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Nov 1996

Volume 14, Issue 6, pp. 3413-4370


Fabrication of gold nanostructures on a vicinal Si(111) 7×7 surface using ultrahigh vacuum scanning tunneling microscope and a gold‐coated tungsten tip

Daisuke Fujita, Qidu Jiang, and Hitoshi Nejoh

J. Vac. Sci. Technol. B 14, 3413 (1996); http://dx.doi.org/10.1116/1.588772 (7 pages) | Cited 20 times

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We have demonstrated that nanometer‐scale gold dots can be deposited on a vicinal Si(111) 7×7 surface using the field‐assisted atom transfer from the gold‐coated tungsten tip of a scanning tunneling microscope operating in ultrahigh vacuum. With the application of negative voltage pulses to the tip, gold nano‐mounds with the size ranging from ∼3 to ∼20 nm across at the base and 0.6–1 nm high can be created on the surface. The deposition is found to be more favored on the step edges than the (111) terraces. Since atomically resolved images of the Si(111) 7×7 structure can be observed even after many cycles of atom transfer using the gold‐coated tip, the shape of the tip apex has been kept very stable. The overall findings clearly suggest that the atom‐transfer technique proposed here is proven to be a good candidate for fabricating nanometer‐scale devices. © 1996 American Vacuum Society
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81.07.-b Nanoscale materials and structures: fabrication and characterization
81.16.-c Methods of micro- and nanofabrication and processing
85.35.-p Nanoelectronic devices
68.37.Ef Scanning tunneling microscopy (including chemistry induced with STM)
68.37.Ps Atomic force microscopy (AFM)
68.37.Rt Magnetic force microscopy (MFM)
68.37.Uv Near-field scanning microscopy and spectroscopy

Characterization of large‐area arrays of nanoscale Si tips fabricated using thermal oxidation and wet etching of Si pillars

C. C. Umbach, B. W. Weselak, J. M. Blakely, and Q. Shen

J. Vac. Sci. Technol. B 14, 3420 (1996); http://dx.doi.org/10.1116/1.588773 (5 pages) | Cited 3 times

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Two‐dimensional periodic arrays containing 108 Si pillars with heights of 600–700 nm, widths of 100 nm, and repeat spacings of 300 nm have been fabricated using electron beam lithography on Si(001) substrates. These pillars have subsequently undergone wet oxidation at 800 °C and etching in hydrofluoric acid to produce an array of sharp tips with a height of ∼4000 Å. The x‐ray diffraction from this array appears to be dominated by scattering from the bases of the tips. Correlated variations in tip shape, observed with scanning electron microscopy, produce a modulated diffuse background in the diffracted x‐ray intensity. These observations demonstrate the feasibility of using high‐resolution x‐ray diffraction for studying defects in large‐area arrays of periodic structures. © 1996 American Vacuum Society
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61.05.cp X-ray diffraction
81.65.Cf Surface cleaning, etching, patterning

Silicon structures for in situ characterization of atomic force microscope probe geometry

K. F. Jarausch, T. J. Stark, and and P. E. Russell

J. Vac. Sci. Technol. B 14, 3425 (1996); http://dx.doi.org/10.1116/1.588774 (6 pages) | Cited 3 times

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Atomic force microscopy (AFM) is increasingly relied on to image and measure micron and submicron scale surface features. Consistent interpretation of AFM information is, however, difficult if the geometry of the probe is not known. In this work, the fabrication of funnel‐like structures and their use in probe characterization were developed from a proof of concept to readiness for field testing. The specifications that determine the structure’s sensitivity to probe shape were identified. The fabrication was tailored to yield large reproducible arrays (>100×100 structure). The geometry of the structures was characterized using low voltage scanning electron microscopy (SEM) techniques. Testing in intermittent contact mode has shown that the structures are stable even at high forces for multiple scans under various conditions. An algorithm was developed that calculates the probe geometry from an image of the structure. The sensitivity of the structures to probe shape was tested by comparing SEM images of probe shape to the probe geometry calculated from the AFM images of the structures. From this analysis it was determined that the structures are sensitive to the cone angle of the probe to within 5° and to the probe radius to within 50 nm. © 1996 American Vacuum Society
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07.79.Lh Atomic force microscopes
68.37.Ef Scanning tunneling microscopy (including chemistry induced with STM)
68.37.Ps Atomic force microscopy (AFM)
68.37.Rt Magnetic force microscopy (MFM)
68.37.Uv Near-field scanning microscopy and spectroscopy
42.30.Va Image forming and processing

Correlation of Raman and optical studies with atomic force microscopy in porous silicon

Adam A. Filios, Susan S. Hefner, and Raphael Tsu

J. Vac. Sci. Technol. B 14, 3431 (1996); http://dx.doi.org/10.1116/1.588775 (5 pages) | Cited 5 times

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Atomic force microscopy images of porous silicon samples prepared with different conditions have been correlated with photoluminescence (PL) and Raman spectra, allowing a clear classification of two types of samples, ‘‘gently’’ etched versus ‘‘heavily’’ etched. The gently etched samples show a significantly improved morphology and uniformity, as well as consistent correlation in PL and Raman results with the quantum confinement model for the light emission. © 1996 American Vacuum Society  
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78.30.Am Elemental semiconductors and insulators
78.55.Mb Porous materials
68.37.Ef Scanning tunneling microscopy (including chemistry induced with STM)
68.37.Ps Atomic force microscopy (AFM)
68.37.Rt Magnetic force microscopy (MFM)
68.37.Uv Near-field scanning microscopy and spectroscopy

Use of multiple analytical techniques to confirm improved optical modeling of SnO2:F films by atomic force microscopy and spectroscopic ellipsometry

P. Ruzakowski Athey, F. K. Urban, and P. H. Holloway

J. Vac. Sci. Technol. B 14, 3436 (1996); http://dx.doi.org/10.1116/1.588776 (9 pages) | Cited 4 times

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Variable angle of incidence spectroscopic ellipsometry, reflectance, and transmittance techniques were used to determine the optical constants of a fluorine doped tin oxide film deposited by chemical vapor deposition onto a hot soda‐lime‐silica glass ribbon. To improve the optical characterization, an additional analytical technique, atomic force microscopy (AFM), was used to incorporate information about surface roughness into the optical model. Our earlier work demonstrated the necessity of including a surface roughness layer as six sublayers in the optical model. The present work further confirms the method and demonstrates its accuracy with additional analytical techniques. These include: (1) cross sectional in‐lens field emission scanning electron microscopy to measure total film thickness, determine presence of interface roughness and extent of surface roughness; (2) secondary ion mass spectrometry to give a first approximation of the film layer structure for optical modeling by depth profiling the film composition; (3) Hall measurements to identify the semiconductor carrier density and mobility; (4) x‐ray diffraction to identify the crystalline phase and preferential growth orientation. The use of AFM surface images and surface roughness plus the other compositional and structural information to improve ellipsometric modeling of thin films has been confirmed. © 1996 American Vacuum Society
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78.66.Li Other semiconductors
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
68.37.Ef Scanning tunneling microscopy (including chemistry induced with STM)
68.37.Ps Atomic force microscopy (AFM)
68.37.Rt Magnetic force microscopy (MFM)
68.37.Uv Near-field scanning microscopy and spectroscopy
73.61.Le Other inorganic semiconductors

Optimal filtering of scanning probe microscope images for wear analysis of smooth surfaces

K. Schouterden, B. M. Lairson, and M. H. Azarian

J. Vac. Sci. Technol. B 14, 3445 (1996); http://dx.doi.org/10.1116/1.588777 (7 pages) | Cited 1 time

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A procedure for removing cumulative drift and white noise from scanning probe microscope images has been constructed. Smooth amorphous carbon overcoats on superpolished hard disk media in particular were examined using a scanning probe microscope. The surfaces typically had a ∼1 nm rms roughness over a scan length of 10 μm. The low roughness yielded a relatively low signal to noise ratio in the unfiltered image. While a conventional filter removes a great deal of noise, an optimal Fourier (Wiener) filter that more selectively removes noise from the image is discussed. White noise and drift were modeled and their contributions to the power spectrum are estimated, resulting in an open clamshell‐shaped two‐dimensional filter. The effect of the filter was demonstrated by subjecting filtered images of unworn and worn areas to a smooth surface to second derivative calculations in different directions. Anisotropy in the wear process associated with the wear direction is apparent in the optimally filtered images. © 1996 American Vacuum Society
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07.79.-v Scanning probe microscopes and components
42.30.Va Image forming and processing
68.37.Ef Scanning tunneling microscopy (including chemistry induced with STM)
68.37.Ps Atomic force microscopy (AFM)
68.37.Rt Magnetic force microscopy (MFM)
68.37.Uv Near-field scanning microscopy and spectroscopy
85.70.Ay Magnetic device characterization, design, and modeling

Atomic structures of Ag2Te studied by scanning tunneling microscopy

M. Ohto and K. Tanaka

J. Vac. Sci. Technol. B 14, 3452 (1996); http://dx.doi.org/10.1116/1.588778 (3 pages) | Cited 2 times

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Atomic structures of Ag2Te in the low‐ and high‐temperature phases have been studied using a scanning tunneling microscope in air and an x‐ray diffraction system. In the low‐temperature phase having a monoclinic lattice, (001) and (01̄0) atomic images are obtained. In the superionic high‐temperature phase, which is stable at temperatures above 145 °C, (100) surfaces of the Te cubic lattice are observed. In both phases, surface atomic reconstructions are not detected. © 1996 American Vacuum Society
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68.35.B- Structure of clean surfaces (and surface reconstruction)
68.55.-a Thin film structure and morphology
68.37.Ef Scanning tunneling microscopy (including chemistry induced with STM)
68.37.Ps Atomic force microscopy (AFM)
68.37.Rt Magnetic force microscopy (MFM)
68.37.Uv Near-field scanning microscopy and spectroscopy

Emission measurements and simulation of silicon field‐emitter arrays with linear planar lenses

Cha‐Mei Tang, T. A. Swyden, K. A. Thomason, L. N. Yadon, D. Temple, C. A. Ball, W. D. Palmer, J. E. Mancusi, D. Vellenga, and G. E. McGuire

J. Vac. Sci. Technol. B 14, 3455 (1996); http://dx.doi.org/10.1116/1.588779 (5 pages) | Cited 10 times

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Results of beam collimation experiments on linear field‐emitter arrays with linear planar lenses are summarized. The electron beam is imaged on a phosphor screen. In general, as lens voltage is reduced relative to the gate voltage, the elliptically shaped screen images narrow, becoming fine lines with emission currents showing only modest reductions. This reduction of emission current can be overcome by increasing the gate voltage only a few volts without affecting beam collimation. As the lens voltage is reduced, screen current decreases relative to emission current while gate current increases, indicating that some emitted electrons in this linear lens geometry cannot propagate to the anode screen. Experimental data and qualitative modeling are in fair agreement. © 1996 American Vacuum Society
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85.45.Bz Vacuum microelectronic device characterization, design, and modeling

Comparative study of the elastic properties of silicate glass films grown by plasma enhanced chemical vapor deposition

G. Carlotti, L. Doucet, and M. Dupeux

J. Vac. Sci. Technol. B 14, 3460 (1996); http://dx.doi.org/10.1116/1.588780 (5 pages) | Cited 12 times

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The Brillouin light scattering technique has been used to study the elastic properties of a number of silicon dioxide films deposited by plasma‐enhanced chemical vapor deposition on Si substrates. In addition to stoichiometric undoped glass films produced from either silane or tetraethylorthosilicate, we have also studied nonstoichiometric Si‐rich films and P‐doped films. The phase velocity of both the surface Rayleigh mode and the longitudinal bulk wave in the film material has been measured and the two independent elastic constants c11 and c44 have been evaluated. The derived values of the Young modulus and the Poisson ratio show appreciable deviations from the values we measured on thermally grown oxide. Moreover, the evolution of the stress during thermal cycles has been analyzed using the substrate curvature method. This permitted us to estimate the thermal expansion coefficient of the films and to distinguish between the intrinsic and thermal components of the stress. © 1996 American Vacuum Society
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68.60.-p Physical properties of thin films, nonelectronic
78.35.+c Brillouin and Rayleigh scattering; other light scattering
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)

Ammonia nitridation of thermal polyoxide to eliminate epitaxial ambient induced dielectric pinhole formation

W. W. Fultz and G. W. Neudeck

J. Vac. Sci. Technol. B 14, 3465 (1996); http://dx.doi.org/10.1116/1.588781 (5 pages) | Cited 2 times

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The incorporation and distribution of nitrogen in ammonia nitrided thermal polyoxide (NPOX) dielectric films and their degradation durability to reduced pressure, dichlorosilane (SiH2Cl2)–HCl–H2 ambient during epitaxial lateral overgrowth (ELO) indicated that the surface nitrogen concentration had no effect. However, a bulk nitrogen concentration as low as 8 at. % significantly reduced the formation of ELO ambient induced pinholes in 250 Å polyoxide films. After 40 min of ELO ambient stress the electrical yield was raised from 0%, for the control polyoxide dielectric capacitors, to 84% for NPOX dielectric capacitors. Analyses of the failed devices suggest that active pinhole generation still exists, however, the bulk nitrogen concentration dramatically reduces the frequency and rate at which these dielectric defects are produced. © 1996 American Vacuum Society
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81.65.Lp Surface hardening: nitridation, carburization, carbonitridation
85.30.-z Semiconductor devices
77.55.-g Dielectric thin films
77.22.Jp Dielectric breakdown and space-charge effects

Selective dry etching of oxide films for spacer applications in a high density plasma

Lynn R. Allen, Victoria Yu‐Wang, and Masyuki Sato

J. Vac. Sci. Technol. B 14, 3470 (1996); http://dx.doi.org/10.1116/1.588782 (3 pages)

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The use of a high density plasma to etch oxide side wall spacers was investigated. Process trends and the optimum process conditions required were determined. Oxide and polysilicon etch rates, uniformities, and the selectivity of oxide to polysilicon were all measured. The resulting etch chemistry had an oxide etch rate of 350 nm/min with a selectivity of oxide to polysilicon of 30:1. © 1996 American Vacuum Society
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81.65.Cf Surface cleaning, etching, patterning
81.05.Je Ceramics and refractories (including borides, carbides, hydrides, nitrides, oxides, and silicides)
85.40.Hp Lithography, masks and pattern transfer

Polysilicon gate etching in high density plasmas. IV. Comparison of photoresist and oxide masked polysilicon etching‐thickness determination of gate oxide layers using x‐ray photoelectron spectroscopy

F. H. Bell and O. Joubert

J. Vac. Sci. Technol. B 14, 3473 (1996); http://dx.doi.org/10.1116/1.588783 (10 pages) | Cited 11 times

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The characteristics of oxide and photoresist masked polysilicon trench etching has been studied by real‐time HeNe laser ellipsometry and quasi in situ x‐ray photoelectron spectroscopy (XPS). Poly‐Si films on SiO2‐covered Si (100) substrates were masked either with a 1‐μm‐thick photoresist or a 200‐nm‐thick oxide hard mask. The 200‐mm‐diam wafers were etched downstream in a helicon high density plasma source using a chlorine‐based gas chemistry. When using an oxide hard mask instead of a photoresist mask, the selectivity of polysilicon over oxide was improved by a factor greater than 3. A new approach to the surface characterization of semiconductor submicron structures by XPS is presented. Photoelectron signals originating from the gate oxide film and the underlying silicon substrate were measured in regular arrays of trenches. The ratio between the SiO2 peak area of the gate oxide film and the Si 2p peak area of the silicon substrate was correlated with the thickness of the SiO2 film. The thickness determined was obtained by calibrating peak area ratios with oxide thickness measurements using spectroscopic ellipsometry. Consequently, the gate oxide thicknesses derived from the area ratios were calculated in patterned areas after etching of photoresist and oxide hard masked polysilicon features as a function of the aspect ratio of the features and mask coverage on the wafer. It was found that the gate oxide consumption is enhanced in high aspect ratio features masked with photoresist as well as in areas with high photoresist coverage; the carbon coverage on the gate oxide film was found to scale with the increased gate oxide etching in the small features. Similar effects were not observed with the oxide masked sample. © 1996 American Vacuum Society
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81.65.Cf Surface cleaning, etching, patterning
81.05.Cy Elemental semiconductors
85.40.Hp Lithography, masks and pattern transfer
82.80.Pv Electron spectroscopy (X-ray photoelectron (XPS), Auger electron spectroscopy (AES), etc.)

Electron‐beam/ultraviolet hybrid exposure combined with novel bilayer resist system for a 0.15 μm T‐shaped gate fabrication process

H. Takano, H. Nakano, H. Minami, K. Hosogi, N. Yoshida, K. Sato, Y. Hirose, and N. Tsubouchi

J. Vac. Sci. Technol. B 14, 3483 (1996); http://dx.doi.org/10.1116/1.588784 (6 pages) | Cited 4 times

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Electron‐beam/ultraviolet (UV) exposure technology to produce undercut T‐shaped resist cavities with bottom openings as small as 0.15 μm is demonstrated with a novel bilayer resist system for AlInAs/InGaAs high electron mobility transistors operated at the millimeter‐wave band. We employed an image reversal resist (AZ5206E) for the top layer and a polydimethyl glutarimide (PMGI) for the bottom layer. The top layer is delineated by UV exposure and the bottom layer is delineated by electron‐beam direct writing. These resist layers are developed layer by layer in different content aqueous tetramethyl ammonium hydroxide solution. Resist profiles are extremely well controlled because exposure and development of both layers are completely independent. A reliable overhang structure for metal liftoff, with a 0.15 μm footprint, was obtained. Gate length variation of less than ±10% on a 3‐in.‐diam InP substrate was successfully accomplished. In addition, an interesting phenomenon was noted. The combination of these two resists leads to an electron‐beam sensitivity decrease of PMGI. This phenomenon is closely related to the change of molecular weight distribution in PMGI. The novel bilayer resist system also allows the further improvement of resolution. This would provide a practical means for electron‐beam lithography in the nanometer region. © 1996 American Vacuum Society
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81.07.-b Nanoscale materials and structures: fabrication and characterization
81.16.-c Methods of micro- and nanofabrication and processing
85.35.-p Nanoelectronic devices
85.30.Tv Field effect devices

Ag2Te/As2S3: A high‐contrast, top‐surface imaging resist for 193 nm lithography

Jerome M. Lavine and Mark J. Buliszak

J. Vac. Sci. Technol. B 14, 3489 (1996); http://dx.doi.org/10.1116/1.588785 (3 pages) | Cited 2 times

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At 193 nm, the Ag2Te/As2S3 inorganic resist system exhibits many of the characteristics previously observed at longer wavelengths, namely, a contrast of the order of 10 and the edge effect, both of which contribute to the printing of narrow linewidths. We have observed 0.3 micron lines limited by the resolution capability of the optical system and not by the resist. Under pulsed excimer laser excitation, this system exhibits a threshold of the order of 3 mJ/cm2/pulse. The system does not exhibit reciprocity. While images were printed with two 17 ns pulses of 4 mJ/cm2/pulse, images could not be printed with a single pulse as large as 50 mJ/cm2/pulse. This behavior is not explained by our previously developed model. © 1996 American Vacuum Society
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81.07.-b Nanoscale materials and structures: fabrication and characterization
81.16.-c Methods of micro- and nanofabrication and processing
85.35.-p Nanoelectronic devices

Neutral shadowing in circular cylindrical trench holes

Barbara Abraham‐Shrauner and Wenjing Chen

J. Vac. Sci. Technol. B 14, 3492 (1996); http://dx.doi.org/10.1116/1.588786 (5 pages) | Cited 9 times

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The neutral flux in the plasma etching of semiconductor wafers has been derived analytically for a simplified model for a circular cylindrical trench hole (circular via). The neutral molecules obey a Maxwellian distribution function and mutual collisions are neglected in the trench. Scattering of the neutrals with the sidewalls and trench bottom is ignored. The flux vector is given at each point on the etching profile surface. The flux vector reduces to the expression previously determined at the center of the trench. Etching profiles of the trench are displayed for neutral flux‐limited etch rates. © 1996 American Vacuum Society
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81.65.Cf Surface cleaning, etching, patterning
85.40.Hp Lithography, masks and pattern transfer
79.20.Rf Atomic, molecular, and ion beam impact and interactions with surfaces

Process technology for monolithic high‐speed Schottky/resonant tunneling diode logic integrated circuits

P.‐M. Lei, S. Subramaniam, G. H. Bernstein, W. Williamson, B. K. Gilbert, and D. H. Chow

J. Vac. Sci. Technol. B 14, 3497 (1996); http://dx.doi.org/10.1116/1.588787 (5 pages)

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A seven‐layer process was developed to fabricate monolithic high‐speed logic circuits, requiring integration of Schottky diodes and resistors with interband resonant tunneling diodes (RTDs). With this process technology, we have demonstrated a functionally complete logic family based on RTDs with a maximum operating frequency in excess of 12 GHz and a minimum power dissipation on the order of 0.5 mW per gate. © 1996 American Vacuum Society
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85.30.Mn Junction breakdown and tunneling devices (including resonance tunneling devices)
85.40.-e Microelectronics: LSI, VLSI, ULSI; integrated circuit fabrication technology

Effect of the Ti/TiN bilayer barrier and its surface treatment on the reliability of a Ti/TiN/AlSiCu/TiN contact metallization

L. Ouellet, Y. Tremblay, G. Gagnon, M. Caron, J. F. Currie, S. C. Gujrathi, and M. Biberger

J. Vac. Sci. Technol. B 14, 3502 (1996); http://dx.doi.org/10.1116/1.588788 (7 pages) | Cited 1 time

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The use of an AlSiCu/TiN bilayer for the metallization of 1.0‐μm‐diam and 1.4‐μm‐deep straight wall contacts to 0.2‐μm‐deep n+ and p+ diffusions, results in a n+/p− and a p+/ṇ− junction leakage lower than 10 pA even after nine heat treatments (60 min each) at 450 °C. However, there is a very important degradation of the contact chain resistance statistics at small contact size. On the other hand, the use of a Ti/TiN bilayer barrier under the AlSiCu/TiN interconnect maintains a n+/p− and a p+/n− junction leakage lower than 20 pA and prevents the degradation of the contact chain resistance statistics after the nine heat treatments. It is finally demonstrated that a vent in nitrogen followed by a momentary air exposure of the Ti/TiN bilayer barrier results in larger contact resistance than a vent in nitrogen followed by a one hour long air exposure of the Ti/TiN bilayer barrier before the deposition of the AlSiCu/TiN interconnect. © 1996 American Vacuum Society
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85.40.Ls Metallization, contacts, interconnects; device isolation
73.40.Cg Contact resistance, contact potential
68.35.Fx Diffusion; interface formation

High stability heterojunction bipolar transistors with carbon‐doped base grown by atomic layer chemical beam epitaxy

R. Driad, F. Alexandre, M. Juhel, and P. Launay

J. Vac. Sci. Technol. B 14, 3509 (1996); http://dx.doi.org/10.1116/1.588789 (5 pages)

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We report the improved thermal stability of heavily C‐doped GaAs layers using atomic layer chemical beam epitaxy (ALCBE). The use of ALCBE improves the crystal quality and reduces hydrogen incorporation in the epilayers by about a factor of 2, resulting in enhanced electrical dopant activity as compared to conventional growth techniques. This process has been successfully applied to the fabrication of InGaP/GaAs heterojunction bipolar transistors (HBTs) with a highly C‐doped base grown by ALCBE and other layers grown by conventional CBE. Dc current gains up to 150, for a base doping layer of 3×1019 cm−3, have been obtained. Moreover, the thermal stability of these devices is increased, as indicated by a post‐growth annealing (650°C, 60 min) which induces only a slight current gain degradation of about 20% at high collector currents, to be compared to a degradation of 60% for HBTs conventionally grown by CBE. © 1996 American Vacuum Society
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85.30.Pq Bipolar transistors
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy

Electrical and microstructure analysis of ohmic contacts to p‐ and n‐type GaSb, grown by molecular beam epitaxy

A. Vogt, H. L. Hartnagel, G. Miehe, H. Fuess, and J. Schmitz

J. Vac. Sci. Technol. B 14, 3514 (1996); http://dx.doi.org/10.1116/1.588790 (6 pages) | Cited 8 times

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Pd based and conventional TiPtAu contacts were realized on GaSb grown by molecular beam epitaxy. For p‐type GaSb, an undoped sample with an acceptor background concentration of 6.6×1016 cm−3 and for n‐type GaSb tellurium‐doped samples with donor concentrations of 7.9×1017 and 1.2×1018 cm−3 were used. Circular transmission line patterns were defined on the samples for determining the specific contact resistivity. On n‐type GaSb, the metallizations consisted of palladium and one of the dopants germanium or sulphur. Rapid thermal annealing lead to values of 4×10−5 Ω cm2. On p‐type GaSb, nonalloyed TiPtAu and alloyed PdGePd contacts were deposited. Values as low as 5.6×10−6 Ω cm2 could be obtained. The interfaces of the TiPtAu, the PdGePd, and PdSPd contacts were studied by high resolution cross‐sectional transmission microscopy. © 1996 American Vacuum Society
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73.40.Cg Contact resistance, contact potential
68.35.Fx Diffusion; interface formation
81.40.Rs Electrical and magnetic properties related to treatment conditions

Thermal stability of W, WSix, and Ti/Al ohmic contacts to InGaN, InN, and InAlN

C. B. Vartuli, S. J. Pearton, C. R. Abernathy, J. D. MacKenzie, R. J. Shul, J. C. Zolper, M. L. Lovejoy, A. G. Baca, and M. Hagerott‐Crawford

J. Vac. Sci. Technol. B 14, 3520 (1996); http://dx.doi.org/10.1116/1.588791 (3 pages) | Cited 5 times

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W, WSi0.44, and Ti/Al contact properties were examined on n+In0.65Ga0.35N, InN, and In0.75Al0.25N. W was found to produce low specific contact resistance (dc∼10−7 Ω cm2) ohmic contacts to InGaN, with significant reaction between metal and semiconductor occurring at 900 °C mainly due to out diffusion of In and N. WSix showed an as‐deposited dc of 4×10−7 Ω cm2 but this degraded significantly with subsequent annealing at ≥600 °C. Ti/Al contacts were stable to ∼600 °C (dc∼4×10−7 Ω cm2 at ≤600 °C). The surfaces of these contacts remained smooth to 800 °C for W and WSix and 650 °C for Ti/Al. InN contacted with W and Ti/Al produced ohmic contacts with dc∼10−7 Ω cm2 and for WSixdc∼10−6 Ω cm2. All remained smooth to ∼600 °C, but exhibited significant interdiffusion of In, N, W, and Ti, respectively, at higher temperatures. The contact resistances for all three metalization schemes were ≥10−4 Ω cm2 on InAlN, and degraded with subsequent annealing. © 1996 American Vacuum Society
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73.40.Cg Contact resistance, contact potential
68.35.Fx Diffusion; interface formation

High temperature surface degradation of III–V nitrides

C. B. Vartuli, S. J. Pearton, C. R. Abernathy, J. D. MacKenzie, E. S. Lambers, and J. C. Zolper

J. Vac. Sci. Technol. B 14, 3523 (1996); http://dx.doi.org/10.1116/1.588792 (9 pages) | Cited 23 times

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The surface stoichiometry, surface morphology, and electrical conductivity of AlN, GaN, InN, InGaN, and InAlN were examined at rapid thermal annealing temperatures up to 1150 °C. The sheet resistance of the AlN dropped steadily with annealing, but the surface showed signs of roughening only above 1000 °C. Auger electron spectroscopy (AES) analysis showed little change in the surface stoichiometry even at 1150 °C. GaN root mean square (rms) surface roughness showed an overall improvement with annealing, but the surface became pitted at 1000 °C, at which point the sheet resistance also dropped by several orders of magnitude, and AES confirmed a loss of N from the surface. The InN surface had roughened considerably even at 650 °C, and scanning electron microscopy showed significant degradation. In contrast to the binary nitrides, the sheet resistance of InAlN was found to increase by ∼102 from the as grown value (3.2×10−3 Ω cm) after annealing at 800 °C and then remain constant up to 1000 °C, while that of InGaN increased by two orders of magnitude between 700 and 900 °C. The rms roughness increased above 800 and 700 °C, respectively, for InAlN and InGaN samples. In droplets began to form on the surface at 900 °C for InAlN and at 800 °C for InGaN, and then evaporate at 1000 °C, leaving pits. AES analysis showed a decrease in the N concentration in the top 500 Å of the sample for annealing ≥800 °C in both materials. © 1996 American Vacuum Society
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68.35.-p Solid surfaces and solid-solid interfaces: structure and energetics
72.80.Ey III-V and II-VI semiconductors
81.40.Rs Electrical and magnetic properties related to treatment conditions

Thermal stability and desorption of Group III nitrides prepared by metal organic chemical vapor deposition

O. Ambacher, M. S. Brandt, R. Dimitrov, T. Metzger, M. Stutzmann, R. A. Fischer, A. Miehr, A. Bergmaier, and G. Dollinger

J. Vac. Sci. Technol. B 14, 3532 (1996); http://dx.doi.org/10.1116/1.588793 (11 pages) | Cited 48 times

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We present results on the thermal stability as well as the thermally induced hydrogen, hydrocarbon, and nitrogen–hydrogen effusion from thin films of Group III nitrides prepared by low‐pressure chemical vapor deposition from organometallic precursors. We have deposited amorphous, polycrystalline, and epitaxial InN, GaN, and AIN films on (0001) Al2O3 substrates using the chemical reaction of azido[bis(3‐dimethylamino)propyl]indium, triethylgallium, and tritertiarybutylaluminium with ammonia. The substrate temperature was varied between 400 °C and 1100 °C. The elemental composition, in particular its dependence on the growth temperature, was investigated by elastic recoil detection analysis (ERDA). The influence of growth rate and crystallite size on the concentration of surface adsorbed hydrocarbons and carbon oxides is determined by a combination of ERDA and thermal desorption measurements. In addition, the stability of and the nitrogen flux from the InN, GaN, and AIN surfaces was determined by x‐ray diffraction and thermal decomposition experiments. © 1996 American Vacuum Society
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68.60.Dv Thermal stability; thermal effects
81.05.Ea III-V semiconductors
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
68.03.Fg Evaporation and condensation of liquids
68.43.Mn Adsorption kinetics

Thermally stable InGaP/GaAs Schottky contacts using low N content double layer WSiN

Kenji Shiojima, Kazumi Nishimura, Masami Tokumitsu, Takumi Nittono, Hirohiko Sugawara, and Fumiaki Hyuga

J. Vac. Sci. Technol. B 14, 3543 (1996); http://dx.doi.org/10.1116/1.588794 (7 pages) | Cited 3 times

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This article describes thermally stable Schottky contacts using low N content double layered WSiN for InGaP/(In)GaAs metal–semiconductor field‐effect transistors with self‐aligned ion‐implanted n+ layers. Transmission electron microscopy observations show that the microscopic interfacial reaction between WSiN and GaAs is completely suppressed when N content in the WSiN is 10% or less. As a result, a WSiN/GaAs‐cap/InGaP Schottky contact shows high thermal stability after annealing at 800 °C for 100 min, even though the GaAs cap is as thin as 25 Å. Moreover, the double‐layer WSiN structure suppresses reduction in the carrier concentration in the channel during activation annealing. The carrier concentration of the GaAs‐cap (40 Å)/InGaP (100 Å)/ InGaAs‐channel (100 Å) film, 6.5×1018 cm−3, decreases to less then 2×1018 cm−3 with low N content WSiN (N=10%, 4000 Å) after annealing at 900 °C for 0.1 s, but it remains 3.8×1018 cm−3 with the double layered WSiN (N=37%, 3800 Å/N=10%, 200 Å). © 1996 American Vacuum Society
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73.30.+y Surface double layers, Schottky barriers, and work functions
85.30.Tv Field effect devices
68.35.Fx Diffusion; interface formation

Improved cathodoluminescence properties of GaAs/Al0.3Ga0.7As tilted T‐shaped quantum wires fabricated on (111)B facet by glancing‐angle molecular beam epitaxy

N. Tomita, M. Tanaka, T. Saeki, S. Shimomura, S. Hiyamizu, K. Fujita, T. Watanabe, T. Higuchi, N. Sano, and A. Adachi

J. Vac. Sci. Technol. B 14, 3550 (1996); http://dx.doi.org/10.1116/1.588795 (5 pages) | Cited 4 times

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GaAs/Al0.3Ga0.7As tilted T‐shaped quantum wires (T‐QWRs) were fabricated by growing Al0.3Ga0.7As/GaAs (well thickness of GaAs Lw=4.4 nm) on a (111)B facet plane that was formed when a GaAs/Al0.3Ga0.7As multi‐quantum well (MQW) layer (Lw=4.5 nm) was grown on a reverse‐mesa etched GaAs(100) substrate by glancing‐angle molecular beam epitaxy (GA‐MBE). Growth conditions of the tilted T‐QWR were optimized, and full width at half‐maximum (FWHM) of a cathodoluminescence (CL) peak from the tilted T‐QWRs was reduced down to 19 meV at 78 K, which is about one‐third of that (61 meV) of previous GaAs/Al0.3Ga0.7As tilted T‐QWRs. © 1996 American Vacuum Society
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85.35.Be Quantum well devices (quantum dots, quantum wires, etc.)
78.60.Hk Cathodoluminescence, ionoluminescence
78.66.Fd III-V semiconductors
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy

Quasiperiodic microfacets on the surface of AlGaAs/GaAs quantum well structures grown by molecular beam epitaxy on (311)A high‐index substrates

S. L. S. Freire, L. A. Cury, F. M. Matinaga, E. C. Valadares, M. V. B. Moreira, A. G. de Oliveira, A. R. Alves, J. M. C. Vilela, M. S. Andrade, T. M. Lima, and J. A. Sluss

J. Vac. Sci. Technol. B 14, 3555 (1996); http://dx.doi.org/10.1116/1.588796 (4 pages) | Cited 2 times

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Standard molecular beam epitaxy is used to demonstrate the growth feasibility and reproducibility on the formation of microfacet array on the top surface of higher‐index (311)A quantum well structures. The quasiperiodic microfacet array was characterized by atomic force microscopy and was observed to be along the [2̄33] direction, whereas for the (100) reference sample the microscopic surface morphology presented the terraces formation. We have used photoluminescence to characterize the optical properties of the samples. The observed redshift of the luminescence from the (311)A sample, in relation to the (100) reference sample, was correlated with the existence of a lateral confinement potential induced by the period of faceting in this structure. The comparative analysis based on photoluminescence measurements have also shown the higher quality and the lower impurity incorporation for the (311)A oriented samples. © 1996 American Vacuum Society
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68.65.-k Low-dimensional, mesoscopic, nanoscale and other related systems: structure and nonelectronic properties
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
78.66.Fd III-V semiconductors
68.37.Ef Scanning tunneling microscopy (including chemistry induced with STM)
68.37.Ps Atomic force microscopy (AFM)
68.37.Rt Magnetic force microscopy (MFM)
68.37.Uv Near-field scanning microscopy and spectroscopy

Layer‐by‐layer removal of GaAs(110) by bromine

C. Y. Cha and J. H. Weaver

J. Vac. Sci. Technol. B 14, 3559 (1996); http://dx.doi.org/10.1116/1.588797 (4 pages) | Cited 3 times

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Scanning tunneling microscopy results show that heating a nearly saturated Br–GaAs(110) 2×1/c(2×2) surface to 600 K leads to a random distribution of single‐layer deep vacancy islands. These islands expand via continued etching upon heating to 700 K. Subsequent exposure to Br2 at 625 K results in complete removal of the first layer via step retreat. Accordingly, monolayer etching can be achieved. The different etching pathways of the exposure‐annealing treatment and that of continuous etching are discussed. © 1996 American Vacuum Society
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81.65.Cf Surface cleaning, etching, patterning
81.05.Ea III-V semiconductors
68.37.Ef Scanning tunneling microscopy (including chemistry induced with STM)
68.37.Ps Atomic force microscopy (AFM)
68.37.Rt Magnetic force microscopy (MFM)
68.37.Uv Near-field scanning microscopy and spectroscopy

Treatment of InP surfaces in radio frequency H2 and H2/CH4/Ar plasmas: In situ compositional analysis, etch rates, and surface roughness

J. E. Parmeter, R. J. Shul, A. J. Howard, and P. A. Miller

J. Vac. Sci. Technol. B 14, 3563 (1996); http://dx.doi.org/10.1116/1.588798 (12 pages) | Cited 6 times

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The surface composition, etch rates, and surface roughness of indium phosphide (InP) surfaces treated in radio frequency (rf) hydrogen and hydrogen/argon/methane plasmas have been investigated using in situ Auger spectroscopy and ex situ scanning electron microscopy and atomic force microscopy. In agreement with most previous studies, hydrogen plasmas are found to completely remove surface carbon and oxygen impurities, but at the expense of some degree of surface phosphorus depletion. This depletion can be minimized by utilizing brief plasma exposure times and low rf power settings. Oxygen removal is found to be rate limiting in the production of a clean surface. InP etching in hydrogen/argon/methane can be performed either in a low density, capacitively coupled plasma mode, or in a high density, inductively coupled plasma mode. For operation in the low density regime, the etched surfaces have a constant and nearly stoichiometric composition, independent of plasma parameters. Etch rates vary from ∼20–400 Å/min, while the root mean square (rms) surface roughness varies from ∼20 to >400 Å. Both of these quantities show definite trends with changing plasma parameters, and, in particular, high etch rates and low surface roughness are both favored by increasing total plasma pressure and methane flow rate. Within the ranges studied, the etch rate is most strongly affected by the amount of hydrocarbon species reaching the surface, which can remove indium in the form of indium alkyl products. However, sputtering effects are also shown to be significant. Etching InP in the high density plasma mode gives an etch rate of ∼700 Å/min, but only at the expense of severe surface phosphorus depletion and rms surface roughness of ∼2000 Å. The breakdown of methane within the plasma under these conditions may serve to inhibit indium alkyl formation, and hence lead to the observed phosphorus depletion. © 1996 American Vacuum Society
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81.65.Cf Surface cleaning, etching, patterning
81.05.Ea III-V semiconductors
68.35.B- Structure of clean surfaces (and surface reconstruction)
52.77.Bn Etching and cleaning
52.77.Dq Plasma-based ion implantation and deposition

Annihilation of monolayer holes on molecular beam epitaxy grown GaAs surface during annealing as shown by in situ scanning electron microscopy

Naohisa Inoue, Keizo Morimoto, Tsutomi Araki, Taichiro Ito, Yoshikazu Homma, and Jiro Osaka

J. Vac. Sci. Technol. B 14, 3575 (1996); http://dx.doi.org/10.1116/1.588545 (7 pages)

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The behavior of monolayer‐deep holes on the surface of (001) GaAs grown by molecular beam epitaxy during post‐growth annealing is observed by in situ scanning electron microscopy. Most small holes disappear immediately after growth in the same way as the islands. However, it is found that some are left for a long time and form big holes with each other. These residual big holes are elongated in the [110] direction initially. They extend in the [110] direction and coalesce with each other, but, at the same time, they shrink in the [1–10] direction and become elongated in the [110] direction. Finally they shrink in both directions and disappear. It takes about 10 min for all the holes to disappear, which is much longer than the growth interruption period usually employed to smooth heterointerfaces. The anisotropic behavior of big holes are discussed in relation to the reported growth anisotropy. © 1996 American Vacuum Society
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68.35.Dv Composition, segregation; defects and impurities
68.37.Hk Scanning electron microscopy (SEM) (including EBIC)
68.37.Lp Transmission electron microscopy (TEM)
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy

Antimony doped GaAs: A model of dominant current transport mechanism

E. Valcheva, T. Paskova, and R. Yakimova

J. Vac. Sci. Technol. B 14, 3582 (1996); http://dx.doi.org/10.1116/1.588546 (6 pages)

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Schottky barrier structures formed on epitaxial GaAs:Sb have been studied at different Sb concentrations (0–1×1020 cm−3) and different temperatures (80–300 K). Current–voltage (I–V) characteristics have been numerically simulated and compared with the experimental measurements in an attempt to reveal the dominant current transport mechanism. Since Sb is a nonelectrically active dopant in GaAs but efficiently influences defect ensemble, the role of the defects on the electrical characteristics of the device structures could be investigated. Three different regions of Sb doping have been considered in accordance with a previous study of the structural and electronic properties of metal organic vapor phase epitaxy‐grown GaAs:Sb. The current transport in the samples containing an optimum amount of Sb (respectively, minimum defects) is dominated by a thermionic field emission in the main operation bias range, although indications of Poole–Frenkel effect are observed, related to the intrinsic near mid‐gap electron levels. In the undoped and highly doped samples the current is mainly due to a carrier diffusion mechanism. In addition, the large amount of defects in these samples results in an electron tunneling component which is present in the I–V characteristics. © 1996 American Vacuum Society
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85.30.De Semiconductor-device characterization, design, and modeling
73.30.+y Surface double layers, Schottky barriers, and work functions
72.20.Jv Charge carriers: generation, recombination, lifetime, and trapping

Misfit dislocations in strained InxGa1−xAs heterostructure on patterned GaAs (001) substrate

W. Zeng, S. S. Jiang, C. Ferrari, S. Gennari, G. Salviati, and J. H. Jiang

J. Vac. Sci. Technol. B 14, 3588 (1996); http://dx.doi.org/10.1116/1.588730 (5 pages)

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〈110〉 60° and 〈100〉 edge misfit dislocations in In0.06Ga0.94As heterostructures grown on patterned GaAs (001) substrates with relatively low misfit f(f=0.0043) have been investigated. The reduction of 〈110〉 misfit dislocation density on mesas is observed by cathodoluminescence, while the 〈100〉 misfit dislocation density on mesas observed by synchrotron radiation double crystal topography remains unchanged. The critical thickness is calculated by modifying the Matthews mechanical equilibrium theory introduced by Chidambarrao et al. The calculated results can be applied to both the nonpatterned area and the sidewalls of the mesa. The critical thickness of one side of the mesa is larger than that of nonpatterned areas. The critical thickness of both sides of mesas is dependent on the angle between the sidewall and (001) GaAs. This is likely due to different values of cos ϕ/sin ψ, which determines the values of the friction force FF with different sidewall angles. It is suggested that the 〈100〉 misfit dislocations are generated by climb and they can cross mesas by climbing along 〈100〉 directions. © 1996 American Vacuum Society
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68.65.-k Low-dimensional, mesoscopic, nanoscale and other related systems: structure and nonelectronic properties
68.35.Ct Interface structure and roughness
78.66.Fd III-V semiconductors
61.05.C- X-ray diffraction and scattering

Surface roughness‐induced artifacts in secondary ion mass spectrometry depth profiling and a simple technique to smooth the surface

S. B. Herner, B. P. Gila, K. S. Jones, H.‐J. Gossmann, J. M. Poate, and H. S. Luftman

J. Vac. Sci. Technol. B 14, 3593 (1996); http://dx.doi.org/10.1116/1.588731 (3 pages) | Cited 7 times

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We report on secondary ion mass spectrometry (SIMS) depth profile artifacts induced by surface roughness. The formation of a TiSi2 film at 800 °C on a boron doping superlattice (DSL) of Si results in a rough (22.0 nm root mean square) interface between the film and Si DSL. After chemically etching off the TiSi2 film, SIMS information is collected while sputtering through the surface of the Si DSL. The resulting depth profiles are irreproducible due to the initial surface roughness. By chemo‐mechanically polishing the Si prior to SIMS analysis, we smooth the surface and the resulting depth profiles are then consistent and easily explained by current diffusion theory. © 1996 American Vacuum Society
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81.70.Jb Chemical composition analysis, chemical depth and dopant profiling
82.80.Ms Mass spectrometry (including SIMS, multiphoton ionization and resonance ionization mass spectrometry, MALDI)
68.35.B- Structure of clean surfaces (and surface reconstruction)
81.65.Ps Polishing, grinding, surface finishing

Rh/n‐GaAs contacts with and without sulfur passivation

G. Eftekhari

J. Vac. Sci. Technol. B 14, 3596 (1996); http://dx.doi.org/10.1116/1.588732 (3 pages)

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The Rh/n‐GaAs contacts with and without sulfur passivation were examined. It was demonstrated that passivation results in contacts of better quality and improved thermal stability. The passivated contacts had higher barrier height, lower reverse current, and lower ideality factor. The formation of thermally stable S–S, S–Ga, and S–As bonds at the GaAs surface, suppression of thermally generated defects, and possible modification in the charge and structure of native oxide were used to explain the observations. © 1996 American Vacuum Society
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73.40.Cg Contact resistance, contact potential
68.35.Fx Diffusion; interface formation
81.65.Rv Passivation

Hydrogen‐induced reconstruction of the GaP(001) surface studied by scanning tunneling microscopy

A. Watanabe, H. Shimaya, M. Naitoh, and S. Nishigaki

J. Vac. Sci. Technol. B 14, 3599 (1996); http://dx.doi.org/10.1116/1.588733 (4 pages) | Cited 2 times

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We report results of a scanning tunneling microscopy investigation on the reconstruction of GaP(001) surfaces. We have observed a 4×2 structure, accompanied locally with c(8×2) domains, at a surface prepared by using ion sputtering and annealing method. On the contrary, both 2×4 [with local c(2×8)] and 4×2 [with local c(8×2)] structures are obtained by hydrogenation followed by annealing. The former consists of a unit structure of three P dimers plus one dimer vacancy, whereas the latter is a parallel arrangement of zig–zag‐chained structures along the [110] direction. It has been shown that the surface hydrogenation before annealing induces new types of reconstruction. © 1996 American Vacuum Society
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68.35.Rh Phase transitions and critical phenomena
68.37.Ef Scanning tunneling microscopy (including chemistry induced with STM)
68.37.Ps Atomic force microscopy (AFM)
68.37.Rt Magnetic force microscopy (MFM)
68.37.Uv Near-field scanning microscopy and spectroscopy

Erratum: Selective wet etching of lattice‐matched InGaAs/InAlAs on InP and metamorphic InGaAs/InAlAs on GaAs using succinic acid/hydrogen peroxide solution [J. Vac. Sci. Technol. B 14, 3400 (1996)]

Hervé Fourre, Frédéric Diette, and Alain Cappy

J. Vac. Sci. Technol. B 14, 3603 (1996); http://dx.doi.org/10.1116/1.588734 (1 page) | Cited 1 time

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Abstract Unavailable
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81.65.Cf Surface cleaning, etching, patterning
81.05.Ea III-V semiconductors
99.10.Cd Errata

Erratum: Surface reaction of trimethylgallium on GaAs [J. Vac. Sci. Technol. B 14, 136 (1996)]

Jun‐ichi Nishizawa, Hiroshi Sakuraba, and Toru Kurabayashi

J. Vac. Sci. Technol. B 14, 3604 (1996); http://dx.doi.org/10.1116/1.588735 (1 page) | Cited 1 time

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Abstract Unavailable
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82.65.+r Surface and interface chemistry; heterogeneous catalysis at surfaces

Erratum: Deep‐etch silicon mm‐waveguide structure for the relativistic acceleration of electrons [J. Vac. Sci. Technol. B 14, 2524 (1996)]

T. L. Willke and A. D. Feinerman

J. Vac. Sci. Technol. B 14, 3605 (1996); http://dx.doi.org/10.1116/1.588736 (1 page)

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41.75.Lx Other advanced accelerator concepts
81.05.Cy Elemental semiconductors

Persistence pays off: Sir Charles Oatley and the scanning electron microscope

T. E. Everhart

J. Vac. Sci. Technol. B 14, 3620 (1996); http://dx.doi.org/10.1116/1.588737 (5 pages) | Cited 2 times

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Shortly after World War II, Sir Charles Oatley initiated research at the Cambridge University engineering laboratories on what has evolved into the modern scanning electron microscope. While much of the research was actually conducted by research students under Oatley’s supervision, he continually provided ideas, resources, and encouragement. He then was instrumental in having this instrument commercialized. His students often continued in the field for some time, making contributions both to the instrument and to its applications that led to improved performance and wider acceptance. This article attempts to capture some of the accomplishments of Sir Charles Oatley as seen by those who worked closely with him. The author believes that Sir Charles deserves the title: ‘‘Father of the Modern Scanning Electron Microscope.’’ © 1996 American Vacuum Society
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01.60.+q Biographies, tributes, personal notes, and obituaries
07.78.+s Electron, positron, and ion microscopes; electron diffractometers

Application of scanning probe methods for electronic and magnetic device fabrication, characterization, and testing

A. Born, C. Hahn, M. Löhndorf, A. Wadas, Ch. Witt, and R. Wiesendanger

J. Vac. Sci. Technol. B 14, 3625 (1996); http://dx.doi.org/10.1116/1.588738 (7 pages) | Cited 3 times

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Selected examples of the application of scanning probe methods for the fabrication, characterization, and testing of electronic and magnetic devices are presented. In particular, promising combinations of conventional photolithography or e‐beam lithography with scanning probe methods are described. The combination of atomic‐scale self‐organization processes with scanning probe microscopy and manipulation experiments possibly can lead to a novel class of atomic‐scale devices which could be fabricated on a reasonable time scale. © 1996 American Vacuum Society
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07.79.-v Scanning probe microscopes and components
81.07.-b Nanoscale materials and structures: fabrication and characterization
81.16.-c Methods of micro- and nanofabrication and processing
85.35.-p Nanoelectronic devices
85.30.De Semiconductor-device characterization, design, and modeling
85.70.Ay Magnetic device characterization, design, and modeling

Low‐energy ion damage in semiconductors: A progress report

Evelyn L. Hu, Ching‐Hui Chen, and Debora L. Green

J. Vac. Sci. Technol. B 14, 3632 (1996); http://dx.doi.org/10.1116/1.588739 (5 pages) | Cited 25 times

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There has been steady progress in understanding the propagation of low‐energy, ion‐induced damage into semiconductor substrates. The availability of specifically designed heterostructure substrates allows us to trace the profile of damage into the material. A number of experiments, together with theoretical simulations, have confirmed the important role played by fortuitous channeling of ions, deep into the material (e.g., >1000 Å deep for incident ions energies ∼300 eV). Recent experiments have also shown the importance of rapid diffusion of ion‐created defects. Using a model that includes the effects of both channeling and defect diffusion, channeling and diffusion in ion damage (CHANDID), we have deduced a room‐temperature diffusion constant of D∼1×10−15 cm2/s. This is an extremely high value for diffusion at room temperature, and is more characteristic of diffusion taking place at temperatures of a few hundred to a few thousand degrees centigrade. One cause of this high value of D may be attributed to radiation enhanced diffusion: the creation of excess electrons and holes during the etch process whose subsequent nonradiative recombination transfers momentum to the defects. Preliminary experiments, which monitor the effects of above band‐gap illumination during ion bombardment, validate this picture. Such understanding, of intrinsic importance, can be used to design material and device structures in which the effects of ion damage may be mitigated. © 1996 American Vacuum Society
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61.82.Fk Semiconductors
61.80.Jh Ion radiation effects
85.30.De Semiconductor-device characterization, design, and modeling

Etching processes for fabrication of GaN/InGaN/AlN microdisk laser structures

J. W. Lee, C. B. Vartuli, C. R. Abernathy, J. D. MacKenzie, J. R. Mileham, S. J. Pearton, R. J. Shul, J. C. Zolper, M. Hagerott‐Crawford, J. M. Zavada, R. G. Wilson, and R. N. Schwartz

J. Vac. Sci. Technol. B 14, 3637 (1996); http://dx.doi.org/10.1116/1.588740 (4 pages) | Cited 6 times

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Several new wet and dry etch processes required for fabrication of microdisk lasers in the III nitrides have been developed. ICl/Ar electron cyclotron resonance plasmas produce etch rates of 1.3 μm/min for GaN and 1.15 μm/min for InN at 1000 W microwave power and 250 W of rf power. These rates are substantially faster than previously investigated Cl2/Ar or CH4/H2 plasma chemistries. Selectivities of 5–6 over AlN are obtained for these materials. Wet chemical etching of AlN and InXAl1−XN in KOH‐based solutions was found to be a strong function of etch temperature and material quality. The activation energy for these materials was in the range 2–6 kcal/mol, typical of diffusion‐controlled processes. The KOH solutions did not etch GaN or InN at temperature as high as 80 °C. © 1996 American Vacuum Society
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81.65.Cf Surface cleaning, etching, patterning
42.82.Cr Fabrication techniques; lithography, pattern transfer
42.55.Px Semiconductor lasers; laser diodes

Quantum dots fabricated in InP/InGaAs by free Cl2 gas etching and metalorganic chemical vapor deposition regrowth

R. Panepucci, E. Reuter, P. Fay, C. Youtsey, J. Kluender, C. Caneau, J. J. Coleman, S. G. Bishop, and I. Adesida

J. Vac. Sci. Technol. B 14, 3641 (1996); http://dx.doi.org/10.1116/1.588741 (5 pages)

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The free Cl2 thermal etching of InGaAs/InP was characterized for the fabrication of quantum well dots (QDs). The effects of mask shape on the three‐dimensional structure of the dot was investigated. Quantum dots with dimensions as small as 56 nm were fabricated using electron beam lithography and free Cl2 etching. The dots were characterized using scanning electron microscopy and low temperature photoluminescence (PL). Metalorganic chemical vapor deposition (MOCVD) regrowth of InP on quantum dots of different mask shapes was investigated. The effect of non‐radiative recombination at the etched sidewall was evaluated through the normalized intensity of the PL. A red shift of the PL peak with decreasing dot sizes was observed for the as‐etched structures and attributed to the effect of residual compressive biaxial strain on the InGaAs layer. Free Cl2 etching is an important etch technique for in situ etch and regrowth processes due to the high quality of the etched interface and the ability to perform selective area regrowth with a SiO2 mask still present. © 1996 American Vacuum Society
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85.35.Be Quantum well devices (quantum dots, quantum wires, etc.)
81.07.-b Nanoscale materials and structures: fabrication and characterization
81.16.-c Methods of micro- and nanofabrication and processing
85.35.-p Nanoelectronic devices
78.66.Fd III-V semiconductors

Reduced nonradiative recombination in etched/regrown AlGaAs/GaAs structures fabricated by in situ processing

S. Kohmoto, Y. Nambu, K. Asakawa, and T. Ishikawa

J. Vac. Sci. Technol. B 14, 3646 (1996); http://dx.doi.org/10.1116/1.588742 (4 pages)

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Effectiveness of in situ processing, which combines Cl2 gas etching with subsequent molecular beam epitaxy regrowth in an ultrahigh vacuum environment, is quantitatively evaluated with nonradiative carrier recombination velocity, S, of etched/regrown AlGaAs/GaAs heterointerfaces. When AlGaAs is in situ regrown on Cl2 gas‐etched flat GaAs surface, the S value is as low as 1.3×103 cm/s. This value is lower than that of air‐exposed/regrown (or ex situ processed) interfaces, thus representing the essential superiority of in situ processing over ex situ. Buried GaAs/AlGaAs multiquantum‐well (MQW) mesa‐stripes are also fabricated by in situ Cl2 gas‐etching/regrowth. The S value at the MQW mesa‐sidewall regrown with AlGaAs is 6.0×103 cm/s, which is reduced by more than one order of magnitude from that of a nonburied case. © 1996 American Vacuum Society
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73.40.Kp III-V semiconductor-to-semiconductor contacts, p-n junctions, and heterojunctions
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
81.65.Cf Surface cleaning, etching, patterning

Etch‐mask of pyrolytic‐photoresist thin‐film for self‐aligned fabrication of smooth and deep faceted three‐dimensional microstructures

G. A. Porkolab, Shih‐Hsiang Hsu, John V. Hryniewicz, Wenhua Lin, Y. J. Chen, Sambhu Agarwala, F. G. Johnson, Oliver King, M. Dagenais, and D. R. Stone

J. Vac. Sci. Technol. B 14, 3650 (1996); http://dx.doi.org/10.1116/1.588743 (4 pages) | Cited 3 times

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Etch‐mask thin‐film material that is particulate‐free and topographically smooth has been created from a standard photoresist spun onto standard semiconductor substrates such as gallium arsenide, indium phosphide, and silicon, and then pyrolyzed by exposing to a temperature of 300 °C in air atmosphere for 1 min on a standard laboratory hot‐plate. The resulting pyrolytic‐photoresist thin‐film is chemically inert to many standard organic solvents including the solvent of photoresist itself and to many inorganic reagents used in semiconductor processing. Therefore the pyrolytic‐photoresist can be patterned by sulfur hexafluoride reactive ion etching via a standard photoresist mask. Upon stripping the standard photoresist in a mixture of 1:1/acetone:developer agitated ultrasonically, the remaining patterned pyrolytic‐photoresist performs as an excellent etch‐mask in chemically assisted ion beam etching and reactive ion etching systems. Thus it can be a key material in the multilayer masking technique used to sculpt self‐aligned three‐dimensional microstructures with deep and smooth facets which are needed for example for photonic integrated circuits and micro‐electro‐mechanical systems. © 1996 American Vacuum Society
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42.82.Cr Fabrication techniques; lithography, pattern transfer
07.10.Cm Micromechanical devices and systems

Photoluminescence blueshift induced by reactive ion etching of strained CdZnSe/ZnSe quantum well structures

L. M. Sparing, P. D. Wang, S. H. Xin, S. W. Short, S. S. Shi, J. K. Furdyna, J. L. Merz, and G. L. Snider

J. Vac. Sci. Technol. B 14, 3654 (1996); http://dx.doi.org/10.1116/1.588744 (4 pages) | Cited 3 times

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A study of the effects of reactive ion etching (RIE) on molecular beam epitaxy‐grown Zn1−xCdxSe/ZnSe strained multiple quantum well samples using low temperature photoluminescence reveals a blueshift in the characteristic peak positions of the wells when etched with CH4/H2. Based on the experimental results, we suggest that the blueshift is not a result of hydrogen incorporation, but that etch induced damage relaxes the compressive strain present in the as‐grown quantum well, producing the observed blueshift. After thermal annealing the energy of the photoluminescence signal returns to its original value, suggesting a restoration of the strain by elimination of the structural damage induced by RIE. However, the original photoluminescence intensity is not recovered by annealing. © 1996 American Vacuum Society
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78.66.Hf II-VI semiconductors
81.65.Cf Surface cleaning, etching, patterning
68.65.-k Low-dimensional, mesoscopic, nanoscale and other related systems: structure and nonelectronic properties

Dry etching damage in III–V semiconductors

S. Murad, M. Rahman, N. Johnson, S. Thoms, S. P. Beaumont, and C. D. W. Wilkinson

J. Vac. Sci. Technol. B 14, 3658 (1996); http://dx.doi.org/10.1116/1.588745 (5 pages) | Cited 19 times

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Dry etching using ions can cause damage to the underlying semiconductor. This paper discusses damage in III–V semiconductors and presents examples of etching conditions under which it can be effectively eliminated. A distinction between surface and sidewall damage is made and methods of measuring both parameters are reviewed. It is noted that the noble gases cause relatively deep damage, while under the correct circumstances, etchants that have a marked chemical effect can cause much less damage. The present state of understanding of the mechanisms for the damage is discussed. © 1996 American Vacuum Society
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81.65.Cf Surface cleaning, etching, patterning
81.05.Ea III-V semiconductors
61.80.Jh Ion radiation effects
85.30.-z Semiconductor devices

Effects of etch‐induced damage on the electrical characteristics of in‐plane gated quantum wire transistors

K. K. Ko, E. W. Berg, and S. W. Pang

J. Vac. Sci. Technol. B 14, 3663 (1996); http://dx.doi.org/10.1116/1.588746 (5 pages) | Cited 3 times

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In‐plane gated (IPG) quantum wire transistors were fabricated using dry etching in a Cl2/Ar plasma generated with an electron cyclotron resonance source. The electrical characteristics of the IPG transistors were correlated with the geometrical dimensions as well as the dry etching and passivation conditions. In‐plane gates with the width of the channel (Wc) and the width of the gate isolation (Wg) ranging from 100 to 850 nm were studied. Good field‐effect transistor characteristics with transconductances up to 371 mS/mm were obtained on these devices. At a gate‐source voltage (VGS) of 2 V, the saturated drain‐source current (IDSAT) increased from 68 to 153 μA as Wc increased from 440 to 800 nm. No current was measured on IPG transistors with Wc ≤−130 nm. The quasi‐one‐dimensional channel can be completely pinched off with VGS ≤−1 V. It was found that the gate leakage current decreased with a wider Wg and a deeper depth for the gate isolation. The leakage current at VGS=2 V decreased significantly from 250 to <0.1 pA when the etch depth increased from 320 to 440 nm. The gate leakage current and IDS were also found to increase with rf power used for etching due to additional defects generated at higher ion energy. These defects, however, can be passivated with low energy chlorine species, and reduction of the gate leakage current from 40 to 4.4 nA was observed after a 1 min Cl2 plasma passivation. © 1996 American Vacuum Society
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85.35.Be Quantum well devices (quantum dots, quantum wires, etc.)
81.65.Cf Surface cleaning, etching, patterning

Effects of O2 addition to SiCl4/SiF4 and the thickness of the capping layer on gate recess etching of GaAs‐pseudomorphic high electron mobility transistors

S. K. Murad, N. I. Cameron, S. P. Beaumont, and C. D. W. Wilkinson

J. Vac. Sci. Technol. B 14, 3668 (1996); http://dx.doi.org/10.1116/1.588747 (6 pages) | Cited 5 times

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The effects of the addition of a small amount of O2 to SiCl4/SiF4 plasma and the thickness of the GaAs capping layer on gate recess etching of GaAs pseudomorphic high electron mobility transistor (p‐HEMT) devices have been studied. During gate recessing of GaAs/AlGaAs p‐HEMTs using a selective reactive ion etching (RIE) process in SiCl4/SiF4 plasma [see S. K. Murad, N. I. Cameron, P. D. Wang, S. P. Beaumont, and C. D. W. Wilkinson, Microelectron. Eng. 27, 439 (1995)], it was found that the profile of the gate changes dramatically from undercut to nearly vertical with no lateral etching when the thickness of the capping layer was reduced below 40 nm. This vertical profile puts the gate metal too close to the recess edges in devices with a ≤30 nm capping layer. The addition of a very small amount of O2 to SiCl4/SiF4 plasma was seen to increase GaAs etch rates remarkably, while maintaining the high selectivity over AlGaAs. This increase in the etch rate agrees well with optical emission spectroscopic observations which indicate that the Cl emission has increased by more than an order of magnitude for the addition of only 1.5% of O2 to SiCl4/SiF4 plasma. This selective RIE process of SiCl4/SiF4/O2 was applied to gate recess etching of GaAs/AlGaAs/InGaAs p‐HEMTs with various capping layer thicknesses. The profile of the T gates changed from nearly vertical (with no undercut or gate offset) to undercut with a lateral etch rate depending on the thickness of the capping layer. The lateral etching rate also strongly depends on the O2 flow. The p‐HEMT devices gate recessed using this process (SiCl4/SiF4/O2) exhibited an ft of 120 GHz, gm of 700 mS/mm and a gain of 9.5 dB at 94 GHz. © 1996 American Vacuum Society
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81.65.Cf Surface cleaning, etching, patterning
85.30.Tv Field effect devices

Investigation of improved regrown material on InP surfaces etched with methane/hydrogen/argon

D. G. Yu, C.‐H. Chen, B. P. Keller, A. L. Holmes, E. L. Hu, and S. P. Den Baars

J. Vac. Sci. Technol. B 14, 3674 (1996); http://dx.doi.org/10.1116/1.588748 (5 pages) | Cited 1 time

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In this work, we study the hydrogen introduced into InP during methane/hydrogen/argon reactive ion etching (RIE) to determine its effect on metalorganic chemical vapor deposition regrowth. We replace hydrogen with deuterium and confirm that deuterium is introduced into the substrate during methane/deuterium/argon RIE with secondary ion mass spectrometry. During regrowth, the deuterium diffuses from deep within the material and clusters at the regrowth interface, strongly indicating the presence of defects. To further understand the role of hydrogen, we investigate the separate effects of ion damage and hydrogenation on subsequent regrowth. We find that photoluminescence of regrown quantum wells is greatly improved on argon ion damaged substrates which have been additionally exposed to hydrogen at −150 V for 3 min. These experiments illustrate that hydrogen interacts with defects in InP, preventing their propagation during regrowth, and improving the photoluminescence quality of regrown quantum wells. © 1996 American Vacuum Society  
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81.65.Cf Surface cleaning, etching, patterning
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
81.05.Ea III-V semiconductors
78.66.Fd III-V semiconductors

Reactive ion etch‐induced effects on 0.2 μm T‐gate In0.52Al0.48As/In0.53Ga0.47As/InP high electron mobility transistors

R. Cheung, W. Patrick, I. Pfund, and G. Hähner

J. Vac. Sci. Technol. B 14, 3679 (1996); http://dx.doi.org/10.1116/1.588749 (5 pages) | Cited 3 times

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The effect of CH4/H2 reactive ion etching on In0.52Al0.48As surfaces and In0.52Al0.48As/ In0.53Ga0.47As/InP heterostructure have been studied using Schottky diode, x‐ray photoelectron spectroscopy, and room temperature transport experiments. The application of CH4/H2 as a dry etch gas for the gate recess step in the fabrication of 0.2 μm T‐gate In0.52Al0.48As/In0.53Ga0.47As/InP high electron mobility transistor has been explored. We show that while the room temperature mobility and the dc and high frequency performance of the dry etched devices are at least comparable to the wet etched ones, their microwave noise behaviours are extremely sensitive to dry etch‐induced defects. © 1996 American Vacuum Society
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85.30.Tv Field effect devices
81.65.Cf Surface cleaning, etching, patterning
84.40.Lj Microwave integrated electronics

Photoluminescence studies on radiation enhanced diffusion of dry‐etch damage in GaAs and InP materials

Ching‐Hui Chen, D. Ginger Yu, Evelyn L. Hu, and Pierre M. Petroff

J. Vac. Sci. Technol. B 14, 3684 (1996); http://dx.doi.org/10.1116/1.588750 (4 pages) | Cited 13 times

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We have investigated the radiation enhanced diffusion of ion defects during reactive ion beam etching of GaAs and InP, using the multiple quantum well (MQW) probe technique. During low energy (sub‐keV) Ar+ ion exposure, illumination with light of energy above the band gap can substantially reduce the photoluminescence efficiency of MQW samples, relative to those which were not laser illuminated; the degradation of luminescence efficiency increases with the intensity of the light. Illumination with light of energy below the band gap produces a slight increase in the damage profiles. The observation of enhanced defect diffusion due to optical radiation in our studies suggests that in ion‐assisted etching of semiconductors, the generation of excess electron‐hole pairs and their subsequent recombination can play an important role in the propagation of defects into the substrate. © 1996 American Vacuum Society
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66.30.Lw Diffusion of other defects
61.80.Jh Ion radiation effects
81.65.Cf Surface cleaning, etching, patterning
78.66.Fd III-V semiconductors

Suppression of electron shading effect by a counter radio frequency bias in plasma etching

T. Kamata and H. Arimoto

J. Vac. Sci. Technol. B 14, 3688 (1996); http://dx.doi.org/10.1116/1.588648 (4 pages) | Cited 4 times

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We investigated the suppression of the charge buildup caused by the electron shading effect using a counter rf bias, which produces high energy electrons reflected from the counter electrode. We expected that these high energy electrons could overcome the potential barrier formed at the entrance of high aspect‐ratio hole patterns and to decrease the charge buildup at the bottom of these patterns. We directly investigated the charge buildup by measuring dc self‐bias potential differences between high aspect‐ratio hole patterns and open‐space pattern. The dc self‐bias potential difference increased, independent of the hole pattern aspect ratio, at the lower substrate rf bias voltage and they tended to saturate at the following higher substrate rf bias voltage. The dc self‐bias potential difference reached about 100 V with a substrate rf bias voltage of 400 V for an aspect ratio of 2. The dc self‐bias potential difference dramatically decreased from 100 to 20 V by increasing the counter rf bias voltage. In addition, we investigated this suppression effect by changing the phase difference between counter and substrate bias voltages when both bias frequencies were set to 13.56 MHz. We found that there is a variation of the suppression effect with respect to the phase difference. This indicates that high energy electrons, which were accelerated in an oscillation sheath, could reach the bottom of the holes. © 1996 American Vacuum Society
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52.77.Bn Etching and cleaning
52.77.Dq Plasma-based ion implantation and deposition
85.40.Hp Lithography, masks and pattern transfer

Fabrication of micromechanical switches for routing radio frequency signals

John N. Randall, Chuck Goldsmith, David Denniston, and Tsen‐Hwang Lin

J. Vac. Sci. Technol. B 14, 3692 (1996); http://dx.doi.org/10.1116/1.588649 (5 pages) | Cited 8 times

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Micromechanical switches have several advantages over other switch technologies for the routing of microwave and mm‐wave signals. They offer low loss, low switching power, very low standby power, and are extremely linear. The switching speeds are very slow compared to solid state switches; however, for a number of applications, their specifications appear attractive. For instance, electronically steerable antenna arrays operating at 10, 20, and 30 GHz need phase shifters for each antenna element. Micromechanical RF switches that offered lower losses could find significant applications as phase shifters for telecommunications applications. We describe the fabrication of membrane micromechanical RF switches that switch signals of 10 GHz and higher. Dry etching plays a critical role in fabrication. In particular the isotropic removal of a sacrificial polymer layer between the bottom electrode and the membrane is a critical process. Reasonable rates must be obtained at moderate temperatures and there must be as little residue as possible. A high degree of selectivity over that of the capacitor dielectric is also a requirement. Our process should be compatible with microwave monolithic integrated circuit (MMIC) processing technology allowing integration with RF amplifiers and other components. © 1996 American Vacuum Society
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84.40.-x Radiowave and microwave (including millimeter wave) technology
07.10.Cm Micromechanical devices and systems

Sharpening Si field emitter tips by dry etching and low temperature plasma oxidation

M. R. Rakhshandehroo and S. W. Pang

J. Vac. Sci. Technol. B 14, 3697 (1996); http://dx.doi.org/10.1116/1.588650 (5 pages) | Cited 4 times

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Dry etching and low temperature plasma oxidation were used to sharpen Si field emitter tips. Si emitters with tip radii of 67 nm were formed by dry etching in a Cl2 plasma at 5 mTorr. An electron cyclotron resonance (ECR) source was used to generate the plasma and erosion of a SiO2 mask was employed to control the Si emitter geometry. The Si emitters were sharpened by dry etching in the Cl2 plasma generated at 0.7 and 5 mTorr after the SiO2 mask was completely eroded. After etching the emitters for 7 min at 0.7 mTorr, the tip radius decreased from 67 to 22 nm. The sharpening effect could be attributed to enhanced sputtering yield at sloped surfaces. At higher pressure of 5 mTorr, the sharpening effect was reduced and the tip radius only decreased from 67 to 62 nm. Optical emission spectroscopy and mass spectrometry were used to monitor the etching and sharpening of Si emitter tips. Sharp increases in the Si emission signal at 288.1 nm and mass spectrometric signal for 63SiCl+ were observed once the SiO2 mask was completely eroded and the sharpening of Si emitters had started. Plasma oxidation was also used to sharpen the emitter tips. With the stage at room temperature, up to 257 nm of plasma oxide was grown in an O2 plasma generated at 0.3 mTorr by the ECR source. After oxide removal, the emitters tip radius was found to decrease from 67 to 8 nm. In comparison, the same amount of oxide grown by thermal dry oxidation at 950 and 1100 °C only reduced the tip radius to 32 and 50 nm, respectively. Sharper emitter tips and faster oxidation rate can be obtained by plasma oxidation. © 1996 American Vacuum Society
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85.45.Db Field emitters and arrays, cold electron emitters
81.65.-b Surface treatments

Realization of atomic layer etching of silicon

Satish D. Athavale and Demetre J. Economou

J. Vac. Sci. Technol. B 14, 3702 (1996); http://dx.doi.org/10.1116/1.588651 (4 pages) | Cited 11 times

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An experimental system and methodology were developed to realize dry etching of single crystal silicon with monolayer accuracy. Atomic layer etching of silicon is a cyclic process composed of four consecutive steps: reactant adsorption, excess reactant evacuation, ion irradiation, and product evacuation. When successful, completion of one cycle results in removal of one monolayer of silicon. The process was self‐limiting with respect to both reactant and ion dose. Control of the ion energy was the most important factor in realizing etching of one monolayer per cycle. © 1996 American Vacuum Society
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81.65.Cf Surface cleaning, etching, patterning
81.07.-b Nanoscale materials and structures: fabrication and characterization
81.16.-c Methods of micro- and nanofabrication and processing
85.35.-p Nanoelectronic devices
81.05.Cy Elemental semiconductors
68.35.B- Structure of clean surfaces (and surface reconstruction)

Precision optical aspheres for extreme ultraviolet lithography

D. R. Kania, D. P. Gaines, D. S. Sweeney, G. E. Sommargren, B. La Fontaine, S. P. Vernon, D. A. Tichenor, J. E. Bjorkholm, F. Zernike, and R. N. Kestner

J. Vac. Sci. Technol. B 14, 3706 (1996); http://dx.doi.org/10.1116/1.588652 (3 pages)

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We have demonstrated significant advances in the production of aspheric optics for extreme ultraviolet lithography. An optic has been fabricated with an aspheric departure of 1.5 μm, a figure error of 0.7 nm rms, and a nanoroughness of 0.25 nm rms. Further improvements are required in the figure and nanoroughness to reach high throughput and near diffraction limited performance in an extreme ultraviolet lithography system. © 1996 American Vacuum Society
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42.79.-e Optical elements, devices, and systems
81.07.-b Nanoscale materials and structures: fabrication and characterization
81.16.-c Methods of micro- and nanofabrication and processing
85.35.-p Nanoelectronic devices

Effects of compaction on 193 nm lithographic system performance

Richard Schenker and William Oldham

J. Vac. Sci. Technol. B 14, 3709 (1996); http://dx.doi.org/10.1116/1.588653 (5 pages) | Cited 1 time

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Ultraviolet radiation induces compaction in fused silica. Using stress‐induced birefringence as a dosimeter, we are able to measure refractive index changes over the range of 20 ppb–1.5 ppm and have found a general description of compaction versus 193 nm dose valid for a wide range of intensities, pulse rates, and fused silicas. Using the experimental data, we evaluate the effect of compaction damage on a model 193 nm optic. Zernike phase aberration terms from compaction in elements near the pupil plane of the system are calculated using Fourier optics while aberrations from other elements are estimated using ray‐tracing. Aerial image simulations show significant distortion and focal shifts occur at the edge of the image field for only a 0.05λ total rms compaction‐induced wave front aberration. The useful life of the model system depends strongly on the throughput, resist sensitivity, and partial coherence. For a system operating at 10 million pulses per day with a 70% clear field mask and sigma of 0.5, we predict a life range of 6 months to 12 years for resist sensitivities ranging from 50 mJ/cm2 to 10 mJ/cm2. This life prediction increases by over factor of 2 for sigma of 0.7. © 1996 American Vacuum Society
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81.07.-b Nanoscale materials and structures: fabrication and characterization
81.16.-c Methods of micro- and nanofabrication and processing
85.35.-p Nanoelectronic devices
42.30.Va Image forming and processing
42.70.-a Optical materials
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
61.80.Ba Ultraviolet, visible, and infrared radiation effects (including laser radiation)

Merit functions for lithographic lens design

Christopher J. Progler and Dale M. Byrne

J. Vac. Sci. Technol. B 14, 3714 (1996); http://dx.doi.org/10.1116/1.588654 (5 pages) | Cited 2 times

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We describe a new approach to the optimization of lithography lenses where lithographic quality factors are enclosed inside the optimization loop. These quality factors are derived from an image simulation program which calculates the relevant lithography metrics each time an optimization cycle is attempted. We find lithographic merit functions strongly impact the final lens performance, and superior lithographic imaging is possible when they are employed. We also show that lens users benefit by understanding the aberration balance inherent in each lithography lens. © 1996 American Vacuum Society
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42.15.Eq Optical system design
85.40.Hp Lithography, masks and pattern transfer
42.79.Bh Lenses, prisms and mirrors

Attenuated phase shift mask materials for 248 and 193 nm lithography

B. W. Smith, S. Butt, Z. Alam, S. Kurinec, and R. L. Lane

J. Vac. Sci. Technol. B 14, 3719 (1996); http://dx.doi.org/10.1116/1.588655 (5 pages) | Cited 6 times

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In order to push resolution toward diffraction limits for 248 and 193 nm lithography, it is likely that some combination of optical enhancement may be needed. The attenuated phase shift mask approach may prove to be one of the less complex techniques available. Four materials are presented which may meet optical and process requirements for use as attenuated phase shift mask films: a molybdenum silicon oxide composite, an aluminum/aluminum nitride cermet, an understoichiometric silicon nitride, and a tantalum silicon oxide composite. All of these materials are shown to be capable of 4%–15% transmission at 193 nm with thicknesses that produce a π phase shift. Evaluation of addition film properties including plasma reactive ion etch and long wavelength transmission helps in establishing materials which may be most production worthy. © 1996 American Vacuum Society
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85.40.Hp Lithography, masks and pattern transfer
81.05.Je Ceramics and refractories (including borides, carbides, hydrides, nitrides, oxides, and silicides)

Propagation effects of partial coherence in optical lithography

R. J. Socha and A. R. Neureuther

J. Vac. Sci. Technol. B 14, 3724 (1996); http://dx.doi.org/10.1116/1.588656 (6 pages) | Cited 5 times

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A method based on optimal expansions is described for making an order of magnitude speed up in the analysis of partial coherence effects of scattering in optical lithography, inspection, and alignment. This method expands the incident mutual intensity from the illumination into coherent nonuniform plane waves whose effects can be added incoherently. For three‐dimensional structures, the CPU time is reduced by an order of magnitude over the uniform plane wave approach of Abbe. For two‐dimensional structures, the number of simulations with the decomposition technique has been found to be about three times smaller than with Abbe’s approach. The method has been incorporated into TEMPEST and shown to give accurate results and reduced CPU time in applications of imaging an attenuated phase shift mask, patterning of gates over an active area well in silicon, and inspection of a trench in silicon dioxide, where the CPU time savings are most significant due to large NA’s and high σ’s. Results for an embedded phase shift mask show the need to generalize Hopkin’s method to include effects of the dependence of the diffraction efficiencies on the angle of incidence. The inclusion of partial coherence in regions of topography scattering show beneficial imaging effects in that reflective notching is reduced as σ is increased. © 1996 American Vacuum Society
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85.40.Hp Lithography, masks and pattern transfer
42.25.-p Wave optics

General aspheric refractive micro‐optics fabricated by optical lithography using a high energy beam sensitive glass gray‐level mask

Walter Däschner, Pin Long, Robert Stein, Chuck Wu, and S. H. Lee

J. Vac. Sci. Technol. B 14, 3730 (1996); http://dx.doi.org/10.1116/1.588657 (4 pages) | Cited 9 times

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General aspheric refractive microlens arrays with an almost 100% fill factor are useful in a wide range of applications ranging from display, optoelectronic interconnections, or improving the efficiency of detector arrays to lithography techniques utilizing microlens arrays. In this article a technique will be discussed which allows the microlithographic fabrication of general aspheric non rotationally symmetric refractive lenses with a 100% fill factor. A gray‐level mask based on high energy beam sensitive (HEBS) glass is used to pattern a thick (4–5 micron) photoresist layer. After development, the refractive structure is transferred into the substrate material using a chemically assisted ion beam etching (CAIBE) process. The HEBS‐glass gray‐level mask is generated by a electron‐beam writer, allowing for complete freedom in terms of the shape and location of the lenses. © 1996 American Vacuum Society
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42.82.Cr Fabrication techniques; lithography, pattern transfer
42.79.-e Optical elements, devices, and systems

Simulation of light propagation in optical linear and nonlinear resist layers by finite difference beam propagation and other methods

A. Erdmann and W. Henke

J. Vac. Sci. Technol. B 14, 3734 (1996); http://dx.doi.org/10.1116/1.588658 (4 pages) | Cited 2 times

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This article presents a new method for the calculation of light propagation in resist layers and compares it with scaled defocus and transfer matrix algorithms. Our method is not restricted to homogeneous resist and substrate layers. For the first time, a simulation of focus drilling is presented. © 1996 American Vacuum Society
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42.25.Bs Wave propagation, transmission and absorption
85.40.Hp Lithography, masks and pattern transfer

Micro‐objective lens with compact secondary electron detector for miniature low voltage electron beam systems

W. Liu, T. Ambe, and R. F. Pease

J. Vac. Sci. Technol. B 14, 3738 (1996); http://dx.doi.org/10.1116/1.588659 (4 pages) | Cited 3 times

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The low voltage scanning electron microscope appears to be attractive for the examination of ultrathin film such as surface contamination. However, achieving high resolution and high secondary electron detection efficiency at, say 100 eV landing energy, meets serious electron optical challenges. We describe a very low aberration micro‐objective lens that is combined with an efficient secondary electron detector to address this issue. The objective lens comprises a mirco‐einzel lens followed by a retarding region (from 10 000 to 100 V) and a final electrode just above the sample to minimize the electric field at the sample surface. The retarding field (a) lowers aberration of the objective lens and (b) accelerates the secondary electrons to improve the detection. Using computer modeling we have optimized the design to minimize the primary beam diameter and maximize secondary electron collection. For a landing energy of 100 eV the minimum beam diameter is about 10 nm at 96 μm working distance when the beam energy spread is 0.1 eV. About 50% of secondary electrons can be collected by the compact p‐n junction detector micromachined to serve also as the bottom electrode of the einzel lens. The depletion region extends from 0.25 to 5 μm at zero bias and experimental results indicate a current gain of more than 2000. © 1996 American Vacuum Society
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41.85.Ne Electrostatic lenses, septa
07.78.+s Electron, positron, and ion microscopes; electron diffractometers

Triangular‐variable‐shaped beams using the cell projection method

Yasuhiro Someda, Yasunari Shoda, and Norio Saitou

J. Vac. Sci. Technol. B 14, 3742 (1996); http://dx.doi.org/10.1116/1.588660 (5 pages) | Cited 1 time

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A triangular variable shaped electron beam lithography method using the cell projection method is proposed. The shaped beams are formed by a conventional rectangular beam method and variable triangular apertures. This method has three significant characteristics: The plural kind of triangles can be made. This increases the pattern flexibility and decreases the number of shots. The position of one corner of the triangles is automatically determined. Therefore, there is no fluctuation of the triangular beam position and the size of the triangle can be varied with high precision. The triangular apertures are located such as to minimize the deflection distance. This realizes high speed and high precision beam formation. With these characteristics, this method is expected to be used for high speed and high precision mask fabrication. © 1996 American Vacuum Society
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85.40.Hp Lithography, masks and pattern transfer
81.07.-b Nanoscale materials and structures: fabrication and characterization
81.16.-c Methods of micro- and nanofabrication and processing
85.35.-p Nanoelectronic devices
41.85.Ew Particle beam profile, beam intensity

Combined calculation of lens aberrations, space charge aberrations, and statistical Coulomb effects in charged particle optical columns

X. R. Jiang, J. E. Barth, and P. Kruit

J. Vac. Sci. Technol. B 14, 3747 (1996); http://dx.doi.org/10.1116/1.588661 (6 pages) | Cited 4 times

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Optimizing a charged particle optical system utilizing a high brightness source requires the inclusion of the effect of Coulomb interactions in the evaluations. A new computer program package, named ANALIC, has been developed to perform the combined calculation of lens aberrations, space charge aberrations, and statistical Coulomb effects in a complete instrument. By making use of an analytical slice method, valid for weak/incomplete collisions, to calculate the Coulomb interactions, the program combines reasonable accuracy with high speed. Using ANALIC, an optical system with an arbitrary number of lenses and apertures, an arbitrary mode of imaging, and an arbitrary distribution of the beam energy can be analyzed directly. The functions, features, organization, and calculation approach of the program are reported. As an example of the use of the program, a four lens electron probe instrument is analyzed for the demonstration of the combined calculation and optimization process of a particle optical system. © 1996 American Vacuum Society
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41.85.-p Beam optics

Optical design of a combined ion and electron beam system for nanotechnology

P. W. H. de Jager and P. Kruit

J. Vac. Sci. Technol. B 14, 3753 (1996); http://dx.doi.org/10.1116/1.588662 (6 pages)

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Nanometer sized structures can be fabricated with an ion beam in several ways, but they would be destroyed if ions were used for observation of the newly made structures. Therefore, they must be observed with an electron beam or scanning probe microscope. A system is developed based on a scanning transmission electron microscope in which both an ion beam and an electron beam can be focused on the specimen. Several design concepts are discussed. In the chosen design, the ion beam is brought on the optical axis of the microscope by means of a 90° deflector which is also used as part of an energy filter. The particles are focused on the specimen by a combined electrostatic and magnetic objective lens. The smallest structure size that can be achieved, is determined by the aberrations of the lenses in the system and the interactions of the ions with each other in the beam (Coulomb interactions) and with the specimen (proximity effect). The system is optimized for these effects resulting in a design which should allow a smallest structure size of 7 nm when using Ar ion sputtering. The spatial resolution when using the electron beam to observe these structures is designed to be 0.6 nm. © 1996 American Vacuum Society
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81.07.-b Nanoscale materials and structures: fabrication and characterization
81.16.-c Methods of micro- and nanofabrication and processing
85.35.-p Nanoelectronic devices

Fundamental limits to imaging resolution for focused ion beams

Jon Orloff, L. W. Swanson, and M. Utlaut

J. Vac. Sci. Technol. B 14, 3759 (1996); http://dx.doi.org/10.1116/1.588663 (5 pages) | Cited 10 times

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This article investigates the limitations on the formation of focused ion beam images from secondary electrons. We use the notion of the information content of an image to account for the effects of resolution, contrast, and signal‐to‐noise ratio and show that there is a competition between the rate at which small features are sputtered away by the primary beam and the rate of collection of secondary electrons. We find that for small features, sputtering is the limit to imaging resolution, and that for extended small features (e.g., layered structures), rearrangement, redeposition, and differential sputtering rates may limit the resolution in some cases. © 1996 American Vacuum Society
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41.85.-p Beam optics
79.20.Rf Atomic, molecular, and ion beam impact and interactions with surfaces

High emittance electron gun for projection lithography

W. DeVore and S. D. Berger

J. Vac. Sci. Technol. B 14, 3764 (1996); http://dx.doi.org/10.1116/1.588664 (6 pages) | Cited 6 times

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The source requirements for a high‐throughput projection electron‐beam stepper are radically different than those for more typical focused beam systems. The SCALPEL®, proof‐of‐concept stepper requires a uniform, 1 mm2 parallel beam at the mask plane with a convergence angle of 0.5 mrad and a beam current on the order of 10 μA. These requirements translate to an axial brightness of ∼1000 A/cm2 sr which is many orders of magnitude less than a typical direct‐write electron‐beam system. Another characteristic of a radiation source is emittance, the product of beam size, and angular extent. Unlike axial brightness, this property is not conserved throughout the optical column but is reduced by the presence of apertures. The required emittance of the SCALPEL system is ∼700 μm mrad at the mask and wafer plane. For comparison, a typical direct‐write system might have an emittance of ∼1 μm mrad at the wafer plane. In principle, the gun emittance requirement can be met with any combination of source size and angular extent. In practice, limitations imposed by spherical aberration in the illumination lenses mean that designs for projection systems need to maximize the source size. In this article we present data from a gun designed to meet the requirements of the SCALPEL® proof‐of‐concept system. This gun has been built and tested at 100 kV. The tests were carried out on a test stand that examines the beam far‐field intensity distribution by means of a yttrium aluminum garnet (YAG) scintillation crystal. Angular intensity uniformity is measured directly by examining the YAG with a calibrated video camera/frame grabber/486PC system. Source size is determined by looking at the penumbral beam rise from the gun aperture edge in the same system. Results to date show the gun producing a virtual source size of >50 μm diameter and a uniform beam of angular extent >12 mrad, which corresponds to an emittance >600 μm mrad. The gun is normally run with temperature‐limited emission from the 〈100〉 lanthanum hexaboride cathode, and it achieves a beam current stability of a few percent per hour. Beam currents of 1–50 μA and larger can be set by changing cathode temperature. Because of the low brightness required by the stepper, normal cathode temperature is about 1250 K. © 1996 American Vacuum Society
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07.77.Ka Charged-particle beam sources and detectors
81.07.-b Nanoscale materials and structures: fabrication and characterization
81.16.-c Methods of micro- and nanofabrication and processing
85.35.-p Nanoelectronic devices

Ultralow voltage imaging

L. S. Hordon and K. M. Monahan

J. Vac. Sci. Technol. B 14, 3770 (1996); http://dx.doi.org/10.1116/1.588665 (4 pages) | Cited 2 times

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Low‐voltage (<1 kV) electron beams have become widely used in the semiconductor industry for nondestructive imaging of integrated circuits. By focusing the electron beam onto the device at an energy close to EII, the unity‐yield point of the material, charging can be minimized. In addition, the penetration depth of the beam into the device is greatly reduced, generating images which carry more surface information and minimizing beam‐induced damage. In this paper we discuss electron beam imaging at ultralow voltages (100–800 V). Within this range, the landing energy is optimal for many insulating materials used in semiconductor devices. Resolution better than or equal to 5 nm is attainable at 600 eV landing energy, and the weak dependence of resolution on landing energy allows the selection of an appropriate energy for a particular material or contrast mechanism. © 1996 American Vacuum Society
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68.37.-d Microscopy of surfaces, interfaces, and thin films
85.40.-e Microelectronics: LSI, VLSI, ULSI; integrated circuit fabrication technology
41.85.-p Beam optics

Electron‐beam microcolumns for lithography and related applications

T. H. P. Chang, M. G. R. Thomson, E. Kratschmer, H. S. Kim, M. L. Yu, K. Y. Lee, S. A. Rishton, B. W. Hussey, and S. Zolgharnain

J. Vac. Sci. Technol. B 14, 3774 (1996); http://dx.doi.org/10.1116/1.588666 (8 pages) | Cited 37 times

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Lithography with an array of miniaturized scanning electron‐beam columns presents one of the most promising high‐throughput possibilities for fabrication of devices with feature sizes less than 100 nm. With scanning electron beams no mask is required and the necessary resolution and alignment of overlay structures are realizable. With arrays of microcolumns, the lithography throughput of a single column can be multiplied. The approach can also be used for a number of lithography related applications such as metrology, inspection, testing, etc. We review the status of the microcolumn program and discuss opportunities and challenges of this approach to high‐throughput nanolithography and related applications. Special emphasis is given to lithography in the 100 nm regime. © 1996 American Vacuum Society
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07.77.Ka Charged-particle beam sources and detectors
81.07.-b Nanoscale materials and structures: fabrication and characterization
81.16.-c Methods of micro- and nanofabrication and processing
85.35.-p Nanoelectronic devices
85.45.Db Field emitters and arrays, cold electron emitters
41.85.-p Beam optics

Semiconductor on glass photocathodes as high‐performance sources for parallel electron beam lithography

J. E. Schneider, A. W. Baum, G. I. Winograd, R. F. W. Pease, M. McCord, W. E. Spicer, K. A. Costello, and V. W. Aebi

J. Vac. Sci. Technol. B 14, 3782 (1996); http://dx.doi.org/10.1116/1.588667 (5 pages) | Cited 16 times

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The throughput of electron beam lithography has historically been limited by electron–electron interactions that cause blurring at high currents. We present a system configuration for maskless parallel electron beam lithography using a new multiple primary source technology that, by employing widely spaced beams, significantly reduces this problem. The proposed source technology, a negative electron affinity (NEA) photocathode, allows us to generate an array of high brightness, low energy spread, independently modulated beams over a large area. In order to assess the effects of electron–electron interactions in this system, Monte Carlo simulations have been performed. The results of these calculations indicate that this configuration enjoys significant advantages over existing maskless systems. By restricting the area of emission for the individual beamlets to submicron dimensions, the blurring due to statistical electron–electron interactions can be significantly reduced for a given current at the wafer. For example, at 50 kV a total current of more than 2.5 μA can be obtained with less than 10 nm beam blurring. Preliminary experimental results suggest that high brightness emission can be maintained from a NEA photocathode in a demountable vacuum system. © 1996 American Vacuum Society
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85.60.Ha Photomultipliers; phototubes and photocathodes
81.07.-b Nanoscale materials and structures: fabrication and characterization
81.16.-c Methods of micro- and nanofabrication and processing
85.35.-p Nanoelectronic devices
41.85.-p Beam optics

Titanium nitride coated tungsten cold field emission sources

W. K. Lo, G. Parthasarathy, C. W. Lo, D. M. Tanenbaum, H. G. Craighead, and M. S. Isaacson

J. Vac. Sci. Technol. B 14, 3787 (1996); http://dx.doi.org/10.1116/1.588668 (5 pages) | Cited 2 times

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Titanium nitride (TiN) thin film coatings were studied by field emission microscopy and spectroscopy. Coated tungsten tips were found to be capable of emitting extremely high currents at low extraction voltages (∼1 mA at 900–1700 V). Current fluctuations for >400 μA total emission from a single tip were 7% rms, measured over ∼ 1 h. Electron energy distributions measured <0.4 eV (full width at half‐maximum). Since TiN thin films are commonly used in the microelectronics industry, TiN coatings have the potential for being a relatively simple and widely accessible method for improving the performance of cold field emission sources. © 1996 American Vacuum Society
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85.45.Db Field emitters and arrays, cold electron emitters
81.05.Je Ceramics and refractories (including borides, carbides, hydrides, nitrides, oxides, and silicides)

Experimental evaluation of a 20×20 mm footprint microcolumn

E. Kratschmer, H. S. Kim, M. G. R. Thomson, K. Y. Lee, S. A. Rishton, M. L. Yu, S. Zolgharnain, B. W. Hussey, and T. H. P. Chang

J. Vac. Sci. Technol. B 14, 3792 (1996); http://dx.doi.org/10.1116/1.588669 (5 pages) | Cited 14 times

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A miniaturized 1 kV electron beam column with a 20×20 mm square footprint for application in arrayed lithography was developed. The actual beam forming optics measured from the electron emitter to the last electrode in the beam focusing Einzel lens is only 3.5 mm in length. The electron source is a miniaturized, high brightness (120 μA/sr), low heating power (<1.5 W) Zr/O/W Schottky field emitter that provides a stable beam current with <1%/h current fluctuations. A custom designed, ultralow profile (0.8 mm high) annular microchannel plate (MCP) detector is fitted into the working distance, which can be varied between 1 and 5 mm, between the Einzel lens and the sample. The MCP provides a high gain, up to 3×104, detector for secondary and backscattered electron detection from solid samples. The beam is scanned over the sample using a prelens double octupole deflector for large field size, ≥100 μm, at low distortions and low deflection aberrations. Using a computer controlled digital pattern generator, patterns with less than 100 nm linewidth were exposed in polymethylmethacrylate resist and reactively ion etched into an underlying tungsten layer. © 1996 American Vacuum Society
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85.45.Db Field emitters and arrays, cold electron emitters
81.07.-b Nanoscale materials and structures: fabrication and characterization
81.16.-c Methods of micro- and nanofabrication and processing
85.35.-p Nanoelectronic devices

Energy distributions of field emitted electrons from carbide tips and tungsten tips with diamondlike carbon coatings

Ming L. Yu, Ho‐Seob Kim, Brian W. Hussey, T. H. Philip Chang, and William A. Mackie

J. Vac. Sci. Technol. B 14, 3797 (1996); http://dx.doi.org/10.1116/1.588670 (5 pages) | Cited 6 times

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We have measured the energy distributions of electrons field emitted from tungsten carbide, HfC〈100〉, and ZrC〈100〉 tips, and tungsten field emitters with diamondlike carbon coatings. Multiple‐peaked energy distributions were observed from instability induced emission sites on the carbide tips. Energy distributions of electrons field emitted from the diamondlike carbon coated tungsten tips were broader than those from metal tips. They also showed a shift towards lower energies with increases in the emission current. © 1996 American Vacuum Society
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79.70.+q Field emission, ionization, evaporation, and desorption
85.45.Db Field emitters and arrays, cold electron emitters

The electrostatic moving objective lens and optimized deflection systems for microcolumns

M. G. R. Thomson

J. Vac. Sci. Technol. B 14, 3802 (1996); http://dx.doi.org/10.1116/1.588671 (6 pages) | Cited 4 times

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The designs of the deflector and the final focusing lens in microcolumns are constrained by the extremely small physical size, and by the low energy of the beam. Because the overall column size and working distance are much smaller, the diameter of the deflection field that can be used without excessive increase in the probe diameter is also smaller. This field size can be improved by incorporating deflectors within the focusing lens. The theory of the ‘‘moving objective lens’’ can be extended to apply to electrostatic lenses and deflectors, and this can lead to greatly increased deflection field sizes when a vertical landing beam is required. The implementation of the moving objective lens requires a pre‐deflector, as well as an electrostatic deflecting field proportional to the second derivative of the axial potential inside the focusing lens. The curvature of field and third order astigmatism must also be dynamically corrected by additional fields, and these can be provided outside the lens. The in‐lens deflecting fields can be obtained by segmenting the lens electrodes so that they can provide both focusing and deflecting fields, and adding shields to shape the fields correctly. In the absence of dynamic correction, the relative magnitudes of the deflecting fields can be optimized to maximize the deflection field size both with and without vertical landing. In the cases that have been analyzed theoretically, the addition of in‐lens deflectors offers increased field size in comparison with optimized prelens double deflectors. The importance of increasing the field size will determine the degree of complexity of the configuration that must be used. © 1996 American Vacuum Society  
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41.85.-p Beam optics

Initial images with a partially micromachined scanning electron microscope

D. A. Crewe, M. M. Ruffin, and A. D. Feinerman

J. Vac. Sci. Technol. B 14, 3808 (1996); http://dx.doi.org/10.1116/1.588672 (5 pages) | Cited 4 times

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The focusing properties of a microfabricated silicon electrostatic electron lens have been tested in a machine tool fabricated assembly. Images of a 200 mesh gold transmission electron microscopy wire grid at a working distance of 4 mm are being obtained in transmission. The electron source is a zirconiated tungsten thermally assisted Schottky field emitter operating at 1800 K. The electron detector is a Faraday cup. The beam is scanned over the sample using parallel plate deflectors. The silicon lens is 1.64 mm long and consists of three silicon die separated by Pyrex optical fibers. Images of the grid at magnifications >10 000 × are being obtained. © 1996 American Vacuum Society
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07.78.+s Electron, positron, and ion microscopes; electron diffractometers
41.85.Ne Electrostatic lenses, septa

Multielectron beam blanking aperture array system SYNAPSE‐2000

Hiroshi Yasuda, Soichiro Arai, Jun‐ichi Kai, Yoshihisa Ooae, Tomohiko Abe, Shigeru Maruyama, and Takashi Kiuchi

J. Vac. Sci. Technol. B 14, 3813 (1996); http://dx.doi.org/10.1116/1.588673 (8 pages) | Cited 19 times

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A blanking aperture array (BAA) has 1024, 25‐μm‐square apertures and blanking electrodes on a 20‐μm‐thick Si membrane with a total aperture ratio of 1/6. These apertures are irradiated with an electron beam, and the electrons passing through the apertures are projected onto a wafer surface in a reduction ratio of about 1 to 200. A signal applied to each blanking electrode turns each beam on and off individually while raster‐scanning the electron flux with a deflector; thereby the desired pattern on the wafer can be drawn. The SYNAPSE‐2000 system uses 512 beams in the center of a BAA and exposes 18 8 in. wafers per hour using a single BAA column. Large convergence semiangle, refocusing, and multicolumns are effective measures to reduce Coulomb interaction and to accomplish higher throughput. This system provides a volume‐production microelectronic device manufacturing method. © 1996 American Vacuum Society
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81.07.-b Nanoscale materials and structures: fabrication and characterization
81.16.-c Methods of micro- and nanofabrication and processing
85.35.-p Nanoelectronic devices
41.85.-p Beam optics

Characterization and application of a low‐profile metal–semiconductor–metal detector for low energy backscattered electrons

G. D. Meier, H. S. Fresser, F. E. Prins, and D. P. Kern

J. Vac. Sci. Technol. B 14, 3821 (1996); http://dx.doi.org/10.1116/1.588674 (4 pages) | Cited 1 time

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A metal–semiconductor–metal (MSM) detector for low energy backscattered electrons has been developed and tested. The effects of detector symmetry, finger spacing, and detection area on signal to dark current ratio were studied in order to determine an optimized detector geometry. The detector assembly consisting of Ni‐GaAs MSM structures with low dark current densities was mounted in a scanning electron microscope on a special sample holder which enabled the test of the detector under conditions which can be expected in electron beam microcolumn applications. With this experimental setup, backscattered electron images of alignment marks of 50‐nm‐thick Au on a Si substrate were obtained. The signal to noise performance of the device has been compared to a commercial Everhart–Thornley detector. It is demonstrated that MSM detectors can be used as backscattered electron detectors in microcolumns. © 1996 American Vacuum Society
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07.77.Ka Charged-particle beam sources and detectors
68.37.-d Microscopy of surfaces, interfaces, and thin films
85.40.-e Microelectronics: LSI, VLSI, ULSI; integrated circuit fabrication technology

Preliminary results from a prototype projection electron‐beam stepper‐scattering with angular limitation projection electron beam lithography proof‐of‐concept system

L. R. Harriott, S. D. Berger, C. Biddick, M. I. Blakey, S. W. Bowler, K. Brady, R. M. Camarda, W. F. Connelly, A. Crorken, J. Custy, R. Dimarco, R. C. Farrow, J. A. Felker, L. Fetter, R. Freeman, et al.

J. Vac. Sci. Technol. B 14, 3825 (1996); http://dx.doi.org/10.1116/1.588675 (4 pages) | Cited 6 times

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We have designed and constructed a proof‐of‐concept projection electron beam lithography system based on the scattering with angular limitation projection electron beam lithography principle. In this system, a thin membrane mask is used in a 4:1 reduction projection system at 100 keV. Image contrast is formed by scattering in the mask and subsequent aperturing of the scattered electrons in the back focal plane of the projection system. We have employed a step‐and‐scan architecture which uses continuously moving mask and wafer stages to trace out the full pattern. The electron beam can thus be kept small (1×1 mm in our case) which greatly simplifies the design of the electron optical system. In addition, the membrane areas can be kept small in linear dimension in one direction, minimizing in‐plane pattern distortions. Our system will be constructed in two stages. In the first stage, the mask stage is static and the wafer stage operates in step‐and‐repeat mode. This initial version of the system allows for critical experiments regarding the mask, resist exposure, and electron optics to be performed. Later, a continuously moving stage system will be integrated. In this article, we report on the initial results from the static system. We have printed features as small as 80 nm and measured a 75 μm depth of focus for nominal 0.25 μm features in negative tone P(SI‐CMS) resist. © 1996 American Vacuum Society
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81.07.-b Nanoscale materials and structures: fabrication and characterization
81.16.-c Methods of micro- and nanofabrication and processing
85.35.-p Nanoelectronic devices

High resolution electron beam lithography using ZEP‐520 and KRS resists at low voltage

D. M. Tanenbaum, C. W. Lo, M. Isaacson, H. G. Craighead, M. J. Rooks, K. Y. Lee, W. S. Huang, and T. H. P. Chang

J. Vac. Sci. Technol. B 14, 3829 (1996); http://dx.doi.org/10.1116/1.588676 (5 pages) | Cited 11 times

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ZEP‐520 and KRS resist systems have been evaluated as candidates for use in low voltage electron beam lithography. ZEP‐520 is a conventional chain scission resist which has a positive tone for over two orders of magnitude in exposure dose. KRS is a chemically amplified resist which can be easily tone reversed with a sensitivity ∼8 μC/cm2 at 1 keV. Both resist systems are shown to have sensitivities ∼1 μC/cm2 for positive tone area exposures to 1 keV electrons. A decrease in contrast in 50 nm thick resist layers is seen when exposure voltage is lowered from 2 to 1 keV, indicating nonuniform energy deposition over the resist thickness. High resolution single pass lines have been transferred into both Si and SiO2 substrates at both low and high voltages in each resist system without using multilayer resist masks. The ZEP‐520 and KRS resists are shown to have resolutions of 50 and 60 nm, respectively, at 1 kV, within a factor of 2 of their high voltage resolutions under identical development conditions. A cusp shaped etch profile in Si allows high aspect ratio 20 nm wide trenches to be fabricated using these resists on bulk Si. Low voltage exposures have been used to pattern gratings with periods as small as 75 and 100 nm in ZEP‐520 and KRS, respectively. Low voltage exposures on SiO2 show no indications of pattern distortion due to charging or proximity effects. © 1996 American Vacuum Society
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81.07.-b Nanoscale materials and structures: fabrication and characterization
81.16.-c Methods of micro- and nanofabrication and processing
85.35.-p Nanoelectronic devices

Electron beam induced damage of silicon germanium

Douglas J. Paul, Joseph M. Ryan, Michael Pepper, Alec N. Broers, Terry E. Whall, Juan M. Fernández, and Bruce A. Joyce

J. Vac. Sci. Technol. B 14, 3834 (1996); http://dx.doi.org/10.1116/1.588677 (5 pages)

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The effect of electron beam irradiation damage to pseudomorphic modulation‐doped SiGe two dimensional hole gas (2DHG) was investigated. For typical poly(methylmethacrylate) type processes with electron energies of 40 keV and doses of 2 C/m2, the material properties were not significantly altered. For 300 keV irradiated electrons, the resistivity of the material increased as the dose of electrons was increased. For 100 keV and higher electron irradiation energies, the material became more resistive as the irradiation energy was increased. The 2DHG material became highly resistive at low temperatures and froze out at between 20 and 30 K. Annealing at 400 °C to 500 °C on 40 keV samples with 2 C/m2 doses could return the resistivity of the material at 300 K to the non‐irradiated value, but the large increase in resistivity for annealing temperatures above 500 °C suggests that the irradiation produced a significant number of defects which accelerated the relaxation of the strained Si0.87Ge0.13 channel by thermal processing. A number of narrow channel devices were fabricated in high mobility modulation‐doped Si/SiGe two dimensional electron gas material and investigated at 4.2 K using the electron beam irradiation to locally damage material into an insulting state. Fluctuations were found in a number of devices with patterned widths below 0.5 μm. © 1996 American Vacuum Society
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61.80.Fe Electron and positron radiation effects
61.82.Fk Semiconductors
73.40.Lq Other semiconductor-to-semiconductor contacts, p-n junctions, and heterojunctions

Theory of beam‐induced substrate heating

T. R. Groves

J. Vac. Sci. Technol. B 14, 3839 (1996); http://dx.doi.org/10.1116/1.588678 (6 pages) | Cited 7 times

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In all electron, ion, and photon beam systems, the beam unavoidably deposits heat in the target substrate. Resist sensitivity varies with temperature, causing unwanted linewidth variation. Substrate heating has been studied by finite element analysis solution of the heat equation. The four‐dimensional nature of the problem, three spatial dimensions together with time, leads to prohibitively long computation time. This limits our ability to obtain a physical understanding of the problem. Alternatively one can superimpose elementary analytic solutions, which have simple space‐time dependency, to construct cases of practical interest. The purpose of this article is to describe mathematically the basic building blocks of a general analytic theory of beam heating, with the aim of efficiently and quickly computing temperature rise due to beam‐induced substrate heating. Beam heating is most critical in writing of quartz reticles. Because of the poor thermal conductivity of quartz, the temperature rise at 10 μC/cm2, 30 A/cm2, and 50 kV is 45–85 °C, depending on pattern density. Heating is also significant for direct writing on silicon. At 10 μC/cm2, 50 A/cm2, and 100 kV, the temperature rise is 0.4–48 °C, depending on pattern density. Beam heating depends directly on the incident energy per unit area, which is given by the dose times the beam voltage. The dose is, in turn, proportional to the beam voltage, due to the increased transparency of resist layers at high voltage. Beam heating therefore increases with the square of the beam voltage. These trends suggest fast resist and low voltage as the best means of containing the effect. The latter conflicts with the need for high resolution, which requires high beam voltage. This suggests an optimum beam voltage for a given set of conditions. © 1996 American Vacuum Society  
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44.40.+a Thermal radiation
85.40.Hp Lithography, masks and pattern transfer

Electron scattering by electron‐beam mask with tapered aperture in cell projection lithography

Hiroshi Yamashita, Takahiro Ema, Katsuyuki Itoh, Hiroshi Nozue, and Eiichi Nomura

J. Vac. Sci. Technol. B 14, 3845 (1996); http://dx.doi.org/10.1116/1.588679 (5 pages) | Cited 6 times

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Electron scattering by stencil‐type masks (electron‐beam mask) of various thicknesses in the cell projection lithography has been studied by Monte Carlo simulation. We also prepared 20‐μm‐thick masks with various taper angles so that we could compare the exposed resist patterns. The simulation study revealed that 30% of the irradiated electrons pass through a 20‐μm‐thick mask with a 5 μm lines‐and‐spaces (L/S) aperture pattern, which corresponds to a 0.2 μm L/S pattern on the wafer. This result has shown that a stencil‐mask forms an image on the wafer by scattering contrast even when its thickness is greater than the electron penetration depth. The simulation study also showed that 70% of incident electrons pass through a 10‐μm‐thick mask. The results have also indicated that more attention must be paid to mask profile, and that a forward tapered profile (in which the electron transmittance has a peak of 85%–90% at the mask taper edge) should be avoided because it may affect a beam profile. When the taper angle is 90° or more, on the other hand, the electron transmittance shows no peak at the mask taper edge and the energy distribution become wider. These transmitted electrons therefore cannot fully contribute to imaging. These scattered electrons, however, can be completely intercepted by an appropriate limiting aperture in order to maintain high contrast. A thinner mask is thus preferable for practical applications. © 1996 American Vacuum Society
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81.07.-b Nanoscale materials and structures: fabrication and characterization
81.16.-c Methods of micro- and nanofabrication and processing
85.35.-p Nanoelectronic devices
41.85.-p Beam optics

Modified mask methods for pattern accuracy enhancement in electron beam lithography

Yasunari Sohda, Yasuhiro Someda, Yoshinori Nakayama, and Norio Saitou

J. Vac. Sci. Technol. B 14, 3850 (1996); http://dx.doi.org/10.1116/1.588680 (5 pages) | Cited 1 time

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In projection‐type lithography, delineated resist patterns differ from original mask shapes. In this article, aperture modification methods are investigated to enhance the pattern accuracy of electron beam cell projection lithography. The modified aperture is easily fabricated by decreasing the mask thickness. Although electrons penetrate the mask, enough high scattering contrast can be obtained. In dot delineation, star‐shape apertures make better square dots near the resolution limit. In line‐and‐space delineation, dividing the pattern into small patterns of lower resolution reduces the electron current. This decreases Coulomb effects. In addition, Monte Carlo simulation results also confirm these results. As a result, these methods are expected to be important in the application of projection‐type charged particle lithography. © 1996 American Vacuum Society
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81.07.-b Nanoscale materials and structures: fabrication and characterization
81.16.-c Methods of micro- and nanofabrication and processing
85.35.-p Nanoelectronic devices
85.40.Hp Lithography, masks and pattern transfer

One step electron‐beam lithography for multipurpose diffractive optical elements with 200 nm resolution

E. Di Fabrizio, L. Grella, M. Baciocchi, M. Gentili, D. Peschiaroli, L. Mastrogiacomo, and R. Maggiora

J. Vac. Sci. Technol. B 14, 3855 (1996); http://dx.doi.org/10.1116/1.588681 (5 pages) | Cited 2 times

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Electron‐beam lithography allows three‐dimensional shaping of polymethylmethacrylate (PMMA) structures with minimum feature size of 200 nm for diffractive optical element fabrication. The key step in fabrication of continuous PMMA profile is the resist process: contrast curve measurement at 40 and 50 kV as well as substrate thickness influence studies (bulk substrates and thin membrane) on resist slope profile were also carried out to determine the best process conditions. Examples of fabricated three‐dimensional resist structures include: eight‐level blazed PMMA profiles for x‐ray focusing elements and a beam shaper for applications at a wavelength of λ=0.633 μm. The intrinsic flexibility and accuracy of the developed process, by which the wide range of diffractive optical elements were fabricated, is a direct consequence of the specifically developed and implemented three‐dimensional proximity correction algorithm. A detailed description of such an algorithm will also be given. © 1996 American Vacuum Society
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42.82.Cr Fabrication techniques; lithography, pattern transfer

Three‐dimensional electron‐beam lithography using an all‐dry resist process

S. Babin and H. W. P. Koops

J. Vac. Sci. Technol. B 14, 3860 (1996); http://dx.doi.org/10.1116/1.588682 (4 pages) | Cited 3 times

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Micromechanics, microelectronics, and micro‐optics favor structurization of three‐dimensional surfaces. Dry resist processes present fewer hazards to personnel and environment than conventional wet resist processes. The negative tone dry resist octavinylsilsesquioxan is investigated in its applicability to three‐dimensional structurization of surfaces having a high relief. This resist, also known as V‐T8, enables coating of arbitrary substrates by evaporation in high vacuum. After exposure it is developed in high vacuum by a dry thermal treatment at 200 °C. The resist is characterized with electron exposures with an energy ranging from 5 to 50 keV. Its sensitivity is 40 μC/cm2 at 20 keV. The resist exhibits high dry etch resistivity. Its contrast is increased from 0.7 to 2.1 using plasma etching in CF4 as a postdevelopment step. The dry resist is employed to structure 250 μm deep steep surface steps and to modify fabricated three‐dimensional structures with dot gratings for metrology applications. © 1996 American Vacuum Society
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81.07.-b Nanoscale materials and structures: fabrication and characterization
81.16.-c Methods of micro- and nanofabrication and processing
85.35.-p Nanoelectronic devices
85.40.Hp Lithography, masks and pattern transfer
06.20.-f Metrology
42.82.Cr Fabrication techniques; lithography, pattern transfer

Modeling of electron elastic and inelastic scattering

C. R. K. Marrian, F. K. Perkins, D. Park, E. A. Dobisz, M. C. Peckerar, K.‐W. Rhee, and R. Bass

J. Vac. Sci. Technol. B 14, 3864 (1996); http://dx.doi.org/10.1116/1.588683 (6 pages) | Cited 11 times

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The role of the form of the elastic and inelastic cross section in Monte Carlo simulations of electron–solid scattering has been studied to understand the processes whereby energy is deposited by electrons as they traverse thin films. Specifically we are interested in these phenomena as they relate to proximity effects in electron‐beam lithography and the detection of electrons by a Schottky diode with a patterned absorber overlayer. Lithographic point and line spread functions have been measured in three resist materials. We show that the inclusion of discrete inelastic scattering events whereby fast secondaries are generated is essential for matching simulation and experiment. The secondaries are crucial in determining the shape of the spread functions in the 0.1–1 μm regime and must be included to model proximity effects. Further, the fitting of line spread function simulations to experiment allows the accurate prediction of dot spread functions and applied dose thresholds as well as three dimensional resist profiles. The form of the elastic cross section is important in determining the energy loss in, and transmission through, thin metallic films. For electron energies where the film transmission is low, the Mott cross section provides a more accurate simulation than the screened Rutherford cross section.
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79.20.Ap Theory of impact phenomena; numerical simulation
81.07.-b Nanoscale materials and structures: fabrication and characterization
81.16.-c Methods of micro- and nanofabrication and processing
85.35.-p Nanoelectronic devices
07.77.Ka Charged-particle beam sources and detectors

Studies on correction accuracy of proximity effect for the pattern area density method in electron beam direct writing

Takashi Kasuga, Morikazu Konishi, Tatsuji Oda, and Shigeru Moriya

J. Vac. Sci. Technol. B 14, 3870 (1996); http://dx.doi.org/10.1116/1.588684 (4 pages) | Cited 2 times

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This article describes the correction accuracy of the pattern area density method for 0.2 μm rule patterning, carrying out simulation and experiments. To enhance the μm correction accuracy at the boundary zone of the different pattern densities, a novel technique using the gradient vectors of the pattern density is proposed and its capability for sub‐0.15‐μm pattern fabrication is demonstrated. © 1996 American Vacuum Society
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81.07.-b Nanoscale materials and structures: fabrication and characterization
81.16.-c Methods of micro- and nanofabrication and processing
85.35.-p Nanoelectronic devices

Region‐wise proximity effect correction for heterogeneous substrates in electron‐beam lithography: Shape modification

Soo‐Young Lee and Bin Liu

J. Vac. Sci. Technol. B 14, 3874 (1996); http://dx.doi.org/10.1116/1.588685 (6 pages) | Cited 2 times

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PYRAMID, a hierarchical rule‐based scheme for proximity effect correction in electron‐beam lithography, has been demonstrated to enable rapid correction of circuit patterns exposed on homogeneous substrates with minimum feature size of 0.1 μm. The current version of PYRAMID modifies the shape of circuit primitives. So far, it has been limited to homogeneous substrates only. This article describes an extension of our pattern shape modification scheme for heterogeneous substrates. The space‐varying nature of a heterogeneous substrate makes exposure estimation and proximity correction more involved than in case of a homogeneous substrate. As a result, the schemes developed for homogeneous substrates cannot be used directly used to deal with heterogeneous substrates. A simple but effective approach has been implemented in an effort to allow our shape modification scheme to correct patterns on heterogeneous substrates. The principal idea is to correct a circuit region‐wise where each region is homogeneous. A transition zone is defined between two adjacent regions of a substrate and additional adjustment is done on primitives within transition zones to get smooth transition between regions. A fuzzy factor, adjustment factor, is introduced to make the convergence of correction faster. This article describes the region‐wise proximity effect correction scheme proposed for heterogeneous substrates and presents preliminary simulation results indicating successful correction. © 1996 American Vacuum Society
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81.07.-b Nanoscale materials and structures: fabrication and characterization
81.16.-c Methods of micro- and nanofabrication and processing
85.35.-p Nanoelectronic devices

Feature contrast in dose‐equalization schemes used for electron‐beam proximity control

Martin Peckerar, Christie Marrian, and F. Keith Perkins

J. Vac. Sci. Technol. B 14, 3880 (1996); http://dx.doi.org/10.1116/1.588686 (7 pages) | Cited 2 times

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Dose equalization by the GHOST technique fails to provide homogeneous contrast when the two‐Gaussian model does not adequately portray the beam‐energy dose distribution. This leads to an undesirable pattern dependence to the contrast obtained. The degree to which this breakdown occurs is shown in computer simulation. The most severe breakdown occurs in enclosed (annular) structures where the effect of ‘‘higher order’’ Gaussian deposition peaks are concentrated. Unanticipated background fluctuations of about 10% of the nominal exposure dose are obtained. As a result of this study, test structures are proposed which can extend the utility of dose equalization.
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81.07.-b Nanoscale materials and structures: fabrication and characterization
81.16.-c Methods of micro- and nanofabrication and processing
85.35.-p Nanoelectronic devices
41.85.-p Beam optics

Electron‐beam‐induced deposition of copper compound with low resistivity

Yukinori Ochiai, Jun‐ichi Fujita, and Shinji Matsui

J. Vac. Sci. Technol. B 14, 3887 (1996); http://dx.doi.org/10.1116/1.588687 (5 pages) | Cited 13 times

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Electron‐beam‐induced deposition of copper was performed using hexafluoro‐acetyoacetonate copper vinyl‐trimethy‐silane (HFA⋅Cu⋅VTMS) gas. The deposition was demonstrated by using a 30 keV environmental scanning electron microscope and a 50 keV electron beam lithography system in an atmosphere of precursor gas: HFA⋅Cu⋅VTMS. The deposition rate, composition, and electrical resistivity of the deposited material were measured. The deposition rate was 6.6 nm/(C/cm2) at a pressure of 160 Pa. The resistivity was 3.6 μΩ cm at room temperature deposited at a pressure of 6.7×10−4 Pa. The resistivity is the lowest so far reported. © 1996 American Vacuum Society
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81.15.Jj Ion and electron beam-assisted deposition; ion plating
85.40.Ls Metallization, contacts, interconnects; device isolation
73.61.At Metal and metallic alloys

Divot defect repair on a deep ultraviolet SiNx halftone mask

H. Nakamura, H. Komano, K. Sugihara, T. Koike, and I. Higashikawa

J. Vac. Sci. Technol. B 14, 3892 (1996); http://dx.doi.org/10.1116/1.588688 (4 pages)

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Divot defect repair on deep ultraviolet SiNx halftone masks in the case of 0.275 μm (on a wafer) line and space patterns was investigated experimentally. The problem regarding imaging is the difficulty of area recognition due to low contrast of halftone masks without the focused ion beam (FIB) irradiation damage. It is overcome by means of limiting the total FIB dose for imaging and by means of image processing with an image filter. Opaque carbon (C) film deposition on a divot defect was found to improve the performance of a defective area. The degree of the improvement was not perfect but allowable for practical use. It was also found that there were other factors that make the performance of the repaired area worse than the nondefective area, except for missing of the phase shift effect. © 1996 American Vacuum Society
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85.40.Hp Lithography, masks and pattern transfer

A proximity ion beam lithography process for high density nanostructures

John C. Wolfe, Sandeep V. Pendharkar, Paul Ruchhoeft, Sudipto Sen, Mark D. Morgan, W. E. Horne, R. C. Tiberio, and John N. Randall

J. Vac. Sci. Technol. B 14, 3896 (1996); http://dx.doi.org/10.1116/1.588689 (4 pages) | Cited 12 times

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Image contrast in proximity ion beam lithography is limited by scattered ions which enter the opaque regions of the mask and exit through the sidewalls of the mask windows. The scattering angles are widely distributed resulting in a ‘‘proximity effect’’ whose range is on the order of the mask‐to‐wafer gap. This problem becomes more severe with increasing pattern density and sets the resolution limit for high density patterns such as interdigital transducers. The only way to counteract this effect is to limit the ion range to a fraction of the mask thickness so that the scattered ions can be recaptured by adjacent sidewalls. This article explores the dependence of image contrast on resolution, pattern density, and beam energy in proximity ion beam lithography. Patterns with feature sizes in the range from 20 to 50 nm and 0.4 μm pitch have been printed with a linewidth change of only 3 nm for a 10% change in dose. © 1996 American Vacuum Society
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81.07.-b Nanoscale materials and structures: fabrication and characterization
81.16.-c Methods of micro- and nanofabrication and processing
85.35.-p Nanoelectronic devices

Stencil mask temperature measurement and control during ion irradiation

James Riordon, Lidia Didenko, and John Melngailis

J. Vac. Sci. Technol. B 14, 3900 (1996); http://dx.doi.org/10.1116/1.588690 (3 pages) | Cited 6 times

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In ion projection lithography a stencil mask consisting of a thin membrane of silicon is irradiated by a broad, uniform beam of ions. The resulting image is demagnified and projected on a resist‐covered substrate. Energy deposited in the stencil mask by the ion beam can lead to temperature distributions resulting in nonuniform stress and unacceptably large feature displacement. Numerical simulations have shown that the presence of a cooled cylinder near the mask during irradiation is an effective means of temperature control. We have experimentally determined the temperature distribution in a thin glass disk which is chosen to be thermally equivalent to a Si stencil mask. We have found temperature distributions that approximately agree with the numerical computations, and have confirmed the effectiveness of a cooled cylinder in reducing the temperature variation over the disk. For example, a graphite coated (ϵ=0.85) glass disk, when irradiated by a 3.3 mW/cm2 ion beam, develops temperature differences of more than 5 °C between the center and edge of the disk. Introduction of a cylinder cooled 35 °C below room temperature reduces the temperature difference to 1.2°C, resulting in thermally induced feature displacement of less than 10 nm. © 1996 American Vacuum Society
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81.07.-b Nanoscale materials and structures: fabrication and characterization
81.16.-c Methods of micro- and nanofabrication and processing
85.35.-p Nanoelectronic devices
07.20.-n Thermal instruments and apparatus

Application of optical filters fabricated by masked ion beam lithography

M. D. Morgan, W. E. Horne, V. Sundaram, J. C. Wolfe, S. V. Pendharkar, and R. Tiberio

J. Vac. Sci. Technol. B 14, 3903 (1996); http://dx.doi.org/10.1116/1.588691 (4 pages) | Cited 21 times

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Masked ion beam lithography (MIBL) was employed to fabricate optical filters as a critical component of an energy conversion system which utilizes semiconductor photovoltaics. This article will describe the operation and novel application of these devices and the MIBL pilot production line being facilitized. The conversion concept, thermophotovoltaics (TPV), when coupled with these MIBL produced bandpass filters, is capable of converting heat to electrical power with >20% conversion efficiency. The EDTEK TPV filter is based on a high density array of slotted antenna elements patterned into a single layer of thin gold film. © 1996 American Vacuum Society
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84.60.Rb Thermoelectric, electrogasdynamic and other direct energy conversion
42.79.Ci Filters, zone plates, and polarizers
42.82.Cr Fabrication techniques; lithography, pattern transfer

High‐brightness ion source for ion projection lithography

S. K. Guharay, W. Wang, V. G. Dudnikov, M. Reiser, J. Orloff, and J. Melngailis

J. Vac. Sci. Technol. B 14, 3907 (1996); http://dx.doi.org/10.1116/1.588692 (4 pages) | Cited 6 times

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A Penning‐type surface plasma source has been developed with the goal to achieve the beam requirements for ion projection lithography (IPL). The present source, with simple, forced air cooling runs up to a duty factor of 1% (pulse length of 1 ms and repetition rate of 10 Hz); a cw Penning source is being planned for IPL. H− emission current density of more than 2 A/cm2 has been obtained with negligibly low noise. The perpendicular temperature is about 0.6 eV for emission current density of about 1 A/cm2—this yields normalized beam brightness of more than 1012 A/(mrad)2. The energy spread full width at half‐maximum (FWHM) for a 5 kV beam with angular current density of 33 mA/sr is about 3.3 eV (close to instrumental resolution). The energy spread increases with beam intensity. In preliminary experiments on positive ion extraction, noiseless H+ beams with emission current density of about 150 mA/cm2 have been achieved. © 1996 American Vacuum Society
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07.77.Ka Charged-particle beam sources and detectors
52.77.Bn Etching and cleaning
52.77.Dq Plasma-based ion implantation and deposition
81.07.-b Nanoscale materials and structures: fabrication and characterization
81.16.-c Methods of micro- and nanofabrication and processing
85.35.-p Nanoelectronic devices

Energy spread in liquid metal ion sources at low currents

J. C. Beckman, T. H. P. Chang, A. Wagner, and R. F. W. Pease

J. Vac. Sci. Technol. B 14, 3911 (1996); http://dx.doi.org/10.1116/1.588693 (5 pages) | Cited 11 times

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In previous work, attempts to lower the energy spread in liquid metal ion sources (LMIS) by resorting to low current operation have rarely been successful. We have found the energy spread of gallium LMIS to be ≊4.5 eV full width at half‐maximum for emission currents from 0.45 μA down to 13 nA. Our experimental results suggest that this occurs because emission <0.45 μA is formed by pulses of height 0.45 μA and an appropriate duty cycle. Several observations support this hypothesis: (1) For sources that had a minimum current, below which they could not be made to operate, the minimum current was always 0.45 μA at room temperature, regardless of apex radius or surface roughness. (2) Emission ≤0.45 μA from blunt sources at room temperature always showed pulses of height 0.45 μA, and a clear transition to dc at 0.45 μA. The pulse height and transition current rose with source temperature. (3) Emission ≤0.45 μA from sharp sources always showed pulsing from the lowest currents up to the current at which the amplifier bandwidth of 1 MHz was exceeded. (4) The angular intensity of emission on axis was in constant proportion to emission current up to 0.45 μA, and in declining proportion at higher currents. © 1996 American Vacuum Society
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07.77.Ka Charged-particle beam sources and detectors

Sub‐100 nm focused ion beam lithography using ladder silicone spin‐on glass

Kohei Suzuki, Motoji Yamashita, Nobuyuki Kawakami, Akihisa Yoshikawa, and Akimitsu Nakaue

J. Vac. Sci. Technol. B 14, 3916 (1996); http://dx.doi.org/10.1116/1.588694 (4 pages) | Cited 4 times

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Focused ion beam lithography using ladder silicone spin‐on glass (LS‐SOG) as a negative‐tone resist was investigated. The use of 200 keV Be2+ ion and tetramethylammoniumhydroxide developer resulted an in 80‐nm‐width line pattern with a vertical profile. The pattern collapse during the development was avoided by the use of fluorocarbon‐based solvent. The development mechanism of LS‐SOG was investigated by using nuclear magnetic resonance and gel permeation chromatography analysis. © 1996 American Vacuum Society
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81.07.-b Nanoscale materials and structures: fabrication and characterization
81.16.-c Methods of micro- and nanofabrication and processing
85.35.-p Nanoelectronic devices

Tetramethoxysilane as a precursor for focused ion beam and electron beam assisted insulator (SiOx) deposition

S. Lipp, L. Frey, C. Lehrer, B. Frank, E. Demm, S. Pauthner, and H. Ryssel

J. Vac. Sci. Technol. B 14, 3920 (1996); http://dx.doi.org/10.1116/1.588695 (4 pages) | Cited 20 times

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Focused ion beams are intensively used for device modification by local material removal and ion beam induced metal deposition. With shrinking dimensions on modern multilayer devices, the need for ion beam induced insulator deposition is increasing. In this article, tetramethoxysilane as a precursor for ion beam induced deposition has been investigated. The influence of beam parameters dwell time and loop time on the material deposition rate will be discussed and compared to model calculations. For optimized scanning conditions, a maximum deposition rate of 0.33 μm3/nC was found. Insulating films were also deposited using an electron beam. The chemical composition and electrical properties of these films were compared with the films deposited by the ion beam. For electron beam deposition, the resistivity of the deposited films was 1×106 Ω cm which is two orders of magnitude higher than for ion beam deposited film. © 1996 American Vacuum Society
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85.40.Sz Deposition technology
81.15.Jj Ion and electron beam-assisted deposition; ion plating
81.05.Je Ceramics and refractories (including borides, carbides, hydrides, nitrides, oxides, and silicides)

HPR 506 photoresist used as a positive tone ion resist

W. H. Bruenger, L.‐M. Buchmann, M. Torkler, and Stephan Sinkwitz

J. Vac. Sci. Technol. B 14, 3924 (1996); http://dx.doi.org/10.1116/1.588696 (4 pages) | Cited 2 times

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A positive tone photo resist HPR 506 (Olin Microelectronic Materials) has been investigated for its performance under ion exposure. Experiments have been conducted with light ions (H+ and He+) in the ion projector IPLM 02 (IMS; Vienna) at an energy of 75 keV. The resist resolution proved to be ∼180 nm which is not as good as the projector resolution of below 80 nm as demonstrated with Polymethylmetacrylate. The sensitivity of HPR 506 resist in positive tone amounts to 1.2×1013 H+ ions/cm2 and 6×1012 He+ ions/cm2 with contrast numbers of 3.3 and 3.2, respectively. The dose gap between positive and negative mode is sufficiently high (factor of 3) to guarantee a good process stability. The exposure latitude for He+ exposure has a value of 15 nm. The sensitivity does not oscillate with resist thickness like in optical lithography. These performance data confirm that HPR 506 resist can be used for mix and match exposure in ion projectors and i‐line steppers. © 1996 American Vacuum Society
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81.07.-b Nanoscale materials and structures: fabrication and characterization
81.16.-c Methods of micro- and nanofabrication and processing
85.35.-p Nanoelectronic devices

Development of focused ion‐beam machining techniques for Permalloy structures

D. M. Thaus, T. J. Stark, D. P. Griffis, and P. E. Russell

J. Vac. Sci. Technol. B 14, 3928 (1996); http://dx.doi.org/10.1116/1.588697 (5 pages) | Cited 2 times

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The ability to micromachine Permalloy (Ni–Fe alloys) has become important for the development of magnetically actuated microelectromechanical systems devices and for the development of computer disk read‐write heads. In this work, focused ion‐beam micromachining (FIBM) of Permalloy using Ga+ and with I and Cl chemical enhancement (CE) has been investigated. Micromachining of Permalloy with Ga+ resulted in a material removal rate of only 0.10 μm3/nC and the topography of the micromachined cuts increased in roughness with increased depth reaching micrometer dimensions for the deeper cuts. In comparison to Ga+ only FIBM, I2 CE‐FIBM increased the material removal rate by a factor of 8–30 (0.83–3.0 μm3/nC) for bulk and edge micromachining, respectively, with much reduced micromachining induced topography. Procedures were developed to prevent the formation of I2 CE‐FIBM related postmicromachining reaction products. Chlorine CE‐FIBM, using C2Cl4, CCl4, and C2HCl5, as noncorrosive chlorine sources, provided a Permalloy material removal rate enhancement versus Ga+‐only FIBM of approximately a factor of 2 and ≊100 Å topography. © 1996 American Vacuum Society
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81.65.Cf Surface cleaning, etching, patterning
07.10.Cm Micromechanical devices and systems

Use of very low energy in situ focused ion beams for three‐dimensional dopant patterning during molecular beam epitaxial growth

P. J. A. Sazio, J. H. Thompson, G. A. C. Jones, E. H. Linfield, D. A. Ritchie, M. Houlton, and G. W. Smith

J. Vac. Sci. Technol. B 14, 3933 (1996); http://dx.doi.org/10.1116/1.588698 (5 pages) | Cited 6 times

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In situ focused ion beam doping during molecular beam epitaxial growth allows the fabrication of novel semiconductor structures and devices otherwise unobtainable using standard lithographic, planar processing. In this technique, the thermal dopant effusion cell used in conventional GaAs molecular beam epitaxy (MBE) is replaced by a scanning Si source focused ion beam column. It is therefore possible to write dopant patterns directly into the semiconductor wafer during crystal growth. Precise control over the elemental composition in the growth (z) direction afforded by MBE is thus combined with the high spatial resolution of the focused dopant ion beam in the lateral (xy) plane. High quality bulk doped GaAs was grown with a Si ion landing energy of 100 eV using this technique, attaining a peak mobility of 3400 cm2 V−1 s−1 (185 K) at a carrier concentration of 1.1 ×1017 cm−3. The dependence of free carrier concentration in GaAs as a function of incident ion energy, and the fabrication of GaAs/AlGaAs modulation doped heterostructures will be discussed. © 1996 American Vacuum Society
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85.40.Ry Impurity doping, diffusion and ion implantation technology
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
73.40.Kp III-V semiconductor-to-semiconductor contacts, p-n junctions, and heterojunctions

Fabrication of laterally selected Si doped layer in GaAs using a low‐energy focused ion beam/molecular beam epitaxy combined system

Junichi Yanagisawa, Hiromasa Nakayama, Fujio Wakaya, Yoshihiko Yuba, and Kenji Gamo

J. Vac. Sci. Technol. B 14, 3938 (1996); http://dx.doi.org/10.1116/1.588699 (4 pages) | Cited 3 times

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A buried conductive layer in GaAs was formed using a low‐energy focused ion beam (FIB) and molecular beam epitaxy (MBE) combined system. The sheet carrier density of the structure was measured as a function of ion dose ranging from 2×1012 to 5×1013 cm−2 and postrapid thermal annealing time at 800 °C. It was shown that implanted Si ions at an ion energy of 200 eV and an ion dose of 2×1012 to 1×1013 cm−2 can be fully activated by choosing an optimum annealing condition. Present results suggest the possibility of fabricating a high quality two‐dimensional electron gas (2DEG) layer in the laterally selected area in GaAs and GaAs/AlGaAs systems. © 1996 American Vacuum Society
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85.40.Ry Impurity doping, diffusion and ion implantation technology
73.40.Kp III-V semiconductor-to-semiconductor contacts, p-n junctions, and heterojunctions
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy

Focused ion beam biased repair of conventional and phase shift masks

Zheng Cui, Philip D. Prewett, and John G. Watson

J. Vac. Sci. Technol. B 14, 3942 (1996); http://dx.doi.org/10.1116/1.588700 (5 pages) | Cited 4 times

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A novel technique, focused ion beam biased sputtering, is used to repair opaque defects in both conventional binary intensity masks and phase shift masks without leaving post‐repair residual defects caused by gallium ion staining. The biased repair involves sputter removal of a defect to an area larger than its original size. The reduction of light transmission due to gallium stain is then effectively compensated by the enlarged repair. Results are presented on the repair of both conventional and attenuated phase shift masks using the biased method in comparison with conventional (no bias) repair. Optimum bias is determined by computer simulation of optical imaging and resist development. Unlike other anti‐staining techniques which require additional equipment and process steps, the biased repair method involves only a change of sputtering strategy and can be implemented in any existing focused ion beam mask repair tools. © 1996 American Vacuum Society
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85.40.Hp Lithography, masks and pattern transfer

Development of ion sources for ion projection lithography

Y. Lee, R. A. Gough, W. B. Kunkel, K. N. Leung, L. T. Perkins, D. S. Pickard, L. Sun, J. Vujic, and M. D. Williams

J. Vac. Sci. Technol. B 14, 3947 (1996); http://dx.doi.org/10.1116/1.588701 (4 pages)

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Multicusp ion sources are capable of generating ion beams with low axial energy spread as required by the ion projection lithography (IPL). Longitudinal ion energy spread has been studied in two different types of plasma discharge: the filament discharge ion source characterized by its low axial energy spread, and the rf‐driven ion source characterized by its long source lifetime. For He+ ions, longitudinal ion energy spreads of 1–2 eV were measured for a filament discharge multicusp ion source which is within the IPL source requirements. Ion beams with larger axial energy spread (∼7 eV) were observed in the rf‐driven source. A double‐chamber ion source has been designed which combines the advantages of low axial energy spread of the filament discharge ion source with the long lifetime of the rf‐driven source. The energy spread of the double chamber source is approximately 2 eV. © 1996 American Vacuum Society
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07.77.Ka Charged-particle beam sources and detectors
81.07.-b Nanoscale materials and structures: fabrication and characterization
81.16.-c Methods of micro- and nanofabrication and processing
85.35.-p Nanoelectronic devices

Nanofabrication technology by gas cluster ion beams

Jiro Matsuo, Noriaki Toyoda, and Isao Yamada

J. Vac. Sci. Technol. B 14, 3951 (1996); http://dx.doi.org/10.1116/1.588621 (4 pages) | Cited 1 time

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Reactive gas cluster ion beam etching, which has many advantages for plasma etching, is proposed. The anisotropic etching of Si is realized with a reactive cluster ion beam. Various kinds of cluster ion beams, from gaseous materials such as Ar, O2, N2, SF6, N2O, and CO2, can be generated by expanding them through a Laval nozzle into a high vacuum. The etching rate of W and Si bombarded by SF6 cluster ions was quite high as the result of reactive sputtering. Surprisingly, the sputtering yield reaches 2200 Si atoms/ion, when Si is sputtered by SF6 cluster ions, with an average size of 2000. This yield is two orders of magnitude larger than the value reported for reactive sputtering using monomer ions. 2.2 μm of Si was etched by SF6 cluster ions, with an energy of 25 keV, at a dose of 5×1015 ions/cm2. Due to the low ion dose, the charge induced damage is reduced. The selectivity of Si to SiO2 increases with decreasing incident energy of cluster ions and finally infinite selectivity can be achieved at 5 keV. This energy corresponds to 2.5 eV per SF6 molecule, when the cluster size is 2000. A 0.5 μm hole was etched by a SF6 ion cluster ion beam and anisotropic etching was demonstrated. © 1996 American Vacuum Society
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81.07.-b Nanoscale materials and structures: fabrication and characterization
81.16.-c Methods of micro- and nanofabrication and processing
85.35.-p Nanoelectronic devices
81.65.Cf Surface cleaning, etching, patterning

Atmospheric metrology using the air turbulence compensated interferometer

Philip D. Henshaw and Donald P. DeGloria

J. Vac. Sci. Technol. B 14, 3955 (1996); http://dx.doi.org/10.1116/1.588622 (5 pages) | Cited 1 time

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Air turbulence affects the performance of the helium‐neon interferometer used to control the wafer stage of stepper or step and scan lithography systems. In this article we describe the principles of operation and performance characterization of an air turbulence compensated interferometer (ATCI) designed to address these problems. Collinear combination of a two‐wavelength compensation system using second harmonic interferometry with the existing HeNe interferometer used for length measurement provides a highly accurate system with real‐time compensation for air turbulence. We characterized the performance of the ATCI system by measuring compensation performance in the presence of four different atmospheres. © 1996 American Vacuum Society
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85.40.-e Microelectronics: LSI, VLSI, ULSI; integrated circuit fabrication technology
07.60.Ly Interferometers

Absolute distance measurement interferometry for alignment systems for advanced lithography tools

Thomas J. Dunn, Teik‐Meng Lee, and Kanti Jain

J. Vac. Sci. Technol. B 14, 3960 (1996); http://dx.doi.org/10.1116/1.588623 (4 pages) | Cited 3 times

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We describe a novel interferometer which enables the absolute measurement of distances between two objects. This system was developed for integration into an alignment system for an x‐ray lithography tool but also has many other potential applications. The absolute distance measuring interferometer system consists of two frequency‐stabilized lasers which probe the resonances of a high‐finesse, Fabry–Pérot (FP) interferometer. The two lasers are independently locked to adjacent resonant peaks of the FP cavity transmission spectrum. The frequency difference between two adjacent longitudinal modes of the cavity is known as the free spectral range (FSR) and is inversely related to the optical path length of the cavity. The FSR of the cavity is measured by analyzing the frequency content of the mixed optical signal from both lasers with a spectrum analyzer. This approach provides a real‐time measurement of the FSR and directly measures the absolute optical path between the two cavity mirrors. We have successfully constructed a working prototype system and measured the FSR of an 8.3‐cm‐long, high‐finesse, optical cavity to within 5 Hz, which translates to a resolution of 2.3 Å. We present an overview of the program, the latest experimental results, and the status of its application to an x‐ray stepper. © 1996 American Vacuum Society
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07.60.Ly Interferometers
81.07.-b Nanoscale materials and structures: fabrication and characterization
81.16.-c Methods of micro- and nanofabrication and processing
85.35.-p Nanoelectronic devices

Initial results from an extreme ultraviolet interferometer operating with a compact laser plasma source

A. K. Ray‐Chaudhuri, K. D. Krenz, R. P. Nissen, S. J. Haney, C. H. Fields, W. C. Sweatt, and A. A. MacDowell

J. Vac. Sci. Technol. B 14, 3964 (1996); http://dx.doi.org/10.1116/1.588624 (5 pages) | Cited 3 times

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When characterizing an extreme ultraviolet (EUV) lithographic optical system, visible light interferometry is limited to measuring wave front aberration caused by surface figure error while failing to measure wave front errors induced by the multilayer coatings. This necessitates the development of interferometric techniques at an EUV camera’s operational wavelength (at‐wavelength testing), which is typically around 13 nm. While a laser plasma source (LPS) is being developed as a lithography production source, it has generally been considered that only an undulator located at a synchrotron facility can provide the necessary laserlike point source brightness for EUV interferometry. Although an undulator‐based approach has been successfully demonstrated, it would be advantageous to test a camera in its operational configuration with an LPS. We are developing the latter approach by utilizing extended source size schemes to provide usable flux throughput. A slit mounted at the source plane can provide the necessary spatial coherence for lateral shearing interferometry. Initial results from an EUV lateral shear interferometer based on the Ronchi test are presented. © 1996 American Vacuum Society
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07.60.Ly Interferometers
81.07.-b Nanoscale materials and structures: fabrication and characterization
81.16.-c Methods of micro- and nanofabrication and processing
85.35.-p Nanoelectronic devices
52.77.Bn Etching and cleaning
52.77.Dq Plasma-based ion implantation and deposition

Simultaneous measurement of gap and superposition in a precision aligner for x‐ray nanolithography

E. E. Moon, P. N. Everett, K. Rhee, and Henry I. Smith

J. Vac. Sci. Technol. B 14, 3969 (1996); http://dx.doi.org/10.1116/1.588625 (5 pages) | Cited 5 times

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Previously we described an x‐ray mask alignment system, capable of nanometer‐level superposition precision, whose alignment signal did not appear to be adversely affected by overlayers of resist, polysilicon, or metal [E. E. Moon, P. N. Everett, and H. I. Smith, J. Vac. Sci. Technol. B 13, 2648 (1995)]. The system, called interferometric broad‐band imaging (IBBI), employs grating and grid type alignment marks on mask and substrate, respectively. These are viewed at an inclined angle, through the mask, using f/10 optics with a working distance of 110 mm. The inclined angle and long working distance avoid interruption of the x‐ray beam. Using a charge‐coupled‐device camera, misalignment is measured from two identical sets of interference fringes (∼50 μm period) that move in opposite directions as the mask is moved relative to the substrate. Alignment corresponds to matching the spatial phases of the two sets of fringes. Here we demonstrate that the same alignment optics and grating type alignment mark on the mask can be used to measure the mask–sample gap, with a sensitivity ∼50 nm, via a diffractive‐Michelson interferometer. No mark is required on the substrate. X‐ray exposures were carried out with the IBBI system. The disparity between (a) the misalignment as measured by the IBBI system and (b) the postprocessing misalignment, as measured on the substrate by a related moiré technique, was evaluated. Mean disparities of 0.1, −0.4, and −0.3 nm were measured for alignment marks of 1, 2, and 4 μm period, respectively. The 3‐σ values of the distributions were 2.4, 7.3, and 5.9 nm. The larger values for the 2 μm period case are attributed to multiple defects in the grating alignment marks. © 1996 American Vacuum Society
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81.07.-b Nanoscale materials and structures: fabrication and characterization
81.16.-c Methods of micro- and nanofabrication and processing
85.35.-p Nanoelectronic devices
06.60.Sx Positioning and alignment; manipulating, remote handling

Latent image formation: Nanoscale topography and calorimetric measurements in chemically amplified resists

L. E. Ocola, D. Fryer, P. Nealey, J. dePablo, F. Cerrina, and S. Kämmer

J. Vac. Sci. Technol. B 14, 3974 (1996); http://dx.doi.org/10.1116/1.588626 (6 pages) | Cited 9 times

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The characterization of photoresists during the image formation process has traditionally relied on bulk methods during or after development. This article shows that it is not necessary to develop the photoresist in order to obtain significant information about the image formation process in x‐ray, electron beam, and UV lithography. The characterization of the image formation process in chemically amplified photoresists prior to development is difficult due to their sensitivity to electrons used in scanning electron microscopy and the weak changes in dielectric constant needed for optical microscopy. The advent and development of the atomic force microscope (AFM) have allowed local surface measurements of exposure induced changed in photoresists with sub‐μm scale resolution and negligible modification of the sample. A series of chemically amplified resists, positive and negative, have been studied with a variety of exposure radiation (electron beam, x‐ray, and UV). The results discussed in this article focus on two of these resists: SAL 605 (−), and TOK 010 (+). Both positive and negative chemically amplified resists exhibit significant changes in topography and calorimetric properties during the image formation process. Interpretation of the resist topography in negative resists is given by a semi‐empirical model that assumes Fickian diffusion of resist material during post‐exposure bake (PEB) and verified with AFM data. The glass transition temperature, Tg, of wafer spun thin films of SAL 605 has been measured, prior to exposure, to be 75±3°C with an ellipsometric technique. The PEB temperature, 105°C, is much greater than the Tg of SAL 605, thereby providing some justification for our Fickian diffusion model. These results are preliminary until a chemical map can be done on the resist at sub‐μm resolution, which at present time is not possible. The need for detecting intrinsic material property changes due to the image formation process motivates the exploration of calorimetric properties of the resist. Interpretation of the calorimetric data is still unclear. Both cases of positive and negative photoresists exhibit an increase of heat absorbed in the exposed regions. Photoacid ions produced by exposure to radiation may be considered responsible for such an increase. © 1996 American Vacuum Society
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81.07.-b Nanoscale materials and structures: fabrication and characterization
81.16.-c Methods of micro- and nanofabrication and processing
85.35.-p Nanoelectronic devices

Minimizing alignment error induced by asymmetric resist coating

Xun Chen and R. F. W. Pease

J. Vac. Sci. Technol. B 14, 3980 (1996); http://dx.doi.org/10.1116/1.588627 (5 pages)

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Asymmetric alignment signal is a major problem in optical lithography. Perhaps the most unavoidable source of such asymmetry is the resist profile covering the alignment marks. Such asymmetry can arise from the spin coating process. We describe a new technique of using TM polarized light and Brewster angle illumination to minimize the reflection from the top resist surface and hence minimize alignment error induced by asymmetric resist coating. A basic model is developed to describe the optical effect of the resist coating and to calculate the alignment signals. The results show that the Brewster angle illumination technique can reduce the alignment error more than tenfold when using standard marks such as 16 μm period gratings. Nearly error‐free alignment can be achieved even on wafer marks that are covered by asymmetric resist, if the alignment marks are suitably designed. © 1996 American Vacuum Society
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85.40.Hp Lithography, masks and pattern transfer

Patterning accuracy estimation during stage acceleration in the electron beam direct writing system EX‐8D

K. Hattori, S. Magoshi, A. Ando, S. Satoh, H. Sunaoshi, M. Suenaga, H. Housai, S. Hashimoto, H. Wada, and K. Sugihara

J. Vac. Sci. Technol. B 14, 3985 (1996); http://dx.doi.org/10.1116/1.588628 (5 pages) | Cited 1 time

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We have evaluated patterning accuracy during stage acceleration of EX‐8D in which a beam deflection control system has been installed to compensate a beam positional shift depending on both the stage velocity and position. From the fact that there is no difference in patterning accuracy between stage acceleration phase and constant velocity phase, it was found that the control system functions accurately. We have also analyzed beam position deviation. The analysis results showed that improvement of the laser interferometer resolution, stabilization of the objection lens, and elimination of the ambient magnetic field change are necessary to achieve 1 Gbit class ultra‐large‐ scale integrated patterning of 0.15 μm within 10% beam position fluctuation. By adopting continuous writing during stage acceleration and deceleration while turning, the improvement of the throughput was also confirmed without reducing the patterning accuracy. © 1996 American Vacuum Society
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81.07.-b Nanoscale materials and structures: fabrication and characterization
81.16.-c Methods of micro- and nanofabrication and processing
85.35.-p Nanoelectronic devices
41.85.-p Beam optics

Characterization of resist profiles using water enhanced focused ion beam micromachining

T. J. Stark, D. P. Griffis, and P. E. Russell

J. Vac. Sci. Technol. B 14, 3990 (1996); http://dx.doi.org/10.1116/1.588629 (6 pages) | Cited 2 times

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The use of water enhanced focused ion beam micromachining has been investigated as a technique to aid in the characterization of resist profiles. The increase in removal rate and the decrease in redeposition associated with the water enhancement allows clean cross sections (no redeposition of substrate material) to be formed at precise locations allowing accurate resist sidewall characterization and eliminates the need for wafer cleaving. The experimental conditions (water flux and beam exposure parameters) were optimized to produce cross sections with minimum artifacts. It was found that water pressure of approximately 80 mTorr, line step distances corresponding to half the beam diameter and dwell time roughly twice that required to clear the resist resulted in nearly vertical cross section faces with minimum edge artifacts. © 1996 American Vacuum Society
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85.40.Hp Lithography, masks and pattern transfer
81.07.-b Nanoscale materials and structures: fabrication and characterization
81.16.-c Methods of micro- and nanofabrication and processing
85.35.-p Nanoelectronic devices

Investigations on the topology of structures milled and etched by focused ion beams

S. Lipp, L. Frey, C. Lehrer, B. Frank, E. Demm, and H. Ryssel

J. Vac. Sci. Technol. B 14, 3996 (1996); http://dx.doi.org/10.1116/1.588630 (4 pages) | Cited 17 times

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For high precision micromachining of micro‐ and nanostructures by focused ion beams, the precision of the material removal process is of great importance. In this article, the topological properties of the ion beam generated structures like slope angles of trenches, surface roughness, and induced defects are investigated. The influence of the beam current and scanning strategy on the topological properties will be discussed. In addition, transmission electron microscopy analysis of thin lamellas generated by focused ion beams will be shown. © 1996 American Vacuum Society
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07.10.Cm Micromechanical devices and systems
81.65.Cf Surface cleaning, etching, patterning

Direct aerial image measurements to evaluate the performance of an extreme ultraviolet projection lithography system

C. H. Fields, W. G. Oldham, A. K. Ray‐Chaudhuri, K. D. Krenz, and R. H. Stulen

J. Vac. Sci. Technol. B 14, 4000 (1996); http://dx.doi.org/10.1116/1.588631 (4 pages)

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We report the application of direct aerial image monitoring to measure the performance of an extreme ultraviolet lithography (EUVL) test bed. There are several issues which might limit the possibility of performing image monitoring experiments on EUVL systems. These issues include: source flux, signal‐to‐noise ratios, and EUV scanning aperture fabrication. We report the results of initial aerial image scans of equal lines and spaces as well as preliminary measurements of scatter produced by the EUV camera. © 1996 American Vacuum Society
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81.07.-b Nanoscale materials and structures: fabrication and characterization
81.16.-c Methods of micro- and nanofabrication and processing
85.35.-p Nanoelectronic devices
42.30.Va Image forming and processing

Atomic force microscopy for cross section inspection and metrology

Kathryn Wilder, Calvin F. Quate, Bhanwar Singh, Roger Alvis, and William H. Arnold

J. Vac. Sci. Technol. B 14, 4004 (1996); http://dx.doi.org/10.1116/1.588632 (5 pages) | Cited 3 times

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Images of integrated circuit cross sections may be acquired with the atomic force microscope (AFM) by introducing material‐dependent topography through a series of selective etches. AFM images of a fully processed complementary metal–oxide–semiconductor inverter structure show excellent qualitative agreement with high resolution scanning electron microscope (SEM) images. Measurements of layer thicknesses and lateral dimensions, however, do not precisely correlate. These discrepancies are attributed to tip–sample convolution due to the finite cone angle and rounding of the probe. We describe a one‐dimensional computer simulator that models the nonlinear geometrical interaction between a tip and sample. Simulation results are used to determine the tip shape from an AFM image of a feature of known dimensions. The tip influence can be subsequently deconvolved from a cross section AFM image, generating a more faithful reflection of the surface topography. We demonstrate that this scheme yields measurements that correlate well with those made by the SEM and suggest that AFM imaging may be a viable alternative for the inspection and metrology of IC cross sections. © 1996 American Vacuum Society
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85.40.Qx Microcircuit quality, noise, performance, and failure analysis
68.37.Ef Scanning tunneling microscopy (including chemistry induced with STM)
68.37.Ps Atomic force microscopy (AFM)
68.37.Rt Magnetic force microscopy (MFM)
68.37.Uv Near-field scanning microscopy and spectroscopy
68.37.Hk Scanning electron microscopy (SEM) (including EBIC)
68.37.Lp Transmission electron microscopy (TEM)

Analysis of distortion in interferometric lithography

Juan Ferrera, M. L. Schattenburg, and Henry I. Smith

J. Vac. Sci. Technol. B 14, 4009 (1996); http://dx.doi.org/10.1116/1.588633 (5 pages) | Cited 19 times

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We present a mathematical model to describe the spatial phase of gratings produced by interferometric lithography, as well as a set of experiments to verify the model’s validity and to measure any distortions introduced when the lithography is performed. The implementation of two methods to measure the phase progression of these gratings is described. We find the results obtained from an initial set of experiments to be in good agreement with the theoretical model, i.e., the absence of significant distortions, such as coherent phase noise, is confirmed. These results are also applicable to the metrology of grids. © 1996 American Vacuum Society
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85.40.Hp Lithography, masks and pattern transfer
42.30.Va Image forming and processing
06.20.-f Metrology

Effects of electron‐beam parameters on critical‐dimension measurements

Fumio Mizuno and Osamu Satoh

J. Vac. Sci. Technol. B 14, 4014 (1996); http://dx.doi.org/10.1116/1.588634 (6 pages) | Cited 4 times

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One of the important requirements for critical‐dimension scanning electron microscopes is to improve the reproducibility of measurement in response to the scaling of features on semiconductor devices. A reproducibility of 3 nm, about 1/100 of the minimum pattern size, will be required for the next generation subquarter‐micron devices. It is clear that the sampling pitch, incident angle, and blurring of the electron beam produce measurement errors in the order of a few nm and the precise control of these parameters is necessary, but not sufficient for achieving a reproducibility of 3 nm. © 1996 American Vacuum Society
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85.40.-e Microelectronics: LSI, VLSI, ULSI; integrated circuit fabrication technology
68.37.Hk Scanning electron microscopy (SEM) (including EBIC)
68.37.Lp Transmission electron microscopy (TEM)
41.85.Ew Particle beam profile, beam intensity

0.1μm complementary metal–oxide–semiconductors and beyond

Akira Toriumi

J. Vac. Sci. Technol. B 14, 4020 (1996); http://dx.doi.org/10.1116/1.588635 (4 pages)

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The size of metal–oxide–semiconductor field effect transistors has been drastically miniaturized to achieve higher performance according to the scaling law. One micron complementary metal–oxide–semiconductor (CMOS) technology is no longer at the frontier of device research; it is being optimized as a real device. The scaling law has been partly modified but the overall direction of device technology is still following that scenario. This article will first review some key messages that have been learned from 0.1μm CMOS development in our laboratories. In the sub‐0.1μm era, there will be a strong demand for new device physics and technologies, including new materials, for a new electronics paradigm. As an example of the new devices, silicon single electron tunneling devices will be discussed here in terms of their gradual assimilation into the current silicon ultralarge scale integration world. © 1996 American Vacuum Society
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81.07.-b Nanoscale materials and structures: fabrication and characterization
81.16.-c Methods of micro- and nanofabrication and processing
85.35.-p Nanoelectronic devices
85.30.-z Semiconductor devices

Fabrication of back‐gated complementary metal‐oxide semiconductor devices using mixed and matched optical and x‐ray lithographies

Isabel Y. Yang, Dimitri A. Antoniadis, and Henry I. Smith

J. Vac. Sci. Technol. B 14, 4024 (1996); http://dx.doi.org/10.1116/1.588636 (5 pages)

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A novel silicon‐on‐insulator‐based technology called silicon‐on‐insulator‐with‐active‐substrate (SOIAS) [I. Y. Yang, C. Vieri, A. Chandrakasan, and D. A. Antoniadis, in International Electron Device Meeting (IEEE, Washington, DC, 1995), p. 877] was developed for high performance and low power electronic systems, which takes advantage of established silicon processes such as chemical mechanical polishing, wafer bonding, and the various lithographic tools used for deep submicrometer patterning. This article demonstrates the fabrication of deep submicrometer back‐gated complementary metal‐oxide semiconductor devices and simple circuits on SOIAS substrates using optical and x‐ray lithographies with our mix‐and‐match strategy [I. Y. Yang, S. Silverman, J. Ferrera, K. Jackson, J. Carter, D. A. Antoniadis, and H. Smith, J. Vac. Sci. Technol. B 13, 2741 (1995)]. © 1996 American Vacuum Society
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81.07.-b Nanoscale materials and structures: fabrication and characterization
81.16.-c Methods of micro- and nanofabrication and processing
85.35.-p Nanoelectronic devices
85.30.Tv Field effect devices

A new high‐performance surface‐micromachined tunneling accelerometer fabricated using nanolithography

R. L. Kubena, G. M. Atkinson, W. P. Robinson, and F. P. Stratton

J. Vac. Sci. Technol. B 14, 4029 (1996); http://dx.doi.org/10.1116/1.588637 (5 pages) | Cited 4 times

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We have fabricated a new class of high‐performance tunneling accelerometers using surface micromachining. The accelerometer structures are fabricated on the surface of a single silicon wafer and consist of a single cantilevered beam with electrostatic deflection electrodes and a sub‐100‐nm‐diam tunneling tip underneath. The noise level resolutions in air of 100‐ and 250‐μm‐long cantilever devices are 8.3×10−4 and 8.5×10−5 g/Hz1/2 at 500 Hz, respectively. The devices are operated in a force rebalance feedback mode using a low noise automatic servo‐control circuit, providing a dynamic range of over 104 g. This new accelerometer technology provides devices with extremely high sensitivity, high bandwidth, and wide dynamic range, in an ultracompact, low‐cost package that is easily integrated with silicon control electronics. © 1996 American Vacuum Society
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07.10.Cm Micromechanical devices and systems
06.30.Gv Velocity, acceleration, and rotation
81.07.-b Nanoscale materials and structures: fabrication and characterization
81.16.-c Methods of micro- and nanofabrication and processing
85.35.-p Nanoelectronic devices

Metal based single electron transistors operating at several Kelvin

S. Altmeyer, A. Hamidi, B. Spangenberg, and H. Kurz

J. Vac. Sci. Technol. B 14, 4034 (1996); http://dx.doi.org/10.1116/1.588638 (4 pages) | Cited 4 times

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Metal based single electron transistors fabricated by the step edge cut off process will be presented. Although standard electron beam lithography, dry etching and lift‐off techniques were used, devices with tunnel capacitances down to 1.5 aF are realized. They are characterized at different temperatures ranging from 50 mK up to 77 K. Transistor operation at 4.2 K is demonstrated. Traces of the Coulomb blockade are observed up to 77 K. © 1996 American Vacuum Society
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85.35.Gv Single electron devices
81.07.-b Nanoscale materials and structures: fabrication and characterization
81.16.-c Methods of micro- and nanofabrication and processing
85.35.-p Nanoelectronic devices
73.23.Hk Coulomb blockade; single-electron tunneling

Fabrication of lateral resonant tunneling devices with heterostructure barriers

John N. Randall, T. P. E. Broekaert, B. D. Smith, E. A. Beam, A. C. Seabaugh, and D. Jovanovic

J. Vac. Sci. Technol. B 14, 4038 (1996); http://dx.doi.org/10.1116/1.588639 (4 pages)

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Lateral resonant tunneling devices that employ heterostructure charge barriers are candidates to replace complementary metal–oxide–semiconductor devices as the basic device type that will drive integrated circuit technology in the next century. We present progress in lateral resonant tunneling device technology including the first lateral resonant tunneling transistor that has heterostructure barriers to be fabricated with planar processing techniques. The devices produced to date are limited to cryogenic operation; however, they do demonstrate that lateral resonant tunneling devices can be fabricated with etch and regrowth techniques and suggest the possibility of an integrated circuit technology that may be scaled down to less than 10 nm and would operate at room temperature. © 1996 American Vacuum Society
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85.30.Mn Junction breakdown and tunneling devices (including resonance tunneling devices)
81.07.-b Nanoscale materials and structures: fabrication and characterization
81.16.-c Methods of micro- and nanofabrication and processing
85.35.-p Nanoelectronic devices

A triangle‐shaped nanoscale metal–oxide–semiconductor device

J. Gondermann, Th. Röwer, B. Hadam, Th. Köster, J. Stein, B. Spangenberg, H. Roskos, and H. Kurz

J. Vac. Sci. Technol. B 14, 4042 (1996); http://dx.doi.org/10.1116/1.588640 (4 pages) | Cited 2 times

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A new fabrication process for ultrasmall high‐current‐density metal–oxide–semiconductor transistors is proposed. The device fabrication is based on anisotropic wet etching of silicon using bonded and etched back silicon‐on‐insulator (BESOI) material and a self‐adjusting polysilicon gate technology. The special feature in the design of the transistor is a small silicon wire with a triangular instead of a planar cross section connecting the source and drain areas. Applying a moderate voltage to the poly‐gate, a high electric field is built up in the top of the triangle which increases the volume of the conducting channel below the gate. For normal operating conditions, the three‐dimensional current flow allows smaller lateral dimensions of the device that offers higher integration. Because of the BESOI material, faster device performance is expected. The physical principle is discussed and the basic fabrication techniques are described. First electrical investigations of the transistors operating at room temperature are presented providing evidence that the current density is considerably higher than in planar transistors. © 1996 American Vacuum Society
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81.07.-b Nanoscale materials and structures: fabrication and characterization
81.16.-c Methods of micro- and nanofabrication and processing
85.35.-p Nanoelectronic devices
85.30.Tv Field effect devices

Charge detector realization for AlGaAs/GaAs quantum‐dot cellular automata

G. Bazán, A. O. Orlov, G. L. Snider, and G. H. Bernstein

J. Vac. Sci. Technol. B 14, 4046 (1996); http://dx.doi.org/10.1116/1.588641 (5 pages) | Cited 1 time

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We perform measurements on an AlGaAs/GaAs double‐quantum‐dot structure, where dots are separated by an opaque barrier and each dot conductance is measured independently and simultaneously. We measure the Coulomb blockade oscillations (CBOs) for each dot when the structure is configured for one and two dots. When configured as a single‐dot device, we sweep the backgate and observe different CBO periods for each dot measured independently, implying dots of different sizes. When the device is configured for two dots, we observe strongly modulated CBOs in the larger dot while CBOs in the smaller dot exhibit almost no influence due to the changing charge of the larger dot. From this experiment, we have realized a charge detection scheme where we observe strong coupling in the detector signal in addition to the detector exhibiting minimal effect on the dot being measured. For an implementation of quantum‐dot cellular automata (QCA), (1) cells must couple capacitively and (2) one must be able to detect electron occupation of a quantum dot within a cell. With this investigation, we demonstrate these two key components required for QCA in AlGaAs/GaAs materials. © 1996 American Vacuum Society
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85.35.Be Quantum well devices (quantum dots, quantum wires, etc.)
73.23.Hk Coulomb blockade; single-electron tunneling
89.20.Ff Computer science and technology

A heavy ion implanted pocket 0.10 μm n‐type metal–oxide–semiconductor field effect transistor with hybrid lithography (electron‐beam/deep ultraviolet) and specific gate passivation process

F. Benistant, S. Tedesco, G. Guegan, F. Martin, M. Heitzmann, and B. Dal’zotto

J. Vac. Sci. Technol. B 14, 4051 (1996); http://dx.doi.org/10.1116/1.588642 (4 pages) | Cited 1 time

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We present a 0.10 μm n‐type metal–oxide–semiconductor process to achieve devices with reduced short channel effect (SCE) and good current drive capability. Full compatible chemical amplified resist process between deep ultraviolet and electron‐beam lithography allowed us to use hybrid lithography at gate level. For the first time, we show that the conventional gate reoxidation is a limiting step to process integration because of the bird’s beak formation at the poly‐gate edge. Consequently, this process is replaced by a low thermal oxide deposition. In addition, indium and gallium pocket implantations have been realized to improve the SCE control. © 1996 American Vacuum Society
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85.30.Tv Field effect devices
81.07.-b Nanoscale materials and structures: fabrication and characterization
81.16.-c Methods of micro- and nanofabrication and processing
85.35.-p Nanoelectronic devices

Fabrication and performance of thin amorphous Si subwavelength transmission grating for controlling vertical cavity surface emitting laser polarization

Lei Zhuang, Steve Schablitsky, Rick C. Shi, and Stephen Y. Chou

J. Vac. Sci. Technol. B 14, 4055 (1996); http://dx.doi.org/10.1116/1.588643 (3 pages) | Cited 4 times

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Amorphous Si subwavelength transmission gratings (SWTGs) with a thickness of 240 nm and a period ranging from 50 to 900 nm were fabricated on a fused silica substrate using electron beam lithography, lift‐off, and reactive ion etching. At certain grating periods, the SWTGs exhibit polarization dependent reflectance and transmittance due to the polarization dependent coupling of the eigenmodes inside the grating. By putting the SWTG in front of the output window of a vertical cavity surface emitting laser (VCSEL), a polarization dependent optical feedback can be achieved. Using this feedback, we demonstrated the locking, switching, and enhancement of the VCSEL’s polarization. A polarization ratio as high as 200:1 was achieved. © 1996 American Vacuum Society
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42.82.Cr Fabrication techniques; lithography, pattern transfer
42.60.-v Laser optical systems: design and operation

Fabrication and investigation of nanostructures and their application in new laser devices

U. A. Griesinger, S. Kronmüller, M. Geiger, D. Ottenwälder, F. Scholz, and H. Schweizer

J. Vac. Sci. Technol. B 14, 4058 (1996); http://dx.doi.org/10.1116/1.588644 (4 pages) | Cited 1 time

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In this article, techniques for the realization of exactly positioned nanostructures are presented and the properties of nanometer scale optic laser devices based on GaInAs/GaInAsP/InP heterostructure are discussed. The fabrication of nanometer scale optic devices requires the precise control of the confinement length of carriers as well as the confinement length of photons, which are different by one order of magnitude. Both requirements can be met by the application of high resolution electron beam lithography in combination with low damage etching techniques and planar epitaxial overgrowth. Lateral structures down to 15 nm with high optical quality at periods around 240 nm suitable for distributed feedback (DFB) devices have been obtained. For the first time, these nanofabrication techniques allow the realization of a new class of semiconductor lasers: gain coupled wire and dot DFB lasers. The reduced dimensionality of the active area shows significant improvements of the gain values and the laser thresholds. The precise definition of dot arrays (array size up to some 100 μm) allows the fabrication of a new device: a gain coupled dot DFB laser, consisting of dots forming a two‐dimensional DFB grating. © 1996 American Vacuum Society
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42.82.Cr Fabrication techniques; lithography, pattern transfer
42.55.Sa Microcavity and microdisk lasers

Fabrication of quantum nanostructures for the measurement of thermoelectric phenomena

M. Hannan, R. Grundbacher, I. Adesida, and R. W. Giannetta

J. Vac. Sci. Technol. B 14, 4062 (1996); http://dx.doi.org/10.1116/1.588645 (6 pages)

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Fabrication of nanostructures has been carried out for the study of thermal and thermoelectric transport properties. The study was done on an electron waveguide, defined as a double‐bend quantum structure in a two‐dimensional electron gas, using a current heating technique. Seebeck and Peltier effects are observed in this structure. © 1996 American Vacuum Society
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81.07.-b Nanoscale materials and structures: fabrication and characterization
81.16.-c Methods of micro- and nanofabrication and processing
85.35.-p Nanoelectronic devices
85.35.Be Quantum well devices (quantum dots, quantum wires, etc.)
73.40.Kp III-V semiconductor-to-semiconductor contacts, p-n junctions, and heterojunctions

Fabrication of Si double barrier structure

K. Yuki, Y. Hirai, K. Morimoto, K. Morita, and T. Uenoyama

J. Vac. Sci. Technol. B 14, 4068 (1996); http://dx.doi.org/10.1116/1.588646 (4 pages) | Cited 2 times

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We have observed an oscillation in the current density–voltage (J–V) characteristics caused by resonant tunneling phenomena by means of a newly developed Si‐based double barrier structure (DBS). In the DBS fabrication, a thin single‐crystal Si plate is used as a quantum well on SIMOX (separation by implanted oxygen) substrate. In order to obtain the Si quantum well, an anisotropic wet chemical etching followed by thermal oxidation is performed. Particularly, a novel advanced shaped etching mask is used to form an extremely thin Si plate. The width of the plate exceeds the resolution limitation of lithography. Accordingly, a quantum well with a width of 9 nm has been successfully obtained. The electrical characteristics of the sample that has around 40 nm wide quantum well and 1.6 nm thick SiO2 barriers are investigated. Oscillation peaks are observed in the J–V characteristics at 4.0 K. The observed peaks are in good agreement with the calculated resonant tunneling diode model. © 1996 American Vacuum Society
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85.30.Mn Junction breakdown and tunneling devices (including resonance tunneling devices)
81.07.-b Nanoscale materials and structures: fabrication and characterization
81.16.-c Methods of micro- and nanofabrication and processing
85.35.-p Nanoelectronic devices

Limit of resolution of a standing wave atom optical lens

R. E. Behringer, Vasant Natarajan, G. Timp, and D. M. Tennant

J. Vac. Sci. Technol. B 14, 4072 (1996); http://dx.doi.org/10.1116/1.588647 (4 pages) | Cited 5 times

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Using a Gaussian standing wave at λ=589 nm as an atom optical lens, we have focused a thermal atomic sodium beam. We have examined the limits of the resolution of this focusing technique, and have made structures with linewidths of 13 nm and contrast of 6:1 with a short focal length atom optical lens. While numerical simulations predict that smaller structures should be attainable with shorter focal lengths, we find that the resolution deteriorates for focal length shorter than f≊16 μm. © 1996 American Vacuum Society
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41.85.Lc Particle beam focusing and bending magnets, wiggler magnets, and quadrupoles
37.10.Vz Mechanical effects of light on atoms, molecules, and ions

Fabrication of a refractive microlens integrated onto the monomode fiber

S. Babin, M. Weber, and H. W. P. Koops

J. Vac. Sci. Technol. B 14, 4076 (1996); http://dx.doi.org/10.1116/1.588594 (4 pages) | Cited 6 times

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The fabrication of microlenses using a dry resist process is described for the first time. Characteristics of the totally dry process were investigated. A technique for lens positioning and exposure was developed for a scanning electron microscope equipped with an image processor beam control system. The microlenses have a computer generated hyperbolic profile. Microlenses of cylindrical, ring, and elliptical geometry were fabricated on a Si wafer and on the end of a monomode quartz fiber. Focusing of visible and infrared light by a fabricated microlens is demonstrated. © 1996 American Vacuum Society
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42.81.Bm Fabrication, cladding, and splicing
42.79.Bh Lenses, prisms and mirrors

Controlling sidewall smoothness for micromachined Si mirrors and lenses

W. H. Juan and S. W. Pang

J. Vac. Sci. Technol. B 14, 4080 (1996); http://dx.doi.org/10.1116/1.588595 (5 pages) | Cited 21 times

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Micromachined vertical mirrors and lenses in Si were fabricated as micro‐optical components. A Cl2 plasma generated by an electron cyclotron resonance source was used to etch these mirrors and lenses in Si and the etched Si sidewalls were characterized by atomic force microscopy and scanning electron microscopy. A trilayer resist process has been developed to provide smooth Ni etch mask edges by postbaking the top imaging resist. The resultant Si etched sidewall showed a roughness of 18.69 nm, as compared to the sidewall roughness of 29.95 nm without postbaking. As the plating current density was varied from 5 to 400 mA/cm2, the etched Si sidewall roughness increased from 24.31 to 43.69 nm. Optimized etch conditions were investigated for smooth Si sidewalls. Sidewall was much rougher with a roughness of 98.99 nm when 50 W rf power was applied for dry etching, whereas the roughness was only 29.95 nm when 100 W rf power was used. Additionally, thermal oxidation followed by oxide removal was able to reduce etched Si sidewall roughness. After oxide removal, the sidewall roughness decreased to 5.93 nm after 135 min wet oxidation at 1100 °C. However, oxide grown at 900 °C was less efficient for reducing the sidewall roughness as compared to 1100 °C. The deep etch‐shallow diffusion process was applied to fabricate micromirrors and microlenses. It was found that B diffusion at 1175 °C for 2 h decreased the Si sidewall roughness from 29.95 to 10.79 nm and selective wet etch lowered sidewall roughness further to 5.01 nm. Vertical micromirrors that were 40 μm tall and 2 μm wide were bonded onto the glass substrate and released. Microlenses that were 40 μm thick with radius of curvature of 50 μm have also been demonstrated. © 1996 American Vacuum Society
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42.82.Cr Fabrication techniques; lithography, pattern transfer

High‐resolution silicon patterning with self‐assembled monolayer resists

M. J. Lercel, C. S. Whelan, H. G. Craighead, K. Seshadri, and D. L. Allara

J. Vac. Sci. Technol. B 14, 4085 (1996); http://dx.doi.org/10.1116/1.588596 (6 pages) | Cited 13 times

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Single crystal and polycrystalline silicon films have been patterned and etched with a novel high‐selectivity process using self‐assembled monolayer resists of octadecylsiloxanes (ODS). The highest resolution patterning of sub‐10 nm features has been demonstrated by scanning force microscopy imaging of ODS layers patterned with a focused electron beam. An all‐dry UV/ozone developer has been used to remove residual carbon from the electron beam exposed regions to improve etch selectivity. The positive tone pattern transfer process consisted of a short buffered hydrofluoric acid wet etch to remove the silicon native oxide followed by a high‐selectivity, low ion energy etch using Cl2 and BCl3 in an electron cyclotron resonance reactive ion etch. Features have been etched up to 90 nm deep into Si(100) wafers and minimum feature sizes obtained are ∼25 nm. Poly‐Si films on SiO2 insulator layers have been similarly patterned and have been used in a combined process with photolithographic definition of microbridges to form narrow conducting channels in the poly‐Si. © 1996 American Vacuum Society
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81.07.-b Nanoscale materials and structures: fabrication and characterization
81.16.-c Methods of micro- and nanofabrication and processing
85.35.-p Nanoelectronic devices

Fabrication of InP‐based wavelength division multiplexing arrayed waveguide filters using chemically assisted ion beam etching

C. Youtsey, I. Adesida, J. B. D. Soole, M. R. Amersfoort, H. P. LeBlanc, N. C. Andreadakis, A. Rajhel, C. Caneau, M. A. Koza, and R. Bhat

J. Vac. Sci. Technol. B 14, 4091 (1996); http://dx.doi.org/10.1116/1.588597 (5 pages) | Cited 4 times

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Chemically assisted ion beam etching using Cl2 has been used to fabricate InP‐based arrayed waveguide filters that demonstrate full polarization independence and excellent performance characteristics. The process is carried out at elevated temperatures of approximately 250 °C to avoid difficulties associated with the low volatility of indium chlorides at lower temperatures. Optimization of the process for smooth, vertical etching is discussed. InP regrowth is successfully carried out on the etched InGaAsP guides, and measurements of the fabricated devices are presented. The adaptation of the process for angled etching is also demonstrated. © 1996 American Vacuum Society
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42.82.Cr Fabrication techniques; lithography, pattern transfer

Fabrication of subwavelength, binary, antireflection surface‐relief structures in the near infrared

J. R. Wendt, G. A. Vawter, R. E. Smith, and M. E. Warren

J. Vac. Sci. Technol. B 14, 4096 (1996); http://dx.doi.org/10.1116/1.588598 (4 pages) | Cited 2 times

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Subwavelength, binary surface‐relief structures are artificial materials with an effective index of refraction that can be tailored by varying the duty cycle of the binary pattern. These structures have the significant advantage of requiring only a single lithography and etch step for fabrication. We demonstrate a specifically designed antireflection structure in a material system (GaAs) and at a wavelength (975 nm) directly integrable with GaAs‐based vertical cavity surface‐emitting lasers and which exhibits strong polarization‐dependent properties. Fabrication is performed using electron beam lithography and reactive‐ion‐beam etching. The observed reflectivity is 2% for TE polarization and 23% for TM polarization, a difference in reflectivity of over a factor of 10 for the two polarizations. © 1996 American Vacuum Society
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42.82.Cr Fabrication techniques; lithography, pattern transfer
42.79.-e Optical elements, devices, and systems

Combined method of electron‐beam lithography and ion implantation techniques for the fabrication of high‐temperature superconductor Josephson junctions

J. Hollkott, S. Hu, C. Becker, J. Auge, B. Spangenberg, and H. Kurz

J. Vac. Sci. Technol. B 14, 4100 (1996); http://dx.doi.org/10.1116/1.588599 (5 pages) | Cited 6 times

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Established semiconductor process technologies are demonstrated to be suitable for the fabrication of high temperature superconductor Josephson junctions. Single YBa2Cu3O7 bridges have been modified by local oxygen ion irradiation through a narrow slit in an implantation mask, which was formed by electron‐beam lithography and reactive ion etching. The influence of the slit dimension, the mask thickness, and the irradiation dose have been investigated systematically. The critical current and the normal resistance of the modified microbridges were found to be controllable by these parameters achieving a great variety of different I/V curves, i.e., resistive or superconductor/normal/superconductor (SNS) Josephson junction behavior. Further investigations were performed on SNS junctions. Microwave irradiation of the microbridges exhibits Shapiro steps in the I/V characteristics. In dc superconducting quantum interference devices a voltage modulation as a function of an applied magnetic flux is observed. © 1996 American Vacuum Society
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85.25.Cp Josephson devices
81.07.-b Nanoscale materials and structures: fabrication and characterization
81.16.-c Methods of micro- and nanofabrication and processing
85.35.-p Nanoelectronic devices

Conductive dots, wires, and supertips for field electron emitters produced by electron‐beam induced deposition on samples having increased temperature

H. W. P. Koops, C. Schössler, A. Kaya, and M. Weber

J. Vac. Sci. Technol. B 14, 4105 (1996); http://dx.doi.org/10.1116/1.588600 (5 pages) | Cited 49 times

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The procedure for three‐dimensional additive lithography with electron‐beam induced deposition is applied in a scanning electron microscope equipped with an image processor beam control system for lithography. Employing organometallic materials, which contain gold or platinum, quantum dots, resistors, and field emitter tips are deposited. Changing the current, the properties of the deposited nanocrystalline compound materials can be selected to be insulating or conducting. High resolution and high aspect ratio structures are grown with this technique. To find the mechanism responsible for conductivity in the deposited material, resistors are characterized at temperatures ranging from −150 °C to +180 °C. Measurements are performed in a high‐vacuum chamber equipped with a gas cooling system cooled with liquid nitrogen and a resistive heater. Poole–Frenkel plots show that field electron emission and hopping of electrons is the dominant mechanism of conduction. The metal content of the deposits is increased with rising sample temperatures ranging from room temperature to 100 °C. The deposited material features zero‐dimensional electron gas in the nanocrystals of the material. Conductive tips with very small tip radius are routinely deposited as supertips on top of etched tungsten tips at elevated temperatures. The tips are investigated in an ultrahigh vacuum field electron microscope. Working supertips have a confined emission and therefore enhanced brightness is obtained routinely. The increase in brightness is at least ninefold for an emission from one site having a confined emission angle of ±7.2°. The emission current may be as large as 10 μA at extraction voltages below 800 V. No single crystalline tip material is needed to generate these supertips. Beam confinement to one emission site is demonstrated the first time for a deposited supertip. © 1996 American Vacuum Society
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81.07.-b Nanoscale materials and structures: fabrication and characterization
81.16.-c Methods of micro- and nanofabrication and processing
85.35.-p Nanoelectronic devices
85.35.Be Quantum well devices (quantum dots, quantum wires, etc.)
85.45.Db Field emitters and arrays, cold electron emitters

Lithographic band gap tuning in photonic band gap crystals

C. C. Cheng, A. Scherer, V. Arbet‐Engels, and E. Yablonovitch

J. Vac. Sci. Technol. B 14, 4110 (1996); http://dx.doi.org/10.1116/1.588601 (5 pages) | Cited 25 times

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We describe the lithographic control over the spectral response of three‐dimensional photonic crystals. By precise microfabrication of the geometry using a reproducible and reliable procedure consisting of electron beam lithography followed by dry etching, we have shifted the conduction band of crystals within the near‐infrared. Such microfabrication has enabled us to reproducibly define photonic crystals with lattice parameters ranging from 650 to 730 nm. In GaAs semiconductor wafers, these can serve as high‐reflectivity (>95%) mirrors. Here, we show the procedure used to generate these photonic crystals and describe the geometry dependence of their spectral response. © 1996 American Vacuum Society
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42.70.Qs Photonic bandgap materials
42.82.Cr Fabrication techniques; lithography, pattern transfer

Reliable fabrication of sub‐40 nm period gratings using a nanolithography system with interferometric dynamic focus control

D. R. S. Cumming, S. Thomas, S. P. Beaumont, and J. M. R. Weaver

J. Vac. Sci. Technol. B 14, 4115 (1996); http://dx.doi.org/10.1116/1.588602 (4 pages) | Cited 2 times

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Electron beam nanolithography tools readily permit the fabrication of ultra small structures. However, the disadvantage of such a system is that the depth of field is very small, making it difficult to maintain the focus of the system as the sample is moved due to sample topography, tilt, and stage run out. This presents a serious limitation to nanofabrication. To overcome this problem, we have built and installed a two color, heterodyne common path interferometer on a converted JEOL 100 CXII scanning transmission electron microscope. The interferometer compensates for the very small depth of field of the system by detecting variations in the sample working distance with respect to the electron optical objective lens, and dynamically correcting the lens current. The advantage of this system is that optical access to the sample can be made in a microscope with a very small working distance or sample space. To demonstrate this system, we have fabricated 38 nm period gratings on a silicon substrate. The process was a conventional one using a single 30 nm layer of 350 k molecular weight poly methyl methacrylate resist. The grating was exposed with a linear dose of 1.6 nC/cm and developed in 3:1 IPA:MIBK for 30 s at 23 °C. Patterns were transferred by lift off of an evaporated Ni/Au film. The gratings have a 1:1 mark:space ratio and a line‐width variation of 5 nm at 4σ. The stage can be moved over large areas and from chip to chip, and the lithography repeated successfully. This system therefore permits reliable state‐of‐the‐art nanolithography. © 1996 American Vacuum Society
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81.07.-b Nanoscale materials and structures: fabrication and characterization
81.16.-c Methods of micro- and nanofabrication and processing
85.35.-p Nanoelectronic devices
07.60.-j Optical instruments and equipment

Dry etching of horizontal distributed Bragg reflector mirrors for waveguide lasers

S. Thomas and S. W. Pang

J. Vac. Sci. Technol. B 14, 4119 (1996); http://dx.doi.org/10.1116/1.588603 (5 pages) | Cited 11 times

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Distributed Bragg reflector mirrors were etched in InP and GaAs. The mirrors were patterned using electron‐beam lithography and etched with an electron cyclotron resonance source. This fabrication technique has the advantage that no regrowth step is required and the length of the passive mirror region is confined to a few micrometers. The structure requires etching vertical profiles with smooth surface morphology and high selectivity to the masking material. The effects of rf power, Cl2 percentage in Ar, chamber pressure, and stage temperature were studied. Increasing the rf power from 100 to 250 W caused the InP selectivity to Ni to decrease from 147 to 55. A similar effect was observed for etching GaAs. For both InP and GaAs, a vertical profile can be obtained by reducing the Cl2 percentage in Ar and by using low chamber pressure of 1 mTorr. Increasing the Cl2 percentage, however, improves selectivity to the Ni mask. With 20% Cl2 in Ar, vertical profiles and high selectivities are obtained for both InP and GaAs. Using high temperature increases the volatility of InClx etch products and improves the selectivity of InP to Ni. For InGaAsP/InP waveguide lasers, 122 nm wide mirrors were etched in InP to a depth of 2.0 μm for maximum reflectivity at 1.55 μm. For AlGaAs/GaAs waveguide lasers, 59 nm wide mirrors were etched in GaAs to a depth of 1.5 μm. Etching of nλ/4 mirrors, where λ is the emission wavelength, was studied and the dependence of gap spacing on etch depth was measured. The variations in etch depth for different gaps were minimized by reducing the pressure. © 1996 American Vacuum Society
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42.82.Cr Fabrication techniques; lithography, pattern transfer
42.55.Px Semiconductor lasers; laser diodes

Mold‐assisted nanolithography: A process for reliable pattern replication

Jan Haisma, Martin Verheijen, Kees van den Heuvel, and Jan van den Berg

J. Vac. Sci. Technol. B 14, 4124 (1996); http://dx.doi.org/10.1116/1.588604 (5 pages) | Cited 107 times

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A process for reproducibly and reliably realizing thin‐layer patterning having details with dimensions of 100 nm or even less is described. This process has been called mold lithography. It is a two‐step process: First, a photopolymerization‐replication step is carried out, after which pattern transfer is realized through, e.g., wet or dry etching into the substrate material. We performed a number of elementary experiments to evaluate this process. Processing conditions are given and the obtained results are discussed. The strengths of this process are its simplicity and low cost while maintaining compatibility with (standard) semiconductor‐technology processing. © 1996 American Vacuum Society
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81.07.-b Nanoscale materials and structures: fabrication and characterization
81.16.-c Methods of micro- and nanofabrication and processing
85.35.-p Nanoelectronic devices

Nanoimprint lithography

Stephen Y. Chou, Peter R. Krauss, and Preston J. Renstrom

J. Vac. Sci. Technol. B 14, 4129 (1996); http://dx.doi.org/10.1116/1.588605 (5 pages) | Cited 241 times

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Nanoimprint lithography, a high‐throughput, low‐cost, nonconventional lithographic method proposed and demonstrated recently, has been developed and investigated further. Nanoimprint lithography has demonstrated 25 nm feature size, 70 nm pitch, vertical and smooth sidewalls, and nearly 90° corners. Further experimental study indicates that the ultimate resolution of nanoimprint lithography could be sub‐10 nm, the imprint process is repeatable, and the mold is durable. In addition, uniformity over a 15 mm by 18 mm area was demonstrated and the uniformity area can be much larger if a better designed press is used. Nanoimprint lithography over a nonflat surface has also been achieved. Finally, nanoimprint lithography has been successfully used for fabricating nanoscale photodetectors, silicon quantum‐dot, quantum‐wire, and ring transistors. © 1996 American Vacuum Society
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81.07.-b Nanoscale materials and structures: fabrication and characterization
81.16.-c Methods of micro- and nanofabrication and processing
85.35.-p Nanoelectronic devices
85.35.Be Quantum well devices (quantum dots, quantum wires, etc.)
85.60.Gz Photodetectors (including infrared and CCD detectors)

Fabrication of nanostructures on silicon surfaces on wafer scale by controlling self‐organization processes

T. Ogino, H. Hibino, and K. Prabhakaran

J. Vac. Sci. Technol. B 14, 4134 (1996); http://dx.doi.org/10.1116/1.588606 (6 pages) | Cited 8 times

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We describe a novel route for future Si integration technology in which atomically controlled nanostructures are designed to the level of full wafers based on self‐organization processes. As an example of the scenario, we present a Ge quantum dot network where individual dots interact with the neighboring dots through tunneling barriers, Schottky junctions, and so on. Ge dots are patterned on Si(111) surfaces by preferential nucleation of Ge islands at atomic steps and boundaries between reconstructed domains. It is then demonstrated that atomic step arrangement can be designed by patterning assisted control; this means that Ge quantum dot network can also be designed. Selective oxidation and silicidation in the Si/Ge systems are effectively utilized to form semiconductor/insulator/metal nanostructures from well‐ordered semiconductor structures. Based on the above processes, we propose a new approach to design nanostructure integration organized on wafer scale. © 1996 American Vacuum Society
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81.07.-b Nanoscale materials and structures: fabrication and characterization
81.16.-c Methods of micro- and nanofabrication and processing
85.35.-p Nanoelectronic devices
85.35.Be Quantum well devices (quantum dots, quantum wires, etc.)

Nanoscale patterning of an organosilane monolayer on the basis of tip‐induced electrochemistry in atomic force microscopy

Hiroyuki Sugimura, Keiko Okiguchi, Nobuyuki Nakagiri, and Masayuki Miyashita

J. Vac. Sci. Technol. B 14, 4140 (1996); http://dx.doi.org/10.1116/1.588607 (4 pages) | Cited 18 times

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An organosilane trimethylsilyl (TMS) monolayer prepared on silicon (Si) substrate by chemical vapor deposition was successfully applied as a self‐developing resist for atomic force microscope (AFM) lithography. The thickness of the monolayer was less than 1 nm. This resist was locally degraded due to electrochemical reactions induced in the junction between a conductive AFM probe and a Si–TMS sample. The generated pattern on the sample was then transferred to the Si substrate by chemical etching using the degraded region as an etching window. Degradation of the monolayer proceeded with both positive and negative sample biases. However, the absolute values of the voltage at which the probe‐scanned region began to show etching were +3.0 for Vs>0 and −5.0 V for Vs<0, in a 60% relative humidity air atmosphere. Faster patterning was achieved through increased current flow by applying a higher bias voltage. A 500 μm/s line drawing at Vs=+20.0 V with 2–3 nA was obtained. The number of injected electrons was estimated to be hundreds of times larger than the number of TMS groups in the scanned area. We therefore concluded that only a small part of the current flowing through the probe‐sample junction is actually responsible for the degradation. © 1996 American Vacuum Society
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81.07.-b Nanoscale materials and structures: fabrication and characterization
81.16.-c Methods of micro- and nanofabrication and processing
85.35.-p Nanoelectronic devices
81.65.Cf Surface cleaning, etching, patterning
82.45.-h Electrochemistry and electrophoresis

The nanoscilloscope: Combined topography and AC field probing with a micromachined tip

D. W. van der Weide and P. Neuzil

J. Vac. Sci. Technol. B 14, 4144 (1996); http://dx.doi.org/10.1116/1.588608 (4 pages) | Cited 14 times

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We introduce a new concept for combined probing of topography and local AC fields, and report preliminary results of tip fabrication and scale‐model measurements. The scanning force microscope (SFM) has been recently used to measure AC fields using the nonlinear response of the cantilever to voltage differences between the sample and scanning tip. By contrast, we extend the concept of near‐field scanning optical microscopy (NSOM) down in frequency by employing a non‐cutoff coaxial micromachined waveguide/tip, maintaining the topographic and tip–sample distance control capabilities of the SFM. Because this instrument will be used to measure both AC fields and topography with nanometer‐level localization and better than nanosecond temporal resolution, we call it a nanoscilloscope. © 1996 American Vacuum Society
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07.79.-v Scanning probe microscopes and components
68.37.Ef Scanning tunneling microscopy (including chemistry induced with STM)
68.37.Ps Atomic force microscopy (AFM)
68.37.Rt Magnetic force microscopy (MFM)
68.37.Uv Near-field scanning microscopy and spectroscopy

Three dimensional electron optical modeling of scanning tunneling microscope lithography in resists

E. A. Dobisz, H. W. P. Koops, F. K. Perkins, C. R. K. Marrian, and S. L. Brandow

J. Vac. Sci. Technol. B 14, 4148 (1996); http://dx.doi.org/10.1116/1.588609 (5 pages) | Cited 1 time

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Three dimensional electron optical simulations were used to model scanning tunneling microscope (STM) lithography in resists under field emission conditions. This work focuses on the effect of resists, as dielectric layers, between the tip and conducting substrate on the operation of the STM. Simulations were run for resist thicknesses of 1–50 nm, which are comparable to our experiments, and tip–resist separations of 1–20 nm. Simulations were run for a ‘‘best’’ tip of radius 10 nm and a typical tip of radius 50 nm. The results show that the presence of a resist layer dramatically reduces the range of stable STM operation, which is observed experimentally. For a given tip–substrate distance and fixed tip–substrate voltage, the interposition of the dielectric layer expels electric field and causes the electric field at the tip to increase. Although the tip will retract from the substrate, the tip–resist distance is less than the prior tip–bare substrate distance, for the same tip–sample voltage and same electric field at the tip. The effect increases with resist thickness. For a 25 nm thick resist layer, the STM will operate a factor of 2 closer to the resist than a bare substrate. In addition, the energy of the electrons entering the resist is 50% less than the applied tip–substrate bias. Estimates of spot size based upon emission centered about the tip–sample axis are ≤15 nm, which is consistent with the best experimental results. © 1996 American Vacuum Society
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81.07.-b Nanoscale materials and structures: fabrication and characterization
81.16.-c Methods of micro- and nanofabrication and processing
85.35.-p Nanoelectronic devices
41.85.-p Beam optics
79.70.+q Field emission, ionization, evaporation, and desorption

Silicon metal‐oxide‐semiconductor field‐effect transistor with gate structures defined by scanned probe lithography

M. S. Hagedorn, D. D. Litfin, G. M. Price, A. E. Gordon, and T. K. Higman

J. Vac. Sci. Technol. B 14, 4153 (1996); http://dx.doi.org/10.1116/1.588610 (4 pages) | Cited 5 times

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We report on the use of scanned probes to define nanolithographic features in the controlling gate structures of silicon metal‐oxide‐semiconductor field‐effect transistors (MOSFETs). By using an atomic force microscope (AFM) with conducting tips (either Ti coated Si3N4 or heavily doped Si cantilevers) in conjunction with surface adsorbed water, we define oxide structures by anodization which are used as masks for subsequent etching. These patterns consist of such things as constrictions and gratings in the gate. When combined with thin oxides, the pattern of the gate is mirrored in the higher mobility MOSFET inversion layer. Pattern transfer into the gate is accomplished by either direct anodization of the gate material (titanium) or by anodization of sacrificial resists consisting of plasma‐deposited organosilicon polymers from methylsilane precursors. The AFM anodization of titanium has been thoroughly described in the literature, and the AFM anodization of the plasma‐deposited organosilicon is thought to be a similar mechanism but the organosilicon is also photo‐oxidizable when exposed to deep‐UV radiation in the presence of oxygen. Using these two methods (direct anodization of gate material and anodization of sacrificial resists) enables AFM lithography to be carried at virtually any step in the process flow. In this way, nanostructure definition can be carried out as a last step in a standard process or may be inserted earlier. Completed devices and their characteristics will be shown. © 1996 American Vacuum Society
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85.30.Tv Field effect devices
81.07.-b Nanoscale materials and structures: fabrication and characterization
81.16.-c Methods of micro- and nanofabrication and processing
85.35.-p Nanoelectronic devices

How practical is 193 nm lithography?

M. Rothschild, J. A. Burns, S. G. Cann, A. R. Forte, C. L. Keast, R. R. Kunz, S. C. Palmateer, J. H. C. Sedlacek, R. Uttaro, A. Grenville, and D. Corliss

J. Vac. Sci. Technol. B 14, 4157 (1996); http://dx.doi.org/10.1116/1.588611 (5 pages) | Cited 2 times

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The use of 193 nm ArF lasers to extend optical projection lithography to its limits was proposed as early as the mid 1980s. Since then steady progress has been made in this area, and the last two years in particular have witnessed an exponentially growing interest in and commitment to its development. At present, 193 nm lithography is a leading candidate for printing 0.18 and 0.13 μm devices. This article reviews the state of development of this technology at Lincoln Laboratory. Significant progress has been made in most areas: qualification of optical materials, characterization of a prototype large‐field projection system, development of photoresist processes, and the fabrication of complementary metal‐oxide semiconductor devices. © 1996 American Vacuum Society
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81.07.-b Nanoscale materials and structures: fabrication and characterization
81.16.-c Methods of micro- and nanofabrication and processing
85.35.-p Nanoelectronic devices
42.82.Cr Fabrication techniques; lithography, pattern transfer
85.30.Tv Field effect devices

Can synthetic aperture techniques be applied to optical lithography?

Hiroshi Fukuda and Rudolf M. von Bunau

J. Vac. Sci. Technol. B 14, 4162 (1996); http://dx.doi.org/10.1116/1.588612 (5 pages) | Cited 1 time

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This article discusses the theoretical feasibility of applying optical aperture synthesis to lithography. A technique involving the insertion of three phase gratings into a conventional projection system is described. While this approach paraxially yields imaging with doubled spatial bandwidth, aberrations introduced by the gratings are shown to be a serious limitation. Image simulations demonstrated that for very restricted pattern types, resolution down to 0.1 μm is theoretically achievable. © 1996 American Vacuum Society
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85.40.Hp Lithography, masks and pattern transfer
42.79.Ag Apertures, collimators
81.07.-b Nanoscale materials and structures: fabrication and characterization
81.16.-c Methods of micro- and nanofabrication and processing
85.35.-p Nanoelectronic devices
42.30.Va Image forming and processing

Large‐area achromatic interferometric lithography for 100 nm period gratings and grids

T. A. Savas, M. L. Schattenburg, J. M. Carter, and Henry I. Smith

J. Vac. Sci. Technol. B 14, 4167 (1996); http://dx.doi.org/10.1116/1.588613 (4 pages) | Cited 59 times

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Achromatic interferometric lithography is the preferred approach for producing large‐area, spatially coherent 100 nm period gratings and grids. We report on improvements to processes which have enabled exposure areas of ≊10 cm2. In addition, we report on the fabrication of 100 nm period free‐standing gold gratings. © 1996 American Vacuum Society
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81.07.-b Nanoscale materials and structures: fabrication and characterization
81.16.-c Methods of micro- and nanofabrication and processing
85.35.-p Nanoelectronic devices
42.79.Dj Gratings

Experimental and simulated estimation of new super resolution technique

Kazuya Kamon and Yasuji Matsui

J. Vac. Sci. Technol. B 14, 4171 (1996); http://dx.doi.org/10.1116/1.588614 (4 pages) | Cited 2 times

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In order to support next‐generation devices, a super resolution technique having wide applicability and effective resolution enhancement has been proposed and some simulation results were demonstrated. It has been experimentally proven that the depth of focus of the new optics is 1.5 times wider than the modified illumination, which shows good agreement to previous simulation results. From the evaluation of the mask stage repeatability, 0.1 μm (on mask) alignment accuracy or lens distortion between the first and second mask is acceptable for the new optics. © 1996 American Vacuum Society
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81.07.-b Nanoscale materials and structures: fabrication and characterization
81.16.-c Methods of micro- and nanofabrication and processing
85.35.-p Nanoelectronic devices
42.30.Va Image forming and processing

Characterization and correction of optical proximity effects in deep‐ultraviolet lithography using behavior modeling

Anthony Yen, Alexander Tritchkov, John P. Stirniman, Geert Vandenberghe, Rik Jonckheere, Kurt Ronse, and Luc Van den hove

J. Vac. Sci. Technol. B 14, 4175 (1996); http://dx.doi.org/10.1116/1.588615 (4 pages) | Cited 1 time

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We present the characterization of optical proximity effects and their correction in deep‐UV lithography using an empirically derived model for calculating feature sizes in resist. The model is based on convolution of the mask pattern with a set of kernels determined from measuring the printed test structures in resist. The fit of the model to the measurement data is reviewed. The model is then used for proximity correction using commercially available proximity correction software. Corrections based on this model is effective in restoring resist linearity and in reducing line‐end shortening. It is also more effective in reducing optical proximity effects than corrections based only on aerial image calculations. © 1996 American Vacuum Society
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81.07.-b Nanoscale materials and structures: fabrication and characterization
81.16.-c Methods of micro- and nanofabrication and processing
85.35.-p Nanoelectronic devices

Application of optical lithography for high aspect ratio microstructures

B. Loechel, R. Demmeler, M. Rothe, W. Bruenger, S. Fehlberg, and G. Gruetzner

J. Vac. Sci. Technol. B 14, 4179 (1996); http://dx.doi.org/10.1116/1.588616 (5 pages) | Cited 1 time

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Interest in thick photoresist applications is steadily growing. Besides the bump fabrication and wire interconnect technology, the process of patterning thick layer photoresists by UV lithography is specially qualified for applications in micro electro mechanical systems. Specialized equipment and new photoresists have been developed or are under development to cope with the new challenges in the field of preparing extremely thick photoresist layers, to plan the process of patterning these thick resists, and to deal with the difficulties of the following galvanoplating step. A technology called three‐dimensional (3D) UV‐microforming was developed, consisting of a resist preparation process for very thick photoresists (positive or negative tone), UV lithographic steps, resist development, moulding procedures by galvanodeposition, and finally stripping and cleaning for finishing the structures. A minimum width of 3 μm for the resist bars was found to be necessary to withstand the fabrication process of lines and spaces in 15 μm thick resist. For thicker layers high aspect ratios of more than 10 as well as steep edges of more than 88° could be fabricated. The resist patterns were moulded by using electroplating. For microsystem applications metals and alloys can be deposited into the resist patterns. 3D UV‐microforming, a combination of UV patterning of thick layer resists and galvanoplating, enables the low‐cost fabrication of a wide variety of micro components for many different users. © 1996 American Vacuum Society
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07.10.Cm Micromechanical devices and systems

Calorimetric measurements of optical materials for 193 nm lithography

A. Grenville, R. Uttaro, J. H. C. Sedlacek, M. Rothschild, and D. Corliss

J. Vac. Sci. Technol. B 14, 4184 (1996); http://dx.doi.org/10.1116/1.588617 (4 pages) | Cited 1 time

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We have developed a new calorimetric method to accurately determine the absorption coefficient at 193 nm of optical materials such as fused silica and calcium fluoride. The amount of absorbed radiation is the power consumed by a thermoelectric cooler that maintains the sample at room temperature during exposure with a 193 nm laser. We report initial results from five types of fused silica which indicate that absorption coefficients are still a factor of 3 higher than the target of 0.001 cm−1 and that batch to batch variations remain common. The absorption coefficient for one grade of calcium fluoride has also been obtained. On one fused silica sample, an upper bound has been placed on the two‐photon absorption coefficient at a factor of 2 lower than those previously reported. Measurements have been performed under a variety of vacuum conditions yielding anomalous losses in transmission. © 1996 American Vacuum Society
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78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
42.70.-a Optical materials
07.20.Fw Calorimeters
81.07.-b Nanoscale materials and structures: fabrication and characterization
81.16.-c Methods of micro- and nanofabrication and processing
85.35.-p Nanoelectronic devices

Fabrication of metal–oxide–semiconductor devices with extreme ultraviolet lithography

K. B. Nguyen, G. F. Cardinale, D. A. Tichenor, G. D. Kubiak, K. Berger, A. K. Ray‐Chaudhuri, Y. Perras, S. J. Haney, R. Nissen, K. Krenz, R. H. Stulen, H. Fujioka, C. Hu, J. Bokor, D. M. Tennant, et al.

J. Vac. Sci. Technol. B 14, 4188 (1996); http://dx.doi.org/10.1116/1.588618 (5 pages) | Cited 4 times

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This article reports results from the successful fabrication of metal–oxide–semiconductor (MOS) devices with extreme ultraviolet lithography. n‐type MOS transistors with gate lengths of 0.1 μm were fabricated and demonstrated good device characteristics. The alignment strategy, mask layout, mask fabrication, and device characteristics will be reported. © 1996 American Vacuum Society
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85.30.-z Semiconductor devices
81.07.-b Nanoscale materials and structures: fabrication and characterization
81.16.-c Methods of micro- and nanofabrication and processing
85.35.-p Nanoelectronic devices

Study on elliptical polarization illumination effects for microlithography

Seong‐Ho Jeon, Bae‐Doo Cho, Kyeong‐Woon Lee, Sung‐Muk Lee, Ki‐Ho Baik, Chang‐Nam Ahn, and Dong‐Gyu Yim

J. Vac. Sci. Technol. B 14, 4193 (1996); http://dx.doi.org/10.1116/1.588619 (6 pages) | Cited 1 time

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The vector image code (VIC) consisting of the vector transmission cross coefficient (TCC) and Fourier transform of the mask function is widely applied to simulate the effects of polarization in microlithography. Until now studies were restricted to the effects of linear polarization. This linear polarization illumination predicts a larger contrast gap between TE polarization and TM polarization as the numerical aperture increases or the critical dimension decreases. In this article, we have studied the effects of elliptical polarization illumination (EPI) as a new method in order to decrease these contrast gaps. We improved VIC by adopting EPI including circular polarization. As a result of using the improved VIC, EPI shows that the contrast and the contrast gap can be tuned by adjusting the angle of polarization and the ratio of the ellipticity. The simulation result also shows that the higher the ratio of ellipticity the lower the contrast gap but at the expense of lowering the contrast somewhat. If this new EPI is adopted into microlithography, the contrast gap can be decreased while the contrast to a specified direction of the mask pattern can be kept high. © 1996 American Vacuum Society
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85.40.Hp Lithography, masks and pattern transfer
42.30.Va Image forming and processing

Passivate SiNx halftone phase shifting mask for deep ultraviolet exposure

S. Ito, T. Iwamatsu, H. Sato, M. Asano, K. Kawano, and F. Miyashita

J. Vac. Sci. Technol. B 14, 4199 (1996); http://dx.doi.org/10.1116/1.588620 (4 pages) | Cited 2 times

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Halftone phase shift masks with a single‐layer SiNx absorption film whose stoichiometric ratio x was controlled were developed at 365 and 248 nm, respectively. Because this stoichiometric ratio x was smaller than 1.33 (Si3N4), the SiNx halftone films were unstable, especially during 248 nm exposure, causing a transmittance error. In this article, we show how to get stable SiNx film for 248 nm exposure. © 1996 American Vacuum Society  
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85.40.Hp Lithography, masks and pattern transfer
81.05.Je Ceramics and refractories (including borides, carbides, hydrides, nitrides, oxides, and silicides)
78.66.Nk Insulators

Prospect and challenges of ArF excimer laser lithography processes and materials

T. Ohfuji, T. Ogawa, K. Kuhara, and M. Sasago

J. Vac. Sci. Technol. B 14, 4203 (1996); http://dx.doi.org/10.1116/1.588575 (4 pages) | Cited 5 times

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Practical chemically amplified resists for 193 nm lithography will be realized from newly developed polar alicyclic base polymers. Their resist performance is likely to be equal to that of resists used for 248 nm lithography, since a 193 nm resist basically follows the same physical rules as a conventional resist. Top surface imaging with a combination of 193 nm exposure and bi‐functional silyation reagent B(DMA)MS was used to produce 0.12 μm L&S patterns. This resolution corresponds to a k1 factor of 0.34. Therefore, the use of dry‐developed resists, which provide excellent resolution and a generous process margin, will help extend the use of 193 nm lithography. However, resolution enhancement techniques must still be developed to improve the process window. © 1996 American Vacuum Society
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85.40.Hp Lithography, masks and pattern transfer

Plasma‐deposited silylation resist for 193 nm lithography

Mark W. Horn, Brian E. Maxwell, Russell B. Goodman, Roderick R. Kunz, and Lynn M. Eriksen

J. Vac. Sci. Technol. B 14, 4207 (1996); http://dx.doi.org/10.1116/1.588576 (5 pages) | Cited 2 times

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Plasma‐enhanced chemical‐vapor‐deposited carbon‐based polymer films are examined for use as an all‐dry positive‐tone photoresist for 193 nm lithography. These films are designed to crosslink upon exposure to 193 nm radiation, enabling selective silicon uptake via reaction with hydroxyl groups. After oxygen plasma pattern transfer, features with resolution below 0.25 μm have been obtained. © 1996 American Vacuum Society
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81.07.-b Nanoscale materials and structures: fabrication and characterization
81.16.-c Methods of micro- and nanofabrication and processing
85.35.-p Nanoelectronic devices
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)

ArF surface modification resist process with enhanced water sorption ability

Takahiro Matsuo, Masayuki Endo, Masamitsu Shirai, and Masahiro Tsunooka

J. Vac. Sci. Technol. B 14, 4212 (1996); http://dx.doi.org/10.1116/1.588577 (4 pages)

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Surface modification resist (SMR) process, which gives negative‐tone image owing to the polysiloxane formation in the exposed resist surface using chemical vapor deposition, was studied for subquarter micron pattern fabrication. SMR was based on the hydrolysis of alkoxysilane and the subsequent condensation reaction in the presence of an acid catalyst and water. This article describes the application of SMR to ArF excimer laser lithography with enhanced water sorption ability. We propose the copolymer of propylideneimino p‐styrenesulfonate (PPISS) and methyl methacrylate with enhanced water sorption ability in order to improve the selectivity of the polysiloxane formation. PPISS generates sulfonic acid and acetone which acts as the diffusion promoter of water molecules. It was demonstrated that the hydrolysis reaction was promoted and the polysiloxane was more selectively formed with high sensitivity by using the proposed polymer. The influence of PPISS units ratio for the selectivity of polysiloxane formation and dry etch durability was investigated. Below 0.2 μm patterns fabrication was demonstrated by optimizing the ratio of the PPISS unit which functioned as the selective generation of acid and acetone. © 1996 American Vacuum Society
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81.07.-b Nanoscale materials and structures: fabrication and characterization
81.16.-c Methods of micro- and nanofabrication and processing
85.35.-p Nanoelectronic devices
82.20.Hf Product distribution
68.43.-h Chemisorption/physisorption: adsorbates on surfaces

Acid‐diffusion suppression in chemical amplification resists by controlling acid‐diffusion channels in base matrix polymers

Toshiyuki Yoshimura, Hiroshi Shiraishi, Tsuneo Terasawa, and Shinji Okazaki

J. Vac. Sci. Technol. B 14, 4216 (1996); http://dx.doi.org/10.1116/1.588578 (5 pages) | Cited 5 times

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We have investigated the suppression of acid diffusion during postexposure baking (PEB) of chemical amplification resists in terms of the molecular control of base matrix polymers to control acid‐diffusion channels. According to a previously proposed model, acid diffuses along acid‐diffusion channels in chemical amplification resists. The acid‐diffusion channels are composed of OH groups outside the base matrix polymers (active OH groups) and vacancies in the matrices. The negative‐type chemical amplification resists used in this work consisted of cresol novolak with controlled molecular‐weight distributions as the base matrix polymers, an acid‐catalyzed crosslinker of melamine resin, and acid generators of onium salt. Measurements of the dependence of the pattern sizes of isolated lines on the PEB time made it clear that acid diffusion defines the resist pattern sizes based on Fick’s law. The densities of the active OH groups play a critical role in acid diffusion, and a base matrix polymer with fewer active OH groups is expected to result in less acid diffusion. Therefore, we can suppress acid diffusion by reducing the number of oligomers in the base matrix polymers by a precipitation method, since these oligomers stereochemically include many active OH groups. We have obtained high resolution by using a resist with an oligomer‐free resin. The acid‐diffusion model was also confirmed based on infrared absorption spectroscopy and thermal analysis. We conclude that acid diffusion can be suppressed by controlling the acid‐diffusion channels. © 1996 American Vacuum Society
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85.40.Hp Lithography, masks and pattern transfer
82.20.Hf Product distribution

Diagnostics of patterning mechanisms in chemically amplified resists from bake dependencies of images

Marco A. Zuniga and Andrew R. Neureuther

J. Vac. Sci. Technol. B 14, 4221 (1996); http://dx.doi.org/10.1116/1.588579 (5 pages) | Cited 8 times

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Measurement and analysis of bake dependencies of resist profiles are used to establish the critical role of diffusion and acid loss in lithographic performance. Imaging experiments carried out with APEX‐E with postexposure bake temperatures above and below its glass transition temperature evidence widely dissimilar feature size dependencies attributable to different acid diffusion mechanisms in the glassy and the rubbery polymer, respectively. Examination of the mechanisms determining e‐beam exposed resist image stability show that, when an acid loss mechanism is present, the initial amount of acid generated the reaction rate, and the diffusion mechanisms are essential in predicting feature size dependence on postexposure bake conditions. © 1996 American Vacuum Society
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85.40.Hp Lithography, masks and pattern transfer

A study of acid diffusion in chemically amplified deep ultraviolet resist

Toshiro Itani, Hiroshi Yoshino, Shuichi Hashimoto, Mitsuharu Yamana, Norihiko Samoto, and Kunihiko Kasama

J. Vac. Sci. Technol. B 14, 4226 (1996); http://dx.doi.org/10.1116/1.588580 (3 pages) | Cited 17 times

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Postexposure bake (PEB) dependence of photogenerated acid diffusion was investigated in a chemically amplified deep ultraviolet positive resist. The resist consisted of a tert‐butoxycarbonyl protected polystyrene as base resin and 2,4‐dimethylbenzenesulfonic acid derivative as photoacid generator. The diffusion length of photoacid increased with increasing PEB temperature or its time. Moreover, the activation energy of acid diffusion reaction within the resist film became smaller, with increased exposure dose. It is considered that hydrophilic OH sites of the base resin generated by the deprotection of hydrophobic protecting groups has a role as one of the diffusion paths in the polymer matrix. Furthermore, it was found that the diffusion coefficient under high PEB conditions was affected by the acid reduction. Based on the analysis of diffusion characteristics, clear correlation between acid diffusion in the resist film and PEB conditions was obtained. These results are useful for improving both resolution capability and pattern profiles. © 1996 American Vacuum Society
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85.40.Hp Lithography, masks and pattern transfer
82.20.Hf Product distribution

A multilayer inorganic antireflective system for use in 248 nm deep ultraviolet lithography

R. A. Cirelli, G. R. Weber, A. Kornblit, R. M. Baker, F. P. Klemens, J. DeMarco, and C. S. Pai

J. Vac. Sci. Technol. B 14, 4229 (1996); http://dx.doi.org/10.1116/1.588581 (5 pages) | Cited 11 times

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We propose a novel technique for reducing substrate reflections in 248 nm deep ultraviolet (DUV) lithography. The method we have developed utilizes a multilayer scheme comprised of layers of silicon rich oxide. Deposition of the film stack is carried out on a production ready PE‐CVD tool in one continuous operation. The combining of multiple layers allows a gradual change in absorption thereby minimizing the reflection coefficient at the resist/ARC interface. The method of operation of these films is one of total absorption rather than the more common destructive interference method of a single layer film which relies on very tight thickness control. Absorption of the combined films is high enough to be effective on even the most highly reflective substrates such as aluminum. Furthermore, this technique does not require the ARC films to be tuned in their optical constants to accommodate the underlying substrate. We have successfully patterned wafers with feature sizes as small as 200 nm with no appreciable change in line width due to the underlying topography. The multilayer ARC system has been successfully integrated into the gate level of a 0.25 μm design rule device with excellent results. A description of the films used, their optical properties, and results from experimental data, as well as numerical simulations, will be reported. © 1996 American Vacuum Society
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81.07.-b Nanoscale materials and structures: fabrication and characterization
81.16.-c Methods of micro- and nanofabrication and processing
85.35.-p Nanoelectronic devices
42.79.Wc Optical coatings

Effect of gaseous permeability of overcoat layer on KrF chemically amplified positive resists

S. Kishimura, J. Sakai, K. Tsujita, and Y. Matsui

J. Vac. Sci. Technol. B 14, 4234 (1996); http://dx.doi.org/10.1116/1.588582 (5 pages) | Cited 1 time

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The process of removing an overcoat (OC) on the tert‐butoxycarbonyl (t‐BOC) type chemically amplified positive resists has been studied, and it has been found that in the case of removing the OC after postexposure bake (PEB), or at development, the decrease in the dissolution rate at the exposed region results in the formation of the surface insoluble layer and scum. This reduction in the rate became larger with increasing the OC thickness and the t‐BOC ratio in the resist, and it was shown by Fourier transform infrared spectra that the t‐BOC group disappeared and a small amount of tert‐butoxy moiety appeared in the fully exposed region. When the OC layer remained on the resist film during PEB, isobutene generated by the deprotection of t‐BOC was prevented from permeating out of the resist film and then recombined with the OH group in the base polymer. Therefore, it was found and verified that by using the acidic OC material which exhibits a high permeability for gases, the resist performance was improved. © 1996 American Vacuum Society
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85.40.Hp Lithography, masks and pattern transfer
82.20.Hf Product distribution

Resist application effects on chemically amplified resist response

Paul M. Dentinger, Carla M. Nelson, Steven J. Rhyner, James W. Taylor, Theodore H. Fedynyshyn, and Michael F. Cronin

J. Vac. Sci. Technol. B 14, 4239 (1996); http://dx.doi.org/10.1116/1.588583 (7 pages) | Cited 8 times

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Chemically amplified negative resist films of Shipley SAL 605 at 1.0 μm thickness show a statistically optimized sensitivity that is twice that observed with 0.5 μm films when exposed to x rays from an electron storage ring. Because of the large ‘‘depth of focus’’ of proximity x‐ray lithography, the differences between thick and thin films are due to resist chemical and physical effects and processing conditions, not to the exposure process. Using identical processing conditions, 1.0‐μm‐thick films showed 34% larger linewidths than 0.5 μm films for isolated lines from one mask with a target linewidth of 0.215 μm. Gel permeation chromatography results indicated that there was no dependence of resin or crosslinker concentration on thickness of the applied film. The photogenerated acid and residual solvent were quantified prior to postexposure bake, and neither was able to explain the apparent sensitivity dependence on thickness. The work suggests that some of the differences arises in the resist application process because of the ability of the thicker film to retain small molecular weight species which facilitate the linewidth production. This implies that thinner films should show better resolution purely because of chemical and physical factors in the resist film. © 1996 American Vacuum Society
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85.40.Hp Lithography, masks and pattern transfer
82.50.Kx Processes caused by X-rays or γ-rays

Impact of reduced resist thickness on deep ultraviolet lithography

T. Azuma, T. Ohiwa, K. Okumura, T. Farrell, R. Nunes, D. Dobuzinsky, G. Fichtl, and A. Gutmann

J. Vac. Sci. Technol. B 14, 4246 (1996); http://dx.doi.org/10.1116/1.588584 (6 pages) | Cited 5 times

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Potential capabilities of a thinner resist process are verified from both points of view—lithography and etch processes. The experimental results for lines and spaces indicate that a larger gain in process window could absolutely go along with reduced resist thickness. It is found that the thinner resist process could successfully improve not only the optical proximity effect in lithography processes but also the microloading effect in etch processes. It is also demonstrated that an application of the thinner resist process would be useful to further extend advantages of higher numerical aperture exposure systems. The thinner resist process is found to be effective to improve the process window of contact holes. Moreover, a novel pattern transfer process could be demonstrated using the practical limit of resolution capability up to k1=0.4. © 1996 American Vacuum Society
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85.40.Hp Lithography, masks and pattern transfer

Application of a reaction‐diffusion model for negative chemically amplified resists to determine electron‐beam proximity correction parameters

N. Glezos, G. P. Patsis, I. Raptis, P. Argitis, M. Gentili, and L. Grella

J. Vac. Sci. Technol. B 14, 4252 (1996); http://dx.doi.org/10.1116/1.588585 (5 pages) | Cited 6 times

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The method of single pixel exposures is applied for the determination of acid diffusion effects in negative chemically amplified resists. The wide range of crosslink density values contained in a single dot is used to determine nonlinear diffusion parameters. A reaction‐diffusion model is developed where the diffusion coefficient D is a function of the crosslink density Θ. This function D(Θ) is evaluated for a given range of postexposure bake parameters in each case and the information obtained is used for proximity correction, also using the e‐beam lithography simulation tool LITHOS. In order to test the model under different circumstances, two resists are studied, namely, the commercially available SAL‐601 and the experimental epoxy novolac resist EPR. The diffusion coefficient is evaluated for each resist under the best processing conditions. The proximity correction procedure is fully demonstrated in the case of SAL‐601. © 1996 American Vacuum Society
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85.40.Hp Lithography, masks and pattern transfer
82.20.-w Chemical kinetics and dynamics

Negative resist corner rounding. Envelope volume modeling

Paul Isaac L. Hagouel, Andrew R. Neureuther, and Andrew M. Zenk

J. Vac. Sci. Technol. B 14, 4257 (1996); http://dx.doi.org/10.1116/1.588586 (5 pages) | Cited 5 times

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A pronounced feature of negative resist developed profiles is corner rounding. Almost all of the current resists are composed of polymeric materials and negative resists depend on cross‐linking during exposure for feature delineation after development. The envelope sphere polymer molecule modeling describes the creation of the rounded profile at corners of resist lines during dissolution. A cellular automata dissolution model incorporates the envelope model, simulates the mechanics of the etching process, and predicts the corner rounding. We used Shipley SNR‐248 negative resist for the experimental profiles. The experimental results confirm the dependence of the dissolution rate Eri,j on the differential etch rate between exposed and unexposed regions (volumes) of the resist. High postexposure bake temperatures and higher development environment temperatures modify the profiles. © 1996 American Vacuum Society
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85.40.Hp Lithography, masks and pattern transfer

Electron‐beam induced etching of resist with water vapor as the etching medium

K. T. Kohlmann‐von Platen and W. H. Bruenger

J. Vac. Sci. Technol. B 14, 4262 (1996); http://dx.doi.org/10.1116/1.588587 (5 pages) | Cited 6 times

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H2O vapor as the etching medium has been investigated for electron beam induced etching of an organic resist. The aim was the determination of the dependencies on the process parameters. The etch rate increases with decreasing beam energy and increasing H2O vapor flux (i.e., molecules per time and area). At 5 keV beam energy, the achieved etch rate is 55 nm/min. By lowering the beam energy to 1 keV (maximum of the secondary electron yield) and increasing the scan speed (approximately 1–5 MHz), a pronounced rise to the etch rate is expected. © 1996 American Vacuum Society
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81.65.Cf Surface cleaning, etching, patterning
85.40.Hp Lithography, masks and pattern transfer

Correlation of UVIIHS resist chemistry to dissolution rate measurements

J. Thackeray, T. H. Fedynyshyn, D. Kang, M. M. Rajaratnam, G. Wallraff, J. Opitz, and D. Hofer

J. Vac. Sci. Technol. B 14, 4267 (1996); http://dx.doi.org/10.1116/1.588588 (5 pages) | Cited 4 times

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This article describes the correlation of UVIIHS resist chemistry to dissolution rate measurements as a function of resist processing conditions. The acid generation efficiency, α, for the UVIIHS photoacid generator is high, 0.027 cm2/mJ. The dissolution rate versus exposure curves show the excellent developer selectivity of UVIIHS, with n values >8 for all processes. The rmax values for this resist are above 20 000 Å/s, which is higher than any positive resist previously reported. The extent conversion for deprotection is directly related to the dissolution rate changes; ∼30% deprotection correlates to the E0 dose for all process conditions evaluated. At 30%–40% acid produced, all of the deprotection chemistry is essentially completed. The chemical contrast, as measured by extent conversion versus exposure dose, is strongly affected by the postexposure bake (PEB) temperature, with 140 °C PEB showing higher chemical and lithographic contrast than the 130 °C PEB. Mack’s dissolution model has been shown to work for these data sets. © 1996 American Vacuum Society
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85.40.Hp Lithography, masks and pattern transfer
82.20.Hf Product distribution

Nanometer‐scale resolution of calixarene negative resist in electron beam lithography

J. Fujita, Y. Ohnishi, Y. Ochiai, E. Nomura, and S. Matsui

J. Vac. Sci. Technol. B 14, 4272 (1996); http://dx.doi.org/10.1116/1.588589 (5 pages) | Cited 19 times

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New nonpolymer materials, calixarene derivatives were tested as high‐resolution negative resists for use in electron beam lithography. Arrays of 12‐nm‐diam dots with a 25 nm pitch were fabricated easily. The sensitivity of calixarene in terms of area dose ranged from 700 to 7000 μC/cm2, and the required dose for dot fabrication was about 105 electrons/dot. The standard area dose for calixarene is almost 20 times higher than that for polymethyl methacrylate (PMMA), but the electron spot dose for dot fabrication by calixarene is almost the same as that for PMMA and other highly sensitive resists such as SAL (chemically amplified negative resist for electron beam made by Shipley). The electron spot dose for such extremely small dots does not seem to depend on standard area dose, but any resist tends to require the same dose under exposure in a 50 keV electron beam writing system. We propose a qualitative exposure model that suggests a tradeoff of dose and dot size. The calixarene seems to be promising material for nanofabrication. © 1996 American Vacuum Society
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81.07.-b Nanoscale materials and structures: fabrication and characterization
81.16.-c Methods of micro- and nanofabrication and processing
85.35.-p Nanoelectronic devices

Measurement of the backscatter coefficient using resist response curves for 20–100 keV electron beam lithography on Si

G. Patrick Watson, Diana Fu, Steven D. Berger, Donald Tennant, Linus Fetter, Anthony Novembre, and Christopher Biddick

J. Vac. Sci. Technol. B 14, 4277 (1996); http://dx.doi.org/10.1116/1.588590 (6 pages) | Cited 6 times

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The effective backscatter coefficient η is a quantity that must be known with precision so that the proximity effect can be adequately compensated to minimize feature size variations in electron beam lithography. A unique technique to measure η that does not require the precise form of the backscatter dose distribution was employed. This method simply compares the resist response near the center of printed features that are much smaller and much larger than the characteristic range of the long range scatter. This technique was already employed to estimate the backscatter coefficient on Si at 100 keV beam energies. We have extended this measurement to determine η at lower beam energies. Results show that η on Si is 0.38, 0.50, 0.55, and 0.46 for 100, 50, 40, and 20 keV beam energies, respectively. Monte Carlo simulations indicate a trend of decreasing η with increasing beam energy, consistent with the experimental results except at 20 keV. © 1996 American Vacuum Society
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85.40.Hp Lithography, masks and pattern transfer
41.75.Fr Electron and positron beams

High voltage electron beam nanolithography on WO3

F. Carcenac, C. Vieu, A. M. Haghiri‐Gosnet, G. Simon, M. Mejias, and H. Launois

J. Vac. Sci. Technol. B 14, 4283 (1996); http://dx.doi.org/10.1116/1.588591 (5 pages) | Cited 1 time

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High voltage electron beam lithography experiments on thin films of tungsten trioxide are reported. For linear doses around 10 mC/cm at 200 kV, a negative resist behavior is observed after development in a NaOH solution. Features with dimensions as low as 15 nm with aspect ratios up to 10, exhibiting weak size fluctuations and vertical sidewalls are routinely achieved. Proximity effects are found to be negligible allowing the fabrication of structures with less than 10 nm separation. The exposure mechanism is investigated by transmission electron microscopy and diffraction. A crystallization process induced by the electron bombardment is clearly evidenced. A model based on the amorphous to crystalline phase transition induced by electron irradiation is proposed to account for the experimental observations. © 1996 American Vacuum Society
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81.07.-b Nanoscale materials and structures: fabrication and characterization
81.16.-c Methods of micro- and nanofabrication and processing
85.35.-p Nanoelectronic devices
61.80.Fe Electron and positron radiation effects
81.05.Je Ceramics and refractories (including borides, carbides, hydrides, nitrides, oxides, and silicides)

Extendibility of x‐ray lithography to ⩽130 nm ground rules in complex integrated circuit patterns

Scott Hector, William Chu, Matthew Thompson, Victor Pol, Bill Dauksher, Kevin Cummings, Doug Resnick, Sandeep Pendharkar, Juan Maldonado, Mark McCord, Azalia Krasnoperova, Lars Liebmann, Jerry Silverman, Jerry Guo, Mumit Khan, et al.

J. Vac. Sci. Technol. B 14, 4288 (1996); http://dx.doi.org/10.1116/1.588592 (6 pages) | Cited 6 times

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Previous experimental and theoretical evidence indicates that x‐ray lithography can be used to pattern ≤180 nm features. In order to be used in manufacturing, x‐ray lithography of complex integrated circuit patterns (i.e., dense two‐dimensional patterns) needs to be demonstrated with a practical proximity gap. However, no large body of experimental evidence exists for the extendibility of x‐ray lithography for complex patterns with ground rules of ≤130 nm at gaps of 10–20 μm. Simulations of image formation and resist dissolution are shown to have good agreement with experimental results. These simulations are then used to predict exposure latitude and gap latitude for printing one‐dimensional 75–125 nm patterns at 10–15 μm gaps. Simulations indicate that at least ±10% exposure dose latitude will exist for simple patterns at these gaps, but significant nested‐to‐isolated linewidth bias will exist. Gaps must be controlled to ±1 μm for ±10% dose latitude. More complex two‐dimensional patterns have been shown to exhibit line end shortening [J. Maldonado, R. Dellaguardia, S. Hector, M. McCord, and L. Liebmann, J. Vac. Sci. Technol. B 13, 3094 (1995)] that simulations qualitatively indicate a rise in part due to image formation. Simple serifs on line ends may be needed to reduce line end shortening. © 1996 American Vacuum Society
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81.07.-b Nanoscale materials and structures: fabrication and characterization
81.16.-c Methods of micro- and nanofabrication and processing
85.35.-p Nanoelectronic devices

Extendibility of synchrotron radiation lithography to the sub‐100 nm region

Kimiyoshi Deguchi, Kazunori Miyoshi, Masatoshi Oda, Tadahito Matsuda, Akira Ozawa, and Hideo Yoshihara

J. Vac. Sci. Technol. B 14, 4294 (1996); http://dx.doi.org/10.1116/1.588593 (4 pages) | Cited 16 times

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This article discusses the resolution of synchrotron radiation lithography in the sub‐100 nm region, taking into consideration the mass production of large‐scale integrated circuits, under attainable conditions for the x‐ray mask, proximity gap, and resist processes. Resolution and exposure latitude for line‐and‐space patterns are markedly improved by using a mask with a contrast of only 2.5. Resolutions of 90, 80, 70, and 60 nm can be achieved with proximity gaps of 30, 20, 15, and 10 μm if a high‐contrast resist and a low‐surface tension developer are used. The latitude will be 10% for pattern sizes as small as 70 nm when the proximity gap is narrower than 15 μm. The effects of mask duty [which is defined to be the ratio of the absorber (line) width to the pattern pitch, i.e., duty cycle] on the optimum exposure dose and mask linearity are also evaluated. © 1996 American Vacuum Society
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81.07.-b Nanoscale materials and structures: fabrication and characterization
81.16.-c Methods of micro- and nanofabrication and processing
85.35.-p Nanoelectronic devices

Replication of near 0.1 μm hole patterns by using x‐ray lithography

Yukiko Kikuchi, Naoko Kihara, Shinji Sugihara, Satoshi Saitoh, Kenzo Kondo, Hiroshi Nomura, and Tohru Ozaki

J. Vac. Sci. Technol. B 14, 4298 (1996); http://dx.doi.org/10.1116/1.589040 (5 pages) | Cited 1 time

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The feasibility of x‐ray lithography in applying device process was studied through fabrication of a small circuit consisting of experimental stacked film and contact holes numbering about 1k with replicated sizes from 0.6 to 0.085 μm. To resolve fine contact holes, in‐house chemically amplified positive resist was used by employing a high contrast post‐exposure‐bake condition. By measuring the resistance and yields of prepared circuits, we have evaluated the reliability of the circuits. High yield of larger than 0.9 was obtained for contact holes larger than 0.15 μm, and prepared circuits were found to be feasible down to 0.085 μm. © 1996 American Vacuum Society
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81.07.-b Nanoscale materials and structures: fabrication and characterization
81.16.-c Methods of micro- and nanofabrication and processing
85.35.-p Nanoelectronic devices

Overlay accuracy of Canon synchrotron radiation stepper XFPA for 0.15 μm process

K. Saitoh, H. Ohsawa, K. Sentoku, T. Matsumoto, N. Mizusawa, Y. Fukuda, K. Uda, H. Sumitani, and T. Hifumi

J. Vac. Sci. Technol. B 14, 4303 (1996); http://dx.doi.org/10.1116/1.589041 (5 pages) | Cited 4 times

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Canon has been developing a synchrotron radiation stepper system for x‐ray lithography feasibility studies. We have developed a novel accurate alignment system using the dual grating lens (DGLs) method. In this article, we explain the principle of the DGL, and the results of the alignment accuracy and process applicability tests. We have evaluated alignment performance for translation (X,Y) and rotation (θ) at the center of every exposure area. We obtained the alignment accuracy 3σ of 19 nm (X), 15 nm (Y) and 0.8 μrad (θ), using etched SiN patterns on Si substrates, and the overlay accuracy in an actual dynamic random access memory fabrication process 3σ of 34 nm (X), 31 nm (Y), and 2.1 μrad (θ). After eliminating the alignment offset in each shot, the values (3σ) are 18 nm, 21 nm, 1.4 μrad, respectively. These results show that the alignment method is promising for 0.15 μm level device fabrication. © 1996 American Vacuum Society
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81.07.-b Nanoscale materials and structures: fabrication and characterization
81.16.-c Methods of micro- and nanofabrication and processing
85.35.-p Nanoelectronic devices
06.60.Sx Positioning and alignment; manipulating, remote handling

Predicting in‐plane distortion from electron‐beam lithography on x‐ray mask membranes

D. L. Laird, R. L. Engelstad, D. M. Puisto, R. E. Acosta, K. D. Cummings, and W. A. Johnson

J. Vac. Sci. Technol. B 14, 4308 (1996); http://dx.doi.org/10.1116/1.589042 (6 pages) | Cited 2 times

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To produce x‐ray masks useable for 0.25 μm lithography and beyond, all sources of mask distortion must be minimized. In order to facilitate the fabrication of high‐quality masks, the phenomenon of changes in resist stress during e‐beam exposure has been studied. Finite element modeling was employed to determine the effects of various geometric and material properties on final image quality. Additionally, writing patterns and multipass exposure were also studied. The results indicate that the stress relief phenomenon can be controlled in a well‐designed system. © 1996 American Vacuum Society
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85.40.Hp Lithography, masks and pattern transfer

Trench isolation at 300 nm active pitch using x‐ray lithography

Asanga H. Perera, M. Thompson, S. Hector, S. Iyer, M. J. Azrak, and M. Zavala

J. Vac. Sci. Technol. B 14, 4314 (1996); http://dx.doi.org/10.1116/1.589043 (4 pages)

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A nanofabrication technology providing device isolation at an active pitch of 300 nm has been developed using x‐ray lithography for pattern definition. The isolation scheme uses oxide filled trenches etched into the silicon substrate, which are 300–350 nm deep and have a 150 nm minimum width. Chemical mechanical polishing is utilized to achieve global planarization. The superior diode leakage and gate oxide (tox=55 Å) performance, excellent metal–oxide–semiconductor field effect transistor characteristics, and robust latch‐up behavior demonstrated by this trench isolation technology, present it as a key enabler for continued scaling of semiconductor technologies. The experimental data presented predicts that with careful attention to process integration, trench isolation can be scaled well into the sub‐0.25 μm size scale. © 1996 American Vacuum Society
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85.40.Ls Metallization, contacts, interconnects; device isolation
85.30.Tv Field effect devices
81.07.-b Nanoscale materials and structures: fabrication and characterization
81.16.-c Methods of micro- and nanofabrication and processing
85.35.-p Nanoelectronic devices

A proposal for maskless, zone‐plate‐array nanolithography

Henry I. Smith

J. Vac. Sci. Technol. B 14, 4318 (1996); http://dx.doi.org/10.1116/1.589044 (5 pages) | Cited 22 times

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We propose a novel form of x‐ray projection lithography that: (1) requires no mask, and hence can be considered an x‐ray pattern generator; (2) is, in principle, capable of reaching the limits of the lithographic process. The new scheme utilizes an array of Fresnel zone plates, and matrix‐addressed micromechanical shutters to turn individual x‐ray beamlets on or off in response to commands from a control computer. Zone plate resolution is approximately equal to the minimum zone width, which can approach 10 nm. Zone plates are narrow‐band lensing elements: For a diffraction limited focus, the source bandwidth Δλ/λ should be less than or equal to the reciprocal of the number of zones N. An undulator having Nu magnetic sections emits collimated radiation in a bandwidth Δλ/λ=1/Nu. Nu is usually in the range 35–100. We present a system design based on 25 nm lithographic resolution using λ=4.5 nm. For N=100 the zone‐plate diameter is 10 μm. Each zone plate of the array would be responsible only for exposure within its ‘‘unit cell.’’ To fill in a full pattern, the stage holding the sample would be scanned in X and Y while the beamlets are multiplexed on and off. A microundulator designed for installation on a commercial compact synchrotron can provide 87 mW within a 2% bandwidth around 4.5 nm in a divergence cone of 0.28 mrad. The calculated efficiency of first‐order focus for a zone plate operating at 4.5 nm is 31%, using 130 nm of spent U as the absorber/phase shifter. An exposure rate of ∼1 cm2/s at 25 nm resolution appears feasible. © 1996 American Vacuum Society
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81.07.-b Nanoscale materials and structures: fabrication and characterization
81.16.-c Methods of micro- and nanofabrication and processing
85.35.-p Nanoelectronic devices

Optimization of the refractory x‐ray mask fabrication sequence

K. D. Cummings, W. J. Dauksher, W. A. Johnson, M. F. Laudon, and R. Engelstad

J. Vac. Sci. Technol. B 14, 4323 (1996); http://dx.doi.org/10.1116/1.589045 (5 pages) | Cited 7 times

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This article discusses the effects different process flows have on the material and control requirements for refractory (subtractive) x‐ray masks. Our investigation of x‐ray masks shows that a film’s stress uniformity is more critical (for distortion) than the magnitude of the stress. In particular, we find for the wafer sequence the requirement on the membrane film’s stress uniformity is the most critical specification. For the membrane sequence, the requirement is for stress uniformity for films that are removed from the membrane (after pattern formation). We find that SiC reduces the distortions from the film stress gradient, however, the frame structure determines the distortions from a film’s mean stress. Finally, we conclude the best choice of an x‐ray mask flow should be decided on our ability to modify wafer equipment and processes, to control the stress uniformity of the membrane film, to control the stress and uniformity of the resist, hardmask, and absorber films, and finally to handle the lithography required to create predistorted mask patterns. © 1996 American Vacuum Society
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85.40.Hp Lithography, masks and pattern transfer

Defect‐free x‐ray masks for 0.2‐μm large‐scale integrated circuits

I. Okada, Y. Saitoh, M. Sekimoto, T. Ohkubo, and T. Matsuda

J. Vac. Sci. Technol. B 14, 4328 (1996); http://dx.doi.org/10.1116/1.589046 (4 pages) | Cited 3 times

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The x‐ray mask fabrication process we developed can be used to make and maintain essentially defect‐free masks consisting of Ta absorbers on SiN membrane. The surface of the deposited SiN substrates is polished to make them as smooth as possible. As Ta is chemically stable, mask fabrication processes are frequently followed with a wet‐cleaning process using a strong acid solution. Inspection of resist patterns printed on a wafer confirms that there are less than 20 printable defects per mask, and there are no defects on the back surface. The inspection and repair are repeated until the mask is defect free. Defects caused by mask handling and x‐ray exposure are immediately washed up by wet cleaning with strong acid. The resulting x‐ray masks have been used in large‐scale integrated circuits fabrication, and fully functional devices have been obtained. © 1996 American Vacuum Society
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81.07.-b Nanoscale materials and structures: fabrication and characterization
81.16.-c Methods of micro- and nanofabrication and processing
85.35.-p Nanoelectronic devices

X‐ray mask distortion correction technology using pattern displacement simulator

S. Uchiyama, M. Oda, and T. Matsuda

J. Vac. Sci. Technol. B 14, 4332 (1996); http://dx.doi.org/10.1116/1.589047 (4 pages) | Cited 2 times

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A new method to correct x‐ray mask distortion was developed. This method uses the correction method of previous analysis of distortion and transformation of coordinates (PAT) and a simulator to calculate pattern displacement caused during backetching. The key advantages of using PAT with a simulator are that no extra time, substrates, or labor are required to fabricate send‐ahead masks. Using this correction method, it was confirmed that the 3σ value of the pattern placement error was reduced to below 76 nm. This indicated that PAT with a pattern displacement simulator was as useful for improving the pattern placement accuracy of x‐ray masks as PAT with send‐ahead masks. In addition, analysis of the remaining error made it clear that the correction error was mainly caused by the lack of e‐beam writing accuracy. © 1996 American Vacuum Society
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85.40.Hp Lithography, masks and pattern transfer
81.07.-b Nanoscale materials and structures: fabrication and characterization
81.16.-c Methods of micro- and nanofabrication and processing
85.35.-p Nanoelectronic devices

X‐ray induced mask contamination and particulate monitoring in x‐ray steppers

C. Capasso, A. Pomerene, W. Chu, J. Leavey, A. Lamberti, S. Hector, J. Oberschmidt, and V. Pol

J. Vac. Sci. Technol. B 14, 4336 (1996); http://dx.doi.org/10.1116/1.589048 (5 pages) | Cited 2 times

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The belief that proximity x‐ray lithography is insensitive to contamination has been based on the assumption that contaminants are small hydrocarbon compounds. However, we will show that x rays may induce photoassisted processes that deposit saltlike films on the mask surface. We will also provide an explanation for the film geometry in the early stages of its growth and suggest some possible solutions to the issue. © 1996 American Vacuum Society
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81.07.-b Nanoscale materials and structures: fabrication and characterization
81.16.-c Methods of micro- and nanofabrication and processing
85.35.-p Nanoelectronic devices
82.50.Kx Processes caused by X-rays or γ-rays
81.65.Cf Surface cleaning, etching, patterning

Multiple‐pass writing optimization for proximity x‐ray mask‐making using electron‐beam lithography

Denise M. Puisto, Mark S. Lawliss, Janet M. Rocque, Kurt R. Kimmel, and John G. Hartley

J. Vac. Sci. Technol. B 14, 4341 (1996); http://dx.doi.org/10.1116/1.589049 (4 pages) | Cited 4 times

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We have evaluated and implemented a multiple‐pass writing scheme that significantly improves the image‐placement performance of masks for proximity x‐ray lithography. Masks were fabricated using a 75 kV EL‐3+ electron‐beam lithography system that separates the data into fields and subfields, and exposes the images by using a variable‐shaped beam. Multiple‐pass writing allows averaging of system noise between multiple exposure passes written at fractional doses [Jpn. J. Appl. Phys. 32, L1707 (1993)]; stitching errors can also be averaged by offsetting the locations of the tool field and subfield boundaries for each pass [Jpn. J. Appl. Phys. 32, 5933 (1993)]. Multiple‐pass writing was evaluated both with and without boundary offsets. Our experiments indicated that the offset method resulted in better image placement but negatively affected image size and defect performance because of the EL‐3+system limitations. The no‐offset method was optimized and implemented and achieved sub‐50 nm (3σ) image placement. The method was then transferred to the EL‐4 electron‐beam lithography system, resulting in image placement of sub‐30 nm (3σ). © 1996 American Vacuum Society
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81.07.-b Nanoscale materials and structures: fabrication and characterization
81.16.-c Methods of micro- and nanofabrication and processing
85.35.-p Nanoelectronic devices

Fabrication of x‐ray lithography masks with optical lithography

D. LaTulipe, J. R. Maldonado, P. Mitchell, R. Leduc, and I. Babich

J. Vac. Sci. Technol. B 14, 4345 (1996); http://dx.doi.org/10.1116/1.589050 (5 pages)

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We describe a technique to fabricate (1×) x‐ray masks utilizing an optical reduction tool (SVGL Micrascan II). A special 1× x‐ray mask chuck was constructed to fit the optical tool. The technique takes advantage of the relatively flat x‐ray mask substrates and the required low throughput which allows replication without compromising the printing tool depth of focus and the resist process. The potential advantages of this technology are: (1) improved placement accuracy relative to conventional e‐beam tools; (2) no (e‐beam) proximity effects; and (3) lower post processing data volumes. The placement distortion and the critical dimension uniformity obtained in the 1× daughter masks on a 22×32 mm field are similar in magnitude to x‐ray masks fabricated with e‐beam lithography utilizing product specific emulation techniques. Furthermore, the distortion seen is believed to be due primarily to the known distortion of the Micrascan tool lenses. This suggests that it may be possible to use the results of lens distortion characterization to adjust the pattern of the reticle so as to correct for the lens distortion. Lens correction in combination with product specific emulation may allow the fabrication of daughter masks with near‐zero placement errors, suitable for sub‐250 nm product applications. © 1996 American Vacuum Society
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85.40.Hp Lithography, masks and pattern transfer

Dynamic motion of mask membrane in x‐ray stepper

Norio Uchida, Nobutaka Kikuiri, and Jun Nishida

J. Vac. Sci. Technol. B 14, 4350 (1996); http://dx.doi.org/10.1116/1.589051 (4 pages) | Cited 2 times

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This article presents a new analysis method and experimental results for the deflection and vibration of x‐ray masks, which are caused by the squeeze effect of the gas film between a mask and a wafer in x‐ray steppers. The deflection and vibration occur when a mask‐to‐wafer gap setting is executed or if the wafer vibrates in the mask direction during stepping motion with a narrow gap. They are not only detrimental to the throughput, but may also damage the mask membrane. Lees’ difference approximation method is applied to a compressible Reynolds’ equation and the equation of motion for the mask membrane. The main results of calculations and experiments, which showed good agreement with each other, are outlined below. (1) When the wafer approaches the mask at a constant velocity, the mask deflection increases in proportion to the velocity, and the mask deflection is larger for a smaller mask tensile stress. (2) When the wafer vibrates in the mask direction, the amplitude of the mask vibration increases with increasing the wafer frequency, and reaches a maximum value at a frequency that depends on the gap size. The maximum amplitude of a tested mask becomes 4 times as large as the wafer amplitude. (3) For a high frequency and narrow gap, the mask vibrates while deflecting convexly in the direction opposite to that of the wafer. © 1996 American Vacuum Society
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85.40.Hp Lithography, masks and pattern transfer
47.40.Dc General subsonic flows

Image placement errors in x‐ray masks induced by changes in resist stress during electron‐beam writing

R. E. Acosta and Denise Puisto

J. Vac. Sci. Technol. B 14, 4354 (1996); http://dx.doi.org/10.1116/1.589052 (5 pages) | Cited 4 times

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Image placement demands for x‐ray masks useable in sub‐0.25 μm applications have prompted a renewed effort to further reduce or eliminate sources of mask distortion. In this work we studied a phenomenon that so far had been overlooked among the contributors to poor image placement: the large change in stress of some resists upon exposure. For instance, it was found that the stress of PMMA films changes from ≂1×108 dyn/cm2 in the unexposed state to ≂1×107 dyn/cm2 after the exposure dose received during electron‐beam (e‐beam) writing. Because e‐beam writing is a serial process, this stress change induces a dynamic distortion of the mask, since the force applied on the membrane by the resist film varies continuously as writing of the pattern progresses. The stress of PMMA films was determined as a function of dose for exposures using e‐beams of 100, 75, and 25 keV energy, broadband UV light (from a Hg lamp), and to x rays from a synchrotron ring with λcharac.=10 Å. In all cases, the stress was found to be a very strong function of the exposure dose at low doses with a slow decay in stress change at larger dose values. The stress changes upon exposure are attributable to changes in molecular weight (MW) distribution, rather than to a reduction in MW only, since the stress of unexposed PMMA films was found to be the same for a wide range (25k to 920k) of initial MW resin. Model experiments demonstrated the correlation between the in‐plane distortion (IPD) of membranes and the lowered resist stress. Because of the drastic stress drop at low doses, fogging prior to writing reduces the distortion problem. Other methods thought to reduce resist stress (various annealing cycles, different solvents, plasticizers) proved unsuccessful. The effect of fogging on IPD was measured for several model cases and found to correlate with the lowered resist stress. Initial evaluation of the changes that fogging induces on the lithographic performance of the resist was performed. © 1996 American Vacuum Society
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81.07.-b Nanoscale materials and structures: fabrication and characterization
81.16.-c Methods of micro- and nanofabrication and processing
85.35.-p Nanoelectronic devices

Fabrication of x‐ray masks for giga‐bit DRAM by using a SiC membrane and W–Ti absorber

Kenji Marumoto, Hideki Yabe, Sunao Aya, Kaeko Kitamura, Kei Sasaki, Koji Kise, and Takeshi Miyachi

J. Vac. Sci. Technol. B 14, 4359 (1996); http://dx.doi.org/10.1116/1.589053 (4 pages) | Cited 5 times

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Advanced x‐ray masks for giga‐bit DRAM require an optimization of the mask fabrication process and a stress‐free absorber. In this article, we will describe the performance of the x‐ray masks fabricated by a membrane process where back‐etch is performed prior to electron beam writing. With other techniques such as stress control by step‐annealing and electron beam (EB) multiple writing, mask‐to‐mask overlay was reduced to less than 40 nm. In spite of multiple EB writing, the pattern size accuracies of 0.14 μm critical dimension were about 10% and 20% for the line and two‐dimensional patterns, respectively. For further improvement in the uniformity of absorber stress and resultant higher placement accuracy, a space variant annealing method is proposed, where the nonuniformity of the absorber stress is corrected by spatially variant temperature distribution during the annealing. Under this method, the uniformity of the amorphous W–Ti absorber improved to about 10 MPa in a 50 mm diam region. © 1996 American Vacuum Society
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81.07.-b Nanoscale materials and structures: fabrication and characterization
81.16.-c Methods of micro- and nanofabrication and processing
85.35.-p Nanoelectronic devices

Sputtered TaX film properties for x‐ray mask absorbers

Takuya Yoshihara, Setsu Kotsuji, and Katsumi Suzuki

J. Vac. Sci. Technol. B 14, 4363 (1996); http://dx.doi.org/10.1116/1.589054 (3 pages) | Cited 10 times

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The characteristics of several elements for binary tantalum alloys, such as crystal structure, x‐ray absorption, and dry‐etching properties were systematically investigated. As a result, TaGe, TaSi, TaRe, and TaTi were selected as potential candidates for x‐ray mask absorbers. We deposited these Ta alloys using conventional magnetron sputtering. The stress in the TaX films was controlled more precisely than in Ta films. It was found that TaGe was one of the most suitable materials based on x‐ray absorption, stress control, and fine pattern fabrication. © 1996 American Vacuum Society
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85.40.Hp Lithography, masks and pattern transfer
81.05.Bx Metals, semimetals, and alloys
81.15.Cd Deposition by sputtering

X‐ray mask fabrication technology for 0.1 μm very large scale integrated circuits

M. Oda, S. Uchiyama, T. Watanabe, K. Komatsu, and T. Matsuda

J. Vac. Sci. Technol. B 14, 4366 (1996); http://dx.doi.org/10.1116/1.589055 (5 pages) | Cited 5 times

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X‐ray mask fabrication using a subtractive process and a 30 kV acceleration voltage electron beam writer was investigated. The dose margin for delineation of fine resist patterns is increased by reducing the resist thickness. Delineation of 0.1 μm patterns in a 0.1‐μm‐thick resist has approximately the same dose margin as that of 0.2 μm patterns in a 0.3‐μm‐thick resist. Width error in SiO2 patterns used as an etching mask is decreased by reducing the thickness and adding SF6 to CF4 etching gas. Tantalum absorbers can be etched very accurately with electron cyclotron resonance ion stream etching by taking microloading effects and undercutting into account. Using the 0.1‐μm‐thick resist, x‐ray masks with 0.1 μm large scale integrated circuit patterns are almost perfectly produced and have a critical dimension accuracy of 13 nm. © 1996 American Vacuum Society
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81.07.-b Nanoscale materials and structures: fabrication and characterization
81.16.-c Methods of micro- and nanofabrication and processing
85.35.-p Nanoelectronic devices
81.65.Cf Surface cleaning, etching, patterning
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