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Nov 1992

Volume 10, Issue 6, pp. 2347-3255


Be diffusion at the emitter‐base junction of graded AlInAs/GaInAs heterojunction bipolar transistors

R. A. Metzger, M. Hafizi, R. G. Wilson, W. E. Stanchina, J. F. Jensen, and L. G. McCray

J. Vac. Sci. Technol. B 10, 2347 (1992); http://dx.doi.org/10.1116/1.586065 (4 pages) | Cited 7 times

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Compositional grading at the emitter‐base junction of Npn heterojunction bipolar transistors (HBTs) has been achieved by using a nine period graded gap AlInAs/GaInAs superlattice of 300 Å thickness. The as designed 500 Å base region was doped using Be fluxes that ranged from 0.8×1012 to 1.4×1012 atoms/cm2 s. Growth over this flux range resulted in a base doping of 4.5×1019 cm−3 with the highest flux producing an additional 160 Å of Be penetration into the graded region as compared with the lowest flux. The dc and rf characteristics of the graded emitter‐base HBTs are found to be tolerant to this degree of Be outdiffusion.
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85.30.Pq Bipolar transistors
73.40.Kp III-V semiconductor-to-semiconductor contacts, p-n junctions, and heterojunctions
61.72.U- Doping and impurity implantation

Observation of the instability of TixGay alloys with respect to GaAs at elevated temperatures

Margaret L. Kniffen and C. Robert Helms

J. Vac. Sci. Technol. B 10, 2351 (1992); http://dx.doi.org/10.1116/1.586066 (3 pages) | Cited 1 time

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The metallurgical reactions occurring at the Ti–GaAs interface between 600 and 850 °C were examined using Auger depth profiling. Between 600 and 720 °C titanium will react with gallium arsenide to form a uniform TixGay /TiAs/GaAs layered structure, similar to that which formed upon annealing Ti–GaAs contacts at much lower temperatures [J. Vac. Sci. Technol. A 5, 1511 (1987); J. Vac. Sci. Technol. A 6, 1473 (1988)]. However above 800 °C the dominant reaction products are a titanium arsenide phase and liquid gallium. This result has significant implications for the development of thermally stable contacts to gallium arsenide using titanium‐based metallizations.  
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68.35.Md Surface thermodynamics, surface energies
84.32.Dd Connectors, relays, and switches

Ohmic contact study for quantum effect transistors and heterojunction bipolar transistors with InGaAs contact layers

W. L. Chen, J. C. Cowles, G. I. Haddad, G. O. Munns, K. W. Eisenbeiser, and J. R. East

J. Vac. Sci. Technol. B 10, 2354 (1992); http://dx.doi.org/10.1116/1.586067 (7 pages) | Cited 6 times

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Two ohmic contact systems for quantum effect devices and heterojunction bipolar transistors (HBTs) were investigated and compared. Ni/Ge/Au/Ti/Au and Pd/Ge/Ti/Al were characterized for diffusion length after annealing and specific contact resistivity on chemical beam epitaxially grown In0.53Ga0.47As. It was found, in general, that the diffusion length could be controlled by varying the total metal thickness and that the specific contact resistivity maintained reasonably low values as long as the compositional ratio of each system remained constant. The diffusion length for Ni/Ge/Au/Ti/Au ranged from 1000 to 2000 Å and that of Pd/Ge/Ti/Al was ∼300 Å. In both cases the specific contact resistivity on n‐type InGaAs was 5×10−7 Ω cm2. Furthermore, the Pd/Ge/Ti/Al was applied to p‐type InGaAs and showed a specific contact resistivity of 3×10−6 Ω cm2. Finally, both systems were used to fabricate an InGaAs/InP hot electron transistor and an InAlAs/InGaAs HBT with excellent direct‐current results.
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73.40.Lq Other semiconductor-to-semiconductor contacts, p-n junctions, and heterojunctions
85.30.Pq Bipolar transistors

Trilayer lift‐off metallization process using low temperature deposited SiNx

J. R. Lothian, F. Ren, S. J. Pearton, U. K. Chakrabarti, C. R. Abernathy, and A. Katz

J. Vac. Sci. Technol. B 10, 2361 (1992); http://dx.doi.org/10.1116/1.586068 (5 pages) | Cited 6 times

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A trilevel resist scheme using low temperature (≤50 °C) deposited SiNx rather than Ge for the transfer layer has been developed. This allows use of an optical stepper for lithographic patterning of the emitter‐base junctions in GaAs/AlGaAs heterojunction bipolar transistors where a conventional lift‐off process using a single level resist often leads to the presence of shorts between metallizations. The plasma‐enhanced chemically vapor deposited (PECVD) SiNx shows a slightly larger degree of Si–H bonding compared to nitride deposited at higher temperature (275 °C), and is under compressive stress (∼5×1010 dyn cm−2) which is considerably relieved upon thermal cycling to 500 °C (∼1.5×1010 dyn cm−2 after cooldown). This final stress is approximately a factor of 2 higher than conventional PECVD SiNx cycled in the same manner. The adhesion of the low temperature nitride to the underlying polydimethylglutarimide base layer in the trilevel resist is excellent, leading to high yields in the lift‐off metallization process. These layers are etched in electron cyclotron resonance discharges of SF6 or O2, respectively, using low additional dc bias (≤−100 V) on the sample. Subsequent deposition of the HBT base metallization (Ti/Ag/Au) and lift‐off of the trilevel resist produces contacts with excellent edge definition and an absence of shorts between metallization.  
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85.40.Hp Lithography, masks and pattern transfer
85.30.Pq Bipolar transistors
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)

Electrical characteristics of Ar‐ion sputter induced defects in epitaxially grown n‐GaAs

F. D. Auret, S. A. Goodman, G. Myburg, and W. E. Meyer

J. Vac. Sci. Technol. B 10, 2366 (1992); http://dx.doi.org/10.1116/1.586069 (5 pages) | Cited 9 times

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Epitaxially grown n‐type GaAs was sputtered by bombarding it with Ar ions at energies of between 0.5 and 5 keV at a dose of 1013 ions/cm2. The fabrication of Au Schottky barrier contacts followed directly after the sputtering. The electrical characteristics of the the sputter induced defects were studied using deep‐level transient spectroscopy (DLTS). Several defects with discrete defect levels ranging from 0.05–0.70 eV below the conduction band, as well as defects with continuously distributed energies in the conduction band, were introduced during sputtering. Concentration depth profiling revealed that whereas some defects are located very close to the interface, others were detected several microns below the interface. The depth of some of these deep lying defects increased with sputter voltage. A possible explanation of the reduction in EL2 DLTS signal previously observed after sputtering is shown to be the sputter induced barrier height lowering.
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71.55.Eq III-V semiconductors
79.20.Rf Atomic, molecular, and ion beam impact and interactions with surfaces

Adsorption and thermal desorption of chlorine from GaAs(100) surfaces

S. M. Mokler, P. R. Watson, L. Ungier, and J. R. Arthur

J. Vac. Sci. Technol. B 10, 2371 (1992); http://dx.doi.org/10.1116/1.586070 (7 pages) | Cited 10 times

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The adsorption and thermal desorption of chlorine on GaAs(100) surfaces prepared either As‐rich or Ga‐rich has been studied using Auger electron spectroscopy, thermal desorption spectroscopy (TDS), and low‐energy electron diffraction (LEED). The initial adsorption occurs more rapidly on the Ga‐rich surfaces, however saturation coverages appear equal on both As‐ and Ga‐rich surfaces. Monitoring the As and Ga Auger signals during adsorption reveals a consistent drop in the As signal while the Ga signal remains constant, which may be a result of a replacement reaction between Cl and As. Sputter damaged surfaces result in more exposed Ga, and hence, 20% more chlorine can be adsorbed onto this surface. LEED and TDS experiments on clean surfaces reveal that desorption of As2 closely follows observed reconstruction changes. Chlorine saturated surfaces, however, show no noticeable reconstruction change from that of the clean surface, and upon heating the saturated surface, only GaCl and As2 are seen as desorption products. Both the adsorption and desorption behavior of chlorine suggest a preferential formation of a Ga–Cl bond at the GaAs surface.
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68.43.-h Chemisorption/physisorption: adsorbates on surfaces

Dry etching of III–V semiconductors in CH3I, C2H5I, and C3H7I discharges

U. K. Chakrabarti, S. J. Pearton, A. Katz, W. S. Hobson, and C. R. Abernathy

J. Vac. Sci. Technol. B 10, 2378 (1992); http://dx.doi.org/10.1116/1.586071 (9 pages) | Cited 4 times

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The characteristics of plasma etching of InP, InAs, InSb, GaAs, AlGaAs, GaSb, AlInAs, InGaAs, and AlInP in microwave (2.45 GHz) discharges of methyl‐, ethyl‐, and propyl‐iodide have been examined with respect to etch rates, surface morphology, damage introduction, and etch anisotropy. The etch rates for all of these semiconductors are somewhat faster than for conventional CH4‐based discharges under the same conditions of direct‐current bias, pressure, and microwave power, but are not as fast as with HI discharges. Polymer deposition on the mask and within the chamber occurs as with CH4‐based mixtures, but is minimized at low pressure (≤10 mTorr) and with H2 dilution. The etched surface morphologies are smooth over a wide range of plasma parameters and show roughness only under conditions of significant polymer deposition. Chemical analysis by Auger electron spectroscopy and x‐ray photoelectron spectroscopy also shows that the near surface of the etched samples retains its stoichiometry under most conditions. While the etch rates are slower than for HI‐based discharges, the halocarbon iodides are significantly less corrosive and much more stable.
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81.65.-b Surface treatments

Fast silicon etching using an expanding cascade arc plasma in a SF6/argon mixture

J. J. Beulens, A. T. M. Wilbers, M. Haverlag, G. S. Oehrlein, G. M. W. Kroesen, and D. C. Schram

J. Vac. Sci. Technol. B 10, 2387 (1992); http://dx.doi.org/10.1116/1.586072 (6 pages) | Cited 6 times

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An expanding cascaded arc is used as a fluorine atom source for fast etching of silicon. Extremely high etch rates up to 1.3 μm/s have been obtained. A reactor parameter study has been performed. The obtained selectivity Si/SiO2 is ∼11 for substrate temperatures of 600 °C, increasing to ∼20 at 100 °C. The etching proces is fully isotropic.
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81.65.-b Surface treatments

Fabrication of sub‐20 nm trenches in silicon nitride using CHF3/O2 reactive ion etching and oblique metallization

T. K. S. Wong and S. G. Ingram

J. Vac. Sci. Technol. B 10, 2393 (1992); http://dx.doi.org/10.1116/1.586073 (5 pages)

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A direct process for fabricating nanometer size trenches in Si3N4 using high voltage electron beam lithography and CHF3/O2 reactive ion etching has been developed and characterized. The process can be used on both bulk and thin membrane substrates and has demonstrated a feature resolution of better than 20 nm. An extension of this process allows 15 nm wide slots to be fabricated in a metal film without performing any metal etching.
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85.40.Hp Lithography, masks and pattern transfer
81.65.-b Surface treatments

Near‐surface residue formation in CF4/H2 reactive ion etching of silicon

Gregg E. Potter, G. H. Morrison, Peter K. Charvat, and Arthur L. Ruoff

J. Vac. Sci. Technol. B 10, 2398 (1992); http://dx.doi.org/10.1116/1.586074 (9 pages) | Cited 7 times

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Surface residues and near‐surface damage present in the surface and near‐surface regions of Si after reactive ion etching with CF4, CF4+H2, and CHF3 were investigated with secondary ion mass spectrometry, laser ellipsometry, x‐ray photoelectron spectroscopy, and cross‐sectional transmission electron microscopy. Specifically, the change in the thickness and composition of the deposited residues with changes in the backfill gas chemistry was investigated. A fluorocarbon (FC) residue was found to develop on all etched samples, with thicknesses ranging from a few angstroms to microns. Two regimes of FC deposition were identified, where (a) a steady‐state FC layer quickly develops during etching, and the net FC deposition rate drops to zero thereafter, and (b) the FC deposition continues at a constant rate throughout the etch. F was found to diffuse to the Si surface to form a fluorinated Si layer between the deposited FC layer and the bulk Si. This layer was taken to be the reaction layer resulting from diffusion‐limited kinetics in this etch system. The diffusion of F or C into the near‐surface region of Si was not observed to change with increasing H2 additions. A simple quantitative model was developed based on rate‐limiting Fickian diffusion through the deposited FC layer. The model was found to agree well the available etch rate data. Si etching with CHF3 was found to behave similiarly to CF4+H2 etching in the steady‐state FC layer regime.
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81.65.-b Surface treatments
82.65.+r Surface and interface chemistry; heterogeneous catalysis at surfaces

Reduction of sidewall roughness during dry etching of SiO2

F. Ren, S. J. Pearton, J. R. Lothian, C. R. Abernathy, and W. S. Hobson

J. Vac. Sci. Technol. B 10, 2407 (1992); http://dx.doi.org/10.1116/1.586075 (5 pages) | Cited 8 times

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The appearance of striations on dry etched semiconductor laser mesas is a common feature of these structures. We describe a number of different methods of reducing the extent of this roughness, including the choice of dielectric etch chemistry, modification of the initial resist processing, and deposition of a SiN sidewall to prevent additional roughening during the plasma etch step. SF6 is found to be preferable to CF4 for dielectric etching because of an absence of polymer formation. This produces smoother SiO2 sidewalls. Flood exposure of theinitial photoresist mask and optimization of the postbake temperature also produces smoother sidewalls on the subsequently etched SiO2. The sidewall can also be protected from roughening that occurs during the dry etch step by coating it with a low temperature SiN layer. A combination of all of these methods produces sidewalls with morphological variations of ≤500 Å.
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85.40.Hp Lithography, masks and pattern transfer
81.65.-b Surface treatments

In situ ellipsometry and reflectometry during etching of patterned surfaces: Experiments and simulations

M. Haverlag and G. S. Oehrlein

J. Vac. Sci. Technol. B 10, 2412 (1992); http://dx.doi.org/10.1116/1.586076 (7 pages) | Cited 3 times

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To address the question whether it is possible to perform in situ end point detection during etching using ellipsometry on patterned wafers, a number of experiments were performed on wafers that were covered with a photoresist line pattern on an oxide‐covered silicon substrate. Two situations were investigated, one in which the probe beam was directed parallel to the line pattern, and one in which the probe beam was perpendicular to the lines. For each situation, a separate ellipsometric model was developed. Employing photoresist and SiO2 etch rates measured with blanket wafers, a good fit between the experimental curves and the simulations was obtained. Though the agreement between modeling and experiment is good, it is shown that the applicability of ellipsometry for end point detection on patterned wafers depends on the aspect ratio of etched holes, the selectivity of the etching process, and the pattern factor (the unmasked area fraction of the wafer). For comparison, experiments and simulations were also performed with a laser interferometer at normal incidence. In this case, only the selectivity and the pattern factor are important. It has been shown that the selectivity of the process becomes less important if the derivative of the reflectivity is used as an end point signal instead of the reflectivity itself. To optimize the end point signal for this method the wavelength can be used to maximize the change in the reflectivity slope at the end point of the process.
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85.40.Hp Lithography, masks and pattern transfer
81.65.-b Surface treatments

Granulation of silicon surface through reactive ion etching

U. S. Tandon and B. D. Pant

J. Vac. Sci. Technol. B 10, 2419 (1992); http://dx.doi.org/10.1116/1.586033 (3 pages)

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A spherelike granular structure has been observed to appear on the surface of single crystal silicon as a result of a two step reactive ion etching (RIE). Fluorocarbon plasma in RIE mode has been found to create a micromasking of bare silicon. Subsequent application of silicon etch recipe produces a texture with submicron spherical granules. Energy dispersion of x ray and Auger spectra analysis reveal that the suspected deposition or adsorption of etchant and effluent species onto the final surface is insignificant. The technique has a potential for controlling the reflectivity of silicon in specific regions of the spectrum and providing a large throughput.
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81.65.-b Surface treatments
68.35.B- Structure of clean surfaces (and surface reconstruction)

Kinetics and mechanism of silicon dioxide deposition through thermal pyrolysis of tetraethoxysilane

Gregory B. Raupp, Frank A. Shemansky, and Timothy S. Cale

J. Vac. Sci. Technol. B 10, 2422 (1992); http://dx.doi.org/10.1116/1.586034 (9 pages) | Cited 15 times

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Intrinsic silicon dioxide deposition rate dependences from tetraethoxysilane (TEOS) thermal pyrolysis were measured in an experimental cold wall low‐pressure chemical vapor deposition reactor designed to minimize reactant depletion and gas‐phase reactions. The apparent activation energy of 90 kJ mol−1±16 kJ mol−1 over the range of temperatures from 873 to 1073 K is significantly lower than that typically measured in commercial or development‐scale hot wall reactors. The reaction rate exhibits a first order dependence on TEOS pressure. Film deposition proceeds without a nucleation‐induced incubation period. Interpretation of deposited film profiles in high aspect ratio trenches through rigorous ballistic transport‐reaction simulation reveals that deposition most likely occurs through a heterogeneous mechanism in which strong readsorption of the byproducts of TEOS decomposition inhibits silicon dioxide deposition.
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81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)

Criteria for use of electron beam charging technique for very large scale integration process inspection

Keith A. Jenkins

J. Vac. Sci. Technol. B 10, 2431 (1992); http://dx.doi.org/10.1116/1.586035 (5 pages)

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A mathematical description of the method of testing by electron beam charging is used to clearly specify its measurement capabilities. The scanning electron microscopy parameters of beam current, frame scan time, and magnification, are used to derive the requirements necessary to distinguish between shorted and isolated structures.  
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85.40.Hp Lithography, masks and pattern transfer
07.79.Cz Scanning tunneling microscopes
61.05.-a Techniques for structure determination

Imaging of submicron index variations by scanning optical tunneling

Daniel Courjon, Claudine Bainier, and Michel Spajer

J. Vac. Sci. Technol. B 10, 2436 (1992); http://dx.doi.org/10.1116/1.586036 (4 pages) | Cited 13 times

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The scanning tunneling optical microscope (SNOM, STOM, PSTM, etc.) is the equivalent of the electron scanning tunneling microscope in the electromagnetic domain. Although it was born at the same time, its actual development is more recent. Here, some new results obtained with the version working in total reflection (STOM/PSTM) are reported. A grating of a periodicity of 417 nm and a thickness of 5 nm have been imaged both in TM and TE modes. It is first noted that the optical image is well resolved. Furthermore, the difference of behavior of the field versus the polarization of the incident light has been shown. More precisely, the TM mode seems to be highly sensitive to small index and topography variations due to surface contaminants. Such effects are generally not imaged by atomic force microscopy working in attractive mode, because they affect the surface topography slightly. The SNOM could be thus a very powerful tool for detecting pollutants over the surface of objects like glasses, lenses, gratings, etc., and in the biology domain.
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07.60.Pb Conventional optical microscopes

Evidence for an Eley–Rideal mechanism in the addition of hydrogen atoms to unsaturated hydrocarbons on Cu(111)

Ming Xi and Brian E. Bent

J. Vac. Sci. Technol. B 10, 2440 (1992); http://dx.doi.org/10.1116/1.586037 (7 pages) | Cited 10 times

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The addition of hydrogen atoms to ethylene and benzene on a Cu(111) surface has been studied by temperature‐programmed desorption and integrated desorption mass spectrometry. The results show that adsorbed ethylene and benzene react with atomic hydrogen from the gas phase at temperatures as low as 110 K. The reaction intermediates, ethyl groups and partially hydrogenated benzene, can be isolated on the surface at this low temperature. When the surface is heated to above 150 K, hydrogen elimination reactions occur to produce ethylene, benzene, cyclohexadiene, and cyclohexene. Complete hydrogenation to alkanes also occurs for larger H‐atom exposures. The absence of these addition reactions when H atoms are adsorbed onto the surface before ethylene or benzene suggests Eley–Rideal mechanisms for these processes.
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73.20.Mf Collective excitations (including excitons, polarons, plasmons and other charge-density excitations)

Efficient microtip fabrication with carbon coating and electron beam deposition for atomic force microscopy

Mariko Yamaki, Tetsuya Miwa, Hideyuki Yoshimura, and Kuniaki Nagayama

J. Vac. Sci. Technol. B 10, 2447 (1992); http://dx.doi.org/10.1116/1.586038 (4 pages) | Cited 6 times

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Abstract Unavailable
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06.60.Sx Positioning and alignment; manipulating, remote handling
07.78.+s Electron, positron, and ion microscopes; electron diffractometers

100 kV field emission electron optics for nanolithography

Mark Gesley

J. Vac. Sci. Technol. B 10, 2451 (1992); http://dx.doi.org/10.1116/1.586039 (8 pages) | Cited 1 time

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A 100 kV optics with field emission source is designed for an electron‐beam nanolithography system. A new electrostatic gun lens permits high‐voltage operation with low aberrations. A demagnifying double‐lens column with fixed magnification and variable aperture is used. The optics are weighted towards 100 kV operation, but the beam voltage can be varied from 25 to 100 kV with resolution maintained below 20 nm. The gun uses a Zr/O/W<100≳ cathode operated near the extended‐Schottky emission regime to achieve 1%/h current stability at a fixed extraction voltage. With the source emitting a 0.5 mA/sr angular intensity, 1.5 nA can be focused to 6 and 10 nm with beam voltages of 100 and 50 kV, respectively. A target current density of 2000 A/cm2 with an effective brightness of 1×108 A/cm2 sr enables 2 MHz pixel rate exposures of PMMA at 100 kV with a vector‐scan deflection system.
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85.40.Hp Lithography, masks and pattern transfer
41.75.Fr Electron and positron beams
41.85.Gy Chromatic and geometrical aberrations
41.85.Ne Electrostatic lenses, septa

Accuracy of proximity correction in electron lithography after development

V. V. Aristov, B. N. Gaifullin, A. A. Svintsov, S. I. Zaitsev, H. F. Raith, and R. Jede

J. Vac. Sci. Technol. B 10, 2459 (1992); http://dx.doi.org/10.1116/1.586040 (9 pages) | Cited 5 times

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The established methods after Parikh [M. Parikh, IBM J. Res. Dev. 24, 438 (1980)] allow a dose correction using the ‘‘Two Gaussian Model’’ by considering the parameters α, β, and η. A guaranteed accuracy after development cannot be given for these methods because the development process, depending on resist type, thickness and contrast, is not taken into account. In order to calculate a final guaranteed accuracy considering α, β, η, and the full resist development process, we did a calculation in following steps. First, we calculated the proximity correction just for backscattered electrons by the method of ‘‘simple compensation’’ [V. V. Aristov, A. A. Svintsov, and S. I. Zaitsev, Microelectron. Eng. 11, 641 (1989)]. In the second step, we simulated the proximity effect after development (modeling) with the before corrected dose distribution, but now considering all parameters: α, β, η, thickness H, and contrast γ of positive resist. This leads to a guaranteed accuracy δ (maximum structure deviation) for a given design rule L using the correction method of simple compensation. This guaranteed accuracy can be expressed in dimensionless coordinates δ/α=f(L/α,H/α,η,γ). So the accuracy of the electron lithography in this approach is determined by the beam size, characterized by α. Simple compensation results in the accuracy equal to a fraction of α. A better proximity correction below the guaranteed accuracy is possible by using simple compensation in iteration and by correcting for α inside a small structure frame.
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85.40.Hp Lithography, masks and pattern transfer

Influence of shifter errors on the printability of L/S structures using the alternated phase‐shifting design: Simulations and experiments

Maaike Op de Beeck, Kurt Ronse, Kazuya Kamon, Masato Fujinaga, Hal Kusunose, and Hiroaki Morimoto

J. Vac. Sci. Technol. B 10, 2468 (1992); http://dx.doi.org/10.1116/1.586041 (12 pages) | Cited 1 time

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It is well‐known that many improvements concerning resolution and focus latitude can be obtained by the use of phase‐shifting masks. Different phase‐shifting mask designs are proposed already, and one of the most suitable designs for periodical structures is the alternated shifter design. If such phase‐shifting masks are investigated, it is assumed that all shifter parameters are ideal. A major problem, however, is the production of such an ideal phase‐shifting mask with perfect shifter parameters. In this work, the influence of shifter parameters such as transparency, thickness, and sidewall slope are studied for the alternated phase‐shifting design. The investigation is carried out by simulations and by experiments, and for various coherence factors. It is found that all shifter deviations cause linewidth differences between shifter and quartz lines, often resulting in a reduced depth‐of‐focus (DOF). Especially if various deviations occur simultaniously, the DOF reductions are important, putting stringent demands on mask processing in order to obtain tolerable shifter deviations. In order to print L/S down to 0.3 μm with reasonable DOF for production applications, the shifter transparency and thickness should not deviate more than 5% from their ideal values.  
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85.40.Hp Lithography, masks and pattern transfer

Antireflective MoSi photomasks

Akira Chiba, Shuichi Matsuda, and Yaichiro Watakabe

J. Vac. Sci. Technol. B 10, 2480 (1992); http://dx.doi.org/10.1116/1.586042 (6 pages) | Cited 2 times

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Antireflective MoSi (AR‐MoSi) photomasks which are produced by applying a thin layer of MoSi oxide directly over the conventional MoSi layer on a quartz substrate has been developed. The thin layer of MoSi oxide is deposited using magnetron dc sputtering. The reflectivity and optical density of the thin layer are not affected by H2SO4 at 120 °C. The layer reflectivity is changed by varying the oxygen partial pressure ratio in argon gas and the layer thickness. To obtain minimum reflectivity, the mechanism of antireflection was studied by using a model of multipath interference with absorption of light. Experimental and theoretical results are in good agreement and show a minimum reflectivity of 6.4% for a 40–60 nm thick MoSi oxide layer. By exposing the photomask, it was found that the AR‐MoSi photomask has practicable resolution performance comparable to conventional photomasks.
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85.40.Hp Lithography, masks and pattern transfer
81.15.Cd Deposition by sputtering
78.66.Fd III-V semiconductors
78.66.Hf II-VI semiconductors

Fabrication of overpass microstructures in GaAs using isotropic reactive ion etching

Katerina Y. Hur and Richard C. Compton

J. Vac. Sci. Technol. B 10, 2486 (1992); http://dx.doi.org/10.1116/1.586043 (2 pages) | Cited 2 times

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85.40.Hp Lithography, masks and pattern transfer
81.65.-b Surface treatments

Influence of silicon nitride cap on the thermal stability of strained Al0.32Ga0.68As/In0.1Ga0.9As high mobility structures grown by metalorganic chemical vapor deposition

A. Kana’ah, P. I. Rockett, J. S. Roberts, M. A. Pate, and M. V. Woodward

J. Vac. Sci. Technol. B 10, 2488 (1992); http://dx.doi.org/10.1116/1.586044 (3 pages)

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Abstract Unavailable
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85.30.Tv Field effect devices
68.60.Dv Thermal stability; thermal effects

New electrostatic micromanipulator which dislodges adhered dust particles in vacuum

Hiroshi Saeki, Takayasu Tanaka, Toshio Fukuda, Ken’ichi Kudou, Toshiro Higuchi, and Hajime Ishimaru

J. Vac. Sci. Technol. B 10, 2491 (1992); http://dx.doi.org/10.1116/1.586045 (2 pages)

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Abstract Unavailable
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06.60.Sx Positioning and alignment; manipulating, remote handling
85.40.-e Microelectronics: LSI, VLSI, ULSI; integrated circuit fabrication technology

Electrical properties of the thermal induced degradation in TiSi2/TiW/AlSi layered structures

R. K. Nahar and P. D. Vyas

J. Vac. Sci. Technol. B 10, 2493 (1992); http://dx.doi.org/10.1116/1.586046 (3 pages)

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Thermal degradation of TiSi2/TiW/AlSi layered structures is studied by the resistivity measurements on samples annealed in the temperature range of 400–550 °C. The effect of using pure TiW and stuffed TiW(N) as a diffusion barrier on the reaction kinetics of the layered structure is studied. The change in the resistivity is correlated to the rate of formation of intermetallic compound. It is shown that the reaction rate of the compound formation is reduced by about 25% for TiW(N) barrier layer compared to pure TiW annealed at 500 °C.  
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73.40.Vz Semiconductor-metal-semiconductor structures
81.40.Rs Electrical and magnetic properties related to treatment conditions
82.65.+r Surface and interface chemistry; heterogeneous catalysis at surfaces

Erratum: ‘‘GaSb‐oxide removal and surface passivation using an electron cyclotron resonance hydrogen source’’ [J. Vac. Sci. Technol. B 10, 1856 (1992)]

Z. Lu, Y. Jiang, W. I. Wang, M. C. Teich, and R. M. Osgood

J. Vac. Sci. Technol. B 10, 2496 (1992); http://dx.doi.org/10.1116/1.586047 (1 page)

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Abstract Unavailable
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81.65.-b Surface treatments
52.50.Gj Plasma heating by particle beams
99.10.Cd Errata

Prospects for x‐ray lithography

D. Fleming, J. R. Maldonado, and M. Neisser

J. Vac. Sci. Technol. B 10, 2511 (1992); http://dx.doi.org/10.1116/1.586048 (5 pages) | Cited 2 times

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The essentials of proximity x‐ray lithography (XRL) have been established and successful alternative implementations have been demonstrated in academic and industrial laboratories worldwide. Results continue to show that XRL can provide simpler and more robust processes than optical or electron beam alternatives. And it is widely accepted that this becomes more true as lithographic dimensions shrink. So why do we still await the introduction of the first commercial use of XRL? Use of a new technology requires its either attaining the unattainable or excelling at cost/performance. For near term application, XRL must leap the latter hurdle. While most concede the superior robustness of XRL to normal process variation, popular lore has it that availability or an adequate infrastructure limits XRL becoming a process of choice. We discuss the current state of XRL against this competitive challenge and project progress forward. In so doing, we find that XRL is now approaching a critical crossroad. While optical approaches struggle to demonstrate technical realization and electron beam approaches are losing ground in the pixel per chip per second race, XRL’s challenge is to mature its infrastructure sufficiently to attract proponents eager to make it the process of choice. The pace of XRL efforts leads us to the conclusion that XRL can be the process of choice for 250 nm applications, most probably beginning with 256 Mb DRAM or NVRAM.
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85.40.Hp Lithography, masks and pattern transfer

Phase holograms in polymethyl methacrylate

P. D. Maker and R. E. Muller

J. Vac. Sci. Technol. B 10, 2516 (1992); http://dx.doi.org/10.1116/1.586049 (4 pages) | Cited 6 times

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Complex computer generated phase holograms (CGPHs) have been fabricated in polymethyl methacrylate (PMMA) by partial exposure and subsequent partial development. The CGPH was encoded as a sequence of phase delay pixels and written by e‐beam (JEOL JBX‐5DII), a different dose being assigned to each value of phase delay. Following carefully controlled, partial development, the pattern appears, rendered in relief, in the PMMA which then acts as the phase‐delay medium. The exposure dose was in the range 20–200 μC/cm2, and very aggressive development in pure acetone led to low contrast. This enabled etch depth control to better than ±20 nm corresponding to an optical phase shift in transmission, relative to air, of ±λvis/60. That result was obtained by exposing isolated 50 μm square patches and measuring resist removal over the central area where the proximity effect dose was uniform and related only to the local exposure. For complex CGPHs with pixel size of the order of the proximity radius, the patterns must be corrected for proximity effects. In addition, the isotropic nature of the development process will produce sidewall etching effects. The devices fabricated were designed with 16 equal phase steps per retardation cycle, were up to 3 mm square, and consisted of up to 10 million 0.3–2.0 μm square pixels. Data files were up to 60 Mb long and exposure times ranged to several hours. No sidewall etch corrections were applied to the pattern and proximity effects were only treated approximately. A Fresnel phase lens was fabricated that had diffraction limited optical performance with 83% efficiency.  
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42.40.Jv Computer-generated holograms
42.79.Bh Lenses, prisms and mirrors
42.70.Ln Holographic recording materials; optical storage media

Deep three‐dimensional microstructure fabrication for infrared binary optics

M. B. Stern and S. S. Medeiros

J. Vac. Sci. Technol. B 10, 2520 (1992); http://dx.doi.org/10.1116/1.586050 (6 pages) | Cited 5 times

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Anisotropic reactive ion etching of deep Si structures (≥8 μm), planarization of deeply stepped topographies, and multilayer resist processes have been developed for fabrication of silicon IR binary optics devices. The effect of adding O2 and C2F6 to the SF6 feed gas on sidewall profile and etch selectivity (Si:photoresist) has been determined. Vertical profiles, without mask undercutting or surface texturing, and high etch selectivity (≥5:1) have been obtained with a 74% SF6–26% O2 mixture. We have successfully fabricated 8‐μm deep Si optics with 16 phase levels and eight‐level structures with a total depth of 14 μm in Si.
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85.40.Hp Lithography, masks and pattern transfer
81.65.-b Surface treatments

Electron beam writing of continuous resist profiles for optical applications

J. M. Stauffer, Y. Oppliger, P. Regnault, L. Baraldi, and M. T. Gale

J. Vac. Sci. Technol. B 10, 2526 (1992); http://dx.doi.org/10.1116/1.586051 (4 pages) | Cited 5 times

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This article reports on progress in the fabrication by e‐beam lithography of high resolution, continuous‐relief microstructures for integrated optical applications in the visible and near infrared. The microstructures are designed for subsequent replications from an electroformed metal shim by embossing into polymer films on glass. The objective of this work is to fabricate complete integrated optical devices and circuits by low‐cost embossing or casting replication technology.
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42.82.Cr Fabrication techniques; lithography, pattern transfer

Characterization of near‐field holography grating masks for optoelectronics fabricated by electron beam lithography

D. M. Tennant, T. L. Koch, P. P. Mulgrew, R. P. Gnall, F. Ostermeyer, and J‐M. Verdiell

J. Vac. Sci. Technol. B 10, 2530 (1992); http://dx.doi.org/10.1116/1.586052 (6 pages) | Cited 16 times

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Direct write e‐beam lithography and reactive ion etching was used to fabricate square‐wave gratings in quartz substrates which serve as pure phase masks in the near‐field holographic printing of gratings. This method of fabricating these masks extends the flexibility of the printing technique by allowing both abrupt phase shifts as well as multiple grating pitches to be simultaneously printed from a single contact mask. Grating masks with periods in the 235–250 nm range have been produced and measured to be within 0.15 nm of the design period. Transmitted and diffracted beam powers have also been measured for various duty cycles and etch depths and are shown to be important parameters for ‘‘balancing’’ these interfering beams. Simple scalar diffraction modeling is used to qualitatively examine the dependence of diffraction on grating parameters, but the need for a more comprehensive modeling is illustrated. Prototype masks have been used to produce grating patterns on InP substrates using two different ultraviolet illumination sources: an argon ion laser and a conventional mercury lamp.
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42.40.Eq Holographic optical elements; holographic gratings

Characteristics of an improved chemically amplified deep‐ultraviolet positive resist

Omkaram Nalamasu, Janet Kometani, May Cheng, Allen G. Timko, Elsa Reichmanis, Sydney Slater, and Andrew Blakeney

J. Vac. Sci. Technol. B 10, 2536 (1992); http://dx.doi.org/10.1116/1.586053 (6 pages)

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Chemically amplified positive resist formulations have been shown to exhibit high photospeed, excellent resolution, and tolerance to process parameters such as softbake, exposure, postexposure bake, developer concentration, and temperature. Many chemically amplified positive resists, however, adhered poorly to some substrates (e.g., Si3N4), required considerable optimization of the etch process to achieve desired etch selectivities and were sensitive to airborne basic contaminants. Many chemically amplified negative resists while not as sensitive to contaminants in the clean room air, show retrograde wall angles especially on antireflection coatings, demonstrate poor latitude in defining contact holes and are difficult to strip after pattern transfer steps. In this article we discuss our efforts toward designing new deep‐ultraviolet (UV) matrix resins and resist formulations as well as efforts toward defining an optimized process. The optimized resist process demonstrates 0.25 μm line and space (L/S) and 0.30 μm contact hole resolution in 0.8 μm thick resist films with a GCA deep‐UV exposure tool. The resist also exhibits excellent adhesion on most semiconductor substrates (e.g., Si, polysilicon, SiO2, Si3N4), thermal stability to at least 140 °C, an order of improvement in postexposure delay latitude over that of CAMP1 (poly t‐butoxycarbonyloxystyrene‐sulfone formulated with photoacid generators) and etch selectivity comparable to that of novolac based resists. In addition, the polymers developed were designed for ease of manufacture with regard to reproducibility, low metal concentration, and cost.
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85.40.Hp Lithography, masks and pattern transfer
81.65.-b Surface treatments

Resist etching kinetics and pattern transfer in a helicon plasma

C. W. Jurgensen, R. S. Hutton, and G. N. Taylor

J. Vac. Sci. Technol. B 10, 2542 (1992); http://dx.doi.org/10.1116/1.586054 (6 pages) | Cited 6 times

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We describe the first commercial etching system based on a helicon ion source and characterize it for etching organic films in an oxygen plasma. This single wafer etching system achieves a throughput of at least 30 fully processed 5 in. wafers per hour, which is comparable to the throughput of batch reactors. The etching chamber is equipped with a 13.56‐MHz 2500‐W helicon source, four low‐field magnets to shape the plasma and support the helicon wave mode, and a 600‐W radio‐frequency chuck with He backside heat exchange and a temperature range from −50 to +125 °C. Etching rates and uniformity were measured on unpatterned resist‐coated wafers, while trilayer resist patterns were used to study pattern transfer effects. Under nearly optimum conditions we obtain an etching rate of 1.31 μm/min, a throughput ≥30 wafers/h, nonuniformity ≤± 3%, selectivity ≊70 relative to SiO2 and nearly vertical etching profiles for all types of features having dimensions down to 0.25 μm. We describe the effect of process variables on etching rate, uniformity, selectivity, and etching profiles. We present a model based on multicomponent adsorption kinetics that fits the observed dependence of etching rate on the process variables. This etching system is being applied to several advanced lithographic schemes including dry‐developed resists, bilayer lithography, and pattern transfer through organic antireflective coatings and planarizing layers.  
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42.82.Cr Fabrication techniques; lithography, pattern transfer
81.05.Lg Polymers and plastics; rubber; synthetic and natural fibers; organometallic and organic materials
81.65.-b Surface treatments

Process optimization of 200 nm wide trenches in SiO2 using a chemically amplified acid catalyzed e‐beam resist

Waldemar W. Kocon, Y. Shacham‐Diamand, Jean M. J. Frechet, and James Fahey

J. Vac. Sci. Technol. B 10, 2548 (1992); http://dx.doi.org/10.1116/1.586325 (6 pages)

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In this article we present a novel acid catalyzed chemically amplified resist and the associated silicon‐dioxide etch process that was developed using that resist. The 200 nm wide and 250 nm deep trenches in the silicon dioxide are part of a multilevel fully planar metallization scheme, where copper lines are fully imbedded in the interlevel dielectric. Conventional resist materials are not sensitive enough to be used in high‐throughput production and in many cases their selectivity versus silicon dioxide reactive ion etching is low. Resist materials based on acid catalyzed chemical amplification show very desirable properties with respect to their sensitivity, flexibility in design, and resolution capability. The resolution capability extends down to 200 nm for 290 nm thick resist presented in this report. Moreover, as such resists meet the requirements of deep UV, x‐ray, and e‐beam exposure tools, it is expected that they will replace the ‘‘standard’’ novolac resists in many applications. A process window for silicon dioxide etching using a single layer resist based on poly(4‐hydroxy styrene‐co‐4‐acetoxymethyl styrene) has been developed. Lithographic sensitivity, resolution, contrast as well as etching characteristics of this resist were evaluated. The resist demonstrated a sensitivity of 2–2.5 μC/cm2 for 50 keV e‐beam exposure by the JEOL 5DIIU system. A contrast value of 5.1 was obtained using a postexposure bake of 130 °C for 2 min. The resist selectivity with respect to thermal oxide in CHF3 plasma reactive ion etching (RIE) was about 1–3. Using this resist and CHF3 RIE we were able to etch 0.25 μm deep and 0.2 μm wide trenches with vertical sidewalls in SiO2. These results showed that the resist system is very feasible for future single layer resist e‐beam pattern definition, and it also has a very promising prospects for deep UV and x‐ray lithographies.
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81.65.-b Surface treatments
85.40.Hp Lithography, masks and pattern transfer

Wet‐developed bilayer resists for 193‐nm excimer laser lithography

R. R. Kunz, M. W. Horn, P. A. Bianconi, D. A. Smith, and J. R. Eshelman

J. Vac. Sci. Technol. B 10, 2554 (1992); http://dx.doi.org/10.1116/1.586326 (6 pages) | Cited 1 time

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A high‐contrast resist process using polysilynes has been developed for 193‐nm excimer laser lithography. Copolymerization allows for control of both polymer molecular weight and the net polymer solubility parameter. Optimal formulations yield sensitivities of 35–60 mJ/cm2 and line‐edge roughness of ≤20 nm. Addition of sensitizers into the resist further improves sensitivity and values from 5 to 30 mJ/cm2 have been demonstrated. Use of high‐density, low‐bias etching sources for the oxygen‐plasma pattern transfer improves process windows. For example, etch rate selectivities of 80:1 for the planarizing layer versus the polysilyne imaging layer have been observed even when the planarizing layer etch rate exceeds 1 μm/min. Under these conditions, the exposure latitude is 40% for k1=0.57 and the development latitude is 100% (20±10 s) for 10% linewidth control.
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42.82.Cr Fabrication techniques; lithography, pattern transfer

Defect studies on single and bilayer resist systems

K. Paul Muller and Harbans S. Sachdev

J. Vac. Sci. Technol. B 10, 2560 (1992); http://dx.doi.org/10.1116/1.586327 (5 pages) | Cited 4 times

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Defect detection equipment and procedures to qualify resist systems with regard to defects have been investigated. An analysis was carried out for two bilayer resist systems which were compared to a single layer resist. One of the bilayer resists was developed for the mid‐UV exposure range, the other for deep‐UV. It showed that the pinhole‐limited yield measured by metal–oxide–semiconductor test structures is approximately 10% lower for one of the bilayer resists compared to a single layer resist. The other bilayer resist scheme was compared to a single layer resist with regard to particulates. Here the dry‐developed bilayer resist scheme showed approximately four times higher additive defect densities than the wet‐developed single layer resist. A short dry etch process for opening an anti reflective coating underneath a single layer resist increased the defect densities. Water rinse steps are capable of reducing these defect levels substantially. The dry‐developed resist schemes had higher defect densities, but it is certainly possible to reduce these to the densities of single layer resists.
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85.40.Hp Lithography, masks and pattern transfer
81.65.-b Surface treatments
68.55.Ln Defects and impurities: doping, implantation, distribution, concentration, etc.

Practical cage‐effect model for crosslinking in a negative chemically amplified resist and its use in comparing e‐beam and optical exposure

N. N. Tam, R. A. Ferguson, and A. R. Neureuther

J. Vac. Sci. Technol. B 10, 2565 (1992); http://dx.doi.org/10.1116/1.586328 (5 pages) | Cited 1 time

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A closed‐form, accurate, and easy to fit model for crosslinking of chemically amplified acid‐hardened resist (Shipley SNR‐248) is presented and used to compare effects of e‐beam and optical exposure. In this model, the saturation of the acid‐catalyzed crosslinking reaction during the postexposure bake is assumed to be caused by the ‘‘cage‐effect’’ mechanism–restriction of segmental diffusion of the polymer chains as the reaction progress. [D. Seligson, S. Das, H. Gaw, and P. Pianetta, J. Vac. Sci. Technol. B 6, 2303 (1988)]. To model this cage effect, the rate coefficient in the rate equation is assumed to be a linearly decreasing function of the extent of the crosslinking with the asymptotic saturation level of the crosslinking as a parameter. According to this cage‐effect model, the order of the acid catalyst in the crosslinking reaction of e‐beam exposed SNR‐248 resists m is 1.37, which is similar to that of the deep‐ultraviolet (DUV) exposed resists (1.42). However, in e‐beam exposed resists, some crosslinking is induced by the electrons during exposure. As a result, this initial crosslinking might contribute to a slightly higher activation energy (0.866 versus 0.694 eV). The equilibrium conversions of the melamine crosslinking sites are also different between the two exposure types. The power of the acid concentration n in the expression for the equilibrium conversion for e‐beam exposed resists is ∼0.49 whereas in DUV exposed resists, n is 1.1. There is also a difference in the activation energies of the equilibrium constants which suggested the cage effect might have a stronger influence on the backward reaction in e‐beam exposed resists.  
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82.35.-x Polymers: properties; reactions; polymerization
85.40.Hp Lithography, masks and pattern transfer

Negative i‐line photoresist for 0.5 μm and beyond

Willard Conley and Jeffery Gelorme

J. Vac. Sci. Technol. B 10, 2570 (1992); http://dx.doi.org/10.1116/1.586329 (6 pages)

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In this article we will discuss a new high‐resolution aqueous base developable negative tone i‐line photoresist system that has demonstrated subhalf‐micron resolution with commerically available i‐line exposure systems. The photoresist system consists of a novolak resin, an aminoplast crosslinker, triphenyl sulfonium triflate as the photoacid generator, and 9‐anthracene methanol, a commercially available aromatic energy transfer compound. Using statistical experimental design, data will be presented showing the experimentation required to optimize the formulation and the process in 2.38% TMAH developer (0.263 N). We will report linewidth, dose, and focus latitude data, energy transfer compound effects on contrast, background dissolution along with linewidth tolerance to changes in postexposure bake temperature. Additionally, we will briefly discuss initial phase‐shift mask work that is currently in progress.
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42.70.Gi Light-sensitive materials
42.70.Jk Polymers and organics

0.35 μm rule device pattern fabrication using high absorption‐type novolac photoresist in single layer deep ultraviolet lithography: Surface image transfer for contact hole fabrication

Y. Tomo, T. Kasuga, M. Saito, A. Someya, and T. Tsumori

J. Vac. Sci. Technol. B 10, 2576 (1992); http://dx.doi.org/10.1116/1.586330 (5 pages)

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0.35 μm design rule device patterns were fabricated using high absorption‐type positive and negative photoresist with a KrF excimer laser stepper. The main reason for using high absorption‐type photoresist was to minimize the thin film interference effect caused by high reflectivity of the substrate in the deep ultraviolet region. The positive photoresist was FH‐EX1 (Fuji‐Hunt) and negative photoresist was SAL601. Both contain novolac resin as the base polymer. The positive photoresist was mainly used for poly‐Si and W–Si layer pattern fabrication and the negative photoresist was used for the contact hole pattern fabrication. In the contact hole fabrication a surface image transfer technique was used. This technique relies on the direct transfer of the surface negative photoresist image to the insulating layer with highly anisotropic etching and is completely different from the so‐called ‘‘surface imaging technique’’ using gas phase silylation and successive dry resist development (O2 reactive ion etching). Although the process was a tentative one, critical dimension controllability of this approach satisfied research and development level device fabrication requirements.
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85.40.Hp Lithography, masks and pattern transfer
85.40.-e Microelectronics: LSI, VLSI, ULSI; integrated circuit fabrication technology

New model of polymer silylation: Application to lithography

C. Pierrat

J. Vac. Sci. Technol. B 10, 2581 (1992); http://dx.doi.org/10.1116/1.586331 (8 pages) | Cited 1 time

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A new model of polymer silylation is proposed. This model takes into account the reaction of the silylating agent with the hydroxyl groups of the polymer and the relaxation rate of the polymer after reaction. The diffusion coefficient of the silylating agent is supposed to be a function of the expansion of the polymer matrix. At the interface between the silylating agent and the polymer, it is assumed that sorption driven by the pressure of the silylating agent, and desorption driven by the concentration of the silylating agent can occur. The resulting differential equations are solved using a finite element technique and the influence of the main parameters, namely, the reaction rate, the relaxation rate, and the diffusion coefficients is studied.
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82.65.+r Surface and interface chemistry; heterogeneous catalysis at surfaces
85.40.Hp Lithography, masks and pattern transfer
82.20.Pm Rate constants, reaction cross sections, and activation energies

Fabrication of submicron conducting and chemically functionalized structures from poly(3‐octylthiophene) by an electron beam

Sui Xiong Cai, Manoj Kanskar, J. C. Nabity, John F. W. Keana, and M. N. Wybourne

J. Vac. Sci. Technol. B 10, 2589 (1992); http://dx.doi.org/10.1116/1.586332 (4 pages) | Cited 2 times

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We present a novel method of using an electron beam to both functionalize and cross‐link poly(3‐octylthiophene) (P3OT) in a single step to produce submicron scale polymer structures carrying functionalized groups. We have shown P3OT to be a negative electron‐beam resist with a sensitivity of 15–30 μC cm−2. The electrical conductivity of doped P3OT wire structures was measured at room temperature and was found to be in the range 4.0–5.9 Ω−1 cm−1. Electron‐beam exposure of P3OT films containing 7 wt % of N‐hydroxysuccinimide (NHS) functionalized perfluorophenyl azide 2 resulted in the incorporation of the NHS functional groups in the polymer, as well as cross‐linking. The functionalized submicron structures were found to be weakly fluorescent under fluorescein excitation (450–490 nm), but after treatment with a solution of 5‐(aminoacetamido)fluorescein in ethanol the structures became strongly fluorescent.
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82.35.-x Polymers: properties; reactions; polymerization
73.61.-r Electrical properties of specific thin films

Characterization of chemically amplified resists for soft x‐ray projection lithography

Glenn D. Kubiak, Eric M. Kneedler, Robert Q. Hwang, Michelle T. Schulberg, Kurt W. Berger, J. E. Bjorkholm, and W. M. Mansfield

J. Vac. Sci. Technol. B 10, 2593 (1992); http://dx.doi.org/10.1116/1.586333 (7 pages) | Cited 5 times

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Sensitivity, lithographic performance, photoabsorption, and photodesorption of chemically amplified novolac‐based resists have been studied at an exposure wavelength of 140 Å and are compared to poly(methylmethacrylate) (PMMA). Monochromatic exposures of the resists AZ PF514, AZ PN114, and SAL 601 yielded D0.9 values of 2.5–3 mJ/cm2 for 0.25 μm thick films. Contrast values ranged from 3 for AZ PN114 to 5 for SAL 601. Photoabsorption measurements of supported AZ PN114 films at 140 Å yield an absorption coefficient of 4.4±0.1 μm−1. Photodesorption of fragment ions induced by 140 Å radiation has been studied in PMMA and AZ PN114 using time‐of‐flight mass spectrometry. It is found that H+, CH2+, CH3+, H2O+, CHO+, C3H5+, and COOCH3+ dominate the ion mass spectra photodesorbed from PMMA, while H+, CH3+, H2O+, and CHO+ dominate the ion mass spectra for AZ PN114. The mass‐integrated ion desorption yield from AZ PN114 is three times less than that measured for PMMA per photon or 90 times less when expressed per exposure. Lithographic performance of AZ PF514 and SAL 601 has been characterized using a multilayer‐coated 20× Schwarzschild objective and a transmissive Ge/Si mask illuminated by a laser plasma source.
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85.40.Hp Lithography, masks and pattern transfer

Characterization of AZ PN114 resist for high resolution using electron‐beam and soft‐x‐ray projection lithographies

K. Early, D. M. Tennant, D. Y. Jeon, P. P. Mulgrew, A. A. MacDowell, and O. R. Wood

J. Vac. Sci. Technol. B 10, 2600 (1992); http://dx.doi.org/10.1116/1.586334 (6 pages) | Cited 4 times

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We report on resolution experiments with the negative chemically amplified resist AZ PN114. Using soft‐x‐ray projection lithography at λ=14 nm, we imaged 0.1‐μm lines and spaces in film thicknesses ranging from 50 to 200 nm with both a 20× reduction Schwarzschild camera and a 1× Offner ring‐field optical system at doses of ∼10 mJ/cm2. High‐resolution electron‐beam lithography was used to study the effect of postexposure bake temperature on resist resolution and to characterize a trilayer structure. We found that at temperatures higher than 105 °C 0.1‐μm features could not be resolved and patterns were distorted. Using e‐beam, we resolved 0.075‐μm lines and spaces in AZ PN114 and transferred the pattern to the underlying levels of the trilayer. We measured feature edge‐noise for 0.1‐ and 0.2‐μm critical dimensions (CDs) over a wide range of doses. We compared the edge noise and linewidth variation with those measured on samples written in poly(methyl methacrylate) (PMMA). We found 3σ values of 24 nm for AZ PN114 and 9 nm for PMMA. These results suggest that AZ PN114, or a resist of similar sensitivity, may be useful for CDs as small as 0.25 μm. To maintain sufficient linewidth control at smaller CDs in manufacturing, less sensitive resists will probably be required.
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85.40.Hp Lithography, masks and pattern transfer

Application of a new analytical technique of electron distribution calculations to the profile simulation of a high sensitivity negative electron‐beam resist

N. Glezos, I. Raptis, D. Tsoukalas, and M. Hatzakis

J. Vac. Sci. Technol. B 10, 2606 (1992); http://dx.doi.org/10.1116/1.586335 (4 pages) | Cited 4 times

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An analytical model for the exposure of electron‐beam sensitive resists is developed. A point beam incident on a multilayer substrate at a right angle is considered. The model uses the diffusion approximation to the Boltzmann transport equation as a starting point for a self‐consistent calculation. Results are applied in the case of a new high sensitivity epoxy‐based resist, and development patterns are effectively simulated using the analytical method.
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71.10.-w Theories and models of many-electron systems
71.20.Rv Polymers and organic compounds
85.40.Hp Lithography, masks and pattern transfer

Wet silylation and dry development with the AZ 5214TM photoresist

Evangelos Gogolides, Elizabeth Tsoi, Androula G. Nassiopoulos, and Michael Hatzakis

J. Vac. Sci. Technol. B 10, 2610 (1992); http://dx.doi.org/10.1116/1.586011 (5 pages) | Cited 1 time

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A positive tone surface imaging process using wet silylation and dry development of AZ 5214TM photoresist was developed. The process steps are spinning and prebake of the photoresist, i‐line exposure, postexposure bake, wet silylation, and dry development in O2 plasma. The process has been developed using statistically designed experiments, starting with a Placket–Burman screening experimental design for six variables. These experiments showed that the composition of the silylating solution was the most important variable. As a result, a mixture experimental design followed, with the concentrations of the silylating agent and solvents as the only variables. Characterization of the process and process window definition were done with ultraviolet spectroscopy of films made on quartz wafers, and scanning electron microscope photographs.
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81.65.-b Surface treatments
85.40.Hp Lithography, masks and pattern transfer

Acid‐diffusion effect on nanofabrication in chemical amplification resist

Toshiyuki Yoshimura, Yoshinori Nakayama, and Shinji Okazaki

J. Vac. Sci. Technol. B 10, 2615 (1992); http://dx.doi.org/10.1116/1.586012 (5 pages) | Cited 16 times

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Acid‐diffusion effect on nanometer pattern fabrication in a chemical amplification resist, SAL601 (Shipley Co.), is investigated with a finely focused electron beam. During postexposure bake (PEB), acid generated by the electron beam exposure diffuses and is assumed to cause pattern size changes. A scanning electron microscope, S‐900 (Hitachi), which has a beam diameter of approximately 2 nm at 5 kV, is used to make latent images of nanometer isolated lines in a resist film. After electron beam exposure, the resist films with a thickness of 20 nm are baked in different conditions before development. The measured linewidths are found to be proportional to the square root of the PEB time. According to a simple acid diffusion model, this can be explained by the diffusion of generated acid during PEB. A minimum feature size of a 20 nm isolated line is obtained by adjusting the PEB conditions. It is therefore important to control the PEB conditions to suppress the acid diffusion for the critical dimension control of nanofabrication when using chemical amplification resist systems. Fine edge roughness is also observed in the delineated patterns. This is thought to originate from the distribution of diffused acid or from the random distribution of the base polymer with finite molecular sizes.
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85.40.Hp Lithography, masks and pattern transfer
82.65.+r Surface and interface chemistry; heterogeneous catalysis at surfaces

Single layer chemically amplified resist processes for device fabrication by x‐ray lithography

D. Seeger, R. Viswanathan, C. Blair, J. Gelorme, and W. Conley

J. Vac. Sci. Technol. B 10, 2620 (1992); http://dx.doi.org/10.1116/1.586013 (8 pages)

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Resist systems using synchrotron radiation x‐ray lithography for the fabrication of 0.25 μm (Leff) devices has been investigated [R. Viswanathan et al. (unpublished)]. In this study, a chemically amplified negative crosslinking IBM resist, CGR [W. Conley and J. Gelorme, J. Vac. Sci. Technol. B 10, XXXX (1992)], for use on the contact level was the focus. Linewidth control and contrast curves of this system have been studied as a function of a number of parameters including changes in formulations. Mask limited resolution to 0.25 μm feature size (line/space array) has been achieved using a 40 μm mask‐to‐wafer gap. More important for device fabrication, reproducibility of exposure latitude and resist bias has been demonstrated and will be discussed. Data on the effect of postapply and postexposure bake conditions on the process will also be presented. It is of interest to note that this resist shows little change in linewidth with respect to postexposure bake temperature. This resist system was modeled using aerial images generated from xmas and a thresholding resist development model. The model indicates that the wall profiles for this resist should be somewhat more tapered for isolated spaces than for isolated lines or line/space arrays and is verified experimentally. It is believed that this is related to the slope of the aerial image at the dose used and not inherent to the resist system. A positive resist was also looked at for application on the polysilicon level. A process that has been previously described was used [(a) A. Katnani, Proc. SPIE XX, XXX (1992); (b) D. Seeger, R. Wood, J. Gelorme, and K. Stewart, KTI Interface ’89 (unpublished), p. 351; (c) R. Wood, C. Lyons, R. Mueller, and J. Conway, KTI Interface ’88 (unpublished), p. 341.] and looked at linewidth control across device wafers. Line widths for the polysilicon gates were measured across topography, across field, and from field‐to‐field and will be described in detail.
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85.40.Hp Lithography, masks and pattern transfer
85.30.Pq Bipolar transistors
85.30.Tv Field effect devices

First x‐ray stepper in IBM advanced lithography facility

A. C. Chen, C. J. Progler, F. F. Couch, T. A. Gunther, R. H. Fair, and K. A. Cooper

J. Vac. Sci. Technol. B 10, 2628 (1992); http://dx.doi.org/10.1116/1.586014 (5 pages) | Cited 2 times

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This article describes the first commercially available state‐of‐the‐art x‐ray stepper, the Karl Suss XRS200/3, installed at the IBM Advanced Lithography Facility (ALF) at the end of 1991. ALF was built for the development of x‐ray lithography for future generations of electronics devices [G. Lesoine, K. Kukkanen, and J. Leavey, Proc. SPIE 1263, 131 (1990)]. This stepper is attached to the first lithography beamline in ALF [J. Oberschmidt, R. Rippstein, R. Ruckel, A. Chen, J. Grandlund, and A. Palumbo, Proc. SPIE 1671, 324 (1992)]. The architecture of the tool and its two main improvements, (a) kinematic mask handling and (b) alignment system, will be discussed. Then the qualification test methodology and resulting data on key lithographic properties and throughput will be presented.
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07.85.-m X- and γ-ray instruments
85.40.Hp Lithography, masks and pattern transfer
81.65.-b Surface treatments
61.80.Cb X-ray effects

Spatial correlation of electron‐beam mask errors and the implications for integrated circuit yield

C. N. Berglund, N. I. Maluf, Jun Ye, G. Owen, R. Browning, and R. F. W. Pease

J. Vac. Sci. Technol. B 10, 2633 (1992); http://dx.doi.org/10.1116/1.586015 (5 pages) | Cited 3 times

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Specifications for masks are usually based on the assumptions that pattern errors can be adequately described by a stationary Gaussian distribution of independent point processes. Critical dimension and feature position errors across chrome‐on‐glass photomask plates were measured, and the results show that a description of these errors in terms of a 3‐sigma variation about a mean value based on the above description is inadequate and often misleading. Mask dimensional errors exhibit considerable spatial correlation across a plate, and have a spatial power spectrum that has implications for integrated circuit yield because of the different ways that photolithography systems can transfer reticle errors to the wafer. Depending on the spatial correlations of the errors and the specific lithography system the implications could be either positive or negative. As a result any quantitative consideration of the effect of mask errors on device performance and yield must consider mask error spatial correlations specifically.
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85.40.Hp Lithography, masks and pattern transfer

Dynamic performance of a scanning X–Y stage for automated electron‐beam inspection

D. J. Clark, J. McMurtry, C. Chadwick, R. Simmons, W. D. Meisburger, L. Veneklasen, A. Chitayat, S. Squires, W. Squires, and M. Levine

J. Vac. Sci. Technol. B 10, 2638 (1992); http://dx.doi.org/10.1116/1.586016 (5 pages) | Cited 1 time

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The design and performance of an X–Y stage for fast electron‐beam inspection of wafers and x‐ray masks is described. The inspection technique involves the comparison of images that are acquired by the raster scan acquisition of long swath images recorded while the stage moves at constant velocity. Pairs of images acquired serially must remain registered to about 0.05 μm net accuracy, requiring interferometer controlled motion with very low vibration. The system design requires high‐vacuum compatible, nonmagnetic construction, with provision for electron and light optical elements above the stage, and additional electron optics and substrate loading elements below it. Accordingly, an open frame stage with internal linear motors and bearings was selected. High stiffness and particular attention to smooth motion results in very low vibration with a relatively large moving mass. The stage is driven by brushless linear motors inside a 20 Hz bandwidth servo loop closed around high‐resolution λ/256=2.5 nm interferometers. Smooth motion contributes to accurate short term position measurement, allowing residual errors to be corrected by beam deflection. Long range accuracy relies largely upon occasional re‐registration using features on the die patterns. At the end of swaths, programmed turnaround trajectories employing position and acceleration feedback allow serpentine paths with a minimum acceleration and overhead time. Using several complementary measurement techniques, overall registration accuracy was shown to be sufficient for detection of 0.05 μm defects.
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85.40.-e Microelectronics: LSI, VLSI, ULSI; integrated circuit fabrication technology
07.78.+s Electron, positron, and ion microscopes; electron diffractometers
81.70.-q Methods of materials testing and analysis
41.75.Fr Electron and positron beams

Analytical description of backscattered electron signal for high‐resolution metrology

E. Di Fabrizio, L. Luciani, L. Grella, M. Baciocchi, M. Gentili, L. Mastrogiacomo, R. Maggiora, and V. White

J. Vac. Sci. Technol. B 10, 2643 (1992); http://dx.doi.org/10.1116/1.586017 (5 pages) | Cited 1 time

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Backscattered electron (BE) signals obtained by scanning fine features with a focused electron beam were studied. A commercial electron beam lithography machine (EBMF10 of Leica Cambridge) equipped with a channel plate detector was exploited for this purpose. The collected signal profile, and in particular the effect of the electron emission from the sidewalls of the feature under inspection (sidewall electrons, SWE) were studied. The variables we investigated include feature material and beam accelerating voltage. The effect of SWE on the BE signal was clarified by making use of Monte Carlo simulations. In particular it was possible to separate the SWE contribution from the global BE signal. Further, a novel analytical representation of the BE signal including the SWE effect was implemented. By this method, a precise linewidth measurement routine was developed and applied for metrology at different voltages on fine metal features of different materials. The application of this method to the metrology of submicron features (down to 0.2 μm) showed an intrinsic accuracy of better than 5% of the actual linewidth value.
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81.70.-q Methods of materials testing and analysis
85.40.-e Microelectronics: LSI, VLSI, ULSI; integrated circuit fabrication technology

Simple metrology scheme with nanometer resolution employed to check the accuracy of an electron beam lithography system

B. Hübner and H. W. P. Koops

J. Vac. Sci. Technol. B 10, 2648 (1992); http://dx.doi.org/10.1116/1.586018 (5 pages)

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The ‘‘self‐comparison method’’ is used to measure positioning errors, thermal and mechanical instabilities as well as field distortions of a high‐resolution electron beam lithography system. For drift measurements, line gratings are overlaid with slightly rotated gratings of the same constant in subsequent exposures. From the position of the moiré patterns we deduce positioning errors with 2.5 nm resolution. Since moiré measurements are equivocal, we use in addition vernier patterns with a resolution of 150 nm to overcome this problem. The measurements are made with an optical microscope but not with a calibrated metrology tool. Distortion measurement is carried out using an image acquisition system with 512×512 pixels together with a video camera and an optical microscope. Images of a point grating filling a full field are taken at various positions in the field. The grating in the center region is taken as a reference for the measurement. Field distortions are measured from differences in the grating constant and rotation between the center region and the outer regions. These are determined by comparing the center of mass of each grating point in the images with the corresponding points in the reference image. Differences in the grating constant down to 0.0003 times the constant and rotations of 0.0003 rad can be measured. These results are then fitted to a polynomial function of fifth order representing the field aberrations. Using this method, the distortions of the image acquisition system have no influence on the result of the evaluations .
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85.40.Hp Lithography, masks and pattern transfer

Pattern placement metrology precision evaluation

S. C. Nash, T. J. Fecteau, and J. S. Cook

J. Vac. Sci. Technol. B 10, 2653 (1992); http://dx.doi.org/10.1116/1.586019 (4 pages)

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Meeting the pattern placement requirement for 0.25‐μm groundrule x‐ray masks is a key development challenge. The e‐beam mask lithography system and process‐induced distortions influence pattern placement. To understand and control these tools and processes, and to disposition finished x‐ray masks, more precise pattern placement metrology is required. This article presents the results of an evaluation of the Leica LMS 2000 Laser Metrology System for pattern placement metrology on x‐ray masks.
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07.85.-m X- and γ-ray instruments
85.40.Hp Lithography, masks and pattern transfer

Novel x‐ray mask distortion measurement technique employing holographic gratings and phase‐shifting interferometry

M. E. Hansen, H. T. H. Chen, G. Chen, R. L. Engelstad, and F. Cerrina

J. Vac. Sci. Technol. B 10, 2657 (1992); http://dx.doi.org/10.1116/1.586020 (5 pages)

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This article presents a new optical metrology technique that has been developed at CXrL to investigate potential distortions induced in x‐ray masks during their fabrication, mounting, and x‐ray irradiation. The technique employs a Zygo phase‐shifting Fizeau interferometer to acquire the in‐plane distortion (IPD) and out‐of‐plane distortion (OPD) present in the masks. The interferometer measures the OPD directly, while IPD measurements are obtained with the aid of holographic gratings that have been printed onto the masks. When positioned at the Littrow angle of the gratings, the interferometer can acquire a retrodiffracted wavefront that contains the IPD information. Subtraction of the pre‐ and postdistortion interferograms yields the induced distortions. Computer models to simulate x‐ray mask distortions have been developed and implemented using ansys, a commercially available finite element analysis software package. Numerical results have shown excellent agreement with interferometric data. The authors believe that these new interferometric techniques and models should prove invaluable as metrologic and predictive tools for the measurement, characterization, and design of x‐ray masks in the 0.25 μm regime.
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81.65.-b Surface treatments
61.80.Cb X-ray effects
85.40.Hp Lithography, masks and pattern transfer

Robust subpixel alignment in lithography

Alan Gatherer and Teresa H.‐Y. Meng

J. Vac. Sci. Technol. B 10, 2662 (1992); http://dx.doi.org/10.1116/1.586021 (5 pages)

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Lithographic alignment is the problem of estimating the position of a feature that has previously been etched onto a wafer. Ideally, the alignment algorithm should be accurate without being computationally complex. In this article we describe an algorithm that, for symmetric pulses, achieves the accuracy of correlation at a fraction of the computational expense. The algorithm will automatically adapt to the minimum error condition for an unknown mark. We show that this algorithm is more robust than simple edge detection.
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85.40.Hp Lithography, masks and pattern transfer

High accuracy electron‐beam grating lithography for optical and optoelectronic devices

C. Dix and P. F. McKee

J. Vac. Sci. Technol. B 10, 2667 (1992); http://dx.doi.org/10.1116/1.586022 (4 pages)

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Much of the development of recent optoelectronic and optical devices has been undertaken using the lithographic tools designed for conventional microelectronic circuits. For the latter, the need for spatial linearity and accuracy is mainly concerned with overlay accuracy and device yield. But the characteristics of optical structures, such as gratings, can be affected by the spatial errors of the tools used to make them. The linearity of a Leica Cambridge EBMF‐10.5 electron beam lithography system has been investigated with particular regard to the writing of gratings for distributed feedback lasers and optical waveguide devices. Since the gratings can be narrow, it is possible to take advantage of the lower distortions associated with scanning in a single axis. The distortion correction system has been shown to provide significant improvements in linearity even at small field sizes of around 1 mm, and an overall beam placement accuracy of 20 nm within the writing field has been demonstrated. The applications illustrated have required different approaches to calibration and writing, and have employed gratings written using both distortion corrected and uncorrected fields.
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42.82.Cr Fabrication techniques; lithography, pattern transfer

Laser‐chemical three‐dimensional writing for microelectromechanics and application to standard‐cell microfluidics

T. M. Bloomstein and D. J. Ehrlich

J. Vac. Sci. Technol. B 10, 2671 (1992); http://dx.doi.org/10.1116/1.586023 (4 pages) | Cited 4 times

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A high‐speed technique has been developed for machining three‐dimensional silicon parts using laser‐induced chlorine etching reactions. Parts are created directly from solid‐modeling computer‐aided‐design/computer‐aided‐manufacturing software. Removal rates exceeding 2×104 and ≥105 μm3/s are achieved at 1 and 15 μm x–y resolution, respectively. This is several orders of magnitude faster than electrodischarge machining methods. Submicrometer resolution has been achieved. Laser‐induced metallization of resulting structures as well as replication through compression molding have been demonstrated. A class of microfluidic flow‐channel devices is under development using a standard‐cell software architecture combined with field stitching.
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85.40.Hp Lithography, masks and pattern transfer
81.65.-b Surface treatments
42.62.Cf Industrial applications

Focused ion beam induced deposition and ion milling as a function of angle of ion incidence

Xin Xu, Anthony D. Della Ratta, Jane Sosonkina, and John Melngailis

J. Vac. Sci. Technol. B 10, 2675 (1992); http://dx.doi.org/10.1116/1.586024 (6 pages) | Cited 17 times

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In the repair of integrated circuits, and x‐ray masks focused ion beam induced deposition, and ion milling often have to be performed over quite nonplanar topography. Thus, the milling and the deposition as a function of the angle of ion incidence are important. The milling yield of Si, SiO2, Au, and W versus angle of incidence using 25 keV Ga+ ions has been measured. In qualitative agreement with simulations, the yield rises with angle and then falls as grazing incidence is approached. Deposition yield versus angle was measured using dimethylgold hexafluoro‐acetylacetonate and W(CO)6 as the precursor gases. The measurements were carried out using cylindrical quartz fibers 30–50 μm in diameter which automatically provide angles of incidence from 0° to 90° or on planar surfaces at various angles. Rippling of the deposited material is observed at angles of incidence greater than 50°.  
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81.15.Cd Deposition by sputtering
79.20.Rf Atomic, molecular, and ion beam impact and interactions with surfaces
85.40.Ls Metallization, contacts, interconnects; device isolation

Etch masks of semimetallic amorphous carbon thin films produced by electron‐beam sublimation of graphitic carbon

G. A. Porkolab and E. D. Wolf

J. Vac. Sci. Technol. B 10, 2681 (1992); http://dx.doi.org/10.1116/1.586025 (4 pages) | Cited 1 time

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Smoothness of etched facets at all angles is a critical requirement for photonic devices in such materials as AlGaAs/GaAs which are etched at variable angles by directed ion beam/reactive gas etching systems such as chemically assisted ion beam etching (CAIBE). Semimetallic amorphous carbon thin films have been found to produce excellent etched facets that are smoother than those etched with other mask materials. This material also exhibits very low CAIBE etch rates and very low chemical reactivity with substrate materials such as AlGaAs/GaAs or silicon. The semimetallic amorphous carbon was deposited up to 400 nm thick by electron beam sublimation of graphitic carbon onto substrates such as polished wafers of GaAs, Si, Ge, and onto glass. The electron‐beam sublimation deposited (EBSD) semimetallic amorphous carbon, EBSD semimetallic a‐C, can be patterned directly by SF6 reactive ion etcher via a standard photoresist mask, it can be used as an etch mask in CAIBE systems, and it can be stripped clean in hydrogen or oxygen plasmas. Etch rate selectivities of approximately 30:1 of (AlGaAs):(EBSD semimetallic a‐C) were observed in CAIBE experiments. The EBSD semimetallic a‐C is being used as the etch mask in a self‐aligned four‐CAIBE steps process to microfabricate surface‐emitting high‐power single‐mode AlGaAs/GaAs laser arrays.
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81.65.-b Surface treatments
85.40.Hp Lithography, masks and pattern transfer

Formation of complex features using electron‐beam direct‐write decomposition of palladium acetate

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

J. Vac. Sci. Technol. B 10, 2685 (1992); http://dx.doi.org/10.1116/1.586026 (5 pages) | Cited 8 times

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A focused electron beam has been used to selectively decompose thin films of palladium acetate, (Pd–Ac), resulting in the formation of ≤50 nm wide conductive Pd‐rich features. The formation of features from various film thicknesses of Pd–Ac has been investigated using a wide range of electron energies. Monte Carlo simulations of electron energy loss distributions in Pd–Ac films were calculated over a wide range of film thicknesses and electron energies. The Monte Carlo calculations were used to predict the volume over which the energy of the electron beam is deposited within the films. Thin conductive wires having profiles from high aspect ratio to almost circular cross sections produced by varying the electron beam energy were in agreement with the Monte Carlo predictions. Complex multilayer Pd–Ac features were then fabricated by performing overlapping exposures of Pd–Ac films with differing electron beam energies.
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82.50.Kx Processes caused by X-rays or γ-rays

Electron‐beam induced tungsten deposition: Growth rate enhancement and applications in microelectronics

K. T. Kohlmann‐von Platen, L.‐M. Buchmann, H.‐C. Petzold, and W. H. Brünger

J. Vac. Sci. Technol. B 10, 2690 (1992); http://dx.doi.org/10.1116/1.586027 (5 pages) | Cited 23 times

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Electron‐beam induced deposition (EBID) of tungsten from the precursor gas W(CO)6 was investigated with the aim of enhancing the growth rate of the process. By varying dwell and loop time over a limited range, experimental deposition rates were compared to a time dependent model developed to describe the focused ion beam induced deposition. We found the cross section σ for EBID at 30 keV beam energy to be 1.2±0.2×10−16 cm−2. Based on these data, we predicted the achievable growth rate as a function of the current density. Moreover, EBID was used for x‐ray and open stencil mask repair, the generation of etch masks and the deposition of electrically conductive lines. The resistivity of the latter was found to be affected by the beam energy and current; the best value achieved was 10−2 Ω cm.
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81.15.Cd Deposition by sputtering

Focused ion beam deposition of Pt containing films

J. Puretz and L. W. Swanson

J. Vac. Sci. Technol. B 10, 2695 (1992); http://dx.doi.org/10.1116/1.586028 (4 pages) | Cited 22 times

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Focused ion beam induced deposition of platinum films from a gas of methylcyclopentadienyl trimethyl platinum is reported. Deposition was carried out with a 25 kV beam of Ga+ with current densities of 2–7 A/cm2 that was controlled by a digital scan generator. Film yields and resistivity were measured as a function of beam current density, gas flux, scan dwell, and loop time. Relatively high yields of 1.4 μm3/nC and resistivities as low as 400 μΩ cm were measured for deposition carried out in 1×10−6 Torr background pressure of residual gas. Auger studies revealed that the films were surprisingly free of oxygen, but contained significant amounts of carbon. A figure‐of‐merit, Fm=ρ/Y, is defined which enables comparison of films used for interconnects. Fm for the Pt films is superior to that of W(CO)6 deposited W films.
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81.15.-z Methods of deposition of films and coatings; film growth and epitaxy
73.61.At Metal and metallic alloys

Large radius new etching system using electron beam excited plasma

Y. Aoyagi, T. Hara, M. Hamagaki, M. Ryoji, and K. Ohnishi

J. Vac. Sci. Technol. B 10, 2699 (1992); http://dx.doi.org/10.1116/1.586029 (4 pages) | Cited 1 time

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A new electron beam excited plasma (EBEP) etching system has been developed. This EBEP system can efficiently generate a high density and uniform plasma by introducing a high current low‐energy electron beam into an etching gas chamber. The uniformity of the Cl plasma density is within ±2.5% over an 8 in. wafer and the uniformity of the plasma and floating potential across the wafer is within ±2 V. This ultrahigh uniformity of the potentials overcomes the problem of the breakdown of thin gate insulators during etching that originate from the nonuniformity of the potential at the substrate. The selectivity of etching obtained is 40:1 for poly‐Si/resist and more than 100:1 for poly‐Si/SiO2. The etch rate is 3600 A/min.
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85.40.Hp Lithography, masks and pattern transfer

Comparison between etching in Cl2 and BCl3 for compound semiconductors using a multipolar electron cyclotron resonance source

S. W. Pang and K. K. Ko

J. Vac. Sci. Technol. B 10, 2703 (1992); http://dx.doi.org/10.1116/1.586030 (5 pages) | Cited 2 times

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Controllable dry etching of GaAs and InP using a multipolar electron cyclotron resonance (ECR) source and a radio frequency (rf)‐powered electrode was investigated. The etch characteristics were studied as a function of microwave power, rf power, distance from the ECR source, pressure, and temperature. Etch rate is found to increase with microwave power initially, then decrease at higher microwave power due to reduction in ion energy. Surface morphology becomes rougher and etch profile is more undercut at higher microwave power, but can be improved using higher rf power or by Ar addition. As the ECR source distance increases, the concentration of ions and neutral species decrease, but the ion energy increases. Therefore, when etching is limited by the arrival rate of reactive radicals, etch rate decreases with source distance. When the process is limited by the ion‐enhanced reaction or removal rates, etch rate increases with source distance. Etch rate and self‐induced dc bias voltage (‖Vdc‖) typically increase with pressure. The increase in ‖Vdc‖ is believed to be caused by the lower ion flux at higher pressure. However, when the reactive species concentrations and the ion energy are low, etch rate decreases with pressure. Low pressure was observed to favor smooth surface morphology and vertical etch profile. Etch rates for both GaAs and InP increase with temperature, with InP etch rate exceeding GaAs at 380 °C. Using a Cl2/Ar mixture with 10% Cl2, 70 W rf power and 25 W microwave power at 0.5 mTorr, 0.1 μm wide features that are 1 μm deep have been fabricated in GaAs with vertical profile and smooth surface morphology.
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81.65.-b Surface treatments

Fabrication of deep submicron patterns with high aspect ratio using magnetron reactive ion etching and sidewall process

Gao Shiping and Chen Mengzhen

J. Vac. Sci. Technol. B 10, 2708 (1992); http://dx.doi.org/10.1116/1.586031 (3 pages) | Cited 1 time

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A method for fabrication of fine patterns by conventional technologies is described. Using the sidewall process for fine pattern transfer and magnetron reactive ion etching, deep submicron and nanometer patterns with high aspect ratio have been prepared.
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85.40.Hp Lithography, masks and pattern transfer
81.65.-b Surface treatments

New in situ electron beam patterning process for GaAs using an electron‐cyclotron‐resonance plasma‐oxidized mask and Cl2 gas etching

N. Takado, S. Kohmoto, Y. Sugimoto, M. Ozaki, M. Sugimoto, and K. Asakawa

J. Vac. Sci. Technol. B 10, 2711 (1992); http://dx.doi.org/10.1116/1.586032 (5 pages) | Cited 1 time

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A new electron beam (EB) patterning process capable of resistless nanofabrication for GaAs has been developed using enclosed continuous‐vacuum processes. These processes are surface oxidation by electron cyclotron resonance (ECR) O2 plasma, oxidized‐surface modification by EB irradiation, and subsequent etching by Cl2 gas. The time and oxygen gas pressure required for the oxidation are greatly reduced, compared to other oxidation methods, by using ECR plasma to form an oxide mask for Cl2 gas etching. The plasma‐oxidized mask without EB irradiation cannot be removed by Cl2 gas etching even for 4 h at a sample temperature of 100 °C. In spite of its resistance to Cl2 gas etching, the mask can be easily removed by thermal treatment of the sample at about 620 °C in an As atmosphere.
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81.65.-b Surface treatments
61.80.Fe Electron and positron radiation effects
85.40.Hp Lithography, masks and pattern transfer

Magnetically enhanced triode etching of large area silicon membranes in a molecular bromine plasma

J. C. Wolfe, S. Sen, S. V. Pendharkar, P. Mauger, and A. R. Shimkunas

J. Vac. Sci. Technol. B 10, 2716 (1992); http://dx.doi.org/10.1116/1.585989 (4 pages) | Cited 1 time

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The optimization of a process for etching 125 mm silicon membranes formed on 150 mm wafers and bonded to Pyrex rings are discussed. A magnetically enhanced triode etching system was designed to provide an intense, remote plasma surrounding the membrane while, at the same time, suppressing the discharge over the membrane itself. For the optimized molecular bromine process, the silicon etch rate is 40 nm/min and the selectivity relative to SiO2 is 160:1.
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85.40.Hp Lithography, masks and pattern transfer
81.65.-b Surface treatments

HCl, H2, and Cl2 radical‐beam ion‐beam etching of AlxGa1−xAs substrates with varying Al mole fraction

J. A. Skidmore, D. G. Lishan, D. B. Young, E. L. Hu, and L. A. Coldren

J. Vac. Sci. Technol. B 10, 2720 (1992); http://dx.doi.org/10.1116/1.585990 (5 pages)

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The possible benefits of H∗ radicals on dry etching characteristics of AlGaAs were explored using HCl and separately mixed H2 and Cl2 radical‐beam ion‐beam etching. H∗ radicals strongly affect the Cl∗–AlGaAs surface chemistry resulting in large changes in etch rate and surface morphology. Etch rates were measured in situ by reflectance interferometry using a quarter‐wavelength structure with varying AlxGa1−xAs mole fraction. The presence of H∗ (from HCl or H2 added to Cl2) increases the Cl∗ etch rate threefold. An increase in surface roughness with H∗ (compared to Cl∗ alone) is correlated with increased Al content.  
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81.65.-b Surface treatments
82.65.+r Surface and interface chemistry; heterogeneous catalysis at surfaces
82.30.Cf Atom and radical reactions; chain reactions; molecule-molecule reactions

Electron cyclotron resonance plasma etching using downstream magnetic confinement

Kent D. Choquette, Robert C. Wetzel, Robert S. Freund, and Rose F. Kopf

J. Vac. Sci. Technol. B 10, 2725 (1992); http://dx.doi.org/10.1116/1.585991 (4 pages) | Cited 3 times

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We demonstrate that electron cyclotron resonance plasma etching with a magnetically confined plasma in the region of the sample produces an enhanced etch rate, an anisotropic etch profile, and low self‐bias voltage. Results are presented for GaAs etch rates, etch profiles, and macroscopic etch uniformity using a SiCl4 plasma, comparing the effects of a confining magnetic field and a diverging magnetic field in the reactor. The etch rates and saturated ion current density to the sample are found to be correlated. An anisotropic near vertical etch profile with smooth‐etched surfaces is obtained with a negative self‐bias voltage of typically 5–25 V for electrically floating samples in a magnetically confined plasma. When the magnetic field lines are perpendicular to the sample surface, the measured macroscopic etch uniformity is ±6% across a 5 cm diam wafer.
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81.65.-b Surface treatments
85.40.Hp Lithography, masks and pattern transfer

Low‐energy electron beam enhanced etching of Si(100)‐(2×1) by molecular hydrogen

H. P. Gillis, J. L. Clemons, and J. P. Chamberlain

J. Vac. Sci. Technol. B 10, 2729 (1992); http://dx.doi.org/10.1116/1.585992 (5 pages) | Cited 3 times

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The use of low‐energy electrons to enhance the rate of the reaction between H2 and Si to produce SiHx has been investigated. Etching was accomplished by steady‐state application of H2 and electrons, with quadrupole mass spectrometer (QMS) detection of etch products. After etching, low‐energy electron diffraction (LEED) was used to check for surface damage. Ultraviolet photoelectron spectroscopy and thermally stimulated desorption were used to determine the surface composition after etching. Experiments of this type have been conducted with electron energies from 200–1000 eV, hydrogen flux held constant, and the sample at room temperature. All have shown qualitatively similar results: the QMS detected species do not represent the fragmentation pattern of SiH4, the thermodynamically predicted product, and LEED shows that the surface has not been damaged.
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81.65.-b Surface treatments
82.65.+r Surface and interface chemistry; heterogeneous catalysis at surfaces
85.40.Hp Lithography, masks and pattern transfer

Electron beam lithography using MEBES IV

F. Abboud, M. Gesley, D. Colby, K. Comendant, R. Dean, W. Eckes, D. McClure, H. Pearce‐Percy, R. Prior, and S. Watson

J. Vac. Sci. Technol. B 10, 2734 (1992); http://dx.doi.org/10.1116/1.585993 (9 pages)

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The lithographic performance of the MEBESR IV maskmaker is described. This raster‐scan electron beam lithography system automates the thermal field emission (TFE) column and makes a number of advances in the electronics and software control subsystems to achieve the stability and accuracy sufficient for 64‐Mbit production and 256‐Mbit development. Key module developments are highlighted, including TFE column vibration reduction, column setup automation, 160 MHz blanking at a high slew rate, low noise, and increased linearity of the deflection control electronics, and multipoint system temperature control. Data on lithographic quality is presented, as well as ghostTM proximity correction results for 1× maskmaking applications with 0.2 μm minimum feature sizes.      
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85.40.Hp Lithography, masks and pattern transfer

Arrayed miniature electron beam columns for high throughput sub‐100 nm lithography

T. H. P. Chang, D. P. Kern, and L. P. Muray

J. Vac. Sci. Technol. B 10, 2743 (1992); http://dx.doi.org/10.1116/1.585994 (6 pages) | Cited 22 times

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In recent years, considerable progress has been made on an approach based on a novel concept which combines scanning tunneling microscope, microfabricated lenses, and field emission technologies to achieve microminiaturized low‐voltage electron beam columns with performance surpassing the conventional column. High throughput lithography is a potentially very important application for these microfabricated columns which measure only millimeters in dimensions. This is to be achieved using an array of these minicolumns in parallel in a multibeam mode with one or more columns per chip. The low‐voltage operation is attractive because proximity effect corrections may not need to be applied. In addition, an arrayed microcolumn system also has the potential of reducing the cost of the overall system through the compaction of the mechanical system. The throughout advantages for such an arrayed system based on different beam forming optics and pattern generation approaches will be discussed. In addition to lithography, a wide range of other applications for such an arrayed system such as testing, metrology, storage, etc., can also be considered.
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85.40.Hp Lithography, masks and pattern transfer
81.65.-b Surface treatments
41.75.Fr Electron and positron beams

Performance measurements of a 1‐keV electron‐beam microcolumn

L. P. Muray, U. Staufer, D. P. Kern, and T. H. P. Chang

J. Vac. Sci. Technol. B 10, 2749 (1992); http://dx.doi.org/10.1116/1.585995 (5 pages) | Cited 2 times

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A complete 1‐keV electron‐beam microcolumn, measuring only 2.5 mm in length, has been assembled and tested. The microcolumn combines a scanning tunneling microscope aligned field‐emission source with a miniaturized octupole scanner and a microfabricated einzel lens. Expected performance of this configuration, at a working distance of 1 mm and semiconvergent angle of 2.5 mrad, has been calculated to be a probe size of 8 nm with current density exceeding 104 A/cm2. The microcolumn has been successfully operated at 1 keV in scanning transmission mode using a 1‐μm grid sample. Images were acquired with scan fields ranging from 10 to 100 μm and preliminary resolution measurements indicated Gaussian beam diameter of 200 nm. Significant improvements are expected in the near term.
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07.78.+s Electron, positron, and ion microscopes; electron diffractometers

Micromachined electrostatic electron source

D. A. Crewe, D. C. Perng, S. E. Shoaf, and A. D. Feinerman

J. Vac. Sci. Technol. B 10, 2754 (1992); http://dx.doi.org/10.1116/1.585996 (5 pages) | Cited 2 times

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A microfabrication technique has been developed that combines the precision of silicon micromachining and fiber optics to allow the construction of large three‐dimensional structures with dimensional tolerances approaching 1 μm [A. D. Feinerman, S. E. Shoaf, and D. A. Crewe, Proceedings of the 180th Annual ECS Conference, Phoenix, AZ, October 1991 (unpublished)]. A miniature scanning electron microscope (MSEM) is being designed using this method. In this article we will present the electron optic calculations of a simple 1 kV MSEM consisting of a source, a three element electrostatic lens, deflectors, and a detector. The MSEM measures less than one cubic centimeter. There are many advantages of a MSEM. The performance of a SEM is improved as its length is reduced. [T. H. P. Chang, D. P. Kern, and L. P. Murray, J. Vac. Sci. Technol. B 8, 1698 (1990)]. The need for mechanical adjustments and motion feedthroughs is eliminated since the microscope components are prealigned to the optic axis. All components are ultrahigh vacuum compatible and can be heated to 500 °C. A small, portable electron microscope can be brought to the sample to be inspected instead of the sample being brought to the microscope. Vacuum hardware requirements are minimized. The fabrication technology is inexpensive compared to the conventional methods of electron microscope construction. Our construction method is easily extended to permit arrays of MSEMs to allow applications in high throughput e‐beam lithography and wafer inspection.
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07.78.+s Electron, positron, and ion microscopes; electron diffractometers
41.85.Ne Electrostatic lenses, septa

Electron‐beam cell‐projection lithography system

Y. Sakitani, H. Yoda, H. Todokoro, Y. Shibata, T. Yamazaki, K. Ohbitu, N. Saitou, S. Moriyama, S. Okazaki, G. Matuoka, F. Murai, and M. Okumura

J. Vac. Sci. Technol. B 10, 2759 (1992); http://dx.doi.org/10.1116/1.585997 (5 pages) | Cited 7 times

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An electron‐beam exposure system HL‐800D has been developed for the mass production of both quarter micron large‐scale integrated memories and application specific integrated circuits (ASICs). To achieve a productive level of throughput, the system utilizes a cell‐projection method combined with variable shaped method and a continuously moving stage at variable speed depending on the pattern density. The system is operated at a 50 kV acceleration voltage and a 1 μC/cm2 dosage. Three stage deflectors have been developed to assure high‐speed deflection and highly accurate positioning. A fast pattern controller generates patern data at 200 ns shot‐cycle‐time with the positioning error correction and proximity effect correction. A high‐speed ceramic XY stage and an automatic wafer loder have been developed. The system is operated by a workstation which also provides data conversion. The estimated throughput of the system is 11 wafers/h for 0.3 μm ASICs and 20 wafers/h for quarter micron memories.
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85.40.Hp Lithography, masks and pattern transfer

100 kV thermal field emission electron beam lithography tool for high‐resolution x‐ray mask patterning

M. A. McCord, R. Viswanathan, F. J. Hohn, A. D. Wilson, R. Naumann, and T. H. Newman

J. Vac. Sci. Technol. B 10, 2764 (1992); http://dx.doi.org/10.1116/1.585998 (7 pages) | Cited 6 times

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High‐voltage (≥50 kV) electron beam lithography (EBL) is the preferred technique for fabrication of additive‐process x‐ray masks, because the high‐voltage minimizes scattering in the resist and membrane, resulting in better resolution, straighter sidewalls, and reduced proximity effect. We have designed and built a new 100 kV column for a vector scan EBL machine for the purpose of writing high‐resolution, high‐precision x‐ray masks in order to explore the technological and fundamental limits of x‐ray lithography. The column features a 100 kV thermal field emission gun with an electrostatic condenser lens, conjugate blanking, and a liquid‐cooled magnetic final lens with high‐precision double magnetic deflection. The two‐lens optics provides a beam diameter of 30 nm at a current of 5 nA, sufficient to expose moderately sensitive resists at pixel rates approaching the maximum deflection speed of 10 MHz. Results obtained include proximity corrected, complex patterns in thin resist with feature sizes down to 50 nm. Comparisons of proximity effects, exposure parameters, and actual resist profiles, show that 100 kV is clearly superior to 50 kV and even 75 kV for feature sizes below 0.25 μm in thick (0.75 μm) resist. Excellent linewidth control has been obtained on plated gold x‐ray masks with feature sizes as small as 75 nm. Problems of patterning nanometer features with aspect ratios as high as 10:1, which include forward scattering, development effects, and plating effects, are discussed.
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85.40.Hp Lithography, masks and pattern transfer

Three‐dimensional electron‐beam resist profile simulator

A. Moniwa, H. Yamaguchi, and S. Okazaki

J. Vac. Sci. Technol. B 10, 2771 (1992); http://dx.doi.org/10.1116/1.585999 (5 pages) | Cited 5 times

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A three‐dimensional (3D) electron‐beam (EB) lithography simulator SEED‐3D (system for evaluating electron‐beam writing and developing 3D) has been developed for resist profile simulation and analysis of proximity effects. SEED calculates an exposure intensity distribution (EID), a 3D accumulated energy distribution after pattern exposure, and a 3D profile of the developed resist. SEED can take into account proximity effects in a wider region, because SEED takes a short time to calculate the 3D accumulated energy distribution. The concept of the 3D accumulated energy calculation is that the proximity effects in the forward scattering region are estimated precisely, and the proximity effects in the backscattering region are evalulated roughly. This 3D EB lithography simulator allows us to examine resist‐pattern profiles of 0.3‐μm line and space patterns. This simulator also gives an acceptable value for η which can be used for dose correction.
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85.40.Hp Lithography, masks and pattern transfer

Choice of system parameters for projection electron‐beam lithography: Accelerating voltage and demagnification factor

J. A. Liddle and S. D. Berger

J. Vac. Sci. Technol. B 10, 2776 (1992); http://dx.doi.org/10.1116/1.586000 (4 pages) | Cited 3 times

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A lithography system that uses Scattering with Angular Limitation Projection Electron Lithography (SCALPEL) allows us to vary the electron‐beam accelerating voltage in a way that was not possible with systems that use absorbing stencil masks. We have discovered that the choice of operating parameters, accelerating voltage, and demagnification factor, as well as many of the subsystem designs, are dominated by the need to control thermal effects within the system. We have derived a model which allows us to find operating parameters that minimize the thermal contribution to the pattern overlay error. This information, when combined with other subsystem constraints, enables us to define a relatively narrow range of possible working conditions. The model is general to high‐throughput electron beam lithography systems; we have applied the model to one example of a SCALPEL system.
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85.40.Hp Lithography, masks and pattern transfer

Mark detection for alignment and registration in a high‐throughput projection electron lithography tool

R. C. Farrow, J. A. Liddle, S. D. Berger, H. A. Huggins, J. S. Kraus, R. M. Camarda, C. W. Jurgensen, R. R. Kola, and L. Fetter

J. Vac. Sci. Technol. B 10, 2780 (1992); http://dx.doi.org/10.1116/1.586001 (4 pages) | Cited 1 time

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The design considerations and performance requirements of an alignment and registration method for high‐throughput projection electron lithography are discussed. We have devised a mark detection system for a lithography tool employing the SCALPEL principle. The process involves scanning the image of a mark from a mask, over a mark that is fabricated on a wafer and measuring the integrated backscattered‐electron intensity. Using a mark that consists of equally spaced lines of tungsten on silicon, we have investigated the effects of spatial and rotational misalignment, and focus in a small field of view SCALPEL machine. We have modeled these and other effects and found agreement between experimental and theoretical results. The measured precision of estimating position from the experimental data is ∼10 nm. By extrapolation we believe that in a practical lithography machine this value can be improved significantly.
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85.40.Hp Lithography, masks and pattern transfer

Calculation of a proximity resist heating in variably shaped electron beam lithography

Ken Nakajima and Naoaki Aizaki

J. Vac. Sci. Technol. B 10, 2784 (1992); http://dx.doi.org/10.1116/1.586002 (5 pages) | Cited 1 time

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In variably shaped electron beam (EB) lithography, the horizontal thermal diffusion in a resist cannot be neglected when, high‐current density, a high‐speed deflector amplifier, and a multiple‐layer resist system are used. These cause a horizontal‐mode resist heating (labeled ‘‘proximity resist heating’’). Calculation of proximity resist heating is accomplished by a finite element method, using ansys (Ver.4.4A) program. The calculation results suggest that the proximity resist heating is caused by the horizontal thermal flux from previous EB shot through a top layer resist. Especially, in case a high‐current acceleration voltage is used, the thermal effect is not caused by the vertical‐mode resist heating, but by the horizontal‐mode resist heating. It is also shown that the shorter settling time, which is the interval between shots, results in a higher resist temperature and a closer position of maximum resist temperature to the previous EB shot position, and that a high‐acceleration voltage in case of using a fixed current density brings out the reduction in resist heating.
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85.40.Hp Lithography, masks and pattern transfer
44.90.+c Other topics in heat transfer (restricted to new topics in section 44)

Multiconcens: An exposure method for submicron contact‐hole layers, using variable‐shape electron‐beam direct‐write and single‐layer resist

F. Heinlein, G. Gross, B. Höfflinger, M. Irmscher, C. Reuter, and R. Springer

J. Vac. Sci. Technol. B 10, 2789 (1992); http://dx.doi.org/10.1116/1.586003 (5 pages)

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With Multiconcens (multiple concentric shots), a novel exposure method is presented, which is especially tailored for variable‐shape electron‐beam lithography of submicron contact‐hole layers, exposed into single‐layer positive resist. The goal is to provide a critical dimension‐accurate, technological processable resist mask with minimum effort in order to generate functioning contact and via holes. Typical experiments demonstrate, after comparison with results from conventional uncorrected single‐shot exposure, the advantage of the method, which guarantees better stability with respect to process fluctuations, for the desired resist profile. Together with a convenient data preparation, the Multiconcens exposure principle can correct topography influences occuring with planarization effects of single layer resist. The feasabilty of contact holes with dimensions required for submicron technologies using thick single‐layer resist is also shown.
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85.40.Hp Lithography, masks and pattern transfer

Electron beam lithography system with new correction techniques

Y. Takahashi, A. Yamada, Y. Oae, H. Yasuda, and K. Kawashima

J. Vac. Sci. Technol. B 10, 2794 (1992); http://dx.doi.org/10.1116/1.586004 (5 pages) | Cited 2 times

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In our electron exposure system, the focal length of the final projection lens is designed to be very short. To decrease aberrations due to beam deflections, which cannot be corrected by a dynamic focus coil or a stigmator, deflection coil parameters are determined by a simulation, which used the conditions: coma length=0, transverse chromatic aberration coefficient=0, and beam incidence is normal to the sample surface. Patterns of the size under 0.2 μm are well resolved inside the whole deflection field of 1.6×1.6 mm. Current density of the system is more than 40 A/cm2. Refocusing and refocus–flyback are necessary to utilize the high current density for spot size between 0.1 and 3.0 μm. Large spot defocusing is refocused by small refocus coils, and refocused beam position shifts are corrected by a refocus–flyback method. Beam‐settling retardation caused by an eddy current occurs after an electromagnetic jump. A differentiated electromagnetic signal is added to electrostatic deflectors to compensate for the transitional beam positions between the jump. The beam‐settling time is less than 100 μs for a 1 mm jump, about a tenth of that without the compensation.
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41.75.Fr Electron and positron beams
81.65.-b Surface treatments

Cell projection column for high speed electron‐beam lithography system

H. Itoh, H. Todokoro, Y. Sohda, Y. Nakayama, and N. Saitou

J. Vac. Sci. Technol. B 10, 2799 (1992); http://dx.doi.org/10.1116/1.586005 (5 pages) | Cited 2 times

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The cell projection column for the high throughput electron‐beam lithography system (HL‐800D) has been developed. This column forms a conventional variable shaped beam and five kinds of cell pattern beams with a maximum 5 μm dimension. A new in‐lens three stage deflection system consisting of a magnetic and two electrostatic deflectors provides low distortion and high speed 5 mm square deflection at 50 kV. Beam shaping optics have a two stage deflector for rectangular beam sizing and cell beam selection. The settling times coincide with three stage deflection system to prevent extra overhead time. The beam shaping system has an inspection function for the cell aperture by switching the crossover focusing. Complicated deflection calibration systems are necessary to correct precisely in advance to exposure. To reduce the correction time, a simplified method which separates time dependent terms from whole correction terms, has been developed. This method decreases the total correction time and procedures, because time dependent terms generally consist of first order terms such as gain and rotation. The correction time is typically reduced to less than 1/10, if the correction term is limited to the first order term. The measured data are statistically averaged and improve the accuracy of the beam correction. Other features of the cell projection column are as follows: (1) long life LaB6 emitter, (2) automatic cell mask handling system, and (3) dry evacuation system. These items provide easy handling and high reliability of the electron beam column.
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85.40.Hp Lithography, masks and pattern transfer

Low‐voltage electron‐optical system for the high‐speed inspection of integrated circuits

W. D. Meisburger, A. D. Brodie, and A. A. Desai

J. Vac. Sci. Technol. B 10, 2804 (1992); http://dx.doi.org/10.1116/1.586006 (5 pages) | Cited 4 times

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Low‐voltage scanning electron microscopes enjoy many advantages over light microscopes for both dimensional measurements and the analysis of small features. Their combination of high‐resolution and large depth‐of‐focus has made them a standard instrument in the semiconductor industry. However, until now, they have been many orders of magnitude too slow to be used for automated wafer inspection. In this article, the authors will determine the optical requirements of high‐speed inspection at low voltage and show how this leads to a novel optical system design. This optical system shares similarities with a 20 keV column designed for an x‐ray mask inspection system [W. D. Meisburger, A. Desai, and A. D. Brodie, J. Vac. Sci. Technol. B 9, 3010 (1991)]. However, the objective lens and electron detection system are unique. The objective lens combines superimposed electric and magnetic fields to decelerate the primary beam from 20 keV to ∼800 eV, and to effectively collimate and reaccelerate the resulting secondary electrons. Auxiliary electrodes are used to control the electric field on the semiconductor’s surface. A Wien filter is used to separate the secondary electrons from the primary beam. A second Wien filter is used to cancel the transverse chromatic aberration of the first filter. This optical system is capable of producing current densities of 1000 A/cm2 at 800 eV into spots as small as 50 nm. Images are acquired at a rate of 100 million pixels/second. Both theoretical and experimental performance results for this system will be presented.
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85.40.-e Microelectronics: LSI, VLSI, ULSI; integrated circuit fabrication technology
07.78.+s Electron, positron, and ion microscopes; electron diffractometers
41.75.Fr Electron and positron beams
41.85.-p Beam optics

Coulomb interactions in a shaped ion beam pattern generator

L. J. Vijgen and P. Kruit

J. Vac. Sci. Technol. B 10, 2809 (1992); http://dx.doi.org/10.1116/1.586007 (5 pages) | Cited 2 times

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The statistical Coulomb interactions between the particles of a focused ion beam can severely reduce the quality of a system. The interactions in the source region of a liquid metal ion source have been studied extensively and lead to the well‐known virtual source diameter of 50 nm and energy width of 5 eV in a Ga source. In this report, the interactions are described in the rest of the column of the Delft ion beam pattern generator, a system using a shaped beam with Köhler illumination. The simulations have been done with the Interac and Montec programs developed by Jansen [G. H. Jansen, Coulomb Interactions in Particle Beams (Academic, San Diego, 1990), Suppl. 22; G. H. Jansen, Montec, and Interac Programs, information obtainable from, Particle Optics Foundation, Lorentzweg 1, 2628 CJ Delft, The Netherlands]. The results show that the Coulomb interactions are a limiting factor for the beam quality, not only in the source region but also in the rest of the column. In particular, long segments with small opening angles cause deterioration of the beam. In these segments, the beam can even tend to thermodynamic relaxation. For the case of a square shape with size 100 nm and edge sharpness 25 nm, for which the normal probe current should be about 1 nA, interactions cause the edge sharpness to deteriorate by a factor of two at 100 pA while for more than 200 pA the square shape is not recognizable anymore.
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41.75.Cn Negative-ion beams
41.85.Ew Particle beam profile, beam intensity

Aberration properties of focused ion‐beam induced by space charge effect

S. Hirohata, T. Kosugi, H. Sawaragi, R. Aihara, and K. Gamo

J. Vac. Sci. Technol. B 10, 2814 (1992); http://dx.doi.org/10.1116/1.586008 (5 pages) | Cited 4 times

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The ion‐beam broadening induced by the space charge effect (SCE) was investigated for conditions relevant to ion beam processes. A Monte Carlo calculation including the effect of lens aberration has been performed. This makes it possible to estimate the beam broadening induced by the SCE following lens aberration changes. Results show that the beam broadening induced by the SCE around the retarding region is less than 8% of the total probe diameter assuming 100 μA/sr of angular current density at the source, 10 eV of energy dispersion, 0.1–10 nA of the probe current, and 0.1–25 keV of landing energy. Results also show that the beam broadening induced by the SCE is more sensitive to angular current density at the source rather than total probe current. The minimum probe diameter at 1 nA of the probe current and 100 eV of landing energy is 0.12 μm at 400 μA/sr of angular current density at the source.
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41.85.Gy Chromatic and geometrical aberrations

Silicon stencil masks for lithography below 0.25 μm by ion‐projection exposure

P. E. Mauger, A. R. Shimkunas, J. C. Wolfe, S. Sen, H. Löschner, and G. Stengl

J. Vac. Sci. Technol. B 10, 2819 (1992); http://dx.doi.org/10.1116/1.586009 (5 pages) | Cited 4 times

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Large‐area silicon stencil masks for demagnifying ion‐projection lithography have been fabricated and characterized. The masks were made by patterning silicon membranes 120 mm in diameter and 2.5 μm in thickness. The membranes, prepared on 150 mm host wafers using a p/n‐junction electrochemical etch stop, were designed with low tensile stress (10 MPa) to obtain minimum pattern distortion. Mask blanks were made by field bonding the membrane‐containing host wafers to pyrex rings. The blanks were patterned by e‐beam lithography over a 60×60‐mm field in a conventional novolak resist. The resist patterns were transferred into the silicon membranes in a magnetically enhanced reactive ion etcher using molecular bromine. The intermediate pattern‐transfer layer was low‐stress chemical vapor deposition silicon dioxide. Mask openings as small as 0.5 μm were achieved. The sidewalls of the openings were smooth and had positive tapers no more than 3° from vertical. The linewidth uniformity across the mask was <±10%, and linewidth bias was small, nearly constant, and uniform across the mask. Mask pattern distortion measurements indicated a pattern‐placement deviation of less than 0.2 μm (3σ).  
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85.40.Hp Lithography, masks and pattern transfer

Ion projector wafer exposure results at 5× ion‐optical reduction obtained with nickel and silicon stencil masks

G. Stengl, G. Bösch, A. Chalupka, J. Fegerl, R. Fischer, G. Lammer, H. Löschner, L. Malek, R. Nowak, C. Traher, P. Wolf, P. Mauger, A. Shimkunas, S. Sen, and J. C. Wolfe

J. Vac. Sci. Technol. B 10, 2824 (1992); http://dx.doi.org/10.1116/1.586010 (5 pages) | Cited 5 times

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A detailed study of the resolution performance of an advanced research type ‘‘Alpha Ion Projector’’ with 5× ion‐optical reduction has been performed. One part of the study was done with a nickel open stencil test mask with an active field of 40 mm×40 mm with smallest line pattern openings of ≊0.7 μm width (2.0 μm periodicity). The other part was done with a silicon stencil test mask (120 mm diam, 2.5 μm thickness, 60 mm×60 mm design field) with smallest line patterns of ≊0.4 μm width (1.0 μm periodicity). The Alpha Ion Projector exposures were performed in positive (PMMA: OEBR‐1000) and negative (SNR‐M4, RAY‐PN) resist materials with subsequent wet chemical development. The 0.15‐μm resolution was obtained in the case of wafer exposures with the nickel stencil mask within the 8 mm×8 mm exposure field whereas in the case of wafer exposures with the silicon stencil mask sub‐0.1‐μm resolution could be achieved near the center of the exposure field at 5.2× ion‐optical reduction.
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85.40.Hp Lithography, masks and pattern transfer
41.85.Ar Particle beam extraction, beam injection

Stability and electronic adjustment of ion images projected at 10×reduction

W. H. Brünger, M. Torkler, and L. M. Buchmann

J. Vac. Sci. Technol. B 10, 2829 (1992); http://dx.doi.org/10.1116/1.585967 (5 pages) | Cited 2 times

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An ion projection system was tested to demonstrate the long‐term stability of lithographic properties. By exposing a resist to He+ ions, the pattern from an open stencil mask was transferred by a surface imaging process into the resist. Even after 12 min exposure the resolution capability still gave patterns of a minimum linewidth of 150 nm. Shifts of the pattern with high accuracy and reproducibility were performed by an octopole deflection unit. A projection mode, which consists of multiple exposures each with a different pattern displacement, was established by activating electric dipole fields. A deflection factor of 3.3 μm/V was obtained. Inducing a quadrupole field, changes in demagnification of opposite signs in x and for y directions (anamorphism) were generated which can be used to compensate for different types of distortion. A relative compression as well as expansion factor of 1.7×10−4 V−1 was determined. Simple two‐dimensional simulation of quadrupole induced pattern displacements were carried out and compared with experiments.
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85.40.Hp Lithography, masks and pattern transfer

Ultrahigh vacuum in situ fabrication of three‐dimensional semiconductor structures using a combination of particle beams

G. A. C. Jones, D. A. Ritchie, E. H. Linfield, J. H. Thompson, A. R. Hamilton, and K. Brown

J. Vac. Sci. Technol. B 10, 2834 (1992); http://dx.doi.org/10.1116/1.585968 (4 pages) | Cited 4 times

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Focused ion beams have been combined with molecular‐beam epitaxy (MBE) in two new in situ processes to produce semiconductor structures. First, a high‐energy focused Ga ion beam has been used, during MBE growth interruption, to produce high‐quality, vertically isolated ohmic contacts to a two‐dimensional electron gas grown in close proximity to an underlying n+ layer. Second, using a focused Sn ion source within the MBE growth chamber, high‐quality, electrically active, selected area, n‐doped GaAs structures have been grown. In this case, a very low incident energy ion beam (≤50 eV) was used in order to prevent ion damage occurring to the crystal. This was achieved using retarded field ion optics.
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81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
81.15.-z Methods of deposition of films and coatings; film growth and epitaxy

In situ distortion measurement of an ion projector with 5× ion‐optical reduction

G. Stengl, G. Bösch, A. Chalupka, J. Fegerl, R. Fischer, G. Lammer, H. Löschner, L. Malek, R. Nowak, C. Traher, P. Wolf, and H. Vonach

J. Vac. Sci. Technol. B 10, 2838 (1992); http://dx.doi.org/10.1116/1.585969 (4 pages) | Cited 5 times

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In situ distortion measurements of an ion projector with 5× ion‐optical reduction were performed. At optimum conditions the measured minimum distortion was less than 0.15 μm within an exposure field of 8 mm×8 mm. This result is in excellent agreement with fifth order ion‐optical calculations.  
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85.40.Hp Lithography, masks and pattern transfer
41.85.Ja Particle beam transport
41.85.Gy Chromatic and geometrical aberrations

Helium field ion source for application in a 100 keV focused ion beam system

Takahide Sakata, Kiyohito Kumagai, Motohiro Naitou, Iwao Watanabe, Yuu Ohhashi, Osamu Hosoda, Yasushi Kokubo, and Kazumitsu Tanaka

J. Vac. Sci. Technol. B 10, 2842 (1992); http://dx.doi.org/10.1116/1.585970 (4 pages) | Cited 2 times

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A He gas‐phase ion source having a three‐electrode acceleration lens that can change the acceleration energy and magnification independently was developed. This source allows application of acceleration voltages up to 100 kV and extraction voltages up to 30 kV. This source is a component of our final objective of development, a nanometer lithography system with a beam diameter of 10 nm and a beam energy of 100 keV. In the present experiment, by using this source, the characteristics of He ion current emitted from W (111) emitter cooled by liquid N2 or liquid He was obtained. Maximum angular intensities of 40 nA/sr and 2.2 μA/sr were obtained at emitter temperatures of ∼100 and 20 K, respectively. In addition, the increase of the gas‐phase ion current by emitter treatment (field‐emission treatment or field‐evaporation treatment) was ascertained.
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41.75.Ak Positive-ion beams

Oxidation of sub‐50 nm Si columns for light emission study

Harvey I. Liu, Nadim I. Maluf, R. F. W. Pease, David K. Biegelsen, Noble M. Johnson, and Fernando A. Ponce

J. Vac. Sci. Technol. B 10, 2846 (1992); http://dx.doi.org/10.1116/1.585971 (5 pages) | Cited 22 times

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Understanding the optical and electrical properties of Si nanostructures is essential for exploring the potential of using structural quantum confinement to induce light emission from crystalline Si. To this end, sub‐50 nm Si columns were fabricated with high resolution electron beam lithography and anisotropic reactive ion etching. The dimensions of the Si nanostructures were further reduced by thermal oxidation. A novel transmission electron microscopy technique was developed to monitor the oxidation progress without removing the oxide structural support. Images of sub‐5 nm crystalline Si cores were obtained. The oxidation rates of the Si nanostructures were characterized. Among the various interesting oxidation phenomena are the nonmonotonic oxidation rate with respect to the column size and an unexpectedly slow change of the outer diameters of the oxidized columns. Several likely mechanisms, including the stress retardation of oxidation for a small radius of curvature, the stress induced generation and diffusion of Si interstitials, the stress induced radial strain in the Si core, and SiO sublimation during oxidation, were proposed to explain the unusual oxidation phenomena. Although not thoroughly understood, a photoluminescence spectrum was also obtained for a sample with a large patterned area.
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78.55.Hx Other solid inorganic materials
81.65.-b Surface treatments
85.60.Jb Light-emitting devices

Evaluation of the etch depth dependence of three‐dimensional confinement in strain‐induced quantum well dot structures

I‐Hsing Tan, Ying‐Lan Chang, Song Shi, Richard Mirin, Evelyn Hu, John Bowers, and James Merz

J. Vac. Sci. Technol. B 10, 2851 (1992); http://dx.doi.org/10.1116/1.585972 (4 pages)

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Strain‐induced quantum well dots (SIQWDs) 120 nm in diameter have been fabricated by laser holography and wet etching. Lateral confinement was generated in the GaAs quantum well (QW) by etching a doubly exposed grating pattern into a strained layer of InGaAs which overlies the QW. Atomic force microscopy was used to examine the surface morphology of the SIQWDs. Photoluminescence spectra of quantum wells located at different distances below the InGaAs stressor probe the etch depth dependence of the strength of the strain modulation. The extent of the strain modulation in the vertical direction falls off within a distance comparable to the lateral dimension of the dot. A maximum redshift of 12 meV is observed for the uppermost QW located 22 nm away from the InGaAs stressor, implying carrier confinement in the SIQWD region. The dots were etched for varying amounts of time, changing the distance between the etched surface and the uppermost QW from 18 to 0 nm. Although the spatial distribution of strain modulation did not change significantly, the luminescence intensities from the uppermost QW decreased by about a factor of 50. This observation suggests that extrinsic causes, such as surface states formed on the etched surfaces are the major cause of diminished luminescence in these SIQWDs, rather than intrinsic causes such as slower electron–phonon interaction rate.  
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73.21.-b Electron states and collective excitations in multilayers, quantum wells, mesoscopic, and nanoscale systems
81.40.Tv Optical and dielectric properties related to treatment conditions

Etch‐rate characterization of irradiated SiO2 and its application in the fabrication of a T‐gate structure

A. C. F. Hoole and A. N. Broers

J. Vac. Sci. Technol. B 10, 2855 (1992); http://dx.doi.org/10.1116/1.585973 (5 pages) | Cited 3 times

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Experiments to determine the effect of the e‐beam irradiation dose on the etch rate enhancement of SiO2 in p etch have been performed. These experiments have been carried out across the dose range of 0–1.5×10−2 C/m and at various acceleration voltages in the 100–350 kV range. The results clearly show the existence of a saturation in the etch rate around a line dose of 3×10−3 C/m. The first direct observation of the resulting trench profiles in the SiO2 have been obtained. These clearly show the effect of the accelerating voltage on the minimum achievable linewidth. Preliminary results of the application of the SiO2 irradiation process to the fabrication of T‐gate type structures are also shown.  
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81.65.-b Surface treatments
85.40.Hp Lithography, masks and pattern transfer

Novel vertical silicon‐membrane structure and its application to Josephson devices

G. E. Rittenhouse, K. Early, B. S. Meyerson, Henry I. Smith, and J. M. Graybeal

J. Vac. Sci. Technol. B 10, 2860 (1992); http://dx.doi.org/10.1116/1.585974 (4 pages)

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The authors present novel techniques for fabricating vertical silicon membranes having thicknesses below 100 nm and, in some cases, ∼40 nm. The combination of extreme membrane facet smoothness, near perfect parallelism, compatibility with epitaxial doped layers, and ability to be fabricated in either single structures or in dense arrays present unusual properties for application. As one specific application of this structure, the authors have fabricated a hybrid superconductor/semiconductor short‐channel Josephson device. Since these vertical membrane structures are also compatible with high‐mobility Si/Ge channel layers, the authors are currently extending this work to study the ballistic transport of Cooper pairs through discrete energy eigenstates formed by the quantum confinement within the thin semiconductor membrane.
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85.25.Cp Josephson devices
81.20.-n Methods of materials synthesis and materials processing
81.65.-b Surface treatments

Selective order–disorder transition in GaInP/AlGaInP: A new approach for the definition of buried quantum wires

Y. Hämisch, R. Steffen, J. Oshinowo, A. Forchel, and P. Röntgen

J. Vac. Sci. Technol. B 10, 2864 (1992); http://dx.doi.org/10.1116/1.585975 (4 pages) | Cited 6 times

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Buried semiconductor wires have been fabricated using the order/disorder transition in GaInP/AlGaInP due to ion implantation and annealing. The transition has been investigated as a function of annealing temperature and implantation dose. In order to induce this transition locally, gold wires were defined as implantation masks by a lift‐off process. After low dose implantation and annealing a lateral potential well is formed, due to the band gap difference between the ordered and the disordered state. The photoluminescence even of the narrowest wire structures shows two sharp and well separated emission bands, due to the recombination in the masked wire areas and in the lateral barrier.
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73.21.-b Electron states and collective excitations in multilayers, quantum wells, mesoscopic, and nanoscale systems
81.40.Tv Optical and dielectric properties related to treatment conditions
78.66.Fd III-V semiconductors
78.66.Hf II-VI semiconductors
81.30.Hd Constant-composition solid-solid phase transformations: polymorphic, massive, and order-disorder

Nanostructure fabrication using lithium fluoride films as an electron beam resist

W. Langheinrich, B. Spangenberg, and H. Beneking

J. Vac. Sci. Technol. B 10, 2868 (1992); http://dx.doi.org/10.1116/1.585976 (5 pages) | Cited 6 times

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Homogeneous and quasiamorphous lithium fluoride based films have been deposited as a new ultrahigh resolution electron beam resist. The exposure characteristics of this self‐developing positive tone resist are discussed. Compared to other metal halide films, a high sensitivity is the most important advantage, while the resolution limit is also far below 10 nm. Concerning pattern transfer, the properties of this resist in various reactive ion etch processes and the capability for a lift‐off process were investigated.
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61.80.Fe Electron and positron radiation effects
85.40.Hp Lithography, masks and pattern transfer
81.65.-b Surface treatments

Nanometer metal–oxide semiconductor field effect transistor structures for studying electron transport

Gongjiu Jin, Y. S. Tang, S. Thoms, C. D. W. Wilkinson, and A. M. Gundlach

J. Vac. Sci. Technol. B 10, 2873 (1992); http://dx.doi.org/10.1116/1.585977 (4 pages)

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Nanostructures including quantum wires and rings based on polycrystalline silicon gate metal–oxide semiconductor field effect transistor system were fabricated for fundamental studies of electron transport. Gate configurations were defined by electron beam lithography and dry etching using whole 3 in. wafers. A good low‐field electron mobility (∼1.5 m2 V−1 s−1) in the inversion channel has been obtained at 4.2 K. Clear steplike quantized conductance has been observed at 4.2 K in the wires fabricated.
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85.30.Tv Field effect devices
85.40.Hp Lithography, masks and pattern transfer
72.20.Fr Low-field transport and mobility; piezoresistance

Electron‐beam lithography with the scanning tunneling microscope

Christie R. K. Marrian, Elizabeth A. Dobisz, and John A. Dagata

J. Vac. Sci. Technol. B 10, 2877 (1992); http://dx.doi.org/10.1116/1.585978 (5 pages) | Cited 17 times

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The scanning tunneling microscope (STM), operated in vacuum in the field emission mode, has been used in lithographic studies of the resist SAL‐601 from Shipley. Patterns have been written by raising the tip–sample voltage above −12 V while operating the STM in the constant current mode. Resist films, 50 nm thick, have been patterned and the pattern transferred into the GaAs substrate by reactive ion etching. The variation of feature size with applied dose and tip–sample bias voltage has been studied. Comparisons have been made to lithography with a 10 nm, 50 kV electron e‐beam in a JEOL JBX‐5DII in the same resist thickness films. In all cases the resist films were processed in the standard fashion before and after exposure. The STM can write smaller minimum features sizes and has a greater process latitude. Proximity effects are absent due to the reduced scattering range of the low energy primary electrons. However, the writing speed is slower, being limited by the response of the piezoelectric scanner. Advances have been made recently in the construction of fast STMs which scan at video rates making the STM comparable in speed to the JEOL for nanolithography. The development of ultralow voltage e‐beam lithography based on STM technology is discussed.
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85.40.Hp Lithography, masks and pattern transfer

Study of the lithographic process in deposited silicon dioxide

Xiaodan Pan, A. N. Broers, and C. Jeynes

J. Vac. Sci. Technol. B 10, 2882 (1992); http://dx.doi.org/10.1116/1.585979 (4 pages) | Cited 2 times

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The lithographic process induced by electron beam irradiation in SiO2 deposited by low‐temperature plasma‐enhanced chemical vapor deposition is studied. It is found that the as‐deposited SiO2 acts as a negative resist when the p‐etch system (15:10:300 HF:HNO3:H2O in volume unit) is used as a developer, but the process is not suitable for lithographic applications because of nonuniform linewidth and relatively poor resolution. Modification of the as‐deposited oxide by 50 keV oxygen ion implantation with a dose of 1×1016/cm2 did not improve the resolution much, but could offer slightly denser structures. However, the linewidth was still inhomogeneous. Annealing the as‐deposited SiO2∼600 °C turned the resist process positive, but again failed to improve the nonuniformity in linewidth and the resolution. A high‐resolution lithographic process was only achieved in the modified oxide films by oxygen ion implantation and subsequent annealing at ∼600 °C. Using this modified oxide as a positive electron beam resist, we have fabricated trenches with feature sizes as small as 10 nm and periods down to 15 nm which are comparable to those previously achieved in thermally grown SiO2.
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85.40.Hp Lithography, masks and pattern transfer
81.65.-b Surface treatments

Effects of a pseudomorphic InGaAs layer on focused ion‐beam modulation doped GaAs–AlGaAs quantum well structures

Y. J. Li, M. Hashemi, M. Wassermeier, U. K. Mishra, J. L. Merz, and P. M. Petroff

J. Vac. Sci. Technol. B 10, 2886 (1992); http://dx.doi.org/10.1116/1.585980 (4 pages)

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GaAs/AlGaAs double heterostructures have been implanted with a focused Si ion beam to directly form a two‐dimensional electron gas in the quantum well (QW). The effects of a strained pseudomorphic In0.3Ga0.7As layer 500 Å above the QW on the electron mobility were studied by magneto‐transport and Hall measurements. The electron mobility improves with the introduction of the strained In0.3Ga0.7As layer and this is tentatively attributed to the dechanneling and localization of the implanted Si ions above the GaAs QW.    
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73.20.Hb Impurity and defect levels; energy states of adsorbed species
73.40.Kp III-V semiconductor-to-semiconductor contacts, p-n junctions, and heterojunctions

Comparative mobility degradation in modulation‐doped GaAs devices after e‐beam and x‐ray irradiation

R. A. Ghanbari, M. Burkhardt, D. A. Antoniadis, Henry I. Smith, M. R. Melloch, K. W. Rhee, and M. C. Peckerar

J. Vac. Sci. Technol. B 10, 2890 (1992); http://dx.doi.org/10.1116/1.585981 (3 pages) | Cited 1 time

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We report on measured Hall mobility versus temperature for high‐quality modulation‐doped AlGaAs/GaAs samples after exposure by electrons and x rays at doses and energies typically used in lithography. We find that bare samples exposed by 50 keV electrons suffered significant mobility degradation over the temperature range of 4.2–300 K (as much as a factor of 30). X‐ray‐exposed samples did not show any mobility degradation. Two‐dimensional electron densities were not dramatically affected by either exposure technique, although e‐beam exposed samples did show a slight decrease in carrier density. Our results are consistent with previous reports of mobility degradation in some e‐beam evaporators.
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73.40.Kp III-V semiconductor-to-semiconductor contacts, p-n junctions, and heterojunctions
81.40.Rs Electrical and magnetic properties related to treatment conditions

Improvement of the quality of InGaAs/InP quantum wires due to epitaxial overgrowth

R. Bergmann, A. Menschig, G. Lehr, P. Kübler, J. Hommel, R. Rudeloff, B. Henle, F. Scholz, and H. Schweizer

J. Vac. Sci. Technol. B 10, 2893 (1992); http://dx.doi.org/10.1116/1.585982 (3 pages)

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Using high‐resolution electron beam lithography and a dry etching process, we fabricated InGaAs/InP quantum wires down to a geometrical wire width of 65 nm. In order to reduce surface recombination and surface depletion effects, the quantum wires were buried in an epitaxial layer of InP by low‐pressure metalorganic vapor phase epitaxy (LPMOVPE). By optical studies and magnetotransport measurements, an overall improvement of the wire properties due to the epitaxial overgrowth is demonstrated. The quantum efficiency determined from luminescence experiments increased by two orders of magnitude for 65 nm wide quantum wires. Magnetotransport measurements yield an improvement of transport properties in overgrown wires. This article presents a recently developed in situ etching and overgrowth process in the LPMOVPE reactor which reduces the surface effects.
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85.40.Hp Lithography, masks and pattern transfer

Investigation of high‐quantum efficiency InGaAs/InP and InGaAs/GaAs quantum dots

A. Schmidt, A. Forchel, J. Straka, I. Gyuro, P. Speier, and E. Zielinski

J. Vac. Sci. Technol. B 10, 2896 (1992); http://dx.doi.org/10.1116/1.585983 (4 pages) | Cited 2 times

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Using selective wet‐chemical etching of the top barrier material of a quantum well, we have fabricated effectively buried quantum dots in the material systems InGaAs/InP and InGaAs/GaAs. The patterning is carried out on InGaAs quantum well samples masked by a high‐resolution negative e‐beam resist which is used as etch mask. A lateral potential well is formed due to the change of the energy barrier between the original quantum well and the surface quantum well regions. The photoluminescence shows a high efficiency as well as a shift of the luminescence signal to higher energy as the structure size is decreased. For InGaAs/InP single quantum well samples the emission of the open surface quantum well is detected. The emission of the lateral barrier regions is blue‐shifted by about 24 meV compared to an unetched reference.
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73.21.-b Electron states and collective excitations in multilayers, quantum wells, mesoscopic, and nanoscale systems
78.66.Fd III-V semiconductors
78.66.Hf II-VI semiconductors
85.40.Hp Lithography, masks and pattern transfer

Fabrication of lateral superlattices using multilayer resist techniques

H. Chang, K. Nummila, R. Grundbacher, I. Adesida, J.‐P. Leburton, and K. Hess

J. Vac. Sci. Technol. B 10, 2900 (1992); http://dx.doi.org/10.1116/1.585984 (4 pages) | Cited 1 time

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A procedure utilizing multilayer resist systems has been developed for the fabrication of artificial lateral surface superlattices (LSSLs) and other structures involving multiple point contacts and split gates. Two electron beam exposures are performed with the first exposure properly adjusted to result in a development down to the surface of the bottom resist layer with suitable undercut profile in the top resist layers. Electron beam exposure of arbitrary geometries at high resolution is then performed on the bottom layer through the opening in the top layers. After metal lift‐off, all these geometries are connected together via an airbridge network. The fabrication of field‐effect devices with split gates and LSSL gates in GaAs/AlGaAs modulation‐doped heterolayers are demonstrated. These devices exhibit quantum conductance at 1.8 K.
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85.40.Hp Lithography, masks and pattern transfer
85.30.Tv Field effect devices
73.40.Kp III-V semiconductor-to-semiconductor contacts, p-n junctions, and heterojunctions

Fabrication and physics of lateral superlattices with 40 nm pitch on high‐mobility GaAs GaAlAs heterostructures

C. G. Smith, W. Chen, M. Pepper, H. Ahmed, D. Hasko, D. A. Ritchie, J. E. F. Frost, and G. A. C. Jones

J. Vac. Sci. Technol. B 10, 2904 (1992); http://dx.doi.org/10.1116/1.585985 (5 pages) | Cited 4 times

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We have shown that a lateral superlattice of dots of period 40 nm can be fabricated and have defined a 60 nm period hexagonal lateral surface superlattice of dots over a high‐mobility two‐dimensional electron gas. With a negative voltage on the gate a honeycomb potential is created around the dots. The pattern is produced with electron beam lithography by stitching together superlattice regions of area (0.5 μm).2 At gate voltages close to zero the Shubnikov–de Haas peaks are split into subbands with corresponding structure in the Hall voltage. Close to pinch‐off, periodic peaks in the conductance versus gate voltage are seen whenever one electron is removed from the 0.5 μm square region. The electrons are localized in this area by the error in the stitching of the fields. There is a sharp drop in conductance when the carrier concentration is such that there is one electron per unit cell, which may indicate the electrons are condensing in a lattice commensurate with the applied periodic potential.
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73.21.-b Electron states and collective excitations in multilayers, quantum wells, mesoscopic, and nanoscale systems
73.20.Fz Weak or Anderson localization
73.40.Kp III-V semiconductor-to-semiconductor contacts, p-n junctions, and heterojunctions

Large‐area, free‐standing gratings for atom interferometry produced using holographic lithography

J. M. Carter, D. B. Olster, M. L. Schattenburg, A. Yen, and Henry I. Smith

J. Vac. Sci. Technol. B 10, 2909 (1992); http://dx.doi.org/10.1116/1.585986 (3 pages) | Cited 5 times

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Interferometers based on matter waves promise orders‐of‐magnitude improvements in metrology over laser‐based systems by virtue of the fact that the de Broglie wavelengths of atoms are about 104 times shorter. To date, the required matched set of four aligned gratings for such atom interferometers has been made using electron beam lithography and, as a result, such gratings suffer from a lack of spatial‐phase coherence. We report on processes we have developed for fabricating free‐standing gratings over large areas using conventional holographic lithography and achromatic holographic lithography to achieve spatial periods of 200 and 100 nm, respectively (i.e., nominal linewidths of 100 and 50 nm, respectively).
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85.40.Hp Lithography, masks and pattern transfer
42.40.My Applications
42.79.Dj Gratings

Fabrication of compact 100 nm‐scale silicon metal–oxide–semiconductor field effect transistors

S. J. Wind, C. M. Reeves, J. J. Bucchignano, Y. T. Lii, T. H. Newman, D. P. Klaus, J. Keller, R. P. Volant, B. Tebin, and F. J. Hohn

J. Vac. Sci. Technol. B 10, 2912 (1992); http://dx.doi.org/10.1116/1.585987 (5 pages) | Cited 1 time

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The fabrication of exploratory silicon metal–oxide–semiconductor field effect transistors in which all device levels meet 100 nm groundrules is reported. The device design incorporates several novel features which allow for an ultracompact structure. These features include shallow trench isolation, over‐the‐gate contacts, fully overlapped source, drain and gate contacts and shallow source and drain extensions. This article offers a detailed description of the fabrication process, with an emphasis on high resolution, high accuracy electron beam nanolithography and new reactive ion etching processes. Complete process integration is described which culminates in the successful fabrication of functional compact devices.
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85.30.Tv Field effect devices
85.40.Hp Lithography, masks and pattern transfer

Design and characterization of compact 100 nm‐scale silicon metal–oxide–semiconductor field effect transistors

C. M. Reeves, S. J. Wind, F. J. Hohn, Y. T. Lii, J. J. Bucchignano, T. H. Newman, D. P. Klaus, R. P. Volant, J. Keller, and B. Tebin

J. Vac. Sci. Technol. B 10, 2917 (1992); http://dx.doi.org/10.1116/1.585988 (5 pages) | Cited 1 time

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Ultracompact n‐channel silicon metal–oxide–semiconductor field effect transistors (MOSFETs) have been fabricated using electron beam nanolithography for all critical levels leading to a first demonstration of silicon MOSFETs which meet 100 nm ground rules. The smallest devices fabricated have active areas which measure only 700 nm×150 nm and are enclosed by a narrow trench isolation scheme. Devices of this size and with physical gate lengths of 120 nm and widths of 150 nm display an extrinsic transconductance of 410 mS/mm at room temperature. This level of miniaturization and performance arises in part from direct application of conventional scaling principles and in part from implementation of a novel device configuration. This article discusses the design of these devices as well as details of their electrical characteristics.
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85.40.Hp Lithography, masks and pattern transfer
85.30.Tv Field effect devices

Gate technology for 89 GHz vertical doping engineered Si metal–oxide semiconductor field effect transistor

D. Y. Jeon, D. M. Tennant, Y. O. Kim, R. H. Yan, K. F. Lee, and K. Early

J. Vac. Sci. Technol. B 10, 2922 (1992); http://dx.doi.org/10.1116/1.586336 (5 pages) | Cited 2 times

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The gate definition performed on a vertical doping engineered metal–oxide semiconductor field effect transistor is described. The fabricated gates were as narrow as 0.15 μm. For writing narrow gates, e‐beam lithography and a chemically amplified negative resist SAL603 were used. The alignment between the gate level and underlying Nikon‐printed levels was made using 0.8 μm deep trenched marks. The gate patterning was done with reactive ion etching (RIE) in CHF3 gas to etch a nitride layer which serves as a gate etch mask and subsequently in a Cl2 gas used to etch the polysilicon gate. A sidewall spacer was formed with a two step etch using CF4 RIE and CHF3 RIE after deposition of a 2000 Å TEOS film. After metallization the n‐channel devices have measured excellent device characteristics.
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85.30.Tv Field effect devices
85.40.Hp Lithography, masks and pattern transfer

T‐gate, Γ‐gate, and air‐bridge fabrication for monolithic microwave integrated circuits by mixed ion‐beam, high‐voltage electron‐beam, and optical lithography

R. G. Woodham, J. R. A. Cleaver, H. Ahmed, and P. H. Ladbrooke

J. Vac. Sci. Technol. B 10, 2927 (1992); http://dx.doi.org/10.1116/1.586337 (5 pages)

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Mixed lithography combining a 140 keV Be++ focused ion beam and a 60 keV electron beam has been applied to fabricate T‐section and Γ‐section structures for gate electrodes in GaAs metal–semiconductor field effect transistors for monolithic microwave integrated circuits. The gates are formed by lift‐off metallization, following successive electron and ion beam exposures of a single resist layer and a single stage of development. Gates with lengths down to 170 nm have been fabricated. Gate resistance parameters given by reverse modeling with data from microwave measurements are consistent with direct measurements on test structures. Forward modeling shows the benefits of the Γ‐gate structure for well‐balanced device design. High‐voltage lithography has been applied also to a novel procedure for generating air‐bridges for monolithic microwave integrated circuits.
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85.40.Hp Lithography, masks and pattern transfer
85.30.Tv Field effect devices

Nanoscale metal–semiconductor–metal photodetectors with subpicosecond response time fabricated using electron beam lithography

M. Y. Liu, S. Y. Chou, T. Y. Hsiang, S. Alexandrou, and R. Sobolewski

J. Vac. Sci. Technol. B 10, 2932 (1992); http://dx.doi.org/10.1116/1.586338 (4 pages) | Cited 5 times

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Metal–semiconductor–metal photodetectors (MSM PDs) with finger spacing and width as small as 25 nm have been fabricated using high‐resolution electron beam lithography. Measurements using an electro‐optic sampling system show that the fastest detector has a full width at half‐maximum response time of 0.87 ps and a 3 dB bandwidth of 510 GHz. Monte Carlo simulation of detector response time is studied and compared with experimental data. Finally, scaling rules for high‐speed MSM PDs are proposed.
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85.60.Gz Photodetectors (including infrared and CCD detectors)
85.40.Hp Lithography, masks and pattern transfer
85.40.-e Microelectronics: LSI, VLSI, ULSI; integrated circuit fabrication technology

Submicron modulation‐doped field‐effect transistor/metal–semiconductor–metal‐based optoelectronic integrated circuit receiver fabricated by direct‐write electron‐beam lithography

A. Ketterson, M. Tong, J.‐W. Seo, K. Nummila, K. Y. Cheng, J. Morikuni, S. Kang, and I. Adesida

J. Vac. Sci. Technol. B 10, 2936 (1992); http://dx.doi.org/10.1116/1.585946 (5 pages) | Cited 3 times

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An all direct‐write electron‐beam fabrication process has been developed for the fabrication of monolithic optoelectronic integrated circuits (OEICs). Various electron‐beam resist technologies are investigated including image reversed AZ5214, PMMA/P[MMA−MAA] bilayer, and PMMA/P[MMA−MAA]/PMMA trilayer. A novel single‐step air‐bridge formation process utilizing selective development is described. These processes are demonstrated in the fabrication of a 0.85‐μm sensitive OEIC receiver comprised of a metal–semiconductor–metal (MSM) detector integrated with a submicron GaAs/InGaAs/AlGaAs pseudomorphic modulation‐doped field‐effect transistor based transimpedance amplifier. A 3‐dB transimpedance bandwidth of 5.6 GHz and a transimpedance bandwidth product of 4.8 THz Ω are measured for the amplifier. Discrete high‐resolution MSM photodetectors with finger/gap spacings ranging from 0.1 to 1.0 μm have been fabricated and characterized.  
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85.60.Gz Photodetectors (including infrared and CCD detectors)
85.40.Hp Lithography, masks and pattern transfer
85.30.Tv Field effect devices
42.82.Ds Interconnects, including holographic interconnects

Fabrication of lateral resonant tunneling devices

J. N. Randall, A. C. Seabaugh, and J. H. Luscombe

J. Vac. Sci. Technol. B 10, 2941 (1992); http://dx.doi.org/10.1116/1.585947 (4 pages) | Cited 3 times

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Lateral resonant tunneling transistors have been fabricated in the InAlAs/InGaAs material system lattice matched to InP. Lateral tunnel barriers are formed in the plane of a two‐dimensional electron gas confined at a modulation‐doped heterointerface by depletion regions induced by top‐contact metal gates. The device is structurally similar to a dual‐gate modulation‐doped field effect transistor with nanoscale gates. The metal gates are written by e‐beam lithography. Device results include multiple negative differential resistance peaks for temperatures as high as 20 K. Using the substrate as a backgate, multiple regions of negative transconductance are also observed.
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85.30.Tv Field effect devices
85.40.Hp Lithography, masks and pattern transfer

Direct‐current and radio‐frequency characterization of submicron striped‐channel field effect transistor structures using focused ion beam and electron‐beam lithography

M. M. Hashemi, Y. Li, K. Kiziloglu, M. Wassermeier, P. M. Petroff, and U. K. Mishra

J. Vac. Sci. Technol. B 10, 2945 (1992); http://dx.doi.org/10.1116/1.585948 (4 pages)

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Submicrometere‐gate GaAs metal–semiconductor field effect transistors (MESFETs) have been fabricated using focused ion beam (FIB) and electron‐beam lithography. The channels of these devices are composed of several high conductance implanted stripes of 1 μm width, connecting source to drain. These conductive stripes are formed by Si implantation using FIB and annealed for 30 s at 850 °C. The region between the conductive stripes are semi‐insulating GaAs having width of ‘‘S.’’ MESFETs with stripe width of 1 μm and stripe separation of 0.1, 1, and 2 μm were fabricated and characterized. The device with 0.1 μm separation represents the control sample with a uniformly doped channel due to overlap of conductive stripes upon the postimplant annealing. Devices with higher stripe separations showed higher effective transconductance (gm), lower output conductance (go), higher breakdown (Vbr), and higher current gain cut‐off frequency (fT). All transistor showed well behaved direct‐current output performance with excellent pinch‐off characteristics and low leakage currents as small as 50 μA for source‐drain voltage of 4 V and gate bias of −9 V without any soft breakdown. Transconductance of 200 mS/mm, gate‐drain breakdown voltage as high as 20 V, output conductance of 4 mS/mm, and fT of 9 GHz from a device with 0.35 μm gate length with stripe separation of 2 μm.
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85.40.Hp Lithography, masks and pattern transfer
85.30.Tv Field effect devices

Dry etching bilayer and trilevel resist systems for submicron gate length GaAs based high electron mobility transistors for power and digital applications

F. Ren, S. J. Pearton, D. M. Tennant, D. J. Resnick, C. R. Abernathy, R. F. Kopf, C. S. Wu, M. Hu, C. K. Pao, B. M. Paine, D. C. Wang, and C. P. Wen

J. Vac. Sci. Technol. B 10, 2949 (1992); http://dx.doi.org/10.1116/1.585949 (5 pages) | Cited 3 times

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Dry‐etching technologies for submicron gate recess and resist pattern transfer are demonstrated with bilayer and trilevel resist systems for power and digital applications, respectively. For power applications, damage‐free, dry‐etched 0.25 μm T‐shaped gate pseudomorphic InGaAs channel high electron mobility transistors (HEMTs) were fabricated. A Freon‐12 based discharge was used in either electron cyclotron resonance or reactive ion etching systems to perform the gate recess process. Etching selectivity of more than 200 was obtained between the GaAs cap layer and the underlying AlGaAs donor layer. Self‐bias voltages of −30 to −50 V were used in the etching process to minimize the damage. Pre‐ and postetch clean steps were utilized to achieve uniform etch and removal of any dry etch related residues. By using the dry etch for gate recess, very tight threshold voltage uniformity across a quarter of a three inch wafer of ±85 mV was obtained in comparison to ±500 mV with our conventional wet recess technology. The extrinsic transconductance was 437 mS/mm with output conductance of 10 mS/mm. With a trilevel resist system, AlGaAs/GaAs single and double heterostructure [high field effect transistors (HFETs) and single quantum wells (SQWs)] were also fabricated as well as pseudomorphic AlGaAs/InGaAs/GaAs [pseudomorphic HEMTs (PHEMTs)] heterojunction FETs to investigate the scaling of the direct‐current performance with gate length for high speed digital applications. Electron‐beam lithography was used to define the gate length from 1 to 0.1 μm. The PHEMT had a consistently higher voltage gain at all gate lengths, with a voltage gain of greater than 30 for a gate length of 0.1 μm.
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85.30.Tv Field effect devices
85.40.Hp Lithography, masks and pattern transfer
81.65.-b Surface treatments

Fabrication of n‐channel metal–oxide–semiconductor field‐effect transistors with 0.2 μm gate lengths in 500 Å thin film silicon on sapphire

P. R. de la Houssaye, B. W. Offord, J. P. Minter, G. P. Imthurn, and G. A. Garcia

J. Vac. Sci. Technol. B 10, 2954 (1992); http://dx.doi.org/10.1116/1.585950 (4 pages)

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n‐Channel metal–oxide–semiconductor field‐effect transistors with gate lengths ranging from 10–0.2 μm were fabricated for the first time on device quality 300–500 Å ultrathin silicon on sapphire (SOS) wafers using electron‐beam exposure for the gate level patterning step. Working devices were found over a large area on a group of six 4 in. wafers, including two wafers with approximately 1000 Å thick silicon films used for comparison, each with slightly different fabrication conditions. An arsenic implant was used to dope the source–drain regions of the devices. Threshold voltages were measured across each wafer for a variety of gate lengths, from which both an average value and spread was obtained. Both the average value and spread were seen to correlate with the silicon film thickness and thickness variations measured directly. Similar measurements were obtained for subthreshold slopes. Extrinsic transconductance was measured to be as high as 42 mS/mm for the smaller devices, heavily reduced due to source and contact resistance from the doped thin silicon (at about 250 Ω/square for the 500 Å films) leading up to the channel. Some of the special difficulties of electron‐beam patterning on thin‐film SOS are addressed.
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85.30.Tv Field effect devices
85.40.Hp Lithography, masks and pattern transfer

Optical and electron beam lithography for electroless copper multilevel metallization

Y. Shacham‐Diamand, M. Angyal, A. Dedhia, and Q. Nasir

J. Vac. Sci. Technol. B 10, 2958 (1992); http://dx.doi.org/10.1116/1.585951 (4 pages)

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Copper fine lines made by electroless deposition are investigated for multilevel metallization in ultra‐large‐scale integration technology. The results are presented using positive patterning, i.e., depositing copper on patterned areas by electroless deposition. Two techniques have been developed: (a) a nonplanar technique that produces 100 nm wide copper lines standing over an interlevel dielectric (ILD); and (b) a fully planar method that produces 0.5 μm copper lines buried in an ILD. Both electron beam and optical lithography processes were developed and are described for the nonplanar process. First, a single layer exposure by e‐beam is described and second, a portable conformal mask (PCM) process with double exposure, the first by i‐line stepper and the second by deep ultraviolet flood exposure. For the fully planar process, the PCM process was modified to produce a capped PCM process. By using two resists of different etch selectivity, an overhang structure was produced which prevented the base metal from being deposited on the sidewalls of the oxide trench. A trilayer resist structure and a single layer structure with isotropic overetch were also developed. Scanning electron microscope pictures of submicron lines are presented followed by a discussion of the problems and highlights of the individual processes.
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85.40.Hp Lithography, masks and pattern transfer
81.05.Bx Metals, semimetals, and alloys
61.80.Ba Ultraviolet, visible, and infrared radiation effects (including laser radiation)

Engineering sub‐50 nm quantum effect devices and single‐electron transistors using electron‐beam lithography

Yun Wang and Stephen Y. Chou

J. Vac. Sci. Technol. B 10, 2962 (1992); http://dx.doi.org/10.1116/1.585952 (4 pages) | Cited 5 times

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Fabrication and characteristics of various nanoscale quantum and single‐electron devices are described. Using high‐resolution electron beam lithography and double layer PMMA resist, we have successfully fabricated a 20 nm split‐gate device, a novel 50 nm single barrier single‐electron transistor, and a 75 nm triple barrier tunneling device. Effects of beam dose and the number of writing passes on the actual lithography pattern were investigated for various device gate geometries. Pronounced quantum and single‐electron effects have been observed in these devices.
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85.40.Hp Lithography, masks and pattern transfer
85.30.Tv Field effect devices

Conductance quantization in a GaAs electron waveguide device fabricated by x‐ray lithography

W. Chu, C. C. Eugster, A. Moel, E. E. Moon, J. A. del Alamo, Henry I. Smith, M. L. Schattenburg, K. W. Rhee, M. C. Peckerar, and M. R. Melloch

J. Vac. Sci. Technol. B 10, 2966 (1992); http://dx.doi.org/10.1116/1.585953 (4 pages)

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We report on the fabrication of AlGaAs/GaAs split‐gate electron waveguide devices of lengths between 0.1 and 2 μm using x‐ray lithography, and the measurements of these devices at liquid‐helium temperatures and up to 15 K. An x‐ray mask (parent mask) was fabricated using e‐beam lithography and replicated using proximity x‐ray lithography (λ=1.32 nm) to generate a replica (daughter) mask. The daughter mask was then aligned to patterns on a high‐mobility AlGaAs/GaAs sample and x ray exposed using a conformable mask fixture. The conductance of the electron waveguides was measured as a function of the split‐gate bias. Sharp 2e2/h conductance steps were observed in devices up to 0.75 μm long at T=2 K. The features in the conductance remain visible up to 15 K.
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85.40.Hp Lithography, masks and pattern transfer
85.40.-e Microelectronics: LSI, VLSI, ULSI; integrated circuit fabrication technology
73.40.Kp III-V semiconductor-to-semiconductor contacts, p-n junctions, and heterojunctions

Fabrication of nonconventional distributed feedback lasers with variable grating periods and phase shifts by electron beam lithography

C. Kaden, U. Griesinger, H. Schweizer, M. H. Pilkuhn, and N. Stath

J. Vac. Sci. Technol. B 10, 2970 (1992); http://dx.doi.org/10.1116/1.585954 (4 pages) | Cited 7 times

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Distributed feedback (DFB) lasers for a wide range in emission frequency have been fabricated in the AlGaAs system. Gratings with periods around 110 nm have been defined by electron beam lithography and dry etching. Two approaches are discussed to reach extremely fine tuning of the emission frequency, which becomes more and more essential the higher the band gap of the material and with that, the emission frequency of the laser. To reach single mode emission, phase shifts in the grating structure have been realized. A flat photon density distribution to reduce spatial hole burning could be achieved by distributing the π/2 phase shift by using four λ/16 phase shifts. In addition, resonators have been fabricated where the phase shift is spread over a wide region in the center of the resonator which corresponds to the introduction of a phase arranging zone with a slightly larger effective grating constant. The laser structures have been tested by optical pumping. DFB emission could be observed over a wide range in frequency at room temperature. The resonators with the distributed phase shifts show stable single mode operation.
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42.55.Px Semiconductor lasers; laser diodes
42.60.Fc Modulation, tuning, and mode locking

Curved grating fabrication techniques for surface‐emitting distributed feedback lasers

Oliver King, Turan Erdogan, Gary W. Wicks, Dennis G. Hall, Erik H. Anderson, Dennis Costello, and Michael J. Rooks

J. Vac. Sci. Technol. B 10, 2974 (1992); http://dx.doi.org/10.1116/1.585955 (5 pages) | Cited 5 times

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We report on techniques for the fabrication of curved waveguide diffraction gratings for use in novel semiconductor laser structures. In particular, we consider the development of concentric‐circle gratings to be employed in circularly symmetric, surface‐emitting semiconductor lasers. The gratings are defined using electron‐beam lithography and subsequently etched into the semiconductor surface by chemically assisted ion‐beam etching. Issues to be addressed include grating design requirements, pattern representation, and scan method. We provide examples of how these techniques can be implemented and their impact on the resulting laser performance.
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42.55.Px Semiconductor lasers; laser diodes
42.82.Cr Fabrication techniques; lithography, pattern transfer
42.82.Et Waveguides, couplers, and arrays

Fabrication of nonlinearly shaped optical waveguide tapers on InP with precise design‐parameter control

H. J. Brückner, H.‐J. Olzhausen, and R. Zengerle

J. Vac. Sci. Technol. B 10, 2979 (1992); http://dx.doi.org/10.1116/1.585956 (5 pages) | Cited 3 times

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An entirely integrated reliable and low‐loss interconnection between an InP‐based optoelectronic circuit and a single‐mode optical fiber is presented. This spot transforming device is characterized by a two‐layer buried waveguide with laterally tapered geometry. Investigations of the characteristics of the negative tone electron beam resist AZ PN 114 show that it is possible to transfer almost any arbitrary shape of an optical waveguide with a width between 80 and 1200 nm to a directly written mask for dry etching without proximity correction or sophisticated writing strategy. The geometries can be maintained to within 20 nm with respect to the structure design. During subsequent reactive ion etching steps for the InGaAsP‐waveguide layers, a very precise etch depth control by a process ellipsometer is possible in the range of 5 nm or less. Optical measurements confirm the spot‐size transformation characteristics of our taper device.
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42.82.Ds Interconnects, including holographic interconnects
42.82.Cr Fabrication techniques; lithography, pattern transfer

Fabrication of encapsulated silicon‐vacuum field‐emission transistors and diodes

C. T. Sune, G. W. Jones, and D. Vellenga

J. Vac. Sci. Technol. B 10, 2984 (1992); http://dx.doi.org/10.1116/1.585957 (5 pages) | Cited 1 time

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We have succeeded in developing encapsulated silicon‐vacuum field‐emission transistors by using integrated circuit technology. This success will accelerate the development of integrated circuit of silicon‐vacuum field‐emission devices. Preliminary electrical characteristics of these encapsulated silicon‐vacuum field‐emission transistors show very similar characteristics to the gated field‐emitter diode. However, the turn‐on voltage and the transconductance are lower compared to the open gated field emitters.  
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85.30.Tv Field effect devices
85.40.Hp Lithography, masks and pattern transfer

Photolithography at 193 nm

M. Rothschild, R. B. Goodman, M. A. Hartney, M. W. Horn, R. R. Kunz, J. H. C. Sedlacek, and D. C. Shaver

J. Vac. Sci. Technol. B 10, 2989 (1992); http://dx.doi.org/10.1116/1.585958 (8 pages) | Cited 1 time

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Photolithography at 193 nm is a natural continuation of the progression from 436 to 365 to 248 nm in lithography, dictated by the requirement for continually higher resolution. It is anticipated that 193‐nm lithography will enable 0.25‐μm patterning in volume production with conventional masks, and 0.18‐μm resolution with phase‐shifting masks. The main issues related to lithography at this new wavelength are being addressed. It has been shown that highly transparent optical materials are available at 193 nm. Also, they are damaged by the laser radiation at a slow enough rate that high‐quality projection optics are expected to perform within specifications for ten years of full‐time operation. Consequently, a 193‐nm step‐and‐scan system is being constructed, and it has been designed to attain 0.25‐μm resolution over a 22 by 35 mm field. A range of 193‐nm photoresist schemes has been demonstrated. They include semitransparent single‐layer resists, positive‐tone surface imaging (silylation), and negative‐tone bilayers using ultrathin silicon‐based polymers. In most instances we have demonstrated sub‐0.25‐μm resolution, high photosensitivity, good exposure–defocus latitude, and very low levels of etch residue. In sum, the first successful steps towards a fully engineered 193‐nm photolithography have been taken, and no major obstacles are anticipated.
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85.40.Hp Lithography, masks and pattern transfer

Lithographic tolerances based on vector diffraction theory

D. G. Flagello and A. E. Rosenbluth

J. Vac. Sci. Technol. B 10, 2997 (1992); http://dx.doi.org/10.1116/1.585959 (7 pages) | Cited 7 times

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The classic rules for scaling lithographic resolution derive from scalar models of image formation in air, and must be reexamined as numerical apertures (NAs) increase beyond 0.5. This article describes a vector image code (VIC) based on plane wave decomposition of the radiation that propagates from the exit pupil, and a modified thin film treatment of propagation into the photoresist. Tolerances on resolution, depth‐of‐focus (DOF), and source polarization can be derived from VIC simulations. The strongest vector diffraction effects arise from polarization in the illumination, producing nonscalar effects in exposure‐to‐clear curves (‘‘swing curves’’), as well as orientation‐dependent asymmetries in printed patterns. Modeling shows that the small asymmetries previously reported [D. Flagello, A. E. Rosenbluth, C. Progler, and J. Armitage, Microcircuit Engineering 1991 (Elsevier, New York, 1991)] at 0.55 NA increase rapidly for NAs beyond 0.7. Resolution increases more slowly than NA−1 at high NA, even with unpolarized illumination and perfect focus control. The contrast loss can largely be ascribed to the in‐plane or parallel component of the E field within any image slice; the out‐of‐plane or perpendicular component actually shows a slight contrast increase. Snell’s law reduces the angular range of E orientations in the resist, so the contrast loss in resist is much less than in air. At high NA, the aerial image loses its relevance as a predictor of lithographic performance. Snell’s law also implies spherical aberration in the refracted field, reducing DOF in thick resist layers. Further, focal tolerances calculated with the traditional ±λ/2 NA2 criterion are shown to be optimistic, since this criterion is derived from the paraxial form for defocus.
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85.40.Bh Computer-aided design of microcircuits; layout and modeling

Optimization of partially coherent optical system for optical lithography

Soichi Inoue, Tadahito Fujisawa, Shuichi Tamaushi, Yoji Ogawa, and Makoto Nakase

J. Vac. Sci. Technol. B 10, 3004 (1992); http://dx.doi.org/10.1116/1.585960 (4 pages) | Cited 3 times

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A new approach, based on the optimization algorithm of ‘‘simulated annealing,’’ is applied to maximize depth of focus for a partially coherent optical system. Optimization is carried out with practical constraints for optical lithography. A phase contrast lithography, consisting of an annular effective source and an annular phase filter on the pupil, is proposed as a definite result of the optimization procedure.
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85.40.Bh Computer-aided design of microcircuits; layout and modeling

Contrast transfer function measurements of deep ultraviolet steppers

Andreas Grassmann and Holger Moritz

J. Vac. Sci. Technol. B 10, 3008 (1992); http://dx.doi.org/10.1116/1.585961 (4 pages) | Cited 6 times

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The aerial image contrast is a key parameter for the evaluation of the performance of optical projection systems. State‐of‐the‐art deep ultraviolet steppers and some i‐line steppers were investigated for comparison by measuring the contrast transfer function, i.e., contrast versus linewidth. Examples are shown how specific weaknesses of an imaging system like astigmatism and sensitivity from internal reflections can be quantified with this technique. For comparison the contrast transfer functions were also calculated, assuming ideal, purely diffraction limited image transfer of the optics, and with the numerical aperture and partial coherence as parameters. Interestingly none of the steppers meet the imaging performance which can be expected from theory.
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85.40.Hp Lithography, masks and pattern transfer

Thin film interference effects in phase shifting masks causing phase and transmittance errors

Kurt Ronse, R. Jonckheere, Ki‐Ho Baik, R. Pforr, and L. Van den hove

J. Vac. Sci. Technol. B 10, 3012 (1992); http://dx.doi.org/10.1116/1.585962 (7 pages)

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Phase shifting masks have proven their potential to enhance resolution and depth‐of‐focus in optical lithography. Nevertheless, many questions still have to be solved, before the phase shifting concept can be introduced in production lines. Controllable mask fabrication is a major concern. This article addresses the influence of physical material properties and process steps in the attempt to fabricate phase shifting masks with acceptable phase shift and transmittance. Spectrophotometer measurements and computer simulations showed the need of matched refractive indices for all transparent materials in the reticle. Second, the sensitivity of the lithographic performance to these shifter deviations was investigated by aerial image simulations. These predicted a high sensitivity to phase errors, especially for negative resists. Using a negative tone top surface imaging resist process and a positive tone wet developed resist, experiments confirmed these predictions. Special attention was paid in finding an accurate and efficient method to measure the transmittance and phase shift deviations of a reticle experimentally.
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85.40.Hp Lithography, masks and pattern transfer

Simulation of projection optic lithography images with finite impulse response filters

L. K. White and J. R. Matey

J. Vac. Sci. Technol. B 10, 3019 (1992); http://dx.doi.org/10.1116/1.585963 (4 pages)

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Finite impulse response (FIR) filters are used to simulate projection optic lithography images. For large arbitrary arrays of imaging data, the FIR filter simulation approach has advantages that lead to dramatic improvements in computation times. The transmission cross‐coefficient (TCC) transfer function is more easily computed, the forward and reverse complex Fourier transforms need not be computed, and, foremost, the application of the TCC can be greatly simplified. Comparisons between FIR and Fourier transform simulation methods for one‐dimensional objects in many cases show excellent agreement to within 1% of the total illumination intensity. The computation of projection optic images for 1000×1000 pixel arrays objects in real time (≤30 ms) appears possible using massively parallel, single‐instruction multiple data computers. This capability provides a powerful design, layout, and design rule checking tool for phase‐shift masks.
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61.80.Ba Ultraviolet, visible, and infrared radiation effects (including laser radiation)
81.65.-b Surface treatments
85.40.Hp Lithography, masks and pattern transfer

High performance optical lithography using a separated light source

Satoru Asai, Isamu Hanyu, and Kohki Hikosaka

J. Vac. Sci. Technol. B 10, 3023 (1992); http://dx.doi.org/10.1116/1.585964 (4 pages) | Cited 2 times

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In projection lithography systems with fly’s‐eye elements, a virtual source is created as an array of approximately mutually incoherent point sources. This article describes light amplitude and phase simulations for an image of a mask illuminated by a point source. This article discusses the dependence on the point‐source location for a plane perpendicular to the optical axis. An image projected by a separated light source, rather than a ring‐shaped light source, improves due to interference effects between multiple apertures is shown. Resolution of 0.25 μm equal lines and spaces was improved experimentally at a wavelength of 365 nm and a numerical aperture of 0.54. Also, how an isolated pattern image can be improved theoretically using an optimally separated light source is shown.
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42.72.Bj Visible and ultraviolet sources
61.80.Ba Ultraviolet, visible, and infrared radiation effects (including laser radiation)

Investigation of single sideband optical lithography using oblique incidence illumination

Emi Tamechika, Seitaro Matsuo, Kazuhiko Komatsu, Yoshinobu Takeuchi, Yoshiaki Mimura, and Katsuhiro Harada

J. Vac. Sci. Technol. B 10, 3027 (1992); http://dx.doi.org/10.1116/1.585965 (5 pages)

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We propose a new method for enhancing the image contrast in oblique illumination lithography. In this article, we analyze the modulation transfer function to clarify the cause of poor contrast in oblique illumination systems. A unique optimization procedure is also proposed. It is carried out for the oblique illumination systems, including single sideband optical lithography. It is found that the contrast enhancing method and optimization can improve the resolution for annular source and four‐point‐type sources. These improvements open up the possibility of 0.25‐μm resolution with i‐line lithography.
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85.40.Hp Lithography, masks and pattern transfer

1/8 μm optical lithography

G. Owen, R. F. W. Pease, D. A. Markle, A. Grenville, R. L. Hsieh, R. von Bünau, and N. I. Maluf

J. Vac. Sci. Technol. B 10, 3032 (1992); http://dx.doi.org/10.1116/1.585966 (5 pages) | Cited 6 times

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The critical bottleneck to extending optical lithography down to the 1/8 μm level is the performance of the projection optics. The Markle–Dyson configuration is virtually free of all geometric and chromatic aberrations. A prototype system has been constructed and characterized. The system uses 248 nm light from a mercury arc lamp at a numerical aperture of 0.7. 0.25 μm resolution has been demonstrated with non phase shifting masks: using phase shifting Levenson‐type masks, a grating consisting of 0.125 μm lines and spaces has been printed. Two possible extensions of the existing design are proposed which would allow general 1/8 μm geometries to be patterned. The first is a 0.7 numerical aperture (NA) system working at a wavelength of 157 nm, and the second is a 1.05 NA immersion system working at 193 nm. At these high NAs the depth‐of‐focus (DOF) of the image becomes very small if a clear aperture is used. However, if the aperture is apodized, the DOF can be increased considerably, and a procedure for optimizing apodization functions has been devised. This makes it possible to consider high NA optical techniques as candidates worthy of further investigation for 1/8 μm lithography.
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85.40.Hp Lithography, masks and pattern transfer

Extending scalar aerial image calculations to higher numerical apertures

Daniel C. Cole, Eytan Barouch, Uwe Hollerbach, and Steven A. Orszag

J. Vac. Sci. Technol. B 10, 3037 (1992); http://dx.doi.org/10.1116/1.585925 (5 pages) | Cited 4 times

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The usual formula for the scalar aerial image of an isolated object due to a projection lens system has been generalized beyond the paraxial approximation in an attempt to extend scalar diffraction theory to include numerical aperture (NA) values up to about 0.6. Beyond this regime, or certainly beyond NA=0.7, polarization effects need to be included, thereby demanding a full vector treatment and invalidating the present scalar formulation. A key point to the present scalar result without the paraxial approximation is the predicted functional dependence of the aerial image on magnification as NA increases. A second key point is that the usual scaling of λ/NA for the object dimensions and λ/NA2 for defocus become invalid for high NA systems. Numerical results of illustrative test cases are shown.
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42.15.-i Geometrical optics
42.30.Va Image forming and processing
42.30.Wb Image reconstruction; tomography

All‐reflective phase‐shifting masks for Markle–Dyson optics

Robert L. Hsieh, Andrew Grenville, Geraint Owen, and R. Fabian Pease

J. Vac. Sci. Technol. B 10, 3042 (1992); http://dx.doi.org/10.1116/1.585926 (5 pages) | Cited 1 time

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Previous work using a Markle–Dyson projection system, operating at 248 nm wavelength, demonstrated 0.19 μm resolution with nonphase‐shifting masks. The use of Levenson‐type phase‐shifting masks should in principle, allow sub‐0.1 μm feature resolution using a k1 of 0.25. To investigate this possibility, a novel reflective phase mask was fabricated and used on the Markle–Dyson system to projection print 0.125 μm lines and spaces in photoresist. An analytical study has been carried out to determine the tolerance of alternating‐phase masks to errors in linewidth and phase.
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85.40.Hp Lithography, masks and pattern transfer

Depth of focus enhancement in optical lithography

R. von Bünau, G. Owen, and R. F. W. Pease

J. Vac. Sci. Technol. B 10, 3047 (1992); http://dx.doi.org/10.1116/1.585927 (8 pages) | Cited 6 times

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Apodization, or pupil plane filtering, can be used to enhance the depth of focus of lithographic projection systems. However, this improvement comes at the expense of decreasing radial concentration of energy in the point spread function. To examine this tradeoff quantitatively, we first define the average encircled energy as a criterion of the energy concentration over a nonzero axial distance. We then derive and numerically solve an integral equation for the apodization function that maximizes the average encircled energy. Finally, we use the eigenfunctions of this equation to construct pupil functions producing an on‐axis intensity profile that is approximately constant over a nonzero axial distance, while maintaining a large value of the average encircled energy within that distance.  
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42.82.Cr Fabrication techniques; lithography, pattern transfer

Exposure characteristics of alternate aperture phase‐shifting masks fabricated using a subtractive process

R. L. Kostelak, C. Pierrat, J. G. Garofalo, and S. Vaidya

J. Vac. Sci. Technol. B 10, 3055 (1992); http://dx.doi.org/10.1116/1.585928 (7 pages) | Cited 8 times

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Exposure characteristics of an alternate aperture phase‐shifting mask fabricated using a subtractive process will be discussed. The subtractive process, where the phase‐shifted regions are etched into a layer below the chromium, is attractive because it allows for the use of conventional chromium‐on‐quartz blanks, as well as providing more processing flexibility. However, recent results using a subtractive fabrication process have determined that a linewidth variation of ∼0.05 μm exists between features imaged with etched and nonetched regions of the alternate aperture pattern. This article examines some of the potential causes for this linewidth variation, including mask linewidth control, surface roughness, contamination during phase‐shift forming etch step, and sidewall profile and position. Results indicate that the sidewall profile and position are critical parameters in defining the wafer feature size. The impact of phase is also investigated. The wafer feature size depends on the depth of the quartz etch and accurate endpointing of the phase‐shift depth is essential for maintaining critical dimension uniformity across all features imaged with a phase‐shifting mask.
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85.40.Hp Lithography, masks and pattern transfer

Proximity effect reduction in x‐ray mask making using thin silicon dioxide layers

Kee W. Rhee, David I Ma, Martin C. Peckerar, R. A. Ghanbari, and Henry I. Smith

J. Vac. Sci. Technol. B 10, 3062 (1992); http://dx.doi.org/10.1116/1.585929 (5 pages) | Cited 2 times

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A novel method is reported for reducing the proximity effect in high‐resolution electron beam patterning of high atomic number materials such as tungsten. The method involves interposing a thin (50–400 nm) layer of SiO2 between the resist and the underlying high‐Z substrate. Examples are shown in which gratings of 0.2 μm lines with a 0.5 μm period were written without proximity effect compensation. Optimal intermediate layer thickness for the best resolution of the gratings is determined to be 200 nm. A Monte Carlo model of electron scattering including inelastic processes has been implemented to interpret our experimental results. The model presented shows that having the low atomic number SiO2 layer between the resist and the tungsten prevents the fast secondary electrons being generated at the surface of the tungsten from propagating back into the resist, suggesting a mechanism for proximity effect reduction. The results presented here have important practical applications for x‐ray mask making.
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85.40.Hp Lithography, masks and pattern transfer

Thin silicon nitride films for reduction of linewidth and proximity effects in e‐beam lithography

E. A. Dobisz, C. R. K. Marrian, L. M. Shirey, and M. Ancona

J. Vac. Sci. Technol. B 10, 3067 (1992); http://dx.doi.org/10.1116/1.585930 (5 pages) | Cited 8 times

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A thin silicon nitride layer (50–300 nm), deposited on a semiconductor substrate, prior to resist deposition, greatly enhances the resist resolution during electron beam lithography. The resolution enhancement was manifested by smaller feature sizes, for a given dose and full resolution of individual array elements at higher doses than on a bare semiconductor substrate. The effect has been observed in 50–100 nm of both SAL‐601 and PMMA spun onto silicon nitride coated Si and GaAs substrates. The samples were patterned with a 50 keV, 15 nm diam probe generated by a JEOL JBX‐5DII system. Improved resolution was found on two types of silicon nitride film grown by chemical vapor deposition: one deposited at 800 °C on Si and the other deposited at 200 °C on GaAs. Linewidth reductions in SAL‐601 of 40% at low doses and an order of magnitude at high doses were observed on silicon nitride coatings of 50–300 nm thickness. In PMMA, the resolution enhancement was less than in SAL‐601, with only a 15% linewidth reduction observed at high doses (≥10 nC/cm). A reduction in proximity effects due to the presence of the nitride layer, is apparent in SAL‐601, for array periods of 1 μm and less. Analysis of the results, combined with Monte Carlo simulations and electron microscopy suggests that fast secondary electrons, generated by the substrate are prevented by the silicon nitride layer from exposing the resist.
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85.40.Hp Lithography, masks and pattern transfer

Fast proximity effect correction method using a pattern area density map

Fumio Murai, Haruo Yoda, Shinji Okazaki, Norio Saitou, and Yoshio Sakitani

J. Vac. Sci. Technol. B 10, 3072 (1992); http://dx.doi.org/10.1116/1.585931 (5 pages) | Cited 13 times

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This article proposes a new method for proximity effect correction that utilizes newly developed hardware. The correction algorithm modifies the exposure dose for each exposure point by referring to a pattern area density map. The only additional process in this method is virtual exposure to make the map. The virtual exposure is carried out once at the first use of the large‐scale integration circuit pattern and can be processed in only 30 s. The pattern area density map makes it possible to correct the proximity effect from the lower‐level patterns by the new map calculated from the two maps of lower level and exposing level. The usefulness of this method is verified by experiments using model patterns.
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85.40.Hp Lithography, masks and pattern transfer

Fast proximity effect correction: An extension of PYRAMID for circuit patterns of arbitrary size

Joseph C. Jacob, Soo‐Young Lee, Jo A. McMillan, and Noel C. MacDonald

J. Vac. Sci. Technol. B 10, 3077 (1992); http://dx.doi.org/10.1116/1.585932 (6 pages) | Cited 5 times

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Previously, we introduced PYRAMID, a hierarchical pattern shape modification scheme for proximity effect correction in electron‐beam lithography, which enabled rapid correction of circuit patterns with linewidths down to 0.1 μm. However, it was limited to relatively small circuit patterns only. This article describes an extension of PYRAMID for circuit patterns of arbitrary size, as well as additional improvements to the previous implementation. PYRAMID is a fast hierarchical pattern modification scheme that can be conceptually partitioned into two phases: local correction to account for circuit components separated by small distances (approximately 1 μm) and global correction for circuit components separated by larger distances. PYRAMID supports input circuits composed of arbitrarily partitioned rectangles, as well as 135° angle path inputs. Also, a segmented mode of operation allows a large circuit to be corrected one segment at a time, thereby reducing computer memory requirements. Experimental results showing the successful correction of a relatively large test pattern (with linewidths as small as 0.1 μm) in 200 nm PMMA resist are provided along with correction times as a function of the number of circuit components.
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85.40.Hp Lithography, masks and pattern transfer
85.40.Qx Microcircuit quality, noise, performance, and failure analysis

Low voltage, high resolution studies of electron beam resist exposure and proximity effect

M. A. McCord and T. H. Newman

J. Vac. Sci. Technol. B 10, 3083 (1992); http://dx.doi.org/10.1116/1.585933 (5 pages) | Cited 19 times

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Resist exposure characteristics have been studied over a voltage range from 1 to 10 kV in order to demonstrate the feasibility of using low voltage electron beam lithography (EBL) to pattern submicron features without the proximity effect problems seen at higher voltages. The exposures were done by modifying a 25 kV thermal field emission EBL machine to run in a retarding field configuration where the sample is biased at a large negative potential, thus reducing the final beam landing energy. After analyzing the linewidths of various proximity test patterns with features as small as 0.15 μm, we conclude that at these dimensions the proximity effect on silicon substrates, compared to 10 kV, is greatly reduced at 5 kV and almost negligible at 3 kV. In order to maintain resolution at these low voltages, it is normally necessary to reduce the beam current due to increased aberrations and reduced source brightness. However, calculations and experiments show that these problems are much less severe in the retarding field configuration, where the electron beam is accelerated to a high potential through most of the optical path length and then reduced to the working voltage just before striking the workpiece. In addition, the reduced beam current is compensated by an almost corresponding increase in the resist sensitivity. Thus, low voltage is shown to be an effective means of avoiding the proximity effect, and a tool using the combination of a thermal field emission electron source and a retarding field final lens is shown to have the resolution and beam current required to expose patterns at the required voltage with reasonable throughput.
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85.40.Hp Lithography, masks and pattern transfer

Low‐voltage electron beam lithography

P. A. Peterson, Z. J. Radzimski, S. A. Schwalm, and P. E. Russell

J. Vac. Sci. Technol. B 10, 3088 (1992); http://dx.doi.org/10.1116/1.585934 (6 pages) | Cited 12 times

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The use of low‐voltage electron beam lithography to reduce proximity effects, improve throughput, and reduce substrate damage caused to underlying materials has been investigated. Various films of PMMA were exposed with a field emission scanning electron microscope adapted with blanking capability and a 16 bit resolution beam control package. The exposure voltages used were from 1 to 15 keV with probe sizes of ≤150 to ≤70 Å, respectively. The dose latitude or working dose range was determined for each voltage on film thicknesses of 0.05, 0.18, and 0.38 μm poly(methylmethacrylate). Optimum beam voltage for a particular thickness which maximizes the energy deposited within the resist has been approximated using Monte Carlo modeling and verified experimentally. Atomic force microscopy showed that at lower voltages the dose required to properly expose a feature is relatively low and as beam voltage increases, the dose required to expose a given area increases. This data also verifies the fact that if the exposing voltage is too low, the resist will not be fully exposed. Because low energy electrons have a smaller interaction volume, there is a significant decrease in the proximity effect that is evident when high energy electrons are used for exposure. Comparison of low energy and higher energy electron beam exposures in this study reveal this decrease. Results indicate that by using low energy electrons for resist exposure the dose can be lowered and thus the throughput increased; the proximity effect is significantly decreased; and because of the limited penetration depth of low energy electrons, the substrate damage is potentially minimized.
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81.05.Lg Polymers and plastics; rubber; synthetic and natural fibers; organometallic and organic materials
81.65.-b Surface treatments
61.80.Fe Electron and positron radiation effects

Low voltage alternative for electron beam lithography

Y.‐H. Lee, R. Browning, N. Maluf, G. Owen, and R. F. W. Pease

J. Vac. Sci. Technol. B 10, 3094 (1992); http://dx.doi.org/10.1116/1.585935 (5 pages) | Cited 14 times

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The current trend in electron beam lithography for patterning submicron features is towards the use of higher beam voltages (20–100 keV). Among the problems often perceived to be associated with the use of low voltages are the poorer resolution, the lower brightness, and the greater sensitivity to electric and magnetic interference. Both by simulation and by experiment at 2 kV it is shown: (1) features of less than 100 nm are clearly resolved in resist of about the same thickness; (2) such features are clearly resolved in both sparse and dense pattern; (3) such features in sparse and dense areas are clearly resolved over a twofold range of exposure doses; (4) such delineation is largely independent of substrate material; (5) there is no evidence of alternating‐current magnetic interference; (6) the lower beam brightness at low voltages is compensated by the increased sensitivity of resists to lower energy electrons. The remaining concerns about low voltage lithography are the reliability of resist with an imaging layer less than 100 nm thick and the extent and effect of charging of such a resist.  
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85.40.Hp Lithography, masks and pattern transfer

Characterization of a positive resist and the application of proximity effect correction in electron‐beam direct write

Z. C. H. Tan, K. Standiford, H. Y. Lem, and C. Nurmi

J. Vac. Sci. Technol. B 10, 3099 (1992); http://dx.doi.org/10.1116/1.585936 (5 pages)

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The resolution capability of a positive resist, TNS, was characterized under optimized process conditions and proximity effect correction. The proximity function is based on a double‐Gaussian scattering model. A ‘‘mesh’’ exposure pattern was used to extract the proximity parameters of the resist. Before parameter determination, the process conditions were optimized by comparing the resist image structures as a function of developer concentration, development time, and temperature. Based on the best process conditions, the proximity parameters were determined and input into the aeble proximity compensation software, where the adequacy of the parameters was investigated. Results demonstrate that both process optimization and proximity effect correction are necessary for resist characterization in fine line lithography.
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85.40.Hp Lithography, masks and pattern transfer

30 nm resolution zero proximity lithography on high‐Z substrates

G. M. Atkinson, F. P. Stratton, R. L. Kubena, and J. C. Wolfe

J. Vac. Sci. Technol. B 10, 3104 (1992); http://dx.doi.org/10.1116/1.585937 (5 pages) | Cited 3 times

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In order to fabricate masks for x‐ray lithography, there is growing interest in subtractive patterning of high atomic mass (high‐Z) materials such as tungsten or gold. Favorable writing speeds and sub‐50 nm resolution without proximity effects combine to make heavy ion focused ion beam lithography an ideal candidate for this area of nanofabrication. Using a 50 keV Ga+ beam with an 8 nm spot diameter, we have exposed a variety of proximity effect test patterns in 60 nm thick PMMA on 0.5 μm thick tungsten films. The results indicate that 30‐nm resolution or better is possible at line/space pitches as small as 80 nm. The test patterns show no apparent proximity effects at these dimensions. An anomalous ‘‘inverse proximity effect’’ was observed, and was determined to be an artifact of the scanning electron microscope technique used to observe the PMMA resist.  
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85.40.Hp Lithography, masks and pattern transfer

Optical detection of multibit logic signals at internal nodes in a flip‐chip mounted silicon static random‐access memory integrated circuit

H. K. Heinrich, N. Pakdaman, J. L. Prince, G. Jordy, M. Belaidi, R. Franch, and D. C. Edelstein

J. Vac. Sci. Technol. B 10, 3109 (1992); http://dx.doi.org/10.1116/1.585938 (3 pages) | Cited 1 time

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We report the first optical measurements of multiple bit‐pattern logic signals at internal nodes in a flip‐chip mounted silicon static random‐access memory integrated circuit. This probing system measures signals by interferometrically detecting the electrically induced charge‐density modulation within devices and parasitic pn junctions. The optical measurements, made on an output driver circuit, compared well with those on an external high‐speed oscilloscope. Measurements made at internal points generally compared well with circuit simulations. However, the bit‐sense circuit measurements suggested internal logic‐level problems in the circuit design.
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85.40.Qx Microcircuit quality, noise, performance, and failure analysis

Ballistic electron emission microscopy investigation of SiGe nanostructures fabricated using reactive‐ion etching

J. G. Couillard, A. Davies, and H. G. Craighead

J. Vac. Sci. Technol. B 10, 3112 (1992); http://dx.doi.org/10.1116/1.585939 (4 pages) | Cited 4 times

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We have applied ballistic electron emission microscopy (BEEM) to microfabricated semiconductor structures in order to study the damage effects of dry etching. Structures were defined in Si0.92Ge0.08 using electron‐beam lithography and reactive‐ion etching. A gold Schottky contact was deposited on the surface, and the transport properties of the metal–semiconductor interface were then characterized using BEEM. BEEM current versus voltage spectra were fit with a two parameter model to determine the local Schottky barrier heights and transmission probabilities of adjacent etched and unetched regions. BEEM enables us to nondestructively examine the electrical nature of the etched surface with nanometer resolution. The results show a lower average barrier height in the etched regions compared to that of the unetched regions, consistent with macroscopic results. This technique also enables us to observe the distribution of local barrier heights with microscopic resolution much higher than conventional techniques.
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81.05.Bx Metals, semimetals, and alloys
85.40.Hp Lithography, masks and pattern transfer
73.30.+y Surface double layers, Schottky barriers, and work functions

Scanning probe microscopy of deposits employed to image the current density distribution of electron beams

M. Weber, H. W. P. Koops, and W. Görtz

J. Vac. Sci. Technol. B 10, 3116 (1992); http://dx.doi.org/10.1116/1.585940 (4 pages) | Cited 3 times

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The current density distribution in the final spot of an electron beam lithography system can be judged from beam diameter measurements performed by means of a knife edge method or recording beam crossover images with conventional lithographic media. Electron beam induced deposition allows to record traces of the current density distribution of the primary beam only, with very small contributions of secondary electrons and x rays. The readout of the focus and stigmation status is obtained by measuring the three‐dimensional appearance of the deposit with a scanning probe microscope. To be able to find the few deposits after transferring the sample to the scanning probe microscope, a ‘‘spotter’’ chip was developed, which supports optical coarse positioning and can be easily scanned by probe microscopes. By scanning a sharp tip structure, deposited by electron beam near the center of the chip, the shape of the probing tip is imaged. This information can be used to unfold the image from the probe tip contributions. Results of beam intensity profiles obtained with this new method using a scanning force microscope are presented.
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41.75.Fr Electron and positron beams
41.85.Ew Particle beam profile, beam intensity
85.40.Hp Lithography, masks and pattern transfer
07.78.+s Electron, positron, and ion microscopes; electron diffractometers

Focused ion beam observation of grain structure and precipitates in aluminum thin films

D. L. Barr, L. R. Harriott, and W. L. Brown

J. Vac. Sci. Technol. B 10, 3120 (1992); http://dx.doi.org/10.1116/1.585941 (6 pages) | Cited 1 time

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Reliability in very large scale integrated circuits is strongly dependent on the grain structure of the aluminum metallization used in interconnection between devices on a chip. Commonly used techniques for grain metrology require the use of time consuming sample preparation. Focused ion beam microscopy is well suited to studying grain size and structure because it needs little or no sample preparation and can give information about grain structure throughout the typical 0.5–1 μm thickness of aluminum films. Measurements of grain size and observations of precipitates in aluminum metallization by using focused ion beam are presented.
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85.40.Hp Lithography, masks and pattern transfer
85.40.Ls Metallization, contacts, interconnects; device isolation

Laser‐produced plasmas for soft x‐ray projection lithography

W. T. Silfvast, M. C. Richardson, H. Bender, A. Hanzo, V. Yanovsky, F. Jin, and J. Thorpe

J. Vac. Sci. Technol. B 10, 3126 (1992); http://dx.doi.org/10.1116/1.585942 (8 pages) | Cited 15 times

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Laser‐produced plasmas are one of the most likely sources to be used for soft x‐ray projection lithography. The characteristics of these sources are described in terms of the expected radiation efficiency within the illumination bandwidth of a lithographic system. Measurements of the plasma particulate emission are described and techniques for interdicting this emission before it reaches the illumination optics are discussed. The laser requirements are obtained for a lithographic system producing a wafer rate of 60, 6 in. wafers per hour.
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85.40.Hp Lithography, masks and pattern transfer
52.25.Os Emission, absorption, and scattering of electromagnetic radiation
81.65.-b Surface treatments

Defect repair for soft x‐ray projection lithography masks

D. M. Tennant, L. A. Fetter, L. R. Harriott, A. A. MacDowell, P. P. Mulgrew, W. K. Waskiewicz, D. L. Windt, and O. R. Wood

J. Vac. Sci. Technol. B 10, 3134 (1992); http://dx.doi.org/10.1116/1.585943 (7 pages) | Cited 2 times

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The most promising option for masks intended for use in soft x‐ray projection lithography (SXPL) at λ=13 nm is a reflective mask which uses a Mo/Si multilayer reflective coating. A variety of multilayer coated reflective mask technologies have been reported which can provide both high‐resolution features and good reflectance contrast between the patterned and unpatterned regions. Repair of defects generated during patterning is a necessary feature of any practical mask technology. We have investigated the application of focused ion beam milling and deposition to programmed defects in the absorber layer of a SXPL Mo/Si multilayer reflection mask. Use of a sacrificial polymer barrier layer is described as well as milling and deposition conditions. The effect of ion implantation of the barrier layer on its removal after absorber repair is also reported. Both reflectivity measurements and resist images comparing repaired and unrepaired regions of masks are used to demonstrate the efficacy of the technique.
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85.40.Hp Lithography, masks and pattern transfer

Metal‐less x‐ray phase‐shift masks for nanolithography

V. White and F. Cerrina

J. Vac. Sci. Technol. B 10, 3141 (1992); http://dx.doi.org/10.1116/1.585944 (4 pages) | Cited 8 times

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In this article the theoretical and experimental results of metal‐less x‐ray phase‐shift masks are reported. Features of 40 nm have been printed using gaps on the order of 5–10 μm, and lines of 0.1 μm have been printed with gaps of 30 μm with synchrotron radiation. A first prototype has been constructed of 2.75 μm of PMMA patterned on 0.8 μm Si3N4. They can be created out of a variety of low‐Z materials. The model predicts a mask contrast between 5–6. Among its advantages is its ability to form nanometer lines without actually having to write them directly, because, with this technique, only the edges of the features are patterned on the mask where the two phases destructively interfere. In addition, the images do not degrade with increasing gap as quickly as a standard metal masks, resulting in a larger process window.
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85.40.Hp Lithography, masks and pattern transfer
81.65.-b Surface treatments
81.05.Lg Polymers and plastics; rubber; synthetic and natural fibers; organometallic and organic materials
61.80.Cb X-ray effects

Application of x‐ray lithography with a single‐layer resist process to subquartermicron large scale integrated circuit fabrication

Kimiyoshi Deguchi, Kazunori Miyoshi, Hiroshi Ban, Hakaru Kyuragi, Shinsuke Konaka, and Tadahito Matsuda

J. Vac. Sci. Technol. B 10, 3145 (1992); http://dx.doi.org/10.1116/1.585945 (5 pages) | Cited 2 times

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The applicability of synchrotron radiation x‐ray lithography to future ultralarge scale integrated circuit fabrication processes is demonstrated by the test fabrication of subquartermicron bipolar‐ complementary metaloxide semiconductor devices (SRAM, gate arrays, and several test element groups) with a total size of two‐million transistors. Synchrotron radiation lithography is used at four critical levels: gate poly, first metal, via hole, and second metal. Both negative and positive chemically amplified resists are used with a single‐layer resist system to simplify the resist process. An overview of the lithography process is presented with emphasis on patterning and overlay performance.
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85.40.Hp Lithography, masks and pattern transfer

Experimental and theoretical study of image bias in x‐ray lithography

Jerry Z. Y. Guo, Quinn Leonard, Franco Cerrina, E. Di Fabrizio, L. Luciani, M. Gentili, and David Gerold

J. Vac. Sci. Technol. B 10, 3150 (1992); http://dx.doi.org/10.1116/1.585901 (5 pages) | Cited 4 times

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The successful application of x‐ray lithography to a manufacturing process requires a detailed understanding of the image formation process. In a series of articles, a theoretical study of the optical processes involved in the definition of the image in proximity printing has been presented. In addition to the diffraction process, it is included here that the image formation in the very near field (microgaps) due to the guiding effects in the absorber which alters the boundary condition for diffraction and thus changes the final image pattern. Also presented here is an experimental study designed to verify the predictions of the models of image formation. Preliminary result shows a very large depth‐of‐focus for 0.25 μm features.
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42.82.Cr Fabrication techniques; lithography, pattern transfer

Stress reduction of gold absorber patterns on x‐ray masks

W. A. Johnson, R. E. Acosta, B. S. Berry, W. C. Pritchet, D. J. Resnick, and W. J. Dauksher

J. Vac. Sci. Technol. B 10, 3155 (1992); http://dx.doi.org/10.1116/1.585902 (4 pages) | Cited 2 times

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A resonance frequency measurement technique has been used to measure the stress at temperature of plated gold films on x‐ray mask membranes over the temperature range of 90–525 K. Room temperature tensile stress increases are observed after above room temperature anneals. Stress relaxations are measured after liquid nitrogen cools. The tensile stress increases and the stress relaxations depend upon the microstructure of the plated films. Focused ion beam imaging shows that grain growth is the dominant mechanism for the tensile stress increases observed for fine grained as‐plated gold films.
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81.40.Jj Elasticity and anelasticity, stress-strain relations
62.40.+i Anelasticity, internal friction, stress relaxation, and mechanical resonances
68.60.Bs Mechanical and acoustical properties

Chemical‐vapor deposition of SiC thin films for x‐ray mask applications

Ricardo I. Fuentes

J. Vac. Sci. Technol. B 10, 3159 (1992); http://dx.doi.org/10.1116/1.585903 (5 pages) | Cited 1 time

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In this article some of the results on growth and application of SiC thin films for x‐ray mask substrates are presented. Aspects of the process that are relevant to the film’s use for x‐ray masks, such as growth defects, roughness, stress, and growth rate versus gas composition, growth temperature, and flow rates are discussed. There are definite regions in composition space within which the growth rate is useful and the growth defect population is minimized. The film’s internal stress is generally tensile and increases with growth temperature, although it can be made compressive by the appropriate choice of growth parameters. The SiC film’s surface roughness also decreases with growth temperature, and growth temperature/gas composition combinations exist which yield smooth films (roughness less than 200 Å) with a desirable stress (less than 300 MPa). Our SiC films are typically 20–500 Å rough (peak‐to‐peak), tensile with a stress in the range of 100–500 MPa, and grow at a nominal rate of 0.8 μm/h. The films appear to be radiation hard up to incident doses of approximately 25 KJ/cm2. The chemical‐vapor deposition system is a cold‐wall‐type with a temperature range of 1423–1673 K. The growth takes place at pressures of 100–700 Torr in a H2–C2H4–SiH4 atmosphere.
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81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
85.40.Hp Lithography, masks and pattern transfer
68.55.-a Thin film structure and morphology
68.60.Bs Mechanical and acoustical properties

Modeling and experimental verification of illumination and diffraction effects on image quality in x‐ray lithography

Scott D. Hector, M. L. Schattenburg, E. H. Anderson, W. Chu, Vincent V. Wong, and Henry I. Smith

J. Vac. Sci. Technol. B 10, 3164 (1992); http://dx.doi.org/10.1116/1.585904 (5 pages) | Cited 9 times

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Most analyses of the effects of diffraction and source coherence on image quality in proximity x‐ray lithography have used Kirchhoff boundary conditions and scalar diffraction theory. In this article we treat the x‐ray absorber as a lossy dielectric and employ the vector form of Maxwell’s equations to calculate image intensity as a function of position for lines, spaces, and gratings, at 100 nm linewidths and below. We show that vector and scalar theories give different results. Simulations are done for two point sources (CuL and an Fe‐plasma) so that calculations could be compared with our experimental results. Agreement was excellent for 80 and 50 nm features at relatively large gaps. We define image contrast and show that, contrary to common intuition, it is enhanced (and spurious ringing is suppressed) as penumbral blurring is increased, reaching a maximum when the extent of blurring is somewhat larger than the minimum feature size.
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85.40.Hp Lithography, masks and pattern transfer
42.30.Va Image forming and processing

Correlation of in‐plane and out‐of‐plane distortion in x‐ray lithography masks

Y. C. Ku, Michael H. Lim, J. M. Carter, M. K. Mondol, A. Moel, and Henry I. Smith

J. Vac. Sci. Technol. B 10, 3169 (1992); http://dx.doi.org/10.1116/1.585905 (4 pages) | Cited 1 time

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The implementation of x‐ray lithography requires that in‐plane distortion caused by absorber stress be eliminated (i.e., be made less than ∼10% of minimum feature sizes). As a rule of thumb, for large‐area membranes (i.e., ≥30 mm diam) stress‐induced distortion is negligible if absorber stress is kept below 108 dynes/cm2 (10 MPa). The most common way of determining absorber stress on membranes is to measure the out‐of‐plane deflection in a Linnik or Mireau interferometer. Out‐of‐plane deflection is caused by absorber bending moment. It is possible, in principle, for an absorber to have a stress that varies with depth in such a way that bending moment is zero but net in‐plane stress is not. To determine if there is a one‐to‐one correspondence between out‐of‐plane and in‐plane distortion, and in order to check the validity of Yanof’s model, we have developed two methods of measuring in‐plane distortion: a moiré method and a holographic interferometry (HI) method. Both require that one etch or lift‐off a grid on one surface of the x‐ray mask membrane using holographic lithography and reactive‐ion etching. On the opposite surface an x‐ray absorber is deposited and patterned. In the moiré method another holographic exposure is performed, at the same spatial period as the grid, but at a small azimuthal rotation. After development, a clear moiré pattern is formed, from which one can calculate the in‐plane distortion and corresponding absorber stress. In the HI method, the mask is placed in the standing wave produced by two intersecting laser beams. A fringe pattern can then be seen on a charge coupled device camera. The HI method provides a higher sensitivity to in‐plane distortion than the moiré method and should enable one to measure in‐plane strain at a level corresponding to in‐plane distortion below 1 nm for typical pattern geometries.
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85.40.Hp Lithography, masks and pattern transfer

Resolution limits in x‐ray lithography

M. Feldman and J. Sun

J. Vac. Sci. Technol. B 10, 3173 (1992); http://dx.doi.org/10.1116/1.585906 (4 pages) | Cited 4 times

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During an x‐ray lithography proximity exposure x rays generate electrons in the resist which deposit energy along a finite range. This range combines with diffraction spreading to degrade the image resolution. The component of resolution arising from electron range is often taken as the Grun range of the most copiously generated photoelectrons, about 0.1 μm at an exposure wavelength of 10 Å. Although some experiments have shown much better resolutions, there is a widespread belief that photoelectron range limits resolution to about 0.1 μm. We have analytically modeled the distribution of energy deposited by Auger and photoelectrons. Near an edge the distribution is well‐fit by an error function. The standard deviation of this error function, which we define as the ‘‘effective range,’’ is about 0.01 μm at 10 Å in poly(methylmethacrylate) (PMMA) resist. For all energies of interest to x‐ray lithography the effective range of the electrons is much smaller than the Grun range, explaining the high‐resolution results. It is diffraction which dominates the resolution of conventional x‐ray lithography. Consequently, reducing the gap in proximity printing should produce resolutions far below 0.1 μm, while retaining all the latitude inherent in the x‐ray lithography process.
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85.40.Hp Lithography, masks and pattern transfer

Projection x‐ray lithography using computer‐generated holograms: A study of compatibility with proximity lithography

Chris Jacobsen and Malcolm Howells

J. Vac. Sci. Technol. B 10, 3177 (1992); http://dx.doi.org/10.1116/1.585907 (5 pages)

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X‐ray projection lithography has recently been explored as a method for the manufacture of ≤200 nm linewidth integrated circuits. A method was previously described [J. Appl. Phys. 71, 2993 (1992)] whereby projected lithographic images can be formed with x rays by means of a transmission hologram. The form of the hologram is computed by an algorithm which eliminates the unwanted signals normally present as systematic errors in in‐line holographic images. Such an approach to projection x‐ray lithography requires an x‐ray beam with very little coherence and is thus compatible with high wafer throughput schemes; in addition, image fidelity remains high even when moderately small contaminant particles block the light from small regions of the hologram. Previous example calculations involved using 5 nm x rays to illuminate a 0–1 μm thick carbon hologram located 200 μm from the wafer to produce simulated 0.06 μm linewidth images with good fidelity and with 6 μm depth of field. Presented here are simulations involving holographic masks made of 0–1 μm of tungsten operating at 1 nm wavelength with 50 μm mask‐to‐wafer gap. Such a configuration can be viewed as a future extension of the existing technology of proximity x‐ray lithography to linewidths as small as 0.02 μm.
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85.40.Hp Lithography, masks and pattern transfer
42.40.My Applications
42.40.Jv Computer-generated holograms

Repair of opaque defects on reflection masks for soft x‐ray projection lithography

Andrew M. Hawryluk and Diane Stewart

J. Vac. Sci. Technol. B 10, 3182 (1992); http://dx.doi.org/10.1116/1.585908 (4 pages) | Cited 1 time

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We have developed a new technique for removing opaque defects on soft x‐ray projection lithography reflection masks using ion beam etching. This technique clears the defect without damaging the multilayer mirror or introducing an absorptive element into the multilayer. Our procedure uses a thin, Si overcoat to protect the multilayers from the kinetic energy of the ion beam, reduced ion beam energy, and a Ar ion beam to avoid absorption losses. A Si ion beam could also be used in this process.
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85.40.Hp Lithography, masks and pattern transfer

Masks for x‐ray lithography with a point source stepper

G. K. Celler, C. Biddick, J. Frackoviak, C. W. Jurgensen, R. R. Kola, A. E. Novembre, L. E. Trimble, and D. M. Tennant

J. Vac. Sci. Technol. B 10, 3186 (1992); http://dx.doi.org/10.1116/1.585909 (5 pages) | Cited 1 time

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We describe some key aspects of proximity x‐ray technology currently being developed at AT&T, from mask fabrication to wafer patterning. The masks are primarily based on polycrystalline Si membranes, 1 μm thick, which are formed directly on optically flat glass disks. A tungsten absorber layer is deposited on the membranes by radio‐frequency diode sputtering, with in situ stress control in the deposition chamber so that stresses ≤10 MPa are routinely achieved. Patterns are defined in an organosilicon negative resist, P(SI‐CMS), using an electron beam writing tool and a neural network based proximity correction algorithm. The patterns are transferred into metallic absorber layers by reactive ion etching in a parallel plate plasma system. Using the above procedure, we have fabricated masks with 0.25 μm features and also some test patterns with lines and spaces as small as 0.1 μm. X‐ray exposures were done with a Hampshire 5000P point source stepper, using AZ PF‐114 resist from Hoechst–Celanese.
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85.40.Hp Lithography, masks and pattern transfer

X‐ray mask development based on SiC membrane and W absorber

M. Chaker, S. Boily, Y. Diawara, M. A. El Khakani, E. Gat, A. Jean, H. Lafontaine, H. Pépin, J. Voyer, J. C. Kieffer, A. M. Haghiri‐Gosnet, F. R. Ladan, M. F. Ravet, Y. Chen, and F. Rousseaux

J. Vac. Sci. Technol. B 10, 3191 (1992); http://dx.doi.org/10.1116/1.585910 (5 pages) | Cited 5 times

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We report a detailed description of x‐ray mask technology based on SiC membrane and tungsten absorber. Amorphous SiC films were prepared using either a 100 kHz plasma‐enhanced chemical vapor deposition (PECVD) system (allowing a high throughput) or a laser ablation deposition (LAD) technique. The PECVD a‐SixC1−x:H films have a maximum Si–C bond density at x=0.5, a hydrogen content of 27 at. % and a high‐compressive stress (1 GPa). The LAD films are stoichiometric, hydrogen‐free, and under high‐compressive stress (1.4 GPa). In order to achieve the tensile stress range (20–40 MPa) required for membrane fabrication, we developed a well‐controlled rapid thermal annealing (RTA) process. At 633 nm, the resulting PECVD and LAD membranes have an optical transparency of 75% and 40%, respectively, and their corresponding biaxial Young’s moduli are 250±30 and 360±60 GPa. A novel approach using RTA for ‘‘fine tuning’’ of the tungsten stress is also proposed. Low stress (≤10 MPa) is obtained for W layers initially under compressive stress lower than 300 MPa. Finally, using an e‐beam patterning process based on a single resist layer and reactive ion etching for the pattern transfer, x‐ray masks with linewidths down to 100 nm were developed.
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85.40.Hp Lithography, masks and pattern transfer

Fabrication of parallel quasi‐one‐dimensional wires using a novel conformable x‐ray mask technology

R. A. Ghanbari, W. Chu, E. E. Moon, M. Burkhardt, K. Yee, D. A. Antoniadis, Henry I. Smith, M. L. Schattenburg, K. W. Rhee, R. Bass, M. C. Peckerar, and M. R. Melloch

J. Vac. Sci. Technol. B 10, 3196 (1992); http://dx.doi.org/10.1116/1.585911 (4 pages) | Cited 1 time

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We report on the fabrication of quasi‐one‐dimensional wires on modulation‐doped GaAs/AlGaAs using a novel conformable x‐ray mask technology which allows us to expose arbitrary sized samples, including samples much smaller than the membrane area, using our laboratory’s standard 31 mm‐diam silicon‐nitride x‐ray mask. After optical alignment, the sample and mask are brought into contact electrically, and then loaded into a specially designed cartridge which allows a vacuum to be pulled between mask and substrate. The vacuum causes the x‐ray mask to conform around the sample. We find that a vacuum hold down is necessary to allow easy separation of the sample from the mask with minimal risk to both.  
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85.40.Hp Lithography, masks and pattern transfer
85.40.-e Microelectronics: LSI, VLSI, ULSI; integrated circuit fabrication technology

Membrane fragility: Fact or illusion?

L. E. Trimble, G. K. Celler, J. Frackoviak, and G. R. Weber

J. Vac. Sci. Technol. B 10, 3200 (1992); http://dx.doi.org/10.1116/1.585912 (4 pages) | Cited 1 time

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Membranes are in wide use today as microsensors, vacuum windows, and lithography mask substrates. They are fragile and difficult to protect, however. We show that membrane strength, and thus process yield, are increased by a newly designed ‘‘skirted’’ membrane. This structure strengthens the attachment of membrane to support, reinforcing a region where fractures usually originate. The skirt design was applied to polysilicon membranes on glass supports, used for x‐ray lithography mask blanks, and was shown to increase strength three times over polysilicon or silicon‐rich nitride membranes on silicon supports, to an average of 1.5 GPa. More significantly, skirted polysilicon membranes exhibit fracture pressure differentials that are six times higher in the same comparison, having tremendous impact on process and application durability.
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68.60.Bs Mechanical and acoustical properties
81.40.Np Fatigue, corrosion fatigue, embrittlement, cracking, fracture, and failure
46.50.+a Fracture mechanics, fatigue and cracks

Impact of different x‐ray mask substrate materials on optical alignment

R. I. Fuentes, C. Progler, S. Bukofsky, and K. Kimmel

J. Vac. Sci. Technol. B 10, 3204 (1992); http://dx.doi.org/10.1116/1.585913 (4 pages) | Cited 1 time

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In this article, results will be presented on how different x‐ray mask substrate materials affect the quality of the alignment signal acquired through them. By affecting the signal quality, the different materials ultimately have a significant impact on the capability of the alignment system to discern the position of the alignment marks precisely. Data will also be presented on position measurement repeatability as a function of mark depth for the different mask materials. In the experiments, in‐house grown SiC and diamond films were used. Vendor SiC and SiN materials were also used. For comparison and reference, signals were acquired through polyimide and B‐doped Si as well. The alignment was done with a lab‐based Suss ALX100 system. Since the primary alignment effect of membrane materials is to reduce signal‐to‐noise ratio, mark recognition repeatability and signal contrast was used as the comparative performance criteria. Experiments were done in both bright field and nonscanning dark field modes from alignment marks with depths between 5 and 150 nm. The effects of the substrate material became more evident when it was attempted to align using shallow marks. The vendor SiC and diamond exhibited poor recognition repeatability when marks of less than 45 nm in depth were used in bright field or 75 nm in dark field. Antireflective coatings seem useful in improving the performance of some of these materials, especially in bright field alignment. With a one sigma repeatability budget of 10 nm, current alignment systems may have difficulties in reproducibly locating shallow marks (below 20 nm), which may be found on some of the very demanding levels, when aligning through any of the candidate materials. The need may exist for careful processing of the marks and/or improvement in the aligners ability to see through rough or highly absorbing mask materials.
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42.82.Cr Fabrication techniques; lithography, pattern transfer

Deformation of x‐ray lithography masks during tool chucking

Alek C. Chen and Juan R. Maldonado

J. Vac. Sci. Technol. B 10, 3208 (1992); http://dx.doi.org/10.1116/1.585914 (4 pages)

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Finite element modeling is used in this article to describe the elastic deformation of x‐ray lithography masks due to chucking in the electron‐beam writer or the lithographic tool. The total overlay budget for the lithography of 0.25 μm ground rule devices is less than 0.1 μm (3 σ) including all possible sources of error. Chuck induced random deformation of x‐ray masks can contribute a significant amount to this overlay error [A. Chen et al., J. Vac. Sci. Technol. B 10, XXXX (1992)]. In addition, errors could arise also if different chucking techniques are used in the writing and exposure tools [A. Chen, S. Lalapet and J. R. Malonado, J. Vac. Technol. B 9, 3306 (1991)]. Based on the state of the art of the precision and accuracy of mask aligners and e‐beam writers, it is required that the mask deformation due to chucking should be kept below 10 nm (3 σ). Several finite element models were constructed to simulate x‐ray lithography masks under different chucking methods: (a) an idealized kinematic chucking, (b) full surface chucking, e.g., chucked by a vacuum ring, and (c) three point chucking. The maximum in‐plane deformation of the x‐ray mask membrane was normalized to the ratio of the modulus of elasticity of the mask support structure (Pyrex; trademark of Cornia Glass) and the chuck material. The calculated in‐plane deformations of the x‐ray mask membrane were compared among the various chucking techniques mentioned above. The results are helpful in the design of aligner and exposure tools from the point of view of selecting proper chuck materials and methods to minimize mask membrane deformations.  
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85.40.Hp Lithography, masks and pattern transfer
81.65.-b Surface treatments
07.85.-m X- and γ-ray instruments

Diffraction effects and image blurring in x‐ray proximity printing

A. D. Dubner, A. Wagner, J. P. Levin, and J. Mauer

J. Vac. Sci. Technol. B 10, 3212 (1992); http://dx.doi.org/10.1116/1.585915 (5 pages) | Cited 2 times

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The influence of diffraction on the shape and size of features printed using x‐ray proximity printing is reviewed, and the effect of image blurring on these results is described. Diffraction can alter the shape of a printed feature, and the systematic shape changes observed in resist images can be explained using simple scaling based on Fresnel diffraction. In addition, the linewidth change with exposure dose is independent of feature type and size, and depends only on the square root of the mask to wafer gap. The shape of printed features and the linewidth change with dose can be modified by smearing the aerial image at the wafer plane. This can be achieved by adding beam divergence or by varying the angle of incidence of the x‐ray beam onto the mask (wobbling). A technique for incorporating wobble into an exposure system is described, and exposures of contact holes, spaces, lines, and line‐space arrays using this technique are presented. For example, 0.35 μm square contact holes normally print diamond shaped at a 40 μm gap. However, the same contact holes are round in resist when 4 mrad of wobble is incorporated into the exposure. The linewidth change for a 10% increase in dose is 24 nm at a 40 μm gap with 5 mrad of wobble. This linewidth change with exposure dose is larger than the 20 nm measured for exposures at a 40 μm gap without wobble. Finally, wobbling during exposure can either increase or decrease the absolute linewidth of a feature in resist at a given exposure dose.
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85.40.Hp Lithography, masks and pattern transfer

Diamond membrane based x‐ray masks

B. Löchel, H.‐L. Huber, C.‐P. Klages, L. Schäfer, and A. Bluhm

J. Vac. Sci. Technol. B 10, 3217 (1992); http://dx.doi.org/10.1116/1.585916 (4 pages) | Cited 3 times

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Diamond layers are of special interest for x‐ray mask fabrication because of their excellent optical and mechanical properties. Using a plasma activated chemical vapor deposition process, 2–5 μm thick diamond layers were deposited and characterized. Microhardness and Young’s modulus are found to be very close to the literature values of bulk diamond. A standard isotropic etching process was applied for membrane fabrication. The optical transparency and the thickness homogeneity were measured. Concerning surface roughness, scanning electron micrographs and atomic force measurements were evaluated. After irradiation of diamond masks with synchrotron light, a slight increase of optical transparency was found.
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78.70.Dm X-ray absorption spectra
78.66.-w Optical properties of specific thin films
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
07.85.-m X- and γ-ray instruments

Novel approach to zero‐magnification x‐ray mask replication

G. M. Wells, A. Krasnoperova, E. A. Haytcher, R. Engelstad, F. Cerrina, R. Fair, and J. Maldonado

J. Vac. Sci. Technol. B 10, 3221 (1992); http://dx.doi.org/10.1116/1.585917 (3 pages)

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A technique for replicating x‐ray masks with no magnification of the master mask pattern has been developed. This technique uses a raster scanning pattern with a synchrotron x‐ray source to eliminate pattern magnification due to the source divergence. Kinematic mounts were employed to reduce clamping induced distortions in the mask replication process and the metrology tool. Finite element analysis of the thermal response of the clamped master and replicate masks during exposure indicates the temperature increase of the two membranes during exposure is matched, so that thermal distortions are not transferred to the printed pattern.
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85.40.Hp Lithography, masks and pattern transfer

Installation and early operating experience with the Helios compact synchrotron x‐ray source

C. N. Archie, J. I. Granlund, R. W. Hill, K. W. Kukkonen, J. A. Leavey, L. G. Lesoine, J. M. Oberschmidt, A. E. Palumbo, C. Wasik, M. Q. Barton, J. P. Silverman, J. M. Warlaumont, A. D. Wilson, R. J. Anderson, N. C. Crosland, et al.

J. Vac. Sci. Technol. B 10, 3224 (1992); http://dx.doi.org/10.1116/1.585918 (5 pages)

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During 1991 the Oxford Instruments’ compact synchrotron x‐ray source Helios was installed at IBM’s Advanced Lithography Facility, following factory tests in Oxford during 1990. The machine has met or exceeded all performance specifications at the East Fishkill site. Since January, 1992 it has been run routinely for lithography development work. Running and reliability statistics are being generated, and the results for the first five months are presented here.
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41.50.+h X-ray beams and x-ray optics
41.60.Ap Synchrotron radiation

CXrL aligner: An experimental x‐ray lithography system for quarter‐micron feature devices

G. Chen, J. Wallace, R. Nachman, G. Wells, D. Bodoh, P. Anderson, M. Reilly, and F. Cerrina

J. Vac. Sci. Technol. B 10, 3229 (1992); http://dx.doi.org/10.1116/1.585919 (6 pages) | Cited 1 time

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This article describes the CXrL aligner, an experimental x‐ray proximity lithography system developed at the University of Wisconsin Center for X‐Ray Lithography. The main features of the aligner are (1) exposure in an atmospheric He environment; (2) mask to wafer alignment error detection and correction during exposure; and (3) mask to wafer continuous gap setting based on capacitance gauges. The aligner consists of a three‐axes two‐state alignment system for continuous alignment error detection and a piezobased precision mechanical stage for alignment error correction. The wafer is held by a flat vacuum chuck and the mask is held by three vacuum suction cups located around the glass ring. Since the optical system is located outside of the synchrotron radiation path, alignment can be performed during the exposure. We have obtained a noise equivalent misalignment of 2 nm with an alignment signal response time less than 10 ms. An alignment signal repeatability (3σ) better than 0.06 μm has been achieved. In the preliminary evaluation of x‐ray printed patterns, we obtained an overlay accuracy of 0.18 μm, to which the measurement error contributes most.  
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85.40.Hp Lithography, masks and pattern transfer

Synchrotron radiation stepper with new alignment system

F. Sato, K. Ito, T. Miyatake, K. Yamazaki, S. Hamada, and Y. Tomita

J. Vac. Sci. Technol. B 10, 3235 (1992); http://dx.doi.org/10.1116/1.585920 (4 pages) | Cited 4 times

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A vertical stepper for synchrotron radiation (SR) x‐ray lithography has been developed. Evaluation tests have been done with SR light from the superconducting compact synchrotron ‘‘AURORA’’ located in SHI‐Tanashi Works, Tokyo. An overlay accuracy of less than 0.08 μm was obtained. A 0.2 μm line‐and‐space pattern was successfully resolved with a high‐aspect ratio. The designed specifications have been attained. The system is ready for the future generation ultra‐large‐scale integration applications.
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85.40.Hp Lithography, masks and pattern transfer

Laser plasma sources for proximity printing or projection x‐ray lithography

M. Chaker, B. La Fontaine, C. Y. Côté, J. C. Kieffer, H. Pépin, M. H. Talon, G. D. Enright, and D. M. Villeneuve

J. Vac. Sci. Technol. B 10, 3239 (1992); http://dx.doi.org/10.1116/1.585921 (4 pages) | Cited 12 times

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In this article, we present a theoretical and experimental study of the x‐ray emission produced by laser plasma sources in different spectral ranges appropriate for x‐ray lithography either in proximity printing (XRL) or projection (XRPL) approaches. For XRPL application, experiments using 10 ns laser pulses show that the maximum conversion efficiency in the (80–250 eV) range is attained at I=1011 W cm−2 whereas for 25 ns pulses and I≤6×1011 W cm−2, it is still increasing with laser intensity. On the other hand, higher laser intensities are required to obtain a high conversion efficiency for XRL (0.9–1.4 keV). Efficient emission peaked at 1.1 keV can be achieved for I≥1013 W cm−2 with copper targets and pulse duration shorter than 5 ns. For iron line emission (peak at 0.9 keV), the laser intensity can be lower (I=5×1012 W cm−2) and the pulse duration longer (τp=10 ns). Finally, we discuss the different approaches which may lead to the appropriate laser design.
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52.25.Os Emission, absorption, and scattering of electromagnetic radiation
52.50.Jm Plasma production and heating by laser beams (laser-foil, laser-cluster, etc.)
85.40.Hp Lithography, masks and pattern transfer

Application of an x‐ray stepper for subquarter micrometer fabrication

Yong Chen, A. M. Haghiri‐Gosnet, D. Decanini, M. F. Ravet, F. Rousseaux, and H. Launois

J. Vac. Sci. Technol. B 10, 3243 (1992); http://dx.doi.org/10.1116/1.585922 (5 pages) | Cited 1 time

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We report on a study of proximity x‐ray lithography with a commercialized x‐ray stepper (Karl Suss XRS200) and synchrotron orbital radiation at Super‐ACO (Orsay, France). Special attention has been paid to the replication capabilities using SiC/W based high‐resolution x‐ray masks. The results show that proximity printing at a gap of 40 μm can result in subquarter micrometer replication. Since the resolution of the proximity printing is limited by the Fresnel diffraction, we use a double exposure technique to generate higher density and higher resolution grating structures. Fabrication of sub‐100 nm linewidth gratings has been achieved using this technique with a wide exposure latitude.
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85.40.Hp Lithography, masks and pattern transfer

Evaluation of heterodyne alignment technique for x‐ray steppers

K. Koga, I. Higashikawa, T. Itoh, K. Araki, K. Fujita, J. Yasui, and S. Aoki

J. Vac. Sci. Technol. B 10, 3248 (1992); http://dx.doi.org/10.1116/1.585923 (4 pages)

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Registration accuracy, as well as resolution capability, is one of the critical factors to identify an appropriate lithography tool. For deep submicron devices represented by the 256 Mbit dynamic random access memory, an alignment accuracy of better than 30 nm is needed. In this article, the alignment accuracy of an x‐ray stepper was evaluated using the double‐exposure method with a posiresist. The alignment accuracy obtained was better than 38 nm (3σ). Moreover, making a quantitative analysis of alignment error factors, we identified the possibility of improvement toward better than 30 nm (3σ).  
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85.40.Hp Lithography, masks and pattern transfer
07.85.-m X- and γ-ray instruments

Measurement of x‐ray absorption spectra of photoresists using a silicon lithium detector

G. M. Wells, J. W. Taylor, F. Cerrina, D. Pearson, and J. MacKay

J. Vac. Sci. Technol. B 10, 3252 (1992); http://dx.doi.org/10.1116/1.585924 (4 pages) | Cited 1 time

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We have developed a simple experimental technique for measuring the absorption spectrum of x‐ray photoresists in the region from 1000 to 3000 eV. Knowledge of the absorption characteristics of a photoresist allows selection of the most efficient range of energies to use for performing x‐ray exposures. The measurements were performed using the Medical Physics beamline on the University of Wisconsin Aladdin synchrotron source. The beamline is equipped with a lithium‐drifted silicon detector that provides an energy resolution of 150 eV. To avoid saturation of the Si(Li) detector, special ‘‘microbeams’’ of approximately 50 circulating electrons in the storage ring were employed. The beam intensity was monitored using a photodiode. The operation of the detector and associated diagnostic equipment will be described. Four by four millimeter square, 1.4 μm thick silicon nitride membranes were used as substrates for the resist films. Photoresist absorption was measured by comparing the transmission of silicon nitride membranes with and without photoresist coatings. Experimental results for both conventional and chemically amplified positive and chemically amplified negative x‐ray photoresists are presented.
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78.70.Dm X-ray absorption spectra
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