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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) | Cited 1 time

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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 23 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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