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Nov 1988

Volume 6, Issue 6, pp. 1621-2311


Reactive ion beam etching of polyimide thin films

William E. Vanderlinde and Arthur L. Ruoff

J. Vac. Sci. Technol. B 6, 1621 (1988); http://dx.doi.org/10.1116/1.584420 (5 pages) | Cited 14 times

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Reactive ion beam etching of polyimide thin films was investigated using x‐ray photoelectron spectroscopy (XPS) and etch rate measurements. The etching mechanism and the near surface damage produced in polyimide by exposure to argon and oxygen ion beams were compared. The etch rate of polyimide by oxygen ions was studied as a function of ion current density and neutral oxygen molecular flux, and the results were found to match a model for the contribution of neutral fluxes to the etch process. Ion beam etching with inert argon ions was found to produce a graphitelike layer on polyimide. Reactive ion beam etching with oxygen ions resulted in much faster etching than for argon ions, and did not produce a graphitized layer.
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81.05.Lg Polymers and plastics; rubber; synthetic and natural fibers; organometallic and organic materials
81.65.-b Surface treatments
79.20.Rf Atomic, molecular, and ion beam impact and interactions with surfaces
82.65.+r Surface and interface chemistry; heterogeneous catalysis at surfaces
61.80.Jh Ion radiation effects

High‐rate ion etching of GaAs and Si at low ion energy by using an electron beam excited plasma system

Jin‐Zhong Yu, Tamio Hara, Manabu Hamagaki, Takashi Yoshinaga, Yoshinobu Aoyagi, and Susumu Namba

J. Vac. Sci. Technol. B 6, 1626 (1988); http://dx.doi.org/10.1116/1.584419 (6 pages) | Cited 2 times

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By using a newly developed electron beam excited plasma (EBEP) system, etching characteristics of GaAs and Si in an ion energy range of 5 to 100 eV were investigated. Anisotropic etching profiles with high aspect ratios were obtained by both Ar ion beam etching (IBE) and Cl2 reactive ion beam etching (RIBE). Etching rates of 1.2 μm/min for GaAs and 0.5 μm/min for Si were demonstrated for the first time by Cl2 RIBE at ultralow ion acceleration voltage of 5 V. Selective ratios of etching rates for Si/SiO2 and GaAs/SiO2 are ∼33 and 80, respectively. Electrical and optical measurements on the etched samples indicated that damage degree introduced by the low‐energy ions is negligible. Therefore, the EBEP system cannot only provide high etching rate because of its high ion current but also realize damageless ion etching due to its low ion energy.
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81.65.-b Surface treatments
79.20.Rf Atomic, molecular, and ion beam impact and interactions with surfaces
61.80.Jh Ion radiation effects

Reaction probability for the spontaneous etching of silicon by CF3 free radicals

Robert M. Robertson, David M. Golden, and Michel J. Rossi

J. Vac. Sci. Technol. B 6, 1632 (1988); http://dx.doi.org/10.1116/1.584421 (9 pages) | Cited 6 times

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The spontaneous thermal etching of silicon by CF3 free radicals has been studied in a very‐low‐pressure photolysis reactor. The radical is produced by infrared multiphoton dissociation of either hexafluoracetone or CF3 I, and is allowed to react with a temperature‐controlled silicon sample (560–745 K). Mass spectrometry is used to measure the extent of dissociation of the precursor gas and the formation of product molecules, C2 F6 and SiF4 . The etch rate of the silicon is determined from the SiF4 production. Resonance‐enhanced multiphoton ionization of CF3 is used to determine the density and time history of the radical in the reactor. The measurements of the etch rate and CF3 density are combined to derive the reaction probability. CF3 etches silicon much more slowly than F atoms and at a rate comparable to molecular F2 . A carbon layer, that is deposited on the silicon by the radicals, inhibits, but does not stop, further etching. Experiments on the etching of silicon by F2 were performed both to validate the reactor design and to prepare the silicon surface for the CF3 studies.
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81.65.-b Surface treatments
82.65.+r Surface and interface chemistry; heterogeneous catalysis at surfaces
79.20.Rf Atomic, molecular, and ion beam impact and interactions with surfaces

Selective dry etching of GaAs over AlGaAs in SF6/SiCl4 mixtures

S. Salimian and C. B. Cooper

J. Vac. Sci. Technol. B 6, 1641 (1988); http://dx.doi.org/10.1116/1.584422 (4 pages) | Cited 9 times

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Reactive ion etching of GaAs with high selectivity over Al0.29Ga0.71As in SF6/SiCl4 mixtures was studied. Selectivity, surface morphology, and anisotropy were investigated over a wide range of pressures (15–100 mTorr), dc bias values (−20 to −300 V), and SF6‐to‐SiCl4 ratios (0–0.5). Higher pressures, lower dc biases, and higher SF6/SiCl4 ratios increase the GaAs‐to‐AlGaAs selectivity. Electron spectroscopy for chemical analysis indicates that the formation of nonvolatile aluminum fluoride on AlGaAs is responsible for the selective etch process.
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81.65.-b Surface treatments
79.20.Rf Atomic, molecular, and ion beam impact and interactions with surfaces
68.35.B- Structure of clean surfaces (and surface reconstruction)
68.55.-a Thin film structure and morphology

The role of aluminum in selective reactive ion etching of GaAs on AlGaAs

K. L. Seaward, N. J. Moll, and W. F. Stickle

J. Vac. Sci. Technol. B 6, 1645 (1988); http://dx.doi.org/10.1116/1.584423 (5 pages) | Cited 4 times

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We have studied the role of aluminum in the formation of an etch barrier at the GaAs/ Alx Ga1−x As interface during reactive ion etching in CCl2 F2 plasma. The minimum Alx Ga1−x As thickness needed to form the barrier is Al mole fraction dependent and was determined with etching experiments monitored by optical emission spectroscopy. Effective Alx Ga1−x As layers for forming an etch barrier are 275 Å for x=0.02, 22 Å for x=0.10, 15 Å for x=0.15, 12 Å for x=0.20, and 9 Å for x=0.30. For all Al mole fractions except x=0.02, these thicknesses correspond to a sheet dose equivalent to 3/4 of a monolayer of Al in the original Alx Ga1−x As layer. Barrier layers for x=0.02, 0.10, 0.25, and 0.30 were examined without air exposure by angle‐dependent x‐ray photoelectron spectroscopy. For samples that are not overetched, the surface is covered with ∼20 Å of AlF3 intermixed with a gallium halide containing chlorine and fluorine and is depleted of arsenic. For substantially overetched barriers, a 30 Å layer is formed with gallium halide present at the surface, AlF3 found farther in, and arsenic depletion throughout the barrier. During extreme overetch, barrier layers on the order of tens of Å in thickness were not etched away and yet did not completely prevent very slow etching of underlying GaAs. Barrier layers on the order of 60 Å in thickness did prevent etching of underlying GaAs. Collectively the data suggest that the role of Al is formation of AlF3 exclusively and that only this compound is responsible for stopping the GaAs etch.
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81.65.-b Surface treatments
79.20.Rf Atomic, molecular, and ion beam impact and interactions with surfaces
82.65.+r Surface and interface chemistry; heterogeneous catalysis at surfaces
68.35.Fx Diffusion; interface formation

Photoemission investigation of Ge and SiGe alloy surfaces after reactive ion etching

S. W. Robey, A. A. Bright, G. S. Oehrlein, S. S. Iyer, and S. L. Delage

J. Vac. Sci. Technol. B 6, 1650 (1988); http://dx.doi.org/10.1116/1.584424 (7 pages) | Cited 6 times

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Photoemission spectra were obtained from Ge surfaces after reactive ion etching with CF4 and CF4/H2 mixtures. These measurements indicate a surface layer of fluorinated Ge species as well as adsorbed carbon and CFx species. The shifted intensity in the Ge(2p3/2) core level suggests a layer of about 1 to 2 layers of GeFx, with x∼2–3. The accumulation of CFx overlayer increases with increasing H2 to CF4, but comparisons with Si etched under identical conditions indicate that there is less steady‐state film deposition of Ge during reactive ion etching than on Si. Thus, an increased thickness of carbonaceous overlayer on Ge compared to Si is unlikely to be the explanation for the observed drop in the selectivity toward etching Ge over Si with increasing hydrogen addition. Reactive ion etching of a Si35Ge65 alloy was also investigated. Here, photoemission indicated a surface layer of GeFx similar to that found on pure Ge, but little evidence of SiFx species. The composition of the surface is enriched in Ge for about 3–5 layers.
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81.65.-b Surface treatments
79.20.Rf Atomic, molecular, and ion beam impact and interactions with surfaces

High‐throughput and fully automated system for molecular‐beam epitaxy

Junro Sakai, Shun‐ichi Murakami, Kimiaki Hirama, Tetsuo Ishida, and Zenjiro Oda

J. Vac. Sci. Technol. B 6, 1657 (1988); http://dx.doi.org/10.1116/1.584425 (5 pages)

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A new high‐throughput and fully automated system for molecular‐beam epitaxy was developed by employing multiple substrate mount pallets and automatic pallet transfer mechanisms. The geometrical configuration between pallet and effusion cells was optimized to achieve the uniformity of thickness and carrier concentration of epitaxial layer better than ±2% within a pallet. The throughput was more than 70 2‐in. wafers per day for the growth of AlGaAs/GaAs two‐dimensional electron gas structure. In a typical two‐dimensional electron gas structure with a 6‐nm spacer layer, the variation of sheet electron mobility closed in 7.5 to 10×104 cm2 /V s at 77 K over growth run to run. By improving the heater structure of the Ga effusion cell, the Ga‐related oval defect density was found to be reduced <1 cm −2. The total surface defect density was reduced to <50 cm−2 by preventing the particulate contamination on the growth surface. Moreover, unintentionally doped GaAs layer was dominated by a donor, whose concentration was lower than 1×1014 cm−3, and electron mobility was 145 000 cm2 /V s at 77 K.
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81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
73.40.Kp III-V semiconductor-to-semiconductor contacts, p-n junctions, and heterojunctions
73.61.Ey III-V semiconductors
68.35.Dv Composition, segregation; defects and impurities

Barrier height modification of metal/germanium Schottky diodes

C. C. Han, E. D. Marshall, F. Fang, L. C. Wang, S. S. Lau, and D. Voreades

J. Vac. Sci. Technol. B 6, 1662 (1988); http://dx.doi.org/10.1116/1.584426 (5 pages) | Cited 3 times

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Germanium is experiencing a resurgence of interest due to superior intrinsic properties and recently overcome technological limitations. This paper addresses the problem of Schottky barrier height control. The Fermi level of metal/Ge contacts is pinned at between 0.54 and 0.61 eV below the conduction‐band edge, independent of the contacting metallization. We compare the modulation of effective barrier height by means of shallow ion implantation, epitaxial growth, and diffusion from a doped level to create a thin, highly doped interfacial region. Lowering of n‐type contacts from 0.54 to 0.4 eV, at room temperature, and enhancement of p‐type contacts from 0.09 to 0.23 eV, at 77 K, have been achieved. Experimental results are compared to computer model calculations.
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73.30.+y Surface double layers, Schottky barriers, and work functions
73.40.Ns Metal-nonmetal contacts
73.20.At Surface states, band structure, electron density of states
73.21.-b Electron states and collective excitations in multilayers, quantum wells, mesoscopic, and nanoscale systems

Baffle‐free refractory dimer arsenic source for molecular‐beam epitaxy

T. J. Mattord, V. P. Kesan, G. E. Crook, T. R. Block, A. C. Campbell, D. P. Neikirk, and B. G. Streetman

J. Vac. Sci. Technol. B 6, 1667 (1988); http://dx.doi.org/10.1116/1.584427 (4 pages) | Cited 2 times

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A refractory, two‐zone, large‐capacity, baffle‐free arsenic cracking source for molecular‐beam epitaxy is presented. The new features of this design include the use of a molybdenum tube to provide efficient cracking, a horizontal sublimator at a right‐angle geometry to the cracking section, a baffle‐free design, and the use of expanded tantalum heating filaments. High‐efficiency cracking is obtained at cracking tube temperatures between 750 and 1050 °C. Bulk GaAs and GaAs/AlGaAs heterostructures grown using this source exhibit good electrical and optical properties, with clear improvements in electrical behavior when compared to an As4 source. We believe this source design can be easily applied to other column V materials such as phosphorus and antimony.
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81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
07.77.-n Atomic, molecular, and charged-particle sources and detectors

Correct substrate temperature monitoring with infrared optical pyrometer for molecular‐beam epitaxy of III–V semiconductors

T. Mizutani

J. Vac. Sci. Technol. B 6, 1671 (1988); http://dx.doi.org/10.1116/1.584428 (7 pages) | Cited 10 times

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Correct GaAs and InP substrate temperatures are monitored with an infrared optical pyrometer. The temperature calibration for the pyrometer is carried out with the help of an emissivity change, produced by an eutectic reaction, in the Al deposited Si substrate. It is found that large apparent temperature differences exist between n+‐ (or p+‐) and semi‐insulating GaAs and InP substrates when constant emissivity is assumed. The temperature difference is ∼60 °C at 500 °C for InP, and 10–30 °C for GaAs. The temperature differences are found to increase with increasing substrate temperature. A model calculation is given for substrate temperature monitoring with an infrared optical pyrometer. The apparent temperature difference is attributed to the presence of optical absorption mechanisms in an n+‐ (and p+‐) substrate and its absence in a semi‐insulating substrate. The limiting temperature of congruent evaporation and the native oxide evaporation temperature for GaAs are measured with an accurately calibrated infrared optical pyrometer. They are found to be 612±10 °C and ∼585 °C, respectively.
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81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
07.20.Ka High-temperature instrumentation; pyrometers
68.35.-p Solid surfaces and solid-solid interfaces: structure and energetics

Characterization and optimization of low‐pressure chemical vapor deposited tungsten silicide using screening and response surface experimental designs

Thomas E. Clark

J. Vac. Sci. Technol. B 6, 1678 (1988); http://dx.doi.org/10.1116/1.584429 (10 pages) | Cited 2 times

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Low‐pressure chemical vapor deposited WSiX has been characterized and optimized through the use of screening and modeling experimental designs. In the screening study, the effects of temperature, pressure, gas flow rates, and a predeposition treatment were determined for a list of properties which included deposition rate, resistivity, stress, stoichiometry, oxidation rate, particle generation, and resistance to chemical attack. Over the process domain covered, temperature, WF6 flow rate, and SiH4 flow rate were found to affect deposition rate, resistivity, film stress, and stoichiometry while stoichiometry was also affected by pressure. WSiX films produced in the screening study ranged in stoichiometry from X=2.1 to 3.0. The oxidation rate of these samples was found to be insensitive to deposition conditions and unrelated to the as‐deposited stoichiometry. As‐deposited and annealed film stress were found to decrease linearly with increasing silicon content of the as‐deposited films. Similarly, the as‐deposited and postannealed resistivity of WSiX films were found to be a function of the initial stoichiometry. Manufacturability related properties such as particle generation, chemical resistance, and uniformity measures involving sheet resistance, resistivity, and film thickness were found to be largely insensitive to the process factors studied. Response surface models were developed for deposition rate, annealed resistivity, annealed stress, and stoichiometry and were used to guide the final process optimization. The optimized process window was relatively large and yielded WSiX films with an annealed (950 °C, 30 min) resistivity of ∼75 μΩ cm, an as‐deposited Si/W atom ratio of ∼2.5, annealed tensile stress of ∼1.2×1010 dyne/cm2, and deposition rates of 9 to 10.5 Å/s.
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81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
68.55.Nq Composition and phase identification
68.60.Bs Mechanical and acoustical properties
73.61.At Metal and metallic alloys

Surface science studies of semiconductor growth processes

D. S. Buhaenko, S. M. Francis, P. A. Goulding, and M. E. Pemble

J. Vac. Sci. Technol. B 6, 1688 (1988); http://dx.doi.org/10.1116/1.584430 (6 pages) | Cited 2 times

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A new approach to the study of semiconductor growth mechanisms is described which utilizes surface science and related photon‐based techniques. It is possible to study growth processes over the pressure range 5×10−11 to 103 mbar through the use of an isolatable atmospheric pressure reactor described briefly. As an illustration of the potential of the surface science approach, the effectiveness of the reducing hydrogen atmosphere employed in the pregrowth bake of a GaAs (100) metal‐organic vapor phase epitaxy (MOVPE) substrate in removing surface carbon and oxygen is determined using Auger electron spectroscopy. It is shown that at a pressure of 0.5 mbar of H2, temperatures as low as 600 K are sufficient to remove the surface carbon and oxygen contamination present on the substrate following wet chemical etching and heating in ultrahigh vacuum. This result implies that the conventional MOVPE sample bake at high temperatures (>850 K), in H2 and AsH3 is not necessary to produce clean substrates. Following the H2 treatment the GaAs(100) surface gives rise to a (1×1) low‐energy electron diffraction pattern suggesting that it has been stabilized towards reconstruction via hydrogen chemisorption.
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68.35.B- Structure of clean surfaces (and surface reconstruction)
81.15.Kk Vapor phase epitaxy; growth from vapor phase
68.55.-a Thin film structure and morphology

Projection patterned Si doping of GaAs in ambient SiH4 gas by a KrF excimer laser

Koji Sugioka and Koichi Toyoda

J. Vac. Sci. Technol. B 6, 1694 (1988); http://dx.doi.org/10.1116/1.584163 (4 pages) | Cited 4 times

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Potential application of a projection system with reduction optics to the patterned doping process has been demonstrated. A KrF excimer laser beam is projected on GaAs substrates enclosed in a SiH4 gas ambient cell to achieve the Si doping with a field size of 5×5 mm2. At a laser fluence of 380 mJ/cm2, the n‐type conduction layer with a surface carrier density of 2.27×1014 cm−2 in the semi‐insulating GaAs substrate and with an activation efficiency of ∼81% can be obtained. The minimum linewidth of 2.5 μm is discussed together with temperature profiles calculated by transient heat conduction in the substrate.
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61.72.U- Doping and impurity implantation

Absorption properties of the bottom novolac layer in multilayer resist systems

Hideo Namatsu

J. Vac. Sci. Technol. B 6, 1698 (1988); http://dx.doi.org/10.1116/1.584164 (4 pages) | Cited 1 time

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A novolac resin suitable for the bottom planarizing layer in multilayer resist systems is discussed from the standpoint of exposure wavelength absorption. Absorption by the bottom planarizing layer is crucial to reduce the reflected light from the resist–substrate interface. It was clarified that the absorption of phenol novolac resin was higher than that of the cresol novolac resin under the same baking conditions. From infrared and nuclear magnetic resonance analysis, it was found that carbonyl structures were formed in the novolac resin after baking. In addition, cross‐linking was found to occur at the methylene bridges in the phenol novolac resins. These factors seem to cause the absorption maxima to shift to a longer wavelength.
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85.40.Hp Lithography, masks and pattern transfer
78.66.Qn Polymers; organic compounds

Properties of WSix using dichlorosilane in a single‐wafer system

T. H. Tom Wu, Richard S. Rosler, Bruce C. Lamartine, Richard B. Gregory, and Harland G. Tompkins

J. Vac. Sci. Technol. B 6, 1707 (1988); http://dx.doi.org/10.1116/1.584165 (7 pages) | Cited 3 times

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Chemical vapor deposition of tungsten silicide (WSix) from WF6 and SiH2Cl2 [JB Price, S. Wu, Y.Chow, and J. Mendonca, Semicon West (1986)] at higher deposition temperatures (450–650 °C) than the conventional WF6 and SiH4 (250–400 °C) process has been characterized using a plasma enhanced, single‐wafer, cold‐wall, radiantly heated system with temperature control utilizing a thermocouple in contact with the backside of the wafer. Film properties such as silicon to tungsten ratio, fluorine and chlorine concentration, resistivity, and film stress were studied as a function of substrate temperature, reactant composition, and flow rates. The film composition was measured by Rutherford backscattering spectrometry. The silicon to tungsten ratio is a function of deposition temperature at a fixed flow (x varying from 2.0–2.8 through the temperature range of 450–650 °C). The as‐deposited resistivity is also a strong function of deposition temperature. The chlorine and fluorine distributions in the WSix film were measured using secondary ion mass spectrometry. The fluorine concentration was found to be much lower than levels reported by conventional WF6/SiH4 chemistry with as‐deposited values of 9×1015 to 3×1018/cm3 compared to 1.3×1020 cm3 by M. Fukumoto and T. Ohzone [Appl. Phys. Lett. 50, 894 (1987)].
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68.55.Nq Composition and phase identification
73.61.At Metal and metallic alloys
68.60.Bs Mechanical and acoustical properties
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)

Study on oxygen behavior during Ti/Si and Ti/SiO2 interactions

Bing‐Zong Li, Shi‐Fang Zhou, Feng Hong, Guo‐Bao Jiang, Ping Liu, Ai‐Ming Zhang, and Ming Chao

J. Vac. Sci. Technol. B 6, 1714 (1988); http://dx.doi.org/10.1116/1.584166 (7 pages) | Cited 1 time

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For practical titanium silicide device application the oxygen behavior in the solid phase interaction is important to study. The Ti/Si and Ti/SiO2 interaction by the NH3 plasma assisted thermal annealing and oxidation of Ti/SiO2 and TiSi2/Si in a wet oxygen ambient were investigated by Auger electron analysis. The characteristic Auger spectral line shapes of Ti, O, and Si and their changes in compounds were measured. The experiment clearly demonstrated the oxygen snowplow effect during TiSi2 and TiN growth, and a stable SiO2 can be grown on TiSi2/Si directly or through a layer of TiO2.
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68.35.Fx Diffusion; interface formation
81.15.-z Methods of deposition of films and coatings; film growth and epitaxy

Tungsten chemical vapor deposition characteristics using SiH4 in a single wafer system

Richard S. Rosler, John Mendonca, and M. John Rice

J. Vac. Sci. Technol. B 6, 1721 (1988); http://dx.doi.org/10.1116/1.584167 (7 pages) | Cited 5 times

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Several workers have recently begun using silane as a high‐rate, low‐temperature alternative to hydrogen for the reduction of WF6 in the chemical vapor deposition of W. The deposition and film characteristics of both selective and blanket W using this new chemistry are explored in a radiantly heated single wafer system using closed‐loop temperature control with a thermocouple in direct contact with the backside of the wafer. Selective W deposition rates of up to 1.5 μm/min were measured over the temperature range 250–550 °C with blanket W rates typically 2–5× lower. Resistivity is in the 10–15 μΩ cm range at 300 °C for SiH4/WF6 ratios of 0.2 to 1.0, while above 400 °C the range is 7.5–8.5 μΩ cm. Si content in the W films is quite low at 1016 to 1017 atoms/cm3. Adhesion to silicon is excellent at temperatures of 350 °C and above. Selective W using SiH4 reduction for doped silicon contact fill shows none of the consumption or encroachment problems common to H2 reduction, although selectivity is more sensitive. Contact resistance for p+ and n+ silicon contacts are comparable to aluminum controls and to previously published data. Blanket deposition into narrow geometries gives ≥90% step coverage and without keyholes in the 250–450 °C deposition temperature range. For low‐SiH4 flows, deposition at 500 °C causes small keyholes, while at 550 °C even larger keyholes result. At higher SiH4 flows, keyholes are typically not seen from 250 to 550 °C. The SiH4‐reduced films are much smoother as indicated by reflectivities that are 2–4×higher than for the H2‐reduced films.
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81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
68.55.Ln Defects and impurities: doping, implantation, distribution, concentration, etc.
73.61.At Metal and metallic alloys
68.60.Bs Mechanical and acoustical properties

Formation and properties of rapid thermally annealed TiSi2 on lightly doped and heavily implanted silicon

K. Shenai, P. A. Piacente, N. Lewis, G. A. Smith, M. D. McConnell, and B. J. Baliga

J. Vac. Sci. Technol. B 6, 1728 (1988); http://dx.doi.org/10.1116/1.584168 (6 pages) | Cited 2 times

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Detailed material and electrical characteristics of rapid thermally annealed (RTA) TiSi2 on doped silicon are presented using transmission electron microscopy, Rutherford backscattering spectrometry, secondary ion mass spectrometry (SIMS), Auger analysis, and four‐point probe measurements. TiSi2 films with varying sheet resistances were formed on lightly doped and heavily arsenic and phosphorus implanted 〈100〉 silicon by rf sputtering titanium and forming the silicide using two‐step flash anneals at different temperatures. It is shown that the silicide sheet resistance is a sensitive function of the silicon surface condition prior to titanium sputtering; in particular, silicide films formed on heavily implanted silicon had significantly higher sheet resistance compared to films formed under identical conditions on lightly doped prime silicon. The higher silicide sheet resistance resulted because of the surface damage created during arsenic and phosphorus implantation and higher silicon dopant concentration. The RTA silicide films showed excellent film properties across 4‐in.‐diam wafers with good thickness uniformity and minimal sheet resistance variations compared to furnace annealed samples. Detailed SIMS and Auger analyses showed minimal film contamination and negligible dopant redistribution for RTA silicided wafers.
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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
73.25.+i Surface conductivity and carrier phenomena
81.15.Cd Deposition by sputtering

TiSi2 strap formation by Ti–amorphous‐Si reaction

H. J. W. van Houtum, A. A. Bos, A. G. M. Jonkers, and I. J. M. M. Raaijmakers

J. Vac. Sci. Technol. B 6, 1734 (1988); http://dx.doi.org/10.1116/1.584169 (6 pages) | Cited 1 time

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This report describes the formation of a TiSi2 strap in combination with the self‐aligned titanium silicide (salicide) technology. The TiSi2 strap is formed by reaction of amorphous silicon (a‐Si) with the underlying Ti layer. It was determined that sputter deposition of the Ti and a‐Si had to be done in one deposition cycle, otherwise interface contamination would prevent the Ti–a‐Si reaction and give rise to extensive silicon diffusion from the active areas. Since TiSi2 straps are formed over diffusion areas as well as over oxide surfaces, the influence of the substrate on the Ti/a‐Si reaction was determined. It was found that for straps deposited on oxide substrate the properties of the silicide layer formed were determined by the Ti/a‐Si atomic ratio. A titanium‐rich strap resulted in a high‐resistivity silicide layer due to TiSi compound formation. Stoichiometric straps formed low‐resistivity TiSi2 layers with a thin‐TiN top layer and silicon‐rich straps also resulted in a low‐resistivity TiSi2 layer but with a silicon enrichment at the surface. On a mono‐Si substrate no influence of the sputtered Ti/a‐Si atomic ratio could be found. Only low‐resistivity TiSi2 layers were formed. In case of silicon‐rich Ti/a‐Si ratio the excess silicon disappears from the layer and regrows onto the Si substrate. The roughness of TiSi2 straps, mainly observed for stoichiometric or silicon‐rich straps on oxide substrates, was found to be related to the presence of argon (and probably hydrogen) incorporated in the layer during sputter deposition. Special attention was paid to strap formation at oxide/diffusion area edges. Possible void formation by local silicon consumption could not be detected. Strap/TiSi2 salicide transitions are also very smooth and showed no substrate defects.
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85.40.Ls Metallization, contacts, interconnects; device isolation
82.65.+r Surface and interface chemistry; heterogeneous catalysis at surfaces
68.55.Nq Composition and phase identification
73.61.Cw Elemental semiconductors
73.61.Jc Amorphous semiconductors; glasses
73.61.Le Other inorganic semiconductors

Selectively silicided vertical power double‐diffused metal–oxide semiconductor field effect transistors for high‐frequency power switching applications

K. Shenai, P. A. Piacente, C. S. Korman, and B. J. Baliga

J. Vac. Sci. Technol. B 6, 1740 (1988); http://dx.doi.org/10.1116/1.584170 (6 pages)

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A new power field effect transistor (FET) structure with selectively silicided gate and source regions is described. This structure simultaneously lowers the gate sheet resistance and source contact resistance. Vertical power double‐diffused metal‐oxide semiconductor field effect transistors fabricated using this technology have a specific on‐resistance of 0.53 mΩ cm2 for devices capable of blocking 50 V in the off‐state. Devices with cell density as high as 4 million cells/in.2 and die size as large as 200×220 mil have been successfully fabricated with excellent gate yield. These results represent the best ever reported forward conductivities for any type of power FET in the 50‐V reverse blocking range. Comparison of selectively silicided power FET’s with state of the art commercial nonsilicided FET’s indicates that the former have an order‐of‐magnitude lower gate sheet resistance, 8× smaller on‐resistance, and 2× smaller input capacitance.
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85.30.Tv Field effect devices
84.32.Dd Connectors, relays, and switches
84.70.+p High-current and high-voltage technology: power systems; power transmission lines and cables

The morphologies and characteristics of reactively formed TaSi2 films

Tao Jiang, Zhang Guobin, Wu Guoying, and Du Anyan

J. Vac. Sci. Technol. B 6, 1746 (1988); http://dx.doi.org/10.1116/1.584171 (3 pages)

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Morphologies and characteristics of the surface and interface of TaSi2/Si and TaSi2/poly‐Si structures reactively formed by furnace annealing and rapid thermal annealing (RTA) have been investigated thoroughly. Scanning electron microscopy and transmission electron microscopy (cross section) results show that the morphologies of the annealed samples were uneven, but the surface and interface of RTA samples were better than that of furnace annealed samples. The specific contact resistivity of TaSi2 to n+ ‐Si substrates with Kelvin structure was measured. The contact resistivity increased as the annealing temperature increased, but was lower for RTA samples than for furnace annealed samples. Sheet resistance measurement, x‐ray diffraction, and Auger electron spectroscopy analysis techniques were used to monitor the formation of TaSi2 films.
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68.55.-a Thin film structure and morphology
73.40.Cg Contact resistance, contact potential
68.35.B- Structure of clean surfaces (and surface reconstruction)
85.40.Ls Metallization, contacts, interconnects; device isolation

A new x‐ray diffractometer design for thin‐film texture, strain, and phase characterization

P. A. Flinn and G. A. Waychunas

J. Vac. Sci. Technol. B 6, 1749 (1988); http://dx.doi.org/10.1116/1.584172 (7 pages) | Cited 15 times

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Powder diffraction techniques are potentially extremely useful for the characterization of a variety of metallic thin films which are used as interconnection materials in very large scale integrated (VLSI) devices. Phase identification, texture determination, elastic strain measurement, and grain size distribution can, in principle, be obtained nondestructively. Although x‐ray techniques have long been applied to bulk materials for these purposes, conventional x‐ray equipment, particularly the widely used Bragg–Brentano powder diffractometer, is often unsuitable for use on these thin films. High‐angle reflections are extremely weak, strong texture renders many reflections inaccessible, and reflections from the silicon single crystal substrate can be a serious interference. The Seemann–Bohlin focusing geometry with a fixed low angle of incidence provides improved intensities and reduced substrate interference, but is unsuitable for texture determinations or strain measurements. We have designed a unique instrument, called a generalized focusing diffractometer (GFD), which combines the intensity advantages of a focusing geometry with the flexibility necessary for texture and strain measurements. The key capability is the arbitrary setting of the incidence beam angle α, independent of the Bragg angle 2θ, which allows accessing of practically any desired set of Bragg diffraction planes in the sample. The focusing condition is achieved in such a geometry by computer control of the sample to detector (receiving) slit distance. Four distinct modes of operation are possible with the GFD: Bragg–Brentano (BB), Seemann–Bohlin (SB), texture analysis (TA), and strain analysis (SA). The BB and SB modes are conventional, except that the incident beam angle α, can be varied arbitrarily in the SB mode, allowing small 2θ values to be explored. In the TA mode, the sample is rocked through a range of incidence angles while the detector is fixed in 2θ, but continuously positioned relative to the sample for optimal focus. In the SA mode, profile scans of particular Bragg reflections are obtained at varying beam incidence angles while the focusing conditions are continuously maintained by
detector positioning. Several examples illustrate the application of the GFD. Untextured powdered Si provides a comparison of BB and SB modes. A film of 5 nm of Au on a glass substrate with well‐developed (111) texture further illustrates the differences between these modes, and indicates the sensitivity of the GFD focusing geometry. A sample consisting of alternating layers of 50‐nm sputtered amorphous TiSi2 and 500 nm of polycrystalline Al–Si on a Si substrate is examined in the BB and SB mode both as synthesized and after two thermal cycles at 450 °C. The scans indicate well‐developed texture in the Al–Si film and the thermally induced growth of silicide crystallites. A sample of highly textured 1000‐nm Al sputtered on Si is examined in TA mode to demonstrate this capability. Finally, SA scans on a sample of highly textured 750‐nm Al‐1% Sm sputtered on Si have been used to determine the strain in the thin film. The results are compared with those obtained by utilizing the wafer curvature method of strain analysis.
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61.05.cp X-ray diffraction
85.40.Ls Metallization, contacts, interconnects; device isolation
68.55.-a Thin film structure and morphology

An investigation of hydrogen concentration profiles in as‐deposited and annealed chemical vapor deposited SiO2 films

Joseph Z. Xie, Shyam P. Murarka, Xin S. Guo, and William A. Lanford

J. Vac. Sci. Technol. B 6, 1756 (1988); http://dx.doi.org/10.1116/1.584173 (7 pages) | Cited 6 times

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Hydrogen concentration depth profiles in as‐deposited and annealed chemical vapor deposited silicon oxide [2% P glass, 8% P glass, tetraethylorthosilicate (TEOS), phosphorous‐doped TEOS and plasma oxide] films were measured using the nuclear reaction profiling technique with a 6.4 MeV 15N ion beam. The H2/Ar annealing of 450 °C for 60 min in furnace and the rapid thermal annealing at 1000 °C for 60 s in O2 or H2/Ar were carried out. It is found that hydrogen concentration is in the range 1021–1022 per cm3 in as‐deposited films. Annealing at high temperatures, even in hydrogen containing medium, lowers the hydrogen concentration in all films. The hydrogen concentration gradually increased with time when the films were left in the room environment. The electrical properties of the oxide are found to be related to the presence of hydrogen. The observed correlation between the flatband voltage and the hydrogen concentration is presented and discussed.
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68.55.Ln Defects and impurities: doping, implantation, distribution, concentration, etc.
73.61.Ng Insulators
81.40.Ef Cold working, work hardening; annealing, post-deformation annealing, quenching, tempering recovery, and crystallization

Thermal stability of polyimidesiloxane (SIM‐2000)

S. P. Sun, S. P. Murarka, and C. J. Lee

J. Vac. Sci. Technol. B 6, 1763 (1988); http://dx.doi.org/10.1116/1.584174 (5 pages)

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Polyimides are finding increased use in integrated circuits as a dielectric and protective layer. Its low dielectric constant, ease of application, and ability to planarize the surfaces, permit their incorporation into very large scale integrated and ultra‐large scale integrated circuit processing. However, there is no single polyimide available which possesses high‐temperature stability at temperature >300 °C. A newer class of polymers called polyimidesiloxane (SIM‐2000), resulting from the modification of polyimides by special equilibrated silicone blocks, has been found superior to commercial polyimides especially with respect to their high‐temperature stability. In this paper, we present the results of our investigation of the high‐temperature stability of a few polyimidesiloxane materials spun on various substrates including Si, SiO2, and Al.
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85.40.Ls Metallization, contacts, interconnects; device isolation
68.60.Dv Thermal stability; thermal effects
77.55.-g Dielectric thin films
81.15.-z Methods of deposition of films and coatings; film growth and epitaxy

Self‐limiting advancing gates for GaAs metal–semiconductor field effect transistors

M. G. Fernandes, C. C. Han, W. Xia, S. S. Lau, and S. P. Kwok

J. Vac. Sci. Technol. B 6, 1768 (1988); http://dx.doi.org/10.1116/1.584154 (5 pages) | Cited 2 times

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The threshold voltage of GaAs metal–semiconductor field effect transistors (MESFET’s) can be controlled by the use of buried gates. The controlling mechanism is through the alloying reaction between the gate material and the GaAs substrate. Although this can be done by choosing suitable annealing conditions, the alloying reaction may continue to proceed if the operating temperature of the device is high and/or for long‐device field service. To overcome this problem a Ni–W alloy is chosen as the gate metallization. The idea here is to utilize the concentration dependence of the interfacial reactivity between the Ni–W alloy and the GaAs to limit the alloying reaction. Below 400 °C Ni leaches out of the Ni–W alloy to react with the GaAs, and W does not participate in the reaction. As Ni leaches out, the composition of W at the interface increases and this appears to choke off the reaction, resulting in a self‐limiting reaction for buried gates. We found that a thin‐Pd (20 Å) layer placed at the GaAs/NiW interface is helpful in improving the interfacial reaction uniformity. It was found that the threshold voltage of GaAs MESFET’s can be adjusted to any desired value using this approach. After the desired threshold voltage has been obtained, the mean value of the threshold voltage of 30 field effect transistors (FET’s) is found to stabilize to ±5 mV with a standard deviation of ±27 mV at a temperature of 235 °C for a period of at least 90 h. The activation energies for the change in threshold voltage at different stages of anneal have also been estimated.
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85.30.Tv Field effect devices
85.30.De Semiconductor-device characterization, design, and modeling
73.40.Ns Metal-nonmetal contacts

Temperature dependence of GaAs metal–semiconductor field effect transistor threshold voltage

C. L. Liang, H. Wong, R. H. Mutikainen, R. M. Fourkas, N. W. Cheung, M. Sokolich, S. P. Kwok, and S. K. Cheung

J. Vac. Sci. Technol. B 6, 1773 (1988); http://dx.doi.org/10.1116/1.584155 (6 pages) | Cited 2 times

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We have investigated the temperature dependence of threshold voltage (Vth) of n‐channel GaAs metal–semiconductor field effect transistors with different gate materials and structures. It is found that Vth increases by 0.3–0.4 V as temperature decreases from 350 to 80 K. The Vth versus temperature relationship is approximately linear. The amount of Vth shift is independent of channel length from 0.8 to 3 μm and it does not strongly depend on the gate material used. Similar Vth increases are observed for different channel doping methods, such as ion implantation and molecular‐beam epitaxy growth. Different GaAs substrates only show a small effect on the Vth temperature dependence. Calculations show that Fermi‐level shift and energy‐gap expansion with decreasing temperature account for only a fraction of the observed change in Vth. Our measurements indicate that the extra Vth shift is not mainly due to deep‐level traps within the channel. Results from C–V measurements on metal/GaAs diodes suggest that build‐in voltage changes with temperature are principally responsible for the Vth shift.
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85.30.Tv Field effect devices
73.40.Ns Metal-nonmetal contacts

The effects of annealing encapsulant and ambient on the barrier height of WNx/GaAs contact and self‐aligned gate field effect transistor fabrication

S. K. Cheung, S. P. Kwok, A. Kaleta, K. M. Yu, J. M. Jaklevic, C. L. Liang, N. W. Cheung, and E. E. Haller

J. Vac. Sci. Technol. B 6, 1779 (1988); http://dx.doi.org/10.1116/1.584156 (6 pages) | Cited 1 time

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It was found that the barrier height of thermally stable WNx /GaAs Schottky contacts can be enhanced by a high‐temperature annealing technique. In this study, the WNx /GaAs contact was annealed under different conditions including (i) furnace annealing under SiO2 encapsulant with N2 and arsine ambient, (ii) furnace annealing under arsine‐overpressure capless annealing, and (iii) rapid thermal annealing (RTA) under SiO2 encapsulant and argon ambient. The temperature range for furnace annealing was 700–850 °C and for RTA, 700–950 °C. RBS analysis of all samples revealed no detectable interdiffusion at the WNx /GaAs interface up to an annealing temperature of 850 °C for furnace annealing and 950 °C for RTA. The Schottky barrier height increased from 0.59 eV, as deposited, to the commonly reported value of 0.72 to 0.74 eV, at the optimum temperatures for all the annealing conditions mentioned, with one exception. Barrier heights as high as 0.8 eV were obtained using furnace annealing under SiO2 encapsulant and arsine ambient. This corresponds to an enhancement up to 80 meV and is significant for improving the noise margin of GaAs integrated circuits, which is typically 200–300 mV. However, such annealing conditions also caused leakage current localized at the perimeter of the WNx /GaAs contact. Such a leakage current can be removed by slight mesa etching of the GaAs at the edges. WNx SAGFET structures were fabricated using both capless furnace annealing in an arsine ambient and RTA in an argon ambient. It was found that capless furnace annealing resulted in significantly better immunity to short‐channel effects than that of RTA. Transconductance as high as 300 mS/mm was obtained with a gate length of 0.5 μm.
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73.30.+y Surface double layers, Schottky barriers, and work functions
81.40.Rs Electrical and magnetic properties related to treatment conditions
85.30.Tv Field effect devices
73.40.Ns Metal-nonmetal contacts

WSix refractory metallization for GaAs metal–semiconductor field‐effect transistors

A. G. Lahav, C. S. Wu, and F. A. Baiocchi

J. Vac. Sci. Technol. B 6, 1785 (1988); http://dx.doi.org/10.1116/1.584157 (11 pages) | Cited 20 times

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WSix thin films on GaAs substrates have been investigated for potential use as refractory gates for self‐aligned metal–semiconductor field‐effect transistor (MESFET) devices. Films with Si/W ratio in the range of 0.19 to 1.76 have been dc magnetron cosputtered. The deposition parameters were optimized to produce adherent films with low stress and minimal impurity content. In order to serve as a refractory gate, the WSix film should perform as a diffusion barrier. The WSi0.45 films satisfied this requirement by having the highest crystallization temperature of 875 °C. Such films remained amorphous following the high‐temperature dopant activation annealing (800 °C), thus reducing Ga and As outdiffusion and preventing pit formation in GaAs under the gate. I–V and C–V measurements were used to characterize contact electrical properties such as barrier height, ideality factor, and carrier concentration. A simulated threshold voltage shift for MESFET structure was obtained by modeling diode results. The WSi0.45 films were characterized by the most stable Schottky contact to GaAs (ϕB =0.75 eV, n=1.1) and showed minimal shift in carrier concentration and threshold voltage after annealing at 800 °C. In addition, the effect of impurities on contact properties was investigated. The presence of Zn at the WSix/ GaAs interface caused drastic reduction in carrier concentration and increased Schottky barrier height up to 0.9 eV.
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85.30.Tv Field effect devices
73.40.Ns Metal-nonmetal contacts
68.35.Fx Diffusion; interface formation
68.55.-a Thin film structure and morphology

Surface micromachining for microsensors and microactuators

Roger T. Howe

J. Vac. Sci. Technol. B 6, 1809 (1988); http://dx.doi.org/10.1116/1.584158 (5 pages) | Cited 43 times

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Micromechanical structures can be made by selectively etching sacrificial layers from a multilayer sandwich of patterned thin films. This paper reviews this technology, termed surface micromachining, with an emphasis on polysilicon microstructures. Micromechanical characteristics of thin‐film microstructures critically depend on the average residual stress in the film, as well as on the stress variation in the direction of deposition. The stress in low‐pressure chemical vapor deposition polysilicon varies with deposition temperature, doping, and annealing cycles. Applications of surface micromachining to fabricate beams, plates, sealed cavities, and linear and rotary bearings are discussed.
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81.65.-b Surface treatments
68.55.-a Thin film structure and morphology
68.60.Bs Mechanical and acoustical properties

High‐speed electron beam testing

George Chiu, Jean‐Marc Halbout, and Paul May

J. Vac. Sci. Technol. B 6, 1814 (1988); http://dx.doi.org/10.1116/1.584159 (6 pages)

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The performance of submicron devices and circuits for the coming decade is advancing at a rapid pace. The emerging requirements to probe the internal nodes of these ultrafast, small and dense circuits give rise to great challenges for high‐speed electron beam testing. In this paper, we review the steps of advancing the electron beam testing to achieve simultaneously: 5‐ps temporal resolution, 0.1‐μm spot size, and 3 mV/Hz1/2 voltage sensitivity. The newly developed instrument, called the picosecond photoelectron scanning electron microscope, is capable of measuring the state‐of‐the art bipolar and field‐effect transistor circuits.
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85.40.Qx Microcircuit quality, noise, performance, and failure analysis
85.30.Tv Field effect devices
07.78.+s Electron, positron, and ion microscopes; electron diffractometers

Electron beam fabrication of high‐performance InGaAs/InAlAs heterojunction insulated gate field effect transistors with submicron refractory airbridge gates

D. M. Tennant, S. C. Shunk, M. D. Feuer, J‐M. Kuo, B. Tell, R. E. Behringer, and T. Y. Chang

J. Vac. Sci. Technol. B 6, 1820 (1988); http://dx.doi.org/10.1116/1.584160 (4 pages)

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Self‐aligned heterojunction insulated gate field effect transistors devices with gate lengths as short as 0.125 μm (nominal) have been fabricated on molecular‐beam epitaxially grown InAlAs/InGaAs/InP heterostructures using electron beam lithography. A bilevel resist comprising poly(methylmethacrylate) (PMMA) and P(MMA/MAA) is exposed in a 50‐kV e‐beam lithography system and is used to liftoff a removable etch mask material. Reactive ion etching is used to define a tungsten gate, followed by implantation of Si+ to form the self‐aligned source and drain contact regions. Tungsten air bridges are formed during the mesa isolation step to provide the lowest gate leakage current and capacitance. Results from preliminary microwave electrical measurements are presented for devices with gate lengths as short as 0.25 μm.
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85.30.Tv Field effect devices
81.65.-b Surface treatments
73.40.Kp III-V semiconductor-to-semiconductor contacts, p-n junctions, and heterojunctions

Lateral‐surface‐superlattice and quasi‐one‐dimensional GaAs/GaAlAs modulation‐doped field‐effect transistors fabricated using x‐ray and deep‐ ultraviolet lithography

K. Ismail, W. Chu, D. A. Antoniadis, and Henry I. Smith

J. Vac. Sci. Technol. B 6, 1824 (1988); http://dx.doi.org/10.1116/1.584161 (4 pages) | Cited 6 times

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We have fabricated and tested lateral‐surface‐superlattice (LSSL) and quasi‐one‐dimensional (Q1D) devices on a modulation‐doped GaAs/GaAlAs heterostructure. The LSSL consists of a 0.2‐μm‐period (0.1‐μm nominal linewidth) Ti/Au grating or grid on top of the GaAlAs layer, forming a Schottky barrier which presents a tunable periodic potential modulation to the electrons traveling from source to drain. The grating gate was fabricated using x‐ray lithography to define the grating lines in poly(methylmethacrylate), and deep‐UV lithography to expose gate contact pads, followed by lift‐off of Ti/Au. Plots of the source–drain current as a function of the grating‐gate bias showed distinct plateaulike features at 4.2 K, providing evidence of a superlattice effect, that is, electron backdiffraction. Minor modifications of the fabrication process permitted Q1D and grid‐gate devices to be made. These also showed the expected structure in the conductance.
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85.30.Tv Field effect devices
73.40.Kp III-V semiconductor-to-semiconductor contacts, p-n junctions, and heterojunctions
81.65.-b Surface treatments

Hybrid lithography of a focused ion beam and an electron beam for the fabrication of a GaAs field effect transistor with a mushroom gate

K. Hosono, T. Fujino, S. Matsuda, K. Nagahama, Y. Sasaki, H. Morimoto, and Y. Watakabe

J. Vac. Sci. Technol. B 6, 1828 (1988); http://dx.doi.org/10.1116/1.584162 (4 pages)

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The hybrid lithography of a 280‐keV Si++ focused ion beam (FIB) and a 20‐keV shaped electron beam (EB) has been applied to fabricate a mushroom‐shaped gate for a high electron mobility transistor. In this process, a resist in the gate region is reduced to ∼0.2 μm by an FIB lithography (corresponding to ‘‘top‐gate’’ formation), and then the center of the top gate is exposed by the EB (corresponding to ‘‘bottom‐gate’’ formation). For a thin resist, patterns with smaller dimensions are more easily delineated by an EB exposure than for a thick resist. A 0.2‐μm pattern can be obtained by using a shaped EB system with a high throughput. The radiation damage is neglected due to the use of EB for the bottom‐gate formation.
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85.30.Tv Field effect devices
41.75.Ak Positive-ion beams
41.75.Cn Negative-ion beams
85.40.Hp Lithography, masks and pattern transfer

Focused ion implantation of gallium arsenide metal–semiconductor field effect transistors with laterally graded doping profiles

A. F. Evason, J. R. A. Cleaver, and H. Ahmed

J. Vac. Sci. Technol. B 6, 1832 (1988); http://dx.doi.org/10.1116/1.584175 (4 pages) | Cited 3 times

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Implantation with finely focused beams of dopant ions scanned under computer control enables laterally graded doping profiles to be formed. A 150‐nm‐diam beam of silicon ions from a gold–silicon–beryllium liquid metal ion source has been used to fabricate GaAs metal–semiconductor field effect transistors (MESFET’s) incorporating a number of different laterally graded doping profiles. It is seen experimentally that, when compared with uniformly implanted devices, these MESFET’s display increased available output power and transductance.
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85.30.Tv Field effect devices
61.72.U- Doping and impurity implantation
85.30.De Semiconductor-device characterization, design, and modeling

Lithography issues in fabricating high‐performance sub‐100‐nm channel metal–oxide semiconductor field effect transistors

D. P. Kern, S. A. Rishton, T. H. P. Chang, G. A. Sai‐Halasz, M. R. Wordeman, and E. Ganin

J. Vac. Sci. Technol. B 6, 1836 (1988); http://dx.doi.org/10.1116/1.584181 (5 pages)

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Specific issues related to achieving high device performance in extremely small channel length field effect transistor circuits are discussed. Ultrahigh resolution electron beam lithography is needed to obtain the ultrashort channels which are key for fast devices, and for the important gate area, double‐layer poly(methylmethacrylate) for lift‐off of a metal reactive ion etching mask has proven to be a suitable technique. Good level to level overlay and dimensional control in the contact process allow miniaturization of all device elements, in particular, reduction of the distance between source/drain contacts and optimization of the contact size and geometry. These are key factors in minimizing parasitic effects. The design considerations are discussed and the fabrication techniques are described which resulted in devices with a maximum measured transconductance of 910 mS/mm at 77 K for a 70‐nm gate device, exhibiting the clearest evidence so far for electron velocity overshoot, and unloaded ring oscillators with 13‐ps switching time per stage.
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85.30.Tv Field effect devices
85.40.Hp Lithography, masks and pattern transfer
85.30.De Semiconductor-device characterization, design, and modeling

Si metal–oxide semiconductor field effect transistor with 70‐nm slotted gates for study of quasi‐one‐dimensional quantum transport

J. H. F. Scott‐Thomas, M. A. Kastner, D. A. Antoniadis, Henry I. Smith, and Stuart Field

J. Vac. Sci. Technol. B 6, 1841 (1988); http://dx.doi.org/10.1116/1.584182 (4 pages) | Cited 2 times

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We have fabricated dual‐gate Si metal–oxide semiconductor field effect transistor devices in which the lower gate is slotted and the upper gate, separated by 45 nm of SiO2, is planar. By appropriate adjustment of the potentials on the two gates, the field lines from the upper gate are pinched, creating an inversion layer about one‐half the slot width. The resist patterning was done by x‐ray lithography, using a mask that combined crystallographic‐template/sidewall‐shadowing techniques with UV lithography. The slotted lower gate was produced by lift‐off. The metallization was a sandwich structure of Cr/W/Cr which permitted high‐temperature annealing. Very high mobilities, ∼15 000 cm2 /V s at 4.2 K, were achieved as a result. The combination of high mobility and extremely narrow inversion channel (∼30 nm) yields very clear structure in the conductance as a function of gate voltage, which cannot be accounted for by either localization effects or universal conductance fluctuations. Although these oscillations may be related to one‐dimensional subband effects, the magnetic field independence of the oscillations is not understood. At very high (12 T) magnetic fields an anomalous magnetoresistance has been seen.
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85.30.Tv Field effect devices
73.40.Qv Metal-insulator-semiconductor structures (including semiconductor-to-insulator)
73.50.-h Electronic transport phenomena in thin films

Electron wave diffraction by nanometer grating and its application for high‐speed transistors

Kazuhito Furuya and Kenji Kurishima

J. Vac. Sci. Technol. B 6, 1845 (1988); http://dx.doi.org/10.1116/1.584183 (4 pages) | Cited 1 time

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This paper describes a new phenomenon about the diffraction of the ballistic electron by a transverse grating in the semiconductor. As a theoretical result, the diffraction efficiency changes almost between one and zero owing to a slight change in the average potential energy of the grating. For the grating of a 19‐nm pitch in GaInAs, we can change the diffraction efficiency between 0.88 and 0.001 by 0.1 V in the grating layer voltage. Applying this phenomenon to control of the electron transport, a new type of transistor is described.
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85.30.De Semiconductor-device characterization, design, and modeling
85.40.Hp Lithography, masks and pattern transfer
85.30.Tv Field effect devices
73.61.Ey III-V semiconductors

Fabrication of submicrometer freestanding single‐crystal gallium arsenide and silicon structures for quantum transport studies

D. G. Hasko, A. Potts, J. R. A. Cleaver, C. G. Smith, and H. Ahmed

J. Vac. Sci. Technol. B 6, 1849 (1988); http://dx.doi.org/10.1116/1.584184 (3 pages) | Cited 8 times

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Freestanding wires of submicrometer width and with lengths up to 40 μm have been fabricated from single‐crystal GaAs and Si for studies of quantum transport. Fabrication techniques are described, and the low‐temperature properties for semiconductors and metals such as AuPd are compared. Fabrication of three‐terminal freestanding GaAs metal–semiconductor field effect transistor structures is demonstrated.
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85.30.Tv Field effect devices
73.40.Ns Metal-nonmetal contacts
84.32.Hh Inductors and coils; wiring

Fabrication and transport characteristics of semiconductor wire and ring structures

K. Ishibashi, Y. Takagaki, K. Gamo, S. Namba, S. Takaoka, K. Murase, S. Ishida, and Y. Aoyagi

J. Vac. Sci. Technol. B 6, 1852 (1988); http://dx.doi.org/10.1116/1.584185 (4 pages) | Cited 4 times

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We have fabricated narrow wires and small rings from GaAs/AlGaAs double heterostructures by using electron beam lithography and dry etching techniques. We describe the nature of universal conductance fluctuations in a single wire and the magnetoresistance oscillations with a period of‐h/e in a ring structure. It is experimentally shown that (i) from a single wire experiment, electrons with energies differing by the correlation energy Ecorr, have quite different magnetoresistance patterns, and (ii) from a ring experiment, the large aspect ratio (diameter/width) is important to obtain well‐defined oscillations.
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84.32.Hh Inductors and coils; wiring
73.40.Kp III-V semiconductor-to-semiconductor contacts, p-n junctions, and heterojunctions

Fabrication and characterization of one‐ and zero‐dimensional electron systems

K. Y. Lee, T. P. Smith, H. Arnot, C. M. Knoedler, J. M. Hong, D. P. Kern, and S. E. Laux

J. Vac. Sci. Technol. B 6, 1856 (1988); http://dx.doi.org/10.1116/1.584186 (5 pages) | Cited 7 times

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One‐ and zero‐dimensional electron systems confined in GaAs/GaAlAs have been fabricated. The starting material consisted of a modulation doped and a double barrier diode heterostructure grown by molecular‐beam epitaxy. Very high resolution electron beam lithography and reactive ion etching were used to pattern lines and dots with widths ranging from 100 to 400 nm. Two measurement techniques have been applied: capacitance measurements of density of states—a novel technique for observing quantum effects in these structures—and resonant tunneling measurements. We have observed oscillations in capacitance spectroscopy which reflect discrete energy levels associated with one‐ and zero‐dimensional electron systems. Preliminary tunneling measurements are presented.
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73.40.Kp III-V semiconductor-to-semiconductor contacts, p-n junctions, and heterojunctions
73.21.-b Electron states and collective excitations in multilayers, quantum wells, mesoscopic, and nanoscale systems
81.65.-b Surface treatments
73.40.Gk Tunneling

Nanostructure fabrication of zero‐dimensional quantum dot diodes

J. N. Randall, M. A. Reed, R. J. Matyi, and T. M. Moore

J. Vac. Sci. Technol. B 6, 1861 (1988); http://dx.doi.org/10.1116/1.584188 (4 pages) | Cited 4 times

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The nanofabrication techniques which are used to create quantum dot diodes will be discussed. The device is a vertical resonant tunneling diode where the lateral dimensions are reduced to ∼1000 Å. Electron beam lithography is used to pattern a small self‐aligned metal dot top contact and etch mask. The semiconductor dot is a cylinder ∼1000 Å in diameter and on the order of 100 Å thick, with the vertical potential defined by the double‐barrier heterostructure and the lateral defined by the Fermi‐level pinning of the free surfaces. Discrete energy states due to the three‐dimensional confinement are observed and are spin degenerate only. Transport measurements through such a device will be presented.
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85.40.-e Microelectronics: LSI, VLSI, ULSI; integrated circuit fabrication technology
85.40.Hp Lithography, masks and pattern transfer
81.65.-b Surface treatments

Selective area nucleation for metal chemical vapor deposition using focused ion beams

R. L. Kubena, F. P. Stratton, and T. M. Mayer

J. Vac. Sci. Technol. B 6, 1865 (1988); http://dx.doi.org/10.1116/1.584189 (4 pages) | Cited 4 times

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Localized growth of metal lines on Si wafers has been demonstrated using a focused Ga+ beam to selectively enhance the nucleation site density during a thermal chemical vapor deposition process. Iron and aluminum lines with thicknesses up to 2 μm have been formed using ion line doses between 4×1010 and 4×1012 Ga+/cm. Thus, the sensitivity of this process can be several orders of magnitude greater than ion beam induced polymerization techniques performed at room temperature. Auger analysis indicated that the total impurity concentration deep within the metal lines was roughly 15%. No Ga was detected in the deposited films.
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81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
81.65.-b Surface treatments
81.15.-z Methods of deposition of films and coatings; film growth and epitaxy

In situ observation on electron beam induced chemical vapor deposition by transmission electron microscopy

Toshinari Ichihashi and Shinji Matsui

J. Vac. Sci. Technol. B 6, 1869 (1988); http://dx.doi.org/10.1116/1.584190 (4 pages) | Cited 17 times

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Electron beam induced chemical vapor deposition of W and Si has been studied in a transmission electron microscope. WF6 and SiH2Cl2 were used as gas sources. Si and W clusters were initially formed. The W clusters, ∼3 nm in size, were β‐W crystal, while the Si clusters were amorphous. Deposition rates can be directly calculated, by using these techniques. For example, a 120‐kV electron beam at 100 A/cm2 current density will deposit W at ∼5 nm/min at 5×10−7 Torr, and Si at 2 nm/min at 5×10−5 Torr. A W rod, 15 nm in diameter, has been deposited using a 3‐nm‐diam focused electron beam.
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81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
79.20.Kz Other electron-impact emission phenomena
81.15.-z Methods of deposition of films and coatings; film growth and epitaxy
68.55.-a Thin film structure and morphology

High‐resolution deposition and etching of metals with a scanning electrochemical microscope

Oskar E. Hüsser, Derek H. Craston, and Allen J. Bard

J. Vac. Sci. Technol. B 6, 1873 (1988); http://dx.doi.org/10.1116/1.584191 (4 pages) | Cited 11 times

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A novel method is described which can be used for both the electrochemical deposition of metals in polymer films and the etching of metals with very high resolution. These faradaic processes are controlled using a scanning electrochemical microscope (similar to the scanning tunneling microscope). Patterns of silver and gold deposited in Nafion and poly(4‐vinylpyridine), respectively, with a linewidth smaller than 0.5 μm, and high‐resolution etching patterns in copper are shown. Extensions of this methodology to depositions of other materials, the use of other conducting polymer films, and possible applications for submicron devices are discussed.
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81.15.-z Methods of deposition of films and coatings; film growth and epitaxy
81.05.Bx Metals, semimetals, and alloys
68.55.Ln Defects and impurities: doping, implantation, distribution, concentration, etc.
82.45.-h Electrochemistry and electrophoresis

Direct deposition of 10‐nm metallic features with the scanning tunneling microscope

M. A. McCord, D. P. Kern, and T. H. P. Chang

J. Vac. Sci. Technol. B 6, 1877 (1988); http://dx.doi.org/10.1116/1.584192 (4 pages) | Cited 44 times

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In this preliminary study we have used a modified scanning tunneling microscope (STM) to directly deposit metallic features as small as 10 nm by decomposing organometallic gases containing tungsten and gold. Dots as well as lines have been formed. Tungsen deposits analyzed by Auger electron spectroscopy contained 48% tungsten, 40% carbon, and 12% oxygen. A resistivity of 0.01 Ω/cm for the deposits was measured by aligning the STM to a metal contact pattern. This is the first reported combination of STM lithography with conventional lithography. A discussion of several interesting physical and chemical mechanisms involved in the deposition process is also presented.
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81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
07.78.+s Electron, positron, and ion microscopes; electron diffractometers
85.40.Hp Lithography, masks and pattern transfer
73.61.At Metal and metallic alloys

Dry etching: From plasma ashing to quantum dots

Hans W. Lehmann

J. Vac. Sci. Technol. B 6, 1881 (1988); http://dx.doi.org/10.1116/1.584193 (4 pages) | Cited 1 time

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First applications of plasma etching in very large scale integration were reported in the literature 20 years ago. After reviewing the early days of dry etching, applications of this technique to high‐resolution pattern transfer are illustrated by the fabrication of deep square‐wave gratings with micron dimensions used in diffractive structures as well as submicron structures with large aspect ratio, both etched into SiO2 in CHF3 plasmas. The importance of pattern distortion by faceting effects, redeposition of sputtered material, and undercutting by isotropic etching is discussed. Modern developments like etching of deep trenches into Si and the fabrication of quantum dots are briefly outlined.
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85.40.Hp Lithography, masks and pattern transfer
81.65.-b Surface treatments

Radical beam/ion beam etching of GaAs

J. A. Skidmore, L. A. Coldren, E. L. Hu, J. L. Merz, and K. Asakawa

J. Vac. Sci. Technol. B 6, 1885 (1988); http://dx.doi.org/10.1116/1.584194 (4 pages) | Cited 5 times

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A novel combined radical beam and ion beam etching (RBIBE) technique that uses a microwave‐excited radical beam combined with an Ar+ ion beam has been developed for smooth, low damage, and rapid etching of GaAs structures. Separate control of both argon ion (Ar+) energy and/or current and chlorine radical (Cl∗) beam flux density has enabled us to realize highly chemically enhanced GaAs etching. This RBIBE technique differs qualitatively from and offers greater flexibility than reactive ion etching (RIE), ion beam assisted etching (IBAE), where the reactive etch gas is not plasma excited, or reactive ion beam etching (RIBE), where independent control of radical and ion beam flux is difficult. Our work examines etch rate as a function of flow rate, temperature, microwave power, and ion beam current. The etch rate and reactive sputter yield are typically eight times greater with the microwave plasma on (RBIBE) than with the plasma off (IBAE). With RBIBE, high etch rates (2.5 μm/min) have been realized at room temperature and for low ion energies (200 eV). Optical emission spectroscopy is used to correlate the etch rate with the concentration of chlorine radicals in the microwave cavity. The reactive sputter yield and degree of anisotropy can be varied over a wide range by varying the microwave power level and the ion beam current density. We demonstrate that this etching technique should be capable of producing smooth, low‐damage structures for applications in optoelectronics.
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81.65.-b Surface treatments
79.20.Rf Atomic, molecular, and ion beam impact and interactions with surfaces

Reactive ion etching of epitaxial ZnSe thin films

E. M. Clausen, H. G. Craighead, L. M. Schiavone, M. C. Tamargo, and J. L. de Miguel

J. Vac. Sci. Technol. B 6, 1889 (1988); http://dx.doi.org/10.1116/1.584195 (3 pages) | Cited 4 times

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Using mixtures of boron trichloride and argon, we show it is possible to reactive ion etch epitaxial thin films of ZnSe grown on GaAs. Optimum etching conditions were determined by the application of a model generated from the multiple linear regression of the independent variables affecting the etching process. These variables included the power, pressure, gas composition, and time of etch. Optimum etching conditions produced etched structures with straight sidewalls and smooth surfaces. Photolithographically defined structures included both micrometer sized stripes and pixel arrays. Cathodoluminescence was measured from the surfaces of these etched structures and from the surface of unetched material at room temperature. Luminescence intensities of broad flat etched surfaces are shown not to be degraded by the etching process. This suggests the possibility of efficient etched light emitting structures.
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81.65.-b Surface treatments
79.20.Rf Atomic, molecular, and ion beam impact and interactions with surfaces
78.60.Hk Cathodoluminescence, ionoluminescence
82.65.+r Surface and interface chemistry; heterogeneous catalysis at surfaces

Mechanistic studies of oxygen plasma etching

M. A. Hartney, W. M. Greene, D. S. Soane, and D. W. Hess

J. Vac. Sci. Technol. B 6, 1892 (1988); http://dx.doi.org/10.1116/1.584196 (4 pages) | Cited 10 times

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Oxygen dissociation was measured in reactive ion etching (RIE) plasmas using a quadrupole mass spectrometer which sampled the particle flux through a pinhole in the lower electrode of a parallel‐plate reactor. The oxygen atom flux increased with increasing power and generally decreased with increasing pressure. Ion currents and bombardment energies also decreased with increasing pressure, while the etch rate of novolac resists increased. In the low‐pressure (20–75 mTorr) regime of oxygen RIE plasmas, etch rates of novolac polymers correlated most directly with the supply of oxygen molecules to the surface.
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81.05.Lg Polymers and plastics; rubber; synthetic and natural fibers; organometallic and organic materials
81.65.-b Surface treatments
79.20.Rf Atomic, molecular, and ion beam impact and interactions with surfaces
82.65.+r Surface and interface chemistry; heterogeneous catalysis at surfaces

Experimental conditions for uniform anisotropic etching of silicon with a microwave electron cyclotron resonance plasma system

J. Hopwood, D. K. Reinhard, and J. Asmussen

J. Vac. Sci. Technol. B 6, 1896 (1988); http://dx.doi.org/10.1116/1.584197 (4 pages) | Cited 7 times

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The etch rate uniformity of a SF6 +Ar plasma is studied for various discharge geometries using an electron cyclotron resonant microwave plasma disk reactor operating at 2.45 GHz. At a distance of 10 mm below the 9‐cm‐diam plasma source 2‐in. (5‐cm) wafers can be etched uniformly in a free‐fall diffusion dominated discharge. The effect of the ratio of SF6 to Ar on vertical and lateral etch rates was investigated and correlated with the 704‐nm F∗ emission line intensity and positive ion flux to the surface. Surface contamination and impurity implantation in etched silicon are documented using Auger electron spectroscopy.
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81.65.-b Surface treatments
79.20.Rf Atomic, molecular, and ion beam impact and interactions with surfaces

A heating model for excimer laser projection processing

S. Palmer and S. Matteson

J. Vac. Sci. Technol. B 6, 1900 (1988); http://dx.doi.org/10.1116/1.584141 (6 pages)

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The reaction rates for laser‐induced desorption, etching, and deposition are dependent on the local substrate temperature. Accurate predictions of the spatial and temporal temperature profiles on the wafer are necessary in order to optimize the process conditions. We report on the solution of the transient heat conduction equation using an adaptation of HEATING5, a program developed at the Oak Ridge National Laboratory.1 The solution includes the full temperature dependence of the material parameters. The aerial and temporal distribution of the incident laser radiation is used in the heating program to calculate the temporal and spatial dependence of the thermal profiles. From the results of the heating model, a process model for laser‐induced etching is constructed and used to explain our results on projection pattern etching of silicon using the KrF laser and fluorine gas mixture.
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44.10.+i Heat conduction
81.65.-b Surface treatments
79.20.Ds Laser-beam impact phenomena
68.03.Fg Evaporation and condensation of liquids
68.43.Mn Adsorption kinetics

Investigation of reactive ion etching induced damage in GaAs–AlGaAs quantum well structures

H. F. Wong, D. L. Green, T. Y. Liu, D. G. Lishan, M. Bellis, E. L. Hu, P. M. Petroff, P. O. Holtz, and J. L. Merz

J. Vac. Sci. Technol. B 6, 1906 (1988); http://dx.doi.org/10.1116/1.584142 (5 pages) | Cited 52 times

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We report on the use of a novel technique to study reactive ion etching (RIE) induced damage using multiple quantum wells of 20‐, 40‐, 60‐, and 90‐Å widths as in situ probes. Cathodoluminescence (CL) at low temperature, using a finely focused electron beam, allows sensitive determination of the quality of individual quantum wells before and after RIE damage. There is a correspondence between individual luminescence peaks and the depth of the particular quantum well. We can therefore use the CL spectral information to provide a sensitive profile of the depth of RIE induced damage. Various etching conditions and the effects of postetch anneals are examined. Pure Ar sputtering and enhanced chemical etching using CCl2F2/BCl3 at different bias voltages are investigated. Our results reveal that the degree and spatial extent of damage increase with increasing ion energy and decreasing ion mass.
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81.65.-b Surface treatments
79.20.Rf Atomic, molecular, and ion beam impact and interactions with surfaces
61.80.Jh Ion radiation effects
82.65.+r Surface and interface chemistry; heterogeneous catalysis at surfaces

Passivation of donors in electron beam lithographically defined nanostructures after methane/hydrogen reactive ion etching

R. Cheung, S. Thoms, I. McIntyre, C. D. W. Wilkinson, and S. P. Beaumont

J. Vac. Sci. Technol. B 6, 1911 (1988); http://dx.doi.org/10.1116/1.584143 (5 pages) | Cited 12 times

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We show that while the methane/hydrogen gas mixture is capable of etching GaAs and AlGaAs controllably and with little residual damange, it leads to the passivation of donors in both semiconductors. The passivation can, however, be annealed out with a short thermal cycle to 300 °C. The effects of passivation are illustrated and characterized by processing uniform epilayers and quantum wires in n+‐GaAs and modulation doped AlGaAs/GaAs heterostructures.
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81.65.-b Surface treatments
79.20.Rf Atomic, molecular, and ion beam impact and interactions with surfaces
73.40.Kp III-V semiconductor-to-semiconductor contacts, p-n junctions, and heterojunctions
85.40.Hp Lithography, masks and pattern transfer

Dry etching induced damage on vertical sidewalls of GaAs channels

S. W. Pang, W. D. Goodhue, T. M. Lyszczarz, D. J. Ehrlich, R. B. Goodman, and G. D. Johnson

J. Vac. Sci. Technol. B 6, 1916 (1988); http://dx.doi.org/10.1116/1.584132 (5 pages) | Cited 14 times

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Damage on the vertical sidewalls of narrow GaAs structures has been investigated. The structures consisted of narrow conducting channels between Ohmic pads. The channels were defined by either masked ion beam lithography or electron beam lithography with channel widths varying from 0.08 to 1.5 μm. Reactive ion etching and ion beam assisted etching were used to remove the epitaxial material outside the channels down to the semi‐insulating substrates. Conduction in the channels was monitored by measuring current–voltage characteristics between the Ohmic pads. It is found that saturation current depends on the dry etching conditions such as ion energy, etching species, and impurity redeposition. Ion beam etching of GaAs substrates at different angles was used to separate out the effects of the inert ion species of reactive ion etching and ion beam assisted etching. Large increases in leakage current and impurity concentrations were obtained when the sample was mounted in the plane parallel to the direction of the ion beam, indicating that redeposition from fixtures and chamber walls can be significant. Controllable etching with minimal damage in GaAs is obtained by using low ion energy, reactive gases, and a contamination‐free environment in the chamber. By optimizing the etching conditions, conduction was observed for channels with mirror‐smooth sidewalls and widths as small as 0.08 μm.
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81.65.-b Surface treatments
61.80.Jh Ion radiation effects
79.20.Rf Atomic, molecular, and ion beam impact and interactions with surfaces

The interference fringe aligner

D. L. White, M. Feldman, T. E. Saunders, and P. Gunter

J. Vac. Sci. Technol. B 6, 1921 (1988); http://dx.doi.org/10.1116/1.584133 (4 pages) | Cited 2 times

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The interference fringe aligner uses interference fringes formed by two crossed laser beams to align each exposure field in a step and repeat camera. The alignment mark is a diffraction grating with a period equal to a multiple of the laser fringe period. The fringes move back and forth across the grating producing variations in the intensity of the several diffraction orders. This amplitude modulation of the diffracted beams contains sufficient information to determine the relative position between the fringes and the grating. Alignment is accomplished with a feedback loop to the stepper stage that moves the grating lines directly under the fringes to produce a symmetrical pattern. The essential optical components of the input are a beam splitter and a phase modulator to move the fringes; the output consists only of photodiodes. Detection and analysis are all electronic, not optical. Thus the system is simple, very sensitive, and stable. The beams strike the wafer at a shallow angle, allowing the aligner to be attached to the bottom of the stepper lens and illuminate a chip under the lens. Chips are aligned in the ‘‘expose’’ position, eliminating stage positioning errors that occur when the chip is aligned at one site and moved to another for exposure. It is thus easy to retrofit existing steppers that have a working distance >1 cm between the lens and the wafer.
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85.40.Hp Lithography, masks and pattern transfer

Measuring overlay errors and critical dimensions by correlating binarized Laplacian of Gaussian convolved images

P. A. Crossley and H. K. Nishihara

J. Vac. Sci. Technol. B 6, 1925 (1988); http://dx.doi.org/10.1116/1.584134 (5 pages)

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A technique is described for measuring alignment and critical dimensions, which is tolerant of noise, defects, and details of target image appearance. The targets are composed of small elements which can be at the minimum feature size of the photolithographic process. Grey‐level images of the targets are bandpass filtered and hard clipped to produce binary patterns representing the clustering structure of the target elements while attenuating details of the individual elements. Correlation of these binary patterns allows extraction of alignment error and critical dimensions without the use of thresholds, stored templates, or edge detection.
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85.40.Hp Lithography, masks and pattern transfer

Proposal for a new submicron dimension reference for an electron beam metrology system

Yoshinori Nakayama, Shinji Okazaki, and Aritoshi Sugimoto

J. Vac. Sci. Technol. B 6, 1930 (1988); http://dx.doi.org/10.1116/1.584135 (4 pages) | Cited 8 times

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A new submicron level reference for an electron beam metrology system is proposed. This reference is a fine rectangular‐profile diffraction grating fabricated by laser interferometer lithography and anisotropic chemical etching of (110) crystalline silicon. The pitch size of the grating is derived from the wavelength of the laser and the angle of incidence of the holographic lithography. The optical diffraction measurement absolutely assures accurate grating pitch size. The measurement error is estimated to be smaller than 0.001 μm. A deep lamellar grating fabricated by anisotropic chemical etching of (110)Si generates a stable and high‐contrast secondary electron signal in an electron beam metrology system. Reference pitch size measurement by optical diffraction and by the electron beam metrology system assures that the pitch size error is smaller than 0.02 μm.
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85.40.Hp Lithography, masks and pattern transfer
41.75.Fr Electron and positron beams
81.65.-b Surface treatments

Patterned wafer inspection using laser holography and spatial frequency filtering

D. L. Cavan, L. H. Lin, R. B. Howe, R. E. Graves, and R. L. Fusek

J. Vac. Sci. Technol. B 6, 1934 (1988); http://dx.doi.org/10.1116/1.584136 (6 pages) | Cited 4 times

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An automatic patterned wafer inspection system for use in integrated circuit fabrication is described. The system is based on the techniques of optical spatial frequency filtering and laser holography. The system can locate defects as small as 0.5 μm over a 150 mm patterned silicon wafer in ∼30 min. The wafer under inspection is placed in front of a lens and is flood illuminated through beam splitting optics with a collimated laser beam. The light reflected and diffracted from the wafer is collected by the lens through the beam splitter. In the back focal plane of the lens, the Fourier transform (spatial frequency) pattern of the wafer circuit is formed. A spatial filter placed in this plane effectively blocks the transmission of the light from the repetitive circuit features of all dies of the wafer. The wave front transmitted through the filter is then recorded in a hologram. The conjugate to the recorded wave front is later reconstructed from the hologram. The reconstructed wave front thus reverse ray traces the filter and the lens, forming a real image of the wafer. In this image, the defects are greatly intensified relative to the filtered circuit features. An analysis of the optical wave fronts in the system is provided. The defect information is obtained by scanning a two‐dimensional photodetector array through the holographic image and recording the size and location of each point of light above a predetermined threshold. Test wafers containing electron beam programmed defects in a trilevel resist structure were prepared and inspected. Performance results are described.
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85.40.Hp Lithography, masks and pattern transfer
85.40.Qx Microcircuit quality, noise, performance, and failure analysis

Scanning ion microscopy and microsectioning of electron beam recrystallized silicon on insulator devices

E. C. G. Kirk, R. A. McMahon, J. R. A. Cleaver, and H. Ahmed

J. Vac. Sci. Technol. B 6, 1940 (1988); http://dx.doi.org/10.1116/1.584137 (4 pages) | Cited 6 times

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Structures fabricated during the development of a process for making three‐dimensionally interconnected integrated circuits using electron beam recrystallization of silicon on insulator have been microsectioned and examined in the scanning ion microscope. This provided detailed information, not accessible by standard analysis techniques, concerning the effects of processing at specific sites in the structures.
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85.40.Hp Lithography, masks and pattern transfer
85.40.Ls Metallization, contacts, interconnects; device isolation
81.65.-b Surface treatments
61.80.Fe Electron and positron radiation effects

Measurement techniques for submicron resist images

Michael G. Rosenfield

J. Vac. Sci. Technol. B 6, 1944 (1988); http://dx.doi.org/10.1116/1.584138 (6 pages)

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Low‐voltage scanning electron microscopes (SEM’s) are primarily used for submicron metrology and inspection of resist images and other processing levels in the fabrication of integrated circuits. The optical confocal laser scanning microscope (CLSM) has recently been introduced as another system for submicron metrology. In this paper, the important issues of submicron resist metrology are investigated. It is shown that SEM based metrology systems can be used to measure the top widths of 0.5‐μm‐thick resist features with an accuracy of 0.02 μm or better, down to ∼0.1 μm, the smallest pattern used in this study. The measurement precision of the SEM was actually better than 0.015 μm, 3σ. The precision was found to be influenced by charging effects and the quality of the SEM signal. The 325‐nm wavelength CLSM was able to make measurements of similar accuracy down to 0.5–0.35 μm using a careful choice of focus height and measurement threshold. Changing the substrate from Si to 0.27‐μm oxide/Si resulted in a significant change in the measurement offset for the CLSM, but had little effect on the SEM measurements. The measurement precision of the CLSM was typically below 0.025 μm, 3σ. The CLSM precision was influenced by small variations in focus height. The accuracy and precision of both systems were dependent on the correct utilization of the measurement algorithms and careful calibration of the measurement signals.
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85.40.Hp Lithography, masks and pattern transfer

Computational tools to analyze voltage contrast detectors

A. Khursheed, A. R. Dinnis, D. J. Hall, and W. R. Knowles

J. Vac. Sci. Technol. B 6, 1950 (1988); http://dx.doi.org/10.1116/1.584139 (3 pages) | Cited 1 time

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Computer programs have been written to analyze the performance of a wide range of ‘‘in the lens’’ voltage contrast detectors. By plotting electron trajectories for emitted secondaries from the specimen, the programs can calculate important figures of merit for different detectors, such as the efficiency of collecting secondaries which leave the specimen. The programs can also calculate third‐order aberrations on the primary beam, and hence determine the spatial resolution capability for each detector.
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41.75.Fr Electron and positron beams
07.05.Hd Data acquisition: hardware and software
07.05.Kf Data analysis: algorithms and implementation; data management
07.05.Rm Data presentation and visualization: algorithms and implementation
07.50.-e Electrical and electronic instruments and components
07.05.Bx Computer systems: hardware, operating systems, computer languages, and utilities

Characteristics of a virtual immersion lens spectrometer for electron beam testing

T. Aton, S. C. J. Garth, J. N. Sackett, and D. F. Spicer

J. Vac. Sci. Technol. B 6, 1953 (1988); http://dx.doi.org/10.1116/1.584144 (5 pages) | Cited 2 times

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Magnetic ‘‘in‐the‐lens’’ secondary electron spectrometers have shown dramatic improvements over conventional spectrometers for high‐resolution voltage measurements on very large scale integrated circuits. In particular, designs incorporating the electron straightening effect of an adiabatic magnetic field have demonstrated considerably improved rejection of local field effects on small geometry devices. A disadvantage of such spectrometers is the need to immerse the sample in a strong magnetic field. This can result in image distortion (due to ferromagnetic lead frame material in the sample) and surface‐charging instability (due to localized charging from returned secondary electrons being refocused close to the emission point). We report on an improved spectrometer that maintains the advantages of the adiabatic straightening of the secondary electrons without the need to set the sample in a magnetic field. This ‘‘virtual’’ immersion lens design gives rise to a spectrometer with similar waveform measurement characteristics to the previous lens type but with greatly superior image resolution, field of view, and beam stability characteristics. We show it to be capable of 0.1‐μ spatial resolution, voltage errors as small as 2% for 5‐V signals on 1‐μ lines and spaces, and a ‘‘detector coefficient’’ as good as 1.42 ×10−8 V(A/Hz)1/2. All of these are among the best reported so far in the electron‐beam testing literature.
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85.40.Qx Microcircuit quality, noise, performance, and failure analysis
07.78.+s Electron, positron, and ion microscopes; electron diffractometers

EBT‐1: A highly automated, practical electron beam tester

K. Koyama, T. Tojo, T. Sugihara, T. Takigawa, T. Sano, M. Ishikawa, and K. Matsuda

J. Vac. Sci. Technol. B 6, 1958 (1988); http://dx.doi.org/10.1116/1.584140 (5 pages)

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A highly automated electron beam testing system EBT‐1 was built for measuring internal voltages of very large scale integrated (VLSI) devices in both wafer and package forms. Voltage measurement and its associated operations are performed by the computer with a minimum of operator intervention. The mother‐board probe‐card system has been incorporated for easy signal connection and the six‐axis stages are specially designed. The upper X, Y stages, Z stage, and piezo‐drive θ stage are used to precisely align the probe card to an arbitrary chip on a 6‐in.‐wafer, whereas the lower X, Y stages are used to shift the area of observation. The electron optical column with four magnetic lenses uses a single‐crystal LaB6 cathode to generate sufficient beam current at low accelerating voltages of 1 to 3 kV. The device drive signals are supplied from conventional LSI testers via more than 160 vacuum‐tight connectors. EBT‐1 has achieved a voltage resolution of < 50 mV and a time resolution of 0.5 ns at the device clock frequency of 25 MHz. The system has been extensively used in the development of VLSI devices, including 1‐Mbit dynamic random access memory.
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85.40.Qx Microcircuit quality, noise, performance, and failure analysis
41.75.Fr Electron and positron beams

Test system timing considerations for electron beam microprobing of logic devices

J. A. Lange

J. Vac. Sci. Technol. B 6, 1963 (1988); http://dx.doi.org/10.1116/1.584145 (3 pages)

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Shrinking geometries, increasing vertical density of standard logic devices and faster execution times are forcing circuit designers and analyzers to depend ever more heavily on electron beam microprobing (EBM) to investigate problem cells in very large scale integrated and ultra large scale integrated logic circuits. However, in the present geometries there are also changes occurring which are forcing designers to look at electron (e‐)beam probing systems as more than a laboratory fascination. The most current of these changes is vertical integration or the addition of more conductive layers to allow for a more dense design, resulting in a more efficient use of silicon area. Currently designs of two‐layer metal and two‐layer polycrystalline silicon are used, with the promise of more on the way, possibly including diffused active regions. The attendant close horizontal spacing between upper layers makes the physical microprobing of underlying layers a delicate proposition at best, if not impossible. The market is also pushing for more speed which means that on‐chip clocks are going to be ever faster, approaching 100 MHz in the foreseeable future. This forces the use of a system with the fewest distributed constants, capable of resolution in the gigahertz region. Effective use of EBM with random logic circuits requires consideration of the test environment external to the e‐beam system itself. Due to the requirement for long patterns of data prior to the particular bit time of interest, very long cycle times are often necessary to allow for internal logic to be setup prior to execution of the offending instruction. In addition, faster clock frequencies require the analyst to be more aware of high‐frequency effects in the distributed constants of the test setup interconnects. Current electron beam microprobe systems are capable of dealing with relatively long cycle times and bandwidth limitations do not present a problem. However the test setup itself can introduce errors due to external hardware and/or software being incompatible with the particular sampling technique in use on most current systems. A brief review of this technique, known generically as boxcar averaging is given along with its unique software and hardware timing requirements, and some common errors to be avoided in interconnection of external systems.
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85.40.Qx Microcircuit quality, noise, performance, and failure analysis
41.75.Fr Electron and positron beams
07.50.-e Electrical and electronic instruments and components

Voltage contrast electron beam testing experiments on very large scale integrated chip packaging substrates

Ollie C. Woodard, Fred Hartnett, Tom Myers, Andrew Ross, and Ronald Thompson

J. Vac. Sci. Technol. B 6, 1966 (1988); http://dx.doi.org/10.1116/1.584146 (5 pages) | Cited 1 time

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Test and inspection are key in reducing costs and increasing reliability of multichip hybrid modules. Increasing very large scale integrated chip packaging densities requiring finer linewidths and more substrate interconnection networks are taxing the probing resolution, throughput, and reliability of conventional mechanical probe test systems. Voltage contrast electron beam test technology was seen as an attractive alternative for high‐throughput, noncontact testing of unpopulated packaging substrates and high‐density printed wiring boards. A conventional scanning electron microscope was modified by adding large‐field vector deflection, a large‐field secondary analyzer, beam blanking, an electron flood gun, and a computer control system, thereby providing the primary test functions required for opens and shorts testing: net charging, net voltage measurement, and global charge removal. Successful substrate test results are shown along with data which highlight potential failure mechanisms such as substrate material variations, charge leakages, and contaminants.
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85.40.Bh Computer-aided design of microcircuits; layout and modeling
85.40.Ls Metallization, contacts, interconnects; device isolation
85.40.Qx Microcircuit quality, noise, performance, and failure analysis

High‐resolution, low‐energy beams by means of mirror optics

E. Munro, J. Orloff, R. Rutherford, and J. Wallmark

J. Vac. Sci. Technol. B 6, 1971 (1988); http://dx.doi.org/10.1116/1.584147 (6 pages) | Cited 4 times

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Electron and ion beam systems with low beam landing energies are needed for many important applications, such as microcircuit inspection and charge storage devices. In this paper, therefore, we have analyzed focusing and deflection systems with strong electrostatic retarding fields immediately in front of the final target plane, with beam landing energies as low as 50 eV. A simple theory is presented, which proves that such strong retarding fields dramatically reduce all the aberration coefficients, including the deflection aberration coefficients as well as the on‐axis ones. The overall spot size (for given beam current) inevitably increases as the beam is retarded, due to the increased aperture angle and increased fractional energy spread at the image plane. Nevertheless, on account of the great reduction in the aberration coefficients, the degradation of spot size at low beam landing energies turns out to be much less severe than might intuitively be expected. Our electron optical design software has been enhanced to compute accurately the aberrations of such retarding field systems. This software has been used to verify the predictions of our theory. A practical retarding field system with 50‐eV beam landing energy has been built and tested, and its experimental performance confirms our computer analysis. The design has been significantly further improved with the aid of our programs. The computed results show that, using a thermal‐field emission source with 1‐eV energy spread, the proposed final design should be capable of producing a 111‐nA beam of <0.3‐μm diameter throughout a 10×10 mm2 deflection field, at a final landing energy of 50 eV.
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41.75.Fr Electron and positron beams
85.40.Qx Microcircuit quality, noise, performance, and failure analysis

Coulomb interactions in particle beams

G. H. Jansen

J. Vac. Sci. Technol. B 6, 1977 (1988); http://dx.doi.org/10.1116/1.584148 (7 pages) | Cited 5 times

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A comprehensive theory has been developed to describe all manifestations of Coulomb interactions between charged particles in low‐ and medium‐density nonrelativistic beams, e.g., as found in electron beam pattern generators and scanning electron microscopes. A survey is given of the analytical prescriptions for the calculation of the Boersch effect, trajectory displacement effect, and space‐charge effect occurring in the drift space of a column. The theory is applied to the IBM EL3 and the Perkin–Elmer aeble 150 shaped spot lithography machines. The results are in close agreement with Monte Carlo simulations as well as the available experimental data.
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41.75.Fr Electron and positron beams
07.77.-n Atomic, molecular, and charged-particle sources and detectors
81.65.-b Surface treatments

A new method for measuring the virtual object diameter of high‐field electron sources

Mark Gesley

J. Vac. Sci. Technol. B 6, 1984 (1988); http://dx.doi.org/10.1116/1.584149 (5 pages) | Cited 2 times

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A new method for measuring the virtual object diameter dν of field emission sources based on the spectral analysis of their flicker noise is described. The nature of the source and the various parameters which influence its size are considered. It is emphasized that the cathode surface does not coincide with the source plane which has a Gaussian current distribution. Extractor electrode aberrations do not make a significant contribution to the virtual source diameter. Extensions of the concentric sphere model of the diode region which modify the spatial electric field distribution do not lead to a larger estimate of the source size. From this discussion comes the relation linking the source diameter dν to the resolution length interval lδ which is defined at the cathode surface. By matching the frequency exponents of the theoretical and measured spectra characteristic frequencies are found which yield lδ and hence provides an estimate of dν. For thermal‐field emission from a tungsten cathode at 1000 K in ultrahigh vacuum a value of dν ≂21±9 Å is obtained.
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79.70.+q Field emission, ionization, evaporation, and desorption
41.75.Fr Electron and positron beams

Novel Monte Carlo simulation of space‐charge‐induced energy broadening in laser irradiated cathodes

D. R. Allee, J. D. Pehoushek, and R. F. W. Pease

J. Vac. Sci. Technol. B 6, 1989 (1988); http://dx.doi.org/10.1116/1.584150 (6 pages) | Cited 1 time

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Laser irradiation is one alternative to the use of a Wehnelt for confining the area of emission of an electron gun. The absence of the retarding Wehnelt electrode allows the direct acceleration of the electrons to the anode, reducing space‐charge‐induced energy broadening in several ways. Fewer crossovers are necessary to achieve a given spot size, and the space‐charge density and total current near the source are reduced. A novel Monte Carlo algorithm has been developed to simulate for the first time the space‐charge interactions in this type of gun for thermionic and photonic emission from various source materials. A novel data structure incorporating a linear ordering of the particles in each of three dimensions allows an efficient determination of particle neighbors. The central processing unit time is proportional to n1.4 instead of n2, where n is the number of particles. This provides a savings in the cost of a simulation or allows more particles to be simulated. The simulation results indicate that, for source current densities up to 20 A/cm2, energy broadening can be practically eliminated by reducing the emission spot size. The predicted energy broadening is significantly less than that reported by Pfeiffer for traditional thermionic electron guns with Wehnelt electrodes. The advantages of a short electron beam lithography column for high‐resolution mask fabrication that incorporates a laser irradiated thermionic source are discussed.
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79.20.Ds Laser-beam impact phenomena
81.65.-b Surface treatments
79.40.+z Thermionic emission
79.60.-i Photoemission and photoelectron spectra

Recent advances with the variable axis immersion lens

M. A. Sturans, H. C. Pfeiffer, W. Stickel, and T. R. Groves

J. Vac. Sci. Technol. B 6, 1995 (1988); http://dx.doi.org/10.1116/1.584151 (4 pages) | Cited 2 times

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The novel variable axis immersion lens (VAIL) magnetic focusing and deflection system has been shown to produce excellent images over large fields. A practical lithography tool, however, requires high throughput (writing speed) which the magnetic deflection alone cannot provide. This paper describes the incorporation of a unique high‐speed electrostatic deflection system in VAIL which maintains perpendicular landing everywhere on the target. In order to keep the beam at optimum focus when the target height or spot size is changing, a high‐speed focus coil was developed which does not produce any positional errors when excited.
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41.75.Fr Electron and positron beams
85.40.Hp Lithography, masks and pattern transfer

Electrostatic focusing and electrostatic deflection systems with reduced aperture aberrations

Kentaro Oku, Masanori Maruyama, and Masakazu Fukushima

J. Vac. Sci. Technol. B 6, 1999 (1988); http://dx.doi.org/10.1116/1.584152 (4 pages)

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Electrostatic focusing and electrostatic deflection (SS) electron beam systems have been investigated to increase the resolution of SS camera tubes. SS camera tubes have pattern electrodes formed on their inner walls. The pattern electrodes comprise deflection electrodes and a cylindrical electrode. The deflection electrodes form a band around the inner wall at one end of the tube. Four leads project longitudinally from this band, dividing the cylindrical electrode into four parts. An octopole lens is created around the leads of the deflection electrodes. To increase tube resolution, the electron optical characteristics were evaluated, taking into account the effects of the octopole lens. It was revealed that, due to the octopole lens, the aberration spot is not isotropic and its diameter is about three times that produced by a cylindrical lens. New pattern electrodes with zig‐zag shaped leads were devised. It was found that the aberration spot became almost round and its diameter was reduced to the value obtained with a cylindrical lens.
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84.47.+w Vacuum tubes
41.75.Fr Electron and positron beams

A voltage‐contrast analyzer using radial magnetic field extraction

A. R. Dinnis and A. Khursheed

J. Vac. Sci. Technol. B 6, 2003 (1988); http://dx.doi.org/10.1116/1.584153 (2 pages) | Cited 1 time

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Quantitative voltage‐contrast work is carried out by detecting the effect which the voltages on conducting tracks on the integrated circuit surface have on the energies of low‐energy secondary electrons, i.e., the electrons having energies below ∼20 eV. It is essential that the final lens and the electron energy analyzer should be designed as a unit if satisfactory performance is to be achieved.
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41.75.Fr Electron and positron beams
07.50.-e Electrical and electronic instruments and components
85.40.Qx Microcircuit quality, noise, performance, and failure analysis

Electron optical characteristics of negative electron affinity cathodes

Colin A. Sanford and Noel C. MacDonald

J. Vac. Sci. Technol. B 6, 2005 (1988); http://dx.doi.org/10.1116/1.584118 (4 pages) | Cited 2 times

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Stable continuous electron emission has been obtained from GaAs electron cathodes which have been activated to a negative electron affinity condition. Negative electron affinity (NEA) photocathodes offer one means of producing very short electron pulses with a high peak brightness necessary for time‐resolved metrology. Despite concerns regarding the stability of such cathodes, we have demonstrated a high degree of short‐term stability through the ability to take scanning electron microscope photographs and Auger spectra using a NEA cathode. We have also demonstrated an effective brightness measured at the sample of 1×105 A/cm2 sr at 3 kV using our prototype electron gun. Room‐temperature operation and laser excitation of this cathode make it particularly well‐suited for low‐voltage time‐resolved electron probe and electron spectroscopy applications.
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85.60.Dw Photodiodes; phototransistors; photoresistors
72.40.+w Photoconduction and photovoltaic effects
79.90.+b Other topics in electron and ion emission by liquids and solids and impact phenomena (restricted to new topics in section 79)

Nanowriter: A new high‐voltage electron beam lithography system for nanometer‐scale fabrication

Z. W. Chen, G. A. C. Jones, and H. Ahmed

J. Vac. Sci. Technol. B 6, 2009 (1988); http://dx.doi.org/10.1116/1.584119 (5 pages) | Cited 9 times

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A new high‐voltage electron beam lithography system, Nanowriter, has been designed and constructed to give a large scan field size without compromising the ability to write nanometer‐scale structures. Nanowriter comprises a 100‐kV LaB6 electron gun with a zoom condenser arrangement consisting of two condenser lenses which are used to provide a system demagnification of up to 10 000 times. To combine a very small on‐axis spot diameter of 4 nm and a large scanned field of 250×250 μm without dynamic correction, a newly developed swinging objective immersion lens (SOIL) concept based on variable axis immersion lens (VAIL) and swinging objective lens (SOL) has been utilized. The SOIL used here has four advantages: first, it is possible to reduce the working distance, thereby decreasing spherical aberration; second, the scanned field is increased without significantly increasing deflection aberrations; third, it permits easy alignment of the column, and fourth, an inherent attribute of the SOIL is the shielding from extraneous magnetic fields given to the target. The substrate resides on an in‐lens stage which is supported on the boreless lower pole piece of the SOIL. The system has been used to delineate nanometer‐scale patterns in poly(methylmethacrylate) (PMMA) resist. Lines of 15‐nm width have been written into 50‐nm‐thick PMMA on thick Si substrates. These linewidths were almost unchanged over the whole scanned area of 250×250 μm.
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81.05.Lg Polymers and plastics; rubber; synthetic and natural fibers; organometallic and organic materials
81.65.-b Surface treatments
85.40.Hp Lithography, masks and pattern transfer

A vector‐scan thermal‐field emission nanolithography system

M. A. Gesley, F. J. Hohn, R. G. Viswanathan, and A. D. Wilson

J. Vac. Sci. Technol. B 6, 2014 (1988); http://dx.doi.org/10.1116/1.584120 (5 pages) | Cited 9 times

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A vector‐scan Gaussian beam lithography system has been retrofitted with a thermal‐field emission electron gun to improve resolution and increase target current density. The design combines a Zr/O/W〈100〉 cathode, three element electrostatic lens, and an octupole stigmator–deflector with the original objective lens and deflection system. Beam voltage is variable up to 25 kV. At high resolution, 1 nA emitted into a gun acceptance semiangle of α0=0.5 mrad is focused to 150 Å at the target with a current density of 500 A/cm2. The current density maximum corresponds to α0=2.2 mrad where a 23 nA, 25 kV probe current is focused to 300 Å with a final convergence angle of 3 mrad at 30‐mm working distance. These values imply a current density of 2.6×103 A/cm2 and an effective brightness of 9×107 A/cm2 sr at the target. The conversion is transparent to the original pattern generation–deflection system. This allows the design change to be rapidly incorporated with the existing subsystems. Proximity corrected 750‐Å features have been developed.
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85.40.Hp Lithography, masks and pattern transfer
79.70.+q Field emission, ionization, evaporation, and desorption

A thermally assisted field emission electron beam exposure system

H. Nakazawa, H. Takemura, M. Isobe, Y. Nakagawa, M. Hassel Shearer, and W. Thompson

J. Vac. Sci. Technol. B 6, 2019 (1988); http://dx.doi.org/10.1116/1.584121 (4 pages)

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Electron beam lithography is widely used to fabricate densely packed devices such as high‐frequency transistors, since optical lithography is unable to write the small patterns required for such devices. One major problem with micropattern writing with an electron beam exposure system, however, is slow writing speed; since the system has to write an extremely large number of patterns on low‐sensitivity resist with a highly focused beam, exposure times are quite long. To speed up the writing process, we have attached a thermal field emission gun to our electron beam exposure system. This gun is designed to increase the electron source brightness and probe current density. In order to determine this new probe current density, we conducted an extensive evaluation on a complete lithography system which uses a thermal field emission gun. We have measured a current density of ∼1000 A/cm2 at an accelerating voltage of 25 kV and conclude that this lithography system can be put to practical use in production areas requiring high throughput and submicron exposures.
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85.40.Hp Lithography, masks and pattern transfer
81.65.-b Surface treatments
85.30.Tv Field effect devices

Microstructures for particle beam control

G. W. Jones, S. K. Jones, M. Walters, and B. Dudley

J. Vac. Sci. Technol. B 6, 2023 (1988); http://dx.doi.org/10.1116/1.584122 (5 pages) | Cited 1 time

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Submicron lithography presents significant challenges to the fabrication of high‐density complex devices. Resolution, speed, critical dimension precision, variable design sets, and registration generally are conflicting goals for a lithography system. In this paper, we will present a new concept in electron or ion beam lithography with the potential to write far submicrometer patterns at speeds well beyond those of single beam systems currently available. This structure serves as a combined multiple aperture and beam deflection structure in a high‐speed multibeam raster scan writing system. The principle device structure to be discussed consists of an array of apertures micromachined into a portion of a silicon substrate with electrostatic deflection lines connected to each aperture. This structure is a key part of a lithography system with targeted 0.1‐μm‐pixel resolution. Apertures of 0.08 μm2 diameter with 10% dimensional control have been fabricated along with multiple multipole lenses using various microfabrication techniques. The paper will focus on the fabrication of these novel structures and will discuss potential system applications.
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85.40.Hp Lithography, masks and pattern transfer
81.65.-b Surface treatments
29.27.-a Beams in particle accelerators

EL3 system for quarter‐micron electron beam lithography

T. R. Groves, H. C. Pfeiffer, T. H. Newman, and F. J. Hohn

J. Vac. Sci. Technol. B 6, 2028 (1988); http://dx.doi.org/10.1116/1.584123 (5 pages) | Cited 1 time

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The introduction of the shaped beam imaging technique has greatly enhanced the exposure efficiency of electron beam (e‐beam) lithography systems. The electron beam lithography systems from IBM provide the throughput capability needed for lithography applications in semiconductor fabrication lines. The resolution of these systems has steadily improved over the past 15 years, in support of the semiconductor trend towards submicron dimensions. This paper describes the latest version EL3 system, capable of fabricating 0.25‐μm dimension features. The technical challenges of submicron e‐beam lithography are discussed. A practical solution is described, with experimental results. The outlook for the future is also highlighted.
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85.40.Hp Lithography, masks and pattern transfer
81.65.-b Surface treatments

A Monte Carlo simulation of electron beam lithography used to create 0.5‐μm structures on GaAs

K. D. Cummings and D. J. Resnick

J. Vac. Sci. Technol. B 6, 2033 (1988); http://dx.doi.org/10.1116/1.584124 (4 pages) | Cited 2 times

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We have used a positive trilevel resist structure on GaAs to verify our general purpose calculations of electron beam lithography. The model uses a single‐scattering Monte Carlo simulation of electron–solid interactions, a simple dissolution rate versus energy model for the resist, and a string model for resist development. The spot size of the electron beam was varied from 0.2 to 0.4 μm in diameter. Experimental results on scanning electron microscopy linewidths and wall profiles are in good agreement with the simulation. Using the model, we have determined the change in process latitude with increasing spot size. However, we find that the lithography process is still able to create 0.5‐μm lines even with large (0.4‐μm) spots.
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81.65.-b Surface treatments
85.40.Hp Lithography, masks and pattern transfer

Optimization of the proximity parameters for the electron beam exposure of nanometer gate‐length GaAs metal–semiconductor field effect transistors

W. Patrick and P. Vettiger

J. Vac. Sci. Technol. B 6, 2037 (1988); http://dx.doi.org/10.1116/1.584125 (5 pages) | Cited 1 time

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Proximity parameters are determined for the electron beam exposure of high‐resolution poly(methylmethacrylate) resist for the particular application of defining submicron gate lengths for GaAs metal–semiconductor field effect transistor (MESFET) structures. A ring‐shaped exposure cell is used to determine the various parameters of the popularly used double Gaussian approximation of the proximity function. The results are shown to be accurate for gate lengths in the range 0.1–0.5 μm. Using this technique for gate delineation, it is shown that very high performance GaAs MESFET devices and circuits can be achieved at sub‐0.5‐μm dimensions.
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85.30.Tv Field effect devices
85.40.Hp Lithography, masks and pattern transfer

Evaluation of the proximity effect and GHOST correction technique for submicron electron beam lithography at 50 and 20 kV

R. L. Kostelak, E. H. Kung, M. G. R. Thomson, and S. Vaidya

J. Vac. Sci. Technol. B 6, 2042 (1988); http://dx.doi.org/10.1116/1.584126 (6 pages)

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The magnitude of proximity effect for submicron electron beam lithography has been experimentally quantified using an electrical proximity effect tester (PET). The PET was delineated in MP 2400‐17 resist in a trilevel stack on aluminum, using an AT&T electron beam exposure system. At 50 kV the proximity exposure on a 0.5‐μm coded feature under the extreme layout conditions in the PET resulted in linewidth variation >0.25 μm. The effective range of the backscattered electrons was measured to be >10 μm. The GHOST proximity correction technique was used to reduce the magnitude of the linewidth variation. Using a 19‐μm defocused beam and a correction dose of 30% of the incident, the magnitude of the linewidth deviation on a 0.5‐μm feature was reduced to ±0.05 μm. However, the smallest feature that could be successfully GHOSTed was 0.375 μm at 50 kV. This was attributed to uncorrected electron scatter associated with the forward traveling electrons. Resolution of finer geometries was unpredictable. At 20 kV the resolution limit for successful proximity correction with GHOSTing was 0.5 μm. In conjunction with the experimental results, a computer model was used to confirm the limitations of the GHOSTing technique, as well as to establish the tolerances on the GHOST parameters, correction dose, and defocused beam size. At 50 kV the correction dose can vary from 27% to 33%, and the defocused beam diameter can vary from 15 to 26 μm with only a ±0.05‐μm linewidth variation on a 0.5‐μm feature.
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85.40.Hp Lithography, masks and pattern transfer
41.75.Fr Electron and positron beams

A parallel processing approach to proximity correction

O. W. Otto and A. K. Griffith

J. Vac. Sci. Technol. B 6, 2048 (1988); http://dx.doi.org/10.1116/1.584127 (5 pages)

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We present an approach to proximity effect computation in which the program is hosted on a parallel processor to accelerate the computation. Our requirements are: (i) factor of 100 speed improvement over a VAX‐11/780 (106 instructions/s), (ii) ability to handle dense patterns with 0.5‐μm design rules, (iii) ability to handle arbitrarily sized chips, and (iv) affordable processing power. We have concluded that parallel processing is a viable approach to realizing these goals. A parallel processing implementation will permit proximity correction of complex very large scale integrated (VLSI) patterns in a few hours instead of hundreds of hours. The proximity correction program is the functional equivalent of the one we have described previously. The program maintains pattern hierarchy insofar as possible, partitions features to permit edge placement control to 0.025 μm, and performs dose computations based on a multiple Gaussian scattering model. We have estimated that the best aggregate computation time per original pattern feature (before partitioning) in a dense pattern environment is ∼100 ms on a VAX‐11/780. We judge that reasonable throughput for real VLSI patterns will require a processing time below 1 ms per original pattern feature; hence, the factor of 100 speed improvement requirement. In this paper we describe our approach to structuring the programs so that a processor node deals with a small portion of the pattern at one time and to managing the computation so that most of the processor nodes are busy most of the time.
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85.40.Hp Lithography, masks and pattern transfer
07.05.Hd Data acquisition: hardware and software
07.05.Kf Data analysis: algorithms and implementation; data management
07.05.Rm Data presentation and visualization: algorithms and implementation
81.65.-b Surface treatments

Electron beam interaction with substrate in electron beam lithography: A scaling experiment to test transport theory

H. Schmoranzer

J. Vac. Sci. Technol. B 6, 2053 (1988); http://dx.doi.org/10.1116/1.584110 (4 pages)

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The interaction of the electron beam with the silicon substrate is studied by means of a scaling electron scattering experiment in gaseous neon. The scaling factor is given by the ratio of the electron ranges in the gas and in solid silicon and exceeds three orders of magnitude. The spatial intensity distribution of neon light emission excited by electron impact has been recorded and was evaluated as a measure of the spatial distribution of energy deposited. From the scaled measurements the range β of resist exposure by backscattered electrons was determined for primary energies from 10 to 40 keV. The analysis of the experimental data was supported by numerical treatment of the electron transport equation.
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85.40.Hp Lithography, masks and pattern transfer
81.65.-b Surface treatments
79.20.Kz Other electron-impact emission phenomena

Monte Carlo calculation of low‐energy electron emission from surfaces

T. E. Allen, R. R. Kunz, and T. M. Mayer

J. Vac. Sci. Technol. B 6, 2057 (1988); http://dx.doi.org/10.1116/1.584111 (4 pages) | Cited 16 times

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Monte Carlo calculations were carried out to estimate the spatial distribution of low‐energy secondary and backscattered electrons emitted from Si bombarded by low‐energy (<4 keV) electron beams. The calculation includes Mott scattering cross sections for elastic scattering, experimental and calculated electron inelastic mean free paths, the Streitwolf excitation function for production of secondary electrons, a simple cascade for transport of secondaries, and a surface refraction condition for emission. The spatial distribution of emitted secondary electrons was observed to be directly related to that of backscattered electrons in peripheral areas. The role of low‐energy electron emission in the efficiency and resolution of direct write electron beam processes is discussed and results of the calculation are presented.
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79.20.Hx Electron impact: secondary emission

Integrated data conversion for the electron beam exposure system EX‐7

K. Koyama, O. Ikenaga, T. Abe, R. Yoshikawa, T. Takigawa, and S. Watanabe

J. Vac. Sci. Technol. B 6, 2061 (1988); http://dx.doi.org/10.1116/1.584112 (5 pages)

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Because pattern data operations for electron beam (EB) lithography requires the knowledge of shape‐to‐shape correlation with adjacent patterns, the hierarchical structure embedded with the input data is usually expanded. Consequently, drastic increase in both the processing time and data amount has resulted. To overcome this problem a novel data conversion technique has been developed. It can exploit the hierarchical structure and repetitiveness originally incorporated into large‐scale integrated designs to efficiently generate EB pattern data. The conversion technique was implemented on a large‐scale computer to make pattern data for the EX‐7 EB exposure system. As a result, the highest density levels of 1‐ and 4‐Mbit direct random access memories (DRAMS), scaled down to 0.5 μm, were converted within 0.5 h of central processing unit (cpu) time, achieving an average data compaction of (1)/(20) . Overlap elimination and tone reversal were performed at a speed of 108 primitive shapes per hour. The data amount increased to 40 from 17 Mbytes of uncorrected data, when the proximity effect correction was performed on the shrinked 4‐Mbit DRAM pattern using this conversion technique.
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85.40.Hp Lithography, masks and pattern transfer
81.65.-b Surface treatments

Spot‐size measurement in an electron‐beam pattern generator.

T. Chisholm

J. Vac. Sci. Technol. B 6, 2066 (1988); http://dx.doi.org/10.1116/1.584113 (4 pages)

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The spot‐size measurement method introduced by Rishton et al. has been successfully adapted for use in any Philips Beamwriter. As the spot is scanned across an etched silicon edge mounted on a substrate holder, the current passing the edge is recorded by a waveform analyzer which then computes the spot size. Apart from initial calibration, the measurements are independent of the Beamwriter. Computer simulations show the influence on the final result of response speed, noise, and stage vibration. Good qualitative agreement between the simulations and measurements allows rules for obtaining accurate results to be formulated. Consistent measurements of spots from 21 to 500 nm have been obtained from several Beamwriters at a number of facilities. It is also shown that the Beamwriter’s internal measurements are accurate when allowance is made for the width of the edge of the marker used.
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85.40.Hp Lithography, masks and pattern transfer
41.75.Fr Electron and positron beams

Active electronic compensation of ambient magnetic fields for electron optical columns

S. D. Golladay

J. Vac. Sci. Technol. B 6, 2070 (1988); http://dx.doi.org/10.1116/1.584114 (4 pages) | Cited 1 time

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In order to reduce ac magnetic field interference with electron beam instruments, a relatively simple and inexpensive electronic field compensation system has been built. The system has a bandwidth extending from ∼8–200 Hz and reduces field strength at the sensor by a factor of about 50 (60 Hz). Because of inhomogeneities in the noise field, the compensated field strength increases with distance from the sensor, but is typically reduced by a factor between 10 and 50 at a distance of 10 cm for the case of a nonmagnetic environment. System performance in a magnetic environment, as in the application to an electron beam instrument, depends on sensor position. Fields within a simulated column consisting of a mu‐metal cylinder are reduced by a factor of 5 or more with sensor position optimized. ac magnetic field interference with an electron beam instrument was reduced by a similar factor.
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41.75.Fr Electron and positron beams
07.77.-n Atomic, molecular, and charged-particle sources and detectors

Quantitative analysis of resolution and stability in nanometer electron beam lithography

E. Kratschmer, S. A. Rishton, D. P. Kern, and T. H. P. Chang

J. Vac. Sci. Technol. B 6, 2074 (1988); http://dx.doi.org/10.1116/1.584115 (6 pages) | Cited 7 times

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A technique for the measurement of the beam diameter and the positional stability of an electron beam with respect to the substrate using an anisotropically etched silicon edge is described. Measurements are done either in a scanning beam mode to measure the beam diameter or in a stationary beam mode to measure beam positional noise. This technique has been used for a quantitative analysis of the resolution and stability in a 8‐nm spot size electron beam lithography system. The detection limit of the beam position stability measurements is <0.1 nm. Applications for the measurement of mechanical vibrations and acoustical noise, deflection amplifier noise, magnetic interference, and eddy currents in magnetic deflection systems are discussed.
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85.40.Hp Lithography, masks and pattern transfer
81.65.-b Surface treatments

Sub‐0.5‐μm lithography with a new ion projection lithography machine using silicon open stencil masks

L.‐M. Buchmann, L. Csepregi, A. Heuberger, K. P. Müller, A. Chalupka, E. Hammel, H. Löschner, and G. Stengl

J. Vac. Sci. Technol. B 6, 2080 (1988); http://dx.doi.org/10.1116/1.584116 (5 pages) | Cited 1 time

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An ion projection lithography system was equipped with an open stencil mask manufactured by applying silicon technology. By exposing poly(methylmethacrylate) and SiO2 to He+ ions, the pattern, transferred with a 9.5:1 reduction, showed structures with a minimum linewidth of 0.25 μm. The emphasis of this work concentrated on the various effects which produce distortion of the mask. Whereas linear dilation of the foil caused by compressive stress and enhanced by the network structure could be offset by means of the ion optical system, anisotropic distortion which resulted from the unequally distributed openings in the pattern had to be minimized by applying a suitable design. With a field effect transistor test pattern, an average distortion of 0.15 μm has been obtained in a 20×21 mm2 area of the mask. Only minor contributions to pattern deviations were expected from the temperature increase and sputter erosion.
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85.40.Hp Lithography, masks and pattern transfer
81.05.Kf Glasses (including metallic glasses)
81.65.-b Surface treatments
81.05.Lg Polymers and plastics; rubber; synthetic and natural fibers; organometallic and organic materials
79.20.Rf Atomic, molecular, and ion beam impact and interactions with surfaces

The dependence of droplet charge distribution on frequency in liquid metal ion sources

A. Bahasadri, W. L. Brown, R. Saedi, and K. Pourrezaei

J. Vac. Sci. Technol. B 6, 2085 (1988); http://dx.doi.org/10.1116/1.584128 (5 pages) | Cited 2 times

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The charge distribution of microdroplets emitted from liquid metal ion sources (LMIS’s) has been investigated as a function of total beam current. For microdroplets with charges of more than 10 000 electronic units, the distribution changes rapidly with total beam current for currents of more than 60 μA. The charge distribution has also been examined when the extractor of the LMIS is driven with an external ac voltage. The total emission of highly charged microdroplets shows a resonance at ∼4 kHz. This resonant behavior may be related to surface wave instabilities that have been suggested as a primary mechanism of droplet formation.
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07.77.-n Atomic, molecular, and charged-particle sources and detectors
85.40.Hp Lithography, masks and pattern transfer
41.75.Ak Positive-ion beams
41.75.Cn Negative-ion beams

Transverse thermal velocity broadening of focused beams from liquid metal ion sources

J. W. Ward, R. L. Kubena, and M. W. Utlaut

J. Vac. Sci. Technol. B 6, 2090 (1988); http://dx.doi.org/10.1116/1.584117 (5 pages) | Cited 7 times

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Experiments have shown that the target current density in focused ion beam columns have long ‘‘tails’’ outside the central submicron region. We show that these tails result from a transverse velocity distribution which has a Holtsmark probability density. Both theory and experiment show that the tails are reduced as the system magnification and source current are reduced.
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41.75.Ak Positive-ion beams
41.75.Cn Negative-ion beams
07.77.-n Atomic, molecular, and charged-particle sources and detectors
85.40.Hp Lithography, masks and pattern transfer

Extraction performance of dual‐grid ion optics: Simulation and experiment

D. Korzec, K. Schmitz, and J. Engemann

J. Vac. Sci. Technol. B 6, 2095 (1988); http://dx.doi.org/10.1116/1.584129 (5 pages) | Cited 4 times

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A comprehensive comparison between experimental and simulated data for the ion beam characteristics of a two‐grid extraction system is presented. An existing description for dc ion sources has been generalized and extended to capacitively coupled rf ion sources. The essential parameter in dc technology—the discharge voltage—was replaced by the plasma edge potential used also by simulation, allowing direct correlation between experimental and simulated data. Experimental results show 50% higher divergence angles if a part of the ion trajectories impinges on the accelerator grid. The reasons for this discrepancy are analyzed. Simple empirical formulas are proposed which describe the performance of the beamlet formed by one hole of a multiaperture extraction optic for a wide range of working conditions. These formulas permit better modeling of the broad beam and optimization of ion optics.
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41.75.Ak Positive-ion beams
41.75.Cn Negative-ion beams
85.40.Hp Lithography, masks and pattern transfer
81.65.-b Surface treatments

Focused ion beam induced optical emission spectroscopy

B. W. Ward, M. Ward, D. Edwards, and N. P. Economou

J. Vac. Sci. Technol. B 6, 2100 (1988); http://dx.doi.org/10.1116/1.584130 (4 pages) | Cited 1 time

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We describe a focused ion beam system and a spectroscopic technique that utilize photons emitted from electronically excited sputtered neutrals for surface element identification and end‐point detection. When a target is bombarded by a focused ion beam, some of the sputtered atoms (as much as 0.2%) leave the surface in electronically excited states and then quickly decay (10−6–10−8 s) by emitting photons of characteristic energies. A sputter‐induced optical emission spectrometer and elemental imaging system were constructed using a focused ion beam in conjunction with a wavelength‐selectable photon detector. Count rates as high as 104/s have been achieved for Al and Si with a 25‐keV, 1.5‐nA Ga+ beam. For these materials, an unambiguous elemental identification and/or end point can be determined by spectral analysis of the emitted photons. Details of the system and its performance will be discussed. In addition, the increase in yield of electronically excited neutrals from oxides or oxidized surfaces is discussed and the utility of a small gas jet to provide oxygen to the target surface is described. Effects of redeposition are considered as they relate to end‐point detection.
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82.80.Ms Mass spectrometry (including SIMS, multiphoton ionization and resonance ionization mass spectrometry, MALDI)
79.20.Rf Atomic, molecular, and ion beam impact and interactions with surfaces
07.60.Rd Visible and ultraviolet spectrometers
07.77.-n Atomic, molecular, and charged-particle sources and detectors

A new approach to simulating the operation of liquid metal ion sources

Cui Zheng and Tong Linsu

J. Vac. Sci. Technol. B 6, 2104 (1988); http://dx.doi.org/10.1116/1.584131 (4 pages) | Cited 7 times

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In order to simulate the electrically driven motion of conducting fluid occurring in the operation of liquid metal ion sources (LMIS’s), an equation system of electrohydrodynamics (EHD) has been set up, which includes gravity, viscosity, electrical stress, and surface tension. A set of numerical methods has been developed to compute the EHD equations. By means of a special technique, the MAC (marker and cell) method, the emitter shape of LMIS can be dynamically described without any assumptions. With the help of the numerical methods, a cylindrical fluid motion driven by electrical force and the liquid metal flow on a needle apex have been calculated. The results have thrown new light on the physical understanding of LMIS operation.
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41.75.Ak Positive-ion beams
41.75.Cn Negative-ion beams
07.77.-n Atomic, molecular, and charged-particle sources and detectors

A new method for improving gallium liquid metal ion source stability

C. S. Galovich and A. Wagner

J. Vac. Sci. Technol. B 6, 2108 (1988); http://dx.doi.org/10.1116/1.584094 (4 pages)

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The influence of backsputtered molybdenum and tin on gallium liquid metal ion source emission and focused currents is examined. In a typical ion gun arrangement, extractor and aperture surfaces act as sources of contaminant material. By selecting appropriate materials for the construction of these components, the stability of focused gallium ion currents is substantially improved. Materials which form a lower melting point solution when mixed with gallium, i.e., indium and tin, yield stable source operation and longer lifetimes. The implications of the long‐term use of these materials in an ion gun are discussed, as well as the increased ability to analyze the effects of residual gases and secondary electrons on source operation.
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07.77.-n Atomic, molecular, and charged-particle sources and detectors
41.75.Ak Positive-ion beams
41.75.Cn Negative-ion beams

High‐resolution fabrication process for silicon ion masks

F‐O. Fong, S. Sen, D. P. Stumbo, J. C. Wolfe, and John N. Randall

J. Vac. Sci. Technol. B 6, 2112 (1988); http://dx.doi.org/10.1116/1.584095 (3 pages) | Cited 1 time

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A process is described for fabricating silicon masks for ion beam lithography. Masks have been fabricated with 0.02‐μm features in 1.5‐μm‐thick silicon membranes.
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85.40.Hp Lithography, masks and pattern transfer
81.65.-b Surface treatments
79.20.Rf Atomic, molecular, and ion beam impact and interactions with surfaces

Applications of a variable energy focused ion beam system

D. H. Narum and R. F. W. Pease

J. Vac. Sci. Technol. B 6, 2115 (1988); http://dx.doi.org/10.1116/1.584096 (5 pages) | Cited 5 times

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A novel ion focused beam system has recently been designed and constructed that employs retarding field, electrostatic optics such that beams of Ga+ ions with energies as low as 25 eV can be focused into a submicron diameter spot. In this paper we review the ion‐optical performance of this system and then describe the interactions of the beam with the target. In the conventional mode (30‐keV landing energy) the system has been used to sputter etch tracks in gold (on a silicon substrate) of width 0.16 μm. However, as the landing energy is reduced below 200 eV, the action of sputter etching gives way to deposition and tracks of gallium 1.5 to 3 μ wide have been laid down in this manner. That the tracks were indeed gallium was confirmed by x‐ray microanalysis. The appearance of the tracks suggested that the interface between the gallium and the substrate affects the morphology of the track. Two obvious and prosaic applications include the repair of both clear and opaque mask defects, and making and breaking integrated circuit electrical interconnections. More ambitious applications include combining the system with molecular‐beam epitaxy to build true three‐dimensional, sub‐0.1‐μm device structures.
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41.75.Ak Positive-ion beams
41.75.Cn Negative-ion beams
85.40.Hp Lithography, masks and pattern transfer
07.77.-n Atomic, molecular, and charged-particle sources and detectors

Preliminary experimental study of the multiple ion beam machine

Masaaki Ando and Julius J. Muray

J. Vac. Sci. Technol. B 6, 2120 (1988); http://dx.doi.org/10.1116/1.584097 (4 pages) | Cited 1 time

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The multiple ion beam machine (MIBM) that we are developing for nanolithography offers important advantages over other nanolithography machines. A focused ion beam machine [R. L. Seliger, R. D. Olney, J. W. Ward, and V. Wang, J. Vac. Sci. Technol. 16, 1610 (1979)] uses a single ion beam to write the pattern. As a result, each chip on a wafer must be written individually thus leading to low throughput for high‐volume production. On the other hand, an ion projection lithography machine (G. Stengel, H. Löshner, and J. J. Muray, Solid State Technol. 1986, 119) has a high throughput; however, it is inconvenient in that it requires a special mask to be made for each lithographic pattern. The MIBM uses multiple focused ion beams, which are deflected and blanked in synchronism, each beam being used to write a single chip. Thus, the exposure time for the whole wafer is the same as is required to write a single chip, resulting in a high throughput.
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85.40.Hp Lithography, masks and pattern transfer
81.65.-b Surface treatments
41.75.Ak Positive-ion beams
41.75.Cn Negative-ion beams
07.77.-n Atomic, molecular, and charged-particle sources and detectors

Defect study in GaAs bombarded by low‐energy focused ion beams

Kenji Gamo, Hideto Miyake, Yoshihiko Yuba, Susumu Namba, H. Kasahara, H. Sawaragi, and Ruso Aihara

J. Vac. Sci. Technol. B 6, 2124 (1988); http://dx.doi.org/10.1116/1.584098 (4 pages) | Cited 8 times

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GaAs was exposed to focused Ga+ beams at various beam energies ranging from 100 eV to 150 keV to investigate properties of defects induced by low‐energy focused ion beams. Defect concentration and distribution profiles were measured by the deep‐level transient spectroscopy technique. It was found that the defect concentration is greatly reduced for irradiation at a beam energy below 1 keV. Defects were observed even at a depth of ≥1500 Å, which is far beyond the ion range (∼15 Å) for 1‐keV Ga+ . This indicates that the defect is induced by diffusion and trapping of mobile primary defects. It was also found that the defects induced by the low‐energy irradiation are easily annealed out at 600 °C, while the defects induced by the high‐energy irradiation still exist after annealing at 850 °C.
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61.80.Jh Ion radiation effects
81.65.-b Surface treatments
61.72.Bb Theories and models of crystal defects

Precisely controlled oscillating mirror system for highly uniform exposure in synchrotron radiation lithography

K. Fujii, K. Okada, M. Nagano, and H. Kuroda

J. Vac. Sci. Technol. B 6, 2128 (1988); http://dx.doi.org/10.1116/1.584099 (4 pages)

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A novel oscillating mirror system in the synchrotron radiation lithography beam line, installed in the Photon Factory storage ring (2.5 GeV), has been studied with special reference to scanning speed control for the synchrotron radiation beam. Concerning an oscillating mirror used in the total reflection region, it should be noted that the cutoff x‐ray wavelength depends on the glancing angle. That is, the total photon energy for the reflected varies as a function of the position of the beam irradiating the wafer. An oscillating mirror system has been investigated, in which the scanning speed for the synchrotron radiation beam can be controlled as a function of the glancing angle of the synchrotron radiation beam with reference to the mirror. Exposure result achieved using the oscillating mirror system, showed that extremely high x‐ray dose uniformity, ∼±3%, was obtained over the 25‐mm‐sq. exposure area.
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85.40.Hp Lithography, masks and pattern transfer
81.65.-b Surface treatments
07.85.-m X- and γ-ray instruments

Experimental results with a scanning stepper for synchrotron‐based x‐ray lithography

E. Cullmann and K. Cooper

J. Vac. Sci. Technol. B 6, 2132 (1988); http://dx.doi.org/10.1116/1.584100 (3 pages) | Cited 1 time

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A second generation of synchrotron‐compatible x‐ray steppers is described which uses the scanning exposure method to minimize overhead time between alignment and exposure. Available x‐ray intensity is increased, since a thin exposure window, only a few mm high, can be used to separate the beam line vacuum from the exposure tool which operates in ambient air. First results indicate sufficient mechanical stability to allow the mask/wafer unit to be scanned in an aligned position.
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07.85.-m X- and γ-ray instruments
85.40.Hp Lithography, masks and pattern transfer

An x‐ray stepper for synchrotron radiation lithography

Eiichi Kouno, Yoshiharu Tanaka, Joji Iwata, Yoshiyuki Tasaki, Emi Kakimoto, Koichi Okada, Katsumi Suzuki, Kiyoshi Fujii, and Eiichi Nomura

J. Vac. Sci. Technol. B 6, 2135 (1988); http://dx.doi.org/10.1116/1.584101 (4 pages) | Cited 1 time

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A prototype synchrotron radiation (SR) stepper for quarter‐micron devices has been developed and installed at the Photon Factory in the National Laboratory for High Energy Physics, Japan. The stepper features are, (i) exposure in an atmospheric environment, (ii) large exposure area (25‐mm sq), and (iii) alignment error detection at all times, including during exposure. The stepper consists of an SR extracting chamber, precision mechanical stages, and an alignment error detection system. An SR beam in UHV goes through a beryllium window into an atmospheric environment, and covers the 25‐mm sq exposure area by using an oscillating mirror. Patterns on a mask are imprinted onto a wafer. Mask and wafer are, respectively, held in place with vacuum chucks. Their subsequent positioning movements are driven in 6 degrees of freedom by piezoelectric actuators for fine alignment and gap setting. The alignment system, based on the previous Fresnel lens optical system, newly employs a differential mode linear Fresnel zone plate alignment method. As the optical system for this method is located at the outside of an SR beam, it can detect an alignment error between a mask and a wafer at all times, including during exposure. Patterns measuring 0.2 μm were completely successfully imprinted on a wafer. Until now, 0.03‐μm (3σ) positioning accuracy and 0.2‐μm (3σ) overlay accuracy were achieved.
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07.85.-m X- and γ-ray instruments
85.40.Hp Lithography, masks and pattern transfer

Magnification corrected imaging in synchrotron radiation x‐ray lithography

K.‐H. Müller, K. Brehm, and K. Werner

J. Vac. Sci. Technol. B 6, 2139 (1988); http://dx.doi.org/10.1116/1.584102 (3 pages) | Cited 1 time

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X‐ray masks for ultra‐large‐scale integration (ULSI) chips having critical dimensions of ∼0.3 μm and field areas of 10 cm2 will be limited by the overlay budget. In this case, a compensation of the linear distortions of mask and wafer can be advantageous. In x‐ray lithography, using point sources with divergent radiation, the magnification adaption can be done by slightly varying the proximity gap between mask and wafer. However, this method is insufficient for synchrotron radiation (SR) where the exposing beam is nearly parallel. The illumination is based on a scan motion of the beam with respect to the mask field. We have developed a new technique of magnification correction for SR lithography. In the vertical direction, the correction is done by synchronous shifting of the mask with respect to the wafer. In the horizontal direction, the correction is achieved by bending the wafer by clamping it on a cylindrical chuck. This method compensates for linear overlay deviations in each direction separately; it also holds for trapezoidal errors. In our experiments we used a Suss x‐ray stepper and SR of the Berlin electron storage ring (BESSY). Magnification variations on the order of 10 ppm were measured using a Leitz MPV‐CD.
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85.40.Hp Lithography, masks and pattern transfer
81.65.-b Surface treatments
07.85.-m X- and γ-ray instruments

Moiré method and zone plate pattern inaccuracies

Y. Vladimirsky and H. W. P. Koops

J. Vac. Sci. Technol. B 6, 2142 (1988); http://dx.doi.org/10.1116/1.584103 (5 pages) | Cited 7 times

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Moiré patterns obtained from superimposed zone plates with common types of pattern inaccuracies are analyzed. Tolerances for the distortions characterized as ellipticity, radial displacement, and nonconcentricity of the zones, are obtained from the corresponding equations for lenses. The formulas for moiré fringes resulting from superimposed zone plate patterns having these defects are derived. The feasibility of moiré pattern techniques to detect and measure inaccuracies of the zone plate is demonstrated. The sensitivity and the limitations of the method are discussed.
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42.79.Ci Filters, zone plates, and polarizers
07.85.-m X- and γ-ray instruments

Fabrication of fully scaled 0.5‐μm n‐type metal–oxide semiconductor test devices using synchrotron x‐ray lithography: Overlay, resist processes, and device fabrication

J. P. Silverman, V. DiMilia, D. Katcoff, K. Kwietniak, D. Seeger, L. K. Wang, J. M. Warlaumont, A. D. Wilson, D. Crockatt, R. Devenuto, B. Hill, L. C. Hsia, and R. Rippstein

J. Vac. Sci. Technol. B 6, 2147 (1988); http://dx.doi.org/10.1116/1.584104 (6 pages) | Cited 2 times

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Functional, fully scaled n‐type metal–oxide semiconductor (NMOS) circuits with 0.5‐μm ground rules have been fabricated using synchrotron radiation x‐ray lithography for all device levels. The exposures were done at the vacuum ultraviolet storage ring of the National Synchrotron Light Source at Brookhaven National Laboratory using a mask/wafer aligner developed at IBM Research. The system is capable of step‐and‐repeat exposures covering 125‐mm wafers. The mask and wafer are held in a near‐vertical plane and a scanning dark‐field alignment technique is used to register mask to wafer with a proximity gap of 40 μm. A scanning mirror in the beamline sweeps the x‐ray beam up and down over the exposure area to achieve uniform exposure over the 25×25 mm2 exposure field used for this experiment. Exposures were done in 20 Torr of helium to provide cooling for the mask. Both positive and negative tone single‐layer resists were used. The mask set consists of four light‐field masks patterned on silicon substrates with electroplated gold absorbers; patterns were written by a vector scan electron beam lithography system. The performance of the aligner on both test wafers and device wafers is discussed, with emphasis on overlay and linewidth control. The repeatability of the alignment and the overall level‐to‐level overlay are described. Characteristics of the fabricated devices are also presented.
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85.30.Tv Field effect devices
85.40.Hp Lithography, masks and pattern transfer
81.65.-b Surface treatments
07.85.-m X- and γ-ray instruments

Applications of microfabrication technology to x‐ray laser cavities

Andrew M. Hawryluk, Natale M. Ceglio, and Daniel G. Stearns

J. Vac. Sci. Technol. B 6, 2153 (1988); http://dx.doi.org/10.1116/1.584105 (5 pages) | Cited 6 times

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We have fabricated new, efficient x‐ray optical components (x‐ray mirrors, beamsplitters, and highly dispersive multilayer mirrors) and have used them to build an x‐ray laser cavity. With our laser cavity, we have demonstrated multipass amplification of soft x rays with significant enhancement (>20×) of the x‐ray laser emission. This is an important first step in the ultimate conversion of x‐ray amplifier media into true x‐ray lasers with optimized coherence and divergence properties. We used advanced microfabrication techniques to fabricate the key laser cavity components which require precise layering of alternating materials, thin‐film membrane technology, and precise patterning. The x‐ray laser requirements, fabrication details, and characterization results for these cavity components are discussed.
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42.60.Da Resonators, cavities, amplifiers, arrays, and rings

Sensitivity‐enhanced x‐ray lithography using radiation‐induced grafting to poly(phenyl methacrylate)

Kozo Mochiji, Hiroaki Oizumi, Yasunari Sooda, Taro Ogawa, and Takeshi Kimura

J. Vac. Sci. Technol. B 6, 2158 (1988); http://dx.doi.org/10.1116/1.584106 (4 pages) | Cited 1 time

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Poly(phenyl methacrylate) (PPhMA) is utilized as a base resist of radiation‐induced graft copolymerization for the purpose of high‐throughput x‐ray lithography. PPhMA has dry‐etching resistance due to the aromatic ring in its side chain and, therefore, it can be used for large‐scale integration (LSI) fabrication. Gaseous acrylic acid is grafted into PPhMA film to produce a copolymer which is insoluble in the solvent of PPhMA. The graft processing enhances the resist sensitivity by three orders of magnitude to the level of 10 mJ/cm2 . The swelling of the grafted resist during development is drastically minimized by formation of a cross‐linked structure in the grafted resist by thermal dehydration of acrylic acids. The above technique successfully provided a negative pattern with feature size down to 0.3 μm.
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85.40.Hp Lithography, masks and pattern transfer
07.85.-m X- and γ-ray instruments

Soft x‐ray projection lithography using an x‐ray reduction camera

Andrew M. Hawryluk and Lynn G. Seppala

J. Vac. Sci. Technol. B 6, 2162 (1988); http://dx.doi.org/10.1116/1.584107 (5 pages) | Cited 18 times

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Soft x‐ray projection lithography can now be realized with recent developments in x‐ray optics. Using new x‐ray optical components and spherical imaging optics, we have designed an x‐ray reduction camera which is capable of projecting with soft x‐ray radiation, a 5× demagnified image of a mask onto a resist coated wafer. The resolution of this design is ∼100 nm with a depth of focus of ±5.6 μm and a 0.5‐cm‐diam image field. We use x‐ray reflecting masks (patterned x‐ray multilayer mirrors) which are fabricated on thick substrates and can be made relatively distortion free. Our design uses a laser produced plasma for the x‐ray source. Better resolution and/or larger areas are possible with improvements in optic figures and source characteristics.
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07.85.-m X- and γ-ray instruments
85.40.Hp Lithography, masks and pattern transfer

Characteristics of optical components for soft x‐ray microscopy and x‐ray holography using an undulator radiation optical system

M. Kakuchi, H. Yoshihara, T. Tamamura, H. Maezawa, Y. Kagoshima, and M. Ando

J. Vac. Sci. Technol. B 6, 2167 (1988); http://dx.doi.org/10.1116/1.584108 (3 pages) | Cited 1 time

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X‐ray optical components, including Fresnel zone plates and transmission gratings, have been fabricated using finely focused electron beam lithography and Ta‐on‐SiN x‐ray mask fabrication technology. The optical components for x‐ray microscopy and x‐ray holography were evaluated in an undulator radiation optical system.
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42.79.Ci Filters, zone plates, and polarizers
07.85.-m X- and γ-ray instruments
42.79.Dj Gratings
42.40.Kw Holographic interferometry; other holographic techniques

Repair of electroplated gold masks for x‐ray lithography

U. Weigmann, H.‐C. Petzold, H. Burghause, R. Putzar, and H. Schaffer

J. Vac. Sci. Technol. B 6, 2170 (1988); http://dx.doi.org/10.1116/1.584109 (4 pages) | Cited 1 time

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X‐ray lithography now enters a stage where its potential is tested by making real circuits. Since defects on x‐ray masks strongly affect the performance of x‐ray lithography, the repair of mask defects becomes very important. This paper discusses results on the repair of opaque and clear defects on electroplated gold‐on‐silicon x‐ray masks using a 100‐kV focused ion beam system from Vacuum Generators and laser‐induced photolytic deposition of tin from a Sn(CH3)4 atmosphere, respectively.
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85.40.Hp Lithography, masks and pattern transfer
85.40.Ls Metallization, contacts, interconnects; device isolation
81.65.-b Surface treatments

Use of ion implantation to eliminate stress‐induced distortion in x‐ray masks

Yao C. Ku, Henry I. Smith, and Irving Plotnik

J. Vac. Sci. Technol. B 6, 2174 (1988); http://dx.doi.org/10.1116/1.584077 (4 pages)

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One of the most important questions with regard to using x‐ray lithography for integrated circuit manufacturing is whether distortion in the x‐ray mask, caused by intrinsic stress in the absorber material, can be made sufficiently small for all types of patterns. Pattern features should deviate from their assigned in‐plane positions by no more than a fraction of the minimum linewidth. Tungsten (W) is a more desirable absorber than gold because of its thermal stability and its closer match to the thermal expansion coefficient of Si. However, it is difficult to reproducibly deposit W films with zero stress. We describe a compensation technique for eliminating distortion, regardless of the initial absorber stress. Experiments were done on 0.3–0.4‐μm‐thick W patterned on 1‐μm‐thick Si and Si3N4 membranes, suitable for x‐ray masks. Distortions caused by tensile stresses ∼109 dyns/cm2 can be eliminated by Si implantation at doses ∼1016 cm−2. Measurements of deflections at an edge were made using a Linnik interferometer, and from this the stress was calculated. Si ions were implanted to a projected range of 10 nm in the W at doses in the range 1015–1016 cm−2. Distortion correction takes place because the implantation produces compressive stress near the upper surface, resulting in a torque that balances a torque of opposite sign at the absorber–membrane interface due to tensile stress in the W. We present a theory for stress compensation together with an empirical prescription for eliminating stress‐induced distortion. We also report crystallographic analysis of the W and describe a method for getting α‐phase W, in either tensile or compressive stress, which appears to be highly stable.
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68.60.Bs Mechanical and acoustical properties
68.55.-a Thin film structure and morphology
85.40.Hp Lithography, masks and pattern transfer
68.55.Ln Defects and impurities: doping, implantation, distribution, concentration, etc.

Mechanical characterization of membranes for x‐ray lithography masks

C. E. Uzoh, J. R. Maldonado, S. S. Dana, R. Acosta, I. Babich, and O. Vladimirsky

J. Vac. Sci. Technol. B 6, 2178 (1988); http://dx.doi.org/10.1116/1.584078 (6 pages) | Cited 3 times

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This paper presents experimental results on the mechanical properties of x‐ray mask substrates. Relevant mechanical properties were determined using an automatic system which plots membrane deformation versus applied differential pressure. In the system, the substrate is held in a leak‐tight chuck, and a differential pressure is applied across the membrane by compressed nitrogen. The resulting bulging of the membrane is measured with a laser gauge. The results obtained allow determination of the Young’s modulus, mechanical hysteresis, tension, and fracture strength of x‐ray lithography mask membranes. Relatively thin (1–7 μm) membranes of different geometries, and of several materials including B‐doped Si and boro–hydro–nitride were characterized. In addition, data that shed light on the role of polyimide coatings on the mechanical integrity of the membranes are presented.
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85.40.Hp Lithography, masks and pattern transfer
68.60.Bs Mechanical and acoustical properties

Sub‐half‐micron critical dimension control in x‐ray lithography mask technology

H.‐L. Huber, S. Pongratz, J. Trube, W. Windbracke, U. Mescheder, and F. Mund

J. Vac. Sci. Technol. B 6, 2184 (1988); http://dx.doi.org/10.1116/1.584079 (6 pages) | Cited 1 time

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The main problems in x‐ray mask fabrication concern the defect density, the pattern placement accuracy, and the critical dimension (CD) control. To demonstrate the performance of x‐ray lithography, it is necessary to fabricate sub‐half‐micron features with high reproducibility and small linewidth variations. This requires an absorber patterning procedure with extremely high stability and homogeneity and additionally a measuring technique with high accuracy in the sub‐half‐micron range in order to control the linewidth quality. It has been shown that mask fabrication can fulfill most of the requirements on x‐ray mask technology using electron beam (e‐beam) writing in a trilevel process with electroplated gold absorbers. Furthermore, a copying procedure was developed which multiplies an e‐beam written master mask by using x‐ray lithography in a single‐layer resist and again gold electroplating. To characterize the linewidths and their variations, an e‐beam based measuring technique is presented, which is able to measure quarter‐micron CD’s with an accuracy of ∼25 nm as a 3σ value. The aim of this paper is to demonstrate the homogeneity of the running mask technology including the mask copying process and the feasibility of the applied measuring technique. Results are presented showing clearly that linewidth variations can be limited to 50 nm for both master mask and mask copy. X‐ray masks with gate lengths down to a quarter‐micron dimension have been fabricated in this quality. The technological ways to achieve these results are summarized in this paper.
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85.40.Hp Lithography, masks and pattern transfer
81.65.-b Surface treatments

Quantitative in situ characterization of x‐ray mask distortions

G. M. Wells, G. Chen, D. So, E. L. Brodsky, K. Kriesel, F. Cerrina, and M. Karnezos

J. Vac. Sci. Technol. B 6, 2190 (1988); http://dx.doi.org/10.1116/1.584080 (6 pages) | Cited 1 time

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The control of x‐ray mask distortion is a central issue in x‐ray lithography technology. Three causes of distortion have been examined: the interaction between a stressed absorber and substrate, the heating of the mask during x‐ray exposure, and the radiation damage resulting from the cumulative absorption of the x rays. Interferometric techniques have been used to measure both in‐plane distortion (IPD) and out‐of‐plane distortion (OPD). To measure OPD, wave fronts reflected from the mask surface are compared with a reference plane wave. For IPD it is necessary to have a diffraction grating on the mask. IPD causes changes in the grating pitch that result in the changes in the interference pattern. For thermal studies, an in situ shear interferometer was used to measure both OPD and IPD. Temperature increases were monitored using an infrared camera. The results have been modeled using the finite element program ansys. The distortion due to aborber substrate interaction was observed to occur at pattern edges. Thermal distortions were observed to cause IPD in regions with no absorber and both IPD and OPD for areas covered with absorber. Radiation damage was found to cause both IPD and OPD. The OPD was in the form of a plateau and can be modeled assuming the relaxation of the material is dependent on the absorbed dose and taking into account the depth dependence on absorption in the mask.
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85.40.Hp Lithography, masks and pattern transfer
07.85.-m X- and γ-ray instruments

Fully scaled 0.5 μm metal–oxide semiconductor circuits by synchrotron x‐ray lithography: Mask fabrication and characterization

R. Viswanathan, R. E. Acosta, D. Seeger, H. Voelker, A. Wilson, I. Babich, J. Maldonado, J. Warlaumont, O. Vladimirsky, F. Hohn, D. Crockatt, and R. Fair

J. Vac. Sci. Technol. B 6, 2196 (1988); http://dx.doi.org/10.1116/1.584081 (6 pages)

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Several sets of x‐ray masks for a metal–oxide semiconductor (MOS) device program were fabricated using boron‐doped silicon as the membrane and gold as the absorber. The metrology of the mask sets was characterized. Mask‐to‐mask overlay error is <0.12 μm (3σ) including measurement error. Absorber induced distortion is not the dominating mask error. (Lack of better measurement systems and techniques preclude exact analysis of errors.) Quarter‐micron patterns have been resolved using a multilayer resist system. Linewidth variations are <0.017 μm (1σ) across the entire membrane. The mask sets have been successfully used to fabricate fully scaled n‐type MOS circuits.
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85.30.Tv Field effect devices
85.40.Hp Lithography, masks and pattern transfer
07.85.-m X- and γ-ray instruments
85.30.De Semiconductor-device characterization, design, and modeling

High‐resolution and high‐fidelity x‐ray mask structure employing embedded absorbers

S. Y. Chou, N. I. Maluf, and R. F. W. Pease

J. Vac. Sci. Technol. B 6, 2202 (1988); http://dx.doi.org/10.1116/1.584082 (5 pages)

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Existing x‐ray masks often suffer from a variety of problems. These include poor adhesion of small absorber features to the substrate, severe undercut in the etching of sub‐half‐micron absorber lines, distortion of absorbing features formed by plating through a resist stencil, distortion of the absorber due to metal migration and due to local stress, and mechanical damage due to handling. Here we describe an x‐ray mask structure in which a high atomic number metal fills trenches etched into a single‐crystal silicon mask membrane. Thus the problems mentioned earlier for conventional x‐ray masks can be either effectively eliminated or greatly reduced. The trenches were formed in the silicon by a combination of ultrathin resist, high‐resolution electron beam exposure, and novel etching techniques involving metal masking. The trenches were half‐micron deep with a sidewall angle of 1.5° to the vertical, and the minimum trench width measured at the top of the trenches was 70 nm, which gives an aspect ratio of 7:1. The trenches were filled with tungsten by both selective and nonselective chemical vapor deposition, and back etching (if any) was performed using reactive ion etching. Scanning electron microscopy reveals that the tungsten features are faithful replicas of the vertically walled trenches. A one‐dimensional stress model shows that for a finite absorber stress, the embedded mask can have zero in‐plane distortion and an out‐of‐plane distortion that is much less than that in a conventional mask.
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85.40.Hp Lithography, masks and pattern transfer
81.65.-b Surface treatments

Optical printability of defects in two‐dimensional patterns

Bachvan Huynh, K. K. H. Toh, W. E. Haller, and A. R. Neureuther

J. Vac. Sci. Technol. B 6, 2207 (1988); http://dx.doi.org/10.1116/1.584083 (6 pages) | Cited 1 time

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Experiments, simulation, and algebraic analysis are used to characterize the printability of defects in various classes of features in optical projection printing. A special test mask was designed with programmed defects located adjacent to isolated lines, arrays of lines, corners, elbows, and nested elbows. These patterns were then projection printed in an exposure–focus matrix in a positive resist process on various substrates and examined in detail via scanning electron micrographs. For small defects of both polarities, the linewidth variation on isolated lines is shown to be K∗ (defect area) where K is 1 and 2.4 for transparent and opaque defects, respectively. For equal line and space arrays of minimum‐sized features [0.8∗ λ/numerical aperture (NA)], opaque defects as small as 0.3∗ λ/NA cause bridging while transparent defects as large as 0.5∗ λ/NA do not cause opens. Elbows and nested elbows are slightly more sensitive than arrays of lines due to intrafeature proximity effects. The interior corners are also sensitive to defects. Underexposure greatly increases the effects of opaque defects while defocus has little impact. The effects on aluminum substrates show similar trends to those on silicon while for thin resist on silicon, even much smaller defects print. The printability of transparent defects in positive resist is easy to model and a constant intensity threshold model is generally adequate. For opaque defects, nonvertical resist development effects typically occur and must be included in the simulation.
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85.40.Hp Lithography, masks and pattern transfer
85.40.Qx Microcircuit quality, noise, performance, and failure analysis

Mask bias in submicron optical lithography

Chris A. Mack and Patricia M. Kaufman

J. Vac. Sci. Technol. B 6, 2213 (1988); http://dx.doi.org/10.1116/1.584084 (8 pages) | Cited 2 times

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The effects of mask bias on the performance of an optical lithographic process are examined theoretically and experimentally. By studying the effects of bias on the aerial image, the fundamental reasons for process improvement with bias are made clear. Simulations are used to examine mask linearity and exposure and focus latitude as a function of bias. Experimental data confirm the improvement in latitude for isolated lines with bias. The proximity effect is investigated and shown to be not well understood. Two possible explanations for the proximity effect: image flare and developer depletion, are studied.
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85.40.Hp Lithography, masks and pattern transfer
81.65.-b Surface treatments

Three‐dimensional photolithography with conformal GeSe resist

Richard G. Vadimsky

J. Vac. Sci. Technol. B 6, 2221 (1988); http://dx.doi.org/10.1116/1.584085 (3 pages) | Cited 2 times

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Arrays of 80‐μm‐high mesas and 250‐μm‐deep wells were formed in silicon using conventional etching techniques. Oxide and metal patterns were photodefined over the sloping walls of these structures using the inorganic resist Ag2Se/Ge0.15Se0.85. A 2000‐Å‐thick conformal coating of the chalcogenide Ge0.15Se0.85 was sputter deposited onto the etched silicon wafers. Sensitized in a Ag(CN)−2 containing aqueous bath, the resist was exposed through a mask on a contact printer. Patterns were delineated using established wet chemical developing procedures and then transferred to underlying oxide or metal to form implant windows or metal conductors, respectively. Image defocusing over the depth of the etched silicon features produced some linewidth changes down the sloping walls, but useful conductors were fabricated.
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81.65.-b Surface treatments
85.40.Hp Lithography, masks and pattern transfer
85.30.De Semiconductor-device characterization, design, and modeling
85.40.Ls Metallization, contacts, interconnects; device isolation

Organometallic materials in lithography: A review

M. Hatzakis, J. Shaw, E. Babich, and J. Paraszczak

J. Vac. Sci. Technol. B 6, 2224 (1988); http://dx.doi.org/10.1116/1.584086 (5 pages) | Cited 3 times

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Organosilicon polymers have found many uses in the electronics industry in the last 25 years due to their low‐dielectric constant and water‐repelling properties. These uses include insulators and encapsulating materials (RTV) for electronic parts. More recently, siloxanes have been incorporated into polyimides for the purpose of increasing the water resistance, improving mechanical properties, and preventing atomic oxygen attack of polyimides [R. H. Bott, J. D. Summers, C. A. Arnold, L. T. Taylor, T. C. Ward, and J. E. McGrath, J. Adhes. 23, 67 (1987)]. In only the last few years, some uses of organosilicon polymers in lithography have been reported. In this paper, a review of these uses will be presented and the requirements for organosilicon materials in lithographic applications will be outlined.
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81.05.Lg Polymers and plastics; rubber; synthetic and natural fibers; organometallic and organic materials
81.65.-b Surface treatments
85.40.Hp Lithography, masks and pattern transfer

Thin titanium dioxide films as interlayers in trilayer‐resist structures

L. E. Stillwagon, A. Kornblit, and G. N. Taylor

J. Vac. Sci. Technol. B 6, 2229 (1988); http://dx.doi.org/10.1116/1.584087 (5 pages) | Cited 1 time

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The use of thin titanium dioxide (TiO2 ) films as interlayers in trilayer‐resist structures was investigated in this paper. TiO2 layers, 30–200 Å thick, were formed on the surface of thick positive photoresist films by the reaction of titanium tetrachloride (TiCl4 ) with water adsorbed on the surface of the films. The TiCl4 ‐treated films served as the bottom two layers in trilayer‐resist structures. Using a thin TiO2 interlayer that acted as the mask in the final reactive ion etching pattern transfer step, 0.5‐μm features were transferred from a top imaging layer to a 1.2‐μm‐thick bottom layer with ∼0.05‐μm linewidth loss. Processing variables that affect the thickness of the TiO2 films were investigated. We discuss these variables, etching techniques for transfer of the resist pattern from the top imaging layer to the TiO2 interlayer and pinhole defects in the TiO2 films.
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68.65.-k Low-dimensional, mesoscopic, nanoscale and other related systems: structure and nonelectronic properties
85.40.Hp Lithography, masks and pattern transfer
68.55.Ln Defects and impurities: doping, implantation, distribution, concentration, etc.

Resist development described by least action principle‐line profile prediction

E. Barouch, B. D. Bradie, and S. V. Babu

J. Vac. Sci. Technol. B 6, 2234 (1988); http://dx.doi.org/10.1116/1.584088 (4 pages) | Cited 1 time

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A new idea is introduced requiring that each development path will be the path of least resistance to developer penetration. Consequently, minimum dissolution time is required for the development of the final line profile. This idea manifests itself in a variational calculation of the path integral along each local development trajectory, from which the dissolution profile is obtained uniquely, as a solution of a nonlinear partial differential equation (PDE). The photoactive compound (PAC) concentration is obtained from the standard Dill’s equations for the exposure–bleaching process for both monotonic as well as standing waves. The procedure has been implemented and tested. It has been found to be very accurate and it eliminates the path crossings inherent in the predictions of the string algorithm. The arbitrary elimination of unfavorable points is avoided as well for all developing times.
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85.40.Bh Computer-aided design of microcircuits; layout and modeling
85.40.Hp Lithography, masks and pattern transfer

Contrast and sensitivity enhancement of resists for high‐resolution lithography

Kaolin Grace Chiong, Karen Petrillo, Fritz J. Hohn, Alan D. Wilson, and Wayne M. Moreau

J. Vac. Sci. Technol. B 6, 2238 (1988); http://dx.doi.org/10.1116/1.584089 (7 pages)

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Novolac based resists have received much attention in the submicron device fabrication area because of their high dry etch resistance. In high‐resolution device fabrication requirements novolac resists suffer from a lack in sensitivity and resolution capability. In order to make use of these high‐quality resists, approaches to improve the resolution capability and sensitivity of conventional positive resists have been a major interest of research. Development techniques such as two‐step and spray development techniques to improve resist contrast have been reported, but neither is well characterized and well understood. In this paper, we report an interrupted development technique which enhances the contrast of an electron beam (e‐beam) exposed diazonapthoquinone novolac, AZ‐type resist. As a result of this enhancement, submicron features varying in density can be controlled properly in size and in image profile. The resolution capability of this resist as a single‐layer system is extended to the one‐quarter micron regime with good linewidth control. In the optically exposed AZ resist, a smaller enhancement in contrast was observed and the resolution improvement is minimal. However, vertical sidewalls are readily obtained by employing appropriate interrupted development schemes on optically as well as e‐beam exposed AZ resists. This difference in response to interrupted development is related to the difference in the energy deposited in the resist film due to electron scattering. In the e‐beam exposed AZ film, the energy deposited in the resist gradually increases through the bulk of the film. On the other hand, because of the UV absorption characteristics of the novolac resist in optical lithography, the energy deposited is attenuated as it penetrates the resist. Sensitivity enhancement by this technique is on the order of 30% to 50%. A sulfone novolac resist with an inductive effect was examined to try to understand the mechanism of contrast enhancement of AZ resist by interrupted development. No response to interrupted development was observed. Possible mechanisms for the delayed lateral erosion of the AZ resist images are proposed, based on the studies of these resists and
developer interactions. Using this interrupted development technique on a single‐layer e‐beam exposed resist system, various profiles can be tailored to fit different applications in device processing requirements, namely an undercut profile for metal lift‐off, straight sidewalls for etch masks or ion implantation masks.
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85.40.Hp Lithography, masks and pattern transfer
81.05.Lg Polymers and plastics; rubber; synthetic and natural fibers; organometallic and organic materials
81.65.-b Surface treatments

Reactive plasticizers in negative electron beam resists

Y. M. N. Namaste, S. K. Obendorf, and F. Rodriguez

J. Vac. Sci. Technol. B 6, 2245 (1988); http://dx.doi.org/10.1116/1.584090 (4 pages)

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Negative electron resists generally exhibit excellent sensitivity, but suffer from swelling during development which results in poor resolution. A new approach to this problem is presented, in which reactive monomers are blended with host polymers to provide sensitive negative resists with improved resolution. Polychloromethylstyrene (PCMS) and VMCH (a terpolymer containing 86% vinyl chloride, 13% vinyl acetate, and 1% maleic acid) were both found to be compatible with two reactive monomers, trimethylolpropanetrimethacrylate and dipentaerythritolpentaacrylate (DPEPA). Addition of 20 wt. % of either monomer to PCMS or VMCH resulted in approximately tenfold increases in sensitivity. Sensitivity increases dramatically with increasing monomer content, with a 1:1 blend of VMCH and DPEPA exhibiting a sensitivity of ∼0.15 μC/cm2. This represents a more than 100‐fold increase in sensitivity over that of VMCH alone. These blends exhibit resolution of 0.5 μm. Blends of the reactive monomers with fractionated base polymers possessing low molecular weight and low polydispersities are promising. Low molecular weight PCMS and VMCH exhibit good contrast and resolution, but suffer from poor sensitivity. Addition of reactive monomers to these base polymers increases their sensitivity, while maintaining contrast and resolution that is superior to the high molecular weight unfractionated polymer alone. These blends exhibit less swelling than the host polymers.
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81.05.Lg Polymers and plastics; rubber; synthetic and natural fibers; organometallic and organic materials
81.65.-b Surface treatments
85.40.Hp Lithography, masks and pattern transfer
79.20.Kz Other electron-impact emission phenomena

PRISM: Process for resist profile improvement with surface modification

Toshiyuki Yoshimura, Fumio Murai, Hiroshi Shiraishi, and Shinji Okazaki

J. Vac. Sci. Technol. B 6, 2249 (1988); http://dx.doi.org/10.1116/1.584091 (5 pages)

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The positive electron beam resist NPR is a composite of a novolac resin and a polymeric dissolution inhibitor. In this resist a surface modified layer is produced on the resist when development is interrupted. The dissolution rate of this layer at low dose is very low. A new process called prism (Process for Resist profile Improvement with Surface Modification) utilizing this layer is proposed. By repetitive development interruption, a steep and accurate resist profile is obtained with sidewall protection. This paper describes an investigation into the effects of development interruption on NPR. The surface modified layer produced by the interruption is investigated with gas analysis and x‐ray photoelectron spectroscopy. It is found that the dissolution inhibitor poly(2‐methylpentene‐1‐sulfone) accumulates at the resist surface. prism can be applied to other resists consisting of aqueous alkaline soluble base resins and polymeric dissolution inhibitors. Improvement of the resist pattern profile is observed in positive‐type photoresists by prism.
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85.40.Hp Lithography, masks and pattern transfer
79.20.Kz Other electron-impact emission phenomena
81.05.Lg Polymers and plastics; rubber; synthetic and natural fibers; organometallic and organic materials
81.65.-b Surface treatments

Analysis by electron energy‐loss spectroscopy of poly(methylmethacrylate) electron beam resist

Jean‐Paul Martinez, Henri Camon, Yolande Kihn, Jean Sevely, and Jean‐Louis Balladore

J. Vac. Sci. Technol. B 6, 2254 (1988); http://dx.doi.org/10.1116/1.584092 (5 pages)

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In electron beam lithography the interactions between the incident electrons and the molecules of the resist lead to a chemical modification of the polymer. In order to understand the various processes which occur, we have used the technique of electron energy‐loss spectroscopy (EELS). The detection of plasmons and characteristic signals associated with atomic deep level excitations in the high‐energy region of the spectrum allows the chemical elements in a given volume of the specimen to be identified and localized. By measuring the intensity of the characteristic signal associated with a given element it is also possible to estimate the number of atoms of this element present in the volume analyzed. The evolution of the energy‐loss spectrum during electron irradiation gives information on the structural modification and on the mass loss of the specimen as a function of the dose. In electron lithography the pattern dimensions vary with the energy deposited in the resist and consequently are related to the time exposure to the beam. The results obtained by EELS allow the evolution of the resist during irradiation to be followed.
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85.40.Hp Lithography, masks and pattern transfer
68.55.Nq Composition and phase identification
61.85.+p Channeling phenomena (blocking, energy loss, etc.)
73.20.Mf Collective excitations (including excitons, polarons, plasmons and other charge-density excitations)

Highly sensitive thermally developable positive resist systems

Hiroshi Ito, Mitsuru Ueda, and Reinhold Schwalm

J. Vac. Sci. Technol. B 6, 2259 (1988); http://dx.doi.org/10.1116/1.584093 (5 pages) | Cited 4 times

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Acid‐catalyzed thermal depolymerization of polyphthalaldehyde derivatives has been utilized in the design of highly sensitive, thermally developable, positive resist systems incorporating two stages of chemical amplification. Poly(4‐chlorophthalaldehyde) mixed with triphenylsulfonium hexafluoroantimonate can be thermally developed to the substrate simply by heating the resist after exposure to <1 mJ/cm2 of 254‐nm radiation or 1 μC/cm2 of 18‐keV electron beam radiation. The images obtained by postbaking at 160 °C do not exhibit any thermal flow. Poly(4‐trimethylsilylphthalaldehyde) (PSPA) sensitized with triphenylsulfonium triflate exhibits a high deep UV sensitivity of <2 mJ/cm2 and a high electron beam sensitivity of 1 to 2 μC/cm2 (20 keV) when the thermal development is performed at 100–130 °C. The high contrast (γ=4.3) of the PSPA resist allows thermal imaging of submicrometer features, which can then be transferred to the bottom planarizing layer by oxygen reactive ion etching (RIE). The combination of the thermal development and oxygen RIE pattern transfer provides a new mode of all dry bilayer processes.
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81.05.Lg Polymers and plastics; rubber; synthetic and natural fibers; organometallic and organic materials
81.65.-b Surface treatments
85.40.Hp Lithography, masks and pattern transfer

Requirements on resist layers in deep‐etch synchrotron radiation lithography

J. Mohr, W. Ehrfeld, and D. Münchmeyer

J. Vac. Sci. Technol. B 6, 2264 (1988); http://dx.doi.org/10.1116/1.584067 (4 pages) | Cited 15 times

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To fabricate microstructures with heights of several hundred micrometers and great aspect ratios by the LIGA (German acronym for LIthographie, Galvanoformung, Abformtechnik) process thick poly(methylmethacrylate) (PMMA) resist layers are produced on a metallic base plate. The requirements these resist layers must fulfill are reported. It is shown that it is possible to achieve defect‐free structuring with high accuracy using cross‐linked PMMA with little content of residual monomer. Good adherence of microstructures with extremely small diameters, even on polished surfaces, is achieved by using an internal coupling agent which establishes a chemical bond between the substrate surface and the PMMA layer. By modifying the resist composition requirements dependent on product specifications can be fulfilled.
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85.40.Hp Lithography, masks and pattern transfer
81.05.Lg Polymers and plastics; rubber; synthetic and natural fibers; organometallic and organic materials
81.65.-b Surface treatments

The impact of high‐sensitivity resist materials on x‐ray lithography

Daniel Seligson, Hiroshi Ito, and C. Grant Willson

J. Vac. Sci. Technol. B 6, 2268 (1988); http://dx.doi.org/10.1116/1.584068 (6 pages) | Cited 1 time

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Major research and development efforts are underway throughout the world that are directed toward establishment of very large scale integrated manufacturing with x‐ray lithography. Point‐source x‐ray lithography was once the favored approach to this technology but point sources have been all but abandoned in favor of synchrotron sources. This paper reviews the reasons for the emphasis on synchrotron sources and reexamines the reasons for this emphasis. Recent developments in point‐source technology and in resist chemistry warrant this reexamination. We conclude that point‐source x‐ray lithography is feasible and renewed effort is warranted in point‐source and high‐resistivity resist research and development.
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85.40.Hp Lithography, masks and pattern transfer
81.65.-b Surface treatments
07.85.-m X- and γ-ray instruments

Ultrathin polymer films for microlithography

S. W. J. Kuan, C. W. Frank, C. C. Fu, D. R. Allee, P. Maccagno, and R. F. W. Pease

J. Vac. Sci. Technol. B 6, 2274 (1988); http://dx.doi.org/10.1116/1.584069 (6 pages) | Cited 9 times

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Ultrathin (14–22 nm) poly(methylmethacrylate) (PMMA) films prepared by both spin casting and Langmuir–Blodgett (LB) techniques and novolac films prepared by spin casting have been explored as high‐resolution electron beam resists. One‐eighth micron lines‐and‐spaces patterns (equal to the smallest beam diameter available) have been achieved by using a Perkin Elmer MEBES I pattern generation system as the exposure tool, and the definition of 45‐nm features has recently been achieved by using a high‐resolution electron beam lithography system. [J. H. Newman, K. E. Williams, and R. F. W. Pease, J. Vac. Sci. Technol. B 5, 88 (1987)]. The etch resistance of such films is sufficiently good to allow patterning of a chromium film suitable for photomask fabrication. The most surprising result has been that the pinhole densities in 14.3‐nm LB PMMA film and 22‐nm spin‐cast novolac film are only a few per cm2, considerably lower than the density in spin‐cast PMMA films of comparable thicknesses.
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85.40.Hp Lithography, masks and pattern transfer
79.20.Kz Other electron-impact emission phenomena
81.05.Lg Polymers and plastics; rubber; synthetic and natural fibers; organometallic and organic materials
81.65.-b Surface treatments

A study of the effect of key processing variables on the lithographic performance of Microposit SAL601‐ER7 resist

Lauren Blum, Marjorie E. Perkins, and Hua‐Yu Liu

J. Vac. Sci. Technol. B 6, 2280 (1988); http://dx.doi.org/10.1116/1.584070 (6 pages) | Cited 1 time

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Two statistically designed experiments were performed to study the effect of the key processing variables on the lithographic properties of Microposit SAL601‐ER7 electron beam resist. A Taguchi L9, nine‐run design with four variables at three levels was used for a screening experiment. The effect of postexposure bake (PEB) temperature, PEB time, and developer normality on the contrast and the sensitivity of the resist was determined. A lithographic test of the process recommended by this experiment suggested that development time should be included as a variable in the next study. A four‐variable central composite design was performed in order to obtain a more complete understanding of the process. These experiments demonstrated that the resist performs well with a broad range of processing conditions. A postexposure bake temperature of 115 °C provides the most robust process. The developer concentration and development time can be modified to attain either shorter development times or lower sensitivities. Many of the effects of the process variables can be explained by the unique chemistry of the resist.
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85.40.Hp Lithography, masks and pattern transfer
81.65.-b Surface treatments

Degradation of poly(methylmethacrylate) by deep ultraviolet, x‐ray, electron beam, and proton beam irradiations

J. O. Choi, J. A. Moore, J. C. Corelli, J. P. Silverman, and H. Bakhru

J. Vac. Sci. Technol. B 6, 2286 (1988); http://dx.doi.org/10.1116/1.584071 (4 pages) | Cited 24 times

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The chemical changes in poly(methylmethacrylate) (PMMA) caused by irradiation with deep ultraviolet (UV), x‐ray, electron, and proton beams were studied by gel permeation chromatography, Fourier‐transform infrared, and UV spectroscopy. The quantitative analysis of spectroscopic changes (Beer’s law) demonstrated a 1:1 correspondence between the disappearance of ester groups and the generation of double bonds in the polymer chain by all types of radiation. The ratio of main chain scission to changes in the number of ester groups and unsaturated bonds was compared to determine the characteristics of degradation of PMMA by the different types of radiation. This ratio for deep UV data was very close to the quantum yield of main chain scission of PMMA as reported in the literature. High‐energy radiation was ∼10× more efficient than deep UV in causing main chain scission with removal of fewer ester groups. Protons induced more main chain scission than electrons. X‐ray irradiation was the most efficient at causing main chain scission of the four different types of radiation.
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82.50.Kx Processes caused by X-rays or γ-rays
82.50.Bc Processes caused by infrared radiation
82.50.Hp Processes caused by visible and UV light
82.80.-d Chemical analysis and related physical methods of analysis
61.80.-x Physical radiation effects, radiation damage

High‐throughput nanolithography using an oxygen‐plasma resistant two‐layer resist system

P. S. D. Lin and A. S. Gozdz

J. Vac. Sci. Technol. B 6, 2290 (1988); http://dx.doi.org/10.1116/1.584072 (4 pages)

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LaB6‐based electron beam nanolithography systems suffer from low beam current, resulting in low throughput for nanometer‐sized patterns. This drawback is further aggravated by the low sensitivity of the standard high‐resolution resist [poly(methylmethacrylate) (PMMA)] and by the reduction of intraproximity effect. We have investigated the lithography aspects (contrast, resolution, exposure latitude, throughput, and statistics) of two‐layer resist systems consisting of a sensitive positive electron beam resist poly(3‐butenyltrimethylsilane sulfone) (PBTMSS) as the top layer, and a variety of materials such as diamondlike carbon film or polyimide as the bottom layer. In these systems, exposed and developed PBTMSS is first oxidized to SiO2, which masks etching of the bottom layer. The pattern is in turn transferred to the substrate either by wet or dry etching using the bottom layer as a mask. Grating patterns with 0.2‐ and 0.1‐μm pitch can be routinely fabricated on semiconductors, and 0.05‐μm pitch patterns have been demonstrated. To achieve such high resolution, a low‐strength developer is used, but a throughput about 30 to 50 times higher than that of PMMA can still be obtained. Gratings now can be patterned in a few hours over square‐centimeter areas. Such a task would require days for PMMA. Implications of our results on lithography system clock rate and resist resolution–sensitivity tradeoff are also discussed.
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85.40.Hp Lithography, masks and pattern transfer
81.65.-b Surface treatments

Contrast enhancement of resist images by surface cross‐linkage

H. Hiraoka, W. Hinsberg, N. Clecak, A. Patlach, and K. N. Chiong

J. Vac. Sci. Technol. B 6, 2294 (1988); http://dx.doi.org/10.1116/1.584073 (4 pages)

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A general method of contrast enhancement which provides control of resist image wall profiles and is applicable to both positive and negative working resists may be obtained by surface cross‐linking. The cross‐linking is used in our process to retard dissolution at the resist surface. The creation of a slower dissolving surface layer affords greater control of wall profiles and enhanced contrast or sensitivity. One method is to use mid‐ and deep‐UV flood exposure. For a negative working electron beam resist this method is the same as surface photo absorption for contrast enhancement. With our experimental resist containing 4,4′‐diazido‐diphenylsulfide as a sensitizer, the improvement in its electron beam sensitivity was not substantial. For a positive working photoresist, the same aromatic bisazide was added to conventional positive working photoresists composed of a diazo‐naphthoquinone‐type photosensitizer and novolac resin. A short‐300‐nm UV flood exposure followed the G‐line imagewise exposures. Another method is to use diffusion‐controlled chemical reactions by treating imagewise exposed resist films in a multifunctional cross‐linking agent prior to image development. Using these methods, a higher contrast and wall profile control have been demonstrated with positive working photo and electron beam resists.
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85.40.Hp Lithography, masks and pattern transfer
81.05.Lg Polymers and plastics; rubber; synthetic and natural fibers; organometallic and organic materials
81.65.-b Surface treatments

High‐resolution electron beam lithography with negative organic and inorganic resists

G. H. Bernstein, W. P. Liu, Y. N. Khawaja, M. N. Kozicki, D. K. Ferry, and L. Blum

J. Vac. Sci. Technol. B 6, 2298 (1988); http://dx.doi.org/10.1116/1.584074 (5 pages) | Cited 2 times

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In this paper, we report the achievement of high‐resolution exposures in the organic negative resist SAL 601‐ER7 (Shipley Co. designation), and also in an optimized inorganic As–S:Ag negative resist system, suitable for in situ processing. Sensitivity curves are presented for the organic material, showing the particularly high sensitivity and contrast of this material at exposure voltages ranging from 10 to 40 keV. High aspect ratio (15:1) patterns were formed with the organic resist but mechanical stability was lacking in these structures. A discussion of optimization of material composition is also given for an inorganic resist system based on As–S chalcogenide. The ultimate resolution attained during this study was 50‐nm lines on a 100‐nm pitch for the organic material and 35‐nm lines on a 70‐nm pitch for the inorganic resist system.
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85.40.Hp Lithography, masks and pattern transfer
81.05.Lg Polymers and plastics; rubber; synthetic and natural fibers; organometallic and organic materials
81.65.-b Surface treatments
79.20.Kz Other electron-impact emission phenomena

Process control with chemical amplification resists using deep ultraviolet and x‐ray radiation

Daniel Seligson, Siddhartha Das, Henry Gaw, and Piero Pianetta

J. Vac. Sci. Technol. B 6, 2303 (1988); http://dx.doi.org/10.1116/1.584075 (5 pages) | Cited 6 times

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Resists for optical electron beam, and x‐ray lithographies that operate on the principles of chemical amplification are entering into widespread use in laboratories. They offer an attractive alternative to conventional positive Novolac photoresists and we may soon see similar use in manufacturing environments. One class of resists within this family is based on acid‐hardening chemistry. We have characterized one such resist (Shipley ECX‐1033) for illumination by excimer laser deep ultraviolet sources and also by x‐ray radiation. A matrix of postexposure bake (PEB) conditions and development conditions was used to examine resist sensitivity and contrast. For all exposure sources we found that contrast is independent of PEB processing and that sensitivity obeys an Arrhenius dependence. Contrast increases with increasing development time while exposed resist loss is minor. A simple kinetic model was developed to explain the observed variations of apparent resist sensitivity with PEB time and temperature. The generality of this model suggests that it is widely applicable to other chemical amplification resists that require a postexposure bake. Together with aerial image calculations for different light sources, the model makes it possible to predict the dependence of linewidth on PEB conditions. In other words, we can anticipate the PEB process control required to achieve a specified critical dimension control. Electrical linewidth measurements of submicron features and their temperature dependence are compared with the predictions of the model.
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81.40.Gh Other heat and thermomechanical treatments
85.40.Hp Lithography, masks and pattern transfer
81.05.Lg Polymers and plastics; rubber; synthetic and natural fibers; organometallic and organic materials
81.65.-b Surface treatments

Nanometer lithography for III–V semiconductor wires using chloromethylated poly‐α‐methylstyrene resist

B. E. Maile, A. Forchel, R. Germann, A. Menschig, H. P. Meier, and D. Grützmacher

J. Vac. Sci. Technol. B 6, 2308 (1988); http://dx.doi.org/10.1116/1.584076 (4 pages) | Cited 11 times

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Chloromethylated poly‐α‐methylstyrene negative resist was investigated for its suitability in the fabrication of nanometer structures for optical studies. Investigating the photoluminescence efficiency of etched GaAs/AlGaAs wires we find a steep decrease with decreasing wire width, whereas for InGaAs/InP the decrease is much smaller. The difference in the behavior of the material systems can be explained by the effectiveness of surface recombination.
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85.40.Hp Lithography, masks and pattern transfer
78.55.Cr III-V semiconductors
84.32.Hh Inductors and coils; wiring
81.65.-b Surface treatments
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