bluuebunny/crossref_metadata_2025 huggingface dataset:
Inner pressure measurement of turbo molecular pump
Authors: Cheng H.-P. , Jou R.-Y. , Lin J.-C. , Chen C.-J. , Huang W.-H.
Published: July 2002

The pressure of the gas including free molecular, transition, slip, and continuum flow inside the turbo booster pump is successfully measured in this study. This pump was developed through the cooperation of Kashiyama Industries Ltd. and Precision Instrument Development Center, with the goal of replacing the mechanical booster pump. The flow-meter method of Japan’s standard JVIS-005 is adopted here to simulate the operating condition of the pump in different pressure ranges. The laboratory and the experimental apparatus are constructed according to the International Standards Organization and JVIS standards. In order to measure the pressure variations from the pump inlet to the outlet, nine holes with 6.5 mm inner diameter are drilled through the pump casing around the periphery along the axial direction. The distances of these holes from the plane of the inlet port are 49.5, 79.5, 107, 127, 147, 167, 187, 207, and 227 mm. The metal gasket face seal fittings with inner diameter 3 mm are welded into the holes using the TIG-tungsten inert gas welding method. The metal bellow tube is used to link the vacuum gauges and the metal gasket face seal fittings. The accuracy range of the vacuum gauges is 1.33×10−4–133 mbar. Six cases of the pump inner pressure with the pump inlet pressure 1.33×10−4, 1.33×10−3, 1.33×10−2, 0.133, 0.665, and 1.33 mbar are performed. The pressure variations along the axial direction are plotted. The pressure trend related to the rotor shape is discussed. The pressure discrepancies between the measured and calculated done by the Computational fluid dynamics method are compared.
Submicrometer contact hole delineation with a two-layer deep-UV portable conformable masking system
Authors: Petrillo K. E. , Chao V. W. , Lin B. J.
Published: July 2002

The two-layer deep-UV portable conformable masking (PCM) system using a novolac resist as the imaging layer on a PMMA planarizing layer was chosen to delineate 1.0×1.25 μm contact holes with a 0.32 NA 405 nm 5× projection lens to support 1 μm MOS circuit fabrication. Measured SiO2 images, delineated with CF4+H2 reactive ion etching, exhibited insignificant biases and small size variations for critical features down to 0.87 ×0.87 μm over typical wafer topography when a near-UV dye was incorporated in the planarizing layer. A comparison of the dyed and undyed deep-UV PCM and a single-layer soaked process will also be given.
A novel bilevel resist system
Authors: McCullough A. W. , Pavelchek E. , Windischmann H.
Published: July 2002

A bilevel system, consisting of PMMA and RD2000N (Hitachi) is described which has no discernable interaction between the resists and no processing interaction. The thin RD2000N resolution layer has very high absorption below 2900 Å and forms a high contrast mask for optical pattern transfer to the thick base PMMA layer. High fidelity step coverage of wet and dry etched oxides 7200 Å high is demonstrated with good linewidth control. The bilevel is capable of resolving 0.75 μm features over steps with good acuity. Preliminary results indicate that linewidth control with the bilevel process is comparable to a single level RD2000N process and has a lσ value of ∼.09 μm nearly independent of linewidth. The RD2000N layer shows a greater sensitivity to process variation than the PMMA. A parametric evaluation shows a dependence of linewidth on development time of 0.02 μm/s and a dependence of 0.11 μm/s for a 17 s exposure time. The resist system has enough dry etch resistance to use plasma etch pattern transfer as a complement to optical pattern transfer.
Reactive ion beam etching: Dissociation of molecular ions upon impact
Authors: Steinbrüchel Ch.
Published: July 2002

This paper reports on etch yield measurements on Au films by ion beams generated from Ar, Ne, O2, N2, CF4, and C2F6 in a Kaufman-type ion gun for ion energies between 0.2 and 1.4 keV. Ions and neutral species emanating from the gun are characterized by mass spectrometry. For CF4 and C2F6 the ion composition is a strong function of the magnetic field in the gun, CF+3 being the major ion only for CF4 at low magnetic field. The physical etch yield of CF+3 is found to be close to that of Ne+, not Ar+. The results on the dependence of the etch yields on ion mass, ion energy, and incident angle can be correlated quantitatively by assuming complete dissociation of molecular ions upon impact on the substrate. The same model is also shown to explain the data by Tachi et al. on etching Si by mass-selected ions of the form CF+x and BF+x. The implications of these results for plasma and reactive ion etching are discussed.
Determination of space charge layer parameters on InSb(110) by electron energy loss spectroscopy
Authors: Ritz A. , Lüth H.
Published: July 2002

The coupled surface phonon (Fuchs–Kliewer)/plasmon polaritons are studied by means of high resolution electron energy loss spectroscopy (HRELS) on cleaved, clean and oxygen-covered InSb(110) surfaces. Intensities and energetic positions of the losses can accurately be described by a layer model in which a surface layer with negligible carrier concentration is assumed. For the oxygen-covered surface this layer is identified as a depletion space charge layer. Thickness and band bending of this depletion layer are determined.
Secondary effects in ion milling
Authors: Moreno-Marin J. C. , Valles-Abarca J. A. , Gras-Marti A.
Published: July 2002

The contribution of secondary processes such as redeposition, resputtering, and ion reflection at the sidewalls, to the transfer by sputter etching of a pattern to a substrate is analyzed. An analytical theory developed by R. Smith and J. M. Walls [Philos. Mag. A 42, 235 (1980)] is used, and the evolution profiles are parametrized.
Reactive ion etching of SiC thin films using fluorinated gases
Authors: Sugiura J. , Lu W.-J. , Cadien K. C. , Steckl A. J.
Published: July 2002

Reactive ion etching (RIE) using fluorinated gases, such as admixtures of CF4 with O2, has been conducted on sputter deposited films of SiC. For comparison purposes, the same experiments with SiO2 films and Si wafers have been conducted. The influence of rf power, pressure, and O2 concentration on etch rate in CF4+O2, SF6+He, and Ar gases has been investigated. RIE mechanisms were studied using in situ monitoring of excited fluorine emission intensity and dc self-bias at the lower electrode. Typical etch rates of Si, SiO2, and SiC are 1220, 600, and 375 Å/min in CF4+4% O2; 8850, 500, and 560 Å/min in SF6+50% He; and 340, 280, and 270 Å/min in Ar, respectively, at P=200 W, p=20 mTorr, and 300 K. Under these conditions the dc self-bias levels are −396 V for CF4+4% O2, −350 V for SF6+50% He, and −414 V for Ar. In both CF4+4% O2 and SF6+50% He, the etch rates of Si, SiO2, and SiC all increase monotonically with the rf power. However, with increasing pressure the Si etch rate increases while the etch rates of SiO2 and SiC decrease. Since the dc self-bias varies proportionally with power and inversely with pressure, it is clear that the etching of Si is chemical reaction rate controlled. On the other hand, the etch rate of SiC depends on the ion bombardment energy and is thus dominantly controlled by a physical reaction. The SiC etch rate exhibits a weak dependence on O2 concentration in CF4+O2 mixtures. The dc self-bias is not affected by increasing O2 concentration, but the SiC etch rate is slightly enhanced. This suggests that a certain etching inhibitor layer exists on the surface of SiC, which can weakly react with the O2 plasma. Auger electron spectroscopy data indicates that this layer consists of carbon atoms.
Resist hardening using a conformable mold
Authors: Lai F. S. , Lin B. J. , Vladimirsky Y.
Published: July 2002

The novolak-based resist image is thoroughly hardened by baking with a conformable mold which is formed by spin coating polymethylmethacrylate (PMMA) over the novolak image. Therefore, instead of a deep-UV hardening exposure or a plasma hardening step followed with a high temperature bake, this hardening process consists of a PMMA coating followed with a high temperature bake. Experimental results show that hardening took place throughout the bulk of the resist. The resist profile remains intact after a 200 °C bake and a second novolak resist image can be delineated on top of the hardened image without any mutual interaction, whereas conventional deep-UV or plasma hardening technique can only harden the resist surface layer. Large features hardened with these conventional techniques tend to deform. Recent results showed stability of resist profile for baking temperature up to at least 500  °C in a nitrogen flushed furnace. The lateral dimension change of the resist image after resist hardening using a conformable mold (RHCM) and 500 °C bake was shown to be less than 0.05 μm.
Excimer laser photoablation of silicon
Authors: Shinn G. B. , Steigerwald F. , Stiegler H. , Sauerbrey R. , Tittel F. K. , Wilson W. L.
Published: July 2002

The ultraviolet and visible emission spectra from excimer laser-produced silicon plasmas were studied and the ablation rate measured as a function of laser energy density and wavelength. A spectroscopic investigation of the laser-produced plasma showed Si i, Si ii, and Si iii spectral lines with higher laser intensity causing a higher degree of ionization in the plasma. Both time-integrated and time-resolved spectroscopic studies showed electronic transitions superimposed on a weak continuum over the entire range from 250 to 640 nm. The photoablation rate of Si was independent of laser wavelength (193 or 248 nm), and had an energy density threshold of ≊1.3 J/cm2. The threshold was almost independent of the buffer gas pressure between vacuum and 1000 Torr. These results are described in the framework recently developed for excimer laser ablation of metals.
Auger electron spectroscopy sputter depth profiles on AlxGa1−xAs protected by As and GaAs ultrathin layers
Authors: Etienne P. , Alnot P. , Rochette J. F. , Massies J.
Published: July 2002

The Auger electron spectroscopy sputter depth profiling technique has been used to evaluate the protective efficiency of ultrathin overlayers of As (∼25 Å) and GaAs (25 Å) against air exposure damaging effect of AlxGa1−xAs (x=0.3) epitaxial layers. It is shown that the As adsorbed overlayer is only partially effective to protect AlxGa1−xAs surface for a short air exposure. The surface of this reactive material can be more efficiently protected by GaAs, even for a very thin overlayer (25 Å). Results dealing with the effects of air and H2 annealings on the AlxGa1−xAs surface are also reported. They confirm the Ga segregation at the AlxGa1−xAs surface recently reported [Stall et al., J. Vac. Sci. Technol. B 3, 524 (1985) and Massies et al., ibid. 3, 613 (1985)].
GaAs–Ge heterojunction interfaces: Cyclical behavior of band discontinuities
Authors: Waldrop J. R. , Grant R. W. , Kraut E. A.
Published: July 2002

The valence band discontinuity ΔEv of (110) and (100) oriented heterojunctions made by growth of GaAs onto Ge (GaAs–Ge) is found to decrease with time after interface formation (on a scale of tens of hours). The thin, abrupt heterojunction samples were prepared by molecular beam epitaxy techniques and characterized by x-ray photoemission spectroscopy. The final room temperature value of ΔEv(GaAs–Ge) is >0.2 eV lower than the ∼0.56 eV value for the stable Ge–GaAs (reverse growth sequence) interface. Annealing a sample for several minutes in vacuum at the growth temperature increases ΔEv(GaAs–Ge) to approximately the Ge–GaAs value. By control of anneal time and an accompanying As overpressure, ΔEv(GaAs–Ge) can be cycled by >0.2 eV. This variation in an interface electrostatic dipole is apparently related to a variable amount of electrically active As that is located at the heterojunction interface. The dipole formation mechanism involved may require the presence of the antiphase disorder that is expected for growth of GaAs on Ge.
Surface and interface optical phonons of a GaAs–AlGaAs superlattice measured by high resolution electron energy loss spectroscopy
Authors: Thiry P. A. , Liehr M. , Pireaux J. J. , Caudano R. , Lambin Ph. , Vigneron J. P. , Lucas A. A. , Kuech T.
Published: July 2002

High resolution electron energy loss spectra have been measured on a GaAs–Al0.3Ga0.7As superlattice. Fuchs–Kliewer-like surface and interface optical phonons were observed with frequencies and intensities in excellent agreement with calculations based on the dielectric theory. The spectra obtained after sputter erosion of the superlattice are discussed in terms of induced defects or segregation of Al at the interface.
Synchrotron radiation-excited chemical-vapor deposition and etching
Authors: Urisu Tsuneo , Kyuragi Hakaru
Published: July 2002

Photoexcited chemical-vapor deposition (CVD) and etching using synchrotron radiation as an exciting light source were experimentally demonstrated. CVD of silicon nitride film and etching of Si and SiO2 by SF6+O2 gases are described in detail. In several reaction systems, it was found that the surface photoexcitation was an important mechanism. Reaction models for gas-phase excitation and surface excitation were proposed.
The evaluation of positive acting resists for lithography at 248 nm
Authors: Wolf T. M. , Hartless R. L. , Shugard A. , Taylor G. N.
Published: July 2002

Two types of positive tone resists were lithographically evaluated using the 248.4 nm emission of a krypton fluoride (KrF) excimer laser by contact printing. These were polymers such as poly(methylmethacrylate) and modified methacrylate copolymers which undergo chain scission upon absorption of light and the dissolution-inhibition resist systems, such as the commercially available naphthoquinonediazide-sensitized novolak-resin-based resists. Our goal was to establish sensitivity and resolution parameters for a variety of resists considered for use in a deep UV stepper operating at 248.4 nm. The sensitivities of the degrading polymers, poly(methylmethacrylate)(>1.2 J/cm2), poly(methylmethacrylate-co-indenone) (450 mJ/cm2), poly(methylmethacrylate-co-oximinobutanone methacrylate) (1.0 J/cm2), and poly(methlymethacrylate-co-oximinobutanone methacrylate-co-methacylonitrile) (350 mJ/cm2) were found to be in the moderate range. In addition, their sensitivity to KrF excimer laser emission was 5–7 times less than previously reported for irradiation with standard Hg-arc emission sources. Three dissolution-inhibition resists, AZ 2415, Microposit 2400-17, and poly(methylmethacrylate-co-methacrylic acid) sensitized with 20% o-nitrobenzylcholate, were evaluated. The latter was found to be more sensitive (150 mJ/cm2) than previously reported. Of the commercially available dissolution-inhibition resists only AZ 2415 and Microposit 2400-17 were considered to have an optical density low enough for use at 248.4 nm. 4600–5000 Å thick films of these resists exhibited good results. 4650 Å thick films of 2400-17 on hard-baked HPR 206 have a sensitivity of 90 mJ/cm2 when developed with 3.5 parts water and 1 part AZ 400K developer concentrate. 0.5 μm resolution is readily obtained with 2400-17. As expected, changes in sensitivity and resolution can be obtained by varying processing conditions.
High resolution patterning system with a single bore objective lens
Authors: Newman T. H. , Williams K. E. , Pease R. F. W.
Published: July 2002

An electron beam microfabrication tool for use in nanometer scale device research has been built incorporating a single bore objective lens. The sample resides in a micrometer-controlled in-lens stage which is an integral part of the boreless lower polepiece. This piece is removed to change samples, a straightforward operation due to the relaxed alignment tolerances between the two polepieces. The focal length of the lens, which has a 4 mm upper bore and a 4 mm gap, is 1.7 mm, with spherical and chromatic aberration coefficients taking on values of 1.0 and 1.2 mm, respectively. At the 40 kV operating voltage of the system with a tungsten hairpin source, 5 pA can be focused into a 50 Å diameter probe. Using ultrasonic liftoff with polymethyl methacrylate (PMMA) resist, we have obtained two-dimensional arrays of 200 Å gold:palladium particles on 500 Å centers on bulk GaAs. As a test of the overall system, which includes a computer-controlled pattern generator, a page of alphabetic characters was written in PMMA on a silicon nitride membrane at a data density of 1010 characters/cm2.
Proximity correction on the AEBLE-150
Authors: Otto O. W. , Griffith A. K.
Published: July 2002

In this paper we describe a method for performing proximity correction of very large scale integrated circuit layout data that is applicable for use on the AEBLE-150 electron-beam lithography system in particular, and other dose modulated systems in general. The algorithm employed saves computation time and program space by retaining, insofar as possible, the pattern hierarchy. The problem of instances of a cell which are in different environments is addressed by high-speed environment estimation through construction of equivalence classes. The dose computation algorithm requires edges to develop at designed locations, rather than requiring constant average exposure as in the so-called ‘‘self-consistent’’ approach. Certain heuristics are employed to accelerate the computation. Dose contributions of rectangular areas are computed via look-up tables and simple arithmetic. A table look-up approach is also applied for trapezoidal areas. The proximity correction computation is based on a multiple Gaussian equivalent scattering function. We will describe measurement techniques we have employed for extracting model parameters for use in the correction program. The performance of the program will be evaluated based on estimates of the various computational components.
X-ray double-crystal diffraction studies of GaInAsP/InP heterostructures
Authors: Wang X. R. , Chi X. Y. , Zheng H. , Miao Z. L. , Wang J. , Zhang Z. S. , Jin Y. S.
Published: July 2002

The lattice mismatch and the half-width of the rocking curves in GaInAsP epitaxial layers grown on (001) InP substrates have been determined by means of x-ray double-crystal diffractometry. The state of strain of GaInAsP epitaxial layers has also been investigated. The relaxed lattice constant of the epilayers in stress-free states has been found from observed lattice deformation using strain relations.
The interference fringe aligner
Authors: White D. L. , Feldman M. , Saunders T. E. , Gunter P.
Published: July 2002

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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u measurement of the composition of molecular-beam epitaxial (Al, Ga)As by Auger electron spectroscopy
Authors: Wright S. L. , Marks R. F. , Savoy R. J.
Published: July 2002

The high-energy Auger spectra were measured for a large number of molecular-beam epitaxial (Al, Ga)As layers, and analyzed for Al composition using electron microprobe and reflection electron diffraction oscillations for calibration. A simple analysis employs this calibration and avoids assumptions of column III/V stoichiometry. Thus the bulk composition can be established to within a few percent from the Auger peak heights, in spite of a large variation in the As surface coverage. An effort is made to account for differences between Auger sensitivity factors determined for as-grown surfaces (this study) and those obtained from measurements performed during Ar+ ion sputtering. Our measurements support recent measurements of the band gap of AlxGa1−xAs which place the direct/indirect crossover composition between x=0.37 and 0.39.
High resolution x-ray lithography using surface-protected development
Authors: Ogawa Taro , Mochiji Kozo , Shiraishi Hiroshi , Kimura Takeshi
Published: July 2002

A new process utilizing a dissolution-blocking layer on a resist surface is proposed for improving developed pattern shape of x-ray lithography. A thin self-developing polymer layer which is coated onto a positive resist almost completely achieves this purpose. This layer can be efficiently decomposed and vaporized by x-ray exposure. As a result, after x-ray exposure, this layer never interferes with development of the exposed portion, while the layer remaining blocks dissolution of the unexposed portion during development. This enhances the development rate ratio between unexposed and exposed portions, thus developed pattern shape is greatly improved. This surface-protected development process has been evaluated for improving the developed pattern shape of novolac based positive resist (NPR). Poly(2-methylpentene–1-sulfone) (PMPS), which is also used as the dissolution inhibitor of the NPR resist, is selected as the dissolution-blocking layer. Application of the post-exposure baking is the key process for improvement of developed pattern shape, because the PMPS layer remaining on the unexposed portion is densified and begins to oppose development, while development of the exposed portion is accelerated by thermal decomposition of the remaining PMPS both on and in the NPR. With this process, 0.3 μm high-aspect-ratio patterns of single-layer NPR can be successfully fabricated at a dosage lower than one-third of that for the current process.
Stress-free and amorphous Ta4B or Ta8SiB absorbers for x-ray masks
Authors: Sugawara Minoru , Kobayashi Masato , Yamaguchi Yoh-ichi
Published: July 2002

We have succeeded in obtaining practical x-ray absorber films, Ta4B and Ta8SiB, using an rf magnetron sputtering method. The internal stress of these films can be controlled precisely within ±1.0×107 N/m2. The stress has thermal stability at 350 °C. The stress is also quite insensitive to the film thickness and substrates used. These excellent stress properties are attributed to the amorphous structure of the film. The amorphous structure also ensures quarter-micron pattern fabrication. Densities of 15.3 g/cm3 for Ta4B and 15.6 g/cm3 for Ta8SiB are high enough to yield sufficient contrast for x-ray exposures.
Large-area silicon–nitride mask technology for x-ray lithography
Authors: Qingyun Dong , Liankui Zhang , Mengzhen Chen , Junru Ma
Published: July 2002

This paper describes a technology for making large area silicon-nitride x-ray masks. We did extensive work for optimizing the LPCVD deposition process. Choosing proper deposition parameters, we obtained silicon-nitride layers with low tensile stress. Using the ion implantation stress compensation technique, the stress of the silicon nitride was reduced until the desirable value was reached. The key parameters of the silicon-nitride mask are satisfactory for the needs of x-ray masks used to fabricate VLSI devices. Because the silicon-nitride film is stoichiometric, a good stability of the mask is expected; tests of its stability to x-ray radiation are being continued at IMT.
Thermal effects in x-ray masks during synchrotron storage ring irradiation
Authors: Vladimirsky Y. , Maldonado J. , Fair R. , Acosta R. , Vladimirsky O. , Viswanathan R. , Voelker H. , Cerrina F. , Wells G. M. , Hansen M. , Nachman R.
Published: July 2002

This paper presents theoretical model and experimental results on radiation heating and thermally induced distortions in x-ray masks. The temperature rise of the mask membranes during x-ray irradiation was measured using metal resistors fabricated directly on the mask. A method was developed to calculate thermal wave effects: thermal distortions of the printed image due to the nonuniformity of temperature distribution in the mask membrane during scanning of the x-ray beam. Experimental results for the thermal wave effects are presented; they indicate that the effects are noticeable only during operation in a vacuum environment. The effects are negligible during normal operation in a helium atmosphere.
Selective metalorganic reactive ion etching of molecular-beam epitaxy GaAs/AlxGa1−xAs
Authors: Law V. J. , Jones G. A. C. , Ritchie D. A. , Peacock D. C. , Frost J. E. F.
Published: July 2002

We report on a metalorganic reactive-ion etch (MORIE) methane and hydrogen process for the selective etching of GaAs, AlxGa1−xAs and GaAs/AlxGa1−xAs heterostructures, grown by molecular-beam epitaxy (MBE). Etch rates, degree of selectivity, and loading effects are examined as a function of aluminium mole fraction(x=0.0–1.0), gas flow rates, pressure, and applied rf power. The etch process employs a specially prepared positive photoresist which can withstand high rf powers (1.1 W cm−2) with plasma potentials of −600 Vdc at 1.3 Pa and prolonged etch times (> 200 min) with little mask erosion, while maintaining a high degree of anisotropy in the etch process. The etch rate ratio of GaAs over AlxGa1−xAs is shown to be a strong function of the methane molecular concentration and by selecting a high methane flow rate, i.e., a low chamber residence time, favorable etch rate ratios are obtained. AlxGa1−xAs layers can either be etched through or an etch-stop achieved, before the onset of plasma polymerisation. This process has been successfully used for etching micron and submicron size mesas and GaAs/AlxGa1−xAs heterostructures, with linear etch rates (Ro) of up to 45 nm min−1 to a depth of 7 μm for GaAs and 0–10 nm min−1 for Al0.3Ga0.7As, depending upon the plasma conditions used.
Proximity effect correction for an electron beam direct writing system EX-7
Authors: Abe Takayuki , Ikeda Naotaka , Kusakabe Hideo , Yoshikawa Ryoichi , Takigawa Tadahiro
Published: July 2002

A new proximity effect correction software system has been developed, which is characterized by the usage of an approximate correction dose formula. The arrayed shot method was developed and a hierarchical data format was used to compact the amount of EB data. An inversion method has also been developed and a hierarchical pattern layout structure was used to accelerate the correction calculation speed. The proximity effect correction system has been installed into a high voltage electron beam direct writing system EX-7 and has been applied to some LSI patterns. The calculation time for correction was about 0.7 h for a 4 MDRAM and about 1 h for a 20 k gate array by using a 14 MIPS computer. The amount of EB data was about 40 Mbytes for the DRAM and about 50 Mbytes for the gate array.
Exploratory test structures for characterization of electron-beam lithography
Authors: Tam Nelson , Nozue Hiroshi , Yu David , Neureuther Andrew R.
Published: July 2002

Electrical testing of electron beam lithography was carried out on the AEBLE-150 in a simulation-calibrating approach to quantitatively study the impact of dose, maximum beam current, and substrate atomic number. The recording thin-film stacks consist of a resist coated thin Ti layer, a thin CVD oxide layer, and a substrate material of polyimide, Si, Mo, or W. The patterns were written using a negative-working chemical amplification resist Shipley SAL-601/ER-7. Electrical data for lines, arrays, serpentine squares, and shorting structures on Si and Mo substrates show no significant dependence on feature orientation or the maximum beam current of the exposure tool. Data from exposures up to five times normal show a lateral line edge growth of about half the Bethe range on Si. On Mo the dose to correctly size a 0.5 μm line drops from 5 to 3 μC/cm2 and the edge growth is much larger than the Bethe range in Mo. Simulation of backscatter electron effects and of the resist profile time evolution were used in the design and interpretation of the experiment.
Mechanisms of band bending at CsOx/GaAs(110) interfaces: Influence of overlayer stoichiometry and interfacial reactivity
Authors: Prietsch M. , Domke M. , Laubschat C. , Remmers G. , Weschke E. , Mandel T. , Ortega J. E. , Kaindl G.
Published: July 2002

The band-bending behavior at interfaces between thin Cs–oxide films and GaAs(110) is studied by photoemission as a function of overlayer stoichiometry and interfacial reactivity. For a substrate temperature of 140 K, nonreactive Cs–oxide/GaAs(110) interfaces with various Cs–oxide stoichiometries were prepared either by successive Cs and oxygen exposure or by codeposition of Cs and oxygen. A remarkable correlation between overlayer stoichiometry and band bending is observed: For both n- and p-type substrates, oxygen-rich overlayers result in almost flat-band conditions, while Cs-rich overlayers lead to Fermi-level positions close to midgap. This behavior is interpreted as a manifestation of a negligible influence of defect states to band bending in the case of these nonreactive interfaces, strongly supporting a mechanism based on virtual gap states. Thermal annealing of the interfaces causes strong interfacial chemical reactions and an increase in band bending for both n- and p-type substrates, signaling non-negligible contributions of reaction-induced defect states in this case.
Electrical properties and defect states in ion beam deposited poly (p-phenylene sulfide) films
Authors: Suzuki Katsuhiko , Matsumoto Kozo , Sakamoto Masatoshi
Published: July 2002

Electrical properties in the ion beam deposited poly(p-phenylene sulfide) (PPS) films, mass spectra in PPS powder and secondary ion mass spectra (SIMS) of Al and Cu have been measured. Sandwich-type cells of the deposited Cu–PPS–Al films show the rectification characteristic of Schottky barrier type. Substrate temperature during evaporation and the vacuum level in a chamber effect the ideality factor and the Schottky barrier, respectively. Ionization voltage increases the value of Schottky barrier, and acceleration voltage decreases one of the ideality factor. Vapor species of PPS, molecule of a benzene ring and a sulfur atom, one of a benzene ring and three sulfur atoms have been found in the mass spectra of PPS powder. The SIMS of the Cu–PPS–Al cell shows the diffusion of Al in PPS film. These values of Schottky barrier, ideality factor, and mass spectra are discussed by a model of which defect states are influenced by the mean polymer chain length.
Flow visualization of a spray develop ultrasonic nozzle using laser techniques
Authors: McIntyre Thomas J. , Via Dr. Giorgio G.
Published: July 2002

The spray develop method achieves the image uniformity required in leading edge lithography processes. At IBM Manassas, we have set up a lithography cell to resist coat, electron beam expose, and spray develop 4-in. wafers. This cell produced the 0.5 μ features found on the fully functional and tested very high speed integrated circuit (VHSIC) microprocessor chips we delivered to the US Government in 1988. An ultrasonic spray develop nozzle was used in the spray develop module of the cell. In order to optimize the process, a method of evaluating the uniformity of the spray aerosol has been devised. A low-powered laser is directed through a cylindrical lens to produce a sheet of laser light. The laser sheet is then directed through the spray aerosol to isolate a cross section of the spray. We compared three different ultrasonic nozzles using this laser sheet visualization technique. Key parameters, such as flow rate and ultrasonic power, were changed to gauge their effect on droplet sizes and spray uniformity. In this paper, we will discuss and present other techniques, such as a strobe synchronized to video and laser interferometry. This study indicates that despite appearances, the ultrasonic spray nozzles do not produce a uniform aerosol. Multiple vortices were found in the spray pattern, as well as numerous large droplets towards the exterior of the spray cone. The addition of a nitrogen shroud around the spray minimized these effects and improved spray stability.
An optical-heterodyne alignment technique for quarter-micron x-ray lithography
Authors: Suzuki Masanori , Une Atsunobu
Published: July 2002

A new optical-heterodyne interferometry alignment technique with diffraction gratings is developed for quarter-micron x-ray lithography. To obtain detection accuracy as good as a few tens of nanometers, a phase signal is utilized instead of a conventional intensity signal. The relative lateral displacement between mask and wafer is detected by measuring the phase difference between heterodyne beat signals generated by projecting two laser beams from + first-order and − first-order diffraction directions on the mask and wafer grating marks. The displacement signal is only slightly influenced by gap variation using symmetric optics. A lateral displacement detection resolution better than 10 nm is obtained by the experimental alignment setup. A nonsymmetric beam from the − third-order diffraction direction is added to the symmetric beams to detect the gap. The phase difference between two beat signals emitted to the second-order diffraction direction from the same mask and wafer marks is used as the gap detection signal. The cyclic gap signal makes it possible to set an arbitrary gap. A gap detection resolution of <20 nm is realized. Using this optical-heterodyne interferometry alignment method, a four-channel alignment system is developed for synchrotron x-ray lithography. Six-axis alignment servo control is established by combining this system with highly accurate stages.
Integrated electron-beam lithography for 0.25 μm device fabrication
Authors: Bucchignano Jim , Rosenfield Michael , Pepper Gwen , Davari Bijan , Holm Fritz , Viswanathan Raman
Published: July 2002

We report on the integration of the lithography related issues necessary for the successful completion of 0.25 μm silicon and GaAs device programs: system configuration and modifications, electron beam/resist interactions, resist and process control, and proximity effect correction. In addition, extended device results will be presented for both device programs. We have successfully completed fully–scaled, all electron beam 0.25 μm NMOS and PMOS runs on silicon and mixed electron beam/optical runs on GaAs. Device performance parameters show linewidth control on silicon of 0.025 μm (3σ). GaAs devices with 0.15 μm gates and 0.25 μm ring oscillators with delays less than 17 ps/stage have been fabricated.
High aspect ratio 0.1 μm tungsten gates for InGaAs/InAlAs heterojunction transistors
Authors: Tennant D. M. , Shunk S. C. , Feuer M. D. , Kuo J-M. , Behringer R. E. , Chang T. Y. , Epworth R. W.
Published: July 2002

High aspect ratio submicron W gate structures as short as 0.1 μm have been made by e-beam lithography and reactive ion etching. An SF6/CHF3 gas mixture has been studied to limit the undercutting observed in SF6 alone. Etch profiles in 1-μm-high tungsten have been systematically studied as a function of gas composition and an optimum ratio found. Data will also be presented on etch selectivity, bias voltage effects, and overetching. High-performance InAlAs/InGaAs heterojunction-insulated-gate FETs (HIGFETs) incorporating W air-bridge gates as short as 0.3 μm have been made using this technology. These devices exhibit a unity current gain frequency ft of 80 GHz, as measured, and an estimated 118 GHz when corrected for pad capacitance. Both pinchoff characteristics and threshold voltage data have been measured for devices with gate lengths from 0.4 to 1.2 μm and are found to be suitable for enhancement mode operation.
Metallic quantum wells grown by molecular-beam epitaxy
Authors: Harbison J. P. , Sands T. , Ramesh R. , Tabatabaie N. , Gilchrist H. L. , Florez L. T. , Keramidas V. G.
Published: July 2002

Ultrathin single crystal buried metal layers of NiAl have been grown within (Al,Ga)As heterostructures. The layers are electrically continuous down to 1 nm in thickness. Furthermore, property changes such as increased in-plane electron–electron interactions, and vertical transport resonant tunneling behavior, attributed to the decreased dimensionality of such ultrathin layers, demonstrate that, in this regime, the films can be considered as metallic quantum wells. The resonant tunneling has been exploited in making a three-terminal buried metallic well device. We discuss initial results of promising experiments aimed at decreasing the lattice mismatch between the metal and the semiconductor (1) by adding In to the GaAs and (2) by substituting the more closely lattice-matched CoAl for NiAl.
Automatic mark detection in electron beam nanolithography using digital image processing and correlation
Authors: Boegli V. , Kern D. P.
Published: July 2002

A method of mark detection for a vector scan eCF1-beam nanolithography system has been developed, in particular, taking into account that fairly low beam currents are used in high resolution writing. The digitally stored image of the scanned mark region is compared to a computer generated template using an advanced correlation technique. This method does not require a threshold determination. It exhibits high immunity to noise and poor contrast in the mark signal. The achieved accuracy is better than one beam step size (LSB) even for partially damaged marks. Due to specially chosen mark shapes, the probability of detecting wrong features is low. This paper describes the method and its hardware implementation along with experimental results for accuracy and repeatability of the mark position evaluation.
Alignment for masked ion beam lithography using ion-induced fluorescence
Authors: Stumbo D. P. , Sen Sudipto , Fong F-O. , Damm G. A. , Engler D. W. , Wolfe J. C. , Randall John N.
Published: July 2002

We show that the bombardment of densified chemical vapor deposited SiO2 by hydrogen ions induces fluorescent defects. A proton dose of 6×1014 /cm2 saturates the fluorescence yield at approximately 0.6 photons/100 keV of absorbed proton energy. A beam rocking technique was used to obtain a fluorescence alignment signal corresponding to the registration of a stencil mask pattern with a corresponding SiO2 mark on a wafer. Simulation of an optimized alignment system implies that 50 nm (3σ) registration can be achieved with a 1 s settling time. This direct approach to alignment has the advantages of being simple, relatively insensitive to resist coating of the marks, and compatible with conventional integrated circuit processing.
Modeling and simulation of a deep-ultraviolet acid hardening resist
Authors: Ferguson Richard A. , Hutchinson John M. , Spence Chris A. , Neureuther Andrew R.
Published: July 2002

A modeling methodology for a class of resist materials that rely on the acid catalyzed crosslinking of the resin matrix during a post-exposure bake is presented. This methodology is used to derive a complete and quantitative model for a production worthy deep-ultraviolet (UV) resist, Shipley XP-8843 (also known commercially as SNR 248). The modeling is based on the chemical and physical mechanisms which determine resist behavior during the exposure, post-exposure bake, and development processes. The IR absorption bands near 990 and 1070 cm−1 are used to monitor the extent of crosslinking during the bake as a function of bake temperature, bake time, and photogenerated acid concentration. The post-exposure bake model consists of a primary crosslinking reaction with an order of 1.42 in photo-generated acid and an acid loss reaction to account for dose dependent saturation of the crosslinking. Resist development is modeled by relating the dissolution rate to the extent of crosslinking during the post-exposure bake and to the number of sites on the crosslinking agent (six for melamine). Good correlation is obtained between simulated development profiles and experimental results with several post-exposure bake conditions.
New compensation method for avoiding proximity resist heating in variably shaped electron beam lithography
Authors: Nakajima Ken , Honda Toshiyuki , Matsumoto Hiroshi
Published: July 2002

A horizontal-mode resist heating is proposed and a suitable method for avoiding it in variably shaped electron beam lithography is described. The horizontal thermal diffusion through a top layer resist between electron beam shots cannot be neglected when using a high current density electron beam, a high speed deflector amplifier, and a multiple layer resist because these cause a horizontal-mode resist heating (labeled ‘‘proximity resist heating’’) which depends on the pattern size and on the time interval between shots. A method, suitable to avoid this resist heating, is proposed where the pattern size dependent optimum repetition number of exposures for each pattern is used. There is a slight throughput degradation of typically 10%–20% increase.
Sensitivity/resolution variables in x-ray chemically amplified resists exposed to synchrotron radiation
Authors: Taylor J. W. , Babcock C. P. , Mancini D. C. , Plumb D. , Olsen R. J. , Fedynyshyn T.
Published: July 2002

New formulations of chemically amplified negative-image photoresists show sensitivities to x rays on the order of 100 mJ/cm2 or less and printed minimum linewidths of 0.25 μm or smaller under electron-beam conditions. Under x-ray exposure, both the resist sensitivity and the contrast are responsive to the processing variables of post-exposure bake temperature, post-exposure bake time, developer normality, and developing time. Initial data are presented for Shipley XP-8933B and several experimental resists to illustrate the major relationships between the listed variables for x-ray exposure. Under optimum conditions all resists produce minimum linewidths of 0.4 μm or better.
Optical properties of x-ray lithography masks
Authors: Vladimirsky Y. , Maldonado J. R. , Vladimirsky O. , Starikov A. , Fuentes R. , Guarnieri D. , Whitehair S. W. , Cuomo J.
Published: July 2002

The purpose of this paper is to present experimental results on optical properties of x-ray mask substrates relevant to x-ray lithography systems utilizing optical alignment between mask and wafer. Data on mask substrates of several materials including B-doped Si, SiC, polyimide, and diamond will be presented. In order to study the light scattering properties of the mask substrate materials, a novel light scattering measuring system was constructed which allows determination of the angular dependence of the transmitted, and reflected light from the mask membranes. The system discriminates between the forwardly transmitted, and specularly reflected light from the sample membranes by the use of perforated solid state light detectors. The detectors are placed on each side of the membrane to obtain simultaneous measurements of forward and back scattering, that otherwise may be affected by thin film interference effects. The data gives information on light scattering due to both the bulk material, and the surface roughness. For the case of B-doped Si membranes, the measured values are in good agreement with a light scattering model also described in this paper. The results shed light on the proper selection of x-ray mask substrate materials from the optical alignment point of view.
Verification of partially coherent light diffraction models in x-ray lithography
Authors: Guo Jerry Z. Y. , Cerrina Franco
Published: July 2002

The image formed in proximity x-ray lithography is normally computed using a physical optics model that takes in explicit account diffraction processes. It is important to understand the assumption implicit in the various models and the effects that they have on the image formation. We concentrate, in particular, on the effect of the type of illumination on the quality of the image that can be obtained in proximity x-ray lithography. In this paper, different methods of calculating the diffraction of partially coherent light are compared and the approximations implicit in each discussed. In a partially coherent system, the properties of the source play an intrinsic role in image formation, so they must be treated together with the imaging process. The full detailed calculations are too complex for implementation on even a supercomputer but, for some types of sources and optical systems it is possible to simplify the problem. Particularly important is the issue of the validity of the linear shift-invariant system approximation, since it allows great improvements in computational time. We prove the validity of the approximation and verify it using a full 4D numerical integration, based on the Rayleigh–Sommerfeld theory and realized on a Cray YMP8 supercomputer. Application of the results to some physical cases of 0.25 and 0.1 μm features is presented and discussed, illustrating the wide process latitude and resolution of x-ray lithography.
The scanning tunneling microscopy combined with the scanning electron microscopy—A tool for the nanometry
Authors: Edel’man V. S. , Troyanovskii A. M. , Khaikin M. S. , Stepanyan G. A. , Volodin A. P.
Published: July 2002

Two scanning tunneling microscopes (STMs) compatible with scanning electron microscope or optical microscope are presented. One STM is based on bimorph piezos and has a scanning range of about 10 μm. The other STM is based on a solid piezoblock with frequencies higher than 8 kHz and with a scanning range of about 3 μm. Some results demonstrate the capabilities of these microscopes. Among them are the observations of the microbridge, of the grain boundary in twinned crystal, the imaging of topography, and tunneling current distribution on the cleaved multilayer GaAs–AlGaAs structure.
Scanning tunneling microscopy of decagonal and icosahedral quasicrystals
Authors: Becker R. S. , Kortan A. Refik , Thiel F. A. , Chen H. S.
Published: July 2002

The scanning tunneling microscope is used under ultrahigh vacuum conditions to image the clean surfaces of decagonal Al65Co20Cu15 and icosahedral Al65Cu20Fe15. The tunneling images show nonperiodic surfaces whose features are adequately described by pentagonal quasilattice for the case of the decagonal material, suggesting that a tiling model accounts for the surface features. The scanning tunneling microscope measurements of the scale of surface features is in good agreement with high resolution x-ray diffraction measurements of the bulk.
Scanning tunneling microscopy observation of crystal growth of deposited gold films during annealing
Authors: Watanabe M. O. , Kuroda T. , Tanaka K. , Sakai A.
Published: July 2002

The crystal growth of deposited gold films by annealing at high temperatures has been studied by scanning tunneling microscopy. The deposited Au film before annealing had a rough surface with an average grain size of about 200 Å. Measurements during annealing at high temperatures have revealed that the small grains grow into larger islands with flatter surfaces, producing even deeper and narrower valleys between the islands. This is considered to be crystal growth near the island edges. The surface after annealing consisted of flat (111) surfaces with steps and deeper valleys.
Scanning tunneling microscopy study of TiOx on Rh(111)
Authors: Wang Hong-Chuan , Ogletree D. Frank , Salmeron Miquel
Published: July 2002

Scanning tunneling microscopy has been used to study submonolayer coverages of titanium oxide on rhodium. After reduction with CO, titania is shown to form one atomic layer thick islands ∼20 Å in size on the Rh(111) surface at submonolayer coverages. High resolution filled state images show enhanced contrast at the island perimeter. The ‘‘ring shaped’’ appearance of the islands is related to the electronic structure of the titania overlayer.