bluuebunny/crossref_metadata_2025 huggingface dataset:
The formation of two aluminum–semiconductor interfaces: A temperature-dependent study
Authors: Stephens C. , McGovern I. T. , McLean A. B. , Braun W.
Published: July 2002

Soft x-ray photoelectron spectroscopy has been used to compare the chemistry of Al/InP(110) and Al/GaSe interfaces at room and low (<120 K) temperatures. For Al/InP(110) at low temperature it was found that the reacted feature of the In 4d spectrum has a coverage dependent binding energy. This is a result of the altered growth mode of the reacted In atoms on the low-temperature surface. The spectral weight of the reacted feature is shown to be equivalent at the two temperatures, but escape depth effects imply that some reduction in reactivity has occurred. The behavior of the Al/GaSe interface is quite different. At low temperature no evidence for reaction was found within the equivalent coverage range. These results are discussed within the cluster-initiated exchange reaction model.
Si crossdoping control and defect control in GaAs/Si heterojunctions grown by molecular-beam epitaxy
Authors: Li A. Z. , Wang J. X. , Qiu J. H. , Liang B. W. , Cheng Y. L. , Li C. C.
Published: July 2002

The effects of growth procedure on the crystal defects and stresses of GaAs/Si polar/nonpolar heterojunctions grown by molecular-beam epitaxy directly on 4° off (100) towards [110], and (211) misoriented Si substrates have been investigated by Raman scattering and Rutherford backscattering channeling. The FWHM of the Raman peak at room temperature and the ion channeling minimum yield Xmin is reduced with cooling rate decrease and with substrate (100) misorientation and (211) misorientation. The stress in (100) growths is about 109 dyn/cm, and in (100) off 4° [110] is 108 dyn/cm. A suitable termination procedure has been described. Si outdiffusion causes a crossdoping problem, and we have studied the effects of temperature on the interface crossdoping by Auger profiles and have found that crossdoping is strongly dependent on the growth temperature and the postgrowth heat treatment. Crossdoping of Si into the GaAs at the interface region can be controlled by using an AlGaAs/GaAs superlattice with an interrupted growth process and relatively low-growth temperatures for AlGaAs/GaAs of 620 °C/570 °C. A multiple step growth procedure for successful growths of GaAs on Si has been developed and is described.
Preparation of molecular-beam epitaxy growth high-quality GaAs–AlGaAs quantum wells and their properties investigation
Authors: Huang Y. H. , Kong M. Y. , Sun D. Z. , Liang J. B. , Zhen Y. P.
Published: July 2002

The quality of molecular-beam epitaxy (MBE) growth GaAs–AlGaAs are essential for the properties of new type microstructural devices. Improved growth conditions in MBE have permitted the fabrication of high-quality ultrathin microstructural materials. In this paper, we report the preparation of MBE grown high-quality GaAs–AlGaAs quantum wells (QW’s) and their properties. The 1.2 meV FWHM of E1h indicates the high quality of the material. Growth conditions (especially growth temperature Ts and precise control of the layer thickness) and the substrate preparation are important factors for MBE growth of high-quality ultrathin microstructural materials. The molecular-beam sources of our MBE system are vertical type Knudsen cells employing PBN crucibles. Entire component parts of our MBE system were made in China.
Examination of fluorocarbon-based plasmas used in the selective and uniform etching of silicon dioxide by response-surface methodology: Effects of helium addition
Authors: Riley Paul E. , Kulkarni Vivek D. , Bishop Sally H.
Published: July 2002

The process parameter space for fluorocarbon plasmas (C2F6/CHF3 and CF4/CHF3, with and without He) which are used to etch SiO2 has been examined with a Lam Research Autoetch 580 parallel plate, single-wafer etching system by response-surface methodology. The response or behavior of the plasmas differs very significantly with reactor pressure, etch gas mixture, and He addition. In particular, substantially higher SiO2 etch rates are obtained with C2F6/CHF3 plasmas than with CF4/CHF3 plasmas at an equivalent radio frequency power density for similar gas flow rates at significantly different reactor pressures: ∼2500 Å/min at ∼400 mTorr with C2F6/CHF3 mixtures and ∼750 Å/min at ∼1500 mTorr with CF4/CHF3 mixtures. Upon addition of He to the plasmas, the SiO2 etch rate maximum for the C2F6-based plasma shifts to ∼800 mTorr and declines to ∼2000 Å/min, while that for the CF4-based plasma remains near 1400 mTorr and increases to ∼1000 Å/min. Whereas the addition of He sharply degrades the etching uniformity with C2F6/CHF3 mixtures, it has no apparent effect on the etching uniformity with CF4/CHF3 mixtures, which is high with or without the addition of He over the parameter space which was explored. For the C2F6/CHF3 plasma, the etch selectivity to silicon is highest at 700–1100 mTorr, while for the CF4/CHF3 plasma the selectivity is highest at 1100–1500 mTorr. Although addition of He substantially improves the selectivity with the CF4/CHF3 plasmas, it has no effect on selectivity with the C2F6/CHF3 plasma. These detailed characterizations of process parameter space have led to a uniform and selective SiO2 sidewall spacer etching process which may be readily extended to other SiO2 etching processes with this equipment and these gas mixtures.
Low-temperature highly preferred polycrystalline Si film growth on crystallized amorphous Si by reactive ion beam deposition
Authors: Yamada Hiroshi
Published: July 2002

Highly preferred polycrystalline Si (polysilicon) film growth on amorphous Si with ion-assisted crystallization by reactive ion beam deposition (RIBD) at the low temperature of 550 °C was investigated. This method uses low-energy controlled ionized species produced from electron-cyclotron-resonance plasma. To achieve highly preferred polysilicon film growth, a new growth process using ion-assisted crystallization was developed as follows: After a thin amorphous Si film was deposited on an amorphous substrate at 100–150 °C and 100 eV by RIBD using SiH4, it was crystallized at 550 °C by 400-eV H+ and H+2 irradiation using the same RIBD system. Then, a polysilicon film was grown at the same temperature and 100 eV by RIBD using SiH4. Polysilicon films grown by this process possess stronger Si(220)-preferred growth orientation and higher Hall mobility than the films grown directly on amorphous substrates.
X-ray spectra in a gas puff plasma x-ray source for x-ray lithography
Authors: Itabashi Seiichi , Okada Ikuo , Saitoh Yasunao , Yoshihara Hideo
Published: July 2002

This paper describes x-ray spectra variation caused by x-ray absorption in columnar high-density plasma which is employed as an x-ray source for x-ray lithography. In the axial direction of the columnar plasma, it is found that x-ray emission from Ne+8 ions is absorbed more intensely than from Ne+9 ions. Thus, the x-ray spectral features vary from the primary profile due to x-ray absorption by high-density plasma. For x-ray lithography, it is necessary to produce high-density plasma near the x-ray extraction side electrode in order to prevent the x-ray output attenuation caused by absorption. An external magnetic field is employed to control the pinched plasma. High-density plasma is localized near the extraction side electrode by the magnetic field. However, pinching becomes weak and x-ray outputs decrease simultaneously. Shortening the electrode gap is effective to prevent the x-ray output attenuation, because plasma density near the extraction side electrode becomes high substantially. However, discharges become unstable if the gap is too narrow. At the optimized electrode gap, x-ray output fluctuation is low and high-density plasma is produced stably. Accordingly, it is necessary to optimize the electrode gap in the plasma source for x-ray lithography.
The effect of LaB6 cathode shape on its performance in a JBX 5DII electron beam lithography system
Authors: Tennant D. M. , Swanson L. W.
Published: July 2002

The focused beam size and current for a JBX 5DII electron beam lithography system was measured for various shaped, (100) single-crystal LaB6 cathodes at 50-kV beam voltage. The performance of a 90° full angle, conically shaped cathode with a 15-μm spherical apex radius was compared with a similar cathode, but with a variable diameter flat at the cathode apex. As the flat size varied from 15 to 30 μm, the minimum beam size (for 50 pA of beam current) varied from 11 to 37 nm for a cathode temperature of 1830 K. The performance of the 15-μm truncated compared favorably with the 15-μm spherical shaped cathode. For larger beam diameters, the beam current for the truncated cathode exceeded that of the 15-μm spherical shaped emitter. The truncated cathode was operated in excess of 3100 h with no performance degradation.
From porous Si to patterned Si substrate: Can misfit strain energy in a continuous heteroepitaxial film be reduced?
Authors: Xie Y. H. , Bean J. C.
Published: July 2002

The use of patterned Si substrates (specifically porous Si) for the reduction of heteroepitaxial film strain energy [S. Luryi and E. Suhir, Appl. Phys. Lett. 49, 140 (1986)] has been studied recently by several research groups. We report experimental studies and discuss the validity of the original concept. We studied molecular beam epitaxial growth of continuous GexSi1−x film on 〈100〉 porous Si substrates using Rutherford backscattering spectrometry, transmission electron microscopy, and x-ray rocking curves. The results show predominantly 60° dislocations with long misfit segments. There is no reduction in either strain in the films or dislocation density compared to the samples grown on regular Si substrates. In order to reduce defect densities, the stress fields from different growth areas of patterned substrate must not interfere. Arguments based on crystallographic considerations are presented which demonstrates that, first, the porous Si substrate is not suitable for such applications because of the nature of interconnected growth areas, and second, any kind of decaying stress field requires a certain degree of wafer warpage which does not always present in a realistic MBE-grown heterostructure. It is the conclusion of this discussion that the strain energy in a continuous heteroepitaxial film grown on patterned substrates does not reach a limiting value, but continues to increase with the film thickness.
A high-accuracy alignment technique using single- and double-pitch dual gratings
Authors: Une A. , Takeuchi N. , Torii Y.
Published: July 2002

This paper describes a mask-to-wafer alignment technique for submicron x-ray lithography. A new gap and lateral alignment method is proposed to avoid the interference of lateral displacement on the gap detection signal and to accurately detect lateral displacement in the wide gap range. This method utilizes a pair of marks: a single grating, which does not have a grating acting as a mark on the wafer, and double-pitch dual gratings, whose wafer grating pitch is twice as large as the mask grating pitch. Gap detection is performed using an interference signal and an envelope signal. The interference signal is produced by superimposing a positive first-order diffraction light beam reflected from the mask grating and that of the wafer surface. The envelope signal makes it possible to set an absolute gap. The linear part of the interference signal is used for precision servocontrol at the gap setting point. The lateral alignment, on the other hand, is performed using the intensity difference between positive first-order and negative first-order diffraction lights generated by the double-pitch dual gratings. A highly sensitive and stable lateral displacement detection signal is obtained at the specific gap. The signal has a triangular waveform and hardly varies for gap fluctuations of a few microns from the specific gap. The gap range where a stable signal can be obtained, is 50 times larger than that of the conventional dual grating method. These experimental results agree quite well with theoretical calculations. By combining the single grating method and the double-pitch dual grating method, accuracies of ±0.02 μm in both gap and lateral alignment servocontrols are realized.
Temperature dependence of current conduction in barrier-enhanced, carbon delta-doped GaAs diodes
Authors: Katz A. , Pearton S. J. , Ren F. , Abernathy C. R.
Published: July 2002

The temperature dependencies of Schottky barrier height, ideality factor, and reverse bias breakdown voltage are reported for Ti/Pt/Au contacts on n-type GaAs containing zero, one, or two near-surface, carbon δ-doped (p=7×1019 cm−3) layers, each ∼50 Å wide. Arrhenius plots of the total current flowing under forward bias in each structure yield effective barrier heights of 0.73, 0.91, and 0.65 eV, respectively, as the transition is made from barrier enhancement (reduced thermionic emission) to barrier lowering (increased tunneling). Both the ideality factor and breakdown voltage degrade with increasing measurement temperature.
Printability of x-ray mask defects at various printing conditions and critical dimensions
Authors: Kluwe A. , Lutzke H. , Stelter Th. , Müller K.-H.
Published: July 2002

Because of the large cost associated with inspection and repair of sub-half-micrometer 1:1 x-ray masks, it is worthwhile to determine precisely the defect requirements. The printed resist image of x-ray mask defects is simulated with the simulator xmas (X-ray lithography Modelling And Simulation) for different mask defect sizes. The printed defect size increases with increasing mask defect size. If it reaches (1)/(10) of the smallest printed linewidth, the corresponding mask defect size is regarded as critical. Mask defects equal to or larger than the critical size must be repaired. The critical sizes of different types of x-ray mask defects are evaluated giving the desired defect requirements. The simulations are confirmed by a comparison between a physical and a simulated print of a designed mask defect. The investigation is confined to the use of a synchrotron as the x-ray source.
Atomically resolved images of bismuth films on mica with an atomic force microscope
Authors: Weisenhorn A. L. , Henriksen P. N. , Chu H. T. , Ramsier R. D. , Reneker D. H.
Published: July 2002

Bi(111) films grown on mica substrates and then exposed to air have been imaged with an atomic force miroscope in 0.01 M HCl. By exposing the Bi(111) to air, layers of Bi oxide are readily formed, which can be removed by imaging in HCl. The images are atomically resolved and show two types of structure: large epitaxial areas of hexagonal structure with a spacing of 7.6 Å, and a few smaller regions with a spacing of 4.5 Å. The former agrees well with the (√3×√3)R30° structure of an overlayer of atomic oxygen atoms adsorbed on Bi(111), and the latter with the uncovered Bi(111) surface.
Scanning tunneling microscopy of chloroplasts
Authors: Mainsbridge B. , Thundat T.
Published: July 2002

Conventional preparation techniques as used in electron microscopy have been used to separate chloroplasts. While still in a buffer solution they have been electrochemically deposited on a gold substrate. Scanning tunneling microscope images of the grana and lamellae of spinach chloroplasts have been found to be consistent with evidence from electron microscopy of their external structure. Possible contact sites, where proteins are imported selectively into the membrane, have been observed, some supporting linear molecular chains approximately 10 nm long.
Magnetron ion etching of InP using mixture of methane and hydrogen and its comparison with reactive ion etching
Authors: Singh Jaspal
Published: July 2002

Magnetron ion etching (MIE) of InP has been studied using methane and hydrogen. These results of the first study are compared with those obtained with reactive ion etching (RIE) using the same gases in the same machine but without the magnet. The advantages of the MIE system demonstrated here include etching rates about three to four times higher and a lower degree of acceptor passivation (reduction in carrier concentration of etched surface), a low self-bias of between 70–200 V, and a resulting etched surface which is very smooth. Moreover, it is found that RIE and MIE give very similar degree of passivation depths, provided sample temperature during etching does not exceed 60 °C. However, MIE is favored because of higher etch rates. The degree of passivation in the MIE also depends on the percentage of methane used in the process. Anisotropic etching of InP with the MIE can be achieved under certain conditions of high pressure, but in conjunction with reduced etch rate and degraded surface morphology.
Characterization of reactive ion etched AlGaAs/GaAs heterostructures by photoluminescence and low temperature Hall measurements
Authors: Joseph M. , Guimaraes F. E. G. , Kraus J. , Tegude F.-J.
Published: July 2002

A low damage dry etch process has been developed for the gate recess of AlGaAs/GaAs heterostructure field effect transistor (HFET) with a selectivity of the etch rates greater than 750:1. The reactive ion etching induced damage has been compared to that reported from other etch processes in literature by the means of photoluminescence (PL) emission from multiple quantum well structures. Better resolution in amount and depth of created defects is obtained by PL measurements of undoped heterostructure layers. The temperature dependent Hall mobility μH and sheet carrier concentration ns of a doped heterostructure layer which directly correspond to the HFET device properties are evaluated in the dark and under illumination. Values of 360.000 cm2/V s for μH and 8.6×1011 cm−2 for ns at 15 K after the etch process show that a residual damage can be neglected.
Dopant migration in silicon during implantation/annealing measured by scanning tunneling microscopy
Authors: Hessel H. E. , Memmert U. , Cerva H. , Behm R. J.
Published: July 2002

The spatial correlation between the lateral distribution of the doping type and the former implantation mask edge was investigated by scanning tunneling microscopy (STM) measurements. The position of the former mask edge was determined from surface steps resolved by STM topography measurements. Current imaging tunneling spectroscopy (CITS) data recorded simultaneously allowed to detect the transition from a high doping level with an ohmic I–V curve to a lower doping level displaying a Schottky barrier behavior. The influence of different annealing treatments on the position of this transition was investigated.
Detection of residual photoresist with the atomic force microscope
Authors: Prater C. B. , Hansma P. K. , Tan I-H. , Lishan D. G. , Hu E. L.
Published: July 2002

We report the use of the atomic force microscope (AFM) for local measurements of photoresist thickness and for the detection of residual photoresist in semiconductor processing. By scraping the photoresist off a small portion of a sample with the AFM stylus, and then imaging a larger area at low force, we have been able to measure the depth of a residual, photoresist masking layer. In addition, the AFM has been used to qualitatively judge the efficiency of three common methods of removing photoresist: a hot acetone bath left the most residual photoresist, a commercial stripper left less, and an oxygen plasma etch left none under our test conditions.
Filling of contacts and interconnects with Cu under XeCl excimer laser irradiation
Authors: Wang Shi-Qing , Ong Edith
Published: July 2002

XeCl excimer laser (λ=308 nm) was used to melt and flow sputter deposited Cu film into contacts and trenches of different depths to fill them and to achieve a planarized surface. The process windows (in terms of laser fluence at substrate temperatures of 20, 365, and 440 °C) for the planarization and complete fill were investigated. We found that it is possible to completely fill the contacts and trenches of 1 μm in width and 1 μm in depth with an appreciable process window. However, we were only able to fill these 1 μm wide contacts and trenches of 2 μm in depth at 440 °C. The results and other phenomena will be discussed.
Photochemistry at adsorbate–metal interfaces: Issues and examples
Authors: White J. M.
Published: July 2002

Some issues and examples of recent progress in the field of photochemistry at adsorbate–metal interfaces are overviewed.
Radio-frequency Ar sputter etch rates: Theory and experiment
Authors: Horwitz C. M. , Puzzer T. , Melngailis J.
Published: July 2002

Radio-frequency (rf) sputter etching rate calculation is difficult because ion fluxes at targets are not well known, and ion-neutral collisions in rf sheaths result in a wide range of particle energies incident on rf targets. In addition, backscattering from the sputtering gas makes experimental etch rates hard to measure. In this article, we present measurements of (a) rf sputter etching and redeposition rates, (b) Ar+ ion beam sputtering rates of Si and SiO2, and (c) ion fluxes and energy distributions for 13.56 MHz Ar discharges. A simple self-consistent model of the rf sheath is used to derive the flux and energy distribution of neutral particles. This is combined with the ion flux to derive theoretical sputtering rates. Experimentally measured etch rates have been corrected for redeposition by comparing rates on planar sufaces with rates inside reentrant masks. Low-density coatings due to redeposition were observed in regions protected from ion bombardment, inside the reentrant masks. Ar sputter etch rates of planar samples were suppressed by factors between 3 and 10 by this redeposition. Agreement between theoretical predictions and observed experimental results is good, inside the range of uncertainty in our theoretical calculations. An overall predictive accuracy within 25% is attained.
Comparison of passivation films: The effect of thermal cycles and comparison of phosphorous doped oxide films
Authors: Wu T. H. Tom , O’Brien Kari , Hemmes Diederik G.
Published: July 2002

Choosing the correct passivation film can be a complicated task. Factors such as sidewall integrity, sodium penetrability, and ability to withstand postpassivation temperature cycles must be considered. Previous studies have defined standard techniques for testing sidewall integrity and sodium barrier ability. In this study, the effect of thermal cycle exposure on the sidewall integrity of plasma enhanced chemical vapor deposition (PECVD) passivation films (TEOS-based oxide, oxynitride, and nitride) by varying factors such as film type, metal sputter temperature, and film stress was examined. It will be shown that metal sputter temperature and film stress are much more important than film type. In addition, the newer generation of TEOS-based phosphorous-doped passivation films was compared to the standard, silane-based phosphosilicate glass which is deposited using atmospheric pressure chemical vapor deposition (APCVD). The conclusion is that APCVD films are slightly better as deposited, but degrade during temperature cycles. The newer TEOS-based PECVD films, however, are not affected by temperature cycling.
Sub-half-micron metal–oxide–semiconductor device fabrication using a compact synchrotron radiation lithography system
Authors: Fujii K. , Tsuboi S. , Yoshihara T. , Tanaka Y. , Suzuki K. , Setoguchi S. , Miyatake T.
Published: July 2002

In order to evaluate the usefulness of the compact synchrotron radiation (SR) lithography system using a superconducting synchrotron light source ‘‘AURORA,’’ sub-half-micron metal–oxide–semiconductor devices were fabricated. This article describes the SR lithography system including x-ray masks, the device fabrication processes, and the characteristics of the resulting devices. Excellent overlay accuracy, better than 90 nm (3 σ), was obtained using chromatic bifocus alignment optics in most levels. Though no radiation effect is observed in initial device characteristics, hot-electron-induced instability is observed in 2000 mJ/cm2-irradiated devices. If high-speed resists with 100–200 mJ/cm2 sensitivity were used, the instability would be reduced to a negligible level.
Nanofabrication of photonic lattice structures in GaAs/AlGaAs
Authors: Wendt J. R. , Vawter G. A. , Gourley P. L. , Brennan T. M. , Hammons B. E.
Published: July 2002

The nanofabrication of two-dimensional photonic lattice structures in GaAs/AlGaAs is reported. The nanofabrication procedure combines direct-write electron-beam lithography and reactive-ion-beam etching to achieve etched features as small as 50 nm. The lattice comprises a hexagonal array of air cylinders etched into a semiconductor surface with a refractive index contrast of 3.54. A range of air volume fractions from 14% to 84% was investigated. The lithographic, masking, and etching processes necessary to fabricate the lattice are described along with practical limitations to achieving a lattice of arbitrary air volume fraction. Initial results from optical characterization of the lattice are also presented.
Overlayer-induced valence states, and evidence for charge transfer in Na/GaP(110) and Na/GaAs(110): A comparative photoemission study
Authors: Evans D. A. , Lapeyre G. J. , Horn K.
Published: July 2002

Core and valence level photoemission experiments for Na overlayers on GaP(110) and GaAs(110) reveal new peaks which are interpreted in terms of Na–Ga charge transfer, as predicted by total energy calculations. New peaks in the region above the valence band are identified with the previously empty Ga surface state which is filled by the charge transfer process. The role of this gap emission in the pinning of the Fermi level at submonolayer to metallic coverages is discussed for both semiconductors.
EL-4, a new generation electron-beam lithography system
Authors: Pfeiffer H. C. , Davis D. E. , Enichen W. A. , Gordon M. S. , Groves T. R. , Hartley J. G. , Quickle R. J. , Rockrohr J. D. , Stickel W. , Weber E. V.
Published: July 2002

The new generation electron-beam lithography system EL-4 is described, designed for direct wafer exposure as well as optical reticle and x-ray mask making. The new architecture features control through workstations and local area network communication between these and the microprocessor-controlled subsystems. The system has on-line error checking and diagnostics. Wafers up to 200 mm diam are handled individually with a Standard Mechanical InterFace-compatible, fully robotic system, and are electrostatically chucked to the stage. Reticles are clamped to the stage with double-sided e/s chucks, ring-bonded membrane masks are kinematically held in a carrier chucked to the stage. The reticle/mask maker has an internal temperature control system in addition to the clean-room climate control for the entire mechanical hardware. The electron optics accommodate triangle as well as rectangle spot formation, and for direct write application a throughput-enhancing third level in the deflection hierarchy. High resolution variable-axis immersion lens optics are used for beam projection and positioning on the target. The column design is significantly advanced over EL-3 for improved integrity and performance as well as automated control through electronics with menu-driven touch screen for user-friendly operation. The first EL-4 system is currently in qualification as a reticle/mask maker for 0.25 μm device technology.
Reactive ion etching of AlInGaP and GaAs in SiCl4/CH4/Ar-based plasmas
Authors: Chang C. V. J. M. , Rijpers J. C. N.
Published: July 2002

The reactive ion etching of AlInGaP and GaAs with a gas mixture of SiCl4, CH4, and Ar is examined. Process parameters such as gas flow composition and radio-frequency power input are varied. The CH4 flow variation in particular has a substantial effect on the morphology of AlInGaP, while generally the effects on GaAs are less dramatic. The etch rates of AlInGaP and GaAs show similar trends. A suitable etching process was found and applied to an AlInGaP/InGaP index-guided 675 nm laser structure.
Ag2Te/As2S3, a top-surface, high-contrast negative-tone resist for deep ultraviolet submicron lithography
Authors: Dumford S. A. , Lavine J. M.
Published: July 2002

The sensitivity of the Ag2Te/As2S3 system has been measured as a top-surface imaging, negative-tone resist between 632.8 and 193 nm. The sensitivity at g-line (435.8 nm) and i-line (365 nm) is of the order of 5 and 0.5 J/cm2, respectively, and is much too low to take advantage of the significant advantages of this resist. These advantages are high contrast (∼10), an edge effect which compensates for the reduction of optical intensity at line edges and latent image formation in a layer whose thickness is significantly less than the depth-of-focus of high resolution stepper optical systems. Measurements at 248 and 193 nm show significantly higher sensitivity of 350 and 80 mJ/cm2, respectively, suggesting that this system may possess practical potential at these wavelengths. Exposures on a GCA XLS-7500 stepper with 0.42 NA at 365 nm have yielded 0.35 μm linewidths.
An analytical model of stochastic interaction effects in projection systems using a nearest-neighbor approach
Authors: Mkrtchyan M. M. , Liddle J. A. , Berger S. D. , Harriott L. R. , Schwartz A. M. , Gibson J. M.
Published: July 2002

Image blurring as a result of stochastic particle interactions has been investigated for projection electron- and ion-beam lithography systems. The investigation was made on the basis of a simple, nearest-neighbor, analytical model, proposed and developed here, for stochastic particle–particle interactions. The results obtained using this model are in close agreement with those given by Jansen [Coulomb Interactions in Particle Beams (Academic, Boston, 1990)] for an extended parallel beam segment in the Holtsmark regime; at the same time they are extendable over a wide range of conditions, unlike Jansen’s results. The results obtained for a parallel beam are applied to more realistic systems by dividing the beam into nearly cylindrical, uncorrelated slices. This method is used to determine the dependence of the image blur on beam parameters for a doublet. Our results correlate well with those obtained by Monte Carlo calculations.
Minimum feature sizes and ion beam profile for a focused ion beam system with post-objective lens retarding and acceleration mode
Authors: Kieslich A. , Reithmaier J. P. , Forchel A.
Published: July 2002

The beam characteristics of a focused Ga+-ion beam (FIB) at ion energies between 10 and 150 keV have been investigated by using a 100 keV focused ion beam system with an additional post-objective lens retarding and acceleration electrode. Line structures with minimum feature sizes down to 20 nm almost independent of the landing energy of the ions could be realized by sputtering line patterns in a gold-coated GaAs substrate. The current density profile was determined over six orders of magnitude by measuring the radii of FIB-exposed dot structures as a function of the ion dose. The beam diameters have been found to be in the range between 30 and 45 nm, nearly independent of the available ion energies. The photoluminescence signal of locally intermixed AlGaAs/GaAs quantum well structures was used to study the spatial resolution of FIB-implanted line patterns. The results were compared with the lateral resolution, which can be calculated from the current density distribution of the beam profile.
Electron cyclotron resonance ion stream etching with high uniformity and accuracy for metal–oxide–semiconductor gate fabrication
Authors: Takahashi Chiharu , Matsuo Seitaro
Published: July 2002

A new system has been constructed for electron cyclotron resonance (ECR) ion stream etching to fabricate metal–oxide–semiconductor (MOS) gates at the quarter-micron level. It has three features: (i) a new ECR plasma source that generates a uniform plasma; (ii) a supplementary coil that makes the ion stream perpendicular over the whole surface of a 6- or 8-in. wafer; and (iii) CF4 and O2 addition to reduce the influence of SiClx by-products formed by the reaction between silicon and the Cl2 etching gas. We have found that reducing the amount of SiClx reaction products desorbed from the chamber wall is essential for significant improvement in etching characteristics. Using this new system, we attained (i) uniformity as good as ±1.6% over a 6 in. wafer with a Si etch rate of 0.17 μm/min; (ii) uniformly vertical profiles over the whole wafer, including the edges; and (iii) stable etching conditions with a high selectivity of over 100.
Efficiency enhancement of Monte Carlo simulation of particle beam interaction by separation of stochastic and continuum contributions
Authors: Groves T. R.
Published: July 2002

In electron and ion beam lithography, the particle–particle interaction in the drift length of the system imposes a fundamental limitation on the useful current obtainable for a given resolution. This is a classical N-body problem, for which Monte Carlo simulation has proven useful for predicting the size of the effect. Monte Carlo simulation is slow, however, due to the fact that N(N−1)/2 computations of the Lorentz force must be done for N particles at each step. The purpose of this study is to investigate the limitation on computational efficiency. Based on this, an efficient algorithm is proposed and demonstrated. The approach consists of separating the interaction force arising from the average charge distribution from that arising from random fluctuations in charge density. These two contributions are computed separately, and the results combined in a way which eliminates ‘‘end effects’’ arising from a finite particle sample length. The results show that a significant reduction is possible in the number of particles needed to obtain a given level of accuracy. This is expected to result in reduced computation time.
High aspect ratio dry etching for microchannel plates
Authors: Snider G. L. , Then A. M. , Soave R. J. , Tasker G. W.
Published: July 2002

Dry etching of GaAs and fused silica for the production of microchannel plates is investigated. Etch methods used are magnetron reactive ion etching, chemically assisted ion beam etching (CAIBE), and electron cyclotron resonance etching (ECR). Extensive characterization of the ECR etcher is carried out with a designed experiment, which uses statistical methods to minimize the number of characterization runs. CAIBE gives high aspect ratio etching of GaAs, but at low etch rates. ECR provides higher etch rates of GaAs and better substrate temperature control. The effect of temperature on sidewall roughness and undercut is examined for temperatures as low as −100 °C. Features with an aspect ratio greater than 30 are presented. Etching of fused silica is difficult due to low etch rates (<0.2 μm/min), and faceting of the metal mask.
Application of lead zirconate titanate thin film displacement sensors for the atomic force microscope
Authors: Fujii Toru , Watanabe Shunji , Suzuki Masatoshi , Fujiu Takamitsu
Published: July 2002

Elimination of optical and tunneling displacement sensors from the atomic force microscope (AFM) is an important breakthrough for improved performance of the AFM. The interaction of an oscillating tip and a surface has become a popular tool for obtaining information which could not be obtained by the conventional repulsive force AFM mode. In this application, lead zirconate titanate (PZT) is one of the most promising materials with large piezoelectric constants which can be used not only for detecting distortions such as the displacement detection of an AFM cantilever, but also oscillations of the cantilever. However, incorporating PZT into the microfabrication process to make the AFM cantilever has not been easily accomplished because PZT has a delicate chemical nature. We have successfully developed an AFM with a microfabricated cantilever which had a PZT thin film applied for displacement sensing. The linearity of the output signal was sufficient for displacement sensing. Images of a compact disk were obtained to assure the capability of the PZT thin film for AFM detection. © 1995 American Vacuum Society
Investigation of silicon transport in the neutral background of a plasma activated reactive evaporation system
Authors: Higgins Ben , Durandet Antoine , Boswell Rod
Published: July 2002

The transport of silicon vapor from an electron-beam evaporation source through argon and hydrogen gas in pressures near 1.0 mTorr has been studied. The flux–distance relationships for the effusion/diffusion of the evaporant through the device are found to vary with the type of filling gas. The investigation includes both a simple theoretical model and experiment. The results of each study are in good agreement. Cross sections for the energy-averaged momentum transfer collisions of silicon with the filling gases (argon, hydrogen) at thermal energies have been determined.
Postgrowth of a Si contact layer on an air-exposed Si1−xGex/Si single quantum well grown by gas-source molecular beam epitaxy, for use in an electroluminescent device
Authors: Kato Y. , Fukatsu S. , Shiraki Y.
Published: July 2002

A Si contact layer for an electroluminescent (EL) diode was successfully grown on a Si1−xGex/Si single quantum well (SQW) layer by ‘‘hybrid’’ Si molecular beam epitaxy (MBE). The ‘‘hybrid’’ MBE was performed by growing the Si contact layer in a solid-source MBE chamber after transferring the sample through air from a gas-source MBE (GSMBE) chamber in which the starting SQW layer was initially grown by using disilane (Si2H6) and germane (GeH4). The growth characteristics of the hybrid MBE were investigated by in situ monitoring of the reflection high energy electron diffraction. A (2×1) reconstruction was observed even after the sample was exposed to air for up to 15 h on a GSMBE-prepared Si(100) surface. Evidence of the excellent quality of the EL device was provided by the sharpest emission lines, a full width at half maximum of ≊5.5 meV. The spectral features of the EL and photoluminescence were found to be almost identical, and a well-resolved acoustic phonon replica was observed. Linear polarization for a no-phonon replica of EL was also observed along SQW plane.
Linear motion oven for variable incident group III flux
Authors: Jones C. R. , Beasley D. L. , Taylor E. N. , Evans K. R. , Solomon J. S.
Published: July 2002

We report on the design, construction, and implementation of the linear motion oven (LIMO), a translatable, elemental source for the generation of thermal molecular and atomic beams of varying incident flux at a fixed position substrate during vapor deposition processing. The robust and smooth relationship between oven position and incident flux, combined with the ease of rapidly and controllably varying the LIMO position, enables three important advances in vapor deposition technology. As demonstrated for an indium atomic beam source in a III–V molecular beam epitaxy growth process, the LIMO is found to provide for (1) controlled production of compositionally graded structures, (2) improved uniformity of flux at the substrate, and (3) complete elimination of conventionally troublesome flux transients.
Initial stages of the nitridation of the Si(111) surface observed by scanning tunneling microscopy
Authors: Yoshimura M. , Takahashi E. , Yao T.
Published: July 2002

The initial stages of the nitridation processes on Si(111) have been investigated by scanning tunneling microscopy. Two nitridation processes are tried: one is an exposure to a clean Si(111)7×7 surface at room temperature followed by annealing, and another is an exposure on the hot substrate. In either case, the initial reaction occurs at the center adatom sites and they tend to pair with each other across the adjacent dimer row. At high coverage, very flat monolayer films with an 8×8 superstructure are clearly observed, the surface of which seems to contain misfit dislocation presumably due to relaxation of the surface stress.
In situ scanning tunneling microscope investigation of passivation and stainless steels and iron
Authors: Schreyer A. , Eng L. , Böhni H.
Published: July 2002

In situ scanning probe microscopy (SPM) is used to characterize passivation of steel alloys [DIN 1.4301 and 1.4529 (DIN is the German characterization number, comparable to AISI numbers)] as well as pure iron in 0.01 M sulfuric acid and boron buffer solution (pH 8.4), respectively. It is shown, that using d(ln i)/ds spectroscopy, semiconducting properties of the growing passive layer can be investigated.
Porous silicon field emission cathode development
Authors: Jessing J. R. , Parker D. L. , Weichold M. H.
Published: July 2002

This article will address the development of a porous silicon cathode technology which shows promise in solving the existing problems, specifically unstable, low current density, nonreproducible and high voltage emission, encountered by other cathode technologies. Monolithic two- and three-terminal devices have been designed, manufactured, and characterized. All of these devices have resulted in stable, reproducible operating characteristics that follow the Fowler–Nordheim model. Vacuum transport of the electrons and temperature independence (to 250 °C) of the current–voltage characteristics have been confirmed. Appreciable emission current has been observed with macroscopic fields on the order of 104 V/cm, thus indicating a large submicroscopic field enhancement due to the geometrical nature of the porous silicon.
Atomic force microscopy of biomolecules
Authors: Hansma Helen G.
Published: July 2002

Biological atomic force microscopy (also known as scanning force microscopy) has advanced in many areas. Some of the new applications of atomic force microscopy to DNA and protein research are outlined. Advances have occurred in both imaging and nonimaging uses of atomic force microscopy. Advances in atomic force microscopy imaging have been seen both in the imaging of immobile samples and in the imaging of motion and processes. Advances in nonimaging atomic force microscopy include the use of force curves to measure intermolecular forces, force mapping, and measurements of protein motion.
Effect of a metallic interfacial layer on peel strength deterioration between a Cu thin film and a polyimide substrate
Authors: Iwamori Satoru , Miyashita Takehiro , Fukuda Shin , Fukuda Nobuhiro , Sudoh Kazufuyu
Published: July 2002

The peel strength of a copper (Cu) thin film deposited on a polyimide (PI) substrate deteriorates after heat treatment at 150 °C in air. The deterioration involves Cu2O microparticles (10–100 nm) penetrating the PI substrate, both the substrate and film being oxidized. To prevent this penetration and oxidation, we introduced an interfacial layer (vanadium, titanium, or cobalt) at the interface between the Cu thin film and PI substrate. Both titanium and cobalt interfacial layers were effective as barriers against the penetration of Cu2O particles. The quality of the interfacial layers (e.g., quantity of dislocations) influenced their effectiveness. By annealing the cobalt interfacial layers at 280 °C for 1 h in a vacuum before sputter deposition of a Cu thin film, we succeeded in keeping the peel strength between the Cu thin film and the PI substrate above 0.1 N/m even after heat treatment of the laminate at 150 °C for three days.
Application of transmission electron detection to SCALPEL mask metrology
Authors: Farrow R. C. , Postek M. T. , Keery W. J. , Jones S. N. , Lowney J. R. , Blakey M. , Fetter L. A. , Griffith J. E. , Liddle J. A. , Hopkins L. C. , Huggins H. A. , Peabody M. , Novembre A.
Published: July 2002

Linewidth measurements were performed on a 4X scattering with angular limitation in projection electron lithography (SCALPEL) e-beam lithography mask using the transmitted electron signal in a modified scanning electron microscope. Features as small as 0.24 μm were measured on the mask. The thin membrane mask structure that was used is found to provide sufficient transmitted signal contrast at energies ranging from 10 to 30 keV. The linewidth measurement accuracy is mostly limited by the variations in the material and not the measurement system. It is concluded that the linewidth measurement technique using transmitted electrons is suitable for the potential certification of SCALPEL mask standards.
Morphological and compositional variations in strain-compensated InGaAsP/InGaP superlattices
Authors: Goldman R. S. , Feenstra R. M. , Silfvenius C. , Stålnacke B. , Landgren G.
Published: July 2002

We have investigated the properties of strain-compensated InGaAsP/InGaP superlattices, grown by metalorganic vapor phase epitaxy, with and without InP interlayers inserted in the InGaP barrier. Using cross-sectional scanning tunneling microscopy and spectroscopy, we observe lateral variations in layer thickness and electronic properties. When the number of superlattice periods is increased from 8 to 16, the growth front develops large undulations in the top two to four superlattice periods. For structures with InP layers inserted in the InGaP barrier, only slight undulations of the top superlattice periods occur. We discuss the origins of the growth front undulations in terms of the elastic relaxation of strain arising from thickness and/or composition variations in the superlattice layers. Finally, we observe a fourfold periodicity of the [001] atomic spacing, presumably arising from atomic ordering in the alloys.
Atomic force microscopy investigations on the surface topographies of aluminum-based composite containing nanocluster diamond
Authors: Ouyang Q. , Wang B. , Okada K.
Published: July 2002

Atomic force microscopy (AFM) has been used to study the rolling effect of ultrafine particles of cluster diamond contained in an aluminum-based composite during a sliding friction process. By analyzing the interaction between the tip of AFM and the spherical particles of diamond, it is estimated that at constant force mode of AFM when a particle is made to rotate, it shows a tendency to leave from the tip and a certain kind of deformed topographies are yielded. Some special images observed are explained by the mechanism based on the rotation of nanoball form particles of cluster diamond during the tip of AFM scanning over the sample surface.
Nanoscale organized assembly of nanoparticulate TiO2-stearate monolayers through the Langmuir–Blodgett method
Authors: Li Lin Song , Zhang Jie , Wang Li Jun , Chen Yongmei , Hui Zheng , Li Tie Jin , Chi L. F. , Fuchs H.
Published: July 2002

Nanoparticulate titanium dioxide-stearate (TiO2-St) monolayer was directly obtained using TiO2 hydrosol as the subphase. The atomic force microscopy images of monolayer, show that the higher coverage were obtained through deposition on the hydrophilic Si(100) surface rather than the hydrophobic Si(100) surface. From the surface photovoltage spectra of TiO2-St monolayer, it can be followed that the photovoltage response of the n-type silicones increased by a factor of 25, and 5 times after a monolayer of TiO2-St Langmuir–Blodgett (LB) films was transferred onto hydrophobic and hydrophilic Si surface, respectively. On the contrary, the photovoltage response value is reduced by ∼40 and 5 times by the deposition of the LB monolayer in the case of the hydrophobic and hydrophilic p-type Si surface, respectively. It is considered that the enhancement of the photovoltage response may be due to the ordered electrostatic potential orientation of the Si(100)/TiO2-St/ITO heterostructures.
X-ray micro- and nanofabrication using a laser–plasma source at 1 nm wavelength
Authors: Turcu I. C. E. , Allot R. M. , Mann C. M. , Reeves C. , Ross I. N. , Lisi N. , Maddison B. J. , Moon S. W. , Prewett P. , Stevenson J. T. M. , Ross A. W. S. , Gundlach A. M. , Koek B. , Mitchell P. , Anastasi P. , McCoard C. , Kim N. S.
Published: July 2002

A picosecond excimer laser–plasma source has been constructed, which generates an x-ray average power of 2.2 and 1.4 W at the wavelengths required for proximity x-ray lithography: 1.4 nm (steel target) and 1 nm (copper target), respectively. The plasma source could be scaled to the 50–75 W x-ray average power required for industrial lithographic production by scaling the total average power of the commercial excimer laser system up to 1 kW. The 1 nm x-ray source is used to micromachine a 2.5 THz microwave waveguide–cavity package with a 48 μm deep, three-dimensional structure, using the LIGA technique. The 1 nm x-ray source is also used to print 180 nm long transistor gates in the fabrication process of field-effect transistors.