bluuebunny/crossref_metadata_2025 huggingface dataset:
A study of the sorption of CO on W and Ni single-crystal surfaces by ion scattering
Authors: Heiland W. , Englert W. , Taglauer E.
Published: July 2002

Helium ion backscattering is used to study the sorption of CO on W(100), Ni(110), and Ni(111) surfaces. It is concluded that the CO molecular axis is oriented normal to the Ni(110) and Ni(111) surfaces. The molecular orientation of CO on W(100) is more complicated, depending on the temperature. No orientation for CO molecules can be obtained at room temperature while at higher temperatures, CO appears to be either oriented parallel to the surface or dissociated.
Electron-beam exposure profiles in polymer films for metallic film mask fabrication
Authors: Kato Tadao , Yahara Toshihiko , Nakata Hidefumi , Murata Kenji , Nagami Koichi
Published: July 2002

The effect of the metallic thin film on energy dissipation profiles in a resist polymer film on a metallic film-clad glass plate as in mask fabrication was investigated experimentally and by Monte Carlo calculations which take an exact account of the above boundary condition for a specific geometry. The thicknesses of the polymer film and metallic films are 8000 Å and 500–800 Å, respectively. Various metals such as Al, Cr, Mo, and Ta are used as mask materials. Both experimental and theoretical results show that the width of the developed profile increases with an increasing atomic number of the metallic film element depending on exposure density as expected due to increasing backscattering from the metallic film. It is concluded that even a very thin metallic film has an appreciable effect on the profile and its effect is exaggerated either by a large dose or by a strong development.
Negative electron resists for direct fabrication of devices
Authors: Thompson L. F. , Stillwagon L. E. , Doerries E. M.
Published: July 2002

The Bell Laboratories electron-beam exposure system (EBES) is currently being used to fabricate master masks and experimental devices using a negative resist based on poly(glycidyl methacrylate-co-ethyl acrylate) (COP) and a positive resist, poly(butene-1-sulfone) (PBS). COP was designed to have a sensitivity of 2–4×10−7 C cm−2 and good wet chemical etching resistance for a variety of thin-film conductors and insulators. The resolution obtained with a 0.6-μm initial COP film exposed with EBES and processed on a routine line is 2.0 μm. These characteristics are satisfactory for current requirements; soon however, machine improvements, smaller device geometries, and new processing procedures are going to place increasing demands on resist systems. In addition to resolution requirements, it is desirable to have a resist which is resistant to ion beam milling, plasma etching, or other dry etching techniques. Each of these requirements will be discussed in detail. This paper summarizes the results of the synthesis and initial lithographic evaluation of several potential negative electron resist systems. These resists were designed to have higher resolution and improved dry etching resistance than the negative resist, COP. Specifically copolymers of glycidyl methacrylate and/or glycidyl acrylate with styrene, and phenyl methacrylate will be discussed.
Surface relief gratings of 3200-Å-period fabrication techniques and influence on thin-film growth
Authors: Flanders D. C. , Smith Henry I.
Published: July 2002

As part of a project to study the effects of surface relief steps on thin-film nucleation and growth, a technology for fabricating 1000-Å-linewidth surface relief gratings with control of sidewall profiles to a resolution of the order of 100 Å is under development. Laser holographic lithography and ion beam etching are used to produce gold gratings on 0.9-μm-thick polyimide membrane masks. Next, these masks are replicated using CuL or CK x-ray lithography, thereby producing high aspect ratio relief gratings in PMMA having well-defined vertical sidewalls. Surface relief structures are then produced on substrates by liftoff, ion beam etching, or reactive ion etching using the PMMA relief gratings. Such structures were decorated with gold nuclei using ion beam sputter deposition. The decoration experiments indicated a periodic variation in nuclei density and showed that the smoothness of the grating edges is of the order of 100 Å.
Transient capacitance in GaAs and InP MOS capacitors
Authors: Stannard J.
Published: July 2002

Capacitance–voltage and transient capacitance measurements were made on MOS capacitors fabricated on bulk n-type GaAs using anodic oxidation. Similar measurements were made on InP–SiO2 capacitors fabricated on bulk n-type InP. The InP structure shows much less charge buildup at the interface upon cooling. A transient response with a new signature (Ec−0.08 eV, 8×10−22 cm2) was observed in GaAs, and previously observed bulk center in InP was also characterized (Ec−0.18 eV, σ−e=6.5×10−15 cm2). A deep center associated with radiation damage appeared prominently in the transient response of the GaAs–anodic-oxide capacitor. Clear evidence was obtained in the InP–SiO2 capacitors of a transient response which has the properties expected of interface states. This response was not observed in GaAs because of high surface fields.
XPS measurements of abrupt Ge–GaAs heterojunction interfaces
Authors: Grant R. W. , Waldrop J. R. , Kraut E. A.
Published: July 2002

A method has been developed to grow thin epitaxial layers of Ge on GaAs substrates within an XPS system by an evaporative MBE technique. Abrupt heterojunctions with Ge layer thicknesses of ?20 Å have been grown on (111), (110), and (100) GaAs crystal faces. By using XPS data obtained on these heterojunctions, variations in band gap discontinuities related to the crystallographic orientation dependence of interface dipoles have been observed directly. The data are also used to make an initial estimate of the valence band discontinuity for the abrupt Ge–GaAs heterojunction and with refinement of the technique, accurate values for this quantity should be obtainable.
Desorption of neutral molecules from Al(6061) by electron and ion bombardment
Authors: Edwards D.
Published: July 2002

The desorption of neutral molecules by ion (1000-eV Ar+) and electron (500 eV) impact on aluminum 6061 surfaces is reported. The molecular desorption yields are determined for the following aluminum treatments: (1) samples prepared with nominally the same laboratory treatments; (2) two types of wet chemistry treatments; (3) various in situ gas exposures (including HC1, C12); (4) glow discharge treatments. In summary, it is found that the various prevacuum treatments have little influence on the desorption yields whereas the in situ Cl2 exposure markedly reduces both the ion and electron desorption yields. In addition, the unit yield energy, E0, is also measured for the above sample conditionings. It is similarly found that neither the prevacuum sample conditionings nor the in situ gas exposures (with the exception of Cl2) affect E0 by more than 10% whereas the in situ Cl2 exposure (1 atm, 10 min) increases E0 by a factor of 2 and provides an example illustrating the possible utility of an in situ chemical treatment for the conditioning of vacuum surfaces of large-scale devices.
Quantitative AES analysis of coevaporated Cu/Ni films and the effects of ion sputtering on them: experiments at liquid nitrogen and room temperature
Authors: Gota K. , Koshikawa T. , Ishikawa K. , Shimizu R.
Published: July 2002

Samples of various concentrations were made by coevaporation of Cu and Ni. The coevaporation was carried out by simultaneous controlled electron bombardment heating of independent evaporation sources. The Auger-electron spectroscopy (AES) measurements were made by using a CMA and could be done following coevaporation or ion sputtering without moving the sample in the UHV system. The absolute composition of the sample was measured by atomic absorption spectroscopy (AAS). A linear relation was found between the AES measurements (700–1000 eV) and the results of AAS when the coevaporation was made onto the substrate at almost liquid nitrogen temperature. It should be mentioned that samples of homogeneous concentration from the surface to the bulk could be obtained, making quantitative AES possible. On the other hand, coevaporation onto substrates at room temperature resulted in Cu-rich surfaces being obtained. Quantitative AES analysis using lower-energy Auger peaks (80–120 eV) was also made using the same samples and results similar to those calculated from the higher-energy Auger transitions (700–1000 eV) were obtained. Samples coevaporated near liquid nitrogen temperature were sputtered by argon ions of 500–2000 eV and no significant difference was observed between sputtering near liquid nitrogen temperature or after allowing the sample to warm to room temperature. The surface of a 60 at. % Cu film became Ni-rich by 4, 8, and 12 at. % for ion energies of 500, 1000, and 2000 eV, respectively.
Materials and techniques used in nanostructure fabrication
Authors: Molzen W. W. , Broers A. N. , Cuomo J. J. , Harper J. M. E. , Laibowitz R. B.
Published: July 2002

A high-resolution electron beam has been used to generate metal structures 8 nm wide and 10 nm high using ’’contamination’’ resist and dense metal patterns with 25 nm linewidths on 50-nm centers using PMMA resist. These resist materials together with standard deposition techniques and ion beam milling have been used to prepare a variety of structures on the order of nanometers in dimension. Present metal structure dimensions are limited by electron backscattering events in the substrate, the microstructure of the metallic thin film, and unknowns in the contamination resist process itself. The processing techniques are discussed as well as the preparation of substrates which are almost transparent to the electron beam.
Effect of high-temperature, postoxidation annealing on the electrical properties of the Si–SiO2 interface
Authors: Revitz M. , Raider S. I. , Gdula R. A.
Published: July 2002

The electrical properties of thin thermal SiO2 films were studied as a function of high-temperature, postoxidation annealing in various ambients. Surface charge measurements were made of SiO2–Si structures after annealing for different time intervals in a N2 ambient at temperatures ?925°C. The oxidation-induced fixed oxide charge rapidly decreased. A more gradually increasing charge was observed that is primarily attributed to fast surface states.
New high-resistivity thin film resistor material for Josephson logic circuits
Authors: Yamada Hajime , Ishida Akira
Published: July 2002

A high-resistivity thin-film resistor for Josephson logic devices has been experimentaly investigated. Resistivity measurements of Au1–xInx evaporated thin films demonstrate the existence of a resistivity maximum around x∠0.16 at liquid He temperature. A maximum resistivity of 0.14 μΩ m has been obtained, which is one order of magnitude higher than that of the previous AuIn2 compound resistor. The temperature dependence and x-ray diffraction experiments suggest that the resistivity maximum appears in the transition region from Au–In solid solution phase (x<0.16) to Au–In compound phase (x≳0.16). This means the resistivity maximum is mainly attributed to the contribution from impurity scattering in the Au–In solid solution.
Fabrication of hemispherical structures using semiconductor technology for use in thermonuclear fusion research
Authors: Wise K. D. , Jackson T. N. , Masnari N. A. , Robinson M. G. , Solomon D. E. , Wuttke G. H. , Rensel W. B.
Published: July 2002

Initial investigations and laboratory experiments in the area of target fabrication using solid state circuit processing techniques to create special target components have indicated the feasibility of a unique advanced manufacturing concept. A question of the applicability of silicon integrated circuit technology and how it might be applied to the fabrication of inertial confinement fusion targets was posed. The combined efforts of the University of Michigan Electron Physics Laboratory, and the Division of Material Sciences of KMS Fusion, Inc. have provided some relatively quick and very encouraging answers and results. The initial efforts to demonstrate electron beam patterning and etching of micron-high letters through the walls of glass microballoons, the fabrication of free-standing thin-walled flanged hemispheres joined to form spherical structures, and a pellet support membrane have been the proof-of-principle milestones and goals.
Chemical and structural properties of the Pd/Si interface during the initial stages of silicide formation
Authors: Ho P. S. , Tan T. Y. , Lewis J. E. , Rubloff G. W.
Published: July 2002

The initial stage of silicide formation at the Pd/Si interface has been investigated during Pd deposition on the Si(111) surface using a combination of AES and TEM techniques. The formation of silicide was found to change the valence state of Si significantly as observed from the shape change of the Si LVV Auger spectra. The ratios of the normalized peak intensities were used to calibrate the composition and the thickness of the reacted layer. The calibration results coupled with TEM phase identification showed uniform formation of the Pd2Si compound even at room temperature up to about 10 Å Pd coverage. Using thin Pd coverages of about 10 Å, epitaxial growth of Pd2Si was not observed on sputter-cleaned Si surfaces. Crystalline order was clearly observed at the Pd2Si/Si interface in annealed samples with less than 4 Å Pd2Si, indicating a relatively sharp interface with no significant amorphous-like structural disorder.
Interface and dielectric properties of the n-indium-phosphide–silicon-oxide system
Authors: Zeisse Carl R.
Published: July 2002

The small signal conductance and capacitance of metal/silicon oxide/n-indium-phosphide structures have been measured as a function of bias voltage at various frequencies from 1 to 100 kHz. The conductance method has been used to determine the surface state density, which rises as the conduction band is approached, passing through 3×1012 cm−2 eV−1 at an energy 30 meV below the conduction band edge. The data display a strong frequency and temperature dependence as the semiconductor approaches accumulation. The dispersion in this region fits a Maxwell–Wagner model suggesting that such effects are caused by the inhomogeneous nature of the dielectric in our samples.
Electronic structure of Ge overlayers on (100) GaAs
Authors: Pollmann J. , Pantelides Sokrates T.
Published: July 2002

We report calculations of the electronic structure of one, two, and three Ge layers on semiinfinite Ga-terminated (100) GaAs using empirical tight-binding Hamiltonians for the bulk-material description. The theoretical approach used to treat these overlayer systems is an extension of our method for the treatment of heterojunction interfaces, which is based on the Koster–Slater idea for treating localized perturbations. Our results show that the wavevector-integrated layer densities of states for the overlayer systems are not strongly influenced by surface–interface interactions. The wavevector-resolved layer densities of states, however, show pronounced features which are induced by surface–interface interactions. In particular, a new peak at about 9 eV below the valence-band top is found to dominate the layer density of states at the zone center (i.e. at the Γ point) and should be detectable by angle-resolved photoemission measurements.
Hybrid e-beam/deep UV exposure using portable conformable masking (PCM) technique
Authors: Lin B. J. , Chang T. H. P.
Published: July 2002

A thin dichroic resist or an opaque metal is directly applied to a deep-UV resist and is delineated with an e-Beam exposure tool conventionally. This intimately contacted pattern now serves as a portable mask that can be carried with the wafer to a deep-UV blanket exposure station for delineation of the deep-UV resist to produce high aspect ratio images with controlled profiles. In particular, AZ1350J/PMMA and AZ1350J/aluminum/PMMA systems are discussed. Sample results showing submicrometer PMMA images in thicknesses ranging from 1.6 to 1.9 μm using a 0.2 μm thick AZ PCM and 0.3-μm-thick aluminum PCM are presented.
Köhler illumination and brightness measurement with lanthanum hexaboride cathodes
Authors: Broers Alec N.
Published: July 2002

An aperture illumination system such as a Köhler system offers the ability to illuminate an electron probe system with the peak brightness from an electron source. It also provides an object with an ideal step-function current distribution. This paper describes results obtained using Köhler illumination on a short focal length final lens SEM. Application of the SEM to brightness measurement is discussed at some length. Examples of overall probe performance for scanning transmission electron microscopy, low-loss surface microscopy, and microfabrication are also given.
Application of a thermal field emission source for high resolution, high current e-beam microprobes
Authors: Tuggle D. , Swanson L. W. , Orloff J.
Published: July 2002

A thermal field emission electron source has been incorporated into a microprobe with two magnetic lenses to produce a 0.10 μm beam spot with 0.11 μA current at 12 kV and a working distance of 13 cm, in agreement with calculated performance assuming a source angular intensity of 1 mA sr−1. The power density and brightness of the beam on the target were 1.6×107 W cm−2 and 5.5×107 A cm−2 sr−1 respectively. The emitter used was 〈100〉 oriented W coated with Zr, operated at 1800 K. Probe current fluctuations (〈ΔI2〉)1/2/IP =0.23% in the frequency interval 1–5000 Hz were measured at the target with I=30 nA. The microprobe was used to construct a scanning Auger microscope which produced submicron resolution Auger elemental maps with scan times of 5 min or less.
Proximity effect dependence on substrate material
Authors: Aizaki Nao-aki
Published: July 2002

The dependence of the proximity effect, which deforms electron-beam exposed patterns, on the substrate material has been investigated theoretically and experimentally. Substrates examined are Si, SiO2, Cr, Mo, Au and their double layers, which are used in LSI fabrication process with a direct writing technique. The proximity effect is approximated as the sum of absorbed energy distributions in a resist layer, which are calculated separately with respect to electron re-incidence number (Ns) from substrate into resist. A Monte Carlo simulation for electron scattering trajectories was used to obtain the spatial distributions of absorbed energy in a resist. The incident beam extent influence was examined. A new evaluation technique was used to obtain the exposed intensity distributions. The absorbed energy distributions, constituting the modeled proximity effect, are in good agreement with experimental results. The absorbed energy distribution for Ns=0 with a Gaussian incident beam is approximated by the function Coexp(−r/σ0). The distribution for Ns?1, expected in the case of a high atomic weight substrate, is approximated by the function Csubexp(−r/σsub).
Ion beam exposure characteristics of resists
Authors: Hall T. M. , Wagner A. , Thompson L. F.
Published: July 2002

The exposure characteristics of six polymer resists to 1.5 MeV H+, He+, and O+ ions and 20 keV electrons were measured. The deposited energy per unit volume required to expose a resist was found to vary by up to a factor of ten between electrons and O+ ions. A model was developed which accounts for the variation in terms of the energy distribution around the particle track in conjunction with whether the resist requires the activation of a single site or two adjacent sites to produce exposure.
Directional oxygen-ion-beam etching of carbonaceous materials
Authors: DeGraff P. D. , Flanders D. C.
Published: July 2002

The results of a comparative study of reactive ion etching in oxygen and oxygen ion beam etching of carbonaceous materials is presented. Scanning electron micrographs are shown of 1600 Å linewidth surface relief structures with vertical sidewalls etched into polyimide, and vitreous carbon. The directional nature of oxygen ion beam etching is demonstrated by the etching of a 3200 Å period grating structure into a polyimide substrate at 45°. It is proposed that the etching of carbonaceous materials in oxygen is an excellent model system for studying etching of materials in reactive gases because of its relative simplicity compared to the more commonly used processes employing fluorocarbon gases.
Ion-beam-sputtered AlOxNy encapsulating films
Authors: Birey Hülya , Pak Sung-Jae , Sites J. R. , Wager J. F.
Published: July 2002

The encapsulating properties of 800–1500 Å aluminum oxynitride (AlOxNy) films, deposited on GaAs by low energy ion beam sputtering, were studied over a range of y from 0.1 to 0.8. Particular attention was given to chemical and sputter cleaning procedures. The structures were characterized by optical microscopy, electrical conductivity, Auger profiling, and ellipsometry. The better films were found to withstand annealing to above 900°C with minimal physical deterioration. The films with a higher proportion of oxygen allowed some oxygen diffusion; those made with inferior cleaning procedures allowed an out-diffusion of arsenic.
Quantitative analysis of Ti–W films
Authors: Hartsough L. D. , Koch A. , Moulder J. , Sigmon T.
Published: July 2002

Resistivity of bias-sputtered Ti–W films was found to depend on the Ti:W ratio in the films, which was controlled by rf substrate bias. Auger depth profiles gave Ti:W about half the expected values. Films deposited at 0, 150, and 300 V bias chosen for further study were analyzed by atomic absorption (AAS), Rutherford backscattering (RBS), and Auger electron (AES) spectroscopies. Large discrepancies were found between techniques. AES tends to give low Ti:W ratios because of preferential Ti sputtering during analysis. The RBS and AES data were used to determine the differential sputtering yield of Ti and W from the film and thus provide a basis for quantitative analysis from AES data. The yield ratio was found to vary linearly with composition of the altered surface layer as r=3.0–4.0 (Ti:W). Advantages, disadvantages, and factors affecting the accuracy of each technique are discussed.
Bonding and diffusion at Al and Au interfaces with CdS
Authors: Brillson L. J. , Bauer R. S. , Bachrach R. Z. , McMenamin J. C.
Published: July 2002

Al and Au interfaces with UHV-cleaved CdS(101̄0) surfaces have been probed via soft x-ray photoemission spectroscopy. We find that Al produces a highly localized reaction at the metal-semiconductor interface, while Au promotes interface diffusion. These bonding differences appear to be characteristic of ionic semiconductor–metal interfaces in general.
Effect of lattice mismatch on the electron mobilities of InAs grown on GaAs by MBE
Authors: Chang Chin-An , Serrano C. M. , Chang L. L. , Esaki L.
Published: July 2002

We have studied the effect of lattice mismatch on the electron mobilities of InAs films grown on GaAs by MBE. The electron mobilities decrease rapidly with decreasing film thickness in the range of 0.2–2 μm. This is attributed to the high density of dislocations observed in the thinner films. Using a step-grading growth technique, the dislocation density is reduced with a simultaneous improvement in mobilities.
Growth of thin platinum films on hydrogenated amorphous silicon and its oxide
Authors: Goldstein Bernard , Szostak Daniel J.
Published: July 2002

We have used Auger electron spectroscopy and low energy electron diffraction to study the growth of thin platinum films on hydrogenated amorphous silicon (a-Si:H), its oxide, and on single crystal (111) silicon. We have identified the growth processes as Frank-van der Merwe on a-Si:H, Stranski–Krastanov on (111) Si, and (tentatively) Volmer–Weber on
Direct anodization of GaAs and Si at extremely low substrate temperature by low pressure oxygen plasma
Authors: Matsuzawa A. , Itoh T. , Ishikawa Y. , Yanagida H.
Published: July 2002

A small scale production system to form clean anodized layers of four 1 in. GaAs wafers is described. Homogeneous oxide films are obtained at a rate of 0.3 to 1.6 nm/s in a low pressure oxygen plasma at a very low substrate temperature of 50 °C or lower. Remarkable improvement on maintaining minimum loss of arsenic and high insulation voltage of 4×106 V/cm are demonstrated. Thickness uniformity of ±5% and a refractive index of 1.80±0.05 is obtained over the entire range of the wafer pedestal (100-mm-diam.). Silicon wafers are also oxidized in the system at the rate of 0.08 nm/s at a substrate temperature of 600 °C. Thickness uniformity of ±5%, refractive indicies between 1.45 and 1.46, and an insulation voltage of 6×106 V/cm are obtained. Characterizations are carried out under AES, ESCA, ellipsometry and under electrical properties of C–V plotting and breakdown voltage.
Systematics on the electron states of silicon d-metal interfaces
Authors: Braicovich L. , Abbati I. , Miller J. N. , Lindau I. , Schwarz S. , Skeath P. R. , Su C. Y. , Spicer W. E.
Published: July 2002

We discuss the trends in photoemission spectra from some silicon d-metal interfaces: Si (111)–Au, Si (111)–Ag, Si (111)–Ni, Si (111)–Pd, Si (111)–Pt. In particular, we discuss the correlation between the chemical processes taking place at the interface and those in the formation of bulk silicon d-metal compounds. Although a general correlation is found, some important differences are seen; in particular, no evidence of the formation of strictly stoichiometric silicides in the interface is found even for the cases in which well defined bulk silicides are known to be stable. We discuss also the role of the hybridization between d-electrons of the metal and (sp) electrons of silicon in the formation of intermixed interface phases. The considerations presented here can be useful as guidelines to interpret future results on other reactive silicon d-metal interfaces.
Si–Pd and Si–Pt interfaces
Authors: Miller J. N. , Schwarz S. A. , Lindau I. , Spicer W. E. , De Michelis B. , Abbati I. , Braicovich L.
Published: July 2002

Photoemission (PS) and Auger electron spectroscopy were used to study the formation of Pd silicide in UHV on Si crystals. The Pd depositions ranged from submonolayer coverages to hundreds of Angstroms thickness. AES sputter depth profiles indicate that room temperature Pd–Si interdiffusion occurs over ∠100 Å and that Pd reduces the native Si oxides, with oxygen appearing at the vacuum surface of the evaporated layer. We have been able to separate out the relative contributions of Si and Pd to the silicide valence band by using a wide range of photon energies in the PS studies. The Pd d-bands in the silicide are filled and, due to the strong Pd–Si interaction, are pulled down more than 2 eV relative to Pd metal. In addition, we suggest that the silicide formed at the surface may be more closely related to that of the glassy metals rather than the well-defined (although closely related) Pd2Si compound. Similar results are also obtained for the system of Pt on Si.
Oxygen adsorption on the GaAs(110) surface
Authors: Su C. Y. , Lindau I. , Skeath P. R. , Chye P. W. , Spicer W. E.
Published: July 2002

The adsorption of nonexcited molecular oxygen on cleaved GaAs(110) surfaces at room temperature has been studied using photoemission techniques. Detailed analysis of the oxygen-induced structure in the valence-band region revealed two different forms of adsorbed oxygen. Adsorption in the first form saturates at a very low coverage (∠0.01 monolayer) and is probably associated with defect sites. Adsorption in the second form occurs at normal surface sites and produces measurable chemical shifts in Ga-3d and As-3d core levels. The nature of the second form of oxygen has been further investigated with core level studies of surfaces oxidized at room temperature and subsequently heated to a high temperature. Annealing to moderately high temperature (∠370°C) causes transfer of oxygen from As–O bonds to form additional Ga–O bonds. Fast heating to high temperature (430°–450°C) leads to desorption of roughly half of the oxygen atoms and all of the chemically affected As atoms, while little change in the Ga-3d core level is observed. Several previously proposed oxidation models are compared based on the present data.
Phosphorus concentration in hydrogenated amorphous silicon using ion-implanted references
Authors: Thomas J. H.
Published: July 2002

The phosphorus content in glow-discharge deposited hydrogenated-amorphous silicon film has been determined using Auger electron spectroscopy. Precision low concentration phosphorus ion-implants into hydrogenated amorphous silicon were used as standards to accurately determine the sensitivity factor for phosphorus in hydrogenated amorphous silicon.
Media for high density optical recording
Authors: Bartolini R. A.
Published: July 2002

There are many high density optical recording systems that require storage media capable of high recording and playback performance. In this paper, the general requirements which govern the selection, design, and optimization of the recording media are described. The use of a high power diode laser as the recording and playback source is also described.
Effects of Ga and Si ionization on the growth of Ga doped Si MBE
Authors: Shimizu S. , Komiya S.
Published: July 2002

Gallium doped Si films were epitaxially grown on Si(100) substrates using a partially ionized Ga molecular beam at various substrate temperatures ranging from 300 to 1000 K with incident Si and Ga beam fluxes of 5×1014 atoms s−1 cm−2, which corresponds to 0.1 nm/s assuming the sticking coefficient to be unity. The surface structure and the surface composition were observed by an in situ RHEED–AES system. Ga ionization produced no observable change in surface structure or surface composition as compared with Ga doping without ionization. However, an increase of the carrier concentration was observed by Ga doping with a partially ionized molecular beam under the following ionization condition: an ion energy of 180 eV with 5% Ga ionization. Moveover, the lowering of the epitaxial temperature was observed using a partially ionized Si molecular beam under the ionization conditions: an ion energy ranging from 30 to 180 eV with ≲7% Si ionization.
Time-resolved charge injection from Al into clean CdS and CdSe
Authors: Slowik J. H.
Published: July 2002

A technique has been developed which unambiguously distinguishes between interfacial and bulk transport. The technique resembles a time-of-flight measurement, but utilizes a higher degree of time-resolution to separate carrier movement in the interfacial region from bulk effects. The injection rate is extremely sensitive to the condition of the interface between Al and ultrapure, high resistivity CdS or CdSe, for which ordinary I–V and C–V characterizations are impossible. When the interface is constructed quickly on single crystals cleaved in UHV, the injection approaches the theoretical maximum rate, the trap-free space-charge-limited current. However, when metal deposition is interrupted at submonolayer coverages, and exposed to UV light, the eventual thick Al electrode forms an altered contact on CdSe. This contact displays an order of magnitude smaller injection rate and is unstable at high field. The larger effective barrier is attributed to a thicker reacted Al layer, whose formation is enhanced by increased bond breaking due to the excess photogenerated carriers.
Surface vacancies in II–VI and III–V zinc blende semiconductors
Authors: Daw M. S. , Smith D.L. , Swarts C.A. , McGill T.C.
Published: July 2002

We present calculations of the bound state energy levels of ideal vacancies near the (110) surface of some zinc blende II–VI and III–V semiconductors: CdTe, ZnTe, GaAs, AlAs, InAs, and some alloys among them. Here we compare vacancies near the surface of II–VI’s with those of III–V’s. In contrast to the III–V’s, where a neutral vacancy has an odd number of electrons, a neutral vacancy in a II–VI semiconductor has an even number. We find that single anion vacancies in III–V’s can behave as both donors and acceptors, and follow observed trends with ionicity and alloy composition. We also find that single cation vacancies in II–VI’s behave as double acceptors and the anion vacancies behave as shallow double donors. We suggest experiments to test the importance of vacancies in determining the Fermi level pinning position for II–VI’s.
Low energy electron loss spectroscopy of Si–Ge interfaces
Authors: Perfetti P. , Nannarone S. , Patella F. , Quaresima C. , Cerrina F. , Capozi M. , Savoia A. , Lindau I.
Published: July 2002

We present energy loss spectra of Si–Ge heterojunctions. The early stage of formation of the interface has been studied by successive evaporations of small amounts of germanium on a silicon substrate heated at 350 °C. The results, compared with theoretical calculations, show that the interface is abrupt on a microscope scale and that germanium induces extrinsic interface states in the main and partial gaps of the projected bulk band structure of silicon on the (111) surface.
A study of Schottky barrier formation for Ga/Si(111)-(2×1) and Sb/Si(111)-(2×1) interfaces
Authors: Freeouf J. L. , Aono M. , Himpsel F. J. , Eastman D. E.
Published: July 2002

We have studied the Schottky barrier formation of Ga/Si(111)-(2×1), Sb/Si(111)-(2×1) and Sb/GaAs(110) interfaces via photoemission measurements of the following coverage-dependent quantities: the Fermi level position at the interface relative to the valence band maximum Ev (i.e., p-type Schottky barrier ΦBP), work function, Si bulk and surface 2p core level binding energies, Ga 3d and Sb 4d core level energies, and Si surface states. Using a lightly-doped (∠15 Ω cm) p-type Si(111)-(2×1) sample which was cleaved with a single-domain (2×1) surface structure, we observe large deviations from the ’’1/3 band gap-rule’’ for p-type Schottky barriers ΦBP with both Ga and Sb; i.e., ΦBP ? 0.07 eV for Ga/Si(111) and ΦBP ? 0.66 eV for Sb/Si(111). The core level spectra for Ga and Sb for coverages in the 0.3 – 12 Å range show very sharp core levels (observed FWHM ∠0.4–0.5 eV), indicative of a ’’simple’’ interface without complex multiple binding sites or displacive reactions; this is in contrast with our studies of the Sb/GaAs(110) interface, for which the Sb core levels are significantly broadened (∠1 eV FWHM). These studies are discussed in view of current models of Schottky barriers on covalent semiconductors.
Protection of molecular beam epitaxy grown AlxGa1−xAs epilayers during ambient transfer
Authors: Kowalczyk S. P. , Miller D. L. , Waldrop J. R. , Newman P. G. , Grant R. W.
Published: July 2002

A method for the protection of reactive compound semiconductor surfaces during transfer from a molecular beam epitaxy apparatus through ambient for further processing or experimental characterization is demonstrated for GaAs and AlAs. This method is likely to be applicable to other compound semiconductors.
Deformation potentials of superlattices and interfaces
Authors: Mon K. K. , Hess K. , Dow J.D.
Published: July 2002

We present a theory of deformation potential electron–phonon scattering in the bulk, in superlattices, and at interfaces of semiconductors. Expressions for the acoustical deformation potential constants are obtained in closed form for bulk semiconductors and for a monolayer superlattice. Deformation potential constants are evaluated numerically for superlattices of various thicknesses. The results are in good agreement with available experiments and provide a detailed understanding of deformation potential scattering.
Nondestructive characterization of Ga1−xAlxAs–GaAs interfaces using nuclear profiling
Authors: Rosner J. S. , Lesser P. M. S. , Pollak F. H. , Woodall J. M.
Published: July 2002

We present a new method for the nondestructive determination of the depth distribution of Al in Ga1−xAlxAs–GaAs heterostructures by means of nuclear profiling. This approach utilizes the 27Al(p,γ)28Si nuclear reaction which has an extremely sharp resonance width for protons incident at 992 keV. The presence of the Al is detected by means of the emitted 10.7 MeV γ ray. Depth profiling is accomplished by varying the energy of the incident proton beam. We have investigated the Al distribution of samples prepared using three different modifications of the liquid phase epitaxy method. Our results, after correction for straggling, are in good agreement with general considerations of the growth conditions.
Volatile metal oxide incorporation in layers of GaAs and Ga1−xAlxAs grown by molecular beam epitaxy
Authors: Kirchner P. D. , Woodall J. M. , Freeouf J. L. , Wolford D. J. , Pettit G. D.
Published: July 2002

A model is presented which relates the observed effects of substrate temperature and growth flux magnitudes upon layer quality to the presence of volatile oxides and the thermodynamics of the formation of nonvolatile oxides on the growth surface. A means for reducing oxide contamination is presented and the consequent benefits explored. Ga2O is shown to be a major contaminant of the gallium growth flux, on the order of 0.1%. Certain conditions, specifically low substrate temperature or high arsenic fluxes, can favor the formation of Ga2O3, a nonvolatile contaminant, on the growth surface and hence in the layer. The presence of aluminum, magnesium, or other highly reactive materials makes oxide incorporation increasingly probable. Drastically lowering the Ga2O pressure by several orders of magnitude by adding 0.1% aluminum to the gallium effusion cell should allow growth at lower substrate temperatures and higher rates. Magnesium doping of GaAs at unity efficiency is demonstrated as proof of the relevance of the model. Photoluminescence data from the doping experiment are presented.
Diffusion barriers in layered contact structures
Authors: Nicolet M-A. , Bartur M.
Published: July 2002

The concept of a diffusion barrier is discussed in the context of thin-film metallization systems. The conditions that an effective thin-film diffusion barrier should meet are enumerated. The dominant role of defects in determining the kinetic properties of a barrier layer is pointed out, and the consequent importance of the method of deposition and the parameters prevailing during deposition are stressed. Examples of the practically important cases of the stuffed barrier, the passive compound barrier, and the sacrificial barrier are given, with special emphasis on the latter as applied to Al contacting of silicide layers. Unconventional ways of forming multiple or novel diffusion barriers are briefly mentioned as well.
Poly(vinylnaphthalene) and its derivatives as e-beam negative resists
Authors: Ohnishi Y.
Published: July 2002

Polymer materials, which contain vinylnaphthalene as monomer units, were developed as e-beam negative resists. Poly(vinylnaphthalene) was found to be highly resistive to dry etching. Under Ar ion milling or CCl4 sputter etching conditions, etching rates for poly(vinylnaphthalene) were found to be about two-thirds of those for polystyrene or AZ resist. For example, etching rates for PMMA, PMIPK, AZ1350J, polystyrene, and poly(2-vinylnaphthalene) in a neutralized 500-eV Ar ion beam (0.83 mA/cm2) at normal incidence, were estimated to be 400, 280, 190, 200, and 150 Å/min, respectively. The contrast (γ value) for poly(2-vinylnaphthalene) is better than that for polystyrene, which had been considered as the highest contrast negative organic resist known. Sensitivity for poly(2-vinylnaphthalene) is insufficient for todays’s requirements. Dig was found to be 2.5×10−4 C/cm2 for Mw = 4×104 polymer. Chloromethylation of this material improved sensitivity. For example, 38.5% chloromethylation attained Dig = 8×10−6C/cm2. Submicrometer fine pattern fabrication is presented. Preliminary results for copolymerization of vinylnaphthalene with other sensitive monomers are presented.
EBCAD—Fully integrated pattern data processing for direct write electron-beam lithography systems
Authors: Otto O. W.
Published: July 2002

EBCAD (Electron–Beam CAD) is the pattern data processing software package for Hughes direct-write electron beam lithography systems. The purpose of EBCAD is to optimize the presentation of pattern data to the e-beam exposure hardware for maximizing throughput and patterning fidelity, and to perform its required functions in the local hardware environment of the exposure system. The EBCAD package, which is an integral part of the e-beam lithography systems, supports all functions associated with pattern preparation for exposure from interactive graphic data creation and manipulation to data reformating for direct use by the exposure hardware. This paper describes the EBCAD package including the major functions, the hierarchical nodal command structure and user interface, and the underlying chaining structure.
Reactive sputter etching of Si, SiO2, Cr, Al, and other materials with gas mixtures based on CF4 and Cl2
Authors: Horwitz C. M. , Melngailis J.
Published: July 2002

All etching processes require control of the relative etch rates of the mask and substrate materials. This is especially important in vacuum-etching processes where directional etching is often obtained at the expense of increased mask etch rate. Etch rate control requires good control of the etching parameters, and here at a constant gas flow of 2×10−2 Pa m3/s we use target voltage (peak-to-peak) and partial pressure of reactant species as controlled variables rather than power density and total pressure, as is common practice. SiO2 and Si etch rates in CF4 with a Si target were found to vary as P1/2V2 where V is the peak-to-peak target voltage (varied between 0.6 kV and 2.9 kV) and P is the reactant gas pressure varied between 0.35 Pa (2.7 μm) and 14.3 Pa (110 μm). Cr and Al rates varied as V3, but were almost independent of pressure. These differences enable accurate selection of relative etch rates and appropriate masks. For instance, SiO2/Cr etch rate ratios as high as 50:1 may be achieved for 3.7 Pa of CF4 at 0.8 kV peak-to-peak target voltage. Chlorine mixed with CF4 enables the properties of the two gases to be combined. Thus, by adjusting only the gas mixture from pure CF4 to pure Cl2, the Si/SiO2 etch rate ratio can be continuously varied between 0.33 and 6, respectively, at 1.3 kV peak-to-peak target voltage, 3.7 Pa pressure, and with substrates on a Si target.
Microstructures for high-energy x-ray and particle imaging applications
Authors: Ceglio N. M. , Stone G. F. , Hawryluk A. M.
Published: July 2002

Coded imaging techniques using thick, micro-Fresnel zone plates as coded apertures have been used to image x-ray emission (2–20 keV) and 3.5 MeV Alpha particle emissions from laser driven micro-implosions. Image resolution in these experiments was 3–8 μm. Extension of this coded imaging capability to higher energy x rays (∠100 KeV) and more penetrating charged particles (e.g., ∠15 MeV protons) requires the fabrication of very thick (50–200 μm), high aspect ratio (10:1), gold Fresnel zone plates with narrow linewidths (5–25 μm) for use as coded apertures. A reactive ion etch technique in oxygen has been used to produce thick zone plate patterns in polymer films. The polymer patterns serve as electroplating molds for the subsequent fabrication of the free-standing gold zone plate structures.
A mass-separating focused-ion-beam system for maskless ion implantation
Authors: Wang V. , Ward J. W. , Seliger R. L.
Published: July 2002

The use of a focused ion beam for direct implantation of dopants into a semiconductor substrate results in appreciable simplification in the processing of semiconductor devices. We have demonstrated that liquid metal (LM) field-ionization sources (based upon the electrostatic formation of an emitting cusp of liquid metal) offer the necessary high brightness to make focused ion beam microfabrication economically feasible. This paper reports upon two developments: (1) the development of eutectic-alloy LM ion sources for the production of boron and arsenic for direct implantation of silicon devices, and (2) the development of a three-lens variable-energy focusing column that incorporates a mass-separator of low aberration. Mass spectra of the ion emission of these sources show that the stoichiometric fraction of boron and arsenic is emitted. We have also demonstrated that the high vapor pressure of arsenic can be suppressed in the eutectic liquid metal, and that boron is predominantly emitted as a singly ionized species, while arsenic is emitted as both singly and doubly ionized species. A new focusing column has been developed that incorporates the new ion sources. It has the capability for focusing to sub-micrometer dimensions with mass-separation, a variable beam voltage of up to 150 kV, and a spot current of near 1 A/cm2. A high-speed electrostatic-deflection system with microprocessor control allows this machine to perform simple pattern exposures. Examples of the operation of this microfabrication system with eutectic alloy sources will be presented.
SiN membrane masks for x-ray lithography
Authors: Suzuki K. , Matsui J. , Torikai T.
Published: July 2002

The fabrication and properties of a new x-ray lithography mask are described. The mask is made of a plasma enhanced chemical vapor deposited (PCVD) silicon nitride (SiN) membrane, which is supported by a silicon frame. The PCVD SiN film, deposited on silicon substrate under appropriate conditions, has a tensile stress of about 1×108 dyn/cm2, which is much lower than that of a Si3N4 film prepared by conventional (pyrolytic) CVD. The strength of the PCVD SiN membrane, stretched over a silicon frame, is as high as that of a Si3N4/SiO2/Si3N4 sandwich structure membrane, and is much higher than that of a conventional CVD Si3N4 membrane. The PCVD SiN film with low stress realizes a low distortion x-ray mask substrate which is expected to be applied to very fine pattern lithography.
Single-crystal GaAs films on amorphous substrates by the CLEFT process
Authors: Bozler C. O. , McClelland R. W. , Salerno J. P. , Fan J. C. C.
Published: July 2002

By using the CLEFT process, epitaxial GaAs films can be grown on a reusable GaAs single-crystal substrate and transferred to amorphous substrates. An essential step in forming the epitaxial films is lateral growth seeded from openings in a mask on the single-crystal substrate. The lateral growth process has been studied as a function of growth conditions and crystal orientation, and optimized to give continuous films with specular surfaces. Very few defects are found in the films by cathodoluminescence and transmission electron microscopy. As an initial demonstration of film quality, solar cells having efficiencies as high as 17% at AM1 and an area of (1)/(2) cm2 have been fabricated. The CLEFT process is advantageous for device applications because amorphous or polycrystalline substrates can be much less expensive than single-crystal substrates, and also because they can have electrical and optical properties leading to improved device performance.
Molecular beam epitaxial growth and electrical transport of graded barriers for nonlinear current conduction
Authors: Gossard A. C. , Brown W. , Allyn C. L. , Wiegmann W.
Published: July 2002

Molecular beam epitaxy (MBE) has been used to grow heterojunction barriers to electrical transport in a number of configurations. Symmetric barriers of square and triangular shape and asymmetric barriers of sawtooth shape were grown by GaAs and AlxGa1−xAs MBE and measured electrically. Temperature dependence of low-voltage conductivity gave conduction-band barrier height ΔEcb≊0.85 ΔEg for undoped barriers of direct-gap AlxGa1−xAs between Si-doped GaAs layers. I-V measurement gave symmetric or asymmetric characteristics as would be expected from the compositional profiles of the barriers.