bluuebunny/crossref_metadata_2025 huggingface dataset:
In situ cleaning of GaAs and AlxGa1−xAs surfaces and production of ohmic contacts using an atomic hydrogen source based on a reflected arc discharge
Authors: Kagadei V. A. , Proskurovsky D. I.
Published: July 2002

A method for the production of ohmic contacts to n-type GaAs and to n-type and p-type AlxGa1−xAs has been proposed where the surface cleaning in atomic hydrogen and the metal film deposition are performed in situ. A feature of the method is that it is realized in a system for vacuum deposition of metal films with the residual pressure kept equal to ∼5×10−4 or ∼(4–10)×10−5Pa when GaAs or AlxGa1−xAs structures, respectively, are cleaned. The atomic hydrogen flow was formed by a source whose operation is based on a reflected arc discharge with a hollow cathode and a self-heating electrode. In the process of cleaning the hydrogen pressure was 10−2 Pa and the temperature of the specimens and the time of their treatment were varied in the ranges from 300 to 400 °C and from 1 to 90 min, respectively. AuGe/GaAs interfaces with the contaminant content below the sensitivity threshold of the method of Auger electron spectroscopy (AES) have been produced. With some technological expedients, an AuGe/Al0.6Ga0.4As interface with the oxygen content <1% and the contents of other impurities below the sensitivity threshold of the AES method have been produced. A comparative investigation of the formation of an ohmic contact by the proposed method and by a conventional technology using “wet” chemical cleaning has shown that the contacts produced with the use of atomic hydrogen cleaning show a better morphology of the surface and a more even edge of the contact pad, high adhesion of the metal film to the semiconductor, and a low contact resistance. The technological process for the production of ohmic contacts is characterized by a high reproducibility. The application of the proposed method together with hydrogenation of the near-surface region of semiconductor structures used in the production of light diodes have raised the output power of the diodes by 30%–40%.
Synthesis and decomposition of formate on Cu(111) and Cu(110) surfaces: Structure sensitivity
Authors: Nakamura I. , Nakano H. , Fujitani T. , Uchijima T. , Nakamura J.
Published: July 2002

The kinetics of both the formate synthesis of hydrogenation of CO2 and the formate decomposition has been studied on clean Cu(111) and Cu(110) surfaces using in situ infrared reflection absorption spectroscopy. It has been found that the formate synthesis does not depend on the surface structure of copper between Cu(111) and Cu(110). The activation energies for the initial formation rate of formate species on Cu(111) and Cu(110) have been determined to be 56.6±4.8 and 59.8±4.1 kJ mol−1, respectively. On the other hand, the activation energy and the pre-exponential factor for the formate decomposition on Cu(111) are widely different from those on Cu(110), indicating that the decomposition of the formate species depends on the Cu surface structure. The position of the neighboring Cu atom is considered to be important for the kinetics of the decomposition since the transition state of the formate decomposition may pass through by the OCO plane vibration toward the surface.
Scanning tunneling microscopy and spectroscopy of tungsten oxide thin films in air
Authors: Santucci S. , Lozzi L. , Passacantando M. , Odorisio L. , Cantalini C.
Published: July 2002

Scanning tunneling spectroscopy and microscopy investigations have been carried out in air on thermally evaporated tungsten oxide thin films deposited onto silicon substrates. The films have been submitted to thermal annealing at different temperatures and for different times. The microscopy images show strong effects of recrystallization and different grain sizes depending on the thermal treatment. The spectroscopic data exhibit a rectifying characteristics and the comparison between the topographic and current images allows a better understanding of the sample morphology in relation to the electrical behavior. X-ray photoelectron spectroscopy valence band measurements have evidenced a structure near the Fermi level, which has been assigned to a structural oxygen deficiency of the deposited films, which is also observed in the conductance curve of some samples.
Oxygen-induced changes in electron-energy-loss spectra for Al, Be and Ni
Authors: Madden H. H. , Landers R. , Kleiman G. G. , Zehner D. M.
Published: July 2002

Electron-energy-loss spectroscopy (EELS) data are presented to illustrate line shape changes that occur as a result of oxygen interaction with metal surfaces. The metals were aluminum, beryllium and nickel. Core-level EELS data were taken for excitations from Al(2p), Be(1s), Ni(3p/3s) and O(1s) levels to the conduction band (CB) density of states (DOS) of the materials. The primary beam energies for the spectra were 300, 450, 300, and 1135 eV, respectively. The data are presented in both the (as measured) first-derivative and the integral forms. The integral spectra were corrected for coherent background losses and analyzed for CB DOS information. These spectra were found to be in qualitative agreement with published experimental and theoretical studies of these materials. One peak in the spectra for Al oxide is analyzed for its correlation with excitonic screening of the Al(2p) core hole. Similar evidence for exciton formation is found in the Ni(3p) spectra for Ni oxide. Data are also presented showing oxygen-induced changes in the lower-loss-energy EELS curves that, in the pure metal, are dominated by plasmon-loss and interband-transition signals. Single-scattering loss profiles in the integral form of the data were calculated using a procedure of Tougaard and Chorkendorff [S. Tougaard and I. Chorkendorff, Phys. Rev. B. 35, 6570 (1987)]. For all three oxides these profiles are dominated by a feature with a loss energy of around 20–25 eV. Although this feature has been ascribed by other researchers as due to bulk plasmon losses in the oxide, an alternative explanation is that the feature is simply due to O(2s)-to-CB-level excitations. An even stronger feature is found at 7 eV loss energy for Ni oxide. Speculation is given as to its source. The line shapes in both the core-level and noncore-level spectra can also be used simply as “fingerprints” of the surface chemistry of the materials. Our data were taken using commercially available surface analysis equipment and serve to complement surface information provided by Auger electron and/or x-ray photoelectron spectroscopy.
Investigation of slider surfaces after wear using photoemission electron microscopy
Authors: Anders Simone , Stammler Thomas , Fong Walton , Bogy David B. , Bhatia C. Singh , Stöhr Joachim
Published: July 2002

The tribo-chemical interactions between the slider and the hard disk surface strongly influence the performance properties of a disk drive. To study these interactions, uncoated and carbon coated sliders were subjected to various wear tests using different disks. After the wear, the test slider surfaces were studied by photoemission electron microscopy (PEEM) using tunable x rays produced by a synchrotron. Using PEEM, one can identify the elemental and chemical state of the surfaces with a high spatial resolution. It was found that wear reduces the thickness of the carbon coating in some local areas of the slider surface. In particular, the coating was removed on elevated areas and in scratches. Scratches were found on the rails of the carbon coated and uncoated sliders after wear that showed the accumulation of a degraded (oxidized) lubricant which was transferred to the slider from the disk. It was also possible to analyze the chemical composition of the debris found on the slider surface. In the present case, the debris had the same chemical composition as the carbon coating of the slider.
Electronic structure, depth profile, and complex impedance spectroscopy of Pd doped ZnO ultrafine particle films
Authors: Dachun Zhao , Zhongkai Qu , Xiaoren Pan
Published: July 2002

Pd doped ZnO ultrafine particle (UFP) films were prepared by combining a direct current gas discharge activated reactive evaporation (direct current-gas discharge activated reactive evaporation) and a vacuum flashing evaporation technique. The electronic state structures and depth profiles of the Pd doped ZnO UFP films were investigated using angle resolved x-ray photoelectron spectroscopy. Three surface states of Zn 3d of Pd doped ZnO UFP films are observed, the positions of these states are located at 10.5, 5.5, and 2.7 eV, the binding energies at 10.5 and 5.5 eV result from Zn 3d state and Zn 4s–O 2p mixed state, the binding energy at 2.7 eV is mostly derived from O 2p, Zn 4p–O 2p or Zn 3d–O 2p. In addition, equivalent circuit of the Ag|Pd doped ZnO UFP film |Ag on the basis of morphology observed by scanning electron microscopy is established. Typical complex impedance spectroscopy at various temperatures is also used to study the Pd doped ZnO UFP film.
Dual ion beam deposited boron-rich boron nitride films
Authors: Chan K. F. , Ong C. W. , Choy C. L. , Kwok R. W. M.
Published: July 2002

BN x films with N content varying from 2 to 40 at. % were deposited by dual ion beam deposition. The films are solid admixtures of a B-rich phase composed of icosahedral atomic clusters, and a graphite-like boron nitride phase. The fraction of the B-rich phase drops, while that of the graphite-like boron nitride phase grows with increasing N content. The hardness of the films first rises, reaches a maximum value of 18.8 GPa at a N content of 20.2 at. %, and falls with further increase in N content. This rise is explained by assuming that some N atoms are located interstitially at the sites surrounded by icosahedral clusters, such that the hardness of the material is enhanced as a result of additional cross-linking of the network by the N atoms. However, the overall N contents are not sufficient to ensure the two phases to have the ideal stoichiometry of B4N and hexagonal BN (h-BN) structures, so that the B-rich phase in the film does not exhibit the theoretical strongest possible cross-linking that has been proposed for the ideal B4N structure. The drop in the hardness of the films with N contents exceeding 20.2 at. % arises from the increasing volume fraction of the graphite-like boron nitride phase.
Mechanism of fluorine reduction in C4F8/Ar parallel-plate-type electron-cyclotron-resonance plasma by a Si top plate
Authors: Hayashi Hisataka , Okigawa Mitsuru , Morishita Satoshi , Sekine Makoto
Published: July 2002

The density of F in C4F8/Ar plasma could be reduced by 34% when the Si top plate was bombarded by energetic ions in a parallel-plate-type 500 MHz electron-cyclotron-resonance plasma reactor, but that in CF4/Ar plasma was not reduced. We measured the densities of CFx (x=1–3), Si, and F in both plasmas as a function of ion-bombardment energy and found that F was generated from CF2 in C4F8/Ar plasma but not in CF4/Ar plasma, and that the CF2 density decreased to a similar extent with increasing ion-bombardment energy in both plasmas. We conclude that the reduction of the F density in C4F8/Ar plasma was caused by the decrease in CF2 density and not by a direct reaction of F with Si when the Si plate was irradiated by energetic ions.
Characterization and enhanced properties of plasma immersion ion processed diamond-like carbon films
Authors: He X. M. , Bardeau J.-F. , Walter K. C. , Nastasi M.
Published: July 2002

The formation and properties of diamond-like carbon (DLC) films prepared on silicon substrates at room temperature, using C2H2–Ar plasma immersion ion processing, are investigated with respect to film deposition parameters. Decreases in the reactive gas-flow ratios of C2H2 to Ar(FC2H2/FAr) or the gas pressure were found to decrease the hydrogen content, increase the density and hardness, and improve the surface finish of the DLC films, all of which led to enhanced tribological properties. Decreasing the friction coefficient requires increasing the hardness of the film and smoothing its surface, whereas increasing the wear resistance correlates with reducing both the hydrogen content and residual stress in DLC films. High hardness and optimum tribological properties were reached as the growth of DLC films was subjected to low-energy ion impingement, which was induced by a −150 V pulsed bias from the C2H2–Ar plasma produced at low reactive gas pressures with low FC2H2/FAr ratios.
Monolayer-level controlled incorporation of nitrogen at Si–SiO2 interfaces using remote plasma processing
Authors: Niimi H. , Lucovsky G.
Published: July 2002

We demonstrate three different ways to incorporate nitrogen at Si–SiO2 interfaces: (i) an O2/He plasma oxidation of the Si surface followed by an N2/He plasma nitridation, (ii) an N2/He plasma nitridation of the Si surface, and (iii) a Si3N4 film deposition on to the Si surface. The two-step interface formation, the O2/He plasma oxidation followed by the N2/He plasma nitridation, is shown to yield significantly better interface device properties than the other two approaches. These differences in interface properties are explained by an application of constraint theory based on comparisons of the average bonding coordination of the dielectric layer at the interface with the Si substrate.
Surface reaction pathways of 1,1,1,5,5,5-hexafluoro-2,4-pentanedione on clean and pre-oxidized Ni(110) surfaces
Authors: Nigg H. L. , Masel R. I.
Published: July 2002

Ni contamination of Si surfaces is an increasing problem for very large scale integrated manufacturers seeking sub-0.25 μm features. Dry etching methods are considered important, potential processes for removal of this contaminant. We and others have recently proposed a chemical vapor etching (CVE) treatment using oxygen and hexafluoropentanedione that could be used to remove Ni. In this article, we have used temperature programmed desorption to examine the surface kinetic pathways of Ni removal by CVE. Ni was successfully dry etched from the pre-oxidized surface by the desorption of Ni(CF3COCHCOCF3)2 between 280 and 480 K with a maximum desorption rate around 390 K. However, above 500 K, a variety of decomposition products appeared and etching ceased. Analysis of the clean (i.e., fully reduced surface) showed these products to be a result of the scission of bonds attached to the β-carbon: C–CF3, C–CH and C=O. Furthermore, stabilization of radical species like CF3 on the clean surface resulted in some unexpected decomposition products observed desorbing between 360 and 540 K. Otherwise, some Ni-fluoride desorption was observed on both surfaces above 800 K and Auger revealed carbon on both surfaces after flashing to 900 K. From these results, it is clear that we need to understand the β-scission process better before we can determine how clean etching can be achieved.
Influence of Mg on the corrosion of Al
Authors: Baer D. R. , Windisch C. F. , Engelhard M. H. , Danielson M. J. , Jones R. H. , Vetrano J. S.
Published: July 2002

This article summarizes a series of experiments to determine the influence of Mg on the corrosion and electrochemical behavior of Al. Magnesium is commonly added to increase the strength of lightweight nonheat treatable Al alloys. However, these alloys are susceptible to grain boundary dissolution, stress corrosion cracking, or hydrogen induced embrittlement due to changes in the alloy structure and elemental distribution during processing, welding, or in-service exposure to elevated temperatures. Auger electron spectroscopy and transmission electron microscopy measurements show that alloys having a distribution of Al3Mg2 (β phase) precipitates and segregated Mg on grain boundaries are more susceptible to cracking. To understand the roles of Mg on the cracking process we compared the corrosion potential and film formation of pure Al, Al implanted with Mg, a 7 wt % Mg–Al alloy and pure Al3Mg2 phase. The surfaces of the specimens were cleaned and prepared in a surface analysis system and transferred in a vacuum transfer system to a corrosion cell. After solution exposure and electrochemical measurement the specimens were returned to the spectrometer and analyzed by x-ray photoelectron spectroscopy. The open circuit potentials for Al, Mg implanted Al, and the 7% alloy were nearly identical. However, the corrosion potential for the β phase differs significantly. The thickness of the film formed on each of the samples is similar. Mg is observed to be depleted in the outer part of the oxide films, but somewhat enhanced near the oxide–metal interface. The results suggest that segregated Mg plays little role in the cracking and that hydrogen production at the β phase particles may be the most significant factor.
Silicon micromachining for millimeter-wave applications
Authors: Guillon B. , Grenier K. , Pons P. , Cazaux J. L. , Lalaurie J. C. , Cros D. , Plana R.
Published: July 2002

We present in this article a very low loss silicon micromachined coplanar technology. The design of the structures was achieved through three dimensional finite element method electromagnetic simulations. A silicon micromachined cavity resonating at 95 GHz with a quality factor greater than 9000 was realized.
Bipolaron formation in para-sexiphenyl thin films upon Cs doping
Authors: Koch N. , Leising G. , Yu L. M. , Rajagopal A. , Pireaux J. J. , Johnson R. L.
Published: July 2002

The semiconducting electroluminescent oligomer para-sexiphenyl (6P) is a promising candidate for application as the active layer in organic light emitting devices. The interaction of Cs atoms evaporated (in a step-wise manner) in ultrahigh-vacuum on thin 6P films has been studied with synchrotron ultraviolet photoelectron spectroscopy. No formation of metallic Cs or of new chemical compounds has been evidenced, but it appears that a doping of the oligomer occurs for the whole range of Cs concentrations we studied. Our data show a progressive growth of new density of states in the (former empty) band gap. Upon progressively increased doping, the material work function decreases, its Fermi-energy remains well below the newly occupied electronic states measured at 5.8 and 3.6 eV (energies relative to the vacuum level). These observations are interpreted as bipolaron formation in the charged 6P material.
Selective etching of GaN over AlN using an inductively coupled plasma and an O2/Cl2/Ar chemistry
Authors: Smith S. A. , Lampert W. V. , Rajagopal P. , Banks A. D. , Thomson D. , Davis R. F.
Published: July 2002

An alternative method for achieving etching selectivity between GaN and AlN has been demonstrated. The etch rate of AlN was significantly decreased by the addition of a low concentration of O2 to a Cl2–Ar mixture in an inductively coupled plasma (ICP) etching system. The etch rate of GaN in the O2-containing plasma was approximately 15% less than the plasma without the O2 for the same parameters. The pressure and the ICP power were varied to achieve a maximum selectivity of 48 at a pressure of 10 mTorr, a direct current bias of −150 V, and an ICP power of 500 W. The etch rates of GaN and AlN at these parameters were 4800 and 100 Å/min, respectively.
Low-temperature growth of Ti(C,N) thin films on D2 steel and Si(100) substrates by plasma-enhanced metalorganic chemical vapor deposition
Authors: Boo Jin-Hyo , Heo Cheol Ho , Cho Yong Ki , Han Jeon-Geon
Published: July 2002

We have deposited Ti(C,N) thin films on Si(100) and D2 steel substrates in the temperature range of 200–300 °C using tetrakis diethylamidotitanium (TDEAT) and titanium isopropoxide (TIP) by pulsed dc plasma-enhanced metalorganic chemical vapor deposition (PEMOCVD). Radical formation and ionization behaviors in plasma are analyzed in situ by optical emission spectroscopy at various pulsed bias voltages and gas conditions. H2 and He+H2 gases are used as carrier gases to compare plasma parameters, and the effect of N2 and NH3 as reactive gas is also evaluated by the reduction of the C content of the films. Polycrystalline Ti(C,N) thin films were successfully grown on either D2 steel or Si(100) surfaces with TDEAT at temperatures as low as 200 °C. For TIP, however, only TiOCN thin films were obtained on Si(100) substrates. The best deposition process is evident for H2 and N2 gas atmospheres and bias voltage of 600 V. The higher film hardness is about 1760 Hk 0.01, but depends on gas species and bias voltage. Compared to TiN films, the Ti(C,N) film grown by PEMOCVD has very good conformability; the step coverage exceeds 85%, with an aspect ratio of more than 3.
A review of recent research on the growth and physical properties of single crystal metastable elemental and alloy semiconductors
Authors: Greene J. E.
Published: July 2002

Several research groups have recently reported the growth of metastable semiconductors which were not only single phase but, in many cases, high quality single crystals. The systems reported to date include the (III–V)1−xIVx alloys (GaAs)1−xSix, (GaAs)1−xGex, and (GaSb)1−x Gex, the nonisostructural alloys Pb1−xCdxS, InSb1−xBix, and Ge1−xSnx, elemental α-Sn, and GaAs1−xSbx with x values within the miscibility gap. Several of these systems have been grown with compositions ranging across the pseudobinary phase diagram and have been found to exhibit good thermal stability against phase separation at temperatures ≥500 °C. In addition to crystal growth studies, structural, optical, electrical, lattice dynamic, and thermodynamic measurements have been carried out. These results are reviewed and an attempt is made to establish a foundation for understanding and modeling crystal growth of this new class of semiconducting materials.
Surface studies of and a mass balance model for Ar+ ion-assisted Cl2 etching of Si
Authors: Barker R. A. , Mayer T. M. , Pearson W. C.
Published: July 2002

An argon ion beam is combined with a Cl2 gas jet to etch silicon. Auger electron spectroscopy is used to measure the surface coverage of chlorine simultaneous with the etch process. This steady state surface chlorine coverage is enhanced by an increase in the Cl2 flux or a decrease in Ar ion flux. The coverage varies from 10% to 100% of saturation as the Ar+ to Cl2 flux ratio varies from 0.4 to 0.004. The Si etch rate increases with increasing Cl2 flux giving an enhancement of as much as a factor of 3 over pure Ar+ sputtering at 500 eV. A general model is presented which is based on the mass balance of ionic and neutral species to and away from the surface region. Assumptions are made to apply the model to the Ar++Cl2+Si system. Expressions for both the surface Cl coverage and silicon etch rate are then obtained as functions of the incident Ar+ and Cl2 fluxes. The model is fit to the data and accounts for all of the observed trends in surface coverage and etch rate.
Proximity effect correction on substrates of variable material composition
Authors: Vettiger Peter , Forster Theo , Kern Dieter P.
Published: July 2002

The main contribution to the proximity effect in electron beam lithography on solid substrates results from electrons backscattered from the substrate. The range around the point of incidence of the primary beam over which these electrons affect the resist as well as their total number depends very much on the substrate material, in particular on the atomic number of the material. In the case of isolated lines it has been shown earlier that the resulting dose variation can be compensated for by modulating the incident dose in accordance with the backscattered electron signal detected during exposure. Shape-to-shape interaction in dense patterns is normally simulated numerically and corrected for on a pattern data level, and this simulation could, in principle, include variable substrate material compositions. The purpose of this paper is to show that a suitable combination of numerical dose compensation for constant substrate composition and real time feedback from the backscattered electron signal can yield significantly improved results compared to either correction alone.
Dot matrix electron beam lithography
Authors: Newman T. H. , Pease R. F. W. , DeVore W.
Published: July 2002

Slow throughput is the major problem of scanning beam lithography. We have investigated a multiple beam approach in which an array of beams is focused and scanned by a common system but the beams are blanked independently. The individual blanking is accomplished using an assembly fabricated with silicon micromachining technology and shadow mask evaporation of blanking electrodes 50 μm wide, 400 μm deep. Analysis and experimental evaluation both indicate that blanking can be achieved with this configuration. Choosing an optimum design involves trade offs between ease of illumination, ease of fabrication, positional control, and space charge blurring. However, extension to 16 or more beams looks quite possible.
Photoemission studies of the band bending on MBE-grown GaAs(001)
Authors: Svensson S. P. , Kanski J. , Andersson T. G. , Nilsson P.-O.
Published: July 2002

The band bending on GaAs(001) surfaces prepared by molecular beam epitaxy (MBE) have been studied for n- and p-type materials. Surfaces with c(4×4), c(2×8), and (4×6) reconstruction ranging from As to Ga rich have been investigated. The surface symmetry was determined by reflection high energy electron diffraction (RHEED) and the position of the valence band maximum relative to the Fermi level was measured using angle resolved UV photoelectron spectroscopy (ARUPS) at normal emission. The position of the Fermi level relative to the valence band maximum was found to be ∼0.7 eV for n-type and ∼0.5 eV for p-type material, with a slightly increasing trend in going from Ga- to As-rich surfaces. For the (4×6) reconstructed n-type samples the growth termination method was found to have a significant influence on the band bending. The results obtained here are in very good agreement with previous measurements of the Al–GaAs(001) Schottky barrier height indicating that the electronic properties of this junction are determined by the properties of the semiconductor.
A nonalloyed, low specific resistance Ohmic contact to n-InP
Authors: Dautremont-Smith W. C. , Barnes P. A. , Stayt J. W.
Published: July 2002

Nonalloyed Ohmic contacts to n-InP have been made by sputter deposition of metals onto sputter-etched InP surfaces. Contacts were Ohmic as deposited without intentional heating. For a 500 Å sputter-etch depth, the contact to 8×1018 cm−3 n-InP was Ohmic up to 5×104 A cm−2 with a specific contact resistance of 4×10−7 Ω cm2 independent of sputter etch energy over the range 200 to 870 eV. To 6×1017 cm−3 n-InP, the corresponding value was 1.8×10−6 Ω cm2. The In rich, degenerate n-type sputter etch damaged surface is responsible for the quality of the contact, which is independent of the particular contacting metal, thus permitting the use of a barrier metal/noble metal combination. Nonalloyed contacts fabricated with Ti/Pt have low stress and excellent adhesion to InP. Even for the lowest etch energy, they are thermally stable, with no change caused by short periods up to 430 °C, or extended periods (∼100 h) at 250 °C. This contacting procedure and the resultant contact has many advantages over the usual Au:Sn or Au:Ge alloyed contact.
Resolution of a three-layer resist using heavy metal as an intermediate layer
Authors: Suzuki Masanori , Namatsu Hideo , Yoshikawa Akira
Published: July 2002

For the purpose of reducing radiation damage and delineating fine patterns in electron beam direct writing lithography, fundamental characteristics of a three-layer resist using heavy metal as an intermediate layer is investigated in detail. An exposure and development simulation program, ELSIS, is extensively used to estimate resolution and linewidth control. The exposure intensity distributions for a line source are calculated to evaluate pattern delineation characteristics and degree of proximity effect in this three-layer resist. The developed pattern profiles of positive-type resist and absorbed energy density profiles in negative-type resist are calculated. Some relevant experimental data also are presented. These results indicate that several advantages can be expected from this three-layer resist, such as an apparent increase in resist sensitivity and a reduction of the interproximity effect.
RHEED oscillation studies of MBE growth kinetics and lattice mismatch strain-induced effects during InGaAs growth on GaAs(100)
Authors: Lewis B. F. , Lee T. C. , Grunthaner F. J. , Madhukar A. , Fernandez R. , Maserjian J.
Published: July 2002

We present the first report of RHEED intensity changes and recovery as a function of monolayer and submonolayer MBE depositions of InxGa1−xAs (x≤0≤0.5) on GaAs(100) substrates. The influence of the lattice mismatch-induced strain on the growth mechanisms and the incorporation behavior of In and Ga is suggested by new and In concentration dependent effects in the RHEED intensity waveform behavior during growth. The monolayer oscillation period is determined by the combined In and Ga fluxes. The initial growth of InGaAs on GaAs(100) is planar, but after an amount of deposition depending upon InAs content and growth conditions, a sudden change from a streaked reflection pattern to a spotty transmission pattern is observed indicating formation of 3D islands. The film thickness at which this transition occurs is strongly influenced by the step density of the GaAs surface when InGaAs growth is initiated. We have examined the recovery behavior of the specular spot intensity after the growth of 0.1 to 15 monolayers of GaAs on an annealed metal-stabilized GaAs(100) surface. In this experiment, the RHEED intensity has dropped from its initial (no-growth) value and, after termination of growth, it slowly recovers to its steady-state value. We report RHEED intensity recovery rates as a function of the number of monolayers of GaAs deposited and compare them to recovery rates after steady-state growth has been reached. The recovery rate is a strong function of the completeness of the surface when growth is stopped.
A novel method of selective SiO2 formation on Mo electrodes
Authors: Kyuragi Hakaru , Oikawa Hideo
Published: July 2002

A novel technique of selective SiO2 formation called the interfacial oxidation method is proposed and proved feasible by experiment. By this technique, a poly-Si/MoO2/Mo structure (poly-Si on MoO2 on Mo) can be converted to a poly-Si/SiO2/Mo structure by annealing in an H2 atmosphere so that SiO2 is selectively formed on only Mo electrodes. The SiO2 film formed by this method is shown to have almost the same properties as thermally grown SiO2 film; the Si(2p) binding energy peak, etching rate for diluted HF(H2O:HF=100:3), and average breakdown strength were 102.9 eV, 102 Å/min, and 3.6×106 V/cm, respectively. In addition, most diodes of 500×500  μm2 area showed a leakage current of less than 10−12 A.
Oxide formation on GaAs exposed to CF4+O2 plasma
Authors: Sugahara Hirohiko , Suzuki Masamitsu
Published: July 2002

The effect of CF4+O2 plasma on GaAs is studied using Auger electron spectroscopy and x-ray photoelectron spectroscopy. AES sputtering profiles and the chemical shift in the Ga 3d photoelectron peak indicate the Ga2O3-rich oxide formation on the GaAs surface through exposure to CF4+O2 plasma. The increase in the Schottky diode ideality factor n and the decrease in GaAs MESFET transconductance gm as functions of plasma exposure time are explained with this oxide formation. The GaAs MESFET I–V characteristics are improved by removing the Ga2O3-rich oxide layer with chemical treatment.
Near surface damage induced in polyimides by ion beam etching
Authors: Vanderlinde William E. , Mills Peter J. , Kramer Edward J. , Ruoff Arthur L.
Published: July 2002

Polyimide layers approximately 10 μm thick on Si wafers were ion beam etched (IBE) by Ar. Ion energies up to 1000 eV and beam current densities as high as 0.3 mA/cm2 were used to a total dose of 54 mC/cm2. After etching, the samples were exposed to iodine vapor for fixed periods of time. The diffusion of iodine into the samples was used to probe for ion induced changes in the polyimide structure. The concentration of the diffused iodine was measured as a function of depth by Rutherford backscattering spectrometry. For the IBE samples the surface concentration of iodine was markedly decreased. The iodine diffusivity in the near surface region of thickness 0.2 μm was reduced by two orders of magnitude. These results indicate that etching appears to cause modification of the polyimide film at depths far greater than the range of the incident ions or their secondary electrons in polyimide.
Near neighbor chemical bonding effects on Si atom native bonding defects in silicon nitride and silicon dioxide insulators
Authors: Lucovsky G. , Lin S. Y.
Published: July 2002

There has been considerable interest in the use of deposited thin films of Si3N4 and SiO2 as gate insulators and/or passivation layers for compound semiconductors. This is contingent on a low temperature deposition process which: (a) produces insulators which are effectively free of native bonding defects and impurity atoms, and at the same time (b) minimizes chemical degradation, and the associated generation of interfacial defect states at the compound semiconductor surfaces. Recently, the group at North Carolina State University and The Research Triangle Institute has developed a low temperature, remote plasma-enhanced chemical vapor deposition (CVD) process for depositing trilayer gate insulators consisting of SiO2–Si3N4–SiO2 layers onto p-type (In,Ga)As to produce high gain, stable, n-channel conducting field-effect transistor (FET) devices. The processing chemistry for the deposition of these Si3N4 and SiO2 layers prevents the incorporation of significant amounts of chemical impurities in the form of oxygen atoms in the Si3N4, and hydrogen and nitrogen atoms in the SiO2. This paper addresses the question of native bonding defects in Si3N4 and SiO2, and considers the effects of near neighbor impurity atoms on the gap state energies of two types of defects, Si dangling bonds and Si–Si bonds.
A simple technique for eliminating hillocks in integrated circuit metallization
Authors: Singh Awatar
Published: July 2002

A simple technique for eliminating hillocks in integrated circuit metallization is reported. In this technique, the aluminium film, after deposition on an oxidized silicon wafer and sintering, is stripped off in orthophosphoric acid. The wafer is thoroughly cleaned in DI water and no HF is used. This treatment forms an A12O3+Si dipole layer on the oxide surface and makes it aluminiumphilic. Further aluminization and sintering generate the adherant composite layers of Al,Al2O3+Si on oxide surface and thereby eliminate hillocks.
The effect of oxygen pressure on volatility and morphology of LaB6 single crystal cathodes
Authors: Davis P. R. , Schwind G. A. , Swanson L. W.
Published: July 2002

Single crystal LaB6 has become an important cathode material for a variety of electron beam systems. At the typical operating pressures of many such systems interaction of the cathode with the residual gases present can cause radical enhancement of the cathode volatility with concomitant change in the usual conical shape, oxygen-bearing gases being the most active in promoting such effects. In this paper we discuss a systematic investigation of the variation of volatility and morphology of heated LaB6 cathodes with oxygen pressure. The results of this study show that at a low operating temperature of 1600 K the volatility enhancement due to PO2=1×10−6 Torr is almost a factor of 100 relative to operation at 1×10−8 Torr or less. In contrast, at a cathode operating temperature of 1900 K the enhancement due to the same oxygen pressure is negligible. The volatility enhancement of LaB6 for PO2=1×10−7 Torr and T=1700 K is only a factor of 2. The volatility enhancement was observed to vary with crystallographic direction and is primarily responsible for the well known formation of facets on an initially conical emitter structure. From the relative rates of growth of the various facets we were able to conclude that crystal face anisotropy of the oxygen enhanced volatility of LaB6 increases in the order (110)<(111)<(100). In the case of a truncated conical cathode the results show the expected increase in rate of change to a pointed pyramid final shape as the cone angle is decreased from 90° to 70°.
Heteroepitaxial molecular beam epitaxial InSb and room temperature operation of its metal-insulator-semiconductor field-effect transistors
Authors: Ohashi T. , Bour D. P. , Itoh T. , Berry J. D. , Jost S. R. , Wicks G. W. , Eastman L. F.
Published: July 2002

Calculations are shown to investigate the possibility of modulating the channel conductance of InSb field-effect transistors (FET’s) at 300 K. Molecular beam epitaxy (MBE) grown InSb metal-insulator-semiconductor field-effect transistors (MISFET’s) were successfully fabricated and exhibited room temperature operation.
Tungsten silicide Schottky contacts on GaAs
Authors: Zhongde Zhu , Cheung Nathan W. , Lemnios Zachary J. , Strathman Michael D. , Stimmell James B.
Published: July 2002

Two types of I–V characteristics for W–Si/GaAs Schottky contacts have been observed. With sputtering deposition from a W–Si composite target (type A), The Schottky contacts have a Schottky barrier height ΦB of 0.64 V and an ideality factor, n of 1.05. The I–V behavior is independent of the WSix composition for x=0.42–2.3. With cosputtering from W and Si targets (type B), an excellent WSi0.6/GaAs Schottky contact is obtained with ΦB equal to 0.8 V and an ideality factor equal to unity. The I–V characteristics of both types of diodes agree with the theoretical thermionic-emission model for both forward and reverse bias. For type B diodes, high-temperature stability has been demonstrated with furnace annealing up to 750 °C. In previous studies, composition of the W–Si film has been emphasized as the single most important factor for GaAs Schottky gates. Our work has shown, besides silicide composition, surface cleaning procedures and silicide deposition techniques will have a greater effect on the diode I–V characteristics, the thermal stability of the Schottky contact, and the silicide adhesion on GaAs substrate. Sputter etching of the GaAs substrate prior to silicide deposition can improve the silicide adhesion up to a heat treatment of 1000 °C but with a degradation of diode performance. A negative substrate bias during deposition was shown to be a better compromise for both adhesion and electrical considerations.
Effects of strain-induced electric fields on the electronic structure of [111] growth axis semiconductor superlattices
Authors: Mailhiot C. , Smith D. L.
Published: July 2002

The presence of internal strains in [111] growth axis strained-layer semiconductor superlattices is responsible for the generation of polarization fields due to the piezoelectric effect. These fields do not occur in [100] growth axis superlattices because the orientation of the lattice-mismatch induced strains is such that they do not produce polarization fields in zinc blende materials. For III–V semiconductor superlattices grown along the [111] direction, the magnitude of these strain-induced electric fields can be of the order of 105 V/cm. We investigate the effects of the strain-induced electric fields on the electronic structure of Ga0.47In0.53As–Al0.70In0.30As strained-layer superlattices grown along the [111] direction. This system is characterized by a lattice mismatch of 1.5%. We demonstrate that the presence of strain-induced electric fields result in sizable Stark shifts on the superlattice electron and hole subbands. This energy shift increases with superlattice layer thickness. Moreover, the presence of these strain-induced electric fields modifies superlattice wave functions and causes a spatial separation of the electrons and the holes within the confining superlattice layers.
Ion beam etching of InGaAs, InP, GaAs, Si, and Ge
Authors: Chen Wei-Xi , Walpita L. M. , Sun C. C. , Chang W. S. C.
Published: July 2002

We have investigated reactive ion beam etching of semiconductor and insulator materials using gases, such as CF4 and C2F6, and compared the etching rates with those of argon ion milling. The ion beam is generated by a Kaufman-type ion source, in a milling system manufactured by the Commonwealth Scientific Corporation. When a number of semiconductors such as InGaAs, InP, GaAs, Si, and Ge are etched with an argon ion beam, the etch rate of these materials increases linearly with the increase of beam current density. Quite different behavior is seen when CF4 or C2F6 ion beams are used; the etch rate deviates from a linear dependence of current density at high beam current density. The etch rates of all the above materials using Ar are higher than the etch rates using CF4 or C2F6. However, for substrates of SiO2, BaO, LiNbO3, and both C2F6 and CF4 give better linearity and higher etching rates than argon. There is some evidence to suggest that at high beam currents, CF4 and C2F6 cause accumulation of carbon on the surface. Carbon buildup on the SiO2, BaO, LiNbO3, and other oxides is minimal since the oxygen in the lattice will form volatile products with carbon in the form of CO, CO2, or COF2, and therefore better linearity is seen. We report that the dependency of III–V compound etching rates on current density can be adjusted both by adjusting the axial magnetic field and introduction of oxygen. We also report the differential etching ratio between photoresist and semiconductor materials for gases C2F6, CF4, Ar/O2, and Ar. We show that the differential etching ratio is best for C2F6 gas.
Low-resistivity W/WSix bilayer gates for self-aligned GaAs metal–semiconductor field-effect transistor large-scale integrated circuits
Authors: Kanamori M. , Nagai K. , Nozaki T.
Published: July 2002

The WSix bilayer gate structure was developed to provide a low-resistivity metallization for GaAs large-scale integrated circuits (LSIs). By the use of 0.1 μm WSi0.4 and 0.4 μm W, 18 μ Ω cm average resistivity could be obtained while maintaining low stress and stable Schottky-barrier characteristics. This resistivity is one order of magnitude lower than that for the conventional WSix single layer. High-performance field-effect transistor characteristics were also confirmed, indicating that this bilayer gate technology is promising for realizing high-speed GaAs LSIs.
Steps on (001) silicon surfaces
Authors: Aspnes D. E. , Ihm J.
Published: July 2002

We investigate a topological method of eliminating antiphase domains in zinc-blende semiconductors heteroepitaxially grown on (001) Si substrates. Antiphase domains cannot occur if only one of the two atomic species of the polar overlayer bonds directly to the substrate at the heteroepitaxial interface (As, in the case of GaAs on Si) and if atoms from only one of the two inequivalent sublattices of the substrate form the termination boundary [only biatomic (a0/2) steps present]. We show that thermal equilibrium is a necessary and sufficient condition to realize this condition for (001) Si, a result of a π-bonded step reconstruction that lowers the relative enthalpy of reconstructed [110] biatomic steps by 0.04 eV per step atom for one type of biatomic step, and of correlation, which freezes out the step configuration entropy thereby suppressing the formation of all other types of steps. Our model explains selection rules and dimer orientations observed in infrared absorption, low-energy electron diffraction, and reflection high-energy electron diffraction measurements of vicinal (001) Si surfaces tilted toward (110). For general vicinal surfaces, competition from the non-π-bonded sides of the atomically flat terraces weakens the thermodynamic driving force. For surfaces tilted toward (100) it vanishes completely, indicating that antiphase-free polar material cannot be grown on these surfaces, in agreement with experiment. If a minimum threshold energy is needed per terrace to form a primitive (001) surface, then the boundaries between antiphase-free and antiphase-dominated regions for spherically figured surfaces should be parabolic. The minimum energy estimated from the results of Akiyama et al. on spherically figured surfaces suggests that terrace–terrace correlations are also important factors in forming the primitive surface.
Interdiffusion of Al and Ga in (Al,Ga)As/GaAs superlattices
Authors: Lee Jyh-Chwen , Schlesinger T. E. , Kuech T. F.
Published: July 2002

We have employed photoluminescence spectroscopy to determine the temperature and composition dependence of the interdiffusion of Al and Ga in (Al,Ga)As/GaAs superlattices. The position of the band to band luminescence in the superlattices was measured both before and after thermal anneal. The diffusion equation was solved with a fixed value of D, to establish the potential profile of the superlattice structure after anneal. A solution of the Schrödinger equation where the electron or hole wave function was expanded in a Fourier series was employed to determine the position of the superlattice band edges both before and after anneal and hence infer the expected luminescence peak positions. The value of D which yielded a calculated shift in agreement with the measured shift in the luminescence was taken to be the actual value of the interdiffusion coefficient. For structures consisting of GaAs wells and AlxGa1−xAs barriers with x=1.0 and 0.3 the interdiffusion process is characterized by an activation energy of 6.0 eV with a value of 4×10−19 cm2/s at 850 °C. For x=0.7 the interdiffusion is characterized by an activation energy of 4.0 eV with a value of 7×10−18 cm2/s at 850 °C.
Atomic-layer growth of GaAs by modulated-continuous-wave laser metal-organic vapor-phase epitaxy
Authors: Aoyagi Yoshinobu , Doi Atsutoshi , Iwai Souhachi , Namba Susumu
Published: July 2002

Atomic-layer epitaxy (ALE) including self-arresting deposition mechanism at 100% surface coverage is realized in GaAs by a modulated-continuous-wave laser metal-organic vapor-phase epitaxy technique. Selective decomposition of trimethylgallium (TMG) or triethylgallium (TEG) on an As-atom layer by laser irradiation is an important mechanism to realize the ALE. The experimental results are well-explained by a calculation based on this selective decomposition mechanism.
Micromachining of optical structures with focused ion beams
Authors: Harriott L. R. , Scotti R. E. , Cummings K. D. , Ambrose A.F
Published: July 2002

For the first generation of lightwave devices, semiconductor lasers and detectors have been used as discrete elements. As the technology continues to evolve, integration of light sources with electronics or other optical elements will be necessary. However, an efficient and reliable method for generating laser facets and other optical elements internal to the integrated system must first be developed. Three dimensional features have been milled into optical materials by scanning a submicron focused gallium ion beam. Different shapes are obtained using computer controlled beam placement and dwell time during sputtering. We have used this technique to create micron-sized facets and reflectors in the active areas of semiconductor lasers. Light output and quantum efficiency measurements indicate that these features are of sufficient quality to fabricate monolithic integrated optical devices. Some of the applications currently being investigated are laser–detector pairs, coupled cavity lasers, lasers with integral lenses, distributed feedback lasers, confocal cavities, and laser cavity length tuning.