bluuebunny/crossref_metadata_2025 huggingface dataset:
Langmuir probe measurements of electron temperature and density scaling in multidipole radio frequency plasmas
Authors: Lai C. , Breun R. A. , Sandstrom P. W. , Wendt A. E. , Hershkowitz N. , Woods R. Claude
Published: July 2002

We have constructed a multidipole rf plasma system in a bell jar with a single planar rf powered electrode inserted at one end of a ‘‘magnetic bucket.’’ Capacitive probe measurements revealed that the rf fluctuations are particularly large in these capacitively coupled plasmas. A Langmuir probe has been developed, in which a large shunting capacitor and several self-resonant inductors are used to allow the probe tip to follow the rf fluctuations. With this new probe, we are able to adequately suppress the effect of these large rf fluctuations and measure time averaged plasma densities and electron temperatures or electron energy distribution functions (EEDFs). We report here a series of experiments in argon with the Langmuir probe fixed at the center of the plasma. The EEDFs were found to be Maxwellian with temperatures from 2 to 5 eV. The value of Te depends primarily on pressure, which was varied from 0.5 to 2.5 mTorr. The plasma density exhibited an approximately linear relationship with AelVrf/Te, where Ael is the area of the powered electrode, and Vrf is the rf voltage on the powered electrode.
Effects of predeposition HF/NH4F treatments on the electrical properties of SiO2/Si structures formed by low-temperature plasma-assisted oxidation and deposition processes
Authors: Yasuda T. , Ma Y. , Chen Y. L. , Lucovsky G. , Maher D.
Published: July 2002

Si(100) and (111) wafers were prepared by a standard RCA cleaning process followed by a treatment in HF/NH4F solutions with different pH values. SiO2/Si structures were formed on these surfaces by a two-step low-temperature, 200–300 °C, plasma-assisted oxidation/deposition process. The SiO2/Si(111) interface, subjected to a predeposition rinse in a 40 wt % NH4F solution, displayed a midgap interface trap density Dit of approximately 5×1010 cm−2 eV−1, which is significantly lower than is generally observed on thermally oxidized Si(111). The Dit values increased systematically up to about 2×1011 cm−2 eV−1 as the pH of the HF/NH4F treatment was decreased. For Si(100) wafers, the absolute level, and the energy distribution of Dit within the Si band gap, were essentially independent of the pH of the HF/NH4F treatment. The micromorphology and perfection of the H passivation of the Si surfaces after the HF/NH4F treatment were characterized by Auger electron spectroscopy and low-energy electron diffraction, and were correlated with the electrical properties of the resulting SiO2/Si structure. It was observed for the first time that the Si(100) surface partially reconstructs into a 2×1 structure after a rinse in 40 wt % NH4F that follows a traditional RCA cleaning treatment.
X-ray photoelectron spectroscopy analysis of the copper/arachidic acid organized molecular assembly interface: Charging phenomena
Authors: King David E. , Czanderna A. W. , Spaulding D.
Published: July 2002

Interactions of evaporated copper with the methyl terminated surfaces of self-assembled monolayers of arachidic acid were studied with x-ray photoelectron spectroscopy (XPS). The arachidic acid [CH3(CH2)19COOH] organized molecular assemblies (OMAs) were self-assembled on native oxide grown on freshly prepared 200 nm thick aluminum films on single crystal silicon wafers. XPS spectra were acquired as a function of evaporated copper thickness. Charging shifts of up to 0.84 eV were observed for the C(1s), O(1s), and Cu(2p) photoemission lines during evaporation of up to 4.0 nm of copper. The thickness of the organized molecular assemblies (OMA) is approximately 2.7 nm on the native oxide surface, yielding a total thickness for the oxide/OMA stack of 6–7 nm.
Point defect structures and energetics in Si using an empirical potential
Authors: Ungar P. J. , Takai T. , Halicioglu T. , Tiller W. A.
Published: July 2002

Statics calculations on silicon using the Tersoff 2 and Tersoff 3 potential energy functions are presented. We have evaluated the following at 0 K: (1) neutral monovacancy and divacancy formation and migration energies; (2) neutral bond-centered, site sharing, tetrahedral, and hexagonal self-interstitial formation and migration energies; and (3) the variation of these energies with distance from a bulk site of Frenkel defect formation and from [100] and [111] surfaces. The structural variations around these defects are also determined and discussed.
CrSi2/Si(111): Growth of monotype domains by solid phase epitaxy on a vicinal surface
Authors: Rocher André , Oustry André , Josée David Marie , Caumont Michel
Published: July 2002

CrSi2 layers grown by solid phase epitaxy on a nominal (111) Si surface exhibit in the same proportion two different orientation relationships, named A and B. When CrSi2 is deposited on a 8° vicinal (111) Si surface, B-type orientation is favored with respect to the A type. This result can be explained by the fact that both the step width introduced by the miscut and the planar coincidence between {11̄00}CrSi2 and {112}Si are nearly equal to 23 Å. 60° misfit dislocations are observed at the interface with the same spacing. Their Burgers vector component along [111] can be almost exactly compensated by steps along the 〈110〉 directions, which make possible a coherent growth of the B-type orientation.
Control of the Fermi-level position on the GaAs(001) surface: Se passivation
Authors: Pashley M. D. , Li D.
Published: July 2002

The performance of some GaAs devices is impaired by a high surface recombination rate brought about by surface states which pin the Fermi level in the middle of the band gap. Passivation of the surface with S or Se can significantly reduce this problem. The pinning on the clean GaAs(001)-(2×4) surface of molecular beam epitaxy grown material is understood from previous scanning tunneling microscopy (STM) studies. We have now used the STM to study the reaction of Se with the GaAs surface and tunneling spectroscopy to determine the change in the Fermi-level position as a result of the Se deposition. Under appropriate deposition and annealing conditions Se forms a well ordered (2×1) reconstructed surface on GaAs(001). The Fermi level on this surface is found to be within 150 meV of the conduction band minimum on heavily n-doped (approximately 6×1018 cm−3 Si) material. STM images show that the kinks in the dimer-vacancy rows of the GaAs(001)-(2×4) reconstruction, which pin the Fermi level on n-type material, are removed when Se is deposited and so the Fermi-level pinning is greatly reduced. In addition, the density of defects (surface vacancies, steps, etc.) is relatively low which will reduce pinning on both n- and p-type material. However, the GaAs(001):Se-(2×1) surface is not sufficiently chemically inert to prevent some oxidation (and presumably pinning) on exposure to the atmosphere. We propose a structural model for the GaAs(001):Se-(2×1) surface that is based on our STM determination of the surface layer composition, published photoemission data which show Se to go below the surface and displace arsenic, and that satisfies electron counting.
Investigation on the effect of isoelectronic substitution in ZnS1−xSex alloys
Authors: Nelson Art J.
Published: July 2002

The composition, structure, and optical properties of thin-film ZnS1−xSex semiconductor alloys were studied by x-ray photoemission spectroscopy, x-ray diffraction, and optical transmission. Nonequilibrium growth of the ternary II–VI semiconductor alloys was accomplished using molecular beam epitaxy with simultaneous electron cyclotron resonance H2S plasma activation to form the ZnS1−xSex alloys. Photoemission measurements were used to identify changes in bulk composition and valence band electronic structure as well as changes in the Zn 3d, Se 3d, and S 2p core lines. X-ray diffraction measurements revealed that these films contain the cubic phase and that the lattice constant decreases with sulfur content. Correlation of these results with growth parameters indicates that substrate temperature, gas flow, and plasma power determine the ZnS1−xSex alloy composition and structure. In addition, optical transmission measurements showed that substitution of S into the ZnSe lattice shifted the cutoff from 460 to 380 nm.
Intrinsic resputtering during film deposition investigated by Monte Carlo simulation
Authors: Bauer Wolfgang , Betz Gerhard , Bangert Herwig , Bergauer Anton , Eisenmenger-Sittner Christoph
Published: July 2002

In sputter deposition intrinsic resputtering is caused by energetic neutral particles which result from the primary sputter events at the target. These energetic particles are target material atoms, known to have energies up to tens of electron volts and sputter gas neutrals backscattered from the target with energies of up to hundreds of electron volts. The yield for each kind of sputter event depends on the mass of the impinging particle and the mass and surface binding energy of the sputtered atom. Therefore, the composition of a binary alloy film with strongly different surface binding energies and masses of the atoms involved in the deposition process varies due to their individual amount of resputter events. To explore the intrinsic resputtering we chose the Cu–Pb system. The gas phase transport of energetic particles from a Cu 2.05 at. % Pb target to a cylindrical substrate and the resputtering effects from the chamber walls as well as the substrate were calculated using the Monte Carlo technique. We observe a Pb concentration of the growing film from zero up to a value six times higher than the target concentration depending on the working gas pressure and the vacuum chamber geometry. Good qualitative agreement between simulations and experiments was observed for several geometries and pressures.
Studies of thin-film growth, adsorption, and oxidation by in situ, real-time, and ex situ ion beam analysis
Authors: Lin Yuping , Krauss A. R. , Auciello O. , Nishino Y. , Gruen D. M. , Chang R. P. H. , Schultz J. A.
Published: July 2002

A time-of-flight (TOF) ion scattering and direct recoil spectrometer (ISS/DRS) has been developed to study the surface composition and reconstruction of metals, metal-oxides, and semiconductors, and to provide in situ characterization of the thin-film deposition process. The in situ, real-time study of Pb, Zr, and Ru ultrathin films produced by ion beam sputter deposition is presented here as the first demonstration of TOF-ISS as a means of characterizing monolayer and submonolayer growth, both in UHV and in mTorr oxygen background. The capability of performing surface analysis at pressures ≳10−3 Torr is unique to pulsed ion beam surface analysis among surface analytical methods and enables the in situ monitoring of oxide thin-film growth processes and surface–gas phase reactions. Using angular-resolved ISS combined with Auger electron spectroscopy, we studied the oxygen adsorption and reconstruction of (001) oriented InSb thin-film surfaces. It was found that the adsorption of molecular oxygen on the InSb (001) surface is consistent with the Langmuir model. Oxygen adsorption preferentially occurs on the antimony sites corresponding to the extension of the lattice into the vacuum and reduces the inward contraction of the first two layers of the clean InSb (001) surface relative to the bulk atomic spacing.
High quality ZnO thin films on InP substrates prepared by radio frequency magnetron sputtering. I. Material study
Authors: Chang S. J. , Su Y. K. , Shei Y. P.
Published: July 2002

High quality ZnO thin films were deposited onto InP substrates by radio frequency magnetron sputtering. It was found that the characteristics of ZnO film depend on deposition parameters, and a detailed study was performed. By adjusting these parameters, we obtained a ZnO thin film with an extremely sharp x-ray diffraction peak with a 0.183° full width at half-maximum. The resistivity of the deposited ZnO film is 1010 Ω cm and its refractive index is close to that of single crystal ZnO. These results indicate that the quality of these ZnO thin films is acceptable for the fabrication of a surface acoustic wave device on InP substrates.
Low outgassing residual gas analyzer with a beryllium–copper-alloy-flanged ion source
Authors: Watanabe Fumio , Kasai Akinari
Published: July 2002

By using a newly developed beryllium–copper (BeCu)-alloy ConFlat flange to house the hot-cathode ion source, a remarkable decrease in the outgassing from a quadrupole residual gas analyzer (RGA) has been achieved. The reduction in outgassing between the new BeCu-flanged RGA and an ordinary stainless-steel RGA of otherwise similar design was a factor of 60 or more in the 10−9 Pa total pressure range. From these results, the possibility of high accuracy residual gas analysis below 10−9 Pa is introduced.
Magnetically confined inductively coupled plasma etching reactor
Authors: Lai C. , Brunmeier B. , Woods R. Claude
Published: July 2002

A planar radio frequency (rf) inductively coupled plasma etching system has been constructed. The plasma is confined by an external multidipole magnetic bucket made of Nd–Fe–B magnets. This magnetically confined inductively coupled plasma system is equipped with a helium backside-cooled electrostatic wafer chuck and a loadlock chamber. A single-sided planar Langmuir probe was used to map electron velocity distribution functions (EVDFs) radially and axially for both Ar and N2 plasmas with rf power up to 1 kW at low pressure (2 mTorr). By rotating the single-sided probe, the authors found that the EVDFs are noticeably anisotropic. The values of the plasma potential, which were highly uniform radially, were independent of the probe orientation, but those of the floating potential depended strongly on it. The radial uniformity and the absolute magnitude of the plasma potential are confirmed by measurements using an emissive probe. The Langmuir probe measurements showed some deviations from Maxwellian EVDFs for both Ar and N2 plasmas. Because of the multidipole confinement the plasma densities are quite uniform axially, and the radial uniformity improves as the axial distance from the quartz window increases. The rf plasma potential fluctuations were also measured, using a capacitive probe.
Methane adsorption and hydrogen isothermal desorption kinetics on a C(001)–(1×1) surface
Authors: Nishimori Toshihiko , Sakamoto Hitoshi , Takakuwa Yuji , Kono Shozo
Published: July 2002

Methane (CH4) adsorption and isothermal hydrogen (H2) desorption kinetics on a C(001)–(1×1) surface have been investigated by observing the surface hydrogen coverage θH which is estimated from the electron-stimulated desorption yield of H+ ions. The time evolution of θH under CH4 exposure, in pressure and temperature ranges of 1×10−8–5×10−7 Torr and 600–800 °C, reveals that the CH4 adsorption is a first-order reaction. The isothermal H2 desorption is conducted in a temperature range of 1095–1270 °C. The time evolution of θH shows that the isothermal H2 desorption is also a first-order reaction. From Arrhenius plots of the reaction coefficients, the activation energies of CH4 adsorption and H2 desorption are evaluated to be 7.3±1.7 and 21±4.9 kcal/mol, respectively. Atomistic kinetics model for CH4 adsorption and H2 desorption are discussed, especially in connection with a recent finding of gas source molecular beam epitaxy of diamond (001) with pure CH4 without any hydrogen or oxygen radicals.
Coadsorption of CO and hydrogen on the Ir(111) surface
Authors: Lauterbach J. , Schick M. , Weinberg W. H.
Published: July 2002

The nonreactive coadsorption of CO and deuterium was investigated with temperature programmed desorption and Fourier transform infrared reflection-absorption spectroscopy. Both chemisorbed CO and deuterium adatoms block the adsorption of one another, and no replacement of either of the adsorbates by the other could be detected. Both the peak position and the linewidth of the CO stretching frequency change upon coadsorption and, together with the thermal desorption spectra, indicate the formation of separate islands of the two adsorbates on the surface.
Process–property relationships between silicon selective epitaxial growth ambients and degradation of insulators
Authors: Gaynor W. , Takoudis C. G. , Neudeck G. W.
Published: July 2002

Comprehensive thermodynamic analyses of the effects of silicon selective epitaxial growth (SEG) environments and low temperature substrate pretreatments on insulator degradation are presented. Silicon nitride is predicted to degrade at about 150 °C higher than silicon dioxide of the same thickness in DCS/H2 ambients at 40 Torr, in agreement with experimental data. Hydrogen/HCl and hydrogen/HCl/dichlorosilane substrate treatments are shown to result in more extensive insulator degradation than a hydrogen bake at the same conditions (e.g., 40–150 Torr, 0.001–1 ppm H2O), also in agreement with experimental data. In low temperature silicon SEG, the addition of ppm levels of a chlorosilane to H2 is predicted to lower the temperature at which substrate surfaces are cleaned in situ by about 150–200 °C, at 0.1–100 Torr, in agreement with experimental observations. Because these thermodynamic analyses take a short computation time (e.g., typically on the order of a few seconds), such results can serve as effective guidelines for substrate surface cleaning and insulator degradation during silicon SEG. Further, these results effectively yield basic process–property relationships between silicon SEG ambients and degradation of insulators with a minimal amount of experimentation.
Preparation of polysiloxane thin films using CO2 laser evaporation assisted by remote radical source
Authors: Fujii Toshiaki , Yokoi Tsuneki , Hiramatsu Mineo , Nawata Masahito , Hori Masaru , Goto Toshio , Hattori Shuzo
Published: July 2002

A simple deposition system using cw CO2 laser for preparation of polysiloxane thin films was demonstrated. Polysiloxane bulk target was evaporated by using CO2 laser irradiation. During film deposition, remote microwave plasma as a radical source was utilized in order to improve the hardness of formed polysiloxane film. Oxygen (O2) gas or water vapor (H2O) was used as a source of reactive species for surface modification of polysiloxane film. The effects of radicals produced by the microwave O2 or H2O plasma on the properties of polysiloxane films were investigated using x-ray photoelectron spectroscopy, Fourier transform infrared spectroscopy, and gel permeation chromatography analyses. Using this system, polysiloxane thin films, of which the chemical structure and composition were close to those of polysiloxane bulk target, were successfully prepared. The molecular weight of the film was about 40 000, which was larger by a factor of 20 than the value of 2100 of the bulk target.
Liquid phase epitaxial growth of Hg1−x−yCdxZnyTe and Hg1−x−yCdxMnyTe from Hg-rich solutions
Authors: Uchino T. , Takita K.
Published: July 2002

Liquid phase epitaxial (LPE) growth from Hg-rich solution is investigated in the case of HgTe-based quaternary semiconductors Hg1−x−yCdxZnyTe and Hg1−x−yCdxMnyTe and the ternary Hg1−xCdxTe. In contrast to the results for Hg1−xCdxTe, the LPE growth can give crystals of quaternary alloys with excellent compositional uniformity. The uniform compositional profiles of the epilayers are revealed by electron probe microanalysis, both in the plane and along the growth direction. The growth of Hg1−xCdxTe by the same LPE method yields a large compositional gradient along the growth direction. Thus we have clearly demonstrated that homogeneity of epilayers are improved by incorporation of Zn or Mn during the crystal growth. A typical sample of as-grown Hg1−x−yCdxZnyTe, with x=0.17 and y=0.10 (Eg≊320 meV at 77 K), showed n-type conduction with a carrier concentration of 1×1016 cm−3 and a mobility of 9×102 cm2/V s at 77 K. As-grown Hg1−x−yCdxMnyTe showed n-type conduction with a carrier concentration of 3×1014 cm−3 and a mobility of 8×104 cm2/V s at 77 K for a typical sample with x=0.16 and y=0.009 (Eg≊150 meV at 77 K).
Si(110)2×3-Sb surface studied with angle-resolved photoemission
Authors: Cricenti A. , LeLay G. , Nesterenko B. , Perfetti P. , Sebenne C.
Published: July 2002

Angle-resolved ultraviolet photoelectron spectroscopy has been used to study the electronic structure of a Si(110)2×3-Sb surface. The surface shows a semiconducting behavior with the highest occupied surface-state band observed around 1.8 eV below the Fermi level (EF). A second state is observed at Γ at 2.2 eV below EF dispersing >2.0 eV towards higher binding energies along the [1̄10] and [1̄11] directions. A third state is observed along the [1̄11] direction around the M point. Surface differential reflectivity experiments showed no optical transitions up to an energy of 3.5 eV, indicating that the minimum energy position of the lowest empty band must be at least 1.8 eV above EF.
Mass spectroscopic study for vaporization characteristics of Ba(TMHD)2 and Sr(TMHD)2 in electron cyclotron resonance-plasma enhanced metal organic chemical vapor deposition
Authors: Lee Joon Sung , Song Han Wook , Kim Kyong Sub , Yu Byoung Gon , Jeong Yon Ho , Jiang Zhong-Tao , No Kwangsoo
Published: July 2002

The decomposition and the degradation characteristics of Ba(TMHD)2 and Sr(TMHD)2 with storage time were analyzed using differential scanning calorimetry. Mass spectrometer monitoring of source vapors with Ar and NH3 carrier gases in an electron cyclotron resonance-plasma enhanced metal organic chemical vapor deposition system was also performed. Introducing NH3 as a carrier gas, significantly improved the volatility and the thermal stability of the precursors, as well as the uniformity and the surface smoothness of strontium carbonate films. Required vaporization temperatures of the precursors were lower with the introduction of NH3 gas than with conventional Ar carrier gas. The degradation with the storage time and with oligmerization at the evaporation temperature for Ba(TMHD)2 was greater compared to Sr(TMHD)2.
Influence of cluster diffusion on the coarsening of Xe films on Pt(111)
Authors: Sholl David S. , Fichthorn Kristen A. , Skodje Rex T.
Published: July 2002

The diffusion of clusters of atoms or vacancies on single-crystal surfaces can have an important impact on the evolution of films. We have investigated the role of cluster diffusion in the coarsening of clusters with a detailed lattice gas model of commensurate Xe films on Pt(111). Both atomic and vacancy clusters can diffuse in this system. We show that, while cluster diffusion and coalescence are the dominant coarsening mechanisms for vacancy clusters, the coarsening of atomic clusters is dominated by Ostwald ripening. We have also used our lattice gas model to test several microscopic assumptions that are made in macroscopic theories of cluster coarsening.
Fabrication of spin-current field-effect transistor structures
Authors: Cabbibo A. , Childress J. R. , Pearton S. J. , Ren F. , Kuo J. M.
Published: July 2002

It has been theoretically proposed that a narrow gap semiconductor field-effect transistor with ferromagnetic contacts for injection of spin-polarized electrons may be used for current modulation. This raises the possibility of electronic devices based on transport of spin-up and spin-down electrons biased and controlled by internal magnetic fields. As an initial step in this direction, we have fabricated GaAs/AlGaAs and InGaAs/AlInAs high electron mobility transistor structures, where the normal AuGeNi source and drain contacts are replaced by sputter-deposited Fe contacts. Mesa fabrication to allow the Fe to contact the two-dimensional electron gas formed at the interface between the doped AlGaAs or AlInAs and the lower bandgap (GaAs or InGaAs) undoped channel was achieved by either wet chemical etching or angled Ar+ ion milling. TiPtAu (1 μm gate width) was employed in both materials systems as a gate contact. The Fe is found to form a rectifying contact to the GaAs channel devices, preventing current injection, but produces a nearly ohmic contact to InGaAs. Improved, bilayer magnetic contacts are currently under investigation for the InGaAs/AlInAs high electron mobility transistor structures in order to produce complete ohmic behavior and establish the feasibility of polarized current injection in these devices.
Microstructural change of TiN films by C and B ion implantations
Authors: Ohara H. , Nakayama A. , Nomura T.
Published: July 2002

C and B ion implantations into TiN films were carried out. The implantation energy was 100 keV, and the ion dose was 1×1018 ions/cm2. Investigations of the implanted layer were carried out by x-ray diffraction analysis and cross-sectional transmission electron microscopy (TEM). Knoop hardness measurements were also made to evaluate the hardness of the modified layer. By x-ray diffraction analysis, TiC was identified in a C ion implanted specimen, and TiB2 was identified in a B ion implanted specimen. From cross-sectional TEM observations of the implanted specimens, it was found that the surface region of the TiN films was not damaged substantially (this was also identified by electron diffraction patterns), and that there was a mixed-textured region with crystalline and amorphous structures in the region with the highest density of implanted elements. However, differences between C and B implantations were also identified in the morphology of the crystalline region and amorphous region. In the C ion implantation, the amorphous region was formed with the lamella structure perpendicular to the ion irradiation direction (parallel to the surface of the film). In the B implantation, the amorphous region was spherically formed. According to the Knoop hardness measurement, the hardness of the TiN film after B implantation increased more than that of the nonimplanted TiN film. On the other hand, the hardness of the TiN films after the C ion implantation tended to decrease compared to the nonimplanted TiN film. The mechanism for improved hardness is presumed to be the result of the formation of a harder compound by reaction between the implanted element and the film element.
Studies of electrical and chemical properties of SiO2/Si after rapid thermal nitridation using surface charge spectroscopy and x-ray photoelectron spectroscopy
Authors: Chan R. W. M. , Kwok R. W. M. , Lau W. M. , Yan H. , Wong S. P.
Published: July 2002

Development of high quality ultrathin dielectric films of thickness less than 100 Å has become an important research subject due to the scaling down of semiconductor devices. In the present study, samples with 20–100 Å SiO2 on silicon were prepared by dry oxidation, and subsequently subjected to rapid thermal nitridation (RTN) using NH3 in the temperature range of 800–1200 °C. X-ray photoelectron spectroscopy and surface charge spectroscopy were applied to study the nitrogen distribution in the dielectric layers, the changes in the interface state density, Dit, and the dielectric breakdown field strength due to the nitrogen incorporation. It was found that nitrogen was mainly incorporated to the dielectric at the dielectric/Si interface without any consumption of silicon in the substrate during RTN. In the study of the electrical properties, we found that RTN led to a slight decrease in Dit and an increase in the breakdown field strength.
Ion-molecule-reaction mass spectrometer for on-line gas analysis
Authors: Bassi D. , Tosi P. , Schlögl R.
Published: July 2002

We describe an apparatus for ion-molecule-reaction mass spectrometry. It is suitable for on-line gas analysis covering the mass range from 1 to 200 amu with a sensitivity of about 1 ppm. The gas to be analyzed is ionized by reaction with a primary ion beam at low collision energy. A mass-selected ion source allows the fast switching among three primary ions beams (Xe+, Kr+, and CF3I+), covering the recombination energy range from 10.23 to 14.67 eV. Calibration measurements and an example of application to the study of heterogeneous catalysis are presented.
Parallel computing and the generation of basic plasma data
Authors: McKoy Vincent , Winstead Carl , Lee Chuo-Han
Published: July 2002

Comprehensive simulations of the processing plasmas used in semiconductor fabrication will depend on the availability of basic data for many microscopic processes that occur in the plasma and at the surface. Cross sections for electron collisions, a principal mechanism for producing reactive species in these plasmas, are among the most important such data; however, electron-collision cross sections are difficult to measure, and the available data are, at best, sketchy for the polyatomic feed gases of interest. While computational approaches to obtaining such data are thus potentially of significant value, studies of electron collisions with polyatomic gases at relevant energies are numerically intensive. In this article, we report on the progress we have made in exploiting large-scale distributed-memory parallel computers, consisting of hundreds of interconnected microprocessors, to generate electron-collision cross sections for gases of interest in plasma simulations.
Fluid simulation of a pulsed-power inductively coupled argon plasma
Authors: Lymberopoulos D. P. , Kolobov V. I. , Economou D. J.
Published: July 2002

A one-dimensional fluid model was developed and used to investigate the spatiotemporal dynamics of a pulsed-power inductively coupled argon plasma at 10 mTorr. Particular attention was devoted to extraction and acceleration of positive ions by a radio frequency (rf) bias applied in the afterglow stage of the discharge. For bias frequencies in the range ω/2π=100 kHz–10 MHz the rf sheath is resistive in nature. Significant oscillations of the ion flux at the driven electrode observed at ωτ≈1 are related to the finite ion transit time τ through the sheath. The latter depends on the sheath thickness which is a complicated function of time in the pulsed plasma. For a constant time-average power, the time-average ion energy flux bombarding the wafer has a minimum with respect to the pulse period. This has implications for the wafer thermal budget.
Role of oxygen in ion-enhanced etching of poly-Si and WSix with chlorine
Authors: Kota Gowri P. , Coburn J. W. , Graves David B.
Published: July 2002

Ion-enhanced etch yields of poly-Si and WSi1.66 with beams of molecular and atomic chlorine and oxygen are reported as a function of neutral-to-ion-flux ratios. The ions used are 500 and 1000 eV Ar+ and 500 eV O2+/O+. Measurements were made in a vacuum chamber with chlorine and oxygen molecules/atoms effusing from an external discharge source as a beam and impacting the selected surface. The etch rates were measured using quartz-crystal microbalances onto which poly-Si and WSi1.66 were deposited. In the ion-flux limited regime, atomic chlorine in comparison to molecular chlorine enhances the etch yield of poly-Si by a factor of 4 and of WSi1.66 by a factor of 9. Therefore, the etch yield selectivity of WSi1.66 over poly-Si, which is 0.7 with molecular chlorine, increased to 1.5 with atomic chlorine in the presence of energetic Ar+ ions. The effect of neutral O/O2 on both molecular and atomic chlorine/Ar+ etching of poly-Si and WSi1.66 is negligible. However, with 500 eV oxygen ions, the etch yields of poly-Si with both Cl and Cl2 are greatly reduced in comparison to those with 500 eV Ar+. The etch yields of WSi1.66 are also lower with oxygen ions, but the reduction is smaller than for the poly-Si case. Therefore, the etch yield selectivity of WSi1.66 over poly-Si increases to 10 with Cl/oxygen ions.
Study of the dynamics of point defects at Si(111)-7×7 surfaces with scanning tunneling microscopy
Authors: Hwang Ing-Shouh , Lo Rong-Li , Tsong Tien T.
Published: July 2002

With a high-temperature scanning tunneling microscope, we study several kinds of point defects at Si(111)-7×7 surfaces. A special type of defect, which we call pseudo-vacancy, appears dark in both tunneling polarities. They are not real vacancies, and they are neither caused by reaction of silicon surface atoms with residual gases, nor due to dopants coming from the Si substrates. On Si(111)-7×7, we can create single vacancies or vacancy clusters at elevated temperatures, which are found to be filled up after a period of time. In addition, we study defects caused by adsorption of O2, CH4, C2H4, and H on clean Si(111)-7×7 surfaces from room temperature to some elevated temperatures. The species produced for adsorption at elevated temperatures are often different from those for adsorption at room temperature. Also, we can observe interesting dynamic behavior, such as site hopping and desorption, at high temperatures. In this work, we find that different surface defects exhibit very different dynamic behavior, which can be used to distinguish between defects.
Inner surface modification of 40Cr steel cylinder with a new plasma source ion implantation method
Authors: Sun Mu , Yang Si-ze , Yao Wen-qing
Published: July 2002

Cylindrical targets of 40Cr steel were immersed in a nitrogen plasma with density 1×1010 cm−3 and implanted at an energy of 30 keV. In order to characterize the inner surface modification effect and the dose uniformity achievable with a new plasma source ion implantation method, the axial distributions of the microhardness, and the implantation dose on the inner surface of the targets were measured, respectively. The experimental results demonstrate that the inner surface of materials can be effectively modified with our method and the measured root-mean-square variations of the retained dose and the microhardness along the axis of the target are well within the acceptable tolerance range for nonsemiconductor applications of ion implantation when the ratio of length to diameter does not exceed 10.
Growth of microcrystalline silicon film by electron beam excited plasma chemical vapor deposition without hydrogen dilution
Authors: Imaizumi Mitsuru , Okitsu Kazuhiko , Yamaguchi Masafumi , Hara Tamio , Ito Tadashi , Konomi Ichiro , Ban Masahito , Tokai Masakuni , Kawamura Kazuhiko
Published: July 2002

Unique characteristics have been obtained for silicon films grown by electron beam excited plasma chemical vapor deposition (EBEP-CVD) in comparison with films grown by conventional plasma CVD. The EBEP-CVD growth of silicon films on single-crystal Si and SiO2 substrates was investigated using SiH4 without hydrogen dilution as a function of SiH4 flow rate, discharge current, chamber pressure, substrate temperature, and electron acceleration voltage. Typical growth rate was ∼0.1 nm/s. Characterization by Raman scattering spectroscopy showed that all the films were microcrystalline with a grain size of approximately 10 nm; the peak intensity ratio of the crystalline portion was greater than 0.6. The hydrogen concentration in the silicon layer under “standard” growth condition was determined by elastic recoil detection analysis to be as much as 19 at. %. This high level of hydrogen incorporation, considered to be facilitated by EBEP of SiH4 gas, seems to play a critical role in the growth process.
Effects of variously configured magnets on the characteristics of inductively coupled plasmas
Authors: Hwang S. W. , Lee Y. J. , Han H. R. , Yoo J. B. , Yeom G. Y.
Published: July 2002

In this study, the effects of axial electromagnet, variously configured multidipole permanent magnets and their combinations, on the characteristics of a square shaped (210 mm×210 mm) inductively coupled plasma source were investigated using a single electrostatic probe for Ar plasmas. The use of multidipole magnets mainly changed the uniformity of the plasma without changing the ion density of the plasma greatly. An optimized shape of the permanent magnets increased the uniformity of the plasma, and the uniformity of the ion density less than 6.0% could be obtained when measured from the center of the chamber to 10 mm before the chamber wall at 600 W of inductive power and 2 mTorr of operational pressure. The use of axial electromagnet mainly increased the ion density with the decrease of the uniformity, and ion density up to 7.5×1011 cm−3 could be obtained with 25 G at 600 W of inductive power and 5 mTorr of operational pressure. The addition of the optimized multidipole magnet to the axial electromagnet also improved the uniformity, and it showed the lowest electron temperature (3 eV) and plasma potential (34VP). The etch uniformities of polysilicon etched using Cl2 gas showed the similar trends as the uniformities of the ion density measured for variously configured magnets.
Production of highly uniform electron cyclotron resonance plasmas by distribution control of the microwave electric field
Authors: Furuse Muneo , Watanabe Seiichi , Tamura Hitoshi , Fukumasa Osamu
Published: July 2002

We have developed the apparatus that can measure the three-dimensional distribution of microwave electric field intensity in electron cyclotron resonance (ECR) plasmas to investigate production and control of ECR plasmas. The relationship between the plasma properties of ECR plasmas and the microwave electric field intensity in plasmas is studied. We have confirmed that the pattern of the radial distribution of the ion saturation current at the electrode is the same as that of the microwave electric field intensity at the ECR zone. If the distribution of microwave electric field intensity at the ECR zone is uniform, the distribution of plasma density on the electrode becomes uniform, even if the distribution of microwave electric field intensity of the other zone is not uniform. Therefore, in order to obtain the optimum distribution of plasma density on the electrode, the distribution of microwave electric field intensity at the ECR zone must be controlled.
Structural analysis of Si(111)-7×7 domain boundaries with takayanaki cores
Authors: Zhao Y. F. , Zhang Z. H. , Yang H. Q. , Xue Z. Q. , Pang S. J.
Published: July 2002

Regular domain boundaries (RDBs) on a Si(111)-7×7 surface are investigated both theoretically and experimentally. Based on the assumption that the RDBs form from a relative shift between two adjacent parts of the perfectly reconstructed lattice, a set of indexes is proposed to classify the RDBs. The irreducible indexes are obtained according to the constraints derived from the lattice-matching condition and the symmetry of the Si(111)-7×7 structure. Along the RDBs, dimer rows should be constructed serving as backbones, and the defects in the RDB should be accompanied by a dimer-adatom stacking fault subunit or unit spanning the RDB as a matching bridge. Most of the RDBs we obtained by direct annealing of the Si(111) surface and through solid phase growth have such features. The atomic structural models compared to the STM images of several examples are presented.
Removal conditions for trapped microparticles in a stored electron beam using electrostatic electrodes
Authors: Saeki Hiroshi , Momose Takashi
Published: July 2002

Microparticle trapping phenomena were observed during beam lifetime decreases in some previously constructed electron storage rings. Fortunately, these harmful phenomena have been rarely observed in recently constructed rings (ESRF, APS, SRRC, SPring-8, etc.) where the vacuum systems are under stricter control for contamination. However, if these phenomena occur in spite of the frequent cleaning of vacuum equipment and stricter contamination controls for the vacuum environment, the harmful particles should be removed. Therefore, we carried out analyses to find the removal conditions for trapped particles using simple electrostatic electrodes for which a voltage is applied during the entire revolution time, except when the bunched electron beam is passing. In the case of the TRISTAN accumulation ring, it was found that trapped microparticles in the range of the continuous trapping condition can be adequately removed using electrodes 30 cm in length, and an applied potential of 30 V, in the passing time of the particle through the electrodes, if the passing time of the particle is more than 0.2 s. The longitudinal motion of the trapped microparticle is also discussed, using a newly developed equation for the longitudinal velocity of a trapped particle. The velocity decides the residence time of the trapped particle passing through the electrodes and the residence time is a key point to remove the particle using the electrostatic electrodes.
Large-diameter microwave plasma source excited by azimuthally symmetric surface waves
Authors: Tuda Mutumi , Ono Kouichi , Ootera Hiroki , Tsuchihashi Masaaki , Hanazaki Minoru , Komemura Toshio
Published: July 2002

This article describes a large-diameter, surface-wave excited plasma (SWP) source designed for materials processing. The plasma reactor employs a launcher of 2.45 GHz azimuthally symmetric surface waves in the field-free region of 24-pole line-cusp magnetic fields, generated by a set of permanent magnets surrounding the reactor chamber walls; the magnets also provide an electron cyclotron resonance (ECR) magnetic field of 875 G near the chamber wall surfaces. Langmuir probe and optical emission measurements were made for characterizing the plasma produced in Ar. After the microwave power was turned on, the discharge was observed to start near the ECR region and then propagate toward the field-free region in the central area of the chamber. Moreover, the discharge was also observed to be excited by ECR at low microwave-power levels, and by surface waves in the field-free region at above a critical power strongly depending on the gas pressure. Such a transition of plasma excitation from ECR to SWP was found to occur under conditions where the plasma electron density exceeds a 2.45 GHz microwave cutoff value of ≈7.4×1010 cm−3. As a result, overdense plasmas with large diameters could be successfully produced with moderate microwave input powers ≲1 kW; the electron density was measured to be Ne∼1−3.5×1011 cm−3 in Ar plasmas, with its spatial variation being ≲5% over a 26-cm-diam area. Furthermore, preliminary experiments of SiO2 etching in pure CF4 plasmas showed that the SiO2 etch rate was typically ∼300 nm/min with a good uniformity ≲3% over an 8-in.-diam wafer.
Intrinsic and extrinsic magnetic properties of the naturally layered manganites
Authors: Berger A. , Mitchell J. F. , Miller D. J. , Jiang J. S. , Bader S. D.
Published: July 2002

Structural and magnetic properties of the two-layered Ruddlesden–Popper phase SrO(La1−xSrxMnO3)2 with x=0.3–0.5 are highlighted. Intrinsic properties of these naturally layered manganites include a “colossal” magnetoresistance, a composition-dependent magnetic anisotropy, and almost no remanence. Above the Curie temperature there is a nonvanishing extrinsic magnetization attributed to intergrowths (stacking faults in the layered structure). These lattice imperfections consist of additional or missing manganite layers, as observed in transmission electron microscopy. Their role in influencing the properties of the host material is highlighted.
Maskless etching of GaAs and InP using a scanning microplasma
Authors: Ochiai Yukinori , Gamo Kenji , Namba Susumu
Published: July 2002

Etching characteristics of GaAs, InP, and other materials using a scanning microplasma have been investigated. This technique utilizes enhanced reaction between a reactive ambient gas and a target at an excited region like a microplasma which is produced by irradiating a scanning focused ion beam. It was observed that the present technique gives an enhanced etching rate over a physical sputter etching and a very smooth etched surface. Dependence of etching rate on bombarding angle and reactant gas flow rate is also measured.
Electronic states of the (100) (2×1) reconstructed Ge surface
Authors: Froelich David V. , Bowen Marshall A. , Dow John D.
Published: July 2002

We present calculations of the surface electronic state dispersion curves E(k̄) of the (100) (2×1) reconstructed surface of Ge, and compare them with recent angle-resolved photoelectron measurements by Nelson et al. We assumed Chadi’s asymmetric dimer model of the surface reconstruction and performed our calculations using the analytic Green’s function technique, with an empirical tight-binding Hamiltonian.
Vibrational study of the SiO2/Si interface by high resolution electron energy loss spectroscopy
Authors: Thiry P. A. , Liehr M. , Pireaux J. J. , Sporken R. , Caudano R. , Vigneron J. P. , Lucas A. A.
Published: July 2002

By using high resolution electron energy loss spectroscopy (HREELS) the surface phonon spectra of SiO2(0001) and of thick amorphous SiO2 layers have been measured. The spectra recorded on the crystalline surface are characterized by three first order peaks at 498, 798, and 1176 cm−1. The HREELS data could be interpreted by the dielectric theory applied to anisotropic material, and the optical constants were compared to infrared spectroscopy values. HREELS spectra as a function of oxide thickness could be obtained from oxidized Si(100) wafers by sputter erosion. Peak positions shifted to lower frequencies and intensities decreased regularly with decreasing oxide thickness. At the interface a transition layer of about 25 Å was observed and carbon contamination was identified. The dielectric theory applied to a thin homogeneous supported film cannot account for the observed frequency shift.
Above-bandgap optical anisotropies in the reflectance spectra of some cubic semiconductors
Authors: Aspnes D. E.
Published: July 2002

I describe some results of the first systematic study of the above-bandgap optical anisotropies of cubic semiconductors. Large anisotropies, of the order of 1% in the differences between reflectances measured for light polarized along different principal axes, are observed. Significant changes are induced by chemical treatments. The effect of microstructure in surface films is described and verified. Analysis of changes induced by exposing H2O-treated (110) Ge surfaces to Br2 in methanol indicates that Br2 is physisorbed on these surfaces with the molecular axes preferentially oriented parallel to 〈11̄0〉.
Electron spectroscopy of vacuum annealing effects on surfaces of some binary and ternary III–V semiconductors
Authors: Massies J. , Rochette J. F. , Delescluse P.
Published: July 2002

It is shown that standard electron spectroscopy techniques such as Auger electron spectroscopy (AES) and electron loss spectroscopy (ELS), when associated with MBE systems, may provide useful information about the clean surface composition changes induced by vacuum annealing of III–V binary or multinary semiconductors. As an illustration of the potential of these types of techniques, annealing experiments were carried out on InP, and on AlxGa1−xAs,AlxIn1−xAs, and GaxIn1−xAs ternary alloy semiconductors grown in situ by MBE. In the case of InP annealing, AES measurements show that phosphorus has a complex behavior near the surface involving several competitive mechanisms. A critical temperature Tc≂450 °C is observed for these mechanisms, leading to an increase of the phosphorus surface concentration for temperature of annealing TaTc. In addition to this result, a study by ELS clearly indicates that indium clustering occurs in the 450–500 °C temperature range. The arsenide alloys exhibit a systematic shift of the surface composition under annealing. For AlxGa1−xAs, above Tc≂550 °C the surface composition evolves towards AlAs with increasing Ta. An even more drastic modification of surface composition is found for AlxIn1−xAs and GaxIn1−xAs: a decrease of In surface concentration is already observed for 450 °C≲Ta≲500 °C. These results are in qualitative agreement with previously reported composition variations of ternary alloy epitaxial layers versus growth temperature determined by Rutherford backscattering and depth profiling Auger analyses.