bluuebunny/crossref_metadata_2025 huggingface dataset:
Contamination by sputtering in mirror field electron cyclotron resonance microwave plasma sources
Authors: Gorbatkin S. M. , Berry L. A.
Published: July 2002

Langmuir probe measurements, visual observation, and Rutherford backscattering spectrometry have been used to investigate source chamber sputtering for electron cyclotron resonance plasma systems operated with Ar, N2, and Cl2. Potentials in the source ≳20 eV combined with high plasma densities (≳1012 cm−3) led to source chamber sputtering and coating of the microwave entrance window. The microwave entrance window coating caused significant absorption of incident microwave power and decreased source efficiency by as much as 50% within 5 min. Operation of the source with an anodized aluminum liner was effective in reducing microwave entrance window coating but resulted in some heavy metal contamination due to sputtering of impurities in the liner itself. Also, checks with secondary ion mass spectrometry indicated some Al contamination from sputtering of the anodized aluminum liner material. Finally, a technique for in situ cleaning of the microwave entrance window was developed and is described in detail.
Langmuir probe and optical emission studies of Ar, O2, and N2 plasmas produced by an electron cyclotron resonance microwave source
Authors: Shatas A. A. , Hu Y. Z. , Irene E. A.
Published: July 2002

An understanding of electron cyclotron resonance microwave plasma discharges requires the measurement of plasma parameters. In argon, nitrogen and oxygen plasmas, cylindrical Langmuir probes were used to determine the variations of plasma parameters (ion density Ni, floating potential Vf, plasma potential Vp, and electron temperature Te) with applied power (100–300 W) and pressures (1–10×10−4 Torr). Simultaneous optical emission (OE) spectra were also obtained, and, using knowledge of excited and neutral peak intensities and transition energies, the electron temperatures were calculated. By the use of the Langmuir probe electron temperature results, the electron temperatures obtained from OE resulted in scaling factors C of 2, 0.15, and 2 eV−0.75 for argon, oxygen, and nitrogen, respectively.
Electronic structure of borane cage molecules adsorbed on Si(111)
Authors: Lee Sunwoo , Li Dongqi , Cendrowski-Guillaume Sophie M. , Dowben P. A. , Perkins F. Keith , Frigo S. P. , Rosenberg R. A.
Published: July 2002

We compare the valence band photoemission resulting from molecular adsorption of nido-decaborane(14) (B10H14) and nido-2,3-diethyl-2,3-dicarbahexaborane on Si(111) at 100 K. The relative shift of the apparent valence band edge with increasing molecular coverage is consistent with the relative energy difference in the highest occupied molecular orbital for these two molecules as inferred from modified neglect of differential overlap calculations. The results suggest that the screening is very similar, despite the very different molecular structures of these two nido cage molecules.
Surface studies of solvent-cast poly(vinyl alcohol-co-vinyl acetate) copolymer films
Authors: Mazzanti John B. , Reamey Robert H. , Helfand Martin A. , Lindley Patricia M.
Published: July 2002

A series of solvent cast poly(vinyl alcohol-co-vinyl acetate) (PVA/PVAc) copolymer films with PVAc concentrations ranging from 0% to 12% have been characterized with bulk nuclear magnetic resonance and surface [variable angle x-ray photoelectron spectroscopy (XPS) and time-of-flight (TOF) secondary ion mass spectroscopy (SIMS)] analytical techniques. PVAc was observed to preferentially segregate to the top most surface region, and despite variations in the bulk levels of PVAc the surface is composed of approximately 40% PVAc. The data suggests segregation is driven by the methyl groups of the acetate functionality and can be predicted based on the minimization of surface energy. TOF–SIMS data aided XPS peak assignments and observed minute manufacturing impurities (Na, K, Ca, and Si) undetected by XPS.
Surface reactions of Ge containing organometallics on Si(100)
Authors: Greenlief C. Michael , Wankum Patricia C. , Klug Debra-Ann , Keeling Lori A.
Published: July 2002

The adsorption and decomposition of germane GeH4 and digermane Ge2H6 on Si(100) have been investigated. Exposure of GeH4 to Si(100) at 110 K results in dissociative chemisorption to GeH3 and H. The adsorption of GeH4 is via a precursor state. Heating to higher temperatures results in the decomposition of GeH3. H2 desorption from GeH4 decomposition exhibits two desorption states. One state is dominated by Si and the second state is influenced by Ge on the surface. The preadsorption of Ge strongly alters the desorption of H2, shifting most of the desorption into the lower temperature state most strongly influenced by Ge. The H2 thermal desorption from the decomposition of Ge2H6 is examined and is qualitatively similar to that of GeH4.
Integration of ferroelectric thin films into nonvolatile memories
Authors: Sinharoy S. , Buhay H. , Lampe D. R. , Francombe M. H.
Published: July 2002

Recent advances in the development of high quality thin films of ferroelectric materials have created renewed interest in ferroelectric random access memory (FERRAM) devices. At the present time, several groups are pursuing the development of FERRAMs, where a thin film ferroelectric capacitor memory element is integrated either adjacent to or directly above the circuit elements in a standard silicon or gallium arsenide integrated circuit. However, these designs provide destructive readout (DRO) only. An alternative monolithic device concept, where the ferroelectric thin film is integrated directly into the semiconductor field effect transistor (FET) element, provides not only nonvolatility, but also nondestructive readout (NDRO). For DRO FERRAM structures, lead–zirconate–titanate is the most widely investigated material at present. At Westinghouse, we are concentrating our efforts on the NDRO ferroelectric memory FET approach, using barium magnesium fluoride (BaMgF4) and bismuth titanate (Bi4Ti3O12) thin films. In this paper, we shall review the current status of the integration of ferroelectric thin films into nonvolatile memory devices, with special emphasis on our own results using BaMgF4 and Bi4Ti3O12.
Pattern transfer onto carbon films on silicon using radio frequency oxygen plasma etching
Authors: Chan K. K. , Amaratunga G. A. J. , Wong T. K. S.
Published: July 2002

Pattern transfer onto semiconducting carbon films with diamondlike properties using optical lithography and radio frequency oxygen plasma etching is reported. Titanium, aluminium, and gold were used as masking materials during oxygen etching. It was found that the titanium mask was most suitable for this process because of better resistance to the oxygen plasma. The microstructures observed were very uniform and well defined.
Chemical beam epitaxy and structural analysis of InAs/InP strained single- and multiquantum well heterostructures
Authors: Freundlich A. , Bensaoula A. , Bensaoula A. H. , Rossignol V.
Published: July 2002

Chemical beam epitaxy growth of pseudomorphically strained InAs/InP (3.1% lattice mismatch) multiquantum wells (SMQW) is studied. Structural properties are investigated as a function of growth temperature within a range of 420–540 °C. The influence of growth interruptions under As flow on the InP interface during the growth of these heterostructures on the interface sharpness is also studied. The interface sharpness when using minimal interruptions, determined through high-resolution x-ray-diffraction analysis of thin (few monolayers) InAs single- and multi-quantum well structures results in less than 1 monolayer roughness over a wide range of growth temperatures (420–490 °C) and high-quality SMQW’s and superlattices were achieved in this manner. Finally the analysis of our data suggests that a small uniform As incorporation (0.6%–1%) in the InP barriers (and buffers) occurs in all the samples presented in this paper. The presence of this As memory effect in the grown heterostructures is related to a much higher As incorporation rate compared to that of P.
Comparison of the operational performance of a compact electron cyclotron resonance plasma source at excitation frequencies of 2.45 GHz or 915 MHz
Authors: Srivastava A. K. , Asmussen J.
Published: July 2002

This article presents the results of a study in which the performance of a compact coaxial electron cyclotron resonance plasma source for molecular-beam epitaxy has been experimentally evaluated and compared at the two microwave excitation frequencies of 2.45 GHz and 915 MHz. Diagnostic measurements, using Langmuir probes and a multigrid energy analyzer, are made at absorbed power levels varying from 80 to 250 W, at flow rates ranging from 2 to 30 sccm and the corresponding pressures of ∼10−5–10−4 Torr. It is seen that the plasma source is capable of producing high density discharges, about high 1010 to low 1011 cm−3, with excitation at either 915 MHz or 2.45 GHz. Also, at either frequency, ion energy distribution functions are relatively narrow, with full width at half-maxima of less than 20 eV for a typical operating condition. However, the average ion energy for a 915 MHz discharge (30–50 eV) is in general higher than the average ion energy of a 2.45 GHz discharge (15–25 eV), when operated at the same power and pressure conditions. As measured by the double Langmuir probe, the electron temperatures of the high energy tail are higher for 915 MHz excitation than similar electron temperatures of a 2.45 GHz excited discharge.
Real-time in situ ellipsometric control of antireflection coatings for semiconductor laser amplifiers using SiOx
Authors: Wu I-Fan , Dottellis J. B. , Dagenais Mario
Published: July 2002

We demonstrate an innovative technique based on real-time in situ ellipsometry to achieve precise monitoring and control of the refractive index of antireflection coatings for semiconductor laser amplifier facets. The refractive index and the layer thickness are extracted every 0.5 s using two thin-film models: the conventional four-medium model which provides an averaged refractive index over the total deposited film, and an adaptive multilayer model which keeps tract of all the previous thin layers that have been deposited and provides a sensitive and instantaneous response to any new refractive index change. A simple procedure to account for polarization effects due to strain in the windows of the evaporator is also described. Using the weighted average of the refractive indices obtained with these two techniques as a feedback parameter, control of the averaged refractive index of SiOx deposited films within ±0.01 and facet reflectivities of order 10−4 or better are reproducibly obtained.
Pregrowth treatment dependence of surface morphology for GaAs grown on exactly oriented (111)A substrates by molecular-beam epitaxy
Authors: Yamamoto Teiji , Inai Makoto , Takebe Toshihiko , Watanabe Toshihide
Published: July 2002

We investigate the dependence of growth layer surface morphology on surface treatment processes, i.e., etching, mounting, and loading wafers before molecular-beam epitaxial growth. The surface morphology of a GaAs growth layer on exactly oriented (111)A GaAs is found to be strongly dependent on stoichiometry and roughness of the surface before growth. Device-quality layers with a good surface morphology were obtained only on the exactly oriented (111)A GaAs wafers etched with NH4OH:H2O2:H2O (2:1:96) etchant, loaded into a growth chamber with little residual As4, and mounted without In. It is very important to use the NH4OH etchant (2:1:96) with (111)A GaAs, because it maintains the surface stoichiometry and smoothness.
Cross-sectional scanning tunneling microscopy and spectroscopy of passivated III–V heterostructures
Authors: Gwo S. , Smith A. R. , Chao K.-J. , Shih C. K. , Sadra K. , Streetman B. G.
Published: July 2002

Structural and electronic properties of Al0.3Ga0.7As/GaAs heterojunction and GaAs pn junction systems are investigated by cross-sectional scanning tunneling microscopy and spectroscopy (XSTM/S). The cross-sectional samples were prepared by passivating ex situ with a sulfide [(NH4)2S] solution and were transferred into an ultra-high vacuum system for STM/S studies. It is found that passivated samples are advantageous for the measurements of scanning tunneling spectroscopy. The STM/S results and the experimental details are reported.
Investigation of thin Ag/Cu-alloy films on Ru(0001)
Authors: Schick M. , Ceballos G. , Pelzer Th. , Schäfer J. , Rangelov G. , Stober J. , Wandelt K.
Published: July 2002

Thin Ag/Cu-alloy films on a Ru(0001) substrate were investigated with respect to the two-dimensional miscibility properties of the two component metals using thermal desorption spectroscopy (TDS), low-energy electron diffraction spectroscopy (LEED), Auger-electron spectroscopy, angle resolved ultraviolet photoemission spectroscopy (ARUPS), and Xe adsorption. The desorption of pure Ag and pure Cu submonolayers from Ru(0001) proceeds with zeroth order kinetics around 1000 and 1200 K, respectively. The Ag-TD spectra from the alloy films show a change from zeroth to first order kinetics as the Cu concentration [ΘAg+ΘCu≤1 ML (monolayer)] increases between 0≤ΘCu≤0.5 ML. TD spectra of adsorbed Xe, in which one clearly can distinguish between submonolayer islands of pure Ag and pure Cu on Ru do not exhibit a distinct heterogeneity in the case of Ag/Cu-alloy films. Instead the desorption peaks shift continuously depending on film composition. Furthermore no Ag induced LEED superstructure typical for pure Ag on Ru(0001) is observed if ΘCu≤0.07 ML is coadsorbed. All the results indicate that Ag is diluted in a Cu matrix, in contrast to the 3D alloy system. Photoemission of adsorbed xenon (PAX) data suggest the formation of densely packed two-dimensional Ag/Cu islands on the Ru(0001) surface. The dispersion of the electronic Ag(4d)- and Cu(3d)-valence bands as derived from ARUPS measurements decreases with decreasing concentration of the respective component again suggesting dilution and increasing interatomic separation between alike atoms. Monte Carlo simulations of the measured Ag-TD spectra yield the lateral interaction parameters, which allows to determine the critical temperature TC, where separation in the Ag/Cu layers should take place. It turns out that TC≤198 K, in agreement with our experimental results.
Silicon oxide deposition in an electron cyclotron resonance plasma with microwave spectroscopic monitoring of SiO
Authors: Chew Kok Heng , Chen Jian , Woods R. Claude , Shohet J. Leon
Published: July 2002

A 2.45 GHz electron cyclotron resonance reactor was used to deposit silicon oxide films using both tetraethoxysilane (TEOS)/O2 and silane/O2. The reactor is equipped with an in situ microwave spectrometer in the frequency range 75–110 GHz, that is used to monitor the gas phase chemical species in this environment. The J=1→2 rotational transition of the vibrational ground state of silicon monoxide (SiO) was detected and monitored in plasmas of both gas mixtures. The integrated intensity of the microwave transition was used to obtain absolute densities of SiO integrated along the path length for both of these plasma chemistries. Silicon oxide films were deposited at pressures of a few mTorr and at low wafer temperature. The properties of the deposited films were characterized using infrared absorption and wet etch rate. The refractive indices of the films were measured by using multicolor ellipsometry. Deposition rates were determined as a function of oxygen/TEOS or oxygen/silane flow ratio. An inverse correlation was found for both sources between SiO abundance and deposition rate. An inverse correlation between SiO abundance and film quality was observed for the silane source.
Processing of PbTiO3 thin films. III. Effects of ion bombardment
Authors: Li Chen C. , Desu Seshu B.
Published: July 2002

The effects of ion bombardment on multicomponent oxides, such as PbTiO3, and multilayer systems have been extensively studied by an in situ stress measurement technique. Energetic ion bombardment was found to accelerate PbTiO3 formation. Both the annealing temperature and the time needed for completion of the reaction were reduced. The apparent activation energy responsible for stress relaxation was found to be 310 kJ/mole for ion-assisted deposition (IAD) films, which is 120 kJ/mole higher than that for non-IAD films. This was attributed to stress reduction in PbTiO3 thin films resulting from ion bombardment. In addition, effects of ion bombardment on the stress of as-deposited multilayers, on the stress development in multilayers during annealing, and on the structure–property-processing interrelationships were also investigated.
Dominant monohydride bonding in hydrogenated amorphous silicon thin films formed by plasma enhanced chemical vapor deposition at room temperature
Authors: Srinivasan Easwar , Lloyd Daniel A. , Parsons Gregory N.
Published: July 2002

Hydrogenated amorphous silicon (a-Si:H) prepared by plasma enhanced chemical vapor deposition (PECVD) with silane, typically shows significant dihydride bonding and high defect density when the substrate temperature is less than 200 °C. Monohydride bonding is associated with low defect densities, and is usually observed only above 250 °C. Using rf (13.56 MHz) PECVD, we have deposited a-Si:H films at a substrate temperature of 35 °C using silane diluted with helium, and found that films with dominant monohydride bonding can be deposited without significant substrate heating. A specific ion enhanced reaction mechanism that is consistent with the results is proposed. As deposited, the films with predominant monohydride bonding show low dark conductivity (10−9 S/cm) and low photoconductivity (10−7 S/cm under 100 mW/cm2 while light illumination). Annealing the films for 3–4 h at 150 °C, resulted in an improved photoconductivity with photo to dark conductivity ratio near 105. These films may be valuable for the fabrication of thin film electronics on novel substrates compatible with only low temperature processes.
Infrared study of Si-rich silicon oxide films deposited by plasma-enhanced chemical vapor deposition
Authors: Sassella A. , Borghesi A. , Corni F. , Monelli A. , Ottaviani G. , Tonini R. , Pivac B. , Bacchetta M. , Zanotti L.
Published: July 2002

A single chamber system for plasma-enhanced chemical vapor deposition was employed to deposit different films of SiOx:N,H with 0.85⩽x⩽1.91, which are studied here by Fourier transform infrared transmission spectroscopy. The sample composition was determined by Rutherford backscattering spectrometry, nuclear reaction, and elastic recoil detection analysis. Moreover, physical properties such as thickness uniformity, deposition rate, density, wet and dry etch rates, and stress are determined. A quantitative study of Si–OH, N–H, and Si–H bonds was performed and interpreted on the basis of the random bonding model; in addition, the presence of NH2, Si–O–Si, H2SiO2, and Si–N groups was detected. The effect of sample annealing at 600 and 900 °C was studied and two species of Si–H bonds were identified, one more stable and the other one easily releasable. A reordering effect of annealing was also detected as a reduction of the amorphous network stress and as the increase of the bond angle in the Si–O–Si groups up to the value typical of thermal SiO2.
X-ray photoemission analysis of chemically treated I–III–VI semiconductor surfaces
Authors: Nelson A. J. , Schwerdtfeger C. R. , Herdt G. C. , King D. , Contreras M. , Ramanathan K. , O’Brien W. L.
Published: July 2002

Device-grade thin-film CuInSe2 was subjected to various chemical treatments commonly used in photovoltaic device fabrication to determine the resulting microscopic surface composi- tion/morphology and the effect on II–VI CuInSe2 heterojunction formation. HCl (38%), Br–MeOH (<1% Br), (NH4)2S, and NH4OH/thiourea solutions were used separately to modify the surface chemistry of the CuInSe2 polycrystalline films. Scanning electron microscopy was used to evaluate the resultant surface morphology. Angle-resolved high-resolution photoemission measurements on the valence band electronic structure and Cu 2p, In 3d, Ga 2p, and Se 3d core lines were used to evaluate the chemistry of the chemically treated surfaces. CdS overlayers were then deposited on these chemically treated surfaces. Photoemission measurements were acquired to determine the resultant heterojunction valence-band discontinuity between the CdS and the chemically modified CuInSe2 surface.
Analysis of the x-ray photoelectron spectrum of Teflon AF 1600
Authors: Sacher E. , Klemberg-Sapieha J. E.
Published: July 2002

The C 1s, F 1s, and O 1s components of the x-ray photoelectron spectroscopy spectrum of Teflon AF 1600 have been obtained, and their constituent peaks were separated and attributed. The effect of an intervening carbon atom on the F 1s spectrum has been shown to decrease the inductive effect of a next-nearest neighbor fragment. An unexpected chemical shift in the O 1s spectrum has been traced to nonbonded steric interactions of close lying rings.
Development of an energetic ion assisted mixing and deposition process for TiNx and diamondlike carbon films, using a co-axial geometry in plasma source ion implantation
Authors: Malik Shamim M. , Fetherston R. P. , Conrad J. R.
Published: July 2002

Plasma source ion implantation (PSII) is a relatively simple technique for the ion implantation/deposition of materials. In PSII a substrate is immersed in a plasma, and high negative voltage pulses are applied to accelerate ions into the substrate resulting in modification of the properties of the material in the near surface region. A technique was developed to produce uniform diamondlike carbon coatings and TiNx films inside and outside a hollow cylinder (substrate). A description of apparatus, experimental methods for this type of deposition process, and preliminary results are presented in this article.
Filtered saddle field fast atom beam deposition of diamondlike carbon films
Authors: Sarangi D. , Panwar O. S. , Kumar Sushil , Dixit P. N. , Bhattacharyya R.
Published: July 2002

An innovation to separate out ionic and neutral radicals from the beam coming out of a saddle field fast atom beam (FAB) source is reported. Diamondlike carbon (DLC) films were grown simultaneously by these ionic and filtered neutral radicals using methane (CH4) as the source gas in the FAB source, on to the substrates placed at different positions inside the deposition chamber. Faraday cup measurements carried out on the two beams confirm the separation of ionic and neutral radicals. It was found that the DLC films deposited by neutral radicals have higher hardness values (980–1070 kg/mm2) than those deposited by ionic radicals (810–970 kg/mm2), whereas, the values of optical band gap and refractive index are found to be higher in DLC films deposited by ionic radicals than those deposited by neutral radicals. It is emphasized that during normal operation of a saddle field source, to grow DLC films, one essentially has a mixed deposition with contributions both from neutral and ionized radicals. Higher hardness values (1050–1150 kg/mm2) of films grown this way may, perhaps, be due to an ion assisted process of network compaction leading to higher degree of overstraining.
Comparison of Si/SiO2 interface roughness from electron cyclotron resonance plasma and thermal oxidation
Authors: Zhao C. , Hu Y. Z. , Labayen T. , Lai L. , Irene E. A.
Published: July 2002

The effects of microwave electron cyclotron resonance (ECR) plasma oxidation on smooth as well as purposely roughened Si surfaces were studied using atomic force microscopy with fractal analysis and the results were compared to thermal oxidation. In addition, spectroscopic immersion ellipsometry was employed to obtain information on the Si/SiO2 interface without the necessity of physically removing the oxide overlayer. The results are concordant and show that during both the ECR plasma and thermal oxidation processes, the Si/SiO2 interface roughness decreases for the purposely roughened Si surfaces, but increases for initially smooth Si surfaces. Besides the initial surface roughness dependence, the change of this interface roughness depends mostly on the extent of oxidation, but also on temperature. The decreasing roughness for plasma oxidation is thought to be driven by the Kelvin equation, but enhanced by an applied external electric field. Ion bombardment, localized defects, and nucleation are eliminated as causative for roughening of initially smooth Si surfaces, and the results suggest a chemically enhanced roughening transition.
Substrate dependence of adlayer optical response in reflectance anisotropy spectroscopy
Authors: Cole R. J. , Frederick B. G. , Weightman P.
Published: July 2002

Reflectance anisotropy spectroscopy (RAS) offers extreme surface sensitivity and can be used to study gas-solid and solid-liquid interfaces. Although the technique has already made a considerable contribution to in situ monitoring of the epitaxial growth of semiconductors, its impact has thus far been limited by difficulties in interpreting experimental results. In particular, RAS spectra are related to both Δε2′ and Δε2″, the real and imaginary parts of the surface dielectric anisotropy, with weighting factors determined by the complex dielectric function of the substrate. Here RAS calculations are performed for a variety of substrates assuming a model overlayer dielectric anisotropy. Three distinct regimes of behavior are observed: RAS spectra can resemble either Δε2′, Δε2″ or −Δε2″ (or some combination of the three) depending on the substrate and the photon energy. It is therefore crucial to properly account for these substrate effects if RAS is to be used to determine the azimuthal orientation of adsorbates or to study the symmetries of surface states, for example. Similar considerations also apply to the related technique of surface differential reflectance. The Fresnel-based theoretical method used here and the substrate optical functions presented should serve as a useful database for future work as RAS is applied to new systems.
Preparation of gold thin films by epitaxial growth on mica and the effect of flame annealing
Authors: Dishner Mark H. , Ivey Michelle M. , Gorer Sasha , Hemminger John C. , Feher Frank J.
Published: July 2002

Highly crystalline thin films of gold were grown on scratch-free mica. Epitaxial growth was accomplished by heating a fleshly cleaved 8 mm×8 mm piece of mica to 380 °C for 12 h at 1.9×10−7 Torr, followed by gold deposition at 1 Å/s and 380 °C until 100 nm was deposited. After flame annealing, these gold films are observed to have grains that are on average 6300 Å in width with a peak to peak topography of a few atomic layers. Adhesion of gold to mica was accomplished by controlling the temperature and length of bakeout in addition to the temperature of deposition. Films prepared in this manner exhibited excellent adhesion when immersed in all solvents except water. The nearly universally [111] terminated gold films were characterized by scanning tunneling microscopy (STM) and transmission electron microscopy (TEM). STM imaging showed that the gold surfaces exhibit the 22×√3 reconstruction. Flame annealing of films removes contaminants and increases the flat surface area by a factor of 25 relative to the unannealed films as was indicated by both STM and TEM.
Recent progress in the functionalization of atomic force microscope probes using electron-beam nanolithography
Authors: Zhou H. , Mills G. , Chong B. K. , Midha A. , Donaldson L. , Weaver J. M. R.
Published: July 2002

We present recent work in which direct-write electron-beam lithography has been used to fabricate near-field optical, thermal and magnetic sensors. Key fabrication issues affecting the performance of these probes are discussed and recent fabrication results are presented.
Formation of large positive silicon-cluster ions in a remote silane plasma
Authors: Kessels W. M. M. , Leewis C. M. , Leroux A. , van de Sanden M. C. M. , Schram D. C.
Published: July 2002

The formation of hydrogen poor cationic silicon clusters SinHm+ with up to ten silicon atoms in an expanding argon–hydrogen–silane plasma has been studied by mass spectrometry and Langmuir probe measurements. Sequential clustering reactions with silane, initiated by silane ions, cause their size to depend on the product of silane density and geometrical path length having possible implications for a-Si:H films deposited by remote plasmas. Reaction rates, estimated by a one-dimensional model, show no strong dependence on the number of silicon and hydrogen atoms present in the ions in contrast with rates determined by ion-cyclotron resonance mass spectrometry studies. Possible causes of the discrepancy are discussed as well as the hydrogen poverty of the clusters. The maximum contribution of the cationic clusters to the growth flux is about 6% for the conditions investigated.
Theoretical studies of surface reactions on metals: I. Ethyl to ethylene conversion on platinum; II. Photodissociation of methane on platinum
Authors: Whitten J. L.
Published: July 2002

An embedding method designed to provide a molecular level understanding of adsorbate energetics and surface reaction mechanisms is presented. Electronic structures, including relativistic effects, are described by an ab initio formalism that permits an accurate determination of energies and adsorbate structure. Applications to catalytic and photochemical reactions on transition metal surfaces are reported. (I) In the catalytic conversion of ethyl adsorbed on platinum surfaces to ethylene, the minimum energy pathway for the transfer of hydrogen to the metal surface is calculated. A detailed description of the transition state is presented. (II) In the photodissociation of methane physisorbed on platinum, results are reported for a methane molecule interacting with an embedded cluster model of Pt(111). Configuration interaction theory is used to sort out states resulting from electron attachment to methane from lower energy states that correspond to metal excitations. Energies of the ground and excited states of the Pt(111)CH4 complex are calculated as a function of geometrical distortions and the distance of methane from the surface. Key steps in the photodissociation process are described.
Dual-doped TMAH silicon etchant for microelectromechanical structures and systems applications
Authors: Paranjape M. , Pandy A. , Brida S. , Landsberger L. , Kahrizi M. , Zen M.
Published: July 2002

Tetra-methyl ammonium-hydroxide (TMAH), is an anisotropic silicon etchant that is gaining considerable use in silicon micromachining due to its excellent silicon etch rate, etch selectivity to masking layers, degree of anisotropy, and relatively low toxicity. However, a shortcoming of TMAH is that it aggressively etches exposed aluminum layers. A dual-doped low concentration TMAH solution is presented, which incorporates a silicate additive for aluminum passivation and an oxidizer additive for improving etch rate and surface quality. Using etch and under-etch experiments, the dual-doped 5 wt % TMAH solution is shown to have characteristics comparable to those of high concentration TMAH solutions with the added benefit of improved etch rate, smoother etched surfaces, and selectivity to silicon over aluminum. Such an etchant can find effective use in batch fabrication and integration of microelectromechanical systems within the framework of standard foundry processes.
Thickness distribution of large-area diamondlike carbon films formed by CH4/H2 supermagnetron plasma chemical vapor deposition with application of a stationary magnetic field
Authors: Kinoshita Haruhisa , Nomura Shyuji , Honda Masahiro
Published: July 2002

Thickness uniformity of diamond-like carbon (DLC) films formed on 5 in. Si wafers by a supermagnetron plasma chemical vapor deposition with applying a static magnetic field was evaluated as a function of radio-frequency (rf) phase difference (RFPD) between two synchronized rf powers (13.56 MHz) supplied to parallel electrodes. When RFPD was 0°, the uniformity of DLC film formed on a lower electrode became poor (about ±9%), and at RFPD of about 180°, it became excellent (about ±3%). Thickness distributions were measured as a function of upper-electrode rf power (UPRF) at lower-electrode rf power (LORF) of 400 W. When UPRF was 0 W (conventional magnetron plasma mode), linearly graded thickness distribution was observed along perpendicular direction to magnetic field lines. At UPRF of 100 W, almost uniform distribution of ±2.9% was obtained, and an inverse thickness distribution to the distribution at UPRF of 0 W was observed at UPRF of 200 W, i.e., inverse magnetron plasma mode. Thickness uniformity also depended on electrode spacing, and good uniformity of ±3% was obtained at a separation of 40–45 mm. By applying a rotating magnetic field, extremely good uniformity of ±1.3% could be obtained.
Simple self-selective method of velocity measurement for particles in impact-based deposition
Authors: Lebedev M. , Akedo J. , Mori K. , Eiju T.
Published: July 2002

A simple, low-cost technique for particles velocity measurement in the gas deposition method (GDM) is reported. The accuracy of the technique is determined only by the precision of measurements of geometrical sizes of deposited pattern. Self-selection of the particles with parameters acceptable for deposition occurs. Under typical deposition conditions the velocities about 200 m/s for ceramic particles and up to 650 m/s for metal ones were detected. The proposed technique allows in situ monitoring during deposition both by GDM and by other deposition methods.
Designs, analyses, and tests of a spiral-grooved turbobooster pump
Authors: Jou Rong-Yuan , Cheng Hong-Ping , Chang Yu-Wen , Chen Fong-Zhi , Iwane Matsume
Published: July 2002

This article shows a spiral-grooved turbobooster pump, which has a momentum transfer-type vacuum pump function, and is capable of operation in a discharge pressure range up to 1000 Pa. Transitional flow pumping speeds are improved by a well-designed midsection element. Pumping performance of this new pump is predicted and examined by both of the computational fluid dynamics method and the direct simulation Monte Carlo method. These two complementary approaches are successfully being used to investigate the whole pumping speed curve from the viscous high-pressure to the molecular low-pressure range. Also, the developed pump is tested on an evaluation system constructed according to JVIS-005 standard. Good agreement between analytical results and experimental data are shown. Furthermore, to achieve a clean, safe, and reliable pumping process, this pump is designed with and operated by an innovative digital magnetic-bearing system.
Microhardness and structural analysis of (Ti,Al)N, (Ti,Cr)N, (Ti,Zr)N and (Ti,V)N films
Authors: Hasegawa Hiroyuki , Kimura Ayako , Suzuki Tetsuya
Published: July 2002

Ti-based binary nitride and ternary nitride films were deposited on cemented carbide by the arc ion plating method and investigated on microhardness, lattice parameter and morphology. Micro-Vickers hardness of TiN, CrN, and ZrN binary films was 2000, 1400, and 1500 HV, respectively. On the other hand, ternary nitrides such as (Ti,Al)N, (TiCr)N, (Ti,Zr)N, and (Ti,V)N with identical atomic ratio against Ti generally had higher hardness of 3100, 3000, 3000, and 2400 HV, respectively. The lattice parameters of both (Ti,Al)N and (Ti,Cr)N were smaller with 4.18 and 4.19 Å. Futhermore, the surface roughness of TiN, CrN, ZrN, (TiAl)N, and (TiZr)N films was all smooth with small number of droplets, while that of (Ti,Cr)N and (Ti,V)N films became rough with large number of droplets.
Epitaxial growth of GaN/AlN heterostructures
Authors: Yoshida S. , Misawa S. , Gonda S.
Published: July 2002

GaN/AlN heterostructures were grown on sapphire by reactive molecular beam epitaxy. The electrical and luminescent properties of the GaN have been studied. The GaN films on AlN have larger Hall mobilities and show more intense cathodoluminescence at the peak of 360 nm, compared with GaN films grown on sapphire. This suggests that the crystalline quality of the GaN is improved by making GaN/AlN heterostructures. The improvement is thought to result from the small mismatch of lattices and the small difference of thermal expansion coefficients between GaN and AlN.
Autocompensation in molecular beam epitaxial gallium arsenide: The (110) orientation
Authors: Ballingall J. M. , Wood C. E. C.
Published: July 2002

Autocompensation has been studied on the (100) and (110) orientations of gallium arsenide. Both n- and p-type silicon-doped (110) gallium arsenide films have been grown by only varying the substrate temperature. Electrical and optical data show that n-type (110) films are heavily autocompensated with silicon.
Copolymers of itaconic acid and methyl methacrylate as positive electron beam resists
Authors: Namasté Y. M. N. , Obendorf S. K. , Anderson C. C. , Krasicky P. D. , Rodriguez F. , Tiberio R.
Published: July 2002

The copolymers of itaconic acid with methyl methacrylate P(MMA–ItA), are expected to perform as highly sensitive electron beam resists based on their high e-beam chain scission efficiencies (Gs). The Gs for P(MMA–20% ItA) was 2.5 times that of PMMA, and the Gs for P(MMA–35% ItA) was nearly 5 times that of PMMA. The copolymers have exhibited improved thermal stability over PMMA, as indicated by a decomposition temperature for P(MMA–20% ItA) that is 30 °C higher than that of PMMA. Infrared analyses of the copolymers showed that anhydride formed during the prebake step of the lithographic evaluation. The anhydride was predominantly a five-membered intramolecular anhydride ring which formed within single monomeric itaconic acid units. Some intermolecular anhydride was suspected because of the reduced solubility of the baked copolymers. The copolymer resists were synthesized to contain 20 and 35 mole% itaconic acid. Copolymers of each composition were evaluated with varying prebake conditions to provide varying amounts of anhydride formation. These resists were then evaluated on the basis of sensitivity, contrast, and resolution. Appropriate solvent systems for developing the lithographic patterns were chosen using a three-dimensional solubility mapping technique based on polar, nonpolar, and hydrogen bonding solubility parameters. P(MMA–20% ItA), with a 160 °C prebake, exposed at 7.5×10−6 C/cm2 with an accelerating voltage of 20 kV, was developed using a mixture of ethyl acetate and MIBK without thinning of the unexposed resist. P(MMA–35% ItA) baked at 120 °C produced 1 μm wide images at 5 to 8 μC/cm2 with a contrast (γ) of 2.5 to 3.5. 10% thinning was observed when developing areas exposed at 8 μC/cm2. Vertical walls were obtained at about 10 μC/cm2, and undercutting was observed with higher doses.
An approach to fabricating sub-half-micrometer-length gates for GaAs metal-semiconductor field-effect transistors
Authors: Holdeman L. B. , Barber R. C. , Abita J. L.
Published: July 2002

A process for fabricating sub-half-micrometer-length gates for GaAs MESFETs is described. This process, which uses conventional photolithography, incorporates a number of special techniques to produce the gates from a photomask having 1-μm-length gate patterns. Gates produced by this process have shapes and cross-sectional areas that are comparable to those of gates produced by liftoff using sub-half-micrometer electron-beam lithography. Gates with lengths less than 0.2 μm have been fabricated.
Atomic and electronic structures of (111), (211), and (311) surfaces of GaAs
Authors: Chadi D. J.
Published: July 2002

The results of calculations on the atomic and electronic structures of relaxed and reconstructed GaAs (111), (211), and (311) surfaces for A and B orientations are presented. Vacancy formation is calculated to be exothermic on the Ga (111) surface but endothermic on the As (1̄1̄1̄) surface. The (211)A surface is nonmetallic and has an occupied surface band near the bulk conduction band minimum for both 1×1 and 2×1 periodicities. The (211)B surface is also nonmetallic but there are no surface states in the band gap. The (311)A- and (311)B 1×1-surfaces are both metallic with 5/8 and 3/8 full surface bands, respectively, in the band gap.
Morphology of GaAs and AlxGa1−xAs grown by molecular beam epitaxy
Authors: Stall R. A. , Zilko J. , Swaminathan V. , Schumaker N.
Published: July 2002

In this paper two major morphological defects that occur in the growth of GaAs and AlxGa1−xAs by molecular beam epitaxy (MBE) are discussed. A uniform, fine scale (<1000 Å period) roughness found on AlxGa1−xAs wafers grown at certain temperatures is shown to result from the presence of a thin Ga layer that has segregated on the surface during growth. The surface roughness leads to high interfacial recombination velocities at GaAs–AlxGa1−xAs heterojunctions and strongly degrades heterostructure device performance, especially lasers. Larger (<20 μm) but localized (density ∼103–105 cm−2) oval defects have been proposed to result from spitting of globules of material from the group III element effusion cells. Here, evidence will be presented in support of this hypothesis. The shape of these oval defects as well as the AlxGa1−xAs surface roughness are shown to be related to the anisotropy of the interfacial energy of the group III elements on GaAs and AlxGa1−xAs.
Ion projection lithography machine IPLM-01: A new tool for sub-0.5-micron modification of materials
Authors: Stengl G. , Löschner H. , Maurer W. , Wolf P.
Published: July 2002

An ion projection lithography machine uses ions as the information carrier in a demagnifying step-and-repeat exposure system. With an IPLM sub-0.2-micron resolution can be obtained combined with an extremely high depth of focus—more than 100 μm. The use of a reliable and stable duoplasmatron ion source with high brightness and high angular current density is significant for this machine. A preprojective lens octupole permits an electrostatic shift of the ion image in x and y directions, and a solenoid at this site enables a rotation of the ion image through the action of the axial magnetic field. Furthermore, the scale of the projected ion image can be adjusted electronically within ±3%. Thus fine adjustment for die-by-die alignment can be done without mechanical movements. An ion projection lithography machine IPLM-01 with a total height of 2.5 m and a floor space of 2 m2 has been built. By inserting a mask consisting of a grid of pinholes an ion multibeam scanning tool (IMBS) is generated. Using demagnifying projection an IMBS enables the production of gratings with sub-0.2-μm periodicity and adjusted scale.
A plasma x-ray source for x-ray lithography
Authors: Okada I. , Saitoh Y. , Itabashi S. , Yoshihara H.
Published: July 2002

Employing a gas-‘‘puff’’ z-pinch plasma, a high brightness and compact plasma x-ray source has been constructed by using a high-repetition-rate discharge and a new x-ray extraction method. The high-repetition-rate discharge (3 Hz) is attained by using a fast-acting gas valve, capable of operating stably under gas plenum pressures below 300 Torr. This low gas pressure discharge makes possible high-conversion efficiency of electrical input to x-rays, highly reliable plasma pinching, and a drastic reduction of debris resulting from electrode vaporization. An axial x-ray exposure is required to reduce the blur in pattern replication caused by the penumbral effect. To carry out the axial exposure, the high-energy particles emitted from the plasma are removed using a plasma reflector plate and magnet. The x rays are efficiently extracted through a window highly transparent to x rays. With this x-ray source, 9–14 Å x rays with 200 J per pulse (600 W average power) are obtained using Ne gas plasma in a 3 Hz operation.
A self-aligned cobalt silicide technology using rapid thermal processing
Authors: Van den hove L. , Wolters R. , Maex K. , De Keersmaecker R. , Declerck G.
Published: July 2002

The feasibility of a self-aligned silicide technology based upon cobalt has been investigated. Silicidation reactions were performed by means of rapid thermal processing. Phase sequence, layer morphology, and reaction kinetics were studied by XRD, SEM, RBS, AES, and TEM. Extremely smooth, highly conductive (16 μΩ cm) CoSi2 films were formed by direct reaction of Co on Si, without significant lateral silicide formation at oxide edges. Shallow arsenic junctions were successfully silicided and low contact resistances were obtained on n+ and p+ Si.
Tight-binding theory of heterojunction band lineups and interface dipoles
Authors: Harrison W. A. , Tersoff J.
Published: July 2002

A tight-binding theory of semiconductor heterojunction band lineups is presented. Interface dipoles are shown to play a crucial role in determining lineups, so that lineups obtained by using the vacuum level as a reference (e.g., the electron affinity rule) are not reliable. Instead, the self-consistent lineup can be obtained approximately by aligning the average sp3 hybrid energies in the respective semiconductors. Numerical results are provided and compared with experiment, and the approximations and accuracy in this approach are discussed. The application of these ideas to Schottky barriers is also considered.
Time-resolved spectroscopic studies of the ultraviolet-laser photolysis of Al alkyls for film growth
Authors: Eres D. , Motooka T. , Gorbatkin S. , Lubben D. , Greene J. E.
Published: July 2002

Time-resolved optical emission spectroscopy, with a resolution of ∼10 ns, was used to investigate the formation of excited photofragments during KrF laser-irradiation of trimethylaluminum (TMA) and triethylaluminum (TEA). The gases were introduced into a vacuum chamber as pulsed molecular beams expanding from a free-jet nozzle. The time-dependence of the fluorescence intensity was measured at various positions, corresponding to different gas pressures P, along the molecular beam. In the case of TMA, the primary peaks observed were the Al 4s 2S→3p 2P atomic transition and the CH A 2Δ→X 2Π (0,0) band. The CH intensity ICH following a laser pulse decreased exponentially with a 1/e decay time τCH ranging from ∼530 ns, in agreement with the radiative lifetime of CH 2Δ(v=0), in the low pressure region of the molecular beam, to ∼150 ns at high pressures. The decrease in τCH with increasing PTMA was due to collisional quenching. The decay of the Al emission intensity IAl was nonexponential since the radiative lifetime of the Al 2S state, 6.8 ns, was less than the laser pulse width, ∼15 ns. The rise times of IAl and ICH, on the other hand, were both <10 ns indicating that CH, like Al, is formed photolytically rather than through subsequent collisions involving photofragments. Substituting TEA for TMA suppressed the CH signal while a new molecular band due to AlH [the (0,0) band of the A 1Π→X 1Σ+ transition] was observed in addition to the atomic Al 2S→2P transition. The rise time of IAlH was also <10 ns indicating that it too was formed photolytically. τAlH was ∼80 ns in agreement with the published AlH radiative lifetime. The significance of these results on the mechanisms of TMA and TEA photodecomposition and C incorporation in Al films grown by KrF-laser photolysis is discussed.
Wavelength dependence of optically induced oxidation of GaAs(100)
Authors: Yu C. F. , Schmidt M. T. , Podlesnik D. V. , Osgood R. M.
Published: July 2002

The wavelength dependence of optically induced, room-temperature oxidation of GaAs (100) is reported. The sample illumination was performed with either continuous wave (cw) or pulsed-laser sources radiating at different wavelengths, in the range of 248–514 nm. The thickness of optically induced oxides, ranging from 1 to >50 Å, was measured with x-ray photoelectron spectroscopy. It was found that the oxidation is always much more rapid in deep-ultraviolet than in near-ultraviolet or visible wavelength regions. This effect is attributed to the generation of hot carriers at the semiconductor surface under ultraviolet light.