bluuebunny/crossref_metadata_2025 huggingface dataset:
Directionality of sputtered Cu atoms in a hollow cathode enhanced planar magnetron
Authors: Turner G. M. , Rossnagel S. M. , Cuomo J. J.
Published: July 2002

Angular distributions of sputtered Cu atoms in a planar magnetron discharge have been measured using a directional quartz microbalance. The discharge, in both Ar and Kr gases, was enhanced at low pressures, e.g., 0.07 Pa, using a hollow cathode electron source. Several means of improving the directionality, i.e., decreasing the angular spread of the sputtered atoms, were investigated. Increasing the discharge voltage to 770 V and increasing the gas pressure to not more than 1 Pa (for a throw distance of 50 mm) marginally improved the directionality of the angular distribution. Significant directionality was achieved using filter collimators which consisted of an array of collimating tubes. Our measurements show that in the absence of gas scattering collisions the collimating effect can be described by geometric shadowing. A Cu cathode with an array of collimating holes machined into the surface was shown to have a collimating effect at high discharge voltages and low current densities. We develop a simple model of the trajectories of ions approaching the cathode to explain the dependence of the angular distribution on the discharge conditions and radial position.
Microstructure of a sputtered Ti film on an indium tin oxide substrate
Authors: Yamashita Hirofumi , Yamaguchi Tetsuya , Miyagawa Ryohei
Published: July 2002

A distinctive dependency of sputtered Ti film qualities on substrate material has been found. A 5000-Å-thick Ti film, deposited by dc magnetron sputtering, on a 350-Å-thick indium tin oxide (ITO) film showed unique properties, such as resistivity, stress, and its microstructure, which were different from those of Ti on other substrates: a bare Si〈100〉 substrate or a borophosphosilicate glass substrate. Results of transmission electron microscopy and x-ray diffraction spectroscopy showed that the morphology and crystallographic properties of Ti films on ITO substrates were quite different throughout 5000 Å thickness from those on other substrates, whereas the deposition environment was identical for all substrates. These results suggest that the first stage of Ti film growth is a conclusive factor for determining the film microstructure and its other qualities.
Highly transparent and conductive group IV impurity-doped ZnO thin films prepared by radio frequency magnetron sputtering
Authors: Sato Hirotoshi , Minami Tadatsugu , Takata Shinzo
Published: July 2002

Highly transparent and conducting group IV impurity-doped ZnO thin films have been prepared on low-temperature substrates below 140 °C by rf magnetron sputtering. Resistivities of 4–8×10−4 Ω cm and an average transmittance above 85% in the visible range were obtained for ZnO films doped with Si, Ge, Ti, Zr, or Hf. The stability of resistivity for use in high-temperature atmospheres was significantly improved by the impurity doping. On the contrary, the resistivity of ZnO films doped with Sn or Pb was higher than that of an undoped ZnO film, and these films were discolored.
Reactive magnetron sputter deposition of niobium nitride films
Authors: Wong M. S. , Sproul W. D. , Chu X. , Barnett S. A.
Published: July 2002

The high-rate reactive magnetron sputtering process by controlling the partial pressure of the nitrogen gas was used to deposit niobium nitride films. Despite the complexity shown in phase diagram of Nb–N, only three different crystalline phases, Nb metal, cubic δ-NbN, and hexagonal δ′-NbN, were observed in the parameter space explored by sputtering a niobium target in an atmosphere of argon and nitrogen. The effects of three deposition parameters including nitrogen partial pressure, target power, and substrate bias voltage were explored. All the deposition parameters affected the formation of different phases, the preferred orientation, and the relative amount of each phase formed, which, in turn, affected the properties of the coatings. The hardness of these reactively sputtered niobium nitrides ranges between 1700 and 4100 kgf/mm2 HV0.025. The highest hardness is significantly higher than the reported hardness value, 1400 kgf/mm2, for bulk niobium nitride, and the primary factor for the hardness increment is due to the effects of low energy ion bombardment during film growth.
Angle-resolved photoemission and band structure of the alloy Al0.5Ga0.5As compared to that of the superlattice [(AlAs)2/(GaAs)2]10
Authors: Zhang X. D. , Riley J. D. , Leckey R. C. G. , Kemister G. , Denecke R. , Faul J. , Ley L.
Published: July 2002

A comparison between the electronic structure of the alloy Al0.5Ga0.5As and that of the superlattice [(AlAs)2/(GaAs)2]10 as determined by angle-resolved photoelectron spectroscopy is presented. Experimental data have been acquired and interpreted according to identical methodologies for the two materials. A mini band gap observed in the superlattice due to the artificially induced periodicity in the growth direction is not present in the alloy. This suggests that the alloy as grown, exhibits no evidence of self-induced long range order. The critical point energy X3v of the alloy is found to lie closer to the value for AlAs than that for GaAs, in agreement with a nonlinear interpolation scheme, and to be higher than the Γ̄4v(X3v) point of the superlattice.
Refrigerator-cooled bakeable-type cryopump at 3 K for extremely high vacuum
Authors: Matsui Y. , Ohzora H. , Yamakawa H.
Published: July 2002

A compact Joule–Thomson (JT) cooling system was adopted to a new type of cryopump which has three cryopanels. The refrigerator system is composed of a JT loop directly connected to the cryopanels and a Gifford–McMahon (GM) refrigerator for precooling. The cryopanels were cooled to the temperatures of 3, 20, and 80 K with circulating cold helium from the closed JT loop. We made an evaluation test of cooling and pumping capabilities and proved its potential capability for the production of extremely high vacuum. Connecting a test dome made of stainless steel to the pump, the volume has been evacuated to extremely low pressure less than 1×10−10 Pa in 11 h after vacuum bakeout.
Ultrahigh vacuum microscopy of the Si(111) boron √3×√3R30° surface
Authors: Marks L. D. , Ai R. , Savage S. , Zhang J. P.
Published: July 2002

The intensities of the diffraction spots for the boron induced √3×√3R30° Si(111) reconstruction in a bulk electron microscope sample examined in ultrahigh vacuum are compared with the results of multislice simulations. The intensities of the spots support the relaxed S5 model. We rule out the existence of any subsurface structure such as the stacking faults present in the Si(111) 7×7 surface.
Influence of energy reflected from the target on thin film characteristics
Authors: Winters Harold F. , Coufal H. J. , Eckstein W.
Published: July 2002

It has been recognized since the 1960’s that bombardment of a growing thin film by energetic particles strongly influences film properties. Particle bombardment has generally been accomplished by accelerating ions into the growing film. However, it has also been recognized since the 1960’s that energetic neutral particles originating at the target also bombard films grown by physical sputtering. It has been frequently suggested that the properties of sputtered films are influenced by bombardment with particles from this source. Nevertheless, a lack of the necessary information has made it difficult to make quantitative (or even semiquantitative) estimates of the magnitude of the energy deposited into the film. A systematic study of the energy reflected from the surface by normally incident, singly charged noble-gas ions on five substrates of different masses has recently been published. These data along with sputter yields from the literature allow estimates to be made which were previously unavailable. The energy reflected from the target is carried away by electrons, sputtered particles, and reflected ions (neutrals). The purpose of this article is to provide basic information which will allow thin film scientists to estimate the influence of various experimental parameters on the amount of energy arriving at the growing film. The energy reflected from the target per sputtered atom will be given as a function of ion mass, target mass, and ion energy. trim.sp Monte Carlo calculations will be used to estimate the ratio of the energy carried away by sputtered atoms to that carried away be reflected ions. Calculations will also be used to estimate the average energy of the sputtered atoms as a function of ion mass, substrate mass, and ion energy. It will be shown how data presented in this article can be used to make estimates for other elements in the periodic table. It will also be shown how this information can be used to guide the adjustment of experimental parameters in sputtering environments so as to control film characteristics.
Structural and morphological characterization of Nb2O5 thin films deposited by reactive sputtering
Authors: Rosenfeld D. , Sanjinés R. , Lévy F. , Buffat P. A. , Demarne V. , Grisel A.
Published: July 2002

Amorphous Nb2O5 thin films of three different thicknesses (10, 100, 400 nm) were deposited onto SiO2/Si substrates by reactive sputtering in an Ar–O2 plasma. Thermal treatments were performed at different temperatures between 500 and 1100 °C. The structural and morphological evolution with temperature is shown to be dependent on the film thickness. At 600 °C, the films essentially crystallize in the TT phase. On the thickest films, the T phase also appears. Annealing at higher temperature progressively increases the concentration of the T phase. The films show large flat grains extending over the whole film thickness. In addition, a large number of polyhedral bubbles is present in the 100 and 400 nm films due to Ar atoms trapped during sputtering. After annealing at 1100 °C the Ar bubbles are no longer present and partial diffusion of the films into the substrate is observed. The modification at high temperature, explained either by the M or the H phase, is favored on the thickest films and leads to plate shaped grains.
Effect of surface microphase-separated structure on interaction between biological components and multiphase polymer surface
Authors: Takahara Atsushi , Korehisa Kinzo , Ge Shou-Ren , Kajiyama Tisato
Published: July 2002

Polystyrene-poly(butadiene-co-hydroxylated butadiene)-polystyrene triblock copolymer (SHBS) with hydrophobic-hydrophilic microdomain structure has been prepared through the hydroxylation of polybutadiene (PBD) block of anionically polymerized SBS triblock copolymer. X-ray photoelectron spectroscopic and contact angle measurements revealed that the environmentally induced surface reorganization took place after exposure of the film to water in the case of low degree of hydroxylation of PBD block. The interaction between plasma protein and the SHBS surface has been studied on the basis of transmission electron microscopic observations of the specimen after immersing it in human serum albumin (HSA) and human fibrinogen (HFN) solutions. The adsorbed HSA and HFN were labeled with colloidal gold and the modified PBD block was stained with osmium tetroxide. Thus, the domain recognition of plasma protein can be analyzed. The amount of plasma protein adsorbed per unit area on PS domain did not depend on the degree of hydroxylation of PBD block. However, the amount of plasma protein adsorbed on the hydroxylated PBD block decreased with an increase in degree of hydroxylation. These behaviors can be ascribed to the selective protein adsorption onto hydrophobic phase in order to minimize the interfacial-free energy between polymer surface and plasma protein solution.
Molecular films from the polymerizable lipid ethyl morpholine pentacosadiynoic amide
Authors: Sullivan Brian , Ribi Hans O. , Tillmann Ralf W. , Hofmann Ulrich G. , Gaub Hermann E.
Published: July 2002

A new polymerizable lipid, ethyl morpholine pentacosadiynoic amide (EMPDA), was synthesized. Monomeric and polymeric films formed from this lipid at the air–water interface were investigated by microfluorescence filmbalance techniques. Below 25 °C, monomeric EMPDA exhibited a pronounced fluid–solid coexistence with a transition enthalpy of ∼100 kJ/mol at room temperature. The coexistence pressure was found to increase with decreasing pH; below pH 4.5 no fluid–solid coexistence was measurable. Microfluorescence revealed that large achiral single-crystalline domains grow in the coexistence regime. Upon ultraviolet exposure only the lipids in the crystalline domains were found to polymerize, indicating that the polymerization is a topochemical reaction. The polymerized domains exhibited a pronounced intrinsic fluorescence with a strong excitation anisotropy which is correlated with the macroscopic crystal axises. Polymerized films transferred onto wafers with thermally grown silicon oxide were investigated by atomic force microscopy. In the polymeric domains, stripelike corrugations were found with an orientation parallel to the fluorescence polarization. At high magnifications molecular resolution images were obtained. The lattice constants of the crystalline arrangement of the lipids are a=0.51±0.03 nm, b=0.48±0.06 nm, α=74±7°. Lateral force images revealed that the friction between tip and sample is dependent on the orientation of the polymer backbone with respect to the fast scan direction.
Low voltage and high speed operating electrostatic wafer chuck using sputtered tantalum oxide membrane
Authors: Nakasuji Mamoru , Shimizu Hiroyasu , Kato Takaaki
Published: July 2002

An insulator figure of merit for an electrostatic wafer holder is introduced. A sputtered Ta2O5 membrane has a maximum figure of merit compared to other candidate dielectric coatings, e.g., Al2O3 and SiO2. The breakdown strength of sputtered Ta2O5 coatings can be optimized by controlling working gas pressure and oxygen concentration: a holding pressure that exceeds 30 gF/cm2 (2942 Pa), when 60 V dc is applied in atmosphere. The pressure is not influenced by the duration of the applied voltage. The residual pressure, after voltage is turned off, decreases to 1/50 of initial pressure within 1 s. The breakdown voltage for 60 cm2 area wafer holder exceeds ±290 V. A sputtered Ta2O5 coating can also be used to smooth relatively rough ceramic substrates. When a polished Al2O3 mixed with ZrO2 ceramic surface is coated with 10 μm thick sputtered Ta2O5 film, good substrate material for an electrostatic chuck is obtained. The sputter rate for the Ta2O5is much larger than that for the Al2O3 or SiO2.
Morphology and bonding measured from boron-nitride powders and films using near-edge x-ray absorption fine structure
Authors: Terminello L. J. , Chaiken A. , Lapiano-Smith D. A. , Doll G. L. , Sato T.
Published: July 2002

Bonding in the hexagonal, cubic (zincblende), rhombohedral, and wurtzite phases of boron nitride was characterized using core-level photoabsorption. In the boron and nitrogen 1s photoabsorption cross section we observed resonances that were unique to each of the phases and that were associated with the sp2 or sp3 bonding present. These spectroscopic standards were then used to characterize the bonding and morphology in an incoherent thin film of BN based on its core-level photoabsorption. The film studied had predominantly sp2 (hexagonal-like) bonding with some evidence of sp3 (cubic-phase) bonds.
Performance of an ionization gauge with a large-angle ion deflector. I. Total pressure measurement in extreme high vacuum
Authors: Oshima C. , Otuka A.
Published: July 2002

Performance of the ionization gauge with a large-angle ion deflector (254.6°) has been examined in extreme high vacuum. We have estimated 4×10−13 Pa to be the lowest measurable limit of the gauge due to soft x-ray noise (1-min period of measurement) and to be less than 2×10−13 Pa for electron stimulated desorption ion noise. The sensitivity of the gauge was 0.018 Pa−1 for hydrogen. By use of a channeltron multiplier for ion detection, the sensitivity of the gauge is improved: hence, a pressure of ∼3×10−11 Pa is easily measured at an emission current <0.1 mA. Deviation from the linear relation of ion current versus emission, allows outgassing from the gauge to be detected.
Critical ion energy and ion flux in the growth of films by plasma-enhanced chemical-vapor deposition
Authors: Martinu L. , Klemberg-Sapieha J. E. , Küttel O. M. , Raveh A. , Wertheimer M. R.
Published: July 2002

Dual-mode microwave/radio frequency plasma-enhanced chemical-vapor deposition allows one to decouple ion bombardment effects from processes in the discharge volume. This approach has been used to deposit three types of hydrogenated amorphous films at low substrate temperature and high deposition rate (∼10–20 Å/s): SiNx, SiO2, and a-C:H. For each of these materials, we have determined critical values of the negative bias potential, VB,C, of the average ion energy, Ēi,c, and of the ion/condensing-atom flux ratio (φi/φn)c, which characterize the transition from a porous to a densely packed microstructure. The evaluations are based on measurements of the films’ resistivity, dielectric loss tangent, microhardness, density, and stress. The Ēi,c, (φi/φn)c values found are: 170 eV, 0.60 for SiNx; 70 eV; 0.26 for SiO2; and 80 eV, 0.28 for a-C:H. Ion bombardment at energies above Ēi,c has been found to account for a large portion of hydrogen in the films which is not chemically bonded. The results are interpreted in terms of a growth process involving surface diffusion of precursor species, and subplantation in hydrogen-rich surfaces.
Deposition and characterization of nanocrystalline diamond films
Authors: Gruen Dieter M. , Pan Xianzheng , Krauss Alan R. , Liu Shengzhong , Luo Jianshu , Foster Christopher M.
Published: July 2002

Highly uniform, smooth nanocrystalline diamond films have been fabricated with a magnetoactive microwave chemical vapor deposition system. The top and bottom magnet currents were 145 and 60 A, respectively, while the microwave power and substrate temperature were controlled at 1500 W and 850 °C, respectively during deposition. The total processing pressure was regulated at 40 Pa (300 mTorr) with gas-flow rates of 30 sccm of hydrogen, 2.4 sccm of methane, and 1 sccm of oxygen. Diamond films obtained under these conditions have grain sizes between 0.1 and 0.3 μm, and a mean roughness of 14.95 nm. The growth rate is 0.1 μm/h. Characterization techniques have involved x-ray diffraction, Raman spectroscopy, scanning electron microscopy, atomic force microscopy, and transmission electron microscopy. Both x-ray and electron diffraction patterns show no evidence of graphitic phase. Although a high density of twins and stacking faults was revealed by high-resolution electron microscopy, compact diamond grains, and clean intergranular boundaries (no graphitic phase) were observed.
Low contamination ultrahigh vacuum system of the Synchrotron Radiation Research Center 1.3 GeV electron storage ring
Authors: Hsiung G. Y. , Huang J. R. , Wang D. J. , Shyy J. G. , Lee J. C. , Sheu R. J. , Tzeng H. S. , Hsu S. N. , Perng S. Y. , Hsiao K. M. , Wey W. D. , Chen J. R. , Liu Y. C.
Published: July 2002

The vacuum system of the Synchrotron Radiation Research Center 1.3 GeV electron storage ring was designed as a low contamination ultrahigh vacuum system. In addition to the standard treatments for the ultrahigh vacuum components, several contamination reduction methods, such as oil-free machining processes, completely oil-free pumping systems, and dust-controlled installation processes, were adopted in the manufacturing processes. The benefits of the low-contamination treatments were verified by the resultant fast-beam cleanup, low degree of dust trapping, and low partial pressures of the carbonaceous residual gases in the vacuum system.
Spherical aberration correction of electrostatic lenses using spherical meshes
Authors: Kato M. , Sekine T.
Published: July 2002

The spherical aberration of electrostatic lenses can be corrected for the aperture angle of up to 60° by introducing spherical meshes. The principle of correction is based on the capability of stigmatic imaging by a spherical refractive surface in light optics. The electrostatic potential distribution around a mesh required for the correction was studied using the analytical expression of the general solution of the Laplace equation, and the amount of aberration was determined by ray tracing. It is shown that the sign of spherical aberration at a virtual image produced by the field near the mesh can be made positive or negative, according to the position of the object and the degree of deformation of the electrostatic field from spherical symmetry when retreating from the mesh surface. It thus becomes possible to cancel the spherical aberration of a focusing field which follows the field near the mesh, and a total lens field without spherical aberration is realized. The possibility of canceling the spherical aberration is verified in a practical design example of an extraction lens for electron spectrometers, which may increase the sensitivity to much higher than that obtained with conventional lenses.
The dependence of the characteristics of a rotating disk vacuum gauge on disk sizes and rotor speed
Authors: Chew A. D. , Chambers A. , Pert G. J. , Troup A. P.
Published: July 2002

The characteristic edge effect loss factor of a rotating disk vacuum gauge has been measured experimentally in hydrogen, helium, nitrogen, and krypton. The results are in good agreement with analytical calculations at low speeds and Monte Carlo calculations at high speeds. The characteristics of the gauge in various unequal size disk configurations measured in nitrogen are also presented.
Formation of C–N thin films by ion beam deposition
Authors: Boyd K. J. , Marton D. , Todorov S. S. , Al-Bayati A. H. , Kulik J. , Zuhr R. A. , Rabalais J. W.
Published: July 2002

Thin carbon–nitrogen films have been formed by direct impingement of 5–100 eV C+ and N+ or N+2 ions upon solid surfaces, as well as by 5–350 eV N+ bombardment of graphite surfaces. The influences of ion energy, N+/C+ arrival rate, and type of substrate have been studied. The films deposited in this manner are found to be essentially amorphous, with some graphitic regions on the scale of a few nm. Two distinct types of C–N bonding, one attributed to graphitelike local structure (C–N π bonds) and one attributed to C3N4-like local structure (C–N σ bonds), have been detected by x-ray photoelectron spectroscopy. Films deposited by dual-beam deposition and single-beam nitridation at 75 eV or less exhibit differences in the single-bonded structure. Total nitrogen concentrations of up to 47 at. % have been measured by Auger electron spectroscopy (AES) and Rutherford backscattering spectrometry. The C KVV Auger line shapes of the two phases have been determined by factor analysis. These line shapes are consistent with the expected band structures for the two phases. Film growth is consistent with a combined surface deposition/subplantation model, with high incident energies resulting preferentially in damage to the C3N4-like phase. A significant amount of disorder is present in all of the films, as indicated by AES line shapes and transmission electron microscopy analysis. Preferential sputtering of N is observed during AES depth profiling with a 1 keV Ar+ beam. Implications of this work for deposition of C–N films by energetic particle bombardment are discussed.
ReSi2 thin-film infrared detectors
Authors: Becker James P. , Mahan John E. , Long Robert G.
Published: July 2002

Two types of thin-film infrared-sensing devices have been investigated using the narrow band-gap semiconductor, rhenium disilicide (Eg∼0.1 eV). These are the ReSi2/n-Si heterojunction internal photoemission (HIP) detector and the ReSi2 thin-film photoconductor. The HIP device was found to be rectifying and to obey a Fowler-type law with a long-wavelength cutoff of ∼2.1 μm (0.59 eV) at room temperature. In hopes of approaching the fundamental limit for a ReSi2-based photonic detector, ∼12 μm (0.1 eV), the ReSi2 photoconductor was explored. Indeed, the spectral response (measured at 10 K) of the ohmic photoconductor was found to extend to 6 μm (the present limit of our measurement equipment), with no indication of a detection cutoff.
Molecular beam epitaxy growth of thin films of SnS2 and SnSe2 on cleaved mica and the basal planes of single-crystal layered semiconductors: Reflection high-energy electron diffraction, low-energy electron diffraction, photoemission, and scanning tunneling microscopy/atomic force microscopy characterization
Authors: Schlaf R. , Louder D. , Lang O. , Pettenkofer C. , Jaegermann W. , Nebesny K. W. , Lee P. A. , Parkinson B. A. , Armstrong N. R.
Published: July 2002

SnS2 and SnSe2 thin films were deposited by molecular beam epitaxy (MBE) methods on a variety of layered semiconductor substrates (freshly cleaved SnS2, SnSe2, WSe2, MoS2, MoTe2, GaSe, InSe) and cleaved mica, for investigation of the interfaces formed as a result of MBE growth. These ultrathin films were characterized in situ by x-ray photoelectron spectroscopy and surface reflection high energy and low energy electron diffraction techniques. The growth modes were verified ex situ by scanning tunneling microscopy and/or atomic force microscopy [scanning probe microscopies (SPM)]. Despite the chemical and structural similarities between SnS2 and SnSe2, SPM measurements show that the two materials as ultrathin films have different growth morphologies in the first few monolayers. Photoelectron spectroscopy (PES) measurements lead to the conclusion that both materials grow on the basal planes of most layered substrates in an epitaxial, layer-by-layer mode. Small deviations from ideal Frank–van der Merwe growth for these thin films could be determined from PES intensity ratios versus coverage. Deposition of both materials on freshly cleaved mica, where the lattice mismatch between the substrate and the overlayer surface unit cell dimension exceeds 40%, yields exclusively 500–1000 Å diameter epitaxial islands with threefold symmetry.
Adsorption induced gas transport phenomena in narrow air channels recorded with work function detectors
Authors: Flietner B. , Doll T. , Lechner J. , Eisele I.
Published: July 2002

Gas transport in narrow air channels (length-to-height ratio 1 mm/1 μm) is characterized by work function detectors like hybrid suspended gate field effect transistors (HSGFETs) with sensitive areas located in the middle of the channel. A thin platinum layer covered one side of the channel. In order to separate the influence of the size of the channel structure on the gas exchange Kelvin probe measurements with platinum coated reference electrodes were carried out simultaneously. For the HSGFET we have observed time lags and suppressions of reactions, which indicate a strong adsorption dependence of gas exchange for the investigated testing gas mixture of hydrogen in nitrogen or synthetic air, respectively. The results are discussed in relation to common models for the flow in thin capillaries. We also point out the special features of narrow air channels for investigating adsorption related phenomena and for improving chemical sensor characteristics by incorporating them into small air gaps.
Argon plasma treatment of polycarbonate: In situ spectroellipsometry study and polymer characterizations
Authors: Vallon S. , Drévillon B. , Poncin-Epaillard F. , Klemberg-Sapieha J. E. , Martinu L.
Published: July 2002

The influence of argon plasma on polycarbonate (PC) was studied in terms of structural changes, reaction mechanisms, and adhesion. In situ ultraviolet-visible ellipsometry reveals formation of a surface layer with a higher refractive index than the untreated polymer. The increase in the refractive index is attributed to polymer densification, which in turn is attributed to crosslinking. However a decrease in the average molecular weight is also observed, and two populations of macromolecules of different sizes are detected by light scattering measurements, revealing a competition between crosslinking and degradation. The reaction mechanisms are investigated using nuclear magnetic resonance and in situ infrared ellipsometry. Degradation is caused by carbonate bond breaking, whereas crosslinking seems to be related to a decrease in methyl groups. In addition, an increase in surface acidity is detected by contact angle measurements and is attributed to photo-Fries rearrangements producing phenolic groups. The adhesion of a 1-μm-thick silica layer on PC is evaluated by the microscratch test, and its enhancement by argon plasma pretreatment is analyzed.
Combined reflectance anisotropy and photoemission spectroscopies of Cs/GaAs(001) interface formation
Authors: Gusev A. O. , Paget D. , Yu. Aristov V. , Soukiassian P. , Berkovits V. L. , Thierry-Mieg V.
Published: July 2002

We have investigated the adsorption of cesium on GaAs(001) using synchrotron radiation excited photoemission spectroscopy and also by monitoring the optical transitions related to gallium dimers and arsenic dimers using reflectance anisotropy spectroscopy (RAS). Cesium adsorption has little effect on the Ga 3d core level shape. In sharp contrast, we observe modifications of the RA signal related to gallium dimers, induced by the modification of the electronic states involved in the corresponding surface optical transitions. The changes of the RA spectrum reveal two adsorption phases at Cs coverages above and below 0.5 monolayers. The origin for the strong sensitivity of RAS to semiconductor/alkali metal interface formation is discussed.
Characteristics of hydrogenated aluminum nitride films prepared by radio frequency reactive sputtering and their application to surface acoustic wave devices
Authors: Yong Yoon-Joong , Lee Jai-Young
Published: July 2002

Hydrogenated aluminum nitride (AlN:H) films have been deposited on silicon wafers by the rf reactive magnetron sputtering method with H2 gas addition to Ar-N2 gas mixture. The changes of physical properties of AlN:H films with different H2 gas addition have been examined by x-ray diffraction, scanning electron microscopy, and x-ray photoelectron spectroscopy. The surface acoustic wave (SAW) filters with wavelength of 60 μm using these films have been fabricated and their SAW velocities and electromechanical coupling coefficients have also been measured by a network analyzer. It is found that as the amount of H2  addition increases, the surface of film becomes smooth, the stress is relieved, the concentration of nitrogen atom increases and that of oxygen atom decreases. We also found that AlN/AlN:H/AlN tri-layered films can prevent the blistering phenomena of AlN:H film. By measuring SAW characteristics of AlN/AlN:H/AlN tri-layered films, the SAW velocity is calculated to be 5280 m/s and electromechanical coupling coefficient is 1.35% which is the highest value reported so far.
Microstructure and corrosion resistance of plasma source ion nitrided austenitic stainless steel
Authors: Lei M. K. , Zhang Z. L.
Published: July 2002

Plasma source ion nitriding has emerged as a low-temperature, low-pressure nitriding approach for implanting nitrogen ions and then diffusing them into metallic materials. In this work, 1Cr18Ni9Ti austenitic stainless steel was nitrided at process temperatures from 280 to 480 °C over a range of nitriding conditions, and the resultant corrosion properties in 1% NaCl solution and in 1 N H2SO4 solution were investigated by cyclic polarization and anodic polarization measurements, respectively. Glancing angle x-ray diffraction and transmission electron microscopy studies were used to determine the crystal structures obtained at different process temperatures. It was found that three different near-surface microstructures were present, they were the face-centered-cubic (fcc)γ-(Fe,Cr,Ni)4N and fcc nitrogen expanded austenite (γN) mixed phases, the γN without precipitation of the nitrides phase, and the α-ferrite, fcc CrN, and γN mixed phase. The hardness-depth profiles exhibit a distinct compound layer with a thickness between 1.5 and 10 μm and the Knoop microhardness varied from 1500 to 2400 HK (0.1 N load), depending on process temperatures. The γN phase layer has a good pitting corrosion resistance in 1% NaCl solution and an equivalent homogeneous corrosion resistance in 1 N H2SO4 solution, compared with the original stainless steel. The formation of the γ-(Fe,Cr,Ni)4N phase from the γN phase layer can be the cause of the poor homogeneous corrosion resistance, while the precipitation of chromium nitride leads to deterioration of both the pitting corrosion resistance and the homogeneous corrosion resistance.
Extreme surface sensitivity in neon–ion scattering from silicon at ejection energies below 80 eV: Evidence for the presence of oxygen on ion bombarded SiO2
Authors: Wittmaack K.
Published: July 2002

Mass resolved ion scattering spectrometry has been used in combination with secondary ion mass spectrometry to study the surface composition of oxidized silicon samples (contaminated and sputter cleaned thin layers of SiO2 on Si and Si exposed to an oxygen jet). Using 1.5–3 keV Ne+20 ions at near-normal incidence and scattering angles around 133 °, the energies of Ne+ and Ne2+ after reflection from Si28 ranged from 46 to 76 eV. Under these conditions the radius of the blocking cone experienced by escaping ions becomes very large (>0.3 nm). Therefore, any adsorbates that may be present at the surface will strongly reduce the scattering signal from target atoms. In accordance with this supposition Si atoms are initially almost undetectable on samples covered with a “natural” adsorbate layer. The scattering yields from Si atoms measured with sputter cleaned SiO2 or oxygen saturated Si amount to only 8%–10% of the yield for clean Si. These numbers are lower by more than a factor of three than what would be expected if the surface composition were reflecting the bulk atomic fraction of Si in SiO2. Apparently, sizable amount of oxygen is residing on the ion bombarded sample. The results were found to be independent of the charge state of the escaping probe ions. Hence neutralization effects do not seem to play an important role.
Characterization of CdTe-Sb co-sputtered films
Authors: Picos-Vega A. , Ramírez-Bon R. , Espinoza-Beltrán F. J. , Zelaya-Angel O. , Farías M.
Published: July 2002

The structure and electrical properties of CdTe-Sb co-sputtered thin films and their relation with composition were studied. The films were grown on glass substrates by radio frequency sputtering deposition. The ternary alloys were deposited by co-sputtering of Sb and CdTe. The substrate temperature was varied from room temperature to 250 °C. The composition measurements show that the Sb content in the films ranges from 8 to 60 at. %, depending on the area fraction covered by the Sb attached to the CdTe target. The Sb content is found to be independent of the substrate temperature. The structure of the films was determined from x-ray diffraction measurements. Three kinds of structures were observed, depending on the Sb content and substrate temperature: (1) CdTe polycrystalline films containing small amounts of Sb, that is probably incorporated in the Cd and Te sites of the CdTe lattice; (2) amorphous CdSbTe films, with high Sb content and low substrate temperatures; and (3) polycrystalline films composed by a mixture of both Sb and CdTe crystallites, with high Sb content and high substrate temperatures. The room temperature electrical resistivity of the films varies from 109 Ω cm in the CdTe polycrystalline films to 10−3 Ω cm in the films composed of Sb and CdTe crystallites.
Insulator-coated sputter gun for growing superconducting oxide films
Authors: Lin R. J. , Chen L. J.
Published: July 2002

Superconducting Y–Ba–Cu–O films have been successfully grown on 2-in.-diam (100) MgO and CeO2-buffered R-plane sapphire substrates using a simple, inexpensive hot-wall dc sputtering system. The deposition chamber was made of a quartz tube and heated by a furnace outside the chamber. A new sputter gun was developed by shielding the surface of a cathode electrode using an insulating layer of alumina. The spatial variations of thickness and composition of films across a 2-in.-diam wafer are 4.9% and 4.2%, respectively. Superconducting properties of the films within a 2-in.-diam area are zero-resistance temperature Tc (zero) of 88–90 K and critical current density Jc (77 K, zero field) of (1.5–3.5)×106 A/cm2.
Primary pressure standard for calibration in the medium vacuum range
Authors: Hinkle L. D. , Provost J. , Surette D. J.
Published: July 2002

Primary standards for gas pressure in the range from ∼0.1 to 10 Pa (1 to 100 mTorr) have received a significant amount of attention in recent years. The interest in the calibration capability in this vacuum range is, to some degree, driven by the increasingly stringent requirements for the semiconductor processing industry. We present a new standard that is based on calculating the gas pressure required to restore a diaphragm to a null position, while the diaphragm is tilted to various, measured inclinations. With this as a basis, the calculations are relatively simple; there are no gas property dependent effects; and the system design is simple, robust, and easily automated. A formal evaluation of uncertainty for the system being developed in this facility is reviewed and compared with other primary standards. For the medium vacuum range, it is anticipated that this standard will offer numerous practical advantages relative to liquid manometers, dead weight testers, volume expansion systems, and conductance-based systems. It is intended that this technique will enable more widespread capability for the calibration, and verification of vacuum gauging in a pressure range of critical interest to many processes.
Study on the growth of biaxially aligned yttria-stabilized zirconia films during ion beam assisted deposition
Authors: Mao Y. J. , Ren C. X. , Yuan J. , Zhang F. , Liu X. H. , Zou S. C.
Published: July 2002

(001)-oriented and in-plane aligned yttria-stabilized zirconia (YSZ) thin films were synthesized on Ni–Cr alloy substrates by ion beam assisted deposition. It was found that it is not the 〈111〉 axial channel but the {110} plane channel that will always follow the direction of the bombarding ion beam and will result in the in-plane aligned structure of the YSZ films. At 55° incident angle, the bombarding ion beam is in the {110} plane channel and the 〈111〉 axial channel simultaneously; this produces the optimal biaxial alignment of YSZ films. On YSZ single crystalline substrates or textured YSZ layers, growth of YSZ films will not be controlled by the bombarding ion beam; rather, but the films continue to grow along the lattice orientation of the substrate. The formation of the biaxial alignment is an evolutionally selected process by ion beam selective bombardment. YSZ grains of (001) orientation are resputtered less than other oriented grains under ion beam bombardment, which causes the (001) orientation to emerge from initial random orientations evolutionally. About a 1000 Å-M20 thickness is needed to develop the alignment. The roughness of the substrate has no obvious influence on the alignment within several hundred Å. Increasing the substrate temperature tends to reduce the (001) orientation and to promote the (111) orientation along the substrate normal. Postannealing of the YSZ films fabricated at ambient temperature can improve the crystalline structure.
Effect of pressure on the deposition of hydrogenated amorphous carbon films using the electron cyclotron resonance chemical vapor deposition
Authors: Rusli  , Yoon S. F. , Yang H. , Zhang Q. , Ahn J. , Fu Y. L.
Published: July 2002

Hydrogenated amorphous carbon (a-C:H) thin films have been deposited from a mixture of methane and hydrogen using the electron cyclotron resonance chemical vapour deposition (ECR-CVD) technique. The films were prepared over a wide range of deposition pressure under a constant microwave power of 200 W, and the rf induced dc bias voltage was maintained constant at −100 V by varying the applied rf power. It was found that changing the deposition pressure in the ECR-CVD process has a profound effect on the properties of the films deposited, as evidenced from their Raman scattering and optical absorption results. The hardness of the films was found to increase remarkably with pressure, whereas the number of bonded hydrogen as deduced from the IR absorption showed only a weak dependence. A hardness of up to 18 GPa was measured for films deposited at 36 mTorr. The sp3 content in the films was also observed to increase with the deposition pressure as deduced from their Raman spectra. The results can be attributed to the efficient excitation of the plasma by the microwave power under the ECR condition, which at increasing pressure leads to a dense plasma and a high ion flux reaching the substrates. The high concentration of atomic hydrogen present in the plasma is also found to be critical in determining the structural properties of the films.
Role of gas feed delivery and dilutent on oxide etching in an inductively coupled plasma etch system
Authors: Lercel M. J. , Dang D. , Marmillion N. , Mlynko W.
Published: July 2002

High-density plasma (HDP) etch systems are advantageous for small-dimension contact and via etch applications because they provide high etch rates and high selectivity between different dielectric films. However, controlling cross-wafer uniformity of the etch rate and selectivity can be difficult in large, single-wafer etch systems. In this article, we examine the effect of gas feed configuration and dilutent gas flow for a high-selectivity silicon oxide-to-silicon nitride etch process in a 200 mm wafer HDP etch system. The oxide etch rate and oxide-to-nitride selectivity were measured for both helium and argon dilution from the top (chamber roof) or bottom (around the base of the wafer chuck) configurations in the applied materials HDP dielectric etch system. These process parameters are compared with the emission spectra and rf parameters obtained during the etch process. The results indicate that the choice of helium or argon has little effect on the process results and increasing dilutent flows tend to make the cross-wafer etch rate and selectivity more nonuniform. However, with no dilutent, cross-wafer uniformity was the poorest and the rf match network could not completely compensate for the plasma impedance. Under all conditions for this process, center gas feed provided more uniform results.
Copper diffusion in amorphous germanium
Authors: Doyle J. P. , Kuznetsov A. Yu. , Svensson B. G.
Published: July 2002

The diffusion coefficient of copper in amorphous germanium is estimated to be larger than 3×10−11 cm2 s−1 and the solubility to be ∼7×1018 cm−3 at 200 °C as determined from secondary mass spectrometry. The observed solubility limit is more than eight orders of magnitude greater than that in crystalline germanium and the enthalpy of a solution of copper in amorphous germanium is estimated to be as low as 0.05 eV in the range of 20–200 °C. Copper is observed to diffuse more readily in amorphous germanium than in amorphous silicon, with an activation enthalpy as low as ∼0.5 eV in the range of 20–200 °C. Interstitial diffusion is assumed to prevail and the trapping enthalpy of defects retarding the motion is found to be significantly lower in amorphous germanium (0.25±0.15 eV) compared to that in amorphous silicon (∼0.8 eV).
Reversible and irreversible control of optical properties of porous silicon superlattices by thermal oxidation, vapor adsorption, and liquid penetration
Authors: Zangooie S. , Jansson R. , Arwin H.
Published: July 2002

Optical properties of porous silicon superlattices are investigated using variable angle spectroscopic ellipsometry. Different phenomena such as in-depth inhomogeneities and interface transition regions are resolved and studied using various optical models. The optical properties of the samples are modified irreversibly by thermal oxidation yielding a blueshift of the reflectance. A reversible redshift of the spectra is obtained by vapor adsorption and liquid penetration into the superlattice. Moreover, existence of different specific internal surface areas and pore size distributions in the low and high index sublayers of the material is proposed.
On the nature of the rate limiting step in the reaction of cracking water molecules on a metallic surface
Authors: Ghezzi F.
Published: July 2002

It is well known that the chemical interaction between gas and solid occurs principally through two steps: surface associated processes (viz. adsorption, dissociation) and bulk dependent processes (viz. diffusion, bulk sorption). Earlier works on metallic alloy–hydrogen systems have shown that the hydrogen sorption rate by the getter alloy is decided by the surface related processes at low pressures and that it is diffusion dependent at higher pressures. In the series of batch conversion experiments conducted on cracking isotopic waters using a metallic (Zr–V–Fe) getter alloy, it has been observed that, over a wide range of pressure (1–500 Pa) and temperature (100–400 °C), the conversion reaction rate remains governed by surface processes (characterized by P1 dependence of the absorption rate) at the beginning of the process, i.e., when the water vapor pressure is high, and that it shifts itself to become diffusion dominated (characterized by the P1/2 dependence) at later times, i.e., when the water vapor pressure becomes low. This observed behavior is attributed to the amount and nature of change in the hydrogen and oxygen concentrations in the alloy occurring during the conversion process. This work presents the experimental observations and discusses the occurrence and relevance of shift in the rate-limiting step during the conversion process.
Dissociation processes in plasma enhanced chemical vapor deposition of SiO2 films using tetraethoxysilane
Authors: Okimura Kunio , Maeda Naohiro
Published: July 2002

Dissociations in plasma enhanced chemical vapor deposition for SiO2 deposition using tetraethoxysilane (TEOS) were investigated by means of mass spectrometry. First, we showed basic dissociation patterns of TEOS as a function of electron energy. It was shown that TEOS dissociates by electron impact at electron energies below 8 eV, removing the ethyl group (C2H5). Next, we presented dissociation patterns in TEOS/He plasma. Finally, dissociation in TEOS/O2 plasma was studied. It was shown that high molecular intermediate products containing carbon and hydrogen, such as Si(OC2H5)2H, Si(OC2H5)2OCH3, and Si(OC2H5)3OCH2, are present only in the TEOS/He plasma but not in the TEOS/O2 plasma. It was also shown that eliminated hydrocarbon gases such as C2H2, C2H4, C2H5, and OC2H5 are converted into H2O and CO2. Fourier-transformed infrared and x-ray photoelectron spectroscopy studies revealed that the degree of impurity concentration in the film decreased with increasing O2 concentration. Characteristics of metal–insulator–semiconductor devices reflected the degree of impurity concentration in the oxide films. It was found that oxygen gas plays an indispensable role for preparing high quality SiO2 films by oxidizing the intermediate dissociation products and eliminating hydrocarbon gases.
Surface roughness and oxide contents of gas-phase and solution-phase polysulfide passivation of III–V surfaces
Authors: Choy W. H. , Kwok R. W. M. , So B. K. L. , Hui G. K. C. , Chen Y. J. , Xu J. B. , Wong S. P. , Lau W. M.
Published: July 2002

A surface etching effect was observed using polysulfide solution for the passivation of III–V semiconductors. The etching rate was found to be 2 Å/min on InP (100). The etching effect increased surface roughness, which enhanced the adsorption of adventitious hydrocarbons and water from the ambient. Such an etching effect was not observed on the samples treated by a gas-phase polysulfide treatment. The surfaces of these samples also showed less adventitious hydrocarbons and water after exposure to the ambient. The presence of sulfide on the surface reduced the sticking coefficient of the adventitious hydrocarbons and water.