bluuebunny/crossref_metadata_2025 huggingface dataset:
Characterization of an ultrahigh vacuum sputtering system
Authors: Brownstein Barry S. , Fraser David B. , O’Hanlon John F.
Published: July 2002

The design and characterization of a custom-designed ultrahigh vacuum sputter deposition system capable of background pressures in the 10−9 Pa range is described. Four pressure gauges, a Bayard–Alpert nude ion gauge, a cold cathode gauge, a capacitance manometer, and a spinning rotor gauge were available to characterize the system performance. The useful lower limit of the 133 Pa capacitance manometer was 3×10−2 Pa. Above that value, it was in good agreement with the spinning rotor gauge. The hot filament ion gauge was compared to the spinning rotor gauge over the range 510−5–5×10−2 Pa. The ion gauge was then used to determine the sensitivities of the partial pressure analyzers. Two residual gas analyzers, an open source and a closed-source instrument were used to measure partial pressures in the system. Both open- and closed-source instruments showed significant scatter in sensitivity at pressures below 10−5 Pa. The useful range of the closed source analyzer was limited to pressures above 10−6 Pa. Below this pressure, background currents prevailed. It was found that these background currents limited the sensitivity of the closed source analyzer when used at sputtering pressures. Finally, the total gas contamination in the system at sputtering pressures was shown to be system, rather than source gas, limited. This contamination was shown to be less, when this system was configured with a helium gas cryogenic pump than with a turbomolecular pump. However, the speed of the cryogenic pump system was somewhat greater than that of the turbomolecular pump system. Some of that reduction in contamination could be attributed to increased pumping speed.
Plasma treated screws for ultrahigh vacuum application
Authors: MacGill R. A. , Castro R. A. , Yao X. Y. , Brown I. G.
Published: July 2002

We describe a method for treating the surface of stainless steel screws to avoid their cold welding in an ultra high vacuum environment. The method involves exposing the screws to an energetic flux of silver plasma produced by a vacuum arc discharge. We find that plasma deposition of about 100 Å or more of silver in this way provides a superior surface.
Adhesion, surface morphology, and gas sensing characteristics of thin-gold-film chemical sensors
Authors: Yoo Kwang Soo , Sorensen Ian W. , Glaunsinger William S.
Published: July 2002

Thin films of the Au, Au/Cr, Au/Ni/Cr, and Au/Pd/Cr systems were deposited on alumina substrates at ambient temperature and 250 °C in a high-vacuum resistance heated evaporator, and annealed at 300, 450, and 600 °C for 1 h in air, respectively. The gold films with a Cr adhesive layer exhibited improved adhesion of the films to the substrate. Pull-off tests demonstrated that the adhesion of the Au/Cr films deposited at ambient temperature more than doubled after annealing at 600 °C. The surface morphology of the gold films was observed using scanning electron microscopy. The sheet resistance of each layer was also investigated using a four-point probe method. Finally, the sensing characteristics as exemplified by observed resistance changes during exposure of the films to a gas were measured at room temperature for hydrogen sulfide (H2S). The sensitivity of the Au/Cr system for H2S is the highest of the four systems. As a result of the Auger-electron spectroscopy analysis, the Au/Ni/Cr and Au/Pd/Cr systems have low sensitivity for H2S due to the interdiffusion between layers.
Kinetics of growth of Cu on Cu(001)
Authors: Ernst H.-J. , Fabre F. , Folkerts R. , Lapujoulade J.
Published: July 2002

Helium atom beam scattering has been used to study the growth of Cu films on Cu(001) surfaces for a wide range of temperatures and coverages. It is shown that this technique provides a powerful means for a detailed structural characterization during growth of the film. Useful information on decisive kinetic parameters, such as the migration coefficient of adatoms, are obtained. The evolving, rough growth front for deposition at low substrate temperatures is analyzed in the light of the dynamical scaling hypothesis. A growth instability is observed, which might be attributed to an asymmetry in the vertical and horizontal mobility of deposited atoms, associated with an excess energy barrier at step edges.
The American Vacuum Society and the people who have guided its development
Authors: Singleton Jack H.
Published: July 2002

As part of the celebration of the first forty years of the American Vacuum Society, a short history of the society has been written, [J. M. Singleton, History of Vacuum Science and Technology (AIP Press, New York, 1993), Vol. 2, p. 1], which provides a detailed account of the society’s development. The present brief article constitutes an attempt to understand the profound effect that individual members of the society have had upon this development by describing a few examples.
Neutrino-recoil induced desorption
Authors: Zhu L. , Avci R. , Lapeyre G. J. , Hindi M. M. , Kozub R. L. , Robinson S. J.
Published: July 2002

Nuclear decay induced 37Cl ion desorption from the electron capture decay 37Ar→37Cl+ν is reported for the first time. A mixture of one part 36Ar and ∼5×10−5 parts 37Ar (36/37Ar) is physisorbed on a gold-plated Si wafer kept at 16 K under ultrahigh vacuum conditions. The time of flight (TOF) of recoiled 37Cl ions is measured using coincidence techniques. The observed kinetic energy distribution of the 37Cl ions is approximately Gaussian in shape, with a maximum at ≊9.0 eV and a full width at half-maximum of ∼3 eV. Considering the binding energy of physisorbed 37Ar is ∼80 meV, the 9-eV peak energy compares well with that of the gas-phase value, where conservation of the energy and momentum fixes the kinetic energy of 37Cl ions at 9.54 eV. Using a combination of TOF and retarding field energy analysis, the charge states of detected ions for 1 ML (monolayer) of 36/37Ar are determined as 53%+1e, 21%+2e, and 26%+ne, where n≥3. The fraction of decaying 37Ar atoms which emerge from the surface as positive 37Cl ions is found to be 10%. Finally, a strong charge exchange reaction between a 37Cl ion and near-neighbor atoms causes a Coulomb explosion within the multilayers, increasing the kinetic energy of desorbing ions by as much as ∼7 eV.
Adsorption of the cyclic ether trioxane on Cu(111)
Authors: Hofmann M. , Wegner H. , Glenz A. , Wöll Ch. , Grunze M.
Published: July 2002

The adsorption of the cyclic ether trioxane, or trioxymethylene (C3H6O3), has been studied on the (111)-oriented single crystal copper surface using photoelectron spectroscopy, thermal desorption spectroscopy and low energy electron diffraction. The large dipole moment of the molecule leads to a rather complex adsorption behaviour, three different adsorption regimes with different molecular orientation and binding energies are found. At all coverages molecular adsorption was observed, in the submonolayer regime trioxane adsorbs with the ring-plane parallel to the surface.
Selectivity variations of electron beam patterned silicon dioxide films*
Authors: Kimball John F. , Allen Patricia E. , Griffis Dieter P. , Radzimski Zbigniew J. , Russell Phillip E.
Published: July 2002

This work is a study of the effect of low-energy e-beam radiation on subsequent wet chemical etching of silicon dioxide (SiO2). The silicon dioxide etch selectivity is examined considering the parameters of electron beam patterning and etching techniques. Electron beam energy optimization considerations for dose minimization were considered following the e-beam exposure and etching of 100 and 50 nm SiO2 films of dry, steam, low-pressure chemical vapor deposition and remote plasma-enhanced chemical vapor deposition samples. The selectivity and etching characteristics of the respective oxides and thicknesses are presented and discussed.
Low dose nitrogen ion implantation in Ti/permalloy bilayer films
Authors: Chaug Yi-Shung , Roy Nripen
Published: July 2002

The layered thin film structures of an element and an alloy has been widely used in fabricating microelectronic devices. The changes in magnetic properties and crystal structure of Ti/permalloy bilayer thin films induced by low dose nitrogen implantation were studied. The nitrogen doses used were at 5, 10, 20, 40, 80, and 160×1014 ions/cm2. X-ray diffraction, optical magnetic domain imaging, and Auger electron spectroscopy were applied in this study. A preferential counter-current diffusion at the interface induced by the ion implantation was found. Increased nitrogen doses resulted in the changes of the lattice parameters, magnetic coercivity, and magnetic domain size. The amorphization of the bilayer films due to ion implantation was also discussed.
Ultrathin self-assembled polymeric films on solid surfaces. III. Influence of acrylate dithioalkyl side chain length on polymeric monolayer formation on gold
Authors: Sun F. , Grainger D. W. , Castner D. G.
Published: July 2002

Self-assembled films of acrylate polymers containing dithioalkyl side chains of varying lengths have been fabricated on gold substrates by adsorption from dilute organic solution. Anchoring alkyl side chain types studied include lipoate (n=4), pentyl dithioundecanoate (n=10), pentyl dithiopalmitate (n=15), and pentyl dithiotricosonate (n=22), where n represents the number of methylene units in the longer arm of the asymmetric disulfide side chain. Comprehensive characterization of polymer monolayers by x-ray photoelectron spectroscopy and reflection Fourier transform infrared spectroscopy showed improved order for structural assemblies of C11 (n=10) side chain polymer monolayers, over shorter and longer side chain polymer analogs, due to a higher percentage of bound thiolate anchors. Monolayer thicknesses range from 20 to 40 Å, primarily depending on side chain length and density along the polymer backbone. Cyclic voltammetry on gold electrodes shows that longer side chain polymer monolayers possess more structural defects resulting from considerable disorder in the films. Despite the less organized structural features for these polymer monolayers, their selective adsorption onto gold via specific side chain terminal disulfide anchors on microlithographed substrate patterns creates well-resolved surface-modified microstructures comparable to those from monomeric analogs, as shown by scanning Auger mapping.
Comparison of angle-resolved x-ray photoelectron spectroscopy/Auger electron spectroscopy with depth profile restoration from inelastic background analysis
Authors: Werner Wolfgang S. M. , Tilinin Igor S.
Published: July 2002

A comparison between usual angle-dependent x-ray photoelectron spectroscopy/Auger electron spectroscopy and a recently developed evaluation procedure based on analysis of the near peak spectral region is presented. The latter procedure is based on the theoretical description of the energy/angular distribution of an arbitrary sample in which the so-called partial escape distributions play a central role. These quantities describe the probability that a signal electron generated in a certain depth interval escapes from the surface with a direction in a certain angular interval after experiencing a certain number of inelastic scattering processes. Using model data to compare the two approaches it was found that analysis of a rather small energy region in the vicinity of the peak recorded at two emission angles (0° and 60° relative to the surface normal) suffices to restore the entire specimen depth profile. In contrast, the usual angle-resolved techniques, based on peak areas or heights only, need to be recorded at more, and more oblique, emission angles. Since measurements at oblique emission are difficult to perform, and the influence of effects like surface roughness, surface excitations, and the like become more pronounced at oblique emission, application of the present method to experimental data seems highly promising.
Directed sputter deposition of AlCu: Film microstructure and microchemistry
Authors: Kim Y.-W. , Moser J. , Petrov I. , Greene J. E. , Rossnagel S. M.
Published: July 2002

The microstructure and microchemistry of AlCu films deposited onto unheated oxidized Si(001) substrates by two recently developed directional sputtering techniques, collimated magnetron sputter deposition (CMSD) and ionized magnetron sputter deposition (IMSD), have been investigated using Rutherford backscattering spectroscopy, x-ray diffraction (XRD), plan-view transmission electron microscopy (TEM), cross-sectional TEM (XTEM), and scanning TEM (STEM). Both sets of films had essentially the same average compositions as the alloy targets while exhibiting dense columnar microstructures with (111) preferred orientation, relatively abrupt film/ substrate interfaces, and no indication of surface faceting. Microstructure evolution pathways, however, were quite different. IMSD layers exhibited competitive column growth resulting in a degree of (111) orientation which was more than an order of magnitude larger than that found in corresponding CMSD films and, for thicker layers (≳1 μm), larger average column sizes. The IMSD films also had a much smaller spread in the azimuthal distribution of (111)-oriented columns. XRD line broadening analyses and TEM/XTEM examinations revealed that IMSD layers contained inhomogeneous strain due to residual ion-irradiation-induced defects and, in the upper near-surface region, Al2Cu precipitates while CMSD layers appeared defect-free in TEM/XTEM images. The IMSD films were slightly tensile (+0.13±0.01 GPa) and the CMSD films were slightly compressive (−0.18±0.06 GPa).
Molecular beam epitaxy grown III–V strain relaxed buffer layers and superlattices characterized by atomic force microscopy
Authors: Howard A. J. , Fritz I. J. , Drummond T. J. , Olsen J. A. , Hammons B. E. , Kurtz S. R. , Brennan T. M.
Published: July 2002

Using atomic force microscopy (AFM), we have investigated the effects of growth temperature and dopant incorporation on the surface morphology of molecular beam epitaxy grown graded buffer layers and strained layer superlattices (SLSs) in the InGaAlAs/GaAs and InAsSb/InSb material systems. Our AFM results show quantitatively that over the temperature range from 380 to 545 °C, graded InxAl1−xAs (x=0.05–0.32) buffer layers grown at high temperatures (∼520 °C) and graded InxGa1−xAs (x=0.05–0.33) buffer layers and In0.4Ga0.6As/In0.26Al0.35Ga0.39As SLSs grown at low temperatures (∼400 °C) have the lowest rms roughness. Also, for SLSs of InAs0.21Sb0.79/InSb, undoped layers grown at 470 °C were smoother than undoped layers grown at 420 °C and Be-doped layers grown at 470 °C. These results illustrate the role of surface tension in the growth of strained layer materials near the melting temperature of the InAsxSb1−x/InSb superlattice. Nomarski interference and transmission electron microscopies, IR photoluminescence, x-ray diffraction, and photocurrent spectroscopy were also used to evaluate the relative quality of the material, but usually the results were not conclusive.
Monte Carlo simulation and measurement of silicon reactive ion etching profiles
Authors: Tait R. N. , Dew S. K. , Smy T. , Brett M. J.
Published: July 2002

A two-dimensional plasma etching model based on the simbad Monte Carlo thin-film growth simulation program has been modified to include ion-enhanced etch processes. The modified program has been applied to a study of sidewall passivation in the etching of silicon in a CF4/O2 plasma. Experimentally measured mask undercut in the etching of 0.8-μm-wide lines was reduced from 150 Å/min to virtually zero with an increase in oxygen from 8% to 45% of total gas flow. The corresponding decrease in etch rate was from about 750 to 325 Å/min. Simulations account for this change based on competition between oxidation and flourine etching of the silicon surface. Reactive gases follow collisionless trajectories at the simulation scale and have a high probability of diffuse re-emission following contact with the surface. This simulation method extends current profile simulation capabilities for a well-known etching chemistry.
Investigation of thick, low-temperature plasma deposited silica films for waveguide fabrication
Authors: Tabasky M. , Bulat E. S. , Tweed B. , Herrick C.
Published: July 2002

Optical devices, such as directional couplers made from silica waveguides, are used to route optical signals at points where optoelectronic conversions are necessary. We report the fabrication of silica waveguides using low-temperature plasma deposition and etching processes. The devices are buried-ridge, single-mode waveguide structures with a refractive index difference (Δn) of 0.03 between the guiding and cladding layers. Two different plasma deposition processes with different reactant chemistries (SiH4/N2/N2O) and 1,3,5,7-tetramethylcyclotetrasiloxane (TMCTS)/O2 were used to fabricate the waveguides. The deposition rates, uniformities, film stress, and refractive index control obtained using the two techniques are discussed. The plasma etching process (CHF3/CF4/Ar chemistry) defining the guiding layer varied from a vertical profile (90°) down to 75°, to minimize void formation in the coupling regions of the devices. The step coverage obtained using the TMCTS process showed marked improvement when compared to silica films deposited using plasma-enhanced chemical-vapor deposition with SiH4/N2/N2O chemistry. The TMCTS chemistry produced plasma deposited films with increased deposition rates and the required precision for both the thickness and refractive index parameters necessary for waveguide device fabrication.
Computer simulation of mass-selective plasma-source ion implantation
Authors: Shohet J. L. , Wickesberg E. B. , Kushner Mark J.
Published: July 2002

The use of plasma source ion implantation (PSII) for impurity sensitive substrates such as semiconductors has been slow to be adopted due to the difficulty of producing low impurity plasmas. In this work the feasibility of producing impurity-free plasmas for PSII using a mass filtering technique is investigated. In this method, an ion cyclotron resonance (ICR) cell is incorporated into a plasma processing reactor to selectively expel unwanted ions. The implementation of ICR in ion implantation is subject to a number of complications, such as ion–neutral collisions, plasma shielding of excitation fields, and nonhomogeneities of the magnetic field. A numerical simulation of ICR-based mass filtering for PSII to investigate these effects has been developed. Mass filtering is potentially effective over a wide range of magnetic field configurations at the pressures typically used for PSII.
Deposition of nonlinear optical films of potassium titanyl phosphate (KTiOPO4) by pulsed excimer laser ablation
Authors: Xiong Fulin , Hagerman M. , Zhou H. , Kozhevnikov V. , Wong G. K. , Poeppelmeier K. , Ketterson J. B. , Chang R. P. H. , White C. W.
Published: July 2002

Nonlinear optical films of potassium titanyl phosphate (KTiOPO4, or KTP) have been, for the first time, fabricated by pulsed excimer laser deposition on several substrates such as sapphire, Si(100) crystals, and fused quartz slides. The properties of the deposited KTP films, such as the chemical stoichiometry, crystallinity, effective index of refraction, and Raman response, have been extensively characterized. All of the results match the values of KTP crystals. The nonlinear optical property of the second harmonic generation of the films has been evaluated, showing a high efficiency comparable to a bulk value of KTP crystals. It is suggested that the success of this deposition relies on the transient congruent process generated by a pulsed UV laser beam.
Compositional and electrical properties of Si metal–oxide–semiconductor structure prepared by direct photoenhanced chemical vapor deposition using a deuterium lamp
Authors: Shei S. C. , Su Y. K. , Hwang C. J. , Yokoyama M. , Pan F. M.
Published: July 2002

High quality SiO2 layers have been grown on (111) Si substrates by direct photoenhanced chemical vapor deposition using monosilane (SiH4) and oxygen (O2) as gas sources under irradiation of a deuterium lamp. The refractive index of the deposited oxide is 1.462 at 250 °C when the gas ratio (O2/SiH4) is 5. The measurements of the Fourier transform infrared spectrum, x-ray photoelectron spectroscopy, and Auger electron spectroscopy show that the dominant components of the oxide are silicon and oxygen and the film is SiO2. Hysteresis free capacitance–voltage characteristics of the metal–oxide–semiconductor diode was observed. After low temperature postoxidation annealing, the minimum interface trap density is 1.5×1011 cm−2 eV−1, which is comparable to that of thermal oxidation.
Bioreactivity of titanium implant alloys
Authors: Kerber Susan J.
Published: July 2002

A study was conducted regarding the adsorption of peptides on commercially pure (cp) Ti and Ti-6Al-4V. The peptides used were arginine-glycine-aspartic acid-alanine (RGDA), arginine-glycine-aspartic acid-serine (RGDS), and arginine-phenylalanine-aspartic acid-serine (RFDS). The tripeptide RGD is known to be important for biologically specific adhesion reactions. This research was conducted to investigate the reason for a tendency toward thrombus formation with Ti-6Al-4V that is not observed with cp Ti. After argon plasma cleaning, coupons of the titanium alloys were inserted into solutions with variable concentrations (0.0625–2 mg/ml) of an individual peptide group under constant temperature and time conditions. The samples were rinsed, dried, and analyzed with x-ray photoelectron spectroscopy (XPS). Adsorption isotherms were obtained by plotting the relative amount of peptide adhesion as a function of solution concentration. It was postulated through the XPS and adsorption isotherm data that the major adhesion mechanism for the peptides to the titanium alloys was hydrogen bonding. CP titanium and Ti-6Al-4V are hypothesized to react differently as implants because Ti-6Al-4V has a more electropositive surface, which allows fewer hydrogen bonds to form. Hydrophilic reactions were proposed to be of secondary importance during bioadhesion, influencing the structure of the second layer adsorbed. There was no correlation found between the net charge of the peptide groups and their adhesion to the alloys.
Modification of overlayer growth kinetics by surface interlayers: The Si(111)√7×√3-indium surface
Authors: Surnev S. L. , Kraft J. , Netzer F. P.
Published: July 2002

The growth of thin films of In on bare Si(111)-type substrate surfaces and on the so-called (√7×√3)–In monolayer structure on Si(111) as an interlayer surface has been studied comparatively by scanning tunneling microscopy (STM), Auger electron spectroscopy, and low-energy electron diffraction (LEED). The In uptake and the morphology of In islands formed on the two surfaces are remarkably different, and a nonwetting behavior of In on the (√7×√3) surface is observed. Due to the very high mobility of In adatoms on the (√7×√3)–In surface very few, but large, In islands are observed; they cover only a minor portion of the surface area, whereas on bare Si(111) surfaces the In islands are more uniformly distributed over the surface, indicating a more limited diffusion rate of In atoms. Epitaxially ordered In islands with In–In distances close to those in bulk In, as revealed by atomically resolved STM images and by LEED, are observed to grow at room temperature on Si(111) surfaces. On the (√7×√3)–In surface metastable In islands in a pseudomorphically grown structure, i.e., with In–In distances determined by the Si(111) lattice, have been detected.
Heating uniformity of a microwave discharge plasma to redistribute a solid fuel layer inside a cryogenic target for inertial confinement fusion
Authors: Chen C. M. , Norimatsu T. , Izawa Y. , Yamanaka T. , Nakai S.
Published: July 2002

In the plasma layering technique, a microwave discharge plasma is turned on in the void of a nonuniform solid fuel layer inside a cryogenic laser fusion target to redistribute the nonuniform layer into a uniform one. The heating uniformity of the plasma initiated by a one-dimensional electric field was examined experimentally and theoretically by making a glow discharge in a quartz shell located in a strong microwave field at room temperature. The heating uniformity on the inner surface of the shell was estimated by measuring the surface temperature of the shell. When the frequency of the external electric field was 2.45 GHz, the resultant measured heating uniformity at the gas density of <0.7 g/m3 should be sufficient to obtain a uniform solid fuel layer for laser implosion experiments. At higher gas densities, the heating uniformity was insufficient because of the nonuniform distribution of the plasma. Countermeasures to improve the uniformity are discussed.
Miniaturized thin film thermal vacuum sensor
Authors: Alvesteffer W. J. , Jacobs D. C. , Baker D. H.
Published: July 2002

A new miniaturized thin film Pirani type vacuum sensor that detects pressure from 1×10−5 to 760 Torr was developed. The compact instrument is attitude insensitive, rugged, and has rapid response to pressure variations. The very small dimension between the heating element and the heat sink prevents the flow from entering into the viscous regime thus resulting in a predominately conductive heat transfer over the entire pressure range. This removes the complexities introduced into the pressure versus output curve by convective heat transfer. The output is linear from 1×10−4 to 1 Torr, and then monotonically increases beyond 760 Torr. A unique feature of this instrument is the use of a microprocessor to compute the sensor power from the analog voltage and current. In the molecular flow regime, the absolute pressure is directly proportional to the power dissipated by the surrounding gas. By measuring the power, the sensor rejects most of the errors introduced by ambient temperature variations. The analog-to-digital converters for both the current and the voltage signals use the ∑–Δ conversion method to reject electrical noise by the averaging technique. This results in the stable signal detection of pressure down to 1×10−5 Torr. The instrument is thermally stable over an ambient temperature range of 0–50 °C when the pressure is between 1×10−4 and 760 Torr.
Competitive halogenation of silicon surfaces in HBr/Cl2 plasmas studied with x-ray photoelectron spectroscopy and in situ, real-time, pulsed laser-induced thermal desorption
Authors: Cheng C. C. , Guinn K. V. , Herman I. P. , Donnelly V. M.
Published: July 2002

Using x-ray photoelectron spectroscopy (XPS) and real-time, laser-induced thermal desorption–laser-induced fluorescence (LD–LIF), we have determined the coverage of Br and Cl on Si(100) surfaces that are etched in mixed HBr/Cl2 plasmas. Halogen coverages measured by XPS after etching are directly proportional to the fraction of the respective halogen in the feed gas. LD–LIF was detected from SiCl(g) and SiBr(g) products with intensities that are a semiquantitative measure of instantaneous Cl and Br coverages. Saturated coverages during etching in Cl2 and HBr plasmas are 1.0×1015 Cl/cm2 and 6.0×1014 Br/cm2, respectively. Etch rates at these two extremes are 2170 and 1330 Å/min, and therefore are proportional to the respective halogen coverages. It therefore appears that the rate of formation of volatile Si–halides, stimulated by ion bombardment, is lower for HBr mainly because less halogen is available on the surface at saturated coverage. Langmuir probe measurements indicate that the ion flux is 17% lower in pure HBr plasmas, compared with Cl2 plasmas at the same power. The plasma potential, direct current bias voltage, and hence ion energy were nearly constant, however, over the range of gas mixtures. The slightly different ion fluxes suggest that the ion bombardment-stimulated process, although similar for Cl2 and HBr plasmas, is actually slightly more efficient on a per halogen basis for Br versus Cl. Positive photoresist surfaces that were also exposed to the plasma differ from Si in that less Br adsorbs on the surface both in pure HBr and mixed HBr/Cl2 plasmas. Apparently the lower reactivity of photoresist with Br (compared with Cl) is at least partly responsible for the widely observed slower etch rate of photoresist in HBr plasmas, and hence enhanced selectivity when etching Si.
The chemistry of a CCl2F2 radio frequency discharge
Authors: Stoffels W. W. , Stoffels E. , Haverlag M. , Kroesen G. M. W. , de Hoog F. J.
Published: July 2002

A systematic study of the chemistry of stable molecules and radicals in a low pressure CCl2F2 radio frequency discharge for dry Si etching has been performed. Various particle densities have been measured and modeled. The electron density, needed as an input parameter to model the CCl2F2 dissociation, is measured by a microwave cavity method. The densities of stable molecules, like CClF3, CF4, 1,2-C2Cl2F4 and the etch product SiF4, are measured by Fourier transform absorption spectroscopy. The density of the CF2 radical is measured by means of absorption spectroscopy with a tunable diode laser. Its density is in the order of 1019 m−3. All density measurements are presented as a function of various plasma parameters. Moreover, optical emission intensities of Cl and F have been recorded as a function of plasma parameters. It appears that the feed gas (CCl2F2) is substantially dissociated (about 70%–90%) in the discharge. Based on the obtained data the dissociation rates of several molecules have been estimated. The measured total dissociation rate of CCl2F2 is 8×10−15 m3 s−1. For this molecule the dissociation rate is substantially higher than the dissociative attachment rate (10−15 m3 s−1). The dissociation rate for CClF3 is 2×10−15 m3 s−1 and for CF4 about 3×10−16 m3 s−1. The total dissociation rate of C2Cl2F4 is higher than 5 ×10−15 m3 s−1, of which 2.5±0.5 × 10−15 m3 s−1 is due to dissociative attachment. Furthermore it has been found that the presence of a silicon wafer strongly affects the plasma chemistry. Optical emission measurements show that the densities of halogen radicals are significantly depleted in presence of Si. Moreover, the densities of several halocarbon molecules display a negative correlation with the density of the etch product SiF4.
Modeling the pump-down of a reversibly adsorbed phase. II. Multilayer coverage
Authors: Redhead P. A.
Published: July 2002

In Part I [J. Vac. Sci. Technol. A 13, 467 (1995)] of this article pressure versus time was calculated for the evacuation of a vacuum system with a reversibly adsorbed phase at coverages less than one monolayer; in Part II this analysis is extended to the multilayer region, i.e., from the saturated vapor pressure (ps) to the pressure corresponding to one monolayer (pm) the gas flow is viscous in this range. In this pressure range the ratio of adsorbed to gas phase molecules is small (less than a few percent). As a practical example, the adsorbed phase is taken to be water at about 300 K. A recently proposed empirical adsorption isotherm is used that is a good fit to experiment from ps to pm, unlike existing isotherms that only cover parts of this range. Using this isotherm, the pressure and coverage as a function of time in the pressure range from ps to pm are calculated. It is shown that, for the reference system chosen (vol 17 ℓ, surface area 4.5×103 cm2), as the system is pumped down, the pressure remains constant for a few seconds at a pressure slightly less than ps and then falls to pm in essentially the same way as in the absence of an adsorbed phase; this occurs because the number of molecules in the adsorbed phase is much less than in the gas phase. For systems with the pumping parameter S/A<5×10−3 (S=pumping speed, ℓ s−1, A=area of adsorbing surface, cm2) the decrease in temperature caused by the desorption of multilayers of water is too small to have any significant effect on the desorption rate; for systems with higher values of S/A the temperature drop may be significant.
CO2 sticking on Pt(111): The role of kinetic energy and internal degrees of freedom
Authors: Kulginov D. , Persson M. , Åkerlund C. , Zorić I. , Kasemo B.
Published: July 2002

CO2 adsorbed on Pt(111) is a system that has several attractive features that make it suitable for studies of the role of internal degrees of freedom on the sticking process. In particular, this relatively long and linear molecule has a low energy vibrational mode. We have carried out measurements of the nondissociative sticking coefficient, S0, of CO2 on the Pt(111) surface in the zero coverage limit as a function of incident kinetic energy, Ei, at different angles of incidence. A most interesting feature of the measured S0 for this physisorption system is its slow decline from 0.6 at Ei=60  meV towards a value of S0≊0.1 at the highest measured energy of 1.2 eV. Our classical trajectory studies suggest that the observed high energy tail of S0 is primarily due to translational–rotational (T–R) energy transfer in the initial collision of the molecule with the surface while the effects of the intramolecular vibrations on S0 are negligible. The calculated S0 depends nonmonotonically on the rotational anisotropy of the molecule–surface interaction. This is shown to be an effect of the dramatic influence of the number of bounces made by the two ends of the molecule against the surface in the initial collision on the T–R energy transfer.
Deposition and modification of titanium nitride by ion assisted arc deposition
Authors: Bendavid A. , Martin P. J. , Wang X. , Wittling M. , Kinder T. J.
Published: July 2002

TiN films were deposited at ambient temperature onto silicon and sapphire substrates using a filtered Ti cathodic arc source and concurrent bombardment from a low energy nitrogen ion beam. The energy and flux of the nitrogen ions were varied and the influence on stress, microhardness, preferred orientation, and surface roughness of the deposited films was investigated. It was found that the stress and microhardness were linearly related and that both decreased with increasing energy of the bombarding ions. The range of TiN microhardness was found to be 26–38 GPa and the compressive stress was found to vary over the range of 0.15–7 GPa. The preferred orientation of the film was sensitive to film thickness, ion energy, and the arrival ratio of nitrogen to titanium ions.
Structural analysis of hydrogenated carbon films obtained by reactive direct current magnetron sputtering
Authors: Fujimaki Shigehiko , Matsumoto Hiroshi , Kokaku Yuichi , Kitoh Makoto , Tsumita Norikazu
Published: July 2002

Amorphous hydrogenated carbon films were prepared by reactive direct current magnetron sputtering in argon plasma containing methane as the reactant gas. The films were characterized using various spectroscopic measurements such as Raman scattering, optical absorption spectroscopy in the ultraviolet–visible region, and infrared (IR) absorption spectroscopy. The spectral analyses indicated that changes in Raman spectroscopy intensity occurring with increasing methane gas content were determined to be caused by changes in optically resonant components in the films. Furthermore, a significant correlation was seen between the relative intensity of IR peaks and wear durability.
Dependence of photochemically etched porous silicon formation on photoetching wavelength and power
Authors: Jones L. A. , Yükseker Ö. , Thomas D. F.
Published: July 2002

It is well known that porous silicon can be formed by the combined chemical action of HNO3 and HF and that this reaction with silicon can be initiated by light. With n-type silicon in a diluted etching solution in the dark, the etching process can be controlled by the exposure of selected areas of the sample to light. In this work, different lasers are used to investigate the wavelength and power dependence of this etching process. It is found that the use of higher energy photons produces fluorescent porous silicon which emits light of a higher energy. It is also observed that increasing etching laser intensity also produces porous silicon which fluoresces at a higher energy. Studies to investigate the effect of etching laser intensity on the fluorescence intensity were inconclusive, suggesting that it plays a minor role compared to other environmental factors. Fluorescence micrographs show that the etched regions, though irradiated by spatially symmetric radiation, were nevertheless irregular in shape, clearly influenced by the reaction-diffusion dynamics of the chemical kinetics. As well, different regions of the etch spots clearly emitted light of different wavelengths, indicating that narrower emission profiles than are normally associated with porous silicon are possible when examined on length scales of tens of microns. Low duty cycle pulsed radiation was not effective in producing porous silicon which provides some indication about the time frame for the etching process to be photoinitiated.
Outgassing rate characteristic of a stainless-steel extreme high vacuum system
Authors: Chun Inkyu , Cho Boklae , Chung Sukmin
Published: July 2002

Using an extremely dry nitrogen venting system, fast return to ultrahigh vacuum condition was achieved. The apparatus is similar to that of our earlier extreme high vacuum publication. The system pumps to 1.1×1−10 and 1.4×10−11 Torr in 5 and 50 h, respectively, after the start of pumpdown and without bakeout. The pressure-time curve for pumpdown shows that the system pressure is determined by surface outgassing which decays algebraically as t−α, where the slope α changes from 2.13 for p≥10−9 Torr, 1.24 for 10−10≤p≤10−9, and 0.82 for p≤10−10 Torr. However, α=0.5, which would be expected for bulk diffusion, was not observed. Curve fitting yields desorption energies of 19, 20, 21, 22, and 23 kcal/mol for five types of adsorption sites on the surface for water. Analysis suggests that the elimination of water with desorption energies of 20 and 21 kcal/mol is essential for rapid pumpdown to the 10−10 Torr decade. A desorption energy of 10.4 kcal/mol for hydrogen was obtained by outgassing rate measurement. This relatively small value is suggestive of a smooth oxide layer formed on the chamber wall.
Cu (In,Ga)Se2 thin films and solar cells prepared by selenization of metallic precursors
Authors: Başol Bülent M. , Kapur Vijay K. , Halani Arvind , Leidholm Craig R. , Sharp Jon , Sites James R. , Swartzlander Amy , Matson Richard , Ullal Harin
Published: July 2002

CuIn(1−x)GaxSe2 (CIGS) thin films with Ga ratio, x, ranging from 0.55 to 0.75 were grown on Mo/glass substrates by the selenization of metallic precursors in a H2Se atmosphere. Without a postdeposition annealing step the films were found to have a highly graded composition that became Ga rich near the absorber/Mo interface. A high-temperature annealing step promoted diffusion of Ga to the surface region of the films. These absorbers were used to fabricate glass/Mo/CIGS/CdS/ZnO thin-film solar cells with open-circuit voltages ranging from 0.4 to 0.74 V and efficiencies approaching 12%. Devices, as well as the absorber layers, were characterized.
Reactive magnetron sputter deposition of polycrystalline vanadium nitride films
Authors: Chu X. , Barnett S. A. , Wong M. S. , Sproul W. D.
Published: July 2002

Polycrystalline vanadium nitride films were deposited onto M2 steel substrates using a high-rate reactive dc magnetron sputtering system by sputtering vanadium metal in an Ar+N2 atmosphere under N2 partial pressure control. The crystal structure, surface morphology, and properties of the films were affected by several process parameters such as nitrogen partial pressure, target power, and negative substrate bias. Analytical techniques including x-ray diffraction and scanning electron microscopy were used to characterize the structure and morphology of the films, and the mechanical properties of the films were measured by a Vickers microhardness and a scratch adhesion testers. The nitrogen partial pressure was found to be the dominant deposition parameter for the formation of different phases which includes crystalline V metal, hexagonal β-V2Nx, and cubic δ-VNx, amorphous V–Nx solid solution, and their mixtures. The film hardness was affected by crystalline phase, and a maximum hardness of 3000 kgf/mm2 Hv0.05 was found at the β-V2Nx phase. The morphology of the films varied in a wide range from cauliflowerlike rough and porous surface to smooth and dense surface, and can be correlated to deposition parameters.
Influence of envelope geometry on the sensitivity of ‘‘nude’’ ionization gauges
Authors: Filippelli Albert R.
Published: July 2002

This article presents the results of some measurements of the influence of envelope size and shape on the N2 sensitivity of two nominally identical ‘‘nude’’ extractor ionization gauges, and three common ‘‘nude’’ versions of the Bayard–Alpert ionization gauge. Measurements were made over the pressure range 10−7–10−1 Pa, using typical gauge operating parameters and with vacuum chamber and gauge envelope at ground potential. Sensitivity values corresponding to the three different envelopes used in this work differed by as much as a factor of 2 (comparing maximum value to minimum value for each gauge) for the Bayard–Alpert gauges. For the extractor gauges, the differences were as large as 7%.
Epitaxial growth of Co3O4 on CoO(100)
Authors: Carson G. A. , Nassir M. H. , Langell M. A.
Published: July 2002

Under mildly oxidizing ultrahigh vacuum conditions, it is possible to form on top of CoO(100) single crystal substrates, thin films that have higher oxygen content but that preserve the overall symmetry of the CoO(100) low-energy electron diffraction pattern. X-ray photoelectron spectroscopy (XPS) and high-resolution electron-energy-loss spectroscopy (HREELS) data indicate that the epitaxial film grown on CoO(100) at 625 K and 5×10−7 Torr is Co3O4-like in both oxygen content and XP/HREEL spectroscopic characteristics. Both materials are closest packed in lattice oxygen, with the mismatch of bulk O2−–O2− distances of approximately 5%. However, the Co3O4 is only able to grow to a thickness of approximately 5 Å before the oxidation process halts. It is proposed that the orientation of Co3O4 that forms most readily on the CoO(100) surface does not present a thermodynamically stable orientation of the bulk Co3O4 substrate but is that which grows under the constraint of the best CoO(100)/Co3O4 epitaxial arrangement. While the mismatch in lattice parameters may in part be to blame for the limitation of higher oxide thickness, thicker oxide films have been grown under conditions with significantly larger mismatch.
Impedance modeling of a Cl2/He plasma discharge for very large scale integrated circuit production monitoring
Authors: Miranda Antonio J. , Spanos Costas J.
Published: July 2002

The objective of this study is to apply a physically based impedance model of a Cl2/He plasma discharge to a commercially available etcher, operating under typical production conditions. This model is to be used in conjunction with a commercial rf monitor for the purpose of process monitoring and diagnosis. A designed experiment was run to extract the impedance model for the Lam Rainbow 4400 plasma etcher. Additional test runs were performed over a range of input rf power and pressure values to determine the accuracy of the extracted impedance model. The results indicate that a nonlinear impedance model can be used to characterize the electrical behavior of a Cl2/He discharge during normal production plasma etch processes. Therefore, once drifts in the electrical signals are detected by the rf sensor, subsequent analysis of the impedance can help determine the cause of the shift and eliminate any lengthy downtime.
Pulsed laser deposition of conductive SrRuO3 thin films
Authors: Jia Q. X. , Foltyn S. R. , Hawley M. , Wu X. D.
Published: July 2002

In this article we describe the pulsed laser deposition of smooth, particulate-free, and high conductivity SrRuO3, which are well suited for use as bottom electrodes in high capacity integrated thin-film capacitors. The films were heteroepitaxially grown on (100) LaAlO3 substrates at temperatures above 650 °C. Scanning tunneling microscopy measurements revealed that higher deposition temperatures produced larger grain sizes, and it was found from x-ray diffraction and four-probe tests that higher temperatures also led to improved film crystallinity and conductivity, respectively. At a deposition temperature of 775 °C, the room-temperature resistivity of SrRuO3 films was 280 μΩ cm, and the residual resistivity ratio was 8.4, making these materials excellent candidates for use as thin-film electrodes.
Combination of a cryopump and a non-evaporable getter pump in applications
Authors: Giannantonio R. , Succi M. , Solcia C.
Published: July 2002

A preliminary study on the pumping performance of a cryopump combined with a high-capacity non-evaporable getter (NEG) pump was performed. The pumping speed, the pump-down time, and the gas composition in a standard UHV chamber were evaluated using the cryopump alone and combined with a high capacity getter pump made from sintered porous getter material. In order to exploit the high specificity of the getter pump for hydrogen and water vapor, the cited quantities were measured both before and after a baking treatment. It was found that the ultimate pressure in the baked chamber could be greatly improved using the getter pump and that pump-down times of the unbaked chamber were consistently reduced due to the very high pumping speed of NEGs for water vapor.
Surface oxidation chemistry of β-SiC
Authors: Pehrsson Pehr E. , Thoms Brian D.
Published: July 2002

Well-ordered, Si- and C-terminated β-SiC (100) surfaces were oxidized at low oxygen pressure and high temperature to elucidate the mechanism of oxidation. The samples were studied by high resolution electron energy loss spectroscopy (HREELS), Auger electron and electron loss spectroscopies, and low energy electron diffraction. Si-terminated surfaces exposed at Tsub=1050 °C to either O2 or hot filament-activated oxygen (O+O2*) and then cooled without oxygen were C-terminated and exhibited similar oxidation rates, surface composition, and HREELS spectra. The change from Si- to C-termination slightly shifted the surface optical phonon. Activated oxygen played no discernible role in the removal of the Si overlayer at this temperature. Samples oxidized under similar conditions but cooled under oxygen were Si-terminated, indicating that the surface lost carbon as CO and CO2 during cooldown. The conversion from Si- to C-termination during oxidation did not occur because of self-limiting etching of a Si monolayer, but rather because the oxidation products of silicon volatilized more rapidly than those of carbon. Oxidation at room temperature resulted in formation of a Si oxide layer.
Characterization of helicon wave plasma for a thin film deposition process
Authors: Kim Seon-Hyo , Kim Ig-Hyeon , Kim Ki-Sung
Published: July 2002

The helicon wave plasma source coupled with a 13.56 MHz rf field has been characterized with the aid of an electrical probe and the retarding field energy analyzer in order to investigate the possibility of application for a thin film process. The high values of Ar plasma density (greater than 1013 cm−3 in the plasma column and 1011 cm−3 in the reaction chamber) can be obtained under the condition of resonant coupling. The uniformity of plasma density around the substrate in the deposition chamber was achieved by surrounding magnetic multipoles in the cusp field configuration. The deposition of BN film on the Si substrate was successfully carried out by dissociating the borazine (B3N3H6) precursor in the plasma. Due to the high density plasma, the deposition proceeds at a satisfactorily fast rate despite the low pressure of 0.3 mTorr.