bluuebunny/crossref_metadata_2025 huggingface dataset:
Sequential deposition of SiO2 and poly-Si in isolation trenches
Authors: Zirkle Thomas E. , Wilson Syd R. , Sundaram Sam L. , Cale Timothy S. , Raupp Gregory B.
Published: July 2002

Low pressure chemical vapor deposition (LPCVD) of SiO2 from tetraethoxysilane followed by LPCVD of polycrystalline silicon (poly-Si) from silane is used to refill isolation trenches. Two important characteristics of the refilled trenches which can adversely affect subsequent processing are the position of the void in the poly-Si and the depth of the groove along the top of the trench. We use evolve, a physically based, low pressure deposition simulator, to study the effects of trench width and the details of the trench profile before refill on void position and groove depth. Simulated SiO2 and poly-Si profiles in trenches with aspect ratios which range from near 4 to 20 are in good agreement with experimental profiles. In particular, evolve’s predictions of (1) the void position as a function of the position of the edge of the nitride film on the wafer’s surface, and (2) the depth of the groove as a function of the trench aspect ratio agree well with available experimental information. The reaction rate expressions used in evolve were developed in independent experiments. We do not adjust any parameters, and our simulations are entirely physically based.
Depth profiling of nonconductive powders using low-pressure radio-frequency plasma
Authors: Dang Tuan A. , Meyers Gail , Cuddy JoAnn
Published: July 2002

Depth-profile analyses of insulating materials have been frequently carried out with an ion gun. The use of an ion gun generally results in preferential sputtering and poor depth resolution. Uniform sputtering of nonconductive powders can be achieved using a low-pressure radio-frequency plasma. The powders were dispersed in a conductive medium to enhance the charge dissipation. The technique was tested with many nonconductive powders including latex spheres, Y2O3, Zn2SiO4, BaSi2O5 and ZrO2. Preferential sputtering caused by charging was not observed in any of the samples studied. In the case of ZnS, preferential sputtering was detected but it was the result of multicrystallite orientations existing in the sample.
Tunnel current controlled atomic force microscope designs
Authors: Kim H. S. , Bryant P. J.
Published: July 2002

The atomic force microscope (AFM) designs described here are based on the high sensitivity of scanning tunneling microscopy (STM) technology. It utilizes short range repulsive contact forces between a small stylus and a sample surface to produce high resolution images of defects and structural features of the surface. An adjacent tunnel gap controls contact forces and provides a very sensitive feedback signal for a Z-direction piezoelectric drive to maintain a constant force value during raster scanning. A STM may serve as an AFM by attaching an AFM adapter. The same piezoelectric drive mechanism, electronics, and recording system can be automatically employed to produce AFM images. This report contains a progression of AFM designs, based on the tunnel current control principle, construction and calibration of AFM levers, AFM applications, and high resolution AFM images.
Adsorption and decomposition of 2-chloroethyl ethyl sulfide on Pt(111): A temperature programmed desorption and laser-induced thermal desorption/Fourier transform mass spectrometry study
Authors: Zhou X.-L. , Sun Z.-J. , White J. M.
Published: July 2002

Using temperature programmed desorption and laser-induced thermal desorption/Fourier transform mass spectrometry, we have investigated the adsorption and thermal decomposition of 2-chloroethyl ethyl sulfide, a simulant for mustard gas, on Pt(111). At 90 K, sulfide adsorption, through the sulfur atom, is molecular and very strong. Molecular desorption does not occur at low coverages, but at high coverages, the multilayer desorbs at 180 K and a small fraction (15%) of the chemisorbed monolayer desorbs between 220 and 380 K. Decomposition, a major reaction channel (85%) for the chemisorbed monolayer, occurs between 280 and 380 K, producing surface ethylidyne (CCH3) and sulfur, and gaseous HCl, H2 , and C2H4 at low coverages and, in addition, C2H6 and S(C2H5)2 at high coverages. The CCH3 decomposes, releasing H2 , between 450 and 700 K. The remaining surface carbon and sulfur poison the surface for further decomposition of the sulfide. We discuss the decomposition mechanism and the effect of adsorbed atomic O on decomposition.
Electronic structure of Au–Ti intermetallics
Authors: Bzowski A. , Sham T. K.
Published: July 2002

Core-level binding energy shifts and valence-band behavior for Au–Ti intermetallic compounds Au2Ti and AuTi3 have been studied with x-ray photoelectron spectroscopy. It is found that the observed Au 4f binding energy shift of the intermetallic compounds, relative to the pure metal, is not consistent with simple electronegativity predictions. The results are interpreted in terms of a charge compensation model, i.e., that there is an increase in the number of sp-like conduction electrons accompanied by a decrease in the d-electron count at the Au site resulting in a small net charge flow onto Au from Ti. Au L2,3 x-ray absorption near edge structure measurements provide independent evidence for d-charge depletion at the gold site. A significant valence-band narrowing as well as a reduction in the spin-orbit splitting of the Au portion of the d band is also observed upon dilution. The implications of these results are discussed.
Predosed oxygen temperature programmed desorption as a kinetic probe of dehydrogenation on Pt(111)
Authors: Zhou X.-L. , White J. M.
Published: July 2002

Based on the propensity of surface atomic oxygen O(a) to react fiercely with H(a) on Pt(111) to form water that desorbs at low temperature, we have developed a thermal reaction and desorption technique—predosed oxygen temperature programmed desorption (POTPD)—which is useful for probing the kinetics of dehydrogenation on Pt(111). The method relies on very low coverages of O(a) which react with available adsorbed atomic H to form water, which desorbs promptly. Thus, the H2O temperature programmed desorption reflects the dehydrogenation process. We have successfully utilized POTPD to determine the dehydrogenation temperatures of methylene (CD2), methyl (CD3), vinyl (CHCH2), ethylene (C2D4), ethyl (C2D5), thioethoxy (SC2H5), and diethyl sulfide [S(C2H5)2] on Pt(111). From the data, a mechanism and kinetic parameters for vinyl to ethylidyne conversion are presented.
Infrared spectroscopic studies of bimetallic electrochemical interfaces: Carbon monoxide coadsorbed with metal overlayers on ordered low-index rhodium and platinum surfaces
Authors: Kizhakevariam Naushad , Weaver Michael J.
Published: July 2002

The influence of underpotential deposited (upd) copper on Rh(111) and (110) electrodes and of predosed antimony on Pt(111) electrodes upon coadsorbed carbon monoxide in aqueous 0.1 M HClO4 has been examined by means of in situ Fourier transform infrared spectroscopy in the C-O stretching (νCO) frequency region as illustrative examples of the use of infrared spectra to discern microscopic interactions in such binary electrochemical systems. Saturation dosages of CO in the presence of small upd copper coverages on Rh(111) yielded segregated coadsorbate domains as evidenced by νCO spectra. In contrast, the corresponding data for CO and copper on Rh(110) are consistent with the presence of intermixed adlayer structures as indicated by the marked decreases in the terminal νCO frequency and the selective removal of the CO bridge band. The irreversibly adsorbed nature of antimony adlayers on Pt(111) enabled the effect of known and adjustable metal coverages, θSb, upon the νCO spectra to be examined for various postdosed CO coverages. Increasing θSb yields approximately commensurate decreases in the saturation CO coverage, along with a progressive shift in site occupancy from twofold bridging to terminal coordination as deduced from the relative infrared band intensities. At the saturation antimony coverage, θSb=0.3, the CO binding is exclusively terminal. These results are consistent with adsorption of antimony chiefly in bridging sites, yielding a microscopically intermixed adlayer with CO. The observed greater tendencies to form intermixed adlayers for Sb–CO than for Cu–CO, and on (110) vs (111) surfaces are consistent with steric and electronic expectations.
Room temperature reaction of thin Ni films with Al(110) surfaces
Authors: Shutthanandan V. , Saleh Adli A. , Smith R. J.
Published: July 2002

We report the results of high-energy ion backscattering and channeling (HEIS) experiments together with x-ray photoemission spectroscopy (XPS) to determine the interface structure for thin Ni films deposited on Al(110) single crystal surfaces at room temperature. Measurements of the Al and Ni surface peak areas (SPA) show that the Ni atoms do not form a simple overlayer on the Al substrate, but react with and displace Al substrate atoms. The reaction continues with two different rates for a range of Ni coverage from 0 to 8 monolayers (ML) before Ni begins to cover the surface, which differs significantly from the thermally reacted Ni/Al systems. For the first 2.3 monolayers of deposited Ni, the NiAl phase is formed with additional displaced Al atoms at the interface, while for Ni depositions between 2.3 and 8.1 ML, a Ni3Al phase is formed. These phase identifications were made using XPS measurements of the Ni-2p3/2 peak chemical shifts and the shape and separation of the energy loss peak. The reaction at the interface is simulated using the embedded atom method to calculate the interaction between Al and Ni atoms. One ML of Ni atoms was initially distributed in small clusters on the Al surface, and a Monte Carlo approach was used to generate snapshots of the evolving interface. Computer simulations of the HEIS yield from these snapshots show an increase in the SPA of Al in good agreement with our experimental measurements.
Face-centered-cubic (111) to body-centered-cubic (110) transition in epitaxial Fe on Cu(111)
Authors: Kief M. T. , Egelhoff W. F.
Published: July 2002

X-ray photoelectron forward scattering and CO-titration measurements show that Fe agglomerates on Cu(111). Deposition of 6 monolayers of Fe at 300 K covers only ∼90% of the substrate. However, deposition of 3 monolayers of Fe at 80 K covers ∼95% of the substrate. The changing film morphology is reflected in the epitaxial phase of the Fe film. Fe deposited on Cu(111) at a substrate temperature of 80 K grows body-centered-cubic (bcc), but Fe deposited at a substrate temperature of 300 K initially grows face-centered-cubic and relaxes to bcc with increasing thickness. The changing epitaxial crystalline phase is discussed in terms of the intrafilm interaction strength relative to the film–substrate bond strength.
Cl2 gas corrosion and outgassing of various surface-treated aluminum alloys
Authors: Iguchi H. , Momose T. , Ishimaru H.
Published: July 2002

We conducted corrosion tests on eight types of surface-treated aluminum alloy sample chambers using chlorine gas (Cl2: 99.5%, H2O: 0.5 wt. %, 2.2 kg/cm2, 20 °C, for 330 h). The outgassing rates before and after baking, both before and after the corrosion test, was measured using the throughput method. Our measuring system can quantify an outgassing rate of 10−14 Torr ℓ s−1 cm−2, which was achieved by lowering total outgassing from the measuring apparatus. Following chlorine gas exposure, the outgassing rates from these samples increased several times to several tens of times before baking, but decreased remarkably after baking. For example, the outgassing rate increased 18 times for the EX-extruded sample, and 1.5 times for Al2O3 coated sample after Cl2 exposure before baking. But after baking, the rates were lower than those before Cl2 exposure. For example, 24 h after baking, the rates for the EX-extruded sample were: 6.2×10−14 Torr ℓ s−1 cm−2 before Cl2 exposure, and 2.5×10−14 Torr ℓ s−1 cm−2 after Cl2 exposure. The rates from the Al2O3-coated sample chamber were: 1.6×10−13 Torr ℓ s−1 cm−2 before Cl2 exposure, and 9.6×10−14 Torr ℓ s−1 cm−2 after Cl2 exposure. The outgassing rates from other surface-treated samples decreased by 1/2–1/3 after Cl2 exposure followed by baking. Scanning electron microscopy and Auger electron spectroscopy analyses support our proposition that the process of corrosion and subsequent baking contribute to the removal of a hydroxide film from the aluminum alloy surfaces and to the growth of a thicker oxide surface film, which further impedes hydrogen diffusion from the aluminum bulk and into the vacuum, resulting in a decrease in the outgassing rate. Through the measurement of outgassing rates from eight different surface-treated aluminum alloy samples before and after corrosion test, we have verified their corrosion resistance and discovered that chlorine gas exposure followed by baking causes their outgassing rates to decrease.
Preparation of microcellular foam in cylindrical gold targets
Authors: Apen Paul G. , Armstrong Sherman V. , Moore Joyce E. , Espinoza Brent F. , Gurule Vivian , Gobby Peter L. , Williams Joel M.
Published: July 2002

The preparation of microcellular foam in submillimeter cylindrical gold targets is described. The gold cylinders were fabricated by electroplating gold onto a silicon bronze mandrel and leaching the mandrel with concentrated nitric acid. After several rinsing and cleaning steps, the cylinders were filled with a solution containing trimethylolpropanetriacrylate (TMPTA). Low density, microcellular polymeric foam was prepared by in situ photopolymerization of the TMPTA solution. Foam preparation was extremely sensitive to metal ion contaminants. In particular, copper ions left behind from ineffective leaching of the silicon bronze mandrels inhibit polymerization and must be removed in order to obtain uniform, nonshrinking foams. A procedure for the effective leaching of the mandrels is described. In addition, a study on the effects of potential contaminants and polymerization inhibitors on TMPTA photopolymerization is presented.
High sensitivity He desorption leak detection method
Authors: Rao M. G.
Published: July 2002

A new high sensitivity leak detection method has been developed for the superconducting radio-frequency (SRF) acceleration cavities for the CEBAF linacs. The vacuum integrity of the SRF cavity pairs and the associated indium-sealed vacuum flanges is essential for the successful operation of the accelerator. These SRF cavity pairs are immersed in superfluid helium to minimize rf heat load to the cryogenic system. Conventional leak detection techniques are not appropriate to leak check these cavity pairs at superfluid helium temperature (2 K), since He will be adsorbed onto the cavity surfaces. Further, the sensitivity of the conventional leak detectors is limited to 10−11 atm cm3 s−1 at 293 K. In this article, the details of the He desorption leak detection procedure and the results with production cavity pairs are presented.
Dissociative chemisorption of oxygen on Ir(110) as a function of angle of incidence: The effects of kinetic energy and surface temperature
Authors: Verhoef R. W. , Kelly D. , Weinberg W. H.
Published: July 2002

Using supersonic molecular beams we have measured the initial probability of dissociative chemisorption of molecular oxygen on the Ir(110) surface as a function of the polar angle of incidence and the incident kinetic energy at surface temperatures of 88, 400, and 1000 K. For incident energies between 4 and 27 kcal/mol (the highest energy investigated) the data can be collapsed onto a single curve by plotting them as a function of the variable Ei cosn θi. This exponent n decreases with increasing surface temperature from 2 (88 K) to 1.56 (1000 K). These results indicate that even for a microscopically rough surface such as Ir(110), the importance of parallel momentum dissipation is dictated by surface temperature and not just by surface geometry.
Mechanism for CO oxidation and oscillatory reactions on Pd(110)
Authors: Bondzie V. , Kleban P. , Browne D. A.
Published: July 2002

The occurrence of kinetic oscillations in the catalytic oxidation of CO on Pd(110) has been attributed to the periodic formation and depletion of subsurface oxygen. Using a Langmuir–Hinshelwood mechanism and the individual reaction steps, Bassett and Imbihl proposed a simple reaction model for the oscillations. In this article, we apply their model to the results of CO titration of a preadsorbed oxygen adlayer on this surface. This shows that the CO–O reaction rate constant used by Bassett and Imbihl is too large by a factor of ≊100. Using corrected values of the reaction constants, however, we can accurately model the results of the titration experiments, both with and without subsurface oxygen. Further, with these changes the model no longer reproduces the oscillatory behavior. These findings imply that the correct mechanism for oscillations on Pd(110) has yet to be identified. Our results also suggest that the reaction of CO with a preadsorbed oxygen overlayer may proceed isotropically rather than one dimensionally.
Novel embedded capacitive sensors for monitoring the cure of polyimide in multichip modules
Authors: Pan Zikang , Hesketh P. J. , Maclay G. J.
Published: July 2002

Efficient and cost-effective manufacturing techniques can be aided by built-in microsensors. In order to monitor the curing of polyimide, an important component of multichip modules two types of embedded capacitive sensors have been developed. One is composed of parallel plates, the other is formed by interdigitated electrodes. The capacitors fabricated on multiple UltradelR 4212 polyimide layers probe the dielectric constant and thickness of the polyimide. Capacitance and loss factor of the sensors are measured after curing the polyinide over the temperature range 100–350 °C, as a function of frequency from 100 kHz to 1 MHz. The interdigitated capacitance decreases during the curing cycle to a stable value indicating that the cure has taken place. Curing time-temperature measurements indicate that a temperature is critical for complete curing. The dielectric constant is calculated from the measured interdigitated capacitance using Schwartz–Christoffel transformation. The film thickness is determined from the parallel plate capacitance. The interdigitated capacitance increases by 4.5% due to humidity, however, when baked at 350 °C the capacitance returns to its initial value. Interdigitated capacitance changes by 10.8% with extra polyimide coating layers.
Oxidation of silicon with a hot oxygen beam
Authors: Ono Tetsuo , Hiraoka Susumu , Suzuki Keizo
Published: July 2002

The oxidation of Si (100) surface with a hot oxygen beam is demonstrated at low substrate temperatures. Oxygen molecules flow through a furnace tube then expand into a vacuum where the beam strikes the Si substrate. The oxidation rate can be controlled to a very slow rate (∼0.1 nm/min) by controlling the thermal dissociation ratio of O2. The oxidizing species that migrates through the oxide is O−. The density of Pb centers at the Si (111)-SiO2 interface measured by electron spin resonance is ∼1.5×1012 cm−2.
Role of contaminants in electron cyclotron resonance plasmas
Authors: Goeckner M. J. , Meyer J. A. , Kim G.-H. , Jenq J.-S. , Matthews A. , Taylor J. W. , Breun R. A.
Published: July 2002

In this article, we examine the influence of contaminants on an electron cyclotron resonance discharge. For our discharge, the measured level of contaminant was highest just after startup, decreasing to a stable level after approximately 20 min.This is consistent with a limited source of gas trapped in the chamber walls. It is shown that the presence of these contaminants cause both the plasma and floating potentials vary by several volts. These potential variations are largest when the contamination is largest. Such variations were found in N2, CF4, and CHF3 discharges. The observed variation in the plasma potential should be of great concern in plasma-aided manufacturing environments. The larger variations represent approximately 10% of the potential that one would typically apply between a device and the plasma. Such large changes in the potential might result in substantial changes in both etch rate and anisotropy. This can have particularly adverse effects on those devices having fine structures. Thus, one should monitor these contaminants and not process devices while the contaminant level varies.
Cosputtering and serial cosputtering using cylindrical rotatable magnetrons
Authors: Belkind A.
Published: July 2002

Cosputtering allows the deposition of a variety of mixed materials. Using a dual cylindrical rotatable magnetron assembly, cosputtering can now be applied to large-area in-line deposition. Inclination of the magnets of the cylindrical magnetron assembly causes increased target cross contamination, modifying the target surfaces and resulting in more uniform compositional depth distribution of the films. The results of deposition of several mixed oxides and nitrides prepared from different pairs of elemental targets are reviewed. Serial cosputtering is another method that provides homogenized composition distributions in depth of mixed material films deposited in an in-line system. Serial cosputtering is based on sequential sputtering of a material from a planar target on top of a rotatable one which is made of another material, then sputtering both materials from the second target onto the substrate. Serial cosputtering does not require one to incline magnet assemblies. That preserves the technologies already developed. In cosputtering with rotatable magnetrons all material components are in the form of cylindrical targets, whereas in serial cosputtering the addition of a new material is realized in the form of a planar target which is much easier to manufacture. Mixed films of some metal alloys and mixed oxides were deposited using serial cosputtering; the process and the materials are discussed.
Application of luminescence techniques to probe surface–adsorbate interactions on oxide single crystals
Authors: Idriss H. , Andrews R. M. , Barteau M. A.
Published: July 2002

Luminescence from semiconducting metal–oxide single crystals can provide important insights into the nature of the surface–adsorbate bond. This study examines cathodoluminescence from a zinc oxide single crystal and changes induced by adsorption and reaction of various oxygen-containing reagents on the (0001) Zn-polar plane. The electron gun on board the UHV surface analysis instrument was used to excite luminescence from the solid; emission spectra were measured with an optical system external to the chamber. Both the band gap emission (in the UV region at 380 nm) and the subband gap emission (in the visible region at 500 nm) characteristic of zinc oxide were monitored in cathodoluminescence from the single crystal. Adsorption at room temperature of methanol, formic acid, acetone, 2-propanol, methyl formate and benzaldehyde on the ZnO(0001) surface produced an irreversible increase of the band gap emission in each case. The UV intensity returned to its original level (i.e., to that of clean zinc oxide before adsorption) after annealing the surface to temperatures high enough to desorb and decompose organic adsorbates (700–800 K). The increase in intensity of the UV emission was proportional to the amount of adsorbate on the surface, demonstrated by the correlation of the integrated C(1s) peak intensity of the adsorbate in x-ray photoelectron spectroscopy with the change in the luminescence intensity. The luminescence peak intensity normalized by the surface coverage, referred to as the ‘‘specific luminescence,’’ decreased with increasing ionization potential of the reactant adsorbed. Failure to normalize the change in luminescence intensity for varying saturation coverages of different adsorbates produced the opposite trend. These results demonstrate that it is essential to calibrate surface coverage independently in order to relate the perturbation of the solid to the electronic properties of the adsorbate. This work demonstrates the application of luminescence to probe reactions on oxide surfaces, it illustrates the advantages of typical UHV surface analysis instruments for such experiments, and it considers the potential for quantitative determination of the extent of charge transfer between adsorbate and surface.
In situ substrate surface cleaning by low-energy ion bombardment for high quality thin film formation
Authors: Aoki Y. , Aoyama S. , Uetake H. , Morizuka K. , Ohmi T.
Published: July 2002

The in situ cleaning of a substrate surface by low-energy ion bombardment is discussed concentrating on the effect on the quality of sputter-deposited metal thin films. The removal of carbon from the wafer surface with the addition of H2 to Ar plasma atmosphere during the in situ cleaning was confirmed by secondary ion mass spectrometry evaluation. High crystallinity Ti films were obtained by deposition using Ar/H2 in situ cleaning by low-energy ion bombardment. By the introduction of the Ar/H2 plasma in situ substrate surface cleaning, Ti film growth by sputtering was confirmed to improve its crystallinity and its surface smoothness.
X-ray photoelectron spectroscopy study of the polypropylene–magnesium interface after in situ plasma and ion treatment: Sticking, bonding, and film growth
Authors: Nowak S. , Collaud M. , Dietler G. , Gröning P. , Schlapbach L.
Published: July 2002

A study on a model system for polymer–metal interface formation after surface treatment is presented. We discuss a comparative x-ray photoelectron spectroscopy analysis of in situ plasma and ion-treated polypropylene surfaces with an evaporated magnesium overlayer. The different surface treatments are found to enhance the sticking probability of the metal vapor on the polymer surface considerably. Depending on the kind of surface treatment, different types of bonding of the Mg with the polymer are observed. The analysis of the excited plasmons is used to gain information about the interface formation. The experimental results suggest an island growth mode of the Mg.
Epitaxial growth of GaP by remote plasma-enhanced chemical vapor deposition
Authors: Choi S. W. , Bachmann K. J. , Lucovsky G.
Published: July 2002

Epitaxial films of gallium phosphide, GaP, have been grown by remote plasma enhanced chemical vapor deposition on GaP and Si substrates. Atomic hydrogen and phosphorus hydrides are generated from molecular hydrogen and phosphorus vapor in a remote radio-frequency plasma. Trimethylgallium is injected downstream from the plasma region where mixing and interaction with activated species extracted from the plasma occur. Homo- and heteroepitaxial GaP films have been produced on GaP and Si substrates respectively, at growth temperatures of 590 °C and higher. Chemical depth profiles of GaP/Si heterostructures indicate that reduced growth temperatures promote abrupt chemical interfaces and improve heterostructure electrical properties. Both homo- and heterodiodes have been fabricated from the above epitaxial structures, and their respective properties are discussed.
Enhanced tribological performance of rigid disk by using chemically bonded lubricant
Authors: Lee H. J. , Zubeck R. , Hollars D. , Lee J. K. , Chao A. , Smallen M.
Published: July 2002

Nonreactive perfluoropolyether lubricants were processed by ultraviolet (UV) radiation to make them chemically bonded to thin film magnetic disks. The tribological performance of these disks was then investigated. Disks with a range of 30–50 Å thick perfluoropolyether lubricant, were treated by using the different sources of UV radiations in air, argon, and nitrogen atmospheres. By changing the power density from 40 mW/cm2 to 50 W/cm2 and UV wavelength 185 to 365 nm, in either dry nitrogen or argon gas, a maximum of 38 Å of lubricant was chemically bonded to the thin film disks. Stiction and friction forces during 1 rpm testing were dramatically decreased with the increase in UV exposure time. Contact-start-stop test performance of disks with ∼15%–30% of chemically bonded lubricant was also significantly enhanced. An optimum amount of chemically bonded lubricant provides excellent tribological performance for thin film disks.
Etching of Si surfaces with hot chlorine beams: Translational and vibrational excitation of the incident chlorine particles
Authors: Szabò Andràs , Engel Thomas
Published: July 2002

A systematic study of etching of Si(100) and Si(111) and Ar+ bombarded Si(100) (surface with defect sites) with chlorine has been carried out. We have compared the reactivity of atomic and molecular chlorine, and studied the effect of translational and vibrational excitation of the etchant on the etch rate. Similar etch rates were obtained on the Si(100) and Si(111) single crystal surfaces. On both surfaces the major etch products were SiCl4 at Ts<500 K and SiCl2 at Ts≳600 K. Some SiCl desorption was obtained at Ts≳1100 K. We have outlined the conditions under which the etch rate, at constant incident flux, is adsorption and desorption limited. On the Si(100) and Si(111) surfaces we found that when the etch rate is reaction limited, higher etch rate can be obtained with atomic chlorine than with molecular chlorine. In the adsorption limited regime, translational excitation of both atomic and molecular chlorine results in a higher etch rate than that obtained with slow atomic and molecular chlorine. Vibrational excitation of Cl2 does not result in an enhancement of the etch rate on the single crystal surfaces studied. In the desorption limited regime the etch rate is primarily determined by the surface temperature. The nature of the etchant particles does not have a significant effect. On Ar+ bombarded Si(100), we obtained a small increase in the etch rate with translationally and vibrationally excited Cl2, and comparable enhancement is obtained with Cl2 that is only translationally excited. The difference in the etch properties of the single crystalline and Ar+ bombarded silicon surfaces points to the importance of surface defects in etching. The present results show that at room temperature the low etch rate of silicon single crystal surfaces with chlorine, as compared to etching with fluorine, is due to the low formation rate of volatile surface products.
Study on electromagnetron for plasma polymerization. II. Magnetic field enhanced radio frequency plasma deposition of organogermanium films from tetraethylgermanium
Authors: Gazicki M. , Schalko J. , Olcaytug F. , Ebel M. , Ebel H. , Wernisch J. , Yasuda H.
Published: July 2002

Construction of a reactive magnetron rf plasma deposition system with cylindrical electrodes is presented. Design of an individual electrode equipped with integrated multiple electromagnet system together with the characteristics of its magnetic field is described. Properties of magnetron discharge and plasma geometry are also presented. Deposition of organogermanium films from tetraethylgermanium in magnetically enhanced rf plasma is discussed in terms of deposition rates and general properties of the films with the particular attention paid to their density. Both, elemental composition of these films by electron spectroscopy for chemical analysis and their chemical functionality by Fourier transform infrared spectroscopy are also given. The main advantage of magnetic field enhancement is local increase of plasma density restricting the discharge, and consequently deposition, to the desired volume. Additionally, the application of a system of integrated electromagnets enables the use of magnetic field intensity as an independent process optimization parameter.
Optical anisotropy of singular and vicinal Si–SiO2 interfaces and H-terminated Si surfaces
Authors: Yasuda T. , Aspnes D. E. , Lee D. R. , Bjorkman C. H. , Lucovsky G.
Published: July 2002

We report the first investigation of the optical anisotropy of H- and SiO2-terminated Si surfaces. We examine six different orientations: (110); several vicinal (111); (113); and vicinal (001). Observed reflectance-difference (RD) spectra fall into two classes according to whether the surface normal is oriented from [111] toward [110] or [001], being consistent with the existence of different step configurations for the two cases. In the (110) class the spectral lineshapes resemble the imaginary part of the Si dielectric function, while in the (001) class they are similar to the energy derivative of the Si reflectance spectrum. To make surface and interface comparison meaningful, we develop an analytic method for correcting interface spectra for the relatively large effects of overlayer thickness. Thickness-corrected RD spectra of Si–SiO2 interfaces are found to differ in small but distinct ways from those of H-terminated surfaces of the same orientation, specifically in the enhancement of spectral features and the appearance of an optical absorption band near 3 eV. Rapid thermal annealing between 900 and 1000 °C increases oxidation-induced interface absorption for the (113) surface and red-shifts the entire spectrum for the (110) surface. We attribute these effects to a relatively high degree of order for (110)-class steps and lower order for (001)-class steps.
Vacuum ultraviolet emission from microwave plasmas of hydrogen and its mixtures with helium and oxygen
Authors: Holländer Andreas , Wertheimer Michael R.
Published: July 2002

The vacuum ultraviolet (VUV) and ultraviolet (UV) emission (112 nm≤λ≤300 nm) from hydrogen-containing microwave plasmas have been investigated, in particular the influence of plasma parameters such as gas composition, pressure, and microwave power. Helium–hydrogen plasma emits a very intense hydrogen Lyman α radiation at 121.5 nm, which is up to 40 times more intense than other lines in the spectrum. Hydrogen–oxygen plasma displays an emission which, within a selected range of the plasma parameters, resembles the absorption of molecular oxygen. We briefly discuss the usefulness of these emissions for investigating the UV photochemistry of polymers.
As capture and the growth of ultrathin InAs layers on InP
Authors: Aspnes D. E. , Tamargo M. C. , Brasil M. J. S. P. , Nahory R. E. , Schwarz S. A.
Published: July 2002

Modification of (001) InP surfaces in the absence of P and by As capture in the absence and presence of In is investigated under chemical beam epitaxy conditions by virtual-interface analysis of real-time kinetic ellipsometric (KE) data. In the absence of anion flux, from 490 to 520 °C the surface roughens microscopically at a rate of 0.06 Å/s at 518 °C, with the rate described by an activation energy of 5.3 eV. Consistent with this stability, As that accumulates on the surface under As exposure in the absence of growth can be completely removed by subsequent exposure to P, showing that As exchange is limited to the outer layer. However, As can be captured permanently by resuming InP growth before the surface has been completely purged of As or by codepositing In, thus producing ultrathin regions of InAs. Using the virtual-substrate approximation, we determine the amounts of captured As to submonolayer precision from the associated displacements of the trajectories of the ellipsometrically measured pseudodielectric function 〈ε〉 without any knowledge about the underlying layers. Photoluminescence data show that these layers are not entirely uniform but exhibit lateral thickness variations. Independent assessments of monolayer amounts of captured As by secondary-ion-mass spectrometry (SIMS) differ by a factor of two from the KE results, which may be due to layer inhomogeneity or a modified SIMS ionization sensitivity for very thin layers.
Optical thin films for waveguide applications
Authors: Mir Jose M. , Agostinelli John A.
Published: July 2002

The development of optical thin films for waveguide applications will enable a variety of new and highly useful optoelectronic functions. Many difficulties must be overcome, however, before optical films can be used in photonics applications. Properties such as polycrystallinity, surface topography, and refractive-index homogeneity can affect the performance of optical thin film waveguides to a much greater extent than in other thin film applications because of the long optical interaction lengths. Even a small degree of polycrystallinity in anisotropic media, for example, can be a significant source of optical scattering. We review recent results of epitaxial lithium tantalate thin films grown as waveguide structures on sapphire and gallium arsenide substrates. Highly oriented crystalline structures with useful optical properties have been demonstrated. Although many challenges still remain before optical thin films are used widely as waveguides, modern thin film technology is beginning to provide the tools and capabilities to make these concepts a reality.
Effect of stoichiometry on the phases present in boron nitride thin films
Authors: Hackenberger L. B. , Pilione L. J. , Messier R. , Lamaze G. P.
Published: July 2002

Boron nitride thin films were deposited by ion-assisted evaporation and characterized by neutron depth profiling (NDP), a nondestructive method for the compositional analysis of solids. The phases present in the films were determined by infrared spectroscopy. Examination of the data presented here and comparison with the work of other authors revealed that stoichiometric or nearly stoichiometric films contained the greatest amount of the cubic phase. This led to the proposition that film stoichiometry is one of the factors that stabilize cubic boron nitride in boron nitride thin films. A shift in the position of the cubic boron nitride infrared absorption was also observed by the present authors which was related to film stoichiometry. Discussion of the various techniques commonly used to determine the stoichiometry of boron nitride thin films emphasized the need for all stoichiometry measurements to be made using the same characterization method in order for all results to be compared with confidence. The advantages of NDP, such as its high accuracy and depth profiling capability, make it a suitable candidate for this application.
Dry etching of palladium thin films in fluorine containing plasmas: X-ray photoelectron spectroscopy investigation
Authors: Fracassi F. , d’Agostino R. , Cacucci A.
Published: July 2002

The dry etching process of palladium thin films has been investigated in Ar–CF4 and Ar–CF4–O2 glow discharges by performing etch rate measurements and x-ray photoelectron spectroscopic analyses. The results indicate that the process is one of physical sputtering and that fluorine atoms react with palladium forming a fluorinated layer (probably PdF) which is characterized by a lower sputtering rate than that of metallic palladium.
The effect of tilt angle on As implants in Si
Authors: Anthony J. M. , Keenan J. A.
Published: July 2002

Si wafers have been implanted with As ions (100 keV, 1.25×1015 at./cm2) at a variety of tilt angles from 0°–80°. BF2 ions (80 keV, 5×1014 at./cm2) were also implanted at 7° in each wafer to establish a consistent depth marker during secondary ion mass spectrometry (SIMS) analysis. Range, straggle, peak location, and peak concentration have been extracted from the SIMS data and are compared to predictions from TRIM. Dose measurements for the steeply angled implants are difficult with SIMS due to surface ion yield transients, so absolute dose measurements have been made using Rutherford backscattering spectroscopy and neutron activation analysis. At high tilt angles backscattering of the As ions greatly reduces the implanted fraction.
Role of C in O removal from ultrathin layers of oxidized La on Pd(100)
Authors: Graham G. W. , Rao B. U. M. , Ahmad M.
Published: July 2002

The complete removal of O from ultrathin layers of oxidized La on Pd(100), effected by heating to temperatures as low as 625 K in ultrahigh vacuum according to previous reports, was found to involve C present at levels not detected by Auger electron spectroscopy due to interference with Pd. Measurements in which Pd was replaced by Rh, where correspondingly small C levels may be detected more easily, show that surface C is indeed able to reduce oxidized La under such conditions. The elimination of C from the Pd(100) surface by means of heat treatments in O2 led to a substantial increase in thermal stability of the oxidized La, but the thermal stability of ultrathin layers of oxidized Al on Pd(100) was less affected. The NO-chemisorption behavior of ultrathin layers of oxidized La on Pd(100) was unchanged (i.e., NO adsorbs both dissociatively and nondissociatively), but the thermal stability of the atomic N was lower, comparable to that of atomic N on Pd(100).
Thin film sensors for automobiles
Authors: Taga Y.
Published: July 2002

A great amount of effort has been devoted to the constant improvement of such basic automobile performance as drivability, safety, and environmental protection. As a result, the total combination of various technologies has made it possible to produce safer and more comfortable automobiles. Among these technologies, surface and thin film techniques are mainly concerned with sensors, optics, electronics and surface modification. This article first describes a new concept of thin film processing in materials synthesis for sensors based on particle–surface interaction during deposition to provide a long life sensor applicable to automobiles. Some examples of practical applications of thin films to sensors are then given. These include (1) a poly(vinylidene fluoride) thin film for integrated pyroelectric infrared sensors, (2) a thin film strain gauge for gravity sensors, and (3) a giant magnetoresistance film for speed sensors.
Surface chemistry of carbon tetrabromide on GaAs(100)
Authors: McEllistrem M. , White J. M.
Published: July 2002

The interaction and decomposition of carbon tetrabromide on GaAs(100) has been investigated with temperature-programmed desorption and x-ray photoelectron spectroscopy. GaBr desorption is observed for all CBr4 doses investigated. The maximum GaBr desorption temperature shifts from 585 K for the lowest doses (5×1013 molecules/cm2) up to 640 K for doses exceeding 2×1014 molecules/cm2. In some cases arsenic is also observed to desorb at a temperature of 665 K. The loss of arsenic appears to be correlated with the evolution of the GaBr. Parent molecule desorption is observed at 190 K for doses exceeding 1×1014 molecules/cm2. The results are consistent with trends observed in GaAs film growth studies in which CBr4 is used as a carbon dopant source.
Effect of substrate symmetry on the preferred magnetization orientation of Ni films on Cu
Authors: Wu S. Z. , Mankey G. J. , Willis R. F.
Published: July 2002

For ultrathin Ni films grown on Cu(100) and Cu(110), the easy axis of magnetization starts out in the plane of the films. Above a critical thickness, the preferred magnetization orientation changes to perpendicular to the films. This behavior is contrary to the spin reorientation transition reported for many thin film ferromagnetic systems where the preferred magnetization orientation starts out perpendicular to the film and then switches to in-plane above a critical thickness. We report in situ surface magneto-optic Kerr effect measurements of the magnetic anisotropy as a function of film thickness. The change in the predominant domain orientation distribution occurs at 8 monolayers (MLs) for Ni on Cu(100) and at 16 ML for Ni on Cu(110). For Ni on Cu(111) no such change is observed down to 3 ML thickness. These results are discussed in terms of competing surface anisotropy and dipole–dipole energy terms.
Bulk Fermi surface determination by tuning the photoelectron kinetic energy
Authors: Avila J. , Casado C. , Asensio M. C. , Perez J. L. , Muñoz M. C. , Soria F.
Published: July 2002

The three-dimensional Fermi surface of a Cu single crystal has been measured by angle-resolved photoemission (ARUPS). Well-defined two-dimensional (2D) cuts through the bulk fcc Cu Brillouin zone have been mapped by adjusting the incident photon energy of a tunable light source. This method, conceived of as an extension of the traditional ARUPS, allows the direct visualization of Fermi surface contours from experimental two-dimensional patterns. The surface shape of constant energy at the Fermi level and its link with the translational bulk symmetries could be clearly seen by the determination of the Fermi photoelectron momentum distribution along several Brillouin zones. In addition, the 2D sections of the Fermi surface measured by photoemission have been well reproduced by a semiempirical tight binding calculation.
Using scanning tunneling microscopy to understand diffraction oscillations: Fe growth on Cu(100)
Authors: Chambliss David D. , Johnson Kevin E.
Published: July 2002

In this article we use scanning tunneling microscope (STM) measurements to improve our understanding of diffraction as a growth diagnostic applied to the complex growth behavior of Fe on Cu(100) at room temperature. We find that kinematical calculations using STM images as input can account quantitatively for many aspects of medium-energy electron diffraction (MEED) results on this system. It is also apparent in the results that an awareness of the different length scales of the problem is important for understanding the MEED data.
Very high quality thin gate oxide formation technology
Authors: Ohmi Tadahiro
Published: July 2002

A new approach to gate oxidation processes, where oxide growth is completely controlled by ultraclean technology, is presented. This approach with chemical preoxide growth in ozonized ultrapure water as a passivation layer, ramp-up in an Ar ambient with a negligible amount of residual water, and formation of high quality oxide in a reductive ambient with H radicals can completely eliminate uncontrolled oxide growth and provide very high quality thin gate oxide. The impact of organic contamination on the gate integrity is also discussed. A newly developed Fourier transform infrared technique is used for the evaluation of organic contamination on the wafer surface.
Optical method for low pressure measurements
Authors: Bello I. , Bederka S. , Haworth L.
Published: July 2002

Pressure measurements from 10−3 to 103 Pa were performed by an optical method. In this method, a radio-frequency electrodeless discharge was initiated in a small glass chamber and the discharge radiation was sensed by a photosensitive element. The radiation intensity, when converted to photovoltage, was found to increase initially with increasing pressure but, above a certain pressure threshold, it decreased. Thus, two pressure values were associated with each photovoltage reading. However, it was also found that the direct current (dc) current passing through the radio-frequency oscillator, which is related to the loss in the electric discharge, could indicate whether the photovoltage (radiation) calibration data were taken above or below the ‘‘deflection point’’ pressure in the photovoltage versus pressure curve. Hence, simultaneous measurements of the radiation intensity and dc oscillator current give a unique pressure. This optical, contactless method could be particularly useful for the determination of pressure in chemically aggressive environments and to provide automatic pressure stabilization in a radio frequency plasma system.
Electrical transport properties of hot electrons at metal, insulator, and semiconductor interfaces
Authors: Ludeke R. , Bauer A.
Published: July 2002

The application of ballistic electron emission microscopy (BEEM) to study hot electron transport phenomena over a kinetic energy range of 0–8 eV is discussed. A basic discussion of hot electron scattering in metals, semiconductors, and insulators precedes the presentation of three case studies, representing examples of transport parameters extracted from BEEM experiments. They include the determination of the energy dependence of (a) the quasielastic and inelastic electron mean free paths in Pd films, (b) the quantum yield of electron–hole pair generation through impact ionization in Si, and (c) the transmission probability of electrons through thin SiO2 layers in metal–oxide–semiconductor structures.