bluuebunny/crossref_metadata_2025 huggingface dataset:
Controlled tuning of periodic morphologies on vicinal Si(111) surfaces
Authors: Szkutnik Pierre-David , Sander Dirk , Dulot Frédéric , d’Avitaya François Arnaud , Hanbücken Margrit
Published: July 2002

Regular hole patterns have been produced on vicinal Si(111) surfaces by optical lithography. Under heat treatment in ultrahigh vacuum, morphological rearrangements of the patterned surfaces occur. In situ light diffraction experiments were carried out during heat treatment to monitor the formation of the desired morphologies by an observation of the diffraction pattern. The surface morphology was characterized by different microscopy techniques after the heat treatment. Structured surfaces with periodic two-dimensional step arrangements and one-dimensional structures of atomically flat terraces uniformly separated by straight steps were obtained. The periodic structures extend over several μm.
Etching of polysilicon in inductively coupled Cl2 and HBr discharges. IV. Calculation of feature charging in profile evolution
Authors: Mahorowala Arpan P. , Sawin Herbert H.
Published: July 2002

The ability to simulate feature charging was added to the Monte Carlo profile evolution simulator described in the companion article of this series [A. P. Mahorowala and H. H. Sawin, J. Vac. Sci. Technol. B 20, 1077 (2002)]. Two electrical assumptions were compared: (1) a perfect insulating feature and (2) a resistive feature. The potential profiles for the entire feature were generated and the ion and electron fluxes were computed along the feature surface. The resistive feature representation enabled the incorporation of bulk conduction and surface leakage that is not possible when using the insulator approximation. For highly resistive surfaces, the solutions for the two assumptions were shown to converge. With the insulator approximation, the potential profiles were calculated by determining the accumulated charge on the feature surface and solving Poisson’s equation over the entire simulation domain. Calculation of the potential profiles with the resistive feature approximation involved the determination of the steady-state current to the feature surface and solution of the current continuity in a resistive feature. Both solutions required the solution of Laplace’s equation with differing boundary conditions. The resistive feature approximation was used to study the role surface and bulk conductivities have on the potential profiles. It was shown for submicron features that the conductivities of most bulk materials could be approximated as perfectly insulating or conducting; however, surface leakage and passivation films could lead to circumstances where realistic conductivities are needed to obtain the correct solution. The charging of features was shown to scale inversely with the feature size. Therefore, charging is more significant in larger features. The materials properties of most materials lead to the conclusion that for current paths on the order of 0.25 μm, bulk materials can be treated as either perfect insulators of conductors. However, surface leakage or ultraviolet radiation may also make bulk oxide significantly conductive. Therefore, modeling it as a resistive material is required. Finally, the deposition of thin insulating layers on conductive materials could easily lead to feature charging.
Model calculations for maximum allowable leak rates of hermetic packages
Authors: Davy J. Gordon
Published: July 2002

Calculations are presented which apply to electronic packages prefilled with helium for leak testing. Depending on the geometry of the leak, the leak rate of the package, while in use in air at ambient pressure, may be equal to or less than that measured while it is tested in vacuum. Two principal flow mechanisms are identified: viscous (including slip), driven by the difference in total pressure between the inside and outside of the package; and diffusive (diffusion and molecular flow), driven by the difference in partial pressure of helium. Air leaks into the package at a rate comparable to the rate at which helium escapes by diffusive flow. An equation is presented which relates leak rate to leak geometry for a capillary leak, and generalization to other leak shapes is made. It is shown that for a 100−cm3 package, with a maximum allowable leak rate of 5×10−6 atm cm3 sec−1, if pressurized to 1 atm (gauge) with helium, most of the pressurization will be lost within a year. If unpressurized, water vapor will accumulate at nearly 3000 ppm/yr. A more stringent standard is proposed of 10−7 atm cm3 sec−1 for a package of this size when pressurized to 1 atm (gauge), or 10−8 atm cm3 sec−1 if unpressurized. The concept is introduced of the ’’marginal gross leaker,’’ defined as a package with the largest leak rate undetectable by a gross−leak test, taken here to be 10−3 atm cm3 sec−1. It is shown that the maximum allowable length of time after filling and sealing a 100−cm3 package with such a leak rate, before it loses enough helium to erroneously pass a helium leak test is 6 days if the standard is 5×10−6 atm cm3 sec−1, and 9 days if the standard is 10−7 atm cm3 sec−1.
Enhancement of field ionization efficiency of 10-μm tungsten filaments caused by the nucleation of carbide particles
Authors: Okuyama F. , Hilt E. , Röllgen F. W. , Beckey H. D.
Published: July 2002

A remarkable enhancement of the field ionization efficiency of 10-μm-diam tungsten filaments due to the nucleation of tungsten carbide particles has been observed. When a filament as the ion source of a mass spectrometer is heated at 1200–1400 K in a flow of benzene vapors while applying a high electric potential, it emits field ions intense enough to produce a mass spectrum of satisfactory quality. In striking contrast to the well-known activation process, a great increase in ion current is achieved in a short time, and very fine particles of tungsten carbide are observed to grow at the surface of the tungsten filament.
Breakdown in silicon oxide−A review
Authors: Solomon Paul
Published: July 2002

A review is given concerning measurement techniques and experimental results obtained on electrical breakdown in SiO2. Breakdown dependence on parameters such as time, thickness, temperature, and electrode material are covered, as well as the effect of various high-temperature processing steps and the effect of ion implantation. The effects of sodium in causing time-dependent breakdown are also reviewed. Special attention is given to the intrinsic breakdown mechanism in MOS capacitors where mechanisms involving impact ionization and positive charge buildup in the insulator are favored.
Solving the ’’stencil’’ problem in vacuum deposition masks using rib-supported structures
Authors: Hammer Robert
Published: July 2002

A technique is described for delineating large metallization patterns, based on the use of non-line-of-sight vacuum techniques through specially designed rib-supported mask structures. These reusable masks were developed to solve problems of fabricating masks containing long and narrow closely spaced apertures, poorly supported cantilever sections, and free-standing islands. The method provides accurate delineation of metallization patterns in a single vacuum deposition step. The masks are fabricated out of graphite by air abrasion machining.
Diagnostic methods for sputtering plasmas
Authors: Thornton John A.
Published: July 2002

This paper reviews the parameters that can be used to characterize glow discharge plasmas of the type used in many sputtering devices, and the methods available to measure those parameters. The review is also generally applicable to the plasmas used in ion plating and plasma-activated reactive evaporation. The objective is to provide a brief overview and a guide to the literature for thin-film specialists. The emphasis is on negative glow-type plasmas, and the diagnostic techniques of optical spectroscopy and electrostatic probes, since these methods are particularly effective for such plasmas and are relatively easy to implement in the laboratory. Guidelines are presented for a corona interpretation of absolute intensity line emission measurements in terms of the density of energetic electrons in an Ar-negative glow. Cases are described in which electrostatic probe measurements were used to investigate performance characteristics of cylindrical-post and cylindrical-hollow magnetron sputtering sources.
An XPS study of the adherence of refractory carbide silicide and boride rf-sputtered wear-resistant coatings
Authors: Brainard William A. , Wheeler Donald R.
Published: July 2002

Radio frequency sputtering was used to deposit refractory carbide, silicide, and boride coatings on 440-C steel substrates. Both sputter etched and pre-oxidized substrates were used and the films were deposited with and without a substrate bias. The composition of the coatings was determined as a function of depth by x-ray photoelectron spectroscopy combined with argon ion etching. Friction and wear tests were conducted to evaluate coating adherence. In the interfacial region there was evidence that bias may produce a graded interface for some compounds. Biasing, while generally improving bulk film stoichiometry, can adversely affect adherence by removing interfacial oxide layers. in all cases but the iron oxide coverage was only complete on the preoxidized substrates. The film and iron oxides were mixed in the MoSi2 and Mo2C films but layered in the Mo2B5 films. In the case of mixed oxides, pre-oxidation enhanced film adherence. In the layered case it did not.
Nondestructive characterization of interface layers between Si or GaAs and their oxides by spectroscopic ellipsometry
Authors: Aspnes D. E. , Theeten J. B. , Chang R. P. H.
Published: July 2002

The mechanism by which spectroscopic ellipsometry is sensitive to semiconductor–dielectric interfaces is discussed, and a systematic method of obtaining overlayer and interface parameters via model fitting is described. Application to the Si/thermally grown SiO2 interface shows 7.7±2.0 Å of chemically mixed a-Si and SiO2 of approximate stoichiometry SiO to be present. The amount of a-As present at GaAs/plasma-grown-oxide interface is dependent upon growth rate. Plasma oxides are found to contain about 2% unoxidized a-As.
GaAs/Ta2O5 and GaAs/Al2O3 interface structures
Authors: Nishi H. , Revesz A. G.
Published: July 2002

Tantalum and aluminum oxides were grown on n-type GaAs by thermal oxidation of Ta and by anodic oxidation of vacuum deposited Ta and Al films. The insulating properties of these films are better than those of the native oxide films on GaAs. The interface properties of the GaAs/Al2O3 interface are better than those of GaAs/Ta2O5 structures obtained so far; this is due to the fact that the interaction between GaAs and Al and/or Al2O3 is less than that occurring during oxidation of Ta on GaAs. Even a relatively small film–substrate interaction can deteriorate the properties of the oxide film and the interface. However, some controlled interaction is desired to obtain good interface properties but it is difficult to achieve. Preliminary C–V measurements at 1 MHz indicate that the properties of the GaAs/Al2O3 interface depend on the original GaAs/Al interface. If a thin native oxide is present, then the accumulation capacitance is lower than the insulator capacitance; this effect is probably due to accumulation of arsenic at the interface. From the capatitance minimum it was also found that the effective donor density at the GaAs surface decreased by about one order of magnitude; this is probably due to Ga migration during the oxidation. However, an important observation was that an accumulation capacitance coinciding with the insulator capacitance could be obtained if a preoxidation heat treatment of the GaAs/Al interface was employed. This allows the incroporation of the room ambient oxide film on GaAs into Al2O3 film; i.e., a new interface is established which has promising properties, but the essential features of the Al2O3 films are maintained.
Practical results of EL2
Authors: Giuffre G. J. , Marquis J. F. , Pfeiffer H. C. , Stickel W.
Published: July 2002

Samples of resist images and device structures are presented, which demonstrate system performance aspects of pattern image fidelity and overlay accuracy of the variable-shape spot (VSS) lithography tool EL2. Test pattern exposure giving qualitative, but more comprehensive information about image fidelity, are compared to quantitative results of resolution measurements with the knife-edge scanning technique. The preeminent resolution limiting electron-optical aberrations determined by complex electron–electron interactions, are explained and put in perspective. Several EL2 systems have been equipped with VSS columns tailored to applications ranging from submicron lithography to 2 μm minimum images over fields of deflection up to 8×8 mm2. Images obtained in test patterns correspond to 10 000 fabricated lines per field. It is shown how the pattern overlay accuracy is determined. The results quoted satisfy technology requirements within an error level of three times the standard deviation.
Variable spot shape control electronics
Authors: Woodard O. C. , Ho C. T. , Michail M. S. , Muir A. W. , Williams M. C.
Published: July 2002

The electronics, calibration, and registration techniques required to dynamically control electron beam spot size, position, and blanking on a spot-by-spot basis to write and overlay integrated circuit patterns are described in this paper. Pattern data which has been converted from a graphic language format to a compressed raster format is supplied to the Digital Control Unit (DCU) where it is expanded to provide control data at a 460 per spot rate to the Analog unit. The analog unit provides deflection voltages to the electron beam column which control retangular spot size and position to a resolution of 0.125 μm in X and Y over an 8 mm field, or 0.0625 μm over a 4 mm field. Pattern accuracy is assured by an automated deflection calibration system. A calibration grid placed underneath the beam is scanned using the same beam deflection pattern and field as that used for writing. Backscatter electrons from the grid are detected and the resultant signal processed to determine the deflection error at 900 points over the field. Corrections are applied to the deflection and the grid is rescanned. This process is repeated until the errors are within specified limits. Overlay of patterns is assured by registering to fiducial marks incorporated into the pattern to be overlayed. Four marks, one in each corner of the pattern, are scanned prior to writing. The resulting backscatter electron signals are processed to determine the errors in the four corners of the field. Corrections are claculated and applied as the pattern is written. Calibration techniques, registration techniques, and circuit performance criteria required to achieve 0.6 um pattern overlay over an 8 mm field are presented.
Anisotropic plasma etching of polysilicon
Authors: Mogab C. J. , Levinstein H. J.
Published: July 2002

Plasma etching of polycrystalline silicon films for fabrication of silicon gate MOS integrated circuits has been studied with emphasis on fine-line devices. CF4–O2 plasmas, commonly used for etching silicon, are unacceptable for very fine features because the etching is isotropic and load dependent. This results in substantial undercutting and insufficient dimensional control. Several alternative gases were investigated in a parallel–plate reactor. CF3Cl and a 70% CF3Br–30% He mixture were found to provide selectivities of 30:1 and 16:1, respectively, over thermal SiO2, freedom from loading effects and a large vertical to lateral etch rate anisotropy which minimizes undercutting. Extensive measurements of etch rate and edge profile as a function of gas composition were made for C2F6–Cl2 plasmas. Fully anisotropic etching (zero lateral etch rate) was observed at low Cl2 concentrations with a selectivity ≳6:1 over thermal SiO2 when using conventional photoresist masks. The vertical and lateral etch rates and the selectivity increase with increasing Cl2 concentration for n-type polysilicon. The dependence of etch rate on Cl2 concentration for p-type polysilicon is nearly identical to that for undoped polysilicon, whereas n-type material etches faster than undoped material with the etch rate ratio (n-type:undoped) increasing with Cl2 concentration. Values for this ratio as large as 15:1 were measured. ’’Pattern sensitivity’’ was observed with photoresist masks such that at low Cl2 concentrations etching was slower in the vicinity of resist features while at high Cl2 concentrations etching was faster near resist features as compared to open (unmasked) areas of the same film. Pattern sensitivity was negligible at an intermediate Cl2 concentration. Results of effluent sampling with IR absorption and mass spectrometry and spectral analysis of optical emission from the plasma suggest that Cl atoms are the likely active species. It is conjectured that the anisotropy in etch rate is a consequence of enhanced chemical reaction between Cl and Si on surfaces which are ion (or electron) bombarded while lateral etching is suppressed by the combination of CF3 radicals and Cl atoms on surfaces which are not ion (or electron) bombarded.
Gas plasma etching of ion implanted chromium films
Authors: Yamazaki T. , Suzuki Y. , Nakata H.
Published: July 2002

The etching characteristics of ion implanted chromium films in gas plasmas have been studied. It was found that in the case of Sb+ and As+ the etching rate of implanted chromium films decreased with increasing ion dose. It was also found that the etching rate depends on the surface impurity concentration, not on the total implanted dose of ions in the film. Using chromium film samples implanted with 20 keV ions at a dose of 1×1016 cm−2, reversely etched LSI photomask patterns have been obtained with good edge profiles. It is speculated that oxides of impurities are responsible for the reversal gas plasma etching.
Ultrasmooth plasma polymerized coatings for laser fusion targets
Authors: Letts S. A. , Myers D. W. , Witt L. A.
Published: July 2002

Coatings for laser fusion targets were deposited up to 135 μm thick by plasma polymerization onto 140 μm diam DT filled glass microspheres. Ultrasmooth surfaces (no defect higher than 0.1 μm) were achieved by eliminating particulate contamination. Process generated particles were eliminated by determining the optimum operating conditions of power, gas flow, and pressure, and maintaining these conditions through feedback control. From a study of coating defects grown over known surface irregularities, a quantitative relationship between irregularity size, film thickness, and defect size was determined. This relationship was used to set standards for the maximum microshell surface irregularity tolerable in the production of hydrocarbon or fluorocarbon coated laser fusion targets.
High temperature annealing of InP anodic oxides
Authors: Fathipour M. , Makky W. H. , McLaren J. , Geib K. M. , Wilmsen C. W.
Published: July 2002

The anodic oxides of InP have previously been reported to be composed of P2O5 and In2O3 even though InPO4 is thermodynamically more favorable. In this paper the composition and topography of annealed anodic oxides were investigated with XPS, SEM, TEM, x-ray diffraction, and x-ray dispersion. It was determined that the P2O5 does not evaporate to any significant extent up to 650 °C the maximum annealing temperature of this study. Little topological change occurs at 500 °C but at 650 °C rapid changes are observed. The conversion to InPO4 or In(PO3)3 was not determined conclusively.
Photoemission spectroscopy study of aluminum–polyimide interface
Authors: Bartha J. W. , Hahn P. O. , LeGoues F. , Ho P. S.
Published: July 2002

X-ray photoemission spectroscopy has been used to investigate the chemical bonding and reactivity of the Al–polyimide interface. At 300 °C substrate temperature, initial deposition of Al reacts with polyimide up to about 3.5 ml. The reaction occurs mainly with the carbonyl group, resulting in the formation of an intermixed layer. The basic reaction continues with reduced rate up to about 11.5 ml, then unreacted Al appeared on the surface. Further deposition of Al caused formation of unreacted Al islands, as confirmed by cross-sectional TEM observations.
Surface precipitation of boron nitride on the surface of type 304 stainless steels doped with nitrogen, boron, and cerium
Authors: Yoshihara K. , Tosa M. , Nii K.
Published: July 2002

The surface compositions of two types of stainless steels in vacuum were observed with AES and XPS at 1000–1100 K; a 304 stainless steel doped with nitrogen and boron (304-NB) and a 304 stainless steel doped with nitrogen, boron, and cerium (304-NBCe). The changes of surface compositions of these steels were compared with that of commercial 304 stainless steel. A thin layer of boron nitride came out from grain boundaries and spread over the surface of the 304-NB, but did not uniformly cover the surface. The spreading mechanism of the boron nitride layer at the initial stage of heating can be explained by Avrami’s model. In the case of 304-NBCe, a boron nitride layer almost uniformly covered the surface at the early stage of heating, and rendered the surface inert to the adsorption of carbon and oxygen. Therefore, the 304-NBCe stainless steel is a candidate material for vacuum vessels.
Laser desorption for hydrogen quantitative analysis: Study by a nuclear method of the laser-induced hydrogen mobility
Authors: Ross G. G. , Terreault B. , Boucher C. , Boivin R.
Published: July 2002

We have conducted an experimental and theoretical study of the desorption, by 25 ns ruby laser pulses, of hydrogen implanted at ∼25 at. % concentration in c-Si. The evolution of the hydrogen depth profile was monitored by elastic recoil detection. The implantation or laser-induced damage was observed by optical microscopy. The heat and hydrogen transport were modeled with a finite-difference code. Desorption sets in at a very sharp threshold of (0.50±0.05) J/cm2 as a function of the laser energy fluence, corresponding to a peak temperature of ∼1000 K, and to minimal laser damage. The rate limiting process is detrapping with an activation energy of 1.2–1.5 eV, and an effective diffusion energy ≤0.1 eV.
Thin films for magnetic recording technology: A review
Authors: Howard J. K.
Published: July 2002

The impact of thin film materials science on disk-drive storage technology is in an evolutionary stage. The transition from ferrite heads and particulate disks to thin film disks and heads is in progress. This paper reviews the novel thin film structures, deposited by sputtering or evaporation, for use in direct-access-storage devices. An overview is presented to describe the issues involved in the deposition of soft magnetic materials, such as permalloy and amorphous alloy films, for yoke structures in the recording head. The future generation of film disks requires high coercivity and high induction. The thin film media must also be smooth and thinner than the present particulate surfaces to achieve higher recording densities. The relationship between deposition, structure, and magnetic properties of oxide and metal film media for longitudinal recording is described. Perpendicular recording appears to be the most promising technology to achieve ultrahigh recording densities (≥200 kBPI). Experimental results for CoCr, Co–X, and CoCr–X alloy films are presented and the correlation between structure and magnetic properties is emphasized. Research in magnetic materials for storage applications is an exciting area of materials science which may rival semiconductor materials studies in the future.
Nucleation of body-centered-cubic tantalum films with a thin niobium underlayer
Authors: Face D. W. , Prober D. E.
Published: July 2002

We discuss the structural and electrical properties of high-quality Ta films prepared by ion beam sputter deposition. The Ta films grow in two different crystal structures, body-centered-cubic (bcc) or tetragonal (β-Ta), depending on the substrate preparation and sputtering conditions. Ta films deposited on a thin (>0.3 nm) Nb underlayer grow in the bcc crystal structure with properties approaching those of clean bulk polycrystalline material. The bcc-Ta films have a superconducting transition temperature of 4.3 K and a low-temperature (10 K) resistivity ρ∼6 μΩ cm. Ta films deposited without a Nb underlayer on Si substrates always grow in the tetragonal (β-Ta) structure. The β-Ta films do not superconduct above 1 K and have a high resistivity ρ∼150 μΩ cm. X-ray diffraction and transmission electron microscope studies of both Ta structures are presented. Both bcc-Ta and β-Ta films are deposited on room-temperature substrates. This allows either type of film to be easily patterned by standard photoresist liftoff methods.
A cryopumped leak detector
Authors: Longsworth Ralph C. , Lahav Yair
Published: July 2002

The potential advantages of using a cryopump with a leak detector have been explored by fabricating and testing an experimental system. The principle advantages of using a cryopump in place of the conventional diffusion pump and cold tap are cleanliness and convenience since liquid nitrogen is not required. In addition, it is possible to selectively pump certain gases. The system tested includes an Alcatel model EA-103 leak detector along with a modified Air Products and Chemicals model HV202-6C cryopump. The ability of the cryopump to retain helium at very low partial pressures and in a quantity sufficient to permit leak checking for several days without regenerating the cryopumps has been investigated. With 0.13 Torr l of helium in the cryopump, leak rates of less than 3×10−10 atm cm3/s can be detected. Right after the cryopump has been regenerated, the minimum detectable leak rate for helium has been measured to be <7×10−12 atm cm3/s.
Experimental performance of a large-scale cryosorption pump
Authors: Coupland J. R. , Hammond D. P. , Bächler W. , Klein H. H.
Published: July 2002

A special compact high-throughput cryosorption pump with pumping speeds of 30 000 and 14 000 l s−1 for hydrogen and helium, respectively, forms an integral part of a diagnostic beam line for the University of Texas at Austin. The design is based on two-stage commercially available refrigerators, the cryogenic performance of which is described in detail. The vacuum performance of the pump, i.e., pumping speed, capacity, and regeneration, is also given.
The pumping of methane by an ionization assisted Zr/Al getter pump
Authors: Shen Gong Lie
Published: July 2002

The pumping of methane by an ionization assisted Zr/Al getter pump has been investigated. This pump consists of 12 pieces of ring getters. A spiral shape W filament is located within the ring getters. A bias voltage is applied across the filament and the getter itself. The experiments have shown that (1) when the bias voltage is turned off, the pumping speed of the getter pump for methane increases exponentially with the filament temperature; (2) when the filament temperature is held constant, its pumping speed varies directly with the ionization electron current; (3) when the filament temperature is 2063 °C and the electron current is 57 mA, the pumping speed of the Zr/Al getter pump is 475 ml/s, and the specific speed is 16.8 ml/s cm2; and (4) an activation energy and critical temperature measured for methane molecules decomposition are, respectively, 47.4 kcal/mol and about 1700 °C. Analysis of the results indicates that methane is pumped by an ionization assisted Zr/Al getter pump not because of the adsorption and the diffusion of methane molecules directly, but because methane molecules are decomposed as C and H2 through a catalysis of the hot W filament, carbon is adsorbed on the surface of the W filament, and is diffused into the interior of the W lattice. H2 is immediately absorbed by the Zr/Al getters. Besides, electron impact with CH4 would result in the additional decomposition and ionization, then the effect of electron bombardment enhances methane pumping by the Zr/Al getters.
Electrical properties of vacuum annealed Si surfaces
Authors: Liehr M. , Renier M. , Wachnik R. A. , Werner J. , Scilla G. S. , Ho P. S.
Published: July 2002

We have measured dopant distribution profiles by spreading resistance and secondary ion mass spectrometry (SIMS) as well as Schottky contact properties at Si surfaces cleaned by a high-temperature anneal in vacuum. After sufficiently long anneal a p-type surface layer forms. The p-type dopant has been identified by SIMS as boron. SIMS and spreading resistance data indicate that the chemically cleaned surface contains boron impurities in the 1012/cm2 range. Metal/silicon (Ag, Al, Ni) contact measurements reveal strong influences on the electrical characteristics due to electrically active p-type accumulation in the near-surface region only after extensive anneal (1150 °C for 5 min). In comparison with nonreacting contacts, silicide formation reduces the influence of the high-temperature anneal due to interface motion into the boron-enriched surface region.
Evidence for oxygen underlayer formation at near-liquid-nitrogen temperatures on Zr(0001)
Authors: Griffiths Keith
Published: July 2002

When a clean Zr(0001) crystal is exposed to oxygen at 82 K, the work function initially decreases by ∼250 mV for an exposure of 0.7 to 0.8 L. Annealing this surface to ∼550 K produces a further decrease in work function of ∼300 mV, and a ‘‘(2×2)-like’’ low-energy electron diffraction pattern is observed. The initial decrease in work function upon oxygen adsorption at 82 K is believed to be due to oxygen incorporation into the Zr lattice.
Structure and composition of ZrN and (Ti,Al)N coatings
Authors: Penttinen I. , Molarius J. M. , Korhonen A. S. , Lappalainen R.
Published: July 2002

Triode ion plated ZrN and (Ti,Al)N thin films were deposited on high-speed steel and stainless-steel substrates. The samples studied in this work were selected on the basis of their cutting performance in turning tests as reported earlier. In cutting tests (Ti,Al)N and ZrN both showed significantly increased wear life as compared to standard TiN. X-ray diffraction studies revealed for (Ti,Al)N a cubic B-1 NaCl structure with strong (200) orientation. The initial morphology was columnar, but by increasing the substrate current density the columnar growth could be suppressed and a finer structure resulted, while wear life in turning also increased. All ZrN coatings showed B-1 NaCl structure with a (111) preferred orientation. Their fracture surface was always noncolumnar and almost featureless as judged by scanning electron microscopy. However, cross-sectional transmission electron microscopy studies revealed a fine columnar structure also with these films. The ZrN coatings had a uniform through-thickness nuclear resonance broadening nitrogen depth profile, whereas irregularities were observed in the (Ti, Al)N coatings and an uneven aluminum distribution was revealed also by backscattering measurements.
Ion beam self-sputtering using a cathodic arc ion source
Authors: Sanders D. M.
Published: July 2002

A low-voltage/high-current vacuum arc offers a means of producing high-current ion beams. These beams can be employed in conjunction with suitable anode and sputter target configurations to permit coating production by self-sputtering without the necessity for adding process gas. This paper describes the influence of sputtering angle and target voltage on coating rate and morphology.
Diamond and diamondlike films: Deposition processes and properties
Authors: Deshpandey C. V. , Bunshah R. F.
Published: July 2002

Considerable interest has been aroused in the synthesis of diamond films due to their potential applications in microelectronics and optoelectronics. Although synthesis of diamond films by a variety of chemical and plasma assisted chemical as well as physical vapor deposition techniques has been reported, the practical applications of these coatings are still very few. The basic reason limiting the applications of these coatings is the inability to deposit films with smooth surface morphology and desired optical and electrical properties at acceptable deposition rates. Published work on diamond films is reviewed to highlight the above issues.
Transmission electron microscopy of scanning tunneling tips
Authors: Garnaes J. , Kragh F. , Mo/rch K. A. , Thölén A. R.
Published: July 2002

The resolution of an scanning tunneling microscope (STM) when used for topographic measurement is mainly limited by the shape of the tip. We here report on the shape and structure of tips observed with high resolution electron microscopy before and after the use in a STM. Tungsten tips made by electropolishing and Pt–Ir tips made by electropolishing, cutting, and ion milling are studied. During electropolishing, the tungsten tips easily get covered with a rather thick, unwanted contamination and/or oxide layer. We have studied such tips as well as clean tips with transmission electron microscopy before and after they were used in a STM working in ambient air. We find that heavily oxide-covered tips often suffer severe bending on a platinum sample, probably because the oxide layer is deformed (broken) before tunneling can occur, or flattening in the STM. On the contrary, oxide free tips normally do not bend, and tunneling condition with a stable tunnel current is easily established.
The deposition of diamond films by filament techniques
Authors: Jansen F. , Machonkin M. A. , Kuhman D. E.
Published: July 2002

Several important aspects of the vapor deposition of diamond thin films by hot filament associated chemical vapor deposition (CVD) are described. This deposition technique is economical and scalable to large areas. However, practical difficulties such as deformation of the filament and its relatively short lifetime often obscure these advantages. Techniques to overcome these difficulties have been developed. Straight rhenium wires, mounted under tension are used for the activation of the precursor gas mixture. The effects of wire diameter, temperature, length, and spacing on the thickness distribution and deposition rate of the diamond films have been determined. For high quality and large area diamond films, deposition rates are generally very low and it is often necessary to overcome a nucleation barrier. The use of submicron diamond powder to provide the necessary nucleation sites is discussed.
X-ray absorption near edge structures of intermediate oxidation states of silicon in silicon oxides during thermal desorption
Authors: Harp G. R. , Han Z. L. , Tonner B. P.
Published: July 2002

X-ray absorption near edge structure (XANES) spectra are measured from silicon oxides using a photoemission microscope. Native oxide overlayers on Si(100) and Si(111) crystals are studied at various stages of the thermal desorption process. Because of the very high energy resolution inherent in the microscope, we are able to resolve for the first time the spin–orbit splitting of the core exciton structure in SiO2. The spectroscopic signature of this transition is unique, and it has enabled us to identify the core exciton XANES structures of two intermediate oxidation states of silicon (Si2+ and Si3+). We have found the Si2+ and Si3+ states existing at the Si–SiO2 interface. We have also found, for the first time, that Si2+ can exist independently on the silicon surface apart from any SiO2.
Silicon migration during the molecular beam epitaxy of delta-doped GaAs and Al0.25Ga0.75As
Authors: Lanzillotto A-M. , Santos M. , Shayegan M.
Published: July 2002

We have investigated the migration of Si in delta (δ)-doped GaAs and Al0.25Ga0.75As structures using secondary ion mass spectrometry. The results demonstrate that: (1) the extent of Si migration strongly depends on the substrate temperature Ts; (2) the profiles for the Si δ layers in GaAs are asymmetric and indicate that Si spreads more towards the surface; this effect can be due to surface segregation; (3) the profiles for the Si δ layers in Al0.25Ga0.75As are symmetric and show substantially larger widths than those in GaAs structures (grown at comparable Ts ). We attribute this enhancement of the Si migration to the larger diffusivity of Si in Al0.25Ga0.75As.
An x-ray photoemission spectroscopy investigation of thermal activation induced changes in surface composition and chemical bonds of two gettering alloys: Zr2Fe versus Zr57V36Fe7
Authors: Sancrotti Massimo , Trezzi Gabriele , Manini Paolo
Published: July 2002

We report comparative XPS (hν=1253.6 eV) core level (Zr 3d; C 1s; O 1s; Fe 2p; V 2p) results from two relevant gettering alloys: Zr2Fe and Zr57V36Fe7. The samples were studied as-received (after in-air fracturing of bulk ingots) and after different annealing treatments (up to 700 °C) performed in ultrahigh vacuum. With increasing temperature both alloys show a progressive dissolution of Zr oxides, an increase in the metallic character of the surface, the gradual loss of C based adsorbates, and a progressive increase in the surface Zr content and at the expense of the C concentration. At temperatures in the range 300–550 °C a fraction of the C atoms form metallic carbides. OH-based groups are depleted from the surface at low temperatures (200 °C), resulting in a sizable decrease of the near surface O content, while a nearly constant O concentration is found at intermediate and high temperatures. Only minor changes are observed for the near surface concentrations of Fe in Zr2Fe and Fe and V in Zr57V36Fe7 as a function of temperature. The two alloys show strong differences in the activation kinetics of these changes, with surface metallization being initiated at lower temperatures and proceeding faster in Zr57V36Fe7. Metallic carbides are found to almost completely dissolve in Zr57V36Fe7 at 600–700 °C, while they are retained even at high temperatures in Zr2Fe. The kinetic differences determined via XPS are consistent with the differences in gettering behavior of Zr2Fe and Zr57V36Fe7.
Scanning tunneling microscopy of one-dimensional periodic corrugated silicon surfaces
Authors: Umbach C. C. , Keeffe M. E. , Blakely J. M.
Published: July 2002

A scanning tunneling microscope has been used to study atomic step arrays associated with periodically corrugated grating structures on Si(001). These gratings have repeat spacings of 1.5 and 2.0 μm, and amplitudes between 65 and 750 Å. The change in morphology of the gratings with annealing is described. The widths of the (001) terraces at the tops and bottoms of the gratings are observed to be as much as four to five times larger than those for perfect sinusoids. This is consistent with a surface tension singularity at the (001) orientation. The relative areas of the (2×1) and (1×2) dimer domains at the extrema indicate that the gratings may produce additional stresses in the surface.
Approach to estimate gettering effects in Ti–O2 reactive sputtering process
Authors: Kusano E. , Baba S. , Kinbara A.
Published: July 2002

In reactive sputtering gettering of reactive gas at the chamber wall plays an important role in process condition changes. In this article, reactive gas mass balance and sputtering yield changes in Ti–O2 reactive sputtering have been analyzed by pressure change observation and film composition analysis to examine gettering effects quantitatively. The obtained results show the drastic change in gettering effects at the mode transition which takes place at a critical O2 partial pressure. Until the mode transition, more than 90% of the introduced O2 is consumed by gettering. The amount of gettered O2 displays a maximum just before target poisoning occurs. At this point the calculated getter pumping speed reaches about ten times larger than the physical pumping speed. After the transition, getter pumping speed ranges between 1/5–1/10 of the physical pumping speed. The sputtering yield also drops by a factor of 17 at the transition. The adsorbed/incident O2 flux ratio is found to decrease from 0.36 to 0.0010 with increasing O2 partial pressure. These results quantitatively indicate the role of gettering in condition changes.
Adsorbate-promoted mass flow on the gold (111) surface observed by scanning tunneling microscopy
Authors: Peale D. R. , Cooper B. H.
Published: July 2002

Using time-lapse sequences of scanning tunneling microscopy images, we have studied the room temperature mass flow from nanoscale nonequilibrium gold structures formed on the gold (111) surface. Isolated clusters of adatoms (islands) and vacancies (pits) formed in air decay in size according to the power law scaling r ∝ (t0 − t)n, where n=1/2, r is the cluster radius, t is the observation time, and t0 is the time at which the cluster vanishes. This behavior is consistent with a model used to describe nucleation and growth in which the mass flow is driven by the curvature of the step edges, and is limited by the generation of adatoms (vacancies) at the edges of the islands (pits). In contrast, we have found no significant mass flow at room temperature for similar structures formed on clean samples under high, and ultrahigh vacuum (UHV) conditions. However, mass flow can be induced on these surfaces by admitting certain gases into the vacuum which adsorb on the surface. The adsorbate-induced mass flow is consistent with a model in which the adsorbates promote the creation of adatoms and vacancies at step edges. Using time-lapse image sequences, we compare the mass flow observed under ambient, UHV, and adsorbate-contaminated conditions, and discuss the role of the adsorbates in promoting the mass flow process at room temperature.
Growth of III–V materials by metalorganic molecular-beam epitaxy
Authors: Abernathy C. R.
Published: July 2002

Metalorganic molecular-beam epitaxy (MOMBE) is a hybrid growth technique which combines the gaseous sources of metalorganic chemical vapor deposition with the ultrahigh vacuum growth environment of molecular-beam epitaxy. This combination greatly alters the growth chemistry relative to that obtained in the parent techniques and hence often mandates the development and use of novel matrix and dopant sources. This paper will discuss how the unique chemistry of MOMBE may be exploited for growth of various III–V materials, paying particular attention to the effect of source chemistry on impurity uptake, dopant control, and uniformity. It will also review variations of the basic MOMBE process, such as electron cyclotron resonance-MOMBE, which allow for growth of nitrogen based materials. Finally the future of this growth technique will be assessed and the key issues which must be resolved in order for this method to achieve its full potential will be discussed.
Nucleation and growth of chemical vapor deposition TiN films on Si (100) as studied by total reflection x-ray fluorescence, atomic force microscopy, and Auger electron spectroscopy
Authors: Hegde Rama I. , Tobin Philip J. , Fiordalice Robert W. , Travis Edward O.
Published: July 2002

We report for the first time the characteristics of the early growth of chemical vapor deposition (CVD) TiN films on Si (100) in the surface reaction limited regime, using total reflection x-ray fluorescence (TXRF), atomic force microscopy (AFM), and Auger electron spectroscopy (AES). Small amounts of CVD TiN from TiCl4 and NH3 reactants were deposited on Si (100) at 650 °C using a rapid thermal CVD system, at a total pressure of 155 mTorr. We examined these small amounts of CVD TiN by introducing TXRF as a tool for observing the initial stages of growth, and AFM for characterizing changes in the overall surface morphology. The nucleation and growth of the resulting CVD TiN films as determined by TXRF, AFM, and AES will be discussed.
Simulation of surface topography evolution during plasma etching by the method of characteristics
Authors: Arnold John C. , Sawin Herbert H. , Dalvie Manoj , Hamaguchi Satoshi
Published: July 2002

Application of the method of characteristics to the general case of ion or plasma etching is reviewed, yielding a topography evolution algorithm which is simultaneously accurate, flexible, and efficient. The behavior of initial slope discontinuities is computed by mapping the characteristic locus in the region of the discontinuity and removing any closed loops which appear in the locus. The new method is shown to produce profiles which satisfy the required entropy and jump conditions for any given variation of etching rate with surface slope, while allowing the use of longer integration time steps than conventional methods. Previously published ‘‘string’’ algorithms [W. G. Oldham, S. N. Nandgaonkar, A. R. Neureuther, and M. O’Toole, IEEE Trans. Electron Devices ED-26, 717 (1979); A. R. Neureuther, C. Y. Liu, and C. H. Ting, J. Vac. Sci. Technol. 16, 1767 (1979)] are compared to the new method, and are shown to be capable of generating correct profiles only under limited conditions, i.e., for specific etching behaviors or if slope discontinuities are artificially removed.
Improved substrate temperature control for growth of twin-free cadmium mercury telluride by molecular beam epitaxy
Authors: Skauli T. , Colin T. , Lo/vold S.
Published: July 2002

The growth of cadmium mercury telluride (CMT) by molecular beam epitaxy requires control of the substrate temperature within a narrow window of a few degrees for growth of twin-free layers on the (111)B and (211)B orientations. It is shown that a thermocouple in contact with the substrate holder does not necessarily provide a sufficient temperature stability and reproducibility. Improving the thermal contact between the substrate holder and the thermocouple by wetting the interface between them with gallium results in a drastic improvement of the substrate temperature control. Reproducible twin-free growth of CMT on (211)B, as well as on misoriented (111)B CdZnTe surfaces have been demonstrated without any change of set points for the substrate or cell temperatures during the growth run. This demonstrates that the growth of twin-free layers does not require a change in the growth conditions with time.
Characterization of defect geometries in multilayer optical coatings
Authors: Tench R. J. , Chow R. , Kozlowski M. R.
Published: July 2002

Laser-induced damage in optical coatings is generally associated with micrometer-scale defects. A simple geometric model for nodule-shaped defects is commonly used to describe defects in optical coatings. No systematic study has been done, however, to prove the applicability of that model to an optical coating deposition process. Not all defects have a classic nodule geometry. The present study uses atomic force microscopy (AFM) and scanning electron microscopy to characterize the topography of coating defects in a HfO2/SiO2 multilayer mirror system. Focused ion-beam cross sectioning is then used to study the underlying defect structure. This work develops a model for defect shape such that the overall geometry of a coating defect, particularly the seed size and depth, can be inferred from nondestructive evaluation measurements such as AFM. The relative mechanical stabilities of nodular defects can be deduced based on the nodule’s geometry. Auger analysis showed that the seed material that causes nodular defects in HfO2/SiO2multilayers is a hafnia oxide. Such characterization capabilities are needed for understanding the enhanced susceptibility of particular defects to laser damage and for developing improved techniques for depositing low-defect density coatings.
Gas-flow experiments in the transition region
Authors: Santeler Donald J.
Published: July 2002

A special gas-flow facility was designed and constructed for the purpose of accurately measuring UF6 gas flow through a variety of gas-flow restrictions. The facility was used to measure the gas flow through 15 different orifices and 20 short tubes over a nominal pressure range from 0.002 to 100 Torr. The intent of the experiments was to confirm a new theoretical approach to gas flow through short tubes in the transition range between laminar viscous flow and molecular flow. The theoretical approach previously discussed [Santeler, J. Vac. Sci. Technol. A 4, 338, 348 (1986)] (1986)] became a part of the basis for several computer programs used for calculating gas flow in vacuum systems. A number of interesting results in turbulent flow were observed during the experiments and are discussed in the paper. The results of the experiments confirmed the proposed model and were used to evaluate specific parameters of the proposed equations.