bluuebunny/crossref_metadata_2025 huggingface dataset:
Analysis of pumping down process
Authors: Kanazawa K.
Published: July 2002

A pumping down process is analyzed considering desorption and adsorption of gas molecules. Starting from a set of equations which describes the surface kinetics of adsorption and desorption and the evacuation of gas phase molecules, a quasi-steady-state condition is defined. Under this condition, if the temperature is constant, the total outgassing rate from the surface is approximately equal to the pumping rate of gas phase molecules out of the system. But with temperature variation the total outgassing rate is considerably different from the pumping rate and the difference contributes to the change of pressure. Under the same condition a single equation which contains an adsorption isotherm explicitly and describes the pressure variation during pumping down including the baking process is obtained. The solution of this equation is defined as a quasi-steady solution. An actual pumping down curve (of water vapor) for an all-metal system including the baking process can be fitted up to just before cool down by the quasi-steady solution with the Freundlich isotherm. With the Temkin isotherm the quasi-steady solution gives a t−1 variation of pressure. As the application of the quasi-steady-state condition for the vacuum system with thermal desorption, it is shown that the Temkin isotherm plays a special role in the consideration of a heterogeneous surface system and in the calculation of a pressure distribution.
Energetic particle bombardment of films during magnetron sputtering
Authors: Rossnagel S. M.
Published: July 2002

The flux of energetic, neutral particles bombarding the sample location during magnetron sputtering has been measured for several cathode–gas systems of general interest. The technique used a differentially pumped detector placed at the sample location, from 5 to 9 cm from the cathode. The detector screens out charged particles, and measures the secondary electrons produced by energetic neutral bombardment of a collector coated with a thin film of cathode material. The energetic neutral flux has been measured as a function of chamber pressure over a range of 5 to 30 mTorr, as a function of discharge power, and as a function of angle (up to 30°) for cathodes of Ti, Cu, Al, Mo, T, and W, in Ar, Ne, and Kr gases. The deposition rate of the film was measured by means of a quartz-crystal oscillator adjacent to the detector. The magnitude of the arriving, energetic neutral flux increased with decreasing gas mass or increasing cathode mass, as expected. The energetic neutral flux was found to increase with decreasing pressure, but the ratio of energetic neutrals to condensing films atoms was found to decrease slightly with decreasing pressure. The arrival rate of energetic neutrals ranged from 2–4% of the depositing atom flux for Ar+→Cu to 12%–20% for Ar+→Ti to 27%–50% for Ne+→Ta. At high discharge powers, the relative arrival rates were higher, due to gas rarefaction in the near cathode region.
Dynamic particulate characterization of a vacuum load-lock system
Authors: Chen Degang , Seidel Thomas , Belinski Steve , Hackwood Susan
Published: July 2002

Particle contamination is an important issue for the development of vacuum interface technology. In this work the relative particle levels between a clean room and a vacuum chamber are compared; once vacuum conditions are reached no particles are detected implying that vacuum environments are intrinsically cleaner than clean rooms. Then the dynamics of particles are systematically studied in a vacuum load-lock chamber during pump down. The relationship between particle count and turbulence is developed through the Reynolds number. Higher particle counts are observed under turbulent conditions and lower particle counts are obtained by reducing the pumping and venting speed. The nature of the chamber ambient is also shown to be a critical parameter. A large reduction in particle density is obtained by preparing the chamber by backfilling with dry nitrogen as compared with (moist) clean room air, even if pumped under turbulent conditions. This and other data suggests a correlative effect between moisture and pumping rate. Particular methodologies of alternate pumping and venting cycles are used to demonstrate lower particle densities. Recommendations are discussed.
Metrological characteristics of a group of quadrupole partial pressure analyzers
Authors: Lieszkovszky L. , Filippelli A. R. , Tilford C. R.
Published: July 2002

Linearity and stability of the pressure response of five different commercial quadrupole partial pressure analyzers and the influence of ion source parameters (emission current, electron energy, and ion energy) on the response has been investigated over the range 10−7–10−1 Pa for He, N2, and Ar. In the 10−3–10−1 Pa range, each instrument developed a maximum (as large as a factor of 100 in one instrument) in the sensitivity versus pressure relation when operated with ‘‘low’’ ion energy (about 2–3 eV). All but one of the instruments also showed significant low-pressure nonlinearity, down to pressures as low as 10−7 Pa in one instrument, when operated at ‘‘high’’ ion energies (greater than about 7 eV). These results bring into question the often-assumed linearity of such instruments at low pressures. The dependence of the signal developed from a constant pressure (10−6 Pa) trace gas as a function of the pressure of another gas (the matrix) was studied using He and Ar as the trace and matrix, and vice versa. The results demonstrated an apparent correlation between the magnitude of this dependence, and an instrument’s nonlinearity as a function of pressure with the matrix gas alone. Brief exposures to certain active gases (O2, C3H8, CO2, CO) were found to cause shifts as large as 10% in the instruments’ inert gas sensitivities (He, N2, Ar). Tens of hours were required to return to pre-exposure sensitivities. Absolute argon sensitivity, monitored over a period of 220 days, for a standard set of operating parameters and with Faraday cup ion detection, showed initial one-directional changes as large as a factor of 2 for one instrument and a scatter of about ±20% in all the instruments. The very large differences among the five test instruments with regard to sensitivity, linearity, and stability, as well as the influence of one gas on the sensitivity to another, point out the need for careful characterization and calibration of such instruments for all except the most qualitative applications.
Methyl radical formation from filament pyrolysis of acetylene and acetylene/hydrogen mixtures within quartz tubes
Authors: Villa E. , Dagata J. A. , Horwitz J. , Squire D. , Lin M. C.
Published: July 2002

Resonance enhanced multiphoton ionization/mass spectrometry and electron impact/mass spectroscopy techniques have been used to probe products from the pyrolysis of C2H2 /He and C2H2 /H2 /He mixtures in the presence of a hot filament in quartz tubes. Methyl radical was found to be the most prominent radical species. The CH3⋅ concentration was highly dependent on the carbon film deposited on the quartz wall, the wall temperature, and hydrogen concentration. The activation energy for the CH3⋅ formation, 39±2 kcal/mol, was independent of the hydrogen concentration and tube diameter.
Amorphous Ta–Si–N thin-film alloys as diffusion barrier in Al/Si metallizations
Authors: Kolawa E. , Molarius J. M. , Nieh C. W. , Nicolet M.-A.
Published: July 2002

Amorphous Ta–Si–N thin films of a wide range of compositions were prepared by rf reactive sputtering of a Ta5Si3 target in a N2/Ar plasma. The relationship between films’ composition and resistivity is reported. All obtained films were tested as diffusion barriers between Al and Si. Backscattering spectrometry combined with cross-sectional transmission electron microscopy were used to determine the barrier effectiveness. It was found that aluminum can be melted on top of the Si/Ta–Si–N structure (675 °C for 30 min) without any evidence of metallurgical interactions between the layers.
Hazardous gas handling in semiconductor processing
Authors: Kumagai H. Y.
Published: July 2002

A variety of hazardous gas reactants are used in the production of semiconductor devices. Silane is an example of a highly flammable and explosive gas. Even dilute mixtures of 3% silane in an inert carrier gas are self-igniting in air. Arsine and phosphine are highly toxic gases while HC1 is widely recognized for its corrosive nature. This paper describes a generalized approach to handling hazardous gases which can be modified to meet the requirements of any specific application. The concept is based on a system design that all but eliminates the possibility of large leaks while providing the means to adequately dilute the modest spillages that may occur. Normal quantities of reactants used in the process are handled so as to maintain their purity and problems such as silane explosions in the mechanical pumps are avoided.
Operation of cryogenic vacuum pumps in severe environments
Authors: Lessard P. A.
Published: July 2002

Because of their high speed, clean vacuum environment, and life cycle cost advantages, cryogenic vacuum pumps have become the pump of choice in many vacuum processes. Since they are concentrating agents rather than throughput pumps, they can pose a potential hazard in some environments. The potentially dangerous environments fall into three categories: first, where severely reactive agents are used as process gases and are cryopumped in significant quantities, second, where hydrogen is used and pumped in large quantities; and third, where hazardous and unsuspected agents are produced by the process itself. Each class of severe environment is discussed and evaluated from a system safety viewpoint.
High throughput tandem turbomolecular pump for extreme high vacuum
Authors: Enosawa H. , Urano C. , Kawashima T. , Yamamoto M.
Published: July 2002

This paper reports on the development and evaluation of a turbomolecular pump for extreme high vacuum which, long awaited by the semiconductor manufacturing industry, can discharge a large volume of process gases. The turbomolecular pump is of the oil-free magnetic suspension type and employs the tandem structure (consisting of two directly and coaxially connected pumps) so as to obtain a high compression ratio which is essential to achieve extreme high vacuum. It has undergone considerable improvements in the roughness of the pump interior and rotor surfaces to suppress the outgassing rate. The evaluation of the new turbomolecular pump revealed that it attained an ultimate pressure of 1×10−9 Pa (8×10−12 Torr). It also achieved a maximum throughput of 2 Pa m3 s−1 (1200 sccm) (N2) at an inlet pressure of 5.3 Pa (4×10−2 Torr).
Controllable leaks using electrically pulsed valves
Authors: Dobson J. L. , Kendall B. R. F.
Published: July 2002

Pulse-modulated electromagnetic on–off valves can be used to deliver repeatable gas flows up to the full flow capability of the valves. The mean gas flow is directly proportional to the pulse repetition rate and to the effective pulse width (open time). Gas flow is also directly proportional to the pressure difference across the valve in the molecular flow region and, in the case of injection into a vacuum, remains predictably related to this pressure difference at higher pressures. A valve can therefore be calibrated in the fully open position and then pulsed electronically to give precise reductions of flow by a known factor of up to 103. Pressure variations provide an additional control factor exceeding 104. Experimental results obtained at flow rates down to the 10−8 Torr ℓ s−1 range are discussed. By using appropriate electronic driving circuits operating at up to hundreds of pulses per second, the technique can be applied to a wide range of small on–off valves including certain inexpensive types not normally used in vacuum applications.
Leak detection in 10−13 Torr aluminum vacuum systems
Authors: Watanabe Fumio , Ishimaru Hajime
Published: July 2002

10−13 Torr aluminum vacuum systems with sputter ion pumps, titanium sublimation pumps, and roughing pumps consisting of turbobacked, turbomolecular pumps have been completed. Leak detection has been accomplished by means of the buildup method of helium monitored with a quadrupole residual gas analyzer. The minimum detectable leak rate is below 2×10−15 Torr ℓ/s. Most leaks below 1×10−10 Torr ℓ/s were found in flange joints with aluminum A1050-H18 gaskets. However, few leaks occurred in flange joints with aluminum A1050-H24 gaskets or in feedthroughs, liquid nitrogen shrouds, aluminum alloy-stainless steel transitions, view ports, or electron beam welded parts.
Large-area industrial vacuum coating in the 1990’s
Authors: Johansen Paul R.
Published: July 2002

Large-area vacuum coating is defined as vacuum processing of thin films and substrate surfaces which are significantly larger in area than integrated circuits. Historically, applications of large-area vacuum coating technology have included roll-to-roll metallized polymer films for capacitors, decorative packaging, and window glazing films; and coatings on rigid discrete substrates for decorative fixtures, precision mirrors and lenses, and antiglare CRT screens. New markets, evolving technologies, and societal concerns will influence the direction and growth of large-area industrial vacuum coating technology in the 1990’s. With the increase of two-worker households and the corresponding popularity of convenience cooking, food packaging materials which provide extended shelf life and enhance microwave preparation will be a growing market. More demanding requirements for recording media, medical applications, and space technology will generate new commercial opportunities for large-area vacuum coating. And concerns relating to control of toxic by-products of industrial coating, plating and etching processes will cast large-area vacuum processing in an attractive new light.
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−-beam deposition of tetragonal ZrO2 films stabilized with alumina and scandia
Authors: Qadri S. B. , Skelton E. F. , Harford M. , Lubitz P. , Aprigliano L.
Published: July 2002

A new method is presented of producing stabilized tetragonal zirconia films based on evaporation of the oxide powders using an electron beam. Both alumina (Al2O3) and scandia (Sc2O3) are used as stabilizing agents. The relative amounts of Al and Sc were gradually increased to find the minimum amount necessary to stabilize the tetragonal phase of zirconia. In the as-deposited state, all films were amorphous, but crystallized following postdeposition heat treatments. As the atomic percent of Al and Sc was increased, the tetragonal phase of zirconia was stabilized. It appeared as a single phase for compositions with more than 24 at. % Al and more than 5 at. % Sc.
Holographic interferometry evidence that β-decay energy can symmetrize solid deuterium–tritium samples
Authors: Ankney Janet S. , Musinski Donald L. , Felmlee William J. , Pattinson Theodore R.
Published: July 2002

Thin solid samples of deuterium–tritium (DT) have been seen to sublime and redistribute within spherical inertial fusion targets due to the heat generated by beta decay. We have frozen thin DT samples within glass shells of 890 and 3750 μm diameter, and observed the evolution of the solid towards more symmetric distributions using real time holographic interferometry. Holographic interferometry provides more sensitivity than direct imaging or classical interferometry to observe the thin (10–30 μm) solid samples in these shells.
Ni/quartz adhesion enhancement: Comparison of Ar+ and Si+ ion mixing
Authors: Galuska A. A.
Published: July 2002

The adhesion between 30 nm Ni films and quartz substrates was examined as a function of the interfacial chemistry and mixing induced by low temperature (<100 °C) 40Ar+ and 28Si+ ion mixing. The Ni/quartz specimens were implanted with either 65 keV 40Ar+ or 55 keV 28Si+ to doses between 1 and 10×1016 atom/cm2. Both types of implants were observed to induce extensive interfacial grading. X-ray photoelectron spectroscopy analyses indicated that Ni–O–Si types of interfacial complexes were present in the as-deposited specimens, but that these complexes were eliminated by the 40Ar+ ion mixing. In contrast, high dose 28Si+ ion mixing was shown to induce the formation of new interfacial complexes (Ni–Si–O and new Ni–O–Si complexes). Adhesion measurements, performed using a scratch tester, indicated that the adhesion of the as-deposited specimens was good (20 N), but that this adhesion got progressively worse (to less than 1 N) with 40Ar+ implantation. In the case of 28Si+ ion mixing, adhesion was reduced (to 5 N) in the low dose specimens, but was substantially increased (to 45 N) in the high dose specimens. Overall, Ni/quartz adhesion was shown to correlate with the concentration of interfacial complexes that could chemically attach the Ni films and quartz substrates.
Transmission electron microscopy analysis of a black copper selective coating
Authors: Richharia Purnima , Chopra K. L. , Sharma S. K.
Published: July 2002

The microstructural analysis of a chemically converted black copper solar selective coating using transmission electron microscopy technique has been presented. The phases present in the as-deposited surfaces are predominantly CuO along with a strong ring pattern of Cu2S and traces of CuCO3, Cu(OH)2, and Cu2O. No noticeable changes in the microstructural and optical properties have been observed up to 300 °C under ambient conditions and up to 250 °C in vacuum conditions. On air annealing above 350 °C, phase transformations occur resulting in change in the microstructural and the optical properties of the coating. No significant microstructural changes have been observed in case of vacuum annealed surfaces above 300 °C. However, a decrease in the optical properties have been observed. Studies with steam and external environment exposed surfaces reveal no significant microstructural and optical changes in the coating.
Stress variation with temperature/time and its correlation to film structure and deposition parameters
Authors: Rastogi Rajiv , Dharmadhikari Vineet , Diebold Alain
Published: July 2002

This study focused on measuring the stress of TiN films prepared by rapid thermal processing, by sputtering, and by furnace annealing. Also included in the study were W and Al alloy films. The stress measurements were done at room temperature, and then further data were collected with temperature up to 870 °C for W and TiN. Al alloy films were temperature cycled up to 500 °C. Film structure was studied by transmission electron microscopy (TEM) analysis prior to and just after thermal cycling. Hysteresis curves were obtained for all films. Graphical stress temperature correlations were made for films of different thicknesses. TEM results of TiN films prepared by rapid thermal processing, furnace annealing, and sputter deposition, indicated a reduction in grain size along with an increase in the tensile stress upon completion of thermal cycling of the films.
Effects of magnetic field and microwave power on electron cyclotron resonance-type plasma characteristics
Authors: Popov Oleg A.
Published: July 2002

Microwave plasmas were excited in cylindrical cavities of 2.5–5.0 cm diam in the presence of magnetic field of 800–1000 G. Microwave cw power of 100–1000 W at a frequency of 2.45 GHz was delivered in the plasma via a matched introduction (quartz) window. It was found that microwaves could propagate in cavities with diameters smaller than cutoff through the overdense plasma (Ne>Ncr,Ncut-off) if the magnetic field in the plasma is higher than electron cyclotron resonance (ECR) field. When the magnetic field is lower than 875 G no detectable microwave propagation through the overdense plasma was observed. The microwave power absorption was located mainly in two sites: (i) near the vacuum window (2–3 cm) where the microwave electric field seems to have a maximum amplitude and plasma density has a steep gradient with a magnitude of Ne≊Ncr (Landau damping), and (ii) at sites along the plasma chamber where the magnetic field has a value of 875 G (ECR heating). Two electron temperatures on the Langmuir probe I–V characteristics −Te1=3–6 eV, and Te2=7–12 eV, and effects of magnetic field and plasma density on the microwave propagation are discussed.
Study of the ionized cluster beam technique
Authors: Urban Frank K. , Bernstein Alfred
Published: July 2002

The unique aspect of Ionized Cluster Beam (ICB) thin film deposition is that material is deposited in the form of ionized, accelerated atom clusters. Unique film properties have been reported for ICB, including high surface adhesion, low temperature epitaxy, and minimal surface damage. The cluster size in much of the early work was not measured directly but was inferred from theory including the following: (1) Thermodynamic description of beam generation using a nozzle source; (2) cluster embryo formation and subsequent growth due to collisions; (3) scaling laws based on gas dynamics; (4) classical nucleation theory coupled with gas flow equations; (5) classical nucleation theory with time dependence; and (6) condensation of vapor atoms on crucible walls, surface migration to form embryos, and establishment of bonds between atoms and embryos. These theories do predict the formation of clusters using a nozzle source even though they are not in complete agreement and have their detractors. Consequently the issues of cluster formation and direct cluster measurement remain of primary importance in ICB. In this presentation, different cluster measurement theories and measurement methods is described. Results of recent cluster size measurements using gold will be reported.
Growth and characterization of ferroelectric BaMgF4 films
Authors: Sinharoy S. , Buhay H. , Francombe M. H. , Takei W. J. , Doyle N. J. , Rieger J. H. , Lampe D. R. , Stepke E.
Published: July 2002

Experimental data are presented that confirm ferroelectric thin films of BaMgF4 can be grown by ultrahigh vacuum (UHV) sublimation on semiconductor and metallized substrates at temperatures below 500 °C. Hysteresis properties of the films are shown to be qualitatively consistent with those measured on thinned single-crystal samples cut perpendicular to the ferroelectric (orthorhombic) a axis. Loops from weakly oriented films on Si(100) display a Pr/Ps ratio of approximately 0.84, with Ps =1.6 μC/cm2 and EC =150 kV/cm. These values are explained on the basis of the film orientation and the measured properties for the bulk crystals. Metal–insulator–semiconductor structures formed with fluoride layers grown on lightly doped Si substrates yielded C–V switching properties indicating their suitability for use in high-performance ferroelectric field-effect transistor memory structures. In particular, switching attributable to polarization charge reversal inside the ferroelectric layer, rather than by tunnel injection of carriers from the Si into the ferroelectric, has been achieved for the first time with this material.
Low-energy (∼100 eV) ion irradiation during growth of TiN deposited by reactive magnetron sputtering: Effects of ion flux on film microstructure
Authors: Hultman L. , Münz W.-D. , Musil J. , Kadlec S. , Petrov I. , Greene J. E.
Published: July 2002

Cross-sectional transmission electron microscopy (XTEM) has been used to investigate the effects of variations in the low-energy ion irradiation flux during the growth of reactively sputter-deposited TiN. The films were deposited on steel substrates with a negative bias of 100 V at 350 °C in mixed Ar–N2 discharges at a pressure of 5 Pa (37 mTorr). The ion-to-Ti arrival rate ratio Jion /JTi at the substrate was varied between 0.3 and 7.1 through the use of a variable external magnetic field. Films grown with Jion /JTi ≲2 had a columnar morphology with a highly underdense microstructure. Increasing Jion /JTi ≳4 was sufficient to cause the growth of dense films with a more equiaxed grain structure due to renucleation. Further increases in Jion /JTi ≳7 resulted in increased TiN grain size and local heteroepitaxy between TiN and the martensitic phase of the substrate.
Magnetic field and substrate position effects on the ion/deposition flux ratio in magnetron sputtering
Authors: Clarke G. A. , Osborne N. R. , Parsons R. R.
Published: July 2002

The dependence of the charged particle flux on the magnetics for magnetron sputtering sources have been systematically studied. Magnetic field line plots were obtained for various magnetic configurations. The magnetrons were increasingly unbalanced as the strength of the center magnet was reduced and the strength of the annular magnet increased. A magnetic bottle along the magnetron axis developed as the magnetron became more unbalanced. This bottle strongly influenced the ion current density. The ion/deposition flux ratio increased with decreasing target-to-substrate distance.
The corrosion resistance of Al–Ni ion plated thin films
Authors: Bushnell Steven E. , Nowak Welville B.
Published: July 2002

The Al–Ni system was investigated for possible passive film formation similar to the Al–Mg, Al–Cu, and Al–Zn systems that have previously been reported. Films of 0–100 wt % Al were coevaporated onto LN2 cooled Ebrite (Fe-26Cr-1Mo) substrates at −1.0 kV in a 3.3 Pa argon glow discharge. As-deposited film morphology, composition, and resistivity were evaluated using SEM, EDS, and a four point probe technique. Potentiodynamic polarization tests were conducted in near neutral, aerated, 3.5% NaCl at room temperature. Some of these tests were terminated prematurely for morphological examination of the film surface. The corrosion resistance of the Al–Ni alloy films was found to increase with Ni content, with high wt % Ni films showing extended regions of stability. In addition, the Ni films were superior to pure bulk (99.8%) Ni, with protection ranges of 0.8 and 0.2 V, respectively, when scanned anodically. Corrosion product film formation was observed for alloy films of higher Ni content, but the products broke down quickly. The enhanced protection of the thin Ni films might be due to the ion plated film structure.
Microstructural evaluations of a Si–Hf–Cr fused slurry coating on graphite for oxidation protection
Authors: Hu H. S. , Joshi A. , Lee J. S.
Published: July 2002

A surface coating of approximate composition Si–30Hf–10Cr (wt. %) was prepared by fused slurry coating method. The metallic particulates in the desired ratio were applied to a graphite specimen in a fluid suspension and vacuum fused at 1450 °C. The metallurgical reactions occurring at the graphite surface were studied by evaluating the coating surface and cross sections using Auger electron spectroscopy, optical metallography, scanning electron microscopy, and x-ray analysis. The results indicate the formation of metal carbides and SiC in a layered structure near the graphite surface. The coating was found to be contiguous and to infiltrate the pores in the substrate, which is essential to improving the oxidation resistance. Oxidation of the coating in air for temperatures up to 1200 °C resulted in the formation of a SiO2 layer at the surface.
Preoxidation Si cleaning and its impact on metal oxide semiconductor characteristics
Authors: Kasi S. R. , Liehr M.
Published: July 2002

SiO2/Si interfaces with minimal defect densities will be required for the proper functioning of field effect transistors (FET) and device isolation schemes in future semiconductor technology. Control of the wafer surface contamination will become critical to meet semiconductor device yield and reliability goals. Future processing strategies to meet these stringent requirements include various vapor-phase preoxidation cleaning and passivating chemistries and clustered-tool processing schemes. In this paper, we summarize results from in situ studies on the prospects of the ultraviolet (UV)/O2 and HF chemical treatments as both preoxidation cleaning procedures and as passivation schemes. HF-cleaned Si surfaces were tested for passivation against hydrocarbon uptake using the surface analytical tools of x-ray photoelectron spectroscopy (XPS), high-resolution electron energy loss spectroscopy (HREELS), and thermal desorption spectrometry (TDS). The impact of organic contamination was studied by fabricating metal oxide semiconductor (MOS) structures on hydrocarbon-contaminated Si surfaces and measuring their electrical characteristics. The gas-phase UV/O2 procedure was studied for organic layer removal. Further, a combined HF+UV/O2 chemistry was studied to understand its effectiveness as a preoxidation treatment for preparing interface hardened MOS structures.
Theory of epitaxial growth onto nonplanar substrates
Authors: Ozdemir M. , Zangwill A.
Published: July 2002

We study epitaxial growth onto a nonplanar substrate by use of phenomenological equations of motion. The substrate is chosen as a periodic sequence of mesa structures composed of well-defined crystallographic facets. Although surface diffusion is not treated explicitly, the problem is formulated at a level of sophistication sufficient to account for the atomistic kinetic processes of deposition, desorption, adatom exchange with kink sites, and interfacet migration. Numerical integration of the final kinetic equations reveals a variety of growth morphologies depending upon the relative rates of these processes. The predictions of our analysis should be amenable to direct experimental test.
Synthesis of boron nitride ultrathin films: The bonding and chemistry of ammonia and hydrazine on Ru(0001) and B/Ru(0001) surfaces
Authors: Rodriguez José A. , Truong Charles M. , Goodman D. Wayne
Published: July 2002

The bonding and chemistry of NH3 and N2H4 on clean and B-covered Ru(0001) surfaces have been studied using surface analytical techniques (thermal desorption spectroscopy, Auger electron spectroscopy, x-ray photoelectron spectroscopy, and Fourier transform infrared reflection absorption spectroscopy) and molecular orbital calculations (INDO/1 method). Both molecules act as electron donors on Ru(0001). Their absorption bonds are mainly a consequence of interactions between the N-lone pairs and the Ru(5p,4d) orbitals. On the basis of these MO calculations, possible UPS spectra for adsorbed ammonia and hydrazine are discussed. B adatoms enhance the binding energies of NH3 and N2H4 on Ru(0001). This is a consequence of attractive interactions (through-metal and through-space) between the negatively charged B adatoms and the positively charged admolecules. The dissociation of NH3 on B/Ru(0001) surface is negligible under ultrahigh vacuum conditions. On the other hand, hydrazine reacts extensively with B, producing boron–nitrogen adlayers with stoichiometries close to 1:1 and decomposition temperatures above 1100 K.
Prevention of overload in high-vacuum systems
Authors: Hablanian M. H.
Published: July 2002

High-vacuum pumps, like other compressors, have basic limitations in regard to the maximum pressure difference (and pressure ratio) and maximum mass (and volume) flow rates that they can produce. Because high-vacuum pumps are usually made to discharge into another pump, their tolerable discharge pressure must be associated with the characteristics of the backing pump. However, it is also necessary to coordinate the performance of the high-vacuum pump with the performance of the pumping system used for pre-evacuation of the vacuum chamber. The traditional concept of a single absolute value for the crossover pressure used for the initiation of high-vacuum pumping is fundamentally incorrect because it is not based on a clear mass flow limitation. To prevent overloading high-vacuum pumps during and immediately after switching from pre-evacuation to high-vacuum pumping, a simple rule must be observed: the crossover must be performed when the gas mass flow from the vacuum chamber is less than the maximum throughput capacity of the high-vacuum pump. Typically, at the end of the pre-evacuation period, there are two somewhat distinct gas quantities associated with the vacuum chamber, the gas in the space of the chamber and the quasisteady outgassing rate. There are distinct pressure decays associated with those two gas quantities. The overloading of the high vacuum pump due to the space gas can be prevented by opening the high-vacuum valve slowly or by using a parallel low-conductance bypass. However, the overload due to the outgassing rate can only be prevented by following the golden rule of mass flow limitation. An immediate corollary of matching mass flows is that the larger the roughing pump, the lower the crossover pressure must be. In capture pumps, the maximum throughput value for the crossover condition must be correlated with the period of regeneration (for cryopumps) or cathode replacement (for ion pumps).
Characterization of as-prepared and annealed W/C multilayer thin films
Authors: Gonzalez-Hernandez J. , Chao B. S. , Pawlik D. A. , Allred D. D. , Wang Qi
Published: July 2002

Tungsten/carbon (W/C) multilayer thin films were prepared by dc magnetron sputtering. All samples consisted of 30 layer pairs with a nominal d spacing varying from 2.5 to 14 nm, the W layer thickness was kept at 2 nm in all samples. The W/C multilayers were subjected to isochronal anneals in a quartz tube furnace at the temperature range from 500 to 950 °C under a flow of high purity Ar gas. X-ray diffraction, Raman scattering, and Auger depth profile were used to characterize the structure of the as-prepared and annealed multilayer films. Both the W and C layers appear to be amorphous as-prepared. An overcoat of 30 nm of plasma enhanced chemical vapor deposited silicon nitride was found to inhibit oxidation during annealing. For those multilayers containing thinner carbon layers (<1 nm), the formation of crystalline W2C occurs at annealing temperature as low as 500 °C and a very small expansion (<2%) in the layer d spacing is observed. On the other hand, for all multilayers with carbon layer thickness equal or greater than 2 nm, crystallization occurs at much higher annealing temperatures and the crystalline phases observed were alpha-W and WC. It is also observed that in the latter group the period increases monotonically with increasing annealing temperature, the total expansion is about 10% and affects both W and C layers approximately equally. The expansion stops at the crystallization temperature which occurs at 900 °C or higher. The expansion is under investigation but may be interpreted as due to the structural ordering processes in the amorphous W and C layers.
Influence of the plasma on substrate heating during low-frequency reactive sputtering of AIN
Authors: Glocker David A.
Published: July 2002

Reports in the literature over the last several years have pointed out the advantages of using low-frequency power for reactive sputtering. In the 10–100 kHz range the impedance of the poisoned target surface is low enough to prevent the charge accumulation that leads to arcing, while the problems associated with rf power are largely avoided. We have found, however, that for a variety of materials the substrate heating at these frequencies is somewhat higher than that observed during dc reactive sputtering under similar conditions. In order to quantify this, we have calorimetrically compared the incident substrate energies while reactively sputtering AlN with both dc and 35 kHz power. In both cases, the power was delivered simultaneously to two 200 cm2 targets. In one set of experiments, they were operated at a total power of 500 W, a total pressure of 10 mTorr, and a N2/Ar flow ratio of 0.18. These conditions were on the knee of the characteristic flow hysteresis curve for our system, and target voltage feedback to the reactive gas flow was used to maintain stability. The average deposition rate and substrate incident energy were 0.82 nm/s and 20.0 eV/atom, respectively, for the dc process and 0.70 nm/s and 32.8 eV/atom for the ac process. Langmuir probe measurements show that the electron energies in the ac plasmas are somewhat higher than the electron energies in comparable dc reactive AlN plasmas and the differences between the plasma and floating potentials are comparable. The ion densities in the ac plasmas we measured averaged 6.4×1016/m3, which is several times greater than the ion densities in similar dc plasmas. We attribute the increased energies and densities to target voltage spikes as the plasma reignites on each half-cycle, causing rapid electron acceleration in the presheath region. This leads to significantly more plasma bombardment of the substrate in the ac case than in the dc case, which our estimates show can partially explain the energy flux difference.
Electrodeposition of copper on Pt(111) and Pt(100) single crystal surfaces
Authors: Markovic N. M. , Ross P. N.
Published: July 2002

The electrodeposition of copper on Pt(100) and Pt(111) in different acid electrolytes was studied by cyclic voltammetry, ex situ Auger electron spectroscopy and low energy electron diffraction (LEED). The specific adsorption of Cl− from HF and HClO4 solutions was found to have a strong effect on the submonolayer deposition process. LEED results from emersed electrodes indicated that for submonolayer deposition from a ‘‘chloride free’’ solution the copper was growing in islands (or ‘‘patches’’) having the lattice constant of the platinum substrate, i.e., pseudomorphic growth as in vapor deposition of Cu on Pt. In the presence of Cl−, submonolayers of Cu were deposited in the form of a Cu–Cl adlattice. After deposition at either the Nernst potential (one monolayer) or at ∼0.2 V negative of it (four monolayers), Cu formed a uniform epitaxial metallic layer with an ordered Cl adlayer on the top of the Cu layer in a structure essentially identical to that for Cl adsorbed from the gas phase onto a bulk Cu crystal to saturation.
Total pressure measurement down to 10−12 Pa without electron stimulated desorption ion errors
Authors: Watanabe Fumio
Published: July 2002

In order to measure a total pressure as low as 10−12 Pa, the avoidance of electron stimulated desorption (ESD) ion errors is more important than the x-ray limit, because even if we can contrive to reduce ESD ions in a gauge, we do not know what fraction the ESD ion error makes in the measured pressure value. This is the largest defect in the reliability of the measurements. Therefore, the development of the ion spectroscopy gauge which avoids ESD ion errors, was recalled with a historical review of the limiting processes in a hot-cathode gauge. The most advanced ion spectroscopy gauge was constructed with a fine platinum alloy spherical grid ion source, immersed in a copper block with stainless steel flanges. Gas phase ions were effectively separated from ESD ions by the actions of electron space charge in the grid and a hemispherical 180° ion energy analyzer. The x-ray limit of the advanced gauge was approximately 2.5×10−13 Pa, and the outgassing rate of 2×10−9 Pa ℓ/s (about 1/100 that of an ordinary nude Bayard–Alpert gauge) was achieved.
Evaluation of aluminum foils, Loctite, ferrites, and ‘‘mirror-finished’’ stainless steel for use in ultrahigh vacuum applications
Authors: Rao Vijendran
Published: July 2002

Aluminum foils have been used for covering UHV components after cleaning and for covering ports in vacuum systems. Traditionally, industrial grade/household variety foils have been used. We have studied different grades for their surface impurities. Similarly, LoctiteR (a polymer of methacrylate) has been used in sealing minute leaks in accelerator rf cavities/separators. Ferrites are being proposed for use in superconducting rf cavities as an absorber. Special surface treatments to get mirror polish on stainless steel (SS) is often used. We have evaluated these materials for their surface topography and composition. Also vacuum/baking treatments have been investigated using a residual gas analyzer (RGA). Summary of our data and a brief analysis is presented.
Scanning tunneling microscope tip–sample interactions: Atomic modification of Si and nanometer Si Schottky diodes
Authors: Avouris Ph. , Lyo I.-W. , Hasegawa Y.
Published: July 2002

In the first part of this article, tip–sample interactions and their use to modify surfaces at the atomic scale are discussed. In particular, a chemically assisted field-evaporation/desorption process, as a general method for breaking strong chemical bonds and inducing atom-transfer, is discussed. This capability is demonstrated using the atomic-scale modification of Si(111). It is further proposed that, due to the elastic coupling between surface atoms, there is a material-dependent limit to how small and how local a scanning tunneling microscope (STM)-induced modification can be. Evidence for large-scale restructuring as a result of ‘‘local’’ modification of the Au(111)-22×√3 surface is presented. The properties of the actual nanometer-size contacts of metal tips with Au, Si(111)-7×7, and Si(100)-2×1 surfaces, and model nanostructures composed of Si epitaxial islands are then considered. The objective is to investigate the behavior of a simple electronic device, the Schottky diode, at the extreme limit of miniaturization. The resistance of the nanometer contacts is found to be a strong function of the semiconductor surface reconstruction, exposure to gases, and subsurface doping changes. The electrical characteristics of the nanometer diodes are very different from those predicted by extrapolation of the behavior of macroscopic devices. These experiments indicate that the STM can be a powerful tool for probing local electrical properties via tip–sample point contacts.
Reactive sputtering using two reactive gases, experiments and computer modeling
Authors: Carlsson P. , Nender C. , Barankova H. , Berg S.
Published: July 2002

The reactive sputtering process is very simple to use as long as one wants to deposit fully formed compounds. If, however, an intermediate composition is required it is necessary to use quite advanced process control. Reactive sputtering from an elemental target in argon with the addition of one reactive gas have been extensively studied. Also studies of reactive cosputtering have been reported. The interest for such studies increased dramatically when the high-temperature superconductive thin films were introduced. In this article we will treat the process of reactive sputtering from an elemental target in argon with the addition of two reactive gases. In such a process, e.g., oxy-nitride films can be formed. The fundamental reactive sputtering model has been modified to handle two reactive gases. By this new model it is possible to simulate two gases having different reactivity and sticking coefficients to the elemental metal involved. It is possible to predict complex effects in the processing region where the two gases compete to form different compounds. The ‘‘hysteresis effect’’ for this two-gas reactive sputtering process differs significantly from the hysteresis effect observed in a single gas reactive sputtering process. Poisoning the target by one gas prevents formation on the target of the compound based on the other gas. It should, however, be possible to ‘‘tune’’ the process to deposit any desired composition. A large fraction of these composition intervals occur inside the ‘‘hysteresis’’ region. The simple one-gas reactive sputtering process operates on a single curve. The two-gas process will operate on a complex processing surface. Results from computer simulations as well as experiments will be reported in order to explain the physical background to the observed complex behavior.
Relationship of crystallographic orientation and impurities to stress, resistivity, and morphology for sputtered copper films
Authors: Burnett Andrew F. , Cech Jay M.
Published: July 2002

Copper has 44% higher conductivity than aluminum, making copper an attractive interconnect metal for advanced multilevel interconnections in integrated circuits (IC) and multichip modules (MCM). Since sputter deposition is widely used in IC and MCM fabrication, the properties of sputtered copper films are investigated in this study. In particular, MCM technology requires relatively thick coatings (5–8 μm), which can result in high stress. Thin film stress can lead to dielectric cracking, wafer bow, and reduced operating lifetime. This study reports the residual stress, morphology, and electrical resistivity of annealed copper coatings as a function of the thin film crystal orientation determined by x-ray diffraction. We found that the stress and electrical resistivity of copper thin films can be significantly reduced by controlling the orientation of the copper crystallites.
Study of band gap and band levels of Cu–In–Se–Te thin films compounds
Authors: Díaz R. , León M.
Published: July 2002

The first direct gap of Cu–In–Se–Te thin films grown by triode sputtering has been determined, showing values in the 0.76–1.42 eV range. The spread of values is explained assuming that the Cu/In atomic ratio of sample composition affects significantly the conduction band minimum whereas the valence band maximum is concerned by the Cu/(Se+Te) atomic ratio. In any case, the variation observed in the energy gap is mainly due to changes in the Cu/In atomic ratio.
Observation of oxygen enrichment in zirconium oxide films*
Authors: Khawaja E. E. , Bouamrane F. , Hallak A. B. , Daous M. A. , Salim M. A.
Published: July 2002

A study of the major deposition parameters, including substrate temperature and oxygen partial pressure, affecting the optical quality of electron beam evaporated zirconium oxide films is presented. The films were found to be optically inhomogeneous. Rutherford backscattering spectroscopy and x-ray photoelectron spectroscopy (XPS) revealed that the films had an excess of oxygen. XPS suggested that the excess oxygen may be due to adsorbed water. However, an increase in the oxygen content with oxygen partial pressure indicated that some of the excess oxygen may have been embedded in the films during deposition.
Magnetic biasing effects while using an unbalanced planar magnetron
Authors: Belkind A. , Orban Z.
Published: July 2002

Magnetic biasing of a floating substrate affects the plasma of an unbalanced magnetron, changing the plasma distribution near the substrate and, therefore, varying the ion bombardment of the substrate. Biasing magnets which focus the plasma flow increase two parameters as measured by electrical probes located in the center of the sputtering zone: floating potential and ion current at the floating potential. Biasing magnets which defocus the plasma flow decrease the floating potential and ion energy flux, but cause little variation of the ion current. In both magnet configurations, a small plasma is confined near the top of the biasing magnets.