bluuebunny/crossref_metadata_2025 huggingface dataset:
Digital heterodyne interference fringe control system
Authors: Heilmann Ralf K. , Konkola Paul T. , Chen Carl G. , Pati G. S. , Schattenburg Mark L.
Published: July 2002

In traditional interference lithography, interference fringes are typically phase locked to a stationary substrate using analog homodyne photodiode signals that are fed back to control a phase-shifting device such as an electro-optic modulator or a piezoelectrically transduced mirror. Commercially available fringe-locking systems based on this approach often achieve stability of the interference fringes to within a small fraction of the fringe period p (typically ±p/20 peak-to-peak). We describe the performance of a heterodyne fringe control system utilizing acousto-optic phase shifters and digital controls that is designed to satisfy the much more stringent fringe control requirements for scanning beam interference lithography. We demonstrate locking to ±p/100, and expect further significant improvements. This versatile system can also be used to lock the phase of moving fringes in almost arbitrary fashion at fringe velocities up to 2.5×107 periods/s and to measure the phase of gratings.
Analysis of SiO2-to-Si3N4 selectivity in reactive ion etching using additional O2 gas
Authors: Matsui Miyako , Uchida Fumihiko , Kojima Masayuki , Tokunaga Takafumi , Yano Fumiko , Hasegawa Masaki
Published: July 2002

The mechanism for control of the Si3N4 etch rate in a self-aligned contact process when C4F8/Ar/O2 gas is used was investigated. The Si3N4 surfaces after dry etching were analyzed by x-ray photoelectron spectroscopy and time-of-flight secondary ion mass spectroscopy. After dry etching, a polymer-like residue film less than 15 nm thick and an oxidized layer between the polymer layer and the Si3N4 surface were observed. In the CF polymer layer, the etching product of CN or CNO was characterized. CN or CNO components are widely distributed in the CF polymer layer, while the SiO2 layer is more localized on the Si3N4 surfaces. We found that the thicknesses of the CF polymer and SiO2 layer strongly depend on the Si3N4 etch rate, which is determined by the flow rate of the additional O2 gas. The thickness of the CF polymer, which was decreased from 10.1 to 4.1 nm, is considered to act as an inhibitor. The thickness of the SiO2 layer, which is easy to etch, was increased from 1.4 to 2.7 nm. The CF polymer thickness and the etching path of Si3N4 oxidation are important factors in controlling the Si3N4 etch rate.
Improvement in partitioning method for electron beam lithography simulation
Authors: Aya S. , Kise K. , Marumoto K.
Published: July 2002

We propose an improved method to calculate the energy deposited in resist for electron beam lithography simulation. The concept of the method is that an exposure intensity distribution (EID) function is partitioned into rings having a constant contribution. The equi-contribution partitioning (ECOP) method decreases the partitioning ring number for the expression of EID and the calculation time dramatically. Using the experimental result of the EID at an acceleration voltage of 100 kV for various patterns, the ECOP method was evaluated for calculation accuracy and calculation time. The time required in this method with a ring number of 50 is ten times shorter than that in the conventional method with the number of rings over 600 while the accuracy obtained by this method is better than that by the conventional method.
Growth of high quality ZnO thin films at low temperature on Si(100) substrates by plasma enhanced chemical vapor deposition
Authors: Li B. S. , Liu Y. C. , Shen D. Z. , Lu Y. M. , Zhang J. Y. , Kong X. G. , Fan X. W. , Zhi Z. Z.
Published: July 2002

High quality ZnO thin films with a c-axis-orientated wurtize structure have been grown on a Si(100) substrate by plasma enhanced chemical vapor deposition using a zinc organic source [Zn(C2H5)2] and carbon dioxide (CO2) gas mixture at low temperature. The dependence of ZnO thin-film quality on the gas flow rate ratio of Zn(C2H5)2 to CO2 (GFRRZC) is studied by x-ray diffraction (XRD), optical transmission spectra (OTS), and photoluminescence spectra (PL). The optical properties show that the GFRRZC has an obvious effect on the band gap of ZnO films. The relationship between the quality of the ZnO thin films and the substrate temperatures is also studied by XRD and PL spectra. The XRD spectra show that the full width at half maximum (FWHM) of the diffraction peak at 34.42° of (0002) oriented ZnO is 0.25° at the optimized condition, indicating the formation of high quality ZnO films. The PL spectra show a strong excitonic emission at about 3.26 eV without the emission around 2.5 eV related to deep-level defects, implying the formation of the stoichiometric ZnO thin films. The smallest FWHM of the PL spectrum of a ZnO thin film is 111 meV at room temperature.
Effect of Ultrahigh Vacuum on the Friction between Metals and Granular Soils
Authors: Karafiath Leslie L. , Mohr George
Published: July 2002

An apparatus has been developed to measure the friction between metals and granular materials in ultrahigh vacuum. Pressures below p=10−9 Torr have been routinely reached with the vacuum system consisting of a turbomolecular, a getter-ion, and a liquid-N2-cooled titanium sublimation pump. The frictional resistance between steel and ground basalt in two particle size ranges was measured under various normal loads. The experiments showed that the ultrahigh vacuum did not affect the coefficient of friction significantly, but increased the frictional resistance by an adhesion ranging from 6 to 24 g/cm2 for the various materials and conditions.
Investigation of Gasket Coating Materials for Ultrahigh-Vacuum Seals
Authors: Danielson P. M.
Published: July 2002

Ultrahigh-vacuum systems are commonly provided with flanged openings that are sealed with copper gaskets. These systems must be baked to at least 250 °C in order to achieve ultrahigh vacuum. This paper presents an investigation of bakeable organic coatings that can be applied to copper gaskets to facilitate sealing conflat flanges on an ultrahigh-vacuum system. The coated gaskets have the advantage over uncoated gaskets in that they require fewer flange bolts and lower bolt torques to provide a leak-free seal. The coatings include polyimide and three silicones. Coating techniques, sealing parameters, and vacuum performance of the coated gasket seals are described. The sealing performance of the coating is characterized in terms of pumpdown performance and residual gas analyses. The results of this investigation show that these organic materials can be used for ultra-high-vacuum gasket coatings. They also show that little variation in the partial pressures of the residual gases (after bakeout) occurs when either uncoated or coated copper gaskets are used.
Defects in silicon substrates
Authors: Hu S. M.
Published: July 2002

This paper reviews some defects of major importance in silicon substrates: their nature and geometrical distribution; the mechanism of formation; their interplays; and their implications. Topics discussed include swirl aggregates of point-defect clusters and dislocation clusters; dislocations generated by thermal stresses; stacking faults generated by thermal oxidation both on the surface and in the bulk of substrates; and clustering and precipitation of oxygen.
Properties and applications of ion-implanted alloys
Authors: Myers S. M.
Published: July 2002

Ion implantation is a controlled and versatile means for near-surface alloying of metals. Supersaturated solutions, meastable compounds, amorphous phases, and equilibrium alloys have been produced. Uses include the investigation of metastable phases, characterization of alloying reactions ocurring in conventional materials, and improvement of surface properties such as hardness, wear, and corrosion. A brief review is given of the physical processes occurring during ion implantation, the types of alloys which result, and representative applications.
Copper distribution in sputtered Al/Cu films
Authors: Denison D. R. , Hartsough L. D.
Published: July 2002

The copper distribution in sputtered aluminum–copper films depends on copper concentration and deposition temperature. At high deposition rates the film temperature is high enough for diffusion to occur without external substrate heating. Targets containing 0.5%, 2%, and 4% copper were used to deposit films by dc magnetron sputtering. No segregation was found in the 0.5% Cu films at film deposition temperatures as high as 460°C. The 2% and 4% Cu films showed segregation, with the peak in the copper content located nearer the film–substrate interface. Auger and SEM data indicate that theta phase particles may form in this region during high rate deposition. These particles apparently redissolve slowly during 500°C postdeposition anneal. In contrast, 4% Cu films deposited by evaporation from a single source showed a similar as-deposited profile, but a more rapid redistribution of the Cu during anneal. The sputtered films are reported to be more resistant to hillock growth and corrosion than the evaporated films. At rates above 10 kÅ/min, and under conditions where film temperature rose toward a steady-state value, film melting or copper-rich whiskers up to several microns in length were observed on the 4% Cu alloy.
Pattern fabrication by oblique incidence ion-beam etching
Authors: Gokan H. , Esho S.
Published: July 2002

Effects of ion-beam incidence angle on etched pattern profiles have been studied. Ion-beam etching was performed using a rotary stage and a Kaufman-type ion gun operated at a 500 V acceleration voltage and a 0.5 mA/cm2 current density. Etched patterns show a unique side wall contour which consists of two distinguishable slopes. The slope angles depend on ion-beam incidence angle and mask thickness. The side wall contour is theoretically interpreted taking into consideration the effects of both ion-beam shadowing and redeposition.
Hydrogen and helium pumping by plasma-wall interaction
Authors: Kerst R. A.
Published: July 2002

Recycling of hydrogen and helium from the SS 304 wall of a plasma discharge experiment has been studied. Hydrogen recycling was dominated by diffusion and recombination; however, helium recycling was dominated by trapping. Detrapping of both hydrogen and helium was observed during a discharge of the opposite species. The density of trapped H from previous hydrogen discharges is estimated to be 1.4×1015 cm−2. Vacancies created in the oxide layer by the implanted ions are suggested as the trapping mechanism.
Reduction of surface states on GaAs by the plasma growth of oxyfluorides
Authors: Ahrenkiel R. K. , Kazmerski L. L. , Ireland P. J. , Jamjoum O. , Russell P. E. , Dunlavy D. , Wagner R. S. , Pattillo S. , Jervis T.
Published: July 2002

Bonding chemistry predicts that native oxides on GaAs produce intrinsic surface state. Native oxyfluoride dielectric are predicted to be stable and free of bonding defects. We have grown native oxides and oxyfluorides on GaAs by a glow discharge plasma process. Oxide MIS structures always have large densities of fast interface states. We have grown oxyfluoride structures in which surface state effects are reduced by about a factor of 50. ESCA and SIMS analysis of the oxyfluoride dielectric showed a uniform fluorine distribution in thermally annealed samples. X- ray photoemission spectroscopy (XPS) indicate that the molecular components of the glass are GaF3 and AsOF3.
Catalysis of carbon methanation by small platinum particles
Authors: Santiesteban J. , Fuentes S. , Yacaman M. J.
Published: July 2002

The reaction of carbon with hydrogen to form methane in the presence of platinum particles is studied. Kinetics studies are combined with TEM techniques that allow particle shape and structure to be obtained. The methane production has two peaks at 800 and 950 °C. The reaction always involves pitting or channeling by particles moving along the substrate surface. The most active particles are found to be platelets with a (110) surface in contact with the basal plane of the graphite. Those particles have a very rough surface containing many kinks.
Effects of ion implantation doping on electrical and chemisorptive properties of tin oxide thin films
Authors: Chang Shih-Chia
Published: July 2002

Antimony and indium were implanted into tin oxide films prepared by reactive rf sputtering from a sintered tin oxide target. A dosage of 2×1015 ions/cm2 of Sb (or In) increased (or decreased) the film conductivity more than two decades after the samples were annealed in air at temperatures ≥350 °C. These implantations reduced the sensitivity of the tin oxide conductivity to the chemisorption of oxidic gases such as NO and O2. This sensitivity reduction is explained in terms of the annihilation of surface chemisorption centers and/or the creation of trapping states by the implantation process.
End point detection in ion milling processes by sputter-induced optical emission spectroscopy
Authors: Lu C. , Dorian M. , Tabei M. , Elsea A.
Published: July 2002

The characteristic optical emission from the sputtered material during ion milling processes can provide an unambiguous indication of the presence of the specific etched species. By monitoring the intensity of a representative emission line, the etching process can be precisely terminated at an interface. Enhancement of the etching end point is possible by using a dual-channel photodetection system operating in a ratio or difference mode. The installation of the optical detection system to an existing etching chamber has been greatly facilitated by the use of optical fibers. Using a commercial ion milling system, experimental data for a number of etching processes have been obtained. The result demonstrates that sputter-induced optical emission spectroscopy offers many advantages over other techniques in detecting the etching end point of ion milling processes.
Modification of the grain size of sputtered copper with additions of oxygen, krypton, silver, or yttrium
Authors: Moss R. W. , Merz M. D.
Published: July 2002

Several 800 to 1100 μm thick films of oxygen-free high-conductivity (OFHC) copper and copper with additions of oxygen, krypton, silver, or yttrium were deposited at rates of 0.5 to 1.2 μm/min using an enhanced thermionically supported-discharge (ETSD) sputtering apparatus. To obtain fine-grained materials, several deposition parameters, such as partial pressure of oxygen in the sputtering gas, bias, and substrate temperature, were varied. Oxygen and krypton were incorporated by trapping the sputtering gas; silver and yttrium were added by means of the target design. The structures and microstructures were examined with standard x-ray diffraction (XRD), transmission electron microscopy (TEM), and optical microscopy techniques. The grain sizes varied from 14 μm for the OFHC copper to 0.0073 μm for the Cu-4 at. % Y deposits. XRD data indicated an amorphous structure for the Cu-9 at. % Y deposits.
Performance comparison of plasma spray and physical vapor deposition BC23 coatings in the LM2500
Authors: Wortman David J.
Published: July 2002

Operation of U. S. Navy Component Improvement Program LM2500 engines on the GTS Callaghan has provided an at-sea test bed for evaluation of hot corrosion on gas turbine engine components. In a presentation at a previous International Conference on Metallurgical Coatings, (ICMC), comparison of several coatings applied by physical vapor deposition (PVD) techniques were compared after LM2500 service. A three-step coating BC23 consisting of PVD CoCrAl followed by codeposition of hafnium and aluminum and an electroplated platinum layer was identified as the most corrosion-resistant coating of several PVD coatings tested. In this paper, a plasma sprayed version of BC23 is compared to the three-step BC23 coating on LM2500 Stage 2 HPT blades from the GTS Callaghan. The plasma sprayed coating PBC23 was produced by an argon-shrouded plasma spray process using prealloyed CoCrAlHfPt powder. The results showed that in this application, where low temperature hot corrosion (type 2) is the predominant mode of corrosion, the plasma sprayed coatings had less attack. These results are compared to laboratory hot corrosion tests and microprobe analysis to explain the improved corrosion resistance of PBC23.
Scanning electron microscope analysis of the microstructure of aluminide diffusion coatings on Ni–Cr alloys
Authors: deLanerolle Nimal , Siegle L. L.
Published: July 2002

Using energy dispersive spectroscopy, a microanalytical study of the coating microstructures in a series of pack-aluminized Ni–15Cr to Ni–35Cr alloys was performed, in order to obtain a more precise chemical analysis of the constituents that can be obtained using the electron microprobe. Composition determinations close to the α/β and α+β/γ phase boundaries were made, as well as across precipitates and the matrix. It was possible to determine the concentration of individual phases present in the diffusion zone of the coatings in the above alloys. It was found that the nonisolated α-Cr lamellar precipitates had a Cr concentration about 95 at. %, whereas the isolated α-Cr had around 60 at. %. Composition traverses on the γ-phase agrees well with the available NiCrAl phase diagram at 1025 °C.
Fabrication of ceramic substrate-reinforced and free forms by mandrel plasma spraying metal–ceramic composites
Authors: Quentmeyer R. J. , McDonald G. , Hendricks R. C.
Published: July 2002

Components fabricated of, or coated with, ceramic have lower parasitic cooling requirements. Techniques are discussed for fabricating thin-shell ceramic components and ceramic coatings for applications in rocket or jet engine environments. Thin ceramic shells with complex geometric forms involving convolutions and re-entrant surfaces were fabricated by mandrel removal. Mandrel removal was combined with electroplating or plasma spraying and isostatic pressing to form a metal support for the ceramic. Rocket engine thrust chambers coated with 0.08 mm (3 mil) of ZrO2–8Y2O3 had no failures and a tenfold increase in engine life. Some measured mechanical properties of the plasma-sprayed ceramic are presented.
A comparison of low-pressure arc and low-pressure plasma sprayed titanium coatings
Authors: Steffens H.-D. , Ertürk E. , Busse K.-H.
Published: July 2002

Titanium coatings for protection in chemical plants are required to withstand severe corrosion attack. Low-pressure plasma spraying (LPPS) and low-pressure arc spraying (LPAS) of titanium were investigated as a means of producing such coatings. Metallographic, mechanical examination, and x-ray diffraction analyses of titanium coatings arc and plasma sprayed in a low pressure atmosphere, show that both coatings are dense and nearly free of contaminating phases. However, results of the comparison show that low-pressure arc sprayed titanium coatings had lower hardness, lower interstitial gas content, higher bond strength with the substrate, and were sprayed with higher efficiency than the low-pressure plasma sprayed titanium coatings.
Frictional and structural characterization of ion-nitrided low and high chromium steels
Authors: Spalvins Talivaldis
Published: July 2002

Low Cr steels AISI 4140, AISI 4340, and high Cr austenitic stainless steels AISI 304. AISI 316 were ion nitrided in a dc glow discharge plasma consisting of a 75% H2–25% N2 mixture. Surface compound layer phases were identified, and compound layer microhardness and diffusion zone microhardness profiles were established. Distinct differences in surface compound layer hardness and diffusion zone profiles were determined between the low and high Cr alloy steels. The high Cr stainless steels after ion nitriding displayed a hard compound layer and an abrupt diffusion zone. The compound layers of the high Cr stainless steels had a columnar structure which accounts for brittleness when layers are exposed to contact stresses. The ion nitrided surfaces of high and low Cr steels displayed a low coefficient of friction with respect to the untreated surfaces when examined in a pin and disk tribotester.
Behavior of Ga atoms on a tungsten surface
Authors: Kim Hyunwoo , Okuno Kimo
Published: July 2002

The variation of the work function and the preexponential term of the Fowler–Nordheim (FN) plots and field emission current from a Ga covered tungsten surface have been studied using a field emission microscope (FEM). The work function and preexponential terms both vary in the same way with coverage and desorption temperature. Both are decreased to 4.25 and −0.6 eV, respectively, at θ=0.2. In spite of a small decrease in work function, the field emission current decreased to about half of its initial value, because of a decrease in the emitting areas of the Ga covered tungsten surface. The polarizability of Ga, at this coverage, is also obtained as ∼3 A3.
Tent-type bakeout oven
Authors: Hess B. V. , Felter T. E.
Published: July 2002

A bakeout oven has been designed and built using quartz infrared lamps bring the vacuum system chamber to a bakeout temperature of 200 C in 75 mi nutes. (AIP)
Deposition of conducting thin films of organometallic monomers by plasma polymerization
Authors: Sadhir R. K. , Saunders H. E.
Published: July 2002

There has been a growing interest in depositing metal-containing thin films by plasma polymerization for various applications. These films have been deposited by two methods (a) by plasma polymerization of volatile organometallic monomers, and (b) by simultaneous plasma etching and polymerization in the same system, resulting in metal-containing fluoropolymers. Heretofore, most films so deposited have had low metal to carbon ratios and are insulating in nature. In our laboratories, we have been working on the plasma polymerization of volatile organometallic monomers with an aim to producing conducting films. We have observed that there is a critical threshold value of metal to carbon composition above which the films become electrically conductive. The key to depositing films having higher metal to carbon ratios is the plasma conditions. In this paper, we will review the work in our laboratories on plasma polymerization of organometallic monomers and discuss the preparation and properties of organotin monomers with various tin to carbon ratios. We will also discuss some of our recent results on plasma polymerization of an organoiron monomer. These films have been characterized by ESCA, IR, SEM, TEM, and x-ray diffractograms.
Size effect of a quartz oscillator on its characteristics as a friction vacuum gauge
Authors: Hirata M. , Kokubun K. , Ono M. , Nakayama K.
Published: July 2002

As the technical basis of the friction vacuum gauge using a quartz oscillator, the electric impedance of various types and sizes of quartz oscillators was measured as a function of pressure from 10−2 Pa to atmospheric pressure. Among the oscillators, the tuning fork showed the highest impedance change of about tenfold in the pressure range. The impedance was a linear function of the pressure in the lower pressure range and was proportional to the square root of the pressure in the higher range. This pressure dependence showed good agreement with the result of theoretical analysis by the authors. In this report, the relation between the change in impedance and the size of the tuning fork was studied experimentally in order to have design data for a gauge of high performance. A semiempirical formula concerning the size effect on the sensitivity was obtained. The formula predicted that an oscillator of a long length and of a small width and thickness has higher sensitivity as a gauge. A few of these oscillators showed the pressure response from 10−2 to 105 Pa or higher.
Surface characterization of a Zr–V–Fe getter by XPS-SIMS—activation process and D2O exposure
Authors: Ichimura Kenji , Ashida Kan , Watanabe Kuniaki
Published: July 2002

To apply hydrogen storage materials (getters) to tritium recovery and storage, it is important to understand the activation process of the getters and their pumping characteristics not only for tritium gas, but also impurity gases such as HTO. From this viewpoint, the activation process of the Zr–V–Fe getter (St-707, SAES Getters) and absorption process of D2O were investigated with XPS-SIMS. An as-received getter surface was observed to be covered with H2O, CO, O2, and hydrocarbons. In addition, the getter components formed respective oxides on the surface. The activation, which consisted of vacuum heating above 500 °C, caused the disappearance of the adsorbed impurities from the surface, forming a metallic surface consisting of Zr(87 at.%) and V(13 at.%). Exposure to D2O vapor at 25 °C resulted in the adsorption of D2O as D2O(a) and/or OD(a). In addition, a part of the surface was oxidized. Elevation of the exposure temperature to 300 °C caused the disappearance of the D2O(a) and/or OD(a). Consequently the O-coverage decreased, although the partially oxidized surface remained. We conclude that both Zr and V function as the active sites for the decomposition of D2O(a) and/or OD(a). However, the Zr sites work more actively for the decomposition reaction than the V sites do. Consequently, these Zr sites determine the absorption rate.
Laser-induced desorption from a temperature-regulated substrate
Authors: Mercier Jacques S. , Cool Terrill A.
Published: July 2002

A surface temperature regulation method is described which demonstrates the feasibility of studying the direct laser-induced quantum desorption of admolecules from surfaces under isothermal substrate conditions. The method is illustrated with an investigation of the desorption of CO molecules from a palladium substrate exposed to cw CO infrared laser radiation at intensities of up to 5 W/cm2. The temperature regulation obtained was sufficiently precise (±0.2 °C) to reduce the thermal desorption background to an upper limit of 3×10−8 desorbed molecules per absorbed photon and to show that, for the adsorption system investigated, nonthermal desorption effects were not present above this threshold.
Exposure characteristics and proximity effect in Ag2Se/GeSe4 inorganic photoresists
Authors: Nakase Makoto , Utsugi Yasushi , Yoshikawa Akira
Published: July 2002

The exposure characteristics and the proximity effect in Ag2Se/GeSe4 inorganic photoresists have been examined through experiment. As a result, high γ and high contrast are confirmed. Reciprocity law failure is not observed. The self-compensation effect of the proximity effect due to the lateral Ag diffusion is verified by measuring the linewidth deviation. In addition, a logarithmic dependence of the Ag-photodoped depth on the exposure dose is derived from the relation between the threshold exposure dose and the removal time of the photodoped layer. This behavior can be explained by a model which demonstrates that the Ag-photodoping is promoted by the recombination of photoexcited electron-hole pairs in GeSe4.
Chemisorption of tritium on graphites at elevated temperatures
Authors: Strehlow R. A.
Published: July 2002

Tritium interactions with graphite will influence the design of procedures for handling graphite components. The tritium sorption capacities of various graphite grades are therefore needed. In a series of measurements, several graphite specimens in different states of oxidation were exposed to tritium gas and to tritium oxide at temperatures ranging from 175 to 750 °C. Higher temperatures were found to result in tritium sorption at concentrations as high as 2.1×1013 cm−2. Sorbed quantities at lower temperatures after exposure to either tritium oxide or tritium gas were found to be in the range of 1×108 cm−2. Oxidized specimens showed the expected profile effects of greater penetration of the tritium into the specimens. The relationship of the BET surface area to the amount adsorbed appeared to be linear for oxidized specimens; however, the amount of tritium sorbed by unoxidized specimens could not be simply related to the BET surface area.
Deposition of silicon dioxide and silicon nitride by remote plasma enhanced chemical vapor deposition
Authors: Lucovsky G. , Richard P. D. , Tsu D. V. , Lin S. Y. , Markunas R. J.
Published: July 2002

We have developed a low temperature process for the deposition of thin films of silicon dioxide and silicon nitride. The process consists of four steps: (a) excitation of an oxygen or nitrogen-containing molecule in an RF plasma; (b) transport of the excited oxygen or nitrogen species out of the plasma region; (c) mixing of the transported excited species with silane (or disilane) out of the plasma region to form precursor species; and (d) a CVD reaction at a heated substrate to form the desired thin film. We call this process remote plasma enhanced CVD (RPECVD). Silicon rich oxide films have been grown at substrate temperatures (Ts) between 100 and 350 °C using an excited O2/He mixture. Two different ‘‘silicon nitrides’’ have been deposited depending on the excited gas, NH3 or an N2/He mixture, and Ts. Using either nitrogen source and Ts greater than 450 °C, we obtain near stoichiometric films of Si3N4. On the other hand, films grown from NH3 and deposited with Ts of about 50 to 100 °C are silicon diimide [Si(NH)2], which is isostructural with respect to SiO2 with bridging NH groups substituted for the bridging oxygen atoms. Films grown from the NH3 source and at Ts between 150 and 450 °C are solid solutions of silicon nitride and silicon diimide. We discuss the application of these dielectric films in device structures.
Kinetics and dynamics of the nitric oxide/ammonia interaction on Pt(111)
Authors: Burgess D. , King D. S. , Cavanagh R. R.
Published: July 2002

The kinetics and dynamics of the nitric oxide/ammonia interaction on Pt(111) were studied using a combination of temperature-programmed desorption (TPD) and laser-excited fluorescence techniques. Although NO desorption kinetics are significantly altered by interaction with preadsorbed NH3, no effect was seen in the dynamical accommodation of rotational energy with the surface. For surface temperatures of 150 to 400 K and NO coverages from 5% to saturation, the rotational temperature of desorbed NO was 90±5% of the surface temperature and independent of coadsorbed ammonia. TPD suggests that a stable NO–NH3 complex exists on the surface and that desorption of NO and NH3 are reaction limited by its dissociation. Our results imply the dissociation and desorption steps are not concerted and NO accommodates with the surface prior to desorption.
Silicide thickness calculations and phase identifications
Authors: Chen Jiann-Ruey
Published: July 2002

A theoretical model on the film thickness calculation is presented in which the thickness of the metal silicide formed after reaction can be expressed in terms of the densities of metal, silicon, and silicide. Results show that the effective thickness of the formed MoSi2 after reaction as calculated by Fomin et al. must be modified by an invariant factor of 0.83. Experimental data on transition-metal silicides conform to our theoretical model, and values of the modifying factor for various metal silicides are in the range from 0.7 to 0.86. This model is further extended into the more general case in which two silicide phases are formed after the reaction. The silicide phases formed after the reaction can be determined from the diagram showing the total thickness of the silicides formed versus the thickness of the metal consumed.
Relation of polymer structure to plasma etching behavior: Role of atomic fluorine
Authors: Cain S. R. , Egitto F. D. , Emmi F.
Published: July 2002

Plasma etching of organic polymers typically involves the use of feed gas mixtures of oxygen with a fluorocarbon. The reactive etchants are generally accepted to be atomic fluorine and atomic oxygen. The roles of these etchants are discussed with special attention being given to the part played by atomic fluorine. Mechanisms are inferred theoretically from a molecular orbital study, and experimentally from the surface composition of plasma treated samples. Hydrogen abstraction by fluorine leads to enhanced etching of saturated polymer structures while addition of fluorine is the dominant mechanism for unsaturated moieties. Etch rate behavior for polyimide, polyisoprene, and polyethylene as a function of gas composition is discussed in terms of the affinity that fluorine has for the surface of the saturated and unsaturated polymers.
Atomic force microscopy and scanning tunneling microscopy with a combination atomic force microscope/scanning tunneling microscope
Authors: Marti O. , Drake B. , Gould S. , Hansma P. K.
Published: July 2002

Since almost all the electronic and mechanical requirements for an atomic force microscope (AFM) are the same as for a scanning tunneling microscope (STM), it is convenient and practical to build a combination AFM/STM with interchangeable heads. The conversion from one to the other can be made in a few minutes. Representative images demonstrate that atomic resolution can be obtained in both modes of operation. With the two modes of operation, it can image conductors, semiconductors, and insulators.
A multiaperture ion source with adjustable optics to provide well-collimated, high-current-density, low- to medium-energy ion beams
Authors: Ray M. A. , Barnett S. A. , Greene J. E.
Published: July 2002

The design, operation, and characterization of a new, adjustable-grid, multiaperture ion source are described. The capability for in situ relative lateral motion of the grids allows beam steering and alignment during source operation. The maximum beam deflection angle is ∼10° at a beam acceleration voltage Vb=1000 V. The grid separation distance dg is also adjustable in situ, allowing independent control over beam current and voltage while maintaining a minimum beam divergence. Decreases in beam divergence angle α, by as much as a factor of 3 over a comparable fixed-grid source, were obtained. Beam accelerating voltages Vb ranging from 200 to 1000 V were investigated for dg values between 1 and 4 mm with a grid hole diameter of 2 mm. Minimum α values ranged from 4° to 7°. The total current density at minimum α for dg=1 mm and Vb=1000 V was 2.2 mA cm−2. The dependence of the measured beam divergence on source operating conditions and grid geometry is explained using a simple ion-optics model.
Structural stability of ZrO2–Al2O3 thin films deposited by magnetron sputtering
Authors: Qadri S. B. , Gilmore C. M. , Quinn C. , Skelton E. F. , Gossett C. R.
Published: July 2002

Thin films of zirconia–alumina were prepared in a variety of compositional ratios and on several different substrates by reactive magnetron sputtering. Thin films were initially amorphous, but they could be crystallized by appropriate heat treatment operations. The conditions for nucleation and the stability of the cubic, tetragonal, and monoclinic phases of ZrO2 were examined over the entire composition range. X-ray diffraction studies suggested that films with Zr:Al atomic ratios up to 0.70:0.30 nucleated first with the zirconia in the cubic phase with subsequent transformation to a tetragonal phase as a function of annealing time. A decrease in volume of the monoclinic phase was observed with increasing alumina content, suggesting that an internal compression results in a reduction of the volume to the point where the monoclinic-to-tetragonal transition is energetically favorable. Freestanding films could be produced by depositing the zirconia–alumina films onto a NaCl substrate and then dissolving the latter in distilled water. High-pressure studies were performed in a diamond anvil to examine the stability of the amorphous and crystallized films.
Outgassing-rate-measurement apparatus for small parts in ultrahigh vacuum
Authors: Ota N. , Watanabe F. , Kanazawa K. , Momose T. , Ishimaru H.
Published: July 2002

An apparatus to measure the outgassing rate of small parts in an ultrahigh vacuum environment was constructed using aluminum alloys. In order to test the reliability of the apparatus, we prepared test pieces and test chambers with various surface areas but with the same surface treatments, and measured the dependence of the outgassing rate on the surface area. The outgassing rate was measured using the throughput method. Before and during baking, the outgassing rate was proportional to the surface area, but after baking, the outgassing from a Bayard–Alpert (BA) gauge modified the proportionality. Residual gas analysis using a quadrupole mass spectrometer (QMS), which was specially prepared for use in extreme-high vacuum [H. Ishimaru, J. Vac. Sci. Technol. A 7, 2439 (1989)], showed that the main component of the outgassing before baking was H2O. After baking, H2 was dominant if the outgassing from the BA gauge was subtracted. The outgassing from the BA gauge was composed of mainly H2 and CO. The outgassing rate of the gauge was the dominant contribution to the background outgassing rate after baking and was about 6×10−10 -2×10−9 Torr ℓ/s. Moreover, the outgassing rate of the gauge depended on the ambient pressure. If the outgassing rate of the gauge is correctly subtracted from the total outgassing rate, the correct outgassing rate of the sample can be determined.
Profiling of Y–Ba–Cu–O radio-frequency sputtering by optical emission spectroscopy
Authors: Klein J. D. , Yen A.
Published: July 2002

The optical emission spectra from species excited during radio-frequency sputtering of a Y–Ba–Cu–O target were observed as a function of position. A collimated optical fiber bundle parallel to the plane of the horizontal sputter target was translated vertically and horizontally to spectroscopically profile the excited species. The Ba and Cu constant intensity contours indicate a significantly different intensity decrease with increasing distance along a line normal to the plane of the target. However, there does exist a region immediately to the side and slightly above the target surface in which the Ba and Cu contours are similar. The pronounced extension of the O contours in a direction perpendicular to the target surface is consistent with negative ion resputtering phenomena.
A reactive sputtering model applied to AlN
Authors: Öfner H. , Zarwasch R. , Rille E. , Pulker H. K.
Published: July 2002

To the model of reactive sputtering of Berg et al. [S. Berg, H.-O. Blom, T. Larsson, C. Nender, J. Vac. Sci. Technol. A 5, 202 (1987)] an energy dependent sputtering yield was introduced. Calculated hysteresis curves were in good agreement with measurements.
A selection principle of phenolic compounds for novolak resins in high performance positive photoresists
Authors: Hanabata Makoto , Furuta Akihiro
Published: July 2002

The relationship between resist performance and the kinds of phenolic compounds for novolak resins was investigated from the standpoint of the image formation process. Dissolution rates were measured on photoresists containing novolak resins made from various phenolic compounds including phenol, cresol, ethylphenol, butylphenol, and their copolymers. It was found that there are suitable combinations of phenolic compounds to exhibit high resist performance. On the basis of the experimental results, we discuss the effect of the kinds of phenolic compounds on the dissolution characteristics and the structure of novolak resins. Finally, we propose a selection principle of phenolic compounds for novolak resins useful to design high performance positive photoresists.
In situ spectroscopic ellipsometry in molecular beam epitaxy
Authors: Maracas G. N. , Edwards J. L. , Shiralagi K. , Choi K. Y. , Droopad R. , Johs B. , Woolam J. A.
Published: July 2002

Noninvasive, real-time material growth monitoring is becoming increasingly important as epitaxial layer structures become more complex and the thickness and alloy composition tolerances are reduced. The technique of spectroscopic ellipsometry has been adapted to a commercial III–V semiconductor molecular beam epitaxy (MBE) system to monitor layer thickness, ternary alloy composition, and substrate temperature in real time during the growth of multilayer structures. Practical system considerations for reliably implementing the rotating analyzer ellipsometer in a hydride source MBE environment that contains a high pressure of dimeric group V species will be discussed. Measurement of substrate temperature from room temperature to typical growth temperatures will then be presented as well as in situ determination of alloy composition and thickness for efficient growth calibration. A growth run of GaAs/AlGaAs epitaxial layers will be examined to observe surface smoothing upon group III pulse deposition and growth interruption at heterointerfaces. The growth of quantum well structures is then monitored and analyzed in attempts to extract heterojunction interface abruptness. Finally, a summary of epitaxial reactor design issues that need to be addressed to implement the spectroscopic ellipsometry (SE) technique in commercial systems is provided.
High-vacuum planar magnetron discharge
Authors: Asamaki T. , Miura T. , Nakamura G. , Hotate K. , Yonaiyama S. , Ishibashi K. , Hosokawa N.
Published: July 2002

The present article demonstrates the possibility of developing a high-vacuum planar magnetron discharge. Until recently, developed cathodes applying a high electric field and a high magnetic field which cross each other in a discharge space enable the discharge to be sustained at 0.1 Pa. Experimental results of this article show that even at pressures lower than 10−3 Pa the discharge can be sustained. The discharge intensity I/P is proportional to the discharge voltage and depends strongly on the magnetic flux density. It is found that the high-vacuum planar magnetron discharge requires a magnetic flux density higher than 0.1 T and a discharge voltage higher than 2 kV, for its effective sustenance. Sputtering of aluminum by this discharge is performed and the deposition rate 0.2 μm/min is obtained.
Ultraviolet ozone oxidation of Si surface studied by photoemission and surface infrared spectroscopy
Authors: Niwano Michio , Suemitsu Maki , Ishibashi Yutaka , Takeda Yuki , Miyamoto Nobuo , Honma Koji
Published: July 2002

It has previously been shown that ultraviolet (UV) ozone oxidation can be utilized for removing carbon contaminants on Si surfaces and forming a thin oxide film which serves as a protective overlayer for chemical attack. In this study, the UV ozone oxidation of a Si surface has been investigated using photoemission spectroscopy with synchrotron radiation and surface infrared spectroscopy in the multiple internal reflection mode. It is shown that during UV ozone oxidation a thin SiO2 film approximately 5 Å thick, which presumably corresponds to one monolayer of six-member rings of SiO4 tetrahedra, is initially formed and subsequently slow oxidation occurs. It is suggested that the formation of this 5-Å-thick oxide film is the key to protecting the Si substrate surface from the adsorption of impurities which would occur if the bare Si surface were exposed to air.
Studies of interactions between NO and CO on a Pd surface by thermal programmed desorption and molecular beam relaxation spectrometry
Authors: Xi Guangkang , Bao Jiangzhong , Shao Shumin , Li Shenglin
Published: July 2002

The catalytic reduction of NO and CO on a Pd (poly) surface has been studied in 300–900 K with thermal programmed desorption and molecular beam relaxation spectrometry methods. Under several ratios of PNO to PCO, the reaction products were CO2, N2, and a bit of N2O. Analysis of data in different temperature regions concludes that the reaction between NO and CO is a true bimolecular reaction rather than unimolecular NO decomposition with CO scavenging of adsorbed oxygen. Best fits to the rate constant parameters characterizing this reaction are given. The activation energies of CO for desorption and of this reaction are Edco= 134.0 and Ebi = 88.4 kJ/mol, respectively. The effects of ratio of PNO to PCO in mixture and coverage of adsorbate are discussed.
Thermally stimulated exoelectron emission from graphite surfaces exposed to oxygen, tetrafluoromethane, and argon plasmas
Authors: Momose Y. , Ohaku T. , Okazaki S. , Fujii Y.
Published: July 2002

We have investigated the thermally stimulated exoelectron emission (TSEE) from graphite surfaces exposed to O2, CF4, and Ar plasmas in combination with the measurements of surface potential (SP) and x-ray photoelectron spectroscopy (XPS). The surfaces exposed to the plasmas were left in the ambient air prior to the measurements. The TSEE glow curves, the change in SP, and the XPS spectra were examined as a function of plasma exposure time and pressure. The TSEE glow curves for each plasma gas exhibited one sharp emission peak (peak I) at ∼98 °C, the intensity of peak I decreasing in the order, O2≳CF4≳Ar. Furthermore, for CF4 plasma a broad peak (peak II) was also observed at ∼250 °C. The SP for the surfaces exposed to the plasmas became highly negative, decreasing in the order, Ar≳O2≳CF4. This can be attributed to an increase in the O and F contents on the surface. The change in SP after the plasma treatment was nearly reversed to the original value in each case after the TSEE measurement. The origins for the TSEE peaks I and II are discussed based on the change in SP and the atomic ratios of O1s/C1s and F1s/C1s measured by XPS.
Recycling and particle control in DIII–D
Authors: Jackson G. L.
Published: July 2002

Particle control of both hydrogen and impurity atoms is important in obtaining reproducible discharges with a low fraction of radiated power in the DIII–D tokamak. The main DIII–D plasma facing components are graphite tiles (40% of the total area and covering regions exposed to the highest heat fluxes) and Inconel. Hydrogenic species desorbed from graphite during a tokamak discharge can be a major fueling source, especially in unconditioned graphite where these species can saturate the surface regions. In this case the recycling coefficient can exceed unity, leading to an uncontrolled density rise. In addition to removing volatile hydrocarbons and oxygen, DIII–D vessel conditioning efforts have been directed at the reduction of particle fueling from the graphite tiles. Conditioning techniques include: baking to ≤400 °C, low power pulsed discharge cleaning, and glow discharges in deuterium, helium, neon, or argon. Helium glow wall conditioning, is now routinely performed before every tokamak discharge. The effects of these techniques on hydrogen recycling and impurity influxes are presented. The Inconel walls, while not generally exposed to high heat fluxes, nevertheless represent a source of metal impurities which can lead to impurity accumulation in the discharge and a high fraction of radiated power, particularly in H-mode discharges at higher plasma currents, Ip ≳ 1.5 MA. To reduce metal influx a thin (∼100 nm) low Z film (carbon or boron) has been applied on all plasma facing surfaces in DIII–D. The application of the boron film, referred to as boronization, has the additional benefit over a carbon film (carbonization) of further reducing the oxygen influx. Following the first boronization in DIII–D a regime of very high confinement (VH-mode) was observed, characterized by low ohmic target density, low Zeff, and low radiated power.
Force microscopy with actively stabilized differential fiber detection mechanism
Authors: Nonnenmacher M. , Vaez-Iravani M. , Wickramasinghe H. K.
Published: July 2002

We present the design and theory of operation of a new fiber-optic detection mechanism for force microscopy. The technique comprises a differential fiber Michelson interferometer, in which most spurious signals due to environmental variations are automatically rejected. Any residual fluctuations are canceled by the action of a feedback mechanism, which also ensures operation at maximum sensitivity. This detection technique is capable of high sensitivity response to both high and low frequency tip variations, and can thus be used in the attractive and repulsive modes. A number of results are presented on the applications of a force microscope utilizing this detection mechanism. Both ac and dc modes of operation are demonstrated.