bluuebunny/crossref_metadata_2025 huggingface dataset:
History of ultrahigh vacuum pressure measurements
Authors: Redhead P. A.
Published: July 2002

The measurement of pressure in the UHV range started in 1950 with the invention of the Bayard–Alpert gauge which reduced the lowest pressure measurable with hot-cathode gauges of the time by a factor of 200 or more. The processes causing limits to the lowest measurable pressure include the x-ray effect, electron stimulated desorption from electron bombarded electrodes, chemical effects at thermionic cathodes, and thermal desorption. This historical review traces from 1950 to the present day the development of gauges, both hot and cold cathode, designed to reduce these lower limits, and emphasizes the research directed to understanding the physical and chemical processes governing these limitations. The development of, and the limiting processes in, residual gas analysers suitable for UHV is also followed over the same period starting with the omegatron, then the magnetic sector instrument, and finally the quadrupole.
Observations of particle layers levitated in a radio-frequency sputtering plasma
Authors: Praburam G. , Goree J.
Published: July 2002

Submicron carbon particles are grown in an argon radio-frequency (rf) sputtering plasma with graphite electrodes. In situ laser light scattering revealed particles levitated in the plasma in stratified layers, which were often thinner than 0.5 mm. Under some conditions, the number of layers was very large. These layers are grouped into clouds. In a pure argon plasma, there is one cloud near the sheath edge above the lower electrode, while adding SF6 results in additional particle clouds near the upper electrode and in the glow region. The different layers appear to separate particles according to size, with the heaviest in the lowest layer. During several hours of plasma operation, the layers collapsed and grew again into more stratified layers. The influence of parameters, such as gas pressure, rf power, electrode separation, and gas mixture was investigated. Scanning electron microscopy revealed that the particles were multisized spheres with a cauliflowerlike surface. Some of the particles were found to be coagulated, due to collisions within the plasma.
Acceleration of high current heavy ions using a variable energy radio-frequency quadrupole linac and measurement of the input beam emittance
Authors: Amemiya Kensuke , Tokiguchi Katsumi , Hakamata Yoshimi , Yamada Satoru , Hirao Yasuo , Tokuda Noboru
Published: July 2002

A high current ion beam injection system and a variable energy radio-frequency quadrupole (RFQ) accelerator with an external LC resonance circuit are tested. A four-rod RFQ electrode of 2.3 m length is newly designed to obtain a milliampere class MeV ion beam. To increase accelerated beam current, injected beam emittance into the RFQ is measured and compared with the designed RFQ acceptance. Injected beam emittance tends to increase with the beam current increase. The beam acceleration tests are carried out with a cw rf power supply of 100 kW (10–30 MHz, continuously variable). Results show that the time-averaged beam currents of N+ and Ar2+ are 1.1 mA (0.4 MeV) and 1.03 mA (1.0 MeV), respectively, and that the peak current of these beams is about 5 mA. As representative ion species for fabricating semiconductor devices, P+ and P2+ are accelerated, and the time-averaged beam current of 0.48 mA (0.56 MeV) and 0.28 mA (0.81 MeV) are obtained, respectively. This high current MeV ion implanter has great potential for application to high-dose implantation and high throughput production of semiconductor devices and material surface modifications.
Flux dependence of in situ electron transport in Ag/Si(111)
Authors: Kimberlin K. R. , Tringides M. C.
Published: July 2002

Electrical transport in ultrathin films of Ag on the Si(111)-7×7 surface has been studied as a function of the incident flux rate in situ at room temperature with a four-probe technique. The origin of conduction in this system is unclear: two dimensional transport after the formation of a percolating cluster or conduction through the substrate via electrons transferred from the film to the substrate has been suggested as possible mechanisms. The four-probe voltage vs deposition time traces obtained at different flux rates collapse into a universal curve that supports conduction through the substrate and not through the film. The film morphology is expected to be smoother at lower flux rates so a steeper drop with time should have been observed if conduction were through the film. No significant dependence on the initial roughness of the clean surface is observed, which further supports conduction controlled by the substrate electronic structure.
Deposition of silicon oxide onto polyethylene and polyethyleneterephthalate: An x-ray photoelectron spectroscopy interfacial study
Authors: Rotger J. C. , Pireaux J. J. , Caudano R. , Thorne N. A. , Dunlop H. M. , Benmalek M.
Published: July 2002

X-ray photoelectron spectroscopy (XPS) and scanning electron microscopy were used to study the physico–chemical interaction between evaporated silicon oxide and polymers. SiO1.5 was shown to deposit as clusters onto polyethylene, not covering the whole surface of the substrate. Argon, oxygen, and nitrogen plasma treatments were tested to improve the reactivity of polyethylene, but only nitrogen was found to be reactive enough to allow for a uniform layer of silicon oxide, as on polyethyleneterephthalate. The high resolution XPS study of the interface between nitrogen plasma treated polyethylene and in situ deposited silicon oxide showed the formation of silicon–oxygen–carbon or silicon–nitrogen–carbon bonds while silicon–carbon bonds were only observed with polyethyleneterephthalate.
Preparation and characterization of ZnO films by an evaporating method
Authors: Ma Jin , Ji Feng , Ma Hong-lei , Li Shu-ying
Published: July 2002

This article describes the preparation of ZnO films by thermal evaporation of zinc acetate [Zn(CH3COO)2⋅2H2O] onto a heated glass substrate. The structure and optical and electrical properties of the deposited films are investigated. Highly transparent films with conductivity as high as 1.3×102 Ω−1 cm−1 can be produced by controlling the deposition parameters. Heat treatment in hydrogen significantly increases the conductivity of these ZnO films by more than six orders of magnitude. The energy gap of ZnO film was evaluated as about 3.3 eV from optical absorption measurements. The electron carrier densities are in the range 1.2–4×1019 cm−3 with mobilities of 20–50 cm2 V−1 s−1.
Quantitative determination of titanium nitride films by high energy resolution Auger electron spectroscopy
Authors: Zhang Qing Yu
Published: July 2002

The major N Auger transition (KLL) overlapping with the Ti LMM peak and the shape of all Ti Auger lines changing by nitride compound formation are the two main difficulties in the quantitative Auger analysis of titanium nitrides. In this article, a linear least-squares method is used to break down the composition of the 420 eV peak (Ti LMV) into separate components and to determine the nitrogen content of the TiNx films by computer fitting the Ti LMV Auger lines. The results obtained by this method are in good agreement with those determined by x-ray photoelectron spectroscopy. The method is also applied to analyze the depth profile of the film and composition change at the interface to the substrate.
Postplasma particle dynamics in a Gaseous Electronics Conference RF Reference Cell
Authors: Collins S. M. , Brown D. A. , O’Hanlon J. F. , Carlile R. N.
Published: July 2002

Particle contamination in plasma tools used for the manufacture of very large scale integrated semiconductor devices on silicon wafers is a major cause of yield loss. Understanding the dynamics of particle movement in the postplasma regime is important to explain the process of their transport to the wafer. The movement of particle contamination in a Gaseous Electronics Conference RF Reference Cell in the postplasma regime was investigated using a novel technique. Particle clouds were observed using laser light scattering together with an image intensifier and a monochromator. This technique allowed particle clouds of low density, that could not otherwise be detected, to be seen. Video analysis of the particles showed movement of the cloud front during the first second after the plasma was extinguished. Using the particle terminal velocity to estimate particle size, we estimate diameters of 0.11 μm in argon and 0.05 μm in krypton. The role of the thermophoretic force on particles during the postplasma was shown to be larger than gravitational forces and to dominate particle transport for small particles under the conditions investigated. A temperature gradient of 12 °C/cm was observed to move these particles away from a warm electrode as the plasma was extinguished and the particles were released from the electrostatic confinement forces generated by the plasma.
Compositionally gradient (Ti1−xAlx)N coatings made by plasma enhanced chemical vapor deposition
Authors: Lee Sang-Hyeob , Lee Jung-Joong
Published: July 2002

Compositionally gradient (Ti1−xAlx)N coatings were deposited by the plasma enhanced chemical vapor deposition technique using a gas mixture of TiCl4, AlCl3, NH3, H2, and Ar. The Al and the Ti concentrations in the coated layer changed linearly with the logarithms of the flow rate ratio of AlCl3 to TiCl4, log(QAlCl3/QTiCl4). Since the vapor pressures of AlCl3 and TiCl4 change exponentially with the temperature within the range where the vaporizers of the source materials were heated for the deposition, the concentrations of Al and Ti in the coatings could be controlled simply by changing the temperatures of the vaporizers. X-ray diffraction (XRD) investigations showed that the compositionally gradient (Ti1−xAlx)N coating has the NaCl structure with a preferred orientation of (200), like TiN, up to the Al concentration of about X=0.8. The broadened XRD peak with its shifted position indicates that the lattice parameter of (Ti1−xAlx)N changed gradually with the concentration change in the coated layer. A suppressed growth of continuous columns and a tetragonally distorted lattice structure, which are supposed to come from the lattice parameter change during the film growth, could be observed in the cross-sectional transmission electron microscopy study.
Sulfur layer formation on GaAs(100) by thermal and photochemical H2S dissociation
Authors: Nooney Matthew G. , Liberman Vladimir , Martin Richard M.
Published: July 2002

We have studied the formation of sulfide layers on the GaAs(100) c(8×2) gallium rich surface through thermal and photoinduced (193 nm) decomposition of H2S. H2S was adsorbed on the sample at 90–95 K. The sulfide layer desorbs as Ga2S beginning at 740 K. For thermal sulfide layer formation, it was found that more sulfur could be built up on the surface by repeated cycles of H2S exposure at low temperature followed by heating to 600 K. Several such cycles gave a sulfide layer saturating at about one monolayer. With photoinduced dissociation of H2S thicker sulfide layers were produced, with no apparent saturation limit after several layers had been formed. Auger data suggests that As remains below the gallium sulfide layer up to at least 600 K. Sulfide layers were found to inhibit oxidation of the substrate by NO2, e.g., sulfide coverages of 1.5 to 2 layers reduced the amount of oxide (Ga2O) formed by 70%–85%.
TiN thin film on stainless steel for extremely high vacuum material
Authors: Saito K. , Inayoshi S. , Ikeda Y. , Yang Y. , Tsukahara S.
Published: July 2002

We have shown that titanium nitride (TiN) coating by activated reactive evaporation using the hollow cathode discharge method is a good surface treatment for stainless steel used in extremely high vacuum (XHV) applications. The TiN film blocks hydrogen diffusion because it has a much lower hydrogen permeation coefficient than stainless steel. By varying the coating and film parameters (e.g., thickness, composition, and substrate bias voltage Vb) the barrier effects on hydrogen permeation of the TiN films were evaluated using small membrane samples. The parameters were varied to optimize the properties of the TiN coating for vacuum materials. The structure of the TiN films was analyzed by an x-ray diffractometry and transmission electron microscopy to clarify the dependence of the barrier effect on the film structure. Stoichiometric TiN films with few defects were shown to have high barrier effects. To demonstrate the use of TiN coatings for XHV applications, the outgassing rates of a stainless steel chamber with and without a TiN film were measured by a modified throughput type apparatus that had a bakeable cryopump for obtaining XHV. The outgassing rates for the chambers were measured using a method which completely eliminated the outgassing contribution of the vacuum gauges. The nitrogen equivalent outgassing rates of the stainless steel chamber with and without a TiN film were 7×10−12 and 9.7×10−10 Pa m s−1, respectively.
Surface flatness of polished metal single crystals
Authors: Tripa C. Emil , Yates John T.
Published: July 2002

The Fizeau interference has been utilized to measure the flatness of a metal single crystal after grinding and polishing by standard techniques. It is postulated that deviations from flatness are due to distortions of flexible abrasive substrates during the grinding step.
Particle trapping, transport, and charge in capacitively and inductively coupled argon plasmas in a Gaseous Electronics Conference Reference Cell
Authors: Collins S. M. , Brown D. A. , O’Hanlon J. F. , Carlile R. N.
Published: July 2002

Particle trapping has been observed for both a capacitively coupled and an inductively coupled Gaseous Electronics Conference Reference Cell. Particles in the system were formed by introducing 10% CCl2F2 into an argon discharge for 5–10 min and sputtering the resulting film during argon-only experiments. The particles generated were 200–600 nm in diameter. Particle transport was observed in the postplasma regime for both capacitively and inductively coupled cases. For the capacitively coupled plasma, particles of positive, negative and neutral charge were found during the postplasma and shown to be affected by the presence of a dc field during the postplasma period. The charge on these particles was determined to be between 1.4 and 12.4 electron charges based on a study of particle motion. This compares to a theoretical value of 800–2600 while the plasma is ignited. For the inductively coupled plasma both a low density mode and a high density mode were observed, being distinguished by a sudden increase in the emission from the plasma as rf power to the inductive coil was increased. In the high density mode of the inductively coupled plasma, the particle cloud was observed to reside less than a millimeter from the powered electrode as the high density plasma mode was established. This was distinguished from a trap height of 4–7 mm for the capacitively coupled plasma which corresponds to the sheath thickness.
Chemical and spectroscopic studies of metal oxide surfaces
Authors: Goodman D. W.
Published: July 2002

Thin oxide films (e.g., 5–10 nm of SiO2, Al2O3, NiO, MgO) supported on a refractory metal substrate (e.g., Mo, W, Ta, Re) have been prepared by deposition of the oxide metal precursor in a background of oxygen. The thin-film nature of these samples facilitates investigation by an array of surface techniques, many of which cannot be effectively utilized on the corresponding bulk oxide. The structural, electronic, and chemical properties of these films have been studied with temperature programmed desorption, Auger electron spectroscopy, X-ray photoelectron spectroscopy, ion scattering spectroscopy, high resolution electron energy loss spectroscopy, and infrared reflection absorption spectroscopy. The results of these studies demonstrate the viability of using thin oxide films as models for the corresponding bulk oxide.
Estimation and verification of the electrical properties of indium tin oxide based on the energy band diagram
Authors: Kulkarni A. K. , Knickerbocker S. A.
Published: July 2002

Indium tin oxide (ITO) is a transparent conducting oxide used in a variety of optoelectronic applications. In order to optimize the electrical conductivity of ITO thin films it is necessary to determine this property as a function of optimum electron concentration (e.g., doping of In2O3 with Sn). A new software program called CRYSTAL 92 is used to determine the energy band diagrams of In2O3 and In2O3 doped with Sn. Using the curvature of the conduction bands, the effective mass of the electrons is estimated and an empirical relationship is established between the effective mass and free carrier concentration using experimentally observed optical effective mass values. The importance of the varying electron effective mass in the prediction of the electron mobility, and hence the electrical conductivity, is shown here by comparing the published experimental results with the estimated results. The limiting factor in the electron mobility appears to be either grain boundary scattering or ion impurity scattering. The mobility due to neutral impurity scattering appears to have a negligible effect on the overall mobility unless the neutral impurity concentration reaches extremely high values.
High-density plasma etching of compound semiconductors
Authors: Shul R. J. , McClellan G. B. , Briggs R. D. , Rieger D. J. , Pearton S. J. , Abernathy C. R. , Lee J. W. , Constantine C. , Barratt C.
Published: July 2002

Inductively coupled plasma (ICP) etching of GaAs, GaP, and InP is reported as a function of plasma chemistry, chamber pressure, rf power, and source power. Etches were characterized in terms of rate and anisotropy using scanning electron microscopy, and root-mean-square surface roughness using atomic force microscopy. ICP etch rates were compared to electron cyclotron resonance etch rates for Cl2/Ar, Cl2/N2, BCl3/Ar, and BCl3/N2 plasmas under similar plasma conditions. High GaAs and GaP etch rates (exceeding 1500 nm/min) were obtained in Cl2-based plasmas due to the high concentration of reactive Cl neutrals and ions generated as compared to BCl3-based plasmas. InP etch rates were much slower and independent of plasma chemistry due to the low volatility of the InClx etch products. The surface morphology for all three materials was smooth over a wide range of etch conditions.
Ultraviolet Raman spectroscopy of catalysts and other solids
Authors: Stair Peter C. , Li Can
Published: July 2002

Resonance Raman spectroscopy measurements, which utilize ultraviolet (UV) excitation, appear to be very useful for the study of catalysts and other solids, which produce strong fluorescence that makes conventional Raman spectroscopy very difficult. In this article, we describe the instrumentation used in our laboratory for ultraviolet Raman spectroscopy and compare measurements using conventional, visible excitation with ultraviolet excitation at 257 nm. We also illustrate the versatility of the UV Raman technique by showing spectra obtained from a variety of solid samples that would be difficult if not impossible to measure using conventional Raman.
Effect of temperature on Ti and TiN films deposited on a BN substrate
Authors: Seal S. , Underwood H. , Uda M. , Osawa H. , Kanai A. , Barr T. L. , Benko E. , Krauss A. , Perera R. C. C.
Published: July 2002

Nitrides (such as BN and TiN) are widely used in various industrial applications because of their excellent wear and corrosion resistance and their thermal and electronic properties. The structural and chemical features formed during plasma vapor deposition of Ti/TiN on BN substrates have been studied using synchrotron radiation near edge absorption spectroscopy (NEXAFS). Various phases of interest have been formed with different annealing temperatures. Diffusion of the nitridation and the interference from oxidation (e.g., TiO2) and boride formation are of particular concern. X-ray photoelectron spectroscopy and secondary ion mass spectroscopy measurements complement our NEXAFS data. Phase formation and chemical bonding between the coating and the substrate are shown to be determining factors for the microhardness.
P
-type transparent conducting In2O3–Ag2O thin films prepared by rf magnetron sputtering
Authors: Minami T. , Shimokawa K. , Miyata T.
Published: July 2002

P -type transparent conducting oxide films consisting of a new multicomponent oxide composed of In2O3 and Ag2O have been prepared by rf magnetron sputtering. After postannealing at a temperature of 500 °C in air, In2O3–Ag2O thin films prepared using In2O3–Ag2O targets with Ag2O contents of 40–60 wt % exhibited p-type conduction. A resistivity of 10−1–10−3 Ω cm and an average transmittance above 20% in the visible range were obtained in the p-type amorphous In2O3–Ag2O films. A resistivity of 8.8×10−3 Ω cm, Hall mobility of 17 cm2/Vs and hole concentration of 4.2×1019 cm−3 were obtained in a film prepared with an Ag2O content of 50 wt %.
Submicron contacts for electrical characterization of semiconducting WS2 thin films
Authors: Ballif C. , Regula M. , Lévy F. , Burmeister F. , Schäfle C. , Matthes Th. , Leiderer P. , Niedermann Ph. , Gutmannsbauer W. , Bucher R.
Published: July 2002

We report a new method to characterize the local electronic properties of polycrystalline semiconducting thin films. A lattice of triangular gold electrodes, with a typical area of 0.2 μm2, is evaporated on a p-type WS2 film. With the help of a conductive atomic force microscope, the current–voltage characteristics of the contacts established between the gold electrodes and the WS2 film are measured. A linear dependence of the current versus voltage is obtained on gold triangles in contact with grain edges. This indicates a high level of doping or degeneracy of the semiconductor at the grain edges. The electrodes deposited on flat WS2 crystallites form rectifying diodes with the underlying grains. Barrier heights of 0.56–0.74 eV and diode ideality factors between 1.15 and 2 are determined. Under illumination, open-circuit voltages up to 500 mV can be measured on some contacts. A short response time of the photocurrent is observed (<0.1 ms) when the diodes are reversed biased, which is related to intrinsic properties of the crystallites. When the diodes are forward biased a longer response time is measured (>100 ms), linked to trapping effects at grain boundaries.
Structural coherence of sputtered Ni3Al/Ni multilayers
Authors: Tixier S. , Böni P. , Van Swygenhoven H.
Published: July 2002

Ni 3 Al/Ni multilayers have been grown by magnetron sputtering at room temperature. Structural coherence and interfacial properties were investigated as a function of deposition conditions by means of high angle x-ray diffraction, as well as specular and nonspecular x-ray reflection. High vertical coherence over 3.5 bilayer thickness is obtained in favorable conditions. It is shown that the structural coherence results from a highly textured growth and from a rather constant bilayer thickness over the whole multilayer stack. Surprisingly, the vertical coherence length does not decrease in samples sputtered at high Ar pressure despite a higher mosaic spread of the grains and rougher interfaces. In contrast, a high base pressure prior to sputtering is found to alter the coherence and to favor sharp and smooth interfaces. In all samples the roughness profiles are partially correlated from one interface to the other. The corresponding vertical correlation length is strongly influenced by the sputtering Ar pressure. In a large lateral length scale range (103–104 Å), a relatively slow decrease of the correlation length with decreasing length scale of the roughness is measured with a correlation length significantly smaller for the sample grown at high Ar pressure.
Interactions of methanol with stoichiometric and defective TiO2(110) and (100) surfaces
Authors: Wang Li-Qiong , Ferris K. F. , Winokur J. P. , Shultz A. N. , Baer D. R. , Engelhard M. H.
Published: July 2002

Interactions of CH3OH with stoichiometric (nearly defect-free) and defective TiO2(110) and (100) surfaces have been studied using x-ray photoelectron spectroscopy and ultraviolet photoemission spectroscopy. The CH3OH saturation coverage was increased by increasing the number of defects created by electron-beam exposure or Ar+ ion bombardment. A small percentage of any defects produced were healed upon the saturation exposure (defect healing means a reduction in defect signal observed by the photoemission measurements). The structural influence on the adsorption and surface defect reactivity was found to be less significant for CH3OH than for H2O. The CH3OH coverages at a given exposure and defect reactivity were comparable for both the (100) and (110) surfaces.
Study of the reactions of Li with tetrahydrofuran and propylene carbonate by photoemission spectroscopy
Authors: Zhuang G. R. , Wang K. , Chen Y. , Ross P. N.
Published: July 2002

The reaction of Li with two organic solvents of technical importance in Li batteries, tetrahydrofuran (THF) and propylene carbonate (PC), were studied in ultrahigh vacuum by photoemission spectroscopy. The organic condensate layers were formed by dosing thin (6–10 nm) films of Li at 120–135 K, with the reactions monitored by x-ray photoemission spectroscopy and ultraviolet photoemission spectroscopy upon subsequent warming of the sample. Activation of the first layer of THF by Li starts at a temperature as low as 120 K. Polymerization of tetrahydrofuran (THF) (forming poly-THF) occurs upon melting near 180 K, but is accompanied by chain-terminating reactions that form lithium alkoxide(s) and hydrocarbon gas(es), such as ethylene and/or propylene. Between 180 and 320 K, there is progressively greater conversion of poly-THF to alkoxide such that at 320 K, the surface film is almost entirely composed of alkoxide. At or near its bulk melting temperature of 220 K, essentially all of the PC remaining on the surface has reacted with Li to form an alkyl carbonate. With increasing temperature, part (25%–33%) of the alkyl carbonate decomposes to form an alkoxide. The alkyl group in the organo–Li compounds derived from PC are most probably propylene. There is no evidence of the formation of any gaseous products containing carbon or oxygen at temperatures below 320 K under the conditions of these experiments. Of particular relevance to battery technology, however, is that in both cases the organo–Li layers that have formed at 270–320 K were formed in the presence of excess unreacted Li, which is the usual circumstance in a real battery, and that no evidence was found of inorganic Li carbonate as a product of the reaction with PC.
Ellipsometric and low energy electron diffraction study of the layer growth of xenon physisorbed on Ag (111) surface
Authors: Igarashi S. , Abe Y. , Irie Y. , Hirayama T. , Arakawa I.
Published: July 2002

We have developed an experimental apparatus for in situ observation of a physisorption system on a metal surface by an ellipsometry and an electron diffraction. In order to observe a physisorption system and a thick insulator film, we have developed an extremely low-current low energy electron diffraction (XLEED) apparatus equipped with a microchannel plate and a position-sensitive detector in place of a phosphor screen in an ordinary LEED optics. The ellipsometric adsorption isotherms of Xe/Ag (111) at substrate temperatures between 50 and 80 K were obtained in the wide pressure range between 10−7 and 1 Pa. We observed the surface structure by XLEED while monitoring the layer growth by the ellipsometry from a submonolayer to a thick film where the equilibrium pressure was nearly equal to the bulk saturation vapor pressure. The Xe overlayer of a sufficiently thick film has clear (111) structure which keeps relative orientation to the Ag (111) substrate.
Surface charge neutralization of insulating samples in x-ray photoemission spectroscopy
Authors: Larson Paul E. , Kelly Michael A.
Published: July 2002

Obtaining high resolution x-ray photoemission spectroscopy (XPS) spectra of insulating samples has long been a problem because of difficulty controlling sample surface potentials. A flood of low energy electrons has traditionally been used to control surface potential, but as monochromatized instruments with small, intense x-ray beams have become available, control has become much more difficult, particularly on larger samples. Increasing the current or energy from the flood gun does not improve the control appreciably. To understand the charging effect in a quantitative way, we have conducted some experiments with a test sample, configured to approximate the geometry present in several commercial XPS instruments using focused x-ray sources. These results show that, because of the energy spread of the flooding electrons, a negative potential is induced by the flood gun in the region surrounding the x-ray beam. This negative potential repels electrons, inhibiting the adequate neutralization of many samples. Based upon an analysis of these results, a neutralizing system is described in which a high current density flood gun with a narrow energy spread (to reduce potential variation on the sample) is used in combination with a source of low energy positive ions (to neutralize the negative potential in the peripheral region). This system has been tried on a wide variety of insulating samples in three commercial instruments, and found to give reproducible spectra with narrow linewidths. We present here spectra taken with the instrument offering the smallest and brightest x-ray beam, the most challenging case of the instruments tried.
Design and performance of an ultrahigh vacuum system for metallic multilayers
Authors: Chaudhari S. M. , Suresh N. , Phase D. M. , Gupta A. , Dasannacharya B. A.
Published: July 2002

This article describes the design, development, and performance testing of a versatile ultrahigh vacuum (UHV) electron-beam deposition system for synthesis of thin films and multilayer structures. Initially, basic design norms required to achieve set objectives are discussed and then a brief description of the system is presented. The fabricated UHV chamber has a number of vacuum ports to accommodate various features and accessories needed to deposit and characterize good quality thin films and multilayer structures of different metals. To demonstrate the capabilities of the system, depositions of thin films and multilayer structures of different materials were carried out. Representative results of hard x-ray reflectivity measurements corresponding to Ni, Au, and Ag thin films and Nb/Si and Fe/Ni multilayer structures are given and discussed. Furthermore, the easy adaptability of the system in order to carry out other investigations related to thin films is also demonstrated by presenting our recent in situ experiments conducted on aging studies of discontinuous silver films deposited on glass substrates under UHV conditions.
Entropic trapping and sieving of long DNA molecules in a nanofluidic channel
Authors: Han J. , Craighead H. G.
Published: July 2002

Entropic trapping of long DNA was demonstrated in an artificial channel, fabricated by silicon based lithography and etching techniques. This channel consisted of alternating thick and thin regions, where the thickness of the thin region was as small as 90 nm. The electrophoretic mobility of long DNA molecules in this channel was measured as a function of the applied electric field. Because the radius of gyration of DNA used was much larger than the thin gap, DNA molecules were trapped when they moved from the thick to the thin region. This trapping determined the mobility of DNA in the system. Surprisingly, longer DNA molecules moved faster than shorter DNA molecules in the channel. This may be due to the fact that a larger DNA molecule has a better chance of escaping entropic traps because of the larger contact area with the thin slit. This device could enable fast manipulation and separation of long polymers.
Studies on passivation behavior of tungsten in application to chemical mechanical polishing
Authors: Tamboli D. , Seal S. , Desai V. , Maury A.
Published: July 2002

Chemical mechanical polishing (CMP) is considered to be the enabling technology for meeting the planarization requirements in <0.35 μm feature sized multilevel semiconductor device fabrication. CMP of tungsten is done in order to planarize and remove excess tungsten in the process to form inter-level contacts. Considerable importance is given to the role played by the passive oxide film formation on the surface during tungsten CMP. In this study, x-ray photoelectron spectroscopy (XPS) is used to understand the oxide growth mechanism in tungsten. Tungsten wafers are polarized to different anodic potentials in static pH 4 solutions of KIO3 and H2O2, two commonly used oxidizers in CMP. XPS measurements are employed to probe the chemical and stoichiometric changes in the surface oxide films treated under these conditions. These results are then compared with the electrochemical polarization results.
Synthesis of hard TiN coatings with suppressed columnar growth and reduced stress
Authors: Lacerda M. M. , Chen Y. H. , Zhou B. , Guruz M. U. , Chung Y. W.
Published: July 2002

Titanium nitride normally grows with a columnar grain structure. In this study, we prepared TiN/CNx multilayered coatings with the intent of using the CNx layers to interrupt the grain growth of TiN to attain an equiaxed grain structure. The TiN/CNx coatings were synthesized by direct current magnetron sputtering. Our investigations showed that three important process conditions are required to obtain superhard and smooth TiN/CNx coatings with low internal stress: (i) a TiN buffer layer with strong (111) texture; (ii) proper bias during the growth of the TiN buffer and TiN/CNx coating; and (iii) small thickness for the CNx layers.
Etching polyimide with a nonequilibrium atmospheric-pressure plasma jet
Authors: Jeong J. Y. , Babayan S. E. , Schütze A. , Tu V. J. , Park J. , Henins I. , Selwyn G. S. , Hicks R. F.
Published: July 2002

An atmospheric-pressure plasma jet has been used to etch polyimide films at 1.0–8.0±0.2 μm/min at 760 Torr and between 50 and 250 °C. The plasma was produced by flowing helium and oxygen between two concentric electrodes, with the inner one coupled to 13.56 MHz rf power and the outer one grounded. The etch rate increased with the O2 partial pressure, the rf power and the substrate temperature. The apparent activation energy for etching was 0.16 eV. Langmuir-probe measurements revealed that the ion densities were between 1×1010 and 1×1011 cm−3, 5 mm from the end of the powered electrode. Biasing the substrate had no effect on the rate. Ozone, singlet sigma metastable oxygen (b 1Σg+), and singlet delta metastable oxygen (a 1Δg) were detected in the plasma by emission spectroscopy. More ozone was produced in the effluent through the recombination of O atoms with O2. Based on the production rate of O3, the concentration of O atoms 6 mm from the powered electrode was estimated to be ∼7×1014 cm−3 at 6.6 Torr O2 and 200 W power. It is proposed that O atoms are the principal reactive species involved in etching polyimide.
Measuring the magnetic field distribution of a magnetron sputtering target
Authors: Santos Edval J. P.
Published: July 2002

The lifetime of a sputtering target is related to the magnetic field distribution near the target surface, which is related to the magnets’ arrangement underneath the target. Therefore, a key design issue is the placement of the magnets to ensure an optimum target lifetime. Even in maintenance procedures it may be necessary to know the magnetic field distribution near the target. This work presents a technique which can be used to map the magnetic field over large targets. The system uses a custom made acquisition board, a modified plotter, and a Hall sensor to measure the two-dimensional magnetic field configuration at different heights near the target. It has been tested with success to measure a 62 mm×226 mm target area in the three coordinates.
Influence of electron shading on highly selective SiO2 to Si etching
Authors: Yonekura Kazumasa , Katayama Toshiharu , Maruyama Takahiro , Fujiwara Nobuo , Miyatake Hiroshi
Published: July 2002

The dependence of the poly-Si etch rates at the bottoms of SiO2 holes on the patterns of the poly-Si films is investigated using fluorocarbon gas plasma. The etch rate of poly-Si film which is separated from large open areas exposed to plasma is higher than that of film which is connected to large open areas. This tendency is exaggerated as the aspect ratio of the hole increases. From Auger electron spectroscopy of the inside of the hole, a carbon peak is detected on the sidewall just above the poly-Si film which is separated from large open areas. This result indicates that low-energy ions, which are a deposition species, are deflected at the bottom of the hole by the positive charge resulting from the electron shading effect. This causes a decrease in the deposition of fluorocarbon polymer on the poly-Si film, resulting in an increase in poly-Si etch rates.
Defect analysis of Cl2/HBr/He/O2 etching process by imaging time-of-flight secondary ion mass spectrometry
Authors: Zhao Jin , Reich D. Fraser , Nguyen Thien T. , Zhao Larry , Hossain Tim Z.
Published: July 2002

Defects appeared during Cl2/HBr/He/O2 etching process were investigated by high laterally resolved imaging time-of-flight secondary ion mass spectrometry (TOF-SIMS). The defects with size of one to several microns appeared after the etching process. These defects are electron-beam sensitive during Auger electron spectroscopy and energy dispersive spectrometry analysis. Imaging TOF-SIMS clearly shows that the defect consists of bromine and H2O. Relatively weak oxygen and silicon signals were detected from the defect site. A negative secondary ion mass spectrum from region of interest (ROI) analysis of the defect area shows a very strong Br− signal. A positive secondary ion mass spectrum from ROI analysis has a very strong H2O+ signal from the defect. These results amply demonstrate that imaging TOF-SIMS enables chemical analysis of small defect at outmost surface with high lateral resolution and submonolayer sputtering damage under static SIMS analytical conditions.
Defect-permeation correlation for ultrathin transparent barrier coatings on polymers
Authors: da Silva Sobrinho A. S. , Czeremuszkin G. , Latrèche M. , Wertheimer M. R.
Published: July 2002

We begin this article by presenting a model for gas permeation through defects in barrier coatings, which is based on a very simple geometrical approach. This model allows us to evaluate permeation through a single- or through multiple circular defects in the coating, and also in special cases of size distributions and noncircular geometries. The model agrees well with published results based on complex computer simulations, and it has proven very useful in the analysis of our permeation measurements for barrier-coated plastic films. We then present correlations between measured O2 transmission rate (OTR) values and the number densities and size distributions of defects in SiO2 and SiN barrier coatings on polyester (PET), results which we compare with published data for aluminized PET. We also show the temperature dependence of OTR and H2O vapor transmission rate for SiO2 and SiN coatings deposited on one and on both sides of PET films. The apparent activation energies evaluated from these measurements support the model of defect-dominated mass transport, but suggest different mechanisms for oxygen and water vapor transmission: Excellent agreement is found between measured and calculated OTR values; these, and the apparent activation energy for OTR through single or double side SiO2 and SiN coatings on PET films, confirm that the observed residual OTR is indeed controlled by the presence of (pinhole) defects in the coatings.
New combination of a three-component gas, Ne–Xe–Ar, for a high efficiency plasma display panel
Authors: Min Byoung-kuk , Lee Seok-Hyun , Park Hun-Gun
Published: July 2002

The luminous efficiency improvement is a key issue for making a plasma display into a large flat panel device. We suggest a new combination of a three-component gas, Ne–Xe–Ar, to achieve a high luminous efficiency of a color plasma display panel. The densities of 26 species and the electron temperature were calculated by zero-dimensional simulation, and we compared the results of zero-dimensional simulation with a measurement of vacuum ultraviolet (VUV) intensity covering a 140–180 nm wavelength range, in order to find the optimum mixing condition of Ne–Xe–Ar gas in a color plasma display panel. Reaction mechanism was analyzed by a computational work to comprehend the mechanism of discharge in Ne–Xe–Ar as well as Ne–Xe. The maximum peak point of the Xe*(1S4) state was obtained in 0.5% of Ar mixing ratio by simulation and the maximum luminous efficiency was measured at the same point of 0.5% Ar mixing ratio in VUV measurement. The luminous efficiency has been improved considerably (about 30%) with a 0.5% Ar addition, compared with the Ne–4% Xe mixing gas.
Low-k Si–O–C–H composite films prepared by plasma-enhanced chemical vapor deposition using bis-trimethylsilylmethane precursor
Authors: Kim Yoon-Hae , Lee Seok-Kiu , Kim Hyeong Joon
Published: July 2002

Low-k Si–O–C–H composite films were prepared using bis-trimethylsilylmethane as a precursor and oxygen in a rf plasma reactor. The growth rate of the Si–O–C–H composite film followed a second-order exponential decay function. This behavior could be explained by the formation of nanosized voids due to Si–CH3 and OH-related bonds included in the film. OH-related bonds were detected in films deposited at 30 °C, but could not be observed for the films deposited above 60 °C. In contrast, Si–CH3 bonds were also detected at 30 °C, but decreased monotonically up to 210 °C and were absent of higher temperatures. After postannealing the film deposited at 30 °C, the Si–CH3 bonds were unchanged, but the OH-related bonds were easily removed. This film showed a low dielectric constant of 2.44 and leakage current density of 4.4×10−7 A/cm2 at 1 MV/cm.
Integration of metal masking and etching for deep submicron patterning
Authors: Gabriel Calvin T. , Kim Robert Y. , Baker Daniel C.
Published: July 2002

Although copper damascene interconnects offer many advantages over conventional subtractive etched Al alloys, the challenges and costs associated with converting to copper have combined to extend the useful life of Al alloy etching into the deep submicron regime. As a result, metal masking and etching are facing new challenges. Deep ultraviolet (DUV) photolithography has replaced the conventional i-line technique for patterning fine metal pitches, but some DUV photoresists are less able to withstand the aggressive plasma environment than their i-line counterparts. Reflectivity increases at DUV wavelength, so dielectric antireflective films are added on top of the metal stack. The mask-open process, where the dielectric film is plasma etched prior to etching the metal stack, alters the photoresist further and influences the subsequent metal etch. Aspect ratio dependent etch effects increase when etching narrow spaces resulting from tightened metal pitches, and gas additives may be required to protect the metal sidewalls. These effects are characterized and the challenges of deep submicron metal etch process development are discussed. The option of true hardmasked etching of the metal stack is also investigated.
MBE growth of GaAs and III-V alloys
Authors: Foxon C. T.
Published: July 2002

The growth of GaAs and III-V alloys by MBE is now a well-established method used to prepare a whole range of devices. One of the advantages of MBE is that the same technology can be used to study the processes controlling growth. This article will discuss the present state of knowledge concerning the growth of binary compounds such as GaAs and of alloys with mixed group III and mixed group V elements. It will also discuss the relation between growth conditions and resulting film properties for binary compounds, alloys, and interfaces.
Measurement of potential at semiconductor interfaces by electron spectroscopy
Authors: Grant R. W. , Kraut E. A. , Kowalczyk S. P. , Waldrop J. R.
Published: July 2002

Electron spectroscopy performed in ultrahigh vacuum can be used to measure potential and heterojunction band discontinuities at abrupt semiconductor interfaces. The technique provides a direct contactless and nondestructive means to determine and correlate interface chemistry and potential. This article discusses some of the factors which affect applications of Auger electron spectroscopy, ultraviolet photoelectron spectroscopy, soft x-ray photoelectron spectroscopy, and x-ray photoelectron spectroscopy for semiconductor interface potential measurements.
Nucleation and strain relaxation at the InAs/GaAs(100) heterojunction
Authors: Schaffer W. J. , Lind M. D. , Kowalczyk S. P. , Grant R. W.
Published: July 2002

The techniques of molecular beam epitaxy have been used to investigate the nucleation and growth of InAs heteroepitaxial thin films lattice mismatched to GaAs(100) substrates. Our previous observations have been that optimum structural and electrical properties are obtained only if the heteroepitaxial nucleation sequence is carried out under experimental conditions leading to the indium stabilized (4×2) InAs(100) surface reconstruction. In this work, reflection electron diffraction, Auger electron spectroscopy and x-ray diffraction have been used to determine the InAs(100) surface phase diagram. The InAs/GaAs(100) heterojunction grown by MBE is abrupt and smooth surfaces are obtained only under indium stabilized nucleation conditions. A residual compressive strain at the crystalline interface occurs which is somewhat relieved by a tetragonal distortion in the direction normal to the film plane. Results of investigations by reflection electron diffraction show that the nucleation of InAs/GaAs(100) occurs via island formation and coalescence, and that the initial in-plane lattice constant observed for InAs at 520 °C is 5.9 Å. The unstrained lattice constant is obtained only after ∼2000 Å of growth under indium stabilized conditions. If the InAs bond length in the vicinity of the interface is estimated from the experimental data, the agreement between our previously measured (via XPS) value for the heterojunction valence-band discontinuity and the calculation based on Harrison’s model (LCAO) is improved.
Electron beam lithography from 20 to 120 keV with a high quality beam
Authors: Howard R. E. , Craighead H. G. , Jackel L. D. , Mankiewich P. M. , Feldman M.
Published: July 2002

We have performed electron beam lithography studies on thick substrates using beam energies of 20–120 keV and a nominal beam diameter of 2 nm in a Philips 400 electron microscope with scanning capability. Metal lines as narrow as 10 nm were fabricated on Si and GaAs substrates using liftoff of a single thin layer of resist. High resolution (approximately 10 nm) patterns could be written at all beam energies with an exposure latitude that remained approximately constant up to energies for which the range of the backscattered electrons became significantly larger than the pattern area. For large area patterns written with the small beam, the proximity effect is greatly reduced, even at 20 keV, because of the sharp edge of the exposure profile. At high beam energies, the range of backscattered electrons is large enough that they contribute only a slowly varying background dose, leading to a relatively simple proximity correction even for complex patterns.
Phase equilibria in thin-film metallizations
Authors: Beyers R. , Sinclair R. , Thomas M. E.
Published: July 2002

The determination of stable tie lines in a ternary phase diagram through a limited number of thin-film reactions is demonstrated. Ternary phase diagrams are then used to explain the stability of refractory metals, silicides, and nitrides during various integrated circuit processing steps. The W–Si–O, Ti–Si–O, Ti–Si–N, and Ti–Al–N systems serve as examples.