bluuebunny/crossref_metadata_2025 huggingface dataset:
Topics in inverse photoemission
Authors: Dose V.
Published: July 2002

Inverse photoemission (IPE) is now a well-recognized addition to the steadily growing arsenal of surface scientific tools. IPE makes accessible empty electronic bands in the energy region between the Fermi level and the vacuum level of solids and at surfaces. It provides the same detailed information on the electronic structure as ordinary photoemission, namely, energy, momentum, spin, and parity of energy bands. Several years of research have provided many results. This suggests addressing the question of what has been learned by these studies that could not have been inferred from our knowledge of ordinary photoemission (PES). Topics include image potential states at metal surfaces, relaxation phenomena in semiconductors, the role of the 2π level in the CO chemisorption bond, and contributions to the controversy ‘‘initial state effects versus final state screening’’ in the photoemission from adsorbed xenon.
TiN hard coatings deposited on high-speed steel substrates by reactive direct current magnetron sputtering
Authors: Schiller S. , Beister G. , Reschke J. , Hoetzsch G.
Published: July 2002

We report on TiN hard coatings deposited on high-speed steel substrates by reactive dc sputtering in an Ar/N2 atmosphere. The sputter parameters lie within the technically interesting coating conditions; i.e., substrate preheating temperatures of 200 or 450 °C, adequate particle scattering by a sputter pressure of 1.3 Pa, and bias voltages of −250 V. With increasing power density on the target the Thornton-model columnar film structure vanishes and the fracture cross sections of the layers are almost structureless. Transmission electron microscopy investigations revealed grain sizes of 15–30 nm or less; and bimodal grain size distributions were not observed. An assessment of the dislocation densities resulted in about 1012 cm−2. At high bias voltages the incorporation of argon in the film comes up to 1 at. % and the compressive residual macrostresses are about 11 GPa.
Plasma polymerization by magnetron glow discharge. I. Effect of magnetic field on breakdown of monomers in low pressure
Authors: Sato K. , Iriyama Y. , Cho D. L. , Yasuda H.
Published: July 2002

The breakdown voltage Vb of glow discharge of an organic monomer generally decreases as the system pressure decreases; however, below a certain threshold pressure, the breakdown voltage increases with decreasing system pressure. In the pressure range below 100 mTorr, the breakdown voltage generally increases as a linear function of 1/p, where p is the system pressure of the reactor. In this region, glow discharge without magnetic enhancement often yields unstable discharge, which is associated with a very steep slope of a line in the Vb vs 1/p plot. The similar plots for glow discharges of non-polymer-forming gases, such as He, Ar, and O2, do not follow the simple linear relationship, but a more or less linear increase is followed by a plateau. Effects of magnetic field on the breakdown phenomena were investigated by using planar parallel electrodes with circular arrangement of permanent magnets. Three different electrode systems with slightly different magnetic field profiles were used to investigate the effects of magnetic field intensity and its profile in the interelectrode space. The increasing intensity of magnetic field generally reduces the slope of Vb vs 1/p and produces more stable glow discharge in the lower pressure region where stable glow discharge cannot be created without magnetic enhancement.
Electrical characterization of radio-frequency parallel-plate capacitively coupled discharges
Authors: Andries B. , Ravel G. , Peccoud L.
Published: July 2002

Measuring the power of electromagnetic waves and their phases is a classical method for the study of microwave circuits. With new apparatus we may use this technique in the 13.56-MHz range. By computation we may derive currents, voltages, and impedances with very good accuracy. In an industrial etching system (GIR 100 made by Alcatel), we measured impedances of glow discharges in argon and SF6 as a function of pressure and power input. We compute voltages on the powered electrode in addition to the current and power actually dissipated in the discharge. We find that the efficiency Weff/W of the generator may be between 10% and 98% depending on the plasma parameters. Real and imaginary parts of impedances relate to the dissipated power and the thickness of the sheaths, respectively. Therefore, one can compare measurements to models of sheaths (Child–Langmuir law, mobility of ions limited by scattering) and to models of glow discharges (power dissipated in the sheath alone or dissipated in the heart of the glow). From our results we discern two types of discharges: discharges in electropositive gases like argon and discharges in very electronegative gases like SF6.
Surface analysis of realistic semiconductor microstructures
Authors: Oehrlein Gottlieb S. , Chan Kevin K. , Jaso Mark A. , Rubloff Gary W.
Published: July 2002

The geometrical and insulating properties of regular arrays of oxide masked silicon trenches formed by reactive ion etching have been utilized to enable in situ x-ray photoelectron spectroscopy of specific parts of the trench structures. Different surface portions of the sample structure are differentiated by using (i) grazing incidence x-ray irradiation which results in shadowing of the trench bottoms and (ii) electrostatic charging of the insulating portions (e.g., the oxide mask) which shifts spectral features. We demonstrate the usefulness of this approach in analyzing the composition of the film passivating the silicon trench sidewall for a SF6/O2 trench etching process.
Etching of silicon (111) with the scanning tunneling microscope
Authors: Ehrichs E. E. , de Lozanne A. L.
Published: July 2002

It has recently been demonstrated that the scanning tunneling microscope can be used to break organometallic molecules on a scale of tens of nanometers [E. E. Ehrichs, S. Yoon, and A. L. Lozanne, Appl. Phys. Lett. 53, 2287 (1988)]. This process has been used to write dots, lines, crisscross patterns, and letters on silicon surfaces. Thus far, dimethyl cadmium, trimethyl aluminum, and tungsten hexafluoride have been used as precursor gases. Organic surface contaminants can also be polymerized by this process, yielding stable structures with linewidths down to 10 nm. All these fabricated structures are conductive enough to drain the tunneling current. More information is currently being obtained by measuring the resistance of lines written by this technique. More recently, it has been observed that WF6 can produce either deposits or etch pits in silicon. The smallest pit obtained thus far is 20 nm in diameter and 12 nm deep. The parameter that determines whether deposition or etching takes place is probably the surface temperature, although this remains to be tested. The results may be useful for archival memory storage, custom interconnects, and for the study of the physics of nanostructures.
Nanometer scale structuring of silicon by direct indentation
Authors: van Loenen E. J. , Dijkkamp D. , Hoeven A. J. , Lenssinck J. M. , Dieleman J.
Published: July 2002

Shallow indentations with diameters of 2–10 nm have been made directly in clean Si(110) and Si(001) surfaces using the W tip of a scanning tunneling microscope. The shape of the holes formed depends on the shape of the tip and is not influenced by the presence or absence of a tunneling current during the indentation process. The sharpness of the tip is not degraded by the intimate tip–sample contact. Arbitrary line and bit patterns can therefore be written and read repeatedly using the same tip.
High resolution secondary ion mass spectrometry depth profiling using continuous sample rotation and its application to superlattice and delta-doped sample analysis
Authors: Cirlin Eun-Hee , Vajo John J. , Hasenberg Thomas C. , Hauenstein Robert J.
Published: July 2002

We report the development of secondary ion mass spectrometry (SIMS) with continuous sample rotation to achieve high resolution that is independent of depth during compositional and dopant sputter depth profiling. Sample rotation reduces the ion beam-induced surface roughness that often limits the depth resolution in SIMS. To illustrate the effects of sample rotation on SIMS analysis, measurements both with and without rotation were performed on a molecular beam epitaxy grown AlGaAs/GaAs superlattice with 100 periods and 5-nm-thick layers, and a boron delta-doped (atomically planar) Si sample, with dopant concentrations from 1016–1021 atoms/cm3 at depths of 0.5–2.0 μm.
Ion beam assisted coating and surface modification with plasma source ion implantation
Authors: Conrad J. R. , Dodd R. A. , Han S. , Madapura M. , Scheuer J. , Sridharan K. , Worzala F. J.
Published: July 2002

Plasma source ion implantation (PSII) is a non-line-of-sight technique which is being developed as an alternative to beamline accelerator technology for ion implantation. The initial development phase of PSII concentrated on implantation of ion species which are gaseous at room temperature (primarily nitrogen ions) and employed a cylindrical vacuum chamber 16 in. high and 14 in. in diameter. A second generation PSII system is being constructed to extend the PSII process to ion beam mixing and ion beam assisted coating modes of operation. The new, larger system (with dimensions 36×36×36 in.) will feature multiple-array sources for sputter deposition concurrent with ion bombardment.
Auger electron spectroscopy as a method of surface potential barrier study
Authors: Klyachko D. V. , Kriegel V. G.
Published: July 2002

Surface cathodo-electromotive force effect was detected and studied using Auger electron spectroscopy in a group of the most common semiconductors (Si, GaAs, InP) of both n- and p-type conductivity. The nature of the effect consists of surface potential barrier changes under electron bombardment. Auger electron energy dependencies on primary beam energy and current are investigated on ion beam sputtered surfaces. Auger line position differences between n- and p-type semiconductors are shown to be zero at low primary beam energy and current and to saturate at high ones. The difference between high and low excitation limits of Auger line position is shown to characterize the sign and height of the initial valence and conduction band bendings. Possible mechanisms of the electromotive force, including electric field separation of the carriers and ballistic effects, are discussed.
Modulated discharges: Effect on plasma parameters and deposition
Authors: Verdeyen J. T. , Beberman J. , Overzet L.
Published: July 2002

The initial motivation for using amplitude modulated (kHz) rf discharges was as an aid for ascertaining the temporal evolution of various transient species which are formed from the feedstock commonly used for the deposition or etching of semiconductors. Such gases are easily dissociated and hence the density of some of the transient molecules may easily exceed the remaining fraction of the donor gas. From a diagnostic point of view, the use of ‘‘time’’ will be shown to be a cheap and a most valuable aid in ascertaining some of the kinetics of such glows. Most surprising was the fact that the use of a modulated discharge can have a profound effect on the processing goal itself. For instance, it has been shown that the bandgap of amorphous silicon deposited from SiH4 is lower with a modulated discharge than that deposited from a continuous wave (cw) one; simultaneously, the amount of ‘‘dust,’’ as measured by Mie scattering, is also much lower. These experiments and others using etching gases point to a role for negative ions, which are usually confined by the sheaths in a cw discharge, but can be extracted during the off period of a modulated one.
Density dependence of the electrochemical characteristics of carbon overcoated thin film media
Authors: Franco Luis P. , Chen Mao-Min , Gorman Grace L. , Castillo Gil , Viswanathan Leela , Duran John
Published: July 2002

The effectiveness of carbon overcoats as a corrosion barrier for thin film media has been studied. The sputtering pressure and power used during the deposition of the carbon overcoat has a direct influence on its density, and thus upon its corrosion protection characteristics for the underlying metal media. Corrosion rates of the carbon overcoated metal media were measured both electrochemically and by exposing disks to conditions of elevated temperature and humidity. Corrosion measurements show that the corrosion rate of the magnetic media, (sputtered at a constant pressure and power), increases with increased deposition pressure (1–30 mTorr) and decreased sputtering power (2.8–0.3 kW) of the carbon film. The increased corrosion rate is caused by a decrease in density of the carbon film. In another experiment, sputtering pressure was varied in both the magnetic and overcoat layers. Corrosion measurements reveal a relatively small change in corrosion rate for sputtering pressure in the range of 1 to 6 mTorr of Ar, but a significant increase at 30 mTorr. This sharp increase was attributed to an increase in surface area of the magnetic layer believed to be generated by the the formation of rough porous films at high pressure. In this study carbon and magnetic films sputtered at high power and low pressure yield media with the lowest corrosion rate.
Room temperature reaction between polycrystalline Ni/Al bilayers deposited in ultrahigh vacuum
Authors: Ruckman M. W. , Jiang L. , Strongin Myron
Published: July 2002

The growth of polycrystalline Ni–Al bilayers deposited in ultrahigh vacuum (P<10−9 Torr), and their modification by annealing are studied by Auger and photoemission spectroscopy. At room temperature, Ni deposition on Al causes a chemical shift of the 68-eV Al Auger line and photoemission shows that the Ni 3d valence-band states for thin Ni overlayers are narrower and shifted away from Ef when compared to Ni metal. For Al deposited on Ni, the 68-eV Al Auger line also undergoes a chemical shift and photoemission shows the Ni 3d valence band is modified by the appearance of a new state at higher binding energy. Based on comparisons with photoemission and Auger data presented by others for Ni–Al intermetallic compounds, and photoemission, ion channeling and ion scattering results published for the chemically similar Pd–Al system, we conclude that polycrystalline Al and Ni films partially intermix and form a NiAl3-like intermetallic compound at room temperature. We believe this Ni–Al compound may be found at the thin-film interface, at grain boundaries or on the surface of 3-D Ni or Al islands. Heating Ni/Al bilayers at 600 K promotes Al out diffusion and heating at higher temperatures leads to the formation of other Ni–Al compounds.
Sharpening of monocrystalline molybdenum tips by means of inert-gas ion sputtering
Authors: Morishita S. , Okuyama F.
Published: July 2002

Monocrystalline Mo tips oriented to [110] are shown to be sharpened into atomic dimensions, by inert-gas ions impinging along the [110] axis. Xe+ ions accelerated to a few keV provided Mo tips less than 50 Å in apex diameter, in a time interval of 10 min or so. Much smaller radii of curvature were achieved by prolonged Ar+ sputtering at lower energies. It is believed that the technique proposed is promising for preparing focused ion and electron beam sources.
High mass resolution surface imaging with a time-of-flight secondary ion mass spectroscopy scanning microprobe
Authors: Schwieters J. , Cramer H.-G. , Heller T. , Jürgens U. , Niehuis E. , Zehnpfenning J. , Benninghoven A.
Published: July 2002

This article describes first applications of a time-of-flight secondary ion mass spectroscopy (TOF-SIMS) scanning microprobe, based on a high mass resolution TOF-SIMS instrument, combined with two pulsed primary ion sources: (a) 10 keV Ga liquid metal ion source (LMIS), probe size: 0.5–1 μm; (b) 10 keV electron impact (EI) ion source (Ar+,Xe+,O+2), probe size 4–10 μm. The detection limits for elemental and molecular surface species as a function of probe size are discussed. At a lateral resolution of 1 μm secondary ion images with about 1000 counts/pixel can be acquired in about 30 min. The high useful yields achieved by TOF-SIMS allows the analysis of submonolayers of inorganic as well as organic materials at high lateral resolution. Currently up to 24 secondary ion images for different masses and a complete mass spectrum can be acquired simultaneously. The performance of the instrument is demonstrated by multielemental and molecular imaging of inorganic and organic patterns on Si wafers. Secondary ion images of a polymer with an average molecular weight of 1400 amu prepared on a silver substrate are presented. As an example for the analysis of insulating materials secondary ion images of an electrically isolated surface mounted device solder pad on an electronic board are shown.
Molecular velocity distribution at large Knudsen numbers
Authors: Jitschin W. , Reich G.
Published: July 2002

It is commonly assumed that the distribution of molecular velocities follows a Maxwellian distribution also in the range of high and ultrahigh vacuum, i.e., at large Knudsen numbers. This distribution is theoretically derived from statistical analysis of an ensemble of molecules with frequent molecule–molecule collisions. Such a situation prevails at higher pressures, i.e., at small Knudsen numbers. However, at smaller pressures the molecule–wall collisions prevail, and due to the different nature of these collisions, the statistical arguments fail. As a consequence, the molecular velocity distribution cannot be predicted a priori at such pressures. In the present paper the applicability of the Maxwellian distribution in vacuum metrology at large Knudsen numbers, i.e., in the molecular regime is investigated. For this purpose, the pressures generated in primary standards of the static and dynamic expansion type are calculated for an arbitrary velocity distribution after expansion. The pressure generated by static expansion is proportional to the expectation value 〈v2z〉, that generated by dynamic expansion proportional to the ratio of expectation values 〈v2z〉/〈‖vz‖〉 (vz denotes the one-dimensional velocity component). Available experimental calibration data obtained by static and dynamic expansion of common gases are compared to each other and with direct pressure measurements with a liquid column manometer. These data provide a decisive test for the expectation values 〈v2z〉 and 〈‖vz‖〉 in the molecular range. Excellent agreement within the uncertainty of less than 1% between experimental values and values calculated assuming a Maxwellian distribution is found. Thus one may conclude that in common vacuum metrology the Maxwellian distribution can be applied for deriving pressures also in the molecular regime with high accuracy.
Zero shift in the differential capacitance diaphragm gauges due to the change in line pressure
Authors: Sharma J. K. N. , Sharma D. R. , Gupta A. C.
Published: July 2002

This paper describes the results of experiments concerning the effect of line pressure on the zero stability of the differential capacitance diaphragm manometers. It is observed that in capacitance manometers with single-sided configuration, the zero shift value varies with different gases for a particular line pressure change and is directly proportional to the dielectric constant of the gases. For the four sensors studied, it is found that the zero shift is positive in nature and varies linearly with the change in line pressure. The linear relationship obtained on the basis of the experimental results is found useful in determining the zero shift values for any gas at any line pressure change. The zero shift at different line pressures with various gases in differential capacitance diaphragm manometers is of great importance for the metrological applications.
Excimer laser ablation of ferroelectric Pb(Zr,Ti)O3 thin films with low pressure direct-current glow discharge
Authors: Roy D. , Krupanidhi S. B. , Dougherty J. P.
Published: July 2002

Thin films of Pb(Zr,Ti)O3 (PZT) were deposited on platinum coated silicon and bare silicon by excimer laser (248 nm) ablation and were in situ crystallized, with and without oxygen discharge. Films deposited at various oxygen discharge voltages exhibited variations in polarization switching, dielectric constant and loss, I–V characteristics and growth temperature as well. Crystalline perovskite PZT films deposited with 300 V discharge offered stoichiometric and crystalline films, with a dielectric constant of 850, a remanent polarization of 22 μC/cm2 and a coercive field of 40 kV/cm and a resistivity of about 1013 Ω cm. Besides the property enhancement, the presence of the O+2 discharge plasma appeared to have reduced the growth temperature to lower values.
Resistivity measurements of thin film iridium on silicon
Authors: Reeves Geoffrey K. , Lawn Malcolm W. , Elliman Robert G.
Published: July 2002

The resistivity of thin iridium films deposited on clean silicon substrates was measured by a four point probe technique. A simple electrical model based on parallel current conduction through the Ir film and the silicon substrate is shown to be valid. This allows the Ir contribution to the conduction to be determined. The effect of varying the film thickness from 0.5 to 16 nm caused the measured film resistivity to decrease from 190 to 35×10−6 Ω cm. This variation agrees well with the variation predicted by the Fuchs–Sondheimer and Lucas models for carrier scattering from the film surfaces.
Si(111)(7×7) dangling bond contribution to surface recombination
Authors: Hsu J. W. P. , Bahr C. C. , vom Felde A. , Downey S. W. , Higashi G. S. , Cardillo M. J.
Published: July 2002

We correlate photoconductivity with surface characterization in order to probe the influence of surface properties of Si(111) on carrier dynamics. Results on the clean (7×7) reconstructed surface indicate that carrier recombination at this surface is fast, with a surface recombination velocity measured to be ≥2×106 cm/s. This is consistent with the notion of midgap dangling bond states acting as effective recombination centers. Combining our results and the present understanding of the (7×7) electronic structure, we estimate the carrier capture cross section for dangling bonds to be ∼10−15 cm2. We also investigate the effect of processing and find that carrier dynamics is strongly influenced by trace impurities below the detection limit of conventional surface characterization techniques.
Rotating disc gauge for absolute total pressure measurement in high vacuum
Authors: Chambers A. , Chew A. D. , Troup A. P.
Published: July 2002

An absolute vacuum gauge exploiting molecular drag between coaxial discs, a configuration suggested by Langmuir, is being further investigated. The device operates in a range similar to that of the spinning rotor gauge. It consists of a silicon disc 92 mm in diameter suspended on a calibrated torsion fiber a few mm above a metal disc of the same size which rotates at speeds up to 50 000 rpm. Molecules leaving this rotor communicate a torque to the suspended disc by molecular drag. The angular deflection thus produced is sensed optically and is about 2° at 10−6 mbar. The critical factors relevant to absolute measurement, such as tangential momentum accommodation, geometry, and edge effects have been investigated and experimental comparisons with a spinning rotor gauge demonstrate that absolute pressure measurements with uncertainty better than ±5% are possible at pressures ∼ 10−6 mbar. Measurements of similar uncertainty will be possible at 10−7 mbar.
Effects of post-deposition annealing ambient on the electrical characteristics and phase transformation kinetics of sputtered lead zirconate titanate (65/35) thin film capacitors
Authors: Chikarmane Vinay , Sudhama Chandra , Kim Jiyoung , Lee Jack , Tasch Al , Novak Steve
Published: July 2002

The fabrication of high dielectric constant lead zirconate titanate thin films for dynamic random access memory application involves post-deposition annealing to convert the low dielectric constant pyrochlore phase to the desired high dielectric constant perovskite phase. The results of our experiments detailing the dielectric characteristics such as degradation field (the electric field at which a sudden increase in leakage takes place), leakage current density, time-dependent dielectric breakdown characteristics, charge storage density, coercive field, and charge storage density are reported. The charge storage density was measured using both double-bipolar pulses and quasistatic capacitance-voltage techniques. The results of these two measurement techniques are discussed for oxygen and nitrogen annealed films. Additionally, a comparative study of the phase transformation kinetics when the post-deposition annealing is carried out in a nonoxidizing ambient such as nitrogen, as against an oxidizing ambient (pure oxygen), is detailed.
Quantitative analysis of deuterium implanted in crystalline silicon and pyrolytic graphite by pulsed XeCl laser desorption
Authors: Guo H. Y. , Ross G. G. , Terreault B.
Published: July 2002

We have investigated the pulsed XeCl laser induced thermal desorption of deuterium implanted in crystalline silicon (c-Si) and highly oriented pyrolytic graphite (HOPG). Calibrations and experimental procedures for the quantitative analysis of deuterium are described. The desorption thresholds are 0.55±0.09 and 0.43±0.07 J/cm2 for c-Si and c-axis HOPG, respectively. However, for a-axis HOPG, deuterium is difficult to desorb because of the higher thermal conductivity. As a desorption product from HOPG, CD4 has also been observed. The deuterium evolution in both c-Si and c-axis HOPG has been modeled with the code dtrlas. It appears to be mainly limited by the detrapping processes with the effective activation energies, EB= 1.2 ± 0.3 eV and EB = 2.35 ± 0.55 eV for c-Si and c-axis HOPG, respectively.
Studies of bimetallic surfaces using infrared reflection absorption spectroscopy
Authors: Kuhn W. Kevin , He Jian-Wei , Goodman D. Wayne
Published: July 2002

Well-defined bimetallic surfaces have been studied using carbon monoxide adsorption in conjunction with infrared reflection–absorption spectroscopy. The vibrational frequency of CO on low Cu coverages [∼0.1 monolayer (ML)] on Rh(100) and Mo(110) is blue-shifted relative to its gas phase stretching frequency of 2143 cm−1. This blue shift is explained as arising from CO adsorbed on well-dispersed Cu adatoms which are slightly positively charged due to polarization arising from the CO–Cu interaction. As the sample temperature is increased to 150–200 K, CO becomes mobile on these surfaces as evidenced by the migration of CO from submonolayer Pd overlayers to a W(110) substrate. Three-dimensional Cu clusters, well-ordered pseudomorphic two-dimensional Cu islands, and single Cu atoms are distinctively characterized by their CO infrared (IR) peaks. In addition, it is found that IR spectra of adsorbed CO show a remarkable sensitivity to surface structural phase transitions. Both order–order and disorder–order transitions are observed for Ni and Co overlayers on a Mo(110) substrate. It is further shown that localized segregation and ordering of C and O on Mo(110), B on Ru(0001) and Co on S/Mo(110) are observable.
Temperature control and measurement for diamond single crystals in ultrahigh vacuum
Authors: Smentkowski V. S. , Yates J. T.
Published: July 2002

A method for reproducibly heating diamond single crystals is described. Measurements of the actual diamond temperature are made using a pair of embedded thermocouples. Both, steady state and temperature programmed heating methods have been characterized. It is demonstrated that diamond temperatures, when estimated by measuring the temperature of the heating support, may be in error by hundreds of degrees K.
Effects of Ar+ sputtering and thermal annealing on optical scatter from Si(100) and Si(111)
Authors: Cohen M. R. , Simonson R. J. , Altamirano M. M. , Critchfield K. L. , Kemp W. T. , Meinhardt J. A.
Published: July 2002

The applications of crystalline silicon in imaging detectors and other devices motivate an interest in the ‘‘macroscopic’’ optical properties of Si surfaces, including reflective scatter. The types of substrate preparation procedures typically employed in Si surface studies can significantly affect the optical scatter at visible wavelengths. Specifically, surface cleaning via sputtering with 500 eV Ar+ ions followed by annealing at approximately 850 °C can increase optical scatter by more than two orders of magnitude. Similar results are obtained through thermal cycling of the Si sample to about 1000 °C. For the results reported herein, scattered light measurements were made in situ in an ultrahigh vacuum system. The incident radiation had a wavelength of 590 nm. The scattering geometry used a detection angle 45° from the specular direction. The measured increase in scatter depends strongly on the sample treatment history. A simple model is proposed to account for these observations. The model is based on standard descriptions of classical optical scatter, combined with defect and impurity diffusion on Si surfaces and step bunching.
Low-pressure ion nitriding of AISI 304 austenitic stainless steel with an intensified glow discharge
Authors: Meletis E. I. , Yan S.
Published: July 2002

Low-pressure ion nitriding of AISI 304 austenitic stainless steel was conducted in the present study by intensifying the glow discharge. Plasma intensification was produced by thermionic emission and by utilizing a triode glow discharge system. The results showed that under the intensified plasma conditions, effective nitriding can be accomplished at relatively low temperatures. The nitride layer had a dense structure, high purity and an ultrafine microstructure with a grain (nucleus) size less than 80 Å. The nitriding treatment produced a thin layer of high nitrides (FeN and Fe2N) followed by a diffusion controlled layer of (Fe,Cr)3N. X-ray and electron-diffraction analysis showed that all nitrides were hexagonal in crystal structure. The intensified plasma treatment caused a significant increase in the nitride layer growth kinetics. The enhancement of the nitrogen diffusion was attributed to the higher surface concentration of vacancies due to the energetic particle bombardment and to grain boundary diffusion in the nitride phase. A simplified diffusion model is developed to estimate the effective nitrogen diffusivity under the intensified plasma ion nitriding.
Copper metalorganic chemical vapor deposition reactions of hexafluoroacetylacetonate Cu(I) vinyltrimethylsilane and bis (hexafluoroacetylacetonate) Cu(II) adsorbed on titanium nitride
Authors: Donnelly V. M. , Gross M. E.
Published: July 2002

Cu is receiving increasing attention as a replacement for Al in future Si ultra-large-scale integrated circuits due to its lower resistivity and potentially better reliability in terms of electromigration resistance and stress-induced voiding. Metalorganic chemical vapor deposition (MOCVD) of Cu offers the advantages of conformal coverage and selective growth. Whatever the means of deposition, a diffusion barrier and adhesion layer such as TiN is required. To understand the nucleation mechanisms of Cu film growth on TiN during MOCVD, we have studied the thermal decomposition of two metalorganic precursors, hexafluoroacetylacetonate Cu(I) vinyltrimethylsilane [CuI(hfac)(vtms)], and bis (hexafluoroacetylacetonate) Cu(II) [CuII(hfac)2] by x-ray photoelectron spectroscopy and temperature programmed desorption mass spectrometry in an ultrahigh vacuum (UHV) system.

Experiments were carried out on polycrystalline air-exposed (i.e., oxidized) TiN and N2 ion beam sputter-cleaned TiN. These surfaces are representative of those found in the traditional stand-alone and newer integrated metallization processing sequences, respectively. Room temperature dosing of TiN with CuI(hfac)(vtms) is accompanied by rapid desorption of the vtms ligand, leaving chemisorbed CuI(hfac). This CuI(hfac) decomposes upon heating to form CO, CO2 and CF4 desorption products, leaving about 90% of the Cu on the surface, along with some F and C. CII(hfac)2 also dissociatively chemisorbs at room temperature to form CuI(hfac) and an adsorbate with the stoichiometry of hfac. Unlike CuI(hfac)(vtms), a Cu(hfac)-containing species desorbs upon heating above 75 °C. Near 200 °C this process ceases and decomposition (and possibly some intact desorption) of hfac takes place, leading to desorption of CO, CO2, and CF4. After desorption of all C-containing species, about 30% of the initially deposited Cu remains on the surface, along with a submonolayer coverage of F. Regardless of the precursor, Cu begins to diffuse into the TiN film, above 280 °C. The results of our studies offer insights into the different mechanisms that may play a role in the nucleation of MOCVD film growth and incorporation of impurities at the interface. Significantly, the disproportionation reaction that dominates the deposition of pure Cu from CuI(hfac)(vtms) at the higher pressures typical of MOCVD does not occur under UHV conditions.
Serial cosputtering of some metal alloys: Enhancement of partial sputtering yields of light metals
Authors: Belkind A. , Orban Z. , Berg S. , Carlsson P.
Published: July 2002

We describe serial cosputtering of Al/W, Ti/W, and Al/Zr metal alloys. Overcoating Al and Ti targets with the heavier metals Zr and W enhances the partial sputtering yield of the host metals. Computer modeling of sputtering from a bilayer structure using a modified t-dyn program indicates mixing of the two elements at the interface that takes place because of recoil implantation. In certain cases, such mixing can lead to the enhancement of the partial sputtering yield of the ground-layer element.
Reflection high-energy electron diffraction intensity monitored homoepitaxial growth of SrTiO3 buffer layer by pulsed laser deposition
Authors: Chern M. Y. , Gupta A. , Hussey B. W. , Shaw T. M.
Published: July 2002

Reflection high-energy electron diffraction (RHEED) has been used to monitor the homoepitaxial growth of SrTiO3 on (001) SrTiO3 by pulsed laser deposition. The RHEED pattern becomes sharp and streaky after deposition, indicating that the smoothness of the SrTiO3 substrate surface is improved by the growth of the buffer layer. High-resolution electron microscopy confirms that the growth of the buffer layer provides a very smooth surface with unit-cell roughness. On a smooth surface, the growth of SrTiO3 occurs in a layer-by-layer mode, as indicated by the damped intensity oscillations of the specular spot in the RHEED pattern. By interrupting the growth the specular beam recovers in intensity, and the oscillations are re-initiated with subsequent growth. Persistent RHEED oscillations, which reach an undamped steady state with superimposed beats, are observed when using a rastered laser beam for deposition. The above results suggest that that pulsed laser deposition is a useful technique for in situ growth of a smooth SrTiO3 buffer layer, which is important for the quality of the film subsequently deposited.
Processing and characterization of large-grain thin-film CdTe
Authors: Nelson Art J. , Hasoon F. , Levi Dean
Published: July 2002

Basic material studies addressing the growth and processing of CdTe have resulted in dense, defect-free as-grown CdTe films on 7059 glass with initial grain sizes of ≊0.2 μm. Innovations in postdeposition processing (no CdCl2) have resulted in films with ≳50 μm grain sizes. Scanning electron microscopy analyses confirm film density while concurrent cathodluminescence reveals a change in the recombination efficiency. Transmission electron microscopy analyses reveal that films grown below 300 °C are defect-free, while films grown above 300 °C contain defects. Photoluminescence lifetime measurements reveal a fivefold increase in lifetime following postdeposition processing of these films. These results were correlated with x-ray photoemission measurements of the Te 4d, Cd 4d, and valence band. This indicates that grain boundaries are the main factor limiting lifetimes. Based on these results, we have developed an understanding of the effects of oxygen and grain boundary oxides on postdeposition processing and enhanced grain growth.
Pt/Ti/Ge/Pd ohmic contacts to GaAs: A structural, chemical, and electrical investigation
Authors: Cole M. W. , Han W. Y. , Casas L. M. , Eckart D. W. , Jones K. A.
Published: July 2002

Interface morphology, phase composition, and elemental diffusion of Pt/Ti/Ge/Pd ohmic contacts to both n+- and p+-GaAs have been investigated as a function of annealing temperature. Structural and chemical results were correlated with specific contact resistances (ρc) measured for each thermal treatment in an attempt to determine how the indiffusion of contact metal and the out-diffusion of Ga and As affect specific contact resistance, and how effective Ti is as a diffusion barrier. Annealing at 450 °C yielded the lowest ρc, ∼6.4×10−7 Ω cm2. The interface was observed to be smooth and abrupt, and there was little As out-diffusion and Pt indiffusion. Two interface phases were detected; a primary phase, PdGe, and a secondary, Ga rich Pd–Ga–As ternary phase. The presence of this ternary phase is believed to be critical to contact formation on n-type GaAs. The Ti and Pt layers remained pristine. Annealing at 550 °C resulted in a slightly higher ρc,∼2.1×10−6Ω cm2. There was significant elemental diffusion within the contact metal and minor diffusion into the GaAs substrate. The interface possessed limited areas of spiking with uniform composition. Annealing at 600 °C proved to have a detrimental effect on the ρc, ∼10−4Ω cm2. This electrical degradation was accompanied by strong chemical intermixing between the contact and substrate, resulting in a continuous nonplanar interface with deep multiphase protrusions, and the Ti layer no longer was effective as a diffusion barrier.
Performance of the cold cathode gauges in a high and misaligned magnetic field
Authors: Hseuh H. C. , Jiang W. S. , Mapes M.
Published: July 2002

Cold cathode gauge tubes without their permanent magnets will be used to monitor the vacuum systems of a muon storage ring, presently under construction at Brookhaven. The fringe field of the storage ring’s superconducting magnet will be used to sustain the gauge discharge. Three commercial cold cathode gauges, a Penning type, a grounded Penning and an inverted magnetron, have been studied for their suitability under this high and misaligned magnetic field. Using an electromagnet, the discharge intensities of these gauges have been measured at pressures from 10−8 to 10−5 Torr, magnetic fields from a few hundred Gauss to 15 kG, and alignment angles from 0° to 50°. The discharge intensity of the Penning gauge increases with increasing magnetic field misalignment and decreases gradually with increasing pressure and magnetic field. At small misalignment, the discharge intensity of the grounded Penning decreases with increasing magnetic field, and if the misalignment is large, it drops off abruptly at high magnetic field. The discharge intensity of the grounded Penning peaks around 1×10−6 Torr if the magnetic field is low; and at a high magnetic field, it drops off gradually with increasing pressure. At lower pressures, the discharge intensity of the inverted magnetron gauge remains fairly constant with an increasing magnetic field, but decreases with increasing magnetic field at higher pressure ranges. Its discharge intensity also decreases rapidly with increasing misalignment.
Analytical performance of a secondary-neutral microprobe with electron-gas postionization and magnetic-sector mass spectrometer
Authors: Bieck W. , Gnaser H. , Oechsner H.
Published: July 2002

A secondary-neutral mass spectrometer has been developed which combines postionization by means of an electron gas (plasma) with a high-transmission magnetic mass spectrometer and a finely focused ion beam produced in a Ga liquid-metal ion source. The instrument can be operated in a large-area direct bombardment-mode extracting the sputtering beam out of the plasma, or in a microprobe mode utilizing the focused Ga+ ion beam to effect sputtering. In the former case secondary-neutral intensities of up to 109 c/s can be realized; together with the high abundance sensitivity those translate in a detection limit in the few-ppb range. In the microprobe mode, secondary-neutral micrographs have been recorded using a focused 20 keV Ga+ beam with a spot size of ≲1 μm and a current of some nA. From these data an elemental detection sensitivity of 10−3 is inferred, necessitating image acquisition times of the order of 2500 s.
Inelastic mean free pathlengths of electrons for quantitative investigations of ultrathin technological surface layers by angle-resolved x-ray photoelectron spectrometry
Authors: Gries Werner H.
Published: July 2002

Angle-resolved self-ratio x-ray photoelectron spectrometry is shown to yield quantitative information on the depth composition of technological surfaces. The inelastic mean free pathlengths (IMFP) of x-ray photoelectrons required for quantification of the experimental data are obtained from a new universal formula (documented here for the first time). For the energy range 200–2000 eV, the two fitting parameters of the formula were deduced from the optical-data-derived IMFP of Tanuma, Powell, and Penn. These ‘‘optical’’ IMFP are presently being checked against IMFP derived from stopping data of high-energy protons and from mean-energy-loss-per-collision data (obtained from electron energy loss spectra). These latter IMFP are found to be significantly shorter than the optical IMFP. Equations are presented for conversion of proton-stopping powers to electron-stopping powers, and thence to IMFP.
Power required to maintain an electron in a discharge: Its use as a reference parameter in magnetized high frequency plasmas
Authors: Margot J. , Moisan M. , Fortin M.
Published: July 2002

Earlier works on discharges sustained by electromagnetic surface waves in absence of a magnetic field have revealed the central role played by the power balance per electron. This balance relation stated that, provided energy transport is negligible, the power θL lost by the electron on the average in collisions with heavy particles is exactly compensated under steady-state conditions by the power θA taken by the electron on the average from the high frequency (hf) field, their common value being the parameter θ. Then, because θL is to a first approximation the same in all hf discharges under given discharge conditions and power density, a simple discharge model valid for all hf plasmas was used. The present article is an extension of this approach to hf magnetized plasmas, using surface-wave plasma columns placed in an axially directed static magnetic field as a means of investigation. We observe that θ decreases monotonously when increasing the magnetic field intensity B0, showing no extremum at or close to the electron cyclotron resonance frequency match over the gas pressure range (5–100 mTorr) investigated. We show that θ is controlled either by classical ambipolar diffusion or anomalous diffusion, the actual diffusion regime depending on whether the novel parameter B0p (p is gas pressure) is small or large. Our measured θ values are further used to estimate the average electron density in helicon sources given the power density, showing fair agreement with the reported values.
Thermal desorption spectroscopic analysis for residual chlorine on Al–Si–Cu after Cl2 electron cyclotron resonance plasma etching
Authors: Teraoka Yuden , Aoki Hidemitsu , Nishiyama Iwao , Ikawa Eiji , Kikkawa Takamaro
Published: July 2002

Thermal desorption spectroscopy is used to measure the amount of residual chlorine on Al–Si–Cu. The Al–Si–Cu surface is etched by Cl2 electron cyclotron resonance (ECR) plasma at substrate temperatures of 30 and −60 °C. The surfaces are then cleaned by one of the following methods: de-ionized water rinsing, H2 ECR plasma irradiation, or annealing in H2/N2 mixed gas. AlCl molecules, which may be responsible for aftercorrosion, are detected. Chlorine compounds, however, cannot be detected by conventional x-ray photoelectron spectroscopy or Auger electron spectroscopy. The low substrate temperature etching reduces the amount of residual chlorine. Moreover, the cleaning ability of the H2 ECR plasma treatment is no less than that of the de-ionized water rinse, and is superior to that of annealing in H2/N2 mixed gas.
Pumping behavior of ion pump elements at high and misaligned magnetic fields
Authors: Hseuh H. C. , Jiang W. S. , Mapes M.
Published: July 2002

The pumping speeds of several diode type ion pump elements with cell radii of 5, 5.5, 6, 9, and 12 mm were measured while being subjected to a magnetic field B, ranging from 500 G up to 15 kG, and misalignment angles (angles between the direction of B and the anode axis) from 0° to 13°. The pumping speeds of elements with the 9 and 12 mm cells peaked around 1–2 kG, then dropped off rapidly with an increasing magnetic field. The pumping speeds of the smaller cell elements remained constant with an increasing magnetic field. The pumping speeds of all the elements decreased with increasing misalignment. The measured pumping speeds from this study are three to four times lower than the calculated pumping speeds using previously reported empirical formulas.
Plasma enhanced chemical vapor deposition of TiO2 in microwave-radio frequency hybrid plasma reactor
Authors: Lee Young H. , Chan Kevin K. , Brady Michael J.
Published: July 2002

A plasma tool and accompanying process have been developed for plasma enhanced chemical vapor deposition of TiO2 thin films for dynamic random access memory application. The microwave-rf (radio frequency) hybrid reactor consists of microwave power (2.45 GHz) for electron cyclotron resonance, a hollow cathode (0.1–30 MHz) for control of the plasma potential, and an additional rf (13.56 MHz) power to the substrate electrode for ion extraction and ion energy control. X-ray diffraction showed the anatase phase at a low deposition temperature below 400 °C, but the rutile phase dominanted above 400 °C. Low energy ion bombardment densifies the TiO2 films and suppresses rutile formation. A dielectric constant of 60(±5) at 1 MHz was obtained, independent of film thickness in a range from 20 to 200 nm. A SiO2 buffer layer was found to be important in order to prevent silicide formation and to keep the leakage current below 10−10 A/cm2.
Ellipsometry for III–V epitaxial growth diagnostics
Authors: Maracas G. N. , Kuo C. H. , Anand S. , Droopad R. , Sohie G. R. L. , Levola T.
Published: July 2002

Spectroscopic ellipsometry’s (SE’s) strength as an in situ semiconductor crystal growth process diagnostic lies in the fact that the material’s dielectric properties (pseudodielectric functions) are dependent upon temperature and alloy composition. These dependencies can be exploited to monitor and control epitaxial growth in real time. This article reviews several aspects of growth and control of III–V semiconductors grown at Arizona State University by molecular beam epitaxy (MBE) using SE. Chamber and manipulator design considerations for implementing SE on a MBE and a gas source MBE with substrate rotation will first be discussed. A commercially available ‘‘ellipsometer-ready’’ MBE system will then be described. It will then be shown that a MBE process can be established without conventional analysis tools such as reflection high energy electron diffraction. Measurement and control of substrate temperature by SE will be shown. This is possible by using the temperature-dependent pseudodielectric functions for GaAs and AlGaAs which we have measured. Calibration of MBE growth will be discussed including in situ measurement of oxide desorption, V/III flux ratio, growth rate, and alloy composition measurements. Tracking the growth of the epitaxial layer provides information on thickness, alloy composition, and surface roughness. Algorithms for deconvoluting these effects from the data will be discussed. Finally, examples of structures used in optoelectronic devices will be presented including quantum well thickness control and microcavity laser device growth.