bluuebunny/crossref_metadata_2025 huggingface dataset:
Secondary ion mass spectrometry analysis of a three-level metal structure using sample rotation
Authors: Stevie F. A. , Moore J. L. , Merchant S. M. , Bollinger C. A. , Dein E. A.
Published: July 2002

Multilevel metal structures are commonly used in submicron semiconductor technology. However, secondary ion mass spectrometry (SIMS) analysis of metal films, such as aluminum and titanium, is complicated by degraded depth resolution due to nonuniform sputtering during analysis. The insulating layers used in multilayer structures cause charging problems that add to the difficulty of the analysis. Sample rotation during analysis has been shown in earlier work to improve depth resolution for a single aluminum layer with a dielectric overlayer. Results are presented here for rotational SIMS analysis to a depth exceeding 5 μm for a three-level metal structure with repeating SiO2/TiN/Al/TiN/Ti segments. Data were obtained using oxygen and cesium primary beams with an electron gun for charge neutralization. The results show that all layers can be identified and that both matrix and impurity species can be monitored. The information obtained permitted evaluation of matrix interdiffusion and the detection of contaminants.
Thermally induced changes in TeOx thin layers
Authors: Podolesheva I. , Platikanova V. , Konstantinov I. , Rösler M.
Published: July 2002

TeOx layers with controlled Te/O ratio and thickness are prepared by thermal coevaporation of TeO2 and Te. Using various transmission and scanning electron microscopy techniques it is shown that the as-deposited layers represent a composite system, consisting of finely dispersed, partly agglomerated crystalline Te particles embedded in an amorphous TeO2 matrix with columnar structure and fine-grained substructure. The effect of annealing and laser exposure on the layers is investigated. A strong correlation of the change in transmission and the Te redistribution is found. It is shown that the variations in the optical properties of the TeOx layers are caused by aggregation of the crystalline Te particles and migration of Te to the upper free surface of the layer.
Reaction layer formation and fracture at chemically vapor deposited diamond/metal interfaces
Authors: Perry Scott S. , Somorjai Gabor A.
Published: July 2002

Chemically vapor deposited (CVD) diamond films have been deposited by a microwave enhanced deposition process on metal substrates including titanium, tungsten, molybdenum, and copper. Boundary reaction layers formed at the interface during the growth of the CVD diamond films have been investigated for each of these systems. In these studies, the interface has been exposed by mechanically deforming the metal substrate to cause film delamination. Where the diamond film has adhered to the substrate through the growth process, delamination procedures have been carried out under controlled conditions in order to preserve the integrity of the interfacial species. The exposed interfaces were characterized by x-ray photoelectron spectroscopy, scanning Auger microscopy, secondary electron microscopy, and Raman microprobe spectroscopy. Reaction layers composed of carbides and oxides of the native metal were detected at the interfaces of titanium, tungsten, and molybdenum while only traces of carbon and oxygen were detected at the diamond/copper interface. We believe that both the chemical composition and morphology of the interface influence the adhesive properties of the diamond coating. Correlated investigations of the interfacial surfaces reveal that fracture of the diamond/metal interface occurs discretely at the diamond nucleation plane or within a reaction layer near the diamond interface.
Oxide film deposition by radio frequency sputtering with electron cyclotron resonance plasma stimulation
Authors: Matsuoka Morito , Tohno Shun-ichi
Published: July 2002

Various oxide films, including SiO2, ZnO, BaTiO3, SrTiO3, and BaFe12O19, are deposited by 13.56 MHz radio frequency mode (rf-mode) sputtering with 2.45 GHz electron cyclotron resonance (ECR) plasma stimulation. The rf plasma is effectively cooled by the ECR plasma as a result of the shielding effect on the rf electric field on the target surface. This causes the self-bias voltage of the target to decrease and the rf-mode sputtering is effectively performed as in a direct current mode (dc-mode) system. There are two stages in the deposition of the oxide films: an oxygen supply-determining stage controlled by the ECR plasma density, and a sputtered-particle supply-determining stage controlled by the rf sputtering power. In the former stage, the film deposition rate is dramatically enhanced by the ECR plasma irradiation onto the substrate surface (ten times higher than without ECR plasma). In the latter stage, the film deposition rate does not change with oxygen plasma density but with the sputtering power. In this stage, the film deposition uniformity depends only on the uniformity of the sputtered particles. Fully oxidized films can be easily deposited by this technique. Changes of film composition are mainly due to anisotropy of the angle at which sputtered atoms of each component are ejected from the target surface, and also to the sticking efficiency of each component on the film surface with ECR plasma irradiation.
Automated Langmuir probe characterization of methane/hydrogen low-pressure radio frequency discharges in a production reactor
Authors: Cali F. A. , Herbert P. A. F. , Kelly W. M.
Published: July 2002

An automated, tuned Langmuir probe has been applied to a commercial, multiply used reactive ion etcher operated by radio frequency-generated 13.56 MHz low-pressure discharges. The probe was used to measure the plasma parameters and electron energy distribution function in a methane/hydrogen plasma, an important etchant of optoelectronic semiconductors. Results have revealed a typical electron temperature of approximately 1.5 eV, an electron density of 6×109 cm−3, and a plasma potential of 28 V. The electron energy distribution function is bi-Maxwellian with a dip appearing at 6 eV, which corresponds to the vibrational state of the methane radical and supports a hypothesis of electron absorption by the radical at this energy. The precautions required to condition both probe and chamber to obtain reliable data are given, and it is shown that the automated Langmuir probe can operate as an in situ diagnostic in polymer producing processing plasmas in operational reactors providing stringent routines are implemented.
Scanning probe visualization of electrostatically immobilized intercalating drug–nucleic acid complexes
Authors: Coury J. E. , McFail-Isom L. , Presnell S. , Williams L. D. , Bottomley L. A.
Published: July 2002

DNA intercalators are planar molecules that insert between the base pairs of duplex DNA. Intercalation into DNA necessarily results in changes in DNA conformation, separating base pairs along the helical axis; thus, intercalators are of great importance as probes of nucleic acid structure and as interferents of DNA replication, transcription, and/or topoisomerase activities. Relationships between structures of intercalators and the changes they cause in DNA conformation are subtle and remain unresolved. An intercalating drug molecule has been synthesized that incorporates markers easily distinguished by atomic force microscopy (AFM). This specially designed psoralen derivative has been intercalated into DNA. To facilitate recognition of the point of intercalation, the psoralen derivative contained a biotin moiety that was exposed and bound readily to streptavidin-coated colloidal gold beads. Atomic force micrographs were obtained following electrostatic immobilization of the DNA/psoralen complexes onto mica surfaces. This article presents AFM images of intercalating drug–DNA complexes which may provide further data for the study of structure/intercalator relationships.
Large volume electron cyclotron resonance plasma generation by use of the slotted antenna microwave source
Authors: Engemann J. , Schott M. , Werner F. , Korzec D.
Published: July 2002

A new electron cyclotron resonance plasma source, the slotted antenna (SLAN) is presented. The microwave power is coupled to the plasma inside a quartz bell jar by ten equally spaced slot antennae positioned equidistantly around the inside wall of a cylindrical ring cavity. A total of 10 SmCo magnet stacks are positioned between each two slots yielding the required 87.5 mT magnetic field strength for electron cyclotron resonance inside the plasma excitation volume. The source plasma ignition/extinction performance and operational range for different atomic (Ar, He) and molecular gases (O2, N2) were studied in detail. Due to the external magnetic field either in toroidal or hybrid symmetry, a shift of the minimum ignition pressure from 0.4 to 2×10−3 mbar and the minimum extinction pressure from 4×10−3 to 2×10−4 mbar for argon was observed. The radial and downstream ion density as well as electron temperature were measured by double-Langmuir-probe techniques. Microwave power coupled to the source was varied from 600 to 2000 W and pressure was ranged from 2×10−4 to 10−2 mbar. Typical data achieved for 1000 W microwave power are ion density 2.8×1011 cm−3 at a pressure of 5×10−3 mbar, corresponding to an ionization ratio of 1.3% (center of SLAN).
Diagnostics and control of radicals in an inductively coupled etching reactor
Authors: Sugai H. , Nakamura K. , Hikosaka Y. , Nakamura M.
Published: July 2002

Comprehensive measurements of charged particles and neutral radicals in an inductively coupled plasma (ICP) are performed to understand and control the etching process using a CF4/H2 gas. The electron density in the ICP reactor decreases exponentially in a downstream region while the most abundant ionic species CF+ increases in proportion to the rf power with the CF+3 density almost constant. The neutral radical diagnostics by appearance mass spectrometry indicate 10 times more F atoms and somewhat fewer CFx radicals (x=1–3) in ICP, compared with a high-pressure capacitively coupled plasma diode. Such a small ratio of the CFx density to the F density is possibly a cause of the low etch selectivity of SiO2 to Si in ICP etching. Two innovative methods to achieve the high selectivity in ICPs are demonstrated. One is wall heating (100–200 °C), which leads to a drastic increase in CFx densities with the F density almost constant. The other is a pulse modulation of rf power at 30–50 μs durations where the time-resolved measurement of electron temperatures indicates a 6 μs rise time and a 70 μs decay time. The density ratio CFx/F (x=2,3) increases with decreasing rf-on time. The mechanisms of the radical composition change and the resultant high selectivity in pulsed plasmas are discussed.
Interaction of 50 eV electrons with D2O on GaAs(100)
Authors: Sloan Derrell W. , Sun Yang-Ming , White J. M.
Published: July 2002

The interaction of 50 eV electrons with D2O, dosed on GaAs(100) at 100 K, has been investigated using temperature programmed desorption (TPD), x-ray photoelectron spectroscopy, and high resolution electron energy loss spectroscopy. There is good evidence that water adsorbs molecularly and does not dissociate thermally in TPD. The TPD spectra change with coverage. At the lowest exposures, the desorption is broad, peaking near 200 K, and exhibits a long tail extending to 600 K, the latter a characteristic of every exposure. As the exposure increases, this peak moves slightly to lower temperatures (196 K) and a second peak appears at 156 K; these two then merge to an unresolved peak at 176 K which moves downward to as low as 169 K. Dissociation and desorption are induced by electron irradiation at 100 K; the O(1s) binding energy shifts downward (533.2–531 eV) and broadens and the vibrational spectra take on characteristics expected for O–D formation and the desorption of molecular water. Electron-induced O–D bond breaking is limited to D2O molecules located at the GaAs interface. During heating (up to 600 K) after electron irradiation, there is (1) some D2O and D2 desorption, (2) depending on the annealing temperature, a lower O(1s) binding energy (530 eV at 400 K, 529 eV at 600 K), and (3) loss of all vibrational features attributable to D. These facts are all consistent with forming a small amount of surface oxide, possibly at defect sites. The D2O removal process is adequately described as first order with an upper bound for the cross section, σ(D2O), of 1.16×10−17 cm2. The measured isotope effect, σ(H 2O)/σ(D2O), was 2.57.
Exoelectron emission from nickel oxide film and its relationship to the reduction by ethanol vapor
Authors: Momose Y. , Iwanami K. , Seki J.
Published: July 2002

The exoelectron emission participating in catalytic reactions on nickel oxide film was investigated using a Geiger counter with an argon–ethanol counting gas. The thermally stimulated exoelectron emission (TSEE) from the metal oxide surfaces was related to the chemical and electrical nature of the surfaces characterized by means of x-ray photoelectron spectroscopy, x-ray diffraction, and surface potential (SP) measurement. Three different metal oxide samples were prepared: metal sheets oxidized by heating in air at various temperatures, and subsequently subjected to treatment in argon or oxygen plasma. The TSEE was observed not only for the plasma treated sheets, but also for the sheets oxidized only, although the intensity of TSEE for the latter was considerably weaker than that for the former with a more negatively charged surface by the plasma treatment. A similar feature was observed for each type of sample: the TSEE activity increased progressively as the SP became more negative and the oxide thickness decreased, being accompanied by the reduction of the oxide and also the deposition of carbon. A mechanism is suggested that the TSEE results from the release of electrons when adsorbed oxygens with a negative charge on the surfaces undergo chemical reduction due to a dehydrogenation of the ethanol, which was used as a quenching gas in the Geiger counter.
A primary standard high vacuum calibration station for industrial applications
Authors: Levine P. D. , Sweda J. R.
Published: July 2002

The Metrology Laboratory at Lockheed Martin Missiles & Space in Sunnyvale, CA, has developed a primary standard high vacuum calibration station. Maintaining an in-house capability for calibrating Bayard–Alpert gauge tubes and spinning rotor gauges (SRGs) at the primary level eliminates the need for external sources of calibration. This not only significantly reduces costs but also provides for continuous monitoring of the reference standards used to support research programs and manufacturing processes. A constant volume, pressure drop flowmeter is used to generate known pressures in a vacuum chamber partitioned by an orifice of calculable conductance. Data are presented which show vacuum chamber pressure to be directly proportional to flowmeter pressure drop in the three decades of vacuum spanned by the SRGs (10−3–10−6 Torr). Using a SRG calibrated at the National Institute of Standards and Technology, the proportionality constant is determined and shown to agree well with the constant calculated from system fixed parameters and measured pressure ratios. A new design of flowmeter is discussed. An estimate of when the system will be fully utilized as a primary reference will be made.
Preparation and characterization of beryllium doped organic plasma polymer coatings
Authors: Brusasco R. , Letts S. , Miller P. , Saculla M. , Cook R.
Published: July 2002

We report the formation of beryllium doped plasma polymerized coatings derived from a helical resonator deposition apparatus, using diethylberyllium as the organometallic source. These coatings had an appearance not unlike plain plasma polymer and were relatively stable to ambient exposure. The coatings were characterized by inductively coupled plasma mass spectrometry and x-ray photoelectron spectroscopy (XPS). Coating rates approaching 0.7 μm h−1 were obtained with a beryllium-to-carbon ratio of 1:1.3. There is also a significant oxygen presence in the coating as well which is attributed to oxidation upon exposure of the coating to air. The XPS data show only one peak for beryllium with the preponderance of the XPS data suggesting that the beryllium exists as BeO. Diethylberyllium was found to be inadequate as a source for beryllium doped plasma polymer, due to thermal decomposition and low vapor recovery rates.
Control of etch profile for fabrication of Si microsensors
Authors: Juan W. H. , Pang S. W.
Published: July 2002

Si has been etched with an electron cyclotron resonance source in a Cl2 plasma to fabricate microsensors with high-aspect-ratio structures. Resonating elements in Si with an aspect ratio of 20 were generated. For these high-aspect-ratio sensing elements, the etch rate and profile strongly depend on feature size and etch depth. When the spacing between elements was increased from 2 to 50 μm, the Si etch depth varied from 21.5 to 24.6 μm for a 156 min etch. Typical etch conditions were 100 W microwave power, 100 W rf power, at 3 mTorr and 8 cm source distance. The Si etch rate decreased linearly from 156 to 119 nm/min as the trench aspect ratio varied from 2 to 34. The etch rate also decreased from 151 to 124 nm/min in 2-μm-wide trenches and from 163 to 141 nm/min in 10-μm-wide trenches as the pressure was increased from 3 to 30 mTorr. Etch profile was vertical at 3 mTorr and it became undercut at pressures ≥10 mTorr. Larger undercut widths were found for trenches with narrower spacings. As microwave power was varied from 50 to 250 W, the etch rate increased from 88 to 206 nm/min for 2-μm-wide openings and from 96 to 251 nm/min for 25-μm-wide features. The amount of undercut increased with microwave power but decreased with trench opening width. The etch profile was also significantly influenced by wafer temperature. For a 2-μm-wide opening with etch depth of 15 μm, the Si etch profile was vertical for temperature ≤40 °C and had 1 μm undercut width at 350 °C. Etch rate increased with temperature and trench width. Wafer clamping and He backside cooling were necessary to provide efficient temperature control. To achieve uniform etch depth and vertical etch profile for various feature sizes, low ion flux, low pressure, and controlled wafer temperature are required.
Study of radiation effects in SiO2/Si by measurement of contact–separation current
Authors: Stacy T. , Burkett S. , Chen C. T. , Charlson E. M. , Charlson E. J.
Published: July 2002

Contact and frictional electrification measurements of insulators have been used for a number of years to characterize insulator surface charging. An instrument developed in our laboratory confirms triboelectric series data derived from the conventional field mill technique by measurement of current when a metal plate contacts and then separates from the insulator. In this work we investigated the measurement of this contact–separation current on unbiased gamma (Co-60) irradiated SiO2 thermally grown on single-crystal silicon. To our knowledge, surface charge measurements have not been previously used to characterize irradiated SiO2. Results on wet and dry thermal oxides show that irradiation with total doses of 1 and 2 Mrad (Si) show consistent decrease in contact current. Comparison to flatband voltage shifts indicates that radiation damage of SiO2 grown on Si can be observed with surface charge measurements, although more work is required to determine the potential of this method for quantitative analysis of radiation effects.
X-ray standing wave study of the S-passivated InP(001) surface
Authors: Sugiyama M. , Maeyama S. , Oshima M.
Published: July 2002

The adsorption position and ordering degree of S atoms on a S-passivated InP(001) surface were investigated by using soft-x-ray standing waves (XSWs) in the photoelectron collection mode. Soft-x-ray photoelectron spectroscopy for a (NH4)2Sx-treated and de-ionized water-rinsed InP(001) surface revealed that a small amount of residual elemental S atoms on the InP(001) surface was completely removed by postannealing at 400 °C in a vacuum. XSW results for the annealed sample showed that most of the S atoms stayed at the bridge site on the In-terminated InP(001) surface, forming In–S–In bridge bonds.
Analysis of surface void fraction using atomic force microscopy
Authors: Lindquist C. S. , Urban F. K.
Published: July 2002

Roughness is present for the majority of surfaces because atomically flat interfaces are not common. Even though the surface ‘‘roughness layer’’ may be very thin, on the order of countable atomic layers, it frequently has a very significant effect on light reflection, chemical reactivity, adhesion, and the like. Consequently the analysis of surface roughness is of interest. Surfaces of metal oxide films deposited by chemical vapor deposition were scanned using an atomic force microscope (AFM). Initial processing of the very large AFM data sets, typically over one megabyte in size in ASCII format, included tilt correction, ‘‘scattering noise’’ removal, surface smoothing, and surface compression. Techniques for enhanced visualization of the surface using hard limited and band images are presented. Histograms (approximate probability density functions) are computed for surface possessing long range order and it is observed that both the long and short range orders are essentially Gaussian. Consequently the void fraction dependency is very close to an error function for these cases. A case (much less common in our data) in which the surface pdf was Gamma rather than Gaussian is also shown for comparison.
Non-self-recognition of metals in blood and peritoneal cavity
Authors: Kanagaraja Sanjiv , Ericson Lars E. , Nygren Håkan
Published: July 2002

To explore the hypothesis that protein adsorption followed by platelet adhesion and activation has an effect on the nature of the subsequent inflammatory response, we studied the cell–implant reactions to Ti and Au in blood and the peritoneal cavity. The metals were exposed to blood (in vitro) and peritoneal fluid (in vivo). In blood the adhesion and activation of platelets and leucocytes were studied by fluorescence microscopy using specific FITC-labeled antibodies or acridine orange. Intraperitoneal leucocyte adhesion was studied by scanning electron microscopy, transmission microscopy, or by staining with acridine orange. The metallic surfaces were exposed to both blood and peritoneal fluid for times varying from 15 s to 4 h. The results show (a) that a significantly larger number of platelets followed by a correspondingly large number of leucocytes initially adhere to Ti rather than to Au, (b) that the rate of the inflammatory response as manifested by the appearance of leucocytes is more rapid in the peritoneal cavity than in blood, and (c) that cells attach directly to the Au surfaces while being separated by an amorphous layer on the Ti surfaces. Thus an interesting nexus exists between the composition of the adsorbed protein layer, platelet adsorption, and activation and the rate and nature of leucocyte recruitment and interaction with implanted materials.
Silicon surfaces treated by CF4, CF4/H2, and CF4/O2 rf plasmas: Study by in situ Fourier transform infrared ellipsometry
Authors: Shirafuji Tatsuru , Stoffels Winfred W. , Moriguchi Hiroshi , Tachibana Kunihide
Published: July 2002

The reaction layer formed on a silicon substrate in a CF4 rf plasma and in its admixtures with hydrogen and oxygen has been investigated by Fourier transform infrared phase-modulated spectroscopic ellipsometry (FTIR-PMSE). The results are compared with x-ray photoelectron spectroscopy spectra of the surface. It is shown that by using FTIR-PMSE, a significant gain in sensitivity is obtained as compared to ordinary reflection absorption measurements. In the case of a CF4 plasma, a large difference in the reaction layer at rf and the grounded electrode has been found. Samples treated on the rf electrode have a thin reaction layer consisting of SiFx (x=1, 2, 3, and 4). The reaction layer of samples treated on the grounded electrode also contain CFx species. In the case of a 50% CF4 50% H2 plasma, a thick carbon layer is formed on both the rf and the grounded electrode. While the layer formed on the grounded electrode contains a high amount of CFx (x=1, 2, and 3) bonds, that on the powered electrode does not contain as much. In the case of a 50% CF4 50% O2 plasma, a thin siliconoxide layer is formed. On the grounded electrode, it takes slightly longer to build up, but the final reaction layer on rf and grounded electrodes is the same. Small amounts of SiF4 are also present in the layer.
Chemistry of actinide and lanthanide metal ions (M+) in laser ablation of dispersions of inorganic compounds in polyimide and polytetrafluoroethylene
Authors: Gibson John K.
Published: July 2002

The positive ions produced during excimer laser ablation of a polyimide (PI) or polytetrafluoroethylene (PTFE) matrix containing a small concentration of a solid compound comprising an actinide (Th, U) and/or lanthanide (La, Ce, Pr, Eu, Tb, Ho, Tm, Yb, Lu) were determined by time-of-flight mass spectrometry. The polyatomic mass spectra were dominated by species of the general form, M+–L, where M+ is the actinide/lanthanide and L is some fragment ligand from the polymer. For PI, primary products were M+–CcHh with c=2 or 4 and h=0 or 1. For PTFE, the main products were generally Mf+ with f=1 or 2. Although the studied metals are largely similar in their condensed phase chemistries, rational differences were evident in the compositions of the ablation products, which often corresponded to molecules identified in high-temperature vaporization of inorganic solids. For the M+–CcHh species, the degree of hydrogenation, i.e., h=0 or 1, consistently reflected the relative thermodynamic stabilities of the binary carbide molecules, MC2, which in turn closely correlate with those of the gaseous MO. Thus, U and Ce form especially robust monoxide and dicarbide molecules and, accordingly, produced primarily the bare dicarbide, MC2+. In contrast, the monoxides and dicarbides of Eu and Tm are relatively weakly bound and their PI ablation products incorporated hydrogen to produce more substantial yields of MC2H+. The compositions of the highly ionic metal fluorides produced from PTFE ablation reflected the relative stabilities of successive metal-ion oxidation states. For example, the yield of the difluoride ion, MF2+(≈M3+F2−), relative to that of the monofluoride, MF+(≈M2+F−), was found to decrease in the order, CeF2+>HoF2+>TmF2+, which is the inverse of the ordering of the +2 to +3 ionization energies: Ce<Ho<Tm. The observation of coherent thermochemical effects in metal-ion chemistry in ablation plumes suggests quasiequilibrium high-temperature conditions. Chemical speciation in laser ablation of metal–polymer aggregates is central to the formation of novel metal-doped polymer materials by pulsed laser deposition, and may be utilized to enhance elemental specificity in direct laser ablation sampling for mass spectrometric analysis. The described techniques are, furthermore, applicable to microscale investigation of the fundamental chemistry of scarce and radioactive transuranic actinides.
Comparison of bromine etching of polycrystalline and single crystal Cu surfaces
Authors: Nakakura C. Y. , Altman E. I.
Published: July 2002

The etching of polycrystalline Cu surfaces by Br2 was studied using temperature programmed desorption and scanning tunneling microscopy, and the results were compared with a recent study of the interaction of Br2 with Cu(100). For both Cu surfaces, the etching mechanism could be described as a two step process: adsorption rate limited CuBr formation followed by CuBr desorption. The adsorption rate was found to be structure sensitive. At 325 K, the sticking coefficient for CuBr formation was higher on Cu(100) than on polycrystalline Cu. For both surfaces, increasing the temperature during dosing decreased the CuBr formation rate. The decrease was larger for polycrystalline Cu and so the structure sensitivity increased with increasing temperature. The removal of CuBr by sublimation was found to depend more strongly on surface structure. For low CuBr coverages on Cu(100), a CuBr desorption peak was observed at 450 K, a temperature lower than anticipated from CuBr vapor pressure data. When the CuBr coverage was increased, the peak at 450 K shifted to higher temperatures and eventually disappeared; the remaining CuBr desorption peaks were consistent with sublimation of bulk CuBr. A CuBr desorption peak at 450 K was also observed on polycrystalline Cu. On the polycrystalline surface, however, this peak saturated at high coverages but did not shift to higher temperatures. The intensity of the 450 K desorption peak depended on the treatment of the polycrystalline surface. Annealing was found to increase the peak intensity while sputtering and Br2 etching were found to decrease the intensity. Scanning tunneling microscopy images following each of these treatments suggested that the 450 K desorption peak is associated with narrow terraces on the surface. The images also revealed that etching greatly increases terrace widths suggesting that steps act as Cu atom sources for CuBr formation, and thus that Br2 etching of Cu can be considered the reverse of step flow growth.
Effects of low-energy electron and ion irradiation on CO/Cu(100): In-situ production and coadsorbate-induced adsorption of CO above room temperature
Authors: Yu H. , Hu D. Q. , Leung K. T.
Published: July 2002

The surface reactions of CO with clean, oxygen-precovered and carbon-precovered surfaces of Cu(100) assisted by low-energy electron or ion irradiation were investigated using high-resolution electron energy loss spectroscopy and temperature programmed desorption mass spectrometry. We observed an anomalous adsorption of “stabilized” CO species on Cu(100) above room temperature that were produced in situ by low-energy electron irradiation of CO/Cu(100) at 120 K and by low-energy ion irradiation of Cu(100) in CO or with pre- or postexposure of O2 in C2H4 at room temperature. The corresponding C–O stretch vibration was found to be redshifted by 73 cm-1 from its nominal position (2084 cm-1) at 120 K. Furthermore, unlike the normal C–O stretch that could only be observed below 200 K, the redshifted peak could be found up to 420 K. From the different mechanisms that could cause the observed redshift and stabilization effects, we propose a direct-interaction bonding model involving a “tilted” CO molecule on an atop site semibridge bonded to an O atom in a four-fold hollow site. Other processes such as reaction activation and creation of defect sites as well as sputtering effects induced by low-energy electron or ion irradiation are discussed.
Simple method for the control of substrate ion fluxes using an unbalanced magnetron
Authors: Telling N. D. , Petty M. , Crapper M. D.
Published: July 2002

Substrate ion fluxes from unbalanced magnetron sources are generally controlled by the use of additional magnetic fields. These methods are not always suitable for differentially controlling the ionic flux from multiple sources. We report here a simple method suitable for attaining such control that can be easily adapted to most unbalanced magnetron systems. The flux leakage from an unbalanced magnetron is controlled by the use of a mild steel keeper with a detachable mild steel annulus. The annulus redirects the unbalanced field lines through the keeper to the rear poles of the magnetron. The flux leakage is thus controlled by varying the thickness of the annulus. Ion saturation currents measured at the substrate, with and without a 0.9 mm thick mild steel annulus, were found to differ by a factor of approximately 3 at an argon partial pressure of 1 mTorr. Furthermore we demonstrate that the changes in ion current density are achieved without alteration to the magnetron operating parameters.
Effect of substrate bias on the properties of a-C:H films by direct current saddle-field plasma-enhanced chemical-vapor deposition
Authors: Yoo Young-Zo , Kim HyoGun , Jang Hong-Kyu , Jeong YoungGeun , Kim Geunsik
Published: July 2002

Hydrogenated amorphous-carbon (a-C:H) films were deposited on p-type Si(100) at room temperature by dc saddle-field plasma-enhanced chemical-vapor deposition using pure methane gas. The effect of substrate bias (Vs) from 0 to 400 V on deposition rate, hydrogen content, and chemical bonding of the films have been investigated. Fourier transform infrared spectrum shows that a-C:H films consist of sp2 and sp3 bondings and the relative intensity ratio of sp2 and sp3 [I(sp2)/I(sp3)] decreases from 0.28 to 0.19 as the substrate bias changes from 0 to 400 V. Deposition rates of the films rapidly decrease with increasing Vs up to 200 V, and then slightly decrease over Vs=200 V. The hydrogen content of the films increases as Vs goes higher and the number of C–H bondings of a-C:H shows same trends. Only in the range of Vs=0 V and Vs=100 V, the Raman band of graphite and disorder is observed. The emission of white photoluminescence (PL) light from the films is observed with the naked eye even at room temperature. The intensity of the PL has a maximum at Vs=200 V, then decreases as the Vs changes from 200 to 400 V. The optical band gap (Eg) determined by the Tauc relation is shifted from 1.48 to 2.9 eV with increasing Vs, while the peak position of the PL spectra is shifted slightly to higher energy.
Characteristic losses in metals: Al, Be, and Ni
Authors: Madden H. H. , Landers R. , Kleiman G. G. , Zehner D. M.
Published: July 2002

Information about the occupied portion of the surface density of states of materials can be derived from electron-excited Auger electron spectroscopy (AES), which is a standard experimental technique in most surface science laboratories. Surface sensitive experimental techniques that provide information regarding the unoccupied portion of the surface density of states are often not standard and are not so readily available. Here we explore the possibility of utilizing the same experimental equipment as in AES to derive information about the unoccupied portion of the surface density of states from a characteristic loss spectroscopy, in particular, from core-level inelastic electron-scattering spectroscopy (CLIESS). An important application of this technique is in comparative studies. CLIESS spectra from clean surfaces of aluminum, beryllium and nickel are presented. These data were taken in the first-derivative mode using the reflection of monoenergetic primary beams of 450 eV energy for Be, and 300 eV for Al and Ni. The Al and Be spectra had to be extracted from overlapping plasmon signals using synthesized plasmon spectra based on the behavior of these spectra between the elastic peak energy and the respective core level threshold energies. After applying loss-deconvolution techniques to remove secondary loss spectral distortions, integral spectra were obtained which compared well to corresponding experimental soft x-ray absorption and transmission electron-energy loss data as well as to theoretical calculations of the unoccupied density-of-states for these materials. Comparison similarities as well as some differences are discussed. Finally, in order to illustrate the potential these signals have in serving as “fingerprints” of surface chemistry, derivative metal-CLIESS curves for the three oxide surfaces of the metals are also presented.
Control of performance and stability of thin film diodes using chromium nitride contacts
Authors: Mc Garvey B. , Curran J. E. , Ford R. A. , Gale I. G. , Hewett J. , Theobald M.
Published: July 2002

We show that reactively sputtered chromium nitride thin films can be used as bottom contact layers in amorphous silicon rich silicon nitride thin film diodes. In common with most amorphous thin film devices the electrical characteristics of these diodes have been found to drift during use. The slope of the thin film diode current–voltage characteristic and its stability can be controlled through manipulation of the chromium nitride deposition parameters. Increasing the nitrogen partial pressure during deposition of chromium nitride causes the nitrogen content of the deposited layer to increase and the oxide growth on the surface of the chromium film to be reduced. This in turn reduces the tunnel barrier and trap density at the metal silicon nitride interface and steepens the current–voltage characteristic. The field through the device can then be reduced below a critical point where it does not affect stability.
Lithium depth profiling in thin electrochromic WO3 films
Authors: Krings L. H. M. , Tamminga Y. , van Berkum J. , Labohm F. , van Veen A. , Arnoldbik W. M.
Published: July 2002

Li profiles in sol-gel prepared electrochromic WO3 thin films have been characterized using three different techniques: neutron depth profiling (NDP), secondary ion mass spectrometry (SIMS), and elastic recoil detection (ERD). The results have been evaluated with respect to their concentration sensitivity and depth resolution. NDP and SIMS led to comparable results in terms of the shape of the profiles. The NDP results were quantified by using a calibration sample. NDP has the advantage that it is a quantitative nondestructive technique while SIMS has a very high sensitivity and depth resolution. Another advantage of NDP is that there is very little risk of neutron-induced Li migration during the measurement because of the very low energy of the incoming thermal neutrons. ERD was found to have a limited depth resolution, attributable to deterioration of the sample as a result of ion bombardment. However, the absolute amount of Li can be very accurately quantified with this technique.
Synthesis and characterization of In–Tl–Sb compounds grown by molecular beam epitaxy
Authors: Antonell M. J. , Abernathy C. R. , Acree W. A. , Berding M. A. , Sher A.
Published: July 2002

The growth of TlSb and InTlSb compounds has been investigated by molecular beam epitaxy. Tl and Sb were found to produce a two phase mixture of elemental Sb and a Tl rich Tl7Sb2 phase. This two phase mixture was the dominant phase produced throughout a variety of substrate temperatures which ranged from 200 to 425 °C. Varying the V/III ratio did not affect the phases produced but rather, only affected the amount of excess Sb found at the surface. The composition of the Tl7Sb2 phase was determined by electron microprobe analysis and confirmed with x-ray diffraction (XRD). XRD also indicated that the Tl7Sb2 phase exists in a complex multiatom per unit cell CsCl structure. Similar to the binary TlSb system, attempts to grow ternary InTlSb did not produce a single phase material. In this case a three phase mixture of InSb, elemental Sb, and Tl7Sb2 was produced throughout a range of growth conditions.
Controller design issues in the feedback control of radio frequency plasma processing reactors
Authors: Rauf Shahid , Kushner Mark J.
Published: July 2002

Feedback control has the potential for improving the reliability and performance of radio frequency (rf) plasma processing reactors for microelectronics etching, deposition, and cleaning applications. Implementation of real-time-control strategies has been slowed by lack of analytic or computational tools to design or optimize systems. To address this need, the virtual plasma equipment model (VPEM) has recently been developed for investigating issues related to feedback control in rf plasma processing equipment. The VPEM has been employed to investigate feedback control of inductively coupled plasma processing reactors for polysilicon etching and, in this article, results from these studies are used in a discussion of controller design, control strategies, and validation of the VPEM. It is demonstrated that response surface based controllers best operate in combination with corrections from an unstructured controller such as a proportional-integral derivative, which relaxes the inherent rigidity of the model-based controller. Since the behavior of plasma processing reactors generally changes over time due to, for example, coatings of the walls, it was found advantageous to make the controllers adaptive.
Study of the dc saddle-field discharge: Application to methane
Authors: Sagnes E. , Szurmak J. , Manage D. , Zukotynski S.
Published: July 2002

The electrical characteristics of a dc saddle-field discharge were studied for methane. The dc saddle-field configuration consists of a semitransparent anode sandwiched between two semitransparent cathodes, and an electrically isolated substrate holder plate positioned behind each of the cathodes. In comparison to the standard dc discharge, the dc saddle-field discharge has a lower breakdown voltage and a lower pressure at the minimum breakdown voltage. This is mainly due to the anode semitransparency which increases the ionization efficiency of the discharge. The electric field between the substrate holder and the semitransparent cathode can be adjusted. This is easily achieved by self-biasing through the adjustment of the substrate–cathode resistance. Increasing the substrate–cathode resistance increases the voltage breakdown at low pressure, and the pressure at the minimum breakdown voltage. When the discharge is used for thin film deposition in the abnormal glow regime, the density of ions reaching the substrate can be controlled independently of ion energy. This added degree of control over ion current density and ion energy should prove very useful in the growth of thin films.
Advances in broadband radio-frequency sensing for real-time control of plasma-based semiconductor processing
Authors: Garvin Craig , Grimard Dennis S. , Grizzle J. W.
Published: July 2002

A novel sensing system based on plasma impedance spectroscopy is compared to standard radio-frequency (rf) metrology. The new system uses an antenna in the glow discharge to excite the bulk plasma over a frequency range of 27.5 MHz to 2.75 GHz. The standard method of rf metrology is implemented by measuring 1000 points of the rf power signal using a digital oscilloscope sampling at 1 GHz. An experiment varying power, pressure, Ar and O2 is constructed. Using a subset of the data to regress a linear model, standard rf sensing reconstructs the experimental variables with a best average R2 of 0.49, whereas the novel sensing system results in a best average R2 of 0.876. A nearest neighbor algorithm is used which results in 70% correct identification of process conditions for standard rf sensing, and 99.5% correct identification of process conditions for the novel sensing system.
Semiconductor and thin film applications of a quadrupole mass spectrometer
Authors: Waits Robert K.
Published: July 2002

Commercial quadrupole mass spectrometer (QMS) residual gas analyzers became available in the late 1960s and have been popular in R&D laboratories, but have found limited use in semiconductor manufacturing. To sample at pressures above 10−5 Torr with ppm sensitivity or better (relative to the total process pressure), differential pumping is usually required. The newly available, small, high-pressure QMS sensors can operate as high as 10–20 mTorr without differential pumping, but provide somewhat lower mass resolution and partial pressure sensitivity than a standard QMS. Applications in semiconductor manufacturing include equipment monitoring, process monitoring, and effluent analysis. Equipment monitoring can include qualification after preventative maintenance, rate-of-rise tests, and leak identification and detection. Usually the burning question is, Why won’t the vacuum chamber pump down? Other uses that are not usually considered include the qualification of replaceable parts: sputter cathodes, electrodes, lamps, shields, etc. In process monitoring, the key question is, Is this process running normally? A manufacturing monitor can be useful simply by providing a comparison between a well-behaved high-yield process and a marginal or failing process. Examples are given for physical vapor deposition (sputtering) processes, chemical vapor deposition, and plasma etching. The effluent from chemical vapor deposition and plasma etch processes can be analyzed to measure the efficiency of process gas utilization or to monitor the efficacy of abatement methods used for the removal of global warming gases.
Density-functional cluster study of K adsorption on GaAs(110) surface
Authors: Panda M. , Ray A. K.
Published: July 2002

Local density approximation of the density-functional theory has been used to investigate K adsorption on a GaAs(110) surface. The surface is modeled by finite hydrogen-bonded clusters and two different formalisms (Slater–Vosko–Wilk–Nusair and Becke–Lee–Yang–Paar) for the exchange-correlation energies are used. All the clusters representing the GaAs(110) surface are found to be stable at the correlated levels of theory and the binding energy, in general, increases with the number of atoms in the cluster. The most stable cluster is found to be the three-layer cluster, Ga4As5H11 followed by Ga5As4H12 which were considered for the study of chemisorption. Of the three sites considered for K adsorption on an ideal surface, sites I and II, are found to be stable, whereas site III is unstable. Site II is the most favorable site for K adsorption with a chemisorption energy of 2.09 eV, which is comparable to the second-order many-body perturbation theory (MP2) value of 2.02 Å. The equilibrium distance of the adatom is found to be 2.35 A from the surface. For the optimized surfaces, site II is again found to be the most stable site. For both sites I and II the height of the adatom and chemisorption energy are higher compared to ideal surfaces, whereas the lattice constants decrease. Our previous MP2 results agree with the current results fairly well. As far as a charge transfer is concerned, there is a significant charge transfer to GaAs surface upon potassium adsorption. In general, gallium atoms lose charge and arsenic atoms gain charges. No significant change in a charge transfer is found in case of an optimized surface, in comparison to an ideal surface. The reductions in the highest occupied molecular orbital–lowest occupied molecular orbital gap upon potassium adsorption indicate the distinct possibilities of metallization.
Reactive ion etching of piezoelectric Pb(ZrxTi1−x)O3 in a SF6 plasma
Authors: Bale M. , Palmer R. E.
Published: July 2002

Reactive ion etching of Pb(ZrxTi1−x)O3 (PZT) is demonstrated using pure SF6 gas. The variation of the etch rate with radio frequency (rf) power and process pressure has been investigated and rates up to 160 nm min−1 were obtained. The dependence of the etch rate on the plasma parameters seems to indicate an ion-induced mechanism. Analysis of photoresist erosion in the process has been performed using an atomic force microscope. It has been found that roughening of the resist surface is accelerated when high rf powers and high process pressures are used. Based on these studies a recipe for PZT etching with a photoresist mask is discussed.
Low temperature polycrystalline silicon film formation with and without charged species in an electron cyclotron resonance SiH4/H2 plasma-enhanced chemical vapor deposition
Authors: Nozawa Ryoichi , Murata Kazuya , Ito Masafumi , Hori Masaru , Goto Toshio
Published: July 2002

We have developed a novel technique to deposit poly-Si films on insulating substrates in an electron cyclotron resonance (ECR) SiH4/H2 plasma-enhanced chemical vapor deposition (PECVD) and investigated the effect of reactive species on polycrystalline silicon (poly-Si) film formation at low substrate temperatures. The charged species incident on the substrate were successfully shut out by using permanent magnets set above the substrate in an ECR SiH4/H2 plasma. As a result, the films formed without charged species were found to have better crystallinity than those formed with charged species at a low substrate temperature of 150 °C. From results of the atomic force microscope, it was found that the surfaces of films formed without charged species were smoother than those of films formed with charged species at a substrate temperature of 300 °C. Therefore, it was clarified that the charged species deteriorated the crystallinity and the surface roughness while the neutral reactive species played an important role for improving them in the poly-Si film formation at low temperatures using the ECR SiH4/H2 PECVD method.