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Journal of Vacuum Science & Technology A: Vacuum, Surfaces, and Films

Issue 4 • Date Jul 1995

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Displaying Results 1 - 25 of 75
  • Adsorption and decomposition of diethylsilane and diethylgermane on Si(100): Surface reactions for an atomic layer epitaxial approach to column IV epitaxy

    Page(s): 1819 - 1825
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    The room‐temperature adsorption and desorption kinetics of diethylsilane (DES) and diethylgermane (DEG) on the Si(100)‐(2×1) surface were investigated under ultrahigh vacuum using temperature programmed desorption, high resolution electron energy loss spectroscopy, and Auger electron spectroscopy. DES and DEG adsorb at room temperature in a self‐limiting fashion, reaching saturation (0.4 and 0.3 monolayers, respectively), at exposures above 30 and 350 L, respectively. Temperature programmed desorption of the DES‐saturated and DEG‐saturated surfaces revealed only two species, hydrogen and ethylene, desorbing from either surface. In both systems, the hydrogen atoms desorbed primarily through the recombinative desorption of monohydride species, while the ethyl groups decomposed via β‐hydride elimination and subsequently desorbed as ethylene. The hydrogen desorption peak temperature was 794 K for the DES‐saturated surface and 788 K for the DEG‐saturated surface. The desorption peak temperature for ethylene was significantly lower in the DEG/Si(100) system (700 K) than in the DES/Si(100) system (730 K) because of a lower activation energy and higher pre‐exponential factor for β‐hydride elimination from DEG‐dosed Si(100). High resolution electron energy loss spectra of the DEG‐saturated surface support an adsorption mechanism in which the ethyl groups remain bonded to the incoming germanium atom throughout the adsorption process. © 1995 American Vacuum Society View full abstract»

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  • Matrix effect of bombardment‐induced Gibbsian segregation on Cu depletion at a CuXNi100-X subsurface

    Page(s): 1826 - 1830
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    A dynamic Monte Carlo program, including an improved bombardment‐induced Gibbsian segregation (BIGS) model was employed to study the matrix effect of BIGS and its influence on Cu depletion at the subsurface under 1 keV Ar ion bombardment of a Cu–Ni alloy. The calculated results show that not only at high fluence (the steady‐state) but also at low fluence the Cu subsurface depletion depends on its bulk composition. This is because the atomic jump rate W21 of Cu from the second layer to the first layer is correlated to Cu bulk composition at any fluence. We also found that the product of the nonsegregating species concentration in the first layer with the segregating species concentration in the second layer plays a more important role than other parameters in determining W21 under low current conditions. © 1995 American Vacuum Society View full abstract»

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  • GaN patterned film synthesis: Carbon depletion by hydrogen atoms produced from NH3 activated by electron impact

    Page(s): 1831 - 1836
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    The electron‐induced reaction of NH3 with a surface layer produced by adsorption of trimethylgallium on SiO2 at 108 K has been investigated by Auger electron spectroscopy. It is shown that atomic hydrogen, produced by electron‐induced dissociation of NH3, to form NHX and H, extracts the methyl groups from the layer leading to carbon removal from the GaN film which is formed. This process is nonthermal. A procedure for the synthesis of GaN is demonstrated and the layer‐by‐layer growth of a GaN film is shown. The method permits GaN to be deposited in a localized region which has been bombarded by the electron beam. © 1995 American Vacuum Society View full abstract»

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  • Sulfur layer formation on GaAs(100) by thermal and photochemical H2S dissociation

    Page(s): 1837 - 1846
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    We have studied the formation of sulfide layers on the GaAs(100) c(8×2) gallium rich surface through thermal and photoinduced (193 nm) decomposition of H2S. H2S was adsorbed on the sample at 90–95 K. The sulfide layer desorbs as Ga2S beginning at 740 K. For thermal sulfide layer formation, it was found that more sulfur could be built up on the surface by repeated cycles of H2S exposure at low temperature followed by heating to 600 K. Several such cycles gave a sulfide layer saturating at about one monolayer. With photoinduced dissociation of H2S thicker sulfide layers were produced, with no apparent saturation limit after several layers had been formed. Auger data suggests that As remains below the gallium sulfide layer up to at least 600 K. Sulfide layers were found to inhibit oxidation of the substrate by NO2, e.g., sulfide coverages of 1.5 to 2 layers reduced the amount of oxide (Ga2O) formed by 70%–85%. © 1995 American Vacuum Society View full abstract»

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  • Importance of the surface oxide layer in the reduction of outgassing from stainless steels

    Page(s): 1847 - 1852
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    Temperature dependence of outgassing was measured for differently surface treated type 316L stainless steel chambers in the temperature range of 25–330 °C. Based on the temperature dependence and outgassing characteristics of major outgassing species, the mechanism of outgassing from the stainless steel surface is discussed and the technique to produce an extremely low outgassing surface is indicated. The following are the important findings. (1) At temperatures below 250 °C, the outgassing species is predominantly hydrogen, which is released by diffusive outgassing from the bulk of the stainless steel. (2) At temperatures above 250 °C, the contribution from water and carbon monoxide outgassing becomes significant because of the enhanced surface reaction to generate these gas species. (3) The surface oxide layer formed by the oxidation in air is predominantly iron oxide and appears to serve as a more effective diffusion barrier for hydrogen outgassing compared with the mixed iron and chromium oxide layer formed on the fully degassed surface. (4) The oxidation reduces carbon contaminants on the surface which are a possible source of carbon containing outgassing species. © 1995 American Vacuum Society View full abstract»

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  • H2O adsorption kinetics on Si(111)7×7 and Si(111)7×7 modified by laser annealing

    Page(s): 1853 - 1860
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    The adsorption kinetics of H2O on Si(111)7×7 and Si(111)7×7 modified by laser annealing were studied using laser‐induced thermal desorption and temperature‐programmed desorption techniques at temperatures between 180 and 800 K. The laser‐annealed Si(111)7×7 surface displayed an enhanced initial reactive sticking coefficient for H2O compared with the unmodified Si(111)7×7 surface. At 180 K, the initial reactive sticking coefficient was S0=6.9×10-1 on laser‐annealed Si(111)7×7 compared with S0=1.9×10-2 on unmodified Si(111)7×7. This larger initial sticking coefficient is attributed to the creation of a more reactive surface structure formed by the laser annealing process. At higher oxygen coverages, the reactivity of the laser‐annealed surface changed and displayed much slower H2O adsorption rates that were similar to the kinetics on Si(111)7×7. The decreasing initial reactive sticking coefficient versus increasing surface temperature suggested a precursor‐mediated adsorption mechanism on both the Si(111)7×7 and laser‐annealed Si(111)7×7 surfaces. After long H2O exposures, the oxygen coverage saturated at θO≊0.35 monolayers on Si(111)7×7 for temperatures between 300 and 700 K. At higher surface temperatures, the saturation coverage increased prior to SiO desorption at temperatures above 900 K. This increase was attributed to the creation of additional dangling bond adsorption sites following H2 desorption at temperatures above 700 K. © 1995 American Vacuum Society View full abstract»

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  • Molecular dynamics simulations of fluorine molecules interacting with a Si{100}(2×1) surface at 1000 K

    Page(s): 1861 - 1866
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    Molecular dynamics simulations are performed to examine the adsorption of fluorine molecules, having incident translational kinetic energies between 0.0195 and 1.67 eV, on a clean Si{100}(2×1) surface at 1000 K. Results using the Stillinger and Weber potential energy function and the Weakliem, Wu, and Carter parameterization of this potential energy function are compared to each other and to experimental results. The initial sticking probability increases as the incident kinetic energy increases. As the incident kinetic energy increases, more difluorination and less monofluorination is observed as barriers to adsorption are overcome. For difluorination, a time delay between the two atom adsorption events is quantified. © 1995 American Vacuum Society View full abstract»

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  • Thermal‐ and electron‐stimulated chemistry of a cyclotriphosphazene lubricant on a magnetic disk with a hard carbon overcoat

    Page(s): 1867 - 1871
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    The thermal and electron induced decomposition of a bis(4‐fluorophenoxy)‐tetrakis(3‐tri‐ fluoromethylphenoxy)cyclotriphosphazene(code‐named X‐1P) lubricant on a magnetic disk are studied by temperature‐programmed desorption spectroscopy, electron‐stimulated desorption, and Auger electron spectroscopy. X‐1P decomposes on the surface with a threshold temperature for dissociation at ∼570 K, ∼100 K lower than the thermal decomposition temperature of fluid molecules. Electron impact also damages X‐1P molecules. Depending on the electron energies, dissociative ionization and dissociative electron attachment are both likely mechanisms for the electron‐induced dissociation. The cross section for the dissociative electron attachment by 3 eV electrons is roughly 9×10-18 cm2. For both 8 and 25 eV electrons the cross sections are larger. © 1995 American Vacuum Society View full abstract»

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  • Modeling of water outgassing from metal surfaces (III)

    Page(s): 1872 - 1878
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    A model of water adsorption on metal oxide layers and water outgassing from metal surfaces has been developed. The oxide layer is assumed to have porous structure and a pore length (l) distribution of 1/l2. Numerical evaluation shows that the quantity of water adsorbed is logarithmic with time within a certain time range as experimentally observed. The outgassing rate from surfaces with adsorbed water distributed uniformly on the inner surfaces of individual pores is shown analytically to be inversely proportional to time. This result is consistent with frequently observed pumpdown curves. © 1995 American Vacuum Society   View full abstract»

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  • Synchrotron radiation induced reactions of a condensed layer of silicon alkoxide on Si

    Page(s): 1879 - 1884
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    The authors have investigated the synchrotron radiation (SR) induced chemical reactions of condensed layers of silicon alkoxides, tetramethoxysilane Si(OCH3)4 and tetraethoxysilane Si(OC2H5)4, adsorbed on a Si substrate at 80 K. Photon stimulated desorption measurements show that irradiation with SR in the vacuum‐ultraviolet region induces the desorption of hydrogen, hydrocarbon, and carbon monoxide from the condensed layer, indicating that the radiation decomposes the alkoxyl group in the silicon alkoxides. Infrared absorption and photoemission data demonstrate that Si‐containing fragments produced by the decomposition of silicon alkoxide molecules are polymerized to form silicon oxide. The experimental results show the possibility of deposition silicon oxide film from silicon alkoxides using intense SR in the VUV region. © 1995 American Vacuum Society View full abstract»

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  • Photodecomposition of poly(methylmethacrylate) thin films by monochromatic soft x‐ray radiation

    Page(s): 1885 - 1892
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    The photofragmentation reaction of poly(methylmethacrylate) (PMMA) by soft x‐ray irradiation was investigated by measuring the yield of released neutral fragments and the changes in the absorption spectra in the carbon and oxygen K‐edge regions. Films of 0.4–1.0 μm thicknesses were irradiated with various doses of monochromatic 300, 400, and 600 eV soft x‐rays. The effect of irradiation was monitored by the yield of the fragment products released from PMMA, as a function of dose. The fragments of mass 15, 28, 29, 31, 44, and 60 amu, corresponding to CH3, CO, CHO, CH3O, CO2, and C2H4O2, were chosen for monitoring this irradiation dose dependence. Each fragment showed a distinct response to irradiation. The etching rates, represented by the yield of the released fragments, are dependent on the original thickness of the sample and gradually decrease with dose. From the analysis of the thickness and dose dependencies, we concluded that secondary reactions in the bulk play an important role in the desorption mechanism. The absorption spectrum after irradiation indicates the abstraction of the ester group and the formation of double bonds. All the observations are in agreement with a degradation mechanism involving the ester group abstraction followed by main chain scission and, at large doses, crosslinking and the formation of a protecting overlayer of chemical nature similar to poly(butadiene). © 1995 American Vacuum Society View full abstract»

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  • X‐ray photoelectron spectroscopy and transmission electron microscopy studies of the NiAl/Al2O3 interfacial chemical compatibility

    Page(s): 1893 - 1900
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    β‐NiAl thin films were prepared by physical vapor deposition (PVD) either on thin PVD Al2O3 films on Si substrates or on sapphire single crystals. These samples were characterized by x‐ray diffraction and electron spectroscopies [Auger electron spectroscopy and x‐ray photoelectron spectroscopy (XPS)]. Crystalline films were obtained after deposition at room temperature. XPS depth profiles and transmission electron microscopy cross sections show that the NiAl–Al2O3 interface is sharp (1 nm) and that NiAl oxidation occurs. Ni remains chemically unaffected by the presence of oxygen while the formation of Al3+ compounds is discussed. Within the film Al and Ni appear in a single chemical environment characterized by binding energies close to those of pure intermetallic compounds. Annealing of these wafers at 600 °C induces surface oxidation and, particularly, the formation of an Al2O3 protective layer. © 1995 American Vacuum Society   View full abstract»

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  • Optical emission study of reaction mechanisms in the deposition of nitrogen‐containing amorphous hydrogenated carbon films

    Page(s): 1901 - 1906
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    The reaction mechanisms taking place in a film‐forming radio frequency discharge of a mixture of acetylene, nitrogen, and helium have been investigated using optical emission spectroscopy. A transient actinometric method was employed, based on the interruption of the flow of one of the feed gases (either C2H2 or N2), and the subsequent observation of the time‐dependent changes in the discharge environment, specifically of the concentrations of CH and CN species, two possible precursors of film formation. Both N2 and C2H2 affect the CH and CN concentrations. Nitrogen strongly enhances the rate of formation of CH, very probably via gas phase reactions between atomic nitrogen and C2H2 or other species containing carbon and hydrogen. On the other hand, the relatively high CH concentration observed in discharges without nitrogen is taken to indicate that fragmentation of the C2H2 molecules by the discharge is another important mechanism of formation of the CH species. For the CN species, gas phase reactions between carbon‐ and nitrogen‐containing species are expected to contribute to its appearance. However, a relatively high CN concentration could be detected even in discharges without C2H2 in the gas feed, so long as a nitrogen‐containing polymer film was previously formed on the inner wall of the chamber. This is taken as evidence that interactions between the plasma and the polymer surface play an important role in the generation of the CN species. Further measurements of the CN concentration in a plasma of 100% He, produced in the chamber immediately after the formation of a nitrogen‐containing polymer film, indicate that a possible reaction mechanism for the formation of the CN species is the detachment of nitrile groups (—C≡N) from the polymer surface upon cleavage of the- - carbon bond linking the nitrile terminations to the polymer chains. © 1995 American Vacuum Society View full abstract»

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  • A study of the interaction between thermally deposited aluminum films and fluoropolymer substrates

    Page(s): 1907 - 1912
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    Aluminum was thermally deposited onto fluoropolymer substrates. The effects of interfacial reaction of aluminum with several fluoropolymeric substrates were investigated. These included PFA (poly[tetrafluoroethylene‐co‐perfluoro(alkoxy vinyl ether)]), FEP (poly(tetrafluoroethylene‐co‐hexa‐ fluoropropylene), and hydroxylated FEP (m‐FEP). The hydroxyl modification was prepared by a previously developed radio frequency glow discharge (RFGD) method. X‐ray photoelectron spectroscopy (XPS) studies of thin (∼30 Å) Al deposited samples showed the formation of new fluorine‐containing species, due to fluorine diffusion into the Al overlayers. Auger and XPS depth profiles of samples with thick (∼200 Å) Al overlayers also suggested the diffusion of fluorine and the formation of Al fluorides at the interface. The RFGD modification process prior to the Al deposition was performed to investigate potential adhesion of Al to the substrates. This is envisioned as a reaction between Al and RFGD introduced oxygen. The resulting Al/oxide interface limits the diffusion of fluorine. © 1995 American Vacuum Society View full abstract»

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  • Surface dielectric function of CdTe(110) obtained by polarized surface differential reflectivity data

    Page(s): 1913 - 1916
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    We present a determination of the complex surface dielectric function (SDF) of CdTe(110) obtained by using polarized surface differential reflectivity (SDR) data. The analysis of SDR data is done in the framework of a macroscopic three‐layer model in which the media involved (vacuum, surface, and substrate) are assumed to have definite anisotropic functions. A relation between SDR data and the complex SDF is obtained under the assumption that the oxide layer is nonabsorbing in the range explored. From the experimental data SDF has been computed for light electric vector along [11¯0] and [001] directions, i.e., parallel and perpendicular to the natural chains of the unreconstructed (110) surface. In the energy range below 3.3 eV the imaginary part of SDF (ϵs) and SDR data are very similar while above 3.3 eV they differ markedly because of the effect of bulk contribution. Three mainly isotropic structures are clearly visible in the deconvolved ϵ‘ spectra at the following photon energies: 2.7, 3.3, and 3.7 eV. Such structures are interpreted in terms of optical transitions between surface state bands as derived from direct and inverse photoemission. The transition at 2.7 eV is assigned at the Γ point in the surface Brillouin zone, the one at 3.3 eV at the Γ and X while the one at 3.7 eV at the X and X’. The effective number of electrons per atom participating in the optical transitions is calculated for energies up to 4.0 eV resulting in slightly more than 0.5. © 1995 American Vacuum Society View full abstract»

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  • Characterization of substrate temperature and damage in diamond growth plasmas by multichannel spectroellipsometry

    Page(s): 1917 - 1923
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    The growth of diamond thin films in enhanced chemical vapor deposition (CVD) processes requires high substrate temperatures (400–1000 °C) and gas pressures (1 Torr to 1 atm), as well as high‐power excitation of the gas source (e.g., 1 kW microwave plasma). Thus determining the substrate temperature in this severe environment is a challenge. The issue is a critical one since substrate temperature is a key parameter for understanding and optimizing diamond film growth. We have developed and utilized methods for precise (∼±5 °C) Si substrate temperature calibration based on rapid‐scanning spectroscopic ellipsometry. In this approach the E1 critical point energy in Si is used to deduce the temperature of the top ∼200 Å of the substrate. In addition, the broadening parameter associated with the critical point transitions can provide information on near‐surface plasma damage. As an application of the temperature calibration, we have measured the kinetics of diamond film growth by the microwave plasma‐enhanced CVD process. © 1995 American Vacuum Society   View full abstract»

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  • Formation of secondary phases in evaporated CuInS2 thin films: A surface analytical study

    Page(s): 1924 - 1929
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    The surface composition of coevaporated Cu‐In‐S films for photovoltaic applications has been investigated by x‐ray and ultraviolet photoelectron spectroscopy. A comparison of the front and back surface, i.e., the interface between the Cu–In–S film and the Mo back contact, is made for films with different stoichiometries. We find that In‐rich films are covered at both surfaces by an In‐rich second phase which has the cation ratio of CuIn3S5. The front surface of Cu‐rich films shows a segregation of CuS that is not found at the back surface. The formation of binary and ternary second phases in nonstoichiometric CuInS2 films and their implications on the growth mechanism are discussed. © 1995 American Vacuum Society View full abstract»

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  • In situ diagnostic for etch uniformity

    Page(s): 1930 - 1934
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    Spatially resolved optical imaging experiments were performed in a parallel plate reactor known as the Gaseous Electronics Conference Reference Cell. They consisted of recording the optical emission discharges at various pressures and powers for 1024 points across the electrode at a height of 7 mm above the bottom powered electrode for the argon neutral line at 750.4 nm. Previously, our experiments [Pender et al., J. Appl. Phys. 74, 3590 (1993)] have shown that argon plasmas are nonuniform, specifically in the shape of annular rings with large intensities originating over the edges of the electrodes. In this work, we examined in situ the plasma uniformity as a single 3 inch silicon wafer with a simple test pattern was etched in a 30 sccm CF4 / 15 sccm Ar plasma environment. The results indicate that the plasma emissivity and etch depth are related. In the pressure range of 50 to 250 mTorr, the emissivity and the etch depth increase linearly with power. For a constant power, both emissivity and etch depth can be fitted to a quadratic polynomial with pressure as the dependent variable. © 1995 American Vacuum Society View full abstract»

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  • Mass spectrometric studies of remote helium plasma dissociation of silane

    Page(s): 1935 - 1940
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    Molecular beam sampling mass spectrometry combined with low‐energy electron impact ionization has been used to detect and quantitate the stable molecules, ions, and silicon radicals created in the interaction of silane with a helium afterglow produced by a microwave discharge in pure helium. The observations are used to understand the afterglow chemistry and to elucidate some important features of the film growth mechanism in the remote plasma‐enhanced chemical vapor deposition of silicon films. © 1995 American Vacuum Society View full abstract»

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  • In situ production of very low density microporous polymeric foams

    Page(s): 1941 - 1944
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    Small, open‐ended, parylene microcylinders of 400 μm diameter, 700 μm length, and 10 μm wall thickness were filled with a solution of a polyfunctional monomer of low concentration. The solution was polymerised in situ with ultraviolet light to produce a gel. Precipitation of these gels in a nonsolvent and subsequent drying by means of a critical point drying apparatus produced microcylinders filled with a low density foam. Radiographic examination of the foam gave a density of the order of 2 mg cm-3, and scanning electron microscopy micrographs showed cell sizes of the order of 1 μm. No shrinkage of the foam was observed with cylinders of the dimensions given, but with larger cylinders of diameter and length of the order of 1000 μm, some axial shrinkage was observed which resulted in cylinders with slightly concave ends (of the order of 20 μm). © 1995 American Vacuum Society View full abstract»

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  • Excimer laser ablation mass spectrometry of inorganic solids: Chemical, matrix, and sampling effects on polyatomic ion yields

    Page(s): 1945 - 1958
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    Positive ions formed directly by excimer laser ablation in vacuum of several lanthanide (Ln) and transition metal solid materials—including Ln2O3, Ln2S3, LnF3, Ta2O5, ZrO2, TiO, and TiO2—were identified by time‐of‐flight mass spectrometry. Variations in ion yields were investigated as a function of the composition of the precursor material, laser irradiance, and ion sampling delay after ablation. The compositions of the observed polyatomic ions reflected the distinctive chemistries of the metal constituents, but the ion yield distributions were not generally indicative of the particular chemical/valence constitution of the target material. For example, the yield of CeO+ relative to Ce+ was substantially greater from the trivalent cerium oxide, Ce2(WO4)3(s), than from tetravalent CeO2(s). Observed ion distributions apparently reflected the chemical composition of the ablation plume and the degree of gas‐phase recombination therein. The observed abundances of polyatomic ions were found to correlate well with their estimated bond strengths. Further obscuring the chemical composition of the progenitor, minor changes in ablation, and sampling parameters—especially irradiance and sampling delay—were often manifested as significant variations in relative ion intensities. © 1995 American Vacuum Society View full abstract»

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  • Quantitative analysis of borophosphosilicate glass films on silicon using infrared external reflection–absorption spectroscopy

    Page(s): 1959 - 1966
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    Borophosphosilicate glass (BPSG) dielectric thin films deposited on both bare and oxide‐coated undoped silicon wafers have been analyzed using infrared external reflection–absorption spectroscopy (IRRAS). The partial least‐squares (PLS1) algorithm was used to simultaneously determine boron content, phosphorous content, and film thickness, with standard errors of prediction of 0.08 wt %, 0.11 wt %, and 24 Å, respectively, in the BPSG films on oxide‐coated wafers (similar results were obtained with the bare wafer BPSG sample set). These results were statistically equivalent to the precisions of the reference methods used to determine each BPSG property, indicating that the precisions of the PLS1 models were limited by the precisions of the reference methods. IRRAS reproducibility and repeatability results verified that the method can be more precise than the reference methods. The reproducibility results were derived from the standard deviation of ten PLS1 predictions of ten IRRAS spectra that were obtained from a single BPSG sample that was moved in and out of the sample chamber between each spectral measurement. The repeatability results were obtained similarly, but the sample was not moved between acquiring the ten spectra. The precision of the IRRAS method from the repeatability data was found to be ±0.006 wt % B, ±0.011 wt % P, and ±4 Å film thickness. The reproducibility results were generally less precise than the repeatability results. Studies done as a function of spectral resolution and signal averaging showed that very rapid IRRAS measurements could be made (up to 2 Hz) with high PLS1 prediction precision for the three calibrated BPSG properties. The results show that the IRRAS technique has great potential for rapid, at‐line quality control monitoring of BPSG thin films on undoped silicon wafers. © 1995 American Vacuum Society View full abstract»

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  • Photoemission studies of K‐promoted nitridation and oxidation of the InP(100) surface using synchrotron radiation

    Page(s): 1967 - 1969
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    The effect of a potassium overlayer on nitridation and oxidation of the InP(100) surface is investigated by core‐level and valence‐band photoemission spectroscopy using synchrotron radiation. In comparison with the K‐promoted nitridation of the InP(110) surface obtained by cleavage in situ, we found that the promotive effect for the InP(100) surface cleaned by ions bombardment is much stronger and that the nitridation products consist of two kinds of complexes: InPNx and InPNx+y. The results confirmed that surface defects play an important part in the promotive effect. Furthermore, in contrast with K‐promoted oxidation of InP(100) where bonding is observed between indium and oxygen, indium atoms did not react directly with nitrogen atoms during the K‐promoted nitridation of InP(100). © 1995 American Vacuum Society View full abstract»

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  • Competitive halogenation of silicon surfaces in HBr/Cl2 plasmas studied with x‐ray photoelectron spectroscopy and in situ, real‐time, pulsed laser‐induced thermal desorption

    Page(s): 1970 - 1976
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    Using x‐ray photoelectron spectroscopy (XPS) and real‐time, laser‐induced thermal desorption–laser‐induced fluorescence (LD–LIF), we have determined the coverage of Br and Cl on Si(100) surfaces that are etched in mixed HBr/Cl2 plasmas. Halogen coverages measured by XPS after etching are directly proportional to the fraction of the respective halogen in the feed gas. LD–LIF was detected from SiCl(g) and SiBr(g) products with intensities that are a semiquantitative measure of instantaneous Cl and Br coverages. Saturated coverages during etching in Cl2 and HBr plasmas are 1.0×1015 Cl/cm2 and 6.0×1014 Br/cm2, respectively. Etch rates at these two extremes are 2170 and 1330 Å/min, and therefore are proportional to the respective halogen coverages. It therefore appears that the rate of formation of volatile Si–halides, stimulated by ion bombardment, is lower for HBr mainly because less halogen is available on the surface at saturated coverage. Langmuir probe measurements indicate that the ion flux is 17% lower in pure HBr plasmas, compared with Cl2 plasmas at the same power. The plasma potential, direct current bias voltage, and hence ion energy were nearly constant, however, over the range of gas mixtures. The slightly different ion fluxes suggest that the ion bombardment‐stimulated process, although similar for Cl2 and HBr plasmas, is actually slightly more efficient on a per halogen basis for Br versus Cl. Positive photoresist surfaces that were also exposed to the plasma differ from Si in that less Br adsorbs on the surface both in pure HBr and mixed HBr/Cl2 plasmas. Apparently the lower reactivity of photoresist with Br (compared with Cl) is at least partly responsible for the widely observed slower etch rate of photoresist in HBr plasmas, and hence enhanced - - selectivity when etching Si. © 1995 American Vacuum Society View full abstract»

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  • A morphology study of the thermal oxidation of rough silicon surfaces

    Page(s): 1977 - 1983
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    A report on the thermal oxidation of rough silicon surfaces as measured by spectroscopic immersion ellipsometry and atomic force microscopy (AFM) is given. It was found that, as the thickness of the thermally grown SiO2 overlayer increases, the average radius of the crystalline silicon protrusions (roughness) at the interface decreases. A fractal analysis shows that a simpler surface results from oxidation. The frequency spectra of AFM images are concordant with the fractal analysis and shows that small features oxidize faster. This is in agreement with the predictions of the Kelvin equation that small features are more reactive. © 1995 American Vacuum Society View full abstract»

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The Journal of Vacuum Science and Technology A is devoted to reports of original research, review articles, and Critical Review articles.

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G. Lucovsky
North Carolina State University