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

Issue 1 • Date Jan 2003

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Displaying Results 1 - 25 of 48
  • Issue Cover

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  • Issue Table of Contents

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  • Growth of highly c-axis textured AlN films on Mo electrodes for film bulk acoustic wave resonators

    Page(s): 1 - 5
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    Highly c-axis textured AlN films on Mo could be obtained using the structural modification of Mo thin films by the reactive rf magnetron sputtering at a low temperature. The correlation of structural properties of Mo and the degree of c-axis texturing in AlN films was studied as a function of sputtering pressure during the dc sputter deposition of Mo. The microstructure and residual stress of Mo films were found to be very dependent on the sputtering pressure. As the pressure decreases and the stress changes from tension to compression, the surface morphology and roughness of Mo films became gradually denser and smoother. It is found that the controlled smooth surface of Mo electrodes plays a key role in the growth of highly c-axis textured AlN films deposited onto them. A full width at half maximum of the x-ray rocking curve of the best AlN film on the surface-controlled Mo electrode was 2.30°. Film bulk acoustic wave resonators with an effective coupling coefficient of 5.6% could be achieved using the improved AlN films. © 2003 American Vacuum Society. View full abstract»

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  • Tribological properties of nitrogen-containing amorphous carbon film produced by dc plasma chemical vapor deposition

    Page(s): 6 - 13
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    The nitrogen-contained amorphous carbon (a-C:N) films were deposited in a dc plasma chemical vapor deposition system with different substrate bias voltages. The structural, mechanical, and tribological properties of the a-C:N films were investigated. The influence of the bias voltage on the tribological behaviors of the a-C:N films was evaluated under various environments (dry air, O2, N2, and vacuum) using a ball-on-disk friction tester. It showed that the sp3 C and hydrogen concentration of the a-C:N films decreases with increasing the bias voltage. However, the nitrogen concentration increases with increasing the bias voltage. As a result, the hardness and internal stress decrease and the critical load for fracturing increases as the substrate bias increases. For the tribological properties of the a-C:N films, the friction coefficient of the films slightly decreases in the environments of N2, O2, or dry air, but increases slightly in the vacuum environment by increasing the bias voltage. It indicates that the incorporated nitrogen in the a-C:N films would decrease the friction coefficient of the films in N2 or O2 environments, but slightly increases the friction coefficient of the films in a vacuum. The excellent wear resistance of the a-C:N films, in the level of 10-9–10-8mm3/Nm, can be observed in N2,<- - /formula> vacuum, and dry air environments. In addition, the effect of the bias voltage on the wear rate of the a-C:N films becomes less obvious by nitrogen incorporation. So, we suggest the incorporated nitrogen, which bonded to carbon and restrained the increase of the fraction of sp2 CC, would restrain the wear of the a-C:N films in different environments, especially in dry air.© 2003 American Vacuum Society. View full abstract»

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  • Changes in photoluminescence of SrS:Ce induced by synchrotron radiation

    Page(s): 14 - 18
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    The effect of x-ray irradiation on the photoluminescence (PL) of SrS:Ce was investigated using synchrotron radiation. SrS films deposited by molecular-beam epitaxy were irradiated by x-ray pulses having an energy of 8.0 keV or 14.5 keV for duration of 17 to 50 ms. PL measurements showed that both the enhancement and deterioration of PL characteristics could be achieved by choosing a combination of shot numbers of x-ray pulses and intervals between pulses. It was found that the enhancement of PL intensity was more remarkable for x-rays of 14.5 keV than for ones of 8.0 keV. The effects of this x-ray irradiation were discussed in terms of x-ray-induced nonthermal atomic movements and thermal annealing by the heat resulting from x-ray absorption. ©2003 American Vacuum Society. View full abstract»

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  • Ionization-assisted deposition of strontium electron injection layer for organic light emitting diode

    Page(s): 19 - 24
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    Strontium (Sr) thin films were prepared by the ionization-assisted deposition (IAD) method for the electron injection layer between tris(8-hydroxyquinolino)aluminum (Alq3) electron transport layer and Al cathode of the organic light emitting diode (LED). The Sr films, around 10 nm in thickness, deposited by IAD were effective in improving the device characteristics such as the luminescence efficiency and, especially, the device lifetime. The best LED characteristics were obtained at the ion acceleration voltage Va of around 800 V. It was found that the deposition condition influences the morphological and chemical properties of the film. The IAD Sr had smaller interdiffusion into Alq3 compared to the standard evaporated one. The film deposited by IAD at higher Va was metallic, and had a densely packed uniform microstructure, while the ones deposited at low Va or by standard evaporation assumed oxide nature, having considerable amount of voids. It is expected that the IAD can optimize the LED characteristics through the control of Sr film properties. © 2003 American Vacuum Society. View full abstract»

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  • Interaction of hydrogen-terminated Si(100), (110), and (111) surfaces with hydrogen plasma investigated by in situ real-time infrared absorption spectroscopy

    Page(s): 25 - 31
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    We have used infrared absorption spectroscopy (IRAS) in the multiple internal reflection (MIR) geometry to investigate the interaction of hydrogen-terminated Si(100), (110), and (111) surfaces with hydrogen plasma at room temperature. We have measured infrared absorption spectra in the Si–H stretching vibration region of the hydrogen-terminated surfaces during H-plasma treatment. IRAS data show that at initial stages of H-plasma treatment, surface hydride species (SiHx,x=1–3) are removed from the surface. A long-term H-plasma treatment of Si(100) and (110) surfaces reproduces monohydride species and creates hydrogen-terminated Si vacancies (VHx) at subsurface regions, i.e., near the surface. On Si(111), no hydride species are reproduced even after a long-term H-plasma treatment. We suggest that monohydride is rather stable against attack of hydrogen radicals as compared to higher hydride species, SiH2 and SiH3. We find that formation of VHx depends on the crystallographic orientation of the Si surface: VHx formation is more favored on Si(110) than on Si(100), and no VHx form on Si(111). © 2003 American Vacuum Society. View full abstract»

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  • Particle-size dependence of alloy phase formation in isolated particles in the In–Sn system

    Page(s): 32 - 36
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    Particle-size dependence of alloy phase formation in isolated particles has been studied by transmission electron microscopy at room temperature, using alloy particles in the In–Sn binary system. In approximately 16-nm-sized particles, essentially the same alloy phases as those in bulk materials formed. Namely, at compositions near the eutectic composition, a mixture of two crystalline phases formed. However, when the size of particles was decreased down to approximately 10 nm in diameter, a liquid phase, which is not an equilibrium phase in bulk materials at room temperature, formed. The formation of a liquid phase is ascribed to the large suppression of the eutectic temperature associated with size reduction. © 2003 American Vacuum Society. View full abstract»

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  • Time-resolved investigation of the surface chemical modification of poly(ethylene naphthalate) by nitrogen plasma treatment

    Page(s): 37 - 46
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    A low rf nitrogen plasma source was used to treat poly(ethylene-2, 6-naphthalate) web material. Nitrogen uptake, the N 1s centroid, the N 1s peak width, rearrangement of the ester (from the O 1s spectrum), and oxygen level were measured using x-ray photoelectron spectroscopy as a function of treatment time at several treatment conditions. The observed changes in surface chemistry with treatment time are roughly consistent with a dose response having a linear regime at low doses and a saturation regime at high doses (where dose is power/width/web speed). Hence, to a first approximation, the flux densities (to the web) of relevant species scale with power. As the dose increases, the distribution of nitrogen groups formed broadens and shifts toward higher N 1s binding energy, suggesting that a larger fraction of the nitrogen-containing species are amines at low doses and amides at higher doses. The breadth of the distribution of nitrogen-containing species appears to be strongly correlated with the amount of nitrogen incorporated in the PEN surface. A surface sites model was applied to the measured nitrogen uptake as a function of treatment time. Phenomenological nitrogen incorporation and loss terms were determined in the context of this model. Both terms increase with treatment power and treatment pressure. The ratio, however, varies to a much smaller degree as a function of process conditions, with high powers and pressures giving the highest ratio. Further elucidation of the incorporation and loss processes should be possible with plasma diagnostic data related to species concentrations. © 2003 American Vacuum Society. View full abstract»

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  • Surface analysis by secondary-ion mass spectroscopy during etching with gas-cluster ion beam

    Page(s): 47 - 58
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    Primary ions from a gas-cluster ion beam (GCIB) are used to investigate metal and silicon surfaces by mass spectroscopy of the secondary ions, as well as to study the nature of cluster-ion interactions with surfaces. The GCIB consists of condensed nanodroplets of either argon, oxygen, or nitrogen gas from which the singly charged cluster ions are generated. The effects of beam acceleration (∼10–25 kV) and flux (ion current density ∼50–500 nA/cm2) are reported. Secondary-ion analysis is done with a quadrupole mass spectrometer in an ultrahigh vacuum chamber. Argon GCIB incident upon metal surfaces of Al, Au, Cu, Ta, and NiFe all result in strong emission of small metal-cluster ions, metal-argon excimers and various other compound ions. Argon GCIB incident upon Al films and Si wafer surfaces generate strong fluxes of small cluster ions (i.e., Aln+ and Sin+ for n=2–10) which decay in emission intensity (with increasing n) approximately by a power law with exponent ∼2.8 and ∼1.0, respectively. Oxygen GCIB upon Al and Si generate strong fluxes of AlnOm+ and SinOm+ compound ions, respectively, with n=1–5 and m≥n. Nitrogen GCIB upon Al and Si generate fluxes of nitride compounds. The beam conditions utilized are similar to those known to significantly reduce fine-scale surface roughness (i.e., ion smoothen) and concurrently etch at a rate of ∼1 nm/min. Native oxide films on Al, Cu, Ta, and NiFe metals are depth profiled under various GCIB conditions, thus characterizing mechanisms of cluster–ion interaction with metals. The native surface of a Ta fi- - lm is investigated in some detail. The TaO+ and C+ ion emissions show a two-part decay and growth, respectively, with accumulating argon-GCIB fluence. These are well fit with exponential functions and the characteristic rates are found to depend linearly on GCIB flux and acceleration. The oxidized surfaces exhibit a minimum threshold in acceleration of ∼7 kV which corresponds to only ∼3 eV per incident argon atom. After the surface oxide is removed by the GCIB, no threshold is observed. The native oxides and Fe/Ni, ratio are depth profiled for a permalloy (NiFe) film showing resolution of the thin oxide layer differentiated from the somewhat thicker metal layer that is enriched with Fe. © 2003 American Vacuum Society. View full abstract»

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  • Characterization of damage in reactive ion etched ZnTe

    Page(s): 59 - 61
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    Reactive ion etching of ZnTe has been carried out at various applied rf powers and CH4/H2 concentrations. The damage induced during dry etching is characterized by low-temperature photominescence (PL) measurements. It is observed that the PL intensity of the free excitons decreases with increasing applied rf power, which is ascribed to the increase of the surface damage by ion bombardment. The amount of the surface damage can be reduced by adding more CH4 in the gas mixture due to the effect of chemical etching. © 2003 American Vacuum Society. View full abstract»

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  • Texture development of CeO2 thin films deposited by ion beam assisted deposition

    Page(s): 62 - 65
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    CeO2 thin films were prepared on amorphous quartz glass substrates by the ion beam assisted deposition (IBAD) technique at room temperature. In order to control both the in-plane and out-of-plane texture of the films, a special geometrical arrangement of the ion sources, the target, and the substrate was used. A new concept, considering the role of reflected particles from the target, which we call self-IBAD, was introduced. The structural properties of the CeO2 films were investigated by x-ray diffraction. Good biaxially textured films were obtained with out-of-plane mosaic spreads of 3.0° and in-plane alignment of 10.8°. © 2003 American Vacuum Society. View full abstract»

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  • Deposition, microstructure, and properties of nanocrystalline Ti(C,O,N) coatings

    Page(s): 66 - 75
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    Chemical vapor deposition of Ti(C,N) coatings from the TiCl4CH3CN–N2H2 system on cemented carbide substrates was studied. The morphology and grain size of the coatings were modified using carbon monoxide (CO). Transmission electron microscopy confirmed that grain refinement of the Ti(C,N) coatings could be obtained by means of CO doping and nanocrystalline coatings were obtained at CO levels exceeding 6%. CO doping resulted in the incorporation of oxygen in the structure, but no segregation of oxygen to grain boundaries was observed. The coatings appeared to be of homogeneous composition even at the highest CO levels. Both improved coating hardness and surface quality were obtained with decreasing grain size. However, the coatings exhibited clearly lower crater wear resistance in the nanograined region. This was explained by an increased tendency for grain-boundary sliding in the nanocrystalline coatings leading to more pronounced plastic deformation. © 2003 American Vacuum Society. View full abstract»

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  • Structure and properties of anatase TiO2 thin films made by reactive electron beam evaporation

    Page(s): 76 - 83
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    Thin, smooth anatase TiO2 films with a thickness of about 100 nm have been made by reactive electron beam evaporation of reduced TiO2. The influence of the oxygen partial pressure is investigated in the range from 2×10-5 to 2×10-3mbar, and the influence of the substrate temperature is studied in the range from 150 to 300 °C. The structure and properties of the films are investigated with x-ray diffraction, transmission electron microscopy, Raman spectroscopy, impedance spectroscopy, and capacitance–voltage profiling. Depending on the type of substrate, two different morphologies are obtained. On titanium-coated fused silica, grains with a preferred (004) orientation and sizes ranging from 40 to 60 nm in directions parallel to the surface, and from 20 to 125 nm perpendicular to the surface are found. On fused silica, a monolayer of randomly oriented single crystal disks with lateral sizes between 0.2 and 2 μm is found. These films may provide a convenient alternative to single crystals in fundamental studies on the properties of anatase TiO2. © 2003 American Vacuum Society. View full abstract»

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  • Effect of gas pressure on reactive pulsed laser ablation of a silicon target

    Page(s): 84 - 86
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    Hydrogenated silicon and silicon nitride films are synthesized by reactive pulsed laser ablation of a silicon target in hydrogen or nitrogen gas. A correlation between gas pressure and morphology or bonding configuration of deposits was investigated. With increasing gas pressure, the surface morphology abruptly changed from film to an assembly of nanoparticles at 30 Pa in hydrogen and 20 Pa in nitrogen gas. The content of Si–H and Si–N bonds in the deposits was maximized at 50 and 5 Pa in hydrogen and nitrogen gas, respectively. The influence of gas type on nanoparticle formation and reaction between silicon and ambient gas are discussed. © 2003 American Vacuum Society. View full abstract»

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  • Monte Carlo simulation method for etching of deep trenches in Si by a SF6/O2 plasma mixture

    Page(s): 87 - 95
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    A Monte Carlo method which determines the evolution of a Si etched surface under an SF6/O2 plasma mixture in a high-density low-pressure reactor is presented. The approach consists of a two-dimensional discretization of the initial target (mask and substrate) in a series of same size cells, to determine the substrate time–space evolution according to plasma-surface interactions. One ion transport model through the sheath is introduced to determine the angular and energetic distribution function of ions near the substrate surface. Spontaneous chemical etching by SiF4 desorption and preferential sputtering are studied. Etch profile simulations were performed to interpret the role of certain parameters such as mask geometry and F sticking probability. The simulation results show that the neutral reemission in the trench is implicated in the undercut formation. Moreover, the predicted etch profiles let a bowing appear at the sidewalls. The model reveals that these zones are sputtered by an incident ion flux reflected from the mask sides. © 2003 American Vacuum Society. View full abstract»

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  • Fundamental beam studies of radical enhanced atomic layer deposition of TiN

    Page(s): 96 - 105
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    TiN films were deposited using radical enhanced atomic layer deposition (REALD) in an ultrahigh vacuum beam system. The REALD cycle used for the film deposition consisted of separate, sequential exposures of TiCl4, deuterium atoms, and nitrogen atoms. By using this three step deposition process with independently controlled beams of TiCl4 molecules, deuterium radicals, and nitrogen radicals, it was possible to monitor each step in the REALD cycle, measuring the sticking and reaction probabilities of each of these species on silicon as a function of surface temperature using a quartz crystal microbalance. Results from the ex situ XPS analysis of the deposited films are promising and suggest that deuterium radicals can abstract Cl from TiClx surface species for substrate temperatures as low as 300 K. The films display low residual chlorine content (≪0.3%) when the D atom exposure is sufficiently large. The results from the third stage in the REALD TiN process are consistent with the addition of approximately stoichiometric amounts of nitrogen. However, the data suggest that during the first few REALD cycles, the nitrogen diffuses into and reacts with the underlying silicon substrate. © 2003 American Vacuum Society. View full abstract»

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  • Soft x-ray photoemission studies of Hf oxidation

    Page(s): 106 - 109
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    Soft x-ray photoemission spectroscopy has been applied to determine the binding energy shifts and the valance band offset of HfO2 grown on Hf metal. Charging of oxide films upon x-ray exposure is found to be very severe and special care is taken to eliminate it. Photoemission results show the presence of metallic Hf (from the substrate) with a 4f7/2 binding energy of 14.22 eV, fully oxidized Hf (from HfO2) with a 4f7/2 binding energy of 18.16 eV, and at least one clearly defined suboxide peak. The position of the valence band of HfO2 with respect to the Hf(metal) Fermi level is 4.23 eV. © 2003 American Vacuum Society. View full abstract»

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  • Nondestructive evaluation of alternative substrate quality using glancing-incidence x-ray diffraction and Raman spectroscopy

    Page(s): 110 - 115
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    Alternate substrate technology holds promise for the growth of high-quality lattice-mismatched epitaxial films. Unfortunately, the technology has been plagued by difficulties in reproducibility of results. Some of this problem resides in a lack of characterization of the thin, twist bonded layer used as the template for subsequent epitaxial growth. In this work, grazing-incidence diffraction (GID) and micro-Raman spectroscopy were used to characterize the alternative substrate prior to growth. The 14- and 50-nm-thin GaAs layers were bonded to (100) GaAs substrates and, subsequently, exposed by standard thinning and etching techniques. The crystalline quality of the thin bonded substrates was studied by GID. The full widths at half maximum (FWHM) of the 004 peaks were used to monitor the optimum bonding condition. The measured FWHM varied from 29 to 601 arc s with smooth surfaces exhibiting the lowest values. The effects of bond pressures on template layers were studied for a series of 50 nm alternative substrates prepared using pressures ranging from 75 to 25 psi with a constant bonding temperature of 450 °C. All transferred template layers prepared within this pressure range showed poor quality (FWHM ranged from 324 to 601 arc s) when compared to bulk GaAs of 15 arc s. Micro-Raman measurements were also carried out on these samples. A transverse optical (TO) phonon line is seen and the intensity ratios of the TO to longitudinal optical phonon were much higher than that of GaAs substrate, confirming that the bonding process is causing damage to the thin template layer. © 2003 American Vacuum Society. View full abstract»

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  • Effect of neutral transport on the etch product lifecycle during plasma etching of silicon in chlorine gas

    Page(s): 116 - 126
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    In this article, we report a computer simulation of silicon etching in chlorine gas. We focus on the lifecycle of silicon containing etch products and how this lifecycle is affected by neutral transport. The lifecycle of silicon in an etch reactor consists of etching, fragmentation by gas phase chemistry, deposition on the walls and wafer, and removal from the reactor. All of these processes are affected by neutral transport. Flow rate and reactor geometry are varied, and the characteristics of the resulting flow fields are analyzed. With the reactor inlet located at the center of the top dielectric, there is significant convective flow at the wafer surface at a chlorine feed rate of 500 sccm. The convective flow helps remove etch products from the reactor. This reduces etch product fragmentation to depositing species in the plasma; thereby reducing wall and wafer deposition. With a showerhead inlet, or with an inlet located at the outer rim of the top dielectric, there is little convective flow at the wafer for any of the simulated flow rates. This results in diffusion dominated transport of etch products. The diffusion is driven by species gradients induced by gas phase and surface reactions. As flow rate decreases, the primary redeposition precursor shifts from SiCl (at 500 sccm) to Si (at 45 sccm), changing the profile of redeposition on the wafer. © 2003 American Vacuum Society. View full abstract»

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  • Temperature dependence in time-of-flight ion scattering spectra of LiTaO3 (0001¯) and surface charge compensation of pyroelectric changes

    Page(s): 127 - 133
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    We used time-of-flight scattering and recoiling spectrometry to study the surface of a LiTaO3 (0001¯) single crystal as a function of temperature (22–200 °C). We found that the variations in surface voltage induced by pyroelectric changes of spontaneous polarization could be quantitatively estimated by computing the effects of surface voltage on the ion optics and scattering events, and measuring scattering and recoiling spectral peak shifts. Generally, when LiTaO3 (0001¯) in a steady state at room temperature was probed, its negative spontaneous polarization charge was compensated by an equivalent amount of positive surface charge and the surface voltage was virtually zero. Raising the sample temperature reduced the spontaneous polarization and indeed a rising positive surface voltage was recorded, which shows that the positive surface charge could not be drained out from the insulating surface instantaneously. However, above 160 °C, the surface voltage returned to around zero, which indicates the presence of a thermally induced surface charge compensation mechanism on LiTaO3 (0001¯) above 160 °C. Cooling the sample both closed this surface charge compensation channel and increased the negative spontaneous polarization charge. A rising negative surface voltage, which is a proper pyroelectric response, was experimentally recorded. However, the spectral changes in the cooling cycle were rather complex. First, peak shifts did not follow the theoretical pyroelectric changes, and second, unexpected additional peaks were observed. These spectral behaviors are attributed to the presence of enhanced ion induced electr- - on and negative ion emission as additional surface charge compensation mechanisms which modified the pyroelectric changes of surface voltage on LiTaO3 (0001¯). In addition, these surface properties were found to be sensitive to surface treatments such as sputtering and proton exchange. © 2003 American Vacuum Society. View full abstract»

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  • Critical Mg doping on the blue-light emission in p-type GaN thin films grown by metal–organic chemical-vapor deposition

    Page(s): 134 - 139
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    The photoluminescence and photocurrent from p-type GaN films were investigated at temperatures of 30 and 297 K for various Mg-doping concentrations. At a low Mg-doping level, there exists a photoluminescence center of the donor and acceptor pair transition at the 3.28 eV band. This center correlates with the defects for a shallow donor of the VGa and for an acceptor of MgGa. The acceptor level shows a binding energy of 0.2–0.25 eV, which was observed by measuring the photocurrent signal at a photon energy of 3.02–3.31 eV. At a high Mg-doping level, we found a photoluminescence center of a deep donor and acceptor pair transition of the 2.76 eV blue band. This center is attributed to the defect structures of MgGaVN for the deep donor and MgGa for the acceptor. For low-doped samples, thermal annealing provides an additional photocurrent signal for unoccupied deep acceptor levels of 0.87–1.35 eV above the valence band, indicating p-type activation. © 2003 American Vacuum Society. View full abstract»

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  • Epitaxial Ti1-xWxN alloys grown on MgO(001) by ultrahigh vacuum reactive magnetron sputtering: Electronic properties and long-range cation ordering

    Page(s): 140 - 146
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    Epitaxial Ti1-xWxN alloys with 0≤x≤0.6 were grown on MgO(001) substrates at 500 °C by ultrahigh vacuum reactive magnetron sputtering from Ti and W targets in pure N2. X-ray diffraction, transmission electron microscopy (TEM), and cross-sectional TEM show that the 0.3-μm-thick Ti1-xWxN(001) alloys are single crystals with the B1-NaCl structure. Rutherford backscattering spectroscopy investigations indicate that alloys with x≥0.05 are slightly overstoichiometric with N/(Ti+W)=1.06±0.05. The alloy lattice parameter a along the film growth direction is 4.251 Å, irrespective of the WN concentration, for x≤0.41 and decreases slightly at higher concentrations. TEM analyses show that Ti0.5W0.5N(001) alloys have long-range CuPt-type atomic ordering on the cation sublattice. The room-temperature resistivity increases linearly from 13 μΩ cm for TiN to 287 μΩ cm for Ti0.42W0.58N due primarily to alloy scattering while the temperature coefficient of resistivity is positive in Ti1-xWxN alloys with x≤0.21 and negative for x≫0.21 due to weak charge carrier localization. The superconducting critical temperature Tc of Ti1-xWxN alloys initially increases with x, due to a larger density of states at the Ferm- - i level, consistent with valence band x-ray photoelectron spectroscopy measurements. Tc reaches a maximum of 6.67 K at x=0.21 and decreases for larger x values.© 2003 American Vacuum Society. View full abstract»

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  • Experimental and theoretical study of ion distributions near 300 μm tall steps on rf-biased wafers in high density plasmas

    Page(s): 147 - 155
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    We present an experimental and theoretical study of ion fluxes, energy distributions, and angular distributions close to 300 μm tall “steps” on rf-biased wafers in high-density argon plasmas. This feature size is important in the etching of microelectromechanical systems. The theory and data show good agreement in most of the trends in the ion distributions as our sampling point approaches the foot of the step: (1) the ion flux decreases, (2) the ions move away from vertical, turning towards the step, and (3) the widths of the double-peaked ion energy distributions become narrower. The theory predicts that the hot neutral flux near the foot of the step is comparable to the ion flux. These hot neutrals may have important effects on the etching process. © 2003 American Vacuum Society. View full abstract»

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  • Gas-efficient deposition of device-quality hydrogenated amorphous silicon using low gas flows and power modulated radio-frequency discharges

    Page(s): 156 - 166
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    Hydrogenated amorphous silicon samples have been deposited by plasma-enhanced chemical-vapor deposition, using a square-wave amplitude-modulated radio-frequency excitation. In this article it will be shown that a combination of amplitude modulation and low gas flows improves the gas-utilization efficiency by a considerable amount. Using a conventional 50 MHz SiH4/H2 plasma with gas flows of 30 sccm, both for SiH4 and H2 at a pressure of 20 Pa, the gas-utilization efficiency is about 8%. It increases up to 50%, by modulating the amplitude of the radio-frequency excitation signal and reducing both gas flows to 10 sccm, keeping the pressure constant. In this case, the deposition rate amounted to 0.55 nm/s. The combination of amplitude modulation and gas flow reduction gives rise to sufficient ion bombardment and hydrogen dilution at low flows. Device-quality optoelectronic properties are obtained under these conditions. The refractive index at 2 eV is about 4.25 and the microstructure parameter has a value around 0.02. The electrical properties were also appropriate for solar cell application. The photo-to-dark-conductivity ratio varied between 105 and 107. The material exhibited a low defect density which is in the order of 1015–1016cm-3. The Urbach energy amounted to 52 meV on the average. © 2003 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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Editor
G. Lucovsky
North Carolina State University