bluuebunny/crossref_metadata_2025 huggingface dataset:
Etching of Si with Cl2 using an electron cyclotron resonance source
Authors: Sung K. T. , Pang S. W.
Published: July 2002

A Cl2 plasma generated by a multipolar electron cyclotron resonance (ECR) source was used to etch Si. Etch rate of Si was found to increase with microwave power and rf power, but decrease with source distance and Ar addition. Etch rate increases with pressure up to 1 mTorr, then decreases at higher pressure. Temperature ranging from − 130 to 100 °C has no significant influence on the etch rate, profile, and morphology. Vertical profile and smooth morphology in Si can be obtained by using low microwave power and low pressure. With a Cl2 plasma at 1 mTorr, 50 W microwave power, 70 W rf power, and 15 cm below the ECR source, 0.15-μm-wide features in Si were etched with 7:1 aspect ratio. Schottky diodes were fabricated on the etched surface to evaluate etch-induced damage. Breakdown voltage was found to increase with microwave power but decrease with rf power and source distance. Ideality factor and barrier height degrade at high rf power and long source distance. One of the most important factors to maintain high quality diode characteristics is by using low self-induced dc bias voltage. In a system with an ECR source and a rf-powered electrode, it has the advantage of generating high density ions at low ion energy, therefore providing high etch rate with minimal surface damage.
Analytic model of the ion angular distribution in a collisional sheath
Authors: Vahedi V. , Stewart R. A. , Lieberman M. A.
Published: July 2002

An analytic model is developed for the ion angular distribution in a collisional sheath. In a previous study, the one-dimensional (normal to the sheath) ion velocity distribution was obtained under the assumption that charge exchange is the dominant ion-neutral collision mechanism. In the present model, we assume λscat≥λcx, where λscat and λcx are the mean free paths for ion-neutral elastic scattering and charge-exchange collisions, respectively. With this assumption, the angular distribution mainly arises from ions that strike the electrode after undergoing only one scattering collision following the last charge-exchange collision. Comparison of the analytic model with results obtained from a particle-in-cell simulation gives excellent agreement. Both the average angle of ions striking the electrode and the ratio of parallel to perpendicular ion flux at the electrode are shown to scale with the ratio of scattering to charge-exchange cross sections σscat/σcx.
Influence of surface-activated reaction kinetics on low-pressure chemical vapor deposition conformality over micro features
Authors: Hsieh Julian J.
Published: July 2002

The coupled effect of molecular scattering and surface-activated reactions on low-pressure chemical vapor deposition (LPCVD) film conformality is investigated. Using a single-precursor two-step surface-activated deposition as an example, film conformality can be found to depend on two first-principle dimensionless parameters–Sc, the intrinsic sticking coefficient, and Sa, the surface saturation factor. An analytical integral material balance formulation, developed for the feature-scale molecular transport, is solved numerically in a wide range of Sc and Sa. The results show that film conformality generally improves with decreasing Sc and increasing Sa. With Sc fixed in most LPCVD processes (due to the nature of the precursor species), the ability to control Sa in the process becomes the key to conformal deposition. The intrinsic surface-activated deposition rate expression shows no apparent reaction order. Therefore, previously reported Monte Carlo schemes and integral-differential models employing a single sticking parameter or a fixed reaction order to characterize LPCVD step coverage behavior are applicable only in limited cases. The two-parameter model has been found useful in understanding the H2-reduced tungsten CVD process, for which the first-principle parameters can be determined from kinetic data reported in the literature.
Power dissipation mechanisms in radio-frequency driven silane discharges: The influence of discharge geometry
Authors: Mataras D. , Cavadias S. , Rapakoulias D.
Published: July 2002

The influence of chamber geometry on the electron impact dissociation and dissociative excitation processes, in a capacitively coupled radio-frequency (rf) silane discharge, is presented. This is achieved by examining the influence of geometry, in conjunction with other macroscopic parameters, on the concentrations of ground state SiH and electronically excited SiH* radicals, recorded simultaneously by spatially resolved laser induced fluorescence and optical emission spectroscopy. The geometry of the discharge is modified, by changing either the interelectrode distance or the electrode diameters, whereas the electric symmetry of the discharge is monitored by the change of the self-bias direct-current potential of the rf electrode. Our observations indicate that the specific path and power consumption of the generation processes of the two radicals are spatially differentiated and sensitive to geometry variations. Thus, emission and fluorescence spatial intensity profiles are differently influenced. In the case of the modification of interelectrode distance, a redistribution of the energy consumed by each of the radical generating processes has been observed.
Two-photon laser-induced fluorescence measurements of absolute atomic hydrogen densities and powder formation in a silane discharge
Authors: Czarnetzki U. , Miyazaki K. , Kajiwara T. , Muraoka K. , Okada T. , Maeda M. , Suzuki A. , Matsuda A.
Published: July 2002

Absolute and spatially resolved hydrogen densities were measured in a silane radio frequency discharge by two-photon laser induced fluorescence spectroscopy. The excitation wavelength was 205 nm and the observation wavelength was 656 nm (Balmer alpha). Titration in a flow tube reactor was used for calibration of the detection system, enabling for the first time the determination of reliable absolute hydrogen densities in a silane discharge. In addition, spontaneous as well as laser induced powder formation was observed.
Diffusion and electrical activity of indium in (Hg,Cd)Te
Authors: Weck G. , Wandel K.
Published: July 2002

Indium diffusion into Hg1−xCdxTe (0.2<x<0.3) was carried out in a two zone furnace in the diffusion temperature range from 240–380 °C. The second zone temperature was chosen to maintain a constant concentration of mercury vacancies if no indium is present. Typical indium profiles consist of an erfc-like segment at higher concentration and an abrupt profile at lower concentration at the diffusion front. The depth of the latter coincides very well with the depth of the n-type region. An electron concentration up to 5×1018 cm−3 was observed. The electrical activation decreases with higher indium concentration as was elucidated by differential Hall measurements. The chemical indium profiles are interpreted in terms of an interstitial diffusion together with two incorporation mechanisms of different net charge transfer: the Frank–Turnbull and the kick-out mechanisms. A numerical diffusion model is outlined based on the assumption of a local equilibrium for site occupation and a linear response of the change of the defect concentration to the deviation from equilibrium. Although the profiles depend strongly on the indium surface concentration, an In-concentration independent diffusion coefficient of interstitial indium DIn,i=(5.4/9.2) ×10−5 cm2 s−1 exp[(−922±20 meV)/kBT] fits the experiments. Large variations of the indium surface concentration are apparently caused by storage in air between wet chemical preparation and enclosure of the specimen in the ampoule.
Hybrid modeling of deposition profiles in magnetron sputtering systems
Authors: Stache J.
Published: July 2002

A three-dimensional hybrid model for calculating sputter deposition profiles has been developed. Both Monte Carlo methods and methods of statistical physics have been used. Due to the negligible mutual interaction of the sputtered particles, the Monte Carlo simulation is only carried out by a point sputtering source. The point source deposition profile and the point source thermalization profile resulting from the Monte Carlo simulation are integrated over all relevant point sources. The spatial distribution of the thermalized particles enters in the well known diffusion equation as a source term. The stationary distribution of concentration of the thermalized particles results in the time invariant solution of the diffusion equation. Therefore, the flux of thermalized particles to the substrate is available. The evaluated model takes into consideration the pressure of the working gas, the initial energy and angular distribution of the sputtered particles, the masses of the working gas atoms and the sputtered particles, the emissivity of the target and the geometry of the sputtering system, and is applicable to all common sputter processes. To verify the model silicon layers have been deposited from a planar magnetron target at an argon pressure of 1.1 and 4.0 Pa. The simulations are in good agreement with experimental data. It is shown that the unexpected decrease in uniformity with increasing pressure is an effect of the pressure dependent source term.
Surface modification of fluoropolymers with vacuum ultraviolet irradiation
Authors: Matienzo L. J. , Zimmerman J. A. , Egitto F. D.
Published: July 2002

Amorphous fluoropolymers (AF) have recently been developed to provide several favorable characteristics not present in the more crystalline materials. However, these polymers have not been fully characterized and reports of surface modification are not extensive. This work presents results of surface analysis and modification with vacuum ultraviolet (VUV) irradiation of Teflon-AF-2400 using contact angle measurements, x-ray photoelectron spectroscopy (XPS), and laser-assisted Fourier transform mass spectroscopy (FTMS). Results are compared to those for other, more crystalline, fluoropolymers, namely, poly(tetrafluoroethylene) (PTFE) and the copolymer of tetrafluoroethylene and perfluoroalkoxyvinyl ether (PFA). These three fluoropolymers differ in structure and amount of oxygen that they contain. Samples were irradiated for sixty minutes downstream from a helium microwave plasma, in some instances through a LiF crystal filter. In the latter case, modification is due solely to photons with wavelengths greater than 104 nm. For films treated without filters, reduction in the advancing contact angle was greatest for AF-2400 and least for PTFE. XPS indicated radiation-induced defluorination for all polymers treated with or without filters. Concurrently, oxygen incorporation occurs upon exposure to air during sample transfer from the plasma reactor to the XPS instrument. Wetting for treated films improved as the ratio of atomic concentrations for oxygen and fluorine, [O]/[F], increased at the surface. As expected, greater modification was achieved with no filter, possibly due to the effect of higher energy photons and/or helium metastable atoms. Small amounts of nitrogen were also incorporated following treatment, upon exposure to nitrogen gas. Laser-assisted FTMS experiments on VUV-treated PTFE and PFA samples resulted in a series of high molecular weight fragments (in increments of 50 amu). This was not observed for untreated films analyzed under similar conditions. It is proposed that VUV irradiation tends to crosslink PTFE and PFA films through defluorination of the –CF2– repeating units, while the AF-2400 is prone to ring cleavage and does not exhibit this tendency toward crosslinking.
Structural characterization of platinum deposits supported on ordered alumina films
Authors: Libuda J. , Bäumer M. , Freund H.-J.
Published: July 2002

Platinum on γ-Al2O3 represents one of the technically important supported catalysts. In order to model such a system, we have prepared a well-ordered 5-Å-thick and atomically flat oxide film with γ-alumina-like structure on NiAl(110). Its defect structure has been subject to a spot-profile analysis–low-energy electron diffraction (SPA-LEED) investigation. The formation of antiphase domains leads to a broadening or splitting of certain superstructure spots, which exhibit unusual intensity up to high diffraction orders. The deposition of small amounts of platinum results in destruction of the oxide superstructure to a great extent. This behavior allows the investigation of small platinum coverages (θ≊0.1). Island sizes and further information about size distributions were extracted from a spot-profile analysis of the (00)-LEED reflex, revealing a high dispersion of platinum with Pt atoms changing the structure of the oxide in their immediate neighborhood. Thermal desorption spectroscopy results suggest an embedding of Pt in the Al2O3 matrix. To a large extent this process can be suppressed by deposition at low temperature (100 K), whereas heating higher than 800 K leads to diffusion of Pt through the oxide into the substate followed by a recovering of the oxide superstructure. Deposition of several monolayers of platinum at 500 K results in the formation of a polycrystalline film. The crystallites grow in (111)-orientation and show preferential azimuthal orientations with respect to the substrate.
Experimental tests of new direct methods for adsorbate structure determination using photoelectron diffraction
Authors: Hofmann Ph. , Schindler K.-M. , Fritzsche V. , Bao S. , Bradshaw A. M. , Woodruff D. P.
Published: July 2002

Two recently proposed methods for approximate but direct adsorbate site determination using scanned-energy mode photoelectron diffraction data have been tested on experimental data from three different adsorption systems. The three systems studied, O, CO, and C2H4 on Ni(111) involve three different local adsorption sites (single hollow, mixed hollows and near-atop) and have all been subjected to separate full quantitative structure determinations. Both the simple Fourier transform approach of Fritsche and Woodruff, and the projection method of Hofmann and Schindler are found to correctly identify all the adsorption sites. The precision of these approximate structure determinations, and the size of the data bases used, are compared with each other and with other proposed methods.
Growth of FeOx on Pt(111) studied by scanning tunneling microscopy
Authors: Galloway H. C. , Benítez J. J. , Salmeron M.
Published: July 2002

We have studied the growth of iron oxide films on Pt(111) using scanning tunneling microscopy. The system has been found to depend sensitively on the temperature and oxygen pressure used to form the oxide. As the coverage is varied from below a monolayer to multilayers of approximately four or five layers thick, three different ordered structures are observed as well as regimes in which the iron oxide appears disordered. For coverages ≤1 ML, the iron oxide is FeO and a large lattice mismatch between the iron oxide and platinum governs the growth process. The first ordered structure occurs at a monolayer coverage and has a large unit cell where ∼8 lattice spacings of the FeO fit ∼9 of the Pt(111) surface. At higher coverages, √3×√3R30° and 2×2 [W. Weiss, A. Barbieri, M. A. Van Hove, and G. A. Somorjai, Phys. Rev. Lett. 71, 1884 (1993)] ordered structures are observed. These can be ascribed to α-Fe2O3 and Fe3O4 phases respectively which are the equilibrium phases for the oxygen pressures and temperatures used in growing the iron oxide. A disordered multilayer growth is also observed.
Elimination of serious artifacts in temperature programmed desorption spectroscopy
Authors: Lu Guangquan , Linsebigler Amy L. , Yates John T.
Published: July 2002

Regurgitation and wall displacement processes are often encountered in temperature programmed desorption measurements. Such effects can lead to misleading interpretations of the surface reaction and desorption products. A simple and useful pumping scheme is described which overcomes this problem by using a cryogenically cooled titanium sublimation pump (TSP) for differential pumping of the mass spectrometer. It is demonstrated that minor wall displacement effects (mainly CO, H2O, and H2) are present in temperature programmed desorption spectroscopy and are insensitive to the mode of differential pumping. In comparison to ion pumping, however, serious methane (CH4) regurgitation and displacement effects can be completely eliminated when the TSP is employed.
An x-ray photoelectron spectroscopy study of the interaction and chemical passivation of chemically etched (100) oriented Hg1−xCdxTe (x=0.226) utilizing chromium and aluminum
Authors: Williams J. P. , Wilks S. P. , Williams R. H. , Tarry H. A.
Published: July 2002

The growth and chemical interaction of both aluminum and chromium interfaces with chemically etched (100) oriented mercury cadmium telluride (MCT) has been studied using x-ray photoelectron spectroscopy (XPS). It is shown that the MCT is chemically passivated with the deposition of Cr, and that there is no outdiffusion of Te and no loss of mercury, as has often been observed. It was found that Cr followed a laminar growth mode with an escape depth of 21 Å. In contrast, the deposition of aluminum onto the etched (100) MCT surface induced an increase in the Te and Cd XPS intensities of approximately 100% and 34%, respectively, of the zero coverage value. This coincided with a rapid loss of mercury from the interfacial region. At high coverage a reacted Te component was observed. A structural model is introduced and is used to account for the trends observed in the core level intensities of the postetched surface. Mathematical expressions derived from this model are utilized to fit the core level intensities as a function of overlayer thickness. We report the success of the model, with excellent fits obtained for both the Cr–MCT and Al–MCT systems and, as a result of this study, a method of chemically passivating the system.
Characterization at different aspect ratios (radius/length) of a radio frequency inductively coupled plasma source
Authors: Wainman P. N. , Lieberman M. A. , Lichtenberg A. J. , Stewart R. A. , Lee C.
Published: July 2002

Ion densities, electron temperatures, plasma potentials, and absorbed powers are measured in a planar inductively coupled argon plasma source at different input powers, pressures, and aspect ratios (radius/length) and are compared to both a global (volume-averaged) model and a two-dimensional (2D) fluid model. Qualitatively, the trends between the models and experiment are similar. Radial ion density profiles at different aspect ratios and pressures are also measured. An ion density peak off-axis is measured at a high aspect ratio and predicted by the 2D fluid model.
Interface reaction of Al/W and chemical properties of Al–W bimetallic bonding
Authors: Tsukada Mitsuo , Ohfuji Shin-ichi
Published: July 2002

Suppression mechanism by a thin interface W oxide layer is investigated for intermetallic reaction at Al/W interfaces. The interface reaction scheme of Al/W was analyzed by in situ x-ray photoemission spectroscopy for the interface formation and subsequent annealing in ultrahigh vacuum. Without the W oxide layer at the interface, annealing at temperatures higher than 450 °C leads to an intermetallic reaction forming the bimetallic compound WAl12 through the entire metal layer, while no reaction between Al and W occurs at room temperature. The intermetallic reaction causes the lowering of W 4f core level by 0.7 eV. This is explained by the donation of a lone electron pair from an Al 3s orbital to a vacant W 6s orbital in bimetallic bonding. The interface thin W oxide layer, composed of WO3, is consumed in the oxidation–reduction reaction with metallic Al. The reaction product Al2O3 inhibits the intermetallic reaction. This results in an increase in annealing temperatures to as high as 600 °C and longer annealing time to form WAl12.
Effect of wall charging on an oxygen plasma created in a helicon diffusion reactor used for silica deposition
Authors: Charles C. , Boswell R. W.
Published: July 2002

A continuous oxygen plasma operating at a radio frequency power of 800 W and a pressure of 2 mTorr has been created in a helicon diffusion reactor used for the deposition of silicon dioxide films. An energy selective mass spectrometer and a Langmuir probe attached to the wall of the silica covered aluminum diffusion chamber below the source have been used to characterize the plasma [ion energy distribution function (IEDF), plasma potential, floating potential, plasma density]. The IEDF of the O+2 ions escaping from the plasma to the sidewalls of the chamber consists of a single peak at an energy corresponding to the plasma potential in the chamber (≊32 V). This rather high value is a consequence of the charging effect of the insulating walls at the initiation of the discharge, and would need to be taken account of when estimating the energy of the ions arriving at a biased substrate.
Sputter deposition of cermet fuel electrodes for solid oxide fuel cells
Authors: Tsai T. , Barnett S. A.
Published: July 2002

We describe the structure and electrochemical properties of cermet thin films composed of 50 vol % Ni and Y-stabilized ZrO2 (YSZ), of interest for solid-oxide fuel cell (SOFC) electrode applications. The Ni–YSZ films—deposited by dc reactive magnetron sputtering of Ni–Zr–Y targets in Ar–O2 mixtures—were porous, two-phase, and exhibited an equiaxed structure with grain sizes of ≊35 nm. The typical conductivity of 103 Ω−1 cm−1 was similar to that of bulk Ni–YSZ. Impedance spectroscopy was used to characterize reactions of H2/H2O fuel gases at the interfaces between Ni–YSZ films and YSZ electrolytes. The spectra typically showed two arcs, attributed to charge transfer and gas diffusion. Either high sputter gas pressures of 40 mTorr or roughened YSZ substrate surfaces were necessary to obtain sufficient film porosity. Electrochemical resistance values of 0.15 to 0.35 Ω cm2 were measured at 750 °C in 97% H2+3% H2O, lower than those for bulk Ni–YSZ and low enough for high-power-density SOFC operation. The low resistance values were probably due to a small grain size. Using a 40 mTorr pressure and a roughened substrate led to film cracking, apparently due to tensile stresses, while using 20 mTorr and a polished substrate led to a too-dense film. Either change increased the electrochemical resistance by ≳100 times.
Plasma chemical vapor deposition and properties of hard C3N4 thin films
Authors: Vepr̆ek S. , Weidmann J. , Glatz F.
Published: July 2002

Compact thin films of stoichiometric, amorphous C3N4 have been prepared by means of chemical transport of carbon in intense nitrogen glow discharge at relatively high deposition temperature of about 800 °C. Their hardness reached 2500 Vickers (kg/mm2).
Interface characterization of an InP/InGaAs resonant tunneling diode by scanning tunneling microscopy
Authors: Wu W. , Skala S. L. , Tucker J. R. , Lyding J. W. , Seabaugh A. , Beam E. A. , Jovanovic D.
Published: July 2002

A lattice-matched InP/InGaAs resonant tunneling diode is studied by scanning tunneling microscopy and spectroscopy. Results show both a structural and chemical asymmetry between the normal and inverted interfaces. The inverted (InP on InGaAs) interface is considerably rougher than the normal interface, and the frequency components of the roughness at both interfaces have been calculated. Additionally, certain images show enhanced and reduced state densities at the normal and inverted interfaces, respectively, which is most likely due to dissimilar bonding types at the interfaces. Spectroscopic observations of evanescent valence-band states tailing into the InP barrier allow for direct measurement of the valence-band offset.
Measurement of the elastic stress of thin films deposited on gallium arsenide
Authors: Mihailovich R. E. , Koscica T. , Zeto R. J.
Published: July 2002

We have measured the elastic stress of thin films of interest in GaAs microdevice processing, particularly for GaAs micromechanical structure fabrication. Stress was determined for films deposited directly on GaAs, in contrast to previous studies examining depositions on other substrates. Stress values were evaluated from the deflection of micron-thick GaAs cantilevers. Films examined include evaporated metals, chemical-vapor-deposition silicon nitride, and sputtered indium tin oxide. Stress values obtained for our films on GaAs are compared to values for these films deposited on other substrates.
Effect of annealing on Ag films on Pt(111)
Authors: Tsay J. S. , Shern C. S.
Published: July 2002

Low-energy electron diffraction (LEED), Auger electron spectroscopy and ultraviolet photoelectron spectroscopy (UPS) were used to study the annealing effect of the silver ultrathin film on a Pt(111) surface. The intensities of the specular beam of LEED versus temperature have abnormal change between 550 and 650 K in a submonolayer range. The irreversibility of this I–T curve gives evidence of a structure change of the surface. The intensity of the specular beam of LEED varying with annealing time plus the Auger signals of Ag and Pt function of temperatures show that a disordered two-dimensional (2D) Ag–Pt alloy is formed in the submonolayer range at a temperature between 600 and 700 K. UP spectra in the growth process show that the d band and the Fermi edge have some interesting changes. On the other hand, UPS in the annealing process also strongly suggests that Ag and Pt atoms mix on the top layer to form a 2D surface alloy at a temperature between 600 and 700 K and a coverage in the submonolayer range.
Synthesis and deposition of silicon nitride films by laser reactive ablation of silicon in low pressure ammonia: A parametric study
Authors: Mihãilescu I. N. , Litã Adriana , Teodorescu V. S. , Gyorgy Eniko , Alexandrescu Rodica , Luches A. , Martino M. , Barboricã A.
Published: July 2002

The UV laser (λ=308 nm) ablation of silicon wafers in 1 mbar ambient ammonia results in the deposition of pure and uniform film of amorphous silicon nitride. At low pressures of NH3 (of several to several tens of μbar), the deposited films are a mixture of amorphous silicon nitride, amorphous nonstoichiometric silicon nitride, and amorphous silicon. The contamination with oxygen is low and is more evident at lower pressures. At ammonia pressures 0.1–1 mbar, the films also contain a certain fraction of hydrogen. Droplets of polycrystalline Si cover the surfaces of some films. This phenomenon is more important at smaller target-collector distances and lower pressures of ambient NH3.
Vacuum ultraviolet emission from radio frequency plasmas of SF6 and CF4
Authors: Li Jan , McConkey J. W.
Published: July 2002

The vacuum ultraviolet and ultraviolet emission (115 nm<λ<300 nm) from radio frequency (rf) discharges through CF4 and SF6 have been investigated as a function of source pressure and rf power. Prominent features of the spectra arise from dissociative excitation of the parent species. Other significant emissions are impurity bands from CO (CF4) or SO (SF6) caused largely by oxygen release from the walls of the discharge tube and subsequent discharge chemistry and excitation. Minor emissions from excited CF+4, CF3, and/or CF2 were obtained from CF4 discharges.
Study of radiation damage and contamination by magnetized inductively coupled plasma etching
Authors: Kim Hyeon-Soo , Nam Wook-Jun , Yeom Geun-Young , Lee Ho-Jun , Kim Jung-Hoon , Whang Ki-Woong
Published: July 2002

Radiation damage and contamination on the silicon surfaces etched by magnetized inductively coupled C4F8 plasmas were investigated. X-ray photoelectron spectroscopy (XPS), secondary ion mass spectrometry, spectroscopic ellipsometry, and transmission electron microscopy were used to characterize contamination and high resolution transmission electron microscopy, and I–V characteristics of Schottky diodes fabricated on the etched and/or annealed silicon surface were used to evaluate radiation damage. As the magnetic field applied to the inductively coupled plasmas increased from 0 to 12 G, the thickness of the residue layer formed on the silicon surface increased with the increase of SiO2 etch rate and selectivity. XPS analysis showed that the composition of the residue layer changed from fluorine rich to carbon rich film by changing the carbon binding state from C–CFx to C–C. Dense defects distributed about 40 Å deep from the etched silicon surface were found for the 0 G condition and thicker but less dense defects were observed for higher magnetic field conditions. The electrical damage estimated from the I–V characteristics of Schottky diodes was reduced with increasing applied magnetic field strength.
Experimental evidence for nanoparticle deposition in continuous argon–silane plasmas: Effects of silicon nanoparticles on film properties
Authors: Roca i Cabarrocas Pere , Gay Patrick , Hadjadj Aomar
Published: July 2002

These last few years a great effort has been made to understand the mechanisms of powder formation in silane discharges. It is now well established that powders are negatively charged and thus confined in the plasma. Therefore, one does not expect powders to contribute to the deposition, unless the plasma is switched off. We present here experimental evidence for the deposition of nanoparticles, even in the case of a continuous discharge. Experimental conditions for nanoparticle formation while avoiding powder formation have been determined from light-scattering and transmission electron microscopy measurements. Nanoparticle deposition has been studied by in situ ellipsometry in silane–argon discharges. From a comparison of the growth kinetics and the optical properties of films obtained under continuous and modulated discharges we conclude that nanoparticle deposition can take place even when the discharge is on. The implications of these discoveries on the properties of hydrogenated amorphous silicon are discussed in the framework of previous studies where we showed that low defect density and well relaxed films are deposited under conditions where nanoparticles and powders are formed in the discharge. The improved properties in these films are attributed to the incorporation of nanoparticles.
Generation of an electron cyclotron resonance plasma using coaxial-type open-ended dielectric cavity with permanent magnets
Authors: Kimura Tadashi , Okazaki Yasunao
Published: July 2002

A high density, uniform, and compact electron cyclotron resonance (ECR) plasma source which utilizes surface-wave radiation and a near-surface magnetic field is described. The microwaves propagated through a coaxial waveguide are introduced circularly into the circumferential side of a dielectric Al2O3 disk, which is placed at the open end of a coaxial-type cavity. The ECR magnetic field is similar to three concentric planar magnetron configurations and is directed away from the dielectric surface by permanent magnets set in the center conductor of the coaxial-type cavity. A surface wave is launched from the dielectric disk surface and generates an ECR plasma. The plasma density and electron temperature are 2.0×1011 cm−3 and 2.2 eV, respectively, at an Ar gas pressure of 10 mTorr and a microwave power of 700 W. The ion saturation current density (Isat) and its uniformity are 8.2 mA/cm2 and ±5.5% within a radius of 10 cm.
In situ study of processes taking place on silicon surface during its bombardment by CFx/Ar ions: Etching versus polymerization
Authors: Šikola T. , Armour D. G. , Van den Berg J. A.
Published: July 2002

The application of a Kaufman ion source in the study of the etching/polymerization processes taking place at the surface of a silicon substrate being exposed to ion beams generated from CF4/Ar gas mixtures is reported. The processes were analyzed by means of in situ mass and energy spectroscopy of the secondary ions sputtered from the substrate surface and the charge-exchange ions, respectively. These analytical methods confirmed the growth of the polymer C–F thin films on the silicon surface at higher concentrations of CF4 in the mixture. It was found that there existed a primary beam threshold energy above which the polymer thin film stopped growing and the etch yield of silicon atoms was increased. The simplified activated growth model presented here describes this behavior qualitatively as a competition between creative and destructive processes leading to deposition and removal of the thin polymer film, respectively.
The role of polymer deposited in differential dielectric etch
Authors: Fang S. , Chiang C. , Fraser D. , Lee B. , Keswick P. , Chang M. , Fung K.
Published: July 2002

Dielectric etch capabilities of a high density plasma etcher have been investigated for the Damascene etch. Here, the patterning of vias, pads, and interconnects by the selective etch stop film approach was evaluated. In particular, the role of fluorocarbon polymer film was studied in etch lag effects and differential dielectric etch (oxide versus nitride). The result shows that the highly selective etch relies on the selective deposition and fluorine scavenging. This article provides the physical insights for the success of the differential dielectric etch. While the investigation is under the Damascene etch, the fundamental understanding can be applied to any highly selective etching of oxide versus nitride.
Detection of hydrogen atoms in silane plasmas using laser-induced fluorescence by Lyman-alpha two-photon and simultaneous Balmer-alpha excitations
Authors: Miyazaki K. , Kajiwara T. , Uchino K. , Muraoka K. , Okada T. , Maeda M.
Published: July 2002

Measurements of atomic hydrogen densities in silane plasmas were accomplished using a two-photon excitation from the ground state (principal quantum number n=1) to the n=2 state at 243 nm, a simultaneous excitation from the n=2 state to the n=3 state at 656 nm, and an observation of fluorescence at 656 nm. First, the influence of the laser-induced dissociation of molecules and radicals in silane plasmas on measurements of hydrogen atoms during the application of this excitation scheme was investigated. Then, we determined the absolute density of hydrogen atoms to be (5±2)×1017 m-3 in a silane plasma at a flow rate of 5 sccm, a pressure of 11 Pa and a rf power of 2 W.
Transient charging and slow trapping in ultrathin SiO2 films on Si during electron bombardment
Authors: Shamir N. , Mihaychuk J. G. , van Driel H. M.
Published: July 2002

Surface charging and electron trapping in ultrathin (1.6 nm) SiO2 films on n-type silicon during bombardment by 350–600 eV electrons are observed by electric-field-induced optical second harmonic generation (SHG). Transient surface charging by fast dissipating electrons (<1 ms charge/discharge time) can be distinguished from oxide electron trapping occurring over hundreds of seconds. The maximum SHG enhancement corresponds to an areal density of trapped electrons of ∼6×1012 cm−2. The gradual recovery of the SHG following electron bombardment suggests the trap sites are “slow traps”, i.e., oxide traps which discharge via tunneling to the Si/SiO2 interface. The effective trap lifetime is about 500 s.
X-ray absorption spectroscopy study of different solid carbon modifications
Authors: Bressler P. R. , Lübbe M. , Zahn D. R. T. , Braun W.
Published: July 2002

Thin chemical vapor deposition (CVD) films of textured diamond (100) and (110) were compared with natural diamond, tetrahedral amorphous carbon, and highly oriented pyrolytic graphite using x-ray absorption spectroscopy at the C 1s absorption edge. Analysis of the intensity ratios of the C 1s→π* and the C 1s→σ* transitions gives a sp2/sp3 ratio of nearly 15% and 40% in the pretempered CVD C(100) and CVD C(110) samples, respectively. The textured samples were exposed to different hydrogen-hot filament treatments for in situ cleaning and for preparing hydrogen-saturated surfaces. After a severe H2  hot filament treatment of the CVD C(110) surface a new peak appears at 286.0 eV, 0.6 eV above the graphite C 1s→π* transition indicating a new hydrocarbon surface compound.
Electron cyclotron resonance plasma enhanced direct current sputtering discharge with magnetic-mirror plasma confinement
Authors: Mišina M. , Setsuhara Y. , Miyake S.
Published: July 2002

Plasma confinement in a mirror magnetic field was applied to the electron cyclotron resonance (ECR) plasma enhanced dc sputtering discharge sustained at pressures below 10−2 Pa. Ion current densities up to 12 mA/cm2, plasma densities about 1011cm−3 and electron temperatures about 25 eV were measured by a Langmuir probe. The cathode current was maximum when the ECR zone was close to the cathodezECR<10 cm (measured from the center of the cathode). A mirror ratio MR⩾3 was necessary for sustaining the discharge at simultaneously large microwave powers and cathode voltages. An application of the system studied to the ion assisted deposition of metallic and compound thin films with a controlled crystal structure is proposed.
Low-temperature deposition of high-quality silicon dioxide films by sputtering-type electron cyclotron resonance plasma
Authors: Nakashima H. , Furukawa K. , Liu Y. C. , Gao D. W. , Kashiwazaki Y. , Muraoka K. , Shibata K. , Tsurushima T.
Published: July 2002

High-quality silicon dioxide films have been deposited at 130 °C by a sputtering technique using an electron cyclotron resonance microwave plasma. Film properties have been studied as a function of O2 flow rate in the range of 2–8 sccm with a constant Ar flow rate of 8 sccm when other plasma conditions were a microwave power of 700 W, and a radio frequency power of 700 W supplied to a target for sputtering. Dielectric breakdown characteristics have been investigated by ramp current–voltage measurements. Films deposited with an O2 flow rate of 5.3 sccm have a dielectric breakdown field of 10 MV/cm, which is close to that of thermally grown silicon dioxide film. The deposition rate was as high as 23 nm/min. Structural properties of films have also been characterized by ellipsometry and infrared absorption spectroscopy, showing that films with O2 flow rates above 4 sccm have near-stoichiometric composition.
Physical damage and contamination by magnetized inductively coupled plasmas and effects of various cleaning and annealing methods
Authors: Nam Wook-Jun , Yeom Geun-Young , Kim Jung-Hun , Whang Ki-Woong , Yoon Jong-Ku
Published: July 2002

Effects of various cleaning and annealing methods on the removal of the residue and physical damage remaining on the exposed silicon surface after the oxide overetching by C4F8 magnetized inductively coupled plasmas were studied. X-ray photoelectron spectroscopy, current–voltage characteristics of Au Schottky diodes, and high resolution transmission electron microscopy were used. The formation of Co silicide was also studied using x-ray diffraction, four-point probe, and Rutherford backscattering spectrometry to investigate the effectiveness of the cleaning and annealing methods on the residue and damage removal. Thicker than 65 Å of polymer and thicker than 40 Å of physical damage remained on the silicon surface etched by C4F8 magnetized inductively coupled plasmas. Among the investigated cleaning methods, SF6/O2 soft cleaning was the most effective in removing the residue. SF6/O2 soft cleaning was also the more effective method in removing the physical damage compared to the annealing methods used in the experiment. Stable Co silicide was formed on the silicon surface after O2 plasma cleaning followed by HF dipping or SF6/O2 soft cleaning. Sheet resistances measured on these silicides were close to those of the silicide formed on the clean control silicon surface. Surface residue not the physical damage appeared to affect the formation of Co silicides, and fluorine rich residue appears to prevent the formation of stable silicide more compared to carbon rich residue.
Proposal for a new self-focusing configuration involving porous silicon for field emission flat panel displays
Authors: Nicolaescu Dan , Filip Valeriu , Okuyama Fumio
Published: July 2002

Field emission displays (FEDs) work in principle in a similar way with conventional cathode ray tubes (CRTs), namely emitted electrons excite phosphors which in turn emit visible light. However, FEDs obtain the electrons through field emission from a distributed network of sharp emitters, and there is no special deflection system for them. The size of the light spot associated with an island of emitters (a pixel) depends on many factors, such as display geometrical dimensions and operating conditions. In this article, a special self-focusing configuration for FEDs is analyzed using a combined analytical and numerical approach. The proposed configuration involves a distributed network of electron emitting areas which are concave in shape and not plane as usual, one for each phosphor pixel. The cathode concave areas are covered with a porous silicon layer, having sharp fibrils with several nanometers radius of curvature. The concave shape has a built-in electron self-focusing feature but, as a by-product, decreases the electric field compared to the plane cathode situation. However, the field multiplication approximation applies in this case, as concerns the electric field enhancement due to both the concave cathode and fibrils. It is shown that high enough electric fields are obtained, allowing electron field emission to occur. Analytical equations are provided for the electric field on the cathode concave surface. These equations are then used in a numerical model, taking into account the electric field enhancement associated with the fibrils, their mutual influence included. This approach allows the computation of the field emitted current as function of model parameters.
Quartz crystal microbalance: A new design eliminates sensitivity outside the electrodes, often wrongly attributed to the electric fringing field
Authors: Cumpson Peter J.
Published: July 2002

Sensitivity outside the electrodes of a quartz crystal microbalance (QCM) is typically 5%–10% of the total sensitivity for the popular planar AT-cut type, and can be a problem in many types of adsorption measurement. This off-electrode sensitivity has sometimes been assumed incorrectly to be due mainly to the electric “fringing field” at the electrode edge, despite the fact that no quantitative theory has been put forward as to how the fringing field could lead to off-electrode sensitivity. In fact, off-electrode sensitivity results from the mass distribution of the electrodes, and is virtually independent of the electric field. Recognition of this fact leads directly to a new QCM design which virtually eliminates the problem altogether; in the new design sensitivity outside the electrode covered area has been reduced from 6% to about 0.3%. Equations previously derived to predict the differential mass sensitivity of existing planar AT-cut QCM sensors are applied to the new design, and compared to experimental calibration measurements obtained using the ink-dot method. Agreement with theory is excellent.
Auger electron spectroscopy analysis of oxidation states of Te in amorphous CdTe oxide thin films
Authors: Zapata-Navarro A. , Bartolo-Pérez P. , Zapata-Torres M. , Castro-Rodriguez R. , Peña J. L. , Farı́as M. H.
Published: July 2002

Amorphous CdTe oxide (a-CdTe:O) thin films with different concentrations of oxygen were grown by rf sputtering and analyzed by Auger electron spectroscopy. A slight change of shape in the Cd MNN peak as a function of oxygen content in a-CdTe:O is observed. This peak resembles the Cd MNN peak of CdTe, at one extreme, and that of CdTeO3, at the other. The Te MNN and the O KLL peaks have similar shapes and lower intensities for a-CdTe:O oxygen saturated films than those in CdTeO3. On the other hand, there is a large and gradual difference in shape, intensity, and energy observed in the Te MNN peak among a-CdTe:O with low, intermediate, and high concentration of oxygen. Different Te oxidation states, as Te−2 and Te+4, contribute to this change as evidenced by a simulation with combinations of CdTe and of CdTeO3 spectra, or by combinations of a-CdTe:O spectra with low and high oxygen content.
Nondestructive depth profiling in Auger electron spectroscopy by means of partial intensity analysis
Authors: Werner Wolfgang S. M.
Published: July 2002

A recently developed method to gain information on the near-surface compositional depth profile via analysis of the spectral line shape of Auger or x-ray photoelectrons has been tested. Electron-excited Auger spectra of a series of thin Au films on a Pt substrate have been subjected to this so-called partial intensity analysis. The overlap of the MNN Auger lines of Pt and Au gives rise to quite complex spectra. Subjecting these spectra to a partial intensity analysis reveals that the Au is present as a homogeneous overlayer. The overlayer thickness provided by the analysis is in good agreement with the values expected from the sample preparation.
Doping of amorphous and microcrystalline silicon films deposited by hot-wire chemical vapor deposition using phosphine and trimethylboron
Authors: Brogueira P. , Chu V. , Ferro A. C. , Conde J. P.
Published: July 2002

The optical, electronic and structural properties of n-type and p-type doped amorphous (a-Si:H) and microcrystalline (μc-Si:H) silicon films prepared by hot-wire chemical vapor deposition are studied. Intrinsic a-Si:H films deposited at filament temperatures Tfil∼1900 °C and 2500 °C using equal silane and hydrogen flow rates, and intrinsic μc-Si:H films deposited either by increasing the hydrogen dilution (FH2/FSiH4⩾10) or decreasing the filament temperature (Tfil∼1500 °C), were doped using phosphine (PH3, n-type doping) or trimethylboron (B(CH3)3, p-type doping). The dependence of the properties of the doped films on Tfil, dopant-to-silane gas flow ratio, and hydrogen dilution is studied. Both p-type and n-type μc-Si:H films were prepared and showed dark conductivities σd∼1  Ω−1 cm−1 and activation energies of σd, Ea,σd∼0.05 eV. N-type a-Si:H films were prepared and showed σd∼10−2  Ω−1 cm−1, Ea,σd∼0.25 eV, whereas p-type doping was less efficient, showing σd∼2×10−6  Ω−1 cm−1, Ea,σd∼0.45 eV. High growth rates (rd⩾15 Å/s) were obtained for all the a-Si:H doped samples. Tungsten (W) contamination of the amorphous samples was kept below the detection limit of the secondary ion mass spectroscopy analysis (∼5×1017 atoms/cm3) for all Tfil. The μc-Si:H samples showed W incorporation close to the detection limit (5–7×1017 atoms/cm3) for Tfil⩾1900 °C. The deep defect density dependence on the dopant-to-silane flow rate ratio was found to be consistent with the defect equilibrium doping model.
Computation of time-dependent temperature distribution along a filament heated in vacuo by electric pulses
Authors: Durakiewicz Tomasz , Halas Stanislaw
Published: July 2002

Numerical solution of the second-order partial differential equation describing the evolution of temperature of a tungsten filament in time allows the simulation of some effects that occur in the case of heating the filament by a series of pulses. Namely, the phenomena investigated are (1) phase shifts between heating current and filament temperature, (2) amplitude of temperature modulation due to variation of supply voltage and (3) the temperature dependence of the time constant of temperature changes. The method presented here may be used for any filament working in vacuo. It may be applied in mass spectrometry, vacuum measurements, thin films deposition by hot filaments and other applications.