Showing papers on "Chemical vapor deposition published in 1988"

Synthesis of diamonds by use of microwave plasma chemical-vapor deposition: Morphology and growth of diamond films

Abstract: An investigation is made of the surface morphology and growth of polycrystalline diamond films deposited on Si substrates using the microwave plasma chemical-vapor-deposition (CVD) method. For the source gas, ${\mathrm{CH}}_{4}$ and ${\mathrm{H}}_{2}$ gases mixed in different concentrations are used. Scanning electron microscope pictures of the diamond films synthesized for 7 h show that the film surface consists of triangular (111) diamond faces for ${\mathrm{CH}}_{4}$ concentrations c0.4 vol %, whereas square (100) faces are predominant above c\ensuremath{\simeq}0.4 vol %. For c\ensuremath{\gtrsim}1.2 vol %, the number density of (100) faces decreases with c and finally at c\ensuremath{\simeq}1.6 vol % the film surface becomes entirely structureless, consisting of microcrystallites only. For characterization of the films, x-ray and electron diffraction are measured along with Raman and infrared spectra. In the study of the evolution of surface morphology during film growth, it is found that diamond particles grown on the substrate initially increase their size almost uniformly until the substrate is entirely covered. Then a secondary growth takes place, followed by surface-restructuring processes such as ``fusion'' and ``absorption'' among secondary crystallites. As a result, well-defined diamond faces are formed progressively on the film surface. Higher-order growths followed by the restructuring processes occur periodically as the CVD synthesis proceeds.

A model for the discharge kinetics and plasma chemistry during plasma enhanced chemical vapor deposition of amorphous silicon

Abstract: A model for the plasma enhanced chemical vapor deposition of amorphous hydrogenated silicon (a‐Si:H) in rf and dc discharges is presented. The model deals primarily with the plasma chemistry of discharges sustained in gas mixtures containing silane (SiH4). The plasma chemistry model uses as input the electron impact rate coefficients generated in a separate simulation for the electron kinetics and therefore makes no a priori assumptions as to the manner of power deposition. Radical densities and contributions to film growth are discussed as a function of gas mixture, electrode separation, and locale of power deposition, and comparisons are made to experiment. A compendium of reactions and rate constants for silane neutral and ion chemistry is also presented.

Cooperative growth phenomena in silicon/germanium low-temperature epitaxy

Abstract: A series of Si:Ge alloys and structures has been prepared by ultrahigh‐vacuum chemical vapor deposition. Alloys of composition 0≤Ge/Si≤0.20 are readily deposited at T=550 °C. Commensurate, defect‐free strained layers are deposited up to a critical thickness, whereupon the accumulated stress in the films is accommodated by the formation of dislocation networks in the substrate wafers. A cooperative growth phenomenon is observed where the addition of 10% germane to the gaseous deposition source accelerates silane’s heterogeneous reaction rate by a factor of 25. A model is proposed where Ge acts as a desorption center for mobile hydrogen adatoms on the Si[100] surface, accelerating heterogeneous silane pyrolysis by the enhanced availability of chemisorption sites.

Growth mechanism of vapor-deposited diamond

Abstract: An elementary-reaction mechanism of diamond growth by a vapor deposition process is proposed. The central postulate is that the main monomer growth species is acetylene. The mechanism basically consists of two alternating steps: surface activation by H abstraction of a hydrogen atom from a surface carbon and the addition of one or two acetylene molecules. During the addition reaction cycle a number of solid C–C bonds is formed and hydrogen atoms migrate from a lower to an upper surface layer. The mechanism is in general agreement with the macroscopic views of the Russian researchers and is consistent with the numerous experimental observations reported in the literature.

Large grain polycrystalline silicon by low‐temperature annealing of low‐pressure chemical vapor deposited amorphous silicon films

Abstract: The crystallization of undoped amorphous silicon films deposited by low‐pressure chemical vapor deposition in the temperature range 580–530 °C and annealed from 550 to 950 °C has been studied by transmission electron microscopy. The average grain size of the crystallized films depends on the annealing temperature and the deposition conditions. The nucleation rate of new grains during annealing decreases as the deposition temperature decreases from 580 to 545 °C and/or when the deposition rate increases. The final grain size is also influenced by the annealing temperature with the largest grain size obtained at low annealing temperatures. A simple model is described which explains the dependence of grain size on the annealing temperature. An average grain size of 500 nm has been obtained in a 200‐nm film deposited at 545 °C and annealed at 550 °C.

Luminescence of heteroepitaxial zinc oxide

Abstract: Thin layers of ZnO were grown on (0001) oriented sapphire by organometallic chemical vapor deposition. Low‐temperature photoluminescence indicates that near‐band‐edge luminescence dominates the spectrum. In contrast to bulk grown material deep level luminescence for the layers is relatively weak.

Surface micromachining for microsensors and microactuators

Abstract: Micromechanical structures can be made by selectively etching sacrificial layers from a multilayer sandwich of patterned thin films. This paper reviews this technology, termed surface micromachining, with an emphasis on polysilicon microstructures. Micromechanical characteristics of thin‐film microstructures critically depend on the average residual stress in the film, as well as on the stress variation in the direction of deposition. The stress in low‐pressure chemical vapor deposition polysilicon varies with deposition temperature, doping, and annealing cycles. Applications of surface micromachining to fabricate beams, plates, sealed cavities, and linear and rotary bearings are discussed.

High rate synthesis of diamond by dc plasma jet chemical vapor deposition

Abstract: This letter describes the first successful attempt at synthesizing diamond by chemical vapor deposition with the use of a dc plasma jet. A plasma jet, formed by the dc arc discharge of CH4 diluted with H2, was sprayed onto a water‐cooled substrate. The growth rate of the diamond film was 80 μm/h. The crystallinity measures well in terms of x‐ray diffraction and Raman spectroscopy. The quenching effect of the thermal plasma is discussed in relation to the high growth rate obtained.

Infrared detection of gaseous species during the filament‐assisted growth of diamond

Abstract: Infrared diode laser absorption spectroscopy is employed as an in situ method to examine gas phase species present during filament‐assisted deposition of diamond films. From a reactant mixture of 0.5% methane in hydrogen, methyl radical (CH3 ), acetylene (C2H2), and ethylene (C2H4 ) are detected above the growing surface, while ethane (C2H6 ), various C3 hydrocarbons, and methylene (CH2) radicals are below our sensitivity levels. The growth of polycrystalline diamond films on Si wafers and polycrystalline Ni is confirmed with x‐ray and Raman scattering, scanning electron microscopy, and Auger electron spectroscopy.

Formation of high Tc superconducting films by organometallic chemical vapor deposition

Abstract: The first growth of superconducting YBaCuO films by organometallic chemical vapor deposition is described. Metal β‐diketonates were decomposed thermally on MgO substrates in an oxygen‐rich atmosphere to produce amorphous brown films. Subsequent annealing in oxygen yielded dull gray films whose thickness corresponded to deposition rates of approximately 8 nm min−1. These films showed semiconductor‐like behavior at higher temperatures, followed by a broad resistive transition from 80 to 36 K with the resistance becoming zero at ∼20 K. Analysis of x‐ray data indicated the presence of the orthorhombic superconducting phase and various other metal oxides. Profilometer measurements yielded film thicknesses up to 950 nm, and scanning electron microscopy revealed faceted grains from 0.5 to 1.0 μm in size.

Measurement of stable species present during filament‐assisted diamond growth

Abstract: We have measured mole fractions of two of the major stable species at the surface of a silicon substrate during filament‐assisted diamond growth as a function of the filament‐to‐substrate distance. Input gases were methane and hydrogen. A quartz probe withdrew gases at the growing surface, and the gases were sampled with an on‐line mass spectrometer. Close to the filament the methane is largely consumed, with most of the remaining gas phase carbon in the form of acetylene. Mass spectral results are compared to compositions calculated with a detailed chemical kinetics model. Our initial analysis suggests that diamond growth comes mainly from reaction of acetylene, ethylene, methane, or methyl radical.

Chemical vapor deposition and characterization of 6H‐SiC thin films on off‐axis 6H‐SiC substrates

Abstract: High‐quality, monocrystalline 6H‐SiC thin films have been epitaxially grown on 6H‐SiC {0001} substrates which were prepared 3° off‐axis from 〈0001〉 towards 〈1120〉 at 1773 K via chemical vapor deposition (CVD). Essentially, no defects were generated from the epilayer/substrate interface as determined by cross‐sectional transmission electron microscopy (XTEM). Double positioning boundaries which were observed in β‐SiC grown on 6H‐SiC substrates were eliminated as confirmed by plan‐view TEM. A strong dependence of the surface morphology of the as‐grown thin films on the tilting orientation of the substrates was observed and reasons for this phenomenon are discussed. The unintentionally doped 6H‐SiC thin films always exhibit n‐type conduction with a carrier concentration on the order of 1016 cm−3. Au‐6H‐SiC Schottky barrier diodes were fabricated on the CVD 6H‐SiC thin films and it was found that the leakage current at a reverse bias of 55 V was only 3.2×10−5 A/cm2. This is compared to SiC films grown on oth...

Method for arc discharge plasma vapor deposition of diamond

Abstract: A method for vapor deposition of diamond by effecting an arc discharge while feeding a discharge gas between an anode and a cathode of a thermal plasma chemical vapor deposition device, radicalizing a gaseous carbon compound by feeding the gaseous carbon compound into a generated plasma jet, and permitting the radicalized plasma jet to impinge on a substrate to be treated, whereby a film of diamond is formed on the substrate.

Defect reduction effects in GaAs on Si substrates by thermal annealing

Abstract: High quality GaAs films with dislocation densities of 2–3×106 cm−2 on (100) Si substrates have been obtained by thermal cycle growth using the metalorganic chemical vapor deposition method. Significant reduction effects of dislocation density in the GaAs layers on Si have been analyzed by a simple model, in which annihilation and coalescence of dislocations are assumed to be caused by dislocation movement under thermal stress. Relaxation of thermal stress in the GaAs films on Si during thermal annealing has also been observed.

Production of high-quality amorphous silicon films by evaporative silane surface decomposition

Abstract: High‐quality hydrogenated amorphous silicon films (a‐Si:H) have been produced by decomposition of low‐pressure silane gas on a very hot surface with deposition on a nearby, typically 210 °C substrate. A high‐temperature tungsten filament provides the surface for heterogeneous thermal decomposition of the low‐pressure silane and subsequent evaporation of atomic silicon and hydrogen. These evaporated species (primarily) induce a‐Si:H growth on nearby substrates which are temperature controlled using a novel substrate holder. The light and dark conductivities, optical band gap, deposition rates, and light‐soaking effects of preliminary films are reported. The decomposition‐evaporation process has been examined using a mass spectrometer to directly detect the decomposition rate and the evaporated radical species. Based on this data and other information, a simplified model for the deposition process is suggested. The excellent film quality and the attributes of the deposition process make this technique, which was originally suggested by Wiessman, viable for the fast rate, large‐area deposition of a‐Si:H for solar cells and other applications.

Diamond crystal growth by plasma chemical vapor deposition

Abstract: We have grown diamond crystals and polycrystalline diamond films from CH4/H2/O2 gas feeds in a simple, high‐power density, 2450‐MHz discharge tube reactor. Single‐crystal growth rates over 20 μm/h have been achieved. The material has been analyzed using Raman spectroscopy, Auger spectroscopy, and x‐ray diffraction. Control of nucleation is a major problem for growing sound films, and the high temperatures currently required for growth will limit applications. Oxygen additions were necessary to deposit diamonds over the range of feed composition we studied.

Raman scattering studies of chemical-vapor-deposited cubic SiC films of (100) Si

Abstract: Raman scattering studies for a series of CVD-grown cubic SiC single-crystal films with film thickness from 600 A to 17 microns are discussed. The results suggest that the crystalline orientations of the Si substrate and the 3C-SiC film are the same. It is found that the Si 522/cm phonon from a Si wafer is enhanced in intensity by a factor of 2-3 due to a CVD overlayer of cubic SiC, and that the 3C-SiC longitudinal optical phonon at the Gamma point from SiC/Si samples is enhanced by a factor of two or three following the removal of the Si substrate. The variation of the Raman spectrum with incident power is investigated, and a method for determining the Raman cross section for 3 C-SiC is proposed.

Handbook of thin-film deposition processes and techniques : principles, methods, equipment, and applications

Abstract: Recent Changes in the Semiconductor Industry Deposition Technologies and Applications: Introduction and Overview Silicon Epitaxy by Chemical Vapor Deposition Chemical Vapor Deposition of Silicon Dioxide Films Metal Organic Chemical Vapor Deposition: Technology and Equipment Feature Scale Modeling The Role of Metrology and Inspection in Semiconductor Processing Contamination Control, Defect Detection, and Yield Enhancement in Gigabit Manufacturing Sputtering and Sputter Deposition Laser and Electron Beam Assisted Processing Molecular Beam Epitaxy: Equipment and Practice Ion Beam Deposition Chemical Mechanical Polishing Organic Dielectrics in Multilevel Metalization of Integrated Circuits Performance, Processing, and Lithography Trends Index

Effects of low‐frequency modulation on rf discharge chemical vapor deposition

Abstract: Low‐frequency square‐wave modulation of a rf discharge in silane diluted with a rare gas brought about an improvement in the deposition rate of amorphous hydrogenated silicon films and in the film quality as well as a drastic suppression of powder concentration in the discharge space. These results can be explained by a SiH3 density in the modulated discharge that is high compared to that without modulation, because of the electron density enhancement resulting from the modulation and also because the lifetime of SiH3 radicals is much longer than those of SiHn radicals (n=0–2).

A model for the surface chemical kinetics of GaAs deposition by chemical‐beam epitaxy

Abstract: Recently we have reported the measurement of reflection high‐energy electron diffraction intensity oscillations during chemical‐beam epitaxy of GaAs using triethylgallium (TEG) and As2 derived from an arsine cracker [Appl. Phys. Lett. 50, 19 (1987)]. In this study we observed a significant variation of the GaAs growth rate with substrate temperature at constant TEG flux. In addition, the variation of growth rate with incident flux at constant temperature was found to be nonlinear below approximately 500 °C and linear above 500 °C for incident fluxes yielding maximum growth rates between 0.2 and 1.8 monolayers/s. We have developed a model of the surface pyrolysis of triethylgallium which explains the qualitative behavior of the above data. The model assumes the existence of adsorbed triethyl, diethyl, and monoethyl gallium species as well as adsorbed ethyl radicals. As a starting point, the rate limiting step to epitaxial incorporation of atomic gallium is assumed to be cleavage of the second ethyl–gallium...

Neutral radical deposition from silane discharges

Abstract: The fractional contributions of the various SiHn radicals (n=0–3) to deposition are calculated for low‐power, pure‐silane rf and dc discharges. This is done using a radical diffusion plus reaction equation, combined with current knowledge of SiH4 dissociation fractionation, of SiHn+SiH4 reactions, and of the distributed source of radicals. The conclusion reached is that more than 98% of neutral radical deposition is by SiH3 for typical deposition pressures (>100 mT at 240 °C). The effect of SiH3+SiH3 reactions at higher power is also evaluated using an estimated reaction rate coefficient (k3). The resulting loss in deposition rate is given as a function of film growth rate and of k3.

Reactive sticking coefficients for silane and disilane on polycrystalline silicon

Abstract: Reactive sticking coefficients (RSCs) were measured for silane and disilane on polycrystalline silicon for a wide range of temperature and flux (pressure) conditions. The data were obtained from deposition‐rate measurements using molecular beam scattering and a very low‐pressure cold‐wall reactor. The RSCs have nonlinear Arrhenius temperature dependencies and decrease with increasing flux at low (710 °C) temperatures. Several simple models are proposed to explain these observations. The results are compared with previous studies of the SiH4/Si(s) reaction and low‐pressure chemical vapor deposition‐rate measurements.

Low‐temperature photoluminescence studies of chemical‐vapor‐deposition‐grown 3C‐SiC on Si

Abstract: Low-temperature photoluminescence studies of 26 cubic SiC films, ranging in thickness from 600 A to 25 microns, grown by CVD on (100)Si are presented. It is suggested that the G band near 1.90-1.92 eV and its phonon side bands G1 and G2 are related to dislocations and extended defects. Formulas for the band-gap shift due to an axial stress have been obtained and applied to the CVD 3C-SiC/Si system. The results indicate that a 1-3-micron transition layer greatly reduces the interface misfit strain, and that biaxial stress in the SiC/Si system depresses the intensity of the no-phonon line.

Thermal conductivity of heavily doped low‐pressure chemical vapor deposited polycrystalline silicon films

Abstract: The lateral thermal conductivity of heavily doped low‐pressure chemical vapor deposited polycrystalline silicon films is measured using polycrystalline silicon microbridges elevated three micrometers above a silicon substrate. The bridges, lightly doped in their central regions and heavily doped elsewhere, are fabricated using a sacrificial silicon‐dioxide layer and phosphorus out‐diffusion from doped oxide. Voltage‐current characteristics measured on the bridges both under high vacuum and in silicone oil are used to calculate lateral thermal conductivity in the polycrystalline silicon. The experimental values for the thermal conductivity of heavily doped polycrystalline silicon range from 0.29 to 0.34 W cm−1 K−1 and average 0.32 W cm−1 K−1. These values agree closely with results obtained by a second method that employs uniformly doped polycrystalline silicon bridges. In the second method, high‐vacuum, voltage‐current characteristics are measured and the indicated thermal conductivities for two samples a...

Electrical characteristics of Schottky diodes fabricated using plasma assisted chemical vapor deposited diamond films

Abstract: Schottky diodes were fabricated using gold and aluminum contacts to thin diamond films obtained by a microwave plasma assisted chemical vapor deposition process. The current‐voltage and capacitance‐voltage‐frequency characteristics of these devices are similar to those fabricated on a crystalline diamond base formed by traditional ultrahigh pressure process.

Y‐Ba‐Cu‐O superconducting films prepared on SrTiO3 substrates by chemical vapor deposition

Abstract: High Tc superconducting YBa2 Cu3 O7−x films were prepared by chemical vapor deposition using β‐diketonates of Y, Ba, and Cu as source materials. The films were epitaxially grown on SrTiO3 (100) substrates. The c‐axis orientation perpendicular to the plane of the substrates was observed. A sharp resistive superconducting transition with Tc (R=0) at 84 K was obtained. The maximum critical‐current density at 77 K was 2×104 A/cm2 .

Metalorganic chemical vapor deposition of PbTiO3 thin films

Abstract: PbTiO3 thin films have been grown successfully for the first time by using purely metalorganic precursors, namely, titanium isopropoxide and tetraethyllead. A scanning electron micrograph showed dense and noncolumnar growth with good surface morphology. Temperature‐dependent x‐ray diffraction studies provide evidences for a reversible tetragonal to cubic phase transition around 540 °C. At room temperature, the dielectric constant is about 180.

Epitaxial Al2O3 films on Si by low‐pressure chemical vapor deposition

Abstract: Heteroepitaxial Al2O3 films were grown successfully on (100)Si substrates at substrate temperatures above 1000 °C by low‐pressure chemical vapor deposition with the use of N2 bubbled Al(CH3)3 and N2O. From reflection high‐energy electron diffraction analysis, the epitaxial films were found to be γ‐Al2O3 with an orientation relation of (100)Al2O3//(100)Si. Capacitors with 700‐A‐thick Al2O3 films as gate insulators were fabricated and showed high‐frequency capacitance‐voltage characteristics without hysteresis. An interface state density of 1.7×1011 cm−2 eV−1 was observed by using quasistatic capacitance‐voltage measurements. The leakage current was 9.7×10−11 A/cm2 at a gate voltage of 3.0 V.