Showing papers on "Chemical vapor deposition published in 1989"

Resistivity of chemical vapor deposited diamond films

Abstract: Diamond films grown by plasma chemical vapor deposition techniques display a fairly low resistivity (∼106 Ω cm). Heat treating the films causes an increase in the resistivity by up to six orders of magnitude. The low resistivity of the as‐grown films is postulated to be due to hydrogen passivation of traps in the films. Annealing causes dehydrogenation resulting in the electrical activation of deep traps with an attendant increase in the resistivity. This mechanism has been confirmed by an observed reduction of the resistivity of the heat‐treated films when they are subjected to a plasma hydrogen treatment.

Effects of the nearest neighbors and the alloy matrix on SiH stretching vibrations in the amorphous SiO r :H (0<r<2) alloy system

Abstract: Hydrogenated silicon suboxides, ${\mathrm{SiO}}_{\mathrm{r}}$:H, for alloy range (0lrl2) have been deposited by remote plasma-enhanced chemical vapor deposition (remote PECVD) under conditions in which hydrogen is incorporated predominantly in monohydride or SiH bonding configurations. We have investigated both the SiH bond-stretching and bond-bending absorption bands by infrared (ir) absorption spectroscopy as a function of r, the alloy composition. In this paper, we have focused on the bond-stretching absorption bands, and have modeled the shape of the bond-stretching band as a function of the alloy composition. There are four distinct local environments for the SiH group in the sub- oxides; these can be written as HSi-${\mathrm{Si}}_{3\mathrm{\ensuremath{-}}\mathrm{n}}$${\mathrm{O}}_{\mathrm{n}}$, for n=0--3. A sum of Gaussian functions, one for each environment, is used to synthesize the absorption in the SiH stretching band. The peak positions of these Gaussians are calculated by an induction model which includes both local and matrix (or alloy) effects; the amplitude weightings are determined from a random statistical model for the local bonding environments of the Si-O groups in the ${\mathrm{SiO}}_{\mathrm{r}}$ alloy. We find that the frequency shifts caused by changes in the matrix, and associated with different values of r, are comparable to the shifts associated with the different local environments. The combination of these effects serves to diminish the discreteness of subband features in the absorption spectrum.

Oxidation studies of SiGe

Abstract: We have studied the kinetics and mechanism of oxidation of SiGe alloys deposited epitaxially onto Si substrates by low‐temperature chemical vapor deposition. Ge is shown to enhance oxidation rates by a factor of about 3 in the linear regime, and to be completely rejected from the oxide so that it piles up at the SiO2/SiGe interface. We demonstrate that Ge plays a purely catalytic role, i.e., it enhances the reaction rate while remaining unchanged itself. Electrical properties of the oxides formed under these conditions are presented, as well as microstructures of the oxide/substrate, Ge‐enriched/SiGe substrate, and SiGe/Si substrate interfaces, and x‐ray photoemission studies of the early stages of oxidation. Possible mechanisms are discussed and compared with oxidation of pure silicon.

Particle bombardment effects on thin‐film deposition: A review

Abstract: In many atomistic film deposition processes, concurrent energetic particle bombardment (ions, atoms, molecules, atom clusters) may occur inadvertently and uncontrollably or bombardment may be used to deliberately modify film properties. These energetic particles can arise from (i) the acceleration of charged particles, (ii) high‐energy neutrals from reflection from bombarded surfaces, or (iii) charge exchange processes. Particle bombardment effects that can affect film formation and growth include (a) modifying the substrate surface (cleaning, defect formation), (b) momentum transfer processes in the surface region (sputtering, desorption, recoil implantation, defect formation), (c) addition of heat to the surface region, and (d) formation of secondary elelctrons that can affect chemical reactions. These in turn affect film properties such as adhesion, residual film stress, film morphology, density, grain size and orientation, surface coverage, pinhole density, and surface area. The understanding of these effects and how to use them advantageously is important to those utilizing processes where concurrent energetic particle bombardment is occurring or can be made to occur.

Hydrogen passivation of electrically active defects in diamond

Abstract: Subjecting natural diamond single crystals to the action of atomic hydrogen in a hydrogen plasma is shown to result in the passivation of interband states in the crystal resulting in a marked reduction in the resistivity to about 105 Ω cm from the expected high resistivity of∼1016 Ω cm. When the hydrogenated crystals are heat treated in a neutral ambient, the hydrogen can be expelled from the crystals, restoring the high resistivity. The behavior of natural diamond crystals, with respect to the effects of hydrogen, is shown to be similar to the behavior of diamond thin films synthesized by plasma‐enhanced chemical vapor deposition techniques.

On the role of oxygen and hydrogen in diamond-forming discharges

Abstract: Plasma emission actinometry has been used to study the mechanism by which small additions of oxygen (∼0.5%) enhance the rate of diamond deposition in a dilute (4%) CH4/H2 discharge at high temperature (900–1300 K). Increasing amounts of CH4 in the feed depress [H], while increasing the O2 concentration, up to ∼5%, produces a fivefold increase in atomic hydrogen in the discharge zone. Invoking a mechanism where diamond growth competes with the formation of an amorphous/graphitic inhibiting layer, these results and earlier studies suggest that oxygen (1) increases [H] which selectively etches amorphous/graphitic carbon, (2) accelerates reaction of this layer with molecular hydrogen, and (3) may itself act as a selective etchant of nondiamond carbon. As a result, the number of active diamond growth sites is increased and enhanced growth rates are observed. We also have grown diamond by alternating a CH4/He discharge with a H2/O2/He discharge and results are consistent with this mechanism. Instantaneous growt...

A Mathematical Model of the Fluid Mechanics and Gas‐Phase Chemistry in a Rotating Disk Chemical Vapor Deposition Reactor

Abstract: We describe a mathematical model of the coupled fluid mechanics and gas‐phase chemical kinetics in a rotating disk chemical vapor deposition reactor. The analysis is for the flow between an infinite radius, heated nonporous rotating disk and a parallel infinite radius porous surface through which reactive fluid is injected normal to the disk. The analysis extends the usual von Karman transformation to allow specification of the normal velocity at the porous disk, and reduces to a stagnation point flow in the limit of zero rotating rate. The deposition of silicon from silane is used as an example system. A new reaction mechanism and set of rate constants are given for the thermal decomposition of silane. We present an RRKM analysis of several of the unimolecular reactions in the mechanism. Calculated velocity and temperature profiles, chemical species density profiles, and deposition rates as functions of susceptor temperature, spin rate, and inlet flow velocity are presented.

Characterization of diamond thin films: Diamond phase identification, surface morphology, and defect structures

Abstract: Thin carbon films grown from a low pressure methane-hydrogen gas mixture by microwave plasma enhanced CVD have been examined by Auger electron spectroscopy, secondary ion mass spectrometry, electron and x-ray diffraction, electron energy loss spectroscopy, and electron microscopy. They were determined to be similar to natural diamond in terms of composition, structure, and bonding. The surface morphology of the diamond films was a function of position on the sample surface and the methane concentration in the feedgas. Well-faceted diamond crystals were observed near the center of the sample whereas a less faceted, cauliflower texture was observed near the edge of the sample, presumably due to variations in temperature across the surface of the sample. Regarding methane concentration effects, threefold {111} faceted diamond crystals were predominant on a film grown at 0.3% CH4 in H2 while fourfold {100} facets were observed on films grown in 1.0% and 2.0% CH4 in H2. Transmission electron microscopy of the diamond films has shown that the majority of diamond crystals have a very high defect density comprised of {111} twins, {111} stacking faults, and dislocations. In addition, cross-sectional TEM has revealed a 50 A epitaxial layer of β3–SiC at the diamond-silicon interface of a film grown with 0.3% CH4 in H2 while no such layer was observed on a diamond film grown in 2.0% CH4 in H2.

Chemical vapor deposition reactor and method of operation

Abstract: A chemical vapor deposition (CVD) reactor and method are disclosed wherein a chamber, preferably configured for receiving a single wafer as a deposition substrate, has multiple gas inlet orifices and exhaust ports which are independently adjustable for dynamically varying and controlling directionality of local gas flow vectors toward and past the deposition substrate. The injection angle of reactant gas being introduced into the chamber is adjusted by baffles for statically deflecting gas flow entering the chamber. Adjustment of the gas inlet orifices and/or exhaust ports and adjustment of the injection angle for the reactant gas is selected for achieving enhanced coating uniformity, and conformality of deposition if necessary or desired, on the substrate.

Hydrogen atom detection in the filament‐assisted diamond deposition environment

Abstract: The resonance‐enchanced multiphoton ionization (REMPI) technique was employed for detection of gas phase atomic hydrogen in the filament‐asisted diamond growth environment. The H atom REMPI signal varied significantly with the reactant CH4/H2 fraction as well as with the filament temperature. We interpret these observations as evidence for the surface role of atomic hydrogen in the diamond growth mechanism. The spatial resolution of the REMPI technique allowed us to confirm that hydrogen atom transport in the deposition region occurs by diffusion.

Characterization of crystalline quality of diamond films by Raman spectroscopy

Abstract: We have measured Raman spectra of diamond films prepared by a hot‐filament method and found that diamond layers on Si substrates are under compressive strain. The degree of the strain is found to increase with increasing nondiamond component in the diamond films. It is shown that Raman spectroscopy is a powerful method to estimate the crystalline quality, especially the strain in the diamond films.

The role of hydrogen in vapor deposition of diamond

Abstract: The effect of hydrogen addition on growth of diamond films under the conditions of chemical vapor deposition was investigated computationally. A detailed chemical kinetic mechanism was composed to describe the evolution of reaction species in pyrolysis of hydrogen‐ and argon‐diluted methane mixtures with imposed temperature profiles, simulating the gas‐phase conditions of diamond film growth in an idealized hot‐filament reactor. The reaction mechanism was comprised of two basic parts: decomposition of methane, and formation and growth of polycyclic aromatic hydrocarbons; it contained a total of 120 elementary reactions and 45 chemical species. The reaction rate coefficients included temperature and pressure dependencies. The computations were performed for a variety of initial conditions, elucidating the effects of critical parameters on the product composition in the regime of diamond deposition. Analysis of the computational results indicated that the key role of the hydrogen addition in the diamond deposition process is to suppress the formation of aromatic species by H2 in the gas phase and thereby to prevent the formation and growth of nondiamond, graphitic phases on the deposition surface.

Surface organometallic chemistry in the chemical vapor deposition of aluminum films using triisobutylaluminum: .beta.-hydride and .beta.-alkyl elimination reactions of surface alkyl intermediates

Abstract: Thermal decomposition of triisobutylaluminum (TIBA) to deposit aluminum films shows promise as a way to form conductive contacts on silicon-based electronic devices. An important step in the steady-state deposition is the reaction of TIBA with the growing aluminum surface. The authors have studied this chemistry by reacting TIBA with single-crystal Al(111) and Al(100) surfaces. A combination of effusive molecular beam scattering, thermal desorption spectroscopy, Auger electron spectroscopy, low-energy electron diffraction, high-resolution electron energy loss spectroscopy, and scanning electron microscopy was used in these studies. The authors find that TIBA decomposes on both of these aluminum surfaces above /approximately/ 470 K by /beta/-hydride elimination reactions to deposit aluminum and evolve hydrogen and isobutylene. This surface /beta/-hydride elimination reaction is the rate-determining step. The authors find that the reaction is 2-5 times faster on Al(111) than on Al(100). In the temperature range of 470-600 K, the growing film is carbon-free, crystalline, and adopts the orientation of the single-crystal substrate. At higher temperatures, the deposited aluminum contains carbon, and they present evidence that a surface /beta/-methyl elimination reaction is responsible, at least in part, for this contamination. Using the kinetic parameters determined from monolayer thermal deposition experiments for this reaction, they are ablemore » to predict the rate of steady-state aluminum deposition for TIBA pressures between 10/sup /minus/6/ and 1 Torr.« less

In situ characterization of diamond nucleation and growth

Abstract: Filament‐assisted chemical vapor deposition (CVD) diamond film growth on Si(100) was studied using x‐ray photoelectron spectroscopy (XPS) to examine the sample at selected intervals during the nucleation and growth processes. The sample was transferred under vacuum from the growth chamber to the attached XPS analysis chamber without exposure to air. Before growth XPS showed that the Si sample is covered by a layer of SiO2 and carbonaceous residue; however, after 15 min of growth both of these substances are removed and replaced by a distinct SiC layer [Si(2p)=100.3 eV and C(1s)=282.7 eV].

Carbon diffusion in undoped, n‐type, and p‐type GaAs

Abstract: The effects of background doping, surface encapsulation, and As4 overpressure on carbon diffusion have been studied by annealing samples with 1000 A p‐type carbon doping spikes grown within 1 μm layers of undoped (n−), Se‐doped (n+), and Mg‐doped (p+) GaAs. The layers were grown by low‐pressure metalorganic chemical vapor deposition using CCl4 as the carbon doping source. Two different As4 overpressure conditions were investigated: (1) the equilibrium pAs4 over GaAs (no excess As), and (2) pAs4 ∼2.5 atm. For each As4 overpressure condition, both capless and Si3N4‐capped samples of the n−‐, n+‐, and p+‐GaAs crystals were annealed simultaneously (825 °C, 24 h). Secondary‐ion mass spectroscopy was used to measure the atomic carbon depth profiles. The carbon diffusion coefficient is always low, but depends on the background doping, being highest in Mg‐doped (p+) GaAs and lowest in Se‐doped (n+) GaAs. The influence of surface encapsulation (Si3N4) and pAs4 on carbon diffusion is minimal.

High‐Temperature Passive Oxidation of Chemically Vapor Deposited Silicon Carbide

Abstract: The oxidation behavior of chemically vapor deposited (CVD) SiC at high temperature was investigated using a thermogravimetric technique in the temperatures range of 1823 to 1948 K. The specimens were prepared by chemical vapor deposition using SiCl4, C3H8, and H2 as source gases. The oxidation behavior of the CVD-SiC indicated “passive” oxidation and a two-step parabolic oxidation kinetics over the entire temperature range. The crystallization of the SiO2 film formed may have caused this two-step parabolic behavior. The parabolic oxidation rate constant (Kp) varied with the square root of the oxygen partial pressure (P1/2O2). The activation energy for the oxidation was determined to be 345 and 387 kJ · mol−1. These values suggest that the diffusion process of the oxygen ion which passes through the SiO2 film is rate-controlling.

Electron and chemical kinetics in methane rf glow‐discharge deposition plasmas

Abstract: Experimental measurements and theoretical modeling of methane deposition plasmas have led to the identification of the most likely homogeneous and heterogeneous reaction paths leading to the deposition of amorphous carbon thin films. Experimental measurements of the voltage, current waveforms, mass flow rates, and pressure are used as inputs to the model. The magnitude and flow‐rate dependence of the discharge luminosity, film deposition rates, and downstream mass spectra are compared with the model predictions and used to identify the dominant reaction paths. The model uses Monte Carlo simulation of the electron kinetics to predict the electron impact dissociation and ionization rates. These rates provide input for a plug flow chemical kinetics model.

Deposition of boron-containing films from decaborane

Abstract: Depopsition of a boron nitride film is carried out by introducing decaborane and dry nitrogen or ammonia into a plasma-assisted chemical vapor deposition chamber. The nitrogen or ammonia partial pressure should provide an excess over the decarborane pressures for example 200 milliTorr of N 2 or NH 3 and 50 MilliTorr of B 10 H 14 . Other film layers can also be produced starting from decaborane.

Electrical Characteristics of Metal Contacts to Boron-Doped Diamond Epitaxial Film

Abstract: Current-voltage characteristics have been obtained for various metal contacts formed on boron-doped diamond epitaxial film prepared on synthesized Ib diamond by the microwave plasma-assisted chemical vapor deposition method. Ti contacts and W contacts have exhibited good ohmic and Schottky properties, respectively. For the first time, we have fabricated Schottky diodes on boron-doped diamond epitaxial films using these contacts and investigated their properties.

Diamond and diamondlike films: Deposition processes and properties

Abstract: Considerable interest has been aroused in the synthesis of diamond films due to their potential applications in microelectronics and optoelectronics. Although synthesis of diamond films by a variety of chemical and plasma assisted chemical as well as physical vapor deposition techniques has been reported, the practical applications of these coatings are still very few. The basic reason limiting the applications of these coatings is the inability to deposit films with smooth surface morphology and desired optical and electrical properties at acceptable deposition rates. Published work on diamond films is reviewed to highlight the above issues.

Critical Currents at 77.3 K under Magnetic Fields up to 27 T for an Y-Ba-Cu-O Film Prepared by Chemical Vapor Deposition

Abstract: Critical currents of an Y1Ba2Cu3O7–δ film prepared by a chemical vapor deposition technique have been measured resistively. Excellent critical current properties in high fields up to 27 T are obtained at 77.3 K. The value of Jc is 4.1×105, 1.9×105, and 6.5×104 A/cm2 at 2, 10, and 27 T, respectively. The upper critical field defined by zero resistivity is estimated to be 35 and 180 T at 77.3 and 0 K, respectively. A peak effect in the critical current is observed at high fields.

Chemical Vapor Deposition of Copper from Copper (II) Hexafluoroacetylacetonate

Abstract: Thermally activated decomposition of the vapor phase of copper (II) hexafluoroacetylacetonate was studied. It was found that the temperature at which the decomposition is carried out influences dramatically the chemical composition of deposits; the higher the temperature, the more carbon is incorporated. Pure copper deposits having resistivities of 3–7 μΩ cm were obtained at substrate temperatures of 340°–390°C. It is believed that in this temperature range, breaking of the metal‐ligand bond of the copper compound takes place while at higher temperatures the onset of the ligand decomposition itself becomes significant. The vapor pressure of liquid copper (II) hexafluoroacetylacetonate was determined over the temperature range 97°‐120°C. The standard enthalpy of evaporation was found to be .

Low temperature organometallic deposition of metals

Abstract: A process for coating metal on a substrate. The process uses organometallic compounds such as (trimethyl)(cyclopentadienyl) platinum in the presence of a reducing fluid such as hydrogen gas to produce high purity films capable of selective deposition on substrates containing, for example, tungsten and silicon. The films are deposited using chemical vapor deposition (CVD) or gas phase laser deposition. The invention also comprises devices made from the process of the invention.

Study on catalytic chemical vapor deposition method to prepare hydrogenated amorphous silicon

Abstract: A new type of thermal chemical vapor deposition (CVD) method is presented. In the method, material gases are decomposed by catalytic or pyrolytic reaction with a heated catalyzer, so that films can be deposited at temperatures less than 300 °C without any plasma or photochemical excitation, and the method is particularly called ‘‘Catalytic‐CVD.’’ Hydrogenated amorphous silicon films are deposited by this method, and the deposition mechanism is also investigated. It is found that device‐quality amorphous silicon films can be obtained and that inactive species, which are generated at the catalyzer and transported without gas‐phase reactions, are key species to make a high‐quality film by this method.

Apparatus for forming thin film

Abstract: Apparatus for forming a thin film on a substrate surface by a CVD (Chemical Vapor Deposition) method which includes diffusing pipes for diffusing and supplying a first reactive gas, and uniformizing plates for supplying uniformly an active species formed through excitation of a second reactive gas The first reactive gas and the active species are mixed uniformly with each other, and the resultant uniform mixture is supplied uniformly to the substrate surface, whereby a uniform film deposition rate is obtained in a reaction zone in which the thin film is formed, and a uniform thin film is formed over the entire substrate surface even when the area of the substrate surface is large

In situ cleaning of silicon substrate surfaces by remote plasma-excited hydrogen

Abstract: We have demonstrated a low‐temperature cleaning technique for removing both carbon and oxygen from a Si surface. It uses a combination of ex situ wet chemical clean and an in situ remote rf plasma‐excited hydrogen clean in an ultrahigh vacuum chamber. Since a remote rf plasma is used, there is insignificant plasma damage or other deleterious effects on surface morphology. A combination of in situ Auger and RHEED analysis has been used to confirm the removal of surface contaminants and the reconstruction of the Si surface. From mass spectroscopy studies, we believe that the hydrogen cleaning is due to a chemical etching of the Si by atomic hydrogen produced by the plasma. This clean is compatible with UHV processing and yields Si substrates that can be used for successful very low temperature (220–400 °C) Si homoepitaxy by remote plasma‐enhanced chemical vapor deposition.

Characterization of filament‐assisted chemical vapor deposition diamond films using Raman spectroscopy

Abstract: Results are presented on a Raman study of diamond films prepared by the filament‐assisted chemical vapor deposition technique from a methane‐hydrogen gas mixture. It is shown that Raman spectroscopy is a useful probe of both the phase of carbon present and of the quality of the diamond component in the films. The study entailed varying the total gas pressure, but holding the ratio of CH4 to H2 constant. It is clearly demonstrated that as the pressure is decreased, the density of defects within the diamond phase increases. The increase in defect density as the pressure is lowered leads eventually to disordered forms of carbon. This result can be understood in terms of the relatively higher electron and ion fluxes at the substrate for films prepared at low pressure.