R. Avni

Boron nitride coatings of steel and graphite produced with a low pressure r.f. plasma

Abstract Boron nitride (BN) coatings were deposited onto die steel and graphite substrates with a low pressure r.f. plasma. The coatings were deposited onto substrates at temperatures of 550–620 °C from a gas mixture of argon, NH 3 and BCl 3 . X-ray diffraction and scanning electron microscopy were employed to identify and to characterize the coatings. The coatings are mostly amorphous; however, the existence of small amounts of hexagonal BN was identified. The influence on the growth rate of the deposition time and the pressure in the reactor is described.

R.F. plasma nitriding of Ti6A14V alloy

Abstract Titanium alloy (Ti6A14V) samples were nitrided in low pressure (7 mbar) inductive r.f. (0.5 MHz) plasmas of nitrogen or nitrogen-hydrogen. The nitriding time was 5 h and the temperatures of the samples during the nitriding process were 470±20°C and 420±20°C in the discharge and afterglow regions respectively. The effect of the sample location in the reactor and of the N2:H2 ratio in the gas mixture was studied. In the centre of the discharge region e-Ti2N plus δ-TiN phases were formed on top of a solid solution of nitrogen in titanium, α-(Ti,N). In the afterglow region an α-(Ti, N) plus e-Ti2N structure was obtained. The effects of nitrogen concentration in the gas mixture and of the sample location on the microhardness, lattice parameters, composition and structure of the nitrided films are presented and discussed.

Deposition of silicon carbide coatings on titanium alloy with a low pressure R.F. plasma

Abstract A low pressure r.f. plasma was applied to deposit SiC coatings onto Ti6A14V substrates. The coatings were deposited onto substrates at temperatures of 140–390°C from a gas mixture of tetramethylsilane (TMS), argon and hydrogen. Scanning electron microscopy, X-ray diffraction and transmission electron microscopy were employed to identify and to characterize the coatings obtained. It was found that the coatings were hexagonal α-SiC of type III. The coating thickness approximately follows a parabolic time law. A maximum rate of deposition was observed in the pressure range 5–6 mbar. The rate of deposition increases with concentration of TMS up to 0.05% and remains approximately constant up to 0.12%

Decomposition and polymerization of silicon tetrachloride in a microwave plasma. A mass-spectrometry investigation

Mass spectrometry has been used to analyze microwave-induced plasmas of silicon tetrachloride diluted in mixtures of hydrogen and argon. The effects of process parameters such as pressure in the reactor, power input, and the composition of the gas mixture were investigated. Sampling by a quadrupole mass-spectrometer along the gas stream showed that the reactions were initiated upstream where the reactants enter the plasma. It was found that the input power had an optimal value for the decomposition rate of SiCl4; above that optimum, recombination occurred downstream. Upstream the concentrations of SiCl4 decrease with increasing pressure in the range 1–10 torr, independent of the input power. The effect of admixing argon to the reaction mixture is discussed, and the results obtained are correlated to experimental results reported in previous works concerning silicon deposition from SiCl4 on a grounded substrate.

Diagnostics of microwave-induced plasmas and polymerization of gaseous hydrocarbons

The microwave plasmas of gaseous mixtures of methane-argon and propyleneargon were analyzed along the flow stream by the electrical double floating probe system, optical spectroscopy, and quadrupole mass spectrometry. The plasma variables measured and considered were current density, electric field strength, electron temperature, positive ion and electron concentrations, and concentration of pyrolyzed and polymerized species. The results indicate that an irreversible process of polymerization of the hydrocarbons takes place in the plasma. The polymerization process reaches its maximum conversion downstream beyond the microwave cavity. The extent of polymerization was correlated to the concentration of positive ions and electrons in the plasma.

Boridation of titanium and steels in a low pressure R.F. plasma

Abstract Boridation of stainless martensitic steel and titanium has been achieved by the reduction of BCl 3 vapour in mixtures with hydrogen and argon in an r.f. (0.5 MHz) induction plasma at low pressures (1–7 Torr). The influence of the plasma macrovariables such as the gas pressure, the BCl 3 concentration in the gas mixtures (3–9 vol.%) and the current in the r.f. coil (30–60 A) was measured for both steel and titanium. The measured temperature of the substrates during the boridation process was lower than 500°C. The boride films identified by X-ray diffraction were orthorhombic for both Ti 3 B 4 and FeB. The optimum formation rate of the films was 4.5 μm h -1 for Ti 3 B 4 and 4 μm h -1 for FeB. The microhardness was above 3000 kgf mm -2 and 2500 kgf mm -2 for Ti 3 B 4 and FeB respectively. The minimum chlorine content was found to be in the range of 1 wt.% for Ti 3 B 4 and 3 wt.% for FeB.

Radical-molecule and ion-molecule mechanisms in the polymerization of hydrocarbons and chlorosilanes in r.f. plasmas at low pressures (below 1.0 Torr)

Abstract Ion-molecule and radical-molecule mechanisms are responsible for the dissociation of hydrocarbons and chlorosilane monomers and for the formation of polymerized species in the plasma state of an r.f. discharge. In the plasma of a mixture of the monomer with argon the rate-determining step for both dissociation and polymerization is governed by an interaction of the ion-molecule type. The addition of H 2 or NH 3 to the monomer-argon mixture converts the rate-determining step from an ion-molecule interaction to a radical-molecule interaction for both monomer dissociation and polymerization processes.

Deposition of silicon nitride from SiCl4 and NH3 in a low pressure r.f. plasma

Silicon nitride coatings were deposited in a low pressure (1–10 Torr) r.f. plasma from SiCl4 and NH3 in the presence of argon onto stainless martensitic steel grounded and floating substrates at 300 °C and 440 °C respectively. The heating of the substrates depends mainly on the position and the induced r.f. power. The coatings were identified as silicon nitride by X-ray investigation and were found to contain chlorine by energy-dispersive analysis of X-rays. The growth rate, the microhardness and the chlorine concentration of the coatings were determined as a function of the total gas pressure, the r.f. power input and the NH3-to-SiCl4 ratio. It was observed that the coatings on the floating substrates have higher deposition rates and are of superior quality.

A comparative study of silicon deposition from SiCl4 in cold plasma using argon, H2 or Ar + H2

Abstract The deposition of silicon by cold plasmas using SiCl 4 as the starting gas was studied using argon, hydrogen or a mixture of both as carrier gases. Electron temperatures and densities in these plasmas, as well as plasma species and growth rates, are compared. A good correlation was found between the reaction rates for the decomposition of the reactant and the growth rates of the films in each kind of plasma. The optimal values were measured when a mixture of argon and hydrogen was used. The differences observed between the three plasmas are attributed to the differences in plasma constituents, as detected by the double floating probes system and by mass spectrometry. A schema for the homogeneous (gas phase) and heterogeneous (plasma-surface) interactions in these plasmas is described.

Preparation of polycrystalline silicon coatings from trichlorosilane

Abstract Polycrystalline silicon was deposited onto graphite substrates by the reduction of trichlorosilane (SiHCl 3 ) in an inductive r.f. (27.12 MHz) plasma in hydrogen and argon gas mixtures. The r.f. plasma was operated at low pressure (up to 10 mbar). The kinetics of the deposition of polycrystalline silicon and its chlorine content were studied as functions of the plasma variables, e.g. the substrate position in the plasma reactor with respect to the r.f. coil and the gas flow direction, the concentrations of SiHCl 3 and H 2 in the gas mixture, the total gas pressure, the net r.f. power and the time of deposition. The plasma variables were optimized such that the maximum deposition rate of silicon (0.9 nm s −1 ) and the minimum chlorine content (1%) were obtained.