A. Grill

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.-sputtered silicon and hafnium nitrides: Properties and adhesion to 440C stainless steel☆

Abstract Silicon nitride and hafnium nitride coatings were deposited by reactive r.f. sputtering onto oxidized and unoxidized 440C stainless steel substrates. The coatings and the interface between the coating and substrate were investigated by X-ray diffractometry, scanning electron microscopy and Auger electron spectroscopy. The Knoop microhardness was measured together with the friction coefficient between a 440C rider and the coatings. Scratch test results demonstrate that the adhesion of hafnium nitride to both oxidized and unoxidized 440C is superior to that of silicon nitride. Oxidized 440C is found to have increased adhesion, to both nitrides, compared with that of unoxidized 440C.

MICROSTRUCTURE AND COMPOSITION OF PLASMA-NITRIDED Ti—6Al-4V LAYERS

Abstract Nitriding of titanium alloys was performed in an r.f. plasma of nitrogen, hydrogen and argon at a substrate temperature of about 500 °C. The microstructure and the composition of the nitrided layers obtained were studied by X-ray diffraction, scanning electron microscopy, transmission electron microscopy (TEM) and Auger electron spectroscopy (AES). Three phases were identified: (a) a solid solution of nitrogen in titanium, α-(Ti, N), (b) tetragonal ϵ-Ti 2 N and (c) cubic δ-TiN (NaCl-type structure). Two distinct layers were formed on top of the plasma-nitrided Ti-6Al-4V alloy, followed by a solid solution of nitrogen in the titanium alloy. The outer layer was identified as δ-TiN while the inner layer was identified as a mixture of δ-TiN and ϵ-Ti 2 N. The ϵ-Ti 2 N was found to be highly oriented (002) while the δ-TiN was obtained as a randomly oriented polycrystalline layer. The outer δ-TiN was found to have a fine structure, while the inner δ-TiN plus ϵ-Ti 2 N comprised large and oriented grains. TEM studies showed that the crystallite size in the upper layer was tens to hundreds of angstroms, while in the inner layer it was one tenth to about half a micrometre. Energy-dispersive analysis performed with the TEM system and AES shows a variation in the bulk composition along the nitride layer. The microstructures and the relative phase content are presented and discussed in relation to the gas feed composition in the plasma.

Nitriding of AISI M2 tool steel in an inductive r.f. plasma

Abstract The nitriding of AISI M2 tool steel in an inductive r.f. plasma was investigated. The plasma was sustained with a 27.12 MHz generator in gas mixtures of N2 and H2 at a pressure of 10 mbar. The ion nitriding was performed at a net r.f. power of 400 W at substrate temperatures of 450–500 °C. X-ray diffraction studies of the treated samples revealed that the most efficient formation of nitride phases was observed in samples nitrided in a pure N2 plasma. As a result of the ion nitriding the surface hardness was substantially increased from a Vickers hardness VHN of 290 kgf mm-2 for untreated samples to a maximum VHN of 1200 kgf mm-2 for samples treated in a plasma sustained in a gas mixture with N2:H2 = 1:1.

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.

Silicon films deposited from SiCl4 by an r.f. cold plasma technique: X-ray photoelectron spectroscopy and electrical conductivity studies☆

Abstract Chemical and electrical characteristics of microcrystalline silicon films deposited from SiCl4 by an r.f. glow discharge were determined using X-ray photoelectron spectroscopy (XPS) and conductivity measurements. The chlorine content in the bulk was found to be about 2–3 at.%, forming partially ionic Siue5f8Cl bonds as reflected by the XPS Cl2p chemical shift. The apparent shift in the Si 2p line is attributed to displacement of the Fermi level induced by the chlorine, which acts as a p-type dopant. This is confirmed by the electrical conductivity measurements carried out for undoped, B2H6- and PH3-doped films. The rather high dark conductivity σ D ≈ 10 -3 Ω -1 cm -1 of the undoped film seems to be associated with the microcrystalline structure. The degree and extent of silicon oxidation across the surface region were studied in detail for two differently air-exposed samples and are discussed in terms of the microcrystalline structure of the film. Compositional variations observed across the silicon-substrate interface are attributed to reactions with the stainless steel substrate during the initial deposition process.

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.

Deposition of silicon from SiCl4 in an inductive r.f. low pressure plasma

Abstract An inductively coupled r.f. plasma was applied to deposit silicon coatings on graphite substrates at 350 °C. The silicon coatings were obtained by reduction of SiCl4 in plasmas excited in gas mixtures of argon, H2 and SiCl4. The kinetics of deposition were investigated and the results indicate that the maximum rate of deposition is obtained inside the r.f. coil, at a position which is a function of the total gas pressure in the reactor. The rate of deposition increases with decreasing [H2]/[SiCl4] ratio, at a constant concentration of SiCl4 in the gas mixture, and it increased with deposition time up to 6h; it showed a maximum at an SiCl4 concentration of 2.5%. The deposited coatings were amorphous. X-ray diffraction indicated 56% crystallinity in samples heat treated at 900 °C for 2h.

Effect of frequency on the deposition of microcrystalline silicon from tetrachlorosilane in low-pressure r.f. plasmas

The efficiency of reduction of silicon tetrachloride and the rate of deposition of Si in a low-pressure r.f. plasma was investigated at two frequencies (0.4 and 27 MHz) as a function of position with regard to the rf coil, pressure, and time of deposition. At 27 MHz the decomposition efficiency of silicon tetrachloride and the deposition rate of Si are about three times higher than at 0.4 MHz.