The growth of silicon nitride crystalline films using microwave plasma enhanced chemical vapor deposition

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Crystalline thin films of silicon nitride have been grown on a variety of substrates by microwave plasma-enhanced chemical vapor deposition using N2, O 2 , and CH 4 gases at a temperature of 800 °C. X-ray diffraction and Rutherford backscattering measurements indicate the deposits are stoichiometric silicon nitride with varying amounts of the a and f3 phases. Scanning electron microscopy imaging indicates /3-Si 3 N 4 possesses sixfold symmetry with particle sizes in the submicron range. In one experiment, the silicon necessary for growth comes from the single crystal silicon substrate due to etching/sputtering by the nitrogen plasma. The dependence of the grain size on the methane concentration is investigated. In another experiment, an organo-silicon source, methoxytrimethylsilane, is used to grow silicon nitride with controlled introduction of the silicon necessary for growth. Thin crystalline films are deposited at rates of 0.1 /tim/h as determined by profilometry. A growth mechanism for both cases is proposed.

I. INTRODUCTION The three-dimensional network of covalently bonded S1N4 tetrahedra in silicon nitride is directly responsible for its exceptional mechanical and physical properties. Intrinsic properties of this material, including a high hot strength and hardness, good thermal shock resistance, chemical inertness, and high electrical resistivity, have led to the use of silicon nitride as an insulating diffusion mask in the microelectronics industry, and as a matrix material for ceramic composite applications as well as eliciting active consideration for machine tool, bearing, and engine applications.1 Several methods have been developed to produce silicon nitride thin films and powders. In the electronics industry, plasma discharges are used to produce thin amorphous layers of silicon nitride.2'3 Silicon nitride in the powder form is produced via direct nitridation of silicon,4'5 the carbothermic reduction of silicon dioxide,6"11 and vapor-phase synthesis of silicon halides.12"17 Crystalline thin films of silicon nitride have been reported only in a few cases.13"17 Hirai and Hayashi13 reported the production of yS-Si 3 N 4 using SiCl 4 -NH 3 -H 2 at temperatures from 1350-1450 °C. Gomez-Aleixandre et al.16 and Lee et al.15 formed crystalline films using SiF4 and NH 3 , while Endler et al.17 used S i C l 4 - N 2 - H 2 to deposit a - S i 3 N 4 on titanium nitride or titanium carbonitride layers at a temperature of 900 °C. In this article, we report the plasma synthesis of crystalline silicon nitride using microwave plasmaenhanced chemical vapor deposition (MPECVD). II. EXPERIMENTAL The reactor used in this experiment has been described previously.18 Experiments were first conducted J. Mater. Res., Vol. 9, No. 9, Sep 1994

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using a mixed N 2 and CH4 plasma and silicon substrates as the source of silicon. Table I lists the experimental parameters for Si 3 N 4 growth on silicon substrates. In later experiments, crystal growth with an organosilicon source,