Optical Emission Analysis of a Si(CH₃)₄-Argon Radio Frequency Plasma for SiC Films Deposition

Abstract
RF glow discharges from tetramethylsilane diluted in an argon flow have been investigated in a cold wall R.F. (2MHz) P.E.C.V.D. reactor. This reactor is used for fast deposition of adherent amorphous silicon carbide films (with Si/C≈1.2) on steel. Optical emission from the plasma was sampled using a high resolution double monochromator (2m focal length, 1800 grooves/mm) coupled with a multichannel CCD detector. Only the lines corresponding to neutral or ionised Argon (Ar, Ar⁺), the broadened hydrogen Balmer (Hα et Hβ) and silicon ionised lines (Si⁺) were clearly pointed out perpendicularly or parallel to the discharge axis. The different broadenings observed were due to Doppler effects and connected with the movement of radical species. With TMS, the fine structure of the hydrogen line is deconvoluted in three gaussian like components, one of which denotes high energy atoms coming from a TMS derived species. Previous mechanisms for hot atom production do explain our results, but the various experimental broadenings could be ascribed to gradients in the cathode sheath adjacent to the substrate, and the hot atoms could be produced by electron impact on intermediate fragments, one bearing silicon, the other bearing carbon.