Glow discharge deposition of tetramethylsilane films

Thin films have been deposited in a low-pressure glow discharge of tetramethylsilane. The study of the deposition kinetics has shown that the determining parameter is the ratio W/P_TMS of the RF power over the TMS partial pressure. The role of oxygenated impurities present in the starting monomer is emphasized. High values of the W/P_TMS ratio give films of low oxygen content as shown by IR spectroscopy measurements (<5% of Si-O bonds). These films have high densities (1.7–2 g/cm³) and refractive indices (1.7) and are similar to amorphous hydrogenated silicon carbide films. On the contrary, low values of W/P_TMS result in the formation of a significant amount of Si-O bonds which are formed at the expense of Si-H bonds. The deposited films show lower densities (0.98–1.6 g/cm³) and lower refractive indices (1.47). It is postulated that this oxygen, which affects the kinetics and the film properties, comes from oxygenated pollutants (H₂O) carried along with the monomer, and that its concentration depends on the temperature of the TMS cooling bath.