Doping and microwave power effects on the properties of a-SiC:H and μc-SiC:H films prepared using ECR-CVD

Hydrogenated amorphous silicon carbide films (a-SiC:H) were deposited using the electron cyclotron resonance chemical vapour deposition (ECR-CVD) technique from a mixture of methane, silane and hydrogen, with diborane as the doping gas. Using two different process pressures (4 and 8 mTorr), the effect of the microwave power on the deposition rate were studied, and variations in the photo and dark conductivities were investigated in conjunction with film analysis using the Raman scattering technique. Samples deposited at both pressures showed rapid increase in the conductivity to a maximum, followed by drastic reduction at high microwave powers. The ratio of the photo to dark conductivity (σph/σd) peaks at microwave powers of ~ 600 and 450 W for samples deposited at 8 and 4 mTorr. respectively. Under conditions of high hydrogen dilution and increasing microwave power, Raman scattering analysis showed evidence of the formation and increase of microcrystalline silicon and diamond-like phases in the films, the former of which could account for the rapid increase and the latter the subsequent decrease in the conductivity. Preliminary investigations of the effect of changes in the diborane levels show that films deposited at a low microwave power of 150 W were all amorphous whereas those deposited at a high microwave power of 800 W contain microcrystalline silicon inclusions and became amorphous as the diborane level is increased.