The effects of process pressure and microwave power on the properties of boron-doped SiC: H films prepared using the ECR-CVD technique

Abstract

Hydrogenated amorphous silicon carbide films (a-SiC:H) were deposited from a mixture of methane, silane and hydrogen, with diborane as the doping gas, using the electron cyclotron resonance chemical vapour deposition (ECR-CVD) technique. The effect of the microwave power on the deposition rate was studied at two different process pressures (4 mTorr and 8 mTorr), and variations in the photoconductivity and dark conductivity were investigated in conjunction with film analysis using the Raman scattering technique. Samples deposited at both process pressures showed a rapid increase in the conductivity to a maximum, followed by a drastic reduction at high microwave powers. The ratio of the photoconductivity to the dark conductivity ( σ ph/ σ d) peaked at microwave powers of about 550 W and 450 W for samples deposited at 8 mTorr 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 for the subsequent decrease in the conductivity.