Control of microstructure in a-SiC:H

Abstract

We demonstrate a means of controlling the microstructure and carbon content in amorphous hydrogenated silicon carbide (a-SiC:H) thin films prepared in a plasma-enhanced chemical vapor deposition system. The capacitively coupled, parallel-plate deposition apparatus includes provision for adjusting the potential of the powered electrode by application of an additional, independent dc voltage. This voltage affects the deposition chemistry. Films prepared when various positive and negative dc voltages are applied are studied with infrared absorption, nuclear magnetic resonance, and electron spin resonance. Their optical band gaps, electrical conductivities, and dark conductivity activation energies are also measured. The films have carbon contents ranging from 1 to 4 at. %. We find that we can alter the microstructure of a-SiC:H by adjusting the powered-electrode potential during deposition, and that these microstructural changes are reflected in the film properties. A small increase in the self-biased voltage of the powered electrode leads to a film with the least amount of infrared-observable microstructure and the highest photoconductivity. Applying an external dc voltage leads to an increase in deposition rate regardless of voltage polarity. The films prepared with externally applied voltage all have lower hydrogen contents than the film prepared with self-biased voltage, which may explain the observed property changes. The addition of an external dc voltage can have beneficial effects on the deposition rate, structure, and properties of a-SiC:H films.