BONDING STRUCTURE AND OPTICAL BANDGAP OF RF-SPUTTERED HYDROGENATED AMORPHOUS-SILICON CARBIDE ALLOY-FILMS

Hydrogenated amorphous silicon carbide (a-Si1-xCx:H) alloy films were deposited by radio frequency (rf) magnetron sputtering at room temperature with variable rf powers. Effects of deposition parameters on the bonding structure and optical properties of the films were measured. Infrared (IR) absorption and optical transmittance measurements of films deposited under methane gas flow rates of 2 and 3 sccm showed that they differed. In the case of 2 sccm flow rate, the optical bandgaps gradually decreased with increasing rf power and slopes, B, of the Tauc plot increased up to a power of 5 W/cm2. In the case of 3 sccm flow rate, optical bandgaps increased and the slopes were invariant with power. This difference is attributed to the differences in the bond structure of the films. Under the condition of flow methane gas flow rate as in the former case, the Si-C bonding concentration is saturated and those of Si-H(n) bonds still increase while those of C-H(n) bonds decrease with power. However in the latter, both concentrations of Si-C and Si-H(n) bonds increase and those of C-H(n) bonds decrease. As a result, optical bandgaps of rf sputtered films which have a high fraction of carbon, greater than 0.65, are more influenced by the Si-C bonds than by the hydrogen-related bonds.