Amorphous hydrogenated-silicon carbide $(a-Si_{1-X}C_X)$ films have been prepared by the r.f sputtering using a silicon target in a gas mixture of Ar and $CH_4$ with varying $CH_4$ gas flow rate in the range of 1.5 to 3.5 sccm at constant Ar flow rate of 30 sccm and r.f power in the range of 3 to 6 W/㎠. The effects of methane flow rate, r.f power and post annealing treatments on the structure and optical properties of $a-Si_{1-X}C_X$ films have been analysed by measuring both the IR absorption spectrum and the UV transmittance for the films. The optical band gap(Eg) of $a-Si_{1-X}C_X$ films have been analysed by measuring both the IR absorption spectrum and the UV transmittance for the films. The optical band gap (Eg) of $a-Si_{1-X}C_X$ films is highly dependent on the $CH_4$ gas flow rate. The Eg of $a-Si_{1-X}C_X$ film increases from 1.6eV to the maximum value of 2.42 eV at a r.f power of 4W/㎠ and a $CH_4$ flow rate of 3 sccm due to an increase in the ratio of carbon to silicon in the films. It appears that a decrease of Eg of films deposited at $CH_4$ gas flow rates greater than 3 sccm is associated with a significant increase in the number of C-Hn bond and a probable formation of carbon clustering.
As the r.f power increases, the number of Si-C and Si-Hn bond significantly increases with an reduction in the nuber of C-Hn bonds. The dependence of Eg on the r.f power is greatly influenced by the $CH_4$ gas flow rate. At the $CH_4$ flow rate of 3 sccm, the Eg has a value of about 2.4eV irrespective of the r.f power. On the other hand, at the $CH_4$ flow rate of 2 sccm, the Eg is significantly decreased from 2.3eV to 1.8eV with increasing the r.f power.
For a-SiC:H film having a relatively low content of carbon, the Eg increases from 2.4eV to 2.7eV by a post annealing at temperature of 300 to 500℃. This is attributed to the competitive difference in rates between a reconstruction of Si-C bond and a formation of dangling bond that occurs by hydrogen evolution from the films during annealing treatment.
