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Summary form only given. Si-C:H film has attracted a lot of attention recently for application in Si-based thin film solar cells, since its bandgap can be easily tunable over a range of 1.5-2.5 eV by simply varying the Si to C ratio in the film. Capacitively coupled SiH4/CH4/H2 plasmas are often employed for deposition of high quality Si-C:H film. A better understanding of the physical and chemical mechanisms in the plasma discharge is desirable. In this study, optical emission spectroscopy of four spectral lines, including Hα (656.2 nm), SiH*(412.8 nm), CH*(430 nm) and H2 Fulcher band (600-630 nm), has been carried out for analyzing the discharge characteristics during the deposition process. The H2 Fulcher band intensity, an indicator of plasma density, is found to increase with rf power, as expected. As the flow rate ratio of CH4/SiH4 increases from 93 to 200, the CH* intensity increases accordingly, as expected, while SiH* intensity remains constant. On the other hand, the Hα and H2 Fulcher band vary little but both intensities drop as the CH4/SiH4 ratio reaches 200. These results indicate that CH4 plays a n less important role for the ionization process in the SiH4/CH4/H2 plasma, as a result of its higher ionization potential than that of SiH4. The detailed experimental results of the parametric analysis by varying, e.g., rf power, gas flow rates, or gas mixtures, as well as their correlation to the film properties, will be presented.