Optical emission spectroscopy analysis of silane/methane/hydrogen plasma for deposition of a-SiC:H film

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 H_α (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 H_α 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.