Investigation of the effect of Acetylene gas flow in plasma mixture on the structural and optical properties of carbon doped Silica thin film

In this study, silica and carbon doped silica thin films were deposited on silicon substrates by plasma polymerization using capacitively coupled system in radio frequency. Organo-silicon TEOS vapor was used as a precursor for synthesizing the films which were mixed by specific flow rate of oxygen gas.In order to combine carbon elements into the silica films, acetylene gas was also added into the plasma gas mixture. The effect of acetylene gas flow rates on thickness and refractive index of the films was studied by spectroscopic ellipsometry. Furthermore, in order to investigate the films transparency, the optical absorption was also determined using the same analysis. Morphological investigation of the films using atomic force microscopy was shown that increasing acetylene into the plasma, causes to increase the surface roughness of the films from 0.1 nm to 5.3 nm. Furthermore, the results of optical analysis were shown that increasing acetylene concentration in the plasma led to increase the films refractive index from 1.447 to 1.485 as well as increase their optical absorption from 0.8% to 9.3%. Moreover, for adding carbon elements into the silica films and changing their properties, the effect of increasing acetylene flow rate was compared by decreasing oxygen flow rate.