Correlation between structure and optical properties of Si-based alloys deposited by PECVD

Si-based thin films, including mu c-Si, Si1-xGex and Si1-xCx alloys, have been deposited by plasma enhanced chemical vapor deposition (PECVD) using SiF4:H-2:He, SiF4:GeH4:H-2 and SiF4:CH4:H-2 plasmas, respectively. When SiF4 is used as Si-precursor, it is found that a low flux of CH4 or GcH(4) results in incorporation of C and Ge in alloys as high as 30%. Correlations between microstructure and optical properties of films are investigated using spectroscopic ellipsometry. The role of fluorine atoms in the growth chemistry and material microstructure is discussed.