Low temperature deposition of nanocrystalline silicon carbide films by plasma enhanced chemical vapor deposition and their structural and optical characterization

Nanocrystalline silicon carbide (SiC) thin films were deposited by plasma enhanced chemical vapor deposition technique at different deposition temperatures (T-d) ranging from 80 to 575 degreesC and different gas flow ratios (GFRs). While diethylsilane was used as the source for the preparation of SiC films, hydrogen, argon and helium were used as dilution gases in different concentrations. The effects of T-d, GFR and dilution gases on the structural and optical properties of these films were investigated using high resolution transmission electron microscope (HRTEM), micro-Raman, Fourier transform infrared (FTIR) and ultraviolet-visible optical absorption techniques. Detailed analysis of the FTIR spectra indicates the onset of formation of SiC nanocrystals embedded in the amorphous matrix of the films deposited at a temperature of 300 degreesC. The degree of crystallization increases with increasing T-d and the crystalline fraction (f(c)) is 65%+/-2.2% at 575 degreesC. The f(c) is the highest for the films deposited with hydrogen dilution in comparison with the films deposited with argon and helium at the same T-d. The Raman spectra also confirm the occurrence of crystallization in these films. The HRTEM measurements confirm the existence of nanocrystallites in the amorphous matrix with a wide variation in the crystallite size from 2 to 10 nm. These results are in reasonable agreement with the FTIR and the micro-Raman analysis. The variation of refractive index (n) with T-d is found to be quite consistent with the structural evolution of these films. The films deposited with high dilution of H-2 have large band gap (E-g) and these values vary from 2.6 to 4.47 eV as T-d is increased from 80 to 575 degreesC. The size dependent shift in the E-g value has also been investigated using effective mass approximation. Thus, the observed large band gap is attributed to the presence of nanocrystallites in the films. (C) 2003 American Institute of Physics.