Laser induced crystallization of hydrogenated amorphous silicon-carbon alloys

Laser induced crystallization of hydrogenated amorphous silicon carbon alloy (a-Si1-xCx:H) films has been investigated by means of synchrotron X-ray diffraction. The a-Si1-xCx:H films were deposited on (100) silicon wafers by Very High Frequency Plasma Enhanced Chemical Vapor Deposition (VHF-PECVD) at 100 MHz in hydrogen diluted silane-methane gas mixtures. The substrate was kept at 250°C or 350°C and the stoichiometry was changed from x = 0.20 to 0.63. The structural characterization of the as-grown films has been carried out by Rutherford Back Scattering (hydrogen concentration) and Infrared Spectroscopy (film ordering). The films were irradiated by a KrF excimer laser (248 nm) with varying energy density and number of pulses. After irradiation, the formation of SiC crystallites has been revealed by synchrotron X-ray diffraction. Besides SiC nanocrystals, the formation of crystalline Si and graphite is observed for under- (x<0.50) and over-stoichiometric (x>0.50) samples respectively. The essential role played by hydrogen concentration and hydrogen bonding configuration in determining the melting threshold and the consequent SiC grain formation is highlighted