Mechanism of Material Removal from Silicon Carbide by Carbon Dioxide Laser Heating

The mechanism of material removal from SiC by CO₂ laser heating was studied using sintered and single-crystal α-SiC. Removal rate and width of the groove showed maxima when plotted as a function of translation speeds. Groove depth decreased as the translation speed of samples increased. Similar results were obtained if argon or air was used as gas assist, which indicated that the material removal mechanism is induced dissociation of SiC. Microstructure of the material deposited in and outside of the groove was studied by SEM. At low scanning speeds, columnar grains 10 to 50 μm long appeared. As the scanning speed increased, columnar grains became smaller and finally only irregular polycrystalline particles were observed. By using Raman spectroscopy, Auger analysis, and X-ray diffraction, phases inside and outside the groove were identified as Si, β-SiC, C, and SiO₂. Columnar grains were identified as β-SiC covered with thin layers of C, Si, and SiO₂. Slow scanning speeds enhanced the growth of β-SiC. At slow scanning speed, free silicon was always found in the grooves of lased single crystals but not in the grooves of lased sintered SiC. It can be concluded that the mechanism of material removal from silicon carbide by CO₂ laser heating is a vaporization process, and material found in the groove and on the surface near the groove is formed by condensation from the vapor.