Laser Ablation of 6H-SiC Single Crystals and Spectral Characterization

Laser micromachining has proven to be a useful tool for precision processing of semiconductors. For Silicon Carbide (SiC) single crystals, ablation with ultraviolet wavelength laser could lead to the maximum absorption efficiency of incident energy. In this paper, laser ablations were performed on 6H-SiC single crystals through a 355 nm solid state laser. Different confining media were also employed to find the optimal processing condition. The surface of SiC after laser ablation was characterized by Raman spectroscopy. Amorphous silicon and nanocrystalline graphite were found to be the main compositions left. For SiC wafers ablation in air, the amorphous silicon exhibited mainly around rather than inside the ablated crater. However, the amorphous silicon showed opposite spatial distribution features for samples processing under liquid. Through analysis of the compositions left on the ablated surface, the ablation mechanism was investigated from another point of view. For liquid confined laser processing,previous studies mainly concentrate on the thickness and viscosity of the liquids, little information has been done on the reducibility of liquids. To investigate the influence of liquid reducibility, the surface morphology and oxygen content of ablation under different confining media were checked by confocal laser scanning microscopy and energy dispersive spectroscopy. Results showed that the reducibility of confining liquid also played a vital role in the ablation process under liquid. Utilizing liquids with deoxidizing ability as confining media will result in a remarkable reduction of surface oxygen content and a more regular morphology.