Study of femtosecond laser ablation effect on micro-processing for 4H-SiC substrate

4H-SiC substrate was ablated by linearly polarized femtosecond (fs) laser in three direct write methods at different parameters, such as repetition rate, scanning velocity and fluence, etc. Two processing modes, transverse scanning mode (TSM) and cross irradiation mode (CIM), were introduced. The surface morphologies were observed by scanning electron microscopy (SEM) for detailed investigation. It was found that the surface morphologies differed remarkably at different processing parameters. Firstly, the shapes of micro craters fabricated at different repetition rates and ablation time duration were respectively investigated. The shape of fs laser spot was demonstrated to play an important role for the generation of micro craters. Secondly, the effect of scanning velocity on the formation of nanoripples and micro grooves were investigated. It was found that the spatial ripples could be refabricated during repeated fs laser ablation; periodic ripples and micro grooves depended on fs laser scanning velocity. Agglomerative substance was fabricated especially at slow scanning velocity. Furthermore, rippled surfaces induced at different fluence were achieved and exhibited. Regular and uniform surfaces with periodic ripples were fabricated at the fluence of 0.31∼0.38 J/cm² . Finally, CMP was carried out to study the effect of fs laser ablation on polishing.