Dynamics of photo-excitation for the ablation of 4H-SiC substrate using femtosecond laser

The authors suggest a low fluence laser processing method for a power semiconductor wafer using a femtosecond double-pulse beam. In this report, we investigate the temporal variation of the surface reflectivity after the ultrafast laser irradiation as a result of a surface photo-excitation. In the double pulse processing method, the surface reflectivity is constantly high until 5 ps after the first pulse irradiation and then gradually decreased with increasing the time interval to shot the second pulse. In addition, the laser induced damage on SiC target is observed at a bottom of the ablated crater by using scanning transmission electron microscope (STEM). The thin amorphous layer whose thickness is about 10 nm can be observed at the ablated area.