Modulation of ultrafast laser-induced modified structure inside silicon carbide for thin wafer dicing

Effective modulation of the internal modification structure is critical for enhancing the quality and efficiency of ultrafast laser dicing in SiC wafer. This paper achieves modulation of the height and width of the modified layer by changing the pulse width and pulse interval. Based on dark-field imaging method, the morphology of the modified layer after laser scanning is non-destructively detected. Transformation of nonlinear absorption modes and heightened thermal effects lead to a stepwise increase in the width of the modified layer. The width of the modified layer with incubation effect is bigger than the width of the modified region with a single pulse of laser action. The height of the modified layer can be significantly increased by multi-focusing, the strength of plasma defocusing determines both the distance between focus points and the total number of focus points. The generation of transverse cracks is determined by the laser pulse width and modification overlap ratio, and transverse cracks are not produced when the laser pulse width is ≤ 2 ps. The sub-picosecond laser monofocal modification dicing process achieves high-quality dicing, the multi-focused laser modification dicing process with pulse widths in the tens of picoseconds range achieves high-efficiency dicing. This study provides a reference for thin SiC wafer dicing and ingot laser slicing.