Formation mechanism of surface quality in 4H-SiC wafers sliced via picosecond laser with gradient Energy-Modulation Multi-Pass modification process

Ultrafast laser slicing is a promising method for slicing silicon carbide (SiC) wafers. However, the surface quality of the sliced wafer significantly impacts subsequent processing efficiency and material utilization. This paper investigates the effects of laser processing parameters on the surface quality of sliced 4H-SiC wafers and proposes a gradient energy-modulation multi-pass strategy. The results indicate that excessive pulse energy or scanning passes degrade the cracked layer morphology and increase surface roughness. Compared to constant-energy multi-pass scanning, gradient energy modulation with ΔE_p = 1.7μJ improves surface quality. The area of the modified region and the boundary defect region decreased by 28 % and 20 %, respectively. By using the gradient energy-modulation scanning strategy, a 5 × 5 mm sample with an average Sa = 224 nm was obtained, and the surface roughness was reduced by 80 %. Boundary defects are refined from micron-scale cracks to nanometer-scale voids. This study offers valuable insights and practical methodologies for high-quality SiC wafer slicing, minimizing material loss and enhancing downstream efficiency.