Taming the boundary effect: Femtosecond laser slicing of 4H-SiC enabled by side scribing for improved processability

Abstract

The 4H polytype of silicon carbide (4H-SiC) has excellent properties such as high electron mobility and high saturation electron velocity; it has therefore become an important material for high-power and high-frequency devices. In the slicing step of wafer fabrication, however, conventional wire-saw cutting is constrained by the inherent high hardness and brittleness of 4H-SiC, causing excessive material removal and surface and subsurface damage. To overcome these limitations, this study proposes a femtosecond laser slicing technology combined with side scribing. A simulation model of the boundary effect in internal laser processing was established to analyze the optical energy distribution under spherical aberration. The simulations revealed boundary regions that resist laser modification because of the coupling between asymmetric focusing and spherical aberration, which degrades the slicing quality of conventional laser processing. Systematic parametric experiments were then used to investigate the influence of the laser processing parameters on the formation of the modified layer. Targeted experiments performed using the optimized processing parameters provided a quantitative characterization of the hard-to-modify regions and guided the application of the side-scribing process. The peeling results demonstrate that the proposed side-scribing-assisted femtosecond laser slicing process effectively reduces the peeling stress and the cracking that occurs during slicing, achieving a 68% reduction in peeling stress and a 27% reduction in the arithmetic mean roughness Sa of the peeled surface, together with the formation of laser-induced periodic surface structures that are better suited to subsequent processing, compared with conventional laser slicing. This study improves the processability of 4H-SiC wafer slicing and provides a new approach to substrate preparation for wide-bandgap semiconductor materials.