Interface weakening mechanism for femtosecond laser slicing of semi-insulating 4H-SiC wafers

Abstract

With the ongoing advancement in power electronics and radio-frequency systems toward higher power density, elevated operating frequencies, and increased integration density, there is a corresponding and growing demand for thinner substrates. Single-crystal 4H‑SiC, owing to its outstanding thermal conductivity and superior electrical characteristics, has emerged as a critical substrate material for next‑generation high‑performance devices. Nevertheless, conventional mechanical wafer‑slicing techniques are constrained by substantial kerf loss, sub‑surface damage, and the need for extensive post‑thinning processing. Femtosecond‑laser‑induced internal modification has arisen as a highly promising non‑contact alternative, enabling precise and high‑quality wafer separation with minimal thermal impact via the induction of the weak bonding interface. However, the insufficient understanding of the formation and failure mechanisms of such interfaces has hindered further improvements in separation quality. This study reveals that two distinct failure paths within the laser-induced weakened interface dictate the final surface morphology. The difference in surface quality originates from two competing failure modes: debonding along the amorphous-crystalline interface and separation within the modified zone. To clarify the underlying interfacial weakening mechanism, a theoretical model based on temporal scale separation was established, elucidating the ultrafast photon energy transfer process responsible for interface degradation. Furthermore, microstructural characterization identified the dominant factors governing each failure path: interface separation initiated by atomic disorder at the amorphous-crystalline boundary, stress concentration induced by nanograting structures, and micro-crack propagation. These insights provide a theoretical foundation for high-quality laser slicing of 4H-SiC.