Morphological evolution of 4H-SiC substrates in stealth dicing by picosecond laser

As a non-contact method, stealth dicing provides an effective solution to the machining challenges of brittle 4H-SiC wafers that replace conventional cutting approaches. In this paper, the morphological evolution of 4H-SiC substrates during stealth dicing was investigated by using a picosecond laser. The results show that the pulse energy is a critical factor to determine the dimensions of the modified structure, with high pulse energy inducing a high aspect ratio laser self-focusing morphology inside the material. Microstructural analysis reveals three types of modified structures: clustered, filamentous, and blocklike structures, which are primarily influenced by the pulse energy and repetition rate. Cracks in the modified structure propagate from the interior of the material toward the cleavage direction, range of which along with the degree of modification are affected by the scanning times. By optimizing the scanning distance, the SiC sample is successfully separated under an applied force of 8.8 N without chipping. Raman spectroscopy analysis confirms that no phase transitions or chemical bond breakage occurred during laser processing. Instead, it confirms that the internal damage and crack propagation of the material are induced by compressive stress.