Abstract: Silicon carbide (SiC) is a highly valued material for power semiconductor devices due to its wide bandgap, high thermal conductivity, and high breakdown electric field. However, its high hardness, brittleness, and chemical stability present substantial challenges for efficient and high-quality processing. This study investigated the effects of picosecond laser surface scanning on 4H-SiC to enhance the material removal performance. The research focused on surface morphology, phase transitions, subsurface/interface characteristics, and material removal mechanisms under varying laser parameters. The results demonstrate that the laser thermal effect decomposes 4H-SiC into amorphous silicon (a-Si), disordered carbon, and graphite, forming a resolidified layer containing Si-O and Si-C-O oxides. Crystalline silicon (c-Si) is produced under high fluences or extensive irradiations. The variation in the resolidified layer thickness with changing laser parameters is revealed. A detailed laser-induced subsurface damage model is developed, encompassing a resolidified layer that includes the above decomposition and oxidation products, and a deformed layer formed primarily under laser-induced stress. The presence of the resolidified layer and the deformed layer leads to a decreased elastic recovery rate and an increased scratching depth, exceeding 2.5 times that of the unmodified condition. Enhanced material removal performance is mainly driven by the resolidified layer at low fluence and by the deformed layer at high fluence. When aligning the total of the ablation depth and the resolidified layer thickness with the subsurface damage depth in the original material, excellent polishing performance is achieved. These findings provide critical insights for understanding the phase evolution, subsurface damage mechanisms, and material removal behavior of 4H-SiC, offering valuable guidance for optimizing the laser surface modification parameters to achieve high-efficiency processing.

Key words: Silicon carbide, Laser surface modification, Laser parameter, Phase transition, Subsurface damage, Ultra-precision machining