Study on surface modification of 4H-SiC wafers induced by nanosecond laser

Due to its high hardness, brittleness, and high melting point, high-precision surface processing of silicon carbide (SiC) presents significant challenges. To improve processing efficiency and surface quality, laser-assisted machining techniques have been widely applied in SiC treatment. In this study, ultraviolet nanosecond laser was used to modify the surface of 4H-SiC wafers, and the effects of laser energy density, scanning speed, and step overlap rate on the surface roughness of SiC were investigated. As the laser energy density increases, the silicon content on the SiC surface remains largely unchanged, while the oxygen content rises (25.27 %) and the carbon content decreases. The thickness of the oxide layer also grows, reaching a maximum of approximately 830 nm. Reducing scanning speed and increasing step overlap rate also enhanced the oxygen content on the SiC surface. Comparing the two wafers, the SiC wafer with a larger surface roughness has a thicker oxide layer and higher oxygen content. The nanoindentation test results show that plastic deformation occurred on the SiC surface during laser treatment, leading to a reduction in hardness, which is beneficial for subsequent processes. For the finished wafers, the optimal process parameters are an energy density of 10 J/cm², scanning speed of 350 mm/s, and step overlap rate of 8 %. For the process wafer, the energy density is 8 J/cm², with the other parameters remaining the same. The research results provide experimental support for the improvement of SiC surface quality and subsequent precision manufacturing processes.