Abstract：In order to achieve the purpose of high efficiency and high quality ultra-smooth and flat processing of sapphire substrate, a new process of pre-treatment and modification of sapphire wafer surface material by femtosecond laser and then cluster magnetorheological polishing is proposed in this paper. The effects of femtosecond laser scanning speed and cluster magnetorheological polishing time on the material removal rate and surface roughness of laser pretreated sapphire wafer were studied. At the same time, the material properties of sapphire surface before and after femtosecond laser treatment were analyzed by means of X-ray photoelectron spectroscopy (XPS) and X-ray diffraction (XRD), and the mechanism of femtosecond laser-assisted cluster magnetorheological polishing was studied. The results show that femtosecond laser pretreatment has a significant effect on cluster magnetorheological polishing of sapphire wafers. The material removal rate of cluster magnetorheological polishing of sapphire wafers pretreated with femtosecond laser is more than doubled, and when the scanning speed of femtosecond laser is 100mm/s, better surface roughness and surface morphology of sapphire can be obtained after polishing. The results of XPS and XRD show that there is no chemical reaction on the surface of sapphire substrate irradiated by femtosecond laser, but the amorphization and microcrystallization of the crystal structure of sapphire surface layer caused by femtosecond laser are beneficial to the material removal in the process of cluster magnetorheological polishing. It is concluded that femtosecond laser can microcrystallize and amorphize the surface layer of sapphire, which is beneficial to improve the polishing efficiency and surface performance of cluster magnetorheological polishing sapphire.
2022, 
