Material removal mechanism of sapphire substrates with four crystal orientations by double-sided planetary grinding

Abstract Sapphire substrates with different crystal orientations are widely used in photoelectric applications. Double-sided planetary grinding is a new process for the rapid thinning and flattening of sapphire, and experiments with it were carried out on sapphire substrates with four commonly used crystal orientations (C-plane (0001), A-plane (11 2 ‾ 0), M-plane (10 1 ‾ 0), and R-plane ( 1 ‾ 012)). By comparing the material removal rates (MRRs), surface topographies, damages, and wear debris among substrates with the four crystal orientations, the removal mechanism for each orientation was revealed. The results showed that the MRR and surface quality of the substrates varied greatly with the four orientations. The R-plane was removed in the form of large pieces of spalled material and had the highest MRR and the largest surface roughness (Sa) of approximately 780 nm among the orientations studied. The C-plane was mainly removed in the form of unique large step-like pieces of spalled material, had the lowest MRR among the orientations observed, and exhibited an Sa of approximately 430 nm. The machinability of the A-plane and M-plane orientations were similar. Both were removed as small pieces of spalled material, and their surface quality was good, with Sa values of 340–390 nm. The experimental results revealed that crystal orientations with lower Young's modulus and fracture toughness values were easier to remove material from, and vice versa. Therefore, to obtain a reasonable material removal rate and a good surface quality of sapphire substrates, different processing techniques are needed for different crystal orientations.