Chemical Polishing Rate Differences Induced by Atomic Arrangement on Polar Surfaces of AIN Crystals

The chemical polishing of AIN wafers typically involves a micro-reaction between the oxidizing agent in the polishing solution and the crystal surface, forming an oxide layer. In the alkaline (or acidic) environment of the polishing solution, further reactions occur, leading to the formation of a softened layer, which is subsequently removed by the physical abrasion of fine particles, resulting in a smooth AIN wafer surface. However, wurtzite AIN crystals, due to their lack of a center of symmetry and the significant electronegativity difference between Al and N atoms, exhibit spontaneous polarization effects. The ABabABab… atomic stacking sequence along the c-axis causes the (0001) and (0001) surfaces to display distinctly different properties. An atomic-level analysis of the atomic arrangement on different polar planes reveals that this difference determines the rate and ease of oxidation and hydrolysis reactions on the surface. It is generally believed that the atomic arrangement on the Al polar surface consists of a top layer of Al atoms. Although, from a structural perspective, the (0001) surface more readily forms an oxide layer, following a series of oxidation, hydrolysis, and the abrasive action of fine particles, the surface exposed on the Al surface is a single layer of nitrogen atoms with a single coordination. The three dangling bonds on these N atoms increase the repulsion toward O and OH, making oxidation and hydrolysis reactions more difficult, and the repulsion effect of these dangling bonds is much smaller for the N polar surface. Consequently, the Al surface exhibits a significantly slower polishing rate during the chemical polishing process.