Cavity etching evolution on the A-plane of sapphire crystal in molten KOH etchant

Chemical wet etching technology is widely applied in semiconductor device fabrication such as the patterned sapphire substrates. However, the etching of pre-formed structure is still lack of investigations, which has potential applications in the preparation of particular devices. By using molten KOH etchant, the present work studied the wet etching behaviors of cavity on the A-plane of sapphire crystal in three-dimensional space and revealed the etching kinetics. It was demonstrated that the cavity will evolve into a complicate symmetric shape with multiple facet planes during etching. The width of the cavity is gradually expanded however the depth of the cavity is stable during etching, where the Arrhenius model was held, indicating that the etching process is realized by step flow removal of atoms. The present results improve the understanding of the morphology evolution and relevant kinetics of a pre-formed structure on sapphire crystal during wet etching, which shed further light on the single crystal wet etching technology for device fabrication.