Mechanism of glycine and H2O action in tribochemical mechanical polishing of single-crystal gallium nitride substrate

• A novel Gly-based TCMP method of SC-GaN substrate is proposed, which exhibits a Ra of 0.80 nm and considerable MRR of 97.1 nm/h without the use of any acid or alkali corrosive solution. • The influence of SC-GaN lattice distortion (friction-induced) on Gly/SC-GaN and H 2 O/SC-GaN reactions is first revealed through analyzing the geometric configurations and interfacial interactions. • Based on TCMP experiments and first-principle calculations, a microscopic material removal model for the TCMP of SC-GaN substrate with Gly is first established. With the rapid development of the third-generation semiconductors, environmentally friendly tribochemical mechanical polishing (TCMP) is in urgent need and has been a research hot-spot. In this work, the mechanism of glycine (Gly) and H 2 O action in TCMP of single-crystal gallium nitride (SC-GaN) substrate is systematically studied. The experimental results indicate that the TCMP of SC-GaN substrate with 0.75 wt% Gly exhibits a higher surface quality and a 3-fold improvement in material removal rate than that with H 2 O. Based on first-principle calculations, the geometric configurations and interfacial interactions of the Gly/SC-GaN and H 2 O/SC-GaN heterostrutures are further explored. Charge transfer analysis shows that SC-GaN with lattice distortion of 0.4 Å transfers more electrons into Gly (0.202 e) than into H 2 O (0.128 e), which suggests the reaction between SC-GaN and Gly is more intense under friction by abrasives. The research of differential charge density and geometric properties (bond angles etc.) demonstrates that the –COOH functional group (Gly) has a higher reactivity than the –OH functional group (H 2 O). Based on the above findings, a microscopic material removal model for the TCMP of SC-GaN substrate with Gly is established. These results have potential applications in the semiconductor and microelectronics industries.