Surface oxidation properties of GaN wafers in chemical magnetorheological polishing process by ultrasonic action

Abstract

To overcome the difficulty of ultraprecision processing of GaN wafers, an ultrasonic chemical magnetorheological composite polishing method using the ultrasonic Fenton method is proposed. The effects of the catalyst type, catalyst concentration and oxidant concentration on the generation of the hydroxyl radical ·OH by ultrasonic Fenton were examined, and the reaction principle of ultrasonic Fenton was determined by using the ·OH and Fe²⁺ content as the main evaluation indices. Compared with those of the ultrasonic Fenton/Fenton reaction under the same conditions, the oxidation‒reduction potential, temperature, ·OH content and Fe²⁺ content all continuously increased within 60 min; thus, ultrasonication promoted the Fenton reaction. A higher catalyst concentration correlated to a higher ionised Fe²⁺ content. A high ·OH content was rapidly generated at the beginning of the reaction, and the ·OH content subsequently decreased after the rapid consumption of the oxidant as the reaction proceeded. The amount of O on the GaN surface increased after oxidation, and the main product of the oxide layer on the GaN surface was Ga₂O₃. Comparative polishing tests have shown that the combination of ultrasound and Fenton action results in higher polishing efficiency and quality.