Improvement of dry etch-induced surface roughness of single crystalline β-Ga₂O₃ using post-wet chemical treatments

Post-wet chemical treatments using sulfuric acid and hydrogen peroxide mixture (SPM) or tetramethyl ammonium hydroxide (TMAH) solutions were performed to reduce dry etch-induced surface damage of β-Ga₂O₃ caused by the inductively coupled plasma-reactive ion etching (ICP-RIE) process using the Cl₂/BCl₃ gas mixture. The addition of BCl₃ to the Cl₂/BCl₃ gas mixture resulted in a significant enhancement of the etch rate of β-Ga₂O₃. However, it increased the surface roughness with the formation of the nonvolatile etch by-product B₂O₃ as a result of the BCl₃/β-Ga₂O₃ reaction. The post-SPM treatment led to the reduction of dry etch-induced surface damage of β-Ga₂O₃ to a certain extent with the removal of B₂O₃. On the other hand, the post-TMAH treatment significantly improved the surface morphology of the dry etched β-Ga₂O₃ surface. During the post-TMAH treatment, the chemical reaction between the damaged β-Ga₂O₃ layer caused by ICP-RIE process and OH⁻ in the TMAH solution led to the formation of the Ga oxide, followed by the simultaneous dissolution of the Ga oxide and the B₂O₃. Thus, the post-TMAH treatment effectively recovered the surface damage of β-Ga₂O₃ induced by the ICP-RIE process using the Cl₂/BCl₃ gas mixture.