Atomically self-limited removal of Cl2-plasma-modified GaN by F2-added Ar plasma at high temperature of 300 °C

Cycle processes of chlorine plasma modification and F2-added Ar plasma removal at a high wafer temperature of 300 °C was examined for self-limited atomic layer etching (ALE) of GaN. The threshold ion energy for etching of GaN by the F2-added Ar plasma was identified at high temperatures and found to decrease with increasing wafer temperature, ultimately reaching 23 eV at 400 °C, despite the low volatility of gallium fluoride. By selecting a wafer temperature of 300 °C and an ion energy of 57 eV, which is equivalent to the threshold energy, ideal self-limited ALE was achieved by combining with the process of surface modification of GaN by chlorine plasma. Then, the etching rate per cycle measured by in situ ellipsometry was 0.14 nm. Consequently, low-damage and precisely rate-controlled etching for GaN are promised.