Etching mechanism of a GaN/InGaN/GaN heterostructure in Cl2- and CH4-based inductively coupled plasmas

The etching mechanism of a GaN/InGaN/GaN heterostructure was studied using Cl2- and CH4-based inductively coupled plasma. The Cl2-based plasmas are effective for fast and smooth etching of the homogeneous GaN layer. However, when the layer has a heterogeneous structure of GaN/InGaN/GaN, Cl2-based plasmas cause many pits or pillars on the surface due to a micromasking effect of low volatile In chlorides. The growth of pillars was accompanied by microtrenching at the bottom of each pillar, which transformed into pits after the pillars were detached from their sites. By adding CH4 gas to the Cl2 plasma, the formation of pillars or pits was reduced, and very smooth surface morphology was demonstrated at the gas condition of 35Cl2+20CH4+5Ar (sccm).