The study of GaAs etching using BCl3/SF6 gas in ECR plasma

The dry etching of GaAs to AlGaAs using BCl3/SF6 gas in ECR (Electron Cyclotron Resonance) plasma is investigated, realizing high selective and negligible damage etching. A selectivity of GaAs to Al0.2Ga0.8As of more than 200 is obtained at a gas ratio (SF6/BCl3 + SF6) of 25% and an RF bias power of 0 W. By plasma emission analysis and XPS (X-ray Photoelectron Spectroscopy) analysis, we found that addition of SF6 to BCl3 has two effects: (1) It promotes BCl3 dissociation, resulting in increased GaAs etch rate. (2) It forms AlF3 on the AlGaAs surface, resulting in a decreased AlGaAs etch rate. Hall effect measurement with a delta-doped heterojunction structure is performed to estimate the penetration depth of damage caused by ECR plasma. The results show no reduction of sheet carrier density and mobility due to plasma damage in more than 38 nm depth after ECR plasma exposure at 50 W microwave power. This dry etching technique using BCl3/SF6 gas in ECR plasma is suitable to gate recess formation on the GaAs based heterojunction field effect transistor.