Inductively Coupled BCl3/Cl2/Ar Plasma Etching of High Al Content AlGaN
Al and Ga chlorides are volatile, making the gas chemistries of BCl3 and Cl2 attractive for use in dry etching. However, obtaining a smooth surface of AlGaN with a dry etch can be difficult due to two compounding effects: AlClx has a lower volatility than GaClx and the bond energy of Ga-N is lower than that of Al-N. This exploratory work aims to document some of the etch characteristics during inductively coupled plasma reactive ion etching (ICP-RIE) of high aluminum content AlGaN with a BCl3/Cl2/Ar plasma. Etch rate and surface morphology were investigated for Al0.85Ga0.15N. Etch rate lends insight into chemical tendencies of AlGaN alloys, while surface morphology is of interest in structures requiring subsequent processing steps such as gate recessing.
Our results show that lowering rf bias and increasing ICP power leads to smoother surfaces while maintaining an attractive etch rate. Also, the ratio of BCl3 to Cl2 significantly affects the surface roughness. In addition, we show significant improvement of surface roughness, even under sub-optimal etch conditions, by implementing a 1min BCl3/Ar plasma pre-treatment dry etch step prior to introducing Cl2 to the main etch using a BCl3/Cl2/Ar plasma.
This work was supported by the Laboratory Directed Research and Development (LDRD) program at Sandia. Sandia National Laboratories is a multi-program laboratory managed and operated by Sandia Corporation, a wholly owned subsidiary of Lockheed Martin Corporation, for the U.S. Department of Energy's National Nuclear Security Administration under contract DE-AC04-94AL85000.