ICP-RIE etching of polar, semi-polar and non-polar AlN: comparison of Cl2/Ar and Cl2/BCl3/Ar plasma chemistry and surface pretreatment

Abstract

We report a comprehensive investigation of inductively-coupled plasma reactive ion etching (ICP-RIE) of polar (0001) c-plane, semi-polar (11–22) and non-polar (11–20) a-plane AlN epilayers and show that under optimized conditions a combination of BCl3-based surface oxide removal pretreatment and Cl2/Ar ICP etching allows fast etch rates (750 nm min−1) with a smooth surface morphology. We compare samples of different orientation etched in Cl2/Ar and Cl2/BCl3/Ar plasmas, with and without BCl3/Ar ICP pretreatment, and show that the effective removal of surface oxide is a crucial step for reliable ICP-RIE etching of AlN layers. For such pretreated samples, optimization of etch parameters such as RF power, ICP power, and chamber pressure then permit very high etch rates to be obtained with a smooth surface morphology. We also study the effect of varying the BCl3 fraction in BCl3/Cl2/Ar plasmas on the etch rate and surface morphology and find that increasing the BCl3 fraction reduces the etch rate for AlN. However, above 20% BCl3 content, samples with and without pre-treatment show similar etch rates.