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Dry etching behavior of unintentionally-doped α-Ga 2 O 3 was investigated in a BCl 3 /Cl 2 /Ar chemistry using inductively-coupled-plasma technique. We systematically studied the impact of various etch conditions such as BCl 3 /Cl 2 /Ar gas ratio, plasma and bias powers, and chamber pressure on etch rate, surface roughness and mask selectivity of α-Ga 2 O 3 with respect to Si 3 N 4 , SiO 2 and photoresist. In contrast to GaN etching, Cl 2 was found to be far less effective than BCl 3 in etching α-Ga 2 O 3 .

This paper reports detailed characterization results of deep reactive ion etching of fused silica with three different masking materials: single-crystal Si, negative photoresist KMPR and SU-8. With an optimized etch recipe, KMPR and SU-8 show higher effective mask selectivity, are easier to integrate and remove than Si, making them better masks for creating high-aspect ratio features. Using a KMPR mask, a high aspect ratio (8:1) etch with a 6-μm mask opening is obtained. SU-8 masks also achieve high aspect ratios of 4.5:1 for 20-μm wide trenches, with mask selectivity of ~2:1. However the polymeric masks cause greater FS sidewall roughness.