We demonstrated heated tetramethylammonium hydroxide (TMAH) etching (25 wt. % concentration, at 90 °C) as an effective post-dry-etch treatment for improving dry-etched trench profiles on (010) β-Ga2O3. This treatment successfully converted rough, tapered dry-etched trench sidewalls into smooth, vertical ones, except for trenches oriented close to the 201 direction, where side etching was most pronounced. In particular, when trenches were oriented along the 102 direction, the exposed vertical sidewalls became exceptionally flat, indicating the preferential development of (2¯01) facets. At the same time, the initially convex trench bottoms were planarized, yielding a well-defined box-like cross-sectional profile. Importantly, both the (2¯01) sidewalls and the (010) bottom surface underwent only minimal material removal, consistent with the very low etch rates of these crystallographic planes. Together with its known ability to alleviate dry-etch damage, TMAH etching can, therefore, be regarded as a highly effective post-treatment for dry-etched fins and trenches on the (010) plane.
Takayoshi Oshima (Sun,) studied this question.