Tetramethylammonium hydroxide (TMAH) treatment of dry-etched trenches on (010) β-Ga2O3 to enhance trench profiles

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.