Heated-H3PO4 etching of (001) β-Ga2O3

Abstract

β-Ga2O3 is a promising ultra-wide bandgap semiconductor with melt-grown substrates that are scalable, particularly in the (001) orientation. In this study, we report on the heated-phosphoric acid etching of (001) β-Ga2O3. A wagon wheel pattern with spokes aligned to a range of specific crystallographic directions was fabricated on (001) β-Ga2O3. At 160 °C, the (001) etch rate was 1.47 μm/h, which is comparable to etch rates obtained via dry etch techniques. The etched (001) surface had a morphology that was smoother than an inductively coupled plasma etched surface. All spokes possessed relatively smooth sidewalls. Spokes oriented along the [100] direction exhibited minimal SiO2 mask undercut rates at lower etch temperatures and symmetric trapezoidal profiles with near vertical (010)-like sidewalls, which are ideal for device structures with a trench geometry. Spokes oriented along the [010] direction exhibited significant SiO2 mask undercut rates and asymmetric trapezoidal profiles with different sidewall angles. These spokes also possessed reduced sidewall angles, which is favorable for field management at device corners and edges. The etch process was used to realize a dense array of [100]-oriented trenches with a height of 1.5 μm, a base width of 2.0 μm, and a mask width of 0.8 μm. The work highlights the potential for ion damage-free, standalone heated-H3PO4 etching as a viable alternative to the dry etching of (001) β-Ga2O3 for high-performance device applications.