| Title |
Fast and Highly Selective GaN-over-AlGaN Etching with Low Surface Damage |
| Authors |
(Kiyoung Jang) ; (Junseok Heo) |
| DOI |
https://doi.org/10.5573/JSTS.2026.26.1.16 |
| Keywords |
Selective etching; ICP-RIE; GaN/AlGaN; low etching damage; 27.12 MHz ICP; BCl3/SF6 |
| Abstract |
Selective etching of GaN over AlGaN is a critical process step in GaN-based high electron mobility transistor (HEMT) fabrication, where precise removal of GaN is required without damaging the thin AlGaN barrier. In this study, we developed a high-selectivity, low-damage etching process using a customized BCl3/SF6 inductively coupled plasma reactive ion etching (ICP-RIE) system. Specifically, a 27.12 MHz helical resonance ICP source was utilized to generate high-density radicals and maximize gas dissociation efficiency, while the substrate temperature was precisely controlled using an external oil-circulating bath. The effects of gas composition and substrate temperature on etch rates, selectivity, and surface properties were systematically investigated. By optimizing the gas ratio to 30% SF6, a record-high GaN-over-AlGaN selectivity of 78:1 was obtained while maintaining a fast GaN etch rate. Temperature-dependent studies revealed that Al-F passivation was stable at low temperatures, whereas it degraded above 40 ?C, resulting in a significant decrease in selectivity. Although low temperatures enhanced passivation, they also promoted AlCl3 residue oxidation, resulting in unintended surface roughening. At an intermediate temperature of ∼30 ?C, the etched surface exhibited the best overall characteristics, including smooth morphology, stable chemical states, and minimized leakage current. These results demonstrate that selective, high-throughput, and low-damage GaN etching can be realized by combining optimized BCl3/SF6 chemistry with precise substrate temperature control and high-frequency ICP operation. |