Effect of Helium Gas Addition to SF6/O2 Chemistry for SiC Dry Etching in AlGaN/GaN/SiC HEMTs

In this study, we present the experiment of the Inductively Coupled Plasma Reactive Ion Etching (ICP-RIE) technique for achieving high etch yield via holes in 100 μm thin Silicon Carbide (SiC) substrate without trenching and micro-masking related issues. Controlled dry etching of the backside via is a challenge in SiC substrate for source grounding in GaN HEMT MMICs. The SiC dry etching using gas chemistry of SF6/O2 was carried out in-house and the formation of by-products on the surface of via sidewalls was investigated. Pillar formation was observed with conventional SF6/O2 gas chemistry. To eliminate unwanted grass formation during via hole etching, Helium (He) gas was introduced in the plasma and its effect was studied. The optimization of He content added to SF6/O2 mixture at different flow rates was carried out through a Design of Experiment (DoE). A high etch rate of ~ 0.42 μm/min of SiC with minimum trenching and micro masking was achieved with approximately 7% He added to the standard SF6/O2 gas mixture. Also, observed its effect on the electrical characteristics of the device and related issues.