Isotropic dry-etching of SiC for AlGaN/GaN MEMS fabrication

We present an isotropic fluorine based process to etch 4H-SiC substrates compatible with standard metallic etch masks and reasonable etching rates. Additionally, a new masking material has been established in order to obtain a stable protection of the layers underneath, based on a combination of sputtered AlN and Ni. The isotropic etching was achieved using a temperature assisted RF plasma etch process. The influence of gas flow, substrate temperature, RF power and working pressure on the etch rate and etch profile was analyzed. An optimized process with a lateral etch rate of 50 nm/min (RF power, working pressure, gas flow and temperature of 50 W, 0.4 mbar, 40 sccm SF6 and 425degC, respectively) was found, which enables the fabrication of novel resonant micro-electromechanical systems (MEMS) based on AlGaN/GaN heterostructures on SiC substrates.