Microtrenching-free two-step reactive ion etching of 4H-SiC using NF ₃/HBr/O₂ and Cl₂/O₂

In this paper, the authors performed a reactive ion etch of a 4H-SiC substrate with a gas mixture of NF₃, HBr, and O₂, resulting in a microtrenching-free etch. The etch rate was 107.8 nm/min, and the selectivity over the oxide hard mask was ∼3.85. Cross-sectional scanning electron microscopy showed no microtrenching compared with etches using plasmas of NF₃, NF₃/HBr, and NF₃/O₂. Analyzing a variety of HBr/O₂ mixing ratios, the authors discuss the additive effect of each gas and their respective potential mechanisms for alleviating microtrenching. To increase the radius of gyration of the bottom corners, they introduced a second etch step with Cl₂/O₂ plasma. Fabricating simple metal-oxide-semiconductor capacitors on the two-step etched surface, the authors found that the electrical characteristics of the etched sample were nearly the same as the nonetched sample.