Advances in High-Aspect-Ratio Deep Reactive Ion Etching of 4H-Silicon Carbide Wafers

This study presents recent advances in high-aspect-ratio Deep Reactive Ion Etching (DRIE) of bulk 4H-SiC and thick 4H-SiC on Insulator (SiCOI) substrates at the wafer level. Utilizing an electroplated nickel mask, we successfully achieved high aspect ratios ranging from 10:1 to 18:1 in deep trenches with critical dimensions in the range of 1- $10~\mu $ m on the wafer. Trenches having an opening of $\sim ~4~\mu $ m were etched to greater than the target depth of $45~\mu $ m, with a tapering angle of 88.5° and smooth sidewalls (roughness <200nm), achieving trench depth uniformity of ~2% ( $\pm 0.85~\mu $ m) across the wafer. These results facilitated batch fabrication of capacitive 4H-SiC bulk acoustic wave disk resonators with high quality factor (Q) approaching 5 million at 3MHz. These achievements in high-aspect-ratio DRIE of 4H-SiC at the wafer level mark a significant stride towards enabling volume manufacturing of ultra-high Q SiC microresonators.[2024-0119]