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-<inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$10~\mu $ </tex-math></inline-formula>m on the wafer. Trenches having an opening of <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\sim ~4~\mu $ </tex-math></inline-formula>m were etched to greater than the target depth of <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$45~\mu $ </tex-math></inline-formula>m, with a tapering angle of 88.5° and smooth sidewalls (roughness <200nm), achieving trench depth uniformity of ~2% (<inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\pm 0.85~\mu $ </tex-math></inline-formula>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]