Mask Influence on the Near-Surface Region of Microstructures Made by Deep Cryogenic Etching of Silicon in SF6/O2 Plasma

The roughness and defects of the side wall surfaces of high-aspect-ratio microstructures formed by cryogenic plasma etching of silicon in SF6/O2 plasma are analyzed. Mask-dependent process is detected for different materials of hard mask (Al2O3 and SiO2), since a mask under ion bombardment is a local source of O atoms flow into the near-mask region. A mechanism for development of the wall roughness is proposed using the modeling of anisotropic plasma etching of silicon in cryogenic conditions.