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.
Rudenko et al. (Wed,) studied this question.