Two types of silicon cryoetching processes are proposed. The first one consists of alternating SF6 plasma isotropic etching steps and SiF4/O-2 passivation steps at low temperature of the silicon substrate. This process only works at very low temperature and avoids reactor wall contamination. A second process alternating long anisotropic SF6/O-2 plasma steps with short SiF4/O-2 over-passivating steps is investigated. This second process gives an etch rate as high as the one obtained in standard cryoetching and allows blocking of the undercut evolution. These two processes offer many advantages in terms of cleanliness, robustness, and performance. (C) 2008 The Electrochemical Society.