Two Cryogenic Processes Involving SF[sub 6], O[sub 2], and SiF[sub 4] for Silicon Deep Etching

Two types of silicon cryoetching processes are proposed. The first one consists of alternating S F 6 plasma isotropic etching steps and Si F 4 ∕ 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 S F 6 ∕ O 2 plasma steps with short Si F 4 ∕ O 2 overpassivating 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.