ON HILLOCKS GENERATED DURING ANISOTROPIC ETCHING OF SI IN TMAH

Hillocks on etched Si{100} surfaces produced by anisotropic etching ar e a common irritant in the creation of micromachined devices, Close in spection of typical pyramidal hillock shapes reveals that they are usu ally bounded by convex [101]-directed edges and {111} or near-{111} pl anes, Underetch experiments at varying TMAH etchant composition confir m that the etch rates of {101} planes and {100} planes vary with etcha nt conditions, Hillocks are suppressed when {101} etches faster than { 100}, which occurs when the TMAH concentration is low, A simple model involving kinks and ledges is proposed and allows direct relation of h illock features to etch anisotropy. Hillocks are hypothesized to be st able due to a lower etch rate for [101] ledges adjacent to the etched surface. The apex of the pyramids may be protected by impurities or de fects. Re-etch experiments indicate that hillock-producing conditions are quite sensitive to etchant conditions.