Contact hole etch model

Summary form only given. A linear relation between the center depth and inverse diameter of a contact hole has been derived approximately. This relation was found experimentally for contact holes etched in silicon dioxide and several models for it were computed. The new feature here is the application of Langmuir kinetics with synergistic etching of neutrals and the ions. The neutrals are modeled for molecular flow in a pipe with a sticking coefficient equal to one. This is supported by a recent finding that the etching (nondepositive) neutrals are not adsorbed appreciably on top of the same neutrals on the passivated walls of contact holes etched in silicon dioxide. The ions are modeled simply by a vertical beam since the directed ion energy fluxes at the center of the contact hole fall off slowly with depth. Etch rates for the neutrals and ions are computed from data.