Method of forming a contact using a trench and an insulation layer

Abstract

A structure and process for forming a contact to a semiconductor substrate on a semiconductor device comprises the step of forming a patterned mask over a semiconductor substrate and over a field oxide region, then etching the semiconductor substrate and the field oxide region to form a trench. The trench comprises a bottom and a first sidewall consisting of silicon and a second sidewall comprising field oxide. The etching step removes a part of a doped region in the substrate. Next, a blanket nitride layer and a blanket oxide layer is formed over the substrate, and a spacer etch is performed on the nitride and oxide layer leaving nitride and oxide over the first and second sidewalls. The trench bottom is oxidized to form a layer of oxide over the bottom of the trench thereby insulating the trench bottom, and the oxide encroaches under the nitride and oxide on the sidewalls to join with the field oxide. The nitride and oxide is removed from the sidewalls, and a conductive layer is formed over the exposed trench sidewalls, the trench bottom being insulated from the conductive layer by the oxide layer over the bottom of the trench. The oxide on the bottom of the trench contacts the field oxide. The contact is isolated from the substrate along the trench bottom and the second sidewall, making contact with the substrate only in the area of the first sidewall.