Self-aligned contact with improved isolation and method for forming

摘要

A method for forming a self-aligned contact in a IC device is disclosed. In the method, a gate oxide layer, a polysilicon layer and a metal silicide layer are first deposited and patterned on a substrate. A first silicon dioxide layer is then deposited on the polysilicon layer followed by the deposition of a silicon nitride cap layer on the first silicon dioxide layer. A second silicon oxide layer is deposited on the silicon nitride cap layer and the stack is patterned forming an oxide-nitride-oxide hard mask. The substrate is then wet etched by an etchant that has low selectivity toward silicon oxide and high selectivity to nitride and silicide, thus forming a toroidal-shaped recess between the silicon nitride layer. A second silicon nitride layer is deposited over the whole substrate. A dielectric layer is formed over the whole substrate.