Self-aligned contact (SAC) etch with dual-chemistry process

摘要

The invention is a two-step dual-chemistry process for etching through a selected portion of an insulating oxide layer of a substrate to create a self-aligned contact opening without damaging underlying field oxide regions. The first etching step uses essentially a C_xF_y (x1)-type chemistry that etches only partially through the oxide layer, since it has very good selectivity to the silicon nitride cap of the gate stacks but a poor selectivity to the field oxide regions. The second etching step employs a second chemistry comprising an H-containing fluorocarbon chemistry. The second chemistry has a good selectivity to the field oxide regions and, at the same time, is able to finish etching the opening.