Process variation resistant self aligned contact etch

Abstract

A method for forming an opening through an interlayer to expose an underlying surface that retains high etch selectivity while having a relatively large process window to accommodate process variations. The method etches an interlayer under a first etching condition that forms a protective layer over portions of exposed surfaces of the opening during the etch process. The formation of the protective layer continues until an etch stop condition is produced, stopping further etching of the interlayer under the first condition prior to exposing the underlying surface. The method continues with etching through the protective layer under a second etching condition to expose a residual interlayer, and etching the exposed residual interlayer under the second etching condition to expose the underlying surface.