Patent ID: 6989317

Claim:
A trench etching method, comprising the steps of: (a) providing a holding layer and a patterned hard mask layer on top of the holding layer; (b) etching first and second trenches in the holding layer using the patterned hard mask layer as a mask, wherein the second trench is wider than the first trench, and wherein the first and second trenches have first and second bottom walls, respectively, in the holding layer; (c) forming a conformal gapfill layer on top of the holding layer and the patterned hard mask layer; (d) etching away first and second portions of the conformal gapfill layer directly above the first and second trenches, respectively, so as to expose the second bottom wall of the second trench to the atmosphere whereas the first bottom wall of the first trench is still covered by the conformal gapfill layer; (e) etching down further into the holding layer at the exposed-to-the-atmosphere surface of the second bottom wall of the second trench so as to make the second trench deeper; and (f) etching away portions of the conformal gapfill layer so as to expose the first bottom wall of the first trench to the atmosphere.