Abstract
This invention relates to a selective etch method for side wall protection, which comprises following steps: (a) providing a substrate; (b) forming a first mask layer on the substrate; (c) forming a second mask layer on the first mask layer; (d) forming a resist layer on the second mask layer and forming a plurality of etch windows in the substrate; (e) performing a first etching to extend the etch windows downwards to reach part of the substrate; (f) performing a second etching to remove the resist layer and etch the substrate to form deep trench structure with various depth; (g) forming a side wall reinforcing structure along the periphery of the deep trench structure with various depth; (h) performing a third etching to remove the second mask layer and to remove the bottom of the side wall reinforcing structure to form a lower structure; and (i) performing a side etching to release an upper structure.