A semiconductor structure and a method for forming a semiconductor structure are provided. The method for forming the semiconductor structure includes: providing a base; forming a first dielectric layer on the base; then forming a plurality of first mask patterns each having zigzag shape on the first dielectric layer, in which the first mask patterns extend in a first direction; forming a plurality of second mask patterns each having zigzag shape on the first mask patterns, in which the second mask patterns extend in a second direction different from the first direction, and projections of the first mask patterns on the first dielectric layer and projections of the second mask patterns on the first dielectric layer overlap with each other to form polygons; and etching the first dielectric layer by using the second mask patterns and the first mask patterns as masks to form openings.