Abstract: A semiconductor structure and a formation method thereof are provided. The formation method includes: providing a base, the base including a pattern dense region and a pattern isolated region; forming a plurality of separate hard mask layers on the base, where adjacent hard mask layers and the base define an opening, and an opening of the pattern isolated region is wider than an opening of the pattern dense region; forming a trimming layer at least on a side wall of the opening of the pattern isolated region, the trimming layer and the hard mask layer constituting a mask structure layer; and etching, using the mask structure layer as a mask, a portion of the thickness of the base exposed by the opening to form a plurality of target pattern layers protruding from the remaining base. Embodiments and implementations of the present disclosure are advantageous for improving a critical dimension uniformity of a target pattern layer in each region.