Method for fabricating shallow trench isolation structures

A method for fabricating shallow trench isolation structures, the method comprising:

• forming a patterned pad layer and a patterned mask layer sequentially on a substrate, wherein the substrate includes a memory region and a periphery region;
• removing a portion of the substrate by using the patterned mask layer as a mask to form a plurality of trenches;
• forming a first liner layer on the substrate to cover surfaces of the patterned mask layer, the patterned pad layer and the trenches;
• removing the first liner layer covering the surfaces of the patterned mask layer, the patterned pad layer and the trenches in the periphery region;
• performing a pull-back process on the patterned mask layer, wherein a pull-back amount of the patterned mask layer in the periphery region is larger than a pull-back amount of the patterned mask layer in the memory region;
• and
• forming an insulating layer in the trenches to form a plurality of shallow trench isolation structures.