Patent ID: 8853093

Claim:
A method for forming a semiconductor structure, comprising: providing a substrate; forming a negative photoresist layer over the substrate; forming a positive photoresist layer on the negative photoresist layer; performing an exposure process to form a first exposure region in the positive photoresist layer and a second exposure region in the negative photoresist layer, wherein the first exposure region having a first width is located directly on the second exposure region having a second width, and the first exposure region and the second exposure region have a same central axis according to the exposure process, and wherein the first width is less than the second width; performing a positive-tone development process to remove the first exposure region from the positive photoresist layer to form one or more first openings to expose the negative photoresist layer; etching the second exposure region of the negative photoresist layer along the one or more first openings to form one or more second openings through both the positive photoresist layer and the negative photoresist layer; removing remaining positive photoresist layer; and performing a negative-tone development process to remove portions of the negative photoresist layer outside of remaining second exposure region to form a double patterned negative photoresist layer.