Semiconductor structure and method of fabricating the same

A method of forming a semiconductor structure, comprising:

• forming a target layer on a substrate;
• sequentially forming a first mask layer, a second mask layer and a first pattern transfer layer on the target layer, wherein the first pattern transfer layer has a plurality of openings;
• forming a second pattern transfer layer in the openings of the first pattern transfer layer;
• patterning the second mask layer, using the first pattern transfer layer and the second pattern transfer layer as a mask, so as to form a patterned second mask layer, wherein a first etch selectivity of the second mask layer to the first pattern transfer layer is greater than about 5;
• patterning the first mask layer, using the patterned second mask layer as a mask, so as to form a patterned first mask layer, wherein a second etch selectivity of the first mask layer to the patterned second mask layer is greater than about 10;
• and
• patterning the target layer using the patterned first mask layer, wherein a third etch selectivity of the target layer to the patterned first mask layer is greater than about 3.