Method for forming self-aligned double pattern and semiconductor structures

A semiconductor structure, comprising:

• a substrate;
• a first mask layer formed on the substrate, the first mask layer having alternate recesses and protrusions;
• a second mask layer formed on the protrusion of the first mask layer;
• and
• a spacer layer covering surfaces of the first mask layer and the second mask layer, an upper surface of the spacer layer located at the recess of the first mask layer being flush with a top surface of the protrusion of the first mask layer.

A semiconductor structure for a Self-Aligned Double Patterning (SADP) etching process, comprising:

• a substrate;
• and
• alternate first mask structures and second mask structures formed on an upper surface of the substrate;
• the first mask structure comprising a first mask layer and a second mask layer sequentially provided on the upper surface of the substrate, the second mask structure comprising a first mask layer, a spacer layer and a fourth mask layer sequentially provided on the upper surface of the substrate, and a second trench being formed between the adjacent first mask structure and second mask structure.