Self-aligned double patterning method

A self-aligned double patterning (SADP) method, comprising:

• providing a substrate with a mask layer formed thereon;
• forming a plurality of line structures on said mask layer, wherein said line structures extend in a first direction and spaced-apart from each other;
• forming a dielectric layer on said line structures and said substrate;
• performing an etch back process so that the top surfaces of said line structures and said dielectric layer are flush;
• forming a layer structure on said line structures and said dielectric layer, wherein the material of said layer structure and said line structures are the same;
• forming a plurality of spacers in a second SADP process on said layer structure, wherein the step of forming said spacers in said second SADP process comprises:
• forming a plurality of mandrels on said layer structure, wherein said mandrels extend in said second direction and spaced-apart from each other;
• forming a conformal spacer layer on said mandrels and said layer structure;
• and
• performing an anisotropic etch process to said spacer layer to form said spacers in said second SADP process, wherein said spacers in said second SADP process extend in a second direction and spaced-apart from each other;
• and
• performing a first etch process with said spacers in said second SADP process as an etch mask to pattern said layer structure, said line structures and said dielectric layer.