Patterning method

A patterning method, comprising:

• forming a hard mask layer on a substrate;
• forming mandrels on the hard mask layer;
• forming mask patterns on the mandrels, wherein each of the mask patterns is formed on one of the mandrels;
• forming spacers on the hard mask layer, wherein each of the spacers is formed on a sidewall of one of the mandrels and on a sidewall of one of the mask patterns;
• forming a cover layer covering the hard mask layer, the spacers and the mask patterns, wherein a material of the mandrels is identical to a material of the cover layer;
• performing a planarization process to remove the cover layer on the mask patterns and the spacers and remove the mask patterns, wherein a part of the cover layer remains between the spacers after the planarization process;
• and
• removing the mandrels and the cover layer after the planarization process.