Method of manufacturing semiconductor device

A method of manufacturing a semiconductor device, comprising:

• forming a core material layer above a target layer;
• forming a patterned mask layer on the core material layer;
• forming a first spacer layer to cover the patterned mask layer and the core material layer;
• performing a first treatment process to form a treated first spacer layer;
• performing a first removal process on the treated first spacer layer and the patterned mask layer to form a plurality of first spacers;
• patterning the core material layer to form a core layer using the first spacers as a mask;
• forming a second spacer layer to cover the core layer;
• performing a second treatment process to form a treated second spacer layer, wherein during the second treatment process, a part of the second spacer layer remains covering the core layer;
• performing a second removal process on the treated second spacer layer and the core layer to form a plurality of second spacers;
• and
• transferring a pattern of the second spacers to the target layer to form a patterned target layer.