Method for improving residue formation after mandrel removal

A method for improving residue formation after mandrel removal, at least comprising:

• step 1, providing a tetraethyl orthosilicate (TEOS) layer, forming mandrel structures on the TEOS layer and spaced apart from each other, and forming spacers on sidewalls of each of the mandrel structures;
• step 2, forming a first spin-on-carbon (SOC) layer to cover the TEOS layer, the mandrel structures, and the spacers of the mandrel structures, and forming an SOC structure by means of photolithography and etch, wherein the SOC structure covers the spacers and exposes top surfaces of the mandrel structures;
• step 3, removing the mandrel structures by etch along sidewalls of the SOC structure, wherein a first groove is formed between two of the spacers formed on the sidewalls of the removed mandrel structures, and wherein after the mandrel structures are removed, residue polymers are attached to a surface of the SOC structure;
• step 4, forming a second SOC layer to cover the SOC structure and fill the first groove;
• step 5, performing top planarization of the second SOC layer until a top surface of the SOC structure is exposed;
• step 6, performing a dry etch-back process on the SOC structure and the second SOC layer, wherein the dry etch-back process is stopped at the top of the spacers, wherein the dry etch-back process removes a portion of the SOC structure that contains the residue polymers attached to the surface of the SOC structure;
• and
• step 7, removing a remaining SOC structure, forming a second groove in an exposed region between two of the spacers once covered by the SOC structure, and removing a remaining second SOC layer to expose the first groove.