Method of double patterning lithography process using plurality of mandrels for integrated circuit applications

A method comprising:

• forming a mandrel layer over a target layer;
• patterning the mandrel layer to form a mandrel strip comprising a first portion and a second portion having lengthwise directions aligned to a straight line, with an first opening separating the first portion and the second portion from each other;
• forming spacers to fill the first opening, wherein the spacers comprises portions on opposite sides of the first portion and the second portion of the mandrel strip;
• partially removing each of the first portion and the second portion of the mandrel strip to form a second opening and a third opening, respectively;
• and
• extending the second opening and the third opening into the target layer, wherein in the extending, the spacers and remaining portions of the mandrel layer in combination are used as an etching mask for etching the target layer.

A method comprising:

• forming a mandrel layer over a target layer;
• performing lithography-and-etching processes to pattern the mandrel layer, with remaining portions of the mandrel layer comprising a first mandrel;
• etching the first mandrel to cut the first mandrel into a second mandrel and a third mandrel, with a first opening separating the second mandrel from the third mandrel, wherein after the second mandrel and the third mandrel are formed, an I-shaped opening is defined by the remaining portions of the mandrel layer, and the first opening is a part of the I-shaped opening;
• and
• depositing a blanket spacer layer over the second mandrel and the third mandrel.