Method for forming patterned mask layer

A method for forming a patterned mask layer, comprising:

• forming a layer over a substrate;
• forming a first strip structure and a second strip structure over the layer;
• forming a spacer layer conformally covering the first strip structure, the second strip structure, and the layer, wherein the spacer layer has a first trench between the first strip structure and the second strip structure;
• removing a first portion of the spacer layer, which is under the first trench, and a second portion of the spacer layer, which is over the first strip structure and the second strip structure, to form a second trench in the spacer layer and under the first trench, wherein after the first portion of the spacer layer is removed, a lower portion of the spacer layer remains under the first trench, the second trench has a first part and a second part, and the lower portion of the spacer layer separates the first part from the second part;
• forming a third strip structure and a fourth strip structure over the layer, wherein the third strip structure is in the second trench, the third strip structure has a third part and a fourth part, the third part and the fourth part are respectively in the first part and the second part of the second trench, and the first strip structure is between the third strip structure and the fourth strip structure;
• removing a side portion of the fourth strip structure to narrow the fourth strip structure;
• and
• removing the spacer layer.

A method for forming a patterned mask layer, comprising:

• forming a first layer over a substrate;
• forming a first strip structure and a second strip structure over the first layer;
• forming a spacer layer covering the first strip structure, the second strip structure, and the first layer, wherein the spacer layer has a first trench between the first strip structure and the second strip structure;
• forming a block structure in the first trench;
• partially removing the spacer layer, wherein the spacer layer remains over a first sidewall of the first strip structure, a second sidewall of the second strip structure, and under the block structure after partially removing the spacer layer;
• forming a third strip structure between the spacer layer remaining over the first sidewall of the first strip structure and the second sidewall of the second strip structure;
• removing the block structure;
• and
• removing the spacer layer, wherein the first strip structure, the second strip structure, and the third strip structure together form a patterned mask layer.