Self aligned multiple patterning

A method for forming a nanostructure on a substrate, the method comprising:

• performing a first lithography-and-etch process, comprising patterning a mandrel layer disposed on a first dielectric layer;
• performing a spacer patterning process, comprising forming a spacer layer on sidewalls of the patterned mandrel layer;
• performing a first gap-filling process, comprising forming a gap-filling layer in openings of the spacer layer on the first dielectric layer and over the patterned mandrel layer;
• performing a second lithography-and-etch process, comprising patterning the gap-filling layer and further patterning the patterned mandrel layer;
• performing a second gap-filling process, comprising further forming the gap-filling layer in openings of the twice patterned mandrel layer;
• performing a third lithography-and-etch process, comprising patterning a first hardmask layer formed over the gap-filling layer;
• performing a fourth lithograph-and-etch process, comprising patterning a second hardmask layer formed over the first hardmask layer, patterning the first hardmask layer through the patterned second hardmask layer, and patterning the gap-filling layer through the patterned first hardmask layer;
• and
• performing a spacer removing process, the spacer removing process comprising removing the patterned spacer layer and the twice patterned mandrel layer.

A nanostructure formed on a substrate, comprising:

• an etch stop layer disposed on a substrate;
• a first dielectric layer disposed on the bottom layer;
• a mandrel layer disposed on the first dielectric layer, the mandrel layer having openings each having a width of less than 14 nm and a pitch of less than 22 nm;
• and
• a spacer layer formed on the first dielectric layer within the openings of the mandrel layer, the spacer layer having a thickness of less than 11 nm.