Patent ID: 8836139

Claim:
A method of forming a feature comprising: providing a substrate with a first device layer with a patterned first hard mask layer on the first device layer, wherein the patterned first hard mask layer includes a first hard mask layer opening to expose a surface of the first device layer, the first hard mask opening having a first critical dimension (CD) which is equal to the CD produced by a lithographic system (CD L ), wherein CD L is larger than a desired CD (CD D ); forming a second device layer over the substrate, the second device layer fills the first hard mask opening having CD L and contacts the first device laver, the second device layer having a top surface which is coplanar with the top surface of the first hard mask layer; removing the first hard mask layer to expose a top surface of the first device layer, the first device layer includes a mesa formed by the second device layer, wherein the CD of the mesa is equal to about the first CD; trimming the mesa to produce a mesa with a second CD, the second CD is equal to about CD D ; forming a second hard mask layer on the exposed surface of the first device layer, the second hard mask layer leaves a top of the mesa exposed, the mesa defines a second hard mask layer opening with a second mask CD equal to about CD D ; and etching the substrate using the second hard mask as the etch mask to remove the mesa and a portion of the first device layer below the mesa to form an opening in the first device layer with CD D .