Techniques herein provide a process to reform or flatten asymmetric spacers to form a square profile which creates symmetric spacers for accurate pattern transfer. Initial spacer formation typically results in spacer profiles with a curved or sloped top surfaces. This asymmetric top surface is isolated while protecting a remaining lower portion of the spacer. The top surface is removed using a plasma processing step resulting in spacers having a squared profile that enables further patterning and/or accurate pattern transfer.

A method for forming a patterned mask layer is provided. The method includes forming a layer over a substrate. The method includes forming a first strip structure and a second strip structure over the layer. The method includes forming a spacer layer over the first strip structure, the second strip structure, and the layer. The method includes forming a third strip structure and a fourth strip structure between the first strip part and the second strip part. The connecting part is between the third strip structure and the fourth strip structure. The method includes removing the spacer layer. The first strip structure, the second strip structure, the third strip structure, and the fourth strip structure together form a patterned mask layer.

A method for forming a patterned mask layer is provided. The method includes forming a layer over a substrate and forming a first strip structure and a second strip structure over the layer. The method also includes forming a spacer layer between the first strip structure, the second strip structure, and the layer. The spacer layer has an H-shape, the spacer layer has a first trench and a second trench spaced apart from each other, and the first trench and the second trench expose portions of the layer. The method further includes forming a third strip structure and a fourth strip structure in the first trench and the second trench, respectively. In addition, the method includes removing the spacer layer. The first strip structure, the second strip structure, the third strip structure, and the fourth strip structure together form a patterned mask layer.

A method includes depositing a hard mask over a target layer. Depositing the hard mask includes depositing a first hard mask layer having a first density and depositing a second hard mask layer over the first hard mask layer, the second hard mask layer having a second density greater than the first density. The method further includes forming a plurality of mandrels over the hard mask; depositing a spacer layer over and along sidewalls of the plurality of mandrels; patterning the spacer layer to provide a plurality of spacers on the sidewalls of the plurality of mandrels; after patterning the spacer layer, removing the plurality of mandrels; transferring a patterning the plurality of spacers to the hard mask; and patterning the target layer using the hard mask as a mask.

A method includes depositing a hard mask over a target layer. Depositing the hard mask includes depositing a first hard mask layer having a first density and depositing a second hard mask layer over the first hard mask layer, the second hard mask layer having a second density greater than the first density. The method further includes forming a plurality of mandrels over the hard mask; depositing a spacer layer over and along sidewalls of the plurality of mandrels; patterning the spacer layer to provide a plurality of spacers on the sidewalls of the plurality of mandrels; after patterning the spacer layer, removing the plurality of mandrels; transferring a patterning the plurality of spacers to the hard mask; and patterning the target layer using the hard mask as a mask.