Achieving interferometric double patterning through wafer rotation

Abstract

Owing to its simplicity and ability to produce line/space gratings with the highest contrast, interferometric lithography is an ideal platform for developing novel double patterning materials and processes. However, lack of sub-10 nm alignment in most interferometric systems impedes its application. In this paper, litho-etch-litho double patterning on a two-beam interferometric system is achieved by converting Cartesian alignment into angular alignment. By concentrically rotating the wafer in the second exposure, the interleaved region between the two exposures allows for the evaluation of double patterning process and materials. Geometric analysis shows that angular alignment has greatly relaxed requirements compared to the Cartesian alignment. It is calculated that for 22 nm double patterning technologies, rotation angle larger than 0.12 degree is sufficient to produce 1 µm long frequency doubled line/space patterns with less than 10% CD variation.