title: Coma measurement by use of an alternating phase-shifting mask mark with a specific phase width.
abstract: The correlation between the coma sensitivity of the alternating phase-shifting mask (Alt-PSM) mark and the mark's structure is studied based on the Hopkins theory of partially coherent imaging and positive resist optical lithography (PROLITH) simulation. It is found that an optimized Alt-PSM mark with its phase width being two-thirds its pitch has a higher sensitivity to coma than Alt-PSM marks with the same pitch and the different phase widths. The pitch of the Alt-PSM mark is also optimized by PROLITH simulation, and the structure of p=1.92lambda/NA and pw=2p/3 proves to be with the highest sensitivity. The optimized Alt-PSM mark is used as a measurement mark to retrieve coma aberration from the projection optics in lithographic tools. In comparison with an ordinary Alt-PSM mark with its phase width being a half its pitch, the measurement accuracies of Z(7) and Z(14) apparently increase.
authors.affiliation: Information Optics Laboratory, Shanghai Institute of Optics and Fine Mechanics, Chinese Academy of Sciences, Shanghai 201800, China.
authors.forename: Zicheng
authors.initials: Z
authors.lastname: Qiu
authors.forename: Xiangzhao
authors.initials: X
authors.lastname: Wang
authors.forename: Qiongyan
authors.initials: Q
authors.lastname: Yuan
authors.forename: Fan
authors.initials: F
authors.lastname: Wang