Influence of coma effect on scanner overlay

A novel method to measure coma aberration of projection system

“…The influence of coma-induced pattern displacement on lithographic tool overlay has been reported [2,3]. As the increasing demand for smaller feature size, the resolution enhancement techniques such as OPC, etc.…”

“…is introduced to extend the resolution-limit [4][5][6]. By using such techniques for smaller feature size, the influence of coma aberration on the lithographic quality has become more obvious [2]. Thus, research on high-accurate in-situ measurement of coma aberration is indispensable.…”

“…In lithography for LSI exposure, coma aberration of projection system is more important for lithographic quality concern [1,2]. The influence of coma-induced pattern displacement on lithographic tool overlay has been reported [2,3].…”

Coma aberration measurement by lateral image displacements at different defocus positions

“…Coma aberration can cause line-width asymmetry, which degrades the critical dimension uniformity [3] . Coma can also cause displacements of the center positions of the printed images, which leads to overlay errors [4][5][6] . As the critical dimension shrinks, the influence of coma aberration on the lithographic quality becomes more obvious.…”