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Study of Alignment & Overlay Strategy in 14 nm Lithography Process

A more accurate and precise control of overlay performance in lithography process is required as design rule shrinks. Overlay performance is mainly determined by alignment and overlay measurement process, of which alignment and overlay marks play an important role. SADP (Self-aligned double patterning) process becomes widely adopted to realize half pitch of original design for 14nm technology node and beyond. The alignment and overlay marks formed by SADP process differ from traditional ones, which should be well designed to better comply with process condition and reduce the pattern loading effect induced by CMP and ETCH process, and eventually improve overlay performance. In this paper, the alignment behavior of different alignment marks formed via SADP process is investigated. On the other side, the overlay performance of segmented overlay marks is designed and compared with traditional ones to reveal the effect of segmentation on improving the overlay measurement precision and accuracy.