The study of overlay mark in self aligned double patterning and solution

Double patterning technology (DPT) has matured as the lithography approach to bridge the gap between ArF water-based immersion lithography and EUV (extreme ultra violet). The adoption of the SADP (self-aligned double patterning) technology relaxes the overlay accuracy requirement compared to LELE (Litho-Etch-Litho-Etch) scheme, especially for flash product. But the traditional BiB(Bar-in-Bar)overlay marks formed by the core mask has been altered, hence the overlay mark recognition could be challenging for the subsequent process layers. This paper will study the overlay mark target design for metrology and will point out the effective solution during fin formation by SADP technology. The result revealed the segmented overlay mark is better than normal overlay mark as for both image contrast and recognition accuracy aspect.