Alt-PSM of Contact with Phase Assist Feature for 65-nm Node

Resolving the very small feature size of contact holes for 65-nm technology node has placed enormous challenge on even the up-to-date optical lithography techniques. Resolution enhancement technique (RET) will be helpful and necessary to alleviate the strain posed by such a task. Here we report that a 193-nm alternating phase shift mask (Alt-PSM) with phase-shifted assist features is used to print the contact holes for 65-nm node. With a novel algorithm of phase assignment, the phases of the main features are assigned properly in the full chip with the assistant features added. The results show that DOF of 110-nm iso-contact hole can be enhanced up to 0.5 μm.