Imaging simulations of optimized overlay marks with deep sub-resolution features

摘要

Bright field imaging based metrology performance enhancement is essential in the quest to meet lithography process control requirements below 65 nm half pitch. Recent work has shown that, in parallel to the lithographic processes themselves, the metrology tools are able to continue to perform despite the fact that the size of the features under test are often below the classical Rayleigh resolution limit of the optical system. Full electromagnetic simulation is a mandatory tool in the investigation and optimization of advanced metrology tool and metrology target architectures. In this paper we report on imaging simulations of overlay marks. We benchmark different simulation platforms and methods, focusing in particular on the challenges associated with bright-field imaging overlay metrology of marks with feature sizes below the resolution limit. In particular, we study the dependence of overlay mark contrast and information content on overlay mark pitch and feature size.