Diffraction-based and image-based overlay evaluation for advanced technology node

The overlay control is one of the main challenges for advanced lithography in sub-28 nm technology node. There are two kind of overlay metrology in use in semiconductor industry: most conventional image-based overlay (IBO) metrology and advanced diffraction-based overlay(DBO) metrology. In this paper we will compare these two methods through 3 critical production layers, focusing on the accuracy and the total measurement uncertainty (TMU) for the standard overlay targets of both techniques. The results show that both the accuracy and TMU of DBO method are superior to the traditional IBO method, which makes DBO method applicable at the 28nm and below technology node.