Litho Process Optimization to Improve Overlay Measurement in Thick PR Layer

Overlay (OVL) is a key index in lithography, which will determine product quality, and its measurement is affected by many factors, such as measurement tool, measurement strategy, OVL mark and STI CMP, etc. For some layers used thick Photoresist(PR), OVL results are out of control due to worse PR profile, especially for asymmetric profile which will cause inaccurate mark signal reading, so it is difficult to guarantee to get actual OVL performance. In this paper, we take some of investigations to optimize OVL measurement accuracy of layer with thick PR, and the corresponding mechanism is also analyzed.