Investigation into PR profile representation through method of OVL focus subtraction based on a case of Overlay AEI-ADI offset on contact layer of advanced technology node

In this paper, we present a study on the overlay (OVL) offset issue in contact (CT) layer aligned to poly-silicon (short as poly) layer (prior layer) in an advanced technology node [1, 2]. We have showed the wafer level OVL AEI-ADI offset (AEI: After Etch Inspection; ADI: After Develop Inspection; AEI-ADI: AEI minus ADI). Within the shot level map, there exists a center-edge difference. The OVL focus subtraction map can well match the OVL AEI-ADI offset map. Investigation into this interesting correlation finally leads to the conclusion of PR tilting. The method of OVL focus subtraction can therefore be a powerful and convenient tool to represent the OVL mark profile.