Enlarge Process Window of BSI in DTI Loop: A Novel OPC Approach to Add Sraf

Compared with conventional Front-Side illuminated (FSI) CMOS image sensor (CIS), the photodiode of back-side illuminated (BSI) has a higher photoconductivity due to its special structure. In order to erase the effect of photoelectron scattering between different photosensitive units, the Deep Trench Isolation (DTI) layer was used to isolate it. However, the main figure of DTI layer is relatively isolated. Under KrF exposure condition, the process window is insufficient. In this paper, the influence of adding different sub-resolution assist features on the process window is discussed.