Integrated OPC approach to line-end shortening effects on the photomask and silicon levels for ArF attenuated PSM lithography

Abstract

Line end shortening (LES) effects and their corrections for ArF attenuated phase shift mask (PSM) technology toward 65 nm node, both in photomask and wafer processes, have been investigated. From critical dimension (CD) measurements on photomasks, it was found that line end distance and line width are the relevant factors for line end deviations on clear field and dark field types, respectively. We confirmed that these mask errors can significantly be reduced by rule base process proximity effect correction (PPC). Subsequently we analyzed resist LES on wafers and found that resist LES shows a down slope in case line end distance is less than 200 nm. We also assessed mask error enhancement factor (MEEF) around line end. Line end MEEF for a clear field mask indicates 3.4 when line end distance is 80 nm. By examining the relation between line end rounding on photomask and corresponding resist LES, we confirmed line end area loss on photomask surely induced larger resist LES. Lastly, we have evaluated a new optical proximity effect correction (OPC) approach in which correction for mask errors is separated from wafer OPC calculation. It is confirmed that new integrated OPC is promising for improving LES.