Advanced Mask Technique to Improve Bit Line CD Uniformity of90 nm node Flash Memory in Low-K1 Lithography

摘要

As devices size move toward 90nm technology node or below, defining uniform bit line CD of flash devices is one ofthe most challenging features to print in KrF lithography. There are two principal difficulties in defining bit line on wafer.One is insufficient process margin besides poor resolution compared with ArF lithography. The other is that asymmetricbit line should be made for OPC(Optical Proximity Correction) modeling. Therefore advanced ArF lithography scannershould be used for define bit line with RETs (Resolution Enhancement Techniques) such as immersion lithography, OPC,PSM(Phase Shift Mask), high NA(Numerical Aperture), OAI(Off-Axis Illumination), SRAF(Sub-resolution AssistantFeature), and mask biasing.. Like this, ArF lithography propose the method of enhancing resolution, however, we mustspend an enormous amount of CoC(cost of ownership) to utilize ArF photolithography process than KrF. In this paper, we suggest method to improve of bit line CD uniformity, patterned by KrF lithographic process in 90nmsFlash(stand alone Flash) devices. We applied new scheme of mask manufacturing, which is able to realize 2 differenttypes of mask, binary and phase-shift, into one plate. Finally, we could get the more uniform bit lines and we expect toget more stable properties then before applying this technique.