CD control in phase-edge lithography - the effects of lens aberration and pattern layout

This paper presents a study of the CD accuracy of phase-edge lithography for 130-nm-node CMOS-gate patterning. In phase-edge lithography, although large process margins are obtained, precise OPC(Optical Proximity effect Correction)is necessary because of large proximity effect. Rule-based OPC was applied to phase-edge gate patterns (Lg=100 nm) with KrF exposure in fabricating 130-nm CMOS LSIs. Proximity effects due to pattern variations in the arrangement of the phase shift mask, the effect of double exposure, the micro-loading effect in dry etching and differences between the etching rates for nMOS and pMOS were all corrected. The variations in CD that were due to the proximity effect decreased from +/-15 nm to +/-5 nm by applying the OPC. Although the error in CD was decreased, process margins for specific pattern arrangements were degraded by lens aberration. Analysis shows that the image performance of an asymmetric pattern is strongly affected by odd-order aberrations and may reduce the process margins for those patterns. The suppression of lens aberration and symmetric phase-shifting mask designs which are less sensitive to aberrations are essential as ways to achieve highly accurate control of CD in applying the phase-edge method.