The attainable road to the lower k1 extension using high transmittance attenuated phase shifting mask in the KrF lithography world

KrF lithography around 0.3k1 was studied using high transmittance attenuated phase shifting mask(att.PSM). Although gradual transition to the more high NA KrF scanner or to the ArF scanner takes place, the strong requests for the timely process development to keep up with the rapid shrinkage of device drive the extension of lithography technology to the lower k1; around 0.3 or even below. Under the given illumination condition, aerial image contrasts for varying design rules (D/R) can be related to the transmittance of att.PSM. In other words, there exists an optimum mask transmittance for each D/R, from which we try to seek the feasible way of extension to the lower k1. We will cover the EL(Exposure Latitude), the MEEF(mask error enhancement factor), and also discuss an interesting behavior of the N-M Offset in utilizing high transmittance att.PSM in the low k1 node. We used the att.PSM of 20% transmittance, as a special case experiment, to investigate the effect of high transmittance around 0.3k1 lithography. This study may facilitate the application of high transmittance att.PSM to the lower k1 and contribute to extending the lifetime of optical lithography.