How large MEEF is acceptable for the low-k 1 lithography?

Abstract

ABSTRACT In the photo-lithography process, a mask is one of the most important items because its imperfection induces the variation of critical dimension (CD) and becomes the source of the CD error on the wafer. The CD error amplification is denoted by using Mask Error Enhancement Factor (MEEF) [1][2] and related to the photo-lithography process. Nowadays MEEF increases conspicuously as the devi ce shrinks so fast. Therefore the mean -to-target (MTT) and the uniformity of the mask CD are very important factors to reduce the effect of high MEEF. In general, the process constant k 1 factor has been cited to denote the capability of the photo process for a certain resolution. However MEEF can describe the process difficulty well because it depend s on the layout design and th e process conditions although the designed patterns have the same design rule. In this study the MEEFs of sub-80nm DRAM patterns [3] are discussed with the process constant k 1 , MTT and the mask CD uniformity. And then the results are compared with the simulation and the wafer process data. Considering the mask specification calculated from the wafer specification and MEEF, the photo tool and process upgrade is necessary to reduce MEEF and to have the mask fabrication tolerance. Key words: MEEF, low k