Improved Margin of Absorber Pattern Sidewall Angle Using Phase Shifting Extreme Ultraviolet Mask

Abstract

Sidewall angle (SWA) of an absorber stack in extreme ultraviolet lithography mask is considered to be 90 ideally, however, it is difficult to obtain 90 SWA because absorber profile is changed by complicated etching process conditions. As the imaging performance of the mask can be varied with this SWA of the absorber stack, more complicated optical proximity correction is required to compensate for the variation of imaging performance. In this study, phase shift mask (PSM) is suggested to reduce the variation of imaging performance due to SWA change by modifying mask material and structure. Variations of imaging performance and lithography process margin depending on SWA were evaluated through aerial image and developed resist simulations to confirm the advantages of PSM over the binary intensity mask (BIM). The results showed that the variations of normalized image log slope and critical dimension bias depending on SWA were reduced by using PSM compared to BIM. Process margin for exposure dose and focus was also improved with PSM.