Influence of a non-ideal sidewall angle of extreme ultra-violet mask absorber for 1 ×-nm patterning in isomorphic and anamorphic lithography

Abstract

The impact of non-ideal absorber sidewall angle (SWA) has been a serious problem as target pattern sizes have been reduced. During mask fabrication, it is difficult to obtain an absorber sidewall angle of 90° due to the imperfect etching process. Furthermore, it is known that repeated mask cleaning processes can worsen this problem. We investigated various patterning results of non-ideal absorbers with sidewall angles <90°. Moreover, we simulated how this affects anamorphic high-numerical aperture (NA) patterning for targeted patterns of 7nm node and smaller. The resist critical dimension (CD) can be varied by about 20% with a 5° variation in the SWA for a horizontal 16nm 1:1 periodic line and space pattern compared to a target CD. For an anamorphic high-NA system, the CD variation caused by the SWA effect is larger in the vertical direction than it is in the horizontal direction due to the asymmetric reduction ratio on the anamorphic mask (4x/8y), which is different from the isomorphic mask (4x/4y). Thus, we must determine the horizontal-vertical bias (H-V bias) generated by non-ideal absorbers in the anamorphic system. Decreasing the SWA from 90° to 85° increased the HV bias of a 10nm 1:1 line and space pattern by 52%.