Lithographic characterization of the printability of programmed extreme ultraviolet substrate defects

Abstract

Extreme ultraviolet lithography, the leading next-generation lithography candidate, has now entered the commercialization phase. One of the most daunting challenges to the commercial viability of this technology is the issue of defect-free multilayer-coated reflection masks. Of great potential interest are multilayer deposition processes that can effectively reduce the printability of substrate defects, thereby relaxing substrate particle cleanliness requirements and facilitating the precoating substrate-inspection task. In particular, ion-beam deposition with additional ion-assisted polishing has been shown to drastically reduce defect sizes as seen after multilayer coating. Here we report on tests performed to lithographically characterize the effectiveness of defect smoothing and to verify defect printability models. The results show that normally printable 50 nm substrate defects are rendered nonprintable through the smoothing process. Moreover, a programmed defect fabrication method enabling controlled proximity printing tests is presented.