Development of highly accurate X-ray mask with high-density patterns

We have previously developed X-ray masks using SiN film as a mask membrane and Ta film, deposited by ECR sputtering, as a mask absorber. However, it is necessary to improve the pattern placement accuracy of X-ray masks for practical fine pattern lithography. In this study, we newly employed (1) a membrane process, (2) SiC film as a membrane, (3) Ru film as an intermediate film between the membrane and the absorber, and (4) a distortion compensation method called PAT by EB writing to reduce the pattern placement distortion. By combining these techniques, highly accurate X-ray masks with high-density patterns, which correspond to 4 Gbit class DRAM patterns, could be fabricated with the distortion of less than 40 nm.