Fabrication of x-ray lithography masks with optical lithography

Abstract

We describe a technique to fabricate (1×) x-ray masks utilizing an optical reduction tool (SVGL Micrascan II). A special 1× x-ray mask chuck was constructed to fit the optical tool. The technique takes advantage of the relatively flat x-ray mask substrates and the required low throughput which allows replication without compromising the printing tool depth of focus and the resist process. The potential advantages of this technology are: (1) improved placement accuracy relative to conventional e-beam tools; (2) no (e-beam) proximity effects; and (3) lower post processing data volumes. The placement distortion and the critical dimension uniformity obtained in the 1× daughter masks on a 22×32 mm field are similar in magnitude to x-ray masks fabricated with e-beam lithography utilizing product specific emulation techniques. Furthermore, the distortion seen is believed to be due primarily to the known distortion of the Micrascan tool lenses. This suggests that it may be possible to use the results of lens distortion characterization to adjust the pattern of the reticle so as to correct for the lens distortion. Lens correction in combination with product specific emulation may allow the fabrication of daughter masks with near-zero placement errors, suitable for sub-250 nm product applications.