FABRICATION OF X-RAY-LITHOGRAPHY MASKS WITH OPTICAL LITHOGRAPHY

We describe a technique to fabricate (1X) x-ray masks utilizing an opt ical reduction tool (SVGL Micrascan II). A special Ix x-ray mask chuck was constructed to fit the optical tool. The technique takes advantag e of the relatively flat x-ray mask substrates and the required low th roughput which allows replication without compromising the printing to ol depth of focus and the resist process. The potential advantages of this technology are: (1) improved placement accuracy relative to conve ntional e-beam tools; (2) no (e-beam) proximity effects; and (3) lower post processing data volumes. The placement distortion and the critic al dimension uniformity obtained in the Ix daughter masks on a 22x32 m m field are similar in magnitude to x-ray masks fabricated with e-beam lithography utilizing product specific emulation techniques. Furtherm ore, 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 adj ust the pattern of the reticle so as to correct for the lens distortio n. Lens correction in combination with product specific emulation may allow the fabrication of daughter masks with near-zero placement error s, suitable for sub-250 nm product applications. (C) 1996 American Vac uum Society.