Progress in x-ray mask technology at NTT

This article overviews NTT's recent progress in membrane and absorber mater ials for x-ray masks and the fabrication of highly accurate masks for synch rotron radiation lithography. As membrane materials, SiC and diamond films are being studied. Experimental results indicate that diamond films are bet ter than SiC from a mask accuracy point of view because of their higher rig idity. As absorber films, Ta films deposited by electron cyclotron resonanc e (ECR) sputtering are studied. The Ta films have the rr structure and larg e grains, and are chemically very stable. All masks are produced by a membr ane process in which the patterning of absorber films is done after backetc hing. The absorbers are patterned by a new electron beam (EB) writer with a n acceleration voltage of 100 kV and ECR ion stream etching with He gas coo ling. Ta patterns with widths below 100 nm are etched accurately. Placement accuracy of absorber patterns produced by this process is confirmed to be about 30 nm, using relatively simple patterns. A technique for inspecting d efects on SiC membrane masks using a scanning electron beam and repair usin g a focused ion beam have also been developed. Ta defects on SiC membrane c an be easily detected with high contrast by the system. (C) 1999 American V acuum Society. [S0734-211X(99)04006-8].