Dry etch processes for the fabrication of EUV masks

The absorber and buffer etching is a crucial step in the manufacture of EUV masks due to the stringent CD and reflectance requirements. Plasma etching of Cr layers, usually applied as an absorber for conventional masks, induces a resolution-limiting line width reduction. Therefore, new absorber materials for extreme ultraviolet lithography (EUVL) masks have to be evaluated. We investigated the etching behaviour of two different layer materials, TaN-I and TaN-II. Dense lines and contact holes down to 100 nm have been realized and an etch bias ≤ +5 nm per feature has been measured. The CD uniformity of lithography and absorber patterning was about 10 nm total range. In addition, etching processes for two different buffer materials, Cr and SiO 2 , have been developed. These dry etch processes for buffer and absorber layer etching have been successfully applied for EUV test mask fabrication. First results of reflectance measurements of patterned masks showed only a minimal reflectance loss due to mask making of ≤ 1%.