Characterization of Ru layer for capping/buffer application in EUVL mask
The glancing incident angle of extreme ultraviolet lithography (EUVL) system requires minimal thickness of absorber patterns. Since a thin (?2nm) Ru top layer improves EUV reflectivity of Mo/Si multilayer, Ru is a good candidate for capping layer material. Moreover, TaN/Ru structure offers a high etch selectivity as well as low EUV reflectivity, which implies Ru can be used as a buffer layer for TaN absorber. This allows single Ru layer approach with merged function as capping/buffer layer. Then mask fabrication process (film deposition and patterning) will be greatly simplified, and the shadow effect will be significantly decreased with much thinner absorber stack. However, deep ultraviolet contrast needs to be further improved for pattern inspection.
ru capping buffer euvl mask absorber stack