Study of CD variation at EUV mask fabrication occurred by electric conduction from top to back side

Extreme Ultra Violet Lithography (EUVL) is the most leading next generation lithographic technology post ArF immersion lithography. The Structure of EUV mask differ from traditional photomask., especially backside coating. E-chuck is employed to fix the EUV mask on the scanner. Therefore a conductive film on backside of the EUV mask blank is needed. We investigated what have an influence on mask manufacturing process caused by the backside coating differed from a traditional photomask. From our experiment, at the mask fabrication process, especially RIE process to etch Ta absorber, the CD variation is occurred by electric conduction between the backside conductive coating and the absorber on the Mo/Si multi-layer. As a result, the EUV mask blank without electric conduction between the backside conductive coating and the absorber on the Mo/Si multilayer is necessary.