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Substrate smoothing for high-temperature condenser operation in EUVL source environments

We are developing polymer smoothing processes on diamond-turned (metal) and ground (metal or ceramic) substrates to reduce high and mid-spatial frequency roughness, for implementation as EUVL condenser optics. Diamond-turning or grinding can be used as relatively inexpensive processes to obtain the specified optic figure, however, the resulting surface has high-spatial roughness in the order of tens or hundreds of Angstroms, which would prohibit normal incidence operation at EUV wavelengths due to extremely low reflectance. Our polymer smoothing process reduces roughness to a few Angstroms, thus enabling normal-incidence operation. The substrate material and smoothing film have to combine a unique set of properties such as chemical compatibility, high thermal stability and low stress to be able to operate inside alternative-fuel EUVL source environments. Experimental results are presented on the development, testing and performance of these novel substrates.