Evaluation of contamination deposition on pinholes used in EUV at-wavelength PDI

Point diffraction interferometry (PDI) is a promising candidate of the wavefront metrology for EUV lithographic projection optics. However, the pinhole used in the PDI is easily filled up with carbon contamination induced by EUV irradiation. We have evaluated the filling rate of pinholes by measuring decreasing rates of intensity of EUV radiation that passed through the pinholes. As a result, we found the filling rates of the pinholes depend on their materials and blowing of the oxygen. The filling rate was the slowest when the pinhole made of Ni was used and oxygen was blown.