EUV mask process development status for full field EUV exposure tool

Abstract

Extreme Ultra Violet Lithography (EUVL) is one of promising candidates for next generation lithography, 32nm node and beyond. Authors are developing EUV mask process targeting full field EUV exposure tool. Unlike the conventional optical mask, EUV mask is reflective type mask. To reflect 13.5nm wavelength light, 40 pairs of Mo/Si multilayer (ML) is used for reflective layer. Reflective layer is covered by capping layer. The capping layer protect reflective layer from absorber etching, defect repair and environmental condition. Top of absorber layer is covered by low reflective (LR) layer to achieve high contrast between the etched and not etched portion. Back side of EUV mask is covered by conductive film for electrostatic chuck use. In this paper, we will report current process development status of EUV mask for full field EUV exposure tool. Absorber patterning process including resist patterning and absorber etching were developed. Thin resist use and small resist damage dry etching process achieved pattern resolution of 32nm node. Defect inspection was also evaluated using DUV reticle inspection tool. Ta-based absorber on ruthenium (Ru) capped ML blanks was used for this evaluation. Because, Ru material has high resistivity to absorber etching plasma, it enable buffer layer less EUV mask structure. Ru also has better property on oxidation resistance compared to standard silicon (Si) capping layer.