Optimized phase-shifting masks for high-resolution resist patterning by interference lithography

The EUV laboratory exposure tool (EUV-LET) is a versatile stand-alone resist patterning tool. Main applications are resist characterization for industrial lithography as well as the patterning of high-resolution arrays over large areas as required in research and small-volume production. High-resolution patterns are achieved by interference lithography based on the achromatic Talbot effect. The theoretical resolution limit for achromatic Talbot lithography (ATL) of 10 nm half-pitch (HP) is mainly resist-limited, as long as necessary high-resolution transmission masks can be fabricated. In this paper we focus on the transmission mask fabrication technology with a low number of process steps that allows to maximize yield and offers high flexibility. Diffraction order efficiencies (DOEs) of the masks are optimized to achieve maximal aerial image contrast (MTF) in the achromatic Talbot distance. The developed four-step mask fabrication process of contact-hole masks with HPs of 50 nm, 40 nm and 30 nm over areas of 1 × 1 mm² is presented. The transmission masks are characterized within the EUV-LET to determine the achievable MTF that can be used for resist patterning and characterization. Based on the carried out in-tool measurements the achievable MTF is 63.7 % and the total diffraction efficiency into the 1^st diffraction orders (DOs) is 41.7 % (both for 50-nm-HP masks) which makes the masks perfectly suited for the achromatic Talbot approach. Furthermore, we demonstrate high-resolution patterning down to 28 nm HP describing an effective in-lab tool that can be used at facilities for the characterization of photoresists for the upcoming lithography generations.