Experimental measurements of telecentricity errors in high-numerical-aperture extreme ultraviolet mask images

TLDR: In this article, a technique to measure telecentricity errors using EUV mask images from an actinic mask inspection tool, called the SEMATECH High NA Actinic Reticle Review Project (SHARP), is presented.

Abstract: Nontelecentric illumination in extreme ultraviolet (EUV) lithography leads to pattern shifts through focus called telecentricity errors. As the industry moves toward finer pitch structures and higher numerical apertures (NA) to improve resolution, the effects of telecentricity errors become more significant. These telecentricity errors are dependent on pattern pitch, pattern type, lens aberrations, mask stack, to name a few. In this paper, a novel technique to measure telecentricity errors using EUV mask images from an actinic mask inspection tool, called the SEMATECH High NA Actinic Reticle Review Project (SHARP) is presented. SHARP is SEMATECH's second generation actinic mask imaging tool developed by Lawrence Berkeley National Laboratory. The SHARP can image masks at different numerical aperture settings, even beyond the currently available scanner NA of 0.33 (high-NA EUV) and also has a set of programmable illuminator choices. A tuned multilayer EUV mask blank was fabricated with test structures optimized for imaging on SHARP. The test structures were designed to cover a variety of critical dimensions and pitches. The mask design was fabricated on a tuned multilayer blank optimized for NA > 0.4. The mask was fabricated at Advanced Mask Technology Center and imaged on the SHARP. SHARP images were analyzed in software customized for edge position extraction of features. Pattern shifts through focus were calculated for a variety of pitches under different NA and illumination settings. The results show a monotonic increase in pattern shifts as NA increases. Also, at a given NA, the pattern shift is dependent on pattern pitch. The paper provides a detailed discussion on the experiment setup, analysis of the results and applicability of these results to high volume manufacturing of semiconductor devices using production EUV scanners.