Stable stitching: impact and mitigation of environment on metal-oxide resist imaging

Due to the anamorphic optics that enable high-numerical aperture (NA) extreme ultraviolet (EUV) lithography, the maximum field size printed on wafers in high NA (EXE) scanners is halved as compared to low NA (NXE) scanners. Two half-field exposures are therefore needed to expose a conventional full-field area, with a method called stitching. The half fields use different reticles, and swapping them introduces overhead between the exposures. Complex wafer and lot operations are implemented to offset throughput loss caused by the reticle swap, but these methods create variable and larger processing delays that may influence imaging performance, specifically pattern critical dimension (CD) drift. We pay attention to the additional delay introduced due to stitching, meaning the duration between half-field exposures. Inpria metal-oxide resists are a leading candidate for high-NA EUV lithography because of their increased resolution capabilities and etch resistance. Due to their sensitivity to ambient conditions after the exposure, the impact of the environment during the various delays has been investigated, with the goal of mitigating the CD drift due to the post-exposure delay involved in high-NA exposure stitching.