Approach for enhancing sensitivity of tin-oxo cluster resist for high NA extreme UV lithography

High numerical aperture (NA) EUV lithography is considered as the most-promising candidate for next generation lithography protocol that will play a crucial role in meeting the demand on the enhanced semiconductor performance and productivity. While this technology enables the fabrication of sub-10 nm patterns, the increased NA has posed challenges, such as reduced depth of focus and narrower process margins. To overcome these hurdles, it is essential to apply thinner resist films while ensuring that the resulting small patterns maintain sufficient physical and chemical durability. Moreover, considering that thinner films absorb fewer photons, the resist molecular structure should be designed to compensate sensitivity burdens. Here, an approach has been proposed to enhance sensitivity by accelerating the solubility change of a well-known tinbased nanocluster resist. To accomplish this goal, it is important to increase not only the number of secondary electrons but also reaction sites and promote radical-based chemical reactions. We aimed at experimentally validating this concept by utilizing elements with high EUV absorbance and highly reactive functional groups with tin radicals. As a model resist, we chose a tin-oxo cage material consisting of a divalent cation containing 12 tin atoms and two counter anions. Our findings indicate that the introduction of unsaturated groups capable of building bridging bonds with radicals leads to fast solubility change at a lower exposure dose, thus enhancing sensitivity. This research offers a promising direction for the development of resists tailored for High NA EUV lithography.