Performance enhancements with High Opacity Multi-Trigger Resist

摘要

The development of an EUV photoresist to support high volume manufacturing remains a challenging issue. Meeting the combined resolution, sensitivity, and line width roughness (RLS) requirements has proved difficult. Furthermore, defectivity issues arising from stochastic effects are becoming increasingly critical as pitches decrease. Whilst traditional chemically amplified resists will likely be used initially, a wide range of materials options are being examined for future nodes, aiming to identify a photoresist that simultaneously meets RLS and defectivity requirements. Irresistible Materials (IM) is developing novel resist systems based on the multi-trigger concept. In a multi-trigger resist, multiple elements of the resist must be simultaneously activated to enable the catalytic reactions to proceed. In high dose areas the resist therefore behaves like a traditional CAR, whilst in low dose areas, such as line edges, the reaction is second-order increasing the chemical gradient. Effectively there is a dose dependent quenching-like behaviour built in to the resist, enhancing chemical contrast and thus resolution and reducing roughness, whilst eliminating the materials stochastics impact of a separate quencher. The multi-trigger material consists of a base molecule and a crosslinker, which represent the resist matrix, together with a photoacid generator (PAG). Research has been undertaken to improve this resist, in particular focusing on improving resist opacity and crosslinking density. A non-metal atom has been incorporated into the crosslinker and the results presented here show three iterations of this high opacity crosslinker. To improve the sensitivity, a mark Ⅱ high-Z crosslinker was synthesised which incorporated longer arms compared to the mark Ⅰ version, to reduce steric hindrance by increasing the distance of the high opacity atom from the reaction site. The results show a dramatic 65% dose-to-size reduction when using the mark Ⅱ crosslinker. Further exposures investigated the effect of PEB temperature on both the mark Ⅰ and mark Ⅱ crosslinkers. This showed that the dose can be reduced by over 50% when using a 90 °C PEB compared to when using no PEB for the mark Ⅰ crosslinker but by only 20% for the mark Ⅱ crosslinker, as would be expected if steric hinderance has been reduced. We present results with the mark Ⅱ crosslinker showing 16 nm half pitch lines using a 28 nm film thickness with a 90 °C PEB which results in a dose to size of 19 mJ/cm~2 and an LWR of 5.2 nm. A Mark Ⅲ version is also presented where the chemistry of the Mark Ⅰ crosslinker has been modified to improve the solubility in industry preferred solvents. We also present work aimed at improving the LWR of the high opacity resist formulation at high resolution, particularly aimed below 16 nm hp using dense lines when patterned using EUV lithography at the Paul Scherrer Institute, Switzerland. We present 13.3 nm lines on a 14 nm half pitch, with an LWR of 2.97 nm and dose of 26 mJ/cm~2 and 14.7 nm lines on a 15 nm half pitch, with an LWR of 2.72 nm and dose of 34 mJ/cm~2.