Irresistible Materials (IM) is developing novel resist systems based on the Multi-trigger concept, which incorporates a dose dependent quenching-like behaviour. The Multi Trigger Resist is a non-metal based negative tone resist, and consists of a base molecule and a crosslinker, which represent the resist matrix, together with a photoacid generator (PAG). Previously presented MTR2 showed 16 nm half pitch lines patterned with a dose of 38 mJ/cm 2 , giving a LER of 3.7 nm on the NXE3300. Since then, research has been undertaken to improve this resist. In particular we are focusing on improved RLS; reduced top-loss and wiggling at high aspect ratios; eliminating the antimony PAG and further reduction of chemical stochastics. In this study, we present the approaches that have been taken to attain these goals and the initial results. Using the EUV Interference Lithography tool at PSI, a multi trigger resist with a high absorbance non-metal element included in the resist matrix, MTR2627, has been patterned at a pitch of 28nm with an estimated dose of 53mJ/cm 2 and LER of 4.2nm. The LWR is improved in the low dose region, and results also show that a thicker film can be used without pattern collapse below pitch 32nm due to increased stiffness. Using the Berkeley MET tool, this resist matrix with a higher MTR ratio has patterned 24nm lines at a pitch of 48nm with an LER of 1.9nm with a dose of 65mJ/cm 2 . Additionally, we present initial results for an MTR resist series where the antimony PAG has been replaced with a carbon based PAG.
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EUV lithography is becoming established in high volume manufacturing but there are still many challenges to be overcome within the ecosystem including next generation exposure tools and the materials used in the patterning stack. EUV photoresists with the appropriate capability to support future roadmap requirements such as high-NA remain a high priority area of research. EUV photons have significantly higher energy than in previous photolithographic techniques, and the resist is exposed by radiation chemistry routes rather than the well-known photochemistry from earlier nodes. In addition, resists must contend with much higher photon-shot noise, require high EUV absorbance to offset the need for very thin films, especially in High-NA EUV, where the depth of focus will be less than 20 nm, and ultimately the theoretical resolution limits of EUV will approach the size of typical photoresist molecules. We are developing a new type of photoresist based on the multi-trigger concept, which seeks to suppress line edge roughness using a new photoresist mechanism, and which is based on molecular rather than polymeric materials to maximize resolution.Here we present results showing improved lithography accomplishments due to the enhancement of the highopacity multi trigger resist system. We present a range of process conditions and formulation variations including substrate changes which impact roughness and defectivity. The lithographic performance at pitch 28 nm patterned on an ASML NXE3400 scanner is presented on a variety of substrates. Lines with a width of 12.5 nm can be patterned at 59 mJ/cm 2 with a biased LWR of 3.9 nm using a resist spun on the Brewer Optistack AL412 underlayer (12 nm thickness). We also present results on SOG/SOC stacks and the optimization required of the substrate to improve LWR and decrease defectivity. We further present results where we have been targeting sub-30 mJ/cm 2 patterning. Introducing an alternative PAG but maintaining constant formulation and process conditions has enabled the patterning of p28 lines lines/spaces, with 12 nm lines having been patterned at a dose of 17.5 mJ/cm 2 and a film thickness of 14.5 nm. Work is continuing to reduce the LWR whilst maintaining a sub 30 mJ/cm 2 dose. Multi-trigger resist has also been used to pattern pillars arranged in a hexagonal pattern. We show results at pitch 36 nm, again patterned on an ASML NXE3400, exposed at 66 mJ/cm 2 to obtain a pillar diameter of 18 nm with a biased LCDU of 3.6 nm. We also show pitch 34 nm hexagonal pillars, patterned at 65 mJ/cm 2 to obtain a pillar diameter of 17 nm with a biased LCDU of 3.6 nm with a focus window of over 60 nm. A film thickness of 22 nm was used. Additionally, carefully controlling the rates of the various reactions in the MTR mechanism, we have shown that we can reduce the dose required for 19 nm diameter hexagonally arranged pillars at p34 to 28 mJ/cm 2 with a biased LCDU of 4.3 nm using a 17 nm resist film thickness.
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