Limitation of blend type of resist platform on EUV lithography

Chemically amplified resist (CAR) system is being widely used not only for 248 nm and 193 nm lithography but for Extreme Ultra Violet Lithography (EUVL).[1] And CAR system is based on blend resist platform which is formulated with polymer and photo-acid generator (PAG) independently. In EUVL to aim at 22 nm node and beyond, EUV resists are required to achieve much higher acid generation efficiency and overcome RLS (Resolution, Line edge roughness, Sensitivity) trade-off using some ideas such as increase in PAG concentration and film absorption coefficient, suppression of acid diffusion length and so on.[2-6] Increase in PAG loading ratio is a promising strategy to improve EUV resist performance,[7-10] however there must be upper limitation of PAG loading ratio on blend resist platform due to lowering film Tg induced by a plasticization effect of blended PAG. This plasticization effect of blended PAG would have another impact to increase acid diffusion length, resulting in low resolution and significant thickness loss, especially on ultra thin film condition. On the other hand, utilizing the PAG having bulky cation structure was beneficial in order to maintain dark loss (in other word, top loss) of the patterned features, however, this type of cation would show low quantum yield driven by the substituent on a cation structure, so that total performance such as ultimate resolution deteriorated. From these results, the bound resist platform which has PAG unit on polymer backbone as branch would be promising platform because of its potential advantages such as suppression of dark loss, no plasticization effect and control of acid diffusion.