Effect of resist polymer molecular weight on EUV lithography

EUV lithography performances of resist materials with different molecular weight of polymer were investigated. EUV exposure experiment using a SFET at Selete clearly showed that line-width roughness (LWR) and 1:1 half-pitch (hp) resolution were each improved using the polymers with middle and low molecular weights. These polymers showed high dissolution contrast relative to polymer with high molecular weight. Mask linearity data also showed that the polymer with low molecular weight gave a linear dependence on critical dimension (CD) against mask size down to hp 26 nm. Thermal analysis of resist film revealed that thermal glass transition temperature (Tg) was dramatically decreased from 190 °C to 110 °C with decreasing molecular weight from high to low. In contrast with Tg which directly reflects mobility of polymer, exposure latitude (EL) was increased from 12.3% to 14.5% at hp 32 nm by decreasing molecular weight of polymer. Similarly, iso-dense bias was also improved by utilizing the low molecular weight polymer. Combination of PAG-B with the low molecular weight polymer caused further improvement in mask linearity, EL, and iso-dense bias at hp 32 nm, although LWR was rather increased.