Molecular nonchemically amplified resists based on spirobixanthene backbone: Sulfoxime oxime esters versus sulfonium salts

Abstract The nonchemically amplified (nonCA) polymer resists, including ionic and non‐ionic types, have achieved higher resolution and smaller line edge roughness (LER) than traditional chemically amplified ones. However, for polymer resists, chain entanglement is an inevitable limitation for the further reduction of LER. To overcome this problem, it is logical to apply the nonCA concept to molecule‐based resists due to their advantages of monodispersity and small size. To date, only a few examples of ionic sulfonium salts‐based nonCA molecular glass resists (nonCAMGRs) have been reported. They demonstrated high resolution and small LER well, but their electron beam sensitivity seemed less than ideal. To our knowledge, non‐ionic sulfoxime oxime esters‐based molecular resists were not reported yet, which leaves room for new round of more in‐depth reserch on nonCAMGRs. Here, employing the excellent spirobixanthene backbone, we have first designed non‐ionic sulfoxime oxime esters‐based nonCAMGRs X4‐NI‐tf and X4‐NI‐tfb, for comparison, sulfonium salts‐based nonCAMGRs X4‐I‐otfdm was designed. All exhibit favorable thermal properties (T d,5% > 200°C) and film‐forming capabilities (RMSs <0.4 nm). Via EBL, X4‐I‐otfdm achieved higher resolution (16 nm, LER 1.4 nm) than X4‐NI‐tf and X4‐NI‐tfb (20 nm, LER 1.6 nm). But contrast curve revealed that the sensitivity of X4‐NI‐tf and X4‐NI‐tfb (D 100 : 370 and 350 μC/cm 2 ) was significantly higher than X4‐I‐otfdm (D 100 : 3300 μC/cm 2 ), demonstrating that the sensitivity of sulfoxime oxime esters exceeds that of sulfonium salts and introduction of bromine can further enhance the sensitivity; based on above, X4‐NI‐tfb exhibited the lowest Z‐factor and demonstrated the best overall performance. We believe that nonCAMGRs based on sulfoxime oxime esters represent a strong candidate for high‐performance photoresists.