Mechanistic insights of Sn-based non-chemically-amplified resists under EUV irradiation

Formulating high sensitivity and resolution in Extreme Ultraviolet (EUV) resists is a serious concern regarding the adaptation of EUV lithography. The incorporation of a high optical density Sn compound in MAPDST-co-ADSM (4-(methacryloyloxy)phenyl) dimethylsulfoniumtrifluoromethane sulfonate-co-acetyldibutylstannyl methacrylate, a non-CAR photoresist, exhibits lithography resolution for sub-15 nm node when patterned under ebeam and Helium ion irradiation. The synthesized resists were irradiated at 103.5 eV (similar to 92 eV) using monochromatic synchrotron radiation. After EUV irradiation and oxidation, the resists were investigated using XPS, NEXAFS and by theoretical calculations (FEFF9 modeling program). It was observed significant changes in the labile CF3SO3- moiety, but interestingly its total dissociation or desorption was not observed after long exposure times. Bonds rearrangements of formation of SnO2 and new S-C/C-F functionalities after irradiation were detected. Those complex processes suggested the existence of important sinks for the high photon energy absorbed, which in turn increased the lithography resolution. The present results highlight the importance of the incorporation of a heavy metal covalently linked to the main polymer structure. The enhanced resolution observed in the MAPDST-co-ADSM resist formulation using standard processing conditions, establishes its potential candidature as a EUVL resist for rapid prototyping of semiconductor devices.