Study of electron-induced chemical transformations in model resists

In extreme ultraviolet (EUV) resists, due to the high energy of the incident photons, most of the radiation chemistry arises from the photon-generated primary and secondary electrons and not the EUV photons themselves. These electrons are generated by a cascade of inelastic scattering events, have a wide range of energies, and play a leading role in EUV patterning by initiating chemical transformations. To characterize electron-induced chemical transformations we exposed photoresist films to an electron beam 7-9 mm in diameter with energies varied from 20 to 80 eV to study the effect of fast primary electrons as well as slow secondary electrons on photoresist materials. Chemical changes of poly-tert-butyl methacrylate (tBMA), poly-methyl methacrylate (PMMA), and poly-4-hydroxystyrene (PHS) were characterized in-situ during exposure using a quadrupole residual gas analyzer (RGA). Full RGA spectra were used to identify the outgassed compounds from samples, and the time dependence of key chemical fragment masses was studied to observe the depletion of fragments from the sample over time. Transmission FTIR data were collected through exposed spots to quantify the changes in chemical bond structure. The number of molecules lost from each resist was estimated by the integrated partial pressure rise observed in RGA and compared to the total thickness change of exposed areas measured using ellipsometry.