Outgassing and photochemical studies of photosensitive films upon irradiation at 13.5 nm

Abstract

Neutral outgassed species from polymethylmethacrylate (PMMA), a model resist (denoted RRR), and three underlayer thin films have been characterized and their absolute outgassing rates determined using a quadrupole mass spectrometer following irradiation at 13.5 nm. The radiation, which was in the extreme ultraviolet (EUV) energy range at 13.5 nm, was delivered from the 08A1-beamline at the National Synchrotron Radiation Research Center in Taiwan. The side chains of acryl-type polymers that are vulnerable to fragmentation and outgassing upon EUV irradiation were characterized and the important outgassed species (H2O and H3O+) were identified from the Si-containing photosensitive materials. The authors propose that the Si-OH formed on the Si-containing surfaces upon EUV irradiation likely undergoes subsequent incremental H2O and H3O+ outgassing upon cumulative EUV irradiation. A benchmark comparison revealed that the absolute outgassing rates of PMMA, RRR, and a Si-containing underlayer sample determined in this work were consistent with values previously reported in the literature. Thus, we have effectively demonstrated that the Taiwanese facility is capable of evaluating absolute resist outgassing rates, making it one of a limited number of EUV resist evaluation sites worldwide. The authors have provided direct evidence that the extent of ionic and neutral outgassing from 80, 100, and 125 nm PMMA and RRR films is not thickness-dependent. The authors have further demonstrated that the absolute outgassing rates of PMMA and RRR films of various thickness and two oxy-hydrocarbon underlayer samples correlated strongly with the 13.5 nm photoabsorption (σabs) and the structural toughness [double-bond-equivalence-per-backbone (DBEPB)] of the polymers. The authors revealed that the formula σabs/DBEPB could be used as a generic metric to predict the resistance of photosensitive films to EUV irradiation for the oxy-hydrocarbons in this work and four previously studied photoresists.