Photo-electron chemistry of photoresist outgassing upon DUV, VUV, EUV, and BEUV irradiation

Abstract This study qualitatively and quantitatively characterized photoresist outgassing upon irradiation with 193 nm (DUV), 103.3 nm (VUV), 13.5 nm (EUV), and 6.7 nm (BEUV) synchrotron light. The photoresist samples used were polymethylmethacrylate (PMMA), poly(4-hydroxystyrene-co-tertbutylacrylate) (HS-TBA) and an EUV model resist denoted as HS-TBA-H (HS-TBA with TPS-Nf, a photoacid generator (PAG), added). The distribution of outgassed species from the resist samples was characterized and found to exhibit a negligible dependence on the film thickness in the 50–125 nm range. Outgassed species from the main-chain scission of PMMA comprised 62% of the overall amount of outgassing upon DUV/VUV irradiation, while outgassing from the methoxycarbonyl side chain were summed up to 83% of outgassing upon EUV/BEUV irradiation. On the other hand, about 68% of outgassing resulting from the ester elimination reaction, and 15–20% of that from the Norrish type I reaction, from the TBA unit of HS-TBA had no observable energy dependence; nevertheless, the distribution gravity shifted toward dehydrogenated species, from DUV/VUV to EUV/BEUV. Benzene outgassing was significant from TPS-Nf in HS-TBA-H at all wavelengths, with 0.13 “PAG reactions” per EUV photon absorbed per 1 wt% TPS-Nf added. A quantitative assessment of the absolute outgassing rates from these photoresist films upon EUV irradiation suggests an escape length of neutral outgassing detected herein on the order of 60–80 nm, and PMMA, HS-TBA-H, and the TBA-H moieties would require ∼11 eV/outgassing, 22.4 eV/outgassing, and 9.4 eV/outgassing following EUV and BEUV photoabsorption, respectively.