Film Quantum Yields of Ultrahigh PAG EUV Photoresists

Abstract

Base titration methods are used to determine C-parameters for twenty EUV photoresist platforms. X-ray reflectometry is used to measure the density of these resists, and leads to the determination of absorbance and film quantum yields (FQY). Ultrahigh levels of Photoacid Generator (PAG) show divergent mechanisms for production of photoacids beyond PAG concentrations of 0.35 moles/liter. The FQY of sulfonium PAGs level off, whereas resists prepared with iodonium PAG show FQYs that increase beyond PAG concentrations of 0.35 moles/liter, reaching record highs of 8-13 acids generated/EUV photons absorbed.

Acid Generation Efficiency of EUV PAGs via Low Energy Electron Exposure

“…Electron cascades produced by EUV exposures allow for quantum yields greater than 1, whereas typical 193 nm photoresists have film quantum yields much less than 1 [13]. Previous research to measure acid generation efficiency has been primarily done by two methods: monitoring acid sensitized dye and base titration [2,14]. Both showed quantum yields of 5-6 acids per absorbed photon are possible, but both indirectly measure the PAG reaction product (acid).…”

“…The PAG contained in OS4, triphenylsulfonium nonaflate (TPS Nf), as well as similar PAGs such as triphenylsulfonium triflate (TPS Tf) and diphenyliodonium triflate (DPI Tf), have been commonly studied within our research group [6,7]. Previous work (Brainard et al and Tagawa et al) contains published values for their respective film quantum yield across various concentrations when exposed to EUV photons [2,14]. TPS Nf, TPS Tf, and DPI Tf (Fig.…”

“…The PAG concentration is reported in terms of molality (moles of PAG per kilogram of ESCAP) which was known through formulation. [2,14]. For most of the sulfonium based PAGs (TPS Nf, F-TPS Tf, M-TPS Tf, and TPS Tf), the limit is 2.5-3 acids generated per incident 80 eV electron.…”

EUV Extendibility: Challenges Facing EUV at 1x and beyond

“…We note that as reported by Stowers et al [13], this has already been achieved with an inorganic EUV resist. For quantum yield, we will assume a value of 6 and note even higher values have been demonstrated by Brainard et al [14]. For photo acid generator loading we will assume 1/nm 3 noting that extremely high loading values have also been reported in [14].…”

“…For quantum yield, we will assume a value of 6 and note even higher values have been demonstrated by Brainard et al [14]. For photo acid generator loading we will assume 1/nm 3 noting that extremely high loading values have also been reported in [14]. For acid blur we will assume 3 nm and 2 nm for the electron blur.…”