Crosslinkable photoacid generators for ultrahigh loading in epoxide functionalized molecular resists

Abstract

A series of ionic onium salt photoacid generators (PAGs) functionalized with epoxide or phenolic groups capable of participating in the cationic polymerization of epoxides have been synthesized and investigated for use in ultrahigh PAG loaded negative tone epoxide functionalized molecular resists. An epoxide functionalized PAG [tris(4-glycidylether-3,5-dimethylphenyl)sulfonium hexafluoroantimonate] was found to be capable of use at loadings up to 100 mol. % in an epoxide functionalized resist [1,1,2,2-tetrakis(4-(oxiran-2-ylmethoxy)phenyl)ethane (4-Ep)] without inhibiting its ability to form fully crosslinked features, and was able to resolve 50 nm features under 100 keV electron-beam lithography at PAG loadings exceeding 50 mol. %. A phenol functionalized PAG [tris(4-hydroxyphenyl)sulfonium hexafluoroantimonate] was similarly capable of use at loadings up to 50 mol. % in 4-Ep without inhibiting cross-linking, and was able to resolve both 50 and sub-50 nm features at PAG loadings exceeding 30 mol. % using 100 keV electron-beam lithography. Initial results from this study indicate that the functionalized PAGs can enable higher PAG loadings in these negative tone resists than was previously possible; however, increasing PAG loading beyond at least 30 mol. % has a negative impact on sensitivity when using 100-keV high energy e-beam exposures.