Photoacid Generator Dispersion in Partially Fluorinated Photoresist Polymers and their Blends
David L. VanderHart, Vivek Prabhu
Solid state proton NMR methods are used to probe the intimacy of mixing in materials relevant to photoresist applications. Bulk blends, made solvent casting, consisted of partially fluorinated polymers and the photoacid generator, di(t-butylphenyl)iodonium perfluorooctanesulfonate (PFOS). Polymers included poly(norbornene hexafluoroisopropanol) (PNBHFA) and the copolymer, poly(norbornene hexafluoroisopropanol-co- t-butyltrifluoromethacrylate) (NBcoTB). Tests for phase separation based on inversion-recovery, solid-echo-spin-diffusion, and chemical-shift-based-spin-diffusion pulse sequences were employed. PFOS, 9% by mass, was shown to be intimately mixed with PNBHFA or with NBcoTB. In 50/50 blends of PNBHFA/NBcoTB, phase separation into domains exceeding 30 nm is observed. However, in the ternary system, containing 9% PFOS to this blend, PFOS is intimately mixed into both phases. Such local scale mixing is necessary to understand for future photoresist materials as feature dimensions are reduced to sub-65 nm.