New photoresist materials for 157-nm lithography. Poly[vinylsulfonyl fluoride-co-4-(1,1,1,3,3,3-hexafluoro-2-hydroxypropyl)-styrene] partially protected with tert-butoxycarbonyl

Our molecular orbital calculations predicted excellent transparencies of molecules having sulfonyl fluoride groups in the vacuum ultraviolet (VUV) region. An optical density (OD) measurement of poly(vinylsulfonyl fluoride) [poly(VSF)] prepared by free radical polymerization of VSF clearly supported this calculation (OD = 2.1μm^-1 at 157 nm). A new copolymer, poly [(VSF)₄₀-co-4-(1,1,1,3,3,3-hexafluoro-2-hydroxypropyl)styrene (HFISt)₆₀] [poly(VSF₄₀-co-HFISt₆₀)] prepared by free radical copolymerization of VSF and HFIST showed good transparency (OD = 2.4μm^-1) as well. Poly(VSF₄₀-co-HFISt₂₂-co-tert-butoxycarbonyl HFISt₃₈) (OD = 2.8μm^-1) was prepared from poly(VSF₄₀-co-HFISt₆₀) and di-tert-butyl dicarbonate in the presence of 4-(dimethylamino)pyridine (DMAP). A resist film consisting of poly(VSF₄₀-co-HFISt₂₂-co-tert-Boc HFISt₃₈) and 5 wt % triphenylsulfonium triflate showed a sensitivity of 7.2 mJ cm^-2 and a contrast of 3.1 when a 150-nm-thick film prebaked at 100 °C for 1 min was exposed to 157-nm laser, postbaked at 130 °C for 1 min, and developed with a 2.38 wt % tetramethylammonium hydroxide (TMAH) aqueous solution.