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 = 2.1 μm-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 = 2.4 μm-1) as well. Poly(VSF40-co-HFISt22-co-tert-butoxycarbonyl HFISt38) (OD = 2.8 μm-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.