Efficiency of Photoacid Generators in Chemically Amplified Resists for 157nm Lithography

The photoacid generation efficiency of six photoacid generators was measured upon exposure to 157nm light in a candidate polymer for 157nm resist formulations of poly(NBHFA-co-NBTBE) using a standard addition technique. The photoacid generators studied were triphenylsulfonium perfluoro-1-butanesulfonate (TPS-Nf), bis(4-tert-butylphenyl)iodonium trifluoromethanesulfonate (BBI-Tf), bis(4-tert-butylphenyl)iodonium perfluoro-1-butanesulfonate (BBI-Nf), bis(4-tert-butylphenyl)iodonium perfluoro-1-octanesulfonate (BBI-PFOS), N-hydroxy-5-norbomene-2, 3-dicarboximide perfluoro-1-butanesulfonate (NDI-Nf), and bis(2-trifluoromethyl-6-dinitrobenzyl) 1, 3-benzene sulfonate (TFMDNBS). For the four ionic salts the photochemical efficiency was in the order BBI-Nf>BBI-Tf> BBI-PFOS>TPS-Nf. The photoacid generators NDI-Nf and TFMDNBS exhibited extremely poor efficiency for photoacid generation in this resist system under exposure to 157nm radiation.