Non-ionic photoacid generators for chemically amplified photoresists: structure effect on resist performance

As reported previously, we developed a novel oxime sulfonate type of photoacid generator (PAG), 2-[2,2,3,3,4,4,5,5,6,6,7,7-dodecafluoro-1-(nonafluorobutylsulfonyloxyimino)-heptyl]-fluorene (DNHF), which generates a strong acid (nonaflic acid) by light irradiation and is applicable to chemically amplified ArF photoresists. Recently we have prepared two DNHF analogues with different fluoroalkyl chains adjacent to the oxime moiety, 2-[2,2,3,3,4,4,4-heptafluoro-1-(nonafluorobutylsulfonyloxyimino)-butyl]-fluorene (HNBF) and 2-[2,2,3,3,4,4,5,5-octafluoro-1-(nonafluorobutylsulfonyloxyimino)-pentyl]-fluorene (ONPF), and investigated the structure effect. The change of the fluoroalkyl chain did not have a strong impact on photo-efficiency and transparency at 193 nm and these PAGs demonstrated superiority to triphenylsulfonium nonaflate (TPSNF) with respect to these criteria. On the other hand, different behaviors were observed in the coating property and contact angle measurement of the photoresists containing these PAGs. The hydrogen atom at the end of the fluoroalkyl chains of DNHF and ONPF was found to have a role in improving the coating property. These non-ionic PAGs were less risky for contamination on the surface of the lens due to insolubility in water. In addition, the effect by these PAGs on increasing hydrophobicity of the photoresist surface was identified. These results suggest that the newly developed non-ionic PAGs are suitable for ArF immersion lithography.