Novel transparent PAGs for 193-nm resists

Transparency of the resist film at exposure wavelength affects lithographic performances, such as sensitivity, profile and resolution. Not only binder polymer, but also photo acid generator (PAG) itself has a significant impact on transparency of the formulated resist. Triphenylsulfonium salt (TPS) or Diphenyliodonium salt (DPI) have been widely used as PAGs in DUV chemically amplified (CA) resists, however, aromatic groups there have strong absorption at 193nm and thereby these PAGs have to suffer from low transparency. In this paper, we will report a novel class of transparent enone sulfonium salt PAGs(ENS-PAG), which we believe useful for 193nm resist. The ENS-PAGs do not have any aromatic groups but have an α,β-unsaturated ketone structure for the absorbing moiety in the backbone. These PAGs showed excellent transparency, thermal stability, and demonstrated an advantage in the line edge roughness (LER).