New ionic photo-acid generators (PAGs) incorporating novel perfluorinated anions

Abstract

A new class of ionic photo-acid generators (PAGs) useful in chemically amplified photoresist formulations has been developed. The new PAGs are salts comprising a photoactive cation and a fluoroorganic sulfonylimide or sulfonylmethide anion. These highly delocalized, nitrogen- and carbon-centered anions are extremely nonbasic and weakly coordinating. Correspondingly, their conjugate acids are powerful superacids. The imide and methide acids produced by photolysis of the corresponding ionic PAGs are highly active in initiating the cationic polymerization of various organic monomers (as in negative resists) and have been shown to catalyze the deprotection of acid-sensitive organic functional groups (as in high activation energy, positive resists) with good photospeeds. The unique balance of reactivity and physical properties provided by the imide and methide anions suggests that they may be useful alternatives to, or replacements for, the organic or inorganic anions commonly employed in existing ionic PAG formulations (e.g., perfluoroalkanesulfonate anions and MF6- anions, where M is Sb, As or P). A family of ionic PAGs based upon these new anions and their combinations with diaryliodonium or triarylsulfonium cations has recently been made available by 3M as experimental products for lithographic evaluations in positive and negative photoresists. In this report we will describe the characterization of these PAGs, including melting points, thermal stabilities, UV extinction coefficients, solubilities and photo-acid volatilities. Potential advantages of these new PAGs in positive and negative photoresist applications will also be presented.