Fundamental Studies of Dissolution Inhibitors in Poly(norbornene-alt-maleic anhydride) Based Resins

Using terpolymers of Poly(norbornene-alt-malefic anhydride-co-acrylic acid) [P(NB/MA/AA)], the dissolution inhibition mechanism for two types of common additives in 193nm resist formulations, tert-butylcarboxylate (e.g. tert-butyl cholate) dissolution inhibitors (DI) and onium salt photoacid generators (PAC's) were examined. For simple cholate ester derivatives, increasing interactions with maleic anhydride repeating units paralleled the dissolution inhibition (tert-butyllithocholate>tert-butyldeoxycholate>tert-butylcholate). For a wider range of cholate derivatives, increasing hydrophobicity as measured by logPoct or the cloud point formation in water/acetone mixtures, is a good predictor of increased dissolution inhibition. Increases in dissolution promotion appeared to track with the number of carboxylic acid moieties and the hydrophobicity of carboxylic acid moieties released upon acidolytic cleavage of carboxylate esters. Finally, for onium salt PAC's, increasing the size of fluorinated anions decreased dissolution inhibition. This may be because these anions offer more steric hindrance, which disfavors interactions with the terpolymer matrix. The nature of this interaction may be that of a PAG with carboxylic acid as judged from modeling studies with acetic acid in which increasing strength of the interaction correlated with increased dissolution inhibition (triflate>nonaflate> perflurooctanesulfonate)