Photochemical Decomposition Mechanisms for AZ-Type Photoresists
by J. Pacansky, J. R. Lyerla
The photochemical decomposition mechanism of orthonaphthoquinonediazides has been investigated principally by infrared and carbon-13 nuclear magnetic resonance spectroscopies. The results demonstrate that the decomposition proceeds via a ketene intermediate to a photoproduct, the nature of which depends on the reaction conditions. Model resist systems were prepared by mixing orthonaphthoquinonediazides and 2,3,6-trimethylphenol or the diazide plus Novolak resin. Under ambient thermal and humidity conditions, ultraviolet (UV) exposure of the diazide yields 3-indenecarboxylic acid as the final photoproduct. However, UV exposure in vacuo results in ester formation via a ketene-phenolic OH reaction. The decomposition pathway and ensuing reactions have been shown to be the same for both 1- and 3-orthonaphthoquinonediazides attached to mono- and trihydroxybenzophenones. The technological implications for resist processing derived from these studies are also discussed.