Structural changes in a resist resulting from plasma exposure during the reactive ion etching process

Structural changes in a resist resulting from plasma exposure during the reactive ion etching (RIE) process were studied using ¹³C-NMR analysis and Fourier transform IR spectroscopy (FT-IR). Two types of resist were chosen containing different amounts of diazonaphthoquinone derivative as an initiator with the same type of base polymer, cresol novolak resin. It was found that a slightly soluble layer was formed by the cross-linking reaction of the main chain of novolak resin as a result of plasma exposure in the case of the resist with a low amount of photosensitizer. The molecular weight concurrently decreased, probably due to the chain-scission of the main chain of novolak resin. On the other hand, in the resist containing a larger amount of photosensitizer, the molecular weight of the material increased, probably due to the occurrence of some type of cross-linking reaction such as thermal condensation. From these results, we obtained some guidelines for developing a resist stripping process without a residue.