Novolak resins: structure elucidation by multidimensional NMR techniques and correlation with lithographic performance

Abstract

AbstractPhoto‐active chemicals blended with novolak resins, solvents and certain other additives serve as photoresists and are the real workhorses of the burgeoning microlithography industry, which plays a key role in making electronic circuits for ICs and VLSIs at micron and sub‐micron levels. It has been realized over the years that the microstructure of these matrix polymers (novolak resins) is very crucial for better lithographic performance. Although various analytical techniques exist for characterizing novolak resins, precise and unambiguous structural details are obtained only through NMR experiments. In this paper, we review the applications of a range of NMR experimental techniques to the structure elucidation of novolak polymers and co‐polymers. Such information is seen to lead to the design of high‐performance photoresists. The optimum percentage of the different phenolic units in novolak resins, which is very crucial for lithographic performance, can also be determined using these spectroscopic techniques. Using DEPT and INEPT 13C NMR spectra of novolak resins, two formulae have been developed for quantitative estimation of the lithographic performance of photoresists. On the basis of a comparison of the NMR spectra of a photoresist before and after photolysis, the mechanism of action of a photoresist can be probed, and this should lead to a deeper insight into the design of high‐performing photoresists. Copyright © 2003 Society of Chemical Industry