The molecular mechanism of novolak–diazonaphthoquinone resists

Novolak–diazonaphthoquinone (DNQ) resists are photosensitive varnishes that are used in the fabrication of more than 80% of todayʹs integrated circuits. They have played a crucial role in an unprecedented technical revolution, yet until quite recently nobody really knew how they work. We have been concerned with this problem for some time and we realize now that the principal functions of novolak resists, namely the inhibition by DNQ derivatives of the dissolution of novolak films, and the cessation of inhibition on exposure to radiation, are essentially physical phenomena. Dissolution inhibition is caused by an electric stress imposed on the phenol groups of the resin by the inhibitor. This effect penetrates deep into the material through the formation of hydrogen-bonded phenolic strings. Exposure relieves the stress by uncoupling the strings from the source of induction. The concept of phenolic strings is new and unusual, but it is essential for the understanding of dissolution inhibition. With it, all the many aspects of novolak resists can be interpreted in a unified manner.