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Volume: 42 | Article ID: art00003
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The Molecular Mechanism of Novolak Resists
  DOI :  10.2352/J.ImagingSci.Technol.1998.42.1.art00003  Published OnlineJanuary 1998
Abstract

The molecular mechanism of Novolak-diazoquinone resists depends on the diffusion of base into the resin matrix. In this context the novolak film may be viewed as a percolation field where the percolation sites are the phenolic OH groups of the resin. The rate of percolation depends on the density (concentration) of percolation sites and on their steric accessibility. When diazonaphthoquinone inhibitors are introduced into the system they cause the formation of hydrogen-bonded strings of phenolic OH groups. The polarized hydroxyls are less available to the advancing base, that lowers the site connectivity of the field, and with it the dissolution rate. On exposure, the photolysis of the diazoquinones is followed by a very fast and very exothermic reaction, the Wolff rearrangement. The heat liberated in this thermal process produces an intense temperature spike, in excess of 200°C at the location of the inhibitor. At the high temperature the phenolic strings are severed from their anchor. The disconnected OH groups are no longer polarized by the inhibitor, and the inhibition effect is suspended. The dissolution rate of the exposed resist returns to that of novolak, except for a slight increase in dissolution rate caused by the presence of newly formed indenecarboxylic acid that contributes some additional percolation sites to the exposed film.

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Arnost Reiser, "The Molecular Mechanism of Novolak Resistsin Journal of Imaging Science and Technology,  1998,  pp 15 - 22,  https://doi.org/10.2352/J.ImagingSci.Technol.1998.42.1.art00003

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