Dissolution Inhibition in Positive Novolak Resists

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Positive novolak resists are by far the most important patterning systems of today's semiconductor technology, yet their functional mechanism is not well understood. This research deals with a mechanistic model of resist function, which if validated and completed would provide a rational basis for the further technical development of these important materials. It was recently shown that novolak dissolution in aqueous alkali is controlled by the rate of diffusion of the base into the solid polymer. It is now suggested that diffusion of the electrolyte into novolak follows a path defined by hydrophilic centers i.e. the OH-groups of the resin, and avoids the hydrophobic regions of the matrix. Dissolution inhibitors function by interrupting these hydrophilic diffusion channels. It is proposed to validate the concept of hydrophilic diffusion pathways by designing resins with a varying concentration of phenols and in this way vary the separation of hydrophilic sites and monitor the effect of site dilution on dissolution rate.