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16 May 1994 Percolation view of novolak dissolution: 3. dissolution inhibition
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The dissolution of novolak films in aqueous alkali is controlled by the diffusion of base through a thin penetration zone that forms at the interface between the developer solution and the solid. Base diffusion is a percolation process in which the ions of the base migrate through the zone by stepping from one hydrophilic site (phenol or phenolate) to the next. Dissolution inhibitors function by blocking some of the hydrophilic sites and thereby interrupting the diffusional pathways. Percolation theory suggests a relation between the strength of inhibition and the percolation characteristics of the resin. The two are linked together by the hydrophobic displacement volume of the inhibitor, which is that volume which the inhibitor occupies in the penetration zone. The hydrophobic displacement volume determines the effectiveness of an inhibitor; it depends not only on the molecular volume of the inhibitor, but also on the mobility of the hydrophilic sites in the zone; it is much smaller above the glass transition temperature of the zone than below it. It is also smaller in systems where some degree of motional freedom persists even below the glass transition of the zone.
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Hsiao-Yi Shih, Tung-Feng Yeh, Arnost Reiser, Ralph R. Dammel, Hans-Joachim Merrem, and Georg Pawlowski "Percolation view of novolak dissolution: 3. dissolution inhibition", Proc. SPIE 2195, Advances in Resist Technology and Processing XI, (16 May 1994);

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