PERCOLATION VIEW OF NOVOLAK DISSOLUTION .6. THE ACCELERATION OF NOVOLAK DISSOLUTION BY PHENOLIC ADDITIVES

Phenols or polyphenols of low molecular weight are added to Novolak re sists to increase the dissolution rate. They function as dissolution p romoters by introducing additional hydrophilic percolation sites (OH g roups) into the system. All low molecular weight phenols accelerate di ssolution, but some are also able to improve lithographic performance by increasing the image contrast of the material, i.e., the difference in dissolution rate between exposed and unexposed areas of the resist film. Additives that function in this way are those that are included in the phenolic clusters formed by the inhibitor. It appears that the criterion for inclusion in the clusters is the acidity of the OH grou ps of the additive.