This paper discusses an insoluble layer which forms on the photoresist surface by pre-exposure treatment. From an analytical result of used developer for pre-exposure treatment, we have found that TBP-NQD triester (triester of trihy-droxybenzophenone with naphthoquinone-1,2-diazide-5-sulfonic acid) and high molecular weight portion of Novolak resin in the positive photoresist were insoluble in the developer. We presume that those components are forming insoluble layer on the photoresist surface. © 1990, The Electrochemical Society, Inc. All rights reserved.