Tailoring of novolac resins for photoresist applications using a two-step synthesis procedure

Abstract

In this paper we report the development of novolak resins suitable for the formulation of positive and negative acting photoresists, which beneficially can be applied in micro- electronical-mechanical systems (MEMS). Based on an extensive screening program, selected properties of the novolaks have been optimized. Special emphasis has been laid on high chemical stability in strongly alkaline systems. The type of the phenolic compounds as well as the arrangement of the phenol moieties within the polymer chain has shown great influence on the resin properties and the performance of the resulting photoresists. The novolak resins have been prepared in laboratory scale and pilot scale using an optimized known two-step synthetic procedure. This procedure ensures for novolaks with reduced polydispersivities and allows the reproduction of the resin quality within a narrow tolerance interval. According to this synthetic procedure novolaks with particular arrangements of the phenolic moieties have been prepared. Novolak resins with alternating and semi-alternating structures have been shown to form a new polymeric matrix for the preparation of special positive and negative tone photoresists. These formulations meet the high requirements of electroplating processes with respect to the accuracy of the structural transformation, layer thickness and metal deposition conditions.