Performance comparison of negative resists for copper rerouting and other electroplating applications

Two types of chemically amplified (CA) negative resists were compared lithographically. An acid catalyzed resist and a photopolymerizable type resist. The optimum lithographic performance of the acid catalyzed resist on Cu is in the thickness range below 15μm, with vertical profiles. This resist exhibits inverted profiles on Cu above 15μm of thickness. The Photopolymer type resist performs best above 25μm thickness, and can be used for 120μm thick applications with single coat. Top line rounding is more observed with this resist as its applied thickness is reduced below 20μm. This effect is believed to be related to oxygen uptake in the resist surface. Thus it has a more pronounced effect at relatively thinner films. Both resists are compatible with the electroplating process.