Effect of Titanium-Polymer Interactions on Adhesion of Polymer-Copper Redistribution Layers in Advanced Packaging

The ever-increasing demand for high-bandwidth interconnects has given rise to the need for high IO-density package redistribution layers (RDL). This necessitates scaling down RDL critical dimensions. There are numerous challenges pertaining to the further miniaturization of polymer RDL. The main challenge is the adhesion of copper RDL to the polymer dielectric. The chemical interactions between polymer and metal seed-layer play an important role in adhesion. This paper presents the study of chemical interactions between titanium and various commercial polymer dielectrics using XPS and FTIR spectroscopy. The effects of pre-deposition processes on chemical interactions and thereby adhesion strength are investigated. It was observed that the chemical interactions between titanium and polymer can be improved by plasma processing leading to a significant enhancement in adhesion strength. In case of ABF dielectric, the mean adhesion strength was increased from 8.9 N/cm to 10.8 N/cm. This adhesion enhancement was attributed to the formation of larger number of Ti-C bonds between the titanium seed and the polymer backbone. XPS and FTIR analyses are presented to elucidate the mechanism of adhesion enhancement.