Development of fine pitch negative tone resist for electro-plating

High density packaging such as 3D-TSV, 2.5D interposers and Flip-chip wafer bumping require fine pitch redistribution layers (RDL). In order to satisfy these requirements, we developed a novel negative tone resist for RDL. Generally, oxygen inhibition for cross-linking reactions is a major issue for negative tone resist, especially at film thickness conditions of <;10um. We found that the sensitivity of the photo initiator and the developing speed of the polymer have major effects on patterning performance. In this study, we developed a new negative tone resist which shows high resolution (<;2.0um line and space), and high aspect ratio (>3) with straight pattern profiles even under 10um film thickness conditions.