Evaluation of ultra thick photo resist for high aspect ratio bumping applications

This paper presents the evaluation results of two positive, thick resist molds for the electroplating of Copper pillar interconnects. Two different resist molds of 100 μm and 58 μm thickness have been fabricated with aspect ratios of 2.5 and 1.3 respectively in a single coat process. Lithography parameters have been optimized using a UV aligner to produce smooth and near vertical sidewall profiles for both resist molds. Through mold electroplating of Copper has also been demonstrated with good uniformity within ± 3% and ±2% respectively. The resist molds were also found to be stripped easily in standard solvent strippers making them suitable for fabrication of high aspect ratio interconnects.