Addition of PEG-Thiol to Cu Electroless Plating Bath for Realizing Perfect Conformal Deposition in Through-Si Via Holes of 3-D Integration

Abstract

Cu electroless plating is one of the most promising methods to form a seed layer of electroplating for Cu filling in TSV of 3-D integration. However, with an increase of the aspect ratio of TSV, a uniformity of Cu thickness at the sidewall of TSV becomes poor due to consumption of Cu ions and reducing agents near the entrance of TSVs. In this study, we have studied an addition of PEG-thiol to an electroless Cu plating bath with a reducing agent of glyoxylic acid. We achieved conformal deposition of Cu for TSV with diameters of 4 to 10 μm by this method. The Cu thickness of the TSV sidewall remained constant with depth even for a high aspect ratio TSVs. This method is very effective for a formation of a thin Cu seed layer prior to the Cu electroplating process of TSV-filling.