The backside via-last through silicon via (TSV) process is a simple and cost-effective approach for three-dimensional integration. However, it has two problems: (1) the notching near the bottom corners of TSVs and (2) the reaction product generated by the etchback step. To overcome these problems and increase TSV yield, we previously proposed a via-last TSV process using notchless Si etching and wet cleaning of the first metal layer. In this process, the notching was suppressed by optimizing the deep Si etching conditions. In addition, wet cleaning of the first metal layer was performed with a novel cleaning solution to remove reaction products on the first metal layer (which was generated by the etchback step) and create good electrical contact between the TSVs and the first metal layer. In this study, we investigated the characteristics of a novel solution used in the wet cleaning process. The wettability between the novel solution and the TSV liner oxide was very good. The cleaning performance of the novel solution was high while the etching rate of the first metal was very small.