Effect of different pretreatments on through silicon via copper filling

Pretreatments have a great effect on the through silicon via (TSV) copper electroplating filling process. In this study, we compared the wetting effect by observing cross-sectional images of samples pretreated with ultrasound and vacuuming method. And the electrochemical test was used to verify the effect of acid plating solution on the oxidation of the Cu seed layer. Without any pretreatment, vias showed a poor wettability that large voids existed at the bottom. The TSV pretreated by ultrasound and vacuuming method both were coated well with copper deposition layer, which showed a good wettability. However, when the Cu seed layer of the TSV was not well sputtered, ultrasound vibration may cause the exfoliation of the Cu seed layer resulting in the formation of void at the bottom of the vias. Diluted additives as prewetting solution made no much difference on filling effect. The acidic plating solution could dissolve the oxide layer at a high speed and react with the Cu seed layer as well.