Extrusion Suppression of TSV Filling Metal by Cu-W Electroplating for Three-Dimensional Microelectronic Packaging

Extrusion behavior of Cu filling in through-silicon-via (TSV) under thermal loading was investigated in this study. In order to suppress the extrusion of Cu-filled TSV, Cu-W was filled in a tapered TSV by electroplating. The Cu-filled TSV was used as a reference for comparison. Defect less filling of Cu-W in TSV was achieved at a composition 92.4 wt pct Cu and 7.6 wt pct W. The coefficients of thermal expansion of both Cu-7.6 pctW and Cu were 10.8 × 10⁻⁶/°C and 16.5 × 10⁻⁶/°C, respectively. Initially, both Cu and Cu-W filled TSVs were annealed for 30 minutes at 723 K (450 °C) and the extrusion heights were measured. The results showed that the extrusion of Cu-W filled was suppressed significantly compared to Cu-filled TSVs. The annealed extrusion heights of Cu and Cu-W were found to be 1.369 and 0.465 µm, respectively. This showed around 34 pct lower extrusion height of Cu-W filled TSV as compared to Cu-filled TSV. The extrusion kinetics with different annealing durations and the mechanism of the suppression of extrusion in Cu-W filled TSV are also reported here.