High speed Cu-Ni filling into TSV for 3-Dimensional Si chip stacking

The effect of Ni addition on high speed Cu filling into a TSV (through-silicon-via) was investigated for three dimensional (3D) Si chip stacking. Tapered vias were prepared in a Si wafer by deep reactive ion etching process. In order to increase the filling ratio of Cu-Ni into the via, a periodic pulse reverse (PPR) current waveform was applied for electroplating. For comparison Cu filling in the via was also carried out using a PPR current waveform. The Cu and Cu-Ni alloy-filled via was observed by field emission scanning electron microscopy (FE-SEM) to investigate the filling ratio of the vias and to observe the deposition characteristics. The calculated rate of Cu-Ni nuclei formation on the cathode surface was increased by about 1.7 times by Ni addition compared to Cu filling and the increased nucleation rate of the Cu-Ni alloy over Cu was confirmed by FE-SEM. The filling ratio of the Cu-Ni alloy was 1.3 times higher than that of Cu at the same time. The Cu-Ni filling process by the PPR current waveform was confirmed to be effective to fill the TSV in a short time.