Microvia Filling By Using Insoluble Anodes in an Acidic Copper Planting Bath with a Novel Accelerator

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To develop copper plating formula for high-speed via filling, a more stable insoluble anode, namely dimensionally stable anode (DSA), was used at high current density. We choose a novel accelerator, 3-(N,N-dimethylthiocarbamoyl)-thio propanesulfonic acid (DPS), which has better acceleration performance on copper superfilling than Bis(3-sulfopropyl) disulfide (SPS) in the DSA plating system. This work investigates the influence of experimental conditions on filling performance and also use numerical simulation method to quantify the filling performance. According to the results, DPS can exhibit excellent acceleration on copper deposition in the DSA plating system only. NMR result shows that DPS is oxidized by the DSA to be more active products which bears -SH and -SO3 - groups, which can accelerate on copper deposition. Putting the DSA in a filter bag can block oxygen which was produced by water electrolysis at the anodes to enter the plating solution and reduce DPS oxidation on the surface of the DSA. As a result, via bottom and top deposition rate was different from that without the filter bag. From the results of microvia filling and numerical simulation method, the inhibition of complex inhibitor (PEG-Cl-) and the filling performance was positive in correlation with convection in the blind via. In a plating system with a strong forced convection and a low temperature exhibited better filling performance. On the other hand, the filling performance was Cu(II) mass-transfer controlled in the weakly forced convection system, so that the filling performance is not good.