Copper Rich Cu1-Xnix Alloys (0.05 < X < 0.15) Electrodeposited From Acid Sulfate-Based Electrolyte With Benzotriazole Additive For Microbump Metallization For 3d Stacked Integrated Circuits

In this paper we report on electrodeposition of CuNi alloys with low Ni content for applications in three-dimensional stacking of integrated circuits (SIC). For practical reasons related to compatibility with SIC processing, a common sulfate-based electrolyte solution was chosen and the high copper/low nickel content in the deposited alloys was achieved through the introduction of organic additive benzotriazole (BTA). BTA is known as a strong inhibitor for Cu deposition, but its effects on CuNi alloy deposition were not known before. We hypothesized that, in addition to bringing the onset potential of Cu closer to that of Ni deposition, the slower diffusion through the BTA passivation layer could enable improved control of the composition of the deposited alloy as well as the current distribution over the substrate. Our hypotheses were tested through systematic electrochemical measurements combined with ex-situ imaging and chemical analysis techniques. As such, CuNi alloys with Ni content between 5-15 at.% were successfully fabricated from a sulfate-based CuNi electrolyte solution with BTA as an organic additive. (C) The Author(s) 2019. Published by ECS.