Comparison of Different Copper Nitride Passivation Layers Fabrication Methodology and Optimal Growth Condition for Low Temperature Copper-to-Copper Bonding in Advanced Packaging

Given the growing demand for heterogeneous integration, achieving low-temperature copper-to-copper bonding has become a pivotal technique. In the context of this bonding technique, the deposition of a passivation layer on metallic interconnects has been demonstrated to enhance bonding quality. Copper nitride film is selective as the passivation layer in this study due to its unique characteristics. We employed both plasma treatment and magnetron sputtering for fabricating copper nitride films. During the plasma treatment, a passivation layer using the optimal plasma condition is selected, and its excellent electrical performance validates the applicability in low temperature bonding. For the sputtering process, different gas ratios are examined, and the optimal condition aligns well with the observed chip-level bonding quality. The bonding mechanism is thoroughly investigated using TEM and EDX. The results from these two distinct approaches affirm the feasibility of employing copper nitride passivation layer in advanced packaging application.