Effect of Ag, Sn, and SiCN Surface Coating Layers on the Reliability of Nanotwinned Cu Redistribution Lines Under Temperature Cycling Tests

Nanotwinned Cu (NT-Cu) is a promising candidate for Cu redistribution lines (RDLs). However, oxidation in NT-Cu lines is of concern because it increases electrical resistance and endangers the reliabilities of semiconductor devices such as temperature cycling tests (TCTs). In order to enhance the reliabilities, the passivation of NT-Cu lines is needed. In this study, immersion Ag/Sn and plasma-enhanced chemical vapor deposition (PECVD) SiCN were used to passivate the surfaces of NT-Cu RDLs at low operating temperatures (60 °C for immersion and 150 °C for PECVD). We found that Ag- and SiCN-capped NT-Cu lines showed negligible changes in microstructures and resistance after TCTs. As for Sn-coated NT-Cu lines, the resistance remained stable after 250 cycles of TCTs, with low oxygen signals detected. These three coating layers can block oxygen and moisture, effectively preventing oxidation and maintaining the resistance of NT-Cu RDLs during the TCT. The findings demonstrate the effectiveness of Ag, Sn, and SiCN coatings in enhancing reliability, providing options for passivation layers of NT-Cu RDLs.