Electrolessly Deposited Co (0.20 at.%)-Modified Cu with Greater Thermal- and Electrical Stress-Induced Reliability than Co

Cobalt (Co) offers superior thermal reliability, yet this study shows that copper (Cu) films with only 0.20 at.% Co, denoted Cu(Co), exceed Co in both thermal and electrical stress reliability. These films were synthesized via electroless plating using a hydrazine-based CuSO₄–CoSO₄ bath. Despite higher Co²⁺ in solution, only 0.20 at.% is incorporated due to preferential Cu²⁺ reduction, as confirmed by electrochemical polarization and mixed potential theory. Sheet resistance and surface morphology analyses reveal that Cu(Co) films maintain structural integrity and exhibit leakage currents two orders lower than Co. The electromigration mechanism is currently under investigation for scalable interconnect development.