Microstructure and reliability of full (Cu,Ni)6Sn5 IMC interconnects fabricated by current driven bonding method with Sn-5Cu-5Ni composite solder

Abstract

Full intermetallic compound (IMC) interconnects have emerged as a promising die-attach solution for third-generation semiconductor power devices that operate at higher temperatures. This study aims to fabricate Cu/(Cu,Ni)₆Sn₅/Cu full IMC interconnects by the current driven bonding (CDB) method with Sn-5Cu-5Ni composite solder to achieve higher reliability. The use of Sn-5Cu-5Ni composite solder reduced the processing time by approximately 1/3 to only 10 min, and significantly refined (Cu,Ni)₆Sn₅ grains from 39.59 to 2.36 μm, compared to common pure Sn solder. Even after current stressing (150 °C, 1.0 × 10⁴ A/cm²) for 500 h, the interfacial (Cu,Ni)₃Sn in full (Cu,Ni)₆Sn₅ IMC interconnect increased by only 0.34 µm in thickness, in comparison to 2.92 μm for Cu₃Sn in full Cu₆Sn₅ IMC interconnect. First-principles calculations indicated that doping Ni increased the diffusion activation energy (\({\text{Q}}_{\text{a}}\)) for Cu atoms diffusing in Cu₆Sn₅ and Cu₃Sn, from 1.60 and 1.56 eV/atom to 2.08 and 1.68 eV/atom, respectively, thereby inhibiting the growth of interfacial (Cu,Ni)₃Sn. The average shear strength of full (Cu,Ni)₆Sn₅ IMC interconnects in as-fabricated state was 64.1 MPa and remained to be 62.8 MPa even after current stressing for 500 h, showing an excellent EM resistance. These findings suggest that the CDB method utilizing the composite solder is expected to realize full IMC interconnects with high strength and high EM reliability.