Study on electrodeposited Ni-Mo alloy barrier films for electronic interconnects

In this study, molybdenum (Mo) is incorporated into nickel (Ni) barrier films by electrodeposition using ammonia-citrate bath. Molybdenum contents in the range of 6-25wt% were investigated for their effectiveness in retarding the diffusion of copper atoms. The effect of the presence of Mo and multiple reflow on the interfacial reactions between Ni-Mo barrier film and Sn-3.8Ag-0.7Cu (SAC387) were investigated. Ni and Ni-W barrier films were also deposited and studied for comparison purpose. Solders spreading rate and contact angle were characterized with the use of optical microscope. Characterization on barrier films was done with energy-dispersive X-ray spectroscopy (EDX) analysis and X-ray diffraction (XRD) analysis. Characterization on interfacial intermetallic compounds (IMCs) was done with field-emission scanning electron microscope (FESEM). Results revealed that only one type of IMC, (Cu, Ni)₆Sn₅ formed at the interface of SAC387 solder and Ni barrier film after 1x and 12x reflow. However, two types of IMCs formed at the interface of SAC387 solder and Ni-Mo/Ni-25wt% W alloy barrier films after 1x and 12x reflow. These IMCs are found to be (Cu, Ni)₆Sn₅ IMC and Sn-Cu-Ni-Mo/ Sn-Cu-Ni-W phase.