Characterization of Ag nanofilm metallization on copper chip interconnect and its ultrasonic bondability

To improve the bondability of copper chip interconnect, a Si/Ti-Cu-Ag structure was designed and fabricated using evaporation method. Some analytical methods such as SEM, AFM, XRD and XPS were used to characterize the Ag nanofilm metallization and its bondability. It was found that the evaporated Ag metallization has good surface state and samll particle size, which could diffuses readily in the wire bonding process and thus improve the bondablilty. XPS showed the Ag metallization was pure silver without oxidation and sulfuration when stored at the room temperature. And XRD showed the crystal face index of the top surface polycrystalline Ag layer was (111), which agree with the principle of minimum surface energy. The bondability and shear strength of the Au ball bump on the Si/Ti-Cu-Ag structure were excellent at room temperature and 150°C, better than the oxygen free copper, and meet the JEDEC Standard 22-B116. After high temperature storage at 200°C for 16 days and temperature cycling for 1000 cycles, the interfaces of the Si/Ti-Cu-Ag structure were still very tight and clear, showing high reliability.