Ultrasonic bondability and antioxidation property of Ti/Cu/Ag metallization on Si substrate

Aluminum has been widely used in integrated circuit (IC) chip interconnect As the IC feature sizes continue to shrink, the RC delay of the interconnect wire has become the main delay of the system, instead of the intrinsic gate delay. For the higher speed responsibility, the resistance of the interconnects should be reduced. Copper interconnect has become the only one option for the semiconductor manufacturing due to its lower resistivity (1.7 vs.2.7μΩ cm) and higher electro-migration resistance. However, there are some problems to be solved in the copper interconnect, especially the bad bondability due to the oxidation of the copper. In this paper, a Ti/Cu/Ag metallization was fabricated on the Si substrate by electron beam evaporating. The Ti-Cu film to simulate copper chip, and the Ag film as the bonding layer to enhance the bond abilities. The Ti/Cu/Ag metallization was characterized by AFM, XPS, XRD and SEM, respectively, and then the ultrasonic bondability of Au wire and antioxidation property of the metallization were measured. The shear test of the Au ball bond was performed by micro-force tester. Ultrasonic bondability test shows that Ti/Cu/Ag metallization has good bonding performance, which was 98% at room temperature and 150°C, and the shear failure was at the interface between Ag layer and Cu layer. High temperate storage test shows that the copper element content increased from 8.1 at.% to 28.9 at.% at surface of the Si/Ti-Cu-Ag structure, and most of them were oxidized.