Ultrasonic bondability and antioxidation property of Ti/Cu/TaN/Ag multi-layers on Si substrate

To improve the ultrasonic bondability and antioxidation property of pure Cu pad, multi-layer structures of Ti/Cu/TaN/Ag are deposited on Si substrate with magnetron sputtering technology. The as-deposited multi-layers had uniform thicknesses and smooth surface with the roughness of 2.098 nm. X-Ray diffraction analysis indicated that both Ag and Cu layers had deposited with (111) preferred orientation, and the grain size of Ag layer was 29.5 nm. The phase composition of TaN layer was Ta₂N. For comparison of antioxidation properties, traditional pad structure Ti/Cu/Ag was also fabricated with the same process. Obvious Cu oxidation occurred on the surface of the Ti/Cu/Ag structure after heating at 150 °C for 30 min. However, no Cu element was detected on the surface of Ti/Cu/TaN/Ag structure even after heating at 300 °C, which indicated that the Ta₂N layer in Ti/Cu/TaN/Ag structure can prevent the underneath Cu pad from oxidation. 100% Au bondability was achieved on Ti/Cu/TaN/Ag structure under both room temperature and 150 °C. The shear fractures mainly occurred in Au bonds, indicating the multi-layers fabricated by magnetron sputtering technology had strong bond interface with Cu pad.