Ultrasonic Bondability And Antioxidation Property Of Nano-film Metallizations On Cu Chip

As the IC package is developing towards miniaturization, high-density and multi-chips, aluminium can not meet the demand. 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 copper.In this paper, several metallizations, Ti-Cu-Ti-Ag,different nitrogen flow Ti-Cu-TiN-Ag, Ti-Cu-TaN-Ag, were fabricated on the Si substrate by magnetron sputtering. The morphology, phase structure and chemical composition of the metallizations were investigated by AFM, XPS, XRD and SEM, respectively, and the influence of ultrasonic and pressure on the ultrasonic bondability was tested. Also the oxidation resistance of different barriers was compared.The results showed that the thickness of the megnetron sputtering Ti-Cu-Ti-Ag, Ti-Cu-TiN(N22.5)-Ag, Ti-Cu-TiN(N21.0)-Ag and Ti-Cu-TaN-Ag films were homogeneous and they had a small surface roughness. XRD analysis of Ag films prepared by sputtering showed a preferred orientation of (111) and an average grain size of 29.2nm. It also showed that the Cu film prepared by sputtering had a preferred orientation of (111), which had a good resistance of electromigration. The TiN film prepared with nitrogen flow 2.5sccm and 1.0sccm existed in the form of TiN and TiN1-x respectively and TaN existed mainly in the form of Ta2N. Ti-Cu-Ti-Ag film, Ti-Cu-TiN(N21.0)-Ag film and Ti-Cu-TaN-Ag film had a good bondability which can reach 100%, while the bondability of Ti-Cu-TiN(N22.5)-Ag was poorer which was only 92%. The shear load of each film increased with the increase of ultrasonic power, while the shear strength increased at first but decreased then; The shear load increased with the increase of bonding pressure and the shear strength increased at first then decreased too. Ti-Cu-TiN(N22.5)-Ag film had a lower shear strength, other film had a higher one. The shear failure of the various films was mainly at the Au bump inside or the interface between Ag layer and the barrier layer. Ti-Cu-TaN-Ag structure and Ti-Cu-TiN (N21.0)-Ag structure had the best blocking performance, after stored in air at 300℃for 30 minutes the diffusion of copper to the surface could not be observed, Ti-Cu-Ti-Ag structure had a lower blocking capability, the content of copper in the surface was 15.93at.% at 250℃in air after stored for 30 minutes, while in the Ti-Cu-TiN (N22.5)-Ag structure,11.77at.% of copper was detected in the edge after holded for 30 minutes in the air at a temperature of 150℃. The content of copper in the surface of the Ti-Cu-Ag structure without barrier layer was 27.52at.%, which was detected after holded in the air for 30 minutes at a temperature of 150℃.