| AVS 54th International Symposium | |
| Thin Film | Thursday Sessions |
| Session TF-ThM |
| Session: | Thin Films for Electronic Applications |
| Presenter: | C. Li, Nanyang Technological University, Singapore |
| Authors: | C. Li, Nanyang Technological University, Singapore J. Hsieh, Ming-Chi University of Technology, Taiwan |
| Correspondent: | Click to Email |
Binary alloys with amorphous structure have been used as diffusion barrier in many electronic components for their better resistance to the movement of thermally and electrically conductive atoms. Some other advantages for using such amorphous films including their high crystallization temperature and good electrical conductivity are also important for the function of electronic components. For instance, films such as Cu100-xTax, Zr40Cu60, Ta50Co50, Ta100-xNix (x=35,50) and Co55W45, all exhibit low resistivity (<200 µ?-cm) and high crystallization temperature (Tx ~800oC, except Ta-Co and Cu-Zr) in literature. However, when they are employed as diffusion barriers for Al, Cu or Au metallization, some of the films (Cu100-xTax, Ta100-xNix (x=35,50) and Co55W45) demonstrate a failure at temperatures much lower than their crystallization point. This may due to the low reaction temperature of these metal with Si substrate which is only around 200-300oC. Based upon these earlier studies, one improvement can be made on the existing amorphous films is to replace the noble or near noble metals (Cu, Ni etc.) with some refractory metals such as Ta, W, Ti or Zr because their reaction temperatures with Si are usually higher than 500oC. Examples of such films as Ta-W and Ti-W can be found in the literature. In this study, a modeling and experimental works on the amorphous binary alloys will be presented for its barrier performance on the metal diffusions. For experiments, a layer of Cu/Ta50Zr50/SiO2/Si stack is made by the deposition of Ta and Zr on thermally oxidized Si substrate by co-sputtering in the Ar plasma. Experimental results indicate that the amorphous barrier can indeed suppress the penetration of Cu atoms into Si substrate upon annealing at temperature higher than 500oC. Further investigations on the thermal stability reveal that the top Cu layer may enhance the formation of metal silicides such as TaSi2 and ZrSi2 inside the barrier. These silicides can increase the activation energy of Cu diffusion and therefore enhance the barrier’s performance. In addition, a failure mechanism of the diffusion barrier is proposed based on both thermal stability and residual tensile stresses. A qualitative model for this proposal shall be analyzed by numerical simulations also.