Ic Cu Interconnect Process Of Ta-based Diffusion Barrier Layer Research

With the development of deep submicron integrated circuits (ICs), copper metallization has been a replacement for conventional aluminum metallization in high density IC manufacture. But Cu is quite mobile in Si and has poor adhesion to Si or SiO2, which could degrade the performance of copper interconnect. Therefore, a diffusion barrier layer between copper interconnect and Si device is necessary. It is very important for the reliability of copper interconnect to conduct research on increasing the stability of barrier layer, finding the failure mechanism and improving the deposition technology. In this paper, Ta-based barrier layers including Ta,TaN,Ta(N implanted)are respectively deposited on Si substrate with deposition technology of magnetron sputtering, reactive sputtering and ion implantation. The surface morphology, reactions, interface, microstructure and depth profile are investigated. The different microstructure due to different deposition technology, failure mechanism and the diffusivity of Cu in barrier layer are discussed. Grain boundary diffusion is dominating for copper diffusion in polycrystalline Ta and TaN films. At high temperature, copper diffuses towards Si substrate through these fast diffusion paths and silicides of Ta and Cu are formed. Based on the grain boundary theory of J. C. Fisher and the approximation solution of Le Claire, thermal diffusivity of copper in Ta and TaN layer was calculated. The diffusion coefficient of Cu in Ta is one order larger than that in TaN (T=630oC). Ta layer with higher oxygen concentration induced by annealing processing showed better performance of impeding copper diffusion. However, oxygen will cause the increase of the resistance of the copper layer and facilitate the silicidation of tantalum and copper. The sputtered Ta layer is modified by N ion implantation to improve the barrier stability, which gives a new way for barrier deposition.Ion implantation changes polycrystalline Ta to amorphous-like. The grain boundaries of Ta layer were diminished and so the performance of the barrier layer is improved significantly.