Advanced Copper Contact Technology Diffusion Barrier Layer

As technology node goes down to 32 nm and beyond, the RC delay of interconnect has overrun the RC delay that comes from the gate, and becomes the bottleneck for further improvement of the device. The large resistance and resistance variances of tungsten plug that come from the difficulty in seamless CVD deposition in 32 nm technology node has caused a great challenge to the contact layer. One solution is to replace tungsten plug using Cu contact structure. Because of the critical demands for the diffusion barriers of Cu contact, the barriers should be thin and efficient in preventing Cu diffusion when working on NiSi substrate. In this thesis, both conventional Ru/TaN barrier and new Ru/TaSiN barrier used on NiSi substrate and Cu contact structure are investigated. The work is new and has practical values, as there is no published scientific research about using TaSiN for Cu contact structure till now.The thermal stability and electrical properties of Ru/TaN were studied, using X-ray Diffraction, X-ray Photoelectron Spectroscopy, Transmission Electron Microscopy analysis, and Current-Voltage tests. The results show that Ru(5nm)/TaN(13nm) barrier can stand 400℃annealing for 30 minutes without degradation, but after a 450℃annealing for 30 minutes, Cu diffusion has occurred, and after 500℃annealing for 30 minutes,Cu3Si is detected at the interface of NiSi/Si.The thermal stabilities of Ru/TaN on NiSi substrate are compoared with that on Si substrate using in-situ XRD. Results show that the failure temperature of Ru/TaN on NiSi is much lower than that on the Si substrate. We further calculate the activation energy (Ea) for Cu diffusion in Cu/Ru/TaN/NiSi/Si and Cu/Ru/TaN/Si system. The Ea is calculated to be 0.65 eV and 1.3 eV respectively for system on NiSi and Si substrate.In this thesis, we are the first to study the properties of Ru/TaSiN barrier for Cu contact structure. By comparing the thermal stabilities of Ru/TaN and Ru/TaSiN, we found that Ru/TaSiN works better on NiSi substrate. By calculating the thermal coefficient of the Cu of different systems, we propose the failure mechanism of the Ru/TaN barrier is caused by the stress exist for the TaN on NiSi during the annealing process. The incorporation of Si in the TaN layer has improved the stress problems of TaN on NiSi substrate. The TaSiN is studied by varying the power of Ta and Si PVD deposition, for varying barrier thicknesses. The diffusion barrier properties do not change much when the proportion of Ta,Si changes from 3.4 to 10.8. Further increasing the Si content can improve the diffusion barrier properties, but the resistivity of TaSiN also increases largly. When further decreasing the thickness of TaSiN to 5 nm, it shows good thermal performance.Considering thickness and diffusion barrier performance requirements, TaSiN is a very good diffusion barrier for Cu contact structure, and worth to be studied thoroughly.