A Study On Contact Tungsten Filling Process For Copper Interconnect Technology

With the entry into the deep sub micron integrated circuit technology, in BEOL, metal interconnection mostly adopts copper interconnection technology. But due to the copper diffusion issue, the contact process still uses tungsten as the filling element. With the line width narrowing, the tungsten gap-filling faces increasing challenges. In productions, there often exists contact void issue for tungsten gap-filling process. Large voids can cause the upper layers of the copper metal diffuses into devices, leading to device failure. Therefore, in order to ensure that the device is stable and reliable, how to improve the tungsten step coverage, and reduce the contact hole seam size is very important and urgent.The main contents of this thesis are:The first part describes the development history of the integrated circuit and the copper interconnect technology, and describes the principle of CVD technology and the basic steps of titanium nitride process, tungsten contact hole process and atomic layer deposition technology. The second part studies characteristics of tungsten contact incomplete filling problem, and explains the principle of copper diffusion and device failure phenomenon in copper interconnect process. The reason of tungsten contact uncompleted filling includes the influence of the substrate of TiN, and many important factors of traditional W CVD process and pulsed nucleation layer (PNL) CVD process. Thirdly, based on the respective experiments of glue layer TiN process, the traditional W CVD and PNL W CVD process, describes several important factors of contact incomplete filling:pre-clean process before the deposition of TiN; TiN thickness and TiN film plasma treatment ratio; the Q-time post TiN deposition and before tungsten process; Tungsten nucleation layer thickness, the temperature and reactive gas flow ratio; B2H6 flow in PNL process and nucleation layer process. Finally, by applying favorable factors of tungsten contact hole filling process into smaller line width process, the thesis describes the improvement of the electrical properties and yield.Through the research, following conclusions can be obtained:Firstly, TiN layer has a very important influence on contact tungsten gap-filling. High density TiN film can be gained by multi-step deposition and plasma treatment, which can reduce the incubation time during Tungsten nucleation process. High density TiN servers the purpose of W step coverage improvement, which can reduce the seam hole of contact filling, and prevent the upper copper metal diffuse through into the device.Secondly, the Art of W nucleation layer film manufacturing process is very important for gap-filling. Denser nucleation layer film with smaller grain size is better for W gap-fill. By B2H6 flow’s optimization of PNL process, good nucleation layer can be gained. It also can improve the seam hole or void issue.Thirdly, in the real production, with application of favorable factors, this process improves the state of W filling and solves copper diffusion issue in the contact hole of 0.11μm technology. It can obtain stable electrical performance, and improve the yield of nearly 20%.