Optimization of tungsten dual poly-metal gates in memory devices with Ti/Wn/WSiN barrier metal

Due to the demand of high-speed/high-density and low power application of memory devices, tungsten dual poly gate (W-DPG; W/barrier metals/n+ and p+ poly-Si) electrode could be a good solution in order to reduce gate sheet resistance (Rs). Process optimization is completed for a diffusion barrier metal in a W-DPG. A new noble WSiN layer is inserted between the Ti/WN barrier metal and the tungsten gate electrode to maintain large grain size of W deposited by physical vapor deposition. The annealed WSiN during post-processing changes into crystallized WSi(x) mixed with SiN, which can make vertical conductive path between top and bottom interface, contributing to low vertical contact resistance (Rc) and low gate Rs adequate for high speed requirement of memory device. The Ti/WN/WSiN barrier is found to have the same electrical performance, ring oscillator singal delay as complicated multi-layes barrier metal, Ti/WN/TiN/WSi(x)/WN reported earlier. Therefore, the gate stack can be optimized by introducing a simpler diffusion barrier metal.