Material and electrical characterization of titanium nitride/silicon dioxide gate stacks

Silicon and silicon dioxide have been driving the enormous growth, the microelectronics industry has experienced over the past four decades. The simplicity and high performance of the silicon-silicon dioxide system have enabled significant scaling up to the ultra-thin gate oxide (1-2nm) regime, which consists of only a few atomic layers of silicon dioxide. Scaling beyond this regime leads to fundamental problems like high gate leakage current, oxide breakdown, boron penetration from the polysilicon gate electrode and degradation of channel mobility. Although strain engineering has effectively addressed mobility improvement, channel material innovations along with the replacement of silicon dioxide/poly-Si system with high-k dielectric/metal gates are seen as the inevitable path of scaling. TiN is an important candidate for a high workfunction metal gate for possible applications in DRAM access devices, control gates in a NAND cell or high performance logic transistors. Reduction in workfunction upon high temperature annealing has been previously reported for the TiN/SiO2 system. In this study, nucleation and growth of sequential-CVD TiN on silicon dioxide has been characterized. The effect of process parameters on the film properties such as resistivity, film stress, impurity concentration and density were studied. Chlorine concentration in the film was observed be a significant influence on the resistivity and yield stress of the film. Effective work function of TiN was found to be significantly influenced by the nitrogen concentration at the interface. The observed reduction in workfunction of TiN post high temperature heat treatment has been correlated to the compositional changes occurring at the TiN-silicon dioxide interface.