The work function engineering and thermal stability of novel metal gate electrodes for advanced CMOS devices

The continuous scaling of Complementary Metal Oxide Semiconductor (CMOS) integrated circuits requires the replacement of the conventional poly-silicon gate electrode and silicon dioxide gate dielectric with metal gate electrodes and high-agate dielectrics, respectively. The most critical requirements for alternative metal gates are proper work function and good thermal stability. This dissertation has focused on the effective work function and thermal stability of molybdenum-based metal gates (Mo, MoN, and MoSiN) and fully silicided (FUSI) NiSi metal gates.; Capacitance-Voltage (C-V) and Current-Voltage (I-V) measurements of MOS capacitors were performed to investigate the electrical properties of molybdenum-based metal gates. Four-point probe resistivity measurements, Rutherford Backscattering Spectroscopy (RBS), X-ray Photoelectron Spectroscopy (XPS), High Resolution Transmission Electron Microscopy (HR-TEM), Electron Nanodiffraction analysis, X-ray Diffraction (XRD) and backside Secondary Ion Mass Spectroscopy (SIMS) methods were performed as well, to characterize the thermal stability of metal gate electrodes.; The effective work function and thermal stability of molybdenum-based metal gates (Mo, MoN and MoSiN) on both SiO2 and Hf-based high-kappadielectrics have been evaluated systematically. The effects of silicon and nitrogen concentrations on the work function and thermal stability are discussed. The effective work function of molybdenum nitrides on both SiO2 and Hf-based high-kappadielectrics can be tuned to ∼4.4-4.5 eV, however, the thermal budgets should be less than 900°C 10 sec due to nitrogen loss and the phase transformation behavior of molybdenum nitrides. Silicon incorporation in the Mo-N system can improve the film thermal stability and diffusion barrier properties at the interface of metal gates/dielectrics due to the presence of Si-N bonds. By optimizing the film composition, the work function of MoSiN gates on SiO2 can be tuned for fully depleted silicon on insulator (FDSOI) NMOS or PMOS with thermal stability up to 1000°C. Compared to MoXSi YNZ (X=46% Y=12%, Z=42%) gates on HfO2, the gates on FlfSiO provides better thermal stability up to 1000°C with no degradation of work function (∼4.4 eV), EOT, fixed charge density, or gate leakage current. These results suggest that MoSiN films with optimized compositions could be promising metal gate candidates for advanced CMOS devices.; The thermal stability of FUSI NiSi metal gate electrodes on both SiON and Hf-based high-kappadielectrics after typical back-end of line (BEOL) thermal annealing has been also investigated. It has been found that the thermal stability of FUSI NiSi metal gates is strongly dependent on the dopants and annealing ambient. The dependence of nickel diffusion on the dielectric thickness and dopants into the silicon channel is discussed in detail. It was found that 5 nm gate dielectric layers are sufficient to inhibit any detectable nickel diffusion from the FUSI NiSi metal gates into the silicon channel.