Thermally Stable Metal Gate Electrodes
Original Publication Date: 2002-Jul-22
Included in the Prior Art Database: 2002-Jul-22
A technique for creating thermally stable metal gate electrode materials is described. As the MOSFET gate lengths scale down to 50 nm and below, the series capacitance from poly-silicon gate electrode depletion significantly reduces the gate capacitance as the dielectric thickness is scaled to 10 Å SiO2 equivalent oxide thickness (EOT) or below. Metal gates show promise to solve this problem and address other gate stack scaling concerns like boron penetration and elevated gate resistance. Extensive simulations have shown that the optimal gate work-functions for the sub-50 nm channel lengths should be 0.2 eV below (above) the conduction (valence) band edge of silicon for n-MOSFETs (p-MOSFETs). In addition to the electrical requirements, metal gates must be thermally stable up to dopant activation temperatures of nearly 1000°C. A thermally stable electrode must exhibit no inter-diffusion between the electrode and the gate oxide, no chemical reaction at the electrode/oxide interface, no microstructure changes in the electrode, and stable electrical properties. Non-crystalline, ternary and quaternary metal gate electrode films that can satisfy the thermal stability requirements for metal gate electrodes are presented.