NMOS gate electrode selection process for advanced silicon devices

In the gate electrode selection process, work function, thermal stability and gate depletion are the critical parameters that need to be satisfied. In our studies we have investigated a) elemental metals, b) metal nitrides, c) metal oxides and d) metal alloys as gate electrodes on SiO2 and high K dielectrics. Sputtered Ta, TaNx, TaSixNy and Ru-Ta alloys were investigated in MOS capacitors as NMOS gate electrodes. Good results were obtained by adding N and Si in Ta films. Excellent thermal stability was obtained up to 1000C. The use of Ru-Ta alloys provided another route in obtaining thermally stable low work function gate electrodes.