Characteristics of Ta-Mo alloy metal gate electrode for nano-scale NMOSFET application

Ta-Mo alloy films with various atomic compositions were fabricated by using the co-sputtering technique. The compositions of the films were measured using field-emission scanning electron microscopy (FESEM). The X-ray diffraction pattern indicated that the alloy was thermally stable up to 900 .deg. C. Capacitance-voltage (C-V) and current-voltage (I-V) characteristics were measured using MOS capacitors fabricated with Ta-Mo alloy gate electrodes. The effective oxide thickness (EOT) and the work function were extracted from the measured C-V curves. The work function varied with the relative compositions of Ta and Mo. If the requirements for a gate electrode, such as thermal stability, an interface layer, and the work function, are considered, the most appropriate atomic composition of the alloy film found in this work for gate electrode applications was about 90 % Ta and 10 % Mo. The work function obtained for that specific atomic composition was 4.25 eV and was appropriate for NMOS gate electrodes. Since the Ta-Mo alloy was found to have a suitable work function and good thermal stability up to 900 .deg. C without any appreciable interface layer and significant EOT change, it is one of the promising metal gate electrodes for NMOSFETs.