Wide Controllability of Flatband Voltage by Tuning Crystalline Microstructures in Metal Gate Electrodes

We propose a novel approach to control the effective workfunction (WF) by taking advantage of crystal structures in metal gate electrodes. The crystal structures determine the predominant material elements at the metal/high-k interface. We have found that, in a Ru-Mo alloy system, a randomly-oriented Ru (fcc) structure promotes the segregation of Mo at the interface, enabling us to achieve a wide controllability of flatband voltage (V
_fb
) from 0.6-0.8 eV In addition, the segregation of Mo within a Ru-rich electrode is a key to reducing Fermi level pinning at metal/HfSiON interfaces. Further tunability in V
_fb
has been examined by employing C-incorporation in the RuMo alloy, thus reducing the crystal grain size and facilitating the control of V
_fb
for a HfSiON (2 nm)/SiO
₂
(0.7 nm)/Si capacitor. These results demonstrate that the crystal structure control in metal gates is essential for realizing the MIS-FET devices with a short gate length in the 32-22 nm node and beyond.