The Role of Rare Earth Metals on Effective Work Function Modulation of Nickel Fully-Silicided Gate/High-k Dielectric Stacks for n-Channel Metal Oxide Semiconductor Device Applications

It was found that the structural properties with gadolinium (Gd) and europium (Eu) incorporation into nickel (Ni) fully silicided (FUSI) gate electrodes are markedly different and resulted in different degrees of effective work function modulation. It was found that Ni–Gd alloys tend to form stable compounds during silicidation and produced a Si-rich layer with amorphous/nanocystalline structure near the FUSI gate electrode/high-k dielectric interface. This compositional and structural change is the main mechanism responsible for effective work function modulation with Gd incorporation. However, in the case of Europium, Eu atoms tend to segregate outside the Ni-FUSI layer during silicidation and resulted in a uniform Ni_xSi_y layer with Eu pile-up layer at the FUSI gate electrode/high-k dielectric interface. This pile-up is believed to be the main cause of effective work function modulation with Eu incorporation. It was also found that the incorporation of Gd and Eu metals into Ni-FUSI gate can remotely scavenge the interfacial oxide layer resulting in lower equivalent oxide thickness (EOT) of the device.