Influence of Ni silicide phases on effective work function modulation with Al-pileup in the Ni fully silicided gate/HfSiON system

Abstract

Influences of Ni silicide phases on the effective work function (Φeff) modulation effect with Al incorporation has been investigated in the Ni silicide/HfSiON systems. We formed metal-insulator-semiconductor capacitors with Al incorporated Ni silicide (NiSi, Ni2Si, and Ni3Si) gates on HfSiON by Al solid-phase diffusion (Al-SPD) process or Al ion implantation (I/I) process. In the Al-SPD process, Al is deposited on Ni silicide gate. In the Al-I/I process, Al ions were doped in the upper part of Ni silicide layer. In both cases, we performed Al drive-in annealing under the condition of 450 °C for 30 min in N2 ambient. It is found that the flat-band voltage (Vfb) values of Al incorporated NiSi and Ni2Si gates shift negatively and identical independent of Al incorporation processes. A highly concentrated Al piled-up layer, which induces Φeff modulation to Al-Φeff value, seems to correspond to the Vfb modulation. On the other hand, Al incorporation has little influence on Φeff at the Ni3Si/HfSiON interface. We revealed that a lower Al diffusion coefficient in Ni3Si phase reduces the Al interface density at the Ni3Si/HfSiON interface. In addition, Al piled-up layer is inherently unstable at the Ni3Si/HfSiON interface, which is confirmed from the detailed investigation about thermal stability of Al piled-up layer by using phase change process from NiSi to Ni3Si phase.