Jaydeb Goswami

EOT, Workfunction, and Vfb Roll-Off in HfO2/Metal Gate Stacks

At a given thickness of HfO 2 , atomic layer deposited (ALD) TaN metal-gates showed higher equivalent oxide thickness (EOT) and flat-band-voltage (V fb ) shift compared to physical vapor deposited (PVD) TaSiN after annealing at 750degC for 30 min in N 2 . TEM data revealed the growth of a thicker interfacial oxide of 1.7 nm for TaN compared to 0.9 nm for TaSiN. In addition, TaN showed higher effective workfunction of 4.7 eV compared to 4.4 eV for TaSiN. However, both TaN and TaSiN exhibited V fb roll-off when the HfO 2 thickness was decreased below 4 nm. XPS measurements showed the presence of 6 atom% oxygen in TaN, whereas no significant amount of oxygen was detected in TaSiN. Electrical results are discussed in terms of the oxygen content in metal-gates and oxygen vacancy in HfO 2 .