On the thermal stability of atomic layer deposited TiN as gate electrode in MOS devices

Abstract

The work function of ALD TiN was found to be above 5 eV after RTP annealing below 800°C in nitrogen atmosphere, while higher annealing temperatures cause a drop in work function by about 0.3-0.5 eV. The effect was found for TiN metal gates on both SiO2 and Al2O3 gate dielecttrics in MOS-capacitors and was seen in C-V as well as in I-V measurements. On the contrary, annealing of SiO2 capacitors in oxygen-enriched N2 atmosphere increased the work function. A variation in EOT of less than 2 Å was demonstrated for the various annealing temperatures, concluding that the ALD TiN is stable in contact with the different dielectric materials. However, the decrease in work function that is found in this investigation may implicate that ALD TiN is less suitable as a metal gate for pMOSFETs.