Mobility Enhancement Induced by Oxygen Gettering of TiAl for Metal Gated NMOSFETs

In this work, the influence of TiAl gate electrodes fabricated by physical vapor deposition (PVD) and atomic layer deposition (ALD) on electron mobility for metal-gated NMOSFETs is respectively investigated. Due to the specific production chemistry, the ALD TiAl film inherently contains lots of C atoms, which further suppresses its O-gettering capability. Compared to the ALD TiAl device, about 15% higher peak mobility for the PVD TiAl device is demonstrated, which is attributed to the lower bulk trap density in gate dielectric layers as revealed by the 1/ ${f}$ noise characteristics analysis. By means of the energy dispersive X-ray spectroscopy (EDX) and X-ray photoelectron spectroscopy (XPS) analysis, the reduced trap density is related to the fact that PVD TiAl can extract more O atoms from gate dielectric layers than ALD TiAl, which weakens the electron trapping/de-trapping process and correspondingly enhances the mobility.