Electrical characteristics of ALD La2O3 capping layers using different lanthanum precursors in MOS devices with ALD HfO2, HfSiOx, and HfSiON gate dielectrics

Abstract

We have investigated the electrical characteristics – flat band voltage (VFB) shift, equivalent oxide thickness (EOT) scaling and charge trapping – of atomic layer deposition (ALD) La2O3 capped high-k gate dielectrics (HfO2, HfSiOx, and HfSiON) in the metal-oxide-semiconductor (MOS) device structure, where two different lanthanum precursors – ① lanthanum formamidinate, La(fAMD)3, and ② lanthanum betadiketonate, La(thd)3, – were used for ALD capping layer. Regardless of precursors, La2O3 capping layer on the ALD high-k films leads to negative VFB shift and thinner EOT as increasing capping thickness. However, more shift and further EOT scaling are observed with La2O3 thin film using La(fAMD)3. In addition, La2O3 capping layer using La(fAMD)3 precursor shows lower interface state density (Dit) and stronger immunity against charge trapping than La2O3 capping layer with La(thd)3 precursor. Similar trends are attained with Si containing HfO2 – HfSiOx and HfSiON, but amount of VFB shift and EOT reduction is smaller than that of HfO2-based device, resulting from suppressed La-diffusion due to stronger Si–O bonds as well as nitrogen blocking in the dielectrics.