Dipole formation to modulate flatband voltage using ALD Al2O3 and La2O3 at the interface between HfO2 and Si or Ge substrates

Abstract

In this study, we have studied the flatband voltage (VFB) modulation by the formation of Al and La-induced dipoles at the interface between Si or Ge substrates and HfO2 gate dielectric in the metal–oxidesemiconductor (MOS) devices. The Al2O3 and La2O3 layers deposited on the HfO2 thin film serve to form dipoles. These Al2O3 and La2O3 thin film layers were atomically deposited using trimethyl-aluminum (TMA) and La(iPrCp)3 for the metal precursor and H2O and O3 for the oxidant, respectively. The dipole, an enabler that modulates the VFB in MOS devices, is formed at the interface between the high-k thin film and substrates upon subsequent annealing. As the thickness of the Al2O3 increases, VFB shifts in the positive direction on both substrates. The VFB shifted by about 230 mV with a 1.5 nm thick Al2O3 capping layer on Si substrate and 610 mV on the Ge substrate. On the other hand, VFB shifted in a negative direction of about 181 mV in the 1.5 nm thick-La2O3 capping layer. Our results indicate that electronegative atoms using Al2O3 and La2O3 are an efficient way to modulate VFB for Si or Ge-based 3D device structures without sufficient space margin for gate stack film formation.