Dipole Formation and Electrical Properties According to SiO2 Layer Thickness at an Al2O3/SiO2 Interface

Interfacial and electrical properties of Al2O3/SiO2/Si were analyzed to determine the change in interfacial defects and suboxide density according to the thickness of the SiO2 layer and to determine the effect on dipole and flat-band voltage. As the thickness of the SiO2 layer increased (5/7/10 nm), the density of the suboxide present at the interface (2.23/3.23/4.73 × 1014 atoms/cm2) also increased, respectively. In addition, the slow state density, fixed oxide charge density, and interface state density calculated through the capacitance–voltage (C–V) curve all differ depending on the thickness of the SiO2 layer and are further reduced by postmetallization annealing (PMA). The flat-band voltages (VFB ) of the SiO2/Si sample with thicknesses of 5, 7, and 10 nm before PMA are −1.27, −1.32, and −2.20 V, respectively, and further decreased after PMA (−0.64, −0.80, and −1.74 V). Consequently, it was demonstrated that there was a difference in interfacial defects and suboxides according to the thickness. In addition, it was confirmed that when the interfacial defects and suboxides were reduced, the oxide charge state density and oxygen diffusion decreased, and thus the dipole layer strength and VFB shift decreased.