Electronic properties of ZrO₂ films fabricated via atomic layer deposition on 4H-SiC and Si substrates

Abstract

Silicon carbide (SiC), an important semiconductor material used in high-power devices, faces the problem of gate oxygen layer formation in traditional Si MOS devices. In view of this, an innovative approach was adopted in the present work to replace the conventional SiO2 as the gate oxygen layer with a high-k material (ZrO2) so as to investigate its effect on the electrical characteristics of the appliance. In particular ZrO2 films were deposited on SiC and Si substrates by atomic layer deposition (ALD), and Al was used as the electrode. The atomic force microscopy (AFM) microregion scan revealed a highly flat surface with Rq<1 nm after the ALD growth of ZrO2 layer. The sample surface analysis via X-ray photoelectron spectroscopy (XPS) suggested the presence of a small amount of ZrOx components. According to the electron energy loss spectrum (EELS), the band gap width (Eg) of this ALD ZrO2 dielectric was 5.45 eV, which met the requirements for high-quality 4H-SiC-related MOS devices. The electrical properties of the samples were then studied, and the maximum breakdown electric field of the MOS capacitor structure on the SiC substrate was obtained to be more than 10 MV/cm, i.e., nearly twice that of the Si substrate. Based on capacitance-voltage (C-V) measurements, the interface defect density (Dit) near the conduction band of the MOS capacitive structure of the SiC substrate was only on the order of 1012 eV-1 cm-2. The movable charge Neffof the oxide layer was also controlled at 1012 cm-2. Therefore, the overall performance of the ZrO2/SiC structure in terms of electrical properties exceeds that of the ZrO2/Si structure and previously reported counterparts. Thus, the combination of the high-k material (ZrO2) and SiC as the substrates in MOS capacitor structures is a very promising research direction.