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

Being an important semiconductor material for high power applications, silicon carbide (SiC) faces the problems while used as a gate oxygen layer in traditional Si MOS devices. In view of this, an innovative approach was adopted in the present work to replace the conventional SiO₂ with a high-k material (ZrO₂) as the gate oxygen layer to investigate its effect on the electrical characteristics of the devices. In particular ZrO₂ films were deposited on Si and SiC 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 R_q < 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 ZrO_x components. According to the electron energy loss spectrum (EELS), the band gap width (E_g) 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 voltage of the Al/ZrO₂/SiC/Al MOS structure was obtained to be 23 V, i.e., nearly twice that of the Si substrate. As for the oxide layer, the interface defect density (D_it) near the conduction band of the Al/ZrO₂/SiC/Al MOS structure was only 10¹² eV⁻¹ cm⁻² orders of magnitude. The N_eff value (the movable charge) of the structure was also controlled at 10¹² cm⁻². Therefore, the overall performance of the ZrO₂/SiC structure in terms of electrical properties exceeded that of the ZrO₂/Si structure and previously reported counterparts. In this respect, the ZrO₂/SiC MOS capacitor structure has great research potential.