Plasma Passivation을 통한 SiC 기반 MOS소자의 계면특성 향상 연구

Abstract

Recently, Si based power electronic devices are faces with obstacle in terms of efficiency improvement because of its theoretical properties. By this reason, researchers have paid attention to wide-bandgap (WBG) materials such as GaN, SiC and diamond in order to overcome the limitations of Si. Among them, SiC has been taken spotlight as a candidate material for power devices due to its outstanding properties such as wider band gap, higher breakdown field, higher thermal conductivity and higher saturated electron velocity than those of Si. Compared to Si based power devices, however, one or two order of magnitude higher interface state density (Dit) at the conduction band edge is a crucial drawback of SiC based power devices. The higher Dit is originated from carbon clusters which are generated during thermal SiO2 growth on SiC. Incomplete oxidation leaves carbon clusters at the interface. They act as defects and increase channel resistance and degrade interface mobility by coulomb scattering. Therefore, Dit reduction is one of the major issues in SiC based Metal-Oxide-Semiconductor (MOS) devices. In this paper, therefore, we fabricated Pt/Al2O3/SiC MOS capacitors applying Remote-Plasma passivation and Remote-Plasma Atomic Layer Deposition (RPALD) techniques and investigated the interface quality. We investigated on the Al2O3 dielectric deposited by RPALD and observed Al2O3 formed uniformly in amorphous state by Scanning Electron Microscopy (SEM), Atomic Force Microscopy (AFM), X-Ray Diffraction (XRD) and After Forming Gas Annealing (FGA) we confirmed that Al2O3 film is more stoichiometric. Then By analysis of X-ray Photoelectron Spectroscopy (XPS), Aeger Electron Spectroscopy (AES), Secondary Ion Mass Spectrometry (SIMS), we confirmed that nitrogen and hydrogen are incorporated into interface during Remote-Plasma Passivation. Especially, NH3 Plasma Passivation leads to form inter layer including nitrogen atoms, which act as oxygen diffusion from High-k. From Capacitance-Voltage and Current-Voltage measurement, we observed smaller hysteresis, lower leakage current on samples with Plasma Passivation and FGA. Although H2 Plasma Passivation sample exhibits poor interface quality, it is improved by FGA. Finally, we extracted interface state density (Dit) by Conductance method. The Dit value is reduced by Plasma Passivation and further improvement is observed by Plasma Passivation in conjunction with FGA. The lowest value is 4.59x1011 cm-2eV-1 from the sample with NH3 Plasma Passivation for 15min and FGA. By these results, we suggested that Remote-Plasma Passivation is effective method to improve interface quality of SiC based MOSCAP for applying to power devices. However, proper process parameters should be applied for further improvement of interface quality.