Materials Science Forum Vols. 645-648

Abstract: A change in the interface state density in 4H-SiC metal–oxide–semiconductor (MOS) structures by incorporation of various elements was systematically investigated. B, N, F, Al, P, and Cl ions were implanted prior to the oxidation and introduced at the SiO2/SiC interface by subsequent thermal oxidation. Interface state density near the conduction band edge for Al-, B-, F-, and Cl-implanted MOS capacitors increased with implantation dose. On the other hand, a strong reduction of the interface state density was observed for N- and P-implanted samples when the implantation dose was larger than 5.0 × 1012 cm−2. It was found that the interface state density can be reduced by P as well as N.

Abstract: The electrical properties of the SiC/SiO2 interface resulting from oxidation of the n-type 6H-SiC polytype were studied by hi-lo CV, temperature dependent CV and constant capacitance deep level transient spectroscopy (CCDLTS) techniques. Several trap species differing in energy and capture cross section were identified. A trap distribution at 0.5 eV below the 6H-SiC conduction band energy and a shallower density of states in both the 6H and 4H polytyes are passivated by post-oxidation NO annealing. However, other ultra-shallow and deeper defect distributions remain after nitridation. The latter may originate from semiconductor traps.

Abstract: We have investigated NH3 plasma pretreatment for Si- and C-face 4H-SiC and characterized interface properties and bond configuration. It is revealed that the NH3 plasma pretreatment is effective to reduce interface state density on C-face. From X-ray photoelectron spectroscopy (XPS) measurements, N- and H-related C bonds were observed. N and H passivate C-related defects and dangling bonds, resulting in improved interface properties.

Abstract: We propose a treatment of nitrogen radical irradiation to 4H-SiC surfaces for improving thermally grown SiO2/SiC interfaces. X-ray photoelectron spectroscopy (XPS) analyses revealed that a 1.7-nm-thick nitride film was formed by nitrogen radical exposure for 30 min and that Si-N bonds were retained after subsequent 10 min oxidation. It was also confirmed by secondary ion mass spectrometry (SIMS) that nitrogen atoms were piled up at the SiO2/SiC interface for the samples fabricated by thermal oxidation for 3 min with nitrogen plasma exposure. The metal-oxide-semiconductor (MOS) capacitors with a thin oxynitride layer formed by nitrogen radical exposure to the SiC surface and subsequent thermal oxidation exhibited excellent capacitance-voltage (C-V) characteristics. The interface state density (Dit) was significantly reduced by nitrogen radical exposure even at the shallow energy level near the conduction band edge. A minimum Dit value of 1.4 × 1011 cm-2eV-1 at Ec – E = 0.44 eV was achieved. Therefore, we can conclude that the treatment of nitrogen radical irradiation to the SiC surface prior to thermal oxidation is a promising method for improving SiC-MOS characteristics.

Abstract: We have investigated the electrical and physical properties of the oxidized-SiN with or without post oxidation annealing (POA) in N2 gas. A significant reduction in interface-trap density (Dit) has been observed in the oxidized-SiN with N2 POA for 60 min if compared with other oxides. The reason for this has been explained in this paper.

Abstract: Characteristics of metal–oxide–semiconductor (MOS) capacitors and MOS field-effect transistors (MOSFETs) fabricated by direct oxidation of C-face 4H-SiC in NO were investigated. It was found that nitridation of the C-face 4H-SiC MOS interface generates near-interface traps (NITs) in the oxide. These traps capture channel mobile electrons and degrade the performance of MOSFETs. The NITs can be reduced by unloading the samples at room temperature after oxidation. It is important to reduce not only the interface states but also the NITs to fabricate high-performance C-face 4H-SiC MOSFETs with nitrided gate oxide.

Abstract: High temperature C-V characterization with and without UV illumination has been performed on n-type 4H-SiC MOS capacitors fabricated using different processing conditions to extract various types of interfacial charges. An anomalous positive flatband voltage shift with temperature has been observed in most of the SiC MOS capacitors measured. We have experimentally identified an extra type of fixed charges at the 4H-SiC/SiO2 interface from the temperature dependence of the flatband voltage, particularly under UV illumination.

Abstract: A novel method based on the analysis of the C-V hysteresis change with increasing charge release time is proposed. The presence of a band of deep traps was demonstrated using this method in 3C-SiC samples. The same band of deep traps was also observed using photo-electric measurements of barrier height EBS in the same samples.

Abstract: We have extended a magnetic resonance based study of MOS devices to include electrically detected magnetic resonance (EDMR) measurements of fully processed MOSFETs from three facilities as well as conventional electron paramagnetic resonance (EPR) resonance measurements on simple SiC/SiO2 structures. We find close similarity between the conventional EPR and the EDMR spectra.

Abstract: Using impedance spectroscopy (IS) for characterization of the electrical properties and gas sensing characteristics of Al2O3/4H-SiC (MOS) structures, insight on the capacitive and resistive contributions in the interfacial region of the MOS structures is obtained. Applying DC bias voltages between accumulation and depletion (corresponding to the interfacial region) allows investigation of the voltage shift of the capacitance versus voltage (CV) curve at different temperatures and atmospheres. This voltage shift forms the basis to use the MOS structure as a gas sensor. The MOS capacitance, as extracted from IS data, is different from the one obtained using CV measurements, due to the ability of distinguishing the resistive contribution (using IS). Voltage shifts between 1 and 2 V are clearly revealed during exposure to hydrogen and oxygen, and this shift exhibits a long-term stability of operation at temperatures up to 500°C. Hence, Al2O3 exhibits great promise as a gate dielectric in MOS-based gas detecting devices for use at elevated temperatures.