Papers by Keyword: SiO₂/SiC

Abstract: The electrical characteristics of the SiC metal-oxide-semiconductor field effect transistor (MOSFET) have been limited by large amount of states at the SiO₂/SiC interface. In this study, the accuracy of the energy level of the interface states extracted by hypothetical high frequency extreme, which is conventionally used, is experimentally examined. Conductance measurements at low temperature between 65 K and 100 K reveal that the extracted energy distribution of the interface states at nitrided SiO₂/SiC interface close to the conduction band edge depends on the measurement temperature. It is demonstrated that conductance method at 65K enables us more accurate evaluation of the interface states at the SiO₂/SiC interface and found that the interface states density (D_it) of nitride SiO₂/SiC interface is over 10¹³ cm^-2eV^-1 at energy level of 0.1 eV below the conduction band edge.

Abstract: In this work, the electrical properties of SiO₂/SiC interfaces onto a 2°-off axis 4H-SiC layer were studied and validated through the processing and characterization of metal-oxide-semiconductor (MOS) capacitors. The electrical analyses on the MOS capacitors gave an interface state density in the low 1×10¹² eV^-1cm^-2 range, which results comparable to the standard 4°-off-axis 4H-SiC, currently used for device fabrication. From Fowler-Nordheim analysis and breakdown measurements, a barrier height of 2.9 eV and an oxide breakdown of 10.3 MV/cm were determined. The results demonstrate the maturity of the 2°-off axis material and pave the way for the fabrication of 4H-SiC MOSFET devices on this misorientation angle.

Abstract: Constant-capacitance deep-level transient spectroscopy was carried out to characterize in detail interface states close to the conduction band edge in SiO₂/SiC structures. The measured results are summarized as follows: (1) The capture of electrons by the interface states proceeds logarithmically with time. (2) The emission of electrons accelerates slightly with increasing density of captured electrons. The oxide trap model explains the logarithmic change in capture with time but not the phenomenon of accelerated emissions. This prompted us to formulate a new model that replicates the logarithmic capture process with time. In this model, we postulated the electron density at the interface decreases exponentially as the trapped electron density increases owing to the interaction between the trapped electrons and the free electrons. In this case, the capture process is almost the same as with the oxide trap model except for the definition of parameters. Further, we do not need to take into account the delay of the emission process caused by tunneling. The phenomenon of accelerated emissions may be explained by interactions among captured electrons in this model.

Abstract: Constant-capacitance deep-level-transient spectroscopy (CCDLTS) characterization of traps (or states) in SiO₂/SiC interfaces on the C-face was carried out to clarify the cause of low-channel mobility of SiC MOSFETs. CCDLTS measurements showed that the interface-state density (D_it) near the conduction band of SiO₂/SiC interfaces fabricated using N₂O oxidation was much higher than that of SiO₂/SiC interfaces fabricated using wet oxidation. The high density of interface states near the conduction band is likely to be the main cause of the low mobility of MOSFETs fabricated using N₂O oxidation.

Abstract: Temperature dependent capacitance-voltage (C-V) and constant capacitance transient spectroscopy (CCDLTS) measurements have been performed to investigate the role of N in improving the transport properties of 4H-SiC MOS transistors. The higher channel mobility in the N pre-implanted transistors is due at least in part to activation of a small fraction of the implanted N near the SiO₂/SiC interface as donors in SiC during oxidation, thus reducing the effects of interface trapping. In addition, the absence of oxidation-induced near-interface defects, which were observed in NO-annealed capacitors, may contribute to the improved mobility in N pre-implanted transistors.

Abstract: Using impedance spectroscopy (IS) for the characterization of SiO2/4H-SiC (MOS) structures, insight on the capacitive and resistive contributions in different physical regions of the MOS structures is obtained. Changing the DC bias conditions, semiconductor, interface as well as oxide traps can be detected. The MOS capacitance, as extracted from IS data, is different from the one obtained using capacitance voltage (CV) measurements, due to the possibility of distinguishing different charge transfer processes using IS. For instance, in the investigated capacitors, a clear contribution is revealed from ionic conduction processes at bias voltages close to zero.

Abstract: The SiO2/4H-SiC hetero-interface was observed using TEM in plan-view geometry. Local roughening of the SiO2/4H-SiC hetero-interface accompanied with local generation of basal-plane dislocations in SiC was observed. In some places, local variations in film thickness of SiO2 as well as the presence of extra carbon and particle-like contrast asociated with the generation of basal-plane dislocations in SiC was observed. The influence of these defect regions on MOSFET properties is discussed.