SiO₂/SiC Interface Transition Region And Plasma Passivation Processes

Silicon carbide (SiC) is a promising semiconductor for high-temperature, high-frequency, and high-power electronic devices due to its wide band-gap, high breakdown field, high thermal conductivity, and high carrier saturation velocity. In addition, SiC is a unique compound semiconductor which can be thermally oxidized to form SiO2. This attribute enables the fabrication of SiC MOSFET by conventional Si technology. SiC MOSFET is an important candidate for power device and an essential component of SiC IGBT. However, SiC MOSFET presents extremely low inversion channel mobility due to the high density of interface traps (A,) at SiO2/SiC interface. The origin of interface traps and the passivation process are two topics of considerable interest.In this work, the composition and structure of SiO2/SiC interface transition region were investigated by X-ray photoelectron spectroscopy (XPS), angle-dependent XPS (ADXPS), electron damping theory, and semiempirical molecular dynamics. N plasma and N-H mixed plasma passivation processes were explored based on electron cyclotron resonance (ECR) microwave plasma system. The effects of these processes on the SiO2/SiC interface properties and the mechanisms involved were examined. In addition, the effects of wet-reoxidation annealing (wet-ROA) on the shallow interface traps of n-type SiC MOS capacitor and the mechanism involved were also studied. The main research contents and results are as follows:(1) The composition and structure of the SiO2/SiC interface transition region. The composition and structure of SiO2/SiC interface transition region were studied by XPS and ADXPS techniques, and a structure model of the interface transition region was proposed. Electron damping theory and semiempirical molecular dynamics simulation were used to verify the structure model. XPS analyses show that SiOC3, SiO2C2, and SiO3C coexist in the SiO2/SiC interface transition region. ADXPS anlyses indicate that SiOC3, SiO2C2, and SiO3C have different depth distributions, and could be described by a nonabrupt structure model. Theoretical calculation and simulation confirm the proposed structure model. This work is helpful for further understanding the origin of SiO2/SiC interface traps and exploring some effective interface passivation processes to improve the performance of SiC MOSFET.(2) The effects and mechanism of ECR microwave N plasma annealing process. ECR microwave N plasma annealing process was proposed for the SiO2/SiC interface. Its effects on the SiO2/SiC interface properties and the mechanism involved were studied by current-voltage (I-V), capacitance-voltage (C-V), secondary ion mass spectrometer (SIMS), and XPS measurements. I-V and C-V analyses indicate that this process could reduce the D,, in the entire upper half of SiC band-gap without degrading the oxide insulating properties. SIMS and XPS analyses show that the reason of this process reducing the Dit is that the incorporated N could transform some SiOxCy and carbon clusters into deep-level Si-N and C-N bonds. This work not only provides an effective SiO2/SiC interface passivation process, which could avoid the introduction of oxygen and the degradation of oxide quality, but also illustrates the mechanism of N plasma reducing Dit. This result is helpful for exploring more effective interface passivation processes to improve the performance of SiC MOSFET.(3) The effects and mechanism of ECR microwave N-H mixed plasma annealing process. ECR microwave N-H mixed plasma annealing process was proposed for the SiO2/SiC interface. Its effects on the SiO2/SiC interface properties and the mechanism involved were investigated by I-V, C-V, and SIMS measurements. I-V and C-V analyses show that this process could not only guarantee the oxide quality, but also significantly reduce the Du in the entire upper half of SiC band-gap by combining the positive roles of N and H. N and H are more effective in passivating the shallow and deep interface traps, respectively. SIMS measurements indicate that N and H are both incorporated and concentrated at the SiO2/SiC interface. The reason of N and H having different roles in reducing the D,, is that N is more inclined to react with shallow-level SiOxCy and carbon clusters to form Si-N and C-N bonds, while H is more inclined to react with the nitrided traps and deep-level carbon dangling bonds. This work provides a new process which could make N and H play roles in passivating the SiO2/SiC interface traps simulataneously, and is helpful for further improving the performance of SiC MOSFET.(4) The effects and mechanism of wet-ROA on shallow interface traps of n-type SiC MOS capacitor. The effects of wet-ROA on shallow interface traps of n-type4H-SiC MOS capacitors and the mechanism involved were studied by temperature-dependent C-V measurements and XPS technique. C-V measurements show that wet-ROA could reduce the shallow-level D,, of n-type4H-SiC MOS capacitors by more than60%. XPS analyses indicate that the reduction in shallow-level Du could be attributed to the reaction between the introduced oxygen and SiOxCy species. This reaction could result in C release from the SiO2/SiC interface and SiOxCy transformation into higher oxidation states, thus reducing the content of SiOxCy. This work clarifies the effects of wet-ROA on shallow interface traps, and illustrates the interrelations among wet-ROA process, SiO2/SiC interface properties, and SiO2/SiC interface traps. This result is helpful for exploring new SiO2/SiC interface passivation processes.