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Irradiation Impact on Optimized 4H-SiC MOSFETs

出版	Universitat Politècnica de Catalunya, 2016
URL	http://books.google.com.hk/books?id=anUjygEACAAJ&hl=&source=gbs_api

註釋Silicon (Si) power device' technologies have reached a high maturity level, but current limitations on mechanic, temperature operation and electric performances require to investigate other semiconductor materials that can potentially compete with and overcome those border issues. This is the case of Silicon Carbide (SiC) and Gallium Nitride (GaN) which are becoming serious competitors to the Si due to their superior physical properties. Concerning SiC, the 4Hpolytype seems to be the best suitable candidate for high power MOSFETs according to its band gap, electric field strength, electron bulk mobility, and attainable threshold voltage, among others. But still, technological processes must be optimized in order to SiC MOSFETS can compete with their Si counterparts. This is the case of the gate oxidation process. A reduction of interface charge density is required for threshold voltage stability, and further improvements of the interface quality are also needed for high inversion mobility values. Once solved these problems, a path toward new perspectives of high power applications will be opened. This work is the direct continuation of the Aurore Constant's work. It is focused on 4HSiC based devices, more specifically on the gate oxidation processes and their behaviour under different harsh environments. Up to now, most of the works carried out were focused on the improvement of the Silicon Dioxide-Silicon Carbide (SiO2/SiC) interface quality. Solving those problems would allow designing high-speed and low-switching losses MOSFETs. In the past work, the main strength was focused on a new surface pre-treatment and on a gate oxidation process. Results showed improved electrical performances. However, we are convinced that better values can be obtained by optimizing the post-oxidation annealing step, by performing surface counter doping or by performing special irradiation treatments. All the efforts of this work will oriented to the development of reliable SiC MOSFETs with improved electrical parameters, which can operate under harsh environments (like high temperature or proton/electron irradiated environment). Thus, the mains guidelines of this Ph. D. Thesis are in accordance with the following lines: 1. State of the art on various SiC related fields. 2. Electrical characterization processes. 3. Proton irradiation impact on 4H-SiC MOSFETs and charge build-up mechanisms theory at the SiO2/SiC interface. 4. Electron irradiation impact on 4H-SiC MOSFETs. 5. Gate oxidation and implantation processes optimization. 6. Robustness limit of the improved processes under irradiation environments.