Aurore Constant

Ph.D. Thesis title:
SiC oxidation processing technology for MOSFET devices fabrication


Aurore Constant




Reading day:

25th July 2011

Power electronic devices are mainly based on the mature and very well established silicon technology. However, silicon exhibits some important limitations regarding power losses, operation temperature and speed of switching. Furthermore, unfortunately the successful silicon technology has almost reached its physical limits. Hence, a new generation of power devices based on new materials must be developed to face the future global energetic challenges. Nowadays, the most promising semiconductor material is silicon carbide (SiC). SiC is increasingly considered as the best candidate to overcome the intrinsic limitations of silicon in developing high-power and high-temperature electronic devices. It shows the best trade-off between theoretical characteristics and real commercial availability of the starting material and maturity of its technological processes.
This thesis is focused on SiC-based power devices, particularly, on one of the major issues in SiC technology: the gate oxidation process. Indeed, SiC can be easily oxidized to form a thin silicon dioxide (SiO2) layer. This provides a unique opportunity to develop power Metal Oxide Semiconductor (MOS) devices, as in the Si-based technology. SiC-based power MOSFETs are expected to have great potential for high-speed and low-loss switching devices. Unfortunately, the oxide/SiC interface quality and oxide reliability are major barriers to the fabrication of advanced SiC power MOSFET devices. Alternative solutions have been developed to overcome these problems. However, SiC MOSFETs have only been recently commercially available, mainly due to reliability concerns. The MOSFET process suitable for mass production is still a challenge. 
The main efforts carried out in the framework of this thesis are addressed towards the development of SiC MOSFETs by improving the current gate oxide process state-of-the-art. A newly gate oxidation process based on rapid thermal processing is demonstrated, and the physical mechanisms associated with oxide formation and the SiO2/SiC interface properties are proposed. This oxidation process has been tested on hexagonal SiC (4H-SiC) and cubic SiC (3C-SiC). Furthermore, the investigated oxidation processing technology is integrated into the fabrication of reliable 4H-SiC MOSFETs, and the bias-stress instability has been evaluated up to operating temperatures of 300 ºC.