Alternative Growth and Interface Passivation Techniques for SiO2 on 4H-SiC
Abstract
Silicon Carbide is a novel wide band gap semiconductor material with excellent thermal, chemical and electrical properties. It also shares its natural oxide SiO2 with Si, which has been widely studied and optimized for decades. These properties make it a perfect candidate for applications in high-temperature, high-power MOS devices. Of over 200 polytypes, 4H-SiC is most commonly used, because it is among the only few commercially available polytypes that are known to be electrically and thermo -dynamically stable for making microelectronic devices. Unfortunately, the performance of such devices is limited by the poor SiO2/SiC interface quality after the standard dry O2 oxidation process. By far, the atomic understanding of the true physical structure and schematic of this interface still remains mystery. After applying most of the conventional passivation techniques such as NO anneal and H2 anneal, improvements on the device performances can be clearly observed, however, the results are still far from satisfactory. In this work, two alternative passivation techniques are applied, in order to obtain better understanding of the interface properties and achieve improved electrical characteristics and higher performance. The first technique is the alumina enhanced oxidation, which by introducing metal impurities via the ceramic alumina during the oxidation, a decreased interface-trap density (DIT) and drastic increase in field effect channel mobility can be observed, however, this is also accompanied by a large amount of mobile ions inside the oxide. The results from electrical measurement of the devices as well as the possible cause and effect of those ions on the interface are discussed. Few other passivation techniques are also applied after this process for potential improvement and optimization, and the results are discussed. Another passivation technique is the nitrogen plasma anneal, which successfully creates atomic nitrogen by microwave induced plasma to achieve an oxygen-free nitridation annealing condition. This helps for further and better understanding of the passivation effect by the sole presence of nitrogen. All the electrical results obtained are discussed in detail and also compared with standard NO results.