Effects Of Nitrogen Plasma POA On TDDB Characteristics Of SiC MOS Dielectric Layer

As a promising third generation semiconductor, SiC have many better properties such as higher thermal conductivity and higher electron mobility compared with Si. SiC is also the only compound semiconductor that could form dielectric layers through oxidation process. However,4H-SiC MOS devices suffer from the problem of instable oxide layers. The reason is that there’re many defects in the oxide layer formed through thermal oxidation, the defects lowered the activation enthalpy needed for the breakdown of oxide layers, which reduced the ability of oxide layers withstanding the electrical stress. Therefore improving the quality and reliability of the oxide layers has become one of the key points in 4H-SiC MOSFET research.In this thesis,4H-SiC MOS devices are made with electron cyclotron resonance (ECR) nitrogen plasma processing technology after the oxidation process. Through current-voltage measurements we found that, the barrier height between SiO2 layer and 4H-SiC substrate of samples undergone the plasma processing have increased to 2.67 eV, close to the theoretic value of 2.7 eV. The breakdown field of SiO2 layer is 10.90 MV/cm. The effects of ECR nitrogen plasma processing on the TDDB characteristics of 4H-SiC MOS was being evaluated using stepped current TDDB technique. Both charge-to-breakdown and lifetime of samples increased dramatically after processing. The charge-to-breakdown and lifetime is respectively 10-100 times and 3-4 magnitudes larger than the samples without processing. In the meantime, the ability to withstand field stress improved after the plasma processing, and the uniformity of the samples increased. In order to explain the effects of ECR nitrogen plasma on the TDDB characteristics of 4H-SiC MOS, we analyzed the physical properties of 4H-SiC MOS using X-ray photoelectron spectroscopy (XPS). The analytical results showed that the process is capable of removing the defects due to insufficient oxidation, and passivate the interface, enlarges the enthalpy of activation need for dielectric breakdown, which increased the value of charge-to-breakdown and lifetime.The above results reveals that ECR nitrogen plasma processing can effectively lower the defects in 4H-SiC MOS dielectric layer, improves the value of charge-to-breakdown, lifetime, uniformity, and enhances the reliability of 4H-SiC MOS dielectric layer.