The Effect Of NH Plasma Treatment On The Reliability Of SiC MOS Dielectric Layer

Silicon Carbon (SiC) is the promising third generation semiconductor due to its wide band gap, high breakdown field and high thermal conductive, and is expected to be widely used in high temperature, high frequency and high power devices field. SiC can form SiO2 dielectric layer through thermal oxidation, which make it possible to use mature Si processes for the fabrication of the SiC MOSFET devices. However, because of the special construction of SiC material, there are lots of defects after thermal oxidation, the reliability of the SiC MOS capacitors which are fabricated by thermal oxidation can not meet the actual demand, and limit the SiC MOSFET application. Therefore, enhancing the reliability of the SiC MOS capacitors by improving the fabrication process become a key issue in the research field of SiC MOSFET devices.In this work, electron cyclotron resonance (ECR) microwave NH plasma surface annealing and post oxidation annealing (POA) are used in the fabrication of SiC MOS capacitors. The reliability of the SiC MOS capacitors was evaluated by current-voltage(?-?) insulating characteristics and time dependent dielectric breakdown (TDDB), and the effects of reliability improvement mechanism were investigated by capacitance-voltage (C-V) characteristics measurements and interface composition analysis. I-V analyses show that the insulating and breakdown characteristics of the samples become better after the NH plasma surface annealing and POA than the samples without any annealing and the samples only have POA. Breakdown field and barrier height of the samples that had the NH plasma surface annealing and POA can reach 11.33 MV/cm and 2.69 eV, which is really close to the theoretic barrier height value of 2.7 eV. TDDB analyses show that breakdown charge of the samples which had the NH plasma surface annealing and POA under the characteristic failure time of 4 C/cm2, is 5 times that of the samples only have NH plasma POA and 50 times that of the samples without annealing. Under the pretended working field 3 MV/cm,80% of the NH plasma surface annealing and POA samples' lifetime can reach 10 years and more, which is 100 times that of the samples without annealing. At the same time, TDDB analyses show that average time dependent dielectric breakdown field and the uniformity of NH plasma surface annealing and POA samples is obviously increased which proved the reliability of the samples' gate oxide is significantly improved. C-V analyses show that the interface state density of the NH plasma surface annealing and POA samples is obviously decreased and the flat band voltage is also decreased to 0.02 V, which proved that H plasma surface annealing and POA processes can significantly improve the SiO2/SiC interface status. Through the interface composition analysis, it is found that POA process passivated SiOxCy, carbon cluster and other interface traps, while the surface pretreatment smoothed the SiC surface, decreased surface state density and suppressed the formation of the interface traps, which increased the actual breakdown thickness of the gate oxide, and finally enhanced the SiC MOS capacitors gate oxide reliability.Above results revealed that ECR microwave NH plasma surface annealing and POA process can effectively lower the SiC/SiO2 interface state density, improved the reliability of the SiC MOS capacitors.