| Pacific Rim Symposium on Surfaces, Coatings and Interfaces (PacSurf 2014) | |
| Thin Films | Tuesday Sessions |
| Session TF-TuP |
| Session: | Thin Films Poster Session |
| Presenter: | Changhyun Kim, Seoul National University, Korea, Republic of Korea |
| Authors: | C. Kim, Seoul National University, Korea, Republic of Korea S. Lee, Seoul National University, Korea, Republic of Korea H. Lee, Seoul National University, Korea, Republic of Korea H. Kim, Seoul National University, Korea, Republic of Korea H.J. Kang, Seoul National University, Korea, Republic of Korea H.J. Kim, Seoul National University, Korea, Republic of Korea |
| Correspondent: | Click to Email |
4H-SiC is a promising wide band gap material which has excellent properties such as high breakdown voltage, high thermal conductivity, and high saturation drift velocity. These characteristics enable 4H-SiC to be used in difficult environments for Si such as processes require high power, high current, high temperature. It also has an advantage in fabrication process because of its native SiO2 from thermal oxidation. However, carbon components are inevitably produced during oxidation, causing high SiO2/SiC interface state density (Dit) and low channel mobility. The nitridation using NO or N2O gas is an effective way to lower Dit and near interface trap density of a SiO2/4H-SiC interface.
In this work, we prepared the atomic layer deposited (ALD) SiO2 with NO post oxidation annealing (POA) to avoid interface oxidation and improve interface properties. We also compared electrical properties of NO POA treated ALD SiO2 with thermally grown oxides with/without NO POA. The NO POA treated ALD SiO2 showed much lower Dit than thermally grown oxides. Also, the metal-oxide-semiconductor (MOS) field effect transistor (FET) with the ALD SiO2 showed high field effect mobility, especially in the high electric field region.
But these methods could not reach the sufficient passivation of the interface traps due to reoxidation by oxygen source of NO gas. Therefore, we employed thin ALD SiO2 layer with NH3 POA for nitridation without reoxidation. Because the NH3 POA oxide had low breakdown field (Eb), we adopted a stacked structure of ALD SiO2 with NH3 POA and ALD SiO2 to exclude oxidation and to improve Eb, respectively. Inert gas annealing or ozone treatment were used to reduce the defects of upper as-deposited SiO2. Oxygen vacancies, a major defect of as-deposited oxide, were effectively reduced by the O3 treatment. The ALD SiO2 with NH3 POA lowered C-V hysteresis and increased the slope of C-V curve, indicating that it reduces the interface defects. It also had low Dit which might be caused by the suppression of reoxidation. The O3 treatment increased Eb effectively, but it did not reached Eb of thermally grown oxide yet.
In conclusion, ALD oxides with proper nitridation process improved the field effect mobility of MOSFET more effectively than thermal one through decreasing Dit induced by carbon component at the SiO2/4H-SiC interface. The NH3 POA instead of NO POA showed low Dit by suppressing of reoxidation, but low Eb problem remains. The O3 treated upper ALD SiO2 increased Eb maintaining low Dit.