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Annealing Behaviors of Void-like Defects in SiO2/SiC Probed by Slow-Positron-Beam

Min Gong 1Jing Yuan 1Haiyun Wang 2Weng Huiming 2Xudong Chen 3S. Fung 3C. D. Beling 3

1. Sichuan University, ChengDu 610064, China
2. University of Science and Technology of China, Hefei 230026, China
3. The University of Hong Kong, Hong Kong, Hong Kong


Silicon carbide has been realized to be one of powerful semiconductors. Various kinds of devices, including Schottky diodes, bipolar-transistors, MOSFETs and some IC units with good properties, have been manufactured using SiC. In these devices, SiO2 films play important roles. However, since the existence of carbon atoms, qualities of thermal oxidation formed SiO2 films on SiC wafers were far from as good as those on Si. The effects of impurities on the C-V characteristics of SiO2/SiC have been investigated by using atoms sensitive probes such as the secondary ion mass spectrometry (SIMS) and the x-ray photoelectron spectroscopy (XPS). These analyzing techniques are not adequate for full understanding of characteristics of SiO2/SiC interface and the structure of SiO2 film since a large of void-type defects will form during thermal oxidation and post-annealing due to the removal or escape of C atoms and CO molecules.
In this work, the technique of Doppler broadening of positron annihilation spectroscopy (PAS) has been used to reveal information on void-type defects of SiO2/SiC system. Variable-energy positron beam makes positrons to different depth in the sample. The value of the S parameter, which reflects the number of positrons annihilated with low momentum electrons, increases since the reduced electron density at open-volume defects narrows the momentum distribution.
The SiC materials used in the experiments were obtained from Cree. The wafers were 6H-SiC (0001) having basic nitrogen and aluminum dopant of 11017 cm-3 in n- and p-type samples, respectively. Dry oxidation was carried out at 1150C for 6 hours. Post-annealing was done at 1100C in nitrogen gas. The thickness of the SiO2 film was about 0.6 nm measured by ellipsometry. Variable energy (0-20 keV) positron beam made the positrons stop and annihilate at different depth from the SiO2 surface to the SiC bulk.
The measurement results obviously showed that the S-parameters


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Presentation: poster at E-MRS Fall Meeting 2004, Symposium C, by Min Gong
See On-line Journal of E-MRS Fall Meeting 2004

Submitted: 2004-04-14 02:28
Revised:   2009-06-08 12:55