Papers by Keyword: Nitrogen Ion Implantation

Abstract: Heavily doped layers were formed in 4H-SiC device epitaxial structures comprised of moderately doped n layer (channel) and heavily doped p⁺ layer (gate). The n⁺ regions were formed by local ion implantation of nitrogen followed by post-implantation annealing with graphite capping layer. It was shown that annealing at 1700 °C is required for complete activation of implanted impurities. The post-implantation anneals were found to have no significant effect on the moderately nitrogen doped channel layer. On the other hand it resulted in noticeable deterioration of electrical propertied of heavily doped epitaxial p⁺ layers leading to the increase of contact resistivity which has to be taken into account in design and processing of SiC devices.

Abstract: 4H-SiC p-type MOS capacitors fabricated by wet oxidation of SiC preamorphized by nitrogen ion (N+) implantation have been investigated. The oxidation rate of the SiC layer preamorphized by high-dose N+ was much larger than that of crystalline SiC, allowing us to reduce the fabrication time of SiC MOS devices. We found that the presence of the surface amorphous SiC layer before the oxidation process did not influence the interface state density in MOS capacitors. Moreover, the shift of the flat-band voltage is not correlated to the amount of nitrogen in the oxide. On the contrary the density of interface states near the valence band edge increased according with the high concentration of the implanted N at the oxide–SiC interface, as in the case of dry oxidation reported by Ciobanu et al. The generation of positive charges due to the nitrogen embedded inside the oxide layer was smaller compared with dry oxidation. We discuss the difference between wet and dry oxidation for MOS capacitors fabricated with N+ implantation.