We examined the atomic concentrations and the weight densities of SiC surfaces irradiated with remote nitrogen plasmas. The unique approach of this work is that we compared the SiC surface irradiated with atomic nitrogen with that irradiated with a mixture of atomic nitrogen and molecular nitrogen in the metastable A 3 Σ + u state. As a result, it was found that molecular nitrogen in the A 3 Σ + u state has a higher efficiency than atomic nitrogen in the nitriding of SiC surfaces. The weight density measurements have revealed the removal of Si and C from the SiC surface by the irradiation of remote nitrogen plasma. These results suggest that the formation of volatile molecules is less significant when the SiC surface is irradiated with molecular nitrogen in the metastable A 3 Σ + u state.
We remotely irradiated a nitrogen plasma onto the carbon-side surface of 4H-SiC at a low temperature, and examined the effect of sample cooling on the characteristics of the nitride layer. An improved nitride layer, which had higher concentrations of carbon and silicon and a lower concentration of oxygen, was formed in the region at depths of more than 0.6-0.9 nm from the top surface. The depth of the fragile nitride layer in the top region, where no improved characteristics of the nitride layer were observed, became smaller with sample cooling. In addition, on the basis of the experimental results, we discussed the difference in the activation energy of the nitriding reaction of 4H-SiC supported by atomic nitrogen and molecular nitrogen in the metastable A 3 Σ + u state.
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