Synthesis of diamond using mode-translation type microwave plasma CVD from a CH
4-H
2-O
2 reaction gas system was investigated. Diamond could not be synthesized by addition of O
2 at low CH
4 flow rate. On the other hand, diamond could be synthesized by addition of small amounts of O
2 at high CH
4 flow rate. The area of film formation was extended by addition of O
2 at high CH
4 flow rate. Moreover, the quality of diamond produced using the CH
4-H
2-O
2 reaction gas system was almost the same as that obtained using the CH
4-H
2 reaction gas system and the diamond deposition rate was increased by addition of small amounts of O
2 at high CH
4 flow rate. In conclusion, the deposition rate and quality of diamond were improved by addition of small amounts of O
2 at high CH
4flow rate in this system.
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