摘要 |
A pulse voltage is applied on a process gas to generate discharge plasma. The pulse voltage has a duty ratio controlled in a range of 0.001 percent or more and 8.0 percent or less. Preferably, the discharge plasma has an electron density of 1x10<SUP>10 </SUP>cm<SUP>-3 </SUP>or larger and an electron temperature of 1.5 eV or lower at a supplied power of 1.0 W/cm<SUP>2 </SUP>or more per a unit area of a discharge electrode.
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