The influence of rare gas dilution on absolute oxygen atom density in O2 radio frequency (RF) capacitively coupled plasma (CCP) was investigated by vacuum ultraviolet absorption spectroscopy (VUVAS) with pulse modulation of main plasma. Helium dilution is effective for raising O atom density at high total pressure (5 Torr) due to the Penning ionization by metastable He. Argon and Krypton dilution keeps O atom density same to pure O2 case at 0.5 Torr while helium dilution lowers the O atom density by the enhanced diffusion flux of O atoms toward walls. The trend is supported by a diffusion model of O atoms.
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