Diagnostic study of low-pressure Ar-O2 remote plasma generated in HCD-L 300 system: Relative density of O atom

The relative density of O atom of Ar-O2 remote plasma excited in a low-pressure 13.56 MHz hollow cathode discharge system has been investigated. The measurements were carried out at a total pressure of 0.05 mbar, radiofrequency (RF) power of 200 W and at three different axial distances in the plasma chamber below the outlet of the discharge source. Using optical emission spectroscopy (OES), the relative density of O ground state was determined from intensity ratio of O(844.6 nm) and Ar(750.4 nm) lines. The electron temperature and O2+ densities have been measured using double langmuir probe measurements. The kinetic study of Ar-O2 plasma, combined with both spectroscopy and langmuir probe measurements, revealed that the main production mechanism of the excited O(3pP3) is direct excitation by electron impact. A maximum of O ground state relative density and correspondingly a minimum of O2+ density are obtained for the ratio O2/Ar:60/40. The maximum O density in the remote zone is found to be 4.5 times higher than at the outlet of source.