Investigations on metastable helium atoms in a capacitively coupled plasma in a mixture of He, Ar and CF4

Spatially resolved density and temperature of helium metastable state 2$^{3}$S$_{1}$ in a parallel plate capacitively coupled plasma in He/Ar/CF4 are measured by laser absorption spectroscopy using a 1083nm distributed feed-back semiconductor laser. Because of lower electron density and possible quenching processes in the sheath, the profile of metastables density shows that the density has a more pronounced fall-off in the sheath than in the bulk plasma. It is also found that the metastables temperature near the powered electrode is higher than that near the grounded one. Other diagnostics are also used to determine related plasma parameters. The electron density is obtained by an emission line-ratio method, and the gas temperature is estimated from rotational spectra of nitrogen molecules. Ion energy distributions, ion fluxes and radical densities are measured by an energy-resolved mass spectrometer. The behavior of metastables helium atoms and the possible kinetic processes will be discussed in this work.