Competing processes on Formation of Negative Ion and Ozone in Recombining Oxygen Plasma

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In this Work, high density oxygen plasma of the order of 10^<12>cm^<-3> has been produced by exciting helicon waves. The plasma was modulated by ON-OFF of RF power, and ionizing and recombining plasmas were produced at the ON and OFF phases of RF, respectively. The aim of the work is to inevestigate comepeting processes on the formation of negative oxygen ion and ozone which would be effectively produced in the afterglow (recombining plasma phase). First, we have investigated behaviors of positive and negative ions by means of time-of-flight mass spectrometry. Negative ions were effectively produced in the afterglow. The O^- ions were mainly produced with a little O_2^- ions. We have also developed two-photon laser-induced fluorescence method to determine absolute density of O-atoms which play an important role in the formation of ozone. It has been found that the degree of oxygen dissociation was about 1% at oxygen of 50mTorr. The decay of O-atoms in the afterglow may be mainly due to processes on the chamber surfases. For ozone, we have tryed to detect it by observing ions of ozone and by laser absorption around 250nm. However we do not yet succeed to do it. It is necessary to improve the detection efficiency for ozone. As a summary, two kinds of diagnostic techniques which are useful to study of basic processes in reactive plasmas could be developed in this research and successfully used for investigating behaviors of ions and radicals in oxygen plasma.