Dominance of Cl2+ or Cl+ ions in time-modulated inductively coupled Cl2 plasma investigated with laser-induced fluorescence technique and probe measurements

Relative densities of chlorine molecular ions Cl₂⁺ and metastable chlorine atomic ions Cl^+* were measured by a laser-induced fluorescence technique in cw and time-modulated inductively coupled chlorine plasma. In the discharge-off period of the time-modulated plasma, a considerable amount of Cl₂⁺ persisted. Under the modulation frequency of 100 kHz, the decrease of the Cl₂⁺ density in the discharge-off period was less than 30% and the decay time constant of Cl₂⁺ density was longer than that of Cl^+*. In order to investigate the dominance between Cl₂⁺ and chlorine atomic ions Cl⁺, the relative densities of Cl₂⁺ and Cl^+* were calibrated as absolute densities along with the Langmuir probe measurements. The dominant ions in the cw plasma were Cl⁺, however, the Cl₂⁺ density became comparable to the Cl⁺ density in the time-modulated plasma.