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 Cl-2(+) 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 Cl-2(+) persisted. Under the modulation frequency of 100 kHz, the decrease of the Cl-2(+) density in the discharge-off period was less than 30% and the decay time constant of Cl-2(+) density was longer than that of CL+*. Tn order to investigate the dominance between Cl-2(+) and chlorine atomic ions Cl+, the relative densities of Cl-2(+) and Cl+* were calibrated as absolute densities along with the Langmuir probe measurements. The dominant ions in the cw plasma were Cl+. however, the Cl-2(+) density became comparable to the Cl+ density in the time-modulated plasma.