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.