Measurements of the Cl atom concentration in radio‐frequency and microwave plasmas by two‐photon laser‐induced fluorescence: Relation to the etching of Si

Atomic chlorine concentrations in Cl₂ plasmas have been measured by two‐photon laser‐induced fluorescence (LIF). Experiments were performed over a wide pressure range in rf, rf magnetron, and microwave electron cyclotron resonance (ECR) discharges. Absolute calibration was achieved by generating Cl atoms through UV photolysis of CCl₄ with the same laser radiation. The LIF measurements showed that in the respective discharges, the Cl concentrations decreased and the corresponding Cl fractions increased with decreasing pressure: the measured fractions ranged from 0.3% to 0.7% in rf discharges, from 0.8% to 8% in magnetron, and from 1% to 2% in ECR. These results, together with electrical measurements of ion and electron energies and densities, demonstrated that the ratio of neutral Cl flux to ion flux toward the substrate decreased from 400:1 to 1:1, almost linearly with decreasing pressure in the three discharges. These results of plasma diagnostics are compared with the etching characteristics of heavily P‐doped polycrystalline Si obtained.