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

Abstract

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.