Metastable chlorine ion kinetics in inductively coupled plasmas

Abstract

Laser induced fluorescence has been used to measure the temperature, radial drift velocity, and relative number density of metastable chlorine ions, Cl+*, in inductively coupled discharges containing mixtures of BCl3, Cl2, N2, and Ar. In the center of the plasma, the Cl+* temperature varied between 2000 and 3000 K for most conditions investigated. The addition of BCl3 to a Cl2 plasma significantly decreased the density of metastable chlorine ions without changing their temperature. Addition of nitrogen to a BCl3 plasma resulted in a factor of 3 increase in the Cl+* density. Spatially resolved measurements of the Cl+* density are compared with Langmuir probe measurements of the spatially resolved electron density and ion saturation current. In general, the normalized Cl+* density was a factor of 2–3 lower than the electron density at the edge of the plasma. Spatially resolved measurements of the ion temperature indicated that the ion temperature increased to between 4500 and 5500 K at the edge of the discharge and increased approximately 600–1400 K moving from the rf source towards the lower electrode. Ion drift velocity in the radial direction was between 5×104 and 8×104 cm/s at the edge of the plasma. Measurements within one millimeter of the biased lower electrode surface showed the ion energy parallel to the biased electrode was independent of rf bias voltage while the density decreased with increased bias voltage. Implications of these measurements on the plasma chemistry and the energy transport in the plasma are discussed.