Diagnostics of inductively coupled chlorine plasmas: Measurement of Cl₂ and Cl number densities

This article presents measurements of absolute Cl₂ and Cl number densities in a chlorine transformer-coupled plasma. It is part of a series of reports on measurements of densities and energy distributions of all charged and neutral species in the same plasma system over an extensive range of pressure and power. Cl₂ and Cl number densities were determined from optical emission spectroscopy and advanced actinometry. Number densities relative to the Xe actinometry gas are reported as a function of pressure (1–20 mTorr) and power (10–1000 W) during slow etching of SiO₂-covered Si wafers. A detailed treatment of the effects of gas temperature on the conversion of these ratios into absolute number densities is also included. Cl₂ is largely (∼90%) dissociated at the highest powers, with a somewhat higher degree of dissociation at low pressure. The Cl number density becomes nearly independent of power at high powers (especially at lower pressure) due to the combination of a higher degree of dissociation of Cl₂ and an overall drop in number density due to heating of the gas. A zero-dimensional (global) model is used to compute Cl₂ and Cl number densities. It gives a Cl wall recombination coefficient of 0.04 on the plasma-seasoned stainless steel walls. © 2000 American Institute of Physics.