Diagnostics of inductively coupled chlorine plasmas: Measurement of CI sub 2 and CI number densities

This paper presents measurements of absolute CI sub 2 and CI number densities in a chlorine transformer-coupled plasma (TCP). 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. CI sub 2 and CI 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 SiO sub 2-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. CI sub 2 is largely (~90%) dissociated at the highest powers, with a somewhat higher degree of dissociation at low pressure. The CI 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 CI sub 2 and an overall drop in number density due to heating of the gas. A zero-dimensional (global) model is used to computer CI sub 2 and CI number densities. It gives reasonable agreement with the observed values for a CI wall recombination coefficient of 0.33 on the stainless steel walls.