Three Dimensional Optical Emission Tomography of an Inductively Coupled Plasma

The three dimensional distribution of the net production rate of excited species in an inductively coupled plasma (ICP) reactor in Ar has been measured as a function of pressure and discharge power. The ICP reactor is driven by a single turn radio-frequency current coil at 13.56 MHz. Robot assisted optical emission tomography was used in order to obtain radial profiles of emission at different distances from the coil thus giving effectively a three dimensional distribution of the net excitation rate as well as the number density of excited states. Under some conditions azimuthal symmetry of the discharge is broken mostly at higher pressures and higher powers. We have covered a range of pressures between 15 and 500 mTorr and powers between 50 W and 400 W. The conditions for producing a uniform distribution of excited atoms as a representative of active species, are discussed.