Optical emission spectroscopy of pulsed inductively coupled plasma in Ar

Optical emission spectroscopy has been used to study the properties of pulsed inductively coupled plasma in Ar. Both spatially resolved computerized tomography and time resolved spectroscopy have been applied. In the range between 5 mTorr and 300 mTorr, it was found that the ratio of time averaged excited state densities in pulsed and CW conditions increases from 1:3 to 3:4. This is larger than the 1:2 ratio which may be expected from the duty cycle. The variation of the emission in the OFF period requires excitation during that period, and its time dependence may be understood by following the decay of the density and mean energy of electrons, and the decay of the metastable density. In the pulsed mode the radial uniformity is generally improved at lower and slightly worse at higher pressures.