Optical emission spectroscopy of pulsed inductively coupled plasma in Ar

Optical emission spectroscopy has been used to study the properties of puls ed inductively coupled plasma in Ar. Both spatially resolved computerized t omography and time resolved spectroscopy have been applied. In the range be tween 5 mTorr and 300 mTorr, it was found that the ratio of time averaged e xcited 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 cy cle. The variation of the emission in the OFF period requires excitation du ring that period, and its time dependence may be understood by following th e decay of the density and mean energy of electrons, and the decay of the m etastable density. In the pulsed mode the radial uniformity is generally im proved at lower and slightly worse at higher pressures.