Abstract
A brief overview of non-perturbing light diagnostics is followed by recent examples of process plasma properties measured via laser-induced fluorescence (LIF), optical emission, and absorption spectroscopy. Examples include radical density measurement via absorption and emission spectroscopy. With LIF, examples show properties of ion beam etching sources and ion velocity angle variations in ICP sheaths near a process surface. Because of the wide range of process plasma parameters, appropriate choice of light diagnostics varies.
Highlights
Process plasmas include many atomic and molecular species in neutral or charged states
Absolute radical densities may be measured using optical absorption spectroscopy, based upon a transition originating in the ground electronic state of the species
In cases for an ICP source without beam accelerating grids but only the plasma sheath near the wafer surface, laser-induced fluorescence (LIF) can show the spread in velocity angles of the ions in the sheath as they approach the wafer
Summary
Process plasmas include many atomic and molecular species in neutral or charged states. Absolute radical densities may be measured using optical absorption spectroscopy, based upon a transition originating in the ground electronic state of the species. This ensures that the measured density closely represents the total amount of that chemical species, though corrections for vibrational and rotational temperature may be needed. Instead an optical emission line intensity may be used to measure relative densities through careful calibration to a rare gas emission line (actinometry) [3] Both methods, absorption and emission, as described [1,2,3], were used to measure radical densities in the present study
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