SPATIAL-DISTRIBUTION AND SURFACE LOSS OF CF3 AND CF2 RADICALS IN A CF4 ETCHING PLASMA

The absolute number density and the spatial distribution of CF3 and CF2 radicals in a radio-frequency CF4 plasma were measured using threshold-ionization mass spectrometry. The time constant of density decay in an afterglow was measured to be almost independent of pressures (15-100 mTorr) and rf powers (10-100 W). This suggests that surface reactions rather than gas phase reactions may primarily be responsibile for the radical loss. The surface loss probability s of CF3 and CF2 radicals was estimated in this well-defined system to be s=0.012 and 0.014, respectively.