MASS-SPECTROMETRIC DETECTION OF F-ATOMS AND CFX RADICALS IN CF4 PLASMAS

Threshold ionization mass spectrometry method has been applied to the study of the neutral radicals in a microwave generated CF4 plasma. Cal ibration of the mass spectrometry signals by comparison with the ion s ignals produced by the dissociative ionization of CF4 allows the estim ation of the absolute concentration of the radicals in a 15 m Torr pla sma, with an emphasis on the cases of atomic fluorine and CFx (x = 1-3 ) radicals. The effect, on the gas phase composition, of the introduct ion of a silicon sample in the plasma chamber is also investigated. Am ong these effects, the introduction of silicon leads to decrease the c oncentration of the F and H atoms as well as HF molecules, and to incr ease the concentration of the SiF3 and CFx radicals.