Mass Spectrometric Detection of F Atoms and CFx Radicals in CF 4 Plasmas

Threshold ionization mass spectrometry method has been applied to the study of the neutral radicals present in a microwave generated CF4 plasma. Calibration of the mass spectrometry signals by comparison with the ion signals produced by the dissociative ionization of CF4 allows the estimation of the absolute concentration of the radicals in a 15 mTorr plasma, with an emphasis on the cases of atomic fluorine and CFx (x = 1–3) radicals. The effect, on the gas phase composition, of the introduction of a silicon sample in the plasma chamber is also investigated. Among these effects, the introduction of silicon leads to decrease the concentration of the F and H atoms as well as HF molecules, and to increase the concentration of the SiF3 and CFx radicals.