A new method of measuring neutral radicals by mass spectrometry

A new method, straight-line fitting, is proposed for measuring neutral radicals in plasma by a residual gas analyzer. Compared to threshold-ionization mass spectrometer, the proposed method is suited to all mass spectrometers, even if the minimum electron energy of the mass spectrometer is larger than the ionization threshold of the radicals. Moreover, the effects of the formation of daughter ions in the mass spectrometry ionization chamber are discussed. The results show that the effects of neutral radicals being ionized into fragment ions can be neglected during the course of deducing plasma depletion fraction within the deviation of the statistical fluctuation. In order to estimate the feasibility and reliability of this method, SiHn (n = 0-3) radicals in an SiH4 plasma and SiCln (n = 0-2) radicals in an SiCl4 plasma are measured. The experimental results demonstrate that this newly proposed method is universal and more accurate than the previous one.