Mass analysis has been conducted on the positive ions and neutral species in the downstream region of Ar/CF4/O2 plasmas. The neutral species have been ionized by Li+ attachment before mass analysis. The CF2O+, C2F5O+ and CnF2n-1O+ (1 ≤n≤ 6) positive ions and the CnF2nO (1 ≤n≤ 7) neutral species have been found as the species composed of C, F and O. The intensity of C2F 4O observed via the Li+-attachment mass spectra has been exceptionally weak in comparison to the intensities of CF2O and C3F6O. In addition, neither C2F4 nor C3F6 have been observed, although CnF 2n (n≥ 4) have been observed as the species composed only of C and F. These findings suggest that CnF2nO (n≥ 3) are produced mainly through the following reactions: CF3(CF 2)mCF = CF2 + O(3P) → CF 2(3B1) + CF3(CF2) mCFO (m≥ 1) and CF3(CF2)mCF = CF(CF2)nCF3 + O(3P) → CF 3(CF2)mCF + CF3(CF2) nCFO (m, n≥ 1), where the CF3(CF2) n- group might have side chains, as in (CF3) 2CF(CF2)n-2-. With the help of quantum chemistry calculations of reaction enthalpies and transition states, the formation mechanisms of the observed species have been discussed in detail.
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