Mass spectrometric investigation and formation mechanisms of high-mass species in the downstream region of Ar/CF₄/O₂plasmas

Abstract

Mass analysis has been conducted on the positive ions and neutral species in the downstream region of Ar/CF(4)/O(2) plasmas. The neutral species have been ionized by Li(+) attachment before mass analysis. The CF(2)O(+), C(2)F(5)O(+) and C(n)F(2n-1)O(+) (1 <or=n<or= 6) positive ions and the C(n)F(2n)O (1 <or=n<or= 7) neutral species have been found as the species composed of C, F and O. The intensity of C(2)F(4)O observed via the Li(+)-attachment mass spectra has been exceptionally weak in comparison to the intensities of CF(2)O and C(3)F(6)O. In addition, neither C(2)F(4) nor C(3)F(6) have been observed, although C(n)F(2n) (n>or= 4) have been observed as the species composed only of C and F. These findings suggest that C(n)F(2n)O (n>or= 3) are produced mainly through the following reactions: CF(3)(CF(2))(m)CF = CF(2) + O((3)P) --> CF(2)((3)B(1)) + CF(3)(CF(2))(m)CFO (m>or= 1) and CF(3)(CF(2))(m)CF = CF(CF(2))(n)CF(3) + O((3)P) --> CF(3)(CF(2))(m)CF + CF(3)(CF(2))(n)CFO (m, n>or= 1), where the CF(3)(CF(2))(n)- group might have side chains, as in (CF(3))(2)CF(CF(2))(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.

Growth of fluorocarbon macromolecules in the gas phase: IV. Li+-attachment mass spectrometric investigation of high-mass neutral radicals in the downstream region of Ar/c-C4F8plasmas

“…In contrast, a lack of C 3 F 6 Li + peak in figure 2 is not due to the sensitivity to C 3 F 6 but due to its truly low concentration, especially of l-C 3 F 6 . The low concentration of l-C 3 F 6 is consistent with the exceptionally low concentration of C 2 F 4 O in the C n F 2n O series observed in the Ar/CF 4 /O 2 plasma, where l-C 3 F 6 is thought to be the main reactant for the C 2 F 4 O formation [14].…”

“…However, we could not observe any neutral radicals with odd-numbered fluorine atoms in the Ar/CF 4 plasma and the pure CF 4 plasma. The growth reactions of C n F 2n+2 and C n F 2n took place around room temperature in the gas phase under our experimental conditions [5,14]. Thus, various radicals such as C n F 2n+1 and C n F 2n−1 may be related to their growth reactions.…”

“…In our preceding paper [14], we pointed out that CF 3 CF plays an important role in the formation of C n F 2n O and C n F 2n−1 O + . CF 3 CF can be produced through the Table 3.…”

“…The translational temperature of ions and neutral species was close to room temperature at a position 30 cm downstream from the centre of the plasmageneration area [5]. Therefore, reactions accompanied by a significant potential barrier do not take place, and exothermic reactions, which lead to the formation of more chemically stable species, take place predominantly in the downstream region of the plasmas [14]. In the following calculations of reaction enthalpy, isomers containing up to four carbon atoms (l-and c-C 3 F 6 ; 1-, trans-2-, cis-2-, iso-and c-C 4 F 8 ; l-and iso-C 4 F 10 ) have been considered.…”

Mass spectrometric investigation of high-mass neutral species in the downstream region of Ar/CH4 plasmas

“…35 The latter method significantly reduces the probability of adduct formation due to the lack of three-body collisions, but allows for measurements under such a low pressure. We have recently found various high-mass neutral molecules in the downstream region of Ar/CF 4 and Ar/CF 4 /O 2 plasmas, 36,37 and radicals in the Ar/c-C 4 F 8 plasma 29 using the low-pressure type Li þ attachment mass spectrometry (Li þ -IAMS).…”