Fourier transform infrared spectroscopy of effluents from pulsed plasmas of 1,1,2,2-tetrafluoroethane, hexafluoropropylene oxide, and difluoromethane

Gas-phase Fourier transform infrared spectroscopy (FTIR) has been used to analyze the effluents from $C2H2F4,$ hexafluoropropylene oxide $(CF3CFOCF2$⁠, HFPO), and $CH2F2$ pulsed plasmas. A series of reference spectra for possible effluent species was used to identify the major species in each. The major species in pulsed $C2H2F4$ plasmas were found to be: $C2H2F4,$ HF, $C2F4$⁠, $C2HF5,$ $CHF3,$ and $SiF4$ (formed from free fluorine). For HFPO pulsed plasmas, the major effluents are: HFPO, $CF3COF3,$ $COF2,$ $C2F4,$ $C2F6,$ CO, $CF4,$ and $C3F8,$ whereas for $CH2F2$ pulsed plasmas, the major effluents are: $CH2F2,$ HF, $SiF4,$ and $CHF3.$ Reaction sets were postulated for each precursor to account for the observed effluents, and these sets were used to explain the trends of species concentrations with pulse on and pulse off time. In each case, most of the effluent concentration trends could be traced back to competition between dissociation pathways of a particular molecule. For both $C2H2F4$ and $CH2F2,$ the main reactions were the competition between $CF2$ production and HF elimination from the original precursor. For $C2H2F4$ pulsed plasmas, the competition between these pathways was found to be ∼1:1, whereas for $CH2F2$ pulsed plasmas, the HF elimination pathway is dominant. For HFPO, the key reactions are the three dissociation pathways of $CF3COF,$ a main product of the initial dissociation of HFPO into $CF2+CF3COF.$ The global warming impact of each of the pulsed plasma enhanced chemical vapor deposition processes was gauged by the million metric tons of carbon equivalent (MMTCE) metric. $CH2F2$ pulsed plasmas were found to have the lowest MMTCE (⁠$min=2.1×106)$⁠, whereas HFPO pulsed plasmas had the highest MMTCE $(max=7.7×107).$ For all three precursors, the MMTCE impact is reduced by decreasing the exposure to plasma excitation through increasing the off time at a fixed on time.