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 a nalyze the effluents from C2H2F4, hexafluoropropylene oxide (CF3CFOCF2, HFP O), and CH2F2 pulsed plasmas. A series of reference spectra for possible ef fluent species was used to identify the major species in each. The major sp ecies in pulsed C2H2F4 plasmas were found to be: C2H2F4, HF, C2F4, C2HF5, C HF3, and SIF, (formed from free fluorine). For HFPO pulsed plasmas, the maj or effluents are: HFPO, CF3COF3, COF2, C2F4, C2F6, CO, CF4, and C3F8, where as for CH2F2 pulsed plasmas, the major effluents are: CH2F2, HF, SiF4, and CHF3. Reaction sets were postulated for each precursor to account for the o bserved effluents, and these sets were used to explain the trends of specie s concentrations with pulse on and pulse off time. In each case, most of th e 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 I-IF el imination from the original precursor. For C2H2F4 pulsed plasmas, the compe tition between these pathways was found to be similar to 1:1, whereas for C H2F2 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 im pact of each of the pulsed plasma enhanced chemical vapor deposition proces ses was gauged by the million metric tons of carbon equivalent (MMTCE) metr ic. CH2F2 pulsed plasmas were found to have the lowest MMTCE (min = 2.1 X 1 0(6)), whereas HFPO pulsed plasmas had the highest MMTCE (max = 7.7 X 10(7) ). 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. (C) 1999 American Vacuum Society. [S0734-2101(99)01706-6].