Plasma-relevant fast electron impact study of difluoromethane

Difluoromethane (CH2F2) is a commonly used etching gas in manufacturing very-large-scale integrated circuits as the fluorine source. Electron impact excitation cross sections for CH2F2 are important input data for modeling the reactive etching plasmas. In this work, we present the experimental generalized oscillator strengths for the 3s ? 2b(2), 1(1)A2 ? X(1)A1, and 3p ? 2b(2) transitions on the absolute scale. The measurement was realized by employing the crossed-beam based relative flow technique at an angle-resolved electron energy loss spectrometer, operating at an incident energy of 1500 eV and a resolution of 80 meV. The dipole-forbidden transition 1(1)A2 ? X(1)A(1) at around 9.7 eV is identified for the first time. The measured data are fitted with the well-known Lassettre formula to yield analytical expressions and optical oscillator strengths at K-2 = 0 for dipole-allowed transitions. The analytical expressions enable integrations over momentum transfer to obtain the Born integral cross sections for electron impact excitations from the threshold to 5000 eV. The integral cross sections for dipole-allowed transitions are scaled to a more reliable level by using the BE-scaling method. The experimental data can benchmark theoretical calculations and supplement the molecular database for plasma modelers.