Laser and mass spectrometric studies of the mechanism of silicon (100) single crystal etching reactions

The thermal etching of Si(100) single crystals by F₂ has been studied by electron impact (EI) and resonance enhanced multiphoton ionization (REMPI) mass spectroscopy. Laser ionization of the gas phase products observed under single collision gas-surface conditions indicates that SiF₂ radicals are formed with an apparent activation energy of 9.9 ± 1.65 kcal/mol. Similarly, EI measurements indicate that SiF₄ is desorbed from the surface with an apparent activation energy of 4.0 ± 1.0 kcal/mol. A comparison of the temperature dependence of the ion currents generated by EI for SiF_x⁺, (x = (1-4)) with MPI of SiF₂ indicate that the SiF_x⁺ signals are derived primarily from SiF₂ and SiF₄ (possibly vibrationally excited). Both n-type and p-type doping apparently have no significant effect in the measured rates and activation energies for SiF₂ and SiF₄ production.