Reaction Products of F Atoms on the Surface of Silicon Dioxide Probed by Synchrotron Photoionization Mass Spectrometry

F atoms etching reaction as an efficient method has been widely used in the fields of optical manufacture, semiconductor and chemistry. But due to the technical challenges of analysis on-line, the products information, especially for the unstable radicals and intermediates, F atoms etching reaction is limited and hinders to understand its detailed mechanisms. The state-of-the-art method of synchrotron vacuum ultraviolet (VUV) photoionization mass spectrometry with high mass reolution and high sensitivity was utilized to probe reaction products of F atoms etching on the surface of silicon dioxide (SiO₂), where a microwave discharge plasma source was combined to produce F atoms with high density. Photoionization efficiency spectra (PIES) corresponding to each mass were measured by scanning synchrotron photon energy continuously, and the ionization energies of the species and the appearance energies of fragment ions were measured, in comparison well to the results of theoretical calculation. Then the ion signals in photoionization mass spectra (PIMS) from different sources, photoionization or dissociative photoionization, were defined and assigned. It was shown that a series of fluorine oxygen silicon compounds (Si_xO_yF_z) were produced and the reaction products of SiF₄, SiF₃OSiF₃ and SiFOSiF₂OF took a large intensity in the PIMS. However, the ion signals of SiF₃⁺ and SiF₃OSiF₂⁺ observed in the PIMS were from dissociative photoionization of their respective precursors. In addition, some fundamental data like the ionization energy of SiF₄ and the appearance energies of SiF₃⁺ and SiF₃OSiF₂⁺ fragment ions from dissociative photoionization of SiF₄ and SiF₃OSiF₃ were measured to be 15.85, 16.20 and 16.40 eV, respectively. This method realizes the efficient detection of products in F atom etching reaction. Because F atom has high chemical reaction activity, the experimental device can also be used to carry out the study of gas phase free radical reaction and simulate the chemical reaction process in atmospheric chemistry and combustion flame system.