Microwave Interferometry of Chemically Active Plasma of RF Discharge in Mixtures Based on Fluorides of Silicon and Germanium

The free electron concentration in hydrogen and chemically active plasmas in H₂ + SiF₄ and H₂ + GeF₄ mixtures was measured by microwave interferometry. The investigations were carried out under conditions of a RF capacitive-coupled discharge at a pressure of 1 Torr. In hydrogen plasma the concentration of free plasma electrons is 1.5 ± 0.03 × 10¹² cm^?3. When the fluoride is added to the hydrogen plasma, the electron concentration is reduced to 1.1 ± 0.05 × 10¹² cm^?3 for SiF₄ and 9.8 ± 0.05 × 10¹¹ cm^?3 for GeF₄. It is suggested that the main mechanism responsible for reducing the concentration of free electrons is the mechanism of dissociative attachment of electrons to SiF₄ and GeF₄ molecules. The difference in the electron concentration for these mixtures is due to the difference in the electron-acceptor ability of the SiF₄ and GeF₄ molecules determined by the affinity for the electron.