In-situ measurement of electron emission yield at silicon surfaces in Ar/CF₄ plasmas

Plasma simulations require accurate data for the ion-induced electron emission yield at plasma-exposed surfaces. For industrially relevant plasmas, however, direct measurement of yields using ion beams is impractical. In contrast, measurements made in situ, during plasma exposure, provide useful values for the total or effective yield produced by all incident ions. Here, in-situ measurements were performed in an icp system in Ar/CF₄ mixtures at 1.3 Pa. The current and voltage across the sheath adjacent to the rf-biased substrate electrode were measured, along with Langmuir probe measurements of ion current density and electron temperature. The measurements are input into a numerical sheath model, which allows the emitted electron current to be distinguished from other currents. The effective yield was determined for thermally oxidized, in-situ etched, and sputter-cleaned silicon surfaces. For thermal oxides in pure Ar, yields agreed with previous measurements [1] on sputtered oxides. By combining measurements made for several mixtures with mass spectrometer data for the relative flux of each ionic species, estimates or bounds were obtained for the individual electron emission yields of the most prevalent ions.

[1] M. A. Sobolewski, Plasma Sources Sci. Technol. 30 025004 (2021).