In situ measurement of electron emission yield at silicon dioxide surfaces exposed to argon plasmas

Abstract

Plasma simulations require accurate yield data to predict the electron flux that is emitted when plasma-exposed surfaces are bombarded by energetic particles. One can measure yields directly using particle beams, but it is impractical to create a separate beam of each particle produced by typical plasmas. In contrast, measurements made in situ, during plasma exposure, provide useful values for the total emitted flux produced by all incident particles. Here, in situ measurements were performed in a radio-frequency (rf) biased, inductively coupled plasma (icp) system in 0.67 Pa and 1.33 Pa (5 mTorr and 10 mTorr) of argon gas. The rf current and voltage across the sheath adjacent to the rf-biased 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 flux to be distinguished from other current mechanisms. The effective yield, i.e., the ratio of the total emitted electron flux to the incident ion flux, is also determined, as a function of incident ion energy. Results for the effective yield of a sputter-deposited SiO2 film are reported and compared with previous work. The measured effective yield can be considered the yield from Ar+ kinetic emission, which, in these experiments, dominates other emission processes. From additional literature data, emission yields for other processes—incident photons, Ar metastables, fast Ar atoms, and Ar+ potential emission—are recommended and are shown to be consistent.