Ion bombardment energy distributions in radio-frequency glow-discharge systems

Abstract

The measurement and interpretation of ion bombardment energies in rf discharges of SF₆, CF₃Cl, and CF₃Br from 0.2 to 1.0 Torr, are discussed. Errors in ion sampling due to disturbances of the electric field and neutral density around the sampling orifice are shown to be most important at higher pressures and with larger orifices. The dependence of the ion bombardment energy distribution on the electric‐field‐to‐pressure ratio is reviewed. Combining this relation with a simple electrical model of a plasma gives estimates of the ion bombardment energies in collisional sheaths. The bombardment energy is proportional to (rf current)/(electrode area×frequency ×pressure) with the proportionality constant for a particular system depending on the collision cross sections and relative ion‐to‐netural mass ratio. The constants found for the three gases studied experimentally are close to theoretical estimates.