Dielectric Breakdown Phenomena during Secondary Electron Emission Measurement of Sputter-Deposited MgO Films

Abstract

The ion-induced secondary electron emission (SEE) characteristics of sputter-deposited magnesium oxide (MgO) films have been investigated. Using an RF magnetron sputtering apparatus, MgO films of 50–200 nm thickness were deposited on Si substrates from a sintered MgO target. Under irradiation of 1 keV of Ar+ ions, secondary electrons were collected at a positively biased electrode. The secondary electron current increased as the bias voltage increased, and saturated to give an SEE coefficient of 2–2.5 in all samples. The deposition condition (gas pressure 2–20 Pa) did not strongly affect this current–voltage (I–V) characteristic of the SEE, while an increase in film thickness resulted in an increase in the voltage at which the SEE current began to rise. This rising voltage depended neither on the energy nor on the current of the primary ion beam. We concluded that the rising voltage was governed by an electric breakdown phenomenon by which the positive charge accumulating on the surface was compensated from the substrate. The field strength was estimated to be as high as 109 V/m.