Sputtering of insulators

Abstract

Ion and electron induced particle emission from insulators will be discussed. Ion bombardment leads to nontransient particle emission for all insulators. For oxides and low to medium ion energies cascade sputtering (momentum transfer collisions) dominates particle emission, while for alkali halides even under ion bombardment non-cascade processes dominate. However, even for oxides pronounced differences in yield, energy distribution and especially in the composition of the sputtered flux can be observed as compared to the results for pure metals. Experimental techniques such as laser-induced fluorescence spectroscopy (LIF), bombardment induced light emission (BLE), secondary ion mass spectrometry (SIMS) and quartz microbalance measurements have been employed to study these effects for oxides as well as alkali halides. For electron bombardment oxides do not show any nontransient particle emission in contrast to alkali halides, where emission is due to electronic excitation induced by the incident particles producing stable defects, which lead to the ejection of the halogen atoms either via diffusion to the surface or through focused collision sequences. In addition, thermal evaporation of the neutralized metal atoms occurs depending on target temperature and will be the rate limiting process. We will discuss differences in the energy distribution of ejected ground-state and excited atoms under electron and ion bombardment and compare the results for two exemplary representatives, i.e. Nad and CaF 2 with the case of the pure metals. In addition, the yield dependence for ground-state and excited atoms will be discussed as a function of the target temperature, which yields information on the origin of excited atoms under electron bombardment.