Effects of low energy particle beam bombardment on solid surfaces

Abstract

Low energy rare gas ion bombardment is used extensively in surface cleaning and conditioning in applications such as semiconductor processing, in surface analytical techniques such as Auger and X-ray photoelectron spectroscopies for cleaning and depth profiling and as a primary beam in other techniques such as ion scattering and secondary ion mass spectrometry. It is always appreciated that such bombardment can produce substantial chemical changes in the surface, particularly in semiconducting and insulating samples. This paper discusses bombardment induced damage in surfaces and describes series of experiments to investigate the importance of beam energy, beam flux density and charge of the bombarding particle. As a vehicle for these investigations, bombardment induced chemical reduction of oxides of niobium and titanium were studied. In these investigations X-ray photoelectron spectroscopy was employed to identify changes in chemical state of the oxides with bombardment. The results of the investigations show little variation in damage with beam energy in the range 1–5 keV, whilst beam flux density has a significant effect. It is further found that neutrals produce substantially less damage in bombarded surfaces than do ions of the same species, energy and flux. Models are proposed which explain the results in terms of surface binding energy effects, mass effects and the influence of charge induced compensating leakage currents.