Ion implantation and sputtering in the presence of reactive gases: Bombardment-induced incorporation of oxygen and related phenomena

Abstract

Medium energy backscattering spectrometry has been used to investigate ion impact-induced incorporation of oxygen in silicon. The sample was first exposed to 20-keV Xe bombardment at base pressure (oxygen-to-xenon flux density ratio ν̇(O2)/Φ̇(Xe)⩽0.5, beam incidence ∼10° off normal). Having arrived at the steady-state level in xenon content, bombardment was continued at deliberately enhanced oxygen partial pressures in the target chamber (5⩽ν̇/Φ̇⩽500). This resulted in significant beam-induced incorporation of oxygen which manifests itself not only in a corresponding signal in the backscattering spectra (aligned geometry) but also in an enhanced reemission of xenon and a reduction in the erosion rate of the substrate (up to a factor of 5). The impact-induced oxygen incorporation efficiency α can become very large. At low (added) fluences and for ν̇/Φ̇≳100 we found α0 = (3±1) atoms/ion. This result is supported by sputtering yield measurements on SiO2 and oxygen-exposed silicon, which indicate that the steady-state partial sputtering yield of oxygen at high flux density ratios is Yp,O = (4.3±0.5) atoms/ion. It is suggested that oxygen incorporation and subsequent migration to larger depths is essentially a defect-controlled process. The high incorporation efficiency is thus due to the large (average) number of defects arriving at the surface after impact of a single ion. Analysis of the experimental data suggests that ion-induced desorption sets an upper limit to the incorporation efficiency. Oxygen reduces the xenon retention capacity of the substrate at all concentration levels. The most pronounced effects are observed near the surface where incorporation of oxygen causes drastic reemission of xenon. The steady-state xenon content of an oxidized sample is controlled by the oxygen concentration and the erosion rate.