Sputtering of metal targets under increased oxygen partial pressure

Abstract

The composition of the sputtered flux from different metal targets (Ca, Cr, Zr, Ti, Cu) under keV rare gas ion bombardment was studied as a function of the oxygen partial pressure. Laser induced fluorescence spectroscopy (LIF) was used to measure the yield as well as the energy distribution of the sputtered ground state (Ca, Cr, Zr) and excited state (Ca, Zr) atoms. Total sputtering yields and the yields of charged and neutral sputtered particles have been obtained from quartz microbalance measurements. The contribution of sputtered excited atoms has been analyzed via bombardment induced light emission (BLE). Total sputtering yields did not decrease by more than a factor of two to four with increasing oxygen partial pressure for all metal targets. The measurements, however, led to the conclusion that with increasing oxygen surface coverage the composition of the sputtered flux changes drastically from almost exclusively neutral ground state atoms without oxygen at the surface to a flux consisting mainly of sputtered neutral molecules and also a sizeable fraction of sputtered ions and ionized molecules. For high oxygen surface coverages the contribution of sputtered ground state atoms to the total flux becomes negligible. The contribution of excited atoms increases with oxygen coverage, however, it always remains a minor contribution to the total flux.