Velocity distributions and sputtering yields of chromium atoms under argon, oxygen and carbon ion bombardment

Abstract

The velocity distribution of sputtered ground-state Cr atoms under 15 keV Ar, O and C ion bombardment has been measured using Doppler-Shift Laser Fluorescence Spectroscopy (DSLFS). Auger analysis of the target surface showed that a clean carbon-free surface could only be obtained under simultaneous Ar ion bombardment and annealing of the Cr target at high temperatures (500 ° C). In the case of Ar ion bombardment we have observed a shift of the velocity distribution to higher values with increasing oxygen partial pressure and, furthermore, a strong density decrease of sputtered Cr ground-state atoms by a factor greater than 50 compared with the results for clean Cr targets. No measurable shift and a density decrease by a factor of only about 2 has been observed for Cr ground-state atoms sputtered by Ar ions and an increased hydrogen background pressure. Contrary to the exposure of Cr targets to an oxygen background atmosphere, under oxygen ion bombardment of up to a few μA/cm2 the density and velocity distributions of sputtered Cr ground-state atoms were comparable with those produced by Ar ion bombardment of Cr targets without oxygen background. A strong density decrease was again observed for simultaneous oxygen exposure and oxygen ion bombardment. The results obtained for carbon ion bombardment in general agree with those for oxygen ion bombardment.The sputtering yield of Cr has been measured for clean and oxygen-covered targets by means of a quartz microbalance (thickness monitor). For clean Cr targets a sputtering yield of 4.2 atoms/ion has been obtained. For increasing oxygen background pressure the sputtering yield decreases. For oxygen pressures of 1 × 10−7 and 1 × 10−6 mbar sputtering yields of 3.8 and about 1, respectively, are obtained.