The effect of oxygen during irradiation of silicon with low energy Cs~+ ions

摘要

The effect of oxygen flooding during ultralow energy SIMS depth profiling of silicon with Cs~+ primary ions is presented. New experimental data show the effective sputtering yield of silicon in the presence of oxygen, as well as the energy distribution of the secondary Si~- ions. It is found that the component sputtering yield of Si is very sensitive to minute amounts of oxygen in the proximity of the sputtered surface. At these very low flooding pressures (in the 10~(-9)-10~(-8) mbar range), one cannot account for a full oxidation in the time frame of a typical measurement; it is concluded that in this particular case, which is technologically very relevant, small traces of oxygen will change the desorption characteristics of cesium as well as silicon. It shows that oxygen that is adsorbed to the silicon surface provides an attachment site for impinging cesium ions and thereby increases the retention capacity of cesium tremendously. Also, oxygen changes the secondary ion yield and can even promote the desorption of Si from the analysis surface.