Influence of the impact angle on the depth resolution and the sensitivity in SIMS depth profiling using a cesium ion beam

Abstract

We have measured the falloff of the SIMS signal of surface impurities (C, O, and F) on Si and GaAs to determine the angular dependence of the depth resolution in sputter profiling under 8-keV Cs+ bombardment. The decay lengths characterizing the exponential tails decreased with increasing impact angle. The relative gain in depth resolution is largest in cases where the resolution is poor at normal beam incidence. The sputtering yield was found to increase approximately as 1/cos2θ, whereas the secondary ion yields of Si− and As− decreased by several orders of magnitude as θ was increased from 0 to 60°. This effect is attributed to a strong angular dependence of the stationary cesium coverage of the ion-bombarded samples. Some information concerning the efficiency for ion-induced desorption is also derived from the experiments.