Optimizing the Depth Resolution of Rutherford Backscattering Through Modeling of Noise Sources

Abstract

AbstractGrazing angle configurations improve the depth resolution of Rutherford Backscattering Spectrometry (RBS) because the path length of scattered particles is geometrically increased. But in the limit of very grazing angles the resolution degrades due to the finite detector acceptance angle and low angle forward scattering of the beam, considerations which are not present in near-normal incidence geometries. The forward scattering, for example, worsens the depth resolution approximately as the square of the depth, rather than the familiar square root dependence of energy straggling. We present a simple computational scheme which predicts the depth resolution in any target as a function of scattering depth, beam energy, and the grazing angle. The calculations are simpler than previous studies because we use analytic expressions in place of numerical inputs without loss of accuracy. The results lead directly to an optimum depth resolution. We find good agreement between the predicted resolution and measurements on thin silicon dioxide and amorphous silicon films. Finally, we calculate the resolution expected with the use of ion beams heavier than He+, and find improved near surface depth resolution if a low noise detector is used.