Application of heavy ions to high depth resolution RBS

Abstract

A detailed study has been made of the use of MeV heavy ions (2 ≤, Z 1 ≤, 10) to improve the limits of depth resolution in surface analysis. While there have been detailed studies of the optimization of the use of He projectiles at glancing angles, heavier ions have received limited attention principally because the energy resolution of surface barrier detectors is significantly degraded for heavy ions and this is a major contributor to limiting the depth resolution of a system near the surface. In this paper the surface barrier detector will be compared with the electrostatic energy analyser (EEA) which does not suffer the same limitations in energy resolution (and hence depth resolution). This work extends a number of limited experimental studies of the application of heavy ions and electrostatic analysers to enhanced depth resolution, though these have rarely been used together. It will be shown that exceptional improvements in depth resolution can be achieved, and subject to the limitations of the theoretical models used in the computer simulation of heavy ion backscattering, it is predicted that depth resolutions of as small as 0.5 nm may be achievable. An algorithm for ascertaining the optimum depth resolution conditions for heavy projectiles is also derived which will identify the best angle of incidence, depth resolution and projectile for a given sample to an accuracy of better than 10%.