The simulation of SIMS measurements of light element profiles in diamond

Abstract

Information about concentrations and profiles of impurities on or near surfaces is commonly obtained from secondary ion mass spectroscopy (SIMS) measurements. These may, however, yield misleading results when sharp profiles are measured. In this work, the results of computer simulations of SIMS measurements of light impurities (hydrogen, deuterium and lithium) on diamond are presented, using a modified version of the transport of ions in matter (TRIM) computer code which has been extended to include the continuously changing material during the SIMS profiling. The simulations show that elastic recoils, induced by the probing beam used in SIMS, can broaden an initially sharp profile and thus induce an apparent diffusion profile. The changes in matrix composition caused by the implantation of the probing beam can modify the depth scale. These are demonstrated by performing detailed computations for the technologically important cases of (i) a hydrogen-passivated diamond surface and (ii) a thin Li layer on top of a diamond surface. The results show that the exponential tail, experimentally measured by SIMS and interpreted as being due to diffusion of Li into diamond, can be fully explained by the art-effect of the SIMS measurement. Very good agreement between the simulated and measured SIMS profiles is obtained when it is assumed that Li is present only on the surface as a thin layer.