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Deltadoped structures represent a powerful class of test structures to investigate the experimental and fundamental factors limiting the depth resolution obtainable in SIMS sputter depth profiling.In this work, tbretical studies of the e&ts on the broadening of an Si delta spike in GaAs as a function of the energy (1.4-4.4 Lev) and angle of incidence (ZO, 45" and 60" off-normal) of the 0, sputter probe beam have been compared with recent experimental data. The theoretical calculations were carried out using the newly developed IMPETUS computer code, which simulates the depth profiling process by taking into account the combined effects of ballistic mixing (treating collisional mixing as a difbion prows), projectile incorporation into the matrix and sputtering. All of these are processes that always occur in any practical sputter depth profiling situation.The IMPETUS model can reproduce low+nergy Si depth profiles with great accuracy by using the wellestablished TRIM calculated range, energy deposition and sputtering data and by making reasonable assumptions for the threshold energy for diffusion in addition to assuming a beam-and sputter statistics-induced surface microtopography, which is described by a Gaussian area versus height distribution having a standard deviation u = 0.8 am. Si@cantly, it is shown that the effects of these parameters on the shape of the sputter profile are largely independent, with u (accounting for microroughaess) mainly affecting the leading edge and the threshold energy (determining mixing processes) the trailing edge of the sputter profile. Good agreement on the energy dependence of the broadening is also obtained. The expected improvement in depth resolution with increasing off-normal bombardment angle is confirmed and can be quantified. The error in the experimental depth scale calibration based on a constant sputter rate, ignoring transient sputtering, is evaluated. Finally, the sputter depth profile observed for an Si delta spike in GaAs subjected to thermal annealing during growth by molecular beam epitaxy (MBE) can be reproduced accurately by considering diffusion broadening of the initial spike followed by a sputter profiling simulation.~

SUMMARYThis paper is concerned with the theoretical determination of the amount of atomic mixing which accompanies the erosion of a solid surface exposed to an energetic ion beam. The work is relevant to sputter depth profiling where such mixing complicates the deduction of the initial depth distributions from the measured ion yields.A mathematical model, which considers the effects of incident ion accumulation, ballistic relocation and diffusion is described. The governing integro-differential equations are solved numerically.Results for a GaAs-AIGaAs multi-layer structure bombarded with 0 : ions are compared with results obtained experimentally.

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