SIMS depth profile correction for the study of the first step of the diffusion of boron in silicon

Abstract

The analysis by secondary ions mass spectrometry (SIMS) is a powerful tool for the study of the diffusion of boron in silicon. It has been extensively used in order to determine diffusion coefficients. Most of the time, the SIMS profiles used to calculate the diffusion coefficients are sufficiently large so that the SIMS analysis do not modify the real concentration distribution in a significant manner. But more and more, the first steps of the diffusion are to be considered in order to obtain very thin diffused structures. In that case, where very thin layers are analyzed by SIMS, it is no more possible to measure directly the real concentration distribution because the SIMS analysis modify it rather significantly. When the real width or the real shape of the analyzed layers is needed, the measured profile has to be corrected in some way. We show that in the case of Gaussian original profiles, the SIMS profiles can be efficiently corrected, and the exact second order moment of the profile determined from the measured profile until the original second order moment is as low as 20 Å. This can be done by the study of the properties of the convolution of the profiles by the SIMS analysis response function. In the case of non-Gaussian profiles, the real shape and width of the profiles can be determined by a deconvolution procedure that we have previously described. (B. Gautier, J.C. Dupuy, G. Prudon, J.P. Vallard, C. Dubois, Proceedings of SIMS X, The International Conference on Secondary Ion Mass Spectroscopy and Related Techniques, Wiley, Chichester, 1996, pp. 443; B. Gautier, R. Prost, J.C. Dupuy, G. Prudon, Surface and Interface Analysis 24 (11) (1996) 733). This procedure is applied to the case of the SIMS measurement of δ-doped layers of boron in silicon before and after rapid thermal annealing (RTA).