Secondary ion mass spectroscopy (SIMS) is one of the most important tools in analyzing dopant profiles in silicon technology. During SfMS analysis, target atoms are sputtered by an ion beam so that, by mass separation, depth profiles of impurities are obtained. When analyzing shallow dopant distributions, the profile shape can be distorted significantly by ion-beam mixing induced by the sputtering process. In this work, the effects of ion-beam mixing on dopant profiles are analyzed experimentally and theoretically via delta-response functions, the SIMS signals of delta-doped layers. Methods for the reconstruction of true dopant profiles are discussed and applied to profiles of arsenic and antimony implanted at low energies.

Secondary Ion Mass Spectroscopy (SIMS) is extensively used in microelectronics in order to measure the depth profiles of dopants in silicon wafers. During the SIMS analysis, the sputtering ion beam induces several mass transport processes (collisional mixing, radiationenhanced diffusion of the dopant atoms) which depend on ion beam characteristics (ion mass, energy, incident angle) and on atomic transport properties of the sample. The atomic transport leads to broader and shifted depth profiles in the measurements compared to the original ones. For a delta distribution of the analyzed impurity in depth, the signal of the SIMS apparatus leads to the response function; this function represents the distortion introduced by the measuring technique. In a first approximation, this response function is assumed to be independent of the initial depth profile. The resulting experimentally measured depth profile can be described as a convolution of the original undistorted profile and the SIMS response function. The SIMS distortion function associated with collisional mixing during SIMS analysis is calculated in the present work using a dynamic version of the TRIM program. As the depth dependence of the response function is important for SIMS analysis of shallow ion-implanted profiles of arsenic, this effect was taken into account to improve the precision of the SIMS profile modeling.

No abstract

No abstract