Distortion of sims profiles due to ion beam mixing: Shallow arsenic implants in silicon

Abstract

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, radiation-enhanced 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.