The permanent decrease of the transistor size to improve the performances of integrated circuits must be accompanied by a permanent decrease of the depth of the source-drain junctions. At the same time, in order to keep acceptable sheet resistance values, the dopant concentration in the source-drain areas has to be continuously increased. A possible technological way to meet the junction depth and abruptness requirements is to use co-implantation of non doping species with classical implantations, especially for light ions as B or P.
In order to clarify the complex interactions occurring during these co-implantation processes, we have performed an extensive experimental study of the effect of Ge, F, N, C and their combinations on boron. A special interest was given to the overall integration issues. We will show that it is required to optimize the respective locations of co-implanted species with respect to the B profiles (more precisely the ion implantation damage locations), as well as the co-implanted species doses, to get an acceptable compromise between the efficient diffusion decrease required for the junction abruptness and depth, and a reasonable current leakages.