Phosphorous degassing from poly silicon under thermal exposure: A ToF-SIMS depth profile investigation

In order to minimize the out-diffusion of phosphorous provided during the poly silicon doping procedure, a possible solution is capping the poly Si with a film with a relatively low P diffusivity with respect to the one in the poly. In fact, P diffusion in poly is normally enhanced by inter granular diffusion that in general is higher than the one due to the Si lattice (bulk diffusion). The aim of this work was to analyze, by ToF-SIMS depth profiling, poly Si samples that have been previously P doped by implantation and than subsequently thermally exposed, with and without a Si oxide capping layer, in order to study the effectiveness of this barrier to prevent the P depletion. The work shows the potential of ToF-SIMS depth profiling in being an efficient vehicle for revealing the goodness of this oxide capping approach in microelectronic applications