Phosphorus in the Polysilicon TiSi2 System: Dopant Redistribution

This work provides direct evidence of a significant reduction in the concentration of phosphorus in silicided polysilicon, due to post-TiSi2 formation at typical process temperatures (e.g BPSG deposition / densification). The phosphorus loss is a thermally activated process, with an activation energy of 1.26 eV, as evidenced by isochronal anneals in the temperature range 750 to 950°C. The reduction in the phosphorus concentration for given anneal conditions is shown to be proportional to the initial concentration in the polysilicon film. Comparison of chemical (SIMS) and electrically active phosphorus concentrations (from CV analysis) yields the percentage of active impurities for various process conditions. The relevance of these new findings to the performance of submicron MOSFETs (i.e., polysilicon depletion effects), and to the voltage linearity of integrated capacitors is discussed.