Point Defect (PD) mediated diffusion of phosphorous in silicon is studied in order to address the long standing open problem of PD-Dopant pair lifetime. A novel experimental method is suggested to increase PD-P pair lifetime for better observability and experimental resolution. In the experiment, phosphorous is implanted, followed by low temperature poly-Si deposition with in-situ doped phosphorous. The P profile shows, after low temperature (<650°C) in-situ phosphorous doped poly-Si deposition, an exponential dependence of two orders of magnitude for a significant depth scale. This indicates that the PD-P pairs survive long-range diffusion before dissociating in the Si lattice. As a result, the lifetime of PD-P pair was extracted and this provides a physical basis for TCAD simulation at the atomic scale.