Phosphorus terminated polystyrene polymers with molar mass ranging from 2 to 25 kg/mol and narrow molar mass distribution were synthesized by Atom Transfer Radical Polymerization (ATRP) followed by phosphorylation reaction. Polymers were grafted onto a native silicon oxide surfaces of a silicon wafers by Rapid Thermal Processing (RTP). The self-limiting nature of the grafting to reaction provides an accurate control of the surface density of P atoms as a function of the molar mass of the polymer grafted. After removing the polymeric part of the grafted layer with by O2 plasma hashing, the phosphorus diffusion in the silicon substrate was promoted by high temperature thermal treatments.