Doping properties of the solid-phase diffusion method (SPD) for an ultra-shallow junction formation was investigated. Phosphorous doped silicon oxide films was used as the SPD source for the fabrication of sub-100nm SOI MOSFET. It was found that diffusion depth of the phosphorous could be controlled to be below 40 nm with temperatures lower than 925° C. The results shows that the SPD method is superior to the plasma doping method to form damage-free ultra-shallow junctions.