In this letter, we have demonstrated phosphorus diffusion into silicon at a temperature of 700 °C using dual spectral source rapid thermal processing (RTP). The optical energy of vacuum ultraviolet irradiation in conjunction with tungsten halogen lamps (light source used in conventional RTP) is responsible for diffusion at low temperatures. Shallow junctions with high surface concentration were formed and no significant degradation in the bulk minority carrier lifetimes was observed. A qualitative explanation for the observed results is offered based on the role of photoeffects in RTP. ©1997 American Institute of Physics.