Phosphorus-doped silicon nanocrystals (Si-NCs) embedded in a silicon nitride matrix were fabricated by post-annealing of silicon-rich silicon nitride (SRN) films deposited by electron cyclotron resonance chemical vapour deposition. The effects of phosphorus addition on the Si crystallization behaviour in SRN films were investigated. From the experimental results, the existence of phosphorus enhances phase separation in SRN and thus Si crystallization rate. As the phosphorus content increases, the Si-NC size increases under the same annealing conditions. The x-ray photoelectron spectroscopy P 2p signal attributed to Si-P or P-P bonds indicates that the phosphorus may exist inside Si-NCs. It was also found that the crystallization temperature decreases when phosphorus concentration is increased, and could be as low as 800°C.