The effect of the silicon thermal nitridation processes, nitridation of SiO2(oxynitridation), and direct nitridation of the silicon surface on boron and phosphorus diffusion is examined. It is found that oxynitridation results in enhanced diffusion of both impurities while direct nitridation of the silicon surface causes retarded diffusion for both. These phenomena are explained by the mechanisms of silicon self‐interstitial injection in the case of oxynitridation and self‐interstitial depletion in the case of direct nitridation.