Diffusion of phosphorus in silicon in an ambient of pure N-2, pure NH3, and mixtures of NH3 and N-2 has been investigated to study the effect of the oxynitridation reaction on the diffusivity. With a thin SiO2 layer on the silicon wafer and a low phosphorus concentration, the diffusion coefficient of phosphorus can be expressed as a function of the partial pressure of NH3 and temperature as D = 0.145 exp (-3.26 eV/kT) + 1.718 x 10(-6) exp (-1.72 eV/kT)p(NH3) cm(2) s(-1) At the same time, the ratio of the interstitial concentration under oxynitridation conditions to the concentration under inert conditions can be expressed as C-I/C-I* = 1 + 1.183 x 10(-5) exp (1.54 eV/kT)p(NH3) By using P diffusion as an interstitial monitor, the data (Ref. 1) of oxynitridatian-enhanced B diffusion are analyzed and the fraction of boron diffusion which occurs through the interstitial mechanism is calculated to be 0.88.