In this work, we study the characteristics of plasma oxynitrided Hf and Zr thin films. A 5-nm-thick Hf or Zr metal film is deposited on the bare Si substrate, followed by plasma oxynitridation on these metal films in a N2O or NH3 ambient. Incorporation of O and N leads to the formation of HfOxNy and ZrOxNy films. The high nitrogen content in the HfOxNy films prepared by NH3 plasma oxynitridation is found to increase the onset of the crystallization temperature, as compared to films prepared by N2O plasma oxynitridation. Nevertheless, the difference in crystallization temperature is not seen for ZrOxNy films. The interlayer (IL) between HfOxNy (or ZrOxNy)and Si is found to be thinner for the films with NH3 plasma oxynitridation than those with N2O plasma oxynitridation. However, the nitrogen incorporated by plasma oxynitridation appears to be depleted after rapid thermal oxidation annealing and is not effective to inhibit the growth of the IL. The activation energy of the IL growth for N2O and NH3 oxynitrided HfOxNy is 0.23 and 0.13 eV, respectively. The activation energy of the IL growth for N2O and NH3 oxynitrided ZrOxNy is 0.19 and 0.14 eV, respectively. (c) 2005 The Electrochemical Society.