In this letter, we report on the reaction between Si andN2in the temperature range of 760–1050 °C, in a rapid thermal processing chamber. Gas phase impurities such asH2O,O2,andH2,which can outgas from the cold walls of the chamber, mediate theSi/N2reaction, resulting in the formation ofSiOxNy.The oxynitridation can be explained by equilibrium chemical thermodynamics, in contrast to the case of oxynitridation usingN2Oor NO, where the nitrogen is incorporated under nonequilibrium conditions. Using nuclear reaction analysis, we have measured nitrogen contents as high as2.5×1015 N/cm2(the equivalent of more than 3 monolayers) in these new dielectrics. They can be reoxidized to form ultrathin (2 to 3 nm) dielectrics. ©1997 American Institute of Physics.