We performed isotopic tracing of O, N, and H during rapid thermal growth of silicon oxynitride films on silicon in two different sequential, synergistic gas environments: O2, followed by NH3, then followed by N2O; and N2O, followed by NH3. Using nuclear reaction analysis and high resolution depth profiling, we demonstrate that the oxynitride films grow by means of thermally activated atomic transport involving the three traced species. Concomitantly, isotopic exchange processes take place. Growth in these sequential gas environments leads to oxynitride films with N concentration profiles and H concentrations different from those obtained by commonly used processes like thermal growth in N2O only or thermal nitridation of SiO2 films in NH3. © 1997 American Institute of Physics.