The influence of nitrogen on the growth of diamond using the gas mixtures of CH4–CO2by microwave plasma chemical vapor deposition was investigated. A clear improvement in the surface morphology and quality of the diamond films indicates the beneficial effect of adding nitrogen to CH4–COgas mixtures. Analysis using Auger electron spectroscopy and secondary ion mass spectroscopy shows very low and uniform levels of nitrogen in the diamond films. Atomic nitrogen plays a dominant role in C/H/O/N plasma chemical vapor deposition processes because of the amount of oxygen atoms increased via the titration reaction of nitrogen atoms (a high‐rate reaction): N+NO→N2+O. This produces a significant influence on diamond synthesis in a CH4–CO2–N2gas mixture. ©1995 American Institute of Physics.