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NdFeAsO films have been grown by a two-step method. First, precursor films that contain a mixture of Nd and Fe oxides were grown by metal–organic chemical vapor deposition. Afterward, the arsenic is incorporated during annealing of these precursor films in the presence of a \NdFeAsO0.75 \F0.25 pellet. The X-ray diffraction and the scanning electron microscopy show that the formation of the quaternary NdFeAsO phase is prevented by the stability of the rare-earth oxides and rare-earth oxyfluorides and that it is synthesized only if the annealing temperature is higher than 1050 ^\circ\C. Although the pellet creates a reaction atmosphere to synthesize the superconducting phase, the fluorine is not incorporated into the quaternary NdFeAsO phase. [ABSTRACT FROM PUBLISHER]