The early stages of diamond film nucleation and growth in a microwave plasma have been studied in detail as a function of important deposition parameters. The influence of the substrate temperature on the diamond nucleation rate, quality, and final film morphology has been elucidated through Raman spectroscopy and scanning electron microscopy measurements. Using transmission infrared spectroscopy and x‐ray diffraction, it is found that a carbide layer is initially formed on the substrate prior to the growth of the diamond film. Furthermore, the final film morphology is also a strong function of the plasma starting condition, the gas composition, and the substrate temperature.