Effects of film thickness and annealing temperature on the properties of molybdenum carbide films prepared using pulsed direct-current magnetron sputtering

Molybdenum carbide (Mo2C) films were prepared using pulsed direct-current (DC) magnetron sputtering. The effects of film thickness on the phase structure, surface morphology, and optical constants of the films were examined using X-ray diffraction (XRD), atomic force microscopy, and extreme ultraviolet reflectivity. XRD analysis showed that the as-sputtered films with thicknesses between 30 nm and 150 nm were almost amorphous. New phase alpha-MoC1-x with the (111), (200), (220), (311), and (222) crystal planes appeared in films with thicknesses between 200 nm and 400 nm. The phase transition and chemical composition of the Mo2C films treated using vacuum heat treatment were analyzed in detail. For 150 nm-thick films, the as-deposited as well as the 600 degrees C-annealed films were amorphous. The phase structures of the 150 nm-thick film annealed at 700 degrees C, 750 degrees C, and 800 degrees C were orthogonal Mo2C (alpha-Mo2C), multiphase structure (beta-Mo2C, monoclinic MoO2, and cubic Mo2N), and monoclinic MoO2, respectively. X-ray photoelectron spectrometry revealed that the Mo-Mo bonds of the films transformed into Mo-C, Mo-O, and Mo-N bonds under 750 celcius-annealing, further confirming the formation of a multiphase structure after annealing. Thus, film thickness and annealing temperature considerably influence the properties of Mo2C films.