Amorphous silicon carbon nitrogen (SiCN) films deposited on stainless steel by radio frequency magnetron sputtering are annealed at different temperatures in hydrogen to investigate the phase transformation kinetics and the impact on film hardness. The SiCN films with polycrystalline structure are formed after annealing at 900 degrees C and the polycrystalline structures contain SiC, Si3N4, and CA phases. The polycrystalline transformation is discussed using a thermodynamics mechanism. Our results reveal that the emergence of homogeneous particle reinforced composite SiCN structure and polycrystalline phases related to SiC, Si3N4, and C3N4 may be responsible for the hardness enhancement of the annealed SiCN films. (c) 2007 American Vacuum Society.