The effect of N content on the structure and properties of rf reactively sputtered amorphous silicon nitride (a-SiNx) has been studied by Rutherford backscattering spectrometry, x-ray reflectivity, ellipsometry, and nano-indentation. The N content in the film increased with the N-2 concentration in the sputtering gas until the Si3N4 stoichiometry was reached. The hardness of a-SiNx increased with density, which in turn increased with the N content. The maximum hardness of 25 GPa and density of 3.2 g/cm(3) were attained at the stoichiometric Si3N4 composition. With the application of a protective overcoat for magnetic disks in mind, thin a - SiNx films were deposited on CoPtCr media to examine their coverage, pinhole density, and wear resistance. According to x-ray photoelectron spectroscopy, the minimum thickness of a - SiNx required to protect the CoPtCr alloy from oxidation was 10 Angstrom, which was 10 Angstrom thinner than that of the reference amorphous nitrogenated carbon (a - CNx). A statistic model showed this lower thickness required- for a - SiNx can be attributed to its high density, which corresponds to 93% bulk density of Si3N4 - Compared with 45 Angstrom a - CNx coated disks, 15 Angstrom a - SiNx coated disks had. lower pinhole defect density and superior wear resistance. (C) 2003 American Vacuum Society.