Pinholes in a silicon oxynitride film are reduced by PECVD deposition of a plurality of silicon oxynitride sub-layers in a PECVD apparatus containing multiple chambers. Embodiments include forming a layer of amorphous carbon over a conductive layer, such as doped polycrystalline silicon, on a substrate, transferring the substrate to a multi-chamber PECVD tool and depositing 2 to 7, e.g., 5, sub-layers of dense silicon oxynitride at a total thickness of 300 to 700 .