Abstract: In a method for forming an interlayer dielectric (ILD) coating on microcircuit interconnect lines of a substrate, the substrate and interconnect lines are annealed prior to deposition of an ILD. A post annealing SiON layer is formed by using plasma-enhanced chemical vapor deposition. The deposition using a plasma formed of nitrogen, nitrous oxide, and silane gases, with the gases being dispensed at regulated flow rates and being energized by a radio frequency power source. The plasma reacts to form SiON which is deposited on a semiconductor substrate. Additionally, during deposition, minor adjustments are made to deposition temperature and process pressure to control the optical characteristics of the SiON layer. The SiON layer is tested for acceptable optical properties and acceptable SiON layers are coated with a SiO2 layer to complete formation of the ILD. Once the ILD is formed the substrate is in readiness for further processing.