A thin silicon nitride layer is deposited at an ultra low deposition rate by PECVD by reducing the NH3 flow rate and/or reducing the SiH4 flow rate. Embodiments include depositing a thin layer of silicon nitride, e.g., 100 Å or less, on a thin silicon oxide liner over a gate electrode, at an NH3 flow rate of 100 to 800 sccm, a SiH4 flow rate of 50 to 100 sccm and a reduced pressure of 0.8 to 1.8 Torr. Embodiments of the present invention further include depositing the silicon nitride layer in multiple deposition stages, e.g., depositing the silicon nitride layer in five deposition stages of 20 Å each.