Method of manufacturing a semiconductor device

A method of manufacturing a semiconductor device, which includes the steps of forming a gate stack structure made up of a floating gate, an inter-poly dielectric, a control gate and a metal layer on a substrate, forming a conformal liner on the gate stack structure, covering a mask layer on the liner, where the mask layer is lower than the metal layer so that a portion of the liner is exposed, and performing a nitridation treatment to transform the exposed liner into a nitrided liner, so that at least the portion of the metal layer in the gate stack structure is covered by the nitrided liner.