A method for forming an oxynitride gate dielectric layer (202, 204) begins by providing a semiconductor substrate (200). This semiconductor substrate is cleaned via process steps (10-28). Optional nitridation and oxidation are performed via steps (50 and 60) to form a thin interface layer (202). Bulk oxynitride gate deposition occurs via a step (70) to form a bulk gate dielectric material (204) having custom tailored oxygen and nitrogen profile and concentration. A step (10) is then utilized to in situ cap this bulk dielectric layer (204) with a polysilicon or amorphous silicon layer (208). The layer (208) ensures that the custom tailors oxygen and nitrogen profile and concentration of the underlying gate dielectric (204) is preserved even in the presence of subsequent wafer exposure to oxygen ambients.