Preventing gate oxice thinning effect in a recess LOCOS process

Embodiments of the present invention relate to a method for preventing gate oxide thinning in a recess LOCOS process. The plurality of trenches are separated by a patterned pad oxide and a patterned silicon nitride layer The patterned silicon nitride layer and the patterned pad oxide layer are removed to expose a surface of the substrate as an active area of the semiconductor device. An ion drive-in to the active area on the substrate is performed by directing a flow of oxygen and nitrogen toward the substrate at a predetermined temperature and with a sufficient amount of oxygen to at least substantially prevent silicon nitride from forming on the field oxide regions. The method further comprises forming a sacrificial oxide layer on the active area, removing the sacrificial oxide layer to expose the active area, and forming a gate oxide layer on the active area.