A system and method is disclosed that prevents the formation of a vertical bird's beak structure in the manufacture of a semiconductor device. A polysilicon filled trench is formed in a substrate of the semiconductor device. One or more composite layers are then applied over the trench and the substrate. A mask and etch process is then applied to etch the composite layers adjacent to the polysilicon filled trench. A field oxide process is applied to form field oxide portions in the substrate adjacent to the trench. Because no field oxide is placed over the trench there is no formation of a vertical bird's beak structure. A gate oxide layer is applied and a protection cap is formed over the polysilicon filled trench to protect the trench from unwanted effects of subsequent processing steps.