Method of manufacturing flash memory device

According to yet another embodiment, a method for forming a non-volatile memory device includes etching a substrate to form first and second trenches. The first and second trenches are filled with an insulating material to form first and second isolation structures. A conductive layer is formed over the first and second isolation structures and between the first and second isolation structures to form a floating gate. The conductive layer and the first isolation structure are etched to form a third trench having an upper portion and a lower portion, the upper portion having vertical sidewalls and the lower portion having sloping sidewalls. The third trench is filled with a conductive material to form a control gate.