A polycrystalline silicon oxidation method, which considerably improves the surface roughness at the oxide/polycrystalline silicon interface, is presented. The surface roughness at the interface is observed by transmission electron microscopy and is also evaluated by atomic force microscopy after the oxide layer is removed using buffered HF acid. The oxide/polycrystalline silicon interface by the new oxidation method with the 50 A˚ thick intermediate oxide has the rms surface roughness of 30 A˚, while that of the interface by the conventional method is 120 A˚. ©1995 American Institute of Physics.