Abstract: The present invention provides the method of manufacturing a dual-gate CMOS device which has high transconductance and improved breakdown voltage, in which depletion in the interface between a gate oxide and a gate electrode is prevented without the increase of the steps of process.A gate oxide film (5) formed on a semiconductor substrate (1) is washed with an aqueous solution, or exposed to a gas atomosphere containing hydrogen, and an amorphous silicon film (3) is formed on the whole surface of the gate oxide film (5). The amorphous silicon film (3) is then crystallized. Alternatively, after a silicon oxide film (53) or a silicon nitrided film is formed on the amorphous silicon film (3), the amorhpous silicon film (3) is crystallized.

Abstract: A semiconductor wafer is placed in a reaction chamber and a cleaning gas is introduced into the reaction chamber. Then, the cleaning gas is excited by irradiation with light rays or heating to produce reactive radicals and a natural oxide film formed on the semiconductor wafer is first removed by the reactive radicals to expose a raw semiconductor wafer surface and then the exposed raw wafer surface is etched by the reactive radicals. Since the natural oxide film is first removed, the exposed raw surface of semiconductor wafer can be etched uniformly over the whole surface, and therefore the highly flat and perfectly crystalline surface can be obtained. It is preferable to introduce a chlorine fluoride series gas such as chlorine trifluoride gas in the cleaning gas. Then, the natural oxide film can be effectively removed by hydrogen fluorine radicals which are produced by irradiating the chloride fluoride series gas with ultraviolet rays.