PROBLEM TO BE SOLVED: To improve the property of silicon oxide and its interface at a low tempera ture in a simple heat treatment process.
SOLUTION: In the atmosphere containing steam or water, a heating process is performed at 150°C or higher and 600°C or bower under the condition of the pressure of the atmosphere of 2 or more atmospheric pressure and 200 atmospheric pressure. Thus, the property of silicon oxide and its interface is improved. At this time, the numerical density of the molecules of the water in suitable atmosphere is set at 2×1019 pieces/cm3 or more and 3.4×1022 pieces/cm3 or less. This method can be applied on the reformation of MOS-type transistors, the manufacture of electronic devices such as a solar bettery or the substrate of silicon oxide.