| 摘要 |
PURPOSE:To improve the quality of an oxide film between a floating gate electrode and a control electrode and improve the device characteristics by a method wherein the oxide film is produced by thermal oxidation in an oxygen atmosphere at a specific high temperature and, during the temperature rise period and the temperature drop period of the oxidizing process, the wafer is kept in a nitrogen atmosphere which contains at least oxygen. CONSTITUTION:The initial temperature T1 of an oxidizing furnace is about 700 deg.C-900 deg.C. Then a wafer is further heated and the temperature is elevated to an oxidization temperature T2. During the temperature rise period, the wafer is kept in a nitride atmosphere which contains at least oxygen in order to avoid nitriding phenomenon or the like specifically. The temperature T2 is limited between 1100 deg.C and 1150 deg.C which is higher than 950 deg.C, the oxidization temperature of the conventional method. By the temperature control like this, memory maintaining characteristics, a dielectric strength and so forth can be improved. From the time t3 to the time t4, the wafer is kept in an oxygen atmosphere. From time t4 to the time t5, which is the temperature drop period, the wafer is again kept in a nitrogen atmosphere which contains a little oxygen.
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