| 摘要 |
PURPOSE:To prevent an impurity from being diffused to the outside during a heat-treatment process or an oxidation process by a method wherein, prior to a process to remove an oxide film, polycrystalline silicon is applied to both faces of a P/P<+> type silicon substrate and the oxide film is wet-etched. CONSTITUTION:An N-type well 3 is formed by using a P/P<+> type silicon substrate; polycrystalline silicon 5a, 5b with 1000-3000 Angstrom are applied to insulating films on both faces of the substrate by a low-pressure CVD method. Then, the polycrystalline silicon 5a is removed by using a parallel-plate type dry etcher. During this process, the P/P<+> type silicon substrate is placed on a target with only its surface exposed to a plasma. An etchant cannot creep to the rear. Accordingly, the polycrystalline silicon 5b on the rear is not removed and only the surface is etched. Then, only an oxide film 4a on the surface is removed by using a mixed solution of hydrofluoric acid and ammonium fluoride. Because an oxide film 4b on the rear is covered with the polycrystalline silicon 5b, it is not removed.
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