| 摘要 |
PURPOSE:To completely remove the residues of a by-product existing in the vicinity of the surface of the silicon substrate and to improve the dielectric withstand voltage of the gate film by a method wherein, when the PAD oxide film is removed with an HF etchant, an overetching is performed. CONSTITUTION:A silicon nitriding oxide film 2 is formed in advance on the prescribed region on a silicon substrate 7 of a semiconductor device through a PAD oxide film 4 and a silicon nitriding film 3. A selective oxidation is performed only on the parts not being covered with this film 2 and selective oxide region 1 are formed. When the PAD oxide film 4 just under this film 2 is removed, an overetching is performed using an HF etchant and selective oxide films 5 are formed on the substrate 7 under the regions 1. The HF etchant is set as HF:NH4F=1:5, the residues of a nitride (by-product) 6 existing in the vicinity of the surface of the substrate 7 are completely removed and the dielectric withstand voltage of a gate oxide film is improved.
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