| 摘要 |
PURPOSE:To obtain an LDD type field effect transistor, whose reliability is improved, by using an isotropic etching method in forming masks and a gate electrode, which are used for forming source and drain regions having high and low impurity concentrations. CONSTITUTION:After a field oxide film 2 is formed on the surface of a silicon substrate 1, a gate oxide film 3 is formed. Then a first mask 5 for forming a gate electrode is formed. Pt ions are implanted as impurities. Then the first mask 5 is removed, and a second mask 6 is formed at the position of the mask 5. A gate electrode 4B comprising a tungsten alloy layer 4A is formed beneath the mask 6 by etching. Then boron is implanted, and P<+> type source and drain regions 7 are formed in an active region. After the second mask 6 is removed, boron ions having low concentration are implanted again, and P<-> type source and drain regions 7A are formed. Thus the source and drain regions having an LDD structure is formed.
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