| 摘要 |
PURPOSE:To simplify floating gate forming processes, when a gate having a double-layer structure comprising a floating gate and a control gate is formed and an ultravoilet-ray erasing type ROM is formed, by depositing a polycrystalline Si layer on a gate-electrode forming region, implanting O<+> ions in the intermediate position in the thickness direction, and then converting the part into SiO2 by heat treatment. CONSTITUTION:A thick field oxide film 2 is formed on the peripheral part of a P type Si substrate 1. A thin gate oxide film 3 is deposited on the surface of the substrate surrounded by the film 2. Then, a polycrystalline Si layer 4 is deposited on the entire surface. A resist film 6, which is to become a mask, is provided on the film 2. O<+> ions are implanted through a hole. An O<+>-ion implanted layer 7 is formed at the intermediate part in the thickness direction of the layer 4. Thereafter, the film 6 is converted into a resist film 8, which has a hole corresponding to the peripheral part of the layer 7. O<+> ions are implanted again, and an implanted layer 9A yielded at the side surface is connected to the layer 7. In this way, the Si film 4 is divided ingot two parts and heat-treated in N2. The layers 9A and 7 are converted into SiO2. Thus a control gate and a floating gate are yielded on the upper and lower sides. |
