| 摘要 |
PURPOSE:To obtain an NANDROM which can be operated at a high speed, by providing a thick insulating film under the gate electrode of an FET under the normally closed state, thereby making the capacity of the gate electrode small. CONSTITUTION:On a P type Si substrate 11, a field oxide film 12 and a gate oxide film 13 are provided, and poly Si 14 is laminated. High concentration P is implanted through a window 16 of an Si3N4 mask 15. Thereafter, wet oxidation is performed at a high temperature, and the entire poly Si 14 is transformed into SiO2. Then, the P breaks through the film 13, and an N layer is formed on the substrate 11. The mask 15 is removed, the poly Si 14 is removed, and an N layer 18 is formed in and under the SiO2 17. Then, by poly Si, a gate electrode 19 for a normally closed FET and a gate electrode 20 for a normally operating FET are provided. By P ion implantation and heat treatment, an N layer 21 and the gate electrodes are completed. At this time, owing to the heat treatment, the source and drain layer 21 and the layer 18 are shorted by the expansion of diffusion, and the normally closed FET is obtained. Then, the surface is coated by PSG and electrodes are provided. In this way, the NANDROM, which can be operated at a high speed is completed. |
