| 摘要 |
PURPOSE:To obtain the final field oxide films, and at the same time, to form the gate oxide films thicken only at the depletion D type transistor part and to reduce the capacities of the polycrystalline Si wirings by a method wherein the selective oxidation to be performed on the field regions is performed being divided into two stages. CONSTITUTION:An SiO2 film (pad oxide film) 2 and an Si3N4 film (nitride film) 3 are superposed on an Si substrate 1, a patterning is performed and selective oxide films 4 are formed. A resist mask 5 is provided, parts of the Si3N4 film 3 are etched away and B ions are implanted. The films 7 of the depletion type transistor are selectively formed. The film 3 and parts of the film 2 are etched away and a gate oxidation is performed. After ions for the control of the Vth of the enhancement type transistor are implanted, the wirings of polycrystalline Si films 8 are provided. After that, the device is completed through a process, wherein P<+> layers (source and drain regions) and the polycrystalline Si films 8 are turned into conductive layers, and the forming process for SiO2 films (oxide films) 10 and a PSG film (interlayer insulating film) 11. By this constitution, the gate oxide films only at the D type transistor part can be formed thicker and the capacities of the polycrystalline Si wirings to affect the mempry readout speed can be made smaller. |
