Mask ROM device having double polycrystalline silicone and process for producing the same

Claim 1

In a process for producing a mask ROM device having a NAND type memory cell and having a high integration double polycrystalline silicon the steps comprising: sequentially forming a pad oxide film and a nitride film on a first conductive type semiconductor substrate and then etching a predetermined region of the nitride film and ion-implanting first conductive type impurities into said substrate thereby forming an ion-implantation region; forming a field oxide film on said ion-implantation region, removing said nitride film and ion-implanting second conductive type impurities thereby forming a depletion type channel; removing the pad oxide film and forming sequentially a first gate oxide film, a first gate electrode substance, an oxide film, a nitride film and an LTO film on the substrate and the field oxide film; etching a predetermined region of said LTO film, nitride film and oxide film, thereby forming a first gate electrode and exposing the substrate; forming a second gate oxide film on said exposed substrate and LTO film and forming a spacer at the side surface of said first gate electrode; depositing a second gate electrode substance on the second gate oxide film, the spacer and the LTO film; sequentially etching said second gate electrode substance, LTO film, nitride film and oxide film on said LTO film thereby forming a second gate electrode; etching a part of a predetermined second gate electrode of said second gate electrode, depositing a photoresist and forming an opening for an ion-implantation into a selected memory cell; ion-implanting said first conductive type impurities into the selected memory cell thereby programming into a compensated enhancement type channel; and forming source and drain regions by ion-implanting said second conductive type impurities into the substrate to be formed source and drain regions, and then forming an insulating film on the whole surface of the second gate oxide film, the first gate electrode and the second gate electrode, and forming a connection opening on said second conductive type diffusion region, and forming a metal film for a bit line.