Monolithic semiconductor mask programmable ROM and a method for manufacturing the same

Claim 1

A monolithic semiconductor mask programmable ROM conprising a matrix array of field effect transistors of insulated gate enhancement type, characterized in that the respective field effect transistors include a semiconductor substrate of one conductivity type, a plurality of strip-like source and drain diffusion regions formed at predetermined intervals in said substrate and having the opposite conductivity type, a plurality of strip-like electroconductive metal layers formed at predetermined intervals through a first relatively thick insulation layer on said substrate so as to intersect said source and drain diffusion regions, and a plurality of gate electrode foils, each gate electrode foil formed through a second insulation layer thinner than said first insulation layer on that portion of said substrate which is situated between the corresponding ones of said respective source and drain diffusion regions so that said gate electrode foil extends integrally with the corresponding one of said electroconductive metal layers with at least one side thereof spaced for a predetermined distance from one of said corresponding source and drain diffusion regions, wherein said field effect transistors are divided into first and second groups, the transistor of the first group being arranged at specific positions corresponding to the information written therein and the transistors of the second group being arranged at specific positions other than those occupied by the first field transistors, and each of said field effect transistors includes an ion implantated region formed beneath said second insulation layer between each gate electrode foil and at least one of the source and drain diffusion regions which are facing the gate electrode foil, the ion implantated regions of the first field effect transistors of the first group having the same conductivity type as said source and drain diffusion regions and the ion implantation regions of the field effect transistors of the second group having the conductivity type opposite to that of the source and drain diffusion regions.