Process for coding and code marking read-only memory

Claim 1

A process for coding and code marking a read-only memory device on a semiconductor substrate of a first conductivity type, comprising: (a) forming a code-marking layer on said semiconductor substrate to define an active region; (b) forming a plurality of spaced-apart and parallel bit lines of a second conductivity type in said substrate within said active region, a longitudinal direction of said bit lines being oriented along a first direction; (c) forming a dielectric layer covering said active region; (d) forming a plurality of spaced-apart and parallel word lines on said dielectric layer, said word lines having a longitudinal direction oriented along a second direction; (e) forming a buffer layer overlying an entire surface of said substrate; and (f) forming a mask layer with a designated pattern of said coding and said code marking of said read-only memory device on said buffer layer; (g) coding said memory device by implanting impurities of said first conductivity type into said substrate through the pattern of said mask layer; and (h) forming a code mark over said code-marking layer by etching said buffer layer using said mask layer as an etch mask.