Process for coding and code marking read-only memory

摘要

A process for coding and code marking a read-only memory device makes use of a buffer layer, such as silicon nitrides (Si3N4) or silicon oxynitrides (SiNxOy), to form a code mark therein. Owing to the etching selectivity between the buffer layer and an underlying layer, for example, silicon oxides, the programmed region not covered by the word lines will not suffer from etching damage while forming the code mark. Therefore, the coding and code marking process can employ the same mask layer, but without the need for two different photomasking procedures to implement code programming and identification code marking.