Method of fabricating self-aligned multilevel mask ROM

摘要

A method of fabricating self-aligned multilevel mask read only memory (ROM). The method can improve the process window to reduce process difficulty by utilizing the self-aligned implantation. Moreover, by utilizing the height difference between different gate polysilicon layers and implantation of the ROM code with self-aligned implatiation to increase the difference between the threshold voltages of different gates, and therefore, multilevel cell transistors with for the mask ROM with multilevel threshold voltages are formed to times the capacity of the mask ROM.