Mask ROM and fabrication thereof

A method for fabricating a Mask ROM, comprising:

• forming a gate oxide layer on the substrate;
• forming a strip conductive structure on the gate oxide layer;
• forming a buried bit line in the substrate beside the strip conductive structure;
• patterning the strip conductive structure perpendicular to the buried bit line to form a plurality of gates;
• forming an insulator on the buried bit lines and between the gates;
• forming a coding layer and a word line thereon over the substrate perpendicular to the buried bit line, wherein the word line is formed over a gate and the insulator, and a portion of the coding layer between the gate and the word line constitutes a coding region of a memory cell;
• forming a coding mask over the substrate;
• and
• performing an implantation using the coding mask as a mask to dope the coding regions of selected memory cells, wherein after the implantation, the selected memory cells are in a logic state of 1 (or 0), and the other memory cells are in a logic state of 0 (or 1).