Mask ROM structure and manufacturing method thereof

A method of manufacturing a mask read-only-memory (ROM), comprising the steps of:

• providing a substrate;
• forming a first dielectric layer, a stopping layer and a second dielectric layer over the substrate to form a stack layer;
• forming a buried bit line in the substrate outside the stack-covered region;
• forming a first photoresist layer over the substrate, wherein the first photoresist layer includes a first line/distance pattern;
• removing the second dielectric layer and the stopping layer to expose the first dielectric layer using the first photoresist layer as a mask;
• removing the first photoresist layer;
• forming a second photoresist layer over the substrate, wherein the second photoresist layer includes a second line/distance pattern, and the second line/distance pattern extends in a direction that differs from the direction of extension of the first line/distance pattern;
• removing a portion of the second dielectric layer and the first dielectric layer to expose the substrate and the stopping layer using the second photoresist layer and the stopping layer as an etching mask;
• forming a gate oxide layer over the exposed substrate;
• and
• forming a word line perpendicular to the direction of extension of the buried bit line to construct a plurality of coding cells, wherein the coding cells having a stack layer thereon are at a first logic state while the coding cells having a gate oxide layer thereon are at a second logic state.