Method of fabricating a mask ROM with raised bit-line on each buried bit-line

A method of fabricating a mask ROM, comprising the steps of:

• forming sequentially a gate dielectric layer, a first conductive layer, and a cap layer on a substrate;
• patterning the cap layer and the first conductive layer to form a plurality of conductive strips with the cap layer formed thereon;
• forming a plurality of lightly doped regions in the substrate between the conductive strips;
• forming a first spacer and a second spacer on the side-walls of each conductive strip, while the substrate under the first spacer is taken as a first coding region and the substrate under the second spacer is taken as a second coding region;
• forming a plurality of buried bit-lines in the substrate between the conductive strips, wherein the buried bit-lines have a conductivity type different from that of the lightly doped regions;
• forming a first coding mask over the substrate, then performing a first tilt coding implantation to dope a part of the first coding regions;
• removing the first coding mask;
• forming a second coding mask over the substrate, then performing a second tilt coding implantation to dope a part of the second coding regions;
• removing the second coding mask;
• forming a raised bit-line on each buried bit-line;
• forming a dielectric layer on each raised bit-line;
• removing the cap layer;
• forming a second conductive layer over the substrate;
• and
• patterning the second conductive layer and the conductive strips successively to form a plurality of word-lines and a plurality of gates, respectively.

A method of fabricating a mask ROM, comprising the steps of:

• forming a plurality of conductive strips on a substrate, wherein each conductive strip is formed with a cap layer on it;
• forming a plurality of buried bit-lines in the substrate between the conductive strips, wherein each bit-line is apart from any of two adjacent conductive strips by a distance and two regions of the substrate between one buried bit-line and the two adjacent conductive strips are a first and a second coding regions, respectively,
• forming a first coding mask over the substrate, then performing a first tilt coding implantation to dope a part of the first coding regions;
• removing the first coding mask;
• forming a second coding mask over the substrate, then performing a second tilt coding implantation to dope a part of the second coding regions;
• removing the second coding mask;
• removing the cap layer;
• forming a conductive layer over the substrate;
• and
• patterning the conductive layer and the conductive strips successively to form a plurality of word-lines and a plurality of gates, respectively.