Non-volatile memory device used for non-overlapping implant and device fabricating method

A method of fabricating a ROM device on a semiconductor substrate with a plurality of parallel buried bit lines, said buried bit lines being oriented in a first direction, a gate oxide layer above the substrate and word lines formed above said gate oxide layer, said word lines being oriented in a second direction, which comprises the steps of:

• forming a dielectric layer over said word lines and said gate oxide layer;
• forming a first photoresist layer over said dielectric layer;
• selectively exposing said first photoresist layer to develop a first opening area over said photoresist layer, said first opening area centered between said adjacent bit lines;
• etching said dielectric layer through said first opening area;
• stripping said first photoresist layer;
• forming a second photoresist layer over said dielectric layer;
• selectively exposing said second photoresist layer to develop a second opening area over said second photoresist layer to define a pattern of code ion implantation;
• ion implanting a code implant dopant through said second opening area down into said substrate;
• and
• stripping said second photoresist layer.