ROM FOR CONSTRAINING 2nd-BIT EFFECT

A read only memory comprising:

• a substrate;
• a source region and a drain region, disposed in the substrate;
• a charge storage structure, located on the substrate between the source region and the drain region;
• a gate, configured on the charge storage structure;
• and
• a local extreme doping region, located in the substrate between the source region and the drain region, the local extreme doping region comprising:
• a low doping concentration region;
• and
• at least one high doping concentration region, disposed between the low doping concentration region and one of the source region and the rain region, wherein
• a doping concentration of the at least one high doping concentration region is three times or more than three times a doping concentration of the low doping concentration region,
• wherein the low doping concentration region is at least located at a center region of the local extreme doping region, and the least one high doping concentration region is located at an edge region of the local extreme doping region.