eDRAM and method for making same

A method for making an embedded dynamic random-access memory (eDRAM), comprising:

• forming a stack of a pad oxide layer and a pad nitride layer above a surface of a substrate;
• forming, in the substrate, at least one active area extending in a first direction and at least one deep trench filled with polysilicon, wherein each deep trench partitions the active area into a first active sub-region and a second active sub-region at opposite sides of the deep trench, wherein the polysilicon in an upper portion of the deep trench is joined to the first active sub-region and the second active sub-region, and wherein the polysilicon has a top surface lower than a top surface of the active area;
• removing the pad nitride layer and the pad oxide layer;
• forming a stack of a re-deposited oxide layer and a re-deposited nitride layer above the substrate;
• etching the second active sub-region and the polysilicon joined to the second active sub-region, thereby forming an isolation recess at a first side of the deep trench opposite to the first active sub-region;
• pulling back the re-deposited nitride layer and the re-deposited oxide layer in the first direction, thereby forming a recess extension on a top of the isolation recess, wherein the recess extension exposes the top surface of the polysilicon and a portion of a top surface of the first active sub-region;
• filling an isolation dielectric into the isolation recess and the recess extension, wherein the isolation dielectric covers the exposed top surfaces of the first active sub-region and the polysilicon;
• and
• forming at least one word line above the substrate, wherein the word line extends in a second direction and crosses over the isolation dielectric.