Patent ID: 6962847

Claim:
A method for forming a self-aligned buried strap, comprising: providing a semiconductor substrate with a trench; conformably forming a collar dielectric layer in a trench bottom portion; filling a conducting layer in the trench bottom portion surrounded by the collar dielectric layer; etching the exposed collar dielectric layer below the level of the surface of the conducting layer, thereby forming a groove between the conducting layer and the trench; forming a thin nitride layer on the groove; filling a doped conducting layer in the groove; diffusing ions into the semiconductor substrate from the doped conducting layer to form a doped area acting as a buried strap; etching the conducting layer and the doped conducting layer below the level of the top surface of the doped area; and forming a trench top insulating layer on the bottom surface of the trench, wherein the trench top insulating layer is lower than the top of the doped area.