Patent ID: 6927123

Claim:
A method for forming a self-aligned buried strap, comprising: providing a semiconductor substrate with a trench, wherein a capacitor wire is formed on the bottom portion of the trench, and a collar dielectric layer is formed between the capacitor wire and the semiconductor substrate to act as an isolation; forming a spacer on a sidewall of the upper portion of the trench; etching the capacitor wire and the collar dielectric layer to a predetermined depth on the same level using the spacer as an etching mask, thereby forming a gap between the spacer and the capacitor wire and the collar dielectric layer to expose a portion of the semiconductor substrate and a portion of the collar dielectric layer; doping ions into the exposed semiconductor substrate to form an ion doped area acting as a buried strap; removing the spacer; after doping ions etching the exposed collar dielectric layer below the level of the surface of the capacitor wire, thereby forming a groove between the capacitor wire and the trench sidewall; filling a conducting layer in the groove; and forming a trench top insulating layer over the trench bottom, wherein the trench top insulating layer is lower than the top surface of the ion doped area.