Method for forming a buried strap by controlled recrystallisation, in a semiconductor memory device, and semiconductor memory device thereby formed

摘要

Forming a coupled capacitor and transistor comprises: (a) forming a trench in a semiconductor substrate; (b) forming an impurity-doped first conductive region by filling the trench with an impurity-doped first conductive material; (c) back etching the impurity-doped first conductive region to a first level within the trench; (d) forming an insulating layer on a side wall of the portion of the trench opened by the back etching; (e) forming a second conductive region by filling the remainder of the trench with a second conductive material; (f) back etching the insulating layer and the second conductive material to a second level within the trench; (g) forming an undoped amorphous Si layer in the portion of the trench opened by the etching back of the insulating layer and the second conductive region; (h) back etching the undoped amorphous Si layer to a third level within the trench; (i) recrystallising the amorphous Si layer; (j) diffusing out impurities from the impurity-doped first conductive region to the semiconductor substrate through the recrystallised Si layer; (k) forming a source/drain region of the transistor adjacent to an intersection of the trench and the surface of the substrate, the diffused out impurities and the recrystallised Si layer constituting a buried strap for electrically connecting the first and second conductive layers in the trench to the source/drain region.