Buried strap formation in a DRAM trench capacitor

A DRAM cell of a type including a trench storage capacitor having a trench formed in a substrate of semiconducting material having a dopant which causes said semiconducting material to be of a first conductivity, said trench being firstly lined with a second semiconducting material having a dopant which causes said second semiconducting material to be of a second conductivity, said dopant of said second conductivity also being partially diffused into said substrate, said trench being secondly lined with a layer of dielectric material and filled with a polysilicon material having a dopant which causes said polysilicon material to be of one of said first and second conductivities, and said trench being recess etched, lined with an oxide collar, and refilled with said polysilicon material which may be either doped or undoped;

• an access transistor formed on said substrate;
• and an electrically conductive region in said substrate, which connects said trench storage capacitor to said access transistor;
• the improvement therewith comprising:
• a layer of single crystalline semiconducting material disposed in said trench wherein said single crystalline semiconducting material selectively controls the size of said electrically conductive region by limiting the outdiffusion of said dopant through said single crystalline semiconducting material during the formation of said access transistor.