A DYNAMIC RANDOM ACCESS MEMORY DEVICE HAVING A SINGLE-CRYSTAL TRANSISTOR ON A TRENCH CAPACITOR STRUCTURE AND A FABRICATION METHOD THEREFOR

摘要

Dynamic random access memory (DRAM) devices are taught wherein individual cells, including an access transistor and a storage capacitor are formed on a single-crystal semiconductor chip, and more particularly a three-dimensional dynamic random access memory (DRAM) device structure is described having a single-crystal access transistor stacked on top of a trench capacitor and a fabrication method therefor wherein crystallization seeds are provided by the single-crystal semiconductor area surrounding the cell and/or from the vertical sidewalls of the trench and wherein the access transistor is isolated by insulator. In the structure, a trench is located in a p+ type substrate containing heavily doped N+ polysilicon. A composite film of SiO2/Si3N4/SiO2 is provided for the capacitor storage insulator. A thin layer of SiO2 is disposed over the polysilicon. A lightly doped p-type epi silicon layer is located over the substrate and SiO2 layer. The access transistor for the memory cell is located on top of the trench capacitor. An N+ doped material connects the source region of the transistor to the polysilicon inside the trench. A medium doped p-region on top of the trench surface may be provided in case there is any significant amount of leakage current along the trench surface.