US Patent 11121135 Structure of memory device

A structure of memory cell includes a substrate. The substrate includes a first active region, a second active region and a first shallow trench isolation (STI) structure between the first active region and the second active region, wherein the first active region is lower than the second active region. A first contact structure is disposed on the first active region. A first stack structure is on the first contact structure. A second contact structure is on the substrate with a bottom portion in the substrate at an interface between the second active region and the first STI structure. A dielectric spacer is at least on a sidewall of the first contact structure. An insulating layer is disposed on the dielectric spacer and between the second contact structure and the first contact structure with the first stack structure, wherein a dielectric constant of the dielectric spacer is lower than a dielectric constant of the insulating layer.