Abstract: A trench capacitor is formed in a substrate and includes a trench having an upper region and a lower region. An insulating collar is formed in the upper region of the trench. The lower region of the trench extends through a buried well. A buried plate is formed around the lower region of the trench as an outer capacitor electrode. A dielectric layer, which forms the capacitor dielectric, lines the lower region of the trench and the insulating collar. A conductive trench filling is put into the trench. A conductive contact layer of tungsten nitride is provided above the insulating collar, between the substrate and the conductive trench filling, and acts as a diffusion barrier. This makes it possible to provide the trench capacitor more closely to the transistor, since the transistor is not damaged by material which is contained in the conductive trench filling.