Fabricating a trench capacitor with an insulation collar in a substrate, which is electrically connected thereto on one side through a buried contact, in particular, for a semiconductor memory cell with a planar selection transistor in the substrate and connected through the buried contact, includes providing a trench using an opening in a hard mask, providing a capacitor dielectric in lower and central trench regions, the collar in central and upper trench regions, and a conductive filling at least as far as the insulation collar topside, completely filling the trench with a filling material, carrying out STI trench fabrication process, removing the filling material and sinking the filling to below the collar topside, forming an insulation region on one side above the collar; uncovering a connection region on a different side above the collar, and forming the buried contact by depositing and etching back a metallic filling.