The present invention provides a fabrication method for a trench capacitor with an insulation collar in a substrate, which is electrically connected to the substrate on one side via a buried contact. After forming and sinking an electrically conductive filling, an insulation collar and, if appropriate, a buried contact that is connected on all sides, the following are effected: providing at least one liner layer in the trench; filling the trench with a filling made of an auxiliary material, which filling is encapsulated by the at least one liner layer in the trench; providing a mask on the filling for defining the structure of the buried contact, the mask having no projections into the trench; removing a part of the filling using the mask; removing an underlying part of the at least one liner layer for uncovering a corresponding part of the insulation collar.