A method for manufacturing a trench capacitor that comprises defining a semiconductor substrate, forming a trench with a lower region and an upper region in the semiconductor substrate, forming a buried conductive region around the lower region, forming a first insulating layer along sidewalls of the trench up to a level between the lower region and the upper region, forming a second insulating layer along the sidewalls of the trench at the upper region, the second insulating layer being separated from the first insulating layer by an intermediate region, and forming an oxide on the sidewalls of the trench at the intermediate region.