A method for forming a trench capacitor includes providing a substrate of a semiconductor material having a hard mask layer; etching the hard mask layer and the substrate to form at least one trench extending into the substrate; and performing pull-back etching on the hard mask layer. In the pull-back etching, a portion of the hard mask layer defining and adjacent to side walls of an opening of the at least one trench is removed. A resulting opening on the hard mask layer has a width dimension larger than a width dimension of an opening of the at least one trench extending into the substrate. The method further comprises doping the semiconductor material defining upper surfaces and sidewalls of the at least one trench to form a doped well region.