Abstract: An insulation region, for example, an oxide collar, is formed in a trench structure for a DRAM as simply as possible by first widening a first trench region of the trench that is to be formed, in particular, a base region thereof, and then providing at least part of the widened region with a material region for the insulation region.

Abstract: A method for fabricating a trench capacitor, that includes steps of: providing a silicon substrate; forming a trench, having a lower region and a surface, in the silicon substrate; and forming a doped layer in the silicon substrate in the lower region of the trench. In addition, a roughened silicon layer that has silicon grains with a diameter ranging from essentially 10 to 100 nm is produced in the lower region of the trench. A dielectric intermediate layer is applied on the roughened silicon layer, and the trench is filled with a doped layer.