A trench capacitor for use in a semiconductor memory cell is formed in a
substrate and includes a trench having an upper region and a lower region.
An insulation collar is formed in the upper region of the trench. The
lower region of the trench extends through a buried well. A dielectric
layer, which is formed from tungsten oxide, serves as a capacitor
dielectric. A conductive trench filling, which is filled into the trench,
is formed from silicon or a tungsten-containing material such as tungsten,
tungsten silicide or tungsten nitride.