Trench capacitor with an intrinsically balanced field across the dielectric

Abstract

The preferred embodiment of the present invention provides an improved capacitor design that overcomes many of the limitations of the prior art. The preferred embodiment of the present invention uses germanium to adjust the work function of the storage node. Specifically, the addition of germanium modifies the fermi level of the storage node, moving the fermi level towards the conduction band. This modification of the fermi level reduces the difference in conduction band-edge potentials between the storage node and the counter electrode, thus reducing the maximum electric potential seen across the capacitor. In the preferred embodiment, p-type doped silicon germanium is formed in the trench capacitor adjacent to the capacitor dielectric layer. A barrier layer is then formed over the doped silicon germanium, and the remaining storage node area is filled with n+-type polysilicon. The p-type doped silicon germanium adjusts the workfunction of the capacitor storage node, moving the fermi level toward the conduction band. This minimizes the maximum difference between conduction band-edge potentials of the storage node and the buried plate, which serves as the counter electrode. This has the effect of balancing the electric potential seen across the dielectric for stored high and stored low situations. This reduces the maximum electric potential seen across the capacitor dielectric. This solution improves the reliability of the capacitor, especially those capacitors with relatively thin dielectric layers, without requiring additional circuitry to bias the buried plate, and without increasing power consumption. The preferred embodiment also reduces leakage current through the capacitor dielectric, thus increasing signal retention time.

Dependencies are inferred from the claim text.