MIM in 3D: dream or reality?

Last decades great effort has been put in the development of 3D capacitors. These capacitors are used for RF decoupling and should therefore have a high capacitance density associated with a sufficient breakdown voltage. Increased capacitance densities have been achieved by exploring the use of the third dimension in silicon, e.g. pores and trenches and considering dielectric layers with a higher dielectric permittivity, so-called higher k dielectrics formed by alternative deposition techniques, e.g. Atomic Layer Deposition (ALD). Starting with the formation of wide pores using the "Bosch" process, we eventually developed high aspect ratio macropore arrays that have been used as the carrier substrate for the capacitors. These arrays have been filled by conventional LPCVD MOS layers with ONO-dielectrics and in situ doped polycrystalline silicon, initially as single layer stack, but also as a double stack capacitor (MOSOS/MIMIM). Further, higher k materials, such as Al ₂O₃, Ta₂O₅, HfO₂ and even rare earth materials with nanoclusters have been considered in our attempt to achieve ultimate capacitance densities. Our current record capacitance density has been realized using a multiple capacitor structure with ALD electrodes and high k dielectric layers, the so-called MIMIMIM capacitor.