Advances in semiconductor manufacturing technology have led to the integration of billions of circuit elements, such as transistors, on a single integrated circuit (IC). In order to integrate increasing numbers of circuit elements onto an integrated circuit it has been necessary to reduce the dimensions of the electronic devices (i.e., a metal-oxide-semiconductor (MOS) transistor).
This scaling down involves making all of the layers in the electronic devices as thin as possible. Silicon dioxide has been the preferred gate dielectric material; however, additional thinning of silicon dioxide compromises the performance and functionality of the electronic devices (e.g., lost function due to charge leakage). One practice has been to substitute the silicon dioxide layer with a higher permittivity gate dielectric since a high permittivity layer can be made thicker and still maintain a high capacitance characteristic. The materials used to form the high permittivity gate dielectric are referred to as high dielectric constant (high-k) dielectric materials.
Most high-k gate dielectric materials however, are not compatible with crystalline silicon or polycrystalline silicon (polysilicon) gate electrodes. In order to switch to the high-k gate dielectric, many manufacturers have replaced the conventional polysilicon gate electrode with a metal gate electrode.