Direct Comparison of ZrO2 and HfO2 on Ge Substrate in Terms of the Realization of Ultrathin High-κ Gate Stacks

Direct comparison of ZrO2 and HfO2 on Ge substrates was performed in terms of the realization of an ultrathin gate stack with low leakage current. Changes in the interfacial layer thickness, film dielectric constant and leakage current upon postdeposition annealing were investigated. Considerable thinning of the interfacial layer due to interdiffusion with ZrO2 was observed after annealing. Moreover, the high dielectric constant of ZrO2 was retained even after Ge incorporation by interdiffusion. These phenomena resulted in a small capacitance equivalent thickness (CET) of 1.2 nm. On the other hand, the interfacial layer under the high-permittivity (high-κ) film remained almost the same for HfO2 on Ge stack, resulting in a relatively large CET of 1.6 nm. Together with the fact that the leakage current is lower for the ZrO2 stack than that for the HfO2 stack, ZrO2 is considered to be preferable to HfO2.