Comparative study on electrical and microstructural characteristics of ZrO2 and HfO2 grown by atomic layer deposition

Ultra-thin ZrO2 and HfO2 dielectric films grown by atomic layer deposition (ALD) are quite promising materials for gate dielectric applications in future transistors, and they exhibit significantly different as-grown microstructures: polycrystalline and amorphous phases, respectively. However, under the identical deposition conditions, both metal oxides show surprisingly similar capacitance-voltage (C-V) characteristics as a function of film thickness, implying that the identities and densities of fixed charge and bulk trapping charge are similar. Factors other than the film microstructure, such as concentration of impurities incorporated during the film deposition, are believed predominantly to control important C-V characteristics. Only the dielectric constant appears to depend significantly on the identity of the dielectric material. It is found that the dielectric constant of ALD-HfO2 (similar to 20) is significantly lower than that of ZrO2 (similar to 30) due to the differences in microstructure and also atomic density of the film. In terms of the leakage Current characteristics, the effective potential barrier heights between Pt and these two dielectric films are identical (similar to 2.3 eV) within the experimental uncertainty. Implications for the electrode/dielectric interface electronic structure are discussed.