Comparative study on electrical and microstructural characteristics of ZrO_2 and HfO_2 grown by atomic layer deposition

摘要

Ultra-thin ZrO_2 and HfO_2 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: poly crystalline 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-HfO_2 (~20) is significantly lower than that of ZrO_2 (~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 (~2.3 eV) within the experimental uncertainty. Implications for the electrode/dielectric interface electronic structure are discussed.