Macroscopic and microscopic electrical characterizations of high-$k$ $ZrO2$ and $ZrO2/Al2O3/ZrO2$ metal-insulator-metal structures

In order for sub-10 nm thin films of $ZrO2$ to have a dielectric constant larger than 30 they need to be crystalline. This is done by either depositing the layer at higher temperatures or by a postdeposition annealing step. Both methods induce high leakage currents in $ZrO2$ based dielectrics. In order to understand the leakage a thickness series of ultrathin $ZrO2$ and nanolaminate $ZrO2/Al2O3/ZrO2$ (ZAZ) films, deposited by atomic layer deposition, was investigated. After deposition these films were subjected to different rapid thermal annealing (RTA) processes. Grazing incidence x-ray diffraction and transmission electron microscopy yield that the crystallization of $ZrO2$ during deposition is dependent on film thickness and on the presence of an $Al2O3$ sublayer. Moreover, the incorporation of $Al2O3$ prevents crystallites from spanning across the entire film during RTA. $C-V$ and $I-V$ spectroscopies show that after a $650°C$ RTA in $N2$ the capacitance equivalent oxide thickness of 10 nm ZAZ films is reduced to 1.0 nm while maintaining low leakage currents of $3.2×10−8A/cm2$ at 1 V. Conductive atomic force microscopy studies yield that currents are not associated with significant morphological features in amorphous layers. However, after crystallization, the currents at crystallite grain boundaries are increased in $ZrO2$ and ZAZ films.