Stabilized formation of tetragonal ZrO2 thin film with high permittivity

We have investigated the effect of the film thickness and lattice spacing of Zr oxides on the crystalline structures of Zr oxide films formed by atomic layer deposition (ALD) and sputtering methods to achieve higher-k tetragonal ZrO2 (t-ZrO2) films. In the ALD case, the t-ZrO2 crystalline structure stably formed over a wide range of film thicknesses (8 to 130 nm). The Zr oxide films with a t-ZrO2 structure prepared by ALD and post-deposition annealing at 350 °C achieved a relative permittivity of 35 ± 2. On the other hand, the ratio of the t-ZrO2 phase to the monoclinic (m-) ZrO2 phase decreases with increasing thickness of the Zr oxide film formed by sputtering, although it can be increased by Ge incorporation. Focusing on the relationship between the lattice spacing and the crystalline phase of Zr oxide, the t-ZrO2 crystalline structures are stably formed with decreasing lattice spacing of the t-ZrO2 crystalline structure. The effect of the lattice spacing on the t-ZrO2 crystalline structure formation is suitably explained in terms of the bulk (volume) energy of the t-ZrO2 phase.