Two-step deposition of TiN capping electrodes to prevent degradation of ferroelectric properties in an in-situ crystallized TiN/Hf_0.5Zr_0.5O₂/TiN device

Abstract Hf0.5Zr0.5O2 (HZO) is an appropriate material for the back-end-of-line (BEOL) process in fabricating ferroelectric TiN/HZO/TiN devices because of its excellent conformality on 3D nanostructures and a suitable crystallization temperature (≥ 350 °C–400 °C). However, in the semiconductor industry, the deposition temperature of TiN is usually higher than 400 °C. Therefore, it is necessary to study the ferroelectric properties of TiN/HZO/TiN devices when the deposition temperature of the TiN top electrode is higher than the HZO film crystallization temperature. In this study, 10-nm-thick TiN top electrodes were deposited at various temperatures on the HZO thin film to investigate the impact of the TiN deposition temperature on the structural features and ferroelectric properties of TiN/HZO/TiN capacitors. Only the sample capped with a TiN top electrode deposited at 400 °C showed ferroelectric properties without subsequent annealing (in situ crystallization). However, this sample exhibited an approximately 40% reduction in the polarization value compared with the other samples that were crystallized after the annealing process. This behavior can be ascribed to the formation of a monoclinic nonpolar phase. To prevent the degradation of the polarization value and suppress the formation of the m-phase in the in situ crystallized HZO thin film, a two-step TiN deposition method was carried out. The sample was fabricated by depositing a 5-nm-thick TiN top electrode at room temperature followed by the deposition of a 5-nm-thick TiN layer at 400 °C, which resulted in strong ferroelectric properties comparable to those of the samples capped with TiN grown at relatively low temperatures (room temperature, 200 °C, and 300 °C). These findings can adequately explain the role of the capping layer in achieving the ferroelectric phase, which is closely related not only during the cooling step of any thermal process but also during the heating and crystallization steps.