How to play on the fabrication process of HfZrO2 ferroelectric thin film to enhance its physical properties

International audience; Various applications have been suggested for fluorite-structure ferroelectrics due to their advantages over the conventional perovskite-structure ferroelectrics [1]. We focus on (Hf,Zr)O2 (HZO) thin films deposition for the capacitor of Ferroelectric Random Access Memories (FRAM) in the 1Transitor-1Capacitor (1T-1C) model. (Hf,Zr)O2 thin films are studied to either fully understand the stabilization of the ferroelectric phase (f-phase) or to fit with industrial requirements. Changing the pressure in our sputtering chamber during the room temperature deposition lead to the deposition of crystalline or amorphous films at room temperature. After a Rapid Thermal Annealing (RTA), only the amorphous films crystallize in the f-phase. Samples are stacks of Si/TiN/Hf0.5Zr0.5O/TiN/Pt. The samples are called NM, and M: NM and M refers to two different architectures, respectively non-mesa and mesa structures. Fabrication and architecture details can be found in reference [2]. The set-up for electrical measurements have been described in reference [3]. We report the fabrication of two samples deposited by magnetron sputtering. Pr values are among the highest for samples deposited by sputtering. Although the N-sample and NM-samples show very close Pr values, the two samples show completely different electrical behaviors. During cycling, the increase of Pr value for the NM-sample is more than an order of magnitude higher than the M-sample. It is accompanied by a decrease of the endurance which is two order of magnitude higher for the NM-sample than for the M-sample. The origins of the different electrical behaviors come from the micro-crystalline structures of the two samples, according to GIXRD results. The crystallization takes place during the annealing step. During annealing, M-sample is built with a TiN TE fully covering the HZO layer whereas the TiN covers only partially the HZO layer in case of the NM-sample. It induces different stress states which lead to two different micro-crystalline patterning. The M-sample shows no monoclinic peak, whereas the NM-sample shows many monoclinic orientations. It can explain the huge reduction of the wake-up effect. A correlation between long-term retention properties and the wake-up effect is also established: the sample with a reduced wake-up effect has a higher extrapolated polarization value and a smaller retention loss after ten years [4]. [1] M.H. Park, et al. MRS Commun. 1 (2018). [2] J. Bouaziz, et al., ACS Appl. Electron. Mater. 1, 1740 (2019). [3] J. Bouaziz, et al., APL Mater. 7, 081109 (2019). [4] J. Bouaziz, et al., Appl. Phys. Lett. 118, 082901 (2021).