Robustness of Ferroelectricity in Hafnium-Zirconium Dioxide Films Deposited By Sputtering and Chemical Solution Deposition for Ferroelectric Transistor Applications

Abstract

Since the discovery of ferroelectricity in HfO2 in 2011, extensive work begin to burst forth on HfO2-based ferroelectric materials and devices. Orthorhombic phase is responsible for ferroelectricity in HfO2, which is usually stabilized by the dopant such as Al, Zr, Si, la and Y. In particular, Zr doped HfO2 (HZO) has large Pr around 20 µC/cm2 and ferroelectricity can be obtained in a wide range of Zr composition. The orthorhombic phase is a metastable phase and Migita et al. [1] reported that the orthorhombic phase of sputtered HZO film was transferred to monoclinic phase by further annealing. In this work, robustness of ferroelectric phase against the further annealing process has been investigated using sputtered HZO and solution-derived Y-doped HZO films [2]. Sputtered HZO films were prepared by room temperature deposition followed by 600 oC, 10 min annealing in N2. Y-doped HZO films were prepared by chemical solution deposition (CSD) by annealing the samples at 800 oC for 3 min in O2.[2] Ferroelectric properties were confirmed by polarization-electric field (P-E) and capacitance-voltage (C-V) measurements for both samples before the second time annealing. Then, both samples were further annealed in 400 and 600 oC in N2 to examine the robustness of ferroelectricity. It was found that sputtered HZO films become paraelectric and that X-ray diffraction (XRD) pattern shows diffraction peak from orthorhombic phase disappeared. On the other hand, CSD HZO films shows ferroelectric nature even after second time annealing with negligible monoclinic phase. Such a significant difference in robustness is presumably due to residual carbon in the CSD films. In addition, In2O3/(Y-)HZO structures are also fabricated for oxide channel thin film transistor applications and characterized, which will be presented at the conference. [1] Shinji Migita et al, Jpn. J. Appl. Phys. 58 SBBA07, 2019. [2] Mohit et al, Jpn. J. Appl. Phys. 59 SMMB02, 2020.

Impact of reduced pressure crystallization on ferroelectric properties in hafnium-zirconium dioxide films deposited by sputtering

“…This indicates the ferroelectric properties of the sputtered HZO film crystallized at 1 atm were degraded by the re-annealing at as low as 400 °C. This is consistent with our previous works, 22,23) demonstrating that the XRD peak from the monoclinic phase in the sputtered HZO film, which had been crystallized at 1 atm of N 2 ambient, was increased by the re-annealing process and that the electrical properties were turned into paraelectric after re-annealing, although clear ferroelectric properties were observed before re-annealing. In addition, a similar observation was reported by Yajma et al They showed that degradation of ferroelectric properties due to the increase of monoclinic phase formation took place by the re-annealing or bake process even at as low as 250 °C for Ge-doped HfO 2 layer prepared by SFFB05-5…”

“…In addition, we have recently reported that the sputtered HZO film became paraelectric after 400 °C, 15 min re-annealing in N 2 ambient, even though good ferroelectric properties had been initially observed. 22,23) This is fatal for some device applications. For example, when the bottom-gate structure ferroelectric gate thin film transistor is fabricated using an oxide semiconductor channel, a thin oxide semiconductor channel layer has to be deposited on the ferroelectric gate insulator, usually followed by the annealing process.…”

Impact of annealing environment on electrical properties of yttrium-doped hafnium zirconium dioxide thin films prepared by the solution process

“…Preliminary experimental results of Y-HZO films annealed in a vacuum and N 2 at 800 °C were presented in the FMA 37 conference extended abstract. 39) In this work, we investigated the ferroelectric properties of Y-HZO films annealed in a vacuum from 600-800 °C prepared by CSD. Later, Y-HZO films were annealed in vacuum, nitrogen and oxygen environments at 800 °C for comparative study.…”

Enhancement of ferroelectricity in sputtered HZO thin films by catalytically generated atomic hydrogen treatment

“…However, we reported that the sputtered HZO film became paraelectric after 400 °C, 15 min of re-annealing in N 2 ambient, even though good ferroelectric properties were initially observed. 22,23) This is in contrast to the films prepared by chemical solution deposition (CSD), which has robust ferroelectricity after the reannealing process and even after the oxide channel layer formation at 600 °C. 24,25) One of the reasons for the discrepancy is that the CSD Y-HZO has more oxygen vacancies than the sputtered HZO.…”