Nanocrystallite Seeding of Metastable Ferroelectric Phase Formation in Atomic Layer-Deposited Hafnia–Zirconia Alloys

Abstract

Hafnia-based ferroelectric thin films are promising for semiconductor memory and neuromorphic computing applications. Amorphous, as-deposited, thin-film binary alloys of HfO 2 and ZrO 2 transform to the metastable, orthorhombic ferroelectric phase during post-deposition annealing and cooling. This transformation is generally thought to involve formation of a tetragonal precursor phase that distorts into the orthorhombic phase during cooling. In this work, we systematically study the effects of atomic layer deposition (ALD) temperature on the ferroelectricity of post-deposition-annealed Hf 0.5 Zr 0.5 O 2 (HZO) thin films. Seed crystallites having interplanar spacings consistent with the polar orthorhombic phase are observed by a plan-view transmission electron microscope in HZO thin films deposited at an elevated ALD temperature. After ALD under conditions that promote formation of these nanocrystallites, high-polarization (P r > 18 μC/cm 2 ) ferroelectric switching is observed after rapid thermal annealing (RTA) at low temperature (350 °C). These results indicate the presence of minimal non-ferroelectric phases retained in the films after RTA when the ALD process forms nanocrystalline particles that seed subsequent formation of the polar orthorhombic phase.

Field‐Induced Ferroelectric Phase Evolution During Polarization “Wake‐Up” in Hf0.5Zr0.5O2 Thin Film Capacitors

“…The ALD 250 °C sample is reported to have majority polar orthorhombic, O‐phase (space group Pca 2 1 ), with the O/T peak at lower Q values while the ALD 200 °C sample has the tetragonal, T‐phase (space group P 4 2 / nmc ), with the O/T peak at higher Q positions. [ 22,23 ] This also explains the different P‐V hysteresis data for the two samples. The switched polarization, as measured by the positive‐up‐negative‐down (PUND) sequence, is plotted in Figure 2c.…”

“…A dissimilarity is observed in the diffraction pattern for the two samples in the pristine state, as presented in Figure a, which matches the previous report. [ 22 ] The main HZO film peak (labeled as the O/T peak) is observed at Q = 2.137 Å −1 for ALD 250 °C and at Q = 2.155 Å −1 for the ALD 200 °C, while the main Pt peak in Figure 2b is consistent for both ALD temperatures at Q = 2.79 Å −1 , eliminating the possibility of any alignment error. The ALD 250 °C sample is reported to have majority polar orthorhombic, O‐phase (space group Pca 2 1 ), with the O/T peak at lower Q values while the ALD 200 °C sample has the tetragonal, T‐phase (space group P 4 2 / nmc ), with the O/T peak at higher Q positions.…”

“…Two otherwise identically processed MFM capacitor arrays are studied with the HZO film grown at different atomic layer deposition (ALD) temperatures and have been examined exhaustively. [ 22 ] The two MFMs, ALD 200 °C sample, and ALD 250 °C sample, show drastically different polarization evolution as a function of the number of switching cycles and, therefore, serve as an ideal observation set. Synchrotron low incidence XRD and capacitance–voltage ( C–V ) measurements are used to test whether the observed evolution of switchable polarization with switching cycle number is caused by a field‐induced HZO phase evolution of TiN/HZO/TiN capacitor stacks.…”

Enhanced Switching Reliability of Hf0.5Zr0.5O2 Ferroelectric Films Induced by Interface Engineering

“…Figure b shows the XRD diffraction patterns of two different samples before and after the wake-up process. At pristine state, the main peak of the HZO sample (light blue curve) is observed at Q = 2.155 Å –1 , which is consistent with the T(101)tetragonal phase (space group P 4 2 / nmc )peak position . By contrast, the main peak of the HZO sample with buffer layers (yellow curve) is located between the O(111)orthorhombic phase (space group Pca 2 1 ), and T(101) peaks, suggesting that it contains fewer nonpolar T-phase domains.…”

“…At pristine state, the main peak of the HZO sample (light blue curve) is observed at Q = 2.155 Å −1 , which is consistent with the T(101)�tetragonal phase (space group P4 2 /nmc)�peak position. 37 By contrast, the main peak of the HZO sample with buffer layers (yellow curve) is located between the O(111)�orthorhombic phase (space group Pca2 1 ), 37 and T(101) peaks, suggesting that it contains fewer nonpolar T-phase domains. After 10 7 cycles, the main peak of the HZO (nonbuffer layer) sample (dark blue curve) shifted to Q = 2.137 Å −1 , which is slightly shifted relative to the O(111) position (Q = 2.135 Å −1 ).…”