Physical chemistry of the TiN/Hf0.5Zr0.5O2 interface

Abstract

Ferroelectric hafnia-based thin films are promising candidates for emerging high-density embedded nonvolatile memory technologies, thanks to their compatibility with silicon technology and the possibility of 3D integration. The electrode–ferroelectric interface and the crystallization annealing temperature may play an important role in such memory cells. The top interface in a TiN/Hf0.5Zr0.5O2/TiN metal–ferroelectric–metal stack annealed at different temperatures was investigated with X-ray photoelectron spectroscopy. The uniformity and continuity of the 2 nm TiN top electrode was verified by photoemission electron microscopy and conductive atomic force microscopy. Partial oxidation of the electrode at the interface is identified. Hf is reduced near the top interface due to oxygen scavenging by the top electrode. The oxygen vacancy (VO) profile showed a maximum at the top interface (0.71%) and a sharp decrease into the film, giving rise to an internal field. Annealing at higher temperatures did not affect the VO concentration at the top interface but causes the generation of additional VO in the film, leading to a decrease of the Schottky Barrier Height for electrons. The interface chemistry and n-type film doping are believed to be at the origin of several phenomena, including wake-up, imprint, and fatigue. Our results give insights into the physical chemistry of the top interface with the accumulation of defective charges acting as electronic traps, causing a local imprint effect. This may explain the wake-up behavior as well and also can be a possible reason of the weaker endurance observed in these systems when increasing the annealing temperature.

On the Origin of Wake‐Up and Antiferroelectric‐Like Behavior in Ferroelectric Hafnium Oxide

“…Furthermore, it can be described by two current peaks popping up at either direction of the current-voltage (I-V ) curve that might even merge to a single peak then resembling the standard distribution of coercive fields (E C ), as shown in Figure 1b. This behavior has been reported already by multiple groups [6,18,22,26,29,[31][32][33][34] and will be referenced to as the classical wake-up effect.…”

Wake‐Up Mechanisms in Ferroelectric Lanthanum‐Doped Hf0.5Zr0.5O2 Thin Films

“…In summary, La doping of Hf 0.5 Zr 0.5 O 2 results into a stronger stabilization of the nonpolar tetragonal phase [ 6,31 ] by introducing oxygen vacancies [ 32 ] in the La‐doped regions (see green layers in the middle of the Hf 0.5 Zr 0.5 O 2 layer in Figure ). The creation of oxygen vacancies at metal/ferroelectric interface due to an oxygen scavenging effect of TiN is also reported in the literature; [ 32–34 ] therefore, a formation of nonpolar tetragonal phase at metal/ferroelectric interface [ 16 ] is also included into figure (see additional green layers at the ferroelectric/metal interface in Figure 5). The field‐cycling at 380 K can result in injection of charges into nonpolar dielectric layer at the metal/ferroelectric interface and into a minor tetragonal to orthorhombic phase change (Figure 5B).…”

Interplay between oxygen defects and dopants: effect on structure and performance of HfO2-based ferroelectrics

“…Recent HAXPES measurements by Szyjka et al 83 also indicated a different oxidation state at the interfaces with the top and the bottom electrode, respectively. Hamouda et al 41,84 measured that the difference in electrode oxidation is accompanied by a V O gradient within the oxide from 0.7 to 0% as a function of probing depth when moving from top to bottom electrode (Fig. 11).…”