Chemical Stability of IrO₂ Top Electrodes in Ferroelectric Hf_0.5Zr_0.5O₂‐Based Metal–Insulator–Metal Structures: The Impact of Annealing Gas

Abstract

The IrO2 top electrode chemistry of ferroelectric IrO2/Hf0.5Zr0.5O2 (HZO)/IrO2 metal–insulator–metal (MIM) structures dependent on rapid thermal annealing in different gas atmospheres (nitrogen, oxygen, and forming gas [FG]) is investigated. Using hard X‐ray photoelectron spectroscopy (HAXPES), the strongly modified chemical states of the IrO2 layer dependent on the choice of annealing gas atmosphere are observed. For O2 and N2 anneals, the IrO2 electrode remains either unaffected or is just slightly chemically attacked at the top. In contrast, FG annealing causes a complete reduction of the IrO2 top electrode into metallic Ir. Surprisingly, oxygen is detected—unbound to Ir—which is incorporated in the metallic Ir layer. This mobile oxygen is thought to affect the electrical behavior of the IrO2/HZO/IrO2 device. In addition, it may serve as a test sample for future studies of the root causes of the role of oxygen‐vacancy interactions at the interface, which can influence the performance instabilities in HZO‐based MIM structures, such as wake‐up, imprint, and fatigue.

Impact of Iridium Oxide Electrodes on the Ferroelectric Phase of Thin Hf0.5Zr0.5O2 Films

“…[30] The nitrogen anneals cause a minor reduction of the oxygen content and the partial formation of metallic Ir at the electrode surface (filled areas in Figure 3a). [31] With HAXPES measurements between the electrode pads, it is possible to study the bottom electrode through the HZO layer. Despite the low intensity of the Ir 4f and 5p peaks, no chemical shift for the different anneals is detectable (Figure 3a inset).…”

The Electrode‐Ferroelectric Interface as the Primary Constraint on Endurance and Retention in HZO‐Based Ferroelectric Capacitors

“…Unfortunately, no MoO 2 bottom electrode was available for hard x-ray photoelectron spectroscopy (HAXPES) measurements, but similar results for the IrO 2 /HZO interface revealed no V O within the measurement limit, as expected for oxide electrodes. [42] The main difference between an electrode material as a top or bottom electrode is that the HZO layer is deposited atop the bottom electrode. This implies an exposition of the BE to the oxygen ALD precursor, which can, in some cases, oxidize the bottom electrode.…”

Hard x-ray photoelectron spectroscopy of tunable oxide interfaces

“…51 Moreover, the choice of different annealing atmospheres has been found to crucially impact the IrO 2 composition and on the crystallization anneal process. 60 In Fig. 13, the Ir 4p and the O 1s core-levels are displayed.…”

“…In addition, the metallic FGA Ir electrode shows an oxygen content at a binding energy of 533 eV, which is related to oxygen unbound to Ir (see the inset). 60 The emergence of metallic Ir electrodes containing unbound oxygen is of special interest to control the ferroelectric behaviour of the Ir/HZO interface during electrical switching of the MIM device. In the inset of Fig.…”