Interface chemistry of pristine TiN/La:Hf0.5Zr0.5O2 capacitors

Abstract

We present a hard and soft x-ray photoelectron spectroscopy study of the interface chemistry in pristine TiN/La-doped Hf0.5Zr0.5O2/TiN capacitors. An oxynitride phase (∼1.3 nm) is formed at the top interface, while a TiO2−δ phase was detected near the bottom interface. The oxygen vacancy (VO) concentration is higher at the top interface than in the film due to oxygen scavenging by the top electrode. The VO concentration was also found to increase from ∼1.5 to 1.9 × 1020 cm−3 when increasing La doping from 1.7 to 2.7 mol. %. Two La dopants are compensated by the formation of one positively charged VO.

Metal Nitride Electrode Stress and Chemistry Effects on Phase and Polarization Response in Ferroelectric Hf0.5Zr0.5O2 Thin Films

“…It has been established that oxygen point defect concentration is a contributor to ferroelectric phase stability and therefore it is likely that the nonstoichiometry of the TaN electrodes leads to differing oxygen vacancy contents in the HZO layers via an oxygen scavenging mechanism. [65,66] While direct examination of defect concentrations in HZO thin films has proven experimentally difficult, leakage current measurements have been utilized to estimate these quantities. [34,67,68] Larger leakage currents have been attributed to higher oxygen point defect concentrations that enable current to flow via compensating electrons and trap-assisted tunneling where the oxygen vacancies serve as traps.…”

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

“…By comparing the works from Islamov et al, 22 it is evident how using lanthanum as a dopant could reduce the defect density in the layer by one order of magnitude i.e. from 10 20 to 10 19 cm −3 with respect to Hf 0.5 Zr 0.5 O 2 layers, leading to a reduction in leakage current 41,42 and to an increase in the number of field cycles before hard breakdown. 43 Nonetheless, opposite results were shown elsewhere, 41 where an increase in La concentration was associated to an increase in V O .…”

“…from 10 20 to 10 19 cm −3 with respect to Hf 0.5 Zr 0.5 O 2 layers, leading to a reduction in leakage current 41,42 and to an increase in the number of field cycles before hard breakdown. 43 Nonetheless, opposite results were shown elsewhere, 41 where an increase in La concentration was associated to an increase in V O . Inconsistencies between reports may be attributed to processing differences.…”

“…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).…”