Si Doped Hafnium Oxide—A “Fragile” Ferroelectric System

Abstract

a wealth of different elements from the periodic table [7][8][9] have since exhibited ferroelectric properties. In their original publication, Böscke et al. [10] used ≈10 nm thick films of Si:HfO 2 and found the electrical behavior to evolve from paraelectric (PE) to ferroelectric (FE) and antiferroelectriclike to paraelectric again with a continuous increase in the Si dopant concentration. A similar electric evolution has also been shown for aluminum doping [11] and for (Hf,Zr)O 2 . [6,12] For the latter, an advanced understanding of the phase stabilization could be established, assisted in part by the very wide concentration window over which the changes occur. Ab initio calculations [13] interrogated the impact of surface energy in this system, revealing a phase transition from monoclinic pure HfO 2 to orthorhombic Hf 0.5 Zr 0.5 O 2 to tetragonal pure ZrO 2 for 10 nm film thickness, which aligns well the experimental observations. Moreover, inclusion of an electric field effect explained the antiferroelectriclike polarization hysteresis of pure ZrO 2 as the result of a fieldinduced phase transition from a nonpolar tetragonal to a polar orthorhombic phase. [6,13,14] Thus, instead of the term antiferroelectricity, field-induced ferroelectricity (FFE) is becoming a more precise and commonly used way to describe this behavior. While Si:HfO 2 and Al:HfO 2 have quickly been used in applications such as ferroelectric field effect transistors in 28 nm technology [15,16] and 3D capacitors, [17] basic material studies of doped ferroelectric HfO 2 have lagged those of the (Hf,Zr) O 2 system. By exploring a wide Si concentration range in fine steps, this work aims to gain insight into the phase transformations that occur in a doped HfO 2 system. Results and Discussion Impact of Annealing ConditionsAs a first step, planar capacitor stacks (Figure 1) with ≈36 nm thick HfO 2 films are deposited using a 22:1 HfO 2 :SiO 2 cycle ratio. As shown later, this results in a Si content that is slightly higher than the one that has produced the highest remanent polarization P r values in this study (Figure 7). As visible in Figure 2, the P r (measured under an electric field of 4 MV cm −1 and 10 kHz) increases for anneals at higher temperatures.Silicon doped hafnium oxide was the material used in the original report of ferroelectricity in hafnia in 2011. Since then, it has been subject of many further publications including the demonstration of the world's first ferroelectric field-effect transistor in the state-of-the-art 28 nm technology. Though many studies are conducted with a strong focus on application in memory devices, a comprehensive study on structural stability in these films remains to be seen. In this work, a film thickness of about 36 nm, instead of the 10 nm used in most previous studies, is utilized to carefully probe how the concentration range impacts the evolution of phases, the dopant distribution, the field cycling effects, and their interplay in the macroscopic ferroelectric response of the films. Si:HfO 2 appear...

Toward Thick Piezoelectric HfO2‐Based Films

“…Figure c shows the trends of remanent polarization P r and relative permittivity ε r with La content. The maximum of relative permittivity occurs at slightly larger dopant concentrations, here 7.5 cat%, as it has been observed repeatedly for HfO 2 ‐based FEs . These observations are in agreement with the density functional theory calculations, which predict a larger permittivity for the higher‐symmetry cubic or tetragonal phases compared with the FE orthorhombic phase.…”

Effect of Annealing Ferroelectric HfO2 Thin Films: In Situ, High Temperature X‐Ray Diffraction

“…[71] The new finding in this study is that a higher RTP temperature can increase the doping concentration range for the o-phase formation. [25,33,35,36] Figure 5 shows the pristine P r -o-phase fraction plot for all the data included in this study. The unit cell volume of the o-phase is about 1.5-2.0% larger than that of the t-phase.…”

“…[31] This shift could be related to a change of lattice parameters, aspect ratio (c/a for t-phase and 2a/(b+c) for o-phase), and unit cell volume. [32][33][34][35][36] Moreover, the time dependent crystallization behavior during annealing has not been previously reported. [31] However, in their work, the effect of annealing temperature was not examined although the annealing temperature is another key factor for the ferroelectric properties of doped HfO 2 thin films.…”

Demonstration of BEOL-compatible ferroelectric Hf0.5Zr0.5O2 scaled FeRAM co-integrated with 130nm CMOS for embedded NVM applications

“…Ferroelectric HfO2-based materials have been intensively studied since 2011 [1], thanks to their excellent CMOS compatibility and potential for scalability. So far, promising performance have been mostly reported on large area (typically 10000µm²) Metal/Ferroelectric/Metal (MFM) capacitors, with thermal budgets larger than 500°C [2,3]. Therefore, ferroelectricity on sub-1µm² capacitors with low thermal budget are yet to be demonstrated for those promising materials in order to integrate them in the Back-End-Of-Line (BEOL).…”