Stabilization of Tetragonal HfO<sub>2</sub> under Low Active Oxygen Source Environment in Atomic Layer Deposition

Cho, Deok‐Yong; Jung, Hyung Suk; Yu, Il-Hyuk; Yoon, Jung Ho; Kim, Hyo Kyeom; Lee, Sang Young; Jeon, Sang-Ho; Han, Seungwu; Kim, Jeong Hwan; Park, Tae Joo; Park, Byeong‐Gyu; Hwang, Cheol Seong

doi:10.1021/cm3001199

Cited by 90 publications

(64 citation statements)

References 52 publications

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“…Independent of the annealing temperature, PVD films contain ten times lower carbon concentration (≈0.1 at%) compared to ALD films (≈1 at%) (Figure S7, Supporting Information). Larger grain sizes of 20 nm in PVD films, compared to grain sizes of 8 nm observed in ALD films (Figure S6, Supporting Information), support this assumption, since a higher carbon concentration would lead to a larger number of grains as well as a suppressed grain growth . In addition, different concentrations of oxygen in ALD versus PVD films as discussed in the later part of the text could impact the crystallization behavior.…”

Section: Discussionmentioning

confidence: 70%

Origin of Ferroelectric Phase in Undoped HfO₂ Films Deposited by Sputtering

Mittmann

Materano

Lomenzo

et al. 2019

Adv Materials Inter

139

151

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the formation of a non-centrosymmetric Pca2 1 orthorhombic phase (o-phase). [1][2][3][4][5][6][7] For increasing doping concentrations, ALD HfO 2 films undergo a phase transition from a non-ferroelectric m-phase to ferroelectric orthorhombic phase and for higher concentrations to the tetragonal phase (t-phase; space group: P4 2 /nmc) if the dopants are smaller than Hf like Si and Al, or to the cubic phase if the dopants are larger than Hf like Gd, La, Sr, and Y. [8] Besides the influence of doping, four other factors are known to promote the stabilization of the ferroelectric phase: surface or interface/grain boundary energy, film stress, and the presence of oxygen vacancies. [9][10][11][12][13] Oxygen vacancies and the related defect states play an important role in the so-called wake-up effect. [14] Wake-up describes the increase of the remanent polarization during electrical field cycling with opening of an initially pinched polarization-voltage hysteresis. [11] In Hf 1−x Zr x O 2 films, Materlik et al. suggested that the bulk and surface free energy of the o-phase is located between those of the m-phase and t-phase. As a result, the o-phase is stabilized in a specific film thickness and grain size region. This suggestion matches well Thin film metal-insulator-metal capacitors with undoped HfO 2 as the insulator are fabricated by sputtering from ceramic targets and subsequently annealed. The influence of film thickness and annealing temperature is characterized by electrical and structural methods. After annealing, the films show distinct ferroelectric properties. Grazing incidence X-ray diffraction measurements reveal a dominant ferroelectric orthorhombic phase for thicknesses in the 10-50 nm range and a negligible non-ferroelectric monoclinic phase fraction. Sputtering HfO 2 with additional oxygen during the deposition decreases the remanent polarization. Overall, the impact of oxygen vacancies and interstitials in the HfO 2 film during deposition and annealing is correlated to the phase formation process.

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Section: Discussionmentioning

confidence: 70%

Origin of Ferroelectric Phase in Undoped HfO₂ Films Deposited by Sputtering

Mittmann

Materano

Lomenzo

et al. 2019

Adv Materials Inter

139

151

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“…The effect of the t f on P r variationcould be ascribed to the change in D ave of the Hf 0.5 Zr 0.5 O 2 films. It has been well known that the polymorphism of polycrystalline HfO 2 and ZrO 2 is governed by the size effects, especially when the D ave is <≈100 nm . The critical D ave to obtain a t‐phase is known to be ≈4 and ≈32 nm for HfO 2 and ZrO 2 , so the critical D ave of Hf 0.5 Zr 0.5 O 2 is estimated as ≈18 nm, from interpolation based on Vegard's law .…”

Section: Origin Of Ferroelectricity and Antiferroelectricity In Dopedmentioning

confidence: 99%

Ferroelectricity and Antiferroelectricity of Doped Thin HfO₂‐Based Films

et al. 2015

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The recent progress in ferroelectricity and antiferroelectricity in HfO2-based thin films is reported. Most ferroelectric thin film research focuses on perovskite structure materials, such as Pb(Zr,Ti)O3, BaTiO3, and SrBi2Ta2O9, which are considered to be feasible candidate materials for non-volatile semiconductor memory devices. However, these conventional ferroelectrics suffer from various problems including poor Si-compatibility, environmental issues related to Pb, large physical thickness, low resistance to hydrogen, and small bandgap. In 2011, ferroelectricity in Si-doped HfO2 thin films was first reported. Various dopants, such as Si, Zr, Al, Y, Gd, Sr, and La can induce ferro-electricity or antiferroelectricity in thin HfO2 films. They have large remanent polarization of up to 45 μC cm(-2), and their coercive field (≈1-2 MV cm(-1)) is larger than conventional ferroelectric films by approximately one order of magnitude. Furthermore, they can be extremely thin (<10 nm) and have a large bandgap (>5 eV). These differences are believed to overcome the barriers of conventional ferroelectrics in memory applications, including ferroelectric field-effect-transistors and three-dimensional capacitors. Moreover, the coupling of electric and thermal properties of the antiferroelectric thin films is expected to be useful for various applications, including energy harvesting/storage, solid-state-cooling, and infrared sensors.

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“…12,[15][16][17] In this report, the higher-k HfO 2 phase is considered the tetragonal phase because the clear distinction between the tetragonal and cubic phases in a very thin HfO 2 ((10 nm) film via laboratory x-ray diffraction is usually difficult. Although the detailed methods for such transformation of HfO 2 to the higher-k phases are diverse, 16,19 they basically rely on the grain size effect (a smaller grain size prefers the higher-k phase) because the surface (or grain boundary) energy of the higher-k phase is lower than that of the monoclinic phase. 18 Therefore, the higher-k phase could be tetragonal, cubic, or even a mixture of them, but clear distinction was not attempted as long as the phase was distinguished from the monoclinic phase.…”

Section: Introductionmentioning

confidence: 99%

“…In addition, the k values of the two phases are not very different and are also dependent on the crystallographic directions. 17,20,21 Therefore, making the grain size smaller is an efficient method of achieving the higher-k phase, which has been achieved by doping aliovalent cations, adding impurities (carbon or hydrocarbon), 19,20,22 alloying with ZrO 2 (ZrO 2 films generally have much smaller grain sizes than HfO 2 films in ALD and thus tend to be tetragonal, 23 and using templates such as a rutile TiO 2 film. Although the detailed methods for such transformation of HfO 2 to the higher-k phases are diverse, 16,19 they basically rely on the grain size effect (a smaller grain size prefers the higher-k phase) because the surface (or grain boundary) energy of the higher-k phase is lower than that of the monoclinic phase.…”

Section: Introductionmentioning

confidence: 99%

“…Although the detailed methods for such transformation of HfO 2 to the higher-k phases are diverse, 16,19 they basically rely on the grain size effect (a smaller grain size prefers the higher-k phase) because the surface (or grain boundary) energy of the higher-k phase is lower than that of the monoclinic phase. The adoption of O 2 as the oxygen source during ALD, however, results in a high carbon impurity concentration, 19 which was actually the reason for making the grain size smaller and thus tetragonal phase, but the high a) Electronic mail: cheolsh@snu.ac.kr carbon concentration largely degraded the electrical performance of the higher-k film. 24 Cho et al reported the transformation of monoclinic HfO 2 to tetragonal phase after PDA by adopting O 2 as the oxygen source during ALD 13 as it has lower oxidizing power than O 3 .…”

Section: Introductionmentioning

confidence: 99%

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Phase control of HfO₂-based dielectric films for higher-k materials

Lee¹,

Yu²,

Lee³

et al. 2014

Journal of Vacuum Science & Technology B, Nanotechnology an

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Articles you may be interested inEffects of rapid thermal annealing on the properties of HfO2/La2O3 nanolaminate films deposited by plasma enhanced atomic layer deposition J. Vac. Sci. Technol. A 33, 01A116 (2015); 10.1116/1.4900935 Engineering crystallinity of atomic layer deposited gate stacks containing ultrathin HfO2 and a Ti-based metal gate: Effects of postmetal gate anneal and integration schemes J. Vac. Sci. Technol. B 32, 03D122 (2014); 10.1116/1.4869162 Physical and electrical characterization of Ce-HfO2 thin films deposited by thermal atomic layer deposition J. Vac. Sci. Technol. B 32, 03D103 (2014); 10.1116/1.4826174 Film properties of low temperature HfO2 grown with H2O, O3, or remote O2-plasma J.In this work, attempts were made to increase the k values of the HfO 2 film by transforming its structure from monoclinic to tetragonal phase. The tetragonal seed HfO 2 layer and multilayer approaches were tested based on the fact that the HfO 2 film deposited via atomic layer deposition (ALD) using O 2 as the oxygen source induced tetragonal-phase HfO 2 after the post deposition annealing (PDA) at temperatures higher than 700 C. Both approaches, however, failed to transform the monoclinic HfO 2 layer grown via ALD using O 3 as the oxygen source, which suggests that the driving force for forming the thermodynamic stable phase (monoclinic) overwhelms the interface energy effect between the two different phases, which would have induced the desired transformation. As another approach, the HfO 2 films were alloyed with ZrO 2 , which was an effective method of changing the structure from monoclinic to tetragonal. While the k values of the Hf 1Àx Zr x O 2 (HZO) film could be tuned by the Zr concentration and the PDA temperature, the increase of the PDA temperature to over 800 C induced the compositional segregation of HZO, which largely increased the leakage current. A critical Zr concentration was found (between 50 and 70%), in which the k-value increase was quite abrupt but the increase in leakage was not very evident after the PDA at 700 C. V C 2014 American Vacuum Society.

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Stabilization of Tetragonal HfO₂ under Low Active Oxygen Source Environment in Atomic Layer Deposition

Abstract: Approximately 13 nm thick HfO2 films are grown on Si wafers by atomic layer deposition under different ozone concentrations at 280 °C using Hf[N(Et)(Me)]4 as Hf precursor.

Cited by 90 publications

References 52 publications

Origin of Ferroelectric Phase in Undoped HfO₂ Films Deposited by Sputtering

Origin of Ferroelectric Phase in Undoped HfO₂ Films Deposited by Sputtering

Ferroelectricity and Antiferroelectricity of Doped Thin HfO₂‐Based Films

Phase control of HfO₂-based dielectric films for higher-k materials

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Stabilization of Tetragonal HfO2 under Low Active Oxygen Source Environment in Atomic Layer Deposition

Abstract: Approximately 13 nm thick HfO2 films are grown on Si wafers by atomic layer deposition under different ozone concentrations at 280 °C using Hf[N(Et)(Me)]4 as Hf precursor.

Cited by 90 publications

References 52 publications

Origin of Ferroelectric Phase in Undoped HfO2 Films Deposited by Sputtering

Origin of Ferroelectric Phase in Undoped HfO2 Films Deposited by Sputtering

Ferroelectricity and Antiferroelectricity of Doped Thin HfO2‐Based Films

Phase control of HfO2-based dielectric films for higher-k materials

Contact Info

Product

Resources

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Stabilization of Tetragonal HfO₂ under Low Active Oxygen Source Environment in Atomic Layer Deposition

Origin of Ferroelectric Phase in Undoped HfO₂ Films Deposited by Sputtering

Origin of Ferroelectric Phase in Undoped HfO₂ Films Deposited by Sputtering

Ferroelectricity and Antiferroelectricity of Doped Thin HfO₂‐Based Films

Phase control of HfO₂-based dielectric films for higher-k materials