Atomic Layer Deposition of SrTiO3 Thin Films from a Novel Strontium Precursor-Strontium-bis(tri-isopropyl cyclopentadienyl)

Vehkamäki, Marko; Hänninen, Timo; Ritala, Mikko; Leskelä, Markku; Sajavaara, Timo; Raühala, E.; Keinonen, J.

doi:10.1002/1521-3862(200103)7:2<75::aid-cvde75>3.0.co;2-b

Cited by 117 publications

(96 citation statements)

References 21 publications

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“…26 In one of the first reports on ALD of STO, the GPC for the SrO process using Sr(C 5 i PrH 2 ) 2 (Hyper-Sr without the DME adduct) and H 2 O was also 0.11 nm/cycle. 9 The GPC of TiO 2 is comparable to those reported in the literature, with values ranging from 0.022 nm/cycle 27 to ∼0.03 nm/cycle 26 for the combination of Ti-Star and O 3 . These values show the variation in GPC reported in the literature for ALD processes employing the same precursors but developed in different equipment, showing the sensitivity of ALD processes to the varying reactor design and experimental conditions.…”

Section: Resultsmentioning

confidence: 97%

Plasma-Assisted Atomic Layer Deposition of SrTiO₃: Stoichiometry and Crystallinity Studied by Spectroscopic Ellipsometry

Longo

Leick

Roozeboom

et al. 2012

ECS J. Solid State Sci. Technol.

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Strontium titanate (SrTiO3, STO) films were deposited by plasma-assisted ALD using cyclopentadienyl-based Sr- and Ti-precursors with O2 plasma as the oxidizing agent. Spectroscopic ellipsometry (SE) was employed to determine the thickness and the optical properties of the layers. As determined from Rutherford backscattering spectrometry (RBS), [Sr]/([Sr]+[Ti]) ratios ranging from 0.42 to 0.68 were achieved for 30–40 nm thick films by tuning the [SrO]/[TiO2] ALD cycle ratio. Films deposited at 250°C were amorphous and required post-deposition annealing to crystallize into the ultrahigh-k perovskite structure. The crystallinity of the films after rapid thermal annealing strongly depended on the film composition as observed by X-ray diffraction measurements. Using RBS data for a set of as-deposited samples, an optical constant library was built to determine the film stoichiometry from SE directly for the amorphous as-deposited films. After rapid thermal annealing the crystalline phase could be determined from the position of critical points of the measured dielectric function and the estimation of the stoichiometry was also possible for crystallized layers. These results open up a new way to use SE as a real-time characterization method to monitor and tune the STO film composition and crystallinity.

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Section: Resultsmentioning

confidence: 97%

Plasma-Assisted Atomic Layer Deposition of SrTiO₃: Stoichiometry and Crystallinity Studied by Spectroscopic Ellipsometry

Longo

Leick

Roozeboom

et al. 2012

ECS J. Solid State Sci. Technol.

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“…After 10 cycles, the GPC steadily decreases until it reaches its ultimate value of 0.05 ± 0.02 nm/cycle after 25 cycles at 250°C, which is consistent with previous studies. 6,13,14 By contrast, at a deposition temperature of 350°C, the GPC continuously increases during the first 10 cycles until it reaches a steady value of 0.30 ± 0.02 nm/cycle.…”

Section: ■ Results and Discussionmentioning

confidence: 99%

Nucleation, Hydroxylation, and Crystallization Effects in ALD SrO

Wang

Jiang

et al. 2013

J. Phys. Chem. C

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The atomic layer deposition (ALD) of SrO thin films from strontium bis(tri(isopropyl)cyclopentadienyl) (Sr-(C 5 i Pr 3 H 2 ) 2 ) and H 2 O was studied by using in situ real-time spectroscopic ellipsometry (RTSE), ex situ X-ray photoelectron spectroscopy (XPS), and grazing-incidence X-ray diffraction (GI-XRD). It is found that with H 2 O as the oxidant, deposition temperature strongly affects film composition. At 250°C films consist of polycrystalline Sr(OH) 2 while at 350°Cpolycrystalline SrO is observed. The growth per cycle (GPC) is found to be sensitive not only to the crystalline phase (Sr(OH) 2 vs SrO) but also the crystalline orientation. For films prepared at high temperatures and subsequently cooled for continued growth at lower temperatures, an unusual transient growth per cycle (GPC) enhancement of over 160% for more than 100 cycles is observed. The enhancement is found to be related to the orientation of the Sr(OH) 2 phase, which is influenced by the underlying crystal texture of the substrate. Substrate nucleation effects were also observed for growth on SiO 2 /Si substrates. A Sr silicate layer with stoichiometry close to Sr 2 SiO 4 forms spontaneously during ALD growth and transiently enhances the GPC. ■ INTRODUCTIONAtomic layer deposition (ALD) has attracted much attention in thin film deposition due to its capability for accurate thickness control and superior conformal growth. 1 Challenges for ALD include nonideal nucleation and substrate effects often encountered at the interfaces between dissimilar materials. 2−4 These substrate effects are particularly problematic for the growth of more complicated materials like ternary systems because of the difficulty encountered in achieving steady, predictable growth. 5 The growth of metal oxides is one of the most extensively studied and promising areas for application of ALD. In particular, SrO ALD is used for the ALD of the ternary strontium titanate (STO), which is of major interest for use with high-density metal−insulator−metal (MIM) capacitors. 6,7 SrO is also of interest for the growth of epitaxial perovskite oxides on semiconductors where it acts as a buffer layer between the reactive semiconductor and metal oxide layers. 8−12 Atomic layer deposition (ALD) of strontium oxide (SrO) has been demonstrated to show nonideal growth characteristics, and properties such as ALD growth window and precursor decomposition temperatures are controversial. 3,6,13,14 The strong basicity of SrO makes ALD-grown SrO films chemically unstable if exposed to air (moisture and CO 2 ). Moreover, traces of Sr(OH) 2 were reported by Vehkamaki et al. in films deposited at 250°C. 13 For films grown at 300°C, crystalline SrO was demonstrated by Rahtu et al. with preferred (111) orientation. 15 At deposition temperatures higher than 300°C, whether the strontium precursor thermally decomposes is still an open question. For example, Rahtu et al. reported that the growth per cycle (GPC) did not saturate as a function of strontium precursor pulse time at 325°C. 3 However, usi...

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“…Both the Sr and Hf metalorganic precursors are commercially available, reactive with water, and have been previously used for ALD. [38][39][40][41][42][43][44][45][46][47][48] Alternating subcycles of Sr and Hf are used to deposit stoichiometric to slightly Sr-rich (56%) films. During each subcycle the metalorganic is dosed for 2 s to ensure complete saturation of the surface, and subsequently purged for 15 s with ultrahigh purity Ar.…”

Section: Methodsmentioning

confidence: 99%

Atomic layer deposition of crystalline SrHfO3 directly on Ge (001) for high-k dielectric applications

McDaniel

et al. 2015

Journal of Applied Physics

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The current work explores the crystalline perovskite oxide, strontium hafnate, as a potential high-k gate dielectric for Ge-based transistors. SrHfO3 (SHO) is grown directly on Ge by atomic layer deposition and becomes crystalline with epitaxial registry after post-deposition vacuum annealing at ∼700 °C for 5 min. The 2 × 1 reconstructed, clean Ge (001) surface is a necessary template to achieve crystalline films upon annealing. The SHO films exhibit excellent crystallinity, as shown by x-ray diffraction and transmission electron microscopy. The SHO films have favorable electronic properties for consideration as a high-k gate dielectric on Ge, with satisfactory band offsets (>2 eV), low leakage current (<10−5 A/cm2 at an applied field of 1 MV/cm) at an equivalent oxide thickness of 1 nm, and a reasonable dielectric constant (k ∼ 18). The interface trap density (Dit) is estimated to be as low as ∼2 × 1012 cm−2 eV−1 under the current growth and anneal conditions. Some interfacial reaction is observed between SHO and Ge at temperatures above ∼650 °C, which may contribute to increased Dit value. This study confirms the potential for crystalline oxides grown directly on Ge by atomic layer deposition for advanced electronic applications.

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Atomic Layer Deposition of SrTiO3 Thin Films from a Novel Strontium Precursor-Strontium-bis(tri-isopropyl cyclopentadienyl)

Cited by 117 publications

References 21 publications

Plasma-Assisted Atomic Layer Deposition of SrTiO₃: Stoichiometry and Crystallinity Studied by Spectroscopic Ellipsometry

Plasma-Assisted Atomic Layer Deposition of SrTiO₃: Stoichiometry and Crystallinity Studied by Spectroscopic Ellipsometry

Nucleation, Hydroxylation, and Crystallization Effects in ALD SrO

Atomic layer deposition of crystalline SrHfO3 directly on Ge (001) for high-k dielectric applications

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Atomic Layer Deposition of SrTiO3 Thin Films from a Novel Strontium Precursor-Strontium-bis(tri-isopropyl cyclopentadienyl)

Cited by 117 publications

References 21 publications

Plasma-Assisted Atomic Layer Deposition of SrTiO3: Stoichiometry and Crystallinity Studied by Spectroscopic Ellipsometry

Plasma-Assisted Atomic Layer Deposition of SrTiO3: Stoichiometry and Crystallinity Studied by Spectroscopic Ellipsometry

Nucleation, Hydroxylation, and Crystallization Effects in ALD SrO

Atomic layer deposition of crystalline SrHfO3 directly on Ge (001) for high-k dielectric applications

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Plasma-Assisted Atomic Layer Deposition of SrTiO₃: Stoichiometry and Crystallinity Studied by Spectroscopic Ellipsometry

Plasma-Assisted Atomic Layer Deposition of SrTiO₃: Stoichiometry and Crystallinity Studied by Spectroscopic Ellipsometry