Review pubs.acs.org/cm
Cite This: Chem. Mater. 2019, 31, 1142−1183
Synthesis of Doped, Ternary, and Quaternary Materials by Atomic Layer Deposition: A Review Adriaan J. M. Mackus,†,‡,# Joel R. Schneider,†,# Callisto MacIsaac,§ Jon G. Baker,† and Stacey F. Bent*,† †
Department of Chemical Engineering, Stanford University, Stanford, California 94305, United States Department of Applied Physics, Eindhoven University of Technology, P.O. Box 513, 5600 MB Eindhoven, The Netherlands § Department of Chemistry, Stanford University, Stanford, California 94305, United States Downloaded via UNIV PARIS-SUD on May 21, 2019 at 14:18:55 (UTC). See https://pubs.acs.org/sharingguidelines for options on how to legitimately share published articles.
‡
ABSTRACT: In the past decade, atomic layer deposition (ALD) has become an important thin film deposition technique for applications in nanoelectronics, catalysis, and other areas due to its high conformality on 3-D nanostructured substrates and control of the film thickness at the atomic level. The current applications of ALD primarily involve binary metal oxides, but for new applications there is increasing interest in more complex materials such as doped, ternary, and quaternary materials. This article reviews how these multicomponent materials can be synthesized by ALD, gives an overview of the materials that have been reported in the literature to date, and discusses important challenges. The most commonly employed approach to synthesize these materials is to combine binary ALD cycles in a supercycle, which provides the ability to control the composition of the material by choosing the cycle ratio. Discussion will focus on four main topics: (i) the characteristics, benefits, and drawbacks of the approaches that currently exist for the synthesis of multicomponent materials, with special attention to the supercycle approach; (ii) the trends in precursor choice, process conditions, and characterization methods, as well as underlying motivations for these design decisions; (iii) the distribution of atoms in the deposited material and the formation of specific (crystalline) phases, which is shown to be dependent on the ALD cycle sequence, deposition temperature, and post-deposition anneal conditions; and (iv) the nucleation effects that occur when switching from one binary ALD process to another, with different explanations provided for why the growth characteristics often deviate from what is expected. This paper provides insight into how the deposition conditions (cycle sequence, temperature, etc.) affect the properties of the resultant thin films, which can serve as a guideline for designing new ALD processes. Furthermore, with an extensive discussion on the nucleation effects taking place during the growth of ternary materials, we hope to contribute to a better understanding of the underlying mechanisms of the ALD growth of multicomponent materials. processes.2 The next step will be the introduction of more complex materials including doped, ternary, and quaternary compounds. Moreover, the success of ALD as an essential technique for semiconductor manufacturing has recently triggered the exploration of other applications in fields as diverse as catalysis,3,4 energy storage,5,6 and photovoltaics.7−9 These new applications also often require complex materials with accurately tuned composition or specific doping profiles.10−12 Due to its atomic-level control of the growth, ALD allows for the creation of homogeneous multicomponent or multilayered thin films by depositing atomic layers of different materials in a specific sequence. ALD relies on the alternating exposure of a surface to a precursor and to a co-reactant, which react with the surface through self-limiting reactions.13 Because of the self-limiting
I. INTRODUCTION In the current era of nanotechnology, the thin film deposition technique of atomic layer deposition (ALD) has emerged as an essential element of the toolbox for processing materials at the atomic level. Although the technique was developed in the 1960s and 1970s,1 it has only in the past decade acquired widespread attention, motivated first by its application for highk gate dielectrics in state-of-the-art transistors and then later expanding to other applications in nanoelectronics.2 With critical dimensions of CMOS electronics currently approaching the sub-5 nm level, the unparalleled conformality and thickness control provided by ALD appear to be required not only for the gate dielectric but also for the deposition of thin films at multiple locations in the CMOS device architecture. Furthermore, the required material properties for these films have become increasingly more demanding, as illustrated by the recent introduction of many new elements into semiconductor processing. The early industrial applications of ALD were almost all based on binary (i.e., two-element) metal oxide ALD © 2018 American Chemical Society
Received: July 8, 2018 Revised: December 9, 2018 Published: December 10, 2018 1142
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the synthesis of multicomponent materials; (ii) the trends in precursor choice, process conditions, and characterization methods; (iii) intermixing of species and phase formation, as influenced by the ALD cycle sequence, deposition, and anneal conditions; and (iv) the nucleation effects that occur when switching between binary ALD processes. These discussions will contribute to a better understanding of the mechanisms at work and to an enhanced ability to reproducibly deposit this class of materials, which can significantly broaden the application possibilities of ALD. This article is organized as follows: First, in Section II, general approaches for ALD of doped, ternary, and quaternary materials are described. Second, in Section III, an overview of the ternary and quaternary materials synthesized by ALD and the processes used is presented. Section IV reviews the literature on intermixing and phase formation. In Section V, various sources of deviation in growth characteristics from those predicted by the rule of mixtures are reviewed, and the ZnAlxOy ALD process is presented as a case study to illustrate how several of these mechanisms can occur in concert.
nature of the surface reactions, the growth is not dependent on the precursor and co-reactant fluxes, resulting in deposition with high conformality even on nanostructured surfaces. Moreover, the cyclic pulsing of ALD provides sub-ångström control of the film thickness. A binary ALD cycle consists of a precursor dose and a subsequent co-reactant dose, separated by purge steps. Precursors are typically metalorganic compounds containing the metal(s) or semimetal(s) of interest, such as trimethylaluminum, tetrakis(dimethylamino)tin, or tetraethyl orthosilicate. As co-reactants, H2O, O3, or O2 plasma are often employed for metal oxides such as Al2O3 and TiO2; NH3 or N2/H2 plasmas for metal nitrides such as TiN and SiNx; and H2S for metal sulfides such as ZnS.14 The most common approach for the synthesis of a doped or ternary material by ALD is to alternate between several cycles of two binary ALD processes in a so-called supercycle. By performing k cycles of binary process ACx and l cycles of binary process BCy, a ternary ABwCz film can be deposited, where C is a nonmetal atom (e.g., O, N, S). This approach allows for the tuning of the composition by choosing a certain cycle ratio k/(k + l). Doping can be achieved by performing supercycles with k ≫ l, such that the ACx process deposits the host material and the BCy process the dopant. A quaternary or quinary material can be synthesized by combining three or more binary ALD processes into a supercycle. In the past decade, many processes for the deposition of doped, ternary, and quaternary materials have been reported. The literature on these materials clearly shows that the development of a ternary or doped process is more complex than just adding two binary processes together. Ideally, the growth rate and the composition should be a linear combination of the growth rate and composition of the employed binary ALD processes, according to the rule of mixtures.15 However, the growth rate of a ternary process is often lower (and sometimes higher) than the growth rate expected from the binary growth rates, and the composition typically deviates from the targeted properties, due to a variety of nonidealities including nucleation effects and precursor ligand interactions. Another important aspect to consider when depositing these materials is the spatial distribution of atoms in the deposited layer. For example, it is often desirable to synthesize a ternary material with a specific perovskite phase.16,17 At first sight, it appears best to switch as often as possible between the two binary processes, such that the elements are well-mixed; however, this also means that any of the nucleation effects that cause the nonidealities described above are amplified. Moreover, ALD at typical substrate temperatures of 100−400 °C generally results in the deposition of amorphous materials,14 while many applications require crystalline phases. It is therefore often needed to perform an anneal after the deposition to facilitate the mixing of atoms or to crystallize the material. In this review article, the deposition of doped, ternary, and quaternary materials by ALD is reviewed. There are many fine reviews of ALD in the literature;11−14,16−24 however, there is to our knowledge no comprehensive review with a focus on multicomponent (ternary and higher) materials. Given the growing importance of these materials, we have therefore written this review to compile the over 475 ALD processes for 207 ternary and 44 quaternary materials demonstrated to date and describe their common fabrication strategies; challenges regarding composition, phase, and nucleation; and future opportunities. The article will mainly focus on (i) the characteristics, benefits, and drawbacks of approaches currently available for
II. APPROACHES FOR DEPOSITION OF DOPED, TERNARY, AND QUATERNARY MATERIALS This section discusses various experimental strategies for producing multicomponent materials, together with their strengths and weaknesses. Relevant terminology is defined, and some literature studies are reviewed. II.A. Supercycle Approach. The most common method for producing doped, ternary, and quaternary materials via ALD involves the combination of multiple binary ALD processes into supercycles. This approach takes the normal ALD cycles of sequential precursor and co-reactant pulses for each constituent process and combines them into a cycle of cycles, as illustrated in Figure 1. An ALD supercycle is defined as the minimum sequence of individual binary cycles that is repeated over the course of the ALD process. A simplified way of picturing this is that each cycle or block of cycles of a binary process results in the deposition of a sublayer of a specific material within the total film. As an example, ZnAlxOy is a ternary material formed by combining the ZnO and Al2O3 binary ALD processes in a supercycle. When the switching between Al2O3 and ZnO ALD occurs after only a small number of cycles as in Figure 1a, then a well-mixed ternary ZnAlxOy film may be formed. Since one ALD cycle leads to deposition of a submonolayer of material with a thickness of 8%) of Cl in the films was observed, but the electrical characteristics were nevertheless deemed reasonable. A drawback of this approach is that because the two precursors must be alternated in an one-to-one ratio, it provides little opportunity for compositional tuning. II.C. Approaches to the Synthesis of Doped Films. The preparation of doped films by ALD has been explored for many material systems. Doped thin films are an increasingly important class of materials, as the addition of small amounts of dopants can dramatically affect the electrical or optical properties of a thin film. This makes doped materials invaluable in fields as varied as photovoltaics, optoelectronics, and catalysis.12,53 However, the supercycle strategy of ALD can result in films that are not homogeneously doped but contain concentration gradients.54 ALD-grown doped films are typically prepared by using supercycles with a small cycle ratio (CR ≪ 0.5; see Figure 1c), such that the concentration of one of the components is low while the other functions as the host material. This means that the supercycle contains several binary ALD cycles of one process to deposit the host material and one binary ALD cycle of another process to deposit the dopant. There are several drawbacks to this approach. First of all, the dopant atoms may be spaced too far apart in the direction normal to the film surface. In addition, one cycle of the dopant ALD process may result in a too high density of dopant atoms in a given lateral plane. The effect of the distribution of the dopants on the material properties is captured by the term doping ef f iciency, which is defined as the number of active charge carriers per dopant atom.55 An increase in doping efficiency results in improved conductance, which can be accomplished either by decreasing defect sites that may trap, recombine, or scatter carriers or by ensuring that the dopant molecules are within a certain critical distance of each other to promote carrier movement.54,56 Figure 4 illustrates how the distribution of dopant atoms influences the doping efficiency. In the case where the range of the effective field of the dopant atoms is smaller than the distance between two layers of dopant atoms as in Figure 4a, the carriers are trapped near the dopant atoms and cannot be transported across the layers, leading to a low doping efficiency. Conversely, having dopants too closely spaced (dopant clustering, as in Figure 4c) can result in lower doping efficiencies through overlapping effective fields or increased carrier scattering. In between these two cases, there is an optimum as shown in Figure 4b, meaning that the distribution of the dopant atoms must be tuned accurately. While the heterogeneity of doped films prepared using the supercycle method has led to a variety of interesting architectures including surface-doped PbS-coated silica microwires57 and P-coated V2O5 oxidative catalysts,58 experimental effort has been focused on in situ and ex situ methodologies to 1146
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Figure 4. Dopant atoms (blue) deposited via the supercycle method, shown with the surrounding orange spheres indicating the effective field for each dopant atom. When S , the distance between the layers of dopant atoms, is larger than d, the effective fields, carriers are trapped within the dopant layer (case a). When the effective fields strongly overlap (case c), carrier transport is possible between dopant layers; however, scattering may lower the doping efficiency. In between there is an optimum that gives a high doping efficiency (case b). This figure was created based on a figure from Advanced Materials with permission.54 Copyright 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Winheim.
produce more homogeneously doped films. These methods can generally be grouped into two broad categories: (i) postdeposition annealing at temperatures high enough to result in dopant species migration59−61 and (ii) decreasing the density of dopant atoms deposited per cycle. Annealing is an effective way to disperse dopant atoms within multicomponent thin films grown using ALD supercycles, the effects of which can be tuned by varying the bilayer thickness, the annealing temperature, and the annealing time.59−63 The influence of these parameters on the intermixing during annealing will be discussed in more detail in Section IV. In situ approaches to produce a homogeneously doped material generally rely on reducing the amount of dopant atoms deposited during the dopant ALD cycle by exploiting the surface chemistry and ligand effects that dominate the in-plane growth of material. When the growth rate of the (one) dopant ALD cycle in the supercycle is reduced, the resulting lateral density of dopant atoms is lower. In addition, the supercycle can contain fewer binary cycles for depositing the host material for a certain volume density of dopants, such that the dopant atoms are spaced less far apart in the direction normal to the film surface. Taken together, a lower lateral density and a reduced distance between dopant layers gives a more uniform distribution of the dopant atoms (more closely representing Figure 4b). Some strategies to yield a less dense dopant layer have focused on utilizing subsaturating dopant precursor exposures,56 but that approach sacrifices the conformality and layerby-layer growth control of ALD, so we will not address it here. One chemical strategy to control the dispersion of dopant molecules across a surface involves tuning the steric bulkiness of the precursor ligands to achieve the desired density of adsorbed precursor molecules. This method was employed in the synthesis of Er-doped photoluminescent Y2O3, where the dopant distribution is especially important because Er−Er interactions can result in nonradiative decay.64 Tris(2,2,6,6tetramethyl-3,5-heptanedionato)Er(III), a bulky β-diketonate ligand, was used to spatially separate the Er atoms as they deposit on the surface, producing superior films (showing roomtemperature photoluminescence). Similarly, the maximum doping efficiency of Al-doped ZnO was increased from approximately 10% to almost 60% by switching from the common ALD precursor TMA to the bulkier precursor dimethylaluminum
Figure 5. The doping efficiency for films deposited using the supercycle approach can be enhanced by reducing the growth rate of the dopant ALD process, which can be accomplished by (a) using a precursor with bulkier ligands65 or (b) employing an ABC-type ALD process in which the number of precursor adsorption sites is reduced by dosing an inhibitor molecule in step A.68 Subfigure (a) reprinted (adapted) with permission from Chemistry of Materials.65 Copyright 2013 American Chemical Society. Subfigure (b) reprinted (adapted) with permission from Chemistry of Materials.68 Copyright 2013 American Chemical Society.
isopropoxide (DMAI).65 As illustrated in Figure 5a, films deposited with the bulkier DMAI resulted in more spatially dispersed Al atoms and, consequently, substantially higher film conductivities.65 Although varying the ligands of the dopant precursor molecule can substantially change the amount of dopants deposited per ALD cycle, it is not a feasible option for all desired combinations of dopant metal atoms, dopant concentrations, and host materials. Yanguas-Gil et al. developed an alternative approach for producing homogeneous doped films that does not rely on altering precursor chemistry but involves preconditioning the surface with so-called inhibitor molecules (e.g., ethanol, acetone) prior to the dopant ALD cycle.66−69 As illustrated in Figure 5b, these inhibitor molecules decrease the number of surface sites available for adsorption of the precursor, thereby influencing the lateral density of the deposited dopant atoms. The approach requires an inhibitor molecule that partly blocks the adsorption sites of the dopant precursor and is resistant to removal by the precursor pulse, while being completely detachable by the co-reactant. ABC-type cycles have been developed in which A is a pulse of the inhibitor molecule, B is a pulse of the dopant precursor, and C is a pulse of a co-reactant that removes both remaining precursor ligands and inhibitor molecules. Such ABC-type processes result in the deposition of a reduced amount of dopant atoms per dopant ALD cycle and, consequently, a higher doping efficiency. This method was successfully demonstrated for Al-doped ZnO using small alcohols like ethanol as saturating inhibitors prior to the TMA dopant pulses.69 The process resulted in a wide range of Al2O3 growth rates and led to Al-doped ZnO films with increased carrier 1147
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Chemistry of Materials densities. It is of note that the films grown were found to be free of additional impurities from the inhibitor molecules. Further research with a larger set of inhibitors including ketones, nitriles, and carbocyclic acids resulted in promising indications that the method could be applied to other metal oxide ALD processes like ZnO, TiO2, Er2O3, ZrO2, and MgO.68 While this approach offers a versatile and robust method to increasing doping efficiency, it has the drawback of extending the ALD cycle by an extra step and potentially introducing contamination into the film. To summarize this section and illustrate the differences between ALD doping methodologies and other thin film depositional methods, we revisit the example process of ZnAlxOy. Literature on ZnAlxOy films grown using ALD supercycles has been plagued by low doping efficiencies (i.e., 10% or less).70 However, a variety of the ALD methods reviewed in this section have been employed to overcome this limitation: doping efficiencies can be increased to 60% by choosing larger precursors that optimize interdoping spacing65 and to 70% by co-dosing of precursors.31 For comparison, doping efficiencies of chemical vapor deposition (CVD) grown Al-doped ZnO are upward of 86%, but it should be noted that the much higher substrate temperature of CVD facilitates a homogeneous profile of dopants in the final film. Few works outside of the field of ALD report performance in terms of doping efficiency, making it difficult to compare doping efficiencies of ALD-grown films to those of other synthesis methods. However, in addition to CVD, using methods like sol−gel or sputtering can result in highly mixed films so it could be predicted that these methods will have higher doping efficiencies. Further discussion of ALD mixing is presented in Section IV.
so for brevity every material appears in the tables only once and is not duplicated in the sections corresponding to every constituent atom. Growth rates for supercycle processes can be reported in terms of growth per supercycle or growth per binary subcycle, and therefore for comparison all growth rates in Tables 1−5 are reported on a per binary subcycle basis. Many of the precursor ligands referenced are simple enough to include their entire chemical formula directly, but some ligands have been abbreviated. Me, Et, Pr, Bu, Ph, and Cp are used as abbreviations for methyl, ethyl, propyl, butyl, phenyl, and cyclopentadienyl groups, respectively, and all other abbreviations are given in Table 6. III.A. Categories of Multicomponent Processes. Ternary metal oxides, consisting of two different metal atoms alloyed with oxygen, are by far the most prevalent materials in the class of ternary materials, and they are detailed in Table 1. The utility of ternary metal oxides in a variety of applications lends them well to multiple frontiers of research, and the number of studies exploring ternary metal oxides has grown dramatically in the past decade. Ternary metal nitrides, presented in Table 2, have been a much more recent development in the field of ALD. Thus far their applications have been primarily limited to the areas of optoelectronics92−95 and diffusion barriers,44,96−101 and the majority of the studies included in the tables have been published in the past five to ten years. Even more recent has been the exploration of ternary metal sulfides by ALD, which are included in Table 3. Other ternary compounds such as Group III−V semiconductors, tellurides, selenides, phosphides, carbonates, and oxysulfides have been explored via ALD, but the body of work on these materials is much smaller, as can be seen in Table 4. Note that ternary oxides, nitrides, and sulfides containing metalloids (e.g., Si or Ge) or two nonmetals (e.g., carbonates or phosphates) instead of two different metal atoms are included in Table 4. Finally, ALD has also been used to synthesize quaternary materials, as listed in Table 5. These materials typically contain oxides, nitrides, or sulfides of three combined metal atoms, allowing for an additional dimension of compositional tuning to affect the properties of the resultant film. However, precise compositional control of these materials has proven challenging in many cases, particularly because the combination of three binary ALD processes provides many more opportunities for chemical phenomena to give rise to nonidealities in growth. We found only two examples of quinary (i.e., five-component) ALD processes in the literature, one studying crystallization and diffusion in perovskites of KNawNbxTayOz and the other investigating crystallization phenomena in solid electrolytes of LiLawZrxAlyOz.102,103 This sparse coverage could result from the fact that the process complexity and opportunity for nonideal behavior observed in ternary and quaternary processes is present to an even greater extent in quinary processes. III.B. Applications. The ternary and quaternary materials described in the tables cover a wide variety of applications, but several are of particular note. A large number of materials have been studied for use as high-k dielectrics,48,104−107 particularly Hf-,86,108−114 Ti-,115−122 and La-containing104,123−127 compounds. Many of these studies have been dedicated to examining compositional effects of various metal atoms in ternary oxides in order to find materials with higher dielectric constants. Ultrahigh-k dielectric materials (e.g., SrTixOy) have also been studied extensively for memory applications.34,46,48,98,114,115,117,118,125,126,128−132 In addition, a number of materials are being explored for usage in buffer
III. OVERVIEW OF TERNARY AND QUATERNARY ALD PROCESSES There is a substantial body of work in the literature that examines a wide variety of ternary and quaternary materials synthesized by ALD. The span of this work is explored in this section, and common trends are discussed. Doped materials are not separately addressed but rather are included as ternary materials. A survey of ternary and quaternary materials synthesized by ALD is presented in Tables 1−5. Although many of the materials have been described in multiple reports, for brevity we have identified the reference representing what is to our knowledge the first paper to present the ALD synthesis of each material using a particular ALD process. Some constraints were imposed to limit the scope of the works included to those most relevant to this review. Molecular layer deposition (MLD)71−76 or hybrid ALD-MLD71,77−82 processes that use one precursor to deposit an entire moleculeusually an organicare not covered here. As can be seen in Tables 4 and 5, ALD has been used to synthesize a number of different phosphates, carbonates, oxysulfides, carbonitrides, and other materials with multiple nonmetal elements. Nonmetal elements like carbon, nitrogen, and halogens are also common impurities found in ALD processes,83−91 so we have only included ALD processes here that were clearly designed such that these elements are intentionally incorporated as significant components of the films. Included in each process entry are the precursors and co-reactants, deposition temperature, post-deposition annealing conditions to yield crystallinity, and growth rates. The tables are organized alphabetically by metal atom contained in the film. Most ternary compounds synthesized by ALD have two metal atoms, A and B, and can be written as either ABxCy or BAzCy, 1148
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Chemistry of Materials Table 1. Previous Work on Ternary Metal Oxides via ALDa material
binary 1
precursor 1
co-reactant 1 binary 2
precursor 2
co-reactant 2 temp. (°C)
anneal to growth rate crystallization (°C) (Å/cyc) ref
AlGaxOy
Al2O3
AlMe3
O3/H2O
Ga2O3
GaMe3
O3/H2O
200
n.r.
1.1
319
AlTaxOy
Al2O3
AlMe3
H2 O
Ta2O5
Ta(OEt)5
H2 O
325
amorphousc
n.r.
320
BaTixOy
BaO
Ba(CpiPr3)2
O2 plasma
TiO2
Ti(OiPr)4
O2 plasma
200−350
crystallineb
0.6−0.8
115
BaO
Ba(Cp Pr3)2
H2 O
TiO2
Ti(O Pr)4
H2 O
225
crystallineb
0.6−0.9
321
BaO
Ba(CpiPr3)2
H2 O
TiO2
Ti(OiPr)4
H2 O
290
500
0.28−0.40
322
BaO
Ba pyrrole
H2 O
TiO2
Ti(OiPr)4
H2 O
180−250
amorphousc
0.17
116
i
i
i
BaO
Ba(CpMe5)2
H2 O
TiO2
Ti(O Pr)4
H2 O
250−325
500
0.5
117
BaO
Ba(CptBu3)2
H2 O
TiO2
Ti(OiPr)4
H2 O
350−350
500
0.4−1.0
323
BaO
Ba(CptBu3)2
H2 O
TiO2
Ti(OMe)4
H2 O
300
600, O2
0.55−0.76
324
BaZrxOy
BaO
Ba(CpPrMe4)2
H2 O
ZrO2
Zr(NMe2)4
H2 O
250−270
600, O2
1.1−1.2
325
BiFexOy
seq.
BiMe3
seq.
C6H8Fe(CO)3
H2 O
490−520
crystallineb
0.55−0.85
38
Bi2O3
Bi(thd)3
H2 O
Fe2O3
Fe(thd)3
H2 O
250
650, O2
0.05
326
Bi2O3
Bi(OCMe2CHMe2)3
H2 O
Fe2O3
Fe(OtBu)3
H2 O
150
500, N2
n.r.
327
Bi2O3
Bi(thd)3
H2 O
Fe2O3
FeCp2
O3
250
650, O2
0.2
328
Bi2O3
Bi(thd)3
O2 plasma
Fe2O3
Fe(thd)3
O2 plasma
210
550, O2
0.61
329
Bi2O3
BiPh3
O3
Fe2O3
FeCp2
O3
290
450
0.2−1.4
330
Bi2O3
Bi(mmp)3
O3
Fe2O3
FeCp2
O3
250−350
600
0.24
331
BiTaxOy
Bi2O3
Bi(N(SiMe3)2)3
H2 O
Ta2O5
Ta(OEt)5
H2 O
190−200
amorphousc
0.3
50
BiTixOy
Bi2O3
BiPh3
O3
TiO2
Ti(OiPr)4
H2 O
250
700−900
n.r.
128
i
BiVxOy
Bi2O3
BiPh3
H2 O
TiO2
Ti(O Pr)4
H2 O
260−325
500−700
0.17−0.23
190
Bi2O3
Bi(N(SiMe3)2)3
H2 O
TiO2
Ti(OMe)4
H2 O
190
750
0.01−0.4
221
Bi2O3
BiPh3
H2 O
V2O5
VO(OiPr)3
H2 O
130
450
0.07
41
Bi2O3
BiPh3
H2 Oe
V2O5
VO(OiPr)3
H2 O
130
450
0.075
332
Bi2O3
BiPh3
O3
V2O5
VO(OiPr)3
H2 O
130
crystallineb
n.r.
41
seq.
BiPh3
seq.
VO(OiPr)3
H2 O
130
n.r.
n.r.
41
Ca(CpiPr3)2
H2 O
HfO2
HfCl4
H2 O
230−300
750, O2
0.55−0.93
333
CaHfxOy CaO CdZnxOy CdO
CdMe2
H2 O
ZnO
ZnEt2
150
crystalline
2.0−2.5
334
CeHfxOy CeO2
Ce(thd)4
O3
HfO2
Hf(CpMe)2(OMe)Me O3
300
900, dry air
0.6−0.9
335
CeO2
Ce(CpiPr)3
H2 O
HfO2
Hf(NMe2)4
H2 O
250
n.r.
n.r.
336
CeO2
Ce(thd)4
O3
Y2O3
Y(thd)3
O3
300
crystallineb
0.39−0.57
337
CoFexOy CoOx
CoCp2
O3
Fe2O3
FeCp2
O3
250
crystallineb
0.4−0.5
239
CoOx
CoCp2
O2
Fe2O3
FeCp2
O2
450
n.r.
n.r.
338
CoOx
Co(thd)2
O radical
Fe2O3
Fe(thd)3
O radical
190−230
450, O2
0.4
339
CoOx
Co(thd)2
O3
Fe2O3
Fe(thd)3
O3
185−310
600, O2
0.11−0.22
27
mcc.
CrO2Cl2
mcc.
AlMe3
100−200
n.r.
4.5
340
CuCrxOy CuOx
Cu(thd)2
O3
Cr2O3
Cr(acac)3
O3
250
700, O2
1.3
341
CuWxOy
CuOx
[Cu(dsbaa)]2
O3
WO3
W(tBuN)2(Me2N)2
H2 O
250
600
0.71
222
DyScxOy
Dy2O3
Dy(thd)3
O3
Sc2O3
Sc(thd)3
O3
300
900
0.18−0.19
104
DyTixOy
Dy2O3
Dy(thd)3
O3
TiO2
TiCl4
O3
300
crystallineb
0.37−0.50
342
CeYxOy
CrAlxOy
H2 O
b
Dy2O3
Dy(thd)3
O3
TiO2
TiCl4
H2 O
300
1000, vacuum
0.41
343
DyZrxOy
seq.
Dy(thd)3
seq.
ZrCl4
H2 O
300
crystallineb
1.6−1.8
344
ErAlxOy
Er2O3
n.r.
n.r.
Al2O3
n.r.
n.r.
n.r.
n.r.
n.r.
345
ErFexOy
Er2O3
Er(thd)3
O3
Fe2O3
Fe(thd)3
O3
280−300
650, N2
1.0
346 223
ErGaxOy
Er2O3
Er(thd)3
O3
Ga2O3
Ga(acac)3
O3
350
900−1000
0.25−0.28
Er2O3
Er(CpMe)3
H2 O
Ga2O3
Ga2(NMe2)6
H2 O
250
900−1000
1.0−1.5
223
ErScxOy
Er2O3
Er(thd)3
O3
Sc2O3
Sc(thd)3
O3
300
600
0.19
104
ErTixOy
Er2O3
Er(CpMe)3
O3
TiO2
Ti(NEt2)4
O3
245
amorphousc
0.51−0.64
118
Er2O3
Er(thd)3
O3
TiO2
TiCl4
H2 O
300
1000, vacuum
0.39
343
Er2O3
Er(CpMe)3
H2 O
Y2O3
YCp3
H2 O
n.r.
n.r.
n.r.
62
Er2O3
Er(thd)3
O2 plasma
Y2O3
Y(thd)3
O2 plasma
200−450
350
n.r.
64
ErZrxOy
Er2O3
Er(thd)3
O3
ZrO2
Zr(CpMe)2(OMe)Me O3
350
crystallineb
0.39−0.47
344
EuTixOy
Eu2O3
Eu(thd)3
O3
TiO2
TiCl4
225−375
crystallineb
0.31−0.74
347
ErYxOy
1149
H2 O
DOI: 10.1021/acs.chemmater.8b02878 Chem. Mater. 2019, 31, 1142−1183
Review
Chemistry of Materials Table 1. continued material
binary 1
precursor 1
co-reactant 1 binary 2
precursor 2
co-reactant 2 temp. (°C)
anneal to growth rate crystallization (°C) (Å/cyc) ref
FeCp2
O3
MgO
Mg(thd)2
O3
400−500
crystallineb
n.r.
348
Fe2O3
Fe(CpCH2NMe2)Cp
O3
MgO
Mg(thd)2
O3
325−450
crystallineb
0.68−3.7
348
Fe2O3
FeCp2
O3/H2O
TiO2
Ti(OiPr)4
H2 O
200
crystallineb
n.r.
349
Fe2O3
FeCp2
O3
TiO2
TiCl4
H2 O
250
amorphousc
0.51−1.08
350
Gd2O3
Gd(CpiPr)3
O3
Al2O3
AlMe3
O3
225−325
amorphousc
0.32−0.5
351
Gd2O3
Gd(CpiPr)3
H2 O
Al2O3
AlMe3
H2 O
225−325
amorphousc
0.8−0.96
351
GdCexOy Gd2O3
Gd(thd)3
O3
CeO2
Ce(thd)4
O3
250
n.r.
n.r.
352
GdScxOy Gd2O3
Gd(thd)3
O3
Sc2O3
Sc(thd)3
O3
300
900
0.21
104
Gd2O3
Gd(CpiPr)3
H2 O
Sc2O3
Sc(CpMe)3
H2 O
300
n.r.
n.r.
105
Gd2O3
Gd(dipaa)3
H2 O
Sc2O3
Sc(deaa)3
H2 O
310
n.r.
1.0
353
HfO2
HfCl4
H2 O
Al2O3
AlMe3
H2 O
300
900
n.r.
197
HfO2
Hf(NMe2)4
H2 O
Al2O3
AlMe3
H2 O
n.r.
950
n.r.
86
HfO2
Hf(NEt2)4
H2 O
Al2O3
AlMe3
H2 O
225
1000
n.r.
110
HfO2
Hf(NEt2)4
O3
Al2O3
Al(NEt2)3
O3
225
600
n.r.
108
HfO2
Hf(NEtMe)4
H2 O
Al2O3
AlMe3
H2 O
240
n.r.
n.r.
354
HfO2
Hf(NEtMe)4
H2 O2
Al2O3
AlMe3
H2 O2
250
900, vacuum
n.r.
355
HfO2
Hf(NEtMe)4
O2 plasma
Al2O3
AlMe3
O2 plasma
250
700
1.03−1.27
356
mcc.
HfCl4
mcc.
Al(OEt)3
400
n.r.
0.6
52
HfO2
Hf(CpMe)2(OMe)Me
O3
Er2O3
Er(thd)3
O3
315
800, N2
n.r.
357
FeMgxOy Fe2O3 FeTixOy GdAlxOy
HfAlxOy
HfErxOy
i
HfGdxOy HfO2
HfCl4
H2 O
Gd2O3
Gd(Cp Pr)3
H2 O
300
1050, N2
0.55
358
HfLaxOy
HfO2
Hf(NEtMe)4
O3
La2O3
La(famd)3
O3
265
900
n.r.
111
HfTaxOy
HfO2
HfCl4
H2 O
Ta2O5
Ta(OEt)5
H2 O
325
amorphousc
n.r.
359
HfO2
HfCl4
H2 O
Ta2O5
TaCl5
H2 O
300
800, Ar or O2
n.r.
360
HfO2
HfCl4
H2 O
TiO2
TiCl4
H2 O
300
400−750
1.0−3.8
114
mcc.
HfCl4
mcc.
Ti(OiPr)4
300
n.r.
0.5
52
HfO2
Hf(CpMe)2(OMe)Me
O3
Y2O3
Y(CpMe)3
O3
350
500, N2
n.r.
361
HfO2
Hf(NEtMe)4
O3
Y2O3
Y(CpMe)3
O3
275
500, N2
n.r.
361
HfO2
Hf(NEt2)4
H2 O
Y2O3
Y(CpMe)3
H2 O
250
600, N2
n.r.
362
HfO2
HfCl4
H2 O
Y2O3
Y(CpMe)3
H2 O
260−420
300
n.r.
363
HfO2
HfTixOy HfYxOy
Hf(NEt2)4
H2 O
Y2O3
Y(CpEt)3
H2 O
250−285
600, N2
1.5−1.7
364
HfZnxOy HfO2
Hf(NEtMe)4
H2 O
ZnO
ZnEt2
H2 O
220
crystallineb
1.74−1.93
365
HfZrxOy
HfO2
HfCl4
H2 O
ZrO2
ZrCl4
H2 O
300
amorphousc
n.r.
360
HfO2
Hf(NEt2)4
H2 O
ZrO2
Zr(NEt2)4
H2 O
250
950
1.2
366
HfO2
Hf(NEt2)4
O3
ZrO2
Zr(NEt2)4
O3
250
n.r.
0.8
367
co-dose
Hf(NEt2)4
H2 O
co-dose Zr(NEt2)4
H2 O
250
n.r.
0.6
367
HoTixOy HoOx
Ho(thd)3
O3
TiO2
TiCl4
H2 O
300
1000, vacuum
0.8
343
InGaxOy
In2O3
InN(SiMe3)2
H2 O2
Ga2O3
GaMe3
H2 O2
200
amorphousc
0.42
368
seq.
InN(SiMe3)2
seq.
GaMe3
H2 O2
200
amorphousc
0.77
368
seq.
GaMe3
seq.
InN(SiMe3)2
H2 O2
200
amorphousc
0.33
368
InSnxOy
b
In2O3
InCl3
H2O2/ H2O SnO2
SnCl4
H2O2/ H2O 500
crystalline
0.2
205
In2O3
InCp
O3
SnO2
Sn(NMe2)4
H2 O2
200−325
crystallineb
1.1−1.7
369
In2O3
InMe3
H2 O
ZnO
ZnEt2
H2 O
200
amorphousc
0.2−1.6
370
In2O3
In(NMe2)Me2
H2 O
ZnO
ZnEt2
H2 O
300
n.r.
n.r.
371
InZrxOy
In2O3
InCl3
H2 O
ZrO2
ZrCl4
H2 O
500
crystallineb
0.27−0.30
372
KAlxOy
KOx
KOtBu
H2 O
Al2O3
AlMe3
H2 O
250−350
n.r.
0.9−2.5
373
KNbxOy
KOx
KOtBu
H2 O
Nb2O5
Nb(OEt)5
H2 O
200−350
500
0.38−0.71
103
KTaxOy
KOx
t
KO Bu
H2 O
Ta2O5
Ta(OEt)5
H2 O
200−350
500
0.40−0.70
103
LaAlxOy
La2O3
La(thd)3
O3
Al2O3
Al(acac)3
O3
325−400
900
0.3−0.5
87
La2O3
La(thd)3
O3
Al2O3
AlMe3
O3
250
650, O2
0.35−0.85
374
La2O3
La(N(SiMe3)2)3
H2 O
Al2O3
AlMe3
H2 O
250
n.r.
0.58
127
La2O3
La(dipaa)3
H2 O
Al2O3
AlMe3
H2 O
300−330
n.r.
0.92
126
La2O3
La(CpiPr)3
H2 O
Al2O3
AlMe3
H2 O
300
900
17
148
InZnxOy
1150
DOI: 10.1021/acs.chemmater.8b02878 Chem. Mater. 2019, 31, 1142−1183
Review
Chemistry of Materials Table 1. continued material
binary 1
precursor 1
co-reactant 1 binary 2
precursor 2
co-reactant 2 temp. (°C)
anneal to growth rate crystallization (°C) (Å/cyc) ref
H2 O
Al2O3
AlMe3
H2 O
300
amorphousc
0.93
[LaAl(O Pr)6( PrOH)]2
H2 O
160−300
amorphousc
0.8−5.1
151
LaCoxOy La2O3
La(thd)3
O3
CoOx
Co(thd)2
O3
200−400
600
0.15−0.65
88
LaCuxOy La2O3
La(thd)3
O3
CuOx
Cu(acac)2
O3
210−300
650
0.31−0.52
376
LaFexOy
La2O3
La(thd)3
O3
Fe2O3
Fe(thd)3
O3
210−350
600, O2
0.2−0.35
149
LaGaxOy
La2O3
La(thd)3
O3
Ga2O3
Ga(acac)3
O3
325−425
850
0.38−0.40
224
LaLuxOy
La2O3
La(thd)3
O3
Lu2O3
Lu(thd)3
O3
300
800−1100
n.r.
123
La2O3
La(dipfa)3
H2 O
Lu2O3
Lu(defa)3
H2 O
300
n.r.
1.2
124
LaMnxOy La2O3
La(thd)3
O3
MnOx
Mn(thd)3
O3
200−400
crystallineb
0.08−0.4
377
LaNixOy
La2O3
La(thd)3
O3
NiO
Ni(thd)2
O3
150−500
600
0.03−0.26
225
La2O3 mcp.
LaScxOy LaTixOy
La(dipfa)3 i
i
375
La2O3
La(dipfa)3
H2 O
Sc2O3
Sc(deaa)3
H2 O
300
n.r.
1.2
124
La2O3
La(thd)3
O3
Sc2O3
Sc(thd)3
O3
300
800
0.26−0.28
104
La2O3
La(thd)3
O3
TiO2
TiCl4
H2 O
225
n.r.
0.17−0.50
240
b
LaYxOy
La2O3
La(dipfa)3
H2 O
Y2O3
Y(dipaa)3
H2 O
280
crystalline
LaZrxOy
La2O3
La(N(SiMe3)2)3
H2 O
ZrO2
Zr(NEt2)4
H2 O
250
n.r.
La2O3
La(CpiPr)3
O3
ZrO2
Zr(CpMe)2(OMe)Me O3
300
600
n.r.
125
mcc.
La(CpiPr)3
mcc.
Zr(CpMe)2(OMe)Me
300
700, air
1.7−3.2
378
Li2O/LiOH
LiOtBu
H2 O
Al2O3
AlMe3
O3 , H2 O
225
n.r.
2.8
135
Li2O/LiOH
LiN(SiMe3)2
H2 O
Al2O3
AlMe3
O3
175−300
950, air
1.0−1.2
167
LiCoxOy
Li2CO3
LiOtBu
O2 plasma
CoOx
CoCp2
O2 plasma
325
700
0.6
139
LiLaxOy
Li2CO3
Li(thd)
O3
La2O3
La(thd)3
O3
225
n.r.
0.22−0.35
89
LiMnxOy Li2O/LiOH
Li(thd)
O3
MnOx
Mn(thd)3
O3
225
crystallineb
0.15−0.23
140
LiNbxOy
Li2O/LiOH
LiN(SiMe3)2
H2 O
Nb2O5
Nb(OEt)5
H2 O
235
650
0.4−0.9
248
Li2O/LiOH
LiOtBu
H2 O
Nb2O5
Nb(OEt)5
H2 O
235
amorphousc
0.51−0.96
379
LiTaxOy
Li2O/LiOH
LiOtBu
H2 O
Ta2O5
Ta(OEt)5
H2 O
225
amorphousc
0.66−1.1
380
LiTixOy
Li2O/LiOH
LiOtBu
H2 O
TiO2
Ti(OiPr)4
H2 O
225
700
0.65−0.8
141
LiAlxOy
LiVxOy
124 127
Li(thd)
O3
V2O5
VO(thd)2
O3
225
crystalline
LuMnxOy Lu2O3
Lu(thd)3
O3
MnOx
Mn(thd)3
O3
275−300
1000
LuScxOy
Lu(thd)3
O3
Sc2O3
Sc(thd)3
O3
300
crystallineb
0.18
104
MgAlxOy MgO
MgCp2
H2 O
Al2O3
AlMe3
H2 O
100−400
800
0.22−0.3
90
MgCaxOy MgO
Mg(dsbaa)2
H2 O
CaO
Ca(dipaa)2
H2 O
310
crystallineb
0.50−0.75
381
MnCoxOy MnOx
Mn(thd)3
O3
CoOx
Co(thd)3
O3
135−275
crystallineb
0.18−0.48
382
NaAlxOy
NaOx
NaOtBu
H2 O
Al2O3
AlMe3
H2 O
250−375
n.r.
0.5−1.6
373
NaOx
NaOtBu
O3
Al2O3
AlMe3
O3
250
n.r.
0.8−1.4
373
NaOx
NaOSiMe3
H2 O
Al2O3
AlMe3
H2 O
250
n.r.
n.r.
373
NaNbxOy NaOx
NaOtBu
H2 O
Nb2O5
Nb(OEt)5
H2 O
200−350
500
0.38−0.50
103
NaTaxOy NaOx
NaOtBu
H2 O
Ta2O5
Ta(OEt)5
H2 O
200−350
500
0.40−0.48
103
NbAlxOy
Nb(OEt)5
H2 O
Al2O3
AlMe3
H2 O
300
amorphousc
1.8−2.7
383
NbSnxOy Nb2O5
Nb(NtBu)(NEt2)3
O3
SnO2
Sn(NMe2)4
O3
120
500
n.r.
384
NbTaxOy Nb2O5
NbF5
H2 O
Ta2O5
TaF5
O3
225
600, N2
n.r.
385
NdAlxOy
Nd2O3
Nd(thd)3
O3
Al2O3
AlMe3
H2 O
300
800, O2
0.45−1.0
386
mcp.
[NdAl(OiPr)6(iPrOH)]2
H2 O
180−350
amorphousc
4.2−5.2
152
NdTixOy Nd2O3
Nd(thd)3
O3
TiO2
TiCl4
H2 O
300
1000, vacuum
0.39
343
NiCoxOy NiO
Ni(thd)2
O3
CoOx
Co(thd)2
O3
200
crystallineb
0.2
387
NiFexOy
NiO
NiCp2
O3
Fe2O3
FeCp2
O3
200
700
0.25−0.3
239
NiTixOy
NiO
Ni(acac)2
O3
TiO2
Ti(OiPr)4
H2 O
250
crystallineb
0.35−0.45
219
PbTixOy
Li2O/LiOH
b
1.0 0.5
Lu2O3
Nb2O5
i
n.r.
140
0.18
226
PbO
PbPh4
O3
TiO2
Ti(O Pr)4
H2 O
250−300
600
0.1−0.6
212
PbO
Pb(tmod)2
H2 O
TiO2
Ti(OiPr)2(thd)2
H2 O
240−300
amorphousc
n.r.
388
PbO
Pb(thd)2
H2 O
TiO2
Ti(OiPr)2(thd)2
H2 O
240
500, O2
n.r.
227
PbO
Pb(dmamp)2
H2 O
TiO2
Ti(OtBu)4
H2 O
200
550, O2
0.55−0.70
228
PbO
Pb(dmamp)2
H2 O
TiO2
Ti(OiPr)4
H2 O
200
n.r.
n.r.
389
PbO
Pb(dmamp)2
H2 O
TiO2
Ti(OiPr)4
O3
200
600, O2
1.09
229
1151
DOI: 10.1021/acs.chemmater.8b02878 Chem. Mater. 2019, 31, 1142−1183
Review
Chemistry of Materials Table 1. continued material PbZrxOy
binary 1 PbO
precursor 1 PbPh4
co-reactant 1 binary 2
precursor 2
co-reactant 2 temp. (°C)
anneal to growth rate crystallization (°C) (Å/cyc) ref
O3
ZrO2
Zr(thd)4
O3
275−300
crystallineb
0.12
129
PrAlxOy
mcp.
[PrAl(O Pr)6( PrOH)]2
H2 O
180−350
amorphousc
1.2−2.5
152
PrTixOy
Pr2O3
Pr(thd)3
O3
TiO2
TiCl4
H2 O
300
1000, vacuum
0.39
343
RbNbxOy RbOx
RbOtBu
H2 O
Nb2O5
Nb(OEt)5
H2 O
250
750
0.1−1.4
390
RbTixOy
RbOx
RbOtBu
H2 O
TiO2
Ti(OiPr)4
H2 O
250
amorphousc
0.4−1.1
390
RuAlxOy
Ru
Ru(imbch)
O2
Al2O3
AlMe3
H2 O
225
mixed phased
n.r.
136
i
i
SmMnxOy Sm2O3
Sm(thd)3
O3
MnOx
Mn(thd)3
O3
275
1000
0.23
226
SmTixOy Sm2O3
Sm(thd)3
O3
TiO2
TiCl4
H2 O
300
1000, vacuum
0.39
343
SnAlxOy
SnO2
Sn(cyam)
H2 O2
Al2O3
AlMe3
H2 O
120
amorphousc
0.13−0.18
391
SnTixOy
SnO2
Sn(acac)2
O3
TiO2
Ti(NEt2)4
O3
200
mixed phased
0.7
392
SrCoxOy
SrO
Sr(thd)2
O3
CoOx
Co(acac)3
O3
290−330
600
0.84
230
SrFexOy
SrO
Sr(thd)2
O3
Fe2O3
Fe(thd)3
O3
260
n.r.
n.r.
149
SrHfxOy
SrO
Sr(CpiPr)2
O2 plasma
HfO2
Hf(CpMe)2(OMe)Me O2 plasma
250
600, air
n.r.
393
SrTaxOy
SrTixOy
mcp.
SrTa2(OEt)10(dmae)2
H2 O
200−350
800
0.25−0.31
46
mcp.
Sr[Ta (OEt)5(OC2H4OMe)]2
O2 plasma
250−300
amorphousc
0.5
33
SrO
Sr(CpiPr3)2
H2 O
TiO2
Ti(OiPr)4
H2 O
250−325
crystallineb
0.7−1.8
117
SrO
Sr(Cp Pr3)2
H2 O
TiO2
Ti(O Pr)2(thd)2
O3
370
crystallineb
1.07
394
SrO
Sr(CpiPr3)2
O3
TiO2
Ti(NEtMe)4
O3
300
550
0.58−1.0
395
SrO
Sr(methd)2
O2 plasma
TiO2
Ti(OiPr)4
O2 plasma
250
n.r.
0.78
120
i
i
i
SrO
Sr(thd)2
O3
TiO2
Ti(O Pr)4
O3
290−325
600, N2
0.52−0.72
213
SrO
Sr(thd)2
H2O/H2O plasma
TiO2
Ti(OiPr)4
H2O/H2O plasma
190−270
600
0.1−0.6
119
SrO
Sr(thd)2
O2 plasma
TiO2
Ti(OiPr)4
O2 plasma
225
600, N2
n.r.
396
co-dose
Sr(thd)2
O2 plasma
co-dose Ti(OiPr)4
O2 plasma
250−350
280
0.3−0.4
170
SrO
Sr(thd)2
H2O/H2O plasma
TiO2
Ti(OiPr)2(thd)2
H2O/H2O plasma
370
600, N2
n.r.
231
SrO
Sr(CptBu3)2
H2 O
TiO2
Ti(OMe)4
H2 O
250
520
n.r.
121
SrO
Sr(CptBu3)2
O3
TiO2
Ti(OMe)4
O3
250
600, N2
n.r.
385
SrO
i
Sr(Cp Pr3)2
H2 O
TiO2
Ti(CpMe5)(OMe)3
O3
370
crystalline
0.1−0.7
397
SrO
Sr2(thd)2(demamp)2
O3
TiO2
Ti(CpMe5)(OMe)3
O3
370
crystallineb
0.5
398
SrO
Sr(CpiPr3)2(Et[OMe]2)
O2 plasma
TiO2
Ti(CpMe5)(OMe)3
O2 plasma
250
500, N2
0.51−0.78
232
SrO
Sr(CpiPr3)2(Et[OMe]2)
O3
TiO2
Ti(CpMe5)(OMe)3
O3
275
n.r.
0.3−1.0
399
SrO
Sr(CpiPr3)2(Et[OMe]2)
O3
TiO2
Ti(CpMe)(OMe)3
O3
275
n.r.
0.27−1.0
399
b
SrZrxOy
SrO
Sr(CpiPr3)2
O3
ZrO2
Zr(CpMe)2(OMe)Me O3
350
700
n.r.
400
TaZrxOy
Ta2O5
Ta(OEt)5
O3
ZrO2
ZrCl4
O3
300
800, N2
0.38−0.45
42
Ta2O5
Ta(OEt)5
H2 O
ZrO2
ZrCl4
H2 O
325
crystallineb
n.r.
320
Ta2O5
TaCl5
H2 O
ZrO2
ZrCl4
H2 O
300
amorphousc
n.r.
360
seq.
Ta(OEt)5
seq.
ZrCl4
O3
300
800, N2
0.50−1.1
42
mcc.
Ta(OEt)5
mcc.
ZrCl4
300
800, N2
0.33−0.45
42
Ta2O5
Ta(NEt2)3NtBu
O2/Ar plasma
ZrO2
Zr(NMe2)3Cp
O2/Ar plasma
250
400
n.r.
401
Tb2O3
Tb(thd)3
O3
Al2O3
AlMe3
O3
350
amorphousc
n.r.
402
0.21−0.25
403
TbAlxOy
b
TbScxOy
Tb2O3
Tb(thd)3
O3
Sc2O3
Sc(thd)3
O3
300
crystalline
TbTixOy
Tb2O3
Tb(thd)3
O3
TiO2
TiCl4
H2 O
300
1000, vacuum
0.33
343
TiAlxOy
TiO2
Ti(OEt)4
H2 O
Al2O3
AlMe3
H2 O
300
700, N2
0.41−0.85
122
TiO2
TiCl4
H2 O
Al2O3
AlMe3
H2 O
200
n.r.
0.4−1.1
404
TiO2
TiCl4
H2 O
Al2O3
AlCl3
H2 O
200−450
amorphousc
n.r.
43
seq.
TiCl4
seq.
AlMe3
H2 O
150−450
amorphousc
n.r.
43
seq.
TiCl4
seq.
AlCl3
H2 O
100−500
amorphousc
n.r.
43
c
TiO2
TiCl4
O3
Al2O3
AlCl3
O3
350
amorphous
n.r.
405
TiO2
Ti(OiPr)4
O3
Al2O3
AlMe3
O3
250
n.r.
0.26−0.28
96
TiO2
Ti(OiPr)4
O2 plasma
Al2O3
AlMe3
O2 plasma
250
n.r.
0.35
406
1152
DOI: 10.1021/acs.chemmater.8b02878 Chem. Mater. 2019, 31, 1142−1183
Review
Chemistry of Materials Table 1. continued material
binary 1
precursor 1
co-reactant 1 binary 2
precursor 2
co-reactant 2 temp. (°C)
anneal to growth rate crystallization (°C) (Å/cyc) ref
TiO2
Ti(OiPr)4
O2 plasma
Al2O3
AlMe3
N2O plasma 250
n.r.
0.59
406
mcc.
Ti(OiPr)4
mcc.
AlCl3
300
n.r.
2.3
52
TiO2
Ti(NMe2)4
H2 O
Al2O3
AlMe3
H2 O
200
amorphousc
n.r.
407
TiO2
Ti(OMe)4
H2 O
CoOx
Co(acac)3
H2 O
300
650, N2/H2
0.14−0.44
408
TiO2
Ti(OMe)4
O3
CoOx
Co(acac)3
O3
300
650, N2/H2
0.37−0.41
408
TiO2
TiCl4
CH3OH
Cr2O3
CrO2Cl2
CH3OH
375
crystallineb, mixed phased
n.r.
409
TiMnxOy TiO2
Ti(OiPr)4
H2 O
MnOx
Mn(CpEt)2
H2 O
200
n.r.
0.2−0.8
410
TiNbxOy TiO2
Ti(OMe)4
H2 O
Nb2O5
Nb(OEt)5
H2 O
215
600
n.r.
233
TiTaxOy
TiO2
Ti(OMe)4
H2 O
Ta2O5
Ta(OEt)5
H2 O
215
600
n.r.
233
TiO2
Ti(OiPr)4
H2 O
Ta2O5
Ta(NCMe2Et) (NMe2)3
H2 O
220
crystallineb
n.r.
411
TiCoxOy TiCrxOy
TmTixOy Tm2O3
Tm(thd)3
O3
TiO2
TiCl4
H2 O
300
1000, vacuum
0.38
343
VCrxOy
V2O5
VOCl3
H2 O
Cr2O3
CrO2Cl2
H2 O
200
n.r.
n.r.
412
WAlxOy
W
WF6
Si2H6
Al2O3
AlMe3
H2 O
177
mixed phased
1.2−4.5
413
YAlxOy
Y2O3
Y(CpEt)3
H2 O
Al2O3
AlMe3
H2 O
300
900, He
0.9−1.7
414
YMnxOy
Y2O3
Y(thd)3
O3
MnOx
Mn(thd)3
O3
250−325
900
0.2−0.3
234
Y2O3
Y(thd)3
O3
Sc2O3
Sc(thd)3
O3
335−350
1000
0.13−0.23
107
Y2O3
Y(CpMe)3
H2 O
Sc2O3
ScCp3
H2 O
300
800
0.8−1.6
107
YbMnxOy Yb2O3
Yb(thd)3
O3
MnOx
Mn(thd)3
O3
275−300
900
0.18
226
YbTixOy
Yb2O3
Yb(thd)3
O3
TiO2
TiCl4
H2 O
300
1000, vacuum
0.38
343
YbVxOy
Yb2O3
Yb(thd)3
O3
V2O5
VO(thd)2
O3
240
500, air
0.8−2.3
415
ZnAlxOy
ZnO
ZnEt2
H2 O
Al2O3
AlMe3
H2 O
177
n.r.
1.25−2.0
315
ZnO
ZnEt2
H2 O
Al2O3
AlCl3
H2 O
200
amorphousc
1.07−1.26
314
YScxOy
i
ZnO
ZnEt2
H2 O
Al2O3
AlMe2O Pr
H2 O
250
n.r.
0.6−1.7
65
ZnO
ZnEt2
H2 O
Al2O3
Al(OiPr)3
H2 O
200
crystallineb
1.16−1.35
211
ZnO
ZnEt2
O3
Al2O3
AlMe3
O3
250
crystallineb
1.4−1.7
29
co-dose
ZnEt2
O3
co-dose AlMe3
O3
250
crystallineb
1.5−1.7
29
b
0.5−2.5
416
ZnEt2
H2 O
Al2O3
AlMe3
H2 O
150−250
crystalline
ZnCoxOy ZnO
ZnMe2
H2 O
CoOx
Co(acac)2
H2 O
160
crystallineb
n.r.
417
ZnFexOy
ZnEt2
H2 O
Fe2O3
FeCp2
O3
250
600, air
0.31−0.32
418
ZnGaxOy ZnO
ZnEt2
H2 O
Ga2O3
GaMe3
H2 O
130−210
n.r.
n.r.
419
ZnO
ZnEt2
H2 O
Ga2O3
GaMe3
O3
250
crystallineb
n.r.
420
ZnO
ZnEt2
H2 O
Ga2O3
GaEt3
H2 O
300
n.r.
n.r.
421
ZnMgxOy ZnO
ZnEt2
H2 O
MgO
MgCp2
H2 O
105−180
crystallineb
0.75−1.75
422
ZnO
ZnO ZnO
ZnEt2
H2 O
MgO
Mg(CpEt)2
H2 O
120
n.r.
1.3−1.5
423
ZnMnxOy ZnO
Zn(MeCOO)2
H2 O
MnOx
Mn(thd)3
H2 O
230−250
crystallineb
n.r.
424
ZnO
Zn(MeCOO)2
H2 O
MnOx
Mn(acac)3
H2 O
230−250
crystallineb
n.r.
424
ZnSnxOy ZnO
ZnEt2
O2 plasma
SnO2
Sn(NMeEt)4
O2 plasma
150
600
1.4−1.9
235
ZnO
ZnEt2
H2 O
SnO2
Sn(OtBu)4
H2 O
120
n.r.
0.18−1.6
422
ZnO
ZnEt2
H2 O
SnO2
Sn(NMe2)4
H2 O
120
amorphousc
0.38−0.41
422
ZnO
ZnEt2
H2 O2
SnO2
Sn(cyam)
H2 O2
170
750, air
n.r.
236
ZnO
ZnEt2
O3
SnO2
SnC12H28N2O2
O3
150
600, air
n.r.
425
ZnO
ZnEt2
O2 plasma
SnO2
Sn(dmamp)2
O2 plasma
100−200
amorphousc
1.4
426
ZnO
ZnEt2
O3
SnO2
SnEt4
O3
250−320
amorphousc
1.3−2.1
427
ZnTaxOy ZnO
ZnEt2
H2 O
Ta2O5
Ta(NMe2)5
H2 O
n.r.
crystallineb
n.r.
428
ZnTixOy
ZnO
ZnEt2
H2 O
TiO2
Ti(NMe2)4
H2 O
90
600
1.8−3.0
216
ZnO
ZnEt2
H2 O
TiO2
Ti(OiPr)4
H2 O
200
600
0.46−0.53
241
ZnZrxOy
ZnO
ZnEt2
H2 O
ZrO2
Z(NMe2)4
H2 O
180
400
n.r.
429
ZrAlxOy
mcc.
ZrCl4
mcc.
Al(OEt)3
400
n.r.
0.45
52
ZrFexOy
ZrO2
Zr(thd)4
O3
Fe2O3
Fe(thd)3
O3
350
600, N2
n.r.
214
ZrTixOy
mcc.
ZrCl4
mcc.
Ti(OiPr)4
300
n.r.
1.2
52
1153
DOI: 10.1021/acs.chemmater.8b02878 Chem. Mater. 2019, 31, 1142−1183
Review
Chemistry of Materials Table 1. continued material ZrYxOy
binary 1
precursor 1
co-reactant 1 binary 2
precursor 2
co-reactant 2 temp. (°C)
anneal to growth rate crystallization (°C) (Å/cyc) ref
ZrO2
Zr(OtBu)4
H2 O
TiO2
Ti(OiPr)4
H2 O
225
1000
n.r.
430
ZrO2
Zr(thd)4
O3
Y2O3
Y(thd)3
O3
375
crystallineb
0.56
130
ZrO2
ZrCp2Me2
O3
Y2O3
Y(thd)3
O3
310−365
crystallineb
0.79
130
ZrO2
ZrCp2Cl2
O3
Y2O3
Y(thd)3
O3
275−350
crystallineb
0.89
130
ZrO2
Z(NMe2)4
H2 O
Y2O3
Y(CpMe)3
H2 O
200−250
crystallineb
2.0
431
ZrO2
ZrCl4
H2 O
Y2O3
YCp3
H2 O
300
950
n.r.
198
a
Each ternary compound appears only once as either ABxCy or BAxCy. Note that ternary oxides containing metalloids (e.g. Si, Ge) are included in Table 4. In cases where a process design omits a precursor or a process, the space only contains a dash. A slash indicates a mixture of two co-reactants. If an alternative approach is used, the approach is indicated in the binary process columns: “co-dose” for co-dosing of metal precursors of different binary processes that share a single co-reactant exposure, “seq.” for sequential pulsing of the indicated precursors in the order listed, “mcp.” for a multiconstituent precursor, and “mcc.” for a multiconstituent co-reactant. All growth rates are presented on a per subcycle basis. Any data not reported by the study is marked n.r. bThis material showed crystalline behavior (partially crystalline, polycrystalline, or epitaxial) as-deposited, with no additional annealing needed. cThis material was amorphous as-deposited. The study either did not find annealing conditions that resulted in crystallization or did not attempt annealing to crystallize the film. dThis material was not a homogeneous ternary compound, either as-deposited or postannealing. The resulting materials instead show some form of significant phase segregation, and the study did not find annealing conditions that caused formation of a homogeneous or nearly homogeneous material. eThis process also included inhibitor molecules in the process to adjust the growth and composition of the films.
Table 2. Previous Work on Ternary Metal Nitrides via ALDa material
binary 1
AlGaxNy
AlN AlN Co InN InN InN InN NbN NbN
CoTixNy InAlxNy InGaxNy
NbTixNy
RuAlxNy RuTaxNy
RuTixNy TiAlxNy
precursor 1
co- reactant 1 binary 2
precursor 2
co-reactant 2
temp. (°C)
anneal to crystallization (°C)
growth rate (Å/cyc)
ref
N2/H2 plasma N2/H2 plasma NH3 N2 plasma NH3 N2 plasma N2 plasma NH3 N2/H2 plasma
GaN GaN TiO2 AlN GaN GaN GaN TiN TiN
GaMe3 GaMe3 Ti(NMe2)4 AlMe3 GaMe3 GaMe3 GaEt3 TiCl4 Ti(NMe2)4
N2/H2 plasma N2 plasma NH3 N2/H2 plasma NH3 N2 plasma N2/H2 plasma NH3 N2/H2 plasma
200 350−450 200 240−300 600−700 240−300 200 450 300
crystallineb crystallineb amorphousc crystallineb crystallineb crystallineb crystallineb crystallineb crystallineb
0.23−0.99 0.2−0.6 n.r. 0.5−0.6 0.2−1.0 0.2−0.5 0.3−0.4 n.r. 0.43−0.76
94 92 432 92 95 92 93 91 433
Ru Ru
AlMe3 AlMe3 Co(bepa)2 InMe3 InEtMe2 InMe3 InMe3 NbCl5 Nb(NtBu) (NEt2)3 Ru(CpEt)2 Ru(CpEtMe)2
NH3 plasma NH3 plasma
AlN TaN
NH3 plasma NH3 plasma
300 300
mixed phased mixed phased
0.45−1.5 n.r.
98 100
Ru
Ru(CpEt)2
NH3 plasma
TaN
NH3 plasma
300
mixed phased
0.32−0.35
101
Ru
Ru(CpEt)2
N2/H2 plasma
TaN
H2 plasma
230
900
0.2−1.3
137
Ru TiN seq. TiN
Ru(CpEt)2 Ti(NMe2)4 TiCl4 TiCl4
N2/H2 plasma N2 plasma NH3
TiN AlN seq. AlN
AlMe3 Ta(NtBu) (NEt2)3 Ta(NtBu) (NEt2)3 Ta(NC5H11) (NMe2)3 Ti(NMe2)4 AlMe3 AlMe3 AlMe3
N2 plasma N2 plasma NH3 NH3
200 200 250−400 300−400
amorphousc amorphousc crystallineb crystallineb
0.4−1.6 0.45 0.15−0.60 0.45−0.85
97 434 435 435
a
Each ternary compound appears only once as either ABxCy or BAxCy. Note that ternary nitrides containing metalloids and nonmetals are included in Table 4. A slash indicates a mixture of two co-reactants. All growth rates are presented on a per subcycle basis. Any data not reported by the study is marked n.r. bThis material showed crystalline behavior (partially crystalline, polycrystalline, or epitaxial) as-deposited, with no additional annealing needed. cThis material was amorphous as-deposited. The study either did not find annealing conditions that resulted in crystallization or did not attempt annealing to crystallize the film. dThis material was not a homogeneous ternary compound, either as-deposited or postannealing. The resulting materials instead show some form of significant phase segregation and the study did not find annealing conditions that caused formation of a homogeneous or nearly homogeneous material.
layers90,100,128,130,133,134 and diffusion barriers97−101,135−138 in electronic device manufacturing. Finally, of particular recent interest have been Li-containing compounds for application in Li-ion batteries as electrodes or solid electrolytes.39,89,139−145 This development is especially interesting given the increasing demand of Li-ion batteries and similar technologies, as well as the growing safety concerns of associated battery fires that could be addressed using solid electrolytes.89,135,139−141 Given the useful contributions the field of ALD has made in providing materials for these applications, together with the continued
importance of effective energy storage and more compact processing devices,13,146,147 further development here is warranted to take advantage of these opportunities. III.C. Processes and Precursors. Several general observations can be made about the ALD strategies used to synthesize the ternary and quaternary films tabulated in Tables 1−5. Figure 6 illustrates a summary of all the ternary metal oxide processes included in Table 1. Across all of the metal atoms used, Al, Ti, Hf, and Zn are some of the metals employed to make the greatest number of different materials. This is 1154
DOI: 10.1021/acs.chemmater.8b02878 Chem. Mater. 2019, 31, 1142−1183
Review
Chemistry of Materials Table 3. Previous Work on Ternary Metal Sulfides via ALDa material
binary 1
precursor 1
co-reactant 1
binary 2
precursor 2
co-reactant 2
temp. (°C)
anneal to crystallization (°C)
growth rate (Å/cyc)
ref
CdZnxSy CuAlxSy CuGaxSy
CdS CuSx co-dose CuSx CuSx CuSx CuSx CuSx ZnS FeSx Li2S SrS SrS ZnS ZnS ZnS
CdMe2 Cu(acac)2 CuCp(PEt3) CuCl CuCl Cu(acac)2 Cu2(dsbaa)2 Cu2(dsbaa)2 ZnEt2 Fe(dipaa)2 LiOtBu Sr(thd)2 Sr(thd)2 ZnEt2 ZnCl2 ZnI2
H2S H2S H2S H2S H2S H2S H2S H2S H2S H2S H2S H2S H2S H2S H2S H2S
ZnS Al2S3 co-dose GaSx In2S3 In2S3 SbSx seq. seq. CoSx Al2S3 CeSx TbSx In2S3 MnSx MnSx
ZnEt2 AlMe3 GaEt3 GaCl3 InCl3 In(acac)3 Sb(NEt2)3 ZnEt2 Cu2(dsbaa)2 Co(dipaa)2 Al(NMe2)3 Ce(thd)4 Tb(thd)3 In(acac)3 Mn(thd)3 Mn(thd)3
H2S H2S H2S H2S H2S H2S H2S H2S H2S H2S H2S H2S H2S H2S
150 140−250 550−600 530−570 350−500 150−200 100 135−150 135−150 120 150 380−420 380−420 200 420 420
crystallineb amorphousc crystallineb 530 crystallineb crystallineb 225, vacuum n.r. n.r. crystallineb amorphousc n.r. n.r. n.r. crystallineb crystallineb
1.0−1.3 0.05−0.14 5.0 1.8−5.9 n.r. 0.23−0.47 n.r. n.r. n.r. 0.22−0.28 0.50 n.r. n.r. n.r. n.r. n.r.
193 194 169 436 206 437 438 262 262 439 440 441 441 133 442 442
CuInxSy CuSbxSy CuZnxSy FeCoxSy LiAlxSy SrCexSy SrTbxSy ZnInxSy ZnMnxSy a
Each ternary compound appears only once as either ABxCy or BAxCy. Note that oxysulfides are included in Table 4. A slash indicates a mixture of two co-reactants. In the binary process columns, “co-dose” marks processes where metal precursors of different binary processes are dosed simultanesouly, sharing a single co-reactant exposure. All growth rates are presented on a per subcycle basis. Any data not reported by the study is marked n.r. bThis material showed crystalline behavior (partially crystalline, polycrystalline, or epitaxial) as-deposited, with no additional annealing needed. cThis material was amorphous as-deposited. The study either did not find annealing conditions that resulted in crystallization or did not attempt annealing to crystallize the film.
precursor with no separate co-reactant (Figure 3d).40,52,175−185 These approaches have allowed for the synthesis of Si-containing compounds that might have otherwise been very challenging to grow via ALD, illustrating that these strategies are worth exploring for other interesting but difficult chemistries. Because of contamination concerns, however, the vast majority of the ternary and quaternary processes outlined above avoid halogenated precursors or precursors containing elements other than C, N, H, and O, which can limit the options for precursor chemistries in multicomponent processes. The choice of precursor in these multicomponent processes also depends on their relative reactivities. One can gain insight into the reactivities of many precursors by examining the ligands. In contrast to O3 and O2 plasma, H2O is not an oxidizing agent and is a source of protons, so ligand elimination can occur via a ligand exchange reaction, replacing the ligand with a hydroxyl group and releasing a protonated form of the ligand. In Tables 1−5, clear trends can be observed as to which precursors are sufficiently reactive to be used with H2O in a multicomponent ALD process. With few exceptionslike Mn(Cp)2186most precursors with alkyl, phenyl, or amine ligands are used with H2O, whereas most precursors in the tables with cyclopentadienyl or diketonate ligands require O3 or O2 plasma to combust the ligands instead. While pKa is not a perfect descriptor of energetics in these ALD systems, alkyl chains, amines, and phenyl groups have significantly higher pKa values (≈35−50) than cyclopentadiene or beta-diketones (≈5−16).187,188 This in turn corresponds to a greater stability of the protonated eliminated alkyl, phenyl, and amine ligands and is reflected in the relative prevalence of H2O as the oxygen source with these precursors. An additional explanation for the difference in reactivity is that the negatively charged cyclopentadienyl and beta-diketonate ligands contain stabilizing aromaticity or resonance that must be broken in order for the ligand to be protonated and eliminated. As seen in Tables 1−5, however, halogenated and alkoxide precursors are almost always used with H2O despite the
perhaps due to the fact that these constituent binary processes are relatively popular, well-understood, and well-behaved. When processes are rendered more complex by combining the binary processes into ternary or quaternary processes, it is advantageous to have well-defined building blocks. Apart from these metal atoms, it can be seen in Figure 6 that La and Li are also used in a number of ternary and quaternary ALD studies. Neither process is as well-behaved, with Li2O and La2O3 both being hygroscopic126,148 and frequently requiring O3 to oxidize ligands in the ALD process. Even with O3 as the oxidizing agent, ternary oxides containing Li or La have been observed to contain carbon contamination via the formation of carbonates.88 La-based ALD is used nonetheless because of its promising applications in microelectronics and because the La atom size lends itself to forming perovskite crystal structures with other metal atoms.26,104,149 Figure 7 summarizes the ternary materials other than metal oxides synthesized thus far by ALD. Most of these are nitrides, sulfides, and phosphides, and Al and Zn are the most commonly used metals in them for similar reasons as stated above. In the majority of cases found in Tables 1−4, the supercycle scheme is used to combine two separate binary ALD processes that share one element (e.g., O, N, S) into a single ternary process. Some studies implement deposition with multiconstituent precursors to introduce more than one atom into the film with a single precursor,33,40,44−46,48,50,51,150−168 and others eschew the supercycle pulsing strategy in other ways29,33,34,36−38,169−172 as discussed in Section II; however, these are far less common among the works shown in the tables. Regarding the use of these alternative approaches, Si-containing compounds are of particular note as SiO2 itself is often difficult to grow on its own.34,40,44,48,106,173,174 A number of studies have successfully deposited Si-containing materials by ALD by using precursor strategies other than supercycles. These strategies include co-dosing multiple precursors simultaneously (Figure 3b),34 combining Si with another element in a multiconstituent precursor (Figure 3c),44,48,150,167,168 or using an alkoxide-containing 1155
DOI: 10.1021/acs.chemmater.8b02878 Chem. Mater. 2019, 31, 1142−1183
Review
Chemistry of Materials
Table 4. Previous Work on Ternary Compounds via ALD, Other than Metal Oxides, Nitrides, Sulfides, and Telluridesa
material
binary 1
precursor 1
co-reactant 1
binary 2
precursor 2
co-reactant 2
temp. (°C)
anneal to crystallization (°C)
growth rate (Å/cyc)
ref
AlGaxAsy
AlAs
AlMe3
AsH3
GaAs
GaMe3
AsH3
550−700
n.r.
2.9
207
AlPxOy
Al2O3
AlMe3
H2O
POx
PO(OMe)3
H2O
250
amorphousc
1.0
144
Al2O3
AlCl3
H2O
POx
PO(OMe)3
H2O
500
n.r.
n.r.
443
Al2O3
AlCl3
H2O
POx
PO(OMe)3
O3
150
amorphousc
1.64
444
Al2O3
AlMe3
H2O
POx
P(NMe2)3
H2O
120
n.r.
1.31
58
mcp.
AlCl3
PO(OMe)3
150−400
825, N2
1.4−2.4
153
mcp.
AlCl3
PO(OEt)3
250
amorphousc
0.82
445
Al2O3
AlCl3
H2O
POx
P2O5
H2O
500
n.r.
n.r.
443
seq.
AlCl3
seq.
P2O5
H2O
500
amorphousc
