Optimization of Bottom Electrodes for Enhancement of Ferroelectric Performance in Hafnia-Based Oxides Using a Back-End-of-Line (BEOL) Compatible Process

Abstract

The disclosed and claimed subject matter relates to a ferroelectric device having a lower electrode, a film including a crystalline ferroelectric material including a mixture of hafnium oxide and zirconium oxide in which a substantial portion (i.e., about 40% or more) or a majority portion of the material remains deposited in a ferroelectric phase, and an upper electrode, and methods of preparing and depositing these materials. The lower electrode is thin and has low roughness. The ferroelectric device is back-end-of-line (BEOL) compatible since all process steps are performed at temperatures of 400° C. or less.

Description

Technical Field

[0001] (Cross - Reference to Related Applications) This application claims the benefit of U.S. Provisional Patent Application No. 63 / 368,891, filed Jul. 20, 2022, which is incorporated herein by reference.

[0002] The disclosed and claimed subject matter relates to ferroelectric materials deposited using vapor phase techniques including atomic layer deposition (ALD). More specifically, the disclosed and claimed subject matter relates to ferroelectric devices having a bottom electrode including tungsten and a thin - film crystalline ferroelectric material including a mixture of hafnium oxide and zirconium oxide in which a substantial portion (i.e., about 40% or more) of the material is in the ferroelectric phase, and methods of preparing and depositing these materials. Importantly, these materials exhibit ferroelectric properties within the thermal budget of a back - end process.

Background Art

[0003] Hafnium oxide and zirconium oxide-based ferroelectric materials enable various computing devices, including non-volatile memories and power-efficient logic devices, due to their strong non-linear capacitance and remanent polarization. These materials may also be useful for a variety of other thermal and magnetic applications. Materials containing hafnium oxide and zirconium oxide are highly desirable for these applications due to their compatibility with many CMOS manufacturing processes and materials. These materials are also desirable due to their ability to be deposited as thin films from the gas phase, including ALD processes that involve the stepwise introduction and removal of precursors, followed by the introduction and removal of reaction gases, as well as those by other known processes (e.g., chemical vapor deposition (CVD) or pulsed CVD). Hafnium oxide and zirconium oxide-based materials are polymorphic. Thus, their atoms can be arranged in several crystal structures (i.e., different orders of atomic arrangements). It is well known that the most stable bulk structure of hafnium oxide and zirconium oxide-based materials is the monoclinic phase. However, this phase does not support ferroelectricity. Other polymorphs (e.g., some orthorhombic and rhombohedral phases) have the symmetries required to support ferroelectric switching behavior, while still others (e.g., the tetragonal phase common in zirconium oxide thin films) can be antiferroelectric-like. References that more particularly describe these general features and aspects of the art are identified by the list of related art appended hereto.

[0004] In many gas-phase deposition processes and atomic layer deposition processes for mixed hafnium oxide and zirconium oxide materials, the materials are amorphous as-deposited.

[0005] Even when heat treatment is used, crystallization into the monoclinic phase or other non-ferroelectric phases is common, thereby reducing the fraction of materials capable of ferroelectric behavior. Several techniques have been developed to preferentially suppress the monoclinic phase in favor of the phase that can support ferroelectricity. For example, incorporating other elements into the material by sequentially or simultaneously introducing precursors of other elements (including, but not limited to, Si, Al, Gd, La, and Y) has been reported as a means of suppressing the monoclinic phase.

[0006] One study has shown that thick films (about 30 nm) of hafnium oxide and zirconium oxide can exhibit weak ferroelectricity from the ferroelectric phase. See Y. Li et al., “A Ferroelectric Thin Film Transistor Based on Annealing-Free HfZrO Film,” in IEEE Journal of the Electron Devices Society, vol. 5, no. 5, pp. 378 - 383, Sept. 2017, doi:10.1109 / JEDS.2017.2732166. This behavior appears to occur because the surface energy effect decreases compared to thinner films in order to produce films of such thickness, and the exposure to heat, which functionally serves as an equivalent role to annealing, becomes longer. However, this study acknowledges what is generally known in the art, namely that thin films (about 20 nm or less) do not exhibit ferroelectric behavior without annealing at high temperatures (either alone or in combination with doping) and the capping techniques described above.

[0007] Therefore, obtaining the desired ferroelectric phase has conventionally depended on a complex and intricate combination of (i) the deposition conditions of the material itself, (ii) dopants, interfaces, and importantly the choice of the top interface, and (iii) the heat treatment after deposition. As can be easily understood, this combination of factors imposes significant limitations on the usefulness of such materials with respect to possible substrates, intermediate layers, electrodes, compositions, and processes. In fact, the thermal profile in a device implementing such a ferroelectric material may not be compatible with all the necessary or desirable applications where the ferroelectric material could be useful. For example, it has been observed that specific electrodes may be required to adjust the electron work function, an interface may be required to create a barrier layer against chemical reactions and atomic diffusion, and the heat treatment conditions can be limited by the stress introduced into other layers within the multilayer stack.

[0008] Ferroelectric devices, including ferroelectric tunnel junctions (FTJs), are two-terminal memory devices in which a ferroelectric material is sandwiched between two similar / dissimilar electrodes, along with other interfacial dielectric materials, and which store data based on the resistance switching of the device (i.e., the low-resistance state and the high-resistance state represent two distinct memory states, thereby storing 1 bit of information). The resistance change is initiated by a change in the tunnel barrier height between the two electrodes due to the switching of the orientation of the permanent charge dipoles within the ferroelectric material. A ferroelectric material is typically a crystalline / polycrystalline material having permanent charge dipoles formed by asymmetric dipole charge centers within the crystal lattice that can be switched (switched) by applying an electric field. Due to the permanent orientation switching of the dipoles, such a material exhibits a polarization (residual polarization) that can change the direct tunnel barrier between the two electrodes without an electric field.

[0009] Typically, for the FTJ to operate, an inherent asymmetry between two electrodes is required. This asymmetry can be achieved by two methods: (i) using two different types of contact materials (either two different metals or one metal and one semiconductor) for the two electrodes, and (ii) using an interfacial dielectric material that is not a ferroelectric.

[0010] The basic concept of the ferroelectric tunnel junction (FTJ) (then called a porous switch) was by Esaki et al. and was formulated in 1971. The FTJ has been widely studied in the literature over the past decade, and several materials such as lead zirconate titanate - Pb(Zr x Ti 1-x )O3 (PZT), bismuth ferrite (BiFeO3 - BFO), barium titanate (BaTiO3 - BTO), lanthanum strontium manganite (La 0.67 Sr 0.33 MnO3 - LSMO), organic polyvinylidene fluoride (PVDF), and organic poly(vinylidene fluoride - trifluoroethylene) - P(VDF - TrFE) have been used. Due to the low BEOL process compatibility and complex integration of these materials, hafnium oxide - based FTJs have been recently studied deeply because of their good compatibility with CMOS processes, especially with specific dopants (Zr, Si), to improve the ferroelectricity of the materials. The use of interfacial layers (SiO2, Al2O3, WO x ) has also been recently introduced to introduce asymmetry into the FTJ stack and improve the memory performance from the perspective of tunnel electrical resistance (TER) window and retention, but still results in less than satisfactory results that do not allow for programming at more than 2 - 3 memory levels with acceptable retention over periods longer than a few hours. SUMMARY OF THE INVENTION

[0011] In a first main aspect, a ferroelectric device is provided. The ferroelectric device includes a substrate, a first electrode and a second electrode, wherein the first electrode is disposed on the substrate, the first electrode and the second electrode, and a thin film including a crystalline material disposed between the first electrode and the second electrode, the crystalline material includes hafnium oxide and zirconium oxide, and the thin film exhibits ferroelectric behavior in the as-deposited state, and the first electrode includes tungsten, titanium nitride, molybdenum, ruthenium, or a combination thereof, and the thin film has a remanent polarization greater than about 50 μC / cm 2 and has a remanent polarization greater than about 50 μC / cm.

[0012] In a further aspect of the first main aspect, the thin film can exhibit ferroelectric activity without a wake-up period. In a further aspect of the first main aspect, the second electrode includes titanium nitride, tungsten, molybdenum, or a combination thereof. In a further aspect of the first main aspect, the first electrode has a thickness of about 4 nm to about 50 nm. In a further aspect of the first main aspect, more than 50% of the total volume of the first electrode is in the α-phase. In a further aspect of the first main aspect, the crystalline material has a hafnium oxide to zirconium oxide ratio of about 1:3 to about 3:1. In a further aspect of the first main aspect, process steps are not performed at temperatures higher than about 400 °C.

[0013] In a further aspect of the first main aspect, the crystalline material is of formula I: [Chemical formula] Formula II: [Chemical formula] Or formula III: [Chemical formula] derived from one or more metallocene precursors having, wherein (i) M is selected from Zr and Hf, (ii) R 1 , R 2 , R 3 , R 4 , R 5 , R6 , R 7 , and R 8 are each independently selected from C1-C6 straight chain alkyl, C1-C6 branched alkyl, C1-C6 halogenated straight chain alkyl, and C1-C6 halogenated branched alkyl; and (iii) R 9 is a C1-C4 group selected from -CH2CH2-, -CH2CH2CH2-, -CH(Me)CH2-, -CH2CH(Me)-, -CH2CH2CH2-, and -CHMeCH2CH2-; (iv) R 10 , R 11 , and R 12 are each independently a C1 to C6 linear alkyl.

[0014] In a further aspect of the first main aspect, the crystalline material has Formula I: [ka] Formula II: [ka] or Formula III: [ka] wherein (i) M is selected from Zr and Hf; and (ii) R 1 , R 2 , R 3 , R 4 , R 5 , R 6 , R 7 , and R 8 are each independently a C1-C6 linear alkyl; and (iii) R 9 is a C1-C4 group selected from -CH2CH2-, -CH2CH2CH2-, -CH(Me)CH2-, -CH2CH(Me)-, -CH2CH2CH2-, and -CHMeCH2CH2-; (iv) R 10 , R 11 , and R 12 are each independently a C1 to C6 linear alkyl.

[0015] In a further aspect of the first main aspect, the crystalline material has the formula I: [Chemical formula] Formula II: [Chemical formula] Or formula III: [Chemical formula] and is derived from one or more metallocene precursors having the formula, wherein (i) M is selected from Zr and Hf, (ii) R 1 , R 2 , R 3 , R 4 , R 5 , R 6 , R 7 , and R 8 are each a methyl group, (iii) R 9 is a C1-C4 group selected from -CH2CH2-, -CH2CH2CH2-, -CH(Me)CH2-, -CH2CH(Me)-, -CH2CH2CH2-, -CHMeCH2CH2-, and (iv) R 10 , R 11 , and R 12 are each independently a C1-C6 straight-chain alkyl.

[0016] In a further aspect of the first main aspect, there is hysteresis and residual polarization in the polarization field measurement. In a further aspect of the first main aspect, the film has a thickness of from about 0.2 nm to about 10 nm.

[0017] In a second main aspect, a method of fabricating a ferroelectric device is provided. The method includes: (i) providing a substrate; (ii) depositing a first electrode on the substrate, the first electrode including tungsten, titanium nitride, molybdenum, ruthenium, or a combination thereof; (iii) depositing a ferroelectric layer on the first electrode at a deposition temperature, the ferroelectric layer including zirconium and hafnium; (iv) depositing a second electrode on the ferroelectric layer; and (v) annealing the first electrode at a temperature of 400 °C or less.

[0018] In a further aspect of the second main aspect, the annealing step is performed at a temperature higher than about 350 °C. In a further aspect of the second main aspect, no process step is performed at a temperature higher than about 400 °C. In a further aspect of the second main aspect, the ferroelectric layer includes hafnium zirconium oxide. In a further aspect of the second main aspect, more than 50% of the total volume of the first electrode is in the α-phase. In a further aspect of the second main aspect, the first electrode has a thickness of from about 4 nm to about 50 nm.

[0019] In a third main aspect, a method of fabricating a ferroelectric device is provided. The method includes: (i) providing a substrate; (ii) depositing a first electrode on the substrate at a first temperature; (iii) depositing a ferroelectric layer on the first electrode at a second temperature; (iv) depositing a second electrode on the ferroelectric layer; and (v) performing a step of annealing at a third temperature, wherein the first temperature, the second temperature, and the third temperature are 400 °C or less.

[0020] In a further aspect of the third main aspect, the first temperature is from about 15 °C to about 400 °C. In a further aspect of the third main aspect, the thickness of the first electrode is from about 4 nm to about 50 nm. In a further aspect of the third main aspect, in the annealing step, the third temperature is from about 350 °C to 400 °C or less. In a further aspect of the third main aspect, no process steps are performed at temperatures higher than about 400 °C. In a further aspect of the third main aspect, the first electrode includes tungsten, titanium nitride, molybdenum, ruthenium, or a combination thereof, and the second electrode includes titanium nitride, tungsten, molybdenum, or a combination thereof.

[0021] In a fourth main aspect, a ferroelectric device is provided. The ferroelectric device is manufactured by a process including: (i) providing a substrate; (ii) depositing a first electrode on the substrate, the first electrode including tungsten; (iii) depositing a ferroelectric layer on the first electrode at a deposition temperature, the ferroelectric layer including zirconium and hafnium; (iv) depositing a second electrode on the ferroelectric layer; and (v) annealing the first electrode at a temperature of 400 °C or less. The first electrode includes tungsten having a remanent polarization greater than 50 μC / cm 2 more.

[0022] In a further aspect of the fourth main aspect, no process steps are performed at temperatures higher than about 400 °C. In a further aspect of the fourth main aspect, the ferroelectric layer is Hf doped with La, Y, Gd, Ge, Si, or Sr x Zr 1-x O2 or HfO2.

[0023] In a further aspect of the fourth main aspect, the ferroelectric device has a critical dimension of 1000 nm or less, preferably about 300 μm or less.

[0024] A unit cell of a ferroelectric random access memory device includes a ferroelectric device described in any of the foregoing aspects.

[0025] A crossbar memory array includes a ferroelectric device of any of the foregoing aspects, or a ferroelectric device created by any of the methods of the foregoing aspects for a memory unit cell.

[0026] A neuromorphic computing chip includes a ferroelectric device described in any of the foregoing aspects, and the ferroelectric device is a synaptic device.

[0027] In another aspect, an advanced metallocene precursor is one or more of the precursors disclosed and / or claimed in U.S. Patent No. 8,568,530, the entire content of which is incorporated herein by reference.

[0028] This summary section of the invention does not specify all embodiments and / or progressively novel aspects of the disclosed and claimed subject matter. Instead, this summary of the invention only provides a preliminary discussion of different embodiments and corresponding points of novelty over the prior art and known techniques. For further details and / or possible aspects of the disclosed and claimed subject matter and embodiments, the reader is referred to the detailed description section and the corresponding figures of this disclosure, as further discussed below.

[0029] The discussion of the order of the different steps described herein is presented for clarity. Generally, the steps disclosed herein can be performed in any suitable order. In addition, each of the different features, techniques, configurations, etc. disclosed herein can be discussed at different places in this disclosure, but it is intended that each concept can be performed independently of each other or in combination with each other as appropriate. Accordingly, the disclosed and claimed subject matter can be embodied and viewed in many different ways.

Brief Description of the Drawings

[0030] The accompanying drawings, which are included to provide a further understanding of the disclosed subject matter, and which are incorporated in and constitute a part of this specification, illustrate embodiments of the disclosed subject matter and, together with the detailed description, serve to explain the principles of the disclosed subject matter.

[0031]

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[0032] definition Unless otherwise stated, the following terms used in the specification and claims have the following meanings in this application:

[0033] In this application, the use of the singular form includes the plural form, and the terms "a", "an", and "the" mean "at least one" unless otherwise specified. Further, the use of the term "including", as well as other forms such as "includes" and "included", is not limiting. Also, terms such as "element" or "component" include both an element or component that includes one unit and an element or component that includes two or more units unless otherwise specified. As used herein, unless otherwise indicated, the conjunction "and" is intended to be inclusive, and the conjunction "or" is not intended to be exclusive. For example, the phrase "or alternatively" is intended to be exclusive. As used herein, the term "and / or" refers to any combination of the foregoing elements, including the use of a single element.

[0034] When the terms "about" or "approximately" are used in connection with a measurable numerical variable, they refer to all values of the variable that are either within the experimental error of the indicated value (e.g., within the 95% confidence limit of the mean) or within a percentage of the indicated value (e.g., ±10%, ±5%), whichever is greater.

[0035] For the purposes of this invention and the claims, the group numbering scheme of the periodic table follows the IUPAC periodic table of the elements.

[0036] As used herein, in phrases such as "A and / or B", the term "and / or" is intended to include "A and B", "A or B", "A", and "B".

[0037] The terms "substituent", "radical", "group", and "moiety" may be used interchangeably.

[0038] As used herein, the terms "metal-containing complex" (or more simply "complex") and "precursor" are used interchangeably and refer to metal-containing molecules or compounds that can be used to prepare metal-containing films by deposition processes such as ALD or CVD. The metal-containing complex can be deposited, adsorbed, decomposed, delivered, and / or passed over a substrate or its surface so as to form a metal-containing film.

[0039] As used herein, the term "metal-containing film" includes not only elemental metal films, which are more fully defined below, but also films that contain a metal together with one or more elements, such as metal nitride films, metal silicide films, metal carbide films, and the like.

[0040] As used herein, the terms "elemental metal", "elemental metal film", and "pure metal film" are used interchangeably and refer to a film consisting of, or consisting essentially of, a pure metal. For example, an elemental metal film may contain a metal with a purity of 100%, or an elemental metal film may contain a metal with a purity of at least about 70%, at least about 80%, at least about 90%, at least about 95%, at least about 96%, at least about 97%, at least about 98%, at least about 99%, at least about 99.9%, or at least about 99.99% together with one or more impurities. However, a film containing an elemental metal is distinguished from a binary film containing a metal and a non-metal (e.g., C, N, O) and a ternary film containing a metal and two non-metals (e.g., C, N, O), although a film containing an elemental metal may contain some amount of impurities. Unless the context dictates otherwise, the term "metal film" is to be construed as meaning an elemental metal film.

[0041] As used herein, the terms "deposition process" and "thermal deposition" are used to refer to any type of deposition technique including, but not limited to, CVD and ALD. In various embodiments, CVD may take the form of conventional (i.e., continuous flow) CVD, liquid injection CVD, plasma enhanced CVD, or photo-assisted CVD. CVD may also take the form of a pulsed technique, i.e., pulsed CVD. ALD is used to form a metal-containing film by vaporizing and / or passing at least one metal complex disclosed herein over a substrate surface. For conventional ALD processes, see, e.g., George S.M., et al., J. Phys. Chem., 1996, 100, 13121-13131. In other embodiments, ALD may take the form of conventional (i.e., pulsed injection) ALD, liquid injection ALD, photo-assisted ALD, plasma-assisted ALD, or plasma enhanced ALD. The term "vapor deposition process" further includes the various vapor deposition techniques described in Chemical Vapour Deposition: Precursors, Processes, and Applications; Jones, A.C.; Hitchman, M.L., Eds. The Royal Society of Chemistry: Cambridge, 2009; Chapter 1, pp. 1-36.

[0042] Unless otherwise indicated, "alkyl" refers to a hydrocarbon group that can be linear, branched (e.g., methyl, ethyl, propyl, isopropyl, tert-butyl, etc.), cyclic (e.g., cyclohexyl, cyclopropyl, cyclopentyl, etc.), or polycyclic (e.g., norbornyl, adamantyl, etc.). Suitable acyclic groups can be methyl, ethyl, n- or iso-propyl, n-, iso, or tert-butyl, linear or branched pentyl, hexyl, heptyl, octyl, decyl, dodecyl, tetradecyl, and hexadecyl. Unless otherwise specified, alkyl refers to a moiety having 1 to 10 carbon atoms. The cyclic alkyl group can be monocyclic or polycyclic. Suitable examples of monocyclic alkyl groups include substituted cyclopentyl, cyclohexyl, and cycloheptyl groups. The substituent can be any of the acyclic alkyl groups described herein. As described herein, the cyclic alkyl group can have any of the acyclic alkyl groups as a substituent. These alkyl moieties can be either substituted or unsubstituted.

[0043] "Alkyl halide" refers to a linear, cyclic, or branched saturated alkyl group as defined above, wherein one or more of the hydrogens are substituted by a halogen (e.g., F, Cl, Br, and I). Thus, for example, alkyl fluoride (also known as "fluoroalkyl") refers to a linear, cyclic, or branched saturated alkyl group as defined above, wherein one or more of the hydrogens are substituted by fluorine (e.g., trifluoromethyl, perfluoroethyl, 2,2,2-trifluoroethyl, perfluoroisopropyl, perfluorocyclohexyl, etc.). Such haloalkyl moieties (e.g., fluoroalkyl moieties) can be unsubstituted or further substituted if not perhalogenated / polyhalogenated.

[0044] The section headings used in this specification are for organization purposes and should not be construed as limiting the subject matter described. All documents or portions of documents cited in this application, including but not limited to patents, patent applications, papers, books, and treatises, are hereby expressly incorporated by reference in their entirety for any purpose. If any of the incorporated documents and similar materials define a term in a manner that conflicts with the definition of the term in this application, this application controls.

[0045] Detailed Description It should be understood that both the foregoing general description and the following detailed description are exemplary and explanatory and are not restrictive of the claimed subject matter. The objectives, features, advantages, and concepts of the disclosed subject matter will be apparent to those skilled in the art from the description provided herein, and the disclosed subject matter is readily practicable by those skilled in the art based on the description appearing herein. The description of any "preferred embodiments" and / or examples showing preferred modes of carrying out the disclosed subject matter is included for illustrative purposes and is not intended to limit the scope of the claims.

[0046] It will also be apparent to those skilled in the art that various modifications can be made to how the disclosed subject matter is practiced based on the aspects described herein without departing from the spirit and scope of the disclosed subject matter.

[0047] I. Ferroelectric Devices with Multilevel Switching The ferroelectric devices of the present disclosure can take many forms. In a preferred embodiment, the ferroelectric device is incorporated into a ferroelectric random access memory (FeRAM, F-RAM, or FRAM (registered trademark)). Further, the ferroelectric device can also be used as a capacitor for programming different residual charge polarization states by applying different electric fields. This particular implementation is generally used in ferroelectric RAM (FeRAM) applications. In an alternative embodiment, the ferroelectric device is a ferroelectric tunnel junction (FTJ). FTJ has recently been studied as one of the best candidates as a memristor or artificial synapse due to its unique analog type of programming principle for neuromorphic computing applications. By using specific Hf and Zr precursors sandwiched between TiN and W electrodes, ALD HZO films deposited at high T, and the use of a specific post-metal anneal (PMA), multi-level programming up to four levels with better retention than the current state-of-the-art for FTJs that generally use a two-layer stack with higher complexity becomes possible. The present disclosure opens the way for future implementation of FTJs in neuromorphic computing chips.

[0048] The present disclosure shows a new technique for introducing asymmetry between the top electrode and the bottom electrode. This is facilitated by high-temperature (>300 °C) atomic layer deposition (ALD) of hafnium zirconium oxide (HZO) using alternating cycles of Hf and Zr precursors and ozone pulses for oxidation therebetween.

[0049] In state-of-the-art systems for manufacturing ferroelectric memory devices, typically, the FE material is deposited using low-temperature ALD that leaves the deposited film amorphous and thus non-FE, and then the film is crystallized, followed by high-temperature annealing (>500 °C) to activate the FE properties of the film. In the case of an FTJ with an interface layer, an additional processing step may be required to deposit the interface material. In the integration and stack of this process, the ability of the precursors to handle high temperatures (>300 °C) enables an as-deposited FE film. Additionally, this process essentially oxidizes the bottom electrode (by its high-temperature and highly reactive ozone process) to produce an interfacial metal oxide that introduces the asymmetry required for FTJ operation. Further annealing at a temperature higher than the deposition temperature can be introduced to improve reliability metrics such as the FE memory window and retention and endurance.

[0050] Additionally, with the optimization of the HZO film, the ferroelectric stack exhibits good tunability. The proper selection of the ALD deposition temperature, ozone dilution, and post-metal annealing conditions is fundamental to obtaining the desired orthorhombic phase necessary for ferroelectric multi-domain switching, which is essential for multi-level switching in ferroelectric devices.

[0051] This disclosure presents for the first time a BEOL-compatible process having a hafnium zirconium oxide (HZO) switching layer sandwiched between symmetric W electrodes with multi-level programming up to four states and good retention of these states for at least 10 4 seconds. During HZO deposition, an oxidized interface layer (WO x ) is generated by oxidizing the W bottom electrode interface. The advantage of this step is that it is performed in conjunction with the deposition process and no additional process steps are required.

[0052] The ferroelectric device 100 of FIG. 1 includes a top electrode 102, a layer 104 of ferroelectric material, a bottom electrode 106, and a substrate 108. In a preferred embodiment, the top and bottom electrodes include tungsten, and the ferroelectric material includes thin-film hafnium oxide and zirconium oxide (HZO).

[0053] Essentially ferroelectric thin film materials and methods of using them to address the foregoing problems are described herein, as well as in U.S. Provisional Patent Application No. 63 / 040,097, filed June 17, 2020 (Attorney Docket No. P20-094 US-PRO), and International Application No. PCT / EP2021 / 066028, filed June 15, 2021 (Attorney Docket No. P20-094 WO-PCT). These applications are incorporated by reference in their entirety. By doing so, the materials and methods described herein shorten processing times and make them particularly suitable for the requirements of current manufacturing procedures. The present disclosure involves FTJs having nine or more different resistance levels. Those skilled in the art can readily appreciate the possibility of subsequent optimization of the interfaces, electrodes, and heat treatment conditions after deposition of these materials.

[0054] II. ESSENTIALLY FERROELECTRIC MATERIALS As described above, the disclosed and claimed subject matter relates to crystalline ferroelectric thin film materials comprising a mixture of hafnium oxide and zirconium oxide in which a substantial portion (i.e., about 40% or more) of the material is in the ferroelectric phase, as well as methods for preparing and depositing these materials. In a further aspect, the ferroelectric material has a majority volume fraction of the ferroelectric phase. Importantly, these materials exhibit ferroelectric properties without the need for further processing such as subsequent capping or annealing steps. The materials produced to be ferroelectric have one or more of (i) a remanent polarization, or (ii) a polarization field curve having hysteresis and a loop opening.

[0055] For the material to be ferroelectric, it should have an atomic arrangement that can support ferroelectricity in some fraction of the film. It is preferred that a substantial portion of the volume of the film has an atomic arrangement that can support ferroelectricity. For thin films, doped materials, and some laminated materials, it is understood that the phase distribution in the material cannot be easily determined by X-ray diffraction. In this case, any other suitable technique for determining the phase of the film, such as Raman spectroscopy, infrared spectroscopy, X-ray absorption spectroscopy, transmission electron microscopy, or a combination thereof, can be used to determine the phase distribution. For example, https: / / onlinelibrary.wiley.com / doi / full / 10.1002 / pssb.201900285 describes techniques for confirming the phase of the film within about 10%.

[0056] This material can be composed of any suitable molar ratio of hafnium oxide and zirconium oxide, and a ratio of 1:3 to 3:1 is preferred. The thickness of the ferroelectric material is any thickness suitable for a given application. The material can be made thicker to increase the remnant polarization or to reduce the leakage current across the thickness of the material, or can be made thinner due to geometric constraints or to increase the capacitance of the film.

[0057] The preferred range of the thickness of this ferroelectric film is from about 0.2 nm to about 20 nm, more preferably from about 0.2 nm to 10 nm. Also, it is preferred that the material forms a film having a thickness of about 10 nm or less. In some embodiments, it is preferred that the material forms a film having a thickness of about 5 nm or less.

[0058] However, as described above, the preferred and / or desired thickness varies depending on the specific application. Thus, as previously mentioned, in some embodiments, the material exhibits ferroelectric properties as a thin film of about 20 nm or less. In a further aspect, the material exhibits ferroelectric properties as a thin film of about 15 nm or less. In a further aspect, the material exhibits ferroelectric properties as a thin film of about 10 nm or less. In a further aspect, the material exhibits ferroelectric properties as a thin film of about 5 nm or less. In a further aspect, the material exhibits ferroelectric properties as a thin film of about 3 nm or less. In a further aspect, the material exhibits ferroelectric properties as a thin film of about 1 nm or less. In a further aspect, the material exhibits ferroelectric properties as a thin film of about 0.5 nm or less. In a further aspect, the material exhibits ferroelectric properties as a thin film of about 0.2 nm or less. In a further aspect, the material exhibits ferroelectric properties as a thin film in the range of about 0.2 nm to about 20 nm. In a further aspect, the material exhibits ferroelectric properties as a thin film in the range of about 0.2 nm to about 15 nm. In a further aspect, the material exhibits ferroelectric properties as a thin film in the range of about 0.2 nm to about 10 nm. In a further aspect, the material exhibits ferroelectric properties as a thin film in the range of about 0.2 nm to about 5 nm. In a further aspect, the material exhibits ferroelectric properties as a thin film in the range of about 0.2 nm to about 3 nm. In a further aspect, the material exhibits ferroelectric properties as a thin film in the range of about 0.2 nm to about 1 nm. In a further aspect, the material exhibits ferroelectric properties as a thin film in the range of about 0.2 nm to about 1 nm.

[0059] Lower electrode The preferred range of the thickness of the lower electrode is from about 1 nm to about 25 nm, more preferably from about 4 nm to 15 nm. Also, it is preferable that the material forms a film having a thickness of about 10 nm or less. In some embodiments, it is preferable that the material forms a film having a thickness of about 5 nm or less.

[0060] In the disclosed and claimed materials, a significant portion, constituting more than about 40% of the crystalline material, is in the ferroelectric phase. Thus, the total of the non-ferroelectric atomic arrangement components is less than about 60% of the total volume of the material. In another embodiment, the total non-ferroelectric atomic arrangement components are less than about 50% of the total volume of the material. In another embodiment, the total non-ferroelectric atomic arrangement components are less than about 40% of the total volume of the material. In another embodiment, the total non-ferroelectric atomic arrangement components are less than about 30% of the total volume of the material. In another embodiment, the total non-ferroelectric atomic arrangement components are less than about 25% of the total volume of the material. In another embodiment, the total non-ferroelectric atomic arrangement components are less than about 20% of the total volume of the material. In another embodiment, the total non-ferroelectric atomic arrangement components are less than about 15% of the total volume of the material. In another embodiment, the total non-ferroelectric atomic arrangement components are less than about 10% of the total volume of the material. In another embodiment, the total non-ferroelectric atomic arrangement components are less than about 5% of the total volume of the material.

[0061] Furthermore, in the disclosed and claimed materials, less than about 60% of the total volume of the material constitutes the non-ferroelectric monoclinic phase component. Thus, in one embodiment of the disclosed and claimed materials, the monoclinic phase component is less than about 50% of the total volume of the material. In another embodiment, the monoclinic phase component is less than about 40% of the total volume of the material. In another embodiment, the monoclinic phase component is less than about 30% of the total volume of the material. In another embodiment, the monoclinic phase component is less than about 25% of the total volume of the material. In another embodiment, the monoclinic phase component is less than about 20% of the total volume of the material. In another embodiment, the monoclinic phase component is less than about 15% of the total volume of the material. In another embodiment, the monoclinic phase component is less than about 10% of the total volume of the material. In another embodiment, the monoclinic phase component is less than about 5% of the total volume of the material.

[0062] The essentially ferroelectric material is derived from the presented metallocene precursor, and the presented metallocene precursor has the formula I (「(R 1 -Cp)(R 2 -Cp)-M-(OR 3 )(R 4 )」(wherein Cp is a cyclopentadienyl group) and / or the formula II (「(R5 -Cp)(R 6 -Cp)-M-(R 7 )(R 8 )」(wherein, Cp is a cyclopentadienyl group), and

Chemical formula

[0063] In another aspect, in formula I, each of R 1 、R 2 、R 3 、R 4 、R 5 、R 6 、R 7 、and R 8 is preferably C1-C6 linear alkyl. In a further aspect, in formula I, each of R 1 、R 2 、R 3 、R 4 、R 5 、R 6 、R 7 、and R 8 is preferably the same C1-C6 linear alkyl. In a further aspect, in formula I, each of R 1 、R 2 、R 3 、R 4 、R 5 、R 6 、R 7 、and R 8 is preferably a methyl group. In a further aspect, in formula I, each of R 1 、R 2 、R 3 、R 4 、R 5 、R 6, R 7 , and R 8 Each of R is preferably an ethyl group. 1 , R 2 , R 5 , and R 6 Each of R is preferably an ethyl group. 3 , R 4 , R 7 , and R 8 Each of R is preferably a methyl group. 1 , R 2 , R 5 , and R 6 is preferably an ethyl group, and R 3 , R 4 , R 7 , and R 8 Each of is preferably a methyl group.

[0064] In another embodiment, in Formula II, R 1 , R 2 , R 3 , R 4 , R 5 , R 6 , R 7 , and R 8 Each of R is preferably a C1-C6 straight chain alkyl. 1 , R 2 , R 3 , R 4 , R 5 , R 6 , R 7 , and R 8 Each of R is preferably the same C1-C6 straight chain alkyl. 1 , R 2 , R 3 , R 4 , R 5 , R 6 , R 7 , and R 8 Each of R is preferably a methyl group. 1 , R 2 , R 3 , R 4 , R5 , R 6 , R 7 , and R 8 Each of is preferably an ethyl group. In a further aspect, in Formula II, R 1 , R 2 , R 5 , and R 6 Each of is preferably an ethyl group. In a further aspect, in Formula II, R 3 , R 4 , R 7 , and R 8 Each of is preferably a methyl group. In a further aspect, in Formula II, R 1 , R 2 , R 5 , and R 6 Each of is preferably an ethyl group, and R 3 , R 4 , R 7 , and R 8 Each of is preferably a methyl group.

[0065] In another aspect, the presented metallocene precursor is one or more of (MeCp)2Zr(OMe)Me, (MeCp)2Hf(OMe)Me, (MeCp)2Zr(Me)2, (MeCp)2Hf(Me)2, (EtCp)2Zr(OMe)Me, (EtCp)2Hf(OMe)Me, (EtCp)2Zr(Me)2, (EtCp)2Hf(Me)2, and combinations thereof.

[0066] In another aspect, the presented metallocene precursor is one or more of a mixture of (MeCp)2Zr(OMe)Me and (MeCp)2Hf(OMe)Me, a mixture of (MeCp)2Hf(Me)2 and (MeCp)2Hf(Me)2, (EtCp)2Zr(OMe)Me and (EtCp)2Hf(OMe)Me, and a mixture of (EtCp)2Hf(Me)2 and (EtCp)2Hf(Me)2.

[0067] In another aspect, the presented metallocene precursor is one or more of the precursors having Formula III.

Chemical formula

[0068] III. Method for Preparing and Depositing Ferroelectric Materials As described above, in another aspect, the disclosed and claimed subject matter relates to a process for preparing and / or depositing the ferroelectric materials disclosed herein. In this process, the disclosed and claimed ferroelectric materials are prepared by (i) repeating the deposition and purge of the metallocene precursor and (ii) the reactants.

[0069] A. Metallocene Precursor As described above, the ferroelectric material is derived from the presented metallocene precursor, and the presented metallocene precursor has the formula I ("(R 1 -Cp)(R 2 -Cp)-M-(OR 3 )(R 4 )" (wherein Cp is a cyclopentadienyl group) and / or the formula II ("(R 5 -Cp)(R 6 -Cp)-M-(R 7 )(R 8 )" (wherein Cp is a cyclopentadienyl group),

Chemical formula

[0070] In another aspect, in formula I, R 1 , R 2 , R 3 , R 4 , R 5 , R 6 , R 7 , and R 8 are each preferably C1-C6 linear alkyl. In a further aspect, in formula I, R 1 , R 2 , R 3 , R 4 , R 5 , R 6 , R 7 , and R 8 are each preferably the same C1-C6 linear alkyl. In a further aspect, in formula I, R 1 , R 2 , R 3 , R 4 , R 5 , R 6 , R 7 , and R 8 are each preferably a methyl group. In a further aspect, in formula I, R 1 , R 2 , R 3 , R 4 , R 5 , R 6 , R 7 , and R 8 are each preferably an ethyl group. In a further aspect, in formula I, R 1 , R 2 , R 5 , and R 6 are each preferably an ethyl group. In a further aspect, in formula I, R 3 , R 4 , R 7 , and R 8 are each preferably a methyl group. In a further aspect, in formula I, R 1 , R 2 , R 5 , and R6 Each of them is preferably an ethyl group, R 3 , R 4 , R 7 , and R 8 are each preferably a methyl group.

[0071] In another aspect, in Formula II, R 1 , R 2 , R 3 , R 4 , R 5 , R 6 , R 7 , and R 8 are each preferably a C1-C6 linear alkyl. In a further aspect, in Formula II, R 1 , R 2 , R 3 , R 4 , R 5 , R 6 , R 7 , and R 8 are each preferably the same C1-C6 linear alkyl. In a further aspect, in Formula II, R 1 , R 2 , R 3 , R 4 , R 5 , R 6 , R 7 , and R 8 are each preferably a methyl group. In a further aspect, in Formula II, R 1 , R 2 , R 3 , R 4 , R 5 , R 6 , R 7 , and R 8 are each preferably an ethyl group. In a further aspect, in Formula II, R 1 , R 2 , R 5 , and R 6 are each preferably an ethyl group. In a further aspect, in Formula II, R 3 , R 4 , R 7 , and R 8 are each preferably a methyl group. In a further aspect, in Formula II, R 1 , R 2, R 5 , and R 6 each is preferably an ethyl group, and R 3 , R 4 , R 7 , and R 8 each is preferably a methyl group.

[0072] In another aspect, the provided metallocene precursor is one or more of (MeCp)2Zr(OMe)Me, (MeCp)2Hf(OMe)Me, (MeCp)2Zr(Me)2, (MeCp)2Hf(Me)2, (EtCp)2Zr(OMe)Me, (EtCp)2Hf(OMe)Me, (EtCp)2Zr(Me)2, (EtCp)2Hf(Me)2, and combinations thereof.

[0073] In another aspect, the provided metallocene precursor is one or more of a mixture of (MeCp)2Zr(OMe)Me and (MeCp)2Hf(OMe)Me, a mixture of (MeCp)2Hf(Me)2 and (MeCp)2Hf(Me)2, (EtCp)2Zr(OMe)Me and (EtCp)2Hf(OMe)Me, and a mixture of (EtCp)2Hf(Me)2 and (EtCp)2Hf(Me)2.

[0074] In another aspect, the provided metallocene precursor is one or more of the precursors having Formula III.

Chemical formula

[0075] Wherein, (i) M is selected from Zr and Hf, (iii) R 9 is a C1-C4 group selected from -CH2CH2-, -CH2CH2CH2-, -CH(Me)CH2-, -CH2CH(Me)-, -CH2CH2CH2-, -CHMeCH2CH2-, (iv) R 10 , R 11 , and R 12 are each independently C1-C6 linear alkyl.

[0076] In another aspect, the presented metallocene precursors having Formula III are one or more mixtures of (MeNCH2CH2Cp)Hf(NMe2)2, (MeNCH2CH2Cp)Hf(NEtMe)2, (MeNCH2CH2CH2Cp)Hf(NMe2)2, (MeNCH2CH2CH2Cp)Hf(NEtMe)2, (MeNC(Me)HCH2Cp)Hf(NMe2)2, (MeNC(Me)HCH2Cp)Hf(NEtMe)2, (MeNCH2CH(Me)Cp)Hf(NMe2)2, (MeNCH2CH(Me)Cp)Hf(NEtMe)2, (MeNCH2CH2Cp)Zr(NMe2)2, (MeNCH2CH2Cp)Zr(NEtMe)2, (MeNCH2CH2CH2Cp)Zr(NMe2)2, (MeNCH2CH2CH2Cp)Zr(NEtMe)2, (MeNC(Me)HCH2Cp)Zr(NMe2)2, (MeNC(Me)HCH2Cp)Zr(NEtMe)2, (MeNCH2CH(Me)Cp)Zr(NMe2)2, (MeNCH2CH(Me)Cp)Zr(NEtMe)2.

[0077] Generally, suitable precursors for preparing ferroelectric materials can be deposited at or near the crystallization temperature of the desired ferroelectric material, typically from about 200 °C to about 570 °C, which depends, inter alia, on the composition of the material, the substrate, and the reactor design. The preferred temperature is about 300 °C (or generally from about 280 °C to about 300 °C), and the preferred temperature range is less than about 450 °C, more preferably less than about 340 °C. However, one skilled in the art should recognize that other temperatures may be possible depending on the particular precursor used, and that such precursors are also within the scope of the disclosed and claimed subject matter. It should be further noted that for specific precursors other than those listed herein, decomposition of the precursor may occur within the described temperature range. Decomposition products, particularly carbonaceous and organic species, can be incorporated into the deposited hafnium oxide or zirconium oxide material. This incorporation of carbon can help to stabilize the ferroelectric phase, but may be undesirable for reasons of material purity. Thus, as described above, the preferred carbon content of the material is less than about 6 atomic percent.

[0078] B. Reactants The reactant is a reaction gas containing one or more of oxygen (e.g., ozone, elemental oxygen, molecular oxygen / O2), water, hydrogen peroxide, and nitrous oxide. In one embodiment, ozone is the preferred reactant gas. In another embodiment, water is the preferred reactant gas.

[0079] C. Process Steps The process for preparing and depositing the ferroelectric material described herein includes a substrate that undergoes a sputtering PVD cycle to deposit a tungsten bottom electrode. Other methods for depositing the bottom electrode include, but are not limited to, CVD, ALD, or electron beam deposition. Following the deposition of the bottom electrode, an ALD cycle is performed, in which the bottom electrode is exposed to vapor and the ferroelectric material is formed and deposited as a thin film layer. Layer 200 is formed and exhibits ferroelectric properties by itself (i.e., as-deposited). Those skilled in the art will of course recognize that the layer can subsequently be annealed and / or capped as desired, but will recognize that doing so is not necessary to observe the ferroelectric behavior of the as-deposited layer. For example, energy can subsequently be applied to the material by heat, plasma, pulsed plasma, helicon plasma, high density plasma, inductively coupled plasma, X-rays, electron beam, photons, remote plasma processes, and combinations thereof, but is not limited thereto.

[0080] The components of the vapor change during the ALD cycle. In particular, the bottom electrode is alternately exposed to a metallocene precursor, followed by purging, then exposed to a reactant, followed by another purge. This process is continued until the desired thickness of the ferroelectric layer is obtained. ALD is the preferred vapor deposition technique, but any suitable vapor deposition technique such as CVD or pulsed CVD can be utilized. Thus, for example, the ALD cycle can be replaced by a CVD process in which the metallocene precursor and the reactant are provided as a mixture in the vapor and simultaneously provided to the substrate.

[0081] An appropriate molar ratio of hafnium oxide to zirconium oxide can be obtained by several methods, including introducing a hafnium-containing precursor during some of these cycles and a zirconium-containing precursor during other cycles. Since both closely blended materials and nanolaminated materials have been shown to have desirable ferroelectric properties, the cycles can be alternated, grouped together, or arranged in any other suitable order to obtain the overall desired molar ratio. It should be noted that other elements may be added to the hafnium oxide-zirconium oxide material by adding appropriate precursors together with the hafnium and zirconium precursors or in separate cycles.

[0082] The bottom electrode on which the ferroelectric material is formed as a layer can include any suitable material, including semiconductor materials such as silicon, germanium, group III-V materials, transition metal dichalcogenides, and mixtures thereof, metals and conductive ceramics such as titanium nitride, titanium, tantalum, tantalum nitride, tungsten, platinum, rhodium, molybdenum, cobalt, ruthenium, palladium, or mixtures thereof, dielectrics such as silicon oxide, silicon nitride, aluminum oxide, titanium oxide, other ferroelectric materials including compositions of hafnium oxide and zirconium oxide, magnetic materials, and mixtures or stacks thereof. In the illustrated embodiment, the bottom electrode includes tungsten.

[0083] Optionally, the bottom electrode can have any suitable topography including a flat surface, trenches, vias, or nanostructured surfaces, and can be patterned or textured as needed. This list represents typical substrates that can be useful in ferroelectric applications, but many other suitable compositions and surface patterns will be apparent to those skilled in the art and should not be considered limiting. In this regard, it is known that the substrate can potentially affect the atomic arrangement and phase of the film, including affecting the crystal orientation and crystallization temperature of the film formed thereon. Regardless of the particular substrate and the extent of this effect, the ferroelectric materials described herein and deposited on such substrates are nonetheless in the ferroelectric phase with a significant fraction of their volume remaining as deposited. In the illustrated embodiment, the bottom electrode has a low roughness.

[0084] Another embodiment of the process for preparing and depositing a ferroelectric material is described herein. In this embodiment, a ferroelectric material of mixed hafnium oxide and zirconium oxide is prepared and deposited as a layer having a thickness of about 7.5 nm on a stack substrate of PVD W (in direct contact with the ferroelectric material), a thermally grown SiO2 layer, and a Si wafer. The layer is formed without further heat treatment or capping. In this embodiment, the molar ratio of hafnium oxide to zirconium oxide is about 1:1, with an error of about 10%. The ferroelectric material is prepared and deposited as layer 301 from the vapor by ALD by alternately performing a first cycle 303 (including steps of (i) pulsing (MeCp)2Zr(OMe)Me 304, (ii) purging, (iii) pulsing ozone 305, and (iv) purging) and a second cycle 306 (including steps of (i) pulsing (MeCp)2Hf(OMe)Me 307, (ii) purging, (iii) pulsing ozone 308, and (iv) purging).

[0085] One skilled in the art would recognize that other precursors, such as (MeCp)2HfMe2 and (MeCp)2ZrMe2, and other reactants, such as water, hydrogen peroxide, or oxygen plasma, could also be, or alternatively, used. One skilled in the art would further recognize that the pulsing time and the purge time can vary depending on the apparatus. In one embodiment, the pulse lasts about 2 seconds to about 3 seconds, followed by a purge of about 10 seconds. In another embodiment, the pulse lasts about 10 seconds to about 15 seconds, followed by a purge of about 30 seconds to about 60 seconds. In another embodiment, the order in which the precursors are deposited can be reversed.

[0086] One embodiment of the process for preparing and depositing the bottom electrode described herein using CVD. The method includes several steps that can be augmented with additional steps and / or optional steps. Step 1 includes providing a substrate at a deposition temperature of about 200 °C to about 500 °C, preferably about 350 °C or in the vicinity thereof (e.g., greater than about 225 °C and less than about 300 °C) and less than 340 °C.

[0087] One embodiment of a process for preparing and depositing the ferroelectric materials described herein using ALD. The method includes several steps that can be augmented with additional steps and / or optional steps. Step 1 includes providing a substrate at a deposition temperature of about 265 °C to about 500 °C, preferably at or near about 300 °C (e.g., greater than about 285 °C and less than or equal to about 300 °C) and less than 340 °C. Step 2 includes (i) exposing the substrate to a first precursor containing hafnium or zirconium or both hafnium and zirconium that does not decompose at the deposition temperature, and (ii) purging. Step 3 includes (i) exposing the substrate to a reactive gas containing oxygen, and (ii) purging. Step 4 includes (i) exposing the substrate to a second precursor containing zirconium or hafnium or both hafnium and zirconium that does not decompose at the deposition temperature, and (ii) purging. Step 5 includes exposing the substrate to a reactive gas containing oxygen. Optional step 6 includes repeating steps 2 - 5 until a film of hafnium oxide and zirconium oxide of the desired thickness is formed in a molar ratio of about 1:3 to about 3:1.

[0088] In the process of the present disclosure, the ferroelectric material is formed and deposited as a film having a significant volume fraction of the ferroelectric phase as-deposited (i.e., without further annealing and / or capping) and as measured by phase determination techniques or electrical tests known to those skilled in the art (e.g., XRD, XAS, TEM, polarization voltage test, piezoresponse force microscopy, or combinations thereof). The metallocene precursors utilized in and / or that can be utilized in the process of FIG. 6 include all those disclosed and discussed above, and in particular, (MeCp)2Zr(OMe)Me, (MeCp)2Hf(OMe)Me, (MeCp)2Zr(Me)2, and (MeCp)2Hf(Me)2. The reactive gas containing oxygen in step 3 and / or step 5 is preferably ozone. Those skilled in the art will recognize that other reactive gases can be used, including those specifically mentioned above (e.g., water, hydrogen peroxide).

[0089] In certain embodiments, the ferroelectric device 100 can be incorporated into a unit cell of a ferroelectric random access memory (FeRAM). In further embodiments, the ferroelectric device can be incorporated into a crossbar array of memory devices or a memory unit cell. In certain embodiments, the ferroelectric device 100 can be incorporated into a neuromorphic computing chip, or a synaptic device such as a synaptic memristor or a synaptic transistor.

[0090] FIG. 1 shows an embodiment of the HZO ferroelectric stack 100 of the present disclosure. FIG. 1 shows an upper electrode 102, a layer 104 of ferroelectric material, a lower electrode 106, and a substrate 108. In a preferred embodiment, the stack includes W(5 nm) / HZO(5 nm) / W(5 nm) after annealing in N2 at 400° C. for 2 minutes.

[0091] The lower (first) electrode and the upper (second) electrode may be metal electrodes or semiconductor electrodes having a thickness that ensures good conductivity. In the illustrated embodiment, the upper electrode includes tungsten. In other embodiments, the upper electrode may include any of titanium nitride, tungsten, molybdenum, nickel, ruthenium, platinum, and aluminum. In the illustrated embodiment, W with a thickness of 5 nm or 10 nm is used. The circular test electrode includes 50 nm of TiN.

Examples

[0092] Here, reference is made to more specific embodiments of the present disclosure and experimental results supporting such embodiments. The examples are given below to more fully explain the disclosed subject matter and should in no way be construed as limiting the disclosed subject matter.

[0093] Device Fabrication The bottom electrode was grown on a coupon having a carrier wafer by a sputtering system. The stated temperature is the chamber setpoint temperature. The HZO film was grown by ALD using bis(methylcyclopentadienyl)methoxymethyl-hafnium and bis(methylcyclopentadienyl)methoxymethyl-zirconium precursors at 330 °C with 4% ozone. Subsequently, following the HZO deposition, a 50 Å deposition of the W top electrode was performed. The circular electrodes for electrical testing were TiN, 500 Å, defined by shadow masking or contact lithography, and grown at 250 °C in an Endura sputtering chamber. After the deposition of the W top electrode, a post-metal annealing was performed at 400 °C for 5 minutes.

[0094] HZO film growth The FE HZO film is grown by atomic layer deposition at 330 °C using an exposure sequence of (bis(methylcyclopentadienyl)methoxymethyl-hafnium) / ozone / (bis(methylcyclopentadienyl)methoxymethyl-zirconium) / ozone including one HZO supercycle. The Hf precursor may also be (MeNCH2CH2Cp)Hf(NMe2)2, and the Zr precursor may also be (MeNCH2CH2Cp)Zr(NMe2)2. Bis(methylcyclopentadienyl)methoxymethyl-hafnium, bis(methylcyclopentadienyl)methoxymethyl-zirconium, (MeNCH2CH2Cp)Hf(NMe2)2, and (MeNCH2CH2Cp)Zr(NMe2)2 are all proprietary chemicals manufactured by EMD Electronics. These cyclopentadienyl precursors have an ALD window at a higher temperature (300 °C to 400 °C) compared to amide-type precursors, enabling a lower temperature PMA process to obtain the desired HZO crystallites. The inventors deposited the film at an ozone concentration of 4%. The bis(methylcyclopentadienyl)methoxymethyl-hafnium and bis(methylcyclopentadienyl)methoxymethyl-zirconium precursors were maintained at ampoule temperatures of 125 °C and 70 °C, respectively, during deposition. (MeNCH2CH2Cp)Hf(NMe2)2 and (MeNCH2CH2Cp)Zr(NMe2)2 were both maintained at an ampoule temperature of 100 °C.

[0095] Example I Figures 2A - 2C show the results of the optimization process of the bottom electrode. In this example, HZO is grown on 50 Å of W. Figure 2A shows the intensity before and after post-metal annealing, which shows the phase transformation of W from the α-phase to the β-phase. The α-phase is more desirable as the bottom electrode because it has a resistance approximately 10 times lower than the β-phase.

[0096] Figure 2C shows the grazing incidence XRD patterns of the essential bottom electrode and the ferroelectric material prepared and deposited on the bottom electrode before and after annealing. As shown in Figure 2B, the crystal peaks of the materials constituting the layer show monoclinic and non-monoclinic components. By fitting the peaks and using the peak areas with the technique described by McBriarty et al. at https: / / onlinelibrary.wiley.com / doi / full / 10.1002 / pssb.201900285, the calculated monoclinic fraction of the volume of the materials constituting the layer is less than 25%, which is the preferred maximum volume fraction of the monoclinic non-ferroelectric material.

[0097] Figure 2B shows the non-monoclinic peak shift after annealing, which indicates a change in the HZO crystallinity. Figure 2C shows the improvement of the remnant polarization after annealing, which indicates the stabilization of the desired ferroelectric phase.

[0098] Example II Figures 3A - 3C show the results of the bottom electrode optimization. Figure 3A shows the surface roughness of the bottom W electrode calculated from X-ray reflectivity, indicating that the roughness increases as the thickness increases. Figure 3B shows that W grown at high temperature has a higher ratio of the α phase. Figure 3C shows the remnant magnetization after annealing of HZO grown on the optimized W electrode (100 Å (10 nm) at 250 °C), indicating a significant improvement.

[0099] Figure 4 shows the significant ferroelectric polarization of the ferroelectric device at the end of the process integration, which does not require a wake-up process to activate the ferroelectricity of the film. After electrical stress, a slight increase in the remnant polarization and a shift in the coercive field are observed.

[0100] For the fabrication of a simple metal-FE-metal (MFM) stack, the inventors deposit W (10 nm) as the bottom electrode (BE) using a PVD process. Subsequently, the HZO film is deposited by ALD. This is followed by capping of the layer (5 nm of W deposited by PVD) and PMA at 400 °C for 5 minutes in an N2 atmosphere. The circular top electrode (TE) for electrical testing is defined by a shadow mask and is 500 Å of TiN grown by an Endura sputtering chamber at 250 °C, followed by SF6 etching of the capping layer on the field.

[0101] In the illustrated embodiment, the bottom electrode contains tungsten. In other embodiments, the top electrode may contain any of titanium nitride, molybdenum, ruthenium, platinum, and aluminum. In the illustrated embodiment, W with a thickness of 5 or 10 nm is used.

[0102] The ferroelectric layer contains Hf x Zr 1-x O2. In alternative embodiments, the ferroelectric layer can contain HfO2 doped with La, Y, Gd, Sr, or combinations thereof.

[0103] In the illustrated embodiment, the post-metal anneal (PMA) is performed at 400 °C for 5 minutes.

[0104] One important observation in Figure 4 is that ferroelectric behavior has been observed even before the wake-up cycle with open-loop hysteresis. Stress 2.5 V 1000 bipolar cycles frequency 1 kHz.

[0105] Figure 5 shows multi-bit programming (>4 states) to adjust the remanent polarization of the ferroelectric capacitor. The device is programmed from + / -1 V to + / -2.75 V in programming steps of + / -0.25 V. The frequency used in all these experiments is 1 kHz.

[0106] Example III Figure 6 shows the effect of the top electrode on the durability of the ferroelectric device. The device was programmed to go through 7.2e+6 cumulative cycles of a sweep from 2.25 V to -2.25 V. The pulse width used in all these experiments was 500 ns. Figure 6 shows the durability without breakdown up to 7.2e+6 cycles of the ferroelectric device with a titanium nitride top electrode, compared to the early breakdown at 4.1e+6 cycles of the ferroelectric device with a tungsten electrode.

[0107] Figure 7 shows the effect of the bottom electrode on the leakage response of the ferroelectric device. Figure 7 shows that the ferroelectric device with a titanium nitride bottom electrode has a lower leakage response (current density in units of amperes / cm 2 at 2 V) compared to the ferroelectric device with a tungsten bottom electrode.

[0108] The ferroelectric layer contains Hf x Zr 1-x O2. In an alternative embodiment, the ferroelectric layer can contain HfO2 doped with La, Y, Gd, Sr, or combinations thereof.

[0109] In the illustrated embodiment, the post-metal annealing (PMA) is performed at 400 °C for 5 minutes.

[0110] In the illustrated embodiment, the top electrode contains tungsten or titanium nitride. In other embodiments, the top electrode can contain any of molybdenum, ruthenium, platinum, and aluminum. In the illustrated embodiment, a top electrode with a thickness of 5 nm is used. 3]

[0111] In the illustrated embodiment, the bottom electrode contains tungsten or titanium nitride. In other embodiments, the bottom electrode can contain any of molybdenum, ruthenium, and platinum. In the illustrated embodiment, a bottom electrode with a thickness of 5 or 20 nm is used.

[0112] A further advantage of the FTJ system of the present invention is a lower total thermal budget. It is important that on-chip back-end-of-the-line (BEOL) compatible memory be fabricated at a temperature below 400 °C at any of its process steps. A typical HZO film is deposited amorphous by a low temperature ALD process and then requires high temperature annealing to activate the FE domains. The process shown utilizes a high temperature ALD precursor, which allows the film to be highly ferroelectric as deposited. Typically, the preferred deposition temperature is 300 °C to 350 °C, in which case annealing at 400 °C is sufficient to make it very stable. This makes the process flow BEOL compatible.

[0113] A further advantage of the FTJ system of the present invention is faster read / write operation. Since the FTJ depends on tunnel electrical resistance, the device is high resistance compared to other non-volatile memory technologies such as ReRAM and PCM in both the low resistance state and the high resistance state. This is desirable from the perspective of energy dissipation, but if the resistance is too high, a high voltage is required for reading, which raises concerns about reliability, and if the pulse is slow, reading and writing become unduly slow and noise is likely to occur. Since a dielectric layer is not required to generate asymmetry and the film has a high remanent polarization, the stack can be designed to be thin and have sufficient FE dipoles to further generate a memory window. This makes the illustrated FTJ stack highly scalable with respect to both the thickness of the ferroelectric material and the area of the device.

[0114] It will be apparent to those skilled in the art that various modifications and variations can be made to the disclosed subject matter and the specific examples provided herein without departing from the spirit and scope of the disclosed subject matter. Accordingly, the disclosed subject matter, including the description provided by the following examples, is intended to cover modifications and variations of the disclosed subject matter that fall within the scope of any claims and their equivalents.

[0115] Materials and Methods: The metallocene precursor was prepared according to U.S. Patent No. 8,568,530 or can be prepared otherwise, the content of which is incorporated herein in its entirety.

[0116] After deposition, the film was identified by grazing incidence XRD using a Bruker D8 Discover diffractometer with a monochromatic Cu X-ray tube (Cu Kα, λ = 1.5418 Å). The incident beam angle was fixed at 0.7°, and the XRD pattern was collected in the range of 2θ 20° - 40° at 0.05° steps using a position-sensitive detector. For the ferroelectric test, a TiN top contact (thickness 50 nm) was deposited in an Applied Materials Endura PVD tool at 250 °C (i.e., at a non-annealing temperature lower than the temperature for ALD growth) by PVD. Circular contacts (diameter 0.203 mm, area 0.032 mm 2 ) were defined by a shadow mask. Polarization curves were collected using a Radiance Precision II ferroelectric tester and a Cascade probe station. Polarization field data were collected using a bipolar triangular waveform (5 kHz, in 0.25 V increments from -3 V to 3 V) before and after applying a wake-up stress of ±3 V for 1 s at 1 kHz. As shown in Figure 3C, the as-deposited layer has a residual polarization (Pr) greater than 30 μC / cm, or a total loop opening 2Pr greater than 60 μC / cm when measured using a triangular bipolar waveform with a maximum applied electric field of about 3.8 MV / cm. Without being bound by theory, the as-deposited layer is expected to have a residual polarization (Pr) of 20 μC / cm or more, or 30 μC / cm or more, or 40 μC / cm or more, or a total loop opening 2Pr of 50 μC / cm or more, or 60 μC / cm or more, or 70 μC / cm or more. 2 greater than, or a total loop opening 2Pr greater than 2 When measured using a triangular bipolar waveform with a maximum applied electric field of about 3.8 MV / cm, the as-deposited layer is expected to have a residual polarization (Pr) of 2 20 μC / cm or more, or 2 30 μC / cm or more, or 2 40 μC / cm or more, or a total loop opening 2Pr of 2 50 μC / cm or more, or 2 60 μC / cm or more, or 2 70 μC / cm or more.

[0117] Although the present invention has been described and illustrated in some detail, it is to be understood that the present disclosure has been made only by way of example, and that numerous changes in the conditions and order of steps can be made by those skilled in the art without departing from the spirit and scope of the invention.

Claims

1. A substrate, a first electrode and a second electrode, wherein the first electrode is disposed on the substrate, the first electrode and the second electrode; a thin film including a crystalline material disposed between the first electrode and the second electrode, wherein the crystalline material includes hafnium oxide and zirconium oxide, and the crystalline material exhibits ferroelectric behavior in the as-deposited state, the thin film; and, The first electrode includes tungsten, titanium nitride, molybdenum, ruthenium, or a combination thereof, and the thin film has a remanent polarization greater than about 50 μC / cm ２ ferroelectric device.

2. The ferroelectric device according to claim 1, wherein the thin film can exhibit ferroelectric activity without a wake-up period.

3. The ferroelectric device according to claim 1, wherein the second electrode includes titanium nitride, tungsten, molybdenum, or a combination thereof.

4. The ferroelectric device according to claim 1, wherein the first electrode has a thickness of about 4 nm to about 50 nm.

5. The ferroelectric device according to claim 1, wherein more than 50% of the total volume of the first electrode is in the α-phase.

6. The ferroelectric device according to claim 1, wherein the crystalline material has a hafnium oxide to zirconium oxide ratio of about 1:3 to about 3:

1.

7. The crystalline material is of formula I: 【Chemical Formula 1】 Formula II: [[Chemical 2]] or formula III: [Chemical Formula 3] Derived from one or more metallocene precursors, wherein (i) M is selected from Zr and Hf, (ii) R １ , R ２ , R ３ , R ４ , R ５ , R ６ , R ７ , and R ８ are each independently selected from C １ to C ６ linear alkyl, C １ to C ６ branched alkyl, C １ to C ６ halogenated linear alkyl, and C １ to C ６ halogenated branched alkyl, (iii) R ９ is a C ２ selected from -CH ２ CH ２ CH ２ CH ２ -, -CH(Me)CH ２ -, -CH ２ CH(Me)-, -CH ２ CH ２ CH ２ -, -CHMeCH ２ CH ２ -, and is a C １ to C ４ group, (iv) R １０ , R １１ , and R １２ are each independently C １ to C ６ linear alkyl, The ferroelectric device according to claim 1.

8. The crystalline material is of formula I: 【Chemical Formula 4】 Formula II: 【Chemical Formula 5】 or formula III: 【Chemical Formula 6】 Derived from one or more metallocene precursors having, wherein, (i) M is selected from Zr and Hf, (ii) R １ R ２ R ３ R ４ R ５ R ６ R ７ and R ８ are each independently a C １ to C ６ linear alkyl, (iii) R ９ is -CH ２ CH ２ -, -CH ２ CH ２ CH ２ -, -CH(Me)CH ２ -, -CH ２ CH(Me)-, -CH ２ CH ２ CH ２ -, -CHMeCH ２ CH ２ - selected from C １ to C ４ groups, (iv) R １０ R １１ and R １２ are each independently a C １ to C ６ linear alkyl, the ferroelectric device according to claim 1.

9. The crystalline material is of formula I: [Chemical Formula 7] Formula II: 【Chemical Formula 8】 or formula III: 【Chemical Formula 9】 derived from one or more metallocene precursors having, wherein (i) M is selected from Zr and Hf, (ii) R １ , R ２ , R ３ , R ４ , R ５ , R ６ , R ７ , and R ８ are each a methyl group, (iii) R ９ is -CH ２ CH ２ -, -CH ２ CH ２ CH ２ -, -CH(Me)CH ２ -, -CH ２ CH(Me)-, -CH ２ CH ２ CH ２ -, -CHMeCH ２ CH ２ - selected from C １ ~C ４ groups, (iv) R １０ , R １１ , and R １２ are each independently C １ ~C ６ linear alkyl, The ferroelectric device according to claim 1.

10. The ferroelectric device according to claim 1, wherein hysteresis and remanent polarization are present in the polarization electric field measurement.

11. The ferroelectric device according to claim 1, wherein the film has a thickness of about 0.2 nm to about 10 nm.

12. A method of fabricating a ferroelectric device, comprising: (i) providing a substrate; (ii) depositing a first electrode on the substrate, wherein the first electrode includes tungsten, titanium nitride, molybdenum, ruthenium, or a combination thereof; (iii) depositing a ferroelectric layer on the first electrode at a deposition temperature, wherein the ferroelectric layer includes zirconium and hafnium; (iv) depositing a second electrode on the ferroelectric layer; and (v) annealing the first electrode at a temperature of 400 °C or lower.

13. The method according to claim 12, wherein the annealing step is performed at a temperature higher than about 350 °C.

14. The method according to claim 12, wherein no process steps are performed at a temperature higher than about 400 °C.

15. The method according to claim 12, wherein the ferroelectric layer contains hafnium zirconium oxide.

16. The method according to claim 12, wherein more than 50% of the total volume of the first electrode is in the α-phase.

17. The method according to claim 12, wherein the first electrode has a thickness of about 4 nm to about 50 nm.

18. A method of manufacturing a ferroelectric device, comprising: (i) providing a substrate; (ii) depositing a first electrode on the substrate at a first temperature; (iii) depositing a ferroelectric layer on the first electrode at a second temperature; (iv) depositing a second electrode on the ferroelectric layer; and (v) performing an annealing step at a third temperature, wherein the first temperature, the second temperature, and the third temperature are 400 °C or less.

19. The method according to claim 18, wherein the first temperature is about 15 °C to about 400 °C.

20. The method according to claim 18, wherein the thickness of the first electrode is about 4 nm to about 50 nm.

21. The method according to claim 18, wherein in the annealing step, the third temperature is about 350 °C or higher and 400 °C or lower.

22. The method according to claim 18, wherein no process step is performed at a temperature higher than about 400 °C.

23. The method according to claim 18, wherein the first electrode contains tungsten, titanium nitride, molybdenum, ruthenium, or a combination thereof, and the second electrode contains titanium nitride, tungsten, molybdenum, or a combination thereof.

24. (i) providing a substrate; (ii) depositing a first electrode on the substrate, wherein the first electrode contains tungsten; (iii) depositing a ferroelectric layer on the first electrode at a deposition temperature, wherein the ferroelectric layer contains zirconium and hafnium; (iv) depositing a second electrode on the ferroelectric layer; and (v) annealing the first electrode at a temperature of 400 °C or less. The first electrode contains tungsten having a remanent polarization greater than 50 μC / cm ２ A ferroelectric device.

25. The ferroelectric device according to claim 24, wherein no process step is performed at a temperature higher than about 400 °C.

26. The ferroelectric layer is Hf doped with La, Y, Gd, Ge, Si, or Sr ｘ Zr １－ｘ O ２ or HfO ２ The ferroelectric device according to claim 24, comprising the same.

27. The ferroelectric device according to claim 24, having a critical dimension of 1000 nm or less, preferably about 300 μm or less.

28. A unit cell of a ferroelectric random access memory device comprising the ferroelectric device according to claim 1.

29. A crossbar memory array comprising the ferroelectric device according to claim 1 and comprising memory unit cells.

30. A neuromorphic computing chip comprising the ferroelectric device according to claim 1, wherein the ferroelectric device is a synaptic device.

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