WO2023231480A1 - 铁电单元、三维铁电结构和铁电存储器 - Google Patents

铁电单元、三维铁电结构和铁电存储器 Download PDF

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WO2023231480A1
WO2023231480A1 PCT/CN2023/078721 CN2023078721W WO2023231480A1 WO 2023231480 A1 WO2023231480 A1 WO 2023231480A1 CN 2023078721 W CN2023078721 W CN 2023078721W WO 2023231480 A1 WO2023231480 A1 WO 2023231480A1
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ferroelectric
ferroelectric layer
electrode
layer
concentration
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PCT/CN2023/078721
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English (en)
French (fr)
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谭万良
李宇星
许俊豪
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华为技术有限公司
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    • H—ELECTRICITY
    • H10—SEMICONDUCTOR DEVICES; ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
    • H10B—ELECTRONIC MEMORY DEVICES
    • H10B51/00—Ferroelectric RAM [FeRAM] devices comprising ferroelectric memory transistors
    • H10B51/30—Ferroelectric RAM [FeRAM] devices comprising ferroelectric memory transistors characterised by the memory core region
    • H—ELECTRICITY
    • H10—SEMICONDUCTOR DEVICES; ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
    • H10B—ELECTRONIC MEMORY DEVICES
    • H10B53/00—Ferroelectric RAM [FeRAM] devices comprising ferroelectric memory capacitors
    • H10B53/20—Ferroelectric RAM [FeRAM] devices comprising ferroelectric memory capacitors characterised by the three-dimensional arrangements, e.g. with cells on different height levels
    • H—ELECTRICITY
    • H10—SEMICONDUCTOR DEVICES; ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
    • H10B—ELECTRONIC MEMORY DEVICES
    • H10B53/00—Ferroelectric RAM [FeRAM] devices comprising ferroelectric memory capacitors
    • H10B53/30—Ferroelectric RAM [FeRAM] devices comprising ferroelectric memory capacitors characterised by the memory core region
    • H—ELECTRICITY
    • H10—SEMICONDUCTOR DEVICES; ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
    • H10N—ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
    • H10N97/00—Electric solid-state thin-film or thick-film devices, not otherwise provided for

Definitions

  • Embodiments of the present application relate to the technical field of semiconductor devices, and in particular to a ferroelectric unit, a three-dimensional ferroelectric structure and a ferroelectric memory.
  • Ferroelectric materials are used in the storage field due to their inherent advantages such as fast erasing and writing speed, ultra-low power consumption, high number of cycles, and non-volatile polarization states.
  • Ferroelectric random access memory (FeRAM) based on ferroelectric materials
  • Ferroelectric devices such as memory
  • ferroelectric tunneling junction (FTJ) have received widespread attention.
  • ferroelectric hafnium oxide materials such as the solid solution HfO 2 :ZrO 2 of hafnium oxide and zirconium oxide, can also be called zirconium-doped hafnium oxide (HfZrOx).
  • This ferroelectric material has a low crystallization temperature and high integration. Compatibility with CMOS technology and other advantages have become research directions.
  • the basic unit structure of FeRAM and FTJ is usually formed by placing a ferroelectric film between two metal electrodes, that is, "metal-ferroelectric layer-metal" sandwich structure.
  • metal-ferroelectric layer-metal sandwich structure
  • the metal electrodes on both sides of the ferroelectric layer are affected by various factors such as metal materials, deposition methods, element ratios, and crystallization levels, the work functions of the metal electrodes on both sides of the ferroelectric layer are usually different. This leads to electrical asymmetry in ferroelectric devices.
  • the electrical asymmetry mainly includes: the polarization curve of the ferroelectric device drifts; under the same electric field strength and different polarity of the external electric field, the leakage current of the ferroelectric device is different. .
  • the electrical asymmetry of ferroelectric devices is not controlled by the outside world. For some ferroelectric devices that require symmetry (such as FeRAM), these electrical asymmetries lead to asymmetry in the positive and negative directions of ferroelectric devices.
  • the performance of the ferroelectric device can be improved.
  • a ferroelectric unit which includes: a first electrode; a first ferroelectric layer disposed on the surface of the first electrode; and a first ferroelectric layer disposed on the surface of the first electrode.
  • the side away from the first electrode a second ferroelectric layer; a second electrode disposed on the surface of the second ferroelectric layer on a side away from the first ferroelectric layer; wherein the concentration of the first element in the first ferroelectric layer is high
  • the concentration of the first element in the second ferroelectric layer, where the first element is one of hafnium element, zirconium element and oxygen element.
  • ferroelectric unit In the ferroelectric unit provided by the embodiment of the present application, two ferroelectric layers are disposed between two electrodes, and the concentration of the first element in the first ferroelectric layer is set to be higher than the concentration of the first element in the second ferroelectric layer. concentration.
  • concentration concentration
  • the oxygen vacancy concentration between the first ferroelectric layer and the second ferroelectric layer can be different, so that the contact between the two ferroelectric layers can be A first built-in electric field is generated between the interfaces; in addition, there is usually a second built-in electric field between the first electrode and the second electrode.
  • the above-mentioned first built-in electric field and the second built-in electric field can be offset or superimposed, so as to improve the electrical symmetry of the ferroelectric device or Reduce the electrical symmetry of ferroelectric devices, that is, the electrical symmetry of ferroelectric devices can be flexibly adjusted, thereby improving the performance of ferroelectric devices.
  • embodiments of the present application change the concentration of the first element in the two ferroelectric layers to generate a built-in electric field between the contact interfaces of the two ferroelectric layers, thereby eliminating the need to introduce elements between the ferroelectric layers and the electrodes.
  • a built-in electric field is generated at the contact interface between the ferroelectric layer and the electrode, thereby avoiding the chaotic state of the contact interface between the electrode and the ferroelectric layer due to element diffusion, thereby improving the feasibility of actual production and use of ferroelectric devices.
  • Embodiments of the present application can achieve different oxygen vacancy concentrations between the first ferroelectric layer and the second ferroelectric layer in a variety of ways.
  • the material of the first ferroelectric layer and the material of the second ferroelectric layer are hafnium zirconium oxide; when the first element is hafnium element, the first ferroelectric layer The concentration of the second element in the ferroelectric layer is lower than the concentration of the second element in the second ferroelectric layer, and the second element is zirconium.
  • the ferroelectric unit when the first electrode is titanium nitride and the second electrode is metal tungsten, since the concentration of oxygen vacancies in the first ferroelectric layer is lower than the concentration of oxygen vacancies in the second ferroelectric layer, the ferroelectric unit
  • the built-in electric field is the superposition of the built-in electric field between the two electrodes and the built-in electric field between the two ferroelectric layers.
  • the non-electrical symmetry of the ferroelectric unit can be improved to improve switching such as FTJ. Compare the performance of the device.
  • the ferroelectric unit when the first electrode is metal tungsten and the second electrode is titanium nitride, since the concentration of oxygen vacancies in the first ferroelectric layer is lower than the concentration of oxygen vacancies in the second ferroelectric layer, the ferroelectric unit
  • the built-in electric field is the built-in electric field between the two electrodes minus the built-in electric field between the two ferroelectric layers.
  • the electrical symmetry of the ferroelectric unit can be improved to improve the performance of ferroelectric devices such as FeROM. performance.
  • the material of the first ferroelectric layer and the second ferroelectric layer are both hafnium and zirconium oxide; when the first element is zirconium, the first iron The concentration of the second element in the electric layer is lower than the concentration of the second element in the second ferroelectric layer, and the second element is hafnium.
  • the first electrode is titanium nitride, and the second electrode is metal tungsten; or the second electrode is titanium nitride, and the first electrode is metal tungsten.
  • the material of the first ferroelectric layer and the material of the second ferroelectric layer are both hafnium zirconium oxygen; the concentration of oxygen element in the first ferroelectric layer is higher than that of the second ferroelectric layer. The concentration of oxygen in the ferroelectric layer.
  • the first electrode is titanium nitride, and the second electrode is metal tungsten; or the second electrode is titanium nitride, and the first electrode is metal tungsten.
  • inventions of the present application provide a three-dimensional ferroelectric structure.
  • the three-dimensional ferroelectric structure includes: a plurality of blunt A first annular region formed by a stack of passivation layers and a plurality of first electrodes; a first ferroelectric layer is provided inside the first annular region, and the first ferroelectric layer is connected with the plurality of passivation layers and the plurality of first electrodes.
  • the first electrodes are all in contact with each other; a second ferroelectric layer is provided on the side of the first ferroelectric layer away from the first annular area; the second ferroelectric layer is provided on a side away from the first ferroelectric layer.
  • a second electrode is provided on the side; wherein the concentration of the first element in the first ferroelectric layer is higher than the concentration of the first element in the second ferroelectric layer, and the first element is hafnium element, One of the elements zirconium and oxygen.
  • multiple first electrodes can share the same ferroelectric layer, thereby forming multiple ferroelectric units.
  • a ferroelectric unit is formed between a first electrode, a first ferroelectric layer, a second ferroelectric layer and a second electrode.
  • the ferroelectric unit provided by the embodiment of the present application sets the concentration of the first element in the first ferroelectric layer to be higher than the concentration of the first element in the second ferroelectric layer by disposing two ferroelectric layers between the two electrodes.
  • the concentration of an element In this way, by setting the first element concentration difference between the two ferroelectric layers, the oxygen vacancy concentration between the first ferroelectric layer and the second ferroelectric layer can be different, so that the contact between the two ferroelectric layers can be A first built-in electric field is generated between the interfaces; in addition, there is usually a second built-in electric field between the first electrode and the second electrode.
  • the above-mentioned first built-in electric field and the second built-in electric field can be offset or superimposed, so as to improve the electrical symmetry of the ferroelectric device or Reduce the electrical symmetry of ferroelectric devices, that is, the electrical symmetry of ferroelectric devices can be flexibly adjusted, thereby improving the performance of ferroelectric devices.
  • embodiments of the present application change the concentration of the first element in the two ferroelectric layers to generate a built-in electric field between the contact interfaces of the two ferroelectric layers, thereby eliminating the need to introduce elements between the ferroelectric layers and the electrodes.
  • a built-in electric field is generated at the contact interface between the ferroelectric layer and the electrode, thereby avoiding the chaotic state of the contact interface between the electrode and the ferroelectric layer due to element diffusion, thereby improving the feasibility of actual production and use of ferroelectric devices.
  • the material of the first ferroelectric layer and the second ferroelectric layer are both hafnium and zirconium oxide; when the first element is hafnium, the first iron The concentration of the second element in the electric layer is lower than the concentration of the second element in the second ferroelectric layer, and the second element is zirconium.
  • the material of the first ferroelectric layer and the second ferroelectric layer are both hafnium and zirconium oxide; when the first element is zirconium, the first ferroelectric layer The concentration of the second element in the layer is lower than the concentration of the second element in the second ferroelectric layer, and the second element is hafnium.
  • the material of the first electrode is tungsten; the second electrode is formed of two metal layers, and the material in contact with the second ferroelectric layer among the two metal layers is Titanium nitride, the material of the two metal layers that is not in contact with the second ferroelectric layer is tungsten.
  • embodiments of the present application provide a ferroelectric memory, which includes a plurality of memory cells arranged in an array; each of the plurality of memory cells includes a transistor and a transistor as described in the first aspect.
  • FIG. 1 is a schematic structural diagram of a ferroelectric unit in the prior art provided by this application.
  • Figure 2A is a schematic diagram showing that the polarization curve of the ferroelectric unit provided by the implementation of this application has not drifted;
  • Figure 2B is a schematic diagram showing the drift of the polarization curve of the ferroelectric unit provided by the implementation of this application;
  • Figure 2C is a schematic diagram showing that the leakage current of the ferroelectric unit provided by the implementation of this application does not drift;
  • Figure 2D is a schematic diagram showing the drift of the leakage current of the ferroelectric unit provided by the implementation of this application;
  • FIG. 3 is another structural schematic diagram of a ferroelectric unit in the prior art provided by this application.
  • Figure 4A is a schematic structural diagram of a ferroelectric unit provided by an embodiment of the present application.
  • Figure 4B is a schematic diagram of the built-in electric field weakening of the ferroelectric unit shown in Figure 4A provided by an embodiment of the present application;
  • Figure 4C is a flow chart for preparing the ferroelectric unit shown in Figure 4A provided by an embodiment of the present application;
  • Figure 5A is another structural schematic diagram of a ferroelectric unit provided by an embodiment of the present application.
  • Figure 5B is a schematic diagram of the built-in electric field enhancement of the ferroelectric unit shown in Figure 5A provided by an embodiment of the present application;
  • FIG. 6 is another structural schematic diagram of the ferroelectric unit provided by the embodiment of the present application.
  • FIG. 7 is another structural schematic diagram of the ferroelectric unit provided by the embodiment of the present application.
  • Figure 8A is a schematic structural diagram of a three-dimensional ferroelectric structure provided by an embodiment of the present application.
  • Figure 8B is a cross-sectional view along AA' of the three-dimensional ferroelectric structure shown in Figure 8A;
  • Figure 9 is a schematic structural diagram of a ferroelectric memory provided by an embodiment of the present application.
  • the ferroelectric unit includes a top metal electrode formed on a substrate, a bottom metal electrode, and a ferroelectric layer disposed between the two metal electrodes.
  • the top metal electrode is a patterned metal layer formed by photolithography.
  • the top electrode is formed of one or more metal materials, such as but not limited to gold (Au), platinum (Pt), tantalum (Ta). ), titanium nitride (TiN), aluminum (Al), tungsten (W) or palladium (Pd), etc.
  • Figure 1 schematically shows that the top electrode is formed of W metal material.
  • the bottom electrode is formed of titanium nitride (TiN) material.
  • the material of the ferroelectric layer is hafnium and zirconium Oxygen (HaZrO, hafnium zirconium oxide).
  • HaZrO hafnium zirconium Oxygen
  • the ferroelectric polarization intensity of the ferroelectric unit is adjusted by changing the material of the top electrode.
  • the abscissa is the external electric field and the ordinate is the ferroelectric polarization intensity.
  • the positive polarization curve and the negative polarization curve of the ferroelectric unit are symmetrical about the ordinate, that is, when the external electric field has opposite polarity and the same magnitude, the positive coercive field and the negative polarization curve are symmetrical about the ordinate.
  • the coercive fields have the same size but opposite polarity.
  • Figure 2B shows the polarization curve of the ferroelectric unit that has drifted.
  • the solid line indicates that the polarization curve of the ferroelectric unit has drifted in the positive direction
  • the dotted line indicates that the polarization curve of the ferroelectric unit has drifted in the negative direction.
  • Figure 2B when the polarization curve of the ferroelectric unit drifts, the positive polarization curve and the negative polarization curve are no longer symmetrical about the ordinate, that is, the applied electric field has opposite polarity and the same magnitude.
  • the positive coercive field and the negative coercive field have different sizes.
  • Figure 2C is the leakage current curve of the ferroelectric unit.
  • the abscissa is the external electric field and the ordinate is the leakage current.
  • FIG. 2C shows the leakage current curve of a drifted ferroelectric unit.
  • the solid line indicates the positive drift of the ferroelectric unit's leakage current, and the dotted line indicates the negative drift of the ferroelectric unit's leakage current. It can be seen from Figure 2D that when the leakage current curve of the ferroelectric unit drifts, the leakage current is different under the same electric field intensity and different polarity of the external electric field.
  • the ferroelectric device will be Issues such as asymmetry in positive and negative erasing, incomplete flipping in a certain direction, and asymmetry in anti-interference performance.
  • the drift of the polarization curve and leakage current needs to be used to achieve the switching ratio of the device. In this case, it is necessary to adjust the drift of the polarization curve and leakage current based on the switching ratio.
  • the industry further proposes to adjust the symmetry of the ferroelectric unit by changing the atoms at the contact interface between the ferroelectric layer and the metal electrode, as shown in Figure 3.
  • the ferroelectric unit includes two layers of TiN electrodes and a ferroelectric layer disposed between the two layers of TiN electrodes.
  • different atoms are introduced into the contact interface between each layer of TiN electrodes and the ferroelectric layer to form a non-zero built-in electric field, thereby adjusting the symmetry of the ferroelectric unit. .
  • the ferroelectric layer material shown in Figure 3 is HfO 2 , Hf atoms are introduced into the contact interface between the TiN electrode and the ferroelectric layer on the left side, and Hf atoms are introduced into the contact interface between the TiN electrode and the ferroelectric layer on the right side. O atoms.
  • the ferroelectric device provided in the embodiment of the present application
  • the unit is configured by arranging two ferroelectric layers between two layers of electrodes, and the concentration of the first element contained in one of the ferroelectric layers is higher than the concentration of the first element contained in the other ferroelectric layer.
  • a first built-in electric field is generated between the contact interface of the two ferroelectric layers; in addition, due to the different materials of the two electrodes, the work functions between the two electrodes are different, that is, a first built-in electric field is generated between the two electrodes.
  • the second built-in electric field by adjusting the positional relationship between the electrode and each ferroelectric layer, the above-mentioned first built-in electric field and the second built-in electric field can be offset or superimposed to improve the electrical symmetry of the ferroelectric device.
  • the embodiment of the present application generates a built-in electric field between the contact interface of the two ferroelectric layers by changing the concentration of the first element in the two ferroelectric layers.
  • the ferroelectric unit provided by the embodiment of the present application will be described in more detail below with reference to the embodiments shown in FIGS. 4A to 8 .
  • FIG. 4A is a schematic structural diagram of the ferroelectric unit 100 provided by an embodiment of the present application.
  • the ferroelectric unit 100 includes an electrode M1, an electrode M2, and a ferroelectric layer F1 and a ferroelectric layer F2 disposed between the electrode M1 and the electrode M2.
  • Both the electrode M1 and the electrode M2 are metal electrodes, and the electrode M1 and the electrode M2 can be made of the same material or different materials.
  • the material of electrode M1 may be tungsten (W), and the material of electrode M2 may be TaN. It should be noted that in other possible implementations of the embodiment of the present application, the materials of the electrode M1 and the electrode M2 can also be other materials.
  • the electrode M1 and the electrode M2 are both TaN, which is not specifically limited in the embodiment of the present application.
  • the material of the ferroelectric layer F1 and the ferroelectric layer F2 may be hafnium oxide (HfO) or hafnium zirconium oxide (HfZrO).
  • the material of the ferroelectric layer F1 and the ferroelectric layer F2 is HfZrO 2 as an example for description.
  • the thickness of the ferroelectric layer F1 and the thickness of the ferroelectric layer F2 may be the same, for example, 5 nm.
  • the concentration of the Zr element in the ferroelectric layer F1 is higher than the concentration of the Zr element in the ferroelectric layer F2; the concentration of the Hf element in the ferroelectric layer F2 is higher than the concentration of the Hf element in the ferroelectric layer F2.
  • the electrode M1 and the electrode M2 shown in Figure 4A since the materials of the electrode M1 and the electrode M2 shown in Figure 4A are W and TaN respectively, the electrode M1 and the electrode M2 have different work functions, and thus the electrode M1 and the electrode M2 have different work functions.
  • Create built-in electric field Since the work function of TaN is about 5.27eV and the work function of W is about 4.55eV, the work function of TaN is higher than the work function of W.
  • the above built-in electric field From electrode M1 to electrode M2 that is, the built-in electric field From the electrode with low work function to the electrode with high work function
  • the ferroelectric unit has the structure shown in Figure 1, the internal electric field of the ferroelectric unit is shown as (1) in Figure 4B.
  • the concentration of the Zr element in the ferroelectric layer F1 is higher than the concentration of the Zr element in the ferroelectric layer F2
  • the concentration of the Hf element in the ferroelectric layer F2 is higher than that of the ferroelectric layer
  • the concentration of the Hf element in F2 that is, the concentration of ZrO 2 in the ferroelectric layer F1 is higher, and the concentration of HfO 2 in the ferroelectric layer F2 is higher.
  • the concentration of oxygen vacancies in ferroelectric layer F1 is higher than the concentration of oxygen vacancies in ferroelectric layer F1, that is, ferroelectric layer F1 and ferroelectric layer F2
  • the built-in electric field From ferroelectric layer F1 to ferroelectric layer F2 (i.e. From the ferroelectric layer with oxygen vacancy concentration to the ferroelectric layer with low oxygen vacancy concentration).
  • the built-in electric field formed between the two electrodes Acts on the ferroelectric layer F1 and the ferroelectric layer F2, and forms a built-in electric field between the ferroelectric layer F1 and the ferroelectric layer F2 Can suppress built-in electric fields The influence of the built-in electric field of the ferroelectric unit 100 for the built-in electric field with built-in electric field The difference, that is, the built-in electric field with built-in electric field cancel each other out.
  • the embodiment of the present application adjusts the concentration of oxygen vacancies in the ferroelectric layer F1 and the ferroelectric layer F2 so that the total built-in electric field of the ferroelectric unit 100 Attenuating, or canceling, the electrical symmetry of ferroelectric cells compared to the existing technology shown in Figure 1 can be improved to improve performance such as FeRAM.
  • the prior art shown in FIG. 3 there is no need to introduce elements between the ferroelectric layer and the electrode to generate a built-in electric field at the contact interface between the ferroelectric layer and the electrode, thereby avoiding the risk of damage due to element diffusion.
  • the contact interface between the electrode and the ferroelectric layer is in a relatively chaotic state, thereby improving the feasibility of actual production and use of ferroelectric devices.
  • the ferroelectric unit 100 shown in Figure 4 can be based on atomic layer deposition (Atomic Layer Deposition) , ALD) process.
  • ALD atomic layer deposition
  • Figure 4C illustrates process steps 200 for preparing the ferroelectric unit 100 shown in Figure 4A.
  • the process steps 200 include:
  • Step 401 Form electrode M1 on the substrate.
  • the material of electrode M1 is W.
  • Step 402 Form ferroelectric layer F1 on electrode M1.
  • each ALD deposition cycle can deposit 1A thickness, and that the deposition rates of HfO 2 and ZrO 2 per ALD deposition cycle are the same, HfO2 of 3ALD deposition cycles and ZrO2 of 7ALD deposition cycles are alternately deposited on the electrode M1 , the ferroelectric layer F1 with a preset thickness can be obtained.
  • the preset thickness is, for example, 5 nm.
  • Step 403 Form a ferroelectric layer F2 on the electrode M1.
  • each ALD deposition cycle can deposit 1A thickness, and that the deposition rates of HfO 2 and ZrO 2 per ALD deposition cycle are the same, HfO2 of 7ALD deposition cycles and ZrO2 of 3ALD deposition cycles are alternately deposited on the ferroelectric layer F1
  • a ferroelectric layer F2 with a predetermined thickness can be obtained.
  • the preset thickness is, for example, 5 nm.
  • Step 404 Form a metal electrode M2 on the ferroelectric layer F2.
  • the material of the metal electrode M2 is TiN.
  • TiN can be prepared based on the principle that TiCl 4 reacts with NH 3 to generate TiN.
  • TiCl 4 is used as the precursor of Ti ions and NH 3 is used as the precursor of N ions.
  • the ratio of TiCl 4 to NH 3 is used as a cycle ratio of 1:1, and atomic deposition technology is used to deposit TiCl respectively. 4 materials and NH 3 materials.
  • the reaction between the deposited TiCl 4 material and NH 3 material produces TiN. After the thickness of the TiN material reaches a preset thickness (for example, 40 nm), stop depositing the TiCl 4 material and NH 3 material.
  • the metal electrode M1 of TiN material is prepared.
  • the ferroelectric unit 100 shown in FIG. 4A can be prepared.
  • the concentration of the Zr element in the ferroelectric layer F1 is higher than the concentration of the Zr element in the ferroelectric layer F2
  • the concentration of the Hf element in the ferroelectric layer F2 is higher than the concentration of the Hf element in the ferroelectric layer .
  • FIGS. 4A to 4C have introduced how to weaken the total built-in capacity of the ferroelectric unit 100 by setting the concentration of oxygen vacancies in the ferroelectric layer F1 to be higher than the concentration of oxygen vacancies in the ferroelectric layer F2 electric field Thereby improving the realization of electrical symmetry of ferroelectric units.
  • the ferroelectric layer F1 can be The concentration of oxygen vacancies in the ferroelectric layer is set lower than the concentration of oxygen vacancies in the ferroelectric layer F2 to increase the total built-in electric field of the electrical unit 100 Thereby improving the electrical asymmetry of the ferroelectric unit.
  • concentration of oxygen vacancies in the ferroelectric layer is set lower than the concentration of oxygen vacancies in the ferroelectric layer F2 to increase the total built-in electric field of the electrical unit 100 Thereby improving the electrical asymmetry of the ferroelectric unit.
  • FIG. 5A is a schematic structural diagram of the ferroelectric unit 300 provided by an embodiment of the present application.
  • the ferroelectric unit 300 also includes an electrode M1, an electrode M2, a ferroelectric layer F1 and a ferroelectric layer F2.
  • the material of electrode M1 is W
  • the material of electrode M2 is TiN.
  • the concentration of the Hf element in the ferroelectric layer F1 is higher than the concentration of the Hf element in the ferroelectric layer F2.
  • the concentration of the Zr element in the ferroelectric layer F2 is higher than the concentration of the Zr element in the ferroelectric layer.
  • the electrode M1 and the electrode M2 have different work functions, thereby forming a direction from the electrode M1 to the electrode M2 in the ferroelectric unit 300 built-in electric field (For more detailed analysis, refer to the relevant description in Figure 4B), as shown in Figure 5B.
  • the ferroelectric unit has the structure shown in Figure 1, the internal electric field of the ferroelectric unit is as shown in (1) in Figure 5B.
  • the concentration of the Hf element in the ferroelectric layer F1 is higher than the concentration of the Hf element in the ferroelectric layer F2
  • the concentration of the Zr element in the ferroelectric layer F2 is higher than that of Zr in the ferroelectric layer F2
  • the concentration of elements that is, the concentration of HfO 2 in the ferroelectric layer F1 is higher, and the concentration of ZrO 2 in the ferroelectric layer F2 is higher.
  • the concentration of oxygen vacancies in ferroelectric F2 is higher than the concentration of oxygen vacancies in ferroelectric layer F1, that is, the difference between ferroelectric layer F2 and ferroelectric layer F1
  • a built-in electric field is formed between the ferroelectric layer F2 and the ferroelectric layer F1 based on the oxygen vacancy concentration difference.
  • the built-in electric field Pointed from ferroelectric layer F2 to ferroelectric layer F1.
  • the built-in electric field formed between the two electrodes Acts on the ferroelectric layer F1 and the ferroelectric layer F2, and forms a built-in electric field between the ferroelectric layer F1 and the ferroelectric layer F2 Can enhance built-in electric field The influence of the built-in electric field of the ferroelectric unit 100 for the built-in electric field with built-in electric field The sum of , that is, the built-in electric field with built-in electric field The superposition between them enhances the built-in electric field of the ferroelectric unit 300.
  • the embodiment of the present application adjusts the concentration of oxygen vacancies in the ferroelectric layer F1 and the ferroelectric layer F2 so that the total built-in electric field of the ferroelectric unit 100 Enhancement, compared with the existing technology shown in Figure 1, can improve the non-electrical symmetry of the ferroelectric unit to improve the performance of devices such as FTJs that achieve on-off ratios.
  • the manufacturing steps of the ferroelectric unit 300 shown in FIG. 5A are similar to the manufacturing steps of the ferroelectric unit 100 shown in FIG. 4A .
  • the difference from the manufacturing steps of the ferroelectric unit 100 shown in FIG. 4A is that , when preparing the ferroelectric unit 300 shown in Figure 5A, interchange steps 402 and 403 shown in Figure 4C, that is, first form an electrode M1 on the substrate; then, 7ALD deposition cycles of HfO2 on the electrode M1 Alternately deposit HfO2 with 3ALD deposition cycles and ZrO2 with 3ALD deposition cycles to obtain a ferroelectric layer F1 with a preset thickness.
  • the ratio of the Zr element and the Hf element between the ferroelectric layer F1 and the ferroelectric layer F2 is adjusted.
  • the concentration of oxygen vacancies to adjust the electrical symmetry of the ferroelectric unit.
  • the concentration of oxygen vacancies in each ferroelectric layer can also be adjusted by adjusting the concentration of oxygen introduced into each ferroelectric layer.
  • FIG. 6 is a schematic structural diagram of the ferroelectric unit 400 provided by an embodiment of the present application.
  • the structure of the ferroelectric unit 400 shown in Figure 6 is the same as the structure of the ferroelectric unit shown in the above embodiments, including an electrode M1, an electrode M2, a ferroelectric layer F1 disposed between the two electrodes M1 and the electrode M2, and Ferroelectric layer F2.
  • the materials of each electrode and each ferroelectric layer are the same as those of the electrodes and ferroelectric layers in the above embodiments, and will not be described again.
  • the concentration of oxygen element introduced into the ferroelectric layer F1 during the preparation process is lower than that introduced into the ferroelectric layer F2 during the preparation process. The concentration of oxygen element.
  • the concentration of the oxygen element used to participate in the oxidation reaction in the ferroelectric layer F1 is lower than the concentration of the oxygen element used to participate in the oxidation reaction in the ferroelectric layer F2. Furthermore, the concentration of oxygen vacancies in the ferroelectric layer F1 is higher than the concentration of oxygen vacancies in the ferroelectric layer F2. As a result, there is a built-in electric field between the ferroelectric layer F1 and the ferroelectric layer F2 The built-in electric field is directed from the ferroelectric layer F1 to the ferroelectric layer F2, thereby improving the electrical symmetry of the ferroelectric unit. As shown in Figure 6 The principle of the ferroelectric unit 400 is the same as that of the ferroelectric unit 100 shown in FIG. 4A. For the specific principle description, refer to the principle description shown in FIG. 4B and will not be described again.
  • the ferroelectric unit 400 shown in FIG. 6 improves the electrical symmetry of the ferroelectric unit by setting the concentration of oxygen element in the ferroelectric layer F1 to be lower than the concentration of oxygen element in the ferroelectric layer F2.
  • the concentration of oxygen element introduced into the ferroelectric layer F1 during the preparation process is higher than the concentration of oxygen element introduced into the ferroelectric layer F2 during the preparation process, as shown in Figure 7 Electrical unit 500. Therefore, the concentration of the oxygen element used to participate in the oxidation reaction in the ferroelectric layer F1 is higher than the concentration of the oxygen element used to participate in the oxidation reaction in the ferroelectric layer F2.
  • the concentration of oxygen vacancies in the ferroelectric layer F1 is lower than the concentration of oxygen vacancies in the ferroelectric layer F2.
  • a built-in electric field ⁇ 2 exists between the ferroelectric layer F1 and the ferroelectric layer F2, and the built-in electric field is directed from the ferroelectric layer F2 to the ferroelectric layer F1, thereby improving the electrical asymmetry of the ferroelectric unit.
  • the principle of the ferroelectric unit 500 shown in FIG. 7 is the same as the principle of the ferroelectric unit 300 shown in FIG. 5A. For the specific principle description, refer to the principle description shown in FIG. 5B, which will not be described again.
  • the ferroelectric unit with a two-dimensional structure has been introduced above through Figures 4A to 7.
  • the ferroelectric unit can also be a three-dimensional structure.
  • multiple electrodes share the same ferroelectric layer, thereby forming multiple ferroelectric units.
  • Figure 8A and 8B Figure 8A is a top view of the three-dimensional ferroelectric structure 600
  • Figure 8B is a cross-sectional view along AA' of the three-dimensional ferroelectric structure 600 shown in Figure 8A.
  • the three-dimensional ferroelectric structure 600 is circular in top view.
  • the outermost layer is a stacked structure composed of a passivation layer 82 and a metal layer 81, in which the material of the metal layer M1 may be W.
  • the ferroelectric layer F1 Inside the laminated structure formed by the passivation layer 82 and the metal layer 81 is the ferroelectric layer F1, the inside of the ferroelectric layer F1 is the ferroelectric layer F2, and the inside of the ferroelectric layer F2 is the metal layer 83.
  • a ferroelectric unit is formed between one metal layer in the multi-layer metal layer 81, the ferroelectric layer F1, the ferroelectric layer F2 and the metal layer 83.
  • the three-dimensional ferroelectric structure 600 includes a plurality of ferroelectric units.
  • the plurality of ferroelectric units share the ferroelectric layer F1, the ferroelectric layer F2 and the metal layer 83.
  • the metal layer 83 may be one or more layers. When the metal layer 83 is one layer, the metal layer may be TiN. When the metal layer 83 is two layers, the two metal layers and the ferroelectric layer F2 The metal layer in contact is TiN, and the other layer is W.
  • the metal layer 83 includes two metal layers.
  • the materials of the ferroelectric layer F1 and the ferroelectric layer F2 and the concentrations of each element are the same as the ferroelectric unit 100 shown in Figure 4A or the ferroelectric unit 100 shown in Figure 6
  • the ferroelectric unit 400 is the same. For details, refer to the relevant descriptions in FIG. 4A or FIG. 6 and will not be described again.
  • the materials of the ferroelectric layer F1 and the ferroelectric layer F2 and the concentrations of each element are the same as the ferroelectric unit 300 shown in Figure 5A or the ferroelectric unit 300 shown in Figure 7
  • the same as the ferroelectric unit 500 shown in Figure 5A please refer to the relevant description of Figure 5A or Figure 7 for details, which will not be described again.
  • an embodiment of the present application also provides a ferroelectric memory 700, as shown in Figure 9.
  • the ferroelectric memory 700 includes a plurality of memory cells 701, 702...70n arranged in an array. Each memory cell includes a transistor M and a ferroelectric cell C.
  • the ferroelectric unit C can be the ferroelectric unit 100 as shown in Figure 4A, the ferroelectric unit 300 as shown in Figure 5A, the ferroelectric unit 400 as shown in Figure 6, or the ferroelectric unit 500 as shown in Figure 7 .
  • the ferroelectric memory 700 also includes a plurality of word lines WL0, WL1...WLm and a plurality of bit lines BL0, BL1..., BLn.
  • Each of the plurality of memory cells is connected to one of the plurality of bit lines.
  • the bit line is connected to one of the plurality of word lines.
  • Each memory cell has the same connection relationship with bit lines and word lines. Taking the memory cell 501 as an example, the gate of the transistor M is connected to the word line WL0, the source of the transistor M is connected to the bit line BL0, the drain of the transistor M is connected to one end of the ferroelectric unit C, and the other end of the ferroelectric unit C Connect to board line PL.

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Abstract

本申请实施例提供了一种铁电单元、三维铁电结构以及铁电存储器，本申请提供的铁电单元，包括：第一电极；设置于所述第一电极表面的第一铁电层；设置于所述第一铁电层表面、远离所述第一电极一侧的第二铁电层；设置于所述第二铁电层表面、远离所述第一铁电层一侧的第二电极；其中，所述第一铁电层中第一元素的浓度，高于所述第二铁电层中所述第一元素的浓度，所述第一元素为铪元素、锆元素和氧元素中的一项。该铁电单元可以灵活调节铁电器件的电学对称性，从而提高铁电器件的性能。

Description

铁电单元、三维铁电结构和铁电存储器
本申请要求于2022年05月30日提交中国专利局、申请号为202210597419.4、申请名称为“铁电单元、三维铁电结构和铁电存储器”的中国专利申请的优先权，其全部内容通过引用结合在本申请中。
技术领域
本申请实施例涉及半导体器件技术领域，尤其涉及一种铁电单元、三维铁电结构和铁电存储器。
背景技术
随着电子技术的发展，对信息处理能力以及信息存储容量的需求也不断提高。铁电材料因其擦写速度快、超低功耗、循环次数多、极化状态非易失等固有优势而被应用于存储领域，基于铁电材料的铁电随机存储器(FeRAM，ferroelectric random access memory)、铁电隧穿结(FTJ，ferroelectric tunneling junction)等铁电器件得到了广泛的关注。其中，铁电氧化铪材料，例如氧化铪与氧化锆的固溶质HfO2:ZrO2，也可以称为锆掺杂氧化铪(HfZrOx)，该铁电材料因其结晶温度低、集成度高、兼容CMOS工艺等优势，成为研究方向。
现有基于铁电氧化铪材料的铁电器件技术中，FeRAM以及FTJ的基本单元结构，通常是在两个金属电极中间设置铁电薄膜而形成的，也即“金属-铁电层-金属”的三明治结构。然而，在该结构中，由于铁电层两侧的金属电极受到金属材料、沉积方式、元素比例以及结晶程度等各种因素的影响，该铁电层两侧的金属电极的功函数通常不同，这就导致铁电器件具有电学非对称性，该电学非对称性主要包括：铁电器件的极化曲线发生漂移；相同电场强度、不同极性的外加电场下，铁电器件的漏电流大小不同。通常，铁电器件的电学非对称性大小不受外界控制，对于某些需要对称性的铁电器件(例如FeRAM)而言，这些电学非对称性导致铁电器件正负向擦写的非对称、某一方向非完全翻转、抗干扰性非对称等问题；另外，对于需要利用电学非对称性实现器件的开关比的铁电器件(例如FTJ)而言，由于铁电器件的电学非对称性不受控，导致目标开关比的铁电器件难以实现。由此，如何有效调节铁电器件的电学非对称性、以提高铁电器件的性能成为需要解决的问题。
发明内容
通过采用本申请实施例所示的铁电单元、三维铁电结构和铁电存储器，可以提高铁电铁电器件的性能。
为达到上述目的，本申请采用如下技术方案：
第一方面，本申请实施例提供一种铁电单元，该铁电单元包括：第一电极；设置于所述第一电极表面的第一铁电层；设置于所述第一铁电层表面、远离所述第一电极一侧 的第二铁电层；设置于所述第二铁电层表面、远离所述第一铁电层一侧的第二电极；其中，所述第一铁电层中第一元素的浓度，高于所述第二铁电层中所述第一元素的浓度，所述第一元素为铪元素、锆元素和氧元素中的一项。
本申请实施例提供的铁电单元，通过在两电极之间设置两层铁电层，将第一铁电层中第一元素的浓度，设置成高于第二铁电层中的第一元素的浓度。这样一来，通过在两层铁电层之间设置第一元素浓度差，可以使得第一铁电层和第二铁电层之间氧空位浓度不同，从而可以在两层铁电层的接触界面之间产生第一内建电场；此外，第一电极和第二电极之间通常具有第二内建电场。这样一来，通过调整电极与各层铁电层之间的位置关系，可以使得上述第一内建电场与第二内建电场可以相抵消或者相叠加，以提高铁电器件的电学对称性或者降低铁电器件的电学对称性，也即可以灵活调节铁电器件的电学对称性，从而提高铁电器件的性能。
此外，本申请实施例通过改变两层铁电层中第一元素的浓度、以在两层铁电层的接触界面之间产生内建电场，可以不需要在铁电层与电极之间引入元素以在铁电层与电极之间的接触界面处产生内建电场，从而避免由于元素扩散导致电极与铁电层的接触界面处于比较混沌的状态，进而提高铁电器件实际生产使用的可行性。
本申请实施例可以通过多种方式实现上述第一铁电层和第二铁电层之间氧空位浓度不同。
在第一种可能的实现方式中，所述第一铁电层的材料和所述第二铁电层的材料均为铪锆氧；当所述第一元素为铪元素时，所述第一铁电层中第二元素的浓度低于所述第二铁电层中第二元素的浓度，所述第二元素为锆元素。
在该种实现方式中，当第一电极为氮化钛、第二电极为金属钨时，由于第一铁电层中氧空位的浓度低于第二铁电层氧空位的浓度，铁电单元内建电场为两电极之间的内建电场以及两铁电层之间的内建电场的叠加，在该实现方式中，可以提高铁电单元的非电学对称性，以提高诸如FTJ等实现开关比的器件的性能。
在该种实现方式中，当第一电极为金属钨、第二电极为氮化钛时，由于第一铁电层中氧空位的浓度低于第二铁电层氧空位的浓度，铁电单元内建电场为两电极之间的内建电场减去两铁电层之间的内建电场，在该实现方式中，可以提高铁电单元的电学对称性，以提高诸如FeROM等铁电器件的性能。
在第二种可能的实现方式中，所述一铁电层的材料和所述第二铁电层的材料均为铪锆氧；当所述第一元素为锆元素时，所述第一铁电层中第二元素的浓度低于所述第二铁电层中第二元素的浓度，所述第二元素为铪元素。
该种可能的实现方式中，所述第一电极为氮化钛，所述第二电极为金属钨；或者所述第二电极为氮化钛，所述第一电极为金属钨。
在第三种可能的实现方式中，所述一铁电层的材料和所述第二铁电层的材料均为铪锆氧；所述第一铁电层中氧元素的浓度高于第二铁电层中氧元素的浓度。
该种可能的实现方式中，所述第一电极为氮化钛，所述第二电极为金属钨；或者所述第二电极为氮化钛，所述第一电极为金属钨。
第二方面，本申请实施例提供一种三维铁电结构，该三维铁电结构包括：由多个钝 化层和多个第一电极堆叠形成的第一环形区域；所述第一环形区域内侧设置有第一铁电层，所述第一铁电层与所述多个钝化层和所述多个第一电极均相接触；所述第一铁电层远离所述第一环形区域的一侧设置有第二铁电层；所述第二铁电层远离所述第一铁电层的一侧设置有第二电极；其中，所述第一铁电层中第一元素的浓度，高于所述第二铁电层中所述第一元素的浓度，所述第一元素为铪元素、锆元素和氧元素中的一项。
本申请实施例通过设置三维铁电结构，多个第一电极可以共用相同的铁电层，从而形成多个铁电单元。例如，其中一个第一电极、第一铁电层、第二铁电层以及第二电极之间形成一个铁电单元。
另外，本申请实施例提供的铁电单元，通过在两电极之间设置两层铁电层，将第一铁电层中第一元素的浓度，设置成高于第二铁电层中的第一元素的浓度。这样一来，通过在两层铁电层之间设置第一元素浓度差，可以使得第一铁电层和第二铁电层之间氧空位浓度不同，从而可以在两层铁电层的接触界面之间产生第一内建电场；此外，第一电极和第二电极之间通常具有第二内建电场。这样一来，通过调整电极与各层铁电层之间的位置关系，可以使得上述第一内建电场与第二内建电场可以相抵消或者相叠加，以提高铁电器件的电学对称性或者降低铁电器件的电学对称性，也即可以灵活调节铁电器件的电学对称性，从而提高铁电器件的性能。
此外，本申请实施例通过改变两层铁电层中第一元素的浓度、以在两层铁电层的接触界面之间产生内建电场，可以不需要在铁电层与电极之间引入元素以在铁电层与电极之间的接触界面处产生内建电场，从而避免由于元素扩散导致电极与铁电层的接触界面处于比较混沌的状态，进而提高铁电器件实际生产使用的可行性。
在一种可能的实现方式中，所述第一铁电层的材料和所述第二铁电层的材料均为铪锆氧；当所述第一元素为铪元素时，所述第一铁电层中第二元素的浓度低于所述第二铁电层中第二元素的浓度，所述第二元素为锆元素。
在一种可能的实现方式中，所述一铁电层的材料和所述第二铁电层的材料均为铪锆氧；当所述第一元素为锆元素时，所述第一铁电层中第二元素的浓度低于所述第二铁电层中第二元素的浓度，所述第二元素为铪元素。
在一种可能的实现方式中，所述第一电极的材料为钨；所述第二电极由两层金属层形成，所述两层金属层中与所述第二铁电层接触的材料为氮化钛，所述两层金属层中与所述第二铁电层不相接触的材料为钨。
第三方面，本申请实施例提供一种铁电存储器，该铁电存储器包括呈阵列排布的多个存储单元；所述多个存储单元中的每一个存储单元包括晶体管以及如第一方面所述的铁电单元。
应当理解的是，本申请的第二方面～第三方面与本申请的第一方面的技术方案一致，各方面及对应的可行实施方式所取得的有益效果相似，不再赘述。
附图说明
为了更清楚地说明本申请实施例的技术方案，下面将对本申请实施例的描述中所需要使用的附图作简单地介绍，显而易见地，下面描述中的附图仅仅是本申请的一些实施 例，对于本领域普通技术人员来讲，在不付出创造性劳动性的前提下，还可以根据这些附图获得其他的附图。
图1是本申请实施提供的现有技术中铁电单元的一个结构示意图；
图2A是本申请实施提供的铁电单元的极化曲线未发生漂移的示意图；
图2B是本申请实施提供的铁电单元的极化曲线发生漂移的示意图；
图2C是本申请实施提供的铁电单元的漏电流未发生漂移的示意图；
图2D是本申请实施提供的铁电单元的漏电流发生漂移的示意图；
图3是本申请实施提供的现有技术中铁电单元的又一个结构示意图；
图4A是本申请实施例提供的铁电单元的一个结构示意图；
图4B是本申请实施例提供的如图4A所示的铁电单元的内建电场减弱示意图；
图4C是本申请实施例提供的用于制备如图4A所示的铁电单元的流程图；
图5A是本申请实施例提供的铁电单元的又一个结构示意图；
图5B是本申请实施例提供的如图5A所示的铁电单元的内建电场增强示意图；
图6是本申请实施例提供的铁电单元的又一个结构示意图；
图7是本申请实施例提供的铁电单元的又一个结构示意图；
图8A是本申请实施例提供的三维铁电结构的一个结构示意图；
图8B是如图8A所示的三维铁电结构沿AA’的一个剖视图；
图9是本申请实施例提供的铁电存储器的一个结构示意图。
具体实施方式
下面将结合本申请实施例中的附图，对本申请实施例中的技术方案进行清楚、完整地描述，显然，所描述的实施例是本申请一部分实施例，而不是全部的实施例。基于本申请中的实施例，本领域普通技术人员在没有做出创造性劳动前提下所获得的所有其他实施例，都属于本申请保护的范围。
本文所提及的"第一"、"第二"以及类似的词语并不表示任何顺序、数量或者重要性，而只是用来区分不同的组成部分。同样，"一个"或者"一"等类似词语也不表示数量限制，而是表示存在至少一个。
在本申请实施例中，“示例性的”或者“例如”等词用于表示例子、例证或说明。本申请实施例中被描述为“示例性的”或者“例如”的任何实施例或设计方案不应被解释为比其它实施例或设计方案更优选或更具优势。确切而言，使用“示例性的”或者“例如”等词旨在以具体方式呈现相关概念。在本申请实施例的描述中，除非另有说明，“多个”的含义是指两个或两个以上。
请参考图1，图1是本申请实施例提供的现有技术中铁电单元的一个结构示意图。在图1中，铁电单元包括在衬底之上形成的顶部金属电极、底部金属电极、以及设置于两层金属电极之间的铁电层。其中，顶部金属电极是通过光刻形成的图案化金属层，该顶部电极由一种或多种金属材料形成，该金属材料例如包括但不限于金(Au)、铂(Pt)、钽(Ta)、氮化钛(TiN)、铝(Al)、钨(W)或钯(Pd)等。图1中示意性的示出了顶部电极由W金属材料形成。底部电极由氮化钛(TiN)材料形成。铁电层的材料为铪锆 氧(HaZrO，hafnium zirconium oxide)。如图1所示的铁电单元中，通过改变顶部电极的材料来调节铁电单元的铁电极化强度。当顶部电极采用多种金属材料、以及顶部电极与底部电极之间采用不同的金属材料时，由于不同金属材料的极化特性曲线均不同，不同金属材料之间的热膨胀系数不同导致铁电单元的极化强度不同，不同金属材料之间的金属功函数不同导致铁电单元的矫顽场不同，这就导致铁电器件的极化曲线发生漂移，以及相同电场强度、不同极性的外加电场下，铁电器件的漏电流大小不同。需要说明的是，当图1所示的铁电单元的顶部电极和底部电极均采用相同的金属材料时，由于金属材料的沉积方式、元素比例、结晶程度、热预算大小等因素的不同，同样导致铁电器件的极化曲线以及漏电流发生漂移。如图2A～图2D所示。图2A为铁电单元的极化曲线，横坐标为外加电场，纵坐标为铁电极化强度。在图2A所示的情形下，铁电单元的正向极化曲线和负向极化曲线关于纵坐标对称，也即外加电场极性相反、大小相同的情况下，正向矫顽场与负向矫顽场大小相同，极性相反。图2B为发生漂移的铁电单元的极化曲线，其中实线为铁电单元的极化曲线发生正向漂移，虚线为铁电单元的极化曲线发生负向漂移。从图2B中可以看出，当铁电单元的极化曲线发生漂移后，正向极化曲线和负向极化曲线不再关于纵坐标对称，也即外加电场极性相反、大小相同的情况下，正向矫顽场与负向矫顽场大小不同。图2C是铁电单元的漏电流曲线，横坐标为外加电场，纵坐标为漏电流。在图2C所示的情形下，相同电场强度、不同极性的外加电场下漏电流相同。图2D为发生漂移的铁电单元的漏电流曲线，其中实线为铁电单元的漏电流发生正向漂移，虚线为铁电单元的漏电流发生负向漂移。从图2D中可以看出，当铁电单元的漏电流曲线发生漂移后，相同电场强度、不同极性的外加电场下漏电流不同。
对于大部分期望极化曲线和漏电流不发生漂移的铁电存储器而言，当铁电单元的极化曲线和漏电流曲线分别如图2B和图2D所示的情形时，将导致铁电器件正负向擦写的非对称、某一方向非完全翻转、抗干扰性非对称等问题。然而，对于某些铁电器件而言，例如FTJ，需要利用极化曲线和漏电流的漂移来实现器件的开关比。在该种情况下，需要基于开关比的大小，调整极化曲线和漏电流的漂移量。为了实现对FTJ等器件开关比的调整，业界进一步提出通过改变铁电层与金属电极接触界面处的原子来调整铁电单元的对称性，如图3所示。在图3中，铁电单元包括两层TiN电极、以及设置于两层TiN电极之间的铁电层。图3所示铁电单元中，基于铁电层的材料，各层TiN电极与铁电层之间的接触界面分别引入不同的原子以形成非零的内建电场，从而调整铁电单元对称性。例如，如图3所示的铁电层材料为HfO2，其左侧TiN电极与铁电层之间的接触界面中引入Hf原子、右侧TiN电极与铁电层之间的接触界面中引入O原子。图3所示的调整铁电单元对称性的方法虽然理论可行，然而在实际生产过程中，通常需要高温退火来诱导铁电单元产生铁电性。在高温退火过程中，由于电极层与铁电层会发生元素扩散，导致电极与铁电层的接触界面处于比较混沌的状态，难以精确控制界面处元素的分布。
综上图1～图3所示的现有技术可以看出，现有技术中仍然无法有效调节铁电器件的电学非对称性、以提高铁电器件的性能，本申请实施例提供的铁电单元，通过在两层电极之间设置两层铁电层，其中一层铁电层中含有的第一元素的浓度，高于另外一层铁电层中所含有的第一元素的浓度。这样一来，由于两层铁电层之间中具有第一元素浓度差， 从而在两层铁电层的接触界面之间产生第一内建电场；此外，由于两层电极的材料不同，该两层电极之间的功函数不同，也即在该两层电极之间产生第二内建电场；通过调整电极与各层铁电层之间的位置关系，可以使得上述第一内建电场与第二内建电场可以相抵消或者相叠加，以提高铁电器件的电学对称性或者降低铁电器件的电学对称性，也即可以灵活调节铁电器件的电学对称性，从而提高铁电器件的性能。此外，本申请实施例通过改变两层铁电层中第一元素的浓度、以在两层铁电层的接触界面之间产生内建电场，与图3所示的现有技术相比，不需要在铁电层与电极之间引入元素以在铁电层与电极之间的接触界面处产生内建电场，从而避免由于元素扩散导致电极与铁电层的接触界面处于比较混沌的状态，进而提高铁电器件实际生产使用的可行性。下面结合图4A-图8所示的实施例，对本申请实施例提供的铁电单元进行更为详细的描述。
请参考图4A，图4A是本申请实施例提供的铁电单元100的一个结构示意图。如图4A所示，铁电单元100包括电极M1、电极M2、设置于电极M1和电极M2之间的铁电层F1和铁电层F2。电极M1和电极M2均为金属电极，电极M1和电极M2可以为相同的材料，也可以为不同的材料。一种可能的实现方式中，电极M1的材料可以为钨(W)，电极M2的材料可以为TaN。需要说明的是，本申请实施例其他可能的实现方式中，电极M1和电极M2的材料也可以为其他材料，例如，电极M1和电极M2均为TaN，本申请实施例对此不做具体限定。铁电层F1和铁电层F2的材料均可以为与氧化铪(HfO)或者铪锆氧(HfZrO)。本申请实施例中以铁电层F1和铁电层F2的材料为HfZrO2为例进行描述。沿图4A所示的方向z，铁电层F1的厚度和铁电层F2的厚度可以相同，例如为5nm。本申请实施例中，铁电层F1中Zr元素的浓度高于铁电层F2中Zr元素的浓度；铁电层F2中Hf元素的浓度高于铁电层F2中Hf元素的浓度。
图4A所示的实施例中，由于图4A所示的电极M1和电极M2的材料分别为W和TaN，从而电极M1和电极M2之间具有不同的功函数，进而电极M1和电极M2之间形成内建电场由于TaN的功函数约为5.27eV、W的功函数约为4.55eV，TaN的功函数高于W的功函数，上述内建电场由电极M1指向电极M2(也即内建电场由功函数低的电极指向功函数高的电极)，如图4B所示。当铁电单元为图1所示的结构时，铁电单元的内部电场如图4B中的(1)所示。当铁电单元为图4A所示的结构时，由于铁电层F1中Zr元素的浓度高于铁电层F2中Zr元素的浓度，并且铁电层F2中Hf元素的浓度高于铁电层F2中Hf元素的浓度，也即铁电层F1中ZrO2的浓度较高，铁电层F2中HfO2的浓度较高。由于ZrO2的氧空位浓度要高于HfO2的氧空位浓度，则铁电层F1中氧空位的浓度高于铁电层F1中氧空位的浓度，也即铁电层F1与铁电层F2之间具有氧空位浓度差，从而基于该氧空位浓度差铁电层F1和铁电层F2之间形成内建电场如图4B中的(2)所示。该内建电场由铁电层F1指向铁电层F2(也即由氧空位浓度的铁电层指向氧空位浓度低的铁电层)。从图4B中的(2)可以看出，两电极之间形成的内建电场作用于铁电层F1和铁电层F2，而铁电层F1和铁电层F2之间形成内建电场可以抑制内建电场的影响，从而，铁电单元100的内建电场为内建电场与内建电场之差，也即内建电场与内建电场之间相互抵消。由此，本申请实施例通过调节铁电层F1和铁电层F2中氧空位的浓度，以使得铁电单元100的总内建电场 减弱或抵消，与图1所示的现有技术相比，可以提高铁电单元的电学对称性，以提高诸如FeRAM的性能。此外，与图3所示的现有技术相比，不需要在铁电层与电极之间引入元素以在铁电层与电极之间的接触界面处产生内建电场，从而避免由于元素扩散导致电极与铁电层的接触界面处于比较混沌的状态，进而提高铁电器件实际生产使用的可行性。
基于图4A所示的铁电单元100、图4B所示的铁电单元100提高铁电单元100对称性的原理，如图4所示的铁电单元100可以是基于原子层沉积(Atomic Layer Deposition，ALD)工艺制备而成的。请继续参考图4C，图4C是用于制备如图4A所示的铁电单元100的工艺步骤200，该工艺步骤200包括：
步骤401，在衬底上形成电极M1。电极M1的材料为W。
步骤402，在电极M1上形成铁电层F1。该步骤中，假设每一个ALD沉积周期可以沉积1A厚度，且HfO2与ZrO2的每ALD沉积周期沉积速率相同时，将3ALD沉积周期的HfO2和7ALD沉积周期的ZrO2交替沉积于电极M1之上，可以得到预设厚度的铁电层F1。该预设厚度例如为5nm。
步骤403，在电极M1上形成铁电层F2。该步骤中，假设每一个ALD沉积周期可以沉积1A厚度，且HfO2与ZrO2的每ALD沉积周期沉积速率相同时，将7ALD沉积周期的HfO2和3ALD沉积周期的ZrO2交替沉积于铁电层F1之上，可以得到预设厚度的铁电层F2。该预设厚度例如为5nm。
步骤404，在铁电层F2之上形成金属电极M2。金属电极M2的材料为TiN。
本申请实施例中，可以基于TiCl4与NH3反应生成TiN的原理来制备TiN。具体工艺中，将TiCl4作为Ti离子的前驱体、NH3作为N离子的前驱体，采用TiCl4与NH3的比例为1:1的循环(cycle)比，利用原子沉积技术，分别沉积TiCl4材料和NH3材料。所沉积的TiCl4材料和NH3材料之间反应生成TiN。待TiN材料的厚度达到预设厚度(例如40nm)后，停止沉积TiCl4材料和NH3材料。由此，制备出TiN材料的金属电极M1。
经过上述步骤401～步骤404，即可制备出如图4A所示的铁电单元100。此外，通过如上工艺步骤200可以看出，铁电层F1中Zr元素的浓度高于铁电层F2中Zr元素的浓度，铁电层F2中Hf元素的浓度高于铁电层Hf元素的浓度。
以上通过图4A～图4C所示的实施例，介绍了通过将铁电层F1中氧空位的浓度，设置成高于铁电层F2氧空位的浓度，以减弱铁电单元100的总内建电场从而提高铁电单元的电学对称性的实现方式。本申请实施例中，为了使得铁电单元100应用于诸如FTJ等需要通过提高铁电单元的电学非对称性来实现开关比的器件中，一种可能的实现方式中，可以将铁电层F1中氧空位的浓度设置成低于铁电层F2氧空位的浓度，以提高电单元100的总内建电场从而提高铁电单元的电学非对称性。下面通过图5所示的实施例进行更为详细的描述。
请参考图5A，图5A是本申请实施例提供的铁电单元300的一个结构示意图。与图4A所示的铁电单元100一样，铁电单元300同样包括电极M1、电极M2、铁电层F1和和铁电层F2。电极M1的材料为W，电极M2的材料为TiN。与图4A所示的铁电单元100不同的是，在图5A中，铁电层F1中Hf元素的浓度高于铁电层F2中Hf元素的浓度， 铁电层F2中Zr元素的浓度高于铁电层Zr元素的浓度。
图5A所示的实施例中，由于电极M1和电极M2的材料分别为W和TaN，电极M1和电极M2之间具有不同的功函数，从而在铁电单元300中形成由电极M1指向电极M2的内建电场(更为详细的分析参考图4B中的相关描述)，如图5B所示。当铁电单元为图1所示的结构时，铁电单元的内部电场如图5B中的(1)所示。图5A所示的铁电单元300中，铁电层F1中Hf元素的浓度高于铁电层F2中Hf元素的浓度，并且铁电层F2中Zr元素的浓度高于铁电层F2中Zr元素的浓度，也即铁电层F1中HfO2的浓度较高，铁电层F2中ZrO2的浓度较高。由于ZrO2的氧空位浓度要高于HfO2的氧空位浓度，则铁电F2中氧空位的浓度高于铁电层F1中氧空位的浓度，也即铁电层F2与铁电层F1之间具有氧空位浓度差，从而基于该氧空位浓度差铁电层F2和铁电层F1之间形成内建电场如图5B中的(2)所示。该内建电场由铁电层F2指向铁电层F1。从图5B中的(2)可以看出，两电极之间形成的内建电场作用于铁电层F1和铁电层F2，而铁电层F1和铁电层F2之间形成内建电场可以增强内建电场的影响，从而，铁电单元100的内建电场为内建电场与内建电场之和，也即内建电场与内建电场之间叠加使得铁电单元300的内建电场增强。由此，本申请实施例通过调节铁电层F1和铁电层F2中氧空位的浓度，以使得铁电单元100的总内建电场增强，与图1所示的现有技术相比，可以提高铁电单元的非电学对称性，以提高诸如FTJ等实现开关比的器件的性能。
如图5A所示的铁电单元300的工艺制备的步骤与图4A所示的铁电单元100的工艺制备的步骤相类似，与制备图4A所示的铁电单元100的工艺步骤不同的是，在制备图5A所示的铁电单元300时，将图4C所示的步骤402和步骤403互换，也即首先在衬底上形成电极M1；接着在电极M1上将7ALD沉积周期的HfO2和3ALD沉积周期的ZrO2交替沉积，可以得到预设厚度的铁电层F1；其次在铁电层F1上将3ALD沉积周期的HfO2和7ALD沉积周期的ZrO2交替沉积，可以得到预设厚度的铁电层F1；最后在铁电层F1上形成电极M2。详细步骤参考图4C所示的制备工艺，不再赘述。
以上图4A和图5A所示的铁电单元中，是通过调整铁电层F1和铁电层F2之间Zr元素的比例以及Hf元素的比例，来调节铁电层F1和铁电层F2中氧空位的浓度，以调节铁电单元的电学对称性。本申请实施例其他可能的实现方式中，还可以通过调节各铁电层中所通入的氧元素的浓度来调节各铁电层中氧空位的浓度。请参考图6，图6是本申请实施例提供的铁电单元400的结构示意图。图6所示的铁电单元400的结构与以上各实施例中所示的铁电单元的结构相同，包括电极M1、电极M2、设置于两电极M1和电极M2之间的铁电层F1和铁电层F2。其中各电极的材料以及各铁电层的材料与以上各实施例中电极的材料以及铁电层的材料相同，不再赘述。与以上各铁电单元不同的是，如图6所示的铁电单元400中，铁电层F1在制备过程中通入的氧元素的浓度，低于铁电层F2在制备过程中通入的氧元素的浓度。从而，铁电层F1中用来参与氧化反应的氧元素的浓度，低于铁电层F2中用来参与氧化反应的氧元素的浓度。进而，铁电层F1中氧空位的浓度高于铁电层F2中氧空位的浓度。由此，铁电层F1和铁电层F2之间存在内建电场该内建电场由铁电层F1指向铁电层F2，从而提高铁电单元的电学对称性。如图6所示 的铁电单元400的原理与图4A所示的铁电单元100的原理相同，具体原理描述参考图4B所示的原理描述，不再赘述。
如图6所示的铁电单元400，是通过将铁电层F1中氧元素的浓度设置为低于铁电层F2氧元素的浓度，以提高铁电单元的电学对称性。在一种可能的实现方式中，铁电层F1在制备过程中通入的氧元素的浓度，高于铁电层F2在制备过程中通入的氧元素的浓度，如图7所示的铁电单元500。从而，铁电层F1中用来参与氧化反应的氧元素的浓度，高于铁电层F2中用来参与氧化反应的氧元素的浓度。进而，铁电层F1中氧空位的浓度低于铁电层F2中氧空位的浓度。由此，铁电层F1和铁电层F2之间存在内建电场φ2，该内建电场由铁电层F2指向铁电层F1，从而提高铁电单元的电学非对称性。如图7所示的铁电单元500的原理与图5A所示的铁电单元300的原理相同，具体原理描述参考图5B所示的原理描述，不再赘述。
以上通过图4A～图7介绍了二维结构的铁电单元。在一种可能的实现方式中，铁电单元也可以为三维结构，在该结构中，多个电极共用相同的铁电层，从而形成多个铁电单元。请参考图8A和图8B，图8A为三维铁电结构600的俯视图，图8B为如图8A所示的三维铁电结构600沿AA’的剖视图。如图8A和图8B所示，三维铁电结构600的俯视图为圆环状。三维铁电结构600中，最外层是由钝化层82和金属层81堆叠而成的层叠结构，其中金属层M1的材料可以为W。在由钝化层82和金属层81形成的层叠结构内侧为铁电层F1，铁电层F1内侧为铁电层F2，铁电层F2内侧为金属层83。三维铁电结构600中，多层金属层81中的一层金属层、铁电层F1、铁电层F2以及金属层83之间形成一个铁电单元。从而，三维铁电结构600包括多个铁电单元。该多个铁电单元共用铁电层F1、铁电层F2以及金属层83。金属层83可以为一层或多层，当该金属层83为一层时，该一层金属层可以为TiN；当金属层83为两层时，该两层金属层中与铁电层F2接触的金属层为TiN，另外一层为W。优选的，金属层83包括两层金属层。三维铁电结构600中，当需要提高铁电单元的电学对称性时，铁电层F1和铁电层F2的材料以及各元素的浓度与图4A所示的铁电单元100或者图6所示的铁电单元400相同，详细参考图4A或者图6的相关描述，不再赘述。三维铁电结构600中，当需要提高铁电单元的非电学对称性时，铁电层F1和铁电层F2的材料以及各元素的浓度与图5A所示的铁电单元300或者图7所示的铁电单元500相同，详细参考图5A或者图7的相关描述，不再赘述。
基于如上各实施例所述的铁电单元，本申请实施例还提供一种铁电存储器700，如图9所示。该铁电存储器700包括呈阵列排布的多个存储单元701、702…70n。每一个存储单元均包括晶体管M和铁电单元C。该铁电单元C可以为如图4A所示的铁电单元100、如图5A所示的铁电单元300、如图6所示的铁电单元400或者如图7所示的铁电单元500。此外，铁电存储器700还包括多条字线WL0、WL1…WLm和多条位线BL0、BL1…、BLn，多个存储单元中的每一个存储单元，分别与多条位线中的其中一条位线和多条字线中的其中一条字线连接。每一个存储单元与位线和字线的连接关系均相同。以存储单元501为例，晶体管M的栅极与字线WL0连接，晶体管M的源极与位线BL0连接，晶体管M的漏极与铁电单元C的一端连接，铁电单元C的另外一端与板线PL连接。
最后应说明的是：以上各实施例仅用以说明本申请的技术方案，而非对其限制；尽管参照前述各实施例对本申请进行了详细的说明，本领域的普通技术人员应当理解：其依然可以对前述各实施例所记载的技术方案进行修改，或者对其中部分或者全部技术特征进行等同替换；而这些修改或者替换，并不使相应技术方案的本质脱离本申请各实施例技术方案的范围。

Claims (10)

  1. 一种铁电单元，其特征在于，包括：
    第一电极；
    设置于所述第一电极表面的第一铁电层；
    设置于所述第一铁电层表面、远离所述第一电极一侧的第二铁电层；
    设置于所述第二铁电层表面、远离所述第一铁电层一侧的第二电极；
    其中，所述第一铁电层中第一元素的浓度，高于所述第二铁电层中所述第一元素的浓度，所述第一元素为铪元素、锆元素和氧元素中的一项。
  2. 根据权利要求1所述的铁电单元，其特征在于，所述第一铁电层的材料和所述第二铁电层的材料均为铪锆氧；
    当所述第一元素为锆元素时，所述第一铁电层中第二元素的浓度低于所述第二铁电层中第二元素的浓度，所述第二元素为铪元素。
  3. 根据权利要求1所述的铁电单元，其特征在于，所述一铁电层的材料和所述第二铁电层的材料均为铪锆氧；
    当所述第一元素为铪元素时，所述第一铁电层中第二元素的浓度低于所述第二铁电层中第二元素的浓度，所述第二元素为锆元素。
  4. 根据权利要求1-3任一项所述的铁电单元，其特征在于，所述第一电极为氮化钛，所述第二电极为金属钨。
  5. 根据权利要求1-3任一项所述的铁电单元，其特征在于，所述第二电极为氮化钛，所述第一电极为金属钨。
  6. 一种三维铁电结构，其特征在于，包括：
    由多个钝化层和多个第一电极堆叠形成的第一环形区域；
    所述第一环形区域内侧设置有第一铁电层，所述第一铁电层与所述多个钝化层和所述多个第一电极均相接触；
    所述第一铁电层远离所述第一环形区域的一侧设置有第二铁电层；
    所述第二铁电层远离所述第一铁电层的一侧设置有第二电极；
    其中，所述第一铁电层中第一元素的浓度，高于所述第二铁电层中所述第一元素的浓度，所述第一元素为铪元素、锆元素和氧元素中的一项。
  7. 根据权利要求6所述的三维铁电结构，其特征在于，所述第一铁电层的材料和所述第二铁电层的材料均为铪锆氧；
    当所述第一元素为铪元素时，所述第一铁电层中第二元素的浓度低于所述第二铁电层中第二元素的浓度，所述第二元素为锆元素。
  8. 根据权利要求6所述的三维铁电结构，其特征在于，所述一铁电层的材料和所述第二铁电层的材料均为铪锆氧；
    当所述第一元素为锆元素时，所述第一铁电层中第二元素的浓度低于所述第二铁电层中第二元素的浓度，所述第二元素为铪元素。
  9. 根据权利要求6-8任一项所述的三维铁电结构，其特征在于，所述第一电极的材 料为钨；
    所述第二电极由两层金属层形成，所述两层金属层中与所述第二铁电层接触的材料为氮化钛，所述两层金属层中与所述第二铁电层不相接触的材料为钨。
  10. 一种铁电存储器，其特征在于，所述铁电存储器包括呈阵列排布的多个存储单元；所述多个存储单元中的每一个存储单元包括晶体管以及如权利要求1-5任一项所述的铁电单元。
PCT/CN2023/078721 2022-05-30 2023-02-28 铁电单元、三维铁电结构和铁电存储器 WO2023231480A1 (zh)

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