HfO2-based ferroelectric film with gradient oxygen vacancy distribution as well as preparation method and application of HfO2-based ferroelectric film

Abstract

The invention discloses a preparation method of an HfO2-based ferroelectric film with gradient oxygen vacancy distribution as well as the film and application of the HfO2-based ferroelectric film. The method comprises the steps that a lower electrode is prepared on a substrate, an amorphous HfO2-based prefabricated film is deposited on the lower electrode through atomic layer deposition, an upper electrode is prepared on the prefabricated film to form a sandwich stacking structure, and crystallization annealing is carried out to induce the prefabricated film to be crystallized into a ferroelectric orthorhombic phase; wherein the atomic layer deposition comprises at least one oxidant modulation period, a first deposition stage and a second deposition stage with different oxidation capacities are alternately carried out, and the oxygen content and oxygen vacancy defect distribution are regulated and controlled in the film thickness direction through the combination of sub-cycles, so that the oxygen vacancy concentration on one side close to the lower electrode and the upper electrode is lower than that in the middle area of the film. The obtained film can be applied to devices such as ferroelectric capacitors and ferroelectric field effect transistors, and is used for improving polarization output, reducing electric leakage and improving consistency and reliability of the devices.

Description

Technical Field

[0001] This invention relates to the field of semiconductor device manufacturing technology, and more specifically, to an HfO2-based ferroelectric thin film with a gradient oxygen vacancy distribution, its preparation method, and its application. Background Technology

[0002] As semiconductor process nodes continue to shrink to 28 nm and below, traditional perovskite-based ferroelectric materials (such as PZT and SBT) are increasingly unable to meet the integration and reliability requirements of next-generation non-volatile memories and logic devices due to their complex material systems, poor compatibility with CMOS processes, and difficulty in achieving ultra-thin films. In contrast, HfO2-based materials are considered important candidate materials for next-generation ferroelectric random access memories (FeRAM), ferroelectric field-effect transistors (FeFETs), and negative capacitance field-effect transistors (NCFETs) due to their high compatibility with existing CMOS processes, good electrical performance at the nanoscale, and suitability for atomic layer deposition. Research shows that the ferroelectricity of HfO2-based materials originates from their metastable, non-centrosymmetric orthorhombic phase structure. However, thermodynamically, HfO2 is more prone to forming a non-ferroelectric monoclinic phase structure. Therefore, effectively suppressing the formation of the monoclinic phase and promoting and stabilizing the orthorhombic phase structure during device fabrication is one of the key technical challenges in realizing high-performance HfO2-based ferroelectric devices. Therefore, existing technologies typically employ elemental doping (such as Zr, Si, Al, La, etc.), mechanical stress engineering (e.g., introducing stress using a metal electrode capping layer), and high-temperature rapid annealing to improve the crystal structure and ferroelectric properties of HfO2 thin films.

[0003] However, further research in existing technologies has revealed that defect states in HfO2-based thin films, especially oxygen vacancy defects, have a significant impact on the crystal phase stability, electrical properties, and device reliability. A suitable amount of oxygen vacancies helps stabilize the metastable orthorhombic phase and improve the polarization reversal characteristics of the device, but excessive oxygen vacancies often form charge transport channels, leading to problems such as increased leakage current, reduced breakdown electric field, and decreased device durability. Therefore, how to promote the formation of the ferroelectric phase while suppressing the adverse electrical effects caused by defects has become a long-standing contradiction in HfO2-based ferroelectric thin film technology. In practical preparation processes, atomic layer deposition (ALD) is widely used for the growth of HfO2-based thin films due to its excellent thickness control and uniformity. However, conventional atomic layer deposition methods typically employ a single and constant oxidant condition throughout the entire thin film deposition process. This results in a uniform stoichiometry and defect distribution in the thickness direction of the HfO2 thin film. This uniform structural feature makes it difficult to balance the different requirements of interfacial insulation and bulk ferroelectric stability. As a result, while improving the residual polarization intensity, leakage current and reliability issues remain prominent, limiting further improvement in the overall performance of the device.

[0004] Therefore, in the preparation of HfO2-based ferroelectric thin films, the existing technology still lacks a means to effectively control the internal defect state of the film while ensuring process compatibility, so as to simultaneously meet the requirements of high ferroelectric performance and low leakage characteristics. Summary of the Invention

[0005] The first technical problem to be solved by the present invention is to provide a method for preparing HfO2-based ferroelectric thin films with gradient oxygen vacancy distribution, so as to solve the problem in the prior art where the oxygen vacancy distribution of the film is uncontrollable due to the single oxidation conditions, the interface leakage current and the stability of the ferroelectric phase are difficult to balance, and thus there is a trade-off between polarization performance and leakage current / reliability.

[0006] To overcome the shortcomings of the prior art, the present invention provides a method for preparing HfO2-based ferroelectric thin films with a gradient oxygen vacancy distribution, comprising the following steps: S1: Provide a substrate and fabricate a lower electrode on the substrate; S2: An amorphous HfO2-based preform is deposited on the lower electrode using atomic layer deposition; S3: An upper electrode is fabricated on the HfO2-based pre-film to form a sandwich stacked structure; S4: Perform crystallization annealing on the sandwich stacked structure to induce the HfO2-based pre-film to crystallize into a ferroelectric orthorhombic phase; In step S2, the atomic layer deposition process includes at least one oxidant modulation cycle, which includes an alternating first deposition stage and a second deposition stage. The oxidant conditions used in the first deposition stage and the second deposition stage have different oxidizing capabilities, so as to control the oxygen content or oxygen vacancy defect distribution along the thickness direction of the HfO2-based pre-film during the thin film deposition process. In this invention, the difference in oxidizing power between the first oxidant condition and the second oxidant condition is reflected in at least one of the following: the chemical types of the oxidant are different, the concentration or partial pressure of the oxidant gas is different, or under one of the conditions, no oxidant is introduced and only inert gas is purged. The first deposition stage involves at least one atomic-layer deposition sub-cycle under the first oxidant condition. The second deposition stage involves at least one atomic layer deposition subcycle under the second oxidant condition.

[0007] Compared with existing technologies, the preparation method of HfO2-based ferroelectric thin films with gradient oxygen vacancy distribution of the present invention has the following advantages: In step S1, the preparation method of the present invention provides a stable growth interface and conductive boundary conditions for the subsequent HfO2-based pre-film by preparing a lower electrode on the substrate, reducing the performance dispersion caused by uneven interface growth and defect enrichment; In step S2, an amorphous HfO2-based pre-film is deposited by atomic layer deposition, and at least one oxidant modulation cycle is introduced. By alternating between a first deposition stage and a second deposition stage with different oxidation capabilities (including changing the type, concentration / partial pressure of the oxidant, or purging with inert gas without introducing an oxidant in one stage), a controllable oxygen content / oxygen vacancy defect gradient is formed along the thickness direction of the film during deposition: the interface region is in a relatively strong oxidizing environment, which can suppress the formation of excessive oxygen vacancies and defect states at the interface and reduce the risk of leakage current; the bulk region is in a relatively weak oxidizing environment. (Or intermittent weak oxidation / non-oxidation) environment can introduce an appropriate amount of oxygen vacancies to facilitate the formation and stabilization of the subsequent ferroelectric phase, achieving a balance between low interface defects and a bulk ferroelectric phase. In step S3, an upper electrode is prepared on the pre-film to form a sandwich stack structure, providing upper and lower interface boundary conditions for annealing. The upper electrode can further act as a capping and stress constraint. In step S4, during crystallization annealing, the synergistic effect of the gradient defect distribution and stack boundary conditions is utilized to promote the crystallization of the HfO2-based thin film into an orthorhombic phase with ferroelectricity. This also improves polarization performance while reducing leakage current, increasing reliability and consistency. The lower electrode / pre-film / upper electrode sandwich stack structure formed in steps S1 and S3 provides clear upper and lower interface boundary conditions for annealing in step S4. The upper electrode can also act as a capping layer to introduce stress constraints, making the gradient oxygen vacancy distribution more effectively transformed into a structural advantage of low interface defects and a stable bulk ferroelectric phase during annealing.

[0008] In one possible implementation, in step S2, the oxidizing power of the first oxidant condition is stronger than that of the second oxidant condition.

[0009] In one possible implementation, in step S2, the oxidant used in the first oxidant condition is selected from one of O3, O2 plasma, and H2O2; the second oxidant condition includes any of the following: (a) using H2O or an alcohol oxidant; (b) not introducing an oxidant, but only performing inert gas purging.

[0010] Compared to existing technologies, which consistently use a single oxidizing agent during deposition (leading to difficulties in simultaneously addressing interfacial insulation and bulk ferroelectricity in controlling oxygen vacancy content and distribution in the thin film), this embodiment sets the first oxidizing agent condition in step S2 to have a stronger oxidizing power than the second oxidizing agent condition. Furthermore, it alternates between a strong oxidation stage and a weak oxidation (or purging without oxidizing agent) stage during the oxidizing agent modulation cycle. The strong oxidation stage enhances the oxidation degree of the surface reaction and provides more sufficient oxygen replenishment, thereby reducing the oxygen vacancy defect density formed in this stage. The weak oxidation or oxidizing-free stages maintain layer-by-layer self-limiting growth. By relatively reducing the degree of oxygen supplementation, a suitable amount of oxygen vacancies is retained in the corresponding thickness region of the film, forming a gradient distribution of low oxygen vacancies in the interface region and a suitable amount of oxygen vacancies in the bulk region along the thickness direction of the film. Therefore, the defect states and potential conductive channels near the electrode interface are reduced, and the leakage current and breakdown risk are reduced. The suitable amount of oxygen vacancies retained in the bulk provides a favorable defect chemical environment for subsequent crystallization annealing to induce and stabilize the ferroelectric orthorhombic phase. Without significantly sacrificing polarization performance, both low leakage current and improved reliability are achieved, realizing the comprehensive optimization of ferroelectric performance and electrical stability. By controlling the ratio and application order of the ALD (atomic layer deposition) sub-cycles under the first and second oxidant conditions, the deposited HfO2-based pre-film has a non-uniform oxygen vacancy concentration distribution in the thickness direction.

[0011] In one possible implementation, in step S2, the material of the HfO2-based preform is HfO2 or doped HfO2, wherein the doping element of the doped HfO2 is selected from at least one of Zr, Si, Al, Gd, La, Sr, Y, and Sc; and the thickness of the HfO2-based preform is 3 nm to 30 nm.

[0012] Compared with the prior art, this embodiment limits the HfO2-based pre-film to HfO2 or doped HfO2, and selects at least one of Zr, Si, Al, Gd, La, Sr, Y, and Sc as the doping element. Doping can change the phase stability of HfO2 by lattice perturbation and defect chemical regulation, making the film more inclined to form or stabilize a ferroelectric orthorhombic phase during annealing, and suppressing the formation of non-ferroelectric phases such as monoclinic phase. At the same time, controlling the film thickness to 3 nm to 30 nm can keep the film in a thickness range that is conducive to polarization reversal and phase stability, avoiding the enhanced leakage / size effect caused by excessively thin film thickness, and also avoiding the increase in the proportion of non-ferroelectric phase or the increase in driving voltage caused by excessively thick film thickness.

[0013] In one possible implementation, in step S2, the temperature of the atomic layer deposition is 200-400°C.

[0014] Compared with the prior art, this embodiment controls the atomic layer deposition temperature in step S2 at 200–400℃, which can ensure that the precursor adsorption / reaction and oxidant reaction processes maintain good self-limitation and reaction completeness, thereby obtaining an amorphous HfO2-based preform with precisely controllable thickness, uniform composition and density; at the same time, within this temperature window, the differential effect of the oxidant modulation cycle on the degree of oxygen replenishment / oxygen vacancy retention is more easily and stably realized, avoiding modulation failure or non-reproducible gradient distribution due to temperature abnormalities.

[0015] In one possible implementation, in step S3, the material of the upper electrode is selected from at least one of TiN, TaN, W, Mo, Ru, Ir, and Pt; and the upper electrode is a composite structure, including a first metal layer that directly contacts the HfO2-based pre-film and a second metal layer located on top of the first metal layer, wherein the chemical inertness of the first metal layer is higher than that of the second metal layer, and the upper electrode acts as a mechanical stress capping layer during the crystallization annealing process in step S4, for applying tensile or compressive stress to the HfO2-based thin film to suppress the formation of the monoclinic phase.

[0016] Compared with the prior art, in this embodiment, the upper electrode material is selected from at least one of TiN, TaN, W, Mo, Ru, Ir, and Pt, and a composite structure composed of a first metal layer and a second metal layer is further adopted. The first metal layer directly contacts the HfO2-based pre-film and its chemical inertness is higher than that of the second metal layer. The first metal layer, as an interface layer, can reduce the interface reaction, element diffusion, or interface defect generation between the electrode and the HfO2-based pre-film during the annealing process, thereby improving the interface stability. At the same time, the composite upper electrode acts as a mechanical stress capping layer during the crystallization annealing process in step S4. By applying tensile or compressive stress to the HfO2-based thin film, it changes the phase transition energy barrier and crystal phase stability of the thin film, suppresses the formation of monoclinic phase, and promotes the formation / retention of ferroelectric related crystal phases. After annealing, the tendency of thin film interface defects and leakage channels to form is reduced, and the proportion of ferroelectric orthorhombic phases is increased or the stability is enhanced.

[0017] In one possible implementation, in step S4, the crystallization annealing process is rapid thermal annealing, with an annealing temperature range of 400-800°C, an annealing time of 1-300 seconds, and an annealing atmosphere of N2, Ar, O2, or a mixture thereof.

[0018] Compared with the prior art, in step S4 of this embodiment, rapid thermal annealing (RTA) is used, with the annealing temperature controlled at 400–800°C and the annealing time controlled at 1–300 seconds. N2, Ar, O2 or a mixture thereof are selected as the atmosphere. RTA provides sufficient crystallization driving force through short-term high temperature, so that the amorphous HfO2-based pre-film can quickly crystallize and form the target ferroelectric phase. At the same time, since the thermal budget is controlled, unwanted interface diffusion, reaction layer growth and defect proliferation can be reduced. In addition, by selecting an inert atmosphere (N2 / Ar) or an oxygen-containing atmosphere (O2 or a mixture), the redox environment during the annealing process can be adjusted, thereby suppressing the generation of excessive defects or leakage-related defects while maintaining the overall advantage of the gradient oxygen vacancy distribution.

[0019] In one possible implementation, in step S4, the crystallization annealing process is carried out in two steps: first, nucleation is performed at a first temperature of 400-550°C for 50-70 seconds, and then the temperature is raised to a second temperature of 600-800°C and held for 8-12 seconds for grain growth.

[0020] Compared with the prior art, this embodiment designs the crystallization annealing as a two-step method: first, nucleation is carried out for a relatively long time at 400–550℃, and then the temperature is raised to 600–800℃ for a short time for grain growth. The first temperature stage mainly promotes a large number of uniform nucleations, reducing the uncertainty caused by subsequent abnormal grain growth and phase competition; furthermore, grain growth and phase transformation are completed in a relatively short time in the second temperature stage, so that the ferroelectric related crystal phase is formed and shaped under a controlled thermal budget, while avoiding the enhanced interface reaction and defect rearrangement caused by long-term high temperature.

[0021] The second technical problem to be solved by the present invention is to provide an HfO2-based ferroelectric thin film with a gradient oxygen vacancy distribution, so as to solve the problem in the prior art that the unreasonable distribution of oxygen vacancy in the film leads to interface leakage, severe defect trapping and insufficient stability of ferroelectric phase, thus making it difficult to balance polarization performance and reliability.

[0022] To overcome the shortcomings of the prior art, the present invention provides an HfO2-based ferroelectric thin film prepared by the above preparation method, wherein the HfO2-based ferroelectric thin film has a non-uniform oxygen vacancy distribution in the thickness direction, wherein the oxygen vacancy concentration in the film region near the lower electrode and the upper electrode is lower than the oxygen vacancy concentration in the central region of the film.

[0023] Compared with existing technologies, the HfO2-based ferroelectric thin film of this invention has the following advantages: Compared with existing technologies where oxygen vacancies are relatively uniformly distributed in the thickness direction or easily enriched at the electrode / film interface, the HfO2-based ferroelectric thin film of this invention exhibits a non-uniform oxygen vacancy distribution in the thickness direction, and the oxygen vacancy concentration in the film region near the lower and upper electrodes is lower than that in the central region of the film. Due to the reduction of oxygen vacancies in the interface region, the formation of interface defect states and charge trapping centers can be reduced, the probability of conductive channel generation can be lowered, thereby suppressing leakage current and improving the interface insulation stability. At the same time, the retention of an appropriate amount of oxygen vacancies in the central part of the film is beneficial to the formation and stability of ferroelectric-related crystal phases and makes the polarization reversal process more complete. Therefore, without significantly sacrificing the ferroelectric polarization capability, the thin film of this invention can achieve lower leakage current and better stability, alleviating the problem that it is difficult to simultaneously achieve high polarization and high leakage current in existing technologies.

[0024] The third technical problem to be solved by the present invention is to provide an HfO2-based ferroelectric thin film with a gradient oxygen vacancy distribution, so as to solve the problems of insufficient polarization output, poor device consistency and limited reliability caused by interface defects and leakage in the prior art ferroelectric capacitors.

[0025] To overcome the shortcomings of the prior art, the present invention provides an application of the HfO2-based ferroelectric thin film, the application including applying the HfO2-based ferroelectric thin film in a ferroelectric capacitor, the ferroelectric capacitor including a lower electrode, an upper electrode, and an HfO2-based ferroelectric thin film located between the lower electrode and the upper electrode.

[0026] Compared with existing technologies, the application of the HfO2-based ferroelectric thin film of this invention has the following advantages: Compared with existing technologies that use conventional HfO2-based thin films to construct ferroelectric capacitors, this invention places the HfO2-based ferroelectric thin film between the lower and upper electrodes, so that the gradient oxygen vacancy distribution of the film is effectively reflected in the device structure. The low-oxygen-vacancy region near the upper and lower electrodes can reduce the tendency for electrode / film interface defects and leakage channels to form, thereby reducing leakage current and improving withstand voltage and operational stability. Meanwhile, an appropriate amount of oxygen vacancy in the middle of the film is beneficial for ferroelectric phase retention and polarization reversal, enabling the capacitor to still obtain good polarization output and switching response under low leakage conditions. In summary, the application scheme of this invention helps to simultaneously improve the polarization performance and reliability of ferroelectric capacitors, improve device parameter dispersion, and meet practical application requirements. Attached Figure Description

[0027] Figure 1 This is a flowchart of a method for preparing an HfO2-based ferroelectric thin film with a gradient oxygen vacancy distribution according to the present invention; Figure 2 This is a schematic cross-sectional view of the film stacking structure of a ferroelectric capacitor; Figure 3 This is a timeline diagram of the oxidant modulation cycle in atomic layer deposition (ALD); Figure 4 This is a schematic diagram comparing the microstructure of HfO2-based ferroelectric thin films prepared by the present invention with those prepared by the conventional single oxidant method after annealing. Figure 5 This is a comparison diagram of the polarization intensity-electric field (PE) characteristics of HfO2-based ferroelectric capacitors prepared by the present invention and the comparative example method. Figure 6 This is a comparison chart of the leakage current density-voltage (JV) characteristics of HfO2-based ferroelectric capacitors prepared by the present invention and the comparative method. Figure 7 This is a schematic diagram of a ferroelectric field-effect transistor (FeFET) integrating the HfO2-based ferroelectric thin film prepared according to the present invention. Detailed Implementation

[0028] First, those skilled in the art should understand that these embodiments are merely illustrative of the technical principles of the present invention and are not intended to limit the scope of protection of the present invention. Those skilled in the art can make adjustments as needed to adapt to specific application scenarios.

[0029] In the description of the embodiments of the present invention, it should be noted that, unless otherwise explicitly specified and limited, the terms "connected" and "linked" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium. Those skilled in the art can understand the specific meaning of the above terms in the embodiments of the present invention based on the specific circumstances.

[0030] In embodiments of the present invention, unless otherwise explicitly specified and limited, "above" or "below" the second feature can mean that the first feature is in direct contact with the second feature, or that the first feature is in indirect contact with the second feature through an intermediate medium. Furthermore, "above," "on top of," and "over" the second feature can mean that the first feature is directly above or diagonally above the second feature, or simply that the first feature is at a higher horizontal level than the second feature. "Below," "below," and "under" the second feature can mean that the first feature is directly below or diagonally below the second feature, or simply that the first feature is at a lower horizontal level than the second feature.

[0031] This invention provides a method for preparing HfO2-based ferroelectric thin films with a gradient oxygen vacancy distribution, such as... Figure 1 As shown, the overall process includes: fabricating a lower electrode on a substrate; depositing an HfO2-based pre-film on the lower electrode using atomic layer deposition (ALD); fabricating an upper electrode on the pre-film to form a sandwich stack structure; and subsequently performing crystallization annealing to induce the formation of a ferroelectric orthorhombic phase in the pre-film. The key is the introduction of at least one oxidant modulation cycle during the ALD deposition process. By alternating between several sub-cycles using the first and second oxidant conditions, in-situ control of the oxygen content or defect density of the film layer is achieved, thus laying the foundation for subsequent annealing to obtain high ferroelectricity. Specifically, the process includes the following steps: S1: Provide a substrate and fabricate a lower electrode on the substrate; S2: An amorphous HfO2-based preform is deposited on the lower electrode using atomic layer deposition; S3: An upper electrode is fabricated on the HfO2-based pre-film to form a sandwich stacked structure; S4: Perform crystallization annealing on the sandwich stacked structure to induce the HfO2-based pre-film to crystallize into a ferroelectric orthorhombic phase; In step S2, the atomic layer deposition process includes at least one oxidant modulation cycle, which includes an alternating first deposition stage and a second deposition stage. The oxidant conditions used in the first deposition stage and the second deposition stage have different oxidizing capabilities, so as to control the oxygen content or oxygen vacancy defect distribution along the thickness direction of the HfO2-based pre-film during the thin film deposition process. The first deposition stage involves at least one atomic-layer deposition sub-cycle under the first oxidant condition. The second deposition stage involves at least one atomic layer deposition subcycle under the second oxidant condition.

[0032] As a preferred embodiment, in step S2, the oxidizing power of the first oxidant condition is stronger than that of the second oxidant condition.

[0033] like Figure 3 As shown, in the ALD process of this invention, the layer-by-layer control of the defect distribution of the thin film is achieved by setting the oxidant modulation cycle: within a modulation cycle, several sub-cycles under the first oxidant condition and several sub-cycles under the second oxidant condition are executed alternately in a predetermined order, and the overall oxygen content and oxygen vacancy concentration of the thin film can be changed by adjusting the ratio of the number of the two types of sub-cycles (N:M) and their application order; furthermore, N:M or the modulation cycle order can be changed at different thickness stages of thin film growth to construct a gradient or step-like non-uniform oxygen vacancy distribution to meet the design requirements of different devices.

[0034] As a preferred embodiment, in step S2, the oxidant used in the first oxidant condition is selected from one of O3, O2 plasma, and H2O2; the second oxidant condition includes any of the following: (a) using H2O or alcohol oxidant; (b) not introducing oxidant, but only performing inert gas purging.

[0035] As a preferred embodiment, in step S2, the material of the HfO2-based preform is HfO2 or doped HfO2, and the doping element of the doped HfO2 is selected from at least one of Zr, Si, Al, Gd, La, Sr, Y, and Sc; and the thickness of the HfO2-based preform is 3 nm to 30 nm.

[0036] As a preferred embodiment, in step S2, the temperature of the atomic layer deposition is 200-400℃.

[0037] As a preferred embodiment, in step S3, the material of the upper electrode is selected from at least one of TiN, TaN, W, Mo, Ru, Ir, and Pt; and the upper electrode is a composite structure, including a first metal layer that directly contacts the HfO2-based preformed film and a second metal layer located on top of the first metal layer, and the chemical inertness of the first metal layer is higher than that of the second metal layer.

[0038] As a preferred embodiment, in step S4, the crystallization annealing treatment is rapid thermal annealing, with an annealing temperature range of 400-800℃, an annealing time of 1-300 seconds, and an annealing atmosphere of N2, Ar, O2, or a mixture thereof.

[0039] As a preferred embodiment, in step S4, the crystallization annealing process adopts a two-step method: first, nucleation is carried out at a first temperature of 400-550℃ for 50-70 seconds, and then the temperature is raised to a second temperature of 600-800℃ for 8-12 seconds to carry out grain growth.

[0040] The present invention provides an HfO2-based ferroelectric thin film prepared by the preparation method described above. The HfO2-based ferroelectric thin film has a non-uniform oxygen vacancy distribution in the thickness direction, wherein the oxygen vacancy concentration in the film region near the lower electrode and the upper electrode is lower than the oxygen vacancy concentration in the central region of the film.

[0041] like Figure 2 As shown, the device structure of this embodiment is preferably a stacked sandwich structure, comprising, from bottom to top: a substrate, a lower electrode layer, an HfO2-based thin film layer, and an upper electrode layer; wherein, the substrate is used to support the device structure and may be a silicon substrate or other semiconductor / insulating substrate; the lower electrode layer is disposed on the substrate and is used to form an electrode pair with the upper electrode layer to form a capacitor structure; the HfO2-based thin film layer is located between the lower electrode layer and the upper electrode layer and serves as a ferroelectric layer or a ferroelectric-related functional layer; the upper electrode layer covers the HfO2-based thin film layer, is disposed opposite to the lower electrode layer and forms a clamping relationship, thereby constituting the lower electrode / HfO2-based thin film layer. The O2-based thin film / top electrode is stacked. The top electrode layer can also act as a capping layer during subsequent crystallization annealing to provide stress constraint or interface stabilization, which is conducive to the formation or stabilization of ferroelectric related crystal phases of the HfO2-based thin film. In a preferred embodiment, different oxidation environments can be set in the film thickness direction (e.g., different oxidant conditions or cyclic combinations of different oxidation intensities are used in the interface region and the bulk region), so that the HfO2-based thin film exhibits a differentiated defect / oxygen vacancy distribution at the interface position near the top and bottom electrodes and the film bulk position, thereby taking into account both the interface insulation characteristics and the bulk ferroelectric performance requirements, and achieving a comprehensive improvement in device performance.

[0042] The present invention provides an application of the HfO2-based ferroelectric thin film, the application including applying the HfO2-based ferroelectric thin film in a ferroelectric capacitor, the ferroelectric capacitor including a lower electrode, an upper electrode, and an HfO2-based ferroelectric thin film located between the lower electrode and the upper electrode.

[0043] like Figure 7 As shown, the HfO2-based ferroelectric thin film prepared by this invention can be used not only in ferroelectric capacitors but also integrated into device structures such as ferroelectric field-effect transistors (FeFETs). The FeFET includes a semiconductor substrate (e.g., Si), a channel region disposed on the surface of the semiconductor substrate, and a source and a drain electrically connected to the channel region and spaced apart in a planar direction, wherein the channel region is located between the source and the drain. A gate dielectric-related stack and a gate electrode (e.g., TiN) are sequentially disposed vertically above the channel region, and the gate dielectric-related stack includes at least the present invention. The invention includes an HfO2-based ferroelectric thin film layer located between the channel region and the gate electrode, thus forming a vertical interlayer positional relationship of "gate electrode / ferroelectric layer / channel region". Optionally, an interface buffer layer (e.g., SiO2) can be provided between the HfO2-based ferroelectric thin film layer and the channel region to improve interface stability or regulate interface electrical properties. By applying a voltage to the gate electrode, the HfO2-based ferroelectric thin film generates different polarization states, and the channel carrier distribution is modulated through the gate dielectric-related stacking, thereby realizing the control of the device conduction state, which is suitable for non-volatile memory or related logic application scenarios.

[0044] The present invention also includes the application of the ferroelectric capacitor in ferroelectric random access memory (FeRAM), ferroelectric field-effect transistor (FeFET) or negative capacitance field-effect transistor (NCFET).

[0045] The following provides more specific embodiments, along with concrete data and operating methods, to further elaborate on the above-mentioned technical solutions of the present invention: It should be noted that the "HfO2-based thin film" mentioned in this invention refers to a pure hafnium dioxide thin film, or a hafnium dioxide thin film doped with elements such as Zr, Si, Al, Gd, La, Sr, and Y to stabilize the ferroelectric phase (e.g., HfO2). 0.5 Zr 0.5 O2). The “ALD sub-cycle” and “atomic layer deposition” described in this invention refer to the standard sequence of steps required to complete the growth of a single atomic layer, which typically includes: metal precursor pulse -> inert gas purging -> oxidant pulse -> inert gas purging.

[0046] Those skilled in the art will understand that by adjusting the ratio (N:M) of the number of sub-cycles under the first oxidant condition (strong oxidation) to the number of sub-cycles under the second oxidant condition (weak oxidation / no oxidation) in the aforementioned oxidant modulation cycle, the overall stoichiometry of the deposited HfO2-based thin film can be precisely controlled. For example, increasing the N:M ratio will lead to an increase in the overall oxygen content of the film and a decrease in the oxygen vacancy concentration. Furthermore, by changing the N:M ratio at different thickness stages of film growth or by changing the order of application of the modulation cycle, the desired non-uniform oxygen vacancy concentration distribution (such as a gradient distribution or a step distribution) can be flexibly constructed to meet the needs of different device designs.

[0047] Furthermore, although subsequent embodiments use Hf 0.5 Zr 0.5 Taking O2 as an example, the oxidant modulation method of this invention is also applicable to pure HfO2 thin films and thin film systems doped with other elements known to stabilize the HfO2 ferroelectric phase, such as Si, Al, Gd, La, Sr, Y, and Sc. Regardless of the type of dopant, the core mechanism of this invention—optimizing the oxygen vacancy defect network by controlling the oxidation environment—remains consistent.

[0048] Example 1 This embodiment provides a method for preparing an HfO2-based pre-film, which can obtain an HfO2-based ferroelectric thin film with specific defect distribution characteristics. The method specifically includes the following steps: S1: Substrate and lower electrode fabrication A heavily doped silicon wafer was selected as the substrate, and a TiN film with a thickness of 20 nm was deposited on the substrate by physical vapor deposition (PVD) as the lower electrode.

[0049] S2: Atomic layer deposition of HfO2-based pre-film The sample obtained in step S1 is placed in the atomic layer deposition reaction chamber and heated to 250 °C.

[0050] Tetra(ethylmethylamino)hafnium (TEMAH) and tetra(ethylmethylamino)zirconium (TEMAZ) were used as metal precursors and introduced alternately in a 1:1 pulse ratio to obtain Hf. 0.5 Zr 0.5 The HfO2-based preform composed of O2 has a target film thickness of approximately 10 nm.

[0051] In this atomic layer deposition process, at least one oxidant modulation cycle is introduced. This oxidant modulation cycle includes alternating first and second deposition stages, wherein the first deposition stage uses a strong oxidant condition, and the second deposition stage uses a weak oxidant condition. Specifically, it includes: First deposition stage (lower interface layer): Under the first oxidant condition, ozone (O3) was used as the oxidant, and 10 atomic layer deposition sub-cycles were performed to form an oxygen-rich Hf layer with a thickness of approximately 1 nm on the lower electrode surface. 0.5 Zr 0.5 O2 thin film layer; Second depositional stage (volume layer): Under the second oxidant condition, water (H2O) was used as the oxidant, and 80 atomic layer deposition sub-cycles were performed to form Hf with a thickness of approximately 8 nm. 0.5 Zr 0.5 O2 bulk thin film layer; First deposition stage (upper interface layer): Again, under the first oxidant condition, ozone (O3) was used as the oxidant for 10 atomic layer deposition sub-cycles, forming an oxygen-rich Hf layer with a thickness of approximately 1 nm. 0.5 Zr 0.5 O2 thin film layer.

[0052] S3: Upper Electrode Preparation On the HfO2-based preform obtained in step S2, a TiN thin film with a thickness of 20 nm is deposited by physical vapor deposition as the top electrode and mechanical stress capping layer.

[0053] S4: Crystallization Annealing Treatment The sandwich stacked structure was subjected to rapid thermal annealing under a nitrogen (N2) atmosphere at a temperature of 600°C for 30 seconds to induce the HfO2-based preform to crystallize into a ferroelectric orthorhombic phase.

[0054] Example 2: Preparation of HfO2:Zr ferroelectric thin films modulated by periodically alternating oxidants This embodiment provides a method for preparing an HfO2-based preform, the difference being the atomic layer deposition method of the HfO2-based preform in step S2.

[0055] S2: Atomic layer deposition of HfO2-based pre-film In step S2, the oxidation conditions are periodically alternating by repeatedly executing the oxidant modulation cycle over the entire film thickness range.

[0056] Specifically, the oxidant modulation cycle is repeated 20 times, and each oxidant modulation cycle includes: Under the second oxidant condition, water (H2O) was used as the oxidant, and four atomic layer deposition subcycles were continuously performed. Under the first oxidant condition, ozone (O3) was used as the oxidant for one atomic layer deposition subcycle.

[0057] The above process involves a total of 100 atomic layer deposition sub-cycles, forming an Hf layer with a thickness of approximately 10 nm. 0.5 Zr 0.5 O2-based preformed film; this embodiment further achieves control over the overall oxygen content of the film by adjusting the alternation frequency of the first deposition stage and the second deposition stage.

[0058] Example 3: Preparation of HfO2-based ferroelectric thin films with composite top electrode structure This embodiment provides a method for preparing an HfO2-based pre-film, which is similar to that of Embodiment 1, except that the upper electrode structure is different in step S3.

[0059] S3: Upper Electrode Preparation On the HfO2-based preform obtained in step S2, a chemically inert metal layer with a thickness of 2 nm is first deposited. The chemically inert metal layer is selected from W or Pt and is used to directly contact the HfO2-based preform. Subsequently, a 30 nm thick TiN film is deposited on the chemically inert metal layer as a second metal layer and a mechanical stress capping layer.

[0060] Example 4: Preparation of HfO2-based ferroelectric thin films using a two-step crystallization annealing process This embodiment provides a method for preparing an HfO2-based preform, which is similar to that of Embodiment 1, except that the crystallization annealing treatment is performed in step S4.

[0061] S4: Crystallization Annealing Treatment First, the film is held at a first temperature of 450 °C for 60 seconds to promote the formation of ferroelectric phase nuclei in the HfO2-based preform. The temperature is then raised to a second temperature of 700 °C and held for 10 seconds to promote grain growth and complete the phase transformation.

[0062] Two comparative examples are provided below to further illustrate the technical solution of the present invention: Comparative Example 1: Preparation of HfO2:Zr thin films using a single weak oxidant Comparative Example 1 is the same as Example 1 in steps S1, S3 and S4, except that the atomic layer deposition process of the HfO2-based pre-film is performed in step S2.

[0063] S2: Atomic layer deposition of HfO2-based pre-film Comparative Example 1 provides a method for preparing an HfO2-based preform. In this comparative example, no oxidant modulation cycle is introduced during the atomic layer deposition process. Instead, a single oxidant with weak oxidizing power is used throughout the entire film deposition process.

[0064] Specifically, using water (H2O) as the sole oxidant, 100 atomic layer deposition subcycles were continuously performed to grow Hf with a thickness of approximately 10 nm. 0.5 Zr 0.5 O2 thin film.

[0065] Apart from the differences mentioned above, the remaining preparation steps are the same as in Example 1.

[0066] Comparative Example 2: Preparation of HfO2:Zr thin films using a single strong oxidant Comparative Example 2 provides a method for preparing an HfO2-based pre-film, which is the same as steps S1, S3 and S4 of Example 1. The difference lies in the atomic layer deposition process of the HfO2-based pre-film in step S2.

[0067] S2: Atomic layer deposition of HfO2-based pre-film In this comparative example, no oxidant modulation cycle was introduced during the atomic layer deposition process; instead, a single oxidant with strong oxidizing power was used throughout the entire thin film deposition process.

[0068] Specifically, using high-concentration ozone (O3) as the sole oxidant, 100 atomic layer deposition subcycles were continuously performed to grow Hf with a thickness of approximately 10 nm. 0.5 Zr 0.5 O2 thin film.

[0069] Apart from the differences mentioned above, the remaining preparation steps are the same as in Example 1.

[0070] Performance test and comparison results: To further verify the electrical properties of the HfO2-based ferroelectric thin films prepared in the above embodiments and comparative examples at the device level, Based on the Hf obtained in Examples 1–2 and Comparative Examples 1–2 0.5 Zr 0.5 An O2 thin film is used to form a TiN lower electrode and a TiN upper electrode on its top and bottom, respectively, thereby preparing a ferroelectric capacitor with a TiN / HZO / TiN structure.

[0071] The electrical performance of the TiN / HZO / TiN ferroelectric capacitors prepared in the above embodiments and comparative examples was tested.

[0072] Figure 5 shows the polarization intensity-electric field (P-E) loop characteristics of each sample, and Figure 6 shows the leakage current density-voltage (J-V) characteristics of each sample.

[0073] The corresponding key electrical performance parameters are summarized in Table 1 below: Table 1: Electrical performance test results of TiN / HZO / TiN ferroelectric capacitors prepared in the examples and comparative examples The performance test results above show that, compared with the comparative samples deposited using a single oxidant, the HfO2-based ferroelectric thin films prepared using the oxidant modulation strategy exhibit a more favorable balance between remanent polarization and leakage current characteristics. In particular, the sample shown in Example 1 achieved a high polarization response while maintaining a low leakage current density, demonstrating its advantages in overall ferroelectric performance.

[0074] like Figure 4 As shown, the oxidant modulation method of the present invention differs from the traditional single oxidant method in terms of the microstructure of the film after annealing: The present invention optimizes the spatial distribution of oxygen vacancies by strong oxidation in the interface region and weak oxidation in the bulk region (or periodically alternating modulation), thereby promoting the formation / stabilization of ferroelectric orthorhombic phases while reducing interface defects and leakage risks; in contrast, deposition of a single weak oxidant may lead to excessive oxygen vacancies and increased leakage, while deposition of a single strong oxidant may reduce leakage but may result in insufficient ferroelectric polarization. The above differences can be corroborated by the comparison results of the electrical performance of the embodiments of the present invention and the comparative examples.

[0075] like Figure 5 As shown, polarization intensity-electric field (P–E) tests were performed on the TiN / HZO / TiN capacitors prepared in the embodiments and comparative examples of the present invention. It can be seen that the oxidant modulation strategy of the present invention can improve the remanent polarization intensity of the device. Among them, the 2Pr of Example 1 with interfacial O3 / bulk H2O modulation can reach about 45 µC / cm under the condition of 3 MV / cm. 2 Example 2, with periodic alternating modulation, has a temperature of approximately 38 µC / cm. 2 In comparison, the 2Pr of the single strong oxidant O3 was significantly lower (approximately 25 µC / cm). 2 This indicates that achieving an appropriate and rationally distributed amount of oxygen vacancies by modulating the oxidation environment is beneficial for obtaining better ferroelectric polarization performance.

[0076] like Figure 6 As shown, leakage current density-voltage (J–V) tests performed on the above devices demonstrate that the oxidant modulation method of the present invention can significantly reduce leakage current while maintaining high polarization: for example, in Example 1, the leakage current density J is approximately 1 × 10⁻⁶ at 2 V.-8 A / cm 2 While the single weak oxidant H2O can achieve a ratio of approximately 1 × 10⁻⁶ under the same conditions, the ratio of J can reach approximately 1 × 10⁻⁶. -6 A / cm 2 This indicates that by employing strong oxidation conditions in the interface region to reduce interface defects and improve interface insulation, leakage channel formation can be effectively suppressed, thereby improving the overall electrical performance of the device.

[0077] Based on the analysis of the preparation process and electrical test results of the above embodiments and comparative examples, the principle of this invention includes: during the thin film growth process, by introducing oxidant conditions with different oxidizing capabilities at different deposition stages, the oxygen content and defect state inside the HfO2-based thin film can be effectively controlled. In the region near the electrode, a stronger oxidizing environment helps to reduce the defect density at the interface, thereby improving the interface insulation properties and suppressing the formation of leakage channels. In the internal region of the thin film, moderate oxygen defects are beneficial to the formation and stabilization of metastable ferroelectric orthogonal phases. This difference in defect distribution along the film thickness direction allows the HfO2-based ferroelectric thin film prepared by this invention to achieve a more reasonable balance between ferroelectric polarization characteristics and leakage suppression, thereby improving the overall electrical performance of the device.

[0078] In the description of the embodiments of the present invention, it should be noted that the terms "inner" and "outer" and other terms indicating the direction or positional relationship are based on the direction or positional relationship shown in the drawings. This is only for the convenience of description and does not indicate or imply that the device or component must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, it should not be construed as a limitation of the present invention.

[0079] In the description of this invention, the references to "one embodiment," "some embodiments," "in this embodiment," "specific example," or "some examples," etc., indicate that a specific feature, structure, material, or characteristic described in connection with that embodiment or example is included in at least one embodiment or example of the invention. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples. Moreover, without contradiction, those skilled in the art can combine and integrate the different embodiments or examples described in this specification, as well as the features of different embodiments or examples.

[0080] The above description is merely a specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the technical scope disclosed in the present invention should be included within the scope of protection of the present invention. Therefore, the scope of protection of the present invention should be determined by the scope of the claims.

Claims

1. A method for preparing an HfO2-based ferroelectric thin film with a gradient oxygen vacancy distribution, characterized in that, Includes the following steps: S1: Provide a substrate and fabricate a lower electrode on the substrate; S2: An amorphous HfO2-based preform is deposited on the lower electrode using atomic layer deposition; S3: An upper electrode is fabricated on the HfO2-based pre-film to form a sandwich stacked structure; S4: Perform crystallization annealing on the sandwich stacked structure to induce the HfO2-based pre-film to crystallize into a ferroelectric orthorhombic phase; In step S2, the atomic layer deposition process includes at least one oxidant modulation cycle, which includes an alternating first deposition stage and a second deposition stage. The oxidant conditions used in the first deposition stage and the second deposition stage have different oxidizing capabilities, so as to control the oxygen content or oxygen vacancy defect distribution along the thickness direction of the HfO2-based pre-film during the thin film deposition process. The first deposition stage involves at least one atomic-layer deposition sub-cycle under the first oxidant condition. The second deposition stage involves at least one atomic layer deposition subcycle under the second oxidant condition.

2. The method for preparing HfO2-based ferroelectric thin films with gradient oxygen vacancy distribution according to claim 1, characterized in that, In step S2, the oxidizing power of the first oxidant condition is stronger than that of the second oxidant condition.

3. The method for preparing HfO2-based ferroelectric thin films with gradient oxygen vacancy distribution according to claim 2, characterized in that, In step S2, the oxidant used in the first oxidant condition is selected from one of O3, O2 plasma, and H2O2; the second oxidant condition includes any of the following: (a) using H2O or alcohol oxidant; (b) not introducing oxidant, but only performing inert gas purging.

4. The method for preparing HfO2-based ferroelectric thin films with gradient oxygen vacancy distribution according to claim 1, characterized in that, In step S2, the material of the HfO2-based pre-film is HfO2 or doped HfO2, and the doping element of the doped HfO2 is selected from at least one of Zr, Si, Al, Gd, La, Sr, Y, and Sc; and the thickness of the HfO2-based pre-film is 3 nm to 30 nm.

5. The method for preparing HfO2-based ferroelectric thin films with gradient oxygen vacancy distribution according to claim 1, characterized in that, In step S2, the temperature of the atomic layer deposition is 200-400℃.

6. The method for preparing HfO2-based ferroelectric thin films with gradient oxygen vacancy distribution according to claim 1, characterized in that, In step S3, the material of the upper electrode is selected from at least one of TiN, TaN, W, Mo, Ru, Ir, and Pt; and the upper electrode is a composite structure, including a first metal layer that directly contacts the HfO2-based preform and a second metal layer located on the first metal layer, and the chemical inertness of the first metal layer is higher than that of the second metal layer.

7. The method for preparing HfO2-based ferroelectric thin films with gradient oxygen vacancy distribution according to claim 1, characterized in that, In step S4, the crystallization annealing process is rapid thermal annealing, with an annealing temperature range of 400-800℃, an annealing time of 1-300 seconds, and an annealing atmosphere of N2, Ar, O2, or a mixture thereof.

8. The method for preparing HfO2-based ferroelectric thin films with gradient oxygen vacancy distribution according to claim 7, characterized in that, In step S4, the crystallization annealing process adopts a two-step method: first, nucleation is carried out at a first temperature of 400-550℃ for 50-70 seconds, and then the temperature is raised to a second temperature of 600-800℃ for 8-12 seconds to carry out grain growth.

9. An HfO2-based ferroelectric thin film prepared by any one of claims 1-8, characterized in that, The HfO2-based ferroelectric thin film has a non-uniform oxygen vacancy distribution in the thickness direction, wherein the oxygen vacancy concentration in the film region near the lower and upper electrodes is lower than the oxygen vacancy concentration in the central region of the film.

10. An application of the HfO2-based ferroelectric thin film according to claim 9, characterized in that, The application includes using the HfO2-based ferroelectric thin film in a ferroelectric capacitor, the ferroelectric capacitor including a lower electrode, an upper electrode, and an HfO2-based ferroelectric thin film located between the lower electrode and the upper electrode, the HfO2-based ferroelectric thin film being the HfO2-based ferroelectric thin film according to claim 9.

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