Preparation method and application of cerium-doped hafnium zirconium oxide ferroelectric film with high remanent polarization strength

Abstract

The present invention provides a method for preparing and applying a cerium-doped hafnium zirconium oxide ferroelectric thin film with high remanent polarization strength. First, an organic hafnium source, an organic zirconium source, and a cerium salt are used as raw materials. A clear and transparent cerium-doped hafnium zirconium oxide precursor solution is prepared by repeated heating and stirring. Finally, the precursor solution is coated on a cleaned platinum substrate according to the experimental design requirements. Drying, preheating, and rapid thermal annealing are performed to obtain a dense and uniform Ce:Hf film. 0.5 Zr 0.5 O2 ferroelectric thin film. The present invention can realize flexible regulation of the film thickness and doping element content, and significantly improves the residual polarization strength of the film.

Description

Technical Field

[0001] The present invention relates to the preparation of ferroelectric thin film materials, and in particular to a preparation method and application of a cerium-doped hafnium zirconium oxide ferroelectric thin film with high residual polarization strength. Background Art

[0002] Hafnium oxide-based ferroelectric materials have widely replaced SiO2 as CMOS transistor gate dielectrics in the field of microelectronics due to their high dielectric constant. Compared with the current perovskite-based ferroelectric materials, they show full scalability and integrability of complementary metal oxide semiconductors, breaking the bottleneck that restricts the development of ferroelectric memory. In the future, they will have broad development space in the field of integrated ferroelectric devices such as non-volatile ferroelectric memory. Hafnium oxide not only has good ferroelectricity, it also has good piezoelectricity, pyroelectricity and compatibility. Research in recent years has shown that the introduction of impurity ions such as Si, Zr, Y, La, Sr, and Ce will induce better ferroelectricity, among which the doping concentration range of Zr ions is the largest, forming Hf 1-x Zr x O2 thin films, due to the similar crystal structures of ZrO2 and HfO2, can form a solid solution system through ion substitution, which helps induce the formation of a highly symmetric phase. Hafnium zirconium oxide ferroelectric films prepared using specialized processes exhibit strong ferroelectricity at the nanoscale. To this end, when preparing HfO2 thin films, researchers typically dope certain elements to achieve a higher remnant polarization strength. They also adjust parameters during preheating and annealing to achieve the desired film thickness and a higher proportion of the ferroelectric phase.

[0003] At present, the main methods for preparing hafnium zirconium oxide thin films are atomic deposition (ALD) and pulsed laser deposition (PLD). The chemical solution deposition method used in the present invention provides the opportunity to manufacture inexpensive devices for various applications at low cost. In addition, a wide range of dopants can be used for CSD-deposited films, which facilitates comparative studies of doped elements. We doped cerium elements into the HfO2-ZrO2 solid solution system to prepare thin films, which also mainly utilizes chemical reactions to generate thin films on the substrate surface. The operation process is simple, low-cost and environmentally friendly, and the raw materials are easily obtained. Compared with the traditional HfO2 thin film preparation process, it has great optimization and significantly improves the residual polarization value of the film. Summary of the Invention

[0004] The purpose of the present invention is to address the deficiencies of existing preparation technologies and provide a method and application for preparing a cerium-doped hafnium zirconium oxide ferroelectric thin film with high remnant polarization strength that is simple to operate, low in cost, environmentally friendly, and can be mass-produced.

[0005] The cerium-doped hafnium zirconium oxide ferroelectric thin film prepared by the present invention is first prepared by adding a hafnium source and a zirconium source as raw materials to an acetic acid solution, and then adding an acetylacetone solution to stabilize the chemical properties of the solution and adjust the pH value. Then, a cerium salt is used as a dopant, and the solution is heated and stirred multiple times to obtain a transparent solution free of visible large particles. The prepared transparent solution is coated on a cleaned platinum substrate, and then dried, heat-treated, and annealed to obtain a solid cerium-doped hafnium zirconium oxide ferroelectric thin film. Finally, an electrode is plated on the surface of the film to prepare a metal-Ce:HZO-metal (MIM) structure capacitor.

[0006] The invention achieves stable generation of orthorhombic phase in the hafnium zirconium oxide ferroelectric thin film by doping with cerium element, improves the initial intrinsic ferroelectric performance of the thin film and the low ferroelectric performance induced under external electric field, and the thickness of the thin film can be controlled.

[0007] The present invention provides a method for preparing a cerium-doped hafnium zirconium oxide ferroelectric thin film with high remnant polarization strength, comprising the following steps:

[0008] (1) adding weighed organic hafnium source and zirconium source to acetic acid solution, heating and stirring until completely dissolved, then adding acetylacetone solution thereto, adjusting the pH value and stabilizing the chemical properties of the solution, to obtain a precursor solution of HfO2-ZrO2 system; then adding a dopant cerium source to the precursor solution, heating and stirring for 20-40 minutes, and standing for 36-40 hours to obtain a clear and transparent cerium-doped hafnium zirconium oxide solution without visible particles;

[0009] (2) Cleaning of substrates: First, ultrasonically clean the cut substrates with deionized water for 3-6 minutes, then ultrasonically clean them with anhydrous ethanol for 8-12 minutes, continue ultrasonically cleaning them with deionized water for 3-6 minutes, and then ultrasonically clean them with acetone for 8-12 minutes. Rinse and soak them with plenty of deionized water, and then dry them. Then, pretreat the surface of the dried substrates and plasma clean them for 3-6 minutes to increase the wettability of the substrate surface with the precursor solution.

[0010] (3) coating and drying: coating the film of step (1) on the cleaned substrate obtained in step (2), and placing the substrate on a baking plate for baking and crystallization after each coating. Then, pre-treating the baked substrate surface to reduce its wetting angle and increase the wettability of the film. Repeat the above operation according to the required film thickness;

[0011] (4) placing the film obtained in step (3) in an annealing furnace filled with a protective atmosphere for preheating treatment, and then performing annealing treatment. After the annealing furnace cools to room temperature, the substrate is taken out to obtain a cerium-doped hafnium zirconium oxide ferroelectric film.

[0012] (5) Plating an electrode on the cerium-doped hafnium zirconium oxide ferroelectric thin film obtained in step (4).

[0013] Furthermore, the organic hafnium source is hafnium acetylacetonate (C 20 H 28 HfO8), the zirconium source is zirconium acetylacetonate (C 20 H 28 ZrO8), and the cerium source is cerium nitrate Ce(NO3)3.

[0014] Furthermore, in step (1), the molar ratio of hafnium and zirconium is 1:1; the pH of the acetylacetone solution is adjusted to 3-5; the acetylacetone solution also plays a role in stabilizing the chemical properties. Therefore, the addition of acetylacetone is very important because the stability of the chemical properties and the pH of the precursor solution play a vital role in the quality of film formation.

[0015] Furthermore, in the cerium-doped hafnium zirconium oxide, the molar percentage of cerium is 5-9%, denoted as 5-9 mol %, excluding endpoints, more preferably 6-8 mol %, and most preferably 7 mol %.

[0016] Furthermore, in step (1), the heating and stirring temperature is 50-60° C., and the stirring rate is 50-70 r / min.

[0017] Furthermore, in step (1), the concentration of the hafnium zirconium oxide precursor solution is controllable, and the concentration of the precursor solution is 0.1-0.2 mol / L. A lower concentration of the acidic precursor solution can obtain a light, thin and dense film.

[0018] Furthermore, the substrate is a Pt(111) / TiN / SiO2 / Si(100) substrate; after each step of ultrasonic cleaning, it is rinsed with a large amount of deionized water to remove surface stains and prevent stains from adhering to the substrate surface; at the same time, plasma cleaning enhances the cleaning effect.

[0019] Furthermore, in step (3), the coating method is spin coating; the spin coating setting parameters are low speed 500rpm*16s, high speed 3000rpm*16s, and the number of coating times can be controlled according to the required film thickness, and the thickness of the cerium-doped hafnium zirconium oxide ferroelectric film is controlled to be less than 40nm.

[0020] Furthermore, in step (4), the protective atmosphere is nitrogen; the annealing process is specifically as follows: first slowly heat from room temperature to 180°C, hold for 3 minutes, then heat to 300°C at a heating rate of 10°C / s, hold for 3 minutes, then heat to 400°C at a heating rate of 10°C / s, hold for 5 minutes, and finally heat to 800°C at a heating rate of 40°C / s, keep warm for 150 seconds, and then wait for cooling to room temperature before taking out.

[0021] Furthermore, in step (5), the electrode is a Pt electrode, and the electrode is deposited on the dry film after annealing.

[0022] The prepared cerium-doped hafnium zirconium oxide ferroelectric film is integrated into a capacitor to facilitate analysis and testing of its ferroelectric properties and electrical properties. The capacitor structure is a MIM structure.

[0023] The present invention prepares a cerium-doped hafnium zirconium oxide precursor solution by a chemical solution method, and in a subsequent preparation process, controls the content of the doping element and the pH value of the precursor solution, optimizes the annealing process, and obtains a stably existing mixed phase (monoclinic phase, orthorhombic phase). The cerium-doped hafnium zirconium oxide ferroelectric thin film prepared by this method has the advantages of uniform film surface, large residual polarization value, low leakage current, etc., and the present invention also has the advantages of simple operation, short cycle, high repeatability, low cost, etc.

[0024] Compared with the prior art, the present invention has the following beneficial effects:

[0025] (1) The present invention achieves a large residual polarization value in the prepared film by controlling the amount of each source and the pH value of the precursor solution, the number of coatings, and the annealing process.

[0026] (2) The cerium-doped hafnium-doped zirconium oxide film prepared by the present invention is dense and uniform and has a small leakage current.

[0027] (3) The operation process of the present invention is simple and clear, and does not require a strict preparation environment. It also does not require advanced and expensive equipment and instruments. It has high reproducibility and can be used for mass production. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1 This is the GIXRD pattern of the sample in Example 1 with a cerium doping concentration of 7 mol% and a film thickness of 34 nm.

[0029] Figure 2 This is the hysteresis loop diagram of the sample in Example 1, where the cerium doping concentration is 7 mol % and the film thickness is 34 nm.

[0030] Figure 3 This is a leakage current diagram of the sample in Example 1 with a cerium doping concentration of 7 mol% and a film thickness of 34 nm. DETAILED DESCRIPTION

[0031] In order to make the process and purpose of the present invention more clear, we will provide a more detailed step-by-step description.

[0032] Example 1

[0033] (1) A method for preparing a cerium-doped hafnium zirconium oxide ferroelectric thin film, comprising the following steps: first, weighing 0.1343 g of hafnium acetylacetonate and 0.1139 g of zirconium acetylacetonate, adding 4 mL of acetic acid solution, placing the mixture on a heating stirrer, setting the temperature to 55°C to facilitate the dissolution of the hafnium source and the zirconium source, and stirring at a rate of 60 r / min. After complete dissolution, adding an appropriate amount of acetylacetone solution, adjusting the pH value to within the range of 3-5 and stabilizing the chemical properties of the solution, and preparing a precursor solution of the HfO2-ZrO2 system. Then, weighing 0.0129 g of cerium nitrate, adding the mixture to the precursor solution of the HfO2-ZrO2 system (the cerium doping molar percentage is 7 mol%), stirring the mixture on a stirrer for 30 minutes at a stirring rate of 60 r / min, and then allowing the mixture to settle for 48 hours to prepare a cerium-doped hafnium zirconium oxide solution with a concentration of 0.1-0.15 mol / L.

[0034] (2) During the preparation process, a Pt(111) / TiN / SiO2 / Si(100) substrate was used; it was first ultrasonically cleaned with deionized water for 5 minutes, then ultrasonically cleaned with anhydrous ethanol for 10 minutes, then ultrasonically cleaned with deionized water for 5 minutes, and then ultrasonically cleaned with acetone for 10 minutes. It was then rinsed with a large amount of deionized water, soaked, and then dried. It was plasma treated for 5 minutes to reduce the contact angle between the substrate surface and the solution and enhance the viscosity of the film and the substrate. After each ultrasonic cleaning step, it was rinsed with a large amount of deionized water to remove surface stains and prevent stains from adhering to the substrate surface.

[0035] (3) Spin coating was used during the coating process; the solution was coated on the surface of the substrate, and then placed in a glue baking machine and heated at 180°C for 3 minutes and 350°C for 5 minutes. The above operation was repeated and two layers were spin-coated to obtain a cerium-doped hafnium zirconium oxide thin film with a thickness of 34 nm;

[0036] (4) The substrate coated in step (3) is placed in an annealing furnace for annealing. The protective atmosphere is nitrogen. The process parameters are set as follows: first slowly heat from room temperature to 180°C, hold for 3 minutes, then heat to 300°C at a heating rate of 10°C / s, hold for 3 minutes, then heat to 400°C at a heating rate of 10°C / s, hold for 5 minutes, and finally heat to 800°C at a heating rate of 40°C / s, keep warm for 150 seconds, and then wait for cooling to room temperature before taking out.

[0037] (5) Electrodes were plated on the film obtained in (4), and the deposited metal was platinum, resulting in a MIM structure capacitor. Finally, the ferroelectric properties were tested. The sample was found to be mainly orthogonal phase, with a remanent polarization value of 16.23 to 20.01 μC / cm 2 The GIXRD patterns, hysteresis loops and leakage currents of the samples are shown in Figure 2. Figure 1 、 Figure 2 and Figure 3shown.

[0038] Example 2

[0039] A cerium-doped hafnium zirconium oxide precursor solution with a cerium doping molar percentage of 5 mol% was prepared. The remaining process steps and process conditions were the same as in Example 1 to obtain a metal-Ce:HZO thin film-metal capacitor. The ferroelectric properties of the capacitor were tested using a ferroelectric analyzer and a semiconductor tester. The sample was found to be a mixture of monoclinic and orthorhombic phases, with a remanent polarization range of 10.25 to 15.70 μC / cm 2 .

[0040] Example 3

[0041] A cerium-doped hafnium zirconium oxide precursor solution with a cerium doping molar percentage of 9 mol% was prepared. The remaining process steps and process conditions were the same as in Example 1 to obtain a metal-Ce:HZO thin film-metal capacitor. The ferroelectric properties of the capacitor were tested using a ferroelectric analyzer and a semiconductor tester. The sample was found to be a mixture of monoclinic and orthorhombic phases, with a remanent polarization range of 8.25 to 10.70 μC / cm 2 .

[0042] In the above embodiments, hafnium zirconium oxide films with different cerium doping concentrations all exhibit ferroelectricity, among which when the cerium doping molar percentage is 7 mol%, the hysteresis loop window is the largest and optimal, and the GIXRD spectrum analysis tested therefrom shows that the film is mainly composed of orthorhombic phase; when the cerium doping molar percentage is 5 mol%, the GIXRD spectrum analysis tested therefrom shows that it is a combination of monoclinic phase and orthorhombic phase; when the cerium doping molar percentage is 9 mol%, the GIXRD spectrum analysis tested therefrom shows that it is a mixed phase of monoclinic phase, orthorhombic phase and cubic phase.

Claims

1. A method for preparing a cerium-doped hafnium zirconium oxide ferroelectric thin film with high remnant polarization strength, characterized in that: The following steps are involved: (1) Add the weighed organic hafnium source and zirconium source to an acetic acid solution, heat and stir until completely dissolved, then add acetylacetone solution, adjust the pH value to 3-5 and stabilize the chemical properties of the solution to obtain a precursor solution of the HfO2-ZrO2 system; then add a dopant cerium source to the precursor solution, heat and stir for 20-40 minutes, and let it stand for 36-60 hours to obtain a clear and transparent cerium-doped hafnium zirconium oxide solution without visible particles; (2) Cleaning of substrates: First, ultrasonically clean the cut substrates with deionized water for 3-6 minutes, then ultrasonically clean them with anhydrous ethanol for 8-12 minutes, continue ultrasonically cleaning them with deionized water for 3-6 minutes, and then ultrasonically clean them with acetone for 8-12 minutes. Rinse and soak them with plenty of deionized water, and then dry them. After drying, pretreat the surface of the substrates and plasma clean them for 3-6 minutes to increase the wettability of the substrate surface with the precursor solution. (3) Coating and drying: The cerium-doped hafnium zirconium oxide solution obtained in step (1) is coated on the cleaned substrate obtained in step (2). After each layer is coated, the substrate is placed on a baking plate for baking and crystallization. The baked substrate is then subjected to surface pretreatment to reduce its wetting angle and increase the wettability of the film. The above operation is repeated according to the required film thickness. (4) placing the film obtained in step (3) in an annealing furnace filled with a protective atmosphere for preheating, and then performing annealing. After the annealing furnace cools to room temperature, the substrate is taken out to obtain a cerium-doped hafnium-zirconium-oxide ferroelectric film; (5) plating an electrode on the cerium-doped hafnium zirconium oxide ferroelectric thin film obtained in step (4); The organic hafnium source is hafnium acetylacetonate, the zirconium source is zirconium acetylacetonate, and the cerium source is cerium nitrate; In the cerium-doped hafnium zirconium oxide, the molar percentage of cerium is 5-9%, denoted as 5-9 mol%, excluding the endpoints; In step (4), the protective atmosphere is nitrogen; the annealing process is specifically as follows: first slowly heat from room temperature to 180 °C, hold for 3 min, then heat to 300 °C at a heating rate of 10 °C / s, hold for 3 min, then heat to 400 °C at a heating rate of 10 °C / s, hold for 5 min, and finally heat to 800 °C at a heating rate of 40 °C / s, hold for 150 s, and then wait to cool to room temperature before taking out.

2. The method for preparing a cerium-doped hafnium zirconium oxide ferroelectric thin film with high remnant polarization strength according to claim 1, characterized in that: In step (1), the molar ratio of hafnium to zirconium is 1:

1.

3. The method for preparing a cerium-doped hafnium zirconium oxide ferroelectric thin film with high remnant polarization strength according to claim 1, wherein: In step (1), the heating and stirring temperature is 50-60°C, and the stirring rate is 50-70 r / min.

4. The method for preparing a cerium-doped hafnium zirconium oxide ferroelectric thin film with high remnant polarization strength according to claim 1, wherein: The substrate is a Pt (111) / TiN / SiO2 / Si (100) substrate.

5. The method for preparing a cerium-doped hafnium zirconium oxide ferroelectric thin film with high remnant polarization strength according to claim 1, wherein: In step (3), the coating method is spin coating; the spin coating setting parameters are low speed 500 rpm*16s, high speed 3000 rpm*16s, and the number of coatings is controlled according to the required film thickness, and the thickness of the cerium-doped hafnium zirconium oxide ferroelectric film is controlled to be less than 40 nm.

6. The method for preparing a cerium-doped hafnium zirconium oxide ferroelectric thin film with high remnant polarization strength according to claim 1, wherein: In step (5), the electrode is a Pt electrode, and the electrode is deposited on the dry film after annealing.

7. Use of the cerium-doped hafnium zirconium oxide ferroelectric thin film obtained by the preparation method according to any one of claims 1 to 6 in capacitors.

Images