High-activity cerium oxide material, and preparation method and application thereof

Abstract

The application relates to a high-activity cerium oxide material and a preparation method and application thereof, and belongs to the technical field of micro-nano powder synthesis. The preparation method comprises the following steps: S1, preparing a cerium nitrate aqueous solution; S2, mixing the cerium nitrate aqueous solution and ethylene glycol and placing them in a high-pressure reaction kettle to perform a solvothermal reaction, so as to obtain a reaction product; S3, performing freeze-drying on the solid separated through suction filtration of the reaction product, so as to obtain a precursor; and S4, grinding the precursor and performing calcination in a vacuum environment, so as to obtain the high-activity cerium oxide. The high-activity cerium oxide material prepared by adopting the method has high Ce 3+ / Ce 4+ Specificity and high surface activity, and is particularly suitable for polishing abrasives used for chemical mechanical polishing.

Description

Technical Field

[0001] This invention relates to the field of micro / nano powder synthesis technology, and in particular to a highly active cerium oxide material, its preparation method, and its applications. Background Technology

[0002] In chemical mechanical polishing (CMP), cerium oxide (CeO2) has become an irreplaceable polishing material for silicon dioxide (SiO2) substrates (such as photomask quartz glass) because its core advantages go far beyond its moderate hardness and regular morphology. The key lies in the dynamic CeO2 content on its crystal surface. 3+ / Ce 4+ Redox pairs. Among them, trivalent cerium (Ce) 3+ The content and activity of () are among the most critical factors determining polishing efficiency and surface quality.

[0003] Traditional methods for preparing cerium oxide include precipitation, hydrothermal methods, and sol-gel methods. While precipitation is simple and low-cost, it is prone to agglomeration, makes grain control difficult, and results in poor product consistency. The sol-gel method struggles to balance purity and activity, is sensitive to process conditions, and exhibits poor batch-to-batch reproducibility. Hydrothermal methods are highly susceptible to significant loss of catalytically active sites during subsequent calcination. Therefore, none of these traditional methods yield highly active cerium oxide materials.

[0004] Therefore, there is an urgent need for a highly active cerium oxide material and its preparation method to solve the problems of low material removal rate, easy scratches and damage on the polished surface, and poor batch stability caused by insufficient chemical reactivity in existing high-end polishing slurries, so as to meet the urgent needs of integrated circuit manufacturing for ultra-precision, low-defect, and high-consistency polishing processes. Summary of the Invention

[0005] Based on the above analysis, the present invention aims to provide a highly active cerium oxide material, its preparation method, and its application, in order to solve the problem of insufficient chemical reactivity of existing cerium oxide materials when applied to polishing fluids.

[0006] In a first aspect, the present invention provides a method for preparing a highly active cerium oxide material, comprising the following steps: S1. Prepare an aqueous solution of cerium nitrate; mix the aqueous solution of cerium nitrate and ethylene glycol, and place it in a high-pressure reactor for a solvothermal reaction to obtain the reactants; S2. The solid separated by filtration of the reactants is freeze-dried to obtain the precursor; S3. After grinding the precursor, it is calcined in a vacuum environment to obtain the highly active cerium oxide.

[0007] Furthermore, in step S1, the cerium nitrate is cerium(III) hexahydrate.

[0008] Further, in step S1, the molar concentration of the cerium nitrate aqueous solution is 0.2~0.8 mol / L.

[0009] Further, in step S1, the volume ratio of the cerium nitrate aqueous solution to ethylene glycol is 1~5:40~80.

[0010] Furthermore, in step S1, the reaction temperature is 155~180℃ and the reaction time is 900~1100 min.

[0011] Further, in step S2, the solid is dried to constant weight at -30~10°C.

[0012] Furthermore, in step S3, the vacuum level is 2~5 Pa.

[0013] Furthermore, in step S3, the calcination temperature is 700~800℃ and the calcination time is 2~5 h.

[0014] Secondly, the present invention provides a highly active cerium oxide material, which is prepared by any of the above-mentioned preparation methods.

[0015] Furthermore, the particle size of the highly active cerium oxide material is 100~200 nm.

[0016] Thirdly, the present invention also provides an application of the above-mentioned highly active cerium oxide material in a chemical mechanical polishing process.

[0017] Compared with the prior art, the present invention can achieve at least one of the following beneficial effects: 1. In the preparation method of this invention, vacuum calcination is used instead of conventional oxidation calcination. By precisely controlling the calcination temperature and time, the oxidizing atmosphere of high-temperature calcination is avoided from "repairing" or annihilating oxygen vacancies in the crystal lattice. At the same time, the weak convective heat transfer under vacuum can effectively suppress the mass transfer and sintering between CeO2 grains, thereby controlling the grain size and obtaining a larger surface area and more surface defects.

[0018] 2. This invention obtains a precursor from the solid obtained by vacuum filtration through a freeze-drying process. Due to the decrease in surface tension under freeze-drying conditions, the drying process uses a solid-gas interface instead of the conventional liquid-gas interface, avoiding structural collapse caused by capillary forces. This further increases the specific surface area of ​​the precursor, creating favorable conditions for subsequent calcination, resulting in a doubling of the specific surface area of ​​the final cerium oxide and exposing more Ce. 3+ Active site.

[0019] 3. The highly active cerium oxide prepared by this invention, when used as a polishing abrasive, exhibits high Ce content. 3+ / Ce4+ High specific gravity and high surface activity are scientific approaches to achieving the synergistic optimization of the contradictory goals of "high material removal rate" and "ultra-low surface damage". Using the highly active cerium oxide prepared in this invention as a polishing abrasive, the removal rate MRR > 200 nm / min and the surface roughness Ra < 0.3 nm are achieved. Compared with conventional materials, it has a higher removal rate while maintaining a roughly equivalent surface roughness.

[0020] In this invention, the above-described technical solutions can be combined with each other to achieve more preferred combinations. Other features and advantages of this invention will be set forth in the following description, and some advantages may become apparent from the description or be learned by practicing the invention. The objectives and other advantages of this invention can be realized and obtained from what is particularly pointed out in the description. Attached Figure Description

[0021] The accompanying drawings are for illustrative purposes only and are not intended to limit the invention. Throughout the drawings, the same reference numerals denote the same parts.

[0022] Figure 1 The images show the XRD patterns of the U-CeO2 material prepared in Example 1 and the CeO2 material prepared in Comparative Example 1 of this invention. Figure 2 This is a SEM image of the U-CeO2 material prepared in Example 1 of the present invention; Figure 3 This is a SEM image of the CeO2 material prepared in Comparative Example 1 of this invention; Figure 4 XPS images of the U-CeO2 material prepared in Example 1 and the CeO2 material prepared in Comparative Example 1 of this invention; Figure 5 Raman images of the U-CeO2 material prepared in Example 1 and the CeO2 material prepared in Comparative Example 1 of this invention; Figure 6 The removal rate (MRR) and surface roughness (Ra) of silicon wafers were measured by using the U-CeO2 material of Example 1 and the CeO2 material of the comparative example as polishing abrasives, respectively. Detailed Implementation

[0023] The technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only a part of the embodiments of the present invention, not all of the embodiments, and are not intended to limit the scope of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention. Furthermore, unless otherwise specified, the raw materials mentioned below are all commercially available products; and the process steps or preparation methods not mentioned in detail are all process steps or preparation methods known to those skilled in the art.

[0024] This invention provides a method for preparing a highly active cerium oxide material, comprising the following steps: S1. Prepare an aqueous solution of cerium nitrate; mix the aqueous solution of cerium nitrate and ethylene glycol, and place it in a high-pressure reactor for a solvothermal reaction to obtain the reactants; Specifically, the cerium nitrate is cerium(III) hexahydrate. The ethylene glycol has a purity of 99%.

[0025] According to some embodiments of the present invention, the molar concentration of the cerium nitrate aqueous solution is 0.2 to 0.8 mol / L. For example, the molar concentrations are 0.2 mol / L, 0.3 mol / L, 0.4 mol / L, 0.5 mol / L, 0.60 mol / L, 0.7 mol / L, and 0.8 mol / L. More preferably, the molar concentration is 0.4 to 0.6 mol / L.

[0026] It should be noted that the concentration of the cerium nitrate aqueous solution needs to be precisely controlled. Too high a concentration (>0.8 mol / L) will lead to an excessively fast subsequent solvothermal reaction rate, uneven nucleation of the precursor, and easy formation of impurities or particle agglomeration; too low a concentration (<0.2 mol / L) will reduce the yield and may affect the specific coordination structure of the precursor.

[0027] According to some embodiments of the present invention, the volume ratio of the cerium nitrate aqueous solution to ethylene glycol is 1~5:40~80. As examples, the volume ratio may be 1:40, 2:45, 3:50, 4:60, 5:80, or any range defined between two ratios. More preferably, the volume ratio is 2~4:50~70.

[0028] It should be noted that by adjusting the ratio window of cerium nitrate aqueous solution to ethylene glycol within a suitable range, a coordination-hydrolysis-alcoholization equilibrium can be achieved. This allows for the control of the precursor from four dimensions: phase, morphology, size, and defect structure, ultimately yielding a product with high oxygen vacancies and high Ce content. 3+ / Ce 4+ Cerium oxide materials with a higher content of trivalent cerium can reach 40-50%.

[0029] According to some embodiments of the present invention, the solvothermal reaction temperature is 155~180°C, and the reaction time is 900~1100 min. As an example, the reaction temperature can be 155°C, 160°C, 165°C, 170°C, 175°C, 180°C, or any range between two values. The reaction time can be 900 min, 950 min, 1000 min, 1050 min, 1100 min, or any range between two values.

[0030] It should be noted that by precisely controlling the reaction temperature and reaction time, incomplete reaction or poor crystallinity caused by excessively low temperature, and premature pyrolysis or excessive growth of precursors caused by excessively high temperature can be avoided.

[0031] According to the preparation method of the highly active cerium oxide material of the present invention, step S1 includes the following specific steps: dissolving cerium(III) hexahydrate in water to prepare a cerium nitrate aqueous solution. After stirring and mixing 1-5 mL of the cerium nitrate aqueous solution with a molar concentration of 0.2-0.8 mol / L with ethylene glycol to dissolve, the mixed solution is placed in a high-pressure reactor for a solvothermal reaction at a reaction temperature of 155-180℃ for a reaction time of 900-1100 min to obtain the reactant.

[0032] S2. The solid separated by filtration of the reactants is freeze-dried to obtain the precursor; Specifically, in step S2, the solid is dried to constant weight at -30 to 10°C. As an example, the drying temperature can be -30°C, -25°C, -20°C, -15°C, -10°C, -5°C, 0°C, 5°C, 10°C, or any range between two values.

[0033] It should be noted that the present invention uses freeze-drying process to replace conventional heating drying. In a low-temperature environment, the drying process uses a solid-gas interface instead of a conventional liquid-gas interface, which reduces the surface tension of the solvent and avoids structural collapse caused by capillary contraction force. This allows the precursor to maintain a better specific surface area, laying a good morphological foundation for obtaining highly active cerium oxide.

[0034] According to the preparation method of the highly active cerium oxide material of the present invention, step S2 includes the following specific steps: drying the solid separated by filtration of the reactants at -30~10℃ to obtain the precursor.

[0035] S3. After grinding the precursor, it is calcined in a vacuum environment to obtain the highly active cerium oxide.

[0036] Specifically, in step S3, the vacuum degree is 2~5 Pa. As an example, the vacuum degree can be 2 Pa, 3 Pa, 4 Pa, 5 Pa, or any range between two values. The calcination temperature is 700~800℃. As an example, the calcination temperature can be 700℃, 720℃, 740℃, 760℃, 780℃, 800℃, or any range between two values. More preferably, it is 700~750℃. The calcination time is 2~5 h. As an example, the calcination time can be 2 h, 2.5 h, 3 h, 3.5 h, 4 h, 4.5 h, 5 h, or any range between two values. More preferably, the calcination time is 2 h.

[0037] It should be noted that in this invention, a suitable vacuum is maintained during the calcination process to create an oxygen-deficient environment. When the organic ligands pyrolyze in this oxygen-deficient environment, they generate reducing gases such as CO, and may also partially carbonize into activated carbon. These components can reduce the CeO2 surface in situ, causing some CeO2 to... 4+ Reduced to Ce 3+ Simultaneously, a large number of oxygen vacancies are generated. The vacuum environment prevents external oxygen from filling these vacancies, preserving these high-defect states and achieving a delicate reaction equilibrium within the system, ultimately resulting in high Ce content. 3+ / Ce 4+ Cerium oxide particles with higher surface activity than those with lower surface activity.

[0038] According to the preparation method of the highly active cerium oxide material of the present invention, step S3 includes the following specific steps: grinding the precursor and then calcining it under vacuum, the calcination temperature being 700~800℃, more preferably 700~750℃, and the calcination time being 2~5 h, more preferably 2 h. Highly active cerium oxide is obtained after calcination.

[0039] The present invention also provides a highly active cerium oxide material, which is prepared by any of the above preparation methods.

[0040] Specifically, the particle size of the highly active cerium oxide material is 100~200 nm.

[0041] It should be noted that the highly active cerium oxide material prepared by the method of this invention has high Ce content. 3+ / Ce 4+ High specific gravity and high surface activity. Based on the advantageous properties of the highly active cerium oxide material provided by this invention, it is particularly suitable as a polishing abrasive for chemical mechanical polishing. Higher Ce content... 3+ The content significantly enhances the chemical reactivity of the polishing interface. Ce 3+Ce readily bonds specifically to the silanol groups (-Si-OH) on the SiO2 surface, forming a Ce-O-Si transition state, effectively softening and "passivating" the polished surface. This "chemical friction"-dominated process significantly reduces the mechanical shear force required for material removal, thereby reducing the generation of mechanical damage such as nanoscale scratches and pits at the source. This is crucial for achieving sub-nanometer surface roughness and zero-defect photomask manufacturing. Secondly, abundant Ce... 3+ The improved site enhances the redox buffering capacity of the material, enabling the polishing process to maintain a stable chemical reaction rate within a wider process window, thus improving the controllability and consistency of the process.

[0042] This invention also provides the application of the aforementioned highly active cerium oxide material in chemical mechanical polishing. Specifically, it can be used as a polishing abrasive to prepare a polishing slurry for polishing third-generation semiconductor materials, silicon wafers, etc. Using the highly active cerium oxide prepared by this invention as a polishing abrasive, the removal rate MRR > 200 nm / min and the surface roughness Ra < 0.3 nm show a higher removal rate compared to conventional materials while maintaining approximately the same surface roughness.

[0043] To more clearly describe the present invention, the following embodiments and comparative examples are provided for further illustration.

[0044] The analysis and detection methods in the following embodiments include: XRD (X-ray diffraction): Tested using an X'Pert PRO X-ray diffractometer.

[0045] SEM (Scanning Electron Microscopy): Tests were performed using a ZEISS Sigma 500 field emission scanning electron microscope.

[0046] XPS (X-ray photoelectron spectroscopy): X-ray photoelectron spectroscopy (XPS) was performed at room temperature using a Thermo Scientific K-Alpha spectrometer.

[0047] Raman: Raman testing was performed using Horiba LabRAM HR Evolution.

[0048] Example 1 A method for preparing a highly active cerium oxide (U-CeO2) material includes the following steps: S1. Prepare a 0.5 mol / L aqueous solution of cerium(III) nitrate by dissolving it in water. Mix 4 mL of the 0.5 mol / L aqueous solution of cerium nitrate with 60 mL of ethylene glycol and stir to dissolve. Place the mixture in a high-pressure reactor for a solvothermal reaction at 160 °C for 960 min to obtain the reactants.

[0049] S2. The solid separated by filtration of the reactants is dried at -30°C to obtain the precursor.

[0050] S3. After grinding the precursor, it is calcined in a vacuum environment (vacuum degree 2 Pa) at a temperature of 700℃ for 2 h to obtain highly active cerium oxide.

[0051] Comparative Example 1 A method for preparing cerium oxide (CeO2) material includes the following steps: S1. Dissolve cerium(III) nitrate hexahydrate in water to prepare... Dispose of a 0.5 mol / L aqueous solution of cerium nitrate. Mix 4 mL of the 0.5 mol / L aqueous solution of cerium nitrate with 60 mL of ethylene glycol and stir to dissolve. Place the mixture in a high-pressure reactor for a solvothermal reaction at 160 °C for 960 min to obtain the reactants.

[0052] S2. The solid separated by filtration of the reactants is dried in an oven at 100°C to obtain the precursor.

[0053] S3. After grinding the precursor, it is calcined in air at a temperature of 700℃ for 2 hours to obtain cerium oxide.

[0054] Performance testing The highly active cerium oxide (U-CeO2) prepared in Example 1 and the cerium oxide (CeO2) prepared in Comparative Example 1 were subjected to XRD, SEM, XPS, and Raman tests, respectively. The results are as follows: Figures 1-5 As shown.

[0055] Depend on Figure 1 It can be seen that the XRD diffraction peaks of U-CeO2 in Example 1 and CeO2 in Comparative Example 1 both correspond to the cerium oxide diffraction peaks identified in the standard PDF card JCPDS No. 34-0394, and the characteristic peaks of the XRD patterns are sharp, indicating that the materials prepared in Example 1 and Comparative Example 1 are both cerium oxide crystals with good crystallinity.

[0056] Depend on Figure 2 and Figure 3 It can be seen that the U-CeO2 particles prepared in Example 1 have good morphology, uniform particle size, and a particle size of 100~200 nm. The CeO2 particles prepared in Comparative Example 1 have uniform morphology, better dispersibility, and a particle size of 100~200 nm.

[0057] Depend on Figure 4It can be seen that the trivalent cerium content of U-CeO2 prepared in Example 1 is 49.95%. The trivalent cerium content of CeO2 prepared in Comparative Example 1 is 37.05%. It is evident that the trivalent cerium content of the highly active cerium oxide material prepared in Example 1 is significantly higher than that in Comparative Example 1.

[0058] Depend on Figure 5 It can be seen that the peak position ratio of U-CeO2 in Example 1 is 0.93, while that of CeO2 in Comparative Example 1 is 0.11. This indicates that the proportion of defect peak intensity to main peak in the U-CeO2 material of Example 1 is significantly higher than that in the CeO2 material of Comparative Example 1. The CeO2 material of Comparative Example 1 has good crystallinity and fewer oxygen vacancies. In contrast, the U-CeO2 material of Example 1 has a large number of oxygen vacancies or lattice defects.

[0059] The materials prepared in Example 1 and Comparative Example 1 were used as polishing abrasives to polish 2-inch silicon wafers. The polishing method employed a known silicon wafer polishing process, and the polishing parameters are shown in Table 1.

[0060] Table 1 Polishing parameters

[0061] Depend on Figure 6 It can be seen that the surface roughness Ra after polishing with the U-CeO2 material of Example 1 is 0.248 nm, while the surface roughness Ra after polishing with the CeO2 material of Comparative Example 1 is 0.221 nm. The surface finish after polishing is not significantly different between the two. However, the removal rate MRR of the U-CeO2 material is 234.12 nm / min, while that of the CeO2 material is 157.36 nm / min. This indicates that the removal rate of the U-CeO2 material of Example 1 is significantly higher than that of the CeO2 material of Comparative Example 1, achieving higher polishing efficiency while maintaining surface finish.

[0062] Example 2 A method for preparing a highly active cerium oxide (U-CeO2) material includes the following steps: S1. Prepare a 0.2 mol / L aqueous solution of cerium(III) nitrate by dissolving cerium(III) hexahydrate in water. Mix 5 mL of the 0.2 mol / L aqueous solution of cerium nitrate with 40 mL of ethylene glycol and stir to dissolve. Place the mixture in a high-pressure reactor for a solvothermal reaction at 180℃ for 900 min to obtain the reactants.

[0063] S2. The solid separated by filtration of the reactants is dried at -10℃ to obtain the precursor.

[0064] S3. After grinding the precursor, it is calcined in a vacuum environment (vacuum degree 5 Pa) at a temperature of 750℃ for 2.5 h to obtain highly active cerium oxide.

[0065] Example 3 A method for preparing a highly active cerium oxide (U-CeO2) material includes the following steps: S1. Prepare a 0.8 mol / L aqueous solution of cerium(III) nitrate by dissolving it in water. Mix 2 mL of the 0.8 mol / L aqueous solution of cerium nitrate with 50 mL of ethylene glycol and stir to dissolve. Place the mixture in a high-pressure reactor for a solvothermal reaction at 160 °C for 960 min to obtain the reactants.

[0066] S2. The solid separated by filtration of the reactants is dried at -30°C to obtain the precursor.

[0067] S3. After grinding the precursor, it is calcined in a vacuum environment (vacuum degree 2 Pa) at a temperature of 700℃ for 2 h to obtain highly active cerium oxide.

[0068] The highly active cerium oxides prepared in Examples 2 and 3 exhibited uniform particle size and good morphology, with trivalent cerium contents of 43.26% and 45.68%, respectively, and chemical activity comparable to that of Example 1. Using the highly active cerium oxides prepared in Examples 2 and 3 as polishing abrasives, silicon wafers were polished according to the polishing parameters in Table 1. Example 2 achieved a removal rate (MRR) of 288.36 nm / min and a surface roughness (Ra) of 0.220 nm. Example 3 achieved a removal rate (MRR) of 215.38 nm / min and a surface roughness (Ra) of 0.230 nm.

[0069] It is evident that the highly active cerium oxide material prepared by the method of this invention, when used as a polishing abrasive, exhibits higher activity and, while ensuring surface smoothness, possesses higher polishing efficiency.

[0070] The above description is only a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any changes or substitutions that can be easily conceived by those skilled in the art within the scope of the technology disclosed in the present invention should be included within the scope of protection of the present invention.

Claims

1. A method for preparing a highly active cerium oxide material, characterized in that, Includes the following steps: S1. Prepare an aqueous solution of cerium nitrate; mix the aqueous solution of cerium nitrate and ethylene glycol, and place it in a high-pressure reactor for a solvothermal reaction to obtain the reactants; S2. The solid separated by filtration of the reactants is freeze-dried to obtain the precursor; S3. After grinding the precursor, it is calcined in a vacuum environment to obtain the highly active cerium oxide.

2. The method for preparing a highly active cerium oxide material according to claim 1, characterized in that, In step S1, the cerium nitrate is cerium(III) hexahydrate.

3. The method for preparing a highly active cerium oxide material according to claim 1, characterized in that, In step S1, the molar concentration of the cerium nitrate aqueous solution is 0.2~0.8 mol / L.

4. The method for preparing a highly active cerium oxide material according to claim 1, characterized in that, In step S1, the volume ratio of the cerium nitrate aqueous solution to ethylene glycol is 1~5:40~80.

5. The method for preparing a highly active cerium oxide material according to claim 1, characterized in that, In step S1, the reaction temperature is 155~180℃ and the reaction time is 900~1100 min.

6. The method for preparing a highly active cerium oxide material according to claim 1, characterized in that, In step S2, the solid is dried to constant weight at -30~10℃.

7. A method for preparing a highly active cerium oxide material according to claim 1, characterized in that, In step S3, the vacuum level is 2~5 Pa.

8. A method for preparing a highly active cerium oxide material according to claim 1, characterized in that, In step S3, the calcination temperature is 700~800℃ and the calcination time is 2~5 h.

9. A highly active cerium oxide material, characterized in that, It is prepared by the preparation method of a highly active cerium oxide material as described in any one of claims 1 to 8.

10. An application of the highly active cerium oxide according to claim 9 in a chemical mechanical polishing process.

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