Preparation of high-uniformity cerium oxide abrasive material and application of high-uniformity cerium oxide abrasive material in chemical mechanical polishing solution

Abstract

The invention discloses preparation of a high-uniformity cerium oxide abrasive material and application of the high-uniformity cerium oxide abrasive material in a chemical mechanical polishing solution. According to a method, cerium nitrate or cerium oxalate is used as a cerium source, a cationic or nonionic surfactant is used as a structure-directing agent, and the high-uniformity cerium oxide abrasive material is prepared in a mixed solvent system formed by water and isopropanol or water and diethylene glycol according to a specific volume ratio. The preparation method comprises the following steps: regulating the particle size and the morphology structure through a solvothermal reaction, carrying out cleaning, drying and high-temperature calcination treatment on a reaction product to obtain sphere-like cerium oxide nano-particles with high particle size concentration ratio, moderate surface roughness and good dispersity, adding cerium oxide powder into deionized water, and carrying out ultrasonic dispersion to obtain the spherical cerium oxide nano-particles. And sequentially adding a dispersing agent and amino acid while stirring, uniformly stirring, fixing the volume, and adding a pH regulator to enable the solution to be weakly acidic, thereby obtaining the chemical mechanical polishing solution. The cerium oxide submicron powder which is different in surface appearance, particle size and distribution uniformity is prepared by adjusting the solvent ratio and other reaction conditions.

Description

Technical Field

[0001] This invention relates to the field of inorganic nanomaterial synthesis and surface treatment technology, and particularly to the preparation of highly uniform cerium oxide abrasives and their application in chemical mechanical polishing slurries. Background Technology

[0002] In chemical mechanical polishing (CMP) processes, cerium oxide is widely used as a polishing abrasive due to its moderate hardness, good chemical activity, and reactivity with various material surfaces. It is one of the key functional components for achieving efficient and low-damage polishing. Since cerium oxide submicron powder plays a major abrasive role in polishing slurry, it needs to have a uniform particle size distribution and an approximately spherical particle morphology to reduce mechanical scratches. Therefore, the preparation method of cerium oxide is crucial. However, cerium oxide abrasives synthesized by traditional methods still have significant deficiencies in terms of particle size uniformity, morphology control, dispersibility, and crystal integrity. This directly affects its dispersion stability, polishing efficiency, and surface treatment effect in polishing slurry. Specifically, the current technology mainly has the following problems: (1) Uneven particle size distribution: Most traditional preparation methods are difficult to control the nucleation rate and grain growth rate at the same time, which easily leads to a wide particle size distribution, a shift in the median particle size, and is not conducive to the stability control of polishing slurry and the optimization of surface morphology in CMP processes. (2) Inconsistent morphology and lack of secondary structure: Cerium oxide particles are prone to forming spherical, rod-shaped or irregular aggregates during the synthesis process. (3) Severe particle agglomeration: Due to the high surface energy during the synthesis process, severe agglomeration often occurs, making it difficult to achieve good particle dispersion, which in turn affects the dispersion stability and process control of the polishing slurry. (4) Single solvent system and poor reaction adjustability: In most conventional hydrothermal or sol-gel methods, only water is used as the solvent. The surface tension of the system is high, the ion migration rate is fast, the reaction process is unstable, the particle morphology and size are difficult to control precisely, and the crystallinity of the product is insufficient. (5) Low specific surface area and limited chemical activity: The CeO2 particles obtained by some methods are dense and smooth, lacking microporous structure and hierarchical structure, resulting in a limited reaction contact area with the workpiece being polished, thereby inhibiting its polishing efficiency. Summary of the Invention

[0003] To address the aforementioned shortcomings, this invention proposes the preparation of highly uniform cerium oxide abrasives and their application in chemical mechanical polishing (CMP) slurries. By adjusting the solvent ratio and other reaction conditions, submicron cerium oxide powders with varying surface morphology, particle size, and uniformity of distribution can be prepared. Furthermore, by controlling the reaction conditions, secondary particles with hierarchical surface structures can be formed. These submicron cerium oxide powders are expected to play an important role in improving CMP efficiency, reducing surface damage, and optimizing the stability of polishing slurries.

[0004] To achieve the above objectives, the present invention provides the following technical solution: preparation of highly uniform cerium oxide abrasive, comprising the following steps: S1: Weigh a soluble cerium source and one or two surfactants and dissolve them together in a first mixed solvent composed of alcohol and water in a volume ratio of 1:1 to 3:1. This allows the alcohol to reduce the polarity of water, thereby slowing down the hydrolysis rate of cerium ions and avoiding uneven particle size caused by rapid precipitation. Stir at room temperature for at least 30 minutes to ensure that all components are completely dissolved and form a stable and homogeneous first solution. S2: After transferring the first solution into a high-pressure reactor lined with polytetrafluoroethylene, heat it at a temperature of 150℃-200℃ for 16-24 hours. The surfactant and the first mixed solvent work together to guide the primary particles to assemble into sheet-like, rod-like, or petal-like secondary structural units, which are then further bent, coiled, or radially assembled to form a relatively dense but porous flower-like spherical multi-level structure. After heating, the structure is allowed to cool naturally to room temperature. S3: Take out the reaction product and wash it several times by centrifuging at 9000-11000 rpm for 1-5 minutes with a second mixed solvent containing pure water and ethanol in a 1:1 volume ratio to remove reaction residues, unreacted substances and surface adsorbed impurities. S4: The cleaned product is vacuum dried at 70℃-90℃ for 9-15 hours to ensure complete drying. Then, the dried product is placed in a muffle furnace and calcined at 500℃-650℃ in air for 1-4 hours to further improve its crystal structure and remove organic residues, ultimately obtaining high-purity cerium oxide particles with uniform particle size distribution and a flower-like multi-level structure.

[0005] As an improvement, the alcohol used in the first mixed solvent in step S1 is any one of ethanol, propanol, isopropanol, n-butanol, octanol, and diethylene glycol.

[0006] As an improvement, the soluble cerium source in step S1 is any one of cerium chloride, cerium nitrate, cerium oxalate, cerium ammonium nitrate, and cerium perchlorate, and the surfactant is any one or any two of octadecyltrimethylammonium chloride, hexadecyltrimethylammonium bromide, tetradecyltrimethylammonium chloride, dodecyltrimethylammonium chloride, benzyldodecyldimethylammonium chloride, hexadecyldimethylphenylammonium chloride, dodecyldimethylamine hydrochloride, sodium disulfosuccinate, and polyvinylpyrrolidone.

[0007] As an improvement, the soluble cerium source is cerium nitrate, the surfactant is polyvinylpyrrolidone, and the alcohol in the first mixed solvent is isopropanol or diethylene glycol, with a volume ratio of alcohol to water of 3:1.

[0008] As an improvement, the heating temperature in step S2 is 160℃-180℃, and the heating time is 18-20 hours.

[0009] As an improvement, the calcination temperature in step S4 is 550℃-600℃, and the calcination time is 1.7-2.2 hours.

[0010] As an improvement, the cerium oxide particles obtained in step S4 have a size of 250-550 nm and a specific surface area of ​​5.44-7.60 m². 2 / g, and the particle size distribution is uniform with no agglomeration.

[0011] For example, the application of highly uniform cerium oxide abrasives in chemical mechanical polishing slurries, as described above, involves the following steps in preparing the chemical mechanical polishing slurry: S5: Weigh the cerium oxide powder obtained in step S4 and add it to deionized water. While stirring, add the dispersant and amino acids in sequence to obtain the third mixed solution. S6: After the third mixed solution is stirred evenly, the volume is adjusted and a pH adjuster is added to make the third mixed solution weakly acidic. Stirring is continued for 50-70 minutes to obtain a chemical mechanical polishing solution.

[0012] As an improvement, the dispersant is any one of polyvinyl alcohol, polyvinylpyrrolidone, sodium polyacrylate, sodium dodecyl sulfonate, and hexadecyltrimethylammonium bromide; the amino acid is any one of alanine, leucine, tryptophan, proline, serine, and threonine; and the pH adjuster is any one or any two of hydrochloric acid, nitric acid, sulfuric acid, acetic acid, citric acid, phosphoric acid, sodium hydroxide, potassium hydroxide, ammonia, triethanolamine, ethanolamine, or phosphate.

[0013] As an improvement, the dispersant is hexadecyltrimethylammonium bromide or polyvinylpyrrolidone, the amino acid is proline, and the pH adjuster is a combination of citric acid and ammonia.

[0014] Compared with the prior art, the advantages of the present invention are as follows: By controlling the solvent polarity using alcohol / water mixed solvents with volume ratios of 1:1 to 3:1, especially at a volume ratio of 3:1, the polarity of water is reduced, the hydrolysis rate of cerium ions is slowed down, and particle uniformity is improved. Combined with specific surfactants (such as polyvinylpyrrolidone and quaternary ammonium salts), the formation and growth of cerium oxide crystal nuclei are precisely guided. Through electrostatic interactions, CeO2 crystal faces are selectively bonded, guiding the product to exhibit a flower-like, multi-level structure, achieving a narrow particle size distribution of 250-550 nm and a particle size of 5.44-7.60 μm. 2The high specific surface area ( / g), lack of agglomeration, and the enhanced flexibility of the hydrophobic chains of surfactant molecules in a high-alcohol environment increase their coating density on the crystal plane, thus solving the problems of agglomeration and morphological distortion. Then, the hydrothermal temperature is precisely controlled at 160-180℃, and the reaction time is 18-20 hours. This method is energy-efficient, simple to operate, and ensures crystallinity and purity. Multiple centrifugal washes using a 1:1 mixture of alcohol and water at 9000-11000 rpm efficiently remove unreacted substances and adsorbed impurities. Finally, high-temperature calcination at 500-650℃ completely decomposes organic matter, resulting in CeO2 particles with low surface impurity content and high crystallinity. These particles are less prone to releasing impurities or forming scratches during polishing, making them suitable for semiconductor wafer materials requiring extremely high surface cleanliness. Furthermore, different amino acids, pH adjusters, and dispersants can be flexibly selected according to different application requirements, exhibiting good versatility and controllability. The surfactant-modified CeO2 particles demonstrate excellent dispersibility in polishing solutions. For example, when combined with a cetyltrimethylammonium bromide / polyvinylpyrrolidone dispersant, the cerium oxide particles, after surfactant modification and appropriate dispersant formulation control, can remain stable in the aqueous polishing solution, resisting sedimentation and aggregation, thus maintaining the uniformity and continuous stability of the polishing solution, improving service life and polishing consistency. Simultaneously, amino acids assist polishing, such as proline, enhancing the chemimechanical synergy to meet the high precision requirements of semiconductors. pH adjusters, such as a citric acid / ammonia combination, make the chemimechanical polishing solution weakly acidic, achieving semiconductor-grade polishing consistency. The preparation process uses water / alcohol as the reaction medium, avoiding toxic organic solvents; the entire process is solvent-free, conforming to the trend of green chemistry. Moreover, the process is simple, the raw materials are readily available, and it has the foundation for large-scale production. Attached Figure Description

[0015] The present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments: Figure 1 The images are scanning electron microscope (SEM) images of CeO2 microspheres, where (a) is a scanning electron microscope (SEM) image of CeO2 microspheres obtained in Example 1, (b) is a scanning electron microscope (SEM) image of CeO2 microspheres obtained in Example 2, (c) is a scanning electron microscope (SEM) image of CeO2 microspheres obtained in Example 3, and (d) is a scanning electron microscope (SEM) image of CeO2 microspheres obtained in Example 4. Figure 2 This is a transmission electron microscope (TEM) image of the CeO2 microspheres obtained in Example 4; Figure 3The figures are the particle size distribution curves of CeO2 microspheres, where (a) is the particle size distribution curve of CeO2 microspheres obtained in Example 1, (b) is the particle size distribution curve of CeO2 microspheres obtained in Example 2, (c) is the particle size distribution curve of CeO2 microspheres obtained in Example 3, and (d) is the particle size distribution curve of CeO2 microspheres obtained in Example 4. Figure 4 The XRD patterns of CeO2 microspheres obtained in Examples 1, 2, 3, and 4 are shown. Figure 5 Fourier transform infrared (FTIR) spectra of CeO2 microspheres obtained in Examples 1, 2, 3, and 4; Figure 6 The precipitation effect of polishing solutions 1-6 after being left for 12h (a), 24h (b), 36h (c), 48h (d), 60h (e), and 72h (f), respectively; Figure 7 Flatness of wafers after polishing with different polishing solutions under different conditions. Detailed Implementation

[0016] Example 1 S1: Weigh 1.304 g (3 mmol) of cerium nitrate hexahydrate (Ce(NO3)3·6H2O) as the cerium source, and weigh 0.72 g (0.2 mmol) of hexadecyltrimethylammonium bromide (CTAB) as the surfactant. Add the two to the first mixed solvent prepared by mixing 10 mL of pure water and 30 mL of isopropanol in a volume ratio of 1:3. The alcohol reduces the polarity of water to slow down the hydrolysis rate of cerium ions, thereby avoiding uneven particle size caused by rapid precipitation. Stir with a magnetic stirrer at room temperature for at least 30 minutes to completely dissolve all components and form a stable, homogeneous, clear and transparent first solution. S2: The first solution is transferred to a high-pressure reactor lined with 100 mL of polytetrafluoroethylene (PTFE), sealed, and placed in a constant temperature oven. The reaction temperature is set to 180°C and heated continuously at this temperature for 18 hours. Hexadecyltrimethylammonium bromide (CTAB) and the first mixed solvent synergistically guide the primary particles to approach and combine with each other in a specific orientation and manner, assembling into sheet-like, rod-like, or petal-like secondary structural units, which are then further bent, coiled, or radially assembled and aggregated to form a relatively dense but porous flower-like spherical multi-level structure. After heating, the mixture is naturally cooled to room temperature to obtain a suspension of the reaction product. S3: Centrifuge the suspension at 10,000 rpm for 3 minutes, collect the precipitate, place the precipitate in a 1:1 mixture of pure water and ethanol, and clean it by ultrasonication. Repeat the centrifugation and cleaning steps 3 to 5 times to effectively remove reaction residues, unreacted raw materials and adsorbed impurities on the surface of particles. S4: The cleaned solid product was vacuum dried at 80℃ for 12 hours to ensure complete drying and dehydration. The dried product was then placed in a muffle furnace and calcined at 600℃ for 2 hours in air to further refine its crystal structure and remove residual organic matter, ultimately yielding a high-purity product with high sphericity and uniform particle size distribution (median particle size D). 50 (510nm) and specific surface area of ​​5.44m² 2 / g of cerium oxide particles; S5: Weigh 1.5g of cerium oxide powder obtained in step S4 and add it to 50mL of deionized water. While stirring, add 0.15g of hexadecyltrimethylammonium bromide and 0.1g of proline to obtain the third mixed solution. S6: After the third mixed solution is stirred evenly, the volume is adjusted to 100 mL, and the pH is adjusted to 4.0 by adding citric acid / ammonia water combination. Stirring is continued for 60 minutes to obtain the chemical mechanical polishing solution, which is labeled as No. 1.

[0017] Example 2 In S1, 1.06 g (1.5 mmol) of cerium oxalate decahydrate (Ce2(C2O4)3·10H2O) was weighed as the cerium source, and 1.30 g (0.13 mmol) of polyvinylpyrrolidone (PVP) with a relative molecular mass of 10000 was weighed as the surfactant. The reaction is carried out in S2 by heating for 20 hours; The median particle size D was obtained in S4. 50 It has a wavelength of 1318 nm and a specific surface area of ​​2.36 m². 2 / g of CeO2 particles; The chemical mechanical polishing fluid obtained in S6 is marked as No. 2.

[0018] The rest is the same as in Example 1, so it will not be repeated here.

[0019] Example 3 In S1, 1.30 g (0.13 mmol) of polyvinylpyrrolidone (PVP) with a relative molecular mass of 10000 was weighed out as a surfactant, and the two were added sequentially to the first mixed solvent prepared by mixing 10 mL of pure water and 30 mL of diethylene glycol in a volume ratio of 1:3. The reaction is carried out in S2 by heating for 20 hours; S4 was calcined at 550℃ for 2 hours in air atmosphere to obtain a product with high purity, high sphericity, and uniform particle size distribution (median particle size D). 50 (296nm) and specific surface area of ​​6.89m² 2 / g of CeO2 particles; The chemical mechanical polishing fluid obtained in S6 is marked as No. 3.

[0020] The rest is the same as in Example 1, so it will not be repeated here.

[0021] Example 4 In S1, the two are added sequentially to the first mixed solvent prepared by 10 mL of pure water and 30 mL of isopropanol in a volume ratio of 1:3. In S2, the reaction temperature is set to 160°C, and the reaction is continuously heated at this temperature for 18 hours. S4 was calcined at 600℃ for 2 hours in air to obtain a product with high purity, high sphericity, and uniform particle size distribution (median particle size D). 50 (510nm) and specific surface area of ​​7.60m² 2 / g of CeO2 particles; In step S5, take three 1.5g portions of CeO2 powder obtained in step S4 and add them to 50mL of deionized water. These samples are numbered 4, 5, and 6. While stirring, add a dispersant. No dispersant is added to sample 4, 0.15g of polyvinylpyrrolidone is added to sample 5, and 0.15g of cetyltrimethylammonium bromide is added to sample 6. The chemical mechanical polishing slurries marked 4, 5, and 6 were obtained in S6.

[0022] The rest is the same as in Example 3, so it will not be repeated here.

[0023] like Figure 1 (a), (b), (c), and (d) are scanning electron microscope images of CeO2 microspheres from Examples 1, 2, 3, and 4, respectively. Figure 1 The particles shown in diagram a have a distinct rough texture on their surface and a particle size of approximately 500 nm. This is consistent with the particle size analysis diagram (median diameter D). 50 The particle size is 510 nm, and the surface is rough with good particle dispersion. No obvious agglomeration was observed. Figure 1 The particles shown in b were formed by the interaction of cerium oxalate precursor and PVP. They are generally spherical, but the particle size distribution is uneven. This is consistent with the particle size analysis diagram (median diameter D). 50 (1318nm), there is obvious agglomeration and particle connection, loose structure, smooth surface, lack of layering, this morphology is not conducive to improving specific surface area and surface activity; Figure 1 The particles shown in c are spherical, uniformly distributed, and densely packed, with a particle size concentrated around 300 nm. This is consistent with the particle size analysis diagram (median diameter D). 50 It has a wavelength of 296 nm and a rough surface with obvious hierarchical structure and three-dimensional fractal characteristics; Figure 1 Image d shows a scanning electron microscope (SEM) image of cerium oxide (CeO2) particles prepared using a specific dispersant and solvent system. The particles exhibit a highly regular spherical structure with a concentrated size distribution and an average particle size of approximately 250 nm. This is combined with a particle size analysis diagram (median diameter D). 50It has a wavelength of 259 nm, and its arrangement is dense and well dispersed with no obvious aggregation, resulting in the best overall performance.

[0024] like Figure 2 This is a transmission electron microscope (TEM) image of the CeO2 microspheres obtained in Example 4. Figure 2 (a) shows that CeO2 microspheres are formed by the aggregation of multiple nanoscale primary particles, exhibiting a regular spherical secondary structure; Figure 2 (b) Clear lattice fringes are visible, and the (111) crystal plane indicated by the arrow corresponds to the typical fluorite-type crystal structure of CeO2 (face-centered cubic (FCC)), indicating its good crystallinity. The presence of lattice fringes suggests that the particles are single crystals or highly oriented crystallized regions, and the interplanar spacing of the (111) crystal plane is approximately 0.30 nm. This microstructure helps to improve the dispersibility and specific surface area of ​​CeO2 powder, thereby enhancing its performance as an abrasive in polishing slurries.

[0025] like Figure 3 As shown in (a), (b), (c), and (d), these are the particle size distribution curves of CeO2 microspheres from Examples 1, 2, 3, and 4, respectively. The main peak position of the particle size distribution of CeO2 microspheres in Example 1 is approximately 510 nm, in Example 2 it is approximately 1318 nm, in Example 3 it is approximately 396 nm, and in Example 4 it is approximately 259 nm. All four curves exhibit a typical normal distribution, with relatively concentrated and narrow particle size distribution and low dispersion.

[0026] Figure 4 The X-ray powder diffraction (XRD) patterns of CeO2 microspheres obtained in Examples 1 to 4 are shown. Comparison with the standard diffraction card PDF#00-034-0394 reveals that all four samples exhibit characteristic diffraction peaks of CeO2, with no impurity peaks observed. This indicates that the prepared samples are all single pure phases with consistent crystal phases and no new phase formation. The sample obtained under optimal synthesis conditions has a calculated lattice constant of a = 5.410 Å, consistent with the lattice parameter (0.5411 nm) of standard cubic CeO2, indicating a stable crystal structure.

[0027] Figure 5 The infrared spectra of CeO2 microspheres from Examples 1 to 4 are shown to analyze the changes in surface functional groups of samples under different synthesis conditions. (Infrared spectra at 3400 cm⁻¹) －1 The broad peaks appearing nearby are attributed to O–H stretching vibrations, mainly from adsorbed water and surface hydroxyl groups; their intensity is affected by drying and sintering conditions; 2800–3000 cm⁻¹ －1 Regional peaks (e.g., 2930 and 2848 cm) －1The corresponding C–H stretching vibration indicates the possible presence of residual organic solvents or precursors in the sample, reflecting the differences in the degree of organic residue under different synthesis conditions; 1650–1570 cm⁻¹ －1 The peaks in this region originate from the bending vibrations of adsorbed water or hydroxyl interactions, and may also involve residual C=O groups; 1500–1400 cm⁻¹ －1 The peaks within the range are associated with carbonate or carbon-oxygen functional groups, indicating that the CeO2 surface readily adsorbs CO2, forming corresponding species. The changes in peak intensity reflect different surface chemical states; in the 400–500 cm⁻¹ range... －1 In this region, a characteristic peak of Ce–O stretching vibration (480 cm⁻¹) appears. －1 The infrared signal ( ) is typical of the CeO2 crystal structure, indicating that the prepared sample has good structural stability.

[0028] like Figure 6 The changes in polishing slurries 1–6 after standing in colorimetric tubes for 12, 24, 36, 48, 60, and 72 hours, as shown, demonstrate the differences in dispersion stability among the samples. Polishing slurry 2 completely precipitated within 24 hours, indicating that the larger CeO2 particles were prone to agglomeration and were unsuitable as abrasives. Polishing slurry 4, although without a dispersant, exhibited good hydrophilicity and dispersibility due to the smaller CeO2 particle size and higher surface hydroxyl density, maintaining good stability for a short period. Polishing slurry 5, with the addition of PVP, showed good initial dispersion, but its settling rate within 72 hours was lower than that of slurry 4, indicating that PVP provided some steric hindrance through physical adsorption. However, the stability of the PVP adsorption layer was poor in an acidic environment, with significant sedimentation and stratification occurring after 48 hours, and the dispersion performance decreasing over time. In contrast, polishing slurries 1, 3, and 6 (with the addition of CTAB) showed better dispersion, especially slurry 6, which maintained good suspension even after 72 hours. This result is attributed to the smaller CeO2 particle size (D... 50 The larger specific surface area (259 nm) is closely related to the adsorption of more dispersant molecules CTAB as cations. Its positive charge can form a stable electrostatic adsorption layer with the negative charge on the CeO2 surface. At the same time, it significantly inhibits particle aggregation through steric hindrance. The small-diameter CeO2 surface is rich in hydroxyl groups and has a uniform charge distribution, which further enhances the binding with CTAB, thereby improving the overall dispersion stability.

[0029] To verify the performance of the polishing slurry in actual wafer removal, we conducted CMP polishing experiments with polishing slurries 1-6 under different pressures and rotation speeds. Here, PS (Platform speed) represents the rotation speed of the polishing disc, HS (Head speed) represents the rotation speed of the polishing head, and the polishing rate is the ratio of the difference in wafer thickness before and after polishing to time. The results are shown in Table 1 below. Table 1 Polishing rates of polishing slurries 1-6 under different conditions We can observe that the optimal polishing slurry (No. 6) formulation is CeO2 + CTAB, with polishing conditions of 117 / 123 rpm and 3 psi, achieving a silica removal rate as high as 3846 Å / min (the highest). This is mainly due to the dispersion effect of small-sized CeO2 combined with CTAB, resulting in optimal particle dispersibility and catalytic activity. Simultaneously, high rotation speed and high pressure enhance the synergistic effect of mechanical and chemical processes. The next best polishing slurry is (No. 5), with polishing conditions of 117 / 123 rpm and 3 psi, achieving a silica removal rate of 3257 Å / min. This is mainly because PVP provides good particle dispersibility, but the dispersibility is slightly weaker than CTAB, resulting in a slightly lower removal rate. The lowest polishing rate (No. 2) formulation, with polishing conditions of 87 / 93 rpm and 3 psi, has a silica removal rate of only 1683 Å / min. This is mainly because large CeO2 particles cause particle agglomeration, reducing particle dispersibility and the effectiveness of the polishing slurry. Furthermore, the abrasive particles are rapidly flushed out of the polishing pad during polishing.

[0030] The following conclusions can be drawn from the study of different formulations and polishing conditions: (1) Small-sized CeO2 particles are superior to large-sized CeO2 particles. Small-sized CeO2 particles, due to their larger specific surface area and higher surface hydroxyl density, exhibit stronger hydrophilicity and dispersion stability. Their surface provides more adsorption sites, which is beneficial for the binding of dispersants. Simultaneously, the uniform surface charge distribution allows for the formation of a stable electrical bilayer, enhancing electrostatic repulsion between particles and inhibiting aggregation and sedimentation. In contrast, large-sized particles are prone to rapid sedimentation due to gravity and surface energy differences, exhibiting poor stability. Furthermore, small particles more readily form a stable adsorption layer with cationic dispersants such as CTAB, further improving dispersion and the performance of the polishing solution. Therefore, considering colloidal stability and surface chemical properties, small-sized CeO2 is significantly superior to large-sized particles in polishing applications.

[0031] (2) Effect of dispersant on particle dispersibility and polishing rate Dispersants are crucial in polishing slurries, effectively improving the dispersibility and stability of abrasive particles, preventing agglomeration and sedimentation, and extending service life. The cationic dispersant CTAB significantly enhances dispersion through electrostatic adsorption on the surface of CeO2 particles, combined with steric hindrance. At pH 4, CTAB firmly adsorbs onto the particle surface, not only inhibiting agglomeration but also improving the contact efficiency between particles and the workpiece surface, thereby accelerating material removal. In contrast, the nonionic dispersant PVP mainly relies on steric hindrance, resulting in slightly inferior dispersion and polishing performance. Overall, the type and mechanism of action of the dispersant have a decisive impact on the performance of the polishing slurry.

[0032] (3) Effect of polishing conditions on removal rate Polishing conditions significantly affect the material removal rate. Higher rotational speeds (117 / 123 rpm) enhance the sliding friction and shear force of the abrasive particles, improving mechanical removal efficiency. Simultaneously, higher pressure (3 psi) strengthens the contact between the particles and the wafer surface, effectively promoting the synergistic effect of mechanical and chemical processes. Under optimized conditions, polishing slurry formulation No. 6, with small-sized CeO2 particles and added CTAB, exhibits the highest polishing rate (3846 Å / min). In contrast, large-sized CeO2 (polishing slurry No. 2) suffers from severe particle agglomeration and poor dispersibility, resulting in a lower removal rate of only 1683 Å / min. These results demonstrate that good dispersibility and reasonable process parameters are crucial for efficient polishing.

[0033] In summary, smaller CeO2 combined with CTAB dispersant exhibits the best polishing performance under high rotation speed and high pressure conditions, providing a theoretical basis and experimental support for optimizing CMP polishing slurry formulations and process design.

[0034] Wafer flatness after CMP To further evaluate the impact of polishing slurries on wafer surface quality, we measured the surface roughness (Sq) of wafers polished with polishing slurries 1 to 6 under different conditions. The results are as follows: Figure 7 As shown, The unpolished sample No. 0 had the highest surface roughness (8.46 nm), reflecting surface defects caused by the original processing, highlighting the importance of chemical mechanical polishing (CMP) in improving wafer flatness.

[0035] The introduction of CTAB dispersant into sample 1 improved the dispersibility and stability of CeO2 particles, reducing the roughness to 0.84 nm. However, due to the large particle size, the mechanical and chemical effects were limited, resulting in a slightly inferior polishing effect. Sample 2 showed severe particle agglomeration and uneven polishing, leading to a roughness increase to 2.31 nm, indicating that dispersibility has a crucial impact on polishing uniformity.

[0036] After adding CTAB dispersant to sample 3, the cationic surfactant improved the particle distribution through electrostatic adsorption, further reducing the roughness to 0.77 nm. Sample 4, although without a dispersant, possessed some self-dispersibility due to the use of smaller CeO2 particles, resulting in a roughness of 1.13 nm. Sample 5, with the same particle size, introduced PVP, further enhancing dispersion stability and reducing the roughness to 0.71 nm.

[0037] Sample 6, using CeO2 particles from Example 4 in combination with CTAB dispersant, achieved the best polishing effect under standard conditions (87 / 93 rpm, 3 psi), with the lowest roughness of only 0.58 nm. Increasing the rotation speed to 117 / 123 rpm (sample 7) improved the material removal rate, but due to excessive shear force, slight over-polishing occurred, resulting in a slight increase in roughness. Reducing the pressure to 2 psi (sample 8) weakened the mechanical effect, leading to insufficient removal and a roughness increase to 1.02 nm.

[0038] Comprehensive analysis shows that the dispersibility, size structure, and polishing parameters of the particles together determine the final surface quality. The best results are derived from the CeO2 particles obtained in Example 4, which exhibited the best smoothness under suitable rotation speed and pressure conditions with the synergistic effect of CTAB dispersant.

[0039] The above description only illustrates the preferred embodiments of the present invention and should not be construed as limiting the scope of the claims. The present invention is not limited to the above embodiments, and variations in its specific structure are permitted. All modifications made within the scope of the independent claims of this invention are also within the scope of protection of this invention.

Claims

1. Preparation of highly uniform cerium oxide abrasive, characterized in that, Includes the following steps: S1: Weigh a soluble cerium source and one or two surfactants and dissolve them together in a first mixed solvent composed of alcohol and water in a volume ratio of 1:1 to 3:1, so that the alcohol reduces the polarity of water to slow down the hydrolysis rate of cerium ions, thereby avoiding uneven particle size caused by rapid precipitation, and stir at room temperature for at least 30 minutes to completely dissolve all components and form a stable and homogeneous first solution. S2: After transferring the first solution to a high-pressure reactor lined with polytetrafluoroethylene, it is heated to a temperature of 150℃-200℃ for 16-24 hours. The surfactant and the first mixed solvent synergistically guide the primary particles to assemble into plate-like, rod-like, or petal-like secondary structural units, which are then further bent, coiled, or radially assembled to form a relatively dense but porous flower-like spherical multi-level structure. After heating, the structure is naturally cooled to room temperature. S3: Take out the reaction product and wash it several times by centrifuging at 9000-11000 rpm for 1-5 minutes with a second mixed solvent containing pure water and ethanol in a 1:1 volume ratio to remove reaction residues, unreacted substances and surface adsorbed impurities. S4: The cleaned product is vacuum dried at 70℃-90℃ for 9-15 hours to ensure complete drying. Then, the dried product is placed in a muffle furnace and calcined at 500℃-650℃ in air for 1-4 hours to further improve its crystal structure and remove organic residues, ultimately obtaining high-purity cerium oxide particles with uniform particle size distribution and a flower-like multi-level structure.

2. The preparation of the highly uniform cerium oxide abrasive according to claim 1, characterized in that: The alcohol used in the first mixed solvent in step S1 is any one of ethanol, propanol, isopropanol, n-butanol, octanol, and ethylene glycol.

3. The preparation of the highly uniform cerium oxide abrasive according to claim 2, characterized in that: The soluble cerium source in step S1 is any one of cerium chloride, cerium nitrate, cerium oxalate, cerium ammonium nitrate, and cerium perchlorate, and the surfactant is any one or any two of octadecyltrimethylammonium chloride, hexadecyltrimethylammonium bromide, tetradecyltrimethylammonium chloride, dodecyltrimethylammonium chloride, benzyldodecyldimethylammonium chloride, hexadecyldimethylphenylammonium chloride, dodecyldimethylamine hydrochloride, sodium disulfosuccinate, and polyvinylpyrrolidone.

4. The preparation of the highly uniform cerium oxide abrasive according to claim 3, characterized in that: The soluble cerium source is cerium nitrate, the surfactant is polyvinylpyrrolidone, the alcohol in the first mixed solvent is isopropanol or diethylene glycol, and the volume ratio of the alcohol to water is 3:

1.

5. The preparation of the highly uniform cerium oxide abrasive according to claim 1, characterized in that: The heating temperature in step S2 is 160℃-180℃, and the heating time is 18-20 hours.

6. The preparation of the highly uniform cerium oxide abrasive according to claim 1, characterized in that: The calcination temperature in step S4 is 550℃-600℃, and the calcination time is 1.7-2.2 hours.

7. The preparation of the highly uniform cerium oxide abrasive according to claim 1, characterized in that: The cerium oxide particles obtained in step S4 have a size of 250-550 nm and a specific surface area of ​​5.44-7.60 m². 2 / g, and the particle size distribution is uniform with no agglomeration.

8. The application of highly uniform cerium oxide abrasive according to any one of claims 1 to 7 in a chemical mechanical polishing slurry, characterized in that: The preparation of the chemical mechanical polishing slurry includes the following steps: S5: Weigh the cerium oxide powder obtained in step S4 and add it to deionized water. While stirring, add the dispersant and amino acids in sequence to obtain the third mixed solution. S6: After the third mixed solution is stirred evenly and brought to a constant volume, a pH adjuster is added to make the third mixed solution weakly acidic. Stirring is continued for 50-70 minutes to obtain the chemical mechanical polishing solution.

9. The application of the highly uniform cerium oxide abrasive according to claim 8 in a chemical mechanical polishing slurry, characterized in that: The dispersant is any one of polyvinyl alcohol, polyvinylpyrrolidone, sodium polyacrylate, sodium dodecyl sulfonate, and hexadecyltrimethylammonium bromide; the amino acid is any one of alanine, leucine, tryptophan, proline, serine, and threonine; and the pH adjuster is any one or any two of hydrochloric acid, nitric acid, sulfuric acid, acetic acid, citric acid, phosphoric acid, sodium hydroxide, potassium hydroxide, ammonia, triethanolamine, ethanolamine, or phosphate.

10. The application of the highly uniform cerium oxide abrasive according to claim 8 in a chemical mechanical polishing slurry, characterized in that: The dispersant is cetyltrimethylammonium bromide or polyvinylpyrrolidone, the amino acid is proline, and the pH adjuster is a combination of citric acid and ammonia.

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