A polishing liquid containing low-crystallinity CeO2 nanoparticles and a method for preparing the same

Abstract

The application relates to a polishing liquid containing low-crystallinity CeO2 nanoparticles and a preparation method thereof, and belongs to the technical field of chemical mechanical polishing. The polishing liquid formula is as follows: 0.1-5.0% of CeO2 nanoparticles, 0.01-0.50% of amino silane coupling agent, 0.01-0.30% of dispersion stabilizer, 0.01-1.00% of pH regulator and the balance of deionized water in percentage by mass; wherein the dispersion stabilizer is composed of hydroxyethylidene diphosphonic acid, gluconic acid and lithium carbonate; the CeO2 nanoparticles have a spherical or octahedral morphology, the particle size ranges from 20 to 250 nm, the crystallinity is 60-80%, and the surface trivalent cerium content is greater than or equal to 30%; the polishing liquid prepared by the application has high dispersion stability and high SiO2 removal rate.

Description

Technical Field

[0001] This invention belongs to the field of chemical mechanical polishing technology, and relates to a polishing slurry containing low-crystallinity CeO2 nanoparticles and its preparation method. Background Technology

[0002] Chemical mechanical polishing (CMP) is currently the only ultra-precision machining technology capable of achieving global wafer planarization, and it occupies an irreplaceable position in semiconductor manufacturing. As the feature size of integrated circuits continues to shrink to 7nm and even more advanced processes, the requirements for wafer surface flatness and polishing precision are becoming increasingly stringent.

[0003] Cerium oxide (CeO2) is widely recognized as one of the most promising abrasives for STI and ILD-CMP applications due to its suitable mechanical properties, high chemical reactivity, and, more importantly, its highly selective removal capability of Si3N4 / SiO2. However, existing cerium oxide polishing slurries still face several technical challenges that urgently need to be addressed in their application: Firstly, the dispersion stability is insufficient. Nano-cerium oxide particles have small sizes and large specific surface areas, resulting in significant surface effects. They are prone to agglomeration in polishing slurries, severely impacting polishing uniformity and surface quality. Traditional methods improve dispersibility by adding dispersants or surfactants; however, excessive dispersants can form bubbles on the oxide surface during polishing, reducing the effective contact area between the abrasive and the workpiece and consequently lowering the polishing rate. Existing patent CN119144237B improves dispersibility by modifying the cerium oxide surface with epoxy carboxylic acid, achieving suspension stability of up to two months; however, this method is cumbersome and costly, and the introduction of the modification layer may affect the chemical activity of the abrasive to some extent.

[0004] Secondly, the trade-off between polishing selectivity and removal rate is difficult to reconcile. STI-CMP requires a high selectivity ratio for SiO2 and Si3N4 to protect the silicon nitride barrier layer while removing excess silicon oxide. In existing technologies, increasing the SiO2 / Si3N4 selectivity ratio often comes at the cost of sacrificing the silicon oxide removal rate. Existing patent CN120230481A achieves selectivity control by adding polishing inhibitors to reduce the SiO2 removal rate, but this approach is a rate-suppressing strategy and fails to fundamentally solve the technical challenge of achieving both high rate and high selectivity.

[0005] Third, controlling surface defects after polishing is difficult. The morphology, particle size, and surface chemical state of cerium oxide abrasives have a decisive influence on the surface roughness and scratch defects of the polished workpiece. Traditional cerium oxide abrasives are mostly irregular in shape with sharp edges, which easily generate scratches and subsurface damage layers on the polished surface. Although some studies have improved the surface roughness of Ce through doping or reduction treatment... 3+ Concentration is used to enhance chemical activity, but the limitation of abrasive morphology on polishing quality has not yet been effectively resolved.

[0006] Fourth, the differences in the activity of cerium oxide crystal faces have not been effectively utilized. Cerium oxide has a cubic fluorite structure, and different crystal faces have different surface energies and chemical activities. However, there are few existing technologies that selectively expose highly active crystal faces to synergistically improve polishing rate and surface quality. Summary of the Invention

[0007] The purpose of this invention is to provide a polishing slurry containing low-crystallinity CeO2 nanoparticles and its preparation method, which has the characteristics of high dispersion stability.

[0008] A polishing slurry containing low-crystallinity CeO2 nanoparticles, the polishing slurry formulation is as follows, by mass percentage: CeO2 nanoparticles 0.1%~5.0%, Aminosilane coupling agent 0.01%~0.50%, Dispersant stabilizer 0.01%~0.30%, pH adjuster 0.01%~1.00%, Deionized water balance; The dispersing stabilizer is composed of hydroxyethylidene diphosphonic acid, gluconic acid and lithium carbonate; The CeO2 nanoparticles have a spherical or octahedral morphology, a particle size range of 20~250nm, a crystallinity of 60%~80%, and a surface trivalent cerium content ≥30%.

[0009] In the technical solution of this invention, the high CeO2 nanoparticles... 3+ The content provides excellent chemical activity. Ce 3+ The presence of these oxygen vacancies and dangling bonds in the CeO2 lattice means that there are more oxygen vacancies and dangling bonds. During polishing, these oxygen vacancies can undergo strong chemical adsorption with bridging oxygen atoms on the SiO2 surface, promoting the breaking and hydrolysis of Si-O-Si bonds, thereby significantly improving the material removal rate of SiO2. Secondly, with a crystallinity in the range of 60% to 80%, CeO2 grains retain a suitable amount of lattice defects and grain boundaries. Under the pressure of CMP polishing, the abrasive particles undergo preferential micro-fracture along the grain boundaries, continuously exposing fresh high-CeO2. 3+ Active surfaces. On the one hand, the abrasive maintains high chemical activity during polishing, preventing loss of polishing ability due to surface contamination or passivation; on the other hand, moderate crushing avoids uncontrolled particle refinement caused by excessive grinding. In contrast, while highly crystalline cerium oxide has high hardness and wear resistance, it lacks self-sharpening properties, and its polishing rate decreases significantly once the surface becomes passivated. Furthermore, high Ce... 3+In synergy with low crystallinity, the polishing slurry of this invention not only exhibits a high initial polishing rate but also a slow rate decay during prolonged polishing or multiple batches of use, thus extending the effective service life of a single batch of polishing slurry. Furthermore, CeO2 enhances selectivity, and high Ce... 3+ Surface reinforcement enhances the chemical reaction of SiO2, but its reinforcing effect on Si3N4 is relatively limited. Meanwhile, the mechanical action generated by the moderate fracturing of low-crystallinity abrasives primarily acts on the softer SiO2 layer rather than the harder Si3N4.

[0010] This invention uses a compound of HEDP, gluconic acid, and lithium carbonate as a dispersant and stabilizer in CeO2-CMP polishing slurry. The three components have complementary functions, resulting in a synergistic effect. HEDP molecules contain two phosphonic acid groups, which can react with CeO2 on the CeO2 surface. 3+ / Ce 4+ Strong coordination occurs. A single HEDP molecule can simultaneously coordinate with surface Ce atoms through two phosphonic acid groups, forming a stable five- or six-membered ring chelate structure. The anchoring strength is much higher than that of adsorption by a single carboxyl or hydroxyl group. After anchoring, the HEDP molecular chain extends into the solution, providing steric hindrance and preventing close contact and aggregation between particles. Simultaneously, the phosphonic acid groups partially ionize under alkaline conditions, becoming negatively charged and contributing electrostatic repulsion.

[0011] Gluconic acid molecules contain one carboxyl group and five hydroxyl groups. The carboxyl group can react with Ce on the surface. 3+ Weak coordination adsorption occurs, and this weak coordination is reversible. When some gluconic acid molecules desorb under polishing shear force, the free gluconic acid in the solution can re-coordinate, endowing the surface modification layer with dynamic self-healing ability. Furthermore, multiple uncoordinated hydroxyl groups of gluconic acid extend into the solution and bind to water molecules through hydrogen bonding, forming a thick hydration film on the particle surface, further enhancing the steric hindrance effect. The carboxyl and hydroxyl groups in the gluconic acid molecules can participate in the surface softening reaction of SiO2 at the polishing interface, helping to increase the polishing rate, rather than the inert coating that leads to a decrease in rate as in traditional dispersants.

[0012] Li in lithium carbonate + With the smallest ionic radius and the highest charge density, it can strongly adsorb onto the Stern layer on the surface of CeO2 particles, modulating the zeta potential to the optimal electrostatic repulsion range. Meanwhile, Li... + The strong hydration capacity forms a dense hydrated lithium-ion layer on the particle surface, further inhibiting particle aggregation through the steric hindrance effect of the hydration film. CO3 2- It has a weak buffering capacity in the polishing solution pH range of 8~10.5, which can maintain the pH stability of the microenvironment at the polishing interface and ensure the uniformity of the polishing rate.

[0013] Furthermore, the mass ratio of hydroxyethylidene diphosphonic acid, gluconic acid, and lithium carbonate in the dispersing stabilizer is 1:(0.5~2):(0.05~0.5).

[0014] In the technical solution of this invention, HEDP:gluconic acid = 1:(0.5~2), where HEDP provides strong coordination anchoring, and gluconic acid provides reversible weak coordination and dynamic self-healing. When the proportion of gluconic acid is too low, the dynamic self-healing ability is insufficient, and the coordination layer cannot be repaired in time after being damaged under shear force, resulting in decreased long-term stability. When the proportion of gluconic acid is too high, excess gluconic acid forms multilayer adsorption on the surface, partially obscuring the phosphonic acid anchoring sites of HEDP and the active surface of CeO2, leading to a decrease in polishing rate. Although lithium carbonate is used in small amounts in the system, its role in regulating the zeta potential is very important. When the proportion of lithium carbonate is too low, the zeta potential regulation is insufficient, the electrostatic repulsion is insufficient to overcome van der Waals attraction, and the sedimentation rate is too high. When the proportion of lithium carbonate is too high, excess Li... + Excessive compression of the electric double layer and an excessively high absolute value of the zeta potential can lead to excessive electrostatic repulsion between particles, which in turn causes the particles to align and form bridging aggregates. At the same time, excessively high ionic strength may change the adsorption conformation of HEDP and gluconic acid on the surface, resulting in decreased dispersibility.

[0015] Furthermore, the method for preparing the CeO2 nanoparticles is as follows: S3-1: Heat deionized water to 35~70℃, add cerium source and stir to dissolve, add dispersant, stir at 35~70℃ for 10~50min, add organic solvent, make up to volume and continue stirring for 10~50min to obtain precursor mixture; S3-2: React the precursor mixture at 90~120℃ for 5~10h; S3-3: The reaction solution was centrifuged and the precipitate was washed sequentially with deionized water and anhydrous ethanol to obtain the CeO2 nanoparticles.

[0016] Furthermore, the cerium source is one or more of cerium chloride, cerium nitrate, cerium acetate, and cerium sulfate; The dispersant is one or more of polyvinylpyrrolidone, polyvinyl alcohol, polyethylene glycol, sodium dodecyl sulfate, and sodium citrate. The organic solvent is one or more of anhydrous ethanol, isopropanol, and polyethylene glycol; The concentration of the cerium source in the precursor solution is 0.05 mol / L to 0.16 mol / L; The volume ratio of the organic solvent to deionized water is 1:9 to 9:1; The amount of dispersant added is 0.1 to 2.5 wt% of the total mass of the precursor solution.

[0017] Furthermore, in step S3-1, the temperature for heating and dissolving the cerium source is 40℃~60℃, the stirring time after adding the dispersant is 20~40min, and the stirring time after adjusting the volume is 20~40min.

[0018] Furthermore, the reaction temperature in S3-2 is 95~115℃, and the reaction time is 6~8h.

[0019] In the technical solution of the present invention, the cerium dioxide nanoparticles prepared by means of the regulating effect of the organic solvent and water mixture system and the steric hindrance effect of the dispersant effectively control the growth habit of cerium dioxide crystals, and can obtain nanoparticles with spherical or near-spherical or octahedral morphology and concentrated particle size distribution.

[0020] The introduction of dispersants significantly improved the surface state of nanoparticles and effectively prevented the formation of hard agglomerates. The resulting powder is easily redispersed in the polishing slurry, forming a uniform and stable suspension system with high static stability, which is beneficial to the stable progress of the polishing process.

[0021] The preparation method used in this invention does not require a precipitant, and this system can completely eliminate the Na+ precipitants introduced by ammonium carbonate, ammonium bicarbonate, sodium hydroxide, ammonia, urea, and other precipitants. + NH4 + Residual impurities are eliminated, thus avoiding particle agglomeration and widening of size distribution caused by rapid nucleation induced by precipitants. Furthermore, high-temperature calcination is unnecessary to remove residues, eliminating hard particle agglomeration and abnormal grain growth during the calcination process. Surface Ce 3+ With higher content and oxygen vacancy concentration, this system exhibits superior polishing activity. At the process level, it reduces the types of raw materials, eliminates the cumbersome steps of precipitant preparation and precise pH control, and significantly reduces human error. Furthermore, it directly yields complete products, eliminating processes such as precipitation aging and high-temperature calcination, shortening the production cycle from the traditional 2-3 days to 12-20 hours. In addition, this system avoids the use of strongly alkaline and corrosive precipitants, resulting in no ammonia release or high-salt wastewater generation. Simultaneously, the reduced cost of precipitant raw materials and calcination energy consumption lowers the overall production cost during large-scale production, combining excellent environmental friendliness and economic benefits.

[0022] The process primarily uses organic solvents and water as the solvent system, resulting in a low environmental impact. The dispersant used is easily removed by washing without affecting the purity of the final product. Furthermore, this method boasts a high cerium salt conversion rate and high raw material utilization, demonstrating good economic benefits and aligning with the principles of green chemistry and sustainable development.

[0023] Furthermore, the aminosilane coupling agent is at least one selected from 3-aminopropyltriethoxysilane, N-(2-aminoethyl)-3-aminopropyltrimethoxysilane, and 3-aminopropyltrimethoxysilane.

[0024] Furthermore, the pH adjuster is at least one of ammonia, tetramethylammonium hydroxide, and potassium hydroxide.

[0025] A method for preparing a polishing slurry containing low-crystallinity CeO2 nanoparticles, the method comprising the following steps: S9-1: Add cerium oxide nanoparticles to half the mass of deionized water and ultrasonically disperse for 10~30 min. During the ultrasonic process, control the system temperature ≤40℃ to obtain a cerium oxide dispersion. S9-2: Add aminosilane coupling agent to cerium oxide dispersion and stir at 400-600 rpm for 1-3 hours at 30-50℃; S9-3: Add a dispersant stabilizer to the system obtained in S9-2, and stir at 400-600 rpm for 0.5-2 hours at a temperature of 20-40℃; S9-4: Adjust the pH of the system to 8.5~10.5 with a pH adjuster, add the remaining deionized water, and continue stirring at 350~450 rpm for 20~60 min to obtain the polishing solution.

[0026] Furthermore, in S9-1, the ultrasonic frequency is 20~40kHz and the ultrasonic power is 200~400W.

[0027] In the technical solution of this invention, S9-2 first involves covalent modification with aminosilane, where the aminosilane is anchored to the CeO2 surface via Si-O-Ce covalent bonds, forming a robust chemical graft layer; S9-3 then involves coordination adsorption, where HEDP binds to Ce via phosphonic acid groups. 3+ / Ce 4+ Coordination adsorption: gluconic acid reacts with Ce via the carboxyl group. 3+ Weak coordination adsorption; the strength of coordination bonds is lower than that of covalent bonds, giving this layer a dynamic and reversible characteristic. After partial desorption under polishing shear force, it can be re-adsorbed, endowing the system with self-healing ability. The covalent bottom layer provides long-term stability, while the coordination top layer provides dynamic self-healing ability; the combination of the two allows the polishing fluid to maintain excellent dispersion during long-term storage and polishing use.

[0028] The beneficial effects of this invention are: (1) This invention employs a low-temperature liquid-phase synthesis method to directly obtain CeO2 nanoparticles without the need for high-temperature calcination. Low-temperature synthesis preserves the high Ce content on the surface. 3+ The high Ce content provides abundant chemically active sites, thus enhancing the SiO2 removal rate. Simultaneously, the 60%–80% crystallinity endows the abrasive with self-sharpening characteristics, selectively micro-fragmenting along grain boundaries under polishing pressure, continuously exposing fresh, high-Ce content abrasive particles. 3+ The active surface solves the problem of rate decay after passivation of traditional highly crystalline cerium oxide surfaces; (2) In this invention, hydroxyethylidene diphosphonic acid, gluconic acid and lithium carbonate are compounded as a dispersing stabilizer. The three have complementary functions. HEDP reacts with Ce through the phosphonic acid group. 3+ / Ce 4+ Strong coordination provides robust anchoring and steric hindrance; gluconic acid, through weak coordination with carboxyl groups, imparts dynamic self-healing capabilities to the modified layer, and its multi-hydroxyl structure enhances the thickness of the hydration film; Li in lithium carbonate... + By precisely controlling the zeta potential, CO3 2- It provides an interface pH buffer, and the ternary compound significantly reduces the sedimentation rate; (3) By strictly controlling the feeding sequence, the present invention constructs a two-layer composite modification structure of covalent bottom layer + coordination top layer on CeO2 surface. The aminosilane coupling agent first forms a stable bottom anchoring layer through Si-O-Ce covalent bonds; HEDP and gluconic acid then form a dynamic and reversible top modification layer through coordination bonds; the covalent bottom layer ensures long-term storage stability, and the coordination top layer provides self-healing ability during the polishing process. Attached Figure Description

[0029] To facilitate understanding by those skilled in the art, the present invention will be further described below with reference to the accompanying drawings.

[0030] Figure 1 X-ray diffraction (XRD) spectra of CeO2 nanoparticles prepared in different embodiments and comparative examples; Figure 2 a is Example 1. Figure 2 b is Example 3. Figure 2 c represents Example 4. Figure 2 d is a scanning electron microscope (SEM) image of the CeO2 nanoparticles prepared in Comparative Example 1; Figure 3 The image shows the X-ray photoelectron spectroscopy (XPS) spectra of the CeO2 nanoparticles prepared in Examples 1 and 2. Detailed Implementation

[0031] To further illustrate the technical means and effects of the present invention in achieving its intended purpose, the following detailed description of the specific implementation methods, structures, features, and effects of the present invention, in conjunction with the accompanying drawings and preferred embodiments, is provided.

[0032] It should be noted that, unless otherwise specified, the present invention does not specifically limit the source of the raw materials used in the following embodiments. Commercially available products or products prepared by conventional preparation methods that are well known to those skilled in the art can be used. Experimental methods that do not specify specific conditions are all conventional methods and conventional conditions well known in the art.

[0033] Example 1

[0034] The preparation method of CeO2 nanoparticles is as follows: Weigh 3.474 g of Ce(NO3)3·6H2O (approximately 0.08 mol) and dissolve it in 25 ml of deionized water. Stir magnetically in a 60°C oil bath until completely dissolved to obtain the first solution. Add 1.00 g of PVP to the first solution. K30 The mixture was magnetically stirred in an oil bath at 60°C until completely dissolved to obtain a second solution. 75 ml of anhydrous ethanol was measured and added to the second solution. The beaker wall was then washed with a small amount of ethanol and the mixture was combined. The final volume was adjusted to 100 ml, and stirring was continued for 30 minutes to obtain a third solution. The third solution was heated to 95°C and reacted at a constant temperature for 9 hours. After the reaction was completed, the product was centrifuged, the precipitate was collected, and washed three times each with deionized water and anhydrous ethanol. The washed sample was transferred to a container to obtain the CeO2 nanoparticles.

[0035] Example 2

[0036] The preparation method of CeO2 nanoparticles is as follows: Weigh 3.474 g of Ce(NO3)3·6H2O (approximately 0.08 mol) and dissolve it in 25 ml of deionized water. Stir magnetically in a 60°C oil bath until completely dissolved to obtain the first solution. Add 1.00 g of PVP to the first solution. K60 The mixture was magnetically stirred in an oil bath at 60°C until completely dissolved to obtain a second solution. 75 ml of anhydrous ethanol was measured and added to the second solution. The beaker wall was then washed with a small amount of ethanol and the mixture was combined. The final volume was adjusted to 100 ml, and stirring was continued for 30 minutes to obtain a third solution. The third solution was heated to 95°C and reacted at a constant temperature for 9 hours. After the reaction was completed, the product was centrifuged, the precipitate was collected, and washed three times each with deionized water and anhydrous ethanol. The washed sample was transferred to a container to obtain the CeO2 nanoparticles.

[0037] Example 3

[0038] The preparation method of CeO2 nanoparticles is as follows: Weigh 3.474 g of Ce(NO3)3·6H2O (approximately 0.08 mol) and dissolve it in 50 ml of deionized water. Stir magnetically in a 60°C oil bath until completely dissolved to obtain the first solution. Add 1.00 g of PVP to the first solution. K60 The mixture was magnetically stirred in an oil bath at 60°C until completely dissolved to obtain a second solution. 50 ml of anhydrous ethanol was measured and added to the second solution. The beaker walls were then washed with a small amount of ethanol and the mixture was combined. The final volume was adjusted to 100 ml, and stirring was continued for 30 minutes to obtain a third solution. The third solution was heated to 100°C and reacted at a constant temperature for 10 hours. After the reaction was completed, the product was centrifuged and the precipitate was collected. The precipitate was washed three times each with deionized water and anhydrous ethanol. The washed sample was transferred to a container to obtain the CeO2 nanoparticles.

[0039] Example 4

[0040] The preparation method of CeO2 nanoparticles is as follows: Weigh 13.896g of Ce(NO3)3·6H2O (approximately 0.08mol) and dissolve it in 100ml of deionized water. Stir the solution magnetically in a 60℃ oil bath until completely dissolved to obtain the first solution. Add 4.00g of PVP to the first solution. K30 The mixture was magnetically stirred in an oil bath at 60°C until completely dissolved to obtain a second solution. 300 ml of anhydrous ethanol was measured, and then the beaker wall was washed with a small amount of ethanol and the mixture was combined. The final volume was adjusted to 400 ml, and stirring was continued for 30 minutes to obtain a third solution. The third solution was heated to 110°C and reacted at a constant temperature for 9 hours. After the reaction was completed, the product was centrifuged, the precipitate was collected, and the precipitate was washed three times each with deionized water and anhydrous ethanol. The washed sample was transferred to a container to obtain the CeO2 nanoparticles.

[0041] Example 5

[0042] The preparation method of CeO2 nanoparticles is as follows: Weigh 4.3425 g of Ce(NO3)3·6H2O (approximately 0.08 mol) and dissolve it in 25 ml of deionized water. Stir the solution magnetically in a 60°C oil bath until completely dissolved to obtain the first solution. Add 1.00 g of CTAB to the first solution and stir magnetically in a 60°C oil bath until completely dissolved to obtain the second solution. Measure 75 ml of anhydrous ethanol and add it to the second solution. Then wash the beaker wall with a small amount of ethanol and combine the solutions, finally adjusting the volume to 100 ml. Continue stirring for 30 minutes to obtain the third solution. Heat the third solution to 100°C and react at this temperature for 8 hours. After the reaction, centrifuge the product, collect the precipitate, and wash the precipitate three times each with deionized water and anhydrous ethanol. Transfer the washed sample to a container to obtain the CeO2 nanoparticles.

[0043] Example 6

[0044] The preparation method of CeO2 nanoparticles is as follows: Weigh 2.97 g of (Ce(CH3COO)3·xH2O) (approximately 0.08 mol) and dissolve it in 25 ml of deionized water. Stir magnetically in a 60°C oil bath until completely dissolved to obtain the first solution. Add 1.00 g of PVP to the first solution. K30The mixture was magnetically stirred in an oil bath at 60°C until completely dissolved to obtain a second solution. 75 ml of anhydrous ethanol was measured and added to the second solution. The beaker walls were then washed with a small amount of ethanol and the mixture was combined. The final volume was adjusted to 100 ml, and stirring was continued for 30 minutes to obtain a third solution. The third solution was heated to 115°C and reacted at a constant temperature for 9 hours. After the reaction was completed, the product was centrifuged, the precipitate was collected, and the precipitate was washed three times each with deionized water and anhydrous ethanol. The washed sample was transferred to a container to obtain the CeO2 nanoparticles.

[0045] Example 7

[0046] The preparation method of CeO2 nanoparticles is as follows: Weigh 3.474 g of Ce(NO3)3·6H2O (approximately 0.08 mol) and dissolve it in 25 ml of deionized water. Stir the solution magnetically in a 60°C oil bath until completely dissolved to obtain the first solution. Add 1.00 g of PVA to the first solution and stir the solution magnetically in a 60°C oil bath until completely dissolved to obtain the second solution. Measure 75 ml of anhydrous ethanol and add it to the second solution. Then wash the beaker wall with a small amount of ethanol and combine the solutions. Finally, adjust the volume to 100 ml and continue stirring for 30 minutes to obtain the third solution. Heat the third solution to 100°C and react at this temperature for 9 hours. After the reaction is complete, centrifuge the product, collect the precipitate, and wash the precipitate three times each with deionized water and anhydrous ethanol. Transfer the washed sample to a container to obtain the CeO2 nanoparticles.

[0047] Example 8

[0048] The preparation method of CeO2 nanoparticles is as follows: Weigh 3.474 g of Ce(NO3)3·6H2O (approximately 0.08 mol) and dissolve it in 25 ml of deionized water. Stir the solution magnetically in a 60°C oil bath until completely dissolved to obtain the first solution. Add 1.00 g of PVA to the first solution and stir the solution magnetically in a 60°C oil bath until completely dissolved to obtain the second solution. Measure 75 ml of isopropanol and add it to the second solution. Then wash the beaker wall with a small amount of ethanol and combine the solutions. Finally, adjust the volume to 100 ml and continue stirring for 30 minutes to obtain the third solution. Heat the third solution to 100°C and react at this temperature for 10 hours. After the reaction is complete, centrifuge the product, collect the precipitate, and wash the precipitate three times each with deionized water and anhydrous ethanol. Transfer the washed sample to a container to obtain the CeO2 nanoparticles.

[0049] Example 9

[0050] A method for preparing a polishing slurry containing low-crystallinity CeO2 nanoparticles, the method comprising the following steps: S9-1: Take 2.0g of CeO2 nanoparticles prepared in Example 1, add them to 400g of deionized water, and ultrasonically disperse for 20min. The ultrasonic frequency is 28kHz, the ultrasonic power is 300W, and the system temperature is controlled to be ≤30℃ to obtain a cerium oxide dispersion. S9-2: Add 0.10 g of 3-aminopropyltriethoxysilane (APTES, purity ≥98%) to the cerium oxide dispersion obtained in S9-1, place the system in a 40℃ water bath, and stir at 500 rpm for 2 h; S9-3: Add dispersant and stabilizer (0.05g hydroxyethylidene diphosphonic acid (HEDP) + 0.05g gluconic acid + 0.01g lithium carbonate) to the system obtained in S9-2, place the system in a 40°C water bath, and stir at 500 rpm for 1 hour; S9-4: Adjust the pH of the system to 9.5 with 25wt% ammonia water, add the remaining deionized water to make up to a total mass of 1000g, and continue stirring at 400rpm for 30min to obtain the polishing solution.

[0051] Example 10

[0052] A method for preparing a polishing slurry containing low-crystallinity CeO2 nanoparticles, the method comprising the following steps: S9-1: Take 2.0g of CeO2 nanoparticles prepared in Example 1, add them to 400g of deionized water, and ultrasonically disperse for 20min. The ultrasonic frequency is 28kHz, the ultrasonic power is 300W, and the system temperature is controlled to be ≤30℃ to obtain a cerium oxide dispersion. S9-2: Add 0.10 g of 3-aminopropyltriethoxysilane (APTES, purity ≥98%) to the cerium oxide dispersion obtained in S9-1, place the system in a 40℃ water bath, and stir at 500 rpm for 2 h; S9-3: Add dispersant stabilizer (HEDP 0.05g + gluconic acid 0.025g + lithium carbonate 0.015g) to the system obtained in S9-2, place the system in a 40℃ water bath, and stir at 500rpm for 1h; S9-4: Adjust the pH of the system to 9.5 with 25wt% ammonia water, add the remaining deionized water to make up to a total mass of 1000g, and continue stirring at 400rpm for 30min to obtain the polishing solution.

[0053] Example 11

[0054] A method for preparing a polishing slurry containing low-crystallinity CeO2 nanoparticles, the method comprising the following steps: S9-1: Take 2.0g of CeO2 nanoparticles prepared in Example 1, add them to 400g of deionized water, and ultrasonically disperse for 20min. The ultrasonic frequency is 28kHz, the ultrasonic power is 300W, and the system temperature is controlled to be ≤30℃ to obtain a cerium oxide dispersion. S9-2: Add 0.10 g of 3-aminopropyltriethoxysilane (APTES, purity ≥98%) to the cerium oxide dispersion obtained in S9-1, place the system in a 40℃ water bath, and stir at 500 rpm for 2 h; S9-3: Add dispersant stabilizer (HEDP 0.05g + gluconic acid 0.10g + lithium carbonate 0.0025g) to the system obtained in S9-2, place the system in a 40℃ water bath, and stir at 500rpm for 1h; S9-4: Adjust the pH of the system to 9.5 with 25wt% ammonia water, add the remaining deionized water to make up to a total mass of 1000g, and continue stirring at 400rpm for 30min to obtain the polishing solution.

[0055] Example 12

[0056] A method for preparing a polishing slurry containing low-crystallinity CeO2 nanoparticles, the method comprising the following steps: S9-1: Take 2.0g of CeO2 nanoparticles prepared in Example 1, add them to 400g of deionized water, and ultrasonically disperse for 25min. The ultrasonic frequency is 35kHz, the ultrasonic power is 350W, and the system temperature is controlled to be ≤30℃ to obtain a cerium oxide dispersion. S9-2: Add 0.15 g of N-(2-aminoethyl)-3-aminopropyltrimethoxysilane to the cerium oxide dispersion obtained in S9-1, place the system in a 40°C water bath, and stir at 500 rpm for 2 h; S9-3: Add dispersant stabilizer (HEDP 0.06g + gluconic acid 0.09g + lithium carbonate 0.006g) to the system obtained in S9-2, place the system in a 40℃ water bath, and stir at 500rpm for 1h; S9-4: Adjust the pH of the system to 9.5 with 25wt% ammonia water, add the remaining deionized water to make up to a total mass of 1000g, and continue stirring at 400rpm for 30min to obtain the polishing solution.

[0057] Example 13

[0058] A method for preparing a polishing slurry containing low-crystallinity CeO2 nanoparticles, the method comprising the following steps: S9-1: Take 2.0g of CeO2 nanoparticles prepared in Example 1, add them to 400g of deionized water, and ultrasonically disperse for 20min. The ultrasonic frequency is 28kHz, the ultrasonic power is 300W, and the system temperature is controlled to be ≤30℃ to obtain a cerium oxide dispersion. S9-2: Add 0.10 g of 3-aminopropyltriethoxysilane to the cerium oxide dispersion obtained in S9-1, place the system in a 40°C water bath, and stir at 500 rpm for 2 h; S9-3: Add dispersant stabilizer (HEDP 0.04g + gluconic acid 0.032g + lithium carbonate 0.01g) to the system obtained in S9-2, place the system in a 40℃ water bath, and stir at 500rpm for 1h; S9-4: Adjust the pH of the system to 9.5 with 25wt% ammonia water, add the remaining deionized water to make up to a total mass of 1000g, and continue stirring at 400rpm for 30min to obtain the polishing solution.

[0059] Example 14

[0060] A method for preparing a polishing slurry containing low-crystallinity CeO2 nanoparticles, the method comprising the following steps: S9-1: Take 4.0g of CeO2 nanoparticles prepared in Example 1, add them to 450g of deionized water, and ultrasonically disperse for 30min. The ultrasonic frequency is 25kHz, the ultrasonic power is 400W, and the system temperature is controlled to be ≤35℃ to obtain a cerium oxide dispersion. S9-2: Add 0.20 g of 3-aminopropyltriethoxysilane to the cerium oxide dispersion obtained in S9-1, place the system in a 45°C water bath, and stir at 600 rpm for 3 h; S9-3: Add dispersant stabilizer (HEDP 0.08g + gluconic acid 0.096g + lithium carbonate 0.012g) to the system obtained in S9-2, place the system in a 40℃ water bath, and stir at 600rpm for 2h; S9-4: Adjust the pH of the system to 10 with 25wt% ammonia water, add the remaining deionized water to make up to a total mass of 1000g, and continue stirring at 450rpm for 50min to obtain the polishing solution.

[0061] Comparative Example 1 The only difference between this comparative example and Example 1 is that no dispersant was added in the preparation of CeO2 nanoparticles; the remaining steps and parameters are exactly the same as in Example 1.

[0062] Comparative Example 2 The only difference between this comparative example and Example 1 is that no organic solvent is added during the preparation of CeO2 nanoparticles; the remaining steps and parameters are exactly the same as in Example 1.

[0063] Comparative Example 3 The only difference between this comparative example and Example 9 is that APTES is not added in the preparation of the polishing slurry; the other steps and parameters are exactly the same as in Example 9.

[0064] Comparative Example 4 The only difference between this comparative example and Example 9 is that HEDP is not added in the preparation of the polishing solution; only 0.10g of gluconic acid and 0.01g of lithium carbonate are used. The remaining steps and parameters are exactly the same as in Example 9.

[0065] Comparative Example 5 The only difference between this comparative example and Example 9 is that gluconic acid is not added in the preparation of the polishing solution; only 0.10g of HEDP and 0.01g of lithium carbonate are used. The remaining steps and parameters are exactly the same as in Example 9.

[0066] Comparative Example 6 The only difference between this comparative example and Example 9 is that lithium carbonate is not added in the preparation of the polishing solution; only 0.05g of HEDP and 0.05g of gluconic acid are used. The remaining steps and parameters are exactly the same as in Example 9.

[0067] Comparative Example 7 The only difference between this comparative example and Example 9 is that gluconic acid and lithium carbonate are not added in the preparation of the polishing solution, and only 0.11g of HEDP is used as a dispersant and stabilizer. The remaining steps and parameters are exactly the same as in Example 9.

[0068] Comparative Example 8 The only difference between this comparative example and Example 9 is that the dispersant stabilizer is added first and then APTES is added in the preparation of the polishing slurry; the other steps and parameters are exactly the same as in Example 9.

[0069] XRD Test and Results X-ray diffraction (XRD) was performed on the CeO2 nanoparticles prepared in Examples 1-3 and Comparative Example 1. The scanning angle range was 10°–80°, and the scanning speed was 5° / min. The XRD analysis results are as follows: Figure 1 As shown, the synthesized sample conforms to the PDF#34-0394 standard card and exhibits diffraction peaks at 28.5°, 33.1°, 47.5°, 56.3°, 59.1°, 69.4°, 76.7°, and 79.1°, corresponding to the (111), (200), (220), (311), (222), (400), (331), and (420) crystal planes, respectively. No other impurity peaks were observed.

[0070] SEM Test and Results The CeO2 nanoparticles prepared in Example 1 were tested using scanning electron microscopy. Figure 2 (a) is Example 1. As can be seen from the figure, the nanoparticles are spherical with a particle size of about 50 nm. By adding PVP, hydrolysis and precipitation are inhibited, and the long PVP chains encapsulate the crystal nuclei to prevent agglomeration and provide physical isolation. The anisotropic growth of the crystals is regulated to form a spherical structure. Figure 2 (b) is Example 3. It can be clearly seen from the figure that the nanoparticles have an octahedral morphology and a particle size of about 150 nm. Figure 2 (c) is Example 4. As can be seen from the figure, the nanoparticles are spherical and have a particle size of about 50 nm. Figure 2 (d) is Comparative Example 1. It can be seen from the figure that the particle size distribution is relatively wide and the morphology is irregular and uneven.

[0071] Introducing organic solvents into the reaction system can reduce the hydrolysis rate of the cerium source, making the crystal nucleation stage more stable and orderly, thus ensuring that the final nanoparticles have uniform size and regular morphology. In addition, the good wettability and low surface tension of organic solvents can also help dispersants such as PVP achieve more uniform dispersion in the solution system, optimizing the coating effect of the dispersant on the particle surface and thus preventing the formation of hard agglomerates between particles.

[0072] XPS Test and Results Figure 3 The above are the peak fitting results of Ce3d orbital X-ray photoelectron spectroscopy for two samples from Examples 1 and 2. All spectra were performed according to standard rules for valence state peaking and fitting. The yellow peak corresponds to Ce. 4+ The six characteristic peaks, with the blue peak corresponding to Ce 3+ The four characteristic peaks showed good agreement between the fitted curve and the original test data, indicating reliable peak division results. Calculations using peak area integration showed that the surface Ce in Example 1... 3+ The relative content is approximately 33%, Ce in Example 2 3+ The peak area increases, and its surface Ce 3+ The relative content is 38%.

[0073] Table 1 Characterization data of CeO2 nanoparticles

[0074] Polishing performance test The test was conducted using a CMP polishing machine. The test conditions were as follows: the wafer was a thermally oxidized SiO2 wafer (the oxide layer thickness was about 1 μm), the polishing disk speed was 80 rpm, the polishing time was 60 seconds, and the polishing temperature was 25℃.

[0075] Removal rate test: The SiO2 film thickness was measured using an ellipsometry before and after polishing. 49 points were measured on each wafer, and the average value was taken. Removal rate (nm / min) = (film thickness before polishing - film thickness after polishing) / polishing time (min).

[0076] Surface roughness test: Atomic force microscopy (AFM) was used for testing, with a scanning range of 10μm×10μm. Ra values ​​were recorded, and measurements were taken at 5 different locations on each wafer, with the average value taken.

[0077] Dispersion stability test: Pour the prepared polishing solution into a 100mL stoppered graduated cylinder, seal it, and place it in a dark place at 25℃. After standing for 60 days, take a 5mL sample from 5cm below the liquid surface in the graduated cylinder using a pipette. Dry the sample in an oven at 105℃ until constant weight, and weigh the solid mass. Sedimentation rate (%) = (initial solid mass - solid mass at sampling point) / initial solid mass × 100%. The lower the sedimentation rate, the better the dispersion stability.

[0078] Table 2 Performance test data of polishing slurry

[0079] As shown in the table above, in Example 9, HEDP, gluconic acid, and lithium carbonate achieved a synergistic equilibrium at a ratio of 1:1:0.2. HEDP provided stable anchoring and steric hindrance, gluconic acid provided dynamic self-healing and a hydration layer, and lithium carbonate regulated the zeta potential to the optimal range, resulting in a low sedimentation rate. In Example 10, the low proportion of gluconic acid led to insufficient dynamic self-healing ability and hydration layer thickness, resulting in a slightly higher sedimentation rate. In Example 11, excessive gluconic acid formed multilayer adsorption on the surface, partially obscuring the HEDP anchoring points and the CeO2 active surface, leading to a decrease in the sedimentation rate; insufficient lithium carbonate resulted in a low absolute value of the zeta potential, increasing the sedimentation rate. Example 12 used N-(2-aminoethyl)-3-aminopropyltrimethoxysilane, whose molecule contains two amino groups, which can introduce a higher density of positively charged functional groups on the CeO2 surface, enhancing electrostatic repulsion and interfacial chemical reaction activity. In Example 13, the relative proportion of lithium carbonate was increased, resulting in more efficient control of the zeta potential and a slightly better sedimentation rate than in Example 9. The slight decrease in gluconic acid led to a slightly insufficient hydration layer thickness and a slightly lower hydration rate. In Example 14, the CeO2 addition was increased to 4.0 g, APTES to 0.20 g, and the total amount of HEDP / gluconic acid / lithium carbonate was correspondingly increased. Higher abrasive concentration meant a greater number of effective abrasive particles participating in polishing per unit time, significantly improving the SiO2 removal rate. However, the high solids content also brought two negative effects: firstly, the frequency of interparticle collisions increased, leading to a higher 60-day sedimentation rate; secondly, the enhanced mechanical removal action increased surface roughness.

[0080] Comparative Example 3 lacks an aminosilane covalent modification layer, relying solely on the coordination adsorption of HEDP / gluconic acid and the electrostatic repulsion of lithium carbonate to maintain dispersion. Although the ternary dispersion stabilizer still plays a role to some extent, the lack of a covalent anchoring layer of APTES leads to insufficient stability of the coordination adsorption layer, making it prone to desorption under polishing shear force. After the active sites on the abrasive surface are exposed, agglomeration occurs, reducing the effective abrasive particles and decreasing the SiO2 removal rate. The absence of amino functional groups also results in the loss of the function of amino groups participating in interfacial reactions to assist polishing.

[0081] Comparative Example 4: Strong phosphonic acid coordination anchoring lacking HEDP, relying solely on weak carboxyl coordination with Ce in gluconate. 3+ Combined, the anchoring strength is insufficient. During polishing shear forces and long-term storage, gluconic acid is easily desorbed from the surface, leading to an increased 60-day settling rate; the lack of stable steric molecular brushes provided by HEDP results in insufficient interparticle repulsion, reduced effective abrasive grains, and decreased abrasive rate.

[0082] Comparative Example 5 lacks the dynamic self-healing ability and hydration layer enhancement function of gluconic acid; although HEDP can provide strong anchoring, once the coordination layer develops local defects under shear force, it lacks reversible weakly coordinated molecules for self-repair, resulting in insufficient long-term stability. Simultaneously, it lacks the carboxyl / hydroxyl-assisted SiO2 softening function of gluconic acid, leading to a reduced softening rate.

[0083] Comparative Example 6 lacks the zeta potential regulation function of lithium carbonate. Although HEDP+gluconic acid can provide electrostatic repulsion through the ionization of phosphonic acid / carboxyl groups, it does not reach the optimal range, and the electrostatic repulsion force is insufficient to effectively overcome the van der Waals attraction between particles. Short-term dispersion is acceptable, but particles slowly aggregate during long-term storage, and the sedimentation rate increases significantly after 60 days.

[0084] Comparative Example 7 uses HEDP as a single dispersant and stabilizer, relying solely on the coordination anchoring of phosphonic acid groups and the electrostatic repulsion provided by partial ionization; it lacks the hydration layer and dynamic repair function of gluconic acid, and lacks the precise control of the zeta potential of lithium carbonate, resulting in limited dispersion effect.

[0085] In Comparative Example 8, the reversed order of feed addition caused HEDP and gluconic acid to occupy the CeO2 surface Ce first. 3+ Active sites: After these coordination molecules form an adsorption layer on the surface, the subsequently added APTES cannot effectively contact the hydroxyl groups on the CeO2 surface, and the formation of Si-O-Ce covalent bonds is hindered, resulting in insufficient APTES modification. Some particle surfaces lack a covalent anchoring layer, leading to an increase in the 60-day sedimentation rate.

[0086] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention in any way. Although the present invention has been disclosed above with reference to preferred embodiments, it is not intended to limit the present invention. Any person skilled in the art can make some modifications or alterations to the above-disclosed technical content to create equivalent embodiments without departing from the scope of the present invention. Any simple modifications, equivalent changes and alterations made to the above embodiments based on the technical essence of the present invention without departing from the scope of the present invention shall still fall within the scope of the present invention.

Claims

1. A polishing slurry containing low-crystallinity CeO2 nanoparticles, characterized in that, The polishing fluid formula is as follows, by weight percentage: CeO2 nanoparticles 0.1%~5.0%, Aminosilane coupling agent 0.01%~0.50%, Dispersant stabilizer 0.01%~0.30%, pH adjuster 0.01%~1.00%, Deionized water balance; The dispersing stabilizer is composed of hydroxyethylidene diphosphonic acid, gluconic acid and lithium carbonate; The CeO2 nanoparticles have a spherical or octahedral morphology, a particle size range of 20~250nm, a crystallinity of 60%~80%, and a surface trivalent cerium content ≥30%.

2. The polishing slurry containing low-crystallinity CeO2 nanoparticles according to claim 1, characterized in that, The mass ratio of hydroxyethylidene diphosphonic acid, gluconic acid, and lithium carbonate in the dispersing stabilizer is 1:(0.5~2):(0.05~0.5).

3. The polishing slurry containing low-crystallinity CeO2 nanoparticles according to claim 1, characterized in that, The method for preparing the CeO2 nanoparticles is as follows: S3-1: Heat deionized water to 35~70℃, add cerium source and stir to dissolve, add dispersant, stir at 35~70℃ for 10~50min, add organic solvent, make up to volume and continue stirring for 10~50min to obtain precursor mixture; S3-2: React the precursor mixture at 90~120℃ for 5~10h; S3-3: The reaction solution was centrifuged and the precipitate was washed sequentially with deionized water and anhydrous ethanol to obtain the CeO2 nanoparticles.

4. The polishing slurry containing low-crystallinity CeO2 nanoparticles according to claim 3, characterized in that, The cerium source is one or more of cerium chloride, cerium nitrate, cerium acetate, and cerium sulfate; The dispersant is one or more of polyvinylpyrrolidone, polyvinyl alcohol, polyethylene glycol, sodium dodecyl sulfate, and sodium citrate. The organic solvent is one or more of anhydrous ethanol, isopropanol, and polyethylene glycol; The concentration of the cerium source in the precursor solution is 0.05 mol / L to 0.16 mol / L; The volume ratio of the organic solvent to deionized water is 1:9 to 9:1; The amount of dispersant added is 0.1 to 2.5 wt% of the total mass of the precursor solution.

5. The polishing slurry containing low-crystallinity CeO2 nanoparticles according to claim 3, characterized in that, In S3-1, the temperature for heating and dissolving the cerium source is 40℃~60℃, the stirring time after adding the dispersant is 20~40min, and the stirring time after adjusting the volume is 20~40min.

6. The polishing slurry containing low-crystallinity CeO2 nanoparticles according to claim 3, characterized in that, The reaction temperature in S3-2 is 95~115℃, and the reaction time is 6~8h.

7. The polishing slurry containing low-crystallinity CeO2 nanoparticles according to claim 1, characterized in that, The aminosilane coupling agent is at least one of 3-aminopropyltriethoxysilane, N-(2-aminoethyl)-3-aminopropyltrimethoxysilane, and 3-aminopropyltrimethoxysilane.

8. The polishing slurry containing low-crystallinity CeO2 nanoparticles according to claim 1, characterized in that, The pH adjuster is at least one of ammonia, tetramethylammonium hydroxide, and potassium hydroxide.

9. A method for preparing a polishing slurry containing low-crystallinity CeO2 nanoparticles as described in any one of claims 1 to 8, characterized in that, The preparation method includes the following steps. S9-1: Add cerium oxide nanoparticles to half the mass of deionized water and ultrasonically disperse for 10~30 min. During the ultrasonication process, control the system temperature ≤40℃ to obtain a cerium oxide dispersion. S9-2: Add aminosilane coupling agent to cerium oxide dispersion and stir at 400-600 rpm for 1-3 hours at 30-50℃; S9-3: Add a dispersant stabilizer to the system obtained in S9-2, and stir at 400-600 rpm for 0.5-2 hours at a temperature of 20-40℃; S9-4: Adjust the pH of the system to 8.5~10.5 with a pH adjuster, add the remaining deionized water, and continue stirring at 350~450 rpm for 20~60 min to obtain the polishing solution.

10. The method for preparing a polishing slurry containing low-crystallinity CeO2 nanoparticles according to claim 9, characterized in that, The ultrasonic frequency in S9-1 is 20~40kHz, and the ultrasonic power is 200~400W.

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