Chemical mechanical polishing liquid containing cerium oxide nanoparticles and method for preparing the same

Abstract

The application relates to a cerium oxide nanoparticle-containing chemical mechanical polishing liquid and a preparation method thereof, and belongs to the technical field of polishing liquids. The polishing liquid contains the following raw materials in mass fractions: 10-30 parts of nano cerium oxide, 2-5 parts of a dispersing agent, 0.1-2 parts of polyquaternary ammonium salt, 1-5 parts of a functional additive, and 80-100 parts of water; the nano cerium oxide has a spherical, spherical-like or octahedral morphology, a particle size of 20-250 nm, a crystallinity of greater than or equal to 75%, and a proportion of trivalent cerium of greater than or equal to 30%; the functional additive is phytic acid, citric acid and ascorbic acid with a mass ratio of 1: (2-5): (2-4). The prepared polishing liquid has excellent storage stability and can reduce surface roughness generated in a chemical mechanical polishing process.

Description

Technical Field

[0001] This invention belongs to the field of polishing fluid technology, and relates to a chemical mechanical polishing fluid containing cerium oxide nanoparticles and its preparation method. Background Technology

[0002] Chemical mechanical polishing (CMP) is an ultra-precision machining technology that can simultaneously achieve global and local planarization of wafer surfaces. Through the synergistic effect of chemical etching and mechanical abrasion, CMP achieves high-precision material removal, thereby obtaining a surface with nanometer-level flatness. It is widely used in key processes such as silicon wafer surface planarization and multilayer metal interconnect planarization.

[0003] In CMP polishing slurries, abrasives serve as a bridge between chemical and mechanical actions, and are key to achieving high-efficiency, atomically smooth manufacturing of various materials. CeO2 nanomaterials, due to their quantum size effect, surface effect, and macroscopic quantum tunneling effect, exhibit superior polishing performance (such as high polishing efficiency, low surface roughness, and no scratch residue) compared to bulk materials, making them one of the most widely used abrasives currently available.

[0004] Currently, the main methods for preparing CeO2 nanoparticles include precipitation, sol-gel, hydrothermal, microwave, and combustion methods. Among these, precipitation is simple but produces a wide particle size distribution and severe agglomeration, which can easily cause scratches on the polished surface. The sol-gel method can obtain high-purity products, but it has a long reaction cycle, high cost, and is difficult to scale up, failing to meet the needs of large-scale applications in the polishing industry. The combustion method has a fast reaction rate, but the product morphology is difficult to control, and agglomeration is a prominent problem, resulting in unstable polishing performance. CeO2 nanoparticles prepared by existing hydrothermal methods have uneven particle size distribution and a wide particle size range, which can easily cause scratches during polishing, affecting the smoothness and gloss of the polished surface.

[0005] Existing cerium oxide CMP polishing slurries still have significant shortcomings in terms of dispersion stability, balance between polishing rate and surface quality, optimization of the microstructure of cerium oxide abrasives, and synergistic design of functional additives.

[0006] Therefore, there is an urgent need to develop a chemical mechanical polishing slurry with good storage stability, high polishing rate, and ultra-low surface roughness. Summary of the Invention

[0007] The purpose of this invention is to provide a chemical mechanical polishing slurry containing cerium oxide nanoparticles and its preparation method. The prepared polishing slurry has excellent storage stability and can reduce the surface roughness generated during chemical mechanical polishing.

[0008] The objective of this invention can be achieved through the following technical solutions: A chemimechanical polishing slurry containing cerium oxide, the slurry comprising the following raw materials in parts by weight: 10-30 parts of nano-cerium oxide; 2-5 parts dispersant; 0.1 to 2 parts of polyquaternium salt; Functional additives: 1-5 parts; 80-100 parts water; The nano-cerium oxide has a spherical, near-spherical, or octahedral morphology, a particle size of 20-250 nm, a crystallinity of ≥75%, and a trivalent cerium content of ≥30%. The functional additives are phytic acid, citric acid and ascorbic acid in a mass ratio of 1:(2~5):(2~4).

[0009] The cerium oxide used in this invention has a spherical, near-spherical, or octahedral morphology. The spherical / near-spherical abrasive can effectively avoid polishing scratches and surface damage, and reduce surface roughness. The octahedral morphology exposes highly active crystal faces, further enhancing chemical activity. At the same time, the sharp edges, after being passivated at the nanoscale, also have high mechanical removal efficiency. The 20~250nm particle size distribution is controllable, ensuring the consistency and planarization effect of the polished surface.

[0010] High crystallinity (≥75%) ensures that cerium oxide abrasives do not break or disintegrate under high-speed polishing shear stress, avoiding secondary scratch defects caused by abrasive fragmentation. Compared with conventional cerium oxide (which typically contains only 10-20% trivalent cerium), the cerium oxide synthesized by the high-pressure hydrothermal method in this invention has a higher concentration of Ce. 3+ And the accompanying oxygen vacancy defects: high concentration of Ce 3 + With more oxygen vacancy defect active centers, it can efficiently catalyze the oxidation of the polished material surface during the polishing process, achieving a chemical etching rate much higher than that of traditional cerium oxide.

[0011] As a preferred embodiment of the present invention, the dispersant is one or more of polyacrylic acid, polyacrylate, triethanolamine and polyethylene glycol.

[0012] As a preferred embodiment of the present invention, the preparation of the nano-cerium oxide includes the following steps: S3.1 Preparation of precursor solution: The cerium source was mixed with deionized water and heated to 35-70°C to dissolve, yielding the first solution. The dispersant was then dissolved in an organic solvent under ultrasonic heating to obtain the second solution. S3.2 Pretreatment: Add the second solution to the first solution and continue stirring for 10-50 minutes to obtain a homogeneous precursor mixture. S3.3, High-pressure hydrothermal reaction: The precursor mixture was placed in a high-pressure reactor and reacted at 120~180℃ for 6~16h. S3.4 Post-processing: The reaction solution was centrifuged and washed to obtain nano-cerium oxide particles.

[0013] This invention uses high-pressure reaction as the core step. The high-pressure environment can promote the full and uniform growth of CeO2 crystal nuclei, forming a cubic fluorite structure with high purity and excellent crystallinity. No impurity phases are generated, and the particle hardness and grinding performance are suitable for polishing requirements. The polishing efficiency is high, and the polished surface can achieve high flatness and high smoothness without scratch residue. It is significantly better than existing preparation methods that do not utilize high-pressure reaction and is suitable for various precision polishing scenarios.

[0014] High-pressure reaction allows dispersant molecules to be more uniformly adsorbed on the CeO2 crystal nucleus surface, enhancing steric hindrance and effectively inhibiting particle growth and agglomeration. The resulting nanoparticles have good dispersibility in both aqueous and organic phases, requiring no subsequent dispersion treatment and can be directly dispersed in polishing liquid, ensuring uniform particle distribution and stable polishing efficiency during the polishing process, and avoiding damage to the polished surface by agglomerates.

[0015] The hydrothermal method directly prepares cerium dioxide with a complete fluorite structure, without the formation of impurity phases. The particles have moderate hardness and can achieve a good balance between efficient mechanical grinding and mild chemical action during polishing.

[0016] As a preferred embodiment of the present invention, the cerium source is one or more of cerium chloride, cerium nitrate, cerium acetate, and cerium sulfate, and the organic solvent is at least one of anhydrous ethanol, isopropanol, and polyethylene glycol.

[0017] This invention uses an organic solvent and water as the solvent system for preparing nano-cerium oxide. The entire reaction process does not use any precipitating agents, resulting in a low environmental impact. This system can completely eliminate the Na+ precipitates 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+ It has a higher content and oxygen vacancy concentration, resulting in better polishing activity.

[0018] As a preferred embodiment of the present invention, the dispersant is at least one selected from polyvinylpyrrolidone, polyvinyl alcohol, polyethylene glycol, sodium dodecyl sulfate, and sodium citrate.

[0019] The dispersant used in this invention is easy to remove by washing without affecting the purity of the final product. This method has a high cerium salt conversion rate, high raw material utilization rate, good economic benefits, and is in line with the concepts of green chemistry and sustainable development.

[0020] As a preferred embodiment of the present invention, the concentration of the cerium source in the precursor mixture is 0.01~0.20 mol / L.

[0021] As a preferred embodiment of the present invention, the organic solvent is 10-90% of the total mass of deionized water and organic solvent, and the dispersant is added at a rate of 0.1-2.5 wt% of the total mass of the precursor solution.

[0022] As a preferred embodiment of the present invention, the nano-cerium oxide is modified with carboxymethyl lignin, and the specific preparation process is as follows: Nano-cerium oxide is dispersed in deionized water and ultrasonically dispersed for 10-30 min to obtain a cerium oxide suspension. Carboxymethyl lignin is dissolved in deionized water to prepare a carboxymethyl lignin solution with a mass fraction of 0.5-5%. The carboxymethyl lignin solution is added to the cerium oxide suspension, wherein the mass ratio of carboxymethyl lignin to cerium oxide is (0.02-0.15):1. The mixture is stirred at 40-80℃ for 1-4 h, and then centrifuged, washed, and dried to obtain carboxymethyl lignin-modified cerium oxide.

[0023] A method for preparing a cerium oxide-containing chemical mechanical polishing slurry includes the following steps: S1. Preparation of suspension: Carboxymethyl lignin-modified cerium oxide was mixed with water to obtain a modified cerium oxide suspension; S2. Add functional additives in stages: S2-1. Add phytic acid to the cerium oxide suspension obtained in step S1 and stir and mix at 20~40℃ for 30~60 min. S2-2. Add citric acid to the system obtained in step S2-1, and continue stirring and mixing at 20~40℃ for 20~40 min; S2-3. Add ascorbic acid to the system obtained in step S2-2, and continue stirring and mixing at 20~40℃ for 10~20 min; S3. Preparation of polishing slurry: Add a dispersant and a polyquaternary ammonium salt to the system obtained in step S2, and adjust the pH to 3-5 to obtain the cerium oxide-containing chemical mechanical polishing slurry.

[0024] As a preferred embodiment of the present invention, steps S2-1, S2-2 and S2-3 are performed under the protection of an inert gas, wherein the inert gas is selected from nitrogen or argon.

[0025] In this invention, the polishing slurry is prepared with inert gas protection. The above process ensures that the highly active state of nano-cerium oxide with a "trivalent cerium ratio ≥ 30%" prepared by the high-pressure hydrothermal method is not oxidized and deactivated during the entire chemical treatment process of preparing the polishing slurry. This ensures that the final product perfectly inherits the high chemical activity of cerium oxide abrasive, thereby achieving efficient chemical-mechanical synergistic polishing.

[0026] In the preparation of the polishing slurry, in step S1, carboxymethyl lignin undergoes chemical grafting with the carboxyl group and Ce site, forming a dense polymer layer on the particle surface. This polymer layer physically widens the distance between particles through strong steric hindrance, fundamentally preventing the formation of hard agglomerates, thus enabling the modified cerium oxide to achieve stable suspension in an aqueous system.

[0027] Step S2-1: Phytic acid is first added to the cerium oxide suspension, allowing phytic acid to chemically bond to the cerium oxide surface through phosphorus-oxygen bonds, thus completing strong coordination anchoring. Step S2-2: Citric acid is then added, allowing citric acid to fill the remaining coordination vacancies after phytic acid anchoring through carboxyl coordination, thus completing medium coordination filling. Step S2-3: Ascorbic acid is then added, allowing ascorbic acid to distribute on the outermost layer through physical adsorption or weak coordination, thus completing weak coordination / reduction treatment. This combination of strong-medium-weak coordination perfectly balances anchoring strength and suspension fluidity.

[0028] Under the high shear force and frictional heat generated during polishing, the outermost layer of ascorbic acid (weakly adsorbed) is most easily detached or activated, initially acting as a lubricant and preventing deposition. As the outer layer is worn away, the inner citric acid and phytic acid are gradually exposed, providing continuous chemical corrosion regulation. This invention forms a "strong-medium-weak" coordination bond energy gradient from the inside out, avoiding the problems of excessive surface rigidity and deteriorated dispersibility caused by a single strong coordinating agent (such as phytic acid alone).

[0029] The carboxymethyl lignin in step S1 consumes excess oxidative defects on the surface of cerium oxide during pretreatment, and improves the thermodynamic stability of the cerium oxide particles in the liquid phase through pretreatment; then the gradient coordination assembly in step S2 solves the problem of spatially ordered distribution of surface active sites.

[0030] This invention utilizes the order-of-magnitude differences in the coordination ability of different ligands with Ce sites, and employs an irreversible adsorption sequence of strong coordination preferential occupation, intermediate coordination gap filling, and weak coordination outer layer detachment; combined with a decreasing time window from 30~60 min to 20~40 min and then to 10~20 min, to precisely match the diffusion rate and adsorption relaxation time of the three molecules at the solid-liquid interface.

[0031] The beneficial effects of this invention are: (1) The present invention can effectively suppress irregular growth of crystal nuclei and particle agglomeration by combining high pressure reaction with stepwise solution preparation and dispersant dispersion, and obtain cerium oxide nanoparticles with uniform particle size in the range of 20~250nm. This particle size range can take into account polishing efficiency and surface quality, and avoid the problems of scratches caused by large particles and low polishing efficiency of small particles. The regulating effect of high pressure reaction can achieve precise control of particle size and improve product consistency.

[0032] (2) This invention solves the problems of easy agglomeration, rapid activity decay, and numerous surface defects in traditional cerium oxide polishing slurries through a complete process of "high-activity abrasive synthesis - surface pre-coating modification - hierarchical and orderly assembly of functional additives - precise control of the final dispersion system". The cerium oxide abrasive in the prepared polishing slurry has excellent dispersion stability, and the polishing slurry itself has excellent storage stability, resulting in extremely low surface roughness. Attached Figure Description

[0033] To facilitate understanding by those skilled in the art, the present invention will be further described below with reference to the accompanying drawings.

[0034] Figure 1 Scanning electron microscope (SEM) images of CeO2 nanoparticles prepared in Examples 1(a), 2(b), 3(c), and Comparative Example 1(d); Figure 2 X-ray diffraction (XRD) spectra of CeO2 nanoparticles prepared in different embodiments and comparative examples. Detailed Implementation

[0035] 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 embodiments, is provided below.

[0036] 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.

[0037] A 5% sodium hydroxide solution was added to a certain amount of water to prepare an alkaline aqueous solution with a pH of 10. 100 g of lignin (phenolic hydroxyl content 2.0 mmol / g) was dissolved in 400 g of the alkaline aqueous solution to prepare a 20% lignin solution. 50 g of sodium cyanoacetate was added at 70°C, and the reaction was allowed to proceed for 2 h to obtain a carboxymethyl lignin solution. The precipitate was separated by centrifugation, dried, and pulverized to obtain carboxymethyl lignin. Example 1

[0038] Weigh 3.474g of Ce(NO3)3·6H2O, heat 25g of deionized water to 60℃, add cerium nitrate hexahydrate to the deionized water, and stir until completely dissolved to obtain the first solution; weigh 1g of PVP K60 75g of anhydrous ethanol was heated to 50℃ and dissolved with ultrasonic assistance under ultrasonic power of 100W to obtain a second solution.

[0039] The first solution was placed in a 60°C oil bath. Under stirring, the second solution was added to the first solution. After stirring for 40 minutes, a homogeneous and transparent precursor mixture was obtained.

[0040] The entire precursor mixture was transferred into a 150 mL stainless steel high-pressure reactor, heated to 140 °C, and reacted at a constant temperature for 12 h. After the reaction was completed, the product was centrifuged, the precipitate was collected, and washed three times each with deionized water and anhydrous ethanol to obtain cerium dioxide.

[0041] Example 2

[0042] Weigh 3.474g of Ce(NO3)3·6H2O, heat 50g of deionized water to 50℃, add cerium nitrate hexahydrate to the deionized water, and stir magnetically until completely dissolved to obtain the first solution; weigh 1g of PVP K30 50g of anhydrous ethanol was heated to 50℃ and dissolved with ultrasonic assistance under ultrasonic power of 100W to obtain a second solution.

[0043] The first solution was placed in a 50°C water bath. Under stirring, the second solution was added to the first solution. After stirring for 40 minutes, a homogeneous and transparent precursor mixture was obtained.

[0044] The entire precursor mixture was transferred into a 150 mL stainless steel high-pressure reactor, heated to 150 °C, and reacted at a constant temperature for 12 h. After the reaction was completed, the product was centrifuged, the precipitate was collected, and washed three times each with deionized water and anhydrous ethanol to obtain cerium dioxide.

[0045] Example 3

[0046] Weigh 2.837g CeCl3·6H2O, heat 25g deionized water to 60℃, add cerium chloride hexahydrate to the deionized water, and stir magnetically until completely dissolved to obtain the first solution; weigh 1g PVP K30 75g of anhydrous ethanol was heated to 50℃ and dissolved with ultrasonic assistance under ultrasonic power of 100W to obtain a second solution.

[0047] The first solution was placed in a 60°C oil bath. Under stirring, the second solution was added to the first solution. After stirring for 40 minutes, a homogeneous and transparent precursor mixture was obtained.

[0048] The entire precursor mixture was transferred into a 150 mL stainless steel high-pressure reactor, heated to 140 °C, and reacted at a constant temperature for 12 h. After the reaction was completed, the product was centrifuged, the precipitate was collected, and washed three times each with deionized water and anhydrous ethanol to obtain cerium dioxide.

[0049] Example 4

[0050] Weigh 3.474g Ce(NO3)3·6H2O, heat 25g deionized water to 60℃, add cerium nitrate hexahydrate to the deionized water, and stir magnetically until completely dissolved to obtain the first solution; weigh 1.00g CTAB, heat 75g anhydrous ethanol to 50℃, and dissolve it with ultrasonic assistance under ultrasonic power of 100W to obtain the second solution.

[0051] The first solution was placed in a 60°C oil bath. Under stirring, the second solution was added to the first solution. After stirring for 40 minutes, a homogeneous and transparent precursor mixture was obtained.

[0052] The entire precursor mixture was transferred into a 150 mL stainless steel high-pressure reactor, heated to 140 °C, and reacted at a constant temperature for 12 h. 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 to obtain cerium dioxide.

[0053] Example 5

[0054] Weigh 2.970g of (Ce(CH3COO)3·xH2O), heat 25g of deionized water to 60℃, add cerium nitrate hexahydrate to the deionized water, and stir magnetically until completely dissolved to obtain the first solution; Weigh 1.00g PVA, heat 75mL of polyethylene glycol to 40℃, and dissolve it with ultrasonic assistance under ultrasonic power of 100W to obtain a second solution.

[0055] Measure 75g of polyethylene glycol and add it dropwise to the second solution while stirring. After the addition is complete, wash the beaker wall with a small amount of polyethylene glycol and combine the solutions. Finally, bring the total volume to 100mL and continue stirring for 30min to obtain the precursor mixture.

[0056] The entire precursor mixture was transferred into a 150 mL stainless steel high-pressure reactor, heated to 150 °C, and reacted at a constant temperature for 12 h. After the reaction was completed, the product was centrifuged, the precipitate was collected, and washed three times each with deionized water and anhydrous ethanol to obtain cerium dioxide.

[0057] Comparative Example 1 This is basically the same as Example 1, except that no dispersant is added in this comparative example.

[0058] Comparative Example 2 This is basically the same as Example 1, except that no organic solvent is added in this comparative example.

[0059] The prepared CeO2 nanoparticles were tested using scanning electron microscopy, and the results are as follows: Figure 1 As shown, (a) is Example 1, and it can be seen from the figure that the nanoparticles are spherical with a particle size of about 50 nm; (b) is Example 2, and it can be clearly seen from the figure that the nanoparticles have an octahedral morphology with a particle size of about 150 nm; (c) is Example 4, and it can be seen from the figure that the nanoparticles are spherical with a particle size of about 50 nm; (d) is Comparative Example 1, and it can be seen from the figure that the particle size distribution is relatively wide and the morphology is irregular and uneven.

[0060] The addition of organic solvents can slow down the hydrolysis rate, making the nucleation process more gradual and conducive to the formation of nanoparticles with more uniform size and regular morphology. At the same time, organic solvents have good wettability and low surface tension, which helps dispersants such as PVP to be evenly distributed in the solution, improve their coating effect on the particle surface, and reduce hard agglomeration.

[0061] X-ray diffraction tests were 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 results are shown in Table 1 below: Table 1

[0062] Combined with XRD analysis results ( Figure 2 The nano-cerium oxide particles prepared by the method of this invention conform to the standard card PDF#34-0394, and diffraction peaks appear 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 are observed, indicating that the cerium oxide prepared by the high-pressure hydrothermal process in this invention is all pure-phase cubic cerium dioxide with excellent phase controllability.

[0063] Example 6

[0064] The polishing solution contains the following raw materials in parts by weight: 20 parts nano-cerium oxide, 3 parts polyacrylic acid, 0.5 parts polyquaternium salt-100, 3 parts functional additives, and 90 parts water; the functional additives are phytic acid, citric acid, and ascorbic acid in a mass ratio of 1:3:3.

[0065] S1. Preparation of suspension: The nano-cerium oxide prepared in Example 1 was dispersed in deionized water and ultrasonically dispersed for 20 min to obtain a cerium oxide suspension. Carboxymethyl lignin was dissolved in deionized water to prepare a 3% carboxymethyl lignin solution. The carboxymethyl lignin solution was added to the cerium oxide suspension, wherein the mass ratio of carboxymethyl lignin to cerium oxide was 0.1:1. The mixture was stirred at 60°C for 3 h, and after centrifugation, washing, and drying, carboxymethyl lignin-modified cerium oxide was obtained. The cerium oxide was mixed with water at a mass ratio of 20:90 and ultrasonically dispersed for 30 min to obtain a cerium oxide suspension. S2. Add functional additives in stages: S2-1. Under nitrogen protection, phytic acid is added to the cerium oxide suspension obtained in step S1 and stirred at 30°C for 45 min. S2-2. Under nitrogen protection, add citric acid to the system obtained in step S2-1 and continue stirring and mixing at 30°C for 30 min. S2-3. Under nitrogen protection, add ascorbic acid to the system obtained in step S2-2, and continue stirring and mixing at 30°C for 15 minutes. S3. Preparation of polishing slurry: Polyacrylic acid and polyquaternary ammonium salt were added to the system obtained in step S2, and the pH was adjusted to 4.5 with nitric acid to obtain a chemical mechanical polishing slurry containing cerium oxide.

[0066] Example 7

[0067] It is basically the same as Example 6, except that the nano-cerium oxide used is prepared in Example 2.

[0068] Example 8

[0069] It is basically the same as Example 6, except that the nano-cerium oxide used is prepared in Example 3.

[0070] Example 9

[0071] The process is basically the same as in Example 6, except that the polishing liquid contains the following raw materials in parts by weight: 10 parts of nano-cerium oxide, 2 parts of polyacrylic acid, 0.1 parts of polyquaternium-10, 1 part of functional additives, and 80 parts of water; the functional additives are phytic acid, citric acid, and ascorbic acid in a mass ratio of 1:2:2.

[0072] Example 10

[0073] The process is basically the same as in Example 6, except that the polishing liquid contains the following raw materials in parts by weight: 30 parts of nano-cerium oxide, 5 parts of polyacrylic acid, 2 parts of polyquaternium-10, 5 parts of functional additives, and 100 parts of water; the functional additives are phytic acid, citric acid, and ascorbic acid in a mass ratio of 1:5:4.

[0074] Comparative Example 3 This is basically the same as Example 6, except that in step S1 of this comparative example, the nano zinc oxide is not modified with carboxymethyl lignin, but is directly mixed with deionized water at a mass ratio of 20:90 and ultrasonically dispersed for 30 min to obtain a cerium oxide suspension.

[0075] Comparative Example 4 The comparison example is basically the same as Example 6, except that in step S2, phytic acid, citric acid and ascorbic acid are added to the cerium oxide suspension obtained in step S1 at the same time in a mass ratio of 1:3:3, and stirred and mixed at 30°C for 90 min.

[0076] Comparative Example 5 This is basically the same as Example 6, except that no polyquaternium salt is added in step S3 of this comparative example.

[0077] Comparative Example 6 It is basically the same as Example 6, except that the mass ratio of phytic acid, citric acid and ascorbic acid in this comparative example functional additive is 1:1:1.

[0078] Performance testing: 1. Stability Test: The polishing slurry was left to stand in a constant temperature environment of 25°C. If significant sedimentation or stratification occurred within 60 days, the time was recorded. 2. Polishing experiment: The polishing target was a 12-inch diameter TEOS wafer with a thickness of 8000 Å. The polishing pad was a WH6000 polishing pad with a polishing disk diameter of 762 mm. The polishing pressure was 2.8 psi, the upper / lower disk rotation speed was 45 / 55 rpm, the polishing slurry was diluted 7.5 times, the flow rate was 300 mL / min, the polishing time was 30 s, and the polishing temperature was 25℃. The polishing rate was measured using a KLA non-metallic film thickness gauge (F50). Specifically, the thickness of the single-crystal silicon wafer was measured before and after polishing, and the polishing rate was calculated by dividing the difference in film thickness before and after polishing by the polishing time. 3. Roughness: The surface of the polished wafer was scanned using an atomic force microscope (AFM) with a scanning range of 5 μm x 5 μm. The root mean square roughness (Rq) was recorded, and the results are shown in Table 2 below. Table 2

[0079] Based on the above data, the polishing rate in Example 6 is 2850 Å / min, corresponding to the cerium oxide used in Table 1 being spherical (20~100 nm, Ce). 3+Although its chemical activity (trivalent cerium) is the highest (35.5%), its round shape means that the polishing process mainly involves rolling friction, and the mechanical cutting force is weaker than that of the edges of the octahedron, so the speed is slightly lower than that of Example 7.

[0080] In Example 7, cerium oxide is octahedral (100-200nm). Because the octahedral morphology exposes the high-energy (111) crystal plane, it has extremely strong chemical activity. At the same time, it has the largest particle size, so it has high mechanical kinetic energy and therefore a high polishing rate.

[0081] In Example 8, the specific surface area and active sites of cerium oxide were less than those in Example 6, resulting in a lower polishing rate.

[0082] In Example 9, the polishing slurry formulation contains a small amount of cerium oxide and additives, resulting in a low probability of cerium oxide abrasive collision, fewer chemical reactants, a decreased polishing rate, but better surface roughness.

[0083] In Example 10, there is more abrasive and the chemical reaction is more intense, resulting in a higher polishing rate. However, its roughness (0.17 nm) is slightly higher than that of Example 6 (0.11 nm). This is because the increased mechanical impact points per unit area between cerium oxide particles under high concentration lead to more micro-scratches.

[0084] In Comparative Example 3, the cerium oxide was not modified, which led to hard agglomeration in the polishing slurry, resulting in a reduction in effective abrasive particles, a decrease in polishing speed, and severe mechanical scratching caused by large agglomerates, thus increasing roughness.

[0085] In Comparative Example 4, the functional additives were added all at once, resulting in disordered competition among the additives. Phytic acid excessively occupied the active sites, sealing off chemical activity. The surface modification layer was disordered, unable to effectively suppress debris, with a roughness of 0.35 nm and decreased stability.

[0086] The polishing rate of Comparative Example 5 was higher than that of Example 6 because the polyquaternium salt, as a cationic surfactant, also forms a small amount of coating on the silicon dioxide (TEOS) surface through physical adsorption. This coating acts as a "protective shield" to slightly inhibit the hydrolysis and removal of TEOS. When the polyquaternium salt is removed, the removal rate of TEOS increases. However, at the same time, because there is no polyquaternium salt to regulate the surface potential of the particles, the electrostatic repulsion between the particles weakens, resulting in reduced dispersion stability and a sharp increase in roughness to 0.31 nm.

[0087] In Comparative Example 6, excessive phytic acid forms a dense passivation film, which prevents citric acid / ascorbic acid from exerting a synergistic effect. The surface charge is excessively reversed, the repulsive force between particles is weakened, and the particle size becomes larger. Therefore, the polishing rate decreases and the roughness increases.

[0088] 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 chemimechanical polishing slurry containing cerium oxide, characterized in that, The polishing liquid contains the following raw materials in parts by weight: 10-30 parts of nano-cerium oxide; 2-5 parts dispersant; 0.1 to 2 parts of polyquaternium salt; Functional additives: 1-5 parts; 80-100 parts water; The nano-cerium oxide has a spherical, near-spherical, or octahedral morphology, a particle size of 20-250 nm, a crystallinity of ≥75%, and a trivalent cerium content of ≥30%. The functional additives are phytic acid, citric acid and ascorbic acid in a mass ratio of 1:(2~5):(2~4).

2. The cerium oxide-containing chemical mechanical polishing slurry according to claim 1, characterized in that, The dispersant is one or more of polyacrylic acid, polyacrylate, triethanolamine, and polyethylene glycol.

3. The cerium oxide-containing chemical mechanical polishing slurry according to claim 1, characterized in that, The preparation of the nano-cerium oxide includes the following steps: S3.1 Preparation of precursor solution: The cerium source was mixed with deionized water and heated to 35-70°C to dissolve, yielding the first solution. The dispersant was then dissolved in an organic solvent under ultrasonic heating to obtain the second solution. S3.2 Pretreatment: Add the second solution to the first solution and continue stirring for 10-50 minutes to obtain a homogeneous precursor mixture. S3.3, High-pressure hydrothermal reaction: The precursor mixture was placed in a high-pressure reactor and reacted at 120~180℃ for 6~16h. S3.4 Post-processing: The reaction solution was centrifuged and washed to obtain nano-cerium oxide particles.

4. The cerium oxide-containing chemical mechanical polishing slurry according to claim 3, characterized in that, The cerium source is one or more of cerium chloride, cerium nitrate, cerium acetate, and cerium sulfate, and the organic solvent is at least one of anhydrous ethanol, isopropanol, and polyethylene glycol.

5. The cerium oxide-containing chemical mechanical polishing slurry according to claim 3, characterized in that, The dispersant is at least one of polyvinylpyrrolidone, polyvinyl alcohol, polyethylene glycol, sodium dodecyl sulfate, and sodium citrate.

6. The cerium oxide-containing chemical mechanical polishing slurry according to claim 3, characterized in that, The concentration of the cerium source in the precursor mixture is 0.01~0.20 mol / L.

7. The cerium oxide-containing chemical mechanical polishing slurry according to claim 3, characterized in that, The organic solvent is 10-90% of the total mass of deionized water and organic solvent, and the dispersant is added at a rate of 0.1-2.5 wt% of the total mass of the precursor solution.

8. The cerium oxide-containing chemical mechanical polishing slurry according to claim 1 or 3, characterized in that, The nano-cerium oxide is modified with carboxymethyl lignin, and the specific preparation process is as follows: Nano-cerium oxide is dispersed in deionized water and ultrasonically dispersed for 10-30 min to obtain a cerium oxide suspension. Carboxymethyl lignin is dissolved in deionized water to prepare a carboxymethyl lignin solution with a mass fraction of 0.5-5%. The carboxymethyl lignin solution is added to the cerium oxide suspension, wherein the mass ratio of carboxymethyl lignin to cerium oxide is (0.02-0.15):

1. The mixture is stirred at 40-80℃ for 1-4 h, and then centrifuged, washed, and dried to obtain carboxymethyl lignin-modified cerium oxide.

9. A method for preparing a cerium oxide-containing chemical mechanical polishing slurry as described in any one of claims 1-8, characterized in that, Includes the following steps: S1. Preparation of suspension: Carboxymethyl lignin-modified cerium oxide was mixed with water to obtain a modified cerium oxide suspension; S2. Add functional additives in stages: S2-1. Add phytic acid to the cerium oxide suspension obtained in step S1 and stir and mix at 20~40℃ for 30~60 min. S2-2. Add citric acid to the system obtained in step S2-1, and continue stirring and mixing at 20~40℃ for 20~40 min; S2-3. Add ascorbic acid to the system obtained in step S2-2, and continue stirring and mixing at 20~40℃ for 10~20 min; S3. Preparation of polishing slurry: Add a dispersant and a polyquaternary ammonium salt to the system obtained in step S2, and adjust the pH to 3-5 to obtain the cerium oxide-containing chemical mechanical polishing slurry.

10. The method for preparing the cerium oxide-containing chemical mechanical polishing slurry according to claim 9, characterized in that, Steps S2-1, S2-2, and S2-3 are performed under the protection of an inert gas, which is selected from nitrogen or argon.

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