A colloidal cerium oxide polishing liquid and a method for preparing the same

Abstract

The application discloses a colloidal cerium oxide polishing liquid and a preparation method thereof, and steps are as follows: S1. Dissolving a soluble cerium salt in deionized water, and respectively dissolving a surfactant, a suspension aid and an imidazole modifier in the deionized water and stirring and clarifying, mixing all the solutions, and performing ultrasonic stirring and high-pressure homogenizer circulation treatment to prepare a modified reaction precursor; S2. Continuously stirring the precursor, adding a precipitant at a uniform speed, and stirring after aging by heating to form a colloidal cerium oxide nanosphere solution with a nanosphere appearance; S3. Centrifuging the solution, washing and freeze-drying the solid to obtain a cerium oxide powder, mixing and stirring the powder and deionized water to disperse, and preparing the colloidal cerium oxide polishing liquid. The polishing liquid has uniform particle size, stable dispersion, a high SiO2 / Si3N4 selection ratio, can reduce wafer scratches, guarantee stable polishing performance, and is suitable for the chemical mechanical polishing demand of a semiconductor wafer shallow trench isolation process.

Description

Technical Field

[0001] This invention belongs to the field of semiconductor materials and chemical mechanical polishing, specifically relating to a colloidal cerium oxide polishing slurry suitable for shallow trench isolation (STI) processes on semiconductor wafers and its preparation method. Background Technology

[0002] As integrated circuit feature sizes continue to shrink to the nanometer level, the requirement for global planarization of wafer surfaces has reached the atomic scale. Chemical mechanical polishing (CMP), as the sole key technology to achieve this goal, relies on the performance of its core material—the polishing slurry—which directly determines the polishing rate, material selectivity, and the final surface defect level. Among numerous polishing abrasives, cerium oxide exhibits uniquely high-efficiency polishing characteristics on silicon-based oxide materials. This is mainly attributed to the "chemical-mechanical" synergistic effect of its surface energy forming special chemical bonds with silicon dioxide and then undergoing breakage, giving it an irreplaceable advantage in key processes such as shallow trench isolation.

[0003] However, cerium oxide abrasives traditionally prepared via solid-state high-temperature calcination generally suffer from problems such as high particle hardness, irregular morphology, and wide particle size distribution. These sharp-edged, hard particles are highly susceptible to causing microscopic scratches and embedded residues on the wafer surface during actual polishing, becoming a fatal defect affecting device reliability and yield. Simultaneously, the particles are prone to uncontrollable hard agglomeration in the slurry system, forming secondary particles with sizes far exceeding design values, further exacerbating the risk of surface damage.

[0004] To overcome these shortcomings, existing technologies attempt to synthesize colloidal cerium oxide via liquid-phase methods, aiming to obtain more uniform and finer particles. However, particles synthesized by such methods often lack sufficient crystallinity, exhibit poor long-term stability in polishing slurries with complex chemical formulations, and are prone to phase transitions or dissolution, leading to a significant decline in polishing performance within the process window. Another common approach is to modify the particle surface by coating it, for example, by encapsulating it with a layer of soft silica or an organic layer to buffer mechanical impact. However, such coatings are at risk of peeling off under high-pressure shear, potentially introducing new contaminants; more importantly, while passivating the particle surface and reducing scratches, they may also shield the unique active sites of cerium oxide, causing the loss of its renowned high polishing efficiency advantage.

[0005] Existing technologies have consistently struggled to balance the fundamental contradiction between the "highly efficient chemical activity" and "mild mechanical properties" of cerium oxide abrasives. The market urgently needs a colloidal cerium oxide polishing slurry and its preparation method that can control the original hardness and morphology of the particles from the source, achieving an intrinsic "soft yet tough" properties, while maintaining highly controllable and accessible surface chemical activity. Furthermore, the synthesis method must possess excellent process repeatability and scalability potential to meet the stringent batch consistency requirements of semiconductor manufacturing. Summary of the Invention

[0006] To address the aforementioned technical problems, this invention provides a colloidal cerium oxide polishing slurry and its preparation method, which is particularly suitable for chemical mechanical polishing in shallow trench isolation (STI) processes on semiconductor wafers.

[0007] The technical solution adopted in this invention is:

[0008] This invention provides a method for preparing colloidal cerium oxide polishing slurry, comprising the following steps:

[0009] S1. Preparation of modified reaction precursor: Dissolve soluble cerium salt in deionized water, and stir ultrasonically until completely dissolved. Then, dissolve surfactant, suspending agent and imidazole modifier in deionized water and stir until clear. Mix all solutions, stir ultrasonically, and then process them in a high-pressure homogenizer.

[0010] S2. Preparation of colloidal cerium oxide nanospheres: The precursor obtained in S1 is continuously stirred, and a precipitant is added dropwise at a uniform rate. After heating, the mixture is aged and stirred to form a colloidal cerium oxide nanosphere solution with nanosphere morphology.

[0011] S3. Preparation of colloidal cerium oxide polishing solution: Centrifuge the solution obtained in S2, wash the obtained solid with deionized water and freeze-dry to constant weight to obtain cerium oxide powder, mix the powder with deionized water and stir to disperse to prepare colloidal cerium oxide polishing solution.

[0012] Furthermore, the imidazole modifier is selected from at least one of 2-methylimidazole, 4-methylimidazole, benzimidazole, and mebendazole.

[0013] Furthermore, the soluble cerium salt is selected from at least one of cerium nitrate and cerium chloride.

[0014] Furthermore, the surfactant is selected from at least one of polyvinylpyrrolidone, hexadecyltrimethylammonium bromide, and sodium dodecyl sulfate; the suspending agent is selected from at least one of polyacrylic acid, sodium carboxymethyl cellulose, and hydroxyethyl cellulose; and the precipitant is selected from at least one of ammonia, sodium hydroxide, and potassium hydroxide.

[0015] Furthermore, the mass ratio of the imidazole modifier to the soluble cerium salt is imidazole modifier: soluble cerium salt = 1:(40-60).

[0016] Furthermore, the ultrasonic stirring time in S1 is 3.5-4.5 hours, and the high-pressure homogenizer is used for 4-6 cycles.

[0017] Furthermore, the precipitant drop rate in S2 is 0.8-1.2 mL / min, and the aging stirring time is 11-13 h.

[0018] Furthermore, the mass ratio of powder to deionized water in S3 is 0.4-0.6%.

[0019] This invention provides a colloidal cerium oxide polishing slurry, which is prepared by the above-described method.

[0020] This invention provides the application of the colloidal cerium oxide polishing slurry described above in the chemical mechanical polishing of shallow trench isolation processes for semiconductor wafers.

[0021] The advantages and positive effects of this invention are:

[0022] 1. By modifying the precursor at the molecular level, the morphology and surface chemical activity of cerium oxide particles can be controlled in a dual manner, which fundamentally solves the technical pain points of large mechanical damage in solid-phase cerium oxide abrasives and insufficient crystallinity and poor controllability of chemical activity in liquid-phase abrasives. This successfully balances the core contradiction between "high-efficiency chemical activity" and "mild mechanical properties" of cerium oxide abrasives.

[0023] 2. Ce on the surface of modified cerium oxide particles 3+ The significantly increased Ce content forms Ce-O-Si bonds with the silanol groups on the SiO2 surface. These chemical bonds are more easily broken under mechanical shearing, greatly improving the SiO2 removal rate and providing a stable chemical driving force for polishing, thus preventing the polishing performance from decaying within the process window. The nitrogen-containing groups of the imidazole modifier form a protective molecular film on the Si3N4 surface, which, along with the high Ce content... 3+ The synergistic effect of chemical selectivity inhibits the mechanical and chemical removal of Si3N4, significantly improves the SiO2 / Si3N4 polishing selectivity ratio, and reduces silicon nitride wafer loss.

[0024] 3. High Ce content 3+ This makes the surface chemical activity of cerium oxide particles more stable, avoids the problem of uneven surface energy, and effectively reduces particle hard agglomeration. Its electrostatic stabilization effect and the steric hindrance effect of the modifier form a dual stabilization mechanism, which significantly improves the dispersion stability of the polishing slurry and avoids wafer scratch defects caused by secondary particles formed by abrasive agglomeration from the source.

[0025] 4. Imidazole modifiers are added in situ during the cerium oxide nucleation growth stage, eliminating the need for secondary modification, simplifying the preparation process and reducing production costs; the process parameters form an effective process window with good repeatability, which is suitable for the batch consistency requirements of semiconductor manufacturing. Attached Figure Description

[0026] Figure 1 The image shows a scanning electron microscope (SEM) image of colloidal cerium oxide nanoparticles prepared in Example 1 of this invention, with a scale bar of 200 nm.

[0027] Figure 2The image shows the Fourier Transform Infrared (FT-IR) spectrum of colloidal cerium oxide prepared in Example 1 of this invention. The horizontal axis represents the wavenumber (cm²). -1 The vertical axis represents absorbance;

[0028] Figure 3 The thermogravimetric (TGA) curve of colloidal cerium oxide prepared in Example 1 of this invention is shown. The horizontal axis represents temperature (°C), and the vertical axis represents mass retention (%). Detailed Implementation

[0029] The present disclosure will now be described more fully with reference to the accompanying drawings, which illustrate exemplary embodiments of the present disclosure. The technical solutions of the embodiments of the present disclosure will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present disclosure, and not all embodiments. All other embodiments obtained by those skilled in the art based on the embodiments of the present disclosure without creative effort are within the scope of protection of the present disclosure.

[0030] I. Experimental Materials and Instruments

[0031] (a) Experimental materials

[0032] Soluble cerium salts: cerium nitrate (Ce(NO3)3·6H2O, electronic grade, purity ≥99.9%), cerium chloride (CeCl3·7H2O, electronic grade);

[0033] Surfactants: polyvinylpyrrolidone (PVP, K30, electronic grade), hexadecyltrimethylammonium bromide (CTAB, purity ≥99%), sodium dodecyl sulfate (SDS, electronic grade), among which polyvinylpyrrolidone is preferred (to improve dispersion stability);

[0034] Suspension aids: polyacrylic acid (PAA, molecular weight 5000~10000), sodium carboxymethyl cellulose (CMC, viscosity 200~300mPa·s), hydroxyethyl cellulose (HEC), among which polyacrylic acid is preferred (to enhance particle suspension).

[0035] Precipitating agent: 25wt% ammonia water (density 0.91g / cm³) 3 ), 10wt% sodium hydroxide aqueous solution, 10wt% potassium hydroxide aqueous solution, with ammonia water being preferred (mildly adjusting pH, which is beneficial for nanosphere nucleation).

[0036] Imidazole modifiers: 2-methylimidazole (purity ≥98%), 4-methylimidazole, benzimidazole, mebendazole, among which 2-methylimidazole is preferred (optimizes the electron cloud density of the imidazole ring and improves the selectivity);

[0037] Solvent: Deionized water (resistivity ≥18.2MΩ·cm, TOC ≤10ppb).

[0038] (II) Experimental Instruments

[0039] Dispersion and mixing equipment: ultrasonic cleaner (500W, 40kHz), high-pressure homogenizer (0-2000bar, 10L / h), top stirrer (0-1500rpm), peristaltic pump (0.1-10mL / min);

[0040] Reaction and post-processing equipment: constant temperature heating chamber (temperature control accuracy ±1℃), high-speed refrigerated centrifuge (maximum speed 15000rpm), vacuum freeze dryer (minimum temperature -80℃, vacuum degree ≤10Pa).

[0041] Characterization equipment: Scanning electron microscope (SEM, resolution 1 nm), Fourier transform infrared spectrometer (FT-IR, 4000-400 cm⁻¹). -1 ), thermogravimetric analyzer (TGA, nitrogen atmosphere, 10℃ / min), Zeta potential analyzer;

[0042] Performance testing equipment: Chemical mechanical polishing machine (CMP-300), film thickness gauge (accuracy ±1) ), optical microscope (magnification 50x).

[0043] II. Core Principles of Process Control

[0044] This invention achieves precise control over the polishing performance of cerium oxide by limiting key process parameters such as the type of imidazole modifier, the timing of its addition, and its mass ratio with the cerium source. The control principles of each parameter are as follows:

[0045] 1. Modifier Type Control Principle: The electronic effect and steric hindrance of the substituents on the imidazole ring jointly determine the modification effect. The methyl group of 2-methylimidazolium is an electron-donating group, which optimizes the electron cloud density of the imidazole ring. It also has moderate steric hindrance, achieving optimal adsorption balance on SiO2 and Si3N4 surfaces, thus exhibiting the highest selectivity (see Table 3, 38.4:1). The adsorption capacity of 4-methylimidazolium decreases slightly due to changes in the methyl substitution site (selectivity 19.1:1). Benzimidazole and tolueneimidazolium contain hydrophobic benzene rings, resulting in excessive steric hindrance and difficulty in effective adsorption (selectivity ratios only 3.1:1 and 2.88:1, respectively).

[0046] 2. Principle of Modifier Addition Timing Control: Adding modifiers during the precursor stage allows them to participate in cerium oxide nucleation and growth, achieving molecular-level modification and forming a uniform coating layer. Aggregation is prevented through steric hindrance and electrostatic stabilization mechanisms (selection ratio 38.4:1, see Table 2). Adding modifiers after nanosphere formation only results in simple surface modification, uneven coating, and weakened effect (selection ratio 33.7:1).

[0047] 3. Principle of Modifier to Cerium Source Mass Ratio Control: A mass ratio of 1:(40-60) is effective, with 1:50 being optimal (see Table 4). At this ratio, the modifier forms a monolayer saturated adsorption on the cerium oxide surface: this prevents aggregation through steric hindrance. Figure 1 The particle size is uniform (verified by SEM), and it can form a protective molecular film on the Si3N4 surface to inhibit its removal, while not hindering the chemical reaction between SiO2 and cerium oxide. Too high a ratio (1:10, 1:25) results in an excessively thick adsorption layer, reducing the SiO2 removal rate; too low a ratio (1:100, 1:200) fails to form a complete protective film, resulting in loss of selectivity.

[0048] 4. Process parameter control principle: ultrasonic stirring for 3.5-4.5h, high-pressure homogenization circulation for 4-6 times, precipitant drop rate of 0.8-1.2mL / min, and heating temperature of 60-100℃. The core function is to ensure the morphology and uniform particle size of the nanospheres. Among them, heating at 60℃ can avoid the decomposition of the modifier and is the optimal parameter (Example 1 has the best performance).

[0049] III. Examples

[0050] Example 1

[0051] S1: Preparation of modified reaction precursors

[0052] 100g of cerium nitrate was dissolved in 200mL of deionized water and placed in an ultrasonic cleaner at 500W and 40kHz until completely dissolved. 2g of polyvinylpyrrolidone, 2g of polyacrylic acid, and 2g of 2-methylimidazole were dissolved in 10mL of deionized water respectively. All the above solutions were combined and placed in an ultrasonic cleaner at 500W and 40kHz for 4 hours. Then, the mixture was transferred to a high-pressure homogenizer and circulated 5 times at 1200bar to obtain the modified reaction precursor.

[0053] S2: Preparation of colloidal cerium oxide nanospheres

[0054] The modified precursor obtained from S1 was transferred to a 500 mL three-necked flask and placed on a top stirrer and stirred continuously at a rate of 500 rpm. 20 mL of 25 wt% ammonia solution was added dropwise to the flask at a rate of 1.0 mL / min using a peristaltic pump. After the addition was completed, the three-necked flask was placed in a constant temperature heating oven at 60 °C and heated for 4 h, followed by aging and stirring for 12 h to obtain a colloidal cerium oxide nanosphere solution.

[0055] S3: Preparation of colloidal cerium oxide polishing slurry

[0056] The colloidal cerium oxide nanosphere solution obtained in S2 was transferred to a 50 mL centrifuge tube and centrifuged at 4 °C and 10,000 rpm for 30 min. The bottom solid was collected. The solid was washed three times with deionized water, and centrifuged at 4 °C and 8,000 rpm for 20 min after each wash. The washed solid was transferred to a vacuum freeze dryer and freeze-dried at -40 °C and a vacuum degree ≤10 Pa for 24 h until constant weight was obtained to obtain cerium oxide powder. The cerium oxide powder was mixed with deionized water at a mass ratio of 0.5% and dispersed by magnetic stirring at 800 rpm for 30 min to prepare a colloidal cerium oxide polishing solution.

[0057] Example 2

[0058] S1: Preparation of modified reaction precursors

[0059] 100g of cerium nitrate was dissolved in 200mL of deionized water and placed in an ultrasonic cleaner at 500W and 40kHz until completely dissolved. 2g of polyvinylpyrrolidone, 2g of polyacrylic acid, and 2g of 2-methylimidazole were weighed and dissolved in 10mL of deionized water respectively, and stirred magnetically at 600rpm until clear. All the above solutions were combined and placed in an ultrasonic cleaner at 500W and 40kHz for 4 hours. Then, the mixture was transferred to a high-pressure homogenizer and circulated 5 times at 1200bar to obtain the modified reaction precursor.

[0060] S2: Preparation of colloidal cerium oxide nanospheres

[0061] The modified precursor obtained from S1 was transferred to a 500 mL three-necked flask and placed on a top stirrer with continuous stirring at a rate of 500 rpm. 20 mL of ammonia water was added dropwise at a rate of 1.0 mL / min, and the mixture was heated at 80 °C for 4 h and then aged and stirred for 12 h to obtain a colloidal cerium oxide nanosphere solution.

[0062] S3: Preparation of colloidal cerium oxide polishing slurry

[0063] The colloidal cerium oxide nanosphere solution obtained in S2 was transferred to a 50 mL centrifuge tube and centrifuged at 4 °C and 10,000 rpm for 30 min. The bottom solid was collected. The solid was washed three times with deionized water, and centrifuged at 4 °C and 8,000 rpm for 20 min after each wash. The washed solid was transferred to a vacuum freeze dryer and freeze-dried at -40 °C and a vacuum degree ≤10 Pa for 24 h until constant weight was obtained to obtain cerium oxide powder. The cerium oxide powder was mixed with deionized water at a mass ratio of 0.5% and dispersed by magnetic stirring at 800 rpm for 30 min to prepare a colloidal cerium oxide polishing solution.

[0064] Example 3

[0065] S1: Preparation of modified reaction precursors

[0066] 100g of cerium nitrate was dissolved in 200mL of deionized water and placed in an ultrasonic cleaner at 500W and 40kHz until completely dissolved. 2g of polyvinylpyrrolidone, 2g of polyacrylic acid, and 2g of 2-methylimidazole were weighed and dissolved in 10mL of deionized water respectively, and stirred magnetically at 600rpm until clear. All the above solutions were combined and placed in an ultrasonic cleaner at 500W and 40kHz for 4 hours. Then, the mixture was transferred to a high-pressure homogenizer and circulated 5 times at 1200bar to obtain the modified reaction precursor.

[0067] S2: Preparation of colloidal cerium oxide nanospheres

[0068] The modified precursor obtained from S1 was transferred to a 500 mL three-necked flask and placed on a top stirrer and stirred continuously at a rate of 500 rpm. 20 mL of ammonia water was added dropwise at a rate of 1.0 mL / min, and the mixture was heated at 100 °C for 4 h and then aged and stirred for 12 h to obtain a colloidal cerium oxide nanosphere solution.

[0069] S3: Preparation of colloidal cerium oxide polishing slurry

[0070] The colloidal cerium oxide nanosphere solution obtained in S2 was transferred to a 50 mL centrifuge tube and centrifuged at 4 °C and 10,000 rpm for 30 min. The bottom solid was collected. The solid was washed three times with deionized water, and centrifuged at 4 °C and 8,000 rpm for 20 min after each wash. The washed solid was transferred to a vacuum freeze dryer and freeze-dried at -40 °C and a vacuum degree ≤10 Pa for 24 h until constant weight was obtained to obtain cerium oxide powder. The cerium oxide powder was mixed with deionized water at a mass ratio of 0.5% and dispersed by magnetic stirring at 800 rpm for 30 min to prepare a colloidal cerium oxide polishing solution.

[0071] Example 4 (modifier is 4-methylimidazole)

[0072] S1: Preparation of modified reaction precursors

[0073] 100g of cerium nitrate was dissolved in 200mL of deionized water and placed in an ultrasonic cleaner at 500W and 40kHz until completely dissolved. 2g of polyvinylpyrrolidone, 2g of polyacrylic acid, and 2g of 4-methylimidazole were dissolved in 10mL of deionized water respectively. All the above solutions were combined and placed in an ultrasonic cleaner at 500W and 40kHz for 4 hours. Then, the mixture was transferred to a high-pressure homogenizer and circulated 5 times at 1200bar to obtain the modified reaction precursor.

[0074] S2: Preparation of colloidal cerium oxide nanospheres

[0075] The modified precursor obtained from S1 was transferred to a 500 mL three-necked flask and placed on a top stirrer and stirred continuously at a rate of 500 rpm. 20 mL of 25 wt% ammonia solution was added dropwise to the flask at a rate of 1.0 mL / min using a peristaltic pump. After the addition was completed, the three-necked flask was placed in a constant temperature heating oven at 60 °C and heated for 4 h, followed by aging and stirring for 12 h to obtain a colloidal cerium oxide nanosphere solution.

[0076] S3: Preparation of colloidal cerium oxide polishing slurry

[0077] The colloidal cerium oxide nanosphere solution obtained in S2 was transferred to a 50 mL centrifuge tube and centrifuged at 4 °C and 10,000 rpm for 30 min. The bottom solid was collected. The solid was washed three times with deionized water, and centrifuged at 4 °C and 8,000 rpm for 20 min after each wash. The washed solid was transferred to a vacuum freeze dryer and freeze-dried at -40 °C and a vacuum degree ≤10 Pa for 24 h until constant weight was obtained to obtain cerium oxide powder. The cerium oxide powder was mixed with deionized water at a mass ratio of 0.5% and dispersed by magnetic stirring at 800 rpm for 30 min to prepare a colloidal cerium oxide polishing solution.

[0078] Example 5 (modifier is benzimidazole)

[0079] S1: Preparation of modified reaction precursors

[0080] 100g of cerium nitrate was dissolved in 200mL of deionized water and placed in an ultrasonic cleaner at 500W and 40kHz until completely dissolved. 2g of polyvinylpyrrolidone, 2g of polyacrylic acid, and 2g of benzimidazole were dissolved in 10mL of deionized water respectively. All the above solutions were combined and placed in an ultrasonic cleaner at 500W and 40kHz for 4 hours. Then, the mixture was transferred to a high-pressure homogenizer and circulated 5 times at 1200bar to obtain the modified reaction precursor.

[0081] S2: Preparation of colloidal cerium oxide nanospheres

[0082] The modified precursor obtained from S1 was transferred to a 500 mL three-necked flask and placed on a top stirrer and stirred continuously at a rate of 500 rpm. 20 mL of 25 wt% ammonia solution was added dropwise to the flask at a rate of 1.0 mL / min using a peristaltic pump. After the addition was completed, the three-necked flask was placed in a constant temperature heating oven at 60 °C and heated for 4 h, followed by aging and stirring for 12 h to obtain a colloidal cerium oxide nanosphere solution.

[0083] S3: Preparation of colloidal cerium oxide polishing slurry

[0084] The colloidal cerium oxide nanosphere solution obtained in S2 was transferred to a 50 mL centrifuge tube and centrifuged at 4 °C and 10,000 rpm for 30 min. The bottom solid was collected. The solid was washed three times with deionized water, and centrifuged at 4 °C and 8,000 rpm for 20 min after each wash. The washed solid was transferred to a vacuum freeze dryer and freeze-dried at -40 °C and a vacuum degree ≤10 Pa for 24 h until constant weight was obtained to obtain cerium oxide powder. The cerium oxide powder was mixed with deionized water at a mass ratio of 0.5% and dispersed by magnetic stirring at 800 rpm for 30 min to prepare a colloidal cerium oxide polishing solution.

[0085] Example 6 (modifier is mebendazole)

[0086] S1: Preparation of modified reaction precursors

[0087] 100g of cerium nitrate was dissolved in 200mL of deionized water and placed in an ultrasonic cleaner at 500W and 40kHz until completely dissolved. 2g of polyvinylpyrrolidone, 2g of polyacrylic acid, and 2g of tolueneimidazole were dissolved in 10mL of deionized water respectively. All the above solutions were combined and placed in an ultrasonic cleaner at 500W and 40kHz for 4 hours. Then, the mixture was transferred to a high-pressure homogenizer and circulated 5 times at 1200bar to obtain the modified reaction precursor.

[0088] S2: Preparation of colloidal cerium oxide nanospheres

[0089] The modified precursor obtained from S1 was transferred to a 500 mL three-necked flask and placed on a top stirrer and stirred continuously at a rate of 500 rpm. 20 mL of 25 wt% ammonia solution was added dropwise to the flask at a rate of 1.0 mL / min using a peristaltic pump. After the addition was completed, the three-necked flask was placed in a constant temperature heating oven at 60 °C and heated for 4 h, followed by aging and stirring for 12 h to obtain a colloidal cerium oxide nanosphere solution.

[0090] S3: Preparation of colloidal cerium oxide polishing slurry

[0091] The colloidal cerium oxide nanosphere solution obtained in S2 was transferred to a 50 mL centrifuge tube and centrifuged at 4 °C and 10,000 rpm for 30 min. The bottom solid was collected. The solid was washed three times with deionized water, and centrifuged at 4 °C and 8,000 rpm for 20 min after each wash. The washed solid was transferred to a vacuum freeze dryer and freeze-dried at -40 °C and a vacuum degree ≤10 Pa for 24 h until constant weight was obtained to obtain cerium oxide powder. The cerium oxide powder was mixed with deionized water at a mass ratio of 0.5% and dispersed by magnetic stirring at 800 rpm for 30 min to prepare a colloidal cerium oxide polishing solution.

[0092] IV. Comparative Examples

[0093] Comparative Example 1 (Blank Control Group)

[0094] S1: Preparation of reaction precursors

[0095] 100g of cerium nitrate was dissolved in 200mL of deionized water and placed in an ultrasonic cleaner at 500W and 40kHz until completely dissolved. 2g of polyvinylpyrrolidone and 2g of polyacrylic acid were dissolved in 10mL of deionized water respectively. All the above solutions were combined and placed in an ultrasonic cleaner at 500W and 40kHz for 4 hours. Then, the mixture was transferred to a high-pressure homogenizer and circulated 5 times at 1200bar to obtain the reaction precursor (without modifier).

[0096] S2: Preparation of colloidal cerium oxide nanospheres

[0097] The reaction precursor obtained from S1 was transferred to a 500 mL three-necked flask and placed on a top stirrer and stirred continuously at a rate of 500 rpm. 20 mL of ammonia water was added dropwise to the flask at a rate of 1.0 mL / min using a peristaltic pump. After the addition was completed, the three-necked flask was placed in a constant temperature heating oven at 60 °C and heated for 4 h. Then, it was aged and stirred for 12 h to obtain a colloidal cerium oxide nanosphere solution.

[0098] S3: Preparation of colloidal cerium oxide polishing slurry

[0099] The colloidal cerium oxide nanosphere solution obtained in S2 was transferred to a 50 mL centrifuge tube and centrifuged at 4 °C and 10,000 rpm for 30 min. The bottom solid was collected. The solid was washed three times with deionized water, and centrifuged at 4 °C and 8,000 rpm for 20 min after each wash. The washed solid was transferred to a vacuum freeze dryer and freeze-dried at -40 °C and a vacuum degree ≤10 Pa for 24 h until constant weight was obtained to obtain cerium oxide powder. The cerium oxide powder was mixed with deionized water at a mass ratio of 0.5% and dispersed by magnetic stirring at 800 rpm for 30 min to prepare a colloidal cerium oxide polishing solution.

[0100] Comparative Example 2 (Group with deteriorated timing of modifier addition)

[0101] S1: Preparation of reaction precursors

[0102] 100g of cerium nitrate was dissolved in 200mL of deionized water and placed in an ultrasonic cleaner at 500W and 40kHz until completely dissolved. 2g of polyvinylpyrrolidone and 2g of polyacrylic acid were dissolved in 10mL of deionized water respectively. All the above solutions were combined and placed in an ultrasonic cleaner at 500W and 40kHz for 4 hours. Then, the mixture was transferred to a high-pressure homogenizer and circulated 5 times at 1200bar to obtain the reaction precursor (without modifier).

[0103] S2: Preparation of modified colloidal cerium oxide nanospheres

[0104] The reaction precursor obtained from S1 was transferred to a 500 mL three-necked flask and placed on a top stirrer and stirred continuously at a rate of 500 rpm. 20 mL of ammonia water was added dropwise to the flask at a rate of 1.0 mL / min using a peristaltic pump. After the addition was completed, the three-necked flask was placed in a constant temperature heating oven at 60 °C and heated for 4 h to complete the formation of colloidal cerium oxide nanospheres.

[0105] Weigh 2g of 2-methylimidazole and dissolve it in 10mL of deionized water. Slowly add the solution dropwise to the above colloidal cerium oxide nanosphere solution and continue to age and stir at a stirring rate of 500rpm for 12h to obtain the modified colloidal cerium oxide nanosphere solution.

[0106] S3: Preparation of colloidal cerium oxide polishing slurry

[0107] The modified colloidal cerium oxide nanosphere solution obtained in S2 was transferred to a 50 mL centrifuge tube and centrifuged at 4 °C and 10,000 rpm for 30 min. The bottom solid was collected. The solid was washed three times with deionized water, and centrifuged at 4 °C and 8,000 rpm for 20 min after each wash. The washed solid was transferred to a vacuum freeze dryer and freeze-dried at -40 °C and a vacuum degree ≤10 Pa for 24 h until constant weight was obtained to obtain cerium oxide powder. The cerium oxide powder was mixed with deionized water at a mass ratio of 0.5% and dispersed by magnetic stirring at 800 rpm for 30 min to prepare a colloidal cerium oxide polishing solution.

[0108] Comparative Example 3 (Group 1 with excess modifier)

[0109] S1: Preparation of modified reaction precursors

[0110] Weigh 100g of cerium nitrate (cerium source) and dissolve it in 200mL of deionized water. Place it in an ultrasonic cleaner and ultrasonically stir at 500W and 40kHz until completely dissolved. Weigh 10g of 2-methylimidazole (modifier) ​​at a mass ratio of 1:10. Weigh 2g of polyvinylpyrrolidone and 2g of polyacrylic acid at the same time. Dissolve each of the three reagents in 10mL of deionized water. Combine all the above solutions and place them in an ultrasonic cleaner and ultrasonically stir at 500W and 40kHz for 4 hours. Then transfer them to a high-pressure homogenizer and cycle them 5 times at a pressure of 1200bar to obtain the modified reaction precursor.

[0111] S2: Preparation of colloidal cerium oxide nanospheres

[0112] The modified precursor obtained from S1 was transferred to a 500 mL three-necked flask and placed on a top stirrer and stirred continuously at a rate of 500 rpm. 20 mL of 25 wt% ammonia solution was added dropwise to the flask at a rate of 1.0 mL / min using a peristaltic pump. After the addition was completed, the three-necked flask was placed in a constant temperature heating oven at 60 °C and heated for 4 h, followed by aging and stirring for 12 h to obtain a colloidal cerium oxide nanosphere solution.

[0113] S3: Preparation of colloidal cerium oxide polishing slurry

[0114] The colloidal cerium oxide nanosphere solution obtained in S2 was transferred to a 50 mL centrifuge tube and centrifuged at 4 °C and 10,000 rpm for 30 min. The bottom solid was collected. The solid was washed three times with deionized water, and centrifuged at 4 °C and 8,000 rpm for 20 min after each wash. The washed solid was transferred to a vacuum freeze dryer and freeze-dried at -40 °C and a vacuum degree ≤10 Pa for 24 h until constant weight was obtained to obtain cerium oxide powder. The cerium oxide powder was mixed with deionized water at a mass ratio of 0.5% and dispersed by magnetic stirring at 800 rpm for 30 min to prepare a colloidal cerium oxide polishing solution.

[0115] Comparative Example 4 (Group 2 with excess modifier)

[0116] S1: Preparation of modified reaction precursors

[0117] Weigh 100g of cerium nitrate (cerium source) and dissolve it in 200mL of deionized water. Place it in an ultrasonic cleaner and ultrasonically stir at 500W and 40kHz until completely dissolved. Weigh 4g of 2-methylimidazole (modifier) ​​at a mass ratio of 1:25. Weigh 2g of polyvinylpyrrolidone and 2g of polyacrylic acid at the same time. Dissolve each of the three reagents in 10mL of deionized water. Combine all the above solutions and place them in an ultrasonic cleaner and ultrasonically stir at 500W and 40kHz for 4 hours. Then transfer them to a high-pressure homogenizer and cycle them 5 times at a pressure of 1200bar to obtain the modified reaction precursor.

[0118] S2: Preparation of colloidal cerium oxide nanospheres

[0119] The modified precursor obtained from S1 was transferred to a 500 mL three-necked flask and placed on a top stirrer and stirred continuously at a rate of 500 rpm. 20 mL of 25 wt% ammonia solution was added dropwise to the flask at a rate of 1.0 mL / min using a peristaltic pump. After the addition was completed, the three-necked flask was placed in a constant temperature heating oven at 60 °C and heated for 4 h, followed by aging and stirring for 12 h to obtain a colloidal cerium oxide nanosphere solution.

[0120] S3: Preparation of colloidal cerium oxide polishing slurry

[0121] The colloidal cerium oxide nanosphere solution obtained in S2 was transferred to a 50 mL centrifuge tube and centrifuged at 4 °C and 10,000 rpm for 30 min. The bottom solid was collected. The solid was washed three times with deionized water, and centrifuged at 4 °C and 8,000 rpm for 20 min after each wash. The washed solid was transferred to a vacuum freeze dryer and freeze-dried at -40 °C and a vacuum degree ≤10 Pa for 24 h until constant weight was obtained to obtain cerium oxide powder. The cerium oxide powder was mixed with deionized water at a mass ratio of 0.5% and dispersed by magnetic stirring at 800 rpm for 30 min to prepare a colloidal cerium oxide polishing solution.

[0122] Comparative Example 5 (Group 1 with insufficient modifier ratio)

[0123] S1: Preparation of modified reaction precursors

[0124] Weigh 100g of cerium nitrate (cerium source) and dissolve it in 200mL of deionized water. Place it in an ultrasonic cleaner and ultrasonically stir at 500W and 40kHz until completely dissolved. Weigh 1g of 2-methylimidazole (modifier) ​​at a mass ratio of 1:100. Weigh 2g of polyvinylpyrrolidone and 2g of polyacrylic acid at the same time. Dissolve each of the three reagents in 10mL of deionized water. Combine all the above solutions and ultrasonically stir at 500W and 40kHz for 4 hours in an ultrasonic cleaner. Then transfer the mixture to a high-pressure homogenizer and cycle it 5 times at a pressure of 1200bar to obtain the modified reaction precursor.

[0125] S2: Preparation of colloidal cerium oxide nanospheres

[0126] The modified precursor obtained from S1 was transferred to a 500 mL three-necked flask and placed on a top stirrer and stirred continuously at a rate of 500 rpm. 20 mL of 25 wt% ammonia solution was added dropwise to the flask at a rate of 1.0 mL / min using a peristaltic pump. After the addition was completed, the three-necked flask was placed in a constant temperature heating oven at 60 °C and heated for 4 h, followed by aging and stirring for 12 h to obtain a colloidal cerium oxide nanosphere solution.

[0127] S3: Preparation of colloidal cerium oxide polishing slurry

[0128] The colloidal cerium oxide nanosphere solution obtained in S2 was transferred to a 50 mL centrifuge tube and centrifuged at 4 °C and 10,000 rpm for 30 min. The bottom solid was collected. The solid was washed three times with deionized water, and centrifuged at 4 °C and 8,000 rpm for 20 min after each wash. The washed solid was transferred to a vacuum freeze dryer and freeze-dried at -40 °C and a vacuum degree ≤10 Pa for 24 h until constant weight was obtained to obtain cerium oxide powder. The cerium oxide powder was mixed with deionized water at a mass ratio of 0.5% and dispersed by magnetic stirring at 800 rpm for 30 min to prepare a colloidal cerium oxide polishing solution.

[0129] Comparative Example 6 (Group 2 with insufficient modifier ratio)

[0130] S1: Preparation of modified reaction precursors

[0131] Weigh 100g of cerium nitrate (cerium source) and dissolve it in 200mL of deionized water. Place it in an ultrasonic cleaner and ultrasonically stir at 500W and 40kHz until completely dissolved. Weigh 0.5g of 2-methylimidazole (modifier) ​​at a mass ratio of 1:200. Weigh 2g of polyvinylpyrrolidone and 2g of polyacrylic acid. Dissolve each of the three reagents in 10mL of deionized water. Combine all the above solutions and ultrasonically stir at 500W and 40kHz for 4 hours in an ultrasonic cleaner. Then transfer the mixture to a high-pressure homogenizer and cycle it 5 times at 1200bar to obtain the modified reaction precursor.

[0132] S2: Preparation of colloidal cerium oxide nanospheres

[0133] The modified precursor obtained from S1 was transferred to a 500 mL three-necked flask and placed on a top stirrer and stirred continuously at a rate of 500 rpm. 20 mL of 25 wt% ammonia solution was added dropwise to the flask at a rate of 1.0 mL / min using a peristaltic pump. After the addition was completed, the three-necked flask was placed in a constant temperature heating oven at 60 °C and heated for 4 h, followed by aging and stirring for 12 h to obtain a colloidal cerium oxide nanosphere solution.

[0134] S3: Preparation of colloidal cerium oxide polishing slurry

[0135] The colloidal cerium oxide nanosphere solution obtained in S2 was transferred to a 50 mL centrifuge tube and centrifuged at 4 °C and 10,000 rpm for 30 min. The bottom solid was collected. The solid was washed three times with deionized water, and centrifuged at 4 °C and 8,000 rpm for 20 min after each wash. The washed solid was transferred to a vacuum freeze dryer and freeze-dried at -40 °C and a vacuum degree ≤10 Pa for 24 h until constant weight was obtained to obtain cerium oxide powder. The cerium oxide powder was mixed with deionized water at a mass ratio of 0.5% and dispersed by magnetic stirring at 800 rpm for 30 min to prepare a colloidal cerium oxide polishing solution.

[0136] V. Performance Testing Methods

[0137] All polishing slurries prepared in the examples and comparative examples were tested for chemical mechanical polishing performance under exactly the same test conditions to ensure that the experimental results were caused only by the target variable:

[0138] Polishing targets: 8-inch silicon oxide (SiO2) wafers and silicon nitride (Si3N4) wafers;

[0139] Polishing equipment: CP-4 chemical mechanical polishing machine, polishing pressure 2psi, polishing disc speed 60rpm, polishing fluid flow rate 150mL / min, polishing time 60s;

[0140] Test parameters: The change in film thickness of the wafer before and after polishing was measured using an ellipsometry, and the material removal rate was calculated (unit: / min); the SiO2 / Si3N4 polishing selectivity ratio is calculated as the ratio of SiO2 removal rate to Si3N4 removal rate;

[0141] Parallel testing: Each group of samples was tested in parallel 3 times, and the average value was taken as the final result.

[0142] VI. Test Results and Data Analysis

[0143] Table 1: Effect of different heating temperatures on the basic properties of polishing slurry

[0144] ;

[0145] As shown in the table above, the heating temperature range of 60℃-100℃ defined in this invention is an effective process window. Polishing slurries prepared within this range have a SiO2 / Si3N4 selectivity ratio ≥28:1 and a cerium oxide particle size variation coefficient ≤15%, which can stably achieve the preparation of colloidal cerium oxide with nanosphere morphology, fully meeting the polishing requirements of semiconductor wafer STI processes.

[0146] As shown in the table above, 60℃ is the optimal heating temperature, corresponding to the best polishing performance in Example 1. Compared to the 80℃ and 100℃ methods, heating at 60℃ avoids the high-temperature decomposition of imidazole modifiers, achieving uniform coating of the modifier on the surface of cerium oxide particles. This ensures a high removal rate of SiO2, minimizes the removal of Si3N4, and achieves optimal particle size uniformity.

[0147] As the heating temperature increases, the selectivity of the polishing slurry decreases. The core reason is that the coordination and binding ability of the modifier is weakened under high temperature conditions, making it impossible to achieve precise molecular-level modification during the cerium oxide nucleation and growth stage. This results in a decrease in particle size uniformity and a weakening of the protective molecular film formation effect on the Si3N4 surface.

[0148] Table 2: Effect of the order of modifier addition on the polishing performance of the polishing slurry

[0149] ;

[0150] As shown in Table 2, the selectivity ratios of both Example 1 and Comparative Example 2 (38.4:1 and 33.7:1, respectively) are significantly higher than those of Comparative Example 1 (2.4:1). This is mainly due to the effective suppression of cerium oxide nanoparticle aggregation by the addition of the modifier, resulting in a more concentrated abrasive particle size distribution and reducing mechanical damage to the silicon nitride surface, which is highly sensitive to large particles, during polishing. Example 1 (in-situ addition of the modifier during the precursor stage) showed the best performance in both SiO2 removal rate and selectivity. Early addition allows the modifier to be more fully adsorbed on the surface of cerium oxide particles, forming a more stable dispersion system, thereby achieving higher material removal efficiency and better selectivity during polishing.

[0151] The selectivity ratio of Example 1 (38.4:1) was significantly higher than that of Comparative Example 2 (33.7:1), indicating that adding the modifier in the early stage of preparation allows the modifier molecules to more uniformly coat the surface of cerium oxide particles, thus exhibiting higher selectivity differences for SiO2 and Si3N4 surfaces with different chemical activities during polishing. This difference is related to the adsorption strength and coverage uniformity of the modifier on the cerium oxide surface. Adding the modifier during the preparation of the modification reaction precursor stage allows the modifier molecules to fully participate in the formation process of cerium oxide nanospheres, achieving surface modification at the molecular level. This addition method allows the modifier molecules to be more uniformly adsorbed on the surface of cerium oxide particles, forming a more complete coating layer, thereby more effectively preventing particle agglomeration through steric hindrance and electrostatic stabilization mechanisms.

[0152] When the mass fraction of the modifier reaches the critical micelle concentration, its effect on the polishing slurry performance reaches saturation. The electronegativity of the particle surface increases, and the electrostatic repulsion strengthens, effectively improving nanoparticle aggregation. Adding the modifier after the formation of cerium oxide nanospheres only modifies the surface of the already formed particles, making it difficult for the modifier to fully penetrate the contact interface between particles, resulting in a relatively weak modification effect. This method of addition may lead to uneven adsorption of the modifier on the particle surface, thus affecting its dispersion stability.

[0153] When the modifier mass fraction is too high, the viscosity of the polishing slurry increases, which is not conducive to material transport and may lead to local product accumulation, thus affecting the polishing effect. The addition of the modifier significantly improves the selectivity ratio of SiO2 to Si3N4, which stems from the synergistic effect of chemical and mechanical actions in chemical mechanical polishing. The modifier achieves a higher selectivity ratio by adjusting the chemical corrosion characteristics and mechanical removal efficiency of the polishing slurry on different material surfaces. Early addition of the modifier may further enhance the protection of the silicon nitride surface by optimizing the surface coating effect, reducing its removal rate, and thus significantly improving the selectivity ratio.

[0154] Table 3: Effects of different modifiers on the polishing performance of polishing slurry

[0155] ;

[0156] As shown in Table 3, the 2-methylimidazole used in Example 1 has the best performance. The core reason is that its molecular size is moderate and the electron-donating effect of the methyl group optimizes the electron cloud density of the imidazole ring, so that its adsorption on the SiO2 and Si3N4 surfaces reaches the best balance. It can form a dense protective molecular film on the Si3N4 surface without excessively hindering the chemimechanical interaction between cerium oxide and the SiO2 surface, thus obtaining the highest polishing selectivity.

[0157] In the polishing environment, the SiO2 surface is rich in silanol groups (Si-OH). Nitrogen atoms in molecules such as 2-methylimidazolium can form hydrogen bonds and other interactions with Si-OH, which can soften the SiO2 surface to some extent or promote the hydrolysis of its Si-O bonds. Therefore, in conjunction with the mechanical wear of cerium oxide abrasive, this maintains or even slightly increases the SiO2 removal rate. Ce in the polishing slurry... 3+ The ratio has a positive impact on the polishing rate because Ce 3+ Ce-O-Si bonds formed on the SiO2 surface are stronger than Si-O-Si bonds and are easier to remove from the material.

[0158] Table 4: Effects of different mass ratios of modifiers and cerium sources on the polishing performance of polishing slurry

[0159] ;

[0160] As shown in Table 4, the polishing slurry achieves the best polishing selectivity when the mass ratio of cerium source is 1:50. This is mainly due to the optimal balance between adsorption coating and chemical activity on the surface of cerium oxide particles at this ratio.

[0161] At this ratio, the modifier molecules can precisely achieve monolayer saturation adsorption on the surface of cerium oxide nanoparticles, forming a dense and stable coating layer. On the one hand, this effectively prevents the agglomeration of nanoparticles during preparation and storage through steric hindrance and electrostatic repulsion, ensuring uniform particle size and stable dispersion of the abrasive particles in the polishing slurry, providing an ideal physical basis for efficient and smooth polishing. On the other hand, and more importantly, this specific adsorption state enables precise control of the chemical reactions at the polishing interface. In particular, 2-methylimidazole, at a ratio of 1:50, can form a complete and dense protective molecular film on the Si3N4 surface through its nitrogen-containing groups. This film effectively blocks direct mechanical contact between the cerium oxide abrasive and the Si3N4 surface and alters its surface reaction kinetics, thereby strongly inhibiting the removal of Si3N4. Simultaneously, this ratio of modifier adsorption layer does not excessively hinder the effective chemimechanical interaction between the cerium oxide abrasive and the SiO2 surface, thus maintaining a high SiO2 removal rate. When the modifier ratio is too high, the SiO2 removal rate decreases significantly. The core reason is that the excessively thick modifier adsorption layer forms a "buffer pad," which hinders the effective contact between the cerium oxide abrasive and the SiO2 surface, resulting in a significant reduction in polishing efficiency. If the modifier ratio is too low, the Si3N4 removal rate increases sharply. The core reason is that the amount of modifier is insufficient, and it is impossible to form a complete protective molecular film on the Si3N4 surface, resulting in a complete loss of polishing selectivity.

[0162] In summary, this invention, through systematic experimental design and optimization, constructs a colloidal cerium oxide polishing slurry preparation system based on "in-situ liquid-phase modification + precise control of core parameters." Examples verify the feasibility and wide temperature window adaptability of the process, while multi-dimensional comparative examples clarify the optimal parameter combination of "adding 2-methylimidazole in the precursor stage at a mass ratio of 1:50," which significantly increases the SiO2 / Si3N4 selectivity of the polishing slurry to 38.4:1, far exceeding existing technologies. This solution not only addresses the core pain points of traditional solid-phase methods (high mechanical damage) and liquid-phase methods (poor stability) at their source, achieving a precise balance between chemical activity and mechanical properties, but also possesses advantages such as simplified process, controllable cost, and strong scalability potential. The comprehensive breakthroughs in particle size uniformity, dispersion stability, and polishing selectivity of the prepared polishing slurry perfectly meet the stringent requirements of shallow trench isolation processes for semiconductor wafers, providing an efficient and reliable solution for global planarization polishing in the context of integrated circuit feature size miniaturization, demonstrating significant technological innovation and industrial application value.

[0163] The embodiments of the present invention have been described in detail above, but the content described is only a preferred embodiment of the present invention and should not be considered as limiting the scope of the present invention. All equivalent changes and improvements made in accordance with the scope of the present invention should still fall within the patent coverage of the present invention.

Claims

1. A method for preparing a colloidal cerium oxide polishing slurry, characterized in that, Includes the following steps: S1. Preparation of modified reaction precursor: Dissolve soluble cerium salt in deionized water, and stir ultrasonically until completely dissolved. Then, dissolve surfactant, suspending agent and imidazole modifier in deionized water and stir until clear. Mix all solutions and stir ultrasonically for 3.5-4.5 hours. Then, process the mixture in a high-pressure homogenizer for 4-6 cycles to obtain the modified reaction precursor. The imidazole modifier is selected from at least one of 2-methylimidazole and 4-methylimidazole; The mass ratio of the imidazole modifier to the soluble cerium salt is 1:(40-60); S2. Preparation of colloidal cerium oxide nanospheres: The precursor obtained in S1 is continuously stirred, and a precipitant is added dropwise at a uniform rate. After heating, the mixture is aged and stirred to form a colloidal cerium oxide nanosphere solution with nanosphere morphology. The precipitant drop rate is 0.8-1.2 mL / min, the temperature is 60-100℃, and the aging and stirring time is 11-13 h. S3. Preparation of colloidal cerium oxide polishing solution: Centrifuge the solution obtained in S2, wash the obtained solid with deionized water and freeze-dry to constant weight to obtain cerium oxide powder, mix the powder with deionized water and stir to disperse to prepare colloidal cerium oxide polishing solution.

2. The preparation method according to claim 1, characterized in that, The soluble cerium salt is selected from at least one of cerium nitrate and cerium chloride.

3. The preparation method according to claim 1, characterized in that, The surfactant is selected from at least one of polyvinylpyrrolidone, hexadecyltrimethylammonium bromide, and sodium dodecyl sulfate; the suspending agent is selected from at least one of polyacrylic acid, sodium carboxymethyl cellulose, and hydroxyethyl cellulose; and the precipitant is selected from at least one of ammonia, sodium hydroxide, and potassium hydroxide.

4. The preparation method according to claim 1, characterized in that, The mass ratio of powder to deionized water in S3 is 0.4-0.6%.

5. A colloidal cerium oxide polishing slurry, characterized in that, It is prepared by any one of the preparation methods described in claims 1-4.

6. The application of the colloidal cerium oxide polishing slurry according to claim 5 in the chemical mechanical polishing of shallow trench isolation process of semiconductor wafers.

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