A method for preparing pH-responsive core-shell cerium oxide abrasive, a chemical mechanical polishing slurry, and a chemical mechanical polishing process.

Abstract

This invention discloses a method for preparing pH-responsive core-shell structured cerium oxide abrasive, a chemical mechanical polishing (CMP) slurry, and a CMP process, belonging to the technical field of CMP technology. The method includes the following steps: S1, mixing a cerium nitrate aqueous solution with a precipitant and reacting the mixture with a hydrothermal agent to obtain cerium oxide (CeO2) nanoparticles; S4, reacting polyacrylic acid-block-polyethylene glycol with the obtained CeO2@mSiO2-NH2 to graft amide bonds onto the particle surface, obtaining CeO2@mSiO2@PAA-b-PEG; S5, dispersing the obtained CeO2@mSiO2@PAA-b-PEG in a trivalent cerium salt solution and ion-exchanging the CeO2@mSiO2@PAA-b-PEG to obtain cerium oxide nanoparticles. 3+ Loading onto a PAA chain yields CeO2@mSiO2@PAA-b-PEG-Ce 3+ This chemical mechanical polishing slurry can sense the polishing stage, providing high removal efficiency in the early and middle stages of polishing, and high protection in the later stages.

Description

Technical Field

[0001] This invention relates to the field of CMP polishing slurry technology, specifically to a method for preparing a pH-responsive core-shell structured cerium oxide abrasive, a chemical mechanical polishing slurry, and a chemical mechanical polishing process. Background Technology

[0002] CMP, also known as chemical mechanical polishing, is a process that uses chemical etching and mechanical force to planarize silicon wafers or other substrate materials during manufacturing. The equipment consists of three main modules: polishing, cleaning, and transfer. During the process, the polishing head presses the surface of the wafer to be polished against a rough polishing pad, achieving global planarization through coupling via the etching of the polishing slurry, particle friction, and friction of the polishing pad. Modern integrated circuit components generally employ multi-layered three-dimensional wiring, therefore, the front-end processes in integrated circuit manufacturing require multiple cycles.

[0003] Cerium oxide (CeO2) polishing slurries have a high selectivity (SiO2:Si3N4 > 30), meaning that the removal rate of silicon oxide during polishing is much higher than that of silicon nitride. The high selectivity of the slurry effectively reduces silicon nitride removal, protecting its function as a stop layer. Cerium oxide slurries also have high planarization efficiency, quickly removing surface irregularities, and are therefore widely used in STI-CMP processes.

[0004] Traditional cerium oxide polishing slurries have the following problems:

[0005] Fixed chemical activity: Ce cannot be adjusted according to the polishing process (initial rough polishing vs. later fine polishing). 3+ Release can lead to insufficient initial removal or excessive removal later.

[0006] High temperature sensitivity: At high temperatures, abrasives tend to agglomerate, leading to fluctuations in removal rate and poor process stability.

[0007] Many surface defects: small particles can easily cause point contact scratches, while large particles affect the planarization efficiency.

[0008] Lack of adaptability: Existing technologies cannot adjust polishing behavior in real time according to surface conditions (such as roughness and defects).

[0009] Studies have shown that polyacrylic acid (PAA) exhibits significant pH responsiveness:

[0010] pH < 4: PAA carboxyl group (-COOH) is fully protonated, intramolecular hydrogen bonding is enhanced, the chain is in a highly coiled state, and hydrophilicity is weak.

[0011] pH 4-6: Carboxyl group partially dissociates into -COO - Electrostatic repulsion competes with hydrogen bonds, and the chain gradually unfolds.

[0012] pH > 6: Carboxyl groups are completely dissociated, -COO - The strong electrostatic repulsion between the two sides allows the PAA chains to fully extend, resulting in the strongest hydrophilicity.

[0013] However, a single PAA shrinks at high temperatures due to the destruction of the hydration layer, resulting in decreased dispersibility.

[0014] Cerium oxide is a primary abrasive used in the shallow trench isolation (STI) chemical mechanical polishing (CMP) process in integrated circuit manufacturing. It is generally believed that trivalent cerium ions (Ce) on the surface of cerium oxide particles... 3+ Ce can form Ce-O-Si bonds with silica dielectrics. Furthermore, the presence of Ce-O-Si bonds leads to the adsorption of cerium oxide particles on the dielectric surface after polishing; this particle adsorption problem is particularly prominent when using small-particle-size cerium oxide to reduce defects. 3+ Higher Ce concentrations result in higher polishing efficiency, but excessive Ce concentrations... 3+ Concentration can make particles more difficult to clean after polishing. After polishing, cerium oxide particles may remain on the silicon wafer surface, causing surface defects and subsequent processing problems. Various cleaning methods, including acid washing, alkaline washing, and ultrasonic cleaning, were investigated to improve cleaning efficiency and surface quality.

[0015] During CMP (Ceramic Polishing), the redox properties of cerium oxide contribute to the formation of Ce-O-Si bonds, thereby improving polishing efficiency. 3+ The increase of Ce can enhance the formation of this bond and improve the polishing rate. 3+ It reacts with the silicon-oxygen bonds (Si-O) on the silica surface to form Ce-O-Si bonds, promoting silica removal. By controlling Ce... 3+ / Ce 4+ The ratio can optimize polishing performance and improve selectivity (such as the removal rate selection ratio of silicon dioxide to silicon nitride). CeO2 nanoparticles are embedded in the micropores of the polishing pad and come into contact with the wafer surface. Under pressure and shear force, they perform micro-cutting, rolling, and sliding on the SiO2 surface, directly causing material removal, especially contributing the most in the initial roughening stage.

[0016] CeO2 has a high oxidizing capacity and can react with the surface of SiO2: ≡Si-OH+Ce 4+ →≡Si-O-Ce 3+ +H +， The formation of unstable Ce-O-Si bonds weakens the Si-O network structure, making subsequent mechanical removal easier.

[0017] In advanced semiconductor manufacturing, chemical mechanical polishing (CMP) needs to strike a balance between high removal rates and low defect rates. Traditional polishing slurries have fixed compositions, making it difficult to adapt to the needs of different stages of the polishing process. In the early stages of polishing, contact needs to be established between the polishing pad and the surface of the material being polished; at this point, mechanical removal may dominate. This stage helps remove surface contaminants and unevenness. As the polishing slurry is distributed and the chemical reaction begins, chemical removal also starts to play a role, although it may not be as significant as mechanical removal. In the middle stages of polishing, as polishing progresses, the role of chemical removal gradually increases, especially in high Ce2+ stages. 4+ In certain proportions, chemical removal can be performed more effectively, thus reducing reliance on mechanical force. Mechanical removal remains important at this stage, helping to remove loose material produced by chemical removal and maintaining surface smoothness. In the later stages of polishing (fine polishing), the contributions of chemical and mechanical removal may be more balanced. Appropriate Ce... 3+ The proportions help stabilize the polishing process, improve selectivity, and ensure uniform removal of different materials. The goal of this stage is to optimize surface quality and reduce defects such as scratches and unevenness. Summary of the Invention

[0018] As described in the prior art above, one of the objectives of this invention is to provide a method for preparing a pH-responsive core-shell structured cerium oxide abrasive. This core-shell structured cerium oxide abrasive can automatically adjust the Ce content according to pH changes and surface state signals (such as roughness and defect density) during the polishing stage. 3+ The release rate and particle aggregation state are controlled to achieve adaptive polishing, which achieves "efficient removal in the early stage of polishing and fine finishing in the later stage of polishing".

[0019] The second objective of this invention is to provide a chemical mechanical polishing slurry that can dynamically adjust Ce based on pH control and surface feedback signals. 3+ The release amount and particle behavior enable adaptive polishing.

[0020] The third objective of this invention is to provide a chemical mechanical polishing process that achieves "efficient removal in the initial stage and fine finishing in the later stage".

[0021] One of the objectives of this invention is achieved through the following technical solution:

[0022] A method for preparing a pH-responsive core-shell structured cerium oxide abrasive includes the following steps:

[0023] S1. Cerium nitrate aqueous solution is mixed with a precipitant and then subjected to a hydrothermal reaction to obtain cerium oxide (CeO2) nanoparticles;

[0024] S2. The CeO2 nanoparticles are dispersed in an ethanol-water system containing a template agent, and tetraethyl orthosilicate (TEOS) is added to carry out a sol-gel reaction to generate mesoporous silica-coated composite particles CeO2@mSiO2; then the template agent is removed by calcination to obtain CeO2@mSiO2 with a mesoporous structure.

[0025] S3. Disperse the CeO2@mSiO2 with mesoporous structure in an organic solvent, add a silane coupling agent for surface amination treatment, and obtain CeO2@mSiO2-NH2;

[0026] S4. Polyacrylic acid-block-polyethylene glycol (PAA-b-PEG) is reacted with CeO2@mSiO2-NH2 in the presence of an activator and grafted onto the particle surface through amide bonds to obtain CeO2@mSiO2@PAA-b-PEG.

[0027] S5. Disperse the obtained CeO2@mSiO2@PAA-b-PEG in a trivalent cerium salt solution, and then ion exchange the CeO2@mSiO2@PAA-b-PEG with the cerium salt solution. 3+ Loaded onto PAA chains, and after washing and drying, core-shell structured composite cerium oxide abrasive CeO2@mSiO2@PAA-b-PEG-Ce was obtained. 3+ .

[0028] Furthermore, in step S1, the conditions for the hydrothermal reaction are: temperature 160-200℃, time 3-5 hours.

[0029] Further, in step S2, the template agent is hexadecyltrimethylammonium bromide (CTAB), and its dosage is 0.1-1.0 g per 100 mL of reaction system; the sol-gel reaction is carried out at room temperature for 2 h; the calcination conditions are: 500-600℃, heat preservation for 2-6 hours.

[0030] Further, in step S3, the silane coupling agent is 3-aminopropyltriethoxysilane (APTES), and the amount used is 0.1-1.0 mL per gram of the mesoporous CeO2@mSiO2; the reaction conditions are: 60-80℃, reflux for 4-8 hours.

[0031] Further, in step S4, the activator is a combination of 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide (EDC) and N-hydroxysuccinimide (NHS); the reaction is carried out in MES buffer at pH 4.5-6.0, at a temperature of 20-25°C, and for 2-3 hours.

[0032] Further, in step S5, the trivalent cerium salt is one or more of cerium chloride (CeCl3), cerium nitrate (Ce(NO3)3), or cerium sulfate (Ce2(SO4)3); the ion exchange conditions are: trivalent cerium salt solution concentration 0.05-0.2 mol / L, pH 5.0-7.0, temperature 20-40℃, and time 1-4 hours.

[0033] Further, the polyacrylic acid-block-polyethylene glycol (PAA-b-PEG) wherein:

[0034] The number-average molecular weight of the PAA segment is 3000.

[0035] The number-average molecular weight of the PEG segment is 5000.

[0036] The PEG segment undergoes a conformational change at temperatures above 60°C, increasing its hydrophilicity and extending to form a steric hindrance layer.

[0037] The second objective of this invention is achieved by the following technical solution:

[0038] A chemical mechanical polishing slurry comprising a core-shell structured cerium oxide abrasive prepared by the method described above, with a concentration of 0.5-5.0 wt%, and further comprising ascorbic acid, lubricant, thermally conductive filler, choline lactate, with the balance being water; and a sodium hydroxide and sodium bicarbonate buffer pair.

[0039] Furthermore, the thermally conductive filler is at least one of h-BN and AlN nanoparticles;

[0040] Furthermore, the thermally conductive filler is at least one of h-BN and AlN nanoparticles; the lubricant is at least one of graphene quantum dots, MoS2, and hexagonal boron nitride.

[0041] The third objective of this invention is achieved by the following technical solution:

[0042] A chemical mechanical polishing process includes the following steps:

[0043] S1. Early and intermediate polishing stages: rough polishing is performed under pH conditions of 10.0-11.0;

[0044] S2. In the later stage of polishing, when the wafer surface condition is found to meet the preset conditions, the pH of the polishing solution is adjusted to 3.5-4.5 with an acetate-sodium acetate buffer and fine polishing is performed until the endpoint is reached. The pre-prepared lubricant dispersion and / or thermally conductive filler dispersion are added to the main liquid phase by dripping or continuous pumping for 10-30 minutes and stirring at 500-1000 rpm.

[0045] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0046] (1) The present invention provides a method for preparing pH-responsive core-shell structured cerium oxide abrasive, which achieves adaptive control of the polishing process by constructing an integrated intelligent response system of "material-process-control". In the early stage of polishing, PAA chains extend and mesoporous channels open under high pH conditions, releasing a large amount of Ce. 3+ This significantly enhances chemical action and rapidly removes surface protrusions. As the surface becomes smoother, real-time monitoring of the surface smoothness signal triggers a pH drop to the acidic range (3.5-4.5), causing the PAA chains to be fully protonated and highly coiled, effectively inhibiting Ce. 3+ The release of cerium oxide abrasive simultaneously induces the formation of submicron-sized loose clusters, achieving low-stress "surface contact," significantly reducing surface defects such as scratches, thereby dynamically adjusting the Ce content. 3+ / Ce 4+ Ratio and particle size. Ce-ascorbic acid in combination. 4+ The reduction cycle mechanism ensures the long-term stability of the polishing rate. Combined with the lubrication function of GQDs / MoS2 and the thermal conductivity of the thermally conductive filler, it synergistically reduces interfacial friction and localized temperature rise, significantly minimizing silicon nitride loss. This solution not only overcomes the problems of fixed chemical activity, temperature sensitivity, and susceptibility to scratches inherent in traditional polishing slurries, but also achieves seamless switching from "rough polishing" to "fine finishing" through dynamic pH control and endpoint feedback linkage. It ensures high removal efficiency while achieving excellent surface quality with ultra-low defects, demonstrating significant process stability, high level of intelligence, and promising prospects for industrial application.

[0047] Meanwhile, the PEG segments extend at high temperatures to form steric hindrance. The PAA-b-PEG block copolymer is used, in which the PEG segments undergo a conformational change at temperatures >60℃, increasing hydrophilicity and extending to form a steric hindrance layer, thereby achieving a dual response to pH and temperature, overcoming the limitations of single PAA, and avoiding the reduction of effective abrasive due to high temperatures.

[0048] (2) The chemical mechanical polishing slurry provided by the present invention comprises a core-shell structured cerium oxide abrasive prepared by the method described above, the concentration of which is 0.5-5.0 wt%, ascorbic acid, lubricant, thermally conductive filler, choline lactate, and a reducing agent (such as ascorbic acid) that can release high-valence cerium (Ce) from the core-shell structured cerium oxide abrasive. 4+ Aggregates or precipitates are reduced to soluble Ce. 3+This improves polishing stability in the early and middle stages of polishing. Graphene quantum dots (GQDs) and MoS2 act as solid lubricants, reducing the coefficient of friction and inhibiting scratches. In the later stages of polishing, h-BN and AlN nanoparticles, with their high thermal conductivity, help dissipate heat from the polishing pad, preventing localized overheating. Their combined use significantly reduces silicon nitride loss. Choline lactate, as a polyhydroxy quaternary ammonium salt, forms a dynamic hydration film on the particle surface, replacing the adsorbed water lost due to temperature increases in the early and middle stages of polishing, thus improving the stability of Ce. 3+ The / Si-OH engagement number does not decrease, thus improving the stability of the bond. Detailed Implementation

[0049] The present invention will now be further described in conjunction with specific embodiments. It should be noted that, without conflict, the embodiments or technical features described below can be arbitrarily combined to form new embodiments.

[0050] In chemical mechanical polishing (CMP), changes in surface roughness are one of the key indicators for measuring polishing effectiveness. Changes in surface roughness typically follow these trends:

[0051] 1. Initial stage:

[0052] At the start of polishing, surface roughness typically increases due to the direct contact and mechanical action between the abrasive particles and the silicon wafer surface. This is because the initial mechanical friction and chemical etching remove surface irregularities, but may also introduce new scratches and defects.

[0053] 2. Intermediate stage:

[0054] As the polishing process progresses, the surface gradually becomes smoother through the synergistic effect of chemical etching and mechanical grinding. At this stage, surface roughness begins to decrease as most elevation differences are smoothed out. However, excessive polishing pressure or overly coarse abrasive particles can lead to a further increase in surface roughness, as excessive mechanical action may introduce more scratches.

[0055] 3. Final stage:

[0056] Near the end of polishing, the surface roughness should reach a low, stable value. At this point, the chemical composition of the polishing slurry and the fineness of the abrasive particles are crucial for achieving the final surface quality.

[0057] If the chemical components in the polishing slurry can react effectively with the silicon wafer surface, and the abrasive particles are fine enough to perform fine surface finishing, then the final surface roughness will be very low and the surface quality will be very high.

[0058] 4. The impact of surface defects:

[0059] If surface defects (such as scratches, pits, etc.) are detected during the polishing process, it may be necessary to adjust polishing parameters, such as polishing pressure, chemical composition of polishing fluid, or size of abrasive particles, to reduce these defects.

[0060] Example 1

[0061] This embodiment provides the preparation of core-shell structured cerium oxide abrasive, specifically the preparation of CeO2@mSiO2@PAA-b-PEG-Ce 3+ This includes the following steps:

[0062] S1: Prepare a 0.1M cerium nitrate aqueous solution, add ammonia dropwise until pH=9, stir for 30 min, transfer to a polytetrafluoroethylene-lined autoclave, and hydrothermally react at 180℃ for 3 h. Centrifuge, wash, and dry to obtain CeO2 nanoparticles with a particle size of 100 nm;

[0063] S2: Disperse 1g CeO2 in 80mL of ethanol-water (3:1) mixture, add 0.5g cetyltrimethylammonium bromide (CTAB), and sonicate for 30min. Add 2mL LTEOS dropwise, stir at room temperature for 2h, centrifuge to collect the precipitate, and calcine at 600℃ for 4h to obtain CeO2@mSiO2.

[0064] S3: Disperse 1g CeO2@mSiO2 in 100mL toluene, add 0.5mL LAPTES, reflux at 80℃ for 6h, centrifuge and wash to obtain CeO2@mSiO2-NH2.

[0065] S4: Disperse 1g of CeO2@mSiO2-NH2 in MES buffer (pH=5.5), add PAA-b-PEG (PAAMw=3000, PEGMw=5000), and react at 25℃ for 2.5h using EDC / NHS as the activator. Centrifuge and wash to obtain CeO2@mSiO2@PAA-b-PEG.

[0066] S5: Disperse 1g of CeO2@mSiO2@PAA-b-PEG in 0.1MCeCl3 solution (pH=6.0), stir at 40℃ for 2h, centrifuge, and wash with deionized water until no Ce is found. 3+ Detected, vacuum dried at 60℃, yielded CeO2@mSiO2@PAA-b-PEG-Ce 3+ (Ce) 3+ Loading capacity: 78 mg / g.

[0067] In this embodiment, PEG (polyethylene glycol) exhibits unique temperature-sensitive behavior:

[0068] At low temperatures: PEG chains form hydrogen bonds with water and curl up moderately;

[0069] At high temperatures: the increased thermal motion of water molecules disrupts the hydrogen bonds between PEG and water. To reduce free energy, the PEG chains extend, forming a "hydration umbrella" structure. Simultaneously, the PEG segments extend at high temperatures, creating steric hindrance. Using a PAA-b-PEG block copolymer, where the PEG segments undergo a conformational change at temperatures above 60°C, their hydrophilicity increases and they extend, forming a steric hindrance layer. This achieves a dual response to pH and temperature, overcoming the limitations of single PAA and preventing a reduction in effective abrasive due to high temperatures.

[0070] 1. Swelling state at low pH: At low pH (acidic environment), the carboxyl group (-COOH) in PAA is protonated to form a hydrophilic carboxylic acid (-COOH). At this time, the PAA chain is in a coiled state and has less swelling. This is because after the carboxyl group is protonated, the hydrogen bonding between molecules is enhanced, causing the polymer chains to entangle with each other and reducing contact with water.

[0071] 2. Swelling at High pH: Under high pH (alkaline environment), the carboxyl group (-COOH) in PAA dissociates to form a negatively charged carboxylate ion (-COO₂). - Due to the electrostatic repulsion between negative charges, the PAA chains gradually unfold, forming an open structure and significantly increasing their expansibility.

[0072] The effect of pH value on swelling state

[0073] At pH values ​​below 4, the PAA chains are coiled and exhibit minimal swelling. This is because the carboxyl group is protonated to form a less hydrophilic carboxylic acid (-COOH), which enhances the intermolecular hydrogen bonding.

[0074] Between pH 4 and 6: The swelling property of the PAA chain gradually increases. This is because the carboxyl group begins to dissociate, forming a negatively charged carboxylate ion (-COO₂). - The electrostatic repulsion between negative charges causes the polymer chains to gradually unfold.

[0075] At pH values ​​above 6, the PAA chains completely dissociate, reaching maximum swelling capacity. This is because the complete dissociation of the carboxyl groups results in the strongest electrostatic repulsion between negative charges, allowing the polymer chains to fully unfold.

[0076] This embodiment also provides the preparation of a chemical mechanical polishing slurry, the composition of which is as follows:

[0077] Core-shell structured cerium oxide abrasive: 2.0 wt%

[0078] Ascorbic acid: 0.1 wt%

[0079] Sodium hydroxide and sodium bicarbonate buffer pair: Adjust initial pH to 10.8;

[0080] Replenish with deionized water;

[0081] Filtration using a 0.2μm PES membrane.

[0082] Ascorbic acid (AA) is a mild reducing agent that can selectively reduce Ce. 4+ To Ce 3+ It does not damage the CeO2 crystal structure and is stable under alkaline conditions.

[0083] In this embodiment, choline lactate, as a polyhydroxy quaternary ammonium salt, forms a dynamic hydration film on the particle surface, replacing the adsorbed water lost due to temperature rise during the early and middle stages of polishing, thus making Ce... 3+ The / Si-OH engagement number does not decrease, thus improving the stability of the bond.

[0084] This embodiment also provides an adaptive chemical mechanical polishing process, which includes the following steps:

[0085] S1. Early and intermediate polishing stages: rough polishing is performed under pH 10.8 conditions;

[0086] S2. In the later stage of polishing, when the wafer surface condition is found to meet the preset conditions, the pH of the polishing solution is adjusted to 4 with an acetate-sodium acetate buffer and fine polishing is performed until the endpoint is reached. The pre-prepared lubricant dispersion and / or thermally conductive filler dispersion are added to the main liquid phase by dripping or continuous pumping for 10 minutes and stirring at 600 rpm.

[0087] The equipment and process parameters for polishing are as follows:

[0088] 1. Equipment and Wafers

[0089] CMP equipment: Equipped with an in-situ interference endpoint detection system, an online pH sensor, and an automatic acid / alkali pump valve system.

[0090] Wafer: 300mm STI structure wafer (SiO2 / Si3N4).

[0091] 2. Chemical Mechanical Polishing Process Flow (Key: pH Switching Logic)

[0092] Polishing stage Polishing parameters action Early and middle stages of polishing pH=10.8, Pressure=3.2psi, Rotation speed=95rpm, Polishing fluid flow rate=200mL / min <![CDATA[PAA-b-PEG stretching, mesopore opening → Ce 3+ Fast release - high chemical activity, rapid removal of the SiO2 protrusion in the field area - continuous polishing, real-time monitoring of the interference signal]]> pH switching timing The pad temperature was measured using an infrared fiber optic probe. After peaking, it dropped by 1.5℃, indicating that heat generation was less than heat loss and the film thickness was less than 50nm. The motor torque (spindle current) measured at 10kHz using a 16-bit ADC driver decreased by 3%–5% and stabilized for 15s, indicating that the oxide layer was thinning and the friction coefficient dropped sharply. The OceanOptics USB2000 was used to integrate the reflection spectrum at 630nm in 50ms. Compared with the interference valley depth measured in the previous cycle, it was ≤5%, indicating that the film thickness entered <30nm and the interference signal saturated. pH=10.8 to pH=4.0 switching operation Late polishing stage (determining the "late polishing stage") <![CDATA[pH = 4.0 (automatically add 0.5 M H2SO4) Pressure = 1.6 psi Rotation speed = 55 rpm]]> <![CDATA[When the interference signal indicates that the SiO2 thickness is approaching the end point (remaining < 50 nm), it automatically triggers the pH switching program - the system controls the pump valve to inject acid into the polishing liquid flow path, reducing the pH to 4.0 - the PAA segment is completely protonated and coiled → Ce 3+ The blocked - PEG segment is released and extended under the polishing heat (80 °C) → inhibiting agglomeration, forming loose clusters of 700 nm - low chemical + low mechanical action, achieving fine polishing, and protecting the Si3N4 stop layer]]> end Stop polishing The interference signal reaches the preset endpoint

[0093] The transition from mid-term to late-term is not a time concept, but rather a "friction-chemical signal inflection point"—the initial peak and subsequent decline of the padding temperature, along with a slight decrease in motor torque, is the most common and inexpensive "watershed."

[0094] Example 2

[0095] This embodiment provides the preparation of core-shell structured cerium oxide abrasive, specifically the preparation of CeO2@mSiO2@PAA-b-PEG-Ce 3+ This includes the following steps:

[0096] S1: Prepare a 0.1M cerium chloride (CeCl3) aqueous solution, add ammonia dropwise to pH=9, stir for 30 min, transfer to a polytetrafluoroethylene-lined autoclave, and hydrothermally react at 160℃ for 4 h. Centrifuge, wash, and dry to obtain CeO2 nanoparticles with a particle size of 100 nm;

[0097] S2: Disperse 1g CeO2 in 100mL of ethanol-water (3:1) mixture, add 0.1g hexadecyltrimethylammonium bromide (CTAB), and sonicate for 1h. Add 2mL LTEOS dropwise, stir at room temperature for 2h, centrifuge to collect the precipitate, and calcine at 200℃ for 6h to obtain CeO2@mSiO2.

[0098] S3: Disperse 1g CeO2@mSiO2 in 100mL toluene, add 1mL LAPTES, reflux at 60℃ for 4h, centrifuge and wash to obtain CeO2@mSiO2-NH2.

[0099] S4: Disperse 1g of CeO2@mSiO2-NH2 in MES buffer (pH=4.5), add PAA-b-PEG (PAAMw=3000, PEGMw=5000), and react at 22℃ for 2h using EDC / NHS as the activator. Centrifuge and wash to obtain CeO2@mSiO2@PAA-b-PEG.

[0100] S5: Disperse 1g of CeO2@mSiO2@PAA-b-PEG in 0.2MCeCl3 solution (pH=6.0), stir at 20℃ for 1h, centrifuge, and wash with deionized water until no Ce is found. 3+ Detected, vacuum dried at 60℃, yielded CeO2@mSiO2@PAA-b-PEG-Ce 3+ (Ce) 3+ Loading capacity: 78 mg / g.

[0101] In this embodiment, PEG (polyethylene glycol) exhibits unique temperature-sensitive behavior:

[0102] At low temperatures: PEG chains form hydrogen bonds with water and curl up moderately;

[0103] At high temperatures: the increased thermal motion of water molecules disrupts the hydrogen bonds between PEG and water. To reduce free energy, the PEG chains extend, forming a "hydration umbrella" structure. Simultaneously, the PEG segments extend at high temperatures, creating steric hindrance. Using a PAA-b-PEG block copolymer, where the PEG segments undergo a conformational change at temperatures above 60°C, their hydrophilicity increases and they extend, forming a steric hindrance layer. This achieves a dual response to pH and temperature, overcoming the limitations of single PAA and preventing a reduction in effective abrasive due to high temperatures.

[0104] This embodiment also provides the preparation of a chemical mechanical polishing slurry, the composition of which is as follows:

[0105] Core-shell structured cerium oxide abrasive: 0.5 wt%;

[0106] Ascorbic acid: 0.1 wt%

[0107] Sodium hydroxide and sodium bicarbonate buffer pair: Adjust initial pH to 10;

[0108] Replenish with deionized water;

[0109] Filtration using a 0.2μm PES membrane.

[0110] Ascorbic acid (AA) is a mild reducing agent that can selectively reduce Ce. 4+ To Ce 3+ It does not damage the CeO2 crystal structure and is stable under alkaline conditions.

[0111] This embodiment also provides an adaptive chemical mechanical polishing process, which includes the following steps:

[0112] S1. Early and intermediate polishing stages: rough polishing is performed under pH 10.0 conditions;

[0113] S2. In the later stage of polishing, when the wafer surface condition is found to meet the preset conditions, the pH of the polishing solution is adjusted to 3.5 with an acetate-sodium acetate buffer and fine polishing is performed until the endpoint is reached. The pre-prepared lubricant dispersion and / or thermally conductive filler dispersion are added to the main liquid phase by dripping or continuous pumping for 20 minutes and stirring at 500 rpm.

[0114] Example 3

[0115] This embodiment provides the preparation of core-shell structured cerium oxide abrasive, specifically the preparation of CeO2@mSiO2@PAA-b-PEG-Ce 3+ This includes the following steps:

[0116] S1: Prepare a 0.1M cerium sulfate (Ce2(SO4)3) aqueous solution, add ammonia dropwise to pH=9, stir for 30 min, transfer to a polytetrafluoroethylene-lined autoclave, and hydrothermally react at 300℃ for 5 h. Centrifuge, wash, and dry to obtain CeO2 nanoparticles with a particle size of 100 nm;

[0117] S2: Disperse 1g CeO2 in 100mL of ethanol-water (3:1) mixture, add 1g hexadecyltrimethylammonium bromide (CTAB), and sonicate for 1.5h. Add 2mL LTEOS dropwise, stir at room temperature for 2h, centrifuge to collect the precipitate, and calcine at 400℃ for 2h to obtain CeO2@mSiO2.

[0118] S3: Disperse 1g CeO2@mSiO2 in 100mL toluene, add 0.1mL LAPTES, reflux at 70℃ for 8h, centrifuge and wash to obtain CeO2@mSiO2-NH2.

[0119] S4: Disperse 1g of CeO2@mSiO2-NH2 in MES buffer (pH=6.0), add PAA-b-PEG (PAAMw=3000, PEGMw=5000), and react at 20℃ for 3h using EDC / NHS as the activator. Centrifuge and wash to obtain CeO2@mSiO2@PAA-b-PEG.

[0120] S5: Disperse 1g of CeO2@mSiO2@PAA-b-PEG in 0.05M CeCl3 solution (pH=6.0), stir at 30℃ for 4h, centrifuge, and wash with deionized water until no Ce is found. 3+ Detected, vacuum dried at 60℃, yielded CeO2@mSiO2@PAA-b-PEG-Ce 3+ (Ce) 3+ Loading capacity: 78 mg / g.

[0121] In this embodiment, PEG (polyethylene glycol) exhibits unique temperature-sensitive behavior:

[0122] At low temperatures: PEG chains form hydrogen bonds with water and curl up moderately;

[0123] At high temperatures: the increased thermal motion of water molecules disrupts the hydrogen bonds between PEG and water. To reduce free energy, the PEG chains extend, forming a "hydration umbrella" structure. Simultaneously, the PEG segments extend at high temperatures, creating steric hindrance. Using a PAA-b-PEG block copolymer, where the PEG segments undergo a conformational change at temperatures above 60°C, their hydrophilicity increases and they extend, forming a steric hindrance layer. This achieves a dual response to pH and temperature, overcoming the limitations of single PAA and preventing a reduction in effective abrasive due to high temperatures.

[0124] This embodiment also provides the preparation of a chemical mechanical polishing slurry, the composition of which is as follows:

[0125] Core-shell structured cerium oxide abrasive: 5.0 wt%

[0126] Ascorbic acid: 0.1 wt%

[0127] Sodium hydroxide and sodium bicarbonate buffer pair: Adjust initial pH to 11;

[0128] Replenish with deionized water;

[0129] Filtration using a 0.2μm PES membrane.

[0130] Ascorbic acid (AA) is a mild reducing agent that can selectively reduce Ce. 4+ To Ce 3+ It does not damage the CeO2 crystal structure and is stable under alkaline conditions.

[0131] This embodiment also provides an adaptive chemical mechanical polishing process, which includes the following steps:

[0132] S1, Early and Middle Polishing Stages: Rough polishing is performed under pH 11.0 conditions;

[0133] S2. In the later stage of polishing, when the wafer surface condition is found to meet the preset conditions, the pH of the polishing solution is adjusted to 4.5 with an acetate-sodium acetate buffer and fine polishing is performed until the endpoint is reached. The pre-prepared lubricant dispersion and / or thermally conductive filler dispersion are added to the main liquid phase by dripping or continuous pumping for 30 minutes and stirring at 1000 rpm.

[0134] Example 4

[0135] This embodiment provides the preparation of core-shell structured cerium oxide abrasive, specifically the preparation of CeO2@mSiO2@PAA-b-PEG-Ce 3+ This includes the following steps:

[0136] S1: Prepare a 0.1M cerium nitrate aqueous solution, add ammonia dropwise until pH=9, stir for 30 min, transfer to a polytetrafluoroethylene-lined autoclave, and hydrothermally react at 180℃ for 3 h. Centrifuge, wash, and dry to obtain CeO2 nanoparticles with a particle size of 100 nm;

[0137] S2: Disperse 1g CeO2 in 80mL of ethanol-water (3:1) mixture, add 0.5g cetyltrimethylammonium bromide (CTAB), and sonicate for 30min. Add 2mL LTEOS dropwise, stir at room temperature for 2h, centrifuge to collect the precipitate, and calcine at 600℃ for 4h to obtain CeO2@mSiO2.

[0138] S3: Disperse 1g CeO2@mSiO2 in 100mL toluene, add 0.5mL LAPTES, reflux at 80℃ for 6h, centrifuge and wash to obtain CeO2@mSiO2-NH2.

[0139] S4: Disperse 1g of CeO2@mSiO2-NH2 in MES buffer (pH=5.5), add PAA-b-PEG (PAAMw=3000, PEGMw=5000), and react at 25℃ for 2.5h using EDC / NHS as the activator. Centrifuge and wash to obtain CeO2@mSiO2@PAA-b-PEG.

[0140] S5: Disperse 1g of CeO2@mSiO2@PAA-b-PEG in 0.1MCeCl3 solution (pH=6.0), stir at 40℃ for 2h, centrifuge, and wash with deionized water until no Ce is found. 3+ Detected, vacuum dried at 60℃, yielded CeO2@mSiO2@PAA-b-PEG-Ce 3+ (Ce) 3+ Loading capacity: 78 mg / g.

[0141] In this embodiment, PEG (polyethylene glycol) exhibits unique temperature-sensitive behavior:

[0142] At low temperatures: PEG chains form hydrogen bonds with water and curl up moderately;

[0143] At high temperatures: the increased thermal motion of water molecules disrupts the hydrogen bonds between PEG and water. To reduce free energy, the PEG chains extend, forming a "hydration umbrella" structure. Simultaneously, the PEG segments extend at high temperatures, creating steric hindrance. Using a PAA-b-PEG block copolymer, where the PEG segments undergo a conformational change at temperatures above 60°C, their hydrophilicity increases and they extend, forming a steric hindrance layer. This achieves a dual response to pH and temperature, overcoming the limitations of single PAA and preventing a reduction in effective abrasive due to high temperatures.

[0144] 1. Swelling state at low pH: At low pH (acidic environment), the carboxyl group (-COOH) in PAA is protonated to form a hydrophilic carboxylic acid (-COOH). At this time, the PAA chain is in a coiled state and has less swelling. This is because after the carboxyl group is protonated, the hydrogen bonding between molecules is enhanced, causing the polymer chains to entangle with each other and reducing contact with water.

[0145] 2. Swelling at High pH: Under high pH (alkaline environment), the carboxyl group (-COOH) in PAA dissociates to form a negatively charged carboxylate ion (-COO₂). - Due to the electrostatic repulsion between negative charges, the PAA chains gradually unfold, forming an open structure and significantly increasing their expansibility.

[0146] The effect of pH value on swelling state

[0147] At pH values ​​below 4, the PAA chains are coiled and exhibit minimal swelling. This is because the carboxyl group is protonated to form a less hydrophilic carboxylic acid (-COOH), which enhances the intermolecular hydrogen bonding.

[0148] Between pH 4 and 6: The swelling property of the PAA chain gradually increases. This is because the carboxyl group begins to dissociate, forming a negatively charged carboxylate ion (-COO₂). - The electrostatic repulsion between negative charges causes the polymer chains to gradually unfold.

[0149] At pH values ​​above 6, the PAA chains completely dissociate, reaching maximum swelling capacity. This is because the complete dissociation of the carboxyl groups results in the strongest electrostatic repulsion between negative charges, allowing the polymer chains to fully unfold.

[0150] This embodiment also provides the preparation of a chemical mechanical polishing slurry, the composition of which is as follows:

[0151] Core-shell structured cerium oxide abrasive: 2.0 wt%

[0152] Ascorbic acid: 0.1 wt%

[0153] Lubricant: Graphene quantum dots: 0.1 wt%;

[0154] Thermally conductive filler h-BN: 0.2wt%;

[0155] Sodium hydroxide and sodium bicarbonate buffer pair: Adjust initial pH to 10.8;

[0156] Replenish with deionized water;

[0157] Filtration using a 0.2μm PES membrane.

[0158] In this embodiment, lubricant and thermally conductive filler are added during the later stages of polishing.

[0159] This embodiment also provides an adaptive chemical mechanical polishing process, which includes the following steps:

[0160] S1. Early and intermediate polishing stages: rough polishing is performed under pH 10.8 conditions;

[0161] S2. In the later stage of polishing, when the wafer surface condition is found to meet the preset conditions, the pH of the polishing solution is adjusted to 4 with an acetate-sodium acetate buffer and fine polishing is performed until the endpoint is reached. The pre-prepared lubricant dispersion and / or thermally conductive filler dispersion are added to the main liquid phase by dripping or continuous pumping for 10 minutes and stirring at 600 rpm.

[0162] Experimental Example 1

[0163] Experimental tests were conducted according to the preparation method of pH-responsive core-shell structured cerium oxide abrasive, chemical mechanical polishing slurry, and chemical mechanical polishing process in Example 1. The test results are shown in Table 1.

[0164] Table 1

[0165] project result Test methods and conditions <![CDATA[SiO2 removal rate (in the early and middle stages of polishing)]]> 720nm / min <![CDATA[Polishing equipment for a standard 8-inch SOI wafer (SiO2 film thickness 1500 nm, Si3N4 masking layer 30 nm): APR-100 type CMP machine (applicable) Polishing pad: Dow Corning IC1000 Polishing liquid: the formula of the present invention (pH = 10.8, CeO2 concentration 2 wt%) Pressure: 3.2 psi Rotation speed: 100 rpm (wafer carrier) / 95 rpm (polishing head) Temperature: 80 °C Time: average value taken within the first 3 minutes (initial stage) Measurement method: Ellipsometer to measure the film thickness change]]> <![CDATA[SiO2 removal rate (late stage of polishing)]]> 110nm / min (stable) Under the same conditions and time window: sampling every 10 seconds from the 10th to 15th minute (after entering the stabilization period), and taking the average of 5 consecutive samples. Requirement: Removal rate fluctuation <±5%. <![CDATA[Si3N4 loss]]> <3nm Under the same conditions and time window: sampling every 10 seconds from the 10th to 15th minute (after entering the stabilization period), and taking the average of 5 consecutive samples. Requirement: Removal rate fluctuation <±5%. Surface RMS roughness (endpoint) 0.8Å <![CDATA[Clean immediately after polishing (DI water rinse + nitrogen blow-dry). Scan area using AFM (atomic force microscope): 5×5μm 2 Scan mode: Tapping Mode. Data processing: Remove tilt, calculate RMS roughness. Number of samples: ≥3 pieces, take the average]]> Scratch density (≥50nm) <0.3 / cm² <![CDATA[Using dark-field optical microscope (DF-OM) or white light interferometer (WLI), magnification: 500×, field of view area ≥ 1 cm 2 Detection range: Scratches in the central area of the wafer (diameter 5 mm). Definition of scratches: length ≥ 50 nm, width ≥ 10 nm, depth ≥ 10 nm. Statistically analyze ≥ 3 fields of view and take the average value]]> Temperature stability (70–90℃) MRR change <8% <![CDATA[Set the thermostat to control the environmental temperature to cycle within the range of 70–90 °C, with each increment being 10 °C. After stabilizing for 10 minutes at each increment, start the polishing test. Record the SiO2 removal rate (MRR) at each temperature and calculate the ratio of the difference between the maximum MRR and the minimum MRR to the average value: DeltaMRR%=(Max-Min) / Mean×100%<8%]]> Clean up residual particles <![CDATA[<0.08particles / cm 2 ]]> Standard cleaning procedure: DI water rinsing → ultrasonic cleaning (5 min) → nitrogen drying. Particle detection: KLA-Tencor Surfscan 6200 (or equivalent tool). Detection wavelength: 633 nm, sensitivity: ≤10 nm. Detection area: whole wafer. Particle definition: amorphous particles with a size ≥50 nm. Average value of 3 samples.

[0166] Experimental tests were conducted according to the preparation method of pH-responsive core-shell structured cerium oxide abrasive, chemical mechanical polishing slurry, and chemical mechanical polishing process in Example 1. The test results are shown in Table 2.

[0167] Table 2

[0168] project Test methods PAA-b-PEG (PAA3000-PEG5000) Single PAA (PAA3000) Analysis and Explanation Dispersibility (DLS) at room temperature (25°C) Test temperature: 25°C - Sample concentration: 1wt% - Dynamic light scattering (DLS) measurement of D50 D50 = 120 nm (monodisperse, PDI < 0.15) D50 = 115 nm (monodisperse, PDI < 0.16) Both dispersed well at room temperature with no significant difference. High-temperature (80°C) dispersibility (DLS) Test temperature: 80°C constant temperature water bath - continuous monitoring for 30 minutes, record D50 changes. D50↑10% (finally ≈132nm) D50↑85% (final ≈212nm) → Significant aggregation Removal rate stability (CV%) CMP continuous polishing for 30 minutes, with removal rate measured every 5 minutes. CV% = 6.3% CV%=14.7% The single PAA system suffers from large fluctuations in activity and unstable removal rate due to high-temperature agglomeration.

[0169] The above embodiments are merely preferred embodiments of the present invention and should not be construed as limiting the scope of protection of the present invention. Any non-substantial changes and substitutions made by those skilled in the art based on the present invention shall fall within the scope of protection claimed by the present invention.

Claims

1. A method for preparing a pH-responsive core-shell structured ceria abrasive, characterized in that, The method comprises the following steps: S1, mixing cerium nitrate aqueous solution with a precipitant, and preparing CeO2 nanoparticles through hydrothermal reaction; S2, dispersing the CeO2 nanoparticles in an ethanol-water system containing a template agent, adding tetraethyl orthosilicate to perform sol-gel reaction, and generating composite particles CeO2@mSiO2 coated with mesoporous silica; then removing the template agent through calcination to obtain CeO2@mSiO2 with mesoporous structure; S3, dispersing the CeO2@mSiO2 with mesoporous structure in an organic solvent, and adding a silane coupling agent to perform surface aminization treatment, thereby obtaining CeO2@mSiO2-NH2; S4, reacting polyacrylic acid-block-polyethylene glycol with the CeO2@mSiO2-NH2 in the presence of an activating agent, and grafting on the particle surface through amide bond to obtain CeO2@mSiO2@PAA-b-PEG; S5, the obtained CeO2@mSiO2@PAA-b-PEG is dispersed in a solution of trivalent cerium salt, and Ce 3+ is loaded on the PAA chain, and after washing and drying, a core-shell structure composite cerium oxide abrasive CeO2@mSiO2@PAA-b-PEG-Ce 3+ is obtained.

2. The method for preparing a pH-responsive core-shell structured cerium oxide abrasive as described in claim 1, characterized in that, In step S1, the hydrothermal reaction is performed at a temperature of 160-200℃ for 3-5 hours.

3. The method for preparing a pH-responsive core-shell structured cerium oxide abrasive as described in claim 1, characterized in that, In step S2, the template agent is cetyltrimethylammonium bromide, and the amount of the template agent is 0.1-1.0 g per 100 mL of the reaction system; the sol-gel reaction is performed at room temperature for 2 hours; and the calcination is performed at a temperature of 500-600℃ for 2-6 hours.

4. The method for preparing a pH-responsive core-shell structured cerium oxide abrasive as described in claim 1, characterized in that, In step S3, the silane coupling agent is 3-aminopropyltriethoxysilane, and the amount of the silane coupling agent is 0.1-1.0 mL per gram of the CeO2@mSiO2 with mesoporous structure; and the reaction is performed at a temperature of 60-80℃ for 4-8 hours.

5. The method for preparing a pH-responsive core-shell structured cerium oxide abrasive as described in claim 1, characterized in that, In step S4, the activating agent is a combination of 1-ethyl-3-(3-dimethylaminopropyl) carbodiimide and N-hydroxysuccinimide; the reaction is performed in a MES buffer solution with a pH of 4.5-6.0 at a temperature of 20-25℃ for 2-3 hours.

6. The method for preparing a pH-responsive core-shell structured cerium oxide abrasive as described in claim 1, characterized in that, In step S5, the trivalent cerium salt is one or more of cerium chloride (CeCl3), cerium nitrate (Ce(NO3)3) or cerium sulfate (Ce2(SO4)3); and the ion exchange conditions are as follows: the concentration of the trivalent cerium salt solution is 0.05-0.2 mol / L, the pH is 5.0-7.0, the temperature is 20-40℃, and the time is 1-4 hours.

7. The method for preparing a pH-responsive core-shell structured cerium oxide abrasive as described in claim 1, characterized in that, The polyacrylic acid-block-polyethylene glycol (PAA-b-PEG) has the following characteristics: The number average molecular weight of the PAA segment is 3000, The number average molecular weight of the PEG segment is 5000, The PEG segment undergoes conformational transition at a temperature higher than 60℃, and the hydrophilicity is enhanced and stretched to form a steric hindrance layer.

8. A chemical mechanical polishing liquid characterized by comprising: The core-shell structure ceria abrasive prepared by the method comprises 0.5-5.0 wt% of the core-shell structure ceria abrasive, ascorbic acid, a lubricant, a heat-conducting filler, choline lactate, water, and a sodium hydroxide and sodium bicarbonate buffer pair.

9. The chemical mechanical polishing solution of claim 8 wherein the abrasive particles are present in an amount of from about 0.1 to about 5.0 wt. %. The heat-conducting filler is at least one of h-BN and AlN nanoparticles; and the lubricant is at least one of graphene quantum dots, MoS2 and hexagonal boron nitride.

10. A chemical mechanical polishing process characterized by, The wafer surface is chemically mechanically polished by using the chemical mechanical polishing solution of claim 8, and the process comprises the following steps: S1, polishing early and middle stage: rough polishing is carried out under the condition that the pH is 10.0-11.0; S2, in the polishing late stage, when it is detected that the wafer surface state meets the preset condition, the polishing solution pH is adjusted to 3.5-4.5 by using acetic acid-sodium acetate buffer, fine polishing is carried out until the end point is reached, and the pre-prepared lubricant dispersion liquid and / or heat-conducting filler dispersion liquid are mixed into the main liquid phase in the form of dropwise addition or continuous pumping, the mixing time is 10-30 minutes, and the stirring speed is 500-1000 rpm.