Composite polishing agent, method for producing the same, and polishing composition and use thereof

Abstract

The application discloses a kind of composite polishing agent and its preparation method and polishing composition and its purposes.The preparation method of the composite polishing agent of the application includes the following steps: (1) silicon sol and quaternary ammonium base aqueous solution are simultaneously added to cerium ammonium nitrate aqueous solution, and precipitation reaction is carried out with pH stabilized at 3.5-5.5, to obtain reaction product; the quaternary ammonium base in the quaternary ammonium base aqueous solution is selected from one or more of tetramethylammonium hydroxide, tetraethylammonium hydroxide; (2) the reaction product is ripened under the condition that stirring rate is 200-300 r / min, to obtain composite polishing agent precursor solution; the composite polishing agent precursor solution is treated using horizontal screw centrifuge, and liquid material is collected; the liquid material is washed and concentrated by ultrafiltration filtration device, to obtain composite polishing agent. The preparation method can obtain core-shell structure cerium dioxide coated silica particles with high coating rate, and the polishing rate of the obtained composite polishing agent is high.

Description

Technical Field

[0001] This invention relates to a composite polishing agent, its preparation method, polishing composition, and its uses. Background Technology

[0002] Chemical mechanical polishing (CMP) is a core process for achieving global planarization of wafer surfaces in semiconductor and integrated circuit manufacturing. It is also an indispensable key step in very large-scale integrated circuits and advanced packaging processes, and its polishing effect directly determines the yield and performance of chips. Polishing particles, as the core functional component of CMP polishing slurries, must possess suitable chemical activity and physical abrasive properties to match the polishing requirements of semiconductor wafers, integrated circuit interlayers, and metal wiring layers.

[0003] Currently, the commonly used single polishing particles are mainly CeO2 particles and SiO2 particles. CeO2 particles have excellent chemical polishing activity, but weak physical polishing ability and low polishing speed. Although SiO2 particles have good physical polishing performance, their strong chemical inertness makes them prone to causing micro-scratches, dents and other defects on the wafer surface during polishing, increasing the risk of chip failure.

[0004] CN102344761A discloses a method for preparing cerium-doped silica sol. Silica sols of different particle sizes obtained by ion exchange are used as seed crystals. A certain amount of alkaline catalyst is added to control the pH value of the seed crystals within 9-10, and the temperature is raised to 60-90℃. A certain amount of cerium ammonium nitrate is dissolved in pure water to form a cerium ammonium nitrate aqueous solution for later use. Using a water bath, the seed crystals are heated to 60-90℃ with stirring, and a certain amount of silicon powder is added initially. Subsequently, a certain amount of silicon powder and cerium ammonium nitrate aqueous solution are added every 30-45 minutes. This method uses NaOH, an inorganic strong alkali, which introduces residual sodium ions, leading to micro-scratches and metal contamination on the polished wafer surface. The reaction is carried out under strong alkalinity and high temperature, and cerium ions exist only as dopants in the SiO2 lattice, failing to form a core-shell structure of CeO2 coating SiO2. The synergistic effect between chemical activity and physical abrasiveness is poor, resulting in a low polishing rate. The product has a wide particle size distribution, requiring subsequent ball milling for refinement, which easily damages the particle structure and introduces impurities from the grinding media. The use of conventional solid-liquid separation methods easily causes particle agglomeration, reducing the dispersion stability of the product.

[0005] CN102417185A discloses a method for preparing silica sol, which involves preparing activated silica powder from silica powder, preparing sodium hydroxide as a sodium hydroxide catalyst, and preparing cerium ammonium nitrate as an aqueous solution of cerium ammonium nitrate. The activated silica powder, sodium hydroxide catalyst, and cerium ammonium nitrate aqueous solution are added sequentially at 80°C, and the reaction is allowed to proceed for 30 minutes. Subsequently, the activated silica powder, sodium hydroxide catalyst, and cerium ammonium nitrate aqueous solution are added every 30 minutes until all the activated silica powder and cerium ammonium nitrate solution are consumed. The silica sol prepared by this method has a low polishing rate. This method also uses NaOH as an alkaline catalyst and adds raw materials in steps, resulting in problems such as local pH abrupt changes, severe product agglomeration, poor particle size uniformity, and a low polishing rate. Summary of the Invention

[0006] One object of the present invention is to provide a method for preparing a composite polishing agent, which can obtain cerium dioxide-coated silicon dioxide particles with a high coating ratio and a high polishing rate. Furthermore, the composite polishing agent obtained by this preparation method can reduce the surface roughness of wafers and reduce scratch defects. Even further, this preparation method can reduce metal ion residue, reduce impurity introduction, and improve particle size uniformity. Another object of the present invention is to provide a composite polishing agent. A further object of the present invention is to provide a polishing composition with a high polishing rate. Furthermore, this polishing composition can reduce the surface roughness of wafers and reduce scratch defects. A final object of the present invention is to provide a use for the polishing composition.

[0007] The above objectives are achieved through the following technical solutions.

[0008] On one hand, the present invention provides a method for preparing a composite polishing agent, comprising the following steps: (1) Silica sol and a quaternary ammonium alkali aqueous solution are simultaneously added to a cerium ammonium nitrate aqueous solution to stabilize the pH at 3.5–5.5 for precipitation reaction to obtain the reaction product; wherein, the particle size D of SiO2 in the silica sol is... 50 The wavelength is 50-150 nm. The mass ratio of SiO2 contained in the silica sol to cerium ammonium nitrate contained in the aqueous solution is (30-45):100; the mass ratio of cerium ammonium nitrate to water in the aqueous solution is 100:(1000-1300); the quaternary ammonium base in the aqueous solution is selected from one or more of tetramethylammonium hydroxide and tetraethylammonium hydroxide. (2) The reaction product is aged for 30 to 60 minutes under a stirring rate of 200 to 300 r / min to obtain a composite polishing agent precursor liquid; the composite polishing agent precursor liquid is processed by a horizontal screw centrifuge and the liquid substance is collected; the liquid substance is washed and concentrated by an ultrafiltration device to obtain a composite polishing agent; wherein the sieve tube diameter of the horizontal screw centrifuge is 150 to 300 mesh.

[0009] According to the preparation method of the present invention, preferably, the concentration of the quaternary ammonium alkali aqueous solution is 8-12 wt%, the dropping rate of the silica sol is 5-10 mL / min, and the dropping rate of the quaternary ammonium alkali aqueous solution is 3-8 mL / min.

[0010] According to the preparation method of the present invention, preferably, in step (1), silica sol and quaternary ammonium base aqueous solution are simultaneously added to cerium ammonium nitrate aqueous solution at 15-25°C; the precipitation reaction is carried out at 15-25°C; In step (2), the aging process is carried out at 15-25°C, and the pH is maintained at 3.5-5.5 during the aging process.

[0011] According to the preparation method of the present invention, preferably, the rotation speed of the horizontal screw centrifuge is 3000-4000 r / min, the separation factor is 1500-2000, and the feed flow rate is 5-10 L / h; The ultrafiltration device has a molecular weight cutoff of 80–120 kDa and a transmembrane pressure of 0.1–0.2 MPa. Water is used as the washing liquid, and a cross-flow washing method is adopted until the conductivity of the washing liquid is ≤5 μS / cm.

[0012] On the other hand, the present invention provides a composite polishing agent prepared by the above-described preparation method.

[0013] According to the composite polishing agent of the present invention, preferably, the particle size D of the particulate matter in the composite polishing agent is... 50 The particle size is 150-200 nm, and the PI value of the particle size is ≤0.2. The particulate matter is a cerium dioxide-silica composite.

[0014] In another aspect, the present invention provides a polishing composition comprising the above-mentioned composite polishing agent, polymeric diol, and water; The repeating unit of the polymer diol contains 2 to 4 carbon atoms.

[0015] According to the polishing composition of the present invention, preferably, the content of particulate matter in the composite polishing agent is 1-10 wt%, and the content of polymeric diol is 0.1-0.9 wt%.

[0016] In another aspect, the present invention provides the use of the above-described polishing composition in polishing wafers.

[0017] According to the present invention, preferably, the process includes the following steps: polishing a wafer using a polishing composition; wherein the polishing pressure is 0.5 to 4 psi, the polishing disc rotation speed is 80 to 110 r / min, and the wafer rotation speed is 70 to 100 r / min.

[0018] Compared with the prior art, the beneficial effects of the present invention are as follows: 1. Catalyst innovation, no metal ion residue: Quaternary ammonium base (tetramethylammonium hydroxide / tetraethylammonium hydroxide) replaces the inorganic bases such as NaOH and ammonia in the existing technology. Quaternary ammonium base is an organic base, without metal ions, and tetramethylammonium hydroxide can decompose and volatilize, eliminating metal ion residue and pollution at the source, and solving the problem of micro-scratches on the wafer polishing surface.

[0019] 2. Process innovation for precise preparation of core-shell structure: The co-precipitation method is used instead of the traditional stepwise addition of raw materials, so that silica sol, quaternary ammonium base and cerium ammonium nitrate aqueous solution are mixed instantly and uniformly, avoiding agglomeration caused by excessive local concentration; combined with constant temperature of 20-25℃ and dynamic pH adjustment of weak acidity of 3.5-5.5, CeO2 is uniformly coated on the SiO2 surface as a monolayer, forming a complete core-shell structure with a coating rate of ≥98%, which is far superior to the cerium doped structure of the prior art, and maximizes the synergistic effect of physical abrasiveness and chemical activity.

[0020] 3. No ball milling or conventional solid-liquid separation, avoiding the introduction of impurities and structural damage: After maturation, the precursor liquid is directly screened for liquid particle size using a horizontal screw centrifuge, eliminating the need for solid-liquid separation and avoiding agglomeration during solid particle separation; there is no ball milling step, and the particle size uniformity is directly controlled through the process, avoiding the core-shell structure damage and introduction of impurities from the grinding media caused by ball milling; subsequent ultrafiltration simultaneously completes washing and concentration, resulting in high product purity and good dispersion stability.

[0021] 4. Excellent product performance and superior polishing effect: The prepared composite polishing agent is in colloidal state with a particle size D 50 The surface roughness is 150–200 nm, PI value ≤ 0.2, dispersion stability ≥ 72 h, and no particle sedimentation. The polishing rate of the composition containing this composite polishing agent is stable at 280–350 nm / min, which is more than 200% higher than the existing technology. After polishing, the wafer surface roughness Ra is ≤ 0.5 nm, with no scratches or dents, and the surface metal ion residue is ≤ 1 × 10⁻⁶. 10 atoms / cm², polishing yield ≥99%.

[0022] 5. High process controllability and high product performance repeatability: By precisely controlling the dropping rate, pH, temperature, centrifuge parameters and ultrafiltration parameters, the entire preparation process can be precisely controlled. The repeatability of product performance indicators such as particle size and coating rate is ≥95%, which is suitable for large-scale industrial production. Attached Figure Description

[0023] Figure 1 This is a SEM image of the particulate matter in the composite polishing agent of Example 1. Detailed Implementation

[0024] The present invention will be further described below with reference to specific embodiments, but the scope of protection of the present invention is not limited thereto.

[0025] Preparation method of composite polishing agent The preparation method of the composite polishing agent of the present invention includes the following steps: (1) preparation of the reaction product; and (2) preparation of the composite polishing agent. The steps are described in detail below.

[0026] Preparation of reaction products Silica sol and quaternary ammonium base aqueous solution are simultaneously added to cerium ammonium nitrate aqueous solution to stabilize the pH at 3.5–5.5 to carry out the precipitation reaction and obtain the reaction product.

[0027] The particle size D of SiO2 in silica sol 50 The wavelength is 50–150 nm; preferably 70–120 nm; more preferably 80–100 nm. The dispersion medium in the silica sol is water.

[0028] The SiO2 content in the silica sol can be 10-30 wt%; preferably 15-25 wt%; more preferably 20-22 wt%.

[0029] The quaternary ammonium base in the aqueous solution can be selected from one or more of tetramethylammonium hydroxide and tetraethylammonium hydroxide; tetramethylammonium hydroxide is preferred. These substances have good water solubility, high catalytic activity, and can be decomposed and volatilized in subsequent processes without any residue, thus eliminating metal ion pollution at the source.

[0030] The concentration of the quaternary ammonium base aqueous solution can be 8–12 wt%; preferably 9–11 wt%; more preferably 10–11 wt%.

[0031] The dropping rate of silica sol can be 5-10 mL / min; preferably 6-9 mL / min; more preferably 7-8 mL / min.

[0032] The dropping rate of the quaternary ammonium base aqueous solution can be 3-8 mL / min; preferably 4-7 mL / min; more preferably 5-6 mL / min.

[0033] At 15–25°C, preferably at 20–25°C, the silica sol and the quaternary ammonium alkali aqueous solution are simultaneously added to the cerium ammonium nitrate aqueous solution.

[0034] The precipitation reaction is carried out at a pH of 3.5–5.5, preferably 4–5, and more preferably 4.3–4.7.

[0035] The precipitation reaction temperature can be 15–25℃; preferably 20–25℃.

[0036] According to one embodiment of the present invention, silica sol and quaternary ammonium alkali aqueous solution are simultaneously added to cerium ammonium nitrate aqueous solution in parallel flow.

[0037] The mass ratio of SiO2 contained in the solid sol to cerium ammonium nitrate contained in the aqueous solution is (30-45):100; preferably (33-42):100; more preferably (35-40):100.

[0038] In the aqueous solution of cerium ammonium nitrate, the mass ratio of cerium ammonium nitrate to water is 100:(800-1150); preferably 100:(900-1100); more preferably 100:(950-1000).

[0039] Under the reaction conditions of this invention, CeO2 can be uniformly deposited and coated on the surface of SiO2, achieving CeO2 monolayer coating with a high coating rate.

[0040] Preparation of composite polishing agent The reaction products were matured to obtain a composite polishing agent precursor liquid; the composite polishing agent precursor liquid was processed using a horizontal screw centrifuge, and the liquid substance was collected; the liquid substance was washed and concentrated through an ultrafiltration device to obtain the composite polishing agent.

[0041] The maturation is carried out under stirring conditions. The stirring rate is 200-300 r / min; preferably 230-280 r / min; more preferably 250-260 r / min.

[0042] The aging process is carried out at a temperature of 15–25°C; preferably at 20–25°C.

[0043] The curing time can be 30 to 60 minutes; preferably 40 to 55 minutes; more preferably 45 to 50 minutes.

[0044] The aging process is carried out at a pH of 3.5 to 5.5, preferably 4 to 5, and more preferably 4.3 to 4.7.

[0045] The rotational speed of the horizontal screw centrifuge is 3000-4000 r / min; preferably 3200-3800 r / min; more preferably 3400-3600 r / min.

[0046] The screening tube diameter of the horizontal screw centrifuge is 150-300 mesh; preferably 170-250 mesh; more preferably 200-220 mesh.

[0047] The separation factor of the horizontal screw centrifuge can be 1500-2000; preferably 1600-1900; more preferably 1700-1800.

[0048] The feed flow rate of the horizontal screw centrifuge can be 5-10 L / h; preferably 6-9 L / h; more preferably 7-8 L / h.

[0049] By controlling the parameters of the horizontal screw centrifuge within the above range, ultrafine / ultra-large particle size impurities can be removed, particle size control can be achieved without solid-liquid separation, and particle agglomeration can be avoided.

[0050] The ultrafiltration device has a molecular weight cutoff of 80–120 kDa; preferably 90–110 kDa; more preferably 100–105 kDa.

[0051] The transmembrane pressure is 0.1–0.2 MPa; preferably 0.12–0.18 MPa; more preferably 0.15–0.16 MPa.

[0052] Water can be used as the washing solution. For example, ultrapure water. A cross-flow washing method can be used.

[0053] Wash until the conductivity of the washing liquid is ≤10μS / cm; preferably, the conductivity is ≤5μS / cm.

[0054] The solid content in the composite polishing agent can be 10-40 wt%; preferably 15-30 wt%; more preferably 20-25 wt%.

[0055] This allows for simultaneous washing and concentration, removing free quaternary ammonium ions and nitrate ions, thus ensuring product purity.

[0056] Composite polishing agent The composite polishing agent of the present invention is prepared by the above method. The composite polishing agent comprises particulate matter and water. The particulate matter is a cerium dioxide-silica composite. In the cerium dioxide-silica composite, cerium dioxide is coated on the surface of silica. The coating rate of cerium dioxide on silica is ≥90%; preferably, the coating rate is ≥95%; more preferably, the coating rate is ≥98%.

[0057] Particle size D of particulate matter 50 The nm size is 150–200 nm; preferably 160–190 nm; more preferably 170–180 nm.

[0058] The particle size index (PI) of the particulate matter of the present invention is ≤0.2; preferably, the particle size index (PI) is ≤0.15. The PI value, also known as the "polydispersity index", characterizes the width of the particle size distribution; the larger the PI value, the wider the particle size distribution; the smaller the PI value, the narrower the particle size distribution and the better the uniformity.

[0059] The specific surface area of ​​particulate matter is 60–90 m². 2 / g; preferably 65-85m 2 / g; more preferably 70-80m 2 / g.

[0060] The composite polishing agent of the present invention shows no particle settling after standing at 25°C for 72 hours; preferably, it shows no particle settling after standing at 25°C for 96 hours.

[0061] The composite polishing agent of the present invention contains no metal ions and / or impurities.

[0062] Polishing Compositions and Their Uses The polishing composition of the present invention comprises a composite polishing agent, a polymeric diol, and water. Preferably, the polishing composition consists of a composite polishing agent, a polymeric diol, and water. The composite polishing agent has been described above and will not be repeated here.

[0063] The content of particulate matter in the composite polishing agent can be 1-10 wt%; preferably 3-8 wt%; more preferably 5-6 wt%.

[0064] The repeating unit of the polymeric diol may contain 2 to 4 carbon atoms; preferably, it contains 2 to 3 carbon atoms. Examples of polymeric diols include, but are not limited to, polyethylene glycol and polypropylene glycol. Preferably, the polymeric diol is polyethylene glycol. The molecular weight of the polymeric diol can be 1000 to 2000 Da; preferably 1400 to 1700 Da. Such polymeric diols have excellent lubricity and dispersibility, and can form a uniform adsorption layer on the surface of core-shell particles, reducing mechanical wear without affecting the chemical activity of CeO2.

[0065] The content of the polymer diol can be 0.1 to 0.9 wt%; preferably 0.3 to 0.7 wt%; more preferably 0.5 to 0.6 wt%.

[0066] The polishing composition of this invention has a pH of 6-8 and a viscosity of 5-10 mPa•s at 25°C. These physicochemical properties match the stability of colloidal composite polishing agents, and there is no agglomeration during storage and use.

[0067] The polishing composition of the present invention can be applied to the polishing of wafers. Therefore, the present invention provides the use of the above composition in polishing wafers. The wafer can be a monocrystalline silicon wafer or a silicon carbide wafer; preferably a monocrystalline silicon wafer. The wafer size can be 4 to 12 inches. The polishing composition of the present invention is suitable for chemical mechanical polishing global planarization processes.

[0068] Specifically, it includes the following steps: polishing the wafer using a polishing composition.

[0069] The polishing pressure can be 0.5 to 4 psi; preferably 1 to 3 psi; more preferably 2 to 3 psi.

[0070] The polishing disc rotation speed can be 80-110 r / min; preferably 80-100 r / min; more preferably 90-95 r / min.

[0071] The wafer rotation speed can be 70-100 r / min; preferably 75-90 r / min; more preferably 80-85 r / min.

[0072] The polishing time can be 30-90s; preferably 40-80s; more preferably 50-70s.

[0073] The flow rate of the polishing fluid can be 100-250 mL / min; preferably 150-240 mL / min; more preferably 200-230 mL / min.

[0074] The polishing rate is greater than or equal to 250 nm / min; preferably, the polishing rate is greater than or equal to 280 nm / min. In some embodiments, the polishing rate is 300–320 nm / min.

[0075] The surface roughness Ra of the polished wafer is ≤0.5nm; more preferably, the surface roughness Ra is ≤0.37nm.

[0076] After polishing, there were no obvious scratches or defects on the wafer surface.

[0077] The test methods used in the following embodiments and comparative examples are as follows: Particle size D 50 Particle size PI value: The test was conducted using the national standard GB / T 34914 "Determination of Particle Size Distribution of Nanoparticles by Laser Dynamic Light Scattering Method" and the testing equipment was HORIBA SZ-100.

[0078] Coating efficiency: The coating efficiency was measured using transmission electron microscopy (TEM) combined with energy dispersive spectroscopy (EDS) on a Tecnai G2 F20 instrument. The coating efficiency was calculated by measuring the area of ​​Ce distribution on the surface of SiO2 particles.

[0079] Metal ion / impurity residues: Detected using inductively coupled plasma mass spectrometry (ICP-MS) on a BRUKER aurora M90 instrument.

[0080] Dispersion stability: Place the composite polishing agent in a sealed container, let it stand at 25°C, observe the particle settling, and record the time without settling.

[0081] Polishing experiment: The polishing composition was used for chemical mechanical polishing of 4-inch single-crystal silicon wafers; the polishing pressure was 3 psi, the polishing disk rotation speed was 90 r / min, the wafer rotation speed was 85 r / min, the polishing fluid flow rate was 220 mL / min, and the polishing time was 60 s. The polishing rate was measured using a profilometer, and the wafer surface roughness Ra was measured using atomic force microscopy (AFM, Bruker Dimension Icon).

[0082] The raw materials are described below: Cerium ammonium nitrate: CeO2 content is 30wt%.

[0083] Ultrapure water: semiconductor grade, resistivity ≥18.2MΩ·cm.

[0084] Silica sol raw material: SiO2 content is 40wt%, particle size D 50 It is 80nm, semiconductor grade. Example 1 100 parts by weight of cerium ammonium nitrate were dissolved in 1000 parts by weight of ultrapure water and stirred until completely dissolved to obtain an aqueous solution of cerium ammonium nitrate. The silica sol raw material was diluted with ultrapure water in a 20°C constant temperature water bath reactor to obtain a silica sol with a SiO2 content of 20 wt%.

[0085] In a constant-temperature water bath reactor at 20℃, silica sol and a 10wt% tetramethylammonium hydroxide aqueous solution were simultaneously added dropwise to a cerium ammonium nitrate aqueous solution, maintaining the pH at 4.5±0.2 to allow for precipitation and yield the reaction product. The dropping rate of the silica sol was 7 mL / min, and the dropping rate of the tetramethylammonium hydroxide aqueous solution was 5 mL / min. The mass ratio of SiO2 in the silica sol to cerium ammonium nitrate was 38:100.

[0086] The reaction product was aged at 20℃ and 250 r / min for 45 min to obtain the composite polishing agent precursor solution. The pH was maintained at 4.5 ± 0.2 during aging. The composite polishing agent precursor solution was processed using a horizontal screw centrifuge; the separated liquid was collected, and the residue was discarded. The horizontal screw centrifuge had a 200-mesh sieve tube, a rotation speed of 3500 r / min, a separation factor of 1800, and a feed flow rate of 7 L / h.

[0087] The collected liquid material was washed and concentrated using an ultrafiltration device with a molecular weight cutoff of 100 kDa to obtain a composite polishing agent with a solid content of 20 wt%. The transmembrane pressure was 0.15 MPa, and cross-flow washing was performed using ultrapure water as the washing solution until the conductivity of the washing solution was ≤5 μS / cm.

[0088] The composite polishing agent comprises water and particulate matter. The particulate matter is a cerium dioxide-silica composite. In the cerium dioxide-silica composite, cerium dioxide coats the surface of silica, forming a core-shell structure, with a cerium dioxide coating rate of 98.5%. The particle size D of the particulate matter contained in the composite polishing agent... 50 The particle size is 175.7 nm, the PI value is 0.148, and the specific surface area is 75 m². 2 / g. The composite polishing agent showed no particle settling after standing at 25℃ for 96 hours. No metal ions or impurities remained in the composite polishing agent.

[0089] Example 2 The composite polishing agent of Example 1, polyethylene glycol (1500 Da), and ultrapure water were mixed to obtain a polishing composition. In the polishing composition, the composite polishing agent contained 5 wt% particulate matter, and the polyethylene glycol contained 0.5 wt%.

[0090] Polishing experiments were conducted using the polishing composition of this embodiment, and the polishing rate was measured to be 320 nm / min. After polishing, the surface roughness of the wafer was Ra = 0.356 nm, with no obvious scratches or dents, and the residual metal ions on the surface were ≤5 × 10⁻⁵. 9 atoms / cm².

[0091] Comparative Example 1 150g of silica sol (30wt% solid silica content) with a particle size of 80nm was added as seed crystals to a glass beaker. While stirring, 2.8g of NaOH was added to adjust the pH of the system to 9.5±0.1. The temperature was raised to 80℃ and maintained for 30min. 45g of cerium ammonium nitrate was dissolved in 300g of deionized water to prepare an aqueous solution. 1700g of deionized water was added to the beaker. Under stirring conditions of 80℃ and 300r / min, 80g of silica powder (total amount 800g) and 30g of cerium ammonium nitrate aqueous solution were added in batches every 30min. After the addition was complete, stirring was continued for 2h to obtain cerium-doped silica sol. The sol was centrifuged at 8000r / min for 20min to remove impurities. The filtrate was vacuum dried at 120℃ and -0.08MPa for 12h to obtain a solid powder. The solid powder was mixed with 5000g of zirconia balls and deionized water (solid-liquid ratio 1:2), and ball-milled at 200r / min for 6h until particle size D was achieved. 50 Stabilized at 170nm±5nm, the particles were centrifuged and vacuum dried at 120℃ for 4h to obtain cerium-doped silicon dioxide polished particles.

[0092] Cerium-doped silica polishing particles were mixed with polyethylene glycol (1500 Da) and ultrapure water to obtain a polishing composition (cerium-doped silica polishing particles content 5 wt%, polyethylene glycol content 0.5 wt%).

[0093] In the polishing particles obtained in this comparative example, the cerium dioxide coating rate of the silicon dioxide particles was 18%, which is a doped structure rather than a core-shell structure. The PI value of the polishing particle size was 0.45. The residual sodium ion content in this polishing composition was 65 ppm.

[0094] Polishing experiments were conducted using the polishing composition of this comparative example, and the polishing rate was measured to be 185 nm / min. After polishing, the wafer surface roughness Ra = 1.32 nm, with obvious micro-scratches, and residual sodium ions ≥ 9 × 10⁻⁹ on the surface. 11 atoms / cm².

[0095] Comparative Example 2 SiO2 polishing particles (particle size D) 50 A polishing composition was obtained by mixing SiO2 polishing particles (150 nm), polyethylene glycol (1500 Da), and ultrapure water. The polishing composition contained 5 wt% SiO2 polishing particles and 0.5 wt% polyethylene glycol.

[0096] Polishing experiments were conducted using the polishing composition of this comparative example, and the polishing rate was measured to be 120 nm / min. The surface roughness Ra of the polished wafer was 0.576 nm, with obvious scratch defects.

[0097] Comparative Example 3 CeO2 polishing particles (particle size D) 50 A polishing composition was obtained by mixing CeO2 polishing particles (147 nm), polyethylene glycol (1500 Da), and ultrapure water. The polishing composition contained 5 wt% CeO2 polishing particles and 0.5 wt% polyethylene glycol.

[0098] Polishing experiments were conducted using the polishing composition of this comparative example, and the polishing rate was measured to be 180 nm / min. The surface roughness Ra of the polished wafer was 0.343 nm, with no obvious scratches or defects.

[0099] This invention is not limited to the above-described embodiments. Any modifications, improvements, or substitutions that can be conceived by those skilled in the art without departing from the essential content of this invention fall within the scope of this invention.

Claims

1. A method for preparing a composite polishing agent, characterized in that, Includes the following steps: (1) Silica sol and a quaternary ammonium alkali aqueous solution are simultaneously added to a cerium ammonium nitrate aqueous solution to stabilize the pH at 3.5–5.5 for precipitation reaction to obtain the reaction product; wherein, the particle size D of SiO2 in the silica sol is... 50 The wavelength is 50-150 nm. The mass ratio of SiO2 contained in the silica sol to cerium ammonium nitrate contained in the aqueous solution is (30-45):100; the mass ratio of cerium ammonium nitrate to water in the aqueous solution is 100:(1000-1300); the quaternary ammonium base in the aqueous solution is selected from one or more of tetramethylammonium hydroxide and tetraethylammonium hydroxide. (2) The reaction product is aged for 30 to 60 minutes under a stirring rate of 200 to 300 r / min to obtain a composite polishing agent precursor liquid; the composite polishing agent precursor liquid is processed by a horizontal screw centrifuge and the liquid substance is collected; the liquid substance is washed and concentrated by an ultrafiltration device to obtain a composite polishing agent; wherein the sieve tube diameter of the horizontal screw centrifuge is 150 to 300 mesh.

2. The preparation method according to claim 1, characterized in that, The concentration of the quaternary ammonium alkali aqueous solution is 8–12 wt%, the dropping rate of the silica sol is 5–10 mL / min, and the dropping rate of the quaternary ammonium alkali aqueous solution is 3–8 mL / min.

3. The preparation method according to claim 1, characterized in that: In step (1), silica sol and quaternary ammonium base aqueous solution are simultaneously added to cerium ammonium nitrate aqueous solution at 15-25℃; the precipitation reaction is carried out at 15-25℃. In step (2), the aging process is carried out at 15-25°C, and the pH is maintained at 3.5-5.5 during the aging process.

4. The preparation method according to claim 1, characterized in that: The horizontal screw centrifuge has a rotational speed of 3000-4000 r / min, a separation factor of 1500-2000, and a feed flow rate of 5-10 L / h. The ultrafiltration device has a molecular weight cutoff of 80–120 kDa and a transmembrane pressure of 0.1–0.2 MPa. Water is used as the washing liquid, and a cross-flow washing method is adopted until the conductivity of the washing liquid is ≤5 μS / cm.

5. A composite polishing agent, characterized in that, The composite polishing agent is prepared by the preparation method according to any one of claims 1 to 4.

6. The composite polishing agent according to claim 5, characterized in that, The particle size D of the particulate matter in the composite polishing agent 50 The particle size is 150-200 nm, and the PI value of the particle size is ≤0.

2. The particulate matter is a cerium dioxide-silica composite.

7. A polishing composition, characterized in that, Includes the composite polishing agent as described in claim 5 or 6, the polymeric diol, and water; The repeating unit of the polymer diol contains 2 to 4 carbon atoms.

8. The polishing composition according to claim 7, characterized in that, In the polishing composition, the content of particulate matter in the composite polishing agent is 1-10 wt%, and the content of polymer diol is 0.1-0.9 wt%.

9. Use of the polishing composition according to claim 7 or 8 in polishing wafers.

10. The use according to claim 9, characterized in that, Includes the following steps: The wafer is polished using a polishing composition; wherein the polishing pressure is 0.5 to 4 psi, the polishing disk speed is 80 to 110 r / min, and the wafer speed is 70 to 100 r / min.

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