Nano cerium oxide polishing solution as well as preparation method and application thereof

Abstract

The invention discloses a nano cerium oxide polishing solution as well as a preparation method and application thereof. The method comprises the following steps: 1) forming cerous carbonate into cerous nitrate solution; dropwise adding the cerous nitrate solution and the ammonium bicarbonate solution into a reaction container in a parallel flow manner for reaction, then aging, and carrying out solid-liquid separation to obtain a cerous carbonate precipitate containing crystal water; 2) mixing the cerium carbonate precipitate containing crystal water, water and polyoxyalkylene, and grinding to obtain a grinding liquid; 3) heating the grinding liquid to 75-100 DEG C, reacting to obtain a reaction liquid, and spray-drying and calcining the reaction liquid to obtain cerium dioxide powder; 4) mixing the crushed cerium dioxide powder, maleic anhydride-containing copolymer salt and water to obtain slurry; 5) treating the slurry with a high-pressure homogenizer to obtain a dispersion liquid, and 6) filtering the dispersion liquid with various filters, and adjusting the pH value of the obtained filtrate to obtain the nano cerium oxide polishing solution. The polishing solution obtained by the preparation method has both polishing effect and cleaning effect.

Description

Technical Field

[0001] The invention relates to a nano cerium oxide polishing liquid and a preparation method and application thereof. Background Art

[0002] Integrated circuits, as the core building block of electronic products, are a key force driving the information technology revolution and industrial transformation and upgrading. With the development of new technologies such as 5G, the Internet of Things, and artificial intelligence, the application scope of integrated circuits continues to expand and market demand continues to grow, making integrated circuits a key engine driving economic growth. In integrated circuit manufacturing, chemical mechanical polishing (CMP) precisely controls the flatness and smoothness of the integrated circuit surface, ensuring the accuracy and consistency of subsequent processes (such as photolithography and etching), making it crucial for improving product yield and reducing failure rates.

[0003] Cerium oxide, an ultra-precision rare earth polishing material, is a core material for achieving global nanoscale planarization of substrate surfaces. It is primarily used in critical processes such as three-dimensional stacked flash memory (3D NAND) and shallow trench isolation (STI) devices. In recent years, the continuous advancement of process nodes has dictated that rare earth polishing materials must simultaneously achieve high speed and high selectivity. With the advancement of global chip manufacturing technology, the requirements for both chip surface roughness and polishing materials have been placed on a high level. Consequently, cerium oxide polishing powders are trending towards smaller sizes, functionalization, and customization.

[0004] Currently, cerium oxide polishing powder serves as a core material for global chip planarization. It interacts with oxidants and complexing agents in the polishing solution to form a chemically reactive system. This chemical reaction with surfaces such as silicon or silicon dioxide forms Ce-O-Si bonds, which then remove the "soft layer." Demand for cerium oxide polishing powder is rapidly growing. As integrated circuit sizes continue to shrink, devices such as fin field-effect transistors (FINFETs) require chemical mechanical polishing processes to achieve higher removal rates and minimize scratches (i.e., reduced surface roughness).

[0005] In addition, there is a problem that it is difficult to clean the polishing material on the device surface after polishing with the polishing liquid.

[0006] CN113201284A discloses a high-polish CMP polishing liquid. Per 100 parts by weight, the polishing liquid comprises 10-45 parts abrasive, 2-7 parts pH adjuster, 0.03-0.3 parts surfactant, 0.5-2.5 parts water-soluble cyclodextrin, 0.03-0.15 parts polyethylene glycol, and water to make up to 100 parts. This patent document does not mention the SiO2 removal rate. Surface roughness alone cannot accurately reflect the polishing effect. Furthermore, devices treated with this polishing liquid are difficult to clean.

[0007] CN108249468A discloses mixing cerium oxide crystals with polyacrylic acid, ball milling the mixture to obtain cerium oxide abrasive particles, and then preparing a polishing slurry. This polishing slurry exhibits a low material removal rate during polishing, failing to meet process requirements. Furthermore, cleaning the polishing material from the device after polishing is difficult.

[0008] CN115433521B discloses a cerium oxide granulated powder polishing liquid, including submicron cerium oxide granulated powder. When used for polishing glass-ceramics, the surface roughness of the polishing liquid remains high. Because the polishing liquid has excessively large granularity, it is not suitable for use in polishing semiconductor silicon wafers.

[0009] CN116694233A discloses a polishing composition comprising 0.2-12 wt% abrasive particles, 0.01-10 wt% poly(meth)acrylate, 0.1-28 wt% C5-C12 polyol, and 0.5-5 wt% C2-C8 carboxylic acid. This polishing composition can be used to effectively polish ITO layers, rather than wafer polishing to remove silicon dioxide. Summary of the Invention

[0010] In view of this, one object of the present invention is to provide a method for preparing a nano-cerium oxide polishing liquid, and the obtained nano-cerium oxide polishing liquid can take into account both polishing effect and cleaning effect. During polishing, the SiO2 removal rate is greater than or equal to 300nm / min, the arithmetic average roughness Ra of the polished device is less than or equal to 0.4nm, and the root mean square roughness Rq is less than or equal to 0.4nm. The average particle size of the obtained nano-cerium oxide polishing liquid is less than or equal to 200nm, and the absolute value of the Zeta potential is greater than or equal to 40mV. Furthermore, the polished device is easy to clean, that is, it is easy to clean off the residual polishing material. Another object of the present invention is to provide a nano-cerium oxide polishing liquid prepared according to the preparation method as described above. Another object of the present invention is to provide an application of the above-mentioned nano-cerium oxide polishing liquid.

[0011] The present invention adopts the following technical solutions to achieve the above-mentioned purpose.

[0012] In one aspect, the present invention provides a method for preparing a nano-cerium oxide polishing liquid, comprising the following steps: 1) dissolving cerium carbonate in nitric acid to form a cerium nitrate solution; adding the cerium nitrate solution and ammonium bicarbonate solution concurrently dropwise to a reaction vessel at 40-85°C for reaction, followed by aging and solid-liquid separation to obtain a cerium carbonate precipitate containing water of crystallization; 2) mixing the cerium carbonate precipitate containing crystal water, water and polyoxyalkylene to obtain a mixed solution; grinding the mixed solution to obtain a grinding solution; 3) heating the grinding liquid to 75-100°C to react and obtain a reaction liquid; then spray drying the reaction liquid to obtain a dry product; and calcining the dry product to obtain cerium dioxide powder; 4) crushing the cerium dioxide powder to obtain crushed cerium dioxide powder; mixing the crushed cerium dioxide powder, a copolymer salt containing maleic anhydride, and water to obtain a slurry; 5) treating the slurry with a high-pressure homogenizer to obtain a dispersion; wherein the pressure of the high-pressure homogenizer is 20,000 to 30,000 psi; 6) filtering the dispersion using a plurality of filters to obtain a filtrate; adjusting the pH value of the obtained filtrate to 3 to 6 to obtain the nano-cerium oxide polishing liquid; The filter element has a precision of less than or equal to 3 μm.

[0013] According to the preparation method of the present invention, preferably, step 1) specifically includes the following process: Cerium carbonate is dissolved in nitric acid with a concentration of 65-68 wt% to form a cerium nitrate solution; the cerium nitrate solution and an ammonium bicarbonate solution with a concentration of 20-25 wt% are co-currently added dropwise to a reaction vessel at 40-85° C. for reaction; after the co-current addition is completed, the pH value of the reaction system is controlled to be 7-10; then, the reaction is aged for 3-6 hours, and the solid is washed with water, and filtered after washing to obtain a cerium carbonate precipitate containing more than 3 crystal waters.

[0014] According to the preparation method of the present invention, preferably, in the mixed solution of step 2), the amount of cerium carbonate precipitate containing crystallization water is 5 to 60 parts by weight, the amount of water is 40 to 99.9 parts by weight, and the amount of polyoxyalkylene is 0.1 to 2 parts by weight; and the pH value of the mixed solution is 7 to 9.

[0015] According to the preparation method of the present invention, preferably, the polyoxyalkylene is selected from one or more of fatty alcohol polyoxyethylene ether, alkylphenol polyoxyethylene ether and polyoxyethylene polyoxypropylene block copolymer.

[0016] According to the preparation method of the present invention, preferably, in step 3), the calcination temperature is 600-900° C., and the calcination time is 3-6 hours.

[0017] According to the preparation method of the present invention, preferably, step 4) specifically includes the following process: The cerium dioxide powder is crushed by a hammer crusher to obtain crushed cerium dioxide powder; 0.5 to 30 parts by weight of the crushed cerium dioxide powder, 0.01 to 1 parts by weight of a copolymer salt containing maleic anhydride and 70 to 99.8 parts by weight of water are mixed to obtain a slurry.

[0018] According to the preparation method of the present invention, preferably, the copolymer salt containing maleic anhydride is selected from one or more of maleic anhydride-styrene copolymer ammonium salt, maleic anhydride-styrene-acrylic acid terpolymer ammonium salt, maleic anhydride-acrylic acid sodium salt and maleic anhydride-vinyl acetate copolymer sodium salt.

[0019] According to the preparation method of the present invention, preferably, in step 5), a high-pressure homogenizer is used for cyclic treatment for more than two times; in step 6), the dispersion is filtered using four filters to obtain filtrates; wherein the filter elements have a precision of 3 μm, 1 μm, 0.5 μm and 0.2 μm, respectively.

[0020] On the other hand, the present invention also provides a nano-cerium oxide polishing liquid, which is prepared according to the preparation method described above.

[0021] In another aspect, the present invention further provides an application of the nano-cerium oxide polishing liquid described above in polishing semiconductors or integrated circuits.

[0022] When the nano-cerium oxide polishing liquid obtained by the preparation method of the present invention is used for polishing, the SiO2 removal rate is greater than or equal to 300 nm / min, the arithmetic mean roughness Ra of the polished device is less than or equal to 0.4 nm, the root mean square roughness Rq is less than or equal to 0.4 nm, and the surface uniformity is good. The nano-cerium oxide polishing liquid of the present invention is suitable for polishing in the field of semiconductors or integrated circuits; the surface of the polished device is easy to clean. Therefore, the nano-cerium oxide polishing liquid of the present invention can achieve both polishing and cleaning effects. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 This is a particle size distribution diagram of the nano-cerium oxide polishing liquid obtained in Example 1 of the present invention.

[0024] Figure 2 This is the Zeta potential distribution diagram of the nano-cerium oxide polishing liquid obtained in Example 1 of the present invention.

[0025] Figure 3 AFM image of a polished silicon oxide wafer before cleaning.

[0026] Figure 4 AFM image of a polished silicon oxide wafer after cleaning. DETAILED DESCRIPTION

[0027] The present invention will be further described below with reference to the accompanying drawings and specific embodiments, but the protection scope of the present invention is not limited thereto.

[0028] The nano-cerium oxide polishing liquid of the present invention can be a CMP nano-cerium oxide polishing liquid. CMP is the abbreviation for Chemical Mechanical Polishing. CMP is a technology that combines chemical etching and mechanical polishing. It is mainly used in the semiconductor manufacturing process to achieve nanoscale planarization of wafer surfaces.

[0029] Generally, the arithmetic mean roughness Ra and the root mean square roughness Rq are height indicators in the one-dimensional profile parameters of surface roughness, and are often used to describe the degree of surface micro-undulation.

[0030] In the present invention, the definition of arithmetic mean roughness (Ra) is: the arithmetic mean of the absolute values of the distances from each point on the profile to the reference line (the least squares midline of the profile) within the sampling length (a specified length used to evaluate surface roughness).

[0031] The definition of root mean square roughness Rq (Root Mean Square Roughness) is: the square root of the arithmetic mean of the squares of the distances from each point on the contour to the reference line (the least squares midline of the contour) within the sampling length.

[0032] Preparation method of nano-cerium oxide polishing liquid The present invention provides a method for preparing a nano-cerium oxide polishing liquid, comprising the following steps: 1) forming a cerium carbonate precipitate containing water of crystallization; 2) forming a grinding liquid from the cerium carbonate precipitate; 3) forming a cerium dioxide powder from the grinding liquid; 4) forming a slurry from the cerium dioxide powder; 5) high-pressure homogenization; and 6) filtering and adjusting the pH to form a final polishing liquid. Extensive research and experimentation have revealed that the technical benefits of the present invention cannot be achieved by directly calcining cerium carbonate to form a cerium dioxide powder, then forming a slurry from the cerium dioxide powder, and then sequentially subjecting the polishing liquid to high-pressure homogenization and filtration. This is described in detail below.

[0033] Steps for forming cerium carbonate precipitate containing crystal water Cerium carbonate is dissolved in nitric acid to form a cerium nitrate solution. The cerium nitrate solution and ammonium bicarbonate solution are then added dropwise to a reaction vessel at 40-85°C for reaction. The resulting product is then aged and subjected to solid-liquid separation to obtain a cerium carbonate precipitate containing water of crystallization. Cerium carbonate containing water of crystallization is easier to precipitate and has a specific crystal form. The resulting cerium carbonate precipitate is advantageous for preparing a nano-cerium oxide polishing solution with a high material removal rate, good surface uniformity, and ease of cleaning.

[0034] In the cerium carbonate of the present invention, TREO ≥ 98%, CeO2 / TREO ≥ 99.9%, preferably, CeO2 / TREO ≥ 99.99%, and more preferably, CeO2 / TREO ≥ 99.995%. TREO stands for Total Rare Earth Oxides.

[0035] In the present invention, cerium carbonate is dissolved in nitric acid with a concentration of 65 to 68 wt % to form a cerium nitrate solution, wherein the mass concentration of cerium nitrate in the cerium nitrate solution is 45 to 65 wt %.

[0036] In the present invention, the ammonium bicarbonate solution is prepared from ammonium bicarbonate and water. The mass concentration of ammonium bicarbonate in the ammonium bicarbonate solution can be 20-25 wt%.

[0037] In the present invention, the reaction temperature during the co-current dropwise addition can be 40-85°C, preferably 45-80°C, more preferably 50-70°C, and even more preferably 55-60°C. After the co-current dropwise addition is completed, the pH of the reaction system is controlled to be 7-10. Preferably, the pH of the reaction system is 8-9, for example, the pH of the reaction system can be 8, 8.5, or 9. After the co-current dropwise addition is completed, the temperature is lowered to room temperature and then aged while standing. The aging time can be 3-6 hours, preferably 3-5 hours, and more preferably 4-5 hours.

[0038] In the present invention, after aging, the solid and liquid are separated, and the solid is washed with water. The water washing may be repeated multiple times, for example, two or three times. After washing, filtration is performed to obtain a cerium carbonate precipitate containing three or more waters of crystallization. The obtained cerium carbonate precipitate preferably contains four or more waters of crystallization, and more preferably contains six or more waters of crystallization. According to one embodiment of the present invention, the cerium carbonate precipitate contains eight waters of crystallization, and its chemical formula is Ce2(CO3)3•8H2O. This facilitates obtaining a nano-cerium oxide polishing liquid that achieves both polishing and cleaning effects.

[0039] Steps for forming grinding fluid by cerium carbonate precipitation The cerium carbonate precipitate containing crystal water, water, and polyoxyalkylene are mixed to obtain a mixed solution. The mixed solution is ground to obtain a grinding solution. This facilitates the dispersion of the cerium carbonate precipitate containing crystal water, thereby facilitating the production of the nano-cerium oxide polishing solution of the present invention.

[0040] In the present invention, polyoxyalkylenes can be commercially available, and their sources are not particularly limited. The polyoxyalkylenes are selected from one or more of fatty alcohol polyoxyethylene ethers, alkylphenol polyoxyethylene ethers, and polyoxyethylene polyoxypropylene block copolymers, preferably selected from one of fatty alcohol polyoxyethylene ethers, alkylphenol polyoxyethylene ethers, and polyoxyethylene polyoxypropylene block copolymers, and more preferably selected from fatty alcohol polyoxyethylene ethers. The present invention has found that the use of these polyoxyalkylenes can achieve a good balance between polishing and cleaning effects in the resulting nano-cerium oxide polishing liquid.

[0041] In the present invention, the carbon number of the fatty alcohol in the fatty alcohol polyoxyethylene ether is 10 to 15, preferably 11 to 14, more preferably 12 to 14. The carbon number of the alkylphenol in the alkylphenol polyoxyethylene ether is 8 to 13, preferably 9 to 11, more preferably 9 to 10.

[0042] In the present invention, the molecular weight of the polyoxyalkylene may be 100 to 3000 Da, preferably 500 to 3000 Da, more preferably 1000 to 3000 Da.

[0043] According to a specific embodiment of the present invention, the polyoxyalkylene is lauryl alcohol polyoxyethylene ether (also known as dodecyl polyoxyethylene ether or lauryl alcohol polyether), CAS No. 68439-50-9, purchased from Kao Corporation of Japan.

[0044] In the mixed solution, the amount of cerium carbonate precipitate containing crystal water is 5 to 60 parts by weight, preferably 10 to 55 parts by weight, and more preferably 20 to 50 parts by weight; the amount of water is 40 to 99.9 parts by weight, preferably 40 to 80 parts by weight, and more preferably 50 to 80 parts by weight; and the amount of polyoxyalkylene is 0.1 to 2 parts by weight, preferably 0.1 to 1 part by weight, and more preferably 0.1 to 0.5 parts by weight. The pH value of the mixed solution can be 7 to 9, and preferably 8 to 9.

[0045] According to a specific embodiment of the present invention, in the mixed solution, the amount of cerium carbonate precipitate containing crystal water is 20-50 parts by weight, the amount of water is 50-80 parts by weight and the amount of polyoxyalkylene is 0.1 part by weight; the pH value of the mixed solution is 8-9.

[0046] In the present invention, the mixed liquid can be ground using a sand mill to obtain a grinding liquid. During the grinding, the grinding medium used is zirconium oxide beads. The maximum particle size Dmax of the particles in the obtained grinding liquid is ≤1 μm.

[0047] Steps for forming cerium dioxide powder from grinding liquid The polishing liquid is heated to 75-100°C and reacted to obtain a reaction solution. The reaction solution is then spray-dried to obtain a dry product. The dry product is calcined to obtain cerium dioxide powder. This facilitates the production of a nano-cerium oxide polishing liquid with excellent polishing and cleaning properties.

[0048] In the present invention, the grinding solution is heated to 75-100°C under normal pressure to produce a reaction solution containing cerium oxycarbonate [Ce2O(CO3)2]. The reaction temperature is preferably 85-100°C, more preferably 95-100°C. The reaction time can be 1-6 hours, preferably 1-4 hours, and more preferably 1-2 hours.

[0049] In the present invention, the reaction solution is spray-dried using a known spray dryer to obtain a dried product. The dried product is calcined at 600-900°C for 3-6 hours to obtain a cerium dioxide powder. The calcination temperature is preferably 630-850°C, more preferably 650-800°C, and more preferably 660-700°C. The calcination time is preferably 3-5 hours, more preferably 3-4 hours.

[0050] Step of forming slurry from cerium dioxide powder The cerium dioxide powder is crushed to obtain crushed cerium dioxide powder. The crushed cerium dioxide powder, a copolymer salt containing maleic anhydride, and water are mixed to obtain a slurry. The present invention has found that the use of a copolymer salt containing maleic anhydride can improve the polishing effect of a polishing liquid and is easy to clean.

[0051] In the present invention, the crushing method is not particularly limited. The obtained cerium dioxide powder can be crushed by using a hammer crusher to obtain crushed cerium dioxide powder.

[0052] In the slurry of the present invention, the amount of crushed cerium dioxide powder can be 0.5 to 30 parts by weight, preferably 1 to 30 parts by weight, more preferably 5 to 30 parts by weight, and further preferably 15 to 29 parts by weight; the amount of copolymer salt containing maleic anhydride can be 0.01 to 1 part by weight, preferably 0.05 to 1 part by weight, more preferably 0.1 to 1 part by weight, and further preferably 0.5 to 1 part by weight; the amount of water can be 70 to 99.8 parts by weight, preferably 70 to 99 parts by weight, more preferably 70 to 89 parts by weight, and further preferably 70 to 80 parts by weight.

[0053] The maleic anhydride-containing copolymer salt can be its ammonium salt or sodium salt; the molecular weight range can be 1,000 to 500,000 Da, preferably 1,500 to 50,000 Da, for example, 10,000 to 30,000 Da. The maleic anhydride-containing copolymer salt is selected from one or more of a maleic anhydride-styrene copolymer ammonium salt, a maleic anhydride-styrene-acrylic acid terpolymer ammonium salt, a maleic anhydride-acrylic acid sodium salt, and a maleic anhydride-vinyl acetate copolymer sodium salt. According to one embodiment of the present invention, the maleic anhydride-containing copolymer salt is a maleic anhydride-styrene copolymer ammonium salt, CAS No. 26022-09-3. The present invention has found that only when polyalkylene oxide is used in step 2) and a maleic anhydride-containing copolymer salt is used in step 4) can both polishing and cleaning effects be achieved; otherwise, both cannot be achieved.

[0054] High-pressure homogenization step The slurry is processed in a high-pressure homogenizer to obtain a dispersion. The pressure of the high-pressure homogenizer can be set to 20,000-30,000 psi. The high-pressure homogenizer performs ultra-high-pressure crushing and impact dispersion to obtain a dispersion. This facilitates particle refinement (down to the nanometer level) and system homogenization.

[0055] In the present invention, the pressure is preferably 25,000 to 30,000 psi, more preferably 28,000 to 30,000 psi. The high-pressure homogenizer can be used for multiple cycles, for example, 2 or more cycles, preferably 3 or more cycles, for example 3 or 4 cycles.

[0056] Filtration and pH adjustment steps to form the final polishing solution The dispersion is filtered through various filters (e.g., filters with two or more levels of precision) to obtain a filtrate. The pH of the filtrate is adjusted to 3 to 6 to obtain the nano-cerium oxide polishing liquid. The filter element has a precision of 3 μm or less. This facilitates obtaining a nano-cerium oxide polishing liquid with good stability and uniformity.

[0057] In the present invention, the dispersion is preferably filtered using three filters (e.g., filters with a precision of grade three or higher) to obtain a filtrate. According to a preferred embodiment of the present invention, four filters are used for filtration, with filter elements having precisions of 3 μm, 1 μm, 0.5 μm, and 0.2 μm, respectively. The precision of the filter element refers to the absolute filtration precision.

[0058] According to one embodiment of the present invention, the pH value of the obtained filtrate is adjusted to 4 to 6, more preferably to 4 to 5, to obtain the nano-cerium oxide polishing liquid of the present invention. The pH adjuster used is selected from any one of citric acid, glacial acetic acid, and nitric acid, preferably nitric acid. The concentration of the pH adjuster can be 1 to 20wt%, preferably 5 to 20wt%, and more preferably 10 to 20wt%.

[0059] Nano-cerium oxide polishing liquid The present invention also provides a nano-cerium oxide polishing liquid, which is prepared according to the above-mentioned preparation method.

[0060] The average particle size of the nano-cerium oxide polishing liquid of the present invention is less than or equal to 200 nm, preferably less than or equal to 180 nm, more preferably less than or equal to 160 nm, and can reach 140 nm and greater than 100 nm.

[0061] The absolute value of the Zeta potential of the nano-cerium oxide polishing liquid of the present invention is greater than or equal to 40 mV, preferably greater than or equal to 45 mV, and more preferably greater than or equal to 48 mV.

[0062] Such nano-cerium oxide polishing liquid can give consideration to both polishing and cleaning effects.

[0063] When the nano-cerium oxide polishing liquid of the present invention is used for polishing, the SiO2 removal rate is greater than or equal to 300 nm / min, preferably greater than or equal to 350 nm / min, and more preferably greater than or equal to 360 nm / min. The arithmetic average roughness Ra of the polished device is less than or equal to 0.4 nm, preferably less than or equal to 0.35 nm. The root mean square roughness Rq is less than or equal to 0.4 nm.

[0064] After polishing with the nano-cerium oxide polishing liquid of the present invention, the surface of the obtained device is easy to clean, thereby avoiding the problem of polishing materials remaining on the device surface in the CMP field.

[0065] application The present invention also provides an application of the nano-cerium oxide polishing liquid described above in polishing semiconductors or integrated circuits. The nano-cerium oxide polishing liquid of the present invention is mainly used in the thinning and fine grinding process of coated wafers and has a good polishing effect on silicon oxide wafers.

[0066] Test Method Particle size distribution (TEM) and Zeta potential test: HORIBA nanoPartica SZ-100V2 nanoparticle size analyzer and Zeta potential analyzer were used respectively; the particle size result is the Z-average particle size value.

[0067] Arithmetic average roughness Ra and root mean square roughness Rq: tested using an atomic force microscope (AFM, NX20, ParkSystem) and obtained by calculation.

[0068] Example 1 1) Dissolve 5 kg of cerium carbonate (CeO₂ / TREO ≥ 99.99%) in 4.5 L of 68 wt% nitric acid to obtain a cerium nitrate solution. Add the cerium nitrate solution and 18 L of 25 wt% ammonium bicarbonate solution dropwise to a reaction vessel at 55°C. After completion of the addition, the pH of the reaction system is 8.5. The mixture is then allowed to age for 4 hours. The precipitate is washed three times with water and filtered to obtain a Ce₂(CO₃)₃·8H₂O precipitate.

[0069] 2) Combine the Ce₂(CO₃)₃·8H₂O precipitate, 5 L of deionized water, and 100 g of polyoxyalkylene (polyoxyethylene lauryl alcohol ether, CAS No. 68439-50-9) to obtain a mixed solution. Control the pH of the mixed solution to 8.6. Grind the mixed solution in a sand mill to obtain a grinding solution.

[0070] 3) Transfer the grinding solution to a reactor, heat to 100°C under atmospheric pressure, and react at 100°C for 2 hours to obtain a reaction solution. Spray dry the reaction solution to obtain a dry product. Place the dry product in a tubular rotary kiln and calcine at 660°C for 3 hours to obtain cerium dioxide powder.

[0071] 4) Crush the cerium dioxide powder using a hammer mill. Mix 29 parts by weight of the crushed cerium dioxide powder, 1 part by weight of a maleic anhydride-containing copolymer salt (maleic anhydride-styrene copolymer ammonium salt, CAS No. 26022-09-3), and 70 parts by weight of deionized water to obtain a slurry.

[0072] 5) The slurry was subjected to ultrahigh pressure crushing and impact dispersion treatment using a high-pressure homogenizer at a set pressure of 30,000 psi, and the treatment was repeated three times to obtain a dispersion.

[0073] 6) Filter the dispersion using four filters with filter cartridges having filter granularities of 3 μm, 1 μm, 0.5 μm, and 0.2 μm, respectively. Collect the final filtrate. While stirring, adjust the pH of the final filtrate to 4.7 using 20 wt% nitric acid to obtain a nano-cerium oxide polishing solution.

[0074] The particle size distribution of the obtained nano-cerium oxide polishing liquid is shown in Figure 1 , Zeta potential results are shown in Figure 2 .Depend on Figure 1 It can be seen that the average particle size of the nano-cerium oxide polishing liquid is 140nm. Figure 2 It can be seen that the zeta potential result is -48.8 mV.

[0075] Comparative Example 1 The raw material cerium carbonate was directly added into a tubular rotary kiln and calcined at 660° C. for 3 h to obtain cerium dioxide powder.

[0076] The cerium dioxide powder obtained above was crushed using a hammer mill. 29 parts by weight of the crushed cerium dioxide powder, 1 part by weight of a copolymer salt containing maleic anhydride (maleic anhydride-styrene copolymer ammonium salt, CAS No. 26022-09-3), and 70 parts by weight of deionized water were uniformly mixed to obtain a slurry.

[0077] The slurry was subjected to ultrahigh pressure crushing and impact dispersion treatment using a high pressure homogenizer at a set pressure of 30,000 psi, and the treatment was circulated three times to obtain a dispersion.

[0078] The dispersion was filtered through four filters with filter cartridges having filter accuracies of 3 μm, 1 μm, 0.5 μm, and 0.2 μm, respectively. The final filtrate was collected. While stirring, the pH of the final filtrate was adjusted to 4.7 using 20 wt% nitric acid to obtain a nano-cerium oxide polishing solution.

[0079] Comparative Example 2 3 kg of abrasive was mixed with 6.42 kg of water, followed by the addition of 0.15 kg of water-soluble cyclodextrin and 0.01 kg of polyethylene glycol. 0.4 kg of a pH adjuster and 0.02 kg of a surfactant were then added and mixed thoroughly to prepare a CMP polishing slurry. The abrasive used was silica sol, the pH adjuster was sodium hydroxide, the surfactant was anionic polyacrylamide, the polyethylene glycol was PEG-2000, and the water-soluble cyclodextrin was hydroxypropyl-β-cyclodextrin.

[0080] Comparative Example 3 At room temperature, a cerium carbonate aqueous dispersion slurry with a solid content of 10 wt % was prepared. The aqueous dispersion slurry also contained 0.1 wt % polyacrylic acid (PAA) as a dispersant, and the pH value of the aqueous dispersion slurry was adjusted to 7.0.

[0081] The prepared cerium carbonate water-dispersed slurry was ball-milled until the average particle size reached 0.3 μm, and then the ball milling was stopped.

[0082] The ball-milled mixture was transferred into a hydrothermal reactor at 50° C. for crystallization reaction for 24 h. The resulting precipitate was washed three times with pure water and filtered to obtain a filter cake.

[0083] The filter cake is dried to obtain cerium carbonate powder, which is then calcined in static air at 500° C. for 10 hours and cooled to obtain cerium oxide powder.

[0084] Water was added to the cerium oxide powder, polyacrylic acid PAA was added as a dispersant, and ball milling dispersion treatment was performed for 30 minutes to obtain a cerium oxide polishing liquid.

[0085] Comparative Example 4 The only difference from Example 1 is that polyacrylamide is used in place of polyalkylene oxide in step 2), and polyacrylic acid is used in place of the copolymer salt containing maleic anhydride in step 4).

[0086] Experimental example 1. Polishing materials and polishing experiments The device to be polished is a silicon oxide wafer, also known as a SiO2 coated wafer. The silicon oxide wafer used is a 4-inch thermal oxide wafer independently produced by Fudan University, with a thickness of 1000nm.

[0087] The polishing machine model was a POLI-400L (G&P Technology, Inc.), equipped with a Gas_Pad_16in_GP polishing pad. The thickness and uniformity of the SiO2-coated films were measured before and after polishing using a Premier 50 dielectric film thickness tester (P50, Futuo Scientific Instrument Co., Ltd.). The polishing conditions were: a pressure of 4 psi, a polishing disk speed of 87 / 93 rpm, and a flow rate of 200 ml / min.

[0088] The polished SiO2-coated wafer was then cleaned and blown away using the polishing machine's built-in water gun (blowing away any residual moisture on the wafer using compressed air or a dedicated air blower). After cleaning, the surface roughness of the wafer was measured using an atomic force microscope (AFM, NX20, Park System). Surface roughness (including Ra and Rq) was measured at three randomly selected areas on the four-inch wafer, using a scanning range of 5μm x 5μm.

[0089] 2. Polishing Experiment Results and Discussion The nano-cerium oxide polishing liquids obtained in Example 1 and Comparative Example 1, and the polishing liquids of Comparative Example 2, Comparative Example 3, and Comparative Example 4 were subjected to polishing experiments and surface roughness (including Ra and Rq) were measured according to the polishing experiments described above. The results are shown in Table 1.

[0090] Table 1

[0091] As can be seen from the table, compared with Comparative Example 1, the device polished with the polishing liquid of the present invention (i.e., the SiO2 coated film after polishing) has smaller surface roughness and better surface uniformity, and the SiO2 removal rate is higher.

[0092] Compared with Comparative Example 2 (silica sol polishing liquid) and Comparative Example 3 (a cerium oxide polishing liquid product currently available on the market), the surface roughness of the device polished using the polishing liquid of the present invention is smaller, the surface uniformity is better, and the SiO2 removal rate is higher.

[0093] Compared with Comparative Example 4, the device polished by the polishing liquid of the present invention has a smaller root mean square roughness Rq, a larger absolute value of the Zeta potential, and a higher SiO2 removal rate.

[0094] Therefore, the surface uniformity of the device polished by the nano-cerium oxide polishing liquid of the present invention is better, and the SiO2 removal rate is higher.

[0095] 3. Cleaning experiment The product polished with the polishing liquid of Example 1 was cleaned with a polishing machine water gun. The actual picture before cleaning and the actual picture after cleaning are compared, respectively. Figure 3 、 Figure 4 However, the devices polished with the polishing solutions of Comparative Examples 1 to 4 could not achieve the cleaning effect of the present invention after cleaning. It can be seen that the devices polished with the polishing solution of Example 1 are more easily cleaned of residual polishing material (i.e., residual nano-cerium oxide polishing material).

[0096] In summary, the nano-cerium oxide polishing liquid prepared by the present invention has a high SiO2 removal rate during polishing, good surface uniformity of the polished device, and is easy to clean. Therefore, the present invention can achieve both polishing and cleaning effects.

[0097] Without departing from the essential content of the present invention, any variation, improvement, or substitution that can be conceived by those skilled in the art shall fall within the scope of the present invention.

Claims

1. A method for preparing a nano-cerium oxide polishing liquid, characterized in that: The following steps are involved: 1) dissolving cerium carbonate in nitric acid to form a cerium nitrate solution; adding the cerium nitrate solution and ammonium bicarbonate solution concurrently dropwise to a reaction vessel at 40-85°C for reaction, followed by aging and solid-liquid separation to obtain a cerium carbonate precipitate containing water of crystallization; 2) mixing the cerium carbonate precipitate containing crystal water, water and polyoxyalkylene to obtain a mixed solution; grinding the mixed solution to obtain a grinding solution; 3) heating the grinding liquid to 75-100°C and reacting to obtain a reaction liquid; The reaction solution is then spray-dried to obtain a dry product; the dry product is calcined to obtain cerium dioxide powder; 4) crushing the cerium dioxide powder to obtain crushed cerium dioxide powder; mixing the crushed cerium dioxide powder, a copolymer salt containing maleic anhydride, and water to obtain a slurry; 5) treating the slurry with a high-pressure homogenizer to obtain a dispersion; wherein the pressure of the high-pressure homogenizer is 20,000 to 30,000 psi; 6) filtering the dispersion using a plurality of filters to obtain a filtrate; adjusting the pH value of the obtained filtrate to 3 to 6 to obtain the nano-cerium oxide polishing liquid; The filter element has a precision of less than or equal to 3 μm.

2. The preparation method according to claim 1, characterized in that Step 1) specifically includes the following process: Cerium carbonate is dissolved in nitric acid with a concentration of 65-68 wt% to form a cerium nitrate solution; the cerium nitrate solution and an ammonium bicarbonate solution with a concentration of 20-25 wt% are co-currently added dropwise to a reaction vessel at 40-85° C. for reaction; after the co-current addition is completed, the pH value of the reaction system is controlled to be 7-10; then, the reaction is aged for 3-6 hours, and the solid is washed with water, and filtered after washing to obtain a cerium carbonate precipitate containing more than 3 crystal waters.

3. The preparation method according to claim 1, characterized in that In the mixed solution of step 2), the amount of cerium carbonate precipitate containing crystal water is 5-60 parts by weight, the amount of water is 40-99.9 parts by weight, and the amount of polyoxyalkylene is 0.1-2 parts by weight; the pH value of the mixed solution is 7-9.

4. The preparation method according to claim 1, characterized in that The polyoxyalkylene is selected from one or more of fatty alcohol polyoxyethylene ether, alkylphenol polyoxyethylene ether and polyoxyethylene polyoxypropylene block copolymer.

5. The preparation method according to claim 1, characterized in that In step 3), the calcination temperature is 600-900° C., and the calcination time is 3-6 hours.

6. The preparation method according to claim 1, characterized in that Step 4) specifically includes the following process: The cerium dioxide powder is crushed by a hammer crusher to obtain crushed cerium dioxide powder; 0.5 to 30 parts by weight of the crushed cerium dioxide powder, 0.01 to 1 parts by weight of a copolymer salt containing maleic anhydride and 70 to 99.8 parts by weight of water are mixed to obtain a slurry.

7. The preparation method according to claim 6, characterized in that The maleic anhydride-containing copolymer salt is selected from one or more of maleic anhydride-styrene copolymer ammonium salt, maleic anhydride-styrene-acrylic acid terpolymer ammonium salt, maleic anhydride-acrylic acid sodium salt and maleic anhydride-vinyl acetate copolymer sodium salt.

8. The preparation method according to claim 1, wherein: In step 5), a high-pressure homogenizer is used for cyclic treatment for more than 2 times; In step 6), the dispersion is filtered using four filters to obtain filtrates; wherein the filter elements have a precision of 3 μm, 1 μm, 0.5 μm and 0.2 μm respectively.

9. A nano-cerium oxide polishing liquid, characterized in that: The invention relates to a novel novel nanostructured carbon foam prepared by the preparation method according to any one of claims 1 to 8.

10. Use of the nano-cerium oxide polishing liquid as claimed in claim 9 in polishing semiconductors or integrated circuits.

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