Preparation method of nanometer cerium oxide for rough polishing of silicon substrate

Abstract

The application discloses a preparation method of nanometer cerium oxide for rough polishing of a silicon substrate, and relates to the technical field of semiconductor material processing; the preparation process is as follows: 1. precursor synthesis: 1) solution preparation: 1) cerium salt solution preparation; 2) lye preparation; 2) synthesis: 1) adding fluxing salt; 2) precipitation; 2. calcination; 3. cleaning; the nanometer cerium oxide for rough polishing of the silicon substrate has the characteristics of simple preparation process, controllable operation process, good repeatability and easy industrialization, and can be used for rough polishing of a silicon substrate wafer.

Description

Technical Field

[0001] This invention relates to the field of semiconductor material processing technology, and in particular to a method for preparing nano-sized cerium oxide for rough polishing of silicon substrates. Background Technology

[0002] As the feature size of very large-scale integrated circuit devices decreases and the integration density increases, the acceptable resolution of the polished surface of single-crystal silicon wafers, which serve as substrate materials, is also increasing, requiring ultra-smooth surfaces. Therefore, in the chemical mechanical polishing of silicon wafers, the size, morphology, particle size distribution, and hardness of the abrasive itself are key factors affecting the quality of the polished surface.

[0003] Silicon substrate polishing typically consists of rough polishing, fine polishing, and precision polishing. Currently, silicon substrate polishing primarily uses silicon oxide polishing slurries. However, silicon oxide polishing slurries still have problems such as low removal rate, the high hardness of silicon dioxide making it prone to scratching the material, difficulty in cleaning after polishing, and difficulty in handling the polished material. Surface damage is caused by the high temperature and pressure during polishing or the influence of metal ions, leading to the agglomeration or crystallization of silicon oxide into hard substances.

[0004] Cerium dioxide has been used as a polishing agent for many years, and it is widely used in the polishing of precision glass and silicon dioxide dielectric layers, exhibiting strong polishing capabilities. Numerous reports have also documented the application of cerium oxide as an abrasive for polishing silicon substrates.

[0005] In existing technologies, the main methods for preparing spherical or near-spherical cerium oxide nanoparticles include the following:

[0006] First, the solid-phase method: The existing solid-phase method can achieve spheroidization or near-spheroidization through fluxing agents, but it is greatly affected by the raw materials, resulting in poor particle uniformity and wide particle distribution;

[0007] Second, the hydrothermal synthesis method: The hydrothermal synthesis method cannot be industrialized because its process is uncontrollable and has poor repeatability;

[0008] Thirdly, the synthesis method: existing synthesis methods result in particles that are prone to agglomeration and have many surface edges and corners. Although the surface edges and agglomeration problems can be improved by adding flux in the later stage, the particle size becomes larger and the uniformity becomes worse.

[0009] Chinese Patent (Patent Application No. 202211028207.0) discloses "A Preparation Method and Application of Nano-Cerium Oxide". The preparation method includes the following steps: feeding a cerium salt solution, a precipitant, and a surfactant into a multiphase interface reactor in a parallel flow and reacting under stirring; then aging, centrifuging, and washing the slurry obtained from the reaction to obtain a nano-cerium carbonate precursor; then calcining the nano-cerium carbonate precursor to obtain the desired product; the molar concentration of Ce3+ in the solution is 0.5-1.8 mol / L; the molar concentration ratio of Ce3+ to precipitant and surfactant in the cerium salt solution is 1:(1-2.0):(0.3%-3%).

[0010] Another Chinese patent (patent application number 202210937597.7) discloses a "method for preparing spherical nano-cerium oxide", which includes the following steps: a) dissolving a certain amount of fluxing salt in water, then adding the undissolved cerium salt to the solution of fluxing salt and water, stirring evenly to obtain a uniformly dispersed slurry; b) drying the slurry obtained in step a while stirring to obtain a dry, uniform, and fine powder; c) calcining the powder obtained in step b to obtain the final product.

[0011] There is also a Chinese patent (patent application number 202210989564.7) that discloses "a highly dispersed spherical nano-cerium oxide polishing slurry and its application", the polishing slurry includes spherical nano-cerium oxide powder; the preparation method of the spherical nano-cerium oxide powder includes the following steps: (1) mixing tetravalent cerium salt with polyvinylpyrrolidone solution to prepare cerium salt solution, adding precipitant and oxidant, and shearing at high speed at 70-90℃ until precipitate is generated to obtain precursor slurry; (2) washing the precursor slurry to neutrality, and then spray drying to obtain cerium oxide precursor, adding fluxing salt to it, refining the material, and spray drying again; (3) calcining the obtained material to obtain nano-cerium oxide powder.

[0012] There is also a Chinese patent (patent application number 202010675867.2) that discloses "a method for preparing 10-50nm high-purity nano-cerium oxide", which includes the following steps: (1) dissolving high-purity cerium nitrate, high-purity glycine and high-purity PEG raw materials in semiconductor-grade ultrapure water, and drying the resulting solution in a closed high-purity protective gas spray dryer to generate micron-sized dry powder; (2) using high-purity oxygen to transport the generated powder to a high-temperature reaction furnace, and the powder undergoes an explosive reaction in the high-temperature furnace to obtain nano-cerium oxide with a particle size of 10-50nm and a purity of 99.9999wt% or higher.

[0013] Another Chinese patent (patent application number 202110667647.X) discloses a "method for low-temperature synthesis of uniform spherical nano-cerium oxide materials." This invention employs a low-temperature hydrothermal method, dissolving a certain amount of cerium nitrate hexahydrate, urea, and polyvinylpyrrolidone-K30 in deionized water at room temperature, mixing and stirring, and then transferring the resulting solution to a stainless steel autoclave for reaction. The autoclave is maintained at 80-120°C for 6-12 hours. After natural cooling to room temperature, uniformly sized spherical nano-cerium dioxide is obtained through centrifugation, washing, and calcination.

[0014] Another Chinese patent (patent application number 201910221796.6) discloses "A method for preparing nano-cerium oxide for silicon wafer polishing", which includes the following steps: a) dissolving a certain amount of silicate in water by stirring, then adding the undissolved cerium salt to the silicate and water solution, and then ball milling to obtain a uniformly dispersed slurry; b) drying the slurry obtained in step a by flash evaporation to obtain a dry, uniform, and fine powder; c) calcining the powder obtained in step b to obtain the final product.

[0015] Another Chinese patent (patent application number 201510966080.0) discloses "A method for preparing ultrafine cerium oxide polishing powder with adjustable average particle size." This method uses a hydrothermal-calcination method to prepare micro / nano cerium oxide polishing powder. First, cerium oxide (Ce(IV)) is hydrothermally synthesized as a precursor. Then, the precursor is calcined and post-treated to obtain the polishing powder product. By adjusting the hydrothermal reaction parameters (system pH value), the size and morphology of the cerium oxide precursor are controlled, thereby achieving control over the morphology and particle size of the finished polishing powder. The prepared cerium oxide polishing powder has a near-spherical morphology, with a median particle size d50 adjustable between 100 nm and 1.5 µm, and 0 < particle size distribution R < 0.8.

[0016] Another US patent, US20110252714, uses potassium hydroxide and cerium nitrate to react. The cerium oxide grains after burning are about 150 nm in size and are spherical. The cutting rate and appearance are acceptable, but the dispersibility and uniformity are average. Summary of the Invention

[0017] In view of the shortcomings of the existing technology, the technical problem to be solved by the present invention is to provide a method for preparing spherical nanoscale cerium oxide powder with simple preparation process, controllable operation, good repeatability and easy industrialization.

[0018] To solve the above-mentioned technical problems, the technical solution adopted by the present invention is to invent a method for preparing nano-sized cerium oxide for rough polishing of silicon substrates, the preparation process of which is as follows:

[0019] Precursor synthesis:

[0020] Solution preparation:

[0021] Preparation of cerium salt solution: Add soluble cerium salt to pure water to prepare a 0.2-0.8 mol / L soluble cerium salt solution for later use;

[0022] Preparation of alkali solution: Add alkali to pure water to prepare an alkali solution with a concentration of 2-8%, and set aside for later use;

[0023] ,synthesis:

[0024] Add fluxing salt: Add fluxing salt to the soluble cerium salt solution and stir to dissolve. The amount of fluxing salt added should be 2-8% of the soluble cerium salt converted to REO. A mixed solution of soluble cerium salt and fluxing salt is obtained for later use.

[0025] Precipitation: At room temperature, slowly add alkali solution to the soluble cerium salt fluxing solution until the pH value is 10-12 to obtain a colloid. Then, stir at 70-90℃ for 4-6 hours. After the reaction is complete, filter and dry the filter cake at 90-120℃ to obtain the precursor for later use.

[0026] Calcination:

[0027] The precursor is placed in a muffle furnace and calcined at 650-800℃. During the calcination process, the temperature is first raised to the calcination temperature in 2-4 hours, and then calcined at the calcination temperature for 0.5-1.5 hours to obtain the calcined precursor for later use.

[0028] Cleaning:

[0029] The calcined precursor was repeatedly centrifuged and washed with pure water in a centrifuge until the conductivity was below 1 mS / cm, thus obtaining cerium oxide.

[0030] Optimally, the soluble cerium salt includes one or both of cerium chloride and cerium nitrate, preferably cerium chloride.

[0031] Optimally, the alkali includes one, two, or three of potassium hydroxide, sodium hydroxide, and ammonia water, with potassium hydroxide being preferred.

[0032] Optimally, the fluxing salt includes one, two, or three of potassium chloride, sodium chloride, and ammonium chloride, with potassium chloride being preferred.

[0033] Ideally, the concentration of the soluble cerium salt solution is 0.4-0.6 mol / L, and it is reserved for use; the content of the alkali solution is 4-6%.

[0034] Ideally, the concentration of the soluble cerium salt solution is 0.5 mol / L, and it is reserved for use; the content of the alkali solution is 5%.

[0035] Ideally, the amount of fluxing salt added is 4-6% of the soluble cerium salt converted to REO.

[0036] Ideally, the amount of fluxing salt added is 5% of the soluble cerium salt converted to REO.

[0037] Ideally, the pH value of the colloid is 11, the stirring temperature of the colloid is 80°C, and the stirring time of the colloid is 5 hours.

[0038] Ideally, the calcination temperature is 700℃, and the calcination process involves: first raising the temperature to 700℃ over 3 hours, and then maintaining the temperature at 700℃ for 1 hour.

[0039] Ideally, the drying temperature of the filter cake is 105°C.

[0040] The cerium oxide obtained by calcination described above, when observed under an electron microscope to determine its morphology, dispersibility, and particle size, can be classified as a near-spherical nanoparticle (see appendix for details). Figure 1-5 As shown in the figure, its subsequent application can be processed into a spherical nano-cerium oxide polishing slurry through ball milling.

[0041] The method for preparing nano-sized cerium oxide for rough polishing of silicon substrates of the present invention involves controlling the process from the beginning of precursor preparation. Specifically, a flux is added before the synthesis reaction, and the particle size, uniformity, and dispersibility of the precursor are controlled by the flux (i.e., fluxing salt). This results in synthesized nano-sized cerium oxide powder with controllable particle size, uniform morphology, excellent dispersibility, and spherical shape. Furthermore, since the reaction process is carried out under atmospheric pressure and heating, the equipment requirements are not high. Therefore, the preparation process is simple, controllable, reproducible, and easily industrialized. Attached Figure Description

[0042] Figure 1 These are electron microscope images of the product obtained in Embodiment 1 of the present invention;

[0043] Figure 2 These are electron microscope images of the product obtained in Embodiment 2 of the present invention;

[0044] Figure 3 These are electron microscope images of the product obtained in Example 3 of the present invention;

[0045] Figure 4 These are electron microscope images of the product obtained in Example 4 of the present invention;

[0046] Figure 5These are electron microscope images of the product obtained in Embodiment 5 of the present invention;

[0047] Figure 6 These are electron microscope images of the product obtained in Comparative Example 1;

[0048] Figure 7 These are electron microscope images of the product obtained in Comparative Example 2;

[0049] Figure 8 The image shown is an electron microscope photograph of the product obtained in Comparative Example 3. Detailed Implementation

[0050] The present invention will be further described below with reference to embodiments. The following description is by way of example, but the scope of protection of the present invention should not be limited thereto.

[0051] Example 1:

[0052] The preparation method of nano-sized cerium oxide for rough polishing of silicon substrates in this embodiment is as follows:

[0053] Precursor synthesis:

[0054] Solution preparation:

[0055] Preparation of cerium salt solution: Add cerium chloride to pure water to prepare a 0.5 mol / L cerium chloride solution for later use;

[0056] Preparation of alkaline solution: Add potassium hydroxide to pure water to prepare a 5% potassium hydroxide solution for later use;

[0057] ,synthesis:

[0058] 1. Add fluxing salt: Add potassium chloride (the added fluxing salt potassium chloride, in which chloride ions and potassium ions are adsorbed by the colloidal particles formed during the subsequent precipitation process, thereby controlling the morphology, dispersibility and particle size of the colloidal particles, the same below) to the cerium chloride solution, stir to dissolve, and add potassium chloride at 5% of the cerium chloride solution (converted to REO) to obtain cerium chloride fluxing solution for later use;

[0059] Precipitation: At room temperature, potassium hydroxide solution is slowly added to cerium chloride flux solution until pH value reaches 11, resulting in a purple colloid. Then, it is stirred at 80℃ for 5 hours (this process is high-temperature aging, the purpose of which is to convert the colloid into a precipitate, solving the problem that hydroxide colloids cannot be separated and are difficult to dry, the same below). After the reaction is complete (at this time, the precipitate settles naturally, reaching a state of solid-liquid separation, the same below), it is filtered and the filter cake is dried at 105℃ to obtain the precursor for later use.

[0060] Calcination:

[0061] The precursor was placed in a muffle furnace and calcined at 700°C. During the calcination process, the temperature was first raised to 700°C over 3 hours, and then calcined at 700°C for 1 hour to obtain the calcined precursor for later use.

[0062] Cleaning:

[0063] The calcined precursor was repeatedly centrifuged and washed with pure water in a centrifuge (during this process, most of the chloride ions and basic metal ions were washed away, the same below) until the conductivity was below 1 mS / cm, thus obtaining cerium oxide.

[0064] The cerium oxide prepared in this embodiment, as determined by electron microscopy, has a primary particle size of approximately 50 nm, good surface sphericity, and good dispersibility. See attached figure for details. Figure 1 As shown, it can therefore be used to prepare nano-cerium oxide for rough polishing of silicon substrates.

[0065] Example 2:

[0066] The preparation method of nano-sized cerium oxide for rough polishing of silicon substrates in this embodiment is as follows:

[0067] Precursor synthesis:

[0068] Solution preparation:

[0069] Preparation of cerium salt solution: Add cerium chloride to pure water to prepare a 0.5 mol / L cerium chloride solution for later use;

[0070] Preparation of alkaline solution: Add potassium hydroxide to pure water to prepare a 5% potassium hydroxide solution for later use;

[0071] ,synthesis:

[0072] 1. Add fluxing salt: Add sodium chloride to the cerium chloride solution and stir to dissolve. The amount of sodium chloride added is 5% of the cerium chloride solution converted to REO. The resulting cerium chloride fluxing solution is ready for use.

[0073] Precipitation: At room temperature, potassium hydroxide solution was slowly added to cerium chloride flux solution until the pH value reached 11, resulting in a purple colloid. Then, the mixture was stirred at 80°C for 5 hours. After the reaction was complete, the mixture was filtered and the filter cake was dried at 105°C to obtain the precursor for later use.

[0074] Calcination:

[0075] The precursor was placed in a muffle furnace and calcined at 700°C. During the calcination process, the temperature was first raised to 700°C over 3 hours, and then calcined at 700°C for 1 hour to obtain the calcined precursor for later use.

[0076] Cleaning:

[0077] The calcined precursor was repeatedly centrifuged and washed with pure water in a centrifuge until the conductivity was below 1 mS / cm, thus obtaining cerium oxide.

[0078] The cerium oxide prepared in this embodiment, as detected by electron microscopy, has a primary particle size of less than 100 nm, and exhibits moderate surface sphericity and dispersibility. See attached figure for details. Figure 2 As shown, it can also be used to prepare nano-cerium oxide for rough polishing of silicon substrates.

[0079] Example 3:

[0080] The preparation method of nano-sized cerium oxide for rough polishing of silicon substrates in this embodiment is as follows:

[0081] Precursor synthesis:

[0082] Solution preparation:

[0083] Preparation of cerium salt solution: Add cerium chloride to pure water to prepare a 0.5 mol / L cerium chloride solution for later use;

[0084] Preparation of alkaline solution: Add sodium hydroxide to pure water to prepare a 5% sodium hydroxide solution for later use;

[0085] ,synthesis:

[0086] 1. Add fluxing salt: Add potassium chloride to the cerium chloride solution and stir to dissolve. The amount of potassium chloride added is 5% of the REO in the cerium chloride solution to obtain a cerium chloride fluxing solution for later use.

[0087] Precipitation: At room temperature, sodium hydroxide solution was slowly added to cerium chloride flux solution until the pH value reached 11, resulting in a purple colloid. Then, the mixture was stirred at 80°C for 5 hours. After the reaction was complete, the mixture was filtered and the filter cake was dried at 105°C to obtain the precursor for later use.

[0088] Calcination:

[0089] The precursor was placed in a muffle furnace and calcined at 700°C. During the calcination process, the temperature was first raised to 700°C over 3 hours, and then calcined at 700°C for 1 hour to obtain the calcined precursor for later use.

[0090] Cleaning:

[0091] The calcined precursor was repeatedly centrifuged and washed with pure water in a centrifuge until the conductivity was below 1 mS / cm, thus obtaining cerium oxide.

[0092] The cerium oxide prepared in this embodiment, as determined by electron microscopy, has a primary particle size of approximately 50 nm, moderate surface sphericity, numerous irregular particles, and generally poor dispersibility. See attached diagram for details. Figure 3 As shown, it can also be used to prepare nano-cerium oxide for rough polishing of silicon substrates.

[0093] Example 4:

[0094] The preparation method of nano-sized cerium oxide for rough polishing of silicon substrates in this embodiment is as follows:

[0095] Precursor synthesis:

[0096] Solution preparation:

[0097] Preparation of cerium salt solution: Add cerium chloride to pure water to prepare a 0.5 mol / L cerium chloride solution for later use;

[0098] Preparation of alkaline solution: Add ammonia water to purified water to prepare a 5% ammonia solution for later use;

[0099] ,synthesis:

[0100] 1. Add fluxing salt: Add ammonium chloride to the cerium chloride solution and stir to dissolve. The amount of ammonium chloride added is 5% of the REO in the cerium chloride solution to obtain a cerium chloride fluxing solution for later use.

[0101] Precipitation: At room temperature, ammonia solution was slowly added to cerium chloride flux solution until the pH value reached 11, resulting in a white colloid. Then, the mixture was stirred at 80°C for 5 hours. After the reaction was complete, the mixture was filtered and the filter cake was dried at 105°C to obtain the precursor for later use.

[0102] Calcination:

[0103] The precursor was placed in a muffle furnace and calcined at 700°C. During the calcination process, the temperature was first raised to 700°C over 3 hours, and then calcined at 700°C for 1 hour to obtain the calcined precursor for later use.

[0104] Cleaning:

[0105] The calcined precursor was repeatedly centrifuged and washed with pure water in a centrifuge until the conductivity was below 1 mS / cm, thus obtaining cerium oxide.

[0106] The cerium oxide prepared in this embodiment, as detected by electron microscopy, has a primary particle size of 50-100 nm, poor surface sphericity, and many sharp edges, but good dispersibility. See attached figure for details. Figure 4 As shown, it can also be used to prepare nano-cerium oxide for rough polishing of silicon substrates.

[0107] Example 5:

[0108] The preparation method of nano-sized cerium oxide for rough polishing of silicon substrates in this embodiment is as follows:

[0109] Precursor synthesis:

[0110] Solution preparation:

[0111] Preparation of cerium salt solution: Add cerium nitrate to pure water to prepare a 0.5 mol / L cerium nitrate solution for later use;

[0112] Preparation of alkaline solution: Add potassium hydroxide to pure water to prepare a 5% potassium hydroxide solution for later use;

[0113] ,synthesis:

[0114] 1. Add fluxing salt: Add potassium chloride to the cerium nitrate solution and stir to dissolve. The amount of potassium chloride added is 5% of the REO content of the cerium nitrate solution, to obtain a cerium nitrate fluxing solution for later use.

[0115] Precipitation: At room temperature, potassium hydroxide solution was slowly added to cerium nitrate flux solution until the pH value reached 11, resulting in a purple colloid. Then, the mixture was stirred at 80°C for 5 hours. After the reaction was complete, the mixture was filtered and the filter cake was dried at 105°C to obtain the precursor for later use.

[0116] Calcination:

[0117] The precursor was placed in a muffle furnace and calcined at 700°C. During the calcination process, the temperature was first raised to 700°C over 3 hours, and then calcined at 700°C for 1 hour to obtain the calcined precursor for later use.

[0118] Cleaning:

[0119] The calcined precursor was repeatedly centrifuged and washed with pure water in a centrifuge until the conductivity was below 1 mS / cm, thus obtaining cerium oxide.

[0120] The cerium oxide prepared in this embodiment, as determined by electron microscopy, has a primary particle size of 50-100 nm, good surface sphericity, good angularity, and good dispersibility. See attached figure for details. Figure 5 As shown, it can also be used to prepare nano-cerium oxide for rough polishing of silicon substrates.

[0121] Based on the test results of the five embodiments above, using sodium chloride as a flux makes it easier for particles to become larger and less uniform. Therefore, overall, potassium ions can better control particle morphology, dispersibility, and size.

[0122] In addition, when cerium nitrate is used as a soluble cerium salt or ammonia is used as a precipitant, a wastewater treatment process is required afterward; otherwise, the ammonia nitrogen in the wastewater will exceed the standard.

[0123] Compare with Example 1:

[0124] The preparation method of cerium oxide in this comparative example is similar to the preparation method of nano-sized cerium oxide for rough polishing of silicon substrates of the present invention, except that no fluxing salt is added. The preparation process is as follows:

[0125] Precursor synthesis:

[0126] Solution preparation:

[0127] Preparation of cerium salt solution: Add cerium chloride to pure water to prepare a 0.5 mol / L cerium chloride solution for later use;

[0128] Preparation of alkaline solution: Add potassium hydroxide to pure water to prepare a 5% potassium hydroxide solution for later use;

[0129] Synthesis (i.e., precipitation):

[0130] At room temperature, potassium hydroxide solution was slowly added to cerium chloride solution until the pH value reached 11, resulting in a purple colloid. Then, the mixture was stirred at 80°C for 5 hours. After the reaction was complete, the mixture was filtered and the filter cake was dried at 105°C to obtain the precursor for later use.

[0131] Calcination:

[0132] The precursor was placed in a muffle furnace and calcined at 700°C. During the calcination process, the temperature was first raised to 700°C over 3 hours, and then calcined at 700°C for 1 hour to obtain the calcined precursor for later use.

[0133] Cleaning:

[0134] The calcined precursor was repeatedly centrifuged and washed with pure water in a centrifuge (in this process, most of the chloride ions and basic metal ions were washed away) until the conductivity was below 1 mS / cm, thus obtaining cerium oxide.

[0135] The cerium oxide prepared in this comparative example, as detected by electron microscopy, has a primary particle size of 50-200 nm, exhibiting uneven size distribution and a wide range. Some particles have a primary particle size exceeding 100 nm, exceeding the scope of nanomaterials. While the surface sphericity is generally moderate, the dispersibility is good. See Appendix for details. Figure 6 As shown.

[0136] Compare with Example 2:

[0137] The preparation method of cerium oxide in this comparative example is similar to the preparation method of nano-sized cerium oxide for rough polishing of silicon substrates of the present invention, except that a fluxing salt is added after aging in the precipitation process. The preparation process is as follows:

[0138] Precursor synthesis:

[0139] Solution preparation:

[0140] Preparation of cerium salt solution: Add cerium chloride to pure water to prepare a 0.5 mol / L cerium chloride solution for later use;

[0141] Preparation of alkaline solution: Add potassium hydroxide to pure water to prepare a 5% potassium hydroxide solution for later use;

[0142] ,synthesis:

[0143] Precipitation: At room temperature, potassium hydroxide solution was slowly added to cerium chloride solution until the pH value reached 11, resulting in a purple colloid. Then, the mixture was stirred at 80°C for 5 hours to obtain an aged colloid for later use.

[0144] Add fluxing salt: Add potassium chloride to the aged colloid, stir to dissolve, and the amount of potassium chloride added is 5% of the amount of REO converted from cerium chloride solution. After the reaction is complete, filter and dry the filter cake at 105℃ to obtain the precursor for later use.

[0145] Calcination:

[0146] The precursor was placed in a muffle furnace and calcined at 700°C. During the calcination process, the temperature was first raised to 700°C over 3 hours, and then calcined at 700°C for 1 hour to obtain the calcined precursor for later use.

[0147] Cleaning:

[0148] The calcined precursor was repeatedly centrifuged and washed with pure water in a centrifuge until the conductivity was below 1 mS / cm, thus obtaining cerium oxide.

[0149] The cerium oxide prepared in this comparative example, as determined by electron microscopy, has a primary particle size of 60-200 nm, exhibiting a wide particle size distribution. Some particles have a primary particle size exceeding 100 nm, falling outside the category of nanomaterials. The surface sphericity and dispersibility are generally poor. See Appendix for details. Figure 7 As shown.

[0150] Compare with Example 3:

[0151] The preparation method of cerium oxide in this comparative example is similar to the preparation method of nano-sized cerium oxide for rough polishing of silicon substrates of the present invention, except that after cleaning to reduce conductivity, it is then filtered; the preparation process is as follows:

[0152] Precursor synthesis:

[0153] Solution preparation:

[0154] Preparation of cerium salt solution: Add cerium chloride to pure water to prepare a 0.5 mol / L cerium chloride solution for later use;

[0155] Preparation of alkaline solution: Add potassium hydroxide to pure water to prepare a 5% potassium hydroxide solution for later use;

[0156] ,synthesis:

[0157] 1. Add fluxing salt: Add potassium chloride to the cerium chloride solution and stir to dissolve. The amount of potassium chloride added is 5% of the REO in the cerium chloride solution to obtain a cerium chloride fluxing solution for later use.

[0158] Precipitation: At room temperature, potassium hydroxide solution was slowly added to cerium chloride flux solution until the pH value reached 11, resulting in a purple colloid. Then, the mixture was stirred at 80°C for 5 hours until the reaction was complete, yielding the precursor for later use.

[0159] Cleaning: The calcined precursor is repeatedly centrifuged and cleaned with pure water in a centrifuge until the conductivity is below 1 mS / cm.

[0160] 1. Filtering: Filter the washed precipitate and dry the filter cake at 105℃ to obtain the precursor for later use;

[0161] Calcination:

[0162] The precursor was placed in a muffle furnace and calcined at 700°C. During the calcination process, the temperature was first raised to 700°C over 3 hours, and then calcined at 700°C for 1 hour to obtain cerium oxide.

[0163] The cerium oxide prepared in this comparative example, as detected by electron microscopy, has a primary particle size of less than 100 nm and a relatively uniform particle distribution. However, it exhibits poor surface sphericity, numerous sharp edges, and poor dispersion. See Appendix for details. Figure 8 As shown.

[0164] The present invention discloses a method for preparing nano-sized cerium oxide for rough polishing of silicon substrates, wherein the prepared nano-sized cerium oxide can be used for rough polishing of silicon substrates.

Claims

1. A method for preparing nano-sized cerium oxide for rough polishing of silicon substrates, characterized in that, Its preparation process is as follows: (i) Precursor Synthesis: (1) Solution preparation: ① Preparation of cerium salt solution: Add soluble cerium salt to pure water to prepare a 0.2-0.8 mol / L soluble cerium salt solution for later use; ② Preparation of alkali solution: Add alkali to pure water to prepare an alkali solution with a concentration of 2-8%, and set aside for later use; (2) Synthesis: ① Add fluxing salt: Add fluxing salt to the soluble cerium salt solution and stir to dissolve. The amount of fluxing salt added should be 2-8% of the soluble cerium salt converted to REO. A mixed solution of soluble cerium salt and fluxing salt is obtained for later use. ② Precipitation: At room temperature, slowly add alkali solution to the soluble cerium salt fluxing solution until the pH value is 10-12 to obtain a colloid. Then, stir at 70-90℃ for 4-6 hours. After the high-temperature aging is complete, filter and dry the filter cake at 105-120℃ to obtain the precursor for later use. ㈡ Calcination: The precursor is placed in a muffle furnace and calcined at 650-700℃. During the calcination process, the temperature is first raised to the calcination temperature in 2-4 hours, and then calcined at the calcination temperature for 0.5-1.5 hours to obtain the calcined precursor for later use. (iii) Cleaning: The calcined precursor was repeatedly centrifuged and washed with pure water in a centrifuge until the conductivity was below 1 mS / cm, thus obtaining cerium oxide. The alkali is potassium hydroxide; The fluxing salt is potassium chloride.

2. The method for preparing nano-sized cerium oxide for rough polishing of silicon substrates according to claim 1, characterized in that: The soluble cerium salt includes one or both of cerium chloride and cerium nitrate.

3. The method for preparing nano-sized cerium oxide for rough polishing of silicon substrates according to claim 1, characterized in that: The concentration of the soluble cerium salt solution is 0.4-0.6 mol / L, and it is for later use; the content of the alkali solution is 4-6%.

4. The method for preparing nano-sized cerium oxide for rough polishing of silicon substrates according to claim 3, characterized in that: The soluble cerium salt solution has a concentration of 0.5 mol / L and is for later use; the alkali solution has a content of 5%.

5. The method for preparing nano-sized cerium oxide for rough polishing of silicon substrates according to claim 1, characterized in that: The amount of fluxing salt added is 4-6% of the soluble cerium salt converted to REO.

6. The method for preparing nano-sized cerium oxide for rough polishing of silicon substrates according to claim 5, characterized in that: The amount of fluxing salt added is 5% of the soluble cerium salt converted to REO.

7. The method for preparing nano-sized cerium oxide for rough polishing of silicon substrates according to claim 1, characterized in that: The pH value of the colloid is 11, the stirring temperature of the colloid is 80℃, and the stirring time of the colloid is 5h.

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