Cerium oxide grinding material as well as preparation method and application thereof

Abstract

The invention discloses a cerium oxide grinding material as well as a preparation method and application thereof. According to the method, high-purity cerium carbonate is taken as a precursor, preliminary crushing is performed before calcination, and cerium oxide particles are prepared by adopting a two-step sintering method during calcination. And carrying out ball milling and particle grading to obtain the cerium oxide abrasive material. The prepared cerium oxide abrasive is used for a CMP STI process, the polishing speed is high and stable during polishing, and meanwhile, the wafer scratch is little.

Description

Technical Field

[0001] The present invention belongs to the field of preparation of nanomaterials, and particularly relates to a method for preparing cerium oxide abrasive by a two-step sintering method, a product thereof, and an application thereof in the field of semiconductor CMP polishing. Background Art

[0002] Chemical mechanical polishing (CMP) is a semiconductor precision processing technology. The wafer is pressed on a rotating polishing pad, and the polishing liquid flows onto the polishing pad and the wafer. The nano-level planarization of the wafer surface is achieved by the physical and chemical actions between the slurry and the wafer surface.

[0003] According to the types of polishing particles, polishing liquids are usually divided into three types: silicon oxide (SiO 2 ), cerium dioxide (CeO 2 ), or aluminum oxide (Al 2 O 3 ). Among them, the cerium oxide polishing liquid forms Ce-O-Si bonds through the Ce 3+ ions on the particle surface and Si-O on the surface of the silicon wafer through the sharing of electron pairs. At the same time, cerium oxide can also undergo dehydration condensation with Si-OH alkali hydrolyzed on the surface of the silicon wafer to form Ce-O-Si bonds. These two chemical mechanisms make the cerium oxide polishing liquid have the characteristic of fast polishing rate. The Mohs hardness of cerium oxide particles is lower than that of silicon oxide, so it is beneficial to reduce wafer scratching during polishing. At the same time, the isoelectric point of the cerium oxide material is between that of silicon oxide and the barrier layer nitride. Therefore, by effectively controlling the pH of the polishing liquid, the cerium oxide particles can be preferentially adsorbed on the oxide layer, showing a repulsive characteristic to the barrier layer nitride layer, thereby reducing the polishing of the nitride layer. Combining the above characteristics, the cerium oxide polishing liquid shows good characteristics in the shallow trench isolation process (STI) in the field of CMP polishing.

[0004] In recent years, with the increase in the size of silicon wafers, the requirements for the polishing quality and precision of CMP have become increasingly stringent, especially the magnitude of the polishing rate and the number of wafer scratches. This has imposed higher requirements on the uniformity, dispersibility, and physical and chemical properties of abrasive particles. Since Japanese Patent Laid-Open No. 11-12561 provided a conventional method for preparing STI CMP cerium oxide abrasive: adding an alkali to an aqueous solution of ammonium cerium(IV) nitrate to produce a cerium hydroxide gel, filtering and washing it to obtain cerium oxide particles. The industry has been continuously optimizing the preparation method of cerium oxide abrasive. Patent No. CN104261454B proposed multi-step heating and obtaining cerium oxide particles with a fast polishing rate of 15-20 μm through quenching. However, the particles obtained by this method are too large and do not meet the requirements for chip polishing applications. Patent No. CN104673098B proposed a precursor crushing process that can effectively avoid the excessive generation during particle calcination and improve the uniformity of particles to a certain extent. However, this method can only increase the specific surface area during particle calcination and make the particles calcined more fully, without controlling the physical and chemical properties of cerium oxide particles.

[0005] Therefore, it is still necessary to continuously optimize the preparation method of cerium oxide particles, continuously put forward higher requirements for the uniformity and physical and chemical properties of nanoparticles, so as to meet the needs of high-process CMP applications. Summary of the Invention

[0006] In view of the above problems, the present invention innovatively proposes a method for preparing cerium oxide abrasive. Using high-purity cerium carbonate as a precursor, preliminary crushing before calcination ensures the sufficiency of the decomposition reaction and improves the true density of the particles after crushing. During calcination, a two-step sintering method is adopted to ensure the uniformity of cerium oxide nanoparticles and a specific Ce 3+ content by changing the heating rate and atmosphere. Cerium oxide abrasive with a primary particle size of 35-50 nm, a secondary particle size of 165-185 nm, a true density of the powder of 5.5-7 g / cm 3 , a Ce 3+ content of 8-27%, and a polishing rate difference of about ±2% is prepared.

[0007] Another object of the present invention is to provide such cerium oxide abrasive.

[0008] Another object of the present invention is to provide the application of such cerium oxide abrasive.

[0009] To achieve the above invention objects, the present invention adopts the following technical solutions:

[0010] A method for preparing cerium oxide abrasive by a two-step sintering method, comprising the following steps:

[0011] 1) Preparation of primary cerium carbonate: Using high-purity cerium carbonate as raw material, reducing the particle size of cerium carbonate to 1-2 μm through air-flow pulverization;

[0012] 2) Preparation of cerium oxide: Obtaining cerium oxide particles through a two-step sintering method by controlling the heating rate, atmosphere, and heat preservation duration;

[0013] 3) Particle dispersion: Adding a certain amount of dispersant and pH regulator to ultrapure water, adding cerium oxide particles and stirring to form a slurry;

[0014] 4) Particle pulverization: Ball-milling the calcined cerium oxide particles to obtain cerium oxide particles with an average particle size of 35-50 nm;

[0015] 5) Particle filtration: Filtering the slurry through a pp filter element to remove large particles.

[0016] In a specific embodiment, the purity of the high-purity cerium carbonate in step 1) is above 4N (99.99%), the morphology has obvious edges, and the particle size d50 is 50-60 μm.

[0017] In a specific embodiment, the air pressure of the air-flow pulverization in step 1) is 0.8-1 MPa.

[0018] In a specific embodiment, in the two-step sintering method of step 2), first raise the temperature of the tube furnace to 350-450 °C at a rate of 2-8 °C / min, and keep it warm for 0.5-1 h; then introduce 10-30 vol% (volume fraction) of N 2 , and raise the temperature to 750-900 °C at a rate of 8-15 °C / min, and keep it warm for 2-4 h; then cool it to room temperature with the furnace.

[0019] In a specific embodiment, the dispersant added in step 3) can be one or more of polyacrylic acid, ammonium polyacrylate, polymethacrylic acid, ammonium polymethacrylate, polyethylene glycol / polyvinyl alcohol, and the addition amount is 0.01-2 wt% of the mass of cerium oxide particles, preferably 0.5-2 wt%.

[0020] In a specific embodiment, the pH regulator added in step 3) is one or more of ammonia water, potassium hydroxide, tetramethylammonium hydroxide, and ethylenediamine; the addition amount is adjusted according to the pH of the slurry to control the pH of the slurry to be 8-10.

[0021] In a specific embodiment, the equipment used in step 4) is a ball mill, the rotation speed is 400-600 rpm, and the duration is 30-60 min.

[0022] In a specific embodiment, the filtration in step 5) is performed using a 0.5-1 μm PP filter element, and the filtration accuracy is preferably 0.5 μm.

[0023] In step 1) of the present invention, the particles before calcination are crushed to intervene in the decomposition process of the cerium carbonate particles and the growth process of the cerium oxide grains.

[0024] In step 2) of the present invention, the first stage of sintering refers to heating from room temperature to 350-450°C at a rate of 2-8°C / min in an air atmosphere in a tubular furnace, and keeping warm for 0.5-1h. The decomposition reaction of cerium carbonate mainly occurs in this stage. Since the decomposition of cerium carbonate starts from the outer surface of the particles, oxygen is then introduced from the outer surface to the inside, and the reaction site absorbs oxygen and decomposes, while releasing carbon dioxide. The speed of the decomposition reaction is mainly determined by the speed of oxygen diffusion and the speed of carbon dioxide diffusion. Therefore, at this stage, reducing the particle size of the particles and increasing the specific surface area of ​​the particles can effectively increase the area of ​​the particle reaction, reduce the mass transfer path of heat and gas, increase the decomposition reaction rate, and the generated cerium dioxide particles have a higher true density. However, in the first sintering stage, it is not necessary to introduce N 2 , is to facilitate the diffusion of carbon dioxide and allow as many reaction sites as possible to react. Finally, by keeping warm for a certain period of time, the decomposition reaction is fully promoted.

[0025] The second stage of the two-step sintering process is to introduce N 2 , and heat to 750-900℃ at a rate of 8-15℃ and keep warm for 2-4h. 2 This is because the inert atmosphere is conducive to inhibiting the Ce in cerium carbonate 3+ Oxidation to Ce 4+ , increasing the Ce on the surface of cerium dioxide particles 3+ Content, since one of the principles of cerium oxide polishing liquid is to form Ce-O-Si bonds through the oxygen vacancies of variable cerium ions, so appropriate Ce 3+ It is conducive to improving the polishing rate. The sintering temperature of the second step is selected between 750-900℃ because: if the temperature is too low, the particle growth is insufficient, the grain development is imperfect, there are still many defects and pores, and the polishing rate is low. If the temperature is too high, the grain size is too large, and the morphology of the particles after crushing is not easy to control. On the other hand, if the temperature is too high, the particle hardness is too high, and it is easy to cause scratches after polishing.

[0026] In step 4) of the present invention, the cerium oxide slurry is poured into a ball mill to crush the particles. The cerium oxide particles are crushed by the collision, extrusion, shearing, etc. of the zirconium beads rotating at high speed. The primary particle size of the cerium oxide particles after ball milling is 30-50 nm. If the rotation speed of the ball mill is too high, the kinetic energy of the zirconium beads is too large, and the destructive effect on the particles is too strong, making it difficult to control the particle morphology and particle size. If the rotation speed of the ball mill is too low, it takes too long to ball mill to a certain particle size, reducing the efficiency.

[0027] In step 5) of the present invention, on the one hand, the filtration operation in this step can filter out large particles and also filter out other possible solid impurities that may be mixed in. The filtration can be atmospheric pressure filtration or pressure filtration, without any particular limitation.

[0028] The present invention also provides the cerium oxide abrasive prepared by the method, which has a primary particle size of 35-50 nm, a secondary particle size of 165-185 nm, and a true density of the powder of 5.5-7 g / cm 3 , and the Ce3+ content is 8-27%.

[0029] On another aspect of the present invention, an application of the aforementioned cerium oxide abrasive in silicon wafer polishing is provided.

[0030] Compared with the prior art, the present invention has the following beneficial effects:

[0031] 1) The present invention prepares cerium oxide particles by controlling the sintering atmosphere and sintering rate during the sintering of cerium carbonate. Compared with the traditional one-step sintering method, the cerium oxide particles prepared by the present invention have a high degree of crystallization, perfect particle development, and more uniform and stable physical and chemical properties.

[0032] 2) The present invention uses an inert atmosphere at a specific stage during the calcination of cerium carbonate to prepare cerium oxide particles, which not only ensures the activity of the cerium oxide particles, but also avoids introducing other impurities to interfere with the later semiconductor CMP application compared with other methods (such as introducing F - ).

[0033] 3) The cerium oxide particles crushed to 30-50 nm by a ball mill form a cerium oxide slurry after adding a dispersant and a pH regulator. Then, through particle classification, large particles are removed to obtain the cerium oxide abrasive. When the cerium oxide polishing liquid prepared by this method is used for chemical mechanical polishing, the polishing rate is more stable, the polishing effect is good, and there are fewer scratches. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] Figure 1 It is a TEM diagram of the cerium oxide particles prepared in Example 1 of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0035] In order to better understand the technical solution of the present invention, the following examples will further illustrate the method provided by the present invention, but the present invention is not limited to the listed examples, and should also include any other known changes within the scope of the claims of the present invention.

[0036] The main raw materials used in the following examples and comparative examples are shown in Table 1:

[0037] Table 1 Main raw materials

[0038] Raw materials Manufacturer Specification Deionized water Self-made 18.2MΩ.cm High-purity cerium carbonate Self-made 99.99％ Ammonium polyacrylate Self-made 99.9％ Polyacrylic acid (MW5000) Aladdin 99.9％ Polymethacrylic acid (MW6000) Aladdin AR Ammonia water Suzhou Jingrui Chemical Co., Ltd. UP grade Tetramethylammonium hydroxide Aladdin AR Ethylenediamine Aladdin AR

[0039] Ammonium polyacrylate is made from Aladdin brand polyacrylic acid (MW5000) and ammonia water.

[0040] Detection method:

[0041] The primary particle size of the cerium oxide particles was measured using TEM and XRD.

[0042] The secondary particle size of cerium oxide particles was tested by dynamic light scattering (DLS) and Malvern laser particle size detector.

[0043] The morphology of cerium oxide particles was observed using TEM.

[0044] The true density of cerium oxide particles was measured using a fully automatic true density analyzer.

[0045] Ce Oxide Particles 3+ The element contents were measured by XPS analysis.

[0046] Each embodiment and comparative example was carried out according to the main process conditions in Table 2:

[0047] Example 1

[0048] Take 2kg of high-purity cerium carbonate and feed it into the hopper of the air flow crushing and classifying machine. The air pressure is 0.8Mpa and the air consumption is 10m 3 / min, crush for 1h to obtain cerium carbonate particles with a d50 of 1.05μm. The crushed cerium carbonate was placed in an alumina crucible and placed in a tube furnace. The heating program was set: from room temperature to 350℃ at a rate of 5℃ / min, and kept at this temperature for 60min. Then the temperature was raised to 750℃ at a rate of 10℃ / min, and 20vol%N was introduced at the same time. 2, and then keep warm for 3 h and cool to room temperature in the furnace to obtain cerium oxide. Weigh 9 g of polyacrylic acid and add it to 1391 g of water. Add ammonia water to adjust the pH of the slurry to 8.0, and add 600 g of cerium oxide and rotate to obtain a slurry. Pour the slurry into the grinding barrel of a ball mill and ball mill at a rate of 500 rmp for 40 min to obtain cerium oxide abrasive with a primary particle size of 45 nm and a secondary particle size d50 of 180 mn. Filter the cerium oxide abrasive through a filter screen with a precision of 0.5 μm to remove large particles. The particle size distribution of the secondary particle size is 83 - 345 nm, and its measured particle true density is 6.09 g / cm 3 , Ce 3+ The content is 17.46%.

[0049] Example 2

[0050] Take 2 kg of high-purity cerium carbonate and feed it into the hopper of a jet mill. The air pressure is 1.0 Mpa and the air consumption is 10 m 3 / min, and crush for 1 h to obtain cerium carbonate particles with d50 of 1 μm. Place the crushed cerium carbonate in an alumina crucible and put it into a tube furnace. Set the heating program: heat from room temperature to 400 °C at a rate of 6 °C / min and keep warm for 1 h. Then heat to 800 °C at a rate of 10 °C / min and simultaneously introduce 10 vol% N 2 , and then keep warm for 3 h and cool to room temperature in the furnace to obtain cerium oxide. Weigh 12 g of ammonium polyacrylate and add it to 1388 g of water. Add ammonia water to make the pH of the slurry 9.0, and add 600 g of cerium oxide and rotate to obtain a slurry. Pour the slurry into the grinding barrel of a ball mill and ball mill at a rate of 550 rmp for 35 min to obtain cerium oxide abrasive with a primary particle size of 43 nm and a secondary particle size d50 of 179 mn. Filter the cerium oxide abrasive through a filter screen with a precision of 0.5 μm to remove large particles. The particle size distribution is 81 - 350 nm, and its measured particle true density is 6.31 g / cm 3 , Ce 3+ The content is 8.01%.

[0051] Example 3

[0052] Take 2 kg of high-purity cerium carbonate and feed it into the hopper of a jet mill. The air pressure is 0.9 Mpa and the air consumption is 10 m 3 / min, and crush for 1 h to obtain cerium carbonate particles with d50 of 1.03 μm. Place the crushed cerium carbonate in an alumina crucible and put it into a tube furnace. Set the heating program: heat from room temperature to 450 °C at a rate of 8 °C / min and keep warm for 0.75 h. Then heat to 800 °C at a rate of 15 °C / min and simultaneously introduce 30 vol% N 2, and then keep it warm for 3 h and then cool it to room temperature in the furnace to obtain cerium oxide. Weigh 9 g of ammonium polymethacrylate and add it to 1391 g of water, then add ethylenediamine to make the pH of the slurry 8.5, and add 600 g of cerium oxide and rotate to obtain the slurry. Pour the slurry into the grinding barrel of the ball mill and ball mill it at a rate of 600 rmp / min for 30 min to obtain cerium oxide abrasive with a primary particle size of 35 nm and a secondary particle size d50 of 168 mn. Filter the cerium oxide abrasive through a filter screen with a precision of 0.5 μm to remove large particles, and the particle size distribution is 79 - 368 nm. The true density of the particles is measured to be 6.25 g / cm 3 ,Ce 3+ The content is 26.04%.

[0053] Example 4

[0054] Take 2 kg of high-purity cerium carbonate and feed it into the hopper of the air flow crushing and classification machine. The air pressure is 1.0 Mpa and the air consumption is 10 m 3 / min, and crush it for 1 h to obtain cerium carbonate particles with d50 of 1 μm. Place the crushed cerium carbonate in an alumina crucible and put it into a tube furnace. Set the heating program: heat from room temperature to 450 °C at a rate of 2.5 °C / min and keep it warm for 0.5 h. Then heat it to 850 °C at a rate of 8 °C / min and simultaneously introduce 20 vol% N 2 , and then keep it warm for 2 h and then cool it to room temperature in the furnace to obtain cerium oxide. Weigh 3 g of ammonium polyacrylate and add it to 1397 g of water, add tetramethylammonium hydroxide to make the pH of the slurry 10.0, and add 600 g of cerium oxide and rotate to obtain the slurry. Pour the slurry into the grinding barrel of the ball mill and ball mill it at a rate of 500 rmp / min for 38 min to obtain cerium oxide abrasive with a primary particle size of 41 nm and a secondary particle size d50 of 176 mn. Filter the cerium oxide abrasive through a filter screen with a precision of 0.5 μm to remove large particles, and the particle size distribution is 83 - 369 nm. The true density of the particles is measured to be 6.59 g / cm 3 ,Ce 3+ The content is 15.46%.

[0055] Example 5

[0056] Take 2 kg of high-purity cerium carbonate and feed it into the hopper of the air flow crushing and classification machine. The air pressure is 1.0 Mpa and the air consumption is 10 m 3 / min, and crush it for 1 h to obtain cerium carbonate particles with d50 of 1 μm. Place the crushed cerium carbonate in an alumina crucible and put it into a tube furnace. Set the heating program: heat from room temperature to 450 °C at a rate of 4 °C / min and keep it warm for 0.5 h. Then heat it to 900 °C at a rate of 12 °C / min and simultaneously introduce 20 vol% N 2, and then keep it warm for 3 h and then cool it to room temperature in the furnace to obtain cerium oxide. Weigh 7 g of polymethacrylic acid and add it to 1393 g of water. Add ammonia water to make the pH of the slurry 9.5, and add 600 g of cerium oxide and rotate to obtain a slurry. Pour the slurry into the grinding barrel of a ball mill and ball mill it at a rate of 450 rmp / min for 43 min to obtain cerium oxide abrasive with a primary particle size of 46 nm and a secondary particle size d50 of 183 mn. Filter the cerium oxide abrasive through a filter screen with a precision of 0.5 μm to remove large particles, and the particle size distribution is 84 - 384 nm. The true density of the particles is measured to be 6.83 g / cm 3 , Ce 3+ The content is 13.99%.

[0057] Comparative Example 1

[0058] Take 2 kg of high-purity cerium carbonate and directly place it in an alumina crucible, and then put it into a tube furnace. Set the heating program: heat from room temperature to 350 °C at a rate of 5 °C / min and keep it warm for 1 h. Then heat it to 750 °C at a rate of 10 °C / min, and then keep it warm for 4 h and then cool it to room temperature in the furnace to obtain cerium oxide. Weigh 9 g of ammonium polyacrylate and add it to 1391 g of water. Add ammonia water to adjust the pH of the slurry to 8.0, and add 600 g of cerium oxide and rotate to obtain a slurry. Pour the slurry into the grinding barrel of a ball mill and ball mill it at a rate of 500 rmp / min for 40 min to obtain cerium oxide abrasive with a primary particle size of 53 nm and a secondary particle size d50 of 212 mn. Filter the cerium oxide abrasive through a filter screen with a precision of 0.5 μm to remove large particles, and the particle size distribution of the secondary particle size is 112 - 387 nm. The true density of the particles is measured to be 5.52 g / cm 3 , Ce 3+ The content is 17.37%.

[0059] Comparative Example 2

[0060] Take 2 kg of high-purity cerium carbonate and directly place it in an alumina crucible, and then put it into a tube furnace. Set the heating program: heat from room temperature to 400 °C at a rate of 6 °C / min and keep it warm for 1 h. Then heat it to 800 °C at a rate of 10 °C / min, and then keep it warm for 4 h and then cool it to room temperature in the furnace to obtain cerium oxide. Weigh 9 g of ammonium polyacrylate and add it to 1391 g of water. Add ammonia water to adjust the pH of the slurry to 9.0, and add 600 g of cerium oxide and rotate to obtain a slurry. Pour the slurry into the grinding barrel of a ball mill and ball mill it at a rate of 550 rmp / min for 35 min to obtain cerium oxide abrasive with a primary particle size of 56 nm and a secondary particle size d50 of 218 mn. Filter the cerium oxide abrasive through a filter screen with a precision of 0.5 μm to remove large particles, and the particle size distribution is 116 - 396 nm. The true density of the particles is measured to be 5.71 g / cm 3 , Ce 3 + The content is 0.31%.

[0061] Comparative Example 3

[0062] Take 2kg of high-purity cerium carbonate and feed it into the hopper of the air flow crushing and classifying machine. The air pressure is 0.9Mpa and the air consumption is 10m 3 / min, crush for 1h to obtain cerium carbonate particles with a d50 of 1.03μm. The crushed cerium carbonate was placed in an alumina crucible and placed in a tubular furnace. Set the heating program: from room temperature to 400℃ at a rate of 8℃ / min, and keep warm for 0.75h. Then heat to 800℃ at a rate of 15℃ / min, then keep warm for 3h and cool to room temperature with the furnace to obtain cerium oxide. Weigh 7g of ammonium polyacrylate and add it to 1393g of water, add ethylenediamine to adjust the slurry pH to 8.5, add 600g of cerium oxide and rotate to obtain a slurry. Pour the slurry into the grinding barrel of the ball mill, ball mill at a rate of 600rmp / min for 30min, and obtain a cerium oxide abrasive with a primary particle size of 33nm and a secondary particle size d50 of 161mn. The cerium oxide abrasive was filtered with a 0.5μm precision filter to remove large particles. The particle size distribution was 74-361nm, and the true density of the particles was measured to be 6.30g / cm 3 ,Ce 3+ The content is 0.29%.

[0063] Comparative Example 4

[0064] Take 2kg of high-purity cerium carbonate and feed it into the hopper of the air flow crushing and classifying machine. The air pressure is 1.0Mpa and the air consumption is 10m 3 / min, crush for 1h to obtain cerium carbonate particles with a d50 of 1μm. The crushed cerium carbonate was placed in an alumina crucible and placed in a tube furnace. The heating program was set: 20vol% N 2 , the temperature was raised from room temperature to 450°C at a rate of 2.5°C / min and kept at this temperature for 0.5h. 2 , let in air, and heat to 850°C at a rate of 8°C / min, then keep warm for 2 hours and cool to room temperature with the furnace to obtain cerium oxide. Weigh 3g of ammonium polyacrylate and add it to 1397g of water, add tetramethylammonium hydroxide to make the slurry pH 10.0, add 600g of cerium oxide and rotate to obtain a slurry. Pour the slurry into the grinding barrel of a ball mill, ball mill at a rate of 400rmp / min for 38min to obtain a cerium oxide abrasive with a primary particle size of 40nm and a secondary particle size d50 of 174mn. Filter the cerium oxide abrasive with a 0.5μm precision filter to remove large particles. The particle size distribution is 81-366nm, and the true density of the particles is measured to be 6.61g / cm 3 ,Ce 3+ The content is 0.30%.

[0065] Comparative Example 5

[0066] Take 2 kg of high-purity cerium carbonate and feed it into the hopper of a pneumatic grinding and classification machine. The air pressure is 1.0 Mpa, and the air consumption is 10 m 3 / min. After grinding for 1 h, cerium carbonate particles with a d50 of 1 μm are obtained. Place the ground cerium carbonate in an alumina crucible and put it into a tube furnace. Set the heating program: Pass 20 vol% of N 2 throughout the process, heat from room temperature to 450 °C at a rate of 2.5 °C / min, and hold for 0.5 h. Then heat to 850 °C at a rate of 8 °C / min, and after holding for 2 h, cool to room temperature with the furnace to obtain cerium oxide. Weigh 3 g of ammonium polyacrylate and add it to 1397 g of water. Add tetramethylammonium hydroxide to make the pH of the slurry 10.0. Add 600 g of cerium oxide and rotate to obtain a slurry. Pour the slurry into the grinding barrel of a ball mill and ball mill at a rate of 500 rmp / min for 38 min to obtain cerium oxide abrasive with a primary particle size of 41 nm and a secondary particle size d50 of 176 mn. Filter the cerium oxide abrasive through a filter screen with a precision of 0.5 μm to remove large particles. The particle size distribution is 81 - 367 nm, and its true particle density is measured to be 6.48 g / cm 3 ,Ce 3+ content is 17.31%.

[0067] Comparative Example 6

[0068] Take 2 kg of high-purity cerium carbonate and feed it into the hopper of a pneumatic grinding and classification machine. The air pressure is 1.0 Mpa, and the air consumption is 10 m 3 / min. After grinding for 1 h, cerium carbonate particles with a d50 of 1 μm are obtained. Place the ground cerium carbonate in an alumina crucible and put it into a tube furnace. Set the heating program: Heat from room temperature to 450 °C at a rate of 8 °C / min, and hold for 0.5 h. Pass 20 vol% N 2 , and then heat to 850 °C at a rate of 2.5 °C / min. After holding for 2 h, cool to room temperature with the furnace to obtain cerium oxide. Weigh 3 g of ammonium polyacrylate and add it to 1397 g of water. Add tetramethylammonium hydroxide to make the pH of the slurry 10.0. Add 600 g of cerium oxide and rotate to obtain a slurry. Pour the slurry into the grinding barrel of a ball mill and ball mill at a rate of 500 rmp / min for 38 min to obtain cerium oxide abrasive with a primary particle size of 49 nm and a secondary particle size d50 of 184 mn. Filter the cerium oxide abrasive through a filter screen with a precision of 0.5 μm to remove large particles. The particle size distribution is 88 - 378 nm, and its true particle density is measured to be 6.65 g / cm 3 ,Ce 3+ content is 13.20%.

[0069] Table 2 Process conditions of each example and comparative example

[0070]

[0071] To evaluate the grinding effect of the abrasive of the present invention, CMP polishing tests were used to evaluate the examples. Nitric acid was added to each group of cerium oxide abrasives, and the pH of the slurry was controlled to be 5. Then the slurry was diluted to a mass fraction of 1%, and polishing tests were carried out. The parameters and models of the polishing equipment are shown in Table 3 below, and the polishing results are shown in Table 4

[0072] Table 3 Polishing Test Equipment Parameters

[0073] Polishing machine model 12”Reflexion LK Polishing pressure 3psi Abrasive flow rate 100ml / min Polishing pad IC1000 Polishing time 120s Wafer diameter 300mm Polishing head / platen rotation speed 20 / 100rpm

[0074] Table 4 Polishing Results

[0075]

[0076] Compared with Comparative Example 1 and Example 1, the precursor can be calcined after being crushed, which can reduce the deviation of the polishing rate to a certain extent. Moreover, the relative roughness of the wafer surface after polishing is lower, the particle size of the particles is smaller, and there is no excessive growth. Thus, it can be seen that the pre-crushing of the precursor of the present invention has a significant effect on the process quality of CMP, and it is an effective method to improve the process quality of CMP..

[0077] Compared with Comparative Examples 2 and 3 and Examples 2 and 3, introducing N 2 (inert atmosphere) during the calcination process of the precursor also has an obvious improvement in the polishing rate, and it will not cause an increase in scratches or an increase in relative roughness. It shows that a certain content of Ce 3+ can improve the polishing rate, and this change is of great significance for cerium oxide polishing liquids with a fast polishing rate as a significant feature.

[0078] Compared with Comparative Example 4 and Example 4, it shows that N 2 (inert atmosphere) should be introduced during the second-stage calcination process of the precursor, which will bring a significant increase in the Ce 3+ content and improve the polishing rate, which should be related to the changes in different stages of calcining cerium carbonate.

[0079] Compared with Comparative Examples 5 and 6 and Example 4, continuously introducing N 2 during the decomposition process of the precursor will reduce the polishing rate, which may be because the diffusion of CO 2 has an important impact on the performance of the particles, indicating that N 2 should be introduced in some stages during the calcination process of cerium carbonate. Delaying the heating rate of the second stage increases the scratches while increasing the polishing rate, which may be due to the formation of large particles caused by excessive growth, indicating that the heating rate of the second-stage calcination process should be faster than that of the first-stage calcination process.

[0080] The influence mechanism of introducing an inert atmosphere during the pre-crushing and calcination of the precursor cerium carbonate on the polishing result is not fully understood, but it can be generally understood from the following aspects: Crushing the precursor cerium carbonate before calcination can increase the specific surface area of the particles, improve the heat-receiving area, and enhance the reaction rate when it undergoes a decomposition reaction. On the other hand, after the particle size is reduced, the heat transfer path from the outside through the dissociation surface into the reaction sites inside the particles and the mass transfer path for the diffusion and discharge of the generated carbon dioxide after decomposition are greatly reduced, making the decomposition of cerium carbonate more complete. At the same time, after the precursor is crushed, the generated cerium oxide grains are smaller, and the particles are not easily agglomerated into large particles during the subsequent sintering process, reducing the number of scratches. Moreover, when the particles are generated, when the surface energy drives the movement of the grain boundaries, the movement path of the grain boundaries is short, and it is not easy to form closed pores, which plays an important role in improving the polishing rate and stabilizing the rate. And introducing an inert atmosphere to increase the polishing rate may be because: Ce 3+ will not be completely oxidized to transform into Ce 4+ , since the currently recognized mainstream polishing mechanisms of cerium oxide polishing liquid are the oxygen vacancy mechanism and the dehydration condensation mechanism. Therefore, the increase in the content of Ce 3+ can fully utilize the oxygen vacancy mechanism, making the vacancy concentration on the surface of cerium oxide particles higher and forming more Ce-O-Si bonds, so the polishing rate is significantly increased.

[0081] Although the content of the present invention has been described in detail through the above preferred embodiments, it should be understood that the above description should not be regarded as a limitation of the present invention. Those skilled in the art can understand that under the teaching of this specification, some modifications or adjustments can be made to the present invention. These modifications or adjustments should also be within the scope defined by the claims of the present invention.

Claims

1. A method for preparing cerium oxide abrasive, comprising the following steps: 1) Preparation of primary cerium carbonate: Using high-purity cerium carbonate as raw material, reducing the particle size of cerium carbonate to 1 - 2 μm by air-flow pulverization; 2) Preparation of cerium oxide: Obtaining cerium oxide particles by two-step sintering method, controlling the heating rate, atmosphere and holding time; 3) Particle dispersion: Adding a certain amount of dispersant and pH regulator into ultrapure water, adding cerium oxide particles and stirring to form a slurry; 4) Particle pulverization: Ball-milling the calcined cerium oxide particles to obtain cerium oxide particles with an average particle size of 35 - 50 nm; 5) Particle filtration: Filtering the slurry through a pp filter element to remove large particles.

2. The method according to claim 1, wherein, the purity of the high-purity cerium carbonate in step 1) is above 99.99%, and the particle size d50 is 50 - 60 μm.

3. The method according to claim 1, wherein, In the two-step sintering method in step 2), first raise the temperature of the tubular furnace from 2 to 8 °C / min to 350 to 450 °C, and keep it warm for 0.5 to 1 h; then introduce 10 to 30 v% of N 2 , raise the temperature to 750 to 900 °C at a rate of 8 to 15 °C / min, and keep it warm for 2 to 4 h; then cool it to room temperature with the furnace.

4. The method according to claim 1, wherein, the dispersant added in step 3) is selected from one or more of polyacrylic acid, ammonium polyacrylate, polymethacrylic acid, ammonium polymethacrylate, polyethylene glycol / polyvinyl alcohol, and the addition amount is 0.01 - 2 wt% of the mass of cerium oxide particles, preferably 0.5 - 2 wt%.

5. The method according to claim 1, wherein, the pH regulator added in step 3) is one or more of ammonia water, potassium hydroxide, tetramethylammonium hydroxide, ethylenediamine; the addition amount is adjusted according to the pH of the slurry to control the pH of the slurry to be 8 - 10.

6. The method according to claim 1, wherein, the equipment used in step 4) is a ball mill, the rotation speed is 400 - 600 rpm, and the time is 30 - 60 min.

7. The method according to claim 1, wherein, in step 5), filtration is carried out using a 0.5 - 1 μm pp filter element, preferably 0.5 μm.

8. Cerium oxide particles prepared by the method according to any one of claims 1 - 7, wherein, The primary particle size is 35 - 50 nm, the secondary particle size is 165 - 185 nm, and the true density of the powder is 5.5 - 7 g / cm 3 , Ce 3+ content is 8 - 27%.

9. The use of the cerium oxide abrasive according to claim 8, wherein, it is used for the application of STI process in silicon wafer polishing.

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