Ordered porous diamond grinding wheel and preparation method and application thereof

Abstract

The invention provides an ordered porous diamond grinding wheel and a preparation method and application thereof. The ordered porous diamond grinding wheel comprises a ceramic diamond grinding wheel body, the ceramic diamond grinding wheel body comprises a plurality of oriented layered structures which are orderly and evenly distributed, oriented large gaps are formed between the adjacent oriented layered structures, and a plurality of transverse partition structures connected with the adjacent oriented layered structures are arranged in each oriented large gap. The directional large gap is separated by the plurality of transverse separation structures to form a plurality of small air holes; therefore, the ordered porous diamond grinding wheel has the characteristics that the porosity can reach more than 70%, the strength is high, the microstructure is uniform, the self-sharpening property and the heat dissipation property are good, and the like. The preparation method of the ordered porous diamond grinding wheel comprises the steps of composite slurry preparation, directional freezing and annealing, sublimation drying, low-temperature sintering, aftertreatment and the like, and the uniformity of the hole structure of the grinding wheel is improved through the directional freezing and annealing process. The invention further provides application of the ordered porous diamond grinding wheel in semiconductor wafer thinning grinding machining.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of mechanical manufacturing and processing, and particularly relates to an ordered porous diamond grinding wheel and a preparation method and application thereof. BACKGROUND

[0002] Diamond grinding wheel ultra-precision grinding is one of the key technologies of semiconductor wafer thinning process, and grinding damage is a major factor affecting the processing efficiency and cost of wafer thinning process. In order to obtain a high-quality wafer grinding surface, a ceramic bond grinding wheel containing ultra-fine diamond abrasive is generally used for grinding in the thinning and fine grinding stage. However, as the particle size of the abrasive in the grinding wheel decreases, it will be wrapped inside the ceramic bond, resulting in a decrease in the grinding capacity of the grinding wheel, and problems such as grinding burn and unstable grinding will occur, which need to be improved by matching the corresponding pore forming process to increase the porosity of the grinding wheel.

[0003] Introducing a large amount of pore-forming agent is the simplest method for preparing a high-porosity grinding wheel. However, traditional dry molding is prone to phenomena such as the agglomeration of abrasive, bond, and pore-forming agent, and the uniformity of the pores is difficult to guarantee. Ultra-fine diamond grinding wheels are prone to phenomena such as the agglomeration of abrasive, bond, and pore-forming agent, and the uniformity of the pores is difficult to guarantee. The "hard block" formed by the agglomeration of ultra-fine particles after sintering can cause wafer burn and scratches. In addition, in the preparation of high-porosity grinding wheels, the amount of pore-forming agent introduced by dry molding is limited, making it difficult to guarantee the self-sharpening and chip and debris removal capabilities of ultra-fine particle grinding wheels.

[0004] Some researchers have used other methods to prepare high-porosity grinding wheels. For example, Kong used gel casting technology to prepare a porous ceramic diamond grinding wheel, which has good sapphire grinding effect (Shuaifei Kong, Yibo Liu, Yang Liu, et al. An experimental investigation of sapphire grinding by porous and vitrified M0.5 / 1.5 diamond grinding wheel[J]. Tribology International, 2023, 185, 108487.). However, the teeth of the grinding wheel are prone to breakage under high-speed rotation, and the recommended grinding wheel grinding speed of this grinding wheel is only 1200 rpm. However, the speed of the semiconductor wafer (such as silicon wafer, silicon carbide, sapphire, gallium arsenide, etc.) during thinning and grinding is generally above 3000 rpm. Non-uniform pores and low strength are the main factors restricting the development of high-porosity wafer thinning grinding wheels, and there is an urgent need to develop porous diamond grinding wheels with high porosity and new organizational structures. SUMMARY

[0005] In view of this, the present application provides an ordered porous diamond grinding wheel and its preparation method and application, mainly based on directional freeze forming technology to prepare an ordered porous diamond grinding wheel with layered microstructure, which has a porosity of more than 70%, high strength, uniform micro-morphology, self-sharpening, good heat dissipation and other characteristics, and can be used as a thinning grinding wheel for semiconductor wafers such as silicon, silicon carbide, sapphire, gallium arsenide, etc.

[0006] Specifically, the present application provides the following technical solutions: In the first aspect, the present application provides an ordered porous diamond grinding wheel, which comprises a ceramic diamond grinding wheel body, the grinding wheel body comprises a plurality of ordered directional layered structures uniformly distributed, the angle between the plurality of ordered directional layered structures and the thickness direction of the grinding wheel body is -10°-10°, a directional large gap is formed between adjacent directional layered structures, a plurality of transverse partition structures connecting adjacent directional layered structures are arranged in each directional large gap, and the plurality of transverse partition structures separate the directional large gap to form a plurality of small pores.

[0007] Further, the plurality of ordered directional layered structures are arranged substantially in parallel, and the angle between the plurality of directional layered structures and the thickness direction of the grinding wheel body is -5°-5°, which is beneficial to improve the chip removal and heat dissipation capacity of the grinding wheel.

[0008] Further, the thickness of the directional layered structure is 3-20 μm, and the distance of the directional large gap is 0-30 μm; in this way, the porosity, strength and self-sharpening of the grinding wheel can be effectively improved, so that the porosity is more than 70% and the strength is 10-15 MPa.

[0009] In the second aspect, the present application provides a preparation method of the ordered porous diamond grinding wheel, which comprises the following steps: Preparation of composite slurry: uniformly mixing annealing medium, water and grinding wheel base raw material by wet ball milling method to obtain a grinding wheel raw material suspension slurry with a solid content of 50-60 wt%, wherein the proportion of the annealing medium in the annealing medium and water is 10-20 wt%; Directional freezing and annealing: first, the grinding wheel raw material suspension slurry is vertically gradiently cooled to a freezing temperature by using a freeze dryer, and a first heat preservation treatment is performed to solidify the grinding wheel raw material suspension slurry; then, the temperature is raised to an annealing temperature, and a second heat preservation treatment is performed; then, the temperature is lowered to the freezing temperature, and a third heat preservation treatment is performed to completely freeze the grinding wheel raw material suspension slurry, wherein the water forms a uniform layered ice crystal structure to obtain a slurry frozen body; Sublimation drying: vacuum sublimation drying treatment is performed on the slurry frozen body to remove the layered ice crystal structure to obtain a porous green body; Low-temperature sintering: first, sinter the porous green body at 200-350 ℃ to remove the organic matter therein; then, sinter at 650-750 ℃ to obtain the grinding wheel block.

[0010] In the step of preparing the composite slurry, the "grinding wheel base material" in the present application refers to the base material required for making the grinding wheel body, which is the prior art. For example, the grinding wheel base material can include ceramic binder, diamond micro-powder, and additives.

[0011] In an embodiment, the grinding wheel base material includes mixed powder, binder, and dispersant, wherein the mixed powder is composed of 18-22 wt% of ceramic binder and 78-82 wt% of diamond micro-powder, the dispersant is added in an amount of 1.5-4 wt% of the mixed powder, and the binder is added in an amount of 4-10 wt% of the mixed powder.

[0012] To increase the order of the ice crystal template and thus the order of the directional large gap in the diamond grinding wheel, the step of directional freezing and annealing includes: first, using the freeze dryer to gradiently lower the temperature of the grinding wheel raw material suspension slurry to the freezing temperature in the vertical direction, and keep the temperature for 140-180 min; then, raise the temperature from the freezing temperature to the annealing temperature, and keep the temperature for 120-160 min; and then, lower the temperature back to the freezing temperature, and keep the temperature for 140-180 min, to obtain the slurry frozen body; wherein the annealing temperature is 20-50 ℃ higher than the freezing temperature. In this way, the crystallization is strengthened while ensuring complete solidification of the grinding wheel raw material suspension slurry, residual stress is eliminated, and a uniform and ordered layered ice crystal structure is formed.

[0013] Preferably, the freezing temperature is -30 ℃ to -50 ℃, the annealing temperature is -10 ℃ to -5 ℃, the gradient lowering rate is 0.5-2 ℃ / min, and the raising rate is 0.5-2 ℃ / min.

[0014] The step of sublimation drying includes: using the vacuum sublimation drying method to gradiently raise the temperature of the slurry frozen body to 10-15 ℃ in the vertical direction, and keep the temperature for 24-30 h, to obtain the porous green body. In this way, the layered ice crystal structure in the slurry frozen body can be fully removed.

[0015] The step of low-temperature sintering includes: first, sintering the porous green body at 200-350 ℃ for 1-3 h; and then, sintering at 650-750 ℃ for 1-3 h and naturally cooling, to obtain the grinding wheel block.

[0016] In a third aspect, the present application provides a use of the ordered porous diamond grinding wheel in semiconductor wafer thinning grinding.

[0017] Therefore, compared with the prior art, the above technical solution provided by the present application has the following characteristics: 1) The ordered porous diamond grinding wheel provided by the present application is a grinding wheel with high porosity and a novel structure, which has a directional layered structure substantially perpendicular to the working surface of the grinding wheel, directional large gaps are formed between the directional layered structures, and small pores are formed in the directional large gaps, so that the ordered porous diamond grinding wheel has high porosity and high strength, and has excellent heat dissipation efficiency and self-sharpening. When the above porous diamond grinding wheel is used in the thinning and grinding process of semiconductor wafers such as silicon wafers and silicon carbide wafers, it has the characteristics of no scratches and burns on the workpiece, high processing quality, high processing efficiency and long service life.

[0018] 2) The preparation method of the ordered porous diamond grinding wheel provided by the present application combines directional freezing technology to form pores, compared with the existing pore forming technology of grinding wheels, the present application first introduces the freeze forming process into the abrasive tool industry, and forms a micro-morphology uniform and layered ordered structure design structure through vertical directional freezing. The ordered diamond grinding wheel prepared has a porosity of ≥70%, and the strength can reach up to 15 MPa, and has excellent heat dissipation efficiency and self-sharpening, and does not produce scratches and burns on the workpiece.

[0019] 3) The preparation method of the ordered porous diamond grinding wheel provided by the present application introduces an annealing process, and the annealing operation is accompanied by a solid phase structure change during rewarming. The phase change behavior and recrystallization process in the annealing process can reduce the size difference of ice crystals and the non-uniformity of the effect on the pore wall. This process strengthens the ice crystal crystallization, improves the pore size and distribution, eliminates residual stress and avoids the generation of micro-cracks, improves the mechanical properties of the diamond grinding wheel, and finally obtains a grinding wheel structure with uniform and ordered structure and excellent mechanical properties.

[0020] Therefore, the above ordered porous diamond grinding wheel provided by the present application has the characteristics of porosity of more than 70%, high strength, uniform and ordered micro-morphology, self-sharpening, and good heat dissipation, and can be used for thinning of semiconductor wafers such as silicon wafers, silicon carbide wafers, sapphire wafers and gallium arsenide wafers. The preparation process is simple and convenient to operate, and can be used to realize the near-net size forming technology of abrasive tool samples, and has low cost. BRIEF DESCRIPTION OF DRAWINGS

[0021] Figure 1 The flowchart for preparing the grinding wheel by freeze forming technology; Figure 2 The SEM images of the microstructure of the grinding wheel blocks provided by Comparative Example 1 (a-a1), Comparative Example 2 (b-b1) and Example 1 (c-c1); Figure 3 The photos and SEM images of the microstructure of the sintered grinding wheel provided by Example 1 (b and d) and Comparative Example 3 (a and c); Figure 4 Photos of the silicon wafer after grinding with the grinding wheel prepared in Comparative Example 1 (a) and Example 1 (b); Figure 5 Photos of the state of the silicon wafer after grinding with the grinding wheel prepared in Comparative Example 1 (a) and Example 1 (b), wherein there are missing teeth in the red frame; Figure 6 Comparison chart of the surface quality of the silicon wafer after grinding with the grinding wheel prepared in Comparative Example 1 (a) and Example 1 (b). DETAILED DESCRIPTION

[0022] In order to make the objects, technical solutions and advantages of the present application clearer, the technical solutions of the present application will be described clearly and completely below in combination with the embodiments of the present application.

[0023] The endpoints of the ranges and any numerical values included in the disclosed ranges are not limited to the precise values stated herein and include any values approximating these. For ranges, the endpoints are included between and around each range as are intervening points to the listed endpoint values. New ranges can be created from the combination of the endpoints from the various ranges and the individual point values, and these new ranges are to be construed as being specifically included in the present application.

[0024] In the present application, unless otherwise specified and / or described, all the numerical values related to the amount of components are "weight". If not specifically indicated, the terms used in the present application are the terms commonly used in the art, and the preparation processes, test methods and the like used in the embodiments are the conventional means known to those skilled in the art, and the raw materials and equipment used can be obtained from public commercial channels.

[0025] The main purpose of the present application is to solve the problems of non-uniform pores and low strength of the current high-porosity thinning grinding wheel. The present application provides an ordered porous diamond grinding wheel with a porosity of 70%, good uniformity of pore structure and high strength. The ordered porous diamond grinding wheel has the characteristics of uniform and ordered micro-morphology, self-sharpening, good heat dissipation, etc. As a thinning grinding wheel for semiconductor wafers, it does not produce scratches and burns on the workpiece, has high processing quality and long service life. The ordered porous diamond grinding wheel can be made by combining the directional freezing technology with the existing grinding wheel manufacturing process. The preparation method is simple, the raw material cost is low, and the process is simple.

[0026] In order to achieve the above-mentioned purpose, the present application adopts the following specific implementation scheme: In a first aspect, the present application provides an ordered porous diamond grinding wheel, comprising a ceramic diamond grinding wheel body, the grinding wheel body comprising a plurality of ordered directional layered structures uniformly distributed, the plurality of ordered directional layered structures having an angle of -10°-10° with the thickness direction of the grinding wheel body, a directional large gap being formed between adjacent directional layered structures, a plurality of transverse partition structures being arranged in each directional large gap to connect adjacent directional layered structures, the plurality of transverse partition structures separating the directional large gap to form a plurality of small pores. The thickness of the directional layered structure is 3-20 μm, and the distance of the directional large gap is 0-30 μm.

[0027] In a specific embodiment, the plurality of directional layered structures are arranged substantially in parallel, and the plurality of directional layered structures have an angle of -5°-5° with the thickness direction of the grinding wheel body, so as to improve the chip removal and heat dissipation capacity of the grinding wheel.

[0028] In a second aspect, the present application provides a preparation method of the ordered porous diamond grinding wheel, comprising the steps of preparing a composite slurry, directional freezing and annealing, sublimation drying, low-temperature sintering, and post-processing. The specific contents of each step are as follows: Preparation of the composite slurry The step of preparing the composite slurry mainly adopts a wet ball milling method to uniformly mix the annealing medium, water, and the base raw material for manufacturing the grinding wheel to prepare a grinding wheel raw material suspension slurry.

[0029] The "base raw material for manufacturing the grinding wheel" in the present application refers to the base raw material required for manufacturing the grinding wheel body, which is a prior art. For example, the base raw material for manufacturing the grinding wheel can include a ceramic binder, diamond micro-powder, and an additive, etc. The ceramic binder and the diamond micro-powder form a mixed powder, and the additive includes a binder and a dispersant, etc. In a specific embodiment, the base raw material for manufacturing the grinding wheel includes a mixed powder, a binder, and a dispersant. The mixed powder is composed of 18-22 wt% of ceramic binder with a particle size of 1-2 μm and 78-82 wt% of diamond micro-powder with a particle size of 0.5-1.5 μm. The addition amount of the dispersant is 1.5-4 wt% of the mixed powder, and the addition amount of the binder is 4-10 wt% of the mixed powder. The dispersant as the additive can be at least one of tetramethylammonium hydroxide, sodium polymethacrylate, sodium polyacrylate, and sodium dodecyl sulfate. The binder as the additive can be at least one of carboxymethyl cellulose, water glass, gelatin, polyacrylic acid, and polyacrylamide.

[0030] In one specific embodiment, the step of preparing the composite slurry includes: adding an aqueous solution of annealing medium, a dispersant, diamond micro powder, and a ceramic binder into a ball mill jar, ball milling and mixing at 300 r / min for 1 to 2 hours, and finally adding a binder and ball milling at 300 r / min for 0.5 to 1 hour to form a uniform suspension slurry of grinding wheel raw materials.

[0031] The main role of the annealing medium aqueous solution is to inhibit further ice crystal growth during the freezing process, as ice crystals continuously precipitate and the concentration and viscosity of the remaining solution gradually increase. When the temperature drops below the glass transition temperature Tg', the system undergoes a glass transition, forming a solid structure composed of partially frozen water and a small amount of water existing in a glassy state. Subsequent annealing, i.e., heating above Tg', reduces the viscosity of the system, restores the molecules' translational and rotational capabilities, and causes a transition from the glassy state to the supercooled liquid state. As the temperature rises, molecular mobility increases, promoting recrystallization, leading to the complete crystallization of unfrozen water and structural reorganization. This phase transition and recrystallization behavior during annealing helps reduce the size difference of ice crystals and alleviates the inhomogeneity of their effect on the ceramic pore walls.

[0032] If the concentration of the annealing medium aqueous solution is too high, it will severely hinder water crystallization, resulting in a large amount of unfrozen water remaining in the glass. During the subsequent drying stage, the slurry will exhibit a "boiling" phenomenon and spray out, causing the sample drying to fail. If the concentration is too low, the annealing effect will be insignificant. Therefore, the concentration of the annealing medium aqueous solution should be controlled at 5–20 wt%, such as 5 wt%, 8 wt%, 10 wt%, 12 wt%, 14 wt%, 15 wt%, 16 wt%, 18 wt%, 20 wt%, etc. The annealing medium includes, but is not limited to, sucrose, glycerol, polyethylene glycol, soluble starch, trehalose, etc. Preferably, the annealing medium aqueous solution is a sucrose aqueous solution with a concentration of 10–20 wt%.

[0033] If the solid content of the grinding wheel raw material suspension slurry is too high, the slurry will be too viscous, resulting in poor casting fluidity and potentially causing ice crystals (pores) to be too small to accommodate grinding chips. If the concentration is too low, slurry stratification is likely to occur, leading to low-density grinding wheel blocks with low strength. Therefore, the solid content of the grinding wheel raw material suspension slurry is preferably 50–60 wt%, such as 50 wt%, 52 wt%, 54 wt%, 55 wt%, 56 wt%, 58 wt%, 60 wt%, etc.

[0034] directional freezing and annealing The main purpose of the directional freezing and annealing steps is to form a uniform, ordered, and oriented ice crystal template in the frozen slurry, enabling the subsequent diamond grinding wheel to have uniformly oriented pores, increasing porosity while maintaining high strength. This step specifically includes the following steps: The grinding wheel raw material suspension slurry is vacuum defoamed and then molded. It is placed in a freeze dryer and first cooled vertically at a rate of 0.5–2 °C / min to a freezing temperature of -30 °C to -50 °C, and held at this temperature for 140–180 min. Then, the temperature is increased from the freezing temperature to an annealing temperature of -10 °C to -5 °C at a rate of 0.5–2 °C / min, and held at this temperature for 120–160 min. Finally, the temperature is lowered back to the freezing temperature and held for 140–180 min, allowing the grinding wheel raw material suspension slurry to completely solidify. The water in the slurry forms a layered ice crystal structure, resulting in a frozen slurry. This process ensures complete solidification of the grinding wheel raw material suspension slurry while simultaneously strengthening crystallization, eliminating residual stress, and forming a uniform layered ice crystal structure.

[0035] Sublimation drying The vacuum sublimation drying method is used to gradually heat the frozen slurry body to 10-15°C in the vertical direction at a heating rate of 0.5-1°C / min, and hold it at that temperature for 24-30 h to fully remove the layered ice crystal structure that serves as an ice crystal template in the frozen slurry body, thereby obtaining the porous preform.

[0036] Low-temperature sintering The porous blank is placed in a sintering furnace and sintered at 200-350 °C for 1-3 hours to remove organic matter; then it is sintered at 650-750 °C for 1-3 hours and cooled in the sintering furnace to obtain the grinding wheel block.

[0037] Post-processing The grinding wheel block obtained in the above steps is cut to form a grinding wheel block of the required size and then bonded to the processed substrate to form a grinding wheel; finally, the prepared grinding wheel is finished to obtain the finished product.

[0038] Thirdly, the present invention provides an application of the above-mentioned ordered porous diamond grinding wheel in semiconductor wafer thinning grinding.

[0039] The technical solution of the present invention will be further described in detail below through specific embodiments. In the following embodiments and comparative examples, the diamond micro-powder abrasive used has a particle size of 0.5 / 1.5 μm, and the ceramic binder is composed of 53.2 wt% SiO2, 9.5 wt% B2O3, 16.5 wt% Al2O3, 7 wt% Li2O, 10.2 wt% Na2O, and 3.6 wt% K2O.

[0040] Example 1 This embodiment provides an ordered porous diamond grinding wheel and its preparation method. The raw material proportions of the ordered porous diamond grinding wheel include: a mixed powder composed of 80 wt% diamond micropowder and 20 wt% ceramic binder; sodium polyacrylate as a dispersant accounting for 1.8 wt% of the mixed powder; polyacrylic acid as a binder accounting for 5 wt% of the mixed powder; a sucrose aqueous solution concentration of 10 wt%; and a solid content of 60 wt% in the grinding wheel raw material suspension slurry.

[0041] Please see Figure 1 The method for preparing the ordered porous diamond grinding wheel includes the following steps: Preparation of composite slurry: The above-mentioned sucrose aqueous solution, dispersant, diamond micro powder and ceramic binder are added to a ball mill jar and ball milled at 300 r / min for 1 h. Finally, the binder is added and ball milled at 300 r / min for 0.5 h to form a uniform grinding wheel raw material suspension slurry with a solid content of 60 wt%. Directional freezing and annealing: After vacuum degassing, the grinding wheel raw material suspension slurry is molded and placed in a freeze dryer. It is first cooled vertically to a freezing temperature of -40°C at a rate of 0.5°C / min, and held at this temperature for 180 min. During annealing, the temperature is increased from the freezing temperature to an annealing temperature of -10°C at a rate of 0.5°C / min, and held for 120 min. Then, it is cooled back to the freezing temperature and held for 180 min. This process allows the grinding wheel raw material suspension slurry to fully solidify while simultaneously strengthening crystallization, eliminating residual stress, and forming a uniform layered ice crystal structure, resulting in a frozen slurry body. Sublimation drying: Vacuum sublimation drying method is adopted, and the temperature of the frozen slurry is gradually increased to 15°C in the vertical direction at a heating rate of 0.5-1°C / min, and held at the temperature for 24 h to obtain a porous green body; Low-temperature sintering: The porous blank is heated in a sintering furnace at a rate of 1°C / min, first held at 350°C for 1 hour, then heated to 740°C and held for 3 hours before being cooled in the furnace to obtain the grinding wheel block. Figure 2 (c-c1) and Figure 3 As shown in (b and d); Post-processing: The grinding wheel block is cut to form a grinding wheel block of the required size and then bonded to an aluminum substrate to form a thinned grinding wheel of the required specifications. After finishing, a diamond grinding wheel is obtained.

[0042] from Figure 2As can be seen, the body of the ordered porous diamond grinding wheel comprises multiple uniformly distributed, essentially parallel, oriented layered structures. The angle between these oriented layered structures and the thickness direction of the grinding wheel body is -5° to 5°. Large oriented gaps are formed between adjacent oriented layered structures. Each large oriented gap contains multiple transverse septa connecting adjacent oriented layered structures, which separate the large oriented gaps to form several small pores. The thickness of the oriented layered structures is 3–20 μm, and the distance between the large oriented gaps is 0–30 μm.

[0043] Example 2 This embodiment provides an ordered porous diamond grinding wheel and its preparation method, which is basically the same as the ordered porous diamond grinding wheel and its preparation method provided in Example 1. The main difference is that the proportions of the raw materials in this embodiment are: 80 wt% diamond micro powder, 20 wt% ceramic binder, 1.7 wt% sodium polyacrylate as dispersant, and 6 wt% polyacrylic acid as binder; the concentration of the sucrose aqueous solution is 12%, and the solid content of the grinding wheel raw material suspension slurry is 55 wt%. The preparation method provided in this embodiment is the same as that in Example 1, with the main difference being: Directional freezing and annealing: the freezing temperature is -30℃, and the annealing temperature is -5℃; the gradient cooling rate is 1℃ / min, and the heating rate is 1℃ / min; Low-temperature sintering: First, hold at 300℃ for 2 hours, then raise the temperature to 700℃ and hold for 2 hours, then cool with the furnace to obtain the grinding wheel block.

[0044] Example 3 This embodiment provides an ordered porous diamond grinding wheel and its preparation method, which is basically the same as the ordered porous diamond grinding wheel and its preparation method provided in Embodiment 1. The main difference is that the proportions of the raw materials in this embodiment are as follows: a mixed powder composed of 80 wt% diamond micro powder and 20 wt% ceramic binder; sodium polyacrylate as a dispersant accounting for 1.5 wt% of the mixed powder; polyacrylic acid as a binder accounting for 8 wt% of the mixed powder; the concentration of the sucrose aqueous solution is 18 wt%; and the solid content of the grinding wheel raw material suspension slurry is 50 wt%. The preparation method provided in this embodiment is the same as that in Embodiment 1, with the main difference being: Directional freezing and annealing: the freezing temperature is -50℃, the annealing temperature is -10℃; the gradient cooling rate is 1℃ / min, and the heating rate is 0.5℃ / min; Low-temperature sintering: First, hold at 220℃ for 3 hours, then raise the temperature to 650℃ and hold for 3 hours, then cool with the furnace to obtain the grinding wheel block.

[0045] Example 4 This embodiment provides an ordered porous diamond grinding wheel and its preparation method, which is basically the same as the ordered porous diamond grinding wheel and its preparation method provided in Example 1. The main difference is that the proportions of the raw materials in this embodiment are as follows: a mixed powder composed of 81 wt% diamond micro powder and 19 wt% ceramic binder, sodium polyacrylate as a dispersant accounting for 1.5 wt% of the mixed powder, and polyacrylic acid as a binder accounting for 5 wt% of the mixed powder; the concentration of sucrose aqueous solution is 15 wt%, and the solid content of the grinding wheel raw material suspension slurry is 60 wt%. The preparation method provided in this embodiment is the same as that in Example 1, with the main difference being: Directional freezing and annealing: the freezing temperature is -35℃, the annealing temperature is -5℃; the gradient cooling rate is 0.5℃ / min, and the heating rate is 1℃ / min.

[0046] Comparative Example 1—Hole-making method This comparative example uses a pore-forming agent method to prepare a high-porosity diamond grinding wheel. The raw material ratio for this diamond grinding wheel is as follows: 80 wt% diamond micro powder, 20 wt% ceramic binder, 55 wt% PMMA pore-forming agent (30 μm) as an additive, and 5 wt% polyethylene glycol as a temporary binder. The preparation method of the diamond grinding wheel includes: 1) Press the above-mentioned diamond abrasive, ceramic binder, PMMA pore-forming agent, and temporary binder into a blank of 30 mm × 20 mm × 6 mm; 2) After natural drying for 12 h, heat the blank in a sintering furnace at 1℃ / min, hold it at 350℃ for 1 hour, then heat it to 740℃ and hold it for 3 hours before cooling it with the furnace to obtain a grinding wheel block; 3) Cut the grinding wheel block to make a grinding wheel block of the required size and bond it to an aluminum substrate to make a thinned grinding wheel of the required specifications. Then, perform fine machining to obtain the finished diamond grinding wheel.

[0047] Comparative Example 2—Fogging Method This comparative example uses a foaming method to prepare a high-porosity diamond grinding wheel. The raw material ratio for this diamond grinding wheel is as follows: 80 wt% diamond micropowder, 20 wt% ceramic binder, 15 wt% calcium carbonate as an external foaming agent (based on the total powder mixture), and 5 wt% polyethylene glycol as a temporary binder. The preparation method of the diamond grinding wheel includes: 1) Press the above-mentioned diamond abrasive, ceramic binder, foaming agent calcium carbonate, and temporary binder into a blank of 30mm×20mm×6mm; 2) After natural drying for 12 hours, heat the blank in a sintering furnace at 1℃ / min, hold it at 350℃ for 1 hour, then heat it to 740℃ and hold it for 3 hours before cooling it in the furnace; 3) Cut the grinding wheel block to make a grinding wheel block of the required size and bond it to an aluminum substrate to make a thinned grinding wheel of the required specifications. Then, perform fine machining to obtain the finished diamond grinding wheel.

[0048] Comparative Example 3—Annexation process omitted This comparative example provides a method for preparing a porous diamond sintered body, which is basically the same as the method for preparing the grinding wheel block in Example 1. The main difference is that this comparative example only replaces the directional freezing and annealing steps in Example 1 with a directional freezing step. Specifically, the directional freezing step in this comparative example includes: after vacuum degassing the grinding wheel raw material suspension slurry, casting it into a mold, placing it in a freeze dryer, and first cooling it vertically at a cooling rate of 0.5 ℃ / min to a freezing temperature of -40 ℃, and then holding it at that temperature for 480 min to obtain a frozen slurry body. The sintered body finally obtained in this comparative example is as follows. Figure 3 As shown in (a and c).

[0049] Figure 3 These are sintered images and microstructure photographs of freeze-formed samples from Examples 1 and 3, using the same formulation, but with or without annealing. From... Figure 3 As can be seen, the macroscopic structure of the sample in Comparative Example 3, which omitted the annealing process, exhibited inhomogeneity during freeze-forming, with fine cracks running from the surface to the bottom. Figure 3 a) It is difficult to prepare it into a grinding wheel; while the sample made by annealing process has a good surface after freeze forming and sintering, without cracks, defects and other phenomena. Figure 3 b). Magnified microstructure revealed that the layered structure of the sample without annealing was poorly oriented and exhibited large pores. Figure 3 c); however, samples processed by annealing do not have these problems ( Figure 3 d). This demonstrates that the annealing process effectively improves the uniformity and order of the microstructure, avoids the formation of large pores, and eliminates forming stress, thus preventing defects and cracks from occurring during ice crystal sublimation. The bulk density, apparent porosity, and flexural strength of Examples 1-4 and Comparative Examples 1-2 after sintering are shown in Table 1.

[0050] Table 1. Physical properties of each embodiment and comparative example. As can be seen from Table 1, the bulk density of the frozen-formed samples ranges from 0.75 to 1 g / cm³. -3Between 68% and 77%, the apparent porosity of the sample was significantly higher than that of the grinding wheels prepared by the pore-forming agent method and the foaming method. This is closely related to its unique layered structure. Since the strength of Comparative Example 2 was too low to be used as a grinding wheel for comparison, only the grinding wheel of Comparative Example 1 was used to compare its grinding performance with that of Example 1 on silicon wafers.

[0051] Figure 2 These are micrographs of the grinding wheels used in Example 1 and Comparative Examples 1-2. From... Figure 2 As can be seen, the porosity of the cryogenically formed grinding wheel is significantly different from that obtained by the pore-forming agent method and the foaming method. The grinding wheel of Comparative Example 1, prepared by compression molding with the introduction of a pore-forming agent, inevitably exhibits the "hard lumps" shown in circles inside, and shows abrasive grain agglomeration (Figures a and a1). The grinding wheel of Comparative Example 2, prepared by the foaming method, also shows uneven pore distribution, even voids, and localized dense aggregates (Figures b and b1). However, Example 1 of this invention, utilizing cryogenic molding without adding any pore-forming agent, obtains ordered, oriented layered pores. The gaps and wall thicknesses of the layered pores are basically consistent, there are no localized hard spots, and the layered abrasive grain deposition effect is excellent. This structure can promote heat dissipation, chip removal, and self-sharpening of the grinding wheel during grinding.

[0052] Figure 4 This is a schematic diagram of a silicon wafer after grinding on a Disco 8540 grinder using grinding wheels of the same specifications prepared in Comparative Example 1 (using the pore-forming agent method) and Example 1 (combined with directional freezing and annealing processes), according to the parameters in Table 2. From... Figure 4 The comparison shows that the silicon wafers prepared by the pore-forming agent method have varying degrees of grinding burn streaks and scratches on the surface of the grinding wheel. Figure 4 a); and the silicon wafers ground by the grinding wheel prepared based on cryogenic forming in Example 1 are more glossy and have better surface quality ( Figure 4 b). Additionally, such as Figure 5 As shown, under the same grinding parameters, the grinding wheel prepared in Comparative Example 1 chipped 3 grinding wheel teeth. Figure 5 a), while the grinding wheel prepared in Example 1 did not exhibit tooth breakage ( Figure 5 b).

[0053] Table 2 Grinding parameters of grinding wheel Grinding parameters Spindle speed / rpm First infeed P1 / μm·s -1 ]]> Second infeed P2 / pm-s -1 ]] Third pass P3 / pm-s -1 ]] Removal / pm Values 3200 0.5 0.5 0.1 50 The surface quality of the silicon wafer after grinding was examined using atomic force microscopy (AFM). Figure 6 The comparison shows the surface quality of silicon wafers after grinding with the thinning grinding wheel prepared by the pore-forming agent method in Example 1 and the thinning grinding wheel prepared in Example 1 of this invention. For example... Figure 6As shown in Figure a, silicon wafers ground using thinning grinding wheels prepared with pore-forming agents exhibit excessively deep or shallow scratches, resulting in poor surface quality and making subsequent processing difficult. In contrast, silicon wafers prepared using a cryogenic forming combined with annealing process, after grinding with thinning grinding wheels from Example 1, have relatively smooth surfaces without excessively deep scratches. Figure 6 As shown in b.

[0054] In summary, the embodiments of this invention utilize cryogenic forming technology to prepare ceramic diamond grinding wheels with high porosity and high strength coupling, combined with annealing to enhance crystallization and improve the uniformity of the wheel's pore structure. Compared with existing thinning grinding wheel pore-forming technologies, the diamond thinning grinding wheels prepared by the method provided in these embodiments exhibit better pore structure uniformity, controllable porosity, and high strength, without causing scratches or burns to the workpiece. The preparation process is simple and cost-effective.

[0055] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and not to limit them; although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications can still be made to the specific implementation of the present invention or equivalent substitutions can be made to some technical features without departing from the spirit of the technical solutions of the present invention, and all such modifications and substitutions should be covered within the scope of the technical solutions claimed in the present invention.

Claims

1. An ordered porous diamond grinding wheel, comprising a ceramic diamond grinding wheel body, characterized in that, The grinding wheel body includes a plurality of uniformly distributed ordered oriented layered structures. The angle between the plurality of ordered oriented layered structures and the thickness direction of the grinding wheel body is -10° to 10°. Large oriented gaps are formed between adjacent oriented layered structures. Each large oriented gap is provided with a plurality of transverse diaphragm structures that connect adjacent oriented layered structures. The plurality of transverse diaphragm structures separate the large oriented gaps to form a number of small pores.

2. The ordered porous diamond grinding wheel according to claim 1, characterized in that, The multiple ordered oriented layered structures are arranged in a basically parallel manner, and the angle between the multiple oriented layered structures and the thickness direction of the grinding wheel body is -5° to 5°.

3. The ordered porous diamond grinding wheel according to claim 1 or 2, characterized in that, The thickness of the oriented layered structure is 3–20 μm, and the distance of the oriented large gaps is 0–30 μm.

4. A method for preparing an ordered porous diamond grinding wheel according to claim 1, 2, or 3, comprising the steps of: Preparation of composite slurry: Annealing media, water, and raw materials for making grinding wheels were uniformly mixed using a wet ball milling method to obtain a grinding wheel raw material suspension slurry with a solid content of 50-60 wt%. The annealing medium comprises 10-20 wt% of both the annealing medium and water. Directional freezing and annealing: First, the grinding wheel raw material suspension slurry is cooled to the freezing temperature in a vertical gradient using a freeze dryer, and then subjected to a first heat preservation treatment to solidify the grinding wheel raw material suspension slurry; Then raise the temperature to the annealing temperature and perform a second heat treatment; Then, the temperature is lowered to the freezing temperature and a third heat preservation treatment is performed to completely freeze the grinding wheel raw material suspension slurry, in which the water forms a uniform layered ice crystal structure, resulting in a frozen slurry body. Sublimation drying: The frozen slurry body is subjected to vacuum sublimation drying to remove the layered ice crystal structure and obtain a porous preform; Low-temperature sintering: First, the porous blank is sintered at a constant temperature of 200-350 ℃ to remove organic matter; then, it is sintered at a constant temperature of 650-750 ℃ ​​to obtain the grinding wheel block.

5. The preparation method according to claim 4, characterized in that, The raw materials for making the grinding wheel include a mixed powder, a binder, and a dispersant. The mixed powder consists of 18-22 wt% ceramic binder and 78-82 wt% diamond micro powder. The amount of dispersant added is 1.5-4 wt% of the mixed powder, and the amount of binder added is 4-10 wt% of the mixed powder.

6. The preparation method according to claim 4 or 5, characterized in that, The directional freezing and annealing steps include: using the freeze dryer to first gradually cool the grinding wheel raw material suspension slurry to the freezing temperature in a vertical direction, and holding it at that temperature for 140–180 min; then raising the temperature from the freezing temperature to the annealing temperature and holding it at that temperature for 120–160 min; and then lowering it back to the freezing temperature and holding it at that temperature for 140–180 min to obtain the frozen slurry body; wherein the annealing temperature is 20–50 °C higher than the freezing temperature.

7. The preparation method according to claim 6, characterized in that, The freezing temperature is -30℃ to -50℃, the annealing temperature is -10℃ to -5℃, the gradient cooling rate is 0.5 to 2℃ / min, and the heating rate is 0.5 to 2℃ / min.

8. The preparation method according to claim 4, 5, or 7, characterized in that, The sublimation drying step includes: using a vacuum sublimation drying method, the temperature of the frozen slurry is gradually increased to 10-15°C in the vertical direction, and kept at that temperature for 24-30 h to obtain the porous preform.

9. The preparation method according to claim 4, 5, or 7, characterized in that, The low-temperature sintering step includes: first sintering the porous blank at a constant temperature of 200-350 ℃ for 1-3 hours; then sintering at a constant temperature of 650-750 ℃ ​​for 1-3 hours and then naturally cooling to obtain the grinding wheel block.

10. The application of an ordered porous diamond grinding wheel as described in claim 1, 2 or 3 in semiconductor wafer thinning grinding.

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