Pva porous foamed material, preparation method and semiconductor wafer cleaning brush

Abstract

The present application belongs to the technical field of polymer porous foaming material and semiconductor precision cleaning consumables, and particularly relates to a PVA porous foaming material, a preparation method and a semiconductor wafer cleaning brush. The preparation method provided by the present application does not need to use solid particle pore-forming medium, polyvinyl alcohol is dissolved in water to form a glue solution, a surfactant and an acidic catalyst are added to adjust pH and filter, inert gas is introduced for foaming, a formaldehyde solution is added, and the product is obtained through gradient temperature solidification, demolding cleaning and drying. The PVA porous foaming material prepared by the present application has a regular and uniform multi-stage pore structure, the main foam holes are nearly spherical and interconnected to form a three-dimensional network structure. The prepared semiconductor wafer cleaning brush has excellent hydrophilicity, flexibility, high elasticity and high rebound characteristics, no particle precipitation and debris shedding occur in the use process, can meet the ultra-high cleanliness requirement of high-end semiconductor processes, simultaneously simplifies the production process, reduces the environmental protection cost, and has a good industrial application prospect.

Description

Technical Field

[0001] This invention belongs to the technical field of polymer porous foam materials and semiconductor precision cleaning consumables, specifically relating to a PVA porous foam material, its preparation method, and a semiconductor wafer cleaning brush. Background Technology

[0002] As semiconductor manufacturing technology rapidly advances towards precision, miniaturization, and high integration, the surface cleanliness of wafers, as the core substrate material for chip fabrication, directly determines chip production yield and operational stability. In the entire wafer fabrication process, contact physical cleaning is a crucial step in removing surface microparticles, organic contaminants, and residual impurities. PVA porous sponge cleaning brushes, with their excellent hydrophilicity, flexible contact characteristics, and porosity adsorption capacity, have become indispensable core consumables in precision semiconductor wafer cleaning scenarios, leading to continuously increasing market demand. Simultaneously, high-end semiconductor processes place extremely high demands on cleaning consumables. They not only require a uniform and regular microporous structure to ensure stable particle capture capabilities but also need to meet core indicators such as no impurity precipitation, high elasticity, deformation resistance, and no debris shedding. The industry's demand for the research and mass production of high-performance, high-cleanliness PVA cleaning brushes is becoming increasingly urgent.

[0003] Currently, PVA sponges used in industrial-scale semiconductor wafer cleaning applications are generally prepared using a polyvinyl alcohol and formaldehyde acid acetalization crosslinking system. However, due to limitations in the foaming technology of existing PVA aqueous reaction systems, it is difficult to prepare a stable, uniformly sized microporous structure in PVA sponges using conventional chemical foaming methods. Therefore, the industry has long used the mainstream preparation method of solid particulate pore formation. This method relies on the dispersion and occupancy of a solid pore-forming medium within a colloidal system. After crosslinking and molding, the solid medium is subsequently removed to form a porous structure, allowing for relatively precise and stable control of the sponge's basic pore structure. This method, with its mature technology and low mass production threshold, has long been the mainstream choice for preparing porous PVA cleaning sponges in the industry.

[0004] Current mainstream solid-state pore-forming processes mostly use starch-based particles as the core pore-forming medium. However, this type of process has inherent cleanliness defects in actual production and application. During the reaction and post-processing stages, the starch matrix easily generates degradation residues, polysaccharide fragments, and other trace solid impurities. Due to the limitations of material bonding characteristics, these solid impurities are easily encapsulated within the internal skeletal structure of the sponge, and even after prolonged and frequent washing, they cannot be completely removed. The latent solid impurities remaining inside the finished sponge are prone to slow precipitation and detachment during wafer contact cleaning, leading to microscopic contamination of the wafer surface and inducing defects such as pitting corrosion and particle residue.

[0005] Meanwhile, the traditional starch-based pore-forming process is cumbersome and lengthy. To reduce the pollution risk caused by residual impurities, the production process must be accompanied by post-treatment steps such as long-term soaking, repeated rinsing, and deep impurity removal, significantly extending the overall production cycle. The lengthy processing not only increases energy consumption and labor costs, but the large amount of solid wastewater generated during the impurity removal process also requires significant investment in purification, increasing the environmental operation pressure on enterprises and hindering the low-carbon, large-scale, and sustainable development of the industry. Summary of the Invention

[0006] To address the shortcomings of existing technologies, this invention provides a PVA porous foam material, a preparation method, and a semiconductor wafer cleaning brush.

[0007] The purpose of this invention is to provide a new preparation method that, while ensuring that the overall performance of the PVA cleaning brush is superior to or at least not inferior to that of products made using traditional starch pore-forming processes, solves the problems of solid impurity residue and slow precipitation in traditional processes, so as to better meet the increasingly higher cleanliness requirements of high-end semiconductor manufacturing processes.

[0008] The first aspect of this invention provides a method for preparing a porous PVA foam material, comprising the following steps: Step S1: Dissolve polyvinyl alcohol in water to form a polyvinyl alcohol gel, add surfactant and acidic catalyst, adjust the pH to 2.0-4.0 to obtain a mixture, and filter the mixture to remove insoluble impurities; Step S2: Place the filtered mixture in a sealed container, and pass inert gas through it while stirring to obtain a foam slurry; add formaldehyde solution to the foam slurry and stir until homogeneous; Step S3: Inject the foam slurry containing formaldehyde solution into the mold and heat it to solidify and shape. Step S4: Demold the cured material, clean and dry it to obtain PVA porous foam material; The preparation method does not use solid particle pore-forming media.

[0009] As a further optimization of the above preparation method, in step S1, the degree of polymerization of polyvinyl alcohol is 1700-2000, the degree of alcoholysis is 88%-99%, and the mass ratio of polyvinyl alcohol to water is 1:8-1:12; the dissolution conditions are stirring at 200-300 rpm for 60-90 min in a water bath at 80-95℃, followed by standing for 10-15 min to remove bubbles after dissolution; the surfactant is sodium dodecylbenzenesulfonate and / or Tween-80, with an addition amount of 0.1%-0.5% of the mass of polyvinyl alcohol; the acid catalyst is an aqueous solution of one or more of sulfuric acid, hydrochloric acid, oxalic acid, and phosphoric acid, with a mass fraction of 5%-10%.

[0010] As a further optimization of the above preparation method, in step S2, the inert gas is high-purity nitrogen with a purity ≥99.999%; the stirring process is first carried out at a high speed of 3000-5000 rpm while nitrogen is introduced, and the system temperature is controlled to 35-45℃ for 10-15 min. Then the stirring speed is reduced to 500-1000 rpm, and formaldehyde solution is added. At the same time, an acidic catalyst is added to maintain the pH at 2.0-4.0. The stirring is continued for 3-5 min, and then the mixture is allowed to stand for 2-3 min. The formaldehyde solution is an aqueous solution of formaldehyde, and the amount of formaldehyde added is 10%-20% of the mass of polyvinyl alcohol.

[0011] As a further optimization of the above preparation method, in step S3, silicone oil is applied to the inner wall of the Teflon mold as a release agent and preheated to 40±2℃. The foam slurry obtained in step S2 is injected into the mold, with the injection volume being 90%-95% of the mold volume. Gradient temperature rise curing is adopted. In the first step, the temperature is raised to 60±3℃, the heating rate is controlled within the range of 2±0.5℃ / min, and the holding time is controlled within the range of 2±0.5h. In the second step, the temperature is raised to 80±3℃, the heating rate is controlled within the range of 1±0.5℃ / min, and the holding time is controlled within the range of 3±0.5h. In the third step, the temperature is raised to 100±3℃, the heating rate is controlled within the range of 2±0.5℃ / min, and the holding time is controlled within the range of 1±0.5h.

[0012] As a further optimization of the above preparation method, in step S4, after the product is naturally cooled to room temperature, it is demolded, then soaked in deionized water for 20-30 hours, centrifuged and dehydrated, rinsed with deionized water for 8-15 minutes, centrifuged and dehydrated again, and dried at 65-75°C.

[0013] As a further optimization of the above preparation method, in step S1, the degree of polymerization of polyvinyl alcohol is 1800, and the mass ratio of polyvinyl alcohol to water is 1:10; after dissolution, the mixture is allowed to stand for 12 minutes to remove bubbles; the surfactant is sodium dodecylbenzenesulfonate, and the amount added is 0.3% of the mass of polyvinyl alcohol; the acid catalyst is a 7% sulfuric acid aqueous solution; the pH is adjusted to 2.0; and the filtration is vacuum filtration through a 0.22μm microporous membrane under a negative pressure of 0.05-0.08MPa.

[0014] As a further optimization of the above preparation method, in step S2, the flow rate of nitrogen gas is 7 L / min, the system temperature is controlled at 40℃, the high-speed stirring speed is 4000 rpm, and the duration is 10 min; after reducing the speed, the stirring speed is 750 rpm, the amount of formaldehyde added is 15% of the mass of polyvinyl alcohol, and after the addition is completed, stirring is continued for 4 min, and then it is allowed to stand for 2.5 min.

[0015] As a further optimization of the above preparation method, in step S3, the mold preheating temperature is 40℃, the preheating time is 30min, and the foam slurry injection volume is 90% of the mold volume; the gradient temperature curing is as follows: the first step is to heat from 40℃ to 60℃ at a heating rate of 2℃ / min and hold for 2h; the second step is to heat from 60℃ to 80℃ at a heating rate of 1℃ / min and hold for 3h; the third step is to heat from 80℃ to 100℃ at a heating rate of 2℃ / min and hold for 1h.

[0016] A second aspect of the present invention provides a PVA porous foam material, which is prepared by any of the above-described preparation methods.

[0017] The third aspect of the present invention provides a semiconductor wafer cleaning brush, which is made of the above-mentioned PVA porous foam material. The PVA porous foam material has a multi-level pore structure, the main pores are nearly spherical, and the pores are interconnected to form a three-dimensional network structure. Secondary fine micropores are distributed in the pore skeleton wall. The PVA porous foam material has no solid phase impurities remaining.

[0018] Beneficial effects The PVA cleaning brush prepared by this invention has a regular and uniform pore arrangement, high pore shape regularity, and no structural defects such as collapsed pores, irregular pores, and large pore interconnections. It forms a stable multi-level pore structure system, which can evenly distribute contact stress, adapt to the flexible cleaning conditions of precision wafer surfaces, and avoid workpiece surface damage caused by rigid contact.

[0019] The molding system of this invention has no solid phase pore-forming medium involved in the entire process, and there are no solid phase residues or hidden impurities inside the finished product. During use, there is no particulate matter precipitation or debris shedding, which fundamentally avoids the risk of wafer micro-contamination caused by the cleaning process and can meet the stringent requirements of ultra-high cleanliness in high-end semiconductor manufacturing processes.

[0020] The PVA cleaning brush prepared by this invention has a dense and stable three-dimensional network structure with excellent high elasticity and resilience. After absorbing water and swelling, it is not easily deformed, delaminated, or collapsed. It has good structural stability after long-term repeated extrusion and has a long service life.

[0021] This invention significantly simplifies the post-processing and impurity removal process of finished products, eliminating the need for prolonged acid and alkali soaking and deep slag removal. It significantly reduces water and energy consumption during production, and the wastewater generated is free of solid suspended matter. The treatment difficulty and environmental protection investment are lower, making it more cost-effective for industrial applications. Attached Figure Description

[0022] Figure 1 This is a photograph of the gas-foamed PVA sponge prepared in Example 1 of the present invention.

[0023] Figure 2 This is a scanning electron microscope image of the gas-foamed PVA sponge prepared according to the present invention.

[0024] Figure 3 Scanning electron microscope image of PVA sponge prepared by traditional starch foaming process.

[0025] Figure 4 This is a physical image of the PVA cleaning brush prepared in Example 2 of the present invention. Detailed Implementation

[0026] This invention discloses a method for preparing a burr-free, high-elastic PVA cleaning brush using a gas foaming process, which mainly includes the following four steps.

[0027] Step S1: Raw material preparation Select high-purity PVA powder (purity ≥ 99.5%) with a degree of polymerization of 1700-2000 and a degree of hydrolysis of 88%-99%. Add deionized water (conductivity ≤ 10 μS / cm) to the PVA powder at a mass ratio of PVA to pure water of 1:8-1:12. Place the above mixture in a constant temperature water bath and control the water bath temperature at 80-95℃ (preferably 85-90℃). Use low-speed mechanical stirring at 200-300 rpm and continue stirring for 60-90 minutes until the PVA powder is completely dissolved, forming a transparent and uniform PVA solution without particles or flocculent matter. Let it stand for 10-15 minutes to remove a small amount of air bubbles in the system.

[0028] Prepare a 37%-40% formaldehyde solution separately as a crosslinking agent. Select one or more of sulfuric acid, hydrochloric acid, oxalic acid, or phosphoric acid to prepare a 5%-10% aqueous solution as an acidic catalyst.

[0029] Add a surfactant to the prepared PVA solution. The surfactant can be one or more of sodium dodecylbenzenesulfonate or Tween-80. The amount added is 0.1%-0.5% of the mass of PVA. Then adjust the pH of the system to 2.0-4.0 with the acidic catalyst aqueous solution prepared above.

[0030] Finally, all the prepared mixed raw materials are vacuum filtered through a 0.22μm microporous membrane under a negative pressure of 0.05-0.08MPa to thoroughly remove tiny particulate impurities and insoluble residues from the raw materials. After filtration, the raw materials are sealed and stored away from light for later use.

[0031] Step S2, Foaming and Mixing First, thoroughly clean the sealed high-pressure foaming kettle with deionized water and dry it until no moisture remains. Check the airtightness of the kettle body to ensure there is no leakage before use. Slowly transfer the PVA adhesive solution filtered in step S1 into the sealed high-pressure foaming kettle, close the kettle lid, and check the airtightness again.

[0032] Turn on the high-speed shear stirring device and adjust the stirring speed to 3000-5000 rpm. Simultaneously, introduce high-purity N2 (≥99.999%) into the reactor at a flow rate of 5-10 L / min to replace air and reduce residual oxygen in the system, preventing PVA oxidation, yellowing, and performance degradation. Control the system temperature to 35-45℃ and continue high-speed stirring for 10-15 min, so that the introduced N2 is sheared into micron-sized bubbles of 50-200 μm. At the same time, the system viscosity increases to initially lock the bubbles. Then, reduce the stirring speed to 500-1000 rpm and slowly add the formaldehyde solution prepared in step S1 to the reactor at a rate of 1-2 mL / min. The amount of formaldehyde added is 10%-20% of the mass of PVA. Simultaneously, slowly add an acidic catalyst aqueous solution to stabilize the pH value of the system at 2.0-4.0. After the addition is complete, maintain medium-speed stirring for 3-5 minutes to ensure that the crosslinking agent (formaldehyde) and PVA molecules are fully contacted and mixed evenly, and to avoid excessive shear force from destroying the stable bubble structure that has been formed; after stirring, let stand for 2-3 minutes to allow the foam system to stabilize.

[0033] Step S3, Injection Molding and Curing Prepare a Teflon mold in advance. Apply a thin layer of silicone oil to the inner wall of the mold as a release agent. Then place the mold in a constant temperature oven and preheat it at a temperature of 40±2℃ for no less than 30 minutes to ensure that the temperature of the inner wall of the mold is uniform.

[0034] The stable foam slurry obtained in step S2 is quickly injected into the preheated Teflon mold. The injection volume is controlled to be 90%-95% of the mold volume, leaving a small amount of space for the foam to expand slightly.

[0035] The mold containing the foam slurry is smoothly placed into a constant temperature oven, and a gradient temperature curing method is used for foaming and curing to ensure sufficient acetalization and cross-linking reaction between PVA and formaldehyde, and permanent stabilization of the bubble structure. Gradient temperature curing: First, the temperature is increased from 40℃ to 60℃ at a rate of 2℃ / min and held for 2 hours to promote further stabilization and initial cross-linking of the bubbles; Second, the temperature is increased from 60℃ to 80℃ at a rate of 1℃ / min and held for 3 hours to accelerate the acetalization and cross-linking reaction and form a stable three-dimensional network structure; Third, the temperature is increased from 80℃ to 100℃ at a rate of 2℃ / min and held for 1 hour to complete the cross-linking and curing, while removing residual moisture and unreacted formaldehyde from the system; During the curing process, good ventilation is maintained in the oven, with the ventilation rate controlled at 5-8 m³ / h.

[0036] Step S4: Demolding and cleaning After curing, turn off the oven power and allow the mold and product inside the oven to cool down to room temperature naturally. Once the mold and product have completely cooled to room temperature, slowly open the mold and completely remove the PVA sponge product from the mold. Trim any excess material remaining on the edges and corners to ensure the product has a neat shape.

[0037] The trimmed PVA sponge product is placed in a deionized water cleaning tank and cleaned by soaking followed by rinsing to remove impurities such as residual acidic catalysts, unreacted formaldehyde, PVA monomers, and surfactants from the product surface and interior. Preferably, the product is first soaked for 20-28 hours, then centrifuged to remove water, rinsed with deionized water for 8-12 minutes, centrifuged again, and finally dried at a temperature of 60-80℃ for 4-6 hours to obtain a burr-free, high-elasticity PVA cleaning brush.

[0038] The present invention is further illustrated below with specific embodiments. These embodiments are exemplary and intended to illustrate the problem and explain the present invention, and are not intended to be limiting.

[0039] Example 1 This embodiment prepares a block-shaped high-elasticity PVA sponge material.

[0040] Step S1: Raw material preparation First, weigh 10g of high-purity PVA powder (degree of polymerization approximately 1800, degree of hydrolysis approximately 99%, purity ≥99.5%). Add 100g of primary deionized water (compliant with GB / T6682-2008 standard, conductivity ≤10μS / cm, mass ratio 1:10) to the PVA powder. Place the mixture in a constant temperature water bath at 85℃ and mechanically stir at 250rpm for 75min until the PVA is completely dissolved to obtain a transparent and homogeneous PVA solution. Let it stand for 12min to remove any small amount of air bubbles. Prepare a 38% formaldehyde solution separately as a crosslinking agent. Prepare a 7% sulfuric acid aqueous solution separately as an acidic catalyst. Add sodium dodecylbenzenesulfonate (0.3% by mass of PVA) as a surfactant to the prepared PVA solution, and then adjust the pH of the system to 2.0 using the above-mentioned sulfuric acid catalyst aqueous solution. Finally, all the mixed raw materials were vacuum filtered using a 0.22μm microporous membrane under a negative pressure of 0.06MPa to remove particulate impurities. After filtration, the mixture was sealed and stored away from light for later use.

[0041] Step S2, Foaming and Mixing Clean the sealed high-pressure foaming vessel with deionized water and dry it thoroughly. Check the vessel's airtightness to ensure there are no leaks. Slowly transfer the filtered PVA solution from step S1 into the high-pressure foaming vessel and close the lid. Turn on the high-speed shear stirring device and adjust the speed to 4000 rpm. Simultaneously, introduce high-purity N2 (≥99.999%) at a uniform flow rate of 7 L / min. Heat the system to 40°C and continue high-speed stirring for 10 min to shear the N2 into microbubbles, while the system viscosity increases. Reduce the stirring speed to 750 rpm and slowly add the formaldehyde solution prepared in step S1 at a rate of 1.5 mL / min, which is 15% of the PVA mass. Simultaneously, slowly add an acidic catalyst aqueous solution to gradually stabilize the pH of the system to 2.0. After the addition is complete, maintain medium-speed stirring for 4 min to ensure the crosslinking agent and PVA are fully mixed. After stirring, let it stand for 2.5 min.

[0042] Step S3, Injection Molding and Curing Prepare a Teflon mold with a rectangular inner cavity. Apply a thin layer of silicone oil to the inner wall of the mold as a release agent, and place the mold in a constant temperature oven to preheat at 40°C for 30 minutes. Quickly inject the stable foam slurry obtained in step S2 into the preheated Teflon mold, filling approximately 90% of the mold's volume. Smoothly place the mold containing the foam slurry into the constant temperature oven for gradient temperature curing: First, increase the temperature from 40°C to 60°C at a rate of 2°C / min and hold for 2 hours; second, increase the temperature from 60°C to 80°C at a rate of 1°C / min and hold for 3 hours; third, increase the temperature from 80°C to 100°C at a rate of 2°C / min and hold for 1 hour.

[0043] Step S4: Demolding and cleaning After curing, turn off the oven power and allow the mold and product to cool naturally to room temperature (25°C). Once the temperature has dropped to room temperature, slowly open the mold and completely remove the PVA sponge product, trimming off any excess material. Place the trimmed sponge product in a deionized water washing tank, soak for 24 hours, centrifuge to remove water, rinse with deionized water for 10 minutes, centrifuge again, and finally dry to obtain a block of high-elasticity PVA sponge.

[0044] After the sponge sample obtained in this embodiment is sliced, it is as follows: Figure 1 As shown, the product has a regular overall shape, no obvious missing material, and a uniform and dense surface, exhibiting the typical white porous material texture of PVA sponge.

[0045] Figure 2Scanning electron microscope (SEM) images of the PVA sponge prepared in this embodiment show that the material has a porous internal structure. The main body of the cells is a regular, nearly spherical shape with high roundness and a relatively uniform pore size distribution. There are no irregular pores or obvious pore wall collapse defects. This regular and uniform cell structure makes the overall mechanical properties of the material more balanced, with stable elasticity and recovery. It is not easy to cause local stress concentration or material fatigue damage during repeated squeezing and cleaning, ensuring the durability and dimensional stability of the cleaning brush. At the same time, the interconnected channels between the cells form a complete three-dimensional network structure without large-sized through defects, providing a uniform skeletal support structure and uniform fluid channels for the material. This helps to uniformly adsorb and discharge the cleaning liquid, improving cleaning efficiency. In addition, the skeleton wall constituting the cells is not a dense solid structure, but rather a dense micropore formed by a large number of secondary microfoamings distributed inside the skeleton, constructing a multi-level porous structure system in which the main cells and skeleton micropores coexist. This structure not only reduces the overall density of the material, making it lighter, but also gives the foam skeleton good flexible buffering ability. When in contact with the surface of precision workpieces such as wafers, it can disperse the contact stress through micro-deformation and avoid rigid scraping from causing scratches on the workpiece surface.

[0046] Figure 3 This is a scanning electron microscope (SEM) image of a PVA sponge prepared using a commercially available traditional starch foaming process. The image shows that it also contains numerous interconnected pores, but the pore shapes are irregular, lacking roundness, and exhibiting many flat pores, irregular shapes, and pore wall wrinkles and collapses. The pore size distribution is uneven. This irregular structure easily leads to uneven mechanical properties, making it prone to localized damage and elasticity loss during use. Furthermore, its pore skeleton wall is a dense, solid structure, lacking the fine micropores formed by secondary micro-foaming within the skeleton, making it more susceptible to scratches when in contact with precision workpieces.

[0047] It is important to note that this embodiment does not use any solid particle pore-forming media such as starch throughout the entire process, completely abandoning the traditional technology path that relies on solid-state site pore formation. This fundamentally solves the inherent defects of traditional starch pore-forming processes, such as residual solid impurities, cumbersome post-processing, and high environmental pressure. Unexpectedly, it also achieves pore structure performance superior to traditional starch-formed products. The superior results are attributed to the synergistic cooperation of each step and process parameter: In step S1, PVA raw materials with specific degrees of polymerization and hydrolysis are selected, and the liquid-to-solid ratio and dissolution conditions are precisely controlled. Combined with vacuum filtration to remove impurities, the physical properties of the adhesive system are controlled at the source, ensuring the purity and uniformity of the components, laying the foundation for obtaining regular pores free of impurities and defects. In step S2, high-purity nitrogen is used as the foaming medium, combined with high-speed shear stirring and precise temperature control, to efficiently disperse nitrogen into uniform micron-sized bubbles. Subsequent medium-speed stirring and simultaneous formaldehyde acetalization under acidic conditions maintain the bubble structure. Without damaging the structure, the crosslinking agent and PVA molecular chains are uniformly blended and initially crosslinked, locking a uniform bubble structure within the system. Step S3 employs a precisely temperature-controlled gradient curing process, using a slow heating rate and step-by-step heat preservation to ensure the acetalization crosslinking reaction proceeds smoothly and gradually. This ensures that the bubble skeleton neither collapses nor over-expands during curing and shaping, and induces the formation of secondary micropores within the skeleton walls. Ultimately, a stable multi-level porous structure without solid phase media involvement and without cleaning dead zones is constructed in one step. Step S4 controls the cleaning and drying conditions to ensure product cleanliness and avoid damage to the pore structure. Finally, precise crosslinking curing and multi-level pore synergistic construction are achieved without solid pore-forming media. This not only avoids the drawbacks of mainstream starch pore-forming processes but also produces a high-quality pore structure with regular pore shape, uniform pore size, and multi-level connectivity.

[0048] Example 2 This embodiment describes the preparation of a highly elastic PVA cleaning brush.

[0049] Compared to Example 1, the only difference in this example is the change in the shape of the mold; the other steps are the same and will not be repeated. In this example, a cleaning brush forming mold is used. The mold is placed vertically, and the slurry is injected into approximately 90% of the mold's volume, leaving a small amount of space at the top for slight foam expansion. The cleaning roller brush product obtained in this example is as follows: Figure 4 As shown. This cleaning roller brush can be used for precision cleaning of semiconductor wafers. It features burr-free, highly elastic and wear-resistant properties, leaves no solid impurities, and has uniform pores. It can efficiently capture particles on the wafer surface and avoid scratching the wafer, making it suitable for the ultra-high cleanliness requirements of semiconductor manufacturing processes.

[0050] The above embodiments are exemplary and are intended to illustrate the technical concept and features of the present invention, so that those skilled in the art can understand the content of the present invention and implement it accordingly. They should not be construed as limiting the scope of protection of the present invention. All equivalent changes or modifications made according to the spirit and essence of the present invention should be covered within the scope of protection of the present invention.

Claims

1. A method for preparing a PVA porous foam material, characterized in that, Includes the following steps: Step S1: Dissolve polyvinyl alcohol in water to form a polyvinyl alcohol gel, add surfactant and acidic catalyst, adjust the pH to 2.0-4.0 to obtain a mixture, and filter the mixture to remove insoluble impurities; Step S2: Place the filtered mixture in a sealed container, and pass inert gas through it while stirring to obtain a foam slurry; add formaldehyde solution to the foam slurry and stir until homogeneous; Step S3: Inject the foam slurry containing formaldehyde solution into the mold and heat it to solidify and shape. Step S4: Demold the cured material, clean and dry it to obtain PVA porous foam material; The preparation method does not use solid particle pore-forming media.

2. The preparation method according to claim 1, characterized in that, In step S1, the degree of polymerization of the polyvinyl alcohol is 1700-2000, the degree of alcoholysis is 88%-99%, and the mass ratio of polyvinyl alcohol to water is 1:8-1:

12. The dissolution conditions are stirring at 200-300 rpm for 60-90 minutes in a water bath at 80-95°C, followed by standing for 10-15 minutes to remove bubbles after dissolution. The surfactant is sodium dodecylbenzenesulfonate and / or Tween-80, and the amount added is 0.1%-0.5% of the mass of polyvinyl alcohol. The acid catalyst is an aqueous solution of one or more of sulfuric acid, hydrochloric acid, oxalic acid, and phosphoric acid, with a mass fraction of 5%-10%.

3. The preparation method according to claim 1, characterized in that, In step S2, the inert gas is high-purity nitrogen with a purity ≥99.999%. The stirring process begins with high-speed stirring at 3000–5000 rpm while nitrogen is introduced, controlling the system temperature to 35–45°C for 10–15 minutes. Then, the stirring speed is reduced to 500–1000 rpm, and the formaldehyde solution is added. Simultaneously, an acidic catalyst is added to maintain the pH at 2.0–4.

0. Stirring continues for 3–5 minutes, followed by standing for 2–3 minutes. The formaldehyde solution is an aqueous solution of formaldehyde, and the amount of formaldehyde added is 10%–20% of the mass of polyvinyl alcohol.

4. The preparation method according to claim 1, characterized in that, In step S3, silicone oil is applied to the inner wall of the Teflon mold as a release agent and preheated to 40±2℃. The foam slurry obtained in step S2 is injected into the mold, with the injection volume being 90%-95% of the mold volume. Gradient temperature curing is adopted. In the first step, the temperature is raised to 60±3℃, the heating rate is controlled within 2±0.5℃ / min, and the holding time is controlled within 2±0.5h. In the second step, the temperature is raised to 80±3℃, the heating rate is controlled within 1±0.5℃ / min, and the holding time is controlled within 3±0.5h. In the third step, the temperature is raised to 100±3℃, the heating rate is controlled within 2±0.5℃ / min, and the holding time is controlled within 1±0.5h.

5. The preparation method according to claim 1, characterized in that, In step S4, after the product has cooled naturally to room temperature, it is demolded, then soaked in deionized water for 20-30 hours, centrifuged to remove water, rinsed with deionized water for 8-15 minutes, centrifuged to remove water again, and dried at 65-75°C.

6. The preparation method according to claim 3, characterized in that, In step S1, the degree of polymerization of the polyvinyl alcohol is 1800, the degree of alcoholysis is 99%, and the mass ratio of polyvinyl alcohol to water is 1:10; after dissolution, the mixture is allowed to stand for 12 minutes to remove bubbles; the surfactant is sodium dodecylbenzenesulfonate, and the amount added is 0.3% of the mass of polyvinyl alcohol; the acid catalyst is a 7% sulfuric acid aqueous solution; the pH is adjusted to 2.0; the filtration is vacuum filtration through a 0.22μm microporous membrane under a negative pressure of 0.05-0.08MPa.

7. The preparation method according to claim 4, characterized in that, In step S2, the flow rate of nitrogen gas is 7 L / min, the system temperature is controlled at 40℃, the high-speed stirring speed is 4000 rpm, and the duration is 10 min; after reducing the speed, the stirring speed is 750 rpm, the amount of formaldehyde added is 15% of the mass of polyvinyl alcohol, after the addition is completed, stirring continues for 4 min, and then standing for 2.5 min.

8. The preparation method according to claim 5, characterized in that, In step S3, the mold preheating temperature is 40℃, the preheating time is 30min, and the foam slurry injection volume is 90% of the mold volume; the gradient temperature rise curing is as follows: the first step is to raise the temperature from 40℃ to 60℃ at a rate of 2℃ / min and hold for 2h; the second step is to raise the temperature from 60℃ to 80℃ at a rate of 1℃ / min and hold for 3h; the third step is to raise the temperature from 80℃ to 100℃ at a rate of 2℃ / min and hold for 1h.

9. A porous PVA foam material, characterized in that, It is prepared by any one of claims 1-8.

10. A semiconductor wafer cleaning brush, characterized in that, The cleaning brush is made of the PVA porous foam material as described in claim 9, and the PVA porous foam material has a multi-level pore structure inside, the main pores are nearly spherical, the pores are interconnected to form a three-dimensional network structure, and secondary fine micropores are distributed in the pore skeleton wall; the PVA porous foam material has no solid phase impurities remaining.

Images