A thiol-modified silica microsphere and a preparation method thereof

Abstract

The present application relates to a kind of mercapto-modified silica microspheres and its preparation method, the present application uses pipeline type continuous reaction process: first, tetraethyl orthosilicate is hydrolyzed under acidic conditions, then nucleated under alkaline conditions by polycondensation, finally, 3-mercapto trimethoxysilane is introduced during the growth of microspheres to carry out shell grafting.The efficient mixing of reactants and precise residence control are achieved by sectional feeding and interval temperature control.The prepared microspheres have core-shell structure, the particle size distribution is 0.3-5 μm and the uniformity is good, the content of metal impurities is less than 1 ppb, and the mercapto grafting amount is 0.2-2.2 mmol / g.The mercapto groups on the surface of the microspheres can specifically capture transition metals, noble metals and heavy metal ions in photoresist at ppb level, and the adsorption removal rate is as high as 94% or more, and it is easy to desorb and regenerate.The whole process of the present application is closed and pollution-free, solves the problem of batch instability of traditional kettle type reaction, can be continuously produced, and effectively improves the purity and process stability of semiconductor photoresist.

Description

Technical Field

[0001] This invention belongs to the field of semiconductor integrated circuit manufacturing technology, and particularly relates to a mercapto-modified silica microsphere and its preparation method. Background Technology

[0002] In semiconductor integrated circuit manufacturing, photolithography is a core process, and the purity of photoresist and its supporting solvents directly determines device performance and yield. As semiconductor manufacturing processes iterate towards advanced nodes such as EUV, KrF, and ArF, feature sizes shrink to the nanometer scale, the purity requirements for photoresist and solvents have increased to electronic-grade ppb or even ppt levels.

[0003] Photoresist systems are prone to introducing trace amounts of metal impurities such as alkali metals, transition metals, and noble metals throughout the entire process. Even at the ppb level, these impurities can interfere with the photosensitivity reaction, reduce device yield, and hinder the development of advanced processes. Existing impurity removal methods (such as ion exchange, membrane separation, distillation, and traditional adsorption) all have limitations: they may introduce secondary pollution, have insufficient purification efficiency, or damage the performance of the photoresist.

[0004] Modified silica microspheres used for photoresist impurity adsorption traditionally rely on complex batch grafting processes, which are prone to residual impurities causing secondary contamination. Furthermore, controlling microsphere particle size uniformity is difficult, leading to problems such as agglomeration and excessively small particle sizes, resulting in low adsorption efficiency. Simultaneously, existing preparation processes suffer from rudimentary environmental control, raw material purity, and impurity removal techniques, resulting in product purity that fails to meet electronic-grade requirements.

[0005] Therefore, developing a method for synthesizing thiol-modified silica microspheres that can control impurities at the source, is closed and pollution-free throughout the entire process, has precise and controllable preparation, and produces products with high purity, uniform particle size, excellent adsorption performance, easy desorption, and reusability has become an urgent issue to be addressed in the field of high-purity semiconductor materials. Summary of the Invention

[0006] The purpose of this invention is to overcome the shortcomings of the prior art and provide a mercapto-modified silica microsphere and its preparation method.

[0007] A thiol-modified silica microsphere includes a silica core and a thiol-modified silica shell coating the silica core.

[0008] In the shell: the amount of thiol grafting is 0.2–2.2 mmol / g, and the particle size of silica microspheres is 0.3–5 μm.

[0009] As a preferred option, the metal impurity content in the mercapto-modified silica microspheres is less than 1 ppb.

[0010] The preparation method of this mercapto-modified silica microsphere includes the following steps:

[0011] Step 1, Acidic Hydrolysis: Solution A and Solution B are simultaneously injected into a polyethylene pipe connected to the outlet at the bottom of the Y-shaped pipe through the inlets on both sides of the upper end of the Y-shaped pipe at the same flow rate; Solution A consists of ethanol, water, and concentrated hydrochloric acid, and the pH of Solution A is 1.5-2; Solution B consists of ethanol and tetraethyl orthosilicate (TEOS); The molar ratio of tetraethyl orthosilicate, water, ethanol, and concentrated hydrochloric acid added to the mixture of Solution A and Solution B in the polyethylene pipe is 1:(3-15):(6-20):(0.01-0.1); The polyethylene pipe is kept warm by a jacketed water bath, and after Solution A and Solution B are mixed in the polyethylene pipe, the reaction is carried out for a set time to obtain a transparent and clear reaction solution without white turbidity or flocculent matter.

[0012] Step 2, alkaline condensation nucleation: Reactant solution one is introduced into the inlet on one side of the upper end of the second Y-shaped pipe, while solution C is simultaneously injected into the inlet on the other side of the upper end of the second Y-shaped pipe. Reactant solution one and solution C are then injected into the polyethylene pipe connected to the outlet at the lower end of the second Y-shaped pipe. Solution C consists of ethanol and 25% ammonia water, and its pH is 9-11. The mixture of reactant solution one and solution C is added to the polyethylene pipe corresponding to the second Y-shaped pipe, with a molar ratio of tetraethyl orthosilicate, ammonia water, and ethanol of 1:(0.02-2.5):(0.25-1.5). The polyethylene pipe corresponding to the second Y-shaped pipe is kept warm using a jacketed water bath. After reactant solution one and solution C are uniformly mixed in the polyethylene pipe corresponding to the second Y-shaped pipe, a rapid reaction is carried out for a set time. Silica microspheres grow rapidly and quickly solidify, forming a milky white suspension-like reactant solution two.

[0013] Step 3, Alkaline Grafting: Introduce reaction solution 2 into the inlet on one side of the upper end of the third-section Y-shaped pipe. Under alkaline conditions, inject solution D into the inlet on the other side of the upper end of the third-section Y-shaped pipe. Inject reaction solution 2 and solution D into a stirred quartz flask connected to the outlet at the lower end of the third-section Y-shaped pipe. Solution D consists of ethanol and 3-mercaptopropyltrimethoxysilane (MPTMS), and is added to the third-section Y-shaped pipe. The molar ratio of tetraethyl orthosilicate, 3-mercaptotrimethoxysilane, and ethanol in a quartz flask with a stirrer at the lower end of the pipe is 1:(0.1~0.25):(0.25~1.5). The stirred quartz flask is kept warm by a jacketed water bath. After the reaction solution two and solution D are uniformly mixed in the stirred quartz flask, the reaction is rapidly carried out for a set time. The 3-mercaptotrimethoxysilane is rapidly hydrolyzed, and the silica microspheres are matured, finally yielding reaction solution three, which has silica microspheres with thiol-grafted shells.

[0014] As a preferred option:

[0015] Step 1 is as follows: Solution A and Solution B are simultaneously injected into the polyethylene pipe connected to the outlet at the bottom of the Y-shaped pipe through the inlets on both sides of the upper end of the Y-shaped pipe at a flow rate of 0.15 ml / min. The polyethylene pipe is kept at 35 ℃ by a jacketed water bath. After Solution A and Solution B are mixed in the polyethylene pipe, they react for 1 h to obtain a transparent and clear reaction solution without white turbidity or flocculent matter. Solution A is composed of ethanol, water and concentrated hydrochloric acid, and the pH of Solution A is maintained within 1.5 to 2. Solution B is composed of ethanol and tetraethyl orthosilicate (TEOS). The molar ratio of tetraethyl orthosilicate, water, ethanol and concentrated hydrochloric acid added to the polyethylene pipe is 1:(3-8):(8-20):(0.01-0.1). The polyethylene pipe is 2 m long, has an inner diameter of 0.5 mm and a wall thickness of 0.1 mm.

[0016] Step 2 is as follows: Reaction solution 1 is introduced into the inlet on one side of the upper end of the second Y-shaped pipe at a flow rate of 0.3 ml / min. Simultaneously, solution C is injected into the inlet on the other side of the upper end of the second Y-shaped pipe at a flow rate of 0.2 ml / min. Reaction solution 1 and solution C are then injected into the polyethylene pipe connected to the outlet at the lower end of the second Y-shaped pipe. The polyethylene pipe corresponding to the second Y-shaped pipe is kept at a temperature of 10–35°C using a jacketed water bath. The injection of ammonia in solution C rapidly transforms the acidic environment of reaction solution 1 into an alkaline environment. Under alkaline conditions (pH=9–11), the transparent reaction solution 1 quickly turns blue or white. Following the pipe length and flow rate, reaction solution 1 and solution C are uniformly mixed within the polyethylene pipe corresponding to the second Y-shaped pipe and react rapidly for 0.5 minutes. h, silica microspheres grow rapidly and quickly form a milky white suspension-like reaction solution two; solution C consists of ethanol and 25% ammonia water, and the pH of solution C is 9-11; the mixture of reaction solution one and solution C is added to the polyethylene pipe corresponding to the second Y-shaped pipe, and the molar ratio of tetraethyl orthosilicate, ammonia water and ethanol is 1:(0.2-0.5):(0.25-1.5); the polyethylene pipe corresponding to the second Y-shaped pipe has a length of 1 m, an inner diameter of 0.5 mm and a wall thickness of 0.1 mm;

[0017] Step 3 is as follows: Reaction solution 2 is introduced into the feed inlet (1 m long) at one side of the upper end of the third Y-shaped pipe. Under alkaline conditions of reaction solution 2, solution D is injected into the feed inlet at the other side of the upper end of the third Y-shaped pipe at a flow rate of 0.05~1 ml / min. Reaction solution 2 and solution D are then injected into a stirred quartz flask connected to the outlet at the lower end of the third Y-shaped pipe. Solution D consists of ethanol and 3-mercaptopropyltrimethoxysilane (MPTMS). The molar ratio of tetraethyl orthosilicate, 3-mercaptopropyltrimethoxysilane, and ethanol added to the stirred quartz flask at the lower end of the third Y-shaped pipe is 1:(0.1~0.25):(0.25~1.5). The stirred quartz flask is then kept at 10~35 ℃ in a jacketed water bath for 1~6 days. h. After uniformly mixing reaction solution 2 and solution D in a stirred quartz flask, they react under the catalysis of ammonia water. 3-Mercaptotrimethoxysilane is rapidly hydrolyzed, and self-polymerization and silanol copolymerization occur on the surface of silica microspheres in reaction solution 2. The silica microspheres are then matured, and finally reaction solution 3 is obtained, which has silica microspheres with shell grafted thiol groups.

[0018] Preferably, step 3 is followed by the following separation and drying steps:

[0019] Silica microspheres with thiol-grafted shells were separated from reaction solution 3 by centrifugation or filtration. The silica microspheres were washed repeatedly 3-4 times with electronic-grade anhydrous ethanol and electronic-grade ultrapure water, and centrifugation or filtration was performed after each wash. The air in the vacuum oven was replaced with high-purity nitrogen with a purity ≥ 99.999%, and nitrogen was continuously introduced for protection during the drying process. The washed silica microspheres were then dried.

[0020] As a preferred option, in step 1:

[0021] Tetraethyl orthosilicate (TEOS) in solution B is completely hydrolyzed into silanol Si(OH)4 and oligomeric silanols under acidic conditions. The hydrolysis is linear under acidic conditions. Branched silanols are also present.

[0022] .

[0023] As a preferred option, in step 2:

[0024] After being injected into solution C, the silanol rapidly undergoes condensation polymerization under alkaline conditions (this is crucial for ensuring the uniformity of the microspheres). The condensation polymerization is much faster than the hydrolysis, and the system quickly changes from a transparent sol with a slight bluish-white tinge to turbidity, and then silica microspheres precipitate out.

[0025] .

[0026] As a preferred option, in step 3:

[0027] After being injected into solution D, 3-mercaptotrimethoxysilane rapidly hydrolyzes under alkaline conditions:

[0028] ;

[0029] The hydrolysis products of 3-mercaptotrimethoxysilane rapidly copolymerize with silanols under alkaline conditions, and some of the hydrolysis products of 3-mercaptotrimethoxysilane undergo self-polymerization.

[0030] The copolymerization reaction is as follows:

[0031] ,

[0032] The self-polymerization reaction is:

[0033] .

[0034] The beneficial effects of this invention are:

[0035] The preparation method of this invention synthesizes silica microspheres with thiol-grafted shells through a pipeline reaction, segmented feeding, and temperature control within specific zones. This method effectively suppresses excessively small particle size and agglomeration during the reaction, controlling the particle size of the silica microspheres to 0.3–5 μm, thereby ensuring the uniformity of the silica microsphere size.

[0036] This invention maintains the metal impurity content in the prepared thiol-modified silica microspheres to less than 1 ppb through high-purity environmental control, screening of electronic-grade raw materials, and selection of precise impurity removal processes. The surface thiol groups (-SH) can specifically adsorb trace transition metals in the photoresist. etc.), precious metals ( etc.) and heavy metals ( (etc.), with high adsorption rate, removing impurities from the source without secondary pollution.

[0037] This invention solves the defects of traditional modified microspheres, such as uneven sphere size, wide particle size dispersion, low purity, and difficulty in removing impurities. Its advantages are prominent: mercapto-encapsulated silica microspheres increase adsorption efficiency and reduce desorption difficulty. They can be directly used in photoresist solvents or photoresist systems, improving material purity and process stability. Attached Figure Description

[0038] Figure 1 This is a SEM image of the mercapto-modified silica microspheres obtained in the embodiments of the present invention. Detailed Implementation

[0039] The present invention will be further described below with reference to embodiments. The description of the embodiments below is only for the purpose of helping to understand the present invention. It should be noted that those skilled in the art can make several modifications to the present invention without departing from the principle of the present invention, and these improvements and modifications also fall within the protection scope of the claims of the present invention.

[0040] As one embodiment, a method for preparing thiol-modified silica microspheres includes the following steps:

[0041] Preparation: The experiment was conducted in a Class 10,000 laboratory. All raw materials, solvents, and high-purity water were of electronic grade. All connection parts were made of PTFE materials. All instruments, pipes, and other auxiliary equipment were cleaned by soaking in electronic grade ethanol and electronic grade high-purity water before use.

[0042] I. Acidic hydrolysis:

[0043] The inlets on both sides of the upper end of the Y-shaped pipe are connected to two syringe pumps, which are respectively filled with solution A and solution B. Solution A consists of 6.9 ml of ethanol, 1.8 ml of water and 0.3 ml of concentrated hydrochloric acid; solution B consists of 6.77 ml of ethanol and 2.23 ml of tetraethyl orthosilicate (TEOS).

[0044] Solution A and solution B are simultaneously injected into a polyethylene pipe connected to the lower outlet of the Y-shaped pipe (the flow rate at the lower outlet of the Y-shaped pipe is 0.3 ml / min) at a flow rate of 0.15 ml / min through the inlets on both sides of the upper end of the Y-shaped pipe; the polyethylene pipe is 2 m long, has an inner diameter of 0.5 mm, and a wall thickness of 0.1 mm.

[0045] The polyethylene pipe is kept at 35 ℃ by a jacketed water bath. Solution A and solution B are uniformly mixed in the polyethylene pipe and reacted for 1 h. After solution A and solution B are mixed, there is a slight milky white turbidity in the first half of the polyethylene pipe. As the reaction proceeds, the solution in the pipe gradually becomes transparent and clear. When there is no white turbidity or flocculent matter in the solution in the pipe, it indicates that the acid hydrolysis reaction has terminated, and reaction solution one is obtained. Under acidic conditions (pH 1.5~2.0), TEOS is stably hydrolyzed, directionally generating linear and branched oligomeric silanols. The acidic conditions inhibit the premature polycondensation of silanols. The residence time in the pipe is fixed, and the degree of hydrolysis is highly uniform, which can yield highly active and highly uniform oligomeric silanols.

[0046] II. Basic condensation nucleation

[0047] Solution C consists of 5.6 ml of ethanol and 0.4 ml of 25% ammonia solution;

[0048] Reaction solution 1 is introduced into the inlet on one side of the upper end of the second Y-shaped pipe at a flow rate of 0.3 ml / min. Simultaneously, solution C is injected into the inlet on the other side of the upper end of the second Y-shaped pipe at a flow rate of 0.2 ml / min. Reaction solution 1 and solution C are then injected into the polyethylene pipe connected to the outlet at the lower end of the second Y-shaped pipe. The polyethylene pipe corresponding to the second Y-shaped pipe is kept at a temperature of 10–35°C using a jacketed water bath. The injection of ammonia in solution C rapidly transforms the acidic environment of reaction solution 1 into an alkaline environment. Under alkaline conditions (pH=9–11), the transparent reaction solution 1 quickly turns blue or white. According to the pipe length and flow rate, reaction solution 1 and solution C are uniformly mixed in the polyethylene pipe corresponding to the second Y-shaped pipe and react rapidly for 0.5 minutes. h, silica microspheres grow rapidly and quickly form a milky white suspension-like reaction solution II; added to the mixture of reaction solution I and solution C in the polyethylene pipe corresponding to the second Y-shaped pipe, the molar ratio of tetraethyl orthosilicate, ammonia and ethanol is 1:(0.02~0.2):(0.25~1.5); the polyethylene pipe corresponding to the second Y-shaped pipe has a length of 1 m, an inner diameter of 0.5 mm and a wall thickness of 0.1 mm; under instantaneous alkaline conditions, silanol undergoes explosive condensation polymerization, nucleation is synchronous, growth is uniform, and the particle size distribution width (PDI) of silica microspheres can be controlled extremely efficiently.

[0049] III. Alkaline grafting:

[0050] Reaction solution 2 is introduced into the feed inlet (1 m long) at the upper end of the third Y-shaped pipe. Under alkaline conditions, solution D is injected into the other feed inlet at a flow rate of 0.1 ml / min. Reaction solution 2 and solution D are then injected into a stirred quartz flask connected to the lower outlet of the third Y-shaped pipe. Solution D consists of 2.8 ml of ethanol and 0.4 ml of 3-mercaptopropyltrimethoxysilane (MPTMS). The molar ratio of tetraethyl orthosilicate, 3-mercaptopropyltrimethoxysilane, and ethanol added to the stirred quartz flask at the lower end of the third Y-shaped pipe is 1:(0.1–0.25):(0.25–1.5). The stirred quartz flask is then kept at 10–35 °C in a jacketed water bath for 1–6 days. h, after reaction solution two and solution D are uniformly mixed in a stirred quartz flask, they react under the catalysis of ammonia water. 3-Mercaptotrimethoxysilane is rapidly hydrolyzed, and self-polymerization and silanol copolymerization on the surface of silica microspheres in reaction solution two occur simultaneously. The silica microspheres are then matured, and finally reaction solution three is obtained. Reaction solution three has silica microspheres with shell grafted thiol groups.

[0051] Under alkaline conditions, the methoxy group of MPTMS is more readily hydrolyzed than the ethoxy group of TEOS, with hydrolysis occurring almost instantaneously. The methoxy group rapidly hydrolyzes to generate a trihydroxysilane intermediate. Under hydroxyl catalysis, the silanol groups undergo rapid dehydration condensation, forming Si–O–Si bonds and constructing a cross-linked network structure. The subsequently added MPTMS forms Si–O–Si bonds containing thiol groups, constructing a cross-linked network structure covering the surface of SiO2 microspheres. Alternatively, newly formed SH–Si–OH bonds directly and rapidly condense with exposed Si–OH bonds on the microsphere surface to produce stable Si–O–Si bonds, ultimately generating size-stable silica microspheres coated with thiol groups. The grafting amount of thiol groups in the shell of the resulting silica microspheres is maintained between 0.2 and 2.2 mmol / g to preserve the stability, dispersibility, uniformity, and thiol group coverage of the spheres. Under alkaline conditions, the hydrolysis and grafting of MPTS are completed in one step, avoiding excessive self-polymerization of MPTS and an excessive amount of free silane. Grafting is performed shortly after the microspheres are formed. This has the advantages of providing numerous surface active sites, a high grafting rate, and resulting in thiol-modified silica microspheres with uniform shell structure, stable density, and consistent surface properties. The thiol groups are primarily grafted onto the outer shell of the microspheres, making them more effective at adsorbing metallic impurities and also easier to desorb and recycle, significantly improving adsorption performance and recycling rate.

[0052] IV. Separation and Drying: Silica microspheres with thiol-grafted shells were separated from reaction solution III by centrifugation or filtration. The microspheres were washed repeatedly 3-4 times with alternating electronic-grade anhydrous ethanol and electronic-grade ultrapure water, followed by centrifugation or filtration after each wash. The air in the vacuum oven was replaced with high-purity nitrogen (≥ 99.999%), and nitrogen was continuously introduced for protection during the drying process. The washed silica microspheres were then dried. SEM images of the resulting thiol-modified silica microspheres are shown below. Figure 1 As shown in the figure, the thiol-modified silica microspheres with shells are generally regular spherical in shape, exhibit excellent monodispersity, no obvious agglomeration, and uniform particle size distribution, with a typical particle size range of 0.3–5 μm. The microspheres have smooth surfaces without obvious defects, and the shell structure is uniform and dense, tightly bound to the core without delamination or detachment. They are regularly shaped and rounded, with good particle dispersibility, no adhesion or breakage, and exhibit uniform overall morphology and strong stability.

[0053] Based on the above embodiments, the prepared thiol-modified silica microspheres were tested to verify the grafting of thiol groups in the thiol-modified silica shell:

[0054] Targeting the specificity of the thiol (-SH) group: Maleimide (Mal) is a highly specific covalent reactive group of thiol (-SH). Under neutral / weakly alkaline conditions (pH 6.5–7.5), at room temperature, and in the dark, it can undergo a Michael addition reaction with the thiol group to form a stable thioether bond (CSC). Therefore, fluorescein-5-maleimide (FAM-Mal) was chosen to react with the thiol group to characterize whether the thiol group is grafted onto the silica microspheres and its distribution. Additionally, the thiol (-SH) group has a characteristic absorption peak in the infrared spectrum, which can also be used to characterize whether the thiol group is grafted onto the silica microspheres.

[0055] Steps (i) to (iii) above all occur within the pipeline, allowing for highly precise control over flow rate, temperature, mixing, and residence time. The rapid mixing speed significantly improves reaction efficiency, eliminating localized over-concentration or excessively high acidity / alkalinity levels, thus achieving continuous and automated operation throughout the entire process. Since the reactions take place entirely within the pipeline, environmental influences are avoided. This prevents batch-to-batch variations and uneven temperature control common in one-pot processes.

[0056] Test Method 1:

[0057] (1) Sample preparation: Sample 1 is silica microspheres prepared from pure TEOS without the addition of MPTMS; Sample 2 is thiol-shell silica microspheres prepared in the above example; Sample 3 is 20 mg of each of the modified silica microspheres prepared by polycondensation of a mixed solution of MPTS and TEOS in the same reaction ratio.

[0058] (2) Solvent: 10 ml of ethanol / PBS buffer (pH=7.0);

[0059] (3) Ultrasound for 5 min to form a uniformly dispersed emulsion;

[0060] (4) Preparation of fluorescent probe solution: Fluorescent maleimide probe: 1 mg, dissolved in 1 ml anhydrous DMSO;

[0061] (5) Labeling reaction: Add 100 μL of probe solvent to the suspension respectively; stir the reaction in the dark at room temperature for 3 h; centrifuge (8000-10000 rpm, 10 min) and discard the supernatant; wash repeatedly with ethanol 3-5 times to remove unreacted free probe.

[0062] (6) Sample preparation and observation: Take a small amount of the washed microspheres, disperse them in ethanol, drop them onto a quartz slide and let them dry. Observe them with a fluorescence microscope. The observation results are shown in Table 1 below:

[0063] Table 1. Fluorescence intensity observation results of samples 1 to 3

[0064]

[0065] As can be seen from Table 1 above, no obvious fluorescence signal was observed in the interior or surface of Sample 1, indicating that the unmodified silica microspheres cannot specifically bind to the fluorescent probe. Sample 2 only exhibited a high-intensity fluorescent ring on the surface of the microspheres, with no obvious fluorescence signal inside, and the fluorescence distribution showed typical shell characteristics. Sample 3 had strong fluorescence signals both inside and outside, with the signal on the outer layer slightly higher than that on the inside, indicating that it is a homogeneous doped structure formed by the co-condensation of TEOS and MPTMS.

[0066] Based on the fluorescence signal data in Table 1, it can be seen that: Sample 1, which has not undergone thiol modification, lacks sites for reaction with the probe; Sample 3 exhibits uniform luminescence, confirming that MPTMS participates in polycondensation simultaneously inside and on the surface of the microspheres; while Sample 2 shows strong fluorescence only on the surface, with virtually no fluorescence inside, clearly indicating that thiol groups are mainly enriched and bonded to the shell region of the silica microspheres. Under the same MPTMS addition amount, the fluorescence intensity of the surface layer of Sample 2 is significantly higher than that of Sample 3, indicating that its surface thiol density is much higher than that of the co-condensation system.

[0067] Test Method 2:

[0068] (1) Sample preparation: Sample 1 is silica microspheres prepared from pure TEOS without the addition of MPTMS; Sample 2 is thiol-shell silica microspheres prepared in the above example;

[0069] (2) Sample drying: Place the sample 1 and sample 2 to be tested in a vacuum drying oven at 60℃ for 2 hours to remove adsorbed water.

[0070] (3) Sample testing: The dried silica microspheres and dried KBr were mixed at a mass ratio of 1:100, ground thoroughly and uniformly, and then pressed into transparent thin films. Pure KBr thin films were used as blank controls. The samples were tested on a Fourier transform infrared spectrometer. Test conditions: Scanning range 4000–400 cm⁻¹ -1 4 cm resolution -1 The number of scans was 32.

[0071] (4) Results analysis: Infrared spectroscopy results show that sample 1 (pure silica microspheres) is only at 1050-1250 cm⁻¹ -1 Strong and broad characteristic absorption peaks of the Si–O–Si framework appear at 3200–3600 cm⁻¹. -1 A broad peak for surface hydroxyl groups and adsorbed water was observed at the 2550–2590 cm⁻¹, but no characteristic signal of thiol groups was found. Sample 2 (after thiol modification) showed a peak for silica microspheres at 2550–2590 cm⁻¹. -1 A distinct S–H stretching vibration characteristic absorption peak appears in the range of 2850–2950 cm⁻¹. -1The presence of a C–H stretching vibration absorption peak indicates that the thiol group has been successfully grafted onto the surface of the silica microspheres.

[0072] Based on the above embodiments, the metal ion adsorption effect of the prepared thiol-modified silica microspheres was tested to verify the grafting of thiol groups in the thiol-modified silica shell, wherein:

[0073] The adsorption conditions were as follows: 0.5 wt% of mercapto-modified silica microspheres were added to the photoresist solvent system (PGMEA / cyclohexanone) and stirred at room temperature for 30 min.

[0074] The detection method was ICP-MS to determine the concentration of metal ions. The detection results are shown in Table 2 below:

[0075] Table 2. Adsorption of metal ions by the thiol-modified silica microspheres prepared in the embodiments of the present invention.

[0076] As can be seen from Table 2 above without any doubt: thiol groups are uniformly embedded in the surface of microspheres through a precise and controllable hydrolysis-condensation reaction, endowing the microspheres with a strong selective adsorption capacity for metal ions; the sulfur atoms in the thiol groups provide lone pairs of electrons, which interact with transition metals ( ), precious metals ( ) and heavy metals ( Ions form stable coordination bonds (generating SiO2-SM) n+ It possesses a high binding constant and is not easily dissociated. In photoresist organic solvent systems, it can efficiently capture trace amounts (ppb level) of various metal ions, achieving adsorption and removal rates exceeding 94%. Among these, it is particularly effective for… The removal rate exceeds 98%, and it is not easily detached due to stirring or temperature fluctuations, effectively removing residual metal impurities in photoresist.

[0077] In summary, during the adsorption performance test, the entire reaction system's generation environment (no impurity contamination, closed and controllable) and the reagents used (electronic-grade anhydrous ethanol, ultrapure water, etc.) are strictly adapted to the photoresist application scenario, with no harmful impurities remaining. The resulting mercapto-modified silica microspheres can be directly used for the adsorption and removal of gold impurities in photoresists without additional modification or purification processes, significantly reducing the process cost and operational difficulty of photoresist preparation, and meeting the stringent requirements of high-precision electronic materials, semiconductor photoresists, and other fields.

Claims

1. A mercapto-modified silica microsphere, characterized in that: It includes a silica core and a mercapto-modified silica shell covering the silica core; In the shell layer: the amount of thiol grafting is 0.2–2.2 mmol / g, and the particle size of the silica microspheres is 0.3–5 μm.

2. The mercapto-modified silica microspheres according to claim 1, characterized in that: The metal impurity content in the thiol-modified silica microspheres is less than 1 ppb.

3. A method for preparing mercapto-modified silica microspheres as described in claim 1, characterized in that, Includes the following steps: Step 1, Acidic Hydrolysis: Solution A and Solution B are simultaneously injected into a polyethylene pipe connected to the outlet at the lower end of the Y-shaped pipe through the inlets on both sides of the upper end of the Y-shaped pipe at the same flow rate; Solution A consists of ethanol, water, and concentrated hydrochloric acid, and the pH of Solution A is 1.5-2; Solution B consists of ethanol and tetraethyl orthosilicate; the molar ratio of tetraethyl orthosilicate, water, ethanol, and concentrated hydrochloric acid added to the mixture of Solution A and Solution B in the polyethylene pipe is 1:(3-15):(6-20):(0.01-0.1); the polyethylene pipe is kept warm by a jacketed water bath, and after Solution A and Solution B are mixed in the polyethylene pipe, the reaction is carried out for a set time to obtain a transparent and clear reaction solution without white turbidity or flocculent matter. Step 2, alkaline condensation nucleation: The reaction solution one is introduced into the feed inlet on one side of the upper end of the second Y-shaped pipe, while solution C is injected from the feed inlet on the other side of the upper end of the second Y-shaped pipe. The reaction solution one and solution C are injected into the polyethylene pipe connected to the discharge port at the lower end of the second Y-shaped pipe. Solution C is composed of ethanol and 25% ammonia water, and the pH of solution C is 9-11. The mixture of reaction solution one and solution C is added to the polyethylene pipe corresponding to the second Y-shaped pipe. The molar ratio of tetraethyl orthosilicate, ammonia water and ethanol is 1:(0.02-2.5):(0.25-1.5). The polyethylene pipe corresponding to the second Y-shaped pipe is kept warm by a jacketed water bath. After the reaction solution one and solution C are uniformly mixed in the polyethylene pipe corresponding to the second Y-shaped pipe, the reaction is carried out for a set time. Silica microspheres are rapidly formed, forming a milky white suspension-like reaction solution two. Step 3, Alkaline Grafting: The reaction solution 2 is introduced into the inlet on one side of the upper end of the third Y-shaped pipe. Under alkaline conditions of the reaction solution 2, solution D is injected into the inlet on the other side of the upper end of the third Y-shaped pipe. The reaction solution 2 and solution D are then injected into a stirred quartz flask connected to the outlet at the lower end of the third Y-shaped pipe. Solution D consists of ethanol and 3-mercaptotrimethoxysilane. The molar ratio of tetraethyl orthosilicate, 3-mercaptotrimethoxysilane, and ethanol added to the stirred quartz flask at the lower end of the third Y-shaped pipe is 1:(0.1~0.25):(0.25~1.5). The stirred quartz flask is kept warm in a jacketed water bath. The reaction solution 2 and solution D are uniformly mixed in the stirred quartz flask and reacted for a set time. The silica microspheres are then matured, finally yielding reaction solution 3, which contains silica microspheres with thiol-grafted shells.

4. The method for preparing thiol-modified silica microspheres according to claim 3, characterized in that: Step 1 specifically involves: simultaneously injecting solutions A and B through the inlets on both sides of the upper end of a Y-shaped pipe into a polyethylene pipe connected to the lower outlet of the Y-shaped pipe at a flow rate of 0.15 ml / min. The polyethylene pipe is then kept at 35 ℃ using a jacketed water bath. Solutions A and B are mixed within the polyethylene pipe and reacted for 1 h to obtain a transparent, clear reaction solution without white turbidity or flocculent matter. Solution A consists of ethanol, water, and concentrated hydrochloric acid, and its pH is maintained between 1.5 and 2. Solution B consists of ethanol and tetraethyl orthosilicate. The molar ratio of tetraethyl orthosilicate, water, ethanol, and concentrated hydrochloric acid added to the polyethylene pipe is 1:(3-8):(8-20):(0.01-0.1). The polyethylene pipe has a length of 2 m, an inner diameter of 0.5 mm, and a wall thickness of 0.1 mm. Step 2 specifically involves: introducing reaction solution one into the inlet on one side of the upper end of the second Y-shaped pipe at a flow rate of 0.3 ml / min, while simultaneously injecting solution C into the inlet on the other side of the upper end of the second Y-shaped pipe at a flow rate of 0.2 ml / min. Reaction solution one and solution C are then injected into the polyethylene pipe connected to the outlet at the lower end of the second Y-shaped pipe. The polyethylene pipe corresponding to the second Y-shaped pipe is kept at a temperature of 10–35°C using a jacketed water bath. The reaction solution one and solution C are then uniformly mixed within the polyethylene pipe corresponding to the second Y-shaped pipe and reacted for 0.5 minutes. h. Silica microspheres are rapidly molded to form a milky white suspension-like reaction solution two; solution C consists of ethanol and 25% ammonia water, and the pH of solution C is 9-11; the mixture of reaction solution one and solution C is added to the polyethylene pipe corresponding to the second Y-shaped pipe, with the molar ratio of tetraethyl orthosilicate, ammonia water, and ethanol being 1:(0.2-0.5):(0.25-1.5); the polyethylene pipe corresponding to the second Y-shaped pipe has a length of 1 m, an inner diameter of 0.5 mm, and a wall thickness of 0.1 mm; Step 3 specifically involves: introducing reaction solution 2 into the inlet on one side of the upper end of the third Y-shaped pipe; under alkaline conditions of reaction solution 2, injecting solution D into the inlet on the other side of the upper end of the third Y-shaped pipe at a flow rate of 0.05~1 ml / min; injecting reaction solution 2 and solution D into a stirred quartz flask connected to the outlet at the lower end of the third Y-shaped pipe; solution D is composed of ethanol and 3-mercaptotrimethoxysilane, and the molar ratio of tetraethyl orthosilicate, 3-mercaptotrimethoxysilane, and ethanol added to the stirred quartz flask at the lower end of the third Y-shaped pipe is 1:(0.1~0.25):(0.25~1.5); and maintaining the stirred quartz flask at 10~35 ℃ in a jacketed water bath for 1~6 days. h, after the reaction solution two and the solution D are uniformly mixed in the quartz flask with a stirrer, they react under the catalysis of ammonia water to finally obtain reaction solution three, which has silica microspheres with shell grafted with thiol groups.

5. The method for preparing thiol-modified silica microspheres according to claim 4, characterized in that, Following step 3, the following separation and drying steps are also included: Silica microspheres with thiol-grafted shells were separated from the reaction solution by centrifugation or filtration. The silica microspheres were washed repeatedly with electronic-grade anhydrous ethanol and electronic-grade ultrapure water 3-4 times, and centrifugation or filtration was performed after each wash. The air in the vacuum oven was replaced with nitrogen gas with a purity of ≥ 99.999%, and nitrogen gas was continuously introduced for protection during the drying process. The washed silica microspheres were then dried.

6. The method for preparing thiol-modified silica microspheres according to claim 3, characterized in that, In step 1: The tetraethyl orthosilicate in solution B hydrolyzes into silanol Si(OH)4 under acidic conditions. 。 7. The method for preparing thiol-modified silica microspheres according to claim 6, characterized in that, In step 2: After injection into the injection solution C, the silanol rapidly undergoes condensation polymerization under alkaline conditions to precipitate silica microspheres: 。 8. The method for preparing thiol-modified silica microspheres according to claim 7, characterized in that, In step 3: After being injected into solution D, 3-mercaptotrimethoxysilane rapidly hydrolyzes under alkaline conditions: ； The hydrolysis products of 3-mercaptotrimethoxysilane copolymerize with the silanol under alkaline conditions, and some of the hydrolysis products of 3-mercaptotrimethoxysilane undergo self-polymerization. The copolymerization reaction is as follows: ， The self-polymerization reaction is as follows: 。

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