CN100363255C - Purification method of special nano-silica sol for VLSI - Google Patents

Abstract

The present invention discloses a purification method of special nanometer silicasol for a very large scale integrated circuit. The present invention has the goal of providing the silicasol purification method for effectively reducing the metallic ion content in silicasol in order to improve the wafer quality. Hydrochloric acid is injected into cation exchange resin and is agitated for preparing acidic cation exchange resin; then, alkali silicasol with high metallic ion content is added into the acidic cation exchange resin for exchange; simultaneously, Zeta electric potential is detected, and acidic silicasol is obtained; sodium hydroxide is injected into the anion exchange resin and is agitated for preparing alkalescence anion exchange resin; the acidic silicasol is added into the alkalescence anion exchange resin for exchange; simultaneously, the Zeta electric potential is detected, and alkaline silicasol is obtained; afterwards, the exchanged alkali silicasol is added into the acidic cation exchange resin for exchange; simultaneously, the Zeta electric potential is detected, and the acidic silicasol with low metallic ion content is obtained. The present invention meets the purity requirement, and has the advantages of low equipment cost and short purification time.

Description

Purification method of special nano-silica sol for VLSI

technical field

The invention belongs to a method for purifying nano-abrasives, in particular to a method for purifying silica sol used for CMP special grinding and polishing in the field of microelectronic processing.

Background technique

With the development of large-scale integrated circuits, the continuous improvement of integration and the continuous reduction of line width, high density, thin lines, and shallow junctions in the development of integrated circuit technology have become the mainstream. If the surface of the silicon substrate is contaminated by harmful heavy metal impurities during processing, it will affect the interface state of the device, increase the static power consumption current of the device, reduce the breakdown strength of the _SiO2 dielectric, weaken the antistatic ability, and drift the threshold voltage. Early failure occurs due to device power aging, especially in sensitive devices such as CMOS and CCD. It can also lead to weakened anti-nuclear radiation capabilities of military devices, product performance, reliability indicators, and device yields. Metal contamination will also destroy the integrity of the thin oxide layer, increase the leakage current density, and reduce the minority carrier lifetime; active ions such as sodium will cause mobile charges in the oxide layer, affecting the stability of MOS devices; heavy metal ions will increase the dark current; Diffused ions, such as copper and nickel, are easy to deposit on the silicon surface and form microstructural defects; iron precipitation will thin the gate oxide layer. In addition, copper will form copper-rich precipitates at the silicon dioxide interface. At high temperatures (1200°C/20s), supersaturated copper silicides will bend and crack the oxide layer until it penetrates, and form at low temperatures (900°C/20s). Lenticular precipitation, thinning the oxide layer. When the metal is seriously contaminated, haze defects (Haze) will also be formed. Alkali metal ions (especially Na ⁺ ) are the most harmful mobile ions in the current microelectronics technology. They will enter the substrate or dielectric layer during the CMP process, causing partial punch-through of the device and increasing the leakage current. The working reliability of the chip is reduced and the life of the device is shortened. Therefore, the microelectronics industry must control the content of harmful metal impurities and the like. At present, for a 64M DRAM device with a line width of 0.35 μm, the critical particle size affecting the circuit is 0.06 μm, and the metal impurities on the surface of the polished sheet should all be less than 5×10 ¹⁵ at/cm ² . The general ULSI process requires The metal contamination on the provided substrate is less than 10 ¹⁰ atom/cm ² .

In the silicon wafer processing and device manufacturing process, all external media in contact with the silicon wafer may cause the silicon wafer to be contaminated by harmful metals. The polishing process is the final and most important process in the wafer processing process, and SiO ₂ Colloidal sol is the most widely used nano-abrasive in CMP with the best effect in the ULSI process. The newly polished wafer will spontaneously absorb various impurities, especially the adsorption of metal ions. If the content of metal ions in the polishing solution is high, after polishing A large number of metal ions remain on the surface of the wafer, which not only increases the burden of the cleaning process, but also increases the metal ions entering the wafer during the polishing process, and these metal ions entering the wafer are difficult to clean. With the development of IC technology, the requirements for the purification of nano- _SiO2 for CMP will become more and more stringent. At present, the production of silica sol mainly uses water glass as a raw material, resulting in a large amount of metal ions (especially Na ⁺ ) contained in silica sol products. Therefore, to remove impurities in silica sol, it is very necessary to purify silica sol.

At present, the purification process of silica sol has not formed its own technology. Quite a few literatures only mention "post-treatment", and only a few literatures mention the method of cationic resin exchange treatment. The micelle structure of silica sol and its schematic diagram are shown in accompanying drawing 1, and the electric double layer structure of silica sol is as shown in accompanying drawing 2, and the micelle of silica sol is to be core by an amorphous mSiO ₂ , and silicon is adsorbed on the surface. Acid and silicic acid negative ions (H ₂ SiO ₄ , H ₃ SiO ₄ ^- ), part of the counterion zNa ⁺ is adsorbed in the compact layer, and the other part (yz) Na ⁺ is distributed in the diffusion layer, forming an electric double layer structure. The charge y is called the total potential, and the charge (yz) is called the zeta potential or Zeta potential, ζ potential. Due to the solvation, the ions around the colloidal particles are all in the solvated form, so that a high-viscosity hydration film is formed, and its thickness is equivalent to the thickness of the diffuse electric double layer. In the early stage of cation exchange, the metal ions in the aqueous phase outside the micelles are free ions in a free state, and the electrostatic force between the metal ions and the colloidal particles on the periphery of the micelles diffusion layer is very weak, and it is very easy to be adsorbed by substances with strong adsorption force. Therefore, the strongly acidic cation exchange resin can quickly absorb and exchange these two parts of the metal ions, and at the same time release the H ⁺ of equal charge, and then neutralize all the OH ^- in the water phase, because the amount of H ⁺ is much greater than that of OH ^- , a large amount of excess H ⁺ makes the pH value of the solution quickly cross the neutral zone and enter the acid zone, so that the exchanged silica sol becomes acidic, the content of metal ions decreases, and the absolute value of Zeta potential increases.

After the silica sol undergoes cation exchange, Na ⁺ and other metal cations on the periphery of the silica sol diffusion layer have been removed, and the remaining Na ⁺ and other metal cations mainly exist in the inner periphery of the diffusion layer and the tight layer. The attraction is strong, and a layer of high viscosity hydration film is attached to the surface of the colloidal particles. This layer of hydration film slows down the speed of H ⁺ diffusion into the tight layer to replace Na ⁺ and other metal cations. H ⁺ slowly enters the compact layer, so that the pH value on the surface of the colloidal particles changes slowly. A large number of Na ⁺ and other metal cations in the silica sol are replaced by H ⁺ , and the hydration ability of H ⁺ is stronger than that of Na ⁺ and other metal cations. These H ⁺ leads to the thickening of the hydration film around the colloidal particles, which seriously hinders the mutual replacement speed of Na ⁺ and other metal cations and H ⁺ . Therefore, purely using cation exchange resin to purify silica sol, although part of the metal ions of silica sol can be removed, there are still a large amount of metal ions inside, the purification effect is not good, and the metal ion content increases with the increase in the number of cation exchange resin treatments. Not much will change.

Contents of the invention

The present invention aims to overcome the deficiencies in the prior art and provide a method for purifying silica sol that can effectively reduce the content of metal ions in silica sol products to improve wafer quality.

The present invention realizes through following technical scheme:

A method for purifying special nano-silica sol for VLSI, characterized in that it comprises the following steps:

(1) At first, 3%-10% hydrochloric acid solution is injected into the cation exchange resin and stirred, so that the cation exchange resin regeneration is complete, wherein the volume exchange capacity of hydrochloric acid and wet cation exchange resin is 1.4-1.8 milliequivalents/ml, leave standstill After layering, the upper layer solution is removed, and the remaining cation exchange resin is rinsed with deionized water until its pH value is in the range of 2-4 to obtain an acidic cation exchange resin;

(2) Then the alkaline silica sol with metal ion content higher than 100ppm is added in the acidic cation exchange resin prepared in the above step (1) under continuous stirring, wherein, the alkaline silica sol and the acidic cation exchange resin The ratio of the amount of the substance is 1:2-1:5, exchange for 10-60min under stirring, and measure the Zeta potential of the exchange solution at the same time, stop stirring after the absolute value is 30mv-60mv, and let it stand for stratification Acidic silica sol is discharged;

(3) inject 3%-10% sodium hydroxide solution into the anion exchange resin and stir to make the anion exchange resin regenerate completely, wherein the volume exchange capacity of sodium hydroxide and wet anion exchange resin is 1.2-1.6 mg equivalent/ml , after static stratification, the upper layer solution is removed, and the remaining anion exchange resin is rinsed with deionized water until its pH value is between 9-10 to obtain a basic anion exchange resin;

(4) Then the acidic silica sol prepared in the above step (2) is added to the basic anion exchange resin prepared in the above step (3), wherein the amount of substance of the acidic silica sol and the basic anion exchange resin The ratio is 1:2-1:5, exchanged for 10-60min while stirring, and at the same time measure the Zeta potential of the exchanged solution so that the absolute value is 30mv-60mv, then stop stirring, and after standing for stratification, the material is discharged to obtain a significant Alkaline silica sol;

(5) Add the exchanged alkaline silica sol prepared in step (4) into the acidic cation exchange resin prepared in step (1) while stirring, wherein the alkaline silica sol and the acidic cation The ratio of the amount of substances in the exchange resin is 1:2-1:5, exchange for 10-60min under the condition of stirring, measure the Zeta potential of the exchange solution at the same time, stop stirring after making its absolute value 30mv-60mv, let it stand and divide After layering, the material is discharged to obtain acidic silica sol with metal ions reaching several ppm.

In order to make the polishing solution whose main component is silica sol better remove metal ions during the polishing process, and at the same time convert the acidic silica sol into alkaline silica sol, after the cation-anion-cation exchange, the above-mentioned cation-anion-cation The acidic silica sol obtained after the exchange is added to the FA/O chelating agent under stirring to obtain the final alkaline silica sol product, wherein the volume ratio of the acidic silica sol to the chelating agent is 1000:2-10.

The used cation exchange resin is strongly acidic styrene type cation exchange resin, and the used anion exchange resin is strongly basic quaternary ammonium anion exchange resin.

The particle size of the purified silica sol is 20nm-60nm.

Principle of action of the present invention is as follows:

Firstly, the metal ions in the outer water phase of the silica sol micelles and the metal ions on the periphery of the micelles diffusion layer are exchanged with a cation exchange resin. After the silica sol undergoes cation exchange, the Na ⁺ and other metal cations on the periphery of the silica sol diffusion layer have been removed, and the remaining Na ⁺ and other metal cations mainly exist in the inner periphery of the diffusion layer and the tight layer. Thickening seriously hinders the mutual replacement speed of Na ⁺ and other metal cations and H ⁺ . Therefore, anion exchange resin is used for exchange. Anion exchange resin exchanges free anions (Cl ^- , silicate negative ions) in the water phase, releases OH ^- and neutralizes with the original H ⁺ of the water phase to generate water, and gradually makes the pH value Rising, so that the exchanged silica sol is alkaline, after the ion exchange balance, there are mainly unneutralized H ⁺ in the water phase, and the electrolyte concentration in the solution is greatly reduced. The thickness of the electric double layer of the colloid is inversely proportional to the concentration of the electrolyte. Therefore, after anion resin exchange, the thickness of the electric double layer of the colloid becomes tens of times of the original, and a large number of cations (Na ⁺ , H ⁺ ) that constitute the electric double layer structure are destroyed. Pushed to a position away from the glue core, the attraction between the glue core and the glue core is greatly weakened, and the viscosity of the hydration film is correspondingly reduced. A large amount of Na ⁺ and other metal cations in the diffusion layer and the tight layer diffuse into the water phase, and then use Cation exchange, adsorbing Na ⁺ and other metal cations in the aqueous phase, continues to reduce the metal ion content in the silica sol. In such a cycle, the control of the hydration film on ion diffusion is effectively released, and silica sol with less impurity content can be obtained. However, due to repeated repetitions to increase costs and reduce production efficiency, considering various factors, three ion exchanges of cation-yin-yang were selected to purify silica sol.

The present invention has following technical effect:

1. According to the exchange mechanism of ion exchange resin and the double electron layer structure of silica sol itself, the present invention utilizes the method of cation-anion-cation exchange resin to purify silica sol alternately. The selectivity order of some common ions in strong acidic cation exchange resins is: Fe ³⁺ Al ³⁺ Ca ²⁺ Mg ²⁺ K ⁺ Na ⁺ H ⁺ , and the selectivity order of some common ions in strongly basic anion exchange resins is: SO ₄ ^2- _NO3 ^- Cl ^- OH ^- F ^- _HCO3 ^- _HSiO3- ^. The first cation exchange removes the metal ions in the aqueous phase outside the silica sol micelles and the metal ions outside the micelles diffusion layer. Then introduce anion exchange resin for exchange, effectively release the control of hydration membrane on ion diffusion, make Na ⁺ and other metal cations in the diffusion layer and tight layer diffuse into the water phase in large quantities, and then use cation exchange to absorb the ions in the water phase Na ⁺ and other metal cations can greatly improve the exchange effect of cation exchange resin, greatly reduce the content of metal ions in silica sol products, and the purification effect is remarkable, which improves the quality of the wafer. The metal ion content of the silica sol obtained by the method can reach several ppm levels, which can meet the purity requirements of the ultra-large-scale integrated circuit processing technology CMP for the grinding material, so that the produced chips have high operating reliability and long service life of the device.

2. The present invention adopts FA/O chelating agent to regulate pH value, and FA/O chelating agent has special structure, and its structural representation is as shown in accompanying drawing 3, and this material chelating ring is many, does not contain metal ion, is soluble in water, It has great chelating ability. While adjusting the pH value, it can also effectively chelate residual metal ions during chemical mechanical polishing, further reduce the content of metal ions, and reduce the pollution of metal ions to the polishing sheet.

3. If the Zeta potential is greater than 30mv, the solution is more stable. The longer the exchange time, the smaller the metal ion content. The present invention controls the exchange time from two aspects of Zeta potential monitoring and ion exchange time, which not only guarantees the requirement of metal ion content, but also takes into account the influence of metal ion content on Zeta potential, ensures the stability of silica sol, and provides industrialization Necessary monitoring conditions are established to ensure the stability of silica sol quality and product repeatability in actual production, so that production can be automated. Considering the quality requirements and production efficiency comprehensively, the Zeta potential is selected to be 30-60mv, and the exchange time is 10-60min.

4. Adopting the method of the present invention has low equipment cost, short purification time and low energy consumption.

Description of drawings

The micelle structure and schematic diagram thereof of accompanying drawing 1 silica sol;

The electric double layer structure of accompanying drawing 2 silica sols;

The structural representation of accompanying drawing 3 chelating agents;

Accompanying drawing 4 Zeta potential test results.

Detailed ways

The present invention will be described in detail below in conjunction with specific examples.

The cation exchange resin used in the present invention is strongly acidic styrene type cation exchange resin, such as Nankai brand 001 × 7 type, U.S. Amber jet 1200Na, Germany Lewatit-100, Japan DiaionSK-1 etc., used anion exchange resin is strong base Non-toxic quaternary amine anion exchange resins, such as Nankai brand 201×7, American Amberlite IRA-400, German Lewatit M500, British Eerolite FF, etc. The ion exchange time should consider the Zeta potential factor of silica sol. When adjusting the pH value of the silica sol, the FA/O chelating agent, which not only has the function of adjusting the pH value, but also has the function of chelating metal ions, is used.

Example 1

Inject 1752ml, 3% hydrochloric acid solution into an ion exchange column equipped with 800ml Nankai brand 001×7 type cation exchange resin and stir. After stirring for 3 minutes, let it stand for stratification, remove the upper layer solution, and rinse the remaining cations with deionized water. Exchange the resin until its pH value is between 2-2.5 to obtain an acidic cation exchange resin.

Then the concentration is 30%, the particle diameter is 22nm, the alkaline silica sol 536g that metal ion content is higher than 100ppm joins in the above-mentioned acidic cation exchange resin of 400ml under the situation of continuous stirring, exchange 15min under the situation of stirring, measure simultaneously Exchange the Zeta potential of the solution so that its absolute value is above 30mv, then stop stirring, leave to stand for stratification, and discharge to obtain acidic silica sol.

Then get 834ml, 3% sodium hydroxide solution and inject in the ion exchange column that 400ml Nankai brand 201 * 7 type wet anion exchange resins are housed and stir, leave standstill layering after stirring for 3min, remove the supernatant solution, use deionized water Rinse the remaining anion exchange resin until its pH value is between 9-9.5 to obtain a basic anion exchange resin. Then the acidic silica sol 536g after the above-mentioned cation resin exchange is added in the above-mentioned 400ml basic anion-exchange resin, exchange 15min under the situation of stirring, measure the Zeta potential of exchange solution simultaneously, stop stirring after its absolute value is more than 30mv, static After layering, the material is discharged to obtain alkaline silica sol.

Add 536g of the above-mentioned alkaline silica sol exchanged by the anion resin into the above-mentioned 400ml acidic cation exchange resin under the condition of stirring, exchange for 15min under the condition of stirring, and measure the Zeta potential of the exchange solution at the same time, and its absolute value is above 30mv Finally, the stirring was stopped, and the material was discharged after standing for stratification to obtain an acidic silica sol with metal ions reaching several ppm.

For users who use acidic polishing liquid, the above-mentioned acidic silica sol is sufficient.

For the alkaline and strict polishing solution, finally add 536g of acidic silica sol after cation-anion-cation exchange into 0.8ml of FA/O chelating agent under stirring to obtain the final silica sol product.

Example 2

Inject 2102.2ml, 5% hydrochloric acid solution into an ion exchange column equipped with 1600ml American Amberjet 1200Na cation exchange resin for stirring, after stirring for 5min, let it stand for stratification, remove the upper layer solution, and rinse the remaining cation exchange resin with deionized water Resin until its pH value is between 2.5-3 to obtain acidic cation exchange resin.

Then the concentration is 32%, the particle diameter is 47nm, the alkaline silica sol 536g that metal ion content is higher than 100ppm joins in the above-mentioned acidic cation exchange resin of 800ml under the situation of continuous stirring, exchange 30min under the situation of stirring, measure simultaneously Exchange the Zeta potential of the solution so that its absolute value is above 40mv, then stop stirring, leave to stand for stratification, and discharge to obtain acidic silica sol.

Then get 1000ml, 5% sodium hydroxide solution and inject in the ion-exchange column that 800ml American AmberliteIRA-400 type wet anion exchange resin is housed and stir, after stirring for 5min, let it stand for stratification, remove the upper layer solution, rinse with deionized water The remaining anion exchange resin is adjusted to a pH value between 9.5-10 to obtain a basic anion exchange resin. Then the acidic silica sol 536g after the above-mentioned cation resin exchange is added in the above-mentioned 800ml basic anion-exchange resin, exchange 30min under the situation of stirring, measure the Zeta potential of exchange solution simultaneously, stop stirring after its absolute value is more than 40mv, static After layering, the material is discharged to obtain alkaline silica sol.

Add 536g of the above-mentioned alkaline silica sol exchanged by the anion resin into the above-mentioned 800ml acidic cation exchange resin under the condition of stirring, exchange for 30min under the condition of stirring, measure the Zeta potential of the exchange solution at the same time, and its absolute value is above 40mv Finally, the stirring was stopped, and the material was discharged after standing for stratification to obtain an acidic silica sol with metal ions reaching several ppm.

Finally, 536 g of acidic silica sol after cation-anion-cation exchange was added into 2.4 ml of FA/O chelating agent under stirring to obtain the final silica sol product.

Example 3

Inject 1325ml, 10% hydrochloric acid solution into an ion exchange column equipped with 2000ml German Lewatit-100 cation exchange resin for stirring. After stirring for 10 minutes, let it stand for stratification, remove the upper layer solution, and rinse the remaining cation exchange resin with deionized water. Resin until its pH value is between 3-3.5 to obtain acidic cation exchange resin.

Then the concentration is 42%, the particle diameter is 60nm, the alkaline silica sol 536g that metal ion content is higher than 100ppm joins in the above-mentioned acidic cation exchange resin of 1000ml under the situation of continuous stirring, exchange 60min under the situation of stirring, measure simultaneously Exchange the Zeta potential of the solution so that its absolute value is above 60mV, then stop stirring, leave to stand for stratification, and discharge to obtain acidic silica sol.

Then take 625ml, 10% sodium hydroxide solution and inject it into an ion exchange column equipped with 1000ml German Lewatit M500 type wet anion exchange resin for stirring. After stirring for 10min, let it stand for stratification, remove the upper solution, and rinse the remaining with deionized water. the anion exchange resin until its pH value is between 9.5-10 to obtain a basic anion exchange resin. Then the acidic silica sol 536g after the above-mentioned cation resin exchange is added in the above-mentioned 1000ml basic anion-exchange resin, exchange 60min under the situation of stirring, measure the Zeta potential of exchange solution simultaneously, stop stirring after its absolute value is more than 60mv, static After layering, the material is discharged to obtain alkaline silica sol.

Add 536g of the above-mentioned alkaline silica sol exchanged by the anion resin into the above-mentioned 1000ml acidic cation exchange resin under the condition of stirring, exchange for 60min under the condition of stirring, measure the Zeta potential of the exchange solution at the same time, and its absolute value is above 60mv Finally, the stirring was stopped, and the material was discharged after standing for stratification to obtain an acidic silica sol with metal ions reaching several ppm.

Finally, 536 g of acidic silica sol after cation-anion-cation exchange was added into 4 ml of FA/O chelating agent under stirring to obtain the final silica sol product.

The detection results of the metal ion content of silica sol are shown in the following table:

A: Before exchange:

Types of metal elements homemade products foreign products domestic products Na(mg/L)Al(mg/L)K(mg/L)Cu(mg/L)Fe(mg/L) 371535321.2608090 317 5348.0--＜0.01   2774321.2--＜0.01

B: Metal ion content after exchange:

Types of metal elements Corresponding content after ion exchange treatment/mg/L NaAlKCuFe   3.4<0.01 Not detected<0.01 Not detected 0.023<0.01 Not detected

Accompanying drawing 4 is the Zeta potential test result, the abscissa is the Zeta potential value, and the ordinate is % class. According to the test results, the absolute value of the Zeta potential is greater than 30mv, which is in the potential range for stable storage of silica sol.

Although the disclosed method for purifying nano-silica sol for VLSI is specifically described with reference to the embodiments, the above-described embodiments are illustrative rather than restrictive, without departing from the spirit and spirit of the present invention. All changes and modifications are within the scope of the present invention.

Claims (4)

1. a method for purifying special nano-silica sol for VLSI, characterized in that it may further comprise the steps: (1) At first inject 3%-10% hydrochloric acid solution into cation exchange resin and stir, make cation exchange resin regenerate completely, wherein the volume exchange capacity of hydrochloric acid and wet cation exchange resin is 1.4-1.8 mg equivalent/milliliter, let stand to divide After layering, the upper layer solution is removed, and then the remaining cation exchange resin is rinsed with deionized water until its pH value is in the range of 2-4 to obtain an acidic cation exchange resin; (2) Then the alkaline silica sol with metal ion content higher than 100ppm is added in the acidic cation exchange resin prepared in the above step (1) under continuous stirring, wherein, the alkaline silica sol and the acidic cation exchange resin The ratio of the amount of the substance is 1:2-1:5, exchange for 10-60min under stirring, and measure the Zeta potential of the exchange solution at the same time, stop stirring after the absolute value is 30mv-60mv, and let it stand for stratification Acidic silica sol is discharged; (3) inject 3%-10% sodium hydroxide solution into the anion exchange resin and stir to make the anion exchange resin regenerate completely, wherein the volume exchange capacity of sodium hydroxide and wet anion exchange resin is 1.2-1.6 mg equivalent/ml , after static stratification, the upper layer solution is removed, and the remaining anion exchange resin is rinsed with deionized water until its pH value is between 9-10 to obtain a basic anion exchange resin; (4) Then the acidic silica sol prepared in the above step (2) is added to the basic anion exchange resin prepared in the above step (3), wherein the amount of substance of the acidic silica sol and the basic anion exchange resin The ratio is 1:2-1:5, exchanged for 10-60min while stirring, and at the same time measure the Zeta potential of the exchanged solution so that the absolute value is 30mv-60mv, then stop stirring, and after standing for stratification, the material is discharged to obtain a significant Alkaline silica sol; (5) Add the exchanged alkaline silica sol prepared in step (4) into the acidic cation exchange resin prepared in step (1) while stirring, wherein the alkaline silica sol and the acidic cation The ratio of the amount of substances in the exchange resin is 1:2-1:5, exchange for 10-60min under the condition of stirring, measure the Zeta potential of the exchange solution at the same time, stop stirring after making its absolute value 30mv-60mv, let it stand and divide After layering, the material is discharged to obtain acidic silica sol with metal ions reaching several ppm levels. 2. the purification method of VLSI special nano-silica sol according to claim 1, is characterized in that, after cation-anion-cation exchange, then FA/O chelating agent is added to above-mentioned cation-anion-cation exchange In the final acidic silica sol, the final silica sol product is obtained, wherein the volume ratio of acidic silica sol and chelating agent is 1000:2-10. 3. according to claim 1 and the purification method of nano-silica sol special for VLSI, it is characterized in that: used cation exchange resin is strongly acidic styrene type cation exchange resin, and used anion exchange resin is strong base Quaternary amine anion exchange resin. 4. The method for purifying nano-silica sol for VLSI according to claim 1, characterized in that: the particle diameter of the purified silica sol is 20nm-60nm.

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