A single crystal silicon polishing liquid and preparation method

Abstract

The present invention discloses a single crystal silicon polishing solution and a preparation method. The silicon wafer polishing solution comprises an imidazole-modified high-purity silica sol, a penetrant and a film-forming agent, a surfactant, a pH regulator, and ultrapure water. The weight percentages of the components are as follows: 0.5% to 20% imidazole-modified high-purity nano-silica sol, 0.01% to 1% chelating agent, 0.01% to 0.5% penetrant, 0.001% to 0.5% film-forming agent, 0.01% to 5% pH regulator, and the balance ultrapure water. The imidazole-modified high-purity silica sol not only improves the dispersibility of the silica sol but also reduces the electrostatic repulsion between the silica sol and the silicon wafer, significantly increasing the polishing rate of the silicon wafer. Under the combined action of the penetrant and film-forming agent, the polishing solution of the present invention not only achieves a polishing rate of up to 550 nm / min, but also exhibits minimal contamination of the silicon wafer surface after polishing, with no scratches or depressions on the surface and a good surface condition. At the same time, the metal impurity ions in the fine polishing liquid of the present invention are controlled below 10 ppb, which meets the fine polishing requirements of single crystal silicon in high-end integrated circuits.

Description

Technical Field

[0001] The present invention relates to the technical field of chemical mechanical polishing (CMP) of single crystal silicon in an integrated circuit, and in particular to a fine polishing liquid for large-size silicon wafers and a preparation method thereof. Technical Background

[0002] Integrated circuits are one of the main high-tech technologies that drive social, economic and information development. Silicon wafers, as the cornerstone of integrated circuits, are widely used as substrates for semiconductor devices and optical components. With the continuous increase in wafer size, the continuous reduction in chip feature size, the increasing number of chip processing steps, and the increasingly high requirements for chip quality, how to improve chip processing efficiency and quality is currently a problem that needs to be solved urgently. Silicon wafers used to manufacture integrated circuits are required to have extremely small surface roughness, extremely high surface flatness and integrity. Chemical mechanical polishing (CMP) is currently the final process to obtain ultra-smooth and damage-free silicon wafers, and has become a crucial step in silicon wafer processing in semiconductor manufacturing technology.

[0003] The mechanism of single-crystal silicon CMP involves using an alkaline polishing solution as an active substance to chemically react with the silicon wafer surface, forming a layer of silicate compounds with a hardness far lower than the wafer itself. Pressure is then applied to the wafer, and the mechanical action of the abrasive in the polishing solution and the polishing pad removes this compound from the wafer surface, resulting in an ultra-smooth surface with low roughness and no damage. In industrial production, the finishing polishing of silicon wafers is a critical step in determining whether a wafer can be used in integrated circuit manufacturing. Generally speaking, a finishing polishing solution requires a high polishing rate, low metal ion content, and excellent surface quality after polishing, with no residual particles. Currently, extensive research has been conducted both domestically and internationally on how to improve the quality of finishing polishing solutions for silicon wafers, with some promising results.

[0004] Patent US010745588B2 discloses a formula for a silicon wafer fine polishing solution consisting of silica sol, polyacryloylmorpholine, ammonia, and deionized water. This polishing solution effectively reduces defects after fine polishing, but the patent does not specify its polishing rate. Patent JP5822356B2 discloses a silicon wafer fine polishing solution consisting of silica particles, a nitrogen-containing alkaline compound, a water-soluble polymer, a pH adjuster, and deionized water. This polishing solution reduces surface roughness and surface defects on silicon wafers after polishing. However, the water-soluble polymer in this patent is complex to synthesize, the polishing rate is low, and the shelf life of the polishing solution is short. Patent CN113881347A discloses a chemical-mechanical fine polishing solution, primarily composed of composite silica sols of varying morphologies, an oxidant, a chelating agent, a surfactant, a pH adjuster, and the balance deionized water, to increase the polishing rate while reducing scratches on silicon wafers. However, the polyspheroidal abrasive used in this patent currently lacks a stable and mature process, making it unsuitable for widespread industrial production.

[0005] It can be seen from the above patent that the fine polishing liquid for silicon wafers is mainly composed of abrasives and additives, among which the abrasive is mainly silica sol. However, under alkaline conditions, the surface of the silicon wafer and the silica sol are both negatively charged. Due to the electrostatic effect, the polishing rate of pure silica sol is very low. Therefore, in order to increase the polishing rate, it is necessary to modify the silica sol so that its surface has a positive charge, thereby reducing the electrostatic repulsion between the silicon wafer and the silica sol.

[0006] Therefore, it is necessary to provide a single crystal silicon fine polishing liquid based on high-purity silica sol with simple synthesis, high polishing rate, good polishing quality and long storage time to overcome the above problems. Summary of the Invention

[0007] The present invention overcomes the problems of low silicon wafer polishing rates and surface defects such as scratches, particles, and depressions in the polishing process of single-crystal silicon fine polishing liquids. Disclosed is a single-crystal silicon fine polishing composition that is simple to synthesize, contains low levels of metallic impurities, has a high polishing rate, and eliminates defects such as scratches, particles, and depressions on the surface of polished silicon wafers.

[0008] The present invention provides a preparation method and application of a large-size silicon wafer fine polishing liquid, which is composed of imidazole-modified high-purity silica sol, a chelating agent, a penetrant, a film-forming agent, a pH regulator and ultrapure water. In terms of mass percentage, the imidazole-modified high-purity nano-silica sol is 0.5% to 20%, the chelating agent is 0.01% to 1%, the penetrant is 0.01% to 0.5%, the film-forming agent content is 0.001% to 0.5%, the pH regulator is 0.01% to 5%, and the balance is ultrapure water.

[0009] The metal ion content in the imidazole-modified high-purity silica sol is less than 10 ppb, and the particle size is 20 to 120 nm.

[0010] The imidazole-modified silica sol is obtained by hydrolyzing an imidazole-based silane coupling agent and then grafting it onto the surface of nano-silica. The imidazole-based silane coupling agent is one or more of N-imidazolepropyltrimethoxysilane and N-[3-(triethoxysilyl)propyl]-4,5-dihydroimidazole.

[0011] The preparation method of the imidazole-modified silica sol is as follows: add the silica sol into a reaction bottle, heat it to 50-80° C., dropwise add the hydrolyzate of the imidazole-based silane coupling agent, and react for 5-6 hours under stirring to obtain the imidazole-modified high-purity silica sol.

[0012] The hydrolyzate of the imidazole silane coupling agent is a hydrolyzate obtained by mixing the imidazole silane coupling agent and water in a mass ratio of 10-20:1;

[0013] The mass ratio of the silica sol to the imidazole silane coupling agent is 10 to 1000:1.

[0014] The chelating agent is selected from organic carboxylic acid or organic phosphoric acid;

[0015] The organic carboxylic acid is selected from any one of acetic acid, citric acid, tartaric acid, malonic acid, diethylenetriaminepentaacetic acid, and ethylenediaminetetraacetic acid;

[0016] The organic phosphoric acid is selected from any one of 2-phosphobutane-1,2,4-tricarboxylic acid, aminotrimethylphosphonic acid, hydroxyethylidene diphosphonic acid, and ethylenediaminetetramethylphosphonic acid;

[0017] The purity of the organic carboxylic acid or organic phosphoric acid is above 99.99%, and the metal ion content is below 10 ppb.

[0018] The penetrant is one or more of octanol polyoxyethylene ether, lauryl alcohol polyoxyethylene ether, isooctyl alcohol polyoxyethylene ether, octylphenol polyoxyethylene ether, isooctyl alcohol polyoxyethylene ether monophosphate, lauryl alcohol phosphate, and isopropyl alcohol amide DF-21.

[0019] The film-forming agent is a cellulose such as hydroxyethyl cellulose, hydroxypropyl methyl cellulose, guar gum, or a polyoxyethylene-polyoxypropylene block copolymer, or polyvinyl pyrrolidone, or one or more polyethylene glycols such as polyethylene glycol-200, polyethylene glycol-400, polyethylene glycol-800; or one or more polyvinyl alcohols such as polyvinyl alcohol 124, polyvinyl alcohol 17-88, etc.

[0020] The pH regulator is an organic base, such as one or more of tetramethylammonium hydroxide, tetraethylammonium hydroxide, tetrapropylammonium hydroxide, tetrabutylammonium hydroxide, ethylenediamine, and ethanolamine.

[0021] The specific steps of preparing the silicon wafer polishing liquid composition are:

[0022] (1) Dispersing imidazole-modified high-purity silica sol in a portion of deionized water and stirring evenly;

[0023] (2) dispersing the chelating agent, penetrant and film-forming agent in the remaining deionized water, stirring and dissolving them, and then slowly adding them to the high-purity silica sol under stirring;

[0024] (3) adding a pH regulator to adjust the pH of the above solution to 9-11;

[0025] (4) The single crystal silicon polishing liquid is filtered through a winding filter element to remove large particles of impurities in the polishing liquid to obtain the final polishing liquid.

[0026] Compared with the prior art, the present invention has the following beneficial effects:

[0027] The abrasive used in the fine polishing liquid of the present invention is imidazole-modified high-purity silica sol, which utilizes the positive charge of the imidazole group under alkaline conditions to not only increase the dispersion stability of the silica sol, but also weaken the electrostatic repulsion between the silica sol and the silicon wafer, thereby accelerating the polishing rate of the silicon wafer;

[0028] The fine polishing liquid of the present invention contains both a penetrant and a film-forming agent. Due to the strong penetrating effect of the penetrant and the film-forming effect of the film-forming agent, the surface of the polished silicon wafer has very few contaminants, no scratches or depressions, and a good surface condition.

[0029] The method for preparing a large-size silicon wafer fine polishing liquid described in the present invention strictly controls the introduction of metal impurity ions starting from the raw materials, so that the metal ions in the fine polishing liquid are controlled below 10ppb, which meets the fine polishing requirements of single crystal silicon in high-end integrated circuits. DETAILED DESCRIPTION

[0030] The present invention is further described below through examples and comparative examples. The embodiments described in the present invention are preferred embodiments. For those skilled in the art, corresponding adjustments and improvements can be made without departing from the technical principles of the present invention. These adjustments and improvements should also be considered as the scope of protection of the present invention.

[0031] The preparation method of imidazole-modified silica sol is as follows: high-purity silica sol is added to a reaction bottle, and then the reaction bottle is placed in a heating jacket with a stirring function, the temperature of the reaction bottle is controlled at 50°C, and the imidazole silane coupling agent is first hydrolyzed to obtain a hydrolyzate, which is a silane hydrolyzate formed by mixing the imidazole silane coupling agent and water in a mass ratio of 10:1, and then the silane hydrolyzate is added dropwise to the high-purity silica sol solution, the mass ratio of the high-purity silica sol to the imidazole silane coupling agent is 10 to 1000, and the mixture is stirred for 6 hours to obtain the imidazole-modified high-purity silica sol.

[0032] The imidazole-based silane coupling agent is N-imidazolepropyltrimethoxysilane, N-[3-(triethoxysilyl)propyl]-4,5-dihydroimidazole.

[0033] Examples 1 to 6

[0034] In Examples 1 to 3, the high-purity silica sol modified with N-imidazolepropyltrimethoxysilane in the above steps was used as the abrasive, and the particle size was 30 nm.

[0035] Examples 4 to 6 use the high-purity silica sol modified with N-[3-(triethoxysilyl)propyl]-4,5-dihydroimidazole in the above steps as the abrasive, with a particle size of 50 nm.

[0036] The weight percentages of the abrasives and additives other than water in the embodiment formula are shown in Table 1, with the remainder being ultrapure water. The sum of the weight percentages of the various components is 100%. The specific preparation steps are as follows:

[0037] (1) Dispersing imidazole-modified high-purity silica sol in a portion of deionized water and stirring evenly;

[0038] (2) dispersing the chelating agent, penetrant and film-forming agent in the remaining deionized water, stirring and dissolving them, and then slowly adding them to the high-purity silica sol under stirring;

[0039] (3) adding a pH regulator to adjust the pH of the above solution to 10.5;

[0040] (4) The single crystal silicon polishing liquid is filtered through a winding filter element to remove large particles of impurities in the polishing liquid to obtain the final polishing liquid.

[0041] Table 1 Composition of the monocrystalline silicon polishing solution in Examples 1 to 6

[0042]

[0043] Comparative Example 1

[0044] The formulation and preparation method of Reference Example 1 were used, except that the abrasive in the formulation was unmodified high-purity silica sol, and other operating conditions and parameters remained unchanged to obtain a fine polishing solution.

[0045] Comparative Example 2

[0046] The formulation and preparation method of Reference Example 1 were used, except that the abrasive in the formulation was high-purity silica sol modified with 4-pyridinetriethoxysilane, and other operating conditions and parameters remained unchanged to obtain a fine polishing solution.

[0047] Comparative Example 3

[0048] The formulation and preparation method of Reference Example 1 were used, except that the abrasive in the formulation was high-purity silica sol modified with methyltrimethoxysilane, and other operating conditions and parameters remained unchanged to obtain a fine polishing solution.

[0049] Comparative Example 4

[0050] The formulation and preparation method of Reference Example 1 were used, except that the abrasive in the formulation was high-purity silica sol modified with 3-(trihydroxysilyl)propanesulfonic acid, and other operating conditions and parameters remained unchanged to prepare a fine polishing solution.

[0051] Comparative Example 5

[0052] The formula and preparation method of Reference Example 3 are different only in that only isopropyl alcohol amide DF-21 penetrant is added to the formula without adding a film-forming agent, and other operating conditions and parameters remain unchanged to obtain a fine polishing solution.

[0053] Comparative Example 6

[0054] The formulation and preparation method of Reference Example 3 were used, except that only guar gum film-forming agent was added to the formulation without penetrant, and other operating conditions and parameters remained unchanged to obtain a fine polishing solution.

[0055] Application of experimental examples and comparative examples

[0056] The prepared single-crystal silicon fine polishing liquid was used in the polishing experiment. The polishing conditions were as follows: polishing machine FD-4603X single-side polishing machine, polishing one 8-inch single-crystal silicon wafer at a time; polishing pressure 25kPa; polishing disk and polishing head speed 50rpm; polishing time 2min; polishing pad Suba 400; polishing liquid flow rate 100mL / min; polishing temperature 25℃.

[0057] The polishing removal rate is calculated by calculating the change in the mass of the silicon wafer before and after polishing, and then the MRR is calculated according to the formula MRR = (△M) / (ρ*S*T)×10 7 (nm / min).

[0058] The surface roughness of the polished silicon wafer was measured using a 3D profilometer. The profilometer used in the experiment was a Sensofer, with an interference resolution of 0.1nm, a scanning frequency of 1.5H, and a scanning range of 168×140μm.

[0059] Detection of surface defects and depressions on polished silicon wafers, using an ultra-depth of field microscope to detect surface scratches and depressions on silicon wafers.

[0060] Table 2 Test results of the embodiment and the comparative example

[0061]

[0062] The comparison between Experimental Example 1 and Comparative Example 1 shows that the imidazole-modified silica sol can significantly increase the polishing rate.

[0063] Comparison of Experimental Example 1 and Comparative Example 2 demonstrates that even though pyridylsilane is positively charged under alkaline conditions, the pyridine group contains only one nitrogen atom, resulting in a lower potential than imidazolylsilane. Therefore, the interaction between the pyridylsilane-modified silica sol and the silicon wafer is weaker than that of the imidazolylsilane-modified silica sol. Consequently, the polishing rate of the pyridylsilane-modified silica sol is lower than that of the imidazolylsilane-modified silica sol. Furthermore, due to its low potential and dispersibility, the polishing rate of the silicon wafer in the pyridylsilane-modified silica sol polishing solution significantly decreases after three months of storage. Comparison of Example 1 and Comparative Example 3 demonstrates that hydrophobic group modification of the silica sol may increase its electric double layer, weakening the interaction between the silica sol and the silicon wafer, thereby reducing the polishing rate. Comparison of Example 1 and Comparative Example 4 demonstrates that the negative charge of the sulfonic acid silane-modified silica sol under alkaline conditions further weakens the interaction between the silica sol and the silicon wafer, resulting in a decrease in polishing rate and reduced contamination. In summary, since the silica sol modified with imidazole silane coupling agent has a stronger positive charge under alkaline conditions, the interaction between it and the silicon wafer is stronger, so its polishing rate is faster, indicating that the silica sol modified with imidazole silane coupling agent is more suitable as an abrasive for silicon polishing solution under alkaline conditions.

[0064] The comparison between Experimental Example 3 and Comparative Examples 2 and 3 shows that the synergy between the penetrant and the chelating agent can effectively reduce the occurrence of defects.

[0065] The above experimental examples show that the optimal polishing liquid formula contains 7% 50nm imidazole-modified high-purity silica sol, 0.5% 2-phosphate butane-1,2,4-tricarboxylic acid chelating agent, 0.5% fatty alcohol polyoxyethylene ether phosphate penetrant, 0.02% hydroxyethyl cellulose film-forming agent, and 0.2% ethanolamine pH regulator. The polishing rate of single crystal silicon polished with this formula is as high as 550nm / min. The surface roughness of the polished silicon wafer is as low as 0.11nm, and there are no scratches, particle residues or depressions on the surface.

[0066] The above description is only a preferred embodiment of the present invention. It should be pointed out that a person skilled in the art can make several modifications and improvements without departing from the inventive concept of the present invention, and these should also be considered within the scope of protection of the invention.

Claims

1. A single crystal silicon polishing liquid, characterized in that: The invention relates to a method for preparing a nano-silica sol modified with imidazole, a chelating agent, a surfactant, a pH regulator and deionized water, wherein the mass percentage of each component is as follows: 0.5% to 20% of imidazole-modified nano-silica sol, 0.01% to 1% of a chelating agent, 0.011% to 1% of a surfactant, 0.01% to 5% of a pH regulator and the balance is deionized water; wherein the surfactant comprises a penetrant and a film-forming agent, the penetrant content is 0.01% to 0.5%, and the film-forming agent content is 0.001% to 0.5%; the imidazole-modified silica sol is obtained by hydrolyzing an imidazole-based silane coupling agent and then grafting it onto the surface of nano-silica; the imidazole-based silane coupling agent is N-imidazole. One or more of propyltrimethoxysilane and N-[3-(triethoxysilyl)propyl]-4,5-dihydroimidazole; the penetrant is selected from one or more of octanol polyoxyethylene ether, lauryl alcohol polyoxyethylene ether, isooctyl alcohol polyoxyethylene ether, octylphenol polyoxyethylene ether, isooctyl alcohol polyoxyethylene ether monophosphate, lauryl alcohol phosphate, and isopropyl alcohol amide DF-21; the film-forming agent is selected from one or more of hydroxyethyl cellulose, hydroxypropyl methylcellulose, guar gum, polyoxyethylene-polyoxypropylene block copolymer, polyvinyl pyrrolidone, polyethylene glycol-200, polyethylene glycol-400, polyethylene glycol-800, polyvinyl alcohol 124, and polyvinyl alcohol 17-88.

2. The single crystal silicon fine polishing liquid according to claim 1, characterized in that The metal ion content in the imidazole-modified silica sol is less than 10 ppb, and the particle size is 20 to 120 nm.

3. The single crystal silicon fine polishing liquid according to claim 1, characterized in that The preparation method of the imidazole-modified silica sol is as follows: add silica sol into a reaction bottle, heat it to 50-80° C., dropwise add the hydrolyzate of the imidazole-based silane coupling agent, and react for 5-6 hours under stirring to obtain the imidazole-modified silica sol.

4. The single crystal silicon fine polishing liquid according to claim 1, characterized in that The hydrolyzate of the imidazole silane coupling agent is a hydrolyzate obtained by mixing the imidazole silane coupling agent and water in a mass ratio of 10-20:1; The mass ratio of the silica sol to the imidazole silane coupling agent is 10 to 1000:

1.

5. The single crystal silicon fine polishing liquid according to claim 1, characterized in that The chelating agent is selected from organic carboxylic acid or organic phosphoric acid; the purity of the organic carboxylic acid or organic phosphoric acid is above 99.99%, and the metal ion content is below 10 ppb.

6. The single crystal silicon fine polishing liquid according to claim 5, characterized in that The organic carboxylic acid is selected from any one of acetic acid, citric acid, tartaric acid, malonic acid, diethylenetriaminepentaacetic acid, and ethylenediaminetetraacetic acid; The organic phosphoric acid is selected from any one of 2-phosphobutane-1,2,4-tricarboxylic acid, aminotrimethylphosphonic acid, hydroxyethylidene diphosphonic acid, and ethylenediaminetetramethylphosphonic acid.

7. The single crystal silicon fine polishing liquid according to claim 1, characterized in that The purity of the penetrant is above 99.99% and the metal ion content is below 10 ppb.

8. The single crystal silicon fine polishing liquid according to claim 1, characterized in that The purity of the film-forming agent is above 99.9%, and the metal ion content is below 5 ppb.

9. The single crystal silicon fine polishing liquid according to claim 1, characterized in that The pH regulator is selected from one or more of tetramethylammonium hydroxide, tetraethylammonium hydroxide, tetrapropylammonium hydroxide, tetrabutylammonium hydroxide, ethylenediamine, and ethanolamine; The purity of the pH adjuster is above 99.9% and the metal ion content is below 8 ppb.

10. The method for preparing a single crystal silicon fine polishing solution according to any one of claims 1 to 9, characterized in that: The following steps are involved: (1) Disperse the imidazole-modified silica sol in a portion of deionized water and stir evenly; (2) Disperse the chelating agent and surfactant in the remaining deionized water, stir and dissolve them, and then slowly add them to step (1) under stirring; (3) adding a pH regulator to adjust the pH of the solution in step (2) to 9-11 to obtain a single crystal silicon polishing solution; (4) The single crystal silicon polishing liquid is filtered through a wound filter element to remove large particles of impurities in the polishing liquid to obtain the final polishing liquid.

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