Chemical mechanical fine polishing liquid for silicon wafer as well as preparation method and application of chemical mechanical fine polishing liquid

Abstract

The invention provides a chemical mechanical fine polishing liquid for a silicon wafer, a preparation method and application, the fine polishing liquid takes high-purity nano silicon dioxide colloid as a polishing abrasive, and is added with a pH regulator, a dispersing agent, stearate, alkyl carbon chain azacyclo-amine and water. Alkyl carbon chain azacyclo-amine and stearate are added into the fine polishing liquid to serve as a surface protective agent, meanwhile, an amino ring structure and an alkoxy carbon chain structure are contained, on one hand, the fine polishing liquid can be adsorbed to the surface of a silicon wafer through hydrogen bonds, on the other hand, alkyl carbon chains among molecules can interact, and therefore a softened film layer can be formed on the surface of the silicon wafer, and the surface of the silicon wafer is protected. And the defects and haze value of the surface of the polished silicon wafer can be effectively improved.

Description

Technical Field

[0001] The invention relates to the technical field of chemical mechanical polishing (CMP), and in particular to a chemical mechanical polishing liquid for final polishing of silicon wafers, a preparation method and application thereof. Background Art

[0002] With the development of semiconductor integrated circuits, the feature size of devices continues to shrink, the integrated circuit manufacturing process steps are becoming more and more complicated, and the requirements for each process technology are becoming higher and higher. Chemical mechanical planarization (CMP) is one of the key technologies in integrated circuit manufacturing and the core technology of global planarization. In the integrated circuit manufacturing process, chemical mechanical polishing of silicon substrates plays a vital role in device performance, and the surface state after polishing directly determines the reliability of the device.

[0003] In order to further improve the surface state of silicon substrates and meet the needs of further technological development, most companies currently use a three-step polishing method to process silicon substrates, mainly including rough polishing, medium polishing and fine polishing. As the feature size of integrated circuits is further reduced, the requirements for the surface state after polishing are also further improved. The purpose of rough polishing of silicon substrates is to quickly remove the damaged layer on the surface of the substrate; the purpose of medium polishing of silicon substrates is to further reduce the damage on the surface of the substrate; the purpose of fine polishing of silicon substrates is to reduce the surface roughness of silicon wafers, remove surface damage, reduce surface defects, and obtain a low haze value and a smooth and smooth surface. Fine polishing is the last step in the chemical mechanical polishing of silicon substrates, and the polishing effect directly determines the processing quality of silicon substrates.

[0004] Therefore, fine polishing of silicon substrate wafers is of great significance for reducing their surface defects (LLS) and haze values. Patent CN 111378378 A discloses a polishing liquid for copper, which improves the roughness of the copper surface after polishing by adding hydrocarbon sulfonate anionic surfactants and metal surface defect improvers, but it is directly used in silicon fine polishing liquid and cannot improve the surface defects of silicon wafers after polishing. Patent CN 113150696 A discloses a polishing liquid for reducing micro scratches on the surface of silicon wafers, using aluminum-coated composite abrasives, combining the advantages and disadvantages of aluminum oxide and silicon oxide abrasives to form a stable colloidal system, and obtaining a low-roughness surface after chemical mechanical polishing. This patent achieves good surface quality by directly modifying better abrasives, which increases costs.

[0005] Therefore, there is still a need to develop a chemical mechanical polishing liquid suitable for silicon wafers so that the abrasive can be better dispersed in the system and the silicon wafers can be smoother after polishing, which is manifested by low surface defects and low haze values. Summary of the invention

[0006] In order to solve the above-mentioned problems existing in the prior art, the purpose of the present invention is to design a chemical mechanical polishing liquid for silicon wafers, by adding stearic acid ester and alkyl carbon chain nitrogen heterocyclic amine as surface protective agents adsorbed on the surface of the silicon wafer, so that a softening film is formed on the surface, scratches are avoided during the chemical mechanical polishing process, the adhesion of particles in the polishing liquid is reduced, and surface defects and haze values ​​are reduced.

[0007] Another object of the present invention is to provide a method for preparing the chemical mechanical polishing liquid.

[0008] Another object of the present invention is to provide an application of the chemical mechanical polishing liquid.

[0009] In order to achieve the above invention object, the present invention adopts the following technical solution:

[0010] A chemical mechanical polishing liquid for silicon wafers uses high-purity nano silicon dioxide sol as polishing abrasive, and is added with a pH regulator, a dispersant, a surface protective agent and water.

[0011] In a preferred embodiment, the invention comprises high-purity nano-silica sol, a pH regulator, a dispersant, stearate, an alkyl carbon chain nitrogen heterocyclic amine and deionized water.

[0012] In a more preferred embodiment, the chemical mechanical polishing liquid includes the following components in percentage by weight: 1% to 20% of high-purity nano-silica sol, 0.1% to 1% of pH regulator, 0.1% to 5% of dispersant, 0.01% to 0.5% of stearate, 0.1% to 1% of alkyl carbon chain nitrogen heterocyclic amine, and the balance is water.

[0013] In a specific embodiment, the metal ion content of the high-purity nano-silica sol is less than 0.1ppm, for example, 90ppt, 80ppt, 70ppt, 60ppt, 50ppt, 40ppt, 30ppt, 20ppt, 10ppt, 5ppt, etc., and the secondary particle size is 10 to 200nm, for example, 20nm, 30nm, 50nm, 60nm, 80nm, 100nm, 120nm, 150nm, 160nm, 180nm, 200nm, etc., preferably 50 to 150nm. In the chemical mechanical polishing liquid, the mass percentage of high-purity nano-silica sol is 1% to 20%, for example, 1%, 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9%, 10%, 11%, 12%, 13%, 14%, 15%, 16%, 17%, 18%, 19%, 20%, etc.

[0014] In a specific embodiment, the pH regulator is selected from any one of potassium hydroxide, sodium hydroxide, ammonium hydroxide, ammonia water, tetramethylammonium hydroxide, tetraethylammonium hydroxide, and tetrabutylammonium hydroxide, preferably ammonia water. In the chemical mechanical polishing liquid, the mass percentage of the pH regulator is 0.1% to 1%, such as 0.1%, 0.2%, 0.3%, 0.4%, 0.5%, 0.6%, 0.7%, 0.8%, 0.9%, 1.0%, etc.

[0015] In the present invention, the pH range of the fine polishing solution is adjusted to 10-11, such as 10.5, by a pH adjusting agent.

[0016] In a specific embodiment, the dispersant is any one of hydroxymethyl cellulose, hydroxyethyl cellulose, hydroxypropyl cellulose and hydroxybutyl cellulose, preferably hydroxyethyl cellulose. In the chemical mechanical polishing liquid, the mass percentage of the dispersant is 0.1% to 5%, for example, 0.1%, 0.2%, 0.3%, 0.4%, 0.5%, 0.6%, 0.7%, 0.8%, 0.9%, 1%, 2%, 3%, 4%, 5%, etc.

[0017] In a specific embodiment, the stearate is any one of ethylene glycol stearate, propylene glycol stearate, butylene glycol stearate, glycerol hydroxystearate, isooctyl stearate, pentaerythritol monostearate, myristic acid stearate, sucrose stearate, xylitol anhydride monostearate, methyl glucoside stearate, and hydroxyacetamide stearate, preferably propylene glycol stearate. In the chemical mechanical polishing liquid, the mass percentage of stearate is 0.01% to 0.5%, such as 0.01%, 0.02%, 0.03%, 0.04%, 0.05%, 0.06%, 0.07%, 0.08%, 0.09%, 0.1%, 0.2%, 0.3%, 0.4%, 0.5%, etc.

[0018] In a specific embodiment, the alkyl carbon chain nitrogen heterocyclic amine contains a cyclic structure having an amine group. Preferably, the structure of the alkyl carbon chain nitrogen heterocyclic amine is as shown in formula (1).

[0019]

[0020] (1), where the R group is -(CH2) n CH3, 2≤n≤10, 1≤x≤3, 0≤y≤2;

[0021] More preferably, the alkyl carbon chain nitrogen heterocyclic amine is selected from any one of 2-propyl nitrogen heterocyclic amine, 2-propyl aziridine, 2-pentyl aziridine, 3-propyl pyrrolidine, 3-butyl nitrogen heterocyclic amine, 2-butyl azetidine, 3-butyl piperidine, and 4-hexyl piperidine, and more preferably 2-propyl nitrogen heterocyclic amine. In the chemical mechanical polishing liquid, the mass percentage of the alkyl carbon chain nitrogen heterocyclic amine is 0.1% to 1%, such as 0.1%, 0.2%, 0.3%, 0.4%, 0.5%, 0.6%, 0.7%, 0.8%, 0.9%, 1%, etc.

[0022] In a specific embodiment, the pH range of the chemical mechanical polishing solution for silicon wafers is 10-11, and the pH range after being diluted 10-40 times with water is 9-11.

[0023] On the other hand, a method for preparing a chemical mechanical polishing solution for final polishing of a silicon wafer comprises the following steps:

[0024] 1) Mix the dispersant, stearate, alkyl carbon chain nitrogen heterocyclic amine and an appropriate amount of water and stir to obtain a pre-dispersion solution.

[0025] 2) After the pH adjuster and the remaining amount of water are mixed evenly, the pre-dispersion liquid is added and stirred for 10 to 180 minutes to obtain an intermediate product;

[0026] 3) Under stirring conditions, high-purity silica sol is added to the intermediate product of step 2), and after being fully mixed, the chemical mechanical polishing solution for final polishing of silicon wafers is obtained.

[0027] The method for using the chemical mechanical polishing liquid for silicon wafers of the present invention can be used for polishing after being diluted 10 to 40 times with ultrapure water, which meets the requirements for chemical mechanical polishing of silicon wafers.

[0028] The silicon wafer chemical mechanical polishing liquid of the present invention is suitable for chemical mechanical polishing of wafers with silicon as substrate.

[0029] In a preferred embodiment, the conditions for fine polishing of silicon wafers are: silicon wafer diameter 200 or 300 nm, polishing pad POLYPAS275NX series, polishing pressure 1.0-5.0 psi, polishing temperature 25-50°C, polishing head and polishing disk rotation speed 50-100 rpm, polishing time 1-10 min, fine polishing liquid flow rate 1-5 L / min.

[0030] In a specific application scheme, the polishing conditions are: polishing machine type OKAMOTO or EBARA, silicon wafer diameter 300nm, polishing pad POLYPAS275NX, polishing pressure 2.5psi, polishing temperature 27°C, polishing head and polishing disk speed 41 / 41rpm, polishing liquid flow rate 1L / min, and the polishing liquid cannot be recycled.

[0031] Compared with the prior art, the technical solution of the present invention has the following beneficial effects:

[0032] 1) The chemical mechanical polishing liquid for silicon wafers of the present invention uses alkyl carbon chain nitrogen heterocyclic amine (such as 2-propyl nitrogen heterocyclic amine) and stearate (such as propylene glycol stearate) small molecules to work synergistically and can be dispersed around the abrasive particles to keep them in a stable state, and the silica sol particles are evenly dispersed in the polishing liquid.

[0033] 2) In the chemical mechanical polishing liquid for silicon wafers of the present invention, during the polishing process, alkyl carbon chain nitrogen heterocyclic amines and stearic acid esters can be adsorbed on the surface of the silicon wafer as surface protective agents to form a softened film layer, thereby preventing particles in the polishing liquid from being adsorbed on the surface of the silicon wafer, while avoiding new scratches on the surface of the silicon wafer during the mechanical polishing process, thereby reducing surface defects and haze values. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] Figure 1 This is a map of the silicon wafer surface after polishing in Comparative Example 4 of the present invention.

[0035] Figure 2 This is a map of the surface of the silicon wafer after polishing in Example 9 of the present invention. DETAILED DESCRIPTION

[0036] In order to better understand the technical solution of the present invention, the following examples will further illustrate the method provided by the present invention, but the present invention is not limited to the listed examples, and should also include any other known changes within the scope of the claims of the present invention.

[0037] The main raw material sources used in the embodiments of the present invention are as follows:

[0038] High-purity nano-silica sol: purchased from Japan FUSO Company, PL series silica sol, particle size 30-120nm;

[0039] Alkyl carbon chain nitrogen heterocyclic amines (2-propyl nitrogen heterocyclic amine, 2-propyl aziridine): purchased from Suzhou Amate Biotechnology Co., Ltd.; (3-propylpyrrolidine): purchased from Jiangsu Aikon Biomedicine Research and Development Co., Ltd.; (3-butyl nitrogen heterocyclic amine) purchased from Zhengzhou Yaoling Pharmaceutical Technology Co., Ltd.

[0040] Stearate: purchased from Beijing Bailingwei Technology Co., Ltd.

[0041] Unless otherwise specified, other reagents were common raw materials purchased from the market.

[0042] Examples 1 to 10

[0043] The chemical mechanical polishing liquid used for preparing silicon wafers has a formula in which the raw material components and percentage compositions other than water are shown in Table 1, the remainder is ultrapure water, and the sum of the mass percentages of each component is 100%. The steps are:

[0044] 1) Mix the dispersant, stearate, alkyl carbon chain nitrogen heterocyclic amine and an appropriate amount of water and stir to obtain a pre-dispersion solution.

[0045] 2) After the pH adjuster and the remaining amount of water are mixed evenly, the pre-dispersed liquid is added and stirred for 10 to 180 minutes to obtain an intermediate product;

[0046] 3) Under stirring conditions, high-purity silica sol is added to the intermediate product of step 2), and after being fully mixed, the chemical mechanical polishing solution for final polishing of silicon wafers is obtained.

[0047] Table 1 Composition of chemical mechanical polishing liquid for silicon wafers in Examples 1 to 10

[0048]

[0049]

[0050] Comparative Example 1

[0051] Referring to the formulation and preparation method of Example 9, 2-propyl azacyclic amine was not added, and other components, operating conditions and parameters remained unchanged to obtain a fine polishing solution with a pH of 10.67.

[0052] Comparative Example 2

[0053] Referring to the formulation and preparation method of Example 9, propylene glycol stearate was not added, and other components, operating conditions and parameters remained unchanged to obtain a fine polishing solution with a pH of 10.75.

[0054] Comparative Example 3

[0055] Referring to the formulation and preparation method of Example 9, the 2-propyl azacyclic amine in the formulation was replaced with acrylic acid monoethanolamide, and the other components, operating conditions and parameters remained unchanged to obtain a fine polishing solution with a pH of 10.71.

[0056] Comparative Example 4

[0057] Referring to the formulation and preparation method of Example 9, 2-propyl azacyclic amine and propylene glycol stearate were not added, and other components, operating conditions and parameters remained unchanged to obtain a fine polishing solution with a pH of 10.81.

[0058] Application of polishing liquids in Examples 1 to 10 and Comparative Examples 1 to 4:

[0059] The silicon wafer used has a diameter of 300 mm and is provided by Xi'an Eswin Materials Technology Co., Ltd.

[0060] Each polishing liquid was diluted 30 times with ultrapure water before use, and the pH after dilution was 9-11, and the solid content was 0.15%-0.85%.

[0061] The polishing conditions are as follows: the polishing machine is a Japanese OKAMOTO PNX332C single-sided polishing machine with two polishing heads, each of which can polish a silicon wafer with a diameter of 300 mm.

[0062] The polishing pad is POLYPAS275NX, the polishing pressure is 2.5 psi, the polishing pad temperature is 27°C, the polishing head and polishing disc speed is 41 / 41 rpm, the polishing time is 5 min, and the polishing liquid flow rate is 1 L / min.

[0063] The statistics of surface defects (LLS) and surface haze values ​​(Haze) of silicon wafers of Comparative Examples 1 to 4 and Examples 1 to 10 of the fine polishing liquid of the present invention are shown in Table 2.

[0064] Silicon wafer surface defects (LLS) and surface haze value (Haze): Use the defect detection device KLA SP5 to count the LLS of all channels and the Haze value of the DW2 channel.

[0065] Table 2 LLS and Haze values ​​of silicon wafer surfaces of Comparative Examples 1 to 4 and Examples 1 to 10.

[0066] Serial number Surface defect LLS (≥26nm) Surface haze value Haze / ppm Comparative Example 1 68 0.080 Comparative Example 2 77 0.053 Comparative Example 3 50 0.063 Comparative Example 4 133 0.16 Example 1 23 0.059 Example 2 17 0.052 Example 3 15 0.053 Example 4 16 0.054 Example 5 19 0.051 Example 6 10 0.053 Example 7 13 0.051 Example 8 11 0.052 Example 9 5 0.048 Example 10 12 0.051

[0067] By comparing Comparative Example 4 with Example 9, it can be seen that when only pH adjuster and dispersant are added, the LLS and Haze of the silicon wafer surface after polishing are the worst. The reason is that the dispersant in Comparative Example 4 cannot form a softening film layer on the silicon wafer surface, and the alkaline additive and high-purity silica sol in the pH adjuster directly contact the wafer. Since chemical corrosion and abrasive mechanical friction directly act on the wafer surface, the surface cannot be better repaired, and new scratches will be generated. After polishing, more polishing liquid particles adhere to the silicon wafer surface. Figure 1 It shows that a large number of surface defects were detected on the surface of the silicon wafer after polishing under the conditions of Comparative Example 4, and after adding stearic acid ester and alkyl carbon chain nitrogen heterocyclic amine, the two acted synergistically to protect the surface of the silicon wafer. Figure 2 The surface defects detected in the process are significantly reduced, and a higher surface quality of the silicon wafer is obtained. The preferred ratio of stearic acid ester to alkyl carbon chain nitrogen heterocyclic amine is in the range of 1:1.5-3, which has a better effect of improving surface defects and reducing haze value.

[0068] By comparing Comparative Example 1, Comparative Example 2 and Example 9, it can be seen that the LLS and Haze of the silicon wafer surface are greatly improved after the stearate and the alkyl carbon chain nitrogen heterocyclic amine are added at the same time. This is due to the synergistic effect of the two, which can be adsorbed on the surface of the silicon wafer to form a softened film layer, and enriched in depressions of different sizes on the surface of the wafer. Therefore, the protrusions on the surface of the silicon wafer can be repaired and smoothed during the polishing process without causing major scratches. At the same time, the depressions will not be over-polished, making the surface of the silicon wafer smoother, and it is easy to fall off from the surface of the silicon wafer during the post-cleaning process, while preventing the particles in the polishing liquid from adhering to the surface of the silicon wafer.

[0069] By comparing Comparative Example 1, Comparative Example 3 and Example 9, it can be seen that by adding acrylic acid monoethanolamide, the LLS and Haze on the surface of the silicon wafer will also be reduced accordingly. In comparison, the synergistic advantage of adding small molecules of alkyl carbon chain nitrogen heterocyclic amines and stearic acid esters is more obvious.

[0070] In summary, the present invention can adsorb the surface of silicon wafers by adding stearate and alkyl carbon chain nitrogen heterocyclic amine as surface protective agents in the polishing liquid, forming a softening film layer during polishing, and reducing the LLS and Haze value of the wafer surface. Using the fine polishing liquid of the present invention, the LLS (≥26nm) of the wafer surface can be reduced to 5 at best, and the Haze value is 0.048ppm.

[0071] Unless otherwise defined, the terms used in the present invention have the meanings commonly understood by those skilled in the art.

[0072] The embodiments described in the present invention are for illustrative purposes only and are not intended to limit the scope of protection of the present invention. Those skilled in the art may make various other substitutions, changes and improvements within the scope of the present invention. Therefore, the present invention is not limited to the above embodiments, but is only limited by the claims.

Claims

1. A chemical mechanical polishing solution for silicon wafers, characterized in that: High-purity nano-silica sol is used as polishing abrasive, and pH regulator, dispersant, surface protective agent and water are added; preferably, high-purity nano-silica sol, pH regulator, dispersant, stearate, alkyl carbon chain nitrogen heterocyclic amine and deionized water are included.

2. The chemical mechanical polishing liquid according to claim 1, characterized in that: The chemical mechanical polishing liquid comprises the following components in percentage by weight based on the total weight of the liquid: 1% to 20% of high-purity nano-silicon dioxide sol, 0.1% to 1% of a pH regulator, 0.1% to 5% of a dispersant, 0.01% to 0.5% of a stearate, 0.1% to 1% of an alkyl carbon chain nitrogen heterocyclic amine, and the remainder is deionized water.

3. The chemical mechanical polishing liquid according to claim 1 or 2, characterized in that: The metal ion content of the high-purity nano-silicon dioxide sol is less than 0.1 ppm, and the secondary particle size is 10 to 200 nm, preferably 50 to 150 nm.

4. The chemical mechanical polishing liquid according to claim 1 or 2, characterized in that: The pH regulator is selected from any one of potassium hydroxide, sodium hydroxide, ammonium hydroxide, aqueous ammonia, tetramethylammonium hydroxide, tetraethylammonium hydroxide, and tetrabutylammonium hydroxide, preferably aqueous ammonia.

5. The chemical mechanical polishing liquid according to claim 1 or 2, characterized in that: The dispersant is any one of hydroxymethyl cellulose, hydroxyethyl cellulose, hydroxypropyl cellulose and hydroxybutyl cellulose.

6. The chemical mechanical polishing liquid according to claim 1 or 2, characterized in that: The stearate is any one of ethylene glycol stearate, propylene glycol stearate, butylene glycol stearate, glyceryl hydroxystearate, isooctyl stearate, pentaerythritol monostearate, myristic acid stearate, sucrose stearate, xylitol monostearate, methyl glucoside stearate, and hydroxyacetamide stearate.

7. The chemical mechanical polishing liquid according to claim 1 or 2, characterized in that: The alkyl carbon chain nitrogen heterocyclic amine contains a cyclic structure having an amine group; preferably, the structure of the alkyl carbon chain nitrogen heterocyclic amine is as shown in formula (1), The R group is -(CH2) n CH3, 2≤n≤10, 1≤x≤3, 0≤y≤2; More preferably, the alkyl carbon chain nitrogen heterocyclic amine is selected from any one of 2-propyl nitrogen heterocyclic amine, 2-propyl aziridine, 2-pentyl aziridine, 3-propyl pyrrolidine, 3-butyl nitrogen heterocyclic amine, 2-butyl azetidine, 3-butyl piperidine, and 4-hexyl piperidine.

8. The chemical mechanical polishing liquid according to any one of claims 1 to 7, characterized in that: The pH range of the polishing liquid is 10 to 11; Preferably, the pH range after dilution 10 to 40 times with water is 9 to 11.

9. The method for preparing a chemical mechanical polishing solution for silicon wafers according to any one of claims 1 to 8, characterized in that: The following steps are involved: 1) mixing the dispersant, stearate, alkyl carbon chain nitrogen heterocyclic amine and an appropriate amount of water and stirring to obtain a pre-dispersion liquid; 2) After the pH adjuster and the remaining amount of water are mixed evenly, the pre-dispersion liquid is added and stirred for 10 to 180 minutes to obtain an intermediate product; 3) Under stirring conditions, high-purity silica sol is added to the intermediate product of step 2), and after being fully mixed, the chemical mechanical polishing solution for final polishing of silicon wafers is obtained.

10. Use of the chemical mechanical polishing liquid for silicon wafers according to any one of claims 1 to 8 or the chemical mechanical polishing liquid obtained by the preparation method according to claim 9 in chemical mechanical polishing of final silicon wafers.

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