Polishing solution and wafer polishing method

Abstract

The invention discloses a polishing solution and a wafer polishing method, and belongs to the field of polishing solutions. Wherein the polishing solution comprises a grinding material, an alkaline substance and sulfonated cellulose; the substitution degree of the sulfonated cellulose is 0.8 to 1.8; the addition amount of the sulfonated cellulose is 500 ppm to 5000 ppm. On the basis of an existing polishing solution, a proper amount of sulfonated cellulose is mainly introduced, and the substitution degree of sulfonated cellulose is further controlled to be 0.8-1.8, so that the residual quantity of particles on the surface of a wafer in the polishing process can be remarkably reduced, and the cleanliness of the surface of the wafer is improved; and meanwhile, the problem of insufficient flowability caused by too high viscosity of the system is avoided, and the subsequent cleaning procedure is facilitated. In addition, by adding sulfonated cellulose, the stability of the polishing solution is enhanced, the applicable pH range of the polishing solution is widened, and the polishing solution is wide in application prospect.

Description

Technical Field

[0001] This application belongs to the field of polishing fluids, specifically relating to a polishing fluid and a method for polishing wafers. Background Technology

[0002] In many fields such as semiconductor manufacturing and photovoltaic industry, different types of wafers, such as silicon wafers and silicon carbide wafers, serve as core basic materials, and their surface quality plays a decisive role in the performance and reliability of the final product. Polishing is a key step in improving wafer surface quality, and polishing slurry, as an important consumable in the polishing process, directly affects the polishing effect of the wafer.

[0003] However, existing polishing slurries have many problems in reducing residual particles on the wafer surface, controlling viscosity, and maintaining stability, making it difficult to meet the increasingly demanding requirements of modern semiconductor manufacturing and the photovoltaic industry for wafer surface quality. Summary of the Invention

[0004] This application aims to at least partially address one of the technical problems in the related art. Therefore, the purpose of this application is to provide a polishing slurry and a method for polishing wafers.

[0005] A first aspect of this application discloses a polishing fluid. According to embodiments of this application, the polishing fluid comprises abrasive particles, an alkaline substance, and sulfonated cellulose; The degree of substitution of the sulfonated cellulose is 0.8-1.8; The amount of sulfonated cellulose added is 500ppm-5000ppm.

[0006] The polishing slurry of the above embodiments of this application, based on existing polishing slurries, mainly introduces an appropriate amount of sulfonated cellulose and further controls its degree of substitution to 0.8-1.8. This not only significantly reduces the amount of residual particles on the wafer surface during polishing, improving the cleanliness of the wafer surface, but also avoids the problem of insufficient fluidity caused by excessively high system viscosity, and facilitates subsequent cleaning processes. In addition, the addition of sulfonated cellulose enhances the stability of the polishing slurry, broadens its applicable pH range, and has broad application prospects.

[0007] In addition, the polishing liquid according to the above embodiments of this application may also have the following additional technical features: In some embodiments of this application, the degree of substitution of the sulfonated cellulose is 1.0-1.6; In some embodiments of this application, the amount of sulfonated cellulose added is 1000ppm-3000ppm.

[0008] In some embodiments of this application, the amount of abrasive added is 0.2 wt.% to 20 wt.% by weight. The physical and chemical properties of the abrasive include: a particle size of 10nm-80nm and a polydispersity index (PDI) of <0.15. The abrasive includes at least one of colloidal silica, aluminum oxide and cerium dioxide, preferably colloidal silica.

[0009] In some embodiments of this application, the alkaline substance is used to adjust the pH of the polishing solution to 9-11; The alkaline substance includes at least one of ammonia, potassium hydroxide, and tetramethylammonium hydroxide.

[0010] In some embodiments of this application, the polishing fluid further includes surfactants and chelating agents.

[0011] In some embodiments of this application, the amount of surfactant added is 0.001 wt.%-0.05 wt.% by weight. The amount of the chelating agent added is 0.001 wt.%-1 wt.% by weight.

[0012] In some embodiments of this application, the surfactant includes at least one of AEO-3, AEO-7, AEO-9, polyoxyethylene octadecyl ether, Tween 20, Tween 80, PEG400, PEG600, sodium dodecylbenzene sulfonate, sodium dodecyl sulfate, sodium fatty alcohol polyoxyethylene ether sulfate, cocamidopropyl betaine, polyvinyl alcohol, and polyvinylpyrrolidone. The chelating agent includes at least one selected from citric acid, tartaric acid, ethylenediaminetetraacetic acid, gluconic acid, aminotriacetic acid, glycine, maleic acid, and malonic acid.

[0013] In some embodiments of this application, the remaining component in the polishing fluid is water.

[0014] A second aspect of this application discloses a method for polishing a wafer. According to embodiments of this application, the polishing agent used in the polishing method includes the polishing slurry described in the first aspect. This significantly reduces the amount of residual particles on the wafer surface and improves the cleanliness of the wafer surface.

[0015] Additional aspects and advantages of this application will be set forth in part in the description which follows, and in part will be obvious from the description, or may be learned by practice of this application. Detailed Implementation

[0016] The embodiments of this application are described in detail below by way of example, and are intended to explain this application, but should not be construed as limiting this application.

[0017] A first aspect of this application discloses a polishing fluid. According to embodiments of this application, the polishing fluid comprises abrasive particles, an alkaline substance, and sulfonated cellulose; The degree of substitution of the sulfonated cellulose is 0.8-1.8, for example, it can be 0.8, 1.0, 1.1, 1.2, 1.5, 1.8 or any of the above values, preferably 1.0-1.6; The amount of sulfonated cellulose added is 500ppm-5000ppm, for example, it can be 500ppm, 800ppm, 1000ppm, 1500ppm, 2000ppm, 3000ppm, 5000ppm or any range between the above values, preferably 1000ppm-3000ppm.

[0018] The polishing slurry of the above embodiments of this application, based on existing polishing slurries, mainly introduces an appropriate amount of sulfonated cellulose and further controls its degree of substitution to 0.8-1.8. This not only significantly reduces the amount of residual particles on the wafer surface during polishing, improving the cleanliness of the wafer surface, but also avoids the problem of insufficient fluidity caused by excessively high system viscosity, and facilitates subsequent cleaning processes. Furthermore, the addition of sulfonated cellulose enhances the stability of the polishing slurry, broadens its applicable pH range, and has wide application prospects. Specifically: This application controls the degree of substitution of sulfonated cellulose between 0.8 and 1.8, which is beneficial for utilizing the strong hydrophilicity of sulfonic acid groups to improve the problem of particle residue after wafer polishing. If the degree of substitution of sulfonated cellulose is too low (e.g., <0.5), the water solubility of sulfonated cellulose will be poor, and it will not be able to effectively improve the wettability of silicon wafer surfaces; if the degree of substitution of sulfonated cellulose is too high (e.g., >2.0), intermolecular cross-linking will occur, which may cause abrasive particles to settle when added to the polishing solution, affecting the wafer polishing effect, and the manufacturing cost will also increase significantly. In addition, the degree of substitution (DS) of sulfonated cellulose refers to the average number of sulfonic acid groups (-SO) on each dehydrated glucose unit (AGU) in the cellulose molecule. 3- The number of hydroxyl groups substituted. Meanwhile, the degree of substitution of sulfonated cellulose can be determined using existing detection methods such as acid-base titration (utilizing the acidity of sulfonic acid groups to titrate the content of sulfonic acid groups with a standard alkaline solution) and nuclear magnetic resonance spectroscopy (calculating DS through chemical shift and integral area ratio).

[0019] This application controls the amount of sulfonated cellulose added to the polishing solution to be between 500ppm and 5000ppm, which ensures that the sulfonated cellulose forms an effective interface protective layer on the wafer surface (if the amount added is less than 500ppm, an effective interface protective layer will not be formed), while avoiding the problem that excessive addition (such as >5000ppm) will cause the viscosity of the polishing solution to be too high, affecting its fluidity and subsequent cleaning effect.

[0020] Furthermore, by introducing sulfonated cellulose, the negatively charged sulfonic acid groups in this application increase the stability of the surface charge of the abrasive and prevent agglomeration. Moreover, sulfonated cellulose maintains good solubility and stability under acidic conditions, has a wider applicable pH range, and can be flexibly adapted to various polishing fluid systems. Additionally, the preparation method of sulfonated cellulose in this application can directly use commercially available products or be self-made using existing preparation processes.

[0021] According to some specific embodiments of this application, the amount of abrasive added, by weight percentage, is 0.2wt.%-20wt.%, for example, it can be 0.2wt.%, 0.5wt.%, 1wt.%, 5wt.%, 8wt.%, 10wt.%, 12wt.%, 15wt.%, 18wt.%, 20wt.%, or any range between the above values, preferably 0.5-5.0wt.%. By controlling the amount of abrasive added within the above-defined range, this application is beneficial to improving the polishing effect of the polishing slurry and controlling the production cost of the polishing slurry.

[0022] According to some specific embodiments of this application, the physicochemical properties of the abrasive include: a particle size of 10nm-80nm, for example, 10nm, 15nm, 20nm, 25nm, 30nm, 40nm, 60nm, 80nm, or any range between the above values, more preferably 20nm-60nm. The use of abrasives with the aforementioned suitable particle size in this application not only provides polishing effect and polishing rate, but also avoids damage to the wafer during the polishing process.

[0023] According to some specific embodiments of this application, the polydispersity index (PDI) of the abrasive is <0.15, for example, it can be 0.05, 0.08, 0.1, etc., preferably PDI <0.08. This application uses the aforementioned abrasive with a narrow particle size distribution to avoid damage to the wafer during polishing. Furthermore, the PDI of the abrasive can be measured using existing detection methods such as dynamic light scattering.

[0024] According to some specific embodiments of this application, the abrasive (or abrasive grain) includes at least one of colloidal silica, aluminum oxide, and cerium dioxide. This application does not specifically limit the selection of the abrasive type; an adaptive selection can be made based on abrasives disclosed in the art, with colloidal silica generally preferred.

[0025] According to some specific embodiments of this application, the alkaline substance is used to adjust the pH of the polishing slurry to 9-11, such as 9.5 or 10; the alkaline substance includes at least one of ammonia, potassium hydroxide, and tetramethylammonium hydroxide. This application does not specifically limit the type or amount of alkaline substance used; it can be adapted to the abrasives disclosed in the art, as long as it can maintain the required pH range of the polishing slurry system and take into account system compatibility.

[0026] According to some specific embodiments of this application, the polishing slurry further includes surfactants and chelating agents. To further improve the process window or adapt to special operating conditions, other additives such as surfactants and chelating agents may also be added to the polishing slurry described above. For example, to further reduce the surface tension of the polishing slurry, surfactants can be added, which helps the polishing slurry penetrate and rinse away residues. Alternatively, to chelate any metal ions (such as Fe) that may be present in the complexing system... 3+ Cu 2+ (etc.), chelating agents can be added.

[0027] According to some specific embodiments of this application, the amount of surfactant added, by weight percentage, is 0.001 wt.%-0.05 wt.%, for example, it can be 0.001 wt.%, 0.005 wt.%, 0.01 wt.%, 0.015 wt.%, 0.02 wt.%, 0.025 wt.%, 0.03 wt.%, 0.04 wt.%, 0.05 wt.%, or any range between the above values; the surfactant includes AEO-3, AEO-7, AEO-9, polyoxyethylene octadecyl ether, Tween 20, Tween 80, PEG400, PEG600, sodium dodecylbenzene sulfonate, and sodium dodecyl sulfate. The chelating agent comprises at least one of sodium fatty alcohol polyoxyethylene ether sulfate, cocamidopropyl betaine, polyvinyl alcohol, and polyvinylpyrrolidone; the amount of the chelating agent added is 0.001 wt.%-1 wt.% by weight, for example, 0.001 wt.%, 0.005 wt.%, 0.01 wt.%, 0.05 wt.%, 0.08 wt.%, 0.1 wt.%, 0.3 wt.%, 0.5 wt.%, 0.8 wt.%, 1.0 wt.%, or any range between the above values; the chelating agent includes at least one of citric acid, tartaric acid, ethylenediaminetetraacetic acid, gluconic acid, aminotriacetic acid, glycine, maleic acid, and malonic acid.

[0028] According to some specific embodiments of this application, the remaining component in the polishing liquid is water, preferably deionized water.

[0029] Furthermore, the preparation method of the polishing slurry described above in this application can be carried out with reference to the preparation process disclosed in the art, such as adding the raw materials in the polishing slurry other than alkaline substances to water and stirring and mixing, and then adding alkaline substances to adjust the pH to a preset range.

[0030] A second aspect of this application discloses a method for polishing a wafer. According to embodiments of this application, the polishing agent used in the polishing method includes the polishing slurry described in the first aspect. This significantly reduces the amount of residual particles on the wafer surface and improves the cleanliness of the wafer surface.

[0031] The embodiments of this application are described in detail below. It should be noted that the embodiments described below are exemplary and are only used to explain this application, and should not be construed as limiting this application. In addition, unless otherwise specified, all reagents used in the following embodiments are commercially available or can be synthesized according to the methods described herein or known methods. For reaction conditions not listed, they are also readily available to those skilled in the art.

[0032] Example 1 This embodiment provides a polishing fluid, comprising the following components: Abrasive: Specifically, colloidal silica (particle size 60nm, PDI=0.08), added at a rate of 2.0 wt.%; Alkaline substance: specifically ammonia water, used to adjust the pH of the polishing solution to 10.00; Sulfonated cellulose: degree of substitution 1.2, addition amount 1000 ppm; the preparation method of this sulfonated cellulose (using sulfur trioxide-pyridine method) includes the following steps: 1.00 g of dry microcrystalline cellulose is added to 30.00 mL of anhydrous DMF, and stirred at 80 °C for 2 h under nitrogen protection. After cooling to 50 °C, 0.56 g of SO3 is slowly added. Py (sulfur trioxide-pyridine complex) was added, and the system temperature was controlled to not exceed 60℃ during the feeding process. After the addition was complete, the temperature was raised to 78℃, and the reaction was continued for 5 hours. After the reaction was completed, 50 mL of ice water was added to the reaction system to terminate the reaction. The pH was adjusted to 7 with 1 mol / L NaOH, and the mixture was placed in a dialysis bag (MWCO=3500) and dialyzed for one week. The resulting dispersion was ultrasonically treated to finally obtain a dispersion of sulfonated cellulose; and its degree of substitution was determined by elemental analysis.

[0033] The remainder is deionized water.

[0034] Example 2 This embodiment provides a polishing liquid, which differs from Embodiment 1 only in that: (1) The degree of substitution of sulfonated cellulose is 0.8; the difference in the preparation method of this sulfonated cellulose is: 0.38g SO3 Py (sulfur trioxide-pyridine complex), heated to 82℃, reacted for 4 hours; the remaining steps were the same.

[0035] Example 3 This embodiment provides a polishing liquid, which differs from Embodiment 1 only in that: (1) The degree of substitution of sulfonated cellulose is 1.8; the difference in the preparation method of this sulfonated cellulose is: 0.84g SO3 Py (sulfur trioxide-pyridine complex), heated to 75°C, reacted for 6 hours; the remaining steps were the same.

[0036] Example 4 This embodiment provides a polishing liquid, which differs from Embodiment 1 only in that: (1) The amount of sulfonated cellulose added is 500 ppm.

[0037] Example 5 This embodiment provides a polishing liquid, which differs from Embodiment 1 only in that: (1) The amount of sulfonated cellulose added is 3000 ppm.

[0038] Example 6 This embodiment provides a polishing liquid, which differs from Embodiment 1 only in that: (1) The amount of sulfonated cellulose added is 5000 ppm.

[0039] Example 7 This embodiment provides a polishing fluid, comprising the following components: Abrasive: Specifically, colloidal silica (particle size 60nm, PDI=0.08), added at a rate of 2.0 wt.%; Alkaline substance: specifically ammonia water, used to adjust the pH of the polishing solution to 10.00; Sulfonated cellulose: degree of substitution 1.2, addition amount 1000ppm; Surfactant: Specifically, AEO-7, added at 20 ppm; Chelating agent: specifically citric acid, added at 20 ppm; The remainder is deionized water.

[0040] Example 8 This embodiment provides a polishing fluid, comprising the following components: Abrasive: Specifically, colloidal silica (particle size 60nm, PDI=0.08), added at a rate of 0.2wt.%; Alkaline substance: specifically ammonia water, used to adjust the pH of the polishing solution to 10.00; Sulfonated cellulose: degree of substitution 0.8, addition amount 500 ppm; Surfactant: Specifically, Tween 20, added at 15 ppm; Chelating agent: specifically tartaric acid, added at 20 ppm; The remainder is deionized water.

[0041] Example 9 This embodiment provides a polishing fluid, comprising the following components: Abrasive: Specifically, colloidal silica (particle size 60nm, PDI=0.08), added at a rate of 20wt.%; Alkaline substance: specifically ammonia water, used to adjust the pH of the polishing solution to 10.00; Sulfonated cellulose: degree of substitution 1.8, addition amount 5000ppm; Surfactant: Specifically, sodium dodecylbenzenesulfonate, added at 20 ppm; Chelating agent: specifically glycine, added at 20 ppm; The remainder is deionized water.

[0042] Comparative Example 1 This comparative example provides a polishing fluid, which differs from Example 1 only in that: (1) The degree of substitution of sulfonated cellulose is 0.5 (i.e., the degree of substitution of sulfonated cellulose is too low); the difference in the preparation method of this sulfonated cellulose is: 0.24g SO3 Py (sulfur trioxide-pyridine complex), heated to 85°C, reacted for 3 hours; the remaining steps were the same.

[0043] Comparative Example 2 This comparative example provides a polishing fluid, which differs from Example 1 only in that: (1) The degree of substitution of sulfonated cellulose is 2.0 (i.e., the degree of substitution of sulfonated cellulose is too high); the difference in the preparation method of this sulfonated cellulose is: 0.94g SO3 Py (sulfur trioxide-pyridine complex), heated to 70℃, reacted for 7 hours; the remaining steps were the same.

[0044] Comparative Example 3 This comparative example provides a polishing fluid, which differs from Example 1 only in that: (1) The amount of sulfonated cellulose added is 100 ppm (i.e., the amount of sulfonated cellulose added is too low).

[0045] Comparative Example 4 This comparative example provides a polishing fluid, which differs from Example 1 only in that: (1) The amount of sulfonated cellulose added is 10,000 ppm (i.e., the amount of sulfonated cellulose added is too high).

[0046] Comparative Example 5 This comparative example provides a polishing fluid, which differs from Example 1 only in that: (1) Replace sulfonated cellulose with carboxymethyl cellulose (the carboxymethyl cellulose was purchased from Aladdin, degree of substitution 1.2, Mw 250000).

[0047] Test Example 1 This test example applies the polishing slurry provided in the above embodiments and comparative examples to wafer polishing. The specific polishing conditions include: 1) Polishing pad: polyurethane; 2) Polishing pressure: 2 psi; 3) Wafer: 4-inch silicon wafer; 4) Grinding head speed: 57 rpm; 5) Grinding disk speed: 63 rpm; 6) Polishing slurry flow rate: 200 mL / min; 7) Polishing time: 2 min; 8) Cleaning after polishing: rinse with deionized water for 1 min.

[0048] Performance testing methods: 1. Detection of residual particles (>45nm) on wafer surface: Surfscan SP5.

[0049] 2. Wafer Polishing Removal Rate Calculation: Weigh the silicon wafers before and after polishing, and calculate the removal rate using the following formula: Where Δm is the difference in silicon wafer quality before and after polishing; ρ is the silicon wafer density; S is the silicon wafer surface area; and T is the polishing time.

[0050] The test results and the content of the main components in the above embodiments and comparative examples are shown in Table 1.

[0051] Table 1

[0052] As shown in Table 1, the polishing fluid provided in this application exhibits superior performance compared to Comparative Examples 1-5. Comparative Examples 1-4 verified that both excessively low and high substitution rates, as well as insufficient or excessive dosage, lead to performance degradation. Comparative Example 5, using carboxymethyl cellulose as a substitute, showed only a slight decrease in polishing rate, but the particle residue increased to 7 particles / cm², indicating that its ability to reduce particle residue is weaker than that of sulfonated cellulose. Examples 7-9 demonstrate the good compatibility of the polishing fluid of this invention with some common polishing aids (such as AEO-7 and Tween 20), achieving multifunctional optimization without sacrificing cleanliness, and is applicable to a wide range of scenarios.

[0053] Test Example 2 This test example performs stability and viscosity tests on the polishing slurries provided in Example 1 and Comparative Examples 1-4. The stability test method includes the following steps: comparing the PDI of the abrasive particles in the initial polishing slurry with the PDI after standing at room temperature for 7 days. Viscosity test: A Bollerfeld viscometer was used.

[0054] The test results are shown in Table 2.

[0055] Table 2

[0056] As shown in Table 2: Example 1: After adding 1000 ppm of sulfonated cellulose with a degree of substitution of 1.2, the initial PDI was 0.082, and the PDI remained basically unchanged after 7 days, indicating that it has excellent colloidal stability.

[0057] Comparative Example 2: The PDI of the abrasive particles increased after 7 days, possibly due to the degradation of the cellulose backbone caused by excessive sulfonation, which weakened the steric hindrance and reduced the stability.

[0058] Comparative Example 3: Although the PDI did not change much after 7 days, the granule residue was too high due to insufficient addition of sulfonated cellulose.

[0059] Comparative Example 4: Although it maintained low particle residue, the viscosity was as high as 4.2 mPa·s, and the PDI rose to 0.262 after 7 days, which posed a risk of long-term storage instability and poor process compatibility.

[0060] In the description of this specification, the references to terms such as "one embodiment," "some embodiments," "example," "specific example," or "some examples," etc., indicate that a specific feature, structure, silicone material, or characteristic described in connection with that embodiment or example is included in at least one embodiment or example of this application. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, silicone materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples. Moreover, without contradiction, those skilled in the art can combine and integrate the different embodiments or examples described in this specification, as well as the features of different embodiments or examples.

[0061] Although embodiments of this application have been shown and described above, it is understood that the above embodiments are exemplary and should not be construed as limiting this application. Those skilled in the art can make changes, modifications, substitutions and variations to the above embodiments within the scope of this application.

Claims

1. A polishing liquid, characterized in that, Including abrasives, alkaline substances, and sulfonated cellulose; The degree of substitution of the sulfonated cellulose is 0.8-1.8; The amount of sulfonated cellulose added is 500ppm-5000ppm.

2. The polishing slurry according to claim 1, characterized in that, The degree of substitution of the sulfonated cellulose is 1.0-1.

6.

3. The polishing slurry according to claim 1, characterized in that, The amount of sulfonated cellulose added is 1000ppm-3000ppm.

4. The polishing slurry according to claim 1, characterized in that, The amount of abrasive added is 0.2 wt.% to 20 wt.% by weight. The physical and chemical properties of the abrasive include: a particle size of 10nm-80nm and a polydispersity index (PDI) of <0.

15. The abrasive includes at least one of colloidal silica, aluminum oxide, and cerium dioxide.

5. The polishing slurry according to claim 1, characterized in that, The alkaline substance is used to adjust the pH of the polishing solution to 9-11; The alkaline substance includes at least one of ammonia, potassium hydroxide, and tetramethylammonium hydroxide.

6. The polishing liquid according to any one of claims 1 to 5, characterized in that, The polishing fluid also includes surfactants and chelating agents.

7. The polishing slurry according to claim 6, characterized in that, The amount of the surfactant added is 0.001 wt.% to 0.05 wt.% by weight. The amount of the chelating agent added is 0.001 wt.%-1 wt.% by weight.

8. The polishing slurry according to claim 7, characterized in that, The surfactant includes at least one of AEO-3, AEO-7, AEO-9, polyoxyethylene octadecyl ether, Tween 20, Tween 80, PEG400, PEG600, sodium dodecylbenzene sulfonate, sodium dodecyl sulfate, sodium fatty alcohol polyoxyethylene ether sulfate, cocamidopropyl betaine, polyvinyl alcohol, and polyvinylpyrrolidone. The chelating agent includes at least one selected from citric acid, tartaric acid, ethylenediaminetetraacetic acid, gluconic acid, aminotriacetic acid, glycine, maleic acid, and malonic acid.

9. The polishing slurry according to claim 6, characterized in that, The remaining component in the polishing solution is water.

10. A method for polishing a wafer, characterized in that, The polishing reagent used in the polishing method includes the polishing liquid according to any one of claims 1 to 9.

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