Composite abrasive-based chemical mechanical polishing liquid, preparation method and application thereof

Abstract

This invention discloses a chemical mechanical polishing slurry based on composite abrasives, its preparation method, and its application, belonging to the field of semiconductor manufacturing technology. The polishing slurry comprises: composite abrasives, specialized chemical additives, and deionized water. The total mass percentage of the composite abrasives is 10-30%, and the composite abrasives include square cerium oxide, round cerium oxide, and α-alumina. The mass percentage of square cerium oxide in the composite abrasives is 40-60%, round cerium oxide is 20-40%, and α-alumina is 10-30%. The specialized chemical additives include surfactants, complexing agents, oxidants, and pH adjusters. The total mass percentage of surfactants is 0.1-1%, complexing agents are 0.05-0.5%, oxidants are 0.1-2%, and the pH adjuster adjusts the pH value of the polishing slurry to 4.0-6.0. The remainder is deionized water. The polishing slurry provided by this invention can achieve high material removal rate, low surface roughness, and low subsurface damage in silicon carbide wafers.

Description

Technical Field

[0001] This invention relates to the field of semiconductor manufacturing technology, and in particular to a chemical mechanical polishing slurry based on composite abrasives, its preparation method, and its application. Background Technology

[0002] Silicon carbide (SiC), as a third-generation wide-bandgap semiconductor material, possesses excellent properties such as high thermal conductivity, high breakdown electric field, and high electron saturation drift velocity, making it suitable for high-temperature, high-frequency, and high-power devices. However, the high hardness and strong chemical inertness of silicon carbide (SiC) material pose significant challenges.

[0003] Existing silicon carbide (SiC) wafer polishing generally uses a single cerium oxide (CeO2) abrasive or a single aluminum oxide (Al2O3) abrasive, and the shape of the abrasive is either square or round.

[0004] Cerium oxide (CeO2) abrasives exhibit hydration reactivity with silicon carbide (SiC) surfaces, enabling chemimechanical polishing; however, pure cerium oxide has relatively weak mechanical properties. Aluminum oxide (Al2O3) abrasives have high hardness and strong mechanical properties, but are prone to surface scratches. Furthermore, the shape of the abrasive significantly impacts polishing results; square abrasives have sharp edges and strong cutting ability but are prone to embedding in the surface, while round abrasives have good flowability but low cutting efficiency. Therefore, existing wafer polishing slurries struggle to achieve low surface roughness and low subsurface damage, significantly hindering the development of the silicon carbide (SiC) semiconductor industry. Summary of the Invention

[0005] The technical problem to be solved by the present invention is to provide a chemical mechanical polishing slurry based on composite abrasives, which has high material removal rate, low surface roughness and low subsurface damage.

[0006] This invention is achieved through the following technical solution: A chemical mechanical polishing slurry based on composite abrasives, comprising composite abrasives, special chemical additives, and deionized water, wherein the total mass percentage of the composite abrasives is 10-30%, and the composite abrasives include square cerium oxide, round cerium oxide, and... Alumina, wherein the square cerium oxide accounts for 40-60% of the mass of the composite abrasive, and the round cerium oxide accounts for 20-40% of the mass of the composite abrasive. The alumina content in the composite abrasive is 10-30% by mass. The special chemical additives include surfactants, complexing agents, oxidants, and pH adjusters. The total mass content of the surfactants is 0.1-1%, the total mass content of the complexing agents is 0.05-0.5%, the total mass content of the oxidants is 0.1-2%, and the pH adjuster adjusts the pH value of the chemical mechanical polishing slurry to 4.0 to 6.0. The remainder is deionized water.

[0007] Optimized, the square cerium oxide particles have a diameter of 50-200 nanometers, the round cerium oxide particles have a diameter of 50-200 nanometers, and the alumina particles have a diameter of 50-150 nanometers.

[0008] The optimized surfactant is a compound of a nonionic surfactant and anionic surfactant.

[0009] In the optimized configuration, the nonionic surfactant is polyethylene glycol, the anionic surfactant is sodium polyacrylate, and the surfactant contains polyethylene glycol at a mass ratio of 16.7%-83.3% and sodium polyacrylate at a mass ratio of 83.3%-16.7%.

[0010] Optimized, the complexing agent is a polydentate phosphonic acid complexing agent.

[0011] Optimized, the oxidant comprises hydrogen peroxide and potassium periodate or hydrogen peroxide and ammonium persulfate, wherein hydrogen peroxide accounts for 10%-40% of the total mass of the oxidant.

[0012] Furthermore, the pH adjuster includes buffer pairs composed of organic acids and their salts, and alkaline pH adjusters.

[0013] A method for preparing a chemical mechanical polishing slurry based on composite abrasives, used to prepare a chemical mechanical polishing slurry based on composite abrasives as described in any one of the above, comprising the following steps: S1: Add the weighed portion of deionized water to a reactor equipped with a stirrer, thermometer and constant temperature water bath jacket, start stirring, control the reactor speed at 200 to 400 rpm, and slowly add the weighed surfactant, complexing agent and oxidant in sequence during stirring, stirring until completely dissolved to complete the preparation of the mother liquor. S2: Slowly add a pH adjuster consisting of a buffer pair of organic acids and their salts to the prepared mother liquor to initially adjust the pH value of the mother liquor to between 3.5 and 4.0; S3: Take a portion of the mother liquor obtained in step S2 and send it to a shear disperser or ball mill for primary high-energy dispersion. Slowly add the weighed α-alumina in batches. The speed of the shear disperser or ball mill is controlled at 3000 to 5000 rpm, and the dispersion time is 20 to 40 minutes until a stable primary dispersion slurry is formed. S4: Return the primary dispersion slurry obtained in step S3 to the remaining mother liquor in the reactor. Adjust the reactor speed to 400 to 600 rpm. While stirring, slowly and evenly add the weighed square cerium oxide abrasive and round cerium oxide abrasive in sequence. After all the abrasive is added, continue stirring for 30 to 60 minutes to ensure that all components are mixed evenly. S5: Continue stirring and slowly add alkaline pH adjuster to adjust the pH value to the target range of 4.0 to 6.0. Then, add the remaining deionized water to the final designed volume and continue stirring for 15 to 30 minutes. S6: Sonicate the prepared polishing solution for 10 to 20 minutes using an ultrasonic oscillator. Then, filter the polishing solution through a bag filter with a rated pore size of 1 to 5 microns or a multi-stage series filter to obtain the final product.

[0014] In the optimized step S1, the reactor temperature is maintained at 25±5℃.

[0015] An application of a composite abrasive-based chemical mechanical polishing slurry, wherein the composite abrasive-based chemical mechanical polishing slurry described above is used for polishing silicon carbide wafers.

[0016] Beneficial effects of the invention: The present invention provides a chemical mechanical polishing slurry based on composite abrasives, its preparation method, and its application, which have the following advantages: 1. Synergistic mechanism of multi-component abrasives: α-alumina has high hardness and can provide strong mechanical cutting, effectively breaking the SiC surface lattice and promoting material removal; cerium oxide undergoes a hydration reaction with the SiC surface under weakly acidic conditions to generate a softer SiO2-CeO2 composite layer, which is easily removed by mechanical action; square cerium oxide has sharp edges and corners, strong cutting ability, and improves the initial removal rate; round cerium oxide has a smooth surface and good rolling properties, which can reduce scratches and promote the discharge of polishing products.

[0017] 2. Extremely high (MRR): Through the synergistic effect of the strong mechanical force of α-alumina and the sharp cutting of square cerium oxide, combined with the surface softening effect of the oxidant.

[0018] 3. Excellent surface quality: The lubricating and filling effect of round cerium oxide combined with the dispersing effect of surfactants can effectively reduce scratches and surface defects, and improve surface quality.

[0019] 4. Low subsurface damage: The precise balance between chemical and mechanical effects avoids simple violent cutting, significantly reduces the depth of lattice damage, and improves device performance and reliability.

[0020] 5. Superior Dispersion: Through a "step-by-step dispersion" strategy, especially the "first-level high-energy dispersion" of α-alumina, the composite abrasive component with the greatest hardness is ensured to be fully dispersed, reducing the risk of surface scratches from the source.

[0021] 6. High stability: Precise pH control process and ultrasonic post-treatment enable the composite abrasive particles to have extremely high absolute potential values ​​in the polishing fluid, thereby achieving excellent suspension stability and storage stability.

[0022] 7. Performance optimization: This preparation method protects the crystal morphology and function of each component of the composite abrasive to the greatest extent, ensuring that the theoretical performance of the polishing slurry is fully reflected in the actual product. Detailed Implementation

[0023] A chemical mechanical polishing slurry based on composite abrasives comprises composite abrasives, special chemical additives, and deionized water, with the total mass percentage being 10-30%. The composite abrasives include square cerium oxide, round cerium oxide, and α-alumina, with the square cerium oxide comprising 40-60% of the composite abrasives, the round cerium oxide comprising 20-40% of the composite abrasives, and the α-alumina comprising 10-30% of the composite abrasives. The special chemical additives include surfactants, complexing agents, oxidants, and pH adjusters, with the surfactants comprising 0.1-1% of the total mass, the complexing agents comprising 0.05-0.5% of the total mass, the oxidants comprising 0.1-2% of the total mass, and the pH adjuster adjusting the pH of the chemical mechanical polishing slurry to 4.0-6.0. The remainder is deionized water.

[0024] Because alumina has a high hardness, reaching 9 on the Mohs scale, it can provide strong mechanical cutting, effectively breaking the SiC surface lattice and promoting material removal. Cerium oxide, on the other hand, is rich in hydroxyl groups (-OH) on its surface, which can undergo a hydration reaction with the surface under weakly acidic conditions to form a softer SiO2-CeO2 composite layer, which is easily removed by mechanical action. Square cerium oxide has sharp edges and corners, strong cutting ability, and can improve the initial removal rate, while round cerium oxide has a smooth surface and good rolling properties, which can reduce scratches and promote the discharge of polishing products.

[0025] Through the synergistic effect of the strong mechanical force of α-alumina and the sharp cutting of square cerium oxide, combined with the surface softening effect of the oxidant, the material removal rate of SiC can be increased by more than 50%, and the polishing speed can reach more than 500 nm / h. The lubricating and filling effect of round cerium oxide combined with the dispersing effect of surfactant can effectively reduce scratches and surface defects. The final surface roughness (Ra) can be better than 0.5 nanometers, achieving atomic-level flatness. Furthermore, the precise balance between chemical and mechanical effects avoids simple violent cutting, significantly reduces the lattice damage depth, and improves the performance and reliability of the device.

[0026] Optimized, the square cerium oxide particles have a diameter of 50-200 nanometers, the round cerium oxide particles have a diameter of 50-200 nanometers, and the α-alumina particles have a diameter of 50-150 nanometers.

[0027] The optimized surfactant is a compound of a nonionic surfactant and anionic surfactant.

[0028] In the optimized form, the surfactant contains polyethylene glycol at a mass ratio of 16.7%-83.3% and sodium polyacrylate at a mass ratio of 83.3%-16.7%.

[0029] Optimized, the complexing agent is a polydentate phosphonic acid complexing agent.

[0030] Optimized, the oxidant comprises hydrogen peroxide and potassium periodate or hydrogen peroxide and ammonium persulfate, wherein hydrogen peroxide accounts for 10%-40% of the total mass of the oxidant.

[0031] Nonionic surfactant polyethylene glycol (PEG) is primarily adsorbed onto composite abrasive particles (especially α-alumina) and wafer surfaces. Through steric hindrance, it prevents the agglomeration of hard abrasive particles, providing lubrication and scratch protection. Anionic surfactant sodium polyacrylate, on the other hand, acts primarily on cerium oxide particles through double-layer repulsion, providing electrostatic stability, preventing flocculation and sedimentation, and maintaining the long-term stability of the polishing slurry. By employing two surfactants and utilizing two mechanisms (steric hindrance + electrostatic repulsion), a more powerful and comprehensive system is formed, offering better performance than a single surfactant and adaptability to a wider range of pH and concentration variations.

[0032] The oxidant used is either hydrogen peroxide or ammonium persulfate, rather than a single oxidant. A combination of oxidants is employed, with one acting rapidly in the initial polishing stage and the other providing continuous and stable oxidation throughout the polishing process. Hydrogen peroxide reacts rapidly in the initial polishing stage, quickly forming a thin softening layer on the SiC surface, laying the foundation for mechanical removal. However, it is unstable and easily decomposes. Potassium periodate or ammonium persulfate, on the other hand, is chemically more stable and can continuously and slowly decompose to release oxidizing active groups during polishing, providing a durable and mild oxidizing environment. This avoids surface over-corrosion or uneven oxidation rates caused by drastic fluctuations in oxidation. The combination of these two achieves a perfect balance between "rapid onset" and "long-lasting effect," making the chemical action throughout the polishing process more stable and controllable.

[0033] Furthermore, the pH adjuster includes buffer pairs composed of organic acids and their salts, and alkaline pH adjusters.

[0034] A method for preparing a chemical mechanical polishing slurry based on composite abrasives, used to prepare a chemical mechanical polishing slurry based on composite abrasives as described in any one of the above, comprising the following steps: S1: Add the weighed portion of deionized water to a reactor equipped with a stirrer, thermometer and constant temperature water bath jacket, start stirring, control the reactor speed at 200 to 400 rpm, and slowly add the weighed surfactant, complexing agent and oxidant in sequence during stirring, stirring until completely dissolved to complete the preparation of the mother liquor. The optimal temperature for the reactor during this stage is 25±5℃, which can prevent some oxidants from decomposing prematurely at high temperatures.

[0035] S2: Slowly add a pH adjuster consisting of a buffer pair of organic acids and their salts to the prepared mother liquor to initially adjust the pH value of the mother liquor to between 3.5 and 4.0; This step can use an online pH meter to monitor the pH value of the mother liquor in real time, and initially adjust the pH value of the mother liquor to an acidic environment between 3.5 and 4.0, which is beneficial to the dispersion of subsequent composite abrasives, especially cerium oxide particles.

[0036] S3: Take a portion of the mother liquor obtained in step S2 and send it to a shear disperser for primary high-energy dispersion. One-third of the total volume of the mother liquor obtained in step S2 can be sent to a shear disperser or ball mill, and the weighed α-alumina can be slowly added in batches. The rotation speed in the shear disperser or ball mill is controlled at 3000 to 5000 rpm, and the dispersion time is 20 to 40 minutes until a stable primary dispersion slurry is formed. Because α-alumina has the highest hardness, high density, and is prone to settling, it is a major risk factor for agglomeration and scratches. This step uses high-energy dispersion to fully break down its primary particles, forming a stable primary dispersion slurry. This is a key prerequisite for obtaining a scratch-free surface, ensuring that the composite abrasive component with the highest hardness is fully dispersed, thus reducing the risk of surface scratches from the source.

[0037] S4: Return the primary dispersion slurry obtained in step S3 to the remaining mother liquor in the reactor. Adjust the reactor speed to 400 to 600 rpm. While stirring, slowly and evenly add the weighed square cerium oxide abrasive and round cerium oxide abrasive in sequence. After all the abrasive is added, continue stirring for 30 to 60 minutes to ensure that all components are mixed evenly. This step involves gentle dispersion, where the composite abrasive is dispersed in two steps: first the "hard" and then the "soft." The hardest and most difficult-to-disperse α-alumina is treated separately, and then the relatively easier-to-disperse cerium oxide abrasive is introduced under gentler conditions. This avoids the agglomeration of hard particles due to insufficient dispersion energy and also prevents the cerium oxide crystal structure from being damaged due to excessive shearing.

[0038] S5: Continue stirring and slowly add alkaline regulator to adjust the pH value to the target range of 4.0 to 6.0. Then, add the remaining deionized water to the final designed volume and continue stirring for 15 to 30 minutes. This step involves monitoring the pH value with a precision pH meter to ensure accuracy, thereby giving the abrasive particles an extremely high absolute Zeta potential in the polishing fluid, resulting in excellent suspension and storage stability.

[0039] S6: The prepared polishing slurry is ultrasonically treated for 10 to 20 minutes using an ultrasonic oscillator, and then filtered through a bag filter or a multi-stage series filter with a rated pore size of 1 to 5 micrometers to obtain the final product.

[0040] The polishing slurry prepared by the above method protects the crystal morphology and function of each component of the composite abrasive to the greatest extent, ensuring that the theoretical performance of the polishing slurry is fully reflected in the actual product.

[0041] An application of a composite abrasive-based chemical mechanical polishing slurry, wherein the composite abrasive-based chemical mechanical polishing slurry described above is used for polishing silicon carbide wafers.

[0042] Using the chemical mechanical polishing slurry based on composite abrasives prepared by the above method for silicon carbide wafer polishing can improve the polishing speed of silicon carbide wafers and result in excellent surface quality of the treated silicon carbide wafers.

[0043] In summary, the chemical mechanical polishing slurry based on composite abrasives provided by this invention can achieve high material removal rate, low surface roughness, and low subsurface damage when used for polishing silicon carbide wafers.

[0044] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A chemical mechanical polishing slurry based on composite abrasives, characterized in that: The chemimechanical polishing solution comprises composite abrasive, specialized chemical additives, and deionized water. The total mass percentage of the composite abrasive is 10-30%. The composite abrasive includes square cerium oxide, round cerium oxide, and α-alumina. The square cerium oxide accounts for 40-60% of the composite abrasive, the round cerium oxide accounts for 20-40%, and the α-alumina accounts for 10-30%. The specialized chemical additives include surfactants, complexing agents, oxidants, and pH adjusters. The total mass percentage of the surfactants is 0.1-1%, the total mass percentage of the complexing agents is 0.05-0.5%, the total mass percentage of the oxidants is 0.1-2%, and the pH adjuster adjusts the pH value of the chemimechanical polishing solution to 4.0-6.

0. The remainder is deionized water.

2. The chemical mechanical polishing slurry based on composite abrasives according to claim 1, characterized in that: The square cerium oxide particles have a diameter of 50-200 nanometers, the round cerium oxide particles have a diameter of 50-200 nanometers, and the α-alumina particles have a diameter of 50-150 nanometers.

3. The chemical mechanical polishing slurry based on composite abrasives according to claim 1, characterized in that: The surfactant is a compound of a nonionic surfactant and anionic surfactant.

4. The chemical mechanical polishing slurry based on composite abrasives according to claim 3, characterized in that: The nonionic surfactant is polyethylene glycol, and the anionic surfactant is sodium polyacrylate. The surfactant contains polyethylene glycol at a mass ratio of 16.7%-83.3% and sodium polyacrylate at a mass ratio of 83.3%-16.7%.

5. The chemical mechanical polishing slurry based on composite abrasives according to claim 1, characterized in that: The complexing agent is a polydentate phosphonic acid complexing agent.

6. The chemical mechanical polishing slurry based on composite abrasives according to claim 1, characterized in that: The oxidant includes hydrogen peroxide and potassium periodate or hydrogen peroxide and ammonium persulfate, wherein hydrogen peroxide accounts for 10%-40% of the total mass of the oxidant.

7. The chemical mechanical polishing slurry based on composite abrasives according to claim 1, characterized in that: The pH adjuster includes buffer pairs composed of organic acids and their salts, and alkaline pH adjusters.

8. A method for preparing a chemical mechanical polishing slurry based on composite abrasives, used to prepare a chemical mechanical polishing slurry based on composite abrasives as described in any one of claims 1 to 7, characterized in that: Includes the following steps: S1: Add the weighed portion of deionized water to a reactor equipped with a stirrer, thermometer and constant temperature water bath jacket, start stirring, control the reactor speed at 200 to 400 rpm, and slowly add the weighed surfactant, complexing agent and oxidant in sequence during stirring, stirring until completely dissolved to complete the preparation of the mother liquor. S2: Slowly add a pH adjuster consisting of a buffer pair of organic acids and their salts to the prepared mother liquor to initially adjust the pH value of the mother liquor to between 3.5 and 4.0; S3: Take a portion of the mother liquor obtained in step S2 and send it to a shear disperser or ball mill for primary high-energy dispersion. Slowly add the weighed α-alumina in batches. The speed of the shear disperser or ball mill is controlled at 3000 to 5000 rpm, and the dispersion time is 20 to 40 minutes until a stable primary dispersion slurry is formed. S4: Return the primary dispersion slurry obtained in step S3 to the remaining mother liquor in the reactor. Adjust the reactor speed to 400 to 600 rpm. While stirring, slowly and evenly add the weighed square cerium oxide abrasive and round cerium oxide abrasive in sequence. After all the abrasive is added, continue stirring for 30 to 60 minutes to ensure that all components are mixed evenly. S5: Continue stirring and slowly add alkaline pH adjuster to adjust the pH value to the target range of 4.0 to 6.

0. Then, add the remaining deionized water to the final designed volume and continue stirring for 15 to 30 minutes. S6: The prepared polishing slurry is ultrasonically treated for 10 to 20 minutes using an ultrasonic oscillator, and then filtered through a bag filter or a multi-stage series filter with a rated pore size of 1 to 5 micrometers to obtain the final product.

9. The method for preparing a chemical mechanical polishing slurry based on composite abrasives according to claim 8, characterized in that: In step S1, the temperature of the reactor is maintained at 25±5℃.

10. An application of a chemical mechanical polishing slurry based on composite abrasives, characterized in that, The chemical mechanical polishing slurry based on composite abrasives as described in any one of claims 1 to 7 is used for polishing silicon carbide wafers.