Silicon carbide polishing liquid and method of making same

Abstract

The application discloses a silicon carbide polishing liquid and a preparation method thereof, and relates to the technical field of semiconductor polishing materials. The silicon carbide polishing liquid comprises 1-20 parts of abrasive, 0.01-5 parts of oxidant, 0.01-0.5 parts of pH regulator and 85-95 parts of water; wherein the abrasive comprises first abrasive and second abrasive, the first abrasive comprises at least one of aluminum oxide and zirconium oxide, and the second abrasive is a lignin / oxidized graphene / nano silicon oxide composite microsphere. The silicon carbide polishing liquid provided by the application can solve the problems of easy agglomeration and sedimentation of conventional silicon carbide polishing liquids due to the use of multiple abrasives, improve the stability of the polishing liquid, and improve the removal efficiency of the polishing liquid and the surface quality of a workpiece after processing.

Description

Technical Field

[0001] This invention relates to the field of semiconductor polishing materials technology, and in particular to a silicon carbide polishing slurry and its preparation method. Background Technology

[0002] In semiconductor manufacturing, chemical mechanical polishing (CMP) is a crucial step in achieving global wafer planarization. CMP combines chemical and mechanical actions to efficiently and controllably remove material from the workpiece surface. During the polishing process, the polishing slurry plays a key role. First, the workpiece surface material reacts chemically with oxidizing agents and other components in the polishing slurry, forming a relatively easy-to-remove soft layer. Subsequently, under the combined mechanical action of the abrasive particles and polishing pads in the slurry, this soft layer is removed, exposing a new workpiece surface. By repeating this chemical-mechanical cycle, the workpiece surface is finally polished, achieving high-precision, high-flatness surface processing.

[0003] Silicon carbide (SiC) is increasingly used in power devices, radio frequency devices, and other fields due to its excellent physical and electrical properties. However, SiC's high hardness and strong chemical inertness make high-quality surface polishing extremely challenging. Currently, SiC polishing slurries mainly use superhard materials such as alumina or zirconium oxide as abrasives. Although these abrasives can provide high material removal rates, their high rigidity and sharp edges easily introduce mechanical damage such as scratches and microcracks into the SiC surface during polishing, resulting in high surface roughness that fails to meet the stringent surface quality requirements of advanced semiconductor devices. Furthermore, due to the inconsistent sedimentation rates of the components in the silicon carbide polishing slurry, instability phenomena such as stratification and sedimentation can occur during storage or use, leading to decreased system homogeneity and severely impacting process repeatability and product yield.

[0004] Therefore, developing a silicon carbide polishing slurry that can achieve high polishing efficiency and excellent surface quality while possessing good dispersion stability remains an important issue that urgently needs to be addressed in this field. Summary of the Invention

[0005] The main objective of this invention is to propose a silicon carbide polishing slurry and its preparation method, aiming to solve the problem that existing silicon carbide polishing slurries cannot simultaneously achieve high polishing efficiency, high surface quality, and stability.

[0006] To achieve the above objectives, the present invention proposes a silicon carbide polishing slurry, comprising the following components by mass: 1-20 parts of abrasive, 0.01-5 parts of oxidant, 0.01-0.5 parts of pH adjuster, and 85-95 parts of water; wherein the abrasive comprises a first abrasive and a second abrasive, the first abrasive comprising at least one of alumina and zirconium oxide, and the second abrasive being lignin / graphene oxide / nano-silica composite microspheres.

[0007] In one embodiment, the particle size of the first abrasive is 0.6 μm to 1.2 μm, and the particle size of the second abrasive is in the range of 200 nm to 500 nm.

[0008] In one embodiment, the mass ratio of the first abrasive to the second abrasive is (3~10):1.

[0009] In one embodiment, the method for preparing the second abrasive includes the following steps:

[0010] A lignin sulfate solution was obtained by mixing N,N-dimethylformamide and water.

[0011] Graphene oxide was dispersed in ethanol to obtain a graphene oxide dispersion.

[0012] Nano-silica, sodium dodecylbenzenesulfonate, and phenylaminomethyltrimethoxysilane were dispersed in ethanol to obtain a modified nano-silica dispersion.

[0013] The lignin solution is stirred, and the graphene oxide dispersion and the modified nano silica dispersion are added dropwise to the lignin solution while maintaining stirring to obtain a self-assembled product. The self-assembled product is then dialyzed and dried to obtain a second abrasive.

[0014] In one embodiment, the volume ratio of N,N-dimethylformamide to water is 7:3 to 9:1; and / or,

[0015] The sulfate lignin accounts for 15% to 30% of the mass in the lignin solution; and / or,

[0016] The mass ratio of sulfate lignin to graphene oxide is (1~4):1; and / or,

[0017] The mass ratio of sulfate lignin to nano-silica is 1:(1.2~2); and / or,

[0018] The mass ratio of the nano-silica, sodium dodecylbenzenesulfonate, and phenylaminomethyltrimethoxysilane is (10~20):10:10.

[0019] In one embodiment, the radial dimension of the graphene oxide is ≤200 nm; and / or,

[0020] The particle size of the nano-silica is 20~100nm.

[0021] In one embodiment, the silicon carbide polishing slurry further includes 0.01 to 0.05 parts of lignin nanoparticles, wherein the lignin nanoparticles have a particle size of 50 to 100 nm.

[0022] In one embodiment, the oxidant includes at least one of potassium permanganate, hydrogen peroxide, hypochlorite, iodate, periodate, and nitric acid.

[0023] In one embodiment, the step of mixing the first abrasive, the second abrasive, the oxidant, and water, and then adjusting the pH of the system to 9-11 using a pH adjuster to obtain the silicon carbide polishing slurry includes:

[0024] This invention also proposes a method for preparing the silicon carbide polishing slurry described in the foregoing technical solution, comprising the following steps:

[0025] The first abrasive, the second abrasive, the oxidant and water are mixed, and then the pH value of the system is adjusted to 9-11 with a pH adjuster to obtain silicon carbide polishing slurry.

[0026] The first abrasive, the second abrasive, the oxidant, the lignin nanoparticles and water were mixed, and then the pH value of the system was adjusted to 9-11 with a pH adjuster to obtain the silicon carbide polishing slurry.

[0027] The polishing slurry provided by the present invention uses at least one of alumina and zirconium oxide as the first abrasive and lignin / graphene oxide / nano silica composite microspheres as the second abrasive. By utilizing the steric hindrance effect between the lignin / graphene oxide / nano silica composite microspheres, the second abrasive can be uniformly dispersed among the first abrasive, thereby effectively improving the problem of easy agglomeration and sedimentation in conventional silicon carbide polishing slurries due to the use of multiple abrasives, and making the entire polishing slurry system have good stability. Meanwhile, the introduction of lignin components into the lignin / graphene oxide / nano silica composite microspheres helps to capture metal ions and other removal products generated during polishing, thereby reducing residual contamination on the wafer surface and facilitating the post-cleaning step of wafer polishing. The lignin molecules themselves have a certain degree of flexibility and elasticity, which can play a "buffering" and "scrubbing" role during polishing. Moreover, different lignin molecules can also form a three-dimensional network structure and undergo elastic deformation to generate tension. During the grinding process, the lignin / graphene oxide / nano silica composite microspheres located at the lower part of the wafer surface have a greater mechanical effect when they are squeezed and deformed compared to the higher parts of the wafer surface. Therefore, the removal rate is higher and the planarization effect of polishing is better. In addition, the graphene component in the lignin / graphene oxide / nano silica composite microspheres not only produces a super-lubricating effect, greatly reducing the coefficient of friction and minimizing surface scratches and subsurface damage, but also acts as a thermally conductive filler. Through the three-dimensional network structure constructed by lignin, it forms an efficient thermally conductive pathway, quickly dissipating heat from the polishing zone. This prevents localized high temperatures from causing surface deformation or polishing fluid failure, further improving the surface quality of the workpiece after processing and enhancing the stability of the polishing fluid. Detailed Implementation

[0028] The technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0029] It should be noted that if the embodiments of the present invention involve directional indicators (such as up, down, left, right, front, back, etc.), the directional indicators are only used to explain the relative positional relationship and movement of the components in a specific posture. If the specific posture changes, the directional indicators will also change accordingly.

[0030] Furthermore, if the embodiments of this invention involve descriptions such as "first" or "second," these descriptions are for descriptive purposes only and should not be construed as indicating or implying their relative importance or implicitly specifying the number of technical features indicated. Thus, a feature defined with "first" or "second" may explicitly or implicitly include at least one of those features. Additionally, the use of "and / or" or "and / or" throughout the text includes three parallel solutions. For example, "A and / or B" includes solution A, solution B, or a solution where both A and B are satisfied simultaneously. Furthermore, the technical solutions of the various embodiments can be combined with each other, but this must be based on the ability of those skilled in the art to implement them. When the combination of technical solutions is contradictory or impossible to implement, it should be considered that such a combination of technical solutions does not exist and is not within the scope of protection claimed by this invention.

[0031] Currently, silicon carbide (SiC) polishing slurries mainly use superhard materials such as alumina or zirconium oxide as abrasives. Although such abrasives can provide a high material removal rate, their high rigidity and sharp edges make them prone to introducing mechanical damage such as scratches and microcracks on the SiC surface during polishing, resulting in high surface roughness and making it difficult to meet the stringent surface quality requirements of advanced semiconductor devices.

[0032] To balance removal efficiency and surface integrity, recent studies have attempted to combine superhard abrasives (such as nanodiamonds and cubic boron nitride) and flexible abrasives (such as colloidal silica and alumina sol) in silicon carbide polishing slurries. While this composite abrasive strategy can achieve a balance between high removal rates and low surface damage to some extent, it still faces the following technical bottlenecks: Firstly, different types of abrasives vary significantly in particle size, density, and surface chemical properties, making them prone to heterogeneous agglomeration after mixing, forming micron-sized aggregates. These aggregates may embed as hard impurities on the surface during polishing, causing deep scratches or micropit defects. Secondly, due to inconsistent sedimentation rates among the components, the polishing slurry is prone to stratification and sedimentation during storage or use, leading to decreased system uniformity and severely affecting process repeatability and product yield. Therefore, developing a silicon carbide polishing slurry that achieves high polishing efficiency and excellent surface quality while also possessing good dispersion stability and process consistency remains a crucial issue that urgently needs to be addressed in this field.

[0033] In conventional polishing slurries, lignin is used sparingly and is mostly added alone as a chelating agent or corrosion inhibitor. Graphene oxide can be added to polishing slurries as a filler, usually alone, as a lubricant. Currently, there are no studies on using composite microspheres made of lignin, graphene oxide, and nano-silica as abrasives in polishing slurries.

[0034] Based on the above background, the present invention proposes a silicon carbide polishing slurry, which, by mass parts, comprises the following components: 1-20 parts abrasive, 0.01-5 parts oxidant, 0.01-0.5 parts pH adjuster, and 85-95 parts water;

[0035] The abrasive includes a first abrasive and a second abrasive. The first abrasive includes at least one of alumina and zirconium oxide, and the second abrasive is a lignin / graphene oxide / nano-silica composite microsphere.

[0036] The polishing slurry provided by the present invention uses at least one of alumina and zirconium oxide as the first abrasive and lignin / graphene oxide / nano silica composite microspheres as the second abrasive. By utilizing the steric hindrance effect between the lignin / graphene oxide / nano silica composite microspheres, the second abrasive can be uniformly dispersed among the first abrasive, thereby effectively improving the problem of easy agglomeration and sedimentation in conventional silicon carbide polishing slurries due to the use of multiple abrasives, and making the entire polishing slurry system have good stability. Meanwhile, the introduction of lignin components into the lignin / graphene oxide / nano silica composite microspheres helps to capture metal ions and other removal products generated during polishing, thereby reducing residual contamination on the wafer surface and facilitating the post-cleaning step of wafer polishing. The lignin molecules themselves have a certain degree of flexibility and elasticity, which can play a "buffering" and "scrubbing" role during polishing. Moreover, different lignin molecules can also form a three-dimensional network structure and undergo elastic deformation to generate tension. During the grinding process, the lignin / graphene oxide / nano silica composite microspheres located at the lower part of the wafer surface have a greater mechanical effect when they are squeezed and deformed compared to the higher parts of the wafer surface. Therefore, the removal rate is higher and the planarization effect of polishing is better. In addition, the graphene component in the lignin / graphene oxide / nano silica composite microspheres not only produces a super-lubricating effect, greatly reducing the coefficient of friction and minimizing surface scratches and subsurface damage, but also acts as a thermally conductive filler. Through the three-dimensional network structure constructed by lignin, it forms an efficient thermally conductive pathway, quickly dissipating heat from the polishing zone. This prevents localized high temperatures from causing surface deformation or polishing fluid failure, further improving the surface quality of the workpiece after processing and enhancing the stability of the polishing fluid.

[0037] In an embodiment of the present invention, the particle size of the first abrasive is 0.6 μm to 1.2 μm, and the particle size of the second abrasive is 200 nm to 500 nm. The technical solution of the present invention controls the particle size of the first abrasive to be larger than that of the second abrasive and sets the particle sizes of the two abrasives within the above-mentioned range. The larger particles of the first abrasive possess sufficient hardness and cutting ability to undertake the main material removal task to ensure the removal rate; the smaller particles of the second abrasive are used to fully fill the gaps between the first abrasive particles, improving the uniformity of abrasive distribution. Through chemical-mechanical synergy, low-damage polishing is achieved, while suppressing deep scratches caused by the large particles of abrasive, which is beneficial to improving surface quality. In one embodiment of the present invention, the particle size of the prepared lignin / graphene oxide / nano-silica composite microspheres is 200 to 300 nm, and the particle size of the first abrasive can be selected from 0.6 μm, 0.8 μm, 1.0 μm, or 1.2 μm.

[0038] In embodiments of the present invention, the mass ratio of the first abrasive to the second abrasive is (3~10):1. Exemplarily, the mass ratio of the first abrasive to the second abrasive can be 3:1, 4:1, 5:1, 6:1, 9:1, or 10:1. If the amount of the second abrasive is too high, it will over-coat the first abrasive, thus weakening the cutting ability of the first abrasive; if the amount of the second abrasive is too low, it cannot effectively fill and passivate the surface, resulting in a poorer improvement in the polishing effect. By setting the amounts of the first and second abrasives within the above ranges, it is beneficial for the first and second abrasives to synergistically exert a chemical-mechanical synergistic effect, achieving a high polishing rate, excellent surface quality, and good stability.

[0039] In an embodiment of the present invention, the method for preparing the second abrasive includes the following steps:

[0040] S1. Mix sulfate lignin, N,N-dimethylformamide and water to obtain a lignin solution; disperse graphene oxide in ethanol to obtain a graphene oxide dispersion; disperse nano silica, sodium dodecylbenzenesulfonate and phenylaminomethyltrimethoxysilane in ethanol to obtain a modified nano silica dispersion.

[0041] S2. Stir the lignin solution, and while maintaining stirring, dropwise add the graphene oxide dispersion and the modified nano silica dispersion into the lignin solution to obtain a self-assembled product. Dialyze and dry the self-assembled product to obtain the second abrasive.

[0042] Sulfate lignin not only contains hydrophilic active groups such as methoxy and hydroxyl groups, but also has a hydrophobic benzene ring skeleton, thus exhibiting excellent amphiphilicity. Graphene oxide has a large number of oxygen-containing functional groups (such as carboxyl, epoxy, and hydroxyl groups) on its surface, exhibiting hydrophilicity, and its own carbon atom matrix structure makes it hydrophobic, thus graphene oxide also exhibits amphiphilicity. Unmodified nano-silica is prone to self-aggregation and has weak interactions with sulfate lignin and graphene oxide, resulting in poor compatibility between unmodified silica and sulfate lignin and graphene oxide, making it difficult to form stable composite nanospheres. Surface modification of nano-silica with sodium dodecylbenzenesulfonate and phenylaminomethyltrimethoxysilane can improve the compatibility between sulfate lignin, graphene oxide, and modified nano-silica, allowing them to self-assemble into stable composite nanospheres (the second abrasive) through hydrogen bonding, electrostatic interactions, and hydrophilic-hydrophobic interactions after mixing.

[0043] The modification principle of using sodium dodecylbenzenesulfonate and phenylaminomethyltrimethoxysilane to modify nano-silica is as follows: Sodium dodecylbenzenesulfonate contains phenyl and sulfonic acid groups, which can improve the compatibility between silica and sulfate lignin after mixing with silica nanoparticles; phenylaminomethyltrimethoxysilane contains both amino and phenyl groups, which can form amino and phenyl groups on the outer surface of silica, making it amphiphilic. Thus, on the one hand, silica binds to carboxyl groups and other groups on the surface of graphene oxide through amino groups, giving it good compatibility with graphene oxide (hydrogen bonding, electrostatic attraction); on the other hand, silica improves its compatibility with sulfate lignin through its surface phenyl groups (hydrophobic interaction, π-relation between benzene rings). (π-stacking effect). Therefore, by adopting the above technical solution, that is, by simultaneously using sodium dodecylbenzenesulfonate and phenylaminomethyltrimethoxysilane to modify nano-silica, the compatibility between silica and sulfate lignin, as well as between silica and graphene oxide, can be improved, making the bonding between the components in the composite nanospheres stronger, thereby improving the stability of the product.

[0044] In embodiments of the present invention, the volume ratio of N,N-dimethylformamide to water is 7:3 to 9:1. Exemplarily, the volume ratio of N,N-dimethylformamide to water can be 7:3, 8:2, or 9:1. Setting the volume ratio of N,N-dimethylformamide to water within the above range is beneficial for forming a uniform lignin solution.

[0045] In embodiments of the present invention, the mass percentage of sulfate lignin in the lignin solution is 15% to 30%. Exemplarily, the mass percentage of sulfate lignin in the lignin solution can be 15%, 20%, or 30%. Sulfate lignin contains a large number of phenolic hydroxyl groups, alcoholic hydroxyl groups, and carboxyl groups, which act as a "bridging" link by forming hydrogen bonds or electrostatic interactions with graphene oxide and silica. If the amount of lignin is insufficient, it will be difficult to stabilize other components, thus making it difficult to form complete and stable composite microspheres; if the amount of lignin is excessive, it may hinder self-assembly due to excessive cross-linking or excessive viscosity, leading to the formation of irregular gels or large precipitates. The technical solution of the present invention sets the amount of sulfate lignin within the above range, which can effectively encapsulate graphene oxide and silica, promote the uniform dispersion of other components, and guide the formation of complete and stable composite microspheres.

[0046] In embodiments of the present invention, the mass ratio of sulfate lignin to graphene oxide is (1~4):1. Exemplarily, the mass ratio of sulfate lignin to graphene oxide can be 1:1, 2:1, 3:1, or 4:1. Controlling the amount of graphene oxide within the above range can avoid the problem of irreversible aggregation due to π–π stacking caused by excessive graphene oxide.

[0047] In embodiments of the present invention, the mass ratio of sulfate lignin to nano-silica is 1:(1.2~2). Exemplarily, the mass ratio of sulfate lignin to nano-silica can be 1:1.2, 1:1.3, 1:1.5, 1:1.8, or 1:2. Controlling the amount of nano-silica within the above range avoids the problem of excessive silica forming free particles in the system, making it difficult to encapsulate them into microspheres.

[0048] In embodiments of the present invention, the mass ratio of the nano-silica, sodium dodecylbenzenesulfonate, and phenylaminomethyltrimethoxysilane is (10~20):10:10. Exemplarily, the mass ratio of the nano-silica, sodium dodecylbenzenesulfonate, and phenylaminomethyltrimethoxysilane can be 10:10:10, 12:10:10, 13:10:10, 15:10:10, 18:10:10, or 20:10:10.

[0049] In embodiments of the present invention, the radial dimension of the graphene oxide is ≤200 nm. Excessively large graphene oxide sheet diameters can lead to severe adhesion between microspheres, making it impossible to obtain independent, dispersed lignin / graphene oxide / nano-silica composite nanospheres. Exemplarily, the graphene oxide can be selected from Beijing Solarbio Science & Technology Co., Ltd., with a sheet diameter of 50~200 nm.

[0050] In embodiments of the present invention, the particle size of the nano-silica is 20-100 nm. Exemplarily, the particle size of the nano-silica can be 20 nm, 30 nm, 40 nm, 50 nm, or 100 nm. Using nano-silica with a particle size within the above range is advantageous for obtaining complete and stable lignin / graphene oxide / nano-silica composite microspheres via self-assembly.

[0051] In an embodiment of the present invention, the silicon carbide polishing slurry further includes 0.01 to 0.05 parts of lignin nanoparticles, wherein the particle size of the lignin nanoparticles is 50 to 100 nm. Exemplarily, the amount of lignin nanoparticles used can be 0.01, 0.02, 0.03, or 0.05 parts; the lignin nanoparticles can be selected from Shandong Baiyuan New Material Technology Co., Ltd., with a particle size of 50 to 100 nm. Adding a small amount of free lignin nanoparticles to fill the gap between the polishing pad and the wafer can make the polishing pressure distribution more uniform, further avoiding pitting caused by local overload; simultaneously, the free lignin nanoparticles can help soften the SiC surface, which helps improve the material removal rate.

[0052] In embodiments of the present invention, the oxidant includes at least one selected from potassium permanganate, hydrogen peroxide, hypochlorite, iodate, periodate, and nitric acid.

[0053] This invention also proposes a method for preparing the silicon carbide polishing slurry described in the foregoing technical solution, comprising the following steps:

[0054] The first abrasive, the second abrasive, the oxidant and water are mixed, and then the pH value of the system is adjusted to 9-11 with a pH adjuster to obtain silicon carbide polishing slurry.

[0055] In an embodiment of the present invention, the step of mixing the first abrasive, the second abrasive, the oxidant, and water, and then adjusting the pH of the system to 9-11 using a pH adjuster to obtain the silicon carbide polishing slurry includes:

[0056] The first abrasive, the second abrasive, the oxidant, the lignin nanoparticles and water were mixed, and then the pH value of the system was adjusted to 9-11 with a pH adjuster to obtain the silicon carbide polishing slurry.

[0057] The technical solution of the present invention will be further described in detail below with reference to specific embodiments. It should be understood that the following embodiments are only used to explain the present invention and are not intended to limit the present invention.

[0058] In the following implementations, sulfate lignin was purchased from Huai'an Hongsen Lignin Technology Co., Ltd.; graphene oxide was purchased from Beijing Solarbio Technology Co., Ltd., with a sheet diameter of 50~200nm; nano silica was purchased from Jiangsu Xianfeng Nanomaterials Technology Co., Ltd., with a particle size of 20nm; and lignin nanoparticles were purchased from Shandong Baiyuan New Material Technology Co., Ltd., with a particle size of 50~100nm.

[0059] Example 1

[0060] A method for preparing lignin / graphene oxide / nano silica composite microspheres includes the following steps:

[0061] (1) Preparation of lignin solution: 15 mg of sulfate lignin was dissolved in a mixed solvent of 50 mg N,N-dimethylformamide / water (volume ratio of 8:2) to obtain lignin solution;

[0062] (2) Preparation of graphene oxide ethanol dispersion: 50 mg of graphene oxide was added to 100 mL of ethanol and ultrasonically dispersed to obtain graphene oxide dispersion.

[0063] (3) Preparation of modified nano silica dispersion: 10 mg sodium dodecylbenzenesulfonate, 10 mg phenylaminomethyltrimethoxysilane, 20 mg nano silica and 60 mL anhydrous ethanol were mixed and ultrasonically dispersed to obtain modified nano silica dispersion.

[0064] (4) Preparation of lignin / graphene oxide / nano silica composite microspheres: The lignin solution was magnetically stirred at 800 rpm. The graphene oxide ethanol dispersion was added dropwise to the lignin solution at 4 mL / min. After adding 20 mL of the graphene oxide ethanol dispersion, the modified nano silica dispersion was added dropwise to the lignin solution at 0.75 mL / min to obtain a mixture. The obtained mixture was poured into a dialysis bag and placed in distilled water to remove the organic solvent. The obtained product was freeze-dried to obtain lignin / graphene oxide / nano silica composite microspheres (particle size of 200~300 nm).

[0065] Example 2

[0066] Compared with Example 1, the difference is that the amount of sulfate lignin used in step (1) is 10 mg;

[0067] The amount of graphene oxide used in step (2) is 20 mg;

[0068] The amount of nano-silica in step (3) is 15 mg.

[0069] Example 3

[0070] A silicon carbide polishing slurry, by mass parts, comprises the following components: 1.5 parts alumina (particle size 800 nm), 0.5 parts composite microspheres of Example 1 (particle size 200~300 nm), 2.5 parts potassium permanganate, and 92 parts water.

[0071] The preparation method of the silicon carbide polishing slurry includes the following steps:

[0072] Alumina, the composite microspheres from Example 1, potassium permanganate, and water were mixed, and then the pH of the system was adjusted to 9-11 with potassium hydroxide to obtain a silicon carbide polishing slurry.

[0073] Example 4

[0074] A silicon carbide polishing slurry, by mass parts, comprises the following components: 4.5 parts alumina, 0.5 parts composite microspheres of Example 1, 2.5 parts potassium permanganate, and 91 parts water; the pH of the silicon carbide polishing slurry is 9.5.

[0075] Example 5

[0076] A silicon carbide polishing slurry, by mass parts, comprises the following components: 1.5 parts alumina, 0.5 parts composite microspheres (particle size 200~300nm) of Example 2, 2.5 parts potassium permanganate, and 92 parts water; the pH of the silicon carbide polishing slurry is 9.6.

[0077] Example 6

[0078] A silicon carbide polishing slurry, by mass parts, comprises the following components: 4.5 parts alumina, 0.5 parts composite microspheres of Example 1, 2.5 parts potassium permanganate, 0.02 parts lignin nanoparticles, and 91 parts water; the pH of the silicon carbide polishing slurry is 9.5.

[0079] Example 7

[0080] Compared with Example 3, the difference is that the amount of composite microspheres used in Example 1 is 1 part.

[0081] Example 8

[0082] Compared to Example 3, the difference is that the amount of alumina used is 5.5 parts.

[0083] Comparative Example 1

[0084] Compared with Example 3, the difference is that all the composite microspheres in Example 1 were replaced with an equal amount of alumina.

[0085] Comparative Example 2

[0086] Compared with Example 3, the difference is that the composite microspheres in Example 1 were replaced with an equal amount of nylon microspheres (particle size 500nm).

[0087] Comparative Example 3

[0088] Compared with Example 3, the difference is that an equal amount of alumina with a particle size of 300 nm is used to replace alumina with a particle size of 800 nm.

[0089] Performance testing

[0090] Stability Test: The appearance of the silicon carbide polishing slurries of Examples 3-8 and Comparative Examples 1-3 was observed after standing at room temperature for 30 and 60 days to evaluate the stability test results. The results showed that the polishing slurries of Examples 3-8 could be stably stored at room temperature for more than 30 days, with the polishing slurry of Example 6 being stably stored for more than 60 days; the silicon carbide polishing slurries of Comparative Examples 1-3 were stably stored at room temperature for less than 30 days. These results indicate that the silicon carbide polishing slurry of the present invention has good dispersion stability.

[0091] Polishing Experiment: Using a CP-4 polishing machine, a 4-inch silicon carbide wafer (semi-insulating, Si side) was attached to the polishing head with wax. The polishing parameters were set as follows: SUBA800 polishing pad; polishing pressure 6 psi; polishing pad rotation speed 100 rpm; polishing disc rotation speed 90 rpm; polishing slurry flow rate 125 mL / min (circulating); polishing time 60 min. After each polishing cycle, the polishing pad was repaired with a 4-inch diamond repair disc for 5 minutes. The polished wafer was then ultrasonically cleaned in cleaning solution for 10 minutes and dried with nitrogen. The test results are shown in Table 1.

[0092] Table 1. Performance test results of silicon carbide polishing slurries in the examples and comparative examples.

[0093]

[0094] The following conclusions can be drawn from Table 1:

[0095] (1) The test results of polishing rate and surface processing quality of Example 6 are better than those of Example 3, indicating that adding a small amount of additional nano-lignin is beneficial to improving the surface quality of the workpiece after processing and to increasing the polishing rate.

[0096] (2) According to the test results of Examples 3 and 7-8, if the amount of lignin / graphene oxide / nano silica composite microspheres is too large and the amount of hard abrasive is too small, the polishing rate will be slowed down; if the amount of lignin / graphene oxide / nano silica composite microspheres is too small, the second abrasive will have a limited effect on improving the polishing effect, and the surface quality will also be worse.

[0097] (3) The test results of Example 3 are better than those of Comparative Examples 1-3. In Comparative Example 1, the surface quality of the workpiece is significantly worse and the polishing rate is slower because only hard abrasive is used. In Comparative Example 2, nylon microspheres are used instead of the lignin / graphene oxide / nano silica composite microspheres provided by the present invention, but the improvement effect on the polishing effect is not as good as that of using the lignin / graphene oxide / nano silica composite microspheres provided by the present invention. The surface quality of the workpiece is significantly worse and the polishing rate is slower. This shows that compared with using nylon microspheres as the second abrasive, using the lignin / graphene oxide / nano silica composite microspheres provided by the present invention as the second abrasive is more conducive to improving the polishing rate and the surface quality of the workpiece after processing. In Comparative Example 3, since the particle size of the first abrasive and the second abrasive are relatively close, it is difficult to fully cover the surface and gaps of the workpiece in the polishing process. Therefore, there are more surface defects, the surface quality after processing is worse, and the polishing rate is slower.

[0098] The above description is merely an exemplary embodiment of the present invention and does not limit the patent scope of the present invention. Any equivalent structural transformations made using the contents of the present invention under the technical concept of the present invention, or direct / indirect applications in other related technical fields, are included within the patent protection scope of the present invention.

Claims

1. A silicon carbide polishing slurry, characterized in that, By weight, it comprises the following components: 1-20 parts abrasive, 0.01-5 parts oxidant, 0.01-0.5 parts pH adjuster, and 85-95 parts water; wherein: The abrasive includes a first abrasive and a second abrasive. The first abrasive includes at least one of alumina and zirconium oxide. The second abrasive is a lignin / graphene oxide / nano-silica composite microsphere. The particle size of the first abrasive is 0.6 μm to 1.2 μm, and the particle size of the second abrasive is 200 nm to 500 nm. The mass ratio of the first abrasive to the second abrasive is (3 to 10):

1. The preparation method of the second abrasive includes the following steps: A lignin sulfate solution was obtained by mixing N,N-dimethylformamide and water. Graphene oxide was dispersed in ethanol to obtain a graphene oxide dispersion. Nano-silica, sodium dodecylbenzenesulfonate, and phenylaminomethyltrimethoxysilane were dispersed in ethanol to obtain a modified nano-silica dispersion. The lignin solution is stirred, and the graphene oxide dispersion and the modified nano silica dispersion are added dropwise to the lignin solution while maintaining stirring to obtain a self-assembled product. The self-assembled product is dialyzed and dried to obtain a second abrasive. The volume ratio of N,N-dimethylformamide to water is 7:3 to 9:1, the mass percentage of sulfate lignin in the lignin solution is 15% to 30%, the mass ratio of sulfate lignin to graphene oxide is (1 to 4):1, the mass ratio of sulfate lignin to nano silica is 1:(1.2 to 2), and the mass ratio of nano silica, sodium dodecylbenzenesulfonate, and phenylaminomethyltrimethoxysilane is (10 to 20):10:

10.

2. The silicon carbide polishing slurry as described in claim 1, characterized in that, The radial dimension of the graphene oxide is ≤200 nm; and / or, The particle size of the nano-silica is 20~100nm.

3. The silicon carbide polishing slurry as described in claim 1, characterized in that, The oxidant includes at least one of potassium permanganate, hydrogen peroxide, hypochlorite, iodate, periodate, and nitric acid.

4. The silicon carbide polishing slurry as described in claim 1, characterized in that, The silicon carbide polishing slurry also includes 0.01 to 0.05 parts of lignin nanoparticles, wherein the particle size of the lignin nanoparticles is 50 to 100 nm.

5. A method for preparing a silicon carbide polishing slurry as described in any one of claims 1 to 3, characterized in that, Includes the following steps: The first abrasive, the second abrasive, the oxidant and water are mixed, and then the pH value of the system is adjusted to 9-11 with a pH adjuster to obtain silicon carbide polishing slurry.

6. The method for preparing the silicon carbide polishing slurry as described in claim 4, characterized in that, Includes the following steps: The first abrasive, the second abrasive, the oxidant, the lignin nanoparticles and water were mixed, and then the pH value of the system was adjusted to 9-11 with a pH adjuster to obtain the silicon carbide polishing slurry.

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