A semiconductor polishing slurry and its preparation method

Abstract

This invention relates to a polishing slurry for semiconductors and its preparation method, belonging to the field of chemical mechanical polishing technology. The polishing slurry comprises the following components by weight: 100 parts silica sol, 0.8-1.4 parts modified complexing agent, 2.2-3.5 parts oxidant, 0.1-0.13 parts corrosion inhibitor, 14-18 parts deionized water, and a certain amount of pH adjuster; the modified complexing agent is prepared by click addition of dimethylallylamine and mercaptoethanol, esterification with ethylenediaminetetraacetic acid, and then quaternization. Its terminal quaternary ammonium positive charge can be electrostatically adsorbed on the surface of negatively charged silica sol particles, realizing polishing contact-triggered release. The branched structure and ethylenediaminetetraacetic acid ester-sulfide structure provide multi-tooth complexing ability and enhance fluid drag to quickly remove complexes. This polishing slurry significantly improves the removal rate and surface planarization accuracy of fine polishing.

Description

Technical Field

[0001] This invention belongs to the field of chemical mechanical polishing technology, specifically, it relates to a polishing slurry for semiconductors and its preparation method. Background Technology

[0002] Polishing is a crucial step in semiconductor material manufacturing to achieve surface planarization. As integrated circuit feature sizes continue to shrink, the requirements for surface planarization have increased from micrometer-level precision to atomic-level precision, posing unprecedented challenges to planarization technology. Chemical mechanical polishing (CMP), a composite processing technology combining chemical etching and mechanical grinding, can simultaneously achieve global planarization of materials and effective control of surface damage, and has become an indispensable core process in semiconductor material manufacturing. The CMP process achieves surface planarization through the synergistic effect of chemical and physical processes: the oxidant in the polishing slurry reacts chemically with the surface material to generate a softer, more easily mechanically removed reaction layer; the abrasive particles in the slurry then remove this reaction layer through mechanical friction, thus forming a cyclical precision polishing process of "chemical oxidation-mechanical removal."

[0003] CMP polishing slurries typically consist of multiple components, including abrasive particles, oxidants, complexing agents, corrosion inhibitors, pH adjusters, and deionized water. The oxidant is responsible for transforming the surface of the material to be polished into a loose oxide layer. The abrasive particles mechanically remove this oxide layer, while the complexing agent complexes and captures the metal ions and their oxides generated during grinding, preventing passivation. Therefore, CMP polishing is a typical dynamic equilibrium process, with the ideal working state being: oxidation rate ≈ removal rate > passivation rate. Matching the oxidation rate and removal rate can be achieved by adjusting the concentration and type of oxidant, and optimizing the abrasive particle size and content. However, controlling the complexing agent is far more complex than simply adjusting the ratio. On the one hand, insufficient complexing ability leads to the accumulation of oxidation products at the polishing interface, reducing polishing efficiency and affecting surface quality. On the other hand, excessive complexing ability causes the complexing agent to strongly bond with the polished surface, forming a composite layer. Furthermore, excessive deposition of complexes on the grinding surface hinders the smooth progress of mechanical grinding. This dilemma of "too much of a good thing" in complexation is particularly prominent in fine polishing processes represented by silica abrasives. Existing complexing agents are unable to achieve precise and timely complexation and removal at the polishing interface, resulting in low polishing efficiency and difficulty in further improving surface flatness accuracy. Summary of the Invention

[0004] In order to solve the technical problems mentioned in the background art, the purpose of this invention is to provide a polishing slurry for semiconductors and a method for preparing the same.

[0005] The objective of this invention can be achieved through the following technical solutions:

[0006] A polishing slurry for semiconductors comprises the following components in parts by weight: 100 parts silica sol, 0.8-1.4 parts modified complexing agent, 2.2-3.5 parts oxidant, 0.1-0.13 parts corrosion inhibitor, 14-18 parts deionized water, and a certain amount of pH adjuster.

[0007] The modified complexing agent is prepared by the following method:

[0008] Step A1: A modifier is prepared by using dimethylallylamine and mercaptoethanol as raw materials in an anhydrous ethanol solvent system and initiating a click addition reaction with a photoinitiator and ultraviolet irradiation.

[0009] Step A2: Using ethylenediaminetetraacetic acid and a modifier as raw materials, an esterification reaction is carried out in a dimethylformamide solvent system with p-toluenesulfonic acid as a catalyst and dicyclohexylcarbodiimide as a dehydrating agent, and the temperature is raised to prepare an intermediate.

[0010] Step A3: Using intermediates and bromopropane as raw materials, a quaternization reaction is carried out in a dioxane solvent system with tetrabutylammonium bromide and diisopropylethylamine as catalysts, and the temperature is raised to prepare a modified complexing agent.

[0011] In step A1, the molar ratio of dimethylallylamine to mercaptoethanol is 1:1.05-1.1, the amount of photoinitiator is 0.15-0.22 wt% of the total amount of both, and the ultraviolet irradiation intensity is 20-25 mW / cm². 2 The specific reaction route is as follows:

[0012]

[0013] In step A2, the molar ratio of ethylenediaminetetraacetic acid (EDTA) to the modifier is 1:4.2-4.4, the amount of p-toluenesulfonic acid is 8-12 wt% of the total amount of both, and the amount of dicyclohexylcarbodiimide is 35-40 wt% of the total amount of both; the specific reaction route is as follows:

[0014]

[0015] In step A3, the molar ratio of the intermediate to bromopropane is 1:4.5-5, tetrabutylammonium bromide accounts for 2-3 wt% of the total amount of both, and diisopropylethylamine accounts for 15-20 wt% of the total amount of both; the specific reaction route is as follows:

[0016]

[0017] Preferably, the particle size of silica in the silica sol is no higher than 10 nm. The fine abrasive particle size is conducive to obtaining a smoother polished surface.

[0018] Preferably, the silica content in the silica sol is 10-15 wt%. A lower silica content results in more stable abrasive dispersion, which is beneficial for improving surface polishing quality.

[0019] Preferably, the oxidant is ammonium persulfate, which has good stability in the silica sol system and relatively strong oxidizing properties. It works synergistically with the modified complexing agent to achieve efficient removal.

[0020] Preferably, the pH adjuster is acetic acid, and the pH value of the polishing solution after adjustment is 7-8.

[0021] A method for preparing a semiconductor polishing slurry specifically involves: premixing a modified complexing agent, an oxidizing agent, and deionized water; adding the premix to a silica sol and mixing; then adding a corrosion inhibitor and a pH adjuster and mixing thoroughly to obtain the polishing slurry.

[0022] The beneficial effects of this invention are:

[0023] This invention introduces a modified complexing agent with a branched quaternary ammonium salt structure into the silica sol polishing system, which changes the way the complexing agent acts in the polishing process, thereby achieving a synergistic improvement in the two core indicators of polishing efficiency and surface precision.

[0024] In traditional polishing slurries, the complexing agent is dispersed throughout the liquid phase as a free molecular, lacking spatial selectivity in its contact with the crystalline material surface. This not only leads to the ineffective adsorption or formation of surface composite layers by a large amount of complexing agent in non-grinding areas (such as depressions and grooves), but also hinders the normal progress of chemical oxidation and mechanical removal. The modified complexing agent of this invention, due to the positive charge of its terminal quaternary ammonium groups and the negative charge of the silica sol particle surface, generates electrostatic attraction between the two, causing the modified complexing agent to be loaded onto the surface of the abrasive particles. This loading state allows the complexing agent to move with the abrasive throughout the polishing process, preventing premature diffusion to non-contact areas of the material surface. Only when the abrasive comes into mechanical contact with the microscopic protrusions of the polished surface is the strong shear stress at the interface sufficient to disrupt the electrostatic balance, causing the complexing agent to detach from the abrasive surface and form a complex with the metal ions generated during grinding. This "contact-triggered" mechanism achieves precise spatial positioning of the complexation reaction, effectively avoiding ineffective consumption and unintended surface contamination, and maximizing the use of the limited complexing agent in the effective processing area.

[0025] Meanwhile, the molecular structure of the modified complexing agent significantly optimizes the removal efficiency of complexation products. Traditional small-molecule complexing agents form small-molecule complexes with metal ions, which tend to accumulate in the narrow fluid boundary layer of the polishing interface, gradually forming an interface layer that hinders mass transfer and causes the polishing rate to decrease over time. In this invention, the branched structure of the modified complexing agent significantly increases its molecular weight, resulting in greater fluid drag in the shear field of the polishing fluid, making it easier to be carried away by the mobile phase. Furthermore, the quaternary ammonium groups at the molecular ends have excellent hydrophilicity, ensuring that the complexes do not adhere to the polishing pad or material surface due to hydrophobic interactions. In addition, the ethylenediaminetetraacetic acid ester in the modified complexing agent molecule and the sulfide structure on the branched chain form a complex chelation mechanism, exhibiting good complexation ability with copper, tantalum, and other metal elements commonly found on semiconductor material surfaces. These characteristics enable the complexed products to quickly detach from the grinding site and diffuse into the main polishing fluid, maintaining the cleanliness of the polishing interface and thus avoiding the self-inhibition effect caused by complex accumulation in traditional processes.

[0026] In summary, this invention optimizes the spatiotemporal characteristics of the complexing agent's action during the polishing process from two dimensions: "precise delivery" and "rapid removal." The former ensures that the chemical complexation reaction is concentrated in the microscopic protrusions where material removal actually occurs, improving the efficiency of the complexing agent and the polishing rate. The latter suppresses the accumulation of interfacial byproducts, ensuring the continuous stability of the polishing process and the accuracy of surface planarization. These two aspects work together to enable the polishing fluid of this invention to achieve comprehensive performance exceeding that of existing formulations with lower additive dosages, demonstrating significant technological advancement. Detailed Implementation

[0027] The technical solutions of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0028] Example 1: Preparation of a polishing slurry for semiconductors. The specific implementation process is as follows:

[0029] 1) Preparation of modified complexing agents

[0030] Step A1: Mix dimethylallylamine, mercaptoethanol, and anhydrous ethanol, then add photoinitiator 1173 and purge with nitrogen gas for protection. Apply an intensity of 25 mW / cm² to the reaction system at room temperature. 2The mixture was irradiated with ultraviolet light at a wavelength of 365 nm and stirred for 3 h. During the reaction, 0.1 mol of dimethylallylamine was used as the quantitative amount, and dimethylallylamine and mercaptoethanol were mixed in a molar ratio of 1:1.1. The amount of photoinitiator 1173 was 0.22 wt% of the total amount of the two, and 55 mL of anhydrous ethanol was added. After the reaction was completed, the ethanol was removed by rotary evaporation to obtain the modifier.

[0031] Step A2: Mix ethylenediaminetetraacetic acid (EDTA), modifier, and dimethylformamide. Then add p-toluenesulfonic acid and dicyclohexylcarbodiimide. Purge with nitrogen and reflux at 115°C for 10 hours. During the reaction, use 20 mmol of EDTA as the quantification. The molar ratio of EDTA to modifier is 1:4.4. The amount of p-toluenesulfonic acid is 12 wt% of the total amount of both. The amount of dicyclohexylcarbodiimide is 40 wt% of the total amount of both. Add 80 mL of dimethylformamide. After the reaction is complete, cool and add 250 mL of deionized water for washing. After removing the aqueous phase, vacuum dry to obtain the intermediate.

[0032] Step A3: Take the intermediate, bromopropane, tetrabutylammonium bromide, diisopropylethylamine and dioxane, stir and mix them, purge with nitrogen, and reflux at 70°C for 12 h; in the reaction, the intermediate is quantified at 10 mmol, the molar ratio of the intermediate to bromopropane is 1:5, and the tetrabutylammonium bromide is 3 wt% of the total amount of the two; after the reaction is completed, remove dioxane and excess bromopropane by rotary evaporation under reduced pressure, dissolve the substrate in ethyl acetate, filter and rotary evaporate to precipitate the precipitate, and dry to obtain the modified complexing agent.

[0033] 2) Preparation of polishing liquid

[0034] The raw materials were prepared according to the following parts by weight: 100 parts of silica sol, using SS1505 type small particle size silica sol, with a silica particle size of 3-5nm and a content of 15%; 1.4 parts of modified complexing agent, which was prepared in this embodiment; 3.5 parts of oxidant, using ammonium persulfate; 0.13 parts of corrosion inhibitor, using benzotriazole; 18 parts of deionized water; and a small amount of pH adjuster to adjust the pH value of the polishing solution to 7.2.

[0035] The modified complexing agent, oxidant and deionized water are stirred and premixed. The premix is ​​then added to the silica sol and stirred and mixed. After that, the corrosion inhibitor is added in sequence and mixed evenly. The pH value is adjusted by adding a pH adjuster to obtain the polishing solution.

[0036] Example 2: Preparation of a polishing slurry for semiconductors. The specific implementation process is as follows:

[0037] 1) Preparation of modified complexing agents

[0038] Step A1: Mix dimethylallylamine, mercaptoethanol, and anhydrous ethanol, then add photoinitiator 1173 and purge with nitrogen gas for protection. Apply an intensity of 20 mW / cm² to the reaction system at room temperature. 2 The mixture was irradiated with ultraviolet light at a wavelength of 365 nm and stirred for 4 h. During the reaction, 0.1 mol of dimethylallylamine was used as the quantitative measure, and dimethylallylamine and mercaptoethanol were prepared in a molar ratio of 1:1.05. The amount of photoinitiator 1173 was 0.15 wt% of the total amount of the two, and 45 mL of anhydrous ethanol was added. After the reaction was completed, the ethanol was removed by rotary evaporation to obtain the modifier.

[0039] Step A2: Mix ethylenediaminetetraacetic acid (EDTA), the modifier, and dimethylformamide. Then add p-toluenesulfonic acid and dicyclohexylcarbodiimide. Purge with nitrogen and reflux at 100°C for 12 hours. During the reaction, use 20 mmol of EDTA as the quantification. The molar ratio of EDTA to the modifier is 1:4.2. The amount of p-toluenesulfonic acid is 8 wt% of the total amount of both. The amount of dicyclohexylcarbodiimide is 35 wt% of the total amount of both. Add 60 mL of dimethylformamide. After the reaction is complete, cool and add 200 mL of deionized water for washing. After removing the aqueous phase, vacuum dry to obtain the intermediate.

[0040] Step A3: Take the intermediate, bromopropane, tetrabutylammonium bromide, diisopropylethylamine and dioxane, stir and mix them, purge with nitrogen for protection, heat to 70℃ and reflux for 15 h; in the reaction, use 10 mmol of intermediate as the quantitative measure, the molar ratio of intermediate to bromopropane is 1:4.5, and tetrabutylammonium bromide is 2 wt% of the total amount of both; after the reaction is completed, remove dioxane and excess bromopropane by rotary evaporation under reduced pressure, dissolve the substrate in ethyl acetate, filter and rotary evaporate to precipitate the precipitate, and dry to obtain the modified complexing agent.

[0041] 2) Preparation of polishing liquid

[0042] The raw materials were prepared according to the following weight proportions: 100 parts of silica sol, using SS1505 type small particle size silica sol, with a silica particle size of 3-5nm and a content of 15%; 0.8 parts of modified complexing agent, which was prepared in this embodiment; 2.2 parts of oxidant, using ammonium persulfate; 0.1 parts of corrosion inhibitor, using benzotriazole; 14 parts of deionized water; and a small amount of pH adjuster to adjust the pH value of the polishing solution to 7.9.

[0043] The modified complexing agent, oxidant and deionized water are stirred and premixed. The premix is ​​then added to the silica sol and stirred and mixed. After that, the corrosion inhibitor is added in sequence and mixed evenly. The pH value is adjusted by adding a pH adjuster to obtain the polishing solution.

[0044] Example 3: Preparation of a polishing slurry for semiconductors. The specific implementation process is as follows:

[0045] 1) Preparation of modified complexing agents

[0046] Step A1: Mix dimethylallylamine, mercaptoethanol, and anhydrous ethanol, then add photoinitiator 1173 and purge with nitrogen gas for protection. Apply an intensity of 20 mW / cm² to the reaction system at room temperature. 2 The mixture was irradiated with ultraviolet light at a wavelength of 365 nm and stirred for 3.5 h. During the reaction, 0.1 mol of dimethylallylamine was used as the quantitative amount, and dimethylallylamine and mercaptoethanol were mixed in a molar ratio of 1:1.08. The amount of photoinitiator 1173 was 0.2 wt% of the total amount of the two, and 50 mL of anhydrous ethanol was added. After the reaction was completed, the ethanol was removed by rotary evaporation to obtain the modifier.

[0047] Step A2: Mix ethylenediaminetetraacetic acid (EDTA), modifier, and dimethylformamide. Then add p-toluenesulfonic acid and dicyclohexylcarbodiimide. Purge with nitrogen and reflux at 110°C for 12 hours. During the reaction, use 20 mmol of EDTA as the quantification. The molar ratio of EDTA to modifier is 1:4.3. The amount of p-toluenesulfonic acid is 10 wt% of the total amount of both. The amount of dicyclohexylcarbodiimide is 40 wt% of the total amount of both. Add 70 mL of dimethylformamide. After the reaction is complete, cool and add 220 mL of deionized water for washing. After removing the aqueous phase, vacuum dry to obtain the intermediate.

[0048] Step A3: Take the intermediate, bromopropane, tetrabutylammonium bromide, diisopropylethylamine and dioxane, stir and mix them, purge with nitrogen for protection, heat to 70℃ and reflux for 13 h; in the reaction, 10 mmol of intermediate is used as the quantitative measure, the molar ratio of intermediate to bromopropane is 1:4.8, and tetrabutylammonium bromide is 2.5 wt% of the total amount of the two; after the reaction is completed, remove dioxane and excess bromopropane by rotary evaporation under reduced pressure, dissolve the substrate in ethyl acetate, filter and rotary evaporate to precipitate the precipitate, and dry to obtain the modified complexing agent.

[0049] 2) Preparation of polishing liquid

[0050] The raw materials were prepared according to the following parts by weight: 100 parts of silica sol, using SS1505 type small particle size silica sol, with a silica particle size of 3-5nm and a content of 15%; 1.1 parts of modified complexing agent, which was prepared in this embodiment; 2.8 parts of oxidant, using ammonium persulfate; 0.11 parts of corrosion inhibitor, using benzotriazole; 15 parts of deionized water; and a small amount of pH adjuster to adjust the pH value of the polishing solution to 7.5.

[0051] The modified complexing agent, oxidant and deionized water are stirred and premixed. The premix is ​​then added to the silica sol and stirred and mixed. After that, the corrosion inhibitor is added in sequence and mixed evenly. The pH value is adjusted by adding a pH adjuster to obtain the polishing solution.

[0052] Comparative Example 1 follows the same procedure as in Example 3, except that the modified complexing agent is replaced with an equal amount of ethylenediaminetetraacetic acid, while the rest remains the same.

[0053] Comparative Example 2: Based on the polishing solution composition of Comparative Example 1, 0.2 parts of dimethyldiethylammonium chloride were added, and the rest were the same.

[0054] The polishing slurry obtained above was used for polishing tests, as detailed below:

[0055] Polishing experiment: 4-inch copper-plated silicon wafers (Cu film thickness approximately 1.2 μm) and tantalum barrier-coated silicon wafers (Ta film thickness approximately 300 nm) were used as polishing objects; IC1000 and Suba IV were used as polishing pads; a single-sided CMP polishing machine was used, and the process parameters were set as follows: polishing pressure 25 kPa, polishing disk speed 60 pm, polishing head speed 55 rpm, polishing fluid flow rate 20 mL / min, and polishing time 180 s.

[0056] The film thickness before and after polishing was measured using a four-probe resistance meter and the polishing rate was calculated; the surface roughness was measured using an atomic force microscope; Tables 1 and 2 below show the polishing test results of Example 3, Comparative Example 1, and Comparative Example 2.

[0057] Table 1 Polishing Test Results of Copper-Coated Silicon Wafers

[0058] Polishing rate (nm / min) Surface roughness (nm) after polishing Example 3 310 0.21 Comparative Example 1 245 0.59 Comparative Example 2 260 0.54

[0059] Table 2 Polishing test results of silicon wafers with tantalum barrier coating

[0060] Polishing rate (nm / min) Surface roughness (nm) after polishing Example 3 205 0.18 Comparative Example 1 130 0.35 Comparative Example 2 140 0.31

[0061] As can be seen from the test results in Tables 1 and 2, the polishing slurry of Example 3, under the same polishing equipment and polishing parameters, has a higher polishing rate for semiconductor materials on copper and tantalum surfaces, and the polishing accuracy is significantly improved.

[0062] In the description of this specification, the references to terms such as "an embodiment," "example," "specific example," etc., indicate that a specific feature, structure, material, or characteristic described in connection with that embodiment or example is included in at least one embodiment or example of the present invention. 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, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples.

[0063] The above description is merely an example and illustration of the present invention. Those skilled in the art can make various modifications or additions to the specific embodiments described, or use similar methods to replace them, as long as they do not deviate from the invention or exceed the scope defined in the claims, all of which should fall within the protection scope of the present invention.

Claims

1. A polishing slurry for semiconductors, characterized in that, It includes the following components by weight: 100 parts silica sol, 0.8-1.4 parts modified complexing agent, 2.2-3.5 parts oxidant, 0.1-0.13 parts corrosion inhibitor, 14-18 parts deionized water, and a certain amount of pH adjuster; The modified complexing agent is prepared by the following method: Step A1: A modifier is prepared by using dimethylallylamine and mercaptoethanol as raw materials in an anhydrous ethanol solvent system and initiating a click addition reaction with a photoinitiator and ultraviolet irradiation. Step A2: Using ethylenediaminetetraacetic acid and a modifier as raw materials, an esterification reaction is carried out in a dimethylformamide solvent system with p-toluenesulfonic acid as a catalyst and dicyclohexylcarbodiimide as a dehydrating agent, and the temperature is raised to prepare an intermediate. Step A3: Using intermediates and bromopropane as raw materials, a quaternization reaction is carried out in a dioxane solvent system with tetrabutylammonium bromide and diisopropylethylamine as catalysts, and the temperature is raised to prepare a modified complexing agent.

2. The semiconductor polishing slurry according to claim 1, characterized in that, The molar ratio of dimethylallylamine to mercaptoethanol is 1:1.05-1.1, and the amount of photoinitiator is 0.15-0.22 wt% of the total amount of both.

3. The semiconductor polishing slurry according to claim 2, characterized in that, The molar ratio of ethylenediaminetetraacetic acid and the modifier is 1:4.2-4.4, the amount of p-toluenesulfonic acid is 8-12 wt% of the total amount of the two, and the amount of dicyclohexylcarbodiimide is 35-40 wt% of the total amount of the two.

4. The semiconductor polishing slurry according to claim 3, characterized in that, The molar ratio of intermediate to bromopropane is 1:4.5-5, tetrabutylammonium bromide is 2-3 wt% of the total amount of both, and diisopropylethylamine is 15-20 wt% of the total amount of both.

5. The semiconductor polishing slurry according to claim 1, characterized in that, The particle size of silica in silica sol is no higher than 10 nm.

6. The semiconductor polishing slurry according to claim 5, characterized in that, The silica content in silica sol is 10-15 wt%.

7. The semiconductor polishing slurry according to claim 1, characterized in that, The oxidizing agent is ammonium persulfate.

8. The semiconductor polishing slurry according to claim 1, characterized in that, The pH adjuster is acetic acid, and the pH value of the polishing solution after adjustment is 7-8.

9. A method for preparing a semiconductor polishing slurry according to any one of claims 1-8, characterized in that, Specifically, the modified complexing agent, oxidant and deionized water are premixed, the premix is ​​added to the silica sol and mixed, and then the corrosion inhibitor and pH adjuster are added and mixed evenly to obtain the polishing solution.

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