A slurry composition for final polishing of silicon wafers to reduce surface defect number and haze, and a final polishing method using the same.

Abstract

This invention relates to a slurry composition for final polishing of silicon wafers and a final polishing method using the same, comprising 1 to 20 wt% colloidal silica as polishing particles, 0.03 to 0.5 wt% surfactant, 0.1 to 10 wt% pH adjuster, 0.02 to 2 wt% water-soluble thickener, 0.05 to 0.2 wt% chelating agent, and 0.1 to 1 wt% organic base, and exhibits excellent performance in reducing the number of defects on the surface of the object being polished and reducing haze.

Description

Technical Field

[0001] This invention relates to a polishing slurry composition for ultimately polishing silicon wafers while reducing the number of defects and haze, and a final polishing method using the same. Background Technology

[0002] Typically, silicon wafers, which serve as substrates in semiconductor manufacturing, are produced through processes such as single crystal growing, slicing, lapping, etching, polishing, and cleaning.

[0003] In wafer manufacturing, polishing is a process that aims to create a mirror-like surface by perfectly removing micro-defects on the wafer surface generated or not removed in time during all processes from the growth of a single-crystal silicon ingot (ingot) to the final CMP (Chemical Mechanical Polishing) process. These defects include scratches, cracks, metallic impurities, particles, LPD (Light Point Defect), and microroughness.

[0004] The CMP process for wafers consists of multiple steps, specifically stock removal polishing, which requires high polishing speeds to remove deep scratches on the wafer surface, and removing any remaining micro-scratches and reducing surface roughness (to several micrometers). The final polishing process, which determines the grade of the mirror surface, is what makes it stand out.

[0005] At this point, hard or soft polyurethane polishing pads and silica slurries can be cited as the main factors determining ultrafine defects in the final polishing process.

[0006] Typically, the final polishing wafer slurry includes: colloidal silica and pH adjuster as polishing agents; organic alkaline compounds that promote polishing; surfactants that improve dispersion stability and cleaning performance; water-soluble thickeners that protect particle stability and wafer surface; and chelating agents that inhibit contamination of the polished object by forming complex ions with metal impurities that may be contained in the polishing slurry.

[0007] Recently, as the high integration of semiconductors has led to a narrowing of the scope for wafer surface defect management, there is active research and development of polishing pads and pastes with suitable quality. In particular, since pastes are considered an important factor in determining the final quality of wafers, products with a variety of physicochemical properties are being released. Summary of the Invention

[0008] Technical problems to be solved

[0009] With the miniaturization of semiconductor wiring, silicon substrates need to be finished with higher-grade surfaces. Therefore, a final polishing paste composition is needed to provide silicon wafer substrates with reduced microparticles and haze.

[0010] Therefore, the object of the present invention is to improve the yield of silicon wafer polishing process by providing a composition for final polishing of silicon wafers and a final polishing method using such a composition, wherein the composition for final polishing of silicon wafers has excellent performance in reducing fine particles and haze on the surface of the silicon wafer substrate to be polished.

[0011] Solution to the problem

[0012] The inventors of this invention explored alkaline compounds and water-soluble polymers for suppressing surface defects and reducing haze on silicon wafers after final polishing. They discovered that using compositions containing compounds with specific structures resulted in excellent reductions in surface defects and haze on silicon wafers, thus completing this invention. In other words, the object of this invention is to provide a slurry composition for final polishing of silicon wafers that provides excellent reductions in surface defects and haze.

[0013] To achieve the above objectives, the present invention provides a slurry composition for final polishing of silicon wafers, comprising ultrapure water, polishing particles, pH adjuster, water-soluble thickener and chelating agent, characterized in that it simultaneously comprises quaternary ammonium ions and monofunctional methacrylate polymer.

[0014] The present invention is characterized in that the quaternary ammonium salt ion is represented by the following chemical formula 1, and the methacrylate polymer includes a substance represented by the following chemical formula 2.

[0015] [Chemical Formula 1]

[0016]

[0017] [Chemical Formula 2]

[0018]

[0019] In the above chemical formula 2, n is between 7 and 22.

[0020] According to an embodiment of the present invention, in the final polishing composition, the average particle size of the particles in the polishing composition, as determined by dynamic light scattering, is 80 nm or less.

[0021] Typically, when the average particle size of the particles in the polishing composition is below 80 nm, the polished surface becomes hydrophobic, thereby increasing the number of surface defects or haze.

[0022] Furthermore, when the average particle size of the particles in the polishing composition is small, due to the repulsive force of the double electric layer, the particles are easily re-attached to the surface of the polished wafer and become granules, thereby increasing the number of defects.

[0023] However, in polishing compositions comprising the aforementioned organic alkaline compounds and water-soluble polymers, even by reducing the particle size in the polishing composition, the cleaning function of the silicon wafer surface can be improved while maintaining the hydrophilicity of the wafer surface. Therefore, according to embodiments of the present invention, it is possible to suppress defects and reduce haze on the polished silicon wafer surface.

[0024] The effects of the invention

[0025] The slurry composition for final polishing of silicon wafers according to the present invention maintains a polishing speed of over 40 nm / min and achieves suppression of fine particle generation and reduction of haze on the silicon wafer surface, thereby significantly improving process reliability and productivity. Attached Figure Description

[0026] Figure 1 This is a surface defect number map of a silicon wafer according to Embodiment 1 of the present invention.

[0027] Figure 2 This is a surface defect count map of a silicon wafer according to Comparative Example 4 of the present invention.

[0028] Figure 3 This is a surface defect count map of a silicon wafer according to Comparative Example 7 of the present invention. Detailed Implementation

[0029] The best way to implement an invention

[0030] The present invention will now be described in further detail. Unless otherwise defined, all technical and scientific terms used in this specification have the same meaning as commonly understood by one of ordinary skill in the art to which this application pertains.

[0031] Generally, the nomenclature used in the specification of this invention is well-known and commonly used in the technical field to which this invention pertains. Throughout the specification of this invention, when a part is referred to as "comprising" a certain constituent element, it indicates, unless specifically stated otherwise, that other constituent elements may be included rather than excluded.

[0032] The techniques disclosed below are applicable to polishing of silicon substrates. They are particularly suitable for polishing of silicon wafers. A typical example of a silicon wafer referred to herein is a single-crystal silicon wafer, such as a single-crystal silicon wafer obtained by slicing a single-crystal silicon ingot.

[0033] In the techniques disclosed herein, the surface to be polished is typically a silicon surface. The polishing methods disclosed herein are preferably applicable to the polishing process of silicon substrates.

[0034] According to the present invention, a slurry composition for final polishing of silicon wafers is provided, characterized in that deionized water is used as a solvent, and the composition includes polishing particles, surfactants, pH adjusters, water-soluble thickeners, chelating agents, and polishing accelerators.

[0035] The composition is characterized by comprising, relative to the total weight of the composition, 1 to 20% by weight of the polishing particles, 0.03 to 0.5% by weight of the surfactant, 0.1 to 10% by weight of the pH adjuster, 0.02 to 2% by weight of the water-soluble thickener, 0.05 to 0.2% by weight of the chelating agent, and 0.1 to 1% by weight of the polishing accelerator.

[0036] In the silicon wafer final polishing slurry composition of this embodiment, water is typically included as a solvent. Ion-exchanged water (deionized water), pure water, ultrapure water, distilled water, etc., are preferably used as water. To minimize interference with the effects of other components contained in the polishing composition, the total metal ion content of the water used is preferably 100 ppb or less.

[0037] The polishing slurry composition of this embodiment includes polishing particles. These polishing particles function to mechanically polish the surface of a silicon wafer. Colloidal silica, fumed silica, colloidal alumina, fumed alumina, and cerium dioxide can be used as polishing particles. From the viewpoint of improving the surface smoothness of the silicon wafer, colloidal silica is preferred.

[0038] In the slurry composition of the present invention, the average particle size of the colloidal silica particles is preferably 30 nm to 70 nm when measured by dynamic light scattering method.

[0039] When the average particle size of colloidal silica particles is less than 30 nm, the polishing speed is too low, making it difficult to apply to the polishing process. Conversely, when the average particle size of colloidal silica particles exceeds 70 nm, a large number of wafer surface defects occur, thus deviating from the purpose of this invention.

[0040] The polishing composition of this embodiment includes a surfactant. The surfactant functions to induce an increase in the zeta potential between polishing particles and to increase the directionality of the polymer arrangement used as a thickener, thereby increasing the dispersion stability of the polishing agent.

[0041] In particular, the cleaning properties of surfactants improve the re-adhesion properties of siloxane particles that detach during polishing.

[0042] Examples of surfactants include carbonate anionic surfactants, sulfonic acid anionic surfactants, phosphoric acid anionic surfactants, betaine amphoteric surfactants, and nonionic surfactants with hydrophilic structures consisting of ethylene alone or ethylene and propylene groups.

[0043] Among these surfactants, nonionic surfactants are preferred from the viewpoint of low foaming properties or ease of pH adjustment.

[0044] Specific examples of nonionic surfactants include single polymers of olefin oxides, block copolymers of various types of olefin oxides, random copolymers of various types of olefin oxides, and polymers of olefin oxides made of methacrylic acid. These nonionic surfactants penetrate the spaces between the molecules of the water-soluble thickener and adhere tightly to the wafer surface. As described above, nonionic surfactants fill the gaps in the protective film, increasing its density and hardness, thereby improving the protective effect on the wafer surface.

[0045] In particular, the methacrylate polymer having the structure of the following chemical formula 2 has strong hydrophilicity, thereby improving the protective effect on the wafer surface and reducing the number of defects and haze value of the polished wafer, and is therefore preferred.

[0046] [Chemical Formula 2]

[0047]

[0048] In the above chemical formula 2, n is between 7 and 22.

[0049] In this invention, ammonia water is used in an amount equivalent to 0.1 to 10% by weight of the total slurry as a pH adjuster to adjust the final pH of the slurry to 10.5 to 12. Furthermore, in addition to its function as a pH adjuster, ammonia water also has the function of forming complexes with metals during the polishing process to inhibit metal residue, thereby achieving the beneficial effect of increasing polishing speed.

[0050] In this invention, to mitigate the effects of mechanical polishing and achieve the desired level of polishing, water-soluble thickeners that promote laminar flow in the slurry can include cellulose-based thickeners, polyvinylpyrrolidone (PVP), PVP-acrylate copolymers, PVP-vinyl acetate copolymers, polyethylene glycol, polyvinyl alcohol, and sorbitan monooleate. Among these water-soluble thickeners, PVP and polyvinyl alcohol are more preferred. These water-soluble thickeners can be used individually or in combination of two or more.

[0051] In this invention, metal contamination of silicon wafers is suppressed by forming a complex by capturing metallic impurity components within the polishing agent, and in particular, a chelating agent capable of suppressing contamination caused by nickel or copper is included.

[0052] Chelating agents include, but are not limited to, glycine, acetic acid, acetone oxime, acrylic acid, adipic acid, alanine, arginine, asparagine, aspartic acid, betaine, dimethylglyoxime, formic acid, fumaric acid, gluconic acid, glutamic acid, glutamine, glutamate, glyceric acid, glycerol, glycolic acid, glyoxylic acid, histidine, iminodiacetic acid, isophthalic acid, itaconic acid, lactic acid, leucine, lysine, maleic acid, maleic anhydride, malic acid, malonic acid, mandelic acid, 2,4-pentanedione, phenylacetic acid, phenylalanine, phthalic acid, proline, propionic acid, catechol, pyromellitic acid, quinic acid, serine, sorbitol, succinic acid, tartaric acid, terephthalic acid, trimellitic acid, pyromellitic acid, tyrosine, valine, xylitol, and their salts and derivatives, and combinations thereof.

[0053] Among these chelating agents, glycine is particularly preferred. These chelating agents can be used alone or in combination of two or more.

[0054] The polishing composition of this embodiment typically contains a silicon wafer polishing accelerator. A silicon wafer polishing accelerator is a component that, when added to a polishing slurry composition, chemically polishes the surface to be polished and helps increase the polishing speed. The silicon wafer polishing accelerator has the effect of chemically etching silicon and is typically an organic basic compound.

[0055] As an organic basic compound, the quaternary ammonium salt is selected from the group consisting of tetramethylammonium hydroxide, tetraethylammonium hydroxide, choline hydroxide, N,N-dimethylpiperidine hydroxide, and tris(2-hydroxyethyl)methylammonium hydroxide. Furthermore, these organic bases function as cleaning agents to remove siloxane particles or metallic impurities detached during polishing from the wafer surface. In particular, tris(2-hydroxyethyl)methylammonium hydroxide (THEMAH), having the structure of Formula 1, exhibits superior cleaning performance compared to other quaternary ammonium salts and is therefore preferred.

[0056] [Chemical Formula 1]

[0057]

[0058] The following describes preferred embodiments and comparative examples of the present invention. However, the following embodiments are merely preferred embodiments of the present invention, and the present invention is not limited to the following embodiments.

[0059] Methods of implementing the invention

[0060] Examples 1 to 5, Comparative Examples 1 to 5

[0061] The present invention will be described in detail using the examples and comparative examples in Table 1.

[0062] The polishing composition shown in Table 1 is obtained by mixing abrasive particles (polishing agent), surfactant, pH adjuster, water-soluble thickener, chelating agent, polishing accelerator and deionized water.

[0063] Specifically, a polishing composition was prepared comprising the following components relative to the total weight of the composition: 10% by weight of abrasive particles, 5% by weight of pH adjuster, 1% by weight of water-soluble thickener, and 0.1% by weight of chelating agent, wherein the types and amounts of surfactants and polishing accelerators are varied as shown in Table 1, and the balance is deionized water.

[0064] [Table 1]

[0065]

[0066]

[0067] *PVA: Polyvinyl alcohol

[0068] Silicon wafers were polished using the polishing compositions listed in Table 1. The number of defects and haze value were measured during polishing. The polishing conditions were as follows:

[0069] - Equipment: 12" 5- Zone pressure polisher & cleaner

[0070] - Pressure: Wafer 1.2psi (2.5 / 1.2 / 1.2 / 1.2 / 1.2) R-ring 4.0psi

[0071] -PAD: Soft pad (H7000HN-PET)

[0072] -Dilution ratio: 1:1 dilution

[0073] - Flow rate: 200 ml / min

[0074] Polishing time: 60 seconds

[0075] Cleaning solution: SC-1

[0076] - Brush type: Roller-type PVA (polyvinyl alcohol)

[0077] Cleaning time: 60 seconds

[0078] Defect count was measured using a 10μm spot size light source from a KLA-Tencor AIT-XP+ device. Haze was evaluated using a wafer inspection unit (KLA-Tencor Surfscan SP2) in DWO mode, with haze values ​​(ppm) measured. The results are shown in Table 2 below.

[0079] [Table 2]

[0080]

[0081]

[0082] In Examples 1 and Comparative Examples 1 and 2, changing the type of polishing accelerator confirmed that THEMAH reduced the number of defects and haze compared to TMAH. Similar reduction trends were also observed in Comparative Examples 3, 4, and 5. In Examples 1 and 5, Comparative Examples 1 and 3, and Comparative Examples 2 and 4, changing the type of surfactant confirmed that PEO-methacrylates reduced the number of defects and haze compared to PEO-PPO-PEO.

[0083] In Examples 1, 2, and 3, increasing the surfactant content resulted in a reduction in both the number of defects and haze. Similar reduction trends were observed in Examples 1, 4, and 5, even with increased polishing accelerator content. However, the reduction in haze was significantly influenced by the surfactant, while the reduction in the number of defects was significantly influenced by the polishing accelerator.

[0084] As shown above, in the slurry composition of the present invention, when an organic base (THEMAH) with increased PEO-methacrylate and OH groups is included, the number of defects and haze are reduced, thereby improving the yield of the polishing process.

[0085] Examples 6 to 11 and Comparative Examples 6 to 9 were prepared by varying the average particle size (nm) and content of colloidal silica as shown in Table 3. Specifically, the compositions were prepared comprising the following components: 1 to 20 wt% abrasive particles, 5 wt% pH adjuster, 1 wt% water-soluble thickener, 0.1 wt% chelating agent, 0.03 wt% PEO-methacrylate, 0.5 wt% THEMAH, and the balance being deionized water, relative to the total weight of the composition. The average particle size after polishing, polishing speed, defect number, and haze were measured and are shown in Table 4.

[0086] [Table 3]

[0087]

[0088] [Table 4]

[0089]

[0090]

[0091] The results of changing the average particle size in Examples 6 to 11 and Comparative Examples 6 and 7 show that the smaller the particle size, the fewer the defects and the less haze. However, at 20 nm, the polishing speed is very low. Therefore, particle sizes of less than 30 nm cannot be used in actual processes.

[0092] Furthermore, while an 80nm particle size increases the polishing speed and shortens the process time, it also reduces the yield of the polishing process due to an increase in the number of defects and haze. Therefore, particle sizes exceeding 70nm cannot be used in practical processes.

[0093] Furthermore, the results of varying the particle content in Examples 7, 10, 11 and Comparative Examples 7, 8, and 9 showed a tendency for lower particle content to reduce polishing speed, defect number, and haze. However, even with reduced defect number and haze, the process efficiency would be significantly reduced due to excessively low polishing speed, making it impractical for real-world applications.

[0094] The foregoing has provided a detailed description of specific aspects of the invention. For those skilled in the art, these specific techniques are merely preferred embodiments, and it is obvious that the scope of the invention is not limited thereto. Therefore, the actual scope of the invention is defined by the claims and their equivalents.

Claims

1. A slurry composition for final polishing of silicon wafers to reduce the number of surface defects and haze, wherein, The composition consists of colloidal silica as polishing particles, surfactant, pH adjuster, water-soluble thickener, chelating agent, polishing accelerator, and the balance being water. The composition comprises, relative to its total weight, 1 to 20% by weight of colloidal silica, 0.03 to 0.5% by weight of surfactant, 0.1 to 10% by weight of pH adjuster, 0.02 to 2% by weight of water-soluble thickener, 0.05 to 0.2% by weight of chelating agent, 0.1 to 1% by weight of polishing accelerator, and the balance being water. The surfactant is a PEO-methacrylate polymer having the structure of the following chemical formula 2. [Chemical Formula 2] In the chemical formula 2, n is between 7 and 22. The polishing accelerator is an organic base, specifically tris(2-hydroxyethyl)methylammonium hydroxide having the structure of the following chemical formula 1. [Chemical Formula 1] ， The colloidal silica has a particle size of 30 nm to 70 nm.

2. The slurry composition for final polishing of silicon wafers according to claim 1, characterized in that, The pH ranges from 10.5 to 12.

3. A final polishing method for silicon wafers, using the composition described in claim 1 or 2.

4. The final polishing method according to claim 3, characterized in that, Polishing speed exceeds 40 nm / min.

Images