Slurry composition for final polishing of silicon wafers for reducing number of surface defects and haze, and final polishing method using the same

Abstract

The present invention relates to a slurry composition for final polishing of silicon wafers, which is excellent in terms of performance of reducing the number of defects and reducing haze on the surface of an object to be polished, and which comprises 1 to 20% by weight of colloidal silica as abrasive grains, 0.03 to 0.5% by weight of a surfactant, 0.1 to 10% by weight of a pH adjuster, 0.02 to 2% by weight of a water-soluble thickener, 0.05 to 0.2% by weight of a chelating agent, and 0.1 to 1% by weight of an organic base, and a method for final polishing using the same.

Description

[Technical field]

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

[0002] Generally, silicon wafers, which serve as substrates in semiconductor manufacturing, are manufactured through processes such as single crystal growing, slicing, lapping, etching, polishing, and cleaning. Among the wafer manufacturing processes, the polishing process is a process that must completely remove scratches, cracks, metal impurities, particles, LPD (Light Point Defects), microroughness, etc., which are minute defects on the wafer surface that have been generated or have not yet been removed during all processes from the growth of silicon single crystal ingots to the final CMP (Chemical Mechanical Polishing) process, to create a mirror-like surface. The CMP process for wafers consists of multiple steps, including stock removal polishing, which requires a high polishing speed to remove deep scratches on the wafer surface, and final polishing, which removes remaining micro-scratches and reduces the micro-roughness of the surface (to a level of a few angstroms) to create a mirror finish. At this time, the main factors that determine the ultra-fine defects in the mirror polishing process include a hard or soft urethane polishing pad and silica slurry. In general, a wafer slurry for mirror polishing contains colloidal silica as an abrasive, a pH adjuster, an organic basic compound that promotes polishing, a surfactant that improves dispersion stability and cleaning performance, a water-soluble thickener for particle stability and protection of the wafer surface, and a chelating agent that forms complex ions with metal impurities that may be contained in the polishing slurry and captures them, thereby suppressing contamination of the object to be polished by metal impurities. Recently, as the degree of integration of semiconductors increases, the scope of control for surface defects on wafers becomes narrower, and active research and development is being conducted on polishing pads and slurries having the appropriate quality. In particular, since slurries are considered to be an important factor that determines the final quality of wafers, products with a variety of physicochemical properties are being released. Summary of the Invention [Problem to be solved by the invention]

[0003] As semiconductor wiring becomes finer, there is a demand for finishing the silicon substrate to a higher quality surface. Therefore, there is a demand for a slurry composition for final polishing that can provide a silicon wafer substrate with reduced fine particles and haze. Therefore, the present invention aims to improve the yield of the silicon wafer polishing process by providing a composition for final polishing of silicon wafers that has excellent performance in reducing fine particles and haze on the surface of a silicon wafer substrate, which is an object to be polished, and a final polishing method using said composition. [Means for solving the problem]

[0004] The present inventors have searched for a basic compound and a water-soluble polymer for suppressing surface defects and reducing haze of silicon wafers after final polishing, and have found that a composition containing a compound having a specific structure is excellent in reducing surface defects and haze of silicon wafers, thereby completing the present invention. That is, an object of the present invention is to provide a composition for final polishing of silicon wafers that is excellent in reducing surface defects and haze of silicon wafers. In order to achieve the above object, the present invention provides a slurry composition for final polishing of silicon wafers, which is characterized in that the slurry composition contains ultrapure water, abrasive grains, a pH adjuster, a water-soluble thickener, and a chelating agent, and simultaneously contains a quaternary ammonium ion (quaternary ammonium cation) and a methacrylate polymer (monofunctional methacrylate). The quaternary ammonium ion of the present invention is characterized by being represented by the following formula (1), and the methacrylate polymer contains a substance represented by the following formula (2). [ka] [ka] (In the formula, n is 7 to 22.) According to an embodiment of the present invention, the final polishing composition has an average particle size of particles in the polishing composition of 80 nm or less as measured by dynamic light scattering. Generally, when the average particle size of the particles in the polishing composition is 80 nm or less, the polished surface becomes hydrophobic, and the number of surface defects or haze increases. Furthermore, when the average particle size of the particles in the polishing composition is small, the particles tend to reattach to the polished wafer surface due to the attractive / repulsive forces of the electric double layer and become particles, which may increase the number of defects. However, in the polishing composition containing the above-mentioned organic basic compound and water-soluble polymer, even if the particles in the polishing composition are made small, the function of cleaning the surface of the silicon wafer is improved and the surface of the wafer can be kept hydrophilic. Therefore, according to the embodiment of the present invention, it is possible to suppress surface defects and reduce haze on the polished silicon wafer. Effect of the Invention

[0005] The slurry composition for final polishing of silicon wafers according to the present invention has a remarkable effect of suppressing the generation of fine particles and reducing haze on the surface of silicon wafers while maintaining a polishing rate of more than 40 nm / min, thereby significantly improving process reliability and productivity. [Brief description of the drawings]

[0006] [Figure 1] 1 is a map showing the number of surface defects of a silicon wafer according to Example 1 of the present invention. [Diagram 2] 1 is a map showing the number of surface defects of a silicon wafer according to Comparative Example 4 of the present invention. [Diagram 3] 13 is a map showing the number of surface defects of a silicon wafer according to Comparative Example 7 of the present invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0007] The present invention will now be described in more detail. Unless otherwise defined, all technical and scientific terms used in the present specification have the same meaning as commonly understood by a skilled artisan in the art to which the present invention belongs. In general, the nomenclature used in the present specification is that which is well known and commonly used in the art to which the present invention pertains. Throughout the present specification, when a part is described as "comprising" a certain component, this does not mean that it excludes other components, but that it can further include other components, unless otherwise specified to the contrary. The technology disclosed below is applied to polishing a silicon substrate as an object to be polished. It is particularly suitable for polishing a silicon wafer as an object to be polished. A typical example of the silicon wafer referred to here is a silicon single crystal wafer, for example, a silicon single crystal wafer obtained by slicing a silicon single crystal ingot. The surface to be polished in the technique disclosed herein is typically a surface containing silicon, and the polishing method disclosed herein can be suitably applied to a polishing process of a silicon substrate. The present invention provides a slurry composition for final polishing of silicon wafers, which is characterized by using deionized water as a solvent and containing abrasive grains, a surfactant, a pH adjuster, a water-soluble thickener, a chelating agent, and a polishing accelerator. The composition is characterized in that it contains, relative to the total weight of the composition, 1 to 20% by weight of the abrasive grains, 0.03 to 0.5% by weight of a surfactant, 0.1 to 10% by weight of a pH adjuster, 0.02 to 2% by weight of a water-soluble thickener, 0.05 to 0.2% by weight of a chelating agent, and 0.1 to 1% by weight of a polishing accelerator. The slurry composition for final polishing of silicon wafers of this embodiment typically contains water as a solvent. As the water, ion-exchanged water (deionized water), pure water, ultrapure water, distilled water, etc. can be preferably used. In order to prevent the action of other components contained in the polishing composition from being inhibited as much as possible, the water used preferably has a total metal ion content of 100 ppb or less.

[0008] The polishing composition of the present embodiment contains abrasive grains. The abrasive grains have the function of mechanically polishing the surface of the silicon wafer. As the abrasive grains, colloidal silica, fumed silica, colloidal alumina, fumed alumina, ceria, and the like can be used. From the viewpoint of improving the surface smoothness of the silicon wafer, it is preferable to use colloidal silica. In the slurry composition of the present invention, the average particle size of the colloidal silica particles is preferably in the range of 30 to 70 nm when measured by dynamic light scattering method. If the average particle size of the colloidal silica particles is less than 30 nm, the polishing rate is too low to be practically applicable to a polishing process. On the other hand, if the average particle size of the colloidal silica particles is more than 70 nm, a large number of defects will occur on the wafer surface, which is beyond the scope of the present invention. The polishing composition of the present embodiment contains a surfactant. The role of the surfactant is to increase the dispersion stability of the polishing agent by inducing an increase in the zeta potential between abrasive grains and increasing the directionality of the arrangement of the polymer used as a thickener. In particular, the cleaning properties of the surfactant enhance the ability to prevent re-adhesion of siloxane particles that are detached during polishing. Examples of the surfactant include carbonate-based anionic surfactants, sulfonic acid-based anionic surfactants, phosphate-based anionic surfactants, betaine-based amphoteric surfactants, and nonionic surfactants having a hydrophilic group structure consisting of ethylene alone or ethylene and propylene groups. Among these surfactants, nonionic surfactants are more preferred from the viewpoint of low foaming properties or ease of pH adjustment.

[0009] Specific examples of nonionic surfactants include homopolymers of oxyalkylene, block copolymers of multiple types of oxyalkylene, random copolymers of multiple types of oxyalkylene, methacrylate oxyalkylene polymers, etc. Such nonionic surfactants penetrate between the molecules of the water-soluble thickener and are densely adsorbed on the surface of the wafer. In this way, the nonionic surfactant fills the gaps in the protective film, improving the density and strength of the protective film and improving the protective effect on the surface of the wafer. Among these, a methacrylate polymer having the structure of the following formula (2) is particularly preferred because it has strong hydrophilicity, enhances the protective effect on the wafer surface, and reduces the number of defects and the haze value of the wafer after polishing. [ka] (In the formula, n is 7 to 22.) In the present invention, the final pH of the slurry is adjusted to 10.5 to 12.0 by using ammonia water as a pH adjuster in an amount equivalent to 0.1 to 10% by weight of the total weight of the slurry. Meanwhile, in addition to its role as a pH adjuster, ammonia water also has a function of suppressing metal residue by forming a complex with metal during the polishing process, and this function can provide a beneficial effect of improving the polishing rate.

[0010] In the present invention, in order to obtain a desired polishing level while mitigating the mechanical polishing effect, the water-soluble thickener that plays a role in making the slurry generate laminar flow includes celluloses, polyvinylpyrrolidone, polyvinylpyrrolidone polyacrylic acid copolymer, polyvinylpyrrolidone vinyl acetate copolymer, polyethylene glycol, polyvinyl alcohol, sorbitan monooleate, etc. Among these water-soluble thickeners, polyvinylpyrrolidone and polyvinyl alcohol are more preferred. These water-soluble thickeners may be used alone or in combination of two or more. The present invention includes a chelating agent that captures metal impurity components in the polishing system to form a complex, thereby suppressing metal contamination of silicon wafers, and in particular suppresses contamination by nickel or copper. 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, glutaric acid, 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, pyrocatechol, pyromellitic acid, quinic acid, serine, sorbitol, succinic acid, tartaric acid, terephthalic acid, trimellitic acid, trimesic acid, tyrosine, valine, xylitol, salts and derivatives thereof, and combinations thereof. Among these chelating agents, it is particularly preferable to use glycine. These chelating agents may be used alone or in combination of two or more. The polishing composition of this embodiment typically contains a silicon wafer polishing accelerator. The silicon wafer polishing accelerator is a component that acts to chemically polish the surface to be polished by being added to the polishing composition, and contributes to improving the polishing rate. The silicon wafer polishing accelerator has the effect of chemically etching silicon, and is typically an organic basic compound.

[0011] The organic basic compound is a quaternary ammonium salt, which is one selected from the group consisting of tetramethylammonium hydroxide, tetraethylammonium hydroxide, choline hydroxide, N,N-dimethylpiperidine hydroxide, and tris(2-hydroxyethyl)methylammonium hydroxide. In addition, such organic bases function as cleaning agents that remove siloxane particles and metal impurities that are released during polishing from the wafer surface. Among these, tris(2-hydroxyethyl)methylammonium hydroxide (THEMAH), which has the structure of the following formula (1), is particularly preferable because it has a superior cleaning function compared to other quaternary ammonium salts. [ka] In the following, preferred examples and comparative examples of the present invention will be described. However, the following examples are merely preferred examples of the present invention, and the present invention is not limited to the following examples. EXAMPLES

[0012] Examples 1 to 5, Comparative Examples 1 to 5 The present invention will be described in detail with reference to the examples and comparative examples in Table 1. Abrasive grains (abrasive), a surfactant, a pH adjuster, a water-soluble thickener, a chelating agent, a polishing accelerator, and deionized water were mixed together to obtain the polishing composition shown in Table 1. Specifically, the composition contained 10% by weight of abrasive grains, 5% by weight of pH regulator, 1% by weight of water-soluble thickener, 0.1% by weight of chelating agent, and the types and amounts of surfactants and polishing accelerators were varied as shown in Table 1, with the remaining amount being deionized water. A polishing composition was prepared. [Table 1] Silicon wafers were polished using the polishing compositions shown in Table 1. The number of defects and the haze value were measured during polishing under the following polishing conditions. -Equipment: 12" 5-zone pressure polisher & cleaner -Pressure: Wafer 1.2psi (2.5 / 1.2 / 1.2 / 1.2 / 1.2) R-ring 4.0psi -PAD: Soft pad (H7000HN-PET) -Dilution ratio: 1:1 dilution -Flow rate: 200mL / min -Polishing time: 60 seconds -Cleaning solution: SC-1 -Brush type: roll type PVA (polyvinyl alcohol) -Cleaning time: 60 seconds

[0013] The number of defects was measured using a light source with a spot size of 10 μm equipped with a product name [AIT-XP+] manufactured by KLA-Tencor Corporation, and the haze evaluation was performed by measuring the haze value (ppm) in DWO mode using a wafer inspection device (product name "Surfscan SP2" manufactured by KLA-Tencor Corporation). The measurement results are shown in Table 2 below. [Table 2] By changing the type of polishing accelerator in Example 1 and Comparative Examples 1 and 2, it was confirmed that THEMAH reduced the number of defects and haze compared to TMAH. A similar reduction trend was also observed in Comparative Examples 3, 4, and 5. By changing the type of surfactant in Example 1 and Comparative Example 5, Comparative Example 1 and Comparative Example 3, and Comparative Example 2 and Comparative Example 4, it was confirmed that the PEO-methacrylate system reduced the number of defects and haze compared to PEO-PPO-PEO. In Examples 1, 2, and 3, the number of defects and haze decreased when the surfactant content was increased, and a similar tendency of decrease was observed when the polishing accelerator content was increased in Examples 1, 4, and 5. However, the decrease in haze tends to be largely influenced by the surfactant, and the decrease in the number of defects tends to be largely influenced by the polishing accelerator. In this way, when the slurry composition of the present invention contains a PEO-methacrylate system and an organic base (THEMAH) with increased OH groups, it is possible to reduce the number of defects and haze, thereby improving the yield of the polishing process.

[0014] In Examples 6 to 11 and Comparative Examples 6 to 9, polishing compositions were prepared with different average particle diameters (nm) and contents of colloidal silica as shown in Table 3. Specifically, the polishing compositions were prepared with 1 to 20% by weight of abrasive grains, 5% by weight of pH regulator, 1% by weight of water-soluble thickener, 0.1% by weight of chelating agent, 0.03% by weight of PEO-methacrylate, 0.5% by weight of THEMAH, and the remaining amount of deionized water. Then, the polishing speed, number of defects, and haze for the average particle diameter after polishing were measured and are shown in Table 4. [Table 3] [Table 4] As a result of changing the average particle size in Examples 6 to 11 and Comparative Examples 6 and 7, the smaller the particle size, the fewer the number of defects and the haze. However, since the polishing speed is very low when the particle size is 20 nm, a particle size of less than 30 nm cannot be adopted in an actual process.

[0015] In addition, a grain size of 80 nm has the advantage of increasing the polishing speed and shortening the process time, but it also increases the number of defects and haze, reducing the yield of the polishing process, so a grain size of over 70 nm cannot be adopted in an actual process. In addition, the particle content was changed in Examples 7, 10, and 11 and Comparative Examples 7, 8, and 9, and the results showed that the lower the particle content, the lower the polishing speed, the number of defects, and the haze. Even if the number of defects and haze are reduced, if the polishing speed is too low, the process efficiency is significantly reduced, and therefore this cannot be adopted in actual processes.

[0016] Although the specific parts of the present invention have been described in detail above, it is clear to those skilled in the art that such specific techniques are merely preferred embodiments and do not limit the scope of the present invention. Therefore, the substantial scope of the present invention should be defined by the claims and their equivalents.

Claims

1. A slurry composition for final polishing of silicon wafers for reducing the number of surface defects and haze, comprising colloidal silica as an abrasive, a surfactant, a pH adjuster, a water-soluble thickener, a chelating agent, a polishing accelerator, and a balance of water, A slurry composition for final polishing of silicon wafers for reducing the number of surface defects and haze, comprising, relative to the total weight of the composition, 1 to 20 wt % of colloidal silica, 0.03 to 0.5 wt % of a surfactant which is a PEO methacrylate polymer having the structure of the following formula (2), 0.1 to 10 wt % of a pH adjuster, 0.02 to 2 wt % of a water-soluble thickener, 0.05 to 0.2 wt % of a chelating agent, 0.1 to 1 wt % of a polishing accelerator which is tris(2-hydroxyethyl)methylammonium hydroxide (THEMAH) having the structure of the following formula (1) as an organic base, and the balance water. 【Chemistry 1】 【Chemistry 2】 (In the formula, n is 7 to 22.)

2. 2. The slurry composition for final polishing of silicon wafers for reducing the number of surface defects and haze according to claim 1, wherein the pH is 10.5 to 12.

3. 2. The slurry composition for final polishing of silicon wafers for reducing the number of surface defects and haze according to claim 1, wherein the colloidal silica has a particle size of 30 to 70 nm.

4. A method for final polishing of silicon wafers, using the composition according to any one of claims 1 to 3.

5. 5. The final polishing method according to claim 4, wherein the polishing rate is more than 40 nm / min.

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