Polishing composition and polishing method

Abstract

The present invention provides a polishing composition and polishing method that enable faster polishing of the object to be polished. [Solution] A polishing composition comprising a polishing speed enhancer that improves the polishing speed of an object to be polished when the object to be polished is polished, an oxidizing agent, and anion-modified silica, wherein the polishing speed enhancer is a salt of a typical metal belonging to group 1, 2, 13, 14, or 15 of the periodic table, and the oxidizing agent is a peroxide, and a polishing method comprising polishing an object to be polished containing tungsten using the polishing composition.

Description

[Technical Field]

[0001] The present invention relates to an abrasive composition and an abrasive method. [Background technology]

[0002] With the increasing use of multilayer wiring on semiconductor substrate surfaces, chemical mechanical polishing (CMP) technology is employed in the manufacturing of devices to flatten and polish the semiconductor substrate. CMP is a method of flattening the surface of a workpiece, such as a semiconductor substrate, using a polishing composition (slurry) containing abrasive particles such as silica, alumina, and ceria, as well as corrosion inhibitors and surfactants. Workpieces include wiring, plugs, and other components made of silicon, polysilicon, silicon oxide, silicon nitride, and metals.

[0003] When polishing substrates containing wiring and plugs made of metal, polishing compositions containing an oxidizing agent are used. Because the metals contained on the substrate are hard and difficult to polish, a sufficient polishing speed cannot be obtained compared to silicon or polysilicon. Therefore, polishing is performed by oxidizing the surface of the metal with an oxidizing agent contained in the polishing composition and then scraping off the formed metal oxide with abrasive grains. Patent Document 1 proposes a polishing composition containing a metal salt containing at least one metal selected from the group consisting of Groups 8, 11, 12, and 13, 1,2,4-triazole, phosphoric acids, an oxidizing agent, and abrasive grains in order to efficiently polish palladium and copper on a substrate.

[0004] On the other hand, with the miniaturization of wiring in semiconductor substrates, tungsten (W) is sometimes used in contact plugs and via plugs. It is known that when a substrate containing tungsten is polished with an abrasive composition containing an oxidizing agent in the CMP process, tungsten corrosion is likely to occur. Patent Document 2 proposes an abrasive composition containing metal ions to achieve both efficient polishing of tungsten and suppression of corrosion. [Prior art documents] [Patent Documents]

[0005] [Patent Document 1] International Publication No. 2011 / 099313 [Patent Document 2] Japanese Patent Publication No. 2020-174083 [Overview of the project] [Problems that the invention aims to solve]

[0006] However, conventional polishing compositions have not provided sufficient polishing speed for tungsten-containing objects. Therefore, there is a need for polishing compositions that can polish tungsten-containing objects at a higher speed.

[0007] The present invention has been made in view of these circumstances, and aims to provide an abrasive composition and abrasive method that can polish a tungsten-containing object at a higher speed. [Means for solving the problem]

[0008] A polishing composition according to one aspect of the present invention comprises a polishing speed enhancer that improves the polishing speed of an object to be polished, an oxidizing agent, and anion-modified silica, wherein the polishing speed enhancer is a salt of a typical metal belonging to group 1, 2, 13, 14, or 15 of the periodic table, and the oxidizing agent is a peroxide.

[0009] A polishing method according to another aspect of the present invention includes a polishing step of polishing an object containing tungsten using the polishing composition according to the present invention. [Effects of the Invention]

[0010] According to the present invention, it is possible to provide an abrasive composition and a polishing method that can polish objects containing tungsten at a faster speed. [Modes for carrying out the invention]

[0011] The polishing composition and polishing method according to this embodiment will be described in detail below. Note that the following embodiments are merely examples of the present invention, and the present invention is not limited to these embodiments. Furthermore, various modifications or improvements can be made to the following embodiments, and such modified or improved forms may also be included in the present invention.

[0012] <Polishing composition> An abrasive composition according to one embodiment of the present invention comprises an abrasive speed enhancer that improves the abrasive speed of an object to be abraded when the object to be abraded is polished, an oxidizing agent, and anion-modified silica. The abrasive speed enhancer is a salt of a typical metal belonging to group 1, 2, 13, 14, or 15 of the periodic table, and the oxidizing agent is a peroxide.

[0013] When using the polishing composition according to this embodiment, the polishing speed for objects containing tungsten can be improved. This is presumed to be because:

[0014] The polishing composition according to this embodiment contains a salt of a typical metal belonging to Group 1, 2, 13, 14, or 15 of the periodic table as a polishing speed enhancer. Anions (for example, nitrate ions (NO3)) are generated from this salt of the typical metal. - )) has oxidizing properties. Therefore, it is thought that this anion promotes oxidation of the tungsten surface, thereby improving the polishing speed of tungsten. In addition, since the surface potential of the tungsten film is negative, metal cations (for example, aluminum ions (Al)) generated from salts of typical metals 3+ It is thought that the silica will adsorb onto the tungsten film surface. This suppresses electrostatic repulsion between the anion-modified silica and the tungsten surface, making it easier for the anion-modified silica to adhere to the tungsten surface, thus enabling more efficient polishing. Therefore, it is presumed that using the polishing composition according to this embodiment will improve the polishing speed for objects containing tungsten compared to polishing compositions without a polishing speed enhancer.

[0015] In other words, the polishing composition according to the present invention may be used to polish an object containing tungsten.

[0016] (Abrasive grains) The polishing composition according to this embodiment contains anion-modified silica as abrasive grains. The abrasive grains have the effect of mechanically polishing the object to be polished. Anion-modified silica is, for example, silica on which an organic acid is fixed to the surface. The type of silica is not particularly limited, but examples include colloidal silica and fumed silica, but colloidal silica is preferred. That is, the abrasive grains may be anion-modified colloidal silica.

[0017] Methods for producing colloidal silica include the sodium silicate method and the sol-gel method. Colloidal silica produced by either method may be used, but from the viewpoint of reducing metal impurities, colloidal silica produced by the sol-gel method is preferred. Colloidal silica produced by the sol-gel method is preferred because it contains less metal impurities that have the property of diffusing in semiconductors and corrosive ions such as chloride ions. Colloidal silica can be produced by the sol-gel method using conventionally known methods. Specifically, colloidal silica can be obtained by using a hydrolyzable silicon compound (for example, alkoxysilane or its derivative) as a raw material and carrying out a hydrolysis-condensation reaction.

[0018] Anion-modified colloidal silica may be colloidal silica on which anionic groups such as carboxylic acid groups, sulfonic acid groups, phosphonic acid groups, and aluminic acid groups are immobilized on the surface, but among these, colloidal silica on which sulfonic acid groups are immobilized on the surface is preferred. In other words, anion-modified silica is preferably sulfonic acid-modified colloidal silica.

[0019] The method for producing the anion-modified colloidal silica is not particularly limited, and examples thereof include a method of reacting a silane coupling agent having an anionic group at the terminal with colloidal silica.

[0020] As a specific example, if the sulfonic acid group is to be immobilized on the colloidal silica, for example, it can be carried out by the method described in “Sulfonic acid-functionalized silica through of thiol groups”, Chem. Commun. 246-247 (2003). Specifically, after coupling a silane coupling agent having a thiol group such as 3-mercaptopropyltrimethoxysilane to the colloidal silica, the thiol group is oxidized with hydrogen peroxide to obtain colloidal silica having a sulfonic acid group immobilized on the surface (sulfonic acid-modified colloidal silica).

[0021] If the carboxylic acid group is to be immobilized on the colloidal silica, for example, it can be carried out by the method described in “Novel Silane Coupling Agents Containing a Photolabile 2-Nitrobenzyl Ester for Introduction of a Carboxy Group on the Surface of Silica Gel”, Chemistry Letters, 3, 228-229 (2000). Specifically, after coupling a silane coupling agent containing a photoreactive 2-nitrobenzyl ester to the colloidal silica, light irradiation is carried out to obtain colloidal silica having a carboxylic acid group immobilized on the surface (carboxylic acid-modified colloidal silica).

[0022] (Zeta potential) In the polishing composition according to this embodiment, the anion-modified silica may have a zeta potential of -10mV or less, or a zeta potential of -15mV or less. If the zeta potential is -10mV or less, the anion-modified silica is less likely to aggregate. Furthermore, the anion-modified silica may have a zeta potential of -70mV or more, or a zeta potential of -45mV or more. If the zeta potential is -70mV or more, the anion-modified silica particles do not disperse too much, so the polishing of the object to be polished can be performed effectively. That is, the anion-modified silica may have a zeta potential of -70mV or more and -10mV or less, or a zeta potential of -45mV or more and -15mV or less.

[0023] (Shape of anion-modified silica) The shape of anion-modified silica is not particularly limited. For example, it may be spherical or non-spherical. Specific examples of non-spherical shapes include polygonal prisms such as triangular and square prisms, cylindrical shapes, cylindrical shapes where the center of the cylinder is wider than the ends, donut shapes where the center of the disk is penetrated, plate shapes, so-called cocoon shapes with a constriction in the center, so-called aggregate spherical shapes where multiple particles are integrated, so-called konpeito shapes with multiple protrusions on the surface, rugby ball shapes, and many other shapes, and are not particularly limited.

[0024] (Average primary particle size) The size of the anion-modified silica is not particularly limited. For example, the average primary particle diameter of the abrasive grains may be 5 nm or more, 10 nm or more, or 15 nm or more. If the average primary particle diameter of the anion-modified silica is 5 nm or more, the polishing speed of the object to be polished with the polishing composition will improve. Also, the average primary particle diameter of the anion-modified silica may be 200 nm or less, 150 nm or less, or 100 nm or less. If the average primary particle diameter of the anion-modified silica is 200 nm or less, it becomes easier to obtain a surface with fewer defects by polishing with the polishing composition. The average primary particle diameter of the anion-modified silica can be calculated, for example, based on the specific surface area (SA) of the anion-modified silica calculated from the BET method, assuming that the shape of the anion-modified silica is a perfect sphere.

[0025] (Average secondary particle size) The average secondary particle diameter of anion-modified silica is not particularly limited. For example, the average secondary particle diameter of anion-modified silica may be 20 nm or more, 30 nm or more, or 40 nm or more. If the average secondary particle diameter of anion-modified silica is 20 nm or more, the resistance during polishing will be reduced, enabling stable polishing. Alternatively, the average secondary particle diameter of anion-modified silica may be 300 nm or less, 200 nm or less, or 100 nm or less. If the average secondary particle diameter of anion-modified silica is 200 nm or less, the surface area per unit mass of anion-modified silica will be increased, improving the frequency of contact with the workpiece and further improving the polishing speed. The average secondary particle diameter of anion-modified silica can be measured by dynamic light scattering methods, such as laser diffraction scattering.

[0026] (Concentration of anion-modified silica) Furthermore, the concentration of anion-modified silica in the polishing composition according to this embodiment is not particularly limited, but the lower limit of the concentration of anion-modified silica may be 0.1% by mass or more, 3% by mass or more, or 5% by mass or more. If the concentration of anion-modified silica is 0.1% by mass or more, a high polishing speed can be obtained. The upper limit of the concentration of anion-modified silica may be 15% by mass or less, 12% by mass or less, or 10% by mass or less. If the concentration of anion-modified silica is 15% by mass or less, not only can the cost of the polishing composition be reduced, but surface defects are less likely to occur on the surface of the object to be polished after polishing with the polishing composition.

[0027] (Polishing speed enhancer) An abrasive composition according to one aspect of the present invention includes a polishing speed enhancer. The polishing speed enhancer is a salt of a typical metal, which is a metal belonging to Group 1, 2, 13, 14, or 15 of the periodic table. The polishing speed enhancer can improve the polishing speed compared to an abrasive composition without the polishing speed enhancer. Examples of typical metals include lithium (Li), beryllium (Be), sodium (Na), magnesium (Mg), aluminum (Al), potassium (K), calcium (Ca), and gallium (Ga). Among these, it is preferable that the typical metal is at least one selected from the group consisting of sodium, magnesium, and aluminum. Examples of salts include nitrates, hydrochlorides, sulfates, and phosphates. Among these, it is preferable that it be one of nitrates, sulfates, and phosphates, and more preferably a nitrate. The salt of the typical metal may be at least one selected from the group consisting of sodium nitrate (NaNO3), magnesium nitrate (Mg(NO3)2), aluminum nitrate (Al(NO3)3), aluminum chloride (AlCl3), lithium nitrate (LiNO3), potassium nitrate (KNO3), and calcium nitrate (Ca(NO3)2).

[0028] The concentration of the polishing speed enhancer in the polishing composition according to this embodiment is not particularly limited, but the lower limit of the concentration of the polishing speed enhancer may be 5 mmol / L (hereinafter, "mol / L" will be written as "M") or higher, and may be 8 mM or higher. If the concentration of the polishing speed enhancer is 5 mM or higher, the oxidation of tungsten can be further promoted. The upper limit of the concentration of the polishing speed enhancer may be 20 mM or lower, and may be 15 mM or lower. If the concentration of the polishing speed enhancer is 20 mM or lower, the corrosion of tungsten can be further suppressed.

[0029] (Oxidizing agent) The polishing composition in one aspect of the present invention contains an oxidizing agent, which is a peroxide. The oxidizing agent oxidizes the surface of the tungsten-containing layer, making the tungsten easier to remove mechanically. The type of peroxide is not particularly limited. Examples of peroxides include hydrogen peroxide (H2O2), peracetic acid (C2H4O3), percarbonate, urea peroxide (CH6N2O3), perchloric acid (HClO4), sodium persulfate (Na2S2O8), and potassium persulfate (K2S2O8). These peroxides may be used individually or in combination of two or more. Among these, hydrogen peroxide is preferred because it can efficiently oxidize tungsten.

[0030] The concentration of the oxidizing agent in the polishing composition is not particularly limited, but the lower limit of the oxidizing agent concentration may be 0.01% by mass or more, 0.1% by mass or more, or 1% by mass or more. If the concentration of the oxidizing agent is 0.01% by mass or more, the polishing speed of the polishing composition tends to improve. Furthermore, the upper limit of the concentration of the oxidizing agent in the polishing composition may be 10% by mass or less, 8% by mass or less, or 6% by mass or less. If the concentration of the oxidizing agent is 10% by mass or less, not only can the material cost of the polishing composition be reduced, but the burden of processing the polishing composition after polishing, i.e., waste liquid treatment, can also be reduced. In addition, excessive oxidation of tungsten on the surface of the object to be polished is less likely to occur, so the surface roughness of the tungsten after polishing tends to be reduced.

[0031] Furthermore, since an oxide film is formed on the surface of the tungsten-containing layer by the oxidizing agent, it is preferable to first prepare a preliminary composition by stirring and mixing the components other than the oxidizing agent, and then add the oxidizing agent to the preliminary composition immediately before polishing.

[0032] (Liquid medium) The polishing composition according to this embodiment may contain a liquid medium. This medium functions as a dispersion medium or solvent for dispersing or dissolving each component of the polishing composition (polishing speed enhancer, oxidizing agent, anion-modified silica, etc.). Examples of liquid media include water and organic solvents. One or more may be used alone or mixed together, but it is preferable that the medium contains water. However, from the viewpoint of preventing the inhibition of the action of each component, it is preferable to use water that contains as few impurities as possible. Specifically, pure water, ultrapure water, or distilled water obtained by removing impurity ions with an ion exchange resin and then removing foreign matter by passing it through a filter is preferred.

[0033] (pH of the abrasive composition) The pH of the polishing composition according to this embodiment may be 5 or less. If the pH is 5 or less, the anion-modified silica will be dispersed, allowing for high-speed polishing of the object to be polished. Alternatively, the pH of the polishing composition may be 1 or higher, or 1.5 or higher. The pH of the polishing composition may also be 3 or lower, or 2.5 or lower. The pH of the polishing composition can be measured by the method described in the examples.

[0034] The polishing composition according to this embodiment may contain a pH adjusting agent to adjust the pH to the above-mentioned range. The pH adjusting agent may be an acid, a base, or both, or an inorganic compound, an organic compound, or both.

[0035] Examples of acids used as pH adjusters include inorganic acids and organic acids. Examples of inorganic acids include sulfuric acid (H2SO4), nitric acid (HNO3), boric acid (B(OH)3), carbonic acid (H2CO3), hypophosphorous acid (H3PO2), phosphorous acid (H3PO3), and phosphoric acid (H3PO4). It is preferable to use inorganic acids as pH adjusters, with nitric acid being particularly preferred. Organic acids include carboxylic acids and organic sulfuric acids. Examples of carboxylic acids include formic acid, acetic acid, propionic acid, butyric acid, valeric acid, 2-methylbutyric acid, n-hexanoic acid, 3,3-dimethylbutyric acid, 2-ethylbutyric acid, 4-methylpentanoic acid, n-heptanoic acid, 2-methylhexanoic acid, n-octanoic acid, 2-ethylhexanoic acid, benzoic acid, glycolic acid, salicylic acid, glyceric acid, oxalic acid, malonic acid, succinic acid, glutaric acid, adipic acid, pimelic acid, maleic acid, phthalic acid, malic acid, tartaric acid, citric acid, and lactic acid. Furthermore, examples of organic sulfuric acids include methanesulfonic acid, ethanesulfonic acid, and isethionic acid. These acids may be used individually or in combination of two or more.

[0036] Examples of bases used as pH adjusters include alkali metal hydroxides or their salts, alkaline earth metal hydroxides or their salts, quaternary ammonium hydroxides or their salts, ammonia, and amines. Examples of alkali metals include potassium and sodium. Examples of alkaline earth metals include calcium and strontium. Examples of salts include carbonates, bicarbonates, sulfates, and acetates. Examples of quaternary ammonium include tetramethylammonium, tetraethylammonium, and tetrabutylammonium.

[0037] Examples of quaternary ammonium hydroxide compounds include quaternary ammonium hydroxide or its salts, such as tetramethylammonium hydroxide, tetraethylammonium hydroxide, and tetrabutylammonium hydroxide. Examples of amines include methylamine, dimethylamine, trimethylamine, ethylamine, diethylamine, triethylamine, ethylenediamine, monoethanolamine, N-(β-aminoethyl)ethanolamine, hexamethylenediamine, diethylenetriamine, triethylenetetramine, anhydrous piperazine, piperazine hexahydrate, 1-(2-aminoethyl)piperazine, N-methylpiperazine, and guanidine. These bases may be used individually or in combination of two or more.

[0038] (Other additives) An abrasive composition according to one aspect of the present invention may further contain known additives such as chelating agents, thickeners, dispersants, surface protectants, wetting agents, and solubilizers, to the extent that the effects of the present invention are not impaired. The content of the above additives may be appropriately set according to the purpose of their addition.

[0039] As described above, the polishing composition according to the present invention can be used to polish objects containing tungsten. By using the polishing composition according to the present invention, objects containing tungsten can be polished at high speed.

[0040] <Method for producing abrasive compositions> The method for producing the polishing composition according to one aspect of the present invention is not particularly limited. For example, first, a polishing speed enhancer, anion-modified silica, and other additives as needed are stirred and mixed in a liquid medium to prepare a preliminary composition. Then, immediately before polishing, an oxidizing agent is added to the obtained preliminary composition and stirred to obtain the polishing composition. The temperature when mixing each component is not particularly limited, but 10°C to 40°C is preferred, and heating may be used to increase the dissolution rate. The mixing time is also not particularly limited as long as uniform mixing is achieved.

[0041] <Object to be polished> Polishing using the polishing composition according to the embodiment of the present invention can improve the polishing speed of objects containing tungsten. For this reason, it is preferable that the object to be polished contains tungsten, but the type of object to be polished is not limited to tungsten. The object to be polished may be elemental silicon, silicon compounds, carbon, metals other than tungsten, materials containing nitrogen, etc. These may be used individually or in combination of two or more types.

[0042] Examples of elemental silicon include single-crystal silicon, polycrystalline silicon (polysilicon), and amorphous silicon. Examples of silicon compounds include silicon nitride (SiN), silicon oxide (SiO2), and silicon carbide (SiC). Silicon compound films include low dielectric constant films with a relative permittivity of 3 or less. Examples of metals include copper, aluminum, hafnium, cobalt, nickel, titanium, tantalum, gold, silver, platinum, palladium, rhodium, ruthenium, iridium, and osmium. These metals may be included in the form of alloys or metallic compounds. Furthermore, examples of nitrogen-containing materials include tantalum nitride (TaN) and titanium nitride (TiN).

[0043] <Polishing method> Another embodiment of the present invention involves polishing an object containing tungsten using the polishing composition according to the present invention.

[0044] The configuration of the polishing apparatus is not particularly limited, but for example, a general polishing apparatus can be used that includes a holder for holding a substrate or the like with the object to be polished, a drive unit such as a motor that can change the rotation speed, and a polishing platen to which a polishing pad (polishing cloth) can be attached. As for the polishing pad, general nonwoven fabrics, polyurethanes, porous fluororesins, etc. can be used without particular limitations. Polishing pads can be made with grooves that allow liquid polishing composition to accumulate.

[0045] There are no particular restrictions on the polishing conditions, but for example, the rotation speed of the polishing platen should be 10 rpm (0.17 s). -1 ) or more 500rpm(8.3s -1 Preferably, the pressure applied to the substrate having the object to be polished (polishing pressure) is preferably 0.5 psi (3.4 kPa) or more and 10 psi (68.9 kPa) or less. The method of supplying the polishing composition to the polishing pad is not particularly limited, and a method of continuously supplying it by a pump or the like is employed. There is no limit to the amount supplied, but it is preferable that the surface of the polishing pad is always covered with the polishing composition according to one aspect of the present invention. The polishing composition according to the embodiment of the present invention may be a one-component type or a multi-component type, including a two-component type. Furthermore, the polishing composition may be prepared by diluting the stock solution of the polishing composition with a diluent such as water, for example, 10 times or more.

[0046] After polishing is complete, the substrate is washed with running water, for example, and dried by removing any water droplets adhering to the substrate using a spin dryer or the like, thereby obtaining a substrate having a layer containing, for example, tungsten. Thus, the polishing composition according to the embodiment of the present invention can be used for the application of polishing substrates. By using the polishing composition according to the embodiment of the present invention to polish the surface of an object to be polished on a semiconductor substrate, the surface of the semiconductor substrate can be polished at a high polishing speed to produce a polished semiconductor substrate. Examples of semiconductor substrates include silicon wafers having layers containing metals such as tungsten, elemental silicon, and silicon compounds. [Examples]

[0047] Examples and comparative examples of the present invention will be described below, but the present invention is not limited to the examples shown below. While the examples shown below have technically preferred limitations for carrying out the present invention, these limitations are not essential requirements of the present invention. Furthermore, various modifications or improvements can be made to the examples below, and such modified or improved forms may also be included in the present invention.

[0048] <Preparation of polishing composition> (Example 1) A preliminary composition was prepared by stirring and mixing sulfonic acid-modified colloidal silica particles (average secondary particle size: 70 nm) as abrasive particles, sodium nitrate as a polishing speed enhancer, nitric acid (HNO3) as a pH adjuster, and water as a liquid medium. Then, immediately before polishing the tungsten-coated wafer described later, the above preliminary composition and 31% by mass hydrogen peroxide solution as an oxidizing agent were stirred and mixed to prepare the polishing composition of Example 1. The components were added so that the concentration of sulfonic acid-modified colloidal silica was 8% by mass, the concentration of sodium nitrate was 10 mM, and the effective concentration of hydrogen peroxide was 1.55% by mass, relative to the total amount of the polishing composition of Example 1. Nitric acid was added so that the pH of the polishing composition of Example 1 was 2.0. The pH of the polishing composition was confirmed using a pH meter (product name: LAQUA®, manufactured by Horiba, Ltd.).

[0049] (Comparative Example 1) The polishing composition for Comparative Example 1 was prepared in the same manner as in Example 1, except that a polishing speed enhancer was not added.

[0050] (Examples 2-4, Comparative Example 2) The polishing compositions for Examples 2-4 and Comparative Example 2 were prepared in the same manner as in Example 1, except that the type of polishing speed enhancer was changed as shown in Table 1.

[0051] (Comparative Example 3) The polishing composition for Comparative Example 3 was prepared in the same manner as for Comparative Example 1, except that silica (average secondary particle size 50 nm) cation-modified with 3-aminopropyltrimethoxysilane (APTES) was used as the abrasive grain, D-camphasulfonic acid was used as the pH adjuster, and the pH was adjusted to 3.0.

[0052] (Comparative Example 4) The polishing composition for Comparative Example 4 was prepared in the same manner as for Comparative Example 3, except that 10 mM aluminum nitrate nonahydrate was added as a polishing speed enhancer.

[0053] <Measuring Zeta Potential> The zeta potential of abrasive grains in the polishing compositions of Examples 1-4 and Comparative Examples 1-4 was measured using a Malvern Zeta sizer nano ZSP. Specifically, the polishing compositions were subjected to a zeta potential / grain size measurement system, and measurements were performed at a measurement temperature of 25°C using a flow cell with laser Doppler (electrophoretic light scattering measurement method). The obtained data was analyzed using Smoluchowski's equation to calculate the zeta potential. These results are shown in Table 1.

[0054] [Table 1]

[0055] <Polishing speed measurement> First, as objects to be polished, 300 mm silicon wafers with a 5000 Å thick tungsten film formed on the surface using the CVD method (tungsten-coated silicon wafers) and 300 mm silicon wafers with a 10000 Å thick TEOS film formed on the surface (TEOS-coated silicon wafers) were prepared. The TEOS film refers to an interlayer dielectric film of silicon dioxide formed from tetraethoxysilane (TEOS). Next, the tungsten-coated silicon wafers and TEOS-coated silicon wafers were polished using the polishing compositions of Examples 1-4 and Comparative Examples 1-4 under the following polishing conditions. • Polishing equipment: 300mm polishing machine (manufactured by Ebara Corporation, model number: F-REX300E) • Polishing pad: Polyurethane pad (manufactured by Nitta DuPont, IC1010) • Polishing pressure: 3 psi (1 psi = 6894.76 Pa) • Polishing platen rotation speed: 90 rpm • Carrier (head) rotation speed: 91 rpm • Supply of polishing composition: flow-through ·Polishing composition supply amount: 300mL / min • Polishing time: 60 seconds

[0056] For silicon wafers with a tungsten film, the film thickness before and after polishing was measured using a sheet resistor VR120_08SD (manufactured by Kokusai Electric Semiconductor Services Co., Ltd.), and for silicon wafers with a TEOS film, the film thickness before and after polishing was measured using an optical interferometry film thickness analyzer Lambda Ace RE-3500 (manufactured by SCREEN). The polishing speed was then calculated from the difference in film thickness and the polishing time. These results are shown in Table 1.

[0057] <Calculation of polishing speed improvement rate> Next, the polishing speed improvement rate using the polishing speed enhancer was calculated. Specifically, the polishing speed improvement rate when using anion-modified silica was calculated by dividing the polishing speed of the tungsten film in Examples 1-4 and Comparative Example 2 by the polishing speed of the tungsten film in Comparative Example 1. In addition, the polishing speed improvement rate when using cation-modified silica was calculated by dividing the polishing speed of the tungsten film in Comparative Example 4 by the polishing speed of the tungsten film in Comparative Example 3. These results are shown in Table 1.

[0058] <Rating> As shown in Table 1, the polishing speed for the tungsten film in Examples 1 to 4 was 750 Å / min or higher, and the polishing speed improvement rate was 1.2 or higher. In contrast, the polishing speed for Comparative Examples 1 to 4 was less than 750 Å / min, and the polishing speed improvement rates for Comparative Examples 2 and 4 were less than 1.2. From this, it was found that Examples 1 to 4 had a higher polishing speed for the tungsten film than Comparative Examples 1 to 4, and the polishing speed for the tungsten film was improved compared to Comparative Examples 2 and 4.

[0059] From the results of Examples 1-4 and Comparative Example 4, it was found that when anionically modified silica is used as the abrasive grain and sodium nitrate, magnesium nitrate, aluminum nitrate, or aluminum chloride is used as the polishing speed enhancer, the polishing speed of the tungsten film can be improved while maintaining the polishing speed of the TEOS film. This can be explained as follows.

[0060] Since the surface potential of the tungsten film is negative, it is thought that the metal cations in the polishing speed enhancer adsorb onto the tungsten film surface. This suppresses the electrostatic repulsion between the anion-modified silica and the tungsten surface, making it easier for the anion-modified silica to adhere to the tungsten surface, thus resulting in efficient polishing.

[0061] On the other hand, it was found that using cation-modified silica as an abrasive significantly reduced the polishing speed of the tungsten film. Since both the metal cations in the polishing speed enhancer and the cation-modified silica have positive surface potentials, they readily adsorb to the tungsten film surface, which has a negative surface potential. However, electrostatic repulsion occurs between the metal cations and the cation-modified silica. When metal cations adsorb to the tungsten film surface, the cation-modified silica repels them. As a result, it is presumed that the cation-modified silica becomes less able to adhere to the tungsten surface, leading to a significant decrease in the tungsten polishing speed.

[0062] From the results of Examples 1-3, it was found that the higher the valence of the cation in the polishing speed enhancer, the higher the polishing speed of the tungsten film. This is thought to be because, for the same period in the periodic table, cations with a higher valence carry a more positive charge. Among Examples 1-3, aluminum ions (Al 3+ ) has the most positive charge, followed by magnesium ions (Mg 2+ ), sodium ions (Na + The cations are positively charged in the order of (a, b, c, y, b, y

[0063] From the results of Example 1 and Comparative Example 2, it was found that the polishing rate of the tungsten film was improved when the cation contained in the polishing rate improver was a metal. The sodium ions (Na + ) in the polishing rate improver of Example 1 have a smaller surface area than the ammonium ions (NH4 + ) in the polishing rate improver of Comparative Example 2, so the ion surface becomes positively charged electrostatically. As described above, the potential of the tungsten surface is negative. Therefore, it is presumed that sodium ions are more likely to suppress electrostatic repulsion than ammonium ions, and thus the polishing rate for the tungsten film is improved.

[0064] From the results of Examples 3 and 4, it was found that when the salt of a typical metal contains nitrate ions, the polishing rate of the tungsten film is further improved. This is considered to be because the nitrate ions contained in the polishing rate improver facilitate the oxidation of the surface of the tungsten film, resulting in an improvement in the polishing rate for the tungsten film.

[0065] Also, for example, the present invention can have the following configurations. [1] A polishing rate improver that improves the polishing rate of the polishing object when polishing the polishing object, an oxidizing agent, and anion-modified silica, and the polishing rate improver is a salt of a typical metal that is a metal belonging to Group 1, Group 2, Group 13, Group 14, or Group 15 of the periodic table, the oxidizing agent is a peroxide, a polishing composition. [2] The polishing composition according to [1], wherein the anion-modified silica is sulfonic acid-modified colloidal silica. [3] The polishing composition according to [1] or [2], wherein the anion-modified silica has a zeta potential of -70 mV or more and -10 mV or less in the polishing composition. [4] The polishing composition according to any one of [1] to [3], wherein the typical metal is at least one selected from the group consisting of sodium, magnesium, and aluminum. [5] The polishing composition according to any one of [1] to [4], wherein the oxidizing agent is hydrogen peroxide. [6] The polishing composition according to any one of items [1] to [5], wherein the pH is 5 or less. [7] The polishing composition according to [6], wherein the pH is 3 or less. [8] An abrasive composition according to any one of [1] to [7], used for polishing an object containing tungsten. A polishing method comprising polishing an object to be polished containing tungsten using an abrasive composition described in any one of items [9] [1] to [8].

Claims

1. A polishing speed enhancer that improves the polishing speed of the object to be polished when the object to be polished is polished, Oxidizing agent, Anionically modified silica, The polishing speed enhancer is a salt of a typical metal belonging to Group 1, Group 2, Group 13, Group 14, or Group 15 of the periodic table. The oxidizing agent is a peroxide, wherein the polishing composition is an abrasive.

2. The polishing composition according to claim 1, wherein the anion-modified silica is sulfonic acid-modified colloidal silica.

3. The polishing composition according to claim 1 or claim 2, wherein the anion-modified silica has a zeta potential of -70 mV or more and -10 mV or less in the polishing composition.

4. The polishing composition according to claim 1 or claim 2, wherein the typical metal is at least one selected from the group consisting of sodium, magnesium, and aluminum.

5. The polishing composition according to claim 1 or claim 2, wherein the oxidizing agent is hydrogen peroxide.

6. The polishing composition according to claim 1 or claim 2, wherein the pH is 5 or less.

7. The polishing composition according to claim 6, wherein the pH is 3 or less.

8. The polishing composition according to claim 1 or claim 2, used for polishing an object containing tungsten.

9. A polishing method comprising polishing an object to be polished containing tungsten using the polishing composition described in claim 1 or claim 2.

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