Polishing composition, polishing method, and method for manufacturing semiconductor substrates

Abstract

To provide a polishing composition that enables high-speed polishing of a silicon nitride film while reducing the polishing rate for a polycrystalline silicon film.SOLUTION: A polishing composition contains abrasive grains and a polyalkylene oxide compound, and has a pH less than 7. The abrasive grains have a negative zeta potential in the polishing composition. The polyalkylene oxide compound is represented by formula (1).SELECTED DRAWING: None

Description

[Technical Field]

[0001] This invention relates to a polishing composition, a polishing method, and a method for manufacturing a semiconductor substrate. [Background technology]

[0002] In recent years, with the increasing use of multilayer wiring on semiconductor substrate surfaces, chemical mechanical polishing (CMP) technology, which involves polishing and planarizing semiconductor substrates, has been utilized during device manufacturing.

[0003] This CMP (Chemical Polishing) has been applied to various processes in semiconductor manufacturing, one example being its application to the gate formation process in transistor fabrication. During transistor fabrication, materials such as metals, silicon, silicon oxide, polycrystalline silicon, and silicon nitride are sometimes polished, and there is a demand to polish each material at high speed in order to improve productivity. For example, there is a demand to polish silicon nitride, which has poor chemical reactivity, at high speed. To meet such demands, for example, Patent Document 1 discloses that silicon nitride can be polished at a high polishing speed using a polishing composition containing colloidal silica with immobilized sulfonic acid and having a pH of 6 or less. [Prior art documents] [Patent Documents]

[0004] [Patent Document 1] Japanese Patent Publication No. 2012-040671 [Overview of the Initiative] [Problems that the invention aims to solve]

[0005] While investigating the application of CMP to various processes in semiconductor manufacturing, the inventors discovered that in some cases it is preferable from a manufacturing perspective to polish a silicon nitride film at high speed in the presence of a polycrystalline silicon film. On the other hand, they also discovered that in some cases it is preferable from a manufacturing perspective to keep the polishing speed of the polycrystalline silicon film as low as possible. However, there is currently no polishing composition that can polish the silicon nitride film at high speed while simultaneously suppressing the polishing speed of the polycrystalline silicon film.

[0006] Therefore, the present invention aims to provide a polishing composition that can polish silicon nitride films at high speed and suppress the polishing speed of polycrystalline silicon films. [Means for solving the problem]

[0007] To solve the above problems, the inventors have diligently conducted research. As a result, they have developed an abrasive composition comprising abrasive grains and a polyalkylene oxide compound, wherein the pH is less than 7, the abrasive grains having a negative zeta potential in the abrasive composition, and the polyalkylene oxide compound having the following formula (1):

[0008] [ka]

[0009] [In equation (1), R 1 and R 3 Each of these independently represents a hydrogen atom or an alkyl group having 1 to 20 carbon atoms; R 2 represents an alkylene group with 4 carbon atoms; n represents an alkylene oxy group (OR 2 This represents the average number of moles added, and is a number between 3 and 100. We have found that the above problems can be solved by an abrasive composition represented by [the formula shown], and have completed the present invention. [Effects of the Invention]

[0010] The present invention provides a polishing composition that can polish silicon nitride films at high speed and suppress the polishing speed of polycrystalline silicon films. Mode for Carrying Out the Invention

[0011] Modes for carrying out the present invention are described in detail below. The embodiments shown herein are exemplifications for embodying the technical idea of the present invention, and do not limit the present invention. Therefore, all other practicable embodiments, usage methods, operation techniques, and the like that can be conceived by those skilled in the art without departing from the gist of the present invention are included in the scope and gist of the present invention, and are also included in the scope of the invention described in the claims and the scope of equivalents thereof. The embodiments described in the present specification can be arbitrarily combined to form other embodiments. In addition, unless otherwise specified in the present specification, measurements of operations, physical properties, and the like are performed under the conditions of room temperature (20°C or higher and 25°C or lower) and a relative humidity of 40% RH or higher and 60% RH or lower.

[0012] The present invention provides a polishing composition comprising abrasive grains and a polyalkylene oxide compound, and having a pH of less than 7, wherein the abrasive grains have a negative zeta potential in the polishing composition, and the polyalkylene oxide compound has an oxyalkylene group having 4 carbon atoms as a repeating unit. Such a polishing composition can polish a silicon nitride film at a high rate and suppress the polishing rate of a polycrystalline silicon film. The present inventor estimates the mechanism by which such effects can be obtained by the present invention as follows. However, the following mechanism is merely a conjecture, and the scope of the present invention is not limited thereby.

[0013] In the present invention, the object to be polished preferably includes at least a silicon nitride film and a polycrystalline silicon film. According to the polishing composition of the present invention, among objects to be polished, an effect of polishing a silicon nitride film at high speed while suppressing the polishing rate of a polycrystalline silicon film can be obtained. In a polishing composition having a pH of less than 7, abrasive grains having a negative zeta potential are easily adsorbed to the silicon nitride film and the polycrystalline silicon film, thereby increasing the amount of abrasive grains present on the surfaces of the silicon nitride film and the polycrystalline silicon film during polishing. However, if the polishing rate of the polycrystalline silicon film is increased, the ratio of the polishing rate of the silicon nitride film to the polishing rate of the polycrystalline silicon film (polishing rate of silicon nitride film / polishing rate of polycrystalline silicon film) (hereinafter also referred to as "polishing selectivity of silicon nitride") will decrease. The present inventors have found that the polishing composition of the present invention, by containing a specific polyalkylene oxide compound in an environment with a pH of less than 7, can improve or maintain the polishing rate of a silicon nitride film while suppressing the polishing rate of a polycrystalline silicon film. That is, since the specific polyalkylene oxide compound is a hydrophobic compound, it is thought that it is easily adsorbed to the polycrystalline silicon film, which is a hydrophobic film, through hydrophobic interaction. It is considered that the specific polyalkylene oxide compound is adsorbed to the polycrystalline silicon film, reducing the contact between abrasive grains and the polycrystalline silicon film, thereby suppressing the polishing rate of the polycrystalline silicon film. On the other hand, the specific polyalkylene oxide compound is less likely to be adsorbed to the silicon nitride film because the silicon nitride film is a hydrophilic film. It is considered that this allows the polishing composition of the present invention to polish a silicon nitride film at high speed while suppressing the polishing rate of a polycrystalline silicon film.

[0014] As described above, the present inventors have found that in a polishing composition having a pH of less than 7, a polishing composition containing abrasive grains having a negative zeta potential and a specific polyalkylene oxide compound solves the problem of polishing a silicon nitride film at high speed while suppressing the polishing rate of a polycrystalline silicon film.

[0015] It should be noted that the above mechanism is based on speculation, and the present invention is not limited in any way to the above mechanism.

[0016] [Object to be polished] The object to be polished according to the present invention preferably contains a silicon nitride (Si3N4) film and a polycrystalline silicon (polysilicon) film. That is, a polishing composition according to a preferred embodiment of the present invention is used for polishing objects containing a silicon nitride film and a polycrystalline silicon film.

[0017] According to one embodiment of the present invention, the application of the object to be polished is not limited and includes semiconductor substrates, solar cell substrates, TFTs for liquid crystal displays (LCDs), etc. It is also suitable for test wafers, monitor wafers, transport check wafers, dummy wafers, etc.

[0018] The object to be polished according to the present invention may contain materials other than silicon nitride film and polycrystalline silicon film. Examples of other materials include silicon oxide and silicon carbonitride (Si x C y N z Examples include doped polycrystalline silicon, undoped amorphous silicon, metals, SiGe, etc.

[0019] Examples of silicon dioxide-containing films include, for example, TEOS (Tetraethyl Orthosilicate) type silicon dioxide films (hereinafter also simply referred to as "TEOS films") produced using tetraethyl orthosilicate as a precursor, HDP (High Density Plasma) films, USG (Undoped Silicate Glass) films, PSG (Phosphorus Silicate Glass) films, BPSG (Boron-Phospho Silicate Glass) films, and RTO (Rapid Thermal Oxidation) films.

[0020] Examples of metal-containing films include tungsten (W) films, titanium nitride (TiN) films, ruthenium (Ru) films, platinum (Pt) films, silver (Ag) films, gold (Au) films, hafnium (Hf) films, cobalt (Co) films, palladium (Pd), iridium (Ir), osmium (Os), nickel (Ni) films, copper (Cu) films, aluminum (Al) films, and tantalum (Ta) films.

[0021] Furthermore, the shape of the object to be polished is not particularly limited. In one embodiment of the present invention, the polishing composition can be preferably applied to polishing objects having flat surfaces, such as plates or polyhedrons.

[0022] [Abrasive grains] The polishing composition according to the present invention contains abrasive grains. The abrasive grains contained in the polishing composition according to the present invention have a negative zeta potential. When the pH is less than 7 and the zeta potential of the abrasive grains is 0 mV or positive, the polishing rate of the silicon nitride film is reduced, and as a result the polishing rate of the silicon nitride film is lower than that of the polycrystalline silicon film (the polishing selectivity ratio of silicon nitride is reduced). The abrasive grains are preferably anionic modified silica (silica having anionic groups), and more preferably anionic modified colloidal silica (colloidal silica having anionic groups). The abrasive grains may be used alone or in combination of two or more types. Furthermore, the abrasive grains may be commercially available or synthetic.

[0023] The polishing composition according to the present invention preferably contains anionically modified colloidal silica as abrasive particles. Anionically modified colloidal silica is colloidal silica whose surface is modified with anionic groups, and in the polishing composition, it has the effect of mechanically polishing the object to be polished.

[0024] Preferred anionically modified colloidal silica includes colloidal silica in which anionic groups such as carboxyl groups, sulfonic acid groups, phosphonic acid groups, and aluminic acid groups are immobilized on the surface. The method for producing such colloidal silica having anionic groups is not particularly limited, and one example is a method of reacting colloidal silica with a silane coupling agent having anionic groups at its terminals.

[0025] For example, if you want to immobilize sulfonic acid groups on colloidal silica, you can do so by the method described in “Sulfonic acid-functionalized silica through quantitative oxidation of thiol groups”, Chem.Commun. 246-247 (2003). Specifically, by coupling a silane coupling agent having a thiol group, such as 3-mercaptopropyltrimethoxysilane, to colloidal silica and then oxidizing the thiol group with hydrogen peroxide, you can obtain colloidal silica on which sulfonic acid groups are immobilized on the surface (sulfonic acid-modified colloidal silica).

[0026] If the goal is to immobilize a carboxyl group on colloidal silica, this can be done, for example, 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, by coupling a silane coupling agent containing a photoreactive 2-nitrobenzyl ester to colloidal silica and then irradiating it with light, colloidal silica with an immobilized carboxyl group on its surface (carboxylic acid-modified colloidal silica) can be obtained.

[0027] The lower limit of the zeta potential of the abrasive grains in the polishing composition is preferably -65mV or higher, more preferably -60mV or higher, even more preferably -55mV or higher, particularly preferably -50mV or higher, and most preferably -45mV or higher. The upper limit of the zeta potential of the abrasive grains in the polishing composition is preferably -5mV or lower, more preferably -10mV or lower, even more preferably -15mV or lower, particularly preferably -20mV or lower, and most preferably -25mV or lower. In other words, the zeta potential of the abrasive grains in the polishing composition is preferably -65mV or higher and -5mV or lower, more preferably -60mV or higher and -10mV or lower, even more preferably -55mV or higher and -15mV or lower, particularly preferably -50mV or higher and -20mV or lower, and most preferably -45mV or higher and -25mV or lower.

[0028] Abrasive grains with the zeta potential described above can polish silicon nitride films at a higher polishing rate, resulting in a higher polishing rate for silicon nitride films compared to polycrystalline silicon films (a higher polishing selectivity for silicon nitride).

[0029] The average primary particle diameter of the abrasive grains is preferably 1 nm or larger, more preferably 3 nm or larger, and even more preferably 5 nm or larger. As the average primary particle diameter of the abrasive grains increases, the polishing speed of the silicon nitride film improves. Furthermore, the average primary particle diameter of the abrasive grains is preferably 100 nm or smaller, more preferably 50 nm or smaller, and even more preferably 30 nm or smaller. As the average primary particle diameter of the abrasive grains decreases, the polishing speed of the silicon nitride film becomes higher than that of the polycrystalline silicon film (the polishing selectivity ratio of silicon nitride becomes higher).

[0030] In other words, the average primary particle diameter of the abrasive grains is preferably 1 nm or more and 100 nm or less, more preferably 3 nm or more and 50 nm or less, and even more preferably 5 nm or more and 30 nm or less. The average primary particle diameter of the abrasive grains can be calculated, for example, based on the specific surface area (SA) of the abrasive grains calculated by the BET method and the density of the abrasive grains.

[0031] Furthermore, the average secondary particle diameter of the abrasive grains is preferably 15 nm or more, more preferably 20 nm or more, and even more preferably 25 nm or more. As the average secondary particle diameter of the abrasive grains increases, the resistance during polishing decreases, enabling stable polishing of the silicon nitride film. Furthermore, the average secondary particle diameter of the abrasive grains is preferably 200 nm or less, more preferably 150 nm or less, and even more preferably 100 nm or less. As the average secondary particle diameter of the abrasive grains decreases, the surface area per unit mass of the abrasive grains increases, the frequency of contact with the object to be polished improves, and the polishing speed of the silicon nitride film improves further. That is, the average secondary particle diameter of the abrasive grains is preferably 15 nm or more and 200 nm or less, more preferably 20 nm or more and 150 nm or less, and even more preferably 25 nm or more and 100 nm or less. In one embodiment, the average secondary particle diameter of the abrasive grains is 20 nm or more and less than 70 nm. The average secondary particle size of the abrasive grains can be measured by dynamic light scattering methods, such as laser diffraction scattering, and specifically, the values ​​measured by the method described in the examples are used.

[0032] The ratio of the average secondary particle diameter to the average primary particle diameter of the abrasive grains (average secondary particle diameter / average primary particle diameter, hereinafter also referred to as "average degree of association") is preferably 1.2 or higher, more preferably 1.5 or higher, even more preferably 1.8 or higher, particularly preferably 2.0 or higher, and most preferably 2.2 or higher. As the average degree of association of the abrasive grains increases, the polishing speed of the polycrystalline silicon film improves further. Furthermore, the average degree of association of the abrasive grains is preferably 5.5 or lower, more preferably 5.0 or lower, even more preferably 4.5 or lower, particularly preferably 4.0 or lower, and most preferably 3.5 or lower. As the average degree of association of the abrasive grains decreases, the polishing speed of the silicon nitride film becomes higher than that of the polycrystalline silicon film (the polishing selectivity ratio of silicon nitride becomes higher). In other words, the average degree of abrasive grain aggregation is preferably 1.2 or more and 5.5 or less, more preferably 1.5 or more and 5.0 or less, even more preferably 1.8 or more and 4.5 or less, particularly preferably 2.0 or more and 4.0 or less, and most preferably 2.2 or more and 3.5 or less.

[0033] The average degree of aggregation of abrasive grains can be obtained by dividing the average secondary particle diameter of the abrasive grains by the average primary particle diameter.

[0034] The upper limit of the aspect ratio of abrasive grains in the polishing composition is not particularly limited, but it is preferably 3.5 or less, more preferably 3.0 or less, even more preferably 2.5 or less, particularly preferably 2.0 or less, and most preferably 1.5 or less. Within this range, defects on the surface of the object to be polished can be further reduced. The aspect ratio is the average of the values ​​obtained by taking the smallest rectangle that circumscribes the image of the abrasive grains using a scanning electron microscope and dividing the length of the longer side of that rectangle by the length of the shorter side of the same rectangle, and can be determined using general image analysis software. The lower limit of the aspect ratio of abrasive grains in the polishing composition is not particularly limited, but it is preferably 1.1 or more.

[0035] The shape of the abrasive grains is not particularly limited and may be spherical or non-spherical. Specific examples of non-spherical shapes include polygonal prisms such as triangular or square prisms, cylindrical shapes, cylindrical shapes with a bulge in the center, donut shapes with a hole in the center, plate shapes, so-called cocoon shapes with a constriction in the center, so-called aggregate spherical shapes where multiple particles are integrated, bead shapes where multiple particles are connected in a nearly straight line, so-called konpeito shapes with multiple protrusions on the surface, rugby ball shapes, needle shapes even thinner than rugby ball shapes, and many other shapes, and are not particularly limited.

[0036] The size of the abrasive grains (average primary particle diameter, average secondary particle diameter, aspect ratio, particle shape, etc.) can be appropriately controlled by selecting the manufacturing method for the abrasive grains.

[0037] In this specification, the zeta potential of the abrasive grains is the value obtained by the method described in the examples. The zeta potential of the abrasive grains can be adjusted by the amount of anionic groups present in the abrasive grains, the pH of the polishing composition, etc.

[0038] In the polishing composition according to the present invention, abrasive grains may be used alone or in a mixture of two or more types. Furthermore, commercially available abrasive grains may be used, or synthetic abrasive grains may be used.

[0039] The abrasive content (concentration) in the polishing composition is not particularly limited, but is preferably 0.1% by mass or more, more preferably 0.2% by mass or more, even more preferably 0.5% by mass or more, and particularly preferably more than 0.5% by mass, relative to the total mass of the polishing composition. Furthermore, the upper limit of the abrasive content (concentration) in the polishing composition is preferably 10% by mass or less, more preferably 5% by mass or less, even more preferably 4% by mass or less, and particularly preferably less than 4% by mass, relative to the total mass of the polishing composition. In other words, the abrasive content (concentration) in the polishing composition is preferably 0.1% by mass or more and 10% by mass or less, more preferably 0.2% by mass or more and 5% by mass or less, even more preferably 0.5% by mass or more and 4% by mass or less, and particularly preferably more than 0.5% by mass and less than 4% by mass, relative to the total mass of the polishing composition. In one embodiment, the abrasive content (concentration) in the polishing composition is 2% by mass or more and 10% by mass or less.

[0040] If the abrasive content is within this range, the polishing rate of the silicon nitride film will be higher than that of the polycrystalline silicon film (the polishing selectivity of silicon nitride will be higher). If the polishing composition contains two or more types of abrasives, the abrasive content refers to the total amount of these abrasives.

[0041] The polishing composition according to the present invention may further contain other abrasive particles other than anion-modified silica, provided that the abrasive particles have a negative zeta potential in the polishing composition, within a range that does not hinder the effects of the present invention. Such other abrasive particles may be inorganic particles, organic particles, or organic-inorganic composite particles. Specific examples of inorganic particles include, for example, unmodified silica, particles made of metal oxides such as alumina, ceria, and titania, silicon nitride particles, silicon carbide particles, and boron nitride particles. Specific examples of organic particles include, for example, polymethyl methacrylate (PMMA) particles.

[0042] [Polyalkylene oxide compounds] The polishing composition according to the present invention contains a polyalkylene oxide compound represented by the following formula (1).

[0043]

Chem.

[0044] In formula (1), R 1 and R 3 each independently represent a hydrogen atom or an alkyl group having 1 to 20 carbon atoms. The alkyl group having 1 to 20 carbon atoms may be a linear alkyl group, a branched alkyl group or a cyclic alkyl group having 1 to 20 carbon atoms, with a linear alkyl group having 1 to 20 carbon atoms being preferred.

[0045] Specific examples of the alkyl group having 1 to 20 carbon atoms include a methyl group, an ethyl group, a propyl group, an isopropyl group, an n-butyl group, an isobutyl group, a sec-butyl group, a tert-butyl group, a pentyl group, an isopentyl group, a neopentyl group, a 2-ethylhexyl group, a hexyl group, a heptyl group, an octyl group, a 3,7-dimethyloctyl group, a nonyl group, a decyl group, an undecyl group, a dodecyl group (lauryl group), a tridecyl group, a tetradecyl group, a pentadecyl group, a hexadecyl group, a heptadecyl group, an octadecyl group, and the like.

[0046] R 1 and R 3 from the viewpoint of the polishing rate of silicon nitride, it is preferred that at least one of them is a hydrogen atom, and it is more preferred that both are hydrogen atoms.

[0047] In formula (1), R 2represents a C4 alkylene group. Examples of C4 alkylene groups include n-butylene group (tetramethylene group, -CH2CH2CH2CH2- group), 1-methyltrimethylene group (-CH(CH3)CH2CH2- group), 2-methyltrimethylene group (-CH2CH(CH3)CH2- group), 1-ethylethylene group (-C(C2H5)CH2), 1,1-dimethylethylene group (-C(CH3)2CH2- group), ethylmethylmethylene group (-C(CH3)(C2H5)-), propylmethylene group (-C(C3H7)-), etc. Of these, n-butylene group (-CH2CH2CH2CH2- group) and 1-methyltrimethylene group (-CH(CH3)CH2CH2- group) are preferred. Compounds of formula (1) are, for example, R 2 If it is an n-butylene group, then "-(OR 2 ) n -" is a compound having a tetramethylene oxide chain, R 2 If it is a 1-methyltrimethylene group, then "-(OR 2 ) n It is a compound having a polybutylene oxide chain (poly-1-methyltrimethylene oxide chain).

[0048] In formula (1), n ​​is an alkylene oxy group (OR 2 This is the average number of moles added, and represents a number between 3 and 100. n is preferably between 3 and 60, more preferably between 5 and 50, even more preferably between 5 and 30, and particularly preferably between 5 and 25. If n is within the above range, the polishing rate of the silicon nitride film will be higher than that of the polycrystalline silicon film (the polishing selectivity ratio of silicon nitride will be higher).

[0049] The polyalkylene oxide compound represented by formula (1) preferably has a weight-average molecular weight (Mw) of 100 to 6000, more preferably 150 to 5000, even more preferably 200 to 4000, particularly preferably 250 to 3500, and most preferably 300 to less than 3000. In one embodiment, the weight-average molecular weight of the polyalkylene oxide compound is less than 3000. If the weight-average molecular weight of the polyalkylene oxide compound is within the above range, the polishing rate of the silicon nitride film will be higher than that of the polycrystalline silicon film (the polishing selectivity of silicon nitride will be higher). Here, the weight-average molecular weight of the polyalkylene oxide compound is measured by gel permeation chromatography (GPC) using polystyrene as a standard substance.

[0050] Specific examples of polyalkylene oxide compounds include polytetramethylene oxide and polybutylene oxide (poly-1-methyltrimethylene oxide). Of these, polytetramethylene oxide is preferred as the polyalkylene oxide compound from the viewpoint of silicon nitride polishing selectivity.

[0051] In the polishing composition according to the present invention, the polyalkylene oxide compound may be used alone or in a mixture of two or more. Furthermore, the polyalkylene oxide compound may be a commercially available product or a synthetic product.

[0052] The content (concentration) of the polyalkylene oxide compound in the polishing composition is not particularly limited, but is preferably 0.0001% by mass or more, more preferably 0.0005% by mass or more, even more preferably 0.001% by mass or more, particularly preferably 0.003% by mass or more, and most preferably 0.005% by mass or more, based on the total mass of the polishing composition. Furthermore, the upper limit of the content (concentration) of the polyalkylene oxide compound in the polishing composition is preferably 5% by mass or less, more preferably 1% by mass or less, even more preferably 0.5% by mass or less, particularly preferably 0.2% by mass or less, and most preferably 0.1% by mass or less, based on the total mass of the polishing composition. In other words, the content (concentration) of the polyalkylene oxide compound is preferably 0.0001% by mass or more and 5% by mass or less, more preferably 0.0005% by mass or more and 1% by mass or less, even more preferably 0.001% by mass or more and 0.5% by mass or less, particularly preferably 0.003% by mass or more and 0.2% by mass or less, and most preferably 0.005% by mass or more and 0.1% by mass or less, based on the total mass of the polishing composition.

[0053] If the polyalkylene oxide compound content (concentration) is within this range, the polishing rate of the silicon nitride film will be higher than that of the polycrystalline silicon film (the polishing selectivity of silicon nitride will be higher). If the polishing composition contains two or more polyalkylene oxide compounds, the content (concentration) of the polyalkylene oxide compounds refers to their total amount.

[0054] [pH and pH adjusters] The pH of the polishing composition according to the present invention is less than 7. When the pH of the polishing composition is 7 or higher, the polishing rate of the polycrystalline silicon film increases and the polishing selectivity ratio of silicon nitride decreases. In one embodiment, the pH of the polishing composition is greater than 1. Therefore, in one embodiment, the pH of the polishing composition is greater than 1 and less than 7. Also, the pH of the polishing composition is preferably 1.5 or higher, more preferably 2.0 or higher, even more preferably 2.5 or higher, particularly preferably 3.0 or higher, and most preferably 3.5 or higher. The pH of the polishing composition is preferably 6.5 or lower, more preferably 6.0 or lower, even more preferably 5.5 or lower, particularly preferably 5.0 or lower, and most preferably 4.5 or lower. That is, the pH of the polishing composition is preferably 1.5 or higher and 6.5 or lower, more preferably 2.0 or higher and 6.0 or lower, even more preferably 2.5 or higher and 5.5 or lower, particularly preferably 3.0 or higher and 5.0 or lower, and most preferably 3.5 or higher and 4.5 or lower. In one embodiment, the pH of the polishing composition is between 2 and 5. When the pH of the polishing composition is within this range, the polishing rate of the polycrystalline silicon film becomes higher than that of the silicon nitride film or silicon oxide film (the polishing selectivity of silicon nitride becomes higher).

[0055] The polishing composition of the present invention may contain a pH adjusting agent to adjust the pH to less than 7. Examples of pH adjusting agents include inorganic acids, organic acids, alkalis, etc. These may be used individually or in combination of two or more.

[0056] Specific examples of inorganic acids that can be used as pH adjusters include hydrochloric acid, sulfuric acid, nitric acid, hydrofluoric acid, boric acid, carbonic acid, hypophosphorous acid, phosphorous acid, and phosphoric acid. Of these, hydrochloric acid, sulfuric acid, nitric acid, or phosphoric acid are preferred, with nitric acid being more preferred. By using nitric acid as a pH adjuster, the polishing selectivity for silicon nitride films can be improved, and the polishing rate for silicon nitride films can be suitably increased.

[0057] Specific examples of organic acids that can be used as pH adjusters include, for example, 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, lactic acid, diglycolic acid, 2-furanic acid, 2,5-franic acid, 3-furanic acid, 2-tetrahydrofuranic acid, methoxyacetic acid, methoxyphenylacetic acid, phenoxyacetic acid, methanesulfonic acid, ethanesulfonic acid, 10-camphorsulfonic acid, and isethionic acid.

[0058] Alkali metal salts of inorganic or organic acids may be used as pH adjusters, either in place of or in combination with inorganic or organic acids. In combinations of weak acids and strong bases, strong acids and weak bases, or weak acids and weak bases, a pH buffering effect can be expected.

[0059] Specific examples of alkalis that can be used as pH adjusters include, for example, ammonia, hydroxides of Group 1 elements (e.g., sodium hydroxide, potassium hydroxide), hydroxides of Group 2 elements (e.g., barium hydroxide), quaternary ammonium hydroxides (e.g., tetramethylammonium hydroxide) or their salts. Examples of salts include carbonates, bicarbonates, sulfates, and acetates.

[0060] In one embodiment, the polishing composition according to the present invention further contains one or more pH adjusting agents selected from organic acids and inorganic acids. That is, in one embodiment, the polishing composition according to the present invention further contains an organic acid or an inorganic acid as a pH adjusting agent. By including an organic acid or an inorganic acid as a pH adjusting agent, the polishing selectivity for silicon nitride films can be improved, and the polishing rate for silicon nitride films can be suitably improved.

[0061] The content of the pH adjusting agent can be selected by appropriately adjusting it within the range that achieves the effects of the present invention. The pH of the polishing composition can be measured, for example, with a pH meter (e.g., a pH meter manufactured by Horiba, Ltd. (model number: LAQUA)).

[0062] [Dispersion medium] The polishing composition according to the present invention preferably contains a dispersion medium for dispersing each component. Examples of dispersion media include water; alcohols such as methanol, ethanol, and ethylene glycol; ketones such as acetone; and mixtures thereof. Of these, water is preferred as the dispersion medium. That is, according to a preferred embodiment of the present invention, the dispersion medium contains water. According to a more preferred embodiment of the present invention, the dispersion medium consists substantially of water. The term "substantially" above means that a dispersion medium other than water may be included insofar as the effects of the present invention can be achieved. More specifically, the dispersion medium preferably consists of 90% to 100% by mass of water and 0% to 10% by mass of a dispersion medium other than water, and more preferably consists of 99% to 100% by mass of water and 0% to 1% by mass of a dispersion medium other than water. Most preferably, the dispersion medium is water.

[0063] From the viewpoint of not inhibiting the action of the components contained in the polishing composition, the dispersion medium should preferably be 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 through a filter is more preferable.

[0064] [Other ingredients] The polishing composition according to the present invention may further contain known additives that can be used in polishing compositions, such as complexing agents, preservatives, fungicides, oxidizing agents, surfactants other than polyalkylene oxide compounds represented by formula (1), water-soluble polymers other than polyalkylene oxide compounds represented by formula (1), and solubilizers, to the extent that they do not impair the effects of the present invention. The polishing composition according to the present invention has a pH of less than 7. For this reason, it is more preferable that the polishing composition contains a fungicide. That is, in one embodiment of the present invention, the polishing composition is substantially composed of abrasive grains, a polyalkylene oxide compound and a dispersion medium, and at least one selected from the group consisting of pH adjusters, solubilizers and fungicides. Here, "the polishing composition is substantially composed of abrasive grains, a polyalkylene oxide compound, a dispersion medium, and at least one selected from the group consisting of pH adjusters, solubilizers, and antifungal agents" means that the total content of abrasive grains, polyalkylene oxide compound, dispersion medium, pH adjuster, solubilizer, and antifungal agent exceeds 99% by mass (upper limit: 100% by mass) relative to the polishing composition. Preferably, the polishing composition is composed of at least one selected from the group consisting of abrasive grains, a polyalkylene oxide compound, a dispersion medium, a pH adjuster, a solubilizer, and antifungal agents (total content = 100% by mass).

[0065] The antifungal agent (preservative) is not particularly limited and can be appropriately selected according to the desired use and purpose. Specifically, examples include isothiazoline preservatives such as 1,2-benzoisothiazole-3(2H)-one (BIT), 2-methyl-4-isothiazolin-3-one, and 5-chloro-2-methyl-4-isothiazolin-3-one, as well as phenoxyethanol.

[0066] A solubilizer is a substance that is added to dissolve a water-soluble polymer in a dispersion medium (solvent) to improve the solubility of the water-soluble polymer. The polishing composition according to one embodiment of the present invention may further contain a solubilizer.

[0067] Examples of solubilizers include alcohol compounds such as methanol, ethanol, 1-propanol, 2-propanol, ethylene glycol, and propylene glycol; ether compounds such as diethylene glycol diethyl ether, 2-methoxyethanol, 2-ethoxyethanol, diethylene glycol, diethylene glycol monomethyl ether, diethylene glycol monoethyl ether, diethylene glycol monobutyl ether, triethylene glycol, triethylene glycol monomethyl ether, tetraethylene glycol, dipropylene glycol, dipropylene glycol monomethyl ether, dipropylene glycol monoethyl ether, tripropylene glycol monomethyl ether, diacetone alcohol, 2-methoxyethyl acetate, 2-ethoxyethyl acetate, and diethylene glycol monoethyl ether acetate; and ketone compounds such as acetone, methyl ethyl ketone, acetylacetone, and cyclohexanone. These solubilizers can be used individually or in combination of two or more.

[0068] [Polishing method and method for manufacturing semiconductor substrates] The polishing composition according to the present invention is suitably used for polishing objects containing, for example, silicon nitride and polycrystalline silicon. Therefore, the present invention provides a polishing method comprising polishing an object containing silicon nitride and polycrystalline silicon using the polishing composition according to the present invention. The present invention also provides a method for manufacturing a semiconductor substrate comprising polishing a semiconductor substrate containing silicon nitride and polycrystalline silicon using the polishing composition according to the present invention. Furthermore, the present invention provides a method for manufacturing a semiconductor substrate comprising the step of polishing a semiconductor substrate containing silicon nitride and polycrystalline silicon by the polishing method according to the present invention.

[0069] As a polishing device, a general polishing device can be used that has a holder for holding a substrate or the like with the object to be polished, a motor with adjustable rotation speed, and a polishing platen to which a polishing pad (abrasive cloth) can be attached.

[0070] As the polishing pad, general nonwoven fabrics, polyurethanes, and porous fluororesins can be used without any particular restrictions. Preferably, the polishing pad has grooves that allow the polishing liquid to accumulate.

[0071] Regarding the polishing conditions, for example, the rotational speed of the polishing platen and carrier should be 10 rpm (0.17 s). -1 ) or more 500rpm (8.33s -1 ) is preferred. 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).

[0072] The method of supplying the polishing composition to the polishing pad is not particularly limited; for example, a method of continuous supply using a pump or the like can be 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 the present invention.

[0073] After polishing is complete, the substrate is washed with running water, and any water droplets adhering to the substrate are removed using a spin dryer or the like to dry it, thereby obtaining a substrate having a layer containing metal.

[0074] The polishing composition according to the present invention may be a one-component type or a multi-component type, including a two-component type. Furthermore, the polishing composition according to the present invention may be prepared by diluting the stock solution of the polishing composition with a diluent such as water to, for example, three times or more (or, for example, five times or more).

[0075] [Polishing speed inhibitor] The polishing composition according to the present invention selectively polishes silicon nitride and suppresses the polishing of polycrystalline silicon when polishing a semiconductor substrate containing silicon nitride and polycrystalline silicon. Therefore, according to the present invention, the following formula (1):

[0076] [ka]

[0077] [In equation (1), R 1 and R 3 Each of these independently represents a hydrogen atom or an alkyl group having 1 to 20 carbon atoms; R 2 represents an alkylene group with 4 carbon atoms; n represents an alkylene oxy group (OR 2 This represents the average number of moles added, and is a number between 3 and 100. A polishing rate inhibitor for polycrystalline silicon films is provided, comprising a polyalkylene oxide compound represented by [formula].

[0078] [Polishing speed] When polishing with the polishing composition according to the present invention, the polishing speed of the silicon nitride film is preferably 150 Å / min to 5000 Å / min, more preferably 200 Å / min to 2500 Å / min, even more preferably 220 Å / min to 2000 Å / min, and particularly preferably 250 Å / min to 1500 Å / min. When polishing with the polishing composition according to the present invention, the polishing speed of the polycrystalline silicon film is preferably 100 Å / min or less, more preferably 50 Å / min or less, even more preferably 45 Å / min or less, and particularly preferably 40 Å / min or less. There is no particular lower limit to the polishing speed of the silicon nitride film and / or silicon oxide film, but in practice it is 5 Å / min or more.

[0079] [Polishing selectivity ratio] When the polishing composition according to the present invention is used to polish an object containing silicon nitride and polycrystalline silicon, the ratio of the polishing rate of silicon nitride to the polishing rate of polycrystalline silicon (polishing rate of silicon nitride / polishing rate of polycrystalline silicon) is preferably 10 or more, more preferably 12 or more, even more preferably 15 or more, particularly preferably 20 or more, and most preferably 30 or more.

[0080] While embodiments of the present invention have been described in detail, these are descriptive and illustrative, and not limiting, and it is clear that the scope of the present invention should be interpreted by the appended claims.

[0081] The present invention encompasses the following embodiments and forms.

[0082] [1] An abrasive composition comprising abrasive grains and a polyalkylene oxide compound, wherein the pH is less than 7, the abrasive grains having a negative zeta potential in the abrasive composition, and the polyalkylene oxide compound having the following formula (1):

[0083] [ka]

[0084] [In equation (1), R 1 and R 3 Each of these independently represents a hydrogen atom or an alkyl group having 1 to 20 carbon atoms; R 2 represents an alkylene group with 4 carbon atoms; n represents an alkylene oxy group (OR 2 This represents the average number of moles added, and is a number between 3 and 100. An abrasive composition represented by [formula].

[0085] [2] The polishing composition according to [1] above, wherein the polyalkylene oxide compound is polytetramethylene oxide.

[0086] [3] The polishing composition according to [1] or [2] above, wherein the weight-average molecular weight of the polyalkylene oxide is less than 3000.

[0087] [4] The abrasive composition according to any one of [1] to [3] above, wherein the abrasive grains are contained in an amount of 2% by mass or more and 10% by mass or less.

[0088] [5] The polishing composition according to any one of [1] to [4] above, wherein the average secondary particle diameter of the abrasive grains is 20 nm or more and less than 70 nm.

[0089] [6] The polishing composition according to any one of [1] to [5] above, wherein the abrasive grains are anionically modified colloidal silica.

[0090] [7] An abrasive composition according to any of [1] to [6] above, wherein the pH is 2 or more and 5 or less.

[0091] [8] The polishing composition according to any one of [1] to [7] above, further comprising an organic acid or an inorganic acid as a pH adjuster.

[0092] [9] A polishing composition according to any one of [1] to [8] above, used for polishing objects containing silicon nitride and polycrystalline silicon.

[0093]

[10] The polishing composition according to [9] above, wherein the ratio of the polishing rate of silicon nitride to the polishing rate of polycrystalline silicon (silicon nitride / polycrystalline silicon) is 20 or more.

[0094]

[11] A polishing method comprising the step of polishing an object to be polished containing silicon nitride and polycrystalline silicon using any of the polishing compositions described in [1] to

[10] above. [Examples]

[0095] The present invention will be described in more detail using the following examples and comparative examples. However, the technical scope of the present invention is not limited to the following examples. Unless otherwise specified, "%" and "parts" mean "mass%" and "parts by mass," respectively.

[0096] <Average primary particle size of abrasive grains> The average primary particle size of the abrasive grains was calculated from the specific surface area of ​​silica particles measured by the BET method using a "Flow Sorb II 2300" manufactured by Micromerities, and the density of the abrasive grains.

[0097] <Average secondary particle size of abrasive grains> The average secondary particle diameter of the abrasive grains was measured as the volume-average particle diameter (volume-based arithmetic mean diameter; Mv) using a dynamic light scattering particle size and particle size distribution analyzer UPA-UTI151 (manufactured by Nikkiso Co., Ltd.).

[0098] <Average degree of aggregation of abrasive grains> The average degree of abrasive particle aggregation was calculated by dividing the average secondary particle diameter of the abrasive particles by the average primary particle diameter of the abrasive particles.

[0099] <Zeta potential of abrasive grains> The zeta potential of abrasive grains in the polishing composition was calculated by subjecting the polishing composition to a Malvern Panalytical Zetasizer Nano and measuring it using laser Doppler (electrophoretic light scattering measurement) at a measurement temperature of 25°C. The obtained data was then analyzed using the Smoluchowski equation.

[0100] <pH of the abrasive composition> The pH of the polishing composition was determined using a glass electrode type hydrogen ion concentration indicator (Horiba, Ltd., Model: F-23). ​​After three-point calibration using standard buffers (phthalate pH buffer pH: 4.01 (25°C), neutral phosphate pH buffer pH: 6.86 (25°C), carbonate pH buffer pH: 10.01 (25°C)), the glass electrode was placed in the polishing composition, and the pH value after stabilization for at least two minutes was taken as the pH value.

[0101] <Electrical conductivity of abrasive compositions> The electrical conductivity (EC) of the polishing composition was measured using a benchtop electrical conductivity meter (manufactured by Horiba, Ltd., model number: DS-71 LAQUA®).

[0102] [Preparation of abrasive grains] As anionically modified colloidal silica, anionically modified colloidal silica grains 1-3 were prepared using the method described in “Sulfonic acid-functionalized silica through quantitative oxidation of thiol groups”, Chem. Commun. 246-247 (2003). Two types of colloidal silica (abrasive grains) were used for sulfonic acid modification (abrasive grain 1 and abrasive grain 2). Abrasive grains 3 and 4 below are the same abrasive grain as abrasive grain 1, differing only in the silane coupling agent concentration (MPS modification amount) relative to the total mass of silica solids: 0.24% by mass, 0.6% by mass, and 0.96% by mass).

[0103] • Abrasive grain 1: (MPS modification amount 0.6 mass%) Average primary particle diameter: 14 nm, Average secondary particle diameter: 14 nm, Average degree of association: 2.4 • Abrasive grain 2: (MPS modification amount 0.6 mass%) Average primary particle diameter: 35 nm, Average secondary particle diameter: 70 nm, Average degree of aggregation: 2.0 • Abrasive grain 3: (MPS modification amount 0.24 mass%) Average primary particle diameter: 14 nm, Average secondary particle diameter: 14 nm, Average degree of association: 2.4 • Abrasive grain 4: (MPS modification amount 0.96 mass%) Average primary particle diameter: 14 nm, Average secondary particle diameter: 14 nm, Average degree of association: 2.4 [Preparation of abrasive compositions] (Example 1) The abrasive grains 1 (anionically modified colloidal silica) obtained above were added to pure water, which was used as the dispersion medium, at room temperature (25°C) to a final concentration of 3% by mass. Furthermore, 2-methyl-4-isothiazolin-3-one (manufactured by THE DOW CHEMICAL COMPANY) was added as an antifungal agent to obtain a mixture to a final concentration of 0.014 mM.

[0104] Subsequently, polytetramethylene oxide (weight-average molecular weight: 1000, manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.) was added as a polyalkylene oxide compound to a final concentration of 0.01% by mass, and nitric acid (HNO3) was added as a pH adjuster to a pH of 4. The mixture was stirred and mixed at room temperature (25°C) for 30 minutes to prepare the polishing composition of Example 1. The pH of the obtained polishing composition was measured to be 4, and the electrical conductivity was 1 mS / cm.

[0105] The zeta potential of abrasive grain 1 (anionically modified colloidal silica) in the obtained polishing composition was measured according to the method described above and was found to be -40 mV. Furthermore, the particle size of abrasive grain 1 (anionically modified colloidal silica) in the polishing composition was similar to that of the abrasive grain 1 (anionically modified colloidal silica) used.

[0106] (Examples 2-10, Comparative Examples 1-4) The polishing compositions for Examples 2-10 and Comparative Examples 1-4 were prepared in the same manner as in Example 1, except that the types and concentrations of each component, as well as the pH, were changed as shown in Table 1 below. The composition of each polishing composition is shown in Table 1 below. Abrasive grain 1 was used in Examples 3, 6, 7, 9, 10 and Comparative Examples 1-4; abrasive grain 2 in Example 2; abrasive grain 3 in Example 4; and abrasive grain 4 in Examples 5 and 8. In Comparative Examples 2 and 3, polyethylene glycol (PEG) was used as the polyalkylene oxide compound (indicated as "PEG200" and "PEG4000" in Table 1). "-" in Table 1 below indicates that the agent was not used. The pH of each polishing composition and the particle size of the abrasive grains in each polishing composition were measured and obtained the values ​​shown in Table 1.

[0107] [evaluation] <Evaluation of polishing speed of polishing compositions> The surface of each object to be polished was polished using each polishing composition under the following conditions. The following (1) and (2) were prepared as objects to be polished.

[0108] (1) Silicon nitride film (Si3N4 film): A silicon wafer (200 mm, blanket wafer) with a silicon nitride film with a thickness of 2000 Å formed on its surface. (2) Polycrystalline silicon film (poly-Si film): A silicon wafer on which a polycrystalline silicon film with a thickness of 5000 Å is formed on the surface.

[0109] (Polishing equipment and polishing conditions) Polishing equipment: Applied Materials Mirra 200mm CMP single-sided polishing machine Polishing pad: Nitta Haas Co., Ltd. Hard polyurethane pad IC1010 Polishing pressure: 4.0 psi (1 psi = 6894.76 Pa) Polishing plate rotation speed: 47 rpm Head (carrier) rotation speed: 43 rpm Supply of polishing composition: flow-through Polishing composition supply amount: 200mL / min Polishing time: 60 seconds.

[0110] (Calculation of polishing speed) For each object to be polished, the thickness before and after polishing was determined using an optical film thickness gauge (ASET-f5x: manufactured by KLA-Tencor Co., Ltd.). The film thickness was determined using an optical film thickness gauge (ASET-f5x: manufactured by KLA-Tencor Co., Ltd.).

[0111] For each object to be polished, the polishing rate was calculated by dividing the difference in film thickness before and after polishing [(thickness before polishing) - (thickness after polishing)] by the polishing time. For silicon nitride films, a polishing rate of 150 Å / min or higher is considered practical. Regarding the polishing rate ratio between silicon nitride films and polycrystalline silicon films, a ratio of the polishing rate of silicon nitride to the polishing rate of polycrystalline silicon (Si3N4 / poly-Si in Table 1) of 10 or more (preferably 20 or more) is considered practical.

[0112] The evaluation results are shown in Table 1. In Table 1, silicon nitride films are indicated by "Si3N4" and polycrystalline silicon films by "poly-Si".

[0113] [Table 1]

[0114] As is clear from Table 1 above, the polishing composition of the example can achieve a high polishing rate for the silicon nitride film and a low polishing rate for the polycrystalline silicon film, resulting in a high polishing rate ratio for the silicon nitride film. On the other hand, the polishing composition of the comparative example cannot achieve a high polishing rate ratio for the silicon nitride film due to factors such as a low polishing rate for the silicon nitride film or an excessively high polishing rate for the polycrystalline silicon film.

[0115] Therefore, it can be seen that the polishing composition according to the present invention can polish silicon nitride films at high speed and suppress the polishing speed of polycrystalline silicon films.

[0116] Table 1 above shows the results obtained by polishing objects with a silicon nitride film and objects with a polycrystalline silicon film separately. However, it is presumed that even when polishing objects with both silicon nitride and polycrystalline silicon, the same polishing speed and polishing selectivity ratio (polishing speed of silicon nitride / polishing speed of polycrystalline silicon) as shown in Table 1 above will be obtained.

Claims

1. An abrasive composition comprising abrasive grains and a polyalkylene oxide compound, having a pH of less than 7, The abrasive grains have a negative zeta potential in the polishing composition. The abrasive grains are contained in an amount of 2% by mass or more and 10% by mass or less. The polyalkylene oxide compound is given by the following formula (1): 【Chemistry 1】 [In equation (1), R １ and R ３ Each of these independently represents a hydrogen atom or an alkyl group having 1 to 20 carbon atoms; R ２ represents an alkylene group with 4 carbon atoms; n is an alkylene oxy group (O-R ２ This represents the average number of moles added, and is a number between 3 and 100. An abrasive composition represented by [formula].

2. An abrasive composition comprising abrasive grains and a polyalkylene oxide compound, wherein the pH is less than 7, The abrasive grains have a negative zeta potential in the polishing composition. The average secondary particle diameter of the abrasive grains is 20 nm or more and less than 70 nm. The polyalkylene oxide compound is given by the following formula (1): 【Chemistry 2】 [In formula (1), R1 and R3 each independently represent a hydrogen atom or an alkyl group having 1 to 20 carbon atoms; R2 represents an alkylene group having 4 carbon atoms; and n is the average number of added moles of alkylene oxy groups (O-R2), and is a number between 3 and 100.] An abrasive composition represented by [formula].

3. An abrasive composition comprising abrasive grains and a polyalkylene oxide compound, wherein the pH is less than 7, The abrasive grains have a negative zeta potential in the polishing composition. The polyalkylene oxide compound is given by the following formula (1): 【Transformation 3】 [In formula (1), R1 and R3 each independently represent a hydrogen atom or an alkyl group having 1 to 20 carbon atoms; R2 represents an alkylene group having 4 carbon atoms; and n is the average number of added moles of alkylene oxy groups (O-R2), and is a number between 3 and 100.] It is represented as, A polishing composition used for polishing objects containing silicon nitride and polycrystalline silicon.

4. The polishing composition according to any one of claims 1 to 3, wherein the polyalkylene oxide compound is polytetramethylene oxide.

5. The polishing composition according to any one of claims 1 to 3, wherein the weight-average molecular weight of the polyalkylene oxide compound is less than 3000.

6. The polishing composition according to claim 2 or 3, wherein the abrasive grains are contained in an amount of 2% by mass or more and 10% by mass or less.

7. The polishing composition according to claim 1 or 3, wherein the average secondary particle diameter of the abrasive grains is 20 nm or more and less than 70 nm.

8. The polishing composition according to any one of claims 1 to 3, wherein the abrasive grains are anionically modified colloidal silica.

9. The polishing composition according to any one of claims 1 to 3, wherein the pH is 2 or more and 5 or less.

10. The polishing composition according to any one of claims 1 to 3, further comprising an organic acid or an inorganic acid as a pH adjuster.

11. The polishing composition according to claim 1 or 2, used for polishing objects containing silicon nitride and polycrystalline silicon.

12. The polishing composition according to claim 11, wherein the ratio of the polishing rate of silicon nitride to the polishing rate of polycrystalline silicon (polishing rate of silicon nitride / polishing rate of polycrystalline silicon) is 20 or more.

13. The polishing composition according to claim 3, wherein the ratio of the polishing rate of silicon nitride to the polishing rate of polycrystalline silicon (polishing rate of silicon nitride / polishing rate of polycrystalline silicon) is 20 or more.

14. A polishing method comprising the step of polishing an object to be polished, which contains silicon nitride and polycrystalline silicon, using the polishing composition described in any one of claims 1 to 3.

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