Composition for polishing, polishing method, and method for manufacturing semiconductor substrate

Abstract

To provide a polishing composition that polishes a silicon nitride film at a high speed and has a sufficiently high ratio of the polishing rate of the silicon nitride film to the polishing rate of a silicon oxide film (that is, polishing selectivity of the silicon nitride film is high).SOLUTION: A polishing composition includes abrasive grains, a pH adjuster, and water, and the abrasive grains have a zeta potential of -25 mV or less, a degree of association of the abrasive grains of more than 3.5, and a pH of 6 or less.SELECTED DRAWING: None

Description

Technical Field

[0001] The present invention relates to a polishing composition, a polishing method, and a method for manufacturing a semiconductor substrate.

Background Art

[0002] In recent years, with the increasing integration and high performance of LSIs (Large Scale Integration), new microfabrication technologies have been developed. The chemical mechanical polishing (CMP) method is one of them and is a technology frequently used in LSI manufacturing processes, particularly in the planarization of interlayer insulating films, the formation of metal plugs, and the formation of embedded wiring (damascene wiring) in the multilayer wiring formation process.

[0003] The CMP has been applied to each process in semiconductor manufacturing. As one aspect, for example, its application to the gate formation process in transistor fabrication can be mentioned. When fabricating transistors, materials such as metals, silicon, silicon oxide, polycrystalline silicon, and silicon nitride films may be polished, and there is a demand to polish each material at high speed in order to improve productivity. To meet such a demand, for example, Patent Document 1 discloses a technique of including colloidal silica (sulfonic acid group (anion) - modified colloidal silica) in which an organic acid is immobilized as abrasive grains in a composition and setting the pH to 6 or less for the purpose of providing a polishing composition capable of polishing a polishing object with poor chemical reactivity such as silicon nitride at high speed.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] Certainly, when using the anionic modified colloidal silica described in Patent Document 1, the silicon nitride film can be polished at a high polishing rate.

[0006] The present inventors have found that in CMP in semiconductor manufacturing, while polishing the silicon nitride film at a high polishing rate, it may be preferable in manufacturing to keep the polishing rate of the silicon oxide film as low as possible.

[0007] Therefore, an object of the present invention is to provide a polishing composition that polishes a silicon nitride film at high speed and has a sufficiently high ratio of the polishing rate of the silicon nitride film to the polishing rate of the silicon oxide film (i.e., a high polishing selectivity for the silicon nitride film).

Means for Solving the Problems

[0008] The present inventors have conducted intensive research to solve the above problems. As a result, it has been found that the above problems can be solved by a polishing composition containing abrasive grains, a pH adjuster, and water, wherein the zeta potential of the abrasive grains is -25 mV or less, the degree of aggregation of the abrasive grains exceeds 3.5, and the pH is 6 or less, and the present invention has been completed.

Effects of the Invention

[0009] According to the present invention, there is provided a polishing composition that polishes a silicon nitride film at high speed and has a sufficiently high ratio of the polishing rate of the silicon nitride film to the polishing rate of the silicon oxide film (i.e., a high polishing selectivity for the silicon nitride film).

Modes for Carrying Out the Invention

[0010] Hereinafter, embodiments according to one embodiment of the present invention will be described. The present invention is not limited only to the following embodiments.

[0011] In this specification, "X to Y" indicating a range means "X or more and Y or less". Also, unless otherwise specified, measurements of operations and physical properties are made under conditions of room temperature (20 to 25 °C) / relative humidity 40 to 50% RH.

[0012] <Abrasive composition> The present invention relates to an abrasive composition used for polishing an object to be polished, which contains abrasive grains, a pH adjuster, and water, wherein the zeta potential of the abrasive grains is -25 mV or less, the degree of aggregation of the abrasive grains exceeds 3.5, and the pH is 6 or less. The abrasive composition of the present invention having such a configuration polishes a silicon nitride film at a high speed, and the ratio of the polishing rate of the silicon nitride film to the polishing rate of the silicon oxide film (hereinafter, also referred to as "polishing selectivity of the silicon nitride film") is sufficiently high. That is, the abrasive composition of the present invention can polish the silicon nitride film at a high speed and suppress the polishing rate of the silicon oxide film.

[0013] The reason why the above effects are achieved by the abrasive composition of the present invention is not necessarily clear, but it is considered as follows. However, the following mechanism is only a speculation and it goes without saying that it does not limit the technical scope of the present invention.

[0014] An abrasive composition generally polishes an object to be polished by a physical action of rubbing the substrate surface, a chemical action of components other than the abrasive grains on the substrate surface, and a combination thereof. Thereby, the form and type of the abrasive grains have a great influence on the polishing rate.

[0015] The abrasive grains contained in the polishing composition of the present invention have a zeta potential of -25 mV or less and an aggregation degree exceeding 3.5. That is, the abrasive grains are negatively charged, and the abrasive grains (secondary particles) are those in which more than 3.5 primary particles are aggregated (agglomerated). On the other hand, silicon nitride has a positively charged surface at a pH of 6 or less. Therefore, due to the electrostatic action between the abrasive grains and the silicon nitride film, the abrasive grains are likely to approach the surface of the silicon nitride film. At this time, since the abrasive grains have more than 3.5 primary particles aggregated and each of the aggregated primary particles is negatively charged, it is considered that the primary particles of the abrasive grains come into contact with the surface of the silicon nitride film so as to spread. Then, on the surface of the silicon nitride film, the contact surface of the abrasive grains becomes large, and a mechanical force can be effectively applied to the surface of the silicon nitride film (polishing surface) which is the object to be polished, and it is considered that polishing can be preferably performed.

[0016] Also, in the present invention, since the pH of the polishing composition is 6 or less, the surface of the silicon oxide film is negatively charged. Therefore, due to the electrostatic repulsion between the abrasive grains and the silicon oxide film, the abrasive grains are less likely to approach the surface of the silicon oxide film. Thus, the abrasive grains are less likely to adhere to the surface of the silicon oxide film, and an efficient polishing cannot be performed. The polishing composition of the present invention can suppress the polishing rate of the silicon oxide film. Thereby, it is considered that the polishing composition of the present invention can increase the polishing selectivity of the silicon nitride film.

[0017] [Object to be polished] The object to be polished according to the present invention preferably includes a silicon nitride film and a silicon oxide film. That is, according to a preferred embodiment of the present invention, the object to be polished includes a silicon nitride film and a silicon oxide film.

[0018] Examples of the silicon oxide film include, for example, a TEOS (Tetraethyl Orthosilicate) type silicon oxide film (hereinafter, also simply referred to as "TEOS film") generated using tetraethyl orthosilicate as a precursor, an HDP (High Density Plasma) film, an USG (Undoped Silicate Glass) film, a PSG (Phosphorus Silicate Glass) film, a BPSG (Boron-Phospho Silicate Glass) film, an RTO (Rapid Thermal Oxidation) film, and the like.

[0019] The object to be polished according to the present invention may contain other materials in addition to the silicon nitride film and the silicon oxide film. Examples of other materials include silicon carbonitride (SiCN), polycrystalline silicon, amorphous silicon, metal, SiGe, and the like.

[0020] Examples of the above metal include tungsten, copper, aluminum, cobalt, hafnium, nickel, gold, silver, platinum, palladium, rhodium, ruthenium, iridium, osmium, and the like.

[0021] [Abrasive grains] The polishing composition of the present invention contains abrasive grains. In the polishing composition of the present invention, the abrasive grains have a zeta potential of -25 mV or less and an aggregation degree exceeding 3.5. Here, the "zeta (ζ) potential" is the potential difference generated at the interface between a solid and a liquid in contact with each other when they perform relative movement. The "aggregation degree" is obtained by dividing the average secondary particle diameter of the abrasive grains by the average primary particle diameter of the abrasive grains.

[0022] In the polishing composition of the present invention, the zeta potential of the abrasive grains is -25 mV or less. By setting the zeta potential of the abrasive grains to -25 mV or less, the electrostatic attractive force between the object to be polished and the abrasive grains can be increased, and the polishing rate of the silicon nitride film can be improved. The zeta potential of the abrasive grains is preferably -30 mV or less, more preferably -32 mV or less, still more preferably -35 mV or less, and particularly preferably -38 mV or less. The zeta potential of the abrasive grains is preferably -65 mV or more, more preferably -60 mV or more, still more preferably -55 mV or more, and particularly preferably -50 mV or more. That is, the zeta potential of the abrasive grains is preferably -65 mV or more and -30 mV or less, more preferably -60 mV or more and -32 mV or less, still more preferably -55 mV or more and -35 mV or less, and particularly preferably -50 mV or more and -38 mV or less. When the abrasive grains have a zeta potential within such a range, the intended effect of the present invention can be further improved.

[0023] Here, the zeta potential of the abrasive grains in the polishing composition is calculated by subjecting a diluted solution of the polishing composition to a zetasizer-nano manufactured by Malvern Panalytical, Spectris Co., using a capillary cell at a measurement temperature of 25°C, measuring by the laser Doppler method (electrophoretic light scattering measurement method), and analyzing the obtained data by Smoluchowski's equation.

[0024] The lower limit of the average primary particle diameter of the abrasive grains is preferably 1 nm or more, more preferably 5 nm or more, still more preferably 7 nm or more, particularly preferably 8 nm or more, and most preferably 10 nm or more. The upper limit of the average primary particle diameter of the abrasive grains is preferably 200 nm or less, more preferably 150 nm or less, still more preferably 100 nm or less, particularly preferably 50 nm or less, and most preferably 30 nm or less. If the average primary particle diameter of the abrasive grains is within such a range, the intended effect of the present invention can be efficiently achieved.

[0025] The value of the average primary particle diameter of the abrasive grains can be calculated based on the specific surface area measured using the BET method.

[0026] The lower limit of the average secondary particle diameter of the abrasive grains is preferably 10 nm or more, more preferably 20 nm or more, further preferably 30 nm or more, still further preferably 40 nm or more, and particularly preferably 50 nm or more. Also, the upper limit of the average secondary particle diameter of the abrasive grains is preferably 700 nm or less, more preferably 530 nm or less, further preferably 350 nm or less, still further preferably 180 nm or less, particularly preferably 120 nm or less, and most preferably 90 nm or less. That is, the average secondary particle diameter of the abrasive grains is preferably 10 nm or more and 700 nm or less, more preferably 20 nm or more and 530 nm or less, further preferably 30 nm or more and 350 nm or less, particularly preferably 40 nm or more and 180 nm or less, and most preferably 50 nm or more and 120 nm or less. Within such a range, the intended effects of the present invention can be achieved efficiently.

[0027] Incidentally, the average secondary particle diameter of the abrasive grains can be measured, for example, by a dynamic light scattering method typified by the laser diffraction scattering method. That is, the average secondary particle diameter of the abrasive grains corresponds to the particle diameter D50 when the integrated particle mass reaches 50% of the total particle mass from the fine particle side in the particle size distribution of the abrasive grains obtained by the laser diffraction scattering method.

[0028] The degree of aggregation of abrasive grains exceeds 3.5. When the degree of aggregation of abrasive grains is 3.5 or less, the area of contact with the silicon nitride film becomes small, so the polishing selectivity of the silicon nitride film (the ratio of the polishing rate of the silicon nitride film to the polishing rate of the silicon oxide film) decreases. By the degree of aggregation of abrasive grains exceeding 3.5, the absolute value of the zeta potential of the negatively charged abrasive grains increases, making it easier to approach the silicon nitride film, so that a sufficient contact area with the silicon nitride film can be obtained, and thus the polishing selectivity of the silicon nitride film is improved. The degree of aggregation of abrasive grains is preferably 4.0 or more, more preferably 4.5 or more, still more preferably exceeding 5.0, particularly preferably 5.5 or more, and most preferably 6.0 or more. As the degree of aggregation of abrasive grains increases, there are advantages such as an improvement in the polishing rate of silicon nitride by the polishing composition and an advantage of suppressing the polishing rate of silicon oxide. The upper limit of the degree of aggregation of abrasive grains is not particularly limited, but is preferably 20 or less, more preferably 10 or less, and still more preferably 8 or less. As the degree of aggregation of abrasive grains decreases, the occurrence of defects on the surface of the object to be polished can be further reduced. Also, it becomes easier to obtain a polishing composition with constant quality and high stability. The degree of aggregation of abrasive grains is obtained by dividing the value of the average secondary particle diameter of the abrasive grains by the value of the average primary particle diameter.

[0029] The size of the abrasive grains (average primary particle diameter, average secondary particle diameter, etc.) can be appropriately controlled by selecting the manufacturing method of the abrasive grains or the like.

[0030] The shape of the abrasive grains is not particularly limited and may be spherical or non-spherical. Specific examples of non-spherical shapes include polyhedral shapes such as triangular prisms and quadrangular prisms, cylindrical shapes, a cocoonshaped cylinder with a swollen central part compared to the ends, a donut-shaped disk with a penetrated central part, a plate shape, a so-called cocoon-shaped with a constriction in the central part, a so-called aggregated spherical shape where a plurality of particles are integrated, a so-called sugar ball shape with a plurality of protrusions on the surface, a rugby ball shape, etc., and there are various shapes and are not particularly limited.

[0031] In the polishing composition of the present invention, examples of the type of abrasive grains include metal oxides such as silica, alumina, zirconia, and titania. The abrasive grains can be used alone or in combination of two or more. As the abrasive grains, commercially available products or synthetic products may be used. The type of abrasive grains is preferably silica, more preferably colloidal silica.

[0032] Hereinafter, preferred embodiments of the colloidal silica used in the present invention will be described.

[0033] The abrasive grains used in the polishing composition of the present invention are preferably those obtained through an ion exchange step of ion-exchanging the raw material colloidal silica described later using an ion exchange resin. The ion exchange step may be carried out once, or may be carried out two or more times as necessary.

[0034] The raw material colloidal silica is the raw material before being anion-modified (reformed) using the modification step described later and contains silica particles. The raw material colloidal silica may be produced by the sodium silicate method or the sol-gel method. The raw material colloidal silica may be synthesized or a commercially available product. The raw material colloidal silica may be unmodified or modified. Examples of the modified raw material colloidal silica include modified colloidal silica treated with aluminate or the like.

[0035] By undergoing the ion exchange step, aggregation of silica particles can be suppressed regardless of the purity of the raw material colloidal silica.

[0036] In one embodiment, the raw material colloidal silica is colloidal silica obtained by the sodium silicate method. The sodium silicate method is typically a method in which active silica obtained by ion-exchanging an aqueous solution of alkali silicate such as water glass is used as a raw material and the particles are grown.

[0037] The average primary particle diameter, average secondary particle diameter, and degree of aggregation of the raw material colloidal silica can be in the same range as that of the abrasive grains described above.

[0038] In the ion exchange step, the concentration of silica particles (solid content) in the raw material colloidal silica is not particularly limited as long as it is a concentration suitable for ion exchange. The concentration of silica particles (solid content) in the raw material colloidal silica is, for example, 1% by mass or more and 40% by mass or less, preferably 5% by mass or more and 30% by mass or less, and more preferably 10% by mass or more and 20% by mass or less.

[0039] The ion exchange resin used in the ion exchange step is not particularly limited, and examples thereof include strongly acidic cation exchange resins, weakly acidic cation exchange resins, strongly basic anion exchange resin type I, strongly basic anion exchange resin type II, weakly basic anion exchange resins, and the like. The ion exchange resin is preferably a strongly acidic cation exchange resin or a weakly acidic cation exchange resin.

[0040] Examples of the exchange group of the strongly acidic cation exchange resin include a sulfonic acid group. Examples of the exchange group of the weakly acidic cation exchange resin include a carboxy group, a phenolic hydroxyl group, and the like. Examples of the exchange group of the strongly basic anion exchange resin type I include a trimethylammonium group. Examples of the exchange group of the strongly basic anion exchange resin type II include a dimethylethanolammonium group. Examples of the exchange group of the weakly basic anion exchange resin include a tertiary amino group.

[0041] Commercially available products may be used as the ion exchange resin, and examples of such commercially available products include SGC650 (manufactured by Purolite Co., Ltd.), Diaion (trademark) series (manufactured by Mitsubishi Chemical Corporation), Amberlite (trademark), Amberjet (trademark) (manufactured by Organo Corporation), and the like.

[0042] The method of ion-exchanging the raw material colloidal silica using an ion-exchange resin is not particularly limited, and conventionally known methods can be used. For example, there are a method of mixing the raw material colloidal silica and the ion-exchange resin, and a method of passing the raw material colloidal silica through a column filled with the ion-exchange resin.

[0043] When mixing the raw material colloidal silica and the ion-exchange resin, the amount of the ion-exchange resin used can be appropriately adjusted according to the raw material colloidal silica to be used. The amount of the ion-exchange resin used is, for example, 10 parts by mass or more and 50 parts by mass or less, preferably 20 parts by mass or more and 30 parts by mass or less, based on 15 parts by mass of the raw material colloidal silica (solid content).

[0044] The temperature for mixing (stirring) the raw material colloidal silica and the ion-exchange resin is, for example, 10°C or higher and 50°C or lower, preferably 20°C or higher and 30°C or lower. Also, the time for mixing (stirring) the raw material colloidal silica and the ion-exchange resin is, for example, 1 hour or longer and 30 hours or shorter, preferably 10 hours or longer and 20 hours or shorter.

[0045] After the ion-exchange is completed, by separating and removing the ion-exchange resin, the ion-exchanged raw material colloidal silica used in the modification step can be obtained. The method of separating and removing the ion-exchange resin is not particularly limited. For example, by allowing the ion-exchange resin to settle naturally and recovering the supernatant liquid, the ion-exchanged raw material colloidal silica can be obtained.

[0046] When passing the raw material colloidal silica through a column filled with the ion-exchange resin, the rate (space velocity) at which the raw material colloidal silica passes through the column is, for example, 1 or more and 30 or less per hour, preferably 5 or more and 15 or less. At this time, the temperature of the raw material colloidal silica is, for example, 0°C or higher and 50°C or lower, preferably 10°C or higher and 30°C or lower.

[0047] The raw material colloidal silica after liquid feeding can be used as the ion-exchanged raw material colloidal silica in the modification process. By using the ion-exchanged raw material colloidal silica, the generation of impurities and the aggregation of silica can be suppressed.

[0048] The abrasive grains used in the polishing composition of the present invention are preferably obtained through a modification process in which the ion-exchanged raw material colloidal silica is anion-modified to obtain an anion-modified colloidal silica. That is, the abrasive grains used in the polishing composition of the present invention are preferably anion-modified colloidal silica.

[0049] In the modification process, there are no particular restrictions on the specific form of the anion-modification treatment, and among the conventionally known modification treatments of colloidal silica, a treatment capable of anion-modifying colloidal silica can be appropriately used. The anion-modification (modification) of colloidal silica means, for example, chemically bonding an organic compound having an anionic functional group (preferably an organic acid) to the surface of colloidal silica.

[0050] Colloidal silica with an immobilized organic acid can be obtained by immobilizing an organic acid on the surface of the colloidal silica. Simply co-existing the colloidal silica and the organic acid does not result in the immobilization of the organic acid on the colloidal silica. If sulfonic acid, which is a kind of organic acid, 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 quantitative oxidation 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 with sulfonic acid immobilized on the surface. Alternatively, if a carboxylic acid 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 and then irradiating with light, colloidal silica with carboxylic acid immobilized on the surface can be obtained.

[0051] In one embodiment, the addition amount of a silane coupling agent having a thiol group such as 3-mercaptopropyltrimethoxysilane used in the modification step 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, still more preferably 0.4% by mass or more and 1.5% by mass or less, based on 100% by mass of the silica particles (solid content) contained in the ion-exchanged raw material colloidal silica. When the lower limit of the addition amount of the silane coupling agent is within the above range, the surface of the silica particles can be sufficiently anionized, and excellent performance can be exhibited when used as an abrasive (abrasive grains in the polishing composition). On the other hand, when the upper limit of the addition amount of the silane coupling agent is within the above range, gelation of the resulting reaction product (anion-modified colloidal silica) over time can be prevented. Further, the amount of the organic solvent (hydrophilic solvent) used to dissolve the silane coupling agent is preferably 300% by volume or more and 7000% by volume or less, more preferably 400% by volume or more and 6000% by volume or less, based on 100% by volume of the silane coupling agent.

[0052] In the present invention, preferably, by using colloidal silica having sulfonic acid immobilized on the surface, it can efficiently adhere to the surface of the silicon nitride film (polishing surface), more effectively apply mechanical force, and can be suitably polished.

[0053] In the polishing composition of the present invention, the abrasive grains may further contain abrasive grains other than those having a zeta potential of -25 mV or less and an aggregation degree exceeding 3.5 (hereinafter, other abrasive grains). The type of other abrasive grains contained in the polishing composition of the present invention is not particularly limited, and examples thereof include oxides such as silica, alumina, zirconia, and titania having an aggregation degree of 3.5 or less. The other abrasive grains can be used alone or in combination of two or more. Each of the other abrasive grains may be a commercially available product or a synthetic product.

[0054] According to one embodiment of the present invention, the lower limit of the content (concentration) of abrasive grains in the polishing composition is preferably 0.2% by mass or more, more preferably 0.3% by mass or more, and even more preferably 0.5% by mass or more with respect to the polishing composition. Further, in the polishing composition of the present invention, the upper limit of the content of abrasive grains is preferably 20% by mass or less, more preferably 15% by mass or less, even more preferably 10% by mass or less, particularly preferably 5% by mass or less, and most preferably 3% by mass or less with respect to the polishing composition. When in such a range, the polishing rate can be further improved. In the case where the polishing composition contains two or more kinds of abrasive grains, the content of abrasive grains means the total amount thereof.

[0055] [pH and pH Adjusting Agent] The pH of the polishing composition of the present invention is 6 or less. When the pH is 6 or less, the magnitude of the electrical repulsion between the silicon oxide film and the abrasive grains becomes better, and the intended effect of the present invention is more likely to be exhibited. The pH of the polishing composition of the present invention may be 6 or less, preferably pH 5.5 or less, more preferably pH 5 or less, and even more preferably pH 4.5 or less. When the pH is 6 or less, there is an advantageous effect that the polishing rate for the silicon nitride film is improved. The lower limit of the pH is preferably 1.0 or more, more preferably 1.5 or more, and even more preferably 2 or more. That is, the pH of the polishing composition of the present invention is preferably 1.0 or more and 5.5 or less, more preferably 1.5 or more and 5 or less, and even more preferably 2 or more and 4.5 or less.

[0056] The polishing composition of the present invention contains a pH adjusting agent. The pH adjusting agent adjusts the pH of the polishing composition to a desired value.

[0057] Examples of the pH adjusting agent contained in the polishing composition of the present invention include inorganic acids, organic acids, alkalis, etc. These may be used alone or in combination of two or more.

[0058] Specific examples of inorganic acids that can be used as pH adjusters include, for example, hydrochloric acid, sulfuric acid, nitric acid, hydrofluoric acid, boric acid, carbonic acid, hypophosphorous acid, phosphorous acid, and phosphoric acid. Among them, hydrochloric acid, sulfuric acid, nitric acid, or phosphoric acid is preferable.

[0059] 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-furancarboxylic acid, 2,5-furandicarboxylic acid, 3-furancarboxylic acid, 2-tetrahydrofuran carboxylic acid, methoxyacetic acid, methoxyphenylacetic acid, and phenoxyacetic acid. Organic sulfonic acids such as methanesulfonic acid, ethanesulfonic acid, and isethionic acid may also be used. Among them, dicarboxylic acids such as malonic acid, succinic acid, glutaric acid, adipic acid, pimelic acid, maleic acid, phthalic acid, malic acid, and tartaric acid, and tricarboxylic acids such as citric acid are preferable.

[0060] Instead of or in combination with an inorganic acid or an organic acid, salts such as alkali metal salts of inorganic acids or organic acids may be used as pH adjusters. In the case of combinations of weak acids and strong bases, strong acids and weak bases, or weak acids and weak bases, a buffering action on pH can be expected.

[0061] Specific examples of alkalis that can be used as pH adjusters include, for example, ammonia, sodium hydroxide, potassium hydroxide, tetramethylammonium hydroxide, and the like. The content of the pH adjuster can be selected by appropriately adjusting within the range where the effects of the present invention are achieved.

[0062] Incidentally, the pH of the polishing composition can be measured, for example, with a pH meter.

[0063] [Dispersion medium] The polishing composition of the present invention contains a dispersion medium for dispersing each component. Examples of the dispersion medium include water; alcohols such as methanol, ethanol, and ethylene glycol; ketones such as acetone; and mixtures thereof. Among 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 essentially of water. The above-mentioned "essentially" is intended to mean that a dispersion medium other than water may be included as long as the object and effect of the present invention can be achieved. More specifically, it preferably consists of 90% by mass or more and 100% by mass or less of water and 0% by mass or more and 10% by mass or less of a dispersion medium other than water, and more preferably consists of 99% by mass or more and 100% by mass or less of water and 0% by mass or more and 1% by mass or less of a dispersion medium other than water. Most preferably, the dispersion medium is water.

[0064] From the viewpoint of not inhibiting the action of the components contained in the polishing composition, water containing as few impurities as possible is preferred as the dispersion medium. Specifically, pure water or ultrapure water obtained by removing impurity ions with an ion exchange resin and then removing foreign substances through a filter, or distilled water is more preferred.

[0065] [Other components] The polishing composition of the present invention may further contain known additives that can be used in the polishing composition, such as oxidizing agents, complexing agents, preservatives, and antifungal agents, as needed, as long as the effect of the present invention is not significantly impaired.

[0066] [Electrical conductivity] The electric conductivity of the polishing composition of the present invention is preferably 0.5 mS / cm or more and 20 mS / cm or less, more preferably 0.5 mS / cm or more and 10 mS / cm or less. The lower limit of the electric conductivity of the polishing composition is preferably 1 mS / cm or more, more preferably 2 mS / cm or more, and still more preferably 3 mS / cm or more. Further, the upper limit of the electric conductivity of the polishing composition is preferably 9 mS / cm or less, more preferably 8 mS / cm or less, and still more preferably 7.5 mS / cm or less. That is, the electric conductivity of the polishing composition of the present invention is preferably 1 mS / cm or more and 9 mS / cm or less, more preferably 2 mS / cm or more and 8 mS / cm or less, and still more preferably 3 mS / cm or more and 7.5 mS / cm or less. When the electric conductivity of the polishing composition is within the above range, the desired effects of the present invention can be achieved efficiently. The electric conductivity of the polishing composition is a value measured by a benchtop electric conductivity meter (manufactured by Horiba, Ltd., model number: DS-71).

[0067] [Method for producing polishing composition] The method for producing the polishing composition of the present invention is not particularly limited, and for example, it can be obtained by stirring and mixing abrasive grains and, if necessary, other components in a dispersion medium (for example, water). Details of each component are as described above.

[0068] The temperature at the time of mixing each component is not particularly limited, but is preferably 10°C or more and 40°C or less, and heating may be performed to increase the dissolution rate. Also, the mixing time is not particularly limited as long as uniform mixing can be achieved.

[0069] [Polishing method and method for manufacturing semiconductor substrate] As described above, the polishing composition of the present invention is suitably used for polishing an object to be polished including a silicon nitride film and a silicon oxide film. Therefore, the present invention provides a polishing method for polishing an object to be polished including a silicon nitride film and a silicon oxide film with the polishing composition of the present invention. That is, the present invention includes a polishing method including a step of polishing an object to be polished including a silicon nitride film and a silicon oxide film using the polishing composition of the present invention. Further, the present invention provides a method for manufacturing a semiconductor substrate including a step of polishing a semiconductor substrate including a silicon nitride film and a silicon oxide film by the polishing method.

[0070] As the polishing apparatus, a general polishing apparatus having a holder for holding a substrate or the like having an object to be polished and a motor or the like capable of changing the rotation speed, and having a polishing platen to which a polishing pad (polishing cloth) can be attached can be used.

[0071] As the polishing pad, general non-woven fabrics, polyurethanes, porous fluororesins, etc. can be used without particular limitation. It is preferable that the polishing pad is grooved so that the polishing liquid can accumulate.

[0072] Regarding the polishing conditions, for example, the rotation speed of the polishing platen is preferably 10 rpm (0.17 s -1 ) or more and 500 rpm (8.3 s -1 ) or less. 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 for example, a method of continuously supplying with a pump or the like is adopted. Although there is no limitation on this supply amount, it is preferable that the surface of the polishing pad is always covered with the polishing composition of the present invention.

[0073] After the polishing is completed, the substrate is washed in running water, and the water droplets adhering to the substrate are removed by a spin dryer or the like and dried, whereby a substrate having a layer containing metal can be obtained.

[0074] The polishing composition of the present invention may be a one-component type or a multi-component type including a two-component type. Further, the polishing composition of the present invention may be prepared by diluting the stock solution of the polishing composition, for example, by 10 times or more using a diluent such as water.

[0075] [Method for polishing a silicon nitride film at a high polishing rate and increasing the polishing selectivity of the silicon nitride film] According to the present invention, there is also provided a method for polishing a silicon nitride film at a high polishing rate and increasing the polishing selectivity of silicon nitride. The specific description of the polishing composition applies to the above description.

[0076] [Polishing rate] In the present invention, the polishing rate of the silicon nitride film is preferably 200 Å / min or more, more preferably 220 Å / min or more. The polishing rate of the silicon oxide film (SiO2 film) is preferably 40 Å / min or less, more preferably 35 Å / min or less, still more preferably 20 Å / min or less, and even more preferably 10 Å / min or less.

[0077] [Polishing selectivity] When the value obtained by dividing the polishing rate (Å / min) of the silicon nitride film (SiN film) by the polishing rate (Å / min) of the silicon oxide film (SiO2 film) is calculated as the polishing selectivity, in the present invention, the polishing selectivity (SiN / SiO2) is preferably more than 50, more preferably 60 or more, still more preferably 70 or more, even more preferably 80 or more, and may be, for example, 85 or more.

Examples

[0078] The present invention will be described in more detail with reference to the following examples and comparative examples. However, the technical scope of the present invention is not limited only to the following examples. Unless otherwise specified, “%” and “parts” mean “mass %” and “parts by mass”, respectively. In the following examples, unless otherwise specified, the operations were carried out under the conditions of room temperature (20 to 25 ° C) / relative humidity 40 to 50% RH. Further, in the following examples, the “TEOS substrate” means a substrate having a silicon oxide film produced using tetraethyl orthosilicate as a precursor.

[0079] [Preparation of abrasive grains] [Preparation of abrasive grain 1] 1 kg of aluminate-modified colloidal silica (silica particle concentration: 15% by mass, average primary particle diameter: 12 nm, average secondary particle diameter: 54 nm, average degree of aggregation: 4.4) produced by the sodium silicate method and 200 mL of an ion exchange resin (strong acid cation exchange resin SGC650; manufactured by Purolite Co., Ltd.) were mixed and stirred for 18 hours for ion exchange. After the ion exchange was completed, the ion exchange resin was allowed to settle naturally, and the supernatant (also referred to as “ion-exchanged colloidal silica”) was recovered.

[0080] 1 mL (specific gravity 1.057) of 3-mercaptopropyltrimethoxysilane mixed with 20 mL of ethanol was added to 900 mL (specific gravity 1.06) (solid content: 15% by mass) of the ion-exchanged colloidal silica, and the mixture was heated at 70 ° C for 18 hours. Then, 80 mL of a 31% by mass hydrogen peroxide solution was added, and the mixture was heated at 65 ° C for 18 hours. After heating, ethanol was removed using an evaporator to prepare anion-modified colloidal silica as abrasive grain 1.

[0081] [Preparation of abrasive grain 2] Anion-modified colloidal silica as abrasive grain 2 was prepared in the same manner as the preparation of abrasive grain 1, except that the addition amount of 3-mercaptopropyltrimethoxysilane was 0.5 mL.

[0082] [Preparation of abrasive grain 3] Except that the addition amount of 3-mercaptopropyltrimethoxysilane was set to 0.4 mL, anionic modified colloidal silica as abrasive grain 3 was prepared in the same manner as the preparation of abrasive grain 1.

[0083] [Preparation of Abrasive Grain 4] Except that aluminic acid-modified colloidal silica with an average primary particle diameter of 15 nm and an average secondary particle diameter of 86 nm (average aggregation degree: 5.73) was used, anionic modified colloidal silica as abrasive grain 4 was prepared in the same manner as the preparation of abrasive grain 1.

[0084] [Preparation of Abrasive Grain 5] Except that aluminic acid-modified colloidal silica with an average primary particle diameter of 14 nm and an average secondary particle diameter of 89 nm (average aggregation degree: 6.36) was used, anionic modified colloidal silica as abrasive grain 5 was prepared in the same manner as the preparation of abrasive grain 1.

[0085] [Preparation of Abrasive Grain 6] Except that aluminic acid-modified colloidal silica with an average primary particle diameter of 25 nm and an average secondary particle diameter of 91 nm (average aggregation degree: 3.64) was used, anionic modified colloidal silica as abrasive grain 6 was prepared in the same manner as the preparation of abrasive grain 1.

[0086] [Preparation of Abrasive Grain 7] Except that colloidal silica with an average primary particle diameter of 12 nm and an average secondary particle diameter of 28 nm (average aggregation degree: 2.3) was used instead of aluminic acid-modified colloidal silica and the addition amount of 3-mercaptopropyltrimethoxysilane was changed to 2 mL, anionic modified colloidal silica as abrasive grain 7 was prepared in the same manner as the preparation of abrasive grain 1.

[0087] [Preparation of Abrasive Grain 8] The aluminic acid-modified colloidal silica produced by the sodium silicate method (silica particle concentration: 15% by mass, average primary particle diameter: 12 nm, average secondary particle diameter: 54 nm, average aggregation degree: 4.4) was used as abrasive grain 8 as it was.

[0088] [Preparation of Abrasive Grain 9] Anionic modified colloidal silica as abrasive grain 9 was prepared in the same manner as the preparation of abrasive grain 1, except that aluminic acid-modified colloidal silica with an average primary particle size of 11 nm and an average secondary particle size of 34 nm (average degree of aggregation: 3.0) was used.

[0089] [Preparation of Polishing Composition] [Example 1: Preparation of Polishing Composition A1] Taking the whole composition as 100 parts by mass, abrasive grain 1 as the abrasive grain, ammonia as the pH adjuster, and water (deionized water) as the dispersion medium were mixed to prepare polishing composition A1. The addition amount (content) of the pH adjuster was set to the amount at which the pH of polishing composition A1 was 4 (liquid temperature: 25 °C). The pH was measured using a pH meter (product name: LAQUA (registered trademark), manufactured by Horiba, Ltd.).

[0090] [Examples 2 - 8: Preparation of Polishing Compositions A2 - A8] Except that the type of abrasive grain was changed as shown in Table 1 below and the amount of the pH adjuster was changed so that the pH of the resulting polishing composition was the pH described in Table 1 below, polishing compositions A2 - A8 were prepared in the same manner as the preparation of polishing composition A1.

[0091] [Comparative Examples 1 - 4: Preparation of Polishing Compositions B1 - B4] Except that the type of abrasive grain was changed as shown in Table 1 below and the amount or type of the pH adjuster was changed so that the pH of the resulting polishing composition was the pH described in Table 1 below, polishing compositions B1 - B4 were prepared in the same manner as the preparation of polishing composition A1.

[0092] Polishing compositions A1 - A8 are the polishing compositions used in the examples, and polishing compositions B1 - B4 are the polishing compositions used in the comparative examples.

[0093] (Evaluation of Average Primary Particle Size) The average primary particle diameter of the anion-modified colloidal silica prepared above was calculated from the specific surface area of the abrasive grains by the BET method measured using "Flow SorbII 2300" manufactured by Micromeritics and the density of the anion-modified colloidal silica.

[0094] (Evaluation of average secondary particle diameter) The average secondary particle diameter of the anion-modified colloidal silica prepared above was measured by a light scattering method using a laser beam. As the measuring instrument, UPA-UT151, a dynamic light scattering type particle size distribution analyzer manufactured by Nikkiso Co., Ltd., was used.

[0095] (Zeta potential measurement) The polishing compositions A1 to A8 and B1 to B4 prepared above were subjected to ELS-Z2 manufactured by Otsuka Electronics Co., Ltd. Measurement was carried out by the laser Doppler method (electrophoretic light scattering measurement method) using a flow cell at a measurement temperature of 25°C. By analyzing the obtained data with Smoluchowski's equation, the zeta potential of the colloidal silica contained in the polishing composition was calculated. The results are shown in Table 1.

[0096] (Electrical conductivity) The electrical conductivity (unit: mS / cm) of the polishing composition (liquid temperature: 25°C) was measured using a desktop electrical conductivity meter (manufactured by Horiba, Ltd., model number: DS-71).

[0097] (Evaluation of polishing rate) As the object to be polished, · 200 mm wafer (SiN (silicon nitride film), manufactured by Advanced Materials Technology Co., Ltd., product name: LP-SiN 3.5KA Blanket), · 200 mm wafer (TEOS (silicon oxide film), manufactured by Advanced Materials Technology Co., Ltd., product name: P-TEOS 10KA Blanket), were prepared, and each wafer was polished under the following polishing conditions using the polishing composition obtained above, and the polishing rate was measured. Also, the polishing selectivity (SiN / SiO2) of the polishing rate of silicon nitride was calculated.

[0098] [Polishing Conditions] Polishing machine: CMP single-sided polishing machine for 200 mm wafers Polishing pad: Polyurethane pad (IC1010: manufactured by Rohm and Haas) Pressure: 1.0 psi (approx. 6.9 kPa) Platen (surface plate) rotation speed: 90 rpm Head (carrier) rotation speed: 87 rpm Flow rate of polishing composition: 200 ml / min Polishing time: 1 minute.

[0099] [Polishing Rate] The polishing rate was calculated by the following formula.

[0100] [Number]

[0101] The film thickness was measured by an optical interference film thickness measuring device (manufactured by KLA-Tencor Corporation, model number: A-SET), and the difference was evaluated by dividing it by the polishing time. The results of the polishing rate are shown in Table 1. In Table 1, the TEOS substrate is shown as SiO2. Also, in Table 1, "-" indicates that the corresponding component was not added.

[0102] [Table 1]

[0103] As shown in Table 1, the polishing compositions of Examples 1 to 8 using abrasive grains with a zeta potential of -25 mV or less and an aggregation degree exceeding 3.5 can polish the silicon nitride film at a high speed and suppress the polishing rate of the silicon oxide film compared to the polishing compositions of Comparative Examples 1 to 4 (that is, the ratio of the polishing rate of the silicon nitride film to the polishing rate of the silicon oxide film; "polishing selectivity SiN / SiO2" is high).

Claims

1. A polishing composition containing abrasive grains, a pH adjuster, and water, wherein the zeta potential of the abrasive grains is -25 mV or less, the degree of aggregation of the abrasive grains exceeds 5.0, and the pH is 6 or less.

2. The polishing composition according to claim 1, wherein the pH is 2 or more and 4.5 or less.

3. The polishing composition according to claim 1 or 2, wherein the abrasive grains are anionic-modified colloidal silica.

4. The polishing composition according to any one of claims 1 to 3, which is used for polishing an object to be polished including a silicon nitride film and a silicon oxide film.

5. A polishing method including a step of polishing an object to be polished including a silicon nitride film and a silicon oxide film using the polishing composition according to any one of claims 1 to 4.

6. A method for manufacturing a semiconductor substrate, which includes a step of polishing a semiconductor substrate including a silicon nitride film and a silicon oxide film by the polishing method according to claim 5.

Images