WO2019193693A1 - Polishing liquid and polishing method - Google Patents

Abstract

A polishing liquid that is used to polish silicon nitride, the polishing liquid comprising cerium-oxide-containing abrasive grains and a liquid medium, wherein the cerium oxide contains an element that has an ionic radius greater than that of cerium.

Description

Polishing liquid and polishing method

The present invention relates to a polishing liquid and a polishing method.

CMP (Chemical Mechanical Polishing) technology is indispensable for forming shallow trench isolation, planarizing a premetal insulating film or an interlayer insulating film, forming a plug, forming a buried metal wiring, etc. in a semiconductor device manufacturing process. It has become a technology.

Various polishing liquids used in CMP are known. When classified according to abrasive grains (polishing particles) contained in the polishing liquid, ceria-based polishing liquid containing cerium oxide (ceria) particles as abrasive grains, silica-based polishing liquid containing silicon oxide (silica) particles as abrasive grains, and abrasive grains Known are an alumina-based polishing liquid containing aluminum oxide (alumina) particles, a resin particle-based polishing liquid containing organic resin particles as abrasive grains, and the like.

As a polishing liquid for polishing an insulating material such as silicon oxide in a manufacturing process of a semiconductor element, a ceria-based polishing liquid is often used in that the polishing speed of an inorganic insulating material is higher than that of a silica-based polishing liquid. (For example, see Patent Document 1 below). Furthermore, in order to control the polishing rate and improve the flatness of the polished film after polishing, a technique for adding an additive to a ceria-based polishing liquid is known (for example, see Patent Document 2 below).

In recent years, the types of materials to be polished have been diversified along with the complicated structures such as 3D devices, and silicon nitride is sometimes used as the material to be polished (for example, Patent Document 3 below). reference).

JP-A-10-106994 Japanese Patent Laid-Open No. 08-22970 International Publication No. 2016/158324

However, when the surface to be polished containing silicon nitride is polished using a conventional polishing liquid, there is a problem that an excellent polishing rate of silicon nitride cannot be obtained.

Therefore, an object of the present invention is to provide a polishing liquid capable of obtaining an excellent polishing rate of silicon nitride. Another object of the present invention is to provide a polishing method capable of polishing silicon nitride at an excellent polishing rate.

The present invention provides, as a first aspect, a polishing liquid used for polishing silicon nitride, comprising abrasive grains containing cerium oxide and a liquid medium, wherein the cerium oxide is an ion larger than cerium. A polishing liquid comprising an element having a radius is provided.

According to the polishing liquid of the first aspect of the present invention, an excellent polishing rate of silicon nitride can be obtained when the surface to be polished containing silicon nitride is polished by providing the above-described configuration. .

Moreover, the present invention provides, as a second aspect, a polishing method for polishing silicon nitride using the above polishing liquid.

According to the polishing method of the second aspect of the present invention, silicon nitride can be polished at an excellent polishing rate.

According to the present invention, a polishing liquid capable of obtaining an excellent polishing rate of silicon nitride can be provided. In addition, according to the present invention, a polishing method capable of polishing silicon nitride at an excellent polishing rate can be provided.

FIG. 1 is a schematic cross-sectional view for explaining an example of a polishing method. FIG. 2 is a diagram showing Raman spectra of abrasive grains obtained by Raman spectroscopy in Example 1 and Comparative Example 1.

Hereinafter, embodiments of the present invention will be described in detail. However, the present invention is not limited to the following embodiments.

In this specification, a numerical range indicated by using “to” indicates a range including the numerical values described before and after “to” as the minimum value and the maximum value, respectively. In the numerical ranges described stepwise in this specification, the upper limit value or lower limit value of a numerical range of a certain step can be arbitrarily combined with the upper limit value or lower limit value of the numerical range of another step. In the numerical range described in this specification, the upper limit value or the lower limit value of the numerical range may be replaced with the values shown in the examples. “A or B” only needs to include either A or B, and may include both. The materials exemplified in this specification can be used singly or in combination of two or more unless otherwise specified. The content of each component in the composition means the total amount of the plurality of substances present in the composition unless there is a specific notice when there are a plurality of substances corresponding to each component in the composition. The term “process” is not limited to an independent process, and is included in this term if the intended effect of the process is achieved even when it cannot be clearly distinguished from other processes.

<Polishing liquid>
The polishing liquid according to this embodiment is a polishing liquid used for polishing silicon nitride, and contains abrasive grains containing cerium oxide and a liquid medium, and the cerium oxide has a larger ionic radius than cerium. Element (hereinafter also referred to as “element A” in some cases). The polishing liquid according to this embodiment can be used as a CMP polishing liquid.

By polishing the surface to be polished containing silicon nitride using the polishing liquid according to this embodiment, an excellent polishing rate of silicon nitride can be obtained. Although the detailed reason for obtaining such an effect is not necessarily clear, the present inventor presumes an example of the reason as follows. That is, when the cerium oxide in the abrasive grains contains the element A, oxygen deficiency of cerium oxide occurs. As a result, the proportion of trivalent cerium atoms in the abrasive grains increases and the electron donating property increases, so that the abrasive grains easily donate electrons to the surface to be polished containing silicon nitride. As a result, the chemical bond between the nitrogen atom and the silicon atom in the silicon nitride is weakened, so that the silicon nitride is easily polished.

(Abrasive grains)
The abrasive grains contain cerium oxide (cerium oxide composition) containing element A having an ionic radius larger than that of cerium (for example, tetravalent cerium). That is, the element A is doped in cerium oxide. In this case, the cerium oxide containing the element A has, for example, a state in which the element A substitutes a cerium atom of cerium oxide, or a state in which the element A enters between lattices of cerium oxide.

The element A is preferably a divalent or trivalent element (divalent or trivalent ion), more preferably a divalent or trivalent rare earth element, from the viewpoint of easily obtaining an excellent polishing rate of silicon nitride. (Divalent or trivalent rare earth element ions). The element A is preferably yttrium (Y), lanthanum (La), praseodymium (Pr), neodymium (Nd), promethium (Pm), samarium (Sm) from the viewpoint of easily obtaining an excellent polishing rate of silicon nitride. , Europium (Eu), gadolinium (Gd), terbium (Tb), dysprosium (Dy), holmium (Ho), erbium (Er), thulium (Tm) and calcium (Ca). More preferably, it is at least one selected from the group consisting of yttrium, lanthanum, samarium and gadolinium, and more preferably at least one selected from the group consisting of lanthanum, samarium and gadolinium. The element A can contain a lanthanoid, for example, can contain lanthanum.

The content of element A in the abrasive grains is preferably in the following range based on the total amount of abrasive grains (total amount of one abrasive grain or total amount of abrasive grains contained in the polishing liquid). The content of element A is preferably 0.001 mol% or more, more preferably 0.1 mol% or more, and further preferably 1 mol%, from the viewpoint of easily obtaining an excellent polishing rate of silicon nitride. That's it. The content of the element A is preferably 50 mol% or less, more preferably 45 mol% or less, and still more preferably 40 mol% or less from the viewpoint of easily obtaining an excellent polishing rate of silicon nitride. From these viewpoints, the content of the element A is preferably 0.001 to 50 mol%, more preferably 0.1 to 45 mol%, still more preferably 0.1 to 40 mol%, Particularly preferred is 1 to 40 mol%.

In the abrasive grains, the content of element A relative to the total of cerium and element A (element A / total of cerium and element A) is preferably in the following range. The content of element A is preferably 5 mol% or more, more than 5 mol%, more than 10 mol%, more than 10 mol%, more than 15 mol%, from the viewpoint of easily obtaining an excellent polishing rate of silicon nitride. , More than 15 mol%, more than 20 mol%, more than 20 mol%, more than 25 mol%, or more than 25 mol%. The content of the element A is preferably 50 mol% or less, less than 50 mol%, less than 45 mol%, less than 45 mol%, less than 40 mol%, 40 mol% or less, from the viewpoint of easily obtaining an excellent polishing rate of silicon nitride. It is less than mol%, less than 35 mol%, less than 35 mol%, or less than 30 mol%. From these viewpoints, the content of the element A is preferably 5 to 50 mol%, 10 to 40 mol%, 20 to 40 mol%, or 30 to 40 mol%. The contents of cerium and element A can be measured, for example, by inductively coupled plasma mass spectrometry (ICP mass spectrometry).

The abrasive grains may be obtained by any manufacturing method. As an abrasive raw material, a compound containing at least one selected from the group consisting of cerium and element A can be used. As such a compound, at least one selected from the group consisting of nitrate, ammonium nitrate, sulfate, ammonium sulfate, acetate, oxalate, carbonate, chloride, acetyl acetate salt, alkoxide and hydroxide is used. be able to. That is, the abrasive is a compound containing at least one selected from the group consisting of cerium and element A, nitrate, ammonium nitrate, sulfate, ammonium sulfate, acetate, oxalate, carbonate, chloride, acetyl acetate salt Cerium oxide obtained using at least one selected from the group consisting of alkoxides and hydroxides, nitrates, ammonium nitrates, sulfates, ammonium sulfates, acetates, oxalates, carbonates And cerium oxide derived from at least one selected from the group consisting of chloride, acetyl acetate salt, alkoxide and hydroxide.

As a method for producing abrasive grains, for example, it can be obtained by oxidizing a mixture containing cerium and element A. That is, the abrasive is a compound containing at least one selected from the group consisting of cerium and element A, nitrate, ammonium nitrate, sulfate, ammonium sulfate, acetate, oxalate, carbonate, chloride, acetyl acetate salt In addition, cerium oxide obtained by oxidizing at least one selected from the group consisting of alkoxides and hydroxides can be contained, and cerium oxide which is an oxide of these compounds can be contained. The mixture can be obtained by mixing a cerium compound (cerium carbonate, cerium nitrate, etc.) and a compound containing element A (lanthanum nitrate, etc.). The mixture may be fired and oxidized, or the mixture may be oxidized with hydrogen peroxide or the like. There is no restriction | limiting in particular as a method of baking, Methods, such as a sintering method using a rotary kiln, an electric furnace, etc., can be used. In this case, the firing temperature is preferably 350 to 900 ° C.

When the abrasive grains produced by these methods are aggregated, the aggregated particles may be mechanically pulverized. Examples of the pulverization method include a dry pulverization method using a jet mill or the like (see, for example, “Chemical Engineering Papers”, Vol. It is done.

When applying such abrasive grains to the polishing liquid, it is preferable to obtain a slurry (cerium oxide slurry) by dispersing the abrasive grains in a liquid medium. Examples of the dispersion method include a method using a homogenizer, an ultrasonic disperser, a wet ball mill, and the like, in addition to a dispersion treatment using a normal stirrer.

The particle size of the abrasive grains in the slurry obtained by the above method may be adjusted by a known method. For example, the slurry can be micronized by centrifuging the slurry with a small centrifuge, forcibly sedimenting, and taking out only the supernatant. In addition, the fine particles can be removed by taking out a precipitate precipitated by decantation and adding a liquid medium (water or the like) to the precipitate. In addition, the abrasive grains may be made fine by causing the abrasive grains in the liquid medium to collide with each other at a high pressure using a high-pressure homogenizer.

The Raman spectrum of the abrasive grains obtained by Raman spectroscopy preferably has a peak derived from oxygen deficiency of cerium oxide from the viewpoint of easily obtaining an excellent polishing rate of silicon nitride. The Raman spectrum may have a peak derived from an oxygen deficiency of cerium oxide in addition to a peak derived from cerium oxide (main peak). From the viewpoint of easily obtaining an excellent polishing rate of silicon nitride, the Raman spectrum preferably has the entire peak or peak top derived from oxygen deficiency of cerium oxide in the following Raman shift range. The peak position is preferably 500 to 650 cm ⁻¹ , more preferably 520 to 630 cm ⁻¹ , and still more preferably 530 to 600 cm ⁻¹ . Measurement by Raman spectroscopy can be performed using a Raman spectrometer.

The abrasive preferably has a positive (greater than 0 mV) zeta potential from the viewpoint of easily obtaining an excellent polishing rate of silicon nitride because the abrasive tends to come into contact with silicon nitride that tends to have a negative potential. . That is, the polishing liquid according to this embodiment preferably contains cationic abrasive grains. The zeta potential of the abrasive is preferably 20 mV or more, more preferably 30 mV or more, still more preferably 40 mV or more, and particularly preferably 50 mV or more from the viewpoint of easily obtaining an excellent polishing rate of silicon nitride. is there. The zeta potential of the abrasive is preferably 100 mV or less, more preferably 90 mV or less, still more preferably 80 mV or less, and particularly preferably 70 mV or less, from the viewpoint of excellent cleanability of the surface to be polished containing silicon nitride. And very preferably 60 mV or less.

The zeta potential (ζ [mV]) can be measured using a zeta potential measuring device (for example, Delsa Nano C (device name) manufactured by Beckman Coulter, Inc.). The zeta potential of the abrasive grains in the polishing liquid can be obtained by, for example, putting the polishing liquid in a concentrated cell unit (cell for high concentration sample) for the zeta potential measuring device.

The average particle diameter of the abrasive grains is preferably 300 nm or less, more preferably 280 nm or less, still more preferably 250 nm or less, and particularly preferably 200 nm or less, from the viewpoint that polishing scratches are less likely to occur. The average grain size of the abrasive grains is preferably 50 nm or more, more preferably 70 nm or more, still more preferably 80 nm or more, and particularly preferably 100 nm or more from the viewpoint of easily obtaining an excellent polishing rate of silicon nitride. It is. From these viewpoints, the average grain size of the abrasive grains is preferably 50 to 300 nm.

Here, the “average particle diameter” is the median value of the volume distribution obtained by directly measuring the polishing liquid with a laser diffraction particle size distribution meter. For example, the average particle diameter (D50) can be obtained using “Microtrac MT3300EXII” manufactured by Microtrack Bell Co., Ltd. The average particle diameter can be controlled by the abrasive production conditions, classification conditions, and the like. The average particle size is the particle size of the abrasive grains contained in the polishing liquid, and can also be adjusted by the type or amount of additives, pH of the polishing liquid, and the like described later.

The content of abrasive grains is preferably in the following range based on the total amount of polishing liquid. The content of the abrasive is preferably 10% by mass or less, more preferably 8% by mass or less, still more preferably 6% by mass or less, and particularly preferably 5% by mass from the viewpoint of preventing the particles from aggregating. Or less, very preferably 4% by mass or less, very preferably 2% by mass or less, and even more preferably 1% by mass or less. The content of the abrasive grains is preferably 0.1% by mass or more, more preferably 0.2% by mass or more, and still more preferably 0.3% by mass from the viewpoint of easily obtaining an excellent polishing rate of silicon nitride. It is at least 0.5 mass%, particularly preferably at least 0.5 mass%. From these viewpoints, the abrasive content is preferably 0.1 to 10% by mass.

(Liquid medium)
The liquid medium is not particularly limited, but preferably contains water as a main component. Examples of water include deionized water, ion exchange water, and ultrapure water. The liquid medium may contain a solvent other than water (for example, a polar solvent such as ethanol, acetic acid, and acetone) and the like as necessary.

(Additive)
The polishing liquid according to this embodiment can contain additives other than abrasive grains and a liquid medium. Examples of the additive include an organic acid component, a pH adjuster, a cationic surfactant, an anionic surfactant, a nonionic surfactant, an amphoteric surfactant, and a water-soluble polymer. By using the additive, it is possible to improve the polishing characteristics such as the polishing selectivity of the polishing rate of silicon nitride with respect to the material to be polished other than silicon nitride.

The polishing liquid according to this embodiment may contain ammonium polyacrylate as a dispersant or the like, but may not contain ammonium polyacrylate. The content of ammonium polyacrylate in the polishing liquid according to the present embodiment is preferably 1 part by mass or less with respect to 100 parts by mass of abrasive grains, from the viewpoint that an excellent polishing rate of silicon nitride is easily obtained. The amount is preferably less than 1 part by mass, more preferably 0.1 part by mass or less, particularly preferably 0.01 part by mass or less, and most preferably 0.001 part by mass or less.

[Organic acid component]
The polishing liquid according to this embodiment can contain an organic acid component. The organic acid component may be at least one selected from the group consisting of organic acids and organic acid salts. The organic acid component may have a role as a dispersant, and the average particle size of the abrasive grains can be controlled by adding the organic acid component. Examples of the organic acid component include monocarboxylic acids such as formic acid, acetic acid, propionic acid, butyric acid, acrylic acid, benzoic acid, and picolinic acid. The organic acid component is preferably acetic acid from the viewpoint of easily obtaining an excellent polishing rate of silicon nitride.

The content of the organic acid component is preferably in the following range based on the total amount of the polishing liquid. The content of the organic acid component is preferably 0.0005% by mass or more, more preferably 0.001% by mass or more, and further preferably 0.001% by mass or more, from the viewpoint of easily obtaining an excellent polishing rate of silicon nitride. It is 003 mass% or more, Most preferably, it is 0.005 mass% or more. The content of the organic acid component is preferably 0.1% by mass or less, more preferably 0.05% by mass or less, and still more preferably 0.8% by mass from the viewpoint of easily obtaining an excellent polishing rate of silicon nitride. 01% by mass or less. From these viewpoints, the content of the organic acid component is preferably 0.0005 to 0.1% by mass, more preferably 0.001 to 0.05% by mass, and still more preferably 0.003 to 0%. 0.01% by mass, particularly preferably 0.005 to 0.01% by mass.

The content of the organic acid component is preferably in the following range with respect to 100 parts by mass of the abrasive grains. The content of the organic acid component is preferably 0.1 parts by mass or more, more preferably 0.3 parts by mass or more, and still more preferably 0. 0 parts by mass from the viewpoint of easily obtaining an excellent polishing rate of silicon nitride. 5 parts by mass or more. The content of the organic acid component is preferably 10 parts by mass or less, more preferably 5 parts by mass or less, and even more preferably 3 parts by mass or less, from the viewpoint that an excellent polishing rate of silicon nitride can be easily obtained. The amount is particularly preferably 1 part by mass or less. From these viewpoints, the content of the organic acid component is preferably 0.1 to 10 parts by mass, more preferably 0.3 to 5 parts by mass, and still more preferably 0.5 to 3 parts by mass. Particularly preferred is 0.5 to 1 part by mass.

[PH adjuster]
The polishing liquid according to this embodiment can contain a pH adjuster. By using a pH adjuster, it is easy to obtain a desired pH of the polishing liquid. Examples of the pH adjuster include inorganic acids and inorganic bases. Examples of inorganic acids include nitric acid, sulfuric acid, hydrochloric acid, phosphoric acid, boric acid and the like. Examples of the inorganic base include sodium hydroxide, potassium hydroxide, calcium hydroxide, ammonia and the like. You may adjust pH using the above-mentioned organic acid component.

The pH of the polishing liquid is preferably 4.0 or more, more preferably 4.3 or more, and even more preferably 4.5 or more, from the viewpoint of easily obtaining an excellent polishing rate of silicon nitride. The pH of the polishing liquid is preferably 12.0 or less, more preferably 11.0 or less, even more preferably 10.0 or less, particularly from the viewpoint of easily obtaining an excellent polishing rate of silicon nitride. Preferably it is 9.0 or less, very preferably 8.0 or less, very preferably 7.0 or less, even more preferably 6.0 or less, even more preferably 5.0 or less. is there. From these viewpoints, the pH of the polishing liquid is preferably 4.0 to 12.0, more preferably 4.3 to 11.0, still more preferably 4.5 to 10.0, Preferably it is 4.5 to 9.0, very preferably 4.5 to 8.0, very preferably 4.5 to 7.0, even more preferably 4.5 to 6.0. More preferably, it is 4.5 to 5.0.

The pH of the polishing liquid according to this embodiment can be measured with a pH meter (for example, model number D-51 manufactured by Horiba, Ltd.). For example, phthalate pH buffer (pH: 4.01), neutral phosphate pH buffer (pH: 6.86) and borate pH buffer (pH: 9.18) are used as standard buffers. After calibrating the pH meter at three points, the electrode of the pH meter is put into the polishing liquid, and the value after being stabilized after 2 minutes or more is measured. At this time, the temperature of the standard buffer solution and the polishing solution is, for example, 25 ° C.

The manufacturing method of the polishing liquid according to this embodiment is not particularly limited. In cases other than being used for polishing (during storage, transportation, etc.), the polishing liquid can have a concentrated form, for example. That is, the polishing liquid according to the present embodiment may be stored as a storage liquid for polishing liquid in which the content of the liquid medium is reduced as compared with that during polishing, and may be diluted with the liquid medium during polishing. That is, the polishing liquid according to the present embodiment may be a polishing liquid obtained by diluting a storage liquid for polishing liquid with a liquid medium.

<Polishing method>
The polishing method according to the present embodiment includes a polishing step of polishing silicon nitride using the polishing liquid according to the present embodiment. In the polishing step, the surface to be polished containing silicon nitride can be polished. The polishing step may be a step of polishing a surface to be polished containing silicon nitride and a conductive material. In the polishing step, film-like silicon nitride (silicon nitride film) may be polished.

In the polishing step, for example, the surface to be polished of the substrate is pressed against the polishing pad of the polishing surface plate, and a predetermined pressure is applied to the substrate from the surface opposite to the surface to be polished (back surface of the substrate). The polishing liquid according to this embodiment is supplied between the surface to be polished of the substrate and the polishing pad, and the surface to be polished can be polished by moving (rotating) the substrate relative to the polishing surface plate. .

An example of a method for polishing a surface to be polished containing silicon nitride is shown in FIG. As shown in FIG. 1A, the object to be polished (base) 10 includes a first insulating material 1 having a groove on the surface, a barrier material 2 having a shape following the surface of the first insulating material 1, And a second insulating material 3 covering the entire barrier material 2 so as to fill the groove. The polishing method of the object to be polished 10 includes a first polishing step (FIGS. 1A to 1B) for polishing the second insulating material 3 until the barrier material 2 is exposed, and a first insulating material. A second polishing step (FIGS. 1 (b) to 1 (c)) for polishing the barrier material 2 and the second insulating material 3 until 1 is exposed. You may have the 3rd grinding | polishing process which grind | polishes the insulating material 1, the barrier material 2, and the 2nd insulating material 3, and finishes a to-be-polished surface flat. Silicon nitride can be used as the second insulating material 3. Examples of the first insulating material 1 include silicon oxide. Examples of the barrier material 2 include polysilicon. Note that the structure to be polished is not limited to the structure shown in FIG. 1 as long as it has a surface to be polished containing silicon nitride.

As the polishing apparatus, a general polishing apparatus having a holder capable of holding a base (such as a semiconductor substrate having a polished surface containing silicon nitride) and a polishing surface plate to which a polishing pad can be attached can be used. Each of the holder and the polishing surface plate may be attached with, for example, a motor capable of changing the rotation speed. Examples of the polishing apparatus include APPLIED MATERIALS polishing equipment (trade names: MIRRA-3400, REFLEXION LK), Ebara Corporation polishing equipment (trade name: F REX-300), and the like.

As the polishing pad, general nonwoven fabric, foam, non-foam, etc. can be used. The material of the polishing pad includes polyurethane, acrylic resin, polyester, acrylic-ester copolymer, polytetrafluoroethylene, polypropylene, polyethylene, poly-4-methylpentene, cellulose, cellulose ester, polyamide (for example, nylon (trade name)) And aramid), polyimide, polyimide amide, polysiloxane copolymer, oxirane compound, phenol resin, polystyrene, polycarbonate, epoxy resin and the like. The material of the polishing pad is preferably at least one selected from the group consisting of foamed polyurethane and non-foamed polyurethane from the viewpoint of easily obtaining an excellent polishing rate and flatness. The polishing pad may be grooved so that the polishing liquid accumulates.

The polishing conditions are not limited, but the rotation speed of the polishing platen is preferably 200 min ⁻¹ (rpm) or less so that the substrate does not jump out, and the polishing pressure (working load) applied to the substrate is not damaged by polishing scratches. From the viewpoint of sufficiently suppressing the occurrence, it is preferably 100 kPa (= about 14.5 psi) or less. During polishing, it is preferable to continuously supply the polishing liquid to the polishing pad with a pump or the like. Although there is no restriction | limiting in this supply amount, it is preferable that the surface of a polishing pad is always covered with polishing liquid.

After the polishing is completed, it is preferable to clean the substrate thoroughly under running water to remove the abrasive grains adhering to the substrate. For cleaning, dilute hydrofluoric acid or ammonia water may be used in addition to water, and a brush may be used to increase cleaning efficiency. Further, after washing, it is preferable to dry the substrate after water droplets adhering to the substrate are removed using a spin dryer or the like.

Hereinafter, the present invention will be specifically described based on examples, but the present invention is not limited to these examples.

<Preparation of polishing liquid>
Example 1
Cerium nitrate and lanthanum nitrate were dissolved in pure water so that the molar ratio of lanthanum to cerium was 7: 3 (cerium: lanthanum) to obtain a mixed solution. To this mixed solution, an aqueous ammonium hydrogen carbonate solution was added to form particles. Next, the precipitate was recovered by solid-liquid separation by centrifugation. Further, the precipitate was calcined in air at 800 ° C. for 1 hour to obtain a lanthanum-containing cerium oxide composition. After mixing the powder of the obtained composition, 1 part by mass of acetic acid (dispersing agent) and 1000 parts by mass of pure water with respect to 100 parts by mass of this powder, the powder was dispersed with an ultrasonic disperser. A dispersion was obtained. Subsequently, the powder in the dispersion was pulverized with a bead mill to prepare a polishing liquid containing 0.5% by mass of abrasive grains containing lanthanum-containing cerium oxide composition and 0.005% by mass of acetic acid.

The Raman spectrum of the abrasive grains was measured based on Raman spectroscopy. As shown by the solid line in FIG. 2, a peak derived from oxygen deficiency of cerium oxide was confirmed in the Raman shift range of 500 to 650 cm ⁻¹ in the Raman spectrum.

(Examples 2 to 4)
A polishing liquid was prepared in the same manner as in Example 1 except that the molar ratio of lanthanum to cerium was changed to the ratio shown in Table 1.

(Example 5)
A polishing liquid was prepared in the same manner as in Example 4 except that lanthanum was changed to gadolinium. Gadolinium nitrate was used as the gadolinium source.

(Example 6)
A polishing liquid was prepared in the same manner as in Example 4 except that lanthanum was changed to samarium. Samarium nitrate was used as the samarium source.

(Example 7)
A polishing liquid was prepared in the same manner as in Example 4 except that lanthanum was changed to yttrium. Yttrium nitrate was used as the yttrium source.

(Comparative Example 1)
A polishing liquid was prepared in the same manner as in Example 1 except that lanthanum nitrate was not used. The Raman spectrum of the abrasive grains was measured based on Raman spectroscopy. As shown by the broken line in FIG. 2, no peak derived from oxygen deficiency of cerium oxide was confirmed in the Raman shift range of 500 to 650 cm ⁻¹ in the Raman spectrum.

<Measurement of abrasive properties>
The pH of the polishing liquid, the average grain size of the abrasive grains, and the zeta potential of the abrasive grains were measured as follows.

(PH)
Measurement temperature: 25 ± 5 ° C
Measuring device: HORIBA, Ltd., model number D-71
Measurement method: Standard buffer (phthalate pH buffer, pH: 4.01 (25 ° C.); neutral phosphate pH buffer, pH: 6.86 (25 ° C.); borate pH buffer, After calibrating three points using pH: 9.18 (25 ° C.), the electrode was placed in a CMP polishing liquid, and the pH after being stabilized for 2 minutes or more was measured with the measuring device. As a result, the pH of all polishing liquids was 4.6.

(Average grain size of abrasive grains)
An appropriate amount of polishing liquid was put into Microtrac MT3300EXII (trade name) manufactured by Microtrack Bell Co., Ltd., and the average particle size of the abrasive grains was measured. The displayed average particle size value was obtained as the average particle size (average secondary particle size, D50). As a result, the average particle diameter of the abrasive grains in all the polishing liquids was 150 nm.

(Zeta potential of abrasive grains)
An appropriate amount of polishing liquid was charged and set in a dense cell unit of Delsa Nano C (device name) manufactured by Beckman Coulter, Inc. The measurement was performed three times at 25 ° C., and the average value of the displayed zeta potential was obtained as the zeta potential. As a result, the zeta potential of the abrasive grains in all the polishing liquids was 55 mV.

<Measurement of polishing rate>
Using each polishing liquid, a circular silicon nitride film having a diameter of 300 mm was polished for 1 minute under the following polishing conditions, and the polishing rate was measured. The polishing rate of the silicon nitride film was the thickness at which the silicon nitride film was removed in 1 minute. When 100 nm or more was removed, it was judged that a good polishing rate was obtained. The results are shown in Table 1.

(CMP polishing conditions)
Polishing device: REFLEXION LK (manufactured by APPLIED MATERIALS)
・ Flow rate of polishing liquid: 250 ml / min
Polishing pad: foamed polyurethane resin with closed cells (Rohm and Haas Japan, model number IC1010)
Polishing pressure: 3.0 psi
-Number of rotations of object to be polished and polishing surface plate: object to be polished / polishing surface plate = 93/87 rpm
・ Polishing time: 1 minute

DESCRIPTION OF SYMBOLS 1 ... 1st insulating material, 2 ... Barrier material, 3 ... 2nd insulating material, 10 ... To-be-polished object.

Claims (13)

A polishing liquid used for polishing silicon nitride,
Containing abrasive grains containing cerium oxide, and a liquid medium,
A polishing liquid, wherein the cerium oxide contains an element having an ionic radius larger than that of cerium. The polishing liquid according to claim 1, wherein the element is divalent or trivalent. 3. The element according to claim 1, wherein the element includes at least one selected from the group consisting of yttrium, lanthanum, praseodymium, neodymium, promethium, samarium, europium, gadolinium, terbium, dysprosium, holmium, erbium, thulium, and calcium. Polishing fluid. The polishing liquid according to any one of claims 1 to 3, wherein the element contains lanthanum. The polishing liquid according to any one of claims 1 to 4, wherein the content of the element is 0.001 to 50 mol% based on the total amount of the abrasive grains. 6. The polishing liquid according to claim 1, wherein the content of the element with respect to the total of cerium and the element is 5 to 50 mol%. The polishing liquid according to any one of claims 1 to 6, wherein the content of the element with respect to the total of cerium and the element is 30 to 40 mol%. The polishing liquid according to any one of claims 1 to 7, wherein the abrasive grains have a positive zeta potential. The abrasive is a compound containing at least one selected from the group consisting of cerium and the elements, nitrate, ammonium nitrate, sulfate, ammonium sulfate, acetate, oxalate, carbonate, chloride, acetyl acetate salt, The polishing liquid according to any one of claims 1 to 8, comprising cerium oxide obtained by using at least one selected from the group consisting of alkoxides and hydroxides. 10. The polishing liquid according to claim 1, wherein the Raman spectrum of the abrasive grains obtained by Raman spectroscopy has a peak derived from oxygen deficiency of cerium oxide. The polishing liquid according to claim 10, wherein the Raman spectrum has the peak in a Raman shift range of 500 to 650 cm ^-1 . The polishing liquid according to any one of claims 1 to 11, further comprising an organic acid component. A polishing method for polishing silicon nitride using the polishing liquid according to any one of claims 1 to 12.

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