JP2022154454A - Polishing composition, polishing method and semiconductor substrate manufacturing method - Google Patents

Abstract

To provide means for suppressing part of a polishing target from being left unpolished and the occurrence of dishing in polishing the target including polycrystalline silicon and silicon nitride.SOLUTION: A polishing composition comprises: abrasive grains; ammonia; and at least one potassium compound selected from a group consisting of potassium hydroxide and a potassium salt. In the polishing composition, a content of the ammonia is 0.002 mass% or more and 0.5 mass% or less to a total mass of the polishing composition, and a content of the potassium compound is 0.004 mass% or more and 0.5 mass% or less to the total mass of the polishing composition.SELECTED DRAWING: None

Description

TECHNICAL FIELD The present invention relates to a polishing composition, a polishing method, and a method for manufacturing a semiconductor substrate.

2. Description of the Related Art In recent years, new microfabrication techniques have been developed as LSIs (Large Scale Integration) have become highly integrated and have high performance. The chemical mechanical polishing (CMP) method is one of them, and is frequently used in the LSI manufacturing process, especially 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. It is a technology that is used.

The CMP has been applied to each step in semiconductor manufacturing, and one aspect thereof is application to a gate formation step in transistor fabrication, for example. Si-containing materials such as silicon, silicon oxide film (silicon oxide), polycrystalline silicon (polysilicon), and silicon nitride (silicon nitride) may be polished during transistor fabrication. There is a need to control the polishing rate of Si-containing materials.

For example, U.S. Pat. No. 5,300,000 discloses a chemistry for polishing polycrystalline silicon films that includes (a) a metal oxide, (b) a quaternary ammonium base; and (c) a fluorosurfactant having a specific structure. A mechanical polishing slurry is disclosed. According to Patent Document 1, by using the slurry, the problem of dishing can be solved and the in-plane uniformity can be improved. Note that dishing refers to a phenomenon in which the central portion of the film is recessed like a dish.

JP 2009-515335 A

Recently, there has been an increasing demand for polishing workpieces containing polysilicon and silicon nitride. For example, polysilicon may be polished to reveal silicon nitride.

However, when such an object to be polished is polished using the technique disclosed in Patent Document 1, it has been found that polysilicon polishing residue may occur on the silicon nitride surface.

SUMMARY OF THE INVENTION Accordingly, it is an object of the present invention to provide means capable of suppressing both polishing residue and dishing in the polishing of a polishing object containing polysilicon and silicon nitride.

In order to solve the above problems, the present inventors have made extensive research. As a result, in the polishing composition containing abrasive grains, ammonia, and a specific potassium compound, the above problems can be solved by controlling the content of ammonia and the content of the potassium compound within specific ranges. and completed the present invention.

That is, the polishing composition according to one aspect of the present invention contains abrasive grains, ammonia, and at least one potassium compound selected from the group consisting of potassium hydroxide and potassium salts. The content of the ammonia is 0.002% by mass or more and 0.5% by mass or less relative to the total mass of the polishing composition, and the content of the potassium compound is relative to the total mass of the polishing composition. is 0.004% by mass or more and 0.5% by mass or less.

According to the present invention, both polishing residue and dishing can be suppressed in polishing an object to be polished including polysilicon and silicon nitride.

FIG. 2 is a diagram showing a confetti-shaped abrasive grain in one embodiment of the present invention. FIG. 2 is a cross-sectional view schematically showing an object to be polished (a silicon wafer having a Poly-Si pattern formed on its surface) used for evaluation of polishing residue and dishing.

TECHNICAL FIELD The present invention relates to a polishing composition containing abrasive grains, ammonia, and at least one potassium compound selected from the group consisting of potassium hydroxide and potassium salts. The content of the ammonia is 0.002% by mass or more and 0.5% by mass or less relative to the total mass of the polishing composition, and the content of the potassium compound is relative to the total mass of the polishing composition. is 0.004% by mass or more and 0.5% by mass or less. According to the polishing composition of the present invention having such a configuration, both polishing residue and dishing can be suppressed in polishing an object to be polished containing polysilicon (polycrystalline silicon) and silicon nitride. More specifically, when a polysilicon film formed so as to cover a silicon nitride film is polished to the surface of the silicon nitride film, polysilicon polishing residue is suppressed from being left on the surface of the silicon nitride film. Dishing of the silicon film can also be suppressed (the amount of dishing can be reduced). Further, according to the polishing composition of the present invention, the polishing rate for polysilicon is sufficiently high, but the polishing rate for silicon nitride remains low. As a result, the effect is obtained that the ratio of the polishing rate of polysilicon to the polishing rate of silicon nitride is sufficiently high (high selectivity).

The mechanism by which the above effects are obtained is considered to be as follows. However, the mechanism described below is merely speculation, and does not limit the scope of the present invention.

Ammonia has the function of extending the inter-bond distance of the Si—Si bond of polysilicon due to the nucleophilic action of the lone pair of electrons present in the nitrogen atoms. Therefore, if the amount of ammonia exceeds a specific amount, the Si--Si bond becomes brittle, and polysilicon is easily polished. Also, for the same reason, polishing residues of polysilicon can be easily removed. On the other hand, if the content of ammonia is high, the above action becomes too large, and dishing tends to occur (the amount of dishing increases).

The potassium compound removes oxides present on the polysilicon surface prior to polishing. If the content of the potassium compound is too small, it will take a long time to remove the oxide film, and the polishing of the polysilicon will tend to be uneven. As a result, this unevenness can become a polishing residue. On the other hand, when the potassium compound content is high, the electrostatic repulsive force between the abrasive grains and the silicon nitride substrate decreases, which increases the silicon nitride polishing rate. can reduce the polishing rate ratio of

When the polishing composition contains a water-soluble polymer, the water-soluble polymer functions as a protective film for polysilicon and can suppress polishing of polysilicon. Therefore, a polishing composition containing a water-soluble polymer tends to cause the problem of polishing residue of polysilicon. The electrical force by which ammonia in the polishing composition interacts with the substrate is greater than the electrical force by which the water-soluble polymer interacts with the substrate. For this reason, ammonia is more likely to be adsorbed to the substrate than the water-soluble polymer, and is thought to exhibit the effect of facilitating the peeling of the water-soluble polymer from the polysilicon. A similar mechanism is also conceivable when the amount of potassium compound in the polishing composition is greater than or equal to a specific amount. That is, since the electrical force with which the potassium compound interacts with the substrate is greater than the electrical force with which the water-soluble polymer interacts with the substrate, the potassium compound is more easily adsorbed to the substrate than the water-soluble polymer. It is thought that the action of facilitating the peeling of the water-soluble polymer from the polysilicon is exhibited. Therefore, when the polishing composition contains ammonia and a specific amount or more of a potassium compound, the scraping of the water-soluble polymer by the abrasive grains is facilitated, and as a result, the polishing of polysilicon is promoted, resulting in a polishing residue. become difficult.

Embodiments of the present invention will be described below. In addition, the present invention is not limited only to the following embodiments.

In this specification, unless otherwise specified, operations and measurements of physical properties are performed under the conditions of room temperature (20° C. or higher and 25° C. or lower)/relative humidity of 40% RH or higher and 50% RH or lower.

In addition, the term "(meth)acryl" as used herein is meant to comprehensively refer to acryl and methacryl. Similarly, "(meth)acrylate" is a generic term for acrylates and methacrylates.

[Object to be polished]
As described above, the polishing composition according to the present invention can suppress both polishing residue and dishing in polishing an object to be polished containing polysilicon and silicon nitride. Further, as described above, when the polishing composition of the present invention is applied to an object to be polished containing polysilicon and silicon nitride, the ratio of the polishing rate of polysilicon to the polishing rate of silicon nitride is sufficiently high (selectivity is high). Therefore, the object to be polished according to the present invention preferably contains polysilicon and silicon nitride. Thus, according to one preferred embodiment of the present invention, the polishing composition is used for polishing objects containing polysilicon and silicon nitride. According to another preferred embodiment of the present invention, the polishing composition is used for selective polishing of polysilicon to silicon nitride.

Objects to be polished according to the present invention may include other materials than polysilicon and silicon nitride. Other materials include, for example, silicon carbonitride (SiCN), silicon oxide, metals, SiGe, and the like.

Examples of polishing objects containing silicon oxide include, for example, a TEOS type silicon oxide (hereinafter also simply referred to as “TEOS-SiO”) film produced using tetraethyl orthosilicate as a precursor, HDP (High Density Plasma), ) film, USG (Undoped Silicate Glass) film, PSG (Phosphorus Silicate Glass) film, BPSG (Boron-Phospho Silicate Glass) film, RTO (Rapid Thermal Oxidation) film, and the like.

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

[Abrasive]
The abrasive grains contained in the polishing composition according to the present invention have the action of mechanically polishing the object to be polished, and improve the polishing rate of the object to be polished by the polishing composition.

In the polishing composition of the present invention, abrasive grains are not particularly limited. Types of abrasive grains include particles made of metal oxides such as silica, alumina, zirconia, and titania. Abrasive grains may be used alone or in combination of two or more. Abrasive grains may be commercially available or synthetic. Among these abrasive grains, silica is preferred, fumed silica and colloidal silica are more preferred, and colloidal silica is even more preferred. Thus, according to one preferred embodiment of the invention, the abrasive grains comprise silica (silica particles). In a more preferred embodiment, the abrasive grain comprises colloidal silica (colloidal silica particles).

Methods for producing colloidal silica include a sodium silicate method, a sol-gel method, and the like, and colloidal silica produced by any of these methods is suitably used as the abrasive grains according to the present embodiment. Among them, colloidal silica produced by a sol-gel method, which can be produced with high purity, is preferable.

The shape of the abrasive grains according to the present invention is not particularly limited, and may be spherical or non-spherical. Specific examples of non-spherical shapes include polygonal prisms such as triangular prisms and square prisms, columnar shapes, bale shapes in which the central portion of a column swells more than the ends, donut shapes in which the central portion of a disc penetrates, and plate shapes. There are various shapes such as a so-called cocoon-shaped shape with a constriction in the center, a so-called association-type spherical shape in which a plurality of particles are integrated, a so-called confetti shape with a plurality of protrusions on the surface, and a rugby ball shape. not. Among them, the shape of the abrasive grains is preferably a confetti shape. When the shape of the abrasive grains is a confetti shape, the polishing rate for polysilicon is improved as compared with the case of using abrasive grains having a smooth surface. As a result, polishing residue can be further suppressed. In this case, since the polishing rate for silicon nitride does not change significantly, the ratio of the polishing rate for polysilicon to the polishing rate for silicon nitride can be further improved (high selectivity). Thus, according to one preferred embodiment of the present invention, the shape of the abrasive grains is a confetti shape.

As used herein, the term “confetti shape” refers to having a plurality of protrusions on the particle surface. In one or a plurality of embodiments, the confetti-shaped abrasive grains have a shape in which two or more grains having a grain size different by five times or more from the grain size of the smallest grain are aggregated or fused together. Preferably, the smaller particles of the two or more particles that differ in particle size by a factor of 5 or more are partially buried in the larger particles.

The average number of protrusions on the surface of the confetti-shaped abrasive grains is preferably 3 or more per grain, more preferably 5 or more.

The projections referred to here have a height and width sufficiently smaller than the particle diameter of the confetti-shaped abrasive grains. Furthermore, the length of the portion shown as curve AB passing through points A and B in FIG. It is a protrusion that does not exceed 1/4 of the circumference length of the largest circle inscribed in the contour of the projection of the outer shape of the abrasive grain. The width of the protrusion means the width at the base of the protrusion, and is expressed as the distance between points A and B in FIG. In addition, the height of the protrusion refers to the distance between the base of the protrusion and the part of the protrusion farthest from the base, and in FIG. It is a thing.

The average value (height of protrusion/width of protrusion) obtained by dividing the height of protrusions on the surface of the confetti-shaped abrasive grains by the width at the base of the same protrusion is 0.17 or more. is preferably 0.20 or more, and still more preferably 0.22 or more. As the average of this value increases, the polishing rate with the polishing composition (particularly, the polishing rate of polysilicon) increases due to the relatively sharp shape of the protrusions.

The average height of protrusions on the surface of the confetti-shaped abrasive grains is preferably 3.5 nm or more, more preferably 4.0 nm or more. As the average height of the protrusions increases, the polishing rate (particularly, the polishing rate of polysilicon) with the polishing composition increases.

The shape (outer shape) of the abrasive grains can be confirmed with a scanning electron microscope. For "average height of protrusions" and "average of (height of protrusions/width of protrusions)", values measured by the method described in Examples are employed.

Konpeito-shaped abrasive grains can be easily produced by those skilled in the art by appropriately referring to known techniques. A preferred embodiment of the method for producing confetti-shaped abrasive grains will be briefly described below. In the following, the production method will be described with reference to confetti-shaped colloidal silica, which is an example of confetti-shaped silica particles. In addition to the confetti-shaped colloidal silica, the confetti-shaped silica particles include fumed silica in the shape of a confetti. From the viewpoint of suppressing the occurrence of polishing scratches, confetti-shaped colloidal silica is preferable.

First, a slurry containing colloidal silica particles is obtained by continuously adding alkoxysilane to a mixed solution of methanol and water to which ammonia water has been added as a catalyst and hydrolyzing the solution. The resulting slurry is heated to distill off methanol and ammonia. After that, an organic alkali is added as a catalyst to the slurry, and then alkoxysilane is added again continuously at a temperature of 70° C. or higher for hydrolysis to form a plurality of protrusions on the surface of the colloidal silica particles. Specific examples of organic alkalis that can be used here include amine compounds such as triethanolamine and quaternary ammonium compounds such as tetramethylammonium hydroxide. According to this method, it is possible to easily obtain silica particles having a plurality of protrusions on the surface and having a metal impurity content of 1 ppm by mass or less.

Incidentally, a general method for producing colloidal silica by hydrolysis of alkoxysilane is described, for example, in Sumio Sakuhana's "Sol-Gel Method Science" (published by Agne Shofusha), pp. 154-156. there is Further, in JP-A-11-60232, methyl silicate or a mixture of methyl silicate and methanol is dropped into a mixed solvent consisting of water, methanol and ammonia or ammonia and an ammonium salt to dissolve methyl silicate and water. There is a disclosure of a method for producing cocoon-shaped colloidal silica that is reacted. Japanese Patent Application Laid-Open No. 2001-48520 discloses a method for producing elongated colloidal silica, in which alkylsilicate is hydrolyzed with an acid catalyst, and then an alkali catalyst is added and heated to promote polymerization of silicic acid and particle growth. There is disclosure. Japanese Patent Application Laid-Open No. 2007-153732 describes a method for producing colloidal silica having a large number of small projections using a specific type of hydrolysis catalyst in a specific amount and using an easily hydrolyzable organosilicate as a raw material. there is Japanese Patent Application Laid-Open No. 2002-338232 describes a method for producing secondary agglomerated colloidal silica by adding a flocculant to monodisperse colloidal silica and causing secondary agglomeration into a spherical shape. Japanese Patent Laying-Open No. 07-118008 and International Publication No. 2007/018069 describe adding a calcium salt or a magnesium salt to active silicic acid obtained from sodium silicate in order to obtain colloidal silica having an irregular shape such as an elongated shape. There is disclosure. Japanese Patent Application Laid-Open No. 2001-11433 discloses that beaded colloidal silica is obtained by adding a calcium salt to active silicic acid obtained from sodium silicate. Japanese Patent Application Laid-Open No. 2008-169102 describes that colloidal silica having a large number of small protrusions like confetti can be obtained by generating and growing fine particles on the surface of seed particles. The confetti-shaped silica particles according to the present invention can also be produced by using the methods described in these documents alone or in combination.

The abrasive grains according to the present invention preferably have a lower silanol group density (a smaller number of silanol groups per unit surface area). A low silanol group density reduces the amount of bound water present between the abrasive grain and the polysilicon surface. As a result, the abrasive grains are more likely to come into contact with the polysilicon surface, and the polysilicon polishing rate can be further improved. As a result, polishing residue can be further suppressed. In this case, since the polishing rate for silicon nitride does not change significantly, the ratio of the polishing rate for polysilicon to the polishing rate for silicon nitride can be further improved (high selectivity). Specifically, the silanol group density of the abrasive grains is preferably 0/nm ² or more and 4/nm ² or less. Therefore, according to a preferred embodiment of the present invention, the abrasive grains have a silanol group density of 0/nm ² or more and 4/nm ² or less. Since the lower the silanol group density is, the more preferable it is, in order of 3.8/nm ² or less, 3.7/nm ² or less, 3.6/nm ² or less, and 3.5/nm ² or less. Since the lower limit of the silanol group density is more preferable, it is 0/nm ² , but when the abrasive grains contain silica (silica particles), a certain amount of silanol groups may be contained. Therefore, the lower limit of the silanol group density may be 0.5/nm ² or more, 1.0/nm ² or more, 1.5/nm ² or more, or 2.0/nm ² or more. Therefore, the silanol group density is preferably 0.5/nm ² or more and 3.8/nm ² or less, more preferably 1.0/nm ² or more and 3.7/nm ² or less. more preferably 1.5/nm ² or more and 3.6/nm ² or less, and particularly preferably 2.0/nm ² or more and 3.5/nm ² or less. The silanol group density can be reduced by performing a heat treatment such as firing in the abrasive grain manufacturing method. In this specification, the value measured by the method described in Examples is adopted as the silanol group density.

Furthermore, the abrasive grains may be surface-modified as long as the silanol group density satisfies the above range. Among them, colloidal silica in which an organic acid is immobilized is particularly preferred. The immobilization of the organic acid on the surface of the colloidal silica contained in the polishing composition is carried out, for example, by chemically bonding the functional groups of the organic acid to the surface of the colloidal silica. Mere coexistence of colloidal silica and an organic acid does not achieve immobilization of the organic acid on the colloidal silica. If sulfonic acid, which is a kind of organic acid, is immobilized on colloidal silica, for example, "Sulfonic acid-functionalized silica through quantitative oxidation of thiol groups", Chem. Commun. 246-247 (2003). Specifically, sulfonic acid is immobilized on the surface 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. colloidal silica can be obtained.あるいは、カルボン酸をコロイダルシリカに固定化するのであれば、例えば、“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, colloidal silica having a carboxylic acid immobilized on the surface can be obtained by coupling a silane coupling agent containing a photoreactive 2-nitrobenzyl ester to colloidal silica and then irradiating with light. .

The abrasive grains according to the present invention preferably have a higher true density. When the true density is high, the mechanical force can be efficiently transmitted to the wafer, and as a result, polishing residue can be further suppressed. In this case, since the polishing rate for silicon nitride does not change significantly, the ratio of the polishing rate for polysilicon to the polishing rate for silicon nitride can be further improved (high selectivity). Specifically, the true density is preferably 1.9 g/cm ³ or more. Therefore, according to a preferred embodiment of the present invention, the abrasive grains have a true density of 1.9 g/cm ³ or more. Since the higher the true density is, the more preferable it is, 2.0 g/cm ³ or more is more preferable, and 2.05 g/cm ³ or more is even more preferable. Although the upper limit is not particularly limited, it is usually 3.0 g/cm ³ or less, preferably 2.5 g/cm ³ or less, more preferably 2.2 g/cm ³ or less. Therefore, the numerical range of the true density is preferably 1.9 g/cm ³ or more and 3.0 g/cm ³ or less, more preferably 2.0 g/cm ³ or more and 2.5 g/cm ³ or less. It is preferably 2.05 g/cm ³ or more and 2.2 g/cm ³ or less. The true density can be controlled by reducing the porosity by adjusting the reaction temperature and reaction time in the abrasive grain manufacturing method (sol-gel method). In this specification, the true density adopts the value measured by the method described in Examples.

The size of abrasive grains is not particularly limited. For example, the average primary particle size of the abrasive grains is preferably 10 nm or more, more preferably 15 nm or more, and even more preferably 20 nm or more. As the average primary particle size of the abrasive grains increases, the polishing rate of the object to be polished with the polishing composition (particularly, the polishing rate of polysilicon) increases. The average primary particle size of the abrasive grains is preferably 300 nm or less, more preferably 100 nm or less, even more preferably 50 nm or less, and particularly preferably 30 nm or less. As the average primary particle size of the abrasive grains decreases, it becomes easier to obtain a surface with fewer defects by polishing with the polishing composition. That is, the average primary particle diameter of the abrasive grains is preferably 10 nm or more and 300 nm or less, more preferably 15 nm or more and 100 nm or less, further preferably 20 nm or more and 50 nm or less, and 20 nm or more and 30 nm or less. is particularly preferred. The average primary particle size 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, assuming that the shape of the abrasive grains is a true sphere. In this specification, the value measured by the method described in the Examples is adopted as the average primary particle size of the abrasive grains.

Also, the average secondary particle size of the abrasive grains is preferably 20 nm or more, more preferably 30 nm or more, and even more preferably 35 nm or more. As the average secondary particle diameter of the abrasive grains increases, the resistance during polishing decreases and stable polishing becomes possible. The average secondary particle size of the abrasive grains is preferably 400 nm or less, more preferably 250 nm or less, even more preferably 100 nm or less, and particularly preferably 70 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 increases, and the polishing speed (especially the polishing speed of polysilicon) improves further. do. That is, the average secondary particle diameter of the abrasive grains is preferably 20 nm or more and 400 nm or less, more preferably 30 nm or more and 250 nm or less, further preferably 35 nm or more and 100 nm or less, and 35 nm or more and 70 nm or less. is particularly preferred. When the shape of the abrasive grains is confetti-shaped, the secondary particles referred to herein refer to particles formed by association of confetti-shaped abrasive grains in the polishing composition. The average secondary particle size of abrasive grains can be measured, for example, by a dynamic light scattering method. In this specification, the value measured by the method described in Examples is adopted as the average secondary particle size of abrasive grains.

In the polishing composition according to the present invention, the content (concentration) of abrasive grains is not particularly limited. It is more preferably at least 0.5% by mass, even more preferably at least 0.5% by mass, and particularly preferably more than 0.5% by mass. The upper limit of the content of abrasive grains is preferably 20% by mass or less, more preferably 10% by mass or less, and 5% by mass or less, relative to the total mass of the polishing composition. is more preferred, and less than 5% by mass is particularly preferred. That is, the content of abrasive grains is preferably 0.1% by mass or more and 20% by mass or less, more preferably 0.2% by mass or more and 10% by mass or less, relative to the total mass of the polishing composition. It is more preferably 5% by mass or less, and particularly preferably more than 0.5% by mass and less than 5% by mass. Within such a range, it is possible to further improve the balance between the polishing rate of polysilicon and the polishing rate of silicon nitride while suppressing costs. Therefore, the ratio (selection ratio) of the polishing rate of polysilicon to the polishing rate of silicon nitride can be further improved. In addition, when the polishing composition contains two or more kinds of abrasive grains, the content of the abrasive grains means the total amount thereof.

[ammonia]
Ammonia contained in the polishing composition according to the present invention has a function of promoting polishing of polysilicon. This is probably because the nucleophilic action of the unshared electron pair of ammonia weakens the Si--Si bonds of polysilicon, facilitating the progress of polishing with abrasive grains.

In the polishing composition according to the present invention, the content (concentration) of ammonia is 0.002% by mass or more and 0.5% by mass or less with respect to the total mass of the polishing composition. If the content of ammonia is less than 0.002% by mass, the action of promoting polishing of polysilicon is not sufficiently exhibited. As a result, there is a possibility that the problem of the present invention of suppressing the polishing residue may not be solved. On the other hand, if the content of ammonia exceeds 0.5% by mass, the effect of promoting the polishing of polysilicon becomes too large. As a result, there is a risk that the problem of the present invention, which is to suppress dishing, will not be solved. From the same viewpoint, the ammonia content is preferably 0.004% by mass or more and 0.2% by mass or less, more preferably 0.008% by mass or more and 0.14% by mass or less, and still more preferably 0 0.01% by mass or more and 0.1% by mass or less, and particularly preferably 0.014% by mass or more and 0.05% by mass or less.

[Potassium compound]
The polishing composition according to the present invention contains at least one potassium compound selected from the group consisting of potassium hydroxide and potassium salts. The potassium compound in the polishing composition has the effect of removing the oxide film present on the polysilicon surface before polishing.

The potassium salt is not particularly limited, and inorganic salts of potassium and organic salts of potassium can be appropriately selected. Inorganic salts of potassium include potassium chloride, potassium bromide, potassium iodide, potassium carbonate, potassium hydrogen carbonate, potassium nitrate, potassium sulfate, potassium hydrogen sulfate, potassium perchlorate, potassium dihydrogen phosphate, and dipotassium hydrogen phosphate. , potassium phosphate, potassium pyrophosphate, potassium etidronate, and the like. Organic salts of potassium include potassium acetate, potassium propionate, potassium citrate and the like.

Among potassium compounds, potassium hydroxide, potassium carbonate, potassium hydrogen carbonate, dipotassium hydrogen phosphate, and potassium phosphate are preferable, and potassium hydroxide, potassium carbonate, and potassium hydrogen carbonate are more preferable, from the viewpoint of improving the selectivity.

These potassium compounds may be used singly or in combination of two or more.

In the polishing composition according to the present invention, the content (concentration) of the potassium compound is 0.004% by mass or more and 0.5% by mass or less with respect to the total mass of the polishing composition. If the content of the potassium compound is less than 0.004% by mass, it takes a long time to remove the oxide film, which tends to cause uneven polishing of the polysilicon. As a result, this unevenness becomes a polishing residue, and there is a possibility that the problem of the present invention, which is to suppress the polishing residue, cannot be solved. On the other hand, when the content of the potassium compound exceeds 0.5% by mass, the electrostatic repulsive force between the abrasive grains and the silicon nitride substrate is reduced, resulting in an increase in the polishing rate of silicon nitride, resulting in an increase in the silicon nitride polishing rate. The ratio of the polishing rate of polysilicon to the polishing rate of polysilicon (selection ratio) may decrease. From the same viewpoint, the content of the potassium compound is preferably 0.005% by mass or more and 0.4% by mass or less, more preferably 0.025% by mass or more and 0.3% by mass or less, and still more preferably It is 0.1 mass % or more and 0.2 mass % or less. In addition, when polishing composition contains 2 or more types of potassium compounds, content of a potassium compound intends these total amounts.

The ratio of the potassium compound content to the ammonia content (potassium compound/ammonia (mass ratio)) in the polishing composition according to the present invention is preferably 0.1 or more and 100 or less, and 0.3 or more and 70 or less. It is more preferably 1 or more and 30 or less, and particularly preferably 10 or more and 20 or less. When the ratio is within the above range, a good balance is achieved between the enhancement of the polishing rate of polysilicon and the reduction of the polishing residue. Therefore, according to a preferred embodiment of the present invention, the ratio of the potassium compound content to the ammonia content (potassium compound/ammonia (mass ratio)) is 0.1 or more and 100 or less.

[Water-soluble polymer]
The polishing composition of the present invention may contain a water-soluble polymer, if desired. The water-soluble polymer adheres to the surface of the object to be polished and protects the surface of the object to be polished from uneven or excessive etching. This can improve the surface quality after polishing. Therefore, according to one preferred embodiment of the present invention, the polishing composition further comprises a water-soluble polymer.

As used herein, “water-soluble” means that the solubility in water (25° C.) is 1 g/100 mL or more, and “polymer” means that the weight average molecular weight is 1,000 or more (common ) refers to polymers. The weight average molecular weight can be measured by gel permeation chromatography (GPC), and specifically, a value measured by the following measuring method is adopted.

(GPC measurement conditions)
Measuring device: HLC-8320GPC (Tosoh)
Sample concentration: 0.01% by mass
Column: TSKgel GMPWXL
Detector: Differential refractometer Eluent: 10 mM lithium bromide/N,N-dimethylformamide Flow rate: 1 mL/min Measurement temperature: 40°C
Molecular weight conversion: Polyethylene glycol conversion Sample injection volume: 200 μL.

The molecular weight calculated from the molecular formula is adopted as the weight-average molecular weight only when it cannot be measured by GPC.

Although the water-soluble polymer according to the present invention is not particularly limited, it preferably has a nitrogen atom, more preferably an amide group, and even more preferably a lactam structure (cyclic amide structure). The use of such a water-soluble polymer facilitates the formation of a protective film on the surface of the object to be polished. Thus, according to one preferred embodiment of the invention, the water-soluble polymer has nitrogen atoms. According to a more preferred embodiment of the invention, the water-soluble polymer has amide groups. According to a further preferred embodiment of the invention, the water-soluble polymer has a lactam structure.

When the water-soluble polymer has a nitrogen atom (preferably an amide group, more preferably a lactam structure), the water-soluble polymer is derived from a monomer having a nitrogen atom (preferably an amide group, more preferably a lactam structure). Structural units can be contained in a ratio of more than 50% by mass based on the total structural units. The content of structural units derived from a monomer having a nitrogen atom (preferably an amide group, more preferably a lactam structure) in the water-soluble polymer is preferably 70% by mass or more, more preferably 80% by mass or more, and further Preferably, it is 90% by mass or more. Particularly preferred is 100% by mass, ie, a homopolymer of a monomer having a nitrogen atom (preferably an amide group, more preferably a lactam structure).

Monomers having a nitrogen atom (preferably an amide group, more preferably a lactam structure) include N-acryloylmorpholine, N-vinylpiperidine, N-vinylimidazole, N-vinylcarbazole, (meth)acrylamide; N-methyl (meth ) acrylamide, N-ethyl (meth)acrylamide, N-isopropyl (meth)acrylamide, Nn-butyl (meth)acrylamide, N-sec-butyl (meth)acrylamide, N-tert-butyl (meth)acrylamide, etc. N-alkyl (meth)acrylamide; N,N-dimethyl (meth)acrylamide, N,N-diethyl (meth)acrylamide, N,N-dipropyl (meth)acrylamide, N,N-diisopropyl (meth)acrylamide, N, N-di(n-butyl)(meth)acrylamide, N,N-dialkyl(meth)acrylamide such as N,N-di(tert-butyl)(meth)acrylamide; N-hydroxymethyl(meth)acrylamide, N- N-hydroxyalkyl (meth)acrylamide such as hydroxyethyl (meth)acrylamide; N-vinylcarboxylic acid amide such as N-vinylacetamide; N-(2-hydroxyethyl) (meth)acrylamide, N-(2-hydroxypropyl) ) (meth)acrylamide, N-(1-hydroxypropyl)(meth)acrylamide, N-(3-hydroxypropyl)(meth)acrylamide, N-(2-hydroxybutyl)(meth)acrylamide, N-(3- hydroxybutyl) (meth)acrylamide, N-hydroxyalkyl (meth)acrylamide such as N-(4-hydroxybutyl) (meth)acrylamide; N-methoxymethyl (meth)acrylamide, N-methoxyethyl (meth)acrylamide, N - N-alkoxyalkyl (meth)acrylamides such as butoxymethyl (meth)acrylamide; N,N-dimethylaminopropyl (meth)acrylamide, N-vinyl-2-pyrrolidone, N-methylvinylpyrrolidone, N-vinyl-2- caprolactam and the like. Among them, N-vinyl-2-pyrrolidone and N-acryloylmorpholine are preferable, and N-vinyl-2-pyrrolidone is more preferable, in consideration of the balance between protecting the surface of the object to be polished, improving the polishing speed of polysilicon and reducing polishing residue. .

These nitrogen atom-containing monomers (preferably amide groups, more preferably lactam structures) may be used singly or in combination of two or more.

A monomer having a nitrogen atom (preferably an amide group, more preferably a lactam structure) may optionally contain a structural unit derived from another copolymerizable monomer copolymerizable with the monomer.

Examples of other copolymerizable monomers include carboxy group-containing monomers such as acrylic acid, methacrylic acid, carboxyethyl acrylate, carboxypentyl acrylate, itaconic acid, maleic acid, fumaric acid, crotonic acid, and isocrotonic acid; maleic anhydride, Acid anhydride group-containing monomers such as itaconic anhydride; methyl (meth) acrylate, ethyl (meth) acrylate, n-butyl (meth) acrylate, sec-butyl (meth) acrylate, t-butyl (meth) acrylate, n- Alkyl (meth)acrylate monomers such as propyl (meth)acrylate, n-hexyl (meth)acrylate, 2-ethylhexyl (meth)acrylate; cyclohexyl (meth)acrylate, cyclohexyloxyalkyl (meth)acrylate, t-butylcyclohexyl (Meth)acrylate monomers having an alicyclic structure such as oxyethyl (meth)acrylate, isobornyl (meth)acrylate, dicyclopentanyl (meth)acrylate; 2-methoxyethyl (meth)acrylate, 2-ethoxyethyl (meth) (Meth)acrylate monomers containing an alkoxy group or an oxyalkylene group such as acrylates, methoxydiethylene glycol (meth)acrylate, ethoxydiethylene glycol (meth)acrylate, methoxypolyethylene glycol (meth)acrylate, polypropylene glycol mono(meth)acrylate; acrylonitrile, cyano group-containing monomers such as methacrylonitrile; olefins such as ethylene, propylene, butadiene, isoprene and isobutylene; dialkyl itaconic acid, dialkyl fumaric acid, vinyl alcohol, allyl alcohol, methyl vinyl ketone, allyltrimethylammonium chloride, dimethyl allyl vinyl ketone, and the like.

These other copolymerizable monomers can be used singly or in combination of two or more.

Preferred specific examples of water-soluble polymers having nitrogen atoms (preferably amide groups, more preferably lactam structures) include poly-N-vinylpyrrolidone (PVP) and polyvinylpyrrolidone-polyvinylalcohol copolymers. Among them, poly N-vinylpyrrolidone (PVP) and polyvinylpyrrolidone-polyvinyl alcohol copolymer are preferable in consideration of the balance between protecting the surface of the object to be polished, improving the polishing speed of polysilicon and reducing polishing residue, and polyN-vinylpyrrolidone (PVP) ) is more preferred.

The lower limit of the weight-average molecular weight (Mw) of the water-soluble polymer is not particularly limited, but is preferably 1000 or more, more preferably more than 1000, still more preferably 1500 or more, even more preferably more than 1500, particularly preferably 5000 or more, Greater than 5000 is most preferred. The upper limit of the weight average molecular weight of the water-soluble polymer is not particularly limited, but is preferably 100,000 or less, more preferably less than 100,000, still more preferably 90,000 or less, even more preferably less than 90,000, particularly preferably 80,000 or less, and less than 80,000. It is particularly more preferred, and 55,000 or less is most preferred. That is, the weight average molecular weight of the water-soluble polymer is preferably 1000 or more and 100000 or less, more preferably more than 1000 and less than 100000, more preferably 1500 or more and 90000 or less, even more preferably 1500 or more and less than 90000, and particularly 5000 or more and 80000 or less. More than 5,000 and less than 80,000 are particularly preferable, and more than 5,000 and 55,000 or less are most preferable. A water-soluble polymer having a weight-average molecular weight within the above range is excellent in solubility and can further improve the ratio (selection ratio) of the polishing rate of polysilicon to the polishing rate of silicon nitride. Moreover, if the water-soluble polymer has a weight-average molecular weight within the above range, the polishing rate of polysilicon can be further improved.

The weight average molecular weight of the water-soluble polymer can be measured by gel permeation chromatography (GPC).

The content (concentration) of the water-soluble polymer is not particularly limited, but is preferably 0.0001% by mass or more, more preferably 0.0005% by mass or more, relative to the total mass of the polishing composition. Preferably, it is more preferably 0.001% by mass or more. The upper limit of the content of the water-soluble polymer is preferably 10% by mass or less, more preferably 1% by mass or less, and 0.1% by mass, relative to the total mass of the polishing composition. More preferably: That is, the content of the water-soluble polymer is preferably 0.0001% by mass or more and 10% by mass or less, more preferably 0.0005% by mass or more and 1% by mass or less, relative to the total mass of the polishing composition. 001% by mass or more and 0.1% by mass or less is more preferable. Within such a content range, the ratio (selection ratio) of the polishing rate of polysilicon to the polishing rate of silicon nitride (selectivity) can be further improved while suppressing costs. Further, within such a content range, the polishing rate of polysilicon can be further improved. In addition, when polishing composition contains 2 or more types of water-soluble polymers, content of water-soluble polymers intends these total amounts.

[Dispersion medium]
The polishing composition of the present invention preferably 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 preferable as the dispersion medium. That is, according to a more preferred form of the invention, the dispersion medium contains water. According to a further preferred form of the invention, the dispersion medium consists essentially of water. In addition, the above-mentioned "substantially" means that a dispersion medium other than water can be included as long as the objective effect of the present invention can be achieved, and more specifically, preferably 90% by mass or more. Consisting of 100% by mass or less of water and 0% by mass to 10% by mass of a dispersion medium other than water, more preferably 99% by mass to 100% by mass of water and 0% by mass to 1% by mass of water other than water and a dispersion medium of As described above, more preferably, the dispersion medium consists only of water.

From the viewpoint of not inhibiting the action of the components contained in the polishing composition, the dispersion medium is preferably water containing as few impurities as possible. It is more preferable to use pure water, ultrapure water, or distilled water from which foreign matter has been removed through a filter.

[pH]
The pH of the polishing composition of the present invention is not particularly limited, but is preferably 9.0 or higher, more preferably 9.0 or higher and 13.0 or lower, and further preferably 9.5 or higher and 12.0 or lower. 10.0 or more and 11.5 or less are particularly preferable, and 10.5 or more and 11.5 or less are most preferable. When the pH is 9.0 or more, the polishing rate of polysilicon can be improved, and when the pH is 13.0 or less, the polishing rate of silicon nitride can be kept low. If the pH is within the above range, the ratio (selection ratio) of the polishing rate of polysilicon to the polishing rate of silicon nitride can be sufficiently increased. For the pH of the polishing composition, the value measured by the method described in Examples below is adopted.

In the polishing composition of the present invention, the ammonia and potassium compounds also serve as pH adjusters. If it is difficult to obtain the desired pH with these components alone, a pH adjuster may be added to adjust the pH within a range that does not impair the effects of the present invention.

The pH adjuster may be any acid or base other than ammonia and potassium compounds, and may be any inorganic or organic compound. The pH adjusters may be used alone or in combination of two or more.

Specific examples of acids used as pH adjusters include inorganic acids such as sulfuric acid, nitric acid, boric acid, carbonic acid, hypophosphorous acid, phosphorous acid, and phosphoric acid; 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-ethyl carboxylic acids such as hexanoic acid, benzoic acid, glycolic acid, salicylic acid, glyceric acid, oxalic acid, malonic acid, succinic acid, glutaric acid, adipic acid, pimelic acid, maleic acid, phthalic acid, malic acid, tartaric acid, citric acid and lactic acid Acids and organic acids such as organic sulfuric acids such as methanesulfonic acid, ethanesulfonic acid and isethionic acid.

Specific examples of bases used as pH adjusters include hydroxides or salts of group 1 elements other than potassium, hydroxides or salts of group 2 elements, quaternary ammonium hydroxides or salts thereof, and the like. is mentioned. Specific examples of salts include carbonates, hydrogen carbonates, sulfates, acetates, and the like.

The amount of the pH adjuster to be added is not particularly limited, and may be appropriately adjusted so that the polishing composition has a desired pH.

[Electrical conductivity (EC) of polishing composition]
The lower limit of the electrical conductivity (EC) of the polishing composition of the invention is preferably 0.01 mS/cm or more, more preferably 0.1 mS/cm or more. The upper limit of the electrical conductivity (EC) of the polishing composition of the invention is preferably 10 mS/cm or less, more preferably 3 mS/cm or less. Within the range described above, the repulsion between abrasive grains can be appropriately adjusted to ensure a sufficient polishing rate and stability (particularly for polysilicon). The electrical conductivity of the polishing composition can be adjusted by adjusting the amount of ammonia, the type and amount of the potassium compound, the type and amount of the pH adjuster, and the like. For the electrical conductivity of the polishing composition, the value measured by the method described in Examples below is adopted.

[Other ingredients]
The polishing composition of the present invention contains known additives that can be used in polishing compositions, such as surfactants, complexing agents, preservatives, and antifungal agents, as long as the effects of the present invention are not significantly hindered. may be further included as necessary.

The polishing composition according to the present invention preferably does not substantially contain an oxidizing agent. If the polishing composition contains an oxidizing agent, the surface of the object to be polished (for example, polysilicon) may be oxidized to form an oxide film, resulting in a longer polishing time. Specific examples of the oxidizing agent here include hydrogen peroxide (H ₂ O ₂ ), sodium persulfate, ammonium persulfate, sodium dichloroisocyanurate and the like. In addition, the fact that the polishing composition does not substantially contain an oxidizing agent means that it does not contain an oxidizing agent at least intentionally. Therefore, a polishing composition that inevitably contains a small amount of oxidizing agent due to its raw material, manufacturing method, or the like is included in the concept of a polishing composition that does not substantially contain an oxidizing agent. For example, the concentration of the oxidizing agent in the polishing composition is preferably 0.001% by mass or less, more preferably 0.0001% by mass or less, and still more preferably 0.00001% by mass or less (lower limit: 0% by mass). be.

[Method for producing polishing composition]
The method for producing the polishing composition of the present invention is not particularly limited. It can be obtained by stirring and mixing in The details of each component are as described above. In general, ammonia is mixed with each component in the form of aqueous ammonia, and the potassium compound is in the form of aqueous potassium solution. Accordingly, the present invention provides a method for producing a polishing composition, comprising the step of mixing abrasive grains, ammonia water and an aqueous potassium compound solution.

The temperature at which each component is mixed is not particularly limited, but is preferably 10° C. or higher and 40° C. or lower, and may be heated to increase the dissolution rate. Also, the mixing time is not particularly limited as long as uniform mixing can be achieved.

[Polishing Method and Semiconductor Substrate Manufacturing Method]
As described above, the polishing composition of the present invention is suitably used for polishing objects containing polysilicon and silicon nitride. Accordingly, the present invention provides a polishing method for polishing an object to be polished containing polysilicon and silicon nitride using the polishing composition.

Furthermore, the present invention provides a method for manufacturing a semiconductor substrate, which includes the above polishing method. Furthermore, the present invention provides a semiconductor substrate obtained by the method for manufacturing the semiconductor substrate.

As a polishing apparatus, a holder that holds a substrate having an object to be polished and a motor that can change the number of rotations are attached, and a polishing surface plate to which a polishing pad (abrasive cloth) can be attached is generally used. Polishing equipment can be used.

As the polishing pad, general non-woven fabric, polyurethane, porous fluororesin, and the like can be used without particular limitation. It is preferable that the polishing pad is grooved so that the polishing liquid is accumulated.

Regarding the polishing conditions, for example, the rotational 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 (polishing pressure) applied to the substrate having the object to be polished 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 also not particularly limited, and, for example, a method of continuously supplying it using a pump or the like is adopted. The amount supplied is not limited, but it is preferred that the surface of the polishing pad is always covered with the polishing composition of the present invention.

After polishing, the substrate is washed in running water, water droplets adhering to the substrate are removed by a spin dryer or the like, and the substrate is dried to obtain a substrate having a layer containing a metal.

The polishing composition of the present invention may be of a one-component type or a multi-component type such as a two-component type. Also, the polishing composition of the present invention may be prepared by diluting a stock solution of the polishing composition with a diluent such as water, for example, 10-fold or more.

(polishing speed)
In an embodiment of the present invention, the polysilicon polishing rate is preferably 2000 Å/min or more, more preferably 3000 Å/min or more, even more preferably 3100 Å/min or more, and 3200 Å/min or more. It is particularly preferred to have Further, in the embodiment of the present invention, the polishing rate of silicon nitride is preferably 100 Å/min or less, more preferably 80 Å/min or less, further preferably 50 Å/min or less, further preferably 20 Å/min. The following are particularly preferred.
(Selection ratio)
When an object to be polished containing polysilicon and silicon nitride is polished using the polishing composition of the present invention, the ratio of the polishing rate of polysilicon to the high polishing rate of silicon nitride (high selectivity of polysilicon to silicon nitride) is achievable. Specifically, in the embodiment of the present invention, the ratio (selection ratio) of the polishing rate of polysilicon to the polishing rate of silicon nitride is preferably 10 or more, more preferably 20 or more, and 30 or more. more preferably 70 or more, particularly preferably 100 or more, and most preferably 150 or more. The ratio (selection ratio) of the polishing rate of polysilicon to the polishing rate of silicon nitride is preferably as high as possible.

In this specification, values calculated by the method described in Examples are used as the polishing rates for polysilicon and silicon nitride. In the present specification, the ratio (selection ratio) of the polishing rate of polysilicon to the polishing rate of silicon nitride is a value calculated by the method described in Examples.

The present invention will be described in more detail with 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 "% by mass" and "parts by mass" respectively.

<Particle size of abrasive grains>
The average primary particle size of the abrasive grains was calculated from the specific surface area of the abrasive grains measured by the BET method using "Flow Sorb II 2300" manufactured by Micromeritex and the density of the abrasive grains. The average secondary particle size of the abrasive grains was measured using a dynamic light scattering type particle size/particle size distribution apparatus UPA-UT151 manufactured by Nikkiso Co., Ltd.

<Shape of abrasive grains>
The shape (outer shape) of the abrasive grains was observed using a scanning electron microscope (SEM) SU8000 (manufactured by Hitachi High-Tech Co., Ltd.) from an image (magnification: 500k times). The height of the protrusion and the width of the protrusion were measured. Then, by calculating the average value of the heights of the protrusions, the "average height of the protrusions" was obtained. Also, the height of the protrusion/the width of the protrusion was determined for each protrusion, and the average value of these values was calculated.

<Silanol group density>
The silanol group density per unit surface area of the abrasive grain (unit: number/nm ² ) was calculated by the following method after each parameter was measured or calculated by the following measurement method or calculation method.

More specifically, C in the following formula is the total mass of the abrasive grains, and S in the following formula is the BET specific surface area of the abrasive grains. More specifically, first, 1.50 g of abrasive grains as a solid content are collected in a 200 ml beaker, 100 ml of pure water is added to make a slurry, and then 30 g of sodium chloride is added and dissolved. Next, after adding 1N hydrochloric acid to adjust the pH of the slurry to about 3.0 to 3.5, pure water is added until the slurry becomes 150 ml. For this slurry, using an automatic titrator (manufactured by Hiranuma Sangyo Co., Ltd., COM-1700), the pH is adjusted to 4.0 using a 0.1N sodium hydroxide aqueous solution at 25 ° C., and further , the volume V [L] of 0.1N aqueous sodium hydroxide solution required to raise the pH from 4.0 to 9.0 by pH titration. The average silanol group density (number/nm ² ) can be calculated by the following formula.

In the above formula,
ρ represents the average silanol group density (number/nm ² );
c represents the concentration (mol/L) of the aqueous sodium hydroxide solution used for titration;
V is the volume of sodium hydroxide solution required to raise the pH from 4.0 to 9.0 (L
) represents;
_NA represents the Avogadro constant (number/mol);
C represents the total mass (solid content) of the abrasive grains (g);
S represents the weighted average value (nm ² /g) of the BET specific surface area of the abrasive grains.

<True density of abrasive grains (g/cm ³ )>
The true density (g/cm ³ ) of abrasive grains is measured by the following method. Specifically, first, an aqueous abrasive dispersion is placed in a crucible so that the solid content (abrasive grains) is about 15 g, and a commercially available hot plate is used to evaporate water at about 200°C. Furthermore, in order to remove moisture remaining in the voids of the abrasive grains, heat treatment is performed at 300°C for 1 hour in an electric furnace (manufactured by Advantech Toyo Co., Ltd., firing furnace), and the dry abrasive grains after treatment are ground in a mortar. crush. Next, 10 g of the dry abrasive grains prepared above were placed in a 100 ml pycnometer (Wa (g)) whose weight was measured in advance with a precision balance (GH-202, manufactured by A&D Co., Ltd.). After measuring (Wb(g)), 20 ml of ethanol is added and degassed for 30 minutes in a desiccator under reduced pressure. Thereafter, the pycnometer is filled with ethanol, stoppered, and the weight is measured (Wc (g)). After the weight measurement of the abrasive grains, the contents of the pycnometer are discarded, and after washing, the pycnometer is filled with ethanol and the weight is measured (Wd). The true density is calculated by equations 1 and 2 from these weights and the temperature of ethanol (t (° C.)) at the time of measurement.

<pH of Polishing Composition>
The pH of the polishing composition (liquid temperature: 25° C.) was measured with a pH meter (model number: F-72 LAQUA (registered trademark) manufactured by Horiba, Ltd.).

<Electrical conductivity of polishing composition>
The electrical conductivity (EC) of the polishing composition was measured with a desktop electrical conductivity meter (manufactured by Horiba, Ltd., model number: DS-71 LAQUA (registered trademark)).

[Example 1]
Colloidal silica as abrasive grains (average primary particle size: 30 nm, average secondary particle size: 60 nm, shape: confetti shape (average height of protrusions: 5 nm, average value of "protrusion height/protrusion width": 0.5 nm). 3), silanol group density: 3.5 groups/nm ² , true density: 2.05 g/cm ³ ) is 3% by mass, and additive 1 is a water-soluble polymer polyvinylpyrrolidone (PVP) (weight average molecular weight ( Mw): 8000) is 10 ppm, 29% by mass of ammonia water as additive 2 is 0.003% by mass in terms of ammonia (NH ₃ ), and 49% by mass of potassium hydroxide aqueous solution is used as additive 3. Add to pure water as a dispersion medium at room temperature (25° C.) to a final concentration of 0.196% by mass in terms of (KOH) and stir and mix for 30 minutes to obtain a polishing composition having a pH of 11. Obtained. The electrical conductivity of the resulting polishing composition was measured and found to be 2.3 mS/cm.

[Examples 2 to 7, Comparative Examples 1 to 8]
Examples 2 to 2 were prepared in the same manner as in Example 1, except that the amount of abrasive grains, the types and amounts of additives 1 to 3, and the pH of the polishing composition were changed as shown in Table 1 below. 7 and Comparative Examples 1 to 8 were prepared. Then, the electrical conductivity of each polishing composition obtained was measured, and the results are shown in Table 1 below. In Table 1 below, "-" indicates that the agent is not included. In Comparative Example 6, tetramethylammonium hydroxide (TMAH) was used as additive 2, and potassium carbonate (K ₂ CO ₃ ) was used as additive 3.

<Evaluation>
The polishing rate, polishing residue and dishing when using each polishing composition were evaluated by the following methods.

(Polishing equipment and polishing conditions)
Polishing device: 200 mm CMP single-sided polishing device Mirra (registered trademark) manufactured by Applied Materials
Polishing pad: Hard polyurethane pad IC1010 manufactured by Nitta DuPont Co., Ltd.
Polishing pressure: 2 psi (1 psi = 6894.76 Pa)
Polishing surface plate rotation speed: 103 rpm
Head (carrier) rotation speed: 97 rpm
Supply of polishing composition: free-flowing Amount of supply of polishing composition: 200 mL/min Polishing time: 60 seconds.

(object to be polished)
The following three types of films were formed respectively.

(1) A polysilicon (Poly-Si) film having a thickness of 5000 Å is formed on the surface of a silicon wafer (200 mm, blanket wafer, manufactured by Advantech Co., Ltd.).

(2) A silicon wafer (200 mm, blanket wafer, manufactured by Advantech Co., Ltd.) on which a silicon nitride (SiN) film having a thickness of 2000 Å is formed.

(3) An 8-inch Poly-Si pattern is formed on the surface of a silicon wafer (200 mm, blanket wafer, manufactured by Advantech Co., Ltd.).
The Poly-Si pattern consists of the following three layers.
The first layer is a plasma TEOS-SiO film with a thickness of 1,000 Å formed on a silicon wafer.
The second layer is a 500 Å thick SiN film formed on the first layer and having a Sematech 854 pattern.
The third layer is a Poly-Si film with a thickness of 2,000 Å formed on the second layer.
FIG. 2 is a cross-sectional view schematically showing the object to be polished of (3) above. As shown in FIG. 2, the object to be polished 10 has three layers, a TEOS-SiO film 2, a patterned SiN film 3, and a Poly-Si film 4, laminated on a silicon wafer 1. As shown in FIG. In FIG. 2, H1 indicates the line width and H2 indicates the space width. 2, T1 indicates the thickness of the SiN film 3, and T2 indicates the thickness of the TEOS-SiO film 2 (the distance from the surface of the TEOS-SiO film 2 to the surface of the SiN film 3 on the line of the SiN film 3). height).

[Polishing speed]
Using each of the polishing compositions obtained above, the test wafers of (1) and (2) above were polished for 60 seconds under the above polishing conditions. Then, the polishing speed (polishing rate) was calculated by the following formula.

The film thickness is determined by an optical film thickness measuring device (ASET-f5x: manufactured by KLA-Tencor Co., Ltd.), and the difference in film thickness before and after polishing is divided by the polishing time to obtain the polishing speed (polishing rate) (Å/min.). ) was evaluated. In Table 1 below, the polishing rate of polysilicon and the polishing rate of silicon nitride are indicated in the columns of "poly-Si" and "SiN", respectively.

[Polishing residue]
Using the polishing rate of polysilicon obtained from the above formula, the time required to polish 2000 Å of polysilicon was calculated, and the above (3) was polished. The film thickness of the polysilicon remaining on the silicon nitride film of (3) after polishing was measured using an optical film thickness measuring device (ASET-f5x: manufactured by KLA-Tencor Corporation). The film thickness at this time was regarded as a polishing residue, and was judged according to the following three-stage judgment criteria. If it is Δ or more, it is practically acceptable.

3-stage judgment criteria (judgment): (remaining polishing)
○: Less than 5 Å △: 5 Å or more and less than 15 Å ×: 15 Å or more [Dishing]
Using the polishing compositions of Examples 1 to 7 and Comparative Examples 1 to 8, the test wafers of (3) above were polished under the above polishing conditions until the entire surface of the silicon nitride film was exposed. Then, the amount of dishing (dishing depth) between the silicon nitride film and the polysilicon film was measured using an atomic force microscope (INSIGHT-CAP manufactured by Bruker Japan Co., Ltd.) at the wiring width portion of 100 μm silicon nitride and 100 μm polysilicon (FIG. 2). H1 and H2 portions in ) were measured and judged according to the following 4-step judgment criteria. If it is Δ or more, it is practically acceptable.

Four-stage judgment criteria (judgment): (dishing amount)
⊚: less than 200 Å ○: 200 Å or more and less than 300 Å Δ: 300 Å or more and less than 400 Å ×: 400 Å or more.

The evaluation results are shown in Table 1 below.

As is clear from Table 1, it was found that the polishing compositions of Examples 1-7 can reduce both polishing residue and dishing compared to the polishing compositions of Comparative Examples 1-8. Among them, the polishing compositions of Examples 1 and 4 to 7 were particularly excellent in the effect of reducing polishing residue as compared with the other Examples. In particular, the polishing compositions of Examples 1, 5 and 6 were particularly excellent in the effect of reducing dishing. Furthermore, the polishing compositions of Examples 1 and 6 also have a high selectivity (polysilicon polishing rate/silicon nitride polishing rate), and therefore are very suitable for polishing objects containing polysilicon and silicon nitride. It is considered suitable for

On the other hand, the polishing compositions of Comparative Examples 1 to 5 and 7 had an ammonia content of less than 0.002% by mass, or a potassium compound content of less than 0.004% by mass or more than 0.5% by mass. Although it is an example, it is not suitable for practical use because there is a lot of polishing residue.

The polishing composition of Comparative Example 6 has the same composition as the polishing composition of Comparative Example 6 except that no chelating agent was added in Example 10 described in JP-A-2015-70008. have. As can be seen from the results of Comparative Example 6, a quaternary ammonium salt such as tetramethylammonium hydroxide (TMAH) is not effective in reducing polishing residue.

The polishing composition of Comparative Example 8, which has an ammonia content of more than 0.5% by mass, is not suitable for practical use because of its large amount of dishing.

Claims (11)

A polishing composition comprising abrasive grains, ammonia, and at least one potassium compound selected from the group consisting of potassium hydroxide and potassium salts,
The ammonia content is 0.002% by mass or more and 0.5% by mass or less with respect to the total mass of the polishing composition,
The polishing composition, wherein the content of the potassium compound is 0.004% by mass or more and 0.5% by mass or less with respect to the total mass of the polishing composition. The polishing composition according to claim 1, further comprising a water-soluble polymer. 3. The polishing composition according to claim 2, wherein said water-soluble polymer has a lactam structure. The polishing composition according to any one of claims 1 to 3, which has a pH of 9.0 or higher. The polishing composition according to any one of claims 1 to 4, wherein the ratio of the content of the potassium compound to the content of the ammonia (potassium compound/ammonia (mass ratio)) is 0.1 or more and 100 or less. thing. The polishing composition according to any one of claims 1 to 5, wherein the abrasive grains have a silanol group density of 0/nm ² or more and 4/nm ² or less. The polishing composition according to any one of claims 1 to 6, wherein the shape of the abrasive grains is a confetti shape. The polishing composition according to any one of claims 1 to 7, wherein the abrasive grains have a true density of 1.9 g/cm ³ or more. A polishing method comprising polishing an object to be polished containing polysilicon and silicon nitride using the polishing composition according to any one of claims 1 to 8. A method of manufacturing a semiconductor substrate, comprising the method of claim 9 . A semiconductor substrate obtained by the method of manufacturing a semiconductor substrate according to claim 10 .

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