JP7508275B2 - Polishing composition, polishing method, and method for producing semiconductor substrate - Google Patents

Description

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

In recent years, with the trend toward multi-layer wiring on semiconductor substrate surfaces, the so-called chemical mechanical polishing (CMP) technology is being used to physically polish and planarize semiconductor substrates when manufacturing devices. CMP is a method of planarizing the surface of an object to be polished (workpiece to be polished) such as a semiconductor substrate using a polishing composition (slurry) containing abrasive grains such as silica, alumina, ceria, etc., an anticorrosive agent, a surfactant, etc. Specifically, it is used in processes such as shallow trench isolation (STI), planarization of interlayer insulating film (ILD film), formation of tungsten plugs, and formation of multi-layer wiring consisting of copper and low dielectric constant film.

For example, Patent Document 1 discloses a polishing composition that contains an alkylene oxide-added water-soluble polymer, polyacrylic acid, and abrasive grains. This technology is said to be capable of polishing at a high polishing rate while suppressing the occurrence of scratches on the polishing surface of the object to be polished during polishing.

JP 2001-185516 A

However, it was found that the technology described in Patent Document 1 still had a problem in that the polishing speed was not improved sufficiently.

Therefore, the present invention aims to provide a polishing composition that can polish an object to be polished at a high polishing rate.

The present inventors have conducted extensive research to solve the above problems. As a result, they have found that the above problems can be solved by a polishing composition that contains an abrasive grain, a basic inorganic compound, an anionic water-soluble polymer, and a dispersion medium, in which the zeta potential of the abrasive grain is negative, the aspect ratio of the abrasive grain is greater than 1.1, and in the particle size distribution of the abrasive grains determined by a laser diffraction scattering method, the ratio D90/D50 of the particle diameter D90 when the cumulative particle mass from the fine particle side reaches 90% of the total particle mass to the particle diameter D50 when the cumulative particle mass from the fine particle side reaches 50% of the total particle mass is greater than 1.3.

The present invention provides a polishing composition that can polish an object to be polished at a high polishing rate.

The following describes the embodiments of the present invention, but the present invention is not limited to the following embodiments. Unless otherwise specified, operations and measurements of physical properties are performed at room temperature (20-25°C) and relative humidity of 40-50% RH. In this specification, the range "X-Y" means "X or more and Y or less."

<Polishing Composition>
The present invention is a polishing composition used for polishing an object to be polished, comprising abrasive grains, a basic inorganic compound, an anionic water-soluble polymer, and a dispersion medium, wherein the abrasive grains have a negative zeta potential and an aspect ratio of more than 1.1, and in a particle size distribution of the abrasive grains determined by a laser diffraction scattering method, the ratio D90/D50 of the particle diameter D90 at which the cumulative particle mass from the fine particle side reaches 90% of the total particle mass to the particle diameter D50 at which the cumulative particle mass from the fine particle side reaches 50% of the total particle mass exceeds 1.3.

The reason why the polishing composition of the present invention exhibits the above-mentioned effects is not necessarily clear, but it is thought to be due to the following reasons.

Polishing compositions generally polish objects by using the physical action of rubbing the substrate surface, the chemical action of components other than the abrasive grains on the substrate surface, or a combination of these. As a result, the shape and type of abrasive grains have a significant effect on the polishing speed.

The polishing composition of the present invention contains abrasive grains having a predetermined shape and a predetermined particle size distribution. That is, the abrasive grains used in the polishing composition are composed of irregularly shaped particles because the aspect ratio exceeds 1.1, and further composed of particles with a wide particle size distribution because the D90/D50 exceeds 1.3. Since the abrasive grains are irregularly shaped particles, rolling on the polishing surface is suppressed, the abrasive grains remain on the polishing surface, and sufficient mechanical force can be applied, allowing suitable polishing. Furthermore, since the particle size distribution of the abrasive grains is wide, abrasive grains of relatively small size and abrasive grains of relatively large size exist. The relatively small abrasive grains are suppressed from rolling on the polishing surface by contacting with the relatively large abrasive grains. As a result, the relatively small abrasive grains can sufficiently apply mechanical force to the object to be polished during polishing, and the polishing speed of the object to be polished can be further improved.

The abrasive grains contained in the polishing composition of the present invention have a negative zeta (ζ) potential. In other words, abrasive grains with a negative zeta potential are used in the polishing composition. Here, the anionic water-soluble polymer contained in the polishing composition of the present invention is a polymer, so it is easy to adhere to the surface of a polishing pad (e.g., polyurethane). When the anionic water-soluble polymer adheres to the surface of the polishing pad, the zeta potential of the polishing pad surface becomes negative. Specifically, if the zeta potential of the pad surface is on the positive side, the zeta potential shifts to the negative side due to the adhesion of the anionic water-soluble polymer, and if the zeta potential of the pad surface is on the negative side, the absolute value of the zeta potential increases due to the adhesion of the anionic water-soluble polymer. Therefore, when the polishing composition is used to polish an object to be polished, a repulsive force due to the negative charges acts between the polishing pad in contact with the polishing composition and the abrasive grains in the polishing composition, and it is presumed that this repulsion further improves the polishing speed for the object to be polished.

Furthermore, the polishing composition of the present invention contains a basic inorganic compound. For example, a basic inorganic compound increases the electrical conductivity of the polishing composition more than a basic organic compound. This is thought to further increase the polishing rate using the polishing composition.

As described above, the polishing composition of the present invention contains highly polishing abrasive grains having a specified shape and a specified particle size distribution in combination with an anionic water-soluble polymer and a basic inorganic compound, which is believed to further improve the polishing properties of the abrasive grains. However, it goes without saying that such a mechanism is merely speculation and does not limit the technical scope of the present invention.

[Polished object]
The material contained in the object to be polished with the polishing composition of the present invention is not particularly limited, and examples thereof include silicon oxide (SiO ₂ ), silicon nitride (SiN), silicon carbonitride (SiCN), polycrystalline silicon (polysilicon), non-crystalline silicon (amorphous silicon), metals, SiGe, etc.

The object to be polished according to the present invention preferably contains silicon oxide or silicon nitride, and more preferably contains silicon oxide. Therefore, the polishing composition of the present invention is preferably used for polishing an object to be polished that contains silicon oxide or silicon nitride, and more preferably used for polishing an object to be polished that contains silicon oxide.

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

Examples of metal-containing films include tungsten (W) film, titanium nitride (TiN) film, ruthenium (Ru) film, platinum (Pt) film, gold (Au) film, hafnium (Hf) film, cobalt (Co) film, nickel (Ni) film, copper (Cu) film, aluminum (Al) film, and tantalum (Ta) film. From the viewpoint of improving electrical conductivity, a W film, a TiN film, a Ru film, a Pt film, or an Au film is preferably used, a W film or a TiN film is particularly preferably used, and a W film is most preferably used. In one embodiment, the polishing composition of the present invention can be used suitably to polish objects containing metals (e.g., tungsten).

[Abrasive grain]
The polishing composition of the present invention contains abrasive grains. The type of abrasive grains used in the polishing composition of the present invention is not particularly limited, and examples thereof include oxides such as silica, alumina, zirconia, and titania. The abrasive grains can be used alone or in combination of two or more kinds. The abrasive grains may be either commercially available products or synthetic products. The type of abrasive grains is preferably silica or alumina. That is, the polishing composition of the present invention contains silica (preferably colloidal silica, which will be described later) or alumina as the abrasive grains.

In the polishing composition of the present invention, the abrasive grains exhibit a negative zeta potential, the aspect ratio of the abrasive grains exceeds 1.1, and in the particle size distribution determined by the laser diffraction scattering method, the ratio D90/D50 of the particle diameter D90 when the cumulative particle mass from the fine particle side reaches 90% of the total particle mass to the particle diameter D50 when the cumulative particle mass from the fine particle side reaches 50% of the total particle mass exceeds 1.3. The preferred form of these abrasive grain characteristics may differ depending on the type of abrasive grain used. In the following, when the preferred form differs depending on the type of abrasive grain, it will be explained each time, but a form that does not specifically mention the type of abrasive grain means a common preferred form regardless of the type of abrasive grain.

The abrasive grains used in the polishing composition of the present invention exhibit a negative zeta potential. Here, "zeta (ζ) potential" refers to the potential difference that occurs at the interface between a solid and a liquid in contact with each other when they undergo relative motion. In the polishing composition of the present invention, the abrasive grains have a negative charge, which can improve the polishing speed of the object to be polished. The zeta potential of the abrasive grains is preferably -80 mV or more and -20 mV or less, and more preferably -60 mV or more and -30 mV or less. By having the abrasive grains have a zeta potential in this range, the polishing speed of the object to be polished can be further improved.

When the abrasive grains are silica, the zeta potential of the abrasive grains is preferably -80 mV or more and -20 mV or less, and more preferably -60 mV or more and -30 mV or less. When the abrasive grains (silica) have a zeta potential in this range, the polishing speed for the object to be polished can be further improved.

When the abrasive grains are alumina, the zeta potential of the abrasive grains is preferably -80 mV or more and -5 mV or less, and more preferably -60 mV or more and -20 mV or less. When the abrasive grains (alumina) have a zeta potential in this range, the polishing speed for the object to be polished can be further improved.

The zeta potential of the abrasive grains in the polishing composition is calculated by subjecting the polishing composition to an ELS-Z2 manufactured by Otsuka Electronics Co., Ltd., measuring the composition at a measurement temperature of 25°C using a flow cell by the laser Doppler method (electrophoretic light scattering measurement method), and analyzing the obtained data using the Smoluchowski formula.

The aspect ratio of the abrasive grains used in the polishing composition of the present invention exceeds 1.1. By using abrasive grains with an aspect ratio exceeding 1.1, rolling on the polishing surface is suppressed, and the polishing rate is improved. If the aspect ratio of the abrasive grains is 1.1 or less, the polishing rate decreases. The aspect ratio of the abrasive grains is preferably 1.2 or more, and more preferably exceeds 1.2. The upper limit of the aspect ratio of the abrasive grains is not particularly limited, but is preferably less than 5, more preferably 4.5 or less, and even more preferably 4 or less. If it is within such a range, the polishing rate can be further improved. The aspect ratio of the abrasive grains is the average of the values obtained by taking the smallest rectangle that circumscribes the image of the abrasive grain particles using a scanning electron microscope, and dividing the length of the long side (long diameter) of the rectangle by the length of the short side (short diameter) of the same rectangle, and can be determined using general image analysis software. Specifically, 100 abrasive grains are randomly selected from an image measured with a scanning electron microscope (SEM) (product name: SU8000, manufactured by Hitachi High-Technologies Corporation), and their average major axis and average minor axis are measured and calculated, and then the aspect ratio can be calculated using the formula "average major axis/average minor axis." Details of the method for measuring and calculating the aspect ratio of the abrasive grains are described in the Examples.

When the abrasive grains are silica, the aspect ratio of the abrasive grains is preferably 1.2 or more, and more preferably exceeds 1.2. When the abrasive grains are silica, the upper limit of the aspect ratio of the abrasive grains is not particularly limited, but is preferably less than 2.0, more preferably 1.8 or less, and even more preferably 1.5 or less. If the aspect ratio of the abrasive grains (silica) is within this range, the polishing speed can be further improved.

When the abrasive grains are alumina, the aspect ratio of the abrasive grains is preferably 2 or more, and more preferably exceeds 2.5. When the abrasive grains are alumina, the upper limit of the aspect ratio of the abrasive grains is not particularly limited, but is preferably less than 5, more preferably 4.5 or less, and even more preferably 4 or less. If the aspect ratio of the abrasive grains (alumina) is within such a range, the polishing speed can be further improved.

In the particle size distribution determined by the laser diffraction scattering method, the abrasive grains used in the polishing composition of the present invention have a ratio D90/D50 of the particle diameter D90 when the cumulative particle mass from the fine particle side reaches 90% of the total particle mass to the particle diameter D50 when the cumulative particle mass from the fine particle side reaches 50% of the total particle mass, which is greater than 1.3. As a result, the polishing composition contains abrasive grains of relatively small size and abrasive grains of relatively large size. The relatively small abrasive grains are in contact with the relatively large abrasive grains, so that the rolling on the polishing surface is suppressed. As a result, the relatively small abrasive grains can fully apply mechanical force to the object to be polished during polishing, and the polishing speed of the object to be polished can be further improved. If the D90/D50 is 1.3 or less, the polishing speed decreases.

D90/D50 is preferably 1.35 or more, more preferably 1.4 or more, and even more preferably 1.6 or more. If it is within this range, the polishing speed can be further improved. In addition, in the particle size distribution of the abrasive grains in the polishing composition, which is determined by the laser diffraction scattering method, the upper limit of the ratio D90/D50 between the particle diameter (D90) when the cumulative particle mass from the fine particle side reaches 90% of the total particle mass and the particle diameter (D50) when the cumulative particle mass from the fine particle side reaches 50% of the total particle mass is not particularly limited, but it is preferably 4 or less. If it is within this range, defects such as scratches that may occur on the surface of the polished object after polishing with the polishing composition can be suppressed.

When the abrasive grains are silica, D90/D50 is preferably 1.35 or more, more preferably 1.4 or more, and even more preferably 1.6 or more. Within such a range, the polishing rate can be further improved. There is no particular upper limit to D90/D50, but when the abrasive grains are silica, it is preferably 2 or less. Within such a range, defects such as scratches that may occur on the surface of the object to be polished after polishing with the polishing composition can be suppressed.

When the abrasive grains are alumina, D90/D50 is preferably 1.4 or more, more preferably 1.5 or more, and even more preferably 2 or more. Within such a range, the polishing rate can be further improved. There is no particular upper limit to D90/D50, but when the abrasive grains are alumina, it is preferably 4 or less. Within such a range, defects such as scratches that may occur on the surface of the object to be polished after polishing with the polishing composition can be suppressed.

The size of the abrasive grains is not particularly limited, but the lower limit of the average primary particle diameter of the abrasive grains determined by image analysis from a photograph observed with a scanning electron microscope is preferably 10 nm or more, more preferably 30 nm or more, and even more preferably 50 nm or more. In addition, in the polishing composition of the present invention, the upper limit of the average primary particle diameter of the abrasive grains is preferably 3000 nm or less, more preferably 2500 nm or less, even more preferably 2000 nm or less, and particularly preferably 1500 nm or less. Within such a range, defects such as scratches that may occur on the surface of the object to be polished after polishing with the polishing composition can be suppressed. That is, the average primary particle diameter of the abrasive grains is preferably 10 nm or more and 3000 nm or less, more preferably 30 nm or more and 2500 nm or less, even more preferably 50 nm or more and 2000 nm or less, and particularly preferably 50 nm or more and 1500 nm or less. The average primary particle diameter of the abrasive grains is calculated, for example, based on the specific surface area of the abrasive grains measured by the BET method.

When the abrasive grains are silica, the lower limit of the average primary particle diameter of the abrasive grains is preferably 10 nm or more, more preferably 30 nm or more, and even more preferably 50 nm or more. In addition, when the abrasive grains are silica, the upper limit of the average primary particle diameter of the abrasive grains in the polishing composition of the present invention is preferably 120 nm or less, more preferably 100 nm or less, and even more preferably 80 nm or less. Within such a range, defects such as scratches that may occur on the surface of the object to be polished after polishing with the polishing composition can be suppressed. That is, when the abrasive grains are silica, the average primary particle diameter of the abrasive grains is preferably 10 nm or more and 120 nm or less, more preferably 30 nm or more and 100 nm or less, and even more preferably 50 nm or more and 80 nm or less.

When the abrasive grains are alumina, the lower limit of the average primary particle diameter of the abrasive grains is preferably 100 nm or more, more preferably 250 nm or more, and even more preferably 300 nm or more. In addition, in the polishing composition of the present invention, when the abrasive grains are alumina, the upper limit of the average primary particle diameter of the abrasive grains is preferably 3000 nm or less, more preferably 2500 nm or less, even more preferably 2000 nm or less, and particularly preferably 1500 nm or less. Within such a range, defects such as scratches that may occur on the surface of the object to be polished after polishing with the polishing composition can be suppressed. That is, when the abrasive grains are alumina, the average primary particle diameter of the abrasive grains is preferably 100 nm or more and 3000 nm or less, more preferably 250 nm or more and 2500 nm or less, even more preferably 300 nm or more and 2000 nm or less, and particularly preferably 300 nm or more and 1500 nm or less.

In the polishing composition of the present invention, the lower limit of the average secondary particle diameter of the abrasive grains is preferably 15 nm or more, more preferably 45 nm or more, even more preferably 50 nm or more, and even more preferably 70 nm or more. In addition, in the polishing composition of the present invention, the upper limit of the average secondary particle diameter of the abrasive grains is preferably 4000 nm or less, more preferably 3500 nm or less, even more preferably 3000 nm or less, even more preferably 2500 nm or less, and most preferably 2000 nm or less. If it is within such a range, defects such as scratches that may occur on the surface of the polished object after polishing with the polishing composition can be suppressed. That is, the average secondary particle diameter of the abrasive grains is preferably 15 nm or more and 4000 nm or less, more preferably 5 nm or more and 3500 nm or less, even more preferably 50 nm or more and 3000 nm or less, even more preferably 70 nm or more and 2500 nm or less, and most preferably 70 nm or more and 2000 nm or less. The average secondary particle diameter of the abrasive grains can be measured, for example, by a dynamic light scattering method, such as a laser diffraction scattering method. In other words, the average secondary particle diameter of the abrasive grains corresponds to the diameter D50 of the particles when the cumulative particle mass from the fine particle side reaches 50% of the total particle mass in the particle size distribution of the abrasive grains determined by the laser diffraction scattering method.

When the abrasive grains are silica, the lower limit of the average secondary particle diameter of the abrasive grains in the polishing composition of the present invention is preferably 15 nm or more, more preferably 45 nm or more, even more preferably 50 nm or more, and even more preferably 70 nm or more. When the abrasive grains are silica, the upper limit of the average secondary particle diameter of the abrasive grains in the polishing composition of the present invention is preferably 250 nm or less, more preferably 200 nm or less, even more preferably 150 nm or less, even more preferably 120 nm or less, and most preferably 100 nm or less. Within such a range, defects such as scratches that may occur on the surface of the object to be polished after polishing with the polishing composition can be suppressed. That is, when the abrasive grains are silica, the average secondary particle diameter of the abrasive grains is preferably 15 nm or more and 250 nm or less, more preferably 45 nm or more and 200 nm or less, even more preferably 50 nm or more and 150 nm or less, even more preferably 70 nm or more and 120 nm or less, and most preferably 70 nm or more and 100 nm or less.

When the abrasive grains are alumina, the lower limit of the average secondary particle diameter of the abrasive grains in the polishing composition of the present invention is preferably 100 nm or more, more preferably 200 nm or more, even more preferably 300 nm or more, and even more preferably 500 nm or more. When the abrasive grains are alumina, the upper limit of the average secondary particle diameter of the abrasive grains in the polishing composition of the present invention is preferably 4000 nm or less, more preferably 3500 nm or less, even more preferably 3000 nm or less, even more preferably 2500 nm or less, and most preferably 2000 nm or less. Within such a range, defects such as scratches that may occur on the surface of the polished object after polishing with the polishing composition can be suppressed. That is, when the abrasive grains are made of alumina, the average secondary particle size of the abrasive grains is preferably 100 nm or more and 4000 nm or less, more preferably 200 nm or more and 3500 nm or less, even more preferably 300 nm or more and 3000 nm or less, even more preferably 400 nm or more and 2500 nm or less, and most preferably 500 nm or more and 2000 nm or less.

The average degree of association of the abrasive grains is preferably 6.0 or less, more preferably 5.0 or less, and even more preferably 4.0 or less. As the average degree of association of the abrasive grains decreases, the occurrence of defects on the surface of the object to be polished can be further reduced. In addition, the average degree of association of the abrasive grains is preferably 1.0 or more, and more preferably 1.2 or more. As the average degree of association of the abrasive grains increases, there is an advantage in that the polishing rate with the polishing composition increases. The average degree of association of the abrasive grains is obtained by dividing the value of the average secondary particle diameter of the abrasive grains by the value of the average primary particle diameter.

When the abrasive grains are silica, the average degree of association of the abrasive grains is preferably 2.0 or less, more preferably 1.8 or less, and even more preferably 1.6 or less. As the average degree of association of the abrasive grains decreases, the occurrence of defects on the surface of the object to be polished can be further reduced. Furthermore, when the abrasive grains are silica, the average degree of association of the abrasive grains is preferably 1.0 or more, and more preferably 1.2 or more. As the average degree of association of the abrasive grains increases, there is an advantage in that the polishing rate with the polishing composition increases.

When the abrasive grains are alumina, the average degree of association of the abrasive grains is preferably 6.0 or less, more preferably 5.0 or less, and even more preferably 4.0 or less. As the average degree of association of the abrasive grains decreases, the occurrence of defects on the surface of the object to be polished can be further reduced. Furthermore, when the abrasive grains are alumina, the average degree of association of the abrasive grains is preferably 1.0 or more, more preferably 1.5 or more, and most preferably 2.0 or more. As the average degree of association of the abrasive grains increases, there is an advantage in that the polishing rate with the polishing composition increases.

The size of the abrasive grains (average particle size, aspect ratio, D90/D50, etc.) can be appropriately controlled by selecting the manufacturing method of the abrasive grains, etc.

When silica is used as the abrasive grains, colloidal silica is preferably used. Methods for producing colloidal silica include the sodium silicate method and the sol-gel method, and colloidal silica produced by either method can be suitably used as the abrasive grains of the present invention. However, from the viewpoint of reducing metal impurities, colloidal silica produced by the sol-gel method is preferred. Colloidal silica produced by the sol-gel method is preferred because it contains less metal impurities that are diffusible in semiconductors and less corrosive ions such as chloride ions. Colloidal silica can be produced by the sol-gel method using a conventionally known method, and specifically, colloidal silica can be obtained by hydrolysis and condensation reaction using a hydrolyzable silicon compound (e.g., alkoxysilane or its derivative) as a raw material.

The colloidal silica may have a cationic group. A preferred example of colloidal silica having a cationic group is colloidal silica having an amino group fixed to the surface. A method for producing colloidal silica having such a cationic group includes a method of fixing a silane coupling agent having an amino group, such as aminoethyltrimethoxysilane, aminopropyltrimethoxysilane, aminoethyltriethoxysilane, aminopropyltriethoxysilane, aminopropyldimethylethoxysilane, aminopropylmethyldiethoxysilane, or aminobutyltriethoxysilane, to the surface of the abrasive grains, as described in JP-A-2005-162533. This makes it possible to obtain colloidal silica having an amino group fixed to the surface (amino group-modified colloidal silica).

The colloidal silica may have an anionic group. As the colloidal silica having an anionic group, a colloidal silica having an anionic group such as a carboxylic acid group, a sulfonic acid group, a phosphonic acid group, or an aluminic acid group fixed to the surface is preferably used. The method for producing such colloidal silica having an anionic group is not particularly limited, and an example of the method is a method in which a silane coupling agent having an anionic group at the end is reacted with colloidal silica.

As a specific example, if sulfonic acid groups are to be fixed to colloidal silica, this can be done by the method described in, for example, "Sulfonic acid-functionalized silica through of thiol groups", Chem. Commun. 246-247 (2003). Specifically, a silane coupling agent having a thiol group, such as 3-mercaptopropyltrimethoxysilane, is coupled to colloidal silica, and then the thiol group is oxidized with hydrogen peroxide to obtain colloidal silica having sulfonic acid groups fixed to the surface.

Alternatively, if carboxylic acid groups are to be fixed to colloidal silica, this can be done, for example, by the method described in "Novel Silane Coupling Agents Containing a Photolabile 2-Nitrobenzyl Ester for Introduction of a Carboxy Group on the Surface of Silica Gel", Chemistry Letters, 3, 228-229 (2000). Specifically, a silane coupling agent containing a photoreactive 2-nitrobenzyl ester is coupled to colloidal silica, and then the resulting product is irradiated with light, thereby obtaining colloidal silica with carboxylic acid groups fixed to the surface.

When alumina is used as the abrasive grains, it can be appropriately selected from various known aluminas. Examples of known aluminas include aluminas containing at least one selected from α-alumina, γ-alumina, δ-alumina, θ-alumina, η-alumina, and κ-alumina. Alumina called fumed alumina (typically alumina fine particles produced when alumina salt is fired at high temperatures) based on classification by manufacturing method may also be used. Furthermore, alumina called colloidal alumina or alumina sol (e.g. alumina hydrate such as boehmite) is also included as an example of the known alumina. The alumina used as the abrasive grains of the polishing composition of the present invention may contain one type of such alumina particles alone or two or more types in combination. Among these, alumina containing an α-phase as a crystal phase (alumina containing α-alumina) is preferable, and alumina containing an α-phase as a main crystal phase (alumina containing α-alumina as a main component) is more preferable.

In this specification, if an α-phase peak appearing at 2θ=25.6° is confirmed in the powder X-ray diffraction spectrum of alumina obtained using a powder X-ray diffractometer, the alumina is determined to "contain α-phase as a crystalline phase." Also, in this specification, if the α-phase ratio described below is more than 50%, the alumina is determined to "contain α-phase as a main crystalline phase" (upper limit 100%). Here, the α-phase ratio [%] can be calculated from the peak height (I25.6) of the α-phase (012) plane appearing at 2θ=25.6° and the peak height (I46) of the γ-phase appearing at 2θ=46° from the powder X-ray diffraction spectrum obtained using a powder X-ray diffractometer using the following formula.

The alpha conversion rate calculated based on the above measurements is the same whether it is measured on the powdered alumina that is the raw material of the polishing composition, or on the alumina extracted from the prepared polishing composition.

The method for producing alumina is not particularly limited, and any known method can be used as appropriate, but a method in which alumina other than the α phase, such as boehmite, is sintered to obtain alumina containing the α phase as the main crystal phase is preferred. In other words, the alumina is preferably alumina produced through a sintering process. The alumina obtained through the sintering process may be crushed to a desired size.

In addition, the alumina used as abrasive grains may contain amorphous alumina as long as the effect of the present invention is not impaired.

In the present invention, the shape of the abrasive grains is preferably non-spherical. Specific examples of non-spherical shapes include polygonal prisms such as triangular prisms and square prisms, cylinders, bale shapes in which the center of a cylinder is more bulging than the ends, donut shapes with a disk penetrating the center, plate shapes, so-called cocoon shapes with a constriction in the center, so-called associative spheres in which multiple particles are integrated, so-called confetti shapes with multiple protrusions on the surface, and rugby ball shapes, and various other shapes are not particularly limited.

The lower limit of the content (concentration) of the abrasive grains in the polishing composition according to one embodiment of the present invention is preferably 1% by mass or more, more preferably 2% by mass or more, and even more preferably 3% by mass or more, based on the polishing composition. The upper limit of the content of the abrasive grains in the polishing composition according to the present invention is preferably 25% by mass or less, more preferably 20% by mass or less, even more preferably 15% by mass or less, and even more preferably 12% by mass or less, based on the polishing composition. Within such a range, the polishing rate can be further improved. When the polishing composition contains two or more types of abrasive grains, the content of the abrasive grains means the total amount of these.

[Basic inorganic compounds]
The polishing composition of the present invention contains a basic inorganic compound. Here, the basic inorganic compound refers to an inorganic compound that has the function of increasing the pH of the polishing composition by being added to the polishing composition. The basic inorganic compound has the function of chemically polishing the surface of the object to be polished and the function of improving the dispersion stability of the polishing composition. In addition, the basic inorganic compound contained in the polishing composition of the present invention increases the electrical conductivity of the polishing composition more than the basic organic compound. It is believed that this further improves the polishing rate by the polishing composition.

In addition, basic inorganic compounds are not as three-dimensionally bulky as basic organic compounds, and as a result, the basic inorganic compounds and the anionic water-soluble polymer are less likely to form aggregates. Therefore, in the polishing composition of the present invention, the anionic water-soluble polymer is in a stable dispersed state, and the anionic water-soluble polymer can be efficiently attached to the polishing pad.

Examples of basic inorganic compounds include alkali metal compounds such as potassium compounds and sodium compounds, and ammonia. Specific examples of alkali metal compounds include potassium hydroxide, potassium carbonate, potassium hydrogen carbonate, potassium sulfate, potassium acetate, potassium chloride, sodium hydroxide, sodium carbonate, sodium hydrogen carbonate, sodium sulfate, sodium acetate, and sodium chloride. Of these, from the viewpoints of pH and slurry stability, potassium hydroxide, sodium hydroxide, and ammonia are preferred as basic inorganic compounds, and potassium hydroxide and ammonia are more preferred.

In an embodiment of the present invention, the content of the basic inorganic compound in the polishing composition is preferably 0.001% by mass or more, more preferably 0.01% by mass or more, even more preferably 0.1% by mass or more, particularly preferably 1.0% by mass or more, and most preferably 1.5% by mass or more, based on the polishing composition. Such a lower limit further improves the polishing rate. The content of the basic inorganic compound in the polishing composition is preferably 10% by mass or less, more preferably 8% by mass or less, and even more preferably 6% by mass or less, based on the polishing composition. Such an upper limit makes it possible to obtain a stable slurry without aggregation.

[Anionic water-soluble polymer]
The polishing composition of the present invention includes an anionic water-soluble polymer. The anionic water-soluble polymer is a water-soluble polymer having an anionic group in the molecule. In this specification, "water-soluble" means that the solubility in water (25°C) is 1 g/100 mL or more. The anionic water-soluble polymer may be used alone or in combination of two or more kinds.

When the polishing composition of the present invention is used to polish an object to be polished, the anionic water-soluble polymer contained in the polishing composition adheres to the polishing pad. At this time, if the zeta potential of the pad surface is on the positive side, the adhesion of the anionic water-soluble polymer shifts the zeta potential to the negative side, and if the zeta potential of the pad surface is on the negative side, the adhesion of the anionic water-soluble polymer increases the absolute value of the zeta potential. For example, if the polishing pad is polyurethane, the zeta potential of the polyurethane surface is about -45 mV, but when the polishing pad comes into contact with the polishing composition of the present invention (i.e., when the anionic water-soluble polymer adheres), the zeta potential of the polishing pad surface can increase to -80 mV. Therefore, the anionic water-soluble polymer adheres to the polishing pad surface, making the surface charge of the polishing pad negative, or increasing the absolute value of the surface charge on the negative side of the polishing pad, which leads to greater repulsion between the polishing pad and the abrasive grains, thereby improving the polishing speed.

According to an embodiment of the present invention, the anionic water-soluble polymer is preferably one that contains at least one functional group selected from the group consisting of a carboxyl group, a sulfo group, a phosphate group, and a phosphonate group in the molecule. In particular, it is preferable that the anionic water-soluble polymer contains a carboxyl group. By containing such a group in the anionic water-soluble polymer, the intended effect of the present invention can be efficiently achieved.

According to an embodiment of the present invention, the anionic water-soluble polymer preferably has a constituent unit derived from a monomer having an ethylenically unsaturated bond. For example, the anionic water-soluble polymer preferably contains one or more monomer-derived constituent units selected from the group consisting of acrylic acid and methacrylic acid. Therefore, it is more preferable that the anionic water-soluble polymer is at least one selected from the group consisting of polyacrylic acid-based polymers and polymethacrylic acid-based polymers. It is presumed that such an embodiment causes the carboxyl group to interact with the basic inorganic compound in the polishing composition, resulting in a stably dispersed state of the abrasive grains.

The anionic water-soluble polymer may be a copolymer containing a structural unit derived from a monomer having an ethylenically unsaturated bond in one molecule and a structural unit derived from another monomer. Examples of such copolymers include a copolymer of (meth)acrylic acid and vinyl alcohol, a copolymer of (meth)acrylic acid and 2-hydroxy-2-phosphonoacetic acid (HPAA), and a copolymer of (meth)acrylic acid and acryloylmorpholine (ACMO). Note that (meth)acrylic acid is a comprehensive term referring to acrylic acid and methacrylic acid.

The anionic water-soluble polymer may also contain an oxyalkylene unit. Examples of oxyalkylene units that the anionic water-soluble polymer may contain include polyethylene oxide (PEO), block copolymers of ethylene oxide (EO) and propylene oxide (PO), and random copolymers of EO and PO. The block copolymers of EO and PO may be diblock or triblock copolymers containing a polyethylene oxide (PEO) block and a polypropylene oxide (PPO) block. The triblock copolymers include PEO-PPO-PEO type triblock copolymers and PPO-PEO-PPO type triblock copolymers.

In an embodiment of the present invention, the lower limit of the molecular weight (mass average molecular weight) of the anionic water-soluble polymer is preferably 1,000 or more, 5,000 or more, 10,000 or more, 50,000 or more, 100,000 or more, 300,000 or more, 500,000 or more, and 800,000 or more. The upper limit of the molecular weight (mass average molecular weight) of the anionic water-soluble polymer is preferably 8,500,000 or less, 6,000,000 or less, 4,000,000 or less, 2,000,000 or less, and 1,500,000 or less, in that order. That is, the molecular weight (mass average molecular weight) of the anionic water-soluble polymer is preferably, for example, 1,000 to 8,500,000, 5,000 to 6,000,000, 10,000 to 4,000,000, 50,000 to 4,000,000, and 100,000 to 2,000,000. If it is within such a range, the polishing rate can be further improved. The molecular weight (mass average molecular weight) of the anionic water-soluble polymer can be a value measured by the GPC method.

In an embodiment of the present invention, the content of the anionic water-soluble polymer in the polishing composition is preferably 0.001% by mass or more, more preferably 0.005% by mass or more, even more preferably 0.01% by mass or more, even more preferably 0.05% by mass or more, and most preferably 0.08% by mass or more, based on the polishing composition. The content of the anionic water-soluble polymer in the polishing composition is 0.8% by mass or less, more preferably 0.5% by mass or less, and particularly preferably 0.4% by mass or less, based on the polishing composition. Within such a range, a high polishing rate can be maintained. When the polishing composition contains two or more types of anionic water-soluble polymers, the content of the anionic water-soluble polymers means the total amount of these.

In an embodiment of the present invention, when the abrasive grains are silica, the content of the anionic water-soluble polymer in the polishing composition is preferably 0.001% by mass or more, more preferably 0.01% by mass or more, even more preferably 0.1% by mass or more, even more preferably 0.15% by mass or more, and most preferably 0.2% by mass or more, based on the polishing composition. When the abrasive grains are silica, the content of the anionic water-soluble polymer in the polishing composition is 0.8% by mass or less, more preferably 0.5% by mass or less, and particularly preferably 0.4% by mass or less, based on the polishing composition. Within such a range, a high polishing rate can be maintained.

In an embodiment of the present invention, when the abrasive grains are alumina, the content of the anionic water-soluble polymer in the polishing composition is preferably 0.001% by mass or more, more preferably 0.005% by mass or more, even more preferably 0.01% by mass or more, even more preferably 0.05% by mass or more, and most preferably 0.08% by mass or more, based on the polishing composition. When the abrasive grains are alumina, the content of the anionic water-soluble polymer in the polishing composition is 0.8% by mass or less, more preferably 0.5% by mass or less, and particularly preferably 0.4% by mass or less, based on the polishing composition. Within such a range, a high polishing rate can be maintained.

[Dispersion medium]
The polishing composition contains a dispersion medium (solvent) for dispersing each component constituting the polishing composition. The dispersion medium has the function of dispersing or dissolving each component. The dispersion medium can be an organic solvent or water, but it is preferable to contain water, and more preferable to be water.

From the viewpoint of suppressing contamination of the object to be polished and inhibiting the action of other components, it is preferable that the dispersion medium contains as few impurities as possible. For example, water having a total transition metal ion content of 100 ppb or less is preferable. Here, the purity of the water can be increased by, for example, removing impurity ions using ion exchange resin, removing foreign matter using a filter, distillation, or other operations. Specifically, it is preferable to use deionized water (ion-exchanged water), pure water, ultrapure water, distilled water, etc. as the water. Usually, it is preferable that 90% by volume or more of the dispersion medium contained in the polishing composition is water, more preferably 95% by volume or more, even more preferably 99% by volume or more, and particularly preferably 100% by volume.

The dispersion medium may be a mixed solvent of water and an organic solvent to disperse or dissolve each component. In this case, examples of organic solvents that can be used include acetone, acetonitrile, ethanol, methanol, isopropanol, glycerin, ethylene glycol, and propylene glycol, which are organic solvents that are miscible with water. These organic solvents may be used without being mixed with water, and then the components may be dispersed or dissolved, and then mixed with water. These organic solvents may be used alone or in combination of two or more kinds.

[Other additives]
The polishing composition of the present invention may further contain known additives such as a pH adjuster, a chelating agent, a thickener, an oxidizing agent, a dispersant, a surface protective agent, a wetting agent, a surfactant, an anti-rust agent, an antiseptic agent, an anti-fungal agent, etc., within a range that does not impair the effects of the present invention. The content of the above additives may be appropriately set depending on the purpose of their addition.

(Oxidant)
The polishing composition of the present invention may contain an oxidizing agent. The oxidizing agent is a component that enhances the effect in polishing, and typically uses a water-soluble one. The oxidizing agent is not particularly limited, but it is considered that the oxidizing agent exhibits the action of oxidizing and altering the surface of the object to be polished in polishing, and contributes to polishing by abrasive grains by weakening the surface of the object to be polished.

When silica is used as the abrasive grains in the polishing composition of the present invention, the polishing speed for silicon nitride (SiN) films can be improved by including an oxidizing agent. Also, when silica is used as the abrasive grains in the polishing composition of the present invention, the polishing speed for metals can be improved by including an oxidizing agent.

Examples of oxidizing agents include peroxides such as hydrogen peroxide; nitric acid and its salts such as iron nitrate, silver nitrate, aluminum nitrate, and its complexes such as cerium ammonium nitrate; persulfates such as potassium peroxomonosulfate and peroxodisulfate, and their salts such as ammonium persulfate and potassium persulfate; chlorine compounds such as chloric acid and its salts, perchloric acid and its salts such as potassium perchlorate; bromine compounds such as bromic acid and its salts such as potassium bromate; iodine compounds such as iodic acid and its salts such as ammonium iodate, periodic acid and its salts such as sodium periodate and potassium periodate; iron compounds such as ferric acid and its salts such as potassium ferrate. Acids: permanganic acid, its salts such as sodium permanganate and potassium permanganate; chromic acid, its salts such as potassium chromate and potassium dichromate; vanadic acid, its salts such as ammonium vanadate, sodium vanadate and potassium vanadate; ruthenic acids such as perruthenic acid or its salts; molybdic acid, its salts such as ammonium molybdate and disodium molybdate; rhenic acids such as perrhenium or its salts; tungstic acid, its salts such as disodium tungstate; etc.

These oxidizing agents may be used alone or in appropriate combination of two or more. Among them, from the viewpoint of polishing efficiency, etc., peroxides, permanganic acid or its salts, vanadic acid or its salts, periodic acid or its salts are preferred, hydrogen peroxide and potassium permanganate are more preferred, and hydrogen peroxide is even more preferred.

In the polishing composition of the present invention, when the polishing composition contains silica (preferably colloidal silica) as an abrasive, the polishing speed for silicon oxide films and silicon nitride films can be improved by including an oxidizing agent (preferably hydrogen peroxide), and the polishing speed for metal films (e.g., tungsten films) can also be improved. More specifically, in the polishing composition of the present invention, the polishing speed for silicon oxide films, silicon nitride films, and metal films (e.g., tungsten films) can be improved by combining silica as an abrasive, a basic inorganic compound (preferably potassium hydroxide), and an oxidizing agent (preferably hydrogen peroxide).

The reason for this effect is unclear, but is speculated as follows. As described above, the polishing composition contains an oxidizing agent, and as a result, the surface of the object to be polished is oxidized and altered, weakening the surface of the object to be polished. Furthermore, when the polishing composition contains an oxidizing agent, the content of basic inorganic compounds is increased (to achieve the same pH) compared to a polishing composition that does not contain an oxidizing agent. In this case, it is considered that the electrical conductivity of the polishing composition increases, and the electrostatic repulsion between the object to be polished and the abrasive grains decreases. This increases the probability of collision between the abrasive grains and the object to be polished. Therefore, it is considered that the abrasive grains efficiently collide with the surface of the object to be polished that has been weakened by the oxidizing agent, thereby efficiently polishing silicon oxide films, silicon nitride films, and metal films (e.g., tungsten films). However, it goes without saying that such a mechanism is merely speculation and does not limit the technical scope of the present invention.

Therefore, in a preferred embodiment, the polishing composition contains silica (preferably colloidal silica) as abrasive grains, a basic inorganic compound (preferably potassium hydroxide), an anionic water-soluble polymer, an oxidizing agent (preferably hydrogen peroxide), and a dispersion medium, the zeta potential of the abrasive grains is negative, the aspect ratio of the abrasive grains is greater than 1.1, and in the particle size distribution of the abrasive grains determined by a laser diffraction scattering method, the ratio D90/D50 of the particle diameter D90 when the cumulative particle mass from the fine particle side reaches 90% of the total particle mass to the particle diameter D50 when the cumulative particle mass from the fine particle side reaches 50% of the total particle mass is greater than 1.3.

The content (concentration) of the oxidizing agent in the polishing composition is preferably 0.03 mass% or more. From the viewpoint of improving the polishing rate, the content of the oxidizing agent is more preferably 0.5 mass% or more, even more preferably 0.8 mass% or more, and particularly preferably 2.5 mass% or more. Furthermore, from the viewpoint of the smoothness of the object to be polished, the content of the oxidizing agent is preferably 10 mass% or less, more preferably 9 mass% or less, even more preferably 8 mass% or less, and more particularly preferably 7 mass% or less.

(pH adjuster)
The polishing composition of the present invention can have a pH adjusted to a desired range by the basic inorganic compound, but may further contain a pH adjuster other than the basic inorganic compound.

As a pH adjuster, a known acid, a base other than a basic inorganic compound, or a salt thereof can be used. Specific examples of acids that can be used as pH adjusters include inorganic acids such as hydrochloric acid, sulfuric acid, hydrofluoric acid, boric acid, carbonic acid, hypophosphorous acid, phosphorous acid, and phosphoric acid, and organic acids such as formic acid, acetic acid, propionic acid, butyric acid, valeric acid, 2-methylbutyric acid, n-hexanoic acid, 3,3-dimethylbutyric acid, 2-ethylbutyric acid, 4-methylpentanoic acid, n-heptanoic acid, 2-methylhexanoic acid, n-octanoic acid, 2-ethylhexanoic acid, benzoic acid, glycolic acid, salicylic acid, glyceric acid, oxalic acid, malonic acid, succinic acid, glutaric acid, adipic acid, pimelic acid, maleic acid, phthalic acid, malic acid, tartaric acid, citric acid, lactic acid, diglycolic acid, 2-furancarboxylic acid, 2,5-furandicarboxylic acid, 3-furancarboxylic acid, 2-tetrahydrofurancarboxylic acid, methoxyacetic acid, methoxyphenylacetic acid, and phenoxyacetic acid.

Examples of bases other than basic inorganic compounds that can be used as pH adjusters include aliphatic amines such as ethanolamine and 2-amino-2-ethyl-1,3-propanediol, aromatic amines, and basic organic compounds such as quaternary ammonium hydroxide.

The above pH adjusters can be used alone or in combination of two or more.

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

The lower limit of the pH of the polishing composition is not particularly limited, but is preferably 9 or more, more preferably 9.5 or more, even more preferably 10 or more, and most preferably 11 or more. By setting the lower limit at such a level, the polishing speed of the object to be polished can be improved. There is also no particular limit to the upper limit of the pH, but it is preferably 13 or less, more preferably 12.5 or less, and even more preferably 12 or less. By setting the upper limit at such a level, the stability of the polishing composition can be improved.

The pH of the polishing composition can be measured, for example, using a pH meter.

<Method of producing polishing composition>
The method for producing the polishing composition of the present invention is not particularly limited, and can be obtained, for example, by stirring and mixing abrasive grains, basic inorganic compound, anionic water-soluble polymer and other additives as necessary in a dispersion medium.The details of each component are as described above.Therefore, the present invention provides a method for producing the polishing composition, which comprises mixing abrasive grains, basic inorganic compound, anionic water-soluble polymer and a dispersion medium.

The temperature at which the components are 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. In addition, there is no particular limit to the mixing time as long as the components can be mixed uniformly.

<Polishing method and semiconductor substrate manufacturing method>
The present invention provides a polishing method comprising a step of polishing an object to be polished with the polishing composition according to one embodiment of the present invention. The present invention also provides a method for producing a semiconductor substrate, comprising the polishing method.

As a polishing device, a general polishing device can be used that is equipped with a holder for holding a substrate or the like having an object to be polished, a motor that can change the rotation speed, and a polishing platen onto which a polishing pad (polishing cloth) can be attached.

As the polishing pad, general nonwoven fabric, polyurethane, porous fluororesin, etc. can be used without any particular restrictions. It is preferable that the polishing pad has grooves to allow the polishing liquid to accumulate.

Regarding the polishing conditions, for example, the rotation speed of the polishing platen is preferably 10 rpm (0.17 s ^-1 ) or more and 500 rpm (8.3 s ^-1 ) or less. The pressure (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. There are no particular limitations on the method of supplying the polishing composition to the polishing pad, and for example, a method of continuously supplying the composition using a pump or the like is adopted. There is no limitation on the amount of supply, but it is preferable that the surface of the polishing pad is always covered with the polishing composition of the present invention.

After polishing is complete, the substrate is washed with running water, and the water droplets adhering to the substrate are removed using a spin dryer or the like, followed by drying to obtain a substrate having a metal-containing layer.

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

The present invention will be described in more detail using the following examples and comparative examples. However, the technical scope of the present invention is not limited to the following examples. Unless otherwise specified, "%" and "parts" mean "% by mass" and "parts by mass", respectively. In the following examples, unless otherwise specified, the operations were carried out under the conditions of room temperature (20-25°C) and relative humidity of 40-50% RH.

The physical properties of each polishing composition were measured according to the following methods.

[Zeta potential measurement]
Each polishing composition prepared below was subjected to measurement by a laser Doppler method (electrophoretic light scattering measurement method) using an ELS-Z2 manufactured by Otsuka Electronics Co., Ltd. and a flow cell at a measurement temperature of 25° C. The obtained data was analyzed by the Smoluchowski equation to calculate the zeta potential of the colloidal silica in the polishing composition.

[aspect ratio]
The abrasive grains in each polishing composition are observed by scanning electron microscope (SEM) (Hitachi High-Technologies Corporation, product name: SU8000). From the image observed by SEM, 100 abrasive grains are randomly selected, and their average major axis and average minor axis are measured and calculated. Then, the aspect ratio of abrasive grains is calculated by the following formula using the average major axis and average minor axis values.

[Measurement of average primary particle size]
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 SorbII 2300" manufactured by Micromeritics, and the density of the abrasive grains.

[Measurement of average secondary particle size]
The average secondary particle diameter of the abrasive grains was measured by light scattering method using laser light, and Microtrac MT3000II (manufactured by Microtrac Bell Co., Ltd.) was used as the measuring device. The powdered abrasive grains were dispersed in water and measured, and the average secondary particle diameter of the polishing composition was measured either as is or diluted with water. At the same time, the ratio D90/D50 of the particle diameter when the cumulative particle mass from the fine particle side reaches 90% of the total particle mass in the particle size distribution of the average secondary particle diameter of the abrasive grains was calculated by analysis using the measuring device, and the particle diameter D90 when the cumulative particle mass from the fine particle side reaches 50% of the total particle mass was calculated.

[Preparation of Polishing Composition]
Example 1
A polishing composition was prepared by mixing and stirring the above components and ion-exchanged water at room temperature (25° C.) for 30 minutes to a final concentration of 7.5% by mass of colloidal silica (average primary particle size 70 nm, average secondary particle size 100 nm, average degree of association 1.4) as abrasive grains, 0.24% by mass of polyacrylic acid (PAA) having a molecular weight (mass average molecular weight) of 1,000,000 as a water-soluble polymer, and 1.7% by mass of potassium hydroxide as a basic compound. The pH of the polishing composition measured with a pH meter was 11. The zeta potential of the colloidal silica in the obtained polishing composition was −47 mV when measured by the above method. The particle size of the abrasive grains (colloidal silica) in the polishing composition was the same as the particle size of the above colloidal silica.

(Examples 2 to 13, Comparative Examples 1 to 10)
Polishing compositions according to Examples 2 to 13 and Comparative Examples 1 to 10 were prepared in the same manner as in Example 1, except that the types and contents of the abrasive grains, water-soluble polymer, and basic compound were changed as shown in Table 1. In Table 1, TMAH represents tetramethylammonium hydroxide, PVP represents polyvinylpyrrolidone, HEC represents hydroxyethyl cellulose, and PEI represents polyethyleneimine. The pH of the obtained polishing composition, as well as the zeta potential, aspect ratio, particle size, and D90/D50 of the abrasive grains (colloidal silica) in the polishing composition are shown in Table 1 below. The particle size of the abrasive grains (colloidal silica) in the polishing composition was the same as the particle size of the colloidal silica measured before preparing the polishing composition.

In addition, in the particle size distribution column in Table 1, "broad" means that D90/D50 exceeds 1.3, and "sharp" means that D90/D50 is 1.3 or less. Furthermore, in the particle shape column in Table 1, "irregular shape" means that the aspect ratio exceeds 1.1, and "spherical" means that the aspect ratio is 1.1 or less. In Table 1, "-" means that the component is not included.

(Examples 14 to 18, Comparative Example 11)
As the abrasive grains, sintered and pulverized α-alumina was prepared. Specifically, as described in paragraph "0013" of JP 2006-36864 A, aluminum hydroxide was calcined under conditions of a calcination temperature in the range of 1100 to 1500° C. and a calcination time in the range of 1 to 5 hours, and then pulverized using aluminum oxide poles with a diameter of 20,000 μm. Abrasive grains (sintered and pulverized α-alumina) were produced by such a method for producing alumina particles (pulverization method) by calcining and then pulverizing as necessary. In producing these abrasive grains, the pulverization time was controlled so as to obtain the average particle diameter values shown in Table 2 below.

Using the obtained sintered and ground α-alumina, the polishing compositions of Examples 14 to 18 and Comparative Example 11 were prepared. The average primary particle size, average secondary particle size, D90/D50, and aspect ratio of the sintered and ground α-alumina used in each polishing composition are shown in Table 2. In addition, the polishing compositions of Examples 14 to 18 and Comparative Example 11 were prepared in the same manner as in Example 1, except that the types and contents of the abrasive grains, water-soluble polymers, and basic compounds were changed as shown in Table 2. The pH of the obtained polishing composition, as well as the zeta potential, aspect ratio, particle size, and D90/D50 of the abrasive grains (sintered and ground α-alumina) in the polishing composition are shown in Table 2 below. The particle size, D90/D50, and aspect ratio of the abrasive grains (sintered and ground α-alumina) in the polishing composition were the same as the particle size, D90/D50, and aspect ratio of the sintered and ground α-alumina measured before preparing the polishing composition. In Table 2, the meanings of "broad" in the particle size distribution column, "irregular shape" in the particle shape column, and "-" in the water-soluble polymer column are the same as in Table 1.

(Example 19)
The polishing composition was prepared by stirring and mixing the above components and ion-exchanged water at room temperature (25° C.) for 30 minutes to obtain a final concentration of 7.5% by mass of colloidal silica (average primary particle size 70 nm, average secondary particle size 100 nm, average degree of association 1.4) as abrasive grains, 0.24% by mass of polyacrylic acid ( _PAA ) having a molecular weight (mass average molecular weight) of 1,000,000 as a water-soluble polymer, 3.4% by mass of potassium hydroxide as a basic compound, and 1.0% by mass of hydrogen peroxide (H 2 O ₂ ) as an oxidizing agent. The pH of the polishing composition measured with a pH meter was 11. The pH of the obtained polishing composition, as well as the zeta potential, aspect ratio, particle size, and D90/D50 of the abrasive grains (colloidal silica) in the polishing composition are shown in Table 4 below. The particle size of the abrasive grains (colloidal silica) in the polishing composition was the same as the particle size of the colloidal silica measured before preparing the polishing composition. In Table 4, the meanings of "broad" in the particle size distribution column, "irregular shape" in the particle shape column, and "-" in the water-soluble polymer column are the same as in Table 1.

(Examples 20 to 25, Comparative Examples 12 to 17)
Polishing compositions according to Examples 20 to 25 and Comparative Examples 12 to 17 were prepared in the same manner as in Example 19, except that the types and contents of the abrasive grains, water-soluble polymer, basic compound, and oxidizing agent were changed as shown in Table 4. In Table 4, H ₂ O ₂ represents hydrogen peroxide, and KMnO ₄ represents potassium permanganate.

The pH of the resulting polishing composition, as well as the zeta potential, aspect ratio, particle size, and D90/D50 of the abrasive grains (colloidal silica) in the polishing composition are shown in Table 4 below. The particle size of the abrasive grains (colloidal silica) in the polishing composition was the same as the particle size of the colloidal silica measured before preparing the polishing composition.

[evaluation]
[Polishing speed]
As the objects to be polished, a silicon wafer (200 mm, blanket wafer, manufactured by Advantech Co., Ltd.) with a TEOS film of 10000 Å on its surface, a silicon wafer (200 mm, blanket wafer, manufactured by Advantech Co., Ltd.) with a SiN (silicon nitride) film of 3500 Å on its surface, and a silicon wafer (200 mm, blanket wafer, manufactured by Advantech Co., Ltd.) with a W (tungsten) film of 4000 Å on its surface were prepared. The TEOS film wafer and the SiN film wafer were each cut into a 60 mm x 60 mm chip coupon as a test piece, and the W film wafer was itself used as a test piece. The three types of objects to be polished were polished under the following polishing conditions using each of the polishing compositions obtained above. The TEOS film wafer and the SiN film wafer were polished using the polishing compositions of Examples 1 to 25 and Comparative Examples 1 to 17, and the W film wafer was polished using the polishing compositions of Examples 1 and 19 to 25 and Comparative Examples 12 to 17.

(Polishing conditions)
TEOS film ( _SiO2 film) wafer: EJ-380IN-CH (Engis Japan Co., Ltd.) was used as the polishing machine, and IC1000 hard polyurethane pad (Rohm and Haas Co., Ltd.) was used as the polishing pad. Polishing was performed for 60 seconds under the conditions of a polishing pressure of 3.05 psi (21.0 kPa), a platen rotation speed of 60 rpm, a carrier rotation speed of 60 rpm, and a supply rate of the polishing composition of 100 ml/min.

SiN film wafer: EJ-380IN-CH (Engis Japan Co., Ltd.) was used as the polishing machine, and IC1000 hard polyurethane pad (Rohm and Haas Co., Ltd.) was used as the polishing pad. Polishing was performed for 60 seconds under the conditions of a polishing pressure of 4.0 psi (27.6 kPa), a platen rotation speed of 113 rpm, a carrier rotation speed of 107 rpm, and a supply rate of the polishing composition of 200 ml/min.

W film wafer: A Mirra (manufactured by Applied Materials) was used as a polishing machine, and a hard polyurethane pad IC1000 (manufactured by Rohm and Haas) was used as a polishing pad. Polishing was performed for 60 seconds under the conditions of a polishing pressure of 4.0 psi (27.6 kPa), a platen rotation speed of 110 rpm, a carrier rotation speed of 107 rpm, and a supply rate of the polishing composition of 200 ml/min.

(Polishing speed)
The removal rate (RR) was calculated according to the following formula.

The film thickness of the TEOS film and the SiN film was measured using an optical interference film thickness measuring device (manufactured by Dainippon Screen Mfg. Co., Ltd., model number: Lambda Ace VM-2030), and the polishing rate was evaluated by dividing the difference in film thickness before and after polishing by the polishing time.

The thickness of the W film was measured using an automatic conveying sheet resistor machine (VR-120/08S, manufactured by Kokusai Electric System Services Co., Ltd.), and the polishing rate was evaluated by dividing the difference in film thickness before and after polishing by the polishing time.

The evaluation results of the polishing speed are shown in Tables 1, 2 and 5 below.

[Number of scratches]
Prepare the polishing object wafer to be evaluated for the number of scratches. First, prepare the silicon wafer (200 mm, blanket wafer, manufactured by Advantech Co., Ltd.) with a TEOS film of 10000 Å thickness on the surface and the silicon wafer (200 mm, blanket wafer, manufactured by Advantech Co., Ltd.) with a SiN film of 3500 Å thickness on the surface as the polishing object. Use the polishing composition of Example 2 and Example 14 obtained above to polish these two kinds of polishing object wafers under the following polishing conditions.

The number of scratches on the surface of the object to be polished after polishing was measured by measuring the coordinates of the entire surface of both sides of the object to be polished (excluding the outer periphery 2 mm) using a wafer inspection device "Surfscan (registered trademark) SP2" manufactured by KLA Tencor Corporation, and observing all of the measured coordinates with a Review-SEM (RS-6000, manufactured by Hitachi High-Tech Corporation). Note that scratches on the substrate surface with a depth of 10 nm or more but less than 100 nm, a width of 5 nm or more but less than 500 nm, and a length of 100 μm or more were counted as scratches. The evaluation results are shown in Table 3 below.

(Polishing conditions for evaluating the number of scratches)
Polishing equipment: Applied Materials 200mm CMP single-sided polishing equipment Mirra
Pad: Nitta Haas Co., Ltd. Hard polyurethane pad IC1010
Polishing pressure: 2.0 psi
Polishing platen rotation speed: 83 rpm
Carrier rotation speed: 77 rpm
Supply of polishing composition: flowing Polishing composition supply amount: 200 ml/min Polishing time: 60 seconds.

As shown in Table 1, when the polishing compositions of Examples 1 to 13 were used, the polishing speed for TEOS films exceeded 3500 Å/min, and the polishing speed for SiN films exceeded 890 Å/min, indicating that both objects could be polished at higher polishing speeds than the polishing compositions of Comparative Examples 1 to 10. In other words, it was found that the polishing compositions containing silica having a specified shape and specified particle size distribution, a basic inorganic compound, and an anionic water-soluble polymer could efficiently polish the objects to be polished, TEOS films and SiN films.

In addition, a comparison between Example 1 and Comparative Example 1 shows that when the polishing composition does not contain a basic inorganic compound, the polishing rate is significantly reduced, and a comparison between Example 1 and Comparative Example 2 shows that when the polishing composition does not contain an anionic water-soluble polymer, the polishing rate is clearly reduced.

Comparing Example 1 with Comparative Examples 6 and 7, when the basic compound contained in the polishing composition is not a basic inorganic compound, the polishing rate with the polishing composition is significantly reduced. Also, comparing Example 1 with Comparative Examples 8 to 10, the polishing rate is clearly reduced with the polishing compositions of Comparative Examples 8 to 10 that contain water-soluble polymers other than anionic water-soluble polymers (nonionic water-soluble polymers, cationic water-soluble polymers).

As shown in Table 2, when the polishing compositions of Examples 14 to 18 were used, the polishing speed for TEOS films exceeded 3000 Å/min, and the polishing speed for SiN films exceeded 600 Å/min, indicating that both objects could be polished at a higher polishing speed than the polishing composition of Comparative Example 1. In other words, it was found that the polishing compositions containing alumina having a specified shape and specified particle size distribution, a basic inorganic compound, and an anionic water-soluble polymer could efficiently polish the objects to be polished, TEOS films and SiN films.

As shown in Table 3, when polishing was performed using the polishing compositions of Example 2 and Example 14, the polishing composition of Example 14 was found to be more likely to form scratches than the polishing composition of Example 2. This is presumably because the irregularly shaped abrasive grains suppress rolling, which makes scratches more likely to form in the case of alumina, which is harder than silica.

This shows that the polishing rate of the object to be polished is improved by the polishing composition containing a basic inorganic compound and an anionic water-soluble polymer.

As shown in Table 5, when the polishing compositions of Examples 19, 20, and 22 to 25 were used, the polishing speed for TEOS films exceeded 3500 Å/min, the polishing speed for SiN films exceeded 1000 Å/min, and the polishing speed for W films exceeded 300 Å/min. This shows that the polishing composition containing silica having a specified shape and specified particle size distribution as abrasive grains, a basic inorganic compound, and an anionic water-soluble polymer, and containing an oxidizing agent, can efficiently polish the TEOS film, SiN film, and W film that are the objects to be polished.

Claims (12)

The abrasive grains include a basic inorganic compound, an anionic water-soluble polymer, and a dispersion medium;
The zeta potential of the abrasive grains is negative;
The aspect ratio of the abrasive grains is greater than 1.1;
In the particle size distribution of the abrasive grains determined by a laser diffraction scattering method, the ratio D90/D50 of the particle diameter D90 when the cumulative particle mass from the fine particle side reaches 90% of the total particle mass to the particle diameter D50 when the cumulative particle mass from the fine particle side reaches 50% of the total particle mass exceeds 1.3,
The polishing composition further comprises an oxidizing agent . The polishing composition according to claim 1 , which is used for polishing an object containing silicon oxide . The abrasive grains include a basic inorganic compound, an anionic water-soluble polymer, and a dispersion medium;
The zeta potential of the abrasive grains is negative;
The aspect ratio of the abrasive grains is greater than 1.1;
In the particle size distribution of the abrasive grains determined by a laser diffraction scattering method, the ratio D90/D50 of the particle diameter D90 when the cumulative particle mass from the fine particle side reaches 90% of the total particle mass to the particle diameter D50 when the cumulative particle mass from the fine particle side reaches 50% of the total particle mass exceeds 1.3,
A polishing composition used for polishing an object containing silicon oxide. The polishing composition according to any one of claims 1 to 3 , wherein the anionic water-soluble polymer is at least one selected from the group consisting of polyacrylic acid-based polymers and polymethacrylic acid-based polymers. The polishing composition according to any one of claims 1 to 4 , wherein the molecular weight of the anionic water-soluble polymer is 5,000 or more and 6,000,000 or less. The polishing composition according to any one of claims 1 to 5 , which has a pH of 9 or more. The polishing composition according to claim 1 , wherein the abrasive grains contain colloidal silica. 8. The polishing composition according to claim 7 , wherein in the particle size distribution of the abrasive grains obtained by a laser diffraction scattering method, the particle diameter D50 at which the cumulative particle mass from the fine particle side reaches 50% of the total particle mass is 50 nm or more. The polishing composition according to claim 1 , wherein the abrasive grains contain alumina. 10. The polishing composition according to claim 9 , wherein in the particle size distribution of the abrasive grains obtained by a laser diffraction scattering method, the particle diameter D50 at which the cumulative particle mass from the fine particle side reaches 50% of the total particle mass is 100 nm or more. A polishing method comprising a step of polishing an object to be polished using the polishing composition according to any one of claims 1 to 10. A method for manufacturing a semiconductor substrate, comprising the polishing method according to claim 11.