JP7666930B2 - Polishing composition - Google Patents

Description

The present invention relates to a polishing composition. More specifically, the present invention relates to a polishing composition for pre-polishing a silicon substrate. This application claims priority based on Japanese Patent Application No. 2019-18930, filed on February 5, 2019, the entire contents of which are incorporated herein by reference.

Conventionally, precision polishing using a polishing composition has been performed on the surfaces of materials such as metals, semi-metals, non-metals, and their oxides. For example, the surface of a silicon substrate used as a component of a semiconductor product is generally finished to a high-quality mirror surface through a lapping process and a polishing process. The polishing process typically includes a preliminary polishing process (preliminary polishing process) and a final polishing process (final polishing process). The preliminary polishing process typically includes a rough polishing process (primary polishing process) and an intermediate polishing process (secondary polishing process). Patent Document 1 is an example of a technical document related to the polishing of this type of silicon substrate.

Japanese Patent Application Publication No. 2015-191966

By the way, for the purpose of identification, etc., a mark such as a barcode, a number, a symbol, etc. (hard laser mark; hereinafter sometimes referred to as "HLM") may be applied to a silicon substrate by irradiating the front or back surface of the silicon substrate with a laser beam. The application of the HLM is generally performed after the lapping process of the silicon substrate is completed and before the polishing process is started. Usually, an altered layer is generated on the surface of the silicon substrate around the HLM by the irradiation of the laser beam for applying the HLM. Although the HLM part of the silicon substrate itself is not used in the final product, if the altered layer is not properly polished in the polishing process after the HLM is applied, it may become a protuberance and the yield may decrease more than necessary. However, since the altered layer is altered to polysilicon or the like by the energy of the laser beam and is difficult to polish, it was difficult to effectively suppress the occurrence of the above-mentioned protuberance with a conventional polishing composition for a general silicon substrate.

In addition, when a silicon substrate having an HLM is polished using a polishing composition exhibiting a high polishing rate (amount of material removed per unit time) in the hope of improving polishing efficiency, the areas other than the periphery of the HLM that are easily polished are selectively polished over the areas of the periphery of the HLM that are difficult to polish, and as a result, it is difficult to improve the elimination of the protuberances on the periphery of the HLM (hereinafter also simply referred to as "protuberances"). For this reason, there is a demand for a polishing composition that has excellent performance in eliminating the protuberances on the periphery of the HLM while satisfying the practical required level of polishing rate.

The present invention has been made in consideration of these points, and aims to provide a polishing composition that can be used in the preliminary polishing process of silicon substrates and can achieve both a high polishing rate and excellent elimination of protuberances around the HLM edges.

According to the present invention, a polishing composition for use in a preliminary polishing step of a silicon substrate is provided. The polishing composition includes an abrasive grain, a basic compound, and a nitrogen-containing organic compound A. Here, the nitrogen-containing organic compound A is a compound in which at least one nitrogen atom contained in the nitrogen-containing organic compound A constitutes a π-conjugated structure. The polishing composition having such a configuration can be used in the preliminary polishing step of a silicon substrate to achieve both a polishing rate that is sufficiently high for practical use and excellent elimination of the protuberance around the HLM.

In this specification, eliminating the protuberance around the HLM means reducing the height from the reference surface (reference plane) around the HLM of the silicon substrate to the highest point of the protuberance. The height from the reference surface around the HLM of the silicon substrate to the highest point of the protuberance can be measured, for example, by the method described in the examples below.

In a preferred embodiment, the polishing composition contains at least one selected from the group consisting of amidine derivative amines, nitrogen-containing heterocyclic aromatic amines, nitrogen-conjugated carboxyl group-containing compounds, and urea as the nitrogen-containing organic compound A. The polishing composition containing such a nitrogen-containing organic compound A can more suitably eliminate the protuberance around the HLM while maintaining a polishing rate that is sufficiently high for practical use.

In a preferred embodiment, the basic compound is an organic basic compound (organic alkali). When an organic alkali is used as the basic compound, the dispersibility of the abrasive grains in the polishing composition is improved, and the polishing rate is likely to be improved.

Another preferred embodiment of the polishing composition contains a quaternary ammonium compound as the basic compound. The polishing composition of this configuration can improve the dispersibility of the abrasive grains in the polishing composition, thereby improving the polishing rate.

A preferred embodiment of the polishing composition contains at least one of arginine, histidine, and tryptophan as the nitrogen-containing organic compound A. When the composition contains such a nitrogen-containing organic compound A, it is possible to effectively eliminate the protuberance around the HLM while maintaining a polishing rate that is sufficiently high for practical use.

In another preferred embodiment, the polishing composition contains at least one selected from the group consisting of imidazole, pyridine, and derivatives thereof as the nitrogen-containing organic compound A. By including such a nitrogen-containing organic compound A, a high polishing rate and excellent elimination of bumps around the HLM can be achieved at the same time.

Another preferred embodiment of the polishing composition contains urea as the nitrogen-containing organic compound A. By including such a nitrogen-containing organic compound A, a high polishing rate and excellent elimination of bumps around the HLM can be achieved at the same time.

In another preferred embodiment of the polishing composition disclosed herein, the abrasive grains are silica grains. In polishing using silica grains as abrasive grains, the nitrogen-containing organic compound A can more effectively eliminate the protuberance around the HLM.

Preferred embodiments of the present invention will be described below. Note that matters other than those specifically mentioned in this specification that are necessary for carrying out the present invention can be understood as design matters for a person skilled in the art based on the prior art in the relevant field. The present invention can be carried out based on the contents disclosed in this specification and the technical common sense in the relevant field.
In this specification, the range "X to Y" means "at least X and at most Y."

In this specification, the average primary particle size of the abrasive grains refers to the particle size calculated from the specific surface area (BET value) measured by the BET method using the formula: average primary particle size (nm) = 6000/(true density (g/ ^cm3 ) x BET value ( ^m2 /g)). For example, in the case of silica particles, the average primary particle size can be calculated from the formula: average primary particle size (nm) = 2727/BET value ( ^m2 /g). The specific surface area can be measured using, for example, a surface area measuring device manufactured by Micromeritics, under the product name "Flow Sorb II 2300".

In this specification, the aspect ratio of each particle constituting an abrasive grain can be determined by dividing the length of the long side of the smallest rectangle circumscribing an image of the particle taken with a scanning electron microscope (SEM) by the length of the short side of the same rectangle.

In this specification, the equivalent circular diameter of a particle means the value obtained by measuring the area of an image of the particle taken with a scanning electron microscope (SEM) and calculating the diameter of a circle with the same area.

<Abrasive grain>
The polishing composition disclosed herein contains abrasive grains. The abrasive grains function to mechanically polish the surface of the object to be polished.

The material and properties of the abrasive grains are not particularly limited and can be appropriately selected according to the purpose and mode of use. Abrasive grains may be used alone or in combination of two or more types. Examples of abrasive grains include inorganic particles, organic particles, and organic-inorganic composite particles. Specific examples of inorganic particles include silicon compound particles such as silica particles, silicon nitride particles, and silicon carbide particles, and diamond particles. Specific examples of organic particles include polymethylmethacrylate (PMMA) particles and polyacrylonitrile particles. Among these, inorganic particles are preferred.

In the technology disclosed herein, silica particles are particularly preferred as abrasive particles. The technology disclosed herein can be preferably implemented, for example, in an embodiment in which the abrasive particles are substantially composed of silica particles. Here, "substantially" means that 95% by weight or more (preferably 98% by weight or more, more preferably 99% by weight or more, and may be 100% by weight) of the particles constituting the abrasive particles are silica particles.

Specific examples of silica particles include colloidal silica, fumed silica, precipitated silica, etc. Silica particles can be used alone or in combination of two or more types. Colloidal silica is particularly preferred because it is less likely to cause scratches on the surface of the object to be polished and can exhibit good polishing performance (performance to reduce surface roughness, ability to eliminate protuberances, etc.). As colloidal silica, for example, colloidal silica produced by ion exchange using water glass (Na silicate) as a raw material, or alkoxide method colloidal silica can be preferably used. Here, alkoxide method colloidal silica is colloidal silica produced by hydrolysis and condensation reaction of alkoxysilane. Colloidal silica can be used alone or in combination of two or more types.

The true specific gravity of the silica constituting the silica particles is preferably 1.5 or more, more preferably 1.6 or more, and even more preferably 1.7 or more. The polishing rate tends to increase as the true specific gravity of the silica increases. From this perspective, silica particles having a true specific gravity of 2.0 or more (e.g., 2.1 or more) are particularly preferred. The upper limit of the true specific gravity of the silica is not particularly limited, but is typically 2.3 or less, for example, 2.2 or less. The true specific gravity of the silica may be measured using a liquid substitution method using ethanol as the substitution liquid.

The average primary particle diameter of the abrasive grains is not particularly limited and may be appropriately selected, for example, from a range of about 10 nm to 200 nm. From the viewpoint of improving the ability to eliminate bumps, the average primary particle diameter is preferably 20 nm or more, and more preferably 30 nm or more. In some embodiments, the average primary particle diameter may be, for example, more than 40 nm, more than 45 nm, or more than 50 nm. In addition, from the viewpoint of preventing the occurrence of scratches, the average primary particle diameter is usually advantageously 150 nm or less, preferably 120 nm or less, and more preferably 100 nm or less. In some embodiments, the average primary particle diameter of the abrasive grains may be 75 nm or less, or may be 60 nm or less.

The shape (external shape) of the abrasive grains may be spherical or non-spherical. Specific examples of non-spherical grains include peanut-shaped (i.e., peanut shell-shaped), cocoon-shaped, confetti-shaped, and other shapes with protrusions, and rugby ball-shaped.

The average aspect ratio of the abrasive grains is not particularly limited. The average aspect ratio of the abrasive grains is, in principle, 1.0 or more, and can be 1.05 or more, or 1.1 or more. As the average aspect ratio increases, the ability to eliminate bumps generally tends to improve. In addition, the average aspect ratio of the abrasive grains is preferably 3.0 or less, more preferably 2.0 or less, from the viewpoint of reducing scratches and improving the stability of polishing. In some embodiments, the average aspect ratio of the abrasive grains may be, for example, 1.5 or less, 1.4 or less, or 1.3 or less.

In some embodiments, the abrasive grains may have a volume fraction of 50% or more of particles having a circular equivalent diameter of 50 nm or more and an aspect ratio of 1.2 or more. The volume fraction may be 60% or more. When the volume fraction is 50% or more, or even 60% or more, the abrasive grains contain a relatively large number of particles with a size and aspect ratio that are particularly effective for eliminating bumps, and this can further improve the ability of the abrasive grains to eliminate bumps through their mechanical action.

In some embodiments, the average circular equivalent diameter of the abrasive grains may be, for example, 25 nm or more, 40 nm or more, 55 nm or more, or 70 nm or more. The average circular equivalent diameter of the abrasive grains may be, for example, 300 nm or less, 200 nm or less, 150 nm or less, or 100 nm or less. The polishing composition disclosed herein may be suitably implemented using abrasive grains having such average circular equivalent diameters.

The content of the abrasive grains is not particularly limited and can be set appropriately according to the purpose. The content of the abrasive grains relative to the total weight of the polishing composition may be, for example, 0.01% by weight or more, 0.05% by weight or more, or 0.1% by weight or more. By increasing the content of the abrasive grains, the bump elimination property generally tends to improve. In some embodiments, the content of the abrasive grains may be 0.2% by weight or more, 0.5% by weight or more, 0.6% by weight or more, 0.7% by weight or more, 0.8% by weight or more, or 0.85% by weight or more. In addition, from the viewpoint of preventing scratches and saving the amount of abrasive grains used, in some embodiments, the content of the abrasive grains may be, for example, 10% by weight or less, 5% by weight or less, 3% by weight or less, or 2% by weight or less. These contents can be preferably applied to the content in the polishing liquid (working slurry) supplied to the polishing object, for example.

<Nitrogen-containing organic compound A>
The polishing composition disclosed herein contains a nitrogen-containing organic compound A. Here, the nitrogen-containing organic compound A is an organic compound containing at least one nitrogen atom in the molecule, and at least one nitrogen atom contained in the nitrogen-containing organic compound A constitutes a π-conjugated structure (a structure in which π electrons are delocalized). With a polishing composition containing such a nitrogen-containing organic compound A, it is easy to achieve both a high removal rate and excellent elimination of the protuberance around the HLM.

The number of nitrogen atoms contained in the nitrogen-containing organic compound A is not particularly limited as long as it is 1 or more. In the technology disclosed herein, the nitrogen-containing organic compound A preferably contains 1 to 10 nitrogen atoms in the molecule. The number of nitrogen atoms contained in the nitrogen-containing organic compound A is more preferably 1 to 6, even more preferably 1 to 5, for example 1 to 4.

Here, when the number of nitrogen atoms contained in the nitrogen-containing organic compound A is two or more, it is not necessary for all of the nitrogen atoms contained in the nitrogen-containing organic compound A to form a π-conjugated structure. In other words, it is sufficient that at least one of the nitrogen atoms contained in the nitrogen-containing organic compound A forms a π-conjugated structure. In a preferred embodiment of the technology disclosed herein, the number of nitrogen atoms forming the π-conjugated structure contained in the nitrogen-containing organic compound A is 1 to 3, more preferably 1 to 2.

In the technology disclosed herein, the structure in which nitrogen atoms form a π-conjugated structure (hereinafter also referred to as "nitrogen conjugated structure") is not particularly limited. For example, examples of the nitrogen conjugated structure include a structure in which nitrogen atoms form part of alternating single bonds and multiple bonds (for example, a nitrogen-containing unsaturated heterocyclic structure, etc.), and a structure in which a non-shared electron pair of a nitrogen atom forms a conjugated system with an atom adjacent to the nitrogen atom. Specific examples of the nitrogen conjugated structure include an amidine structure, a nitrogen-containing unsaturated heterocyclic structure, and a urea (carbamide) structure. A polishing composition containing a nitrogen-containing organic compound A having such a structure in its molecule is likely to improve the performance of eliminating the protuberance around the HLM.

As long as the nitrogen-containing organic compound A disclosed herein contains a structure in which nitrogen atoms form a π-conjugated system, the structure (structure, substituents, etc.) of the portion other than the nitrogen-conjugated structure is not particularly limited. Specific examples of the nitrogen-containing organic compound A that can be suitably used in the technology disclosed herein include amidine derivative amines, nitrogen-containing heterocyclic aromatic amines, nitrogen-conjugated carboxyl group-containing compounds, urea, etc. Among them, from the viewpoint of the ability to eliminate the protuberance around the HLM, one or more selected from the group consisting of nitrogen-containing heterocyclic aromatic amines, nitrogen-conjugated carboxyl group-containing compounds, and urea can be preferably used. Here, the nitrogen-conjugated carboxyl group-containing compound refers to a compound that contains a nitrogen-conjugated structure in the molecule and at least one carboxyl group.

Examples of the amidine derivative amines include amines having an amidine moiety (e.g., heterocyclic amines having an amidine partial structure). Specific examples include 1,8-diazabicyclo[5.4.0]undec-7-ene (DBU) and 1,5-diazabicyclo[4.3.0]-5-nonene (DBN). Among these, DBU is preferred from the viewpoint of eliminating the protuberance around the HLM.

The nitrogen-containing heterocyclic aromatic amine refers to an amine containing at least one aromatic heterocycle containing a nitrogen atom in the molecule. Here, the size of the aromatic heterocycle is not particularly limited. In a preferred embodiment of the technology disclosed herein, the aromatic heterocycle is preferably a six-membered ring or less, more preferably a five-membered ring or a six-membered ring. The nitrogen-containing heterocyclic aromatic amine may have two or more unsaturated heterocycles (typically aromatic heterocycles) in the molecule. Preferably, the nitrogen-containing heterocyclic aromatic amine has one or two nitrogen-containing unsaturated heterocycles in the molecule.

Examples of the nitrogen-containing heterocyclic aromatic amine include nitrogen-containing six-membered aromatic amines and nitrogen-containing five-membered aromatic amines. Suitable examples of the nitrogen-containing six-membered aromatic amine include pyridine and its derivatives. Suitable examples of pyridine derivatives include 4-aminopyridine, picolinic acid, pyridine, and the like. Of these, pyridine is preferably used. Suitable examples of the nitrogen-containing five-membered aromatic amine include imidazole and its derivatives. Suitable examples of imidazole derivatives include 1-(3-aminopropyl)imidazole, 2-methylimidazole, and the like. Of these, 1-(3-aminopropyl)imidazole is preferably used.

Non-limiting examples of the nitrogen-conjugated carboxyl group-containing compounds include guanidine derivatives such as guanidinobenZoic acid, guanidinoglutaric acid, guanidinosuccinic acid, guanidinacetic acid, creatine, and guanidinop ionic acid, imidazole derivatives such as 1-imidazoleacetic acid, and picolinic acid.

Further, examples of the nitrogen-conjugated carboxyl group-containing compound include nitrogen-conjugated amino acids. The nitrogen-conjugated amino acids refer to amino acids in which at least one nitrogen atom in the molecule constitutes a π-conjugated structure. The nitrogen-conjugated amino acids are preferably used from the viewpoint of eliminating the protuberance around the HLM. Specific examples of the nitrogen-conjugated amino acids include arginine, histidine, tryptophan, etc.

The nitrogen-containing organic compound A in the technology disclosed herein may be any one of the compounds described above or a mixture of two or more of them.

The content of the nitrogen-containing organic compound A in the polishing composition (the total amount of the nitrogen-containing organic compounds A when multiple types of the nitrogen-containing organic compounds A are contained) is not particularly limited, and can be appropriately set so as to obtain the desired effect according to the purpose of use, the mode of use, etc. In a preferred embodiment, the content of the nitrogen-containing organic compound A in the polishing composition can be, for example, 0.0001% by weight or more, and may be 0.001% by weight or more from the viewpoint of better exerting the bump-eliminating effect, preferably 0.003% by weight or more, and more preferably 0.004% by weight or more. In addition, the content of the nitrogen-containing organic compound A in the polishing composition can be, for example, 0.5% by weight or less, and may be 0.1% by weight or less from the viewpoint of polishing efficiency, etc., preferably 0.05% by weight or less, more preferably 0.03% by weight or less, and even more preferably 0.02% by weight or less. These contents can be preferably applied, for example, to the content in the polishing liquid (working slurry) supplied to the polishing object.

Although not particularly limited, the content of the nitrogen-containing organic compound A in the polishing composition disclosed herein can be 0.01 parts by weight or more per 100 parts by weight of the abrasive grains, and may be 0.05 parts by weight or more from the viewpoint of better exerting the bump-eliminating effect, preferably 0.1 parts by weight or more, more preferably 0.3 parts by weight or more, and even more preferably 0.5 parts by weight or more. The content of the nitrogen-containing organic compound A in the polishing composition can be 20 parts by weight or less per 100 parts by weight of the abrasive grains, and may be 15 parts by weight or less from the viewpoint of polishing efficiency, etc., preferably 10 parts by weight or less, more preferably 5 parts by weight or less, and even more preferably 3 parts by weight or less (for example, 2.5 parts by weight or less).

<Basic Compound>
The polishing composition according to the present invention contains a basic compound. Here, the basic compound refers to a compound that has the function of increasing the pH of the polishing composition by being added to the polishing composition. The basic compound acts to chemically polish the surface to be polished, and can contribute to improving the polishing rate. In the present invention, the basic compound does not include the nitrogen-containing organic compound A in which the nitrogen atom forms a π-conjugated structure.

As the basic compound, an organic or inorganic basic compound containing nitrogen, an alkali metal or alkaline earth metal hydroxide, etc. can be used. For example, the basic compound can be an alkali metal hydroxide, a quaternary ammonium hydroxide or a salt thereof, ammonia, an amine, etc. Specific examples of the alkali metal hydroxide include potassium hydroxide and sodium hydroxide. Specific examples of the quaternary ammonium hydroxide or a salt thereof include tetramethylammonium hydroxide, tetraethylammonium hydroxide, tetrabutylammonium hydroxide, etc. Specific examples of the amine include methylamine, dimethylamine, trimethylamine, ethylamine, diethylamine, triethylamine, ethylenediamine, monoethanolamine, N-(β-aminoethyl)ethanolamine, hexamethylenediamine, diethylenetriamine, triethylenetetramine, anhydrous piperazine, piperazine hexahydrate, 1-(2-aminoethyl)piperazine, N-methylpiperazine, etc. In this way, by using a combination of a basic compound in which nitrogen atoms do not form a π-conjugated structure and the nitrogen-containing organic compound A, it is easy to achieve both an improvement in the polishing rate and an improvement in the elimination of protuberances around the HLM.

In the technology disclosed herein, the basic compound preferably used is an organic basic compound (organic alkali). When an organic alkali is used as the basic compound, the dispersibility of the abrasive grains is improved, and the polishing rate tends to increase.

A quaternary ammonium compound is a preferred basic compound from the viewpoint of improving the swelling-resolving property. As the quaternary ammonium compound, a quaternary ammonium salt (typically a strong base) such as a tetraalkylammonium salt or a hydroxyalkyltrialkylammonium salt can be preferably used. The anion component in such a quaternary ammonium salt can be, for example, OH ^- , F ^- , Cl ^- , Br ^- , I ^- , ClO ₄ ^- , BH ₄ ^- , etc. Among them, a preferred example is a quaternary ammonium salt whose anion is OH ^- , that is, a quaternary ammonium hydroxide. Specific examples of the quaternary ammonium hydroxide include tetraalkylammonium hydroxides such as tetramethylammonium hydroxide, tetraethylammonium hydroxide, tetrapropylammonium hydroxide, tetrabutylammonium hydroxide, tetrapentylammonium hydroxide, and tetrahexylammonium hydroxide; hydroxyalkyltrialkylammonium hydroxides such as 2-hydroxyethyltrimethylammonium hydroxide (also called choline); and the like. A particularly preferred example is tetraalkylammonium hydroxide (for example, tetramethylammonium hydroxide). The above basic compounds may be used alone or in combination of two or more.

The content of the basic compound relative to the total amount of the polishing composition is preferably 0.01% by weight or more, more preferably 0.02% by weight or more, and even more preferably 0.03% by weight or more, from the viewpoint of promoting the polishing rate. By increasing the content of the basic compound, the dispersion stability of the polishing composition can also be improved. The content of the basic compound is preferably 1% by weight or less, and from the viewpoint of surface quality, etc., it is preferably 0.5% by weight or less, more preferably 0.1% by weight or less. In addition, when two or more basic compounds are used in combination, the above content refers to the total content of two or more basic compounds. These contents can be preferably applied to the content in the polishing liquid (working slurry) supplied to the polishing object, for example.

Although not particularly limited, the content of the basic compound in the polishing composition disclosed herein can be 0.01 parts by weight or more per 100 parts by weight of the abrasive grains, and may be 0.05 parts by weight or more from the viewpoint of accelerating the polishing rate, preferably 0.1 parts by weight or more, more preferably 0.3 parts by weight or more, and even more preferably 0.5 parts by weight or more. The content of the basic compound in the polishing composition can be 20 parts by weight or less per 100 parts by weight of the abrasive grains, and may be 15 parts by weight or less from the viewpoint of surface quality, etc., preferably 12 parts by weight or less, and more preferably 10 parts by weight or less. For example, the content of the basic compound may be 8 parts by weight or less, or 5 parts by weight or less per 100 parts by weight of the abrasive grains. When two or more kinds of basic compounds are used in combination, the above content refers to the total content of two or more kinds of basic compounds.

<Water>
In a preferred embodiment, the polishing composition disclosed herein contains water. As the water, ion-exchanged water (deionized water), pure water, ultrapure water, distilled water, etc. can be preferably used. In order to avoid as much as possible the inhibition of the action of other components contained in the polishing composition, the water used preferably has a total transition metal ion content of, for example, 100 ppb or less. For example, the purity of water can be increased by removing impurity ions with an ion exchange resin, removing foreign matter with a filter, distillation, etc.
The polishing composition disclosed herein may further contain an organic solvent (such as a lower alcohol or a lower ketone) that can be uniformly mixed with water, if necessary. Usually, it is preferable that 90% by volume or more of the solvent contained in the polishing composition is water, and more preferably 95% by volume or more (typically 99 to 100% by volume) is water.

<Other ingredients>
The polishing composition disclosed herein may further contain, as necessary, known additives that can be used in polishing compositions (typically polishing compositions used in the polishing process of silicon substrates), such as water-soluble polymers, surfactants, acids, chelating agents, preservatives, and anti-fungal agents, to the extent that the effects of the present invention are not significantly impeded.

Examples of the water-soluble polymer include cellulose derivatives, starch derivatives, polymers containing oxyalkylene units, polymers containing nitrogen atoms, vinyl alcohol-based polymers, etc. Specific examples of the water-soluble polymer include hydroxyethyl cellulose, pullulan, random copolymers or block copolymers of ethylene oxide and propylene oxide, polyvinyl alcohol, polyisoprene sulfonic acid, polyvinyl sulfonic acid, polyallyl sulfonic acid, polyisoamylene sulfonic acid, polystyrene sulfonate, polyacrylate, polyvinyl acetate, polyethylene glycol, polyvinyl imidazole, polyvinyl carbazole, polyvinyl pyrrolidone, polyvinyl caprolactam, polyvinyl piperidine, etc. The water-soluble polymer may be used alone or in combination of two or more. The polishing composition disclosed herein may also be preferably implemented in an embodiment that does not substantially contain a water-soluble polymer, that is, an embodiment that does not contain a water-soluble polymer at least intentionally.

The polishing composition disclosed herein may contain a surfactant (typically a water-soluble organic compound having a molecular weight of less than 1×10 ⁴ ) as an optional component. The use of a surfactant may improve the dispersion stability of the polishing composition. The surfactant may be used alone or in combination of two or more.
As the surfactant, anionic or nonionic surfactants can be preferably used. From the viewpoint of low foaming and ease of pH adjustment, nonionic surfactants are more preferable. For example, nonionic surfactants include oxyalkylene polymers such as polyethylene glycol, polypropylene glycol, and polytetramethylene glycol; polyoxyalkylene adducts such as polyoxyethylene alkyl ethers, polyoxyethylene alkylphenyl ethers, polyoxyethylene alkylamines, polyoxyethylene fatty acid esters, polyoxyethylene glyceryl ether fatty acid esters, and polyoxyethylene sorbitan fatty acid esters; copolymers of multiple types of oxyalkylenes (diblock type, triblock type, random type, alternating type); and the like.
The amount of the surfactant used is suitably 5 g or less per kg of abrasive grains, preferably 2 g or less, and more preferably 1 g or less. The polishing composition disclosed herein can also be preferably implemented in an embodiment that does not substantially contain a surfactant.

Examples of the above acids include inorganic acids such as hydrochloric acid, phosphoric acid, sulfuric acid, phosphonic acid, nitric acid, phosphinic acid, and boric acid; and organic acids such as acetic acid, itaconic acid, succinic acid, tartaric acid, citric acid, maleic acid, glycolic acid, malonic acid, methanesulfonic acid, formic acid, malic acid, gluconic acid, alanine, glycine, lactic acid, hydroxyethylidene diphosphonic acid (HEDP), nitrilotris[methylene phosphonic acid] (NTMP), and phosphonobutane tricarboxylic acid (PBTC). The acid may be used in the form of a salt of the acid. The salt of the acid may be, for example, an alkali metal salt such as a sodium salt or a potassium salt, or an ammonium salt.

Examples of the chelating agent include aminocarboxylic acid chelating agents and organic phosphonic acid chelating agents. Examples of aminocarboxylic acid chelating agents include ethylenediaminetetraacetic acid, sodium ethylenediaminetetraacetate, nitrilotriacetic acid, sodium nitrilotriacetate, ammonium nitrilotriacetate, hydroxyethylethylenediaminetriacetic acid, sodium hydroxyethylethylenediaminetriacetate, diethylenetriaminepentaacetic acid, sodium diethylenetriaminepentaacetate, triethylenetetraminehexaacetic acid, and sodium triethylenetetraminehexaacetate. Examples of organic phosphonic acid chelating agents include 2-aminoethylphosphonic acid, 1-hydroxyethylidene-1,1-diphosphonic acid, aminotri(methylenephosphonic acid), ethylenediaminetetrakis(methylenephosphonic acid), diethylenetriaminepenta(methylenephosphonic acid), ethane-1,1-diphosphonic acid, ethane-1,1,2-triphosphonic acid, ethane-1-hydroxy-1,1-diphosphonic acid, ethane-1-hydroxy-1,1,2-triphosphonic acid, ethane-1,2-dicarboxy-1,2-diphosphonic acid, methanehydroxyphosphonic acid, 2-phosphonobutane-1,2-dicarboxylic acid, 1-phosphonobutane-2,3,4-tricarboxylic acid, and α-methylphosphonosuccinic acid. Of these, organic phosphonic acid chelating agents are more preferred. Among them, preferred are ethylenediaminetetrakis(methylene phosphonic acid), diethylenetriaminepenta(methylene phosphonic acid) and diethylenetriaminepentaacetic acid. Particularly preferred chelating agents are ethylenediaminetetrakis(methylene phosphonic acid) and diethylenetriaminepenta(methylene phosphonic acid). The chelating agents can be used alone or in combination of two or more. The amount of the chelating agent used can be set so that the content of the chelating agent in the working slurry is, for example, about 0.0001 to 1 wt%, about 0.001 to 0.5 wt%, or about 0.005 to 0.1 wt%, but is not limited thereto. The polishing composition disclosed herein can also be preferably used in an embodiment that does not contain a chelating agent.

Examples of the above preservatives and antifungal agents include isothiazolinone compounds, paraoxybenzoic acid esters, phenoxyethanol, etc.

The polishing composition disclosed herein preferably does not substantially contain an oxidizing agent. If an oxidizing agent is contained in the polishing composition, the surface of the silicon substrate may be oxidized by the supply of the composition, resulting in an oxide film, which may result in a decrease in the polishing rate. Here, the polishing composition substantially does not contain an oxidizing agent means that an oxidizing agent is not intentionally blended, and it is acceptable that a trace amount of an oxidizing agent is inevitably contained due to the raw materials, manufacturing method, etc. The above-mentioned trace amount means that the molar concentration of the oxidizing agent in the polishing composition is 0.0005 mol/L or less (preferably 0.0001 mol/L or less, more preferably 0.00001 mol/L or less, particularly preferably 0.000001 mol/L or less). A preferred embodiment of the polishing composition does not contain an oxidizing agent. The polishing composition disclosed herein may be preferably implemented in an embodiment that does not contain any of hydrogen peroxide, sodium persulfate, ammonium persulfate, and sodium dichloroisocyanurate, for example.

<Polishing Composition>
The polishing composition disclosed herein is typically supplied to an object to be polished in the form of a polishing liquid (working slurry) containing the polishing composition, and used to polish the object to be polished. The polishing composition disclosed herein may be used, for example, as a polishing liquid after dilution (typically with water), or may be used as a polishing liquid as is. That is, the concept of the polishing composition in the technology disclosed herein includes both a working slurry that is supplied to an object to be polished and used to polish the object to be polished, and a concentrated liquid (undiluted liquid) of the working slurry. The concentration ratio of the concentrated liquid may be, for example, about 2 to 100 times on a volume basis, and is usually about 5 to 50 times.

The pH of the polishing composition is typically 8.0 or more, preferably 8.5 or more, more preferably 9.0 or more, even more preferably 9.5 or more, for example 10.0 or more. As the pH increases, the polishing rate and the ability to eliminate bumps tend to improve. On the other hand, from the viewpoint of preventing dissolution of the abrasive grains (e.g., silica particles) and suppressing a decrease in the mechanical polishing action of the abrasive grains, the pH of the polishing liquid is usually appropriate to be 12.0 or less, preferably 11.8 or less, more preferably 11.5 or less, and even more preferably 11.0 or less. These pH values can be preferably applied to both the pH of the polishing liquid (working slurry) supplied to the object to be polished and the concentrated liquid thereof.

The pH of the polishing composition can be determined by using a pH meter (for example, a glass electrode type hydrogen ion concentration indicator (model number F-23) manufactured by Horiba, Ltd.) and performing three-point calibration using standard buffer solutions (phthalate pH buffer solution, pH: 4.01 (25°C), neutral phosphate pH buffer solution, pH: 6.86 (25°C), carbonate pH buffer solution, pH: 10.01 (25°C)), then placing the glass electrode into the polishing composition and measuring the value after it has stabilized for at least two minutes.

The polishing composition disclosed herein may be a one-component type or a multi-component type, including a two-component type. For example, the polishing liquid may be prepared by mixing at least part A containing abrasive grains with part B containing the remaining components, and diluting the mixture at an appropriate time as necessary.

The method for producing the polishing composition disclosed herein is not particularly limited. For example, the components contained in the polishing composition may be mixed using a well-known mixing device such as a blade stirrer, ultrasonic disperser, or homomixer. The manner in which these components are mixed is not particularly limited, and for example, all the components may be mixed at once or in an appropriately set order.

<Polishing>
The polishing composition disclosed herein can be used for polishing an object to be polished, for example, in an embodiment including the following steps.
That is, a working slurry containing any of the polishing compositions disclosed herein is prepared. Then, the polishing composition is supplied to an object to be polished, and polished by a conventional method. For example, the object to be polished is set in a general polishing device, and the polishing composition is supplied to the surface (surface to be polished) of the object to be polished through the polishing pad of the polishing device. Typically, the polishing pad is pressed against the surface of the object to be polished while the polishing composition is continuously supplied, and the two are moved relatively (for example, rotated). Through this polishing process, the polishing of the object to be polished is completed.

The polishing pad used in the polishing process is not particularly limited. For example, any of foamed polyurethane type, nonwoven fabric type, suede type, abrasive type, and abrasive type may be used. In addition, the polishing device may be a double-sided polishing device that polishes both sides of the object to be polished simultaneously, or a single-sided polishing device that polishes only one side of the object to be polished.

The polishing composition may be used in a manner in which it is used once for polishing and then disposed of (so-called "flow-through"), or may be recycled and used repeatedly. An example of a method for recycling a polishing composition is a method in which the used polishing composition discharged from a polishing device is collected in a tank and the collected polishing composition is supplied to the polishing device again. When recycling the polishing composition disclosed herein, new components, components that have decreased due to use, or components that are desired to be increased may be added to the polishing composition during use at any time. For example, examples of adding components include adding only the nitrogen-containing organic compound A to the polishing composition during recycling, adding only the basic compound, or adding both of these.

<Applications>
The polishing composition disclosed herein has excellent performance in eliminating the ridges around the HLM (ridge elimination). Taking advantage of this feature, the polishing composition can be preferably applied to polishing a surface to be polished, including a surface to which an HLM is applied. The polishing composition disclosed herein can be particularly preferably used in a preliminary polishing step, i.e., the first polishing step (primary polishing step) in a polishing step, or the subsequent intermediate polishing step (secondary polishing step).

The polishing composition disclosed herein is suitable for use in polishing silicon substrates. The silicon substrate may be subjected to a general treatment that can be applied to silicon substrates, such as lapping, etching, or application of the above-mentioned HLM, before the polishing process using the polishing composition disclosed herein.
The silicon substrate typically has a surface made of silicon. A typical example of such a silicon substrate is a silicon single crystal wafer, for example, a silicon single crystal wafer obtained by slicing a silicon single crystal ingot. The polishing composition disclosed herein is suitable for polishing a silicon single crystal wafer with an HLM.
In addition, the polishing composition disclosed herein can be suitably used for polishing an object that does not have an HLM.

Several examples of the present invention are described below, but it is not intended that the present invention be limited to those examples.

<Preparation of Polishing Composition>
(Example 1)
The polishing composition of Example 1 was prepared by stirring and mixing the above components and ion-exchanged water at room temperature of about 25° C. for about 30 minutes so that the content of colloidal silica (average primary particle diameter: 55 nm) as abrasive grains was 0.9 wt %, the content of tetramethylammonium hydroxide (TMAH) was 0.04 wt %, and the content of L-arginine as nitrogen-containing organic compound A was 0.016 wt %.

(Examples 2 to 6)
Polishing compositions of Examples 2 to 6 were prepared in the same manner as the polishing composition of Example 1, except that the type and content of nitrogen-containing organic compound A were changed to those shown in Table 1.

(Example 7)
The polishing composition of Example 7 was prepared in the same manner as in the polishing composition of Example 1, except that the nitrogen-containing organic compound A was not used.

(Examples 8 to 11)
The polishing compositions of Examples 8 to 11 were prepared in the same manner as the polishing composition of Example 1, except that the type and content of the nitrogen-containing organic compound were changed to those shown in Table 1.

<Polishing of silicon substrate>
The polishing liquid according to each example was used as a working slurry to polish the surface of the object to be polished (test piece) under the following conditions. The test piece was a commercially available silicon single crystal wafer (thickness: 525 μm, conductivity type: P type, crystal orientation: <100>, resistivity: 0.1 Ω cm or more and less than 100 Ω cm) with a diameter of 100 mm that had been lapped and etched. The wafer was provided with an HLM.

(Polishing conditions)
Polishing equipment: Single-sided polishing equipment manufactured by Engis Japan Co., Ltd., model number "EJ-380IN"
Polishing pressure: 12 kPa
Rotation speed of the platen: 50 rpm
Head rotation speed: 45 rpm
Polishing pad: Nitta Haas, product name "SUBA800"
Polishing liquid supply rate: 100 mL/min (flowing)
Polishing environment temperature: 25°C
Polishing allowance: 4 μm

<Evaluation of bump elimination>
For the polished silicon wafer, the surface shape of the site including the HLM was measured using a stylus surface roughness profiler (SURFCOM 1500DX, manufactured by Tokyo Seimitsu Co., Ltd.), and the height from the reference plane around the HLM to the highest point of the protuberance was measured. The evaluation result indicates that the greater the protuberance height, the worse the protuberance elimination. The results are shown in the "Protuberance Height" column of Table 1. In addition, the protuberance height of each example obtained was converted into a relative value (relative protuberance height) with the protuberance height of Example 7 taken as 100%. The results are shown in the "Relative Protuberance Height" column of Table 1.
<Polishing rate evaluation>
The polishing rate [nm/min] for each example was calculated based on the time required for the polishing, i.e., the time required for the polishing stock removal to reach 4 μm. The results were converted into relative values (relative polishing rates) with the polishing rate of Example 7 taken as 100%. The results are shown in the "relative polishing rate" column of Table 1.

The abbreviations in Table 1 refer to the following compounds.
Arg: L-arginine His: L-histidine Trp: L-tryptophan APP: 1-(3-aminopropyl)imidazole Py: pyridine TEA: triethylamine AEP: N-(2-aminoethyl)piperazine

As shown in Table 1, the polishing compositions of Examples 1 to 6, which contain a nitrogen-containing organic compound A whose nitrogen atoms form a π-conjugated structure, exhibited significantly improved bump elimination while maintaining a sufficiently high polishing rate compared to the polishing composition of Example 7, which does not contain a nitrogen-containing organic compound A.

On the other hand, the polishing compositions of Examples 8 to 11, which did not contain nitrogen-containing organic compound A but instead contained a nitrogen-containing organic compound in which the nitrogen atom did not form a π-conjugated structure, had worse bump-eliminating properties than the polishing compositions of Examples 1 to 6, which contained nitrogen-containing organic compound A.

Although specific examples of the present invention have been described in detail above, these are merely examples and do not limit the scope of the claims. The technology described in the claims includes various modifications and variations of the specific examples exemplified above.

Claims (6)

A polishing composition for use in a pre-polishing step of a silicon substrate, comprising:
The method comprises the steps of:
The nitrogen-containing organic compound A is
At least one nitrogen atom contained in the nitrogen-containing organic compound A constitutes a π-conjugated structure, and
one or more selected from the group consisting of pyridine, 1-(3-aminopropyl)imidazole and nitrogen-conjugated carboxy group-containing compounds;
The content of the nitrogen-containing organic compound A is 0.01 parts by weight or more and 10 parts by weight or less based on 100 parts by weight of the abrasive grains. The polishing composition according to claim 1, wherein the basic compound is an organic alkali. The polishing composition according to claim 2, wherein the organic alkali comprises a quaternary ammonium compound. The polishing composition according to any one of claims 1 to 3, wherein the nitrogen-containing organic compound A is a nitrogen-conjugated carboxyl group-containing compound. The polishing composition according to claim 4, wherein the nitrogen-containing organic compound A contains at least one of arginine, histidine, and tryptophan. The polishing composition according to claim 1 , wherein the abrasive grains are silica grains.