JP7440423B2 - polishing composition - Google Patents

Description

The present invention relates to a polishing composition. More specifically, the present invention relates to a composition for preliminary polishing of silicon wafers. This application claims priority based on Japanese Patent Application No. 2018-212314 filed on November 12, 2018, and the entire contents of that application are incorporated herein by reference.

Conventionally, precision polishing using a polishing composition has been performed on the surfaces of materials such as metals, semimetals, nonmetals, and their oxides. For example, the surface of a silicon substrate used as a component of a semiconductor product is generally finished into a high-quality mirror surface through a lapping process or 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). As a technical document regarding the above-mentioned preliminary polishing composition, for example, Patent Document 1 can be mentioned.

Japanese Patent Application Publication No. 2015-233031

For example, silicon wafers are marked with barcodes, numbers, symbols, etc. (hard laser marks; hereinafter referred to as "HLM") by irradiating the front and back surfaces of the silicon wafer with laser light for purposes such as identification. ) may be added. HLM is generally applied after the lapping process of the silicon wafer is completed and before the polishing process is started. Normally, irradiation with laser light for attaching HLM produces a degraded layer on the surface of the silicon wafer at the periphery of the HLM. Although the HLM portion of the silicon wafer itself is not used in the final product, if the deteriorated layer is not properly polished in the polishing process after HLM application, it may become a bump and lower the yield unnecessarily. . However, the deteriorated layer changes into polysilicon or the like due to the energy of the laser beam, making it difficult to polish. Therefore, a silicon wafer pre-polishing composition that flattens the bulges on the HLM periphery (hereinafter also simply referred to as ``bumps'') may have a composition suitable for eliminating the bulges. For example, in Patent Document 1, bulge-resolving properties are investigated using a specific composition containing silica particles as abrasive grains, potassium carbonate as a weak acid salt, and a quaternary ammonium compound as a basic compound.

On the other hand, it is conventionally known that a polishing apparatus vibrates during polishing (hereinafter referred to as "polishing vibration") depending on the polishing conditions. Polishing vibrations may become a load on the apparatus and cause deterioration of the constituent members, which may adversely affect the life of the apparatus. It would be beneficial if a polishing composition could be provided that can prevent or suppress polishing vibrations while ensuring the ability to eliminate protuberances around the HLM periphery.

The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a silicon wafer pre-polishing composition that has excellent ability to eliminate bumps on the HLM periphery and is capable of preventing or suppressing polishing vibrations. .

According to this specification, a silicon wafer pre-polishing composition is provided. This polishing composition contains abrasive grains, a basic compound, a water-soluble polymer, and water, and further contains an organic acid or a salt thereof. The above-mentioned polishing composition has excellent ability to eliminate upheaval around the HLM periphery. Furthermore, in polishing using the polishing composition described above, polishing vibrations do not occur or are suppressed.

Note that in this specification, eliminating the protrusion on the HLM periphery refers to reducing the height from the reference plane (reference plane) around the HLM of the silicon wafer to the highest point of the protrusion. The height from the reference plane around the HLM of the silicon wafer to the highest point of the protuberance can be measured, for example, by a method described in Examples described below.

In one preferred embodiment, the organic acid is a polyhydric carboxylic acid. Additionally, the organic acid may be a hydroxy acid. By using a polyhydric carboxylic acid, a hydroxy acid, or both as the organic acid, the effects of the technology disclosed herein, that is, both the ability to eliminate bumps and the prevention or suppression of polishing vibrations, are preferably achieved. can do.

In one preferred embodiment, the abrasive grains are silica particles. In polishing using silica particles as abrasive grains, the effect of eliminating bumps can be more effectively exhibited.

A polishing composition according to a preferred embodiment includes quaternary ammonium hydroxide or a salt thereof as the basic compound. By using a quaternary ammonium hydroxide compound as the basic compound, the prominence of the HLM periphery can be preferably eliminated. The polishing composition having the above composition is also preferable in terms of improving the polishing rate.

In the polishing composition according to a preferred embodiment, the ratio (A _OA /A _HM ) of the content of the organic acid and its salt (A _OA ) to the content of the water-soluble polymer (A _HM ) is 1 or more and 100. It is as follows. By setting the ratio of the content of the water-soluble polymer to the content of the organic acid and its salt in the polishing composition within the above range, the protuberance at the periphery of the HLM can be more preferably eliminated.

Hereinafter, preferred embodiments of the present invention will be described. Note that matters other than those specifically mentioned in this specification that are necessary for implementing the present invention can be understood as matters designed by those skilled in the art based on the prior art in the relevant field. The present invention can be implemented based on the content disclosed in this specification and the common general knowledge in the field.
In this specification, the range "X to Y" means "more than or equal to X and less than or equal to Y."

In this specification, the average primary particle diameter of abrasive grains is calculated from the specific surface area (BET value) measured by the BET method, and the average primary particle diameter (nm) = 6000/(true density (g/cm ³ ) x BET It refers to the particle diameter calculated by the formula (m ² /g). For example, in the case of silica particles, the average primary particle size can be calculated from average primary particle size (nm)=2727/BET value (m ² /g). The specific surface area can be measured using, for example, a surface area measuring device manufactured by Micromeritex, trade name "Flow Sorb II 2300".

In this specification, the aspect ratio of each particle constituting an abrasive grain is defined as the length of the long side of the smallest rectangle circumscribing the image of the particle in a scanning electron microscope (SEM), and the length of the short side of the same rectangle. It can be found by dividing by. The average aspect ratio and standard deviation of the aspect ratio of abrasive grains are the average value and standard deviation of the aspect ratio of multiple grains within the field of view of a scanning electron microscope, and these are calculated using common image analysis software. can be found.

In this specification, the equivalent circle diameter of a particle refers to a value obtained by measuring the area of an image of the particle using a scanning electron microscope and determining the diameter of a circle with the same area. The average circularly equivalent diameter and standard deviation of the circularly equivalent diameter of the particles constituting the abrasive grains are the average value and standard deviation of the circularly equivalent diameter of multiple particles within the field of view of a scanning electron microscope, and these are also commonly used. It can be determined using suitable image analysis software.

<Abrasive>
The polishing composition disclosed herein contains abrasive grains. 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 depending on the purpose of use, manner of use, etc. One type of abrasive grain may be used alone, or two or more types may be used in combination. 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 polymethyl methacrylate (PMMA) particles, polyacrylonitrile particles, and the like. Among them, inorganic particles are preferred.

Particularly preferred abrasive grains in the technology disclosed herein include silica particles. The technique disclosed herein can be preferably implemented, for example, in an embodiment in which the abrasive grains essentially consist 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 grains. It means that it is a silica particle.

Specific examples of silica particles include colloidal silica, fumed silica, precipitated silica, and the like. Silica particles can be used alone or in combination of two or more. 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 (ability to reduce surface roughness, ability to eliminate bumps, etc.). As the colloidal silica, for example, colloidal silica produced using water glass (Na silicate) as a raw material by an ion exchange method or colloidal silica produced by an alkoxide method can be preferably employed. Here, the alkoxide method colloidal silica is colloidal silica produced by a hydrolytic condensation reaction of alkoxysilane. One type of colloidal silica can be used alone or two or more types can be used in combination.

The true specific gravity of silica constituting the silica particles is preferably 1.5 or more, more preferably 1.6 or more, still more preferably 1.7 or more. As the true specific gravity of silica increases, the polishing rate tends to increase. From this viewpoint, silica particles having a true specific gravity of 2.0 or more (for example, 2.1 or more) are particularly preferred. The upper limit of the true specific gravity of silica is not particularly limited, but is typically 2.3 or less, for example 2.2 or less. As the true specific gravity of silica, a value measured by a liquid displacement method using ethanol as a displacement liquid can be adopted.

The average primary particle diameter of the abrasive grains is not particularly limited, and can 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, more preferably 30 nm or more. In some embodiments, the average primary particle size can be, for example, greater than 40 nm, greater than 45 nm, or greater than 50 nm. Furthermore, from the viewpoint of preventing 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 size may be 75 nm or less, or 60 nm or less.

The shape (outer shape) of the abrasive grains may be spherical or non-spherical. Specific examples of non-spherical particles include a peanut shape (ie, peanut shell shape), a cocoon shape, a confetti candy shape, a rugby ball shape, and the like.

The average aspect ratio of the abrasive grains is not particularly limited. In principle, the average aspect ratio of the abrasive grains is 1.0 or more, and can be 1.05 or more, or 1.1 or more. As the average aspect ratio increases, bulge resolving properties generally tend to improve. Further, 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 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, abrasive grains in which the volume ratio of particles having a circular equivalent diameter of 50 nm or more and an aspect ratio of 1.2 or more is 50% or more can be employed. The volume ratio can also be set to 60% or more. When the volume ratio value is 50% or more, more specifically, 60% or more, the abrasive grains contain a relatively large amount of particles with a size and aspect ratio that are particularly effective for eliminating bumps. The ability to eliminate bumps due to the mechanical action of the abrasive grains can be further improved.

In some embodiments, the average equivalent circular 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. Further, the average 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 can be suitably implemented using abrasive grains having such an average circular diameter.

The content of abrasive grains is not particularly limited, and can be appropriately set depending on the purpose. The content of abrasive grains based on 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. As the content of abrasive grains increases, the ridge resolving ability generally tends to improve. In some embodiments, the content of abrasive grains may be 0.2% by weight or more, 0.5% by weight or more, or 0.6% by weight or more. Further, from the viewpoint of preventing scratches and saving the amount of abrasive grains used, in some embodiments, the content of abrasive grains may be, for example, 10% by weight or less, 5% by weight or less, or 3% by weight or less. Generally, it may be 2% by weight or less, 1.5% by weight or less, 1.2% by weight or less, or 1.0% by weight or less. These contents can be preferably applied to, for example, the contents in the polishing liquid (working slurry) supplied to the object to be polished.

In addition, in the case of a polishing composition (i.e., a concentrated solution) that is diluted and used for polishing, the content of abrasive grains is usually 50% by weight or less from the viewpoint of storage stability and filterability. It is suitable, and more preferably 40% by weight or less. Further, from the viewpoint of taking advantage of the advantage of forming a concentrated liquid, the content of abrasive grains is preferably 1% by weight or more, more preferably 5% by weight or more.

<Basic compound>
The polishing composition disclosed herein contains a basic compound. Here, the basic compound refers to a compound having the function of increasing the pH of the polishing composition by being added to the polishing composition. The basic compound functions to chemically polish the surface to be polished, and can contribute to improving the polishing rate.

As the basic compound, organic or inorganic basic compounds containing nitrogen, hydroxides of alkali metals or alkaline earth metals, and the like can be used. Examples include alkali metal hydroxides, quaternary ammoniums such as quaternary ammonium hydroxide, ammonia, and amines. Specific examples of alkali metal hydroxides include potassium hydroxide, sodium hydroxide, and the like. Specific examples of quaternary ammoniums include tetramethylammonium hydroxide, tetraethylammonium hydroxide, and tetrabutylammonium hydroxide. Specific examples of amines 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, guanidine, and azoles such as imidazole and triazole.

Preferred basic compounds from the viewpoint of improving the ability to eliminate bumps include quaternary ammonium hydroxides. Particularly preferably used is tetramethylammonium hydroxide. The above basic compounds can be used alone or in combination of two or more.

The content of the basic compound based on 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 from the viewpoint of polishing rate and protrusion elimination properties. % or more. Stability may also be improved by increasing the content of basic compounds. The upper limit of the content of the basic compound is suitably 1% by weight or less, and from the viewpoint of surface quality etc., preferably 0.5% by weight or less, more preferably 0.1% by weight or less. , more preferably 0.06% by weight or less. In addition, when using two or more types in combination, the above content refers to the total content of the two or more types of basic compounds. These contents can be preferably applied to, for example, the contents in the polishing liquid (working slurry) supplied to the object to be polished.

In addition, in the case of a polishing composition (i.e., a concentrated solution) that is diluted and used for polishing, the content of basic compounds is usually 10% by weight or less from the viewpoint of storage stability and filterability. It is suitable, and more preferably 5% by weight or less. In addition, from the viewpoint of taking advantage of the advantage of forming a concentrated liquid, the content of the basic compound is preferably 0.1% by weight or more, more preferably 0.5% by weight or more, and even more preferably 0.9% by weight or more. It is.

<Water-soluble polymer>
The polishing composition disclosed herein contains a water-soluble polymer. According to a polishing composition containing a water-soluble polymer, the ability to eliminate protrusions around the HLM edge is likely to be improved. In implementing the technology disclosed herein, it is not necessary to elucidate the mechanism by which a water-soluble polymer contributes to improving the ability to eliminate upheavals around the HLM edge, but it is not necessary to elucidate the mechanism by which a water-soluble polymer contributes to improving the ability to eliminate upheavals around the HLM edge. It is conceivable that the region is selectively protected with the water-soluble polymer compared to the HLM periphery, and polishing of this region is suppressed. However, the interpretation is not limited to this mechanism alone.

Examples of the water-soluble polymer include cellulose derivatives, starch derivatives, polymers containing oxyalkylene units, polymers containing nitrogen atoms, vinyl alcohol polymers, and the like. Specific examples include hydroxyethyl cellulose, pullulan, random copolymers and block copolymers of ethylene oxide and propylene oxide, polyvinyl alcohol, polyisoprene sulfonic acid, polyvinyl sulfonic acid, polyallylsulfonic acid, and polyisoamylene sulfonic acid. , polystyrene sulfonate, styrene-maleic acid copolymer, polyacrylate, polyvinyl acetate, polyethylene glycol, polyvinylimidazole, polyvinylcarbazole, polyvinylpyrrolidone, polyacryloylmorpholine, polyvinylcaprolactam, polyvinylpiperidine, and the like. One type of water-soluble polymer can be used alone or two or more types can be used in combination.

In the technology disclosed herein, the molecular weight of the water-soluble polymer is not particularly limited. For example, the weight average molecular weight (Mw) of the water-soluble polymer can be approximately 200×10 ⁴ or less, and 150×10 ⁴ or less is appropriate. From the viewpoint of suppressing polishing vibrations and surface defects, the Mw may be approximately 100×10 ⁴ or less, or approximately 50×10 ⁴ or less. In addition, from the viewpoint of protecting the silicon wafer surface, the above Mw is usually about 0.2×10 ⁴ or more, suitably about 0.5×10 ⁴ or more, and about 0.8× It may be 10 ⁴ or more.

Note that as the Mw of the water-soluble polymer, a value based on aqueous gel permeation chromatography (GPC) (aqueous, polyethylene oxide equivalent) can be adopted.

The content of the water-soluble polymer in the polishing composition disclosed herein is not particularly limited, and from the viewpoint of eliminating bumps and improving surface quality, the content of the water-soluble polymer is approximately 1×10 ^-5 % by weight or more (for example, approximately 1× 10 ⁻⁴ % by weight or more), preferably approximately 5×10 ⁻⁴ % by weight or more. The upper limit of the water-soluble polymer content in the polishing composition can be, for example, approximately 1% by weight or less. From the viewpoint of polishing effect, cleaning performance, etc., the content of the water-soluble polymer is preferably about 0.1% by weight or less, more preferably about 0.05% by weight or less, and still more preferably about 0.01% by weight or less. (For example, approximately 0.005% by weight or less).

Moreover, the content of the water-soluble polymer in the polishing composition disclosed herein can also be specified by the relative relationship with the abrasive grains contained in the polishing composition. Specifically, it is appropriate that the content of the water-soluble polymer in the polishing composition be approximately 0.001 part by weight or more per 100 parts by weight of the abrasive grains, and the From the viewpoint of protecting the area, the amount is preferably about 0.01 part by weight or more, more preferably about 0.05 part by weight or more (for example, about 0.1 part by weight or more). In addition, from the viewpoint of polishing effect, etc., the content of the water-soluble polymer is suitably about 10 parts by weight or less, preferably about 1 part by weight or less, and more preferably about 1 part by weight or less per 100 parts by weight of the abrasive grains. It is about 0.5 part by weight or less (for example, about 0.3 part by weight or less).

<Organic acid or its salt>
The polishing composition disclosed herein is characterized by containing an organic acid or a salt thereof. By using an organic acid or a salt thereof, polishing vibration can be prevented or suppressed while achieving excellent bulge resolving properties. In carrying out the technology disclosed herein, it is not necessary to elucidate the mechanism by which organic acids or their salts contribute to prevention of polishing vibration, etc. However, compared to inorganic acids or their salts, organic acids or their salts are It is thought that this contributes to improving the uniformity of the abrasive grains on the wafer surface, thereby making the mechanical polishing action smoother and eliminating polishing vibrations. However, the interpretation is not limited to this mechanism alone.

The organic acid or its salt is not particularly limited, and typically a carboxylic acid or its salt can be used. Although not particularly limited, polyvalent acids such as polyvalent carboxylic acids are preferably used as the organic acid. The number of acid groups per molecule of polyhydric acid (the number of carboxyl groups in the case of polyhydric carboxylic acid) is 2 to 5, more preferably 2, 3 or 4 (typically 2 or 3). The organic acid may be a monovalent acid such as a monocarboxylic acid. Furthermore, the organic acid according to a preferred embodiment may be a hydroxy acid (typically a hydroxycarboxylic acid) having one or more hydroxyl groups in one molecule. By using a polyhydric carboxylic acid having a hydroxyl group or a salt thereof, it is possible to suitably achieve both of the protrusion resolving property and the prevention of polishing vibration by the technique disclosed herein. Note that the organic acids and their salts in this specification are different from aminocarboxylic acid compounds and organic phosphonic acid compounds used as chelating agents, and therefore do not have an amine structure such as secondary amines or tertiary amines. It can be something that doesn't.

Further, the organic acid or its salt is preferably one that can exhibit a buffering effect in combination with a basic compound. A polishing composition configured to exhibit such a buffering effect has less pH fluctuation during polishing, and can maintain polishing efficiency better. It is possible to achieve both improvement and maintenance of the polishing rate more favorably.

Organic acids include 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, tartronic acid, and glyceric acid. , hydroxybutyric acid, isocitric acid, hydroxyethylidene diphosphonic acid (HEDP), nitrilotris [methylene phosphonic acid] (NTMP), phosphonobutane tricarboxylic acid (PBTC), etc. Acids may be used in the form of their salts. The salt of the above acid may be, for example, an alkali metal salt such as a sodium salt or a potassium salt, or an ammonium salt. Among these, citric acid or a salt thereof is preferred. As the salt of citric acid, an ammonium salt is preferable from the viewpoint of suppressing metal contamination, and examples thereof include diammonium hydrogen citrate and triammonium citrate. One type of organic acid or a salt thereof can be used alone or two or more types can be used in combination. From the viewpoint of anti-polishing vibration properties, it is preferable to select and use only one type from organic acids and their salts.

The content of the organic acid and its salt is not particularly limited, and may be, for example, 0.001% by weight or more, and 0.002% by weight, based on the total weight of the polishing composition, from the viewpoint of resolving protrusions. It may be more than 0.005% by weight. Further, from the viewpoint of dispersion stability of the polishing composition, in some embodiments, the above-mentioned total content may be, for example, 5% by weight or less, 1% by weight or less, 0.3% by weight or less. It may be 0.1% by weight or less, or 0.05% by weight or less (for example, 0.02% by weight or less). These contents can be preferably applied to, for example, the contents in the polishing liquid (working slurry) supplied to the object to be polished.

Moreover, the content of the organic acid and its salt in the polishing composition disclosed herein can also be specified by the relative relationship with the abrasive grains contained in the polishing composition. Specifically, it is appropriate that the content of the organic acid and its salt in the polishing composition be approximately 0.01 parts by weight or more per 100 parts by weight of the abrasive grains, and from the viewpoint of resolving protrusions, It is preferably about 0.1 part by weight or more, more preferably about 0.5 part by weight or more (for example, about 1 part by weight or more). In addition, from the viewpoint of dispersion stability, etc., it is appropriate that the content of organic acids and their salts be approximately 50 parts by weight or less, preferably approximately 10 parts by weight or less, and more preferably approximately 10 parts by weight or less per 100 parts by weight of abrasive grains. Preferably, it is about 5 parts by weight or less (for example, about 3 parts by weight or less).

Moreover, the content of the organic acid and its salt in the polishing composition disclosed herein can also be specified by the relative relationship with the content of the water-soluble polymer contained in the polishing composition. Specifically _, the ratio ₍ A _OA /A _HM ) is suitably about 0.1 or more, and from the viewpoint of preventing polishing vibrations, it is preferably about 1 or more, more preferably about 5 or more. Further, from the viewpoint of dispersion stability, etc., it is appropriate that the above ratio (A _OA /A _HM ) is approximately 500 or less, preferably approximately 100 or less, more preferably approximately 50 or less (for example, approximately 30 or less). It is.

In addition, in the case of a polishing composition (i.e., a concentrated solution) that is diluted and used for polishing, the content of organic acids and their salts is usually 10% by weight or less from the viewpoint of storage stability and filterability. Suitably, the amount is 5% by weight or less, more preferably 3% by weight or less (for example, 1% by weight or less). In addition, from the viewpoint of utilizing the advantage of forming a concentrated liquid, the content of the organic acid and its salt is preferably 0.01% by weight or more, more preferably 0.1% by weight or more, and even more preferably 0.3% by weight. % or more.

<Water>
The polishing composition disclosed herein contains water. As water, ion exchange water (deionized water), pure water, ultrapure water, distilled water, etc. can be preferably used. The water used preferably has a total content of transition metal ions of 100 ppb or less, for example, in order to avoid as much as possible inhibiting the functions of other components contained in the polishing composition. For example, the purity of water can be increased by removing impurity ions using an ion exchange resin, removing foreign substances using a filter, and distilling.
The polishing composition disclosed herein may further contain an organic solvent (lower alcohol, lower ketone, etc.) 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 contain polishing compositions (such as inorganic acids, salts thereof, surfactants, chelating agents, preservatives, antifungal agents, etc.) to the extent that the effects of the present invention are not significantly impaired. Typically, known additives that can be used in polishing compositions (polishing compositions used in silicon wafer polishing steps) may be further included as necessary.

Examples of the inorganic acids include hydrochloric acid, phosphoric acid, sulfuric acid, phosphonic acid, nitric acid, phosphinic acid, boric acid, and the like. Acids may be used in the form of their salts. The salt of the above acid may be, for example, an alkali metal salt such as a sodium salt or a potassium salt, or an ammonium salt. Other examples of the inorganic acid salts include sodium carbonate, potassium carbonate, sodium hydrogen carbonate, potassium hydrogen carbonate, sodium orthosilicate, potassium orthosilicate, calcium carbonate, calcium hydrogen carbonate, and the like. The polishing composition disclosed herein can be preferably implemented in an embodiment that is substantially free of inorganic acid salts, that is, in an embodiment that does not contain inorganic acid salts at least intentionally.

As the above surfactant, any type of surfactant can be used, including amphoteric surfactants, cationic surfactants, anionic surfactants, and nonionic surfactants. The molecular weight of the surfactant is typically less than 2000, preferably 1500 or less. Further, the lower limit of the molecular weight of the surfactant is not limited to a specific range, and may be, for example, 200 or more. As the molecular weight of the surfactant, a value calculated from a chemical formula can be adopted. The polishing composition disclosed herein can be preferably implemented in an embodiment that is substantially free of surfactants, that is, in an embodiment that does not contain surfactants at least intentionally.

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, and diethylenetriaminepentaacetic acid. , sodium diethylenetriaminepentaacetate, sodium triethylenetetraminehexaacetate, 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), 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-methylphosphonic acid Contains nosuccinic acid. Among these, organic phosphonic acid-based chelating agents are more preferred. Among these, preferred are ethylenediaminetetrakis (methylenephosphonic acid), diethylenetriaminepenta (methylenephosphonic acid), and diethylenetriaminepentaacetic acid. Particularly preferred chelating agents include ethylenediaminetetrakis (methylenephosphonic acid) and diethylenetriaminepenta (methylenephosphonic acid). One type of chelating agent can be used alone or two or more types can be used in combination.

Examples of the above-mentioned preservatives and antifungal agents include isothiazoline compounds, paraoxybenzoic acid esters, phenoxyethanol, and the like.

It is preferable that the polishing composition disclosed herein does not substantially contain an oxidizing agent. If the polishing composition contains an oxidizing agent, the supply of the composition may oxidize the silicon wafer surface and form an oxide film, which may reduce the polishing rate. It is. Here, "the polishing composition does not substantially contain an oxidizing agent" means that it does not contain an oxidizing agent, at least intentionally, and it inevitably contains a small amount of oxidizing agent due to the raw materials, manufacturing method, etc. It is permissible to be 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 0.0001 mol/L or less, particularly preferably 0.0001 mol/L or less). 000001 mol/L or less). The polishing composition according to a preferred embodiment does not contain an oxidizing agent. The polishing composition disclosed herein can 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 for polishing the object. The polishing composition disclosed herein may be used as a polishing liquid after being diluted (typically, with water), or it may be used as a polishing liquid as it is. Good too. 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 for polishing the object, and a concentrated solution (undiluted solution) of the working slurry. is included. The concentration ratio of the above-mentioned concentrate may be, for example, about 2 times to 100 times by volume, and usually about 5 times to 70 times is appropriate.

The pH of the polishing composition is typically 8.0 or higher, preferably 8.5 or higher, more preferably 9.0 or higher, even more preferably 9.5 or higher, for example 10.0 or higher. 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 abrasive grains (for example, silica particles) and suppressing a decrease in the mechanical polishing action of the abrasive grains, it is appropriate that the pH of the polishing liquid is usually 12.0 or less. , is preferably 11.8 or less, more preferably 11.5 or less. These pH values can be preferably applied to both the pH of the polishing slurry (working slurry) supplied to the object to be polished and its concentrated solution.

The pH of the polishing composition can be determined using a pH meter (for example, Horiba's glass electrode hydrogen ion concentration indicator (model number F-23)) and a standard buffer solution (phthalate pH buffer solution pH: 4.01 (25°C), neutral phosphate pH buffer pH: 6.86 (25°C), carbonate pH buffer pH: 10.01 (25°C)). This can be determined by placing a glass electrode in a polishing composition and measuring the value after the polishing composition has stabilized for 2 minutes or more.

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

The method for producing the polishing composition disclosed herein is not particularly limited. For example, each component contained in the polishing composition may be mixed using a well-known mixing device such as a blade stirrer, an ultrasonic disperser, or a 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 may be mixed in an appropriately set order.

<Polishing>
The polishing composition disclosed herein can be used for polishing an object to be polished, for example, in a mode including the following operations.
That is, a working slurry containing one of the polishing compositions disclosed herein is prepared. Next, the polishing composition is supplied to the object to be polished, and the object is polished by a conventional method. For example, a polishing target is set in a general polishing device, and a polishing composition is supplied to the surface of the polishing target (surface to be polished) through a polishing pad of the polishing device. Typically, while continuously supplying the polishing composition, a polishing pad is pressed against the surface of the object to be polished and the two are moved relative to each other (for example, rotated). After this polishing step, polishing of the object to be polished is completed.

The polishing pad used in the polishing step is not particularly limited. For example, any one of foamed polyurethane type, nonwoven fabric type, suede type, one containing abrasive grains, one without abrasive grains, etc. may be used. Further, as the polishing device, a double-sided polishing device that simultaneously polishes both sides of the object to be polished may be used, or a single-sided polishing device that polishes only one side of the object to be polished may be used.

The above-mentioned polishing composition may be used in a manner that once it is used for polishing, it is discarded (so-called "sprinkling"), or it may be circulated and used repeatedly. An example of a method for recycling a polishing composition is a method in which used polishing composition discharged from a polishing device is collected in a tank, and the collected polishing composition is again supplied to the polishing device. .

<Application>
The polishing composition disclosed herein is suitable for polishing semiconductor substrates such as silicon wafers. The above-mentioned polishing composition has an excellent ability to eliminate the protuberances around the HLM periphery (protuberance resolving ability), and therefore can be preferably applied to polishing a surface to be polished, including a surface to which an HLM has been applied. The polishing composition disclosed herein can be used in a preliminary polishing process, more specifically, in a rough polishing process (primary polishing process) which is the first polishing process in a polishing process, and in a subsequent intermediate polishing process (secondary polishing process). ) can be particularly preferably used.

The silicon wafer is subjected to general treatments that can be applied to silicon wafers, such as lapping, etching, and application of the above-mentioned HLM, before the polishing process using the polishing composition disclosed herein. Good too.
The silicon wafer typically has a surface made of silicon. Such a silicon wafer is typically 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 silicon single crystal wafers coated with HLM.
Furthermore, the polishing composition disclosed herein can also be suitably used for polishing objects to be polished that do not have HLM.

Hereinafter, some examples relating to the present invention will be described, but the present invention is not intended to be limited to what is shown in these examples.

<Preparation of polishing composition>
(Example 1)
Colloidal silica as abrasive grains, tetramethylammonium hydroxide (TMAH) as a basic compound, triammonium citrate, polyvinylpyrrolidone (PVP) as a water-soluble polymer, and ion-exchanged water were heated at room temperature at 25°C. A polishing composition was prepared by stirring and mixing at about 0.degree. C. for about 30 minutes. The obtained polishing composition was diluted 50 times with ion-exchanged water to obtain a polishing liquid containing each component at the concentrations shown in Table 1. Wt% in the table is weight%. The colloidal silica has an average primary particle diameter of 55 nm, an average circular diameter of 93 nm as determined by SEM observation, a standard deviation of the circular diameter of 38.5, an average aspect ratio of 1.3, and an aspect ratio of 1.3. The standard deviation of the ratio is 0.320, the volume percentage of particles with a circular equivalent diameter of 50 nm or more and an aspect ratio of 1.2 or more is 77%, and the volume content of particles with a circular equivalent diameter of 1 to 300 nm is 100%. %Met. Further, the pH of the polishing composition according to this example was 10.2.

(Comparative example 1)
A polishing liquid according to this example was prepared in the same manner as in Example 1, except that triammonium citrate was replaced with potassium carbonate (K ₂ CO ₃ ) and the concentrations were as shown in Table 1.

(Comparative Examples 2 to 4)
Regarding the polishing liquid of Comparative Example 1, Comparative Example 2 did not use a water-soluble polymer, Comparative Example 3 did not use potassium carbonate, and Comparative Example 4 did not use abrasive grains. Prepared.

[Elevation height]
(Silicon wafer polishing)
Using the polishing liquid according to each example as a working slurry, the surface of the object to be polished (test piece) was polished under the following conditions. The test piece was a commercially available silicon single crystal wafer with a diameter of 100 mm that had been wrapped and etched (thickness: 525 μm, conductivity type: P type, crystal orientation: <100>, resistivity: 0.1 Ω·cm or more and 100 Ω·cm). (less than) was used. HLM is attached to the wafer.
(polishing conditions)
Polishing device: Single-sided polishing device manufactured by Nippon Engis Co., Ltd., model “EJ-380IN”
Polishing pressure: 12kPa
Surface plate rotation speed: 50 rpm
Head rotation speed: 40rpm
Polishing pad: Manufactured by Nitta Haas, product name "SUBA800"
Polishing liquid supply rate: 100mL/min (using continuous flow)
Holding temperature of polishing environment: 25℃
Polishing time: 20 minutes

(evaluation)
After polishing, the surface profile of the site containing the HLM was measured using a stylus-type surface roughness profile measuring machine (SURFCOM 1500DX, manufactured by Tokyo Seimitsu Co., Ltd.) for the silicon wafer after polishing. The height [μm] to the point was measured. The evaluation results indicate that the larger the height of the bump, the worse the ability to eliminate the bump. The obtained results are shown in the "Upheaval Height" column of Table 1.

[Polishing vibration]
(Silicon wafer polishing)
Using the polishing liquid according to each example as a working slurry, the surface of the object to be polished (test piece) was polished under the following conditions. The test piece was a commercially available silicon wafer with a diameter of 300 mm that had been wrapped and etched (thickness: 775 μm, conductivity type: P type, crystal orientation: <100>, resistivity: 0.1 Ω·cm or more and less than 100 Ω·cm). used.
(polishing conditions)
Polishing device: Double-sided polishing device manufactured by Speed Fam, model “20B”
Polishing pad: Manufactured by Nitta Haas, product name "SUBA800"
Polishing pressure: 15kPa
Slurry flow rate: 4.5L/min Upper surface plate rotation speed: -13.4rpm
Lower surface plate rotation speed: +35.0 rpm (rotation direction opposite to that of the upper surface plate)
Carrier revolution speed: 11.2 rpm
Holding temperature of polishing environment: 25℃
Polishing time: 5 minutes

(evaluation)
During the above-mentioned polishing, if polishing vibration was observed, it was evaluated as "present," and if no polishing vibration was observed, it was evaluated as "absent." The obtained results are shown in the "polishing vibration" column of Table 1.

As shown in Table 1, Comparative Example 1, which used a polishing composition containing abrasive grains, a basic compound, a water-soluble polymer, and water but not containing an organic acid or its salt, had excellent protrusion elimination properties. However, polishing vibration occurred. On the other hand, Example 1 using an organic acid or its salt showed the same level of protrusion resolving ability as Comparative Example 1, and no polishing vibration occurred. In Comparative Example 2, in which no water-soluble polymer was used, the bulge elimination properties were poor and polishing vibrations also occurred. In Comparative Example 3 in which no acid or its salt was used, good protuberance elimination properties were not obtained, and polishing vibrations also occurred. In Comparative Example 4, in which no abrasive grains were used, polishing vibration did not occur, but the ridge elimination performance was poor. From these results, it was found that a polishing composition containing abrasive grains, a basic compound, a water-soluble polymer, and water, and further containing an organic acid or its salt, achieves excellent protrusion elimination properties and polishing vibration prevention properties. I know what I'm getting.

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

Claims (7)

A silicon wafer pre-polishing composition used for polishing a silicon wafer including a surface with a hard laser mark, the composition comprising:
Contains abrasive grains, basic compounds, water-soluble polymers and water,
Furthermore, it contains an organic acid or its salt,
A composition for preliminary polishing of silicon wafers, wherein the ratio (A _OA /A _HM ) of the content of the organic acid and its salt (A _OA ) to the content of the water-soluble polymer (A _HM ) is 1 or more and 100 or less. . The polishing composition according to claim 1, wherein the abrasive grains have a volume ratio 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 polishing composition according to claim 1 or 2, wherein the water-soluble polymer includes a polymer having a nitrogen atom. The polishing composition according to any one of claims 1 to 3 , wherein the organic acid is a polycarboxylic acid. The polishing composition according to any one of claims 1 to 4 , wherein the organic acid is a hydroxy acid. The polishing composition according to any one of claims 1 to 5 , wherein the abrasive grains are silica particles. The polishing composition according to any one of claims 1 to 6 , wherein the basic compound contains quaternary ammonium hydroxide or a salt thereof.