JP7074525B2 - Polishing composition and polishing method - Google Patents

Description

The present invention relates to a polishing composition used for rough polishing a silicon wafer and a polishing method using the polishing composition.

Conventionally, precision polishing using a polishing composition has been performed on the surface of materials such as metals, metalloids, non-metals, and oxides thereof. For example, the surface of a silicon wafer used as a component of a semiconductor device is generally finished into a high-quality mirror surface through a wrapping process and a polishing process. The polishing step typically includes a pre-polishing step (pre-polishing step) and a final polishing step (final polishing step). The pre-polishing step typically includes a rough polishing step (primary polishing step) and an intermediate polishing step (secondary polishing step).

In recent years, with the increase in performance and integration of semiconductor devices, improvement in quality of silicon wafers is required. For example, Patent Document 1 discloses a polishing composition containing silicon dioxide, a nitrogen-containing water-soluble polymer, and a basic compound in a specific ratio, and the polishing composition makes it possible to obtain a silicon wafer. It is stated that the shape of the edges is maintained and surface roughness and steps are reduced.

Japanese Unexamined Patent Publication No. 2013-165173

However, when a silicon wafer is roughly polished using the polishing composition described in Patent Document 1, excessive polishing (drip) at the edge of the wafer is reduced, but the flatness of the entire wafer is still insufficient. , Further quality improvement was required.

The present invention has been made in view of such circumstances, and is a polishing composition in which when a silicon wafer is roughly polished, sagging of edges is reduced and overall flatness is improved while maintaining a high polishing rate. The purpose is to provide things.

The present inventors have found that the above-mentioned problems can be solved by a polishing composition containing silica, two or more water-soluble polymers having different adsorptivity to silica, a basic compound, and water. The invention was completed.

By performing rough polishing of a silicon wafer using the polishing composition according to the present invention, sagging of edges is reduced and overall flatness is improved while maintaining a high polishing rate.

The present invention is a polishing composition used for rough polishing a silicon wafer, which comprises silica, a water-soluble polymer, a basic compound, and water, and the water-soluble polymer is silica. Includes two or more species with different adsorptivity to. Here, the adsorptivity to silica is a value calculated by the method described later.

Usually, in the rough polishing step of a silicon wafer, a method of relatively moving (for example, rotating) the wafer and the polishing pad to polish is used. The polishing pad is pressed against the surface of the wafer set in the polishing apparatus, and the polishing composition containing abrasive grains such as silica is continuously supplied. At this time, the polishing composition is supplied between the wafer and the polishing pad so as to flow mainly from the outer peripheral portion to the central portion of the substrate. The present inventors have added two or more kinds of water-soluble polymers having different adsorptivity to silica to the polishing composition, so that when a silicon wafer is roughly polished, both the end shape and the overall shape can be obtained. I found that it could be improved.

The water-soluble polymer having high adsorptivity to silica (hereinafter, also referred to as “first water-soluble polymer”) is adsorbed on the surface of silica which is an abrasive grain to buffer the mechanical action of silica. In other words, when the polishing composition is supplied to the wafer as described above, the silica first comes into contact with the outer peripheral portion of the wafer, but the first water-soluble polymer is adsorbed on the silica and covers the surface thereof. The impact of silica on the outer periphery of the wafer is mitigated. Therefore, excessive polishing of the outer peripheral portion is suppressed, sagging of the end portion (edge roll-off) is reduced, and the shape of the end portion is improved. On the other hand, a water-soluble polymer having a lower adsorptivity to silica than the first water-soluble polymer (hereinafter, also referred to as “second water-soluble polymer”) is difficult to be adsorbed on the surface of silica which is an abrasive grain. Most of them are present in the polishing composition in a free state. Therefore, it flows into the center of the wafer and diffuses over the entire surface of the wafer. As a result, the etching action of the entire wafer is controlled, and the wafer is uniformly polished. Therefore, the flatness of the entire wafer is improved and the overall shape is improved.

The above mechanism is speculative, and the present invention is not limited to the above mechanism.

In the present specification, unless otherwise specified, the operation and the measurement of physical properties are measured under the conditions of room temperature (20 to 25 ° C.) / relative humidity of 40 to 50% RH.

[Abrasion target]
The polishing composition according to the present invention is used for rough polishing a silicon wafer. By acting on the silica and the silicon surface by two or more kinds of water-soluble polymers having different adsorptivity to silica contained in the polishing composition, a silicon wafer having an excellent end and overall shape can be obtained.

Here, the silicon wafer may be made of simple substance silicon such as single crystal silicon or polycrystalline silicon, or may be composed of a layer made of simple substance silicon and a layer other than that. good. Further, it is permissible for the silicon wafer to contain elements other than silicon with a content of impurities. Therefore, the silicon wafer may contain dopants such as boron and phosphorus.

Next, the constituents of the polishing composition of the present invention will be described.

[Water-soluble polymer]
The polishing composition according to the present invention contains two or more kinds of water-soluble polymers having different adsorptivity to silica. Here, two types of water-soluble polymers are preferable. As described above, the water-soluble polymer (first water-soluble polymer) having high adsorptivity to silica suppresses excessive polishing of the outer peripheral portion by buffering the mechanical action of silica, and causes sagging of the end portion. It is thought that it will be reduced. On the other hand, the water-soluble polymer (second water-soluble polymer), which has lower adsorptivity to silica than the first water-soluble polymer, diffuses over the entire surface of the wafer to control the etching action and flatten the entire wafer. Is thought to improve.

Here, "adsorbability to silica" means the following 1. ~ 4. It is a value calculated based on:
1. 1. A slurry containing 0.004% by weight of the water-soluble polymer to be measured, 0.08% by weight of silica (primary particle diameter by the BET method) 0.08% by weight, and 0.005% by weight of ammonia was prepared, and the balance was water. Let stand for 24 hours;
2. 2. Above 1. The total organic carbon content (TOC) C ₀ in the subsequent slurry is measured;
3. 3. Above 1. After the slurry has been allowed to stand for 24 hours, the slurry is centrifuged (23000 rpm) to collect the supernatant, and the total organic carbon content (TOC) C ₁ in the supernatant is measured;
4. From C ₀ and C ₁ above, the adsorptivity to silica is measured based on the following formula (1).

(First water-soluble polymer)
The adsorptivity of the first water-soluble polymer to silica is preferably 70% or more, more preferably 75% or more, further preferably 80% or more, and even more preferably 85% or more. Is particularly preferable. Within such a range, excessive polishing of the outer peripheral portion of the wafer is suppressed, sagging of the end portion is reduced, and the shape of the end portion is improved. The adsorptivity of the first water-soluble polymer to silica is preferably 95% or less, more preferably 90% or less. Within such a range, the outer peripheral portion of the wafer is appropriately polished and the warp of the end portion is suppressed.

The first water-soluble polymer preferably contains a nitrogen atom. A water-soluble polymer containing a nitrogen atom has excellent adsorptivity to silica. Therefore, it is considered that the mechanical action of silica can be effectively buffered and the excessive polishing of the outer peripheral portion can be further suppressed. Examples of the water-soluble polymer containing a nitrogen atom include polyvinylpyrrolidone (PVP), polyvinylimidazole (PVI), polyvinylcarbazole, polyvinylcaprolactam, polyvinylpiperidin, polyacryloylmorpholine (PACMO) and the like. Above all, from the viewpoint of further reducing the sagging of the end portion and further improving the flatness of the whole, the first water-soluble polymer preferably contains at least one of polyvinylpyrrolidone and polyvinylimidazole, and may contain polyvinylpyrrolidone. More preferred. These may be used alone or in combination of two or more. That is, in a preferred embodiment of the present invention, the first water-soluble polymer is polyvinylpyrrolidone.

The weight average molecular weight of the first water-soluble polymer is preferably 5,000 or more, more preferably 8,000 or more, still more preferably 10,000 or more, still more preferably 15,000 or more. It is particularly preferably 17,000 or more. The weight average molecular weight of the first water-soluble polymer is preferably 3,000,000 or less, more preferably 1,000,000 or less, still more preferably 500,000 or less, and even more. It is preferably 250,000 or less, and particularly preferably 100,000 or less. The weight average molecular weight can be measured by gel permeation chromatography (GPC) using polyethylene oxide as a standard substance.

(Second water-soluble polymer)
The adsorptivity of the second water-soluble polymer to silica is preferably less than 70%, more preferably less than 60%, and even more preferably 50% or less. Above all, from the viewpoint of further improving the flatness of the entire wafer, it is preferably less than 30%, more preferably less than 20%, and even more preferably less than 10% (lower limit value: 0%).

From the viewpoint that the etching action of the entire wafer can be suitably controlled, the second water-soluble polymer preferably contains a hydroxyl group. In particular, it is preferable that the repeating unit of the water-soluble polymer contains a hydroxyl group. Specific examples thereof include a polymer having a structural unit derived from vinyl alcohol, a polymer having a structural unit derived from glycerin, a cellulose derivative and the like. Among them, polyvinyl alcohol (PVA), polyglycerin, hydroxyethyl cellulose (HEC) and the like are preferable. Further, from the viewpoint of further improving the flatness of the entire wafer, it is preferable to contain at least one of polyvinyl alcohol and polyglycerin, and it is more preferable to contain polyvinyl alcohol. These may be used alone or in combination of two or more. That is, in a preferred embodiment of the present invention, the second water-soluble polymer is polyvinyl alcohol. Further, in a preferred embodiment of the present invention, the second water-soluble polymer is polyglycerin.

The weight average molecular weight of the second water-soluble polymer is preferably 500 or more. The weight average molecular weight of the second water-soluble polymer is preferably 2,000,000 or less, and more preferably 1,500,000 or less. Above all, from the viewpoint of further improving the flatness of the entire wafer, the weight average molecular weight of the second water-soluble polymer is preferably less than 200,000, more preferably less than 100,000, and even more preferably 50. It is less than 000, particularly preferably less than 15,000. The weight average molecular weight can be measured by gel permeation chromatography (GPC) using polyethylene oxide as a standard substance.

When the second water-soluble polymer contains polyvinyl alcohol, the saponification degree of the polyvinyl alcohol is preferably 80% or more and 100% or less, and more preferably 90% or more and 100% or less. It is even more preferably 95% or more and 100% or less, and particularly preferably 98% or more and 100% or less.

In the polishing composition of the present invention, the weight ratio of the first water-soluble polymer and the second water-soluble polymer (weight of the first water-soluble polymer: weight of the second water-soluble polymer) is determined. It is preferably 5: 1 to 1: 5, and more preferably 3: 1 to 1: 3. Above all, it is even more preferably 1: 1 to 1: 3, and particularly preferably 1: 1 to 1: 2. Within such a range, a sufficient amount of the second water-soluble polymer is diffused over the entire surface of the wafer, so that the etching action of the entire wafer is better controlled, and the flatness of the entire wafer is further improved. When two or more kinds of water-soluble polymers are used as the first water-soluble polymer, the total weight of these is taken as the weight of the first water-soluble polymer. Similarly, when two or more kinds of water-soluble polymers are used as the second water-soluble polymer, the total weight of these is taken as the weight of the second water-soluble polymer.

When the polishing composition is used as it is as a polishing liquid, the content of the water-soluble polymer is preferably 0.002% by weight or less, more preferably 0.001% by weight or less, based on the polishing composition. It is even more preferably 0.0008% by weight or less. Within such a range, a high polishing rate can be maintained, and it can be suitably used in the rough polishing process. When the polishing composition is used as it is as a polishing liquid, the content of the water-soluble polymer is preferably 0.0001% by weight or more, more preferably 0.0003% by weight, based on the polishing composition. % Or more, and even more preferably 0.0006% by weight or more. Within such a range, a silicon wafer having an excellent end shape and overall shape can be obtained. The content of the water-soluble polymer refers to the total content of the first water-soluble polymer and the second water-soluble polymer.

Further, when the polishing composition is diluted and used for polishing, that is, when the polishing composition is a concentrated liquid, the content of the water-soluble polymer is 1 from the viewpoint of storage stability, filterability and the like. It is preferably 0% by weight or less. Further, from the viewpoint of taking advantage of the concentrated solution, the content of the water-soluble polymer is preferably 0.001% by weight or more.

In the polishing composition of the present invention, the content of the water-soluble polymer is preferably 0.1 part by weight or less, more preferably 0.08 part by weight or less, based on 100 parts by weight of the silica content. Yes, more preferably 0.06 parts by weight or less, and particularly preferably less than 0.058 parts by weight. Within such a range, a high polishing rate can be maintained, and it can be suitably used in the rough polishing process. The content of the water-soluble polymer is preferably 0.01 parts by weight or more, more preferably 0.03 parts by weight or more, and even more preferably 0, based on 100 parts by weight of the silica content. It is .04 parts by weight or more, and particularly preferably 0.045 parts by weight or more. Within such a range, a silicon wafer having an excellent end shape and overall shape can be obtained. That is, in a preferred embodiment of the present invention, the content of the water-soluble polymer is 0.01 parts by weight or more and 0.1 parts by weight or less with respect to 100 parts by weight of the silica content. The content of the water-soluble polymer refers to the total content of the first water-soluble polymer and the second water-soluble polymer.

[silica]
The polishing composition of the present invention contains silica. Silica contained in the polishing composition has an action of mechanically polishing a silicon wafer. As silica, colloidal silica is preferable. Unless otherwise specified in the present specification, silica refers to silica that has not been surface-modified.

The lower limit of the average primary particle size of silica is preferably 10 nm or more, more preferably 15 nm or more, further preferably 20 nm or more, further preferably 30 nm or more, and further preferably 40 nm or more. Is even more preferable, and 50 nm or more is particularly preferable. Within such a range, a high polishing rate can be maintained, so that it can be suitably used in the rough polishing process. The upper limit of the average primary particle size of silica is preferably 200 nm or less, more preferably 150 nm or less, and further preferably 100 nm or less. Within such a range, it is possible to further suppress the occurrence of defects on the surface of the silicon wafer after polishing. The average primary particle size of silica is calculated, for example, based on the specific surface area of silica measured by the BET method.

The lower limit of the average secondary particle diameter of silica is preferably 15 nm or more, more preferably 30 nm or more, and further preferably 50 nm or more. Within such a range, a high polishing rate can be maintained, so that it can be suitably used in the rough polishing process. The upper limit of the average secondary particle size of silica is preferably 300 nm or less, more preferably 260 nm or less, and further preferably 220 nm or less. Within such a range, it is possible to further suppress the occurrence of defects on the surface of the silicon wafer after polishing. The average secondary particle size of silica can be measured, for example, by a dynamic light scattering method.

When the polishing composition is used as it is as a polishing liquid, the content of silica is preferably 0.1% by weight or more, more preferably 0.5% by weight or more, based on the polishing composition. Even more preferably, it is 1.0% by weight or more, and particularly preferably 1.4% by weight or more. Within such a range, a high polishing rate can be maintained, and it can be suitably used in the rough polishing process. When the polishing composition is used as it is as a polishing liquid, the silica content is usually preferably 10% by weight or less, preferably 5% by weight or less, and preferably 3% by weight or less from the viewpoint of scratch prevention and the like. Is more preferable, and 2% by weight or less is particularly preferable. Reducing the silica content is also preferable from the economical point of view.

Further, when the polishing composition is diluted and used for polishing, that is, when the polishing composition is a concentrated liquid, the silica content is usually 50 from the viewpoint of storage stability, filterability and the like. It is suitable to be 10% by weight or less, and more preferably 40% by weight or less. Further, from the viewpoint of taking advantage of the concentrated liquid, the silica content is preferably 1% by weight or more, more preferably 5% by weight or more.

[Basic compound]
The polishing composition according to the present invention contains a basic compound. Here, the basic compound refers to a compound having a function of raising the pH of the composition by being added to the polishing composition. The basic compound functions to chemically polish the surface to be polished, and may contribute to the improvement of the polishing speed. In addition, the basic compound may help improve the dispersion stability of the polishing composition.

As the basic compound, an organic or inorganic basic compound containing nitrogen, an alkali metal or a hydroxide of a Group 2 metal, various carbonates, hydrogen carbonate and the like can be used. Examples thereof include hydroxides of alkali metals, quaternary ammonium hydroxides or salts thereof, ammonia, amines and the like. Specific examples of alkali metal hydroxides include potassium hydroxide and sodium hydroxide. Specific examples of the carbonate or hydrogen carbonate include ammonium hydrogencarbonate, ammonium carbonate, potassium hydrogencarbonate, potassium carbonate, sodium hydrogencarbonate, sodium carbonate and the like. Specific examples of the quaternary ammonium hydroxide or a salt thereof include tetramethylammonium hydroxide, tetraethylammonium hydroxide, tetrabutylammonium hydroxide and the like. Specific examples of amines include methylamine, dimethylamine, trimethylamine, ethylamine, diethylamine, triethylamine, ethylenediamine, monoethanolamine, N- (β-aminoethyl) ethanolamine, hexamethylenediamine, diethylenetriamine, triethylenetetramine, and anhydrous piperazine. , Piperazine hexahydrate, 1- (2-aminoethyl) piperazine, N-methylpiperazine, guanidine, azoles such as imidazole and triazole, and the like.

From the viewpoint of improving the polishing speed, preferred basic compounds include ammonia, potassium hydroxide, sodium hydroxide, tetramethylammonium hydroxide, tetraethylammonium hydroxide, ammonium hydrogencarbonate, ammonium carbonate, potassium hydrogencarbonate, potassium carbonate, and carbonic acid. Examples include sodium hydrogen and sodium carbonate. Of these, ammonia, potassium hydroxide, sodium hydroxide, tetramethylammonium hydroxide and tetraethylammonium hydroxide are exemplified as more preferable ones. Further preferred are potassium carbonate and tetramethylammonium hydroxide. Such basic compounds may be used alone or in combination of two or more. When two or more kinds are used in combination, for example, a combination of potassium carbonate and tetramethylammonium hydroxide is preferable.

When the polishing composition is used as it is as a polishing liquid, the content of the basic compound is preferably 0.01% by weight or more, more preferably 0.05% by weight or more, still more preferably, with respect to the polishing composition. Is 0.1% by weight or more. Within such a range, a high polishing rate can be maintained, so that it can be suitably used in the rough polishing process. In addition, the stability may be improved by increasing the content of the basic compound. When the polishing composition is used as it is as a polishing liquid, the upper limit of the content of the basic compound is appropriately 1% by weight or less, and is preferably 0.5% by weight from the viewpoint of surface quality and the like. % Or less. When two or more kinds are used in combination, the content refers to the total content of two or more kinds of basic compounds.

Further, when the polishing composition is diluted and used for polishing, that is, when the polishing composition is a concentrated solution, the content of the basic compound is usually determined from the viewpoint of storage stability, filterability and the like. It is appropriate that it is 10% by weight or less, and more preferably 5% by weight or less. Further, from the viewpoint of taking advantage of the concentrated solution, the content of the basic compound is preferably 0.1% by weight or more, more preferably 0.5% by weight or more, still more preferably 0.9% by weight or more. Is.

[water]
The polishing composition according to the present invention contains water as a dispersion medium for dispersing or dissolving each component. Water preferably contains as little impurities as possible from the viewpoint of preventing contamination of the silicon wafer and inhibition of the action of other components. As such water, for example, water having a total content of transition metal ions of 100 ppb or less is preferable. Here, the purity of water can be increased by, for example, operations such as removal of impurity ions using an ion exchange resin, removal of foreign substances by a filter, distillation and the like. Specifically, as the water, for example, deionized water (ion-exchanged water), pure water, ultrapure water, distilled water and the like are preferably used.

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

[Other ingredients]
The polishing composition according to the present invention is a known additive that can be used in the polishing composition, such as a surfactant, a chelating agent, a preservative, and an antifungal agent, as long as the effect of the present invention is not significantly impaired. May be further contained if necessary. The polishing composition here typically means a polishing composition used in the polishing step of a silicon wafer.

(Surfactant)
The polishing composition of the present invention may further contain a surfactant such as a nonionic surfactant, a cationic surfactant, and an anionic surfactant, if necessary. From the viewpoint of suppressing the precipitation of the water-soluble polymer and maintaining the performance of the polishing composition, the polishing composition of the present invention preferably further contains a nonionic surfactant.

Examples of nonionic surfactants that can be used in the present invention include alkylbetaine, alkylamine oxides, polyoxyethylene alkyl ethers, polyoxyalkylene alkyl ethers, sorbitan fatty acid esters, glycerin fatty acid esters, polyoxyethylene fatty acid esters, and polyoxy. Examples thereof include ethylene alkylamine and alkylalkanolamide. Of these, polyoxyalkylene alkyl ethers are preferable, and polyoxyethylene alkyl ethers are more preferable, from the viewpoint of improving the dispersion stability of the polishing composition. These may be used alone or in combination of two or more.

When the polishing composition is used as it is as a polishing liquid, the content of the nonionic surfactant is preferably 0.00001% by weight or more, more preferably 0.00002% by weight or more, based on the polishing composition. More preferably, it is 0.00003% by weight or more. Within such a range, the dispersion stability of the polishing composition is improved, so that it can be suitably used in the rough polishing step. When the polishing composition is used as it is as a polishing liquid, it is appropriate that the upper limit of the content of the nonionic surfactant is 0.0002% by weight or less, which is preferable from the viewpoint of surface quality and the like. It is 0.0001% by weight or less. When two or more kinds are used in combination, the content refers to the total content of two or more kinds of nonionic surfactants.

Further, when the polishing composition is diluted and used for polishing, that is, when the polishing composition is a concentrated liquid, the content of the nonionic surfactant is determined from the viewpoint of storage stability, filterability and the like. Usually, it is suitable to be 0.1% by weight or less, and more preferably 0.05% by weight or less. Further, from the viewpoint of taking advantage of the concentrated solution, the content of the basic compound is preferably 0.0001% by weight or more, more preferably 0.0002% by weight or more, still more preferably 0.0005% by weight or more. Is.

(Chelating agent)
Examples of the chelating agent that can be contained in the polishing composition include an aminocarboxylic acid-based chelating agent and an organic phosphonic acid-based chelating agent. Examples of aminocarboxylic acid-based chelating agents include ethylenediamine tetraacetic acid, sodium ethylenediamine tetraacetate, nitrilotriacetic acid, sodium nitrilotriacetate, ammonium nitrilotriacetic acid, hydroxyethylethylenediamine triacetic acid, sodium hydroxyethylethylenediamine triacetate, and diethylenetriaminepentaacetic acid. , Diethylenetriamine pentaacetate sodium, triethylenetetramine hexaacetic acid and triethylenetetramine hexaacetate sodium. Examples of organic phosphonic acid-based chelating agents include 2-aminoethylphosphonic acid, 1-hydroxyethylidene-1,1-diphosphonic acid, aminotri (methylenephosphonic acid), ethylenediaminetetrakis (methylenephosphonic acid), and diethylenetriaminepenta (methylenephosphonic acid). Acid), Etan-1,1-diphosphonic acid, Etan-1,1,2-triphosphonic acid, Etan-1-hydroxy-1,1-diphosphonic acid, Etan-1-hydroxy-1,1,2-triphosphonic acid , Etan-1,2-dicarboxy-1,2-diphosphonic acid, methanehydroxyphosphonic acid, 2-phosphonobutane-1,2-dicarboxylic acid, 1-phosphonobutane-2,3,4-tricarboxylic acid and α-methylphospho Contains nosuccinic acid. Of these, organic phosphonic acid-based chelating agents are more preferable. Of these, ethylenediaminetetrakis (methylenephosphonic acid), diethylenetriaminepenta (methylenephosphonic acid) and diethylenetriaminepentaacetic acid are preferable. Particularly preferred chelating agents include ethylenediamine tetrakis (methylenephosphonic acid) and diethylenetriaminepenta (methylenephosphonic acid). The chelating agent may be used alone or in combination of two or more.

Examples of preservatives and fungicides that can be contained in the polishing composition include isothiazolin-based agents such as 2-methyl-4-isothiazolin-3-one and 5-chloro-2-methyl-4-isothiazolin-3-one. Preservatives, paraoxybenzoic acid esters, phenoxyethanol and the like can be mentioned. These preservatives and fungicides may be used alone or in admixture of two or more.

[Characteristics of polishing composition]
The polishing composition according to the present invention is typically supplied to the above-mentioned silicon wafer in the form of a polishing liquid containing the polishing composition, and is used for rough polishing of the silicon wafer. The polishing composition according to the present invention may be, for example, diluted and used as a polishing liquid, or may be used as it is as a polishing liquid. Here, the dilution is typically a dilution with water. The concept of the polishing composition in the technique according to the present invention includes a polishing liquid (working slurry) supplied to a silicon wafer and used for polishing, and a concentrated liquid (stock solution of working slurry) diluted and used for polishing. Both are included. The concentration ratio of the concentrated solution can be, for example, about 2 to 100 times on a volume basis, and usually about 5 to 50 times is appropriate.

When the polishing composition is used as it is as a polishing liquid, the pH of the polishing composition is preferably 9.0 or more, more preferably 9.5 or more, still more preferably 10.0 or more. , Particularly preferably 10.5 or more. As the pH of the polishing liquid increases, the polishing rate increases. On the other hand, when the polishing composition is used as it is as a polishing liquid, the pH of the polishing liquid is preferably 12.0 or less, more preferably 11.5 or less. When the pH of the polishing liquid is 12.0 or less, it is possible to suppress the dissolution of silica and prevent the silica from deteriorating the mechanical polishing action.

Further, when the polishing composition is diluted and used for polishing, that is, when the polishing composition is a concentrated solution, the pH of the polishing composition is preferably 9.5 or more, more preferably 10. It is 0.0 or more, and even more preferably 10.5 or more. The pH of the polishing composition is preferably 12.0 or less, preferably 11.5 or less.

The pH of the polishing composition can be measured using a pH meter. After calibrating the pH meter at 3 points with standard buffer, the glass electrodes are placed in the polishing composition. Then, the pH of the polishing composition can be grasped by measuring the value after it has stabilized after 2 minutes or more. For example, as the pH meter, a pH glass electrode type hydrogen ion concentration indicator (model number F-23) manufactured by HORIBA, Ltd. can be used. The standard buffers are (1) phthalate pH buffer pH: 4.01 (25 ° C), (2) neutral phosphate pH buffer pH: 6.86 (25 ° C), (3) carbonate. pH buffer pH: 10.01 (25 ° C.) can be used.

The polishing composition according to the present invention may be a one-component type or a multi-component type including a two-component type. The multi-component type is a combination of liquids in which a part or all of the polishing composition is mixed at an arbitrary mixing ratio. Further, when a polishing device having a plurality of supply paths for the polishing composition is used, two or more polishing compositions prepared in advance so that the polishing composition is mixed on the polishing device may be used. good.

[Manufacturing method of polishing composition]
The method for producing a polishing composition of the present invention can be obtained, for example, by stirring and mixing each component in water. However, it is not particularly limited to this method. The temperature at which each component is mixed is not particularly limited, but is preferably 10 ° C. or higher and 40 ° C. or lower, and may be heated in order to increase the dissolution rate. Further, the mixing time is not particularly limited.

[Polishing method]
The polishing composition according to the present invention can be used in a rough polishing step (primary polishing step) of a silicon wafer, for example, in an embodiment including the following operations. That is, the present invention also provides a polishing method for rough polishing a silicon wafer using the above polishing composition.

That is, a working slurry containing the polishing composition according to the present invention is prepared. Next, the polishing composition is supplied to a silicon wafer, and rough polishing is performed by a conventional method. For example, a silicon wafer is set in a general polishing device, and a polishing composition is supplied to the surface (polishing target surface) of the silicon wafer through the polishing pad of the polishing device. Typically, while continuously supplying the polishing composition, a polishing pad is pressed against the surface of the silicon wafer to relatively move (for example, rotationally move) the two. Rough polishing of the silicon wafer is completed through such a polishing step.

The polishing pad used in the above process is not particularly limited. For example, any of foamed polyurethane type, non-woven fabric type, suede type, silica-containing type, silica-free type, and the like may be used. Further, as the polishing device, a double-sided polishing device that simultaneously polishes both sides of the silicon wafer may be used, or a single-sided polishing device that polishes only one side of the silicon wafer may be used.

The polishing conditions are not particularly limited, but for example, the rotation speed of the polishing surface plate is preferably 10 rpm or more and 500 rpm or less, and the pressure (polishing pressure) applied to the silicon wafer is preferably 3 kPa or more and 70 kPa or less, for example, 3.45 kPa or more and 69 kPa or less. .. The method of supplying the polishing composition to the polishing pad is also not particularly limited, and for example, a method of continuously supplying the polishing composition with a pump or the like is adopted. Although the supply amount is not limited, it is preferable that the surface of the polishing pad is always covered with the polishing composition of the present invention.

The polishing composition may be used in a so-called "flowing" manner, or may be circulated and used repeatedly. Here, the “flowing” refers to a mode in which once used for polishing, it is thrown away. The following methods are mentioned as an example of the method of circulating and using the polishing composition. In this method, the used polishing composition discharged from the polishing device is collected in a tank, and the collected polishing composition is supplied to the polishing device again. When the polishing composition is recycled, the environmental load can be reduced as compared with the case where the polishing composition is used by flowing. This is because the amount of used polishing composition treated as waste liquid is reduced. In addition, the cost can be suppressed by reducing the amount of the polishing composition used.

[Use]
As described above, the polishing composition of the present invention is excellent in the ability to shape the edges and the entire shape of the silicon wafer while maintaining a high polishing rate. Taking advantage of these features, the polishing composition of the present invention is suitably used in a rough polishing step of a silicon wafer, that is, in a first polishing step (primary polishing step) in a polishing step. The rough polishing step is typically carried out as a double-sided polishing step in which both sides of the wafer are polished at the same time. The polishing composition according to the present invention can also be preferably used in such a double-sided polishing step.

The present invention will be described in more detail with reference to the following examples and comparative examples. However, the technical scope of the present invention is not limited to the following examples.

[Evaluation of adsorptivity of water-soluble polymer to silica]
The components and ion-exchanged water have a final concentration of 0.004% by weight of the water-soluble polymer to be measured, 0.08% by weight of colloidal silica (average primary particle diameter by the BET method) 0.08% by weight, and 0.005% by weight of ammonia. Was stirred and mixed at room temperature (25 ° C.) for 30 minutes to prepare an evaluation slurry. After allowing the slurry to stand at 25 ° C. for 24 hours, the total organic carbon content (TOC) C ₀ in the slurry was measured using a total organic carbon meter (TOC-5000A manufactured by Shimadzu Corporation). In addition, the slurry after standing was centrifuged (23000 rpm, 30 minutes, 25 ° C.) to recover the supernatant, and the total organic carbon content (TOC) C ₁ in the supernatant was measured. From C ₀ and C ₁ , the adsorptivity to silica was calculated based on the following formula (1).

The water-soluble polymers to be measured are as follows:
-Polyvinylpyrrolidone (weight average molecular weight 45,000, referred to as "PVP" in Table 2)
-Polyvinylpyrrolidone (weight average molecular weight 2.5 million, referred to as "PVP high molecular weight" in Table 2)
-Polyvinylimidazole (weight average molecular weight 17,000, referred to as "PVI" in Table 2)
-Polyvinyl alcohol (weight average molecular weight 10,000, saponification degree 98%, referred to as "PVA" in Table 2)
Hydroxyethyl cellulose (weight average molecular weight 1.2 million, referred to as "HEC" in Table 2)
-Polyglycerin (weight average molecular weight 750).

[Preparation of polishing composition]
(Example 1)
Colloidal silica (average primary particle diameter 55 nm by BET method) 1.4% by weight, polyvinylpyrrolidone (PVP) (weight average molecular weight 45,000) 0.0003% by weight as the first water-soluble polymer, second water-soluble Final concentration of polyvinyl alcohol (PVA) (weight average molecular weight 10,000) 0.0005% by weight as a sex polymer, 0.07% by weight of tetramethylammonium hydroxide (TMAH) as a basic compound, and 0.04% by weight of potassium carbonate. The components and ion-exchanged water were stirred and mixed at room temperature (25 ° C.) for 30 minutes, and then allowed to stand for 1 day or more. KOH (pH adjuster) was added to the static solution to adjust the pH to 10.5 to prepare a polishing composition.

(Examples 2 to 5 and Comparative Examples 1 to 4)
The polishing compositions according to Examples 2 to 5 and Comparative Examples 1 to 4 were prepared in the same manner as in Example 1 except that the type and content of the water-soluble polymer were changed as shown in Table 2.

[Polishing performance]
Using the above polishing composition, a silicon wafer (Bare Si P- <100>) having a size of 60 mm × 60 mm was polished under the polishing conditions shown in Table 1 below.

(Polishing rate)
The weight of the silicon wafer before and after polishing was measured, and the polishing rate was calculated using the following formula from the difference in weight before and after polishing.

Here, the density of silicon was 2.33 [g / cm ³ ], and the area to be polished was 36 [cm ² ]. Table 2 shows the relative values of the polishing composition of Comparative Example 1 with the polishing rate as 100.

(Wafer thickness difference)
Using DIGIMICRO MH-15M manufactured by Nikon Corporation, the thickness in the wafer surface after polishing was measured. The measurement points are set at intervals of 10 mm in length and width in a region (50 mm × 50 mm) starting from a position 5 mm from the outer periphery of the wafer, for a total of 36 points. Then, the difference between the maximum value and the minimum value among the 36 points was defined as "wafer thickness difference". Table 2 shows the relative values when the wafer thickness difference of Comparative Example 1 is 100. In Table 2, it can be said that the smaller the value of the wafer thickness difference, the higher the flatness of the entire wafer and the better the overall shape.

(Roll-off amount)
The roll-off amount was evaluated by measuring the shape displacement amount of the wafer surface after polishing using New View 5032 manufactured by Zygo. Specifically, a relatively flat region at a position of 2.0 mm to 4.0 mm from the outer peripheral edge of the wafer toward the center is set as a reference region, and a straight line (reference straight line) that approximates the amount of shape displacement in the region is set. Subtract using the least squares method. Next, a point on the reference straight line at a position 2.0 mm from the outer peripheral edge is set as a reference point, and the difference between the shape displacement amount of the wafer and the reference point at the 2.0 mm position is measured, and this is referred to as "roll-off amount". Was defined. Table 2 shows the relative values when the roll-off amount of Comparative Example 1 is 100. In Table 2, it can be said that the smaller the value of the roll-off amount, the smaller the sagging of the wafer end portion, and the better the end portion shape.

Table 2 shows the results of the wafer thickness difference and the roll-off amount after polishing using each polishing composition. Table 2 also shows the adsorptivity of each water-soluble polymer calculated by the above method to silica.

As shown in Table 2, the silicon wafers polished using the polishing compositions according to Examples 1 to 5 had small edge sagging and good overall flatness. Further, it shows the same polishing rate as that of Comparative Example 1 containing no water-soluble polymer, and it can be seen that a high polishing rate can be maintained.

On the other hand, as shown in Comparative Example 1, when the water-soluble polymer was not contained, the sagging of the end portion was large and the overall flatness was also inferior. It is suggested that the absence of the water-soluble polymer promotes excessive polishing of the edges, and the etching action of the entire wafer is not controlled and is uniformly polished. Further, as shown in Comparative Examples 2 to 4, when a water-soluble polymer is contained but two types having different adsorptivity to silica are not contained as in the present invention, sagging of the wafer end is relatively suppressed. However, the result was that the flatness of the entire wafer was poor. In Comparative Example 2, it is considered that the flatness of the entire wafer was poor because the water-soluble polymer was consumed by adsorption to silica and the etching suppression ability of the entire wafer could not be controlled. In Comparative Example 3, two types of water-soluble polymers having the same adsorptivity for silica and different molecular weights adsorb to silica, so that the edge shape is good, but the etching action of the entire wafer is not controlled. It is probable that the overall flatness was poor. In Comparative Example 4, it is considered that the flatness of the entire portion was improved, but the shape of the end portion became poor because the excessive polishing of the end portion could not be suppressed.

Claims (11)

A polishing composition used for rough polishing of silicon wafers.
Containing silica, a water-soluble polymer, a basic compound, and water,
The water-soluble polymer contains two or more kinds having different adsorptivity to silica.
A polishing composition having a water-soluble polymer content of 0.0001% by weight or more and 0.002% by weight or less . The water-soluble polymer includes a first water-soluble polymer and a second water-soluble polymer, and includes a second water-soluble polymer.
The first water-soluble polymer has an adsorptivity to the silica of 70% or more, and the second water-soluble polymer has an adsorptivity to the silica of less than 70%, according to claim 1. A composition for polishing. The polishing composition according to claim 2, wherein the weight ratio of the first water-soluble polymer to the second water-soluble polymer is 5: 1 to 1: 5. The polishing composition according to claim 2 or 3, wherein the second water-soluble polymer contains a hydroxyl group. The polishing composition according to any one of claims 2 to 4, wherein the first water-soluble polymer contains a nitrogen atom. The polishing composition according to any one of claims 2 to 5, wherein the first water-soluble polymer is polyvinylpyrrolidone. The polishing composition according to any one of claims 2 to 6, wherein the second water-soluble polymer is polyvinyl alcohol. The polishing composition according to any one of claims 2 to 6, wherein the second water-soluble polymer is polyglycerin. The polishing composition according to any one of claims 1 to 8 , wherein the silica has an average primary particle diameter of 50 nm or more. The content of any one of claims 1 to 9 , wherein the content of the water-soluble polymer is 0.01 parts by weight or more and 0.1 parts by weight or less with respect to 100 parts by weight of the silica content. Polishing composition. A polishing method for rough polishing a silicon wafer using the polishing composition according to any one of claims 1 to 10 .