JP5985083B2 - Polishing composition and method for producing semiconductor wafer - Google Patents

Description

<Technical field>
The present invention relates to a polishing composition and a method for producing a semiconductor wafer by polishing the semiconductor wafer using the same.

<Related technologies>
Conventionally, various polishing compositions have been proposed as compositions for polishing semiconductor wafers and the like.

  For example, in Patent Document 1, silica sol and silica gel are proposed as polishing compositions. Furthermore, Patent Document 2 discloses that the polishing rate is increased by setting the pH of the suspension within the range of 10.5 to 12.5.

  However, in these techniques, the processing speed is generally slow and the production efficiency is inferior, and the pH is likely to change due to a change in external conditions and the processing stability is often lacking. In other words, these techniques are time-consuming and difficult processing methods, and are difficult to say as complete methods. However, in particular, with the recent high integration of electronic circuits and the increase in size of the wafer itself, high level planarization of silicon wafers and semiconductor device wafer surfaces is indispensable. Furthermore, in order to improve production efficiency, a polishing composition and a polishing method having a high processing speed are desired.

  In order to solve such problems, a colloidal solution containing 1 to 15% by weight of colloidal silica having an average primary particle size of 8 to 500 nm is formed by combining tetramethylammonium hydroxide and potassium bicarbonate. Is added as a buffer solution having a buffering action between pH 9.5 and 10.6, and the conductivity at 25 ° C. is 20 mS / m or more and 101 mS / m per 1% by weight of silicon oxide as colloidal silica. A polishing composition characterized by the following is disclosed. Thus, by using the polishing composition as a buffer solution and increasing the electrical conductivity, a polishing composition having a small pH change and a high polishing rate is formed. It is disclosed that if the polishing composition of the present invention is used, silicon wafers and semiconductor device wafers can be stably polished at a high speed without degrading the quality of the polished surface (Patent Document 3).

U.S. Pat. No. 3,170,273 U.S. Pat. No. 3,328,141 Japanese Patent No. 4163785

<Outline of the invention>
However, even in the technique of Patent Document 3, a sufficient polishing rate cannot be realized, and it cannot be said that a stable polishing composition having a low performance change is provided even after repeated use.

  Accordingly, an object of the present invention is to provide a stable polishing composition that realizes a sufficient polishing rate and has a low performance change even when used repeatedly.

  The present inventors diligently studied the cause of inferior polishing rate even when polished with the polishing composition disclosed in Patent Document 3, and instability in repeated use. In the process, attention was paid to the presence of water-soluble quaternary ammonium hydroxide (quaternary ammonium compound) adsorbed with colloidal silica in the polishing composition and not liberated in the polishing composition. The present invention was completed by preparing a polishing composition in consideration of such a quaternary ammonium compound that has not been focused on in the past.

That is, the problem to be solved by the present invention is a polishing composition for use in polishing a semiconductor wafer, comprising colloidal silica, a weak acid salt, and a quaternary ammonium compound, and the content of the weak acid salt Is 1.0 × 10 ^{−7 to} 1.0 × 10 ⁻⁵ mol / m ² —SiO ₂ with respect to the total surface area of the colloidal silica, and the content of the quaternary ammonium compound is represented by the following formula (1) And by providing a polishing composition that satisfies the relationship of (2).

<Description of Preferred Embodiment>
Embodiments of the present invention will be described below. In addition, this invention is not limited only to the following embodiment. In this specification, “X to Y” indicating a range means “X or more and Y or less”, “weight” and “mass”, “wt%” and “mass%”, and “part by weight” and “part by mass”. Is treated as a synonym. Unless otherwise specified, measurement of operation and physical properties is performed under conditions of room temperature (20 to 25 ° C.) / Relative humidity 40 to 50%.

The present invention is a polishing composition for use in polishing a semiconductor wafer, comprising colloidal silica, a weak acid salt, and a quaternary ammonium compound, wherein the content of the weak acid salt is the total surface area of the colloidal silica. On the other hand, it is 1.0 × 10 ^{−7 to} 1.0 × 10 ⁻⁵ mol / m ² —SiO ₂ , and the content of the quaternary ammonium compound satisfies the relationship of the following formulas (1) and (2): A polishing composition.

  With the above configuration, a sufficient polishing rate can be realized, and in particular, the initial polishing efficiency can be improved. Further, according to the polishing composition of the present invention, it is possible to provide a stable polishing composition having a low performance change even after repeated use, in particular, excellent in polishing efficiency maintenance rate.

  The polishing object to be polished by the polishing composition of the present invention is not particularly limited as long as it is a semiconductor wafer, and can be applied to semiconductor wafers such as silicon, aluminum, nickel, tungsten, copper, tantalum, titanium, and stainless steel. . Above all, the polishing composition of the present invention is suitable for polishing a silicon semiconductor wafer. Further, the shape of the object to be polished is not particularly limited. For example, it can be preferably applied to polishing a polishing object having a flat surface such as a plate shape or a polyhedron shape. Of these, a polishing object composed of a plurality of materials may be used. Among these, the polishing composition of the present invention is useful for polishing a polishing object having a surface made of single crystal or polycrystalline silicon.

  The technical idea of the present invention will be described in detail below.

  What is required for a polishing composition (particularly a double-sided polishing composition) has controllability of the flatness of the object to be polished, improvement of polishing efficiency, resistance to recycling, and the like, which the present invention is trying to solve. However, the present invention is to provide a polishing composition that improves a sufficient polishing rate, particularly an initial polishing efficiency, and is resistant to recycling (that is, having a stable polishing efficiency maintenance rate). This recycling resistance means that the polishing composition can be used repeatedly a plurality of times when it is circulated and polished.

In a preferred embodiment of the present invention, the polishing mechanism can be described as follows. That is, the polishing proceeds when the alkali component contained in the polishing composition directly attacks the semiconductor wafer and chemically etches it. Further, as an effect other than the above, an action by the alkali component being carried to the surface of the object to be polished by adsorbing to the abrasive grains is also important. In the present invention, although the polishing composition contains colloidal silica as abrasive grains, “—OH” in the silanol group possessed by the colloidal silica is extracted from the “H” by the action of the alkali component. , “−O ⁻ ”. The polishing composition of the present invention contains a quaternary ammonium compound, and a cation derived from the quaternary ammonium compound (tetramethylammonium ion in a preferred embodiment) is a counter of “—O ⁻ ”. It is thought that the polishing force is further accelerated by adsorbing as cations.

  In addition, when the semiconductor wafer has a surface made of silicon, silicon becomes polishing waste (silicate derivative) as the polishing process proceeds, and is released into the solvent constituting the polishing composition. The alkali component also has an effect of solubilizing the polishing scraps and suppressing clogging of the polishing pad. From the above viewpoint, it can be said that it is important to stably supply the alkali component to the abrasive grains, the substrate and the polishing scraps, that is, to provide stability of pH, in order to proceed polishing efficiently.

In order to stabilize the pH of the polishing composition, that is, in order to keep the supply of “OH ⁻ ” stable while “OH ⁻ ” is consumed, the pH buffering action is used in the present invention.

For example, when considering a buffer of carbonic acid (H ₂ CO ₃ ) and tetramethylammonium hydroxide (TMAOH), as can be seen from the following formula,

Carbonic acid (H ₂ CO ₃ ) and tetramethylammonium hydroxide (TMAOH) are considered to have a maximum buffer at 1: 2.

  By maximizing this buffering action, even if the alkaline component is supplied to the abrasive grains, the substrate and the polishing scrap as the polishing progresses, the pH can be quickly reduced, so that the change is minimized. Can be kept to the limit. That is, the buffer ratio of the alkali buffer component free in the solvent of the polishing composition, excluding the amount of the alkali component adsorbed on the surface of the abrasive grains, is set to weak acid: strong base (mol ratio) = 1: A. The present invention has been completed based on the idea that the maximum effect can be obtained.

The amount (B) of the quaternary ammonium compound that is not adsorbed on the abrasive grains is taken into consideration, and the content (X) of the weak acid salt is multiplied by the theoretical buffer ratio (A) of the quaternary ammonium compound and the weak acid salt. Thus, the optimum value (that is, optimum concentration) (Y ₀ ) of the content of the quaternary ammonium compound can be calculated. And, under the intensive research of the present inventors, if the quaternary ammonium compound content (Y) falls within the range of -20 to 100% of the optimum concentration (Y ₀ ), a sufficient polishing rate can be obtained. It has been found that it is possible to provide a stable polishing composition that can achieve realization, in particular, can improve the initial polishing efficiency, and has a low performance change even during repeated use, in particular, excellent in the polishing efficiency maintenance rate.

  Hereinafter, each component contained in the polishing composition of the present invention will be described.

<Colloidal silica>
The colloidal silica in the polishing composition has a function of giving a physical action to the surface to be polished, and physically polishes the surface to be polished. There are various types of abrasive grains, but when colloidal silica is used as in the present invention, scratches generated on the surface of the semiconductor wafer due to polishing are reduced, which is preferable in this respect. These colloidal silicas may be used individually by 1 type, and may be used in combination of 2 or more type. The colloidal silica used in the present invention is preferably produced from water glass (silicate Na) as a raw material by an ion exchange method.

  The average primary particle diameter (BET particle diameter) obtained from the specific surface area measured by the BET method of colloidal silica in the polishing composition is preferably 10 nm or more, more preferably 20 nm or more, and further preferably 30 nm. It is above, Especially preferably, it is 40 nm or more. When the average primary particle diameter (BET particle diameter) obtained from the specific surface area measured by the BET method of colloidal silica is such a size, it is particularly easy to reduce the surface roughness or the level difference. Further, the flatness of the wafer measured by, for example, sagging of the edge of the silicon wafer, GBIR, ESFQR, etc. is improved. In addition, by using relatively large abrasive grains of 40 nm or more, there is an effect of improving the elimination of locally existing protrusions on the wafer.

  The average primary particle diameter (BET particle diameter) determined from the specific surface area measured by the BET method of colloidal silica in the polishing composition is preferably 80 nm or less, more preferably 70 nm or less, and even more preferably 60 nm or less. . When the average primary particle diameter (BET particle diameter) obtained from the specific surface area measured by the BET method of colloidal silica is such a size, the storage stability of the colloidal silica in the polishing composition is further maintained. Here, the storage stability refers to the stability of the physical properties of the composition itself after storing the polishing composition in a container for a certain period of time, and the stability relating to the polishing characteristics when the composition is used for polishing. . In addition, there is an effect of alleviating silica sedimentation when the polishing composition is stored for a long time.

Further, the total surface area (a) of the colloidal silica contained per 1 kg of the polishing composition is preferably 150 (m ² —SiO ₂ / kg-Slurry) or more, more preferably 250 (m ² —SiO ₂ / kg-Slurry) or more, more preferably 500 (m ² —SiO ₂ / kg-Slurry) or more, and most preferably 1500 (m ² —SiO ₂ / kg-Slurry) or more. When the total surface area of the colloidal silica contained in 1 kg of the polishing composition is such a size, there is an effect that the polishing characteristics of the polishing composition are further maintained. The total surface area (a) of the colloidal silica contained per 1 kg of the polishing composition is preferably 50000 (m ² —SiO ₂ / kg-Slurry) or less, more preferably 25000 (m ² —SiO ₂ / kg-Slurry) or less, more preferably 5000 (m ² -SiO ₂ / kg-Slurry) or less, and most preferably 3500 (m ² -SiO ₂ / kg-Slurry) or less. When the total surface area of the colloidal silica contained in 1 kg of the polishing composition is such a size, there is an effect that the storage stability of the colloidal silica in the polishing composition is further maintained. As described above, by adjusting the content of colloidal silica and the particle size thereof (a) in such a range, there is an effect that the polishing characteristics of the polishing composition can be further maintained over the long term. .

  The total surface area (a) of the colloidal silica can be measured using a surface area measuring device manufactured by Micromeritex, Inc., trade name “Flow Sorb II 2300”.

  The true specific gravity of the colloidal silica in the polishing composition is preferably 1.7 or more, more preferably 2.0 or more, and further preferably 2.1 or more. As the true specific gravity of the colloidal silica increases, it becomes easier to obtain a high polishing rate, and it becomes easier to enhance the effect of reducing the surface roughness or the level difference. In addition, for example, there is an effect of improving the flatness of the wafer measured by sagging of the edge of the silicon wafer, GBIR, ESFQR, and the like, and improving the resolvability of abnormal protrusions that exist locally. The true specific gravity of the colloidal silica is calculated from the weight when the colloidal silica particles are dried and the weight when the colloidal silica particles are filled with ethanol having a known capacity. In addition, although there is no restriction | limiting in particular as an upper limit, 2.3 or less are preferable and 2.2 or less are more preferable.

  The content of colloidal silica in the polishing composition is preferably 0.3% by mass or more, more preferably 0.5% by mass or more, and further preferably 1.0% by mass or more. The higher the colloidal silica content, the easier it is to obtain a high polishing rate and the higher the effect of reducing the surface roughness or level difference.

Moreover, since colloidal silica itself functions as a weak acid, another buffering effect is expressed by the presence of a strong base. That the colloidal silica as the silica surface is large content of OH ^- groups is increased, the stronger the buffering action and the like weak acid salt or a quaternary ammonium compound which will be described later, further stabilize the effect of the pH of the polishing composition There is. The content of colloidal silica in the polishing composition is preferably 50% by mass or less, more preferably 30% by mass or less, and still more preferably 10% by mass or less. If the content of the colloidal silica is about this level, the storage stability of the polishing composition is further maintained and it is economical.

<Weak acid salt>
The polishing composition of the present invention contains a weak acid salt.

  As an example of a weak acid salt used in the polishing composition having a buffering action of the present invention, as the weak acid salt, the valence is not limited, and from the viewpoint of effectively exhibiting the intended effect of the present invention. The divalent carbonate is preferable, and the divalent carbonate is particularly preferable.

  What can be used as a weak acid salt in the polishing composition of the present invention is as follows. That is, as the anion component constituting the salt, carbonate ion, bicarbonate ion, monocarboxylate ion (for example, acetate ion), dicarboxylate ion (for example, oxalate ion, maleate ion), and tricarboxylate ion (for example, Citrate ion), borate ion, phosphate ion and the like.

  Examples of the cation component constituting the salt include potassium ion, sodium ion, calcium ion, magnesium ion, manganese ion, cobalt ion, tetraalkylammonium ion and tetraalkylphosphonium ion.

  Among these, potassium, sodium, and the like are preferable as the cationic component from the viewpoint of increasing the pH value after addition of the weak acid salt (hereinafter referred to as “alkali strength”). Further, potassium is more effective than sodium from the viewpoint of the storage stability of colloidal silica in the polishing composition (hereinafter also referred to as “silica dispersion stability”).

  When an anion component having an acid dissociation constant (pKa) close to pH 10 of the polishing composition is selected, the buffering action of the polishing composition works more effectively. As such, the anion component is preferably carbonate ion, hydrogen carbonate ion or dicarboxylate ion.

  In view of the above, specifically, for example, sodium carbonate, potassium carbonate, sodium bicarbonate, potassium bicarbonate, sodium acetate, potassium acetate, sodium propionate, potassium propionate, calcium carbonate, calcium bicarbonate, calcium acetate, propion Examples include calcium acid, magnesium acetate, magnesium propionate, zinc propionate, manganese acetate, and cobalt acetate. Of these, potassium carbonate or potassium hydrogen carbonate is preferred from the viewpoint of alkali strength during dissolution and silica dispersion stability.

Further, the amount (mol / kg-SiO ₂ ) of alkali metal weak acid salt per kg of colloidal silica in the polishing composition is preferably 0.02 mol / kg-SiO ₂ or more, more preferably 0.8. 04 mol / kg-SiO ₂ or more, more preferably 0.07 (mol / kg-SiO ₂ ) or more. Such an amount is effective in stabilizing the polishing efficiency when the slurry is circulated. Further, the amount (mol / kg-SiO ₂ ) of alkali metal weak acid salt per kg of colloidal silica in the polishing composition is preferably 2.0 (mol / kg-SiO ₂ ) or less, more preferably. Is 1.0 (mol / kg-SiO ₂ ) or less, more preferably 0.4 (mol / kg-SiO ₂ ) or less. With such an amount, the silica dispersion stability is effective.

  The molar concentration (b) (mol / kg-Slurry) of the alkali metal weak acid salt contained in 1 kg of the polishing composition is preferably 0.0001 (mol / kg-Slurry) or more, and more preferably. Is 0.002 (mol / kg-Slurry) or more, more preferably 0.003 (mol / kg-Slurry) or more. Such an amount is effective in stabilizing the polishing efficiency during polishing. Further, the molar concentration (b) (mol / kg-Slurry) of the weak salt of alkali metal contained per kg of the polishing composition is preferably 1.0 (mol / kg-Slurry) or less, more preferably. Is 0.1 (mol / kg-Slurry) or less, more preferably 0.02 (mol / kg-Slurry) or less. With such an amount, the silica dispersion stability is effective.

Here, the content (X) of the weak acid salt is the molar concentration (b) of the alkali metal weak acid salt contained in 1 kg of the polishing composition, and the total surface area of the colloidal silica contained in 1 kg of the polishing composition ( It can be calculated by dividing by a). That is, the content (X) of the weak acid salt indicates the content (mol) of the weak acid salt with respect to the total surface area (m ² —SiO ₂ ) of the colloidal silica. In the present invention, the content (X) of the weak acid salt is 1.0 × 10 ^{−7 to} 1.0 × 10 ⁻⁵ mol / m ² —SiO ₂ . If the content (X) of the weak acid salt is less than 1.0 × 10 ⁻⁷ , the optimum content of the quaternary ammonium compound is reduced and the pH of the polishing composition is lowered. There arises a problem that cannot be sufficiently obtained. On the other hand, if it exceeds 1.0 × 10 ⁻⁵ , the optimum content of the quaternary ammonium compound is increased, and the pH of the polishing composition is increased. As the content (X) is less than 1.0 × 10 ^−7, there arises a problem that the polishing efficiency cannot be sufficiently obtained.

Thus, the content (X) of the weak acid salt contained in the polishing composition of the present invention is 1.0 × 10 ^{−7 to} 1.0 × 10 ⁻⁵ mol / m ² —SiO ₂ , The desired effect of the present invention can be achieved, but preferably 1.0 × 10 ^{−7 to} 1.0 × 10 ⁻⁵ mol / m ² —SiO ₂ , more preferably 2.0 × 10 ^−7. ˜2.0 × 10 ⁻⁵ mol / m ² —SiO ₂ , more preferably 5.0 × 10 ^{−7 to} 5.0 × 10 ⁻⁵ mol / m ² —SiO ₂ .

<Quaternary ammonium compound>
The polishing composition of the present invention contains a quaternary ammonium compound.

  The quaternary ammonium compound has a function of chemically polishing the surface to be polished and a function of improving the storage stability of the polishing composition.

  The quaternary ammonium compounds include tetramethylammonium hydroxide, hydroxyethyltrimethylammonium hydroxide (commonly called “choline”), tetraethylammonium hydroxide, tetrapropylammonium hydroxide, tetrabutylammonium hydroxide, tetrapentylammonium hydroxide, and Examples include tetrahexylammonium hydroxide.

The amount (mol / kg-SiO ₂ ) of the quaternary ammonium compound per kg of colloidal silica is preferably 0.1 (mol / kg-SiO ₂ ) or more, more preferably 0.3 (mol / kg). -SiO ₂₎ or more, further preferably _{0.5 (mol / kg-SiO 2} ) or more. With such an amount, there is an effect of increasing the polishing efficiency during polishing and stabilizing the polishing efficiency. The amount (mol / kg-SiO ₂ ) of the quaternary ammonium compound per kg of colloidal silica is preferably 5.0 (mol / kg-SiO ₂ ) or less, more preferably 2.5 (mol / kg). -SiO ₂₎ or less, more preferably _{1.2 (mol / kg-SiO 2} ) or less. With such an amount, the silica dispersion stability is effective.

  Further, the molar concentration (c) (mol / kg-Slurry) of the quaternary ammonium compound contained per 1 kg of the polishing composition is preferably 0.0005 (mol / kg-Slurry) or more, more preferably. Is 0.005 (mol / kg-Slurry) or more, more preferably 0.02 (mol / kg-Slurry) or more. With such an amount, there is an effect of increasing the polishing efficiency during polishing and stabilizing the polishing efficiency. The molar concentration (c) (mol / kg-Slurry) of the quaternary ammonium compound contained per 1 kg of the polishing composition is preferably 2.5 (mol / kg-Slurry) or less, more preferably 1 .2 (mol / kg-Slurry) or less, more preferably 0.6 (mol / kg-Slurry) or less. With such an amount, the silica dispersion stability is effective.

Here, the content (Y) of the quaternary ammonium compound is the molar concentration (c) of the quaternary ammonium compound contained in 1 kg of the polishing composition, and the colloidal silica contained in 1 kg of the polishing composition. It can be calculated by dividing by the total surface area (a). That is, the content of the quaternary ammonium compound (Y) shows the total surface area of the colloidal silica ^(m ₂ -SiO 2), the content of the quaternary ammonium compound (mol).

On the other hand, the optimum concentration (optimum value) (Y ₀ ) of the quaternary ammonium compound can be calculated as follows according to the mechanism described at the beginning.

Optimum value of Y: Y ₀ = A * X + B
A: Theoretical buffer ratio of quaternary ammonium compound and weak acid salt B: The amount of quaternary ammonium compound adsorbed to colloidal silica and not released in the polishing composition (in other words, the amount of quaternary ammonium compound Adsorption on colloidal silica)
Then, by calculating (Y−Y ₀ ) / Y ₀ (%), it is possible to indicate what percentage deviates from the optimum concentration of the quaternary ammonium compound contained in the polishing composition. . In other words, if it falls within -20 to 100%, the buffering action is efficiently exhibited, so that both the “initial polishing efficiency” and the “polishing efficiency maintenance rate” are excellent.

The lower limit of the _{(Y-Y 0) / Y} 0 (%) is preferably 10%, more preferably -8%, more preferably 5%. The upper limit of (Y−Y ₀ ) / Y ₀ (%) is preferably + 80%, more preferably + 50%, still more preferably + 20%, even more preferably + 10%, and most preferably + 5%.

  As the preferable range is reached, a more ideal buffering effect can be exhibited, so that a sufficient polishing rate can be realized, and in particular, the initial polishing efficiency can be improved. Further, according to the polishing composition of the present invention, it is possible to provide a stable polishing composition having a low performance change even after repeated use, in particular, excellent in polishing efficiency maintenance rate.

As can be seen from the above, the content (Y) of the quaternary ammonium compound is such that the content of the weak acid salt ((Y−Y ₀ ) / Y ₀ (%) is within −20 to 100% ( X) may be set in consideration.

  Subsequently, components that can be contained in the polishing composition of the present invention will be described below.

<Nitrogen-containing water-soluble polymer>
The polishing composition of the present invention may contain a nitrogen-containing water-soluble polymer. By including such a nitrogen-containing water-soluble polymer, the flatness of the end portion from the center of the semiconductor wafer can be maintained.

  The nitrogen-containing water-soluble polymer that can be used is preferably one having one or more nitrogen atoms in the monomer unit, or one having one or more nitrogen atoms in a part of the side chain. , Imine, amide, imide, carbodiimide, hydrazide, urethane compound and the like are used, and any of linear, cyclic, primary, secondary, and tertiary may be used.

  Further, it may be a nitrogen-containing water-soluble polymer having a salt structure formed with a nitrogen atom as a cation. Examples of the nitrogen-containing water-soluble polymer having a salt structure include quaternary ammonium salts. Examples of the nitrogen-containing water-soluble polymer include polycondensation polyamides such as water-soluble nylon, polycondensation polyesters such as water-soluble polyesters, polyaddition polyamines, polyaddition polyimines, polyaddition (meth) acrylamides, and alkyls. Examples thereof include a water-soluble polymer having a nitrogen atom in at least a part of the main chain and a water-soluble polymer having a nitrogen atom in at least a part of the side chain. The water-soluble polymer having a nitrogen atom in the side chain also includes a water-soluble polymer having a quaternary nitrogen in the side chain.

  Specific examples of the polyaddition type nitrogen-containing water-soluble polymer include polyvinyl imidazole, polyvinyl carbazole, polyvinyl pyrrolidone, polyvinyl caprolactam, polyvinyl piperidine and the like. Further, the nitrogen-containing water-soluble polymer may have a partially hydrophilic structure such as a vinyl alcohol structure, a methacrylic acid structure, a vinyl sulfonic acid structure, a vinyl alcohol carboxylic acid ester structure, or an oxyalkylene structure. Good. Moreover, the polymer which has multiple types of structures, such as these diblock type | molds, a triblock type | mold, a random type | mold, and an alternating type | mold, may be sufficient. The nitrogen-containing water-soluble polymer may be either one having a cation in part or all of the molecule, one having an anion, one having both an anion and a cation, and one having a nonion. One of these nitrogen-containing water-soluble polymers may be used alone, or two or more thereof may be used in combination.

  Among the nitrogen-containing water-soluble polymers, polyvinyl pyrrolidone, a copolymer containing polyvinyl pyrrolidone as a part of the structure, polyvinyl caprolactam, polyvinyl caprolactam has a structure from the viewpoint that it has a good function of controlling the processability of the edge. A copolymer contained in a part of is preferable. Of these nitrogen-containing water-soluble polymers, polyvinyl pyrrolidone is most preferred.

  The weight average molecular weight of the nitrogen-containing water-soluble polymer in the polishing composition is preferably less than 1500,000 in terms of polyethylene oxide, more preferably less than 500,000, still more preferably less than 100,000, more preferably less than 80000, most preferably. Is less than 50000. When the molecular weight of the nitrogen-containing water-soluble polymer is less than 1500,000, the storage stability of the polishing composition is easily maintained.

  In addition, the weight average molecular weight of the nitrogen-containing water-soluble polymer in the polishing composition is preferably 1000 or more, more preferably 20000 or more. When the molecular weight of the nitrogen-containing water-soluble polymer is 1000 or more, the shape of the end portion of the semiconductor wafer is further easily maintained.

  The content of the nitrogen-containing water-soluble polymer compound in the polishing composition is preferably 0.0001% by mass or more. When the content of the nitrogen-containing water-soluble polymer compound is 0.0001% by mass or more, the shape of the end portion of the semiconductor wafer is more easily maintained.

  The content of the nitrogen-containing water-soluble polymer in the polishing composition is preferably less than 0.002% by mass, more preferably less than 0.001% by mass, and still more preferably less than 0.0005% by mass. is there. When the content of the nitrogen-containing water-soluble polymer is less than 0.002% by mass, a high polishing rate is further easily obtained.

<Chelating agent>
A chelating agent can be contained in the polishing composition of the present invention. The chelating agent in the polishing composition suppresses the remaining metal impurities on the semiconductor wafer by capturing metal impurities in the polishing system to form a complex.

  Examples of chelating agents include aminocarboxylic acid chelating agents and organic phosphonic acid chelating agents. Specific examples of the aminocarboxylic acid chelating agent include ethylenediaminetetraacetic acid, sodium ethylenediaminetetraacetate, nitrilotriacetic acid, sodium nitrilotriacetate, ammonium nitrilotriacetate, hydroxyethylethylenediaminetriacetic acid, sodium hydroxyethylethylenediaminetriacetate, diethylenetriamine Examples include acetic acid, sodium diethylenetriaminepentaacetate, triethylenetetraminehexaacetic acid, sodium triethylenetetraminehexaacetate, and the like.

  Specific examples of the organic phosphonic acid chelating agent include 2-aminoethylphosphonic acid, 1-hydroxyethylidene-1,1-diphosphonic acid, aminotri (methylenephosphonic acid), ethylenediaminetetrakis (methylenephosphonic acid), diethylenetriaminepenta (methylene Phosphonic acid), triethylenetetramine hexa (methylenephosphonic acid), ethane-1,1, -diphosphonic acid, ethane-1,1,2-triphosphonic acid, ethane-1-hydroxy-1,1-diphosphonic acid, ethane- 1-hydroxy-1,1,2-triphosphonic acid, ethane-1,2-dicarboxy-1,2-diphosphonic acid, methanehydroxyphosphonic acid, 2-phosphonobutane-1,2-dicarboxylic acid, 1-phosphonobutane-2 , 3,4-tricarboxylic acid, α-methylphosphonosucci Etc. The. These chelating agents may be used individually by 1 type, and may be used in combination of 2 or more type.

  Among chelating agents, organic phosphonic acid-based chelates are preferable, and ethylenediaminetetrakis (methylenephosphonic acid) is more preferable.

  The content of the chelating agent in the polishing composition is preferably 0.0001% by mass or more, and more preferably 0.0005% by mass or more. By increasing the content of the chelating agent, the effect of suppressing residual metal impurities in the semiconductor wafer is enhanced.

  Moreover, it is preferable that content of the chelating agent in polishing composition is less than 0.01 mass%, More preferably, it is less than 0.005 mass%. By reducing the content of the chelating agent, the storage stability of the polishing composition is better maintained.

<Water>
It is particularly preferable that the polishing composition of the present invention contains water.

  Water in the polishing composition has a function of dissolving or dispersing other components. In order to avoid that the function of other components is inhibited as much as possible, the water preferably has a total content of transition metal ions of 100 ppb or less. For example, the purity of water can be increased by operations such as removal of impurity ions using an ion exchange resin, removal of foreign matters by a filter, and distillation. Specifically, for example, ion exchange water, pure water, ultrapure water, distilled water or the like is preferably used.

  The pH of the polishing composition is preferably in the range of 8-12, more preferably in the range of 9-11.

  For the preparation of the polishing composition described above, for example, a well-known stirring and mixing device such as a blade-type stirrer, an ultrasonic disperser, a homomixer or the like can be used. Each raw material of polishing composition may be mixed simultaneously, and a mixing order may be set suitably.

  Next, a method for polishing a semiconductor wafer using the polishing composition of the present invention will be described together with the action of the polishing composition. That is, the manufacturing method of a semiconductor wafer including the grinding | polishing process of grind | polishing a semiconductor wafer using polishing composition is demonstrated.

  When polishing the surface of a semiconductor wafer using the polishing composition, the polishing pad is pressed against the surface of the semiconductor wafer while rotating the semiconductor wafer and the polishing pad while supplying the polishing composition to the surface of the semiconductor wafer. As the polishing apparatus, for example, a double-side polishing apparatus that simultaneously polishes both surfaces of a semiconductor wafer can be used. In particular, in preliminary polishing, a double-side polishing apparatus is preferably used from the viewpoint of improving flatness.

  In addition, the present invention takes into account the presence of a water-soluble quaternary ammonium hydroxide that is adsorbed with colloidal silica in the polishing composition and is not liberated in the polishing composition, and is used for polishing. Since the idea is that the composition is prepared, it is possible to improve the initial polishing efficiency in both single-sided and double-sided polishing, and the effect of low performance change even in repeated use, in particular, excellent polishing efficiency maintenance rate. Have Therefore, whether to perform single-side polishing or double-side polishing may be selected in accordance with the actual situation.

  The polishing process for polishing both or one side of the semiconductor wafer includes a first polishing process that is an initial polishing process, a second polishing process that is performed after the polishing process, and a final polishing process that is performed as a final finish. Has the following stages. Among such polishing processes, in the polishing process after the second polishing process, single-side polishing for polishing one side of the semiconductor wafer is often performed.

The polishing composition of the present invention is a polishing composition used for polishing a semiconductor wafer, comprising colloidal silica, a weak acid salt, and a quaternary ammonium compound, wherein the content of the weak acid salt is colloidal. 1.0 × 10 ^{−7 to} 1.0 × 10 ⁻⁵ mol / m ² —SiO ₂ with respect to the total surface area of silica, and the content of the quaternary ammonium compound is represented by the following formulas (1) and (2) Polishing composition which satisfy | fills the relationship of these.

  By having such a configuration, the polishing composition of the present invention achieves a sufficient polishing rate, and is stable with low performance change even after repeated use. This is usually required for the first polishing step and the second polishing step, and is a required performance mainly required for the first polishing step. Therefore, the present invention is preferably a silicon wafer having a size of mainly 300 mm or more in the first polishing step or the second polishing step of the semiconductor wafer, more preferably the first polishing step of the semiconductor wafer, more preferably the first polishing of the semiconductor wafer. Used for double-side polishing. The reason is that the required polishing rate increases in the order of the second polishing step, the single-side polishing in the first polishing step, and the double-side polishing in the first polishing step, and the amount of silicon scraped by one polishing increases. Then, the amount of silicon dissolved in the polishing composition increases, and a large amount of silicate ions is contained in the polishing composition. This acts to lower the pH of the polishing composition. Even under such circumstances, the present invention can suppress fluctuations in pH during circulation use of the polishing composition.

  In addition, the polishing composition of the present invention can maximize the buffering effect by taking into account quaternary ammonium adsorbed on colloidal silica, which has not been noticed conventionally. As a result, a sufficient polishing speed can be achieved, especially the initial polishing efficiency can be improved, the performance change is small even after repeated use, and the maintenance efficiency of the polishing efficiency is particularly excellent, contributing to the realization of high wafer flatness and low defect performance. To do. Therefore, since it can polish efficiently and stably with respect to the surface of a semiconductor wafer, the performance of a semiconductor wafer also becomes stable, and also to the user who uses a constituent for polish. It will be very reliable. In addition, the polishing composition of the present invention is very suitable for long-term storage because the pH is stable.

  The embodiment of the present invention may be modified as follows.

  -You may make the said polishing composition contain well-known additives, such as antiseptic | preservative and a fungicide, as needed. Specific examples of the antiseptic and antifungal agent include isothiazoline compounds, paraoxybenzoates, phenoxyethanol and the like.

  -The polishing composition may be a one-part type or a multi-part type composed of two or more parts.

  The polishing composition may be prepared by diluting a stock solution of the polishing composition with water. For example, after storing or transporting the stock solution of the polishing composition, it can be diluted at the time of use to prepare the polishing composition.

  -The polishing composition may be used for polishing again after being used for polishing once. When the used polishing composition is used again for polishing, components lacking in the polishing composition may be added.

  The polishing pad used in polishing using the polishing composition is not particularly limited, and any of polyurethane type, non-woven fabric type, suede type, those containing abrasive grains, and those not containing abrasive grains may be used. .

  Next, the embodiment will be described more specifically with reference to examples and comparative examples. However, it goes without saying that the present invention is not limited to the following examples.

Colloidal silica (SiO ₂ ) (true specific gravity: 2.1 to 2.2), weak alkali metal salt and quaternary ammonium compound are added to ion-exchanged water and stirred at room temperature of about 25 ° C. for about 30 minutes. By mixing, polishing compositions (2 kg) of Examples and Comparative Examples were prepared. Details of the polishing composition of each example are shown in Table 1. Comparative Example 1 and Comparative Example 2 correspond to Example 1 Experiment No. 1 and Example 1 Experiment No. 2 disclosed in Patent Document 3, respectively.

  In addition, colloidal silica was produced using water glass (silicic acid Na) as a raw material by an ion exchange method.

“BET particle diameter (nm)” in Table 1 is an average primary particle calculated from “BET specific surface area (m ² / g-SiO ₂ )” measured using “Flow SorbII 2300” manufactured by Micromeritex. The diameter is shown. Specifically, the colloidal silica of the polishing compositions of Comparative Example 1 and Comparative Example 2 has a BET particle diameter of 15.0 nm, and the polishing compositions of Examples 1 to 6 and Comparative Examples 3 to 5 The colloidal silica had a BET particle size of 55.0 nm.

  In addition, pH of Examples 1-6 and Comparative Examples 1-5 is 10.32, 10.35, 10.30, 10.34, 10.33, 10.36, 9.82, 9.88, respectively. 10.04, 10.15, 10.28. The pH was measured at room temperature of 25 ° C. using a model number F-23 manufactured by Horiba, Ltd.

“Concentration (wt%)” in the “SiO ₂ ” column of Table 1 indicates the concentration (% by weight) of colloidal silica in the polishing composition. Specifically, the concentration of colloidal silica in each polishing composition was adjusted to 5% by weight.

“Silica surface area per 1 kg of slurry (a) (m ² —SiO ₂ / kg-Slurry)” in the “SiO ₂ ” column of Table 1 is the total surface area of colloidal silica contained in 1 kg of the polishing composition. (A) is shown.

In the “content of alkali metal II-valent weak acid salt” column in Table 1, type “K ₂ CO ₃ ” indicates potassium carbonate, and “KHCO ₃ ” indicates potassium hydrogen carbonate.

In addition, in Table 1, the “concentration of alkali metal II weak salt per kg of silica (mol / kg-SiO ₂ )” in the column “Content of alkali metal II weak weak acid salt” is the value per kg of colloidal silica. The amount (mol) of weak alkali metal salt is shown.

  In addition, “Molar concentration of alkali metal II weak salt per kg of slurry (b) (mol / kg-Slurry)” in the column “Content of alkali metal II weak salt” in Table 1 is the polishing composition. The molar concentration (b) of the weak salt of alkali metal contained per kg of the product is shown.

In addition, “X (= (b) / (a)) (mol / m ² —SiO ₂ )” in the “content of alkali metal II-valent weak acid salt” column in Table 1 represents (b) as (a ), That is, the content (mol) of the weak salt of the alkali metal with respect to the total surface area (m ² ) of the colloidal silica. In the table, “E” represents an index, and “E-06” means “10 ⁻⁶ ”. The same applies hereinafter.

  The type “TMAOH” in the “Content of quaternary ammonium compound” column in Table 1 represents tetramethylammonium hydroxide.

Further, in Table 1, “Content of quaternary ammonium compound” column, “mol concentration of quaternary ammonium salt per kg of silica (mol / kg-SiO ₂ )” is quaternary ammonium per kg of colloidal silica. The amount (mol) of the compound is shown.

  In addition, in Table 1, the “quaternary ammonium salt mol concentration (c) (mol / kg-Slurry) per kg of slurry” in the “content of quaternary ammonium compound” column is 1 kg of polishing composition. The molar concentration (c) of the quaternary ammonium compound contained is shown.

In addition, “Y (= (c) / (a)) (mol / m ² —SiO ₂ )” in the “Content of quaternary ammonium compound” column in Table 1 is the same as (c) in (a). That is, the content (mol) of the quaternary ammonium compound with respect to the total surface area (m ² ) of the colloidal silica is shown.

“Y ₀ (mol / m ² —SiO ₂ )” in the “optimum value of Y” column in Table 1 indicates the optimum concentration of TMAOH. More specifically, it is calculated from the following equation.

Optimum value of TMAOH: Y ₀ = A * X + B
A: Theoretical buffer ratio of TMAOH and weak acid salt (= 2)
B: Amount of TMAOH adsorbed with colloidal silica and not liberated in the polishing composition (= 8.0 × 10 ⁻⁶ mol / m ² —SiO ₂ )
“B” is a value calculated by dividing “adsorption amount of quaternary ammonium compound to abrasive grains measured by TOC” by “specific surface area of silica abrasive grains by BET measurement method”. Glass (Na silicate) raw silica has a certain value. More specifically, the polishing composition is centrifuged and the supernatant organic substance (that is, carbon content) is measured. That is, since the amount of organic carbon can be quantified by TOC, it can be measured by how much the quaternary ammonium compound is reduced with respect to the charged amount of the quaternary ammonium compound.

“(Y−Y ₀ ) / Y ₀ (%)” in the “deviation from the optimum value of Y” column in Table 1 indicates the optimum concentration of the quaternary ammonium compound contained in the polishing composition. It shows what percentage deviates. If this is within -20 to 100%, as will be described later, both the “initial polishing efficiency” and the “polishing efficiency maintenance ratio” are excellent polishing compositions.

  Subsequently, 600 ml of the polishing composition of each example was used in a circulating manner, and a silicon wafer was polished under the polishing conditions described in Table 2 using a small polishing machine, EJ-380IN manufactured by ENGIS. Note that the silicon wafer has a size of 60 mm × 60 mm, a conductivity type of P type, a crystal orientation of <100>, and a resistivity of 0.1 Ω · cm to less than 100 Ω · cm. The polishing performance was evaluated by “initial polishing efficiency” and “polishing efficiency maintenance rate”.

<Polishing efficiency during cumulative machining allowance polishing (μm / min)>
The column “10 μm” in “Cutting efficiency (μm / min) at cumulative machining allowance polishing” in Table 1 means the average polishing efficiency when polishing 10 μm from the start of polishing, that is, 10 μm polishing from the start of polishing. It shows how much it was polished per minute (polishing efficiency). Similarly, the “20 μm” column indicates how much polishing (polishing efficiency) is performed in one minute in the section of the accumulated machining allowance of 10 to 20 μm. The columns “30 μm”, “40 μm”, and “50 μm” mean the same thing.

<Initial polishing efficiency>
“Initial polishing efficiency” in Table 1 refers to the polishing efficiency with a cumulative machining allowance of 10 μm, that is, the same as the “10 μm” column, and the higher the polishing efficiency, the better. The standard shown in Table 1 is “0”. The evaluation was made on a 6-point scale of "5".

<Polishing efficiency maintenance rate>
“Polishing efficiency maintenance ratio” in Table 1 shows the difference between the polishing efficiency of 50 μm (“50 μm” column) and the polishing efficiency of 10 μm (“10 μm” column) as a percentage based on the initial polishing efficiency. With respect to the value, the larger the value, the better, and the six-level evaluation of “0” to “5” based on the criteria shown in the table below.

  In the cyclic use of the polishing composition (slurry), both the initial polishing efficiency and its maintainability (polishing efficiency maintenance ratio) are required to have good characteristics. Therefore, as an overall evaluation, “initial polishing efficiency”, “ The average value of “polishing efficiency maintenance rate” was evaluated.

  In addition, this application is based on the Japan patent application 2014-000554 for which it applied on January 6, 2014, The content of an indication is referred as a whole by reference.

Claims (7)

Colloidal silica, weak acid salt, and a quaternary ammonium compound, used for polishing the plane of the semiconductor wafer having a flat surface, a polishing composition,
The content of the weak acid salt is 1.0 × 10 ^{−7 to} 1.0 × 10 ⁻⁵ mol / m ² —SiO ₂ with respect to the total surface area of the colloidal silica,
Polishing composition with which content of the said quaternary ammonium compound satisfy | fills the relationship of the following Formula (1) and (2).
Y ₀ = A * X + B (1)
−20 ≦ (Y−Y ₀ ) / Y ₀ ≦ 20 (%) (2)
A: Theoretical buffer ratio between quaternary ammonium compound and weak acid salt B: The amount of quaternary ammonium compound adsorbed with colloidal silica and not released in the polishing composition Y: Content of quaternary ammonium compound Y ₀ : Optimum amount of quaternary ammonium compound X: Content of weak acid salt   The polishing composition according to claim 1, wherein the weak acid salt is a divalent weak acid salt.   The polishing composition according to claim 1 or 2, wherein the weak acid salt is a carbonate or a dicarboxylate.   The quaternary ammonium compound is selected from the group consisting of tetramethylammonium hydroxide, tetraethylammonium hydroxide, tetrapropylammonium hydroxide, tetrabutylammonium hydroxide, tetrapentylammonium hydroxide and tetrahexylammonium hydroxide, The polishing composition according to any one of claims 1 to 3. The polishing composition according to claim 1, wherein the semiconductor wafer has a surface made of single crystal silicon. The manufacturing method of a semiconductor wafer including the grinding | polishing process of grind | polishing a semiconductor wafer using the polishing composition of any one of Claims 1-5 . A method for stabilizing a polishing efficiency maintenance rate when polishing a flat surface of a semiconductor wafer having a flat surface using a polishing composition containing colloidal silica, a weak acid salt and a quaternary ammonium compound,
The content of the weak acid salt is 1.0 × 10 4 with respect to the total surface area of the colloidal silica. ^-7 ~ 1.0 × 10 ^-5 mol / m ² -SiO ₂ age,
A method of stabilizing the polishing efficiency maintenance rate, wherein the content of the quaternary ammonium compound is adjusted so as to satisfy the relationship of the following formulas (1) and (2).
Y ₀ = A * X + B (1)
−20 ≦ (Y−Y ₀ ) / Y ₀ ≦ 20 (%) (2)
A: Theoretical buffer ratio of quaternary ammonium compound and weak acid salt
B: Amount of quaternary ammonium compound adsorbed with colloidal silica and not liberated in the polishing composition
Y: Content of quaternary ammonium compound
Y ₀ : Optimum amount of quaternary ammonium compound
X: content of weak acid salt