WO2015190065A1

WO2015190065A1 - Polishing composition

Info

Publication number: WO2015190065A1
Application number: PCT/JP2015/002790
Authority: WO
Inventors: 匠学井出; 誠田畑; 高見　信一郎
Original assignee: 株式会社フジミインコーポレーテッド
Priority date: 2014-06-09
Filing date: 2015-06-02
Publication date: 2015-12-17
Also published as: TW201612284A; KR20170017877A; CN106463382A; TWI668301B; JP2015233031A; JP6357356B2; CN106463382B; KR102394765B1

Abstract

To provide a polishing composition which exhibits excellent performance of eliminating a bulge in the periphery of a hard laser mark. Provided is a polishing composition for silicon wafers. This polishing composition contains silica particles having a BET average particle diameter of 50 nm or less, a weak acid salt and a quaternary ammonium compound. The content (Y) (mol/L) of the quaternary ammonium compound satisfies formula (1). 0.80 ≤ (Y/Y₀) (1) (In the formula, Y₀ (mol/L) represents an amount that is defined by the following formula Y₀ = AX + B, where A is the theoretical buffer ratio, X is the content (mol/L) of the weak acid salt, and B is the adsorption (mol/L) of the quaternary ammonium compound onto the silica particles.)

Description

Polishing composition

The present invention relates to a polishing composition, and more particularly to a polishing composition for polishing a silicon wafer.

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 product is generally finished to a high-quality mirror surface through a lapping process (rough polishing process) and a polishing process (precision polishing process). The polishing process typically includes a preliminary polishing process (preliminary polishing process) and a final polishing process (final polishing process). Patent Documents 1 to 3 are listed as technical documents related to the polishing composition.

JP-A-11-302634 Special table 2011-523207 gazette JP 2013-165173 A

In Patent Document 1, a polishing composition containing colloidal silica as abrasive grains is prepared as a buffer solution with a combination of a weak acid and a strong base, a strong acid and a weak base, or a combination of a weak acid and a weak base. It is described that a polishing composition having a high speed can be formed. Specifically, a polishing composition using a buffering action by a combination of tetramethylammonium hydroxide and potassium bicarbonate (KHCO ₃ ) is disclosed.

Incidentally, a mark (hard laser mark) such as a bar code, a number, or a symbol may be attached to a silicon wafer by irradiating the surface of the silicon wafer with laser light for the purpose of identification or the like. Such a hard laser mark is generally applied after the lapping process of the silicon wafer is finished and before the polishing process is started.

Usually, a laser beam for attaching a hard laser mark causes a bulge (swell) on the silicon wafer surface around the hard laser mark. Although the hard laser mark portion itself of the silicon wafer is not used in the final product, the yield may be lowered more than necessary if the above-mentioned bumps are not properly eliminated in the polishing process after the hard laser mark is applied. However, since the raised portions are often hardened due to alteration such as polysilicon due to the energy of the laser beam, the above-mentioned raised portions are effectively eliminated by conventional polishing compositions for silicon wafers. It was difficult to do.

The present invention has been made in view of such circumstances, and an object of the present invention is to provide a polishing composition excellent in performance for eliminating the bulge at the periphery of the hard laser mark.

According to this specification, a polishing composition for use in polishing a silicon wafer is provided. The polishing composition contains silica particles having a BET average particle diameter of 50 nm or less, a weak acid salt, and a quaternary ammonium compound. The content Y [mol / L] of the quaternary ammonium compound in the polishing composition satisfies the following formula (1).
0.80 ≦ (Y / Y ₀ ) (1)
Here, Y ₀ [mol / L] is
The theoretical buffer ratio A between the quaternary ammonium compound and the weak acid salt;
The content X [mol / L] of the weak acid salt in the polishing composition;
Based on the amount B [mol / L] adsorbed on the silica particles in the quaternary ammonium compound contained in the polishing composition, the amount is defined by the following formula (2).
Y ₀ = AX + B (2)

According to such a polishing composition, by effectively utilizing the buffering action of the quaternary ammonium compound and the weak acid salt, the pH variation of the polishing composition during polishing is suitably suppressed, and good polishing is achieved. Efficiency can be maintained. This makes it possible to efficiently eliminate the bulge around the hard laser mark. Further, the polishing composition is excellent in dispersion stability because the BET average particle diameter of the silica particles is 50 nm or less.

In this specification, to eliminate the bulge on the periphery of the hard laser mark means to reduce the height from the reference surface (reference plane) around the hard laser mark of the silicon wafer to the highest point of the bulge. The height from the reference surface around the hard laser mark of the silicon wafer to the highest point of the bulge can be measured, for example, by the method described in the examples described later.

The polishing composition disclosed herein includes the content X [mol / L] of the weak acid salt, the content Y [mol / L] of the quaternary ammonium compound in the polishing composition, and the silica. The relationship with the particle content W [kg / L] preferably satisfies the following formula (3).
0.5 [mol / kg] ≦ (AX + Y) / W [mol / kg] (3)
In such a polishing composition, the balance between the mechanical polishing action and the chemical polishing action is adjusted so as to be suitable for eliminating the bulge at the periphery of the hard laser mark. According to such a polishing composition, it is possible to effectively eliminate the bulge at the periphery of the hard laser mark.

In the polishing composition disclosed herein, the ratio of the quaternary ammonium compound content Y [mol / L] to the silica particle content W [kg / L] is 1.00 [mol / kg]. It is preferable that it is above. That is, a polishing composition having a Y / W [mol / kg] of 1.00 [mol / kg] or more is preferable. According to such a polishing composition, it is possible to effectively eliminate the bulge at the periphery of the hard laser mark.

In the polishing composition disclosed herein, the ratio of the weak acid salt content X [mol / L] to the silica particle content W [kg / L] is 0.20 [mol / kg] or more. Preferably there is. That is, a polishing composition having X / W [mol / kg] of 0.20 [mol / kg] or more is preferable. According to such a polishing composition, it is possible to effectively eliminate the bulge at the periphery of the hard laser mark.

The polishing composition disclosed herein preferably contains a weak acid salt having at least one acid dissociation constant (pKa) value in the range of 8.0 to 11.8 as the weak acid salt. The polishing composition is typically used for polishing a silicon wafer as a working slurry having a pH of about 8.0 to 11.8. By containing a weak acid salt having a pKa value in the range of 8.0 to 11.8, the buffering action between the weak acid salt and the quaternary ammonium compound is effectively exhibited in such a working slurry. Can do.

A polishing composition according to a preferred embodiment includes at least one selected from the group consisting of carbonates and dicarboxylates as the weak acid salt. By utilizing the buffering action between the weak acid salt and the quaternary ammonium compound, the bulge around the hard laser mark can be effectively eliminated.

A polishing composition according to another preferred embodiment includes, as the quaternary ammonium compound, tetramethylammonium hydroxide, tetraethylammonium hydroxide, tetrapropylammonium hydroxide, tetrabutylammonium hydroxide, tetrapentylammonium hydroxide, and It contains at least one selected from the group consisting of tetrahexylammonium hydroxide. By utilizing such a buffering action between the quaternary ammonium compound and the weak acid salt, it is possible to effectively eliminate the bulge around the hard laser mark.

In the polishing composition disclosed herein, the BET average particle size of the silica particles is preferably 25 nm or more and less than 50 nm. According to such a polishing composition, it is possible to effectively eliminate the bulge at the periphery of the hard laser mark.

The polishing composition disclosed herein can be excellent in performance (hereinafter also referred to as “protrusion elimination”) that eliminates the protuberance at the periphery of the hard laser mark. Therefore, it is suitable for use in polishing a silicon wafer with a hard laser mark.

Hereinafter, preferred embodiments of the present invention will be described. Note that matters other than matters specifically mentioned in the present specification and necessary for the implementation of the present invention can be grasped as design matters of those skilled in the art based on the prior art in this field. The present invention can be carried out based on the contents disclosed in this specification and common technical knowledge in the field.
In the present 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”. Are treated as synonyms. Unless otherwise specified, measurement of operation and physical properties shall be performed under conditions of room temperature (20 to 25 ° C.) and relative humidity of 40 to 50%.

<Silica particles>
The polishing composition disclosed herein contains silica particles as abrasive grains. Specific examples of the silica particles include colloidal silica, fumed silica, precipitated silica and the like. These silica particles can be used alone or in combination of two or more. Colloidal silica is particularly preferable because scratches are unlikely to occur on the surface of the object to be polished, and good uplifting properties can be exhibited. For example, colloidal silica produced from water glass (silicate Na) as a raw material by an ion exchange method can be preferably employed. Colloidal silica can be used alone or in combination of two or more.

The true specific gravity of silica constituting the silica particles is preferably 1.5 or more, more preferably 1.6 or more, and even more preferably 1.7 or more. Due to the increase in the true specific gravity of silica, the bulge resolution tends to increase. From these viewpoints, silica particles having a true specific gravity of 2.0 or more (for example, 2.1 or more) are particularly preferable. The upper limit of the true specific gravity of silica is not particularly limited, but is typically 2.3 or less, for example, 2.2 or less. As the true specific gravity of silica, a measured value by a liquid substitution method using ethanol as a substitution liquid can be adopted.

The BET average particle diameter of the silica particles contained in the polishing composition disclosed herein is 50 nm or less. Here, the BET average particle diameter of the silica particles refers to a particle diameter calculated from the specific surface area S (m ² / g) measured by the BET method according to an equation of average particle diameter (nm) = 2727 / S. . The specific surface area can be measured using, for example, a surface area measuring device manufactured by Micromeritex Corporation, a trade name “Flow Sorb II 2300”.

The lower limit of the BET average particle diameter of the silica particles is not particularly limited. The BET average particle diameter of the silica particles contained in the polishing composition disclosed herein is usually preferably 10 nm or more, and more preferably 20 nm or more. From the viewpoint of obtaining higher bulge resolution, the BET particle diameter of the silica particles is preferably 25 nm or more, and more preferably 30 nm or more. The polishing composition disclosed herein can also be preferably implemented in an embodiment containing silica particles having a BET average particle size of 40 nm or more.

The BET average particle diameter of the silica particles contained in the polishing composition disclosed herein is 50 nm or less (typically from the viewpoint of the storage stability of the polishing composition (for example, the dispersion stability of the silica particles). Less than 50 nm), more preferably 48 nm or less, and even more preferably 45 nm or less. Here, the storage stability means that when the polishing composition is stored, there is little deterioration of the polishing composition over time. Degradation of the polishing composition includes, for example, sedimentation and aggregation of silica particles, change in pH of the polishing composition, and decrease in polishing performance when the polishing composition is used for polishing (for example, decrease in bulge resolution) ) Etc.

The shape (outer shape) of the silica particles in the technology disclosed herein may be spherical or non-spherical. Specific examples of the non-spherical silica particles include a peanut shape (that is, a peanut shell shape), a bowl shape, a confetti shape, a rugby ball shape, and the like. For example, silica particles in which most of the particles have a peanut shape can be preferably used.

Although not particularly limited, the average value (average aspect ratio) of the major axis / minor axis ratio of the silica particles is preferably 1.05 or more, and more preferably 1.1 or more. By increasing the average aspect ratio, higher ridge resolution can be achieved. The average aspect ratio of the silica particles is preferably 3.0 or less, more preferably 2.0 or less, and further preferably 1.5 or less, from the viewpoint of reducing scratches.

The shape (outer shape) and average aspect ratio of the silica particles can be grasped by, for example, observation with an electron microscope. As a specific procedure for grasping the average aspect ratio, for example, each particle image of a predetermined number (for example, 200) of silica particles capable of recognizing the shape of independent particles using a scanning electron microscope (SEM) is used. Draw the smallest rectangle that circumscribes. For the rectangle drawn for each particle image, the value obtained by dividing the length of the long side (major axis value) by the length of the short side (minor axis value) is the major axis / minor axis ratio (aspect ratio). ). An average aspect ratio can be obtained by arithmetically averaging the aspect ratios of the predetermined number of particles.

The content of silica particles in the polishing composition disclosed herein is not particularly limited.
As will be described later, in the case of a polishing composition (typically a slurry-like polishing liquid, sometimes referred to as a working slurry or a polishing slurry) used for polishing a polishing object as it is as a polishing liquid. The amount W [kg / L] of silica particles contained per liter (L) of the polishing composition is preferably 0.0001 kg / L or more, more preferably 0.0005 kg / L or more. preferable. By increasing the content of silica particles, higher bulge resolution tends to be obtained. From this viewpoint, the content W of the silica particles can be set to 0.001 kg / L or more, for example, 0.003 kg / L or more, and further 0.005 kg / L or more. Further, from the viewpoint of preventing scratches, the content W of silica particles is usually suitably 0.1 kg / L or less, preferably 0.05 kg / L or less, more preferably 0.01 kg / L or less. It is also preferable from the viewpoint of economy to reduce the content W of the silica particles. From this viewpoint, the content W of silica particles in the working slurry may be 0.008 kg / L or less, and may further be 0.005 kg / L or less. The polishing composition disclosed herein can exhibit practically sufficient uplifting properties even at such a low silica particle content W.

In the case of a polishing composition (that is, a concentrated liquid) diluted and used for polishing, the content W [kg / L] of silica particles is usually from the viewpoint of storage stability, filterability, and the like. The amount is suitably 5 kg / L or less, preferably 0.4 kg / L or less, and more preferably 0.3 kg / L or less. Further, from the viewpoint of taking advantage of the concentrated liquid, the content W [kg / L] of the silica particles is preferably 0.01 kg / L or more, more preferably 0.03 kg / L or more, and still more preferably 0. .05 kg / L or more.

<Quaternary ammonium compound>
The polishing composition disclosed herein 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. A quaternary ammonium compound can be used individually by 1 type or in combination of 2 or more types.

As the quaternary ammonium compound, a quaternary ammonium salt (typically a strong base) such as a tetraalkylammonium salt or a hydroxyalkyltrialkylammonium salt can be preferably used. The anionic component in such a quaternary ammonium salt can be, for example, OH ⁻ , F ⁻ , Cl ⁻ , Br ⁻ , I ⁻ , ClO ₄ ⁻ , BH ₄ ^{− and the} like. Among them, a preferred example is a quaternary ammonium salt whose anion is OH—, that is, a quaternary ammonium hydroxide. Preferable examples of the cation component in the quaternary ammonium salt include tetraalkylammonium ions and hydroxyalkyltrialkylammonium ions. The number of carbon atoms of the alkyl group in the tetraalkylammonium ion is preferably 1 to 6, and more preferably 1 to 4, each independently. In the hydroxyalkyltrialkylammonium ion, the number of carbon atoms of the hydroxyalkyl group and the number of carbon atoms of the alkyl group are each independently preferably 1 to 6, and more preferably 1 to 4.

Specific examples of preferable quaternary ammonium compounds in the polishing composition disclosed herein include tetramethylammonium hydroxide, tetraethylammonium hydroxide, tetrapropylammonium hydroxide, tetrabutylammonium hydroxide, and tetrapentylammonium hydroxide. And tetraalkylammonium hydroxide such as tetrahexylammonium hydroxide; hydroxyalkyltrialkylammonium hydroxide such as 2-hydroxyethyltrimethylammonium hydroxide (also referred to as choline); and the like. Of these, tetraalkylammonium hydroxide is preferable, and tetramethylammonium hydroxide is particularly preferable.

<Weak acid salt>
As the weak acid salt in the technique disclosed herein, one that can be used for polishing using silica particles and can exhibit a desired buffering action in combination with a quaternary ammonium compound can be appropriately selected. The weak acid salts can be used alone or in combination of two or more.
For example, carbonate ions, hydrogen carbonate ions, borate ions, phosphate ions, phenol ions, monocarboxylate ions (eg acetate ions), dicarboxylate ions (eg oxalate ions, maleate ions) Ion) and tricarboxylate ion (for example, citrate ion) and the like. Examples of the cation component constituting the weak acid salt include alkali metal ions such as potassium ion and sodium ion; alkaline earth metal ions such as calcium ion and magnesium ion; transition metals such as manganese ion, cobalt ion and zinc ion. Ions; ammonium ions such as tetraalkylammonium ions; phosphonium ions such as tetraalkylphosphonium ions; and the like. Specific examples of weak acid salts include sodium carbonate, potassium carbonate, sodium bicarbonate, potassium bicarbonate, sodium acetate, potassium acetate, sodium propionate, potassium propionate, calcium carbonate, calcium bicarbonate, calcium acetate, calcium propionate, Examples include magnesium acetate, magnesium propionate, zinc propionate, manganese acetate, and cobalt acetate.

From the viewpoint of obtaining a polishing composition exhibiting a good buffering action in a pH range suitable for polishing using silica particles (for example, polishing of a silicon wafer), at least one of the acid dissociation constant (pKa) values is 8.0 to Weak acid salts in the range of 11.8 (eg 8.0 to 11.5) are preferred. Suitable examples include carbonates, bicarbonates, borates, phosphates and phenol salts. Of these, weak acid salts in which the anion component is carbonate ion or hydrogen carbonate ion are preferable, and weak acid salts in which the anion component is carbonate ion are particularly preferable. Moreover, as a cation component, alkali metal ions, such as potassium and sodium, are suitable. Particularly preferred weak acid salts include sodium carbonate, potassium carbonate, sodium bicarbonate and potassium bicarbonate. Of these, potassium carbonate (K ₂ CO ₃ ) is preferable. As the value of pKa, the value of the acid dissociation constant at 25 ° C. described in known materials can be adopted.

<Content of quaternary ammonium compound>
The amount Y [mol / L] of the quaternary ammonium compound contained per liter (L) of the polishing composition disclosed herein satisfies the following formula (1).
0.80 ≦ (Y / Y ₀ ) (1)
Here, Y ₀ [mol / L] is
The theoretical buffer ratio A between the quaternary ammonium compound and the weak acid salt;
The content X [mol / L] of the weak acid salt in the polishing composition;
Based on the amount B [mol / L] adsorbed on the silica particles in the quaternary ammonium compound contained in the polishing composition, the following formula (2):
Y ₀ = AX + B (2);
Is an amount defined by

The theoretical buffer ratio A is such that the weak acid salt can dissociate in a pH range (typically in the range of pH 8.0 to 11.8) in which the polishing composition disclosed herein can be used for polishing a silicon wafer. It can be grasped as a value obtained by dividing the number of stages by the valence of a strong base that exhibits a buffering action in relation to the weak acid salt. Here, the valence of the quaternary ammonium compound is 1. Therefore, for example, when carbonate is used as the weak acid salt, the theoretical buffer ratio A is 2 because the acid dissociation constant (pKa2) related to the second-stage dissociation of carbonic acid is about 10.25.

The silica particles in the polishing composition are converted to “—O ⁻ ” by “H” being extracted from the silanol group “—OH” by the action of the alkali component. The cations derived from the quaternary ammonium compound in the polishing composition are adsorbed on the silica particles as a counter cation whose amount is “—O ⁻ ”. That is, the cation (quaternary ammonium ion) derived from the quaternary ammonium compound in the polishing composition is not completely released in the aqueous phase, but a part of the cation is adsorbed on the silica particles. It has become a state. The amount of quaternary ammonium ions liberated in the aqueous phase is the amount obtained by subtracting the adsorption amount B on the silica particles from the amount Y of the quaternary ammonium compound contained in the polishing composition, that is, Y—B. It becomes.
In order to realize the theoretical buffer ratio A in the aqueous phase of the polishing composition, the amount Y ₀ of the quaternary ammonium compound represented by the above formula (2) is set in consideration of the amount B adsorbed on the silica particles. It can be grasped as indicating the amount of the quaternary ammonium compound that is desirably contained in the polishing composition. Hereinafter, the amount Y ₀ [mol / L] of the quaternary ammonium compound defined by the formula (2) may be referred to as “target content Y ₀ ”.

The amount of adsorption B of the quaternary ammonium compound on the silica particles is usually proportional to the surface area of the silica particles based on the BET method. The adsorption amount of the quaternary ammonium compound per surface area of the silica particles can be grasped as follows, for example. That is, after adding a known amount of a quaternary ammonium compound to a dispersion containing silica particles having a known surface area and stirring and mixing, the silica particles are precipitated by centrifugation. The total amount of organic carbon (TOC) contained in the supernatant was analyzed to determine the amount of quaternary ammonium ions contained in the supernatant, and how much the amount was reduced from the amount of quaternary ammonium compound charged. Is calculated. Thereby, the quantity of the quaternary ammonium ion which adsorb | sucked to the silica particle and settled with this silica particle can be estimated. Then, by dividing the amount of quaternary ammonium ions precipitated together with the silica particles by the surface area of the silica particles, the adsorption amount of the quaternary ammonium compound per surface area of the silica particles can be obtained.
In the case of colloidal silica prepared using water glass (silicate silicate) as a raw material, the adsorption amount [mol] of tetramethylammonium ions per surface area [m ² ] of the colloidal silica is 8.0 × 10 ⁻⁶ [mol / m ² ].

Satisfying the above formula (1) means that the quaternary ammonium compound actually contained in the polishing composition with respect to the target content Y ₀ [mol / L] of the quaternary ammonium compound described above. It means that the amount Y [mol / L] is 0.80 times or more. According to the polishing composition containing the quaternary ammonium compound and the weak acid salt in an amount satisfying the formula (1), the buffering action between the quaternary ammonium compound and the weak acid salt can be effectively exhibited. Such a polishing composition has little pH variation of the polishing composition during polishing and can be excellent in maintainability of polishing efficiency. Therefore, even in a polishing composition that uses silica particles having a BET average particle diameter of 50 nm or less as abrasive grains, it is possible to achieve good bulge resolution.

The _{value of} Y / Y ₀ (hereinafter, “Y / Y ₀ ” may be referred to as “α”) is ₀ from the viewpoint of more efficiently exerting the buffering action by the quaternary ammonium compound and the weak acid salt. It is preferably 0.85 or more, more preferably 0.90 or more, and even more preferably 0.95 or more. The polishing composition disclosed herein can be preferably implemented, for example, in an embodiment in which α is 1.00 or more.

The polishing composition disclosed herein may be a composition containing more quaternary ammonium compounds than the amount that realizes the theoretical buffer ratio A in the aqueous phase. That is, α may be larger than 1.00. According to such a polishing composition, the chemical polishing action by the quaternary ammonium compound can be exhibited better. As a result, better uplifting can be achieved. From this point of view, the value of α can be, for example, 1.20 or more, may be 1.40 or more, and may be 1.50 or more.

In the polishing composition disclosed herein, the upper limit of α is not particularly limited. From the viewpoint of avoiding an excessively high pH and easily obtaining good uplifting properties, it is usually appropriate to set α to 5.00 or less, and to 4.00 or less. Preferably, it is 3.50 or less (for example, 3.00 or less).

The content (concentration) of the weak acid salt in the polishing composition disclosed herein is not particularly limited. The content of the weak acid salt can be set so that the above formula (1) is satisfied in consideration of the content of the quaternary ammonium compound and the amount adsorbed on the silica particles.

In a preferred embodiment, the content X [mol / L] of the weak acid salt per liter (L) of the polishing composition is 0.0001 mol / L or more from the viewpoint of pH maintenance of the polishing composition. Appropriately, 0.0003 mol / L or more is preferable. From the viewpoint of obtaining better uplifting ability, the content X of the weak acid salt is preferably 0.0005 mol / L or more, more preferably 0.001 mol / L or more, and further preferably 0.0015 mol / L or more. It is. In a preferred embodiment, the content X of the weak acid salt may be 0.002 mol / L or more. Further, from the viewpoint of the dispersion stability of the polishing composition, the content of the weak acid salt contained per liter of the polishing composition is usually 1.0 mol / L or less. In the polishing composition used as a polishing liquid as it is, the content X of the weak acid salt contained in 1 liter of the polishing composition is preferably 0.1 mol / L or less, preferably 0.05 / L mol or less, more preferably 0.02 mol / L or less.

The content X / W [mol / kg] of weak acid salt per kg of silica particles contained in the polishing composition is set to, for example, 0.10 mol / kg or more from the viewpoint of pH maintenance of the polishing composition. Usually, 0.20 mol / kg or more is suitable, and 0.40 mol / kg or more is preferable. From the viewpoint of obtaining better uplifting ability, the content of weak acid salt per 1 kg of silica particles can be 0.50 mol / kg or more, may be 0.80 mol / kg or more, and is 1.00 or more. Or even 1.50 mol / kg or more. The upper limit of the content X / W of weak acid salt per 1 kg of silica particles is not particularly limited, but usually 5.00 mol / kg or less is appropriate, 3.00 mol / kg or less is preferable, and 1.00 mol / Kg or less is more preferable. The polishing composition disclosed herein can be preferably implemented, for example, in an embodiment in which X / W is in the range of 0.20 to 0.60 mol / kg.

The content (concentration) of the quaternary ammonium compound in the polishing composition disclosed herein is not particularly limited. In consideration of the content of the weak acid salt and the like, the above formula (1) can be set.

In a preferred embodiment, the content Y [mol / L] of the quaternary ammonium compound per liter (L) of the polishing composition is 0.0002 mol / L from the viewpoint of the pH maintenance property of the polishing composition. L or more is appropriate, and 0.0005 mol / L or more is preferable. From the viewpoint of improving the initial polishing efficiency and obtaining better bulge resolution, the content Y of the quaternary ammonium compound is preferably 0.001 mol / L or more, more preferably 0.003 mol / L or more, More preferably, it is 0.005 mol / L or more. In a preferred embodiment, the content Y of the quaternary ammonium compound may be 0.01 mol / L or more. Further, from the viewpoint of the dispersion stability of the polishing composition, the content of the quaternary ammonium compound contained per liter of the polishing composition is usually suitably 2.0 mol / L or less. In a polishing composition used as a polishing liquid as it is, the content Y of the quaternary ammonium compound contained in 1 liter of the composition is preferably 0.2 mol / L or less, preferably 0.1 / L mol or less, more preferably 0.05 mol / L or less.

The content Y / W [mol / kg] of the quaternary ammonium compound per kg of silica particles contained in the polishing composition is, for example, 0.30 mol / kg from the viewpoint of the pH maintainability of the polishing composition. Usually, 0.50 mol / kg or more is appropriate, and 1.00 mol / kg or more is preferable. From the viewpoint of improving the initial polishing efficiency and obtaining better bulge resolution, the content Y / W of the quaternary ammonium compound per 1 kg of silica particles can be 1.20 mol / kg or more. It may be 40 mol / kg or more, and may be 1.50 mol / kg or more. The upper limit of the content Y / W [mol / kg] of the quaternary ammonium compound per 1 kg of silica particles is not particularly limited, but is usually 10.00 mol / kg or less, and 8.00 mol / kg. The following is preferable, and 5.00 mol / kg or less (for example, 3.00 mol / kg or less) is more preferable. The polishing composition disclosed herein can be preferably implemented, for example, in an embodiment in which Y / W is in the range of 1.20 to 2.50 mol / kg.

In a preferred embodiment of the polishing composition disclosed herein, the content is calculated from the content X [mol / L] of the weak acid salt, the theoretical buffer ratio A, and the content Y [mol / L] of the quaternary ammonium compound. The value of “AX + Y [mol / L]” is suitably 0.005 mol / L or more, preferably 0.008 mol / L or more, and 0.010 mol / L or more. Is more preferably 0.013 mol / L or more. When the value of AX + Y increases, the chemical polishing action of the polishing composition increases, and the polishing efficiency at the beginning of polishing (initial polishing efficiency) tends to improve. Furthermore, by satisfy | filling said Formula (1), the high polishing efficiency in an initial stage can be maintained suitably. As a result, a good ridge-dissolving property can be realized. Moreover, when the value of AX + Y is too large, the pH of the polishing composition may be too high. For this reason, the value of AX + Y is usually preferably 3 mol / L or less, and more preferably 1 mol / L or less.

The polishing composition disclosed herein has a weak acid salt content X [mol / L], a theoretical buffer ratio A, a quaternary ammonium compound content Y [mol / L], and a silica particle content W [ It is preferable that the value of “(AX + Y) / W [mol / kg]” calculated from kg / L] is within a predetermined range. Hereinafter, “(AX + Y) / W” may be expressed as “β”. The value of β [mol / kg] is suitably 0.5 mol / kg or more, preferably 0.8 mol / kg or more, more preferably 1.0 mol / kg or more. Preferably, it is 1.5 mol / kg or more. The value of β [mol / kg] is usually suitably 10.0 [mol / kg] or less, preferably 7.0 [mol / kg] or less, and preferably 5.0 [mol / kg] or less. Mol / kg] or less, more preferably 2.5 [mol / kg] or less.
The value of (AX + Y) / W (= β) can be understood as representing the ratio of the chemical polishing action contribution to the mechanical polishing action contribution. As the value of β increases, the contribution of the chemical polishing action tends to be greater than the contribution of the mechanical polishing action. In the polishing composition disclosed herein, by making the value of β within a predetermined numerical range, mechanical polishing action and chemical polishing action are compared with the case where the value of β is too large or too small. This balance is suitable for relieving uplift. This makes it possible to realize a polishing composition that exhibits good uplifting resistance even when silica particles of 50 nm or less are used.

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

<Other ingredients>
The polishing composition disclosed herein is a polishing composition (typically a water-soluble polymer, a surfactant, a chelating agent, an antiseptic, an antifungal agent, etc.) as long as the effects of the present invention are not significantly hindered. Specifically, a known additive that can be used in a polishing composition used in a polishing process of a silicon wafer may be further contained as necessary.

Examples of water-soluble polymers include cellulose derivatives, starch derivatives, polymers containing oxyalkylene units, polymers containing nitrogen atoms, vinyl alcohol polymers, and the like. Specific examples include hydroxyethyl cellulose, pullulan, random copolymer or block copolymer of ethylene oxide and propylene oxide, polyvinyl alcohol, polyisoprene sulfonic acid, polyvinyl sulfonic acid, polyallyl sulfonic acid, polyisoamylene sulfonic acid. , Polystyrene sulfonate, polyacrylate, polyvinyl acetate, polyethylene glycol, polyvinyl imidazole, polyvinyl carbazole, polyvinyl pyrrolidone, polyvinyl caprolactam, polyvinyl piperidine and the like. A water-soluble polymer can be used singly or in combination of two or more.

Examples of chelating agents include aminocarboxylic acid chelating agents and organic phosphonic acid chelating agents. Examples of aminocarboxylic acid chelating agents include ethylenediaminetetraacetic acid, ethylenediaminetetraacetic acid sodium, nitrilotriacetic acid, nitrilotriacetic acid sodium, nitrilotriacetic acid ammonium, hydroxyethylethylenediaminetriacetic acid, hydroxyethylethylenediamine sodium triacetate, diethylenetriaminepentaacetic acid Diethylenetriamine sodium pentaacetate, triethylenetetramine hexaacetic acid and sodium triethylenetetramine hexaacetate. Examples of organic phosphonic acid chelating agents include 2-aminoethylphosphonic acid, 1-hydroxyethylidene-1,1-diphosphonic acid, aminotri (methylenephosphonic acid), ethylenediaminetetrakis (methylenephosphonic acid), diethylenetriaminepenta (methylenephosphonic). Acid), ethane-1,1-diphosphonic acid, ethane-1,1,2-triphosphonic acid, ethane-1-hydroxy-1,1-diphosphonic acid, ethane-1-hydroxy-1,1,2-triphosphonic acid Ethane-1,2-dicarboxy-1,2-diphosphonic acid, methanehydroxyphosphonic acid, 2-phosphonobutane-1,2-dicarboxylic acid, 1-phosphonobutane-2,3,4-tricarboxylic acid and α-methylphospho Nosuccinic acid is included. Of these, organic phosphonic acid chelating agents are more preferred. Of these, ethylenediaminetetrakis (methylenephosphonic acid), diethylenetriaminepenta (methylenephosphonic acid) and diethylenetriaminepentaacetic acid are preferable. Particularly preferred chelating agents include ethylenediaminetetrakis (methylenephosphonic acid) and diethylenetriaminepenta (methylenephosphonic acid). A chelating agent can be used individually by 1 type or in combination of 2 or more types.

Examples of preservatives and fungicides include isothiazoline compounds, paraoxybenzoates, phenoxyethanol and the like.

The polishing composition disclosed herein can contain a base other than the quaternary ammonium compound as required, as long as the effects of the present invention are not significantly hindered. Examples of the base as such an optional component include alkali metal hydroxide, quaternary phosphonium hydroxide, amine, ammonia and the like. When a base as an optional component is included, the content [mol / L] is suitably ½ or less of the quaternary ammonium compound, and preferably ¼ or less. From the viewpoint of simplification of the composition and stability of performance, the polishing composition disclosed herein can be preferably implemented in an embodiment that does not substantially contain a base (potassium hydroxide, piperazine, etc.) as an optional component. Here, “substantially not containing” means not at least intentionally contained in the polishing composition.

<Polishing composition>
The polishing composition disclosed herein is typically supplied to a polishing object in the form of a polishing liquid containing the polishing composition, and used for polishing the polishing object. The polishing composition disclosed herein may be used, for example, as a polishing liquid after being diluted (typically diluted with water) or as it is as a polishing liquid. Also good. That is, the concept of the polishing composition in the technology disclosed herein includes a polishing composition (working slurry) that is supplied to a polishing object and used for polishing the polishing object, and diluted for use in polishing. And a concentrated liquid (working slurry stock solution). The concentration ratio of the concentrated liquid can be, for example, about 2 to 100 times on a volume basis, and usually about 5 to 50 times is appropriate.

The pH of the polishing composition is typically 8.0 or more, preferably 8.5 or more, more preferably 9.0 or more, still more preferably 9.5 or more, for example 10.0 or more. As the pH of the polishing liquid increases, the bulge elimination tends to improve. On the other hand, the pH of the polishing liquid is suitably 12.0 or less from the viewpoint of preventing the dissolution of silica particles as abrasive grains and suppressing the reduction of the mechanical polishing action by the abrasive grains. It is preferably 8 or less, more preferably 11.5 or less, and even more preferably 11.0 or less.
In addition, the pH of the polishing composition was measured using a pH meter (for example, a glass electrode type hydrogen ion concentration indicator (model number F-23) manufactured by Horiba, Ltd.) and a standard buffer solution (phthalate pH buffer solution pH: 4.01 (25 ° C), neutral phosphate pH buffer pH: 6.86 (25 ° C), carbonate pH buffer pH: 10.01 (25 ° C)) It can be grasped by putting the glass electrode into the polishing composition and measuring the value after 2 minutes or more has been stabilized.

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

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

The polishing pad used in the above polishing process is not particularly limited. For example, any of polyurethane foam type, non-woven fabric type, suede type, those containing abrasive grains, and those not containing abrasive grains may be used. Further, as the polishing apparatus, a double-side polishing apparatus that simultaneously polishes both surfaces of an object to be polished, or a single-side polishing apparatus that polishes only one surface of the object to be polished may be used.

The above polishing composition may be used in a disposable form (so-called “flowing”) once used for polishing, or may be repeatedly used after circulation. As an example of a method of circulating and using the polishing composition, there is a method of collecting a used polishing composition discharged from the polishing apparatus in a tank and supplying the recovered polishing composition to the polishing apparatus again. . When the polishing composition is used in a circulating manner, the environmental load can be reduced by reducing the amount of the used polishing composition to be treated as a waste liquid, compared with the case of using the polishing composition by pouring. Moreover, cost can be suppressed by reducing the usage-amount of polishing composition. Since the polishing composition disclosed here is excellent in pH maintainability, it is suitable for the usage mode in which it is used in this manner. According to such a use mode, the significance of adopting the configuration of the present invention can be exhibited particularly well.

<Application>
The polishing composition disclosed here is excellent in the performance (uplift-removability) of eliminating the uplift of the peripheral edge of the hard laser mark. Taking advantage of this feature, the polishing composition can be preferably applied to polishing of a surface to be polished including a surface with a hard laser mark. For example, it is suitable as a polishing composition used in a preliminary polishing step of a silicon wafer with a hard laser mark. It is desirable to eliminate the bulge around the hard laser mark at the beginning of the polishing process. For this reason, the polishing composition disclosed herein can be particularly preferably used in the first polishing step (primary polishing step) after applying the hard laser mark. The first polishing step is typically performed as a double-side polishing step in which both sides of a silicon wafer are simultaneously polished. The polishing composition disclosed herein can be preferably used in such a double-side polishing step.

The polishing composition disclosed herein can also be used for polishing a surface to be polished that does not have a hard laser mark. For example, the present invention can be preferably applied to preliminary polishing of a lapped silicon wafer regardless of the presence or absence of a hard laser mark. In the preliminary polishing step, since the required polishing rate is higher than that in the final polishing step, the scraped silicon is dissolved in the polishing composition in a large amount. Accordingly, the polishing composition tends to contain a large amount of silicate ions. This acts to lower the pH of the polishing composition. When the polishing composition is recycled, the above action is particularly strong. The polishing composition disclosed herein is preferable because it can be one having little pH fluctuation (high pH maintainability) even under such circumstances.

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

<Preparation of polishing composition>
(Examples 1 to 5)
A polishing composition having the composition shown in Table 1 was prepared by stirring and mixing colloidal silica, potassium carbonate (K ₂ CO ₃ ), tetramethylammonium hydroxide (TMAH) and ion-exchanged water at room temperature of about 25 ° C. for about 30 minutes. Prepared. As colloidal silica, those having a BET average particle diameter of 40.0 nm were used in Examples 1 to 4, and those having a BET average particle diameter of 50.0 nm were used in Example 5. The polishing compositions according to Examples 1 to 5 constitute a buffer system of K ₂ CO ₃ and TMAH. The theoretical buffer ratio A in this buffer system is 2.

(Comparative Examples 1 to 3)
A polishing composition having the composition shown in Table 1 was prepared by stirring and mixing colloidal silica, TMAH and ion-exchanged water at room temperature of about 25 ° C. for about 30 minutes. As the colloidal silica, one having a BET average particle diameter of 40.0 nm was used.

(Comparative Examples 4 and 5)
A polishing composition having the composition shown in Table 1 was prepared by stirring and mixing colloidal silica, K ₂ CO ₃ , TMAH and ion exchange water at room temperature of about 25 ° C. for about 30 minutes. As the colloidal silica, one having a BET average particle diameter of 40.0 nm was used.

About each polishing composition of Examples 1-5 and Comparative Examples 1-5, content W [kg / L] of colloidal silica in each polishing composition, content X [mol / L] of K ₂ CO ₃ ] And TMAH content Y [mol / L] and the amount B [mol / L] adsorbed on colloidal silica in TMAH contained in the polishing composition, Y ₀ (= 2X + B) [mol / L], Y / Y ₀ (= α) and (2X + Y) / W (= β) [mol / kg] were calculated. The results are shown in Table 1. Table 1 also shows the pH of the polishing composition measured immediately before being used for polishing a silicon wafer described later.
Of the TMAH contained in the polishing composition, the amount B [mol / L] adsorbed on the colloidal silica is the TMAH adsorption amount [mol] per surface area [m ² ] of the colloidal silica and the polishing composition. It calculated from the surface area [m < ² > / L] of the colloidal silica contained per 1L. The TMAH adsorption amount [mole] per surface area [m ² ] of the colloidal silica was 8.0 × 10 ⁻⁶ [mole / m ² ] for any polishing composition as measured by the method described above. .

<Polishing of silicon wafer>
The polishing composition according to each example was directly used as a polishing liquid (working slurry), and the surface of the polishing object (test piece) was polished under the following conditions. As a test piece, a commercially available silicon wafer having a diameter of 300 mm (thickness: 798 μm, conductivity type: P type, crystal orientation: <100>, resistivity: 0.1 Ω · cm or more and less than 100 Ω · cm) as a test piece. used. This wafer is engraved with a back hard laser mark based on the SEMI M1 (T7) standard.

(Polishing conditions)
Polishing device: Double-side polishing device manufactured by Speedfam, model “DSM20B-5P-4D”
Polishing pressure: 15.0kPa
Upper surface plate rotation speed: -13 rotations / minute Lower surface plate rotation speed: 35 rotations / minute
Internal gear rotation speed: 7 rotations / minute Sun gear rotation speed: 25 rotations / minute Polishing pad: Product name “MH S-15A” manufactured by Nitta Haas
Polishing liquid: A total of 100 L of polishing liquid is circulated at a rate of 4.5 L / min. Polishing environment temperature: 20 ° C.
Polishing time: 60 minutes

<Washing>
A silicon wafer after polishing is washed with a cleaning solution having a composition of ammonia water (ammonia concentration 29 mass%): hydrogen peroxide water (hydrogen peroxide concentration 31 mass%): deionized water = 1: 1: 30 (volume ratio). Washed with (SC-1 wash). More specifically, two cleaning tanks equipped with an ultrasonic oscillator with a frequency of 950 kHz were prepared, and the cleaning liquid was accommodated in each of the first and second cleaning tanks and maintained at 60 ° C. Then, after immersing the polished silicon wafer in the first cleaning tank for 6 minutes in a state where the ultrasonic oscillator is operated, the ultrasonic oscillator is operated in a rinse tank containing ultra pure water at 25 ° C. In the second cleaning tank, the ultrasonic oscillator was operated and immersed for 6 minutes.

<Uplift erasure evaluation>
For the cleaned silicon wafer, the surface shape of the site including the hard laser mark was measured, and the ridge elimination property was evaluated. The measurement was performed by obtaining SFQD (Site Front least-squares site Deviation) using “WaferSight 2” manufactured by KLA Tencor. Here, SFQD is a 26 mm × 8 mm size (in order to improve evaluation accuracy, the part from the edge to 1 mm in the inner circumferential direction is excluded from the evaluation range). Of the calculated + side thickness from the reference plane and − side thickness from the reference plane, this is the numerical value with the larger absolute value. The “+ side” refers to the upper side when the silicon wafer is placed horizontally with the surface facing upward. The “− side” refers to the lower side when the surface of the silicon wafer is placed horizontally with the surface facing upward. The obtained SFQD value (unit: nm) is shown in the column of “bulge resolution” in Table 1.
The results obtained by the above measurements or tests are shown in Table 1.

As shown in Table 1, all of the polishing compositions of Examples 1 to 5 having α of 0.80 or more showed good bulge elimination properties. Among the polishing compositions of Examples 1 to 4 using silica particles having a BET average particle diameter of 40.0 nm, the polishing compositions of Examples 2 to 4 having α greater than 1.00 have higher bulges. Resolvability was obtained. In Examples 2 and 3 in which β was 1.0 mol / kg or more and 5 mol / kg or less, particularly excellent uplifting property was obtained.
On the other hand, the polishing composition of Comparative Example 2 was inferior to the bulge-removing property as compared with Example 1, although the value of β was larger than that of Example 1. This is probably because the polishing composition of Comparative Example 2 could not utilize the buffering action of TMAH and weak acid salt, and the maintenance efficiency of the polishing efficiency was lower than that of the polishing composition of Example 1. The polishing compositions of Comparative Examples 1 and 3 that did not contain a weak acid salt and had a small β value compared to Comparative Example 2 were further less prone to bulging. Further, the polishing compositions of Comparative Examples 4 and 5 were too small to achieve a sufficient buffering action because α was too small, and were not as good as those of Examples 1 to 5 in terms of bulge elimination.

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

Claims

A polishing composition for use in polishing a silicon wafer,
Comprising silica particles, a weak acid salt and a quaternary ammonium compound,
The BET average particle diameter of the silica particles is 50 nm or less,
Polishing composition in which content Y [mol / L] of the said quaternary ammonium compound in the said polishing composition satisfy | fills following formula (1).
0.80 ≦ (Y / Y 0 ) (1)
(Where Y 0 [mol / L] is
The theoretical buffer ratio A between the quaternary ammonium compound and the weak acid salt;
Content of the weak acid salt in the polishing composition X [mol / L];
Based on the amount B [mol / L] adsorbed on the silica particles in the quaternary ammonium compound contained in the polishing composition, the following formula (2):
Y 0 = AX + B (2);
Is an amount defined by )
The weak acid salt content X [mol / L], the quaternary ammonium compound content Y [mol / L], and the silica particle content W [kg / L] in the polishing composition Of the following formula (3):
0.5 [mol / kg] ≦ (AX + Y) / W [mol / kg] (3);
The polishing composition according to claim 1, wherein
The ratio of the content Y [mol / L] of the quaternary ammonium compound to the content W [kg / L] of the silica particles is 1.00 [mol / kg] or more. Polishing composition.
4. The ratio of the content X [mol / L] of the weak acid salt to the content W [kg / L] of the silica particles is 0.20 [mol / kg] or more. 5. The polishing composition according to 1.
5. The polishing composition according to claim 1, wherein the weak acid salt includes a weak acid salt having at least one acid dissociation constant (pKa) value in the range of 8.0 to 11.8.
The polishing composition according to any one of claims 1 to 5, comprising at least one selected from the group consisting of carbonates and dicarboxylates as the weak acid salt.
The quaternary ammonium compound is at least selected from the group consisting of tetramethylammonium hydroxide, tetraethylammonium hydroxide, tetrapropylammonium hydroxide, tetrabutylammonium hydroxide, tetrapentylammonium hydroxide and tetrahexylammonium hydroxide. Polishing composition as described in any one of Claim 1 to 6 containing 1 type.
Polishing composition as described in any one of Claim 1 to 7 whose BET average particle diameter of the said silica particle is 25 nm or more and less than 50 nm.
The polishing composition according to any one of claims 1 to 8, which is used for polishing a silicon wafer having a hard laser mark.