JP2014216368A - Polishing agent and polishing method - Google Patents

Abstract

An object of the present invention is to provide a polishing agent and a polishing method excellent in stability during long-term polishing use, such as suppressing fluctuations in pH and improving the sustainability of polishing rate in polishing a sapphire substrate. An abrasive for polishing a surface to be polished of a sapphire substrate, comprising at least selected from silicon oxide fine particles, amino acids having an amino group pKa of 8 to 10.5, boric acid, and sodium bicarbonate. An abrasive comprising one kind of pH adjuster and water. [Selection] Figure 1

Description

The present invention relates to an abrasive and a polishing method for polishing a surface to be polished of a sapphire (α-Al ₂ O ₃ ) substrate. More specifically, the present invention relates to a polishing agent having excellent stability when used for a long time in polishing a surface to be polished of a sapphire substrate, and a polishing method using the same.

Sapphire (α-Al ₂ O ₃ ) substrate manufacturing and processing techniques are attracting attention as substrates for LEDs and power devices that are expected to grow significantly in the future. Since a crystal thin film such as GaN is formed on a sapphire substrate to form a device, it is important to have a low defect / high quality surface crystallographically, and to obtain a low defect / high smooth surface. Therefore, a chemical mechanical polishing (hereinafter also referred to as CMP) technique has attracted attention. However, since sapphire is very hard and has high chemical stability, it is difficult to polish with high efficiency while ensuring quality, especially in the final stage of polishing that determines quality, and the polishing process is very difficult. Had the problem of getting longer.

  In the chemical mechanical polishing, silicon oxide fine particles have been used as polishing abrasive grains in many cases. Here, in the chemical mechanical polishing, the abrasive is generally circulated. However, when the circulator is used for a long period of time, there is a problem that the pH of the abrasive is reduced and the polishing efficiency is greatly lowered. Thus, for example, a method has been proposed in which an alkaline agent such as sodium hydroxide or an amine-based substance is added to a circulating abrasive using a pH adjuster to adjust the pH of the abrasive (see Patent Document 1). .

  Further, as a method for adjusting the pH of a polishing agent using silicon oxide fine particles as polishing abrasive grains, a method using a polishing agent in which an amino acid is added to the polishing abrasive grains together with an oxidizing agent and an inhibitor is known in polishing semiconductor metal wiring. ing. (See Patent Document 2).

JP-A-11-10540 JP 2000-133621 A

  Even when polishing a sapphire substrate, when a polishing agent for polishing silicon oxide fine particles is used in a circulating manner, there is a problem that the pH of the polishing agent is lowered and the abrasive particles are easily aggregated, and the polishing rate is reduced. In the method using a pH adjuster, there are problems that the polishing rate varies depending on the timing of addition of the alkaline agent, and that the apparatus configuration becomes complicated due to the use of the automatic dropping apparatus. In addition, the method using an amine compound as an alkaline agent has a problem that its use is regulated by law in consideration of the environment.

  The present invention has been made to solve the above-mentioned problems, and in the polishing of the surface to be polished of the sapphire substrate, it is possible to suppress the fluctuation of pH and improve the durability of the polishing rate. An object of the present invention is to provide an abrasive and a polishing method excellent in properties.

The present invention provides an abrasive for polishing a surface to be polished of a sapphire substrate having the following configuration.
[1] A polishing agent for polishing a surface to be polished of a sapphire (α-Al ₂ O ₃ ) substrate, comprising silicon oxide fine particles, amino acids having a pKa of an amino group of 8 to 10.5, boric acid, and An abrasive comprising at least one pH adjuster selected from sodium hydrogen carbonate and water.
[2] The abrasive according to [1], wherein the pH of the abrasive is in the range of 8 to 10.5.
[3] The silicon oxide fine particles include first silicon oxide fine particles having an average primary particle diameter of 5 to 20 nm and second silicon oxide fine particles having an average primary particle diameter of 40 to 110 nm, and the first The polishing agent according to [1] or [2], wherein a ratio of the first silicon oxide fine particles to a total amount of the silicon oxide fine particles and the second silicon oxide fine particles is 0.7 to 40% by mass.
[4] The abrasive according to any one of [1] to [3], wherein the pH adjuster is at least one selected from glycine, alanine, cysteine, boric acid, and sodium bicarbonate.
[5] The abrasive according to any one of [1] to [4], wherein the content of the pH adjuster is 0.001 to 15% by mass with respect to the total amount of the abrasive.

[6] The abrasive according to any one of [1] to [5], wherein the silicon oxide fine particles are colloidal silica.
[7] The abrasive according to any one of [1] to [6], wherein the content of the silicon oxide fine particles is 0.01 to 50% by mass with respect to the total amount of the abrasive.
[8] The abrasive according to any one of [3] to [7], wherein an average primary particle diameter of the second silicon oxide fine particles is 45 to 110 nm.
[9] The abrasive according to any one of [3] to [8], wherein the average primary particle diameter of the first silicon oxide fine particles is 8 to 20 nm.

The present invention also provides a polishing method for polishing a surface to be polished of a sapphire substrate having the following configuration.
[10] A method of supplying a polishing agent to a polishing pad, bringing a polishing target surface of a sapphire substrate into contact with the polishing pad, and polishing by relative movement between the two, and the polishing agents [1] to [1] 9] A polishing method using any of the polishing agents.
[11] The polishing agent supplied to the polishing pad and used for polishing is recovered, and the polishing agent is circulated and used by repeatedly supplying the recovered polishing agent to the polishing pad again. Method.

  According to the polishing agent of the present invention and the polishing method using the same, it is possible to suppress pH fluctuation and improve the durability of the polishing rate even during repeated use in polishing the surface to be polished of the sapphire substrate. Therefore, it can be used stably for a long time.

It is a figure which shows an example of the grinding | polishing apparatus which can be used for the grinding | polishing method of this invention.

Hereinafter, embodiments of an abrasive and a polishing method according to the present invention will be described.
[Abrasive]
Polishing agent of the present embodiment is a polishing agent for polishing a sapphire (α-Al 2 _{O 3)} the polished surface of the substrate, and silicon oxide particles, pKa of the amino group is a 8 to 10.5 It contains at least one pH adjusting agent selected from amino acids, boric acid and sodium hydrogen carbonate, and water.

Abrasive of the present embodiment is made of a single crystal of α-Al ₂ O _3, a polishing agent for hardness polishing a sapphire substrate which is 12 by modified Mohs hardness.

  In the polishing agent of the present embodiment, silicon oxide fine particles are used as polishing abrasive grains, and the pH adjuster described above can be used to change the pH of the polishing agent when used for a long time in polishing a sapphire substrate. It suppresses and improves the sustainability of the polishing rate.

  As described above, in the polishing of the sapphire substrate, when the abrasive is circulated, the polishing waste of the sapphire substrate may be mixed as aluminate and the pH of the abrasive may be lowered. For this reason, there is a problem that the silicon oxide fine particles which are abrasive grains easily aggregate and the polishing rate is lowered. At this time, in the method in which an alkali agent or the like is added to the abrasive according to the change in pH of the abrasive, the pH of the abrasive varies depending on the timing of the addition, and the polishing rate may vary.

The abrasive according to the present embodiment contains silicon oxide fine particles, the above-described specific pH adjuster, and water, and the pH of the abrasive varies due to the high buffering action of the specific pH adjuster. And the dispersion stability of the silicon oxide fine particles in the dispersion medium can be improved. Furthermore, since the pH adjuster is non-volatile, the concentration of the silicon oxide fine particles, which are abrasive grains, in the abrasive can be kept stable, and the polishing rate can be kept stable. Thus, the abrasive | polishing agent of this embodiment is excellent in stability at the time of long-term use. Furthermore, since an automatic dripping device is unnecessary, the configuration of the device used for polishing can be simplified, and there is no problem of environmental burden because no amine compound is used.
Hereafter, each element which comprises the abrasive | polishing agent of this embodiment is demonstrated.

(1) pH adjuster In the abrasive | polishing agent of this embodiment, a pH adjuster is from amino acid (henceforth an amino acid (A)) whose pKa of an amino group is 8-10.5, boric acid, and sodium hydrogencarbonate. At least one selected.
An amino acid is a compound having an amino group and a carboxyl group, and usually has an amino group pKa and a carboxyl group pKa. The amino acid (A) used as a pH adjuster in this embodiment may be any amino acid having an amino group pKa of 8 to 10.5, and the carboxyl group pKa is not particularly limited. The amino acid (A) may have two or more amino groups, and in this case, the pKa of the amino group refers to any one pKa of two or more amino groups.
Also, boric acid and sodium bicarbonate have pKa values of 9.2 and 10.3, respectively, and have a pKa value similar to the pKa value of the amino group of amino acid (A).

  Amino acid (A), boric acid and sodium bicarbonate have the above-mentioned pKa value, thereby suppressing the decrease in pH of the abrasive due to the mixing of polishing waste on the sapphire substrate in the abrasive using silicon oxide fine particles as abrasive grains. It is a compound that exhibits a pH buffering action that keeps the pH constant. The amino acid (A) is preferably an amino acid (A) having an amino group with a pKa of 9 to 10.5. The amino acid (A) is preferably a water-soluble compound, preferably a solubility in water of 5 mg / 100 mL or more and a nonvolatile compound. Boric acid and sodium bicarbonate are sufficiently non-volatile compounds with sufficient water solubility.

  In the polishing agent of the present embodiment, as the amino acid (A) used as a pH adjuster, for example, glycine (9.2), alanine (9.69), methionine (9.06), arginine (9.01), Phenylalanine (9.19), proline (10.38), asparagine (8.72), cysteine (8.15, 10.29), tyrosine (9.04, 10.14), glutamine (9.01), Histidine (9.08), isoleucine (9.56), leucine (9.57), lysine (9.08), threonine (8.97), tryptophan (9.33), serine (9.06), valine (9.49), cystine (8.03, 8.8), hydroxyproline (9.46), hydroxylysine, thyroxine, o-phosphoserine, desmosine, β-alanine 10.10), sarcosine (9.97), ornithine (8.74), creatine, .gamma.-aminobutyric acid, opine, theanine, Torikoromin acid, kainic acid, domoic acid, ibotenic acid, and acromelic acid. In addition, about the above-mentioned amino acid, the value in parentheses is the pKa value of the amino group.

  Among the above, the pH adjuster is at least selected from glycine, alanine, cysteine, boric acid and sodium bicarbonate because it is easily available, has excellent pH stability, and excellent polishing rate sustainability during long-term polishing. One type is preferable.

  In addition, as a pH adjuster, 1 type mentioned above may be used independently and 2 or more types may be used together.

  In the abrasive of this embodiment, the content of the pH adjuster is preferably 0.001 to 15% by mass and more preferably 0.005 to 10% by mass with respect to the total amount of the abrasive.

(2) Silicon oxide fine particles In the abrasive of this embodiment, the silicon oxide fine particles are used as abrasive grains. As the silicon oxide fine particles, those produced by various known methods can be used. For example, fumed silica obtained by vapor phase synthesis of silicon tetrachloride in an oxygen and hydrogen flame, colloidal silica obtained by ion exchange or neutralization of sodium silicate, or colloidal silica obtained by hydrolyzing silicon alkoxide in the liquid phase, etc. And silicon oxide fine particles. Among these, in the abrasive | polishing agent of this embodiment, the colloidal silica which uses sodium silicate as a starting material from a viewpoint of the diversity of a kind is more preferable. In addition, colloidal silica is supplied in a state in which silicon oxide fine particles are dispersed in water in advance, and the pH is preferably 7 to 11, and more preferably 8 to 10.5.

  In the abrasive of this embodiment, the average primary particle diameter of the silicon oxide fine particles is preferably 5 to 110 nm, and more preferably 8 to 110 nm. When using silicon oxide fine particles as abrasive grains, it is preferable to use a combination of two or more types of silicon oxide fine particles having different average primary particle sizes from the viewpoint of stability during long-term use.

  Specifically, the combination of such silicon oxide fine particles includes first silicon oxide fine particles having an average primary particle diameter of 5 to 20 nm and second silicon oxide fine particles having an average primary particle diameter of 40 to 110 nm. A combination is preferable, and in this case, the ratio of the first silicon oxide fine particles to the total amount of the first silicon oxide fine particles and the second silicon oxide fine particles is preferably 0.7 to 40% by mass.

  The first and second silicon oxide fine particles are used as the silicon oxide fine particles, and the average primary particle diameter of the first silicon oxide fine particles and the average primary particle diameter of the second silicon oxide fine particles are within the above ranges, respectively, and polishing is performed at the above blending ratio. By blending with the agent, a small amount of the first silicon oxide fine particles having a small particle diameter is present together with the second silicon oxide fine particles having a large particle size as shown in the above blending ratio, and the large specific surface area of the first silicon oxide fine particles Due to the buffering effect, it is possible to further improve the stability during long-term use by further suppressing pH fluctuations. Further, the first silicon oxide fine particles having a small particle diameter present between the second silicon oxide fine particles having a large particle size, which occupies most of the above-mentioned blending proportions as polishing abrasive grains during polishing, increase the polishability. A high polishing rate can be obtained by acting on the above.

  These first silicon oxide fine particles and second silicon oxide fine particles can be the same silicon oxide fine particles except that the average primary particle diameter is different.

  When the first and second silicon oxide fine particles are used as the silicon oxide fine particles, the average primary particle diameter of the first silicon oxide fine particles is more preferably 8 to 20 nm.

  The average primary particle diameter of the second silicon oxide fine particles is more preferably 45 to 110 nm.

  In the present specification, the average primary particle diameter of the silicon oxide fine particles is obtained by converting the specific surface area measured by the nitrogen adsorption BET method into the diameter of the spherical particles.

  As a blending ratio of the first and second silicon oxide fine particles in the polishing agent of the present embodiment, the ratio of the first silicon oxide fine particles to the total amount of the first silicon oxide fine particles and the second silicon oxide fine particles is as follows: 1-40 mass% is more preferable, and 3-40 mass% is especially preferable.

  The content of silicon oxide fine particles in the abrasive of this embodiment is in the range of 0.01 to 50% by mass with respect to the total mass of the abrasive, taking into consideration the polishing rate, uniformity, material selectivity, dispersion stability, and the like. Therefore, it is preferable to set appropriately. When the content of the silicon oxide fine particles is less than 0.01% by mass with respect to the total mass of the abrasive, a sufficient polishing rate may not be obtained. When the content exceeds 50% by mass, the increase in abrasive concentration is commensurate. In some cases, the polishing rate is not improved, the viscosity of the abrasive is excessively increased, or the gelation of the abrasive is promoted. The content of silicon oxide fine particles is more preferably in the range of 1 to 30% by mass.

  When the first and second silicon oxide fine particles are used as the silicon oxide fine particles, the content of the silicon oxide fine particles in the abrasive is such that the first silicon oxide fine particles contained in the entire abrasive and It is a ratio of the total mass of the second silicon oxide fine particles.

(3) Water The water contained in the abrasive of this embodiment disperses the silicon oxide fine particles that are abrasive grains, dissolves the pH adjuster, and disperses other optional components that are added as necessary. It is a medium for dissolution. Although there is no restriction | limiting in particular about water, A pure water or deionized water is preferable from the influence with respect to another compounding component, mixing of an impurity, pH, etc. Since water has a function of controlling the fluidity of the abrasive, the content thereof can be appropriately set according to the target polishing characteristics such as the polishing rate and the flattening characteristics.

  In the abrasive of this embodiment, water is preferably contained in the range of 40 to 99 mass% with respect to the total mass of the abrasive. When the water content is less than 40% by mass with respect to the total mass of the abrasive, the viscosity of the abrasive may be increased and the fluidity may be impaired. In some cases, the concentration of the fine particles becomes low and a sufficient polishing rate cannot be obtained.

(4) Preparation of polishing agent and optional components The polishing agent of the present embodiment contains the pH adjusting agent (1), the silicon oxide fine particles (2), and the water (3) contained as essential components, for example. , And can be prepared by weighing and mixing to achieve the above content.

  Here, when colloidal silica is used as the silicon oxide fine particles, an aqueous dispersion of colloidal silica containing the silicon oxide fine particles is mixed in a desired ratio, a predetermined amount of (1) a pH adjuster is added, and water is appropriately added. It can be adjusted by diluting.

  In addition, when the first silicon oxide fine particles and the second silicon oxide fine particles are used as the silicon oxide fine particles, colloidal silica containing the first silicon oxide fine particles and colloidal silica containing the second silicon oxide fine particles are desired. And a predetermined amount of (1) pH adjuster may be added and appropriately diluted with water.

  In addition, the abrasive | polishing agent of this embodiment contains the abrasive | polishing agent for normal chemical mechanical polishing in addition to the essential component of said (1)-(3) in the range which does not impair the effect of the said this invention. Such optional components may be included.

  Thus, it is preferable that the pH of the abrasive | polishing agent of this embodiment obtained exists in the range of 8-10.5, and 8.5-10.5 is more preferable. If (1) pH adjuster, (2) silicon oxide fine particles, and (3) water, which are essential components of the abrasive of the present embodiment, are mixed at a predetermined ratio, the pH is generally within the above range, which will be described later. It can function as a buffer solution.

  In the embodiment, in order to adjust the pH of the abrasive to the above range, a pH adjusting auxiliary agent such as a strong acid or a strong base may be further added as an optional component. The addition amount of the pH adjustment auxiliary agent in the abrasive is in a range where the abrasive functions sufficiently with the buffer solution, and (1) 20% by mass or less is preferable with respect to the content of the pH adjuster. As the pH adjustment aid, an aqueous solution of a strong acid such as hydrochloric acid, nitric acid, sulfuric acid, a strong base such as sodium hydroxide or potassium hydroxide, or an aqueous solution thereof can be used. In addition, as a method for preparing an abrasive by arbitrarily adding a pH adjusting auxiliary to the essential components (1) to (3), specifically, an abrasive adjusted without blending a pH adjusting auxiliary. For the above, a method of adding the above-mentioned pH adjusting auxiliary agent to an aqueous solution having an appropriate concentration while measuring the pH and adding each in an appropriate amount, preferably not more than the upper limit shown above, so that the pH becomes a desired value. It is done.

  Moreover, it is preferable that the abrasive | polishing agent of this embodiment is a buffer solution. In the abrasive | polishing agent of this embodiment, when grind | polishing a sapphire substrate using this, it acts as a buffer solution. That is, when the sapphire substrate is chemically and mechanically polished using the polishing agent of this embodiment, polishing waste is discharged into the polishing agent in the form of aluminate, but even after taking a certain amount of aluminate into the pH. It is preferable that the polishing agent has a small change in.

For example, the abrasive according to the present embodiment has a pH in the above-described preferable range, and sodium aluminate Na [Al (OH) ₄ ] is used with respect to the total mass after mixing the sodium aluminate and the abrasive. The difference between the pH after addition of 0.04 mass% and the pH before addition of sodium aluminate is preferably within ± 1.5, more preferably within ± 1. Moreover, it is preferable that pH after adding this sodium aluminate is the range of 6.5-12.

  As described above, in the polishing agent of this embodiment, even if polishing scraps of the sapphire substrate are mixed during polishing, (1) the pH adjuster functions as a pH buffering agent alone or together with components added as necessary. Since the polishing agent is a buffer solution, the pH can be maintained within the above-described preferable pH range, and stable use for a long period of time becomes possible.

[Polishing method]
As a method for polishing the surface to be polished of the sapphire substrate using the polishing agent of the present embodiment, the surface to be polished of the sapphire substrate and the polishing pad are brought into contact with each other while supplying the polishing agent to the polishing pad. A polishing method in which polishing is performed by relative motion is preferable.

  In the above polishing method, a conventionally known polishing apparatus can be used as the polishing apparatus. FIG. 1 shows an example of a polishing apparatus that can be used in the present embodiment and circulates an abrasive. The polishing apparatus used in the present invention is limited to the structure described above. It is not a thing.

  The polishing apparatus 10 includes a polishing head 2 that holds a sapphire substrate 1, a polishing surface plate 3, a polishing pad 4 that is attached to the surface of the polishing surface plate 3, a tank 8 that stores an abrasive 5, and a tank 8 is provided with an abrasive supply pipe 6 for supplying the abrasive 5 to the polishing pad 4 using the abrasive supply means 7. The polishing apparatus 10 brings the polishing surface of the sapphire substrate 1 held by the polishing head 2 into contact with the polishing pad 4 while supplying the polishing agent 5 from the polishing agent supply pipe 6. It is comprised so that grinding | polishing may be carried out by rotating relatively.

  The polishing surface of the sapphire substrate 1 can be polished using such a polishing apparatus 10. Here, the polishing apparatus 10 is a polishing apparatus that polishes one surface of a sapphire substrate as a surface to be polished. For example, a double-sided simultaneous polishing apparatus in which polishing pads similar to the polishing apparatus 10 are arranged on the upper and lower surfaces of the sapphire substrate is used. It is also possible to polish the polished surface (both sides) of the sapphire substrate.

  The polishing head 2 may perform a linear motion as well as a rotational motion. Further, the polishing surface plate 3 and the polishing pad 4 may be as large as or smaller than the sapphire substrate 1. In that case, it is preferable that the entire surface to be polished of the sapphire substrate 1 can be polished by relatively moving the polishing head 2 and the polishing surface plate 3. Furthermore, the polishing surface plate 3 and the polishing pad 4 do not have to perform rotational movement, and may move in one direction, for example, by a belt type.

The polishing conditions of the polishing apparatus 10 are not particularly limited, but by applying a load to the polishing head 2 and pressing it against the polishing pad 4, it is possible to increase the polishing pressure and improve the polishing rate. The polishing pressure is preferably about 10 to 50 kPa, and more preferably about 10 to 40 kPa from the viewpoint of the polishing surface uniformity of the sapphire substrate 1 having a polishing rate, flatness, and prevention of polishing defects such as scratches. The number of rotations of the polishing surface plate 3 and the polishing head 2 is preferably about 50 to 500 rpm, but is not limited thereto. The supply amount of the abrasive 5 is appropriately adjusted and selected depending on the composition of the abrasive, each of the above polishing conditions, and the like. For example, when polishing a sapphire wafer having a diameter of 50 mm, it is approximately 5 to 300 cm ³ / A supply amount of about a minute is preferable.

  As the polishing pad 4, one made of a general nonwoven fabric, foamed polyurethane, porous resin, non-porous resin or the like can be used. Further, in order to promote the supply of the polishing agent 5 to the polishing pad 4 or to collect a certain amount of the polishing agent 5 on the polishing pad 4, the surface of the polishing pad 4 has a lattice shape, a concentric circle shape, a spiral shape, or the like. Groove processing may be performed.

  In addition, if necessary, polishing may be performed while bringing the pad conditioner into contact with the surface of the polishing pad 4 and conditioning the surface of the polishing pad 4.

  The polishing apparatus 10 shown in FIG. 1 has a recovery means (not shown) for recovering the polishing agent 5 used for polishing from the polishing pad 4, and the recovered polishing agent 5 is transported to the tank 8. It has become. The abrasive 5 returned to the tank 8 is supplied to the polishing pad 4 through the abrasive supply pipe 6 again using the abrasive supply means 7. The abrasive 5 is circulated and used in this way.

  In the polishing method of the present embodiment, after the abrasive supplied to the polishing pad is used for polishing, it is recovered in the same manner as described above, but is discarded after each polishing use. It is also possible to use this polishing apparatus.

  A polishing method in which the abrasive is used in a circulating manner is preferable because the consumption of the abrasive can be reduced as compared with a polishing method in which the abrasive is discarded for each polishing use. However, as the polishing progresses, polishing scraps on the sapphire substrate are mixed into the abrasive due to polishing, so conventional abrasives tend to cause aggregation and gelation of abrasive grains, leading to pad clogging. There was a problem that the polishing rate gradually decreased. If the abrasive | polishing agent of this embodiment is used, the fall of the polishing rate at the time of circulation use will be suppressed by suppressing the fall of pH which causes aggregation of an abrasive grain.

  That is, the abrasive according to the present embodiment has a feature that a decrease in the polishing rate when used in a circulation system is suppressed. This not only improves the efficiency of the polishing process, but also reduces the consumption of abrasives, shortens downtime by reducing the frequency of pad dressing and flushing, etc., and also reduces the pad consumption. Therefore, it can be said that it has great significance for improving the mass productivity of various device manufacturing.

Hereinafter, the present invention will be described using examples, but the present invention is not limited to the following description. Examples 1 to 13 are Examples, and Examples 14 to 16 are Comparative Examples.
In each example, when the first silicon oxide fine particles and the second silicon oxide fine particles were blended as abrasive grains in the abrasive, the following colloidal silica aqueous dispersion was used.
(Abrasive grains)
For the first silicon oxide fine particles, a 30% by weight solid dispersion of colloidal silica having an average primary particle diameter of 10 nm (hereinafter referred to as “first colloidal silica dispersion”) was used.
For the second silicon oxide fine particles, a 40% by weight solid dispersion of colloidal silica having an average primary particle diameter of 110 nm (hereinafter referred to as “second colloidal silica dispersion”) was used.
The average primary particle diameter of the first and second silicon oxide fine particles is a value obtained by measuring the specific surface area by the nitrogen adsorption BET method.

(Example 1)
(1) 0.1% by mass of alanine as a pH adjuster, (2) 25% by mass of second silicon oxide fine particles, and (3) water (ion exchange) with respect to the total mass of the abrasive obtained finally. The second colloidal silica dispersion, alanine and water were mixed and stirred so that the water was 70% by mass. The pH of this mixed solution (pH during mixing of (1), (2) and (3)) was 8.5.

Next, add a pH adjustment aid (10% by weight aqueous solution of KOH) until the pH reaches 9.5, then add water so that the total amount becomes 100% by weight, and adjust the abrasive by stirring well. did. The addition amount of the pH adjustment aid at this time was 0.06% by mass with respect to the total amount of the abrasive. The pH of the abrasive was measured using a portable pH meter (manufactured by TOADKK).
Table 1 shows the composition of the abrasive obtained in Example 1 above.

(Examples 2 to 16)
Using each of the compounds in Table 1 as a pH adjuster, the first and second silicon oxide fine particles, the pH adjuster, water, and the pH adjuster auxiliary shown in Table 1 as necessary (10% by mass of KOH) The mixing ratio of the aqueous solution and the 10% by weight aqueous solution of HNO ₃ was as shown in Table 1, and the abrasives of Examples 2 to 16 were prepared in the same manner as in Example 1. Moreover, about each example, the pH adjuster, the silicon oxide microparticles | fine-particles, and water were mixed, and pH of the liquid mixture before adding a pH adjustment adjuvant was measured.
In Examples 9 and 11, the pH when the silicon oxide fine particles, the pH adjuster (glycine), and water were mixed was 9.5, and thus no pH adjusting aid was added.

[Evaluation]
The polishing characteristics of the abrasives of Examples 1 to 16 obtained above were evaluated by the following methods.
As evaluation of the polishing characteristics, the sustainability of the polishing rate when the abrasive was used in circulation and the change in pH when the abrasive contained sapphire substrate polishing scraps were evaluated.

<Polished object>
As the object to be polished, a 2-inch wafer of a single crystal sapphire substrate (manufactured by Shinko, (0001) plane, substrate thickness of 420 μm) was used.

<Polishing method>
As a polishing machine, a table polishing apparatus manufactured by SPEEDFAM was used. As a polishing pad, SUBA800-XY-groove (manufactured by Nitta Haas) was used, and conditioning was performed using MEC100-PH3.5L (manufactured by Mitsubishi Materials) and a brush before the test.

Polishing was carried out at a polishing agent supply rate of 100 cm ³ / min, a polishing plate speed of 90 rpm, and a polishing pressure of 5 psi, ie 34.5 kPa. The abrasive was circulated and the polishing head was set not to rotate alone but to rotate with the rotation of the polishing platen.

<Polishing speed>
The polishing rate was evaluated by the amount of change in the thickness of the substrate per unit time (μm / hr). Specifically, for the single crystal sapphire substrate used for the above evaluation, the mass of an unpolished substrate with a known thickness and the substrate mass after polishing each time are measured, and the mass change is obtained from the difference, and further the mass change The change per time of the thickness of the substrate obtained from the above was calculated using the following formula.

(Calculation formula of polishing rate (V))
Δm = m0−m1
V = Δm / m0 × T0 × 60 / t (1)
(In the formula, Δm (g) is the mass change before and after polishing, m0 (g) is the initial mass of the unpolished substrate, m1 (g) is the mass of the substrate after polishing, V is the polishing rate (μm / hr), and T0 is (The substrate thickness (μm) of the unpolished substrate, and t represents the polishing time (min).)

<Initial polishing rate>
First, with respect to the abrasives of Examples 1 to 16, the polishing rate after polishing for 15 minutes was measured and calculated, and used as the initial polishing rate. That is, the substrate after polishing for 15 minutes was removed from the polishing head and its mass was measured. The initial polishing rate was calculated by subtracting the mass of the substrate after 15 minutes polishing from the mass of the unpolished substrate as Δm (g) in the equation (1). The initial polishing rate was expressed by calculating the ratio when the first and second silicon oxide fine particles prepared in Example 15 were used as abrasive grains and the initial polishing rate of an abrasive containing no pH adjuster was set to 1.00. . The results are shown in Table 2.

<Polishing speed after 240 minutes polishing>
About the abrasive | polishing agent of Example 1- Example 16, the grinding | polishing speed after 240-minute grinding | polishing was measured and calculated, and it was set as the grinding | polishing speed after 240-minute grinding | polishing. That is, following the measurement of the initial polishing rate, the substrate after polishing for 15 minutes after the mass measurement is again held by the polishing head, and after the polishing for a total of 225 minutes from the start of polishing, the substrate is removed from the polishing head and the mass is measured. The substrate mass after polishing for 225 minutes. Next, the substrate after the mass measurement is held again on the polishing head and further polished for 15 minutes (after polishing for a total of 240 minutes from the start of polishing), then the substrate is removed from the polishing head, the mass is measured, and the 240-minute polishing is performed. It was set as the substrate mass. In formula (1), Δm is a value obtained by subtracting the substrate mass after 240 minutes polishing from the substrate mass after 225 minutes polishing, and the polishing rate after 240 minutes polishing was calculated.
<Durability of polishing rate>
Next, the polishing rate after the 240 minute polishing was compared with the initial polishing rate in Example 15 (the polishing rate after 15 minutes from the start of polishing), and the polishing rate was evaluated by the following formula. Specifically, it shows that the larger the numerical value, the lower the polishing rate and the better the polishing rate persistence.
Persistence of polishing rate = (value of polishing rate after 240 minutes polishing) / (value of initial polishing rate in Example 15)

<Method for evaluating pH change of abrasive>
The pH of the abrasive before polishing and after polishing for 240 minutes was measured using a portable pH meter (manufactured by TOADKK). From the obtained pH measurement value, a difference in pH before and after polishing use, ΔpH, was calculated by the following equation. The results are shown in Table 1. Note that the abrasive is not subjected to operations such as removal of polishing debris during circulation for 240 minutes.
ΔpH = (pH of polishing agent before polishing) − (pH of polishing agent after 240 minutes polishing)

  As can be seen from Table 1, the polishing agents of Examples 1 to 13 which are examples are small in decrease in the polishing rate after 240 minutes of polishing from the initial stage of polishing and are excellent in sustainability of the polishing rate. Moreover, the fall of pH of the abrasive | polishing agent at this time is also suppressed. That is, it is understood that the long-term use stability is excellent.

  On the other hand, in Examples 14 to 16, which are comparative examples, the initial polishing rate is low with the abrasive of Example 14, and the polishing rate after 240 minutes of polishing with the abrasives of Examples 15 and 16 is greatly reduced from the initial polishing rate. ing.

  According to the present invention, it is possible to efficiently polish the surface to be polished of a sapphire single crystal substrate with high hardness, excellent polishing rate sustainability, and pH fluctuations are also suppressed. Stability can be improved. Thereby, it can contribute to the improvement of productivity of a sapphire substrate.

  DESCRIPTION OF SYMBOLS 1 ... Sapphire substrate, 2 ... Polishing head, 3 ... Polishing surface plate, 4 ... Polishing pad, 5 ... Polishing agent, 6 ... Abrasive supply piping, 7 ... Abrasive supply means, 8 ... Tank, 10 ... Polishing apparatus

Claims (11)

A polishing agent for polishing a surface to be polished of a sapphire (α-Al ₂ O ₃ ) substrate, comprising silicon oxide fine particles, amino acid pKa of 8 to 10.5, amino acid, boric acid and sodium hydrogen carbonate An abrasive comprising at least one pH adjusting agent selected from the group consisting of water and water.   The abrasive | polishing agent of Claim 1 whose pH of the said abrasive | polishing agent is the range of 8-10.5.   The silicon oxide fine particles include first silicon oxide fine particles having an average primary particle diameter of 5 to 20 nm and second silicon oxide fine particles having an average primary particle diameter of 40 to 110 nm, and the first silicon oxide fine particles. The abrasive | polishing agent of Claim 1 or 2 whose ratio of the said 1st silicon oxide microparticles | fine-particles which occupies for the total amount of 2nd silicon oxide microparticles | fine-particles is 0.7-40 mass%.   The abrasive according to any one of claims 1 to 3, wherein the pH adjuster is at least one selected from glycine, alanine, cysteine, boric acid and sodium bicarbonate.   5. The abrasive according to claim 1, wherein the content of the pH adjuster is 0.001 to 15% by mass with respect to the total amount of the abrasive.   The abrasive according to claim 1, wherein the silicon oxide fine particles are colloidal silica.   7. The abrasive according to claim 1, wherein the content of the silicon oxide fine particles is 0.01 to 50 mass% with respect to the total amount of the abrasive.   The abrasive according to any one of claims 3 to 7, wherein an average primary particle diameter of the second silicon oxide fine particles is 45 to 110 nm.   The abrasive according to any one of claims 3 to 8, wherein an average primary particle diameter of the first silicon oxide fine particles is 8 to 20 nm.   A method of supplying a polishing agent to a polishing pad, bringing the polishing surface of a sapphire substrate into contact with the polishing pad, and polishing by relative movement between the two, wherein the polishing agent is any one of claims 1 to 9. A polishing method using the abrasive according to item 1.   The polishing method according to claim 10, wherein the polishing agent is circulated and used by repeatedly performing an operation of recovering the polishing agent supplied to the polishing pad and used for polishing, and supplying the recovered polishing agent to the polishing pad again.

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