JP2017197670A - Polishing liquid for sapphire, stock solution, and polishing method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a polishing liquid for sapphire capable of suppressing generation of a chatter vibration of a polishing device in a CMP process of a sapphire substrate, suppressing evaporation of a polishing liquid and agglomeration of an abrasive grain, performing polishing at a high polishing rate for a long time, and polishing a sapphire substrate surface lubricously.SOLUTION: The polishing liquid of the present invention includes: a polar aprotic organic compound having a specific permittivity of not less than 30; an abrasive grain containing colloidal silica; an organic acid; and a liquid medium containing not less than 80 mass% of water, and the polishing liquid has a pH of 8.0-11.0. Further, the content of the polar aprotic organic compound having a specific permittivity of not less than 30 is preferably in a range of 0.05-1.0 in terms of a total mass of the polishing liquid.SELECTED DRAWING: None

Description

  The present invention relates to a polishing liquid for sapphire used for polishing sapphire, a storage liquid for obtaining the polishing liquid, and a polishing method using these.

  Sapphire has been used mainly for LED substrates, but it is transparent, has high hardness, and is not easily damaged. It has also been used for camera cover glass and the like, and its demand is increasing year by year.

  As a method for manufacturing a sapphire substrate, for example, first, a sapphire lump is formed by the Bernoulli method, the Czochralski method, the EFG (Edge-defined Film-fed Growth Method) method, etc., and then the substrate is hollowed out and sliced thinly. The method of manufacturing is mentioned. When slicing, since a thin wire or the like (for example, a multi-wire saw) to which diamond particles are attached is cut out, there are fine scratches on the cut surface.

  Since the LED base is manufactured by crystal growth of GaN on the sapphire base, the surface of the sapphire is required to be very smooth for its use. In addition, even when the sapphire substrate is used for a cover glass of an electronic device housing, if the surface of the sapphire has scratches or the like, the design is deteriorated and the appearance is not beautiful. It is required to be.

  CMP (Chemical Mechanical Polishing) is indispensable for removing such scratches on the sapphire surface and smoothing it. CMP is a technique for mechanically polishing with abrasive grains and a polishing pad (polishing cloth) contained in the polishing liquid while chemically modifying the surface of the workpiece easily with a polishing liquid. However, since sapphire is very stable chemically and thermally and has a high hardness, it is difficult to perform CMP, takes a long processing time, and has a high production cost.

  In order to reduce the production cost, it is desired to improve the polishing rate of sapphire in the polishing process and shorten the polishing time. The polishing rate can be increased by increasing the pressure during polishing. However, in order to shorten the processing time, if the pressure is increased during CMP and polishing is performed under a condition that places a burden on the polishing apparatus, there may be a problem that the polishing apparatus vibrates. This vibration of the polishing apparatus is referred to as “chatter vibration”, and if polishing is continued for a long time while chatter vibration is generated, there is a possibility that problems such as breakage of the apparatus may occur. This chatter vibration is considered to occur due to an increase in friction generated between the polishing pad filled with the polishing liquid and the sapphire substrate. When the friction increases, the temperature of the surface plate and head of the polishing apparatus and the polishing liquid rises due to the frictional heat generated between the polishing pad and the sapphire substrate, and the amount of polishing liquid evaporation increases and at the same time the abrasive grains agglomerate. As a result, the polishing rate is significantly reduced, and the usable time of the polishing liquid may be shortened. For this reason, by improving the polishing liquid used for polishing, the friction generated between the polishing pad and the sapphire substrate during polishing is reduced to suppress chatter vibration of the polishing apparatus, and to suppress evaporation of the polishing liquid and aggregation of abrasive grains. It is desired to maintain a high polishing rate for a long time.

  Several polishing liquids for sapphire are known, but the types are not abundant. For example, Patent Document 1 describes polishing sapphire with a polishing liquid containing a high concentration of colloidal silica. In Patent Document 2, the sapphire polishing composition contains a surfactant, a detergent, a rust inhibitor, a surface modifier, a viscosity modifier, an antibacterial agent, a dispersant, and the like as necessary. It is described that it may be.

JP 2008-44078 A Japanese Patent No. 5384037

  However, even if sapphire is polished using the polishing liquid described in Patent Document 1 or the polishing liquid composition described in Patent Document 2, chatter vibration of the polishing apparatus cannot be suppressed. The polishing rate of sapphire is not sufficient.

  The present invention has been made in view of the above circumstances, and can suppress the occurrence of chatter vibrations of the polishing apparatus in the CMP process of the sapphire substrate, suppress evaporation of the polishing liquid and agglomeration of abrasive grains, and increase the speed at a high polishing rate. An object of the present invention is to provide a polishing liquid for sapphire that can be polished for a long time and can smooth the surface of the sapphire substrate, a storage liquid thereof, and a polishing method using them.

  One embodiment of the present invention contains a polar aprotic organic compound having a relative dielectric constant of 30 or more, abrasive grains containing colloidal silica, an organic acid, and a liquid medium containing 80% by mass or more of water. The present invention relates to a polishing liquid for sapphire having a pH of 8.0 to 11.0. The content of the organic compound having a polar aprotic property having a relative dielectric constant of 30 or more is preferably in the range of 0.05 to 1.0% by mass based on the total mass of the polishing liquid. By using such a polishing liquid, it is possible to suppress the occurrence of chatter vibration of the polishing apparatus in the CMP process of the sapphire substrate, and to suppress the evaporation of the polishing liquid and agglomeration of abrasive grains and to polish for a long time at a high polishing rate. And the surface of the sapphire substrate can be polished smoothly.

  In one embodiment of the present invention, the polar aprotic organic compound having a relative dielectric constant of 30 or more is preferably at least one of glycerin and dimethyl sulfoxide. In this case, generation of chatter vibrations of the polishing apparatus in the CMP process of the sapphire substrate can be further effectively suppressed, and evaporation of the polishing liquid and aggregation of the abrasive grains are further effectively suppressed, and polishing is continued for a longer time at a high polishing rate. be able to.

  In one embodiment of the present invention, the abrasive grains containing colloidal silica are obtained by mixing first particles having an average primary particle size of 60 to 150 nm and second particles having an average primary particle size of 10 to 50 nm. The ratio of the blending amount of the first particles to the blending amount of the second particles preferably exceeds 1 on a mass basis. In this case, generation of chatter vibrations of the polishing apparatus in the CMP process of the sapphire substrate can be further effectively suppressed, and evaporation of the polishing liquid and aggregation of the abrasive grains are further effectively suppressed, and polishing is continued for a longer time at a high polishing rate. And the surface of the sapphire substrate can be polished smoothly.

  In one embodiment of the present invention, the content of abrasive grains containing the colloidal silica is preferably 6 to 50% by mass based on the total mass of the polishing liquid. In this case, generation of chatter vibrations of the polishing apparatus in the CMP process of the sapphire substrate can be further effectively suppressed, and evaporation of the polishing liquid and aggregation of the abrasive grains are further effectively suppressed, and polishing is continued for a longer time at a high polishing rate. And the surface of the sapphire substrate can be polished smoothly.

  One aspect of the present invention is a storage liquid used when preparing the polishing liquid, wherein the content of the liquid medium containing 80% by mass or more of water is less than that of the polishing liquid, and each component excluding the liquid medium Relates to a storage liquid contained in the same blending ratio as the polishing liquid. According to such a storage liquid, it is possible to reduce the cost related to the storage and transportation of the polishing liquid.

  One embodiment of the present invention relates to a polishing method including a step of polishing a surface to be polished containing sapphire using the polishing liquid. According to such a polishing method, generation of chatter vibration of the polishing apparatus in the CMP process of the sapphire substrate can be further effectively suppressed, evaporation of the polishing liquid and aggregation of the abrasive grains can be further effectively suppressed, and a high polishing rate can be achieved. Can be polished for a longer time and the surface of the sapphire substrate can be polished smoothly.

  One embodiment of the present invention is a process of preparing the polishing liquid by diluting the storage liquid with a liquid medium containing 80% by mass or more of water, and polishing a surface to be polished containing sapphire using the polishing liquid. And a polishing step. According to such a polishing method, sapphire can be polished smoothly at a high polishing rate. In addition, since the costs related to the storage, transportation, storage, etc. of the polishing liquid can be suppressed, the overall production cost can be reduced.

  According to the present invention, it is possible to suppress the occurrence of chatter vibration of the polishing apparatus in the CMP process of the sapphire substrate, suppress evaporation of the polishing liquid and aggregation of abrasive grains, and polish at a high polishing rate for a long time, and It is possible to provide a polishing liquid for sapphire that can smoothly polish the surface of a sapphire substrate, a storage liquid thereof, and a polishing method using these.

  Hereinafter, preferred embodiments of the present invention will be described. However, the present invention is not limited to the following embodiment.

<Polishing liquid>
The polishing liquid according to the present embodiment includes a polar aprotic organic compound having a relative dielectric constant of 30 or more, abrasive grains containing colloidal silica, an organic acid, and a liquid medium containing 80% by mass or more of water. And the pH is 8.0 to 11.0, and the content of the polar aprotic organic compound having a relative dielectric constant of 30 or more is 0.05 to 1.0 on the basis of the total mass of the polishing liquid. It is practical to be in the mass% range.

(Organic compounds having polar aprotic properties)
Organic compounds with polar aprotic properties include amides (fully substituted, with nitrogen lacking bonded hydrogen atoms), urea (fully substituted, without hydrogen atoms attached to nitrogen), ethers, cyclic ethers, nitriles, It is selected from the group consisting of ketones, sulfones, sulfoxides, fully substituted phosphorus salts, phosphonic acid esters, phosphoramides, and nitro compounds. For example, dimethyl sulfoxide (DMSO), N, N-dimethylformamide (DMF), acetonitrile, acetone, tetrahydrofuran, N-methyl-2-pyrodinone (NMP), 2-pyrrolidinone, 1,3-dimethyl-2-imidazolidone (DMI) , Dioxane, tetramethylene sulfone (sulfolane), hexamethylphosphoramide (HMPA), nitromethane, 1,2-propylene glycol carbonate, and the like. Moreover, glycerin which is a polyhydric alcohol can also be used. Glycerin contains an OH proton donating group, but generally does not function as proton donation and is treated as an organic compound having polar aproticity in the present invention.

(Relative permittivity)
The relative dielectric constant is the ratio ε / ε ₀ = ε _r between the dielectric constant of the medium and the dielectric constant of the vacuum. The relative permittivity is a dimensionless quantity and takes a certain value specific to the substance regardless of the unit system used. Among the organic compounds having polar aprotic properties, examples of the organic compound having a relative dielectric constant of 30 or more include compounds such as glycerin, dimethyl sulfoxide, N, N-dimethylformamide, and acetonitrile.

  Although the clear knowledge about the reason why the effect of suppressing the chatter vibration of the polishing apparatus in the CMP process is obtained by containing an organic compound having a polar aprotic property has not been obtained, the present inventors It is estimated as follows.

  The chatter vibration of the polishing apparatus in sapphire CMP increases the friction generated at the interface between the surface to be polished containing sapphire and the polishing pad, and this stress is applied to the surface to be polished including sapphire (for example, attached to the head of the polishing apparatus). It is thought that this is caused by the fact that it is impossible to escape from the surface of the substrate to be polished) and the surface of the polishing pad (for example, the polishing pad mounted on the surface plate of the polishing apparatus and rotating). For this reason, the lower the number of rotations of the surface plate of the polishing apparatus and the higher the pressure of the head, the easier the vibration is generated.

  Here, it is considered that the abrasive grains in the polishing liquid play a role of relaxing friction at the interface between the surface to be polished containing sapphire and the polishing pad. And a sufficient amount of the polar aprotic organic compound has the effect of suitably supplementing the ability to relieve friction at the interface between the polishing surface containing sapphire and the polishing pad, such as abrasive grains in the polishing liquid. Conceivable. About this mechanism, it intervenes between abrasive grains so as to loosen the bonding of abrasive grains, acts as a lubricant to reduce friction between the surface to be polished and the polishing pad in the presence of abrasive grains, etc. It is presumed that the effect of reducing chatter vibration of the polishing apparatus is exerted by the combination thereof, but further research is required for its true / false.

  By containing an organic compound having a polar aprotic property, it is possible to polish the surface of the sapphire substrate smoothly by suppressing evaporation of the polishing liquid and agglomeration of abrasive grains in the CMP process, and polishing at a high polishing rate for a long time. As described above, as described above, the polar aprotic organic compound preferably has the ability to relieve friction at the interface between the polishing target surface containing sapphire and the polishing pad, such as abrasive grains in the polishing liquid. By exerting a compensating effect, frictional heat generated between the polishing pad and the sapphire substrate is reduced, and the temperature of the surface plate and head of the polishing apparatus and the polishing liquid are kept low. Accordingly, it is considered that the evaporation amount of the polishing liquid is reduced, and at the same time, the aggregation of the polishing abrasive grains is suppressed, and it is possible to avoid that the polishing speed is remarkably lowered and the usable time of the polishing liquid is shortened.

  As described above, the polishing apparatus can be vibrated by reducing the friction at the interface between the polishing surface and the polishing pad containing an organic compound having a polar aprotic property, such as abrasive grains in the polishing liquid. Although it has been explained that the generation of vibration is suppressed and the frictional heat is reduced, the following explanation is given by the present inventors regarding the reason why the polishing rate does not decrease even if the friction is relaxed and is maintained fast. To do.

  It is thought that CMP of sapphire proceeds as follows. When abrasive grains containing silica are pressed against sapphire on the polishing pad, the hydroxyl group of sapphire and the hydroxyl group of silica form a hydrogen bond, and the bonding site reacts to generate an aluminosilicate. Since the aluminosilicate is soft, the aluminosilicate is mechanically removed when the polishing pad and the sapphire substrate are rotated relative to each other.

  Here, the polar aprotic organic compound is considered to act on the aluminum atom of sapphire or the silicon atom of silica directly bonded to the hydroxyl group on the surface of sapphire to increase the electron density on the hydroxyl group. It is considered that this action facilitates the formation of hydrogen bonds, which accelerates the subsequent aluminosilicate production reaction and improves the polishing rate. It is believed that the effect of improving the polishing rate works so as to counteract the action of reducing the polishing rate by reducing the friction, so that the polishing rate can be maintained fast even if the friction is reduced.

  As a result of diligent research, the present inventors have found that among the organic compounds having polar aprotic properties, organic compounds having a relative dielectric constant of 30 or more are excellent in the effect of maintaining a high polishing rate even when friction is relaxed. It came to discover. Although this detailed mechanism requires further research, when the relative dielectric constant is 30 or more, it acts on the aluminum atom of sapphire or the silicon atom of silica directly connected to the hydroxyl group on the sapphire surface described above. It is considered that this is because it is excellent in the action of increasing the electron density on the hydroxyl group, preferably the aluminosilicate formation reaction is accelerated, and the polishing rate is improved.

In addition, in order to achieve the effect that the polishing rate can be maintained fast even if the friction is relaxed, it is essential that water is contained in an amount of 80% by mass or more as a liquid medium used in the sapphire polishing liquid. Although this detailed mechanism has not been clarified, among polar polar protic solvents used as abrasives, water has no influence on the fact that the relative dielectric constant is larger than that of organic solvents such as ethanol. I think. The relative permittivity of water is 80, and the relative permittivity of ethanol is 24.

  The relative dielectric constant of the organic compound having a polar aprotic property is more preferably 35 or more, and still more preferably 40 or more, from the viewpoint of suitably expressing the effect of maintaining a high polishing rate even when friction is relaxed. In addition, the upper limit of the relative dielectric constant of an organic compound having polar aprotic properties is currently in a range of about 80 or less, which corresponds to the relative dielectric constant of water, although research is insufficient at present. It turns out to be preferable.

  From this point of view, among organic compounds having polar aproticity with a relative dielectric constant of 40 or more, glycerin and dimethyl sulfoxide, both of which have a relative dielectric constant of about 47, are capable of maintaining a high polishing rate even when friction is relaxed. Therefore, it is more preferably used in the sapphire polishing liquid of the present invention.

  The content of the organic compound having a polar aprotic property having a relative dielectric constant of 30 or more in the polishing liquid is from 0.05 to 2 in terms of suitably expressing the effect of maintaining the polishing rate fast even when the friction is relaxed. A range of 0% by mass is practical. If the amount is less than 0.05% by mass, the friction can be reduced and the effect of suppressing the occurrence of chatter vibration of the polishing apparatus cannot be obtained. If the amount exceeds 2.0% by mass, the effect of reducing the friction is too strong and polishing is performed. The speed is remarkably lowered and the function as a polishing liquid for sapphire is insufficient.

  In this respect, the content of the organic compound having a polar aprotic property having a relative dielectric constant of 30 or more in the polishing liquid is preferably 0.10 to 1.0% by mass, and 0.15 to 0.50% by mass. It is more preferable that it is 0.17-0.40 mass%, and it is especially preferable that it is 0.18-0.30 mass%.

  It can be easily understood that the amount of evaporation of the polishing liquid can be reduced by reducing the frictional heat generated between the polishing pad and the sapphire substrate, but at the same time, the aggregation of abrasive grains in the polishing liquid is reduced. The fact that it can be suppressed is a phenomenon that cannot be explained only by the effect of the temperature rise of the polishing liquid.

  Aggregation of abrasive grains in the polishing liquid varies depending on the type of abrasive grains. In the present invention, as a result of selecting colloidal silica capable of suitably polishing a sapphire substrate and studying conditions for suppressing this aggregation using colloidal silica as an essential component, polar aprotic properties having a relative dielectric constant of 30 or more are studied. It has been found that an organic compound having a sapphire not only can reduce frictional heat but also suppresses aggregation of colloidal silica even under conditions where the polishing liquid for sapphire is intentionally heated. Furthermore, the polishing liquid containing the polar aprotic organic compound having a relative dielectric constant of 30 or more in the range of 0.05 to 2.0% by mass has a pH in the range of 8.0 to 11.0. It has been discovered that a suitably high polishing rate can be obtained and that aggregation of colloidal silica during polishing can be suppressed. At the same time, as the pH adjuster for adjusting the pH to the range of 8.0 to 11.0, the inorganic acid has a large aggregation of colloidal silica during polishing, and the organic acid preferably has an aggregation of colloidal silica during polishing. It was discovered that it can be suppressed.

  That is, the present invention has as essential components a polar aprotic organic compound having a relative dielectric constant of 30 or more, abrasive grains containing colloidal silica, an organic acid, and a liquid medium containing 80% by mass or more of water, pH Are essential components, and the content of the organic compound having a polar aprotic property having a relative dielectric constant of 30 or more is based on the total mass of the polishing liquid. It is defined in the range of 0.05 to 2.0% by mass. By using such a polishing liquid, it is possible to suppress the occurrence of chatter vibration of the polishing apparatus in the CMP process of the sapphire substrate, and to suppress the evaporation of the polishing liquid and agglomeration of abrasive grains and to polish for a long time at a high polishing rate. And the surface of the sapphire substrate can be polished smoothly.

(Abrasive grains)
The abrasive used in the present invention contains colloidal silica. As other constituents of the abrasive grains, the effects of the present invention (the generation of chatter vibrations in the polishing apparatus in the CMP process of the sapphire substrate can be suppressed, evaporation of the polishing liquid and aggregation of the abrasive grains can be suppressed, and the polishing speed can be increased. Fume silica, alumina, and ceria that are well known in the art can be used as long as they can be polished for a long time and the surface of the sapphire substrate can be polished smoothly). As an abrasive grain, it can be used individually by 1 type from which an average particle diameter, a shape, a constituent material, etc. differ, or in combination of 2 or more types.

  From the viewpoint of smoothly polishing sapphire at a further excellent polishing rate, the abrasive grains containing the colloidal silica have an average primary particle diameter of 60 to 150 nm (large particles containing colloidal silica and the like) and an average. Second particles having a primary particle size of 10 to 50 nm (small particles containing colloidal silica or the like), and the ratio of the content of the first particles to the content of the second particles (of the first particles It is preferable that (content / content of second particle) exceeds 1 on a mass basis. That is, the abrasive contains at least one kind of large particles having an average primary particle diameter of 60 to 150 nm and at least one kind of small particles having an average primary particle diameter of 10 to 50 nm, and the content of the large particles is increased. It is preferable that the value divided by the content of small particles exceeds 1. Each of the contents of the first particles and the second particles is the total amount of the contents of each particle when there are a plurality of corresponding particles. Content of 1st particle | grains and 2nd particle | grains can be adjusted with the compounding quantity of 1st particle | grains and 2nd particle | grains. The abrasive is obtained by mixing the first particles and the second particles, and the ratio of the blend amount of the first particles to the blend amount of the second particles exceeds 1 on a mass basis. It is preferable that it is an aspect.

A method for measuring the average primary particle size is not particularly limited, and a method of converting from the specific surface area measured by the BET method can be used. For example, using the specific surface area and silica density measured by the BET method according to JIS Z 8830, it was calculated from the following formula (1) on the assumption that the particles are spherical and have no pores. The value may be the average primary particle size of the particles.
Average primary particle size (nm) = 6000 / (specific surface area (m ² / g) × silica density (g / cm ³ )) Formula (1)

  The reason why the polishing rate is improved by containing the specific amount of the large first particles and the small second particles is not clear, but the present inventors presume as follows.

  As described above, in sapphire CMP, sapphire and colloidal silica undergo a solid-phase reaction during polishing to form an aluminosilicate that is relatively more fragile than sapphire.

  Here, when only the large first particles are present, the gap between the particles is larger than when only the small second particles are present, so that the contact area between the sapphire and the particles is small. Conceivable. On the other hand, when only small second particles are present, the contact area between the sapphire and the particles is larger than when only large first particles are present, but the load transmitted from the polishing pad to the particles is large. It will be smaller.

  On the other hand, when the polishing liquid contains a large amount of the first particles and the small second particles, the contact area between the sapphire and the particles increases because the small particles enter the gaps between the large particles. At the same time, when the large particles transmit the load to the adjacent small particles, the load on the sapphire increases even for the small particles, which is considered to improve the polishing rate.

  The ratio of the content of the first particles to the content of the second particles is preferably 1.01 to 2.00 from the viewpoint of further improving the polishing rate of sapphire, and 1.03 to 1. More preferably, it is 50, and it is still more preferable that it is 1.04-1.20. That is, the ratio of the blending amount of the first particles to the blending amount of the second particles is preferably 1.01 to 2.00, more preferably 1.03 to 1.50. More preferably, it is 0.04 to 1.20.

  The average primary particle size of the first particles is preferably 65 to 140 nm, more preferably 70 to 130 nm, and even more preferably 75 to 120 nm.

  The average primary particle size of the second particles is preferably 10 to 40 nm, more preferably 10 to 30 nm, and still more preferably 10 to 25 nm.

  The content of the abrasive grains containing colloidal silica in the polishing liquid is 8 to 40% by mass based on the total mass of the polishing liquid from the viewpoint of further improving the polishing rate of sapphire and making the abrasive grains less likely to aggregate during polishing. Is preferable, 10-30 mass% is more preferable, and 12-20 mass% is still more preferable. Since the content of abrasive grains containing colloidal silica is a factor that directly affects the cost of the polishing liquid, the lower the abrasive content, the lower the cost.

(Sub-additive)
The polishing liquid according to the present embodiment, if necessary, is effective to suppress the effects of the present invention (the generation of chatter vibrations of the polishing apparatus in the CMP process of the sapphire substrate, and the evaporation of the polishing liquid and the aggregation of the abrasive grains are fast. Surfactant, detergent, rust inhibitor, surface modifier, viscosity modifier, antibacterial agent as long as it can be polished at a polishing rate for a long time and the surface of the sapphire substrate can be polished smoothly) , And may contain a secondary additive such as a dispersant.

(PH)
The pH of the polishing liquid according to this embodiment is set to 8.0 to 11.0 from the viewpoint of suppressing aggregation of colloidal silica during polishing. Moreover, from this viewpoint, 8.2-10.5 are preferable, 8.4-10.2 are more preferable, 8.6-10.0 are still more preferable, 8.8-9.8 are especially preferable. The pH is defined as the pH at a liquid temperature of 25 ° C.

  The pH of the polishing liquid can be measured with a pH meter (for example, manufactured by HORIBA, Ltd., model number: pH MATE F-50). As pH measurement values, standard buffer solution (phthalate pH buffer solution pH: 4.01 (25 ° C), neutral phosphate pH buffer solution pH: 6.86 (25 ° C), borate pH buffer solution After calibrating three points using the liquid pH: 9.18 (25 ° C.), the electrode is placed in the polishing liquid, and the value after 2 minutes or more has elapsed is adopted.

(PH adjuster)
As the pH adjuster of the polishing liquid according to this embodiment, an organic acid is used from the viewpoint of suppressing aggregation of colloidal silica during polishing. Examples of the organic acid include malic acid, malonic acid, acetic acid, oxalic acid, picolinic acid and the like, and these can be used alone or in combination of two or more. Among these, malic acid and malonic acid are preferably used from the viewpoint of suppressing aggregation of colloidal silica during polishing. On the other hand, in the case of inorganic acids such as sulfuric acid, hydrochloric acid, nitric acid, and phosphoric acid, the aggregation of colloidal silica during polishing is large, which is not preferable as a pH adjuster for the polishing liquid according to this embodiment.

  Examples of the pH adjuster prepared to be alkaline include alkali components such as ammonia, sodium hydroxide, potassium hydroxide, TMAH (tetramethylammonium hydroxide), and imidazole. The pH of the polishing liquid can be adjusted with these pH adjusters. In order to stabilize the pH, the polishing liquid may contain a buffer solution. Examples of such a buffer include acetate buffer and phthalate buffer.

  Since many of these alkali components and buffer solutions promote the aggregation of colloidal silica during polishing, the amount of addition thereof is the effect of the present invention (the occurrence of chatter vibration of the polishing apparatus in the CMP process of the sapphire substrate). Can be used as long as the evaporation of the polishing liquid and the aggregation of the abrasive grains are suppressed, the polishing can be performed for a long time at a high polishing rate, and the surface of the sapphire substrate can be polished smoothly). Needed.

(Liquid medium)
The polishing liquid according to this embodiment contains a liquid medium containing 80% by mass or more of water. The liquid medium acts as a dispersion medium for abrasive grains. More specifically, water is preferably deionized water, ion exchange water, ultrapure water, or the like. Examples of the liquid medium include water and a mixed solvent of water and a water-soluble organic solvent. Examples of the water-soluble organic solvent include alcohols. Examples of alcohols include ethyl alcohol and ethylene glycol.

  When the liquid medium is a mixed solvent, the content of the liquid medium other than water is essential to be less than 20% by mass with respect to the total mass of the liquid medium from the viewpoint that the polishing rate can be maintained fast even if friction is eased. It is said. From this viewpoint, the content of the liquid medium other than water is preferably less than 10% by mass, more preferably less than 5% by mass, still more preferably less than 2% by mass with respect to the total mass of the liquid medium. It is particularly preferred.

<Storage solution>
The polishing liquid according to this embodiment can be stored as a storage liquid that is diluted with a liquid medium containing 80% by mass or more of water during use. That is, the storage liquid according to this embodiment is a storage liquid used when preparing the above-described polishing liquid, and the content of the liquid medium containing 80% by mass or more of water is less than that of the polishing liquid, and the liquid state Each component excluding the medium is included in the same blending ratio as the polishing liquid. In the present embodiment, the difference between the storage liquid and the polishing liquid is only the content of the liquid medium, and the blending ratio of each component excluding the liquid medium is the same. Using this stock solution, a polishing liquid is obtained by diluting with a liquid medium containing 80% by mass or more of water (for example, diluting twice or more on a mass basis). By storing the polishing liquid as a stock solution, costs associated with storage, transportation, storage, etc. can be suppressed. The storage liquid may be diluted with a liquid medium containing 80% by mass or more of water immediately before polishing to form a polishing liquid, or a storage medium and a liquid medium containing 80% by mass or more of water are supplied on a polishing platen, A polishing liquid may be prepared on a polishing surface plate.

  As the dilution ratio of the storage liquid is higher, a larger amount of the polishing liquid can be prepared with a smaller amount of the storage liquid. Therefore, it is possible to reduce costs related to storage, transportation, storage, and the like of the storage liquid. Therefore, the lower limit of the dilution ratio of the stock solution is preferably 2 times or more and more preferably 3 times or more on a mass basis. The upper limit of the dilution ratio of the stock solution is not particularly limited, but is preferably 10 times or less, more preferably 7 times or less, and still more preferably 5 times or less on a mass basis. When the dilution ratio is less than or equal to these upper limit values, the content of abrasive grains contained in the stock solution is prevented from becoming too high, and the stability of the stock solution during storage tends to be easily maintained. When the dilution ratio is d, each content of the abrasive grains in the storage liquid and the compound having a polar aprotic organic compound having a relative dielectric constant of 30 or more is determined by the abrasive grains and the relative dielectric constant in the polishing liquid. It is d times of each content of the compound which has 30 or more polar aprotic organic compounds.

<Polishing method>
The polishing method (sapphire polishing method) according to the present embodiment includes a polishing step of polishing a surface to be polished containing sapphire using the above-described polishing liquid. The polishing step may be a step including a step of polishing a surface to be polished containing sapphire using a polishing liquid obtained by diluting the above-described storage liquid with a liquid medium containing 80% by mass or more of water.

  In the polishing method according to this embodiment, a known polishing apparatus can be widely used. For example, when polishing a substrate having a surface to be polished (sapphire substrate) containing sapphire, a polishing apparatus that can be used is connected to a holder for holding the sapphire substrate on the head, a motor whose rotation speed can be changed, and the like. A general polishing apparatus having a surface plate with a polishing pad attached thereto can be used.

Although it does not specifically limit as a polishing pad, A general nonwoven fabric, a polyurethane foam, a porous fluororesin, etc. are mentioned. The polishing conditions for the substrate are not limited, but the rotation speed of the surface plate is preferably 200 min ⁻¹ or less in order to easily prevent the substrate from popping out. Further, the polishing pressure is preferably 700 gf / cm ² or less in order to easily suppress the generation of scratches on the substrate surface after polishing.

  In the polishing method according to the present embodiment, for example, while supplying the polishing liquid between the surface to be polished and the polishing pad with a pump or the like in a state where the sapphire substrate is pressed against the polishing pad attached to the surface plate, Move the base and the surface plate relatively. By these operations, the surface to be polished containing sapphire is polished. The method for supplying the polishing liquid to the polishing apparatus is not particularly limited as long as the polishing liquid can be continuously supplied to the polishing pad during polishing. The supply amount of the polishing liquid is not limited, but it is preferable that the surface of the polishing pad is always covered with the polishing liquid. Supply the storage liquid and a liquid medium such as water between the surface to be polished and the polishing pad, and perform polishing while diluting the storage liquid on the polishing surface plate (for example, diluting it twice or more on a mass basis). Also good. Further, the supplied polishing liquid may be collected and supplied to the polishing pad again, and used after circulation.

  The substrate after polishing is preferably washed with water, ethanol, isopropyl alcohol, other cleaning agents, etc., and then dried after removing water droplets adhering to the substrate using a spin dryer or the like.

  EXAMPLES Hereinafter, although an Example demonstrates this invention in more detail, this invention is not restrict | limited to these Examples, unless it deviates from the technical idea of this invention.

<Abrasive>
<Average particle size of abrasive grains>
Among the abrasive grains containing colloidal silica used in Examples and Comparative Examples, cataloid SI-80P (“Cataloid” is a registered trademark, the same applies hereinafter) as large first particles having an average primary particle diameter of 60 to 150 nm containing colloidal silica. As a small second particle having an average primary particle size of 10 to 50 nm containing colloidal silica using JGC Catalysts & Chemicals Co., Ltd., an average primary particle size of 80 nm and a colloidal silica abrasive particle content of 40% by mass. Cataloid SI-40 (“Cataloid” is a registered trademark, the same applies hereinafter. JGC Catalysts & Chemicals, Inc., average primary particle size 18 nm, colloidal silica abrasive (true spherical) content 40% by mass) was used.

<Example 1>
(Storage solution 1)
Cataloid SI-80P 49 parts by mass, cataloid SI-40 47 parts by mass, glycerin (relative dielectric constant 47, organic compound having polar aproticity (hereinafter the same)) 0.2 parts by mass, malic acid 0.02 A stock solution 1 was prepared by dissolving and mixing parts by mass and 3.78 parts by mass of deionized water.

(Polishing liquid 1)
By mixing 1 part by mass of the stock solution 1 and 2 parts by mass of deionized water, the stock solution 1 was diluted 3 times to prepare a polishing liquid 1. The pH in the polishing liquid 1 is 9.2, the content of colloidal silica is 12.8% by mass, and the ratio of the amount of large first particles to the amount of small second particles is 1.04. The glycerin content was 0.067% by mass and the malic acid content was 0.0067% by mass. The “content” is the content based on the total mass of the polishing liquid (the same applies hereinafter).

<Example 2>
(Stock solution 2)
49 parts by mass of Cataloid SI-80P, 47 parts by mass of Catalloid SI-40, 0.8 parts by mass of glycerin, 0.02 parts by mass of malic acid, and 3.18 parts by mass of deionized water were dissolved and mixed. 2 was produced.

(Polishing liquid 2)
By mixing 1 part by mass of the storage liquid 2 and 2 parts by mass of deionized water, the storage liquid 2 was diluted 3 times to prepare a polishing liquid 2. The pH in the polishing liquid 2 is 9.2, the content of colloidal silica is 12.8% by mass, and the ratio of the amount of large first particles to the amount of small second particles is 1.04. The glycerin content was 0.267% by mass and the malic acid content was 0.0067% by mass.

<Example 3>
(Stock solution 3)
49 parts by mass of Cataloid SI-80P, 47 parts by mass of Catalloid SI-40, 2.0 parts by mass of glycerin, 0.02 parts by mass of malic acid, and 1.98 parts by mass of deionized water were dissolved and mixed. 3 was produced.

(Polishing liquid 3)
By mixing 1 part by mass of the storage liquid 3 and 2 parts by mass of deionized water, the storage liquid 3 was diluted 3 times to prepare a polishing liquid 3. The pH in the polishing liquid 3 is 9.2, the content of colloidal silica is 12.8% by mass, and the ratio of the amount of large first particles to the amount of small second particles is 1.04. The glycerin content was 0.667% by mass and the malic acid content was 0.0067% by mass.

<Example 4>
(Stock solution 4)
Cataloid SI-80P 49 parts by mass, cataloid SI-40 47 parts by mass, dimethyl sulfoxide (relative permittivity 47, organic compound having polar aproticity (hereinafter the same)) 0.8 parts by mass, malic acid 0. A stock solution 4 was prepared by dissolving and mixing 03 parts by mass and 3.17 parts by mass of deionized water.

(Polishing liquid 4)
By mixing 1 part by mass of the storage liquid 4 and 2 parts by mass of deionized water, the storage liquid 4 was diluted 3 times to prepare a polishing liquid 4. The pH in the polishing liquid 4 is 9.2, the content of colloidal silica is 12.8% by mass, and the ratio of the amount of large first particles to the amount of small second particles is 1.04. The content of dimethyl sulfoxide was 0.267% by mass, and the content of malic acid was 0.010% by mass.

<Comparative Example 1>
(Storage solution X1)
49 parts by mass of catalloid SI-80P, 47 parts by mass of cataloid SI-40, 0.02 parts by mass of malic acid, and 3.98 parts by mass of deionized water were dissolved and mixed to prepare a stock solution X1.

(Polishing liquid X1)
By mixing 1 part by mass of the storage liquid X1 and 2 parts by mass of deionized water, the storage liquid X1 was diluted 3 times to prepare a polishing liquid X1. The pH in the polishing liquid X1 is 9.2, the content of colloidal silica is 12.8% by mass, and the ratio of the amount of large first particles to the amount of small second particles is 1.04. The content of malic acid was 0.0067% by mass.

<Comparative example 2>
(Storage solution X2)
Cataloid SI-80P 49 parts by mass, cataloid SI-40 47 parts by mass, tetrahydrofuran (an organic compound having a relative dielectric constant of 8, polar aproticity (hereinafter the same)) 0.8 part by mass, and malic acid 0.01 A stock solution X2 was prepared by dissolving and mixing parts by mass and 3.19 parts by mass of deionized water.

(Polishing liquid X2)
By mixing 1 part by mass of the storage liquid X2 and 2 parts by mass of deionized water, the storage liquid X2 was diluted 3 times to prepare a polishing liquid X2. The pH in the polishing liquid X2 is 9.2, the content of colloidal silica is 12.8% by mass, and the ratio of the amount of large first particles to the amount of small second particles is 1.04. The tetrahydrofuran content was 0.267% by mass, and the malic acid content was 0.0033% by mass.

<Comparative Example 3>
(Storage solution X3)
Cataloid SI-80P 49 parts by mass, cataloid SI-40 47 parts by mass, formic acid (relative dielectric constant 58, organic compound having polar proticity (hereinafter the same)) 0.4 parts by mass, deionized water 3.60 A mass part was dissolved and mixed to prepare a stock solution X3.

(Polishing liquid X3)
By mixing 1 part by mass of the storage liquid X3 and 2 parts by mass of deionized water, the storage liquid X3 was diluted 3 times to prepare a polishing liquid X3. The pH in the polishing liquid X3 is 8.8, the content of colloidal silica is 12.8% by mass, and the ratio of the amount of large first particles to the amount of small second particles is 1.04. The formic acid content was 0.133% by mass.

<Comparative Example 4>
(Storage solution X4)
Cataloid SI-80P 49 parts by mass, cataloid SI-40 47 parts by mass, methanol (relative dielectric constant 33, polar protic organic compound (hereinafter the same)) 0.8 parts by mass, malic acid 0.02 parts by mass Then, 3.18 parts by mass of deionized water was dissolved and mixed to prepare a stock solution X4.

(Polishing liquid X4)
By mixing 1 part by mass of the storage liquid X4 and 2 parts by mass of deionized water, the storage liquid X4 was diluted 3 times to prepare a polishing liquid X4. The pH in the polishing liquid X4 is 9.2, the content of colloidal silica is 12.8% by mass, and the ratio of the amount of large first particles to the amount of small second particles is 1.04. The methanol content was 0.267% by mass, and the malic acid content was 0.0067% by mass.

<Measurement of pH of polishing liquid>
The pH at 25 ° C. of the polishing liquids of Examples and Comparative Examples was measured using a pH meter “pH MATE F-50” manufactured by Horiba, Ltd. Specifically, standard buffer solution (phthalate pH buffer solution pH: 4.01 (25 ° C), neutral phosphate pH buffer solution pH: 6.86 (25 ° C), borate pH buffer solution pH : 9.18 (25 ° C.)), three points were calibrated, and then the electrode was put into the polishing liquid, and the value after 2 minutes or more had been stabilized was measured. The evaluation results are shown in Table 1 below.

<Sapphire substrate used for CMP evaluation>
In the CMP evaluation, a sapphire wafer having a diameter of 101.6 mm (4 inches) and a thickness of 0.65 mm is used as the sapphire substrate having a surface orientation A plane, the polishing condition is 1, the diameter is 50.8 mm (2 inches), and the thickness is 0.50 mm. The sapphire wafer was used for polishing conditions 2 and 3. The average surface roughness (Ra) before polishing was 0.2 nm for all sapphire wafers. The average surface roughness (Ra) was measured using a scanning probe microscope (“SPI3800N / SPA500” manufactured by Seiko Instruments Inc.) in a measurement region of 1 micron.

<Sapphire polishing evaluation by CMP>
While the polishing liquids 1 to 4 and X1 to X4 obtained above were dropped onto a pad attached to a surface plate, CMP treatment was performed under the following polishing conditions 1, 2 and 3. In polishing condition 1, the presence or absence of chatter vibration, the maximum value of the friction coefficient, the polishing rate [10 minutes] and the average average surface roughness [Ra] are evaluated. In polishing condition 2, the amount of abrasive grains aggregated and the evaporation of the polishing liquid are evaluated. With respect to the evaluation of the amount, in the polishing condition 3, the polishing rate [360 minutes] was evaluated. The evaluation results are shown in Table 1 below.

(Polishing condition 1)
Polishing apparatus: RDP-500, manufactured by Fujikoshi Machinery Co., Ltd.
Polishing pad: Nitta Haas Co., Ltd., SUBA800 Pad20 ″ DPJ; XA04
Polishing pressure: 500 gf / cm ²
Flow rate of polishing liquid: 500 ml / min (1000 g of polishing liquid was circulated)
Polishing time: 10 minutes Sapphire substrate: 1 sheet Rotating speed (rotation speed) of polishing surface plate: 70 min ⁻¹
Polishing fluid heating: None (room temperature approx. 25 ° C)

(Polishing condition 2, polishing condition 3)
Polishing device: FACT-200, manufactured by Nano Factor Co., Ltd.
Polishing pad: Nitta Haas Co., Ltd., SUBA800 Pad20 ″ DPJ; XA04
Polishing pressure: 300 gf / cm ²
Flow rate of polishing liquid: 100 ml / min (500 g of polishing liquid was circulated)
Polishing time: 120 minutes (polishing condition 2), 360 minutes (polishing condition 3)
Sapphire substrate: 1 sheet Polishing surface plate rotation speed: 184 min ⁻¹
Polishing liquid heating: 40 ° C water bath

(With or without chatter vibration)
The presence / absence of chatter vibration was determined by listening to the presence / absence of chatter vibration of the polishing apparatus during the CMP process under the polishing condition 1 described above. The results are shown in Table 1 below.

(Maximum friction coefficient)
As described above, chatter vibration is considered to occur due to increased friction generated between the polishing pad filled with the polishing liquid and the sapphire substrate. By evaluating the coefficient of friction during the CMP process, it was determined as an index of the ease of chatter vibrations that the polishing liquid has. The polishing apparatus RDP-500 is equipped with an X-axis load cell and a Z-axis load cell so that the X-axis direction force and the Z-axis direction force applied to the object to be polished can be measured. The friction coefficient is a value obtained by dividing the force in the X-axis direction by the force in the Z-axis direction, and is automatically calculated / recorded by the RDP-500. The maximum value of the friction coefficient was set to the maximum value of the friction coefficient recorded during the CMP process under the polishing condition 1 described above. The results are shown in Table 1 below. The maximum value of the friction coefficient was considered to be good when it was less than 0.70.

(Polishing speed)
The polishing rate is determined by measuring the mass of the polished sapphire substrate before and after the CMP treatment, and using the surface area of the substrate to be polished and the sapphire density of 3.97 g / cm ^3. The film thickness was calculated from the relationship between the reduced film thickness and the polishing time (10 minutes for polishing condition 1 and 360 minutes for polishing condition 3). The results are represented by a polishing rate [10 minutes] and a polishing rate [360 minutes], respectively, and are shown in Table 1 below. The polishing rate of condition 1 [10 minutes] was assumed to be 1.7 μm / h or higher, and the polishing rate of polishing condition 3 [360 minutes] was determined to be 1.0 μm / h or higher.

(Average surface roughness [Ra])
The average surface roughness (Ra) of the polished surface of the sapphire substrate after the CMP treatment was measured by the same method as described in <Sapphire substrate used for CMP evaluation>. The results are shown in Table 1 below. An average surface roughness [Ra] of less than 0.3 nm was considered good.

(Agglomeration amount of abrasive grains)
The amount of agglomeration of the abrasive grains is determined by preliminarily measuring all the paths through which the polishing liquid flows, that is, the polishing apparatus and the piping of the polishing liquid, and the abrasive agglomerates generated in the service tank after the CMP treatment under the polishing condition 2 described above. Made by Mitsubishi Rayon Co., Ltd., which had been measured for mass, filtered with human silk feather double (approx. 50 μm mesh), dried and then measured for the mass of human silk feather double together with the aggregate of the filtered abrasive grains. The agglomeration amount of the abrasive grains was determined from the difference in mass before and after filtration. The results are shown in Table 1 below. The amount of abrasive grains aggregated was less than 0.8 g.

(Evaporation amount of polishing liquid)
The amount of abrasive agglomeration is determined by collecting the polishing liquid remaining in the polishing apparatus, the polishing liquid piping, and the service tank after the CMP treatment under the polishing condition 2 shown above, that is, the polishing apparatus, the polishing liquid piping, and the service tank. The mass was measured, and the mass of the evaporated polishing liquid was determined from the difference from 500 g of the polishing liquid charged first. The amount of evaporation of the polishing liquid was expressed by mass% obtained by dividing the mass of the evaporated polishing liquid by 500 g of the polishing liquid first charged. The results are shown in Table 1 below. The amount of evaporation of the polishing liquid was considered to be less than 40% by mass.

  From the results in Table 1, the polishing liquids of Examples 1 to 4 can suppress chatter vibrations of the polishing apparatus in the CMP process of the sapphire substrate, suppress evaporation of the polishing liquid and aggregation of abrasive grains, and at a high polishing rate. It can be seen that polishing can be performed for a long time and the surface of the sapphire substrate can be polished smoothly. Table 1 shows Examples 1 to 4 in which glycerin and dimethyl sulfoxide are used singly, but Example 2 and Example 4 have almost the same evaluation results. It can be easily assumed that the same effect can be obtained even when both organic compounds are contained simultaneously.

  On the other hand, the polishing liquids of Comparative Examples 1 to 4 all had a maximum friction coefficient exceeding 0.07, and some chatter vibrations were generated. Further, in the evaluation results of the polishing rate, the polishing rate of 10 minutes under the polishing condition 1 was particularly good in Comparative Example 1 in which no additive was blended and in Comparative Example 3 in which formic acid was blended. In the polishing for 360 minutes, the decrease in the polishing rate was large, and good results were not obtained. This tendency was conspicuous in Comparative Example 3 in which formic acid was blended. In Comparative Example 3 in which formic acid was blended, as shown in the evaluation results of polishing condition 2, the amount of abrasive grains aggregated and the amount of evaporation of the polishing liquid were large. This is thought to be part of the reason.

  A sapphire polishing liquid (CMP polishing liquid), a storage liquid, and a polishing method using these are suitable for CMP of a surface to be polished containing sapphire, and display an electronic device such as an LED base or a smartphone. Since it is suitable for CMP of a sapphire substrate (substrate having a polished surface containing sapphire) used for a part cover, its usefulness is extremely high.

Claims (8)

  It contains a polar aprotic organic compound having a relative dielectric constant of 30 or more, abrasive grains containing colloidal silica, an organic acid, and a liquid medium containing 80% by mass or more of water, and has a pH of 8.0 to 8.0. A polishing liquid for sapphire which is 11.0.   2. The polishing liquid for sapphire according to claim 1, wherein the organic compound having a polar aprotic property having a relative dielectric constant of 30 or more is in a range of 0.05 to 1.0 mass% based on the total mass of the polishing liquid.   The polishing liquid according to claim 1 or 2, wherein the organic compound having a polar aprotic property having a relative dielectric constant of 30 or more is at least one of glycerin and dimethyl sulfoxide.   The abrasive grains containing the colloidal silica are obtained by mixing first particles having an average primary particle size of 60 to 150 nm and second particles having an average primary particle size of 10 to 50 nm. The polishing liquid according to any one of claims 1 to 3, wherein a ratio of a blending amount of the first particles to a blending amount exceeds 1 on a mass basis.   The polishing liquid according to any one of claims 1 to 4, wherein the content of abrasive grains containing the colloidal silica is 6 to 50 mass% based on the total mass of the polishing liquid.   A storage liquid used when preparing the polishing liquid according to any one of claims 1 to 5, wherein the liquid medium containing water in an amount of 80% by mass or more is less than the polishing liquid, and the liquid Each component except for the medium is a storage solution containing the same blending ratio as the polishing solution.   A grinding | polishing method provided with the process of grind | polishing the to-be-polished surface containing sapphire using the polishing liquid as described in any one of Claims 1-5.   A step of preparing the polishing liquid by diluting the stock solution according to claim 6 with a liquid medium containing 80% by mass or more of water, and a step of polishing a surface to be polished containing sapphire using the polishing liquid. A polishing method comprising: