JP6582601B2 - Polishing liquid, storage liquid and polishing method - Google Patents

Description

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

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

  As a method of manufacturing a sapphire substrate, 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 cut into a substrate and thinly sliced to manufacture. A method is mentioned. When slicing, since a thin wire or the like (multi-wire saw) with diamond particles attached is used for cutting, there are fine scratches on the cut surface.

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

  A CMP (Chemical Mechanical Polishing) process is indispensable in order to remove such scratches on the sapphire surface and make it smooth. CMP is a technique of mechanically polishing with abrasive grains and a polishing pad contained in the polishing liquid while chemically modifying the surface of the workpiece easily with the polishing liquid. However, since sapphire is very stable chemically and thermally and has high hardness, there is a problem that CMP is difficult, processing time is long, and production cost is high.

  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 number of rotations and pressure of the polishing platen during polishing. However, the sapphire substrate that is required year by year tends to become thinner, and if the rotation speed and pressure of the polishing platen are increased to a certain level or more, the sapphire substrate may be broken or chipped. Therefore, it is desired to improve the polishing rate by improving the polishing liquid used for polishing.

  Several polishing liquids for sapphire are known, but the types are not abundant. For example, Patent Document 1 discloses polishing sapphire with a polishing liquid containing a high concentration of colloidal silica. Patent Document 2 discloses a polishing liquid for sapphire substrate comprising at least one of an alkanolamine compound and a fluorine-based compound having a perfluoroalkyl group, silica particles, and water. Further, Patent Document 3 discloses a polishing liquid containing 2% by mass or more of silica having a particle size of 10 nm to 50 nm and 2% by mass or more of silica having a particle size of 60 nm to 300 nm. ing.

JP 2008-44078 A JP 2009-297818 A International Publication No. 2013/069623

  However, for example, when sapphire is polished with the polishing liquid described in Patent Documents 1 to 3, the polishing rate is relatively slow and the polishing rate is not sufficient.

  The present invention has been made in view of the above circumstances, and an object thereof is to provide a polishing liquid capable of polishing sapphire at a high polishing rate, a storage liquid thereof, and a sapphire polishing method using these.

  One aspect of the present invention includes at least one or more types of large silica having an average primary particle size of 60 to 150 nm, at least one or more types of small silica having an average primary particle size of 40 nm or less, water, and a polishing accelerator. The value (L / S) obtained by dividing the large silica content (L) by the small silica content (S) is more than 1, the polishing accelerator contains a nitrogen-containing aromatic heterocyclic compound, and the pH is 7 It is related with the polishing liquid for grind | polishing the base | substrate containing sapphire which is 0.0-10.4. By using such a polishing liquid, the surface of sapphire can be polished at an excellent polishing rate.

  In one aspect of the present invention, the total content of the large silica and the small silica is preferably 1 to 40% by mass based on the total mass of the polishing liquid. Thereby, the surface of sapphire can be polished at a higher polishing rate.

  One aspect of the present invention relates to a storage liquid that can obtain the polishing liquid according to any one of claims 1 to 3 by being diluted two or more times with a liquid medium. According to such a storage liquid, it is possible to reduce costs related to storage / transport of the CMP polishing liquid.

  One embodiment of the present invention relates to a polishing method including a step of polishing a substrate containing sapphire using the polishing liquid. According to such a polishing method, a substrate containing sapphire can be polished at an excellent polishing rate.

  One embodiment of the present invention relates to a polishing method including a step of polishing a substrate containing sapphire using a polishing liquid obtained by diluting the above storage liquid with a liquid medium at least twice. As a result, the costs associated with storage, transportation, storage, etc. of the polishing slurry for CMP can be suppressed, so that the overall manufacturing cost can be reduced.

  According to the present invention, it is possible to provide a polishing liquid capable of polishing sapphire at a high polishing rate, a storage liquid thereof, and a sapphire polishing method using these.

FIG. 1 is a diagram for explaining a method of calculating an average particle diameter of particles.

  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 an embodiment of the present invention includes at least one kind of large silica having an average primary particle diameter of 60 to 150 nm, at least one kind of small silica having an average primary particle diameter of 40 nm or less, water, and A value (L / S) obtained by dividing the content of large silica (L) by the content of small silica (S) (L / S) is greater than 1 and contains a polishing accelerator, and the polishing accelerator is a nitrogen-containing aromatic heterocyclic compound. A polishing liquid for polishing a sapphire-containing substrate having a pH of 7.0 to 10.4.

(silica)
The polishing liquid according to this embodiment contains silica. Silica acts as an abrasive. Conventionally, silica and alumina are well known as abrasive grains, but silica is excellent in smoothing the surface of sapphire.

  From the viewpoint of improving the polishing rate for sapphire, the polishing liquid is composed of at least one kind of large silica having an average primary particle diameter of silica of 60 to 150 nm and at least one kind of small silica having an average primary particle diameter of 40 nm or less. Contains silica. In this embodiment, the value (L / S) obtained by dividing the addition amount (L) of large silica by the addition amount (S) of small silica is a value exceeding 1. The average primary particle size of large silica is preferably 65 nm or more, more preferably 70 nm or more, and even more preferably 75 nm or more. The average primary particle size is preferably 140 nm or less, more preferably 130 nm or less, and still more preferably 120 nm or less. The average primary particle size of the small silica is preferably 2 nm or more, more preferably 4 nm or more, and further preferably 6 nm or more. The average primary particle size is preferably 35 nm or less, more preferably 30 nm or less, and even more preferably 25 nm or less.

  In the present embodiment, the average primary particle diameter of the particles can be measured from an SEM image obtained by observation with a scanning electron microscope. Specifically, for example, a plurality of (for example, 20) particles are randomly selected from the SEM image of the particles. About the selected particle | grains, a particle size is measured on the basis of the reduced scale displayed by SEM. The particle diameter can be obtained as the square root (biaxial average particle diameter) of the product of the maximum diameter of the particle and the short diameter perpendicular thereto. The average value of the measured values obtained is taken as the average primary particle size of the particles.

  Specifically, for example, an appropriate amount of abrasive liquid to be measured is taken, a chip containing a 2 cm square wafer with a pattern wiring is immersed in the container containing the liquid for about 30 seconds, and then a container containing pure water And rinse for about 30 seconds and blow dry the chips. Thereafter, the sample is placed on a sample stage for SEM observation, an acceleration voltage of 10 kV is applied, particles are observed at an appropriate magnification (for example, 200,000 times), and an image is taken. Arbitrary 20 particles are selected from the obtained image.

  For example, when the selected particle has a shape as shown in FIG. 1, a rectangle (circumscribed rectangle 2) that circumscribes the particle 1 and has the longest diameter is guided. Then, the biaxial average particle diameter of one particle is calculated as “√ (X × Y)” where X is the major axis of the circumscribed rectangle 2 and Y is the minor axis. This operation is carried out on any 20 particles, and the average value obtained is taken as the average primary particle size of the particles.

  The reason why the polishing rate is improved when the polishing liquid contains large silica and small silica is not clear, but the inventors consider as follows.

  It is said that sapphire undergoes solid phase reaction with silica at the time of polishing, forming a relatively weak aluminosilicate than sapphire, and polishing proceeds. At this time, it is considered that the polishing rate is not improved only with large silica because a gap is generated between the silica particles and the contact area between sapphire and silica is not large. On the other hand, with small silica alone, the contact area increases compared to polishing with large silica alone, but the load transmitted from the polishing pad to silica seems to be relatively small, and it is assumed that the polishing rate does not improve. . In contrast, the inclusion of large silica and small silica in the polishing liquid increases the contact area because the small silica enters the gaps between the large silica particles, and the large silica functions to transmit the load to the adjacent small silica. Therefore, it is considered that the polishing rate is improved because the load on sapphire increases even with small silica. From such a viewpoint, the L / S is preferably more than 1, and more preferably 1.1 or more. The upper limit of L / S is not particularly limited, but can be 8 or less from the viewpoint of improving the polishing rate.

  The content of silica in the polishing liquid (total content of large silica and small silica) is preferably 1 to 40% by mass, more preferably 5 to 30% by mass based on the total mass of the polishing liquid. . From the viewpoint of easily achieving a polishing rate that is significantly different from the polishing rate when the polishing liquid does not contain abrasive grains, the content of the abrasive grains is preferably 1% by mass or more based on the total mass of the polishing liquid. . Moreover, when the content of abrasive grains is 40% by mass or less based on the total mass of the polishing liquid, there is a tendency that the polishing rate is easily improved as the content increases.

(water)
The water that is the medium of the polishing liquid is not particularly limited, and examples thereof include deionized water, ion exchange water, and ultrapure water.

(Polishing accelerator)
The polishing liquid according to this embodiment contains a nitrogen-containing aromatic heterocyclic compound as a polishing accelerator for polishing a substrate containing sapphire. Thereby, the polishing rate can be improved.

  The nitrogen-containing aromatic heterocyclic compound is preferably a compound represented by the following general formula (I).

式（Ｉ）中、点線で囲まれたＡｒは芳香環を示し、Ｒ^１は、水素原子、ヒドロキシル基又はアルキル基を示す。

In formula (I), Ar surrounded by a dotted line represents an aromatic ring, and R ¹ represents a hydrogen atom, a hydroxyl group or an alkyl group.

  The reason why the polishing rate of sapphire is improved by adding the nitrogen-containing aromatic heterocyclic compound to the polishing liquid is not clear, but the inventors consider as follows. In other words, when sapphire is polished, when silica is pressed against sapphire, the hydroxyl group on sapphire and the hydroxyl group on silica form hydrogen bonds, and then react to produce aluminosilicate, which is soft. For this reason, it is considered that polishing is progressed by mechanical removal by CMP. At this time, the nitrogen-containing aromatic heterocyclic compound acts on the aluminum atom of sapphire directly bonded to the hydroxyl group or the silicon atom of silica to increase the electron density on the hydroxyl group and facilitate hydrogen bonding, so that the subsequent aluminosilicate It is thought that the production reaction of this proceeds rapidly and the polishing rate is improved.

  Examples of the nitrogen-containing aromatic heterocyclic compound represented by the general formula (I) include pyrazole, 1,2,4-triazole, 1-hydroxybenzotriazole, benzotriazole, cinnoline, tetrazole, 5-methyltetrazole, and 5-amino. Examples include tetrazole, 5-mercapto-1-phenyl-1H-tetrazole, and derivatives thereof. Among these, 1-hydroxybenzotriazole and 5-methyl-1H-tetrazole are more preferable from the viewpoints of low cost, high safety, high solubility in water, and improvement in the polishing rate for sapphire. These can be used alone or in combination of two or more.

  The polishing accelerator may further contain an aluminum silicate additive, a cationic surfactant, a wettability improver, and the like.

  As the aluminum silicate-based additive, kaolin-based or smectite-based natural minerals or synthetic products can be used, and examples thereof include bentonite, kaolin, saponite, and aluminum magnesium silicate. These can be used alone or in combination of two or more.

  The cationic surfactant acts to improve the polishing rate of the sapphire substrate by lowering the surface potential of silica negatively charged in the polishing liquid and increasing the attractive force between the sapphire substrate and silica. Examples of such cationic surfactants include alkylamines, alkylamine salts, polyalkylamines, polyalkylamine salts, and alkylphosphonium salts. These can be used alone or in combination of two or more.

  The wettability improver reduces the surface tension of the polishing liquid, thins the liquid film of the polishing liquid on the polishing pad, and improves the polishing rate of the sapphire substrate by bringing the silica and sapphire substrate into more contact. To do. Examples of such wettability improvers include higher alcohols, phenols, alkylphenols, alkylene oxide adducts such as fatty acids and aliphatic amines, fatty acid esters of alcohols, fatty acid alkanolamides, alkylphosphoniums, and alkylphosphonium salts. These can be used alone or in combination of two or more.

  Each component (nitrogen-containing aromatic heterocyclic compound, aluminum silicate additive, cationic surfactant, wettability improver, etc.) that can be contained in the polishing accelerator is independent of the amount of the polishing liquid. It is preferable that it is 0.01 mass% or more and less than 1.0 mass% on the basis of the total mass. Thereby, the polishing rate of the sapphire substrate can be further improved. From the viewpoint of obtaining a superior polishing rate, the content is more preferably 0.05% by mass or more, and further preferably 0.1% by mass or more. Similarly, the content is more preferably 0.7% by mass or less from the viewpoint of obtaining a superior polishing rate.

(PH)
The pH of the polishing liquid according to this embodiment is in the range of 7.0 to 10.4. Thereby, the polishing rate can be improved. From the same viewpoint, the pH is preferably 7.5 or more, more preferably 8.0 or more, and even more preferably 9.0 or more. The pH is preferably 10.2 or less, more preferably 10.0 or less, and even more preferably 9.8 or less.

  pH is inorganic acid such as sulfuric acid, hydrochloric acid, nitric acid, phosphoric acid, organic acid such as acetic acid, oxalic acid, malic acid, malonic acid, picolinic acid, or ammonia, sodium hydroxide, potassium hydroxide, TMAH (tetrahydroxide). It can be adjusted by adding alkali components such as methylammonium) and imidazole.

  The pH of the polishing liquid can be measured with a pH meter (for example, model number: PHL-40, manufactured by Electrochemical Instrument Co., Ltd.). As the pH measurement value, 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 buffer)
The sapphire substrate is generally polished while circulating the polishing liquid for a long time. The pH of the polishing liquid is usually set so that the polishing rate of sapphire is high, but by polishing for a long time, the pH of the polishing solution gradually deviates from the appropriate range for polishing sapphire, and the polishing rate It has been found that may decrease. From this, it is preferable that the polishing liquid according to the present embodiment includes a pH buffering agent in order to stabilize the pH of the polishing liquid during polishing. As a result, sapphire can be polished stably for a long time at an excellent polishing rate.

  Particularly effective buffer solutions in the pH range of 7.0 to 10.4 include buffers composed of a combination of alkalis such as boric acid and sodium hydroxide, and combinations of alkalis such as sodium tetraborate and sodium hydroxide. A buffer consisting of a combination of alkalis such as potassium dihydrogen phosphate and sodium hydroxide, a buffer consisting of a combination of ammonium chloride and ammonia, and a combination of acids such as tris (hydroxymethyl) aminomethane and hydrochloric acid. Examples of the buffer include a buffer and a buffer comprising a combination of glycine and an alkali such as sodium hydroxide.

  The content of the pH buffering agent is preferably 0.01% by mass or more, more preferably 0.05% by mass or more based on the total mass of the polishing liquid from the viewpoint of further stabilizing the pH of the polishing liquid during polishing. . Further, when the buffer is added in a large amount, the silica in the polishing liquid is aggregated and the storage stability tends to be remarkably impaired. From the viewpoint of further stabilizing the pH without impairing storage stability, the content of the pH buffer in the polishing liquid is preferably 1.0% by mass or less, and more preferably 0.5% by mass or less. In addition, content here refers to content in the polishing liquid of the pH buffer formed by combining said each component.

[Stock solution]
The polishing liquid according to the present embodiment can be stored as a storage liquid that is used by being diluted two or more times with a liquid medium such as water at the time of use, from the viewpoint of suppressing the cost related to storage, transportation, storage, and the like. . The storage liquid may be diluted with a liquid medium immediately before polishing to form a polishing liquid. When a sapphire substrate is polished, the storage liquid and the liquid medium are supplied onto the polishing surface plate and polished on the polishing surface plate. A liquid may be prepared. Examples of the liquid medium include methanol, ethanol, isopropyl alcohol and the like in addition to the water.

  The dilution rate of the stock solution is preferably 2 times or more and more preferably 3 times or more because the higher the magnification is, the higher the cost suppressing effect relating to storage, transportation, storage, etc. is. The upper limit of the dilution rate 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. When the dilution factor is less than or equal to these upper limit values, the content of abrasive grains and nitrogen-containing compounds 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. . In addition, when the dilution rate is d, the respective contents of the abrasive grains and the organic acid in the storage liquid are d times the respective contents of the abrasive grains and the organic acid in the polishing liquid.

[Polishing method]
In the polishing method according to this embodiment, a known polishing apparatus can be widely used. For example, when polishing a sapphire substrate, a polishing apparatus that can be used includes a holder for holding the sapphire substrate and a surface plate (platen) to which a polishing cloth (polishing pad) is attached, or a fixed plate made of cast iron, copper, and tin. A general polishing apparatus having a board or the like can be used. A motor or the like for changing the number of rotations is attached to the surface plate.

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 from the viewpoint of easily preventing the substrate from popping out, the rotational speed of the base plate is preferably 200 rpm (min ⁻¹ ) or less. From the viewpoint of easily suppressing the occurrence of scratches on the substrate surface after polishing, the polishing load is preferably 20 psi (34.5 kPa) or less.

  In the polishing method according to the present embodiment, while the polishing pad affixed to the surface plate is pressed against the substrate containing sapphire, the polishing liquid is supplied between the substrate and the polishing pad by a pump or the like, Move relative to the surface plate. By these operations, the substrate surface 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. Polishing may be performed by supplying a stock solution and a liquid medium such as water between the substrate and the polishing cloth and diluting the stock solution by a factor of 2 or more on a polishing platen. Further, the supplied polishing liquid may be recovered and supplied to the polishing pad again, and used by circulating.

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

  Hereinafter, the present invention will be described in more detail by way of examples. However, the present invention is not limited to these examples without departing from the technical idea of the present invention.

As the abrasive particles, silica shown in Table 1 was used.

  A stock solution is prepared by adding silica A (average primary particle size 11 nm), silica B (average primary particle size 25 nm), and silica C (average primary particle size 80 nm) to deionized water. A polishing liquid was prepared by diluting twice (mixing the stock solution with deionized water of the same mass as the stock solution). The concentration of silica A in the polishing liquid was 1% by mass, the concentration of silica B was 3.5% by mass, and the concentration of silica C was 5% by mass. That is, the value (L / S) obtained by dividing the content (L) of silica C by the content (S) of silica A and B was 1.1. A predetermined polishing accelerator was added to the polishing liquid so that the content described in Table 2 was obtained. The polishing liquid was adjusted with an aqueous potassium hydroxide solution or malic acid so that the pH was 9.2.

[CMP method and polishing characteristic evaluation method]
The substrate was subjected to chemical mechanical polishing with a polishing liquid for CMP using the polishing apparatus in the following procedure.

  A CMP polishing liquid (polishing liquid) is supplied at a room temperature (25 ° C.) between the base and the polishing pad with a pump while pressing the following base on the polishing pad affixed to the platen. The platen was rotated. At this time, polishing was performed while circulating the polishing liquid. By these operations, CMP of the substrate surface was performed.

  As a substrate to be polished, a sapphire wafer having a polished surface with an A-plane or C-plane orientation was used. The substrate had a diameter of 4 inches (100 mm) and a thickness of 0.65 mm.

  A model RDP-500 manufactured by Fujikoshi Machinery Co., Ltd. was used as a polishing apparatus. As a polishing pad, SUBA800 having a grid-like groove made by Rohm and Haas was used. The polishing conditions were as follows.

<Polishing conditions>
Polishing pressure: 7.1 psi
Platen diameter: 50.8cm
Platen rotation speed: 110 rpm (min ⁻¹ )
Flow rate (supply amount) of polishing liquid for CMP: 750 mL / min
Polishing time: 30 min

<Polishing speed>
The polished mass was determined by measuring the mass of the substrate before and after CMP using each polishing liquid, and the area and density of the polished surface of the substrate (using a value of 3.97 g / cm ³ for sapphire) were used. Was converted into a film thickness and the polishing rate was calculated. A sapphire substrate with an A-plane orientation is considered to be good when the polishing rate is 1.8 μm / h, and a sapphire substrate with a C-plane is 4.0 μm / h or more. Table 2 shows the evaluation results of the polishing rate.

[Evaluation results]
From Table 2, it was confirmed that a CMP polishing liquid capable of polishing the surface of sapphire at high speed can be obtained by including a predetermined polishing accelerator in the polishing liquid.

  The polishing liquid (CMP polishing liquid), the storage liquid, and the polishing method using these according to the present invention are suitable for CMP of a substrate containing sapphire used in an electronic device casing such as an LED substrate or a smartphone.

  1 ... particle, 2 ... circumscribed rectangle.

Claims (5)

Including at least one or more types of large silica having an average primary particle size of 60 to 150 nm, at least one or more types of small silica having an average primary particle size of 40 nm or less, water, and a polishing accelerator,
A value (L / S) obtained by dividing the content (L) of the large silica by the content (S) of the small silica is more than 1, and the polishing accelerator is pyrazole, 1,2,4-triazole, 1 -Containing at least one selected from the group consisting of -hydroxybenzotriazole, benzotriazole, cinnoline, tetrazole, 5-methyl-1H-tetrazole, 5-aminotetrazole and 5-mercapto-1-phenyl-1H-terazole , and has a pH of Polishing liquid for grind | polishing the base | substrate containing sapphire which is 7.0-10.4.   The polishing liquid according to claim 1, wherein the total content of the large silica and the small silica is 1 to 40% by mass based on the total mass of the polishing liquid.   A storage liquid that can obtain the polishing liquid according to claim 1 or 2 by being diluted two or more times with a liquid medium.   A polishing method comprising a step of polishing a substrate containing sapphire using the polishing liquid according to claim 1.   A polishing method comprising a step of polishing a substrate containing sapphire using a polishing liquid obtained by diluting the storage liquid according to claim 3 with a liquid medium at least twice.

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