JP2018154789A - Composition for polishing and polishing method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a composition for polishing which is more suitably usable for use in polishing lithium tantalate or lithium niobate.SOLUTION: A composition for polishing a lithium tantalate or lithium niobate substrate contains colloidal silica, a potassium salt of an ethylenediaminetetraacetic acid or a potassium salt of a diethylenetriamine pentaacetic acid, and water, where a ratio of a content of the colloidal silica to the composition is 10-35 mass%, a neutralization rate of a hydrogen atom in the carboxyl group with the potassium atom in the potassium salt of the ethylenediaminetetraacetic acid or the potassium salt of the diethylenetriamine pentaacetic acid is 60-100 mol%, a ratio of a content of the potassium salt of ethylenediaminetetraacetic acid or the potassium salt of the diethylenetriamine pentaacetic acid in the contents is 0.2-4.0 mass%, and pH is 7 to 12.SELECTED DRAWING: None

Description

  The present invention relates to a polishing composition used for polishing a polishing object of lithium tantalate or lithium niobate, and a polishing object of lithium tantalate or lithium niobate using such a polishing composition. Regarding the method.

  Demand for piezoelectric wafers constituting surface acoustic wave devices using surface acoustic waves generated by the piezoelectric effect in piezoelectric bodies is increasing as electronic component materials for television intermediate frequency filters and resonators. As such piezoelectric wafer materials, hard and brittle materials such as lithium tantalate materials and lithium niobate materials excellent in piezoelectricity, pyroelectricity, and electro-optic effect are widely used.

  The above lithium tantalate and lithium niobate materials are hard and brittle, but if a hard abrasive such as alumina or diamond having coarse and hard particles is used as the abrasive, the polishing rate will increase. There have been problems such as pits and scratches on the polished surface, processing distortion remaining inside the wafer surface, and extremely poor surface accuracy. In addition, since it is a chemically stable material, the polishing effect by mechanochemical action is extremely low, and no effective polishing accelerator has been found.

  In order to improve the polishing characteristics of such a hard and brittle material, Patent Document 1 discloses at least one of an abrasive and an acid obtained by oxidation of aldose such as uronic acid, aldonic acid, and aldaric acid, and a salt thereof. A polishing composition containing one of the aldose derivatives and water has been proposed.

  Patent Document 2 proposes a polishing composition containing colloidal silica as a base, colloidal silica having a particle diameter different from that of the base abrasive, and a chelating compound.

  However, the polishing compositions disclosed in Patent Documents 1 and 2 sufficiently satisfy the demand for polishing with high accuracy and a high polishing rate for hard and brittle materials of lithium tantalate materials and lithium niobate materials. Not satisfied.

JP 2006-150482 A JP2007-32159A

  An object of the present invention is to provide a polishing composition that can be more suitably used in applications for polishing lithium tantalate or lithium niobate, and a polishing method for polishing a polishing object using such a polishing composition Is to provide.

In order to achieve the above object, one embodiment of the present invention provides a polishing composition for lithium tantalate or lithium niobate containing the following components (a), (b) and (c).
(A): Colloidal silica (b): Compound (c) which is a potassium salt of ethylenediaminetetraacetic acid or potassium salt of diethylenetriaminepentaacetic acid and has a neutralization rate of 60 to 100 mol% of the hydrogen atom of the carboxyl group with the potassium atom :water

  In another embodiment of the present invention, in the polishing composition of the above embodiment, the proportion of (a) in the total of (a), (b) and (c) is 10 to 35% by mass, (a Polishing composition for lithium tantalate or lithium niobate, wherein the proportion of (b) in the total of (b), (b) and (c) is 0.2-4.0% by mass and the pH is 7-12 Offer things.

  ADVANTAGE OF THE INVENTION According to this invention, the polishing composition which can be used more suitably in the use which grind | polishes a lithium tantalate or a lithium niobate board | substrate is provided. The present invention also provides a polishing method for polishing a lithium tantalate or lithium niobate substrate using such a polishing composition.

Hereinafter, an embodiment of the present invention will be described.
One embodiment of the present invention is the following component (a) colloidal silica, (b) potassium salt of ethylenediaminetetraacetic acid or potassium salt of diethylenetriaminepentaacetic acid, and the neutralization rate of the hydrogen atom of the carboxyl group by the potassium atom is 60 Provided is a polishing composition for lithium tantalate or lithium niobate containing a compound that is ˜100 mol%, and (c) water. Hereinafter, each content is demonstrated.

<Colloidal silica>
The average particle diameter of colloidal silica is not specified. However, in general, colloidal silica having an average particle diameter of less than 15 nm, more specifically colloidal silica of less than 25 nm, does not have a very high ability to polish an object to be polished. Therefore, in order to improve the polishing rate, the average particle diameter of colloidal silica is preferably 15 nm or more, more preferably 25 nm or more. On the other hand, colloidal silica having an average particle diameter larger than 100 nm, and more specifically colloidal silica larger than 80 nm, is expensive to manufacture. Therefore, for cost reduction, the average particle size of colloidal silica is preferably 100 nm or less, more preferably 80 nm or less. The average particle diameter of colloidal silica is, for example, a volume average particle diameter (volume-based arithmetic mean; expressed by a dynamic light scattering method using a model “UPA-UT151” manufactured by Nikkiso Co., Ltd .; Mv).

  Moreover, when content of colloidal silica in polishing composition is less than 10 mass%, there exists a possibility that polishing composition may not have very high polishing capability. Therefore, in order to improve the polishing rate, the content of colloidal silica in the polishing composition is 10% by mass or more. On the other hand, when the content of colloidal silica in the polishing composition is more than 35% by mass, the dispersion stability of the polishing composition is lowered, and there is a possibility of gelation with time. Therefore, in order to prevent a decrease in dispersion stability of the polishing composition, the content of colloidal silica in the polishing composition is 35% by mass or less. The content of colloidal silica in the polishing composition is preferably 15 to 30% by mass, more preferably 15 to 25% by mass.

  Polishing composition of one Embodiment of this invention contains the potassium salt of ethylenediaminetetraacetic acid or the potassium salt of diethylenetriaminepentaacetic acid, and the neutralization rate by the potassium atom of the hydrogen atom of a carboxyl group is 60-100 mol% at this time It is a requirement that As the potassium salt of ethylenediaminetetraacetic acid or potassium salt of diethylenetriaminepentaacetic acid, commercially available ones may be used, or ethylenediaminetetraacetic acid or diethylenetriaminepentaacetic acid and potassium or potassium hydroxide may be separately blended. Good. The addition of potassium ethylenediaminetetraacetic acid or potassium diethylenetriaminepentaacetic acid as a polishing accelerator to colloidal silica has a favorable polishing rate due to moderate relaxation of polishing resistance during polishing. In addition, the polishing rate is maintained over a long period of time and an excellent polishing life is realized.

  The neutralization rate by the potassium atom of the hydrogen atom of the carboxyl group of the potassium salt of ethylenediaminetetraacetic acid or potassium salt of diethylenetriaminepentaacetic acid is 60 to 100 mol%, preferably 60 to 90 mol%. When the neutralization rate of the potassium atom of the carboxyl group of the potassium salt of ethylenediaminetetraacetic acid or potassium salt of diethylenetriaminepentaacetic acid is less than 60 mol%, the polishing composition has a marked increase in viscosity over time or gel If the amount exceeds 100 mol%, the pH of the polishing composition tends to increase and problems such as dissolution of the abrasive in the polishing composition tend to occur.

  The content of the potassium salt of ethylenediaminetetraacetic acid or potassium salt of diethylenetriaminepentaacetic acid is added at a rate of 0.2 to 4.0% by mass, preferably 0.3 to 3.0% by mass. More preferably, the blending ratio of 0.4 to 2.5% by mass is good, and thereby even better polishing efficiency can be obtained. When the blending ratio is less than 0.2% by mass, the improvement of the polishing rate tends not to be expressed. When the blending ratio is more than 4.0% by mass, the viscosity increases or gels with time. This is because there is a tendency.

  The water blended in the polishing composition of the present embodiment plays a role as a medium for dispersing or dissolving components other than water in the polishing composition. The water may be industrial water, tap water, distilled water, or those obtained by filtering them, and preferably contains as little impurities as possible.

  When the pH of the polishing composition is lower than 7, more specifically, lower than 8, the dispersion stability of the polishing composition decreases, and the viscosity tends to increase or gel with time. is there. Therefore, in order to prevent the dispersion stability of the polishing composition from being lowered, the pH of the polishing composition is 7 or more, preferably 8 or more. On the other hand, when the pH of the polishing composition is higher than 12, more specifically, higher than 11, the abrasive in the polishing composition tends to dissolve. Therefore, the pH of the polishing composition is 12 or less, preferably 11 or less, in order to prevent dissolution of the abrasive.

  In order to adjust the pH of the polishing composition, various pH adjusting agents can be appropriately blended depending on the abrasive and the blending agent blended in the polishing composition.

  Another embodiment of the present invention provides a method for polishing a lithium tantalate or lithium niobate substrate surface using the polishing composition for a lithium tantalate or lithium niobate substrate of the above embodiment. At this time, for example, the polishing object such as a polishing pad is brought into contact with the polishing object which is a lithium tantalate or lithium niobate substrate, and the polishing object of the above embodiment is supplied to the contact portion and the polishing object and Either one of the polishing members is slid with respect to the other.

This embodiment has the following advantages.
The polishing composition according to this embodiment contains a potassium salt of ethylenediaminetetraacetic acid or a potassium salt of diethylenetriaminepentaacetic acid that contributes to improving the polishing ability of the polishing composition. Therefore, the polishing composition according to this embodiment has a higher polishing ability than the conventional polishing composition, and can quickly polish the lithium tantalate substrate and the lithium niobate substrate.

  Further, the neutralization rate of the potassium atom of the carboxyl group of the potassium salt of ethylenediaminetetraacetic acid or potassium salt of diethylenetriaminepentaacetic acid is 60 to 100 mol%, thereby improving the dispersion stability of the polishing composition. Therefore, the polishing composition according to this embodiment has higher dispersion stability than the conventional polishing composition. That is, even when the abrasive is contained at a high concentration, the abrasive in the polishing composition is less likely to be gelled or solidified.

  The neutralization rate is the number of moles of the basic substance that forms a neutralization salt with the carboxyl group of ethylenediaminetetraacetic acid or diethylenetriaminepentaacetic acid in the polishing composition, and the number of moles of carboxyl group of ethylenediaminetetraacetic acid or diethylenetriaminepentaacetic acid. Divide and calculate. Alternatively, the molar equivalent of the potassium atom of ethylenediaminetetraacetic acid or diethylenetriaminepentaacetic acid in the polishing composition may be divided by the molar equivalent of the carboxyl group of ethylenediaminetetraacetic acid or diethylenetriaminepentaacetic acid.

  The embodiment may be modified as follows. The polishing composition according to the above embodiment may contain alumina, fumed silica, amorphous silica powder, ceria or manganese dioxide as an abrasive instead of or in addition to colloidal silica. However, in order to improve the polishing rate, the polishing composition preferably contains at least colloidal silica or ceria as an abrasive.

  The polishing composition according to the embodiment may further contain a pH adjuster, an antifungal agent, a surfactant and the like. The pH adjuster may be an inorganic acid such as sulfuric acid, hydrochloric acid, nitric acid, or carbonic acid, or an organic acid such as acetic acid or oxalic acid, or a salt of an inorganic acid or an organic acid. Alternatively, the pH adjuster may be an alkaline compound such as potassium hydroxide, sodium hydroxide, ammonia, tetramethylammonium hydroxide. The fungicide is preferably an organic fungicide containing nitrogen and sulfur. The content of the antifungal agent in the polishing composition is preferably 0.001 to 1.0% by mass, more preferably 0.01 to 0.1% by mass. The surfactant may be, for example, any of an anionic surfactant, a nonionic surfactant, and a fluorosurfactant. The surfactant has an effect of improving the dispersibility of the abrasive in the polishing composition.

  The polishing composition according to the embodiment may be used for polishing an object to be polished other than a lithium tantalate or lithium niobate substrate. For example, the polishing composition according to the embodiment may be used in an application for polishing an oxide substrate other than a lithium tantalate or lithium niobate substrate, or in an application for polishing an oxide other than an oxide substrate. May be used. Alternatively, it may be used in an application for polishing a glass substrate for a magnetic disk.

  The polishing composition according to the embodiment may be prepared by diluting the stock solution with water.

Next, the present invention will be described more specifically with reference to examples and comparative examples.
Example 1
<Preparation of polishing composition and measurement of physical properties>
Into a 200 mL resin cup, put 84.2 g of water, 0.80 g of ethylenediaminetetraacetic acid tripotassium salt, 15.0 g of colloidal silica having an average particle diameter D50 of 69 nm, and stir at room temperature for 30 minutes. The polishing composition of Example 1 was obtained. It was 8.8 when pH of the said polishing composition was measured. Further, the neutralization rate was calculated as follows by dividing the molar equivalent of the potassium atom in the potassium salt of ethylenediaminetetraacetic acid by the molar equivalent of the carboxyl group of ethylenediaminetetraacetic acid.
Neutralization rate (%) = 3/4 × 100 = 75

<Measurement of viscosity>
The viscosity of the prepared polishing composition of Example 1 at 25 ° C. was 1 mPa · s. After the polishing composition was allowed to stand at 25 ° C. for 3 months, the viscosity at 25 ° C. was 1 mPa · s. In Table 1, when the viscosity at 25 ° C. is 300 mPa · s or less, “◯”, when the viscosity at 25 ° C. exceeds 300 mP · s, or when gelled, “×” indicates change with time Evaluation of was shown. The results are shown in Table 1.

<Measurement of polishing rate>
10 kg of the polishing composition was prepared in the same manner as the preparation of the polishing composition described above, the polishing test was performed with the equipment and conditions shown below, and after sufficient cleaning, the area of the object to be polished and before and after polishing The polishing rate was calculated from the weight change at.
Polishing machine: Double-side polishing machine (DSM 12B-8PV 4MH manufactured by Speedfam)
Polishing pad: Polyurethane polishing pad (SUBA 800 manufactured by Nitta Haas Co., Ltd.)
Polishing object: 3 inch diameter, 0.5 mm thick lithium tantalate wafer (manufactured by Yamato Ceramics Co., Ltd.), 9 wafers / batch
Upper platen rotation speed: 5rpm
Lower platen rotation speed: 16rpm
Polishing composition supply rate: 3 L / min (circulation use)
Polishing time: 30 minutes The polishing rate was 14.3 μm / hour. In Table 1, the case where the polishing rate exceeded 13.0 μm / hour was evaluated as “◯”, and the case where the polishing rate was 13.0 μm / hour or less was evaluated as “x”. The results are shown in Table 1.

<Measurement of surface roughness>
Using a non-contact surface shape measuring instrument (New View 5032 manufactured by ZYGO), the arithmetic average value Ra of the surface height at a viewing angle of 289 × 217 μm of the lithium tantalate substrate after the polishing test was measured as the surface roughness. Ra was 0.232 nm. In Table 1, regarding the evaluation of the surface roughness, the case where Ra was 0.500 nm or less was evaluated as “◯”, and the case where Ra exceeded 0.500 nm was evaluated as “x”. The results are shown in Table 1.

(Examples 2-9)
In the same manner as in Example 1, the average particle size and blending ratio of colloidal silica shown in Table 1, the blending ratio of potassium salt of ethylenediaminetetraacetic acid or potassium salt of diethylenetriaminepentaacetic acid, and blending ratio of water 1-9 polishing compositions were prepared. By the same method as in Example 1, the neutralization rate of the potassium salt of ethylenediaminetetraacetic acid or the potassium salt of diethylenetriaminepentaacetic acid was calculated. Further, the physical properties (pH, viscosity) of the polishing composition and the performance (polishing rate, surface roughness) of the polishing composition were measured, and the obtained results and evaluation are shown in Table 1. In addition, as potassium salt of ethylenediaminetetraacetic acid or potassium salt of diethylenetriaminepentaacetic acid, Examples 2 to 4, 7 and 9 used tripotassium salt of ethylenediaminetetraacetic acid, and Example 8 used pentapotassium salt of diethylenetriaminepentaacetic acid. In Example 5, 0.37 g of ethylenediaminetetraacetic acid dipotassium salt and 0.43 g of ethylenediaminetetraacetic acid tripotassium salt were used, and the blending ratio of ethylenediaminetetraacetic acid potassium salt was set to the blending ratio shown in Table 1. In Example 6, 0.38 g of tripotassium salt of ethylenediaminetetraacetic acid and 0.42 g of tetrapotassium salt of ethylenediaminetetraacetic acid were used, and the blending ratio of the potassium salt of ethylenediaminetetraacetic acid was the blending ratio shown in Table 1.

(Comparative Examples 1-9)
In the same manner as in Example 1, as shown in Table 1, the average particle diameter, blending ratio, potassium, sodium or ammonium salt of ethylenediaminetetraacetic acid, or blending ratio of potassium salt of diethylenetriaminepentaacetic acid, and blending of water shown in Table 1 The polishing composition of Comparative Examples 1-9 was prepared with the ratio. The neutralization rate was calculated by dividing the molar equivalent of potassium atom, sodium atom or ammonium molecule in potassium, sodium or ammonium salt of ethylenediaminetetraacetic acid or potassium salt of diethylenetriaminepentaacetic acid by the molar equivalent of carboxyl group. Further, the physical properties (pH, viscosity) of the polishing composition and the performance (polishing rate, surface roughness) of the polishing composition were measured by the same method as in Example 1, and the obtained results and evaluation were shown in Table 1. It was shown to. In addition, instead of the potassium salt of ethylenediaminetetraacetic acid or the potassium salt of diethylenetriaminepentaacetic acid, trisodium salt of ethylenediaminetetraacetic acid was used in Comparative Example 1, triammonium salt of ethylenediaminetetraacetic acid was used in Comparative Example 2, and ethylenediaminetetraacetic acid was used in Comparative Example 9. The diammonium salt of was used.

  As shown in Table 1, the polishing compositions of Examples 1 to 9 satisfying the composition specified in the present invention and the neutralization rate of the potassium salt of ethylenediaminetetraacetic acid or potassium salt of diethylenetriaminepentaacetic acid are time-varying characteristics ( Viscosity characteristics) were good, the polishing rate was high, and the surface roughness of the resulting polished surface was also good.

  On the other hand, since the polishing composition of Comparative Example 1 used a sodium salt of ethylenediaminetetraacetic acid, the polishing rate was insufficient. Since the polishing composition of Comparative Example 2 used an ammonium salt of ethylenediaminetetraacetic acid, the polishing rate was insufficient. In the polishing composition of Comparative Example 3, since the neutralization rate of the potassium salt of ethylenediaminetetraacetic acid was smaller than the range of the present invention, the polishing composition gelled with time. The polishing composition of Comparative Example 4 had an insufficient polishing rate because the proportion of colloidal silica in the polishing composition was smaller than the range of the present invention. In the polishing composition of Comparative Example 5, since the proportion of colloidal silica in the polishing composition was larger than the range of the present invention, the polishing composition gelled with time. The polishing composition of Comparative Example 6 had an insufficient polishing rate because the proportion of colloidal silica in the polishing composition was smaller than the range of the present invention. The polishing composition of Comparative Example 7 had an insufficient polishing rate because the proportion of ethylenediaminetetraacetic acid potassium salt in the polishing composition was smaller than the range of the present invention. In the polishing composition of Comparative Example 8, the polishing composition gelled with time because the ratio of the potassium salt of ethylenediaminetetraacetic acid in the polishing composition was larger than the range of the present invention. The polishing composition of Comparative Example 9 uses an ammonium salt of ethylenediaminetetraacetic acid, and since the proportion of colloidal silica in the polishing composition is larger than the range of the present invention, the polishing composition gelates with time. did.

Claims (2)

Colloidal silica,
A potassium salt of ethylenediaminetetraacetic acid or a potassium salt of diethylenetriaminepentaacetic acid;
A polishing composition for a lithium tantalate or lithium niobate substrate, comprising water,
The neutralization rate of the hydrogen atom in the carboxyl group in the potassium salt of ethylenediaminetetraacetic acid or potassium salt of diethylenetriaminepentaacetic acid is 60 to 100 mol%, the colloidal silica, the potassium salt of ethylenediaminetetraacetic acid or the The proportion of the colloidal silica content in the total content of potassium salt of diethylenetriaminepentaacetic acid and water is 10 to 35% by mass, the colloidal silica, the potassium salt of ethylenediaminetetraacetic acid or the diethylenetriaminepentaacetic acid The ratio of the content of potassium salt of ethylenediaminetetraacetic acid or potassium salt of diethylenetriaminepentaacetic acid in the total content of potassium salt and water is 0.2 to 4.0% by mass, and the pH is 7 to Twelve Le lithium or polishing composition for a lithium niobate substrate.   A method for polishing a surface of a lithium tantalate or lithium niobate substrate using the polishing composition for a lithium tantalate or lithium niobate substrate according to claim 1.