JP2003188121A - Polishing liquid composition for oxide single crystal substrate and polishing method using the same - Google Patents

Abstract

(57) Abstract: A polishing liquid capable of improving a polishing rate without causing surface defects on the surface of a workpiece in precision polishing of an oxide single crystal substrate such as lithium tantalate or lithium niobate. A composition, a polishing method using the polishing composition, and an oxide single crystal substrate having excellent surface quality. The present invention relates to water, colloidal silica, and polyaminocarboxylic acid compounds, polyamine compounds, phosphonic acid compounds, bipyridine compounds, polycarbonyl compounds, aromatic polyhydroxy compounds, and salts thereof. A polishing composition for an oxide single crystal substrate comprising at least one selected chelating compound, a method for polishing an oxide single crystal substrate for polishing a substrate to be polished using the polishing composition, and An oxide single crystal substrate obtained by polishing by the polishing method.

Description

Detailed Description of the Invention

[0001]

The present invention relates to a surface of an oxide single crystal substrate, such as lithium tantalate or lithium niobate, which is widely used as a ferroelectric substrate for a surface acoustic wave device, an electro-optical device or the like. The present invention relates to a polishing liquid composition used for polishing, a polishing method using the polishing liquid composition, and an oxide single crystal substrate obtained by polishing by the polishing method.

[0002]

2. Description of the Related Art Oxide single crystals such as lithium tantalate and lithium niobate, which are excellent in piezoelectricity, pyroelectricity, and electro-optic effect, have been conventionally used as substrates for various surface acoustic wave devices for video equipment such as televisions and video equipment. Although it has been used as a material, it has been used as a substrate material for various surface acoustic wave devices used in mobile communication devices (cell phones, PHS, pagers, etc.), which are rapidly expanding their markets in recent years. Has become.

On the surface of the substrate for various surface acoustic wave devices,
Usually, polishing is performed to obtain a mirror surface. Oxide single crystals such as lithium tantalate and lithium niobate have a high hardness (5 to 6 Mohs hardness) and are chemically very stable materials, so that the polishing rate is very slow, , Industrially, supply polishing liquid,
Although it is used in a circulating supply system by repeating collection,
In some cases, a polishing time of nearly 10 hours is required to obtain a desired thickness, and its productivity and low efficiency have been problems.

Therefore, various polishing compositions have been proposed to date for this problem. For example, Japanese Patent Laid-Open No. 6-1
No. 91988, a polishing agent made of colloidal silica, colloidal alumina or colloidal zirconia is used, and KOH, NaOH, NaClO and Br are used as working fluids.
-It has been proposed to use with the addition of methanol. However, since the oxide single crystal made of lithium tantalate and lithium niobate has a high hardness as described above and is a chemically very stable compound, the polishing rate has not been sufficiently improved.

On the other hand, in Japanese Patent Laid-Open No. 3-54287,
A polishing composition containing calcined alumina powder is disclosed in JP-A-5-1.
In Japanese Patent No. 279, the BET specific surface area is 10 to 60 m ² /
g, and a method of using an aqueous slurry dispersion of finely divided silicon dioxide having a secondary particle diameter of 0.5 to 5 μm as a polishing composition, and in JP 2001-239652 A, a method of Have an average particle size (D50),
Further, there has been proposed a polishing composition in which α-alumina having a BET specific surface area of 15 to 50 m ² / g is dispersed in an aqueous medium. However, these methods have a problem that a highly accurate mirror surface cannot be obtained because many abrasive grains having a relatively large average particle diameter are used, and scratches often occur.

Further, in Japanese Patent Laid-Open No. 2001-93866, silicon oxide particles having an average primary particle diameter of 8 to 150 nm and an average secondary particle diameter of 12 to 400 nm are included, and 10 mS / m per 1% by weight of silicon oxide. The polishing composition provided with the above-mentioned conductivity is also disclosed in JP-A 2001-15213.
According to Japanese Patent Laid-Open No. 4, the average primary particle diameter A is 40 to 150 nm, the ratio B / A of the diameter to the average secondary particle diameter B is 1 or more and less than 1.4, and the silicon oxide particles are 1 wt%. Although a polishing composition having a conductivity of 10 mS / m or more has been proposed, none of them has sufficiently improved the polishing rate and the surface quality.

[0007]

SUMMARY OF THE INVENTION An object of the present invention is to perform a precision polishing process on an oxide single crystal substrate such as lithium tantalate or lithium niobate without causing surface defects on the surface of the object to be polished. A polishing liquid composition capable of improving the above, a polishing method using the polishing liquid composition, and an oxide single crystal substrate excellent in surface quality are provided.

[0008]

The summary of the present invention is as follows.
[1] Water, colloidal silica, and selected from the group consisting of polyaminocarboxylic acid compounds, polyamine compounds, phosphonic acid compounds, bipyridine compounds, polycarbonyl compounds, aromatic polyhydroxy compounds and salts thereof. An oxide single crystal substrate polishing composition containing at least one chelating compound
[2] A method for polishing an oxide single crystal substrate, which comprises polishing a substrate to be polished using the polishing composition of [1], and [3] an oxide obtained by polishing by the polishing method of [2]. It relates to a single crystal substrate.

[0009]

BEST MODE FOR CARRYING OUT THE INVENTION In the present invention, colloidal silica is used from the viewpoint of improving the surface quality of an oxide single crystal substrate. The colloidal silica used in the present invention is not particularly limited to the production method, for example, colloidal silica produced by dealkalization from water glass (sodium silicate aqueous solution), an organosilicon compound such as ethyl silicate is hydrolyzed. Colloidal silica produced, colloidal silica produced by dispersing fumed silica in water, and the like can be used.

The average particle size of colloidal silica is preferably 10 nm or more from the viewpoint of achieving a sufficient polishing rate.
More preferably 20 nm or more, further preferably 30 nm
From the viewpoint of improving surface quality such as scratch reduction and surface roughness reduction, the thickness is preferably 200 nm or less, more preferably 180 nm or less, and further preferably 1 nm or less.
It is 50 nm or less. The average particle size is preferably 10 n
m-200 nm, more preferably 20 nm-180 n
m, and more preferably 30 nm to 150 nm.

The average particle size of the colloidal silica in the present invention can be determined by the following method using a scanning electron microscope (hereinafter referred to as SEM). The polishing liquid composition containing the colloidal silica of the present invention is diluted with ethanol so that the colloidal silica concentration becomes 0.5% by weight. This diluted solution was heated to about 50 ° C by SEM
Apply evenly to the sample stand. Then, the excess solution is sucked with a filter paper and air-dried uniformly so that the solution does not aggregate. Pt-P on naturally dried colloidal silica particles
d is vapor-deposited and the magnification is 3000 times so that about 500 colloidal silica particles can be observed in the visual field using a field effect scanning electron microscope (FE-SEM: S-4000 type) manufactured by Hitachi, Ltd. Adjust at 100,000 times and observe two points on one sample stand to take a picture. Take a photo (4 inches x 5 inches) with a copy machine, etc.
Expand to 4 sizes and measure the particle size of each colloidal silica with a caliper and tabulate. The number of colloidal silica to be measured by repeating this operation several times is set to 2000 or more. Increasing the number of measurement points by SEM is more preferable from the viewpoint of obtaining an accurate average particle size. The particle size distribution was aggregated, the frequency (%) was added from the smallest particle size, and the particle size at which the value was 50% was taken as the average particle size.

The content of colloidal silica in the polishing composition is preferably 1% by weight or more, more preferably 3% by weight or more, further preferably 5% by weight or more, from the viewpoint of achieving a sufficient polishing rate. From the viewpoint of improving surface quality such as scratch reduction and surface roughness reduction, and from the viewpoint of economy, the amount is preferably 60% by weight or less, more preferably 55% by weight or less, and further preferably 50% by weight or less. The colloidal silica content is preferably 1 to
It is 60% by weight, more preferably 3 to 55% by weight, still more preferably 5 to 50% by weight.

The chelating compound used in the present invention is
It is a compound having a polydentate ligand capable of binding to a metal ion to form a complex. The molecular weight of the chelating compound used in the present invention is preferably 1,000 or less from the viewpoint of solubility in water. The chelating compound used in the present invention has, as a coordinating group, an —OH group, a —COOH group, a> C═O group, a —CO group.
O- group, -COOR group (wherein, R represents an alkyl group such as methyl group, ethyl group), - CONH ₂ group, -NO group,
-NO ₂ group, -SO ₃ H group, -PHO (OH) group, -P
O (OH) ₂ group, -NH ₂ group,> NH group,> N- group,-
It is a compound having two or more functional groups selected from the group of N = N- group,> C = N-OH group and> C = NH group.
Among these coordination groups, -OH group, -COOH group,> C
= O group, -NH ₂ group,> NH group,> N-group, -PO (O
H) ₂ groups and> C = NH groups are preferred. In the present invention, specific examples of the chelating compound include polyaminocarboxylic acid compounds, polyamine compounds, phosphonic acid compounds, bipyridine compounds, polycarbonyl compounds, aromatic polyhydroxy compounds and salts thereof. To be

More specifically, the polyaminocarboxylic acid compounds include nitrilotriacetic acid, diethylenetriaminepentaacetic acid, ethylenediaminetetraacetic acid, diethylenetriaminepentaacetic acid, propylenediaminetetraacetic acid, ethylenediaminetetrapropionic acid, hydroxyethylethylenediaminetriacetic acid, glycol ether. Diamine tetraacetic acid,
Examples thereof include nitrilotriacetic acid, hydroxyethyliminodiacetic acid, dihydroxyethylglycine, triethylenetetraaminehexaacetic acid and the like, and salts thereof such as ammonium salts, amine salts, sodium salts and potassium salts.

Examples of the polyamine compound include monomers such as ethylenediamine and diethylenetriamine, and salts such as hydrochlorides thereof.

The phosphonic acid compounds include diethylenetriaminepentamethylenephosphonic acid, phosphonobutanetricarboxylic acid, phosphonohydroxyacetic acid, hydroxyethyldimethylenephosphonic acid, aminotrismethylenephosphonic acid, hydroxyethanediphosphonic acid, ethylenediaminetetramethylenephosphonic acid. Examples thereof include acids, hexamethylenediaminetetramethylenephosphonic acid and the like, and salts thereof such as ammonium salts, amine salts, sodium salts and potassium salts.

As the bipyridine compound, 2,2'-
Examples include bipyridine and O-phenanthroline.

Examples of polycarbonyl compounds include acetylacetone and acetylacetic acid.

As the aromatic polyhydroxy compound,
Catechol, pyrogallol, 2-aminophenol, etc. are mentioned.

Of these, polyaminocarboxylic acid compounds and phosphonic acid compounds are preferred from the viewpoints of chelate stability, anti-clogging property of polishing debris, polishing rate and improvement of surface quality.

In the present invention, the chelating compound to be used may be used alone or in combination of two or more kinds. The content of the chelating compound in the polishing composition depends on the polishing rate. From the viewpoint of improving, it is preferably 0.05% by weight or more, more preferably 0.1% by weight or more, further preferably 0.2% by weight or more, and preferably 20% by weight from the viewpoint of improving the surface quality. Or less, more preferably 10% by weight or less, and further preferably 5
It is less than or equal to wt. The content is preferably 0.05 to 2
It is 0% by weight, more preferably 0.1 to 10% by weight, still more preferably 0.2 to 5% by weight.

In the present invention, clogging of the polishing pad with polishing debris is considered as one of the causes of the slow polishing rate of the oxide substrate (long processing time). It is presumed that it is sometimes adsorbed on the surface of the polishing debris, increasing the dispersibility of the polishing debris and suppressing the clogging of the pad, which makes it possible to maintain the original polishing rate of the polishing liquid and, as a result, reduce the processing time. It is estimated that it will be possible. Further, the chelating compound is presumed to be rapidly adsorbed on the surface of the polishing waste and prevent the adhesion of the polishing waste to the object to be polished, thereby showing the effect of improving the polishing rate and the surface quality of the object to be polished. It is estimated that

Further, additives other than the chelating compound may be added, and examples thereof include thickeners, dispersants, rust preventives, surfactants and the like.

The water in the polishing composition of the present invention is used as a medium, and the content thereof is preferably 20% by weight or more from the viewpoint of efficiently polishing an object to be polished.
It is more preferably 35% by weight or more, still more preferably 45% by weight or more, preferably 98.95% by weight or less, more preferably 96.9% by weight or less, still more preferably 94.8% by weight or less. . The content is preferably 20 to 98.95% by weight, more preferably 35 to 96.
It is 9% by weight, and more preferably 45-94.8% by weight.

The concentration of each component in the polishing composition may be either the concentration at the time of producing the composition or the concentration at the time of use. Usually, the composition is produced as a concentrated solution, and it is often used by diluting the composition.

From the viewpoint of improving the dispersibility of the colloidal silica particles and improving the surface quality, the pH of the polishing composition of the present invention is preferably 6 or more, more preferably 7 or more, still more preferably 8 or more. And preferably 12 or less, more preferably 11.5 or less, and further preferably 11 or less. The pH is preferably 6-1
2, more preferably 7 to 11.5, even more preferably 8
~ 11. The pH is a monomer such as an inorganic acid such as nitric acid and sulfuric acid, an organic acid such as formic acid and acetic acid, a metal salt such as lithium, sodium, potassium, calcium and nickel, an ammonium salt, an amine salt, hydrogen peroxide and the like. The basic substance such as the above-mentioned peroxide, ammonia, potassium hydroxide, sodium hydroxide, and amine can be adjusted by appropriately mixing them in desired amounts.

The oxide single crystal substrate targeted by the polishing composition of the present invention includes lithium tantalate, lithium niobate, doped products of these MgO and ZnO, sapphire, lithium tetraborate, and a chemical formula A ₃ BC. A single crystal substrate such as a Langasite compound represented by ₃ D ₂ O ₁₄ is preferable.

The shape of the object to be polished is not particularly limited. For example, a shape having a flat surface portion such as a disk shape, a plate shape, a slab shape, a prism shape, or a shape having a curved surface portion such as a lens is used for the polishing of the present invention. It becomes the object of polishing using the liquid composition.

The method for polishing an oxide single crystal substrate of the present invention is as follows:
Using the polishing liquid composition of the present invention, or a step of polishing the substrate to be polished by preparing a polishing liquid by mixing each component so that the composition of the polishing liquid composition of the present invention, An oxide single crystal substrate can be manufactured suitably.

As a polishing method using the polishing composition of the present invention, for example, the substrate is sandwiched by a polishing plate having a non-woven organic polymer polishing cloth attached thereto, and the polishing composition is supplied to the polishing surface. Examples include a method of polishing by moving a polishing disk or a substrate while applying a constant pressure. As a supply form of the polishing composition, from the viewpoint of economy, a circulation supply system in which the polishing composition is repeatedly used may be used.

The oxide single crystal substrate produced by the polishing method of the present invention has excellent surface quality with very few surface defects.

[0032]

EXAMPLES Example 1 A scanning electron microscope (S, manufactured by Hitachi, Ltd.) was used as an abrasive.
-4000 type) and a 50 wt% aqueous slurry (pH 9) of colloidal silica having an average particle size of 60 nm calculated by the method described in the detailed description of the invention was prepared. This colloidal silica 50% by weight aqueous slurry 52
Dissolve 100 g of ethylenediaminetetraacetic acid disodium as a chelating compound in 1150 g of ion-exchanged water to 00 g, add 25% ammonia water 50 g to adjust the pH to about 9, and sufficiently stir and mix. A slurry of wt% and disodium ethylenediaminetetraacetate 1.5 wt% was obtained. This slurry was diluted with ion-exchanged water to a volume of 2 times to obtain a polishing liquid-1.

Example 2 A scanning electron microscope (S, manufactured by Hitachi, Ltd.) was used as an abrasive.
The polishing liquid was prepared by the same method as in Example 1 except that colloidal silica having an average particle size of 100 nm calculated by the method described in the detailed description of the invention was used. This was designated as polishing liquid-2.

Example 3 A scanning electron microscope (S, manufactured by Hitachi, Ltd.) was used as an abrasive.
-4000 type) and a 50 wt% aqueous slurry (pH 9) of colloidal silica having an average particle size of 60 nm calculated by the method described in the detailed description of the invention was prepared. This colloidal silica 50% by weight aqueous slurry 52
To OO g, 166 g of a 60 wt% aqueous solution of 1-hydroxyethane-1,1-diphosphonic acid as a chelating compound
Was dissolved in 1022 g of ion-exchanged water, pH of which was adjusted to about 9 with 112 g of 25% ammonia water was added, and the mixture was sufficiently stirred and mixed, and 40% by weight of colloidal silica was added.
A slurry of 1.5% by weight of hydroxyethane-1,1-diphosphonic acid was obtained. This slurry was diluted with ion-exchanged water to a volume of 2 times to obtain a polishing liquid-3.

Comparative Example 1 A scanning electron microscope (S, manufactured by Hitachi, Ltd.) was used as an abrasive.
-4000 type) and a 50 wt% aqueous slurry (pH 9) of colloidal silica having an average particle size of 60 nm calculated by the method described in the detailed description of the invention was prepared. This colloidal silica 50% by weight aqueous slurry 52
To 300 g, 1300 g of ion-exchanged water was added and sufficiently stirred and mixed to obtain a slurry containing 40% by weight of colloidal silica. This slurry was diluted with ion-exchanged water to a volume of 2 times to obtain a polishing liquid-A.

Comparative Example 2 A scanning electron microscope (S, manufactured by Hitachi, Ltd.) was used as an abrasive.
The polishing liquid was prepared in the same manner as in Comparative Example 1 except that colloidal silica having an average particle size of 100 nm calculated by the method described in the detailed description of the invention was used. This was designated as Polishing Liquid-B.

<Polishing Test and Evaluation Method> A lithium tantalate substrate (thickness: 0.5 mm, diameter: 3 inches) was used as a work to be polished, and a polishing test was conducted under the following conditions for evaluation.

Polishing test Polishing object: Lithium tantalate substrate (thickness: 0.5 m
m, diameter: 3 inches) Polishing tester: Speedfam's 9B type double-sided polishing machine Polishing pad: Rodel Nitta's suba 800 Plate speed: 30r / min Slurry supply rate: 500ml / min (circulation supply method) Polishing time: 60 minutes Polishing load: 12.7 kPa Number of loaded substrates: 10

Evaluation / polishing speed: Determined from the weight change of the lithium tantalate substrate before and after polishing.・ Flatness (LTV: Local Thickness)
Variation, TTV: Total Thick
(Nest Variation): Measured over the entire area of the lithium tantalate substrate (diameter 3 inches) by "Laser interference type flatness measuring device FM100XR" manufactured by TROPEL.

The LTV represents the difference between the maximum value and the minimum value of the thickness (distance from the back reference plane to the surface) in a square divided area of 5 mm in length and 5 mm in width of the substrate fixed by suction. LT showing the maximum value at about 140 sites
The V value was evaluated. On the other hand, TTV represents the difference between the maximum value and the minimum value of the thickness of the suction-fixed substrate, and was evaluated by the TTV value over the entire substrate.

The smaller the values of LTV and TTV are, the higher the flatness is. The LTV is 1 μm or less, and T
A TV having a TV of 5 to 10 μm or less is a generally required level for an oxide single crystal substrate, and a TV having an LTV of 1 μm or less and a TTV of 5 μm or less is a passing product. -Scratch: evaluated by visual observation under irradiation with a halogen lamp. The results of these evaluations are shown in Table 1.

[0042]

[Table 1]

As is clear from the results shown in Table 1, those using the polishing liquid of the present invention have a high polishing rate, and no defects such as scratches are observed on the polished surface of the substrate, and high flatness is obtained. Having a high quality surface.

[0044]

EFFECTS OF THE INVENTION The polishing composition of the present invention has a high flatness mirror surface without causing surface defects such as scratches in precision polishing of an oxide single crystal substrate such as lithium tantalate or lithium niobate. The processed substrate can be efficiently manufactured.

Front page continuation (51) Int.Cl. ⁷ Identification code FI theme code (reference) C09K 3/14 C09K 3/14 550Z

Claims (3)

[Claims] 1. A group consisting of water, colloidal silica, and polyaminocarboxylic acid compounds, polyamine compounds, phosphonic acid compounds, bipyridine compounds, polycarbonyl compounds, aromatic polyhydroxy compounds, and salts thereof. A polishing liquid composition for an oxide single crystal substrate, which comprises at least one chelating compound selected from 2. A method for polishing an oxide single crystal substrate, which comprises polishing a substrate to be polished using the polishing composition of claim 1. 3. An oxide single crystal substrate obtained by polishing by the polishing method according to claim 2.