JP2001152134A - Composition and process for grinding oxide single crystal wafer - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain an abrasive composition for conducting efficient polishing processing of oxide single crystal wafers having relatively high hardness such as lithium tantalate, lithium niobate, or the like. SOLUTION: The abrasive composition for oxide single crystal wafers is a colloidal solution with a pH of from 8 to 11 which contains from 3 to 25 wt.% silica oxide particle and a component which imparts an electrical conductivity at 25 deg.C of >=10 mS/m per 1 wt.% silica oxide. Here, the silica oxide particle has an average primary particle size A, obtained from the specific area measured by BET method by calculating the particle as a sphere, of from 40 to 150 nm, and a ratio B/A of the average secondary particle size B, measured by laser-scattering method using microtrack UPA, to A of 1 or larger but smaller than 1.4. In a grinding process, this abrasive composition is used.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a mirror-finished surface of an oxide single crystal wafer such as lithium tantalate or lithium niobate widely used as a ferroelectric wafer serving as a substrate for a surface acoustic wave device or an electro-optical device. It relates to a method for polishing. In particular, the present invention uses a polishing composition mainly composed of an aqueous dispersion of colloidal silica having high electrical conductivity to form a hard oxide single crystal wafer made of lithium tantalate or lithium niobate at a high speed. The present invention relates to a method for performing mirror polishing with excellent surface roughness.

[0002]

2. Description of the Related Art With the rapid development of mobile communications such as mobile phones, cordless horns, and automobile phones in recent years, the production of oxide single crystal wafers made of lithium tantalate or lithium niobate has been rapidly increasing. Since these oxide single crystals such as lithium tantalate and lithium niobate have high hardness (5 to 6 in Mohs hardness), the polishing rate is low in a normal polishing method, and it takes nearly 10 hours to obtain a predetermined thickness. In some cases, polishing time is required, and low productivity and low efficiency have been pointed out.

[0003] As a general polishing method, for example, 10 of “Ultra-precision production technology system 2” (published by Fuji Techno System)
On page 25, "... a stable surface state is obtained by an alkali slurry based on colloidal silica. The average particle diameter of a commercially available product is 20 to 120 n.
m, pH 9.0 to 1 with organic amine, NaOH, etc.
Abrasives prepared at the 0.5 level have become widespread. There is a description, and this is a method used for polishing of a normal silicon wafer or the like almost directly followed, and at present, as described above, the low polishing rate by this method has been pointed out. Is what it is.

Conventionally, various polishing compositions have been proposed as polishing compositions for mirror-polishing an oxide single crystal comprising lithium tantalate and lithium niobate. For example, Japanese Unexamined Patent Publication (Kokai) No. 6-1988 discloses that an abrasive made of colloidal silica, colloidal alumina or colloidal zirconia is added with KOH and Na
It has been proposed to use OH, NaClO, Br-methanol in addition. However, the oxide single crystal composed of lithium tantalate and lithium niobate has a high hardness as described above, and is a very chemically stable compound. Is hardly eroded, so
Even if a mechanochemical polishing method is used, the polishing rate is hardly improved.

[0005] Japanese Patent Application Laid-Open No. 3-54287 proposes a polishing composition containing calcined alumina powder.
Further, in Japanese Patent Application Laid-Open No. H5-1279, the BET specific surface area is 10
In ~60m ² / g, a method of using as a polishing composition an aqueous slurry dispersion of precipitated silica secondary particle size of 0.5~5μm is proposed. However, these methods use abrasive grains with a relatively large average particle size, do not provide a high-precision mirror surface, and often generate scratches, with the aim of improving the polishing rate in final mirror surface finishing. It's not something that I did.

One method for improving the polishing rate is as follows.
There is also a method of increasing the concentration of abrasive grains as an abrasive.
However, if this method also exceeds a certain concentration, the polishing rate reaches a saturation value, the expected effect is not obtained, but rather the generation of scratches and the adverse effect on the polishing liquid circulation work become conspicuous, and the complete is not. Further, as a method for improving the polishing rate, a method using ultra-hard abrasive grains such as diamond and boron nitride can be considered, but it is difficult to obtain an ultrafine powder suitable for obtaining a final mirror surface.

[0007]

SUMMARY OF THE INVENTION In view of the above-mentioned problems of the prior art, the present inventors have proposed silicon dioxide (Si).
As a result of intensive research on a method of improving the polishing rate by a method based on using colloidal particles (hereinafter referred to as colloidal silica) of O ₂ : hereinafter referred to as silicon oxide) as polishing abrasives, An oxide composed of lithium tantalate or lithium niobate by placing colloidal silica having a certain range of particle diameters and secondary aggregation in a narrow range under certain conditions of conductivity and pH. The present inventors have found that a polishing composition suitable for mirror finishing of a single crystal wafer can be obtained, and have completed the present invention. That is, an object of the present invention is to provide a polishing composition suitable for performing mirror polishing at a high speed with extremely excellent surface roughness on the surface of an oxide single crystal wafer. Still another object of the present invention is to provide a method for mirror-polishing the surface of an oxide single crystal wafer using the polishing composition.

[0008] The above-mentioned object is to obtain an average primary particle diameter A of 40, which is calculated from the specific surface area measured by the BET method in terms of sphere.
And silicon oxide particles having a diameter ratio B / A of from 1 to 150 nm and an average secondary particle diameter B measured by a laser scattering method using a Microtrack UPA of 1 to less than 1.4,
A colloidal solution having a silicon oxide particle content of 3 to 25% by weight based on the entire solution, and a component for imparting conductivity such that the conductivity at 25 ° C. is 10 mS / m or more per 1% by weight of silicon oxide. Contains and pH is 8-11
And a polishing composition for an oxide single crystal wafer, wherein Further, another object of the present invention is to provide a polishing machine having a rotatable platen on which polishing pads made of synthetic resin foam, synthetic leather or nonwoven fabric are stuck on both upper and lower surfaces or one surface, an oxide single crystal wafer. By placing and pressing, while supplying the polishing composition according to claim 1 to claim 3, by rotating both or one of the platen and the oxide single crystal wafer, This is achieved by a method of performing polishing for the oxide single crystal wafer.

[0009]

DETAILED DESCRIPTION OF THE INVENTION The essential point of the present invention is that the average primary particle diameter of silicon oxide particles contained in the polishing composition used for polishing is 40 to 150 nm, and the secondary aggregation of the particles is as follows.
The ratio B / A of the diameter A of the primary particles to the diameter B of the secondary particles is 1.
It is in that it is less than 4, and furthermore, it is a liquid that has been given conductivity by adding a conductive component. This form of abrasive grains in the polishing composition, that is, by making it nearly monodisperse with little secondary agglomeration, there are no large particles that lead to the occurrence of defects such as scratches, extremely excellent finished surface roughness Is obtained, and the polishing rate can be remarkably improved by adding a conductive component.

In the present invention, the average primary particle diameter is measured using a value calculated in terms of a sphere from the specific surface area measured by the BET method, and the average secondary particle diameter is determined by Microtrac UPA (manufactured by Honeywell). The volume average particle diameter measured by the laser scattering method according to the present invention is used. When the average primary particle diameter of colloidal silica is 40 nm or less, the polishing rate is not sufficiently improved. When the average primary particle size exceeds 150 nm or more, defects such as scratches are likely to occur, and the finished surface roughness is not good, which is not preferable. Generally, when fine particles are aggregated, they tend to flocculate and become giant particles, but in the present invention, the ratio of the average primary particle diameter A to the average secondary particle diameter B, B / A, is less than 1.4. It is important to use what is in the point of being suppressed. When the ratio B / A of the particle diameters is 1.4 or more, scratches are likely to occur, and the effect is insufficient in that a finished surface having extremely excellent surface roughness is created.

The colloidal silicon oxide used in the present invention is:
Colloidal silica produced by dealkalization from water glass, colloidal silica obtained by hydrolyzing an organosilicon compound, colloidal silica obtained by dispersing fumed silica in water can be used, and the production method is particularly limited. Instead, extremely fine silicon oxide fine particles are dispersed in a colloidal state. The silica concentration during polishing is 3
It must be between ２５25% by weight, preferably between 10-18% by weight. When the silica concentration is 3% by weight or less, the polishing rate is low and the silica is not practical. When the silica concentration is 25% by weight or more, coarse aggregated particles are easily generated and scratches and the like are easily generated. If the concentration of silicon oxide during polishing increases, the polishing speed itself increases, but the value reaches a saturation value when it exceeds about 15% by weight.

In the present invention, the value of the conductivity per unit length (micro Siemens) is represented by a value converted to 1% by weight of silicon oxide, and the value at 25 ° C. is 10 mS / m / 1% -SiO _2. It is necessary to be above. Preferably, the polishing rate is further increased by setting it to 15 mS / m / 1% -SiO ₂ or more. The component for imparting conductivity to the polishing composition is not particularly limited, but at least one of alkali metal, choline, tetramethylammonium and ammonium salts can be used as an additive. Alkali metal, choline, tetramethylammonium or ammonium salt forms include fluoride, chloride, bromide, sulfate, nitrate, carbonate, bicarbonate, bromate,
Inorganic salts such as iodate, perchlorate, borate, phosphate, etc., and organic acid salts such as citrate, oxalate, tartrate, etc. From the viewpoint, nitrate is particularly preferable. These salts may be used in combination.

In the present invention, the polishing composition has a pH of 8
It is important to be within the range of ~ 11. When the pH is 8 or less, the polishing rate is remarkably reduced and is out of a practical range. Further, when the pH becomes 11 or more, the colloidal silica is out of the range of the present invention for the first time due to agglomeration, so that the stability of the polishing composition is lowered and also out of the practical range. Also, this pH should not readily change due to possible changes in external conditions, such as friction, heat, contact with the outside air, or mixing with other components. It is also effective to make the polishing composition solution itself a liquid having a small variation in pH with respect to a change in external conditions, that is, a so-called strong buffering action, for stabilizing and maintaining polishing performance. Salts effective for forming a solution having a strong buffering action include, for example, salts of carbonic acid, boric acid, phosphoric acid, citric acid, oxalic acid and tartaric acid.

In order to improve the physical properties of the polishing composition of the present invention and to improve the quality of the polished surface of the polished material, a surfactant, a dispersant and the like may be used in combination. Specific examples of the surfactant and the dispersant include water-soluble organic substances. Although the polishing composition of the present invention is in the form of an aqueous dispersion, an organic solvent may be added. The polishing composition of the present invention may be prepared by mixing colloidal silica, an alkali metal, choline, tetramethylammonium or ammonium salt, an additive, and water during polishing. In addition, as a colloidal silica, a concentrated composition of 15 to 65% may be prepared and used after being diluted with water or a mixture of water and an organic solvent.

The method for polishing the mirror surface of an oxide single crystal wafer made of lithium tantalate or lithium niobate using the polishing composition of the present invention is, for example, an SH-24 manufactured by Speedfam IPEC Co., Ltd.
And a DSM-12B type duplex machine. With these polishing apparatuses, the polishing composition of the present invention was used to maintain a polishing rate of a single oxide wafer of lithium tantalate, lithium niobate or the like at a constant high level, and also had an excellent finished surface roughness. A mirror surface can be obtained.

[0016]

EXAMPLES Next, the polishing composition of the present invention and the polishing method using the polishing composition of the present invention will be described specifically with reference to Examples and Comparative Examples, but the present invention is not particularly limited thereto. The equipment and conditions used for the polishing experiment are as follows. Polishing equipment: Doctor-made small table-top polishing machine, Doctor Wrap, made by Maruto Co., Ltd. Surface rotation speed: 82 RPM Polishing cloth: SUBA800 (manufactured by Rodel Nitta) Flow rate of polishing composition: 20 ml / min Processing load: 326 gf / cm ² Processing time: 30 Minute Workpiece: Simultaneous polishing of three pieces cut to 15 mm square The polishing rate was determined from the difference in weight before and after polishing. The pH of the polishing composition was measured using a pH meter. In the measurement, the pH electrode was calibrated in advance with pH standard solutions of pH 6.86 and 9.18, and then measured. The conductivity per 1% by weight of silicon oxide was used by dividing the value measured by a conductivity meter by the concentration of silicon oxide. Further, for the evaluation of the polished surface, the surface roughness (Ra) was measured using AFM.

Examples 1 to 10 and Comparative Examples 1 to 5 Tables 1, 2 and 3 show the compositions and physical properties of the polishing compositions used in the examples and comparative examples, and the polishing compositions obtained in accordance with the above methods. The results of the polishing test are also shown.

[0018]

[Table 1]

Table 1 shows the results of the example of the present invention in which the additive was added and the result of the comparative example in which the additive was not added. By adding an additive of a salt such as sodium chloride or sodium sulfate, the conductivity was increased in Examples 1 to 3.
As shown in the figure, it can be adjusted to a range of 10 mS / m-1% SiO ₂ or more, and a good polishing rate and surface roughness can be obtained. On the other hand, when no additive was added, the conductivity was less than 10 mS / m-1% SiO _{2 as} shown in Comparative Examples 1 and 2, and the polishing rate was about half the value of the example. Absent.

[0020]

[Table 2]

In Table 2, Comparative Examples 3 and 4 show the particle size ratio B /
A is an example in which A is larger than the present invention range 1.4,
Comparative Example 5 is an example in which the primary particle diameter is smaller than 40 nm, which is the range of the present invention. As is clear from the results in Table 2, when the particle size ratio B / A exceeds 1.4, scratches are generated, which is not preferable, and when the primary particle size is 40 nm or less, the polishing rate is reduced according to the present invention. About half of Examples 4 and 5, which is not preferable.

[0022]

[Table 3]

Table 3 shows examples in which the additives were nitrates or carbonates. In each case, a good polishing rate and surface roughness can be obtained.

[0024]

As can be seen from the results of the above Examples and Comparative Examples, when the polishing composition according to the present invention is used, for example, a mirror surface of a hard oxide single crystal wafer such as lithium tantalate or lithium niobate can be obtained. It is clear that a higher polishing rate than conventional one can be obtained in the final polishing, and it is possible to obtain a mirror-finished surface with high precision in terms of surface roughness. The polishing composition according to the present invention makes it possible to reduce the time and efficiency of the mirror finish polishing (polishing) process, which has conventionally required a great deal of time and labor, and this can be achieved, for example, in mobile communication. This greatly contributes to productivity improvement and cost reduction of surface acoustic wave devices and electro-optical devices, which are important components.

 ──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor Shinya Ichikawa 2647 Hayakawa Hayakawa, Ayase City, Kanagawa Prefecture Inside (72) Inventor Takahito Kojima 2647 Hayakawa Hayakawa, Ayase City, Kanagawa Prefecture Inside Speed Fam Ipec Corporation

Claims (4)

[Claims] 1. An average primary particle diameter A of 40 to 150 nm calculated as a sphere from a specific surface area measured by a BET method, and an average secondary particle diameter B measured by a laser scattering method using Microtrac UPA. Diameter ratio B / A is 1
A colloidal solution containing silicon oxide particles of at least 1.4 and having a total content of the silicon oxide particles of 3 to 25% by weight, and a conductivity at 25 ° C. of 1% by weight of silicon oxide
A polishing composition for an oxide single crystal wafer, comprising a component that imparts conductivity so as to be 10 mS / m or more per unit area, and having a pH of 8 to 11. 2. The polishing method for an oxide single crystal wafer according to claim 1, wherein the component imparting conductivity is at least one of alkali metal, choline, tetramethylammonium and ammonium salts. Composition. 3. The polishing composition for an oxide single crystal wafer according to claim 1, wherein the oxide single crystal wafer is a lithium tantalate or lithium niobate single crystal wafer. A polishing composition for an oxide single crystal wafer, which is characterized in that: 4. An oxide single crystal wafer is placed and pressed on a polishing machine having a rotatable platen having a polishing pad made of synthetic resin foam, synthetic leather or non-woven fabric adhered to both upper and lower surfaces or one surface, The oxide single crystal is formed by rotating both or one of the platen and the oxide single crystal wafer while supplying the polishing composition according to claim 1. A method for polishing a wafer.