JP6481589B2 - Polishing slurry for oxide single crystal substrate and method for producing the same - Google Patents

Description

  The present invention relates to a polishing slurry for an oxide single crystal substrate and a method for producing the same, and more specifically, the polishing rate can be improved by combining a specific additive with colloidal silica, such as lithium tantalate or lithium niobate. The present invention relates to a polishing slurry for an oxide single crystal substrate and a manufacturing method thereof.

  Surface acoustic wave devices are used in mobile communication devices (cell phones, smartphones, etc.), which have been rapidly expanding in recent years. As substrate materials, oxide single crystals such as lithium tantalate and lithium niobate are used. Has become an indispensable material.

  A substrate for a surface acoustic wave device is usually subjected to mirror polishing, and a polishing process called mechanochemical polishing (or simply polishing) is widely employed as a technique for the substrate. In mechanochemical polishing, a slurry in which fine silicon dioxide (silica particles) called colloidal silica is dispersed in water is used as an abrasive, and the surface is mirror-polished by pressing the substrate against a polishing pad made of nonwoven fabric or urethane (for example, , See Patent Document 1).

  According to Patent Document 1, since the wafer container is improved, excellent processing accuracy such as flatness can be obtained. However, oxide single crystals such as lithium tantalate (LT) and lithium niobate (LN) have Mohs hardness. Since the material has a high hardness of 5 to 6 and is extremely chemically stable, the polishing rate is very slow and sufficient productivity is not obtained.

In polishing of oxide single crystal substrates such as LT and LN, it is known that the additive in colloidal silica greatly affects the polishing rate.
For example, Patent Document 2 proposes a polishing composition containing, as an additive, uronic acid obtained by oxidation of aldose, and polishing by adding a chelating agent such as a chelating agent or an organic acid. It describes that the speed is improved. Among them, gluconate and DHEG (dihydroxyglycine) are supposed to show a high effect, whereas in the case of citric acid, the polishing rate is about 70% of gluconic acid. It indicates that it has not been done.

However, gluconic acid, which has good polishing performance, is an organic acid with a small amount of circulation, and the world production is less than 1/10 compared with citric acid. Although the risk of a supply shortage due to the distribution volume of gluconic acid is low, considering the future market expansion of mobile communication devices, it is necessary to select raw materials with a higher distribution volume and reduce the supply risk .
In addition, DHEG is much less expensive and more expensive than organic acids such as gluconic acid and citric acid. Electronic component materials such as LT and LN are highly cost-competitive, and using expensive raw materials such as DHEG is problematic in terms of cost.

  Under such circumstances, it is possible to reduce the supply risk by selecting raw materials with a large amount of circulation, and there is no cost problem, but also high hardness such as lithium tantalate and lithium niobate, and extremely chemically There is a need for a polishing slurry containing colloidal silica that can increase the polishing rate of a stable oxide single crystal material and improve productivity.

JP 2011-206871 A JP 2006-150482 A

  An object of the present invention is to provide a polishing slurry for an oxide single crystal substrate such as lithium tantalate or lithium niobate, which has an improved polishing rate by combining a specific additive with colloidal silica, and a method for producing the same. is there.

  In order to achieve the above object, the present inventor conducted intensive studies on the influence on the polishing rate by mixing an additive exhibiting a chelating action and an additive exhibiting an aggregating action. As a result, only citric acid was added. Then, although it did not reach the polishing rate of gluconic acid, it was found that a polishing rate equivalent to that of gluconic acid can be obtained by mixing citric acid and sulfate, and the present invention has been completed.

That is, according to the first aspect of the present invention, there is provided a slurry for polishing an oxide single crystal substrate containing colloidal silica having an average particle size of 100 nm or less as abrasive particles and containing a citric acid compound as an additive, It contains a sulfate as an agent, the citrate compound is sodium citrate or potassium citrate, the sulfate is sodium sulfate or potassium sulfate, and the addition amount of the citrate compound is 0.01 relative to the slurry . There is provided a slurry for polishing an oxide single crystal substrate , which is ˜0.12 mol / L and the addition amount of the sulfate is 0.02 mol / L or less with respect to the slurry .

According to a second aspect of the present invention, there is provided the slurry for polishing an oxide single crystal substrate according to the first aspect, wherein the concentration of the colloidal silica is 10 to 50% by mass. .

According to a third invention of the present invention, in the first invention, the oxide single crystal substrate is an oxide single crystal wafer of lithium tantalate or lithium niobate. A slurry for polishing a crystalline substrate is provided.

According to a fourth aspect of the present invention, in any one of the first to third aspects, the citric acid compound as an additive is added to the slurry containing colloidal silica having an average particle diameter of 100 nm or less in an amount of 0. Oxide single crystal characterized in that it is set in the range of 01 to 0.12 mol / L, adjusted according to the average particle diameter of colloidal silica, added, and then sulfate is added and mixed until uniform A method for producing a slurry for polishing a substrate is provided.

According to the fifth invention of the present invention, the slurry for polishing an oxide single crystal substrate according to any one of the first to third inventions is used, and the slurry is supplied to the oxide single crystal substrate attached to the polishing apparatus. A method for polishing an oxide single crystal substrate, which is characterized in that polishing is performed.

According to the present invention, a specific additive is blended with colloidal silica for use in mirror polishing of an oxide single crystal substrate. However, since the additive is relatively inexpensive and easily available, the supply risk is low. A polishing slurry capable of obtaining a high polishing rate can be provided.
Further, since the amount of the additive relative to the colloidal silica is small, the manufacturing cost of the polishing slurry can be suppressed.

  Hereinafter, specific embodiments of the polishing slurry for an oxide single crystal substrate of the present invention will be described in detail. It should be noted that the present invention is not limited only to the following embodiments without departing from the object of the present invention.

1. Polishing slurry for oxide single crystal substrate The slurry for polishing an oxide single crystal substrate of the present invention contains colloidal silica having an average particle diameter of 100 nm or less as abrasive particles, contains a citric acid compound and a sulfate as additives, and The citrate ion concentration is 0.01 to 0.12 mol / L.

  That is, the polishing slurry composition in the present invention mainly comprises colloidal silica, a chelating agent (citrate), sulfate, and water.

(1) Colloidal silica The colloidal silica preferably has an average primary particle diameter of 100 nm or less. This is because colloidal silica having an average particle size larger than 100 nm does not have a high polishing ability of the object to be polished. The average particle diameter of colloidal silica is more preferably 25 nm or more and 90 nm or less.

  The particle diameter of the silica particles is preferably in the range of 5 to 150 nm, more preferably in the range of 10 to 140 nm. Here, the particle diameter of the silica particles is obtained by directly measuring the particle diameter from observation images of a BET method, a dynamic light scattering method (DLS method), a scanning electron microscope (SEM), or a transmission electron microscope (TEM). be able to. The method for measuring the particle diameter is not particularly limited, but there may be a case where the measured value varies between the methods.

  That is, in the BET method, when the particles are aggregated, the specific surface area becomes small, so that there is a tendency to be measured smaller than the actual particle diameter. In the DLS method, when the particles are aggregated, the lump is detected as one particle, so that there is a tendency that small particles are not detected and large particles that are not actually included are detected. In SEM, if the particles are biased in the process of drying the sample, the particle size distribution may shift. In addition, in TEM, since it is necessary to dilute at a magnification smaller than the above three methods, aggregation and unevenness of particles may occur in the dilution process. For this reason, the above-mentioned particle size takes into account a measurement error of a maximum of 20%.

  In the present invention, the particle diameter may be measured by any method, but the particle diameter is accurately measured so that the measurement error due to the above problem is reduced. In the present invention, it is preferable to use SEM from the viewpoint that the most stable measurement value can be obtained.

  In the present invention, the silica particles can be produced by a water glass method or an alkoxide method. However, these are merely examples of a method for producing a colloidal silica slurry, and any other known method can be employed in the present invention.

  The concentration of colloidal silica is not particularly limited, but if it is less than 10% by mass, the silica fine particles and the object to be polished are not sufficiently in contact with each other, and the original polishing ability may not be exhibited. On the other hand, if it is larger than 50% by mass, the dispersion stability of the silica fine particles is lowered, and the colloidal silica may be aggregated. Therefore, the concentration of colloidal silica is preferably 10% by mass or more and 50% by mass or less, and more preferably 15% by mass or more and 30% by mass or less. Yes.

(2) Citric acid compound As described above, gluconic acid is known as a chelate having good polishing performance, but it is an organic acid having a smaller circulation amount than citric acid. Although there is no high risk of a supply shortage due to the current distribution volume of gluconic acid, considering the future market expansion of mobile communication devices, we will select raw materials with a higher distribution volume and reduce supply risks. It is necessary to connect to.

  For this reason, in this invention, a citric acid compound with much circulation is used as a chelate additive. The citric acid compound refers to citric acid that generates citrate ions when dissolved in water, or an alkali metal salt of citric acid, and acts as a chelating agent. Hereinafter, it is also simply referred to as citric acid.

Specific examples include trisodium citrate, monosodium citrate, disodium citrate, or alkali metal salts such as monopotassium citrate, dipotassium citrate, tripotassium citrate, and lithium citrate. In addition, citrate metal salts such as calcium citrate, magnesium citrate, copper citrate, and ammonium iron citrate can also be used.
In the present invention, the various sodium citrates and potassium citrates are preferable from the viewpoint of being inexpensive, safe and easy to handle.

  Since citric acid has a higher concentration and a higher polishing rate, it is 0.01 mol / L or more, preferably 0.03 mol / L or more. However, since excessive addition causes gelation of colloidal silica and decreases the polishing rate, the citrate ion concentration should not exceed 0.12 mol / L. 0.03-0.10 mol / L is preferable and 0.03-0.08 mol / L is more preferable.

  Colloidal silica has a tendency to be easily gelled as the particle size is large, and this is considered to be because the influence of gelation by the additive is strongly influenced as the particle size is large. Since citric acid has a chelating action, the amount of citric acid added to colloidal silica varies depending on the particle size of the silica. For example, when comparing the case where the particle diameter of silica is 60 nm and 80 nm, the applicant has confirmed that it is easier to improve the polishing rate with a smaller addition amount when the particle diameter is 80 nm than when it is 60 nm.

(3) Sulfate In the present invention, examples of the sulfate include a compound of sulfuric acid and an alkali metal such as sodium sulfate, potassium sulfate, and lithium sulfate. In addition, beryllium sulfate, magnesium sulfate, calcium sulfate, and the like can be used. Since it suffices to generate sulfate ions by dissolving in water, sulfuric acid or sodium hydrogen sulfate can be used if the pH is adjusted.
In the present invention, sodium sulfate and potassium sulfate are preferred from the viewpoints of being inexpensive and requiring no pH adjustment.

  The citric acid compound exerts a chelating action on metal ions, but since sulfates give an aggregating action, the action mechanism for improving the polishing rate is different. Thus, it has hardly been studied to mix persons having different action mechanisms.

The present invention is intended to obtain a polishing rate improvement effect equal to or higher than that of gluconic acid by mixing a specific amount of citric acid and sulfate, and is high while reducing the supply risk of chelating additives. It is possible to obtain a polishing rate.
The addition amount of the sulfate is not particularly limited, and the sulfate ion concentration is 0.005 mol / L or more as a guide, but 0.020 mol / L or less is preferable. Even if it exceeds this, since the effect is not improved, 0.015 mol / L or less is preferable.

In the case of citric acid, as described above, since it has a chelating action, the amount of addition to colloidal silica is changed depending on the particle size of silica. However, such knowledge is not obtained with sulfate.
Considering the polishing effect of the sulfate inhibiting the gelation of colloidal silica by citric acid, even if the silica particle size is compared between 60 nm and 80 nm as described above, There seems to be no big difference.

2. Manufacturing method of polishing slurry The polishing slurry manufacturing method of the present invention sets the amount of a citric acid compound as an additive in a range of 0.01 to 0.12 mol / L with respect to colloidal silica having an average particle size of 100 nm or less. And adjusting and adding according to the average particle diameter of colloidal silica, and then adding a sulfate and mixing until uniform.

  That is, colloidal silica in which silica particles are dispersed in water is first prepared. Silica particles that are raw materials for colloidal silica are generally produced by a water glass method and an alkoxide method.

The water glass method is a technique in which sodium silicate is ion-exchanged to adjust active silicon, and then this is added to a seed particle-containing aqueous solution whose pH is adjusted with caustic soda under heating to grow particles. The alkoxide method is a method for producing silica particles while hydrolyzing an alkyl silicate (tetraalkoxysilane) in the presence of a basic catalyst and simultaneously performing condensation and particle growth. In addition, for relatively large particles of 100 nm or more, a method can be used in which large silica particles are prepared in advance, and then pulverized and classified to make the particle diameter uniform.
And a desired particle size distribution can also be obtained in a manufacturing stage by control of temperature, pH, etc. Thus, colloidal silica in which silica particles having an average particle diameter of 100 nm or less are dispersed in water or the like is obtained.

  The obtained colloidal silica may be used alone or in combination of two or more. For example, a predetermined amount of two kinds of silica particles A having an average particle diameter of 60 nm or less and silica particles B having an average particle diameter of 110 nm or more are mixed, or silica particles C having an average particle diameter of 50 to 90 nm are added thereto. The three kinds can be produced by mixing a predetermined amount.

  Next, the addition amount of the citric acid compound is set in the range of 0.01 to 0.12 mol / L with respect to the colloidal silica. In order to improve the polishing rate, it is necessary to set it to 0.03 mol / L or more. On the other hand, if it is added excessively, gelation of colloidal silica is caused and the polishing rate is lowered. / L or less is desirable.

  Since citric acid has a chelating action, the amount added to the colloidal silica varies depending on the particle size of the silica, so the amount added is adjusted according to the average particle size of the colloidal silica.

  Specifically, when the silica particle size is 60 nm and 80 nm, the 80 nm particle size can improve the polishing rate with a smaller amount of citric acid than the 60 nm particle size. It is preferable to increase or decrease the set value in the range of 0.01 to 0.03 mol / L.

  Then, add sulfate and mix well until homogeneous. By adding the sulfate subsequent to citric acid, gelation of colloidal silica by citric acid is suppressed. The mixing apparatus and stirring conditions may be general and are not particularly limited. Although it may be normal temperature, you may heat to about 30-80 degreeC.

  When sulfate is added to a citric acid compound, the higher the concentration, the greater the effect of improving the polishing rate. However, the sulfate ion concentration is preferably 0.020 mol / L or less. This is because the polishing effect is not improved even if the amount exceeds this, and 0.015 mol / L or less is more preferable.

3. Polishing Method of Oxide Single Crystal Substrate In order to polish an oxide single crystal substrate using the polishing slurry of the present invention, the substrate is attached to a substrate (wafer) housing portion of a polishing apparatus with wax or the like and then polished. A polishing cloth is affixed to the upper surface of the surface plate, and the polishing slurry is supplied onto the polishing cloth for polishing.

The object to be polished is an oxide single crystal substrate such as LT or LN. The size is not particularly limited, and it can be polished from a small size of 4 inches or less to a large size exceeding 5 inches.
The polishing surface plate is rotationally driven at an arbitrary rotational speed by a motor control or the like via a drive shaft connected to the surface plate.

  Then, while rotating the polishing platen, the polishing slurry is supplied onto the polishing cloth, and the pressing mechanism is rotated in the opposite direction to the polishing platen, so that the mirror surface of the wafer substrate surface pressed against the polishing cloth Polishing is performed.

Although the rotation speed of a surface plate is based also on the kind of apparatus etc., it can be 50-200 rpm, for example, and a grinding | polishing load can be 300-800 g / cm < ² >.
The polishing time is difficult to define, but can be set to, for example, 30 to 120 minutes. In the present invention, as described above, since a polishing slurry in which a specific amount of citric acid and sulfate is mixed is used, remarkable polishing performance can be obtained by the chelating effect of citric acid and the gelation suppression effect of colloidal silica by sulfate. Polishing is sufficiently performed, and the polishing process is terminated when the substrate reaches a predetermined thickness. Since the polishing slurry of the present invention has a high polishing rate, depending on the type of substrate, polishing may be completed within 30 minutes.

  As mentioned above, although the method of grind | polishing the board | substrate of LT or LN was described, since it is said that the grinding | polishing mechanism is the same also in the case of sapphire by colloidal silica, the polishing slurry of this invention should be used also for grinding | polishing of a sapphire board | substrate similarly. Can do.

  Examples of the present invention will be specifically described below in comparison with comparative examples. However, the present invention is not limited to these examples.

  In the following examples, polishing was performed under the conditions shown in Table 1, and the substrate thickness after polishing was measured with a micrometer, and the polishing rate was calculated for evaluation.

(Examples 1-5)
What prepared colloidal silica with an average particle size of 60 nm to 20% by mass (manufactured by Sumiishi Materials Co., Ltd., CMP-30CN) was prepared, and organic acid trisodium citrate (Fuso Chemical Industries ( Polishing of the present invention by mixing with “purified sodium citrate”) and sodium sulfate (“neutral anhydrous sodium sulfate” manufactured by Shikoku Kasei Kogyo Co., Ltd.) in an amount uniform as shown in Table 2. A slurry was prepared.
Next, a 4-inch lithium tantalate substrate was prepared as a polishing material in a polishing apparatus (SPM-12 manufactured by Fujikoshi Machine Industry Co., Ltd.) and attached to a block using wax. Thereafter, SUBA800 manufactured by Rodel Co., Ltd. was used as a polishing pad, the polishing material was polished under the conditions shown in Table 1, and the effect of improving the polishing rate of each additive added to colloidal silica was evaluated. The results are shown in Table 2.

(Comparative Example 1)
What prepared the colloidal silica whose average particle diameter is 60 nm same as Example 1 in 20 mass% was prepared, and it was set as the polishing slurry, without using any additive. Polishing was performed under the conditions shown in Table 1 in the same manner as in Example 1. The results are shown in Table 2.

(Comparative Examples 2 to 4)
The amount shown in Table 2 was mixed with the slurry of Comparative Example 1 using potassium gluconate of an organic acid salt (“Potassium Gluconate” manufactured by Wako Pure Chemical Industries, Ltd.) as a chelating agent. Polishing was performed under the conditions shown in Table 1 in the same manner as in Example 1. The results are shown in Table 2.

(Comparative Examples 5-7)
The slurry of Comparative Example 1 was mixed with DHEG (dihydroxyglycine (“Kyrest GA” manufactured by Chubu Kirest Co., Ltd.)) as a chelating agent in the amounts shown in Table 2. As in Example 1, Table 1 was used. The results are shown in Table 2.

(Comparative Examples 8 to 10)
The slurry of Comparative Example 1 was mixed with organic acid trisodium citrate (“Purified Sodium Citrate” manufactured by Fuso Chemical Industry Co., Ltd.) as a chelating agent in the amounts shown in Table 2. Polishing was performed under the conditions shown in Table 1 in the same manner as in Example 1. The results are shown in Table 2.

(Comparative Examples 11-13)
The slurry of Comparative Example 1 was mixed in the amount shown in Table 2 using sodium sulfate (“Neutral anhydrous sodium sulfate” manufactured by Shikoku Kasei Kogyo Co., Ltd.) without using a chelating agent. Polishing was performed under the conditions shown in Table 1 in the same manner as in Example 1. The results are shown in Table 2.

(Comparative Examples 14-16)
To the slurry of Comparative Example 1, potassium sulfate (“Potassium sulfate, powder” manufactured by Wako Pure Chemical Industries, Ltd.) was used in the amount shown in Table 2 without using a chelating agent. Polishing was performed under the conditions shown in Table 1 in the same manner as in Example 1. The results are shown in Table 2.

(Examples 6 to 10)
Instead of colloidal silica having an average particle size of 60 nm used in Example 1, colloidal silica having an average particle size of 80 nm adjusted to 20% by mass (Nissan Chemical Co., Ltd., Snowtex YL) was added. As the chelating agent, trisodium citrate, an organic acid salt as a chelating agent ("purified sodium citrate" manufactured by Fuso Chemical Industry Co., Ltd.), and sodium sulfate ("neutral anhydrous sodium sulfate" manufactured by Shikoku Chemicals Co., Ltd.) as a flocculant ) And mixed so as to be uniformly dispersed in the amount shown in Table 2 to prepare a polishing slurry of the present invention.
Next, a 4-inch lithium tantalate substrate as a polishing material was affixed to the block with a wax in a polishing apparatus (SPM-12 manufactured by Fujikoshi Machine Industry Co., Ltd.). Thereafter, SUBA800 manufactured by Rodel Co., Ltd. was used as a polishing pad, the grinding material was ground under the conditions shown in Table 1, and the effect of improving the polishing rate of each additive added to colloidal silica was evaluated. The results are shown in Table 2.

(Examples 11 to 12)
Instead of trisodium citrate used in Examples 1 to 5, tripotassium citrate of an organic acid salt (“Wood Pure Chemical Industries, Ltd.“ Tripotassium citrate monohydrate ”) was used as a chelating agent. Sodium sulfate (“Medieval anhydrous sodium sulfate” manufactured by Shikoku Kasei Kogyo Co., Ltd.) was used as the flocculant, and mixed so as to be uniform in the amounts shown in Table 2 to prepare the polishing slurry of the present invention.
Next, a 4-inch lithium tantalate substrate was prepared as a polishing material in a polishing apparatus (SPM-12 manufactured by Fujikoshi Machine Industry Co., Ltd.) and attached to a block using wax. Thereafter, SUBA800 manufactured by Rodel Co., Ltd. was used as a polishing pad, the polishing material was polished under the conditions shown in Table 1, and the effect of improving the polishing rate of each additive added to colloidal silica was evaluated. The results are shown in Table 2.

(Examples 13 to 14)
Instead of sodium sulfate used in Examples 1 to 5, potassium sulfate ("potassium sulfate, powder" manufactured by Wako Pure Chemical Industries, Ltd.) was used as a flocculant, and sodium citrate (Fuso Chemical Industries ( Co., Ltd. “purified sodium citrate”) was used and mixed so as to be uniform in the amounts shown in Table 2 to prepare the polishing slurry of the present invention.
Next, a 4-inch lithium tantalate substrate was prepared as a polishing material in a polishing apparatus (SPM-12 manufactured by Fujikoshi Machine Industry Co., Ltd.) and attached to a block using wax. Thereafter, SUBA800 manufactured by Rodel Co., Ltd. was used as a polishing pad, the polishing material was polished under the conditions shown in Table 1, and the effect of improving the polishing rate of each additive added to colloidal silica was evaluated. The results are shown in Table 2.

"Evaluation"
The following can be seen from Table 2 showing the results of Examples and Comparative Examples. Although the target value of the polishing rate is 0.42 μm / min, there is no practical problem if it is about 0.40 μm / min.

When colloidal silica having an average particle diameter of 60 nm is used, as compared with Comparative Example 1 that does not contain an additive, as Comparative Examples 5 to 7 show, the polishing rate improved with increasing amount of addition in DHEG. No improvement in speed was observed at 06 mol / L or more.
In addition, as Comparative Examples 2 to 4 and Comparative Examples 8 to 10 showed that the polishing rate improved with increasing amount of addition of potassium gluconate and trisodium citrate, but at 0.06 mol / L or more, the rate increased. A decrease was seen. When the addition concentration is 0.12 mol / L, gelation of colloidal silica can be confirmed, and it is considered that the polishing rate is reduced. Among Comparative Examples 2 to 10, Comparative Examples 3, 6, and 7 had a polishing rate of 0.43 μm / min. The result of Patent Document 2 was reproduced. However, as mentioned above, there are concerns about supply concerns.

  In Comparative Examples 11 to 16 to which only the sulfate was added, a slight improvement in the polishing rate was observed although not as much as the chelating agent or the organic acid salt. The polishing rate was improved by adding a flocculant such as sulfate to colloidal silica, and the polishing rate was improved as the addition amount was increased, but no improvement in the rate was observed at an addition concentration of 0.01 mol / L or more. It was.

  Examples 1-5 showed the high grinding | polishing rate in each trisodium citrate density | concentration compared with Comparative Examples 8-10, and have confirmed the synergistic effect by mixing with sodium sulfate. Compared to Comparative Example 3 (potassium gluconate 0.06 mol / L), Comparative Example 9 (trisodium citrate simple substance 0.06 mol / L) was 9% inferior in polishing rate, whereas Example 3 (Quen Trisodium acid 0.06 mol / L + sodium sulfate 0.01 mol / L) had an equivalent polishing rate. In Examples 1 to 5, the polishing rate was improved as the amount of trisodium citrate added was increased, but in Examples 4 and 5 at 0.06 mol / L, a reduction in the polishing rate was observed. This is the same tendency as in Comparative Example 10.

Examples 6 to 10 are the results of comparison with colloidal silica having an average particle diameter of 80 nm, but Example 8 shows a polishing rate equivalent to that of Example 3, and the trisodium citrate and sodium sulfate It was confirmed that the effect of mixing appeared regardless of the particle size of colloidal silica.
However, it was confirmed that the colloidal silica having an average particle diameter of 80 nm was gelled at a lower additive concentration than the colloidal silica having an average particle diameter of 60 nm. It is considered that colloidal silica has a tendency to be easily gelled as the particle size is large, and that the influence of gelation by the additive is strongly influenced as the particle size is large.

  Therefore, in the present invention, the concentration of the citric acid compound added to the colloidal silica is 0.01 to 0.12 mol / L. However, when the silica particle diameter is too large or the additive concentration is too high, the polishing rate by gelation is used. Colloidal silica having an average particle diameter of 100 nm or less is used so as not to cause a decrease, and the addition amount is 0.06 mol / L or less, and depending on the particle diameter, the addition concentration is suppressed to 0.03 mol / L or less, and sulfate is added. Can be polished under more optimal conditions.

  Examples 11-14 are the results when the trisodium salt of citric acid was changed to the tripotassium salt, or the sodium salt of sulfuric acid was changed to the potassium salt of sulfuric acid. A polishing rate equivalent to that of Example 1 and Example 3 where the ion concentration was the same was obtained. That is, in the present invention, it is important to contain citrate ions and sulfate ions, and it can be said that any salt may be used.

  The polishing slurry of the present invention can be used when mirror-polishing an oxide single crystal substrate, and contributes to productivity improvement.

Claims (5)

An oxide single crystal substrate polishing slurry containing colloidal silica having an average particle size of 100 nm or less as abrasive particles and containing a citric acid compound as an additive,
Furthermore, it contains sulfate as an additive,
The citric acid compound is sodium citrate or potassium citrate;
The sulfate is sodium sulfate or potassium sulfate;
That the addition amount of the citric acid compound is a 0.01~0.12mol / L with respect to the slurry, and the addition amount of the sulfate is not more than 0.02 mol / L with respect to the slurry A slurry for polishing an oxide single crystal substrate.   2. The slurry for polishing an oxide single crystal substrate according to claim 1, wherein the concentration of the colloidal silica is 10 to 50 mass%.   The slurry for polishing an oxide single crystal substrate according to claim 1, wherein the oxide single crystal substrate is an oxide single crystal wafer of lithium tantalate or lithium niobate. Against slurry containing an average particle diameter 100nm or less of the colloidal silica, the amount of the citric acid compound is set in a range of 0.01~0.12mol / L as an additive, the average particle diameter of the colloidal silica Adjust according to the addition,
Next, the said sulfate is added and it mixes until it becomes uniform, The manufacturing method of the slurry for oxide single crystal substrate polishing in any one of Claims 1-3 characterized by the above-mentioned. The oxide single crystal substrate polishing according to any one of claims 1 to 3 , wherein polishing is performed while supplying the slurry to the oxide single crystal substrate attached to a polishing apparatus. A method for polishing a substrate.