JP3514397B2 - Method for producing composite oxide single crystal - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing a composite oxide single crystal from a melt, and more particularly to a method for producing a lithium niobate or lithium tantalate single crystal used in a surface acoustic wave device. Is.

[0002]

2. Description of the Related Art A composite oxide single crystal composed of two or more kinds of metal ions such as a lithium tantalate single crystal and a lithium niobate single crystal is a single crystal useful as a substrate for a surface acoustic wave (hereinafter abbreviated as SAW) device. Is usually the Czochralski method, that is, filling the raw material in the crucible,
It is manufactured by a method of heating and melting, bringing the seed crystal into contact with the surface of the raw material, and then pulling the seed crystal while rotating.
As a raw material composition in this case, for example, when a crystal is continuously pulled and grown for a lithium tantalate single crystal, as shown in FIG. 1 of Japanese Patent Publication No. 3-24438, the melt composition is crystallographically engineered. It is preferred to use a congruent composition which is defined as a match between the crystal composition and the crystal composition. However, as described in Japanese Patent Publication No. 3-24438, it is difficult to accurately determine the congruent composition. As a result, when the manufactured single crystal substrate is used as a SAW device, There was a large variation in manufacturing yield.

Usually, in the production of the above-mentioned composite oxide single crystal, a noble metal crucible is filled with a raw material having a congruent composition,
After performing crystal growth by the Czochralski method, for the next pulling growth, the crucible residual raw material is filled with the calcined powder or the growing crystal mass corresponding to the weight of the previously pulled and grown crystal, and the next batch of crystal is pulled up. Grow and continue to do the above. Therefore, if the raw material composition deviates from the true congruent composition, the crystal composition gradually changes as the number of continuous pulling increases, and SAW characteristic fluctuations within and between crystal batches increase, resulting in a decrease in device yield. Is said to lead to. Therefore, Japanese Patent Publication No. 3-24438
In the publication, the measured value of the Curie point of the grown crystal corresponding to the crystal composition is analyzed, the congruent composition is rigorously determined, and the final raw material composition is determined in consideration of the fluctuation record in the single crystal manufacturing process. There is.

However, even if the raw material composition is set to the optimum value in advance, for example, in the gadolinium gallium garnet single crystal manufacturing process, Ga ₂ O ₃ is grown during the raw material firing process and the melting of the raw material in the crucible during the crystal growth. Up to the above process, and Li ₂ O scatters during the same process in the lithium tantalate and lithium niobate single crystal manufacturing processes. Further, strictly speaking, this scattering amount is not always constant, and in the raw material firing step, for example, it varies depending on the firing temperature, the firing time, the particle size of the raw material, the degree of mixing of the raw materials, and the crucible is filled with the raw material in the crucible. It is considered that the size, the thickness of the crystal, the filling amount of the raw material, the flow rate of the atmosphere gas, and the time from the temperature rise to the contact with the seed crystal change, and it is not possible to establish a manufacturing method that keeps these conditions constant. This is very difficult industrially.

Further, the recent applications of lithium tantalate and lithium niobate single crystals are increasing in fields such as automobile phones and mobile phones whose operating frequency band exceeds 800 MHz.
It is said that the device yield will deteriorate unless the range of the sound velocity is further limited for use in this application. Therefore, there is an increasing demand for a substrate crystal in which the crystal composition corresponding to the speed of sound is strictly controlled. For this purpose, it is not possible to deal with the conventional management of the raw material composition alone, while the crystal is being manufactured, its crystal composition, or the physical property values closely related to the crystal composition are rapidly measured, and the melt composition of the next batch is measured. There is a demand for a specific method of feeding back to.

[0006]

DISCLOSURE OF THE INVENTION The present invention is a method for producing a composite oxide single crystal in which a composite oxide single crystal having a congruent composition is continuously grown from a melt by the Czochralski method, and particularly, the single crystal is Lithium niobate, Lithium tantalate, which provides a method for reproducibly producing a composite oxide single crystal having a crystal composition within a predetermined range by controlling the composition variation between crystal batches to a minimum. Is.

[0007]

That is, the present invention SUMMARY OF THE INVENTION may, upon growing the composite oxide single crystal having a congruent composition from the melt continuously by the Czochralski method, said plurality
The raw material of the compound oxide single crystal is melted by heating to pull up the single crystal.
Difference between the measured lattice constant and the target lattice constant.
The calculated, based on the difference, determine the oxides or carbonates of the metal components constituting the should be added a composite oxide single crystal
The present invention is directed to a method for producing a composite oxide single crystal, which comprises adding the compound oxide into a raw material for growing the composite oxide single crystal and then growing the next batch of the composite oxide single crystal. For example, in the next batch to the difference of the obtained lattice constant
Depends on the amount of crystal raw material used and single crystal pulling conditions
Adjust the deviation from the congruent composition by multiplying by a coefficient
Obtain the amount of raw material components and use this to grow a complex oxide single crystal.
The next batch of complex oxide single crystal after being added to the raw material
May grow. Next batch of complex oxide single crystals
The raw material is the firing raw material and the residue after pulling the single crystal of the previous batch.
Based on the difference in the lattice constant and the crystal raw material composed of
The oxide of the metal component that constitutes the obtained composite oxide single crystal was obtained.
Rui is considered to have carbonate added. Complex oxide single bond
If the crystal is a lithium tantalate single crystal, tantalum pentoxide
And lithium carbonate are added, and the composite oxide single crystal is niobium.
In the case of lithium oxide single crystal, niobium pentoxide or lithium carbonate
Um is added. Also, the initial composition of the firing material is
It is preferable to use a composition with more lithium than the gradient composition.
Good This will be described in more detail below.

The production of the single crystal according to the present invention is carried out by the Czochralski method, that is, by using a Czochralski method to form a complex oxide crystal composed of two or more kinds of metal ions such as gadolinium / gallium / garnet single crystal, lithium tantalate single crystal and lithium niobate single crystal. Fill the crucible with firing raw material, heat and melt,
After the seed crystal is brought into contact with the surface of the raw material, the seed crystal is pulled while rotating. In order to strictly control the crystal composition in the above, it is necessary to accurately grasp the crystal composition, but it is difficult to accurately analyze the amount of the metal element forming the composite oxide crystal. Further, as a physical property value for controlling the crystal composition, corresponding to the crystal composition,
Moreover, measuring the sound velocity, which is directly related to the device yield, takes a long measuring time after the pattern is formed on the substrate, and is not practical as a process control method of continuously pulling up. It takes a long time to measure the Curie temperature.

Therefore, the lattice constant is taken up as a physical property value which corresponds to the crystal composition and also to the sound velocity corresponding to the device characteristics. The relationship between the lattice constant and the speed of sound is disclosed in Japanese Patent Laid-Open No.
As disclosed in Japanese Patent Publication No. 1-128619, it is found that the desirable lattice constant range is 5.1534 to 5.1540 nm at a temperature of 25 ° C. in the a-axis direction of a lithium tantalate single crystal.
( × 10 ⁻¹ ) , but 5.15365 to 5.15395 nm ( × 10 ⁻¹ ) is preferable for further use in the frequency band in which the frequency exceeds 800 MHz. A single crystal having such a very limited and narrow lattice constant cannot be produced only by using a raw material having a congruent composition. Therefore, the present inventors cut out a sample from the single crystal grown for each batch, measure the lattice constant of the sample, find the deviation of the lattice constant from the target value, and obtain a crystal corresponding to the deviation found in advance. The present invention was completed by finding that a raw material composition having a composition close to the congruent composition can be obtained by adding the constituent raw material components to the raw material of the next batch.

As a composition close to the congruent composition, in the case of lithium tantalate or lithium niobate, the composition of Ta ₂ O ₅ or Nb ₂ O ₅ is easier to control than the addition of Li ₂ CO ₃ which tends to scatter. Since it is preferable to add
It is better to set the composition with more Li than the congruent composition as the initial composition. The composition of this firing material differs depending on the manufacturing method because the amount of Li ₂ O scattered depends on the single crystal pulling method, but in the case of lithium tantalate, Li / Ta = 0.942 ~
It is 0.944 (molar ratio), preferably Li / Ta = 0.943 (molar ratio).

Hereinafter, lithium tantalate will be described. The above-mentioned firing raw material, a crystal raw material consisting of the remaining melt after pulling the single crystal of the previous batch, and a melt consisting of Ta ₂ O ₅ in an amount determined with reference to the lattice constant value of the single crystal of the previous batch According to the Czochralski method, a single crystal having a congruent composition having a lattice constant in a target range can be obtained.

As the firing raw material, powders of Li ₂ CO ₃ and Ta ₂ O ₅ were weighed so that the molar ratio was Li / Ta = 0.943, and these were mixed.
What is baked at 900 ° C or higher may be used.

As a result of various studies on Ta ₂ O ₅ to be added, the addition amount can be obtained by the formula (1). Addition amount Ta ₂ O ₅ amount [g] = -Lattice constant [ nm ( × 10 ^-1 ) ]-5.15385) × Crystal raw material [g] × F …… Equation (1) where F is the crucible size and crystal Is a coefficient that depends on the outer diameter, the filling degree of the raw material, the flow rate of the atmospheric gas, and the time from the temperature rise to the seed crystal contact, and is a number that is experimentally obtained. The amount of lithium niobate added can also be determined by the same method as for lithium tantalate.

[0014]

As described above, the deviation of the congruent composition can be controlled more easily than the control of measuring the speed of sound and the Curie point. That is, the lattice constant of a sample cut out from a grown single crystal is measured, the amount of raw material component that adjusts the deviation from the congruent composition is calculated by the formula (1), and the amount of the raw material component is added to the raw material of the next batch. The lattice constant corresponding to can be controlled within a certain range.

[0015]

EXAMPLES Examples and comparative examples will be described below. Example: An iridium crucible with a diameter of 180 mm and a height of 180 mm has an outer diameter.
Place an iridium reflector on a donut plate with a diameter of 185 mm φ, an inner diameter of 130 mm φ, and a thickness of 2 mm.
A cylindrical after heater made of iridium with a diameter of 5 mm and a height of 180 mm was placed. Next, as batch 1, 6500 g of a firing raw material in which powders of Li ₂ CO ₃ and Ta ₂ O ₅ were mixed and fired in the crucible so that the composition ratio was Li / Ta = 0.943 (molar ratio), and the crystal raw material of the previous batch A total of 8500 g of 15000 g was charged, and after heating and melting, 10500 g of a 4-inch diameter lithium tantalate single crystal was pulled by the Czochralski method. A wafer with a thickness of 1 mm is cut out from the tail part of this crystal with an inner peripheral cutting machine.
The lattice constant in the a-axis direction was measured at 25 ° C.
It was 15380 nm ( × 10 ^-1 ) .

Next, as batch 2, 6300 g of a burning raw material having the same composition as batch 1, 2200 g of a crystalline raw material composed of the residual melt of batch 1, and F in the formula (1) were experimentally determined to be 40, which was obtained in batch 1. 4.4 g of Ta ₂ O ₅ obtained by calculating the formula (1) together with the value of the lattice constant of the obtained single crystal was charged into a crucible, and 8450 g of lithium tantalate single crystal was pulled by the Czochralski method. The lattice constant of this single crystal is 5.
It was 15378 nm ( × 10 ^-1 ) . In the same manner, batch 10 was performed as shown in Table 1. The results are shown in Table 1.

[0017]

[Table 1]

As shown in Table 1, the obtained lithium tantalate single crystal has a lattice constant of 5.15374 to 5.15383 nm ( ×
We were able to obtain a very narrow range of 10 ^-1 ) .

Comparative Example Five batches of lithium tantalate single crystal were prepared in the same manner as in Example except that additional Ta ₂ O ₅ based on the formula (1) was not added. The results are shown in Table 2.

[0020]

[Table 2]

As a result of Table 2, as a result of continuing pulling while using the firing raw material and the crystal raw material having a composition ratio of Li / Ta = 0.943 (molar ratio), the lattice constant of the obtained lithium tantalate single crystal was batch by batch. It became smaller, and in the fourth batch, it fell outside the target range of 5.15365 to 5.15395 nm ( × 10 ^-1 ) .

[0022]

According to the method of the present invention, the melt composition is strictly controlled, and the range of the lattice constant of the single crystal thus produced is, for example, in the case of lithium tantalate single crystal.
It can be set to an extremely narrow range of 5.15365 to 5.15395 nm ( × 10 ^-1 ) , and it becomes possible to manufacture a SAW device substrate crystal particularly suitable for applications where the operating frequency exceeds 800 MHz.

─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Toshihiko Nagao 2-13-1, Isobe, Annaka-shi, Gunma Shin-Etsu Chemical Co., Ltd. Precision Materials Research Laboratory (56) Reference JP-A-54-8199 ( JP, A) JP 61-128619 (JP, A) JP 1-122996 (JP, A) JP 6-48896 (JP, A) JP 3-24438 (JP, B2) (58) ) Fields investigated (Int.Cl. ⁷ , DB name) C30B 1/00-35/00

Claims (6)

(57) [Claims] 1. When a composite oxide single crystal having a congruent composition is continuously grown from a melt by the Czochralski method, a raw material of the composite oxide single crystal is melted by heating.
To pull up the single crystal and measure this lattice constant to set the target.
The difference between the lattice constant and the lattice constant is calculated.
Seeking oxides or carbonates of the metal components constituting the composite oxide single crystal can raw material for growing a composite oxide single crystal
A method for producing a composite oxide single crystal, which comprises growing the next batch of the composite oxide single crystal after being added therein. 2. When the composite oxide single crystal having a congruent composition is continuously grown from the melt by the Czochralski method , the raw material of the composite oxide single crystal is heated and melted.
To pull up the single crystal and measure this lattice constant to set the target.
Calculate the difference from the lattice constant and use this value for the next batch
Multiply a coefficient that depends on the amount of crystal raw material and the single crystal pulling conditions
Raw material components that adjust the deviation from the congruent composition
A method for producing a composite oxide single crystal, which comprises: determining an amount, adding this to a raw material for growing the composite oxide single crystal, and then growing the next batch of the composite oxide single crystal. 3. A raw material for a composite oxide single crystal is a firing raw material.
And the remaining melt after pulling the single crystal of the previous batch
Complex oxides obtained based on the difference in crystal raw materials and lattice constants
Add oxides or carbonates of the metal components that make up the single crystal.
The method for producing a composite oxide single crystal according to claim 1 or 2 , further comprising: 4. The method for producing a composite oxide single crystal according to claim 1, wherein the composite oxide single crystal is a lithium tantalate single crystal, and the added component is tantalum pentoxide or lithium carbonate. . 5. The method for producing a composite oxide single crystal according to claim 1, wherein the composite oxide single crystal is a lithium niobate single crystal, and the added component is niobium pentoxide or lithium carbonate. . 6. The firing raw material is more preferable than the congruent composition.
6. A composition containing a large amount of lithium as an initial composition.
The method for producing a composite oxide single crystal according to any one of claims .