JP2022050890A - Manufacturing method of oxide single crystal wafer - Google Patents

Abstract

To provide a manufacturing method of an oxide single crystal wafer capable of increasing a number of single crystal ingots produced from single seed crystal and improving a productivity of a single crystal wafer per seed crystal.SOLUTION: A manufacturing method of an oxide single crystal wafer according to the invention includes the steps of: forming a neck part 9a while a seed crystal 7 is lifted after contacting the seed crystal 7 to a raw material melt 8; growing a single crystal ingot 9 under the neck part 9a; cutting/separating the seed crystal 7 and the single crystal ingot 9 at a mid of the neck part 9a to prepare a seed crystal with a left part neck 9a of 4 mm or more in length; and preparing a single crystal wafer by slicing the single crystal ingot 9.SELECTED DRAWING: Figure 1

Description

The present invention relates to a method for producing an oxide single crystal wafer from an oxide single crystal produced by the Czochralski method.

There is a Czochralski method (CZ method) as a method for producing an oxide single crystal (see, for example, Patent Document 1). The CZ method is a method for growing a single crystal by bringing a seed crystal into contact with a raw material melt and pulling it up at a predetermined speed, and is a method widely used industrially.

Japanese Unexamined Patent Publication No. 2020-1937

When the seed crystal is brought into contact with the melt, the melt erodes the seed crystal due to surface tension, so that the seed crystal becomes shorter with repeated use. Therefore, the number of single crystal ingots produced from one seed crystal is about 3 to 4, and the productivity of the single crystal ingot per seed crystal is poor. Therefore, it was necessary to prepare a large amount of seed crystals at the manufacturing site. Then, it has been desired to improve the productivity of the single crystal ingot per seed crystal.

Therefore, the present invention provides a method for producing an oxide single crystal wafer, which can increase the number of single crystal ingots that can be produced from one seed crystal and improve the productivity of the single crystal wafer per seed crystal. With the goal.

The present invention provides the following method for producing an oxide single crystal wafer in order to achieve the above object. That is,
[1] A step of forming a neck portion while pulling up the seed crystal after contacting the seed crystal with a raw material melt, a step of growing a single crystal ingot under the neck portion, the seed crystal and the single crystal ingot. A step of cutting and separating the seed crystal in the middle of the neck portion to produce a seed crystal in which a part of the neck portion remains with a length of 4 mm or more, and a step of slicing the single crystal ingot to produce a single crystal wafer. A method for manufacturing an oxide single crystal wafer including.
[2] The oxide single crystal according to the above [1], in which the step of producing a seed crystal in which a part of the neck portion remains is cut and separated with the seed crystal having a neck portion having a length of at least 6 mm or more. Wafer manufacturing method.
[3] The step of forming the neck portion is the method for producing an oxide single crystal wafer according to the above [1] or [2], wherein the neck portion has a length of 10 mm or more.
[4] A step of bringing the neck portion remaining in the seed crystal into contact with the raw material melt and then growing the neck portion while pulling up the seed crystal, a step of growing a single crystal ingot under the neck portion, the seed. A step of cutting and separating a crystal and the single crystal ingot in the middle of the neck portion to produce a seed crystal in which a part of the neck portion remains, and slicing the single crystal ingot to prepare a single crystal wafer. The method for producing an oxide single crystal wafer according to any one of the above [1] to [3], further comprising a step.
[5] The method for producing an oxide single crystal wafer according to any one of the above [1] to [4], wherein the oxide single crystal is lithium tantalate or lithium niobate.

According to the present invention, it is provided a method for producing an oxide single crystal wafer capable of increasing the number of single crystal ingots that can be produced from one seed crystal and improving the productivity of the single crystal wafer per seed crystal. Can be done.

FIG. 1 is a diagram showing an example of a single crystal manufacturing apparatus. 2 (a) and 2 (b) are diagrams for explaining the pulling down of the seed crystal. FIG. 3 is a diagram for explaining the erosion of the seed crystal by the melt. FIG. 4 is a diagram for explaining melting of the tip portion of the seed crystal. FIG. 5 is a diagram for explaining the formation of the neck portion. FIG. 6 is a diagram for explaining the formation of the straight body portion. FIG. 7 is a diagram for explaining a single crystal ingot separated from the liquid surface. FIG. 8 is a diagram for explaining the separation of the single crystal ingot and the seed crystal. FIG. 9 is a diagram for explaining a slice of a single crystal ingot. FIG. 10 is a diagram for explaining the reuse of a seed crystal in which a part of the neck portion is integrated.

[Manufacturing method of single crystal ingot]
Hereinafter, a method for producing an oxide single crystal according to an embodiment of the present invention will be described. The method for producing an oxide single crystal according to an embodiment of the present invention is a step of forming a neck portion while pulling up the seed crystal after contacting the seed crystal with the raw material melt, and placing a single crystal ingot under the neck portion. The step of growing, the step of cutting and separating the seed crystal and the single crystal ingot in the middle of the neck part to produce a seed crystal in which a part of the neck part remains with a length of 4 mm or more, and the step of slicing the single crystal ingot to make a single crystal. It includes a step of producing a crystal wafer. In the step of forming the neck portion and the step of growing the single crystal ingot, for example, the neck portion can be formed by the CZ method using the single crystal manufacturing apparatus shown in FIG. 1, and the single crystal ingot can be grown.

[Single crystal manufacturing equipment]
The single crystal manufacturing apparatus 100 is a high-frequency induction heating type apparatus, and the crucible 1 is arranged in the chamber 10. The crucible 1 is placed on a refractory crucible stand 4. In the chamber 10, the heat insulating material 5 is arranged so as to surround the crucible 1. Further, the work coil 2 is arranged so as to surround the crucible 1, and an eddy current flows through the crucible 1 due to the high frequency magnetic field generated by the work coil 2, and the crucible 1 generates heat. That is, the crucible 1 itself becomes a heating element. A seed rod 3 is provided on the upper part of the chamber 10 so as to be rotatable and vertically movable.

In the Czochralski method (CZ method), the seed crystal 7 attached to the tip of the seed rod 3 is brought into contact with the melt surface of the raw material melt 8 in the pit 1, and then the seed crystal 7 is brought into contact with the shaft of the seed rod 3. By pulling upward while rotating horizontally around the seed crystal 7, a neck portion 9a, a cone portion 9b, and a straight body portion 9c can be formed, and a cylindrical single crystal ingot 9 having the same orientation as the seed crystal 7 can be grown. can. By forming the neck portion 9a, dislocations from the seed crystal 7 can be removed. Further, as the single crystal grows, the single crystal can be suspended and held by the seed crystal 7.

After growing the single crystal to a desired size, the grown single crystal is separated from the raw material melt 8 by performing operations such as changing the pulling speed and gradually increasing the melt temperature.
Then, by reducing the output of the work coil 2 at a predetermined speed, the grown single crystal is slowly cooled, and after the temperature in the chamber 10 becomes close to room temperature, the grown single crystal is taken out from the chamber 10.

Further, in the single crystal manufacturing apparatus 100, in order to move and rotate the seed rod 3 up and down, for example, a pull-up shaft driving means equipped with a motor (not shown) may be provided. The rotation speed and pulling speed of the seed rod 3 can be appropriately set depending on the size of the diameter of the single crystal to be formed, the length of the straight body portion, and the like.

Further, instead of the high frequency induction heating method using the work coil 2, the crucible 1 may be heated by the resistance heating method using a resistance heating heater. As the resistance heating heater, a heating element using carbon, nichrome (alloy of nickel and chromium), molybdenum disilicate, or the like that generates heat due to electric resistance can be appropriately used.

The crucible stand 4 may be provided with a hole in the center thereof, for example, so as to be in contact with a thermocouple 6 for measuring the temperature of the bottom of the crucible 1. The material of the crucible stand 4 is heat-resistant ceramics such as zirconia and alumina.

Next, regarding the method for producing an oxide single crystal by the CZ method, a production method using the single crystal production apparatus 100 will be described as an example.
[Seed crystal]
The quality of the seed crystal affects the quality and manufacturing yield of the single crystal ingot, and even the device characteristics when it is made into a wafer. Therefore, it is important to grow a single crystal using a seed crystal with excellent quality. It is preferable to prepare seed crystals of excellent quality selected in advance and grow single crystals. For example, in Japanese Patent No. 400072 (selection of seeds not containing lineage by XRT) and Japanese Patent Application Laid-Open No. 8-310899 (selection of seed crystals without defects by observing a mirror surface with a microscope), seed crystals having excellent quality can be obtained. The method is described.

[Single crystal manufacturing method]
(Seeding)
The prepared seed crystal 7 is attached to the tip of the seed rod 3, the crucible 1 is filled with a predetermined amount of calcined powder of the raw material prepared to have a congluent composition, and heated to make a melt 8. For example, lithium tantalate (LT) may be melted at about 1700 ° C. In the case of lithium niobate (LN), it is preferable to melt at about 1300 ° C, which is 400 ° C lower than LT. After that, the temperature of the melt 8 is adjusted to near the melting point (near 1650 ° C. for LT, around 1250 ° C. for LN), the seed crystal 7 is lowered while rotating at 10 rpm (FIG. 2), and the lower end thereof is melted. It is brought into contact with the surface of No. 8 (seed) to prepare for the start of growth of a single crystal. At this time, the surface of the melt 8 is attracted to the seed crystal 7 by surface tension and erodes the lower end of the seed crystal 7 by about 3 mm (FIG. 3). Hold this state for a while and observe the surface of the melt. This is to determine whether the melt temperature is suitable for crystal growth, and the seed crystal may be separated from the melt (the melt temperature is higher than the optimum temperature), or crystallization progresses rapidly. If the seed crystals are separated from the melt 8 once (the melt temperature is lower than the optimum temperature), the temperature of the melt 8 is adjusted again, and then seeding is performed.

(Melting seed crystals)
When the melt temperature is determined to be appropriate, the seed rod 3 is lowered and the lower end of the seed crystal 7 is further inserted into the melt 8 by A [mm] to melt the tip portion of the seed crystal 7 (FIG. 4). By doing so, the tip of the seed crystal 7 can be completely brought into contact with the melt. As a result, the residual strain of the tip portion generated when the seed crystal 7 is cut out and the heat shock strain caused by the temperature difference between the seed crystal 7 and the melt 8 when they are brought into contact with each other are reduced, and the quality is reduced. You can pull up a good single crystal.

Since the effect of reducing strain on the seed crystal 7 is enhanced, the insertion length A [mm] at this time is preferably 1 mm or more, and more preferably 2 mm or more. However, since the strain reducing effect is almost the same even if A exceeds 3 mm, it is particularly preferable to set A = about 3 mm, which consumes less seed crystals. When these operations are performed, the seed crystal is shortened by at least (3 + A) mm each time one single crystal is grown due to erosion due to surface tension and insertion for dissolution. That is, when A is 3 mm, it is shortened by 6 mm.

Then, the growth of a single crystal is started.
(Formation of neck)
The neck portion 9a is formed by pulling the seed crystal 7 upward at a speed of about 8 mm / hour or less while rotating the seed crystal 7 at a rotation speed of about 7 rpm (FIG. 5). The diameter of the neck portion 9a is a thickness that can withstand holding the single crystal to be formed, and a thickness of 5 mm or more is preferable. The length B [mm] of the neck portion 9a to be formed is preferably B ≧ (3 + A) [mm]. By doing so, it is possible to prevent the length of the seed crystal that can be reused from being shortened by cutting so that a part of the neck portion remains at the tip of the seed crystal in the subsequent step (FIG. 6). That is, when A = 3 mm, it is preferable that B ≧ 6 mm.

When the neck portion is separated in a later process, if the blade of a cutting tool such as a micro grinder hits the cone portion or the vicinity of the cone portion, cracks may occur toward the straight body portion. Therefore, it is preferable to cut in the middle of the neck portion. Further, it is more preferable that the length B of the neck portion 9a to be formed has a margin of about 4 mm. That is, it is more preferable that B ≧ (3 + 4 + A) [mm]. When A = 3 mm, it is more preferable that B ≧ 10 mm. Further, from the viewpoint of further preventing cracking of the straight body portion, it is more preferable that B ≧ 12 mm. Further, from the viewpoint of productivity, it is preferable that B ≦ 20 mm.

(Growth of single crystal ingot)
After forming the neck portion, the crystal diameter is gradually increased until the desired crystal diameter is reached to form the cone portion. Subsequently, a straight body portion is formed (FIG. 6). When forming the cone portion and the straight body portion, it is desirable to grow the single crystal at a growth rate of 10 mm / h or less because it is easy to obtain a single crystal with few defects. When the straight body reaches the desired length, it is separated from the liquid level. Then, the single crystal ingot can be obtained by slowly cooling to room temperature (FIG. 7).

(Preparation of seed crystal)
Next, the obtained single crystal ingot and the seed crystal are separated (FIG. 8). For cutting, for example, a micro grinder is used. The cutting is performed in the middle of the neck portion 9a so that a part of the neck portion 9a'is integrated with the seed crystal and remains. By doing so, it is possible to produce a seed crystal in which a part of the neck portion 9a'is integrated. Then, the entire seed crystal in which a part of the neck portion 9a'is integrated can be reused as the seed crystal 7'in the next batch, and the length of the seed crystal is suppressed to be shortened for each production batch. be able to. In this way, it is possible to increase the number of single crystal ingots that can be produced from one seed crystal. The length C [mm] of the neck portion 9a'left integrated with the seed crystal is preferably C ≧ 4 [mm], and more preferably C ≧ (3 + A) [mm]. In this way, it becomes possible to substantially continue to use one seed crystal for production semi-permanently. That is, when A = 3 mm, it is more preferable that C ≧ 6 mm. Further, from the viewpoint of suppressing the length of the seed crystal from becoming shorter for each production batch, it is more preferable to set C ≧ 8 [mm], and even more preferably C ≧ 10 [mm]. Further, from the viewpoint of productivity, it is preferable to set C ≦ 18 [mm].

(Making a single crystal wafer)
The produced single crystal ingot is sliced to a desired thickness and polished to obtain a single crystal wafer 11 (FIG. 9).

(Reuse of seed crystals)
Using the seed crystal 7'in which a part of the neck portion obtained in the above ingot cutting and separating step is integrated as a seed crystal as it is, the above seeding-growth of a single crystal ingot-preparation of a seed crystal-single crystal wafer A single crystal wafer can be produced by performing the process of producing the above (FIG. 10). That is, in the method for producing an oxide single crystal according to an embodiment of the present invention, the neck portion 9a'remaining in the seed crystal 7'is brought into contact with the raw material melt 8, and then the neck portion is pulled up while pulling up the seed crystal 7'. A step of growing a single crystal ingot under the neck part, a step of cutting and separating the seed crystal and the single crystal ingot in the middle of the neck part to produce a seed crystal in which a part of the neck part remains. , And it is preferable to further include a step of slicing the single crystal ingot to prepare a single crystal wafer. Specifically, at this time, a part of the neck portion remains integrated at the tip of the seed crystal, and the seed crystal is attached to the tip of the seed rod so that a part of the neck portion faces downward. When the seeding operation is performed, the seed crystal is shortened due to the surface tension generated when the seed crystal comes into contact with the melt and the seed crystal is melted for the purpose of removing strain, but there is a neck part that remains integrated. It is possible to suppress the shortening of the seed crystal body. In particular, it is preferable to leave the neck portion length C of 4 mm or more, preferably 6 mm or more, because it is possible to prevent shortening of the seed crystal body.

Here, it is preferable to grow the single crystal after forming the neck portion length of 10 mm or more again with respect to the seed crystal as in the previous batch. Similarly, it is preferable to cut the seed crystal with a part of the neck portion remaining at the tip of the seed crystal using, for example, a micro grinder to separate the single crystal ingot. It is preferable to slice the single crystal ingot to produce a single crystal wafer.

In this way, by repeating the above steps, it is possible to manufacture a single crystal ingot and manufacture a single crystal wafer by repeatedly utilizing one seed crystal many times.

The oxide single crystal produced by the method for producing an oxide single crystal wafer according to an embodiment of the present invention is preferably lithium tantalate or lithium niobate.

[Modification example]
The method for producing an oxide single crystal wafer according to an embodiment of the present invention is a step of forming a neck portion while pulling up the seed crystal after contacting the seed crystal with the raw material melt, and a single crystal ingot under the neck portion. The step of growing the seed crystal and the single crystal ingot are cut and separated in the middle of the neck part to produce a seed crystal in which a part of the neck part remains with a length of 4 mm or more, and the single crystal ingot is sliced. It is not particularly limited as long as it includes a step of producing a single crystal wafer.

The method for producing an oxide single crystal wafer according to an embodiment of the present invention is merely an example of the method for producing an oxide single crystal wafer of the present invention, and does not limit the method for producing an oxide single crystal wafer of the present invention.

Hereinafter, examples and comparative examples of the present invention described above will be given, but the present invention is not limited to the following examples.

[Examples and Comparative Examples]
In Examples and Comparative Examples, a LiTaO ₃ (LT) single crystal having a crystal orientation of 42 ° RY, a straight body length of about 90 mm, and a diameter of 4 inches was grown by the CZ method using a single crystal manufacturing apparatus 100. ..

(Preparation of LT single crystal ingot)
The raw material powder adjusted to the congluent composition of Li ₂ O-Ta ₂ O ₅ was filled in a crucible made of iridium, and the raw material powder was melted by high frequency heating. The tip of the prepared seed crystal was brought into contact with the melt, and when the melt was judged to have an appropriate seeding temperature, the seed crystal was inserted into the melt by 3 mm to remove the strain on the tip of the seed crystal. Then, after confirming that the melt had an appropriate temperature again, the seed crystal was gradually pulled up to obtain an LT single crystal ingot having the above-mentioned shape. The seed crystal was pulled up in a mixed gas of nitrogen and oxygen under the conditions of a pulling speed of 1 to 5 mm / h and a rotation speed of 5 to 20 rpm.
The prepared seed crystal was a square having a cross section of 1 cm × 1 cm and a size of 8 cm in length, and a plurality of such seed crystals were prepared and Examples and Comparative Examples were carried out.
Hereinafter, the production of the LT single crystal ingot in Examples and Comparative Examples will be described in detail.

(Example)
In carrying out the pulling, in the example, the tip of the seed crystal was brought into contact with the melt, and when the melt was judged to have an appropriate temperature, the seed crystal was inserted into the 3 mm melt, and it was confirmed again that the melt was at an appropriate temperature. Then, first, the neck portion was formed by 15 mm. The neck part was grown at a rotation speed of 7 rpm and a pulling speed of 3 mm / h of the seed crystal, and the diameter of the neck part was 10 mm.

After forming the neck portion, the crystal diameter was gradually increased until the crystal diameter reached 105 mm to form a cone portion, and then a straight body portion was formed. Then, when the length of the straight body portion was pulled up to 90 mm, the single crystal was separated from the melt and the crystal growth was completed. The cone portion and the straight body portion were formed while adjusting the rotation speed in the range of 5 to 20 rpm and the pulling speed in the range of 1 to 5 mm / h.

Then, the obtained single crystal was cooled to room temperature, and the middle of the neck portion was cut off using a micro grinder to obtain a seed crystal remaining by integrating a part of the neck portion and a first single crystal ingot. .. The length of the neck portion remaining in the seed crystal was 6 mm.

A single crystal wafer was produced by slicing the straight body portion of a single crystal ingot.

The seed crystal with a neck portion of 6 mm left was reused when growing the next single crystal ingot. That is, after confirming that the melt had an appropriate temperature by the above procedure again, the neck portion left in the seed crystal grew to a length of at least 10 mm or more, and then the LT single crystal was grown. Then, the seed crystal and the single crystal ingot were separated with a neck portion of 6 mm or more left in the seed crystal. By repeating such operations, the single crystal ingots were grown 142 times in total, and single crystal wafers were produced for each of the grown single crystal ingots.

After growing the single crystal ingot, the seed crystal may crack when the single crystal ingot and the seed crystal are separated, or the melt temperature before growing the single crystal ingot may be too high and the seed crystal may melt and shorten. There was something. In this case, the seed crystal became non-reusable, and a new seed crystal was used in place of the non-reusable seed crystal. Then, three seed crystals were used to grow the single crystal ingot 142 times.

Of the single crystal ingots obtained by growing the single crystals 142 times, 11 of them had a part of the single crystal ingots polycrystallized or cracks occurred in the single crystal ingots, but the remaining 131. The single crystal ingot of the book was a good product. On average, 43.6 good single crystal ingots could be obtained from one seed crystal.

(Comparative example)
In the comparative example, the tip of the seed crystal was brought into contact with the melt, and when the temperature of the melt was determined to be appropriate, the seed crystal was inserted into the melt by 3 mm. After confirming that the melt had an appropriate temperature again, first, a neck portion of 5 mm was formed, and then single crystal growth was started. The neck portion was grown at a rotation speed of 7 rpm and a pulling speed of 3 mm / h, and the diameter of the neck portion was set to 10 mm.

After forming the neck portion, the crystal diameter was gradually increased until the crystal diameter reached 105 mm to form a cone portion, and then a straight body portion was formed. Then, when the length of the straight body portion was pulled up to 90 mm, the crystal was separated from the melt and the single crystal growth was completed. The cone portion and the straight body portion were formed while adjusting the rotation speed in the range of 5 to 20 rpm and the pulling speed in the range of 1 to 5 mm / h.

Then, the obtained single crystal was cooled to room temperature, and the middle of the neck portion was cut off using a micro grinder to obtain a seed crystal remaining by integrating a small part of the neck portion and a first single crystal ingot. .. The length of the neck portion remaining in the seed crystal was about 1 mm.

A single crystal wafer was produced by slicing the straight body portion of a single crystal ingot.

The seed crystal with a neck portion of 1 mm left was reused when growing the next single crystal ingot. That is, after confirming that the melt had an appropriate temperature by the above procedure again, the neck portion left in the seed crystal grew to a length of 5 mm, and then the LT single crystal was grown. Then, the seed crystal and the single crystal ingot were separated with the neck portion of 1 to 3 mm left in the seed crystal. By repeating such operations, the single crystal ingots were grown 112 times in total, and single crystal wafers were produced for each of the grown single crystal ingots.

When the same seed crystal was continued to be used, the seed crystal became shorter by several mm compared to the initial state, and the seed crystal became unreusable. For this reason, a new seed crystal was used instead of the non-reusable seed crystal. Then, 30 seed crystals were used for 112 single crystal ingot growths.

Of the single crystal ingots obtained by growing the single crystal ingots 112 times, 87 single crystal ingots were good products. On average, 2.9 good single crystal ingots could be obtained from one seed crystal.

From the above Examples and Comparative Examples, in the method for producing an oxide single crystal wafer of the present invention, more seed crystals can be used repeatedly than in the conventional case, and a single crystal ingot having excellent quality can be efficiently produced. I found that I could do it. As a result, it can be seen that a single crystal wafer having excellent quality can be efficiently manufactured.

1 坩 堝 2 work coil 3 seed rod 4 坩 堝 stand 5 heat insulating material 6 thermoelectric pair 7 seed crystal 7'next batch seed crystal 8 raw material melt 9 cylindrical single crystal ingot 9a neck part 9a'remaining integrated with seed crystal Neck part 9a ”Neck part 9b that remains integrated with the single crystal ingot 9b Cone part 9c Straight body part 10 Chamber 100 Single crystal manufacturing equipment

Claims (5)

A step of forming a neck portion while pulling up the seed crystal after contacting the seed crystal with the raw material melt.
The process of growing a single crystal ingot under the neck,
A step of cutting and separating the seed crystal and the single crystal ingot in the middle of the neck portion to produce a seed crystal in which a part of the neck portion remains with a length of 4 mm or more, and slicing the single crystal ingot. The process of producing a single crystal wafer,
A method for producing an oxide single crystal wafer containing. The method for producing an oxide single crystal wafer according to claim 1, wherein in the step of producing a seed crystal in which a part of the neck portion remains, cutting and separation is performed with the seed crystal having a neck portion having a length of at least 6 mm or more. .. The method for producing an oxide single crystal wafer according to claim 1 or 2, wherein the step of forming the neck portion is a step of forming the neck portion with a length of 10 mm or more. A step of growing the neck portion while pulling up the seed crystal after contacting the neck portion remaining on the seed crystal with the raw material melt.
The process of growing a single crystal ingot under the neck,
A step of cutting and separating the seed crystal and the single crystal ingot in the middle of the neck portion to produce a seed crystal in which a part of the neck portion remains, and slicing the single crystal ingot to obtain a single crystal wafer. Manufacturing process,
The method for producing an oxide single crystal wafer according to any one of claims 1 to 3, further comprising. The method for producing an oxide single crystal wafer according to any one of claims 1 to 4, wherein the oxide single crystal is lithium tantalate or lithium niobate.

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