JP5888631B2 - Method for producing single crystal ingot - Google Patents

Description

  The present invention relates to a method for producing a single crystal ingot, more specifically, a single crystal using a connection structure of a seed shaft and a seed holder in a single crystal pulling apparatus suitable for pulling a single crystal by the Czochralski method, particularly an oxide single crystal. The present invention relates to a method for producing a crystal ingot.

  For example, the Czochralski method (CZ method) is generally known for producing an ingot of single crystal sapphire, which is a kind of oxide single crystal. In pulling up the single crystal sapphire ingot by the CZ method, first, aluminum oxide filled in the crucible is heated by a heater to obtain an alumina melt. Thereafter, the seed crystal mounted on the lower end of the seed holder is immersed in an alumina melt, and the seed holder is gradually pulled up while rotating the seed holder and the crucible, and a single crystal sapphire ingot is grown on the lower end of the seed crystal (Patent Document) 1).

  This seed holder is a member for mounting and holding a seed crystal. Although there is no description of the configuration in Patent Document 1, the conventional seed holder is firmly fastened to the lower end portion of a rod-shaped seed shaft that is pulled up vertically by a lifting mechanism via three screws. Specifically, three horizontal screw holes are formed at the lower end portion of the seed shaft from the outer peripheral surface thereof toward the holder holding hole in the center portion, and three screw screws are adjusted in each screw hole, respectively. By screwing the screw, the seed holder is held at the lower end of the seed shaft. The seed crystal is firmly fastened to the lower end of the sea holder. These seed shafts, seed holders, and seed crystals are adjusted in connection so that the respective axes are arranged on a virtual virtual straight line in a normal temperature environment.

JP 2010-265150 A

  As described above, in the conventional technique such as Patent Document 1, when the ingot is pulled up, the seed shaft is thermally expanded due to the radiant heat from the alumina melt and the like, and the seed shaft is bent (deformed) and loosened in three screws. Had occurred. As a result, the vertical seed crystal mounted on the seed holder in a room temperature environment was deposited obliquely with respect to the alumina melt surface, and the temperature gradient in the alumina melt was changed. Thereby, when the shoulder portion of the single crystal sapphire ingot is pulled up, the shoulder portion grows rapidly, and the shoulder portion may not be grown concentrically.

  Therefore, as a result of intensive research, the inventors have established that the seed shaft and the seed crystal are connected by a seed holder having a universal joint structure, so that the seed shaft is caused by thermal expansion due to radiant heat from the alumina melt. It has been found that the tilt of the seed crystal can be eliminated by the respective weights of the seed holder and the seed crystal even when the screws are deformed or the screws are loosened. That is, the seed crystal is kept vertical immediately above the alumina melt, and the seed crystal is deposited vertically to the liquid surface. Therefore, in the initial stage of pulling up the ingot, it was found that the rapid shoulder growth, which was a conventional problem, was eliminated, and it was possible to grow a single crystal sapphire ingot having a smooth shoulder. I let you.

  The present invention provides a single crystal that can deposit a seed crystal perpendicularly to the melt surface even if, for example, a connection portion between the seed shaft and the seed holder is bent due to radiant heat from the melt or the like. It aims at providing the manufacturing method of an ingot.

The invention according to claim 1 is a manufacturing method of a single crystal ingot in which a single crystal ingot is pulled up from a melt by a Czochralski method. an upper end portion of the seed holder being connected by a universal joint scheme, pulling the single crystal ingot from the melt, said universal joint system divides the seed holder 3 over n number of partial seed holder The connection between the seed shaft and the seed holder that supports the lower end portion of the seed shaft and the partial seed holder or the adjacent partial seed holders by n rotational pins whose axes are horizontal. It is a manufacturing method of a single crystal ingot which is a structural method .

  According to this invention, since the seed shaft and the seed crystal are connected by the universal joint type seed holder, when pulling up the single crystal ingot from the melt by the Czochralski method, temporarily by radiant heat from the melt, etc. For example, even if a bending or the like occurs at the connecting portion between the seed shaft and the seed holder, the length direction of the seed holder with the seed crystal is vertical due to its own weight. As a result, the seed crystal is kept perpendicularly above the melt and can be deposited perpendicularly to the liquid surface. As a result, in the initial stage of pulling up the single crystal ingot, the sharp shoulder growth, which has been a conventional problem, is eliminated, and a single crystal ingot having a smooth shoulder can be grown.

It is a front view of the connection structure of the seed axis | shaft and seed holder which concern on Example 1 of this invention. It is a longitudinal cross-sectional view of the single crystal pulling apparatus by which the connection structure of the seed axis | shaft and seed holder which concerns on Example 1 of this invention was mounted. It is a perspective view which shows the centering state in the room temperature of the connection structure of the seed axis | shaft and seed holder which concern on Example 1 of this invention. It is a perspective view which shows the use condition of the connection structure of the seed axis | shaft and seed holder which concern on Example 1 of this invention. It is a perspective view which shows the centering state in the room temperature of the connection structure of the seed axis | shaft and seed holder which concern on Example 2 of this invention. It is a perspective view which shows the use condition of the connection structure of the seed axis | shaft and seed holder which concern on Example 2 of this invention. It is a perspective view which shows the centering state in the room temperature of the connection structure of the seed shaft and seed holder which concerns on the conventional method. It is a perspective view which shows the use condition of the connection structure of the seed shaft and seed holder which concerns on the conventional method. It is a perspective view which shows the centering state in the room temperature of the connection structure of the seed shaft and seed holder which concerns on another conventional method. It is a perspective view which shows the use condition of the connection structure of the seed axis | shaft and seed holder which concerns on another conventional method.

The present invention relates to a method for producing a single crystal ingot in which a single crystal ingot is pulled up from a melt by the Czochralski method. connecting the upper end at the universal joint type, pulling the single crystal ingot from the melt, said universal joint system divides the seed holder 3 over n number of partial seed holder, of the seed shaft It is a simple structure of a seed shaft and a seed holder that supports the lower end portion and the partial seed holder or the adjacent partial seed holders by n rotational pins whose axes are horizontal. It is a manufacturing method of a crystal ingot.

  According to this invention, since the seed shaft and the seed crystal are connected by the universal joint type seed holder, when pulling up the single crystal ingot from the melt by the Czochralski method, for example, by radiant heat from the melt, for example, Even if a bending or the like occurs at the connecting portion between the seed shaft and the seed holder, the length of the seed holder with the seed crystal is vertical due to its own weight. As a result, the seed crystal can be held vertically immediately above the melt, and thereafter can land on the liquid surface perpendicularly. Therefore, in the initial stage of pulling up the ingot, the rapid shoulder growth, which has been a conventional problem, is eliminated, and a single crystal ingot having a smooth shoulder can be grown.

As the single crystal ingot, for example, an oxide single crystal ingot such as a single crystal sapphire ingot can be employed. In addition, single crystal silicon or the like may be used.
As a single crystal pulling apparatus to which the present invention is applied, various Czochralski-type single crystal pulling apparatuses can be employed. For example, there is an MCZ type that pulls up a single crystal ingot in a high magnetic field application state.
The seed shaft is a bar material extending linearly. As specific materials for the seed shaft and the seed holder, for example, tungsten, molybdenum, molybdenum alloy, tantalum, or the like can be employed. Also, if the seed shaft and the seed holder are made of different materials, mutual fusion can be prevented.

Here, the universal joint system means that three or more n partial seed holders rotate freely around their corresponding rotation pins by the dead weight of the seed crystal and the seed holder immediately below the seed shaft. This is a system in which the length direction of the seed crystal mounted on the lower end of the seed holder is oriented in the vertical direction.
The number n of partial seed holders constituting the seed holder may be 3 or more.
The material of the seed crystal is the same as that of the single crystal ingot to be pulled up.
The number n of rotating pins is the same as the number of partial seed holders.
Each rotation pin is coaxially inserted into a plurality of pin holes formed between two members to be connected, such as partial seed holders. The diameter of each rotation pin is 0.5 mm to 2 mm smaller than the hole diameter of the corresponding pin hole in order to obtain a degree of freedom of rotation as a universal joint around the n rotation pins of the seed holder.

In the universal joint system, the n rotation pins are based on the one for the uppermost partial seed holder, and the lower arrangement pin is centered on the axis of the seed holder by an angle obtained by dividing 180 ° by n. It is preferable to change the angle around one direction.
“An angle obtained by dividing 180 ° by n” means that the numerical value “n” indicating the number of partial seed holders and the number of rotating pins is 60 ° in the case of 3 , for example 45 ° in the case of 4. Become.
For example, n is 3 when the angle of 180 ° divided by n is changed in one direction around the axis of the seed holder with the uppermost rotation pin as a reference. Means the following: That is, when the length direction of the first rotation pin connecting the lower end portion of the seed shaft and the upper end portion of the uppermost partial seed holder is a reference angle of 0 °, the lower end portion of the uppermost partial seed holder is The second rotation pin that connects the upper end of the partial seed holder one step below (second from the top) is rotated 60 ° counterclockwise around the axis of the seed holder, for example, from the reference angle. Arranged at the moved position. In addition, the third pivot pin from the top connecting the lower end of the second stage partial seed holder from the top and the upper end of the third stage partial seed holder from the upper side makes the axis of the seed holder from the reference angle. It is arranged at a position rotated 120 ° counterclockwise as the center.

Next, a connection structure between the seed shaft and the seed holder according to Embodiment 1 of the present invention will be described with reference to FIGS.
1 and 2, reference numeral 10 denotes a connection structure (hereinafter referred to as a seed connection structure) between a seed shaft and a seed holder according to Embodiment 1 of the present invention. The seed connection structure 10 is a single crystal for a single crystal sapphire ingot. It is mounted on the pulling device 30.

Hereinafter, these components will be specifically described.
The single crystal pulling apparatus 30 includes a hollow cylindrical chamber 11. The chamber 11 includes a main chamber 12 and a pull chamber 13 that is continuously fixed on the main chamber 12 and has a smaller diameter than the main chamber 12. A molybdenum crucible 14 is fixed on a support shaft (pedestal) 15 that can be rotated and moved up and down in the center of the main chamber 12.

On the outside of the crucible 14, a heating resistance heater 21 is arranged concentrically with the wall of the crucible 14. On the outside of the heater 21, a cylindrical heat insulating cylinder 22 is disposed along the inner surface of the peripheral side wall of the main chamber 12. A circular heat insulating plate 23 is disposed on the bottom surface of the main chamber 12.
On the center line of the crucible 14, a round rod seed shaft 25 made of molybdenum that can rotate and move up and down in the Z direction (vertical direction) on the same axis as the support shaft 15 is suspended through the pull chamber 13. Yes. A seed holder 24 made of molybdenum is connected to the lower end portion of the seed shaft 25, and a seed crystal C made of single crystal sapphire is attached to the lower end portion of the seed holder 24.

Next, the seed coupling structure 10 will be described in detail with reference to FIG.
The seed connection structure 10 of the first embodiment is characterized in that the seed holder 24 is of a universal joint type. This will be specifically described below.
The seed holder 24 includes two partial seed holders 24A and 24B obtained by dividing the seed holder 24 in the vertical direction, and a first turn that rotatably supports the upper end portion of the upper partial seed holder 24A on the lower end portion of the seed shaft 25. Lower shaft having an upper shaft support portion 29A having a moving pin 28A and a second rotation pin 28B for rotatably supporting the upper end portion of the lower partial seed holder 24B on the lower end portion of the upper partial seed holder 24A. And a branch.

Both the rotating pins 28A and 28B are pin members made of molybdenum alloy and having a horizontal axis. Among these, the axial direction of the second rotating pin 28B is 180 ° counterclockwise about the axis of the seed holder 24 with respect to the axial direction (Y direction) of the first rotating pin 28A. The direction is changed by 90 degrees divided by (X direction). As the material of the rotating pins 28A and 28B, a molybdenum alloy which has a high melting point (about 2600 ° C.) and is softer than tungsten is adopted. It is hard to do. In addition, since the material of the second rotation pin 28B is made of a material different from that of the seed shaft 25 and the seed holder 24, fusion is unlikely to occur at the contact portions even when heated at a high temperature.
An insertion hole for the upper end portion of the seed crystal C is formed at the center portion of the lower end surface of the lower partial seed holder 24B. By inserting the upper end portion of the seed crystal C into the insertion hole and firmly fixing the seed crystal C, the seed crystal C is mounted on the lower end portion of the seed holder 24.

  The upper shaft support portion 29A has a short prismatic shape protruding downward from the center portion of the lower end surface of the seed shaft 25 in addition to the first rotation pin 28A, and when the lower portion is viewed from the front in the drawing of FIG. Is provided with a semicircular shaft support protrusion 31A and a shaft support groove 32A formed through both end portions in the X direction of the upper end portion of the upper partial seed holder 24A. A protrusion-side pin hole 31a that penetrates both side surfaces in the Y direction is formed at the lower end of the shaft support protrusion 31A. Further, groove-side pin holes 24a penetrating both end portions in the Y direction are formed in the upper end portion of the upper partial seed holder 24A. When assembling the upper shaft support portion 29A, the first rotation pin 28A is coaxially inserted from one groove side pin hole 24a through the projection side pin hole 31a to the other groove side pin hole 24a, thereby The upper partial seed holder 24 </ b> A is pivotally coupled (supported) to the seed shaft 25 around the rotation pin 28 </ b> A. The diameter of the first rotation pin 28A is about 0.5 mm smaller than the inner diameters of the projection-side pin hole 31a and the groove-side pin hole 24a. This prevents the rotation pin 28A from being locked due to thermal expansion between the first rotation pin 28A, the seed shaft 25 and the seed holder 24, and the universal joint type seed holder 24 is being pulled up while the ingot is being pulled up. It is possible to ensure the degree of freedom of rotation (swing).

  In addition to the second pivot pin 28B, the lower shaft support portion 29B has a shaft support protrusion 31B having substantially the same shape as that of the seed shaft 25 protruding downward from the center of the lower end surface of the upper partial seed holder 24A. And the shaft support groove 32B having substantially the same shape as that formed at the upper end of the lower partial seed holder 24B. However, the lower portion of the shaft support protrusion 31B is semicircular when viewed from the side in the drawing of FIG. 1, and the length direction of the shaft support groove 32B is the Y direction. The length directions of the side pin hole 31b and the groove side pin hole 24b are in the X direction.

Next, a single crystal sapphire ingot growth method using the single crystal pulling apparatus 30 will be specifically described with reference to FIGS.
First, as shown in FIG. 1 and FIG. 3, at room temperature, the axis direction of each member of the seed shaft 25, the seed holder 24 consisting of the upper and lower partial seed holders 24A and 24B, and the seed crystal C is set to the Z direction. The centering is made to match.
Thereafter, as shown in FIG. 2, the inside of the chamber 11 is decompressed to 25 Torr, and 100 L / min of argon gas is introduced. Next, the aluminum oxide in the crucible 14 is melted by heating to 2020 ° C. with the heater 21, thereby forming an alumina melt 26 in the crucible 14.

After centering, the seed shaft 25 is gradually lowered by the pulling mechanism, and the tip of the seed crystal C attached to the lower end of the seed holder 24 is immersed in the alumina melt 26.
At this time, the seed shaft 25 and the seed crystal C are connected by a universal joint type seed holder 24. Therefore, when the single crystal sapphire ingot S is pulled up from the alumina melt 26 by the subsequent Czochralski method, the connecting portion between the seed shaft 25 and the seed holder 24 is bent by the radiant heat from the alumina melt 26 or the like. However, in the seed holder 24 with the seed crystal C, the upper partial seed holder 24A and the lower partial seed holder 24B can freely move by their own weights around the two rotation pins 28A and 28B whose angles are changed by 90 °. Rotate. Thereby, the length direction of the seed holder 24 is held in the Z direction with no power.

As a result, the seed crystal C is kept vertical immediately above the alumina melt 26, and the seed crystal C can be deposited vertically to the liquid surface. As a result, in the initial stage of pulling up the single crystal sapphire ingot S, the rapid shoulder growth, which has been a conventional problem, is eliminated, and the single crystal sapphire ingot S with a smooth shoulder can be grown.
In addition, since the universal joint type seed connection structure 10 is a pin multipoint structure, depending on the furnace temperature, the connection portion of the seed shaft 25 and the seed holder 24 each made of molybdenum may be welded. Therefore, the shaft support portions 29A and 29B having both the rotating pins 28A and 28B are always spaced apart by 200 mm or more upward from the liquid surface of the alumina melt 26 and are disposed in the internal space of the pull chamber 13 at 1500 ° C. or less. Is preferred.
Thereafter, while rotating the crucible 14 and the seed shaft 25 in opposite directions, the seed shaft 25 is pulled up in the Z direction (vertical) to grow a single crystal sapphire ingot S below the seed crystal C.

Next, with reference to FIG. 5 and FIG. 6, the connection structure of the seed axis | shaft and seed holder which concern on Example 2 of this invention is demonstrated.
As shown in FIGS. 5 and 6, the seed connection structure 10A according to the second embodiment of the present invention is characterized in that the seed holder 24 is added to the upper and lower partial seed holders 24A and 24B, and the middle partial seed holder 24C is added. Thus, it is configured in three divisions using three rotation pins 28A to 28C.

Here, with the first rotating pin 28A for the upper partial seed holder as a reference, the lower partial seed holders are arranged at an angle obtained by dividing 180 ° by n, specifically 60 °, in the lower stage. The second rotation pin 28B for the first and the third rotation pin 28C for the lower partial seed holder are arranged at positions rotated counterclockwise about the axis of the seed holder 24.
Other configurations, operations, and effects are within a range that can be estimated from the first embodiment, and thus description thereof is omitted.

  Here, the tilt of the seed crystal during pulling of the single crystal sapphire ingot and the single crystal being pulled due to the difference in the connection structure between the seed shaft and the seed holder (Comparative Examples 1 and 2 and Test Examples 1 and 2). For each comparative example and each test example, an experiment was performed three times under the same conditions to determine how the growth of the shoulder of the sapphire ingot changes. Note that the inclination of the seed crystal is a value obtained by capturing an image with a CCD camera from above the seed holder and performing a numerical calculation process on the captured image.

(Comparative Example 1)
In Comparative Example 1, a screw connection method was adopted as a connection structure between the seed shaft and the seed holder. Specifically, as shown in FIG. 7, the connection protrusion 33 protruding from the center portion of the upper end surface of the seed holder 24 is inserted into the holder holding hole 25 a formed in the center portion of the lower end surface of the seed shaft 25, Three screws P were screwed into the lower end portion of the seed shaft 25 from the outer peripheral surface toward the holder holding hole 25a in the center portion. As a result, the seed holder 24 was firmly sandwiched between the lower end portion of the seed shaft 25 via the connection protrusion 33. Note that the seed shaft 25, the seed holder 24, and the seed crystal C that were connected to each other were adjusted in advance so that the respective axes are oriented in the vertical direction in an environment at room temperature.

  Thereafter, the single crystal sapphire ingot S was pulled up from the alumina melt 26 of the crucible 14 under the ingot pulling conditions of Example 1. At this time, the seed shaft 25 was thermally expanded by radiant heat from the alumina melt 26 and the like, and the seed shaft 25 was bent and the three screws P were loosened. This is because the seed holder 24 is screwed to the seed shaft 25. As a result, the vertical seed crystal C mounted on the seed holder 24 under the room temperature environment is deposited obliquely with respect to the surface of the alumina melt 26, and the temperature gradient in the alumina melt 26 changes (FIG. 8). Therefore, when the shoulder portion of the single crystal sapphire ingot S was pulled up, the shoulder portion grew rapidly, and the shoulder portion could not be grown concentrically. Table 1 shows the results of performing the above experiment three times.

(Comparative Example 2)
In Comparative Example 2, as a connecting structure between the seed shaft and the seed holder, instead of the universal joint system of the two rotation pins of Example 1, as shown in FIGS. A single pin method was adopted. One shaft support portion 34 rotatably supports the shaft support protrusion 31 of the seed shaft 25, the shaft support groove of the seed holder 24 that accommodates the shaft support protrusion 31, and the shaft support protrusion 31 in the shaft support groove. And one rotating pin 28D that is long in the X direction. Note that the seed shaft 25, the seed holder 24, and the seed crystal C that were connected to each other were adjusted in advance so that the respective axes are oriented in the vertical direction in an environment at room temperature. The results are shown in Table 1.
In Comparative Example 2, the seed shaft 25 and the seed holder 24 are pivotally supported by a single rotation pin 28D. However, when the seed crystal C is rotated around the rotation pin 28D, the seed crystal C is moved in the X direction. It was easy to tilt because there was no degree of freedom. That is, as shown in Table 1, during the three experiments, only the second time was able to suppress the inclination of the seed crystal C and the rapid growth of the shoulder.

(Test Example 1)
In Test Example 1, according to Example 1 shown in FIG. 1, FIG. 3, and FIG. 4, the seed holder 24 is composed of partial seed holders 24A and 24B that are divided into upper and lower stages, and the axial direction differs by 90 °. A universal joint system having two rotating pins 28A and 28B was adopted. When the single crystal sapphire ingot S is pulled up under the same conditions as in Example 1, the seed holder 24 has a degree of freedom of rotation in the X direction and the Y direction, and even if the seed shaft 25 is slightly deformed in a high temperature environment, Further, even when the seed crystal C was rotated in a predetermined direction integrally with the seed holder 24, the seed crystal C could always be kept vertical by its own weight. The results are shown in Table 1.

(Test Example 2)
In Test Example 2, according to Example 2 shown in FIGS. 5 and 6, the seed holder 24 is composed of partial seed holders 24 </ b> A to 24 </ b> C divided into upper, middle, and lower stages, and the axial direction is different by 60 °. A universal joint system having the rotating pins 28A to 28C was adopted. When the single crystal sapphire ingot S is pulled up under the same conditions as in the second embodiment, it has the same degree of freedom of rotation in the X direction and the Y direction as in the first embodiment, thus increasing the number of rotating pins. In addition, it was confirmed that the seed crystal C was deposited vertically on the alumina melt 26 and the shoulder portion of the single crystal sapphire wafer S could be stably grown. The results are shown in Table 1.

In the present invention, the seed holder C and the seed crystal C have their own weights, so that the seed crystal C can always maintain the perpendicular to the liquid surface of the alumina melt 26 regardless of the room temperature and the high temperature. The centering work for aligning the length direction of the seed crystal in the vertical direction at room temperature, which was essential in the past, is no longer necessary.
In addition, during the experiment, the inclination of the seed crystal C was confirmed on the screen of the CCD camera. By using two or more rotating pins, the inclination of the seed crystal C is below the detection lower limit of 1.2E-04 °. I was able to confirm.

  According to the present invention, in the initial stage of pulling up the ingot, the rapid shoulder growth, which has been a conventional problem, is eliminated, and a single crystal ingot having a smooth shoulder can be grown.

10, 10A Seed shaft and seed holder connection structure,
24 seed holder,
24A-24C partial seed holder,
25 seed axis,
26 Alumina melt (melt),
28A-28C Rotating pin,
C seed crystal,
S Single crystal sapphire ingot (single crystal ingot).

Claims (1)

In the method for producing a single crystal ingot that pulls the single crystal ingot from the melt by the Czochralski method,
The lower end of the rod-shaped seed shaft that is pulled up vertically and the upper end of the seed holder on which the seed crystal is attached to the lower end are connected by a universal joint method, and the single crystal ingot is pulled up from the melt,
In the universal joint method , the seed holder is divided into three or more n partial seed holders, and the lower end portion of the seed shaft and the partial seed holder, or the adjacent partial seed holders, the axis is horizontal. A manufacturing method of a single crystal ingot which is a connection structure system of a seed shaft and a seed holder that are rotatably supported by n rotational pins .

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