JP2024088149A - Single crystal pulling apparatus and method - Google Patents

Abstract

To provide an apparatus for pulling a single crystal, capable of applying a horizontal magnetic field to pull a silicon single crystal by the Czochralski method and capable of suppressing dislocation after forming a shoulder part.SOLUTION: An apparatus for pulling a single crystal includes: a rotary drive control part for rotating a crucible 3 around a vertical axis by a rotary drive part and; a magnetic field application control part 8a for controlling a horizontal magnetic field applied to a silicon melt M. The rotary drive control part rotates the crucible at a first rotation number when forming the neck part of a single crystal and controls the rotation number of the crucible to be a second rotation number smaller than the first rotation number when starting to form the straight body part of the single crystal; and the magnetic field application control part starts to apply the horizontal magnetic field when the diameter of the shoulder part of the single crystal is 3/4 or more and less than 1 of the straight body part without applying the magnetic field when forming the neck part of the single crystal and controls to apply the horizontal magnetic field of 0.1 tesla or more when starting to form the straight body part.SELECTED DRAWING: Figure 2

Description

The present invention relates to a single crystal pulling device and a single crystal pulling method, and in particular to a single crystal pulling device and a single crystal pulling method for pulling silicon single crystals by the Czochralski method.

In growing silicon single crystals by the Czochralski method (CZ method), as shown in FIG. 5 , a quartz glass crucible 51 installed in a chamber 50 is filled with polysilicon as a raw material, and the polysilicon is heated and melted by a heater 52 provided around the quartz glass crucible 51 to form a silicon melt M.
Thereafter, a seed crystal P (seed) attached to a seed chuck is immersed in the silicon melt M, and the seed chuck and the quartz crucible 51 are rotated in the same direction or in the opposite direction. When the seed crystal P is immersed in the silicon melt M, dislocations are generated due to thermal shock, so a drawing process called "necking" (a process for forming a neck portion CN) is performed to prevent the dislocations from affecting the subsequent crystal growth.
Next, the crystal diameter is gradually increased to grow a shoulder portion C1, and then the diameter is increased to a predetermined straight body diameter to form a straight body portion C2, and the silicon single crystal C is pulled and grown.

When growing silicon single crystals using high-concentration dopants, it is necessary to suppress dislocations caused by compositional supercooling. Compositional supercooling is a phenomenon that occurs when producing silicon single crystals with a high concentration of dopant added, and the degree of freezing point depression, which is the difference between the freezing point of silicon melt M and the freezing point of the dopant-added melt in which the dopant is added to silicon melt M, becomes very large due to the introduction of a large amount of dopant into silicon melt M.

In order to suppress the occurrence of compositional supercooling, as disclosed in Patent Document 1, for example, it is necessary to maintain the relationship GL/V>A·CL, which is determined by the melt vertical temperature gradient GL immediately below the interface (solid-liquid interface) between the silicon single crystal and the silicon melt, the crystal pulling speed V, and the dopant concentration CL in the melt (A is a coefficient depending on the dopant type).
That is, it is important to increase the temperature gradient GL and slow the pulling speed V. However, when the dopant concentration CL itself in the melt increases, it is necessary to increase GL/V. One method for increasing the temperature gradient GL is to suppress the convection of the silicon melt by applying a horizontal magnetic field. For this reason, applying a horizontal magnetic field is an effective method for suppressing the compositional supercooling that is likely to occur when a high concentration dopant is used.
However, in the shoulder formation process in the stage of expanding the crystal diameter, there was a problem that dislocations frequently occurred in the shoulder even if the above-mentioned relationship GL/V>A·CL was satisfied.

Patent Document 2 discloses a method for manufacturing silicon single crystals in which a high concentration of dopant is used to grow low resistivity silicon single crystals by adjusting the distance (gap) between the bottom end of an inert Ar gas straightening tube and the surface of the silicon melt, thereby suppressing the occurrence of dislocations during shoulder formation. According to the method disclosed in Patent Document 2, the Ar gas keeps the volatilized dopant away from the crystal, reducing the thermal stress generated in the single crystal and suppressing the occurrence of dislocations during shoulder formation.

JP 2017-222551 A Japanese Patent No. 5262346

However, when a silicon single crystal is grown by applying a horizontal magnetic field, the method disclosed in Patent Document 2 also has a problem in that dislocations occur during shoulder formation.
As a result of extensive research by the applicant into this issue, it was discovered that the occurrence of dislocations during shoulder formation is closely related to the suppression of convection in the silicon melt by application of a horizontal magnetic field and slowing down the rotation speed of the crucible.

That is, similar to the effective means of suppressing compositional supercooling in the body, the application of a horizontal magnetic field also suppresses the convection of the silicon melt during the formation of the neck. Furthermore, when the crystal of the neck with a small diameter is pulled up while the crucible rotation speed is low, the solid-liquid interface is pulled up in the pulling direction, and the solid-liquid interface shape is likely to become an upward convex shape. Here, dislocations generated during the formation of the neck tend to extend in the crystal growth direction, and since the dislocations gather at the center of the neck, it is difficult to eliminate them. As a result, it was found that under the horizontal magnetic field application condition, dislocations extending vertically remain at the center of the neck, and dislocations are likely to occur after the formation of the shoulder.
In addition, when the crucible rotation speed is slowed down, the stirring of the silicon melt is suppressed, and the temperature fluctuations directly below the solid-liquid interface become large. In this case, when the crystal diameter is small, such as in the early stages of the formation of the neck and shoulder, it is affected by the temperature fluctuations and dislocations are likely to occur.

The present invention has been made in light of the above circumstances, and aims to provide a single crystal pulling apparatus and single crystal pulling method that can suppress dislocations after shoulder formation in a single crystal pulling apparatus that adds a high concentration of dopant and pulls silicon single crystals by the Czochralski method in order to produce low-resistance silicon single crystals.

The single crystal pulling apparatus according to the present invention, which has been made to solve the above problems, forms a silicon melt in a crucible by heating from a heater surrounding the crucible, adds a dopant to the silicon melt and applies a horizontal magnetic field to the silicon melt, and pulls a silicon single crystal from the silicon melt by the Czochralski method. The apparatus includes a rotation drive control unit that rotates the crucible around a vertical axis by a rotation drive unit, and a magnetic field application control unit that controls the horizontal magnetic field applied to the silicon melt. The rotation drive control unit controls the rotation speed of the crucible to rotate at a first rotation speed when the neck of the single crystal is formed, and to a second rotation speed smaller than the first rotation speed when the formation of the straight body of the single crystal begins. The magnetic field application control unit does not apply a magnetic field when the neck of the single crystal is formed, starts applying a horizontal magnetic field when the diameter of the shoulder of the single crystal is 3/4 or more and less than 1 of the straight body, and controls to apply a horizontal magnetic field of 0.1 Tesla or more when the formation of the straight body begins.

It is preferable that the rotation drive control section performs control so as to gradually decrease the rotation speed when changing the rotation speed of the crucible from the first rotation speed to the second rotation speed.
It is also preferable that the rotation drive control section controls the rotation speed of the crucible to be constant at a second rotation speed during the formation of the body portion.
It is also desirable that the first rotation speed is equal to or greater than 10 rpm and equal to or less than 20 rpm, and the second rotation speed is equal to or less than 1 rpm.
It is also preferable that the magnetic field application control unit performs control so as to apply a horizontal magnetic field of 0.2 Tesla or more and 0.3 Tesla or less in forming the straight body portion.

According to the single crystal pulling apparatus configured in this way, the solid-liquid interface can be made downwardly convex by rotating the crucible at high speed during the formation of the neck. As a result, dislocations generated in the neck due to thermal shock are formed on the outer periphery of the neck, and the dislocations can be eliminated during the neck formation process. In addition, since no horizontal magnetic field is applied, convection under the solid-liquid interface is promoted, and the temperature of the silicon melt can be stabilized by rotating the crucible at high speed, preventing the occurrence of dislocations due to large temperature fluctuations.
In addition, when forming the shoulder portion, while the diameter of the shoulder portion is small, the crucible rotation is accelerated to stabilize the temperature of the silicon melt, as in the case of forming the neck portion, thereby suppressing large temperature fluctuations below the solid-liquid interface and preventing the occurrence of dislocations.
Furthermore, when starting to form the body portion, a horizontal magnetic field is applied to suppress convection in the silicon melt, increasing the temperature gradient and slowing down the crucible rotation speed, thereby making it possible to suppress the occurrence of dislocations due to constitutional supercooling during the process of forming the body portion.

The method for pulling a single crystal according to the present invention, which has been made to solve the above problems, is a method for pulling a single crystal by forming a silicon melt in a crucible by heating from a heater surrounding the crucible, adding a dopant to the silicon melt and applying a horizontal magnetic field, and pulling a silicon single crystal from the silicon melt by the Czochralski method, and is characterized in that it includes the steps of: rotating the crucible at a first rotation speed without applying a horizontal magnetic field in forming a neck portion of the single crystal; starting to apply a horizontal magnetic field when the diameter of the shoulder portion of the single crystal is 3/4 or more and less than 1/1 of the diameter of the straight body portion in forming the straight body portion of the single crystal; and applying a horizontal magnetic field of 0.1 Tesla or more before the start of formation of the straight body portion and setting the rotation speed of the crucible to a second rotation speed smaller than the first rotation speed in forming the straight body portion of the single crystal.

In addition, it is desirable to control the rotation speed of the crucible to gradually decrease from the first rotation speed to the second rotation speed during the process from rotating the crucible at a first rotation speed in forming the neck portion of the single crystal to the process of changing the rotation speed of the crucible to a second rotation speed smaller than the first rotation speed at the start of forming the straight body portion of the single crystal.
In addition, in forming the body portion of the single crystal, it is desirable to control the rotation speed of the crucible to a constant value at the second rotation speed.
It is also desirable that the first rotation speed is equal to or greater than 10 rpm and equal to or less than 20 rpm, and the second rotation speed is equal to or less than 1 rpm.
In addition, it is preferable to control the application of a horizontal magnetic field of 0.2 Tesla or more and 0.3 Tesla or less during the formation of the straight body portion.
It is also preferable to add a dopant to the silicon melt to pull up a silicon single crystal having a resistivity of 0.5 mΩcm or more and 1.1 mΩcm or less.
The dopant is preferably red phosphorus.

According to the single crystal pulling method configured as above, in forming the neck portion, the solid-liquid interface can be made to have a downward convex shape by rotating the crucible at a high speed. As a result, dislocations generated in the neck portion by thermal shock are formed on the outer periphery of the neck portion, and the dislocations can be eliminated in the neck portion forming process.
In addition, since no horizontal magnetic field is applied, convection below the solid-liquid interface is promoted, and by rotating the crucible at high speed, the temperature of the silicon melt can be stabilized and the occurrence of dislocations due to large temperature fluctuations can be prevented.
In addition, when forming the shoulder portion, while the diameter of the shoulder portion is small, the crucible rotation is accelerated to stabilize the temperature of the silicon melt, as in the case of forming the neck portion, thereby suppressing large temperature fluctuations below the solid-liquid interface and preventing the occurrence of dislocations.
Furthermore, when starting to form the body portion, a horizontal magnetic field is applied to suppress convection in the silicon melt, increasing the temperature gradient and slowing down the crucible rotation speed, thereby making it possible to suppress the occurrence of dislocations due to constitutional supercooling during the process of forming the body portion.

In order to produce low-resistance silicon single crystals, a high concentration of dopant is added and a single crystal pulling apparatus that pulls up silicon single crystals using the Czochralski method can provide a single crystal pulling apparatus and single crystal pulling method that can suppress dislocations after shoulder formation.

FIG. 1 is a cross-sectional view showing an example of a single crystal pulling apparatus according to the present invention. FIG. 2 is a flow chart showing the process of an embodiment of the single crystal pulling method of the present invention. FIG. 3 is a graph showing an example of the control of the magnetic field application in the single crystal pulling method of the present invention. FIG. 4 is a graph showing an example of crucible rotation control in the single crystal pulling method of the present invention. FIG. 5 is a cross-sectional view of a conventional single crystal pulling apparatus.

The following describes an embodiment of the single crystal pulling apparatus and single crystal pulling method according to the present invention with reference to the drawings. However, this embodiment is described as an example of the present invention, and the present invention is not limited thereto.

Figure 1 is a cross-sectional view showing an example of a single crystal pulling apparatus according to the present invention. This single crystal pulling apparatus 1 has a furnace body 10 formed by stacking a pull chamber 10b on a cylindrical main chamber 10a, and is equipped with a carbon crucible (or graphite crucible) 2 that is rotatable around a vertical axis and can be raised and lowered within the furnace body 10, and a quartz glass crucible 3 (hereinafter simply referred to as crucible 3) held by the carbon crucible 2. This crucible 3 is rotatable around the vertical axis together with the rotation of the carbon crucible 2.

Further, below the carbon crucible 2, there are provided a rotation drive unit 14 such as a rotation motor for rotating the carbon crucible 2 around a vertical axis, and an elevation drive unit 15 for moving the carbon crucible 2 up and down.
The rotation drive unit 14 is connected to a rotation drive control unit 14a, and the elevation drive unit 15 is connected to an elevation drive control unit 15a.

The single crystal pulling apparatus 1 also includes a side heater 4 using a resistance heating method or a high-frequency induction heating method for heating and melting the semiconductor raw material (raw material polysilicon) loaded in the crucible 3 to produce silicon melt M, and a bottom heater 5. As shown in the figure, the side heater 4 is disposed so as to surround the crucible 3 from the side thereof, and the bottom heater 5 is disposed below the crucible 3. The heating output of the side heater 4 is controlled by a side heater control unit 4a, and the heating output of the bottom heater 5 is controlled by a bottom heater control unit 5a.

In addition, in this single crystal pulling apparatus 1, a magnetic field application electromagnetic coil 8 is installed outside the furnace body 2. When a predetermined current is applied to this magnetic field application electromagnetic coil 8, a horizontal magnetic field of a predetermined strength is applied to the silicon melt M in the crucible 3. The magnetic field application electromagnetic coil 8 is connected to an electromagnetic coil control unit 8a (magnetic field application control unit) that controls its operation.

That is, in this embodiment, the MCZ method (magnetic field applied CZ method) is carried out, in which a horizontal magnetic field is applied to the molten liquid M to grow a single crystal, thereby controlling the convection of the silicon molten liquid M and stabilizing the single crystallization.

The single crystal pulling device 1 also includes a pulling mechanism 9 that winds up the wire 6 and pulls up the single crystal C being grown. A seed crystal P is attached to the tip of the wire 6 of the pulling mechanism 9. A rotation drive control unit 9a that controls the rotation drive of the pulling mechanism 9 is connected to the pulling mechanism 9.

A radiation shield 7 is placed above the silicon melt M formed in the crucible 3 to surround the single crystal C. This radiation shield 7 has openings at the top and bottom, and serves to block excess radiant heat from the side heaters 4 and the silicon melt M to the single crystal C being grown, and to straighten the gas flow inside the furnace.

The single crystal pulling device 1 also includes an optical diameter measuring sensor (diameter measuring device) 16, such as a CCD camera, for measuring the diameter of the single crystal being grown. A small observation window 10a1 is provided on the top surface of the main chamber 10a, and the change in position of the crystal end (position indicated by the dashed arrow) at the solid-liquid interface can be detected from outside this small window 10a1.

The single crystal pulling device 1 also includes a controller 11 having a memory device 11a and an arithmetic and control device 11b, and the side heater control unit 4a, bottom heater control unit 5a, electromagnetic coil control unit 8a, rotation drive control unit 14a, lift drive control unit 15a, rotation drive control unit 9a, and diameter measurement sensor 16 are each connected to the arithmetic and control device 11b.

In the single crystal pulling apparatus 1 thus constructed, when a single crystal C having a diameter of, for example, 200 mm is grown, pulling is performed as follows.
That is, first, raw polysilicon (for example, 150 kg) is loaded into the crucible 3, and a crystal growing process is started based on the program stored in the storage device 11a of the controller 11.

First, a predetermined atmosphere (mainly an inert gas such as argon gas) is created inside the furnace body 10. For example, a furnace atmosphere with an internal furnace pressure of 65 torr and an argon gas flow rate of 90 liters/min is created.
Then, while the crucible 3 is rotated in a predetermined direction at a high rotation speed (a first rotation speed of 10 rpm to 20 rpm), for example, 15 rpm (step S1 in FIG. 2), the raw material polysilicon loaded in the crucible 3 is melted by heating with the side heater 4 and the bottom heater 5 to form silicon melt M (step S2 in FIG. 2). In order to grow a silicon single crystal with a low resistivity of 0.5 mΩcm to 1.1 mΩcm, 1000 g of red phosphorus is added to the silicon melt M as a dopant.
The first rotation speed is set to 10 rpm or more and 20 rpm or less for the following reason: if the first rotation speed of the crucible 3 is smaller than 10 rpm, there is a risk that the temperature fluctuation of the silicon melt M will be large, and if the first rotation speed is larger than 10 rpm, there is a risk that the liquid surface vibration of the silicon melt M will occur.

Once the silicon melt M is formed, the pulling conditions are adjusted using parameters such as the initial power supply to the side heater 4 and bottom heater 5 and the pulling speed, and the seed crystal P begins to rotate around its axis at a predetermined rotation speed. The rotation direction is opposite to that of the crucible 3.

Next, the wire 6 is lowered to bring the seed crystal P into contact with the silicon melt M (step S3 in FIG. 2). After the tip of the seed crystal P is melted, necking is performed to form a neck portion P1 (step S4 in FIG. 2).
Here, since the horizontal magnetic field has not yet been applied, the convection of the silicon melt M is not suppressed. Therefore, in the neck forming process, the convection below the solid-liquid interface is promoted, and the crucible rotation speed is high at 15 rpm, and the solid-liquid interface shape can be stably formed into a downward convex shape without increasing the dopant concentration in the diffusion boundary layer immediately below the solid-liquid interface more than necessary. As a result, dislocations generated in the neck due to thermal shock are formed on the outer periphery of the neck, and the dislocations can be eliminated in the neck forming process.
In addition, since no horizontal magnetic field is applied, convection of the silicon melt M is not suppressed, and since the crucible rotation speed is high at 15 rpm, the silicon melt M is stirred and the temperature of the silicon melt M is kept stable. Therefore, no large thermal fluctuation occurs, and it is possible to prevent the occurrence of dislocations due to thermal fluctuation.

Next, the shoulder C1 starts to form as the crystal diameter gradually expands (step S5 in FIG. 2). When the shoulder C1 starts to form, the crucible rotation speed starts to decrease from 15 rpm as the crystal diameter increases, as shown in the graph in FIG. 4 (the vertical axis is the crucible rotation speed (rpm), and the horizontal axis is the crystal diameter (mm)) (step S6 in FIG. 2).
Here, while the diameter of the shoulder portion C1 is small, it is preferable to rotate the crucible at a high speed, similar to that of the neck portion, to stabilize the temperature of the silicon melt M, thereby suppressing large temperature fluctuations and preventing the occurrence of dislocations.

When the diameter of the shoulder portion C1 reaches 3/4 of the diameter of the body portion C2, which is 150 mm in this example (step S7 in FIG. 2), as shown in the graph in FIG. 3 (the vertical axis is the magnetic field strength (tesla), and the horizontal axis is the crystal diameter (mm)), a predetermined current is passed through the magnetic field application electromagnetic coil 8, and application of a horizontal magnetic field to the molten liquid M in order to suppress convection (step S8 in FIG. 2).
Also, as shown in the graph of FIG. 3, by the time the diameter of the shoulder portion C1 reaches 200 mm, which is the diameter of the straight body portion C2, the magnetic field of the horizontal magnetic field is set to 0.1 Tesla (1000 Gauss) or more (preferably 0.2 Tesla (2000 Gauss) or more and 0.3 Tesla (3000 Gauss) or less), in this example, 0.2 Tesla (2000 Gauss) (step S9 in FIG. 2).
Furthermore, as shown in FIG. 4, before the diameter of the shoulder portion C1 reaches 200 mm, which is the diameter of the body portion C2, the crucible rotation speed is reduced to 1 rpm or less (second rotation speed) (step S10 in FIG. 2).

In this way, when the diameter of the shoulder portion C1 reaches the diameter of the straight body portion C2, the controller 11 controls the lift drive unit 15 via the lift drive control unit 15a, keeps the pulling speed constant at, for example, 0.55 mm/min, and proceeds to the process of forming the straight body portion C2, which will become the product part (step S11 in Figure 2).
In forming this straight body portion C2, a horizontal magnetic field of 0.2 Tesla (2000 Gauss) is applied, and the crucible rotation speed is slowed down to 1 rpm (a second rotation speed lower than the first rotation speed).
That is, the application of the horizontal magnetic field suppresses the convection of the silicon melt and increases the temperature gradient GL. In addition, since the crucible rotation speed is small, the stirring of the silicon melt can be suppressed and the decrease in the temperature gradient GL can be suppressed. As a result, the occurrence of dislocations due to compositional supercooling is suppressed in the process of forming the straight body portion C2. In addition, in the pulling of the straight body portion C2, the second rotation speed of the crucible 3 is set to 1 rpm or less while the horizontal magnetic field is applied because the temperature of the silicon melt M is stable at 1 rpm or less and the temperature of the silicon melt M may become unstable at more than 1 rpm.

Once the body C2 has been formed to a predetermined length, the process moves to the final tail process (step S12 in FIG. 2). In this tail process, the contact area between the bottom end of the crystal and the silicon melt M gradually decreases, and the single crystal C is separated from the silicon melt M, producing a silicon single crystal.

As described above, according to the embodiment of the present invention, in forming the neck portion, the solid-liquid interface shape can be made downwardly convex by rotating the crucible at high speed. As a result, dislocations generated in the neck portion due to thermal shock are formed on the outer periphery of the neck portion, and the dislocations can be eliminated in the neck portion forming process. In addition, since no horizontal magnetic field is applied, convection under the solid-liquid interface is promoted, and by rotating the crucible at high speed, the temperature of the silicon melt can be stabilized, and the occurrence of dislocations due to large temperature fluctuations can be prevented.
In addition, in forming the shoulder portion C1, the crucible rotation speed is gradually decreased, but while the diameter of the shoulder portion C1 is small, the crucible rotation is increased to a high speed in the same manner as in forming the neck portion to stabilize the temperature of the silicon melt M. This makes it possible to suppress large temperature fluctuations below the solid-liquid interface and prevent the occurrence of dislocations.
Furthermore, when the formation of the body portion C2 starts, a horizontal magnetic field is applied to suppress convection of the silicon melt, increasing the temperature gradient GL and slowing down the crucible rotation speed, thereby making it possible to suppress the occurrence of dislocations due to constitutional supercooling in the process of forming the body portion C2.

The single crystal pulling apparatus and single crystal pulling method according to the present invention will be further explained based on examples.

(Experiment 1)
In experiment 1, when pulling up a low-resistivity silicon single crystal using the single crystal pulling apparatus shown in Figure 1, the neck portion was formed in a magnetic field-free state, and the timing of applying a horizontal magnetic field thereafter was examined by changing the conditions.

Example 1
In Example 1, a silicon single crystal doped with red phosphorus and having a diameter of 200 mm and a resistivity of 1.3 mΩcm was grown. As shown in Figures 3 and 4, the process started with no magnetic field from the time of neck formation, and the timing of magnetic field application was set to the time when the shoulder diameter was 150 mm (3/4 of the straight body diameter), and the timing of the reduction in the rotation speed of the crucible was set to the time when the shoulder diameter was 50 mm, and the rotation speed was controlled to be 1 rpm from 15 rpm when the straight body was reached. After that, a horizontal magnetic field of 0.3 Tesla (3000 Gauss) was applied to the straight body, and the presence or absence of dislocations in the pulled silicon single crystal was inspected. The number of pulling trials was three.
Example 2
In Example 2, a silicon single crystal doped with red phosphorus and having a resistivity of 1.2 mΩcm and a diameter of 200 mm was grown. The other conditions were the same as those in Example 1.
Example 3
In Example 3, a silicon single crystal doped with red phosphorus and having a resistivity of 1.1 mΩcm and a diameter of 200 mm was grown. The other conditions were the same as those in Example 1.

Example 4
In Example 4, a silicon single crystal doped with red phosphorus and having a resistivity of 1.0 mΩcm and a diameter of 200 mm was grown. The other conditions were the same as those in Example 1.
Example 5
In Example 5, a silicon single crystal doped with red phosphorus and having a resistivity of 0.9 mΩcm and a diameter of 200 mm was grown. The other conditions were the same as those in Example 1.

(Comparative Example 1)
In Comparative Example 1, a silicon single crystal doped with red phosphorus and having a diameter of 200 mm and a resistivity of 1.3 mΩcm was grown. The neck was formed without a magnetic field, and the timing for starting the magnetic field application was set to the point where the shoulder diameter was 50 mm, and the rotation speed was controlled to be 1 rpm from 15 rpm when the straight body was reached. After that, a horizontal magnetic field of 0.3 Tesla (3000 Gauss) was applied to the straight body, and the presence or absence of dislocations in the pulled silicon single crystal was inspected. The number of pulling trials was three.
(Comparative Example 2)
In Comparative Example 2, a silicon single crystal doped with red phosphorus and having a resistivity of 1.2 mΩcm and a diameter of 200 mm was grown. The other conditions were the same as those of Comparative Example 1.
(Comparative Example 3)
In Comparative Example 3, a silicon single crystal doped with red phosphorus and having a resistivity of 1.1 mΩcm and a diameter of 200 mm was grown. The other conditions were the same as those of Comparative Example 1.

(Comparative Example 4)
In Comparative Example 4, a silicon single crystal doped with red phosphorus and having a resistivity of 1.0 mΩcm and a diameter of 200 mm was grown. The other conditions were the same as those of Comparative Example 1.
(Comparative Example 5)
In Comparative Example 5, a silicon single crystal doped with red phosphorus and having a resistivity of 0.9 mΩcm and a diameter of 200 mm was grown. The other conditions were the same as those of Comparative Example 1.

(Comparative Example 6)
In Comparative Example 6, a silicon single crystal doped with red phosphorus and having a diameter of 200 mm and a resistivity of 1.3 mΩcm was grown. The neck was formed without a magnetic field, and the timing for starting the magnetic field application was set to the point where the shoulder diameter was 100 mm, and the rotation speed was controlled to be 1 rpm from 15 rpm when the straight body was reached. After that, a horizontal magnetic field of 0.3 Tesla (3000 Gauss) was applied to the straight body, and the presence or absence of dislocations in the pulled silicon single crystal was inspected. The number of pulling trials was three.
(Comparative Example 7)
In Comparative Example 7, a silicon single crystal doped with red phosphorus and having a resistivity of 1.2 mΩcm and a diameter of 200 mm was grown. The other conditions were the same as those of Comparative Example 6.
(Comparative Example 8)
In Comparative Example 8, a silicon single crystal doped with red phosphorus and having a resistivity of 1.1 mΩcm and a diameter of 200 mm was grown. The other conditions were the same as those of Comparative Example 6.

(Comparative Example 9)
In Comparative Example 9, a silicon single crystal doped with red phosphorus and having a resistivity of 1.0 mΩcm and a diameter of 200 mm was grown. The other conditions were the same as those of Comparative Example 6.
(Comparative Example 10)
In Comparative Example 10, a silicon single crystal doped with red phosphorus and having a resistivity of 0.9 mΩcm and a diameter of 200 mm was grown. The other conditions were the same as those of Comparative Example 6.

(Comparative Example 11)
In Comparative Example 11, a silicon single crystal doped with red phosphorus and having a diameter of 200 mm and a resistivity of 1.3 mΩcm was grown. The neck was formed without a magnetic field, and the timing of magnetic field application was set to the point where the length of the straight body was 0 mm, and the rotation speed was controlled to be 1 rpm from 15 rpm when the straight body was reached. After that, a horizontal magnetic field of 0.3 Tesla (3000 Gauss) was applied to the straight body, and the presence or absence of dislocations in the pulled silicon single crystal was inspected. The number of pulling trials was three.
(Comparative Example 12)
In Comparative Example 12, a silicon single crystal doped with red phosphorus and having a resistivity of 1.2 mΩcm and a diameter of 200 mm was grown. The other conditions were the same as those of Comparative Example 11.
(Comparative Example 13)
In Comparative Example 13, a silicon single crystal doped with red phosphorus and having a resistivity of 1.1 mΩcm and a diameter of 200 mm was grown. The other conditions were the same as those of Comparative Example 11.

(Comparative Example 14)
In Comparative Example 14, a silicon single crystal doped with red phosphorus and having a resistivity of 1.0 mΩcm and a diameter of 200 mm was grown. The other conditions were the same as those of Comparative Example 11.
(Comparative Example 15)
In Comparative Example 15, a silicon single crystal doped with red phosphorus and having a resistivity of 0.9 mΩcm and a diameter of 200 mm was grown. The other conditions were the same as those of Comparative Example 11.

(Comparative Example 16)
In Comparative Example 16, a silicon single crystal doped with red phosphorus and having a diameter of 200 mm and a resistivity of 1.3 mΩcm was grown. The neck was formed without a magnetic field, and the timing of magnetic field application was set to the point where the length of the straight body was 0 mm, and the rotation speed was controlled to be 1 rpm from 15 rpm when the straight body was reached. After that, a horizontal magnetic field of 0.3 Tesla (3000 Gauss) was applied to the straight body, and the presence or absence of dislocations in the pulled silicon single crystal was inspected. The number of pulling trials was three.
(Comparative Example 17)
In Comparative Example 17, a silicon single crystal doped with red phosphorus and having a resistivity of 1.2 mΩcm and a diameter of 200 mm was grown. The other conditions were the same as those of Comparative Example 16.
(Comparative Example 18)
In Comparative Example 18, a silicon single crystal doped with red phosphorus and having a resistivity of 1.1 mΩcm and a diameter of 200 mm was grown. The other conditions were the same as those of Comparative Example 16.

(Comparative Example 19)
In Comparative Example 19, a silicon single crystal doped with red phosphorus and having a resistivity of 1.0 mΩcm and a diameter of 200 mm was grown. The other conditions were the same as those of Comparative Example 16.
(Comparative Example 20)
In Comparative Example 20, a silicon single crystal doped with red phosphorus and having a resistivity of 0.9 mΩcm and a diameter of 200 mm was grown. The other conditions were the same as those of Comparative Example 16.

The results of Examples 1 to 5 and Comparative Examples 6 to 20 are shown in Table 1. In the evaluation column of Table 1, if all three of the three pulling trials were dislocation-free, they were marked with an O; if one or two of the three had dislocations, they were marked with a △; and if three of the three had dislocations, they were marked with an X.

As shown in Table 1, in the pulling (Examples 1 to 5) in which the magnetic field application was started from a shoulder diameter of 150 mm, which corresponds to 3/4 of the diameter, which is the condition according to the present invention, crystals could be grown without dislocations regardless of the resistivity. Although not shown in Table 1, even in the pulling in which the magnetic field application was started from a shoulder diameter of 150 mm, which corresponds to 3/4 of the diameter, when the magnetic field strength at the start of the formation of the straight body portion was set to less than 0.1 Tesla (1000 Gauss), such as 0.03 Tesla (300 Gauss), 0.05 Tesla (500 Gauss), 0.09 Tesla (900 Gauss), and 0.095 Tesla (950 Gauss), dislocations occurred in one or three out of three crystals. Specifically, dislocations occurred in three out of three crystals at magnetic field strengths of 0.03 Tesla (300 Gauss) and 0.05 Tesla (500 Gauss). Furthermore, at magnetic field strengths of 0.09 Tesla (900 Gauss) and 0.095 Tesla (950 Gauss), dislocations occurred in only one of the three crystals. On the other hand, when the magnetic field strength was set to 0.1 Tesla (1000 Gauss) at the start of the formation of the straight body portion, crystals could be grown without dislocations in all three of the three crystals, confirming that it is desirable to apply a horizontal magnetic field of 0.1 Tesla (1000 Gauss) or more at the start of the formation of the straight body portion.
Furthermore, although not shown in Table 1, when pulling up a straight body portion having a resistivity of 0.5 mΩcm, which is lower than that of Example 5 (other conditions were the same as in Example 1), three out of three were dislocation-free. This confirms that the single crystal pulling apparatus of the present invention can pull up a silicon single crystal having a low resistivity of 0.5 mΩcm or more and 1.1 mΩcm or less without dislocations.

In contrast, when the magnetic field was applied with a shoulder diameter of 100 mm or less (Comparative Examples 1 to 10), dislocations occurred in the crystal regardless of the level of resistivity. On the other hand, when the magnetic field was applied after the crystal reached the straight body (Comparative Examples 11 to 20), dislocations occurred under conditions of low resistivity.
It was also confirmed that dislocations were more likely to occur if the timing of reducing the crucible rotation speed was when the crucible reached the straight body or after it had reached the body.
Additionally, although red phosphorus is preferred as the dopant in the present invention, arsenic and antimony are also applicable.

REFERENCE SIGNS LIST 1 Single crystal pulling device 3 Silica glass crucible 4 Side heater 5 Bottom heater 6 Wire 7 Radiation shield 8a Electromagnetic coil control unit (magnetic field application control unit)
14 Rotation drive unit 14a Rotation drive control unit C Silicon single crystal M Silicon melt C1 Shoulder C2 Body CN Neck

Claims (12)

A single crystal pulling apparatus for forming a silicon melt in a crucible by heating the crucible from a heater surrounding the crucible, adding a dopant to the silicon melt and applying a horizontal magnetic field to the silicon melt, and pulling a silicon single crystal from the silicon melt by a Czochralski method,
a rotation drive control unit that rotates the crucible around a vertical axis by a rotation drive unit;
a magnetic field application control unit for controlling a horizontal magnetic field applied to the silicon melt;
Equipped with
the rotation drive control unit controls the rotation speed of the crucible to be rotated at a first rotation speed when a neck portion of the single crystal is formed, and to be rotated at a second rotation speed lower than the first rotation speed when formation of a body portion of the single crystal is started;
the magnetic field application control unit applies no magnetic field when the neck of the single crystal is formed, starts applying a horizontal magnetic field when the diameter of the shoulder of the single crystal is 3/4 or more and less than 1/1 of the diameter of the straight body, and controls so as to apply a horizontal magnetic field of 0.1 Tesla or more when formation of the straight body begins. The single crystal pulling apparatus according to claim 1, characterized in that the rotation drive control unit controls the rotation speed of the crucible to be gradually reduced when changing the rotation speed from the first rotation speed to the second rotation speed. The single crystal pulling apparatus according to claim 1, characterized in that the rotation drive control unit controls the rotation speed of the crucible to be constant at a second rotation speed during the formation of the straight body portion. The single crystal pulling apparatus described in claim 1, characterized in that the first rotation speed is 10 rpm or more and 20 rpm or less, and the second rotation speed is 1 rpm or less. The single crystal pulling apparatus according to claim 1, characterized in that the magnetic field application control unit controls the application of a horizontal magnetic field of 0.2 Tesla or more and 0.3 Tesla or less during the formation of the straight body portion. A method for pulling a single crystal, comprising the steps of forming a silicon melt in a crucible by heating the crucible from a heater surrounding the crucible, adding a dopant to the silicon melt and applying a horizontal magnetic field to the silicon melt, and pulling a silicon single crystal from the silicon melt by a Czochralski method,
In forming a neck portion of the single crystal, a step of rotating the crucible at a first rotation speed without applying a horizontal magnetic field;
In forming a shoulder of the single crystal, a step of starting to apply a horizontal magnetic field when the diameter of the shoulder of the single crystal is 3/4 or more and less than 1/1 of the diameter of the straight body of the single crystal;
In forming a straight body portion of the single crystal, a horizontal magnetic field of 0.1 Tesla or more is applied before the start of formation of the straight body portion, and a rotation speed of the crucible is set to a second rotation speed which is smaller than the first rotation speed;
A method for pulling a single crystal comprising the steps of: During a period from a step of rotating the crucible at a first rotation speed in forming a neck portion of the single crystal to a step of changing the rotation speed of the crucible to a second rotation speed lower than the first rotation speed at the start of forming a body portion of the single crystal,
7. The method for pulling a single crystal according to claim 6, wherein the rotation speed of the crucible is controlled to be gradually decreased from the first rotation speed to the second rotation speed. The method for pulling a single crystal according to claim 6, characterized in that the rotation speed of the crucible is controlled to a constant second rotation speed during the formation of the straight body portion of the single crystal. The method for drawing a single crystal according to claim 6, characterized in that the first rotation speed is 10 rpm or more and 20 rpm or less, and the second rotation speed is 1 rpm or less. The method for pulling a single crystal according to claim 6, characterized in that a horizontal magnetic field of 0.2 Tesla or more and 0.3 Tesla or less is applied during the formation of the straight body portion. The method for pulling a single crystal according to claim 6, characterized in that a silicon single crystal having a resistivity of 0.5 mΩcm or more and 1.1 mΩcm or less is pulled by adding a dopant to the silicon melt. The method for pulling a single crystal according to claim 6, characterized in that the dopant is red phosphorus.

Images