JP2013199387A - Apparatus and method for pulling single crystal - Google Patents

Abstract

PROBLEM TO BE SOLVED: To control an opening diameter of a radiation shield along with pulling; to suppress generation of dislocation of a crystal; and to improve pulling speed.SOLUTION: This apparatus includes: a radiation shield 7 formed cylindrically having openings on the upper and lower sides respectively, and arranged over silicon molten liquid M in a crucible 3 so as to enclose a silicon single crystal C; an annular separation inner member 12 provided engageably with a lower opening 7c of the radiation shield; and a lifting means 14 for lifting and lowering the separation inner member with respect to the lower opening of the radiation shield; wherein the separation inner member lowered by the lifting means is engaged with the lower opening of the radiation shield, and thereby a lower opening diameter of the radiation shield is reduced.

Description

  The present invention relates to a single crystal pulling apparatus and a single crystal pulling method for pulling up while growing a single crystal by the Czochralski method (hereinafter referred to as “CZ method”).

  The CZ method is widely used for the growth of silicon single crystals. In this method, as shown in FIG. 7, a silicon melt M is formed in the crucible 50 by the heat of the heater 52, the seed crystal P is brought into contact with the surface thereof, the crucible 50 is rotated, and the seed crystal P The single crystal C is formed at the lower end of the seed crystal P by pulling upward while rotating in the opposite direction. Specifically, necking P1 is formed by melting the tip of the seed crystal P, the neck P1 is formed, the diameter of the crystal is expanded from the neck P1, and the shoulder C1 is formed. Part C2 is formed. Further, when the straight body portion C2 is formed, the diameter of the crystal is reduced and a bottom portion (not shown) is formed.

  In the single crystal pulling apparatus that performs this CZ method, as disclosed in Patent Document 1, a radiation shield 51 is provided above the crucible so as to surround the pulling region of the single crystal C. The radiation shield 51 effectively blocks the radiant heat to the outer peripheral surface of the single crystal C to be grown, thereby promoting the solidification of the single crystal C being pulled up and quickly cooling the single crystal C. be able to. Moreover, in the case of the structure which has arrange | positioned the water cooling body 53 inside the radiation shield 51 so that it may show in figure, since the heat removal effect from a crystal | crystallization improves, pulling-up speed can be made quick.

JP-A-11-92272

By providing the radiation shield 51 as described above, radiation heat to the outer peripheral surface of the single crystal C to be grown can be effectively blocked, and in particular, the edge of the lower opening 51a of the radiation shield 51 and the crystal peripheral surface. If the distance between the two is small, the crystal cooling capacity is further improved, and the pulling speed can be further increased.
However, in order to obtain the above effect, when the lower opening diameter of the radiation shield 51 is slightly larger than the diameter of the straight body portion of the single crystal C and the crystal cooling capacity is set high, for example, when the neck portion P1 is formed. When the crystal is cooled rapidly, the thermal stress inside the crystal increases, and when dislocations occur, it is difficult to escape outwards and cannot be removed, resulting in a low dislocation rate (cannot suppress dislocations). There was a problem.
Further, in the growing process of the straight body portion C2 in the first half of the crystal pulling, the free surface area where oxygen evaporates in the melt M is constant even when the pulling progresses, whereas the residual liquid decreases with the pulling and melts. Since the area for supplying oxygen to the liquid M (the contact area between the melt M and the crucible) is gradually reduced, the oxygen concentration gradually decreases along the crystal axis, and the oxygen concentration distribution is simply uniform in the crystal axis direction. There was a problem that crystals could not be obtained.

  The present invention has been made under the circumstances as described above. In a single crystal pulling apparatus and single crystal pulling method for pulling a silicon single crystal from a crucible by the Czochralski method, radiation is accompanied by pulling. Single crystal pulling that can control the opening diameter of the shield, suppress dislocations in the crystal and improve pulling speed, and can obtain a single crystal with a uniform oxygen concentration distribution in the crystal axis direction. An object is to provide an apparatus and a method for pulling a single crystal.

A single crystal pulling apparatus according to the present invention, which has been made to solve the above problems, applies a magnetic field to a silicon melt in a crucible and pulls up the silicon single crystal from the silicon melt by the Czochralski method. A single crystal pulling apparatus, which is formed in a cylindrical shape having openings on the top and bottom, and is disposed above the silicon melt in the crucible so as to surround the silicon single crystal, and the radiation An annular separation inner member provided so as to be engageable with the lower opening of the shield, and an elevating means for moving the separation inner member up and down with respect to the lower opening of the radiation shield. When the separated inner member is engaged with the lower opening of the radiation shield, the lower opening diameter of the radiation shield is reduced. Having the features.
The lower opening of the annular radiation shield has an end surface having a predetermined thickness dimension and is opposed to each other in the radial direction, and when the diameter of the silicon single crystal is Φ _cry , It is desirable that the diameter Φ ₁ of the separation inner member, the lower end side diameter Φ ₂ of the lower opening of the radiation shield, and the upper end side diameter Φ ₃ are respectively defined by equations (1) to (3).

Φ ₁ = Φ _cry +10 to 100 mm (1)
Φ ₂ = Φ ₁ +10 to 100 mm (2)
Φ ₃ = Φ ₂ +10 to 100 mm (3)

By configuring in this way, the size of the lower opening diameter of the radiation shield becomes variable.For example, if the lower opening diameter is large when growing the neck, shoulder and bottom of the crystal, the cooling capacity can be increased. Can be small. For this reason, the thermal stress inside the crystal is reduced, and when dislocations occur during the formation of the neck, shoulder and bottom, it can be easily removed outwards, improving the dislocation-free rate of the crystal can do.
In addition, when the straight body portion of the crystal is grown, the cooling capacity can be increased if the lower opening diameter of the radiation shield is made small. Thereby, the pulling speed of the crystal can be increased, and the productivity can be improved.
Also, if the lower opening diameter of the radiation shield is made small, the oxygen concentration in the crystal will decrease, and if the lower opening diameter is made large, the oxygen concentration in the crystal will rise. Thus, the oxygen concentration in the crystal can be controlled.
Furthermore, when a transverse magnetic field is applied to the melt and the crystal is pulled up, the melt convection changes due to a rapid decrease in the free surface area if the melt surface is below the small R portion directly below the straight body of the crucible. However, if the lower opening diameter of the radiation shield is small, the temperature of the melt immediately below the crystal periphery increases rapidly. It is possible to effectively suppress dislocation induced from supercooling.

In addition, the single crystal pulling method according to the present invention, which has been made to solve the above-described problems, includes forming a silicon melt in a crucible and applying a magnetic field to the silicon melt. A method of pulling a single crystal from a silicon melt by a Czochralski method, wherein a cylindrical radiation shield having openings above and below is disposed so as to surround the silicon single crystal at the top, An annular separation member that can be engaged with the lower opening of the shield and reduces the diameter of the lower opening by being engaged is moved up and down in accordance with the growth process of the silicon single crystal, thereby It is characterized in that the distance between the peripheral surface of the crystal and the lower opening is changed.
In the process of growing the silicon single crystal, at least in the neck portion forming step, the separation inner member is disposed above the radiation shield and is not engaged with the lower opening of the radiation shield, thereby forming a straight body portion. In the step, the separation inner member is engaged with the lower opening of the radiation shield. In the crystal bottom forming step, the separation inner member is disposed above the radiation shield and is not engaged with the lower opening of the radiation shield. It is desirable.

According to such a method, since the size of the lower opening diameter of the radiation shield is variable, at least in the process of forming the neck portion and the bottom portion of the crystal, if the lower opening diameter is made large, the cooling capacity is reduced. can do. For this reason, the thermal stress inside the crystal is reduced, and when dislocations occur during the formation of the neck and the bottom, it can be easily removed outward, and the dislocation-free rate of the crystal can be improved. it can.
In addition, when the straight body portion of the crystal is grown, the cooling capacity can be increased if the lower opening diameter of the radiation shield is made small. Thereby, the pulling speed of the crystal can be increased, and the productivity can be improved.

Further, in the step of forming the straight body portion of the silicon single crystal, the separation inner member is moved up and down with respect to the lower opening of the radiation shield, and the distance between the lower opening and the crystal peripheral surface is changed. The oxygen concentration may be controlled.
Specifically, if the distance between the lower opening of the radiation shield and the peripheral surface of the crystal is small, the gas flow rate at the meniscus surface of the melt near the crystal periphery is increased, and oxygen is easily evaporated. Flows directly under the crystal and solidifies, so that the oxygen concentration in the crystal can be lowered. On the other hand, if the distance between the lower opening and the crystal peripheral surface is large, the gas flow velocity at the meniscus surface of the melt near the crystal periphery is reduced, making it difficult for oxygen to evaporate, and the high oxygen melt flows directly under the crystal. As it solidifies, the oxygen concentration in the crystal can be increased.
For this reason, a single crystal having a uniform oxygen concentration distribution along the crystal axis can be obtained by performing predetermined control for moving the separation inner member up and down along with the process of growing the straight body portion.

  According to the present invention, in a single crystal pulling apparatus that pulls a silicon single crystal from a crucible by the Czochralski method, the opening diameter of the radiation shield is controlled along with the pulling, and the dislocation of the crystal is suppressed and pulled. The upper speed can be improved, and a single crystal having a uniform oxygen concentration distribution in the crystal axis direction can be obtained. Furthermore, when a transverse magnetic field is applied to the melt and the crystal is pulled up, if the lower opening diameter of the radiation shield is made small, the temperature of the melt immediately below the outer periphery of the crystal rises rapidly. It is possible to effectively suppress dislocation induced from the supercooling of the liquid.

FIG. 1 is a cross-sectional view showing a configuration of a single crystal pulling apparatus according to the present invention. FIG. 2 is a cross-sectional view showing a state where the separation inner member is lowered from the state shown in FIG. 1 and engaged with the lower opening of the radiation shield in the single crystal pulling apparatus of FIG. FIG. 3 is a flow showing a series of steps of the single crystal pulling method in the single crystal pulling apparatus of FIG. FIG. 4 is a partially enlarged cross-sectional view of the single crystal pulling apparatus of FIG. FIG. 5 is a cross-sectional view showing a state where the separation inner member is lowered from the state shown in FIG. 1 and arranged above the lower opening of the radiation shield in the single crystal pulling apparatus of FIG. FIG. 6 is a graph showing the results of Example 4. FIG. 7 is a cross-sectional view showing a configuration of a conventional single crystal pulling apparatus.

  Hereinafter, embodiments of a single crystal pulling apparatus and a single crystal pulling method according to the present invention will be described with reference to the drawings. FIG. 1 is a sectional view showing a partial configuration of a single crystal pulling apparatus according to the present invention.

This single crystal pulling apparatus 1 includes a furnace body 2 formed by superposing a pull chamber 2b on a cylindrical main chamber 2a, a crucible 3 provided in the furnace body 2, and a semiconductor loaded in the crucible 3. A resistance heater 4 (hereinafter simply referred to as a heater) that melts a raw material (raw material polysilicon) to form a silicon melt M (hereinafter simply referred to as melt M) and a single crystal that is grown by winding up a wire 6 And a pulling mechanism 5 for pulling up C.
The crucible 3 has a double structure, and is composed of a quartz glass crucible 3a on the inside and a graphite crucible 3b on the outside. Further, the inner quartz glass crucible 3a has a straight body portion 3a1, and a bottom portion (large R portion) 3a3 via a small R portion 3a2 therebelow. A seed crystal P is attached to the tip of the wire 6 included in the pulling mechanism 5.

Further, in the single crystal pulling apparatus 1, although not shown in FIG. 1, a magnetic field applying electromagnetic coil (not shown in FIG. 1) is installed outside the main chamber 2a.
When a predetermined current is applied to the magnetic field application electromagnetic coil, a transverse magnetic field having a predetermined intensity is applied to the silicon melt M in the crucible 3.
That is, in the present embodiment, the MCZ method (Magnetic field applied CZ method) in which a magnetic field is applied to the melt M to grow a single crystal is implemented, thereby controlling the convection of the silicon melt M and It is made to stabilize.

In addition, above the melt M formed in the crucible 3, a cylindrical shape having openings up and down to shield the extra radiant heat from the heater 4 and the melt M with respect to the growing single crystal C. A radiation shield 7 is provided.
The radiation shield 7 has an outer cylinder member 8 formed to a predetermined thickness fixed to the furnace body 2 and a heat insulating member 9 (9a and 9b are laminated in two stages) inside the outer cylinder member 8. Is provided. The outer cylinder member 8 is made of, for example, high-purity graphite or graphite having a surface coated with SiC. Moreover, the said heat insulation member 9 is formed with the felt material which consists of carbon fibers, for example.

Further, the radiation shield 7 composed of the outer cylindrical member 8 and the heat insulating member 9 as described above includes a cylindrical straight body portion 7a surrounding the periphery of the single crystal C as shown in the figure, and an inner side from the lower end of the straight body portion 7a. And a lower shoulder 7b that forms a lower opening 7c. The lower opening 7c has a predetermined thickness dimension and is formed so as to face each other in the radial direction.
The gap Gap (see FIG. 4) between the lower end of the radiation shield 7 and the melt surface is controlled so as to maintain a predetermined distance according to desired characteristics of the single crystal to be grown.
In addition, a cylindrical water-cooled body 10 is disposed inside the radiation shield 7. Cooling water is supplied to the water-cooled body 10 by the cooling water supply means 11 and is circulated to maintain a predetermined temperature.

A separation inner member lifting / lowering device 14 (lifting / lowering means) is provided on the upper portion of the pull chamber 2b. The separation inner member lifting / lowering device 14 supports the separation inner member 12 formed in an annular shape around the pulling shaft so as to be movable up and down by a plurality of wires 13. .
The separation inner member 12 is provided with a heat insulating member 12b made of the same material as the heat insulating member 9a on an annular support member 12a having the same material and thickness as the outer cylindrical member 8 of the radiation shield 7. When the separation inner member 12 is lowered by the separation inner member lifting device 14, the separation inner member 12 is formed in a shape that can be engaged with the lower opening 7c of the radiation shield 7, as shown in FIG. That is, when the separation inner member 12 is lowered to the position of the lower opening 7c of the radiation shield, the support member 12a of the separation inner member 12 and the outer cylinder member 8 of the radiation shield 7 are connected to each other as shown in the figure. The 12 heat insulating members 12b and the heat insulating member 9a of the radiation shield 7 are connected.

As shown in FIG. 4, when the diameter of the single crystal C to be grown is Φ _cry , the diameter Φ ₁ of the separation inner member 12, the lower end diameter Φ ₂ of the lower opening 7 c of the radiation shield 7, and the upper end diameter Φ ₃ is defined by the equations (1) to (3), respectively.

Φ ₁ = Φ _cry +10 to 100 mm (1)
Φ ₂ = Φ ₁ +10 to 100 mm (2)
Φ ₃ = Φ ₂ +10 to 100 mm (3)

  Further, as shown in FIG. 1, the single crystal pulling apparatus 1 includes a heater control unit 20 that controls the amount of power supplied to the heater 4 that controls the temperature of the melt M, and a motor 21 that rotates the crucible 3 around the pulling axis. And a motor control unit 21a for controlling the rotational speed of the motor 21. Also, a lifting device 22 that controls the height of the crucible 3, a lifting device control unit 22 a that controls the lifting device 22, and a pulling control unit 23 that controls the pulling speed, rotation, and the like of the single crystal C by the pulling mechanism 5. And. Furthermore, an elevating control unit 24 that controls the elevating movement of the separated inner member 12 by the separated inner member elevating device 14 is provided. These control units 20, 21 a, 22 a, 23, and 24 are connected to the computer 30.

In the single crystal pulling apparatus 1 configured as described above, for example, when growing a single crystal C having a diameter of 300 mm and a straight body length of 500 mm, the pulling is performed as follows. That is, the raw material polysilicon is first loaded into the quartz glass crucible 3a, and the crystal growth process is started along the flow of FIG. 3 based on the program stored in the storage means of the computer 30.
First, the inside of the furnace body 2 is set to a predetermined atmosphere (mainly argon gas atmosphere), and the raw material polysilicon charged in the crucible 3 is melted by heating by the heater 4 to be a melt M. Further, the motor control unit 21a and the lifting device control unit 22a are operated by a command from the computer 30, and the crucible 3 is rotated at a predetermined rotational speed (rpm) at a predetermined height position (step S1 in FIG. 3). .

Next, a predetermined current is passed through a magnetic field applying electromagnetic coil (not shown) according to a command from the computer 30, and application of a transverse magnetic field having a predetermined strength into the melt M is started (step S2 in FIG. 3).
Moreover, the pulling-up control part 23 operates the winding mechanism 5a by the command of the computer 30, and the wire 6 is lowered. Then, the seed crystal P attached to the wire 6 is brought into contact with the melt M, necking for dissolving the tip portion of the seed crystal P is performed, and formation of the neck portion P1 is started (step S3 in FIG. 3).

  When the neck portion P1 is formed, the pulling conditions are adjusted by parameters of the power supplied to the heater 4, the pulling speed (usually a speed of several millimeters per minute), the magnetic field application intensity, and the like according to commands from the computer 30. The seed crystal P starts to rotate at a predetermined rotation speed in the direction opposite to the rotation direction. Then, the crystal diameter is expanded to form the shoulder C1 (step S4 in FIG. 3), and the process proceeds to a straight body process (step S5 in FIG. 3) for forming the straight body C2 to be a product part.

Here, the grown crystal length from the neck part P1 to the shoulder part C1 and the straight body part C2 is L, and as shown in FIG. 4, the gap between the lower end of the radiation shield 7 and the melt surface M1 is Gp (for example, 20 mm). ), While satisfying the condition of the following formula (4), that is, at least while forming the neck portion P1 and the shoulder portion C1 (step S7 in FIG. 3), the separation inner member 12 as shown in FIG. Control is performed so as to be positioned above the pull chamber 2b (step S6 in FIG. 3).
Thus, the lower opening diameter of the radiation shield 7 is maintained large, and the crystal cooling capacity is small, so that the pulling speed is controlled to be low. According to such pulling control, since the thermal stress inside the crystal is reduced, the dislocations generated during the formation of the neck portion P1 and the shoulder portion C1 are likely to escape outward, and no dislocation is formed until the straight body portion C2 is formed. The rate can be improved.

L ≦ Gap + 100 mm (4)
L> Gap + 100 mm (5)

Further, when the growth of the straight body C2 progresses and the condition of the expression (5) is satisfied, the separation inner member 12 is gradually lowered by the separation inner member elevating device 14, and the radiation shield 7 as shown in FIG. Is engaged with the lower opening 7c (step S8 in FIG. 3).
As a result, the lower opening diameter of the radiation shield 7 is reduced and the crystal cooling capacity is increased, and accordingly, the straight body C2 is grown at a higher pulling speed.

  When the straight body process is completed (step S9 in FIG. 3), a diameter reducing process (step S10 in FIG. 3) for reducing the crystal diameter to form a crystal bottom (not shown) is performed. When this diameter reduction process is started, the separation inner member 12 is separated from the radiation shield 7 and moved upward, and is disposed above the pull chamber 2b until the pulling of the single crystal C is completed (step S11 in FIG. 3). As a result, the lower opening diameter of the radiation shield 7 returns to a large state, and the crystal cooling capacity decreases, so that the pulling speed is controlled to be low. According to such pulling control, when a dislocation occurs during the formation of the crystal bottom, it can be easily removed outward.

As described above, according to the present embodiment, the single crystal pulling apparatus 1 includes the annular separation inner member 12 that can be engaged with the lower opening 7c of the radiation shield 7, and the single crystal pulling process. Accordingly, the separation inner member 12 is engaged or separated with respect to the lower opening 7c of the radiation shield 7. Thereby, the size of the lower opening diameter of the radiation shield 7 becomes variable, and when the crystal neck portion P1, shoulder portion C1 and bottom portion are grown, the lower opening diameter becomes large, and the cooling capacity is controlled to be small. For this reason, when the thermal stress inside the crystal is reduced and dislocations are generated during the formation of the neck portion P1, the shoulder portion C1, and the bottom portion, it can be easily removed outward, and the dislocation-free rate of the crystal Can be improved.
Further, when growing the straight body portion C2 of the crystal, the lower opening diameter of the radiation shield 7 is set to a small state, and the cooling capacity is controlled to be increased. Thereby, the pulling speed of the crystal can be increased, and the productivity can be improved.

In the above embodiment, a transverse magnetic field capable of forming a strong magnetic field is applied in the step of growing the single crystal C. However, the present invention is not limited to this, and other magnetic field application methods may be used.
For example, a cusp magnetic field that forms a weaker magnetic field may be used. In this case, since the melt M can be more stabilized, the separation inner member 12 is lowered immediately after the neck portion P1 is formed to emit radiation. The shield 7 may be engaged with the lower opening 7 c of the shield 7.

Moreover, in the said embodiment, in the formation process of the straight body part C2, the raising / lowering control of the separation inner member 12 was performed for the purpose of increasing the pulling speed, but along the crystal axis direction. The raising / lowering control of the separation inner member 12 may be performed for the purpose of obtaining a single crystal having a uniform oxygen concentration.
Specifically, when growing the straight body portion C2, if it is desired to increase the oxygen concentration, the separation inner member 12 is disposed above the pull chamber 2b, and the distance between the lower opening 7c of the radiation shield 7 and the crystal peripheral surface is set. Just make it bigger. This slows down the gas flow velocity at the meniscus surface of the melt near the crystal periphery, making it difficult for oxygen to evaporate, and the high oxygen concentration melt flows directly under the crystal and solidifies, increasing the crystal oxygen concentration. Can be made.
On the other hand, when it is desired to reduce the oxygen concentration, the separation inner member 12 is lowered and engaged with the lower opening 7c of the radiation shield 7 to reduce the lower opening diameter of the radiation shield 7. As a result, the gas flow velocity at the meniscus surface of the melt near the outer periphery of the crystal increases, oxygen evaporates easily, and the low oxygen concentration melt flows directly under the crystal and solidifies, reducing the crystal oxygen concentration. Can be made.
For this reason, a single crystal having a uniform oxygen concentration distribution along the crystal axis direction can be obtained by performing predetermined control for moving the separation inner member 12 up and down along with the growing process of the straight body portion C2.

Further, as shown in FIG. 5, the separation inner member 12 and the lower opening 7c of the radiation shield 7 form a wall having a predetermined length with respect to the single crystal C, and the oxygen concentration distribution in the crystal length direction becomes more uniform. Control may be performed as described above.
Furthermore, when a transverse magnetic field is applied to the melt M and the crystal is pulled up, if the melt surface falls below the small R portion of the crucible 3, the melt convection changes due to a rapid decrease in the free surface area, and the crystal periphery Although the supercooling of the melt M immediately below is likely to occur, if the lower opening diameter of the radiation shield 7 is made small, the melt temperature immediately below the crystal periphery rises rapidly. It is possible to effectively suppress dislocation induced from supercooling.

  The single crystal pulling apparatus and single crystal pulling method according to the present invention will be further described based on examples. In this example, single crystal pulling was performed using the single crystal pulling apparatus described in the above embodiment, and the pulled crystal was verified.

[Example 1]
As specific conditions of Example 1, the charge amount of the raw material silicon to the 32-inch crucible is 300 kg, the diameter of the single crystal to be grown is 300 mm, the length of the straight body of the crystal is 500 mm, and the strength (magnetic flux density) of the transverse magnetic field is 3000 Gauss and the magnetic field position were 0 mm. Further, the gap Gap between radiation shield bottom and melt surface shown in FIG. 4 and 20 mm, the diameter [Phi ₁ separate inner member and 330 mm, a lower end diameter [Phi ₂ of the lower opening of the radiation shield 380 mm, the upper end diameter the Φ ₃ was 430mm.
Under these conditions, 10 single crystals were pulled up according to the steps of FIG. 3 in the same manner as in the above embodiment, and the neck portion was formed with a diameter average of 5 mm to a length of 300 mm, and the number of dislocations achieved at that time was verified. In addition, the dislocation-free achievement rate after completion of crystal pulling was verified.

[Comparative Example 1]
As Comparative Example 1, the separation inner member was not used, and the lower opening diameter of the radiation shield was fixed to 330 mm (that is, the opening diameter was small), and the single crystal was pulled up. Other conditions are the same as in the first embodiment.
Table 1 shows the results of Example 1 and Comparative Example 1.

As shown in Table 1, in Example 1 according to the present invention, the number of dislocation-free when forming a 300 mm long neck portion was 8, and in Comparative Example 1, the number was 1. That is, in Example 1, when the neck portion is formed, the lower opening diameter of the radiation shield is larger than in the case of Comparative Example 1, so that the cooling effect is reduced, and even if dislocation occurs, it falls out. It was found that it was easily removed.
Further, the dislocation-free rate after completion of the pulling was 80% in Example 1 and 10% in Comparative Example 1, and it was confirmed that the dislocation-free rate can be significantly improved in the straight body portion formation after the neck portion formation.

[Example 2]
In Example 2, a transverse magnetic field was applied to the melt, and the dislocation-free rate in the latter half of the crystal growth was verified. Specifically, before the molten liquid surface (free surface) passes through the small R portion of the quartz crucible, 10 dislocation-free crystals are selected and the separation inner member is pulled up while being engaged with the lower opening of the radiation shield. Then, the number of dislocations achieved when the melt surface passed through the small R portion of the crucible and the dislocation-free achievement rate upon completion of pulling were verified. Other conditions are the same as those in the first embodiment.

[Comparative Example 2]
In Comparative Example 2, as in Example 2, 10 dislocation-free crystals were selected before the molten liquid surface (free surface) passed through the small R portion of the quartz crucible, and the separation inner member was placed in the upper portion of the pull chamber. The number of dislocations achieved when the melt surface passed through the small R portion of the crucible and the dislocation-free achievement rate when the pulling was completed were verified. Other conditions are the same as those in the first embodiment.
Table 2 shows the results of Example 2 and Comparative Example 2.

As shown in Table 2, in Example 2, the dislocation-free achievement rate after pulling was as high as 90%, but in Comparative Example 2, it was 50%, and it was present in the latter half of crystal growth induced by supercooling of the melt. It was confirmed that dislocations can also be effectively suppressed.
[Example 3]
In Example 3, the same conditions as in Example 1 were used, and the single crystal pulling was performed according to the steps of FIG. 3 as in the above embodiment, the relative pulling speed of the crystal body (relative to Comparative Example 3), and the crystal The relative density of the glow-in defect (relative to Comparative Example 3) was verified.
In this straight body process, the separation inner member is engaged with the lower opening of the radiation shield, and the opening diameter is small.

[Comparative Example 3]
As Comparative Example 3, the separation inner member was not used, and the lower opening diameter of the radiation shield was fixed to 380 mm (that is, the opening diameter was large), and the single crystal was pulled up. Other conditions are the same as in Example 3.
Table 3 shows the results of Example 2 and Comparative Example 2.

  As shown in Table 3, in Example 3 according to the present invention, the crystal pulling speed can be improved by 30% as compared with Comparative Example 3, and the density of glow-in defects (large size defects) is also greatly reduced. It was confirmed.

[Example 4]
In Example 4, in order to apply a cusp magnetic field and make the oxygen concentration uniform in the crystal length direction, the single crystal was pulled up while changing the position of the separation inner member with respect to the radiation shield. Other conditions were the same as in Example 1, and the oxygen concentration in the crystal was verified.

[Comparative Example 4]
In Comparative Example 4, the lower opening diameter of the radiation shield was fixed to 330 mm (that is, the opening diameter was small), and the single crystal was pulled up. Other conditions are the same as in Example 4.

[Comparative Example 5]
In Comparative Example 5, the lower opening diameter of the radiation shield was fixed at 380 mm (that is, the opening diameter was large), and the single crystal was pulled up. Other conditions are the same as in Example 4.
In FIG. 6, the result of Example 4 and Comparative Examples 4 and 5 is shown as a graph. The horizontal axis of the graph of FIG. 6 is the crystal solidification rate, and the vertical axis is the oxygen concentration.
In Example 4, the separation inner member is engaged with the lower opening of the radiation shield until the solidification rate of 0.1 in FIG. 6 is reached, and thereafter, the separation inner member is gradually raised to gradually increase the solidification rate. At the time of 0.6, the bottom of the separation inner member was controlled to be Gap (20 mm) +100 mm from the melt surface. Further, after that, the separation inner member was further raised and arranged at the position above the pull chamber.
As shown in this graph, in Comparative Examples 4 and 5, as the solidification rate increases, the oxygen concentration significantly decreases. However, according to Example 4, the oxygen concentration distribution is substantially uniform along the crystal length direction. It was confirmed that

  From the results of Examples 1 to 4 above, according to the single crystal pulling apparatus and pulling method according to the present invention, it is possible to suppress dislocation of the crystal and improve the pulling speed. It was confirmed that a single crystal having a uniform oxygen concentration distribution in the axial direction can be obtained.

DESCRIPTION OF SYMBOLS 1 Single crystal pulling apparatus 2 Furnace body 3 Crucible 4 Heater 5 Pulling mechanism 6 Wire 7 Radiation shield 7c Lower opening 8 Outer cylinder member 9 Heat insulation member 10 Water-cooled body 12 Separation inner member 13 Wire 14 Separation inner member raising / lowering device (elevating means)
C single crystal C1 shoulder C2 straight body M silicon melt P seed crystal P1 neck

Claims (5)

A single crystal pulling apparatus that applies a magnetic field to the silicon melt in the crucible and pulls up the silicon single crystal from the silicon melt by the Czochralski method,
It is formed in a cylindrical shape having openings at the top and bottom, and can be engaged with a radiation shield disposed above the silicon melt in the crucible so as to surround the silicon single crystal and a lower opening of the radiation shield. An annular separation inner member provided in the upper and lower lift means for moving the separation inner member up and down with respect to the lower opening of the radiation shield,
The single crystal pulling apparatus according to claim 1, wherein the diameter of the lower opening of the radiation shield is reduced by engaging the separation inner member moved downward by the lifting means with the lower opening of the radiation shield. The lower opening of the annular radiation shield is formed so that its end face has a predetermined thickness dimension and is opposed to the radial direction,
When the diameter of the silicon single crystal is Φ _cry ,
The diameter Φ ₁ of the separation inner member, the lower end side diameter Φ ₂ of the lower opening of the radiation shield, and the upper end side diameter Φ ₃ are respectively defined by equations (1) to (3). The single crystal pulling apparatus according to claim 1.
Φ ₁ = Φ _cry +10 to 100 mm (1)
Φ ₂ = Φ ₁ +10 to 100 mm (2)
Φ ₃ = Φ ₂ +10 to 100 mm (3) A silicon melt is formed in the crucible and a magnetic field is applied to the silicon melt, and a cylindrical radiation shield having openings above and below is disposed so as to surround the silicon single crystal above the silicon melt. A single crystal pulling method for pulling up a silicon single crystal from the silicon melt by the Czochralski method,
An annular separation member that can be engaged with the lower opening of the radiation shield and reduces the diameter of the lower opening by being engaged is moved up and down according to the growth process of the silicon single crystal, A method for pulling a single crystal, wherein the distance between the peripheral surface of the silicon single crystal and the lower opening is changed. In the process of growing the silicon single crystal,
At least in the step of forming the neck portion, the separation inner member is disposed above the radiation shield, and is not attached to the lower opening of the radiation shield.
In the step of forming the straight body portion, the separation inner member is engaged with the lower opening of the radiation shield,
4. The single crystal pulling method according to claim 3, wherein, in the crystal bottom portion forming step, the separation inner member is disposed above the radiation shield and is not engaged with a lower opening of the radiation shield. In the step of forming the straight body of the silicon single crystal,
The oxygen concentration in the crystal is controlled by moving the separation inner member up and down relative to the lower opening of the radiation shield and changing the distance between the lower opening and the crystal peripheral surface. The single crystal pulling method according to claim 4.

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