JP6604440B2 - Single crystal manufacturing method and apparatus - Google Patents

Description

  The present invention relates to a method and an apparatus for producing a single crystal by an FZ (Floating Zone) method, and more particularly, to a method for supporting a single crystal that has been weighted as crystal growth proceeds.

  The FZ method is known as one method for producing a silicon single crystal that is a semiconductor material. The FZ method is a method in which a part of a raw material rod made of polycrystalline silicon is heated at a high frequency to form a molten zone, and a single crystal is gradually grown while moving the molten zone. Unlike the CZ (Czochralski) method, since the FZ method does not use a quartz crucible, it is possible to produce a high-purity silicon single crystal that does not contain impurities such as oxygen.

  In the production of a silicon single crystal by the FZ method, a cylindrical ingot is grown by growing the raw material rod and the single crystal while rotating them, respectively. In particular, the concentration distribution of the dopant in the cross section perpendicular to the crystal growth direction is made uniform. For this reason, alternate rotation is performed to periodically reverse the rotation direction of the single crystal. For example, Patent Document 1 discloses an alternating rotation that alternately repeats a base rotation that rotates a single crystal at a predetermined base angle and a counter rotation that rotates the single crystal at a counter angle smaller than the base angle in a direction opposite to the base rotation. The method describes a method of reducing in-plane variation in resistivity of a single crystal by changing a combination of a base angle and a counter angle in accordance with the diameter of a raw material rod.

  In the FZ method, if the growth of the silicon single crystal progresses to a certain extent and the weight increases, it becomes impossible to support the entire silicon single crystal with the support shaft of the seed crystal alone. Therefore, the support method of the single crystal may be changed during the growth process. It has been broken. For example, Patent Document 2 describes holding a grown silicon single crystal with a single crystal weight holder. Since the single crystal weight holder receives most of the weight of the silicon single crystal, the weight of the silicon single crystal can be prevented from being applied to the support shaft of the seed crystal. Patent Document 3 describes a method of supporting a growing single crystal by applying a cylindrical ring support to a conical region of the growing single crystal.

JP2015-229612A JP 2012-106882 A Japanese Patent Laid-Open No. 2006-52983

  In the intermediate support of silicon single crystal by the single crystal weight holder, the drive for rotating and lowering the single crystal after pressing multiple support pins against the taper part of the single crystal at the predetermined timing when the single crystal is weighted Connect the system to the support shaft side of the support pin. By switching to single crystal support with a plurality of support pins in this manner, the single crystal can be lowered while rotating with the support pins, and the single crystal growth process can be continued.

  However, in the method of supporting a single crystal with a plurality of support pins, the crystal vibration increases after switching the support of the single crystal from the support shaft of the seed crystal to the plurality of support pins, and the support of the single crystal becomes very unstable. There is a problem of becoming. In particular, when single crystals are rotated alternately, a strong centrifugal force is applied to the tip of the support pin due to a sudden change in the direction of rotation, which results in insufficient support of the single crystal and tends to cause crystal bending.

  Therefore, the object of the present invention is to stably support a single crystal with a plurality of support pins even when the single crystal is rotated alternately, and to prevent the occurrence of crystal bending after switching to a multi-point support with a plurality of support pins. An object of the present invention is to provide a method and an apparatus for producing a single crystal that can be prevented.

  In order to solve the above-mentioned problem, a method for producing a single crystal according to the present invention comprises heating a part of a raw material rod to form a molten zone, and then forming the raw material rod and the single crystal located above and below the molten zone, respectively. A method of producing a single crystal by FZ method in which the single crystal is grown by lowering, wherein the single crystal is grown above the seed crystal while rotating a crystal axis that supports a lower end of the seed crystal; Switching the support body of the single crystal from the crystal axis to the support means by bringing a support means into contact with the outer peripheral surface of the tapered portion of the single crystal grown into a crystal shape; and After switching to the support means, the support means is pushed against the single crystal by lowering the crystal axis while fixing the vertical position of the support means. And having the steps of strengthening the body, and a step of further growing the single crystal while supported by the support means.

  In addition, the single crystal manufacturing apparatus according to the present invention includes a raw material shaft that supports a raw material rod, a raw material feed mechanism that drives the raw material shaft up and down, and a rotation, a crystal shaft that supports the lower end of a seed crystal, and the raw material rod An induction heating coil that supports the single crystal by contacting an outer peripheral surface of the taper portion of the single crystal, a crystal feed mechanism that moves the crystal axis or the support means up and down, and rotates, and the crystal axis. And a control unit that controls switching of the main support of the single crystal from the support unit to the support unit, and the control unit abuts the support unit on the outer peripheral surface of the tapered portion of the single crystal grown in a predetermined crystal shape. The support body of the single crystal is switched from the crystal axis to the support means by a lock mechanism that locks the movement of the support means in a state where After the body is switched to the support means, the crystal axis is lowered while the vertical position of the support means is fixed to strengthen the pushing of the support means against the single crystal, and the single crystal is supported while being supported by the support means. It is characterized by further growing.

  According to the present invention, the support force of the single crystal by the support means can be enhanced. Therefore, even when the single crystals are alternately rotated, the single crystal can be stably supported by the support means, and the occurrence of crystal bending and melt spillage can be prevented after the support is switched.

In the present invention, the descending amount of the crystal axis for strengthening the pushing of the support means to the single crystal is preferably larger than 0 mm and not larger than 0.5 mm, and not smaller than 0.1 mm and not larger than 0.5 mm. Is more preferable. If the descending amount of the crystal axis is larger than 0 mm, the support force necessary for supporting the single crystal by the support means can be ensured. If the crystal axis drop is 0.5 mm or less, it is possible to avoid the risk of cracking or breaking near the connection point between the seed crystal and the crystal axis. Furthermore, if the amount of crystal axis descent is 0.1 mm or more, the support force of the single crystal by the support means can be reliably strengthened.

The method and apparatus for producing a single crystal according to the present invention preferably further grows while alternately rotating the single crystal supported by the support means. If the single crystal is rotated alternately, the single crystal will be shaken at the time of reversal, so if the support means applied from the side is not firmly bitten into the single crystal, the deviation of the central axis of the single crystal will increase and the central axis will tilt. As a result, the crystal may bend and the melt on the single crystal may be spilled. However, according to the present invention, it is possible to prevent a decrease in yield and damage to the crystal growth equipment due to the occurrence of crystal bending in the subsequent crystal growth process.

  In the present invention, the support means includes a plurality of support pins provided slidably along the radial direction of the single crystal, and each of the plurality of support pins is slidable along the radial direction of the single crystal. It is preferable that a plurality of fixed pieces are respectively arranged behind the plurality of movable pieces supported on the base plate to lock the movement of each support pin along the radial direction of the single crystal. According to this, the weighted single crystal can be reliably supported. Further, the support means can be reliably pressed with a relatively simple configuration, and the pressed state can be locked.

  In the present invention, the movable piece has a tapered surface having an inclination angle of 20 to 25 ° with respect to a vertical plane, and the fixed piece has an inverted tapered surface having the same inclination angle as the tapered surface of the movable piece. It is preferable that the reverse taper surface of the fixed piece is brought into contact with the taper surface of the movable piece when the plurality of support pins are locked. According to this, a fixed piece can be arrange | positioned in an appropriate position with respect to the arbitrary positions of a movable piece, and the force with which a fixed piece presses a movable piece can be strengthened. Therefore, the support pin can be securely fixed, and the support force of the support pin can be strengthened so as not to lose the centrifugal force when the single crystal rotates.

  In the present invention, the support means may include a support ring that is in contact with substantially the entire circumference of the outer peripheral surface of the tapered portion of the single crystal. In this case, the support ring is made of a first material and is in contact with the outer peripheral surface of the tapered portion of the single crystal, and the outer ring member is made of a second material and is located on the outer peripheral side of the inner ring member. It is preferable to have. Even with such a configuration, the weighted single crystal can be reliably supported. Further, the support means can be reliably pressed with a relatively simple configuration, and the pressed state can be locked.

  In the method and apparatus for producing a single crystal according to the present invention, the vicinity of the contact position between the support means and the outer peripheral surface of the tapered portion of the single crystal is photographed with a camera, and the support means is based on the photographed image of the camera. It is preferable to determine whether or not the outer peripheral surface of the tapered portion of the single crystal is in contact. According to this, it is possible to automatically switch the support subject of the single crystal.

  The method and apparatus for producing a single crystal according to the present invention determines whether the support means is in contact with the outer peripheral surface of the tapered portion of the single crystal based on a change in load applied to the crystal axis or the support means. Is also preferred. According to this, it is possible to automatically switch the support subject of the single crystal.

  According to the present invention, even when single crystals are alternately rotated, the single crystal can be stably supported by the support means, and a single crystal manufacturing method and apparatus capable of preventing the occurrence of crystal bending after support switching. Can be provided.

FIG. 1 is a schematic diagram showing a configuration of a single crystal manufacturing apparatus 10 according to a preferred embodiment of the present invention. FIG. 2 is a plan view showing the configuration of the single crystal weight holder 16 according to the first embodiment. 3A to 3C are side views showing the configuration of the lock mechanism 16L of the support pin 16a. FIG. 4 is a flowchart schematically showing the manufacturing process of the single crystal 3 by the FZ method. FIG. 5 is a schematic diagram for explaining the manufacturing process of the single crystal 3 together with FIG. FIG. 6 is a side view schematically showing the shape of a single crystal ingot 3I manufactured by the FZ method. FIG. 7 is a side view for explaining a support switching method of the single crystal 3. FIG. 8 is a side view for explaining a support switching method of the single crystal 3. FIG. 9 is a schematic cross-sectional view showing a single crystal weight holder 16 according to the second embodiment. 10A and 10B are diagrams showing the configuration of the support ring 16r, where FIG. 10A is a plan view, FIG. 10B is a cross-sectional view, and FIG. 10C is a cross-sectional view showing a state in which the single crystal 3 is supported.

  Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings.

  FIG. 1 is a schematic diagram showing a configuration of a single crystal manufacturing apparatus 10 according to a preferred embodiment of the present invention.

As shown in FIG. 1, the single crystal manufacturing apparatus 10 includes a raw material shaft 11 having a raw material rod 1 attached to the lower end, a raw material feed mechanism 12 that feeds the raw material shaft 11 while rotating the raw material shaft 11, and a lower end of the seed crystal 2. A crystal axis 13 supported at one point, a crystal feed mechanism 14 that feeds the crystal axis 13 while rotating the crystal axis 13, an induction heating coil 15 for heating the raw material rod 1, and a plurality of weights supporting the weighted single crystal 3 A single crystal weight holder 16 having a support pin 16a, a CCD camera 17 for photographing a contact state between the support pin 16a and the single crystal 3, an image processing unit 18 for processing image data photographed by the CCD camera 17, and a raw material A control unit 19 that controls the feed mechanism 12, the crystal feed mechanism 14, the induction heating coil 15, and the single crystal weight holder 16 is provided.

  The raw material feed mechanism 12 has a raising / lowering function and a rotation function of the raw material shaft 11 and controls the feed speed and the rotational speed of the raw material rod 1, respectively. The crystal feeding mechanism 14 has a lifting function and a rotating function of the crystal axis 13 and the single crystal weight holder 16 and controls the feed speed and the rotational speed of the single crystal 3 or the single crystal weight holder 16, respectively. The induction heating coil 15 is a loop conductor surrounding the periphery of the raw material rod 1, and the melting zone 4 is generated by induction heating of the raw material rod 1.

  The crystal feeding mechanism 14 has a resolver 14a attached to a motor for driving the crystal axis 13 up and down, and the amount of movement of the crystal axis 13, that is, the crystal length can be obtained from the pulse integrated value detected by the resolver 14a. it can. A load sensor 20 is provided below the crystal feeding mechanism 14, and the load sensor 20 can detect the weight of the single crystal 3. Further, the diameter of the single crystal 3 can be measured from an image taken by the CCD camera 17. Thus, the shape of the silicon single crystal can be determined from the outputs of the resolver 14a, the load sensor 20, the CCD camera 17, and the like.

  The rotation support shaft 16 z that supports the single crystal weight holder 16 has a configuration that can rotate coaxially with the crystal shaft 13. The crystal feeding mechanism 14 is connected to at least one of the crystal shaft 13 and the rotation support shaft 16z that supports the single crystal weight holder 16 via the clutch 16y. For example, the rotation support shaft 16z that supports the single crystal weight holder 16 is additionally connected to the crystal feed mechanism 14 by a clutch 16y, whereby the crystal axis 13 and the single crystal weight holder 16 are driven together. . That is, when only the crystal axis 13 is connected to the crystal feed mechanism 14, the single crystal weight holder 16 is disconnected from the crystal feed mechanism 14, and the single crystal weight holder 16 is connected to the crystal feed mechanism 14. Sometimes, both the crystal axis 13 and the single crystal weight holder 16 are connected to the crystal feeding mechanism 14.

  The crystal feeding mechanism 14 may be connected to either the crystal shaft 13 or the rotation support shaft 16z via the clutch 16y. That is, when the crystal axis 13 is connected to the crystal feed mechanism 14, the single crystal weight holder 16 is disconnected from the crystal feed mechanism 14, and when the single crystal weight holder 16 is connected to the crystal feed mechanism 14. The crystal axis 13 may be separated from the crystal feed mechanism 14. The crystal axis 13 separated from the crystal feed mechanism 14 can be rotated and lifted independently of the crystal feed mechanism 14, and is rotated and lifted together with the single crystal 3.

  FIG. 2 is a plan view showing the configuration of the single crystal weight holder 16 according to the first embodiment.

  As shown in FIG. 2, the single crystal weight holder 16 has three support pins 16a. The support pins 16a are arranged at equal intervals (here, 120 ° intervals) in the circumferential direction, whereby the single crystal 3 is supported at three points. The three support pins 16a are mounted on a ring-shaped base 16c, and their vertical positions (heights) are simultaneously controlled by the crystal feeding mechanism 14. Further, the support pins 16a are driven to rotate by the crystal feeding mechanism 14 and can rotate alternately as indicated by an arrow A1. Alternating rotation is a method of alternately rotating clockwise and counterclockwise at a predetermined cycle. In this case, the counterclockwise and clockwise rotations may be different rotation amounts, or the same rotation amount.

  The tip portion of the support pin 16a comes into contact when the single crystal 3 reaches a predetermined crystal shape, and thereby the tapered portion 3b of the single crystal 3 reaches a predetermined diameter R1 at the same height as the support pin 16a. Is set to The predetermined diameter R1 of the tapered portion 3b of the single crystal 3 is smaller than the diameter (maximum diameter) R2 of the straight body portion 3c of the single crystal 3. The support pin 16a can move forward and backward in the radial direction of the single crystal 3 indicated by the arrow A2, but the position of the support pin 16a is fixed by the lock mechanism 16L while the single crystal 3 is supported.

  3A to 3C are side views showing the configuration of the lock mechanism 16L of the support pin 16a.

  As shown in FIG. 3A, the lock mechanism 16L of the support pin 16a is mainly composed of a movable piece 16b that slidably supports the support pin 16a and a fixed piece 16d that restricts the movement of the movable piece 16b. The The rear end portion of the support pin 16a is fixed to the movable piece 16b, and the movable piece 16b can be moved forward and backward in the radial direction (arrow A2) of the single crystal 3 along a guide rail (not shown) provided on the base 16c. have. A fixed piece 16d is arranged behind the movable piece 16b, and the fixed piece 16d is lifted upward in the unlocked state. A post 16e is provided below the fixed piece 16d, and the lower end of the post 16e is supported by a plate 16f. In FIG. 3A, the tip of the support pin 16a is not yet in contact with the single crystal 3.

  As shown in FIG. 3B, when the single crystal 3 descends as it grows, the tip of the support pin 16 a comes into contact with the outer peripheral surface of the tapered portion 3 b of the single crystal 3. When the growth of the single crystal 3 further progresses and the crystal diameter further increases, the support pin 16a is pushed in the direction indicated by the arrow A3 by the outer peripheral surface of the single crystal 3, but the unlocked support pin 16a and the movable piece 16b are It is possible to slide in the backward direction that is the direction of A3.

  As shown in FIG. 3C, the support pin 16a is locked by lowering the fixed piece 16d to restrict the backward movement of the support pin 16a. The fixed piece 16d can be lowered by pulling out the plate 16f to release the drop restriction of the post 16e, and dropping the fixed piece 16d together with the post 16e. As a result, the movement of the support pin 16a shown in FIG. 3A in the direction of the arrow A2 is restricted. That is, the movement of the slidable support pin 16a can be locked.

  The support pin 16a and the movable piece 16b may be configured to be manually advanced and retracted. In this case, the operator may manually advance the support pin 16a at the timing when the single crystal 3 grows into a predetermined crystal shape, and the tip thereof may contact the single crystal 3. Then, when the contact of the tip of the support pin 16a could be visually confirmed, the crystal pin 13 was slightly lowered while the vertical position of the support pin 16a was fixed, and the pushing of the support pin 16a into the single crystal 3 was strengthened. Thereafter, the single crystal weight holder 16 is connected to the crystal feeding mechanism 14 to continue the single crystal growth process. Therefore, it is possible to further grow the single crystal by lowering the single crystal 3 together with the support pins 16a while rotating it alternately.

  Further, when it can be determined from the output of the resolver 14a, the output of the load sensor 20, the photographed image of the camera 17 and the like that the single crystal 3 has grown into a predetermined crystal shape, the support pin 16a is automatically advanced to move the tip thereof. The single crystal 3 may be contacted.

  The side surface of the movable piece 16b facing the fixed piece 16d constitutes a tapered surface Sb having an inclination angle θ of 20 to 25 ° with respect to the vertical surface, and the side surface of the fixed piece 16d fits this tapered surface. It has an inversely tapered surface Sd with an inclination angle θ. In the unlocked state, the fixed piece 16d is disposed obliquely above the movable piece 16b, and the support pin 16a is locked by lowering the fixed piece 16d and placing it on the base 16c. At this time, the reverse taper surface Sd of the fixed piece 16d slides down in the direction indicated by the arrow A4 in FIG. 3B while contacting the taper surface Sb of the movable piece 16b, so that the fixed piece 16d is moved to an arbitrary position of the movable piece 16b. On the other hand, the fixed piece 16d can be dropped and arranged at an appropriate position. In addition, compared to the case where the vertical end surfaces of the movable piece 16b and the fixed piece 16d are brought into contact with each other, the force by which the fixed piece 16d presses the movable piece 16b can be increased. Therefore, the support pin 16a can be securely fixed, and the support force of the support pin 16a can be strengthened so as not to lose the centrifugal force when the single crystal 3 rotates.

  FIG. 4 is a flowchart schematically showing the manufacturing process of the single crystal 3 by the FZ method. FIG. 5 is a schematic diagram for explaining the manufacturing process of the single crystal 3 together with FIG. FIG. 6 is a side view schematically showing the shape of the single crystal ingot 3I manufactured by the FZ method.

  As shown in FIGS. 4 to 6, in the growth of the single crystal 3 by the FZ method, by melting the tip of the raw material rod 1 and fusing it to the seed crystal 2, the single crystal 3 is narrowed down. A drawing step S2 for eliminating dislocations in the single crystal, a tapered portion growing step S3 for growing a tapered portion 3b in which the crystal diameter is gradually expanded to a target diameter, and a straight body portion 3c in which the crystal diameter is maintained constant are grown. The straight body part growing step S4, the bottom part growing step S5 for growing the bottom part 3d whose crystal diameter has been gradually reduced, and the cooling step S6 for finishing and cooling the growth of the single crystal 3 are sequentially performed.

  In the fusing step S1, the raw material rod 1 attached to the lower end of the raw material shaft 11 is lowered and placed inside the induction heating coil 15, and the narrowed tip of the raw material rod 1 is heated to a molten state. The melt portion is fused to the seed crystal 2 attached to the upper end of the crystal axis 13. Thereafter, the seed crystal 2 is slowly lowered and moved away from the induction heating coil 15 to crystallize the solid-liquid interface between the seed crystal 2 and the melt portion. The melt portion is maintained by lowering the raw material rod 1 together with the seed crystal 2. In the taper part growing step S3, the single crystal 3 is grown while gradually increasing the crystal diameter by controlling the raw material feed rate and the crystal feed rate. In the straight body part growing step S4, the single crystal 3 is grown while maintaining the crystal diameter constant by controlling the raw material feed rate and the crystal feed rate. At this time, the crystal axis 13 supports the single crystal 3 while rotating alternately. The vertical position of the crystal axis 13 is controlled by the crystal feed mechanism 14.

  As described above, the narrowed portion 3a in which the crystal diameter is narrowed, the tapered portion 3b in which the diameter gradually increases from the upper end of the narrowed portion 3a, the straight body portion 3c having a constant diameter, and the bottom in which the diameter gradually decreases. A single crystal ingot 3I having a portion 3d is completed. In the FZ method, the single crystal ingot 3I is formed in the order of the narrowed portion 3a, the tapered portion 3b, the straight body portion 3c, and the bottom portion 3d. Usually, the diameter of the straight body portion 3c of the single crystal 3 is larger than the diameter of the raw material rod 1, and the straight body portion 3c is a portion that is actually provided as a product. The length of the single crystal 3 depends on the amount of the raw material rod.

  7 and 8 are side views for explaining a support switching method of the single crystal 3.

  As shown in FIG. 7A, immediately after the start of the straight body part growing step S4, the weight of the single crystal 3 has not yet advanced so much, and the single crystal 3 can be supported only by the crystal axis 13. Therefore, in the early stage of the crystal growth process, the crystal axis 13 supports the single crystal 3 at a single point, and the crystal axis 13 descends while alternately rotating, and the single crystal 3 is sent downward. Be nurtured. The alternate rotation and the vertical position of the crystal axis 13 are controlled by the crystal feed mechanism 14.

  As shown in FIG. 7 (b), the single crystal 3 grows into a predetermined crystal shape, whereby the diameter of the tapered portion 3b of the single crystal 3 at the same height as the support pin 16a is a predetermined diameter R1 (see FIG. 2). ), The tip portions of the plurality of support pins 16a come into contact with the outer peripheral surface of the tapered portion 3b of the single crystal 3.

  As shown in FIG. 8A, when the contact state between the tip of the support pin 16a and the single crystal 3 is confirmed by image determination or visual observation of the camera 17, the position of the support pin 16a is fixed by the lock mechanism 16L. Is done. That is, when the fixed piece 16d is lowered, the backward sliding of the support pin 16a is restricted. Thus, the main support body of the single crystal 3 is switched from the crystal axis 13 to the plurality of support pins 16a. The operation of dropping the fixed piece 16d may be performed manually by the operator or automatically based on the image determination result of the camera 17.

  As shown in FIG. 8 (b), after completing the switching of the support method of the single crystal 3, with the vertical position of the support pin 16a fixed, the crystal axis 13 is slightly lowered as shown by the arrow A5, The pushing of the support pin 16a into the single crystal 3 is strengthened. Since the support pin 16a is in contact with the tapered surface of the single crystal 3, the pressing force (arrow A6) against the support pin 16a can be increased by lowering the tapered surface. The support switching operation refers to locking the advance / retreat movement of the support pin in a state where the tip of the support pin is in contact with the single crystal.

  Here, the descent amount d of the crystal axis 13 is preferably greater than 0 and 0.5 mm or less (0 mm <d ≦ 0.5 mm). If the descent amount d of the crystal axis 13 is larger than 0 mm, the support force of the single crystal 3 by the support pins 16a can be strengthened. If the descent amount d of the crystal axis 13 is 0.5 mm or less, it is possible to avoid the risk that the tensile stress applied to the seed crystal 2 becomes too strong and cracks and fractures occur near the connection point with the crystal axis 13. .

  After the crystal axis 13 is slightly lowered to strengthen the support force of the single crystal 3 by the support pins 16 a, the crystal feed mechanism 14 is connected not only to the crystal axis 13 but also to the single crystal weight holder 16. When the single crystal weight holder 16 is connected to the crystal feeding mechanism 14 via the clutch 16y, the single crystal 3 is rotated and moved up and down by the support pin 16a, and the support pin 16a rotates coaxially with the crystal axis 13. When the single crystal weight holder 16 is connected to the crystal feed mechanism 14, the crystal axis 13 may be driven together with the single crystal weight holder 16 or may be disconnected from the crystal feed mechanism 14. When the crystal axis 13 is separated from the crystal feeding mechanism 14, the crystal axis 13 loses its function as a driving source and becomes a member that can only freely follow the movement of the single crystal 3.

  Thereafter, as shown in FIG. 1, the straight body part growing step S4 is continued while supporting the single crystal 3 with a plurality of support pins 16a. Since the single crystal 3 is supported by the support pins 16a, the vertical position of the single crystal 3 is controlled by the crystal feed mechanism 14 that drives the support pins 16a. Further, since the support pin 16a supports the single crystal 3 while rotating alternately as indicated by the arrow A1, the single crystal 3 can be rotated alternately, thereby reducing in-plane variation in the concentration distribution of the dopant in the crystal. can do.

  As described above, in the method for manufacturing a single crystal according to the present embodiment, after the support switching operation by the support pin 16a is completed, the crystal axis 13 is lowered while the vertical position of the support pin 16a is fixed to the single crystal 3. Since the pushing of the support pin 16a is strengthened, the support force of the single crystal 3 by the support pin 16a can be strengthened, and crystal vibration after switching the support main body of the single crystal 3 from the crystal axis 13 to the support pin 16a can be suppressed. Can do. Therefore, it is possible to prevent the occurrence of crystal bending when the single crystal 3 is alternately rotated while being supported by the support pins 16a.

  FIG. 9 is a schematic cross-sectional view showing a single crystal weight holder 16 according to the second embodiment.

  As shown in FIG. 9, the single crystal weight holder 16 is characterized in that the support means for supporting the weighted single crystal is constituted by a support ring 16r instead of the support pins 16a. The support ring 16r is an annular member and plays a role of supporting the single crystal 3 by contacting the entire outer periphery of the tapered portion 3b of the single crystal 3. The support ring 16r is coaxially arranged with the crystal axis 13, and is mounted on the rotation support shaft 16z via a plurality of shafts 16s capable of driving the support ring 16r up and down.

  10A and 10B are diagrams showing the configuration of the support ring 16r, where FIG. 10A is a plan view, FIG. 10B is a cross-sectional view, and FIG. 10C is a cross-sectional view showing a state in which the single crystal 3 is supported.

  As shown in FIGS. 10A to 10C, the diameter R3 of the opening of the support ring 16r is smaller than the diameter R2 of the straight body 3c of the single crystal 3. Therefore, when the single crystal 3 is lowered or the support ring 16r is raised and the support ring 16r is inserted into the lower end portion of the single crystal 3, the support ring 16r hits the entire circumference of the outer peripheral surface of the tapered portion 3b. The single crystal 3 is supported in contact and cannot move upward from the contact position with the tapered portion 3b. In this state, the support main body of the single crystal 3 is switched from the crystal axis 13 to the support ring 16r.

  The support ring 16r is made up of an inner ring member made of the first material and in contact with the outer peripheral surface of the tapered portion 3b of the single crystal 3, and an outer ring member made of the second material and positioned on the outer peripheral side of the inner ring member. May be. In this case, the first material is preferably borosilicate glass, and the second member is preferably a metal or a ceramic material. According to this configuration, it is possible to further enhance the support force by increasing the degree of adhesion between the support ring 16r and the single crystal 3 while ensuring a desired strength.

  As described above, the support ring 16r is used as the support means of the single crystal 3 in the present embodiment, but the same effects as in the first embodiment can be obtained. That is, after the support switching operation by the support ring 16r is completed, the crystal axis 13 is lowered while the vertical position of the support ring 16r is fixed, and the pushing of the support ring 16r into the single crystal 3 is strengthened. 3 can be strengthened, and the crystal vibration after the support main body of the single crystal 3 is switched from the crystal axis 13 to the support ring 16r can be suppressed. Therefore, when the single crystals 3 are alternately rotated while being supported by the support ring 16r, it is possible to prevent the occurrence of crystal bending.

  The preferred embodiments of the present invention have been described above, but the present invention is not limited to the above-described embodiments, and various modifications can be made without departing from the spirit of the present invention. Needless to say, it is included in the range.

  For example, in the above embodiment, the movable piece 16b and the fixed piece 16d are used as a method of locking the slide along the radial direction of the single crystal 3 of the support pin 16a, but the present invention is not limited to such a method. Various locking methods can be employed.

  Moreover, in the said embodiment, although the change of the support method of the single crystal 3 is performed during the straight body part growing process S4, you may perform it during the taper part growing process S3. The timing of switching the support method of the single crystal 3 may be determined by a method using the load sensor 20 in addition to a method of judging from visual observation or an image taken by the camera 17. When the single crystal 3 is supported by the support pin 16a, the load sensor 20 attached to the lower end of the crystal shaft 13 detects a sudden decrease in the weight of the single crystal 3, and thus supports at the timing when such a weight change is detected. The support of the single crystal 3 may be switched by locking the pin 16a. It is also possible to provide the load sensor 20 on the support pin 16a side instead of the crystal axis 13 side. In this case, since the load sensor 20 detects a sudden increase in load when the single crystal 3 is supported by the support pin 16a, the support pin may be locked at the timing when such a weight change is detected.

  Moreover, the detection timing of the support method of the single crystal 3 may be detected by electrical detection. When a voltage is applied to the support pin 16a and the support pin 16a comes into contact with the single crystal 3, a current flows slightly and the voltage drops. Therefore, the support pin 16a is locked at the timing when this change in voltage is detected, The support of the single crystal 3 may be switched.

  Further, the single crystal produced in the present invention is not limited to a silicon single crystal, and various single crystals grown by the FZ method can be targeted.

  In the production of a silicon single crystal having a diameter of 200 mm by the FZ method, the influence of the presence or absence of a crystal pushing step performed after completion of switching from support by a crystal axis to support by a support pin was evaluated on the quality of the single crystal. In manufacturing a silicon single crystal by the FZ method, six types of silicon single crystal samples with different manufacturing conditions were manufactured.

  The first and second samples T1 and T2 (Comparative Example 1) of the silicon single crystal have a single-crystal rotation method, a rotation speed of 20 rpm, and the support pin is pushed down by lowering the silicon single crystal. No process was performed.

  In the third and fourth samples T3 and T4 (Comparative Example 2), the rotation method of the single crystal is alternate rotation, the crystal rotation speed is 20 rpm, and the step of pushing the support pin by lowering the silicon single crystal is not performed. It was.

  In the fifth and sixth samples T5 and T6 (examples), the rotation method of the single crystal was changed alternately, and the single crystal was lowered by 0.1 mm together with the crystal axis, and the support pin was pushed in.

  The crystal shapes of the silicon single crystal samples T1 to T6 thus manufactured were visually evaluated. The results are shown in Table 1.

  As is apparent from Table 1, even in the support method without the step of pushing the support pin that did not cause crystal bending in one-way rotation, crystal bending occurred in alternate rotation. Furthermore, when the support pin was pushed in, no crystal bending occurred even with alternate rotation.

  Next, six types of silicon single crystal samples T7 to T12 having different single crystal drop amounts in the step of pushing the support pins were manufactured. The rotation method of the silicon single crystal was alternate rotation, and the rotation speed was 20 rpm. The descending amounts for pushing the support in the seventh to twelfth samples T7, T8, T9, T10, T11, T12 are 0.1 mm, 0.2 mm, 0.3 mm, 0.4 mm, 0.5 mm,. It was 6 mm. The silicon single crystal samples T7 to T12 thus manufactured were visually evaluated for crystal shape and crystal breakage. The results are shown in Table 2.

  As is clear from Table 2, the single crystal was not damaged when the drop amount was 0.1 to 0.5 mm, but the single crystal was broken when the drop amount was 0.6 mm.

DESCRIPTION OF SYMBOLS 1 Raw material rod 2 Seed crystal 3 Single crystal 3I Single crystal ingot 3a Constriction part 3b Tapered part 3c Straight body part 3d Bottom part 4 Melt zone 10 Single crystal production apparatus 11 Raw material axis | shaft 12 Raw material feeding mechanism 13 Crystal axis 14 Crystal feeding mechanism 14a Resolver 15 induction heating coil 16 single crystal weight holder 16L lock mechanism 16a support pin 16b movable piece 16c base 16d fixed piece 16e post 16f plate 16y clutch 16z rotation support shaft 17 for single crystal weight holder Camera (CCD camera)
18 Image processing unit 19 Control unit 20 Load sensor R1 Tapered part diameter R2 Straight body diameter S1 Fusion process S2 Drawing process S3 Tapered part growing process S4 Straight body growing process S5 Bottom part growing process S6 Cooling process Sb Tapered surface Sd Reverse taper surface θ Inclination angle of taper surface and reverse taper surface

Claims (18)

A method for producing a single crystal by FZ method, in which a part of a raw material rod is heated to form a melting zone, and the raw material rod and the single crystal located above and below the melting zone are lowered to grow the single crystal. Because
Growing a single crystal above the seed crystal while rotating a crystal axis supporting the lower end of the seed crystal;
Switching the support main body of the single crystal from the crystal axis to the support means by bringing a support means into contact with the outer peripheral surface of the tapered portion of the single crystal grown into a predetermined crystal shape;
After the main support body of the single crystal is switched to the support means, the step of lowering the crystal axis while fixing the vertical position of the support means to strengthen the pushing of the support means against the single crystal;
And further growing the single crystal while being supported by the support means.   2. The method for producing a single crystal according to claim 1, wherein a descending amount of the crystal axis for strengthening the pushing of the support means against the single crystal is greater than 0 mm and 0.5 mm or less.   The method for producing a single crystal according to claim 1, wherein the single crystal supported by the support means is further grown while being alternately rotated.   The support means includes a plurality of support pins provided slidably along the radial direction of the single crystal, and a plurality of support pins are slidably supported along the radial direction of the single crystal. The single crystal production according to any one of claims 1 to 3, wherein a plurality of fixed pieces are respectively arranged behind the movable piece to lock the movement of each support pin along the radial direction of the single crystal. Method.   The movable piece has a tapered surface having an inclination angle of 20 to 25 ° with respect to a vertical surface, and the fixed piece has an inversely tapered surface having the same inclination angle as the tapered surface of the movable piece, The method for producing a single crystal according to claim 4, wherein when the plurality of support pins are locked, the reverse tapered surface of the fixed piece is brought into contact with the tapered surface of the movable piece.   4. The method for producing a single crystal according to claim 1, wherein the support means includes a support ring that contacts substantially the entire circumference of the outer peripheral surface of the tapered portion of the single crystal.   The support ring includes an inner ring member made of a first material and in contact with an outer peripheral surface of the tapered portion of the single crystal, and an outer ring member made of a second material and positioned on the outer peripheral side of the inner ring member. Item 7. A method for producing a single crystal according to Item 6.   Whether the support means is in contact with the outer peripheral surface of the tapered portion of the single crystal based on a photographed image of the camera by photographing the vicinity of the contact position between the support means and the outer peripheral surface of the tapered portion of the single crystal. The manufacturing method of the single crystal as described in any one of Claims 1 thru | or 7 which judges whether.   9. The method according to claim 1, wherein it is determined whether the support means is in contact with an outer peripheral surface of the tapered portion of the single crystal based on a change in a load applied to the crystal axis or the support means. A method for producing a single crystal. A single crystal manufacturing apparatus for manufacturing a single crystal by an FZ method,
A raw material shaft that supports the raw material rod;
A raw material feed mechanism for raising and lowering and rotating the raw material shaft;
A crystal axis supporting the lower end of the seed crystal;
An induction heating coil for heating the raw material rod;
Support means for supporting the single crystal in contact with the outer peripheral surface of the tapered portion of the single crystal;
A crystal feed mechanism for moving up and down and rotating the crystal axis or the support means;
A control unit that controls switching of the support body of the single crystal from the crystal axis to the support means;
The controller is
The support main body of the single crystal is moved from the crystal axis by the lock mechanism that locks the movement of the support means in a state where the support means is in contact with the outer peripheral surface of the tapered portion of the single crystal grown into a predetermined crystal shape. Switch to support,
After switching the support body of the single crystal to the support means, the crystal means is lowered while the vertical position of the support means is fixed to strengthen the pushing of the support means against the single crystal,
A single crystal manufacturing apparatus, wherein the single crystal is further grown while being supported by the support means.   11. The single crystal manufacturing apparatus according to claim 10, wherein a descending amount of the crystal axis for strengthening pushing of the support means with respect to the single crystal is greater than 0 mm and equal to or less than 0.5 mm.   The single crystal manufacturing apparatus according to claim 10 or 11, wherein the control unit further grows the single crystal supported by the support means while alternately rotating the single crystal. The support means includes
A plurality of support pins slidably provided along the radial direction of the single crystal;
A plurality of movable pieces that slidably support each of the plurality of support pins along the radial direction of the single crystal;
When the tip of each of the plurality of support pins comes into contact with the outer peripheral surface of the tapered portion of the single crystal, the support pins are arranged behind the plurality of movable pieces and extend along the radial direction of the single crystal of each support pin. The single crystal manufacturing apparatus according to claim 10, further comprising a plurality of fixed pieces that lock the movement.   The movable piece has a tapered surface having an inclination angle of 20 to 25 ° with respect to a vertical surface, and the fixed piece has an inversely tapered surface having the same inclination angle as the tapered surface of the movable piece, The single crystal manufacturing apparatus according to claim 13, wherein the reverse tapered surface of the fixed piece is brought into contact with the tapered surface of the movable piece when a plurality of support pins are locked.   The single crystal manufacturing apparatus according to any one of claims 10 to 12, wherein the support means includes a support ring that abuts substantially the entire circumference of the outer peripheral surface of the tapered portion of the single crystal.   The support ring includes an inner ring member made of a first material and in contact with an outer peripheral surface of the tapered portion of the single crystal, and an outer ring member made of a second material and positioned on the outer peripheral side of the inner ring member. Item 16. The single crystal manufacturing apparatus according to Item 15. A camera for photographing the vicinity of the contact position between the support means and the outer peripheral surface of the tapered portion of the single crystal;
The single unit according to any one of claims 10 to 16, wherein the control unit determines whether the support means has contacted an outer peripheral surface of the tapered portion of the single crystal based on a captured image of the camera. Crystal manufacturing equipment. A load sensor for detecting a load applied to the crystal axis or the support means;
18. The control unit according to claim 10, wherein the control unit determines whether the support unit is in contact with an outer peripheral surface of the tapered portion of the single crystal based on a change in a load applied to the crystal axis or the support unit. The single crystal manufacturing apparatus according to claim 1.