Method for producing single crystal silicon ingot

Abstract

Provided is a method for producing a single crystal silicon ingot, with which it is possible to suppress deterioration in speed controllability accompanying an increase in the number of pulls in a CZ method using a multi-pulling method. The method for producing a single crystal silicon ingot according to the present invention is characterized in that a horizontal magnetic field is applied by a plurality of conductive coils provided around a quartz crucible in a pulling step of a CZ method using a multi-pulling method, and the Bp / Bc in at least one pulling step among the second and subsequent pulling steps of the single crystal silicon ingot is smaller than the Bp / Bc in the first pulling step of the single crystal silicon ingot. In a horizontal plane including the surface of the silicon melt, the direction of the magnetic line of force at the center point of the quartz crucible is defined as the X-axis, the direction passing through the center point of the quartz crucible and perpendicular to the X-axis is defined as the Y-axis, and the ratio of the magnetic flux density Bp at the intersection of the Y-axis and the inner wall surface of the quartz crucible to the magnetic flux density Bc at the center point of the quartz crucible is defined as Bp / Bc.

Description

Technical Field

[0001] The present invention relates to a method for manufacturing a single crystal ingot using the Czochralski (CZ) method, and particularly to a so-called multi-pulling method for continuously manufacturing multiple single crystal ingots using the same quartz crucible. Background Art

[0002] As a representative method for manufacturing a single crystal ingot, the Czochralski method (CZ method) can be cited. In the manufacture of a single crystal ingot using the CZ method, a silicon raw material such as polysilicon is filled in a quartz crucible, and the silicon raw material is heated and melted in a chamber to form a silicon melt. Next, a seed crystal is brought into contact with the silicon melt in the quartz crucible, and the seed crystal and the quartz crucible are rotated in a predetermined direction while the seed crystal is slowly raised, whereby a single crystal ingot is grown below the seed crystal.

[0003] In the manufacture of a single crystal ingot, it is important that the manufactured silicon has no defects, and techniques for suppressing the convection of the silicon melt in the crucible and increasing the oxygen concentration in the single crystal are known. Patent Document 1 discloses a single crystal pulling apparatus that applies a horizontal magnetic field to a molten single crystal material to suppress the convection of the molten single crystal material in the crucible. In addition, the stable control of the growth rate of a single crystal is important for improving the yield of defect-free crystals, and is a technique necessary for further defect-free processing accompanying the miniaturization and high integration of semiconductor silicon devices in the future.

[0004] On the other hand, as an application of the CZ method, a multi-pulling method is known. In the multi-pulling method, after pulling the first single crystal ingot, silicon raw material is additionally supplied and melted in the same quartz crucible, and the second single crystal ingot is pulled from the resulting silicon melt. By repeating such a raw material supply process and a pulling process, multiple single crystal ingots are manufactured using one quartz crucible. By using the multi-pulling method, the cost of the quartz crucible per ingot can be reduced. In addition, since the frequency of disassembling the chamber and replacing the quartz crucible can be reduced, the work efficiency can be improved.

[0005] Prior Art Documents

[0006] Patent Documents

[0007] Patent Document 1: Japanese Unexamined Patent Application Publication No. 2021-98622 Summary of the Invention

[0008] Problems to be Solved by the Invention

[0009] However, the inventors of the present invention have found through research that in the CZ method using the multi-pulling method, even when a horizontal magnetic field is applied, the rate controllability deteriorates as the number of pulling times increases.

[0010] In view of the above problems, an object of the present invention is to provide a method for manufacturing a single crystal ingot, which can suppress the deterioration of speed controllability accompanying an increase in the number of pulling operations in the CZ method using the multi-pulling method.

[0011] Means for Solving the Problems

[0012] To solve the above problems, the present inventors conducted in-depth research and obtained the following insights. That is, in the CZ method using the multi-pulling method, when a horizontal magnetic field is applied to the silicon melt in the quartz crucible by a plurality of conductive coils, by controlling the Bp / Bc ratio in the second and subsequent pulling steps of the single crystal ingot to be smaller than the Bp / Bc ratio in the first pulling step, the deterioration of speed controllability accompanying an increase in the number of pulling operations can be suppressed. In addition, by controlling the Bp / Bc ratio in the nth (n is at least one of integers of 2 or more) pulling step to be smaller than the Bp / Bc ratio in the (n-1)th pulling step, the deterioration of speed controllability in the nth pulling can be suppressed. It should be noted that Bp / Bc is the magnetic flux density ratio described later.

[0013] [1] A method for manufacturing a single crystal ingot, which is a method for manufacturing a single crystal ingot using the CZ method. The CZ method repeats the steps of filling a silicon raw material in a quartz crucible, heating the silicon raw material to melt it and forming a silicon melt in the quartz crucible, and a pulling step of pulling a single crystal ingot from the silicon melt, so as to pull a plurality of single crystal ingots using the same quartz crucible. The feature of this manufacturing method is that

[0014] In the pulling step, a horizontal magnetic field is applied to the silicon melt in the quartz crucible by a plurality of conductive coils provided around the quartz crucible.

[0015] In a horizontal plane including the surface of the silicon melt, the direction of the magnetic field line at the center point of the quartz crucible is set as the X axis, the direction passing through the center point of the quartz crucible and perpendicular to the X axis is set as the Y axis, and the ratio of the magnetic flux density Bp at the intersection of the Y axis and the inner wall surface of the quartz crucible to the magnetic flux density Bc at the center point of the quartz crucible is set as Bp / Bc.

[0016] The Bp / Bc in at least one of the second and subsequent pulling steps of the single crystal ingot is set to be smaller than the Bp / Bc in the first pulling step of the single crystal ingot.

[0017] It should be noted that the direction of the magnetic field line at the center point of the quartz crucible in the horizontal plane refers to the direction of the component on the horizontal plane when the magnetic field line is decomposed into a component perpendicular to the horizontal plane and a component on the horizontal plane.

[0018] [2]The manufacturing method of a single crystal silicon ingot is a manufacturing method of a single crystal silicon ingot using the Czochralski method (CZ method). The CZ method forms a silicon melt in a quartz crucible by repeating the steps of filling the quartz crucible with silicon raw materials, heating the silicon raw materials to melt them, and pulling a single crystal silicon ingot from the silicon melt, so as to pull multiple single crystal silicon ingots using the same quartz crucible. The feature of this manufacturing method is that,

[0019] In the pulling step, a horizontal magnetic field is applied to the silicon melt in the quartz crucible by a plurality of conductive coils arranged around the quartz crucible.

[0020] In the horizontal plane including the surface of the silicon melt, the direction of the magnetic field line at the center point of the quartz crucible is set as the X-axis, the direction passing through the center point of the quartz crucible and perpendicular to the X-axis is set as the Y-axis, and the ratio of the magnetic flux density Bp at the intersection of the Y-axis and the inner wall surface of the quartz crucible to the magnetic flux density Bc at the center point of the quartz crucible is set as Bp / Bc.

[0021] The Bp / Bc in the nth (n is at least one of integers greater than or equal to 2) pulling step of the single crystal silicon ingot is set to be smaller than the Bp / Bc in the (n - 1)th pulling step.

[0022] [3]According to the manufacturing method of the single crystal silicon ingot described in the above [1] or [2], wherein the Bp / Bc in the first pulling step of the single crystal silicon ingot is 1.2 or more and 1.5 or less.

[0023] [4]According to the manufacturing method of the single crystal silicon ingot described in any one of the above [1] to [3], wherein the magnetic flux density Bc is 500 G or more and 4000 G or less.

[0024] Advantages of the Invention

[0025] According to the manufacturing method of the single crystal silicon ingot of the present invention, in the CZ method using the multi-pulling method, it is possible to suppress the deterioration of the speed controllability accompanying the increase in the number of pulling times, and further improve the yield. Description of the Drawings

[0026] Figure 1 : It is a sectional view along the pulling axis Z, which schematically shows the configuration of the silicon single crystal pulling device 100 used in one embodiment of the present invention.

[0027] Figure 2 : It is a perspective view of the magnetic field generating device.

[0028] Figure 3 : It is a sectional view along the horizontal plane including the surface of the silicon melt, which shows an example configuration of three pairs of superconducting coils in the magnetic field generating device.

[0029] Figure 4 : (A) is the condition of the magnetic flux density ratio in an embodiment of the present invention, and (B) to (D) are the results obtained by measuring the change in the speed deviation of Bc recorded in the upper part of each figure with the increase in the number of pulling operations.

[0030] Figure 5 : (A) is the condition of the magnetic flux density ratio in an embodiment of the present invention, and (B) is the result obtained by measuring the change in the speed deviation with the increase in the number of pulling operations. Detailed implementation mode

[0031] (Silicon single crystal pulling device)

[0032] First, with reference to Figure 1 , the configuration of the silicon single crystal pulling device 100 used in an embodiment of the present invention will be described.

[0033] The silicon single crystal pulling device 100 includes: a main chamber 10, a pulling chamber 11, a crucible 16, a shaft 18, a shaft drive mechanism 20, a cylindrical thermal shield 22, a cylindrical heater 24, a cylindrical heat insulator 26, a seed crystal chuck 28, a pulling wire 30, a wire lifting mechanism 32, and a magnetic field generating device 34.

[0034] The main chamber 10 is a bottomed cylindrical chamber that houses the crucible 16 inside. The pulling chamber 11 has the same central axis as the main chamber 10 and is a cylindrical chamber with a smaller diameter than the main chamber 10, which is provided above the main chamber 10. A gate valve 12 is provided between the main chamber 10 and the pulling chamber 11. Through the opening and closing of this gate valve 12, the spaces inside the main chamber 10 and the pulling chamber 11 are interconnected and separated. A gas inlet 13 for introducing an inert gas such as Ar gas into the main chamber 10 is provided at the upper part of the pulling chamber 11. In addition, a gas outlet 14 for sucking and discharging the gas inside the main chamber 10 by driving a vacuum pump (not shown) is provided at the bottom of the main chamber 10.

[0035] The crucible 16 is provided at the central part of the main chamber 10 and houses the silicon melt M. The crucible 16 has a double structure of a quartz crucible 16A and a graphite crucible 16B. The quartz crucible 16A directly supports the silicon melt M on its inner surface. The graphite crucible 16B supports the quartz crucible 16A on the outside of the quartz crucible 16A. As Figure 1 shown, the upper end of the quartz crucible 16A is higher than the upper end of the graphite crucible 16B, that is, the upper end portion of the quartz crucible 16A protrudes from the upper end of the graphite crucible 16B.

[0036] The shaft 18 penetrates the bottom of the main chamber 10 in the vertical direction and supports the crucible 16 at the upper end. Subsequently, the shaft drive mechanism 20 rotates and lifts the crucible 16 through the shaft 18.

[0037] A thermal shield 22 is disposed above the crucible 16 to surround the single crystal ingot I pulled from the silicon melt M. Specifically, the thermal shield 22 includes: a shield main body 22A having an inverted frustum shape, an inner flange portion 22B extending horizontally from the lower end portion of the shield main body 22A toward the pulling axis Z side (inside), and an outer flange portion 22C extending horizontally from the upper end portion of the shield main body 22A toward the chamber side (outside), and the outer flange portion 22C is fixed to the heat insulator 26. With respect to the ingot I being grown, the thermal shield 22 adjusts the incident amount of high-temperature radiant heat from the silicon melt M, the heater 24, and the side wall of the crucible 16, or adjusts the amount of heat diffusion near the crystal growth interface. In addition, the thermal shield 22 functions to control the temperature gradient in the pulling axis Z direction of the central portion and the outer peripheral portion of the single crystal ingot I.

[0038] The cylindrical heater 24 is located in the main chamber 10 at a position surrounding the crucible 16. The heater 24 is a resistance heating type heater using carbon as a raw material, melts the silicon raw material put into the crucible 16 to form the silicon melt M, and further performs heating for maintaining the formed silicon melt M.

[0039] The cylindrical heat insulator 26 is disposed along the inner side surface of the main chamber 10 separately from the outer peripheral surface of the heater 24 below the upper end of the thermal shield 22. The heat insulator 26 gives a heat preservation effect to the region inside the chamber 10, especially the region below the thermal shield 22, and has a function of easily maintaining the silicon melt M in the crucible 16.

[0040] Above the crucible 16, a pulling wire 30 holding the seed crystal S at the lower end and a seed crystal chuck 28 are arranged coaxially with the shaft 18, and the wire lifting mechanism 32 rotates and lifts the pulling wire 30 at a predetermined speed in a direction opposite to or the same as the shaft 18.

[0041] The magnetic field generating device 34 is located outside the main chamber 10 in a height range including the crucible 16. By passing an electric current through a plurality of superconducting coils constituting the magnetic field generating device 34, a horizontal magnetic field that forms a horizontal magnetic field distribution for the silicon melt M can be generated. It should be noted that the magnetic flux density can be controlled by the magnitude of the current flowing through the superconducting coil.

[0042] In one embodiment, the magnetic field generating device 34 includes a plurality of superconducting coils. By using a magnetic field generating device having a plurality of superconducting coils, a horizontal magnetic field can be applied. Figure 2 A perspective view of the magnetic field generating device 34 described in an example of the present embodiment is shown, Figure 3A cross-sectional view showing an example configuration of three pairs of superconducting coils in the magnetic field generating device 34. Here, two superconducting coils arranged to sandwich the quartz crucible 16A (with a common coil axis) are defined as one pair. That is, the superconducting coils 40A and 40C, 40B and 40D, and 40E and 40F are respectively defined as one pair of coils. In addition, the central axes of the respective superconducting coils are all arranged to be included in one horizontal plane. It should be noted that in the present invention, the magnetic field generating device 34 may have a plurality of conductive coils, or normal conducting coils may be used instead of superconducting coils.

[0043] Conventionally, a magnetic field generating device using two pairs of superconducting coils equivalent to Figure 3 the superconducting coils 40A and 40C, 40B and 40D is used. By using two pairs of a total of four superconducting coils, a horizontal magnetic field is applied to the quartz crucible 16A. Here, as Figure 3 shown, in the horizontal plane including the surface of the silicon melt, the direction of the magnetic field line 41 at the center point (position of the pulling axis Z) of the quartz crucible 16A is set as the X-axis, and the direction passing through the center point of the quartz crucible and perpendicular to the X-axis is set as the Y-axis. The inventors of the present invention found that in addition to the above two pairs of superconducting coils, by having one pair of superconducting coils on the X-axis, the control of Bp / Bc described later can be easily performed. Therefore, the magnetic field generating device 34 preferably has three pairs of a total of six superconducting coils. Here, the one pair of superconducting coils on the X-axis is defined as the sub-coils, and the two pairs of superconducting coils symmetrically arranged with respect to the X-axis are called the main coils. That is, Figure 3 the superconducting coils 40A to 40D are defined as the main coils, and the superconducting coils 40E and 40F are defined as the sub-coils.

[0044] As Figure 3 such, by arranging the superconducting coils and controlling the ratio of the current value of the sub-coils to the current value of the main coils, the control of Bp / Bc described later can be achieved. Specifically, if the current value of the sub-coils is increased, Bc increases, and if the current value of the main coils is increased, Bp increases. It should be noted that even in the case of applying a horizontal magnetic field using two pairs of superconducting coils, the control of Bp / Bc can be performed by changing the setting angle of the superconducting coils, but it is difficult to make such a change during the pulling of a single crystal ingot.

[0045] As Figure 3 shown, the angle between the common coil axis of the first pair of main coils 40A and 40C and the common coil axis of the second pair of main coils 40B and 40D sandwiching the X-axis is set as α. When α is 100 degrees or more, during the cultivation of a single crystal with a low oxygen concentration, the reduction of the oxygen concentration can be appropriately performed. Therefore, α is preferably 100 degrees or more. On the other hand, when α is 120 degrees or less, the collision between adjacent main coils can be appropriately prevented. Therefore, α is preferably 120 degrees or less.

[0046] (Method for manufacturing single crystal silicon ingot using multi-pulling method)

[0047] The method for manufacturing a single crystal silicon ingot according to an embodiment of the present invention can be suitably implemented using the silicon single crystal pulling device 100 described above. Here, the method for manufacturing a single crystal silicon ingot according to an embodiment of the present invention will be described.

[0048] [Raw material filling process]

[0049] First, a silicon raw material such as a polysilicon block is filled in the quartz crucible 16A located in the main chamber 10. At this time, the gate valve 12 is opened, and the main chamber 10 and the pulling chamber 11 are maintained under reduced pressure in an inert gas atmosphere such as Ar gas. In addition, the crucible 16 is located below in the main chamber 10 so that the silicon raw material does not contact the heat shield 22.

[0050] [Raw material melting process]

[0051] Next, the silicon raw material in the crucible 16 is heated and melted by the heater 24 to form a silicon melt M in the quartz crucible 16A. Then, the crucible 16 is raised to the pulling start position. This "raw material melting process" is defined as the period from the start of heating of the heater 24 until the raising of the crucible 16 is completed.

[0052] [Pulling process]

[0053] Next, the pulling wire 30 is lowered by the wire lifting mechanism 32 so that the seed crystal S is immersed in the silicon melt M, and the single crystal silicon ingot I is pulled from the silicon melt M. Specifically, while rotating the crucible 16 and the pulling wire 30 in a predetermined direction, the pulling wire 30 is lifted upward to grow the single crystal silicon ingot I below the seed crystal S. It should be noted that as the single crystal silicon ingot I grows, the amount of the silicon melt M decreases, but the crucible 16 is raised to maintain the level of the melt surface. In this specification, the "pulling process" is defined as the period from the start of the raising of the pulling wire 30 until the completion of the growth of the single crystal silicon ingot I (the moment when the single crystal silicon ingot I is separated from the silicon melt M).

[0054] In the pulling process, first, in order to make the single crystal dislocation-free, seed crystal reduction (necking) based on the Dash method is performed to form a neck. Next, the shoulder is grown, and when the silicon single crystal reaches the desired diameter, the diameter is maintained constant and the main body is grown. After growing the main body to a predetermined length, in order to separate the single crystal from the silicon melt M in a dislocation-free state, tail reduction is performed to form a tail. In the pulling process, especially when growing the main body, precise control of crystal defects and control of the diameter of the silicon single crystal are required. Therefore, in the pulling process, especially when growing the main body, good controllability of the pulling speed is required.

[0055] [Ingot lifting process in the main chamber]

[0056] Next, the lifted single-crystal silicon ingot I is separated from the silicon melt M and lifted within the main chamber 10, and is accommodated in the lifting chamber 11 above the main chamber 10. In this specification, the "ingot lifting process in the main chamber" is defined as the period from the moment when the single-crystal silicon ingot I is separated from the silicon melt M until the entire single-crystal silicon ingot I is moved into the lifting chamber 11 and the gate valve 12 is closed. The lifting speed in this process is appropriately determined according to the required crystal quality characteristics.

[0057] [Cooling process in the lifting chamber]

[0058] Next, the single-crystal silicon ingot I is placed and cooled in the lifting chamber 11 with the gate valve 12 closed until the take-out temperature of preferably 500 °C or lower.

[0059] [Ingot take-out process]

[0060] Next, the cooled single-crystal silicon ingot I is taken out from the lifting chamber 11. Specifically, with the gate valve 12 closed, the lifting chamber 11 is lifted and rotated, and the ingot I descends within the lifting chamber 11 and is loaded onto the transport cart. Through the above processes, one single-crystal silicon ingot I is manufactured.

[0061] [Lifting using the multi-lifting method]

[0062] This embodiment relates to a multi-lifting method of lifting multiple single-crystal silicon ingots I using the same quartz crucible 16A. Therefore, after the first single-crystal silicon ingot I is taken out, in order to perform the next lifting, the raw material filling process to the ingot take-out process is performed again to manufacture the second single-crystal silicon ingot I. By repeating these processes, n single-crystal silicon ingots I are manufactured. n is at least one of integers of 2 or more and is not particularly limited. When the next lifting is not performed, the operation using the same quartz crucible 16A is ended and the crucible is replaced.

[0063] It should be noted that in this embodiment, during the period from the end of the first to the (n - 1)th crystal growth process until the filling process of the new silicon raw material required for the next crystal growth process is performed, it is necessary to maintain the silicon melt M in the quartz crucible 16A. Therefore, in the first to the (n - 1)th ingot lifting process in the main chamber, the cooling process in the lifting chamber, and the ingot take-out process, the heater 24 is not stopped, and the heating of the silicon melt M is continued. Further, in the second to the nth raw material filling process, the heater 24 is also not stopped, and the heating of the silicon melt M is performed.

[0064] [Application of magnetic field]

[0065] In this embodiment, in the pulling process, an electric current is passed through the superconducting coils 40A to 40F of the magnetic field generating device 34 to apply a horizontal magnetic field to the silicon melt M. By performing the pulling process in this state, the thermal convection of the silicon melt M during single crystal growth is suppressed, and the change over time in the temperature near the surface of the melt (the temperature of the solid-liquid interface of crystal growth) is reduced. Therefore, a single crystal ingot with suppressed generation of dislocations and defects can be easily obtained.

[0066] Figure 3 In this case, the magnetic flux density at the intersection of the Y-axis and the inner wall surface of the quartz crucible 16A is designated as Bp, and the magnetic flux density at the center point of the quartz crucible (the position of the pulling axis Z) is designated as Bc. It should be noted that there are two intersections of the Y-axis and the inner wall surface of the quartz crucible 16A, but the applied horizontal magnetic field is symmetric about the X-axis and the Y-axis. Therefore, either intersection can be selected to set Bp.

[0067] In this embodiment, Bp / Bc in at least one of the pulling processes in the second and subsequent pulling processes of the single crystal ingot is set to be smaller than Bp / Bc in the first pulling process of the single crystal ingot. In particular, in the pulling process, it is preferable to set the magnitude relationship of Bp / Bc at the start time of the cultivation of the main body part in this way. By controlling Bp / Bc in this manner, it is possible to suppress the deterioration of speed controllability accompanying an increase in the number of pulling times at the start of the cultivation of the main body part where good controllability of the pulling speed is particularly required. In particular, when Bp / Bc in the third and subsequent pulling processes is set to be smaller than Bp / Bc in the first pulling process, the effects of the present invention can be significantly obtained, so this is preferable. Furthermore, it is more preferable to set Bp / Bc in all of the pulling processes in the second and subsequent pulling processes to be smaller than Bp / Bc in the first pulling process.

[0068] In addition, in another embodiment of the present invention, Bp / Bc in the nth (n is at least one of integers of 2 or more) pulling process of the single crystal ingot is set to be smaller than Bp / Bc in the (n - 1)th pulling process. In particular, in the pulling process, it is preferable to set the magnitude relationship of Bp / Bc at the start time of the cultivation of the main body part in this way. By controlling Bp / Bc in this manner, it is possible to suppress the deterioration of speed controllability in at least the nth pulling process compared to that in the (n - 1)th pulling process at the start of the cultivation of the main body part where good controllability of the pulling speed is particularly required. It should be noted that n is preferably 5 or less.

[0069] It should be noted that Bp / Bc in the pulling process only needs to satisfy any one of the above two embodiments, and it may also satisfy both.

[0070] In addition, in actual operation, it is expected that the position of the crucible (i.e., the position of the molten liquid surface) changes during the pulling process. At this time, the relative positional relationship between the conductive coil and the molten liquid surface changes. Therefore, during the pulling process, Bp / Bc will change slightly. Even in the case where Bp / Bc changes during the pulling process, the effects of the present invention can be obtained by setting the magnitude relationship of Bp / Bc at the start time of cultivating the main body part as described above. Therefore, during the pulling process, especially when Bp / Bc changes, it is preferable to set the magnitude relationship of Bp / Bc at the start time of cultivating the main body part as described above.

[0071] Furthermore, the inventors found that when the number of pulling operations is set to n, Bp / Bc is more preferably a value that satisfies -0.057n + 1.56. Considering the deviation, Bp / Bc is preferably in the range of -0.057n + 1.56 ± 0.2. That is, Bp / Bc in the nth pulling process more preferably satisfies the following formula (1). By making Bp / Bc satisfy the following formula (1), the deterioration of the rate controllability accompanying the increase in the number of pulling operations can be further appropriately suppressed.

[0072] -0.057n + 1.36 ≤ Bp / Bc ≤ -0.057n + 1.76 · · · (1)

[0073] If Bp / Bc in the first pulling process of the single crystal ingot is 1.2 or more, the deterioration of the rate controllability accompanying the increase in the number of pulling operations can be appropriately suppressed. Therefore, Bp / Bc in the first pulling process is preferably set to 1.2 or more. On the other hand, if Bp / Bc in the first pulling process is 1.5 or less, the deterioration of the rate controllability accompanying the increase in the number of pulling operations can be appropriately suppressed. Therefore, Bp / Bc in the first pulling process is preferably set to 1.5 or less.

[0074] If Bp / Bc in the second and subsequent pulling processes of the single crystal ingot is 1.0 or more, the deterioration of the rate controllability accompanying the increase in the number of pulling operations can be appropriately suppressed. Therefore, Bp / Bc in the second and subsequent pulling processes is preferably set to 1.0 or more, and more preferably set to 1.1 or more. On the other hand, if Bp / Bc in the second and subsequent pulling processes is 1.6 or less, the deterioration of the rate controllability accompanying the increase in the number of pulling operations can be appropriately suppressed. Therefore, Bp / Bc in the second and subsequent pulling processes is preferably set to 1.6 or less, and more preferably set to 1.2 or less. In particular, in the fourth and fifth pulling processes, Bp / Bc is preferably set to be 1.1 or more and 1.2 or less.

[0075] If Bc in each pulling process is 500 G or more, the deterioration of speed controllability accompanying an increase in the number of pulling times can be appropriately suppressed. Therefore, Bc is preferably 500 G or more, more preferably 2500 G or more, and still more preferably 3000 G or more. On the other hand, if Bc in each pulling process is 4000 G or less, the output range on the equipment can be appropriately ensured. Therefore, Bc is preferably 4000 G or less, more preferably 3500 G or less, and still more preferably 3400 G or less.

[0076] Let the magnetic flux density at the intersection of the X-axis and the inner wall surface of the quartz crucible 16A be Bp2. In Figure 3 such a superconducting coil configuration, if the value of Bp / Bc is fixed, the value of Bp2 / Bc is also fixed.

[0077] In the present invention, the speed controllability in each pulling process is evaluated by the speed deviation σ. The speed deviation σ refers to obtaining the actual crystal growth speed v in the crystal length direction act relative to the crystal growth speed v set in the pulling process set The difference Δv = v act - v set is the standard deviation of Δv at that time. The smaller Δv is, the better the speed controllability, and the manufacturing yield of the single crystal ingot is improved.

[0078] In the cultivation of a single crystal ingot, the crystal growth speed is set so that v / G, that is, the ratio of the growth speed v during crystal growth to the temperature gradient G in the growth axis direction near the melting point, reaches its critical value (ξcri). On the other hand, since the crystal growth speed also serves to keep the crystal diameter of the single crystal ingot constant, when the stability of the diameter is impaired due to unstable fluidity of the molten liquid or the like during pulling, it is sometimes necessary to change the crystal growth speed. The deviation between the set growth speed and the actual growth speed is evaluated by the speed deviation σ.

[0079] The stability of the diameter of the single crystal ingot in the pulling process is the stability of the flow of the molten liquid. Although the flow of the molten liquid can be stabilized by increasing the magnetic flux density ratio of the applied magnetic field, it is also affected by the interference during crystal growth. Especially in the multi-pulling method, it is considered that with an increase in the number of pulling times, the attachment and deterioration of impurities on the furnace internal components and the thinning of the wall thickness (change in shape) due to the melting of the quartz crucible in the molten liquid will have an impact. These problems are inevitable when performing the multi-pulling method. Therefore, ensuring the diameter stability of the single crystal ingot in the pulling process, that is, suppressing the deterioration of speed controllability, is important.

[0080] In the present invention, the inventors believe that the mechanism for suppressing the deterioration of speed controllability by adjusting Bp / Bc corresponding to the number of liftings as described above is as follows. By making Bp / Bc a high value (e.g., 1.4), the flow of the molten liquid can be stabilized. However, when Bp / Bc is high, a non-uniform magnetic flux density distribution is formed in the silicon molten liquid. Therefore, due to the influence of interference, the non-uniformity of the Lorentz force distribution in the molten liquid becomes extreme, and the speed controllability deteriorates instead. Therefore, in the case of being strongly affected by interference, that is, in the lifting process after multiple liftings in the multi-lifting method, by reducing Bp / Bc, the deterioration of speed controllability can be suppressed.

[0081] It should be noted that processes and conditions not described in the present invention can be carried out using conventional methods.

[0082] [Examples]

[0083] As examples and comparative examples of the present invention, a silicon single crystal pulling apparatus having the configuration shown in Figure 1 was used, and Bp / Bc and Bc were changed, and the multi-lifting method for manufacturing single crystal ingots five times in repetition was carried out respectively.

[0084] First, a silicon raw material (polycrystalline silicon block) was filled in a quartz crucible, heated and melted to form a specified amount of silicon molten liquid. Then, a horizontal magnetic field was applied to the silicon molten liquid, and a crystal growth process was carried out starting from the liquid contact process to manufacture a single crystal ingot (diameter 310 mm). At this time, the rotation speed of the crucible was set to 0.5 rpm.

[0085] Figure 4 (A) shows the magnetic flux density ratio Bp / Bc of the horizontal magnetic field applied in each lifting of the example and comparative example of the present invention. In the example of the present invention, Bp / Bc was made to decrease by 0.04 each time with the minimum change amount. On the other hand, in the comparative example, Bp / Bc was set to be constant in each lifting.

[0086] Figure 4 (B) to (D) show the ratio of the speed deviation σ in each lifting of the example and comparative example of the present invention when Bc is set to 3400 G, 3000 G, and 2500 G respectively, to the speed deviation σ in the first lifting of the example of the present invention when Bc is set to 3400 G. In the comparative example, the ratio of the speed deviation increased each time as the number of liftings elapsed. In contrast, in the example of the present invention, it was shown that the speed deviation was a substantially constant value regardless of the number of liftings. Therefore, it is obvious that by reducing Bp / Bc corresponding to the increase in the number of liftings, an increase in the speed deviation can be suppressed, that is, the deterioration of speed controllability accompanying the increase in the number of liftings can be suppressed.

[0087] Next, in order to verify the case where Bp / Bc is set to a small value from the first lift, a single crystal silicon ingot was manufactured in the same manner as described above. Figure 5 (A) shows the magnetic flux density ratio Bp / Bc of the horizontal magnetic fields applied in each lift of the inventive example and the comparative example. In the comparative example, Bp / Bc = 1.0 was set in each lift. Figure 5 (B) shows the ratio of the speed deviation σ in each lift of the inventive example and the comparative example when Bc is 3400 G to the speed deviation σ in the first lift of the inventive example when Bc is 3400 G. As Figure 5 (B) shows, it is clear that the speed deviation of the inventive example is smaller than that of the comparative example, and the deterioration of speed controllability accompanying an increase in the number of lifts can be suppressed.

[0088] Industrial Applicability

[0089] According to the present invention, a method for manufacturing a single crystal silicon ingot capable of suppressing deterioration of speed controllability accompanying an increase in the number of lifts in the CZ method using the multi-lift method can be provided.

[0090] Symbol Explanation

[0091] 100 Single crystal silicon pulling device

[0092] 10 Main chamber

[0093] 11 Pulling chamber

[0094] 12 Gate valve

[0095] 13 Gas inlet

[0096] 14 Gas outlet

[0097] 16 Crucible

[0098] 16A Quartz crucible

[0099] 16B Graphite crucible

[0100] 18 Shaft

[0101] 20 Shaft drive mechanism

[0102] 22 Thermal shield

[0103] 22A Shield main body

[0104] 22B Inner flange portion

[0105] 22C Outer flange portion

[0106] 24 Heater

[0107] 26 Heat insulator

[0108] 28 Seed crystal chuck

[0109] 30 Pulling wire

[0110] 32 Wire lifting mechanism

[0111] 34 Magnetic field generating device

[0112] 40A Superconducting coil (main coil)

[0113] 40B Superconducting coil (main coil)

[0114] 40C Superconducting coil (main coil)

[0115] 40D Superconducting coil (main coil)

[0116] 40E Superconducting coil (secondary coil)

[0117] 40F Superconducting coil (secondary coil)

[0118] 41 Magnetic lines of force

[0119] 42 Coil axis

[0120] S Seed crystal

[0121] M Molten silicon

[0122] I Single crystal silicon ingot

[0123] Axis in the direction of the magnetic lines of force at the center point of the quartz crucible on the X horizontal plane

[0124] Axis in the Y direction on the horizontal plane passing through the center point of the quartz crucible and perpendicular to the X axis

[0125] Z Pulling axis

Claims

1. A method for manufacturing a single crystal silicon ingot, which is a method for manufacturing a single crystal silicon ingot using a CZ method, wherein the CZ method comprises repeatedly performing a step of filling a quartz crucible with a silicon raw material, a step of heating and melting the silicon raw material to form a silicon melt in the quartz crucible, and a step of pulling the single crystal silicon ingot from the silicon melt, thereby pulling up a plurality of single crystal silicon ingots using the same quartz crucible, wherein: In the pulling step, a horizontal magnetic field is applied to the silicon melt in the quartz crucible by a plurality of conductive coils disposed around the quartz crucible. In a horizontal plane including the surface of the silicon melt, the direction of the magnetic field lines at the center point of the quartz crucible is set as the X-axis, the direction passing through the center point of the quartz crucible and perpendicular to the X-axis is set as the Y-axis, and the ratio of the magnetic flux density Bp at the intersection of the Y-axis and the inner wall surface of the quartz crucible to the magnetic flux density Bc at the center point of the quartz crucible is set as Bp / Bc, Bp / Bc in at least one of the pulling steps after the second pulling step of the single crystal silicon ingot is set to be smaller than Bp / Bc in the first pulling step of the single crystal silicon ingot.

2. A method for manufacturing a single crystal silicon ingot, which is a method for manufacturing a single crystal silicon ingot using a CZ method, wherein the CZ method comprises repeatedly performing a step of filling a quartz crucible with a silicon raw material, a step of heating the silicon raw material and melting it to form a silicon melt in the quartz crucible, and a step of pulling a single crystal silicon ingot from the silicon melt, thereby pulling a plurality of single crystal silicon ingots using the same quartz crucible, wherein the method is characterized in that: In the pulling step, a horizontal magnetic field is applied to the silicon melt in the quartz crucible by a plurality of conductive coils disposed around the quartz crucible. In a horizontal plane including the surface of the silicon melt, the direction of the magnetic field lines at the center point of the quartz crucible is set as the X-axis, the direction passing through the center point of the quartz crucible and perpendicular to the X-axis is set as the Y-axis, and the ratio of the magnetic flux density Bp at the intersection of the Y-axis and the inner wall surface of the quartz crucible to the magnetic flux density Bc at the center point of the quartz crucible is set as Bp / Bc, Bp / Bc in the nth (n is at least one of an integer greater than or equal to 2) pulling step of the single crystal silicon ingot is set to be smaller than Bp / Bc in the (n-1)th pulling step.

3. The method for manufacturing a single crystal silicon ingot according to claim 1 or 2, wherein: Bp / Bc in the first pulling step of the single crystal silicon ingot is greater than or equal to 1.2 and less than or equal to 1.

5.

4. The method for manufacturing a single crystal silicon ingot according to claim 1 or 2, wherein: The magnetic flux density Bc is greater than or equal to 500G and less than or equal to 4000G.

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