Method for manufacturing single crystal silicon ingot

Abstract

To provide a method for manufacturing single crystal silicon ingot in which deterioration of speed controllability with an increase of the number of pulling can be suppressed in CZ method using a multipulling method.SOLUTION: A method for manufacturing a single crystal silicon ingot includes a pulling step of a CZ method using a multipulling method in which a horizontal magnetic field is applied from a plurality of superconducting coils provided around a quartz crucible. Bp / Bc in at least a single pulling step out of the second and further pulling steps of a single crystal silicon ingot is smaller than Bp / Bc in the first pulling step of a single crystal silicon ingot.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to a method for manufacturing a single crystal silicon ingot by the Czochralski (CZ) method, and more particularly to a so-called multiplication method for continuously manufacturing a plurality of single crystal silicon ingots using the same quartz crucible.

Background Art

[0002] As a typical method for manufacturing a single crystal silicon ingot, the Czochralski method (CZ method) can be mentioned. In the manufacture of a single crystal silicon ingot by the CZ method, a silicon raw material such as polycrystalline silicon is filled in a quartz crucible, and the silicon raw material is heated and melted in a chamber to obtain 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 gradually raised, whereby a single crystal silicon ingot is grown below the seed crystal.

[0003] In the manufacture of a single crystal silicon ingot, it is important that the manufactured silicon is defect-free, and techniques for suppressing the convection of the silicon melt in the crucible and the increase in 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 single crystal silicon is important for improving the manufacturing yield of defect-free crystals, and is also a necessary technique for further defect reduction accompanying the miniaturization and high integration of future semiconductor silicon devices.

[0004] On the other hand, as an application of the Czochralski method, the multiplication method is known. In the multiplication method, after pulling up the first single-crystal silicon ingot, silicon raw material is additionally supplied and melted in the same quartz crucible, and then the second single-crystal silicon ingot is pulled up from the obtained silicon melt. By repeating such a raw material supply process and a pulling process, a plurality of single-crystal silicon ingots are manufactured using one quartz crucible. According to the multiplication 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 operation efficiency can be improved.

Prior Art Documents

Patent Documents

[0005]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0006] However, as a result of the inventors' study, it has been found that in the Czochralski method using the multiplication method, even when a horizontal magnetic field is applied, the speed controllability deteriorates as the number of pulls increases.

[0007] In view of the above problems, an object of the present invention is to provide a method for manufacturing a single-crystal silicon ingot capable of suppressing deterioration of speed controllability accompanying an increase in the number of pulls in the Czochralski method using the multiplication method.

Means for Solving the Problems

[0008] To solve the above problems, the present inventors have conducted intensive research and obtained the following findings. That is, in the Czochralski method using the multiplication method, when applying a horizontal magnetic field from a plurality of conductive coils to the silicon melt in the quartz crucible, by controlling Bp / Bc in the second and subsequent pulling steps of the single crystal silicon ingot to be smaller than Bp / Bc in the first pulling step, it is possible to suppress the deterioration of the speed controllability with an increase in the number of pulling times. Further, by controlling Bp / Bc in the nth (n is at least one of integers of 2 or more) pulling step to be smaller than Bp / Bc in the (n - 1)th pulling step, it is possible to suppress the deterioration of the speed controllability in the nth pulling. Note that Bp / Bc is a magnetic flux density ratio defined later.

[0009] [1] A method for manufacturing a single crystal silicon ingot by the Czochralski method, comprising repeatedly performing a step of filling a silicon raw material into a quartz crucible, a step of heating and melting the silicon raw material to form a silicon melt in the quartz crucible, and a pulling step of pulling a single crystal silicon ingot from the silicon melt, so as to pull a plurality of single crystal silicon ingots using the same quartz crucible, In the pulling step, applying a horizontal magnetic field from a plurality of conductive coils provided around the quartz crucible to the silicon melt in the quartz crucible, In a horizontal plane including the surface of the silicon melt, taking the magnetic field line direction at the center point of the quartz crucible as the X axis, and the direction passing through the center point of the quartz crucible and perpendicular to the X axis as the Y axis, 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, A method for manufacturing a single crystal silicon ingot, characterized in that Bp / Bc in at least one of the second and subsequent pulling steps 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. Note that the magnetic field line direction at the center point of the quartz crucible in the horizontal plane is the direction of the component of the magnetic field line 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.

[0010] [2] A method for manufacturing a single crystal silicon ingot by the CZ method in which a silicon raw material is filled into a quartz crucible, the silicon raw material is heated and melted to form a silicon melt in the quartz crucible, and a pulling step of pulling a single crystal silicon ingot from the silicon melt is repeatedly performed to pull a plurality of single crystal silicon ingots using the same quartz crucible, In the pulling step, a horizontal magnetic field is applied to the silicon melt in the quartz crucible from a plurality of conductive coils provided around the quartz crucible. In a horizontal plane including the surface of the silicon melt, with the magnetic field line direction at the center point of the quartz crucible as the X-axis and the direction passing through the center point of the quartz crucible and perpendicular to the X-axis as the Y-axis, 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. A method for manufacturing a single crystal silicon ingot, characterized in that Bp / Bc in the nth (n is at least one integer of 2 or more) pulling step of the single crystal silicon ingot is set to be smaller than Bp / Bc in the (n - 1)th pulling step.

[0011] [3] The method for manufacturing a single crystal silicon ingot according to [1] or [2] above, wherein Bp / Bc in the first pulling step of the single crystal silicon ingot is 1.2 or more and 1.5 or less.

[0012] [4] The method for manufacturing a single crystal silicon ingot according to any one of [1] to [3] above, wherein the magnetic flux density Bc is 500 G or more and 4000 G or less.

Advantages of the Invention

[0013] According to the method for manufacturing a single-crystalline silicon ingot of the present invention, in the CZ method using the multipulling method, it is possible to suppress the deterioration of speed controllability accompanying an increase in the number of pulling operations, and thus the yield can be improved.

Brief Description of the Drawings

[0014]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Embodiments for Carrying Out the Invention

[0015] (Silicon Single-Crystal Pulling Apparatus) First, with reference to FIG. 1, the configuration of a silicon single-crystal pulling apparatus 100 used in one embodiment of the present invention will be described.

[0016] The silicon single-crystal pulling apparatus 100 includes a main chamber 10, a pull chamber 11, a crucible 16, a shaft 18, a shaft drive mechanism 20, a cylindrical heat shield 22, a cylindrical heater 24, a cylindrical heat insulator 26, a seed chuck 28, a pulling wire 30, a wire lifting mechanism 32, and a magnetic field generating device 34.

[0017] The main chamber 10 is a bottomed cylindrical chamber in which the crucible 16 is accommodated. The pull 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, provided above the main chamber 10. A gate valve 12 is provided between the main chamber 10 and the pull chamber 11. By opening and closing this gate valve 12, the spaces in the main chamber 10 and the pull chamber 11 are communicated with and blocked from each other. At the upper part of the pull chamber 11, a gas inlet 13 for introducing an inert gas such as Ar gas into the main chamber 10 is provided. Also, at the bottom of the main chamber 10, a gas outlet 14 is provided for sucking and discharging the gas in the main chamber 10 by driving a vacuum pump (not shown).

[0018] The crucible 16 is arranged at the center of the main chamber 10 and accommodates 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 outside the quartz crucible 16A. As shown in FIG. 1, 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.

[0019] The shaft 18 vertically penetrates the bottom of the main chamber 10 and supports the crucible 16 at the upper end. Then, the shaft drive mechanism 20 raises and lowers the crucible 16 while rotating it via the shaft 18.

[0020] The heat shield 22 is provided above the crucible 16 so as to surround the single crystal silicon ingot I pulled up from the silicon melt M. Specifically, the heat shield 22 includes an inverted frustum-shaped shield body 22A, an inner flange portion 22B extending horizontally from the lower end portion of the shield 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 body 22A toward the chamber side (outside). The outer flange portion 22C is fixed to the heat insulator 26. This heat shield 22 adjusts the amount of incident high-temperature radiant heat from the silicon melt M, the heater 24, and the side wall of the crucible 16 to the growing ingot I, and adjusts the amount of heat diffusion near the crystal growth interface, and plays a role in controlling the temperature gradient in the pulling axis Z direction at the center and outer periphery of the single crystal silicon ingot I.

[0021] The cylindrical heater 24 is positioned in the main chamber 10 so as to surround the crucible 16. The heater 24 is a resistance heating type heater made of carbon, melts the silicon raw material charged into the crucible 16 to form the silicon melt M, and further performs heating to maintain the formed silicon melt M.

[0022] The cylindrical heat insulator 26 is provided along the inner surface of the main chamber 10, below the upper end of the heat shield 22 and spaced apart from the outer peripheral surface of the heater 24. The heat insulator 26 has a function of imparting a heat retention effect to the region in the chamber 10, particularly below the heat shield 22, and making it easier to maintain the silicon melt M in the crucible 16.

[0023] Above the crucible 16, a pulling wire 30 that holds the seed chuck 28 holding the seed crystal S at the lower end is arranged coaxially with the shaft 18, and the wire lifting mechanism 32 raises and lowers the pulling wire 30 while rotating it in the opposite direction or the same direction as the shaft 18 at a predetermined speed.

[0024] The magnetic field generating device 34 is located in a height range outside the main chamber 10 and encompassing the crucible 16. By passing an electric current through a plurality of superconducting coils of this magnetic field generating device 34, a horizontal magnetic field that forms a horizontal magnetic field distribution with respect to the silicon melt M can be generated. Note that the magnetic flux density can be controlled by the magnitude of the current flowing through the superconducting coil.

[0025] In one embodiment, the magnetic field generating device 34 has 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. FIG. 2 shows a perspective view of the magnetic field generating device 34 according to an example of this embodiment, and FIG. 3 shows a cross-sectional view of an example of the arrangement of three pairs of superconducting coils in the magnetic field generating device 34. Here, two superconducting coils arranged so as to face each other with the quartz crucible 16A interposed therebetween (the coil axes being common) are defined as one pair. That is, the superconducting coils 40A and 40C, 40B and 40D, and 40E and 40F are each one pair of coils. Also, the central axes of all the superconducting coils are arranged so as to be included in a single horizontal plane. Note that in the present invention, the magnetic field generating device 34 only needs to have a plurality of conductive coils, and a normal conducting coil may be used instead of the superconducting coil.

[0026] Conventionally, a magnetic field generating device having two pairs of superconducting coils corresponding to the superconducting coils 40A and 40C, and 40B and 40D in FIG. 3 has been used. By using two pairs of four superconducting coils in total, a horizontal magnetic field is applied to the quartz crucible 16A. Here, as shown in FIG. 3, in the horizontal plane including the surface of the silicon melt, the direction of the magnetic field line 41 at the center point of the quartz crucible 16A (the position of the lifting axis Z) is defined as the X-axis, and the direction passing through the center point of the quartz crucible and perpendicular to the X-axis is defined as the Y-axis. The inventors of the present invention discovered that by having a pair of superconducting coils on the X-axis in addition to the above two pairs of superconducting coils, the control of Bp / Bc described later can be easily performed. Therefore, it is preferable that the magnetic field generating device 34 has a total of six superconducting coils in three pairs. Here, a pair of superconducting coils on the X-axis is referred to as an auxiliary coil, and two pairs of superconducting coils arranged symmetrically with respect to the X-axis are referred to as main coils. That is, in FIG. 3, the superconducting coils 40A to 40D are main coils, and the superconducting coils 40E and 40F are auxiliary coils.

[0027] As shown in FIG. 3, by arranging the superconducting coils and controlling the ratio of the current value of the auxiliary coil to the current value of the main coil, the control of Bp / Bc described later becomes possible. Specifically, when the current value of the auxiliary coil is increased, Bc increases, and when the current value of the main coil is increased, Bp increases. In addition, even when a horizontal magnetic field is applied by two pairs of superconducting coils, the control of Bp / Bc is possible by changing the installation angle of the superconducting coils, but it is difficult to make such a change during the pulling of the single crystal silicon ingot.

[0028] As shown in FIG. 3, let the angle between the common coil axis of the first pair of main coils 40A and 40C and the X-axis, and the common coil axis of the second pair of main coils 40B and 40D be α. When α is 100 degrees or more, in the growth of a single crystal with a low oxygen concentration, the reduction of the oxygen concentration can be preferably performed. Therefore, α is preferably 100 degrees or more. On the other hand, when α is 120 degrees or less, it is possible to preferably prevent the adjacent main coils from colliding with each other. Therefore, α is preferably 120 degrees or less.

[0029] (Method for manufacturing single-crystal silicon ingot by multiplication method) The method for manufacturing a single-crystal silicon ingot according to an embodiment of the present invention can be preferably implemented using the silicon single-crystal pulling apparatus 100 described above. Here, the method for manufacturing a single-crystal silicon ingot according to an embodiment of the present invention will be described.

[0030] [Raw material filling step] First, a silicon raw material such as a polycrystalline silicon ingot is filled into the quartz crucible 16A located in the main chamber 10. At this time, the gate valve 12 is open, and the inside of the main chamber 10 and the pull chamber 11 is maintained in an inert gas atmosphere such as Ar gas under reduced pressure. Further, the crucible 16 is positioned below in the main chamber 10 so that the silicon raw material does not contact the heat shield 22.

[0031] [Raw material melting step] 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 start position of pulling. This "raw material melting step" is defined as the period from the time when heating by the heater 24 is started to the time when the raising of the crucible 16 is completed.

[0032] [Pulling step] Next, the pulling wire 30 is lowered by the wire lifting mechanism 32 to attach the seed crystal S to 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 pulled upward to grow the single-crystal silicon ingot I below the seed crystal S. As the growth of the single-crystal silicon ingot I progresses, 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 step" is defined as the period from the time when the raising of the pulling wire 30 is started to the time when the growth of the single-crystal silicon ingot I is completed (the time when the single-crystal silicon ingot I is separated from the silicon melt M).

[0033] In the pulling-up process, first, in order to make the single crystal dislocation-free, seed necking (necking) is performed by the Dash method to form a neck portion. Next, the shoulder portion is grown, and when the silicon single crystal reaches the desired diameter, the diameter is made constant and the body portion is grown. After growing the straight body portion to a predetermined length, tail necking is performed to separate the single crystal from the silicon melt M in a dislocation-free state and form a tail portion. In the pulling-up process, especially when growing the body portion, it is necessary to precisely control the crystal defects and the diameter of the silicon single crystal. Therefore, when growing the body portion in particular in the pulling-up process, good controllability of the pulling speed is required.

[0034] [Ingot lifting process in the main chamber] Next, the pulled-up single crystal silicon ingot I is separated from the silicon melt M, lifted inside the main chamber 10, and accommodated in the pull 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 time when the single crystal silicon ingot I is separated from the silicon melt M until the entire single crystal silicon ingot I moves into the pull chamber 11 and the gate valve 12 closes. The pulling speed in this process is appropriately determined according to the required crystal quality characteristics.

[0035] [Cooling process in the pull chamber] Next, the single crystal silicon ingot I is left in the pull chamber 11 with the gate valve 12 closed and cooled until it reaches a take-out temperature of preferably 500°C or lower.

[0036] [Ingot take-out process] Next, the cooled single crystal silicon ingot I is taken out of the pull chamber 11. Specifically, with the gate valve 12 kept closed, the pull chamber 11 moves up and down and rotates, the ingot I is processed inside the pull chamber 11, and loaded onto a transport cart. Through the above processes, one single crystal silicon ingot I is manufactured.

[0037] [Pulling by the Multiplication Method] This embodiment relates to a multiplication method for pulling a plurality of single crystal silicon ingots I using the same quartz crucible 16A. Therefore, after taking out the first single crystal silicon ingot I, in order to perform the next pulling, the raw material filling process to the ingot taking-out process are carried out again, and the second single crystal silicon ingot I is manufactured. By repeating this, n single crystal silicon ingots I are manufactured. n is at least one integer of 2 or more and is not particularly limited. If the next pulling is not performed, the operation using the same quartz crucible 16A is terminated and the crucible is replaced.

[0038] In this embodiment, after the crystal growth process from the first to the (n - 1)th time is completed, it is necessary to maintain the silicon melt M in the quartz crucible 16A until a new silicon raw material filling process required for performing the next crystal growth process is carried out. Therefore, in the ingot lifting process, the cooling process in the pull chamber, and the ingot taking-out process in the main chamber from the first to the (n - 1)th time, the heating of the silicon melt M is continued without stopping the heater 24. Further, in the raw material filling process from the second to the nth time, the heating of the silicon melt M is continued without stopping the heater 24.

[0039] [Application of Magnetic Field] In this embodiment, in the pulling process, a 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. In this state, by performing the pulling process, the thermal convection of the silicon melt M during the growth of the single crystal is suppressed, and the temporal variation of the temperature near the melt surface (the temperature of the crystal growth solid-liquid interface) is reduced. Therefore, a single crystal silicon ingot with suppressed generation of dislocations and defects can be easily obtained.

[0040] In FIG. 3, let the magnetic flux density at the intersection of the Y-axis and the inner wall surface of the quartz crucible 16A be Bp, and the magnetic flux density at the center point of the quartz crucible (the position of the pulling axis Z) be Bc. Although there are two intersections between the Y-axis and the inner wall surface of the quartz crucible 16A, since the applied horizontal magnetic field is symmetric about the X-axis and the Y-axis, either intersection can be used as Bp.

[0041] In this embodiment, 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. In particular, it is preferable to set the magnitude relationship of Bp / Bc at the start of the growth of the body portion in the pulling step in this way. By controlling Bp / Bc in this way, it is possible to suppress the deterioration of the speed controllability accompanying the increase in the number of pulling times at the start of the growth of the body portion, where good controllability of the pulling speed is particularly required. In particular, setting Bp / Bc in the pulling steps after the third time to be smaller than Bp / Bc in the first pulling step is preferable because the effects of the present invention can be obtained remarkably. Further, it is more preferable to set Bp / Bc in all the pulling steps after the second pulling step to be smaller than Bp / Bc in the first pulling step.

[0042] Further, in another embodiment of the present invention, Bp / Bc in the n-th (n is at least one integer of 2 or more) pulling step of the single crystal silicon ingot is set to be smaller than Bp / Bc in the (n - 1)-th pulling step. In particular, it is preferable to set the magnitude relationship of Bp / Bc at the start of the growth of the body portion in the pulling step in this way. By controlling Bp / Bc in this way, it is possible to suppress the deterioration of the speed controllability in at least the n-th pulling step from being worse than the speed controllability in the (n - 1)-th pulling step at the start of the growth of the body portion, where good controllability of the pulling speed is particularly required. Note that n is preferably 5 or less.

[0043] In addition, Bp / Bc in the pulling-up process only needs to satisfy any one of the above two embodiments, and may satisfy both of them.

[0044] Also, in actual operation, it is assumed that the position of the crucible (i.e., the position of the melt surface) changes during the pulling-up process. In this case, since the relative positional relationship between the induction coil and the melt surface changes, Bp / Bc will change slightly during the pulling-up process. Even when Bp / Bc changes during the pulling-up process like this, by setting the magnitude relationship of Bp / Bc at the start point of growing the body part as described above, the effects of the present invention can be obtained. Therefore, in the pulling-up process, especially when Bp / Bc changes, it is preferable to set the magnitude relationship of Bp / Bc at the start point of growing the body part as described above.

[0045] Furthermore, the inventors found that it is more preferable that Bp / Bc is a value satisfying -0.057n + 1.56, where n is the number of pull-ups. Considering the variation, it is preferable that Bp / Bc is in the range of -0.057n + 1.56 ± 0.2. That is, it is more preferable that Bp / Bc in the n-th pulling-up process satisfies the following formula (1). By Bp / Bc satisfying the following formula (1), the deterioration of speed controllability accompanying the increase in the number of pull-ups can be more suitably suppressed. -0.057n + 1.36 ≦ Bp / Bc ≦ -0.057n + 1.76 ···(1)

[0046] When Bp / Bc in the first pulling-up process of the single crystal silicon ingot is 1.2 or more, the deterioration of speed controllability accompanying the increase in the number of pull-ups can be suitably suppressed. Therefore, it is preferable that Bp / Bc in the first pulling-up process is 1.2 or more. On the other hand, when Bp / Bc in the first pulling-up process is 1.5 or less, the deterioration of speed controllability accompanying the increase in the number of pull-ups can be suitably suppressed. Therefore, it is preferable that Bp / Bc in the first pulling-up process is 1.5 or less.

[0047] In the pulling process after the second time of pulling a single-crystal silicon ingot, when Bp / Bc is 1.0 or more, the deterioration of the rate controllability associated with the increase in the number of pulling times can be suitably suppressed. Therefore, it is preferable that Bp / Bc in the pulling process after the second time is 1.0 or more, and more preferably 1.1 or more. On the other hand, when Bp / Bc in the pulling process after the second time is 1.6 or less, the deterioration of the rate controllability associated with the increase in the number of pulling times can be suitably suppressed. Therefore, it is preferable that Bp / Bc in the pulling process after the second time is 1.6 or less, and more preferably 1.2 or less. In particular, in the pulling process of the fourth or fifth time, it is preferable that Bp / Bc is 1.1 or more and 1.2 or less.

[0048] When Bc in each pulling process is 500 G or more, the deterioration of the rate controllability associated with the increase in the number of pulling times can be suitably suppressed. Therefore, it is preferable that Bc is 500 G or more, more preferably 2500 G or more, and even more preferably 3000 G or more. On the other hand, when Bc in each pulling process is 4000 G or less, the output range on the equipment can be suitably ensured. Therefore, it is preferable that Bc is 4000 G or less, more preferably 3500 G or less, and even more preferably 3400 G or less.

[0049] 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 the arrangement of the superconducting coil as shown in FIG. 3, when the value of Bp / Bc is determined, the value of Bp2 / Bc is also determined.

[0050] In the present invention, the rate controllability in each pulling process is evaluated by the rate variation σ. The rate variation σ is the difference Δv = v set - v act between the actual crystal growth rate v act and the crystal growth rate v set set in the pulling process, and is the standard deviation of Δv when obtained in the crystal longitudinal direction. The smaller Δv is, the better the rate controllability is, and the production yield of the single-crystal silicon ingot is improved.

[0051] In the growth of a single crystal silicon ingot, the crystal growth rate is set such that v / G, that is, the ratio of the growth rate v during crystal growth to the temperature gradient G in the growth axis direction near the melting point, becomes its critical value (ξcri). On the other hand, since the crystal growth rate also plays a role in keeping the crystal diameter of the single crystal silicon ingot constant, when the diameter stability is impaired for reasons such as unstable melt fluidity during pulling, it may be necessary to vary the crystal growth rate. The variation in the difference between the set growth rate and the actual growth rate is evaluated by the rate variation σ.

[0052] The diameter stability of the single crystal silicon ingot in the pulling process means, that is, the stability of the melt flow. The melt flow can be stabilized by increasing the magnetic flux density ratio of the applied magnetic field, but it is also affected by disturbances during crystal growth. In particular, in the multiplication method, it is considered that with an increase in the number of pulls, impurity adhesion and deterioration to the internal furnace components and the reduction of the quartz crucible due to dissolution into the melt (change in shape) have an impact. Since these cannot be avoided in performing the multiplication method, it is important to ensure the diameter stability of the single crystal silicon ingot in the pulling process, that is, to suppress the deterioration of the speed controllability.

[0053] In the present invention, regarding the mechanism by which the deterioration of the speed controllability can be suppressed by adjusting Bp / Bc as described above in accordance with the number of pulls, the inventors consider as follows. By setting Bp / Bc to a high value (for example, 1.4), the melt flow can be stabilized. However, when Bp / Bc is high, a non-uniform magnetic flux density distribution is formed in the silicon melt, so depending on the influence of disturbances, the non-uniformity of the Lorentz force distribution in the melt becomes extreme and rather the speed controllability deteriorates. Therefore, when strongly affected by disturbances, that is, in the pulling process after multiple pulls in the multiplication method, the deterioration of the speed controllability can be suppressed by lowering Bp / Bc.

[0054] Note that conventional methods can be used for the processes and conditions not described in the present invention.

Example

[0055] As examples and comparative examples of the present invention, using a silicon single crystal pulling apparatus having the configuration shown in FIG. 1, a multiplication method of repeatedly manufacturing a single crystal silicon ingot 5 times was performed by changing Bp / Bc and Bc, respectively.

[0056] First, a quartz crucible was filled with a silicon raw material (polycrystalline silicon lump), which was heated and melted to form a predetermined amount of silicon melt. Thereafter, a horizontal magnetic field was applied to the silicon melt, and the liquid landing process to the crystal growth process was performed to manufacture a single crystal silicon ingot (diameter 310 mm). At that time, the rotation speed of the crucible was set to 0.5 rpm.

[0057] FIG. 4(A) shows the magnetic flux density ratio Bp / Bc of the horizontal magnetic field applied in each pulling run of the present invention example and the comparative example. In the present invention example, Bp / Bc was decreased for each pulling run with a minimum change amount of 0.04. On the other hand, in the comparative example, Bp / Bc was made constant for each pulling run.

[0058] FIGS. 4(B) to (D) show the ratios of the speed variations σ in each pulling run of the present invention example and the comparative example when Bc is set to 3400 G, 3000 G, and 2500 G, respectively, with respect to the speed variation σ in the first pulling run of the present invention example where Bc is 3400 G. In the comparative example, the ratio of the speed variation increased with the number of pulling runs, whereas in the present invention example, the speed variation showed a substantially constant value regardless of the number of pulling runs. From this, it is clear that by decreasing Bp / Bc in accordance with the increase in the number of pulling runs, an increase in the speed variation can be suppressed, that is, a deterioration in the speed controllability accompanying an increase in the number of pulling runs can be suppressed.

[0059] Next, in order to verify the case where Bp / Bc is set to a small value from the first pulling cycle, single crystal silicon ingots were produced in the same manner as described above. Fig. 5(A) shows the magnetic flux density ratio Bp / Bc of the horizontal magnetic fields applied in each pulling cycle of the inventive example and the comparative example. In the comparative example, Bp / Bc = 1.0 was set for each pulling. Fig. 5(B) shows the ratio of the speed variations σ of each pulling cycle of the inventive example and the comparative example, for the case where Bc is 3400 G, with respect to the speed variation σ of the first pulling cycle of the inventive example where Bc is 3400 G. As shown in Fig. 5(B), it is clear that the inventive example has less speed variation and can suppress the deterioration of speed controllability associated with an increase in the number of pulling cycles.

Industrial Applicability

[0060] According to the present invention, in the CZ method using the multiplication method, it is possible to provide a method for manufacturing a single crystal silicon ingot that can suppress the deterioration of speed controllability associated with an increase in the number of pulling cycles.

Explanation of Reference Numerals

[0061] 100 Silicon single crystal pulling apparatus 10 Main chamber 11 Pull chamber 12 Gate valve 13 Gas inlet 14 Gas outlet 16 Crucible 16A Quartz crucible 16B Graphite crucible 18 Shaft 20 Shaft drive mechanism 22 Heat shield 22A Shield body 22B Inner flange portion 22C Outer flange portion 24 Heater 26 Heat insulator 28 Seed chuck 30 Pulling wire 32 Wire lifting mechanism 34 Magnetic field generator 40A Superconducting Coil (Main Coil) 40B Superconducting Coil (Main Coil) 40C Superconducting Coil (Main Coil) 40D Superconducting Coil (Main Coil) 40E Superconducting Coil (Auxiliary Coil) 40F Superconducting Coil (Auxiliary Coil) 41 Magnetic Flux 42 Coil Axis S-Type Crystal M Silicon Melt I Single Crystal Silicon Ingot X Axis in the Direction of the Magnetic Flux at the Center Point of the Quartz Crucible on the Horizontal Plane Y Axis Passing Through the Center Point of the Quartz Crucible on the Horizontal Plane and Perpendicular to the X Axis Z Pulling Axis

Claims

1. A method for manufacturing a single crystal silicon ingot by the CZ method, in which a silicon raw material is filled into a quartz crucible, the silicon raw material is heated and melted to form a silicon melt in the quartz crucible, and a pulling step of pulling a single crystal silicon ingot from the silicon melt is repeatedly performed to pull a plurality of single crystal silicon ingots using the same quartz crucible, comprising: In the pulling step, a horizontal magnetic field is applied to the silicon melt in the quartz crucible from a plurality of conductive coils provided around the quartz crucible, In a horizontal plane including the surface of the silicon melt, with the magnetic field line direction at the center point of the quartz crucible as the X-axis and the direction passing through the center point of the quartz crucible and perpendicular to the X-axis as the Y-axis, 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, A method for manufacturing a single crystal silicon ingot, characterized in that 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 by the CZ method, in which a silicon raw material is filled into a quartz crucible, the silicon raw material is heated and melted to form a silicon melt in the quartz crucible, and a pulling step of pulling a single crystal silicon ingot from the silicon melt is repeatedly performed to pull a plurality of single crystal silicon ingots using the same quartz crucible, comprising: In the pulling step, a horizontal magnetic field is applied to the silicon melt in the quartz crucible from a plurality of conductive coils provided around the quartz crucible, In a horizontal plane including the surface of the silicon melt, with the magnetic field line direction at the center point of the quartz crucible as the X-axis and the direction passing through the center point of the quartz crucible and perpendicular to the X-axis as the Y-axis, 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, A method for manufacturing a single-crystalline silicon ingot, characterized in that Bp / Bc in the n-th (n is at least one integer of 2 or more) pulling step of the single-crystalline silicon ingot is set to be smaller than Bp / Bc in the (n - 1)-th pulling step.

3. The method for manufacturing a single-crystalline silicon ingot according to claim 1 or 2, wherein Bp / Bc in the first pulling step of the single-crystalline silicon ingot is 1.2 or more and 1.5 or less.

4. The method for manufacturing a single-crystalline silicon ingot according to claim 1 or 2, wherein the magnetic flux density Bc is 500 G or more and 4000 G or less.

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