METHOD FOR PRODUCING A SILICON SINGLE CRYSTAL

Abstract

Method for producing a silicon single crystal by a CZ process using a cusp magnetic field formed by an upper coil and a lower coil provided in a drawing furnace, the method comprising the following steps: Seeding by bringing a seed crystal into contact with a silicon melt; and Pulling up a straight body after increasing the diameter of the silicon single crystal, wherein The seeding is carried out with a position of a magnetic field minimal plane on a central axis of the drawing furnace as the first position below a surface of the silicon melt, Before proceeding with the raising of the straight body, the position of the magnetic field minimum plane on the central axis of the drawing furnace is brought to a second position above the first position. The lifting of the straight body takes place with the position of the magnetic field minimal plane on the central axis of the drawing furnace as the second position, The first position lies between 30 mm and 80 mm below the surface of the silicon melt, The second position lies between 10 mm below and 100 mm above the surface of the silicon melt. During seeding, the intensity of the magnetic field at an intersection of an intermediate plane between the upper coil and the lower coil and an inner wall of a crucible is 0.15 T or more and 0.20 T or less, and When the straight body is pulled upwards, the intensity of a magnetic field at an intersection of an intermediate plane between the upper coil and the lower coil and an inner wall of a crucible is 0.075 T or more and 0.18 T or less.

Description

TECHNICAL AREA

[0001] The present invention relates to a method for producing a silicon single crystal by a CZ process using a Cusp magnetic field. BACKGROUND

[0002] In recent years, power devices have gained attention as a means of saving energy. The area where an electric current flows in a power device can be located in the thickness range of a few dozen or hundreds of micrometers from a surface layer, or in some cases, the electric current flows across an entire wafer. If an oxygen deposit or a bulk microdefect (BMD) is present in the area where the electric current flows, it can lead to a breakdown voltage failure or a leakage defect. To avoid the aforementioned defects, silicon single-crystal wafers for power devices must have such a low oxygen concentration that no oxygen deposit forms, as well as a flat distribution of oxygen and resistance in the plane.

[0003] The Czochralski process (CZ process) is one of the leading methods for producing a silicon single crystal for a power device. In the CZ process, the silicon single crystal is grown by bringing a seed crystal into contact with a heated silicon melt and gradually drawing the seed crystal upwards above the melt. Assuming a significant temperature difference between the seed crystal and the silicon melt, a thermal shock occurs when the seed crystal comes into contact with the silicon melt, and this thermal shock generates a sliding dislocation. The method for eliminating the sliding dislocation that occurs when the seed crystal comes into contact with the silicon melt, by narrowing the crystal diameter to 3 to 5 mm, is called the dash necking process and is widely used in the production of silicon single crystals using the CZ process.

[0004] Recently, with the development of a larger diameter and heavier silicon single crystal, a dislocation-free seeding method was also introduced that does not use the dash necking method described in Patent Document 1. According to the method described in Patent Document 1, a seed crystal with a pointed shape, where the angle of the tip is 28° or less, is used. The seed crystal is heated to nearly the same temperature as the raw material melt before contact with the silicon melt, and then the seed crystal is brought into contact with the silicon melt, thus suppressing the occurrence of thermal shock. Applying this method to grow a single crystal enables the efficient production of a large-diameter, heavy single crystal with a diameter of 300 mm or more.

[0005] Patent document 6 discloses a silicon single crystal, a method for its production, as well as a silicon wafer and in particular a method for producing a silicon single crystal using an MCZ (CZ with applied magnetic field) process, as well as a silicon single crystal and a silicon wafer produced therein.

[0006] Patent document 7 discloses a method for growing a silicon single crystal according to the Czochralski method.

[0007] Patent document 8 discloses a Czochralski puller utilizing a magnetic field, and a method for growing a single-crystal block using the same; more precisely, a Czochralski puller utilizing a peak magnetic field used for growing a single-crystal block, and a method for growing a single-crystal block using the same to improve the pulling speed of a single-crystal block and the growth of pure silicon. Patent document 9 discloses a method for producing single crystals and a device for producing single crystals for producing a dislocation-free silicon single crystal according to the Czochralski method. QUOTE LIST PATENT LITERATURE Patent Document 1: JP 4151580 B2 Patent Document 2: JP 2009-18984 A Patent document 3: WO 2009 / 025340 Patent Document 4: JP 2001-89289 A Patent Document 5: JP 2020-33200 A Patent document 6: DE 11 2018 006 080 T5 Patent document 7: JP 2013-023 415 A Patent document 8: KR 10 2002 011 956 A Patent Document 9: JP H10-273 376 A SUMMARY OF THE INVENTIONAL PROBLEM

[0008] In the production of a silicon single crystal using the CZ process, the magnetic field Czochralski process (MCZ process) is the main method, in which a single crystal is grown while a magnetic field is applied to a molten raw material. For growing an oxygen-deficient crystal for a power device, a process using a horizontal magnetic field and a process using a cusp magnetic field are known.

[0009] As a method utilizing a horizontal magnetic field, patent document 2, for example, discloses a process for obtaining an oxygen-depleted crystal by setting the rotational speed of the crystal and the rotational speed of the crucible under a horizontal magnetic field. However, this method targets a diameter of 200 mm and is not suitable for growing a silicon single crystal with a large diameter of 300 mm or more. Furthermore, as disclosed in patent document 3, there is a method in which the intensity of the magnetic field is set to 0.20 T (2000 G) or more and the rotational speed of the crystal is set to 5 rpm or less. In this method, hydrogen doping is performed during the single crystal's production, followed by neutron irradiation.However, the problem is that carrying out these processes increases the cost of manufacturing the crystal. Furthermore, producing the oxygen-depleted crystal with a diameter of 300 mm or more in a horizontal magnetic field requires a low crystal rotation rate, as disclosed in patent document 3. However, a low crystal rotation rate degrades the distribution of resistivity and oxygen in the plane, leading to defects in the device.

[0010] On the other hand, as disclosed, for example, in patent document 4, there is a method using the Cusp magnetic field to shift a central position of the Cusp magnetic field (position of a magnetic field minimum plane) to a position where a temperature is stabilized, depending on the amount of reduced silicon melt. In this method, the position of the magnetic field plane of the Cusp magnetic field is also raised with an increase in the solidification ratio of the single crystal. A change in the position of the magnetic field minimum plane within the product part (straight body part) causes an increase in the magnitude of the change in oxygen concentration in the product part, which leads to a problem where the yield is significantly reduced when the crystal is produced with a narrow specification range of oxygen concentration or a low-oxygen crystal.

[0011] Furthermore, patent document 5 presents a method in which the rotational speed of the crystal, the rotational speed of the crucible, the central position of the magnetic field (position of the plane of minimum magnetic field), and the intensity of the magnetic field are determined, thereby obtaining the oxygen-deficient crystal. In this way, the position of the plane of minimum magnetic field is positioned near a solid-liquid interface, and the intensity of the magnetic field, defined as 0.05 to 0.07 T (500 to 700 G), allows the single crystal with a low oxygen concentration of 4 × 10⁻⁶ to be produced. 17 atoms / cm² 3or less. As described above, for the production of a heavy single crystal with a diameter of 300 mm or more, the dislocation-free seeding process without dash necking is preferable. However, under the conditions disclosed in patent document 5, the temperature variation on the surface of the raw material melt during seeding is considerable, and this leads to a problem where the success of the seeding becomes difficult; therefore, the single crystal productivity is reduced.

[0012] The present invention was made with regard to the problem described above. One objective of the present invention is to provide a method for producing a silicon single crystal in order to produce a single crystal with a lower oxygen concentration and better in-plane distribution, with an improved success rate and production efficiency than the prior art. SOLUTION TO THE PROBLEM

[0013] To achieve this goal, the present invention provides a method for producing a silicon single crystal by a CZ process using a cusp magnetic field formed by an upper coil and a lower coil in a drawing furnace, the method comprising the following steps: Seeding by bringing a seed crystal into contact with a silicon melt; and Pulling up a straight body after increasing the diameter of the silicon single crystal, wherein the seeding is carried out with a position of a magnetic field minimal plane on a central axis of the drawing furnace as the first position below a surface of the silicon melt, Before the straight body is drawn up, the position of the magnetic field minimum plane on the central axis of the drawing furnace is brought to a second position above the first position. The lifting of the straight body takes place with the position of the plane with minimal magnetic field on the central axis of the drawing furnace as the second position.

[0014] In this method for producing silicon single crystals, the surface temperature fluctuation of the raw material melt (silicon melt) during seeding is minimal, thus significantly improving the seeding success rate. Furthermore, when drawing the straight body of a product part, oxygen tends to be readily incorporated into the single crystal from an oxygen-depleted layer on the surface of the silicon melt by changing the position of the plane of minimum magnetic field strength. This allows for the production of a silicon single crystal with a low oxygen concentration and excellent in-plane distribution. As a result of the combination of these effects, a single crystal with low oxygen concentration and excellent in-plane distribution can be efficiently produced.

[0015] In this case, the first position can be between 30 mm and 80 mm below the surface of the silicon melt, and the second position can be between 10 mm below and 100 mm above the surface of the silicon melt.

[0016] This enables a more stable and reliable production of the silicon single crystal with a low oxygen concentration and excellent in-plane distribution, resulting in an improved seeding success rate and higher production efficiency.

[0017] In this case, the intensity of the magnetic field at the intersection of an intermediate plane between the upper coil and the lower coil and an inner wall of a crucible can be 0.15 T (1500 G) or more.

[0018] This allows for a more stable and reliable improvement in vaccination success rates and production efficiency.

[0019] In this case, when the straight body is pulled upwards, the intensity of the magnetic field at the intersection of an intermediate plane between the upper coil and the lower coil and an inner wall of the crucible can be 0.075 T (750 G) or more and 0.18 T (1800 G) or less.

[0020] This enables a more stable and reliable production of silicon single crystals with a low oxygen concentration and excellent in-plane distribution.

[0021] In this case, vaccination can be carried out using a procedure that does not involve transferring patients.

[0022] This enables the efficient production of silicon single crystals with a stable low oxygen concentration and excellent in-plane distribution, even for silicon single crystals with a larger diameter, resulting in an improved seeding success rate.

[0023] In this case, a constriction can be carried out after inoculation, while the position of the magnetic field minimum plane on the central axis of the drawing furnace is the first position below the surface of the silicon melt.

[0024] Thus, even when using the Dash Necking method, a silicon single crystal with a stable low oxygen concentration and excellent in-plane distribution can be efficiently produced, while simultaneously improving the seeding success rate. ADVANTAGEOUS EFFECTS OF THE INVENTION

[0025] As described above, the inventive method for producing the silicon single crystal can improve the seeding success rate by reducing temperature fluctuations on the surface of the silicon melt during seeding. Furthermore, the method can efficiently produce the single crystal with the low oxygen concentration and excellent in-plane distribution required for, e.g., a power component on a straight body segment. BRIEF DESCRIPTION OF THE DRAWINGS Fig. Figure 1 is a view showing an example of a single-crystal pulling device. DESCRIPTION OF THE EXECUTION FORMS

[0026] The present invention is described in detail below. However, the present invention is not limited to this.

[0027] As described above, in recent years the quality of low-oxygen crystals used in power components, etc., has been required to be at a higher level than conventional ones. In particular, the desired oxygen concentration should be 3 x 10⁻⁶. 17 atoms / cm² 3(ASTM'79) or less to eliminate the effect of a thermal donor created by low-temperature heat treatment. Furthermore, a uniform distribution of oxygen concentration in the plane is desirable to eliminate chip-to-chip quality variations. For example, if the oxygen concentration is low at the periphery of a wafer, sliding dislocations can occur during heat treatment, which in some cases negatively impacts the yield of a device process. In this case, doping with impurities such as nitrogen can increase strength, but since nitrogen also influences defect and donor formation, it is important to uniformize the oxygen concentration in the plane so that it is independent of doping.

[0028] Furthermore, the radial oxygen gradient (ROG) can be used as an indicator of excellent in-plane oxygen distribution. ROG is a value determined by measuring the oxygen concentration at at least two locations: in the wafer center and 5 mm from the wafer edge, using a formula: (Maximum value - minimum value) x 100 / maximum value. In recent years, a better ROG value than the conventional value has been required, and an excellent distribution is demanded where the ROG value is less than 15%.

[0029] In the CZ process, a silicon melt is placed in a quartz crucible, and oxygen is incorporated into a silicon single crystal by eluting an oxygen component from the quartz crucible into the silicon melt while the crystal is pulled. In the MCZ process with a horizontal magnetic field, when viewing a surface layer of the silicon melt from a vertical perspective, convection parallel to the magnetic field lines is suppressed because the magnetic field acts in this direction. However, convection is activated perpendicular to the magnetic field lines because there is almost no magnetic field in this direction. This creates a region where convection is locally active, and the oxygen component can be more easily eluted from the quartz crucible in the horizontal magnetic field, resulting in a high oxygen concentration in the silicon single crystal.

[0030] On the other hand, in the case of a cusp magnetic field, the magnetic field acts near an inner wall of the crucible across its entire circumference; therefore, convection near the inner wall of the crucible is suppressed across its entire circumference. Consequently, the relative velocity between the quartz crucible and the silicon melt in a cusp magnetic field becomes high if the rotational speed of the crucible is sufficiently high and the magnetic field intensity is high. This favors the elution of the oxygen component. Conversely, the relative velocity between the quartz crucible and the silicon melt becomes slow if the rotational speed of the crucible is sufficiently low and the magnetic field intensity is low. Then, the elution of oxygen is suppressed.In addition to the factors described above, the natural convection inherent in the Cusp magnetic field facilitates the incorporation of oxygen components into the single crystal from a low-oxygen layer on the surface of the silicon melt by positioning the minimum plane of the magnetic field in the Cusp magnetic field near or above a solid-liquid interface of the single crystal. Therefore, the inventor has found that by using the Cusp magnetic field and positioning the minimum plane of the magnetic field near or above the solid-liquid interface of the single crystal, an improvement in low oxygen enrichment and crystal uniformity can be achieved.

[0031] To produce an oxygen-depleted crystal that meets all the required properties for a high-productivity power device, an improvement in the seeding success rate is necessary. The present inventor has conducted thorough investigations and found that when seeding is performed while the position of the magnetic field minimum plane of the cusp magnetic field is defined near or above the solid-liquid interface, similar to the condition described above for the product portion, temperature fluctuations on the silicon melt surface increase, consequently significantly reducing the seeding success rate and decreasing the crystal's productivity.

[0032] Therefore, the inventor has developed a method for producing a silicon single crystal by a CZ process using a Cusp magnetic field, in which the seeding is carried out while the position of the magnetic field minimum plane on the central axis of a drawing furnace is below the surface of the silicon melt (raw material melt), and then, before proceeding with the drawing of a straight body to a product section, the position of the magnetic field minimum plane is moved upwards, and then the drawing of the straight body of the product section is carried out.

[0033] To solve the above problem, the present inventors have seriously investigated and found a method for producing a silicon single crystal by a CZ process using a cusp magnetic field formed by an upper coil and a lower coil in a drawing furnace, wherein the method comprises: seeding by bringing a seed crystal into contact with a silicon melt, and drawing up a straight body after increasing the diameter of the silicon single crystal, wherein the seeding is carried out with a position of a magnetic field minimum plane on a central axis of the drawing furnace as a first position below a surface of the silicon melt, before proceeding with the drawing up of the straight body, the position of the magnetic field minimum plane on the central axis of the drawing furnace is moved to a second position above the first position.The drawing up of the straight body is carried out with the position of the plane of minimum magnetic field on the central axis of the drawing furnace as the second position, thus enabling the efficient production of the single crystal with a low oxygen concentration and excellent in-plane distribution. Based on this finding, the present invention was further developed.

[0034] The following is a description with reference to the drawings. [Single crystal pulling device]

[0035] First, a single-crystal pulling device is described which is suitable for the inventive method for producing a silicon single crystal. Fig. Figure 1 shows an example of a single-crystal pulling device. A Fig.The single-crystal drawing furnace 1 shown in Figure 1 is configured to include a heat-insulating material 9, a heating element 8 within the heat-insulating material 9, and a heat-shielding element 13 facing a silicon melt 5 (raw material melt) contained in a quartz crucible 6 within a graphite crucible 7 at the lower end of a cylindrical part 12. Furthermore, a magnetic field generator 30 with an upper coil 30a and a lower coil 30b, which are upper and lower superconducting coils, is installed nearby, and the Cusp magnetic field is applied to the silicon melt 5 by exciting the upper coil 30a and the lower coil 30b. A seed crystal 2, held by a seed crystal holder 3 which is connected by a wire on a central axis 10 of the drawing furnace 1, is brought into contact with the silicon melt 5, thereby inoculating the crystal.The diameter of the silicon single crystal is then increased. A silicon single crystal 4 is then produced by a configuration in which a straight body segment is pulled in a tensile direction as the product segment.

[0036] The magnetic field generator 30 is installed on a lifting device 30c, which can be moved up and down vertically and is equipped with the upper coil 30a and the lower coil 30b. The Cusp magnetic field is generated by applying electric currents in opposite directions to the upper and lower coils. When the electric current values ​​of the upper coil 30a and the lower coil 30b are equal and the electric current flows in opposite directions, the magnetic field distribution is symmetrical from top to bottom and from left to right. In this case, the intensity of the magnetic field at the position of the magnetic field minimum plane 31 at the intersection of a central axis 10 and an intermediate plane 11 between the upper and lower coils is 0 Tesla (0 Gauss).

[0037] If the electric current values ​​of the upper coil 30a and the lower coil 30b are defined differently, and by applying electric currents in opposite directions to two upper and lower coils, the magnetic field distribution becomes asymmetrical from top to bottom and symmetrical from left to right, and the position of the magnetic field minimum plane 31 changes compared to the case where the electric current values ​​of the upper and lower coils are the same (hereinafter referred to as “asymmetrical excitation”).For example, if the electric current value of the upper coil is greater than the electric current value of the lower coil, the position of the magnetic field minimum plane 31 moves to a lower side compared to the case where the electric current values ​​of the upper and lower coils are defined as the same value, and if the electric current value of the upper coil is less than the electric current value of the lower coil, the position of the magnetic field minimum plane 31 moves to a higher side compared to the case where the electric current values ​​of the upper and lower coils are defined as the same value.

[0038] Incidentally, a structure like HZ (Hot Zone), unlike the one described above, can be a similar structure to a conventional process for a silicon single crystal production plant by CZ. [Method for the production of silicon single crystals]

[0039] The inventive method for producing a silicon single crystal is then described. The inventive method for the silicon single crystal comprises seeding, in which a seed crystal is brought into contact with a silicon melt, and drawing a straight body after increasing the diameter of the silicon single crystal. Seeding is carried out with a magnetic field minimal plane positioned on a central axis of the drawing furnace as a first position below the surface of the silicon melt. Before proceeding with the drawing of the straight body, the magnetic field minimal plane on the central axis of the drawing furnace is moved to a second position above the first position. The drawing of the straight body is then carried out with the magnetic field minimal plane on the central axis of the drawing furnace as the second position. A detailed description follows. (Vaccinate)

[0040] During seeding, the constriction is achieved by positioning a magnetic field-minimal plane 31 on a central axis 10 of the single-crystal growing furnace 1 as the first position, below a surface of the silicon melt 5 (raw material melt). In this case, a seed crystal 2 is preferably heated directly above a silicon melt 5 for approximately 5 to 60 minutes prior to seeding. This heating reduces the temperature difference between the seed crystal 2 and the silicon melt 5, thus mitigating thermal shock upon contact between the melt and the seed crystal. Consequently, the success rate in growing the dislocation-free silicon single crystal is further improved, thereby increasing productivity.

[0041] During seeding, the initial position of the magnetic field minimum plane of a Cusp magnetic field is preferably located below the surface of the silicon melt at a depth of between 30 mm and 80 mm (30 mm or more and 80 mm or less). Such a depth makes the seeding process more stable and further improves the success rate.

[0042] Furthermore, as described above, in the MCZ process, the magnetic field distribution and the intensity of the magnetic field near the inner wall of the crucible are factors that determine the amount of oxygen incorporated into the single crystal. Specifying these conditions is therefore preferred to produce a low-oxygen crystal with high productivity. Consequently, the inventive process for producing the silicon single crystal determines the intensity of the magnetic field according to a value at the intersection of the intermediate plane between the upper and lower coils and the inner wall of the crucible.

[0043] In the seeding process according to the invention for producing the silicon single crystal, the constriction is preferably carried out after applying a magnetic field in order to increase the intensity of the magnetic field at the intersection of the intermediate plane between the upper and lower coils and the inner wall of the crucible to 0.15 T (1500 G) or more. Such a region stabilizes the seeding and significantly improves the success rate.

[0044] In this way, during inoculation, the first position of the magnetic field minimum plane is located between 30 mm and 80 mm below the surface of the silicon melt (raw material melt), and / or the magnetic field intensity at the intersection of the intermediate plane between two upper and lower coils and the inner wall of the crucible is 0.15 T (1500 G) or more. As a result, the magnetic field acts on the entire surface of the silicon melt, and temperature fluctuations at the surface of the silicon melt are reduced. This significantly improves the inoculation success rate. If the first position of the magnetic field minimum plane of the Cusp magnetic field is located between 30 mm and 80 mm below the surface of the silicon melt, and the magnetic field intensity at the intersection of the intermediate plane between two upper and lower coils and the inner wall of the crucible is 0.15 T (1500 G), the following applies:When the magnetic field strength is 15 T (1500 G) or greater, the convection-suppressing force in the silicon melt increases with increasing magnetic field intensity, and the temperature fluctuations on the surface of the silicon melt decrease. Therefore, it is not necessary to set an upper limit for the magnetic field strength during seeding, but the upper limit can be defined based on the capabilities and structure of the device (the coils forming the cusp magnetic field) and may, for example, be 0.50 T (5000 G) or less.

[0045] Seeding can be carried out using a dislocation-free seeding method, in which no necking occurs after seeding (dash necking method). The seed crystal with a tapered tip is used when the dislocation-free seeding method is performed, and at this point, the angle of the tip of the seed crystal is preferably 28° or less. A seed crystal with such a shape can more effectively mitigate the thermal shock that occurs when the silicon melt and the seed crystal come into contact, thereby further improving the success rate of dislocation-free growth of the silicon single crystal.

[0046] After seeding, the dash necking process can be performed, whereby the position of the plane with minimal magnetic field strength remains unchanged and is maintained at the initial position. In the inventive method for producing silicon single crystals, the seeding success rate can be stably improved and efficient production enabled, even when the dash necking process is carried out. (Raising the straight body)

[0047] After seeding and before pulling the straight body, the position of the magnetic field-minimal plane 31 on the central axis 10 of the single-crystal pulling furnace 1 is moved to a second position above a first position, and the pulling of the straight body is carried out with the position of the magnetic field-minimal plane 31 on the central axis 10 of the single-crystal pulling furnace 1 in the second position. Consequently, the silicon single crystal with a low oxygen concentration and excellent in-plane distribution can be produced.

[0048] During the pull-up of the straight body, when the position of the magnetic field minimum plane is in the first position as during seeding, the convection of a silicon melt near a quartz crucible is suppressed. This increases the relative velocity between the quartz crucible and the silicon melt, facilitating elution of the oxygen component from the quartz crucible into the silicon melt. To further suppress the elution of the oxygen component described above, after increasing the diameter of the silicon single crystal, the position of the magnetic field minimum plane is shifted to the second position above the first position before the pull-up of the straight body, thus creating a product section.

[0049] In this case, the second position is preferably located between 10 mm below and 100 mm above (10 mm or less downwards and 100 mm or less upwards) the surface of the silicon melt. Within such a range, the single crystal can be produced more stably with a low oxygen concentration and excellent in-plane distribution.

[0050] If the second position of the plane of minimum magnetic field during the lifting of the straight body of the product part is defined as a position 10 mm below and 100 mm above the surface of the silicon melt, the magnetic field can be suppressed with a direction that intersects the melt surface at a right angle, so that it does not become too strong (near the VMCZ). As a result, a more uniform boundary diffusion layer thickness at the solid-liquid interface can be maintained more stably, and a high degree of uniformity in the distribution of oxygen concentration in the plane can be preserved.

[0051] Furthermore, the strength of the magnetic field is preferably set to a predetermined value. When lifting the straight body, the strength of the magnetic field at the intersection of the intermediate plane between the upper coil and the lower coil and the inner wall of the crucible is preferably 0.075 T (750 G) or more and 0.18 T (1800 G) or less. The silicon single crystal with the low oxygen concentration and excellent in-plane distribution can be produced more stably in such a range. If the intensity of the magnetic field is 0.075 T (750 G) or more, crystal deformation can be suppressed more effectively when lifting the straight body of the product part, and operation can continue stably. If the intensity is 0.If the temperature is 18 T (1800 G) or less, the convection of the silicon melt near the quartz crucible is not suppressed too much, and the relative velocity between the quartz crucible and the silicon melt becomes slow. This makes it less likely that the oxygen component from the quartz crucible will elute into the silicon melt, and the increase in oxygen concentration can be suppressed more effectively.

[0052] As described above, in the inventive process for producing the silicon single crystal, prior to drawing up the straight body of the product portion, the second position of the plane of minimum magnetic field is preferably located between 10 mm below and 100 mm above the surface of the silicon melt, and / or the intensity of the magnetic field at the intersection of the intermediate plane between two upper and lower coils and the inner wall of the crucible is preferably 0.075 T (750 G) or more and 0.18 T (1800 G) or less. Accordingly, the relative velocity between the quartz crucible and the silicon melt is slowed, which suppresses the leaching of oxygen and facilitates the incorporation of oxygen into the single crystal from an oxygen-deficient layer on the surface of the silicon melt. This ensures a stable realization of the low oxygen concentration of 3 × 10⁻⁶. 17 atoms / cm² 3 (ASTM'79) or less.

[0053] In the inventive method for producing the silicon single crystal, the position of the magnetic field minimum plane is moved upwards before the transition from the seeding or necking step, which is a non-product part step, to the product part step (straight body part). The position of the magnetic field minimum plane can be moved upwards by an upward movement of a magnetic field generator 30 using a lifting device 30c, or the position of the magnetic field minimum plane can be moved upwards by an unbalanced excitation resulting from the definition of the electric current values ​​of the upper coil 30a and the lower coil 30b, since the electric current value of the upper coil is smaller than the electric current value of the lower coil. EXAMPLE

[0054] The present invention is described below, particularly with reference to examples. However, the present invention is not limited to these examples.

[0055] 340 kg of raw silicon material were melted in a 32-inch (800 mm) diameter crucible in a CZ drawing furnace and a Cusp magnetic field was applied. A silicon single crystal with a crystal diameter of 300 mm was then pulled. After pulling the single crystal, the samples were sliced ​​at positions with solidification rates of 20%, 35%, 50%, and 65%, and the in-plane oxygen concentration distribution was subsequently investigated using Fourier transform infrared (FT-IR) spectroscopy. ROG was used as an indicator of the excellence of the in-plane oxygen concentration distribution.

[0056] In this context, ROG was defined as a value determined by a formula: (Maximum value - minimum value) x 100 / maximum value, where the oxygen concentration was measured at a minimum of two locations in the wafer center and 5 mm from a wafer edge. In the following examples and comparison examples, an average value for each position at solidification rates of 20%, 35%, 50%, and 65% was used for the ROG values ​​given in the tables.

[0057] In the following description, the position of a magnetic field minimum plane is described as "~ mm below / above the surface," where the melt surface of the silicon melt (melt surface) serves as the reference point. Incidentally, when the description "0 mm below the melt surface" is used, this means that the surface coincides with the position of the magnetic field minimum plane. [Examples 1 to 4]

[0058] In Examples 1-4, silicon single crystals were produced under the following conditions. (Vaccinate)

[0059] A position of a magnetic field minimum plane (a position between upper and lower coil has 0 T (0 G)): 30 mm below the melting surface or 70 mm below the melting surface. Intensity of the magnetic field at the intersection of an intermediate plane between the upper coil and the lower coil and an inner wall of a crucible: 0.15 T (1500 G). A Crucible rotation speed: 1.0 rpm. A single crystal with a rotational speed of 8 rpm. (Raising the straight body)

[0060] A position of a plane with minimal magnetic field: 10 mm below the melting surface or 100 mm above the melting surface. Magnetic field intensity at the intersection of an intermediate plane between the upper coil and the lower coil and an inner wall of a crucible: 0.15 T (1500 G) A Crucible rotation speed: 1.0 rpm A single crystal with a rotational speed of 8 rpm

[0061] In Examples 1 to 4, during seeding, the position of the magnetic field minimum plane of a cusp magnetic field was set to 30 mm or 70 mm below the surface of the silicon melt (melt surface), and necking (dash necking procedure) was performed after seeding. The position of the magnetic field minimum plane was shifted upwards before proceeding to the pulling of the straight body of the product portion. Then, during the pulling of the straight body of the product portion, the position of the magnetic field minimum plane was defined as 10 mm below or 100 mm above the silicon melt surface (melt surface). The single crystals were pulled under a total of four different pulling conditions. Additionally, before transitioning to pulling the straight body of the product portion, the position of the magnetic field minimum plane was moved using a lifting device. The results of Examples 1 to 4 are presented in Table 1. [Table 1] Seeding: Position of the magnetic field minimum plane Vaccination: Intensity of the magnetic field [T] Vaccination failure rate Product portion: Position of the magnetic field minimum plane [mm] Product portion: Intensity of the magnetic field [T] Oxygen concentration [atoms / cm³] 3 ] ROG[%] feasibility Crystal quality Example 1 30mm below surface 0.15(1500 G) 0 10mm below surface 0.15(1500 G) 2.5E17~2.7E17 5,2 good good Example 2 70mm below surface 0.15(1500 G) 0 10mm below surface 0.15(1500 G) 2.5E17~2.6E17 10,8 good good Example 3 30mm below surface 0.15(1500 G) 0 100mm above surface 0.15(1500 G) 2.7E17~2.8E17 11,0 good good Example 4 70mm below surface 0.15(1500 G) 0 100mm above surface 0.15(1500 G) 2.6E17~2.8E17 13,5 good good

[0062] As shown in Table 1, single crystals were successfully grown without dislocations during seeding under the conditions of Examples 1 to 4. Regarding the crystal quality of a product batch, the oxygen concentration was 3 x 10 17 atoms / cm² 3 (ASTM'79) or less, ROG was less than 15%, and an in-plane distribution with excellent dispersion was achieved. The low-oxygen crystal, meeting the required quality for a power device, was successfully grown without affecting production output. [Examples 5 to 8]

[0063] In Examples 5 to 8, the seeding magnetic field intensity was changed to 0.20 T (2000 G), and the pulling magnetic field intensity was changed to 0.18 T (1800 G). The other conditions were the same as in Examples 1 to 4, and a total of four pulling conditions were used for single crystal pulling. The results of Examples 5 to 8 are listed in Table 2. [Table 2] Seeding: Position of the magnetic field minimum plane Vaccination: Intensity of the magnetic field [T] Vaccination failure rate Product portion: Position of the magnetic field minimum plane [mm] Product portion: Intensity of the magnetic field [T] Oxygen concentration [atoms / cm³] 3 ] ROG[%] feasibility Crystal quality Example 5 30mm below surface 0.20(2000 G) 0 10mm below surface 0.18(1800 G) 2.5E17~2.8E17 5, 1 good good Example 6 70mm below surface 0.20(2000 G) 0 10mm below surface 0.18(1800 G) 2.4E17~2.7E17 5,8 good good Example 7 30mm below surface 0.20(2000 G) 0 100mm above surface 0.18(1800 G) 2.6E17~2.8E17 10,2 good good Example 8 70mm below surface 0.20(2000 G) 0 100mm above surface 0.18(1800 G) 2.5E17~2.8E17 11,3 good good

[0064] As can be seen from Table 2, the pulling of single crystals was also carried out successfully under the conditions of Examples 5 to 8 without dislocations during seeding, and the quality of the crystals of one product batch had an oxygen concentration of 3x10 17 atoms / cm² 3(ASTM'79) or less, and the ROG was less than 15%. Then, an in-plane distribution with excellent distribution was achieved. The low-oxygen crystal, meeting the required quality for a power device, was successfully grown without affecting production output. [Examples 9 to 12]

[0065] In Examples 9 to 12, only the intensity of the magnetic field during the pulling of a straight body from a product portion was changed to 0.075 T (750 G), and the other conditions were the same as in Examples 1 to 4. The single crystals were pulled under a total of four pulling conditions. The results of Examples 9 to 12 are shown in Table 3. [Table 3] Seeding: Position of the magnetic field minimum plane Vaccination: Intensity of the magnetic field [T] Vaccination failure rate Product portion: Position of the magnetic field minimum plane [mm] Product portion: Intensity of the magnetic field [T] Oxygen concentration [atoms / cm³] 3 ] ROG[%] feasibility Crystal quality Example 9 30mm below surface 0.15(1500 G) 0 10mm below surface 0.075(750 G) 2.1E17~2.3E17 10,2 good good Example 10 70mm below surface 0.15(1500 G) 0 10mm below surface 0.075(750 G) 2.2E17~2.5E17 10,8 good good Example 11 30mm below surface 0.15(1500 G) 0 100mm above surface 0.075(750 G) 2.4E17~2.6E17 14,5 good good Example 12 70mm below surface 0.15(1500 G) 0 100mm above surface 0.075(750 G) 2.4E17~2.7E17 14,8 good good

[0066] As can be seen from Table 3, the pulling of single crystals was also carried out successfully under the conditions of Examples 9 to 12 without dislocations during seeding, and the quality of the crystals of one product batch had an oxygen concentration of 3x10 17 atoms / cm² 3 (ASTM'79) or less, and ROG was less than 15%. Then, an in-plane distribution with excellent dispersion was achieved. The low-oxygen crystal, meeting the required quality for a power device, was successfully grown without affecting production output. [Examples 13 and 14]

[0067] In Examples 13 and 14, a dislocation-free, dash-necking seeding procedure was performed, and the other conditions were the same as in Examples 1 and 2. The single crystals were grown under a total of two pulling conditions. The results of Examples 13 and 14 are shown in Table 4. [Table 4] Seeding: Position of the magnetic field minimum plane Vaccination: Intensity of the magnetic field [T] Vaccination failure rate Product portion: Position of the magnetic field minimum plane [mm] Product portion: Intensity of the magnetic field [T] Oxygen concentration [atoms / cm³] 3 ] ROG[%] feasibility Crystal quality Example 13 30mm below surface 0.15(1500 G) 0 10mm below surface 0.15(1500 G) 2.4E17~2.6E17 5,4 good good Example 14 70mm below surface 0.15(1500 G) 0 10mm below surface 0.15(1500 G) 2.5E17~2.6E17 10,2 good good

[0068] As can be seen from Table 4, the pulling of single crystals was also carried out successfully under the conditions of Examples 13 and 14 without dislocations at the seeding site, and the quality of the crystals of one product portion showed an oxygen concentration of 3x10 17 atoms / cm² 3(ASTM'79) or less, and the ROG was less than 15%. Excellent in-plane distribution was then achieved. The low-oxygen crystal, meeting the required quality for a power device, was successfully grown without affecting production output. [Comparison examples 1 to 4]

[0069] In comparative examples 1 to 4, the position of the plane of minimum magnetic field during seeding was defined as 0 mm below the surface or 15 mm below the melt surface. The intensity of the magnetic field at the intersection of an intermediate plane between the upper and lower coils and an inner wall of a crucible was defined as 0.15 T (1500 G) or 0.20 T (2000 G). The condition for pulling a straight body from a product portion was the same for the position of the plane of minimum magnetic field and the intensity of the magnetic field during seeding. A total of four pulling conditions were used for single crystal pulling. Furthermore, in comparative examples 1 to 4, all other conditions were the same as in example 1. The results of comparative examples 1 to 4 are listed in Table 5. [Table 5] Seeding: Position of the magnetic field minimum plane Vaccination: Intensity of the magnetic field [T] Vaccination failure rate Product portion: Position of the plane with minimum magnetic field [mm] Product portion: Intensity of the magnetic field [T] Oxygen concentration [atoms / cm³] 3 ] ROG[%] feasibility Crystal quality Comparative example 1 0mm below surface 0.15(1500 G) 10 0mm below surface 0.15(1500 G) - - bad - Comparative example 2 15mm below surface 0.15(1500 G) 6 15mm below surface 0.15(1500 G) 3.2E17~3.5E17 12,6 sufficient bad Comparative example 3 0mm below surface 0.20(2000 G) 10 0mm below surface 0.20(2000 G) - - bad - Comparative example 4 15mm below surface 0.20(2000 G) 5 15mm below surface 0.20(2000 G) 3.5E17~3.8E17 9,2 sufficient bad

[0070] As can be seen from Table 5, of the comparison examples 1 to 4, examples 1 and 3, in which the position of the magnetic field minimum plane was set to 0 mm below the melt surface, failed 10 times during seeding, regardless of the magnetic field strength, making it difficult to maintain operation. When the position of the magnetic field minimum plane was 15 mm below the melt surface, the number of failed attempts decreased to 6 when the magnetic field intensity at seeding was 0.15 T (1500 G) (comparison example 2), and to 5 when the magnetic field intensity at seeding was 0.20 T (2000 G) (comparison example 4). Setting the position of the magnetic field minimum plane at 15 mm below the melt surface during seeding resulted in fewer seeding failures than setting the position of the magnetic field minimum plane at 0 mm below the surface.In comparative examples 2 and 4, however, the position of the plane with minimum magnetic field and the intensity of the magnetic field during the lifting of the straight body of the product portion had the same condition as during seeding; an oxygen concentration of the product portion was higher than 3×10. 17 atoms / cm² 3 , so that it was not possible to grow the oxygen-depleted crystal that meets the required quality for a power component. [Comparative examples 5 and 6]

[0071] In comparative examples 5 and 6, a dislocation-free, dash-necking seeding method was used, and the position of the plane of minimum magnetic field during seeding was either 0 mm below the melt surface or 15 mm below the melt surface. The magnetic field intensity at the intersection of an intermediate plane between the upper and lower coils and an inner wall of a crucible was 0.15 T (1500 G). The condition for pulling the straight body of the product portion was the same for the position of the plane of minimum magnetic field and the magnetic field intensity during seeding, and single crystal pulling was performed based on these two conditions. Meanwhile, the other conditions in comparative examples 5 and 6 were the same as those in example 1. The results of comparative examples 5 and 6 are presented in Table 6. [Table 6] Seeding: Position of the magnetic field minimum plane Vaccination: Intensity of the magnetic field [T] Vaccination failure rate Product portion: Position of the magnetic field minimum plane [mm] Product portion: Intensity of the magnetic field [T] Oxygen concentration [atoms / cm³] 3 ] ROG [%] feasibility Crystal quality Comparative example 5 0mm below surface 0.15(1500 G) 10 0mm below surface 0.15(1500 G) - - bad - Comparative example 6 15mm below surface 0.15(1500 G) 5 15mm below surface 0.15(1500 G) 3.2E17~3.4E17 10,4 sufficient bad

[0072] As shown in Table 6, in comparative example 5, where the magnetic field minimum plane was located 0 mm below the surface, seeding failed 10 times, making it difficult to maintain operation. In contrast, in comparative example 6, where the magnetic field minimum plane was located 15 mm below the surface, the number of failed attempts was reduced to 5. Positioning the magnetic field minimum plane 15 mm below the surface during seeding resulted in a reduction in the number of seeding failures compared to positioning the magnetic field minimum plane 0 mm below the surface. Consequently, it was also found that, in the case of dislocation-free seeding without necking (dash necking) in a cusp magnetic field, the magnetic field minimum plane must be located below the surface of a silicon melt during seeding.In comparative example 6, where the position of the magnetic field minimum plane and the intensity of the magnetic field at the product part during seeding were set to the same condition, the oxygen concentration of the product part was higher than 3×10. 17 atoms / cm² 3 and therefore it was not possible to grow the oxygen-depleted crystal that meets the required quality for a power component.

[0073] As described above, according to the examples of the present invention, the single crystal with the low oxygen concentration and the excellent in-plane distribution could be efficiently produced with the improved seeding success rate.

[0074] It should be noted that the present invention is not limited to the embodiments described above. The embodiments are merely examples, and all examples that exhibit essentially the same features and demonstrate the same functions and effects as those in the technical concept disclosed in the claims of the present invention are included within the technical scope of the present invention.

Claims

[1] Method for producing a silicon single crystal by a CZ process using a cusp magnetic field formed by an upper coil and a lower coil provided in a drawing furnace, the method comprising the following steps: Seeding by bringing a seed crystal into contact with a silicon melt; and Pulling up a straight body after increasing the diameter of the silicon single crystal, wherein The seeding is carried out with a position of a magnetic field minimal plane on a central axis of the drawing furnace as the first position below a surface of the silicon melt, Before proceeding with the raising of the straight body, the position of the magnetic field minimum plane on the central axis of the drawing furnace is brought to a second position above the first position. The lifting of the straight body takes place with the position of the magnetic field minimal plane on the central axis of the drawing furnace as the second position, The first position lies between 30 mm and 80 mm below the surface of the silicon melt, The second position lies between 10 mm below and 100 mm above the surface of the silicon melt. During seeding, the intensity of the magnetic field at an intersection of an intermediate plane between the upper coil and the lower coil and an inner wall of a crucible is 0.15 T or more and 0.20 T or less, and When the straight body is pulled upwards, the intensity of a magnetic field at an intersection of an intermediate plane between the upper coil and the lower coil and an inner wall of a crucible is 0.075 T or more and 0.18 T or less. [2] Method for producing the silicon single crystal according to claim 1, wherein the seeding is carried out by a dislocation-free seeding method in which a seeding crystal with a tapered seeding crystal tip is used. [3] Method for producing a silicon single crystal according to claim 1 or 2, wherein after seeding a constriction is carried out, while the position of the magnetic field minimum plane on the central axis of the drawing furnace is the first position below the surface of the silicon melt.

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