Silicon single crystal manufacturing method

Abstract

To provide a method for efficiently producing a silicon single crystal which has a lower oxygen concentration compared to the prior art, while having an improved in-plane distribution of oxygen concentration.SOLUTION: The present invention provides a method for producing a silicon single crystal by a CZ process that uses a cusp magnetic field that is formed by an upper coil and a lower coil, the coils being provided in a pulling furnace. In a straight body formation step, a silicon single crystal is pulled while setting a rotation speed of the silicon single crystal to 7 rpm or more and 12 rpm or less, a rotation speed of a quartz crucible to 1.0 rpm or less, a position of a magnetic field minimum plane of the cusp magnetic field within a range from 10 mm below a surface of a raw material melt to 5 mm above it, and a magnetic field strength of the cusp magnetic field at an intersection point of an inner wall of the quartz crucible and the plane of the same height as the magnetic field minimum plane to 800 G to 1,200 G.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a method for producing a silicon single crystal by the CZ method using a cusp magnetic field formed by an upper coil and a lower coil provided in a pulling furnace. [Background technology]

[0002] In recent years, power devices have been attracting attention as devices that can achieve power savings. The region through which current flows in a power device can be in the thickness range of several tens to several hundreds of micrometers from the surface, and in some cases, the current flows throughout the entire wafer. If oxygen precipitates or BMDs (bulk micro defects) exist in this region through which current flows, it can cause breakdown voltage defects or leakage defects.

[0003] In order to prevent the above defects, silicon single crystal wafers for power devices are required to have a low oxygen concentration that does not cause oxygen precipitates and a flat in-plane distribution of oxygen concentration.Furthermore, because the presence of oxygen donors in RF (radio frequency) devices used for communications such as smartphones deteriorates their high-frequency characteristics, silicon single crystal wafers for RF devices are also required to have a low oxygen concentration and a flat in-plane distribution of oxygen concentration.

[0004] The Czochralski (CZ) method is one of the most common methods for producing silicon single crystals for power and RF devices. When producing silicon single crystals using the CZ method, the mainstream method is the magnetically coupled CZ (MCZ) method, in which a magnetic field is applied to the raw material melt to pull the single crystal. Known methods for growing low-oxygen crystals for power devices include a method using a horizontal magnetic field and a method using a cusp magnetic field.

[0005] As methods using a horizontal magnetic field, for example, Patent Document 1 discloses a method for obtaining low-oxygen crystals by specifying the crystal rotation speed and crucible rotation speed under a horizontal magnetic field, and Patent Document 2 discloses a method for setting the magnetic field strength to 2000 G or more, the quartz crucible rotation speed to 0.2 rpm or less, and the crystal rotation speed to 5 rpm or less.

[0006] On the other hand, as a method using a cusp magnetic field, for example, there is a method described in Patent Document 3 in which the magnetic field center position (=magnetic field minimum plane position) of the cusp magnetic field is moved to a position where the temperature is stable according to the amount of silicon melt reduced.

[0007] Patent Document 4 discloses a method in which the center of the magnetic field (=minimum plane) is positioned 10 to 100 mm above the liquid surface and the crystal rotation is set to 15 to 20 rpm, while Patent Document 5 discloses a method in which the distance from the bottom end of the heat shielding material to the melt surface is set to 50 to 120 mm, the center of the magnetic field is positioned between the melt surface and half the melt depth, and the crystal rotation is set to 13 rpm or more.

[0008] Patent Document 6 discloses a method in which the magnetic field strength of the cusp magnetic field is 0.05 T to 0.12 T, the magnetic field center position is 0 mm to -30 mm relative to the melt surface, the crystal rotation is 8 to 14 rpm, and the crucible rotation speed is 1.3 to 2.2 rpm. [Prior art documents] [Patent documents]

[0009] [Patent Document 1] Japanese Patent Application Laid-Open No. 2009-18984 [Patent Document 2] International Publication No. 2009 / 025340 [Patent Document 3] Japanese Patent Application Laid-Open No. 2001-89289 [Patent Document 4] JP 2020-33200 A [Patent Document 5] Patent No. 3783495 [Patent Document 6] Japanese Patent Application Publication No. 2019-31436 Summary of the Invention [Problem to be solved by the invention]

[0010] In the methods described in Patent Document 1 and Patent Document 2, the crystal rotation speed is set to about 5 rpm (Patent Document 1) or lower (Patent Document 2). However, slowing the crystal rotation speed leads to deterioration of resistivity and in-plane oxygen distribution, which can cause device defects.

[0011] In the method described in Patent Document 3, the position of the magnetic field minimum plane of the cusp magnetic field is raised as the solidification rate of the single crystal increases. However, changing the position of the magnetic field minimum plane in the product portion results in a large change in the oxygen concentration in the product portion, which poses a problem of significantly reducing yield when producing crystals with a narrow oxygen concentration specification range or low-oxygen crystals.

[0012] When producing a small diameter single crystal of 200 mm or less, the crystal rotation speeds described in Patent Documents 4 and 5 are not a problem. However, when producing a large diameter single crystal of 300 mm or more, if the crystal rotation speed is set to 13 rpm or more, the diameter fluctuations during pulling of the single crystal become so large that it becomes impossible to continue operation.

[0013] The oxygen concentration described in Patent Document 6 is the result of a model prediction (based on numerical analysis), and the oxygen concentration is measured only at one point near the center. In the production of large-diameter single crystals of 300 mm or more, if the rotation speed of the quartz crucible is set to a high speed of 1.3 rpm or higher as described in Patent Document 6, the oxygen concentration value increases, and the in-plane distribution of the oxygen concentration deteriorates, which is a problem.

[0014] The present invention has been made to solve the above problems, and aims to provide a method for efficiently producing silicon single crystals having a lower oxygen concentration and a better in-plane distribution of oxygen concentration than conventional techniques. [Means for solving the problem]

[0015] The present invention has been made to achieve the above-mentioned object, and provides a method for producing a silicon single crystal by the CZ method using a cusp magnetic field formed by an upper coil and a lower coil provided in a pulling furnace, wherein in the straight body process, the silicon single crystal is pulled by setting the rotation speed of the silicon single crystal to 7 rpm or more and 12 rpm or less, the rotation speed of the quartz crucible to 1.0 rpm or less, the position of the magnetic field minimum plane of the cusp magnetic field within a range of 10 mm below to 5 mm above the surface of the raw material melt, and the magnetic field strength of the cusp magnetic field at the intersection of a plane at the same height as the magnetic field minimum plane and the inner wall of the quartz crucible to 800 to 1200 G.

[0016] This method for producing silicon single crystals eliminates problems such as an increase in oxygen concentration and a deterioration in the in-plane distribution of oxygen concentration when the crucible rotation speed is increased, making it possible to efficiently produce single crystals with a low oxygen concentration and a good in-plane distribution of oxygen concentration that meet the quality requirements for power devices and RF devices.

[0017] At this time, the silicon single crystal has an oxygen concentration of 2×10 based on ASTM '79. 17 atoms / cm 3 or less, and the ROG in a crystal cross section perpendicular to the growth direction of the silicon single crystal is 8% or less.

[0018] The method for producing a silicon single crystal according to the present invention can stably produce such high-quality silicon single crystals. [Effects of the Invention]

[0019] As described above, the method for producing a silicon single crystal of the present invention eliminates problems such as an increase in oxygen concentration and a deterioration in the in-plane distribution of oxygen concentration when the crucible rotation speed is increased, and therefore makes it possible to efficiently produce single crystals with a low oxygen concentration that meets the quality requirements for power devices and RF devices and with a good in-plane distribution of oxygen concentration. [Brief explanation of the drawings]

[0020] [Figure 1] FIG. 1 is a diagram illustrating an example of a single crystal manufacturing apparatus. [Figure 2] 1 shows the in-plane distribution of oxygen concentration obtained at 100 cm from the straight body in Examples 1 and 2. [Figure 3] 1 shows the dependence of the oxygen concentration in a single crystal on the crucible rotation speed. [Figure 4] 1 shows the in-plane distribution of oxygen concentration obtained at 100 cm from the straight body of Comparative Example 2. DETAILED DESCRIPTION OF THE INVENTION

[0021] The present invention will be described in detail below, but the present invention is not limited thereto.

[0022] As described above, there has been a demand for a method for producing silicon single crystals that can efficiently produce single crystals with a lower oxygen concentration and a better in-plane distribution of oxygen concentration than conventional techniques.

[0023] As a result of extensive research into the above-mentioned problems, the present inventors have discovered that a method for producing a silicon single crystal by the CZ method using a cusp magnetic field formed by an upper coil and a lower coil provided in a pulling furnace, in which in the straight body process, the rotation speed of the silicon single crystal is 7 rpm or more and 12 rpm or less, the rotation speed of the quartz crucible is 1.0 rpm or less, the position of the magnetic field minimum plane of the cusp magnetic field is within a range of 10 mm below the surface of the raw material melt and 5 mm above, and the magnetic field strength of the cusp magnetic field at the intersection of a plane at the same height as the magnetic field minimum plane and the inner wall of the quartz crucible is 800 to 1200 G, eliminates problems such as an increase in oxygen concentration and a deterioration in the in-plane distribution of oxygen concentration when the crucible rotation speed is set to a high speed, and therefore makes it possible to efficiently produce a single crystal with a low oxygen concentration and a good in-plane distribution of oxygen concentration that meets the quality requirements for power devices and RF devices, and have completed the present invention.

[0024] As mentioned above, in recent years, a higher level of quality than conventional levels is required for low-oxygen crystals for power devices and RF devices. In particular, the oxygen concentration is required to be 2×10 to eliminate the influence of thermal donors generated during low-temperature heat treatment. 17 atoms / cm 3 It is desirable for the oxygen concentration to be equal to or less than ASTM '79. In addition, it is desirable to make the oxygen concentration distribution uniform across the wafer to eliminate quality variations between chips. For example, if the oxygen concentration is low on the outer periphery of the wafer, slip dislocations may occur in the outer periphery during heat treatment, which can have a negative impact on the yield of the device process.

[0025] To address this issue, it is important to make the oxygen concentration uniform across the wafer. Hereafter, ROG (Radial Oxygen Gradient) is used as an index to measure the quality of the oxygen concentration distribution across the wafer. ROG is calculated by measuring the oxygen concentration at at least two locations, one at the center of the wafer and the other at a predetermined position from the wafer periphery. (Maximum value - Minimum value) x 100 / Maximum value In recent years, higher levels of ROG have been required than in the past, and a good distribution that satisfies ROG < 8% is required.

[0026] In the CZ method, single crystals are grown while rotating the crystal during crystal pulling. When using the CZ method with a cusp magnetic field to pull large single crystals (diameters of 300 mm or more), excessively high crystal rotation speeds can cause large diameter fluctuations during crystal pulling, leading to operational disruption. Conversely, excessively low crystal rotation speeds can lead to poor in-plane resistivity and oxygen concentration distributions, potentially resulting in device failure. To avoid these problems, excessively high or low crystal rotation speeds must be avoided when using the CZ method with a cusp magnetic field.

[0027] Furthermore, in the MCZ method, silicon melt (hereinafter also referred to as "raw material melt") is contained in a quartz crucible. During crystal pulling, oxygen dissolves from the quartz crucible and is incorporated into the silicon melt, increasing the oxygen concentration in the single crystal. Looking at the silicon melt surface (melt surface) from a vertical perspective, in the MCZ method using a horizontal magnetic field, the magnetic field acts in a direction parallel to the magnetic field lines, suppressing convection. However, in a direction perpendicular to the magnetic field, almost no magnetic field acts, resulting in active convection. As a result, localized regions of active convection are created, making it easier for oxygen to dissolve from the quartz crucible in a horizontal magnetic field, resulting in a high oxygen concentration in the crystal.

[0028] On the other hand, in the case of a cusp magnetic field, the magnetic field acts on the entire periphery near the inner wall of the quartz crucible (hereinafter sometimes simply referred to as the "crucible wall" or "crucible inner wall"), so convection near the crucible wall is suppressed all around. Therefore, in a cusp magnetic field, when the crucible rotation speed is sufficiently fast and the magnetic field strength is strong, the relative velocity between the quartz crucible and the raw material melt increases, promoting the dissolution of oxygen, but conversely, when the crucible rotation speed is sufficiently slow and the magnetic field strength is weak, the relative velocity between the quartz crucible and the raw material melt decreases, suppressing the dissolution of oxygen.

[0029] In addition to the above, by positioning the magnetic field minimum plane in the cusp magnetic field near or above the solid-liquid interface between the single crystal and the silicon melt, the natural convection inherent to the cusp magnetic field facilitates oxygen absorption from the low-oxygen-concentration layer on the surface of the silicon melt into the single crystal. Therefore, by using the cusp magnetic field to sufficiently slow down the crucible rotation speed, weaken the magnetic field strength, and position the magnetic field minimum plane near or above the solid-liquid interface between the single crystal and the silicon melt, it is possible to achieve a low oxygen concentration in the crystal for the first time.

[0030] That is, the present invention is characterized in that, in a method for producing a silicon single crystal by the CZ method using a cusp magnetic field, the crystal rotation speed of the single crystal in the straight body process is 7 rpm or more and 12 rpm or less, the position of the magnetic field minimum plane of the magnetic field is within a range of 10 mm below to 5 mm above the surface of the raw material melt, the rotation speed of the quartz crucible is 1.0 rpm or less, and the magnetic field strength of the cusp magnetic field (hereinafter sometimes simply referred to as "magnetic field strength") at the intersection of a plane at the same height as the magnetic field minimum plane and the inner wall of the quartz crucible is 800 to 1200 G.

[0031] An example of a single crystal manufacturing apparatus suitable for use in the method for manufacturing a silicon single crystal according to the present invention will be described below with reference to the drawings. Note that descriptions of the same components as those in conventional apparatuses may be omitted as appropriate.

[0032] FIG. 1 shows an example of a single crystal manufacturing apparatus (single crystal pulling apparatus). The single crystal manufacturing apparatus (single crystal pulling apparatus) 100 shown in FIG. 1 includes a heat insulating material 9, a heater 8 therein, and a heat shielding member 12 disposed at the bottom end of a cylindrical portion 11 so as to face a silicon raw material melt 5 contained in a quartz crucible 6 disposed within a graphite crucible 7. The apparatus includes a pulling furnace 1 having a central axis 10 and a magnetic field generator 30 disposed around the pulling furnace 1 and having an upper coil 30a and a lower coil 30b. A cusp magnetic field is applied to the silicon melt by energizing the upper coil 30a and the lower coil 30b, thereby pulling the single crystal in the direction of the central axis. A seed crystal 2 held by a seed holder 3 connected to a wire and located on the central axis 10 of the pulling furnace 1 is brought into contact with the raw material melt 5 for seeding, and the silicon single crystal is expanded in diameter. The straight body portion, which will become the product portion, is pulled in the pulling direction to produce a silicon single crystal 4.

[0033] The magnetic field generator 30 is installed on a vertically movable elevator 30c, and the upper coil 30a and the lower coil 30b are arranged to surround the side of the pulling furnace 1. In a cusp magnetic field, repulsive magnetic field lines are generated by passing currents in opposite directions through the upper and lower coils. The magnetic field distributions generated by the upper and lower coils 30a and 30b create a region (magnetic field minimum surface 32) where the magnetic field strength is at its lowest near the central axis 10 between the upper and lower coils 30a and 30b. For example, setting the current values ​​of the upper and lower coils 30a and 30b to the same value and passing currents in opposite directions through the upper and lower coils 30a and 30b results in a magnetic field distribution that is vertically and horizontally symmetrical. In this case, the magnetic field strength is weakest at the intersection of the central axis 10 and the magnetic field minimum surface 32. Note that FIG. 1 illustrates a case where the height position of the magnetic field minimum surface 32 (i.e., the height position of the surface 31 at the same height as the magnetic field minimum surface) is the same as the height position of the raw material melt surface 33.

[0034] Furthermore, by setting the current values ​​of the upper coil 30a and the lower coil 30b to different values ​​and passing currents in opposite directions through the two upper and lower coils, an asymmetrical and symmetrical magnetic field distribution is obtained (hereinafter referred to as "unbalanced excitation"), and the position of the magnetic field minimum surface 32 changes compared to when the current values ​​of the upper and lower coils are set to the same value. For example, Upper coil current value > Lower coil current value In this case, the magnetic field minimum surface 32 shifts downward compared to when the current values ​​of the upper and lower coils are set to the same value, Upper coil current value < Lower coil current value In this case, the magnetic field minimum surface 32 shifts upward compared to when the current values ​​of the upper and lower coils are set to the same value.

[0035] In the present invention, the position of the magnetic field minimum surface 32 in the product section (straight body process) is set within a range of 10 mm below and 5 mm above the raw material melt surface 33, but it is necessary to move the position of the magnetic field minimum surface before pulling up the product section (straight body process). The means for moving the magnetic field minimum surface at this time may be to move the magnetic field generator 30 up and down using the lifting device 30c, or to move the position of the magnetic field minimum surface by performing unbalanced excitation with different current values ​​in the upper and lower coils 30a, 30b.

[0036] As mentioned above, the strength of the convection suppression force near the inner wall of the quartz crucible is determined by the magnetic field strength near the inner wall of the quartz crucible, and therefore the magnetic field strength near the inner wall of the quartz crucible is an important factor in determining the oxygen concentration in the MCZ method using a cusp magnetic field. Therefore, the magnetic field strength in the present invention is specified as a value of 800 to 1200 G at the intersection 35 between the surface 31 at the same height as the magnetic field minimum surface and the quartz crucible inner wall. Note that the surface 31 at the same height as the magnetic field minimum surface is a surface including the magnetic field minimum surface 32, and the intersection 35 can be rephrased as a point at the same height as the magnetic field minimum surface 32 on the inner wall of the quartz crucible.

[0037] The structure of the HZ (hot zone) other than that described above can be the same as that of a general CZ silicon single crystal manufacturing device, except that the rotation speed of the quartz crucible must be set to 1.0 rpm or less.

[0038] In the CZ method, the single crystal is grown while being rotated. In order to obtain a single crystal with a low oxygen concentration and a good in-plane distribution of oxygen concentration without impairing operability, in the present invention, the crystal rotation speed of the single crystal in the straight body process is set to 7 rpm or more and 12 rpm or less.

[0039] In addition, in the CZ method, the quartz crucible is rotated while growing the single crystal, but in a cusp magnetic field, the magnetic field acts on the entire circumference near the crucible wall, so convection near the crucible wall is suppressed all around. Therefore, if the rotation speed of the quartz crucible is increased too much in a cusp magnetic field, the relative velocity between the quartz crucible and the raw material melt increases, promoting oxygen dissolution and increasing the oxygen concentration in the single crystal.

[0040] In addition to the above problems, if the rotation speed of the quartz crucible is too high, especially in the production of single crystals with a large diameter, for example, a diameter of 300 mm or more, the in-plane distribution will deteriorate. To solve these problems, in the present invention, the rotation speed of the quartz crucible is set to 1.0 rpm or less.

[0041] In this way, the crystal rotation speed of the single crystal in the straight body process is set to 7 rpm or more and 12 rpm or less, the position of the magnetic field minimum plane of the magnetic field is set within a range of 10 mm below to 5 mm above the surface of the raw material melt, the rotation speed of the quartz crucible is set to 1.0 rpm or less, and the magnetic field strength of the cusp magnetic field is set to 800 to 1200 G, thereby achieving a 2 × 10 17 atoms / cm 3 A good in-plane distribution of oxygen concentration can be obtained while maintaining a low oxygen concentration below (ASTM'79). [Example]

[0042] The present invention will be specifically explained below with reference to examples, but the present invention is not limited to these examples.

[0043] 360 kg of raw material was melted in a 32-inch (approximately 800 mm) crucible in a CZ puller, and a cusp magnetic field was applied to pull a single crystal with a diameter of 300 mm. In this example and comparative example, symmetrical excitation was performed in which the current values ​​of the upper and lower coils of the cusp magnetic field were the same, and unbalanced excitation was performed in which the current values ​​of the upper and lower coils were different. When unbalanced excitation was performed in the product section, the magnetic field position was set in advance using an elevator device so that the magnetic field minimum plane was 70 mm below the surface of the raw material melt, and then the degree of unbalance was set to a predetermined value in the non-product section before moving to the product section. At this time, the unbalance between the upper and lower coils is Unbalance = Lower coil current value / Upper coil current value The value is obtained by the following formula.

[0044] After pulling, samples were cut from the straight body at 20cm, 50cm, 75cm, and 100cm, and the in-plane distribution of oxygen concentration was examined using FT-IR. The oxygen concentration values ​​shown below are those at the center of the wafer.

[0045] ROG also measures the oxygen concentration at two locations: the center of the wafer and 2 mm from the wafer periphery. (Maximum value - Minimum value) x 100 / Maximum value In addition, ROG in the table is the average value between 20cm and 100cm from the straight body position.

[0046] (Examples 1 and 2) In Examples 1 and 2, silicon single crystals were produced under the following conditions. [Direct body process (product department)] Position of magnetic field minimum surface: 10 mm below the melt surface Unbalance between upper and lower coils: 1.00 (upper and lower symmetric excitation) Magnetic field strength at the intersection of the surface at the same height as the magnetic field minimum surface and the crucible inner wall: 1000G Crucible rotation speed: 0.5 rpm (Example 1), 1.0 rpm (Example 2) Single crystal rotation speed: 10 rpm

[0047] In Examples 1 and 2, in the straight body process, the magnetic field minimum plane position of the cusp magnetic field, the imbalance between the upper and lower coils, the magnetic field strength, and the single crystal rotation speed were fixed, and a total of two single crystals were produced with the crucible rotation speed set to 0.5 rpm (Example 1) and 1.00 rpm (Example 2). The conditions and results for Examples 1 and 2 are shown in Table 1, and the in-plane distribution of oxygen concentration obtained at 100 cm of the straight body for Examples 1 and 2 is shown in Figure 2.

[0048] [Table 1]

[0049] When the conditions of Examples 1 and 2 of the silicon single crystal manufacturing method according to the present invention were used, a single crystal was successfully pulled without any dislocations occurring during the straight body process. 17 atoms / cm 3 (ASTM'79) or lower, and ROG <8% was achieved. We succeeded in pulling single crystals with low oxygen concentration and good in-plane distribution of oxygen concentration without impairing workability.

[0050] (Examples 3 and 4) In Examples 3 and 4, silicon single crystals were produced under the following conditions. [Direct body process (product department)] Position of magnetic field minimum plane: 5 mm above the melt surface Unbalance degree: 1.00 (vertical symmetrical excitation) Magnetic field strength at the intersection of the plane at the same height as the magnetic field minimum plane and the crucible inner wall: 800 G (Example 3), 1200 G (Example 4) Crucible rotation speed: 1.00 rpm Single crystal rotation speed: 10 rpm

[0051] In Examples 3 and 4, the magnetic field minimum plane position of the cusp magnetic field in the straight body process, the degree of imbalance, the crucible rotation speed, and the single crystal rotation speed were fixed, and a total of two single crystals were produced at magnetic field strengths of 800 G (Example 3) and 1200 G (Example 4). The conditions and results for Examples 3 and 4 are shown in Table 2.

[0052] [Table 2]

[0053] Even when the conditions of Examples 3 and 4 of the silicon single crystal manufacturing method according to the present invention were used, single crystals were successfully pulled without any dislocations occurring during the straight body process. Regarding the crystal quality of the product part, in all cases, the oxygen concentration was 2×10 17 atoms / cm 3(ASTM'79) or lower, and ROG <8% was achieved. We succeeded in pulling single crystals with low oxygen concentration and good in-plane distribution of oxygen concentration without impairing workability.

[0054] (Examples 5 and 6) In Examples 5 and 6, silicon single crystals were produced under the following conditions. [Direct body process (product department)] Position of magnetic field minimum plane: 5 mm above the melt surface Unbalance degree: 1.00 (vertical symmetrical excitation) Magnetic field strength at the intersection of the surface at the same height as the magnetic field minimum surface and the crucible inner wall: 1000G Crucible rotation speed: 1.00 rpm Single crystal rotation speed: 7 rpm (Example 5), 12 rpm (Example 6)

[0055] In Examples 5 and 6, the magnetic field minimum plane position of the cusp magnetic field, the degree of imbalance, the magnetic field strength, and the crucible rotation speed in the straight body process were fixed, and a total of two single crystals were produced at single crystal rotation speeds of 7 rpm (Example 5) and 12 rpm (Example 6). The conditions and results for Examples 5 and 6 are shown in Table 3.

[0056] [Table 3]

[0057] Even when the conditions of Examples 5 and 6 of the silicon single crystal manufacturing method according to the present invention were used, single crystals were successfully pulled without any dislocations occurring during the straight body process. Regarding the crystal quality of the product part, in all cases, the oxygen concentration was 2×10 17 atoms / cm 3 (ASTM'79) or lower, and ROG <8% was achieved. We succeeded in pulling single crystals with low oxygen concentration and good in-plane distribution of oxygen concentration without impairing workability.

[0058] (Examples 7 and 8) In Examples 7 and 8, silicon single crystals were produced under the following conditions. [Direct body process (product department)] Position of magnetic field minimum surface: 10 mm below the melt surface Unbalance degree: 1.10 (unbalanced excitation) Magnetic field strength at the intersection of the surface at the same height as the magnetic field minimum surface and the crucible inner wall: 1000G Crucible rotation speed: 0.5 rpm (Example 7), 1.0 rpm (Example 8) Single crystal rotation speed: 10 rpm

[0059] In Examples 7 and 8, the excitation mode was changed to unbalanced excitation, and the magnetic field minimum plane position, unbalance, magnetic field strength, and single crystal rotation speed in the straight body process were fixed, and a total of two single crystals were produced with the crucible rotation speed set to 0.5 rpm (Example 7) and 1.0 rpm (Example 8). The conditions and results for Examples 7 and 8 are shown in Table 4.

[0060] [Table 4]

[0061] Even when the conditions of Examples 7 and 8 of the silicon single crystal manufacturing method according to the present invention were used, single crystals were successfully pulled without any dislocations occurring during the straight body process. Regarding the crystal quality of the product part, in all cases, the oxygen concentration was 2×10 17 atoms / cm 3 (ASTM'79) or lower, and ROG <8% was achieved. We succeeded in pulling single crystals with low oxygen concentration and good in-plane distribution of oxygen concentration without impairing workability.

[0062] (Examples 9 and 10) In Examples 9 and 10, silicon single crystals were produced under the following conditions. [Direct body process (product department)] Position of magnetic field minimum surface: 10 mm below the melt surface Unbalance degree: 1.10 (unbalanced excitation) Magnetic field strength at the intersection of the plane at the same height as the magnetic field minimum plane and the crucible inner wall: 800 G (Example 9), 1200 G (Example 10) Crucible rotation speed: 1.0 rpm Single crystal rotation speed: 10 rpm

[0063] In Examples 9 and 10, the excitation mode was changed to unbalanced excitation, and the magnetic field minimum plane position, unbalance, crucible rotation speed, and single crystal rotation speed in the straight body process were fixed, and a total of two single crystals were produced with magnetic field strengths of 800 G (Example 9) and 1200 G (Example 10). The conditions and results for Examples 9 and 10 are shown in Table 5.

[0064] [Table 5]

[0065] Even under the conditions of Examples 9 and 10 of the silicon single crystal manufacturing method according to the present invention, single crystals were successfully pulled without any dislocations occurring during the straight body process. 17 atoms / cm 3 (ASTM'79) or lower, and ROG <8% was achieved. We succeeded in pulling single crystals with low oxygen concentration and good in-plane distribution of oxygen concentration without impairing workability.

[0066] (Examples 11 and 12) In Examples 11 and 12, silicon single crystals were produced under the following conditions. [Direct body process (product department)] Position of magnetic field minimum surface: 10 mm below the melt surface Unbalance degree: 1.10 (unbalanced excitation) Magnetic field strength at the intersection of the surface at the same height as the magnetic field minimum surface and the crucible inner wall: 1000G Crucible rotation speed: 1.0 rpm Single crystal rotation speed: 7 rpm (Example 11), 12 rpm (Example 12)

[0067] In Examples 11 and 12, the excitation mode was changed to unbalanced excitation, and the magnetic field minimum plane position, unbalance, magnetic field strength, and crucible rotation speed in the straight body process were fixed, and a total of two single crystals were produced with single crystal rotation speeds of 7 rpm (Example 11) and 12 rpm (Example 12). The conditions and results for Examples 11 and 12 are shown in Table 6.

[0068] [Table 6]

[0069] Even under the conditions of Examples 11 and 12 of the silicon single crystal manufacturing method according to the present invention, single crystals were successfully pulled without any dislocations occurring during the straight body process. 17 atoms / cm 3 (ASTM'79) or lower, and ROG <8% was achieved. We succeeded in pulling single crystals with low oxygen concentration and good in-plane distribution of oxygen concentration without impairing workability.

[0070] (Comparative Example 1) In Comparative Example 1, the crucible rotation speed in the body process (product section) was set to 1.5 rpm, and the other conditions were all the same as in Example 1 to produce a single crystal. The conditions and results of Comparative Example 1 are shown in Table 7.

[0071] [Table 7]

[0072] Under the conditions of Comparative Example 1, a single crystal was successfully pulled without any dislocations occurring during the straight body process. However, the oxygen concentration was 2×10 17 atoms / cm 3 It is higher than that, with ROG>8%.

[0073] As a precaution, single crystals were produced by varying the crucible rotation speed within a range of 1.0 to 2.2 rpm, with the other conditions remaining the same as those in Comparative Example 1. As a result, the oxygen concentration monotonically increased with an increase in the crucible rotation speed, as shown in Figure 3. This shows that in order to obtain single crystals with a low oxygen concentration that meets the quality requirements for power devices and RF devices and with a good in-plane distribution of oxygen concentration, it is necessary to set the crucible rotation speed to 1.0 rpm or less, as in the method for producing silicon single crystals according to the present invention.

[0074] (Comparative Examples 2 and 3) In Comparative Examples 2 and 3, the crystal rotation speed in the body process (product section) was set to 6 rpm (Comparative Example 2) or 13 rpm (Comparative Example 3), and the other conditions for pulling single crystals were the same as those in Example 1. The conditions and results for Comparative Examples 2 and 3 are shown in Table 8, and the in-plane distribution of oxygen concentration obtained at 100 cm of the body in Comparative Example 2 is shown in Figure 4.

[0075] [Table 8]

[0076] When the crystal rotation speed in the body process (product section) was set to 6 rpm, a single crystal was successfully pulled without any dislocations occurring during the body process, but the in-plane oxygen distribution deteriorated, making it impossible to achieve ROG≦8%. Furthermore, when the crystal rotation speed in the body process (product section) was set to 13 rpm, crystal deformation became severe during pulling, making it difficult to continue operation. Therefore, in order to obtain a single crystal with a low oxygen concentration and a good in-plane oxygen concentration distribution that meets the quality requirements for power devices and RF devices, it is necessary to set the crystal rotation speed in the body process (product section) to between 7 rpm and 12 rpm, as in the silicon single crystal manufacturing method of the present invention.

[0077] (Comparative Examples 4-7) In Comparative Examples 4 to 7, the magnetic field strength in the body process (product portion) was 700 G (Comparative Example 4) or 1300 G (Comparative Example 5), and the position of the magnetic field minimum plane in the body process was 10 mm above the melt surface (Comparative Example 6) or 15 mm below the melt surface (Comparative Example 7), and the other conditions were the same as in Example 2, and single crystals were pulled. The conditions and results for Comparative Examples 4 to 7 are shown in Table 9.

[0078] [Table 9]

[0079] When the magnetic field strength in the body process (product section) was set to 700 G, the crystal deformation during pulling became so severe that it was difficult to continue operation. On the other hand, when the magnetic field strength in the body process (product section) was set to 1300 G, the oxygen concentration was 2 × 10 17 atoms / cm 3 In addition, even when the position of the magnetic field minimum plane in the straight body process (product part) was set to 10 mm above the melt surface and 15 mm below the melt surface, the oxygen concentration was 2 × 10 17 atoms / cm 3 Therefore, in order to obtain a single crystal with a low oxygen concentration that satisfies the quality requirements for power devices and RF devices and has a good in-plane distribution of oxygen concentration, it is necessary to set the absolute value of the magnetic field strength to 800 G or more and 1200 G or less in the straight body process (product part) and to set the position of the magnetic field minimum plane within a range of 10 mm below to 5 mm above the surface of the raw material melt, as in the method for producing a silicon single crystal according to the present invention.

[0080] (Comparative Example 8) In Comparative Example 8, the crucible rotation speed in the body process (product section) was set to 1.5 rpm, and all other conditions were the same as in Example 7 (unbalanced excitation), to produce a single crystal. The conditions and results of Comparative Example 8 are shown in Table 10.

[0081] [Table 10]

[0082] Under the conditions of Comparative Example 8, a single crystal was successfully pulled without any dislocations occurring during the straight body process. However, the oxygen concentration was 2×10 17 atoms / cm 3 Therefore, even when the excitation mode is unbalanced excitation, in order to obtain a single crystal with a low oxygen concentration that satisfies the quality requirements for power devices and RF devices and with a good in-plane distribution of oxygen concentration, it is necessary to set the crucible rotation speed to 1.0 rpm or less, as in the method for producing a silicon single crystal according to the present invention.

[0083] (Comparative Examples 9 and 10) In Comparative Examples 9 and 10, the crystal rotation speed in the body process (product part) was set to 6 rpm (Comparative Example 9) or 13 rpm (Comparative Example 10), and the other conditions were the same as in Example 7, and single crystals were pulled. The conditions and results for Comparative Examples 9 and 10 are shown in Table 11.

[0084] [Table 11]

[0085] When the crystal rotation speed in the straight body process (product section) was set to 6 rpm, cranking occurred during the straight body process, making it difficult to continue operation. Furthermore, when the crystal rotation speed in the straight body process (product section) was set to 13 rpm, crystal deformation became so severe during pulling that it was difficult to continue operation. Therefore, even when the excitation mode is unbalanced excitation, in order to obtain a single crystal with a low oxygen concentration and a good in-plane distribution of oxygen concentration that meets the quality requirements for power devices and RF devices, it is necessary to set the crystal rotation speed in the straight body process (product section) to between 7 rpm and 12 rpm, as in the silicon single crystal manufacturing method according to the present invention.

[0086] (Comparative Examples 11-14) In Comparative Examples 11 to 14, the magnetic field strength in the body process (product part) was 700 G (Comparative Example 11) or 1300 G (Comparative Example 12), and the position of the magnetic field minimum plane in the body process (product part) was 10 mm above the melt surface (Comparative Example 13) or 15 mm below the melt surface (Comparative Example 14), and the other conditions were the same as in Example 8, and single crystals were pulled. The conditions and results of Comparative Examples 11 to 14 are shown in Table 12.

[0087] [Table 12]

[0088] When the magnetic field strength in the body process (product section) was set to 700 G, the crystal deformation during pulling became so severe that it was difficult to continue operation. On the other hand, when the magnetic field strength in the body process (product section) was set to 1300 G, the oxygen concentration was 2 × 10 17 atoms / cm 3 In addition, even when the position of the magnetic field minimum plane in the straight body process (product part) was set to 10 mm above the melt surface and 15 mm below the melt surface, the oxygen concentration was 2 × 10 17 atoms / cm 3 Therefore, even when the excitation mode is unbalanced excitation, in order to obtain a single crystal with a low oxygen concentration that satisfies the quality requirements for power devices and RF devices and with a good in-plane distribution of oxygen concentration, it is necessary to set the absolute value of the magnetic field strength to between 800 G and 1200 G inclusive in the straight body process (product part) and to set the position of the magnetic field minimum plane within a range of 10 mm below and 5 mm above the surface of the raw material melt, as in the method for producing a silicon single crystal according to the present invention.

[0089] As described above, according to the examples of the present invention, problems such as an increase in oxygen concentration and a deterioration in the in-plane distribution of oxygen concentration when the crucible rotation speed is increased are eliminated, and it is possible to efficiently produce single crystals with a low oxygen concentration and a good in-plane distribution of oxygen concentration that meet the quality requirements for power devices and RF devices.

[0090] The present invention is not limited to the above-described embodiments. The above-described embodiments are merely examples, and anything that has substantially the same configuration as the technical idea described in the claims of the present invention and that exhibits similar effects is included within the technical scope of the present invention. [Explanation of symbols]

[0091] 1...pulling furnace, 2...seed crystal, 3...seed holder, 4...silicon single crystal, 5...raw material melt, 6...quartz crucible, 7...graphite crucible, 8...heater, 9...heat insulating material, 10...center axis, 11...tubular portion, 12...heat shielding member, 30...magnetic field generator, 30a...upper coil, 30b...lower coil, 30c...lifting device, 31...surface at the same height as the magnetic field minimum surface, 32... Minimum magnetic field surface, 33... Raw material melt surface, 35...Intersection of the plane at the same height as the magnetic field minimum plane and the inner wall of the quartz crucible, 100...Single crystal manufacturing equipment (single crystal pulling equipment).

Claims

1. A method for producing a silicon single crystal by a CZ method using a cusp magnetic field formed by an upper coil and a lower coil provided in a pulling furnace, A method for producing a silicon single crystal, characterized in that in the straight body step, the silicon single crystal is pulled up by setting the rotation speed of the silicon single crystal to 7 rpm or more and 12 rpm or less, the rotation speed of the quartz crucible to 1.0 rpm or less, the position of the magnetic field minimum plane of the cusp magnetic field within a range of 10 mm below to 5 mm above the surface of the raw material melt, and the magnetic field strength of the cusp magnetic field at the intersection of a plane at the same height as the magnetic field minimum plane and the inner wall of the quartz crucible to 800 to 1200 G.

2. The silicon single crystal has an oxygen concentration of 2×10 based on ASTM '79 １７ atoms / cm ３ 2. The method for producing a silicon single crystal according to claim 1, wherein the silicon single crystal has an ROG of 8% or less in a crystal cross section perpendicular to the growth direction.

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