Method for growing single crystal silicon, method for manufacturing silicon wafer, and single crystal pulling apparatus

Abstract

To suppress a variation in oxygen concentration in each silicon single crystal without increasing a production cost of a single crystal pulling-up apparatus.SOLUTION: A growing method of a silicon single crystal for pulling up a silicon single crystal while applying a horizontal magnetic field to a silicon melt M uses a single crystal pulling-up apparatus 1 equipped with a chamber 2, a crucible 3 for storing the silicon melt M, a heating unit 4 for heating the silicon melt M, and a cylindrical heat insulator 7 arranged inside the chamber 2. The central axis C of the heat insulator 7 is arranged so as to be deviated from the rotation center axis A of the crucible 3 by 1.5 mm or more in the horizontal direction orthogonal to the application direction MD of the magnetic field center of the horizontal magnetic field, thereby growing the silicon single crystal.SELECTED DRAWING: Figure 3

Description

Technical Field

[0001] The present invention relates to a method for growing a silicon single crystal, a method for manufacturing a silicon wafer, and a single crystal pulling apparatus.

Background Art

[0002] As a method for growing a silicon single crystal, the Czochralski method is known. In recent years, a so-called MCZ method in which a silicon single crystal is grown while applying a horizontal magnetic field to a silicon melt has been increasingly used. When a horizontal magnetic field is applied to a silicon melt using the MCZ method, as shown in FIG. 1(a), when the clockwise convection C1 becomes dominant in the crucible 3 (hereinafter referred to as the right vortex mode), and as shown in FIG. 1(b), when the counterclockwise convection C2 becomes dominant in the crucible 3 (hereinafter referred to as the left vortex mode), either one of the convection modes is initially formed. In FIG. 1, the symbol MD is the applied direction of the magnetic field center of the horizontal magnetic field.

[0003] Whether the convection mode becomes the right vortex mode or the left vortex mode is random, and the oxygen concentration incorporated into the crystal varies depending on the convection mode and the furnace environment. In order to obtain a silicon single crystal having a stable oxygen concentration, it is important to control the convection mode of the silicon melt during pulling. For this reason, various studies have been conducted on methods for controlling the convection mode of the silicon melt in the crucible (see, for example, Patent Document 1).

[0004] Patent Document 1 discloses a method for eliminating variations in oxygen concentration caused by the convection mode by stably selecting one of the two convection modes (right vortex mode or left vortex mode). Specifically, the convection mode is fixed to one side by making the thermal environment in the furnace asymmetric by varying the resistance value of the heater and the thickness of the heat insulating material on the left and right of the apparatus, thereby suppressing variations in oxygen concentration for each silicon single crystal.

Prior Art Documents

Patent Documents

[0005] Patent Document 1 Japanese Patent Application Laid-Open No. 2019-151502 Summary of the Invention Problems to be Solved by the Invention

[0006] However, in the method described in Patent Document 1 above, there is a problem that special members such as "a heater having different resistance values on the left and right" and "a heat insulating material having different thicknesses on the left and right" are required, increasing the manufacturing cost of the apparatus.

[0007] An object of the present invention is to provide a method for growing a silicon single crystal, a method for manufacturing a silicon wafer, and a single crystal pulling apparatus that can suppress variations in oxygen concentration for each silicon single crystal without increasing the manufacturing cost of the single crystal pulling apparatus. Means for Solving the Problems

[0008] The method for growing a silicon single crystal according to the present invention uses a single crystal pulling apparatus including a chamber, a crucible for storing a silicon melt, a heating unit for heating the silicon melt, and a cylindrical heat insulating material disposed inside the chamber, and grows the silicon single crystal while applying a horizontal magnetic field to the silicon melt, wherein the heat insulating material is arranged such that the central axis of the heat insulating material is displaced by 1.5 mm or more in a horizontal direction orthogonal to the application direction of the magnetic field center of the horizontal magnetic field with respect to the rotation center axis of the crucible to grow the silicon single crystal.

[0009] In the method for growing a silicon single crystal described above, it is preferable that the heat insulating material is formed of carbon fiber.

[0010] The method for manufacturing a silicon wafer according to the present invention includes the method for growing a silicon single crystal described above, and is characterized by cutting out a silicon wafer from the grown silicon single crystal.

[0011] The single crystal pulling apparatus of the present invention includes a chamber, a crucible for storing a silicon melt, a heating unit for heating the silicon melt, a cylindrical heat insulating material disposed inside the chamber, and a magnetic field applying unit for applying a horizontal magnetic field to the silicon melt in the crucible, wherein the heat insulating material is disposed such that the central axis of the heat insulating material is displaced by 1.5 mm or more in a horizontal direction perpendicular to the application direction of the magnetic field center of the horizontal magnetic field with respect to the rotation center axis of the crucible.

[0012] In the above single crystal pulling apparatus, it is preferable that the heat insulating material is formed of carbon fiber.

Brief Description of the Drawings

[0013]

Figure 1

Figure 2

Figure 3

Embodiments for Carrying Out the Invention

[0014] 〔Configuration of Single Crystal Pulling Apparatus〕 The configuration of the single crystal pulling apparatus according to an embodiment of the present invention will be described. As shown in FIG. 2, the single crystal pulling apparatus 1 is an apparatus for pulling a silicon single crystal SM while applying a horizontal magnetic field to a silicon melt M by the MCZ method. The single crystal pulling apparatus 1 includes a chamber 2, a crucible 3 disposed in the chamber 2 for storing the silicon melt M, a heater 4, a pulling unit 5 for pulling the silicon single crystal SM, a heat shield 6 provided above the crucible 3 so as to surround the silicon single crystal SM, a heat insulating material 7, a crucible driving unit 8, and a magnetic field applying unit 9 (see FIG. 3) for applying a horizontal magnetic field to the silicon melt M.

[0015] The crucible 3 has a double structure composed of a quartz crucible 3A and a graphite crucible 3B that houses the quartz crucible 3A. The crucible driving unit 8 includes a support shaft 11 that supports the crucible 3 from below, and rotates and raises and lowers the crucible 3 at a predetermined speed around the rotation center axis A.

[0016] The chamber 2 includes a main chamber 12 and a pull chamber 13 connected to the upper part of the main chamber 12. The main chamber 12 and the pull chamber 13 are connected via a gate valve 14.

[0017] The main chamber 12 includes a main body portion 12A where the crucible 3, the heater 4, the heat shield 6, etc. are arranged, and a lid portion 12B that closes the upper surface of the main body portion 12A. The main body portion 12A has a cylindrical shape. An opening 15 for introducing an inert gas such as argon gas into the main chamber 12 is provided in the lid portion 12B. A support portion 17 extending inward is provided between the main body portion 12A and the lid portion 12B.

[0018] The pull chamber 13 is provided with a gas inlet 20 for introducing an inert gas into the main chamber 12. A gas exhaust port 21 for sucking and discharging the gas in the main chamber 12 is provided at the lower part of the main body portion 12A of the main chamber 12 by driving a vacuum pump (not shown). The inert gas introduced into the chamber 2 from the gas inlet 20 descends between the growing silicon single crystal SM and the heat shield 6. Next, the inert gas flows through the gap between the lower end of the heat shield 6 and the liquid surface of the silicon melt M, then flows outside the heat shield 6 and further outside the crucible 3. Thereafter, the inert gas descends outside the crucible 3 and is discharged from the gas exhaust port 21.

[0019] The heater 4 is a heating part by resistance heating and heats the silicon melt M. The heater 4 is arranged around the crucible 3 and inside the heat insulating material 7. The heater 4 is formed so as to be cylindrical as a whole.

[0020] The pulling-up unit 5 includes a pulling-up shaft 24 to which a seed crystal SC is attached at one end, and a pulling-up driving unit 23 that raises and lowers and rotates the pulling-up shaft 24. The central axes of the chamber 2 and the heater 4 coincide with the rotation central axis A of the crucible 3, and the rotation central axis A of the crucible 3 coincides with the lifting axis 24.

[0021] The heat insulator 7 is cylindrical and has a predetermined thickness in the radial direction. The heat insulator 7 is disposed outside the heater 4 and inside the chamber 2. When the heat insulator 7 is arranged such that the central axis C (see FIG. 3) of the heat insulator 7 coincides with the rotation central axis A, at least a 1.5 mm gap is formed between the outer peripheral surface of the heat insulator 7 and the inner peripheral surface of the main body portion 12A of the main chamber 12.

[0022] The heat insulator 7 is placed on the bottom surface 12C of the main chamber 12. A graphite ring 16 is interposed between the heat insulator 7 and the bottom surface 12C of the main chamber 12. The ring 16 can also be omitted. The heat insulator 7 is a carbon fiber heat insulator formed of carbon fiber. The heat insulator 7 can be moved in the radial direction (horizontal direction) within the chamber 2. The single crystal pulling apparatus 1 may include a fixture for fixing the position of the heat insulator 7 after moving the heat insulator 7.

[0023] The heat shield 6 blocks the high-temperature radiant heat from the silicon melt M, the heater 4, and the side wall of the crucible 3 in the crucible 3 from the growing silicon single crystal SM. Further, the heat shield 6 suppresses the diffusion of heat to the outside with respect to the vicinity of the solid-liquid interface which is the crystal growth interface, and controls the temperature gradient in the vertical direction of the central portion and the outer peripheral portion of the silicon single crystal SM. Furthermore, the heat shield 6 functions as a rectifying cylinder for exhausting the evaporant from the silicon melt M to the outside of the furnace by the inert gas introduced from above the furnace.

[0024] The upper end of the heat shield 6 is supported by the support portion 17 of the chamber 2. The heat shield 6 is formed in a frustum-shaped cylindrical shape with a diameter decreasing toward the lower end. Note that the shape of the heat shield 6 is not limited to the shape described above. For example, it may be provided with a cylindrical main body and a protruding portion that protrudes inward in a flange shape from the entire circumference of the lower end of the main body, and may be formed in a frustum-shaped cylindrical shape in which the diameter of the protruding portion decreases as it goes downward.

[0025] The magnetic field application unit 9 (see FIG. 3) includes a first magnetic body 9A and a second magnetic body 9B configured by electromagnetic coils. The magnetic bodies 9A and 9B are provided so as to face each other with the crucible 3 interposed therebetween outside the chamber 2. In this way, the magnetic field application unit 9 is arranged such that the application direction MD of the magnetic field center is in the horizontal direction passing through the rotation center axis A of the crucible 3. That is, the magnetic field center is in the horizontal direction passing through the rotation center axis A of the crucible 3.

[0026] [Method for growing single crystal silicon] Next, a method for growing a single crystal silicon using the above-described single crystal pulling apparatus 1 will be described. FIG. 3 is a schematic plan view for explaining the arrangement position of the heat insulating material 7 in the method for growing a single crystal silicon. In FIG. 3, in order to explain the arrangement method of the heat insulating material 7, the deviation amount Δx (movement amount) of the heat insulating material 7 is emphasized.

[0027] First, as shown in FIG. 3, the operator arranges the heat insulating material 7 so that the central axis C of the heat insulating material 7 is displaced in the horizontal direction (x-axis direction) orthogonal to the application direction MD of the magnetic field center of the horizontal magnetic field with respect to the rotation center axis A of the crucible 3. Specifically, when the vertical direction is the z-axis, the application direction MD of the magnetic field center of the horizontal magnetic field is the y-axis, and the horizontal direction orthogonal to the z-axis and the y-axis is the x-axis, the heat insulating material 7 is arranged so that the central axis C of the heat insulating material 7 is displaced in the x-axis direction. The deviation amount Δx of the heat insulating material 7 is 1.5 mm or more (|Δx|≧1.5 mm). In FIG. 3, the heat insulating material 7 is displaced in the -x direction, but the heat insulating material 7 may be displaced in the +x direction. Further, the upper limit of the deviation amount Δx of the heat insulating material 7 is 3.0 mm (|Δx|≦3.0 mm). This upper limit is due to the heat insulating material 7 interfering with the inner peripheral surface of the chamber 2 or the outer peripheral surface of the heater 4.

[0028] Next, without applying a horizontal magnetic field, an inert gas is introduced into the chamber 2 and the crucible 3 is rotated while maintaining an inert gas atmosphere under reduced pressure, and a solid raw material such as polycrystalline silicon stored in the crucible 3 is melted by heating with the heater 4 to generate a silicon melt M.

[0029] Next, the magnetic field application unit 9 is driven to apply a horizontal magnetic field. Here, since the heat insulating material 7 is installed with a shift in the x-axis direction, the gap between the heat insulating material 7 and the heater 4 is non-uniform in the circumferential direction. In the present embodiment, since the heat insulating material 7 is shifted in the -x direction, the gap on the right side (+x direction) in FIG. 3 is narrowed. When the silicon melt M is heated in this state, the right side of the silicon melt M becomes relatively hotter than the left side. Specifically, the gap between the heat insulating material 7 and the heater 4 is smaller on the right side, and the heat transfer by radiation becomes larger, so the temperature of the silicon melt M closer to it becomes higher. When the right side of the silicon melt M becomes relatively hotter than the left side, the buoyancy of the silicon melt M becomes larger on the right side than on the left side, and the convection mode is more likely to form the left vortex mode than the right vortex mode.

[0030] In the present embodiment, the heat insulating material 7 is shifted in the -x direction to facilitate the formation of the left vortex mode. However, when the heat insulating material 7 is shifted in the +x direction, the right vortex mode is more likely to be formed.

[0031] Thereafter, based on the pre-set process conditions, after the seed crystal SC is dropped onto the silicon melt M, the silicon single crystal SM is pulled up.

[0032] 〔Method for manufacturing a silicon wafer〕 A silicon wafer is cut out from an ingot of the silicon single crystal SM grown by the above-described method for growing a silicon single crystal using a wire saw (not shown), and the silicon wafer can be manufactured through general wafer manufacturing processes such as chamfering, polishing, and cleaning.

[0033] According to the above embodiment, the heat insulating material 7 can be easily arranged so as to be displaced in the horizontal direction orthogonal to the application direction MD of the magnetic field center of the horizontal magnetic field, and the convection mode can be easily fixed to one mode (right vortex mode or left vortex mode) regardless of the symmetry of the structure of the lifting device 1. Therefore, by fixing the convection mode, the variation in the oxygen concentration for each silicon single crystal SM can be suppressed.

[0034] In addition, when using a heat insulating material with a special shape that has different thicknesses in the circumferential direction, it is necessary to distinguish between the heat insulating material for the right vortex mode and the heat insulating material for the left vortex mode. However, if the thickness and structure of the heat insulating material are the same in the circumferential direction as in the above embodiment, the design, manufacture, and management of the heat insulating material are easy.

[0035] Further, since the heat insulating material 7 is a carbon fiber heat insulating material formed of carbon fiber, it is possible to obtain a heat insulating material having a high heat resistance temperature and excellent heat insulating performance.

[0036] In this embodiment, the operator moves the heat insulating material 7, but the present invention is not limited to this. At the manufacturing stage of the single crystal pulling device 1, the heat insulating material 7 may be arranged such that the central axis C of the heat insulating material is displaced by 1.5 mm or more in the horizontal direction orthogonal to the application direction MD of the magnetic field center of the horizontal magnetic field with respect to the rotation center axis A of the crucible 3.

[0037] 〔Example〕 Silicon single crystals were grown while changing the displacement amount of the heat insulating material, and the oxygen concentrations of the silicon single crystals were compared. As shown in Table 1, the displacement amounts Δx of the heat insulating material to be changed were Δx = -3.0 mm, -2.0 mm, -1.5 mm, -1.0 mm, +1.0 mm, +1.5 mm, +2.0 mm, and +3.0 mm. Under these conditions, silicon single crystals with a diameter of 300 mm and a crystal length of 2000 mm were grown. Twenty silicon single crystals were grown under each condition.

[0038]

Table 1

[0039] The generation rates of the right vortex mode / left vortex mode under each condition and the oxygen concentration at a position 1000 mm below the top of the grown silicon single crystal were measured by Fourier Transform Infrared Spectroscopy (FTIR), and the results are shown in Table 1. The right vortex mode / left vortex mode was determined by measuring two points T1 and T2 on the surface of the silicon melt using the temperature measurement unit 30 (see Fig. 2), and judging from the magnitude of the temperatures. The temperature measurement unit 30 includes a pair of reflection parts 30A and a pair of radiation thermometers 30B, and measures the temperature on the surface of the silicon melt M. Also, the oxygen concentrations in Table 1 are shown as the ratios of the minimum value to the maximum value of the oxygen concentrations of 20 silicon single crystals under each condition to the reference value, with the average value of the oxygen concentration in Comparative Example 1 (Δx = 0 mm) as the reference value.

[0040] As can be seen from Table 1, when |Δx| ≧ 1.5 mm (Examples 1 to 6), the convection mode generation rate becomes 100% of the left vortex mode or 100% of the right vortex mode, indicating that it can be fixed to the right vortex mode or the left vortex mode. On the other hand, when |Δx| = 1.0 (Comparative Examples 2 and 3), it cannot be fixed to the right vortex mode or the left vortex mode, and the width of the maximum value and the minimum value of the oxygen concentration is also as large as 0.3. Depending on whether it is the right vortex mode or the left vortex mode, the average value of the oxygen concentration increases or decreases from the reference value (1.0), but the width of the maximum value and the minimum value decreases significantly from 0.4 (Comparative Example 1) to 0.05 (Examples 1 to 6), indicating that the controllability of the oxygen concentration has been improved. To grow a crystal with a desired oxygen concentration, after fixing it to the right vortex or left vortex mode, other process conditions such as the crucible rotation speed and the crystal rotation speed during crystal growth may be adjusted.

Explanation of symbols

[0041] 1... Single crystal pulling apparatus, 2... Chamber, 3... Crucible, 4... Heater (heating section), 5... Pulling section, 6... Thermal shield, 7... Heat insulating material, 9... Magnetic field applying section, 23... Pulling drive section, 24... Pulling shaft, A... Rotation center axis, C... Central axis, M... Silicon melt, MD... Applying direction of magnetic field center of horizontal magnetic field, SC... Seed crystal, SM... Silicon single crystal.

Claims

1. A method for growing a silicon single crystal, which uses a single crystal pulling apparatus including a chamber, a crucible for storing a silicon melt, a heating unit for heating the silicon melt, and a cylindrical heat insulating material disposed outside the heating unit and inside the chamber, and pulls up a silicon single crystal while applying a horizontal magnetic field to the silicon melt, wherein the silicon single crystal is grown by disposing the heat insulating material such that the central axis of the heat insulating material is displaced by 1.5 mm or more in a horizontal direction orthogonal to the application direction of the magnetic field center of the horizontal magnetic field with respect to the rotation central axis of the crucible.

2. In the method for growing a silicon single crystal according to Claim 1, the heat insulating material is formed of carbon fiber.

3. A method for manufacturing a silicon wafer, which includes the method for growing a silicon single crystal according to Claim 1 or Claim 2, and cuts out a silicon wafer from the grown silicon single crystal.

4. A single crystal pulling apparatus including a chamber, a crucible for storing a silicon melt, a heating unit for heating the silicon melt, a cylindrical heat insulating material disposed outside the heating unit and inside the chamber, and a magnetic field applying unit for applying a horizontal magnetic field to the silicon melt in the crucible, wherein the heat insulating material is disposed such that the central axis of the heat insulating material is displaced by 1.5 mm or more in a horizontal direction orthogonal to the application direction of the magnetic field center of the horizontal magnetic field with respect to the rotation central axis of the crucible.

5. In the single crystal pulling apparatus according to Claim 4, the heat insulating material is formed of carbon fiber. ​

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