JP2023170513A - Growing method of silicon single crystal, production method of silicon wafer, and single crystal pulling-up apparatus - Google Patents

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

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

The Czochralski method is known as a method for growing silicon single crystals. In recent years, the so-called MCZ method, in which a silicon single crystal is grown while applying a horizontal magnetic field to a silicon melt, has come into widespread use. When a horizontal magnetic field is applied to the silicon melt using the MCZ method, the clockwise convection C1 becomes dominant in the crucible 3 (hereinafter referred to as right-handed vortex mode) as shown in Fig. 1(a). , as shown in FIG. 1(b), when the counterclockwise convection C2 becomes predominant in the crucible 3 (hereinafter referred to as the left vortex mode), one of the convection modes is initially formed. In FIG. 1, the symbol MD indicates the direction of application of the center of the horizontal magnetic field.

It is random whether the convection mode is the right vortex mode or the left vortex mode, and the oxygen concentration taken into the crystal varies depending on the convection mode and the furnace environment. In order to obtain a silicon single crystal with 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).

Patent Document 1 discloses a method of eliminating variations in oxygen concentration caused by the convection mode by stably selecting one of two convection modes (right vortex mode or left vortex mode). Specifically, by making the thermal environment inside the furnace asymmetric by changing the heater resistance and the thickness of the insulation material on the left and right sides of the device, the convection mode is fixed to one side, and the variation in oxygen concentration for each silicon single crystal is reduced. is suppressed.

JP 2019-151502 Publication

However, the method described in Patent Document 1 requires special members such as "heaters with different resistance values on the left and right sides" and "insulating materials with different thicknesses on the left and right sides," which poses a problem in that the manufacturing cost of the device increases. .

The present invention provides a method for growing a silicon single crystal, a method for manufacturing a silicon wafer, and a single crystal pulling device that can suppress variations in oxygen concentration among silicon single crystals without increasing the manufacturing cost of the single crystal pulling device. The purpose is to

The silicon single crystal growth method of the present invention includes a chamber, a crucible for storing a silicon melt, a heating section for heating the silicon melt, and a cylindrical heat insulating material disposed inside the chamber. A method for growing a silicon single crystal by pulling the silicon single crystal while applying a horizontal magnetic field to the silicon melt using a single crystal pulling apparatus equipped with the above, The silicon single crystal is grown so as to be shifted by 1.5 mm or more in a horizontal direction perpendicular to the direction of application of the center of the horizontal magnetic field with respect to the rotation center axis of the horizontal magnetic field.

In the method for growing a silicon single crystal, the heat insulating material is preferably formed of carbon fiber.

The method for manufacturing a silicon wafer of the present invention includes the method for growing a silicon single crystal described above, and is characterized in that a silicon wafer is cut out from the grown silicon single crystal.

The single crystal pulling apparatus of the present invention includes a chamber, a crucible for storing a silicon melt, a heating section for heating the silicon melt, a cylindrical heat insulating material disposed inside the chamber, and a crucible for storing a silicon melt. a magnetic field applying unit that applies a horizontal magnetic field to the silicon melt, and the heat insulating material has a central axis of the heat insulating material that is aligned with a direction in which the center of the magnetic field of the horizontal magnetic field is applied with respect to a central axis of rotation of the crucible. It is characterized by being arranged so as to be shifted by 1.5 mm or more in the orthogonal horizontal direction.

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

It is a schematic diagram explaining convection mode. FIG. 1 is a schematic cross-sectional view of a single crystal pulling apparatus according to an embodiment of the present invention. FIG. 2 is a schematic plan view illustrating the placement position of a heat insulating material in a silicon single crystal growth method.

[Single crystal pulling equipment configuration]
The configuration of a single crystal pulling apparatus according to an embodiment of the present invention will be described.
As shown in FIG. 2, the single crystal pulling device 1 is a device that pulls a silicon single crystal SM while applying a horizontal magnetic field to a silicon melt M using the MCZ method. The single crystal pulling apparatus 1 includes a chamber 2, a crucible 3 disposed in the chamber 2 and storing a silicon melt M, a heater 4, a pulling section 5 for pulling up a silicon single crystal SM, and a silicon single crystal pulling unit 5 above the crucible 3. It includes a heat shield 6 provided to surround the crystal SM, a heat insulating material 7, a crucible driving section 8, and a magnetic field applying section 9 (see FIG. 3) that applies a horizontal magnetic field to the silicon melt M. There is.

The crucible 3 has a double structure consisting of a quartz crucible 3A and a graphite crucible 3B that accommodates the quartz crucible 3A.
The crucible drive unit 8 includes a support shaft 11 that supports the crucible 3 from below, and rotates the crucible 3 around the rotation center axis A at a predetermined speed and moves it up and down.

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.

The main chamber 12 includes a main body portion 12A in which a crucible 3, a heater 4, a 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. The lid portion 12B is provided with an opening 15 for introducing an inert gas such as argon gas into the main chamber 12. A support portion 17 extending inward is provided between the main body portion 12A and the lid portion 12B.

The pull chamber 13 is provided with a gas introduction port 20 for introducing an inert gas into the main chamber 12 . A gas exhaust port 21 is provided at the lower part of the main body portion 12A of the main chamber 12, which sucks and exhausts gas in 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 silicon single crystal SM being grown and the heat shield 6 . Next, the inert gas passes through the gap between the lower end of the heat shield 6 and the surface of the silicon melt M, and then flows toward the outside of the heat shield 6 and further to the outside of the crucible 3. Thereafter, the inert gas descends outside the crucible 3 and is discharged from the gas exhaust port 21.

The heater 4 is a heating section using a resistance heating type, 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 to have a cylindrical shape as a whole.

The pulling section 5 includes a pulling shaft 24 to which a seed crystal SC is attached to one end, and a pulling drive section 23 that raises and lowers and rotates the pulling shaft 24.
The central axes of the chamber 2 and the heater 4 coincide with the rotational central axis A of the crucible 3, and the rotational central axis A of the crucible 3 coincides with the pulling shaft 24.

The heat insulating material 7 has a cylindrical shape and has a predetermined thickness in the radial direction. The heat insulating material 7 is arranged outside the heater 4 and inside the chamber 2. When the heat insulating material 7 is arranged so that the central axis C (see FIG. 3) of the insulating material 7 coincides with the rotation center axis A, the outer circumferential surface of the insulating material 7 and the inner circumferential surface of the main body 12A of the main chamber 12 A gap of at least 1.5 mm is formed between the two.

The heat insulating material 7 is placed on the bottom surface 12C of the main chamber 12. A graphite ring 16 is interposed between the heat insulating material 7 and the bottom surface 12C of the main chamber 12. Ring 16 can also be omitted.
The heat insulator 7 is a carbon fiber heat insulator made of carbon fiber.
The heat insulator 7 can be moved in the radial direction (horizontally) within the chamber 2 . The single crystal pulling apparatus 1 may include a fixture that fixes the position of the heat insulating material 7 after the heat insulating material 7 is moved.

The heat shield 6 blocks high-temperature radiant heat from the silicon melt M in the crucible 3, the heater 4, and the side wall of the crucible 3 from the growing silicon single crystal SM. In addition, the heat shield 6 suppresses the diffusion of heat to the outside near the solid-liquid interface, which is the crystal growth interface, and reduces the temperature gradient in the vertical direction at the center and outer periphery of the silicon single crystal SM. Control.
Further, the heat shield 6 functions as a rectifying tube that exhausts the evaporated material from the silicon melt M to the outside of the furnace using an inert gas introduced from above the furnace.

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 into a truncated conical tube shape whose diameter decreases toward the lower end.
Note that the shape of the heat shield 6 is not limited to the above-described shape, and includes, for example, a cylindrical main body and a protrusion that protrudes inward from the entire lower end of the main body in a brim shape. It may be formed into a truncated conical tube shape whose diameter decreases toward the bottom.

The magnetic field application unit 9 (see FIG. 3) includes a first magnetic body 9A and a second magnetic body 9B, each of which is composed of an electromagnetic coil. The magnetic bodies 9A and 9B are provided outside the chamber 2 so as to face each other with the crucible 3 in between. In this way, the magnetic field applying section 9 is arranged so that the application direction MD of the center of the magnetic field passes through the rotation center axis A of the crucible 3 and is in the horizontal direction. That is, the center of the magnetic field is in the horizontal direction passing through the rotation center axis A of the crucible 3.

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

First, as shown in FIG. (x-axis direction). Specifically, the heat insulating material 7 are arranged so that the central axis C of is shifted in the x-axis direction.
The amount of deviation Δx of the heat insulating material 7 is 1.5 mm or more (|Δx|≧1.5 mm). Note that in FIG. 3, the heat insulating material 7 is shifted in the -x direction, but the heat insulating material 7 may be shifted 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 interference of the heat insulating material 7 with the inner peripheral surface of the chamber 2 and the outer peripheral surface of the heater 4.

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

Next, the magnetic field applying section 9 is driven to apply a horizontal magnetic field. Here, since the heat insulating material 7 is disposed offset 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 this 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 narrower. 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 due to radiation is larger, so the temperature of the silicon melt M near the right side 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 left vortex mode is formed more than the right vortex mode in the convection mode. It becomes easier.

Note that in this embodiment, the heat insulating material 7 is shifted in the −x direction to facilitate the formation of the left vortex mode, but if the heat insulating material 7 is shifted in the +x direction, the right vortex mode is more likely to be formed.

Thereafter, a seed crystal SC is deposited on the silicon melt M based on process conditions set in advance, and then the silicon single crystal SM is pulled up.

[Silicon wafer manufacturing method]
A silicon wafer is cut out using a wire saw (not shown) from a silicon single crystal SM ingot grown using the silicon single crystal growth method described above, and is subjected to common wafer manufacturing processing steps such as chamfering, polishing, and cleaning. Silicon wafers can be manufactured.

According to the above embodiment, the heat insulating material 7 can be simply arranged so as to be shifted in the horizontal direction perpendicular to the application direction MD of the magnetic field center of the horizontal magnetic field, regardless of the symmetry of the structure of the pulling device 1. , it is easy to fix the convection mode to one mode (right vortex mode or left vortex mode). Therefore, by fixing the convection mode, variations in oxygen concentration among silicon single crystal SMs can be suppressed.

Furthermore, when using a specially shaped heat insulating material with different thicknesses in the circumferential direction, it is necessary to use heat insulating material for right vortex mode and heat insulating material for left vortex mode. If the thickness and structure of the insulation material are the same in the circumferential direction, it is easy to design, manufacture, and manage the insulation material.

Further, by using a carbon fiber heat insulating material formed of carbon fibers as the heat insulating material 7, it is possible to obtain a heat insulating material with a high heat resistance and excellent heat insulation performance.

In this embodiment, the worker moves the heat insulating material 7, but the invention is not limited to this, and in the manufacturing stage of the single crystal pulling apparatus 1, the center axis C of the heat insulating material 7 is moved by the rotation of the crucible 3. The heat insulating material 7 may be arranged so as to be shifted from the central axis A by 1.5 mm or more in the horizontal direction perpendicular to the direction MD of the magnetic field center of the horizontal magnetic field.

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

The table shows the occurrence rate of 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 measured by Fourier Transform Infrared Spectroscopy (FTIR). Shown in 1.
The right vortex mode/left vortex mode was determined by measuring two locations T1 and T2 on the surface of the silicon melt using the temperature measurement unit 30 (see FIG. 2), and based on the magnitude of the temperature. The temperature measurement unit 30 includes a pair of reflection units 30A and a pair of radiation thermometers 30B, and measures the temperature of the surface of the silicon melt M.
In addition, the oxygen concentrations in Table 1 are the ratios of the minimum to maximum oxygen concentrations of 20 silicon single crystals under each condition to the standard value, with the average value of the oxygen concentration of Comparative Example 1 (Δx = 0 mm) as the standard value. It was shown as

As can be seen from Table 1, if |Δx|≧1.5 mm (Examples 1 to 6), the convection mode occurrence rate becomes 100% left vortex mode or 100% right vortex mode, and the right vortex mode or left vortex mode It can be seen that it can be fixed to On the other hand, when |Δx| = 1.0 (Comparative Examples 2 and 3), it is not possible to fix the mode to right vortex mode or left vortex mode, and the width of the maximum and minimum values of oxygen concentration is as large as 0.3. .
Depending on whether the mode is right vortex mode or left vortex mode, the average value of oxygen concentration increases or decreases from the standard value (1.0), but the width of the maximum and minimum values is 0.4 (comparison). There is a large decrease from Example 1) to 0.05 (Examples 1 to 6), indicating that the controllability of the oxygen concentration is improved. In order to grow a crystal with a desired oxygen concentration, it is sufficient to fix the mode to right-handed or left-handed vortex mode, and then adjust other process conditions such as crucible rotation speed and crystal rotation speed during crystal growth.

DESCRIPTION OF SYMBOLS 1... Single crystal pulling apparatus, 2... Chamber, 3... Crucible, 4... Heater (heating part), 5... Pulling part, 6... Heat shield, 7... Heat insulating material, 9... Magnetic field application part, 23... Pulling drive part , 24... Pulling axis, A... Rotation center axis, C... Central axis, M... Silicon melt, MD... Application direction of the magnetic field center of the horizontal magnetic field, SC... Seed crystal, SM... Silicon single crystal.

Claims (5)

Using a single crystal pulling apparatus including a chamber, a crucible for storing silicon melt, a heating section for heating the silicon melt, and a cylindrical heat insulating material disposed inside the chamber, the silicon A method for growing a silicon single crystal, the method comprising: pulling the silicon single crystal while applying a horizontal magnetic field to the melt;
The silicon single crystal is grown by arranging the heat insulating material such that the center axis of the heat insulating material is shifted from the rotation center axis of the crucible by 1.5 mm or more in a horizontal direction perpendicular to the direction of application of the center of the magnetic field of the horizontal magnetic field. A method for growing silicon single crystals. The method for growing a silicon single crystal according to claim 1,
The method for growing a silicon single crystal in which the heat insulating material is made of carbon fiber. Including the method for growing a silicon single crystal according to claim 1 or claim 2,
A method for manufacturing a silicon wafer, comprising cutting a silicon wafer from the grown silicon single crystal. a chamber;
A crucible that stores silicon melt,
a heating section that heats the silicon melt;
a cylindrical heat insulator disposed inside the chamber;
a magnetic field applying unit that applies a horizontal magnetic field to the silicon melt in the crucible,
The heat insulating material is a pulled single crystal that is arranged such that the central axis of the heat insulating material is shifted from the central axis of rotation of the crucible by 1.5 mm or more in a horizontal direction perpendicular to the direction of application of the center of the magnetic field of the horizontal magnetic field. Device. In the single crystal pulling apparatus according to claim 4,
In the single crystal pulling device, the heat insulating material is made of carbon fiber.

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