WO2019184129A1

WO2019184129A1 - Magnet for magnetic control of czochralski single crystals and method for magnetic control of czochralski single crystals

Info

Publication number: WO2019184129A1
Application number: PCT/CN2018/094315
Authority: WO
Inventors: 汤洪明; 傅林坚; 刘黎明; 刘赛波
Original assignee: 苏州八匹马超导科技有限公司
Priority date: 2018-03-30
Filing date: 2018-07-03
Publication date: 2019-10-03
Also published as: JP7029733B2; JP2020522457A; CN110129883A

Abstract

Disclosed is a magnet for the magnetic control of Czochralski single crystals, the magnet comprising multiple coils, wherein the multiple coils are connected in series and are arranged around the outer periphery of a single crystal furnace, two oppositely arranged coils of the multiple coils are arranged in a centrally symmetrical manner about the central axis of the single crystal furnace, and the central axis of each of the coils passes through the central point of the single crystal furnace; each of the coils comprises a main coil and a secondary coil which are coaxially arranged, and the secondary coil is provided further away from the single crystal furnace than the main coil; and when the coil is energized, the current direction in the main coil is the opposite to that in the secondary coil. Further disclosed is a method for the magnetic control of Czochralski single crystals.

Description

Magnet for magnetron Czochralski single crystal and method for magnetron controlled Czochralski single crystal

Technical field

The present disclosure relates to the field of semiconductor technology, for example, to a magnet for magnetically controlled Czochralski single crystal and a method of magnetron controlled Czochralski.

Background technique

Monocrystalline silicon is an important component in crystalline materials. It is a raw material for manufacturing semiconductor silicon devices and is widely used in semiconductor technologies such as large-scale integrated circuits, rectifiers, high-power transistors, diodes, and solar panels.

The method of producing single crystal silicon includes a Czochralski method and a suspension zone melting method. At present, single crystal silicon is usually prepared by a Czochralski method, and a rod-shaped single crystal silicon is grown from a melt by a Czochralski method using a single crystal furnace. The basic characteristics of the Czochralski method are mature technology, easy control of crystal shape and electrical parameters, and suitable for growing large diameter single crystal silicon. In recent years, the development of very large scale integrated circuits has higher requirements on the size and quality of single crystal silicon. However, as the crystal size increases and the thermal convection of the melt increases, temperature fluctuations in the melt and local remelting of the crystal may occur, resulting in uneven distribution of impurities such as carbon and oxygen in the crystal, thereby deteriorating the quality of the single crystal silicon. .

In order to solve the above problems, the magnetron straight pull single crystal technology has been gradually developed. On the basis of the Czochralski method, a strong magnetic field is applied outside the single crystal furnace, and the strong magnetic field has the ability to suppress the thermal convection of the melt. By adding a magnetic field of a certain strength and uniformity to the growth system of the Czochralski silicon, it is possible to effectively suppress the heat convection in the silicon melt and control the transport of impurities in the molten silicon. A properly distributed magnetic field can reduce impurities such as oxygen, boron, and aluminum from the quartz crucible into the melt, thereby improving the quality of the single crystal silicon.

The magnetic field generating device of the conventional magnetron-controlled direct drawing method generally uses a permanent magnet material and a conventional electromagnet, and the magnetron straight-drawing method is limited by the saturation magnetization of the permanent magnet material and the power of the conventional electromagnet, so that the magnetic field strength is generated. Often not high, the effect of heat convection suppression on the melt is more common. With the development of superconducting magnet technology, more and more superconducting magnets have replaced conventional electromagnets. Superconducting magnets can generate stronger magnetic fields, and the effect of suppressing the thermal convection of the melt is more obvious. The process can produce larger size or higher quality single crystal silicon.

The magnetic fields generated by the superconducting magnet in the magnetron Czochralski method include a hook magnetic field, a transverse magnetic field, and a longitudinal magnetic field. Among them, the effect of the longitudinal magnetic field on the thermal convection of the melt is not obvious, and has been replaced by the hook magnetic field and the transverse magnetic field.

Since the magnet is disposed outside the single crystal furnace, it is necessary to consider the electromagnetic compatibility problem with the single crystal furnace. The leakage magnetic field generated by the simple coil is generally large, and cannot meet the requirements of the use of general electronic devices or power supplies, and the safety requirements for the human body. Therefore, the superconducting magnet reduces the leakage magnetic field by passively shielding the iron yoke outside the magnet, which causes the weight of the magnet to increase sharply. Generally, the weight of the iron yoke reaches 50% or more of the entire magnet, which increases the manufacturing cost. .

Summary of the invention

The present application proposes a magnet for magnetically controlled Czochralski single crystal and a method of magnetically controlled Czochralski single crystal, which can effectively reduce the leakage magnetic field while avoiding an increase in the weight of the magnet.

The present application provides a magnet for a magnetron Czochralski single crystal, comprising: a plurality of coils connected in series and surrounding an outer circumference of a single crystal furnace, two coils disposed opposite to each other of the plurality of coils Arranging symmetrically about a central axis of the single crystal furnace, and a central axis of each of the coils passes through a center point of the single crystal furnace; each of the coils includes a main coil and a secondary coil disposed coaxially, The secondary coil is disposed away from the single crystal furnace with respect to the primary coil; when the coil is energized, a current direction in the primary coil and a current in the secondary coil are opposite.

Optionally, a preset distance is set between the primary coil and the secondary coil.

Optionally, the central axis of each of the coils is perpendicular to a central axis of the single crystal furnace.

Optionally, a central axis of each of the coils is at a first angle to a central axis of the single crystal furnace.

Optionally, an angle between the central axes of each of the two adjacent ones of the plurality of coils is the same.

Optionally, an angle is formed between central axes of each of the two adjacent coils of the plurality of coils, and the adjacent angles are different, and the opposite angles are the same.

Optionally, the number of the plurality of coils is four; two of the four coils are disposed on a first side of the single crystal furnace, and two of the four coils are oppositely disposed On the second side of the single crystal furnace.

Optionally, an angle between the central axes of the adjacent two coils on the first side of the single crystal furnace and the fourth of the four coils in the single crystal furnace The angle between the central axes of the adjacent two coils on the two sides is a predetermined angle.

Optionally, the preset angle ranges from 50° to 70°.

Optionally, the plurality of coils are superconducting coils.

Optionally, the magnet further comprises a cryogenic vessel; the cryogenic vessel is placed at a periphery of the single crystal furnace.

Optionally, the cryocontainer is filled with a cryogenic liquid, and the plurality of coils are placed in the cryogenic liquid.

Optionally, the plurality of coils are sequentially connected in series, and the main coils of the plurality of coils are sequentially connected in series, and the secondary coils of the plurality of coils are sequentially connected in series, and the primary coil and the secondary coil are connected in series to form a positive pole and a negative pole. Two ports.

Optionally, the plurality of coils are sequentially connected in series, and the first main coil and the secondary coil of the plurality of coils are respectively connected in series, and then connected in series to form two ports of a positive electrode and a negative electrode.

Optionally, the cryogenic container is provided with a pair of binary current leads, which are respectively a first current lead and a second current lead;

The normal temperature end of the first current lead is connected to the positive pole of the power source, and the superconducting end of the first current lead is connected to the positive pole port after the plurality of coils are connected in series;

The normal temperature end of the second current lead is connected to the negative pole of the power source, and the superconducting end of the second current lead is connected to the negative pole port after the plurality of coils are connected in series.

Optionally, the superconducting end of the first current lead is connected to the positive terminal after the plurality of coils are connected in series, and includes:

The first current lead includes a first copper wire end and a first superconducting end connected to the first copper wire end, the first superconducting end extending into the cryogenic liquid and being connected in series with the plurality of coils Positive port connection;

Optionally, the superconducting end of the second current lead is connected to the negative port after the plurality of coils are connected in series, and includes:

The second current lead includes a second copper wire end and a second superconducting end connected to the second copper wire end, the second superconducting end extending into the cryogenic liquid and being connected in series with the plurality of coils Negative port connection;

Optionally, the cryogenic vessel is provided with a refrigerator, and the refrigerator is provided with a cold head stage and a cold head stage which are sequentially arranged from top to bottom;

The cold head stage is configured to cool the first current lead and the second current lead;

The cold head is configured to condense the cryogenic liquid in the cryogenic vessel.

The present application also provides a magnetically controlled Czochralski single crystal method, the magnetic control Czochralski single crystal method comprises:

Arranging the above magnets outside the single crystal furnace and energizing the magnets;

Providing a heater in the single crystal furnace, the heater heating the crucible on which the ingot is placed;

Single crystal silicon was obtained by a Czochralski method.

In the present application, the coil is set as the primary coil and the secondary coil, and currents in opposite directions are respectively transmitted to the primary coil and the secondary coil, so that the magnetic field generated by the secondary coil can effectively cancel the magnetic field generated by the primary coil externally, and is actively shielded. The way to reduce the leakage magnetic field of the magnet. And reduce the weight of the magnet, saving the manufacturing cost of the magnet.

DRAWINGS

1 is a schematic structural view of a magnet and a single crystal furnace according to an embodiment of the present application;

2 is a cross-sectional view of a magnet and a single crystal furnace provided by an embodiment of the present application;

3 is a schematic structural view of the exterior of the magnet and the single crystal furnace provided by the embodiment of the present application;

4 is a comparison diagram of the field strength generated by the magnet provided by the embodiment of the present application and the field strength generated by other forms.

In the picture:

10, single crystal furnace; 20, heater; 30, 坩埚;

1, the coil; 11, the main coil; 12, the secondary coil;

2, a cryogenic container; 21, a first current lead; 22, a second current lead; 23, a pressure relief valve; 25, a signal line interface; 26, a vacuum valve;

24, refrigerator; 241, cold head level; 242, cold head level two.

detailed description

The present embodiment provides a magnet for a magnetron Czochralski single crystal. As shown in FIGS. 1 and 2, the magnet for magnetron CZ pulling single crystal includes a plurality of coils 1, and the plurality of coils 1 Arranged in series and around the outer circumference of the single crystal furnace 10, the two coils 1 disposed opposite to each other in the plurality of coils 1 are symmetrically disposed centering on the central axis of the single crystal furnace 10, and the central axis of each coil 1 passes through a single crystal. a center point of the furnace 10; each of the coils 1 includes a main coil 11 and a secondary coil 12 disposed coaxially, the secondary coil 12 being disposed away from the single crystal furnace 10 with respect to the main coil 11; When the current is applied, the current direction in the main coil 11 and the current in the sub coil 12 are opposite.

In the present embodiment, by providing the coil 1 as the main coil 11 and the sub coil 12, and supplying currents in opposite directions to the main coil 11 and the sub coil 12, the magnetic field generated by the sub coil 12 can effectively cancel the external coil 11 to be externally generated. The magnetic field reduces the leakage magnetic field of the magnet by active shielding, reduces the weight of the magnet, saves the manufacturing cost of the magnet, and avoids the passive shielding method of adding ferromagnetic material outside the coil to reduce the leakage magnetic field. The case where the weight of the magnet is increased.

In an embodiment, a preset distance is provided between the primary coil 11 and the secondary coil 12. In the present embodiment, by providing the sub-coil 12 outside the main coil 11, the effect of the sub-coil 12 canceling the leakage magnetic field generated outside the main coil 11 can be improved. In addition, the preset distance is not limited in this embodiment. In the actual production process, adjustment may be performed as needed to ensure that the secondary coil 12 can cancel the external magnetic field generated by the primary coil 11, thereby reducing the leakage magnetic field of the magnet.

In an embodiment, the center axis of each coil 1 is perpendicular to the central axis of the single crystal furnace 10. In an embodiment, the center axis of each coil 1 is at a first angle to the central axis of the single crystal furnace 10. Since the two coils disposed opposite to each other in the plurality of coils 1 are symmetrically disposed centering on the central axis of the single crystal furnace 10, and the central axes of the adjacent coils 1 are provided with an angle therebetween, each coil 1 is in a single crystal A transverse magnetic field is formed in the furnace 10 to ensure that high quality crystals can be produced by the single crystal furnace 10. In one embodiment, the main coil 11 provides the main magnetic field required for the Czochralski crystal, the secondary coil 12 is the active shielding coil, and the opposite current is supplied to the main coil 11, and the main coil 11 is reduced while reducing the leakage magnetic field. The co-generated magnetic field provides a transverse magnetic field for the Czochralski single crystal.

In one embodiment, the number of coils 1 is four, wherein the four coils 1 comprise two pairs of correspondingly disposed coils 1, two of the four coils 1 being disposed on the first side of the single crystal furnace 10. The other two coils 1 of the four coils 1 are oppositely disposed on the second side of the single crystal furnace 10. An angle between the central axes of the adjacent two coils 1 of the first side of the single crystal furnace 10 in the four coils 1 and the four coils 1 in the single crystal furnace 10 The angle between the central axes of the adjacent two coils 1 on the second side is a predetermined angle. In one embodiment, the preset angle ranges from 50° to 70°.

The preset angle is not limited in this embodiment, and may be adjusted according to actual needs to ensure that the transverse magnetic field generated by the interaction of the primary coil 11 and the secondary coil 12 has a certain strength and uniformity, thereby improving the crystal in the single crystal furnace 10. Manufacturing quality.

As shown in FIG. 2 and FIG. 3, the magnet provided in this embodiment further includes a low temperature container 2, and the low temperature container 2 is disposed at the periphery of the single crystal furnace 10, and the coil 1 is disposed in the low temperature container 2. Wherein, the cryocontainer 2 is filled with a cryogenic liquid, and the coil 1 is placed in a cryogenic liquid. In one embodiment, the cryocontainer 2 is provided with a vacuum interlayer, and the cryocontainer 2 is further provided with a vacuum valve 26, through which the vacuum environment outside the cryogenic liquid can be ensured, thereby providing a heat insulating effect and allowing the cryogenic liquid to be Zero consumption status. In one embodiment, the cryogenic liquid is liquid helium and the vacuum layer is liquid helium dewar. In one embodiment, the coil is cooled by a cryogenic liquid, or may be directly cooled by a refrigerator. The cryogenic liquid and the vacuum interlayer may be of other types, which is not limited in this embodiment.

The cryocontainer 2 is provided with a first current lead 21 and a second current lead 22 connected to a power source. The first current lead 21 and the second current lead 22 are binary current leads, and the first current lead 21 and the second current lead 22 both include a copper end and a superconducting end connected to the copper end, superconducting. The end extends into the cryogenic liquid and is connected to the coil 1. The first current lead 21 and the second current lead 22 are respectively connected to the coil 1 and the power source to form a closed loop, and the power source supplies the coil 1 with a current of a magnetic field.

In addition, the pressure relief valve 23 is also disposed on the cryogenic vessel 2, and since the energy storage of the coil 1 is large, when the coil 1 loses superconductivity under an unexpected situation, a large amount of heat is released, and a large amount of liquid helium is evaporated, causing a large The air pressure can cause damage to the magnet and personal injury in severe cases. At this time, pressure relief is performed through the pressure relief valve 23 to ensure the safety of the magnet.

By setting each of the primary coil 11 and the secondary coil 12 as a superconducting coil, the present embodiment achieves a superconducting state at an ultra-low temperature ambient temperature, and can carry a higher current than a conventional coil, thereby generating a higher magnetic field, thereby ensuring The quality of single crystal silicon production.

The cryogenic vessel 2 is further provided with a refrigerator 24, and the refrigerator 24 is provided with a cold head stage 241 and a cold head stage 242 arranged in order from top to bottom, wherein the cold head stage 241 is arranged to cool the first current. The lead 21 and the second current lead 22 and a radiation shield (not shown) are disposed to condense the cryogenic liquid in the cryocontainer 2.

The low temperature container 2 is further provided with a signal line interface 25, and the signal line is connected to the low temperature container 2 by the signal line interface 25 for detecting signals such as temperature and voltage drop of the coil 1.

As shown in Fig. 4, a comparison chart of leakage magnetic fields in the case of unshielded, ferromagnetic material shielding and active shielding is shown. Among them, the abscissa indicates the distance from the test point to the central magnetic field. Under normal circumstances, when located between 1.6 m and 1.8 m, the strength of the magnetic field is required to be less than 500 Gauss (GS). The requirements for human safety are: the magnetic field strength within 3 meters in the radial direction is less than 60 Gauss (GS). Referring to FIG. 4, the active shielding method of the embodiment can effectively reduce the leakage magnetic field and meet the human body safety requirements.

This embodiment also passes a magnetically controlled Czochralski single crystal method, comprising:

Step 1: Arranging the above magnets outside the single crystal furnace 10 and energizing the magnets.

Among them, energizing the magnet includes energizing the coil 1 and the refrigerator 24 and the like. When the coil 1 in the magnet is energized, a current in the opposite direction is passed through the main coil 11 and the secondary coil 12, so that the magnetic field generated by the secondary coil 12 can effectively cancel the magnetic field generated by the main coil 11 externally, thereby reducing The leakage magnetic field of the magnet. In addition, the use of a passive shielding method of adding a ferromagnetic material outside the coil 1 to reduce the leakage magnetic field, thereby increasing the weight of the magnet, while saving the manufacturing cost of the magnet is avoided.

Step 2: A heater 20 is disposed in the single crystal furnace 10, and the heater 20 heats the crucible 30 on which the ingot is placed. By heating the ingot to a molten state, the transverse magnetic field provided by the coil 1 acts on the melt, and under the action of the magnetic field, the conductive melt has a vortex when flowing, and is subjected to Lorentz force. Under the action of Lenze force, the thermal convection of the melt is suppressed, and oxygen, point defects and other impurities at the melt level are suppressed.

Step 3: Single crystal silicon is obtained by a Czochralski method. Wherein, since the transverse magnetic field generated by the coil 1 has a high magnetic field uniformity (about 3 ‰ to 1%) in a region from about 50 mm (mm) below the liquid level to the liquid surface, the heat convection of the melt is high. The suppression is uniform, so that the obtained single crystal silicon has high purity, the distribution of trace impurities is more uniform, and the quality of single crystal silicon is improved.

Wherein, the Czochralski method refers to, after heating the melt to a molten state, a chemically etched seed crystal is lowered and brought into contact with the melt, and the single crystal furnace 10 is rotated to make the melt on the seed crystal. Crystallize continuously until a certain diameter of crystal is reached.

Claims

A magnet for a magnetron Czochralski single crystal, comprising: a plurality of coils (1) connected in series and surrounding an outer circumference of a single crystal furnace (10), the plurality of coils (1) The two coils (1) disposed opposite each other are symmetrically disposed centering on the central axis of the single crystal furnace (10), and the central axis of each of the coils (1) passes through the center of the single crystal furnace (10) a point; each of the coils (1) includes a main coil (11) and a secondary coil (12) disposed coaxially, the secondary coil (12) being disposed away from the single crystal with respect to the main coil (11) Furnace (10);

When the coil (1) is energized, the direction of current flow in the primary coil (11) and the direction of current flow in the secondary coil (12) are opposite.
The magnet according to claim 1, wherein a predetermined distance is provided between the primary coil (11) and the secondary coil (12).
The magnet according to claim 1 or 2, wherein a central axis of each of said coils (1) is perpendicular to a central axis of said single crystal furnace (10).
A magnet according to claim 1 or 2, wherein a central axis of each of said coils (1) is at a first angle to a central axis of said single crystal furnace (10).
The magnet according to any one of claims 1 to 4, wherein an angle between central axes of each of the two adjacent coils (1) of the plurality of coils (1) is the same.
The magnet according to any one of claims 1 to 4, wherein an angle is formed between central axes of each of the two adjacent coils (1) of the plurality of coils (1), and adjacent The included angles are different, and the opposite angles are the same.
The magnet according to claim 6, wherein the number of the plurality of coils (1) is four; two of the four coils (1) are disposed in the single crystal furnace (10) On the first side, the other two coils (1) of the four coils (1) are oppositely disposed on the second side of the single crystal furnace (10).
The magnet according to claim 7, wherein a sandwich between the central axes of the adjacent two coils (1) of the first side of the single crystal furnace (10) of the four coils (1) An angle between the corner and the central axis of the two adjacent coils (1) of the second side of the single crystal furnace (10) in the four coils (1) is a predetermined angle, wherein The preset angle ranges from 50° to 70°.
The magnet according to any of claims 1-8, wherein the plurality of coils (1) are superconducting coils.
A magnet according to any one of claims 1 to 9, further comprising a cryogenic vessel (2); said cryogenic vessel (2) being disposed at a periphery of said single crystal furnace (10).
The magnet according to claim 10, wherein said cryogenic vessel (2) is filled with a cryogenic liquid, and said plurality of coils (1) are placed in said cryogenic liquid.
A magnet according to claim 10 or 11, further comprising:

a normal temperature end of the first current lead (21) is connected to a positive pole of the power source, and a superconducting end of the first current lead (21) is connected to a positive terminal of the coil;

A normal temperature end of the second current lead (22) is connected to a negative pole of the power source, and a superconducting end of the second current lead (22) is connected to a negative terminal of the coil.
The magnet of claim 12, wherein the superconducting end of the first current lead (21) is coupled to the positive terminal of the coil, comprising:

The first current lead (21) includes a first copper wire end and a first superconducting end connected to the first copper wire end, the first superconducting end projecting into the cryogenic liquid and with the coil Positive port connection;

The superconducting end of the second current lead (22) is connected to the negative port of the coil, and includes:

The second current lead (21) includes a second copper wire end and a second superconducting end connected to the second copper wire end, the second superconducting end projecting into the cryogenic liquid and the coil Negative port connection;
A magnet according to claim 12 or 13, further comprising:

The cryogenic vessel (2) is provided with a refrigerator (24), and the refrigerator (24) is provided with a cold head stage (241) and a cold head stage (242) arranged in order from top to bottom;

The cold head stage (241) is configured to cool the first current lead (21) and the second current lead (22);

The cold head secondary (242) is arranged to condense the cryogenic liquid in the cryogenic vessel (2).
A method for magnetically controlled Czochralski single crystal, comprising:

Arranging the magnet of any of claims 1-14 outside the single crystal furnace (10) and energizing the magnet;

A heater (20) is disposed in the single crystal furnace (10), and the heater (20) heats the crucible (30) on which the ingot is placed;

Single crystal silicon was obtained by a Czochralski method.