CN116206846A - Superconducting magnet for magnetically controlled Czochralski single crystal and cooling method thereof - Google Patents

Abstract

The application discloses a superconducting magnet and a cooling method thereof for magnetically controlled Czochralski single crystal. The superconducting magnet includes: a superconducting coil; a cold conducting plate, the superconducting coil is arranged on the side of the cold plate; a liquid nitrogen tank, The interior is used to store liquid nitrogen, one end of the cold guide plate is connected to the liquid nitrogen tank, and the liquid nitrogen tank is used to cool the superconducting coil to the first temperature through liquid nitrogen; GM refrigerator, the cold head of the GM refrigerator and the cold guide plate connected, the GM refrigerator is used to cool down the cold plate, and then cool the superconducting coil to a second temperature, the second temperature is lower than the first temperature, and the second temperature is lower than or equal to the critical temperature of the superconducting coil. This application first uses liquid nitrogen to cool the superconducting coil to a temperature of about 77K, and then uses a GM refrigerator to cool the superconducting coil to a temperature of about 4.2K. The combination of the two cooling methods not only has a lower cooling cost , and can shorten the cooling time to 8‑10 days, which can greatly save time and cost compared to simply using GM refrigerators.

Description

Superconducting magnet for magnetron Czochralski single crystal and its cooling method

technical field

The present application relates to the technical field of semiconductor production equipment, in particular to superconducting magnets for magnetron Czochralski single crystals and cooling methods thereof.

Background technique

As an important raw material for semiconductor devices, monocrystalline silicon is widely used in large-scale integrated circuits. Adding a certain strength magnetic field to the growth system of Czochralski single crystal silicon can effectively improve the uniformity and quality of single crystal silicon rods.

A superconducting magnet used for magnetically controlled Czochralski single crystal needs to place a single crystal furnace and supporting lifting devices in its central hole, so it takes up a lot of space. Moreover, in order to increase the magnetic field strength and the range of the uniform magnetic field, superconducting magnets are generally large in size, with a diameter of about 1.6 meters to 2.4 meters. The superconducting coil needs to be cooled from room temperature 300K to 4.2K. Liquid helium or GM refrigerators can be used for cooling. Although liquid helium can cool down quickly, liquid helium is a scarce resource, so it is expensive, resulting in higher cooling costs. Although the cost of using GM refrigerators is lower, it consumes more energy for cooling. Even if four refrigeration machines are used to cool down at the same time, it will take about 17 days to cool down.

Contents of the invention

The embodiment of the present application provides a superconducting magnet for magnetron Czochralski single crystal and its cooling method, which are used to solve the problems of high cooling cost of liquid helium and long cooling time of GM refrigerator in the prior art.

On the one hand, the embodiment of the present application provides a superconducting magnet for magnetron Czochralski single crystal, including:

superconducting coils;

The cold plate, the superconducting coil is arranged on the side of the cold plate;

The liquid nitrogen box is used to store liquid nitrogen inside, and one end of the cold guide plate is connected to the liquid nitrogen box, and the liquid nitrogen box is used to cool the superconducting coil to the first temperature through liquid nitrogen;

GM refrigerator, the cold head of the GM refrigerator is connected to the cold guide plate, and the GM refrigerator is used to cool the cold guide plate, thereby cooling the superconducting coil to the second temperature, the second temperature is lower than the first temperature, and the second The temperature is lower than or equal to the critical temperature of the superconducting coil.

On the other hand, the embodiment of the present application also provides a cooling method for a superconducting magnet of a magnetron Czochralski single crystal, including:

Transport liquid nitrogen to the liquid nitrogen tank;

Conduct cooling from the liquid nitrogen tank to the superconducting coil through the cold conducting plate, so that the superconducting coil is cooled to the first temperature;

After the superconducting coil is cooled to the first temperature, start the GM refrigerator to cool down the cold plate;

The cold conduction plate continues to conduct cold to the superconducting coil, so that the superconducting coil is cooled to the second temperature.

The superconducting magnet and its cooling method for magnetron Czochralski single crystal in the present application have the following advantages:

First use liquid nitrogen to cool the superconducting coil to a temperature of about 77K, and then use a GM refrigerator to cool the superconducting coil to a temperature of about 4.2K. The combination of the two cooling methods not only has a lower cooling cost, but also The cooling time can be shortened to 8-10 days, which can greatly save time and cost compared to simply using GM refrigerators.

Description of drawings

In order to more clearly illustrate the technical solutions in the embodiments of the present application or the prior art, the following will briefly introduce the drawings that need to be used in the description of the embodiments or the prior art. Obviously, the accompanying drawings in the following description are only These are some embodiments of the present application. Those skilled in the art can also obtain other drawings based on these drawings without creative work.

FIG. 1 is a schematic structural diagram of a superconducting magnet used for magnetron Czochralski single crystal provided in an embodiment of the present application.

Description of reference numerals: 1 - superconducting coil, 2 - cryostat, 3 - cold guide plate, 4 - liquid nitrogen tank, 5 - liquid nitrogen tube, 6 - GM refrigerator.

Detailed ways

The following will clearly and completely describe the technical solutions in the embodiments of the application with reference to the drawings in the embodiments of the application. Apparently, the described embodiments are only some of the embodiments of the application, not all of them. Based on the embodiments in this application, all other embodiments obtained by persons of ordinary skill in the art without making creative efforts belong to the scope of protection of this application.

FIG. 1 is a schematic structural diagram of a superconducting magnet used for magnetron Czochralski single crystal provided in an embodiment of the present application. The embodiment of the present application provides a superconducting magnet for magnetron Czochralski single crystal, including:

superconducting coil 1;

The cold conducting plate 3, the superconducting coil 1 is arranged on the side of the cold plate 1;

The liquid nitrogen tank 4 is used to store liquid nitrogen inside, and one end of the cold guide plate 3 is connected to the liquid nitrogen tank 4, and the liquid nitrogen tank 4 is used to cool the superconducting coil 1 to the first temperature through liquid nitrogen;

GM refrigerator 6, the cold head of the GM refrigerator 6 is connected to the cold conducting plate 3, and the GM refrigerator 6 is used to cool the cold conducting plate 3, thereby cooling the superconducting coil 1 to a second temperature, which is lower than the first temperature a temperature, and the second temperature is lower than or equal to the critical temperature of the superconducting coil 1 .

Exemplarily, there may be multiple superconducting coils 1. In the embodiment of the present application, there are four superconducting coils 1, and the four superconducting coils 1 are arranged around the periphery of a vertical axis in a center-symmetric manner. And the radial direction of each superconducting coil 1 is parallel to the vertical axis. When the superconducting coil 1 is cooled to the second temperature, it is in a superconducting state. In the superconducting state, the resistance is zero, so it can withstand strong current without generating Joule heat, and the magnetic fields generated by the four superconducting coils 1 act together on the inner area surrounded by them, so that a strong magnetic field can be provided to the Czochralski single crystal environment set in the inner area.

The cold-conducting plate 3 can be made of copper, and the superconducting coil 1 is fixedly arranged on the outer surface or the inner surface of the cold-conducting plate 3. After the cold-conducting plate 3 and the liquid nitrogen tank 4 are connected, the liquid nitrogen in the liquid nitrogen tank 4 That is, the heat of the superconducting coil 1 can be absorbed by the cold conducting plate 3 , thereby reducing the temperature of the superconducting coil 1 .

In the embodiment of the present application, the first temperature is 77K, and the second temperature is 4.2K. The quantity of liquid nitrogen tank 4 is identical with the quantity of superconducting coil 1, also is four, and four liquid nitrogen tanks 4 are divided into two groups, two liquid nitrogen tanks 4 in each group are fixedly connected together, and one group of liquid nitrogen tanks A nitrogen box 4 is set between two adjacent superconducting coils 1 , and another group of liquid nitrogen boxes 4 is set between the other two adjacent superconducting coils 1 .

Specifically, the two liquid nitrogen tanks 4 in one group can also be connected by a copper-made cold guide plate 3, so that heat can also be transferred between the two liquid nitrogen tanks 4, and the cold conduction plate connecting the liquid nitrogen tank 4 The plate 3 can be directly connected with the cold conducting plate connected to the superconducting coil 1, or integrally formed, so that the heat can be delivered more quickly.

Further, the number of GM refrigerators 6 is also four, and each GM refrigerator 6 is connected to one cold guide plate 3 respectively.

In a possible embodiment, the superconducting magnet also includes: a cryostat 2, the superconducting coil 1, the cold conducting plate 3 and the liquid nitrogen tank 4 are all arranged inside the cryostat 2, and the cryostat 2 is used to isolate external heat.

For example, since the ambient temperature of the superconducting coil 1 is very low, only about 4.2K, and the external temperature is very high relative to this low temperature environment, about 300K, it is necessary to use a cryostat 2 to place the superconducting coil The environment where 1 is located is thermally isolated from the external environment, so as to avoid or reduce the thermal load on the superconducting coil 1 caused by the external high temperature environment.

In the embodiment of the present application, the cryostat 2 includes: a radiation screen, located outside the superconducting coil 1, the cold guide plate 3 and the liquid nitrogen tank 4; a vacuum Dewar, arranged outside the radiation screen, and the vacuum Dewar and radiation The space between the screens is in a vacuum state.

Since the superconducting magnet needs to be equipped with equipment such as a single crystal furnace, the superconducting magnet has a circular cylindrical structure as a whole, and correspondingly, the cryostat 2 also has a circular cylindrical structure. Both the radiation screen and the vacuum dewar can be made of materials with low thermal conductivity, and the vacuum environment between the radiation screen and the vacuum dewar can greatly reduce the superconducting coil 1 located inside the radiation screen and the superconducting coil 1 located outside the vacuum dewar. The heat exchange between the external environments creates a low-temperature and constant environment for the superconducting coil 1 .

In a possible embodiment, the GM refrigerator 6 is a secondary refrigerator, the primary cold head of the GM refrigerator 6 is connected to the radiation screen, and the secondary cold head of the GM refrigerator 6 is connected to the cold guide plate 3 .

Exemplarily, the GM refrigerator 6 in the form of two-stage refrigeration has a primary cold head and a secondary cold head, wherein the primary cold head can reach a low temperature of 35K at the lowest, and the secondary cold head can reach a low temperature of 2K at the lowest, so it can Meet the cooling needs in this application. This application uses a primary cold head to reduce the temperature of the radiation screen to about 77K, reducing the temperature difference between the radiation screen and the superconducting coil 1, thereby reducing the heat exchange between the two. The temperature of the plate 3 is lowered to about 4.2K, so that the temperature of the superconducting coil 1 installed on the heat conducting plate 3 is also lowered to the critical temperature or below, and then enters the superconducting state.

In a possible embodiment, a liquid nitrogen pipe 5 is provided on the outer surface of the radiation shield, and the end of the liquid nitrogen pipe 5 is connected to the liquid nitrogen tank 4 .

Exemplarily, there are two liquid nitrogen pipes 5 , one of which is used to transport liquid nitrogen into the liquid nitrogen tank 4 , and the other liquid nitrogen pipe 5 is used to discharge the vaporized nitrogen in the liquid nitrogen tank 4 .

When there are multiple liquid nitrogen tanks 4, each liquid nitrogen tube 5 needs to be connected to each liquid nitrogen tank 4, and the connection can be in series or in parallel. In the embodiment of the present application, the liquid nitrogen pipe 5 is made of a material with low thermal conductivity, such as stainless steel. And the liquid nitrogen tube 5 is solidified on the outer surface of the radiation screen by low-temperature glue, and the low-temperature glue can not only connect the liquid nitrogen tube 5 and the radiation screen fixedly, but also form a thermal barrier between the liquid nitrogen tube 5 and the radiation screen to reduce heat exchange resulting in heat leakage.

The working process of the superconducting magnet in this application is as follows: the superconducting coil 1 needs to drop from room temperature 300K to 4.2K to enter the superconducting state of zero resistance, and then provide a strong magnetic field environment for Czochralski single crystal silicon under the action of a large current. But in the 300K～77K temperature zone, the heat capacity of the superconducting coil 1 is larger than that of 77K～4.2K, and the temperature drop is also slower. Therefore, this application first performs liquid nitrogen precooling, and the liquid nitrogen is input from the infusion port of the liquid nitrogen pipe 5, and Open the exhaust port of the liquid nitrogen pipe 5 to prevent the internal liquid nitrogen from vaporizing and suppressing pressure. The liquid nitrogen flows from the liquid nitrogen pipe 5 into the liquid nitrogen tank 4 to quickly cool down the radiation screen and the superconducting coil 1 at 300K-77K, and this process takes about 2 days. When the superconducting coil 1 reaches 77K, pressurize the liquid nitrogen tube 5 to discharge excess liquid nitrogen, and then turn on the GM refrigerator 6 to start conduction cooling. This process takes about 6-8 days. The whole cooling process takes about 8-10 days.

The embodiment of the present application also provides a cooling method for a superconducting magnet for magnetron Czochralski single crystal, comprising the following steps:

Transport liquid nitrogen to the liquid nitrogen tank 4;

Conduct cooling from the liquid nitrogen tank 4 to the superconducting coil 1 through the cold conducting plate 3, so that the superconducting coil 1 is cooled to the first temperature;

After the superconducting coil 1 is cooled to the first temperature, start the GM refrigerator 6 to cool down the cold plate 3;

The cold conduction plate 3 continues to conduct cold to the superconducting coil 1, so that the superconducting coil 1 is cooled to the second temperature.

While preferred embodiments of the present application have been described, additional changes and modifications to these embodiments can be made by those skilled in the art once the basic inventive concept is appreciated. Therefore, the appended claims are intended to be construed to cover the preferred embodiment and all changes and modifications which fall within the scope of the application.

Obviously, those skilled in the art can make various changes and modifications to the application without departing from the spirit and scope of the application. In this way, if these modifications and variations of the present application fall within the scope of the claims of the present application and their equivalent technologies, the present application is also intended to include these modifications and variations.

Claims (8)

1. A superconducting magnet for magnetron Czochralski single crystal, characterized in that it comprises: superconducting coil (1); A cold conducting plate (3), the superconducting coil (1) is arranged on the side of the cold plate (1); Liquid nitrogen box (4), inside is used for storing liquid nitrogen, and one end of described cold guide plate (3) is connected with described liquid nitrogen box (4), and described liquid nitrogen box (4) is used for passing all The superconducting coil (1) is cooled to a first temperature; GM refrigerator (6), the cold head of the GM refrigerator (6) is connected to the cold guide plate (3), and the GM refrigerator (6) is used to cool the cold guide plate (3), Further, the superconducting coil (1) is cooled to a second temperature, the second temperature is lower than the first temperature, and the second temperature is lower than or equal to the critical temperature of the superconducting coil (1). 2. the superconducting magnet for magnetron CZ single crystal according to claim 1, is characterized in that, also comprises: A cryostat (2), the superconducting coil (1), the cold conducting plate (3) and the liquid nitrogen tank (4) are all arranged inside the cryostat (2), and the cryostat (2) Used to insulate from external heat. 3. the superconducting magnet for magnetron Czochralski single crystal according to claim 2, is characterized in that, described cryostat (2) comprises: Radiation screen, located outside the superconducting coil (1), cold conducting plate (3) and liquid nitrogen tank (4); A vacuum dewar is arranged outside the radiation screen, and the space between the vacuum dewar and the radiation screen is in a vacuum state. 4. The superconducting magnet for magnetron Czochralski according to claim 3, characterized in that, the GM refrigerator (6) is a secondary refrigerator, and one of the GM refrigerators (6) The secondary cold head is connected with the radiation screen, and the secondary cold head of the GM refrigerator (6) is connected with the cold guide plate (3). 5. the superconducting magnet for magnetron CZ single crystal according to claim 3, is characterized in that, the outer surface of described radiation shield is provided with liquid nitrogen tube (5), and described liquid nitrogen tube (5) ) is connected with the liquid nitrogen tank (4). 6. the superconducting magnet for magnetron Czochralski according to claim 5, is characterized in that, the quantity of described liquid nitrogen tube (5) is two, and wherein one described liquid nitrogen tube (5) It is used to deliver liquid nitrogen into the liquid nitrogen tank (4), and the other liquid nitrogen pipe (5) is used to discharge the vaporized nitrogen in the liquid nitrogen tank (4). 7. The superconducting magnet for magnetron Czochralski single crystal according to claim 5, characterized in that, the liquid nitrogen tube (5) is solidified on the outer surface of the radiation screen by low-temperature glue. 8. be applied to the cooling method of the superconducting magnet that is used for magnetron Czochralski single crystal described in any one of claim 1-7, it is characterized in that, comprises the following steps: Delivering liquid nitrogen to the liquid nitrogen tank (4); The liquid nitrogen tank (4) conducts cooling to the superconducting coil (1) through the cold conducting plate (3), so that the superconducting coil (1) is cooled to a first temperature; After the superconducting coil (1) is cooled to the first temperature, start the GM refrigerator (6) to cool down the cold conducting plate (3); The cold conduction plate (3) continues to conduct cold to the superconducting coil (1), so that the superconducting coil (1) is cooled to a second temperature.

Images