Single crystal furnace and monocrystalline silicon preparation method

Abstract

The invention provides a single crystal furnace and a monocrystalline silicon preparation method, and belongs to the technical field of semiconductors. The single crystal furnace comprises a furnace body; the graphite crucible is positioned in the furnace body; the quartz crucible is positioned in the graphite crucible and is used for containing a multi-silicon crystal material to be molten; the cylindrical side heater is coaxial with the furnace body and is arranged on the outer side of the graphite crucible in a sleeving manner; the bottom heater is arranged at the bottom of the graphite crucible; the guide cylinder is positioned above the quartz crucible; the controller is connected with the side heater and the bottom heater through electrodes and used for controlling power output to the side heater and the bottom heater. According to the invention, a uniform and controllable thermal environment can be provided, the yield of the silicon single crystal rod is improved, and the quality of the drawn silicon single crystal rod is ensured.

Description

Technical Field

[0001] The present invention relates to the field of semiconductor technology, in particular to a single crystal furnace and a method for preparing single crystal silicon. Background Art

[0002] Nowadays, most of the single crystal silicon is prepared by the Czochralski method. The Czochralski method (CZ method) is to put a high-purity polysilicon block into a quartz crucible, and in a vacuum environment, use argon as a protective gas to heat the polysilicon to above 1420°C, and then maintain this temperature for a period of time to allow the silicon material to melt and change from solid to liquid. After the temperature stabilizes to the target temperature, a rod-shaped crystal seed (seed crystal) with a diameter of only about 10mm is immersed in the melt, so that the seed crystal with a certain crystal orientation is melted with the melt to lead out a thin-necked crystal with a diameter of 3 to 5mm to eliminate crystal dislocations, and then the shoulder release, shoulder rotation, equal diameter, tailing, cooling and other processes are performed to complete the growth process of single crystal silicon.

[0003] The heaters in the thermal field of a traditional vertical pulling furnace include bottom heaters and side heaters, which are controlled together. If the bottom heater is used for heating, the side heater cannot heat up again when the temperature in the crystal pulling furnace has met the requirements, resulting in premature crystallization of the tail part due to insufficient temperature supply during the process of pulling the crystal rod, causing wire breakage, yield loss and quality abnormalities. Summary of the invention

[0004] The technical problem to be solved by the present invention is to provide a single crystal furnace and a method for preparing single crystal silicon, which can provide a uniform and controllable thermal environment, improve the yield of single crystal silicon rods, and ensure the quality of the drawn single crystal silicon rods.

[0005] To solve the above technical problems, the embodiments of the present invention provide the following technical solutions:

[0006] In one aspect, an embodiment of the present invention provides a single crystal furnace, comprising:

[0007] Furnace body;

[0008] a graphite crucible located in the furnace body;

[0009] A quartz crucible located inside the graphite crucible, the quartz crucible being used to contain polysilicon crystal material to be melted;

[0010] A cylindrical side heater coaxial with the furnace body and sleeved on the outside of the graphite crucible;

[0011] A bottom heater disposed at the bottom of the graphite crucible;

[0012] a flow guide tube located above the quartz crucible;

[0013] A controller is connected to the side heater and the bottom heater through electrodes respectively, and is used for controlling power output to the side heater and the bottom heater.

[0014] In some embodiments, the side heater includes an upper side heater and a lower side heater sequentially arranged along the axial direction of the furnace body, and the upper side heater and the lower side heater are independent of each other.

[0015] In some embodiments, a height ratio of the upper side heater to the lower side heater is 3:1.

[0016] In some embodiments, the upper side heater and the lower side heater are supported by conductive graphite feet, respectively, and are disposed on the furnace bottom of the furnace body.

[0017] In some embodiments, the bottom heater is shaped like a basin structure that fits the bottom of the graphite crucible.

[0018] In some embodiments, the side heater includes at least three heating coils.

[0019] In some embodiments, the heating coil is made of a resistive heating material, and the resistive heating material includes at least one of the following: silicon carbide coated graphite, high purity graphite, tungsten, metal, and carbon fiber composite.

[0020] The embodiment of the present invention further provides a method for preparing single crystal silicon, which is applied to the single crystal furnace as described above, comprising:

[0021] The polysilicon material to be melted is placed in the quartz crucible, the furnace body is sealed and evacuated to allow inert gas to pass through, the side heater and the bottom heater are started to melt the polysilicon material; after the polysilicon material is completely melted, the seed crystal is lowered to the vicinity of the silicon melt surface to carry out a growth process including welding, shoulder release, shoulder rotation and equal diameter.

[0022] In some embodiments, it also includes:

[0023] The power output to the side heater and the bottom heater is controlled respectively by a controller.

[0024] In some embodiments, when the crystal rod is pulled to the end, the power of the bottom heater is reduced, and the power of the bottom heater is reduced by 1 to 20 KW every 1 to 10 minutes, and the bottom heater is turned off after the crystal rod is pulled to the end.

[0025] The embodiments of the present invention have the following beneficial effects:

[0026] In the above scheme, a bottom heater and a side heater are set for the thermal field of the single crystal furnace. The controller can control the power output to the side heater and the bottom heater respectively, optimize the thermal field, better maintain the stability of the thermal field, and provide a stable and uniform thermal environment. When the crystal rod is pulled to the tail stage, the bottom heater can be reduced or gradually turned off, and heat is provided to the tail crystal rod only by increasing the power of the side heater, without the problem of insufficient heat supply at the tail causing premature crystallization and disconnection. In addition, each heater can be separated independently, which is convenient for later disassembly, maintenance, installation and replacement; in addition, the power of different heaters can be controlled separately at different preparation stages of single crystal silicon, which is convenient for controlling the temperature gradient of the crystal and the melt at the solid-liquid interface, improving heat transfer efficiency, increasing the service life of the thermal field, and reducing energy consumption. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 It is a structural schematic diagram of a single crystal furnace in the related art;

[0028] Figure 2 It is a schematic structural diagram of a heater of a single crystal furnace according to an embodiment of the present invention.

[0029] The following are the descriptions of the reference numerals:

[0030] 1 Water cooling jacket

[0031] 2 Guide tube

[0032] 3 Quartz crucible

[0033] 4 Graphite Crucible

[0034] 5 Bottom heater

[0035] 6 Ventilation pipe

[0036] 7 Base

[0037] 8 Side heater

[0038] 9 Support

[0039] 10. Heat Insulator

[0040] 11 Furnace bottom

[0041] 12 Electrodes

[0042] 13 Graphite foot board

[0043] 14 Bottom heater

[0044] 15 Lower side heater

[0045] 16 Upper side heater DETAILED DESCRIPTION

[0046] In order to make the technical problems, technical solutions and advantages to be solved by the embodiments of the present invention more clear, a detailed description will be given below with reference to the accompanying drawings and specific embodiments.

[0047] In order to make the purpose, technical solution and advantages of the embodiment of the present invention clearer, the technical solution of the embodiment of the present invention will be clearly and completely described below in conjunction with the drawings of the embodiment of the present invention. Obviously, the described embodiment is a part of the embodiment of the present invention, not all of the embodiments. Based on the described embodiment of the present invention, all other embodiments obtained by ordinary technicians in this field belong to the scope of protection of the present invention.

[0048] Nowadays, most of the single crystal silicon is prepared by the Czochralski method. The Czochralski method (CZ method) is to put a high-purity polysilicon block into a quartz crucible, and in a vacuum environment, use argon as a protective gas to heat the polysilicon to above 1420°C, and then maintain this temperature for a period of time to allow the silicon material to melt and change from solid to liquid. After the temperature stabilizes to the target temperature, a rod-shaped crystal seed (seed crystal) with a diameter of only about 10mm is immersed in the melt, so that the seed crystal with a certain crystal orientation is melted with the melt to lead out a thin-necked crystal with a diameter of 3 to 5mm to eliminate crystal dislocations, and then the shoulder release, shoulder rotation, equal diameter, tailing, cooling and other processes are performed to complete the growth process of single crystal silicon.

[0049] The thermal field structure of the single crystal furnace mainly includes a heating assembly for heating and melting polysilicon materials, a heat shield for blocking heat loss, a graphite heater surrounding the quartz crucible, a crucible support rod and a crucible tray, etc. In order to prepare high-quality single crystal silicon, a uniform thermal environment around the interface is formed and maintained, so that the single crystal can grow to a larger length while maintaining the quality and pulling speed of the single crystal and making it easy to control the pulling speed. More specifically, the polysilicon material and the silicon melt continuously receive heat from the heater, and the heat loss is blocked by the heat shield structure to maintain a predetermined temperature gradient.

[0050] In the process of preparing large-size silicon single crystals by Czochralski method, due to the large amount of polysilicon feed, in order to meet the requirements of thermal field temperature gradient and ensure small temperature fluctuation during crystal pulling, heaters located on the side of the crucible and heaters located at the bottom of the crucible are often used to heat and melt the polysilicon material to achieve control of the temperature field. Figure 1 As shown, the single crystal furnace of the related art includes a water cooling jacket 1, a guide tube 2, a quartz crucible 3, a graphite crucible 4, a bottom heater 5, a ventilation pipe 6, a base 7, a side heater 8, a support 9 and a heat insulator 10. Among them, the bottom heater 5 and the side heater 8 are controlled uniformly, resulting in premature crystallization of the tail part due to insufficient temperature supply during the process of pulling the crystal rod, thereby causing a wire breakage problem, resulting in yield loss and quality abnormality.

[0051] The embodiments of the present invention provide a single crystal furnace and a method for preparing single crystal silicon, which can provide a uniform and controllable thermal environment, improve the yield of single crystal silicon rods, and ensure the quality of the drawn single crystal silicon rods.

[0052] An embodiment of the present invention provides a single crystal furnace, comprising:

[0053] Furnace body;

[0054] a graphite crucible located in the furnace body;

[0055] A quartz crucible located inside the graphite crucible, the quartz crucible being used to contain polysilicon crystal material to be melted;

[0056] A cylindrical side heater coaxial with the furnace body and sleeved on the outside of the graphite crucible;

[0057] A bottom heater disposed at the bottom of the graphite crucible;

[0058] a flow guide tube located above the quartz crucible;

[0059] A controller is connected to the side heater and the bottom heater through electrodes respectively, and is used for controlling power output to the side heater and the bottom heater.

[0060] In this embodiment, a bottom heater and a side heater are set for the thermal field of the single crystal furnace. The controller can control the power output to the side heater and the bottom heater respectively, optimize the thermal field, better maintain the stability of the thermal field, and provide a stable and uniform thermal environment. When the crystal rod is pulled to the tail stage, the bottom heater can be reduced or gradually turned off, and heat is provided to the tail crystal rod only by increasing the power of the side heater, without the problem of insufficient heat supply at the tail causing premature crystallization and disconnection. In addition, each heater can be separated independently, which is convenient for later disassembly, maintenance, installation and replacement; in addition, the power of different heaters can be controlled separately at different preparation stages of single crystal silicon, which is convenient for controlling the temperature gradient of the crystal and the melt at the solid-liquid interface, improving heat transfer efficiency, increasing the service life of the thermal field, and reducing energy consumption.

[0061] In this embodiment, Figure 2As shown, the side heater includes an upper side heater 16 and a lower side heater 15 arranged in sequence along the axial direction of the furnace body. The upper side heater 16 and the lower side heater 15 are independent of each other, and the controller can control the power output to the upper side heater 16 and the lower side heater 15 respectively, so that the power of different heaters can be controlled separately according to demand, the thermal field can be optimized, the stability of the thermal field can be better maintained, and a stable and uniform thermal environment can be provided. The height ratio of the upper side heater 16 to the lower side heater 15 is 3:1, which is conducive to fully mobilizing the heat supply of the crystal rod in the later stage. The main force of the late heater is mainly the upper side heater. When the crystal rod is pulled to the tail stage, heat can be provided to the tail crystal rod only by increasing the power of the upper side heater 16, and there will be no premature crystallization and wire breakage due to insufficient heat supply at the tail.

[0062] In an exemplary embodiment of the present invention, the side heater includes at least three heating coils, and the multiple heating coils are independent of each other, so that the power of different heating coils can be controlled according to needs, the thermal field can be optimized, the stability of the thermal field can be better maintained, and a stable and uniform thermal environment can be provided. The heating coil can be a block ring coil, a double circular coil or other shapes, and the heating coil is made of resistive heating material, such as silicon carbide coated graphite, high purity graphite, tungsten, metal, carbon fiber composite or other suitable materials, and the coil spacing, material, and power are adjusted according to needs.

[0063] In this embodiment, Figure 2 As shown, the bottom heater 13 is shaped like a basin-shaped structure that fits the bottom of the graphite crucible, which can effectively wrap the graphite crucible. While improving the stability of the graphite crucible, it can effectively increase the heating area of ​​the crucible, so that the crucible is heated evenly, which can effectively improve and preserve the heat loss problem, thereby saving energy loss. In addition, it can also effectively shorten the melting time of the silicon material, thereby effectively improving the production efficiency in the crystal pulling process, and can also improve the quality of the crystal rod.

[0064] like Figure 2 As shown, the upper side heater 16 and the lower side heater 15 are supported by conductive graphite foot plates 14, respectively, and are arranged on the furnace bottom 11 of the furnace body. The heaters can be connected to the graphite foot plates 14 by bolts; in addition, the bottom heater 13 is also arranged on the furnace bottom 11 of the furnace body. Six electrodes 12 are arranged on the furnace bottom 11, the upper side heater 16 is connected to two electrodes 12 on the furnace bottom 11 through the graphite foot plates 14, the lower side heater 15 is connected to two electrodes 12 on the furnace bottom 11 through the graphite foot plates 14, and the bottom heater 13 is connected to two electrodes 12 on the furnace bottom 11, that is, each heater needs two electrodes 12 to be controlled, and different heaters are controlled by independent electrodes without interfering with each other.

[0065] In the technical solution of this embodiment, the side heater is changed to two-stage heating, making full use of the independent control heating function to achieve segmented temperature control. After pulling to the tail of the crystal rod, the power of the bottom heater 13 can be reduced or the bottom heater 13 can be turned off, and only the upper side heater 16 is used for heating, which can effectively save energy. The technical solution of this embodiment only requires the heater to be modified, and the cost is low.

[0066] An embodiment of the present invention further provides a method for preparing single crystal silicon, which is applied to the single crystal furnace as described above, comprising:

[0067] The polysilicon material to be melted is placed in the quartz crucible, the furnace body is sealed and evacuated to allow inert gas to pass through, the side heater and the bottom heater are started to melt the polysilicon material; after the polysilicon material is completely melted, the seed crystal is lowered to the vicinity of the silicon melt surface to carry out a growth process including welding, shoulder release, shoulder rotation and equal diameter.

[0068] In some embodiments, it also includes:

[0069] The power output to the side heater and the bottom heater is controlled by the controller. Each heater can be separated independently, which is convenient for later disassembly, maintenance, installation and replacement; in addition, the power of different heaters can be controlled separately at different stages of single crystal silicon preparation, which is convenient for controlling the temperature gradient of the crystal and the melt at the solid-liquid interface, improving heat transfer efficiency, increasing the service life of the thermal field, and reducing energy consumption.

[0070] In some embodiments, when the crystal rod is pulled to the end, the power of the bottom heater is reduced, and the power of the bottom heater is reduced by 1 to 20 KW every 1 to 10 minutes, and the bottom heater is turned off after the crystal rod is pulled to the end.

[0071] After being pulled to the tail of the crystal rod, the power of the bottom heater 13 can be gradually reduced, and only the side heaters such as the upper side heater 16 can be used for heating, which can effectively save energy; and the power of the side heaters such as the upper side heater 16 can be increased to provide sufficient heat to the tail crystal rod, without insufficient heating at the tail causing premature crystallization and wire breakage.

[0072] The tail of the crystal rod is about 2000 mm in length, and the interval duration of the power reduction of the bottom heater 13 and the adjustment step length of the power reduction can be determined according to the actual length of the crystal rod after the tail is completed.

[0073] Unless otherwise defined, the technical terms or scientific terms used in this disclosure should be understood by people with ordinary skills in the field to which the present invention belongs. "First", "second" and similar words used in this disclosure do not indicate any order, quantity or importance, but are only used to distinguish different components. "Include" or "comprise" and similar words mean that the elements or objects appearing before the word cover the elements or objects listed after the word and their equivalents, without excluding other elements or objects. "Connect" or "connected" and similar words are not limited to physical or mechanical connections, but may include electrical connections, whether direct or indirect. "Up", "down", "left", "right" and the like are only used to indicate relative positional relationships. When the absolute position of the described object changes, the relative positional relationship may also change accordingly.

[0074] The above is a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principles of the present invention. These improvements and modifications should also be regarded as the scope of protection of the present invention.

Claims

1. A single crystal furnace, characterized in that: include: Furnace body; a graphite crucible located in the furnace body; A quartz crucible located inside the graphite crucible, the quartz crucible being used to contain polysilicon crystal material to be melted; A cylindrical side heater coaxial with the furnace body and sleeved on the outside of the graphite crucible; A bottom heater disposed at the bottom of the graphite crucible; a flow guide tube located above the quartz crucible; A controller is connected to the side heater and the bottom heater through electrodes respectively, and is used to control the power output to the side heater and the bottom heater.

2. The single crystal furnace according to claim 1, characterized in that: The side heater includes an upper side heater and a lower side heater which are sequentially arranged along the axial direction of the furnace body, and the upper side heater and the lower side heater are independent of each other.

3. The single crystal furnace according to claim 2, characterized in that: A height ratio of the upper side heater to the lower side heater is 3:

1.

4. The single crystal furnace according to claim 2, characterized in that: The upper side heater and the lower side heater are supported by conductive graphite foot plates respectively and are arranged on the furnace bottom of the furnace body.

5. The single crystal furnace according to claim 1, characterized in that: The bottom heater is in the shape of a basin-shaped structure that fits the bottom of the graphite crucible.

6. The single crystal furnace according to claim 1, characterized in that: The side heater includes at least three heating coils.

7. The single crystal furnace according to claim 6, characterized in that: The heating coil is made of a resistive heating material, and the resistive heating material includes at least one of the following: silicon carbide coated graphite, high-purity graphite, tungsten, metal, and carbon fiber composite.

8. A method for preparing single crystal silicon, characterized in that: A single crystal furnace as claimed in any one of claims 1 to 7, comprising: The polysilicon material to be melted is placed in the quartz crucible, the furnace body is sealed and evacuated to allow inert gas to pass through, the side heater and the bottom heater are started to melt the polysilicon material; after the polysilicon material is completely melted, the seed crystal is lowered to the vicinity of the silicon melt surface to carry out a growth process including welding, shoulder release, shoulder rotation and equal diameter.

9. The method for preparing single crystal silicon according to claim 8, characterized in that: Also includes: The power output to the side heater and the bottom heater is controlled respectively by a controller.

10. The method for preparing single crystal silicon according to claim 8, characterized in that: When the crystal rod is pulled to the tail, the power of the bottom heater is reduced, and the power of the bottom heater is reduced by 1 to 20 KW every 1 to 10 minutes. After the crystal rod is pulled to the end, the bottom heater is turned off.

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