CN115198348B

CN115198348B - Monocrystalline silicon preparation method and device

Info

Publication number: CN115198348B
Application number: CN202110396723.8A
Authority: CN
Inventors: 欧子杨; 白枭龙; 张昕宇
Original assignee: Zhejiang Jinko Solar Co Ltd; Jinko Solar Co Ltd
Current assignee: Zhejiang Jinko Solar Co Ltd; Jinko Solar Co Ltd
Priority date: 2021-04-13
Filing date: 2021-04-13
Publication date: 2023-06-23
Anticipated expiration: 2041-04-13
Also published as: CN115198348A

Abstract

The application provides a monocrystalline silicon preparation method and device, wherein the monocrystalline silicon preparation device at least comprises a monocrystalline furnace, a crucible, a heater, a guide cylinder, a crystal pulling device and a thermal cover plate; the crucible is used for accommodating the silicon raw material, and the silicon raw material is melted under the action of the heater to form a silicon melt; the thermal cover plate is detachably connected to the crystal pulling device and comprises a plurality of fan blades which are sequentially arranged at intervals along the circumferential direction, and the fan blades are obliquely arranged along the horizontal direction; the crystal lifting device is used for driving the thermal cover plate to move towards the opening near the lower end of the guide cylinder and driving the thermal cover plate to rotate. The monocrystalline silicon preparation method and the monocrystalline silicon preparation device can inhibit heat loss and remarkably improve melting efficiency; volatile matters in the effectively pressed silicon melt volatilize from the top, so that the crystal pulling environment of monocrystalline silicon is improved, and the quality of the monocrystalline silicon is improved.

Description

Monocrystalline silicon preparation method and device

Technical Field

The application relates to the technical field of photovoltaic cells, in particular to a monocrystalline silicon preparation method and device.

Background

Currently, single crystal silicon for solar cells is mainly manufactured by a Czochralski method, and in the melting stage of silicon materials, the silicon materials need to be changed from solid state to liquid state, and a great amount of heat is required to be constantly absorbed in the process, and the part of heat is sourced from a side heater and a bottom heater of a crucible, and the upper temperature of a furnace cover in a thermal field is greatly dissipated, so that the side heater and the bottom heater need to provide higher power to maintain melting materials, and the melting materials are low in efficiency.

Disclosure of Invention

In view of this, the present application provides a method and apparatus for producing monocrystalline silicon, which can inhibit heat dissipation, improve melting efficiency, and improve quality of monocrystalline silicon.

In a first aspect, an embodiment of the present application provides a single crystal silicon preparation apparatus, where the single crystal silicon preparation apparatus at least includes a single crystal furnace, a crucible, a heater, a guide cylinder, a crystal pulling apparatus, and a thermal cover plate;

the crucible is used for accommodating a silicon raw material, and the silicon raw material is melted under the action of the heater to form a silicon melt;

the thermal cover plate is detachably connected to the crystal pulling device and comprises a plurality of fan blades which are sequentially arranged at intervals along the circumferential direction, and the fan blades are obliquely arranged along the horizontal direction;

the crystal lifting device is used for driving the thermal cover plate to move towards the opening near the lower end of the guide cylinder and driving the thermal cover plate to rotate.

With reference to the first aspect, in a possible implementation manner, an inclination angle between the fan blade on the thermal cover plate and the horizontal plane is 20 degrees to 45 degrees.

In combination with the first aspect, in a feasible implementation manner, the crystal pulling device is provided with N layers of heat cover plates, N is more than or equal to 1 and less than or equal to 10, the inclination directions of the fan blades of two adjacent layers of heat cover plates are opposite, and the inclination angles of a plurality of fan blades on the same layer of heat cover plates are consistent.

With reference to the first aspect, in a possible implementation manner, the single-layer thickness of the thermal cover plate is 20mm to 50mm, and/or the overall thickness of the N-layer thermal cover plate is 20mm to 100mm.

With reference to the first aspect, in a possible implementation manner, the outer edge of the thermal cover plate is circular, and the diameter of the thermal cover plate is 250 mm-300 mm.

With reference to the first aspect, in a possible implementation manner, the shape of the outer edge of the thermal cover plate matches the shape of the opening at the lower end of the guide cylinder, and the diameter of the thermal cover plate is smaller than the inner diameter of the opening at the lower end of the guide cylinder.

With reference to the first aspect, in a possible implementation manner, the material of the fan blade includes at least one of carbon-carbon material, graphite, silicon, molybdenum or tungsten.

With reference to the first aspect, in a possible implementation manner, the crystal pulling device is connected with the heavy hammer through a metal wire;

a clamping device is arranged in a secondary chamber at the top of the single crystal furnace, the clamping device comprises a driver and a telescopic clamping block connected with the driver, and the telescopic clamping block is used for locking the thermal cover plate;

when the driver drives the telescopic clamping block to unlock the thermal cover plate, the thermal cover plate can be clamped and fixed on the heavy hammer.

In a second aspect, the present application provides a method for producing single crystal silicon, the method comprising the steps of:

after the silicon raw material is put into a crucible in a single crystal furnace, a crystal pulling device drives a hot cover plate to move to an opening at the lower end of a guide cylinder, wherein the hot cover plate comprises a plurality of fan blades which are sequentially arranged at intervals along the circumferential direction, and the fan blades are obliquely arranged along the horizontal direction;

vacuumizing the single crystal furnace, introducing protective gas, driving the hot cover plate to rotate by the crystal pulling device, and melting silicon raw materials by using a heater under the action of the protective gas to obtain a silicon melt;

after the temperature of the silicon melt is stable, immersing a seed crystal into the silicon melt, and then sequentially carrying out seeding, shouldering and isodiametric growth;

after the completion of the isodiametric growth, a final stage is carried out to gradually reduce the diameter of the crystal until the crystal is separated from the silicon melt, and the crystal is taken out after being cooled to room temperature to obtain monocrystalline silicon.

With reference to the second aspect, in a possible implementation manner, the method further includes the following steps:

after the monocrystalline silicon is taken out, the crystal pulling device drives the thermal cover plate to move downwards and pass through the opening at the lower end of the guide cylinder, and the rotation speed of the thermal cover plate is controlled to be 1-10 revolutions/min.

With reference to the second aspect, in a possible implementation manner, after the thermal cover plate passes through the lower end opening of the guide cylinder, the thermal cover plate descends to a distance between 50mm and 400mm from the lower end opening of the guide cylinder.

With reference to the second aspect, in a possible implementation manner, the rotation speed of the thermal cover plate is 1-5 rpm during the melting material and the single crystal silicon drawing process.

With reference to the second aspect, in a possible implementation manner, during the melting process, the bottom heater power of the crucible is controlled to be 80 kw-90 kw, and the side heater power of the crucible is controlled to be 100 kw-120 kw.

With reference to the second aspect, in a possible implementation, the method fulfils at least one of the following features a to d:

a. the inclination angle between the fan blades on the hot cover plate and the horizontal plane is 20-45 degrees;

b. the outer edge of the thermal cover plate is circular, and the diameter of the thermal cover plate is 250-300 mm;

c. the shape of the outer edge of the thermal cover plate is matched with the shape of the opening at the lower end of the guide cylinder, and the diameter of the thermal cover plate is smaller than the inner diameter of the opening at the lower end of the guide cylinder;

d. the fan blade is made of at least one of carbon-carbon material, graphite, silicon, molybdenum or tungsten.

With reference to the second aspect, in a possible implementation manner, the crystal pulling device is connected with the heavy hammer through a metal wire;

the clamping device is arranged in the auxiliary chamber at the top of the single crystal furnace and comprises a driver and a telescopic clamping block connected with the driver, and the thermal cover plate is locked in the auxiliary chamber through the telescopic clamping block.

With reference to the second aspect, in a possible implementation manner, before the crystal pulling device drives the thermal cover plate to move to the opening at the lower end of the guide cylinder, the method further includes:

the crystal lifting device drives the heavy hammer to move upwards to the position below the thermal cover plate;

and the driver is utilized to drive the telescopic clamping block to unlock the thermal cover plate, and the thermal cover plate moves downwards and is clamped and fixed on the heavy hammer.

The technical scheme of the application has the following beneficial effects:

in the melting process, the thermal cover plate is lowered to the opening at the lower end of the guide cylinder, so that the thermal cover plate has a heat insulation effect, heat dissipation can be restrained, and melting efficiency is remarkably improved; and the swirl-shaped polymer airflow is formed under the rotation of the hot cover plate, so that the deposition of volatile matters can be restrained, and in the whole single crystal silicon drawing process, the polymer airflow takes away oxides from the two sides of the left side of the crucible through the air outlets at the bottom, so that the volatile matters in the silicon melt can be effectively pressed to volatilize from the top, the crystal pulling environment of the single crystal silicon is improved, and the quality of the single crystal silicon is improved.

Drawings

For a clearer description of embodiments of the present application or of the prior art, the drawings that are used in the description of the embodiments or of the prior art will be briefly described, it being apparent that the drawings in the description that follow are only some embodiments of the present application, and that other drawings may be obtained from these drawings by a person of ordinary skill in the art without inventive effort.

Fig. 1 is a schematic structural view of a single crystal silicon manufacturing apparatus according to the present embodiment;

FIG. 2 is a schematic diagram showing the installation state of the thermal cover plate and the weight according to the present embodiment;

fig. 3a and fig. 3b are schematic diagrams of fan blade structures of the heat cover plate according to the present embodiment;

FIG. 3c is a schematic view of a multi-layered thermal cover plate according to the present embodiment;

fig. 4 is a schematic structural diagram of a clamping device in a monocrystalline silicon preparation apparatus according to an embodiment of the present disclosure;

FIG. 5 is a thermodynamic diagram of a single crystal silicon manufacturing apparatus according to an embodiment of the present application;

fig. 6 is a schematic flow chart of a method for preparing monocrystalline silicon according to an embodiment of the present application.

Detailed Description

For a better understanding of the technical solutions of the present application, embodiments of the present application are described in detail below with reference to the accompanying drawings.

It should be understood that the described embodiments are merely some, but not all, of the embodiments of the present application. All other embodiments, based on the embodiments herein, which would be apparent to one of ordinary skill in the art without making any inventive effort, are intended to be within the scope of the present application.

The terminology used in the embodiments of the application is for the purpose of describing particular embodiments only and is not intended to be limiting of the application. As used in this application and the appended claims, the singular forms "a," "an," and "the" are intended to include the plural forms as well, unless the context clearly indicates otherwise.

It should be understood that the term "and/or" as used herein is merely one relationship describing the association of the associated objects, meaning that there may be three relationships, e.g., a and/or B, may represent: a exists alone, A and B exist together, and B exists alone. In addition, the character "/" herein generally indicates that the front and rear associated objects are an "or" relationship.

In a first aspect, the present application provides a monocrystalline silicon preparation apparatus, and fig. 1 is a schematic diagram of an operating state of the monocrystalline silicon preparation apparatus provided in the present application; as shown in fig. 1, the single crystal silicon manufacturing apparatus includes at least: 1 of a single crystal furnace, 2 of a crucible, 3 of a crystal pulling device, 4 of a guide cylinder, and 6 of a heater and a thermal cover plate.

The crucible 2 is used for accommodating silicon raw materials and dopants, and the silicon raw materials in the crucible 2 are melted to form a silicon melt under the action of the heater.

The crystal pulling device 3 is used for pulling the crystal bar. In some embodiments, the crystal pulling apparatus 3 is connected to the weight 7 by a wire, which may be, for example, a steel wire. As shown in fig. 2, the weight 7 is provided with a mounting assembly 72, and the mounting assembly 72 is used for mounting the thermal cover plate 6. Alternatively, the mounting assembly 72 may be coupled to the thermal cover plate 6 by a snap-fit, engagement, welding, or the like. Preferably, the connection means is snap-fit so that the thermal cover plate 6 is easy to install and remove. The bottom of the heavy hammer 7 is also provided with a seed clamp 71, and the seed clamp 71 is used for clamping a seed crystal bar.

Because of strict requirements on the oxygen content in the silicon wafer, for example, the higher the oxygen content is, the lower the minority carrier lifetime is, and thus the efficiency of the solar cell is reduced, the oxygen concentration in the silicon melt needs to be reduced in the crystal pulling process, and the oxygen element in the silicon melt exists in the form of SiO, in this embodiment, by arranging the guide cylinder 4 (only part of the structure is shown in fig. 1), the shielding gas (argon and/or nitrogen) is converged into the crucible 2, so that the volatilization of SiO is accelerated, and the oxygen concentration in the melt can be greatly reduced. Meanwhile, the guide cylinder 4 can also play a role of heat shielding, and the converged shielding gas can accelerate the cooling of crystals, increase the axial temperature gradient of the crystals and improve the crystal growth rate.

The guide cylinder 4 is of a hollow structure, the lower end of the guide cylinder 4 is open, and the hollow structure of the guide cylinder can be used as an airflow channel and a crystal bar growth channel, so that the volatilization of oxides in the crystal bar drawing process is facilitated. In this embodiment, the thermal cover plate 6 can pass through the lower end opening of the guide cylinder 4.

The heater includes a bottom heater 52 provided at the bottom of the crucible 2 and a side heater 51 provided at the side of the crucible 2 for heating the silicon raw material and the dopant in the crucible 2 so that the silicon raw material is melted to form a silicon melt.

In the melting process, the power of the bottom heater 52 of the crucible is controlled to be 80-90 kw, and the power of the side heater 51 of the crucible is controlled to be 100-120 kw.

Further, the thermal cover plate 6 is detachably connected to the crystal pulling device 3, in particular to the mounting assembly 72 of the weight 7. The crystal pulling device 3 can drive the thermal cover plate 6 to move towards the opening near the lower end of the guide cylinder 4 and drive the thermal cover plate 6 to rotate.

As shown in fig. 3a, 3b and 3c, the thermal cover plate 6 includes a plurality of blades 61 sequentially spaced apart from each other in the circumferential direction, and the plurality of blades 61 are disposed obliquely in the horizontal direction. In the present embodiment, the inclination angle a between the fan blade 61 on the heat cover plate 6 and the horizontal plane is 20 degrees to 45 degrees, specifically, may be 20 degrees, 25 degrees, 30 degrees, 32 degrees, 35 degrees, 38 degrees, 40 degrees, 45 degrees, or the like, and may be any other value within the above range, which is not limited herein. By arranging the blades 61 obliquely, a swirl-like polymer gas flow is formed, and the gas flow is facilitated to flow from top to bottom; in the process of pulling the monocrystalline silicon, deposition of volatile matters can be restrained, and polymer gas flow takes oxide away from the two sides of the left side of the crucible 2 through the gas outlets at the bottom, so that the volatile matters in the silicon melt can be effectively pressed to volatilize from the top, the crystal pulling environment of the monocrystalline silicon is improved, the quality of the monocrystalline silicon is improved, and the oxygen content of the monocrystalline silicon is reduced. Preferably, the inclination angle between the fan blades 61 on the thermal cover plate 6 and the horizontal plane is 30 degrees.

In some embodiments, the crystal pulling apparatus 3 is provided with N layers of thermal cover plates, where N is 1-10, i.e. the number of layers of the thermal cover plate 6 may be 1, 2, 3, 5, 6, 7, 8, 9 or 10, etc., and of course, other values within the above range may be used, which is not limited herein.

As shown in fig. 3c, the inclined directions of the blades 61 of the adjacent two layers of heat cover plates 6 are opposite, and the inclined angles of the blades 61 on the same layer of heat cover plate 6 are consistent. Illustratively, the tilt angle a may be 30 degrees.

Specifically, the thickness of the single layer of the thermal cover plate 6 is 20mm to 50mm, specifically, the thickness of the single layer of the thermal cover plate 6 may be 20mm, 25mm, 30mm, 35mm, 40mm, 45mm, 50mm, or the like, and other values within the above range may be used, which is not limited herein. The thickness is too thick, increases the load of weight, reduces the life of device. Preferably, the thermal cover plate 6 is a single layer cover plate.

When the thermal cover plate 6 has N layers, the overall thickness of the N layers of thermal cover plate 6 is 20mm to 100mm, specifically, the single layer thickness of the thermal cover plate may be 20mm, 30mm, 40mm, 50mm, 60mm, 70mm, 80mm or 100mm, or the like, and other values within the above range may be used, which is not limited herein.

The thermal cover plate 6 includes a plurality of fan blades 61, and the fan blades 61 may also have a fan shape, an arc shape, a square shape, a circular shape, etc., which is not limited herein.

The outer edge of the thermal cover plate 6 is circular, and the diameter of the thermal cover plate 6 is 250mm to 300mm, specifically, may be 250mm, 260mm, 270mm, 280mm, 290mm or 300mm, or the like, and of course, may be other values within the above range, and is not limited thereto. The shape of the outer edge of the heat cover plate 6 is matched with the shape of the opening at the lower end of the guide cylinder 4, and the diameter of the heat cover plate 6 is smaller than the inner diameter of the opening at the lower end of the guide cylinder 4, so that the heat cover plate 6 can conveniently penetrate through the opening at the lower end of the guide cylinder 4.

As an optional technical solution of the present application, the material of the fan blade 61 includes at least one of carbon-carbon material, graphite, silicon, molybdenum or tungsten. Preferably, the lower surface of the fan blade 61 near the silicon melt has a heat reflecting layer, which can suppress heat dissipation and is advantageous for improving the melting rate.

Further, as shown in fig. 4, a clamping device 8 is arranged on the auxiliary chamber 11 at the top of the single crystal furnace 1, the clamping device 8 comprises a driver 81 and a telescopic clamping block 82 connected with the driver 81, and the telescopic clamping block 82 is used for locking the thermal cover plate 6; when the driver 81 drives the telescopic clamping block 82 to unlock the thermal cover 6, the thermal cover 6 can be fastened and fixed on the mounting assembly 72 of the weight 7.

Fig. 5 is a flowchart of a single crystal silicon preparation method according to an embodiment of the present application, which may be implemented by means of the single crystal silicon preparation apparatus described in fig. 1 to 4. As shown in fig. 5, the present application provides a method for preparing single crystal silicon, comprising the steps of:

step S10, after a silicon raw material is put into a crucible in a single crystal furnace, a crystal pulling device drives a hot cover plate to move to an opening at the lower end of a guide cylinder, wherein the hot cover plate comprises a plurality of fan blades which are sequentially arranged at intervals along the circumferential direction, and the fan blades are obliquely arranged along the horizontal direction;

step S20, vacuumizing the single crystal furnace, introducing protective gas, driving the hot cover plate to rotate by the crystal pulling device, and melting silicon raw materials by using a heater under the action of the protective gas to obtain a silicon melt;

step S30, after the temperature of the silicon melt is stable, immersing a seed crystal into the silicon melt, and then sequentially carrying out seeding, shouldering and isodiametric growth;

and step S40, after the constant diameter growth is completed, performing a final stage to gradually reduce the diameter of the crystal until the crystal is separated from the silicon melt, and taking out the crystal after the crystal is cooled to room temperature to obtain monocrystalline silicon.

In the scheme, in the melting process, the heat cover plate 6 is lowered to the opening of the lower end of the guide cylinder 4, so that the heat cover plate 6 has a heat insulation effect, heat loss can be restrained, and the melting efficiency is remarkably improved; and under the rotation of the hot cover plate 6, vortex-shaped polymer airflow is formed, so that the deposition of volatile matters can be restrained, and in the whole single crystal silicon drawing process, the polymer airflow takes oxide away from the two sides of the left side of the crucible and through the air outlets at the bottom, so that the volatile matters in the silicon melt can be effectively pressed to volatilize from the top, the crystal pulling environment of the single crystal silicon is improved, and the quality of the single crystal silicon is improved.

The present solution is described in detail below with reference to examples:

step S10, after the silicon raw material is put into the crucible 2 in the single crystal furnace 1, the crystal pulling device 3 drives the hot cover plate 6 to move to the opening at the lower end of the guide cylinder 4, wherein the hot cover plate 6 comprises a plurality of fan blades 61 which are sequentially arranged at intervals along the circumferential direction, and the fan blades 61 are obliquely arranged along the horizontal direction.

Prior to step S10, the method comprises:

the crystal pulling device 3 drives the heavy hammer 7 to move upwards to the lower part of the thermal cover plate 6;

the driver 81 is used to drive the telescopic clamping block 82 to unlock the thermal cover plate 6, and the thermal cover plate 6 moves downward and is clamped and fixed on the weight 7.

In this embodiment, the weight 7 is provided with a mounting assembly 72, and the thermal cover plate 6 can be mounted and fixed on the mounting assembly 72 so as to rotate with the weight 7 under the action of the crystal pulling apparatus 3.

It will be appreciated that the weight 7 is raised into the sub-chamber 11 at the top of the single crystal furnace 1 when the silicon feedstock is charged. At this time, the heat cover plate 6 is locked by the retractable latch 82 of the engaging device 8, and is accommodated in the sub chamber 11. When the silicon raw material is completely filled, the driver 81 drives the telescopic clamping block 82 to unlock the thermal cover plate 6, so that the thermal cover plate 6 can descend and be clamped and fixed on the mounting assembly 72 of the heavy hammer 7. The driver 81 may be a cylinder or a motor, for example.

After the silicon raw material is put into the crucible 2 in the single crystal furnace 1, the crystal pulling device 3 drives the thermal cover plate 6 to move to the opening at the lower end of the guide cylinder 4, and at the moment, the shape of the outer edge of the thermal cover plate 6 is matched with the shape of the opening at the lower end of the guide cylinder 4, so that heat dissipation can be inhibited, and the melting efficiency is remarkably improved.

As an optional technical solution of the present application, the thermal cover plate 6 includes a plurality of fan blades 61 that are sequentially spaced along the circumferential direction, and the plurality of fan blades 61 are obliquely disposed along the horizontal direction. In the present embodiment, the inclination angle a between the fan blade 61 on the heat cover plate 6 and the horizontal plane is 20 degrees to 45 degrees, specifically, may be 20 degrees, 25 degrees, 30 degrees, 32 degrees, 35 degrees, 38 degrees, 40 degrees, 45 degrees, or the like, and may be any other value within the above range, which is not limited herein. Preferably, the inclination angle a between the fan blades 61 on the thermal cover plate 6 and the horizontal plane is 30 degrees.

The crystal pulling device 3 is provided with N layers of thermal cover plates 6, N is not less than 1 and not more than 10, i.e. the number of layers of the thermal cover plates 6 can be 1, 2, 3, 5, 6, 7, 8, 9 or 10, etc., and of course, other values within the above range can be also used, and the crystal pulling device is not limited herein.

As shown in fig. 3c, the inclined directions of the blades 61 of the adjacent two layers of heat cover plates 6 are opposite, and the inclined angles of the blades 61 on the same layer of heat cover plate 6 are consistent.

When the thermal cover plate 6 has N layers, the overall thickness of the N layers of thermal cover plate 6 is 20mm to 100mm, specifically, the single layer thickness of the thermal cover plate 6 may be 20mm, 30mm, 40mm, 50mm, 60mm, 70mm, 80mm or 100mm, or the like, and of course, other values within the above range may be used, which is not limited herein.

The thermal cover plate 6 includes a plurality of fan blades 61, and the fan blades 61 may be arc-shaped, square-shaped, circular-shaped, etc., which are not limited herein.

Step S20, vacuumizing the single crystal furnace 1, introducing protective gas, driving the hot cover plate 6 to rotate by the crystal pulling device 3, and melting silicon raw materials by using a heater under the action of the protective gas to obtain a silicon melt.

In the melting process, the power of the bottom heater 52 of the crucible is controlled to be 80-90 kw, and the power of the side heater 51 of the crucible is controlled to be 100-120 kw. It will be appreciated that the bottom heater 52, in combination with the side heater 51, helps to maintain the temperature of the silicon level of the silicon melt in the crucible 2 and ensures the growth rate of the silicon single crystal throughout the silicon single crystal pulling process.

In the melting and monocrystalline silicon drawing process, the rotation speed of the thermal cover plate 6 is 1-5 rpm, specifically, the rotation speed of the thermal cover plate 6 may be 1-, 2-, 3-, 4-, or 5-rpm, which may be other values within the above range, but not limited thereto.

It will be appreciated that, as shown in fig. 6, a swirl-shaped polymer gas flow is formed in the single crystal furnace under the rotation of the hot cover plate 6, so that the deposition of volatile matters can be inhibited, and in the whole single crystal silicon drawing process, the polymer gas flow takes away oxide from the two sides of the left side of the crucible through the gas outlet at the bottom, so that the volatile matters in the silicon melt can be effectively pressed to volatilize from the top, the crystal pulling environment of the single crystal silicon is improved, and the quality of the single crystal silicon is improved.

As an optional technical scheme, the shielding gas comprises any one of argon, krypton and nitrogen. The flow rate of the protective gas is 85 slpm-95 slpm. Specifically, the flow rate may be 85slpm, 86slpm, 87slpm, 88slpm, 89slpm, 90slpm, 91slpm, 92slpm, 93slpm, 94slpm, or 95slpm, or the like, and of course, may be other values within the above range, which is not limited herein, and preferably, the flow rate of the shielding gas in the single crystal furnace 1 is adjusted to 88slpm to 92slpm. Through a plurality of experiments, the flow direction of the shielding gas is from top to bottom by adjusting the flow rate of the shielding gas, the shielding gas is favorable for forming vortex-shaped polymer gas flow, and the volatile deposition can be restrained.

And step S30, after the temperature of the silicon melt is stable, immersing the seed crystal into the silicon melt, and then sequentially carrying out seeding, shouldering and isodiametric growth.

In the seeding process, the seeding speed is 200-290mm/h, the seeding length is 200-260 mm, and the crystal diameter is 5-8 mm.

Alternatively, the seeding speed may be 200mm/h, 210mm/h, 220mm/h, 240mm/h, 250mm/h, 260mm/h, 270mm/h, 280mm/h, and 290mm/h, without limitation. In the seeding process, the crystal diameter may be 5mm, 6mm, 7mm, 8mm, etc., and the crystal length may be 200mm, 210mm, 220mm, 230mm, 240mm, 250mm, 260mm, etc., without limitation.

The temperature in the single crystal furnace 1 is 1250-1300 sp. Illustratively, the temperature in the single crystal furnace 1 may be 1250sp, 1255sp, 1260sp, 1265sp, 1270sp, 1275sp, 1280sp, 1285sp, 1290sp, 1295sp, 1300sp, preferably, the temperature in the single crystal furnace 1 is 1300sp, and it is understood that the appropriate seeding temperature may effectively improve the seeding success rate, and of course, the temperature in the single crystal furnace 1 may be other values, which is not limited herein.

In the shouldering process, the first pulling speed of the crystal is 50-80mm/h, so that the diameter of the crystal is gradually increased to 230-310mm.

Alternatively, the first pulling speed may be 50mm/h, 60mm/h, 70mm/h, 80mm/h, etc., and the diameter of the crystal is gradually increased to 230mm, 240mm, 250mm, 260mm, 270mm, 280mm, 290mm, 300mm, 310mm, etc., without limitation. It will be appreciated that to ensure crystal pull stability, the crystal growth rate is slower and the crystal pull rate is also slower. In addition, in the whole shouldering process, the temperature in the single crystal furnace 1 can be gradually reduced, and the temperature cannot be increased.

The diameter range of the crystal can be designed and controlled according to the size requirement of the battery piece on the silicon wafer, and the crystal is not limited in this way.

In order to improve the uniformity of the distribution of the doping elements in the silicon melt, the silicon melt needs to be fully stirred, and the seed crystal and the crucible 2 can be reversely rotated, so that the stirring effect can be achieved.

Specifically, in the process of the equal diameter growth, the second pulling speed of the crystal is 80-130mm/h, specifically, 80mm/h, 90mm/h, 100mm/h, 110mm/h, 120mm/h, 130mm/h, etc., without limitation.

It can be understood that during the isodiametric growth, the impurity speed of the impurity at each point in the radial direction of the crystal near the solid-liquid interface is unequal to the impurity speed of the impurity separated and condensed to the silicon melt side near the interface, so that the radial doping concentration distribution of the crystal is uneven, and the pulling speed in the isodiametric growth stage is controlled to be smaller than the pulling speed in the seeding process. Along with the decrease of the pulling speed, enough time is available for the doping elements at all parts of the crystal in the radial direction to diffuse into the melt, so that the radial doping elements of the crystal are distributed more uniformly.

Likewise, in the equal-diameter growth process, the rotation speed of the thermal cover plate 6 is 1-5 rpm, and it can be understood that the thermal cover plate 6 rotates, and the heat conduction to the crystal rod can be accelerated by the flow of the protective gas, so that the heat on the crystal rod is taken away, and a temperature gradient is easier to form, thereby improving the crystal growth rate and accelerating the drawing efficiency of the crystal rod.

In the finishing stage, the third pulling rate of the crystal is 20-80mm/h, and may be, for example, 20mm/h, 30mm/h, 40mm/h, 50mm/h, 60mm/h, 70mm/h, or 80mm/h.

In this embodiment, the oxygen content of the single crystal silicon is 12ppma or less, specifically 12ppma, 10ppma, 9ppma, 8ppma, 7ppma, 6ppma, 5ppma, 4ppma, 3ppma, 2ppma, or the like. It can be understood that, in the whole process of pulling the monocrystalline silicon, due to the swirling polymeric airflow formed in the monocrystalline furnace 1 under the rotation action of the thermal cover plate 6, the deposition of volatile matters can be restrained, in the whole process of pulling the monocrystalline silicon, the polymeric airflow takes away volatile oxides from the left two sides of the crucible 2 through the air outlets at the bottom, the volatile matters in the silicon melt can be effectively pressed to volatilize from the top, the crystal pulling environment of the monocrystalline silicon is improved, oxygen impurities are difficult to enter the monocrystalline silicon rod, and the oxygen element source of the monocrystalline silicon can be effectively reduced.

After step S40, the method further comprises the steps of:

after the monocrystalline silicon is taken out, the crystal pulling device 3 drives the thermal cover plate 6 to move downwards and pass through the opening at the lower end of the guide cylinder, and the rotation speed of the thermal cover plate 6 is controlled to be 1-10 revolutions/min.

As an optional technical solution of the present application, the rotation speed of the thermal cover plate 6 may specifically be 1 rotation/min, 2 rotation/min, 3 rotation/min, 4 rotation/min, 5 rotation/min, 6 rotation/min, 7 rotation/min, 8 rotation/min, 9 rotation/min, or 10 rotation/min, and the like, which is not limited herein. It will be appreciated that by lowering the thermal cover plate 6 to a position below the opening in the lower end of the guide cylinder 4, i.e. the thermal cover plate 6 extends into the crucible 2, the thermal cover plate 6 rotates to accelerate the heat dissipation in the crucible 2, so that the single crystal furnace 1 can be rapidly cooled to the furnace opening temperature.

Optionally, after the monocrystalline silicon is taken out, the flow rate of the protective gas is 85 slpm-95 slpm. Specifically, the flow rate may be 85slpm, 86slpm, 87slpm, 88slpm, 89slpm, 90slpm, 91slpm, 92slpm, 93slpm, 94slpm, or 95slpm, or the like, and of course, may be other values within the above range, which is not limited herein. Preferably, the flow rate of the shielding gas in the single crystal furnace 1 is adjusted to 88slpm to 92slpm. Through a plurality of experiments, the shielding gas is beneficial to accelerating the heat dissipation in the crucible 2, so that the single crystal furnace 1 can be rapidly cooled to the furnace opening temperature.

As an optional technical scheme of the application, after the thermal cover plate 6 passes through the opening at the lower end of the guide cylinder 4, the thermal cover plate 6 descends to a distance of 50-400 mm from the opening at the lower end of the guide cylinder 4. Specifically, the value may be 50mm, 100mm, 150mm, 200mm, 250mm, 300mm, 350mm, 400mm, or the like, but other values within the above range are also possible, and the present invention is not limited thereto.

The following are test data for the specific examples:

example 1

Step (1), placing silicon raw material and dopant into a crucible 2;

step (2), the crystal lifting device 3 drives the thermal cover plate 6 to move to the opening at the lower end of the guide cylinder 4;

step (3), vacuumizing the single crystal furnace 1, introducing protective gas, driving the hot cover plate 6 to rotate by the crystal pulling device 3, controlling the rotating speed of the hot cover plate 6 to be 5 revolutions per minute, and melting silicon raw materials by using a heater under the action of the protective gas, wherein the power of a bottom heater 51 of the crucible 2 is 85kw, and the power of a side heater 52 of the crucible 2 is 110kw, so as to obtain silicon melt; the structure of the thermal cover plate 6 is shown in fig. 3 a;

step (4), after the temperature of the silicon melt is stable, immersing a seed crystal into the silicon melt by a crystal pulling device 3 to start seeding, setting the temperature in the single crystal furnace 1 to 1300sp during seeding, and controlling the seeding speed to 250mm/h;

step (5), after seeding, starting shouldering, reducing the pulling speed to 50mm/h, gradually increasing the diameter of the crystal to 250mm, then starting isodiametric growth, controlling the lifting speed of the crystal to 100mm/h, and keeping the rotating speed of the hot cover plate 6 to 5 revolutions/min;

step (6), after the isodiametric growth is completed, entering a final stage, controlling the lifting speed of the crystal to be 50mm/h, so that the diameter of the crystal is gradually reduced until the crystal is separated from the silicon melt, and taking out the grown crystal after the crystal is cooled to room temperature in a furnace chamber, wherein the crystal is monocrystalline silicon;

and (7) after the monocrystalline silicon is taken out, closing the crucible bottom heater 52 and the side heater 51, and driving the thermal cover plate 6 to move downwards by the crystal pulling device 3 and pass through the opening at the lower end of the guide cylinder 4, so as to control the rotation speed of the thermal cover plate 6 to be 10 revolutions per minute.

Example 2

Step (1), placing silicon raw material and dopant into a crucible 2;

step (3), vacuumizing the single crystal furnace 1, introducing protective gas, driving the hot cover plate 6 to rotate by the crystal pulling device, controlling the rotation speed of the hot cover plate 6 to be 5 revolutions per minute, and melting silicon raw materials by using a heater under the action of the protective gas, wherein the power of a bottom heater 51 of the crucible 2 is 85kw, and the power of a side heater 51 of the crucible 2 is 110kw, so as to obtain silicon melt; the thermal cover plate 6 in the embodiment is circular, and no fan blade is arranged;

step (4), after the temperature of the silicon melt is stable, immersing a seed crystal into the silicon melt by a crystal pulling device 3 to start seeding, setting the temperature in a single crystal furnace to 1300sp during seeding, and controlling the seeding speed to 250mm/h;

and (7) after the monocrystalline silicon is taken out, closing a crucible bottom heater 51 and a side heater 52, and driving the thermal cover plate 6 to move downwards by the crystal pulling device 3 and pass through the opening at the lower end of the guide cylinder 4, and controlling the rotation speed of the thermal cover plate 6 to be 10 revolutions per minute.

Comparative example 1

Step (1), placing silicon raw material and dopant into a crucible 2;

step (2), vacuumizing the single crystal furnace 1, introducing protective gas, and melting silicon raw materials by using a heater under the action of the protective gas, wherein the power of a bottom heater 51 of the crucible 2 is 85kw, and the power of a side heater 52 of the crucible 2 is 110kw, so as to obtain silicon melt;

step (3), after the temperature of the silicon melt is stable, immersing a seed crystal into the silicon melt by a crystal pulling device 3 to start seeding, setting the temperature in the single crystal furnace 1 to 1300sp during seeding, and controlling the seeding speed to 250mm/h;

step (4), after seeding, starting shouldering, reducing the pulling speed to 50mm/h, gradually increasing the diameter of the crystal to 250mm, then starting isodiametric growth, and controlling the lifting speed of the crystal to be 100mm/h;

step (5), after the isodiametric growth is completed, entering a final stage, controlling the lifting speed of the crystal to be 50mm/h, so that the diameter of the crystal is gradually reduced until the crystal is separated from the silicon melt, and taking out the grown crystal after the crystal is cooled to room temperature in a furnace chamber, wherein the crystal is monocrystalline silicon;

and (6) after the monocrystalline silicon is taken out, the crucible bottom heater 51 and the side heater 52 are turned off.

Experimental data of the above example 1, example 2 and comparative example 1 are shown in tables 1 and 2.

TABLE 1

Parameters (parameters)	Example 1	Example 2	Comparative example 1
				Melt Rate (kg/h)	80	70	60
Crystal growth rate (mm/h) at constant diameter stage	95	90	90
				Single crystal silicon oxygen content (ppma)	12	13	13
Cooling time of furnace shutdown (h)	8	9	10
				Whole bar rate (%)	50	35	35

TABLE 2 constant diameter growth phase parameters

According to the data in table 1, in the melting process, by lowering the thermal cover plate to the opening at the lower end of the guide cylinder, the thermal cover plate has a heat insulation effect, so that heat dissipation can be inhibited, and compared with comparative example 1, the melting rate is improved by 20kg/h, and the melting efficiency is remarkably improved. Example 1 also showed a significant increase in the crystal growth rate at the isodiametric stage relative to comparative example 1. In addition, the oxygen content of the monocrystalline silicon prepared in example 1 is lower than that of comparative example 1, which shows that the rotation of the hot cover plate can effectively suppress the volatilization of the volatile matters in the silicon melt from the top in the whole monocrystalline silicon drawing process, so that the crystal pulling environment of the monocrystalline silicon is improved, and the quality of the monocrystalline silicon is improved. During the furnace shutdown treatment, the heat cover plate can accelerate the heat dissipation of the single crystal furnace, and can accelerate the temperature reduction in the furnace, so that the furnace shutdown cooling time is shortened.

It should be noted that the whole bar ratio refers to the continuous wire rod ratio, because the volatilization of oxide from the top is suppressed, the wire rod is less likely to break.

According to the data in Table 2, in the equal diameter growth stage of monocrystalline silicon preparation, vortex-shaped polymer gas flow is formed under the rotation of the hot cover plate, so that the convection heat dissipation effect can be effectively enhanced, the formation of a temperature gradient is facilitated, and the crystal growth speed can be effectively improved by about 5mm/h.

While the preferred embodiment has been described, it is not intended to limit the scope of the claims, and any person skilled in the art can make several possible variations and modifications without departing from the spirit of the invention, so the scope of the invention shall be defined by the claims.

Claims

1. The monocrystalline silicon preparation device is characterized by at least comprising a monocrystalline furnace, a crucible, a heater, a guide cylinder, a crystal pulling device and a thermal cover plate;

2. The apparatus according to claim 1, wherein an inclination angle between the blade on the thermal cover plate and a horizontal plane is 20 degrees to 45 degrees.

3. The monocrystalline silicon preparation device according to claim 1, wherein the crystal pulling device is provided with N layers of heat cover plates, N is more than or equal to 1 and less than or equal to 10, the blade inclination directions of two adjacent layers of heat cover plates are opposite, and the inclination angles of a plurality of blades on the same layer of heat cover plate are consistent.

4. A single crystal silicon production apparatus according to claim 3, wherein the single layer thickness of the thermal cover plate is 20mm to 50mm, and/or the entire thickness of the N-layer thermal cover plate is 20mm to 100mm.

5. The apparatus for producing silicon single crystal according to claim 1, wherein the outer edge of the thermal cover plate is circular, and the thermal cover plate has a diameter of 250mm to 300mm.

6. The apparatus for producing silicon single crystal according to claim 1, wherein the shape of the outer edge of the thermal cover plate matches the shape of the opening at the lower end of the guide cylinder, and the diameter of the thermal cover plate is smaller than the inner diameter of the opening at the lower end of the guide cylinder.

7. The apparatus according to any one of claims 2 to 6, wherein the blade is made of at least one of carbon-carbon material, graphite, silicon, molybdenum, or tungsten.

8. The apparatus for producing single crystal silicon according to claim 1, wherein the crystal pulling means is connected to a weight by a wire;

9. A method for producing single crystal silicon, characterized by comprising the steps of:

10. The method for producing a single crystal silicon according to claim 9, characterized in that the method further comprises the steps of:

11. The method for producing a silicon single crystal according to claim 10, wherein the thermal cover plate is lowered to a distance of 50mm to 400mm from the opening of the lower end of the guide cylinder after passing through the opening of the lower end of the guide cylinder.

12. The method of producing silicon single crystal according to claim 9, wherein the rotation speed of the thermal cover plate is 1 to 5 rotations/min during melting and pulling of silicon single crystal.

13. The method of producing a single crystal silicon according to claim 9, wherein during the melting, the bottom heater power of the crucible is controlled to be 80 to 90kw, and the side heater power of the crucible is controlled to be 100 to 120kw.

14. The method for producing a single crystal silicon according to claim 9, wherein the method satisfies at least one of the following features a to d:

15. The method for producing a single crystal silicon according to claim 9, wherein the crystal pulling means is connected to a weight through a wire;

16. The method for producing a silicon single crystal according to claim 15, wherein before the crystal pulling apparatus moves the thermal cover plate to the opening at the lower end of the guide cylinder, the method further comprises: