CN113061982A

CN113061982A - Continuous direct-pulling single crystal furnace and method capable of controlling content of monocrystalline silicon oxygen

Info

Publication number: CN113061982A
Application number: CN202110300588.2A
Authority: CN
Inventors: 丁欣
Original assignee: Shanghai Yinwan Photoelectric Technology Co ltd
Current assignee: Shanghai Yinwan Photoelectric Technology Co ltd
Priority date: 2021-03-22
Filing date: 2021-03-22
Publication date: 2021-07-02
Also published as: WO2022199286A1

Abstract

The invention relates to the technical field of monocrystalline silicon straight pulling, and provides a continuous monocrystalline silicon pulling furnace for controlling the oxygen content in monocrystalline silicon, which comprises a crucible, an inner crucible dam and a feeder, wherein the feeder comprises a molten silicon feeder which is arranged above the crucible and used for supplying liquid silicon to the crucible according to a preset speed; and the sealed shell surrounds and vacuum seals the whole structure of the continuous czochralski crystal growing furnace. Wherein the level of liquid molten silicon in the crucible has a depth less than 1/2 the diameter of the crucible and the maximum amount of molten silicon in the crucible is less than the total molten silicon demand of a single pull 2/3. The invention also provides a continuous Czochralski single crystal method for controlling the oxygen content and/or inhibiting COP of the single crystal silicon. The method can inhibit the exchange of oxygen atoms inside and outside the dam, reduce impurities such as oxygen atoms and the like to inhibit the COP of the monocrystalline silicon, and is effective and simple.

Description

Continuous direct-pulling single crystal furnace and method capable of controlling content of monocrystalline silicon oxygen

Technical Field

The invention relates to the technical field of monocrystalline silicon straight pulling. In particular to a continuous czochralski crystal growing furnace and a method capable of controlling the content of monocrystalline silicon oxygen.

Background

The Czochralski method is a crystal growth method for obtaining single crystal materials such as semiconductors, metals, salts, and synthetic gemstones. The most primitive czochralski method is the single-pass czochralski method in which a single ingot is pulled from a single crucible, and the crucible is broken by cooling after the pulling and cannot be reused.

At present, the industrial production of monocrystalline silicon mostly adopts a multiple-time repeated czochralski method, and is improved by adding a feeding device on equipment on the basis of a single czochralski method. In the multiple re-feeding czochralski method, the crucible is kept at a high temperature after each silicon crystal rod is pulled, and polycrystalline silicon granular raw material (or crushed material of the siemens method) is added in batches to the remaining silicon melt in the crucible by the repeated feeding device to be melted for the next silicon crystal rod pulling. The repeated-feeding multi-time Czochralski method does not cause the breakage of the crucible due to the cooling of the crucible like the single-time Czochralski method, so that the crucible can be fully utilized for multiple times in the service life.

At present, the repeated-feeding multi-time Czochralski method is the mainstream of the application in the industry, the improvement is made based on the repeated-feeding multi-time Czochralski method, and the method for continuously adding the polycrystalline silicon raw material in the crystal pulling process is the continuous Czochralski method. The silicon crystal rod produced by the continuous Czochralski method has better quality, more uniform resistivity and narrower distribution, and is more suitable for high-efficiency battery processes such as P-type PERC and the like and more efficient N-type battery processes, thereby being more beneficial to the production of high-power components. Based on the consideration of multiple factors such as efficiency, quality, cost and the like, the continuous Czochralski method gradually replaces the existing repeated-casting multiple Czochralski method.

Meanwhile, in the Czochralski single crystal pulling process, oxygen (oxygen atoms are components of quartz) and other impurities in the quartz crucible enter the melt under the scouring of the high-temperature molten silicon. In P-type solar cells, boron and oxygen atoms as dopants constitute a boron-oxygen complex causing a decline in cell efficiency. In electronic grade single crystal silicon wafers, oxygen precipitation is the major factor responsible for COP. Magnetic field MCZ (magnetic field czochralski) is mainly used in the integrated circuit industry to improve COP. The high temperature molten silicon in the magnetic field acts as a conductor to cut magnetic lines of force, and the generated Lorenz force can obstruct convection of the melt to reduce oxygen atoms entering the crystal, thereby reducing oxygen precipitation and finally inhibiting COP generation.

Although the magnetic field MCZ has good effects, it is extremely expensive in price and cost, and in addition to the power consumption of the magnetic field, the superconducting coil needs low-temperature excitation, and is also very expensive.

The crystal bar produced by the continuous Czochralski method has better quality, more uniform resistivity and narrower distribution. The beneficial effects are of great significance to the application of the solar cell and the electronic grade chip. However, the most significant effect is that a shallow crucible is used in the pulling process of the continuous czochralski method, and the convection suppression effect of the shallow crucible is significant, and the suppression effect on cop (crystal aligned crystal) grown-in defects is significant. Therefore, a 12-inch integrated circuit large silicon wafer with extremely high quality can be manufactured.

The current industry's major continuous czochralski process is developed by Solaicx and confluent Solar, respectively. The former is purchased by MEMC corporation and the latter becomes part of GTAT corporation.

Fig. 9 is a schematic cross-sectional view of a continuous czochralski crystal growing furnace of the prior art. Fig. 10 is a schematic cross-sectional view of another continuous czochralski crystal growing furnace of the prior art. As shown in FIGS. 9 and 10, the single crystal furnace is enclosed by a casing, the inside of which is in a vacuum state, and solid silicon raw material is continuously added from the outside into a crucible of the single crystal furnace by a transfer device.

However, the continuous Czochralski method described above involves continuously charging a crystal pulling crucible with a solid polycrystalline silicon charge, which is based on the solid polycrystalline silicon charge meeting a certain particle size maximum dimension requirement and thus flowability requirement, and which can be controlled by vibration or a flap mechanism. For example, GTAT corporation provides a vibratory conveying apparatus for continuous czochralski equipment, as shown in fig. 11, wherein the physical dimensions of the conveyed solid polysilicon material must meet the critical dimensional requirements of the transport path to avoid clogging or seizing.

Generally speaking, good flow properties are obtainable in industry, the quality of granular silicon which can be fed continuously is poor, the productivity is low, and the feeding amount cannot exceed 20% of the total feeding amount. Polycrystalline silicon produced by a Siemens method which is the mainstream in industrial production is rod-shaped, and the crushed shape is irregular large blocky inclusion part fine particles. If the size of the blocky polycrystalline silicon is too large, the blocky polycrystalline silicon needs to be further crushed to obtain small-grained polycrystalline silicon so as to carry out continuous feeding control through a traditional mechanical feeding device, wherein the traditional feeding device comprises a vibrating hopper and a flap valve port. The hardness of polysilicon is high, the fine particles generated during the crushing process are lost, and if a large amount of particles meeting the flowability requirement are crushed for flowability, the loss of powder is more, and the loss amount is from 1% to 5%. The crushing process enlarges the specific surface area (the ratio of the surface area to the volume) and also brings various potential surface pollutions, the common wet chemical cleaning can remove the surface pollutions, but the used chemical substances not only bring environmental pollution, but also lose a certain proportion of silicon due to corrosion. The ability to use near-original size Siemens polycrystalline silicon rods or chunks is therefore a requirement of the continuous Czochralski single crystal process, whereby charging with molten silicon is an option. However, current fluid control (valve, pipe) technology cannot meet the requirement of high purity under high temperature molten silicon conditions.

Disclosure of Invention

Aiming at the problems that the granular silicon and the Siemens polycrystalline silicon in the prior art can not meet the quality requirement or the fluidity required by continuous feeding, and the fluid control technology can not meet the high purity requirement under the condition of high-temperature molten silicon, the invention provides the method for controlling the conveying speed of the molten silicon by the melting crucible heater without the traditional valve technology. And further controlling the content of oxygen atoms in the single crystal by combining the design of the crucible.

According to one embodiment of the invention, a continuous czochralski crystal growing furnace for adjusting the silicon oxygen content of a single crystal according to requirements is provided, which is characterized by comprising:

a crucible;

a device for lifting and rotating the crucible;

the sealed shell surrounds and seals the whole structure of the continuous czochralski crystal growing furnace in vacuum; and

the inner dam is arranged in the crucible, the middle lower part of the inner dam is provided with an opening or the upper edge of the inner dam is provided with an overflow gap, so that the convection inside and outside the dam are mutually isolated and the liquid level is communicated,

the inner dam isolates the crucible as: the inner dam is made of non-silicon oxide high-purity materials resistant to molten silicon corrosion, or the inner dam is made of non-silicon oxide high-purity materials resistant to molten silicon corrosion.

In one embodiment of the invention, the shape of the inner dam comprises a cylinder or U-shape provided with openings and/or crenels.

In one embodiment of the invention, the material of the inner dam is silicon nitride.

In one embodiment of the invention, the continuous czochralski crystal growing furnace for regulating the content of the monocrystalline silicon oxygen according to requirements further comprises one or more of the following devices:

crucible supports arranged at the outer side and the bottom of the crucible;

one or more first heaters disposed outside and at the bottom of the crucible;

a magnetic field applying device which applies a magnetic field MCZ to the crucible, the magnetic field comprising a cusp-type, horizontal or vertical magnetic field.

In one embodiment of the invention, the continuous czochralski crystal growing furnace for adjusting the content of the monocrystalline silicon oxygen according to the requirement further comprises:

a silicon feeder installed above the crucible and supplying liquid silicon or solid polycrystalline silicon to the crucible according to a predetermined speed;

wherein the level of liquid molten silicon in the crucible has a depth less than 1/2 the diameter of the crucible and the maximum amount of molten silicon in the crucible is less than the total molten silicon requirement of a single pull 2/3.

In one embodiment of the invention, the silicon feeders are two or more silicon feeders arranged in parallel, and the same crucible is alternately or simultaneously filled,

wherein the silicon feeder comprises:

an open crucible having a top opening at a top and a sprue at a bottom, the open crucible receiving and containing solid silicon feedstock.

In one embodiment of the present invention, the silicon feeder comprises:

a hopper, said hopper being a container for holding solid polysilicon feedstock, said hopper having a bottom opening at the bottom thereof, said hopper bottom opening being in abutment with the open crucible top opening, said hopper being of a material that is quartz or high purity ceramic, or having a high purity coating on the inside surface thereof, said hopper further comprising:

the silicon material plug is arranged on the opening at the bottom of the hopper and comprises a silicon wafer, a silicon block, a raised key, a pin, a tooth or a mortise and tenon structure with the same diameter as the hopper.

In one embodiment of the invention, the continuous czochralski crystal growing furnace for adjusting the content of the monocrystalline silicon oxygen according to the requirement further comprises: an isolation device arranged at the connection position of the hopper and the open crucible, wherein when the isolation device is closed, the inside of the shell is isolated into two airtight spaces to make the hopper hermetically isolated from other devices, when the isolation device is opened, the two airtight spaces are communicated, the bottom opening of the hopper is butted with the top opening of the open crucible, and the isolation device comprises a body flange or an isolation valve

a second heater disposed at the periphery of the open crucible and heating the inside of the open crucible;

and the water cooling device is arranged on the shell adjacent to the heater.

In one embodiment of the invention, the material of the open crucible is silicon nitride, the upper part of the open crucible is a material melting area, the lower part of the open crucible is a superheat area, the injection port is positioned at the bottom of the superheat area, the size of the top opening of the open crucible is larger than that of the injection port, the material melting area directly melts solid silicon raw materials, the superheat area overheats molten silicon, and the overheated molten silicon enters the crucible through the injection port.

According to another embodiment of the invention, a method for controlling the silicon oxygen content of a single crystal is provided, which comprises the following steps:

melting the polycrystalline silicon by a molten silicon feeder;

injecting molten silicon into the crucible, wherein the level of liquid molten silicon in the crucible has a depth less than the crucible diameter of 1/2;

continuous Czochralski single crystal silicon is pulled by continuously injecting molten polycrystalline silicon to ensure that the maximum amount of molten silicon in the crucible is less than the total molten silicon demand of single pull 2/3, and the demand for molten silicon above single pull 1/3 is replenished by the molten silicon feeder.

In another embodiment of the present invention, injecting molten silicon into the crucible comprises:

controlling the melting speed of the solid polycrystalline silicon by the second heater so as to control the position and pressure of the liquid level of the molten silicon and the outlet pressure of the injection port; and

controlling the rate of injection of molten silicon into the crucible based on the position and pressure of the molten silicon level and the outlet pressure of the injection port, as expressed by the following equation:

wherein g represents the gravitational acceleration, ρ represents the density of the molten polysilicon, and z₁Denotes the height, u, of the molten silicon level₁Flow rate, p, representing the position of the surface of molten silicon₁Pressure, z, representing the position of the surface of the molten silicon₂Indicating the height of the outlet of the injection port, u₂Represents the implantation velocity, p₂Indicating the pressure at the outlet of the injection port, w_eRepresents the external work of the molten silicon feeder during the injection, w_fRepresenting the loss of flow resistance.

In another embodiment of the invention, when the hopper needs to be replaced,

closing the isolation device to isolate the hopper;

introducing gas to balance the air pressure of the space where the hopper is located with the external atmospheric pressure;

removing the hopper and inserting another hopper filled with solid polycrystalline silicon;

vacuumizing the space where the other hopper full of solid polycrystalline silicon is positioned to balance pressure, and opening an isolating device; and

the other solid-laden polysilicon hopper is docked with the open crucible and heated to melt the plug of silicon material.

In another embodiment of the invention, the exchange between the fluid molten silicon in the dam and the high oxygen volatilization region outside the dam where the bottom and the wall of the crucible are positioned is controlled by adjusting the size of the opening of the dam in the crucible, so that the oxygen atom concentration in the monocrystalline silicon can be controlled according to the requirement.

In another embodiment of the present invention, the method of controlling the content of single crystal silicon oxygen further comprises applying a magnetic field MCZ to the crucible, the magnetic field comprising a cusp-type, horizontal or vertical magnetic field.

The invention can obtain the effects of better quality of the silicon crystal rod, more uniform resistivity and narrower distribution in the continuous Czochralski technology, is more suitable for the high-efficiency battery process such as P-type PERC and the like and the high-efficiency N-type battery process, and is more beneficial to the output of high-power components. The defects that the Siemens method polycrystalline silicon lump material always puzzles the continuous straight pulling technology is poor in flowability and transport performance, continuous and stable feeding is difficult to carry out, the quality of granules with good transport performance is poor, the yield is low, the granules cannot be fed completely and the like are overcome. According to the invention, the polysilicon rod obtained after the Siemens reduction furnace is disassembled can be directly added into the hopper without being crushed for use, so that the production efficiency is improved, the probability of silicon pollution is reduced, and the cost is reduced. Meanwhile, the invention can obviously reduce the oxygen content of the Czochralski single crystal and reduce COP (coefficient of performance) primary defects and boron-oxygen complexes caused by oxygen, thereby improving the performance of the electronic silicon wafer and improving the conversion efficiency of the solar cell.

Drawings

To further clarify the advantages and features that may be present in various embodiments of the present invention, a more particular description of various embodiments of the invention will be rendered by reference to the appended drawings. It is appreciated that these drawings depict only typical embodiments of the invention and are therefore not to be considered limiting of its scope. In the drawings, the same or corresponding parts will be denoted by the same or similar reference numerals for clarity.

FIG. 1A shows a schematic view of the structure of a molten silicon feeder according to an embodiment of the present invention.

FIG. 1B shows a variation of the molten silicon feeder shown in FIG. 1A, according to one embodiment of the present invention.

FIG. 2 is a schematic view showing the structure of a single crystal pulling furnace for continuous pulling of a single crystal according to an embodiment of the present invention.

Figure 3 shows a schematic diagram of the structure of a hopper in one embodiment of the invention.

Figure 4 shows a schematic view of the shape of a hopper bottom plug in one embodiment of the invention.

FIG. 5 shows a flow chart for performing a fast swap in one embodiment of the present invention.

FIG. 6 illustrates convection currents in a single crystal silicon crucible in one embodiment of the present invention.

FIG. 7A shows a schematic view of a shallow crucible and its inner dam according to one embodiment of the present invention.

FIG. 7B shows a schematic view of a shallow crucible and its inner dam according to another embodiment of the present invention.

FIG. 8A shows a schematic view of a shallow crucible and its inner dam according to one embodiment of the present invention.

FIG. 8B shows a schematic view of a shallow crucible and its inner dam according to another embodiment of the present invention.

Fig. 9 is a schematic cross-sectional view of a continuous czochralski crystal growing furnace of the prior art.

Fig. 10 is a schematic cross-sectional view of another continuous czochralski crystal growing furnace of the prior art.

FIG. 11 shows a schematic view of a vibratory conveying apparatus of a continuous Czochralski method apparatus of the prior art.

Detailed Description

It should be noted that the components in the figures may be exaggerated and not necessarily to scale for illustrative purposes. In the figures, identical or functionally identical components are provided with the same reference symbols.

In the present invention, "disposed on …", "disposed over …" and "disposed over …" do not exclude the presence of an intermediate therebetween, unless otherwise specified. Further, "disposed on or above …" merely indicates the relative positional relationship between two components, and may also be converted to "disposed below or below …" and vice versa in certain cases, such as after reversing the product direction.

In the present invention, the embodiments are only intended to illustrate the aspects of the present invention, and should not be construed as limiting.

In the present invention, the terms "a" and "an" do not exclude the presence of a plurality of elements, unless otherwise specified.

It is further noted herein that in embodiments of the present invention, only a portion of the components or assemblies may be shown for clarity and simplicity, but those of ordinary skill in the art will appreciate that, given the teachings of the present invention, required components or assemblies may be added as needed in a particular scenario. Furthermore, features from different embodiments of the invention may be combined with each other, unless otherwise indicated. For example, a feature of the second embodiment may be substituted for a corresponding or functionally equivalent or similar feature of the first embodiment, and the resulting embodiments are likewise within the scope of the disclosure or recitation of the present application.

It is also noted herein that, within the scope of the present invention, the terms "same", "equal", and the like do not mean that the two values are absolutely equal, but allow some reasonable error, that is, the terms also encompass "substantially the same", "substantially equal". By analogy, in the present invention, the terms "perpendicular", "parallel" and the like in the directions of the tables also cover the meanings of "substantially perpendicular", "substantially parallel".

The numbering of the steps of the methods of the present invention does not limit the order of execution of the steps of the methods. Unless specifically stated, the method steps may be performed in a different order.

The invention is further elucidated with reference to the drawings in conjunction with the detailed description.

One embodiment of the present invention provides a molten silicon feeder 100 having three working zones, as shown in FIG. 1A. The molten silicon feeder 100 includes a hopper 110, a heater 120, an open crucible 130, a partition 140, and a housing 150.

The inner walls of the charger 100 (including the inner layer of the hopper 110 and the inner layer 131 of the open crucible 130) are high temperature resistant, high purity materials. The high-temperature-resistant high-purity material comprises quartz, high-purity ceramic or molten silicon corrosion-resistant high-purity material and material with a high-purity coating resistant to molten silicon corrosion. By open crucible is meant a crucible having an open mouth at the lower portion such that it can only dynamically contain molten silicon such that it can continuously replenish the crystal growth crucible with molten silicon at a given rate. The openings in the lower portion include openings in the bottom or lateral openings in the lower portion of the side edges. The open crucible is small and does not need to bear the gravity of a large amount of molten silicon, and silicon nitride ceramics can be used. The silicon nitride is non-infiltrated with the melt silicon and does not contain oxygen, which is beneficial to reducing oxygen atoms entering the melt and can improve COP of the electronic grade single crystal and boron-oxygen recombination of the solar silicon wafer.

The operational zones of the feeder 100 include a solid feed zone, a melting zone, and a superheating zone. The hopper 110 is in the solid feedstock area. The bottom opening of the hopper 110 interfaces with or partially overlaps the top opening of the open crucible 130. The outer layer 132 of the open crucible 130 is a thermally insulating material such as graphite, carbon felt composite, or ceramic refractory. In some cases, the outer layer 132 is not necessarily designed (e.g., in the case where the material of 131 is quartz, the quartz softens under the temperature condition of the molten silicon and may be broken after cooling, and thus the outer layer 132 is required to physically support and protect the quartz (to prevent the molten silicon from leaking). in the case where the outer heater is an induction coil, the induction coil cannot be directly exposed to high temperature, and the insulation material of the outer layer 132 may be used to insulate the high temperature crucible, and in general, the induction coil itself needs to be water-cooled). if a graphite resistance heater is used as in a conventional czochralski crystal growing furnace, the insulation material needs to be disposed outside the heater 120 to insulate the heater. In this case, if 131 is made of quartz, it still needs 132 to physically support and protect 131. The heater 120 is disposed at the periphery of the open crucible 130, and heats the silicon material inside the open crucible 130. The open crucible 130 has an upper portion in the melting zone and a lower portion in the superheating zone. In some embodiments of the present invention, the diameter of the hopper 110 is configured to be suitably larger than the diameter of the bar-shaped silicon (the primary bar of the polysilicon reduction furnace is usually 100mm to 200mm), so that the Siemens method polysilicon with a larger lump can be directly put into the inner barrel of the feeder for melting and using, without being limited to the crushed Siemens polysilicon, but the same can also be applied to the granular polysilicon.

In an embodiment of the present invention, the hopper 110 may further include a loading port 111 and a top ram 112. In the solid feedstock region, unmelted silicon is conveyed by gravity or by a pusher 112 to the lower melting region, or to indicate the height of the remaining silicon charge in the hopper 110.

In some embodiments of the present invention, heater 120 may comprise a plurality of independently controlled heaters. Each heater may be an induction coil or a resistive (graphite, silicon carbide or refractory metal, etc.) heater. These induction coils or heaters are disposed at the periphery of the melting zone and the superheating zone of the open crucible 130. The diameter of the material melting area is changed to a certain extent from the overheating area, so that the material melting area can directly melt a large primary Siemens silicon rod and the size of the injection port 133 is kept small, and the silicon liquid can enter the monocrystalline silicon crucible at a set flow rate to finish growth.

In the embodiment shown in FIG. 1A, the heater 120 is three independently controlled induction coils, however, it should be understood by those skilled in the art that the heater of the present invention is not limited to the specific configuration shown in FIG. 1A. The type and number of heaters can be selected by those skilled in the art according to the actual heating needs.

Since high purity silicon is nearly non-conductive at room temperature, the induction coil cannot directly heat the room temperature silicon. Thus, the induction heater 120 needs to be designed with a microwave or resistive heater as a part of the silicon material to preheat, the preheated silicon can be heated by the induction coil, and the pre-conduction process is also called as breakdown. The broken silicon material can be heated by an induction heater. In other embodiments of the invention, the required breakdown heat of the silicon material can be introduced from the lower high temperature crystal pulling crucible, so that a part of the silicon material is heated by the induction coil after reaching the breakdown temperature.

In the material melting area, due to the skin effect of induction heating or uneven heat transfer, a certain solid-liquid mixing phenomenon may exist in the area.

The rate of melting of silicon is controlled by the heating power of the heater 120. The heating power, the minimum pipe diameter of the injection port 133, and the molten silicon level (outlet pressure) of the injection pipe determine the maximum outflow rate of silicon.

Because the inner diameter of the lower opening of the crucible is reduced, a plurality of heaters with outward centers can be arranged; the heater may be multi-zone independent heating; the power of the single heater is 100w-500 kw. The height of the molten silicon (outlet pressure) can be adjusted by varying the power of the plurality of independently controlled heaters 120. When the silicon injection speed needs to be increased, the power is increased, and the silicon in the high area is further melted, so that the liquid level of the molten silicon is increased, the outlet pressure is increased, and the silicon injection speed is increased. When a smaller silicon injection flow rate is required, the number of heaters to be put in can be reduced and only the lower heater is used. The lower part of the open crucible 130 is a superheat region, and the injection port 133 is positioned at the bottom end of the superheat region, so that the molten silicon flows to the crucible of the czochralski crystal growing furnace, and the molten silicon is properly superheated, so that the molten silicon is not blocked due to supercooling condensation.

Assuming a 310mm round bar is drawn, the draw rate is assumed to be 1mm/min, and the draw rate is increased or decreased, and the required exit injection is increased or decreased accordingly, as shown in the following table:

TABLE 1

The injection port diameter is enlarged to 2 cm and the required exit flow rate can be reduced to 24 cm/min.

An excessively large opening may cause a large mass of silicon liquid or even unmelted silicon blocks to directly fall into the crucible and splash out of the crucible to cause potential safety hazards. An excessively small opening may not allow a sufficient flow rate to be obtained only by the molten silicon level. Therefore, a moderate opening can compromise injection rate, silicon fluid splash and safety, and in summary, the opening inner diameter is set to be between about 1mm and about 100mm in embodiments of the present invention.

The heating power of the heating zone controls the melting speed of the solid polysilicon so as to control the position and pressure of the molten silicon liquid level and the pressure of the injection port outlet.

According to the control of the rate of injection of molten silicon into a single crystal silicon crucible, expressed as follows:

The housing 150 surrounds the hopper 110, the heater 120, and the open crucible 130, and is vacuum-sealed. The interior of the housing 150 is placed in a vacuum state by a vacuum device in operation. The isolation device 140 is provided at a connection position of the hopper 110 and the open crucible 130. The isolation device 140 is used to hermetically isolate the hopper 110 from other devices when the hopper 110 is replaced. That is, the isolation device 140 may isolate the interior of the housing 150 into two airtight spaces: an upper hopper space and a lower open crucible space. The isolation device 140 may be an isolation flange, body flange, plug-in valve, or other gas-tight device.

The housing 150 may be a metal container and a cooling water jacket needs to be added at a portion near the heater.

The open crucible 130 is optionally supported on the housing 150 by an open crucible support unit 160.

When the reinforced hopper is replenished to needs, both can still use traditional vibration, turn over the hopper through the traditional charge door 111 in the upper right corner and carry out reinforced transport, also can carry out quick reloading through directly changing the hopper.

In particular, fig. 5 shows a flow diagram of a method of quickly replacing a hopper according to one embodiment of the invention. Directly change the hopper includes: lifting the existing hopper, closing the isolation device 140, and hermetically isolating the hopper 110 from other devices; the space in which the hopper 110 is located is vented so that it is in equilibrium with the ambient atmospheric pressure. Opening the housing 150, removing the original hopper, and inserting a new fully loaded hopper; vacuumizing the reloading hopper to balance pressure, and opening the isolating device 140; and a new hopper is butted against the open crucible 130 and the refueling is completed.

In one embodiment of the invention, in order to prevent the hopper device from being replaced and solid silicon material in the hopper from spilling, silicon wafers with the same diameter as the hopper can be used as a disposable bottom plate at the bottom of the hopper, wherein the silicon bottom plate (silicon wafer) with the diameter smaller than 300mm is easy to manufacture for the solar industry, and czochralski monocrystalline polycrystal with the diameter of 400mm-600mm also belongs to products which can be produced in mass production. A 1000mm dimension block of silicon can be easily obtained if ingot casting techniques are used. When the new hopper is butted with the open crucible, the silicon wafer bottom plate is melted, and the solid silicon material can enter the material melting area.

In other embodiments of the invention, other shapes of hopper bottom structures may be used, as will be described in more detail below.

FIG. 1B shows a variation of the molten silicon feeder shown in FIG. 1A, according to one embodiment of the present invention. As shown in fig. 1B. The molten silicon feeder 1001 includes a heater 1201, an open crucible 1301, and a housing 1501. The heater 1201, open crucible 1301 and enclosure 1501 are similar to the corresponding heater 120, open crucible 130 and enclosure 150 shown in FIG. 1A and therefore will not be described in detail.

The feeder 100 shown in fig. 1B differs from the feeder shown in fig. 1A in that no hopper and isolation device need be used. The solid feedstock is placed directly in an open crucible.

Fig. 2 shows a schematic view of a czochralski crystal growing furnace 200 for continuous czochralski crystal growth, according to an embodiment of the present invention. The Czochralski crystal growing furnace 200 includes a crucible 210 and a silicon feeder 220, as shown in FIG. 2. The silicon feeder 220 is similar in structure to the molten silicon feeder described in connection with FIG. 1A and will not be described again in order to simplify the present description. The silicon feeder 220 is installed above the crucible 210 of the Czochralski crystal growing furnace, and has a housing 221 made of metal and attached to a housing of the Czochralski crystal growing furnace or formed as a part of the Czochralski crystal growing furnace, the housing being resistant to a vacuum necessary for pulling the single crystal. In the embodiment shown in fig. 2, only a portion of the crucible and the housing are shown for simplicity of illustration, and those skilled in the art can conceive of the overall structure of the single crystal furnace based on the portion of the illustration shown in fig. 2.

The silicon feeder 220 is internally provided with a heating zone and a hopper (barrel) above the heating zone, and the hopper is made of high-purity materials such as high-purity quartz or high-purity ceramic and the like.

It will be appreciated by those skilled in the art that the silicon feeder 220 may be the feeder shown in FIG. 1B or other types of feeders. As long as the crucible 210 can be supplied with the solid or liquid raw material, it can be used as a feeder of the czochralski crystal growing furnace 200 of the present invention. Therefore, any feeder that can supply solid or liquid raw material to the crucible falls within the scope of the present invention.

Crucible 210 is a long crystal crucible similar to conventional czochralski single crystal techniques for holding molten silicon, and may be made of quartz, high purity ceramic, silicon nitride, or other high melting point materials. The crucible 210 has an inner crucible dam 211 therein. The crucible inner dam 211 and the crucible 210 are concentrically driven to rotate and/or (lift) by a crucible driving shaft 240 at the bottom, and the lower part of the crucible inner dam 211 is provided with an opening or the upper edge is provided with an overflow gap, so that the convection inside and outside the dam is mutually isolated and the liquid level is communicated. The structure and function of the inner crucible dam 211 will be described in detail hereinafter.

In one embodiment of the present invention, a susceptor 212 may be provided outside the crucible 210. For example, when the crucible 210 is a quartz crucible, the susceptor 212 is a graphite, carbon felt composite, or ceramic susceptor. The susceptor 212 may serve as a support and insulation.

One or

more heaters

231, 232 may be provided at the bottom and sides of the crucible 210. Each heater may be an induction coil or a resistive heater such as a graphite, silicon carbide or refractory metal. The heater may be multi-zone independent heating; the power of the single heater is 100w-500 kw.

At the bottom of the crucible 210, there is a crucible shaft 240 for rotating the crucible. If there is a metal shell outside the heating zone, the shell needs water cooling protection.

The inner dam 211 can be conveniently realized by using silicon nitride ceramics due to small size, the silicon nitride is non-infiltrated with melt silicon, and does not contain oxygen, thereby being beneficial to reducing oxygen atoms entering the melt and improving COP of electronic grade single crystal and boron-oxygen recombination of solar silicon wafers. Nitrogen atoms in the silicon nitride enter the molten silicon, and nitrogen-doped single crystals in the semiconductor can be realized.

The heating zones of the silicon feeder 220 are: a solids addition zone, a digestion zone (possibly a solid-liquid mixing zone) and a superheat injection zone; the superheat injection zone injects molten silicon into the crucible; the overheating injection area can be a downward opening of the open crucible, and the diameter of the opening is smaller than the diameter of the hopper (the diameter of the opening at the upper part of the crucible); the part of the quartz open type crucible injection port, which is not subject to the gravity of the molten silicon, can be free from designing a crucible support; the lower inner diameter of the heater (open crucible lower opening) and the upper inner diameter of the heater (open crucible lower opening) are between 1mm and 500 mm.

A body flange (body flap) or an isolation valve (gate valve and the like) which can be isolated is arranged in the middle of the silicon feeder 220 and serves as an isolation device, so that the upper part and the lower part of the valve or the flange can be closed or isolated or disassembled after being closed; the body flange or the isolation valve can separate the hopper after the polycrystalline silicon in the hopper above is consumed, and close the valve or isolate the body flange; the interior of the feeder above the flange or the valve is refilled to the atmospheric pressure and then opened, and a new hopper is loaded; the effective inner diameter of the body flange or the isolation valve is between 5mm and 500 mm.

And the bottom of the new hopper is a plug made of silicon wafers or silicon materials, after the pressure is balanced, the isolation valve is opened, the silicon bottom plate at the bottom of the hopper is inserted into the open crucible, and the silicon bottom plate or the silicon plug is heated until the silicon bottom plate or the silicon plug is melted. The second addition is complete.

In one embodiment of the invention, 2 or more than 2 feeders are used to operate alternately to ensure continuous growth through a minimum of shallow crucibles. 2 or more than 2 feeders can be placed at different positions above the crucible.

In one embodiment of the invention, a shallow crucible is used to suppress convection.

In conventional crystal pulling techniques, the convection mode differs greatly as the crystal grows, the molten silicon is consumed, and the melt depth in the crucible varies. Particularly, as the crucible rises, boundary layers of molten silicon and the crucible wall and bottom are positioned at different positions of the cusp type magnetic field, the direction of the magnetic field, the field intensity and the like can be greatly changed, so that the convection mode is greatly changed, and the axial and radial oxygen distribution in the crystal is a very complicated mode. In the continuous Czochralski technique, the reduced height of the charge in the crucible is reduced to a so-called shallow crucible, the crucible no longer needs to be raised by a large amount to match the silicon level drop after the molten silicon consumption (which is compensated for by the continuous charge), and the crystal growth interface is maintained at the same silicon level and the same position of the magnetic field (if present) to maintain the same convection pattern. The single convection mode is easily optimized for crystal growth parameters, so that the boundary layer of oxygen diffusion at the pot bottom and the pot wall is thickest and the oxygen diffusion is least; while the oxygen atoms volatilized by free convection to the crucible surface are maximized, thereby minimizing the oxygen atoms entering the crystal growth.

The Gravax Gr is a dimensionless number in fluid dynamics and heat transfer that approximates the ratio of buoyancy to viscous forces acting on the fluid to characterize buoyancy-driven natural thermal convection due to temperature gradients within the melt, and is expressed by the following equation:

wherein alpha is_vThe volume change coefficient is expressed, the ideal gas is equal to the reciprocal of absolute temperature, g represents the gravity acceleration, L represents the characteristic scale, delta t is the temperature difference, and v represents the kinematic viscosity.

The cause of the primary crystal defect COP is the accumulation of empty-site defects,oxygen atoms from the quartz crucible enter a melt through convection to grow and precipitate in the silicon crystal to form vacancies, which are important causes of COP; the convection can be obviously reduced by reducing the depth of the crucible, and foreign impurities such as oxygen atoms brought by the convection can be inhibited, so that the original COP defect can be inhibited; from Gravaxiafu number G_rThe formula shows that when the liquid level of the crucible is reduced, the convection intensity is correspondingly reduced; whereas shallow crucible pulling corresponds to the state when the pulling is near the end and the molten silicon is about to be depleted. Namely, the shallow crucible can inhibit convection and reduce the oxygen content in the crystal, thereby reducing COP defects;

convection is suppressed to produce COP-free single crystal silicon using a shallow crucible in which the level of liquid molten silicon is at a depth less than the crucible diameter of 1/2. During crystal pulling, the maximum amount of molten silicon in the shallow crucible is less than the total molten silicon demand of single pull 2/3, and the demand of molten silicon above single pull 1/3 is replenished by the charge.

The shallow crucible is used to suppress convection and to combine a magnetic field MCZ, including cusp, horizontal, and vertical magnetic fields, to produce a COP-free single crystal.

Fig. 3 shows a schematic view of a hopper 300 according to an embodiment of the invention. The hopper 300 may use quartz. The polycrystalline silicon rod may be directly put into the hopper 300. The bottom of the hopper 300 has a silicon plug 310.

Figure 4 shows a schematic view of a number of variations of a hopper according to an embodiment of the invention. As shown in fig. 4, 410 represents a section of the hopper and 420 represents a top view of the hopper, with four variants of the stopper of the bottom of the hopper, respectively indicated as 430 to 460. The mechanical design of the plug at the bottom of the hopper can be designed into a plurality of different shapes including a cylinder, a cone, a square and an inverted trapezoid.

The plug can also be added with a convex key or a pin, tooth and tenon structure.

The plug may be of other master alloy materials for doping or may already contain doped silicon material. The plug may be monocrystalline silicon or polycrystalline silicon, or other crystalline silicon or silicon alloy, or even semiconductor materials such as germanium.

Based on the processing cost of the silicon wafer, during transition processing, the machining equipment possibly causes pollution to the system, and the circular silicon wafer with proper thickness capable of bearing the weight of the silicon material in the feeding hopper is the best choice for cost, realization difficulty and impurity contamination risk.

Casting polycrystalline (or quasi-single crystal) allows large-size silicon ingots to be easily obtained, which is an important option for manufacturing plugs (bottom plates).

In one embodiment of the present invention, a silicon nitride crucible internal dam is used to prevent oxygen atoms from the quartz crucible walls and bottom from entering the dam by convection to produce a COP-free single crystal.

In the process of the convection of the czochralski single crystal, the upward extraction and lifting of the molten silicon are realized by the czochralski crystal, and the forced convection is caused by combining the rising buoyancy of the natural thermal convection and the rotation of the crucible and the crystal. Convection currents from the crucible can be generalized to two flow cells Cs and Cf as shown in fig. 6. The oxygen atoms exchanged into the molten silicon come from the crucible bottom and the crucible wall. Wherein Cf obtains oxygen atoms at the bottom and the side wall of a crucible below, and simultaneously, oxygen in Cf can be volatilized on the liquid level of Cf in a large amount, so that the oxygen content is reduced. The oxygen in Cs comes from the bottom of the crucible below Cs and exchanges with the material on the interface layer of the Cf flow cell, and finally the oxygen content in Cs determines the oxygen content of the crystal.

Embodiments of the present invention therefore use a dam of silicon nitride material in the shallow crucible to isolate as much of the crucible wall as possible from the crucible bottom. FIG. 7A shows a schematic view of a shallow crucible and its inner dam according to one embodiment of the present invention. The inner dam 710 is a U-shaped inner dam having an opening 711 at the bottom. FIG. 7B shows a schematic view of a shallow crucible and its inner dam according to another embodiment of the present invention. The inner dam 720 is a U-shaped inner

dam having openings

721 and 722 at the bottom and side top. FIG. 8A shows a schematic view of a shallow crucible and its inner dam according to one embodiment of the present invention. The inner dam 810 has only side walls with an opening 811 at the bottom of the side walls. FIG. 8B shows a schematic view of a shallow crucible and its inner dam according to another embodiment of the present invention. Inner dam 820 has only side walls with

openings

821 and 822 at the bottom and bottom of the side walls. The molten silicon consumed for compensation crystallization enters only through the opening of the dam, i.e. the mass exchange is limited to the molten silicon entering the inner dam from outside the dam, at a rate equal to the rate of crystal growth, and the amount of oxygen atoms entering Cs per unit time is only equal to the rate of crystal growth per unit Cf of oxygen content in the molten silicon. The mass of oxygen atoms of Cs is the mass exchange rate of the melt convection per Cf oxygen content of the molten silicon. Since the rate of crystal growth is much lower than the flux exchange rate of convection of the crucible melt, the oxygen content in Cs is greatly reduced. If the exchange holes of the inner dam are opened so that the fluid exchange rate of the melt convection is higher than the rate of the crystal growth, a specified oxygen atom content between the two can be obtained.

The forming and processing of high purity materials resistant to erosion by molten silicon and the cost have been a problem in the industry. Based on the principle of the invention, various complex shapes can be designed to achieve the purpose of controlling the exchange of fluid substances. Practitioners in the art should and will understand that the design of these contoured dams is within the scope of the present invention. However, in combination with industrial practice, cost and feasibility, an open tubular or U-shaped design is the most economically feasible implementation.

Silicon nitride is not infiltrated with molten silicon and is different from a quartz crucible; and the inner dam is open and leaks, so that damage caused by expansion coefficient when the residual molten silicon in the crucible is condensed can be avoided through proper design, and the silicon nitride ceramic inner dam can be used at multiple positions after being cooled.

Conventional silicon nitride ceramics require bonding using sintering agents composed of metal oxides, which can be a source of contamination for crystal growth. The reaction sintering silicon nitride without sintering agent, which is combined by the nitridation reaction of the high-purity silicon powder, can achieve high purity and is a good choice for pulling crystal. Generally, reaction bonded silicon nitride contains a proportion of unreacted free silicon, which when heated to near the melting point of silicon results in a decrease in the strength of the ceramic. Therefore, the reaction bonded silicon nitride ceramic has potential safety hazard when being used for bearing dozens or even hundreds of kilograms of high-temperature molten silicon, but is enough to be used as a non-bearing crucible inner dam.

The nitrogen-doped single crystal usually uses silicon nitride powder, and the silicon nitride crucible in the invention can also play a certain role in nitrogen doping.

FIGS. 7A, 7B, 8A and 8B illustrate different sizes of the inner dam opening in the crucible inner dam, wherein the opening in FIGS. 8A and 8B is larger relative to the opening in FIGS. 7A and 7B, with more oxygen atoms entering the inner dam.

For electronic grade single crystals, completely oxygen free single crystals are not a technical pursuit. In defect engineering of monocrystalline silicon, internal gettering is achieved by oxygen precipitation. At the same time, the literature also shows that the oxygen content is related to the mechanical strength of the single crystal rod. By utilizing defect engineering technology, reasonable and proper amount of oxygen is added to be beneficial to the quality of the crystal. Therefore, the material exchange of the quartz crucible (bottom and wall) to the molten silicon in the inner dam is regulated by reporting the opening size of the inner dam, so as to obtain the oxygen content with a set proportion, thereby realizing defect engineering to improve the quality of the monocrystalline silicon.

Because the dam mainly has the function of isolating material exchange caused by convection, the dam can be formed by splicing, joggling or even separating a plurality of non-integrated materials. It is only necessary that a large displacement is not generated in the crucible by rotation of the crucible or convection.

While various embodiments of the present invention have been described above, it should be understood that they have been presented by way of example only, and not limitation. It will be apparent to persons skilled in the relevant art that various combinations, modifications, and changes can be made thereto without departing from the spirit and scope of the invention. Thus, the breadth and scope of the present invention disclosed herein should not be limited by any of the above-described exemplary embodiments, but should be defined only in accordance with the following claims and their equivalents.

Claims

1. A continuous czochralski crystal growing furnace for adjusting the content of monocrystalline silicon oxygen according to requirements is characterized by comprising:

a crucible;

a device for lifting and rotating the crucible;

2. The continuous czochralski crystal growing furnace for conditioning the content of monocrystalline silicon oxygen as required according to claim 1, wherein the shape of the inner dam comprises a cylinder or a U-shape provided with openings and/or crenels.

3. The continuous czochralski crystal growing furnace for conditioning the silicon oxygen content of single crystals as required according to claim 1, wherein the material of said inner dam is silicon nitride.

4. The continuous czochralski crystal growing furnace for conditioning the silicon oxygen content of single crystals as required of claim 1, further comprising one or more of the following means:

crucible supports arranged at the outer side and the bottom of the crucible;

one or more first heaters disposed outside and at the bottom of the crucible;

5. The continuous czochralski crystal growing furnace for conditioning the silicon oxygen content of single crystals as required of claim 1, further comprising:

6. The continuous direct crystal pulling furnace for adjusting the silicon oxygen content as required in claim 5, wherein the silicon feeders are two or more silicon feeders arranged in parallel and feed the same crucible alternately or simultaneously,

wherein the silicon feeder comprises:

7. The continuous direct crystal pulling furnace for conditioning silicon oxygen content of a single crystal as required of claim 6 wherein said silicon feeder comprises:

8. The continuous czochralski crystal growing furnace for conditioning the silicon oxygen content of single crystals as required of claim 7, further comprising: and the isolating device is arranged at the connecting position of the hopper and the open crucible, separates the inside of the shell into two airtight spaces when the isolating device is closed so as to enable the hopper to be airtight isolated from other devices, communicates the two airtight spaces when the isolating device is opened, and is in butt joint with the top opening of the open crucible through the bottom opening of the hopper, and the isolating device comprises a body flange or an isolating valve.

9. The continuous czochralski crystal growing furnace for conditioning the silicon oxygen content of single crystals as required of claim 6, further comprising:

and the water cooling device is arranged on the shell adjacent to the heater.

10. The continuous direct pulling single crystal furnace for adjusting the content of single crystal silicon oxygen as required in claim 6, wherein the material of the open crucible is silicon nitride, the upper part of the open crucible is a melting region, the lower part of the open crucible is a superheating region, the sprue is arranged at the bottom of the superheating region, the opening size at the top of the open crucible is larger than that of the sprue, the melting region directly melts the solid silicon raw material, the superheating region superheats the molten silicon, and the superheated molten silicon enters the crucible through the sprue.

11. The continuous czochralski crystal growing furnace for conditioning the silicon oxygen content of single crystals as required according to claim 1, wherein the inner dam is a non-integral multi-piece material mosaic structure, joggle structure or multi-piece independent structure.

12. A method for controlling the content of monocrystalline silicon oxygen using the continuous czochralski crystal growing furnace of any one of claims 1 to 11, comprising:

melting the polycrystalline silicon by a molten silicon feeder;

13. The method of controlling silicon oxygen content of a single crystal of claim 11, wherein injecting molten silicon into the crucible comprises:

14. The method of claim 11 wherein when the hopper needs to be replaced,

closing the isolation device to isolate the hopper;

15. The method of claim 11 wherein the oxygen concentration in the single crystal silicon is controlled on demand by adjusting the size of the openings in the internal dam of the crucible to control the exchange of the fluid molten silicon in the dam with the high oxygen volatilization zone outside the dam where the bottom and walls of the crucible are located.

16. The method of claim 1, further comprising applying a magnetic field MCZ to the crucible, wherein the magnetic field comprises a cusp-type, horizontal, or vertical magnetic field.