CN110923807A - Thermal field and method for improving quality of monocrystalline silicon - Google Patents
Thermal field and method for improving quality of monocrystalline silicon Download PDFInfo
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- CN110923807A CN110923807A CN201911410265.8A CN201911410265A CN110923807A CN 110923807 A CN110923807 A CN 110923807A CN 201911410265 A CN201911410265 A CN 201911410265A CN 110923807 A CN110923807 A CN 110923807A
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- C—CHEMISTRY; METALLURGY
- C30—CRYSTAL GROWTH
- C30B—SINGLE-CRYSTAL GROWTH; UNIDIRECTIONAL SOLIDIFICATION OF EUTECTIC MATERIAL OR UNIDIRECTIONAL DEMIXING OF EUTECTOID MATERIAL; REFINING BY ZONE-MELTING OF MATERIAL; PRODUCTION OF A HOMOGENEOUS POLYCRYSTALLINE MATERIAL WITH DEFINED STRUCTURE; SINGLE CRYSTALS OR HOMOGENEOUS POLYCRYSTALLINE MATERIAL WITH DEFINED STRUCTURE; AFTER-TREATMENT OF SINGLE CRYSTALS OR A HOMOGENEOUS POLYCRYSTALLINE MATERIAL WITH DEFINED STRUCTURE; APPARATUS THEREFOR
- C30B15/00—Single-crystal growth by pulling from a melt, e.g. Czochralski method
- C30B15/14—Heating of the melt or the crystallised materials
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- C—CHEMISTRY; METALLURGY
- C30—CRYSTAL GROWTH
- C30B—SINGLE-CRYSTAL GROWTH; UNIDIRECTIONAL SOLIDIFICATION OF EUTECTIC MATERIAL OR UNIDIRECTIONAL DEMIXING OF EUTECTOID MATERIAL; REFINING BY ZONE-MELTING OF MATERIAL; PRODUCTION OF A HOMOGENEOUS POLYCRYSTALLINE MATERIAL WITH DEFINED STRUCTURE; SINGLE CRYSTALS OR HOMOGENEOUS POLYCRYSTALLINE MATERIAL WITH DEFINED STRUCTURE; AFTER-TREATMENT OF SINGLE CRYSTALS OR A HOMOGENEOUS POLYCRYSTALLINE MATERIAL WITH DEFINED STRUCTURE; APPARATUS THEREFOR
- C30B29/00—Single crystals or homogeneous polycrystalline material with defined structure characterised by the material or by their shape
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- C30B29/06—Silicon
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Abstract
The invention discloses a thermal field and a method for improving the quality of monocrystalline silicon. The thermal field comprises a quartz crucible, a main heater and an auxiliary heater which are coaxially arranged in an equal diameter mode, wherein the main heater is arranged relative to the middle upper portion of the quartz crucible and is formed by a plurality of main heating valve rings with equal length; the auxiliary heater is arranged opposite to the lower part of the quartz crucible and is formed by a plurality of auxiliary heating rings with equal length, and the surfaces of the main heater and the auxiliary heater are also sprayed with high-temperature resistant water-based nano coatings for avoiding carbon volatilization. The method comprises the steps of cleaning polycrystalline silicon materials, cleaning a furnace, charging, melting materials, secondarily charging, guiding a neck, shouldering, equalizing the diameter, ending and extracting. The thermal field provided by the invention can reduce thermal convection and the content of impurities such as monocrystalline oxygen element and the like in monocrystalline silicon, and the monocrystalline silicon prepared by the method has low content of impurities such as oxygen, carbon, metal and the like, and when the thermal field is used for producing a battery piece, the efficiency of the battery can be effectively improved, and the attenuation of the battery piece is reduced.
Description
Technical Field
The invention relates to the technical field of monocrystalline silicon growth and semiconductor manufacturing, in particular to a thermal field and a method for improving the quality of monocrystalline silicon.
Background
In solar cell products, the cell mainly comprises silicon semiconductor materials, and is generally divided into monocrystalline silicon, polycrystalline silicon and amorphous silicon. The most rapidly developed solar cell is a single crystal silicon solar cell, which is prepared from a high-purity single crystal silicon rod as a raw material and has high conversion efficiency and reliability, so that the solar cell is widely accepted by the market. However, with the rapid development of the photovoltaic industry, the production of monocrystalline silicon solar cells tends to mature, the construction and production process thereof is established, the photovoltaic industry is competitive, and in order to reduce the production cost, solar cells and the like applied to the ground at present adopt solar-grade monocrystalline silicon rods with relaxed material performance indexes, and some monocrystalline silicon rods special for solar cells are prepared by redrawing head and tail materials and waste monocrystalline silicon materials processed by semiconductor devices.
However, it is not always reasonable to reduce the cost and seize the market share by simply adopting the raw materials with lower quality, and the competition and the elimination between enterprises or industries still need to ensure the quality, that is, the cost is reduced and the quality of the monocrystalline silicon raw materials is improved by improving the process or the equipment, so that the high-quality low-attenuation and high-efficiency battery piece is produced, and the larger market share is obtained.
It is known that the success and quality of the growth of a silicon single crystal are determined by the temperature distribution of a thermal field in the growth of a silicon single crystal by the Czochralski method. The thermal field with proper temperature distribution not only ensures smooth growth of the silicon single crystal, but also has higher quality; if the temperature distribution of the thermal field is not reasonable, various defects are easily generated in the process of growing the silicon single crystal, the quality is affected, and the phenomenon of crystal transformation can be caused under serious conditions, so that the single crystal can not grow.
At present, the quartz crucible used for receiving and melting the primary silicon material traditionally is used as the only device contacting the silicon material and the silicon liquid, and most of the devices contain metal impurities, although barium carbonate can react with the liquid silicon to form a protective film on the quartz crucible
But also partial metal impurities enter the single crystal, so that the conversion efficiency of the finished battery piece at the later stage is reduced; in addition to this, SiO of quartz crucible2The reaction is continuously carried out at high temperature to generate O2Leading to the oxygen content of the head of the silicon rod produced by the conventional thermal fieldThe amount exceeds the standard, the head of the silicon rod which is higher than the standard can not be used as a qualified finished product and can only be cut off, and waste is caused.
Disclosure of Invention
The invention aims to overcome the defects in the prior art, and provides a thermal field and a method for improving the quality of monocrystalline silicon, wherein the thermal field can reduce thermal convection and the content of impurities such as monocrystalline oxygen element in the monocrystalline silicon, the content of impurities such as oxygen, carbon, metal and the like in the monocrystalline silicon prepared by the method is low, and when the thermal field is used for producing a battery piece, the efficiency of the battery can be effectively improved, and the attenuation of the battery piece can be reduced.
In order to achieve the above purpose, the invention provides the following technical scheme:
a thermal field for improving the quality of monocrystalline silicon comprises a quartz crucible, a main heater and an auxiliary heater, wherein the main heater and the auxiliary heater are coaxially arranged in an equal diameter mode; the auxiliary heater is arranged opposite to the lower part of the quartz crucible and is formed by a plurality of auxiliary heating rings with equal length, and high-temperature-resistant water-based nano coatings for avoiding carbon volatilization are sprayed on the surfaces of the main heater and the auxiliary heater.
The invention mainly improves the quality of monocrystalline silicon by adjusting a heating area in a thermal field, and specifically comprises the following steps: different from the main heaters in the prior art, in which the main heating lobes are arranged at intervals, in the application, the main heating lobes of the heating area of the main heater are arranged at equal length, so that the thermal convection vortex in the thermal field can be reduced; secondly, the high-temperature resistant water-based nano coating for avoiding carbon volatilization is sprayed on the surfaces of the main heater and the auxiliary heater, so that carbon elements can be prevented from entering the single crystal, the content of carbon element impurities is reduced, and the efficiency of the cell is improved.
In one embodiment, the quartz crucible is a high-purity quartz crucible, the inner layer sand of the high-purity quartz crucible is high-purity quartz sand, and the ratio of the inner layer sand is 90-100 wt%.
According to the application, a high-purity quartz crucible is used as a bearing container of a polycrystalline silicon material, the ratio of inner-layer sand in the whole high-purity quartz crucible is 90-100 wt%, the introduction of metal impurities in monocrystalline silicon can be fundamentally reduced, and the reduction of thermal convection can reduce the movement speed of metal atoms by combining with the adjustment of a heating area of a thermal field, so that the content of the metal impurities in the monocrystalline silicon is reduced, and the service life of the monocrystalline silicon is prolonged.
The quartz sand is quartz particles formed by crushing quartz stone, and the main mineral component is SiO2Hard, wear resistant, chemically stable, insoluble in acid, slightly soluble in KOH solution, melting point 1750 ℃. The common specifications of the quartz sand are 0.5-1mm, 1-2mm, 2-4mm, 4-8mm, 8-16mm, 16-32mm, 10-20 meshes, 20-40 meshes, 40-80 meshes and 100-120 meshes. The quartz sand has large mineral content change, mainly comprises quartz, and then feldspar, mica, rock debris, heavy minerals, clay minerals and the like, and is industrially divided into common quartz sand, refined quartz sand, high-purity quartz sand, fused quartz sand, silicon micropowder and the like. The common quartz sand is generally prepared by crushing, washing, drying and secondary screening natural quartz ore; refined quartz sand also known as pickled quartz sand, SiO2≥99-99.5％、Fe2O3Less than or equal to 0.005 percent and is made of high-quality natural quartz sand and mortar; SiO in high-purity quartz sand2≥99.5-99.9％、Fe2O3Less than or equal to 0.001 percent; the chemical composition of the fused quartz sand is SiO299.9-99.95% of Fe2O3The content is 5-25PPM max, Li2O content of 1-2PPM max and Al2O3The content is 20-30PPM max, K2O content of 20-25PPM max and Na2The O content is 10-20PPM max (PPM is a unit of millionth); the chemical composition of the microsilica is shown in the following table:
| item | SiO2 | Al2O3 | Fe2O3 | MgO | CaO | NaO | PH |
| Mean value of | 75-96％ | 1.0±0.2％ | 0.9±0.3％ | 0.7±0.1％ | 0.3±0.1％ | 1.3±0.2％ | Neutral property |
In one embodiment, the preparation method of the high-purity quartz crucible comprises the steps of forming a quartz crucible blank by using quartz sand, and then forming quartz crucible inner-layer sand by high-temperature priming by using the high-purity quartz sand through an electric arc method.
In one embodiment, the striking power of the priming forming is 800-.
The melting time of 6-10s is used in this application because: at this melting power, if the melting time is less than 6 seconds, the use effect of the high purity silica sand is poor, and if the melting time is more than 10 seconds, a thick high purity silica layer is formed, and since the high purity silica sand has a high purity and contains less impurities, the mechanical strength of the high purity silica layer is reduced, which is not favorable for long-term high temperature use.
In one embodiment, the thermal field further comprises a heat-preserving cylinder and a large cover, the heat-preserving cylinder, the large cover and the main heater and the secondary heater are all made of graphite pieces, and the surfaces of the heat-preserving cylinder and the large cover are respectively coated with a high-temperature-resistant water-based nano coating for avoiding carbon volatilization.
Graphite is preferred for the components of the thermal field in this embodiment because graphite can increase conductivity, strength and service life.
In one embodiment, the material of the high temperature resistant water-based nano coating is zirconium dioxide.
Zirconium oxide (ZrO)2) Chinese alias: c.i. pigment white 12; zirconium dioxide; zirconium dioxide (stable insulation grade); zirconia (nanometer); fully stabilized zirconia; zirconium dioxide (stable); zirconium dioxide (IV); zirconia (beads), and the like. The zirconia can be used as a high-efficiency high-temperature heat insulation material; the zirconia fiber is used for ultra-high temperature heat insulation protective materials and ceramic matrix composite reinforced materials in the fields of aerospace, national defense and military industry, atomic energy and the like; the method is used for manufacturing ultrahigh temperature industrial kilns, ultrahigh temperature experimental electric furnaces and other ultrahigh temperature heating devices resistant to high temperature higher than 1500 ℃ in the fields of ceramic sintering, metal smelting, pyrolysis, semiconductor manufacturing, quartz melting and the like.
A method for improving the quality of monocrystalline silicon by adopting the thermal field comprises the following steps:
and installing a thermal field, cleaning the polycrystalline silicon material, and performing the steps of furnace cleaning, charging, material melting, secondary charging, neck guiding, shoulder placing, diameter equalization, ending and extraction.
In one embodiment, the method further comprises the step of adjusting the thermal field; the adjustment is as follows: shortening the length of the main heating lobe while reducing the height of a heating center formed by the main heater and the sub-heater; in the equal-diameter link, the auxiliary heater is shut down, and the temperature of the thermal field is maintained only by the main heater.
The length of the main heating valve is shortened, the height of the heating center is reduced, the growth temperature of the monocrystalline silicon can be met, and the length of the main heating valve is shortened and the heating center of the thermal field is reduced, so that the thermal convection in the thermal field is reduced, the reaction rate of a silicon material and a quartz crucible is slowed down, and the oxygen content is reduced; in addition, in the step of shoulder-putting, turning and casting isometric, the heating area of the thermal field is further adjusted, namely the auxiliary heater is turned off, and the temperature of the thermal field is maintained in the isometric state only through the main heater, so that the strength of thermal convection is reduced, the reaction rate of silicon materials and a quartz crucible is further slowed down, the oxygen content of monocrystalline silicon is reduced, and the LID attenuation of the cell link is reduced.
In one embodiment, the adjusting further comprises shortening the length of the secondary heating lobes while decreasing the pull rate in the constant diameter segment.
Under the condition that the main heating lobe and the auxiliary heating lobe are both shortened, the power of the main heater is increased to maintain the temperature required by a thermal field, the pulling speed in the constant diameter link is reduced, the success rate of crystal formation can be improved, and the damage of a single crystal caused by the higher pulling speed is avoided.
In one embodiment, the material melting link adopts split type two-step heating, the secondary feeding link is annular combined feeding firstly and then feeding by a feeder, and inert gases for taking away silicon oxide and impurity volatiles are simultaneously introduced in the second-step heating process of the material melting link and the feeding process of the feeder.
Compared with the prior art, the invention has the following beneficial effects:
(1) the thermal field adopts the heaters with the same length of each main heating lobe as the main heater, avoids forming temperature gradient, reduces thermal convection vortex in the thermal field, and simultaneously sprays the high-temperature resistant water-based nano coating for avoiding carbon volatilization on the surfaces of the main heater and the auxiliary heater, so that carbon elements can be prevented from entering a single crystal, the content of carbon element impurities is effectively reduced, and the efficiency of the cell piece is improved. The zirconium dioxide is preferably used as the high-temperature resistant water-based nano coating for avoiding carbon volatilization, the coating structure mainly comprises two parts, namely, columnar structure and nanoscale equiaxed structure, it is known that, as the content of the nanoscale equiaxed structure increases, i.e. the reduction of the grain size, the average grain size of the coating is gradually reduced, i.e. the thermal conductivity of the material is reduced, therefore, the high-temperature-resistant water-based nano zirconium dioxide coating not only can effectively avoid carbon volatilization, but also has better heat-insulating property, and in addition, researches show that, the content of the nanoscale equiaxed tissue can be controlled by changing spraying parameters (such as main gas, auxiliary gas, current, powder feeding, carrier gas, spray distance and the like) during spraying, therefore, the zirconium dioxide is adopted as the high-temperature-resistant water-based nano coating for avoiding carbon volatilization, so that the heat conduction performance of each component in a thermal field can be better controlled.
(2) The adjusting method provided by the invention comprises the steps of shortening the length of the heating lobe, reducing the heating area, reducing the heat convection, reducing the oxygen content and reducing the attenuation of the single crystal; in the crystal waiting process, on the basis that the main heating flap is shortened, the operation of the auxiliary heater is stopped, so that the heat convection is further reduced, the reaction rate of silicon and the quartz crucible is reduced, the temperature of the thermal field is maintained by increasing the power of the main heater and combining the reduction of the height of the heating center, and the height of the heating center is reduced, so that the consumed power of the main reactor can be reduced on the premise of maintaining the temperature of the thermal field, and the reduction of the height of the heating center means that the height of the quartz crucible for bearing silicon liquid can be integrally reduced, the crystal forming liquid level is reduced along with the reduction of the height of the heating center, and the crystal forming liquid level is more favorable for reducing the heat convection and reducing the.
Drawings
In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the embodiments or the prior art will be briefly described below, it is obvious that the drawings in the following description are only some embodiments of the present invention, and for those skilled in the art, other drawings can be obtained according to the drawings without creative efforts.
FIG. 1 is a schematic diagram of a thermal field provided in the prior art;
fig. 2 is a schematic structural diagram of a thermal field according to an embodiment of the present invention.
Description of reference numerals:
1. a main heater; 11. a main heating flap; 2. a sub-heater; 21. and a secondary heating flap.
Detailed Description
The technical solutions of the present invention will be described clearly and completely with reference to the accompanying drawings, and it should be understood that the described embodiments are some, but not all embodiments of the present invention. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.
In the description of the present invention, it should be noted that the terms "center", "upper", "lower", "left", "right", "vertical", "horizontal", "inner", "outer", etc., indicate orientations or positional relationships based on the orientations or positional relationships shown in the drawings, and are only for convenience of description and simplicity of description, but do not indicate or imply that the device or element being referred to must have a particular orientation, be constructed and operated in a particular orientation, and thus, should not be construed as limiting the present invention. Furthermore, the terms "first," "second," and "third" are used for descriptive purposes only and are not to be construed as indicating or implying relative importance.
In the description of the present invention, it should be noted that, unless otherwise explicitly specified or limited, the terms "mounted," "connected," and "connected" are to be construed broadly, e.g., as meaning either a fixed connection, a removable connection, or an integral connection; can be mechanically or electrically connected; they may be connected directly or indirectly through intervening media, or they may be interconnected between two elements. The specific meanings of the above terms in the present invention can be understood in specific cases to those skilled in the art.
In addition, the technical features involved in the different embodiments of the present invention described below may be combined with each other as long as they do not conflict with each other.
Comparative example
First, a prior art mature process for preparing single crystal silicon (taking 10t yield as an example) is provided, comprising the following steps:
s1, mounting a thermal field:
the method comprises the steps of coaxially installing a main heater 1 and an auxiliary heater 2 with the same diameter in a heat preservation cylinder, covering a large cover to form a thermal field, and placing a quartz crucible in the thermal field, wherein the main heater 1 is arranged relative to the middle upper part of the quartz crucible, the distance between the main heater 1 and a lower cover plate is 345mm, the auxiliary heater 2 is arranged relative to the lower part of the quartz crucible, as shown in figure 1, the main heater 1 is formed by annularly arranging a plurality of main heating petals 11 which are arranged at intervals, the length of the shortest main heating petal 11 is 280mm to form a temperature gradient, a heating area of the auxiliary heater 2 is formed by annularly arranging a plurality of auxiliary heating petals 21, the length of the auxiliary heating petal 11 is 130mm, the length of the main heating petal 11 is greater than that of the auxiliary heating petal 21, and the power of the main heater 1 is greater.
S2 preparation of monocrystalline silicon
Cleaning the polysilicon material: selecting a no-clean polycrystalline silicon material with the diameter of 50-80mm and the purity of 99.99999 percent to carry out ultrasonic pure water cleaning, and eliminating silicon powder generated by friction and collision among silicon materials; placing the cleaned polysilicon material in a container with the cleanliness of 100 grade for air cooling treatment for not less than 2 hours, and then slowly pouring the polysilicon material into a quartz charging container;
cleaning the furnace and charging: a pre-charging mode is adopted, the loaded finished furnace burden is slowly lowered into a high-purity quartz crucible by a clamp, the furnace is closed and evacuated, an 1/3 ball valve is opened for 15 minutes, a 2/3 ball valve is opened for 10 minutes, and then the ball valves are all opened, so that the problem that the cleanliness in the furnace is insufficient due to the fact that silicon materials are extracted at an excessively high air draft rate is avoided;
material melting: adopting split type two-step heating, wherein the total power of the first step is 60-70kw, the power of the main heater is 35-40kw, the power of the auxiliary heater is 25-30kw, after heating for 40-50 minutes, the total power of the second step is increased to 110-120kw/h, the power of the main heater is 70-80kw, and the power of the auxiliary heater is 40 kw;
secondary feeding: the method is carried out by adopting an annular combined type plus feeder feeding mode, the combined diameter is controlled to be between 220 and 235mm through reasonable calculation, and the melting time can be shortened by 40 minutes;
neck drainage: opening a main heater, controlling the power of the main heater within a range of 58-63kw, controlling the power of an auxiliary heater within a range of 4.5-5.5kw, adopting a high-connection low-leading mode, fully contacting for 40-50 minutes, reducing the temperature, controlling the pulling speed within a range of 0.5-8mm/min, the length within a range of 80-100mm, the crystal rotation within a range of 8-12r/min, the crucible rotation within a range of 7-10r/min, the argon flow within a range of 40-50min/min, simultaneously fully eliminating dislocation and reducing the occurrence of bract dropping;
shouldering: the power of the main heater and the auxiliary heater is kept unchanged, the crystal rotation parameter is 8-12r/min, the crucible rotation is 8-10r/min, the argon flow is 45L/min, the crucible lift ratio is 0.130mm/min, the water flow is 30-40L/min, the water temperature is 25-35 ℃, and the pulling speed is unchanged;
and (3) constant diameter: different from the shoulder-laying link, the link reduces the power of the main heater to 53-58kw, and the power of the auxiliary heater is unchanged; the average constant-diameter drawing speed is adjusted to 1.22-1.72 mm/min;
ending: the power of the main heating is 58-63kw/h, the power of the auxiliary heater is unchanged, the crucible is lifted to zero, meanwhile, the power is increased by 5-10kw, the pulling speed is reduced to the minimum pulling speed in the equal diameter, after the aperture is retracted, the pulling speed is reduced to 0.03mm/min, the crystal is rotated by 4 revolutions per minute, the crucible is rotated by 2 revolutions per minute, and after 30 minutes, the end is finished after the crucible is separated from the liquid level;
it proposes: in order to prevent the high-temperature single crystal from entering a low-temperature region to cause internal defects or damage, the high-temperature single crystal needs to be lifted to the auxiliary chamber at the pulling speed of 4-6mm/min after 1 hour, and the high-temperature single crystal can be obtained after the auxiliary chamber is kept still for 30 min.
S4, preparing a battery piece from the monocrystalline silicon by adopting a conventional method.
Example 1
Unlike the comparative example, in the thermal field provided in the present embodiment, as shown in fig. 2, the main heater 1 of the thermal field is formed by surrounding a plurality of main heating fins 11 having the same length, and the heat generating region of the sub-heater 2 is formed by surrounding a plurality of sub-heating fins (refer to 21 in fig. 1), in the present embodiment, the length of the main heating fin 11 is 280mm, and the length of the sub-heating fin is 130 mm.
Before installing the thermal field, the outer surfaces of the main heater, the auxiliary heater, the heat-insulating bucket and the large cover are uniformly sprayed with the high-temperature-resistant water-based nano coating for avoiding carbon volatilization, in the embodiment, in order to increase the conductivity and prolong the service life, the main heater, the auxiliary heater, the heat-insulating bucket and the large cover are all made of graphite materials, and the high-temperature-resistant water-based nano coating for avoiding carbon volatilization is made of zirconium dioxide, which is not limited to the listed materials, but can be made of other high-temperature-resistant water-based nano coatings capable of avoiding carbon volatilization;
the spraying steps mainly comprise: firstly, cleaning the graphite piece and wiping the graphite piece; preparing a coating, wherein the coating needs to be shaken up and down for about 4-8 times before spraying to ensure uniform mixing; preparing a handheld spray gun for spraying, confirming the surface of the graphite piece to be clean and free of impurities again, finally putting the coating into the spray gun to start spraying, ensuring that the periphery of the graphite piece is sprayed completely when spraying is carried out, wherein the spraying is uniform, the spraying is preferably carried out for a small number of times, at least twice, and after the first spraying is finished, naturally drying for 2-5 hours until the surface of the graphite piece is dried completely; after the second spraying is finished, naturally drying for 3-6 hours until the surface of the graphite piece is completely dried; the sprayed graphite piece can be directly loaded into a furnace for calcination, and the spraying of the graphite piece needs to be repeated every 2-4 months.
The method of producing single crystal silicon using this thermal field is the same as the comparative example.
Example 2
Different from the example 1, the quartz crucible in the thermal field of the application is a high-purity quartz crucible, and the preparation method comprises the following steps:
the method comprises the following steps of forming a quartz crucible blank by using quartz sand, and forming inner-layer sand of the quartz crucible by using high-purity quartz sand through high-temperature priming by an arc method, wherein the inner-layer sand accounts for 90-100 wt%, and the specific preparation process comprises the following steps:
vacuumizing: starting an arc by adopting 800KW power, wherein the arc starting position is on the upper side 3/4, and the arc starting position is on the lower side of the opening of the heat-shielding water jacket; after the vacuum pressure rises (seals), the electrode gap is opened rapidly to raise the power to 1400-1600 KW; then starting to open the crucible bottom, melting for 8-12 seconds (about 150mm) along the lower part of a stainless steel die opening, firing for 18-25 seconds, then lowering the power to 900 and 1200KW from the upper electrode to the arc starting position, continuing to melt, and starting to close the vacuum and deflate when the electric energy reaches 50-70KWs for about 3 minutes and 20 seconds;
normally melting: after the vacuum is closed, the power is increased to 1000-class 1500KW, then the first air blowing process is carried out, and the crucible burning position is flexibly mastered according to the crucible opening receiving condition; and starting a secondary air blowing process at the left and right of 5-9 minutes, reducing the power to 1200KW after air blowing is finished, starting the electrode from the upper edge position of the mold for 6 seconds, starting crucible bottom striking for 1 minute (counting time from the electrode to the crucible bottom position), then starting the electrode to the upper crucible burning position, increasing the power to 1000 KW, continuing melting, and flexibly grasping the air blowing frequency. Finally, the power is reduced to 800-100KW 1 minute before the furnace is discharged, and the arc breaking is finished. It is to be understood that the actual production may be performed by determining the specific melting time in accordance with the consumption of electric energy and the production state of the conventional crucible, for example, the conventional crucible may be required to consume about 360 degrees of electric energy and the firing time may be about 16 minutes, thereby adjusting the melting time.
The method of producing single crystal silicon using this thermal field is the same as the comparative example.
Example 3
This example provides a method for improving the quality of single-crystal silicon, different from the comparative example: the thermal field provided in example 2 is used to produce single crystal silicon, the thermal field is adjusted during the production process, and the specific adjustment steps are as follows:
the length of the main heating lobe 1 is shortened to be adjusted to 260mm, that is, the length of the main heating lobe 11 is shortened by 20mm in the present embodiment compared to the shorter main heating lobe in embodiment 1 or the comparative example; meanwhile, the height of a heating center formed by the main heater 1 and the auxiliary heater 2 is reduced by 10mm, correspondingly, compared with the traditional main heater 1, the distance between the main heater 1 and the lower cover plate is reduced from 345mm to 335mm, the whole high-purity quartz crucible for bearing silicon liquid is reduced by 10mm, and the crystal forming liquid surface is reduced by 10 mm; it should be noted that the length of the main heating lobe 11 can be shortened and the height of the heating center can be adjusted according to the actual production yield, but the adjustment is performed based on the mature preparation process (ensuring the crystal forming conditions such as crystal pulling temperature) and the supporting equipment;
in the second material melting stage, inert gas with the flow rate of 50-60L/min, such as argon and the like, is introduced for melting, so that the gas flow circulation can be promoted, and the content of silicon oxide and impurity volatile matters in the furnace can be reduced; an upper inflation mode is adopted in the charging link of the charger, argon with the flow rate of 50-70L/min is introduced at the same time, and the airflow guide is adjusted to smoothly take away impurities such as SiO, CO, C and the like in the furnace;
in the equal diameter stage, the present embodiment further adjusts the thermal field, i.e. stops the sub-heater 2, only turns on the main heater 1, and controls the power of the main heater 1 to 60-65kw to meet the temperature required by the thermal field.
Example 4
Unlike example 3, the length of the main heating lobe 11 is 210mm, the length of the main heating lobe 11 is shortened by 50mm with respect to example 1, and the length of the sub-heating lobe 21 is also shortened in the present example, and the length of the sub-heating lobe 21 is shortened by 20mm with respect to both the comparative example and example 1, that is, the length of the sub-heating lobe 21 is adjusted to 110 mm. The average pulling speed is reduced by 0.05mm/min at the same time in the equal diameter stage, and the success rate of crystal formation is improved by reducing the pulling speed under the condition that the main heating valve 11 and the auxiliary heating valve 21 are both shortened, so that the single crystal is not damaged due to higher pulling speed.
Example 5
Different from the embodiment 4, the auxiliary heater can be closed in the steps of neck leading, shoulder putting, diameter equalizing and ending, and the crystal pulling can be realized by controlling the power of the main heater, wherein the main heater of the neck leading step is controlled within the range of 65-70 kw; the power of a main heater in the shouldering link is kept unchanged; in the constant diameter link, the power of the main heater is reduced to 60-65kw, which is different from the shoulder-laying link; in the ending link, the power of the main heater is increased to 65-70 kw.
Detection assay
The quality of the single crystal silicon produced in examples 2 to 4 and the comparative example was analyzed by comparing the comparative examples, and the indexes to be analyzed and the specific analysis method were as follows:
1. detecting the oxygen content in the monocrystalline silicon: an infrared absorption measurement method of the interstitial oxygen content in GB/T1557 silicon crystal;
2. detecting the carbon content in the monocrystalline silicon: an infrared absorption measurement method for the content of substitutional carbon atoms in GB/T1558 silicon;
3. detecting the service life of the monocrystalline silicon: GB/T1553 method for measuring the lifetime of minority carriers in silicon and germanium bodies by using a photoconductive decay method.
The results of the experiments are shown in the following table:
TABLE 1 ＊
The data are the average values of 20 furnaces of monocrystalline silicon data.
It can be seen from the table that the contents of the head oxygen, the tail oxygen, the head carbon and the tail carbon in the single crystal silicon prepared in the examples 2 to 4 of the present invention are reduced to different degrees compared to the comparative example, and the average values of the head life and the tail life in the single crystal silicon prepared in the examples 2 to 4 are improved compared to the comparative example, and it can also be seen from the table that the head oxygen content of all the single crystal silicon is higher than the tail oxygen content, wherein the structure of the main heating lobe is changed compared to the comparative example in example 1, the high temperature resistant water-based nano coating for avoiding carbon volatilization is sprayed, and the high purity quartz crucible is adopted in example 2 compared to example 1; in example 4, compared with example 2, the heating zones of the main heater and the sub-heater, the pulling speeds of the equal-diameter links, and the like are adjusted, and it can be seen from the numerical values in the table that the contents of the head oxygen, the tail oxygen, the head carbon, and the tail carbon of the single crystal silicon prepared in example 1, example 2, and example 4 are sequentially reduced, but the average values of the head life and the tail life are sequentially increased, so that the invention can improve the quality of the single crystal silicon, reduce the oxygen content and the carbon content, and prolong the service life. From the example 1 and the comparative example, it can be seen that the influence of the increase of the high-temperature resistant water-based nano coating on the head oxygen and the tail oxygen is small, but the contents of the head carbon and the tail carbon are greatly reduced, so that the spraying of the high-temperature resistant water-based nano coating can effectively control the content of the carbon element in the monocrystalline silicon; as can be seen from comparison of the comparative example, the example 1 and the example 2, the content of the head oxygen can be controlled to a certain extent by adopting the high-purity quartz crucible to prepare the monocrystalline silicon, the head service life and the tail service life can be greatly improved, and the contents of the head oxygen and the tail oxygen can be greatly reduced by adjusting the heating area as can be seen from the comparative example, the example 1, the example 2 and the example 4.
The above description is only for the specific embodiments of the present invention, but the scope of the present invention is not limited thereto, and any changes or substitutions that can be easily conceived by those skilled in the art within the technical scope of the present invention are included in the scope of the present invention. Therefore, the protection scope of the present invention shall be subject to the protection scope of the appended claims.
Claims (10)
1. The utility model provides an improve thermal field of monocrystalline silicon quality, its characterized in that, includes quartz crucible and coaxial constant diameter setting's primary heater and auxiliary heater, the primary heater for the setting of the well upper portion of quartz crucible is established by the isometric primary heating valve ring of a plurality of and is formed, the auxiliary heater for the setting of the lower part of quartz crucible is established by the isometric auxiliary heating valve ring of a plurality of and is formed, the primary heater with the surface of auxiliary heater still spraying has the high temperature resistant water base nanometer coating that is used for avoiding carbon to volatilize.
2. The thermal field according to claim 1, characterized in that the quartz crucible is a high-purity quartz crucible, the inner layer sand of the high-purity quartz crucible is high-purity quartz sand, and the ratio of the inner layer sand is 90-100 wt%.
3. The thermal field according to claim 2, characterized in that the preparation method of the high-purity quartz crucible comprises the steps of forming a quartz crucible blank by using quartz sand, and then forming quartz crucible inner-layer sand by high-temperature priming by using the high-purity quartz sand through an electric arc method.
4. The thermal field according to claim 3, wherein the arc starting power of the priming is 800-.
5. The thermal field according to claim 1, further comprising a thermal insulating cylinder and a large cover, wherein the thermal insulating cylinder, the large cover and the main heater and the secondary heater are all made of graphite, and the surfaces of the thermal insulating cylinder and the large cover are respectively coated with a high-temperature resistant water-based nano-coating for avoiding carbon volatilization.
6. The thermal field according to claim 5, wherein the high temperature water-based nano-coating is made of zirconium dioxide.
7. A method of upgrading single crystal silicon using the thermal field of any one of claims 1-6, comprising the steps of:
and installing a thermal field, cleaning the polycrystalline silicon material, and performing the steps of furnace cleaning, charging, material melting, secondary charging, neck guiding, shoulder placing, diameter equalization, ending and extraction.
8. The method of claim 7, further comprising the step of adjusting the thermal field; the adjustment is as follows: shortening the length of the main heating lobe while reducing the height of a heating center formed by the main heater and the sub-heater; in the equal-diameter link, the auxiliary heater is shut down, and the temperature of the thermal field is maintained only by the main heater.
9. The method of claim 8, wherein said adjusting further comprises shortening the length of said secondary heating lobes while decreasing the pull rate in said constant diameter segment.
10. The method as claimed in claim 7, wherein the material melting step adopts two-step heating, the secondary feeding step comprises annular combined feeding and feeding by a feeder, and inert gases for removing silicon oxide and impurity volatiles are simultaneously introduced during the second heating step and the feeding by the feeder in the material melting step.
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