WO2014056157A1 - 多晶硅锭及其制造方法、坩埚 - Google Patents

多晶硅锭及其制造方法、坩埚 Download PDF

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Publication number
WO2014056157A1
WO2014056157A1 PCT/CN2012/082709 CN2012082709W WO2014056157A1 WO 2014056157 A1 WO2014056157 A1 WO 2014056157A1 CN 2012082709 W CN2012082709 W CN 2012082709W WO 2014056157 A1 WO2014056157 A1 WO 2014056157A1
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Prior art keywords
silicon
crucible
coating
crystal
polycrystalline silicon
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PCT/CN2012/082709
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English (en)
French (fr)
Inventor
郑志东
王朋
翟蕊
李娟�
范立伟
Original Assignee
浙江昱辉阳光能源有限公司
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Application filed by 浙江昱辉阳光能源有限公司 filed Critical 浙江昱辉阳光能源有限公司
Priority to PCT/CN2012/082709 priority Critical patent/WO2014056157A1/zh
Priority to CN201280076314.9A priority patent/CN104703914B/zh
Priority to KR1020157011114A priority patent/KR101779267B1/ko
Publication of WO2014056157A1 publication Critical patent/WO2014056157A1/zh

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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
    • C30B29/02—Elements
    • C30B29/06—Silicon
    • 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
    • C30B11/00—Single-crystal growth by normal freezing or freezing under temperature gradient, e.g. Bridgman-Stockbarger method
    • C30B11/002—Crucibles or containers for supporting the melt
    • 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
    • C30B11/00—Single-crystal growth by normal freezing or freezing under temperature gradient, e.g. Bridgman-Stockbarger method
    • C30B11/14—Single-crystal growth by normal freezing or freezing under temperature gradient, e.g. Bridgman-Stockbarger method characterised by the seed, e.g. its crystallographic orientation
    • 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
    • C30B28/00—Production of homogeneous polycrystalline material with defined structure
    • C30B28/04—Production of homogeneous polycrystalline material with defined structure from liquids
    • C30B28/06—Production of homogeneous polycrystalline material with defined structure from liquids by normal freezing or freezing under temperature gradient

Definitions

  • the present invention relates to the field of manufacturing technology and photovoltaics of single crystal silicon and polycrystalline silicon, and more particularly to a polycrystalline silicon ingot, a method for producing the same, and a crucible.
  • Solar cells can convert light energy into electrical energy. Photoelectric conversion efficiency and attenuation are important parameters to measure the quality of solar cells, and the cost of production has become an important factor restricting the development of solar cells. At present, solar cells are mainly classified into single crystal silicon solar cells and polycrystalline silicon solar cells, depending on materials. Monocrystalline silicon solar cells have high conversion efficiency, but the production cost is 4 ⁇ , and the cost of polycrystalline silicon solar cells is low, but the conversion efficiency is relatively low. At present, polycrystalline silicon solar cells have an advantage in the photovoltaic market share due to higher cost performance.
  • the directional solidification method is mostly used to produce the polycrystalline silicon ingot.
  • the process is mainly to deposit the silicon material in the flat crucible on the inner surface, and then melt the silicon material completely, and control the temperature in the ingot furnace to make the polycrystalline silicon ingot from the bottom.
  • a polycrystalline silicon ingot is obtained.
  • the present invention provides a polycrystalline silicon ingot and a method for manufacturing the same, which are used to make the crystal grain size in the grown polycrystalline silicon ingot more uniform, the crystal orientation is more uniform, and the defect density inside the crystal is lowered, thereby The conversion efficiency of polycrystalline silicon solar cells is improved.
  • the embodiment of the present invention provides the following technical solutions:
  • the inner surface of the crucible is coated with at least one coating layer, and the crucible bottom surface coating has A particulate matter of heterogeneous nucleation sites of silicon, the inner surface comprising an inner wall and a bottom surface, the bottom surface being a bottom surface of the inner surface of the crucible.
  • the coating comprises at least one of a silicon nitride coating, a composite coating of silicon nitride and silicon carbide, and a composite coating of silicon nitride and silicon dioxide.
  • the particulate matter in the middle is silicon nitride particles
  • the particulate matter in the composite coating of silicon nitride and silicon carbide is silicon nitride particles and silicon carbide particles
  • the particulate matter in the layer is silicon nitride particles and silica particles.
  • the weight ratio of silicon carbide is 0-5%, including the endpoint value; in the composite coating of silicon nitride and silicon dioxide, silicon dioxide The weight ratio is 0-5%, including the endpoint value.
  • the bottom surface of the crucible is a composite coating of silicon nitride and silicon carbide, or a composite coating of silicon nitride and silicon dioxide, and the inner wall of the crucible is a silicon nitride coating.
  • the coating has a thickness of 10 ⁇ m to 500 ⁇ m, including the endpoint value.
  • the bottom surface has a roughness Ra greater than 5 ⁇ m and less than 5 mm, inclusive.
  • the three-dimensional geometric shape is irregularly arranged on the bottom surface of the crucible, and the three-dimensional geometric shape is a hollow structure with an apex downward and an open upward.
  • the spatial distribution of the plurality of three-dimensional geometric shapes is such that the vertices of the plurality of three-dimensional geometric shapes and/or the distances of the openings from the bottom surface of the outer surface of the outer surface are not equal.
  • the spatial distribution of the plurality of three-dimensional geometric shapes is such that the plurality of three-dimensional geometric shapes are irregularly arranged in a direction along the mouth portion toward the bottom of the crucible.
  • the openings of the plurality of three-dimensional geometric shapes are the same or different.
  • the embodiment of the invention further discloses a method for manufacturing a polycrystalline silicon ingot, which adopts the above-mentioned crucible, the manufacturing method comprises: closely laying a silicon material at the bottom of the crucible to obtain a first silicon material layer, wherein the first silicon material layer
  • the silicon material is a bulk silicon material, a crushed silicon material or a silicon powder; the silicon material is continuously filled on the first silicon material layer until the silicon material is filled; the silicon material in the crucible is melted to obtain a silicon liquid Controlling the thermal field in the polycrystalline silicon ingot furnace, crystallizing the silicon liquid until crystal growth is completed, and obtaining a polycrystalline silicon ingot.
  • the gap between the silicon materials in the first silicon material layer is 0-20 mm.
  • the embodiment of the invention also discloses a polycrystalline silicon ingot manufactured by the above method, the polycrystalline silicon ingot having a dislocation density of 10 2 -10 5 /cm 2 .
  • the polycrystalline silicon ingot has a long side length of 2 mm to 30 mm, inclusive.
  • the bottom surface of the crucible provided by the embodiment of the present invention is coated with at least one coating layer, and the granular material in the coating layer can be used as a nucleation point of silicon in the subsequent crystal growth process, and the crucible is located at the initial stage of crystallization.
  • the rough surface of the crucible has a certain guiding effect on the crystallographic orientation of the crystal grains.
  • the crystal grains of the nucleation begin to compete at the pits on the bottom surface of the crucible, and a certain crystal orientation is obtained.
  • the crystal grains have an advantage in the competition process, and finally remain, so that the orientation of the crystal nucleus tends to be uniform. Therefore, the crystal grain size of the polycrystalline silicon ingot grown by the method is uniform, and the grain orientation is relatively uniform, and The dislocation density inside the crystal is lowered, and the minority carrier lifetime is improved, thereby improving the conversion efficiency of the polycrystalline silicon solar cell.
  • FIG. 1 is a cross-sectional view of a crucible disclosed in an embodiment of the present invention.
  • FIG. 2 is a top plan view of a bottom portion of a crucible disclosed in an embodiment of the present invention
  • FIG. 3 is a partial cross-sectional enlarged view of a bottom portion of a crucible disclosed in an embodiment of the present invention
  • FIG. 4 is a flow chart of a method for manufacturing a polycrystalline silicon ingot according to an embodiment of the present invention.
  • FIG. 5 is a schematic view showing a crystal of a central portion of a polycrystalline silicon ingot in the prior art
  • FIG. 6 is a schematic view showing a crystal of a central portion of a polycrystalline silicon ingot disclosed in an embodiment of the present invention.
  • FIG. 7 is a dislocation distribution diagram on a polycrystalline silicon wafer in the middle of a polycrystalline silicon ingot in the prior art
  • FIG. 8 is a diagram showing dislocation distribution on a polycrystalline silicon wafer in the middle of a polycrystalline silicon ingot disclosed in an embodiment of the present invention. detailed description
  • the quality of the polycrystalline silicon ingot obtained by the ingot casting process of the prior art is poor, and the conversion efficiency of the solar cell fabricated by using the polycrystalline silicon ingot of the prior art is low, and the inventors have found that such a problem arises.
  • the reason is that in the prior art polycrystalline silicon ingot, crystals are randomly nucleated and grown during crystal growth, resulting in a large difference in grain size in the finally formed silicon ingot, and some inclusions between large crystal grains. Small crystal grains, or defects such as subgrain boundaries distributed in the large crystal grains, the size of the small crystal grains is too small, resulting in many grain boundaries inside the silicon ingot, and many dislocations. These subgrains and dislocations are extremely defective. It is easy to become a recombination center of photo-generated carriers, especially dislocations, and has a resilience of composite activity, resulting in low lifetime of the minority carriers in the fabricated solar cell, which greatly reduces the conversion efficiency of the battery.
  • the present invention provides a crucible, and a polycrystalline silicon ingot manufacturing method and a polycrystalline stone in which the crucible is formed, wherein the inner surface of the inner surface is thick and has a large distribution therebetween. a three-dimensional geometric shape; the inner surface of the crucible is coated with at least one coating having a particulate matter as a heterogeneous nucleation point of silicon, the inner surface including an inner wall and a bottom surface.
  • the polycrystalline silicon ingot manufacturing method comprises: laying a silicon material tightly at the bottom of the crucible to obtain a first silicon material layer, wherein the silicon material in the first silicon material layer is a bulk silicon material, a crushed silicon material or a silicon powder; The silicon material is continuously filled on the silicon layer until the silicon material is filled; the silicon material in the crucible is melted to obtain the silicon liquid; the thermal field in the polycrystalline silicon ingot furnace is controlled, and the silicon liquid is crystallized. Until the crystal growth is completed, a polycrystalline silicon ingot is obtained.
  • the dislocation density of the polycrystalline silicon ingot produced by this method is reduced by 1-3 orders of magnitude from the prior art polycrystalline silicon ingot, and is 10 2 - 10 5 /cm 2 . And the length of the long side of the crystal grain of the polycrystalline silicon ingot is 2 mm-30 mm, including the end point value. Obviously, the quality of the polycrystalline silicon ingot obtained by the embodiment of the present invention is greatly improved.
  • the above solution adopts a crucible with a rough bottom surface and a coated crucible to place the silicon material.
  • the coating material has a granular substance as a heterogeneous nucleation point of silicon, especially the bottom surface of the crucible.
  • the position of the particulate matter preferentially nucleates and grows, and in the subsequent growth process, the formation of crystal nuclei in other regions is suppressed.
  • the silicon crystal After the nucleation of the depressed region on the bottom surface of the crucible, the silicon crystal has a specific nucleation position, thereby making the crystal distribution uniform. Further, since the bottom surface of the crucible is rough, a plurality of crystal nuclei formed in the same recessed region of the bottom surface are also preferentially competitive before being grown to the top of the recessed region. In the process, a certain crystal grain in the crystal orientation is in competition. The process has an advantage, and finally retains, so that the orientation of the grains tends to be consistent. After the preferential competition, the number of crystal nuclei retained in the same 1HJ trap region is reduced before the subsequent columnar growth. Further increasing the uniformity of the grain distribution, the orientation of the crystal tends to be uniform, thereby reducing the dislocation density inside the crystal, prolonging the lifetime of the minority carrier, thereby improving the conversion efficiency of the polycrystalline silicon solar cell.
  • particulate matter as the heterogeneous nucleation point may be derived from strontium or may be Subsequent artificial coated coatings are described in the following examples only as the latter.
  • the embodiment of the present invention provides a crucible, the cross-sectional view thereof is shown in FIG. 1, the top view is shown in FIG. 2, and FIG. 3 is a partial enlarged view of the bottom of the crucible.
  • the bottom surface 11 of the inner surface of the crucible is rough, and the bottom surface 11 has a plurality of three-dimensional geometric shapes 12 of irregular spatial distribution, and the inner surface of the crucible is coated with at least one coating layer 14, the inner surface
  • the inner wall 13 and the bottom surface 11 are provided, and the coating of the crucible bottom surface 11 has a particulate matter (not shown) as a heterogeneous nucleation point of silicon, and the bottom surface is a bottom surface of the inner surface of the crucible.
  • the roughness in the figure is only used to show the structure and distribution of the three-dimensional geometric shape 12 at the bottom of the crucible, and the size and proportion of each part are not limited as to the actual crucible structure.
  • the existing solid phase particle surface nucleation (the existing solid phase particle is also called heterogeneous nucleation point), which reduces the preferential nucleation of the silicon crystal at this position, and thus the growth of the subsequent ingot In the process, the formation of crystal nuclei in other regions in the silicon liquid can be suppressed, thereby reducing the grain boundary and the dislocation density to some extent.
  • the difficulty of nucleation is related to the size of the nucleation work, and the depression of the bottom surface of the crucible can reduce the nucleation work of the silicon crystal, that is, the energy potential required for the nucleation of the crystal at the recessed area of the crucible bottom surface.
  • the barrier is lower than other regions, and preferentially grows after nucleation, thereby further inhibiting the formation and growth of crystal nuclei in other regions, thereby increasing the order of the finally formed crystals, and at the same time, because the preferentially nucleated particulate matter is located in the crucible. In the recessed area on the bottom surface, the crystals that are first nucleated begin to compete at the pits on the bottom surface of the crucible.
  • the crystals of a certain crystal orientation have an advantage in the competition process and eventually remain, which makes the orientation of the crystal nucleus tend to Consistently, the crystal orientation of the finally obtained polycrystalline silicon ingot is more uniform, crystal
  • the increase in the order of the body reduces the dislocation density inside the crystal, thereby prolonging the life of the minority carrier and improving the conversion efficiency of the polycrystalline silicon solar cell.
  • the coating 14 in this embodiment comprises at least one of a silicon nitride coating, a composite coating of silicon nitride and silicon carbide, and a composite coating of silicon nitride and silicon dioxide, specifically, ⁇
  • the bottom surface and the inner wall may be the same coating, such as silicon nitride coating, or any of the above composite coatings, or different coatings may be used, such as using any of the above composite coatings on the bottom surface and nitrogen on the inner wall. Silicon coating, or silicon nitride coating on the bottom, and any composite coating on the inner wall.
  • the particulate matter in the silicon nitride coating is silicon nitride particles
  • the particulate matter in the composite coating of silicon nitride and silicon carbide is silicon nitride particles and silicon carbide particles
  • the particulate matter in the composite coating with silica is silicon nitride particles and silica particles.
  • the coating is applied to the rough bottom surface of the crucible, and the polycrystalline silicon is grown compared to the simple coating of the silicon nitride coating on the flat bottom surface and the simple roughening of the crucible.
  • the performance of the ingot is better.
  • the crucible used for ingots is quartz crucible, but the use of quartz crucibles alone is prone to cracking during ingot casting.
  • the main reason is that molten silicon reacts with the silica it contacts to form silicon monoxide and Oxygen; wherein, oxygen can contaminate silicon, and silicon monoxide is volatile; and it can also form silicon carbide and carbon monoxide with the graphite component in the furnace, and the generated carbon monoxide can then react with the molten silicon to form volatile silicon monoxide, Carbide, oxide and carbon of silicon carbide or dopants, carbon can contaminate silicon.
  • the above reaction between silica and molten silicon causes the silicon to adhere to the crucible. However, due to the difference in thermal expansion coefficient between silicon dioxide and silicon, the silicon ingot is prone to cracking upon cooling.
  • the inner surface of the crucible is coated with thick silicon nitride to prevent the silicon dioxide from reacting with the molten silicon liquid, and at the same time, it is also convenient to release the polycrystalline silicon ingot.
  • the purity of the silicon nitride is required to be higher. The better.
  • the size of the nucleation work is also related to the contact angle of the parent phase and the solid phase particles.
  • the contact angle is related to the material of the parent phase and the solid phase particles.
  • the heterogeneous shape of the suitable material The nuclear point, the required nucleation work is small, and the nucleation is easier.
  • silicon carbide and silicon oxide particles have a smaller contact angle with silicon liquid, and silicon carbide and silicon oxide particles are used as heterogeneous nucleation sites of silicon, and silicon crystal nucleation requires less energy.
  • the formation performance is more Adding a good polycrystalline silicon ingot while avoiding the introduction of new impurities, preferably doping a small amount of silicon carbide or silicon dioxide in the silicon nitride, that is, in this embodiment, it is preferred to apply a composite coating on the inner surface of the crucible, and During the ingot casting process, the influence of silicon carbide and silicon dioxide on niobium and the contamination of the silicon ingot must strictly control the content of silicon carbide or silicon dioxide.
  • the weight ratio of silicon carbide is less than 5%, including the end point value, such as 2%, 3% or 4%; composite of silicon nitride and silicon dioxide In the coating, the weight ratio of silica is below 5%, including endpoint values such as 2%, 3% or 4%.
  • the preferential nucleation region is the depressed portion of the crucible bottom surface, and once the grain orientation of the crucible bottom surface is determined, The subsequent crystal growth process can be guided. In the subsequent crystal growth process, the nucleation of the sidewall of the crucible should be minimized. For this reason, in this embodiment, it is more preferable to use any of the above composite coatings on the bottom surface of the crucible, and the inner wall is nitrided. Silicon coating.
  • the thickness of the coating in this embodiment is 10 ⁇ - 500 ⁇ , including the endpoint value, to reduce the effect of impurities of the ruthenium itself on the ingot process.
  • the coating in this embodiment may be a single layer coating and a multilayer coating.
  • the silicon carbide or silicon dioxide particles may be directly mixed after being mixed with the silicon nitride particles.
  • a separate silicon carbide or silicon dioxide solution may be applied to the inner surface of the crucible, and then a silicon nitride solution may be additionally coated.
  • the coating order of the different solutions is not limited, that is, the nitride may be first coated.
  • the silicon solution is recoated with a silicon carbide or silica solution, or the different solutions are cross-coated.
  • the roughness Ra of the bottom surface of the inner surface of the crucible in this embodiment is greater than 5 ⁇ m and less than 5 mm, including the end point value, more preferably Ra is greater than 10 ⁇ m and less than 2 mm.
  • the three-dimensional geometric shape 12 in this embodiment is a hollow structure with a vertex downward and an opening upward.
  • the three-dimensional geometric shape of the bottom surface of the crucible in this embodiment may be a regular arrangement or an irregular arrangement.
  • the three-dimensional geometric shape is irregularly arranged on the bottom surface of the crucible, that is, the plane of the opening of the three-dimensional geometric shape 12 and the bottom of the crucible may not Parallel, and along the mouth of the mouth toward the bottom of the raft
  • the shape of the opening of the hollow inverted structure may be a triangle, a quadrangle, a pentagon or the like, and the shape of the opening of the hollow inverted structure of the entire bottom surface may be the same or different, as seen from a plan view.
  • the arrangement may be irregular.
  • the thickness of the crucible bottom is not required, and the thickness of the crucible bottom may be the same as the thickness of the conventional crucible, or slightly larger than the thickness of the conventional crucible. In the present embodiment, it is preferable that the bottom of the crucible has a thickness of 10 to 50 mm.
  • the rough bottom surface is formed in various ways. For example, before the compaction of the crucible is sintered, a bottom brush or the like may be used to brush the bottom surface, and a groove mark may be left on the bottom surface, and then sintering and setting may be performed; Sprinkle some gravel on the bottom of the crucible, then use the binder to fix the gravel to the bottom of the crucible.
  • the process of forming the bottom roughness of the crucible is not specifically limited. That is, the manufacturing process of the crucible in this embodiment is simpler, and the processing precision is very low.
  • Another embodiment of the present invention further discloses a method for manufacturing a polycrystalline silicon ingot, which adopts the crucible described in the above embodiment, and the flow chart thereof is as shown in FIG. 4, and the manufacturing method includes:
  • Step S11 Titanium material is closely laid at the bottom of the crucible to reduce the gap between the silicon materials to obtain a first silicon material layer.
  • the silicon material in the first silicon material layer is a bulk silicon material, a crushed silicon material or a silicon powder. In this embodiment, it is preferably silicon powder;
  • the gap between the silicon materials in the first silicon material layer is 0-20 mm. Since the gap between the silicon materials is small, the time of crystal nucleation of the bottom surface of the crucible is relatively uniform, and it is easy to obtain a uniform size and a regular shape. Grain
  • Step S12 continuing to fill the silicon material on the first silicon material layer until the silicon material is filled, and the silicon material or the bulk silicon material may be used in the step;
  • Step S13 melting all the silicon materials in the crucible to obtain a silicon liquid;
  • Step S14 controlling a thermal field in the polycrystalline silicon ingot furnace, and crystallizing the silicon liquid until crystal growth is completed to obtain a polycrystalline silicon ingot.
  • the solid-liquid interface formed during the crystallization of the silicon liquid is an arc-shaped interface (collectively referred to as a partially convex solid-liquid interface) which is convex from the edge of the crucible to the interior of the crucible.
  • the curved interface may have a plurality of protrusions, or only a raised.
  • the crystal grains formed are relatively small, but due to the solid-liquid interface with local protrusions, the crystal grains gradually increase during the directional growth process.
  • the localized solid-liquid interface can inhibit the formation and proliferation of defects such as dislocations and grain boundaries to a certain extent, and improve the quality of the polycrystalline silicon ingot.
  • Another embodiment of the present invention also discloses a polycrystalline silicon ingot formed by the above method, wherein the crystal grain diagram of the middle portion is as shown in FIG. 6, using a conventional process and a conventional crucible (a quartz having an inner surface flat and coated with a silicon nitride coating) ⁇ )
  • the crystal grain in the middle of the produced polycrystalline silicon ingot is shown in Fig. 5. It can be directly seen from the figure that the grain orientation in the silicon ingot produced by the conventional crucible and the conventional process is inconsistent, and the grain size is very different. Big.
  • the inventors have found that the grain sizes in polycrystalline silicon ingots grown using conventional crucibles and conventional processes vary widely, and the long sides of the grains on a single wafer are distributed between 1 mm and 100 mm, and the same size of crystal grains. The location of the distribution is very scattered. However, the grain size difference in the polycrystalline silicon ingot produced by the method disclosed in the embodiment of the present invention is small, and the length of the long side of the crystal on the single silicon wafer is 2 mm to 30 mm, including the end point value, and the same size of the crystal grain. The distribution location is more concentrated.
  • the dislocation density of the polycrystalline silicon ingot in the prior art is 10 5 -10 6 /cm 2 , taking the middle of the polycrystalline silicon ingot as an example, and the dislocation distribution is as shown in FIG. 7 , as can be seen from the figure, the dislocation The density distribution of the polycrystalline silicon ingot produced by the enthalpy method disclosed in the embodiment of the present invention is as shown in FIG. 8. The dislocation density is significantly lower than that in the prior art, from the polycrystalline silicon ingot.
  • the dislocation density of the polycrystalline silicon ingot in the embodiment of the present invention is reduced by 1-3 orders of magnitude compared with the prior art, and the performance of the ingot is greatly improved, and the orientation of the crystal nucleus is more uniform, and the crystal grain is more uniform.
  • the size is uniform and the dislocation density is greatly reduced.
  • the inventor has seen through many experiments that the sun made by the polysilicon ingot in the prior art is obtained.
  • the conversion efficiency of the energy battery is generally about 17%, and the conversion efficiency of the solar cell produced by using the polycrystalline silicon ingot in the embodiment of the present invention can reach 17.5%, or even larger, that is, the polycrystalline silicon ingot in the embodiment of the present invention is used.
  • the conversion efficiency of the solar cell is improved by more than 0.5% than that of the conventional solar wafer.
  • the method for fabricating bismuth and polycrystalline silicon ingots in the embodiment of the present invention makes the grain size in the grown polycrystalline silicon ingot more uniform, the crystal orientation of the crystal nucleus is more uniform, and the dislocation density inside the crystal is lowered. And the grain boundary density, thereby improving the conversion efficiency of the polycrystalline silicon solar cell.

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Abstract

本发明公开了一种多晶硅锭及其制造方法、坩埚，其中该坩埚底面粗糙，且具有空间分布的多个三维几何形状；该坩埚内表面涂覆有至少一层涂层，所述坩埚底面涂层中具有作为硅的异质形核点的颗粒状物质。本发明实施例的坩埚底面涂覆至少一层涂层，涂层中的颗粒状物质可以在后续长晶过程中作为硅的形核点，抑制其它区域晶核的形成，使晶粒的分布更均匀，并且，首先形核的晶粒在坩埚底面的凹坑处即开始进行竞争，一定晶向的晶粒在竞争过程中占有优势，并最终被保留，从而使晶核的取向趋于一致，即采用该方法生长的多晶硅锭中的晶粒大小均匀，晶粒取向较为一致，并降低了晶体内部的位错密度，提高了少子寿命，从而提高了多晶硅太阳能电池的转换效率。

Description

多晶硅键及其制造方法、 坩埚
技术领域
本发明涉及单晶硅、 多晶硅的制造技术和光电领域， 尤其涉及一种多晶硅 锭及其制造方法、 坩埚。
背景技术
太阳能电池可将光能转换为电能 ,光电转换效率和衰减是衡量太阳能电池 质量好坏的重要参数，而生产成本的高低也成为了制约太阳能电池发展的重要 因素。 目前， 根据材料的不同， 太阳能电池主要分为单晶硅太阳能电池和多晶 硅太阳能电池两种。 单晶硅太阳能电池转换效率高， 但是生产成本 4艮高， 多晶 硅太阳能电池成本低， 但转换效率则相对较低。 目前， 由于较高的性价比， 多 晶硅太阳能电池在光伏市场份额上占据优势。
现有技术中多采用定向凝固法生产多晶硅锭， 其过程主要为，在内表面平 坦的坩埚中投放硅料， 之后将硅料全部熔化， 通过控制铸锭炉内的温度， 使多 晶硅锭自下而上的定向凝固， 得到多晶硅锭。
但是，采用现有技术中生产的多晶硅锭制作的太阳能电池的转换效率一直 难以提高， 出现这种情况很大一部分原因在于多晶硅锭的质量， 因此， 如何制 作性能良好的多晶硅锭成为业界热门的研究方向。
发明内容
为解决上述技术问题， 本发明提供了一种多晶硅锭及其制造方法、 坩埚， 使生长得到的多晶硅锭中的晶粒大小更均匀， 晶向更加一致， 并降低了晶体内 部的缺陷密度， 从而提高了多晶硅太阳能电池的转换效率。
为解决上述问题， 本发明实施例提供了如下技术方案：
一种坩埚， 应用于多晶硅锭的铸造过程， 该坩埚底面粗糙， 且具有空间分 布的多个三维几何形状； 该坩埚内表面涂覆有至少一层涂层， 所述坩埚底面涂 层中具有作为硅的异质形核点的颗粒状物质， 所述内表面包括内壁和底面， 所 述底面为坩埚内表面的底面。 优选的， 所述涂层包括氮化硅涂层、 氮化硅与碳化硅的复合涂层、 和氮化 硅与二氧化硅的复合涂层中的至少一种，所述氮化硅涂层中的颗粒状物质为氮 化硅颗粒 ,所述氮化硅与碳化硅的复合涂层中的颗粒状物质为氮化硅颗粒和碳 化硅颗粒，所述氮化硅与二氧化硅的复合涂层中的颗粒状物质为氮化硅颗粒和 二氧化硅颗粒。
优选的， 所述氮化硅与碳化硅的复合涂层中， 碳化硅的重量比为 0-5%, 包括端点值； 所述氮化硅与二氧化硅的复合涂层中， 二氧化硅的重量比为 0-5%, 包括端点值。
优选的， 所述坩埚的底面为所述氮化硅与碳化硅的复合涂层、或氮化硅与 二氧化硅的复合涂层， 所述坩埚的内壁为氮化硅涂层。
优选的， 所述涂层的厚度为 10 μ ιη-500 μ ηι, 包括端点值。
优选的， 所述底面的粗糙度 Ra大于 5 μ ιη, 且小于 5mm , 包括端点值。 优选的， 所述三维几何形状在坩埚底面为不规则排布，且所述三维几何形 状为顶点向下， 开口向上的空心结构。
优选的， 所述多个三维几何形状的空间分布方式为， 所述多个三维几何形 状的顶点和 /或开口距坩埚外表面的底面的距离不等。
优选的， 所述多个三维几何形状的空间分布方式为，在沿坩埚口部向坩埚 底部的方向， 所述多个三维几何形状呈不规则排布。
优选的， 所述多个三维几何形状的开口形状相同或不同。
本发明实施例还公开了一种多晶硅锭制造方法， 采用以上所述的坩埚， 该 制造方法包括： 在坩埚底部紧密铺设硅料， 得到第一硅料层， 所述第一硅料层 中的硅料为块状硅料、碎硅料或硅粉； 在所述第一硅料层上继续填装硅料， 直 至硅料填装完成； 熔化所述坩埚内的所有硅料， 得到硅液； 控制多晶硅铸锭炉 内的热场， 对所述硅液进行结晶， 直至晶体生长完成， 得到多晶硅锭。
优选的， 所述第一硅料层中的硅料间的间隙为 0-20mm。
本发明实施例还公开了一种多晶硅锭， 采用以上方法制造， 该多晶硅锭的 位错密度为 102-105个 /cm2。 优选的， 该多晶硅锭的晶粒长边长度为 2mm-30mm, 包括端点值。
与现有技术相比， 上述技术方案具有以下优点：
本发明实施例所提供的坩埚底面涂覆有至少一层涂层，涂层中的颗粒状物 质可以在后续长晶过程中作为硅的形核点， 在结晶初始时， 由于底面粗糙， 位 于坩埚底面凹陷的位置，尤其是三维几何形状的顶或底区域附近的涂层中的硅 晶粒会优先形核并长大，并在后续的生长过程中，会抑制其它区域晶核的形成， 从而使晶粒的分布更均匀， 进一步的，底面粗糙的坩埚对晶粒的晶体学取向有 一定的引导作用， 首先形核的晶粒在坩埚底面的凹坑处即开始进行竟争， 一定 晶向的晶粒在竟争过程中占有优势， 并最终保留了下来，从而使晶核的取向趋 于一致， 因此， 采用该方法生长的多晶硅锭中的晶粒大小均匀， 晶粒取向较为 一致， 并降低了晶体内部的位错密度， 提高了少子寿命， 从而提高了多晶硅太 阳能电池的转换效率。
附图说明
图 1为本发明实施例公开的坩埚的剖面图；
图 2为本发明实施例公开的坩埚底部的俯视图；
图 3为本发明实施例公开的坩埚底部的局部剖面放大图；
图 4为本发明实施例公开的多晶硅锭制造方法流程图；
图 5为现有技术中多晶硅锭中部区域的晶体示意图；
图 6为本发明实施例公开的多晶硅锭中部区域的晶体示意图；
图 7为现有技术中的多晶硅锭中部的多晶硅片上的位错分布图；
图 8为本发明实施例公开的多晶硅锭中部的多晶硅片上的位错分布图。 具体实施方式
正如背景技术部分所述，采用现有技术中的铸锭工艺得到的多晶硅锭质量 较差， 采用现有技术中的多晶硅锭制作的太阳能电池的转换效率低，发明人研 究发现，出现这种问题的原因在于，现有技术中的多晶硅锭在晶体生长过程中， 晶体随机形核并生长，造成最后形成的硅锭中的晶粒大小存在很大的差异， 在 大晶粒之间会夹杂一些小晶粒， 或者在大晶粒内部分布着亚晶界等缺陷， 小晶 粒的尺寸又过小， 导致硅锭内部晶界多， 位错多， 这些亚晶和位错等缺陷又极 易成为光生载流子的复合中心， 尤其是位错， 具有艮强的复合活性， 从而导致 制作出的太阳能电池中的少子寿命低， 大大降低了电池的转换效率。
为解决上述问题， 本发明提供了一种坩埚， 以及采用这种坩埚的多晶硅锭 制造方法和制作出的多晶石圭键, 其中, 该; ¾"呙内表面的底面粗 , 且具有 间 分布的多个三维几何形状； 该坩埚内表面涂覆有至少一层涂层， 所述涂层中具 有作为硅的异质形核点的颗粒状物质， 所述内表面包括内壁和底面。
该多晶硅锭制造方法包括， 在坩埚底部紧密铺设硅料， 得到第一硅料层， 所述第一硅料层中的硅料为块状硅料、碎硅料或硅粉； 在所述第一硅料层上继 续填装硅料， 直至硅料填装完成； 熔化所述坩埚内的所有硅料， 得到硅液； 控 制多晶硅铸锭炉内的热场， 对所述硅液进行结晶， 直至晶体生长完成， 得到多 晶硅锭。采用该方法制作出的多晶硅锭的位错密度较现有技术中的多晶硅锭的 位错密度降低了 1-3个数量级， 为 102-105个 /cm2。且该多晶硅锭的晶粒长边长 度为 2mm-30mm, 包括端点值。 显然， 本发明实施例得到的多晶硅锭的质量 得到了很大的提高。
上述方案通过采用底面粗糙且涂覆有涂层的坩埚来放置硅料，硅料熔化后 的长晶过程中， 涂层中具有作为硅的异质形核点的颗粒状物质， 尤其是坩埚底 面凹陷区域的涂层中具有颗粒状物质的位置处会优先形核并长大，在后续的生 长过程中， 抑制其它区域晶核的形成。
在坩埚底面的凹陷区域形核后，使硅晶体具有了特定的形核位置，从而使 晶粒分布均匀。 进一步的， 由于坩埚的底面粗糙， 在底面的同一凹陷区域形成 的多个晶核在生长到凹陷区域顶部前， 同样会经过择优竟争， 在该过程中， 一 定晶向的晶粒在竟争过程中占有优势， 并最终保留了下来，从而使晶粒的取向 趋于一致， 经过该择优竟争之后， 使得晶体在后续进行柱状生长之前， 在同一 1HJ陷区域保留的晶核数量减少，从而进一步增加了晶粒分布的均匀性，使晶体 的取向趋于一致， 进而降低了晶体内部的位错密度， 延长了少子寿命， 从而提 高了多晶硅太阳能电池的转换效率。
需要说明的是，作为异质形核点的颗粒状物质可能来源于坩埚，也可以为 后续人为涂覆的涂层， 在以下实施例中仅以后者为例进行说明。
以上是本申请的核心思想， 下面将结合本发明实施例中的附图，对本发明 实施例中的技术方案进行清楚、 完整地描述， 显然， 所描述的实施例仅仅是本 发明一部分实施例， 而不是全部的实施例。 基于本发明中的实施例， 本领域普 通技术人员在没有做出创造性劳动前提下所获得的所有其它实施例 ,都属于本 发明保护的范围。
基于上述研究的基础上， 本发明实施例提供了一种坩埚， 其剖面图如图 1 所示， 俯视图如图 2所示， 图 3为坩埚底部的局部放大图， 该坩埚应用于多晶 硅锭的铸造过程， 该坩埚内表面的底面 11粗糙， 且底面 11上具有不规则的空 间分布的多个三维几何形状 12, 并且， 该坩埚内表面涂覆有至少一层涂层 14, 所述内表面包括内壁 13和底面 11 , 所述坩埚底面 11涂层中具有作为硅的异 质形核点的颗粒状物质（图中未示出）， 所述底面为坩埚内表面的底面。 其中， 图中的粗糙程度仅用来示出坩埚底部三维几何形状 12的结构及分布方式， 各 部分的尺寸及比例并不作为对实际坩埚结构的限制。
需要说明的是， 在多晶硅锭结晶生长过程中， 由于坩埚的存在， 硅液（即 母相）中存在着其他固相颗粒， 新的形核晶粒会依附于已有的固相颗粒， 在已 有的固相颗粒表面形核（该已有的固相颗粒又称为异质形核点）， 这就降低了 硅晶体可以在该位置处优先形核， 并从而在后续硅锭的生长过程中， 能够抑制 硅液内其它区域晶核的形成， 从而在一定程度上降低了晶界和位错密度。
进一步的， 形核的难易程度与形核功的大小有关， 坩埚底面凹陷区域能够 降低硅晶体的形核功，也就是说，位于坩埚底面凹陷区域处晶粒成核所需越过 的能量势垒要低于其它区域， 并且成核后优先生长，从而进一步的抑制其它区 域晶核的形成和生长，从而使最终形成的晶体的有序性增加， 同时由于优先形 核的颗粒状物质位于坩埚底面凹陷区域，首先形核的晶体在坩埚底面的凹坑处 即开始进行竟争，一定晶向的晶体在竟争过程中占有优势，并最终保留了下来， 这就使晶核的取向趋于一致， 进而使最终得到的多晶硅锭的晶向更加一致， 晶 体的有序度增加， 使晶体内部的位错密度降低， 从而延长了少子寿命， 提高了 多晶硅太阳能电池的转换效率。
其中， 本实施例中的涂层 14包括氮化硅涂层、 氮化硅与碳化硅的复合涂 层、 和氮化硅与二氧化硅的复合涂层中的至少一种， 具体的， 坩埚底面和内壁 可以采用相同的涂层， 如均为氮化硅涂层、 或以上任一种复合涂层， 也可以采 用不同的涂层， 如底面采用以上任一种复合涂层， 内壁采用氮化硅涂层， 或底 面采用氮化硅涂层， 内壁采用以上任一种复合涂层。
所述氮化硅涂层中的颗粒状物质为氮化硅颗粒，所述氮化硅与碳化硅的复 合涂层中的颗粒状物质为氮化硅颗粒和碳化硅颗粒，所述氮化硅与二氧化硅的 复合涂层中的颗粒状物质为氮化硅颗粒和二氧化硅颗粒。
根据以上分析可知， 本实施例中将涂层涂覆在坩埚粗糙的底面，相比于单 纯的在平坦的坩埚底面涂覆氮化硅涂层和单纯制作底面粗糙的坩埚来说，生长 的多晶硅锭的性能更好。
一般铸锭用的坩埚多为石英坩埚，但是单纯的使用石英坩埚，在铸锭时容 易出现开裂的问题， 其主要原因为， 熔融的硅可与其接触的二氧化硅反应， 形 成一氧化硅和氧； 其中， 氧可污染硅， 一氧化硅具有挥发性； 并且其还可与炉 内的石墨部件形成碳化硅和一氧化碳， 生成的一氧化碳继而可与熔融的硅反 应， 形成挥发性一氧化硅、 碳化硅或掺杂剂的碳化物、 氧化物和碳， 碳可污染 硅。二氧化硅与熔融硅之间的上述反应促使硅黏附在坩埚上。但由于二氧化硅 和硅之间的热膨胀系数不一样， 导致硅锭在冷却时易发生开裂。
为此，在坩埚内表面涂覆较厚的氮化硅， 以阻止二氧化硅与熔融的硅液反 应， 同时也便于多晶硅锭脱模， 要起到这种作用要求氮化硅的纯度越高越好。
但是， 形核功的大小还与母相和固相颗粒的接触角有关，接触角的大小与 母相和固相颗粒的材质有关，在母相材料固定的情况下，合适材料的异质形核 点， 所需的形核功小， 形核更加容易。 相对于氮化硅颗粒来说， 碳化硅和氧化 硅颗粒与硅液的接触角更小， 采用碳化硅和氧化硅颗粒作为硅的异质形核点， 硅晶体形核所需的能量更低， 即更加易于形核， 因此本实施例中为形成性能更 加良好的多晶硅锭， 同时避免引入新的杂质，优选在氮化硅中掺杂少量的碳化 硅或二氧化硅， 即本实施例中优选在坩埚内表面涂覆复合涂层， 并且为降低在 铸锭过程中，碳化硅和二氧化硅对坩埚的影响和对硅锭的污染情况， 必须严格 控制碳化硅或二氧化硅的含量。
本实施例中优选氮化硅与碳化硅的复合涂层中， 碳化硅的重量比在 5%以 下， 包括端点值， 如 2%、 3%或 4%; 氮化硅与二氧化硅的复合涂层中， 二氧 化硅的重量比在 5%以下， 包括端点值， 如 2%、 3%或 4%。
进一步的， 为了最大限度的减小碳化硅或二氧化硅对铸锭过程的影响， 同 时由于在长晶初期，优先形核的区域为坩埚底面凹陷部位， 一旦坩埚底面晶粒 取向确定后， 即可引导后续的长晶过程， 在后续长晶过程中， 应尽量减少坩埚 侧壁的成核， 为此， 本实施例中更优选在坩埚底面采用以上任一种复合涂层， 内壁采用氮化硅涂层。
本实施例中优选涂层的厚度为 10 μ ιη-500 μ ηι, 包括端点值， 以减小坩埚 本身的杂质对铸锭过程的影响。
并且，本实施例中的涂层可以为单层涂层和多层涂层，对于复合涂层来说， 可将碳化硅或二氧化硅颗粒与氮化硅颗粒混合在一起后，直接涂覆在坩埚内表 面，也可以将单独的碳化硅或二氧化硅溶液涂覆在坩埚内表面后，再另外涂覆 氮化硅溶液， 不同溶液的涂覆顺序不限， 即也可先涂氮化硅溶液， 再涂碳化硅 或二氧化硅溶液， 或者不同溶液交叉多层涂覆。 为了在粗糙的坩埚底面形成均 勾的涂层， 本实施例中优选采用喷涂工艺将涂层所用溶液涂覆在坩埚内表面。
本实施例中坩埚内表面的底面的粗糙度 Ra大于 5 μ m, 且小于 5mm, 包 括端点值， 更优选为 Ra大于 10 μ m, 且小于 2mm。
本实施例中的三维几何形状 12为顶点向下， 开口向上的空心结构， 需要 说明的是， 本实施例中的坩埚底面的三维几何形状可以为规则排布，也可以不 规则排布， 本实施例中为了减小加工难度， 降低对坩埚底面的三维几何形状的 精细度的要求，优选三维几何形状在坩埚底面为不规则排布， 即三维几何形状 12 的开口所在平面与坩埚底部可以不平行， 且在沿坩埚口部向坩埚底部的方 向 （以下简称俯视）， 该空心倒立结构的开口形状任意， 可以为三角形、 四边 形、 五边形等， 并且， 从俯视图上看， 整个底面的空心倒立结构的开口形状可 以相同， 也可以不同， 并且可呈不规则排布， 在剖面图上看， 多个三维几何形 状的顶点和 /或开口距坩埚外表面的底面的距离可以相等或不等。
由于石英坩埚表面的微结构也在微米量级，而本实施例中的坩埚底面的粗 糙度 (与三维几何形状的径向尺寸近似 )与石英坩埚表面的微结构的数量级相 差不大， 坩埚底面的三维几何形状产生的应力对坩埚底面的影响不大， 因此， 本实施例中对坩埚底部的厚度要求不大，该坩埚底部厚度可与常规坩埚的厚度 相同， 或稍大于常规坩埚的厚度， 本实施例中优选所述坩埚底部的厚度为 10-50mm。
并且， 由于本实施例中坩埚底面的三维几何形状的排列不规则，且尺寸不 大， 因此， 在坩埚制作过程中， 对坩埚底面的加工精度没有任何要求， 即可避 免制作复杂的模具， 本实施例中粗糙的坩埚底面的形成方式有多种， 比如在坩 埚烧结致密前， 可采用细毛刷等工具刷坩埚底面， 在底面留下凹槽痕迹即可， 之后再进行烧结定型； 也可在坩埚底部撒些砂砾，之后采用粘结剂将砂砾固定 在坩埚底部即可。 本实施例中对形成坩埚底部粗糙结构的工艺不做具体限定。 即本实施例中的坩埚的制作工艺更简单， 对加工精度的要求很低。
本发明另一实施例还公开了一种多晶硅锭制造方法 ,该方法采用以上实施 例所述的坩埚， 其流程图如图 4所示， 该制造方法包括：
步骤 S11 : 在坩埚底部紧密铺设硅料， 以减小硅料间的空隙， 得到第一硅 料层， 所述第一硅料层中的硅料为块状硅料、碎硅料或硅粉， 本实施例中优选 为硅粉；
本实施例中优选第一硅料层中的硅料间的间隙为 0-20mm, 由于硅料间的 间隙艮小， 坩埚底面晶粒形核的时间较为一致， 容易得到大小均匀， 形状规则 的晶粒；
步骤 S12: 在所述第一硅料层上继续填装硅料， 直至硅料填装完成， 该步 骤中可采用碎硅料或大块硅料； 步骤 S13: 熔化所述坩埚内的所有硅料， 得到硅液；
步骤 S14: 控制多晶硅铸锭炉内的热场， 对所述硅液进行结晶， 直至晶体 生长完成， 得到多晶硅锭。
硅液结晶过程中形成的固液界面为由坩埚边缘处向坩埚内部凸起的弧形 界面 （统称局部凸起的固液界面）， 该弧形界面可有多个凸起， 也可仅有一个 凸起。在晶体生长初期，形成的晶粒比较小，但由于具有局部凸起的固液界面， 使得晶体在定向生长过程中， 晶粒会逐渐增大。 同时， 局部凸起的固液界面可 在一定程度上抑制位错、 晶界等缺陷的形成和增殖， 提高了多晶硅锭的质量。
本发明另一实施例还公开了采用上述方法形成的多晶硅锭，其中部的晶粒 示意图如图 6所示， 采用常规工艺和常规坩埚（内表面平坦且涂覆有氮化硅涂 层的石英坩埚）制作得到的多晶硅锭中部的晶粒示意图如图 5所示，从图中可 以直接看出， 使用常规坩埚和常规工艺制作得到的硅锭中的晶粒取向不一致， 晶粒的大小差别很大。
发明人统计得到，使用常规坩埚和常规工艺生长的多晶硅锭中的晶粒大小 相差很大，单张硅片上的晶粒长边在 1mm到 100mm之间都有分布，且同样尺 寸的晶粒分布的位置很分散。而采用本发明实施例公开的坩埚和方法制作出的 多晶硅锭中的晶粒大小相差很小， 单张硅片上晶粒长边长度为 2mm-30mm, 包括端点值， 且同样尺寸的晶粒分布位置较为集中。
并且， 现有技术中的多晶硅锭的位错密度为 105-106个 /cm2, 以多晶硅锭 中部为例， 其位错分布如图 7所示， 从图中可以看出， 位错的密度 ^艮大； 而采 用本发明实施例公开的坩埚和方法制作出的多晶硅锭中部的位错分布如图 8 所示， 位错密度比现有技术中的明显降低了很多， 从多晶硅锭整体上来看， 本 发明实施例中的多晶硅锭的位错密度较现有技术降低了 1-3 个数量级， 约为 锭的性能得到了很大的提高， 晶核的取向更加趋向一致， 晶粒的大小均匀， 位 错密度得到的很大的降低。
发明人经过多次试验对比得知，采用现有技术中的多晶硅锭制作出的太阳 能电池的转换效率一般在 17%左右，而采用本发明实施例中的多晶硅锭制作出 的太阳能电池的转换效率可达 17.5%, 甚至更大， 即采用本发明实施例中的多 晶硅锭制作出的太阳能电池的转换效率比常规多晶硅片制作的太阳能电池的 转换效率提高了 0.5%以上。
综上所述， 采用本发明实施例中的坩埚、 多晶硅锭制作方法， 使生长得到 的多晶硅锭中的晶粒大小更均匀， 晶核的晶向更加一致， 并降低了晶体内部的 位错密度和晶界密度， 从而提高了多晶硅太阳能电池的转换效率。
对所公开的实施例的上述说明，使本领域专业技术人员能够实现或使用本 发明。 对这些实施例的多种修改对本领域的专业技术人员来说将是显而易见 的， 本文中所定义的一般原理可以在不脱离本发明的精神或范围的情况下， 在 其它实施例中实现。 因此， 本发明将不会被限制于本文所示的实施例， 而是要 符合与本文所公开的原理和新颖特点相一致的最宽的范围。
+

Claims

权 利 要 求
1、 一种坩埚， 应用于多晶硅锭的铸造过程， 其特征在于， 该坩埚底面粗 糙，且具有空间分布的多个三维几何形状；该坩埚内表面涂覆有至少一层涂层 , 所述坩埚底面涂层中具有作为硅的异质形核点的颗粒状物质，所述内表面包括 内壁和底面， 所述底面为坩埚内表面的底面。
2、根据权利要求 1所述的坩埚， 其特征在于， 所述涂层包括氮化硅涂层、 氮化硅与碳化硅的复合涂层、 和氮化硅与二氧化硅的复合涂层中的至少一种 , 所述氮化硅涂层中的颗粒状物质为氮化硅颗粒 ,所述氮化硅与碳化硅的复合涂 层中的颗粒状物质为氮化硅颗粒和碳化硅颗粒 ,所述氮化硅与二氧化硅的复合 涂层中的颗粒状物质为氮化硅颗粒和二氧化硅颗粒。
3、 根据权利要求 2所述的坩埚， 其特征在于， 所述氮化硅与碳化硅的复 合涂层中， 碳化硅的重量比为 0-5%, 包括端点值； 所述氮化硅与二氧化硅的 复合涂层中， 二氧化硅的重量比为 0-5%, 包括端点值。
4、 根据权利要求 3所述的坩埚， 其特征在于， 所述坩埚的底面为所述氮 化硅与碳化硅的复合涂层、或氮化硅与二氧化硅的复合涂层， 所述坩埚的内壁 为氮化硅涂层。
5、根据权利要求 3所述的坩埚，其特征在于，所述涂层的厚度为 10 μ m-500 μ ιη, 包括端点值。
6、根据权利要求 1所述的坩埚， 其特征在于， 所述底面的粗糙度 Ra大于 5 μ ιη, 且小于 5mm , 包括端点值。
7、 根据权利要求 1所述的坩埚， 其特征在于， 所述三维几何形状在坩埚 底面为不规则排布， 且所述三维几何形状为顶点向下， 开口向上的空心结构。
8、 根据权利要求 7所述的坩埚， 其特征在于， 所述多个三维几何形状的 空间分布方式为， 所述多个三维几何形状的顶点和 /或开口距坩埚外表面的底 面的距离不等。
9、 根据权利要求 8所述的坩埚， 其特征在于， 所述多个三维几何形状的 空间分布方式为，在沿坩埚口部向坩埚底部的方向， 所述多个三维几何形状呈 不规则排布。
10、 根据权利要求 9所述的坩埚， 其特征在于， 所述多个三维几何形状的 开口形状相同或不同。
11、 一种多晶硅锭制造方法， 其特征在于， 采用权利要求 1-10任一项所 述的坩埚， 该制造方法包括：
在坩埚底部紧密铺设硅料，得到第一硅料层， 所述第一硅料层中的硅料为 块状硅料、 碎硅料或硅粉；
在所述第一硅料层上继续填装硅料， 直至硅料填装完成；
熔化所述坩埚内的所有硅料， 得到硅液；
控制多晶硅铸锭炉内的热场， 对所述硅液进行结晶， 直至晶体生长完成， 得到多晶硅锭。
12、 根据权利要求 11所述的方法， 其特征在于， 所述第一硅料层中的硅 料间的间隙为 0-20mm。
13、 一种多晶硅锭， 采用权利要求 11所述的方法制造， 其特征在于， 该 多晶硅锭的位错密度为 102-105个 /cm2。
14、 根据权利要求 13所述的多晶硅锭， 其特征在于， 该多晶硅锭的晶粒 长边长度为 2mm-30mm, 包括端点值。
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