WO2012126255A1 - 定向凝固法生长硅晶体时控制坩埚底面结晶成核的方法和装置 - Google Patents

定向凝固法生长硅晶体时控制坩埚底面结晶成核的方法和装置 Download PDF

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WO2012126255A1
WO2012126255A1 PCT/CN2011/083149 CN2011083149W WO2012126255A1 WO 2012126255 A1 WO2012126255 A1 WO 2012126255A1 CN 2011083149 W CN2011083149 W CN 2011083149W WO 2012126255 A1 WO2012126255 A1 WO 2012126255A1
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silicon
crystal
crucible
seed crystal
spacer
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PCT/CN2011/083149
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English (en)
French (fr)
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李乔
马远
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浙江碧晶科技有限公司
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Priority claimed from CN 201110067923 external-priority patent/CN102146580B/zh
Priority claimed from CN201110162568XA external-priority patent/CN102191536A/zh
Application filed by 浙江碧晶科技有限公司 filed Critical 浙江碧晶科技有限公司
Publication of WO2012126255A1 publication Critical patent/WO2012126255A1/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
    • C30B11/006—Controlling or regulating
    • 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

Definitions

  • the invention belongs to the field of solar grade silicon manufacturing, and in particular relates to a method and device improvement for growing silicon crystal by directional solidification method.
  • Silicon single crystal and silicon polycrystalline ingots are the most commonly used materials for crystalline silicon solar cells.
  • a solar cell fabricated using a silicon single crystal material has higher photoelectric transshipment efficiency than a solar cell fabricated using a silicon polycrystalline material.
  • silicon polycrystals the larger the crystalline particles of the silicon polycrystal, the higher the efficiency of the fabricated solar cell.
  • a silicon single crystal is produced, and a silicon polycrystal is produced by a directional solidification method (ie, a casting method or an ingot casting method).
  • the directional solidification method is to place the silicon raw material in a crucible in a polycrystalline ingot furnace, and the silicon raw material is crystallized from the bottom upward by changing the temperature field.
  • the silicon crystal grown by the directional solidification method is usually silicon polycrystal, and the silicon single crystal cannot be obtained.
  • the main reason is that the initial process of directional solidification is not guided by a seed crystal of a specific crystal orientation, and solidification is usually Starting from the wall surface of the quartz crucible, a plurality of solidified cores spontaneously form and gradually grow, so that the finally formed crystal is polycrystalline rather than single crystal.
  • a specific seeding technique for example, the patent number is In the Chinese utility model patent disclosed in ZL 200920115886.9, the seed crystal is placed in the crucible to carry out the seed crystal growth ingot, and the ingot casting method can also grow the silicon single crystal. But the patent number is ZL
  • the Chinese utility model patent of 200920115886.9 requires special processing of quartz crucibles, which increases the manufacturing cost of quartz crucibles.
  • the crucible is usually a quartz crucible, and in order to facilitate the separation of the silicon ingot from the crucible after the growth is completed, It is necessary to spray a silicon oxide coating on the inner wall of the quartz crucible.
  • the temperature is suitable, a large number of nucleation cores are formed, resulting in the grain size of the silicon polycrystalline ingot formed in the initial stage of growth. Small and large, it is not conducive to the final formation of silicon polycrystalline materials with large crystalline particles.
  • the invention provides a method for controlling crystal nucleation of a crucible bottom surface when a silicon crystal is grown by a directional solidification method.
  • the polycrystalline silicon ingot or single crystal silicon of large crystal grains can be efficiently grown without changing the structure of the existing directional solidification furnace and quartz crucible.
  • the present invention also provides a device for controlling the crystal nucleation of the crucible bottom surface when the silicon crystal is grown by the directional solidification method, and is suitable for growing the silicon single crystal ingot by the directional solidification method.
  • One kind The method of controlling the crystal nucleation of the crucible bottom surface when the silicon crystal is grown by the directional solidification method, and the spacer substance is placed in the crucible at or before the silicon raw material is melted to form the silicon melt, and the spacer substance is melted at a temperature above the melting point of the silicon.
  • the liquid form is deposited at the bottom of the crucible to separate the silicon melt from the bottom of the crucible to control the amount and quality of the crystal nucleation of the crucible bottom surface;
  • the spacer material is a substance having a melting point lower than that of silicon, a density greater than silicon, and a non-reactive and non-miscible with silicon at 1000 to 2000 °C.
  • the spacer material is one or more of IV cluster elements such as Ge (Ge), tin (Sn), and lead (Pb), and may also be used, for example, CaF 2 , CaCl 2 , BaF 2 .
  • Barium (Ba) may also be used as a chloride or fluoride which does not react with silicon such as BaCl 2 . That is, the spacer substance may be one or more of bismuth, tin, lead, CaF 2 , CaCl 2 , BaF 2 , BaCl 2 , Ba.
  • the F element or the Cl element in the compound is corrosive to the tantalum material or the seeding mold, it is most preferable to use one of ⁇ (Ge ), tin (Sn), lead (Pb), ⁇ (Ba) or A variety.
  • the preferred spacer material is used because the melting point is lower than that of silicon and the density is higher than that of silicon; it can ensure that the isolation material is liquid when the silicon crystal grows, always at the bottom of the crucible; and does not react with silicon, nor does it affect the use of silicon material as a solar photovoltaic material. Quality at the time.
  • the spacer material may be placed in advance in the crucible, or the spacer material may be added to the crucible when the silicon material is melted to form a silicon melt. Since the insulating material has a lower melting point than silicon and a higher density than silicon, When the crucible to which the separator and the silicon raw material are added is heated at a high temperature, the separator will first melt and precipitate to the bottom of the crucible. When the temperature is further increased, the silicon raw material will also be turned into a silicon melt and floated on top of the liquid spacer to completely isolate the bottom of the crucible from the silicon melt.
  • the silicon melt crystallizes and nucleates at the interface where the spacer material contacts the silicon melt liquid phase. Due to the isolation of the substance and the silicon melt (or / The interface with the silicon crystal) is smooth, and there are no defects inherent in the wall surface of the quartz crucible, such as surface bumps and surface depressions, which induce defects in the formation of new crystal nuclei, resulting in fewer crystal nucleation cores, which is beneficial to Formation of large-sized crystalline particles. Finally, the solidification interface is moved upward by temperature field control to grow into a higher quality silicon ingot. Another significant benefit of the barrier material is that it reduces the contamination of the silicon wall material by the bottom wall of the crucible.
  • the temperature field control is realized by changing the heating and heat preservation manner to move the temperature gradient of the thermal field, so that the solidification interface at the crystallization nucleation gradually moves upward, directional solidification, and finally generates a large size.
  • the crucible is usually a quartz crucible having a surface coated with silicon nitride. Namely, a polycrystalline silicon ingot which efficiently grows large crystal particles can be realized by using a quartz crucible which is common in the prior art. It can be seen that the above method is used for growing polycrystalline silicon ingots without changing the structure of the existing directional solidification furnace and quartz crucible.
  • the above method can also be used for the growth of silicon single crystal ingots, in which case it is necessary to fix the silicon single crystal seed crystals to the bottom of the crucible before the silicon raw material is melted to form a silicon melt. That is, the silicon single crystal seed crystal is fixed at the bottom of the crucible, and the single crystal of the crystal orientation is induced by the seed crystal seeding. Since the density of silicon is less than the density of the spacer material, when the spacer material is melted, the silicon single crystal seed crystal may float away from the bottom of the crucible, so the silicon single crystal seed crystal must be fixed at the bottom of the crucible.
  • a mold can be used to fix the seed crystal, and various methods such as binding a material having a density much higher than that of the spacer material (for example, tungsten) to the seed crystal can be employed.
  • the spacer material for example, tungsten
  • the directional solidification method for growing a silicon single crystal ingot can be realized without changing the structure of the existing directional solidification furnace and the quartz crucible.
  • a device for controlling crystal nucleation of the crucible bottom surface when the silicon crystal is grown by the directional solidification method will be provided, which is suitable for use in the method of fixing the seed crystal by the mold described above.
  • a device for controlling crystal nucleation of a crucible bottom surface when a silicon crystal is grown by a directional solidification method comprising a quartz crucible, wherein a seed crystal mold is placed or disposed at a bottom portion of the quartz crucible, and the seed crystal mold includes seeds a crystal container and a spacer liquid container, the seed crystal container being provided with a first cavity for placing a seed crystal, the spacer liquid container being constituted by a cavity connected around the seed crystal container for placing the isolation substance;
  • the shape of the outer wall of the spacer liquid container is adapted to the shape of the inner wall of the quartz crucible such that the outer wall of the seed crystal mold is in close contact with the inner wall of the quartz crucible; Bottom shape with the stated
  • the bottom shape of the quartz crucible is adapted such that the bottom of the seed crystal mold covers the bottom of the quartz crucible so that the spacer material placed in the spacer liquid container can be in a liquid state during crystal growth.
  • the spacer liquid container is used for storing a liquid isolation material with an effective height of 5 to 100 mm. It can occupy as little as possible the capacity of the quartz crucible to hold the silicon raw material, and it can effectively isolate it.
  • a cavity is provided on the bottom wall of the spacer liquid container, so that the temperature of the position of the seed crystal and the quartz are The temperature difference around the crucible is larger, so that the temperature of the seed crystal is just near the melting point while the silicon melt is kept overheated.
  • the central axis of the first cavity of the seed crystal container is the same as the central axis of the seed crystal mold, and when the seed crystal mold is placed at the bottom of the quartz crucible, And will be described When the seed crystal is placed in the first cavity, the seed crystal is located in the The center of the bottom of the quartz crucible is beneficial to the formation of silicon single crystal by seed crystal, and to ensure the uniformity and consistency of the quality of the silicon single crystal, which is more conducive to the growth of high quality silicon single crystal.
  • the shape of the first cavity is adapted to the shape of the seed crystal, and thus the shape of the first cavity is mainly designed for the shape of the existing seed crystal.
  • the cross section of the first cavity is preferably circular or square. If a large seed crystal (cross-sectional area greater than 2500 mm 2 ) is used, the round seed crystal may be a segmented single crystal grown by the Czochralski method, and the square seed crystal may be a single crystal grown by the directional solidification method. A section of the cut single crystal obtained after (cut).
  • the first cavity is cylindrical, preferably an elongated tubular shape of equal section, that is, the cross section of the first cavity is the same everywhere, and the cylinder is generally selected in consideration of convenience of processing. Or square tube.
  • the cross-sectional area of the first cavity determines the size of the cross-sectional area of the seed crystal placed therein.
  • the diameter of the first cavity is not strictly limited, but too large a seed crystal increases the cost of purchasing the seed crystal, and too small a seed crystal may cause difficulty in processing the seed crystal. Therefore, the cross-sectional area of the first cavity can be selected in the range of 0.25 to 40,000 mm 2 , which is easy to process and can appropriately control the cost.
  • the seeding mold Since the seeding mold is placed or disposed inside the quartz crucible, its volume occupies the effective capacity of the original quartz crucible. In order to minimize the capacity of the quartz crucible to hold the silicon raw material, the overall height of the seed crystal mold should be as low as possible. However, a too low seed crystal height (corresponding to the height of the first cavity) is not conducive to controlling the temperature in crystal growth, and it is difficult to achieve partial melting of the seed crystal and to eliminate dislocations during crystal growth.
  • the height of the first cavity is preferably 5 ⁇ 100mm It does not occupy too much volume of quartz crucible, but also facilitates temperature field control of seed crystal seeding. Meanwhile, in order to prevent the liquid spacer from covering the seed crystal, it is preferable that the height of the first cavity is larger than the spacer liquid container for storing the liquid state. The effective height of the isolating substance.
  • the first cavity is contracted at least in a portion near the top end thereof to form a neck portion.
  • the constricted section itself may be of equal diameter or may be tapered. Since the neck portion has a gradually decreasing diameter, the disc grows through the elongated passage of the neck portion, and the dislocations which grow from the seed crystal can be better eliminated.
  • the main raw material for preparing the seed crystal mold may be a conventional graphite or carbon carbon composite material (CFC).
  • CFC carbon carbon composite material
  • the seeding mold When fabricated from a graphite material, the seeding mold can be machined by a single piece of graphite to form a first cavity of the seed container.
  • the seed crystal mold can also be made of boron nitride, quartz, carbon carbon composite material (CFC ) and other materials are processed.
  • the seeding mold is processed by using quartz as a material, the seeding mold can be made into a part of a quartz crucible, that is, a quartz crucible having a crystallizing mold structure.
  • the surface of the seed crystal mold is spray coated with a layer of silicon nitride (Si 3 N 4 ) or boron nitride (BN) coating.
  • the thickness of the coating described is 0.001 to 5 mm.
  • the present invention it is only necessary to provide or place a seed crystal mold at the bottom of the prior art quartz crucible to realize the directional solidification method for growing a silicon single crystal ingot.
  • the crystal introducing mold is placed at the bottom of the quartz crucible, there is no need to improve the quartz crucible; when the crystal introducing mold is placed at the bottom of the quartz crucible, it is only necessary to perform a simple template improvement when processing the quartz crucible, and at this time, the quartz crucible is provided.
  • the quartz crucible of the seeding mold is provided.
  • the method for controlling crystal nucleation of the crucible bottom surface when the silicon crystal is grown by the directional solidification method by using the above device the specific steps are as follows: a spacer substance is placed in the spacer liquid container, the spacer substance is completely melted and filled with the spacer liquid container; in the first cavity of the seed crystal container The seed crystal is placed therein, and the silicon raw material is placed in the quartz crucible, and the insulating material and the silicon raw material are all melted, the seed crystal portion is partially melted, and the silicon melt is directionally solidified by temperature field control. Producing monocrystalline silicon / Single crystal silicon.
  • the above-mentioned isolation of the wall surface of the quartz crucible is only for the bottom wall surface of the quartz crucible, and the side wall surface of the quartz crucible is not required to be isolated, as long as the temperature field is reasonably designed to form a micro-convex solidification interface during the crystal growth process,
  • the spontaneous nucleation nucleus formed on the wall cannot diffuse into the interior of the crystal to avoid damaging the single crystal structure.
  • the isolation material is liquid when the silicon crystal grows, if there is no container to contain the liquid isolation substance, the liquid is likely to cover the entire seed crystal during the seed crystal seeding, resulting in the seed crystal cannot be combined with silicon.
  • the raw materials are in contact, resulting in failure of seeding.
  • the above apparatus is used for directional solidification to grow single crystal silicon, because the spacer substance is placed in the spacer liquid container of the seed crystal mold, and the height of the first cavity in the seed crystal container is set to be larger than the spacer liquid container. It is used to store the effective height of the liquid isolating material, which can effectively avoid the failure of seeding.
  • the silicon crystal (with the / And the silicon melt) will be in contact with the surface of the liquid barrier material, at which point the free surface of the spacer material will act as a wall of the quartz crucible and effectively avoid spontaneous nucleation of the wall.
  • the single crystal grown from the seed crystal needs to cross the upper end of the wall surface of the seed crystal container before being in contact with the free surface of the liquid spacer material, so that there is a great possibility that the wall surface of the seed crystal container is formed.
  • a spontaneous nucleation nucleation region destroys the original single crystal structure. For this reason, it is necessary to strengthen the surface treatment for preventing spontaneous nucleation at this place, for example, it is necessary to enhance the surface finish of the seed hole and the like.
  • the temperature field control is realized by changing the heating and heat preservation manner to move the temperature gradient of the thermal field, so that the solidification interface at the seed crystal gradually moves upward, directional solidification, and finally generates large-sized single crystal silicon / Monocrystalline silicon.
  • the method of the invention comprises placing a spacer substance in the crucible, the spacer substance being at a high temperature
  • the silicon melt or / and silicon crystal
  • the silicon melt can be isolated from the bottom wall of the crucible in a liquid state, so that less crystal nuclei are formed.
  • a polycrystalline silicon ingot or single crystal silicon which can efficiently grow large crystalline particles.
  • the method of the present invention can improve the quality of the silicon crystal product without changing the structure of the existing directional solidification furnace and quartz crucible. The improvement in the application of the present invention to production is low in cost and effective.
  • the seed crystal can be fixed by placing or placing a seed crystal mold in the quartz crucible, and is suitable for controlling the crystal nucleation of the crucible bottom surface when the silicon single crystal ingot is grown by the directional solidification method, which effectively solves the seed crystal placement problem and makes The seed crystal eliminates dislocations during the seeding process, and also avoids the spontaneous nucleation of the melt originating from the bottom wall of the crucible.
  • the apparatus of the present invention can be appropriately modified to satisfy the distribution of the temperature field required for crystal growth.
  • the thermal insulation structure or the thermal insulation sandwich material may be added at a suitable place of the seed crystal mold to change the heat distribution lost from the bottom of the quartz crucible to achieve the purpose of changing the shape of the solidification interface. This change is very easy to implement, but it works well, and therefore, the apparatus of the present invention leaves a very large room for improvement in addition to the object of the present invention.
  • Figure 1 is a schematic view of a first embodiment of the present invention.
  • FIG. 2 is a schematic view of a second embodiment of the present invention.
  • Figure 3 is a statistical comparison of the crystal grain size of the ingot produced in Example 1 and Comparative Example 1.
  • Figure 4 is a cell photoelectric efficiency comparison box line manufactured by using the ingots produced in Example 1 and Comparative Example 1 (boxplot) ) Figure.
  • Figure 5 is a schematic view of a third embodiment of the present invention.
  • Figure 6 is a perspective view showing the structure of a device used in the third embodiment of the present invention.
  • Figure 7 is a schematic cross-sectional view of the apparatus of Figure 6.
  • Figure 8 is a schematic cross-sectional view showing another apparatus employed in the third embodiment of the present invention.
  • Seeding die 2 quartz crucible 3, silicon melt 4, silicon seed crystal 5, tungsten block 6, silicon crystal 7 , spacer material 8 , the seed crystal container 9, the spacer liquid container 10, the wall surface end of the seed crystal container 11 .
  • the quartz crucible 3 is a rectangular parallelepiped having a cavity size of 840 mm (length) ⁇ 840 mm (width) ⁇ 420 mm (height).
  • the temperature is raised above the melting point of the silicon by heating, and the spacer material (tin) and the silicon raw material are all melted by the control of the temperature field, at which time the spacer substance 8 (tin melt) will remain at the bottom of the crucible and the silicon melt 4 will remain in the spacer material 8 Above the (tin melt). Then, by changing the heating and heat preservation mode, the temperature gradient of the thermal field is moved, so that the nucleation of the silicon melt first occurs at the contact interface between the tin melt and the silicon melt, and the silicon crystal is formed. .
  • the (liquid) spacer substance 8 (tin melt) will always remain at the bottom of the crucible, which serves the purpose of isolating the bottom wall of the quartz crucible 3 from the silicon crystal (or / and silicon melt), effectively preventing the silicon from being in the quartz crucible 3
  • the bottom spontaneously forms a phenomenon of numerous nucleation cores, directional solidification, and growth to obtain polycrystalline silicon ingots having large-sized crystalline particles.
  • the polycrystalline silicon ingot was prepared by the procedure of Example 1, and the crystal growth was carried out by using 420 kg of silicon raw material and the inner cavity size was 840 mm. (length) ⁇ 840mm (width) ⁇ 420mm (height) in the quartz crucible. Unlike Example 1, no separator other than the silicon raw material was placed in the crucible.
  • Example 1 After removing the skin (the portion of the ingot that is not qualified for the life of the ingot), use Comparative Example 1 and Example 1 The resulting ingot is produced in a manner to carry out statistics on crystal particles.
  • Silicon crystal grown in a proportional 1 manner (ingot A
  • the grain size is much smaller than that of the silicon crystal (ingot B) obtained in Example 1.
  • the difference in grain size is also reflected in the efficiency of photoelectric conversion.
  • ingot B The average efficiency of the cell for the raw material is 0.56% higher than the average efficiency of the cell produced by the same process using Ingot A as the raw material.
  • the silicon crystal when the crystal grows, the silicon crystal can grow from the seed crystal, form a solidification interface convex to the liquid phase growth interface through the temperature field, and suppress the spontaneous nucleation of the tin melt to grow a single crystal silicon. / class of single crystal silicon.
  • Example 2 In the same manner as in Example 1, except that the spacer 8 used was 6N high purity germanium (Ge, purity was 99.9999%) and 5N high purity lead (Pb, purity 99.999%) in a mass ratio of 1:1 mixture.
  • the spacer 8 used was 6N high purity germanium (Ge, purity was 99.9999%) and 5N high purity lead (Pb, purity 99.999%) in a mass ratio of 1:1 mixture.
  • the seeding mold 2 is placed at the bottom of the quartz crucible 3, and an appropriate mass of 6N pure high purity tin (Sn, purity 99.9999%) is used as the spacer material 8 in the seeding mold 2
  • the spacer fluid is in the container 10.
  • the seed crystal mold 2 is processed from a graphite material and placed in the bottom of the quartz crucible 3, and its structure is as shown in Figs. 6 and 7, including a seed crystal container 9 and a spacer liquid container 10, and a square cylinder shape in the middle of the seed crystal container 9.
  • the spacer liquid container 10 is constituted by a cavity connected around the seed crystal container 9, which is surrounded by a graphite wall, and the shape of the outer wall of the spacer liquid container 10 is adapted to the shape of the inner wall of the quartz crucible 3, so that the outer wall of the spacer liquid container 10 is tight
  • the inner wall of the quartz crucible 3 is attached;
  • the bottom shape of the spacer liquid container 10 is adapted to the bottom shape of the quartz crucible 3, so that the (liquid) insulating substance 8 placed in the spacer liquid container 10 can melt the silicon melt and the bottom of the quartz crucible 3.
  • the walls are separated.
  • the upper portion of the spacer fluid container 10 is open to communicate with the inner cavity of the quartz crucible
  • the tin After the temperature of the quartz crucible 3 is heated to above the melting point of the tin, the tin is completely melted, and after cooling, the high-purity tin re-solidifies into a solid state and is filled with the seeding mold. 2 spacer container 10 . Then, the silicon seed crystal 5 is placed in the first cavity of the seed crystal container 9, at which time the silicon seed crystal 5 is located at the center of the bottom of the quartz crucible 3, and is directed toward the quartz crucible 3 Place the silicon material inside. The spacer material 8 (tin) in the seed crystal mold 2 and the seed crystal mold 2 is held at the bottom of the crucible.
  • the temperature is raised above the melting point of silicon by heating, and the tin and silicon raw materials are all melted by the control of the temperature field, and the silicon seed crystal 5 The upper part melts. Then, by changing the heating and holding methods, the temperature gradient of the thermal field is moved, so that the solidification interface at the silicon seed crystal 5 gradually moves upward. In this process, the density of tin melt is much larger than that of silicon melt 4 With the density of the silicon crystal 7, the (liquid) spacer material 8 (tin melt) will remain in the spacer container 10 of the seeding mold. As shown in Figure 5, the (liquid) barrier material 8 The (tin melt) serves to isolate the bottom wall of the quartz crucible 3 from the silicon crystal (or / and silicon melt), effectively preventing the spontaneous nucleation of silicon at the bottom of the quartz crucible 3.
  • the single crystal grown from the silicon seed crystal 5 is separated from the (liquid) material 8 Before the free surface of the (tin melt) is in contact, it is necessary to span the upper end 11 of the wall surface of the seed container 9, so that the wall end 11 of the seed container 9 There is a great possibility that a nucleation forming region of spontaneous nucleation is formed, and the original single crystal structure is destroyed. For this reason, the surface treatment for preventing spontaneous nucleation is reinforced at this point, that is, the wall end of the seed container 9 is reinforced 11 The finish.
  • Forming a crystal nucleus on the sidewall to destroy the silicon single crystal structure requires adjusting the thermal field to maintain a stable temperature field and a slowly rising solidification interface inside the quartz crucible 3, and keep the temperature at the center of the solidification interface lower than that of the quartz crucible 3 The temperature around the periphery causes the solidification interface to protrude toward the liquid phase, so that the finally formed silicon crystal 7 is a large-sized single crystal silicon/monocrystalline silicon.
  • the seed crystal container in the seeding die 2 of the present embodiment 9 has a section of diameter near the top end thereof which is contracted to form a length of 10 mm.
  • the necking section itself is of equal diameter, but since the necking section has a gradually decreasing diameter, when the seed crystal grows through the elongated passage of the necking section, the position growing from the seed crystal can be better eliminated. wrong.
  • a cavity is provided at the bottom of the seed crystal container 9, so that the temperature of the silicon seed crystal 5 and the quartz crucible 3 The temperature difference around the four is greater, so that the temperature of the silicon seed crystal 5 is just near the melting point while the silicon melt is kept overheated.
  • Further improvements include placing a radiant heat shield in the bottom cavity of the seed container 9 described above, or in the seed container 9 described above.
  • the insulating material is placed in the bottom cavity to change the heat distribution lost from the bottom of the quartz crucible 3, so as to change the shape of the solidification interface.
  • Example 4 In the same manner as in Example 4, except that the seeding mold 2 and the quartz crucible 3 It is made in one piece, and the material for manufacturing the seed crystal mold 2 is quartz.
  • the invention is suitable for industrial applications and mass production.

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Description

定向凝固法生长硅晶体时控制坩埚底面结晶成核的方法和装置 技术领域
本发明属于太阳能级硅制造领域，具体涉及一种采用定向凝固法生长硅晶体的方法和装置改进。
背景技术
硅单晶和硅多晶铸锭是晶体硅太阳能电池最常用的材料。通常，使用硅单晶材料制造的太阳能电池比使用硅多晶材料制造的太阳能电池具有更高的光电传换效率。当采用硅多晶制造太阳能电池时，硅多晶的结晶颗粒越大，则制造的太阳能电池效率越高。
通常采用提拉法（ Czochralski 法）和区熔法（ Floating Zone 法）制造硅单晶，采用定向凝固法（即铸造法、铸锭法）制造硅多晶。定向凝固法是将硅原料放置在多晶铸锭炉内的坩埚中，通过改变温度场使硅原料从下向上定向结晶。目前，采用定向凝固法生长而成的硅晶体通常为硅多晶，而不能得到硅单晶，其主要原因在于，定向凝固的初始过程并没有采用特定晶向的籽晶进行引导，凝固通常是从石英坩埚壁面开始，自发形成多个凝固核心并逐渐长大，使其最终形成的晶体为多晶而不是单晶。如果采用特定的引晶技术（例如在采用专利号为 ZL 200920115886.9 的中国实用新型专利中公开的坩埚中放置籽晶进行引晶生长铸锭），铸锭法也可以生长出硅单晶。但专利号为 ZL 200920115886.9 的中国实用新型专利中需要对石英坩埚做特殊的加工，增加了石英坩埚的制造成本。
另外，在硅多晶制造方面，虽然光伏行业倾向于使用具有大结晶颗粒的硅多晶作为原料来制造高效率的太阳能电池，但是生长出大结晶颗粒的硅多晶却存在各种困难。温度场及凝固界面的控制是使硅多晶铸锭形成大结晶颗粒的一个必要条件；此外，在晶体成核的初期，也需要控制成核的数量尽可能地少，使得结晶颗粒在初始阶段就可以长得比较大。
然而在采用定向凝固法生长硅铸锭（包括单晶铸锭和多晶铸锭）时，通常所采用的坩埚为石英坩埚，同时为了使硅铸锭在生长完成后与坩埚能方便脱离，还需要在石英坩埚内壁喷涂氧化硅涂层。这使得不光洁的石英坩埚表面形成众多的促进硅熔液自发成核的条件，当温度合适时，形成众多数量的成核核心，导致硅多晶铸锭在生长的初始阶段形成的晶粒尺寸小而数量多，不利于最终形成具有大结晶颗粒的硅多晶材料。
 技术问题
本发明提供了一种 定向凝固法生长硅晶体时控制坩埚底面结晶成核的方法， 无需改变现有的定向凝固炉和石英坩埚的结构，即可有效地生长大结晶颗粒的多晶硅铸锭或单晶硅。
此外，本发明还提供了一种用于定向凝固法生长硅晶体时控制坩埚底面结晶成核的装置，适用于定向凝固法生长硅单晶铸锭。
 技术解决方案
一种 定向凝固法生长硅晶体时控制坩埚底面结晶成核的方法，在硅原料熔化形成硅熔液之时或之前，将隔离物质放置在坩埚内，在硅熔点以上的温度下，隔离物质熔化后以液态的形式沉淀在坩埚底部，实现硅熔液与坩埚底部相互隔离，以控制坩埚底面结晶成核的数量和质量； 所述的隔离物质为熔点低于硅、密度大于硅、且在 1000~2000°C 下与硅不反应且不互溶的物质。
优选的技术方案中，所述的隔离物质采用锗（ Ge ）、锡（ Sn ）、铅（ Pb ）等 IV 簇元素中的一种或多种，也可以采用如 CaF2 、 CaCl2 、 BaF2 、 BaCl2 等与硅不反应的氯化物或氟化物，还可以采用钡（ Ba ）。即：所述的隔离物质可以为锗、锡、铅、 CaF2 、 CaCl2 、 BaF2 、 BaCl2 、 Ba 中的一种或多种。由于化合物中的 F 元素或 Cl 元素对坩埚材料或引晶模具有一定的腐蚀性，因此最优选采用锗（ Ge ）、锡（ Sn ）、铅（ Pb ）、钡（ Ba ）中的一种或多种。采用优选的隔离物质，由于熔点比硅低且密度高于硅；可以保证硅晶体生长时隔离物质为液态，始终处于坩埚的底部；并且不与硅反应，也不影响硅材料作为太阳能光伏材料使用时的品质。
本发明中，可以 在坩埚内预先放置隔离物质，也可以在硅原料熔化形成硅熔液时向坩埚内加入隔离物质。 由于所述的隔离物质熔点低于硅、密度大于硅， 当加入有隔离物质和硅原料的坩埚在高温下加热时，隔离物质将首先融化，沉淀到坩埚的底部。当温度进一步升高后，硅原料也将化为硅熔液，并浮在液态隔离物质的上面，使坩埚底部与硅熔液完全隔离。然后，通过温度场的控制，硅熔液将在隔离物质与硅熔液相接触的界面结晶成核。由于隔离物质与硅熔液（或 / 和硅晶体）相接触的界面光滑，不存在通常石英坩埚壁面所固有的缺陷，例如表面凸点和表面凹陷等诱发形成新的晶核的缺陷，使得形成的结晶成核核心较少，有利于大尺寸结晶颗粒的形成。最终通过温度场控制实现凝固界面向上移动，生长成质量较高的硅铸锭。隔离物质的另一个明显的好处在于，可以减少坩埚底部墙面对硅原料的污染。
所述的温度场控制，是通过改变加热和保温方式使热场的温度梯度移动来实现，从而使得结晶成核处的凝固界面逐渐向上移动，定向凝固，最终生成 大 尺寸 结晶颗粒的多晶硅铸锭 。
上述的方法中，所述的坩埚通常采用表面喷涂有氮化硅的石英坩埚。即，采用现有技术中通用的石英坩埚，就可实现 有效地生长大结晶颗粒的多晶硅铸锭。 可见，上述方法用于生长多晶硅铸锭时， 无需改变现有的定向凝固炉和石英坩埚的结构。
上述的方法也可用于硅单晶铸锭生长，这种情况下就需要在硅原料熔化形成硅熔液之前，将硅单晶籽晶固定在所述坩埚底部。即：在坩埚底部固定硅单晶籽晶，再通过籽晶引晶来诱发生长固定晶向的单晶。由于硅的密度小于隔离物质的密度，当隔离物质熔化后，硅单晶籽晶可能浮离坩埚底部，所以必须将硅单晶籽晶固定在坩埚底部。可采用模具来固定籽晶，也可以采用将密度远高于隔离物质的材料（例如钨）与籽晶捆绑等各种方法。当采用后者时，也 无需改变现有的定向凝固炉和石英坩埚的结构，即可 实现定向凝固法生长硅单晶铸锭 。
以下将提供一种用于定向凝固法生长硅晶体时控制坩埚底面结晶成核的装置，适合用在上文所述的模具固定籽晶的方法中。
一种用于定向凝固法生长硅晶体时控制坩埚底面结晶成核的装置，包括石英坩埚，其中，在所述石英坩埚内的底部放置或设置有引晶模具，所述的引晶模具包括籽晶容器和隔离液容器，所述的籽晶容器设有用于放置籽晶的第一空腔，所述的隔离液容器由连接在所述的籽晶容器周围的空腔构成，用于放置隔离物质； 所述的隔离液容器的外壁的形状与所述的 石英 坩埚的内壁的形状相适应，使得所述的引晶模具的外壁与所述的 石英 坩埚的内壁紧贴；所述的隔离液容器的底部形状与所述的 石英 坩埚的底部形状相适应，使得所述的引晶模具的底部覆盖所述的 石英 坩埚的底部， 从而使得放置在所述的隔离液容器内的隔离物质能 在晶体生长时以液态的方式 将硅晶体（或 / 和硅熔液）与所述的石英坩埚内的底部壁面隔开 ；所述的隔离液容器的上部敞开，与所述的 石英 坩埚的内部空腔 以尽可能大的面积 相联通。
优选的技术方案中，所述的隔离液容器 用于 存放液态 隔离物质 的有效高度为 5~100mm ，既 能尽量少地占用石英坩埚盛放硅原料的容量，又能起到有效隔离的作用。
优选的技术方案中，为了更好地引晶，更好地控制温度梯度，在所述的隔离液容器的底部壁面设有空腔，使得籽晶所在位置的温度与所述的 石英 坩埚四周的温差更大，使硅熔液在保持过热的状态下，籽晶处的温度正好在熔点附近。
优选的技术方案中，所述的籽晶容器的第一空腔的中心轴线与所述的引晶模具的中心轴线相同，当所述的引晶模具放置在所述的 石英坩埚内的底部，并且将所述的 籽晶放置在所述的第一空腔内时，所述的籽晶位于所述的 石英坩埚的底部的中心，这样有利于借助籽晶诱发形成硅单晶，并保证硅单晶品质的均匀性和一致性，更利于高品质硅单晶的生长。
本发明中，所述的第一空腔的形状与籽晶的形状相适应，因此所述的第一空腔的形状主要是针对现有籽晶的形状而设计的。对于大型籽晶而言，规则的方形或圆形籽晶更容易获得。所以，所述的第一空腔的横截面优选为圆形或正方形。如果采用大型籽晶（截面积大于 2500mm 2 ），则圆籽晶可为采用提拉法（ Czochralski 法）生长的一段截断单晶，方籽晶可为采用定向凝固法生长的单晶经过开方（切方）后得到的一段截断单晶。
优选的技术方案中，所述的第一空腔为筒状，优选为等截面的细长筒状，即所述的第一空腔的横截面处处相同，考虑到加工的方便一般选用圆筒或方筒状。
本发明中，所述的第一空腔的截面面积决定了放置在其中的籽晶的截面积的大小。所述的第一空腔直径没有严格限制，但是太大的籽晶增加了采购籽晶的成本，而太小的籽晶会导致籽晶的加工困难。因此，所述的第一空腔的截面面积可在 0.25 ～ 40000mm2 范围内选择，既容易加工获得，又能适当控制成本。
本发明中， 由于所述的引晶模具是放置或设置在石英坩埚内部的，它的体积占用了原有石英坩埚的有效容量。为了尽量少地占用石英坩埚盛放硅原料的容量，所述的引晶模具的整体高度要尽量低。然而，太低的籽晶高度（对应于第一空腔的高度），不利于控制晶体生长中的温度，难以实现籽晶的部分熔化和在晶体生长时消除位错。 所述的第一空腔的高度优选为 5~100mm ，既不会占用太多石英坩埚的容积，又便于籽晶引晶的温度场控制。同时，为了避免液态隔离物质覆盖籽晶，优选所述的第一空腔的高度大于所述的隔离液容器 用于 存放液态 隔离物质 的有效高度。
优选的技术方案中，为了提高所述的引晶模具的引晶质量，所述的第一空腔在靠近其顶端的部分至少一段直径收缩形成缩口段。就缩口段本身而言可以是等径的也可以是锥形的。由于所述的缩口段具有逐渐缩小的直径，籽晶生长时通过缩口段的细长通道时，可以更好地消除从籽晶增长出的位错。
本发明中，制备所述的引晶模具的主要原料可选用常用的石墨或炭炭复合材料（ CFC ）。 当采用石墨材料制造时，所述的引晶模具可采用整块石墨通过机加工的方法做出籽晶容器的第一空腔。所述的引晶模具也可以采用氮化硼、石英、炭炭复合材料（ CFC ）等其他材料加工而成。当引晶模具采用石英为材料进行加工时，可将引晶模具制成石英坩埚的一部分，即 带 有引晶模具结构的石英坩埚。
优选的技术方案中，为了便于硅晶体制备完成后的脱模，所述的引晶模具表面用喷涂法覆盖有一层氮化硅（ Si3N4 ）或氮化硼（ BN ）涂层，所述的涂层的厚度为 0.001~5mm 。
本发明中，只需要在现有技术的石英坩埚底部设置或放置引晶模具，即可实现 定向凝固法生长硅单晶铸锭。在 石英坩埚底部放置引晶模具时，石英坩埚无需进行改进；在石英坩埚底部设置引晶模具时，只需要在加工石英坩埚时，进行简单的模板改进即可，此时，该石英坩埚为带有引晶模具的石英坩埚。
采用上述装置 进行定向凝固法生长硅晶体时控制坩埚底面结晶成核的方法，具体步骤如下： 将所述的 隔离物质放置在所述的隔离液容器中，所述的隔离物质完全熔融后充满所述的隔离液容器；在所述的籽晶容器的 第一空腔 中放置籽晶，并向所述的石英坩埚内放置硅原料，加热使所述的隔离物质和硅原料全部熔化、所述的籽晶部分熔化，再通过温度场控制，使硅熔液定向凝固生成单晶 硅 / 类单晶 硅。
在单晶硅生长过程中，需要通过籽晶引晶来诱发生长固定晶向的单晶，同时还需避免在石英坩埚壁面形成的自发成核核心破坏晶体的单晶结构。当采用液态隔离物质将硅晶体（或 / 和硅熔液）与石英坩埚壁面隔离之后，由于液态隔离物质与硅晶体（或 / 和硅熔液）接触的界面不存在通常石英坩埚壁面所固有的缺陷，例如表面凸点和表面凹陷等诱发形成新的晶核的缺陷，从而避免硅晶体生长时可能导致的坩埚壁面的自发成核现象，可有效地防止固定晶向的单晶体被破坏。
上述的对石英坩埚壁面的隔离只针对石英坩埚的底部壁面，而对石英坩埚的侧壁面则无需进行隔离，只要合理地设计温度场，使晶体生长过程形成一个微凸的凝固界面，即可使壁面形成的自发成核的晶核无法向晶体内部扩散，避免破坏单晶结构。
在定向凝固法生长单晶硅中，由于硅晶体生长时隔离物质为液态，如果没有容器容纳液态隔离物质，液体很可能在籽晶引晶的过程中覆盖整个籽晶，造成籽晶无法与硅原料相接触，导致引晶失败。而采用上述装置进行定向凝固法生长单晶硅，由于将隔离物质放置在引晶模具的隔离液容器中，并且设置籽晶容器中第一空腔的高度大于所述的隔离液容器 用于 存放液态 隔离物质 的有效高度，可有效避免引晶失败。
此外，当放置在籽晶容器内的籽晶完成引晶后，随着凝固界面的不断扩大，硅晶体（或 / 和硅熔液）将与液态隔离物质的表面相接触，这时隔离物质的自由表面将起到石英坩埚壁面的作用，并有效避免壁面的自发成核。
需要进一步说明的是，从籽晶处生长出的单晶，在与液态隔离物质的自由表面相接触之前，需要跨越籽晶容器壁面的上端，因此籽晶容器的壁面上端存在着很大可能形成自发成核的晶核形成区域，破坏原来的单晶结构。为此，需要在该处加强防止自发成核的表面处理，例如需要加强籽晶孔的壁面上端区域的光洁度等。
其中，所述的温度场控制，是通过改变加热和保温方式使热场的温度梯度移动来实现，从而使得籽晶处的凝固界面逐渐向上移动，定向凝固，最终生成大尺寸的 单晶硅 / 类单晶硅 。
 有益效果
本发明方法通过在坩埚内放置隔离物质， 所述的隔离物质在 高温下 晶体生长时能够以液态的方式将硅熔液（或 / 和硅晶体）与坩埚底部壁面隔离，使得形成的结晶核少， 可有效地生长大结晶颗粒的多晶硅铸锭或者单晶硅。本发明方法可以在不改变现有定向凝固炉和石英坩埚的结构的情况下提高硅晶体产品的质量。将本发明应用到生产中的改进成本低，效果明显。
本发明装置 采用在石英坩埚内设置或放置引晶模具，可以实现对籽晶的固定，适用于定向凝固法生长硅单晶铸锭时控制坩埚底面结晶成核，既有效解决了籽晶放置问题，并使籽晶在引晶过程中消除位错，同时还避免了源自坩埚底部壁面的熔液自发成核现象。
而且，在满足上述的进行引晶和用液态隔离物质隔离石英坩埚壁面与硅晶体的作用外，还可以通过对本发明装置进行适当的改良，以满足晶体生长所需的温度场的分布。例如，可以在引晶模具的适当地方增加保温结构或保温夹心材料，从而改变从石英坩埚底部散失的热量分布，达到改变凝固界面形状的目的。这一改变非常容易实现，但又能起到很好的效果，因此，本发明装置在实现本发明目的之外，还留有非常大的改进空间。
 附图说明
图 1 是本发明的第一种实施方式的示意图。
图 2 是本发明的第二种实施方式的示意图。
图 3 是实施例 1 和对比例 1 生产的铸锭结晶颗粒尺寸的统计对照图。
图 4 是采用实施例 1 和对比例 1 生产的铸锭制造的电池片光电效率对照箱线（ boxplot ）图。
图 5 是本发明的第三种实施方式的示意图。
图 6 是本发明的第三种实施方式中所采用的一种装置的立体结构示意图。
图 7 是图 6 的装置的剖面结构示意图。
图 8 是本发明的第三种实施方式中采用的另一种装置的剖面结构示意图。
图中：
引晶模具 2 、石英坩埚 3 、硅熔液 4 、硅籽晶 5 、钨块 6 、硅晶体 7 、隔离物质 8 、籽晶容器 9 、隔离液容器 10 、籽晶容器的壁面上端 11 。
 本发明的最佳实施方式
本发明的实施方式
下面结合实施例和附图来详细说明本发明，但本发明并不仅限于此。
实施例 1 ：
如图 1 所示，在晶体生长之前，将 420 公斤 硅原料与作为隔离物质的 20 公斤 锡（ Sn ，纯度 99.999% ）放置在石英坩埚 3 内。石英坩埚 3 为长方体，内腔尺寸为 840mm （长）× 840mm （宽）× 420mm （高）。
通过加热升温到硅的熔点之上，并通过温度场的控制使隔离物质（锡）和硅原料全部熔化，这时隔离物质 8 （锡熔液）将保持在坩埚底部，硅熔液 4 保持在隔离物质 8 （锡熔液）的上面。然后通过改变加热和保温方式，使热场的温度梯度移动，从而使得硅熔液的成核首先在锡熔液与硅熔液的接触界面处发生，并形成硅晶体 7 。在这一过程中，由于隔离物质 8 （锡熔液）的密度远大于硅熔液 4 和硅晶体 7 的密度，（液态的）隔离物质 8 （锡熔液）将始终保持在坩埚底部，起到了隔离石英坩埚 3 底部壁面与硅晶体（或 / 和硅熔液）的目的，有效地防止了硅在石英坩埚 3 底部的自发形成众多成核核心的现象，定向凝固，生长得到 具有大尺寸结晶颗粒的多晶硅铸锭 。
对比例 1
采用实施例 1 的流程制备多晶硅铸锭，晶体生长采用 420 公斤 硅原料放置在内腔尺寸为 840mm （长）× 840mm （宽）× 420mm （高）的石英坩埚中。与实施例 1 不同的是，坩埚内没有放置任何除硅原料之外的隔离物质。
去边皮（铸锭四周少子寿命不合格部分）后，对采用对比例 1 和实施例 1 方式生产所得的铸锭进行结晶颗粒的统计。结晶颗粒尺寸用平均颗粒面积的方式（平均颗粒面积 = 截面面积 / 截面上颗粒数量）表示，在晶体生长方向相垂直在铸锭上任意取 3 个截面后，统计结果如图 3 所示。采用对比例 1 方式生长的硅晶体（铸锭 A ）的晶粒尺寸比实施例 1 中得到的硅晶体（铸锭 B ）的晶粒尺寸要小很多。晶粒尺寸的不同也同时体现在光电转换的效率上。如图 4 所示，以铸锭 B 为原料的电池片效率平均值要比以铸锭 A 为原料以同样工艺生产的电池片效率平均值高 0.56% 。
实施例 2 ：
如图 2 所示，采用 与 实施例 1 相同的方式，不同之处在于为了生长硅单晶，在石英坩埚 3 底部固定有硅籽晶 5 ，加入坩埚内的锡（ Sn ，纯度 99.999% ）的质量为 60 公斤 。硅籽晶 5 通过钨块 6 压放在石英坩埚 3 底部，以防止因浮力而上浮。当温度升高后，隔离物质 8 （锡熔液）将保持在石英坩埚 3 底部，起到隔离石英坩埚 3 底部壁面与硅晶体（或 / 和硅熔液）的目的。这样，当晶体生长时，硅晶体就能够从籽晶处开始生长，通过温度场形成凝固界面凸向液相生长界面，以及锡熔液对自发成核的抑制作用，生长出一个 单晶硅 / 类单晶硅 。
实施例 3 ：
采用 与 实施例 1 相同的方式，不同之处在于所用的隔离物质 8 为 6N 高纯锗 (Ge ，纯度为 99.9999%) 和 5N 高纯铅 (Pb ，纯度为 99.999%) 以质量比为 1:1 的混合物。
实施例 4 ：
如图 5 所示，在晶体生长之前，将引晶模具 2 放置在石英坩埚 3 的底部，并将适当质量的 6N 纯度的高纯锡（ Sn ，纯度 99.9999% ）作为隔离物质 8 放置在引晶模具 2 的隔离液容器 10 中。引晶模具 2 由石墨材料加工而成并放置在石英坩埚 3 内的底部，其结构如图 6 和 7 所示，包括籽晶容器 9 和隔离液容器 10 ，籽晶容器 9 中间有方筒形的第一空腔，用于放置硅籽晶 5 ，第一空腔截面积为 10000mm 2 ，高度为 30mm , 截面形状为正方形，第一空腔的中心轴线与引晶模具 2 的中心轴线相同；隔离液容器 10 由连接在籽晶容器 9 周围的空腔构成，该空腔由石墨壁围成，隔离液容器 10 外壁的形状与石英坩埚 3 内壁的形状相适应，使得隔离液容器 10 外壁紧贴石英坩埚 3 内壁；隔离液容器 10 的底部形状与石英坩埚 3 的底部形状相适应，使得放置在隔离液容器 10 内的（液态的）隔离物质 8 能将硅熔液与石英坩埚 3 的底部壁面隔开。隔离液容器 10 的上部敞开，与石英坩埚 3 的内部空腔以尽可能大的面积相联通。隔离液容器 10 可存放液体的最大高度为 18mm 。
将石英坩埚 3 温度加热到锡的熔点以上后，锡完全熔化，冷却之后高纯锡重新凝固为固态，并充满了引晶模具 2 的隔离液容器 10 。然后，向籽晶容器 9 的第一空腔中放置硅籽晶 5 ，此时，硅籽晶 5 位于石英坩埚 3 的底部的中心， 并向石英坩埚 3 内放置硅原料。引晶模具 2 和引晶模具 2 内的隔离物质 8 （锡）保持在坩埚的底部。
通过加热升温到硅的熔点之上，并通过温度场的控制使锡和硅原料全部熔化，而硅籽晶 5 的上半部分熔化。然后通过改变加热和保温方式，使热场的温度梯度移动，从而使得硅籽晶 5 处的凝固界面逐渐向上移动。在这一过程中，由于锡熔液的密度远大于硅熔液 4 和硅晶体 7 的密度，（液态的）隔离物质 8 （锡熔液）将始终保持在引晶模具的隔离液容器 10 内。如图 5 所示，（液态的）隔离物质 8 （锡熔液）起到了隔离石英坩埚 3 底部壁面与硅晶体（或 / 和硅熔液）的目的，有效地防止了硅在石英坩埚 3 底部的自发成核现象。
需要进一步说明的是，从硅籽晶 5 处生长出的单晶，在与（液态的）隔离物质 8 （锡熔液）的自由表面相接触之前，需要跨越籽晶容器 9 壁面的上端 11 ，因此籽晶容器 9 的壁面上端 11 存在着很大可能形成自发成核的晶核形成区域，破坏原来的单晶结构。为此，在该处加强了防止自发成核的表面处理，即加强了籽晶容器 9 的壁面上端 11 的光洁度。
另外，为了能够保证硅晶体不在石英坩埚 3 侧壁上形成结晶核而破坏硅单晶结构，需要通过调节热场，使石英坩埚 3 内部保持一个稳定温度场和缓慢上升的凝固界面，并且保持凝固界面中央的温度低于石英坩埚 3 周边的温度，使得凝固界面凸向液相，这样最终形成的硅晶体 7 为一个大尺寸的 单晶硅 / 类单晶硅 。
实施例 5 ：
采用 与 实施例 4 相同的方式，不同之处仅在于采用的装置不同，即装置中采用了另一种引晶模具，其结构如图 8 所示。
为了引晶，更好地控制温度梯度，本实施例的引晶模具 2 中籽晶容器 9 的第一空腔在靠近其顶端的部分有一段直径收缩形成 长 10mm 的 缩口段，缩口段本身是等径的，但由于缩口段具有逐渐缩小的直径，籽晶生长时通过缩口段的细长通道时，可以更好地消除从籽晶增长出的位错。
另外，在籽晶容器 9 的底部均设有空腔，使得硅籽晶 5 所在位置的温度与石英坩埚 3 四周的温差更大，使硅熔液在保持过热的状态下，硅籽晶 5 处的温度正好在熔点附近。
进一步的改良还包括在上述的籽晶容器 9 的底部空腔内放置挡辐射热屏，或在上述的籽晶容器 9 的底部空腔内放置保温材料，从而改变从石英坩埚 3 底部散失的热量分布，达到改变凝固界面形状的目的。
实施例 6 ：
采用 与 实施例 4 相同的方式，不同之处在于所用的隔离物质 8 为 6N 高纯锗 (Ge ，纯度为 99.9999%) 和 5N 高纯铅 (Pb ，纯度为 99.999%) 以质量比为 1:1 的混合物。
实施例 7 ：
采用 与 实施例 4 相同的方式，不同之处在于引晶模具 2 与石英坩埚 3 制成一个整体，并且用于制造引晶模具 2 的材料为石英。
 工业实用性
本发明适于工业化应用和大规模生产。

Claims (10)

  1. 一种 定向凝固法生长硅晶体时控制坩埚底面结晶成核的方法，其特征在于：在硅原料熔化形成硅熔液之时或之前，将隔离物质放置在坩埚内，在硅熔点以上的温度下，隔离物质熔化后以液态的形式沉淀在坩埚底部，实现硅熔液与坩埚底部相互隔离，以控制坩埚底面的结晶成核； 所述的隔离物质为熔点低于硅、密度大于硅、且在 1000~2000°C 下与硅不反应且不互溶的物质。
  2. 如权利要求 1 所述的定向凝固法生长硅晶体时控制坩埚底面结晶成核的方法，其特征在于：在硅原料熔化形成硅熔液之前，将硅单晶籽晶固定在所述坩埚底部。
  3. 如权利要求 1 或 2 任一所述的定向凝固法生长硅晶体时控制坩埚底面结晶成核的方法，其特征在于：所述的隔离物质为锗、锡、铅、钡中的一种或多种。
  4. 如权利要求 1 或 2 任一所述的定向凝固法生长硅晶体时控制坩埚底面结晶成核的方法，其特征在于：所述的隔离物质为 CaF2 、 CaCl2 、 BaF2 、 BaCl2 中的一种或多种。
  5. 如权利要求 1 或 2 任一所述的定向凝固法生长硅晶体时控制坩埚底面结晶成核的方法，其特征在于：所述的坩埚为表面喷涂有氮化硅的石英坩埚。
  6. 一种用于定向凝固法生长硅晶体时控制坩埚底面结晶成核的装置，包括石英坩埚，其特征在于：在所述石英坩埚内的底部放置或设置有引晶模具，所述的引晶模具包括籽晶容器和隔离液容器，所述的籽晶容器设有用于放置籽晶的第一空腔，所述的隔离液容器由连接在所述的籽晶容器周围的空腔构成，用于放置隔离物质； 所述的隔离液容器的外壁的形状与所述的 石英 坩埚的内壁的形状相适应，使得所述的引晶模具的外壁与所述的 石英 坩埚的内壁紧贴；所述的隔离液容器的底部形状与所述的 石英 坩埚的底部形状相适应，使得所述的引晶模具的底部覆盖所述的 石英 坩埚的底部；所述的隔离液容器的上部敞开，与所述的 石英 坩埚的内部空腔相联通。
  7. 如权利要求 6 所述的 用于定向凝固法生长硅晶体时控制坩埚底面结晶成核的装置， 其特征在于：所述的隔离液容器 用于 存放液态 隔离物质 的有效高度为 5~100mm 。
  8. 如权利要求 6 所述的用于 定向凝固法生长硅晶体时控制坩埚底面结晶成核的装置 ，其特征在于：所述的籽晶容器的第一空腔的中心轴线与所述的引晶模具的中心轴线相同。
  9. 如权利要求 6 所述的用于 定向凝固法生长硅晶体时控制坩埚底面结晶成核的装置 ，其特征在于：所述的第一空腔的横截面为圆形或正方形。
  10. 如权利要求 6 所述的用于 定向凝固法生长硅晶体时控制坩埚底面结晶成核的装置 ，其特征在于：所述的第一空腔在靠近其顶端的部分至少一段直径收缩形成缩口段。
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CN201506711U (zh) * 2009-09-30 2010-06-16 常州天合光能有限公司 铸锭用坩埚
CN102146580A (zh) * 2011-03-21 2011-08-10 浙江碧晶科技有限公司 用于定向凝固法生长硅晶体的引晶模具及晶体生长方法
CN102191536A (zh) * 2011-06-16 2011-09-21 浙江碧晶科技有限公司 定向凝固法生长硅晶体时控制坩埚底面结晶成核的方法

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* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
CN201506711U (zh) * 2009-09-30 2010-06-16 常州天合光能有限公司 铸锭用坩埚
CN102146580A (zh) * 2011-03-21 2011-08-10 浙江碧晶科技有限公司 用于定向凝固法生长硅晶体的引晶模具及晶体生长方法
CN102191536A (zh) * 2011-06-16 2011-09-21 浙江碧晶科技有限公司 定向凝固法生长硅晶体时控制坩埚底面结晶成核的方法

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