Method for producing multicrystalline silicon ingot with oxygen evacuation channel inside the crucible

Abstract

This invention relates to a method for preparing polycrystalline silicon ingots by forming oxygen venting channels inside a crucible using single-crystal or polycrystalline rods, comprising the following steps: preparing silicon square pillars; arranging the single-crystal or polycrystalline square pillars adjacent to the inner circumferential surface of the crucible according to the crucible shape, thereby forming a space within the space surrounded by the single-crystal or polycrystalline square pillars that can accommodate large blocks, and inserting the silicon square pillars into the crucible by forming oxygen venting holes between one side of the single-crystal or polycrystalline square pillar and the inner surface of the crucible; inserting silicon blocks into the crucible within the large space that can accommodate the single-crystal or polycrystalline square pillars; and performing bulk melting and crystallization. Therefore, it has the advantages of minimizing partial breakage of the ingot or minimizing the formation of various sizes and shapes of bubble venting channels on the surface of the ingot facing the interior of the ingot.

Description

Technical Field

[0001] This invention relates to a method for preparing polycrystalline silicon ingots by forming oxygen-removing channels inside a crucible using single-crystal rods or polycrystalline rods. Background Technology

[0002] Polycrystalline silicon ingots are typically used as substrates for solar cells.

[0003] That is, polycrystalline silicon wafers are prepared by slicing polycrystalline silicon ingots to a specified thickness, and then substrates for solar cells are prepared by processing the polycrystalline silicon wafers.

[0004] The ingot preparation process is one of the most important and critical processes in the production of semiconductor devices such as solar cell substrates.

[0005] In particular, when the molten silicon is stored in a silicon crucible, oxygen will mix into the molten silicon from the silicon dioxide that makes up the crucible, and the oxygen in the molten silicon will be released from the liquid surface in the form of silicon monoxide (SiO) gas.

[0006] As solidification begins, oxygen will mix in from the bottom and sides of the crucible, thus increasing the amount of oxygen in the molten silicon at the start of solidification, particularly at the bottom where solidification begins.

[0007] If solidification occurs on the bottom side of the crucible, causing the solid-liquid interface to rise, oxygen can only enter from the side, thus gradually reducing the amount of oxygen mixed into the molten silicon.

[0008] As mentioned above, during the polycrystalline silicon crystallization process, impurities such as oxygen generated in the molten silicon or flowing in from the crucible are released to the outer surface, which can cause partial breakage of the ingot or the formation of bubble discharge grooves of various sizes and shapes on the surface of the ingot toward the interior of the ingot.

[0009] As a result, the usable area of ​​the ingot is reduced, leading to a decrease in wafer production yield and an adverse impact on ingot production efficiency.

[0010] As described above, in order to minimize the following situations during the production process of polycrystalline silicon ingots, namely, the ingot is partially damaged due to the release of impurities such as oxygen generated in the molten silicon or flowing in from the crucible to the outer surface, or the formation of bubble discharge grooves of various sizes and shapes on the surface of the ingot towards the interior of the ingot, a method for preparing the ingot by forming a silicon nitride (Si3N4) coating layer and a silicon monoxide (SiO) multilayer coating layer inside a silicon dioxide crucible is disclosed in Korean Patent Publication No. 10-2012-0135284, etc.

[0011] The following is a brief description of the polycrystalline silicon ingot preparation method disclosed in Korean Patent Publication No. 10-2012-0135284.

[0012] First, the polycrystalline silicon ingot apparatus for preparing polycrystalline silicon ingots disclosed in Korean Patent Publication No. 10-2012-0135284 is as follows.

[0013] Figure 1 The polycrystalline silicon ingot preparation apparatus 10 shown includes: a crucible 20 for storing molten silicon L; a base 12 for mounting the crucible 20; an under-bed heater 13 for supporting the base 12 from below; and a ceiling heater 14 disposed above the crucible 20.

[0014] Furthermore, an insulating material 15 is formed around the crucible 20.

[0015] The aforementioned chassis 12 forms a hollow structure and a structure through which argon (Ar) gas is supplied to the interior via a supply pipe 16.

[0016] The crucible 20 described above can be formed into a square (quadrilateral) or annular (circular) horizontal cross-sectional shape.

[0017] like Figure 2 and Figure 3 As shown, the crucible 20 includes: a crucible body 21 made of silicon dioxide; a silicon nitride coating layer 22 formed on the inner side wall of the crucible body 21; and a silicon dioxide multilayer coating layer 27 formed on the bottom surface 20a of the crucible body 21.

[0018] The silicon nitride coating layer 22 has the following structure: 50 μm to 300 μm micro-molten silica sand 26 is dispersed in a mixture of silicon nitride powder 24 of 0.2 μm to 4.0 μm and sodium-containing silica 25 containing 10 ppm to 6000 ppm sodium.

[0019] Furthermore, a mixture of silicon nitride powder 24 and sodium-containing silicon dioxide 25 is disposed (exposed) on the outermost surface of the silicon nitride coating layer 22.

[0020] The silica multilayer coating 27 is composed of a slurry layer 28 and a plaster layer 29 stacked together to form a multilayer structure.

[0021] The aforementioned silica multilayer coating 27 is stacked with a total of three or more but less than four slurry layers 28 and plaster layers 29.

[0022] The slurry layer 28 is formed by coating an aqueous dispersion of filler with a particle size of 10μm or larger and 50μm or smaller and colloidal silica.

[0023] Furthermore, the plaster layer 29 is formed by dispersing (coating) silica particles with a particle size of 0.3 mm or more and 3 mm or less.

[0024] By observing the preparation process of polycrystalline silicon ingot using the silicon ingot preparation apparatus 10, a silicon nitride coating layer 22 is first formed on the inner surface of the side wall, and silicon raw materials are loaded into the crucible 20, which has a silicon dioxide multilayer coating layer 27 formed on the bottom surface.

[0025] Among them, as a silicon raw material, a block-shaped substance called "chunk" is obtained by crushing high-purity silicon of 11N (purity 99.9999999999).

[0026] For example, the particle size of the silicon raw material in this block is 30 mm to 100 mm.

[0027] The silicon raw material is heated by energizing the ceiling heater 14 and the under-bed heater 13.

[0028] Thus, molten silicon L is stored in crucible 20.

[0029] Next, the power supply to the under-bed heater 13 is stopped, and argon gas is supplied to the interior of the chassis 12 through the supply pipe 16.

[0030] This allows the bottom surface of the crucible 20 to be cooled.

[0031] Furthermore, by gradually reducing the power supply to the ceiling heater 14, the molten silicon L in the crucible 20 is cooled from the bottom of the crucible 20 and solidifies unidirectionally from the bottom upwards.

[0032] In this case, the solidification rate of the silicon molten liquid L in the crucible 20, that is, the speed at which it moves upward to the solid-liquid interface, is adjusted by controlling the amount of argon gas supplied to the chassis 12 and the amount of electricity supplied to the ceiling heater 14.

[0033] Moreover, such as Figure 2 As shown, the solidification process of the silicon molten liquid L in the crucible 20 is divided into three regions, and a solidification rate is set in each region.

[0034] Specifically, taking the bottom surface 20a of the crucible 20 as a reference, the solidification process inside the crucible 20 is divided into a first region A1 from 0 mm to height X, a second region A2 from height X to height Y, and a third region A3 above height Y. Height X is set to the range of 10 mm ≤ X < 30 mm, and height Y is set to the range of 30 mm ≤ Y < 100 mm.

[0035] Furthermore, the height Y-X of the second region A2 is set within the range of 10mm≤Y-X≤40mm.

[0036] For example, if X=20mm and Y=40mm are set, the height Y-X of the second area A2 can be set to 20mm.

[0037] For each region, the solidification rate is set as follows.

[0038] The solidification rate V1 in the first region A1 is set in the range of 10 mm / h ≤ V1 ≤ 20 mm / h.

[0039] The solidification rate V2 in the second region A2 is set in the range of 1 mm / h ≤ V2 ≤ 5 mm / h.

[0040] The solidification rate V3 in the third region A3 is set within the range of 5 mm / h ≤ V3 ≤ 30 mm / h.

[0041] However, even if polycrystalline silicon ingots are prepared using the polycrystalline silicon ingot preparation apparatus and preparation method described above, the following problems will occur during the polycrystalline silicon crystallization process: impurities such as oxygen flowing in from the crucible or generated from inside the silicon solution will be released to the outer surface, which will cause partial breakage of the ingot, or bubble discharge grooves of various sizes and shapes will be formed on the surface of the ingot towards the inside of the ingot. Summary of the Invention

[0042] The present invention addresses the problems of the prior art as described above, and aims to provide a method for preparing polycrystalline silicon ingots by forming oxygen-removing channels inside a crucible using a single crystal rod or a polycrystalline rod, so as to minimize the following situations during the polycrystalline silicon crystallization process: partial breakage of the ingot due to the release of impurities such as oxygen flowing from the crucible or generated inside the silicon solution to the outer surface; or the formation of bubble discharge channels of various sizes and shapes on the surface of the ingot facing the interior of the ingot.

[0043] To achieve the above objectives, the method for preparing polycrystalline silicon ingots by forming oxygen-removing channels inside a crucible using single-crystal or polycrystalline rods according to the present invention is characterized by comprising the following steps: preparing silicon square pillars; arranging the single-crystal or polycrystalline square pillars adjacent to the inner circumferential surface of the crucible according to the crucible shape, thereby forming a space within the space surrounded by the single-crystal or polycrystalline square pillars that can accommodate large blocks, and inserting the silicon square pillars into the crucible by forming oxygen-removing holes between one side of the single-crystal or polycrystalline square pillar and the inner surface of the crucible; inserting silicon blocks into the crucible within the large space that can accommodate the single-crystal or polycrystalline square pillars; and performing bulk melting and crystallization.

[0044] The present invention is characterized in that the single-crystal square pillar or polycrystalline square pillar is trapezoidal in shape. ) a pillar or a quadrilateral shape with a concave side on one side of a rectangle ( ) Any of the pillars.

[0045] The present invention is characterized in that when the above-mentioned single crystal square pillar or polycrystalline square pillar is a trapezoidal pillar, it is configured such that the short side faces the inner surface of the crucible.

[0046] The present invention is characterized in that, when the above-mentioned single-crystal square pillar or polycrystalline square pillar is a quadrilateral shape with one side concave, it is configured such that the concave part of the pillar faces the inner surface of the crucible.

[0047] According to the present invention having the aforementioned structure, during the polycrystalline silicon crystallization process, oxygen (O2) generated on the bottom and sides of the crucible is smoothly discharged to the upper part of the crucible through the oxygen venting channel between the single crystal column, the polycrystalline column and the inner wall of the crucible. Therefore, it has the following advantages: the occurrence of partial breakage of the ingot can be minimized, or the formation of bubble venting channels of various sizes and shapes facing the interior of the ingot on the surface of the ingot can be minimized. Attached Figure Description

[0048] Figure 1 This is a side cross-sectional view of an apparatus for preparing polycrystalline silicon ingots by forming oxygen-removing channels inside a crucible using single or multiple crystal rods.

[0049] Figure 2 To show in Figure 1 The solidification process of the silicon melt in the crucible in the polycrystalline silicon ingot preparation apparatus is divided into three regions in the side cross-sectional view.

[0050] Figure 3 In order to be in Figure 1 A simplified schematic diagram of the crucible used in the polycrystalline silicon ingot preparation apparatus.

[0051] Figure 4a The following are top and side cross-sectional views illustrating a structural example in which a single-crystal silicon rod or a polycrystalline silicon rod is arranged on the inner circumferential surface of a crucible in a square column shape with one side recessed in the silicon ingot preparation apparatus of the present invention.

[0052] Figure 4b This is a top view illustrating a structural example in which a single-crystal silicon rod or a polycrystalline silicon rod is arranged in a trapezoidal shape on the inner circumferential surface of a crucible in the silicon ingot preparation apparatus of the present invention.

[0053] Figure 5a To illustrate a three-dimensional view of a square-prism shaped silicon rod with one concave side, Figure 5b A three-dimensional view showing a trapezoidal silicon rod.

[0054] Figure 6 A diagram illustrating the surface state of silicon ingots prepared by the preparation method of the present invention and the preparation method of a comparative object. Detailed Implementation

[0055] Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings.

[0056] First, in this invention, the polycrystalline silicon ingot preparation apparatus disclosed in the prior art can be utilized.

[0057] That is, the silicon ingot preparation apparatus used for implementing the polycrystalline silicon ingot preparation method of the present invention, which involves forming oxygen-removing channels inside a crucible using a single crystal rod or a polycrystalline rod, can also be used. Figure 1 The preparation apparatus shown.

[0058] like Figure 1 As shown, the silicon ingot preparation apparatus 10 for implementing the polycrystalline silicon ingot preparation method of the present invention, which forms an oxygen-removing channel inside a crucible by a single crystal rod or a polycrystalline rod, includes: a crucible 20 for storing molten silicon L; a base 12 for mounting the crucible 20; an under-bed heater 13 for supporting the base 12 from below; and a ceiling heater 14 disposed above the crucible 20.

[0059] Furthermore, an insulating material 15 is formed around the crucible 20.

[0060] The aforementioned chassis 12 forms a hollow structure and is designed to supply argon gas to the interior through a supply pipe 16.

[0061] The crucible 20 described above has a square (quadrilateral) or annular (circular) horizontal cross-sectional shape, and in this embodiment it is circular.

[0062] like Figure 2 As shown, the crucible 20 includes a crucible body 21 made of silicon dioxide. Silicon nitride (SiN4) is coated on the inner sidewall and bottom surface 20a of the crucible body 21, followed by silicon dioxide (SiO2), or silicon dioxide is coated and then silicon nitride is coated, or silicon dioxide, yttrium oxide (Y2O3), or zirconium oxide (ZrO2) is coated, or the same structure as described in Korean Patent Publication No. 2012-0135284 is applied.

[0063] As described above, the silicon ingot preparation apparatus of the present invention has been explained, but this is for the purpose of understanding the present invention. Various silicon ingot preparation apparatuses known in the art or commercially available can be used.

[0064] The following describes the method of preparing polycrystalline silicon ingots according to the present invention, which uses a single crystal rod or a polycrystalline rod to form an oxygen-removing channel inside a crucible.

[0065] The crucible used in the silicon ingot preparation apparatus is made of silicon dioxide (SiO). Therefore, during the process of heating the silicon raw material (bulk) and achieving solidification, oxygen generated in the crucible and oxygen generated from the coating agent of the crucible flow into the silicon melt. The oxygen that flows in is discharged to the outside during the crystallization process, which will cause the ingot to break as described above and will create grooves on the surface.

[0066] The ingot preparation process of the present invention, which is used to solve this problem, will be described below.

[0067] First, the first step is the preparation of silicon square pillars.

[0068] Specifically, the single-crystal silicon rod or polycrystalline silicon rod disposed on the inner circumferential surface of the crucible 20 of the silicon ingot preparation apparatus 10 is processed into a trapezoidal shape. , refer to Figure 4b ), or it can be processed into a quadrilateral shape with a concave side on one side of a rectangle. , refer to Figure 4a (The shape of a pillar.)

[0069] For example, when using a circular crucible, the width of the processed square column is as follows.

[0070] When the aforementioned monocrystalline silicon rod or polycrystalline silicon rod is a quadrilateral shape with one side concave ( Figure 4a When the circumference of the circular crucible is 3600 mm, the width of the square column is 100 mm, its thickness is 10 mm, and the concave part is an arc shape with a central depth of about 3 mm.

[0071] Furthermore, when the aforementioned monocrystalline silicon rod or polycrystalline silicon rod is trapezoidal in shape ( Figure 4b When the long side is 100mm, the short side is 70mm, and the crucible thickness is 10mm.

[0072] The height of the square column is less than or equal to the height of the crucible used.

[0073] However, the size of the square column is only provided for illustration. Those skilled in the art can adjust the size by simple design changes depending on the size and shape of the crucible in the ingot preparation apparatus.

[0074] Furthermore, for ease of explanation, the description is based on a square pillar, but it is reasonable to change it to a shape that allows oxygen to be released during the melting of silicon by placing it on the side wall of the crucible.

[0075] The square pillars described above can be prepared using techniques known in the art, such as cutting or grinding single or polycrystalline ingots.

[0076] The second step is to load the silicon square pillar into the crucible.

[0077] Specifically, the plurality of single-crystal square pillars or polycrystalline square pillars are arranged adjacent to each other along the inner circumferential surface of the crucible, thereby forming a space within the space surrounded by the single-crystal square pillars or polycrystalline square pillars that can accommodate large blocks.

[0078] In this case, such as Figure 4a and Figure 4b As shown, multiple single-crystal or polycrystalline square pillars are arranged vertically adjacent to the inner circumferential surface of the crucible.

[0079] In the case of a crucible, a single-crystal trapezoidal shape or a polycrystalline trapezoidal shape is formed along the inner surface of the crucible. Figure 5b ) or a quadrilateral shape with one side concave ( Figure 5a ( ) Single-crystal square pillars or polycrystalline square pillars.

[0080] In one embodiment of the present invention, the trapezoidal shape ( Figure 5b In the case of a single-crystal square prism or a polycrystalline square prism, the short side of the trapezoidal shape is configured as ( Figure 4b The inner side of the crucible is concave, forming a quadrilateral shape. Figure 5a In the case of a single-crystal square prism or a polycrystalline square prism, the recessed quadrilateral-shaped recess is configured as ( Figure 4a ( ) The inner side facing the circular crucible.

[0081] Therefore, it can be seen that after placing a single-crystal or polycrystalline square pillar in a circular crucible, oxygen venting holes can be appropriately formed when the bulk material is loaded (refer to...). Figure 4a , Figure 4b ).

[0082] Set a trapezoidal shape for single or polycrystalline materials in a circular or quadrilateral crucible. Figure 4b and Figure 5b ), set a quadrilateral shape with one side concave ( Figure 4a and Figure 5a When constructing a single-crystal square pillar or a polycrystalline square pillar, as mentioned above, it is obvious that oxygen venting pores should be appropriately formed, so detailed explanation is omitted.

[0083] The third step is to load the silicon block into the crucible.

[0084] Specifically, in the second step, the quadrilateral crucible is provided with a trapezoidal shape of single crystal or polycrystalline material. Figure 4b ), towards a quadrilateral shape with one side concave ( Figure 4a Silicon blocks are packed into the internal space of a single-crystal or polycrystalline square pillar.

[0085] In this case, since the inserted bulk material is the same as the bulk material known in the art for the preparation of polycrystalline silicon ingots, its description is omitted.

[0086] Next, the fourth step is to melt and crystallize the large blocks.

[0087] Specifically, the steps of large-scale melting and crystallization involve placing a single-crystal square pillar or polycrystalline square pillar and a large-scale ingot inside the crucible in the state described in the third step above. Then, the ingot is prepared using the ingot preparation process disclosed in Korean Patent Publication No. 2012-0135284, or by heating the upper and lower heaters of the silicon ingot preparation apparatus used in this technical field to achieve melting. The silicon is then crystallized through a series of processes, such as controlling the temperature of the upper and lower heaters, to prepare the ingot. These methods include the Kyropoulos Method (hereinafter referred to as "KY method"), the Czochralski Method (hereinafter referred to as "CZ method"), the Edge-defined Film-fed Growth (EFG) method, the Heat Exchange Method, and the Vertical Horizontal Gradient Freezing method. Therefore, detailed descriptions of these methods are omitted.

[0088] In the absence of an oxygen venting channel inside the crucible, when a large block of silicon is melted inside a silicon dioxide (SiO) crucible, the oxygen (O2) component of the coating agent or the oxygen component that can flow into the silicon dioxide (SiO) crucible mixes into the dissolved silicon melt. The oxygen in the silicon melt, as oxygen gas, rises from the bottom surface to the top surface in the form of bubbles and is released.

[0089] When the silicon molten liquid begins to solidify, oxygen from the coating on the bottom and sides of the silicon dioxide crucible will mix in as the polycrystalline silicon ingot is grown unidirectionally, thus increasing the oxygen content in the silicon molten liquid.

[0090] Moreover, due to the characteristics of silicon crystal growth, impurities inside the silicon are pushed to the outside, resulting in oxygen being concentrated and mixed into the bottom and sides of the polycrystalline silicon ingot.

[0091] However, according to the polycrystalline silicon ingot preparation method that forms an oxygen removal channel inside the crucible by using a single crystal rod or a polycrystalline rod, oxygen (O2) generated from the bottom and sides of the crucible is successfully discharged to the upper part of the crucible through the oxygen removal channel between the single crystal column, the polycrystalline column and the inner wall of the crucible.

[0092] This inhibits the incorporation of oxygen (O2) into the polycrystalline ingot and suppresses ingot breakage and the formation of grooves on the surface.

[0093] In order to determine the effect of the ingot preparation method according to the present invention on suppressing the breakage of other ingots and the generation of grooves on the surface, the inventor conducted the following experiments.

[0094] First, the experimental conditions were the same: using the same materials, the same process conditions, and the same preparation equipment. The preparation method of the comparison object did not form an oxygen emission channel through the polycrystalline silicon square pillar.

[0095] like Figure 6 As shown, the results indicate that, compared with the preparation method of the comparative object, the surface of the silicon ingot prepared by the preparation method of the present invention is reduced in terms of bubble state, number of bubbles and bubble size.

Claims

1. A method for preparing polycrystalline silicon ingots by forming oxygen-removing channels inside a crucible using single-crystal rods or polycrystalline rods, characterized in that, Includes the following steps: Preparation of silicon square pillars; The single-crystal or polycrystalline square pillars are arranged adjacent to the inner circumferential surface of the crucible according to the shape of the crucible, so as to form a space that can accommodate large blocks inside the space surrounded by the single-crystal or polycrystalline square pillars. The silicon square pillars are inserted into the crucible by forming an oxygen venting hole between one side of the single-crystal or polycrystalline square pillar and the inner side of the crucible. The silicon block is loaded into the crucible in a large space that can fit inside a single-crystal square pillar or a polycrystalline square pillar. as well as Large-scale melting and crystallization are carried out. Among them, single-crystal square prisms or polycrystalline square prisms are trapezoidal in shape. A column or a rectangular shape with a concave side. Any of the pillars, When the aforementioned single-crystal or polycrystalline square pillar is a trapezoidal pillar, it is configured with its short side facing the inner surface of the crucible.

2. A method for preparing polycrystalline silicon ingots by forming oxygen-removing channels inside a crucible using single-crystal rods or polycrystalline rods, characterized in that, Includes the following steps: Preparation of silicon square pillars; The single-crystal or polycrystalline square pillars are arranged adjacent to the inner circumferential surface of the crucible according to the shape of the crucible, so as to form a space that can accommodate large blocks inside the space surrounded by the single-crystal or polycrystalline square pillars. The silicon square pillars are inserted into the crucible by forming an oxygen venting hole between one side of the single-crystal or polycrystalline square pillar and the inner side of the crucible. The silicon block is loaded into the crucible in a large space that can fit inside a single-crystal square pillar or a polycrystalline square pillar. as well as Large-scale melting and crystallization are carried out. Among them, single-crystal square prisms or polycrystalline square prisms are trapezoidal in shape. A column or a rectangular shape with a concave side. Any of the pillars, When the aforementioned single-crystal square pillar or polycrystalline square pillar is a quadrilateral shape with one side concave, it is configured such that the concave part of the pillar faces the inner surface of the crucible.

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