Quality determination method of cast single crystal silicon block and cast single crystal silicon block

Abstract

The present invention discloses a quality determination method for a cast single crystal silicon block and a cast single crystal silicon block, the steps of which include: (1) uniformly removing about 30-60 mm of the head of the cast single crystal silicon block; (2) measuring a photoluminescence test image of the head end face of the cast single crystal silicon block by using a photoluminescence tester, and calculating a black silk area ratio value D of the photoluminescence test image. S ; (3) Measure and calculate the end surface area S of the ingot single crystal silicon block; (4) Establish a black wire growth calculation model to determine the silicon block removal length L and the preset end surface black wire area ratio value D L The relationship L (D L ,⍺), where ⍺ is the dislocation growth angle; (5) According to the preset end face black wire area ratio value D L and the relation L(D L ,⍺), calculate the value of the silicon block removal length L; (6) remove the head of the cast single crystal silicon block according to the value of the silicon block removal length L. This method combines the photoluminescence test with the growth characteristics of the cast single crystal silicon ingot to propose a new method for removing different black wire ratios at the head of the cast single crystal silicon block.

Description

Technical Field

[0001] The invention relates to the technical field of preparation of cast single crystal silicon ingots, and in particular to a quality determination method for a cast single crystal silicon block and a cast single crystal silicon block. Background Art

[0002] The growth of ingot polycrystalline nuclei is small grain nucleation, and it grows in vertical columnar crystals. The growth quality of different regions is similar, and due to the segregation effect, there are more impurities in the head. Therefore, the method for determining the head removal of ingot polycrystalline silicon blocks is mainly based on the judgment of the minority carrier lifetime that characterizes the amount of impurities in the silicon block. The CZ-pulled single crystal is generally a dislocation-free single crystal. Once impurities or dislocations exist, it will break and grow into polycrystalline. The defective head is mainly caused by poor resistivity caused by oxygen donors or diameter defects caused by pulling. Therefore, the method for determining the head removal of CZ-pulled single crystal silicon blocks is mainly based on the judgment of poor resistivity and poor diameter.

[0003] Ingot single crystal is a silicon crystal product that has developed rapidly in recent years. Its performance is between that of ingot polycrystalline and Czochralski single crystal. It can be applied to the alkali texturing process of single crystal, and its efficiency is much higher than that of ingot polycrystalline. The single feeding amount is large, and the production cost is much lower than that of Czochralski single crystal. However, since the raw materials of ingot single crystal silicon block are of lower grade than those of Czochralski single crystal (the impurity content in the raw materials is higher), and the growth mode is different from that of Czochralski single crystal, there will be some dislocations inside it, which seriously affect the efficiency of the battery cells prepared subsequently from the ingot single crystal silicon block. If the head is removed according to the determination method of the minority carrier lifetime of the ingot polycrystalline silicon block and the determination method of the resistivity of the Czochralski single crystal, there will be a large error. In addition, the existing dislocation detection method is mainly through chemical corrosion, physical polishing and then observation under a microscope. It can only detect the dislocation density of a local area of ​​a single silicon wafer each time. It is mainly used for research and development guidance and cannot be used for quality control of large-scale production products. Summary of the invention

[0004] To solve the above problems, the purpose of the present invention is to propose a method for determining the quality of a cast single crystal silicon block and an ingot single crystal silicon block. The method combines photoluminescence testing technology with the growth characteristics of an ingot single crystal silicon ingot to propose a new way to remove the head of an ingot single crystal silicon block. The method is simple and convenient, has a high accuracy rate, and can effectively remove defects in the head of the silicon block, thereby significantly improving the quality of the silicon block after removal.

[0005] One aspect of the present invention provides a method for determining the quality of a cast single crystal silicon block, the steps of which include:

[0006] (1) Remove about 30-60 mm from the head of the ingot single crystal silicon block.

[0007] (2) Using a photoluminescence tester to measure the photoluminescence test image of the head end surface of the ingot single crystal silicon block, and calculating the black wire area ratio value D of the photoluminescence test image S ;

[0008] (3) measuring and calculating the end surface area S of the ingot single crystal silicon block;

[0009] (4) Establish a black wire growth calculation model to determine the silicon block removal length L and the preset end face black wire area ratio D L The relationship L(D L ,α), where α is the dislocation growth angle;

[0010] (5) According to the preset end face black wire area ratio value D L and the relation L(D L ,α), calculate and obtain the value of the silicon block removal length L;

[0011] (6) The head of the cast single crystal silicon block is removed according to the value of the silicon block removal length L.

[0012] By constructing a black filament growth calculation model, utilizing existing photoluminescence technology, and combining the growth characteristics of dislocations in cast single silicon blocks, an effective method for removing the silicon block head was determined, thereby ensuring the overall quality of the cast single crystal silicon block.

[0013] Furthermore, in step (4), the relation L(D L ,α) is:

[0014]

[0015] Where L is the length of silicon block removed; S is the end surface area of ​​silicon block, D S is the black wire area ratio of the silicon block head end surface, D L is the black wire area ratio of the preset silicon block end face, and α is the dislocation growth angle.

[0016] Furthermore, in step (4), the crystal orientation of the cast single crystal silicon block is (100), and the formula for determining the dislocation growth angle α is: α=45 / 2v, where v is the crystal growth rate.

[0017] Alternatively, the crystal growth rate v is calculated from the height of the original silicon ingot and the solidification time of the original silicon ingot.

[0018] Optionally, the value of v is 0.50-1.2 cm / h.

[0019] Optionally, the v value of the cast single crystal silicon block that is a central region silicon block is greater than the v value of the cast single crystal silicon block that is an edge region silicon block or a corner region silicon block.

[0020] Furthermore, when the ingot single crystal silicon block is the central region silicon block, D L The value is 15%-20%; when the ingot single crystal silicon block is an edge area silicon block or a corner area silicon block, D L The value is 10%-15%.

[0021] In another aspect of the present invention, the present invention discloses a cast single crystal silicon block, which is prepared by any of the above-mentioned determination methods for the cast single crystal silicon block.

[0022] Additional aspects and advantages of the present invention will be given in part in the following description and in part will be obvious from the following description, or will be learned through practice of the present invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 is a flow chart of one embodiment of the present invention.

[0024] Figure 2 It is a scan diagram of minority carrier lifetime of the cast single crystal silicon block of the present invention.

[0025] Figure 3 It is a schematic diagram of the construction of the black silk model of the present invention.

[0026] Figure 4 This is a black silk surface image of the ingot single crystal silicon block of the first embodiment of the present invention.

[0027] Figure 5 This is a black silk surface image of the ingot single crystal silicon block of the second embodiment of the present invention. DETAILED DESCRIPTION

[0028] Embodiments of the present invention are described in detail below, examples of which are shown in the accompanying drawings, wherein the same or similar reference numerals throughout represent the same or similar elements or elements having the same or similar functions. The embodiments described below with reference to the accompanying drawings are exemplary and are intended to be used to explain the present invention, and should not be construed as limiting the present invention.

[0029] One aspect of the present invention, as Figure 1 As shown, a method for determining the quality of a cast single crystal silicon block is provided, the steps of which include:

[0030] (1) Remove about 30-60 mm from the head of the ingot single crystal silicon block.

[0031] In this step, after the original ingot is squared, the head of the ingot monocrystalline silicon block is uniformly removed by 30-60 mm, for example, 30 mm, 35 mm, 40 mm, 45 mm, 50 mm, 55 mm or 60 mm. Due to the segregation effect, there are more impurities in the head of the silicon block, and because the ingot monocrystalline silicon ingot is grown by directional solidification, there will be some obvious inclusions or dirt at the head of the silicon block. These areas are generally not used to prepare solar cells, and will affect the detection results of the photoluminescence tester. The head of the silicon block is uniformly removed by 30-60 mm, so that the photoluminescence test picture measured by the photoluminescence tester will be more representative of the black silk area ratio, thereby further improving the quality of the final ingot monocrystalline silicon block.

[0032] (2) Use a photoluminescence tester to measure the photoluminescence test image of the head end surface of the ingot single crystal silicon block, and calculate the black wire area ratio value D of the photoluminescence test image S ;

[0033] In this step, photoluminescence tester (PL) is a technical detection and analysis method commonly used by technicians in this field. It is mainly used to detect hidden cracks, fragments, growth defects, etc. of silicon wafers and solar cells. Among them, growth defect detection is the most widely used. The PL test results reflect the surface quality of the test surface and can show surface dislocations, grain boundaries and other crystal structure defects. The photoluminescence test graph measured by the photoluminescence tester is mainly as follows: Figure 4 , as shown in Figure 5, the black lines that gather in the figure are generally called "black silk" (such as Figure 4 As shown in the circle in the left figure, referring to the electronic industry standard SJ / T11629-2016 of the People's Republic of China "Online Photoluminescence Analysis Method for Silicon Wafers and Cells for Solar Cells", it can be known that this black wire is mainly considered to be a dislocation. The photoluminescence tester can calculate the black wire area ratio value based on the pixel difference between the black wire and the silicon wafer background after setting the pixel threshold, that is, the ratio of the black wire area to the entire silicon wafer area in the figure.

[0034] In this step, a photoluminescence test image is performed on the head of the single crystal silicon block, and the black wire area ratio value D of the photoluminescence test image is calculated. S , so as to make subsequent quality judgment of silicon blocks.

[0035] (3) Measure and calculate the end surface area S of the ingot single crystal silicon block;

[0036] In this step, the end surface area S of the ingot single crystal silicon block can be calculated by measuring the side width of the silicon block.

[0037] It can be understood that there is no particular order in which step (1) and step (2) are performed. They can be performed simultaneously, or step (1) can be performed first and step (2) can be performed later, or step (2) can be performed first and step (1) can be performed later.

[0038] (4) Establish a black wire growth calculation model to determine the silicon block removal length L and the preset end face black wire area ratio D L The relationship L(D L ,α), where α is the dislocation growth angle;

[0039] In this step, as mentioned above, the black silk in the ingot single crystal is mainly composed of dislocations, and the inventors found that the black silk, that is, dislocations, are mainly generated during the preparation process of the ingot single crystal. Since it adopts a combination of directional solidification and seed crystal splicing and bottoming seeding, there are gaps in the seed crystal splicing process, and dislocations are easily generated in a certain part of the silicon block during the growth process. Moreover, since the dislocations have no grain boundary barriers like traditional polycrystalline, the dislocations slip and multiply very rapidly, and the dislocations slip and multiply at a certain angle.

[0040] The minority carrier lifetime is also a technical detection and analysis method commonly used by technicians in this field. The minority carrier lifetime is mainly an indicator of metal impurities or lattice defects (grain boundaries, dislocations, etc.) inside the silicon block. The inventor further analyzed the minority carrier lifetime diagram of the ingot single crystal silicon block and found that Figure 2 , Figure 2 It is the minority carrier lifetime on the side of the single crystal silicon block, that is, the minority carrier lifetime picture from the beginning to the end of the silicon block, where the upper end face is the head of the silicon block and the lower end face is the tail of the silicon block. It can be seen from the figure that the straight line indicated by the arrow in the figure is the lattice defect growing from the bottom to the top at a certain angle and diverging around. In view of the above findings, the construction of the black wire model will be mainly based on the dislocation slip proliferation growth theory. The growth surface of the ingot single crystal silicon block is generally in the (100) direction, and dislocations are prone to appear in the low-energy surface (111) direction. The angle α between the (111) crystal direction and the (100) growth surface is constant. Therefore, under ideal conditions, once a dislocation is generated, it will slip and proliferate at a constant angle α inside the silicon block. Therefore, the black wire theoretical model established by the inventor is as follows Figure 3 As shown, the left figure is a stereoscopic diagram of the black wire (i.e. dislocation) growth model, and the right figure is a front view of the black wire growth model. From the left figure, it can be seen that the end surface area of ​​the silicon block is S, if the black wire area ratio is D S , then the black wire area is S×D S , if the predetermined black wire area ratio reaching the predetermined dislocation position is D L , the black silk area is S×D L , then the dislocation radius of the end face is:

[0041]

[0042] Dislocation radius at a predetermined location:

[0043]

[0044] As can be seen from the figure on the right, Tanα=r S / L0, where L0 is the height of the ingot single crystal silicon block (i.e. the height from the tail to the head of the silicon block), and r S / r L =L0 / (L0-L), from which we can know:

[0045] L=(r S -r L ) / Tanα (3)

[0046] Combining (1), (2) and (3), we can see that

[0047]

[0048] Where: L is the length of silicon block removed; S is the end surface area of ​​silicon block, D S is the black wire area ratio of the silicon block head end surface, D L is the black wire area ratio of the preset silicon block end face, and α is the dislocation growth angle.

[0049] In some specific embodiments, the crystal orientation of the cast single crystal silicon block is (100), and the formula for determining the dislocation growth angle α is: α=45 / 2v, where v is the crystal growth rate. The growth plane of the cast single crystal silicon block is generally in the (100) direction, and dislocations are prone to appear in the low-energy plane (111) direction. Ideally, the angle between the (111) crystal direction and the (100) growth plane is 45 degrees, that is, ideally, the silicon block dislocation slips at a dislocation angle of 45 degrees, then α=45 / 2=22.5 degrees, but in actual situations, by comparing the dislocation growth characteristics of the center and the edge of the silicon ingot, it is found that the growth rate of the silicon ingot will affect the dislocation angle, and there is an inversely proportional relationship, that is, the slower the growth, the larger the dislocation angle, and the faster the growth, the smaller the angle. Specifically, α=45 / 2v, where the crystal growth rate v is calculated by the height of the original silicon ingot and the solidification time of the original silicon ingot. In some specific embodiments, the value of v can be 0.50-1.20 cm / h, for example, 0.5 cm / h, 0.6 cm / h, 0.7 cm / h, 0.8 cm / h, 0.9 cm / h, 1.0 cm / h, 1.1 cm / h or 1.2 cm / h. Furthermore, in the same furnace of cast single crystals, the v value of the cast single crystal silicon block as the central region silicon block is greater than the v value of the cast single crystal silicon block as the edge region silicon block or the corner region silicon block.

[0050] (5) According to the preset end face black wire area ratio value D L and the relation L(D L,α), calculate and obtain the value of the silicon block removal length L;

[0051] In this step, by the above relationship L(D L ,α), and according to D L The value of L can be effectively calculated. In some specific embodiments, D L The value of can be between 0-100%. Preferably, D L The value of may be 10%-20%, for example, 10%, 11%, 12%, 13%, 14%, 15%, 16%, 17%, 18%, 19% or 20%. L When the value of is greater than 20%, the silicon wafers cut from the head silicon block will be inefficient when made into solar cells, resulting in a high defective rate of solar cells; if D L When the value is less than 10%, too much length is removed and the cost is too high.

[0052] Furthermore, when the ingot single crystal silicon block is the central region silicon block, D L The value of may be 15%-20%, for example, 15%, 16%, 17%, 18%, 19% or 20%; when the ingot single crystal silicon block is an edge region silicon block or a corner region silicon block, D L The value can be 10%-15%, for example, 10%, 11%, 12%, 13%, 14%, 15%. The ingot single crystal silicon block is generally prepared into a cube, which is cut into 5×5=25 blocks or 6×6=36 blocks according to the subsequent size of the silicon wafer. For example, in a 5×5=25 silicon wafer, there will be 4 corner silicon blocks, 12 edge silicon blocks and 9 center silicon blocks. Due to the segregation of impurities and the diffusion of the crucible wall, the quality of the silicon blocks in the center area is better than that of the edge silicon blocks, especially the impurity content of metals with a smaller segregation coefficient will be slightly lower than that of the edge and corner silicon blocks. Therefore, even if the proportion of black silk area is slightly higher, the efficiency of the battery prepared subsequently will be within the qualified range. And this judgment method can further reduce costs.

[0053] (6) The head of the cast single crystal silicon block is removed according to the value of the silicon block removal length L.

[0054] In this step, the head of the silicon block is removed using the L value calculated as described above.

[0055] In another aspect of the present invention, the present invention discloses a cast single crystal silicon block, which is prepared by any of the above-mentioned determination methods for the cast single crystal silicon block.

[0056] The present invention is described below with reference to specific embodiments. It should be noted that these embodiments are merely illustrative and do not limit the present invention in any way.

[0057] Example 1

[0058] Select a silicon block in the center area of ​​the original ingot single crystal with a (100) crystal orientation, and remove 30 mm from its head;

[0059] like Figure 4 As shown in the left figure, the photoluminescence image of the head end face of the ingot single crystal silicon block is measured by a photoluminescence tester, and the black wire area ratio value D of the head end face photoluminescence image is calculated. S 66.5%;

[0060] Measure and calculate the end surface area S of the ingot single crystal silicon block = 158 × 158;

[0061] The crystal growth rate was calculated to be 0.86 cm / h based on the height of the silicon ingot and the solidification completion time of the silicon block in the central area.

[0062] Set the black wire area ratio value D of the preset end face L is 15.25%, and S = 158 × 158, D S =66.5%, α = 45 / (2×0.86) Substitute into L(D L ,α) can be known:

[0063]

[0064] After removing 77mm of the silicon block head, the photoluminescence tester is used to measure the black silk area ratio of the silicon block head end face again, such as Figure 4 As shown in the right figure, the black silk area ratio is 15.22% as measured and calculated.

[0065] Example 2

[0066] Select a silicon block at the edge of the original ingot single crystal with a (100) crystal orientation, and remove 50 mm from its head;

[0067] like Figure 5 As shown in the left figure, the photoluminescence image of the head end face of the ingot single crystal silicon block is measured by a photoluminescence tester, and the black wire area ratio value D of the head end face photoluminescence image is calculated. S 84%

[0068] Measure and calculate the end surface area S of the ingot single crystal silicon block = 158 × 158;

[0069] The crystal growth rate was calculated to be 0.778 cm / h based on the height of the silicon ingot and the solidification completion time of the silicon block in the central area.

[0070] Set the black wire area ratio value D of the preset end face L is 11.5%, and S = 158 × 158, D S=84%, α = 45 / (2×0.778) Substitute into L(D L ,α) can be known:

[0071]

[0072] After removing 93mm of the silicon block head, the photoluminescence tester was used to measure the black silk area ratio of the silicon block head end face again, such as Figure 5 As shown in the figure on the right, the black silk area ratio is measured and calculated to be 11.75%.

[0073] Evaluation index: Error rate = | black wire area ratio of the preset end face - black wire area ratio of the actual end face | / black wire area of ​​the preset end face

[0074] Calculation shows that the error between the black wire area ratio value of the preset end face in Example 1 and Example 2 and the black wire area ratio value of the actual end face does not exceed 0.3%. The determination method of the present invention is simple and convenient, has high accuracy, and can effectively remove defects at the head of the silicon block, so that the quality of the silicon block after removal is significantly improved.

[0075] In the description of this specification, the description with reference to the terms "one embodiment", "some embodiments", "example", "specific example", or "some examples" etc. means that the specific features, structures, materials or characteristics described in conjunction with the embodiment or example are included in at least one embodiment or example of the present invention. In this specification, the schematic representations of the above terms do not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials or characteristics described may be combined in any one or more embodiments or examples in a suitable manner. In addition, those skilled in the art may combine and combine the different embodiments or examples described in this specification and the features of the different embodiments or examples, without contradiction.

[0076] Although the embodiments of the present invention have been shown and described above, it is to be understood that the above embodiments are exemplary and are not to be construed as limitations of the present invention. A person skilled in the art may change, modify, replace and vary the above embodiments within the scope of the present invention.

Claims

1. A method for determining the quality of a cast single crystal silicon block, characterized in that: The steps include: (1) uniformly remove 30-60 mm from the head of the ingot single crystal silicon block; (2) Using a photoluminescence tester to measure the photoluminescence test image of the head end surface of the ingot single crystal silicon block, and calculating the black wire area ratio value D of the photoluminescence test image S ; (3) measuring and calculating the end surface area S of the ingot single crystal silicon block; (4) Establish a black wire growth calculation model to determine the silicon block removal length L and the preset end face black wire area ratio D L The relationship L(D L ,α), where the relation L(D L ,α) is: L is the length of silicon block removed; S is the end surface area of ​​silicon block, D S is the black wire area ratio of the silicon block head end surface, D L is the black wire area ratio of the preset silicon block end surface, and α is the dislocation growth angle; (5) According to the preset end face black wire area ratio value D L and the relation L(D L ,α), calculate and obtain the value of the silicon block removal length L; (6) The head of the cast single crystal silicon block is removed according to the value of the silicon block removal length L.

2. The method for determining the quality of a cast single crystal silicon block according to claim 1, characterized in that: In step (4), the crystal orientation of the cast single crystal silicon block is (100), and the formula for determining the dislocation growth angle α is: α=45 / 2v, where v is the crystal growth rate.

3. A method for determining the quality of a cast single crystal silicon block according to claim 2, characterized in that: The crystal growth rate v is calculated according to the height of the original silicon ingot and the solidification time of the original silicon ingot.

4. A method for determining the quality of a cast single crystal silicon block according to claim 3, characterized in that: The value of v is 0.50-1.20 cm / h.

5. The method for determining the quality of a cast single crystal silicon block according to claim 2, wherein: The v value of the cast single crystal silicon block that is a central region silicon block is greater than the v value of the cast single crystal silicon block that is an edge region silicon block or a corner region silicon block.

6. The method for determining the quality of a cast single crystal silicon block according to claim 1, characterized in that: When the ingot single crystal silicon block is the central region silicon block, the D L The value of D is 15%-20%; when the ingot single crystal silicon block is an edge area silicon block or a corner area silicon block, the D L The value is 10%-15%.

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