A finishing process for reducing crack dislocations in a single crystal silicon rod

Abstract

The application provides a finishing process for reducing crack dislocation of a single crystal silicon rod, which comprises the following steps: S1: instantaneously increasing a heating power, instantaneously reducing a pulling speed to a first pulling speed, reducing the first pulling speed to a second pulling speed at a first acceleration, keeping a crystal rotation and a crucible rotation unchanged as an equal-diameter section crystal rotation and crucible rotation, and keeping a first crystal rotation and a first crucible rotation unchanged, and gradually reducing a single crystal diameter; S2: increasing the second pulling speed to a third pulling speed at a second acceleration, increasing the first crystal rotation and the first crucible rotation to a second crystal rotation and a second crucible rotation at a third acceleration, and continuing to reduce the single crystal diameter; and S3: increasing the third pulling speed to a fourth pulling speed at the second acceleration, increasing the second crystal rotation and the second crucible rotation to a third crystal rotation and a third crucible rotation at a fourth acceleration, and ending the finishing process. The application has the beneficial effects of effectively reducing the broken edge of the single crystal, shortening the finishing time, effectively controlling the dislocation and crack of the single crystal, and improving the qualified rate of the single crystal product.

Description

Technical Field

[0001] This invention belongs to the field of single-crystal silicon rod technology, and in particular relates to a finishing process for reducing crack dislocations in single-crystal silicon rods. Background Technology

[0002] The Czochralski method for growing monocrystalline silicon is currently the most widely used technology for producing monocrystalline silicon. However, with increasing market competition and cost pressures, monocrystalline silicon manufacturers are now increasing the diameter of the pulled single crystals to maximize throughput and increase theoretical production capacity in order to reduce costs. However, increasing the diameter of the pulled single crystal significantly increases the temperature difference between the center and the edge of the single crystal during the pulling process. The temperature at the center of the single crystal cannot be quickly conducted away, leading to increased stress. This stress exceeds the elastic stress of the single crystal, causing plastic deformation and resulting in dislocations and cracks.

[0003] In existing technologies, the heater power gradually increases during the finishing process to control the growth rate of the single crystal edge, in conjunction with the increased pulling speed, until the diameter shrinks to <80mm, completing the finishing work with a circular cross-section. To avoid dislocations affecting the effective single crystal silicon rod, the finishing length must be greater than the finishing diameter, allowing dislocations to extend to the single crystal surface within the finishing diameter range. This process has a long finishing time, and the increased temperature during finishing increases the temperature difference between the single crystal center and edge, easily leading to edge breakage. The dislocation extension length at the edge breakage point is equal to the single crystal cross-sectional diameter at the breakage point, which can easily affect the yield of single crystal products. Summary of the Invention

[0004] To address the aforementioned technical problems, this invention provides a finishing process that reduces dislocation cracks in monocrystalline silicon rods, effectively solving the problems of long finishing times and the tendency for monocrystalline silicon rods to develop broken edges and dislocation cracks.

[0005] The technical solution adopted in this invention is: a finishing process for reducing dislocation cracks in single-crystal silicon rods, comprising the following steps after constant-diameter growth:

[0006] S1: Instantly increase the heating power, instantaneously decrease the pulling speed to the first pulling speed, and then decrease the first pulling speed to the second pulling speed with the first acceleration. The crystal rotation and crucible rotation are crystal rotation and crucible rotation of equal diameter segments, and remain unchanged as the first crystal rotation and first crucible rotation. The single crystal diameter gradually shrinks.

[0007] S2: The second pulling speed is increased to the third pulling speed by the second acceleration, the first crystal rotation and the first crucible rotation are increased to the second crystal rotation and the second crucible rotation by the third acceleration, and the diameter of the single crystal continues to shrink;

[0008] S3: The third pulling speed is increased to the fourth pulling speed by the second acceleration, and the second crystal rotation and the second crucible rotation are increased to the third crystal rotation and the third crucible rotation by the fourth acceleration, and the process ends.

[0009] Furthermore, the heating power is increased instantaneously by 5-15kW and then remains constant until the process is completed.

[0010] Furthermore, in S1, the first pulling speed is 50%-80% of the pulling speed of the equal diameter section, and the second pulling speed is 80%-90% of the first pulling speed.

[0011] Furthermore, in S1, the termination time of the single crystal is 50% of the total termination time, and the termination length of the single crystal is 1 / 3 of the total termination length.

[0012] Furthermore, in S2, the third pulling speed is the pulling speed of the constant diameter section, and the second crystal rotation and the second crucible rotation are 110%-120% of the first crystal rotation and the first crucible rotation.

[0013] Furthermore, in step S2, the termination time of the single crystal is 30% of the total termination time, and the termination length of the single crystal is 1 / 3 of the total termination length.

[0014] Furthermore, in S3, the fourth pulling speed is 130%-150% of the third pulling speed, and the third crystal rotation and the third crucible rotation are 105%-110% of the second crystal rotation and the second crucible rotation.

[0015] Furthermore, in S3, the termination time of the single crystal is 20% of the total termination time, and the termination length of the single crystal is 1 / 3 of the total termination length.

[0016] Furthermore, the second acceleration is greater than the first acceleration, and the fourth acceleration is greater than the third acceleration.

[0017] The advantages and positive effects of this invention are: by adopting the above technical solution, the breakage of single crystals is effectively reduced, the finishing time is shortened, the dislocations and cracks in single crystals are effectively controlled, and the yield of single crystal products is improved. Attached Figure Description

[0018] Figure 1 This is a front view of a tailing structure for reducing crack dislocations in a single-crystal silicon rod according to an embodiment of the present invention.

[0019] Figure 2 This is a bottom view of a tail structure for reducing crack dislocations in a single-crystal silicon rod according to an embodiment of the present invention.

[0020] In the picture:

[0021] 1. Upper section 2. Lower section 3. Equal diameter section

[0022] 4. Edge line 5. First curved surface 6. Second curved surface Detailed Implementation

[0023] This invention provides a finishing process for reducing dislocation cracks in single-crystal silicon rods. The embodiments of this invention are described below with reference to the accompanying drawings.

[0024] like Figure 1 and Figure 2 As shown, this embodiment of the invention provides a tailing structure for reducing dislocation cracks in a single-crystal silicon rod, comprising an integrally formed first segment 1 and a second segment 2. The maximum diameter of the first segment 1 is the same as the diameter of the crystal constant-diameter segment 3, and the maximum diameter of the second segment 2 is the same as the minimum diameter of the first segment 1. Edges 4 are provided on the surface of the second segment 2 along the single-crystal tailing length, and the edge lines 4 are arranged in pairs. The cross-section of the end of the second segment 2 away from the first segment 1 is a polygon. The polygon can be a regular polygon or a twisted polygon. The tailing length is 100-150mm, and the final tailing diameter is d, where 80mm < d < 120mm.

[0025] Specifically, the first segment 1 is a frustum structure. The end of the first segment 1 closest to the equal diameter section is the large diameter surface, and the other end is the small diameter surface.

[0026] Specifically, a single crystal typically has four growth ridges. Four growth ridges extend from the top of the second segment 2. Each growth ridge gradually splits into two paired ridges 4 along the end of the second segment away from the first segment, extending all the way to the tail of the single crystal. The cross-section of the end of the second segment 2 away from the first segment is octagonal. A first curved surface 5 is provided between the paired ridges 4, with the first curved surface 5 concave inwards. A second curved surface 6 is provided between two adjacent first curved surfaces, with the second curved surface 6 convex outwards.

[0027] Specifically, since the crystal plane (111) is more likely to grow as the supercooling increases compared to other crystal planes, as the four growth edges separate, the (111) plane gradually emerges between the separated growth edges, and the first curved surface 5 is the crystal plane (111).

[0028] Specifically, the diameter of the second segment 2 gradually decreases along the end length of the single crystal, shrinking to 1 / 3 of the diameter of the equal-diameter segment, and the length of the first segment 1 is twice the length of the second segment 2.

[0029] Example: A tailing structure for reducing dislocation cracks in a single-crystal silicon rod, with a total tailing length of 110mm, comprising an integrally formed first segment 1 and a second segment 2. The first segment 1 is a frustum structure, with its large-diameter surface as the upper end face and its small-diameter surface as the lower end face. The diameter of the upper end face is 245mm, the same as the diameter of the crystal constant-diameter segment 3. The maximum diameter of the second segment 2 is the same as the minimum diameter of the first segment 1. The diameter of the second segment 2 gradually decreases along the tailing length of the single crystal. The length of the first segment 1 is twice that of the second segment 2. The side of the second segment 2 has four pairs of ridges 4 along the tailing length of the single crystal, formed by the four growth ridges of the single crystal gradually splitting towards the tail of the single crystal. Each growth ridge is divided into two ridges 4. The tailing cross-section of the second segment 2 is a regular octagon. The pairs of ridges 4 are connected by a first curved surface 5, and adjacent first curved surfaces 5 are connected by a second curved surface 6. The first curved surface 5 is a crystal plane (111). The larger interplanar spacing and higher areal density of the crystal plane (111) are more conducive to the release of dislocations, and dislocations are less likely to invert. In this embodiment, the diameter d of the circumcircle of the final cross-section of the single crystal is 85 mm.

[0030] This closing structure, through the release of the crystal plane (111) in the second segment 2, is more conducive to the release of dislocations, prevents the generation of cracks, and improves the quality of single crystal.

[0031] This invention also provides a finishing process for reducing crack dislocations in single-crystal silicon rods, which includes the following steps after constant-diameter growth:

[0032] S1: Instantly increase the heating power, instantaneously decrease the pulling speed to the first pulling speed, and then decrease the pulling speed to the second pulling speed with the first acceleration. The crystal rotation and crucible rotation are equal in diameter and remain unchanged as the first crystal rotation and the first crucible rotation, and the single crystal diameter gradually shrinks.

[0033] Specifically, the heating power is instantaneously increased by 5-15 kW and then maintained at that level until the end of the finishing process. This increase in heating power causes the single crystal diameter to gradually shrink during the finishing process. At the start of the finishing process, the pulling speed is instantaneously reduced to 50%-80% of the constant-diameter pulling speed (the first pulling speed). The pulling speed then decreases at the first acceleration, reaching 80%-90% of the first pulling speed (the second pulling speed). During this stage, the pulling speed continues to decrease to reclaim the diameter and prevent the single crystal tail from detaching from the molten silicon surface. At this point, the crystal rotation and crucible rotation remain the same as in the constant-diameter section 3. The finishing shape in this stage is a frustum structure, with a finishing length of 1 / 3 of the total length and a finishing time of 50% of the total time.

[0034] S2: Increase the second pulling speed to the third pulling speed with the second acceleration, and increase the first crystal rotation and the first crucible rotation to the second crystal rotation and the second crucible rotation with the third acceleration, so that the single crystal diameter continues to shrink.

[0035] The second acceleration is greater than the first acceleration. When the pulling speed drops to the second pulling speed, it begins to increase to the third pulling speed at the second acceleration. The third pulling speed is the pulling speed for the constant diameter section. At this time, the first crystal rotation and the first crucible rotation continue to increase at the third acceleration to the second crystal rotation and the second crucible rotation. The second crystal rotation and the second crucible rotation are 110%-120% of the first crystal rotation and the first crucible rotation, increasing the undercooling and enabling the single crystal to be rapidly finished. The finishing shape in this stage is a frustum structure, the finishing length is 1 / 3 of the total length, and the finishing time is 30% of the total time.

[0036] The above two stages form the first segment 1 of the final shape. The first segment 1 is a frustum structure. The large diameter surface of the first segment 1 is the upper end surface, and the small diameter surface is the lower end surface. The diameter of the upper end surface is the diameter of the crystal equal diameter segment 3.

[0037] S3: Increase the third pulling speed to the fourth pulling speed with the second acceleration, and increase the second crystal rotation and the second crucible rotation to the third crystal rotation and the third crucible rotation with the fourth acceleration, until the end of the second segment 2.

[0038] The fourth pulling speed is 130%-150% of the third pulling speed, and the third crystal rotation and third crucible rotation are 105%-110% of the second crystal rotation and second crucible rotation. In stages S2 and S3, the heating power remains constant, while the crystal rotation and crucible rotation continue to increase with the fourth acceleration. The fourth acceleration is greater than the third acceleration, so the temperature decreases and the supercooling increases. Four growth ridges grow at the top of the second segment 2. As the crystal rotation and crucible rotation continue to increase and the pulling speed increases, the supercooling continues to increase, and one growth ridge splits into two ridges 4 until the end. The increase in supercooling makes the crystal face (111) easier to grow between the paired ridges 4 than other crystal faces. The first curved surface 5 between the two paired ridges 4 is the crystal face (111). At this time, the cross-section of the second segment 2 is octagonal. The crystal face (111) has a larger interplanar spacing and a larger surface density, which is more conducive to the release of dislocations to the single crystal surface and makes it less likely for dislocations to invert. The finishing stage accounts for 1 / 3 of the total length and takes 20% of the total time.

[0039] Example 1: Single crystal diameter is 245mm

[0040] S1: When the equal diameter section 3 is completed, the single crystal pulling speed is 85 mm / hr, the heating power is 68 kW, the crystal rotation is 10 r / min, and the crucible rotation is 10 r / min.

[0041] At the start of the finishing process, the crystal rotation and crucible rotation remain constant when the first crystal rotation and the first crucible rotation are of equal diameter. The power is instantaneously increased to 78kW and then remains constant until the finishing process is complete. The increase in heating power causes the single crystal diameter to gradually decrease during the finishing process. At the start of the finishing process, the pulling speed is instantaneously reduced to 51mm / hr as the first pulling speed, and then increased to a first acceleration of 0.004mm / min. 2The pulling speed is gradually reduced to 41 mm / hr for the second stage. During this stage, the pulling speed continues to decrease to reclaim the diameter and prevent the single crystal tail from detaching from the molten silicon surface. At this point, the crystal rotation, crucible rotation, and constant diameter section 3 are maintained. The tail shape in this stage is a frustum structure with a tail length of 36.7 mm and a tailing time of 0.7 h.

[0042] S2: with a second acceleration of 0.03 mm / min 2 Increase the pulling speed to the third pulling speed, i.e., the pulling speed of the constant diameter section is 85 mm / hr, with a third acceleration of 0.04 r / min. 2 Increase the crystal rotation and crucible rotation to 11 r / min for the second crystal rotation and 11 r / min for the second crucible rotation to increase the undercooling and enable rapid single crystal termination. After this stage, the termination length is 36.5 mm and the termination time is 0.4 h.

[0043] S3: with a second acceleration of 0.03 mm / min 2 Increase the pulling speed to the fourth pulling speed of 115 mm / hr, and accelerate the crystal rotation and crucible rotation at the fourth acceleration of 0.06 r / min. 2 The rotation speed is increased to 12 r / min for the third crystal rotation and 12 r / min for the third crucible rotation, ending at the end of the second stage 2. Four growth ridges emerge at the top of the second stage 2. As the crystal and crucible rotation speeds increase and the pulling speed rises, the undercooling increases, and one growth ridge splits into two ridges 4, until the end of the stage. The first curved surface 5 between the two ridges 4 is the crystal plane (111), which facilitates dislocation release to the single crystal surface. The cross-section of the second stage 2 is octagonal. The end length of this stage is 36.8 mm, and the end time is 0.28 h.

[0044] In this embodiment, the total length after finishing is 110mm, the total finishing time is 1.38h, and the final finishing diameter is 85mm.

[0045] Example 2: Single crystal diameter 350mm

[0046] S1: When the equal diameter section 3 is completed, the single crystal pulling speed is 75 mm / hr, the heating power is 64 kW, the crystal rotation is 10 r / min, and the crucible rotation is 10 r / min.

[0047] At the start of the finishing process, the crystal rotation and crucible rotation remain constant when the first crystal rotation and the first crucible rotation are of equal diameter. The power is instantaneously increased to 75kW and then remains constant until the finishing process is complete. The increase in heating power causes the single crystal diameter to gradually decrease during the finishing process. At the start of the finishing process, the pulling speed is instantaneously reduced to 45mm / hr as the first pulling speed, and then increased to a first acceleration of 0.003mm / min. 2The pulling speed is gradually reduced to 38 mm / hr for the second stage. During this stage, the pulling speed continues to decrease to reclaim the diameter and prevent the single crystal tail from detaching from the molten silicon surface. At this time, the crystal rotation, crucible rotation, and constant diameter section 3 are maintained. The tail shape in this stage is a frustum-shaped cone structure with a tail length of 46.7 mm and a tailing time of 0.65 h.

[0048] S2: with a second acceleration of 0.03 mm / min 2 Increase the pulling speed to the third pulling speed, i.e., the pulling speed of the constant diameter section is 75 mm / hr, with a third acceleration of 0.04 r / min. 2 The crystal rotation and crucible rotation were continuously increased to a second crystal rotation speed of 11 r / min and a second crucible rotation speed of 11 r / min to increase the undercooling and enable rapid single crystal termination. After this stage, the termination length was 46.5 mm and the termination time was 0.39 h.

[0049] S3: with a second acceleration of 0.03 mm / min 2 Increase the pulling speed to the fourth pulling speed of 100 mm / hr, and accelerate the crystal rotation and crucible rotation at the fourth acceleration of 0.06 r / min. 2 The rotation speed is increased to 12 r / min for the third crystal rotation and 12 r / min for the third crucible rotation, ending at the end of the second stage 2. Four growth ridges emerge at the top of the second stage 2. As the crystal and crucible rotation speeds increase and the pulling speed rises, the undercooling increases, and one growth ridge splits into two ridges 4, until the end of the stage. The first curved surface 5 between the two ridges 4 is the crystal plane (111), which facilitates dislocation release to the single crystal surface. The cross-section of the second stage 2 is octagonal. The end length of this stage is 46.8 mm, and the end time is 0.26 h.

[0050] In this embodiment, the total length after finishing is 140mm, the total finishing time is 1.3h, and the final finishing diameter is 115mm.

[0051] The advantages and positive effects of this invention are as follows:

[0052] 1. By increasing the pulling speed in conjunction with crystal rotation and crucible rotation, the undercooling is increased, which allows the second segment 2 of the tail structure to release the crystal plane (111), making it more conducive to the release of dislocations to the single crystal surface.

[0053] 2. In the later stages of the process, the power remains constant, while the continuous increase in crystal rotation and crucible rotation lowers the temperature, reduces the temperature difference between the center and edge of the single crystal, and prevents edge breakage.

[0054] 3. The continuous increase in pulling speed has improved the finishing rate and increased the finishing diameter, further shortening the finishing time.

[0055] The embodiments of the present invention have been described in detail above, but the content described is only a preferred embodiment of the present invention and should not be considered as limiting the scope of the present invention. All equivalent changes and improvements made in accordance with the scope of the present invention should still fall within the patent coverage of the present invention.

Claims

1. A finishing process for reducing dislocations in cracks of single-crystal silicon rods, characterized in that, After the isodiameter growth is completed, the following steps are included: S1: Instantly increase the heating power and keep it constant until the end. Instantly reduce the pulling speed to the first pulling speed, and then reduce the first pulling speed to the second pulling speed with the first acceleration. The crystal rotation and crucible rotation are crystal rotation and crucible rotation of equal diameter segments, and remain constant as the first crystal rotation and first crucible rotation. The single crystal diameter gradually shrinks. S2: The second pulling speed is increased to the third pulling speed by the second acceleration, the first crystal rotation and the first crucible rotation are increased to the second crystal rotation and the second crucible rotation by the third acceleration, and the diameter of the single crystal continues to shrink; S3: The third pulling speed is increased to the fourth pulling speed by the second acceleration, and the second crystal rotation and the second crucible rotation are increased to the third crystal rotation and the third crucible rotation by the fourth acceleration, and the process ends.

2. The finishing process for reducing crack dislocations in single-crystal silicon rods according to claim 1, characterized in that: The heating power is increased instantaneously by 5-15kW and then remains constant until the end of the process.

3. The finishing process for reducing crack dislocations in single-crystal silicon rods according to claim 2, characterized in that: In S1, the first pulling speed is 50%-80% of the pulling speed of the equal diameter section, and the second pulling speed is 80%-90% of the first pulling speed.

4. The finishing process for reducing crack dislocations in single-crystal silicon rods according to claim 3, characterized in that: In step S1, the termination time of the single crystal is 50% of the total termination time, and the termination length of the single crystal is 1 / 3 of the total termination length.

5. The finishing process for reducing crack dislocations in single-crystal silicon rods according to claim 2, characterized in that: In S2, the third pulling speed is the pulling speed of the constant diameter section, and the second crystal rotation and the second crucible rotation are 110%-120% of the first crystal rotation and the first crucible rotation.

6. The finishing process for reducing crack dislocations in single-crystal silicon rods according to claim 5, characterized in that: In step S2, the termination time of the single crystal is 30% of the total termination time, and the termination length of the single crystal is 1 / 3 of the total termination length.

7. The finishing process for reducing crack dislocations in single-crystal silicon rods according to claim 2, characterized in that: In S3, the fourth pulling speed is 130%-150% of the third pulling speed, and the third crystal rotation and the third crucible rotation are 105%-110% of the second crystal rotation and the second crucible rotation.

8. The finishing process for reducing crack dislocations in single-crystal silicon rods according to claim 7, characterized in that: In step S3, the single crystal's termination time is 20% of the total termination time, and the single crystal's termination length is 1 / 3 of the total termination length.

9. A finishing process for reducing crack dislocations in single-crystal silicon rods according to any one of claims 1-8, characterized in that: The second acceleration is greater than the first acceleration, and the fourth acceleration is greater than the third acceleration.

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