A process for controlling the axial resistivity of a single crystal

Abstract

The application provides a process method for controlling the axial resistivity of a single crystal. In the constant diameter stage, the pulling speed is reduced as the residual material weight in the crucible decreases; when the residual material weight in the crucible decreases to a critical weight, the pulling speed decreases to a minimum speed; as the residual material weight in the crucible continues to decrease, the pulling speed increases; and in the process of gradually decreasing the residual material weight in the crucible, the temperature of the thermal field gradually increases. The beneficial effect of the application is that the resistivity of the tail section of the single crystal is improved without affecting the head resistance of the single crystal, the length of the single crystal in the target resistance range is increased, the output of the single crystal per furnace is improved, and the competitiveness of the product is increased.

Description

Technical Field

[0001] This invention belongs to the field of Czochralski single crystal technology, and in particular relates to a process method for controlling the axial resistivity of single crystals. Background Technology

[0002] Competition within the industry is intensifying, leading to a growing demand for low-light-decay silicon wafers for monocrystalline silicon modules. Pulling monocrystalline silicon involves adding gallium alloys, which reduces light-decay in silicon monocrystalline silicon. Currently, the monocrystalline silicon industry primarily manufactures gallium-doped monocrystalline silicon. Because gallium's segregation coefficient is only 0.08, far lower than boron's 0.8 (a difference of 100 times), the solid-liquid alloy concentration difference during the pulling process of gallium-doped monocrystalline silicon is enormous. During the pulling process, the amount of gallium alloy entering the solid phase interface is much smaller than that in the liquid phase, with a ratio of only 0.08. Therefore, an alloy-rich region forms on the liquid phase side of the solid-liquid interface, unable to diffuse to the low-concentration region in time. The formation of this region results in the actual alloy concentration at the solid-liquid interface in the later stages of monocrystalline silicon pulling being higher than the theoretical calculation. This leads to an increase in the amount of alloy entering the monocrystalline silicon, causing the resistivity to drop to the target lower limit, making further crystal pulling impossible. Summary of the Invention

[0003] In view of the above problems, the present invention provides a process method for controlling the axial resistivity of a single crystal to solve the above or other problems existing in the prior art.

[0004] To solve the above-mentioned technical problems, the technical solution adopted by the present invention is: a process method for controlling the axial resistivity of single crystals, wherein, in the constant diameter stage, the crystal pulling speed is reduced as the weight of the remaining material in the crucible decreases;

[0005] When the weight of the remaining material in the crucible drops to the critical weight, the crystal pulling speed drops to the minimum speed;

[0006] As the weight of the remaining material in the crucible continues to decrease, the crystal pulling speed is increased;

[0007] As the weight of the remaining material in the crucible gradually decreases, the temperature of the thermal field gradually increases.

[0008] Furthermore, before the weight of the remaining material in the crucible drops to the critical weight, for every decrease in the weight of the remaining material by one unit of weight change, the crystal pulling speed decreases by one unit of speed change.

[0009] Furthermore, the weight change ranges from 1 to 30 kg, and the speed change ranges from 0 to 50 mm / hr.

[0010] Furthermore, as the weight of the remaining material in the crucible decreases to the critical weight, the change in weight gradually decreases while the change in velocity gradually increases.

[0011] Furthermore, after the weight of the remaining material in the crucible drops to the critical weight, the crystal pulling speed increases by a first speed change for every decrease in the weight of the remaining material by a first weight change.

[0012] Furthermore, the first weight change is 1-30 kg, and the first speed change is 0-50 mm / hr.

[0013] Furthermore, as the weight of the remaining material in the crucible continues to decrease, the first change in weight gradually increases, while the first change in velocity first increases and then decreases.

[0014] Furthermore, as the weight of the remaining material in the crucible gradually decreases, the temperature of the thermal field increases according to a certain temperature change, and the temperature change is the largest when the weight of the remaining material in the crucible drops to the critical weight.

[0015] Furthermore, the temperature change is 1-20℃ / hr, and the temperature change first increases and then decreases.

[0016] Furthermore, the critical weight is 80-130 kg.

[0017] Furthermore, when the crystal pulling speed is at its lowest, the first time is maintained, which is 2-4 hours.

[0018] By adopting the above technical solution, during the constant diameter stage, the single crystal pulling speed is reduced and the thermal zone temperature is increased before the remaining material weight in the crucible drops to the critical weight. When the remaining material weight reaches the critical weight, the single crystal pulling speed is at its lowest to ensure volatilization and reduce the alloy concentration in the remaining material. During this process, the single crystal still grows slowly in the silicon melt without edge breakage, and the diameter remains within the usable range. This increases the alloy volatilization rate, reduces the alloy concentration, and increases the single crystal pulling length. After volatilization, the single crystal growth rate is increased, and the thermal zone temperature is increased to ensure that the single crystal diameter remains within the required range. Without affecting the resistance at the head of the single crystal, the resistivity of the tail section of the single crystal is increased, and the pulling length of a single single crystal is increased within the target resistance range, thereby increasing the output of a single crystal per furnace and enhancing the competitiveness of the product. Detailed Implementation

[0019] The present invention will be further described below with reference to specific embodiments.

[0020] One embodiment of the present invention relates to a process method for controlling the axial resistivity of a single crystal, used for Czochralski single crystal growth, especially for use with alloys whose dopants have extremely low segregation coefficients, such as gallium-doped single crystals. In the constant diameter stage, as the weight of the remaining material in the crucible decreases, the crystal pulling speed and thermal field temperature are controlled. During this process, when the weight of the remaining material in the crucible decreases to a critical weight, the single crystal growth rate is reduced to a sufficiently low level to ensure that the alloy diffusion rate on the liquid phase side of the single crystal growth interface is greater than the alloy increase rate caused by the single crystal growth, thereby reducing the alloy concentration at the growth interface, increasing the resistivity of the tail section of the single crystal, and improving the raw material utilization rate of the single crystal.

[0021] A process for controlling the axial resistivity of a single crystal, applicable to gallium-doped single crystals, is disclosed. During the single crystal pulling process, by controlling the single crystal pulling speed, the alloy diffusion rate in the alloy-rich region of the solution is accelerated in the later stage of single crystal pulling, the alloy concentration on the liquid side of the solid-liquid interface in single crystal growth is reduced, a reasonable resistivity is ensured for the continued growth of gallium-doped single crystals, the length of gallium-doped single crystal segments is increased, and the output is increased.

[0022] The process for controlling the axial resistivity of single crystals involves reducing the crystal pulling speed during the constant diameter stage as the weight of the remaining material in the crucible decreases; during the constant diameter process, as the single crystal pulling progresses, the weight of the remaining material in the crucible gradually decreases, and the crystal pulling speed is gradually reduced as the weight of the remaining material gradually decreases, in order to control the rate of alloy increase caused by single crystal growth during the single crystal growth process.

[0023] When the weight of the remaining material in the crucible drops to the critical weight, the crystal pulling speed is reduced to the minimum speed. As the single crystal is pulled, the alloy enrichment on the liquid phase side of the solid-liquid interface caused by the single crystal growth becomes increasingly severe. When the weight of the remaining material in the crucible reaches the critical weight, the alloy concentration on the liquid phase side far exceeds the theoretical calculation value, resulting in the single crystal alloy content exceeding the specification requirement and the single crystal resistance being lower than the target value, making the pulled single crystal unqualified. Therefore, as the single crystal is pulled, the weight of the remaining material in the crucible gradually decreases. During this process, the crystal pulling speed is gradually reduced. When the weight of the remaining material in the crucible drops to the critical weight, the crystal pulling speed is reduced to the minimum speed, reducing the single crystal growth rate to the minimum. This ensures that the alloy diffusion rate on the liquid phase side of the single crystal growth interface is greater than the alloy increase rate caused by the single crystal growth, thereby reducing the alloy concentration at the growth interface and increasing the resistivity of the tail section of the single crystal.

[0024] As the weight of the remaining material in the crucible continues to decrease, the crystal pulling speed is increased to raise the growth rate of the single crystal to a normal level, ensuring that the resistance of the single crystal is raised back to the target range.

[0025] As the weight of the remaining material in the crucible gradually decreases, the temperature of the hot zone gradually increases. Before the weight of the remaining material in the crucible decreases to the critical weight, the temperature of the hot zone gradually increases as the weight of the remaining material decreases. During this process, the temperature of the hot zone is controlled and gradually increased to increase the internal temperature of the single crystal furnace, so as to ensure that the problem of uncontrolled single crystal diameter does not occur during the process of reducing the crystal pulling speed.

[0026] When the weight of the remaining material in the crucible is reduced to the critical weight, the temperature of the thermal field is relatively high, the temperature inside the single crystal furnace is maintained at a high level, and the single crystal pulling speed is at the minimum speed to ensure that the single crystal will not grow too large in diameter.

[0027] After the weight of the remaining material in the crucible is reduced to the critical weight, the temperature of the thermal field is gradually increased to ensure that the diameter of the single crystal remains within the required range after the single crystal pulling speed is increased.

[0028] The critical weight mentioned above refers to the weight of remaining material in the crucible when the alloy concentration on the liquid phase side of the solid-liquid interface during single-crystal growth is equal to or greater than the theoretically calculated value. This critical weight ranges from 80 to 130 kg and can be selected and set according to actual needs.

[0029] This process for controlling the axial resistivity of single crystals is applied in the constant diameter stage. Preferably, in the later stage of the constant diameter stage, this process accelerates the alloy diffusion rate in the alloy-rich region of the solution by controlling the single crystal pulling speed, thereby reducing the alloy concentration on the liquid phase side of the solid-liquid interface in single crystal growth and ensuring the resistivity of the single crystal. The later stage of the constant diameter stage is when the weight of the remaining material in the crucible is reduced to below 180 kg.

[0030] Specifically, as the weight of the remaining material in the crucible decreases, the crystal pulling speed is reduced. In this step, the crystal pulling speed can decrease linearly, in a curved manner, in stages, or in other ways, depending on the actual needs. No specific requirements are specified here. In this embodiment, before the weight of the remaining material in the crucible drops to the critical weight, the crystal pulling speed decreases by one unit for every unit decrease in the weight of the remaining material. That is, when the weight of the remaining material in the crucible decreases by one unit, the crystal pulling speed decreases by one unit. Then, when the weight of the remaining material in the crucible decreases by another unit, the crystal pulling speed decreases by another unit, and so on, until the weight of the remaining material in the crucible decreases to the critical weight.

[0031] The weight change ranges from 1 to 30 kg, and can be selected based on actual needs; no specific requirements are specified here. During the reduction of the remaining material weight in the crucible, the weight change can be a constant or a variable value, depending on actual needs; no specific requirements are specified here. In this embodiment, preferably, the weight change is a variable value. As the remaining material weight in the crucible gradually approaches the critical weight, the weight change gradually decreases. The closer the remaining material weight is to the critical weight, the smaller the weight change, and the smaller the reduction in the remaining material weight in the crucible. This ensures that when the remaining material weight in the crucible decreases to the critical weight, the crystal pulling speed drops to the minimum speed, and the crystal pulling speed rapidly decreases to the minimum speed within a short period of time.

[0032] The speed variation ranges from 0 to 50 mm / hr, and can be selected and set according to actual needs; no specific requirements are specified here. As the weight of the remaining material in the crucible decreases, the crystal pulling speed gradually decreases. This speed variation can be a constant or a variable value, depending on actual needs; no specific requirements are specified here. In this embodiment, preferably, the speed variation is a variable value. As the weight of the remaining material in the crucible gradually approaches the critical weight, the crystal pulling speed gradually decreases. The closer the remaining material weight is to the critical weight, the faster the crystal pulling speed decreases, and the larger the speed variation. This ensures that when the remaining material weight decreases to the critical weight, the crystal pulling speed drops to its minimum. When the remaining material weight is at the critical weight, crystal pulling is performed at the minimum speed, reducing the single crystal growth rate to a sufficiently low level to ensure that the alloy diffusion rate on the liquid phase side of the single crystal growth interface is greater than the alloy increase rate caused by single crystal growth.

[0033] As the weight of the remaining material in the crucible continues to decrease, the crystal pulling speed is increased. In this step, the crystal pulling speed can increase linearly, curvilinearly, in stages, or in other ways, depending on the actual needs; no specific requirements are specified here. In this embodiment, preferably, the crystal pulling speed increases in stages. After the weight of the remaining material in the crucible drops to a critical weight, the crystal pulling speed increases by one first change amount for every decrease in the remaining material weight. That is, when the remaining material weight decreases by one first change amount, the crystal pulling speed increases by one first change amount; then, when the remaining material weight decreases by another first change amount, the crystal pulling speed increases by another first change amount, and so on. For every decrease in the weight of the remaining material in the crucible by one first change amount, the crystal pulling speed increases by one first change amount.

[0034] The first weight change ranges from 1 to 30 kg. This first weight change can be a constant value or a variable value, and the choice is made according to actual needs. No specific requirements are specified here. In this embodiment, preferably, the first weight change is a variable value. The further the remaining weight is from the critical weight, the larger the value of the first weight change. The further the remaining weight in the crucible is from the critical weight, the faster the remaining weight in the crucible decreases.

[0035] The first speed change is 0-50 mm / hr. This first speed change can be a constant value or a variable value, and the choice can be made according to actual needs. No specific requirements are made here. In this embodiment, preferably, the first speed change is a variable value. The further the weight of the remaining material in the crucible is from the critical weight, the crystal pulling speed gradually increases, and the first speed change of the crystal pulling speed gradually decreases. That is, as the weight of the remaining material decreases, the crystal pulling speed increases rapidly in the early stage, increases rapidly in the later stage, and increases slowly in the later stage. The first speed change in the early stage is greater than the first speed change in the later stage. The first speed change gradually decreases, and the crystal pulling speed rapidly increases to the normal level in a short time.

[0036] As the weight of the remaining material in the crucible gradually decreases, the temperature of the thermal field increases according to a certain temperature change. The temperature change is greatest when the weight of the remaining material in the crucible drops to a critical weight. In other words, the thermal field temperature is constantly increasing as the weight of the remaining material in the crucible decreases, but the magnitude of the temperature change and the rate of increase vary at different stages. The temperature change initially increases and then decreases. Before the weight of the remaining material in the crucible drops to the critical weight, the temperature change gradually increases, and the closer the remaining material weight is to the critical weight, the greater the temperature change. After the weight of the remaining material drops to the critical weight, the temperature change decreases, and the closer the remaining material weight is to the critical weight, the smaller the temperature change. The less the remaining material weight is than the critical weight, the greater the temperature change. In other words, after the weight of the remaining material in the crucible drops to the critical weight, the temperature change first decreases and then increases. The thermal field temperature first increases slowly and then rapidly, ensuring that the diameter of the single crystal remains within the required range at a high crystal pulling speed.

[0037] The temperature change range is 1-20℃ / hr, and the selection should be made according to actual needs. No specific requirements are given here.

[0038] When growing a single crystal at the lowest crystal pulling speed, maintain the first time, which is 2-4 hours. The setting can be selected according to actual needs. When the weight of the remaining material is reduced to the critical weight, the crystal pulling speed is reduced to the lowest speed. At this time, the thermal field temperature is maintained at a relatively high temperature. The crystal pulling speed is maintained at the lowest speed and the first time is maintained to ensure that the single crystal does not become too large in diameter.

[0039] The following describes several specific embodiments.

[0040] Example 1

[0041] A process for controlling the axial resistivity of a single crystal involves reducing the crystal pulling speed and increasing the thermal field temperature during the constant diameter stage as the weight of the remaining material in the crucible decreases. For every increase in the weight of the remaining material by a certain amount, the crystal pulling speed decreases by a certain amount and the thermal field temperature increases by a certain amount.

[0042] When the weight of the remaining material in the crucible drops to a critical weight, the crystal pulling speed is reduced to a minimum speed; in this embodiment, the critical weight is 98 kg, the minimum speed is 20 mm / hr, and the minimum pulling speed is maintained for 3 hours.

[0043] As the weight of the remaining material in the crucible continues to decrease, the crystal pulling speed and the thermal field temperature are increased. For every decrease in the weight of the remaining material by a first weight change, the crystal pulling speed increases by a first speed change, and the thermal field temperature increases by a temperature change.

[0044] The relevant parameters are summarized in the table below:

[0045]

[0046]

[0047] Using the above process parameters, the resistivity of the pulled single crystal is:

[0048]

[0049] When single crystals are pulled using the above-mentioned process, the resistivity at the tail of the single crystal increases, and the length of the single crystal increases.

[0050] Example 2

[0051] A process for controlling the axial resistivity of a single crystal involves reducing the crystal pulling speed and increasing the thermal field temperature during the constant diameter stage as the weight of the remaining material in the crucible decreases. For every increase in the weight of the remaining material by a certain amount, the crystal pulling speed decreases by a certain amount and the thermal field temperature increases by a certain amount.

[0052] When the weight of the remaining material in the crucible drops to a critical weight, the crystal pulling speed is reduced to a minimum speed; in this embodiment, the critical weight is 90 kg, the minimum speed is 20 mm / hr, and the minimum speed is maintained for a first time of 4 hours.

[0053] As the weight of the remaining material in the crucible continues to decrease, the crystal pulling speed and the thermal field temperature are increased. For every decrease in the weight of the remaining material by a first weight change, the crystal pulling speed increases by a first speed change, and the thermal field temperature increases by a temperature change.

[0054] The relevant parameters are summarized in the table below:

[0055]

[0056]

[0057] Using the above process parameters, the resistivity of the pulled single crystal is:

[0058]

[0059] When single crystals are pulled using the above-mentioned process, the resistivity at the tail of the single crystal increases, and the length of the single crystal increases.

[0060] By adopting the above technical solution, during the constant diameter stage, the single crystal pulling speed is reduced and the thermal zone temperature is increased before the remaining material weight in the crucible drops to the critical weight. When the remaining material weight reaches the critical weight, the single crystal pulling speed is at its lowest to ensure volatilization and reduce the alloy concentration in the remaining material. During this process, the single crystal still grows slowly in the silicon melt without edge breakage, and the diameter remains within the usable range. This increases the alloy volatilization rate, reduces the alloy concentration, and increases the single crystal pulling length. After volatilization, the single crystal growth rate is increased, and the thermal zone temperature is increased to ensure that the single crystal diameter remains within the required range. Without affecting the resistance at the head of the single crystal, the resistivity of the tail section of the single crystal is increased, and the pulling length of a single single crystal is increased within the target resistance range, thereby increasing the output of a single crystal per furnace and enhancing the competitiveness of the product.

[0061] 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 within the scope of the present invention should still fall within the patent coverage of the present invention.

Claims

1. A process for controlling the axial resistivity of a single crystal, characterized in that: This method is applicable to gallium-doped single crystals. In the constant diameter stage, the crystal pulling speed is reduced as the weight of the remaining material in the crucible decreases. When the weight of the remaining material in the crucible drops to the critical weight, the crystal pulling speed drops to the minimum speed; As the weight of the remaining material in the crucible continues to decrease, the crystal pulling speed is increased; As the weight of the remaining material in the crucible gradually decreases, the temperature of the thermal field gradually increases.

2. The process method for controlling the axial resistivity of a single crystal according to claim 1, characterized in that: Before the weight of the remaining material in the crucible drops to the critical weight, the crystal pulling speed decreases by one speed change for every decrease in the weight of the remaining material.

3. The process method for controlling the axial resistivity of a single crystal according to claim 2, characterized in that: The weight change is 1-30 kg, and the speed change is 0-50 mm / hr.

4. The process method for controlling the axial resistivity of a single crystal according to claim 3, characterized in that: As the weight of the remaining material in the crucible decreases to the critical weight, the change in weight gradually decreases, while the change in speed gradually increases.

5. The process method for controlling the axial resistivity of a single crystal according to claim 2, 3, or 4, characterized in that: After the weight of the remaining material in the crucible drops to the critical weight, the crystal pulling speed increases by a first speed change for every decrease in the weight of the remaining material by a first weight change.

6. The process method for controlling the axial resistivity of a single crystal according to claim 5, characterized in that: The first weight change is 1-30 kg, and the first speed change is 0-50 mm / hr.

7. The process method for controlling the axial resistivity of a single crystal according to claim 6, characterized in that: As the weight of the remaining material in the crucible continues to decrease, the first change in weight gradually increases, while the first change in velocity first increases and then decreases.

8. The process method for controlling the axial resistivity of a single crystal according to any one of claims 1-4, 6 and 7, characterized in that: As the weight of the remaining material in the crucible gradually decreases, the temperature of the thermal field increases according to a certain temperature change, and the temperature change is the largest when the weight of the remaining material in the crucible drops to a critical weight.

9. The process method for controlling the axial resistivity of a single crystal according to claim 6, characterized in that: The temperature change is 1-20℃ / hr, and the temperature change first increases and then decreases.

10. The process method for controlling the axial resistivity of a single crystal according to claim 1, characterized in that: The critical weight is 80-130 kg.

11. The process method for controlling the axial resistivity of a single crystal according to claim 9, characterized in that: Maintain the crystal pulling speed at its lowest setting for a first time, which is 2-4 hours.

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