A necking method for reducing the oxidation at the bottom of single crystal silicon based on the Czochralski method

Abstract

The present invention discloses a necking method for reducing the oxidation of the bottom of single crystal silicon based on the Czochralski method, which includes loading materials, melting materials, seeding, shoulder formation, constant diameter growth, tailing and furnace shutdown. When a wire break occurs during the constant diameter operation, the following steps are included: S1. Open the pump opening of the vacuum pump to 100% for crystal pulling; S2. On the basis of step S1, set the flow rate of argon to more than 120 sL / min; S3. On the basis of step S2, use a speed of 10 - 160 mm / min to lower the position of the crucible; S4. On the basis of step S3, set the flow rate of argon to 100 sL / min; S5. On the basis of step S4, set the speed of lowering the position of the crucible to 280 mm / min; S6. After completing the necking, perform tailing and furnace shutdown. By improving the sequence of the necking method and optimizing the crystal pulling speed and necking speed during necking, and at the same time, each step is carried out simultaneously in sequence, the occurrence of oxidation of the bottom single crystal silicon is effectively reduced, the quality of the single crystal silicon recycled material is improved, and the cleaning cost is saved.

Description

Technical Field

[0001] This application relates to the technical field of single crystal silicon manufacturing production, and specifically relates to a breaking method for reducing the bottom oxidation of single crystal silicon based on the Czochralski method. Background Art

[0002] Solar energy is an ideal clean energy source. Developing the photovoltaic industry is of great significance for adjusting the energy structure, promoting the transformation of energy production and consumption methods, and promoting the construction of ecological civilization. In recent years, with the continuous decline of the cost of photovoltaic power generation, the photovoltaic industry has a broader market space. Low-cost and high-quality single crystal silicon wafers are the core competitiveness of single crystal silicon manufacturing enterprises. To further reduce costs, the industry has taken various cost reduction measures.

[0003] Currently, the single crystal silicon industry mostly uses the Czochralski method for crystal pulling. The Czochralski method includes loading materials, melting materials, seeding, necking down, constant diameter, ending, and furnace shutdown. During the constant diameter operation, a wire break situation may occur. A wire break means that due to dislocation accumulation, the crystal changes from a single crystal state to a polycrystalline state, and the manifestation is that the single crystal edge line disappears. When the conventional process performs a breaking operation in this step, the accumulation of bottom oxides is serious, presenting as yellow powder accumulating at the bottom of the single crystal silicon ingot. The oxidized bottom brings great trouble to the subsequent cleaning of the single crystal silicon, reduces the grade quality of the recycled materials, leads to an increase in cleaning work, an increase in the chemicals and labor costs required, and an increase in production costs and other problems. Summary of the Invention

[0004] The purpose of the present invention is to provide a breaking method for reducing the bottom oxidation of single crystal silicon based on the Czochralski method. When a wire break occurs during the constant diameter of the Czochralski method, a breaking operation is performed. By improving the crystal pulling speed, increasing the argon gas flow rate, reducing the speed of the crucible position and the breaking speed, and when performing the breaking operation, each step is carried out simultaneously in sequence, solving the oxidation existing at the bottom of the single crystal ingot, as well as the problems of the decline in the quality of recycled materials caused by oxidation and the increase in cleaning and labor costs.

[0005] To solve the above technical problems, the present invention adopts the following solutions:

[0006] A breaking method for reducing the bottom oxidation of single crystal silicon based on the Czochralski method, including loading materials, melting materials, seeding, necking down, constant diameter, ending, and furnace shutdown. When a wire break occurs during the constant diameter operation, it includes the following steps:

[0007] S1. Open the pump opening of the vacuum pump to 100% for crystal pulling;

[0008] S2. On the basis of step S1, set the flow rate of argon gas to more than 120 sL / min;

[0009] S3. On the basis of step S2, use a speed of 10 - 160 mm / min to reduce the position of the crucible;

[0010] S4. Based on the step S3, set the flow rate of argon to 100 sL / min;

[0011] S5. Based on the step S4, set the speed of lowering the crucible position to 280 mm / min;

[0012] S6. After completing the breaking, perform the finishing and furnace shutdown.

[0013] Preferably, in the steps S1 to S5, the pump opening of the vacuum pump is maintained at 100%, the crystal pulling speed in the step S1 is 1.65 mm / min, and the duration is 0.5 - 5 min.

[0014] Preferably, the duration of the step S1 is 1 min.

[0015] Preferably, in the step S2, the flow rate of argon is 120 sL / min, the crystal pulling speed is 1.65 mm / min, and the duration is 0.5 - 5 min.

[0016] Preferably, the duration of the step S2 is 1.5 min.

[0017] Preferably, in the step S3, the speed of lowering the crucible position is 150 mm / min, the crystal pulling speed is 2 mm / min, and the duration is 2 - 15 min.

[0018] Preferably, the speed of lowering the crucible position is 150 mm / min.

[0019] Preferably, in the step S4, perform the breaking, the breaking speed is 4 - 5 mm / min, and the duration is 15 - 30 min.

[0020] Preferably, in the step S5, the speed of lowering the crucible position is 280 mm / min, the breaking speed is 5 - 6 mm / min, and the duration is 30 - 60 min.

[0021] The beneficial effects of the present invention are as follows: By improving the sequence of the breaking method to open the vacuum pump to 100%, increasing the argon flow rate to 120 sL / min, reducing the speed of lowering the crucible position to 150 mm / min, reducing the argon flow rate to 100 sL / min, increasing the speed of the crucible position to 280 mm / min, and optimizing the crystal pulling speed and breaking speed during breaking, and at the same time, each step is carried out simultaneously, the occurrence of oxidation of the bottom single crystal silicon is effectively reduced, the quality of the single crystal silicon recycled material is improved, and the cleaning cost is saved. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 is the process flow chart of the present invention;

[0023] Figure 2 is the working schematic diagram of the present invention;

[0024] Figure 3 is the working schematic diagram of the single-crystal silicon ingot of the present invention detaching from the liquid surface;

[0025] Figure 4 is the bottom part of the finished single-crystal silicon ingot prepared by the present invention;

[0026] Figure 5 is the bottom part of the finished single-crystal silicon ingot prepared by the conventional process. The part shown by the circle (a) in the figure is the yellow area presented during oxidation.

[0027] Reference numerals: 10 - single-crystal silicon ingot, 12 - crucible, 14 - argon, 16 - vacuum pump, 18 - seed crystal, 20 - crucible bracket. Detailed implementation manners

[0028] In order to more clearly present the purpose, technical solution and advantages of the present invention, the following will further illustrate the present application in combination with embodiments.

[0029] Embodiment

[0030] The embodiment of the present invention is a comparison between the lift-off method of the present invention and the conventional lift-off method.

[0031] A lift-off method for reducing the oxidation of the bottom of single-crystal silicon based on the Czochralski method. The Czochralski method is also known as the Cz method. The characteristic of the Czochralski method is that in a straight-cylindrical thermal system, the polysilicon contained in a high-purity quartz crucible is melted by graphite resistance heating, and then the seed crystal is inserted into the melt surface for welding. The rotating seed crystal is lowered to contact the melt by infiltration and then gradually lifted. The crystal pulling is completed through steps such as necking, necking down, shoulder forming, equal-diameter control, and tailing. When a wire break occurs during the equal-diameter operation, the lift-off method of the present invention is used to reduce the oxidation of the bottom of single-crystal silicon. As Figure 1 shown, it mainly includes the following steps:

[0032] 1) Open the pump opening of the vacuum pump 16 to 100% for crystal pulling. At this time, the crystal pulling speed is 1.65 mm / min, and the duration of this step is 1 min;

[0033] 2) On the basis of step 1, set the flow rate of argon 14 to 120 sL / min. At this time, the crystal pulling speed is 1.65 mm / min, and the duration of this step is 1.5 min;

[0034] 3) On the basis of step 2, lower the position of the crucible 12 at a speed of 150 mm / min. At this time, the crystal pulling speed is 2 mm / min, and the duration of this step is 2 - 15 min;

[0035] 4) On the basis of Step 3, set the flow rate of argon gas 14 to 100 sL / min. At this time, the lifting and breaking speed is 4 - 5 mm / min, and the duration of this step is 15 - 30 min;

[0036] 5) On the basis of Step 4, set the speed of lowering the position of crucible 12 to 280 mm / min, and the lifting and breaking speed is 5 - 6 mm / min. The duration of this step is 30 - 60 min;

[0037] 6) After the lifting and breaking in Step 5 is completed, carry out the finishing work and furnace shutdown.

[0038] Furthermore, in Steps 1 to 5, the pump opening of vacuum pump 16 is maintained at 100%.

[0039] Furthermore, the purpose of Step 1 is to melt the oxide on the silicon liquid surface, fully open the vacuum pump 16, and quickly remove the excess oxide through the suction of the vacuum pump 16.

[0040] Furthermore, on the basis of Step 1, in Step 2, argon gas 14 is introduced, and at the same time, the flow rate of argon gas 14 is set to be above 120 sL / min, preferably 120 sL / min. The role of argon gas 14 during single crystal growth is to remove impurities, including the oxides generated during single crystal growth. Increasing the flow rate of argon gas 14 can further enhance the ability of argon gas 14 to remove oxides, and further reduce the oxides on the single crystal liquid surface, as Figure 2 shown. Since when the amount of argon gas is 120 sL / min, the oxides on the single crystal liquid surface have already been reduced, increasing the flow rate of argon gas will increase the manufacturing cost. Therefore, when ensuring the reduction of oxides on the single crystal liquid surface, argon gas with a flow rate of 120 sL / min is preferably used to save processing costs.

[0041] Furthermore, on the basis of Step 2, lower the position of crucible 12, and at the same time use a lower speed to lower it. A certain lifting speed during lifting and breaking will not cause the single crystal to directly break away from the liquid surface, while lowering the crucible 12 can change the thermal field state of single crystal growth, that is, lowering the position of crucible 12 can cause the single crystal to break away from the liquid surface more quickly. By controlling the speed at which the position of crucible 12 drops during single crystal growth, the speed at which the single crystal breaks away from the liquid surface can be further reduced. This step reduces the accumulation of oxides at the bottom of the single crystal, as Figure 3 shown, and by slowly lowering the position of crucible 12, the single crystal silicon rod 10 is separated from the liquid surface.

[0042] Furthermore, on the basis of Step 3, restore the flow rate of argon gas 14 to the normal flow rate, that is, 100 sL / min. The interface between the single crystal and the molten silicon has been completely separated and has risen for a period of time. Oxides can no longer accumulate at the bottom of the single crystal, and the flow rate of argon gas 14 gradually returns to the normal flow rate.

[0043] Further, based on step 4, the speed of lowering the pot position of the crucible 12 is set to a normal speed of 280 mm / min. At this time, there is no oxide on the bottom of the single crystal. The lowering speed of the pot position of the crucible 12 is increased so that the crucible 12 reaches a safe position for lifting and breaking.

[0044] Test example

[0045] The finished single crystal silicon ingot prepared by the cutting method of the present invention is as follows: Figure 4 The bottom part of the finished single crystal silicon ingot is shown.

[0046] Comparative Example

[0047] The comparative example of this embodiment is a conventional process when a wire break occurs in the step of manufacturing single crystal silicon equal diameter by Czochralski method, including the following steps:

[0048] 1) Open the vacuum pump to 100%, set the argon flow rate to 100sL / min, lower the crucible to 280mm / min, and lift the crucible to 4-5mm / min for 0-20min;

[0049] 2) Based on step 1, the lifting and breaking speed is increased to 5-6 mm / min, and the duration is 30-60 min;

[0050] 3) After the lifting and breaking is completed, the finishing and furnace shutdown are carried out.

[0051] Figure 5 It is the bottom part of the finished single crystal silicon ingot produced by conventional technology.

[0052] from Figure 4 and Figure 5 By comparison, it can be concluded that the bottom of the finished single crystal silicon ingot produced by the present invention has no yellow powder attached, and the bottom shows the color of the single crystal silicon itself. Figure 5 The bottom of the finished single crystal silicon ingot produced by the conventional process has a large area of ​​yellow attachment ( Figure 5 The area marked in the middle circle a) indicates that the conventional process produces a large amount of oxidation during the preparation of single crystal silicon, resulting in yellowing of the bottom, while the preparation process of the present invention greatly reduces the occurrence of bottom oxidation, ensures the quality of the single crystal, and reduces the cleaning cost caused by the oxidation of the bottom of the single crystal silicon rod.

[0053] The above description is only a preferred embodiment of the present invention and does not limit the present invention in any form. According to the technical essence of the present invention, within the spirit and principles of the present invention, any simple modification, equivalent replacement and improvement made to the above embodiment still falls within the protection scope of the technical solution of the present invention.

Claims

1. A necking method for reducing the oxidation at the bottom of single crystal silicon based on the Czochralski method, including charging, melting, seeding, necking down, constant diameter growth, tailing and furnace shutdown, characterized in that, When a wire break occurs during the equal-diameter operation, the following steps are included: S1. Open the pump opening of the vacuum pump (16) to 100% for crystal pulling; S2. On the basis of step S1, set the flow rate of argon (14) to be above 120 sL / min; S3. On the basis of step S2, lower the crucible position of the crucible (12) at a speed of 10 - 160 mm / min, and the speed of lowering the crucible position of the crucible (12) is 150 mm / min; S4. On the basis of step S3, set the flow rate of argon (14) to 100 sL / min for wire break lifting, the wire break lifting speed is 4 - 5 mm / min, and the duration is 15 - 30 min; S5. On the basis of step S4, set the speed of lowering the crucible position of the crucible (12) to 280 mm / min, the wire break lifting speed is 5 - 6 mm / min, and the duration is 30 - 60 min; S6. After completing the wire break lifting, perform the finishing work and furnace shutdown.

2. The necking method for reducing the oxidation at the bottom of a single crystal silicon based on the Czochralski method according to claim 1, characterized in that, In steps S1 to S5, the pump opening of the vacuum pump (16) remains at 100%, the crystal pulling speed in step S1 is 1.65 mm / min, and the duration is 0.5 - 5 min.

3. A necking method for reducing the oxidation at the bottom of a single crystal silicon based on the Czochralski method according to claim 2, characterized in that, The duration of step S1 is 1 min.

4. A necking method for reducing the oxidation of the bottom of a single crystal silicon based on the Czochralski method according to claim 2, characterized in that In step S2, the flow rate of argon (14) is 120 sL / min, the crystal pulling speed is 1.65 mm / min, and the duration is 0.5 - 5 min.

5. A necking method for reducing the oxidation at the bottom of a single crystal silicon based on the Czochralski method according to claim 4, characterized in that, The duration of step S2 is 1.5 min.

6. A necking method for reducing the oxidation at the bottom of a single crystal silicon based on the Czochralski method according to claim 4, characterized in that, In step S3, the crystal pulling speed is 2 mm / min, and the duration is 2 - 15 min.

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