N-type single crystal rod and preparation method thereof

Abstract

The invention provides an N-type single crystal rod and a preparation method thereof, and the preparation method comprises the following steps: in temperature regulation, seeding, shouldering and shouldering, a constant crucible is changed into 5 crucible rotation, the constant furnace pressure is 11Torr, and the constant argon flow is 100slpm; entering a 0-300mm stage of an equal-diameter head part, lifting the crucible by 10mm / h constantly to jack the crucible, and after an equal-diameter liquid opening distance is reached, increasing the pulling speed and rotating the crucible; s3, at the stage of equal diameter of 300-500 mm, the crucible rotation is maintained, and the pulling speed is increased again; when the diameter is equal to 500-2000mm, reducing the crucible rotation, and cooling again; at the stage of equal diameter of 2000-3000 mm, the furnace pressure is reduced, and the argon flow is increased; after the diameter is equal to 3000mm, the pulling speed is reduced; and raising the temperature when the diameter is 4500mm, and completing crystal pulling to obtain the N-type single crystal rod. The oxygen content in the crystal bar is low, and the resistivity concentration ratio is improved; the resistivity ratio of the head to the tail is reduced, and the purposes of reducing cost and increasing efficiency are achieved.

Description

Technical Field

[0001] The invention belongs to the technical field of photovoltaic manufacturing, and in particular relates to an N-type single crystal rod and a preparation method thereof. Background Art

[0002] Solar power generation plays a significant role in promoting energy transformation, protecting the ecological environment, and mitigating climate change. Crystalline silicon cells are already in a period of technical iteration where N-type cells take over P-type cells for a new generation of battery technology. The theoretical efficiency limits of N-type TOPCon and HJT cells are 28.7% and 27.5%, respectively. In addition, N-type single crystals also have the advantages of no light decay, good weak light effect, and low temperature coefficient, making them the most promising battery materials in the future. However, N-type cells have relatively high requirements for silicon wafer quality, especially stable photoelectric conversion efficiency requires high-quality single crystal silicon wafers as support. At the manufacturing end, the quality of N-type silicon wafers can be effectively improved by reducing the oxygen content of silicon wafers, increasing minority carrier lifetime, reducing carbon content, and increasing resistivity concentration.

[0003] At present, the mainstream process of N-type cells is the Topcon process. The oxygen content of N-type silicon wafers affects the conversion efficiency of Topcon cells to a certain extent. At high temperatures, the interstitial oxygen in the silicon wafer reaches an oversaturated state and precipitates after heat treatment (concentric circles), which reduces the efficiency of the cell. Therefore, in order to ensure the high efficiency of the cell, the oxygen content in the silicon wafer must be strictly controlled. Summary of the invention

[0004] In view of this, an object of the present invention is to provide an N-type single crystal rod and a preparation method thereof, which can improve the quality of the N-type single crystal rod, reduce the oxygen content of the crystal rod, and improve the resistivity concentration.

[0005] The present invention provides a method for preparing an N-type single crystal rod, comprising the following steps:

[0006] S1: During temperature adjustment, seeding, shoulder release and shoulder rotation, the constant crucible rotation is 5 crucible rotations, the constant furnace pressure is 11 Torr and the constant argon flow rate is 100 slpm;

[0007] S2: Entering the stage of equal diameter head 0-300mm, the crucible is lifted at a constant crucible height of 10mm / h to push the crucible. After reaching the equal diameter liquid mouth distance, the pulling speed and crucible rotation are increased;

[0008] S3: At the stage of equal diameter of 300-500mm, keep the crucible rotating and increase the pulling speed again;

[0009] S4: In the stage of equal diameter 500-2000mm, the crucible rotation is reduced and the temperature is lowered again;

[0010] S5: In the stage of equal diameter 2000-3000mm, reduce the furnace pressure and increase the argon flow rate;

[0011] S6: After the equal diameter reaches 3000mm, the pulling speed is reduced; when the equal diameter reaches 4500mm, the temperature is increased to complete the crystal pulling and obtain an N-type single crystal rod.

[0012] Preferably, in step S2, the pulling speed is increased to 95 mm / h;

[0013] Lift the crucible and turn it to 6-7 crucible turns.

[0014] Preferably, in step S3, the pulling speed is increased again to 108 mm / h.

[0015] Preferably, in step S4, the temperature is lowered again by reducing the power;

[0016] When the diameter reaches 2000mm, the power reduction is 0.5-1.0kW.

[0017] Preferably, in step S5, the furnace pressure is reduced to 9 Torr and the argon flow rate is increased to 120 slpm.

[0018] Preferably, in step S6, the temperature is increased by increasing the power;

[0019] When the diameter reaches 4500mm, the power increase is 1.5kW.

[0020] Preferably, in step S3, the furnace pressure is 11 Torr and the argon gas is 100 slpm;

[0021] In step S4, the furnace pressure is 11 Torr and the argon gas is 100 slpm.

[0022] Preferably, in step S2, the distance between the equal-diameter liquid ports is 20 to 22 mm.

[0023] Preferably, in step S4, the crucible speed is lowered to 5 crucible speeds.

[0024] The present invention provides an N-type single crystal rod, which is prepared by the preparation method described in the above technical solution;

[0025] The head / tail resistivity ratio of the N-type single crystal rod is less than 1.5; and the oxygen content of the tail is less than 10 ppm.

[0026] The invention provides a method for preparing an N-type single crystal rod, comprising the following steps: S1: in temperature adjustment, crystal seeding, shoulder release and shoulder rotation, the constant crucible rotation is 5 crucible rotations, the constant furnace pressure is 11 Torr and the constant argon flow rate is 100 slpm; S2: when entering the stage of equal diameter head of 0-300 mm, the crucible is lifted by a constant crucible of 10 mm / h to push the crucible, and after reaching the equal diameter liquid mouth distance, the pulling speed and the crucible rotation are increased; S3: in the stage of equal diameter of 300-500 mm, the crucible rotation is maintained and the pulling speed is increased again; S4: in the stage of equal diameter of 500-2000 mm, the crucible rotation is reduced and the temperature is reduced again; S5: in the stage of equal diameter of 2000-3000 mm, the furnace pressure is reduced and the argon flow rate is increased; S6: after the equal diameter is 3000 mm, the pulling speed is reduced; when the temperature is increased to the process of equal diameter of 4500 mm, the crystal pulling is completed to obtain the N-type single crystal rod. This method reduces the oxygen content in the obtained crystal rod and improves the resistivity concentration by comprehensively controlling parameters such as crucible rotation, furnace pressure and argon gas flow rate; it reduces the head-tail resistivity ratio and achieves the purpose of reducing costs and increasing efficiency. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 This is a diagram showing the oxygen content distribution of a crystal rod prepared by conventional process in Comparative Example 1 of the present invention;

[0028] Figure 2 This is the oxygen content distribution diagram of the crystal rod prepared in Example 1 of the present invention. DETAILED DESCRIPTION

[0029] The present invention provides a method for preparing an N-type single crystal rod, comprising the following steps:

[0030] S1: During temperature adjustment, seeding, shoulder release and shoulder rotation, the constant crucible rotation is 5 crucible rotations, the constant furnace pressure is 11 Torr and the constant argon flow rate is 100 slpm;

[0031] S2: Entering the stage of equal diameter head 0-300mm, the crucible is lifted at a constant crucible height of 10mm / h to push the crucible. After reaching the equal diameter liquid mouth distance, the pulling speed and crucible rotation are increased;

[0032] S3: At the stage of equal diameter of 300-500mm, keep the crucible rotating and increase the pulling speed again;

[0033] S4: In the stage of equal diameter 500-2000mm, the crucible rotation is reduced and the temperature is lowered again;

[0034] S5: In the stage of equal diameter 2000-3000mm, reduce the furnace pressure and increase the argon flow rate;

[0035] S6: After the equal diameter reaches 3000mm, the pulling speed is reduced; when the equal diameter reaches 4500mm, the temperature is increased to complete the crystal pulling and obtain an N-type single crystal rod.

[0036] In order to ensure the survival rate during the crystal pulling process, the present invention maintains a constant crucible rotation, a constant furnace pressure and a constant argon flow rate during temperature adjustment, crystal seeding, shoulder release and shoulder rotation; that is, the constant crucible rotation is 5 crucible rotations, the constant furnace pressure is 11 Torr and the constant argon flow rate is 100 slpm.

[0037] The present invention enters the stage of equal-diameter head 0-300mm, adopts a constant crucible lift of 10mm / h to push the crucible, and after reaching the equal-diameter liquid mouth distance, increases the pulling speed and crucible rotation. The present invention reduces the liquid mouth distance to a suitable distance as soon as possible, so that the crystallization latent heat released by the melt being converted into crystals can be taken away in time; the liquid mouth distance, that is, the distance from the liquid surface to the lower mouth of the guide tube, that is, the equal-diameter liquid mouth distance, is preferably reduced from 35mm to 20-22mm. During the process of pushing the crucible, the system needs to gradually increase the pulling speed, preferably to 95mm / h, and more preferably from 78mm / h to 95mm / h. The present invention requires cooling to coordinate with increasing the pulling speed to keep the diameter of the crystal rod constant; the present invention preferably achieves cooling by increasing the crucible rotation, and the crucible rotation is preferably increased from 5 crucible rotations at the head to 6-7 crucible rotations, and more preferably to 7 crucible rotations.

[0038] The present invention enters the stage of equal diameter of 300-500mm, maintains the crucible rotation, and increases the pulling speed again. The present invention enters the stage of equal diameter of 300-500mm. Due to the rapid decrease of the distance between the liquid mouth of the fast top crucible, the oxygen content often reaches the lowest point at this stage. The crucible rotation is maintained, preferably maintained at 7 crucible rotations, the furnace pressure is still 11Torr, and the argon gas is 100slpm. The equal diameter pulling speed is slowly increased to 108mm / h, reaching the maximum pulling speed. The pulling rate is related to the actual crystal rod length.

[0039] The present invention enters the stage of equal diameter of 500-2000mm, reduces the crucible rotation, and cools down again. According to the longitudinal distribution of oxygen content in the crystal in the early stage, the oxygen content will rise linearly after the equal diameter of 500mm. For this reason, the present invention slowly reduces the crucible rotation from 7 crucible rotations to 5 crucible rotations to reduce the generation of oxygen. In order to ensure the stable progress of crystal pulling, the variables are minimized as much as possible, and the furnace pressure and argon flow rate are maintained constant, that is, the furnace pressure is 11Torr and the argon is 100slpm. The crucible rotation is reduced, and the forced heat dissipation effect is reduced. In order to maintain the diameter of the crystal rod and the pulling speed, the main power is adjusted for forced cooling. When the equal diameter node is 2000mm, the power is cumulatively reduced by 0.5-1.0kw.

[0040] The present invention enters the stage of equal diameter of 2000-3000mm, reduces the furnace pressure and increases the argon flow rate. The present invention maintains the crucible rotation at 5 crucible rotations in the stage of equal diameter of 2000-3000mm; in order to prevent the oxygen content from continuing to increase, the furnace pressure and argon flow rate are adjusted at this time to promote the volatilization of oxygen; the furnace pressure is preferably slowly reduced to 9Torr, and the argon flow rate is slowly increased from 100slpm to 120slpm. Due to the reduction of furnace pressure and the increase of argon flow rate, the melt is cool as a whole, and there is no need to adjust the power for forced cooling at this time.

[0041] After the equal diameter reaches 3000mm, the pulling speed is reduced; the temperature is increased during the process of equal diameter reaching 4500mm, and the crystal pulling is completed to obtain an N-type single crystal rod. After the equal diameter reaches 3000mm, there is less residual material in the crucible, resulting in a lower melt temperature; and in the later stage of crystal pulling, the equal diameter pulling speed is slowly reduced to 102mm / h to prevent dislocation increment and improve the crystallization rate. At this time, the crucible rotation is still 5 crucible rotations, the furnace pressure is still 9Torr, the argon gas flow rate is 120slpm, the heater power is adjusted to increase the temperature, and the cumulative increase is 1.5kw at the end of the equal diameter of about 4500mm, and the crystal pulling is completed.

[0042] The present invention can achieve a better improvement effect only through process improvement, avoiding the cost problem caused by equipment improvement and the problem of unstable crystal pulling caused by thermal field transformation. The process provided by the present invention achieves the purpose of improving quality; while reducing the oxygen content, the concentration of resistivity distribution is increased, which has a great effect on improving the efficiency of the back-end battery process.

[0043] The present invention prepares an N-type single crystal rod, and adds a group V element to the melt. Taking a phosphorus alloy as an example, after an equal diameter of 2000 mm, the reduction of the furnace pressure and the increase of the argon gas flow rate promote the volatilization of the impurity elements in the melt; due to the segregation effect of the phosphorus element, as the crystal pulling proceeds, the impurity concentration will become higher and higher, resulting in a sharp decrease in resistivity; the volatilization of the phosphorus element can be promoted through the volatilization of low-pressure and large-flow argon gas, the tail resistivity of the crystal rod can be increased, the head and tail resistivity ratio of the crystal rod can be reduced, and the resistivity concentration can be improved.

[0044] The present invention provides an N-type single crystal rod, which is prepared by the preparation method described in the above technical solution;

[0045] The head / tail resistivity ratio of the N-type single crystal rod is less than 1.5; and the oxygen content of the tail is less than 10 ppm.

[0046] In the present invention, the tail is defined as occupying more than 80% of the rod length or feed amount.

[0047] The method for testing the oxygen content in the crystal rod prepared by the present invention is the Fourier infrared transform method; the resistivity test adopts the tester BCT-400.

[0048] In order to further illustrate the present invention, an N-type single crystal rod and a preparation method thereof provided by the present invention are described in detail below in combination with embodiments, but they should not be construed as limiting the protection scope of the present invention.

[0049] Comparative Example

[0050] General implementation steps:

[0051] S1: During temperature adjustment, seeding, shoulder release and shoulder rotation, the constant crucible rotation is 5 crucible rotations, the constant furnace pressure is 11 Torr and the constant argon flow rate is 100 slpm;

[0052] S2: Entering the stage of equal diameter head 0-300mm, the crucible is lifted at a constant crucible height of 10mm / h to push the crucible. After reaching the equal diameter liquid mouth distance, the pulling speed and crucible rotation are increased;

[0053] S3: At the stage of equal diameter of 300-500mm, the crucible is rotated for 7 times and the pulling speed is increased again;

[0054] S4: Constant diameter 500-4500 mm stage, constant 7 crucible revolutions, constant furnace pressure of 11 Torr and constant argon flow rate of 100 slpm;

[0055] S5: When the diameter reaches 4500mm, the temperature is raised to complete the crystal pulling and obtain an N-type single crystal rod.

[0056] The specific parameters for preparing the N-type single crystal rod by the conventional method are set as shown in Table 1:

[0057] Table 1

[0058]

[0059] Example 1

[0060] S1: During temperature adjustment, seeding, shoulder release and shoulder rotation, the constant crucible rotation is 5 crucible rotations, the constant furnace pressure is 11 Torr and the constant argon flow rate is 100 slpm;

[0061] S2: Entering the stage of equal diameter head 0-300mm, the crucible is lifted at a constant crucible height of 10mm / h to push the crucible. After reaching the equal diameter liquid mouth distance, the pulling speed and crucible rotation are increased;

[0062] S3: At the stage of equal diameter of 300-500mm, the crucible rotation is maintained at 7 crucible rotations, and the pulling speed is increased again;

[0063] S4: When the diameter is 500-2000 mm, the crucible is lowered to 5 crucible revolutions and the temperature is lowered again;

[0064] S5: In the stage of equal diameter 2000-3000mm, reduce the furnace pressure and increase the argon flow rate;

[0065] S6: After the equal diameter reaches 3000mm, the pulling speed is reduced; when the equal diameter reaches 4500mm, the temperature is increased to complete the crystal pulling and obtain an N-type single crystal rod.

[0066] The specific parameter settings of the above steps are as shown in Table 2:

[0067] Table 2

[0068]

[0069] The resistivity test results of the crystal rod prepared according to the process of Example 1 are shown in Table 3:

[0070] Table 3

[0071]

[0072] It can be seen from Table 3 that under the same rod length condition, the head resistivity is basically the same. With the embodiment 1 of the process of changing furnace pressure and argon gas in the middle and late stages of equal diameter, the resistivity is more evenly distributed than that under the conventional process (fixed furnace pressure and fixed argon gas process), the head / tail resistivity is reduced by 23% compared with the conventional process, and the resistivity concentration is greatly improved.

[0073] Figure 1 The oxygen content distribution diagram of the crystal rod prepared by the conventional process of Comparative Example 1 of the present invention is shown in FIG. 1 ; the test results of the oxygen content in the crystal rod prepared by the process of Example 1 are shown in FIG. Figure 2 , Figure 2 This is the distribution diagram of oxygen content in the crystal rod prepared in Example 1. Figure 1 and Figure 2 Comparison shows that the oxygen content distribution in the middle and late stages of the crystal rod prepared by the improved process is more uniform, and the oxygen content in the tail is more uniform than that in the conventional process (constant furnace pressure, constant argon flow process), and the overall oxygen content concentration is greatly improved; after the equal diameter 500, that is, after S4, the crucible rotation is gradually reduced, the SiO generated by the reaction between the melt and the inner wall of the quartz crucible is reduced, and the increase in oxygen content is reduced.

[0074] It can be seen from the above embodiments that the present invention provides a method for preparing an N-type single crystal rod, comprising the following steps: S1: during temperature adjustment, crystal induction, shoulder release and shoulder rotation, the constant crucible speed is 5 crucible speeds, the constant furnace pressure is 11 Torr and the constant argon flow rate is 100 slpm; S2: entering the stage of equal-diameter head of 0 to 300 mm, a constant crucible lift of 10 mm / h is used to push the crucible, and after reaching the equal-diameter liquid mouth distance, the pulling speed and crucible speed are increased; S3: in the stage of equal-diameter of 300 to 500 mm, the crucible rotation is maintained and the pulling speed is increased again; S4: in the stage of equal-diameter of 500 to 2000 mm, the crucible speed is reduced and the temperature is lowered again; S5: in the stage of equal-diameter of 2000 to 3000 mm, the furnace pressure is reduced and the argon flow rate is increased; S6: after the equal-diameter is 3000 mm, the pulling speed is reduced; when the temperature is increased to the process of equal-diameter of 4500 mm, the crystal pulling is completed to obtain an N-type single crystal rod. The method reduces the oxygen content of the obtained crystal rod and improves the resistivity concentration by comprehensively controlling parameters such as crucible rotation, furnace pressure and argon gas flow rate; reduces the head-tail resistivity ratio, and achieves the purpose of reducing costs and increasing efficiency.

[0075] The above is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principle of the present invention. These improvements and modifications should also be regarded as the scope of protection of the present invention.

Claims

1. A method for preparing an N-type single crystal rod, comprising the following steps: S1: During temperature adjustment, seeding, shoulder release and shoulder rotation, the constant crucible rotation is 5 crucible rotations, the constant furnace pressure is 11 Torr and the constant argon flow rate is 100 slpm; S2: Entering the stage of equal diameter head 0-300mm, the crucible is lifted at a constant crucible height of 10mm / h to push the crucible. After reaching the equal diameter liquid mouth distance, the pulling speed and crucible rotation are increased; S3: At the stage of equal diameter of 300-500mm, keep the crucible rotating and increase the pulling speed again; S4: In the stage of equal diameter 500-2000mm, the crucible rotation is reduced and the temperature is lowered again; S5: In the stage of equal diameter 2000-3000mm, reduce the furnace pressure and increase the argon flow rate; S6: After the equal diameter reaches 3000mm, the pulling speed is reduced; when the equal diameter reaches 4500mm, the temperature is increased to complete the crystal pulling and obtain an N-type single crystal rod.

2. The preparation method according to claim 1, characterized in that: In step S2, the pulling speed is increased to 95 mm / h; Lift the crucible and turn it to 6-7 crucible turns.

3. The preparation method according to claim 2, characterized in that: In step S3, the pulling speed is increased again to 108 mm / h.

4. The preparation method according to claim 1, characterized in that: In step S4, the temperature is lowered again by reducing the power; When the diameter reaches 2000mm, the power reduction is 0.5-1.0kW.

5. The preparation method according to claim 1, characterized in that: In step S5, the furnace pressure is reduced to 9 Torr and the argon flow rate is increased to 120 slpm.

6. The method according to claim 1, characterized in that In step S6, the temperature is increased by increasing the power; When the diameter reaches 4500mm, the power increase is 1.5kW.

7. The preparation method according to claim 1, characterized in that: In step S3, the furnace pressure is 11 Torr and the argon gas is 100 slpm; In step S4, the furnace pressure is 11 Torr and the argon gas is 100 slpm.

8. The preparation method according to claim 1, characterized in that: In step S2, the distance between the equal-diameter liquid ports is 20 to 22 mm.

9. The preparation method according to claim 2, characterized in that: In step S4, the crucible is lowered to 5 crucible revolutions.

10. An N-type single crystal rod, prepared by the preparation method according to any one of claims 1 to 9; The head / tail resistivity ratio of the N-type single crystal rod is less than 1.5; and the oxygen content of the tail is less than 10 ppm.

Images