Czochralski silicon and preparation method thereof

Abstract

The invention discloses czochralski silicon and a preparation method thereof. The preparation method of the czochralski silicon comprises the following steps: 1) melting materials; 2) seeding: immersing the seed crystal into a silicon liquid, and stretching the silicon liquid to grow into a neck crystal; 3) shouldering: stretching and growing the neck crystal into a shouldered crystal; 4) shoulder rotation: stretching and growing the shouldered crystal until the diameter of the crystal is equal-diameter growth diameter to obtain a shoulder rotation crystal; 5) performing equal-diameter growth: performing equal-diameter growth on the shouldered crystal under the condition that the first crystal rotation speed is 2-6 rpm greater than the first crucible rotation speed to obtain a middle equal-diameter crystal; performing equal-diameter growth on the intermediate equal-diameter crystal under the condition that the second crystal rotation speed is 1-5 rpm lower than the second crucible rotation speed to obtain an equal-diameter growth crystal bar; and 6) ending: ending the equal-diameter growth crystal bar at a second crystal rotation speed to obtain the czochralski silicon. The uniformity of the transverse resistance of the czochralski silicon prepared by the method is relatively good.

Description

Technical Field

[0001] This invention relates to a Czochralski-grown single-crystal silicon and its preparation method. Background Technology

[0002] Monocrystalline silicon is a crucial basic material for industries such as information, electronics, and photovoltaics. It can be grown from solution or gas, employing diverse methods with high-quality growth. In this field, the Czochralski method is commonly used. Existing methods for preparing monocrystalline silicon typically involve adding dopants to suppress light-induced degradation and improve the long-term stability and photoelectric conversion efficiency of the silicon used in solar cells. However, doped monocrystalline silicon prepared using the existing Czochralski method generally suffers from uneven lateral resistivity distribution (characterized by low resistance in the center and high resistance at the edges). This is because the segregation coefficient of dopants in silicon is relatively low (approximately 0.008 for gallium), leading to significant differences in lateral resistivity during the growth process, which in turn affects the photoelectric conversion efficiency of the solar cell module. Summary of the Invention

[0003] In view of this, one object of the present invention is to provide a method for preparing Czochralski single-crystal silicon. The Czochralski single-crystal silicon prepared by this method has a resistivity difference of less than 0.02 Ω between its center and edge, and exhibits good uniformity in lateral resistivity. Another object of the present invention is to provide Czochralski single-crystal silicon prepared by the above-described method.

[0004] The present invention achieves the above objectives using the following technical solutions.

[0005] On one hand, the method for preparing Czochralski single-crystal silicon according to the present invention includes the following steps:

[0006] 1) Molten material: Polycrystalline silicon and dopant are added to the crucible of a single crystal furnace and melted to obtain molten silicon; wherein, the dopant is selected from at least one of gallium, indium, antimony, boron, phosphorus and arsenic;

[0007] 2) Seed crystal growth: The seed crystal is immersed in molten silicon, and the molten silicon is stretched and grown into a neck crystal under protective gas conditions; wherein the length of the neck crystal is 230-300 mm.

[0008] 3) Shoulder growth: The neck crystal is stretched and grown into a shoulder-grown crystal under protective gas conditions;

[0009] 4) Shoulder rotation: The shouldered crystal is stretched and grown under a protective gas condition until the crystal diameter is the same as the growth diameter, thus obtaining a shouldered crystal;

[0010] 5) Constant diameter growth: The shoulder crystal is grown with constant diameter under the condition that the first crystal rotation speed is 2-6 rpm greater than the first crucible rotation speed and the first protective gas is used to obtain an intermediate constant diameter crystal; wherein, the length of the intermediate constant diameter crystal is 100-500 mm.

[0011] An intermediate constant-diameter crystal is grown under the condition that the second crystal rotation speed is 1-5 rpm less than the second crucible rotation speed and a second protective gas is used to obtain a constant-diameter grown crystal rod; wherein, the second crystal rotation speed is 1-8 rpm less than the first crystal rotation speed.

[0012] 6) Finishing: The constant diameter growth rod is finished under the second crystal rotation speed and protective gas conditions to obtain Czochralski single crystal silicon.

[0013] In this invention, the single crystal furnace can be any type of single crystal furnace known in the art, and no particular limitation is made here.

[0014] In step 1) of this invention, the dopant can be selected from at least one of gallium, indium, antimony, boron, phosphorus, and arsenic, preferably at least one of gallium, indium, and antimony. The weight of the dopant can be 3 to 10 wt% of the weight of polycrystalline silicon, preferably 5 to 8 wt%. The melting time can be 8 to 25 hours, preferably 10 to 20 hours.

[0015] According to the preparation method of the present invention, preferably, in step 2), the crystal rotation speed of the crystal driver can be 5-15 rpm, more preferably 6-13 rpm. The crucible rotation speed can be 6-12 rpm, more preferably 7-11 rpm. The flow rate of the protective gas can be 80-180 slpm, more preferably 90-160 slpm. The crystal pulling speed can be 200-400 mm / min, more preferably 220-380 mm / min.

[0016] In step 2) of the present invention, the length of the neck crystal can be 230-300 mm, preferably 230-250 mm.

[0017] Reasonable crystal-leading conditions can prevent the formation of polycrystalline silicon during growth, improve the crystal integrity of monocrystalline silicon, and significantly improve the quality of monocrystalline silicon.

[0018] According to the preparation method of the present invention, preferably, in step 3), the crystal rotation speed of the shoulder formation can be 5-15 rpm, more preferably 6-13 rpm. The crucible rotation speed can be 6-12 rpm, more preferably 7-11 rpm. The flow rate of the protective gas can be 80-180 slpm, more preferably 90-160 slpm. The shoulder pulling speed can be 50-90 mm / min, more preferably 55-85 mm / min.

[0019] In step 3) of the present invention, the length of the shoulder crystal can be 170-300 mm, preferably 170-200 mm.

[0020] Reasonable shoulder conditions can ensure precise control of crystal diameter, stabilize the solid-liquid interface, and prevent dislocation defects, thereby improving the quality and utilization rate of crystal rods and facilitating the high-quality completion of subsequent constant-diameter growth.

[0021] According to the preparation method of the present invention, preferably, in step 4), the crystal rotation speed of the shoulder can be 9-15 rpm, more preferably 10-13 rpm. The crucible rotation speed of the shoulder can be 6-12 rpm, more preferably 7-11 rpm. The flow rate of the protective gas for the shoulder can be 80-180 slpm, more preferably 90-160 slpm. The pulling speed of the shoulder can be 70-180 mm / min, more preferably 75-160 mm / min. The constant diameter growth diameter can be 100-500 mm, more preferably 200-400 mm.

[0022] Reasonable shoulder conditions can ensure that the crystal diameter smoothly transitions to the initial value of constant diameter growth, reduce thermal stress and dislocation defects, and facilitate the high-quality completion of subsequent constant diameter growth.

[0023] According to the preparation method of the present invention, preferably, in step 5), the first crystal rotation speed can be greater than the first crucible rotation speed by 2-6 rpm, more preferably 3-5 rpm. The second crystal rotation speed can be less than the second crucible rotation speed by 1-5 rpm, more preferably 1-3 rpm. The second crystal rotation speed can be less than the first crystal rotation speed by 1-8 rpm, more preferably 2-7 rpm. In step 5), the first crystal rotation speed can be 9-15 rpm, more preferably 10-13 rpm. Further, the first crucible rotation speed can be 3-13 rpm, more preferably 5-10 rpm. The second crystal rotation speed can be 1-14 rpm, more preferably 3-11 rpm. The second crucible rotation speed can be 2-19 rpm, more preferably 4-14 rpm.

[0024] According to the preparation method of the present invention, preferably, in step 5), the flow rate of the first protective gas can be 120-180 slpm, more preferably 130-160 slpm. The flow rate of the second protective gas can be 50-100 slpm, more preferably 60-95 slpm.

[0025] In step 5) of the present invention, an intermediate constant-diameter crystal is obtained at a first constant-diameter growth rate, which can be 45-150 mm / min, preferably 50-140 mm / min. A constant-diameter growth rod is obtained at a second constant-diameter growth rate, which can be 45-150 mm / min, preferably 50-140 mm / min.

[0026] In this invention, the length of the intermediate constant-diameter crystal can be 100–500 mm, preferably 200–450 mm. The length of the constant-diameter growth rod can be 450 mm or more, preferably 450–500 mm. Limiting the constant-diameter growth conditions to the above range ensures a low resistance difference between the center and edge of the Czochralski single-crystal silicon, which is beneficial for the uniform distribution of lateral resistance.

[0027] According to the preparation method of the present invention, preferably, in step 5), the crystal rotation speed during the finishing process can be 1-14 rpm, more preferably 3-11 rpm. The crucible rotation speed during the finishing process can be 2-19 rpm, more preferably 4-14 rpm. The flow rate of the protective gas during the finishing process can be 50-100 slpm, more preferably 60-95 slpm. The pulling speed during the finishing process can be 80-200 mm / min, more preferably 85-190 mm / min. During the finishing process, the power of the bottom heater can be increased by 10-40 kW, more preferably 15-30 kW. The finishing length can be at least 180 mm, more preferably 180-500 mm.

[0028] Reasonable finishing conditions can prevent dislocations from extending to the constant-diameter region, ensuring crystal integrity and improving yield; at the same time, it is conducive to optimizing the utilization of crystal raw materials.

[0029] In this invention, the protective gas used in each step can be selected from at least one of nitrogen and inert gases. The inert gases involved in this invention include helium (He), neon (Ne), argon (Ar), krypton (Kr), and xenon (Xe). Preferably, the inert gas is helium or argon. According to a preferred embodiment of the invention, the protective gas can be selected from at least one of nitrogen and argon.

[0030] This invention leverages the characteristic of the crystal surface transforming from a convex to a concave interface during the constant-diameter growth of single-crystal silicon. By adjusting crystal rotation, crucible rotation, and protective gas flow rate according to different interface morphologies, the degree of dopant volatilization is controlled, thereby ensuring the consistency of the crystal's lateral resistance. Specifically: During the constant-diameter growth of single-crystal silicon, when the growth length is 0-100 mm, the crystal surface morphology transforms from a convex to a flat interface, resulting in a lateral resistance distribution that is high at the center and low at the edges. By controlling high crystal rotation, low crucible rotation, and a larger protective gas flow rate, dopant volatilization can be enhanced, thereby increasing the edge resistance and making the center resistance and edge resistance more consistent. When the constant-diameter growth length exceeds 400 mm, the single-crystal silicon crystal surface becomes concave. At this point, controlling the growth conditions with low crystal rotation, high crucible rotation, and a smaller protective gas flow rate reduces dopant volatilization, thereby lowering the edge resistance and making the center resistance and edge resistance more consistent.

[0031] On the other hand, the present invention also provides Czochralski single-crystal silicon prepared by the above-described preparation method. The resistance difference between the center and the edge of the Czochralski single-crystal silicon can be less than 0.02Ω, preferably less than 0.018Ω.

[0032] This invention controls the crystal rotation, crucible rotation, and protective gas flow rate during the uniform diameter growth process of single-crystal silicon to obtain Czochralski single-crystal silicon with a resistance difference of less than 0.02Ω between the center and the edge, and good uniformity of lateral resistance. Detailed Implementation

[0033] The present invention will be further described below with reference to specific embodiments, but the scope of protection of the present invention is not limited thereto.

[0034] The “crystal rotation speed” mentioned in this invention refers to the angular velocity of a growing single-crystal silicon rod (crystal) rotating about its vertical axis, and the unit is revolutions per minute (rpm).

[0035] The "cruise speed" mentioned in this invention refers to the angular velocity of the crucible containing molten silicon rotating about its axis, measured in revolutions per minute (rpm).

[0036] <Testing Methods>

[0037] Resistance difference measurement: The measurement was performed using a BCT-400 minority carrier lifetime tester manufactured by Sinton Instruments, Inc., USA.

[0038] <Ingredient Description>

[0039] Unless otherwise specified, all raw materials used in the following examples are commercially available products.

[0040] Example 1

[0041] The following steps are used to prepare Czochralski-grown single-crystal silicon:

[0042] 1) Melting: Polycrystalline silicon and gallium are added to the crucible of the single crystal furnace and melted to obtain molten silicon. The amount of gallium added is 7 wt% of the weight of polycrystalline silicon. During melting, the power of the main heater is 95 kW, the power of the bottom heater is 90 kW, and the melting time is 13 h.

[0043] 2) Seed crystal growth: The seed crystal is immersed in the molten silicon and stretched to grow a neck crystal with a seed crystal length of 230 mm under the conditions of crystal rotation speed of 12 rpm, crucible rotation speed of 8 rpm, argon flow rate of 150 slpm, and stretching speed of 240-360 mm / min.

[0044] 3) Shoulder formation: The neck crystal is stretched and grown into a shoulder crystal with a length of 170 mm under the conditions of crystal rotation speed of 12 rpm, crucible rotation speed of 8 rpm, argon flow rate of 150 slpm, and stretching speed of 60-80 mm / min.

[0045] 4) Shoulder growth: The shouldered crystal is stretched and grown into a shouldered crystal with a diameter of 300 mm under the conditions of crystal rotation speed of 12 rpm, crucible rotation speed of 8 rpm, argon flow rate of 150 slpm, and stretching speed of 80-150 mm / min.

[0046] 5) Constant diameter growth: The shouldered crystal is grown to a diameter of 300 mm under the conditions of a first crystal rotation speed of 12 rpm, a first crucible rotation speed of 8 rpm, an argon flow rate of 150 slpm, and a pulling speed of 55-135 mm / min to obtain an intermediate constant diameter crystal with a length of 400 mm.

[0047] The intermediate constant-diameter crystal was further grown under the conditions of a second crystal rotation speed of 6 rpm, a second crucible rotation speed of 7 rpm, an argon flow rate of 90 slpm, and a pulling speed of 55–135 mm / min. The constant-diameter growth was terminated when the length of the constant-diameter crystal reached 450 mm, and a constant-diameter grown crystal rod was obtained.

[0048] 6) Finishing: Increase the power of the bottom heater by 21KW, and finish the growth of the equal diameter crystal rod under the conditions of a speed of 6rpm, a crucible rotation speed of 7rpm, an argon flow rate of 90slpm, and a pulling speed of 90~180mm / min. Stop the growth when the length of the crystal reaches 300mm to obtain Czochralski single crystal silicon.

[0049] The test results showed that the resistance difference between the interface center and the edge of the prepared Czochralski single crystal silicon was 0.012Ω.

[0050] Example 2

[0051] The only difference from Example 1 is the constant diameter growth step. The constant diameter growth step is as follows:

[0052] The shouldered crystal was grown at a constant diameter of 300 mm under the conditions of a first crystal rotation speed of 12 rpm, a first crucible rotation speed of 7 rpm, an argon flow rate of 150 slpm, and a pulling speed of 55-135 mm / min to obtain an intermediate constant diameter crystal with a length of 400 mm.

[0053] The intermediate constant-diameter crystal was further grown under the conditions of a second crystal rotation speed of 5 rpm, a second crucible rotation speed of 7 rpm, an argon flow rate of 90 slpm, and a pulling speed of 55–135 mm / min. The growth was stopped when the length of the constant-diameter crystal reached 450 mm, and Czochralski single-crystal silicon was obtained.

[0054] The test results showed that the resistance difference between the interface center and the edge of the prepared Czochralski single crystal silicon was 0.018Ω.

[0055] Comparative Example 1

[0056] The only difference from Example 1 is the constant diameter growth step. The constant diameter growth step is as follows:

[0057] The shoulder-shaped crystal was grown at a constant diameter of 300 mm under the conditions of a first crystal rotation speed of 6 rpm, a first crucible rotation speed of 8 rpm, an argon flow rate of 100 slpm, and a pulling speed of 55-135 mm / min to obtain an intermediate constant diameter crystal with a length of 400 mm.

[0058] The intermediate constant-diameter crystal was further grown under the conditions of a second crystal rotation speed of 5 rpm, a second crucible rotation speed of 8 rpm, an argon flow rate of 120 slpm, and a pulling speed of 55-135 mm / min. The growth was stopped when the length of the constant-diameter crystal reached 460 mm, and Czochralski single crystal silicon was obtained.

[0059] Testing revealed that the resistance difference between the interface center and edge of the prepared Czochralski single crystal silicon was 0.036Ω, significantly higher than that of the example.

[0060] This invention is not limited to the above-described embodiments. Any modifications, improvements, or substitutions that can be conceived by those skilled in the art without departing from the essential content of this invention fall within the scope of this invention.

Claims

1. A method for preparing Czochralski-grown single-crystal silicon, characterized in that, Includes the following steps: 1) Molten material: Polycrystalline silicon and dopant are added to the crucible of a single crystal furnace and melted to obtain molten silicon; wherein, the dopant is selected from at least one of gallium, indium, antimony, boron, phosphorus and arsenic; 2) Seed crystal growth: The seed crystal is immersed in molten silicon, and the molten silicon is stretched and grown into a neck crystal under protective gas conditions; 3) Shoulder growth: The neck crystal is stretched and grown into a shoulder-grown crystal under protective gas conditions; 4) Shoulder rotation: The shouldered crystal is stretched and grown under a protective gas condition until the crystal diameter is the same as the growth diameter, thus obtaining a shouldered crystal; 5) Constant diameter growth: The shoulder crystal is grown with constant diameter under the condition that the first crystal rotation speed is 2-6 rpm greater than the first crucible rotation speed and the first protective gas is used to obtain an intermediate constant diameter crystal; wherein, the length of the intermediate constant diameter crystal is 100-500 mm. An intermediate constant-diameter crystal is grown under the condition that the second crystal rotation speed is 1-5 rpm less than the second crucible rotation speed and a second protective gas is used to obtain a constant-diameter grown crystal rod; wherein, the second crystal rotation speed is 1-8 rpm less than the first crystal rotation speed. 6) Finishing: The constant diameter growth rod is finished under the second crystal rotation speed and protective gas conditions to obtain Czochralski single crystal silicon.

2. The preparation method according to claim 1, characterized in that, In step 2), the crystal rotation speed is 5-15 rpm, the crucible rotation speed is 6-12 rpm, the flow rate of the protective gas is 80-180 slpm, and the crystal pulling speed is 200-400 mm / min.

3. The preparation method according to claim 1, characterized in that, In step 2), the length of the neck crystal is 230-300 mm.

4. The preparation method according to claim 1, characterized in that, In step 3), the crystal rotation speed of the shoulder-forming process is 5-15 rpm, the crucible rotation speed is 6-12 rpm, the flow rate of the protective gas is 80-180 slpm, the shoulder-forming pulling speed is 50-90 mm / min, and the length of the shoulder-forming crystal is 170-300 mm.

5. The preparation method according to claim 1, characterized in that, In step 4), the crystal rotation speed of the rotating shoulder is 9-15 rpm, the crucible rotation speed is 6-12 rpm, the flow rate of the protective gas is 80-180 slpm, and the pulling speed of the rotating shoulder is 70-180 mm / min.

6. The preparation method according to claim 1, characterized in that, In step 5), the flow rate of the first protective gas is 120-180 slpm, and the flow rate of the second protective gas is 50-100 slpm.

7. The preparation method according to claim 1, characterized in that, In step 5), the first crystal rotation speed is 3-5 rpm greater than the first crucible rotation speed, the second crystal rotation speed is 1-3 rpm less than the second crucible rotation speed, and the second crystal rotation speed is 2-7 rpm less than the first crystal rotation speed; the first crystal rotation speed is 9-15 rpm.

8. The preparation method according to claim 1, characterized in that, In step 5), the length of the constant diameter growth rod is 450 mm or more.

9. The preparation method according to claim 1, characterized in that, In step 6), the crystal rotation speed at the tailing point is 1-14 rpm, the crucible rotation speed is 2-19 rpm, the flow rate of the protective gas is 50-100 slpm, and the pulling speed at the tailing point is 80-200 mm / min.

10. A Czochralski-grown single-crystal silicon prepared by any one of the preparation methods described in claims 1 to 9, characterized in that, The resistance difference between the center and the edge of the Czochralski single crystal silicon is less than 0.02Ω.