Method for improving crystallization rate of drawn large-size crystal bar

Abstract

A method for improving the crystal forming rate of drawn large-size crystal bars relates to the technical field of crystal bar drawing, and comprises a material melting process, a stabilizing process, a seeding process, a shouldering process, a shoulder rotating process, an equal-diameter process and an ending process, in the material melting process, argon is blown into the upper part of an auxiliary chamber of a single crystal furnace and the lower part of a main chamber of the single crystal furnace at the same time; the ratio of the upper argon flow to the lower argon flow is (5: 1)-(7: 1); in the stabilizing procedure, the argon flow is 40-60 L / min, and the temperature of molten silicon is reduced at the rate of 3-5 DEG C. According to the method, the crystal bar crystallization rate is increased to 92.3%.

Description

Technical Field

[0001] The present invention relates to the technical field of large-size ingot pulling, and specifically to a method for improving the crystallization rate of large-size ingots during pulling. Background Art

[0002] With the development of the photovoltaic industry, the demand for large-size ingots is gradually increasing. When using traditional ingot pulling methods to pull large-size ingots, due to the increase in melt volume, the thermal convection intensifies, causing impurities (such as oxygen and metal ions) to accumulate at the negative electrode at the bottom of the melt. These impurity regions will affect the stability of the crystallization cross-section; the increase in melt depth leads to an increase in the vertical temperature gradient, causing fluctuations in the solid-liquid interface. The enrichment of impurities, the instability of the crystallization cross-section, and the fluctuations in the solid-liquid interface all affect the crystallization rate of the ingot, resulting in a decrease in the crystallization rate. Summary of the Invention

[0003] The purpose of the present invention is to provide a method for improving the crystallization rate of large-size ingots during pulling, which improves the crystallization rate of the ingots.

[0004] To achieve the above purpose, the specific solution adopted by the present invention is as follows: A method for improving the crystallization rate of large-size ingots during pulling includes a material melting process, a stabilization process, a seed crystal introduction process, a shoulder forming process, a shoulder turning process, an equal diameter process, and a finishing process. In the material melting process, argon gas is blown into the upper part of the auxiliary chamber of the single crystal furnace and the lower part of the main chamber of the single crystal furnace at the same time, and the ratio of the argon gas flow rate in the upper part to the argon gas flow rate in the lower part is 5:1 - 7:1; in the stabilization process, the argon gas flow rate is 40 - 60 L / min, and the temperature of the molten silicon is decreased at a rate of 3 - 5 °C / min.

[0005] As an optimized scheme of the above method for improving the crystallization rate of large-size ingots during pulling: Before the material melting process, the raw materials are soaked in a hydrofluoric acid-nitric acid mixed solution for 12 minutes.

[0006] As another optimized scheme of the above method for improving the crystallization rate of large-size ingots during pulling: The content ratio of hydrofluoric acid to nitric acid in the hydrofluoric acid-nitric acid mixed solution is 1:2.

[0007] As another optimized scheme of the above method for improving the crystallization rate of large-size ingots during pulling: In the material melting process, the argon gas flow rate in the upper part is 80 - 100 L / min, the argon gas flow rate in the lower part is 15 L / min, and the furnace pressure is 8 torr.

[0008] As another optimized scheme of the above method for improving the crystallization rate of large-size ingots during pulling: In the stabilization process, the temperature of the molten silicon is decreased in stages. First, the temperature of the molten silicon is decreased by 50 °C at a rate of 5 °C / min, and then the temperature of the molten silicon is decreased by 100 °C at a rate of 3 °C / min.

[0009] As another optimization solution for the above method of improving the crystal growth rate of large-sized crystal rods: the furnace pressure when the temperature of molten silicon is reduced by 50 °C at a rate of 5 °C / min is 3 torr.

[0010] As another optimization solution for the above method of improving the crystal growth rate of large-sized crystal rods: the furnace pressure when the temperature of molten silicon is reduced by 100 °C at a rate of 3 °C / min is 2 torr.

[0011] As another optimization solution for the above method of improving the crystal growth rate of large-sized crystal rods: a seed crystal with micro-grooves at the bottom is used in the crystal seeding process.

[0012] As another optimization solution for the above method of improving the crystal growth rate of large-sized crystal rods: the depth of the micro-grooves is 5 - 10 μm.

[0013] Compared with the prior art, the present invention has the following beneficial effects:

[0014] 1. The present invention provides a method for improving the crystal growth rate of large-sized crystal rods. Argon is introduced simultaneously above the auxiliary chamber and below the main chamber to accelerate the volatilization of SiO at the bottom of molten silicon, reduce the accumulation of oxygen in molten silicon, and at the same time inhibit the precipitation of metal impurities. Combining with gradually reducing the temperature of molten silicon in stages promotes the precipitation of oxygen in molten silicon, and the diffusion coefficient is increased to 3.5×10 -5 cm 2 / s, improving the crystal growth rate of the crystal rod to 92.3%.

[0015] 2. In the present invention, a seed crystal with micro-grooves at the bottom is used for crystal seeding. The micro-grooves provide oriented nucleation sites, which not only improve the crystal growth rate of the crystal rod but also reduce the crystal orientation deviation.

[0016] 3. In the present invention, the raw materials are soaked in a mixed solution of hydrofluoric acid and nitric acid to remove the surface oxide layer and metal impurities, reducing the impurities in molten silicon from the source. Detailed implementation manners

[0017] The technical solutions of the present invention will be further elaborated in detail below in combination with specific embodiments. For parts not detailedly recorded and disclosed in the following embodiments of the present invention, they should all be understood as the prior art known or should be known to those skilled in the art.

[0018] Embodiment 1

[0019] A method for improving the crystal growth rate of large-sized crystal rods, including a material melting process, a stabilization process, a crystal seeding process, a shoulder releasing process, a shoulder turning process, an equal diameter process, and a finishing process, specifically including the following steps:

[0020] In the material melting process, argon gas is blown into the upper part of the auxiliary chamber of the single crystal furnace and the lower part of the main chamber of the single crystal furnace simultaneously, and the ratio of the argon gas flow rate in the upper part to the argon gas flow rate in the lower part is 5:1 - 7:1. In this embodiment, the argon gas flow rate in the upper part is 90 L / min, the argon gas flow rate in the lower part is 15 L / min, the furnace pressure is 8 torr, and the remaining process parameters are all in the prior art and will not be elaborated here. The argon gas flow rate in the upper part combines with the argon gas flow rate in the lower part to accelerate the volatilization of SiO at the bottom of the molten silicon, reduce the accumulation of oxygen in the molten silicon, and simultaneously inhibit the precipitation of metal impurities.

[0021] In the stabilization process, the argon gas flow rate is 40 - 60 L / min, and the temperature of the molten silicon is decreased at a rate of 3 - 5 °C / min. In this embodiment, the argon gas flow rate is 50 L / min, and the temperature of the molten silicon is decreased by 150 °C at a rate of 4 °C / min to promote the precipitation of oxygen in the molten silicon. The remaining process parameters are all in the prior art and will not be elaborated here.

[0022] The processes of crystal seeding, shoulder formation, shoulder turning, equal diameter growth, and end process are the processes in the traditional Czochralski method to obtain a single crystal ingot.

[0023] Example 2

[0024] A method for improving the crystal formation rate of pulling large-size crystal ingots includes a material melting process, a stabilization process, a crystal seeding process, a shoulder formation process, a shoulder turning process, an equal diameter growth process, and an end process, and specifically includes the following steps:

[0025] In the material melting process, argon gas is blown into the upper part of the auxiliary chamber of the single crystal furnace and the lower part of the main chamber of the single crystal furnace simultaneously. The argon gas flow rate in the upper part is 80 L / min, the argon gas flow rate in the lower part is 15 L / min, the furnace pressure is 8 torr, and the remaining process parameters are all in the prior art and will not be elaborated here.

[0026] In the stabilization process, the argon gas flow rate is 40 L / min, and the temperature of the molten silicon is decreased by 150 °C at a rate of 3 °C / min. The remaining process parameters are all in the prior art and will not be elaborated here.

[0027] The processes of crystal seeding, shoulder formation, shoulder turning, equal diameter growth, and end process are the processes in the traditional Czochralski method to obtain a single crystal ingot.

[0028] Example 3

[0029] A method for improving the crystal formation rate of pulling large-size crystal ingots includes a material melting process, a stabilization process, a crystal seeding process, a shoulder formation process, a shoulder turning process, an equal diameter growth process, and an end process, and specifically includes the following steps:

[0030] During the material preparation process, argon gas is blown into the upper part of the secondary chamber and the lower part of the main chamber of the single crystal furnace simultaneously. The argon gas flow rate in the upper part is 100 L / min, the argon gas flow rate in the lower part is 15 L / min, and the furnace pressure is 8 torr. The remaining process parameters are all in the prior art and will not be elaborated here.

[0031] During the stabilization process, the argon gas flow rate is 50 L / min, and the temperature of the molten silicon is decreased by 150 °C at a rate of 5 °C / min. The remaining process parameters are all in the prior art and will not be elaborated here.

[0032] The processes of crystal seeding, shoulder formation, shoulder turning, equal diameter growth, and ending are the processes in the traditional Czochralski method to obtain a single crystal ingot.

[0033] Example 4

[0034] A method for improving the crystal formation rate of pulling large-sized crystal ingots, including a material preparation process, a stabilization process, a crystal seeding process, a shoulder formation process, a shoulder turning process, an equal diameter growth process, and an ending process, specifically includes the following steps:

[0035] During the material preparation process, argon gas is blown into the upper part of the secondary chamber and the lower part of the main chamber of the single crystal furnace simultaneously. The argon gas flow rate in the upper part is 100 L / min, the argon gas flow rate in the lower part is 15 L / min, and the furnace pressure is 8 torr. The remaining process parameters are all in the prior art and will not be elaborated here.

[0036] During the stabilization process, the temperature of the molten silicon is decreased in stages by argon. First, the temperature of the molten silicon is decreased by 50 °C at a rate of 5 °C / min, and the furnace pressure at this stage is 3 torr; then, the temperature of the molten silicon is decreased by 100 °C at a rate of 3 °C / min, and the furnace pressure at this stage is 2 torr. The remaining process parameters are all in the prior art and will not be elaborated here.

[0037] The processes of crystal seeding, shoulder formation, shoulder turning, equal diameter growth, and ending are the processes in the traditional Czochralski method to obtain a single crystal ingot.

[0038] Example 5

[0039] A method for improving the crystal formation rate of pulling large-sized crystal ingots, including a material preparation process, a stabilization process, a crystal seeding process, a shoulder formation process, a shoulder turning process, an equal diameter growth process, and an ending process, specifically includes the following steps:

[0040] Before the material preparation process, the raw materials are soaked in a hydrofluoric acid-nitric acid mixture for 12 min, and the content ratio of hydrofluoric acid to nitric acid in the hydrofluoric acid-nitric acid mixture is 1:2.

[0041] In the material melting process, argon gas is blown into the upper part of the secondary chamber of the single crystal furnace and the lower part of the main chamber of the single crystal furnace simultaneously. The argon gas flow rate in the upper part is 100 L / min, the argon gas flow rate in the lower part is 15 L / min, and the furnace pressure is 8 torr. The remaining process parameters are all prior arts and will not be elaborated here.

[0042] In the stabilization process, the argon gas flow rate is 50 L / min, and the temperature of the molten silicon is reduced by 150 °C at a rate of 5 °C / min. The remaining process parameters are all prior arts and will not be elaborated here.

[0043] The processes of crystal seeding, shoulder formation, shoulder turning, equal diameter growth, and end process are the processes in the traditional Czochralski method to obtain a single crystal ingot.

[0044] Example 6

[0045] A method for improving the crystal formation rate of pulling large-size crystal ingots includes a material melting process, a stabilization process, a crystal seeding process, a shoulder formation process, a shoulder turning process, an equal diameter growth process, and an end process, and specifically includes the following steps:

[0046] Before the material melting process, the raw materials are soaked in a hydrofluoric acid-nitric acid mixed solution for 12 min, and the content ratio of hydrofluoric acid to nitric acid in the hydrofluoric acid-nitric acid mixed solution is 1:2.

[0047] In the material melting process, argon gas is blown into the upper part of the secondary chamber of the single crystal furnace and the lower part of the main chamber of the single crystal furnace simultaneously. The argon gas flow rate in the upper part is 100 L / min, the argon gas flow rate in the lower part is 15 L / min, and the furnace pressure is 8 torr. The remaining process parameters are all prior arts and will not be elaborated here.

[0048] In the stabilization process, the argon gas flow rate is 50 L / min, and the temperature of the molten silicon is reduced by 150 °C at a rate of 5 °C / min. The remaining process parameters are all prior arts and will not be elaborated here.

[0049] In the crystal seeding process, a seed crystal with micro-grooves at the bottom is used, and the depth of the micro-grooves is 5 - 10 μm.

[0050] The processes of shoulder formation, shoulder turning, equal diameter growth, and end process are the processes in the traditional Czochralski method to obtain a single crystal ingot.

[0051] The above description of the disclosed embodiments enables those skilled in the art to implement or use the present invention. Various modifications to these embodiments will be apparent to those skilled in the art. The general principles defined herein can be implemented in other embodiments without departing from the spirit or scope of the present invention. Therefore, the present invention will not be limited to these embodiments shown herein, but rather to the broadest scope consistent with the principles and novel features disclosed herein.

Claims

1. A method for improving the crystallization rate of pulling a large-size crystal rod, comprising a material processing step, a stabilization step, a seeding step, a shoulder release step, a shoulder transfer step, a diameter equalization step and a finishing step, characterized in that: During the material chemical process, argon is blown into the upper part of the single crystal furnace sub-chamber and the lower part of the single crystal furnace main chamber at the same time, and the ratio of the upper argon flow rate to the lower argon flow rate is 5:1-7:1; during the stabilization process, the argon flow rate is 40-60L / min, and the temperature of the molten silicon is reduced at a rate of 3-5℃ / min.

2. A method for improving the crystallization rate of pulling a large-size crystal rod according to claim 1, characterized in that: Before the chemical process, the raw materials are soaked in a hydrofluoric acid-nitric acid mixture for 12 minutes.

3. A method for improving the crystallization rate of pulling a large-size crystal rod according to claim 2, characterized in that: The content ratio of hydrofluoric acid to nitric acid in the hydrofluoric acid-nitric acid mixture is 1:

2.

4. A method for improving the crystallization rate of pulling a large-size crystal rod according to claim 1, characterized in that: In the chemical process, the upper argon flow rate is 80-100L / min, the lower argon flow rate is 15L / min, and the furnace pressure is 8torr.

5. A method for improving the crystallization rate of pulling a large-size crystal rod according to claim 1, characterized in that: In the stabilization process, the temperature of the molten silicon is lowered in stages. First, the temperature of the molten silicon is lowered by 50°C at a rate of 5°C / min, and then the temperature of the molten silicon is lowered by 100°C at a rate of 3°C / min.

6. A method for improving the crystallization rate of pulling a large-size crystal rod according to claim 5, characterized in that: The furnace pressure was 3 torr when the temperature of the molten silicon was reduced by 50°C at a rate of 5°C / min.

7. A method for improving the crystallization rate of pulling a large-size crystal rod according to claim 5, characterized in that: The furnace pressure was 2 torr when the temperature of the molten silicon was reduced by 100°C at a rate of 3°C / min.

8. A method for improving the crystallization rate of pulling a large-size crystal rod according to claim 1, characterized in that: The seeding process uses a seed crystal with micro grooves on the bottom.

9. A method for improving the crystallization rate of pulling a large-size crystal rod according to claim 8, characterized in that: The depth of the micro groove is 5-10 μm.