Ending process method for purifying polycrystalline silicon by zone melting method

Abstract

The invention discloses an ending process method for purifying polycrystalline silicon by a zone melting method, which is characterized in that a waist-like shape is formed during ending operation. When the length of the upper polycrystal material is 35-40mm, starting to carry out ending operation; when the diameter of the purified polycrystal is reduced by 15-20mm, stopping ending, and starting to increase the power and the moving speed of the upper polycrystal material, so that the diameter of the purified polycrystal starts to grow; after the purified polycrystal grows to the target diameter again, starting to slowly reduce the power, and meanwhile, stopping the downward movement of the polycrystal raw material, and at the moment, gradually reducing the diameter of the lower polycrystal rod; and when the diameter of the lower purified polycrystal is reduced by 15-20mm, moving the upper polycrystal material upwards, separating the upper polycrystal rod from the lower polycrystal rod, continuously moving the lower polycrystal material downwards, slowly keeping away from the thermal field, naturally cooling and ending. According to the ending process method disclosed by the invention, the tail part of the polycrystal can be directly hung into the single crystal furnace again to continue to draw the single crystal or perform purification operation again without grooving and corroding treatment, so that the production efficiency is greatly improved, and the waste generated in the process is also reduced.

Description

Technical Field

[0001] The present invention relates to a finishing process method for purifying polysilicon by a zone melting method, which reduces the waste caused by cutting tail grooves and re-etching after polycrystalline purification, thereby improving efficiency and reducing waste, and has high practical value. Background Art

[0002] At present, silicon single crystals used in the semiconductor industry are mainly grown by the Czochralski method (CZ) and the flux zone method (FZ). Among them, single crystals grown by the flux zone method (FZ) are suitable for use in high-power devices due to their low oxygen content and almost no metal contamination.

[0003] The resistivity of polycrystalline raw materials used in the production of zone-melting silicon single crystals is generally high, and the growth environment of zone-melting single crystals is clean and pollution-free, so the resistivity of zone-melting native single crystals is relatively high. The resistivity of zone-melting silicon single crystals currently produced in industry is generally around 2000-5000Ω·cm. With the rapid development of semiconductor and microelectronics technology, higher requirements are also put forward for semiconductor materials. High-quality zone-melting silicon single crystals are important materials for making various radiation detectors and photoelectric detectors, which can greatly improve the performance stability and safety of devices.

[0004] The single crystal silicon used in semiconductor silicon photodetectors requires very high purity and lattice integrity to ensure that the detector can achieve the goal of low dark current and high DC and pulse response. This places very high demands on material purity. At this time, the purification effect of the zone melting method needs to be applied to purify the polysilicon once or even multiple times to further reduce the phosphorus content, so that the zone melting high-resistance silicon single crystal can be pulled normally.

[0005] After the purified polycrystal is subjected to normal finishing operations, the tail needs to be grooved and etched before it can be hung in the single crystal furnace to continue pulling single crystals or to be purified again, which is time-consuming, labor-intensive, and material-consuming. Therefore, it is necessary to improve the finishing process method to improve production efficiency and reduce waste caused by the corresponding process. Summary of the invention

[0006] The object of the present invention is to provide a finishing process method for purifying polysilicon by a zone melting method, so as to reduce the waste caused by cutting tail grooves and re-etching after polycrystalline purification and improve production efficiency.

[0007] To achieve the above object, the present invention adopts the following technical solutions:

[0008] A finishing process method for purifying polysilicon by zone melting method, during the finishing operation, a waist-like shape is formed, and after the purified polysilicon is naturally cooled, it is taken out, and then a clamp is used to clamp the waist position of the polysilicon tail, and it is directly hung in the furnace again to continue pulling single crystals or to perform purification operations again.

[0009] Furthermore, the finishing process method for purifying polycrystalline silicon by the zone melting method comprises the following steps:

[0010] (1) Hang the etched polycrystals into the furnace and perform normal shoulder expansion operations. After the polycrystals are purified to the target diameter, they begin to grow stably;

[0011] (2) When the remaining length of the upper polycrystalline material is 35-40 mm, the finishing operation begins;

[0012] (3) When the diameter of the purified polycrystal is reduced by 15-20 mm, the tailing is stopped and the power and the moving speed of the upper polycrystal material are increased to make the diameter of the purified polycrystal begin to grow, similar to step (1) and the shoulder expansion operation is repeated;

[0013] (4) After the purified polycrystal grows to the target diameter again, the power is slowly reduced and the downward movement of the polycrystal raw material is stopped. At this time, the diameter of the lower polycrystal rod gradually decreases. When the diameter of the lower purified polycrystal is reduced by 15-20 mm, the upper polycrystal material is moved upward, the upper and lower polycrystal rods are separated, and the lower purified polycrystal material continues to move downward, slowly away from the heat field, and naturally cools to the end.

[0014] Preferably, in step (2), at the end, the power and the moving speed of the upper polycrystalline material are slowly reduced, the power reduction amplitude is 10%-15%, and the reduction frequency is 2-3% / min; the moving speed of the upper polycrystalline material is reduced to 70-80% of the speed during equal diameter growth, and the frequency is 4-6% / min.

[0015] Preferably, in the step (3), the power and the moving speed of the upper polycrystalline material are increased synchronously until the power and the moving speed of the upper polycrystalline material are increased to a state of equal diameter.

[0016] Preferably, the power increase frequency is 2-3% / min, and the upper polycrystalline material moving speed increase frequency is 4-6% / min.

[0017] Preferably, in step (4), after growing to the target diameter again, the power is slowly reduced by 10%-15% and the frequency of reduction is 2-3% / min; at the same time, the downward moving speed of the polycrystalline raw material is reduced to 50-60% and the speed reduction is 10-12% / min; when the diameter of the lower purified polycrystalline is reduced by 15-20mm, the upper polycrystalline material is started to be moved upward and the moving speed of the upper polycrystalline material is adjusted to 2-3.5mm / min upward.

[0018] Beneficial effects of the present invention:

[0019] The finishing process method of the present invention is different from the conventional single crystal finishing process operation of only one step. After the polycrystalline is purified, the tail needs to be folded into a waist-like shape. After the purified polycrystalline silicon is naturally cooled, it is packaged and taken out with a clean packaging bag, and then the waist position of the polycrystalline tail is clamped with a clamp, and it can be directly hung in the furnace again for use. The finishing process method of the present invention does not require grooving or corrosion treatment of the polycrystalline tail, and can be directly hung in the single crystal furnace again to continue pulling the single crystal or perform purification operations again, which greatly improves production efficiency and also reduces waste generated in the process. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 Flow chart of the existing zone melting method for preparing single crystals.

[0021] Figure 2 This is a schematic diagram of the shape change of polysilicon using the finishing process method of the present invention. DETAILED DESCRIPTION

[0022] The present invention is further described below in conjunction with the accompanying drawings and embodiments, but this does not limit the protection scope of the present invention.

[0023] like Figure 1 As shown, the existing process of purifying polysilicon by zone melting method includes: preparation work, furnace loading, furnace sealing, evacuation, inflation, preheating, material processing, crystal seeding, diameter reduction, shoulder expansion, shoulder rotation, holding and clamping device release, finishing, furnace shutdown, furnace dismantling, furnace cleaning and other processes.

[0024] The difference between the present invention and the prior art is that, during the finishing operation, a waist-like shape is formed at the tail. After the purified polysilicon is naturally cooled, it is wrapped in a clean packaging bag and taken out. Then, a clamp is used to clamp the waist position of the polycrystalline tail, and it can be directly hung in the furnace again to continue pulling single crystals or perform purification operations again.

[0025] Example

[0026] like Figure 2 As shown, the process of purifying polysilicon by zone melting method in this embodiment includes the following steps:

[0027] Step 1: Hang the etched polycrystalline into the furnace and perform normal shoulder expansion operation, such as Figure 2 As shown in 1→.

[0028] Step 2: After purification to the target diameter, the polycrystal begins to grow stably, such as Figure 2 As shown in 2→.

[0029] Step 3: When the remaining length of the upper polycrystalline material is 35-40mm, start the finishing operation, such as Figure 2As shown in 3→, the operating equipment slowly reduces the power and the moving speed of the upper polycrystalline material, the power reduction amplitude is 10%, and the reduction frequency is 2% / min. The moving speed of the upper polycrystalline material is reduced to 70% of the current speed, and the reduction frequency is 6% / min.

[0030] Step 4: When the power is reduced to 90% of the equal diameter power and the upper polycrystalline material moving speed is reduced to 70%, the lower purified polycrystalline diameter is reduced by 15-20mm, and the tailing is stopped. The power and the upper polycrystalline material moving speed are increased to make the polycrystalline diameter grow, similar to the shoulder expansion operation in step 1. Increase the power and the upper polycrystalline material moving speed simultaneously, and increase the power and the upper polycrystalline material moving speed to the equal diameter state. The power increase frequency is 2% / min, and the upper polycrystalline material moving speed increase frequency is 6% / min. Figure 2 As shown in Figure 4→.

[0031] Step 5: After growing to the target diameter again, slowly reduce the power by 10% and the frequency of reduction is 2% / min. At the same time, reduce the downward movement speed of the polycrystalline raw material to 50% and the speed reduction amplitude is 10% / min. At this time, the diameter of the lower polycrystalline rod gradually decreases. When the movement speed of the upper polycrystalline material is reduced to 50%, start to move the upper polycrystalline material upward and adjust the movement speed of the upper polycrystalline material to 3mm / min upward. Separate the upper and lower polycrystalline rods, and the lower polycrystalline material continues to move downward at the same speed, slowly away from the heat field, and cool naturally to end, such as Figure 2 As shown in Figure 5→.

[0032] After the purified polysilicon cools naturally, it is taken out by wrapping it in a clean packaging bag, and then the polysilicon tail waist is clamped by a fixture, and it can be directly hung in the furnace again for use. This reduces the need to cut grooves and etch the polysilicon tail after purification, improves production efficiency, and also reduces the waste generated in this process.

[0033] Each time the finishing process method of the present invention is used for purification, the loss of the purified polycrystalline cutting groove can be reduced by 0.5kg-1.5kg, the time consumption can be reduced by 8 hours, and the acid used for corrosion can be reduced by 4L.

Claims

1. A finishing process method for purifying polycrystalline silicon by a zone melting method, characterized in that: During the finishing operation, a waist-like shape is formed at the end. After the purified polysilicon cools naturally, it is taken out and the waist position of the polysilicon tail is clamped with a fixture. It is then directly hung in the furnace again to continue pulling single crystals or to perform purification operations again.

2. The finishing process method for purifying polysilicon by zone melting method according to claim 1, characterized in that: The following steps are involved: (1) Hang the etched polycrystals into the furnace and perform normal shoulder expansion operations. After the polycrystals are purified to the target diameter, they begin to grow stably; (2) When the remaining length of the upper polycrystalline material is 35-40 mm, the finishing operation begins; (3) When the diameter of the purified polycrystal is reduced by 15-20 mm, the tailing is stopped and the power and the moving speed of the upper polycrystal material are increased synchronously to make the diameter of the purified polycrystal begin to grow, similar to step (1) and the shoulder expansion operation is repeated; (4) After the purified polycrystal grows to the target diameter again, the power is slowly reduced and the downward movement of the polycrystal raw material is stopped. At this time, the diameter of the lower polycrystal rod gradually decreases. When the diameter of the lower purified polycrystal decreases by 15-20 mm, the upper polycrystal material is moved upward, the upper and lower polycrystal rods are separated, and the lower polycrystal material continues to move downward, slowly away from the heat field, and naturally cools to the end.

3. The finishing process method for purifying polysilicon by zone melting method according to claim 2, characterized in that: In the step (2), at the end, the power and the moving speed of the upper polycrystalline material are slowly reduced, the power reduction range is 10%-15%, and the reduction frequency is 2-3% / min; the moving speed of the upper polycrystalline material is reduced to 70-80% of the speed during equal diameter growth, and the frequency is 4-6% / min.

4. The finishing process method for purifying polysilicon by zone melting method according to claim 2, characterized in that: In the step (3), the power and the moving speed of the upper polycrystalline material are increased synchronously until the power and the moving speed of the upper polycrystalline material are increased to a state of equal diameter.

5. The finishing process method for purifying polycrystalline silicon by zone melting method according to claim 4, characterized in that: The power increase frequency is 2-3% / min, and the upper polycrystalline material moving speed increase frequency is 4-6% / min.

6. The finishing process method for purifying polycrystalline silicon by zone melting method according to claim 2, characterized in that: In the step (4), after growing to the target diameter again, the power is slowly reduced by 10%-15% and the frequency is 2-3% / min; at the same time, the downward moving speed of the polycrystalline raw material is reduced to 50-60% and the speed reduction is 10-12% / min; when the diameter of the lower purified polycrystalline is reduced by 15-20mm, the upper polycrystalline material is started to be moved upward and the moving speed of the upper polycrystalline material is adjusted to 2-3.5mm / min.

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