Method for preparing phosphorus-doped silicon master alloy

Abstract

The application belongs to the technical field of solar photovoltaic materials, and particularly discloses a preparation method of phosphorus-doped silicon master alloy. A double-temperature-zone horizontal furnace is used, and zinc phosphide is used as a dopant. A sealed quartz horizontal ampoule is arranged in the double-temperature-zone horizontal furnace. A graphite boat is arranged in the high-temperature section of the quartz horizontal ampoule, and polycrystalline silicon material is arranged in the graphite boat. A quartz crucible is arranged in the low-temperature section, and zinc phosphide is arranged in the quartz crucible. Different temperatures of the high-temperature section and the low-temperature section are set, and the temperature is kept for a period of time, and then the temperature is reduced to obtain the phosphorus-doped silicon master alloy. The speed of synthesizing the phosphorus-doped silicon master alloy is fast, the method is safe and reliable, the requirement for equipment is low, and the manufacturing cost of the phosphorus-doped silicon master alloy is greatly reduced.

Description

Technical Field

[0001] This invention belongs to the field of solar photovoltaic materials technology, specifically relating to a method for preparing silicon alloys. Background Technology

[0002] Solar photovoltaic (PV) is a semiconductor device that directly converts sunlight into electrical energy. With the advancement of technology, more and more solar PV applications are being developed.

[0003] In the photovoltaic industry, silicon solar cells dominate. Currently, most monocrystalline silicon is manufactured using the Czochralski method, which involves heating and melting polycrystalline silicon, adding dopants, and then pulling it into monocrystalline silicon. Monocrystalline silicon has a wide resistivity range. For solar photovoltaics, monocrystalline silicon with lower resistivity achieves higher open-circuit voltage and photoelectric conversion efficiency, while solar cells made from monocrystalline silicon with higher resistivity have lower open-circuit voltages, resulting in very low conversion efficiency. Heavily phosphorus-doped monocrystalline silicon has extremely low resistivity. Currently, elemental phosphorus is mainly used as a dopant. Phosphorus is doped into high-purity silicon material, and the doped silicon rod is pulled using the Czochralski method to obtain a uniform phosphorus-doped silicon master alloy. This method requires placing the phosphorus directly in a single-crystal furnace. Because of its high vapor pressure, phosphorus volatilizes in large quantities during single crystal growth, making it difficult to effectively incorporate into silicon single crystals. This is especially true for heavily phosphorus-doped single crystal silicon, where the more phosphorus required for doping, the greater the amount of phosphorus volatilized during doping. This not only pollutes the thermal field inside the furnace, but also produces a large amount of white smoke when the furnace is turned on, which has a significant negative impact on safety and environmental protection. Summary of the Invention

[0004] In view of the problems existing in the prior art, the purpose of this invention is to provide a new method for preparing phosphorus-doped silicon master alloy.

[0005] To achieve the above objectives, the present invention adopts the following specific technical solutions.

[0006] A method for preparing a phosphorus-doped silicon master alloy, using zinc phosphide as a dopant.

[0007] Furthermore, in some preferred embodiments of the present invention, the preparation method of the phosphorus-doped silicon master alloy is carried out in a dual-temperature zone horizontal furnace.

[0008] Furthermore, in some preferred embodiments of the present invention, the high-temperature section of the dual-temperature zone horizontal furnace is the polycrystalline silicon discharge zone, and the low-temperature section is the zinc phosphide discharge zone.

[0009] Furthermore, in some preferred embodiments of the present invention, the dual-temperature zone horizontal furnace is equipped with a sealed quartz horizontal ampoule, the high-temperature section of the quartz horizontal ampoule is equipped with a graphite boat, which is a discharge container for polycrystalline silicon; the low-temperature section of the quartz horizontal ampoule is equipped with a quartz crucible, which is a discharge container for zinc phosphide.

[0010] Furthermore, in some preferred embodiments of the present invention, the mass ratio of polycrystalline silicon to zinc phosphide is 100:1~2.

[0011] Furthermore, in some preferred embodiments of the present invention, the quartz horizontal ampoule is sealed by vacuum sealing.

[0012] Furthermore, in some preferred embodiments of the present invention, the temperature of the high-temperature section of the dual-temperature zone horizontal furnace is 1410~1450°C, and the temperature of the low-temperature section is 400~418°C.

[0013] Furthermore, in some preferred embodiments of the present invention, the heat preservation time of the high-temperature section and the low-temperature section of the quartz horizontal ampoule is 48~72h.

[0014] Furthermore, in some preferred embodiments of the present invention, after the quartz horizontal ampoule has finished being kept warm, it is cooled down at a rate of 20~30℃ / h.

[0015] This invention uses zinc phosphide as a dopant in solar photovoltaic silicon materials. Zinc phosphide can be effectively decomposed at relatively low temperatures, releasing phosphorus vapor, which diffuses into the silicon melt. The zinc produced during decomposition is solid with a very low vapor pressure, thus avoiding contamination of the silicon material. This invention provides a fast, safe, and reliable synthesis of phosphorus-doped silicon master alloys with low equipment requirements, significantly reducing the manufacturing cost of phosphorus-doped silicon master alloys. Detailed Implementation

[0016] To facilitate understanding of the present invention, the present invention will be described more fully and in detail below with reference to preferred embodiments and comparative examples, but the scope of protection of the present invention is not limited to the following specific embodiments.

[0017] Unless otherwise defined, all technical terms used herein have the same meaning as commonly understood by those skilled in the art. The technical terms used herein are for the purpose of describing particular embodiments only and are not intended to limit the scope of the invention.

[0018] Unless otherwise specified, all raw materials, reagents, instruments and equipment used in this invention can be purchased from the market or prepared by existing methods.

[0019] This invention uses zinc phosphide as a dopant to prepare a phosphorus-doped silicon master alloy.

[0020] In the preparation of the phosphorus-doped silicon master alloy, a dual-temperature zone horizontal furnace was used, containing a sealed quartz horizontal ampoule. The high-temperature zone of the quartz ampoule contained a graphite boat holding polycrystalline silicon material, while the low-temperature zone contained a quartz crucible holding zinc phosphide. Different temperatures were set for the high-temperature and low-temperature zones of the dual-temperature zone, and the temperatures were maintained for a period of time before cooling to obtain the phosphorus-doped silicon master alloy.

[0021] In a specific embodiment, the quartz horizontal ampoule is sealed using a vacuum seal. The vacuum-sealed quartz ampoule effectively seals the phosphorus within the ampoule, preventing contamination of the furnace body.

[0022] In a specific embodiment, the mass ratio of polycrystalline silicon to zinc phosphide is 100:1~2.

[0023] In a specific embodiment, the temperature of the high-temperature section of the quartz horizontal ampoule is 1410~1450℃, preferably 1430℃. In the high-temperature section, the polycrystalline silicon material is melted.

[0024] In a specific embodiment, the low-temperature range of the quartz horizontal ampoule is 400~418℃. Within this temperature range, zinc phosphide begins to decompose effectively and slowly releases phosphorus vapor. The zinc produced during decomposition is solid at this temperature, with a very low vapor pressure, and will not contaminate the polycrystalline silicon material.

[0025] Zinc phosphide is a powdered material, facilitating accurate weighing; it is non-flammable in air, making the operation safer and more reliable. Furthermore, zinc phosphide is a compound that acts as a slow-release agent, moderating the release of phosphorus, lowering its saturated vapor pressure, reducing the risk of quartz ampoule breakage, and ensuring smooth production. If phosphorus is used directly as a dopant, its high saturated vapor pressure can cause quartz ampoules to break, even when used in quartz ampoules.

[0026] In a specific embodiment, the heat preservation time for both the high-temperature and low-temperature sections of the quartz horizontal ampoule is 48-72 hours, preferably 60-72 hours. During these heat preservation times, the molten silicon absorbs sufficient phosphorus vapor and reaches equilibrium.

[0027] In this specific implementation, after the reaction is complete, the temperature is lowered. The cooling rate is 20~30℃ / h. Lowering the temperature at this level can prevent the graphite boat containing the silicon raw material from cracking.

[0028] The technical solution of the present invention will be further described in detail below through specific embodiments and comparative examples.

[0029] Example 1

[0030] Design and fabricate a silicon master alloy with a resistivity of 0.006 Ω·cm.

[0031] A dual-temperature zone horizontal furnace is used, within which sealed quartz horizontal ampoules are placed. The high-temperature zone of the quartz horizontal ampoules contains a graphite boat containing 8 kg of 7N pure polycrystalline silicon material, while the low-temperature zone contains a quartz crucible containing 80 g of zinc phosphide. The quartz horizontal ampoules are vacuum-sealed.

[0032] The high-temperature zone of the dual-temperature horizontal furnace was set to 1410℃, and the low-temperature zone to 400℃, and the temperature was held for 72 hours. Then, the temperature was reduced to room temperature at a rate of 20℃ / h.

[0033] Comparative Example 1

[0034] The only difference between Comparative Example 1 and Example 1 is that the quartz horizontal ampoule is sealed with nitrogen.

[0035] Comparative Example 2

[0036] The only difference between Comparative Example 2 and Example 1 is that the quartz horizontal ampoule is located in a vacuum environment, is not sealed, and is open.

[0037] Comparative Example 3

[0038] The only difference between Comparative Example 3 and Example 1 is that the quartz horizontal ampoule is located in a nitrogen atmosphere, is not sealed, and is open.

[0039] Comparative Example 4

[0040] The only difference between Comparative Example 4 and Example 1 is that the high-temperature section of the dual-temperature zone horizontal furnace has a temperature of 1450°C.

[0041] Comparative Example 5

[0042] The only difference between Comparative Example 5 and Example 1 is that the high-temperature section of the dual-temperature zone horizontal furnace has a temperature of 1400°C.

[0043] Comparative Example 6

[0044] The only difference between Comparative Example 6 and Example 1 is that the temperature of the low-temperature section of the dual-temperature zone horizontal furnace is 380°C.

[0045] Comparative Example 7

[0046] The only difference between Comparative Example 7 and Example 1 is that the holding time of the dual-temperature zone horizontal furnace is 40 hours.

[0047] Comparative Example 8

[0048] The only difference between Comparative Example 8 and Example 1 is that the cooling rate is 40°C / h.

[0049] Comparative Example 9

[0050] The only difference between Comparative Example 9 and Example 1 is that the cooling rate is 10°C / h.

[0051] Comparative Example 10

[0052] The only difference between Comparative Example 10 and Example 1 is that the quartz crucible contains 5g of phosphorus instead of 80g of zinc phosphide.

[0053] Example 2

[0054] Design and fabricate a silicon master alloy with a resistivity of 0.01 Ω·cm.

[0055] A dual-temperature zone horizontal furnace is employed, within which sealed quartz horizontal ampoules are contained. The high-temperature zone of each quartz horizontal ampoule contains a graphite boat containing 10 kg of 7N pure polycrystalline silicon material, while the low-temperature zone contains a quartz crucible containing 150 g of zinc phosphide. The quartz horizontal ampoules are vacuum-sealed.

[0056] The high-temperature zone of the dual-temperature horizontal furnace was set to 1410℃, and the low-temperature zone to 418℃, and the temperature was held for 60 hours. Then, the temperature was reduced to room temperature at a rate of 20℃ / h.

[0057] Example 3

[0058] Design and fabricate a silicon master alloy with a resistivity of 0.015 Ω·cm.

[0059] A dual-temperature zone horizontal furnace is employed, within which sealed quartz horizontal ampoules are contained. The high-temperature zone of each quartz horizontal ampoule contains a graphite boat containing 10 kg of 7N pure polycrystalline silicon material, while the low-temperature zone contains a quartz crucible containing 200 g of zinc phosphide. The quartz horizontal ampoules are vacuum-sealed.

[0060] The high-temperature zone of the dual-temperature horizontal furnace was set to 1410℃, and the low-temperature zone to 410℃, and the temperature was held for 48 hours. Then, the temperature was reduced to room temperature at a rate of 30℃ / h.

[0061] The phosphorus content and resistivity of the products obtained in Examples 1-3 and Comparative Examples 1-9 were determined.

[0062] Measurement of phosphorus content in phosphorus-doped silicon master alloy: The method of secondary ion mass spectrometry for measuring the content of P, As and Sb donor impurities in silicon materials for photovoltaic cells was adopted according to GB / T 29852-2013.

[0063] Measurement of the electrical properties of phosphorus-doped silicon master alloy: measured in accordance with GB / T 1551 Method for Determination of Resistivity of Single Crystal Silicon.

[0064] The measurement results are shown in Table 1.

[0065] Table 1

[0066]

[0067] As can be seen from the data in Table 1, using zinc phosphide as a dopant changes the situation where polycrystalline silicon cannot be doped when phosphorus is used as a dopant. Furthermore, by adjusting the appropriate process parameters, a phosphorus-doped silicon master alloy with low resistivity can be obtained.

[0068] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A method for preparing a phosphorus-doped silicon master alloy, characterized in that, Zinc phosphide was used as a dopant in a dual-temperature zone horizontal furnace. The high-temperature zone of the dual-temperature zone horizontal furnace was the polycrystalline silicon feeding zone, and the low-temperature zone was the zinc phosphide feeding zone. The temperature of the high-temperature zone of the dual-temperature zone horizontal furnace was 1410~1450℃, and the temperature of the low-temperature zone was 400~418℃. The holding time of the high-temperature zone and the low-temperature zone was 48~72h. After the holding time was completed, the temperature was lowered at a rate of 20~30℃ / h.

2. The method for preparing the phosphorus-doped silicon master alloy as described in claim 1, characterized in that, The dual-temperature zone horizontal furnace contains sealed quartz horizontal ampoules. The high-temperature section of the quartz horizontal ampoules contains a graphite boat, which serves as a discharge container for polycrystalline silicon. The low-temperature section of the quartz horizontal ampoules contains a quartz crucible, which serves as a discharge container for zinc phosphide.

3. The method for preparing the phosphorus-doped silicon master alloy as described in claim 1, characterized in that, The mass ratio of polycrystalline silicon to zinc phosphide is 100:1~2.

4. The method for preparing the phosphorus-doped silicon master alloy as described in claim 2, characterized in that, The quartz horizontal ampoule is sealed by vacuum sealing.

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