High-purity silicon chemical vapor deposition system and method based on composite ceramic lining

Abstract

The invention provides a high-purity silicon chemical vapor deposition system based on a composite ceramic lining. The high-purity silicon chemical vapor deposition system comprises a reaction cavity, a heating unit, a gas inlet unit, a tail gas treatment unit and a control unit, the reaction cavity comprises a lining made of a silicon carbide-hexagonal boron nitride composite ceramic material. The invention further provides a method for preparing high-purity silicon by using the chemical vapor deposition system. The method comprises the steps of lining surface pretreatment, deposition temperature field establishment, silicon vapor deposition and the like. The lining of the reaction cavity is made of the silicon carbide-boron nitride composite ceramic material, pollution impurities cannot be generated, the sealing performance of the working environment in the reaction cavity can be better maintained, and impurities generated by other metal materials outside the lining are prevented from entering the reaction cavity. According to the preparation method, the surface of the lining is pretreated, an atomic-scale passivation layer is generated on the reaction surface of the lining in situ, cation impurities in the lining body are prevented from diffusing into a gas phase and deposited silicon, and the effect of reducing the impurities is further achieved.

Description

Technical Field

[0001] This invention relates to the field of chemical vapor deposition for the preparation of high-purity silicon, and particularly to a high-purity silicon chemical vapor deposition system and method based on a composite ceramic liner. Background Technology

[0002] High-purity polycrystalline silicon is a semiconductor core material with a purity of ≥99.9999% (6N) and existing in a polycrystalline form. It is divided into electronic grade (≥9N-11N) and solar grade (≥6N). It is mainly used in semiconductor chips and photovoltaic cells, and is also the basic raw material for power devices, MEMS sensors and infrared optical components.

[0003] Currently, the mainstream high-purity silicon preparation technologies are the modified Siemens process (trichlorosilane hydrogen reduction) or the silane process. Their core principle is a closed-loop process of trichlorosilane (SiHCl3) purification by distillation followed by chemical vapor deposition (CVD) reduction, which can stably produce 9N+ electronic-grade polycrystalline silicon. The main equipment used is a CVD reactor, where a silicon core (usually a slender rod) placed in the reactor's reaction chamber comes into contact with the gas, gradually depositing high-purity silicon on the core's surface. However, during the high-temperature (typically >1000℃) deposition process, the reactor liner or carrier can become a significant source of impurities contaminating the silicon material. Traditional liner materials, such as high-purity graphite, can introduce carbon, metals, and other impurities into the silicon at high temperatures due to the volatilization of trace impurities, particle shedding, or interaction with the reacting gases, affecting the electrical properties of the silicon ingot. Quartz glass liners, on the other hand, have low strength, poor thermal shock resistance, are prone to breakage, and have a short lifespan.

[0004] Current technological improvements primarily focus on optimizing external process parameters (such as airflow design and heating uniformity) or purifying post-deposition silicon materials, representing passive responses. For example, Chinese invention patent CN116282036B discloses a polycrystalline silicon cold hydrogenation catalyst recovery and separation device and a polycrystalline silicon production system. This device utilizes magnetic separation for efficient catalyst separation, reducing production costs and product impurity content, thereby ensuring product purity and quality. Chinese invention patent CN112374502B proposes a polycrystalline silicon cold hydrogenation method using a gas-solid co-current flowing fluidized bed reactor. This eliminates the gas-solid ring core structure of the upward fluidized bed reactor, resulting in a more thorough and uniform reaction with higher efficiency. Less silicon powder and catalyst are carried away during the reaction, allowing for recycling and higher silicon powder utilization, significantly reducing slurry generation. However, these advancements do not address the pollution source—the interfacial chemical properties of the reactor lining material. Therefore, a novel reactor lining and associated deposition technology is urgently needed to suppress impurity migration at its source and positively impact silicon crystal growth. Summary of the Invention

[0005] To address the shortcomings of existing technologies, this invention provides a high-purity silicon chemical vapor deposition system and method based on a composite ceramic liner. This system solves the problem in existing technologies where the reactor liner or carrier introduces impurities into the silicon at high temperatures due to the volatilization of trace impurities, particle shedding, or interaction with reaction gases, thus affecting product purity.

[0006] In a first aspect, the present invention proposes a high-purity silicon chemical vapor deposition system based on a composite ceramic liner, comprising a reaction chamber, a heating unit, an air intake unit, an exhaust gas treatment unit, and a control unit.

[0007] The reaction chamber includes a liner made of silicon carbide-hexagonal boron nitride composite ceramic material. The liner constitutes the entire inner wall surface of the reaction chamber and the base supporting the silicon seed crystal, or it may only constitute the entire inner wall surface of the reaction chamber. On the working surface of the liner, the hexagonal boron nitride phase is dispersed in the silicon carbide matrix in the form of micron-sized lamellar crystals.

[0008] The heating unit is a multi-segment independent temperature-controlled heater surrounding the reaction chamber, which can form a precisely controlled temperature gradient in the axial and radial directions of the liner.

[0009] The air intake unit is used to introduce a mixture of silane gas and hydrogen gas into the reaction chamber;

[0010] The exhaust gas treatment unit uses a dust removal and purification method to remove silicon particles and harmful gaseous pollutants contained in the exhaust gas.

[0011] The control unit is electrically connected to the reaction chamber, heating unit, air intake unit, and exhaust gas treatment unit, respectively, thereby controlling the automated operation of the entire system.

[0012] Furthermore, the liner is prepared in the following manner:

[0013] Silicon carbide micro powder, flake-shaped hexagonal boron nitride powder, and a composite sintering aid containing aluminum nitride and yttrium oxide are mixed to prepare a ceramic slurry. The slurry is then formed into a green body according to the shape of the reaction chamber using direct-write 3D printing technology. The green body is then pre-oxidized at 800℃-1000℃ in an air atmosphere. Finally, it is sintered in two stages at 1400℃-1600℃ and 1850℃-2000℃ under a protective atmosphere to form a composite ceramic lining.

[0014] Furthermore, it also includes a surface pretreatment unit connected to the reaction chamber, which can introduce a pretreatment gas containing a boron source or a nitrogen source into the reaction chamber.

[0015] Preferably, the pretreatment gas is a mixture of diborane and hydrogen or ammonia.

[0016] Furthermore, the exhaust gas treatment unit includes a cyclone dust collector, a cryogenic condenser gas-liquid separator, an HCl absorption tower, a PSA hydrogen purification chamber, and a combustion alkaline washing tank arranged in sequence. First, dust is removed, and chlorosilane is recovered by cooling and condensation. Then, HCl and high-purity hydrogen are separated and purified to achieve raw material recycling. Finally, the residual waste gas is burned and neutralized by alkaline washing.

[0018] The present invention also proposes a method for preparing high-purity silicon using the above-mentioned chemical vapor deposition system, comprising the following steps:

[0019] S1. Surface pretreatment of the inner lining: After the silicon seed crystal is loaded into the reaction chamber, the system is sealed and a vacuum is drawn. A pretreatment gas containing a boron source or a nitrogen source is introduced into the reaction chamber. The pretreatment gas reacts with the working surface of the inner lining at 600℃-900℃ for 0.5h-4h, thereby generating a boron-rich or nitrogen-rich passivation layer on its surface in situ.

[0020] S2. Deposition temperature field establishment: After the pretreatment is completed, switch to the deposition process, raise the temperature of the lining of the reaction chamber to the deposition temperature through the heating unit, and establish the required axial temperature gradient in the reaction chamber.

[0021] S3. Silicon vapor deposition: A mixture of high-purity silane gas and hydrogen is introduced into the reaction chamber. The gas flow rate and pressure are controlled to allow the silicon crystal to grow continuously. After the predetermined deposition time or predetermined silicon ingot size is reached, the silane is stopped, and the temperature is programmed to cool down in a hydrogen atmosphere to obtain a high-purity silicon ingot product.

[0022] Furthermore, in step S2, when silane is used as a raw material, the deposition temperature is 1050℃-1150℃.

[0023] Furthermore, in step S2, the temperature at the top of the reaction chamber is higher than the temperature at the bottom, forming a temperature gradient within a range of 50°C that gradually decreases from top to bottom, which is conducive to gas phase transport and deposition.

[0024] Furthermore, in step S3, the gas flow rate is 45-55 L / min, and the system pressure is maintained at 0.04 MPa-0.06 MPa.

[0025] Compared with the prior art, the present invention has the following beneficial effects:

[0026] 1. The reaction chamber lining of this invention is made of silicon carbide-boron nitride composite ceramic material. This ceramic material, characterized by high density, extremely low chemical reactivity, and strong high-temperature stability, constructs an active "chemical barrier" on the reactor lining surface. This ensures that the lining not only prevents the generation of contaminating impurities but also better maintains the sealing of the internal working environment of the reaction chamber, preventing impurities from other metal materials outside the lining from entering the reaction chamber. This can reduce the carbon and metal impurity content in the silicon ingot by more than an order of magnitude.

[0027] 2. In this invention, hexagonal boron nitride is introduced as the liner material. Its crystal structure has a specific lattice matching relationship with some polycrystalline silicon crystal planes. Its diffuse distribution on the liner reaction surface can provide heterogeneous nucleation sites for silicon deposition, which helps to obtain a silicon crystal structure with more uniform grain size and fewer defects, and potentially improves the electrical performance of silicon wafers.

[0028] 3. In the high-purity silicon preparation method proposed in this invention, the inner liner surface is first pretreated using a boron or nitrogen source gas. A boron-rich or nitrogen-rich atomic-level passivation layer is generated in situ on the inner liner reaction surface. Through the passivation layer and its inherent low surface energy characteristics, cationic impurities in the inner liner body (such as Y from sintering aids) can be effectively blocked. 3+ Al 3+ It diffuses into the gas phase and deposited silicon, further reducing impurities. Detailed Implementation

[0029] The technical solutions of the present invention will be further described below with reference to the embodiments.

[0030] Example 1:

[0031] This embodiment of a high-purity silicon chemical vapor deposition system based on a composite ceramic liner includes a reaction chamber, a heating unit, an air intake unit, an exhaust gas treatment unit, and a control unit. The reaction chamber includes a liner made of silicon carbide-hexagonal boron nitride composite ceramic material. This liner forms the entire inner wall surface of the reaction chamber and the base supporting the silicon seed crystal, or it may only form the entire inner wall surface of the reaction chamber. On the working surface of the liner, the hexagonal boron nitride phase is dispersed in the silicon carbide matrix in a micron-sized lamellar morphology.

[0032] The heating unit consists of a multi-segment, independently temperature-controlled heater surrounding the reaction chamber, employing resistance heating to create a precisely controlled temperature gradient along the axial and radial directions of the lining. The air intake unit is a metering pump connected to a gas tank, used to introduce a mixture of silane and hydrogen into the reaction chamber. The exhaust gas treatment unit comprises, in sequence, a cyclone dust collector, a cryogenic condenser gas-liquid separator, an HCl absorption tower, a PSA hydrogen purification chamber, and a combustion alkaline washing tank. It first removes dust, cools and condenses to recover chlorosilane, then separates and purifies HCl and high-purity hydrogen for raw material recycling, and finally combusts and neutralizes the residual waste gas through alkaline washing. The control unit is a microprocessor electrically connected to the reaction chamber, heating unit, air intake unit, and exhaust gas treatment unit, thereby controlling the automated operation of the entire system.

[0033] It also includes a surface pretreatment unit connected to the reaction chamber, which can introduce pretreatment gas into the reaction chamber. The pretreatment gas is a mixture of diborane and hydrogen or ammonia.

[0034] In this embodiment, the liner is prepared in the following manner:

[0035] Silicon carbide micro powder, flake-shaped hexagonal boron nitride powder, and a composite sintering aid containing aluminum nitride and yttrium oxide are mixed to prepare a ceramic slurry. The slurry is then formed into a green body according to the shape of the reaction chamber using direct-write 3D printing technology. The green body is then pre-oxidized at 800℃-1000℃ in an air atmosphere. Finally, it is sintered in two stages at 1400℃-1600℃ and 1850℃-2000℃ under a protective atmosphere to form a composite ceramic lining.

[0036] Based on the above system, high-purity silicon is prepared using the following steps in this embodiment:

[0037] (1) After the high-purity polycrystalline silicon fine rods are loaded into the reaction chamber as seed crystals, the system is sealed and a vacuum is drawn. A pretreatment gas composed of 5% diborane and 95% hydrogen is introduced into the reaction chamber and the pretreatment gas reacts with the inner lining working surface at 800°C for 2 hours.

[0038] (2) After the pretreatment is completed, the temperature in the reaction chamber is raised to 1100℃. A mixture of 20% silane and 80% hydrogen is introduced, with a gas flow rate of 50 L / min under standard conditions, and the system pressure is maintained at 0.05 MPa.

[0039] (3) After continuous deposition for 200 hours, the reaction was stopped to obtain a polycrystalline silicon ingot with a diameter of about 220 mm.

[0041] Example 2:

[0042] The structure of the chemical vapor deposition system in this embodiment is the same as that in Example 1. The difference is that high-purity silicon is prepared using the following steps in this embodiment:

[0043] (1) After the high-purity polycrystalline silicon fine rods are loaded into the reaction chamber as seed crystals, the system is sealed and a vacuum is drawn. A pretreatment gas composed of 4% diborane and 96% hydrogen is introduced into the reaction chamber and the pretreatment gas reacts with the working surface of the inner lining at 600°C for 0.5h.

[0044] (2) After the pretreatment is completed, the temperature in the reaction chamber is raised to 1050℃. A mixture of 15% silane and 85% hydrogen is introduced, with a gas flow rate of 45 L / min under standard conditions, and the system pressure is maintained at 0.04 MPa.

[0045] (3) After continuous deposition for 200 hours, the reaction was stopped to obtain a polycrystalline silicon ingot with a diameter of about 220 mm.

[0047] Example 3:

[0048] The structure of the chemical vapor deposition system in this embodiment is the same as that in Example 1. The difference is that high-purity silicon is prepared using the following steps in this embodiment:

[0049] (1) After the high-purity polycrystalline silicon fine rods are loaded into the reaction chamber as seed crystals, the system is sealed and a vacuum is drawn. A pretreatment gas formed by ammonia is introduced into the reaction chamber and the pretreatment gas reacts with the inner lining working surface at 900°C for 4 hours.

[0050] (2) After the pretreatment is completed, the temperature in the reaction chamber is raised to 1150℃. A mixture of 25% silane and 75% hydrogen is introduced, with a gas flow rate of 55 L / min under standard conditions, and the system pressure is maintained at 0.06 MPa.

[0051] (3) After continuous deposition for 200 hours, the reaction was stopped to obtain a polycrystalline silicon ingot with a diameter of about 220 mm.

[0053] Comparative example:

[0054] Using the standard modified Siemens process, polycrystalline silicon ingots of the same size (approximately 220 mm in diameter) were prepared in a graphite-lined chemical deposition reactor.

[0056] The polycrystalline silicon ingot products of Examples 1-3 and the comparative examples were compared in terms of parameters, and the contents of key metal impurities such as iron (Fe), chromium (Cr), and nickel (Ni) were tested. At the same time, minority carrier lifetime tests were performed on the silicon ingots. The results are shown in Table 1.

[0057]

[0058] As can be seen from Table 1, the metal impurity content of the product prepared by the present invention is significantly lower than that of the product prepared by the prior art, and its minority carrier lifetime is also significantly improved, which fully demonstrates the advantages of the present invention in reducing the introduction of impurities.

[0059] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit it. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of the present invention without departing from the spirit and scope of the technical solutions of the present invention, and all such modifications or substitutions should be covered within the scope of the claims of the present invention.

Claims

1. A high-purity silicon chemical vapor deposition system based on a composite ceramic liner, characterized in that: It includes a reaction chamber, a heating unit, an air intake unit, an exhaust gas treatment unit, and a control unit; The reaction chamber includes a liner made of silicon carbide-hexagonal boron nitride composite ceramic material. The liner constitutes the entire inner wall surface of the reaction chamber and the base supporting the silicon seed crystal, or it may only constitute the entire inner wall surface of the reaction chamber. On the working surface of the liner, the hexagonal boron nitride phase is dispersed in the silicon carbide matrix in the form of micron-sized lamellar crystals. The heating unit is a multi-segment independent temperature-controlled heater surrounding the reaction chamber, which can form a precisely controlled temperature gradient in the axial and radial directions of the liner. The air intake unit is used to introduce a mixture of silane gas and hydrogen gas into the reaction chamber; The exhaust gas treatment unit uses a dust removal and purification method to remove silicon particles and harmful gaseous pollutants contained in the exhaust gas. The control unit is electrically connected to the reaction chamber, heating unit, air intake unit, and exhaust gas treatment unit, respectively, thereby controlling the automated operation of the entire system.

2. The high-purity silicon chemical vapor deposition system based on a composite ceramic liner as described in claim 1, characterized in that, The liner is prepared in the following manner: Silicon carbide micro powder, flake-shaped hexagonal boron nitride powder, and a composite sintering aid containing aluminum nitride and yttrium oxide are mixed to prepare a ceramic slurry. The slurry is then formed into a green body according to the shape of the reaction chamber using direct-write 3D printing technology. The green body is then pre-oxidized at 800℃-1000℃ in an air atmosphere. Finally, it is sintered in two stages at 1400℃-1600℃ and 1850℃-2000℃ under a protective atmosphere to form a composite ceramic lining.

3. The high-purity silicon chemical vapor deposition system based on a composite ceramic liner as described in claim 1, characterized in that: It also includes a surface pretreatment unit connected to the reaction chamber, which can introduce pretreatment gas containing a boron source or a nitrogen source into the reaction chamber.

4. The high-purity silicon chemical vapor deposition system based on a composite ceramic liner as described in claim 3, characterized in that: The pretreatment gas is a mixture of diborane and hydrogen or ammonia.

5. The high-purity silicon chemical vapor deposition system based on a composite ceramic liner as described in claim 1, characterized in that: The exhaust gas treatment unit includes a cyclone dust collector, a cryogenic condenser gas-liquid separator, an HCl absorption tower, a PSA hydrogen purification chamber, and a combustion alkaline washing tank arranged in sequence. First, dust is removed, and chlorosilane is recovered by cooling and condensation. Then, HCl and high-purity hydrogen are separated and purified to achieve raw material recycling. Finally, the residual waste gas is burned and neutralized by alkaline washing.

6. A method for preparing high-purity silicon using a chemical vapor deposition system as described in any one of claims 1-5, characterized in that, Includes the following steps: S1. Surface pretreatment of the inner lining: After the silicon seed crystal is loaded into the reaction chamber, the system is sealed and a vacuum is drawn. A pretreatment gas containing a boron source or a nitrogen source is introduced into the reaction chamber. The pretreatment gas reacts with the working surface of the inner lining at 600℃-900℃ for 0.5h-4h, thereby generating a boron-rich or nitrogen-rich passivation layer on its surface in situ. S2. Deposition temperature field establishment: After the pretreatment is completed, switch to the deposition process, raise the temperature of the lining of the reaction chamber to the deposition temperature through the heating unit, and establish the required axial temperature gradient in the reaction chamber. S3. Silicon vapor deposition: A mixture of high-purity silane gas and hydrogen is introduced into the reaction chamber. The gas flow rate and pressure are controlled to allow the silicon crystal to grow continuously. After the predetermined deposition time or predetermined silicon ingot size is reached, the silane is stopped, and the temperature is programmed to cool down in a hydrogen atmosphere to obtain a high-purity silicon ingot product.

7. The method for preparing high-purity silicon as described in claim 6, characterized in that: In step S2, when silane is used as a raw material, the deposition temperature is 1050℃-1150℃.

8. The method for preparing high-purity silicon as described in claim 6, characterized in that: In step S2, the temperature at the top of the reaction chamber is higher than that at the bottom, forming a temperature gradient within a range of 50°C that gradually decreases from top to bottom, which is beneficial for gas phase transport and deposition.

9. The method for preparing high-purity silicon as described in claim 6, characterized in that: In step S3, the gas flow rate is 45-55 L / min, and the system pressure is maintained at 0.04 MPa-0.06 MPa.

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