Gas guide heat shield and method for enhancing uniformity of single crystal product and single crystal furnace

Abstract

The invention provides a gas guide heat shield and method for enhancing uniformity of a single crystal product and a single crystal furnace, and belongs to the technical field of semiconductor processing. Comprising a gas guide heat insulation cover for enhancing uniformity of a single crystal product, the gas guide heat insulation cover is provided with an axially through hollow cavity, the bottom of a guide cylinder is sleeved with the gas guide heat insulation cover, the gas guide heat insulation cover is axially communicated with the guide cylinder, and the bottom of the gas guide heat insulation cover protrudes out of the bottom of the guide cylinder; a through hole is formed in the side wall of the air guide heat insulation cover. According to the invention, the air guide heat shield is arranged on the guide cylinder, and the through holes are formed in the side wall of the air guide heat shield, so that effective heat insulation and directional airflow guide between the heat shield and the crystal bar are realized, and thermal field distribution and impurity discharge in the monocrystalline silicon growth process are optimized.

Description

Technical Field

[0001] This invention relates to the field of semiconductor processing technology, specifically to a gas-conducting heat shield, method, and single-crystal furnace for enhancing the uniformity of single-crystal products. Background Technology

[0002] As a fundamental material for integrated circuits and the photovoltaic industry, the crystal quality of semiconductor single-crystal silicon directly affects device performance. In the Czochralski method of single-crystal growth, melt convection, temperature distribution, and impurity transport are key factors influencing single-crystal uniformity. The flow guide tube is an important component in the thermal field, primarily serving to guide gas flow and dissipate heat. Gas guidance involves directing the argon gas flow, thus influencing the transport path of gaseous impurities; heat dissipation involves shielding the single-crystal silicon rod from some of the heat radiated by the surrounding heaters, creating an axial temperature gradient. Therefore, the flow guide tube has a decisive influence on single-crystal uniformity through its control of the thermal field, gas flow field, and impurity transport process. However, traditional flow guide tubes have limited thermal field adjustment capabilities and cannot precisely control the axial temperature gradient; furthermore, gas guidance relies on natural convection, leading to turbulent protective gas flow that causes temperature fluctuations on the crystal surface, and the argon gas flow cannot effectively remove volatile dopants, resulting in low impurity removal efficiency. Summary of the Invention

[0003] In view of this, the present invention provides a gas-conducting heat insulation cover, method and single crystal furnace to enhance the uniformity of single crystal products, so as to solve the technical problems of limited thermal field adjustment capability and low impurity discharge efficiency of traditional flow guide tubes.

[0004] The technical solution adopted by this invention to solve its technical problem is:

[0005] A gas-conducting heat insulation cover for enhancing the uniformity of single crystal products, the gas-conducting heat insulation cover having an axially penetrating hollow cavity and being sleeved on the bottom of a flow guide tube, and being axially penetrating the flow guide tube, wherein the bottom of the gas-conducting heat insulation cover protrudes from the bottom of the flow guide tube; and the side wall of the gas-conducting heat insulation cover is provided with a through hole.

[0006] Preferably, the distance between the bottom of the gas-conducting heat insulation cover and the liquid surface of the silicon melt is 20-30 mm.

[0007] Preferably, the air-guiding heat insulation cover includes a connecting part and an air-guiding heat insulation part; the connecting part is frustum-shaped, and the upper diameter of the connecting part is larger than the diameter of the bottom of the guide tube; the air-guiding heat insulation part is cylindrical, and the diameter of the air-guiding heat insulation part is smaller than the diameter of the bottom of the guide tube, and the bottom of the air-guiding heat insulation part protrudes from the bottom of the guide tube.

[0008] Preferably, a connector is provided on the inner wall of the guide tube at the position corresponding to the connecting part, and the connecting part and the connector are connected in a fitting manner.

[0009] Preferably, the connector includes a connecting boss protruding from the inner wall of the guide tube.

[0010] Preferably, the material of the air-guiding heat insulation cover is quartz.

[0011] The present invention also provides a method for enhancing the uniformity of single crystal products. Before crystal pulling, a gas-conducting heat insulation cover is fitted onto the bottom of the guide tube, and the bottom of the gas-conducting heat insulation cover is adjusted to a preset distance from the liquid surface of the silicon melt. The crystal pulling program is started, and the liquid outlet distance and pulling speed are controlled accordingly so that the ratio of pulling speed to temperature gradient is controlled within the critical value range.

[0012] Preferably, the distance between the liquid outlets is 50-60 mm.

[0013] Preferably, the pulling speed is 0.5-0.6 mm / s.

[0014] The present invention also provides a single crystal furnace, including a flow guide tube, wherein a gas guide heat insulation cover as described above is provided on the flow guide tube.

[0015] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0016] This invention optimizes the thermal field distribution and impurity removal during the growth of single crystal silicon by setting a gas-guiding heat shield on the flow guide tube and opening through holes on the side wall of the gas-guiding heat shield, thereby achieving effective heat insulation and directional airflow guidance between the heat shield and the crystal rod. Attached Figure Description

[0017] Figure 1 This is a schematic diagram of the thermal field structure in an embodiment.

[0018] Figure 2 This is a schematic diagram of the thermal field structure for comparison.

[0019] Figure 3 This is a comparison chart of product yield between the examples and the comparative examples.

[0020] Figure 4 This is a comparison chart of oxygen content between the examples and the comparative examples.

[0021] In the figure: air guide heat insulation cover 10, through hole 11, connecting part 12, air guide heat insulation part 13, flow guide tube 20. Detailed Implementation

[0022] The technical solutions and effects of the embodiments of the present invention will be further described in detail below with reference to the accompanying drawings.

[0023] Please refer to Figure 1A gas-conducting heat insulation cover 10 for enhancing the uniformity of single crystal products. The gas-conducting heat insulation cover 10 has an axially penetrating hollow cavity and is sleeved on the bottom of the flow guide cylinder 20, and is axially penetrating the flow guide cylinder 20. The bottom of the gas-conducting heat insulation cover 10 protrudes from the bottom of the flow guide cylinder 20. The side wall of the gas-conducting heat insulation cover 10 is provided with a through hole 11.

[0024] This invention incorporates a gas-guiding heat shield 10 at the bottom of a traditional guide tube 20. Because the bottom of the gas-guiding heat shield 10 protrudes from the bottom of the guide tube 20, a heat insulation layer is formed between the crystal rod and the heat shield. This effectively blocks high-temperature heat from the crucible and heating zone from being conducted or radiated to the upper part of the crystal rod through the heat shield, helping to maintain the stable axial temperature gradient required for the crystal rod growth interface. Simultaneously, by controlling the temperature distribution above the crystal rod and reducing radial and axial temperature differences, the internal thermal stress of the crystal can be significantly reduced, thereby reducing defects such as dislocations and vacancies, and improving the structural integrity and electrical properties of single-crystal silicon. Furthermore, it reduces heat loss to the crystal rod region, enhancing the thermal insulation effect, reducing the power required by the heater, thus reducing energy consumption, and improving the stability and continuity of the crystal pulling process. Further, the gas-guiding heat shield can also isolate reactive gases and impurities released from components such as the crucible and heater, preventing them from entering the crystal rod growth region through convection, helping to reduce the concentration of impurities such as oxygen and improve the purity of the crystal rod. However, the original gap between the heat shield and the liquid surface was relatively wide, resulting in a large space area and slow airflow velocity. With the addition of the gas-guiding heat shield 10, the airflow velocity increased, easily leading to backflow or turbulence between the bottom of the gas-guiding heat shield 10 and the bottom of the guide tube 20. Therefore, this invention also provides through holes on the side wall of the gas-guiding heat shield 10 to enhance the flow between the gas inside and outside the gas-guiding heat shield 10, making the airflow more uniform on both sides of the gas-guiding heat shield 10. This helps stabilize the solid-liquid interface shape, reduce interface deflection, improve the crystal pulling success rate, and simultaneously enhance impurity removal, maintaining the stability of the growth interface. Thus, by setting the gas-guiding heat shield 10 in the guide tube and providing through holes on its side wall, effective heat insulation and directional airflow guidance between the heat shield and the crystal rod are achieved, thereby optimizing the thermal field distribution and impurity removal during the single-crystal silicon growth process.

[0025] In some embodiments, the sidewall of the gas-guiding heat insulation cover 10 is provided with multiple through holes at equal intervals to further enhance gas flow. Furthermore, since the bottom of the gas-guiding heat insulation cover 10 protrudes beyond the bottom of the guide cylinder 20, turbulence is easily formed between the protruding portion of the bottom of the gas-guiding heat insulation cover 10 and the bottom of the guide cylinder 20. Therefore, multiple through holes can be provided only on the sidewall of the protruding portion of the bottom of the gas-guiding heat insulation cover 10 to improve the utilization rate of the through holes.

[0026] Furthermore, the distance between the bottom of the gas-conducting heat shield 10 and the liquid surface of the silicon melt is 20-30 mm. When the distance between the bottom of the gas-conducting heat shield 10 and the liquid surface of the silicon melt is too far, the heat insulation effect of the gas-conducting heat shield 10 will be reduced, affecting the axial temperature gradient of the crystal rod; while when the distance is too close, the low-temperature surface of the gas-conducting heat shield 10 will strongly reflect the heat radiation from the surface of the melt, causing the surface temperature of the melt to drop sharply, while the lower layer of melt remains at a high temperature, thus forming an abnormally steep vertical temperature gradient inside the melt, exciting strong natural convection, and seriously interfering with the stability of the solid-liquid interface. Moreover, when the bottom of the gas-conducting heat shield 10 is too close to the liquid surface, the argon gas flow channel is compressed, the gas flow velocity increases sharply, and the laminar flow is transformed into turbulent or vortex flow, which inhibits the discharge of impurities. Therefore, the present invention sets the distance between the bottom of the gas-guiding heat shield 10 and the surface of the silicon melt to 20-30mm, so as to effectively block the radiative heat from the melt and the lower part of the thermal field and guide the airflow, thereby creating a more stable environment with a more uniform temperature gradient for the crystal growth area.

[0027] Further, please see Figure 1 The gas-guiding heat insulation cover 10 includes a connecting part 12 and a gas-guiding heat insulation part 13. The connecting part 12 is frustoconical, and its upper diameter is larger than the bottom diameter of the guide tube 20. The gas-guiding heat insulation part 13 is cylindrical, and its diameter is smaller than the bottom diameter of the guide tube 20. The bottom of the gas-guiding heat insulation part 13 protrudes from the bottom of the guide tube 20. Since the upper diameter of the connecting part 12 is larger than the bottom diameter of the guide tube 20, when the gas-guiding heat insulation cover 10 is fitted onto the bottom of the guide tube 20, the connecting part 12 fits snugly against the inner wall of the guide tube 20, thus realizing the assembly of the gas-guiding heat insulation cover 10 and the guide tube 20. The assembly process is convenient and the structure is simple.

[0028] Furthermore, a connector is provided on the inner wall of the guide tube 20 at a position corresponding to the connecting part 12, and the connecting part 12 and the connector are connected in a mating manner. By providing the connector, on the one hand, it can prevent the gas-guiding heat insulation cover 10 from being directly stuck on the guide tube 20, thus avoiding damage to the inner wall of the guide tube 20; on the other hand, the mating between the connecting part 12 and the connector can improve the assembly stability of the gas-guiding heat insulation cover 10 and the guide tube 20. In some embodiments, the connector includes a connecting boss protruding from the inner wall of the guide tube, which allows the connecting part 12 to overlap onto the connecting boss, completing the assembly of the gas-guiding heat insulation cover 10 and the guide tube 20. Because the connecting boss is provided, the gas-guiding heat insulation cover 10 is prevented from directly exerting force on the inner wall of the guide tube 20, and at the same time, the connecting boss provides a reaction support force for the gas-guiding heat insulation cover 10, improving the stability of the gas-guiding heat insulation cover 10.

[0029] In other embodiments, the connecting part 12 is provided with a first connecting hole, and the connecting boss is provided with a second connecting hole. The connecting part 12 overlaps with the side surface of the connecting boss near the top, and connecting pins are inserted into the corresponding first and second connecting holes. The connecting pins are inserted into the corresponding connecting holes in the connecting part 12 and the connecting boss to achieve a tight connection between the gas-guiding heat insulation cover 10 and the guide cylinder 20, preventing the gas flow inside the single crystal furnace from causing displacement of the gas-guiding heat insulation cover 10, which would affect the heat insulation and gas guiding effect. The first and second connecting holes serve to position and connect the connecting pins. Multiple connecting bosses can be provided on the inner sidewall of the guide cylinder 20, and multiple first connecting holes are opened on the connecting part 12 at positions corresponding to the second connecting holes of the connecting bosses to further enhance the tight connection between the gas-guiding heat insulation cover 10 and the guide cylinder 20.

[0030] Furthermore, the air-conducting heat insulation cover 10 is made of quartz material, which can further prevent crystal rod contamination and ensure the quality of the crystal rod.

[0031] In some embodiments, the gas-conducting heat insulation cover 10 can also be configured as a cylinder, and the upper part of the gas-conducting heat insulation cover 10 is connected to the lifting mechanism to control the distance of the bottom protrusion of the gas-conducting heat insulation part 10 according to different crystal growth stages, thereby realizing dynamic thermal field optimization of the growth interface.

[0032] This invention also provides a method for enhancing the uniformity of single-crystal products. Before crystal pulling, a gas-guided heat shield is fitted onto the bottom of the guide tube, and the bottom of the gas-guided heat shield is adjusted to a preset distance from the surface of the silicon melt. The crystal pulling program is then started, and the liquid outlet distance and pulling speed are controlled accordingly to keep the ratio of pulling speed to temperature gradient within a critical range. During crystal growth, two types of intrinsic point defects inevitably occur: vacancies and interstitial silicon atoms. The dominant defect type in the crystal is ultimately determined by the axial temperature gradient at the solid-liquid interface and the crystal growth rate, following the classical V / G (pulling speed / temperature gradient) theory. Its core is the existence of a critical ratio (V / G)*. When the actual V / G > (V / G)*, the oversaturation of vacancies is much higher than that of interstitial atoms, and the oversaturated vacancies will aggregate to form microvoid defects. This is the most common defect type in crystals. When the actual V / G < (V / G)*, interstitial atoms become overly dominant, and they will aggregate to form extended defects such as dislocation loops. When V / G is precisely controlled within a very narrow range near the critical value (V / G), the supersaturation of vacancies and interstitial atoms is comparable. They meet through diffusion and recombine, effectively suppressing the aggregation and growth of any macroscopic defects, resulting in a near-perfect crystal structure. Therefore, the core theoretical task of growing a perfect single crystal is to maintain the V / G value stably within the aforementioned narrow critical range throughout the entire growth process by synergistically and precisely controlling the thermal field (to control the axial temperature gradient G) and the pulling speed (V). Since the temperature gradient G changes after adding the gas-conducting heat shield, the pulling speed also needs to be controlled to maintain the V / G value close to the critical value for a perfect crystal. Simultaneously, because the bottom of the gas-conducting heat shield 10 protrudes from the bottom of the guide tube 20, altering the gas flow field above the liquid surface, the liquid outlet distance needs to be adjusted to accommodate the influence of the gas-conducting heat shield 10 on the airflow.

[0033] Furthermore, the liquid outlet distance is 50-60mm. Since the bottom of the gas-guiding heat shield 10 protrudes beyond the bottom of the guide tube 20, maintaining the original liquid outlet distance would increase the disturbance to the melt surface when the airflow blows from the gas-guiding heat shield 10 to the melt surface, disrupting the melt surface stability and inhibiting SiO volatilization, which is detrimental to reducing oxygen content. Appropriately increasing the liquid outlet distance enhances the blowing effect of the airflow on the melt surface, promoting SiO volatilization and reducing the oxygen content in the crystals.

[0034] Furthermore, the pulling speed is 0.5-0.6 mm / s. Since the gas-conducting heat shield 10 increases the temperature gradient G, the pulling speed needs to be appropriately increased to maintain the V / G value close to the critical value for a perfect crystal. In traditional Czochralski pulling processes, because the edges crystallize before the center, a resistivity distribution of "low at the center and high at the edges" is typically formed. Appropriately increasing the pulling speed can make the solid-liquid interface more flat, thereby improving the radial resistivity uniformity. Simultaneously, increasing the pulling speed accelerates the crystal growth rate and reduces the contact time between the melt and the quartz crucible, which can reduce the amount of oxygen introduced.

[0035] The present invention also provides a single crystal furnace, including a flow guide tube, on which a gas-guiding heat insulation cover as described above is disposed.

[0036] The beneficial effects of the present invention will be described below with reference to specific comparative examples and embodiments.

[0037] Example

[0038] Adopting such Figure 1 The thermal field design shown involves first installing a gas-conducting heat shield 10 at the bottom of the guide tube 20 before crystal pulling, and adjusting the distance between the bottom of the gas-conducting heat shield 10 and the surface of the molten silicon to 25mm. The crystal pulling program is then set, with the liquid outlet distance set to 55mm, the pulling speed set to 0.5mm / s, and other crystal pulling parameters set as usual. After the program is set, crystal pulling begins, yielding a single-crystal silicon rod A.

[0039] Comparative Example

[0040] Adopting such Figure 2 The thermal field design shown is used to set the crystal pulling program, with the liquid outlet distance set to 35mm and the pulling speed set to 0.4mm / s. Other crystal pulling parameters are consistent with the example. After the program is set, crystal pulling begins, and a single crystal silicon rod B is obtained.

[0041] The yields of single-crystal silicon rods A and B were measured respectively, and the results were as follows: Figure 3 The comparison chart shown shows that the yield of single-crystal silicon rod B is [missing information]. Figure 3 Before improvement, the yield was only 70%, while the yield of single-crystal silicon rod A was... Figure 3 After improvement, the yield reached 95%. Further, the oxygen content of single-crystal silicon rod A and single-crystal silicon rod B were measured respectively, and the results were as follows: Figure 4 The comparison chart shown shows that the oxygen content of single-crystal silicon rod B is... Figure 4 Before improvement, the oxygen content of the single crystal silicon rod A was: Figure 4The improved oxygen content shows a significant reduction compared to the original oxygen content. This demonstrates that this application, by installing a gas-guiding heat shield on the flow guide tube, creating through holes in the sidewall of the heat shield, and coordinating the control of the pulling speed and liquid outlet distance, couples the thermal field, flow field, and concentration field to achieve global optimization. This effectively improves the oxygen content control precision of monocrystalline silicon, enhances monocrystalline uniformity, and ultimately improves the quality of semiconductor-grade silicon monocrystalline products.

[0042] The above description discloses only preferred embodiments of the present invention and should not be construed as limiting the scope of the invention. Those skilled in the art will understand that implementing all or part of the above embodiments and making equivalent changes in accordance with the claims of the present invention are still within the scope of the invention.

Claims

1. A gas-conducting heat insulation cover for enhancing the uniformity of single-crystal products, characterized in that, The gas-guiding heat insulation cover has an axially penetrating hollow cavity and is sleeved on the bottom of the flow guide tube, communicating axially with the flow guide tube. The bottom of the gas-guiding heat insulation cover protrudes from the bottom of the flow guide tube. The side wall of the gas-guiding heat insulation cover has through holes.

2. The gas-conducting heat insulation cover for enhancing the uniformity of single-crystal products according to claim 1, characterized in that, The distance between the bottom of the gas-conducting heat insulation cover and the liquid surface of the silicon melt is 20-30mm.

3. The gas-conducting heat insulation cover for enhancing the uniformity of single-crystal products according to claim 2, characterized in that, The air-guiding heat insulation cover includes a connecting part and an air-guiding heat insulation part; the connecting part is frustum-shaped, and the upper diameter of the connecting part is larger than the bottom diameter of the guide tube; the air-guiding heat insulation part is cylindrical, and the diameter of the air-guiding heat insulation part is smaller than the bottom diameter of the guide tube, and the bottom of the air-guiding heat insulation part protrudes from the bottom of the guide tube.

4. The gas-conducting heat insulation cover for enhancing the uniformity of single-crystal products according to claim 3, characterized in that, A connector is provided on the inner wall of the guide tube at the position corresponding to the connecting part, and the connecting part and the connector are connected together.

5. The gas-conducting heat insulation cover for enhancing the uniformity of single-crystal products according to claim 4, characterized in that, The connector includes a connecting boss that protrudes from the inner wall of the guide tube.

6. The gas-conducting heat insulation cover for enhancing the uniformity of single-crystal products according to claim 1, characterized in that, The air-conducting heat insulation cover is made of quartz.

7. A method for enhancing the uniformity of single-crystal products, characterized in that, Before crystal pulling, a gas-conducting heat shield is placed on the bottom of the guide tube, and the bottom of the gas-conducting heat shield is adjusted to a preset distance from the liquid surface of the silicon melt; the crystal pulling program is started, and the liquid outlet distance and pulling speed are controlled accordingly so that the ratio of pulling speed to temperature gradient is controlled within the critical value range.

8. The method for enhancing the uniformity of single-crystal products according to claim 7, characterized in that, The distance between the liquid outlets is 50-60 mm.

9. The method for enhancing the uniformity of single-crystal products according to claim 8, characterized in that, The pulling speed is 0.5-0.6 mm / s.

10. A single crystal furnace, characterized in that, It includes a flow guide tube, on which a gas-guiding heat insulation cover as described in any one of claims 1-6 is provided.

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