Single crystal furnace with double heat shields

Abstract

The invention discloses a single crystal furnace with double heat shields, which belongs to the technical field of single crystal silicon growth of photovoltaic equipment, and is characterized in that a double heat shield structure is introduced into the single crystal furnace to guide an argon flow path near a free surface of a melt so as to eliminate argon vortex on the outer sides of the heat shields; and the risk of melt pollution and crystal breaking caused by the fact that volatilized impurity gas deposits on the outer side of the heat shield and then falls back into the melt is avoided. A first flow channel is formed between the double heat shields, a second flow channel is formed between the auxiliary heat shield and the inner wall of the quartz crucible, and a divergent channel is formed among the first flow channel, the second flow channel and the free surface of melt, so that the flow velocity of argon above the free surface is integrally improved, and the discharge of foreign gas and the heat dissipation of crystals are accelerated; therefore, the growth rate of the crystal is improved while the oxygen content of the crystal is reduced.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of single crystal silicon growth, in particular to a double-heat-shield single crystal furnace. BACKGROUND

[0002] With the continuous progress of science and technology and the continuous development of 5G, artificial intelligence, new energy vehicles and other industries, as one of the most important raw materials in the photovoltaic, semiconductor and other industries, under the promotion of the global low-carbon and intelligent development trend, the demand for semiconductors is growing. Silicon wafer is the basis of microchips, and larger silicon wafers can produce more chips per wafer, thereby improving manufacturing efficiency and reducing costs. Therefore, improving the growth rate of large-diameter silicon wafers is crucial to reducing costs.

[0003] With the development of large-size silicon rods, the number of crucibles and melts increases. In order to avoid the condensation of silicon melt in the quartz crucible due to the temperature drop below the melting point, a larger heater power is needed to maintain the thermal field in the furnace, which inevitably leads to an increase in oxygen impurities. Excessive oxygen impurities can form oxygen precipitates, affecting the performance of the product.

[0004] The existing single crystal furnace has a high oxygen impurity content in the produced crystal. A distance is usually reserved between the bottom of the heat shield and the crucible wall. During the crystal pulling process, a large space is formed between the heat shield and the silicon liquid surface. During the flow of argon, the sudden increase in the cross-sectional area of the flow channel will cause the flow rate to decrease rapidly, and a low-flow argon vortex will be formed above the free surface. This vortex not only delays the normal flow of argon, reduces the heat and impurity removal efficiency, and leads to a high oxygen content in the crystal and a decrease in growth rate, but also causes the deposition of volatile SiO gas outside the heat shield. When the deposited SiO falls onto the free surface of the melt, it can also cause the risk of "crystal breakage". SUMMARY

[0005] The present application provides a double-heat-shield single crystal furnace, which effectively solves the technical problems of high energy consumption, slow growth rate and high oxygen impurity content of existing large-size single crystal silicon. By setting double heat shields in the single crystal furnace, the flow path of argon gas flow is guided, the argon vortex area is eliminated, the blowing capacity of argon is enhanced, the heat and impurity removal efficiency is improved, and the risk of contamination of the melt and "crystal breakage" caused by the deposition of volatile impurity gas on the outside of the heat shield and then falling back into the melt is avoided.

[0006] The first object of the present application is to provide a double-heat-shield single crystal furnace, which comprises a furnace body, a heat shield and a quartz crucible. The heat shield comprises a main heat shield and a secondary heat shield. The main heat shield and the secondary heat shield are both arranged in the furnace body and located above the quartz crucible.

[0007] The first flow channel is formed between the main heat shield and the secondary heat shield, and the second flow channel is formed between the secondary heat shield and the inner wall of the quartz crucible.

[0008] Through the first flow channel and the second flow channel, the impurity gas and heat generated by the melt in the quartz crucible are discharged with the argon gas flow.

[0009] As a preferred embodiment, the difference between the height of the bottom of the main heat shield from the free surface of the melt in the quartz crucible and the height of the bottom of the secondary heat shield from the free surface of the melt in the quartz crucible is 0mm-80mm.

[0010] As a preferred embodiment, the width of the first flow channel is 20mm-50mm, and the width of the second flow channel is 40mm-70mm.

[0011] As a preferred embodiment, the inner part of the main heat shield and the inner part of the secondary heat shield are both provided with a felt layer, and the felt layer is nested with a graphite layer outside.

[0012] As a preferred embodiment, the main heat shield is detachably arranged on the inner wall of the furnace body.

[0013] As a preferred embodiment, the furnace body is further provided with a heat preservation layer, and the secondary heat shield is connected with the heat preservation layer.

[0014] As a preferred embodiment, the outer wall of the quartz crucible is provided with a graphite crucible.

[0015] As a preferred embodiment, the furnace body is further provided with a first heater and a second heater, and the first heater and the second heater are located outside the graphite crucible.

[0016] As a preferred embodiment, the top wall of the furnace body is provided with an argon gas inlet.

[0017] As a preferred embodiment, the bottom of the furnace body is provided with a support frame, and the graphite crucible is arranged on the support frame.

[0018] Compared with the prior art, the present application has the following advantages: The application provides a double-heat-screen single crystal furnace, which comprises a furnace body, a heat screen and a quartz crucible, the heat screen comprises a main heat screen and a secondary heat screen, the main heat screen and the secondary heat screen are arranged in the furnace body and are located above the quartz crucible, a first flow channel is formed between the main heat screen and the secondary heat screen, and a second flow channel is formed between the secondary heat screen and the inner wall of the quartz crucible; through the first flow channel and the second flow channel, impurity gas and heat generated by a melt in the quartz crucible are discharged along an argon gas flow. Compared with a traditional single-heat-screen, the double-heat-screen structure is introduced into the single crystal furnace, the first flow channel is formed between the double heat screens, the second flow channel is formed between the secondary heat screen and the inner wall of the quartz crucible, the cross-sectional area of the gas flow channel is significantly reduced, the gas flow velocity is improved, the flow path of argon gas near the free surface of the melt in the quartz crucible is guided, the first flow channel, the second flow channel and the free surface of the melt form a gradually expanding channel, the gas flow velocity is further improved, the argon gas vortex outside the heat screen is eliminated, the argon gas flow is accelerated, the impurity gas and heat generated by the melt are discharged, the discharge efficiency of the impurity gas is improved, the heat dissipation of the crystal is accelerated, the risk that the deposited impurity gas outside the heat screen falls back into the melt to cause the pollution of the melt and the risk of "crystal breaking" are avoided, and thus the impurity content of the crystal is reduced and the growth rate of the crystal is improved.

[0019] The double-heat-screen structure (the main heat screen and the secondary heat screen) has a double-layer heat insulation effect on a crystal zone, the heat radiation of a heater to the crystal is weakened, the heat dissipation of the crystal is accelerated, and the growth rate of the crystal is improved. BRIEF DESCRIPTION OF DRAWINGS

[0020] Figure 1 It is a structural schematic diagram of the double-heat-screen single crystal furnace.

[0021] Figure 2 It is a position relation schematic diagram of the first flow channel, the second flow channel and the main heat screen, the secondary heat screen and the quartz crucible.

[0022] Figure 3 It is a width diagram of the first flow channel and the second flow channel.

[0023] Figure 4 It is a schematic diagram of argon flow guiding and oxygen reduction of the heat screen structure of the single crystal furnace, wherein (a) is a single-heat-screen single crystal furnace, and (b) is the double-heat-screen single crystal furnace.

[0024] Figure 5 It is a heat field distribution diagram in the single crystal furnace, wherein (a) is a single-heat-screen single crystal furnace, and (b) is the double-heat-screen single crystal furnace.

[0025] Figure 6 It is a temperature distribution diagram in the crystal, wherein (a) is a single-heat-screen single crystal furnace, and (b) is the double-heat-screen single crystal furnace.

[0026] Figure 7 Figure (a) is a single heat shield single crystal furnace, and figure (b) is a double heat shield single crystal furnace according to the present application.

[0027] Figure 8 Figure A is a double heat shield structure according to embodiment 1, figure B is a double heat shield structure according to embodiment 3, and figure C is a double heat shield structure according to embodiment 2. DETAILED DESCRIPTION

[0028] In order to enable a person skilled in the art to better understand the technical solutions of the present application and to implement them, the present application will be further described below in conjunction with specific embodiments, but the embodiments are not limiting of the present application. The following test methods and detection methods are conventional methods unless otherwise specified; the reagents and raw materials are commercially available unless otherwise specified.

[0029] For the existing single crystal furnace: first, the silicon melt in the quartz crucible in the single crystal furnace will condense when the temperature drops below the melting point, which requires a larger heater power to maintain the thermal field in the furnace, thereby inevitably causing an increase in oxygen impurities, and too many oxygen impurities will form oxygen precipitates, affecting the performance of the product; second, the existing single crystal furnace uses a heat shield structure to produce a crystal with generally high oxygen impurities, and a distance is usually reserved between the bottom of the heat shield and the crucible wall, so that a large space is formed between the heat shield and the silicon liquid surface during crystal pulling, and the sudden increase in the cross-sectional area of the flow channel during the flow of argon gas will cause the flow rate to rapidly decrease, forming a low-flow argon vortex above the free surface. The vortex not only delays the normal flow of argon gas, reduces the heat and impurity removal efficiency, and causes the oxygen content in the crystal to be high and the growth rate to decrease, but also causes the deposited SiO gas to fall onto the free surface of the melt, which may cause the risk of "crystal breakage". In view of the above technical problems, the present application provides a double heat shield single crystal furnace.

[0030] The technical content of the present application will be described in detail below.

[0031] The present application provides a double heat shield single crystal furnace, which comprises a furnace body 1, a heat shield and a quartz crucible 5, the heat shield comprises a main heat shield 2 and a secondary heat shield 3, the main heat shield 2 and the secondary heat shield 3 are arranged in the furnace body 1 and located above the quartz crucible 5.

[0032] A first flow channel 10 is formed between the main heat shield 2 and the secondary heat shield 3, and a second flow channel 11 is formed between the secondary heat shield 3 and the inner wall of the quartz crucible 5.

[0033] Through the first flow channel 10 and the second flow channel 11, the impurity gas and heat generated by the melt in the quartz crucible 5 are discharged with the argon gas flow.

[0034] In the above technical solution, the double heat shield structure is introduced into the single crystal furnace, the first flow channel 10 is formed between the double heat shields, the second flow channel 11 is formed between the auxiliary heat shield and the inner wall of the quartz crucible, the cross-sectional area of the gas flow channel is significantly reduced, thereby the gas flow rate is increased, the flow path of the argon gas near the free surface of the melt in the quartz crucible 5 is guided, the first flow channel, the second flow channel and the free surface of the melt form a gradually expanding channel, the gas flow rate is accelerated, thereby the argon gas vortex outside the heat shield is eliminated, the argon gas flow is accelerated, and the impurity gas and heat generated by the melt are discharged, the impurity gas discharge efficiency is improved, and the heat dissipation of the crystal is accelerated, thereby the risk of the deposited impurity gas outside the heat shield falling back into the melt to cause the melt pollution and "crystal breaking" is avoided, so that the impurity content of the crystal is reduced and the growth rate of the crystal is increased.

[0035] In order to further improve the flow rate of the argon gas above the free surface, the difference between the height of the bottom of the main heat shield 2 from the free surface of the melt in the quartz crucible 5 and the height of the bottom of the auxiliary heat shield 3 from the free surface of the melt in the quartz crucible 5 is 0mm~80mm.

[0036] In order to further ensure the discharge of the argon gas and impurities above the free surface, the width of the first flow channel 10 is 20mm~50mm, and the width of the second flow channel 11 is 40mm~70mm. The width of the first flow channel 10 greater than 20mm can ensure the normal flow of the argon gas and the smooth discharge of the impurities, and the width less than 50mm can avoid the generation of the vortex on the side wall of the main heat shield; the width of the second flow channel 11 greater than 40mm can ensure the normal flow of the argon gas and the smooth discharge of the impurities, and the width less than 70mm can avoid the generation of the vortex on the side wall of the auxiliary heat shield. Figure 3 .

[0037] It should be noted that the inside of the main heat shield 2 and the inside of the auxiliary heat shield 3 are both provided with a felt layer, and the graphite layer is nested outside the felt layer.

[0038] In order to facilitate the maintenance and cleaning of the dirt on the surface of the heat shield, the main heat shield 2 is detachably arranged on the inner wall of the furnace body 1.

[0039] It should be noted that the furnace body 1 is also provided with a heat preservation layer 7, and the auxiliary heat shield 3 is connected with the heat preservation layer 7. Since the gas in the first flow channel 10 flows out between the heat preservation layer 7 and the furnace body 1, the auxiliary heat shield 3 cannot be connected with the furnace body 1.

[0040] In order to prepare the silicon raw material in the quartz crucible 5 into a melt, the outer wall of the quartz crucible 5 is provided with a graphite crucible 6. The furnace body 1 is further provided with a first heater 4 and a second heater 8, which are located outside the graphite crucible 6. The silicon raw material is placed in the quartz crucible 5, and the first heater 4 and the second heater 8 are started to heat. The heat is transmitted to the quartz crucible 5 through the graphite crucible 6 to heat the silicon raw material until the silicon raw material is completely melted and has a certain fluidity. During the heating and melting of the silicon raw material, the graphite crucible 6 plays a good supporting role for the quartz crucible 5, avoiding the softening of the quartz crucible 5 at high temperature, which leads to the leakage of the melt, affecting the production. The peripheral graphite crucible 6 can also make the heat generated by the first heater 4 more uniformly distributed around the quartz crucible 5, making the temperature distribution more symmetrical, avoiding the solidification of the melt at the bottom due to low temperature during the crystal pulling process, which not only affects the fluidity of the melt, but also leads to the decline of production efficiency and the quality of the single crystal silicon rod.

[0041] In order to introduce argon gas flow into the single crystal furnace to avoid the generation of oxygen impurities in the melt, the top wall of the furnace body 1 is provided with an argon gas inlet.

[0042] In order to realize the support of the quartz crucible 5 and the graphite crucible 6, the bottom of the furnace body 1 is provided with a support frame 9, and the graphite crucible 6 is arranged on the support frame 9.

[0043] The content of the application will be specifically described below through the following examples and comparative examples.

[0044] Example 1 A double-heat-shield single crystal furnace includes a furnace body 1, a main heat shield 2, a secondary heat shield 3, a first heater 4, a quartz crucible 5, a graphite crucible 6, a heat preservation layer 7, a second heater 8 and a support frame 9. The top wall of the furnace body 1 is provided with an argon gas inlet.

[0045] The main heat shield 2 is detachably arranged on the inner wall of the furnace body 1, and the furnace body 1 is further provided with a heat preservation layer 7. The secondary heat shield 3 is connected with the heat preservation layer 7, and the main heat shield 2 and the secondary heat shield 3 are both located above the quartz crucible 5. The inside of the main heat shield 2 and the secondary heat shield 3 is provided with a felt layer, and the outside of the felt layer is nested with a graphite layer. The main heat shield 2 and the secondary heat shield 3 are arranged in parallel, the height from the bottom of the main heat shield 2 to the free surface of the melt in the quartz crucible 5 is less than the height from the bottom of the secondary heat shield 3 to the free surface of the melt in the quartz crucible 5, and the difference is 40 mm, that is, the liquid port distance of the main heat shield 2 is less than that of the secondary heat shield 3, and the difference is 40 mm. The outer wall of the quartz crucible 5 is provided with a graphite crucible 6. The bottom of the furnace body 1 is provided with a support frame 9, and the graphite crucible 6 is arranged on the support frame 9. The furnace body 1 is further provided with a first heater 4 and a second heater 8, and the first heater 4 and the second heater 8 are located outside the graphite crucible 6.

[0046] The first flow channel 10 with a width of 40 mm is formed between the main heat shield 2 and the secondary heat shield 3, and the second flow channel 11 with a width of 60 mm is formed between the secondary heat shield 3 and the inner wall of the quartz crucible 5. Through the first flow channel 10 and the second flow channel 11, the impurity gas and heat generated by the melt in the quartz crucible 5 are discharged with the argon gas flow.

[0047] In the production of single crystal silicon by using the above-mentioned double-heat-shield single crystal furnace, the silicon raw material is placed in the quartz crucible 5, and the first heater 4 and the second heater 8 are started to heat. The heat is transmitted to the silicon raw material in the quartz crucible 5 through the graphite crucible 6 to heat the silicon raw material until it is completely melted and has a certain fluidity. During the heating and melting of the silicon raw material, the graphite crucible 6 plays a good supporting role for the quartz crucible 5, avoiding the softening of the quartz crucible 5 at high temperature, which leads to the leakage of the melt and affects the production. The outer graphite crucible 6 can also make the heat generated by the first heater 4 more uniformly distributed around the quartz crucible 5, making the temperature distribution more symmetrical, avoiding the solidification of the melt at the bottom due to low temperature during the crystal pulling process, which not only affects the fluidity of the melt, but also leads to the decline of production efficiency and the quality of the single crystal silicon rod.

[0048] After the silicon raw material is completely melted, it is kept for a period of time. During this process, the argon gas flows through the first flow channel 10 and the second flow channel 11 with the main heat shield 2 and the secondary heat shield 3, carrying out the impurities generated in the melt and part of the heat in the furnace cavity, which can effectively reduce the impurity content in the furnace and avoid the melting of the seed crystal during the seed crystal descending process due to the high temperature, which has not yet contacted the silicon melt.

[0049] After a period of time, the production of single crystal silicon rod is started. During the preparation process, the argon gas flow is divided by the main heat shield 2 and the secondary heat shield 3, and the main heat shield 2 and the secondary heat shield 3 form a flow channel for the smooth expansion of the argon gas flow between them and the free surface of the melt. Above the free surface of the melt, the overall argon gas flow rate can maintain a relatively high flow rate, avoiding the problem of impurity retention and hindering the flow of argon gas due to argon vortex area, and avoiding the risk of contamination of the melt and "crystal breaking" caused by the deposition of volatile impurity gas on the outside of the heat shield and then falling back into the melt.

[0050] During the single crystal silicon pulling stage, the change of the argon gas flow field also affects the transport of oxygen impurities, thereby affecting the impurity content in the single crystal silicon rod. Higher argon gas flow rate can more quickly and timely carry out the volatilized impurities out of the furnace, reducing the oxygen concentration near the crystal rod.

[0051] In the crystal growth area, the double heat shield structure has a double-layer heat insulation effect on the crystal area, which weakens the heat radiation of the heater on the crystal, accelerates the heat dissipation of the crystal, and the increase of the argon gas flow rate can greatly promote the discharge of the latent heat of crystallization, which indirectly affects the solid-liquid interface. Under the comprehensive action of the two, it is helpful to improve the crystal growth rate and the stability of the crystal growth.

[0052] In the specific production process of single crystal silicon rod, the first heater 4 and the second heater 8 are started to heat, the quartz crucible 5 and the graphite crucible 6 are rotated at 5r / min, and when the silicon raw material in the quartz crucible 5 is completely melted, the heat preservation is 3min. During this process, the argon gas inlet flow rate is 150mL / min, the main heat shield 2 and the auxiliary heat shield 3 are divided into two parts, the impurities generated in the melt and part of the heat in the furnace cavity are discharged from the furnace body with the argon gas flow through the first flow channel 10 and the second flow channel 11, which can effectively reduce the impurity content in the furnace, and can avoid the melting of the seed crystal due to the too high temperature during the descending process of the seed crystal.

[0053] After 3min of heat preservation, the production of single crystal silicon rod is started, and in the production process, the single crystal silicon crystal rotates in the opposite direction of the quartz crucible 5 at a speed of 10r / min, the argon gas flow is divided by the main heat shield 2 and the auxiliary heat shield 3, and the main heat shield 2 and the auxiliary heat shield 3 form a smooth expansion flow channel with the free surface of the melt. Above the free surface, the overall argon gas flow rate can maintain a relatively high flow rate.

[0054] The results show that, compared with the traditional single heat shield structure, the argon gas flow rate at the second flow channel 10 inlet of the double heat shield structure of the embodiment 1 is increased from 6.57m / s to 9.73m / s, and the argon gas flow rate near the top of the crucible is increased from 7.81m / s to 11.87m / s, with an increase of 52%, which effectively avoids the problem of impurity retention and hindering of argon gas flow caused by argon gas vortex area, and avoids the risk of contamination of the melt and "crystal breaking" caused by the deposition of volatile impurity gas outside the heat shield.

[0055] During the single crystal silicon pulling stage, the change of the argon gas flow field also affects the transport of oxygen impurities, thereby affecting the impurity content in the single crystal silicon rod. Higher argon gas flow rate can more quickly and timely carry out the volatilized impurities out of the furnace, thereby reducing the oxygen concentration near the crystal rod. As a result, compared with the traditional single heat shield structure, the oxygen impurity content at the solid-liquid interface under the double heat shield structure is reduced by 1.22ppma.

[0056] In the crystal growth area, the double heat shield structure of the embodiment 1 of the present application has double heat insulation effect on the crystal area, which weakens the heat radiation of the heater to the crystal, accelerates the heat dissipation of the crystal, and the increase of the argon gas flow rate greatly promotes the discharge of the latent heat of crystallization, which indirectly affects the solid-liquid interface. Under the comprehensive action of the two, the crystal growth rate is increased by about 20%, the maximum deformation of the solid-liquid interface is decreased from 24.44 mm to 12.17 mm, the growth stability of the single crystal silicon is improved, and the thermal stress at the solid-liquid interface is decreased from 22.992 Mpa to 18.766 Mpa when the double heat shield is used.

[0057] Embodiment 2 A double heat shield single crystal furnace, comprising a furnace body 1, a main heat shield 2, a secondary heat shield 3, a first heater 4, a quartz crucible 5, a graphite crucible 6, a heat preservation layer 7, a second heater 8 and a support frame 9; the top wall of the furnace body 1 is provided with an argon gas inlet.

[0058] The main heat shield 2 is detachably arranged on the inner wall of the furnace body 1, and the furnace body 1 is further provided with a heat preservation layer 7, and the secondary heat shield 3 is connected with the heat preservation layer 7, and the main heat shield 2 and the secondary heat shield 3 are located above the quartz crucible 5; the inside of the main heat shield 2 and the secondary heat shield 3 is provided with a felt layer, and the felt layer is nested with a graphite layer outside; the main heat shield 2 and the secondary heat shield 3 are arranged in parallel, the height of the bottom of the main heat shield 2 from the free surface of the melt in the quartz crucible 5 is greater than the height of the bottom of the secondary heat shield 3 from the free surface of the melt in the quartz crucible 5, and the difference is 40 mm, that is, the liquid port distance of the main heat shield 2 is greater than that of the secondary heat shield 3, and the difference is 40 mm. The outer wall of the quartz crucible 5 is provided with a graphite crucible 6; the bottom of the furnace body 1 is provided with a support frame 9, and the graphite crucible 6 is arranged on the support frame 9; the furnace body 1 is further provided with a first heater 4 and a second heater 8, and the first heater 4 and the second heater 8 are located outside the graphite crucible 6.

[0059] The first flow channel 10 with a width of 30 mm is formed between the main heat shield 2 and the secondary heat shield 3, and the second flow channel 11 with a width of 70 mm is formed between the secondary heat shield 3 and the inner wall of the quartz crucible 5; through the first flow channel 10 and the second flow channel 11, the impurity gas and heat generated by the melt in the quartz crucible 5 are discharged with the argon gas flow.

[0060] In the specific production process of the single crystal silicon rod, the first heater 4 and the second heater 8 are started to heat, the quartz crucible 5 and the graphite crucible 6 rotate at 5 r / min, when the silicon raw material in the quartz crucible 5 is completely melted, the heat preservation is 3 min, in this process, the argon inlet flow is 150 mL / min, the main heat shield 2 and the auxiliary heat shield 3 are divided to flow, the impurities generated in the melt and part of the heat in the furnace cavity are discharged from the furnace body along with the argon flow through the first flow channel 10 and the second flow channel 11, which can effectively reduce the impurity content in the furnace, and can avoid the melting of the seed crystal due to the too high temperature during the descending process of the seed crystal before the seed crystal contacts the silicon melt.

[0061] After heat preservation for 3 min, the single crystal silicon rod is started to be produced, in the production process, the single crystal silicon crystal rotates in the opposite direction of the quartz crucible 5 at a rotating speed of 10 r / min, the argon flow is divided by the main heat shield 2 and the auxiliary heat shield 3, the main heat shield 2 and the auxiliary heat shield 3 form a flow channel for smooth expansion of the argon gas flow between the main heat shield 2 and the auxiliary heat shield 3 and the free surface of the melt, and the overall argon gas flow speed above the free surface can be kept relatively high.

[0062] The results show that, compared with the traditional single heat shield structure, the argon flow speed at the second flow channel 10 inlet of the double heat shield structure of the embodiment 2 is increased from 6.57 m / s to 11.66 m / s, with an increase of 77.47%, and the argon flow speed near the top of the crucible is increased from 7.81 m / s to 8.74 m / s, which effectively avoids the problems of impurity retention and hindering of argon flow caused by argon vortex area, and avoids the risk of contamination of the melt and "crystal breaking" caused by the deposition of volatile impurity gas outside the heat shield.

[0063] In the single crystal silicon pulling stage, the change of the argon flow field also affects the transport of oxygen impurities, thereby affecting the impurity content in the single crystal silicon rod, and a higher argon flow speed can more quickly and timely carry out the volatile impurities out of the furnace, thereby reducing the oxygen concentration near the crystal rod. The results show that, compared with the traditional single heat shield structure, the oxygen impurity content at the solid-liquid interface under the double heat shield structure is reduced by 1.56 ppma.

[0064] In the crystal growth area, the double heat shield structure of the embodiment 2 has a double heat insulation effect on the crystal area, which weakens the heat radiation of the heater to the crystal, accelerates the heat dissipation of the crystal, and the increase of the argon flow speed greatly promotes the discharge of the latent heat of crystallization, which indirectly affects the solid-liquid interface. Under the comprehensive action of the two, the crystal growth speed is increased by about 20%, the maximum deformation amount of the solid-liquid interface is reduced from 24.44 mm to 13.81 mm, the growth stability of the single crystal silicon is improved, and the thermal stress at the solid-liquid interface is reduced from 22.992 Mpa to 21.316 Mpa under the double heat shield.

[0065] Embodiment 3 The application discloses a double-heat-screen single crystal furnace, which comprises a furnace body 1, a main heat screen 2, a secondary heat screen 3, a first heater 4, a quartz crucible 5, a graphite crucible 6, a heat preservation layer 7, a second heater 8 and a supporting frame 9.

[0066] The main heat screen 2 is detachably arranged on the inner wall of the furnace body 1, the furnace body 1 is further provided with the heat preservation layer 7, the secondary heat screen 3 is connected with the heat preservation layer 7, and the main heat screen 2 and the secondary heat screen 3 are both located above the quartz crucible 5; the inner part of the main heat screen 2 and the secondary heat screen 3 is provided with a felt layer, and the outer part of the heat preservation layer is nested with a felt layer; the main heat screen 2 and the secondary heat screen 3 are arranged in parallel, the height from the bottom of the main heat screen 2 to the free surface of the melt in the quartz crucible 5 is equal to the height from the bottom of the secondary heat screen 3 to the free surface of the melt in the quartz crucible 5, that is, the liquid port distance of the main heat screen 2 is equal to the liquid port distance of the secondary heat screen 3; the outer wall of the quartz crucible 5 is provided with the graphite crucible 6; the bottom of the furnace body 1 is provided with the supporting frame 9, and the graphite crucible 6 is arranged on the supporting frame 9; the furnace body 1 is further provided with the first heater 4 and the second heater 8, and the first heater 4 and the second heater 8 are located outside the graphite crucible 6.

[0067] The first flow channel 10 with a width of 35mm is formed between the main heat screen 2 and the secondary heat screen 3, and the second flow channel 11 with a width of 65mm is formed between the secondary heat screen 3 and the inner wall of the quartz crucible 5; through the first flow channel 10 and the second flow channel 11, the impurity gas and heat generated by the melt in the quartz crucible 5 are discharged along the argon gas flow.

[0068] In the specific production process of the single crystal silicon rod, the first heater 4 and the second heater 8 are started to heat, the quartz crucible 5 and the graphite crucible 6 rotate at 5r / min, and after the silicon raw material in the quartz crucible 5 is completely melted, the heat preservation is carried out for 3min; in this process, the argon gas inlet flow is 150mL / min, the main heat screen 2 and the secondary heat screen 3 are divided into flows, the impurities generated in the melt and part of the heat in the furnace cavity are discharged from the furnace body along the argon gas flow through the first flow channel 10 and the second flow channel 11, the impurity content in the furnace can be effectively reduced, and the seed crystal can be prevented from melting before contacting the silicon melt due to the excessively high temperature in the seed crystal descending process.

[0069] After the heat preservation is carried out for 3min, the single crystal silicon rod is produced, and in the production process, the single crystal silicon crystal rotates in the opposite direction of the quartz crucible 5 at a rotating speed of 10r / min, the argon gas flow is divided into flows through the main heat screen 2 and the secondary heat screen 3, the main heat screen 2 and the secondary heat screen 3 form the flow channel for the smooth expansion of the argon gas flow between the free surface of the melt, and above the free surface, the argon gas flow can maintain a relatively large flow speed as a whole.

[0070] The results show that, compared with the traditional single heat shield structure, the argon gas flow rate at the inlet of the second flow channel 10 of the double heat shield structure of embodiment 3 is increased from 6.57 m / s to 10.23 m / s, and the argon gas flow rate near the top of the crucible is increased from 7.81 m / s to 12.39 m / s, with an increase of 58%, effectively avoiding the problem of impurity retention and hindering the flow of argon gas caused by the argon gas vortex area, and avoiding the risk of contamination and "crystal breakage" caused by the deposited volatile impurity gas falling back into the melt.

[0071] During the single crystal silicon pulling stage, the change of the argon gas flow field also affects the transport of oxygen impurities, thereby affecting the impurity content in the single crystal silicon rod. Higher argon gas flow rate can more quickly and timely carry out the volatilized impurities out of the furnace, thereby reducing the oxygen concentration near the crystal rod. As a result, compared with the traditional single heat shield structure, the oxygen impurity content at the solid-liquid interface is reduced by 1.16 ppma under the double heat shield structure.

[0072] In the crystal growth area, the double heat shield structure of embodiment 1 has a double heat insulation effect on the crystal area, which weakens the heat radiation of the heater to the crystal, accelerates the heat dissipation of the crystal, and the increase of the argon gas flow rate greatly promotes the discharge of the latent heat of crystallization, which indirectly affects the solid-liquid interface. Under the comprehensive action of the two, the crystal growth rate is increased by about 20%, the maximum deformation of the solid-liquid interface is reduced from 24.44 mm to 12.27 mm, the growth stability of the single crystal silicon is improved, and the thermal stress at the solid-liquid interface is reduced from 22.992 Mpa to 19.22 Mpa under the double heat shield structure.

[0073] The performance of the double heat shield single crystal furnace set according to the above embodiments 1-3 is detected, and the results are as follows.

[0074] Effect of double heat shield structure on argon gas flow and oxygen reduction As shown in Figure 4 , on the outside of the traditional single heat shield, due to the sudden increase of the flow channel cross-sectional area, the flow rate is significantly reduced, which causes the formation of a vortex on the outside of the heat shield. The vortex not only delays the normal flow of argon gas, reduces the heat and impurity discharge efficiency, but also may cause the deposition of volatilized SiO gas on the outside of the heat shield. When the deposited SiO falls to the free surface of the melt, it may also cause the risk of "crystal breakage". However, in the double heat shield structure, due to the flow guiding effect of the double heat shield, the generation of vortex on the outside of the heat shield is avoided, which greatly improves the stability of crystal growth.

[0075] In addition, the double heat shield structure forms a gradually expanding flow passage with the free surface, and the argon flow rate slowly decreases. After the flow is guided through the double heat shield, the gas flow rate outside the heat shield significantly increases, such as the argon flow rate near the top of the crucible increases from 7.81 m / s to 11.87 m / s, with an increase of 52%. This will greatly promote the crystallization latent heat and the discharge of impurities, and improve the crystal growth rate and crystal growth stability. Compared with the single heat shield structure, the oxygen impurity at the solid-liquid interface decreases by 1.22 ppma, and the silicon oxide content above the free surface decreases by 1238.857 ppma. Therefore, compared with the traditional single heat shield structure, the double heat shield structure can significantly optimize the argon flow field, eliminate the vortex outside the heat shield, and thus improve the heat and impurity discharge efficiency.

[0076] Effect of double heat shield structure on double-layer thermal insulation of crystal zone and acceleration of crystal growth The double heat shield structure will affect the temperature field in the furnace. The double heat shield structure has a double-layer thermal insulation effect. It can be seen that the temperature in the heater area increases with the double heat shield structure, which blocks the radiation heating of the heater to the crystal, and the heat dissipation of the crystal is accelerated. As shown in Figure 6 , the minimum temperature in the crystal decreases from 1214 K to 1135 K. The axial temperature gradient in the crystal changes, and the efficiency of latent heat removal by argon gas flow increases, and the crystal growth rate is improved by 19.2% compared with the traditional single heat shield structure.

[0077] In addition, as shown in Figure 5 , the temperature field in the melt also changes with the change of the heat shield structure. Compared with the single heat shield, the temperature in the center area and the bottom of the melt in the double heat shield structure increases as a whole, which can effectively improve the fluidity of the melt and avoid the solidification of the melt during the single crystal silicon pulling process, which leads to the decline of production efficiency and crystal quality.

[0078] Effect of double heat shield structure on crystal thermal stress and point defect control As shown in Figure 7As shown, the difference in thermal stress distribution in the crystal under the two structures mainly manifests in two aspects: one is that the thermal stress distribution at the solid-liquid interface is significantly different. In the double heat shield structure, the thermal stress value on the solid-liquid interface is lower as a whole, and the maximum value is reduced from 22.992 Mpa in the single heat shield to 18.766 Mpa in the double heat shield. The decrease in thermal stress may be related to the lower interface fluctuation in the double heat shield, and in the double heat shield structure, the maximum fluctuation value of the solid-liquid interface is reduced from 24.44 mm in the single heat shield structure to 12.17 mm. In the double heat shield structure, the solid-liquid interface shape is more gentle. Two is that the maximum thermal stress value at the crystal side wall is different. In the single heat shield, the maximum thermal stress value is 19.025 Mpa, while in the double heat shield structure, it increases to 20.546 Mpa, which may be due to the larger heat dissipation capacity of the crystal in the double heat shield, the stress increase at the side wall is smaller, compared with the change of thermal stress at the solid-liquid interface in the center of the crystal, the increase at the side wall is acceptable, and in the actual application process, the crystal side wall can be cut to obtain a low-stress wafer.

[0079] Figure 8 The gas flow guide comparison diagram of the double heat shield structure in the embodiment 1~embodiment 2 and the comparative example 1 of the application, wherein, A diagram is embodiment 1, B diagram is embodiment 3, C diagram is embodiment 2. From Figure 8 It can be seen that: three kinds of double heat shield structure can guide the flow of argon, at the same time, eliminate vortex and increase argon flow rate, with the change of the length of the auxiliary heat shield, the flow rate of argon will also change with the change of the cross-sectional area of the flow channel, and the impurities flowing into the flow channel 1 (first flow channel 10) and flow channel 2 (second flow channel 11) will also change, compared with comparative example 1, the oxygen impurity removal effect of embodiment 2 is better.

[0080] Obviously, those skilled in the art can make various modifications and variations to the present application without departing from the spirit and scope of the present application. Thus, if these modifications and variations of the present application fall within the scope of the claims of the present application and their equivalent technologies, the present application also intends to include these modifications and variations.

Claims

1. A dual-heatscreen single-crystal furnace, comprising a furnace body (1), a heatscreen, and a quartz crucible (5), characterized in that, The heat screen includes a main heat screen (2) and a secondary heat screen (3), both of which are located inside the furnace body (1) and above the quartz crucible (5). A first flow channel (10) is formed between the main heat screen (2) and the secondary heat screen (3), and a second flow channel (11) is formed between the secondary heat screen (3) and the inner wall of the quartz crucible (5); Impurity gases and heat generated by the melt in the quartz crucible (5) are discharged with the argon gas flow through the first flow channel (10) and the second flow channel (11).

2. The dual-heatscreen single-crystal furnace according to claim 1, characterized in that, The difference between the height of the bottom of the main heat screen (2) from the free surface of the melt in the quartz crucible (5) and the height of the bottom of the auxiliary heat screen (3) from the free surface of the melt in the quartz crucible (5) is 0mm to 80mm.

3. The dual-heatscreen single-crystal furnace according to claim 1, characterized in that, The width of the first flow channel (10) is 20mm~50mm, and the width of the second flow channel (11) is 40mm~70mm.

4. The dual-heatscreen single-crystal furnace according to claim 1, characterized in that, Both the main heat shield (2) and the secondary heat shield (3) have a felt layer inside, and a graphite layer is nested outside the felt layer.

5. The dual-heatscreen single-crystal furnace according to claim 1, characterized in that, The main heat shield (2) is detachably mounted on the inner wall of the furnace body (1).

6. The dual-heatscreen single-crystal furnace according to claim 1, characterized in that, The furnace body (1) is also provided with a heat insulation layer (7), and the auxiliary heat shield (3) is connected to the heat insulation layer (7).

7. The dual-heatscreen single-crystal furnace according to claim 1, characterized in that, A graphite crucible (6) is provided on the outer wall of the quartz crucible (5).

8. The dual-heatscreen single-crystal furnace according to claim 7, characterized in that, The furnace body (1) is also provided with a first heater (4) and a second heater (8), which are located outside the graphite crucible (6).

9. The dual-heatscreen single-crystal furnace according to claim 1, characterized in that, The top wall of the furnace body (1) is provided with an argon gas inlet.

10. The dual-heatscreen single-crystal furnace according to claim 7, characterized in that, The bottom of the furnace body (1) is provided with a support frame (9), and the graphite crucible (6) is placed on the support frame (9).

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