Cooling method of monocrystalline silicon crystal bar

Abstract

The invention relates to a cooling method of a monocrystalline silicon crystal bar. The cooling method of the monocrystalline silicon crystal bar comprises the following steps: providing a monocrystalline silicon crystal bar which finishes growing, wherein the monocrystalline silicon crystal bar is positioned in a single crystal furnace; and synchronously reducing the furnace pressure in the single crystal furnace to the cooling furnace pressure, increasing the flow of the protective gas transmitted into the single crystal furnace to the cooling flow and increasing the pulling speed of the monocrystalline silicon crystal bar to the cooling pulling speed, so that the temperature of the monocrystalline silicon crystal bar is reduced to 350 DEG C or below. According to the invention, the concentration of thermal donors in the cooled monocrystalline silicon crystal bar is obviously reduced, and the growth process of the monocrystalline silicon crystal bar does not need to be improved or adjusted.

Description

Technical Field

[0001] This invention relates to the field of semiconductor manufacturing technology, and in particular to a cooling method for a single-crystal silicon ingot. Background Technology

[0002] Semiconductor-grade monocrystalline silicon is used as a substrate material for integrated circuits. The Czochralski (CZ) method is currently the mainstream technology for industrial production of monocrystalline silicon rods. Its principle involves placing high-purity polycrystalline silicon raw material into a quartz crucible and then heating the polycrystalline silicon raw material to form a molten silicon melt. Next, a seed crystal is immersed in the surface of the molten silicon, and by pulling and rotating the seed crystal upwards, the molten silicon solidifies and crystallizes at the interface between the seed crystal and the molten silicon, forming a monocrystalline silicon rod.

[0003] In the CZ process of growing single-crystal silicon ingots, the cooling of the single-crystal silicon ingot is one of the key factors affecting product quality. Since the silicon melt inevitably contains a certain amount of oxygen, some of this oxygen dissolves into the single-crystal silicon lattice during the growth process, forming interstitial oxygen. During the cooling process, the single-crystal silicon ingot inevitably passes through a temperature range of 350℃ to 550℃. Within this temperature range, the interstitial oxygen rapidly forms thermal donors. The formation of thermal donors has a serious negative impact on the electrical properties of the single-crystal silicon ingot. For example, it can cause drift in electrical parameters (such as threshold voltage) at the wafer and even device level formed from the single-crystal silicon ingot, severely affecting stability. For P-type single-crystal silicon ingots, thermal donors, as shallow donor levels, can compensate for boron acceptor impurities in the lattice, leading to a decrease in effective acceptor concentration, which in turn increases the resistivity of the single-crystal silicon ingot. In severe cases, it may even cause P-type to N-type inversion. Furthermore, the thermal donor concentration is strongly dependent on the thermal history. In actual production, the cooling rate often varies at different locations on a monocrystalline silicon ingot. This variation leads to significant fluctuations in the thermal donor concentration at different locations, resulting in differences in resistivity and compromising product consistency. Therefore, pre-suppressing the formation of thermal donors in the monocrystalline silicon ingot is crucial. However, intervention during the crystal growth stage is not only technically challenging but also costly.

[0004] Therefore, how to effectively suppress the formation of thermal donors in monocrystalline silicon rods, reduce the cost of suppressing the formation of thermal donors in monocrystalline silicon rods, simplify the suppression operation, thereby improving the quality of monocrystalline silicon rods and increasing the uniformity of resistivity distribution in monocrystalline silicon rods, is a technical problem that urgently needs to be solved. Summary of the Invention

[0005] This invention provides a cooling method for monocrystalline silicon ingots, which effectively suppresses the formation of thermal donors in monocrystalline silicon ingots and reduces the cost of suppressing the formation of thermal donors in monocrystalline silicon ingots, thereby improving the quality of monocrystalline silicon ingots and increasing the uniformity of resistivity distribution in monocrystalline silicon ingots.

[0006] According to some embodiments, the present invention provides a cooling method for a single-crystal silicon ingot, comprising the following steps: A single-crystal silicon ingot with its growth completed is provided, the single-crystal silicon ingot being located inside a single-crystal furnace; Simultaneously, the furnace pressure inside the single crystal furnace is reduced to a cooling furnace pressure, the flow rate of the protective gas transmitted to the single crystal furnace is increased to a cooling flow rate, and the pulling speed of the single crystal silicon ingot is increased to a cooling pulling speed, so that the temperature of the single crystal silicon ingot is reduced to below 350°C, the cooling furnace pressure is lower than the furnace pressure during the growth process of the single crystal silicon ingot, the cooling flow rate is higher than the preset flow rate during the growth process of the single crystal silicon ingot, and the cooling pulling speed is higher than the pulling speed during the growth process of the single crystal silicon ingot.

[0007] In some embodiments, the single-crystal silicon ingot, after growth has ended, is located in a quartz crucible within the single-crystal furnace, and the quartz crucible is located within a graphite crucible. Before simultaneously reducing the furnace pressure within the single-crystal furnace to a cooling furnace pressure, increasing the flow rate of the protective gas transmitted to the single-crystal furnace to a cooling flow rate, and increasing the pulling speed of the single-crystal silicon ingot to a cooling pulling speed, the following steps are further included: Stop lifting the graphite crucible and the single-crystal silicon ingot upwards, and reduce the rotational speed of the single-crystal silicon ingot to below 5 rpm.

[0008] In some embodiments, the single crystal furnace further includes a bottom heater located below the graphite crucible for heating the bottom of the graphite crucible; before simultaneously implementing the reduction of furnace pressure in the single crystal furnace to cooling furnace pressure, the increase of the flow rate of the protective gas transmitted to the single crystal furnace to cooling flow rate, and the increase of the pulling speed of the single crystal silicon ingot to cooling pulling speed, the following steps are also included: The graphite crucible is lowered to the lower limit at a speed of 50 mm / min, and the heating power of the bottom heater is adjusted to 5 kW to 10 kW.

[0009] In some embodiments, before simultaneously implementing the reduction of furnace pressure in the single crystal furnace to cooling furnace pressure, the increase of the flow rate of the protective gas transmitted to the single crystal furnace to cooling flow rate, and the increase of the pulling speed of the single crystal silicon ingot to cooling pulling speed, the following steps are further included: The single-crystal silicon ingot, now at the end of its growth, is lowered at a speed of 30 mm / min until the distance between its tail and the surface of the remaining molten silicon in the quartz crucible is 100 mm.

[0010] In some embodiments, the single crystal furnace further includes a main heater located on the outer side of the graphite crucible for heating the graphite crucible; before simultaneously implementing the reduction of the furnace pressure in the single crystal furnace to the cooling furnace pressure, the increase of the flow rate of the protective gas transmitted to the single crystal furnace to the cooling flow rate, and the increase of the pulling speed of the single crystal silicon ingot to the cooling pulling speed, the following steps are also included: The heating power of the main heater is reduced to 30kW and maintained for 30 to 60 minutes.

[0011] In some embodiments, the specific steps of simultaneously reducing the furnace pressure in the single crystal furnace to the cooling furnace pressure, increasing the flow rate of the protective gas transmitted to the single crystal furnace to the cooling flow rate, and increasing the pulling speed of the single crystal silicon ingot to the cooling pulling speed include: Determine whether the temperature of the single crystal silicon ingot is stable at 650°C. If so, simultaneously reduce the furnace pressure in the single crystal furnace to the cooling furnace pressure, increase the flow rate of the protective gas transmitted to the single crystal furnace to the cooling flow rate, and increase the pulling speed of the single crystal silicon ingot to the cooling pulling speed.

[0012] In some embodiments, the cooling furnace pressure is 3 kPa, the cooling flow rate is 150 slm~180 slm, and the cooling lifting speed is 50 mm / min.

[0013] In some embodiments, the single crystal furnace includes a lower furnace cylinder, a middle furnace cylinder located above the lower furnace cylinder, and an upper furnace cylinder located above the middle furnace cylinder; the specific steps of simultaneously implementing the reduction of furnace pressure in the single crystal furnace to cooling furnace pressure, increasing the flow rate of the protective gas transmitted to the single crystal furnace to cooling flow rate, and increasing the pulling speed of the single crystal silicon ingot to cooling pulling speed further include: Increase the pulling speed of the single crystal silicon ingot to the cooling pulling speed to pull the single crystal silicon ingot upwards into the upper furnace cylinder.

[0014] In some embodiments, while simultaneously implementing the reduction of furnace pressure in the single crystal furnace to cooling furnace pressure, the increase of the flow rate of the protective gas transmitted to the single crystal furnace to cooling flow rate, and the increase of the pulling speed of the single crystal silicon ingot to cooling pulling speed, the following steps are also included: The rotational speed of the single-crystal silicon ingot is adjusted to 12 rpm.

[0015] In some embodiments, while simultaneously implementing the reduction of furnace pressure in the single crystal furnace to cooling furnace pressure, the increase of the flow rate of the protective gas transmitted to the single crystal furnace to cooling flow rate, and the increase of the pulling speed of the single crystal silicon ingot to cooling pulling speed, the following steps are also included: Remove the external magnetic field applied to the single crystal furnace, which is used to suppress thermal convection of the silicon melt in the quartz crucible.

[0016] The cooling method for monocrystalline silicon ingots provided by this invention, after completing the monocrystalline silicon ingot growth process, simultaneously reduces the furnace pressure in the monocrystalline furnace, increases the flow rate of the protective gas transported to the monocrystalline furnace, and increases the pulling speed of the monocrystalline silicon ingot. Through the synergistic effect of the adjustments in furnace pressure, the flow rate of the protective gas, and the pulling speed, the temperature of the monocrystalline silicon ingot is rapidly reduced to below 350°C. This significantly increases the cooling rate of the monocrystalline silicon ingot within the thermal donor formation temperature range of 350°C to 550°C, preventing interstitial oxygen from fully accumulating to form thermal donors and inhibiting thermal donor formation. Consequently, the thermal donor concentration in the cooled monocrystalline silicon ingot is significantly reduced, improving the quality of the monocrystalline silicon ingot and enhancing the uniformity of the axial resistivity distribution. Furthermore, since the cooling method for monocrystalline silicon ingots provided by this invention is implemented in situ after the complete growth process of the monocrystalline silicon ingot is finished, no additional cooling equipment is required, and there is no need to pay attention to the growth process of the monocrystalline silicon ingot, nor is it necessary to improve or adjust the growth process of the monocrystalline silicon ingot, thus not affecting the growth process of the monocrystalline silicon ingot. Compared with thermal treatment of wafers to attract thermal donors, this simplifies the process and reduces the difficulty of suppressing the formation of thermal donors in monocrystalline silicon ingots. Attached Figure Description

[0017] To more clearly illustrate the technical solutions in the embodiments of the present invention, the accompanying drawings used in the description of the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0018] Figure 1 This is a flowchart of a cooling method for a single-crystal silicon ingot in a specific embodiment of the present invention; Figure 2 This is a schematic diagram of the structure inside the single crystal furnace in a specific embodiment of the present invention.

[0019] Explanation of reference numerals in the attached figures 20 Quartz Crucible 21 Graphite crucibles 22 Single Crystal Silicon Ingot 23 Lower furnace tube 24 furnace tubes 25 upper furnace tube 26 graphite crucible shaft 27 Thermal insulation layer 28 Main Heater 29 Bottom Heater 30 guide tube 31 Silicon Melt 32 Isolation Valve Chamber Detailed Implementation The specific embodiments of the cooling method for single-crystal silicon ingots provided by the present invention will be described in detail below with reference to the accompanying drawings.

[0020] This specific embodiment provides a cooling method for a single-crystal silicon ingot. Figure 1 This is a flowchart illustrating the cooling method for a single-crystal silicon ingot in a specific embodiment of the present invention. (For example...) Figure 1 As shown, the cooling method for the single-crystal silicon ingot includes the following steps: Step S11: Provide a single-crystal silicon ingot after growth has ended, the single-crystal silicon ingot being located inside a single-crystal furnace; Step S12 involves simultaneously reducing the furnace pressure in the single crystal furnace to a cooling furnace pressure, increasing the flow rate of the protective gas transmitted to the single crystal furnace to a cooling flow rate, and increasing the pulling speed of the single crystal silicon ingot to a cooling pulling speed. This results in the temperature of the single crystal silicon ingot being reduced to below 350°C, the cooling furnace pressure being lower than the furnace pressure during the growth process of the single crystal silicon ingot, the cooling flow rate being higher than the flow rate during the growth process of the single crystal silicon ingot, and the cooling pulling speed being higher than the pulling speed during the growth process of the single crystal silicon ingot.

[0021] Figure 2 This is a schematic diagram of the structure inside the single crystal furnace in a specific embodiment of the present invention. In some embodiments, such as... Figure 2 As shown, the single-crystal silicon ingot 22, after growth has ended, is located in a quartz crucible 20 within the single-crystal furnace, and the quartz crucible 20 is located within a graphite crucible 21. Before simultaneously reducing the furnace pressure in the single-crystal furnace to the cooling furnace pressure, increasing the flow rate of the protective gas transmitted to the single-crystal furnace to the cooling flow rate, and increasing the pulling speed of the single-crystal silicon ingot to the cooling pulling speed, the following steps are also included: Stop the upward lifting of the graphite crucible 21 and the single crystal silicon rod 22, and reduce the rotational speed of the single crystal silicon rod 22 to below 5 rpm.

[0022] Specifically, the single-crystal silicon ingot 22 is grown inside the single-crystal furnace, which includes a lower furnace cylinder 23, a middle furnace cylinder 24 located above the lower furnace cylinder 23, and an upper furnace cylinder 25 located above the middle furnace cylinder 24. An isolation valve chamber 32 is also provided between the upper furnace cylinder 25 and the middle furnace cylinder 24, which isolates the middle furnace cylinder 24 from the upper furnace cylinder 25 to prevent mutual influence between the thermal environments inside the middle furnace cylinder 24 and the upper furnace cylinder 25. A graphite crucible 21 is located inside the middle furnace cylinder 24, and a quartz crucible 20 is located inside the graphite crucible 21. The quartz crucible 20 contains molten silicon 31. A guide tube 30 is also provided above the quartz crucible 20. The guide tube 30 is used to introduce protective gases such as argon from top to bottom above the silicon melt 31 to remove the SiO above the silicon melt 31 and cool the single crystal silicon rod 22, increasing its axial temperature gradient and enabling rapid single crystal growth. During the growth of the single crystal silicon rod 22, the pressure inside the single crystal furnace is maintained at a preset furnace pressure, and the grown single crystal silicon rod is pulled upward at a preset pulling speed, while a preset flow rate of protective gas is continuously supplied to the single crystal furnace. After the growth process of the single crystal silicon rod 22 is completely completed, the remaining silicon melt 31 in the quartz crucible 20 serves as the bottom material. In this specific embodiment, after the growth process of the monocrystalline silicon ingot 22 is completely completed, a rapid secondary cooling process is performed on the entire formed monocrystalline silicon ingot 22 in situ within the monocrystalline furnace. This process does not require adjustment of the parameters of the existing monocrystalline silicon ingot growth process and is a cooling process independent of the monocrystalline silicon ingot growth process. It will not affect the growth process of the monocrystalline silicon ingot, thereby simplifying the process of suppressing the formation of thermal donors in the monocrystalline silicon ingot and reducing the difficulty of suppressing the formation of thermal donors in the monocrystalline silicon ingot.

[0023] In this specific embodiment, after the growth process of the single-crystal silicon ingot 22 is completely completed, and before simultaneously reducing the furnace pressure in the single-crystal furnace to the cooling furnace pressure, increasing the flow rate of the protective gas transmitted to the single-crystal furnace to the cooling flow rate, and increasing the pulling speed of the single-crystal silicon ingot to the cooling pulling speed, the upward lifting of the graphite crucible 21 and the single-crystal silicon ingot 22 is stopped, and the rotational speed (i.e., crystal rotation speed) of the single-crystal silicon ingot 22 is reduced to below 5 rpm. This is to maintain the relative stability of the formed single-crystal silicon ingot 22 and the remaining silicon melt 31 in the quartz crucible 20, and to avoid damage to the surface of the single-crystal silicon ingot 22 or excessive internal stress caused by sudden movement, thereby further ensuring the quality of the single-crystal silicon ingot 22 after cooling.

[0024] In some embodiments, the single crystal furnace further includes a bottom heater 29 located below the graphite crucible 21 for heating the bottom of the graphite crucible 21; before simultaneously implementing the reduction of the furnace pressure in the single crystal furnace to the cooling furnace pressure, the increase of the flow rate of the protective gas transmitted to the single crystal furnace to the cooling flow rate, and the increase of the pulling speed of the single crystal silicon ingot 22 to the cooling pulling speed, the following steps are also included: The graphite crucible 21 is lowered to the lower limit at a speed of 50 mm / min, and the heating power of the bottom heater 29 is adjusted to 5 kW to 10 kW.

[0025] Specifically, the single crystal furnace also includes a bottom heater 29 located at the bottom of the graphite crucible 21 for heating the bottom of the graphite crucible 21. The bottom heater 29 heats the bottom of the silicon melt 31 within the quartz crucible 20 by heating the bottom of the graphite crucible 21 and transferring heat. The single crystal furnace also includes a heat-insulating layer 27 distributed around the outer periphery of the graphite crucible 21, with the bottom heater 29 located between the heat-insulating layer 27 and the bottom of the graphite crucible 21. In one example, the heat-insulating layer 27 can be an insulating felt. Below the graphite crucible 21, there is a graphite crucible shaft 26 connected to the graphite crucible 21. The graphite crucible shaft 26 drives the graphite crucible 21 to move vertically up and down, thereby causing the quartz crucible 20 and the silicon melt 31 within the quartz crucible 20 to move vertically up and down.

[0026] In this specific embodiment, after stopping the upward lifting of the graphite crucible 21 and the single-crystal silicon ingot 22 and reducing the rotational speed of the single-crystal silicon ingot 22 to below 5 rpm, and simultaneously reducing the furnace pressure in the single-crystal furnace to cooling furnace pressure, increasing the flow rate of the protective gas transmitted to the single-crystal furnace to cooling flow rate, and increasing the pulling speed of the single-crystal silicon ingot 22 to cooling pulling speed, the graphite crucible 21 is driven by the graphite crucible shaft 26 to descend to the lower limit position at a speed of 50 mm / min, thereby increasing the distance between the graphite crucible 21 and the single-crystal silicon ingot 22. At the same time, the heating power of the bottom heater 29 is adjusted to 5 kW to 10 kW to maintain the basic temperature of the bottom of the graphite crucible 21 and the bottom of the quartz crucible 20, while avoiding damage to the quartz crucible 20 due to a sudden temperature drop, and maintaining a stable temperature field at the bottom of the furnace.

[0027] In some embodiments, before simultaneously implementing the reduction of furnace pressure in the single crystal furnace to cooling furnace pressure, the increase of the flow rate of the protective gas transmitted to the single crystal furnace to cooling flow rate, and the increase of the pulling speed of the single crystal silicon ingot 22 to cooling pulling speed, the following steps are further included: The single-crystal silicon ingot 22, after growth has ended, is lowered at a speed of 30 mm / min until the distance between its tail and the liquid surface of the remaining silicon melt 31 in the quartz crucible 20 is 100 mm.

[0028] Specifically, after lowering the graphite crucible 21 to the lower limit at a speed of 50 mm / min and adjusting the heating power of the bottom heater 29 to 5 kW~10 kW, and simultaneously reducing the furnace pressure in the single crystal furnace to the cooling furnace pressure, increasing the flow rate of the protective gas transmitted to the single crystal furnace to the cooling flow rate, and increasing the pulling speed of the single crystal silicon rod 22 to the cooling pulling speed, the single crystal silicon rod 22 is driven to descend at a speed of 30 mm / min until the distance between the tail of the single crystal silicon rod 22 (i.e. the end of the single crystal silicon rod 22 facing the quartz crucible 20) and the liquid surface of the remaining silicon melt 31 (i.e. the bottom material) in the quartz crucible 20 is 100 mm, so as to avoid the single crystal silicon rod 22 contacting the remaining silicon melt 31 in the quartz crucible 20.

[0029] In some embodiments, the single crystal furnace further includes a main heater 28 located on the outer side of the graphite crucible 21 for heating the graphite crucible 21; before simultaneously implementing the reduction of the furnace pressure in the single crystal furnace to the cooling furnace pressure, the increase of the flow rate of the protective gas transmitted to the single crystal furnace to the cooling flow rate, and the increase of the pulling speed of the single crystal silicon ingot 22 to the cooling pulling speed, the following steps are also included: The heating power of the main heater 28 is reduced to 30kW and maintained for 30min~60min.

[0030] Specifically, after the monocrystalline silicon ingot 22 is lowered at a speed of 30 mm / min to a point where the distance between its tail and the surface of the remaining molten silicon 31 in the quartz crucible 20 is 100 mm, and simultaneously the furnace pressure in the monocrystalline furnace is reduced to a cooling furnace pressure, the flow rate of the protective gas transmitted to the monocrystalline furnace is increased to a cooling flow rate, and the pulling speed of the monocrystalline silicon ingot 22 is increased to a cooling pulling speed, the heating power of the main heater 28 is reduced to 30 kW within 3 minutes and maintained for 30 to 60 minutes. This rapid reduction in the heating power of the main heater 28 reduces the heating effect on the monocrystalline silicon ingot 22. Simultaneously, by maintaining the heating power of the main heater 28 at 30 kW for 30 to 60 minutes, the temperature gradient between the surface and interior of the monocrystalline silicon ingot 22 becomes more gradual, reducing thermal stress within the monocrystalline silicon ingot 22.

[0031] In some embodiments, the specific steps of simultaneously reducing the furnace pressure in the single crystal furnace to the cooling furnace pressure, increasing the flow rate of the protective gas transmitted to the single crystal furnace to the cooling flow rate, and increasing the pulling speed of the single crystal silicon ingot 22 to the cooling pulling speed include: Determine whether the temperature of the single crystal silicon ingot 22 is stable at 650°C. If so, simultaneously reduce the furnace pressure in the single crystal furnace to the cooling furnace pressure, increase the flow rate of the protective gas transmitted to the single crystal furnace to the cooling flow rate, and increase the pulling speed of the single crystal silicon ingot 22 to the cooling pulling speed.

[0032] Specifically, the temperature of the monocrystalline silicon ingot 22 can be detected by a temperature sensor. After confirming that the temperature of the monocrystalline silicon ingot 22 is stable at 650°C, the furnace pressure in the monocrystalline furnace is simultaneously reduced to a cooling furnace pressure, the flow rate of the protective gas transmitted to the monocrystalline furnace is increased to a cooling flow rate, and the pulling speed of the monocrystalline silicon ingot 22 is increased to a cooling pulling speed. After confirming that the temperature of the monocrystalline silicon ingot 22 is stable at 650°C, the furnace pressure in the monocrystalline furnace is again simultaneously reduced to a cooling furnace pressure, the flow rate of the protective gas transmitted to the monocrystalline furnace is increased to a cooling flow rate, and the pulling speed of the monocrystalline silicon ingot 22 is increased to a cooling pulling speed. This avoids premature entry into the temperature range for inducing thermal donor formation (i.e., 350°C~550°C) and avoids excessive time spent in the thermal donor formation region, thereby further improving the quality of the monocrystalline silicon ingot.

[0033] In some embodiments, the cooling furnace pressure is 3 kPa, the cooling flow rate is 150 slm~180 slm, and the cooling lifting speed is 50 mm / min.

[0034] For example, the preset furnace pressure is 5 kPa. After the temperature of the monocrystalline silicon ingot 22 is stabilized at 650°C, the furnace pressure inside the single-crystal furnace is reduced from 5 kPa to 3 kPa, thereby increasing the thermal conductivity of the gas inside the single-crystal furnace and increasing the amount of heat carried away from the monocrystalline silicon ingot 22 by the gas inside the single-crystal furnace, thus improving the heat dissipation rate of the monocrystalline silicon ingot 22. The preset flow rate is 100 slm. By increasing the flow rate of the protective gas transmitted to the single-crystal furnace from 100 slm to 150 slm~180 slm, the flow rate of the protective gas inside the single-crystal furnace is accelerated, enhancing the convective heat transfer effect, thereby improving the heat dissipation rate of the monocrystalline silicon ingot 22. At the same time, the monocrystalline silicon ingot 22 is pulled upward at a cooling pulling speed of 50 mm / min, so that the monocrystalline silicon ingot 22 is moved away from the heating area, further enhancing the heat dissipation effect of the monocrystalline silicon ingot 22. This specific embodiment simultaneously reduces the furnace pressure inside the single crystal furnace, increases the flow rate of the protective gas transmitted to the single crystal furnace, and increases the pulling speed of the single crystal silicon ingot. Through the synergistic effect of adjusting the furnace pressure, the flow rate of the protective gas, and the pulling speed, the cooling rate of the single crystal silicon ingot 22 in the temperature range of 350℃ to 550℃ is improved, allowing the temperature of the single crystal silicon ingot 22 to drop rapidly to below 350℃. This significantly increases the cooling rate of the single crystal silicon ingot in the thermal donor formation temperature range of 350℃ to 550℃, preventing interstitial oxygen from fully accumulating to form thermal donors and inhibiting thermal donor formation. This significantly reduces the thermal donor concentration in the cooled single crystal silicon ingot, improving the quality of the single crystal silicon ingot and increasing the uniformity of the axial resistivity distribution of the single crystal silicon ingot. The rapid temperature drop of the monocrystalline silicon ingot 22 to below 350°C in this specific embodiment means that the rate at which the monocrystalline silicon ingot drops from the temperature range of 650°C to below 350°C in this specific embodiment is faster than the rate at which the monocrystalline silicon ingot drops from the temperature range of 650°C to below 350°C in conventional processes (such as natural cooling processes).

[0035] In some embodiments, the single crystal furnace includes a lower furnace cylinder 23, a middle furnace cylinder 24 located above the lower furnace cylinder 23, and an upper furnace cylinder 25 located above the middle furnace cylinder 24; the specific steps of simultaneously implementing the reduction of furnace pressure in the single crystal furnace to cooling furnace pressure, increasing the flow rate of the protective gas transmitted to the single crystal furnace to cooling flow rate, and increasing the pulling speed of the single crystal silicon ingot 22 to cooling pulling speed further include: Increase the pulling speed of the single crystal silicon ingot 22 to the cooling pulling speed to pull the single crystal silicon ingot 22 upward to the upper furnace cylinder 25.

[0036] In some embodiments, while simultaneously implementing the reduction of furnace pressure in the single crystal furnace to cooling furnace pressure, the increase of the flow rate of the protective gas transmitted to the single crystal furnace to cooling flow rate, and the increase of the pulling speed of the single crystal silicon ingot 22 to cooling pulling speed, the following steps are also included: The rotational speed of the single-crystal silicon ingot 22 is adjusted to 12 rpm.

[0037] Specifically, by lifting the monocrystalline silicon ingot 22 upwards into the upper furnace cylinder 25, the distance between the monocrystalline silicon ingot 22 and the bottom heater 29 and the main heater 28 can be maximized, thereby further improving the heat dissipation effect of the monocrystalline silicon ingot 22. Simultaneously, adjusting the rotation speed of the monocrystalline silicon ingot 22 to 12 rpm facilitates more uniform heat exchange between the surface of the monocrystalline silicon ingot 22 and the surrounding gas, enhancing the cooling effect of the monocrystalline silicon ingot 22.

[0038] In some embodiments, while simultaneously implementing the reduction of furnace pressure in the single crystal furnace to cooling furnace pressure, the increase of the flow rate of the protective gas transmitted to the single crystal furnace to cooling flow rate, and the increase of the pulling speed of the single crystal silicon ingot 22 to cooling pulling speed, the following steps are also included: Remove the external magnetic field applied to the single crystal furnace, which is used to suppress thermal convection of the silicon melt 31 in the quartz crucible 20.

[0039] Specifically, by demagnetizing the single-crystal furnace, the influence of the external magnetic field on the cooling process of the single-crystal silicon ingot 22 is eliminated, ensuring the stability of the cooling rate of the single-crystal silicon ingot 22. After removing the external magnetic field applied to the single-crystal furnace, the furnace pressure in the single-crystal furnace is maintained at the cooling furnace pressure, and the flow rate of the protective gas is maintained at the cooling flow rate, so that the single-crystal silicon ingot 22 located in the upper furnace cylinder 25 is cooled for 12 hours. Afterwards, the single-crystal furnace is opened, the single-crystal silicon ingot 22 is removed, and the single-crystal silicon ingot 22 is sliced ​​to form a wafer. The resistivity and other parameters of the wafer are tested to verify the cooling effect of the single-crystal silicon ingot 22.

[0040] The cooling method for monocrystalline silicon ingots provided in this specific embodiment, after completing the monocrystalline silicon ingot growth process, simultaneously reduces the furnace pressure in the monocrystalline furnace, increases the flow rate of the protective gas transmitted to the monocrystalline furnace, and increases the pulling speed of the monocrystalline silicon ingot. Through the synergistic effect of the adjustments in furnace pressure, the flow rate of the protective gas, and the pulling speed, the temperature of the monocrystalline silicon ingot is rapidly reduced to below 350°C. This significantly increases the cooling rate of the monocrystalline silicon ingot within the thermal donor formation temperature range of 350°C to 550°C, preventing interstitial oxygen from fully accumulating to form thermal donors and inhibiting thermal donor formation. Consequently, the thermal donor concentration in the cooled monocrystalline silicon ingot is significantly reduced, improving the quality of the monocrystalline silicon ingot and enhancing the uniformity of the axial resistivity distribution of the monocrystalline silicon ingot. Furthermore, since the cooling method for the monocrystalline silicon ingot provided in this specific embodiment is implemented in situ after the complete completion of the monocrystalline silicon ingot growth process, no additional cooling equipment is required, and there is no need to pay attention to the monocrystalline silicon ingot growth process, nor is it necessary to improve or adjust the monocrystalline silicon ingot growth process, thus not affecting the monocrystalline silicon ingot growth process. Compared with thermal treatment of the wafer as a thermal donor, the process is simplified, and the difficulty of suppressing the formation of thermal donors in the monocrystalline silicon ingot is reduced.

[0041] It should be noted that the terms "comprising" and "having," and their variations, used in this invention document are intended to cover non-exclusive inclusion. The terms "first," "second," etc., are used to distinguish similar objects and are not necessarily used to describe a specific order or sequence, unless explicitly indicated by the context; it should be understood that such use of data can be interchanged where appropriate. The term "one or more" depends at least in part on the context and can be used to describe features, structures, or characteristics in a singular sense, or in a plural sense to describe combinations of features, structures, or characteristics. The term "based on" can be understood as not necessarily intended to express an exclusive set of factors, but can instead, also at least in part on the context, allow for the presence of other factors that are not necessarily explicitly described. Furthermore, embodiments and features in embodiments of this invention can be combined with each other without conflict. In addition, descriptions of well-known components and technologies have been omitted in the above description to avoid unnecessarily obscuring the concepts of this invention. In the various embodiments described above, each embodiment focuses on its differences from other embodiments; similar / identical parts between embodiments can be referred to mutually.

[0042] The above description is only a preferred embodiment of the present invention. It should be noted that those skilled in the art can make several improvements and modifications without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A cooling method for a single-crystal silicon ingot, characterized in that, Includes the following steps: A single-crystal silicon ingot with its growth completed is provided, the single-crystal silicon ingot being located inside a single-crystal furnace; Simultaneously, the furnace pressure inside the single crystal furnace is reduced to a cooling furnace pressure, the flow rate of the protective gas transmitted to the single crystal furnace is increased to a cooling flow rate, and the pulling speed of the single crystal silicon ingot is increased to a cooling pulling speed, so that the temperature of the single crystal silicon ingot is reduced to below 350°C, the cooling furnace pressure is lower than the furnace pressure during the growth process of the single crystal silicon ingot, the cooling flow rate is higher than the flow rate during the growth process of the single crystal silicon ingot, and the cooling pulling speed is higher than the pulling speed during the growth process of the single crystal silicon ingot.

2. The cooling method for a single-crystal silicon ingot according to claim 1, characterized in that, The single-crystal silicon ingot, after growth has ended, is located in a quartz crucible within the single-crystal furnace, and the quartz crucible is located within a graphite crucible. Before simultaneously reducing the furnace pressure in the single-crystal furnace to a cooling furnace pressure, increasing the flow rate of the protective gas transmitted to the single-crystal furnace to a cooling flow rate, and increasing the pulling speed of the single-crystal silicon ingot to a cooling pulling speed, the following steps are also included: Stop lifting the graphite crucible and the single-crystal silicon ingot upwards, and reduce the rotational speed of the single-crystal silicon ingot to below 5 rpm.

3. The cooling method for a single-crystal silicon ingot according to claim 2, characterized in that, The single crystal furnace also includes a bottom heater located below the graphite crucible for heating the bottom of the graphite crucible; before simultaneously reducing the furnace pressure in the single crystal furnace to the cooling furnace pressure, increasing the flow rate of the protective gas transmitted to the single crystal furnace to the cooling flow rate, and increasing the pulling speed of the single crystal silicon ingot to the cooling pulling speed, the following steps are also included: The graphite crucible is lowered to the lower limit at a speed of 50 mm / min, and the heating power of the bottom heater is adjusted to 5 kW to 10 kW.

4. The cooling method for a single-crystal silicon ingot according to claim 2, characterized in that, Before simultaneously reducing the furnace pressure in the single crystal furnace to the cooling furnace pressure, increasing the flow rate of the protective gas transmitted to the single crystal furnace to the cooling flow rate, and increasing the pulling speed of the single crystal silicon ingot to the cooling pulling speed, the following steps are also included: The single-crystal silicon ingot, now at the end of its growth, is lowered at a speed of 30 mm / min until the distance between its tail and the surface of the remaining molten silicon in the quartz crucible is 100 mm.

5. The cooling method for a single-crystal silicon ingot according to claim 2, characterized in that, The single crystal furnace also includes a main heater located on the outer side of the graphite crucible for heating the graphite crucible; before simultaneously reducing the furnace pressure in the single crystal furnace to the cooling furnace pressure, increasing the flow rate of the protective gas transmitted to the single crystal furnace to the cooling flow rate, and increasing the pulling speed of the single crystal silicon ingot to the cooling pulling speed, the following steps are also included: The heating power of the main heater is reduced to 30kW and maintained for 30 to 60 minutes.

6. The cooling method for a single-crystal silicon ingot according to claim 1, characterized in that, The specific steps for simultaneously implementing the reduction of furnace pressure in the single crystal furnace to cooling furnace pressure, the increase of the flow rate of the protective gas transmitted to the single crystal furnace to cooling flow rate, and the increase of the pulling speed of the single crystal silicon ingot to cooling pulling speed include: Determine whether the temperature of the single crystal silicon ingot is stable at 650°C. If so, simultaneously reduce the furnace pressure in the single crystal furnace to the cooling furnace pressure, increase the flow rate of the protective gas transmitted to the single crystal furnace to the cooling flow rate, and increase the pulling speed of the single crystal silicon ingot to the cooling pulling speed.

7. The cooling method for a single-crystal silicon ingot according to claim 1, characterized in that, The cooling furnace pressure is 3 kPa, the cooling flow rate is 150 slm~180 slm, and the cooling lifting speed is 50 mm / min.

8. The cooling method for a single-crystal silicon ingot according to claim 2, characterized in that, The single crystal furnace includes a lower furnace cylinder, a middle furnace cylinder located above the lower furnace cylinder, and an upper furnace cylinder located above the middle furnace cylinder; the specific steps of simultaneously reducing the furnace pressure in the single crystal furnace to the cooling furnace pressure, increasing the flow rate of the protective gas transmitted to the single crystal furnace to the cooling flow rate, and increasing the pulling speed of the single crystal silicon ingot to the cooling pulling speed also include: Increase the pulling speed of the single crystal silicon ingot to the cooling pulling speed to pull the single crystal silicon ingot upwards into the upper furnace cylinder.

9. The cooling method for a single-crystal silicon ingot according to claim 2, characterized in that, Simultaneously implementing the reduction of furnace pressure in the single crystal furnace to cooling furnace pressure, the increase of the flow rate of the protective gas transmitted to the single crystal furnace to cooling flow rate, and the increase of the pulling speed of the single crystal silicon ingot to cooling pulling speed, the process also includes the following steps: The rotational speed of the single-crystal silicon ingot is adjusted to 12 rpm.

10. The cooling method for a single-crystal silicon ingot according to claim 2, characterized in that, Simultaneously implementing the reduction of furnace pressure in the single crystal furnace to cooling furnace pressure, the increase of the flow rate of the protective gas transmitted to the single crystal furnace to cooling flow rate, and the increase of the pulling speed of the single crystal silicon ingot to cooling pulling speed, the process also includes the following steps: Remove the external magnetic field applied to the single crystal furnace, which is used to suppress thermal convection of the silicon melt in the quartz crucible.

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