Quartz crucible and method for improving hydroxyl uniformity of quartz crucible

Abstract

The invention discloses a quartz crucible and a method for improving hydroxyl uniformity of the quartz crucible, and belongs to the technical field of quartz crucibles. According to the method, a bubble layer is obtained through repeated operation of a melting circulation unit, the vacuum degree of a first sub-stage in the melting circulation unit ranges from-0.005 MPa to-0.010 MPa, the current ranges from 4300 A to 4500 A, the electric arc action time ranges from 0.25 min to 0.3 min, the distance between electrodes ranges from 30 mm to 35 mm, and the vertical distance between the arcing end of each electrode and an upper end opening of a rotary mold ranges from 150 mm to 200 mm; in the second sub-stage, the vacuum degree is-0.030 MPa to-0.040 MPa, the current is 2100 A to 2300 A, and the rest are the same as those in the first sub-stage. According to the method, the uniformity of hydroxyl in the quartz crucible can be improved, so that the service life of the crucible can be prolonged, the defect rate of a silicon single crystal rod is reduced, and the yield of the silicon single crystal rod is improved.

Description

A quartz crucible and a method for improving its hydroxyl uniformity Technical Field

[0001] This invention relates to the field of quartz crucible technology, and more specifically, to a quartz crucible and a method for improving the uniformity of its hydroxyl groups. Background Technology

[0002] Quartz crucibles are vessels made primarily from high-purity quartz sand. They possess characteristics such as high purity, strong temperature resistance, large size and high precision, good heat insulation, energy saving, and stable quality, and can be used below 1450℃. The performance of the quartz crucible directly affects the quality of single-crystal silicon. Hydroxyl groups, as one of the main elements affecting crucible performance, have a particularly significant negative impact. For example, hydroxyl groups may generate bubbles during the preparation process, affecting the quality of single crystals. Furthermore, they may also cause crucible deformation. Currently, there is no effective method to control the content and uniformity of hydroxyl groups in quartz crucibles.

[0003] In view of this, the present invention is proposed. Summary of the Invention

[0004] The purpose of this invention is to provide a quartz crucible and a method for improving the uniformity of its hydroxyl groups, so as to solve or improve the above-mentioned technical problems.

[0005] This invention can be implemented as follows: In a first aspect, this invention provides a method for improving the uniformity of hydroxyl groups in a quartz crucible, comprising the following steps: laying quartz sand in a rotating mold, removing air from the rotating mold and from the gaps between the quartz sand; sequentially preparing a transparent layer and a bubble layer under vacuum and electric arc conditions; wherein the bubble layer is obtained by repeated melting cycle units, each melting cycle unit including a first sub-stage and a second sub-stage, and the total electric arc time during the bubble layer preparation process is 10 min to 15 min; the conditions of the first sub-stage include: a vacuum degree of -0.005 MPa to -0.010 M... The conditions for the second sub-stage are: a vacuum of -0.030MPa to -0.040MPa, a current of 2100A to 2300A, an arc duration of 0.25min to 0.3min, an electrode spacing of 30mm to 35mm, and a vertical distance between the arc-starting end of the electrode and the upper port of the rotating mold of 150mm to 200mm;

[0006] In an optional embodiment, the preparation of the transparent layer includes two stages: the preparation conditions of stage one include a vacuum of -0.035MPa to -0.095MPa, a current of 2000A to 2300A, an arc duration of 2 to 3 minutes, an electrode spacing of 20mm to 25mm, and a vertical distance of 150mm to 200mm between the arc-starting end of the electrode and the upper port of the rotating mold, so that the quartz sand in the arc-acting area forms a sealing layer; the preparation conditions of stage two include a vacuum of -0.095MPa to -0.099MPa, a current of 2000A to 2300A, an arc duration of 6 to 8 minutes, an electrode spacing of 20mm to 25mm, and a vertical distance of 150mm to 200mm between the arc-starting end of the electrode and the upper port of the rotating mold, so that the quartz sand in the arc-acting area and the sealing layer together form a transparent layer.

[0007] In an optional embodiment, the quartz sand used to prepare the transparent layer and the bubble layer includes both coarse-grained quartz sand and fine-grained quartz sand; wherein the particle size of the coarse-grained quartz sand is 230μm~325μm; and the particle size of the fine-grained quartz sand is 75μm~125μm.

[0008] In an optional embodiment, the mass ratio of coarse-grained quartz sand to fine-grained quartz sand is (1~1.2):(2~2.3).

[0009] Secondly, the present invention provides a quartz crucible prepared by any of the methods described in the foregoing embodiments.

[0010] In an optional embodiment, the hydroxyl content in the quartz crucible is 18ppm to 25ppm.

[0011] In an optional embodiment, the hydroxyl content in the straight-wall region of the quartz crucible is 22 ppm to 24 ppm.

[0012] In an optional embodiment, the hydroxyl content in the R-corner region of the quartz crucible is 21ppm to 22.5ppm.

[0013] In an optional embodiment, the hydroxyl content in the bottom wall region of the quartz crucible is 20ppm to 21.5ppm.

[0014] In an optional embodiment, the thickness of the transparent layer of the quartz crucible is 3mm to 5mm, and the thickness of the bubble layer is 10mm to 12mm.

[0015] The beneficial effects of this invention include: By employing a specific melting process, this invention effectively improves the bubble composition content within the bubble layer of a quartz crucible. Specifically, during the bubble layer preparation process, a high-current ablation and vacuum frequency conversion scheme is introduced. First, a short period of high-current ablation is performed, followed by a short period of low-current ablation, using the residual heat of the high-current to melt the bubble layer. Repeating this alternating high-current and low-current melting process ensures that the bubbles in the prepared bubble layer are uniform and free of water vapor and hydrogen gases. During the high-current ablation process, the vacuum limit is low, making it difficult for the quartz sand to melt quickly. The intermittent high-current ablation improves upon the problem of insufficient volatilization of hydroxyl groups on the straight wall caused by the low-current ablation, and avoids the situation where continuous high-current ablation causes rapid melting of the quartz sand, resulting in excessively rapid melting of small bubbles in the bubble layer and an increase in the content of water vapor and hydrogen gases.

[0016] The solution provided by the invention can effectively reduce the content of hydroxyl groups in the quartz crucible and improve the uniformity of hydroxyl groups in the quartz crucible, thereby helping to extend the service life of the crucible, reduce the defect rate of the single crystal silicon rod and improve the yield of the single crystal silicon rod. Attached Figure Description

[0017] To more clearly illustrate the technical solutions of the embodiments of the present invention, the accompanying drawings used in the embodiments will be briefly introduced below. It should be understood that the following drawings only show some embodiments of the present invention and should not be regarded as a limitation on the scope. For those skilled in the art, other related drawings can be obtained based on these drawings without creative effort.

[0018] Figure 1 is a schematic diagram of the structure of the quartz crucible provided by the present invention.

[0019] Icons: 1-Transparent layer; 2-Bubble layer. Detailed Implementation

[0020] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below. Where specific conditions are not specified in the embodiments, conventional conditions or conditions recommended by the manufacturer shall apply. Reagents or instruments whose manufacturers are not specified are all conventional products that can be purchased commercially.

[0021] The quartz crucible and the method for improving the uniformity of its hydroxyl groups provided by the present invention will be described in detail below.

[0022] In quartz crucibles, the presence of hydroxyl groups disrupts the Si-O-Si network structure of the quartz glass, significantly reducing the viscosity of the molten silica. This reduced viscosity makes the inner wall of the crucible more susceptible to erosion and dissolution by the molten silicon at high temperatures, resulting in thinner crucible walls and a shorter lifespan. Furthermore, the reduced viscosity makes the crucible more prone to high-temperature creep and softening deformation under its own weight and the hydrostatic pressure of the molten silicon. This deformation alters the thermal field distribution, also negatively impacting crystal growth. Additionally, quartz glass is metastable and tends to transform into cristobalite at high temperatures—a process known as crystallization or devitrification. The presence of hydroxyl groups accelerates this crystallization process. The precipitated cristobalite crystals have different coefficients of thermal expansion than the quartz glass matrix, leading to microcracks during cooling and fragmentation. These cristobalite fragments falling into the molten silicon become fatal defects, causing dislocations, wire breaks, and even rendering the single-crystal silicon rod unusable. Furthermore, at high temperatures, hydroxyl groups decompose to form water vapor and hydrogen gas, generating tiny bubbles. These bubbles are released into the molten silicon through the crucible walls, causing instability in the silicon flow and affecting the solid-liquid interface of crystal growth, thus disrupting crystal uniformity. More importantly, the hydrogen and oxygen introduced by the decomposition of hydroxyl groups enter the silicon melt and eventually the crystal lattice, severely reducing the electrical properties and mechanical strength of the silicon wafer. Moreover, during crystal pulling, water molecules and hydrogen gas react at high temperatures, directly introducing hydroxyl groups.

[0023] Based on this, the present invention creatively proposes a method for improving the uniformity of hydroxyl groups in a quartz crucible. As shown in Figure 1, the quartz crucible includes a transparent layer 1 and a bubble layer 2 arranged sequentially from the inside to the outside. The method for improving the uniformity of hydroxyl groups includes the following steps: laying quartz sand in a rotating mold to form a shape, removing air from the rotating mold and the gaps between the quartz sand; and preparing the transparent layer 1 and the bubble layer 2 sequentially under vacuum and electric arc.

[0024] In this invention, the quartz sand used to prepare the transparent layer 1 and the bubble layer 2 includes both coarse-grained quartz sand and fine-grained quartz sand.

[0025] The coarse-grained quartz sand has a particle size of 230μm~325μm, such as 230μm, 250μm, 280μm, 300μm or 325μm, or other values ​​within the range of 230μm~325μm.

[0026] The particle size of fine-grained quartz sand can be 75μm~125μm, such as 75μm, 100μm or 125μm, or other values ​​within the range of 75μm~125μm.

[0027] In some alternative embodiments, the mass ratio of coarse-grained quartz sand to fine-grained quartz sand is (1~1.2):(2~2.3), such as 1:2, 1:2.1, 1:2.2, 1:2.3, 1.1:2, 1.2:2, etc., or other values ​​within the range of (1~1.2):(2~2.3).

[0028] The purity of the aforementioned quartz sand is not less than 99.9999%.

[0029] It should be noted that, after extensive research on existing quartz crucibles, the inventors proposed that the type and proportion of quartz sand used in the preparation of the crucible have a certain impact on the hydroxyl content of the crucible body, and the excessive use of coarse quartz sand is also one of the main sources of increased hydroxyl content. Specifically, fine-grained quartz sand, due to its small particle size, has a significantly larger specific surface area compared to coarse-grained quartz sand, theoretically resulting in more adsorbed water molecules and the generation of more hydroxyl groups. However, during the melting process, the high packing density of fine particles, the close contact between particles, and the more uniform heat transfer can accelerate the volatilization of hydroxyl groups in localized high-temperature areas. In addition, the short-range diffusion path of fine particles makes it easier for hydroxyl groups to migrate from the interior of the particles to the surface and escape, thereby reducing the overall hydroxyl content. Furthermore, fine-grained quartz sand (especially those treated by ball milling or air jet milling) has a more uniform particle shape and fewer surface defects, reducing the aggregation points of hydroxyl groups. In contrast, coarse-grained quartz sand has a rough surface with more microcracks and pores, where hydroxyl groups tend to accumulate and are difficult to volatilize. Therefore, this invention creatively improves the hydroxyl content of the crucible body by appropriately controlling the ratio of coarse and fine quartz sand.

[0030] However, if too little coarse-grained quartz sand is used, such as a mass ratio of coarse to fine quartz sand of 0.5:2, it is easy for the material to melt before all internal moisture is expelled, thus locking more hydroxyl groups inside the material. If too much coarse-grained quartz sand is used, such as a mass ratio of coarse to fine quartz sand of 1:1, it is not conducive to the treatment of air bubbles during the melting process. If the fine particles are insufficient to fill these pores, the resulting transparent layer will have more air bubbles, which is not conducive to vacuuming and will easily lead to insufficient moisture removal.

[0031] In some alternative embodiments, the rotational speed of the mold can be 70 rpm to 72 rpm throughout the entire preparation process of the quartz crucible, such as 70 rpm, 71 rpm or 72 rpm, or other values ​​within the range of 70 rpm to 72 rpm.

[0032] It should be noted that feasible methods for laying and shaping quartz sand and removing air can be found in relevant existing technologies. As long as the above effects can be achieved, this application will not elaborate on or limit the above operations.

[0033] In this invention, the preparation of transparent layer 1 includes two stages: stage one and stage two.

[0034] The preparation conditions for stage one include: a vacuum degree of -0.035MPa to -0.095MPa, a current of 2000A to 2300A, an arc duration of 2 to 3 minutes, an electrode spacing of 20mm to 25mm, and a vertical distance of 150mm to 200mm between the arc-starting end of the electrode and the upper port of the rotating mold, so that the quartz sand in the arc-acting area forms a sealing layer.

[0035] For example, the vacuum level of stage one can be -0.035MPa, -0.045MPa, -0.055MPa, -0.065MPa, -0.075MPa, -0.085MPa or -0.095MPa, or other values ​​within the range of -0.035MPa to -0.095MPa.

[0036] The current in stage one can be 2000A, 2050A, 2100A, 2150A, 2200A, 2250A or 2300A, or other values ​​within the range of 2000A to 2300A.

[0037] The arc duration in stage one can be 2 min, 2.5 min, or 3 min, or other values ​​within the range of 2 min to 3 min.

[0038] The electrode spacing in stage one can be 20mm, 21mm, 22mm, 23mm, 24mm or 25mm, or other values ​​within the range of 20mm to 25mm.

[0039] In stage one, the vertical distance between the arc-starting end of the electrode and the upper port of the rotating mold can be 150mm, 160mm, 170mm, 180mm, 190mm or 200mm, or other values ​​within the range of 150mm to 200mm.

[0040] The preparation conditions for stage two include: a vacuum of -0.095MPa to -0.099MPa, a current of 2000A to 2300A, an arc duration of 6 to 8 minutes, an electrode spacing of 20mm to 25mm, and a vertical distance of 150mm to 200mm between the arc-starting end of the electrode and the upper port of the rotating mold, so that the quartz sand in the arc-acting area and the sealing layer together form a transparent layer 1.

[0041] For example, the vacuum degree of stage two can be -0.095MPa, -0.096MPa, -0.097MPa, -0.098MPa or -0.099MPa, or other values ​​in the range of -0.095MPa to -0.099MPa.

[0042] If the vacuum level in stage two does not reach the ultimate vacuum pressure of -0.095MPa to -0.099MPa, such as -0.08MPa, it will not be conducive to the removal of bubbles in the transparent layer, resulting in an increase in the bubble content inside the transparent layer.

[0043] The current in stage two can be 2000A, 2050A, 2100A, 2150A, 2200A, 2250A or 2300A, or other values ​​within the range of 2000A to 2300A.

[0044] The arc duration in stage two can be 6 min, 6.5 min, 7 min, 7.5 min or 8 min, or other values ​​within the range of 6 min to 8 min.

[0045] The electrode spacing in stage two can be 20mm, 21mm, 22mm, 23mm, 24mm or 25mm, or other values ​​within the range of 20mm to 25mm.

[0046] In stage two, the vertical distance between the arc-starting end of the electrode and the upper port of the rotating mold can be 150mm, 160mm, 170mm, 180mm, 190mm or 200mm, or other values ​​within the range of 150mm to 200mm.

[0047] In the aforementioned transparent layer 1 stage, by compounding coarse-grained quartz sand with fine-grained quartz sand, and then using near-limit vacuum extraction to remove air bubbles from the gaps, it is easier to remove air bubbles, thus obtaining a transparent layer 1 with almost no air bubbles. In contrast, the conventional method of preparing transparent layer 1 using fine-grained quartz sand is difficult to remove because the fine-grained quartz sand melts quickly.

[0048] In this invention, the bubble layer 2 is obtained by repeated melting cycle units. Each melting cycle unit includes a first sub-stage and a second sub-stage. The total arc time during the preparation of the bubble layer 2 is 10 min to 15 min, such as 10 min, 11 min, 12 min, 13 min, 14 min or 15 min, or other values ​​within the range of 10 min to 15 min.

[0049] The conditions for the first sub-stage may include: a vacuum of -0.005MPa to -0.010MPa, a current of 4300A to 4500A, an arc duration of 0.25min to 0.3min, an electrode spacing of 30mm to 35mm, and a vertical distance of 150mm to 200mm between the arc-starting end of the electrode and the upper port of the rotating mold.

[0050] For example, the vacuum degree of the first sub-stage can be -0.005MPa, -0.006MPa, -0.007MPa, -0.008MPa, -0.009MPa or -0.010MPa, or other values ​​in the range of -0.005MPa to -0.010MPa.

[0051] If the vacuum level in the first sub-stage is below -0.005MPa (e.g., -0.002MPa), it is not conducive to the effective adsorption of molten quartz into the inner layer of the mold, and the quartz is prone to collapse under the action of gravity and impact. If the vacuum level in the first sub-stage is above -0.005MPa (e.g., -0.015MPa), in the high current stage, some quartz sand melts faster, resulting in the inability to effectively remove water vapor, hydrogen and other gases in the gaps of the quartz sand.

[0052] The current of the first sub-stage can be 4300A, 4350A, 4400A, 4450A or 4500A, or other values ​​within the range of 4300A to 4500A.

[0053] If the current in the first sub-stage is lower than 4300A, it is not conducive to the volatilization of gases such as water vapor and hydrogen in the gaps between the bubble layers, as well as the volatilization of hydroxyl groups in the quartz sand itself. If the current in the first sub-stage is higher than 4500A, under the action of a small vacuum, due to the excessively high temperature and rapid melting, gases such as water vapor and hydrogen in the gaps between the bubble layers cannot be discharged in time and remain in the bubbles, increasing the risk of increased hydroxyl content during the later crystal pulling process.

[0054] The arc duration of the first sub-stage can be 0.25 min, 0.26 min, 0.27 min, 0.28 min, 0.29 min, or 0.3 min, or other values ​​within the range of 0.25 min to 0.3 min.

[0055] If the arc duration in the first sub-stage exceeds 0.3 minutes, such as 1 minute, some of the quartz sand will continue to melt during the high current stage, resulting in the inability to effectively remove gases such as water vapor and hydrogen from the gaps in the quartz sand.

[0056] The electrode spacing of the first sub-stage can be 30mm, 31mm, 32mm, 33mm, 34mm or 35mm, or other values ​​within the range of 30mm to 35mm.

[0057] In the first sub-stage, the vertical distance between the arc-starting end of the electrode and the upper port of the rotating mold can be 150mm, 160mm, 170mm, 180mm, 190mm or 200mm, or other values ​​within the range of 150mm to 200mm.

[0058] The conditions for the second sub-stage may include: a vacuum of -0.030MPa to -0.040MPa, a current of 2100A to 2300A, an arc duration of 0.25min to 0.3min, an electrode spacing of 30mm to 35mm, and a vertical distance of 250mm to 300mm between the arc-starting end of the electrode and the upper port of the rotating mold.

[0059] For example, the vacuum degree of the second sub-stage can be -0.030MPa, -0.032MPa, -0.035MPa, -0.038MPa or -0.040MPa, or other values ​​in the range of -0.030MPa to -0.040MPa.

[0060] If the vacuum level of the second sub-stage is below -0.030MPa (e.g., -0.020MPa), it is not conducive to the timely removal of gases such as water vapor and hydrogen from the gaps in the quartz sand; if the vacuum level of the second sub-stage is above -0.040MPa (e.g., -0.050MPa), it is easy for gases such as water vapor and hydrogen to be melted into the bubbles in the bubble layer.

[0061] The current in the second sub-stage can be 2100A, 2150A, 2200A, 2250A or 2300A, or other values ​​within the range of 2100A to 2300A.

[0062] If the current in the second sub-stage is below 2100A, the current is too small and the quartz sand cannot melt, thus failing to effectively form a bubble layer; if the current in the second sub-stage is above 2300A, it is difficult to effectively reduce the content of harmful gases melted in the bubbles.

[0063] The arc duration in the second sub-stage can be 0.25 min, 0.26 min, 0.27 min, 0.28 min, 0.29 min, or 0.3 min, or other values ​​within the range of 0.25 min to 0.3 min.

[0064] If the arcing time in the second stage exceeds 0.3 minutes, such as 1 minute, the temperature is prone to drop during the melting process, which can lead to the ineffective volatilization of hydroxyl groups in the molten quartz and the quartz sand itself. Therefore, a short period of high current and high temperature, combined with a suitable period of low current vacuuming, can not only effectively volatilize hydroxyl groups, but also effectively remove water vapor, hydrogen, and other gases from the gaps in the quartz sand under a small vacuum.

[0065] The electrode spacing of the second sub-stage can be 30mm, 31mm, 32mm, 33mm, 34mm or 35mm, or other values ​​within the range of 30mm to 35mm.

[0066] In the second sub-stage, the vertical distance between the arc-starting end of the electrode and the upper port of the rotating mold can be 250mm, 260mm, 270mm, 280mm, 290mm or 300mm, or other values ​​within the range of 250mm to 300mm.

[0067] It should be noted that in the conventional process, a small-scale vacuum was not performed when melting the bubble layer 2, resulting in uneven bubbles in the bubble layer 2. Furthermore, because no vacuum was performed, some water vapor and hydrogen gases remained in the gaps between the quartz sand. During the crystal pulling process, these water molecules and hydrogen gases reacted at high temperatures, directly introducing hydroxyl groups. In addition, the conventional process usually uses a small current to melt the bubble layer 2, which prevents the hydroxyl groups at the ends from being fully volatilized.

[0068] In this invention, a specific melting process effectively improves the bubble composition content within the bubble layer 2 of the quartz crucible. Specifically, by introducing a high-current ablation and vacuum frequency conversion scheme, a short period of high-current ablation is performed first, followed by a short period of low-current ablation, using the residual heat of the high-current to melt the bubble layer 2. This alternating high-current and low-current melting process is repeated, resulting in uniformly distributed bubbles in the prepared bubble layer 2, and ensuring that the bubble layer 2 is free of water vapor and hydrogen gases. During the high-current ablation process, the vacuum level is low, making it difficult for the quartz sand to melt quickly. The intermittent high-current ablation improves the problem of insufficient volatilization of hydroxyl groups on the straight wall caused by the low current, and avoids the situation where continuous high-current ablation leads to rapid melting of the quartz sand, resulting in excessively rapid melting of the small bubbles in the bubble layer 2 and an increase in the content of water vapor and hydrogen gases.

[0069] Accordingly, the present invention also provides a quartz crucible prepared by the above method.

[0070] The hydroxyl content in this quartz crucible is 18ppm to 25ppm.

[0071] In some optional embodiments, the hydroxyl content in the straight wall region of the quartz crucible is 22ppm~24ppm, the hydroxyl content in the rounded corner region is 21ppm~22.5ppm, and the hydroxyl content in the bottom wall region is 20ppm~21.5ppm.

[0072] In some alternative embodiments, the thickness of the transparent layer 1 of the quartz crucible can be 3mm to 5mm, such as 3mm, 3.5mm, 4mm, 4.5mm or 5mm, or other values ​​within the range of 3mm to 5mm.

[0073] The thickness of bubble layer 2 can be 10mm to 12mm, such as 10mm, 10.5mm, 11mm, 11.5mm or 12mm, or other values ​​within the range of 10mm to 12mm.

[0074] In some alternative embodiments, the outer diameter of the quartz crucible can be 808mm to 813mm, such as 808mm, 809mm, 810mm, 811mm, 812mm or 813mm, or other values ​​within the range of 808mm to 813mm.

[0075] In some alternative embodiments, the height of the quartz crucible can be 500mm to 550mm, such as 500mm, 510mm, 520mm, 530mm, 540mm or 550mm, or other values ​​within the range of 500mm to 550mm.

[0076] As mentioned above, the quartz crucible provided by this invention has a low and uniform hydroxyl content, which is beneficial for extending the service life of the crucible, reducing the defect rate of single crystal silicon rods, and improving the yield of single crystal silicon rods.

[0077] The features and performance of the present invention will be further described in detail below with reference to embodiments.

[0078] Example 1 This example provides a quartz crucible with an outer diameter of 810 mm and a height of 550 mm. The preparation of the quartz crucible includes: laying quartz sand in a rotating mold to form a shape, removing air from the rotating mold and the gaps between the quartz sand; under vacuum and electric arc action, sequentially preparing a transparent layer 1 with a thickness of 3 mm and a bubble layer 2 with a thickness of 10 mm, and then removing it from the furnace.

[0079] The quartz sand is composed of coarse quartz sand and fine quartz sand in a mass ratio of 1:2. The coarse quartz sand has a particle size of 230μm~325μm and a purity of 99.9999%; the fine quartz sand has a particle size of 75μm~125μm and a purity of 99.9999%.

[0080] The preparation of transparent layer 1 includes two stages.

[0081] The preparation conditions for Stage 1 include: a vacuum of -0.065 MPa, a current of 2150 A, an arc duration of 2.5 min, an electrode spacing of 22 mm, and a vertical distance of 175 mm between the arc-starting end of the electrode and the upper port of the rotating mold, so that the quartz sand in the arc-acting area forms a sealing layer. The preparation conditions for Stage 2 include: a vacuum of -0.098 MPa, a current of 2150 A, an arc duration of 7 min, an electrode spacing of 22 mm, and a vertical distance of 175 mm between the arc-starting end of the electrode and the upper port of the rotating mold, so that the quartz sand in the arc-acting area and the sealing layer together form a transparent layer 1.

[0082] The bubble layer 2 is obtained by repeating the melting cycle unit. Each melting cycle unit includes a first sub-stage and a second sub-stage. The total arc time during the preparation of the bubble layer 2 is 12 minutes.

[0083] The conditions for the first sub-stage include: a vacuum of -0.008 MPa, a current of 4500 A, an arc duration of 0.3 min, an electrode spacing of 32 mm, and a vertical distance of 175 mm between the arc-initiating end of the electrode and the upper port of the rotating mold. The conditions for the second sub-stage include: a vacuum of -0.035 MPa, a current of 2300 A, an arc duration of 0.3 min, an electrode spacing of 32 mm, and a vertical distance of 275 mm between the arc-initiating end of the electrode and the upper port of the rotating mold.

[0084] Example 2 This example provides a quartz crucible with an outer diameter of 808 mm and a height of 500 mm. The preparation of the quartz crucible includes: laying quartz sand in a rotating mold to form a shape, removing air from the rotating mold and the gaps between the quartz sand; and preparing a transparent layer 1 with a thickness of 4 mm and a bubble layer 2 with a thickness of 10 mm in sequence under vacuum and electric arc.

[0085] The quartz sand is composed of coarse-grained quartz sand and fine-grained quartz sand in a mass ratio of 1:2.3. The coarse-grained quartz sand has a particle size of 230μm~325μm and a purity of 99.9999%; the fine-grained quartz sand has a particle size of 75μm~125μm and a purity of 99.9999%.

[0086] The preparation of transparent layer 1 includes two stages.

[0087] The preparation conditions for Stage 1 include: a vacuum of -0.035 MPa, a current of 2000 A, an arc duration of 3 min, an electrode spacing of 20 mm, and a vertical distance of 150 mm between the arc-starting end of the electrode and the upper port of the rotating mold, so that the quartz sand in the arc-acting area forms a sealing layer; the preparation conditions for Stage 2 include: a vacuum of -0.095 MPa, a current of 2000 A, an arc duration of 8 min, an electrode spacing of 20 mm, and a vertical distance of 150 mm between the arc-starting end of the electrode and the upper port of the rotating mold, so that the quartz sand in the arc-acting area and the sealing layer together form a transparent layer 1.

[0088] The bubble layer 2 is obtained by repeating the melting cycle unit. Each melting cycle unit includes a first sub-stage and a second sub-stage. The total arc time during the preparation of the bubble layer 2 is 10 minutes.

[0089] The conditions for the first sub-stage include: a vacuum of -0.005 MPa, a current of 4300 A, an arc duration of 0.3 min, an electrode spacing of 30 mm, and a vertical distance of 150 mm between the arc-initiating end of the electrode and the upper port of the rotating mold. The conditions for the second sub-stage include: a vacuum of -0.030 MPa, a current of 2100 A, an arc duration of 0.25 min, an electrode spacing of 35 mm, and a vertical distance of 250 mm between the arc-initiating end of the electrode and the upper port of the rotating mold.

[0090] Example 3 This example provides a quartz crucible with an outer diameter of 813 mm and a height of 520 mm. The preparation of the quartz crucible includes: laying quartz sand in a rotating mold to form a shape, removing air from the rotating mold and the gaps between the quartz sand; and preparing a transparent layer 1 with a thickness of 5 mm and a bubble layer 2 with a thickness of 12 mm in sequence under vacuum and electric arc.

[0091] The quartz sand is composed of coarse quartz sand and fine quartz sand in a mass ratio of 1.2:2. The coarse quartz sand has a particle size of 230μm~325μm and a purity of 99.9999%; the fine quartz sand has a particle size of 75μm~125μm and a purity of 99.9999%.

[0092] The preparation of transparent layer 1 includes two stages.

[0093] The preparation conditions for Stage 1 include: a vacuum of -0.095 MPa, a current of 2300 A, an arc duration of 2 min, an electrode spacing of 25 mm, and a vertical distance of 200 mm between the arc-starting end of the electrode and the upper port of the rotating mold, so that the quartz sand in the arc-acting area forms a sealing layer; the preparation conditions for Stage 2 include: a vacuum of -0.099 MPa, a current of 2300 A, an arc duration of 6 min, an electrode spacing of 25 mm, and a vertical distance of 200 mm between the arc-starting end of the electrode and the upper port of the rotating mold, so that the quartz sand in the arc-acting area and the sealing layer together form a transparent layer 1.

[0094] The bubble layer 2 is obtained by repeating the melting cycle unit. Each melting cycle unit includes a first sub-stage and a second sub-stage. The total arc time during the preparation of the bubble layer 2 is 15 minutes.

[0095] The conditions for the first sub-stage include: a vacuum of -0.010 MPa, a current of 4400 A, an arc duration of 0.25 min, an electrode spacing of 35 mm, and a vertical distance of 200 mm between the arc-initiating end of the electrode and the upper port of the rotating mold. The conditions for the second sub-stage include: a vacuum of -0.040 MPa, a current of 2200 A, an arc duration of 0.3 min, an electrode spacing of 30 mm, and a vertical distance of 300 mm between the arc-initiating end of the electrode and the upper port of the rotating mold.

[0096] Comparative Example 1 differs from Example 1 in that the fine-grained quartz sand is replaced with an equal amount of coarse-grained quartz sand. That is, all the quartz sand used in this comparative example is coarse-grained quartz sand.

[0097] Comparative Example 2 differs from Example 1 in that coarse-grained quartz sand is replaced with an equal amount of fine-grained quartz sand. That is, all the quartz sand used in this comparative example is fine-grained quartz sand.

[0098] The difference between Comparative Example 3 and Example 1 is that the mass ratio of coarse-grained quartz sand to fine-grained quartz sand is 0.5:2.

[0099] The difference between Comparative Example 4 and Example 1 is that the mass ratio of coarse-grained quartz sand to fine-grained quartz sand is 1:1.

[0100] The difference between Comparative Example 5 and Example 1 is that the preparation of bubble layer 2 was carried out continuously only under the conditions of the first sub-stage.

[0101] The difference between Comparative Example 6 and Example 1 is that the current in the second sub-stage of bubble layer 2 is also 4500A.

[0102] The difference between Comparative Example 7 and Example 1 is that the current in the first sub-stage of bubble layer 2 is also 2300A.

[0103] The difference between Comparative Example 8 and Example 1 is that the vacuum degree of the first sub-stage in bubble layer 2 is -0.002 MPa.

[0104] The difference between Comparative Example 9 and Example 1 is that the vacuum degree of the first sub-stage in bubble layer 2 is -0.015 MPa.

[0105] The difference between Comparative Example 10 and Example 1 is that the arcing time in the first sub-stage of bubble layer 2 is 1 minute.

[0106] The difference between Comparative Example 11 and Example 1 is that the vacuum degree of the second sub-stage in bubble layer 2 is -0.020 MPa.

[0107] The difference between Comparative Example 12 and Example 1 is that the vacuum degree of the second sub-stage in bubble layer 2 is -0.050 MPa.

[0108] The difference between Comparative Example 13 and Example 1 is that the arcing time in the second sub-stage of bubble layer 2 is 1 minute.

[0109] In the experimental examples, the hydroxyl content of the quartz crucibles prepared in Examples 1-3 and Comparative Examples 1-13 was tested. The test method was in accordance with GB / T 12442-2019 "Test Method for Hydroxyl Content in Quartz Glass". The test results are shown in Table 1.

[0110] Wherein, "W1" represents the average of the results obtained from three randomly selected test points at the port of the straight wall area, with at least a 100mm interval between each test point; "W2" represents the average of the results obtained from three randomly selected test points at a height of 100mm from the port in the straight wall area, with at least a 100mm interval between each test point; "W3" represents the average of the results obtained from three randomly selected test points at a height of 200mm from the port in the straight wall area, with at least a 100mm interval between each test point.

[0111] “R” represents the average value of the results obtained from three randomly selected test points at the height of the center of the R-angle region's arc, with at least 100mm between each test point.

[0112] “B1” represents the test result at the center of the bottom wall area; “B2” represents the average of the results obtained by randomly selecting 3 test points on a circle 100mm apart from the center of the bottom wall area, with each test point at least 100mm apart; “B3” represents the average of the results obtained by randomly selecting 3 test points on a circle 200mm apart from the center of the bottom wall area, with each test point at least 100mm apart.

[0113] Table 1 Test Results

[0114] As can be seen from Table 1, the method provided in the embodiments of the present invention can obtain quartz crucibles with low and uniform hydroxyl content.

[0115] In summary, the solution provided by this invention can effectively reduce the content of hydroxyl groups in the quartz crucible and improve the uniformity of hydroxyl groups in the quartz crucible, thereby helping to extend the service life of the crucible, reduce the defect rate of the single crystal silicon rod, and improve the yield of the single crystal silicon rod.

[0116] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A method for improving the uniformity of hydroxyl groups in a quartz crucible, characterized in that, Includes the following steps: Quartz sand is laid and shaped in a rotating mold, and air inside the rotating mold and in the gaps between the quartz sand is removed. A transparent layer and a bubble layer are sequentially prepared under vacuum and electric arc conditions. The bubble layer is obtained by repeated melting cycle units, each of which includes a first sub-stage and a second sub-stage. The total electric arc time during bubble layer preparation is 10-15 minutes. The conditions for the first sub-stage include: vacuum degree of -0.005 MPa to -0.010 MPa, current of 4300 A to 4500 A, and electric arc... The action time is 0.25min~0.3min, the electrode spacing is 30mm~35mm, and the vertical distance between the arc-starting end of the electrode and the upper port of the rotating mold is 150mm~200mm; the conditions of the second sub-stage include: vacuum degree of -0.030MPa~-0.040MPa, current of 2100A~2300A, arc action time of 0.25min~0.3min, electrode spacing of 30mm~35mm, and the vertical distance between the arc-starting end of the electrode and the upper port of the rotating mold is 250mm~300mm.

2. The method according to claim 1, characterized in that, The preparation of the transparent layer includes two stages: Stage 1 includes the following conditions: vacuum degree of -0.035MPa to -0.095MPa, current of 2000A to 2300A, arc duration of 2min to 3min, electrode spacing of 20mm to 25mm, and vertical distance between the arc-starting end of the electrode and the upper port of the rotating mold of 150mm to 200mm, so that the quartz sand in the arc-acting area forms a sealing layer; Stage 2 includes the following conditions: vacuum degree of -0.095MPa to -0.099MPa, current of 2000A to 2300A, arc duration of 6min to 8min, electrode spacing of 20mm to 25mm, and vertical distance between the arc-starting end of the electrode and the upper port of the rotating mold of 150mm to 200mm, so that the quartz sand in the arc-acting area and the sealing layer together form a transparent layer.

3. The method according to claim 1 or 2, characterized in that, The quartz sand used to prepare the transparent layer and the bubble layer includes both coarse-grained quartz sand and fine-grained quartz sand; wherein the particle size of the coarse-grained quartz sand is 230μm~325μm; and the particle size of the fine-grained quartz sand is 75μm~125μm.

4. The method according to claim 3, characterized in that, The mass ratio of the coarse-grained quartz sand to the fine-grained quartz sand is (1~1.2):(2~2.3).

5. A quartz crucible, characterized in that, It is prepared by the method described in any one of claims 1 to 4.

6. The quartz crucible according to claim 5, characterized in that, The hydroxyl content in the quartz crucible is 18ppm to 25ppm.

7. The quartz crucible according to claim 5, characterized in that, The hydroxyl content in the straight-walled region of the quartz crucible is 22ppm~24ppm.

8. The quartz crucible according to claim 5, characterized in that, The hydroxyl content in the R-corner region of the quartz crucible is 21ppm~22.5ppm.

9. The quartz crucible according to claim 5, characterized in that, The hydroxyl content in the bottom wall region of the quartz crucible is 20ppm to 21.5ppm.

10. The quartz crucible according to claim 5, characterized in that, The transparent layer of the quartz crucible has a thickness of 3mm to 5mm, and the bubble layer has a thickness of 10mm to 12mm.

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