Quartz crucible and preparation method and application thereof

Abstract

The application discloses a quartz crucible and a preparation method and application thereof, and belongs to the technical field of quartz crucibles. The preparation of the quartz crucible comprises the following steps: bubble layer quartz sand and transparent layer quartz sand are laid and formed in a rotating mold in the order from outside to inside; air in the rotating mold and air in the gap between the quartz sands are removed; under the conditions of vacuumizing and starting arc, the sealing layer quartz sand is introduced into the rotating mold by a scattering method so that the sealing layer quartz sand is melted and deposited on the surface of the transparent layer quartz sand, and then the temperature is lowered to obtain the sealing layer on the inner surface of the transparent layer; then the transparent layer quartz sand is melted to form the transparent layer; and then the bubble layer quartz sand is melted to form the bubble layer. By preparing the sealing layer on the inner wall of the transparent layer, impurities introduced by the rupture of bubbles of the crucible itself in the crystal pulling process can be avoided, and problems such as the reduction of the whole single crystal silicon rod rate, the appearance of pinholes and broken lines and the like can be avoided.

Description

Technical Field

[0001] The present invention relates to the technical field of quartz crucibles, and in particular to a quartz crucible and a preparation method and application thereof. Background Art

[0002] Single crystal silicon, the starting material for most semiconductor electronic component manufacturing, is typically produced using the so-called Czochralski ("CZ") method. Using the CZ method, crystal growth is most commonly performed in a crystal pulling furnace, where polycrystalline silicon is loaded into a crucible and melted by heaters surrounding the outer surface of the crucible's sidewalls. A seed crystal is brought into contact with the molten silicon, and a single crystal ingot is extracted by a crystal puller.

[0003] Crucibles used in conventional crystal pulling are typically made of quartz due to its purity, temperature stability, and chemical resistance. The mainstream method for manufacturing quartz crucibles is to introduce quartz feedstock into a rotating hollow mold. After the feedstock is introduced, a heat source, such as an electric arc, is introduced into the mold to melt the quartz. While heating, a vacuum is applied to the outside of the mold during continuous rotation to extract any interstitial gases, with the goal of collapsing the voids. The vacuum is maintained during melting and rotation, after which the finished crucible can be vented by replacing the vacuum with compressed air outside the mold. During this process, residual gases can cause unwanted bubbles to form in the quartz glass.

[0004] However, during the crystal growth process, the inner sidewall of the crucible is exposed to the high-temperature silicon melt for a long time, causing the silicon melt to react with the quartz crucible and dissolve the inner surface of the crucible sidewall. The silicon melt continues to dissolve into the crucible wall, especially into the wall containing bubbles. At some point, the bubble-containing wall is destroyed or dented, gas is released from the inside of the bubble, and quartz particles are released from the bubble sidewall into the melt. The released quartz particles may destroy the single crystal structure, thereby limiting crystal growth and single crystal yield. In addition, the bubble cavities or bubble voids along the inner surface of the crucible may become sites for gas nucleation. When the gas nucleates and grows into small bubbles, these bubbles may enter the growing silicon, resulting in crystals with voids and non-compliant crystals.

[0005] Therefore, the reduction or elimination of bubbles in the crucible is beneficial to ensure that the voids in the crystal are minimized to obtain acceptable crystal performance within the specifications. The method of reducing bubbles in the crucible in the prior art includes: preparing a quartz crucible by using a quartz crucible vacuum arc suction casting method, but because the inner surface layer of the quartz crucible is in contact with the air, the bubbles cannot be completely removed by vacuum, so there are still certain microbubbles in the surface layer. These microbubbles will expand and rupture due to heat during the crystal pulling process, and tiny quartz particles will fall into the silicon liquid when ruptured, reducing the purity of the single crystal silicon. In addition, the rupture of microbubbles on the inner surface of the quartz crucible also greatly causes the liquid level to fluctuate more during crystal pulling, which makes crystal pulling difficult and easy to break. Moreover, the ruptured area is more likely to induce crystallization, and the shedding of the crystallized part will also affect the purity of the single crystal silicon.

[0006] In view of this, the present invention is proposed. Summary of the Invention

[0007] The object of the present invention is to provide a quartz crucible and a preparation method and application thereof, so as to solve or improve the above-mentioned technical problems.

[0008] The present invention can be achieved like this:

[0009] In a first aspect, the present invention provides a method for preparing a quartz crucible, comprising the following steps: laying out a bubble layer of quartz sand and a transparent layer of quartz sand in a rotating mold in order from the outside to the inside to form a shape; removing air from the rotating mold and air in the gaps between the quartz sands; under vacuum and arcing conditions, introducing a cover layer of quartz sand into the rotating mold by a dispersion method so that the cover layer of quartz sand melts and deposits on the surface of the transparent layer of quartz sand, and then cooling to obtain a cover layer located on the inner surface of the transparent layer; then melting the transparent layer of quartz sand to form a transparent layer; and then melting the bubble layer of quartz sand to form a bubble layer.

[0010] In an optional embodiment, excluding air includes: introducing monatomic gas or a mixture of monatomic gas and oxygen into the rotating mold, the mixture comprising 80 wt% to 90 wt% of monatomic gas and 10 wt% to 20 wt% of oxygen.

[0011] In an optional embodiment, the scattering method includes: introducing the cover layer quartz sand into the rotating mold through an introduction device, the vertical distance between the discharge port of the introduction device and the upper port of the rotating mold is 45mm~55mm; the horizontal distance between the discharge port of the introduction device and the transparent layer is 100mm~150mm.

[0012] In an optional embodiment, the conditions for preparing the envelope layer include: a vacuum condition of -0.20 MPa to -0.3 MPa, an arc striking power of 10 Kw to 15 Kw, an arc acting time of 2 min to 3 min, an electrode spacing of 20 mm to 25 mm, and a vertical distance between the arc striking end of the electrode and the upper port of the rotating mold of 150 mm to 200 mm.

[0013] In an optional embodiment, the conditions for the cooling process include: a vacuum condition of -0.20 MPa to -0.4 MPa, an arc striking power of 5 Kw to 10 Kw, an arc acting time of 2 min to 3 min, an electrode spacing of 10 mm to 15 mm, and a vertical distance between the arc striking end of the electrode and the upper port of the rotating mold of 150 mm to 200 mm.

[0014] In an optional embodiment, the conditions for preparing the transparent layer include: a vacuum condition of -0.95 MPa to -0.99 MPa, an arc striking power of 25 Kw to 35 Kw, an arc acting time of 4 min to 6 min, an electrode spacing of 20 mm to 30 mm, and a vertical distance between the arc striking end of the electrode and the upper port of the rotating mold of 100 mm to 150 mm.

[0015] In an optional embodiment, the conditions for preparing the bubble layer include: an arc striking power of 16 Kw to 20 Kw, an arc acting time of 6 min to 10 min, an electrode spacing of 35 mm to 45 mm, and a vertical distance between the arc striking end of the electrode and the upper port of the rotating mold of 70 mm to 100 mm.

[0016] In an optional embodiment, the particle size of the bubble layer quartz sand is 120 μm to 250 μm, the particle size of the transparent layer quartz sand is 75 μm to 100 μm, and the particle size of the envelope layer quartz sand is 75 μm to 100 μm.

[0017] In an optional embodiment, the method further includes: after the bubble layer is formed, the arc is turned off, the electrode position is raised until the quartz crucible cools, and then the furnace is discharged and the mold is demolded.

[0018] In a second aspect, the application provides a quartz crucible prepared by the method of any one of the preceding embodiments.

[0019] In an optional embodiment, the quartz crucible has at least one of the following characteristics:

[0020] Characteristic 1: the thickness of the envelope layer is 0.3 mm to 0.8 mm.

[0021] Characteristic 2: the number of bubbles in the envelope layer is not more than 1 per 17 mm 2 .

[0022] In a third aspect, the present invention provides a use of the quartz crucible of the aforementioned embodiment in preparing single crystal silicon.

[0023] In a fourth aspect, the present invention provides a single crystal silicon, which is prepared using the quartz crucible of the aforementioned embodiment.

[0024] The beneficial effects of the present invention include:

[0025] By forming a cover layer on the inner wall of the transparent layer, the present invention avoids the introduction of impurities from bubbles rupturing on the inner surface of the quartz crucible during the crystal pulling process, a problem encountered in the prior art. This in turn avoids problems such as reduced single crystal silicon purity, the formation of pinholes, and liquid level fluctuations caused by bubble rupture. The single crystal silicon produced using this quartz crucible exhibits a high whole-rod rate, few pinholes, and a low breakage rate. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the following briefly introduces the drawings required for use in the embodiments. It should be understood that the following drawings only illustrate certain embodiments of the present invention and therefore should not be regarded as limiting the scope. For ordinary technicians in this field, other relevant drawings can be obtained based on these drawings without paying any creative work.

[0027] Figure 1 A schematic diagram of the structure involved in the preparation process of the quartz crucible provided in Example 1;

[0028] Figure 2 A photograph showing the number of bubbles in a portion of the transparent layer of the quartz crucible provided for Comparative Example 1;

[0029] Figure 3 This is a photo of the number of bubbles in a portion of the envelope layer of the quartz crucible provided in Example 1.

[0030] Icon: 1-graphite electrode; 2-mixed gas; 3-exhaust hole; 4-rotating mold; 5-bubble layer; 6-transparent layer; 7-covering layer; 8-quartz sand for covering layer; 9-conduit. DETAILED DESCRIPTION

[0031] To make the purpose, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention are described clearly and completely below. Where specific conditions are not specified in the embodiments, conventional conditions or conditions recommended by the manufacturer are used. Where the manufacturer of the reagents or instruments is not specified, all are conventional products that can be purchased commercially.

[0032] The quartz crucible provided by the present invention and its preparation method and application are described in detail below.

[0033] The present invention provides a method for preparing a quartz crucible, comprising the following steps:

[0034] S1: Lay the bubble layer quartz sand and the transparent layer quartz sand in a rotating mold in order from outside to inside to form.

[0035] In some optional embodiments, the particle size of the bubble layer quartz sand may be 120 μm to 250 μm, such as 120 μm, 150 μm, 180 μm, 200 μm, 220 μm or 250 μm, or other values ​​within the range of 120 μm to 250 μm.

[0036] The particle size of the transparent layer of quartz sand can be 75 μm to 100 μm, such as 75 μm, 80 μm, 85 μm, 90 μm, 95 μm, or 100 μm, or other values ​​within the range of 75 μm to 100 μm. Controlling the particle size of the transparent layer of quartz sand within this range is conducive to eliminating microbubbles.

[0037] The rotary mold can be made of steel, and its inner diameter can be 825 mm to 830 mm by way of example but not limitation. The rotary mold is also provided with an exhaust hole.

[0038] It should be noted that the related operations of laying the bubble layer quartz sand and the transparent layer quartz sand in the present invention can be referred to in the existing technology, and the present invention does not make any special limitation to this step.

[0039] For example, laying the bubble layer of quartz sand can be performed as follows: tilt the rotating mold to 45° to 56° from vertical and rotate it at 65 rpm to 70 rpm. Then, pour the bubble layer of quartz sand into the mold and use a forming rod to spread the bubble layer of quartz sand on the straight wall area and shape it. Subsequently, set the rotating mold vertically (0° from vertical) and rotate it at 65 rpm to 70 rpm. Use the forming rod to scrape off some of the quartz sand on the straight wall area and let it fall to the bottom, until the bubble layer of quartz sand is laid and formed on the entire crucible area.

[0040] The transparent quartz sand layer can be laid as follows: Use a molding machine to lay some of the transparent quartz sand on the inner straight wall area of ​​the bubble layer quartz sand and shape it. Then manually lay the remaining transparent quartz sand on the inner bottom and R corner of the bubble layer quartz sand and shape it.

[0041] S2: Expel the air in the rotating mold and the air in the gaps of the quartz sand.

[0042] In some optional embodiments, removing air may include: introducing monatomic gas or a mixture of monatomic gas and oxygen into the rotating mold to remove as much air as possible from the interior of the mold and the gaps in the quartz sand.

[0043] Monatomic gases, such as helium, argon, neon, or deuterium, can purify quartz sand through the principle of selective permeation. For example, helium can penetrate into the gaps in the sand, and the air displaced by the helium can then be expelled through vacuuming. Furthermore, after the air is expelled, the helium that has penetrated into the gaps in the sand can also be expelled through vacuuming.

[0044] The mixed gas may include 80wt% to 90wt% of monatomic gas and 10wt% to 20wt% of oxygen. Oxygen can play a role in supporting combustion and assisting the electrode to increase heat.

[0045] When only monatomic gas is introduced, the introduction rate of the monatomic gas can be 0.25 MPa / min to 0.5 MPa / min, such as 0.25 MPa / min, 0.3 MPa / min, 0.35 MPa / min, 0.4 MPa / min, 0.45 MPa / min, or 0.5 MPa / min, or other values ​​within the range of 0.25 MPa / min to 0.5 MPa / min. Similarly, when a mixed gas is introduced, the introduction rate of the mixed gas can also be 0.25 MPa / min to 0.5 MPa / min.

[0046] S3: Under vacuum and arc conditions, the cover layer quartz sand is introduced into the rotating mold by a dispersion method to melt the cover layer quartz sand and deposit on the surface of the transparent layer quartz sand, and then cooled to obtain the cover layer located on the inner surface of the transparent layer.

[0047] In some optional embodiments, the particle size of the quartz sand in the cover layer may be 75 μm to 100 μm, such as 75 μm, 80 μm, 85 μm, 90 μm, 95 μm or 100 μm, or other values ​​within the range of 75 μm to 100 μm.

[0048] The purity and particle size of the quartz sand of the cover layer and the quartz sand of the transparent layer are equal, thereby effectively avoiding the formation of air bubbles between the transparent layer and the cover layer.

[0049] In some optional embodiments, the spreading method may include introducing the cover layer quartz sand into the rotating mold via an introduction device. The introduction device may be, for example, a conduit with a valve. The conduit has a feed end and a discharge end. The discharge end is used to introduce the cover layer quartz sand into the rotating mold. The feed end is connected to a cover layer quartz sand storage device, which may be equipped with a stirring mechanism.

[0050] The quartz sand of the cover layer is discharged from the discharge port of the introduction device, melted under the action of the electric arc, and then spread on the inner surface of the rotating mold based on gravity and vacuum suction. It should be noted that in the prior art, based on the limitations of graphite electrode discharge, the temperature brought by the electric arc is relatively low, and it is difficult to ensure that the quartz sand is completely ablated after laying and forming. In addition, due to the centrifugal force at the bottom of the crucible, the bottom will move, and the movement of the bubbles at the bottom will converge at the R corner, causing a serious problem of bubbles at the R corner. The present invention melts and deposits a cover layer with nearly zero bubbles by a dispersion method, thereby avoiding the impurities introduced by the rupture of bubbles on the inner wall of the crucible during the crystal pulling process due to the presence of bubbles on the inner surface of the quartz crucible, thereby avoiding the problems of reduced purity of single crystal silicon, the appearance of pinholes, and liquid level jitter caused by bubble rupture.

[0051] In some optional embodiments, the vertical distance between the discharge port of the introduction device and the upper port of the rotating mold is 45mm~55mm, such as 45mm, 48mm, 50mm, 52mm or 55mm, etc., or other values ​​within the range of 45mm~55mm.

[0052] If the vertical distance between the discharge port of the introduction device and the upper port of the rotating mold is too short, it is not conducive to the uniform dispersion and deposition of the molten quartz sand at the port; if the vertical distance between the discharge port of the introduction device and the upper port of the rotating mold is too far, it is not conducive to the uniform dispersion and deposition of the molten quartz sand at the bottom.

[0053] In some optional embodiments, the horizontal distance between the discharge port of the introduction device and the transparent layer can be 100mm~150mm, such as 100mm, 110mm, 120mm, 130mm, 140mm or 150mm, or other values ​​within the range of 100mm~150mm.

[0054] If the horizontal distance between the discharge port of the introduction device and the transparent layer is too short, it is not conducive to the uniform dispersion and deposition of the fused quartz sand at the port; if the horizontal distance between the discharge port of the introduction device and the transparent layer is too far, it is not conducive to the uniform dispersion and deposition of the fused quartz sand at the bottom.

[0055] In some optional embodiments, the conditions for preparing the cover layer may include: a vacuum condition of -0.20 MPa to -0.3 MPa (such as -0.2 MPa, -0.25 MPa, or -0.3 MPa), an arc starting power of 10 kW to 15 kW (such as 10 kW, 11 kW, 12 kW, 13 kW, 14 kW, or 15 kW), an arc action time of 2 min to 3 min (such as 2 min, 2.5 min, or 3 min), an electrode spacing of 20 mm to 25 mm (such as 20 mm, 21 mm, 22 mm, 23 mm, 24 mm, or 25 mm), and a vertical distance between the arc starting end of the electrode and the upper port of the rotating mold of 150 mm to 200 mm (such as 150 mm, 160 mm, 170 mm, 180 mm, 190 mm, or 200 mm).

[0056] If the arc-starting power is less than 10Kw during the preparation of the cover layer, the quartz sand in the cover layer will not be completely melted, forming a "cold zone", resulting in an uneven cover layer or the generation of unmelted particles, which will not effectively serve as a cover for the transparent layer; if the arc-starting power is greater than 15Kw during the preparation of the cover layer, the cover layer will be too thick, resulting in a bubble interlayer between the cover layer and the transparent layer. It should be noted that there is a large amount of air in the gaps on the inner surface of the quartz crucible after molding, which makes it very easy to generate microbubbles in the transparent layer. The bubbles in the area far away from the inner surface of the crucible can be improved by vacuuming, but the bubbles in the area close to the inner surface of the crucible are difficult to be effectively removed because they are in contact with air. Therefore, if the cover layer is too thick, bubbles are likely to remain in the area of ​​the cover layer close to the transparent layer.

[0057] If the vacuum is drawn too slowly during the preparation of the cover layer, the bubbles will not be completely removed; if the vacuum is drawn too quickly, the cover layer will be broken and the cover layer will not be effectively sealed.

[0058] If the arc action time is shorter than 2 minutes during the preparation of the cover layer, the fused quartz will not be evenly deposited on the inner surface of the crucible, and some places will not be fully deposited; if the arc action time is longer than 3 minutes during the preparation of the cover layer, the cover layer will be poorly uniform and the cover layer will be thickened in some areas.

[0059] In the present invention, the number of electrodes is three, and they may be graphite electrodes. If the electrode spacing during the preparation of the cover layer is less than 20 mm, it is not conducive to arcing. The arc cannot be opened in time, and arcing will occur, resulting in arc instability. If the electrode spacing during the preparation of the cover layer is longer than 25 mm, it is not conducive to arcing. If the electrode spacing is too large, arcing will occur, resulting in arc instability.

[0060] If the vertical distance between the arc-starting end of the electrode and the upper port of the rotating mold during the preparation of the cover layer is less than 150 mm, it is not conducive to the uniform dispersion and deposition of the molten quartz sand at the port; if the vertical distance between the arc-starting end of the electrode and the upper port of the rotating mold during the preparation of the cover layer is greater than 200 mm, it is not conducive to the uniform dispersion and deposition of the molten quartz sand at the bottom.

[0061] In some optional embodiments, the conditions of the cooling process include: vacuum conditions of -0.20MPa~-0.4MPa (such as -0.2MPa, -0.25MPa, -0.3MPa, -0.35MPa or -0.4MPa, etc.), arc power of 5Kw~10Kw (such as 5Kw, 6Kw, 7Kw, 8Kw, 9Kw or 10Kw, etc.), arc action time of 2min~3min (such as 2min, 2.5min or 3min, etc.), electrode spacing of 10mm~15mm (such as 10mm, 11mm, 12mm, 13mm, 14mm or 15mm, etc.), and the vertical distance between the arc end of the electrode and the upper port of the rotating mold is 150mm~200mm (such as 150mm, 160mm, 170mm, 180mm, 190mm or 200mm, etc.).

[0062] By cooling the film, the integrity of the cover layer is ensured. The vacuum should not be too high during this process to prevent the surface from becoming unstable immediately after the casting, which could lead to the rupture of the deposited cover layer. Furthermore, cooling the film can prevent bubbles from forming under the cover layer due to excessively high temperatures when the vacuum pumping speed is low during vacuum arc casting.

[0063] S4: melting the transparent layer quartz sand to form a transparent layer.

[0064] In some optional embodiments, the conditions for preparing the transparent layer may include: a vacuum condition of -0.95 MPa to -0.99 MPa (such as -0.95 MPa, -0.96 MPa, -0.97 MPa, -0.98 MPa or -0.99 MPa, etc.), an arc power of 25 Kw to 35 Kw (such as 25 Kw, 28 Kw, 30 Kw, 32 Kw or 35 Kw, etc.), an arc action time of 4 min to 6 min (such as 4 min, 5 min or 6 min, etc.), an electrode spacing of 20 mm to 30 mm (such as 20 min, 22 min, 25 min, 28 min or 30 min, etc.), and a vertical distance between the arc end of the electrode and the upper port of the rotating mold of 100 mm to 150 mm (such as 100 mm, 110 mm, 120 mm, 130 mm, 140 mm or 150 mm, etc.).

[0065] During this process, the electrodes are positioned lower than during the preparation of the cover layer, facilitating the uniform growth of the transparent layer along the entire inner wall. Furthermore, this process is performed after the cover layer is prepared, and the vacuum pumping speed is greater than the melting speed of the quartz sand, thus preventing the formation of bubbles in the transparent layer.

[0066] S5: melting the bubble layer quartz sand to form a bubble layer.

[0067] In some optional embodiments, the conditions for preparing the bubble layer may include: the arc power is 16Kw~20Kw (such as 16Kw, 17Kw, 18Kw, 19Kw or 20Kw, etc.), the arc action time is 6min~10min (such as 6min, 7min, 8min, 9min or 10min, etc.), the electrode spacing is 35mm~45mm (such as 35min, 38min, 40min, 42min or 45min, etc.), and the vertical distance between the arc end of the electrode and the upper port of the rotating mold is 70mm~100mm (such as 70mm, 75mm, 80mm, 85mm, 90mm, 95mm or 100mm, etc.).

[0068] In this process, vacuum is turned off, the electrode spacing becomes larger, and the electrode position is further lowered, which shortens the melting time to avoid impurity contamination caused by excessive melting time.

[0069] It should be noted that appropriate electrode position and electrode spacing not only help to improve the consistency of the quartz crucible and reduce the bubble content, but also help to shorten the production cycle and improve production efficiency.

[0070] S6: Turn off the arc and raise the electrode position until the quartz crucible cools down, then take it out of the furnace and demold it.

[0071] Correspondingly, the present invention provides a quartz crucible, which is prepared by the above preparation method.

[0072] In some optional embodiments, the thickness of the cover layer is 0.3 mm to 0.8 mm, such as 0.3 mm, 0.4 mm, 0.5 mm, 0.6 mm, 0.7 mm or 0.8 mm, etc., and may also be other values ​​within the range of 0.3 mm to 0.8 mm.

[0073] If the cover layer is too thin, it is difficult to ensure its integrity and it is easy to break, which will cause bubbles to be sucked into the transparent layer; if the cover layer is too thick, a bubble layer will easily form between it and the transparent layer.

[0074] In some optional embodiments, the number of bubbles in the cover layer does not exceed 1 / 17mm 2 , which can effectively avoid the adverse effects of bubbles on single crystal silicon during the crystal pulling process.

[0075] In addition, the application further provides the use of the quartz crucible in the preparation of single crystal silicon.

[0076] Correspondingly, the application further provides single crystal silicon prepared by using the quartz crucible.

[0077] The features and performances of the application are further described in detail below in combination with examples.

[0078] Example 1

[0079] This example provides a quartz crucible, the preparation process of which involves a structural schematic diagram as shown in Figure 1 The preparation method is as follows:

[0080] S1: bubble layer quartz sand and transparent layer quartz sand are laid and formed in the rotating mold 4 in the order from outside to inside.

[0081] S11: bubble layer quartz sand is laid.

[0082] The rotating mold 4 is inclined to 50° with the vertical direction, rotated at a speed of 70 rpm, then the bubble layer quartz sand is poured into the mold, and the bubble layer quartz sand is laid and formed to the straight wall area by using a forming rod. Subsequently, the rotating mold 4 is vertically arranged (0° with the vertical direction), rotated at a speed of 70 rpm, and part of the quartz sand in the straight wall area is scraped off by using a forming rod to fall into the bottom until the bubble layer quartz sand in the whole crucible area is laid and formed. The particle size of the bubble layer quartz sand is 120 μm~150 μm, and the purity is 99.9999%. The rotating mold 4 is a steel mold, the inner diameter of which is 830 mm, and the rotating mold 4 is provided with an exhaust hole 3.

[0083] S12: transparent layer quartz sand is laid.

[0084] The mold is kept rotating at a speed of 70 rpm, part of the transparent quartz sand is laid and formed to the inner straight wall area of the bubble layer quartz sand by using a forming machine. Subsequently, the remaining transparent quartz sand is laid and formed to the inner bottom and R angle part of the bubble layer quartz sand manually. The particle size of the transparent layer quartz sand is 75 μm~80 μm, and the purity is 99.9999%.

[0085] S2: air in the rotating mold 4 and air in the gap between the quartz sands are excluded.

[0086] The mixed gas 2 composed of 85wt% helium and 15wt% oxygen is introduced into the rotating mold 4, and the introduction speed of the mixed gas 2 is 0.4 MPa / min.

[0087] S3: Under vacuum and arc conditions, the cover layer quartz sand 8 is introduced into the rotating mold 4 by a dispersion method so that the cover layer quartz sand 8 is melted and deposited on the surface of the transparent layer quartz sand, and then cooled to obtain the cover layer 7 located on the inner surface of the transparent layer 6.

[0088] S31: preparing the cover layer 7 by combining the dispersion method with vacuum arc suction casting.

[0089] Quartz sand 8 for the cover layer is introduced into the rotating mold 4 through a conduit 9 equipped with a valve. The vertical distance between the discharge port of conduit 9 and the upper end of the rotating mold 4 is 50 mm, and the horizontal distance between the discharge port of conduit 9 and the transparent layer 6 is 120 mm. The vacuum condition is -0.25 MPa, the arc power is 15 kW, the arc action time is 2.5 minutes, and the electrodes are three graphite electrodes 1 with a 25 mm spacing. The vertical distance between the arc-starting end of the electrode and the upper end of the rotating mold 4 is 200 mm. The particle size of the quartz sand 8 for the cover layer is 75 μm to 80 μm, and the purity is 99.9999% (the quartz sand 8 for the cover layer is the same as the quartz sand for the transparent layer).

[0090] S32: Cooling down.

[0091] The vacuum condition is -0.3 MPa, the arc power is 10 Kw, the arc action time is 2.5 min, the electrode spacing is 15 mm, and the vertical distance between the arc end of the electrode and the upper port of the rotating mold 4 is 200 mm.

[0092] S4: melting the transparent layer quartz sand to form a transparent layer 6.

[0093] The vacuum condition is -0.99 MPa, the arc power is 30 Kw, the arc action time is 5 min, the electrode spacing is 25 mm, and the vertical distance between the arc end of the electrode and the upper port of the rotating mold 4 is 150 mm.

[0094] S5: Melting the bubble layer quartz sand to form a bubble layer 5.

[0095] The arc power is 18 Kw, the arc action time is 8 minutes, the electrode spacing is 40 mm, and the vertical distance between the arc end of the electrode and the upper port of the rotating mold 4 is 85 mm.

[0096] S6: Turn off the arc and raise the electrode position until the quartz crucible cools down, then take it out of the furnace and demold it.

[0097] In the quartz crucible, the bubble layer 5 has a thickness of 13.5 mm, the transparent layer 6 has a thickness of 3 mm, and the cover layer 7 has a thickness of 0.4 mm.

[0098] Example 2

[0099] This embodiment provides a quartz crucible, and the preparation method thereof is as follows:

[0100] S1: Lay the bubble layer quartz sand and the transparent layer quartz sand in a rotating mold in order from outside to inside to form.

[0101] S11: Laying bubble layer quartz sand.

[0102] The rotating mold is tilted to a 45° angle from vertical and rotated at 65 rpm. Then, a bubble layer of quartz sand is poured into the mold and spread over the straight wall area using a forming rod to form the bubble layer. Subsequently, the rotating mold is set vertically (at a 0° angle from vertical) and rotated at 65 rpm. A forming rod is used to scrape off some of the quartz sand from the straight wall area, allowing it to fall to the bottom, until the bubble layer of quartz sand is laid and formed over the entire crucible area. The particle size of the bubble layer quartz sand is 150 μm to 200 μm, with a purity of 99.9999%. The inner diameter of the rotating mold is 825 mm.

[0103] S12: Laying a transparent layer of quartz sand.

[0104] While the mold rotates at 65 rpm, a portion of the transparent quartz sand is applied to the inner straight wall area of ​​the bubble layer using a molding machine. The remaining transparent quartz sand is then manually applied to the inner bottom and rounded corners of the bubble layer and formed. The particle size of the transparent quartz sand is 80 to 90 μm, with a purity of 99.9999%.

[0105] S2: Expel the air in the rotating mold and the air in the gaps of the quartz sand.

[0106] A mixed gas consisting of 80 wt% helium and 20 wt% oxygen was introduced into the rotating mold at a rate of 0.25 MPa / min.

[0107] S3: Under vacuum and arc conditions, the cover layer quartz sand is introduced into the rotating mold by a dispersion method to melt the cover layer quartz sand and deposit on the surface of the transparent layer quartz sand, and then cooled to obtain the cover layer located on the inner surface of the transparent layer.

[0108] S31: The cover layer is prepared by the dispersion method combined with vacuum arc suction casting.

[0109] The quartz sand for the cover layer is introduced into the rotating mold through a conduit. The vertical distance between the conduit outlet and the upper port of the rotating mold is 45 mm, and the horizontal distance between the conduit outlet and the transparent layer is 100 mm. The vacuum conditions are -0.2 MPa, the arc power is 10 kW, the arc action time is 3 minutes, the electrode spacing is 20 mm, and the vertical distance between the arc-starting end of the electrode and the upper port of the rotating mold is 150 mm. The particle size of the quartz sand for the cover layer is 80 μm to 90 μm, and the purity is 99.9999% (the quartz sand for the cover layer is the same as the quartz sand for the transparent layer).

[0110] S32: Cooling down.

[0111] The vacuum condition was -0.2 MPa, the arc power was 5 kW, the arc action time was 3 min, the electrode spacing was 10 mm, and the vertical distance between the arc end of the electrode and the upper port of the rotating mold was 150 mm.

[0112] S4: melting the transparent layer quartz sand to form a transparent layer.

[0113] The vacuum condition was -0.99 MPa, the arc power was 25 Kw, the arc action time was 6 min, the electrode spacing was 20 mm, and the vertical distance between the arc end of the electrode and the upper port of the rotating mold was 100 mm.

[0114] S5: melting the bubble layer quartz sand to form a bubble layer.

[0115] The arc power is 16 Kw, the arc action time is 10 min, the electrode spacing is 35 mm, and the vertical distance between the arc end of the electrode and the upper port of the rotating mold is 70 mm.

[0116] S6: Turn off the arc and raise the electrode position until the quartz crucible cools down, then take it out of the furnace and demold it.

[0117] The bubble layer in the quartz crucible has a thickness of 13.4 mm, the transparent layer has a thickness of 3.1 mm, and the cover layer has a thickness of 0.6 mm.

[0118] Example 3

[0119] This embodiment provides a quartz crucible, and the preparation method thereof is as follows:

[0120] S1: Lay the bubble layer quartz sand and the transparent layer quartz sand in a rotating mold in order from outside to inside to form.

[0121] S11: Laying bubble layer quartz sand.

[0122] The rotating mold is inclined to 56° with the vertical direction, and rotates at a speed of 68 rpm, then the bubble layer quartz sand is poured into the mold, and the bubble layer quartz sand is laid to the straight wall area by a forming rod and formed. Subsequently, the rotating mold is vertically arranged (0° with the vertical direction), and rotates at a speed of 68 rpm, and the part of the quartz sand in the straight wall area is scraped by a forming rod to fall into the bottom until the bubble layer quartz sand in the whole crucible area is laid and formed. The particle size of the bubble layer quartz sand is 200 μm-250 μm, and the purity is 99.9999%. The inner diameter of the rotating mold is 830 mm.

[0123] S12: Laying transparent layer quartz sand.

[0124] The mold is kept rotating at a speed of 68 rpm, and part of the transparent quartz sand is laid to the inner straight wall area of the bubble layer quartz sand by a forming machine and formed. Subsequently, the remaining transparent quartz sand is laid to the inner bottom and R angle part of the bubble layer quartz sand by hand and formed. The particle size of the transparent layer quartz sand is 90 μm-100 μm, and the purity is 99.9999%.

[0125] S2: Excluding air in the rotating mold and air in the gap between the quartz sands.

[0126] The mixed gas composed of 90wt% helium and 10wt% oxygen is introduced into the rotating mold, and the introduction speed of the mixed gas is 0.5 MPa / min.

[0127] S3: Under the conditions of vacuumizing and starting arc, the envelope layer quartz sand is introduced into the rotating mold by the scattering method to make the envelope layer quartz sand melt and deposit on the surface of the transparent layer quartz sand, and then cooled to obtain the envelope layer on the inner surface of the transparent layer.

[0128] S31: Preparing the envelope layer by the scattering method combined with vacuum arc suction casting.

[0129] The envelope layer quartz sand is introduced into the rotating mold through a pipe. The vertical distance between the discharge port of the pipe and the upper port of the rotating mold is 55 mm, and the horizontal distance between the discharge port of the pipe and the transparent layer is 150 mm. The vacuum condition is -0.3 MPa, the arc power is 12 Kw, the arc action time is 2 min, the electrode spacing is 22 mm, and the vertical distance between the arc end of the electrode and the upper port of the rotating mold is 180 mm. The particle size of the envelope layer quartz sand is 90 μm-100 μm, and the purity is 99.9999% (the envelope layer quartz sand is the same as the transparent layer quartz sand).

[0130] S32: Cooling.

[0131] The vacuum condition is -0.4 MPa, the arc power is 8 Kw, the arc action time is 2 min, the electrode spacing is 12 mm, and the vertical distance between the arc end of the electrode and the upper port of the rotating mold is 180 mm.

[0132] S4: The transparent layer quartz sand is fused to form a transparent layer.

[0133] The vacuum condition is -0.95 MPa, the arc power is 35 Kw, the arc action time is 4 min, the electrode spacing is 30 mm, and the vertical distance between the arc end of the electrode and the upper port of the rotating mold is 120 mm.

[0134] S5: The bubble layer quartz sand is fused to form a bubble layer.

[0135] The arc power is 20 Kw, the arc action time is 6 min, the electrode spacing is 45 mm, and the vertical distance between the arc end of the electrode and the upper port of the rotating mold is 100 mm.

[0136] S6: The arc is turned off, the electrode position is raised until the quartz crucible cools, and then the furnace is discharged and demolded.

[0137] The bubble layer thickness in the quartz crucible is 13.4 mm, the transparent layer thickness is 2.9 mm, and the envelope layer thickness is 0.6 mm.

[0138] Example 4

[0139] The difference between this example and Example 1 is that the mixed gas in S2 is replaced by helium gas only.

[0140] Comparative Example 1

[0141] The difference between this comparative example and Example 1 is that the envelope layer is not prepared on the inner wall of the transparent layer.

[0142] Comparative Example 2

[0143] The difference between this comparative example and Example 1 is that the S32 step is not performed, that is, the envelope layer is not cooled.

[0144] Comparative Example 3

[0145] The difference between this comparative example and Example 1 is that in S31, the vertical distance between the discharge port of the conduit and the upper port of the rotating mold is 20 mm.

[0146] Comparative Example 4

[0147] The difference between this comparative example and Example 1 is that in S31, the vertical distance between the discharge port of the conduit and the upper port of the rotating mold is 80 mm.

[0148] Comparative Example 5

[0149] The difference between this comparative example and Example 1 is that in S31, the horizontal distance between the discharge port of the conduit and the transparent layer is 80 mm.

[0150] Comparative Example 6

[0151] The difference between this comparative example and Example 1 is that in S31, the horizontal distance between the discharge port of the conduit and the transparent layer is 180 mm.

[0152] Comparative Example 7

[0153] The difference between this comparative example and Example 1 is that in S31, the vacuum condition is -0.1 MPa.

[0154] Comparative Example 8

[0155] The difference between this comparative example and Example 1 is that in S31, the vacuum condition is -0.4 MPa.

[0156] Comparative Example 9

[0157] The difference between this comparative example and Example 1 is that in S31, the arc starting power is 8Kw.

[0158] Comparative Example 10

[0159] The difference between this comparative example and Example 1 is that in S31, the arc starting power is 18Kw.

[0160] Comparative Example 11

[0161] The difference between this comparative example and Example 1 is that in S31, the arcing time is 5 minutes.

[0162] Comparative Example 12

[0163] The difference between this comparative example and Example 1 is that in S31, the electrode spacing is 15 mm.

[0164] Comparative Example 13

[0165] The difference between this comparative example and Example 1 is that in S31, the vertical distance between the arc starting end of the electrode and the upper port of the rotating mold is 120 mm.

[0166] Comparative Example 14

[0167] The difference between this comparative example and Example 1 is that in S31, the vertical distance between the arc starting end of the electrode and the upper port of the rotating mold is 240 mm.

[0168] Comparative Example 15

[0169] The difference between this comparative example and Example 1 is that in S32, the vacuum condition is -0.6 MPa.

[0170] Test example

[0171] (1) The thickness of the cover layer in the quartz crucibles prepared in Examples 1 to 4 and Comparative Examples 2 to 15 was counted, and the number of bubbles in the inner surface layer of the quartz crucibles in each Example and each Comparative Example was counted. The results are shown in Tables 1 and Figure 2 and Figure 3 The number of bubbles was obtained by optical microscope observation.

[0172] Figure 2 The number of bubbles in the inner surface area of ​​the quartz crucible of Comparative Example 1 is 46 / 17mm 2 ; Figure 3 The number of bubbles in the inner surface layer (skin layer) of the quartz crucible of Example 1 is 1 / 17 mm. 2 .

[0173] Depend on Figure 2 and Figure 3 By comparison, it can be seen that the method provided by the present invention can successfully produce a bubble number of no more than 1 / 17mm 2 The sealing layer can effectively serve as a seal for the transparent layer, preventing bubbles in the transparent layer from affecting the production of single crystal silicon.

[0174] (2) The quartz crucibles prepared in Examples 1 to 4 and Comparative Examples 1 to 15 were used to prepare single crystal silicon using the same crystal pulling method. The whole rod rate, pinhole rate, and wire break rate of the single crystal silicon obtained by crystal pulling were compared, and the results are shown in Table 1. The whole rod rate is calculated as the percentage of the obtained whole rod single crystal silicon in the total amount of the measured single crystal silicon, the pinhole rate is calculated as the percentage of the single crystal silicon with visible pinholes in the total amount of the measured single crystal silicon, and the wire break rate is calculated as the percentage of the single crystal silicon with broken wires in the total amount of the measured single crystal silicon.

[0175] Table 1 Test results

[0176]

[0177] The above “ / ” means that the cover layer cannot be uniformly deposited.

[0178] It can be seen from Table 1 that the sealing layer of the quartz crucible provided by the present invention substantially contains no bubbles, which is beneficial to improving the quality of the single crystal silicon produced thereby.

[0179] It can be seen from Example 1 and Comparative Examples 1 to 15 that the quartz crucible with a cover layer (Example 1 and Comparative Examples 2 to 15) is more conducive to improving the quality of single crystal silicon than the quartz crucible without a cover layer (Comparative Example 1).

[0180] It can be seen from Example 1 and Comparative Examples 2 to 15 that when the conditions for preparing the cover layer are inappropriate, the quality of the single crystal silicon will be affected even if the cover layer is formed.

[0181] In summary, the present invention adopts a dispersion method combined with a vacuum arc suction casting method to prepare a cover layer that is basically free of bubbles on the inner surface of the transparent layer, which can avoid impurities introduced by the bursting of bubbles in the crucible itself during the crystal pulling process, and thus avoid and improve problems such as the reduction of the single crystal silicon whole rod rate, the occurrence of pinholes and wire breaks.

[0182] The foregoing description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Those skilled in the art will readily appreciate that various modifications and variations of the present invention are possible. Any modifications, equivalent substitutions, or improvements made within the spirit and principles of the present invention are intended to be within the scope of protection of the present invention.

Claims

1. A method for preparing a quartz crucible, characterized in that: The method comprises the following steps: laying a bubble layer of quartz sand and a transparent layer of quartz sand in a rotating mold in order from outside to inside to form a shape; Expelling air from the rotating mold and air in the gaps between the quartz sands; introducing the cover layer quartz sand into the rotating mold by a dispersion method under vacuum and arcing conditions so that the cover layer quartz sand is melted and deposited on the surface of the transparent layer quartz sand, and then cooling to obtain a cover layer located on the inner surface of the transparent layer; Then, the transparent layer quartz sand is melted to form a transparent layer; Then, the bubble layer quartz sand is melted to form a bubble layer; The spreading method includes: introducing the cover layer quartz sand into the rotating mold through an introduction device, wherein the vertical distance between the discharge port of the introduction device and the upper end of the rotating mold is 45 mm to 55 mm; the horizontal distance between the discharge port of the introduction device and the transparent layer is 100 mm to 150 mm; and the rotation speed of the rotating mold is 65 rpm to 70 rpm; The conditions for preparing the cover layer include: vacuum condition of -0.20MPa to -0.3MPa, arc starting power of 10Kw to 15Kw, arc action time of 2min to 3min, electrode spacing of 20mm to 25mm, and a vertical distance between the arc starting end of the electrode and the upper end of the rotating mold of 150mm to 200mm; The conditions of the cooling process include: vacuum condition of -0.20MPa to -0.4MPa, arc power of 5Kw to 10Kw, arc action time of 2min to 3min, electrode spacing of 10mm to 15mm, and a vertical distance between the arc end of the electrode and the upper port of the rotating mold of 150mm to 200mm; The thickness of the cover layer is 0.3mm~0.8mm; the number of bubbles in the cover layer does not exceed 1 / 17mm 2 ; The purity and particle size of the quartz sand of the cover layer and the quartz sand of the transparent layer are equal.

2. The preparation method according to claim 1, characterized in that Expelling air includes: introducing monatomic gas or a mixture of monatomic gas and oxygen into the rotating mold; The mixed gas includes 80 wt% to 90 wt% of monatomic gas and 10 wt% to 20 wt% of oxygen.

3. The preparation method according to claim 1, characterized in that The conditions for preparing the transparent layer include: vacuum conditions of -0.95MPa~-0.99MPa, arc power of 25Kw~35Kw, arc action time of 4min~6min, electrode spacing of 20mm~30mm, and a vertical distance between the arc end of the electrode and the upper port of the rotating mold of 100mm~150mm.

4. The preparation method according to claim 1, characterized in that The conditions for preparing the bubble layer include: arc power of 16Kw~20Kw, arc action time of 6min~10min, electrode spacing of 35mm~45mm, and a vertical distance between the arc end of the electrode and the upper port of the rotating mold of 70mm~100mm.

5. The preparation method according to claim 1, characterized in that The particle size of the quartz sand in the bubble layer is 120 μm to 250 μm, the particle size of the quartz sand in the transparent layer is 75 μm to 100 μm, and the particle size of the quartz sand in the cover layer is 75 μm to 100 μm.

6. A quartz crucible, characterized in that: The product is prepared by the preparation method according to any one of claims 1 to 5.

7. Use of the quartz crucible according to claim 6 in preparing single crystal silicon.

8. A single crystal silicon, characterized in that: The single crystal silicon is prepared using the quartz crucible according to claim 6.

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