Quartz crucible as well as preparation method and application thereof

Abstract

The invention discloses a quartz crucible as well as a preparation method and application thereof, and belongs to the technical field of quartz crucibles. The preparation method of the quartz crucible comprises the following steps: laying and molding the bubble layer quartz sand and the transparent layer quartz sand in a rotary mold from outside to inside; air in the rotary mold and air in gaps of the quartz sand are exhausted; under the conditions of vacuumizing and arcing, the cover layer quartz sand is guided into the rotary mold through a dispersion method so that the cover layer quartz sand can be fused and deposited on the surface of the transparent layer quartz sand, then cooling is conducted, and a cover layer located on the inner surface of the transparent layer is obtained; melting the transparent layer quartz sand to form a transparent layer; and melting the bubble layer quartz sand to form a bubble layer. The sealing layer is prepared on the inner wall of the transparent layer, so that impurities introduced by bubble breakage of the crucible in the crystal pulling process can be avoided, and the problems of reduction of the whole rod rate of monocrystalline silicon, pinholes, 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, a preparation method thereof, and an application thereof. Background Art

[0002] Monocrystalline silicon, which is the starting material for the manufacture of most semiconductor electronic components, is usually prepared by the so-called Czochralski method ("CZ"). Using the CZ method, the growth of the crystal is most commonly carried out in a crystal pulling furnace, in which polysilicon is loaded into a crucible and melted by a heater around the outer surface of the crucible sidewall. A seed crystal is brought into contact with the molten silicon, and the growing single crystal ingot is extracted by a crystal pulling machine.

[0003] The crucibles used in conventional crystal pulling are usually made of quartz because of its purity, temperature stability, and chemical resistance. The mainstream method for manufacturing quartz crucibles is to introduce quartz raw materials into a rotating hollow mold. After introducing the raw materials, 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 evacuate any interstitial gases, with the aim of collapsing the voids. The vacuum is maintained during melting and rotation, and thereafter, the finished crucible can be discharged by replacing the vacuum with compressed air outside the mold. In this process, residual gases may cause the formation of unwanted bubbles in the fused quartz.

[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, resulting in the reaction between the silicon melt and the quartz crucible and the dissolution of the inner surface of the crucible sidewall. The silicon melt continues to dissolve into the wall of the crucible, especially into the wall containing bubbles. At a certain moment, the wall containing bubbles is damaged or dented, and gas is released from inside the bubbles and quartz particles are released from the sidewall of the bubbles into the melt. The released quartz particles may damage the single crystal structure, thereby limiting crystal growth and the yield of single crystals. In addition, the bubble cavities or bubble voids present 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 voids in the crystal, which do not meet the specifications.

[0005] Therefore, the reduction or elimination of bubbles in the crucible is beneficial to ensuring the minimization of voids in the crystal to obtain acceptable crystal properties within specifications. Methods for reducing bubbles in the prior art include: preparing a quartz crucible by the vacuum arc casting method using a quartz crucible. However, since the inner surface layer of the quartz crucible is in contact with air, bubbles cannot be completely evacuated by vacuum, so there are still some micro-bubbles in the surface layer. These micro-bubbles will expand and burst when heated during the crystal pulling process. When bursting, tiny quartz particles fall into the silicon melt, reducing the purity of the single-crystal silicon. In addition, the bursting of micro-bubbles on the inner surface of the quartz crucible greatly causes the liquid surface to fluctuate more during crystal pulling, resulting in difficult crystal pulling and easy wire breakage. Moreover, the bursting places are 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 specifically proposed. Summary of the Invention

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

[0008] The present invention can be implemented as follows: In a first aspect, the present invention provides a preparation method of a quartz crucible, including the following steps: laying bubble layer quartz sand and transparent layer quartz sand in a rotating mold in the order from outside to inside to form a mold; evacuating the air in the rotating mold and the air in the gaps between the quartz sands; under the conditions of vacuum pumping and arc starting, introducing the sealing layer quartz sand into the rotating mold by a spreading method so that the sealing layer quartz sand melts and deposits on the surface of the transparent layer quartz sand, and then cooling to obtain a sealing layer on the inner surface of the transparent layer; then melting the transparent layer quartz sand to form a transparent layer; and then melting the bubble layer quartz sand to form a bubble layer.

[0009] In an optional embodiment, evacuating the air includes: introducing a monoatomic gas or a mixed gas composed of a monoatomic gas and oxygen into the rotating mold, and the mixed gas includes 80wt% - 90wt% of the monoatomic gas and 10wt% - 20wt% of oxygen.

[0010] In an optional embodiment, the spreading method includes: introducing the sealing layer quartz sand into the rotating mold through an introducing device, and the vertical distance between the discharge port of the introducing device and the upper port of the rotating mold is 45mm - 55mm; the horizontal distance between the discharge port of the introducing device and the transparent layer is 100mm - 150mm.

[0011] In an alternative embodiment, the conditions for preparing the sealing layer include: a vacuum condition of -0.20 MPa to -0.3 MPa, an arc starting power of 10 Kw to 15 Kw, an arc action time of 2 min to 3 min, an electrode spacing of 20 mm to 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.

[0012] In an alternative embodiment, the conditions for the cooling process include: a vacuum condition of -0.20 MPa to -0.4 MPa, an arc power of 5 Kw to 10 Kw, an arc action time of 2 min to 3 min, an electrode spacing of 10 mm to 15 mm, and a vertical distance between the arc end of the electrode and the upper port of the rotating mold of 150 mm to 200 mm.

[0013] In an alternative embodiment, the conditions for preparing the transparent layer include: a vacuum condition of -0.95 MPa to -0.99 MPa, an arc power of 25 Kw to 35 Kw, an arc action time of 4 min to 6 min, an electrode spacing of 20 mm to 30 mm, 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.

[0014] In an alternative embodiment, the conditions for preparing the bubble layer include: an arc power of 16 Kw to 20 Kw, an arc action time of 6 min to 10 min, an electrode spacing of 35 mm to 45 mm, and a vertical distance between the arc end of the electrode and the upper port of the rotating mold of 70 mm to 100 mm.

[0015] In an alternative embodiment, 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 sealing layer is 75 μm to 100 μm.

[0016] In an alternative embodiment, it further includes: after forming the bubble layer, turning off the arc, raising the electrode position until the quartz crucible cools, and then taking it out of the furnace and demolding.

[0017] In a second aspect, the present invention provides a quartz crucible prepared by the preparation method according to any one of the foregoing embodiments.

[0018] In an alternative embodiment, the quartz crucible has at least one of the following characteristics: Characteristic 1: The thickness of the sealing layer is 0.3 mm to 0.8 mm; Characteristic 2: The number of bubbles in the sealing layer does not exceed 1 per 17 mm 2 。

[0019] In a third aspect, the present invention provides an application of the quartz crucible according to the foregoing embodiment in the preparation of monocrystalline silicon.

[0020] Fourthly, the present invention provides a single crystal silicon, which is prepared by using the quartz crucible of the foregoing embodiment.

[0021] The beneficial effects of the present invention include: By preparing a sealing layer on the inner wall of the transparent layer, the present invention avoids the impurities introduced by the rupture of bubbles during the crystal pulling process due to the presence of bubbles on the inner surface of the quartz crucible in the prior art, and further avoids problems such as the reduction of the purity of single crystal silicon, the appearance of pinholes, and the liquid surface jitter caused by the rupture of bubbles. The single crystal silicon prepared by using the above quartz crucible has a high whole rod rate, few pinholes, and a low wire break rate. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings required for use 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 therefore should not be regarded as limiting the scope. For those of ordinary skill in the art, other related drawings can be obtained based on these drawings without creative efforts.

[0023] Figure 1 It is a schematic structural diagram involved in the preparation process of the quartz crucible provided in Embodiment 1; Figure 2 It is a photo of the number of bubbles in a partial area of the transparent layer of the quartz crucible provided in Comparative Example 1; Figure 3 It is a photo of the number of bubbles in a partial area of the sealing layer of the quartz crucible provided in Embodiment 1.

[0024] Reference numerals: 1 - graphite electrode; 2 - mixed gas; 3 - exhaust hole; 4 - rotating mold; 5 - bubble layer; 6 - transparent layer; 7 - sealing layer; 8 - sealing layer quartz sand; 9 - conduit. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0025] In order 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. Those not specified in the embodiments are carried out according to conventional conditions or conditions recommended by the manufacturer. The reagents or instruments not specified by the manufacturer are all conventional products that can be obtained through commercial purchase.

[0026] The quartz crucible provided by the present invention, its preparation method, and application will be specifically described below.

[0027] The present invention provides a method for preparing a quartz crucible, including the following steps: S1: Lay and form bubble layer quartz sand and transparent layer quartz sand in a rotating mold in the order from outside to inside.

[0028] 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, etc., or may be other values within the range of 120 μm to 250 μm.

[0029] The particle size of the transparent layer quartz sand can be 75 μm to 100 μm, such as 75 μm, 80 μm, 85 μm, 90 μm, 95 μm or 100 μm, etc., or other values within the range of 75 μm to 100 μm. Controlling the particle size of the transparent layer quartz sand within this range is conducive to the elimination of microbubbles.

[0030] The rotating mold may be made of steel, and its inner diameter may be 825 mm to 830 mm by way of example but not limitation. The rotating mold may also be provided with an exhaust hole.

[0031] 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 refer to the existing technology, and the present invention does not make any special limitation to this step.

[0032] For example, the laying of the bubble layer quartz sand can be carried out in the following manner: the rotating mold is tilted to 45° to 56° from the vertical direction, rotated at a speed of 65rpm to 70rpm, and then the bubble layer quartz sand is poured into the mold, and the bubble layer quartz sand is laid to the straight wall area with a forming rod and formed. Subsequently, the rotating mold is set vertically (0° from the vertical direction), rotated at a speed of 65rpm to 70rpm, and a part of the quartz sand in the straight wall area is scraped off with a forming rod to make it fall to the bottom, until the bubble layer quartz sand laying and forming of the entire crucible area is completed.

[0033] The transparent layer of quartz sand can be laid in the following manner: part of the transparent quartz sand is laid to the inner straight wall area of the bubble layer of quartz sand by a molding machine and formed. Then the remaining transparent quartz sand is manually laid to the inner bottom and R corner part of the bubble layer of quartz sand and formed.

[0034] S2: Expel the air in the rotating mold and the air in the gaps of quartz sand.

[0035] 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 inside of the mold and the gaps in the quartz sand.

[0036] Among them, monatomic gases may include, for example, helium, argon, neon, deuterium, etc. The above-mentioned monatomic gases can purify quartz sand through the principle of selective permeation. For example, taking helium as an example, it can penetrate into the gaps of quartz sand, and then the air displaced by helium can be discharged by means of vacuum pumping, etc. Moreover, after the air is discharged, the helium that has penetrated into the gaps of quartz sand can also be discharged in the form of vacuum pumping.

[0037] The mixed gas may include 80wt% - 90wt% of monatomic gas and 10wt% - 20wt% of oxygen. Oxygen can play a role in supporting combustion and assist the electrode in increasing heat.

[0038] When only the monatomic gas is introduced, the introduction speed of the monatomic gas can be 0.25MPa / min - 0.5MPa / min, such as 0.25MPa / min, 0.3MPa / min, 0.35MPa / min, 0.4MPa / min, 0.45MPa / min or 0.5MPa / min, etc., or other values within the range of 0.25MPa / min - 0.5MPa / min. Similarly, when the mixed gas is introduced, the introduction speed of the mixed gas can also be 0.25MPa / min - 0.5MPa / min.

[0039] S3: Under the conditions of vacuum pumping and arc ignition, the quartz sand of the sealing layer is introduced into the rotating mold by the spreading method so that the quartz sand of the sealing layer melts and deposits on the surface of the quartz sand of the transparent layer, and then cools down to obtain the sealing layer on the inner surface of the transparent layer.

[0040] In some alternative embodiments, the particle size of the quartz sand of the sealing layer can be 75μm - 100μm, such as 75μm, 80μm, 85μm, 90μm, 95μm or 100μm, etc., or other values within the range of 75μm - 100μm.

[0041] The purity, particle size, etc. of the above-mentioned quartz sand of the sealing layer and the quartz sand of the transparent layer are equal, so that air bubble interlayers between the transparent layer and the sealing layer can be effectively avoided.

[0042] In some alternative embodiments, the spreading method may include: introducing the quartz sand of the sealing layer into the rotating mold through an introducing device. Among them, the introducing device can be, for example, a conduit with a valve. The conduit has a feed end and a discharge end, and the discharge end is used to introduce the quartz sand of the sealing layer into the rotating mold. The feed end is connected to the quartz sand storage device, and a stirring structure may be provided in the quartz sand storage device.

[0043] The quartz sand in the sealing layer is discharged from the discharge port of the feeding device, melted under the action of an electric arc, and then dispersed on the inner surface of the rotating mold based on gravity and vacuum suction. It should be noted that in the prior art, due to the limitations of graphite electrode discharge, the temperature brought by the electric arc is relatively low, making it difficult to ensure that the quartz sand after laying and forming is completely ablated. And due to the centrifugal force at the bottom of the crucible, the bottom will move, and the movement of the bottom bubbles will converge at the R corner, resulting in serious R corner bubble problems. The present invention melts and deposits a sealing layer with almost zero bubbles through the dispersion method, avoiding the impurities introduced due to the rupture of the bubbles on the inner wall of the crucible during the single crystal pulling process due to the presence of bubbles on the inner surface of the quartz crucible, thereby avoiding problems such as a decrease in the purity of single crystal silicon, the appearance of pinholes, and the liquid surface jitter caused by the rupture of bubbles.

[0044] In some alternative embodiments, the vertical distance between the discharge port of the feeding device and the upper port of the rotating mold can be 45 mm to 55 mm, such as 45 mm, 48 mm, 50 mm, 52 mm or 55 mm, etc., or other values within the range of 45 mm to 55 mm.

[0045] If the vertical distance between the discharge port of the feeding 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 feeding device and the upper port of the rotating mold is too long, it is not conducive to the uniform dispersion and deposition of the molten quartz sand at the bottom.

[0046] In some alternative embodiments, the horizontal distance between the discharge port of the feeding device and the transparent layer can be 100 mm to 150 mm, such as 100 mm, 110 mm, 120 mm, 130 mm, 140 mm or 150 mm, etc., or other values within the range of 100 mm to 150 mm.

[0047] If the horizontal distance between the discharge port of the feeding device and the transparent layer is too short, it is not conducive to the uniform dispersion and deposition of the molten quartz sand at the port; if the horizontal distance between the discharge port of the feeding device and the transparent layer is too long, it is not conducive to the uniform dispersion and deposition of the molten quartz sand at the bottom.

[0048] In some alternative embodiments, the conditions for preparing the sealing layer may include: the vacuum condition is -0.20 MPa to -0.3 MPa (such as -0.2 MPa, -0.25 MPa or -0.3 MPa, etc.), the arc starting power is 10 Kw to 15 Kw (such as 10 Kw, 11 Kw, 12 Kw, 13 Kw, 14 Kw or 15 Kw, etc.), the arc action time is 2 min to 3 min (such as 2 min, 2.5 min or 3 min, etc.), the electrode spacing is 20 mm to 25 mm (such as 20 mm, 21 mm, 22 mm, 23 mm, 24 mm or 25 mm, etc.), and the vertical distance between the arc starting end of the electrode and the upper port of the rotating mold is 150 mm to 200 mm (such as 150 mm, 160 mm, 170 mm, 180 mm, 190 mm or 200 mm, etc.).

[0049] If the arc starting power is less than 10 Kw during the preparation of the sealing layer, it will cause incomplete melting of the quartz sand in the sealing layer, forming a "cold zone", resulting in unevenness of the sealing layer or the generation of unmelted particles, and unable to effectively seal the transparent layer; if the arc starting power is greater than 15 Kw during the preparation of the sealing layer, it will cause the sealing layer to be too thick, resulting in the appearance of a bubble sandwich between the sealing 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 forming, which makes it extremely easy to generate microbubbles in the transparent layer. The bubbles in the area far from the inner surface of the crucible can be improved by vacuum pumping, 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 sealing layer is too thick, bubbles are also likely to remain in the area of the sealing layer close to the transparent layer.

[0050] If the vacuum is pumped too slowly during the preparation of the sealing layer, the bubbles cannot be exhausted completely; if the vacuum is pumped too quickly, the sealing layer will be broken and the sealing layer cannot be effectively sealed.

[0051] If the arc action time is shorter than 2 min during the preparation of the sealing layer, the molten quartz will not be evenly deposited on the inner surface of the crucible, and some places cannot be fully deposited; if the arc action time is longer than 3 min during the preparation of the sealing layer, it will cause poor uniformity of the sealing layer and the sealing layer will thicken locally.

[0052] In the present invention, the number of electrodes is 3, and they can be graphite electrodes. If the electrode spacing is less than 20 mm during the preparation of the sealing layer, it is not conducive to the arc light. The arc cannot open in time and arcing will occur, resulting in unstable arc light; if the electrode spacing is longer than 25 mm during the preparation of the sealing layer, it is not conducive to the arc light. The electrode spacing is too large and arcing will occur, resulting in unstable arc light.

[0053] If the vertical distance between the arc starting end of the electrode and the upper port of the rotating mold is less than 150 mm during the preparation of the sealing layer, it is not conducive to the uniform dispersion and deposition of fused 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 is greater than 200 mm during the preparation of the sealing layer, it is not conducive to the uniform dispersion and deposition of fused quartz sand at the bottom.

[0054] In some alternative embodiments, the conditions of the cooling process include: the vacuum condition is -0.20 MPa to -0.4 MPa (such as -0.2 MPa, -0.25 MPa, -0.3 MPa, -0.35 MPa or -0.4 MPa, etc.), the arc power is 5 Kw to 10 Kw (such as 5 Kw, 6 Kw, 7 Kw, 8 Kw, 9 Kw or 10 Kw, etc.), the arc action time is 2 min to 3 min (such as 2 min, 2.5 min or 3 min, etc.), the electrode spacing is 10 mm to 15 mm (such as 10 mm, 11 mm, 12 mm, 13 mm, 14 mm or 15 mm, etc.), and the vertical distance between the arc end of the electrode and the upper port of the rotating mold is 150 mm to 200 mm (such as 150 mm, 160 mm, 170 mm, 180 mm, 190 mm or 200 mm, etc.).

[0055] By cooling, the integrity of the sealing layer is ensured. The vacuum should not be too high during this process to avoid the instability of the surface layer just after the process and the breaking of the deposited sealing layer by pumping. In addition, by cooling, it can also prevent the situation where there are bubbles remaining below the sealing layer due to excessive temperature when the vacuum pumping speed is not high during vacuum arc suction casting.

[0056] S4: Melt the transparent layer quartz sand to form the transparent layer.

[0057] In some alternative embodiments, the conditions for preparing the transparent layer may include: the vacuum condition is -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.), the arc power is 25 Kw to 35 Kw (such as 25 Kw, 28 Kw, 30 Kw, 32 Kw or 35 Kw, etc.), the arc action time is 4 min to 6 min (such as 4 min, 5 min or 6 min, etc.), the electrode spacing is 20 mm to 30 mm (such as 20 min, 22 min, 25 min, 28 min or 30 min, etc.), and the vertical distance between the arc end of the electrode and the upper port of the rotating mold is 100 mm to 150 mm (such as 100 mm, 110 mm, 120 mm, 130 mm, 140 mm or 150 mm, etc.).

[0058] During this process, the electrode position is lower than that during the preparation of the sealing layer to facilitate the uniform growth of the entire inner wall transparent layer. Moreover, this process is carried out after the preparation of the sealing layer, and the pumping speed of the vacuum during this process is greater than the melting speed of the quartz sand, thereby avoiding the generation of bubbles in the transparent layer.

[0059] S5: Melt the quartz sand in the bubble layer to form the bubble layer.

[0060] In some alternative embodiments, the conditions for preparing the bubble layer may include: the arc power is 16 Kw to 20 Kw (such as 16 Kw, 17 Kw, 18 Kw, 19 Kw or 20 Kw, etc.), the arc action time is 6 min to 10 min (such as 6 min, 7 min, 8 min, 9 min or 10 min, etc.), the electrode spacing is 35 mm to 45 mm (such as 35 min, 38 min, 40 min, 42 min or 45 min, etc.), and the vertical distance between the arc end of the electrode and the upper port of the rotating mold is 70 mm to 100 mm (such as 70 mm, 75 mm, 80 mm, 85 mm, 90 mm, 95 mm or 100 mm, etc.).

[0061] During this process, the vacuum pumping is turned off, the electrode spacing becomes larger, and the electrode position is further lowered, shortening the melting time to avoid impurity contamination caused by too long melting time.

[0062] It should be noted that appropriate electrode positions and electrode spacings not only help improve the consistency of the quartz crucible and reduce the bubble content, but also help shorten the production cycle and improve production efficiency.

[0063] S6: Turn off the arc, raise the electrode position until the quartz crucible cools, and then take it out of the furnace and demold it.

[0064] Correspondingly, the present invention provides a quartz crucible prepared by the above preparation method.

[0065] In some alternative embodiments, the thickness of the sealing 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 can also be other values within the range of 0.3 mm to 0.8 mm.

[0066] If the thickness of the sealing layer is too thin, it is difficult to ensure its integrity and it is easy to break, and after breaking, bubbles will be sucked into the transparent layer; if the thickness of the sealing layer is too thick, it is easy to form a bubble sandwich layer between it and the transparent layer.

[0067] In some alternative embodiments, the number of bubbles in the sealing layer does not exceed 1 per 17 mm 2 , thereby effectively avoiding the adverse effects of bubbles on monocrystalline silicon during the crystal pulling process.

[0068] In addition, the present invention also provides an application of the above quartz crucible in the preparation of monocrystalline silicon.

[0069] Correspondingly, the present invention also provides a monocrystalline silicon, which is prepared by using the above quartz crucible. This monocrystalline silicon has a high whole rod rate, few defects, and a low wire breakage rate.

[0070] The features and performance of the present invention will be further described in detail below in conjunction with embodiments.

[0071] Embodiment 1 This embodiment provides a quartz crucible, and the structural schematic diagram involved in its preparation process is as Figure 1 shown, and its preparation method is as follows: S1: Lay and form the bubble layer quartz sand and the transparent layer quartz sand in the rotary mold 4 in the order from outside to inside.

[0072] S11: Lay the bubble layer quartz sand.

[0073] Tilt the rotary mold 4 to an angle of 50° with the vertical direction, rotate it at a speed of 70 rpm, then pour the bubble layer quartz sand into the mold, and use a forming rod to lay the bubble layer quartz sand to the straight wall area and form it. Subsequently, set the rotary mold 4 vertically (at an angle of 0° with the vertical direction), rotate it at a speed of 70 rpm, and use a forming rod to scrape off part of the quartz sand in the straight wall area so that it falls to the bottom until the laying and forming of the bubble layer quartz sand in the entire crucible area is completed. Among them, the particle size of the bubble layer quartz sand is 120 μm to 150 μm, and the purity is 99.9999%. The rotary mold 4 is a steel mold, its inner diameter is 830 mm, and the rotary mold 4 is provided with exhaust holes 3.

[0074] S12: Lay the transparent layer quartz sand.

[0075] Keep the mold rotating at a speed of 70 rpm, and use a forming machine to lay part of the transparent quartz sand to the inner straight wall area of the bubble layer quartz sand and form it. Subsequently, manually lay the remaining transparent quartz sand to the inner bottom and R corner parts of the bubble layer quartz sand and form it. Among them, the particle size of the transparent layer quartz sand is 75 μm to 80 μm, and the purity is 99.9999%.

[0076] S2: Exclude the air in the rotary mold 4 and the air in the gaps between the quartz sands.

[0077] Introduce a mixed gas 2 composed of 85 wt% helium and 15 wt% oxygen into the rotary mold 4, and the introduction speed of the mixed gas 2 is 0.4 MPa / min.

[0078] S3: Under the conditions of vacuum pumping and arc initiation, introduce the quartz sand 8 of the sealing layer into the rotating mold 4 by the spreading method so that the quartz sand 8 of the sealing layer melts and deposits on the surface of the quartz sand of the transparent layer, and then cool down to obtain the sealing layer 7 on the inner surface of the transparent layer 6.

[0079] S31: Prepare the sealing layer 7 by combining the spreading method with vacuum arc suction casting.

[0080] Introduce the quartz sand 8 of the sealing layer into the rotating mold 4 through a conduit 9 provided with a valve. The vertical distance between the discharge port of the conduit 9 and the upper port of the rotating mold 4 is 50 mm, and the horizontal distance between the discharge port of the conduit 9 and the transparent layer 6 is 120 mm. The vacuum condition is -0.25 MPa, the arc initiation power is 15 Kw, the arc action time is 2.5 min, the number of electrodes is 3 graphite electrodes 1, the electrode spacing is 25 mm, and the vertical distance between the arc initiation end of the electrode and the upper port of the rotating mold 4 is 200 mm. Among them, the particle size of the quartz sand 8 of the sealing layer is 75 μm - 80 μm, and the purity is 99.9999% (the quartz sand 8 of the sealing layer is the same as the quartz sand of the transparent layer).

[0081] S32: Cool down.

[0082] 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.

[0083] S4: Melt the quartz sand of the transparent layer to form the transparent layer 6.

[0084] 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.

[0085] S5: Melt the quartz sand of the bubble layer to form the bubble layer 5.

[0086] The arc power is 18 Kw, the arc action time is 8 min, 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.

[0087] S6: Turn off the arc, raise the position of the electrode until the quartz crucible cools, and then take out of the furnace and demold.

[0088] In this quartz crucible, the thickness of the bubble layer 5 is 13.5 mm, the thickness of the transparent layer 6 is 3 mm, and the thickness of the sealing layer 7 is 0.4 mm.

[0089] Example 2 This example provides a quartz crucible, and its preparation method is as follows: S1: Lay and form the bubble layer quartz sand and the transparent layer quartz sand in a rotating mold in the order from outside to inside.

[0090] S11: Lay the bubble layer quartz sand.

[0091] Tilt the rotating mold to an angle of 45° with the vertical direction, rotate it at a speed of 65 rpm, then pour the bubble layer quartz sand into the mold, and use a forming rod to lay the bubble layer quartz sand to the straight wall area and form it. Subsequently, set the rotating mold vertically (at 0° with the vertical direction), rotate it at a speed of 65 rpm, and use a forming rod to scrape off part of the quartz sand in the straight wall area so that it falls to the bottom until the laying and forming of the bubble layer quartz sand in the entire crucible area is completed. Among them, the particle size of the bubble layer quartz sand is 150 μm - 200 μm, and the purity is 99.9999%. The inner diameter of the rotating mold is 825 mm.

[0092] S12: Lay the transparent layer quartz sand.

[0093] Keep the mold rotating at a speed of 65 rpm, and use a forming machine to lay part of the transparent quartz sand to the inner straight wall area of the bubble layer quartz sand and form it. Subsequently, manually lay the remaining transparent quartz sand to the inner bottom and R - corner part of the bubble layer quartz sand and form it. Among them, the particle size of the transparent layer quartz sand is 80 μm - 90 μm, and the purity is 99.9999%.

[0094] S2: Exclude the air in the rotating mold and the air in the gaps between the quartz sands.

[0095] Introduce a mixed gas composed of 80 wt% helium and 20 wt% oxygen into the rotating mold, and the introduction speed of the mixed gas is 0.25 MPa / min.

[0096] Under the conditions of vacuum pumping and arc starting, introduce the seal layer quartz sand into the rotating mold by the dispersion method so that the seal layer quartz sand melts and deposits on the surface of the transparent layer quartz sand, and then cool down to obtain the seal layer on the inner surface of the transparent layer.

[0097] S31: Prepare the seal layer by combining the dispersion method with vacuum arc suction casting.

[0098] Introduce the seal layer quartz sand into the rotating mold through a conduit. The vertical distance from the discharge port of the conduit to the upper port of the rotating mold is 45 mm, and the horizontal distance from the discharge port of the conduit to the transparent layer is 100 mm. The vacuum condition is - 0.2 MPa, the arc starting power is 10 Kw, the arc action time is 3 min, the electrode spacing is 20 mm, and the vertical distance from the arc - starting end of the electrode to the upper port of the rotating mold is 150 mm. Among them, the particle size of the seal layer quartz sand is 80 μm - 90 μm, and the purity is 99.9999% (the same as the transparent layer quartz sand).

[0099] S32: Cooling down.

[0100] The vacuum condition is -0.2 MPa, the arc power is 5 Kw, the arc action time is 3 min, the electrode spacing is 10 mm, and the vertical distance between the arc end of the electrode and the upper port of the rotating mold is 150 mm.

[0101] S4: Melting the transparent layer quartz sand to form a transparent layer.

[0102] The vacuum condition is -0.99 MPa, the arc power is 25 Kw, the arc action time is 6 min, the electrode spacing is 20 mm, and the vertical distance between the arc end of the electrode and the upper port of the rotating mold is 100 mm.

[0103] S5: Melting the bubble layer quartz sand to form a bubble layer.

[0104] 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.

[0105] S6: Turning off the arc, raising the electrode position until the quartz crucible cools down, and then taking it out of the furnace and demolding.

[0106] In this quartz crucible, the thickness of the bubble layer is 13.4 mm, the thickness of the transparent layer is 3.1 mm, and the thickness of the sealing skin layer is 0.6 mm.

[0107] Example 3 This example provides a quartz crucible, and its preparation method is as follows: S1: Laying and molding the bubble layer quartz sand and the transparent layer quartz sand in a rotating mold in the order from outside to inside.

[0108] S11: Laying the bubble layer quartz sand.

[0109] Tilting the rotating mold to 56° with respect to the vertical direction, rotating at a speed of 68 rpm, then pouring the bubble layer quartz sand into the mold, and using a forming rod to lay the bubble layer quartz sand to the straight wall area and form it. Subsequently, setting the rotating mold vertically (at 0° with respect to the vertical direction), rotating at a speed of 68 rpm, and scraping off part of the quartz sand in the straight wall area with a forming rod so that it falls to the bottom until the laying and molding of the bubble layer quartz sand in the entire crucible area is completed. Among them, 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.

[0110] S12: Laying the transparent layer quartz sand.

[0111] Keep the mold rotating at a speed of 68 rpm, and use a molding machine to lay a part of the transparent quartz sand on the inner straight wall area of the bubble layer quartz sand and form it. Subsequently, manually lay the remaining transparent quartz sand on the inner bottom and R corner parts of the bubble layer quartz sand and form it. Among them, the particle size of the transparent layer quartz sand is 90μm - 100μm, and the purity is 99.9999%.

[0112] S2: Exclude the air in the rotating mold and the air in the gaps between the quartz sands.

[0113] Introduce a mixed gas composed of 90wt% helium and 10wt% oxygen into the rotating mold at a feeding rate of 0.5MPa / min.

[0114] S3: Under the conditions of vacuum pumping and arc ignition, introduce the sealing layer quartz sand into the rotating mold by the spreading method to melt and deposit the sealing layer quartz sand on the surface of the transparent layer quartz sand, and then cool down to obtain the sealing layer on the inner surface of the transparent layer.

[0115] S31: Prepare the sealing layer by combining the spreading method with vacuum arc suction casting.

[0116] Introduce the sealing layer quartz sand into the rotating mold through a conduit. The vertical distance from the outlet of the conduit to the upper port of the rotating mold is 55mm, and the horizontal distance from the outlet of the conduit to the transparent layer is 150mm. The vacuum condition is -0.3MPa, the arc power is 12Kw, the arc action time is 2min, the electrode spacing is 22mm, and the vertical distance from the arc end of the electrode to the upper port of the rotating mold is 180mm. Among them, the particle size of the sealing layer quartz sand is 90μm - 100μm, and the purity is 99.9999% (the same as the transparent layer quartz sand).

[0117] S32: Cool down.

[0118] The vacuum condition is -0.4MPa, the arc power is 8Kw, the arc action time is 2min, the electrode spacing is 12mm, and the vertical distance from the arc end of the electrode to the upper port of the rotating mold is 180mm.

[0119] S4: Melt the transparent layer quartz sand to form the transparent layer.

[0120] The vacuum condition is -0.95MPa, the arc power is 35Kw, the arc action time is 4min, the electrode spacing is 30mm, and the vertical distance from the arc end of the electrode to the upper port of the rotating mold is 120mm.

[0121] S5: Melt the bubble layer quartz sand to form the bubble layer.

[0122] 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.

[0123] S6: Turn off the arc, raise the electrode position until the quartz crucible cools, and then take it out of the furnace and demold it.

[0124] The thickness of the bubble layer in the quartz crucible is 13.4 mm, the thickness of the transparent layer is 2.9 mm, and the thickness of the sealing layer is 0.6 mm.

[0125] Example 4 The difference between this example and Example 1 is that in S2, the mixed gas is replaced with only helium.

[0126] Comparative Example 1 The difference between this comparative example and Example 1 is that the sealing layer is not prepared on the inner wall of the transparent layer.

[0127] Comparative Example 2 The difference between this comparative example and Example 1 is that step S32 is not carried out, that is, the sealing layer is not cooled down.

[0128] Comparative Example 3 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.

[0129] Comparative Example 4 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.

[0130] Comparative Example 5 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.

[0131] Comparative Example 6 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.

[0132] Comparative Example 7 The difference between this comparative example and Example 1 is that in S31, the vacuum condition is -0.1 MPa.

[0133] Comparative Example 8 The difference between this comparative example and Example 1 is that in S31, the vacuum condition is -0.4 MPa.

[0134] Comparative Example 9 The difference between this comparative example and Example 1 is that in S31, the arc starting power is 8 Kw.

[0135] Comparative Example 10 The difference between this comparative example and Example 1 is that in S31, the starting arc power is 18 Kw.

[0136] Comparative Example 11 The difference between this comparative example and Example 1 is that in S31, the starting arc action time is 5 min.

[0137] Comparative Example 12 The difference between this comparative example and Example 1 is that in S31, the electrode spacing is 15 mm.

[0138] Comparative Example 13 The difference between this comparative example and Example 1 is that in S31, the vertical distance between the starting arc end of the electrode and the upper port of the rotating mold is 120 mm.

[0139] Comparative Example 14 The difference between this comparative example and Example 1 is that in S31, the vertical distance between the starting arc end of the electrode and the upper port of the rotating mold is 240 mm.

[0140] Comparative Example 15 The difference between this comparative example and Example 1 is that in S32, the vacuum condition is -0.6 MPa.

[0141] Test Example (1) The thickness of the sealing layer in the quartz crucibles prepared in Examples 1 to 4 and Comparative Examples 2 to 15 was statistically analyzed, and the number of bubbles in the inner surface layer of the quartz crucibles in each example and each comparative example was statistically analyzed. The results are shown in Table 1 and Figure 2 and Figure 3 as shown. Among them, the number of bubbles was obtained by observing with an optical microscope.

[0142] Figure 2 shows the number of bubbles in a partial area of the inner surface layer of the quartz crucible of Comparative Example 1, which is 46 bubbles / 17 mm 2 ; Figure 3 shows the number of bubbles in a partial area of the inner surface layer (sealing layer) of the quartz crucible of Example 1, which is 1 bubble / 17 mm 2 .

[0143] From Figure 2 and Figure 3 comparison, it can be seen that the method provided by the present invention can successfully prepare a sealing layer with no more than 1 bubble / 17 mm 2 , which can effectively seal the transparent layer and avoid the influence of bubbles in the transparent layer on the production of single crystal silicon.

[0144] (2)The quartz crucibles prepared in Examples 1-4 and Comparative Examples 1-15 were used to prepare monocrystalline silicon by the same crystal pulling method. The whole rod rate, pinhole rate, and wire break rate of the monocrystalline silicon obtained by crystal pulling were compared, and the results are shown in Table 1. Among them, the whole rod rate is calculated as the percentage of the obtained whole rod monocrystalline silicon in the total amount of the measured monocrystalline silicon, the pinhole rate is calculated as the percentage of the monocrystalline silicon with visible pinholes in the total amount of the measured monocrystalline silicon, and the wire break rate is calculated as the percentage of the monocrystalline silicon with wire breaks in the total amount of the measured monocrystalline silicon.

[0145] Table 1 Test Results

[0146] The above " / " means that a uniformly deposited sealing layer could not be obtained.

[0147] As can be seen from Table 1, the sealing layer in the quartz crucible provided by the present invention basically contains no bubbles, which is beneficial to improving the quality of the monocrystalline silicon produced therefrom.

[0148] As can be seen from Example 1 and Comparative Examples 1-15, the quartz crucibles with a sealing layer (Example 1 and Comparative Examples 2-15) are more conducive to improving the quality of monocrystalline silicon than those without a sealing layer (Comparative Example 1).

[0149] As can be seen from Example 1 and Comparative Examples 2-15, when the conditions for preparing the sealing layer are improper, even if a sealing layer is formed, it will affect the quality of monocrystalline silicon.

[0150] In summary, by using the dispersion method in combination with the vacuum arc suction casting method to prepare a sealing layer with basically no bubbles on the inner surface of the transparent layer, the present invention can avoid the impurities introduced by the rupture of the bubbles in the crucible itself during the crystal pulling process, and thus can avoid and improve problems such as a decrease in the whole rod rate of monocrystalline silicon, the appearance of pinholes, and wire breaks.

[0151] The above are only the preferred embodiments of the present invention and are not intended to limit the present invention. For those skilled in the art, the present invention can have various changes and modifications. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A method for preparing a quartz crucible, characterized in that, It includes the following steps: laying the bubble layer quartz sand and the transparent layer quartz sand in a rotating mold in the order from outside to inside to form a shape; Removing the air in the rotating mold and the air in the gaps between the quartz sands; under the conditions of vacuum extraction and arc ignition, introducing the sealing layer quartz sand into the rotating mold by the dispersion method so that the sealing layer quartz sand melts and deposits on the surface of the transparent layer quartz sand, and then cooling down to obtain a sealing layer on the inner surface of the transparent layer; Subsequently, melting the transparent layer quartz sand to form a transparent layer; and then melting the bubble layer quartz sand to form a bubble layer.

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

3. The preparation method according to claim 1 or 2, characterized in that, The dispersion method includes: introducing the sealing layer quartz sand into the rotating mold through an introducing device, and the vertical distance from the discharge port of the introducing device to the upper port of the rotating mold is 45mm - 55mm; the horizontal distance from the discharge port of the introducing device to the transparent layer is 100mm - 150mm.

4. The preparation method according to claim 3, wherein The conditions for preparing the sealing layer include: the vacuum condition is -0.20MPa - -0.3MPa, the arc ignition power is 10Kw - 15Kw, the arc action time is 2min - 3min, the electrode spacing is 20mm - 25mm, and the vertical distance from the arc ignition end of the electrode to the upper port of the rotating mold is 150mm - 200mm.

5. The preparation method according to claim 1, characterized in that, The conditions for the cooling process include: the vacuum condition is -0.20MPa - -0.4MPa, the arc power is 5Kw - 10Kw, the arc action time is 2min - 3min, the electrode spacing is 10mm - 15mm, and the vertical distance from the arc end of the electrode to the upper port of the rotating mold is 150mm - 200mm.

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

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

8. The preparation method according to claim 1, wherein, The particle size of the bubble layer quartz sand is 120μm - 250μm, the particle size of the transparent layer quartz sand is 75μm - 100μm, and the particle size of the sealing layer quartz sand is 75μm - 100μm.

9. A quartz crucible, characterized in that, Prepared by the preparation method according to any one of claims 1 - 8.

10. The quartz crucible according to claim 9, wherein, The quartz crucible has at least one of the following characteristics: Characteristic 1: The thickness of the sealing layer is 0.3mm - 0.8mm; Feature 2: The number of air bubbles in the sealing layer does not exceed 1 per 17 mm 2 .

11. Use of the quartz crucible according to claim 9 or 10 in the preparation of monocrystalline silicon.

12. A single crystal silicon, characterized in that, The single crystal silicon is prepared by using the quartz crucible described in claim 9 or 10.

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