Necking-down type crucible structure and crystal growth process
By designing a necked opening structure and an outer annular insulation layer in the crucible structure, the problem of difficulty in adjusting the radial temperature field when growing SiC crystals is solved, and the crystal quality and service life of the insulation material are improved.
Patent Information
- Application Number
- CN202411646665.X
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2024-11-18
- Publication Date
- 2025-02-18
AI Technical Summary
When the prior art grows SiC crystals, it is difficult to adjust the axial temperature ladder and the radial temperature field at the same time, resulting in poor crystal quality and the insulation material is easily corrosive and needs to be replaced frequently, resulting in waste of materials.
Design a necked crucible structure, by setting a necked open structure and annular insulation layer on the segmented crucible, the radial temperature gradient in the growth area of the crucible is controlled, and the radial temperature under different coils or crucible positions are achieved. Flexible adjustment of the field. The insulation layer is arranged outside the crucible structure to avoid corrosion of the silicon atmosphere.
The fine adjustment of the radial temperature field in the SiC single crystal growth area is achieved, the crystal quality and yield are improved, the service life of the insulation material is extended, and material waste is reduced.
Smart Images
Figure CN119465406A_ABST
Abstract
Description
Technical Field
[0001] The invention belongs to the technical field of semiconductors and relates to a necked crucible structure and a crystal growth process. Background Art
[0002] 4H-SiC, as a third-generation semiconductor material, has the characteristics of large bandgap, low on-resistance, good heat dissipation and high saturated electron drift velocity. It is widely used in high-power, high-frequency and high-temperature electronic devices and has good development prospects.
[0003] At present, the mainstream preparation of large-scale commercial silicon carbide single crystals is mainly based on the physical vapor transport method (PVT method). The preparation process of this method is to fix the seed crystal on the top of the graphite crucible, and the silicon carbide raw material (mostly silicon carbide powder or polycrystalline silicon carbide) is placed under the graphite crucible, and the bottom raw material is decomposed and sublimated by heating. Driven by the axial temperature difference, the sublimated SimCn gas phase components are then transported to the surface of the seed crystal with the air flow, and deposited and crystallized on the growth surface of the seed crystal. As the growth time increases, the growth interface gradually advances to the raw material area, and finally forms a silicon carbide ingot.
[0004] As is known to all, when growing SiC crystals by the PVT method, the temperature control of the axial diameter is a difficult point in crystal growth. Usually, under the condition that the thermal field structure inside the crucible is fixed, the axial temperature gradient is adjusted by adjusting the coil height or the crucible position, but this causes changes in the radial temperature gradient in the growth area, and it is difficult to take into account the radial temperature change requirements while adjusting the axial temperature gradient. Although the existing technology, such as adding annular insulation felt or graphite parts with special structures in the growth area of the crucible to adjust the radial temperature field, as the crystal growth time increases, under the action of impurities or other atmospheres, especially silicon atmosphere, the corrosion of such materials will increase, which will cause the distribution of the temperature field in the growth area to change, increase the difficulty of thermal field adjustment, and thus affect the crystal quality, and need to replace the insulation material used to adjust the internal radial temperature gradient with the furnace or at a high frequency, which greatly causes material waste.
[0005] Therefore, it is urgent to design a necked crucible structure to overcome the defects of the prior art and meet the needs of practical applications. Summary of the invention
[0006] In view of the deficiencies in the prior art, the purpose of the present invention is to provide a necked crucible structure and a crystal growth process. In the present invention, by specifically designing the necked opening structure and the thermal insulation layer on the segmented crucible, the radial temperature gradient of the growth area inside the crucible structure can be regulated, and the radial temperature field under different coil or crucible positions can be easily adjusted. Fine adjustments can be made for different thickness stages of crystal growth, which is convenient for preparing high-quality SiC single crystals. The crucible structure can be recycled, and the thermal insulation layer is arranged on the outside of the crucible structure, which effectively avoids corrosion from the silicon atmosphere, avoids high-frequency replacement of thermal insulation materials, and greatly improves the service life of the material.
[0007] To achieve this object, the present invention adopts the following technical solutions:
[0008] In a first aspect, the present invention provides a necked crucible structure, which comprises a lower crucible and an upper crucible, wherein the upper crucible is threadedly connected to the top of the lower crucible to form a reaction chamber; an end of the upper crucible away from the lower crucible is a necked opening structure, and an insulation layer is arranged circumferentially on the outer side of the necked opening structure.
[0009] In the present invention, by specifically designing the neck opening structure and the insulation layer on the segmented crucible, the radial temperature gradient of the growth area inside the crucible structure can be controlled, the radial temperature field under different coil or crucible positions can be easily adjusted, and fine-tuning can be performed for different thickness stages of crystal growth, so as to facilitate the preparation of high-quality SiC single crystals. The crucible structure can be recycled, and the insulation layer is arranged on the outside of the crucible structure, which effectively avoids corrosion from the silicon atmosphere, avoids high-frequency replacement of insulation materials, and greatly improves the service life of the material.
[0010] It should be noted that the crucible structure of the present invention is based on the PVT method, and a thermal insulation layer is placed outside the necking opening structure to adjust the radial gradient of the crystal in the growth area inside the crucible, and the thermal insulation layer used has a ring structure. The inner diameter of the thermal insulation layer fits the outer diameter of the necking opening structure, and the outer diameter and specific thickness of the thermal insulation layer can be adjusted according to actual conditions. It can be designed as a thermal insulation structure that is wide at the top and narrow at the bottom to adjust the radial gradient changes during the crystal growth and thickness process. The thermal field structure can be adjusted more flexibly to meet the thermal field requirements of various complex crystal growths. At the same time, it can prevent the thermal field parameter disturbance caused by the internal silicon atmosphere corrosion of the thermal insulation layer, protect the thermal insulation layer, and improve the service life of the thermal insulation felt, which greatly saves material costs.
[0011] As a preferred technical solution of the present invention, the crucible structure further comprises a crucible cover, and the crucible cover is threadedly connected to an end of the upper crucible away from the lower crucible.
[0012] As a preferred technical solution of the present invention, the height of the necked opening structure is 45mm to 65mm, for example, it can be 45mm, 47mm, 49mm, 50mm, 52mm, 54mm, 56mm, 58mm, 60mm, etc., but is not limited to the listed values, and other unlisted values within the numerical range are also applicable.
[0013] The height of the necked opening structure in the present invention is 45mm to 65mm, which is mainly designed based on the height and thickness of the equal-diameter ring and the seed crystal holder. Generally, the thickness of the crystal after growth is between 20mm and 30mm. The length of the equal-diameter ring will be greater than the crystal thickness, between 40mm and 50mm, plus the thickness of the seed crystal holder. Therefore, the height of the necked opening structure can be more conducive to crystal growth.
[0014] Preferably, the ratio of the inner diameter of the neck opening structure to the inner diameter of the lower crucible is 1:(1.4-1.6), for example, it can be 1:1.4, 1:1.45, 1:1.48, 1:1.5, 1:1.53, 1:1.56, 1:1.58, 1:1.6, etc., but is not limited to the listed values, and other unlisted values within the numerical range are also applicable.
[0015] In the present invention, the ratio of the inner diameter of the necking opening structure to the inner diameter of the lower crucible is 1:(1.4-1.6) because within this range, the inner diameter of the lower crucible can be prevented from being too large relative to the necking growth area, thereby causing the powder loaded in the side area to crystallize on the crucible wall in the non-necking area of the upper crucible.
[0016] As a preferred technical solution of the present invention, the height of the lower crucible is 90 mm to 110 mm, for example, it can be 90 mm, 92 mm, 94 mm, 96 mm, 98 mm, 100 mm, 102 mm, 104 mm, 106 mm, 108 mm, 110 mm, etc., but is not limited to the listed values, and other unlisted values within the numerical range are also applicable.
[0017] Preferably, the height of the upper crucible excluding the neck opening structure is 70 mm to 90 mm, for example, it can be 70 mm, 72 mm, 74 mm, 76 mm, 78 mm, 80 mm, 82 mm, 84 mm, 86 mm, 88 mm, 90 mm, etc., but is not limited to the listed values, and other unlisted values within the numerical range are also applicable.
[0018] In the present invention, the height of the lower crucible is 90 mm to 110 mm and the height of the upper crucible excluding the neck opening structure is 70 mm to 90 mm, because a suitable axial gradient can be guaranteed within this range, and the distance between the material surface and the growth surface can effectively reduce the floating of fine carbon particles generated in the charging area to the crystal growth area.
[0019] Preferably, the thread depth of the threaded connection between the upper crucible and the lower crucible is 10 mm to 15 mm, for example, it can be 10 mm, 10.5 mm, 11 mm, 11.5 mm, 12 mm, 12.5 mm, 13 mm, 13.5 mm, 14 mm, 14.5 mm, 15 mm, etc., but is not limited to the listed values, and other unlisted values within the numerical range are also applicable.
[0020] As a preferred technical solution of the present invention, the inner diameter of the upper crucible except the neck opening structure is the same as the inner diameter of the lower crucible.
[0021] As a preferred technical solution of the present invention, the insulation layer is provided with at least one layer, for example, it can be 1 layer, 2 layers, 3 layers, 4 layers, 5 layers, etc., but it is not limited to the listed values, and other unlisted values within the numerical range are also applicable.
[0022] Preferably, the thickness of the insulation layer is the same or gradually increases in a direction away from the lower crucible.
[0023] It should be noted that when the thickness of the insulation layer in the present invention is the same along the direction away from the lower crucible, as the crystal grows thicker, the radial temperature gradient of the growth surface becomes larger, which can be suitable for the large-diameter growth conditions of the crystal; when it gradually increases, it ensures that the radial temperature gradient of the growth surface changes less as the crystal grows thicker, which is suitable for equal-diameter growth. This combinability is conducive to more flexible adjustment of the thermal field structure to meet the thermal field requirements of various complex crystal growths.
[0024] Preferably, the thermal insulation layer is made of soft graphite felt or hard graphite felt.
[0025] As a preferred technical solution of the present invention, an annular partition layer is arranged in the lower crucible, and the annular partition layer divides the interior of the lower crucible into a central charging area and an annular charging area which are distributed in concentric circles from the center to the outside.
[0026] Preferably, the ratio of the diameter of the central charging area to the inner diameter of the lower crucible is 1:(1.4-1.6), for example, it can be 1:1.4, 1:1.45, 1:1.48, 1:1.5, 1:1.53, 1:1.56, 1:1.58, 1:1.6, etc., but is not limited to the listed values, and other unlisted values within the numerical range are also applicable.
[0027] The ratio of the diameter of the central loading area to the inner diameter of the lower crucible of the present invention is 1:(1.4-1.6) because it can avoid the inner diameter of the lower crucible being too large relative to the necking growth area, thereby causing the powder filled in the side area to crystallize on the crucible wall in the non-neck area of the upper crucible, thereby ensuring the uniformity of the atmosphere.
[0028] Preferably, the annular separation layer is a porous graphite plate or a graphite mesh.
[0029] Preferably, a cover sheet is provided on the top of the central charging area and the annular charging area.
[0030] Preferably, the cover sheet is made of porous graphite.
[0031] It should be noted that the lower crucible in the present invention is a charging crucible, and its charging area is a central charging area and an annular charging area, so as to carry out the reaction of silicon carbide powder with different particle sizes. Different areas are separated by porous graphite plates or graphite meshes. Usually, the annular charging area is close to the crucible wall during the crystal growth process, the temperature is high, the powder is easy to sublimate, the SiC raw material with small particle size sublimates quickly, and it is easy to produce fine carbon particles. Therefore, SiC powder with larger particle size can be loaded in the annular charging area to reduce the carbon particles generated in the edge area. At the same time, a cover sheet made of porous graphite material is placed above the raw material to filter large particles. The central charging area can be filled with SiC powder with small particle size to increase the crystal growth rate.
[0032] Preferably, the thickness of the cover sheet is 2 mm to 3 mm, for example, 2 mm, 2.2 mm, 2.4 mm, 2.6 mm, 2.8 mm, 3 mm, etc., but is not limited to the listed values, and other unlisted values within the numerical range are also applicable.
[0033] The thickness of the cover sheet in the present invention is 2 mm to 3 mm because within this range, impurities (mainly carbon particles) in the powder can be effectively filtered, while the cover sheet will not be too thick to cause crystal blockage under the material plate, affecting the upward transport of gas and reducing the utilization rate of the powder.
[0034] As a preferred technical solution of the present invention, an equal-diameter ring is circumferentially arranged on the inner wall of the necked opening structure, and the equal-diameter ring is used to carry the seed crystal holder.
[0035] Preferably, the height of the equal-diameter ring is smaller than the height of the necked opening structure.
[0036] It should be noted that the necked opening structure of the upper crucible is internally equipped with an equal-diameter ring to receive the seed crystal holder. The height of the equal-diameter ring can be adjusted according to needs. The seed crystal and the equal-diameter ring are in a non-contact state, and the seed crystal is bonded to the bottom of the seed crystal holder. After the material and seed crystal are assembled, the crucible structure is placed in a crystal growth furnace, and the crucible structure is adjusted to a suitable position (relative position with the heater or induction coil) by a stepper motor, and then vacuuming, back-pressurizing, reducing pressure, heating and other crystal growth processes are carried out.
[0037] Exemplarily, the specific assembly method of the crucible structure in the present invention includes:
[0038] The lower crucible is filled with silicon carbide raw materials. The particle size of the powder in the annular loading area is 8-20 mesh, and the particle size of the powder in the central loading area is 20-40 mesh. The material surface is 80-100 mm away from the seed crystal of the upper crucible. A cover sheet is placed on the upper part of the powder. The upper and lower crucibles are tightened. The equal-diameter ring is placed in the necking opening structure. The bottom is supported by the steps inside the upper crucible. The protruding part of the step is flush with the inner diameter of the equal-diameter ring. The seed crystal holder is placed on the equal-diameter ring. The seed crystal holder is matched with the equal-diameter ring. The assembly error does not exceed 0.1 mm. The annular insulation layer is placed on the outer wall of the necking opening structure. After filling, the crucible cover and the upper crucible are tightened.
[0039] In a second aspect, the present invention provides a crystal growth process, wherein the crystal growth process is performed using a crystal growth furnace, wherein the crucible structure described in the first aspect is placed in the crystal growth furnace.
[0040] It should be noted that the present invention does not specifically limit the specific structure and model of the crystal growth furnace. Those skilled in the art can make adaptive adjustments according to actual conditions, and all crystal growth furnaces can be included in the scope of protection of the present invention.
[0041] As a preferred technical solution of the present invention, the crystal growth process includes:
[0042] (1) Place the crucible structure with the assembled materials in the crystal growth furnace, check for leaks and evacuate the crystal growth furnace. When the internal pressure drops to 0.5Pa~5Pa, turn on the molecular pump to evacuate to 5×10 -3 Pa~5×10 -2 Pa;
[0043] (2) The crystal growth furnace is heated at a rate of 6°C / min to 7°C / min. When the temperature reaches 1100°C to 1250°C, the molecular pump is turned off and the mechanical pump continues to pump gas;
[0044] (3) On the basis of step (2), heating is continued at a heating rate of 2°C / min to 3°C / min. When the temperature reaches 1500°C to 1650°C, argon and nitrogen are introduced into the crystal growth furnace at the same time. The gas flow rate of argon is 100mL / min to 200mL / min, and the gas flow rate of nitrogen is 5mL / min to 10mL / min. The gas pressure is set to 300mbar. The temperature is kept at a target temperature of 1800°C to 2000°C. The heating time is 2h, and the pressure is kept at 100mbar to 200mbar.
[0045] (4) On the basis of step (3), continue heating for 10 hours. When the target temperature reaches 2100° C., perform step-by-step pressure reduction. The first pressure reduction time is 1 hour, from 100 mbar to 200 mbar to 50 mbar to 100 mbar. The second pressure reduction time is 1 hour, from 50 mbar to 100 mbar to 25 mbar to 50 mbar. The third pressure reduction time is 5 hours, from 25 mbar to 50 mbar to 5 mbar to 10 mbar. Keep the temperature and pressure for 90 hours to 110 hours.
[0046] (5) After step (4) is completed, the crystal growth furnace is subjected to a temperature reduction treatment and a pressure return treatment. The temperature reduction treatment includes naturally cooling the furnace to room temperature within 10 to 20 hours. The pressure return treatment includes restoring the pressure in the crystal growth furnace to 800 mbar. After the temperature reduction is completed, the internal pressure of the crystal growth furnace is released to atmospheric pressure.
[0047] (6) Open the crystal growth furnace and take out the crystal that has completed the crystal growth process.
[0048] It should be noted that the present invention reduces the microtube density of the crystal to 0.1 / cm by adopting a crystal growth process with specific steps and parameters. 2 The total number of dislocations is less than 5000. Compared with the traditional crystal growth process, the quality and yield of the crystal are greatly improved.
[0049] It should be noted that in step (1), 0.5Pa to 5Pa, for example, can be 0.5Pa, 1Pa, 2Pa, 3Pa, 5Pa, etc.; 5×10 -3 Pa~5×10 -2Pa, for example, can be 0.006Pa, 0.008Pa, 0.02Pa, 0.04Pa, 0.05Pa, etc.; in step (2), 6℃ / min~7℃ / min, for example, can be 6℃ / min, 6.5℃ / min, 7℃ / min, etc.; 1100℃~1250℃, for example, can be 1100℃, 1150℃, 1200℃, 1250℃, etc.; in step (3), 2℃ / min~3℃ / min, for example, can be 2℃ / min, 2 .5℃ / min, 3℃ / min, etc.; 1500℃~1650℃, for example, 1500℃, 1550℃, 1600℃, 1650℃, etc.; 100mL / min~200mL / min, for example, 100mL / min, 150mL / min, 200mL / min, etc.; 5mL / min~10mL / min, for example, 5mL / min, 8mL / min, 10mL / min, etc.; 1800℃~2000℃ , for example, it can be 1800°C, 1850°C, 1900°C, 2000°C, etc.; 100mbar~200mbar, for example, it can be 100mbar, 150mbar, 200mbar, etc.; in step (4), 100mbar~200mbar, for example, it can be 100mbar, 150mbar, 200mbar, etc.; 50mbar~100mbar, for example, it can be 50mbar, 80mbar, 100mbar, etc.; 25mbar~50mbar, for example, it can be 25mbar, 40mbar, 50mbar, etc.; 5mbar~10mbar, for example, it can be 5mbar, 8mbar, 10mbar, etc.; 90h~110h, for example, it can be 90h, 100h, 110h, etc.; in step (5), 10h~20h, for example, it can be 10h, 15h, 20h, etc.; but it is not limited to the listed values, and other values not listed within the numerical range are also applicable.
[0050] Compared with the prior art, the present invention has the following beneficial effects:
[0051] Through the specific design of the neck opening structure and the insulation layer on the segmented crucible, the radial temperature gradient of the growth area inside the crucible structure can be controlled, and the radial temperature field under different coil or crucible positions can be easily adjusted. Fine-tuning can be performed for different thickness stages of crystal growth, which is convenient for preparing high-quality SiC single crystals. The crucible structure can be recycled, and the insulation layer is arranged on the outside of the crucible structure, which effectively avoids corrosion from the silicon atmosphere and avoids high-frequency replacement of insulation materials, greatly improving the service life of the material.
[0052] The overall components of the crucible structure are easy to manufacture, easy to assemble, and extremely easy to industrialize. The insulation layer can be used multiple times to reduce thermal field material loss. Insulation felts of different sizes and thicknesses can be flexibly matched to adjust the radial temperature gradient while reducing the impact on the axial temperature gradient to meet various complex crystal growth needs. BRIEF DESCRIPTION OF THE DRAWINGS
[0053] Figure 1 A schematic diagram of a necked crucible structure provided in accordance with a specific embodiment of the present invention;
[0054] Figure 2 A schematic diagram of a necked crucible structure including a crucible cover provided in a specific embodiment of the present invention;
[0055] Figure 3 A schematic diagram of different insulation layer designs in a necked crucible structure provided in one specific embodiment of the present invention;
[0056] Among them, 1-upper crucible; 2-lower crucible; 3-crucible cover; 4-seed crystal holder; 5-neck opening structure; 6-equal diameter ring; 7-insulation layer; 8-central loading area; 9-annular loading area; 10-cover sheet. DETAILED DESCRIPTION
[0057] It should be understood that, in the description of the present invention, the terms "center", "longitudinal", "lateral", "up", "down", "front", "back", "left", "right", "vertical", "horizontal", "top", "bottom", "inside", "outside", etc., indicating the orientation or positional relationship are based on the orientation or positional relationship shown in the drawings, and are only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore cannot be understood as a limitation on the present invention. In addition, the terms "first", "second", etc. are only used for descriptive purposes, and cannot be understood as indicating or implying relative importance or implicitly indicating the number of technical features indicated. Therefore, the features defined as "first", "second", etc. may explicitly or implicitly include one or more of the features. In the description of the present invention, unless otherwise specified, "multiple" means two or more.
[0058] It should be noted that in the description of the present invention, unless otherwise clearly specified and limited, the terms "disposed", "connected", and "connected" should be understood in a broad sense, for example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be a direct connection, or it can be indirectly connected through an intermediate medium, or it can be the internal communication of two elements. For ordinary technicians in this field, the specific meanings of the above terms in the present invention can be understood by specific circumstances.
[0059] Those skilled in the art should understand that the present invention necessarily includes necessary pipelines, conventional valves and general pump equipment for realizing a complete process, but the above content does not belong to the main inventive point of the present invention. Those skilled in the art can add layouts on their own based on the process flow and equipment structure selection, and the present invention does not make special requirements and specific limitations on this.
[0060] The technical solution of the present invention is further described below with reference to the accompanying drawings and through specific implementation methods.
[0061] In a specific embodiment, the present invention provides a necked crucible structure, such as Figure 1 , Figure 2 As shown, the crucible structure includes a lower crucible 2 and an upper crucible 1, the upper crucible 1 is threadedly connected to the top of the lower crucible 2 to form a reaction chamber; the end of the upper crucible 1 away from the lower crucible 2 is a necked opening structure 5, and an insulation layer 7 is circumferentially arranged on the outer side of the necked opening structure 5.
[0062] In the present invention, by specifically designing the neck opening structure 5 and the insulation layer 7 on the segmented crucible, the radial temperature gradient of the growth area inside the crucible structure can be controlled, and the radial temperature field under different coil or crucible positions can be easily adjusted. Fine-tuning can be performed for different thickness stages of crystal growth, which is convenient for preparing high-quality SiC single crystals. The crucible structure can be recycled, and the insulation layer 7 is arranged on the outside of the crucible structure, which effectively avoids corrosion from the silicon atmosphere, avoids high-frequency replacement of insulation materials, and greatly improves the service life of the material.
[0063] It should be noted that the crucible structure of the present invention is based on the PVT method, and a heat-insulating layer 7 is placed outside the neck opening structure 5 to adjust the radial gradient of the crystal in the growth area inside the crucible, and the heat-insulating layer 7 used has a ring structure. The inner diameter of the heat-insulating layer 7 fits the outer diameter of the neck opening structure 5, and the outer diameter and specific thickness of the heat-insulating layer 7 can be adjusted according to actual conditions. It can be designed as a heat-insulating structure that is wide at the top and narrow at the bottom, which is used to adjust the radial gradient change during the crystal growth and thickness process. The thermal field structure can be adjusted more flexibly to meet the thermal field requirements of various complex crystal growths. At the same time, it can prevent the heat-insulating layer 7 from being disturbed by the thermal field parameters caused by the internal silicon atmosphere corrosion, protect the heat-insulating layer 7, and improve the service life of the heat-insulating felt, which greatly saves material costs.
[0064] In one embodiment, the crucible structure further includes a crucible cover 3 , which is threadedly connected to an end of the upper crucible 1 away from the lower crucible 2 .
[0065] In one embodiment, the height of the necked opening structure 5 is 45 mm to 65 mm, for example, 45 mm, 47 mm, 49 mm, 50 mm, 52 mm, 54 mm, 56 mm, 58 mm, 60 mm, etc., but is not limited to the listed values, and other unlisted values within the numerical range are also applicable.
[0066] In the present invention, the height of the necked opening structure 5 is 45 mm to 65 mm, which is mainly designed based on the height and thickness of the equal-diameter ring 6 and the seed crystal holder 4. Generally, the thickness of the crystal after growth is between 20 mm and 30 mm. The length of the equal-diameter ring 6 will be greater than the crystal thickness, between 40 mm and 50 mm, plus the thickness of the seed crystal holder 4. Therefore, the height of the necked opening structure 5 can be more conducive to crystal growth.
[0067] In one embodiment, the ratio of the inner diameter of the neck opening structure 5 to the inner diameter of the lower crucible 2 is 1:(1.4-1.6), for example, it can be 1:1.4, 1:1.45, 1:1.48, 1:1.5, 1:1.53, 1:1.56, 1:1.58, 1:1.6, etc., but is not limited to the listed values, and other unlisted values within the numerical range are also applicable.
[0068] In the present invention, the ratio of the inner diameter of the necking opening structure 5 to the inner diameter of the lower crucible 2 is 1:(1.4-1.6) because within this range it is possible to avoid the inner diameter of the lower crucible 2 being too large relative to the necking growth area, thereby causing the powder loaded in the side area to crystallize on the crucible wall of the non-necking area of the upper crucible 1.
[0069] In one embodiment, the height of the lower crucible 2 is 90 mm to 110 mm, for example, it can be 90 mm, 92 mm, 94 mm, 96 mm, 98 mm, 100 mm, 102 mm, 104 mm, 106 mm, 108 mm, 110 mm, etc., but is not limited to the listed values, and other unlisted values within the numerical range are also applicable.
[0070] In one embodiment, the height of the upper crucible 1 excluding the neck opening structure 5 is 70 mm to 90 mm, for example, 70 mm, 72 mm, 74 mm, 76 mm, 78 mm, 80 mm, 82 mm, 84 mm, 86 mm, 88 mm, 90 mm, etc., but is not limited to the listed values, and other unlisted values within the numerical range are also applicable.
[0071] In one embodiment, the thread depth of the threaded connection between the lower crucible 2 and the lower crucible 2 is 10 mm to 15 mm, for example, it can be 10 mm, 10.5 mm, 11 mm, 11.5 mm, 12 mm, 12.5 mm, 13 mm, 13.5 mm, 14 mm, 14.5 mm, 15 mm, etc., but is not limited to the listed values, and other unlisted values within the numerical range are also applicable.
[0072] In one embodiment, the inner diameter of the upper crucible 1 excluding the neck opening structure 5 is the same as the inner diameter of the lower crucible 2 .
[0073] In one embodiment, the thermal insulation layer 7 is provided with at least one layer, for example, it can be 1 layer, 2 layers, 3 layers, 4 layers, 5 layers, etc., but it is not limited to the listed values, and other unlisted values within the numerical range are also applicable.
[0074] In one embodiment, the thickness of the heat-insulating layer 7 is the same or gradually increases in a direction away from the lower crucible 2 .
[0075] In one embodiment, the material of the thermal insulation layer 7 is soft graphite felt or hard graphite felt.
[0076] In one embodiment, an annular partition layer is disposed in the lower crucible 2 , and the annular partition layer divides the interior of the lower crucible 2 into a central charging area 8 and an annular charging area 9 which are distributed in concentric circles from the center to the outside.
[0077] In one embodiment, the ratio of the diameter of the central charging area 8 to the inner diameter of the lower crucible 2 is 1:(1.4-1.6), for example, it can be 1:1.4, 1:1.45, 1:1.48, 1:1.5, 1:1.53, 1:1.56, 1:1.58, 1:1.6, etc., but is not limited to the listed values, and other unlisted values within the numerical range are also applicable.
[0078] The ratio of the diameter of the central loading area 8 to the inner diameter of the lower crucible 2 of the present invention is 1:(1.4-1.6) because it can avoid the inner diameter of the lower crucible 2 being too large relative to the necking growth area, thereby causing the powder filled in the side area to crystallize on the crucible wall of the non-neck area of the upper crucible 1, thereby ensuring the uniformity of the atmosphere.
[0079] In one embodiment, the annular separator layer is a porous graphite plate or a graphite mesh.
[0080] In one embodiment, a cover sheet 10 is provided on top of the central charging area 8 and the annular charging area 9 .
[0081] In one embodiment, the cover sheet 10 is made of porous graphite.
[0082] It should be noted that the lower crucible 2 in the present invention is a loading crucible, and its loading area is a central loading area 8 and an annular loading area 9, so as to carry out the reaction of silicon carbide powders of different particle sizes. Different areas are separated by porous graphite plates or graphite meshes. Usually, during the crystal growth process, the annular loading area 9 is close to the crucible wall, the temperature is high, and the powder is easy to sublimate. The small-particle SiC raw material sublimates quickly and is easy to produce fine carbon particles. Therefore, a larger-particle SiC powder can be loaded in the annular loading area 9 to reduce the carbon particles generated in the edge area. At the same time, a porous graphite cover sheet 10 is placed above the raw material to filter large particles. The central loading area 8 can be filled with small-particle SiC powder to increase the crystal growth rate.
[0083] In one embodiment, the thickness of the cover sheet 10 is 2 mm to 3 mm, for example, 2 mm, 2.2 mm, 2.4 mm, 2.6 mm, 2.8 mm, 3 mm, etc., but is not limited to the listed values, and other unlisted values within the numerical range are also applicable.
[0084] In one embodiment, a ring of equal diameter 6 is circumferentially arranged on the inner wall of the neck opening structure 5 , and the ring of equal diameter 6 is used to support the seed crystal holder 4 .
[0085] In one embodiment, the height of the equal diameter ring 6 is smaller than the height of the neck opening structure 5 .
[0086] It should be noted that an equal-diameter ring 6 is assembled inside the necked opening structure 5 of the upper crucible 1 to receive the seed crystal holder 4. The height of the equal-diameter ring 6 can be adjusted as needed, wherein the seed crystal and the equal-diameter ring 6 are in a non-contact state, and the seed crystal is bonded to the bottom of the seed crystal holder 4. After the assembly of the material and the seed crystal is completed, the crucible structure is placed in a crystal growth furnace, and the crucible structure is adjusted to a suitable position (relative position with the heater or induction coil) by a stepper motor, and then vacuuming, back-pressurizing, reducing pressure, heating and other crystal growth processes are carried out.
[0087] Exemplarily, the specific assembly method of the crucible structure in the present invention includes:
[0088] The lower crucible 2 is filled with silicon carbide raw materials. The powder particle size in the annular loading area 9 is 8-20 meshes, and the powder particle size in the central loading area 8 is 20-40 meshes. The material surface is 80-100 mm away from the seed crystal of the upper crucible 1. A cover sheet 10 is placed on the upper part of the powder. The upper crucible 1 and the lower crucible 2 are screwed tightly. The equal-diameter ring 6 is placed in the necking opening structure 5. The bottom is supported by the steps provided inside the upper crucible 1. The protruding part of the steps is flush with the inner diameter of the equal-diameter ring 6. The seed crystal holder 4 is placed on the equal-diameter ring 6. The seed crystal holder 4 is adapted to the equal-diameter ring 6. The assembly error does not exceed 0.1 mm. The annular insulation layer 7 is placed on the outer wall of the necking opening structure 5. After the filling is completed, the crucible cover 3 and the upper crucible 1 are screwed tightly.
[0089] In another specific embodiment, the present invention provides a crystal growth process, which is performed using a crystal growth furnace, in which the above-mentioned crucible structure is placed.
[0090] It should be noted that the present invention does not specifically limit the specific structure and model of the crystal growth furnace. Those skilled in the art can make adaptive adjustments according to actual conditions, and all crystal growth furnaces can be included in the scope of protection of the present invention.
[0091] The crystal growth process specifically includes:
[0092] (1) Place the crucible structure with the assembled materials in the crystal growth furnace, check for leaks and evacuate the crystal growth furnace. When the internal pressure drops to 0.5Pa~5Pa, turn on the molecular pump to evacuate to 5×10 -3 Pa~5×10 -2 Pa;
[0093] (2) The crystal growth furnace is heated at a rate of 6°C / min to 7°C / min. When the temperature reaches 1100°C to 1250°C, the molecular pump is turned off and the mechanical pump continues to pump gas;
[0094] (3) On the basis of step (2), heating is continued at a heating rate of 2°C / min to 3°C / min. When the temperature reaches 1500°C to 1650°C, argon and nitrogen are introduced into the crystal growth furnace at the same time. The gas flow rate of argon is 100mL / min to 200mL / min, and the gas flow rate of nitrogen is 5mL / min to 10mL / min. The gas pressure is set to 300mbar. The temperature is kept at a target temperature of 1800°C to 2000°C. The heating time is 2h, and the pressure is kept at 100mbar to 200mbar.
[0095] (4) On the basis of step (3), continue heating for 10 hours. When the target temperature reaches 2100° C., perform step-by-step pressure reduction. The first pressure reduction time is 1 hour, from 100 mbar to 200 mbar to 50 mbar to 100 mbar. The second pressure reduction time is 1 hour, from 50 mbar to 100 mbar to 25 mbar to 50 mbar. The third pressure reduction time is 5 hours, from 25 mbar to 50 mbar to 5 mbar to 10 mbar. Keep the temperature and pressure for 90 hours to 110 hours.
[0096] (5) After step (4) is completed, the crystal growth furnace is subjected to a temperature reduction treatment and a pressure return treatment. The temperature reduction treatment includes naturally cooling the furnace to room temperature within 10 to 20 hours. The pressure return treatment includes restoring the pressure in the crystal growth furnace to 800 mbar. After the temperature reduction is completed, the internal pressure of the crystal growth furnace is released to atmospheric pressure.
[0097] (6) Open the crystal growth furnace and take out the crystal that has completed the crystal growth process.
[0098] Example 1
[0099] This embodiment provides a necked crucible structure, wherein:
[0100] The crucible structure includes a lower crucible 2 and an upper crucible 1, and the upper crucible 1 is threadedly connected to the top of the lower crucible 2 to form a reaction chamber; the end of the upper crucible 1 away from the lower crucible 2 is a necked opening structure 5, and a layer of insulation layer 7 is circumferentially arranged on the outer side of the necked opening structure 5. The crucible structure also includes a crucible cover 3, which is threadedly connected to the end of the upper crucible 1 away from the lower crucible 2.
[0101] The height of the necked opening structure 5 is 45 mm, the ratio of the inner diameter of the necked opening structure 5 to the inner diameter of the lower crucible 2 is 1:1.4, the height of the lower crucible 2 is 90 mm, the height of the upper crucible 1 excluding the necked opening structure 5 is 70 mm, the thread depth of the threaded connection between the lower crucible 2 and the lower crucible 2 is 10 mm, and the inner diameter of the upper crucible 1 excluding the necked opening structure 5 is the same as the inner diameter of the lower crucible 2.
[0102] The thickness of the heat-insulating layer 7 is the same along the direction away from the lower crucible 2 , and the material of the heat-insulating layer 7 is graphite soft felt.
[0103] An annular partition layer is provided in the lower crucible 2, and the annular partition layer divides the interior of the lower crucible 2 into a central charging area 8 and an annular charging area 9 which are distributed in concentric circles from the center to the outside. The ratio of the diameter of the central charging area 8 to the inner diameter of the lower crucible 2 is 1:1.4, and the annular partition layer is a porous graphite plate. A cover sheet 10 is provided on the top of the central charging area 8 and the annular charging area 9, and the cover sheet 10 is made of porous graphite and has a thickness of 2 mm.
[0104] An equal-diameter ring 6 is circumferentially arranged on the inner wall of the necked opening structure 5 . The equal-diameter ring 6 is used to carry the seed crystal holder 4 . The height of the equal-diameter ring 6 is smaller than the height of the necked opening structure 5 .
[0105] Example 2
[0106] This embodiment provides a necked crucible structure, such as Figure 3 As shown, where:
[0107] The crucible structure includes a lower crucible 2 and an upper crucible 1, and the upper crucible 1 is threadedly connected to the top of the lower crucible 2 to form a reaction chamber; the end of the upper crucible 1 away from the lower crucible 2 is a necked opening structure 5, and three layers of insulation layers 7 are circumferentially arranged on the outer side of the necked opening structure 5. The crucible structure also includes a crucible cover 3, which is threadedly connected to the end of the upper crucible 1 away from the lower crucible 2.
[0108] The height of the necked opening structure 5 is 50 mm, the ratio of the inner diameter of the necked opening structure 5 to the inner diameter of the lower crucible 2 is 1:1.5, the height of the lower crucible 2 is 100 mm, the height of the upper crucible 1 excluding the necked opening structure 5 is 80 mm, the thread depth of the threaded connection between the lower crucible 2 and the lower crucible 2 is 12 mm, and the inner diameter of the upper crucible 1 excluding the necked opening structure 5 is the same as the inner diameter of the lower crucible 2.
[0109] The thickness of the heat-insulating layer 7 gradually increases in a direction away from the lower crucible 2 , and the material of the heat-insulating layer 7 is graphite hard felt.
[0110] An annular partition layer is provided in the lower crucible 2, and the annular partition layer divides the interior of the lower crucible 2 into a central charging area 8 and an annular charging area 9 which are distributed in concentric circles from the center to the outside. The ratio of the diameter of the central charging area 8 to the inner diameter of the lower crucible 2 is 1:1.5, and the annular partition layer is a graphite mesh. A cover sheet 10 is provided on the top of the central charging area 8 and the annular charging area 9, and the cover sheet 10 is made of porous graphite, and the thickness of the cover sheet 10 is 2.5 mm.
[0111] An equal-diameter ring 6 is circumferentially arranged on the inner wall of the necked opening structure 5 . The equal-diameter ring 6 is used to carry the seed crystal holder 4 . The height of the equal-diameter ring 6 is smaller than the height of the necked opening structure 5 .
[0112] Example 3
[0113] This embodiment provides a necked crucible structure, wherein:
[0114] The crucible structure includes a lower crucible 2 and an upper crucible 1, and the upper crucible 1 is threadedly connected to the top of the lower crucible 2 to form a reaction chamber; the end of the upper crucible 1 away from the lower crucible 2 is a necked opening structure 5, and two layers of insulation layers 7 are circumferentially arranged on the outer side of the necked opening structure 5. The crucible structure also includes a crucible cover 3, which is threadedly connected to the end of the upper crucible 1 away from the lower crucible 2.
[0115] The height of the necked opening structure 5 is 65 mm, the ratio of the inner diameter of the necked opening structure 5 to the inner diameter of the lower crucible 2 is 1:1.6, the height of the lower crucible 2 is 110 mm, the height of the upper crucible 1 excluding the necked opening structure 5 is 90 mm, the thread depth of the threaded connection between the lower crucible 2 and the lower crucible 2 is 15 mm, and the inner diameter of the upper crucible 1 excluding the necked opening structure 5 is the same as the inner diameter of the lower crucible 2.
[0116] The thickness of the heat-insulating layer 7 is the same along the direction away from the lower crucible 2 , and the material of the heat-insulating layer 7 is graphite soft felt.
[0117] An annular partition layer is provided in the lower crucible 2, and the annular partition layer divides the interior of the lower crucible 2 into a central charging area 8 and an annular charging area 9 which are distributed in concentric circles from the center to the outside. The ratio of the diameter of the central charging area 8 to the inner diameter of the lower crucible 2 is 1:1.6, and the annular partition layer is a graphite mesh. A cover sheet 10 is provided on the top of the central charging area 8 and the annular charging area 9, and the cover sheet 10 is made of porous graphite and has a thickness of 3 mm.
[0118] An equal-diameter ring 6 is circumferentially arranged on the inner wall of the necked opening structure 5 . The equal-diameter ring 6 is used to carry the seed crystal holder 4 . The height of the equal-diameter ring 6 is smaller than the height of the necked opening structure 5 .
[0119] Example 4
[0120] This embodiment provides a necked crucible structure, which is different from Embodiment 1 in that the ratio of the inner diameter of the necked opening structure 5 to the inner diameter of the lower crucible 2 is 1:1.3, and other test parameters are the same as those of Embodiment 1.
[0121] Example 5
[0122] This embodiment provides a necked crucible structure, which is different from Embodiment 1 in that the ratio of the inner diameter of the necked opening structure 5 to the inner diameter of the lower crucible 2 is 1:1.7, and other test parameters are the same as those of Embodiment 1.
[0123] Example 6
[0124] This embodiment provides a necked crucible structure, which is different from the embodiment 1 in that the height of the necked opening structure 5 is 40 mm, and other test parameters are the same as those of the embodiment 1.
[0125] Example 7
[0126] This embodiment provides a necked crucible structure, which is different from the embodiment 1 in that the height of the necked opening structure 5 is 70 mm, and the other test parameters are the same as those of the embodiment 1.
[0127] Example 8
[0128] This embodiment provides a necked crucible structure, which is different from the first embodiment in that no annular separation layer is provided, and other test parameters are the same as those of the first embodiment.
[0129] Comparative Example 1
[0130] This comparative example provides a crucible structure. The difference from Example 1 is that the crucible as a whole is of the same diameter structure, and a heat-insulating layer 7 is designed inside the crucible. Other test parameters are the same as those of Example 1.
[0131] The crucible structures in the above embodiments and comparative examples were placed in a crystal growth furnace, and the same crystal growth process was used to produce crystals. The obtained crystals were tested for corrosion dislocations, microtubes, and inclusions. The results are shown in Table 1 below.
[0132] Table 1 Test results of crystals in the embodiments and comparative examples
[0133]
[0134]
[0135] From Table 1 above, we know that:
[0136] The crystals produced by the crucible structure in Examples 1-8 are better than the crystals produced by the crucible structure in Comparative Example 1. This is because the present invention can regulate the radial temperature gradient of the growth area inside the crucible structure through the specific design of the neck opening structure 5 and the insulation layer 7 on the segmented crucible, and can easily adjust the radial temperature field under different coil or crucible positions. It can be fine-tuned for different thickness stages of crystal growth, which is convenient for preparing high-quality SiC single crystals. The insulation layer 7 is arranged on the outside of the crucible structure, which effectively avoids corrosion from the silicon atmosphere and avoids high-frequency replacement of insulation materials, greatly improving the service life of the material.
[0137] The above description is only a specific implementation mode of the present invention, but the protection scope of the present invention is not limited thereto. Those skilled in the art should understand that any changes or substitutions that can be easily thought of by those skilled in the art within the technical scope disclosed by the present invention are within the protection scope and disclosure scope of the present invention.
Claims
1. A necked crucible structure, characterized in that: The crucible structure comprises a lower crucible and an upper crucible, wherein the upper crucible is threadedly connected to the top of the lower crucible to form a reaction chamber; One end of the upper crucible away from the lower crucible is a necked opening structure, and a heat-insulating layer is arranged on the outer circumference of the necked opening structure.
2. The crucible structure according to claim 1, characterized in that: The crucible structure further comprises a crucible cover, which is threadedly connected to an end of the upper crucible away from the lower crucible.
3. The crucible structure according to claim 1 or 2, characterized in that: The height of the necked opening structure is 45 mm to 65 mm; Preferably, the ratio of the inner diameter of the neck opening structure to the inner diameter of the lower crucible is 1:(1.4-1.6).
4. The crucible structure according to any one of claims 1 to 3, characterized in that: The height of the lower crucible is 90 mm to 110 mm; Preferably, the height of the upper crucible excluding the neck opening structure is 70 mm to 90 mm; Preferably, the thread depth of the threaded connection between the upper crucible and the lower crucible is 10 mm to 15 mm.
5. The crucible structure according to any one of claims 1 to 4, characterized in that: The inner diameter of the upper crucible except the neck opening structure is the same as the inner diameter of the lower crucible.
6. The crucible structure according to any one of claims 1 to 5, characterized in that: The thermal insulation layer is provided with at least one layer; Preferably, the thickness of the insulation layer is the same or gradually increases in a direction away from the lower crucible; Preferably, the thermal insulation layer is made of soft graphite felt or hard graphite felt.
7. The crucible structure according to any one of claims 1 to 6, characterized in that: An annular partition layer is provided in the lower crucible, and the annular partition layer divides the interior of the lower crucible into a central charging area and an annular charging area which are distributed in concentric circles from the center to the outside; Preferably, the ratio of the diameter of the central charging area to the inner diameter of the lower crucible is 1:(1.4-1.6); Preferably, the annular separation layer is a porous graphite plate or a graphite mesh; Preferably, a cover sheet is provided on the top of the central loading area and the annular loading area; Preferably, the cover sheet is made of porous graphite; Preferably, the cover sheet has a thickness of 2 mm to 3 mm.
8. The crucible structure according to any one of claims 1 to 7, characterized in that: An equal-diameter ring is circumferentially arranged on the inner wall of the necked opening structure, and the equal-diameter ring is used to carry the seed crystal holder; Preferably, the height of the equal-diameter ring is smaller than the height of the necked opening structure.
9. A crystal growth process, characterized in that: The crystal growth process is carried out in a crystal growth furnace, and the crucible structure according to any one of claims 1 to 8 is placed in the crystal growth furnace.
10. The crystal growth process according to claim 9, characterized in that: The crystal growth process comprises: (1) Place the crucible structure with the assembled materials in the crystal growth furnace, check for leaks and evacuate the crystal growth furnace. When the internal pressure drops to 0.5Pa~5Pa, turn on the molecular pump to evacuate to 5×10 -3 Pa~5×10 -2 Pa; (2) The crystal growth furnace is heated at a rate of 6°C / min to 7°C / min. When the temperature reaches 1100°C to 1250°C, the molecular pump is turned off and the mechanical pump continues to pump gas; (3) On the basis of step (2), heating is continued at a heating rate of 2°C / min to 3°C / min. When the temperature reaches 1500°C to 1650°C, argon and nitrogen are introduced into the crystal growth furnace at the same time. The gas flow rate of argon is 100mL / min to 200mL / min, and the gas flow rate of nitrogen is 5mL / min to 10mL / min. The gas pressure is set to 300mbar. The temperature is kept at a target temperature of 1800°C to 2000°C. The heating time is 2h, and the pressure is kept at 100mbar to 200mbar. (4) On the basis of step (3), continue heating for 10 hours. When the target temperature reaches 2100° C., perform step-by-step pressure reduction. The first pressure reduction time is 1 hour, from 100 mbar to 200 mbar to 50 mbar to 100 mbar. The second pressure reduction time is 1 hour, from 50 mbar to 100 mbar to 25 mbar to 50 mbar. The third pressure reduction time is 5 hours, from 25 mbar to 50 mbar to 5 mbar to 10 mbar. Keep the temperature and pressure for 90 hours to 110 hours. (5) After step (4) is completed, the crystal growth furnace is subjected to a temperature reduction treatment and a pressure return treatment. The temperature reduction treatment includes naturally cooling the furnace to room temperature within 10 to 20 hours. The pressure return treatment includes restoring the pressure in the crystal growth furnace to 800 mbar. After the temperature reduction is completed, the internal pressure of the crystal growth furnace is released to atmospheric pressure. (6) Open the crystal growth furnace and take out the crystal that has completed the crystal growth process.