WO2023201934A1 - 基于pvt法生长碳化硅单晶的设备及方法 - Google Patents

基于pvt法生长碳化硅单晶的设备及方法 Download PDF

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Publication number
WO2023201934A1
WO2023201934A1 PCT/CN2022/111456 CN2022111456W WO2023201934A1 WO 2023201934 A1 WO2023201934 A1 WO 2023201934A1 CN 2022111456 W CN2022111456 W CN 2022111456W WO 2023201934 A1 WO2023201934 A1 WO 2023201934A1
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crucible
lifting rod
growth
storage
crystal
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PCT/CN2022/111456
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English (en)
French (fr)
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马远
薛卫明
潘尧波
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中电化合物半导体有限公司
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Publication of WO2023201934A1 publication Critical patent/WO2023201934A1/zh

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    • C—CHEMISTRY; METALLURGY
    • C30—CRYSTAL GROWTH
    • C30B—SINGLE-CRYSTAL GROWTH; UNIDIRECTIONAL SOLIDIFICATION OF EUTECTIC MATERIAL OR UNIDIRECTIONAL DEMIXING OF EUTECTOID MATERIAL; REFINING BY ZONE-MELTING OF MATERIAL; PRODUCTION OF A HOMOGENEOUS POLYCRYSTALLINE MATERIAL WITH DEFINED STRUCTURE; SINGLE CRYSTALS OR HOMOGENEOUS POLYCRYSTALLINE MATERIAL WITH DEFINED STRUCTURE; AFTER-TREATMENT OF SINGLE CRYSTALS OR A HOMOGENEOUS POLYCRYSTALLINE MATERIAL WITH DEFINED STRUCTURE; APPARATUS THEREFOR
    • C30B29/00—Single crystals or homogeneous polycrystalline material with defined structure characterised by the material or by their shape
    • C30B29/10—Inorganic compounds or compositions
    • C30B29/36—Carbides
    • C—CHEMISTRY; METALLURGY
    • C30—CRYSTAL GROWTH
    • C30B—SINGLE-CRYSTAL GROWTH; UNIDIRECTIONAL SOLIDIFICATION OF EUTECTIC MATERIAL OR UNIDIRECTIONAL DEMIXING OF EUTECTOID MATERIAL; REFINING BY ZONE-MELTING OF MATERIAL; PRODUCTION OF A HOMOGENEOUS POLYCRYSTALLINE MATERIAL WITH DEFINED STRUCTURE; SINGLE CRYSTALS OR HOMOGENEOUS POLYCRYSTALLINE MATERIAL WITH DEFINED STRUCTURE; AFTER-TREATMENT OF SINGLE CRYSTALS OR A HOMOGENEOUS POLYCRYSTALLINE MATERIAL WITH DEFINED STRUCTURE; APPARATUS THEREFOR
    • C30B23/00—Single-crystal growth by condensing evaporated or sublimed materials

Definitions

  • the present invention relates to the technical field of silicon carbide single crystal growth, and in particular to an equipment and method for growing silicon carbide single crystal based on the PVT method.
  • SiC silicon carbide
  • the main growth methods of silicon carbide single crystal include physical vapor transport method (PVT), high-temperature chemical vapor deposition method and solution method.
  • PVT physical vapor transport method
  • the PVT method has gradually become the standard method for growing silicon carbide single crystals due to its higher growth rate, more stable growth process and cost advantages.
  • the growth process of the PVT method mainly involves the sublimation of polycrystalline silicon carbide under high temperature and low pressure conditions, and the generated gas phase components (mainly Si, Si 2 C, SiC 2 ) reach the lower temperature seed crystal driven by the temperature gradient. , generating supersaturation and crystallizing on the seed crystal to continuously grow single crystals.
  • silicon carbide powder is generally placed at the bottom of the graphite crucible, and the silicon carbide seed crystal is placed near the crucible cover.
  • the crucible is heated by radio frequency induction and insulated by graphite felt or porous graphite to generate a certain temperature. Gradient, the gas phase components that sublimate driven by the temperature gradient can condense and crystallize on the seed crystal to obtain silicon carbide single crystal.
  • the 6-inch silicon carbide crystal that dominates large-scale production has a raw material utilization rate of about 40%. That is, 3kg of raw material can produce a 6-inch crystal with a thickness of about 20mm and a weight of about 1.2kg.
  • the crucible diameter is between 150mm and 200mm. Between them, under typical thermal field design conditions, the temperature difference between the center of the raw material and the edge of the raw material is close to 12 degrees Celsius.
  • relevant domestic literature has shown (Reference: Lu Jiazheng, Zhang Hui, Zheng Lili, Ma Yuan, et al. Design and optimization of thermal field for large-size resistance heating silicon carbide crystal growth[J] . Journal of Artificial Crystallography.
  • the difference between the center temperature of the raw material and the temperature near the inner wall of the crucible will be greater than 15 degrees Celsius. Due to this temperature difference, when the gas phase raw material rises from the bottom of the crucible to the center, the gas phase reaches saturation and is in the upper layer. The crystallization on the raw material cannot reach the crystal growth interface, resulting in a decrease in raw material utilization; at the same time, due to the agglomeration of the middle and upper raw materials and the evaporation of the lower raw materials, the agglomerated parts will suddenly collapse during the crystal growth process, causing a sudden change in the heat transfer mechanism, causing Crystal quality issues.
  • This method can indeed produce to produce more crystals, but as the crystal size continues to increase, it may not always work; for example, in some plans, graphite columns are used to disperse the raw materials in the crucible (refer to Chinese patent CN202111361145.0) to avoid the crystallization of the gas phase raw materials in the raw material area, but The size of the uniform temperature zone in the crucible is fixed, so the amount of feed is limited.
  • the purpose of the present invention is to provide an equipment and method for growing silicon carbide single crystal based on the PVT method to solve the problem of raw material utilization in the silicon carbide single crystal growth technology in the prior art.
  • Low there is a large temperature difference between the edge and center of the crucible, and the crystal quality is reduced due to the collapse of the crystalline part.
  • the present invention provides a device for growing silicon carbide single crystal based on the PVT method, including a growth chamber, a crucible, a lifting rod and a silo for carrying raw materials.
  • the crucible, lifting rod and The silos are all located in the growth chamber; the silos are located in the crucible, and the silos include a plurality of mutually independent storage bins; the lifting rod passes upward from the bottom of the crucible through the bottom of the storage bins and extends to By lifting the lifting rod up and down on the top of the storage bin, the top of the storage bin can be sealed or the gas phase raw material channel can be ejected from the sealed top of the storage bin.
  • the top of the storage bin is provided with an exhaust hole as a gas-phase raw material passage
  • the top of the lifting rod is provided with an end surface matching the exhaust hole, and the lifting rod is raised When the end surface is against the exhaust hole, the exhaust hole can be sealed, and the lifting rod is lowered to the end surface away from the exhaust hole, so that the storage chamber can discharge the gas phase raw material through the exhaust hole.
  • the diameter of the exhaust hole is 0.1mm-5mm, and the lower part of the exhaust hole is provided with a tapered surface that matches the top end surface of the lifting rod, and the cone angle of the tapered surface is 5°-85°. .
  • the top of the lifting rod is provided with a boss with a height of 1mm-5mm and a diameter of 1mm-10mm, and a tapered surface matching the tapered surface of the exhaust hole is connected below the boss.
  • the top of the storage bin is sealed by a thin graphite cover and/or several layers of graphite paper.
  • the thickness of the graphite cover is 0.1mm-2mm.
  • the end surface of the lifting rod is arc-shaped, and the roughness of the end surface is not greater than 1.6um.
  • each storage chamber is a concentric circular ring structure or a concentric polygonal ring structure, and is arranged sequentially from the inside to the outside of the crucible according to the inner diameter; or the planar shape of each storage chamber is selected from triangles. , quadrilateral, hexagonal and circular, and each storage bin is arranged in a honeycomb shape.
  • the top of the silo is in a parabolic shape with a low middle and high edges.
  • the side wall thickness of the crucible is 5mm-25mm
  • the side wall thickness of the storage chamber is 0.5mm-3mm
  • the lifting rod is a graphite rod with a diameter of 2mm-15mm.
  • the bottom of the crucible is provided with a number of threaded holes.
  • a number of lifting rods are arranged in the threaded holes one by one to match the threads of the bottom of the crucible. By adjusting the length of the threads of the lifting rod and the bottom of the crucible, the lifting rod can be realized. of lifting.
  • the invention also provides a method for growing silicon carbide single crystal based on the PVT method, which includes:
  • the raw material storage capacity of different storage bins is adjusted to It can selectively reduce the amount of C released into the gas phase raw material of the storage chamber below the facet, thereby achieving non-axisymmetric concentration growth under an axisymmetric temperature distribution.
  • the initial atmosphere in the thermal field has a pressure of 500mbar-800mbar, heat the crucible to 2200-2450°C, and after stabilizing for 30min-5h, use 1h-15h to reduce the pressure to 0.5mbar. to 50mbar; the first and second times are both 5h-50h; after completing the single crystal growth, inflate the thermal field to 100mbar-600mbar, reduce the heating power to 0 for 5h-10h, cool to room temperature naturally, and then take it out crystal.
  • the silicon carbide single crystal grown by the method is greater than or equal to 8 inches, and the thickness of the single crystal is greater than or equal to 15 mm.
  • the equipment and method for growing silicon carbide single crystal based on the PVT method of the present invention have the following beneficial effects: the improved structural design of the present invention divides the silo into multiple independent storage silos.
  • lift rods are used to release gas-phase raw material channels at the top of different storage chambers, thereby realizing the gradual evaporation of raw materials in different temperature zones, ensuring that the concentration of each component remains basically the same throughout the single crystal growth process; therefore The raw materials at the low temperature in the center can also be fully utilized in the later stages of crystal growth.
  • the utilization rate of raw materials can be increased by more than 10%.
  • asymmetric growth can be more effectively achieved to suppress defects, and crystal cracking caused by stress asymmetry can be effectively avoided, which can significantly improve the quality of crystal growth.
  • Figure 1 shows a typical gas phase transport diagram in a crucible in the comparative example.
  • Figure 2 shows a typical crucible isotherm diagram in the comparative example.
  • Figure 3 shows the defect distribution diagram under the non-axisymmetric temperature distribution in the comparative example.
  • Figure 4 shows a schematic diagram of an exemplary equipment structure in Embodiment 1 of the present invention.
  • Figure 5 shows an exemplary top view of the silo in Embodiment 1 of the present invention.
  • Figure 6 is a schematic diagram showing the positional relationship between the storage bin and the lifting rod in Embodiment 1 of the present invention.
  • FIG. 7 is a partially enlarged schematic view of the positional relationship between the storage bin and the lifting rod in Embodiment 2 of the present invention.
  • Figure 8 shows a defect distribution diagram of asymmetric growth with axially symmetric temperature distribution in Example 2 of the present invention.
  • Figure 9 shows a schematic diagram of the top of the graphite paper sealed storage compartment in Embodiment 3 of the present invention.
  • spatial relationship words such as “below”, “below”, “below”, “below”, “above”, “on”, etc. may be used herein to describe an element or element shown in the drawings.
  • a layer is referred to as being “between” two layers, it can be the only layer between the two layers, or one or more intervening layers may also be present.
  • structures described as having a first feature "on" a second feature may include embodiments in which the first and second features are formed in direct contact, as well as may include additional features formed between the first and second features. Embodiments between second features such that the first and second features may not be in direct contact.
  • the present invention provides an equipment for growing silicon carbide single crystal based on the PVT method, including a growth chamber 21, a crucible 22, a lifting rod 24 and a silo 23 for carrying raw materials.
  • the lifting rod 24 and the material bin 23 are both located in the growth cavity 21; the material bin 23 is located in the crucible 22, and the material bin 23 includes a plurality of mutually independent material storage chambers 231.
  • This The concept of "mutual independence" mainly means that the raw materials stored in each storage warehouse 231 do not contact each other and do not interfere with each other during the supply process. Therefore, during the single crystal growth process, specific storage warehouses 231 can be selected as needed.
  • each storage bin 231 can be an independent entity that is detachable physically.
  • Each storage bin 231 can also be integrally connected to each other, or each storage bin 231 can also be described as A complete silo 23 is divided into multiple independent and closed areas by spacing materials.
  • each storage silo 231 is not strictly limited; the lifting rod 24 passes upward from the bottom of the crucible 22 Through the bottom of the storage bin 231 (the bottom of the storage bin 231 is sealed) and extending to the top 234 of the storage bin 231, by lifting the lifting rod 24 up and down, the storage bin can be The top 234 of 231 is sealed or the gas phase raw material channel is ejected from the sealed top of the storage bin 231; that is, depending on the specific shape of the top of the storage bin 231, the results of the lifting of the lifting rod 24 are also different.
  • the top 234 of the storage chamber 231 is provided with an exhaust hole 235 as a gas phase raw material passage, and the top of the lifting rod 24 is provided with an end surface matching the exhaust hole 235.
  • the lifting rod 24 is raised until the end surface is against the exhaust hole 235, so that the exhaust hole 235 can be sealed.
  • the lifting rod 24 is lowered until the end surface of the lifting rod 24 is away from the exhaust hole 235, so that The storage chamber 231 can discharge the gas phase raw material through the exhaust hole 235; and in another example, the top 234 of the storage chamber 231 is originally closed, for example, through a graphite thin cover 233 (refer to Figure 7 (shown in Figure 9), more specifically, for example, through an isobaric graphite thin cover, or through a single or multiple layers of graphite paper 232 to achieve sealing, or as shown in Figure 9, using both graphite thin cover 233 and graphite paper 232 to achieve sealing;
  • a hole serving as the gas phase raw material channel is formed on the top 234 of the storage chamber 231, for example, in the graphite cover and/or graphite paper.
  • the improved structural design of the present invention divides the silo into multiple independent storage silos.
  • a lifting rod is used to release gas phase raw material channels at the top of different storage silos, thereby achieving Raw materials in different temperature zones are gradually evaporated to ensure that the concentration of each component remains basically the same throughout the entire single crystal growth process; because the raw materials at the low temperature in the center can also be fully utilized in the later stages of crystal growth, compared with using existing equipment, the utilization of raw materials The rate can be increased by more than 10%.
  • asymmetric growth can be more effectively achieved to suppress defects, and crystal cracking caused by stress asymmetry can be effectively avoided, which can significantly improve the quality of crystal growth.
  • the diameter of the exhaust hole 235 is preferably 0.1mm-5mm, and in a further example, as shown in Figure 5
  • the lower part of the exhaust hole 235 is provided with a tapered surface that matches the top end surface of the lifting rod 24.
  • the cone angle of the tapered surface is, for example, 5°-85°, more preferably 30°-60°; and in order to make the lift
  • the rod 24 better matches the exhaust hole 235.
  • the top of the lifting rod 24 is provided with a boss with a height of 1mm-5mm and a diameter of 1mm-10mm. The lower part of the boss is connected to the row of the exhaust hole 235.
  • the tapered surface of the air hole 235 matches the tapered surface.
  • the tapered surface at the top of the lifting rod 24 is also a conical surface, for example, and the cone angle is, for example, 5°-85°, more preferably 30°-60°.
  • the thickness of the thin graphite cover is preferably 0.1mm-2mm (including the endpoint value.
  • endpoint values such as 0.1mm, 0.5mm, 1mm, 2mm or any value in this range.
  • the thin graphite cover 233 can be located below the graphite paper 232, and the size of the graphite paper 232 is consistent with the size of the top opening of the storage bin 231, that is, graphite The paper 232 seals the top of the storage bin 231, and the size of the graphite cover 233 is smaller than the size of the top opening of the storage bin 231.
  • the graphite cover 233 can be a circle slightly larger than the end face size of the lifting rod 24 in contact with it.
  • the end surface of the lifting rod 24 is preferably arc-shaped, and the roughness Ra of the end surface is not greater than 1.6um, so that the lifting rod 24 can eject a relatively small space at the top of the storage bin 231 Regular holes; when the lift rod 24 rises, it first contacts the graphite cover 233.
  • the graphite cover 233 is pressured by the lift rod 24 and transmits the force to the graphite paper 232, so that the graphite paper 232 corresponds to the part of the graphite cover 233.
  • the rupture forms holes that act as channels for the gas phase feedstock.
  • the top of the storage chamber 231 can be prevented from being completely broken at once, and the size of the holes can be better controlled, thereby better controlling the release of gas phase raw materials, which helps to improve the utilization rate of raw materials and the quality of single crystal growth. .
  • each storage chamber 231 is a concentric annular structure or a concentric polygonal annular structure, and is arranged sequentially from the inside to the outside of the crucible 22 according to the inner diameter.
  • the planar shape of each storage bin 231 is selected from several types including triangle, quadrilateral, hexagon and circle, and each storage bin 231 is arranged in a honeycomb shape. cloth, and the shapes of the multiple storage bins 231 of the same bin 23 can be the same or different.
  • the number of storage bins 231 and the specific size of each storage bin 231 can be set as needed, and there is no strict restriction on this, but it is preferably divided into at least three storage bins 231 to correspond to the bins respectively.
  • the top of the bin 23 is a parabola with a low middle and a high edge (refer to Figure 4) to correspond to the isotherm cloud diagram of the crucible 22 during the single crystal growth process, thereby enabling better control.
  • Thermal field distribution improves raw material utilization.
  • the storage bin 231 and the lifting rod 24 may have a one-to-one correspondence, that is, each storage bin 231 is provided with a lifting rod 24. In other examples, there may be a single storage bin 231. A plurality of lifting rods 24 are provided correspondingly. For example, when the storage bin 231 has the aforementioned annular structure, the lifting rods 24 can be provided in different corresponding areas of the same storage bin 231, or as needed, only Lifting rods 24 are provided in part of the storage bins 231. This is not strictly limited in this embodiment, but it is preferable to provide at least one lifting rod 24 corresponding to each storage bin 231.
  • the lifting rod 24 needs to be made of high-temperature and corrosion-resistant materials to avoid impurity contamination due to corrosion and wear of the lifting rod 24 .
  • the lifting rod 24 is a graphite rod, that is, made of pure graphite, and its diameter (dimensions except the end face) is preferably 2 mm to 15 mm.
  • the thickness of the side wall of the crucible 22 is preferably 5 mm-25 mm, and the thickness of the side wall of the storage chamber 231 is preferably 0.5 mm-3 mm.
  • the lifting and lowering of the lifting rod 24 can be manually adjusted or mechanically controlled, preferably mechanically controlled.
  • a number of threaded holes are provided at the bottom of the crucible 22, and the bottom of the crucible 22 thread-seales the bottom of each storage chamber 231.
  • a through hole is provided at the bottom of each storage chamber 231, and the lifting rod 24 and the bottom of the crucible 22 The threads match and penetrate from the bottom of the crucible 22 into the through holes of each storage chamber 231 to form a piston structure.
  • the lifting rod 24 can be raised and lowered, for example, by The lifting rod 24 is raised and lowered by mechanically rotating the thread.
  • an elastic structure such as a bellows connected to the bottom of the crucible 22 can also be provided in the crucible 22 .
  • the lifting rod 24 passes through the bellows from the bottom of the crucible 22 and extends upward to the storage chamber 231 to ensure that the storage chamber 231 is stored.
  • the top of the silo chamber 231 is sealed, and a lifting device (such as a piston rod of a cylinder) is used to lift the lifting rod 24 from the bottom of the lifting rod 24.
  • the lifting of the lifting rod 24 can also be adjusted.
  • the equipment also includes structures such as heaters and heat insulation devices. Since this part is not the focus of the present invention, it will not be discussed in detail.
  • the equipment provided by the present invention can effectively avoid the non-uniformity of raw material transportation caused by the radial temperature gradient caused by the increase in crucible size, and at the same time facilitate the transportation of axially symmetrical or non-axially symmetrical raw materials, especially for crystals with a diameter exceeding 8 inches. Crystal growth with a thickness exceeding 15mm can effectively improve raw material utilization while providing stable process conditions.
  • the present invention also provides a method for growing silicon carbide single crystal based on the PVT method.
  • This method is particularly suitable for the growth of large-sized silicon carbide single crystals, for example, suitable for growing silicon carbide single crystals greater than or equal to 8 inches and with a single crystal thickness greater than or equal to 15 mm.
  • the method includes:
  • the lifting rod 24 is inserted upward from the bottom of the crucible 22 into the storage bin 231, and extends to the top of the storage bin 231, so that the storage bin The top of the chamber 231 remains sealed; in this step, the seed crystal holder 25 with the 8-12 inch silicon carbide seed crystal 26 can be fixed on the growth chamber 21 first, and then the lifting rod 24 is inserted into each storage bin 231 , and add a total of 3.5kg-12kg of raw materials (depending on the specifications of the silicon carbide single crystal to be grown), put the entire silo 23 into the crucible 22, and use the threads at the bottom of the crucible 22 to seal each storage silo 231, and then Fix the crucible 22 and the growth chamber 21, and put the entire crucible 22 into the thermal field;
  • steps 2) and 3) include: after placing the crucible 22 in the thermal field, the initial atmosphere in the thermal field is at a pressure of 500mbar-800mbar, heating the crucible 22 to 2200-2450°C, and then stabilizing for 30min-5h , use 1h-15h to reduce the pressure in the thermal field to 0.5mbar to 50mbar; adjust the height of the lifting rod 24 so that the top of the storage chamber 231 near the edge of the crucible 22 releases the gas phase raw material, and the surface of the seed crystal 26 begins to nucleate After stable growth for 5h-50h; increase the temperature by 0-50°C (if the outside temperature is high enough, the inside will have begun to evaporate without heating up, but because the inside crucible 22 is sealed, the raw materials cannot come out.
  • the temperature needs to be gradually raised , in order to achieve gradual evaporation from the outside to the inside, that is, this temperature rise step is optional according to process needs), so that the top of the silo 23 near the center releases the gas phase raw material and grows stably for 5h-50h again; preferably, when using silicon carbide
  • the seed crystal 26 grows a crystal with a deflection angle of C direction [0001] and A direction [1120] greater than 2°
  • the amount of gas phase raw material released from C to the storage chamber 231 below the facet can be selectively reduced, for example, in C There are several storage warehouses 231 facing downwards.
  • the opposite storage warehouse 231 may hold no material, or the opposite storage warehouse 231 may hold less material, or the opposite storage warehouse 231 may hold less material. Put less of some of them, or not put them at all, that is, by adjusting the raw material storage amounts of different storage bins 231, you can selectively reduce the amount of gas phase raw materials released by C to the storage bin 231 below the facet, thereby Achieve non-axisymmetric concentration growth in axisymmetric temperature distribution;
  • an inert gas such as argon
  • an inert gas such as argon
  • the gas phase raw material 17 in the high-temperature zone 12 of the crucible gradually diffuses to the seed crystal 13, and at the same time, it also continuously solidifies in the low-temperature zone 14.
  • the high-temperature zone 12 is completely cavitated, and the solidified raw materials in the low-temperature zone will suddenly fall into the high-temperature zone 12, causing a sudden change in the crystal growth conditions.
  • the silicon carbide composition in the crystal growth area 16 is also constantly changing. In the early stage of decomposition of the raw materials, silicon-rich gas phase raw materials are released to nucleate.
  • the crystal is not axially symmetrical, so there is The solution is to use an asymmetric thermal field to adapt to the asymmetric crystal, so that the defects will be less at one end and more at the other, resulting in a high probability of cracking of the generated crystal.
  • a device with multiple independent storage chambers 231 for example, including the third A storage warehouse 231a, a second storage warehouse 231b, a third storage warehouse 231c, a fourth storage warehouse 231d and a fifth storage warehouse 231e.
  • Each storage warehouse is located in the crucible 22 according to the inner diameter.
  • the bin 23 is arranged concentrically from the inside to the outside), and the top surface of the bin 23 presents a parabolic shape with a low middle and a high edge.
  • the silicon carbide single crystal growth steps in this embodiment include:
  • the top 234 of the storage bin 231 is provided with an exhaust hole 235 with a diameter of 2 mm as a gas phase raw material channel, and an exhaust hole 235 is provided below the exhaust hole 235.
  • step (4) Repeat step (4) until the first to fifth storage chambers 231a to 231e in the crucible are released in sequence;
  • the thickness of the 8-inch silicon carbide crystal obtained reached 24mm, the mass reached 3.2kg, and the conversion efficiency of raw materials reached 64%.
  • formula 1 is the formula for the decomposition and generation of silicon carbide
  • formula 2 is the thermophoretic force formula of particles, where F ⁇ is the thermophoretic force, R is the radius of graphite powder, and Cs is the thermal slip coefficient. is the temperature gradient, ⁇ is the density of graphite, T is the temperature, Cm is the momentum exchange coefficient, and ⁇ is the free path of gas molecules.
  • step (4) Repeat step (4) until the raw materials in all storage compartments are released sequentially from outside to inside;
  • the silicon carbide crystal with a diameter of 200mm has a thickness of 22mm and a mass of about 2.9kg. Due to the increased diffusion area of the raw material, there are fewer inclusions in the crystal. At the same time, refer to the asymmetric growth of the axially symmetric temperature distribution in Figure 8. It can be seen from the defect distribution diagram that this embodiment uses an axially symmetric temperature distribution to achieve asymmetric growth, which can effectively reduce microscopic defects in the crystal.
  • the storage bin 231 adopts the structure shown in Figure 9 for top closure, including Sealed graphite paper 232 of 1mm and graphite sheet 233 with a diameter of 5mm and a thickness of 2mm.
  • the graphite sheet 233 is located below the graphite paper 232, so it will first contact the lifting rod 24.
  • the top of the lifting rod 24 is arc-shaped and has a roughness of 1.6 um; during the growth process, the lifting rod 24 exerts pressure on the graphite sheet 233, which can ensure that the graphite paper 232 has an opening surface of at least 5mm in diameter, ensuring that each storage bin has a relatively consistent raw material evaporation area, thereby further stabilizing the process.
  • the improved structural design of the present invention divides the silo into multiple independent storage silos.
  • the lifting rod is used to release the gas phase at the top of the different storage silos.
  • raw material channels thereby realizing the gradual evaporation of raw materials in different temperature zones, ensuring that the concentration of each component remains basically consistent during the entire single crystal growth process; because the raw materials at the low temperature in the center can also be fully utilized in the later stages of crystal growth, compared with the existing The utilization rate of equipment and raw materials can be increased by more than 10%.
  • the present invention effectively overcomes various shortcomings in the prior art and has high industrial utilization value.

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Abstract

一种基于PVT法生长碳化硅单晶的设备及方法，设备包括生长腔体、坩埚、升降杆和用于承载原料的料仓，所述坩埚、升降杆和料仓均位于生长腔体内；所述料仓位于所述坩埚内，料仓包括多个相互独立的存料仓室；升降杆由坩埚底部向上穿过所述存料仓室的底部并延伸至存料仓室的顶部，通过上下升降所述升降杆，可将所述存料仓室的顶部密封或在存料仓室的密封顶部顶出气相原料通道。可根据单晶不同生长阶段的需要，利用升降杆在不同的存料仓室顶部释放出气相原料通道，从而实现不同温区的原料逐步蒸发，确保整个单晶生长过程中，各组分浓度基本保持一致，有助于提高原料利用率和提高晶体生长质量。

Description

基于PVT法生长碳化硅单晶的设备及方法 技术领域
本发明涉及碳化硅单晶生长技术领域，特别是涉及一种基于PVT法生长碳化硅单晶的设备及方法。
背景技术
第三代半导体材料逐渐成为新一代信息技术的核心支撑。随着半导体技术的不断革新，第三代宽禁带材料中的碳化硅(SiC)由于自身材料的优良特性和SiC器件呈现出的巨大应用前景而得到飞速发展，使得SiC晶体的生长以及相关器件的研究一直是国内外的前沿研究热点，国外已有企业宣布8英寸碳化硅进入投产阶段。
碳化硅单晶的生长方法主要有物理气相传输法(physical vapor transport method，PVT)、高温化学气相沉积法和溶液法等。目前，PVT法因其较高的生长速率、较为稳定的生长工艺和成本优势逐渐成为碳化硅单晶生长的标准方法。PVT法的生长过程主要包括多晶碳化硅在高温低压的条件下升华，产生的气相组分(主要为Si，Si 2C，SiC 2)在温度梯度的驱动下到达较低温度的籽晶处，产生过饱和度而在籽晶上结晶不断生长单晶。PVT法生长单晶过程中，一般是将碳化硅粉料放置在石墨坩埚底部，碳化硅籽晶放置在坩埚埚盖附近，坩埚通过射频感应加热，通过石墨毡或多孔石墨绝热，产生一定的温度梯度，在温度梯度的驱动下升华的气相组分可以在籽晶上凝结并结晶得到碳化硅单晶。
目前规模化生产占主导地位的6英寸碳化硅晶体，其原料利用率在40％左右，即3kg原料可获厚度为20mm左右，重量在1.2kg左右的6英寸晶体，其坩埚直径在150mm-200mm之间，典型的热场设计条件下，原料中心与原料边缘温度相差接近12摄氏度。而对于8英寸以上的碳化硅晶体生长，国内已有相关文献表明(参考文献：卢嘉铮,张辉,郑丽丽,马远,等.大尺寸电阻加热式碳化硅晶体生长热场设计与优化[J].人工晶体学报.2022.)，坩埚直径超过200mm，原料中心温度与靠近坩埚内壁的温度差将大于15摄氏度，由于此温差，当气相原料从坩埚底部上升到中心时，气相达到饱和并在上层原料上结晶，无法到达晶体生长界面处，造成原料利用率的下降；同时由于中上部原料结块，下部原料蒸发，晶体生长过程中，结块部分会突然垮塌，造成传热机制的突变，引起晶体质量问题。
另一方面，由于4H型碳化硅多采用C向[0001]晶面与A向[1120]晶面(即[0001]和[1120]都表示碳化硅单晶的晶面，下同)偏转4度生长，且有研究及相关技术证实非对称生长更有有利于减少晶体中某些缺陷的增生(张福生,杨昆,刘新辉,等.无微管缺陷六英寸碳化硅单晶的 制备[J].硅酸盐学报,2021.，U.S.Pat.No.7,364,617B2)。然而，此种非对称温度分布的生长方式，给超过8英寸的晶体生长产生了更多的非对称热应力的分布，增加了晶体开裂的几率。
在碳化硅晶体直径达到100mm时，已有不少公司遇到原料利用率下降和由于结晶部分垮塌造成晶体质量降低的情况，为此Cree公司提供了相关的技术方案(参考美国专利U.S.Pat.No.8,741,413B2)，随着国内碳化硅晶体产业的发展，有越来越多的方案解决此类问题，如将原料置于等温区，以尽量避免原料边缘与中心存在较大的温差(参考中国专利CN111424320A)、原料低温处布置发热装置以减少温差(参考中国专利CN201921527970.1和CN201610175716.4)，这些方案虽然可以一定程度缓解中心与边缘温差引起的气相原料过早达饱和的问题，然而面对8英寸以上，厚度超过20mm的晶体，其投料空间就不足以支撑晶体生长；又如有些方案中将少量原料置于均温区，利用载气将原料带入生长区(参考中国专利CN202111448112.X和CN202111446990.8)，这类方案与CVD法有异曲同工之好处，但CVD的原料由有机气源提供，其浓度不随生长时间发生明显改变，且生长厚度仅以微米计算，而PVT法无法保证各组分随时间一致，因此也不能获得稳定的大尺寸晶体生长；又如有些方案中通过增加原料密度(参考中国专利CN202120267484.1)来提高单位体积原料的晶体产量，这种方法确实可以产出更多晶体，但随着晶体尺寸不断增加恐怕无法一直奏效；又如有些方案中，利用石墨柱将原料分散于坩埚内(参考中国专利CN202111361145.0),避免气相原料在原料区结晶，但坩埚内均温区尺寸是固定的，因而投料量受限。
此外，上述技术方案均未解决非对称热场对晶体产生非对称应力的问题。
发明内容
鉴于以上所述现有技术的缺点，本发明的目的在于提供一种基于PVT法生长碳化硅单晶的设备及方法，用于解决现有技术中的碳化硅单晶生长技术存在的原料利用率低、坩埚边缘与中心存在较大温差、由于结晶部分垮塌造成晶体质量降低等问题，尤其是在用于超过8英寸的碳化硅单晶生长时会产生更多的非对称热应力的分布，增加晶体开裂几率等问题。
为实现上述目的及其他相关目的，本发明提供一种基于PVT法生长碳化硅单晶的设备，包括生长腔体、坩埚、升降杆和用于承载原料的料仓，所述坩埚、升降杆和料仓均位于生长腔体内；所述料仓位于所述坩埚内，料仓包括多个相互独立的存料仓室；升降杆由坩埚底部向上穿过所述存料仓室的底部并延伸至存料仓室的顶部，通过上下升降所述升降杆，可将所述存料仓室的顶部密封或在存料仓室的密封顶部顶出气相原料通道。
在一可选方案中，所述存料仓室的顶部设置有作为气相原料通道的排气孔，所述升降杆 顶部设置有与所述排气孔相匹配的端面，将所述升降杆上升至端面抵住所述排气孔，可将所述排气孔密封，将所述升降杆下降至端面远离所述排气孔，使得所述存料仓室可以通过所述排气孔排出气相原料。
更可选地，所述排气孔的直径为0.1mm-5mm，排气孔的下部设置有与升降杆的顶部端面相匹配的锥形面，锥形面的圆锥角为5°-85°。
更可选地，所述升降杆的顶端设置有高度为1mm-5mm且直径为1mm-10mm的凸台，凸台下方连接有与所述排气孔的锥形面相匹配的锥形面。
在另一可选方案中，所述存料仓室顶部通过石墨薄盖和/或若干层石墨纸实现密封，石墨薄盖的厚度为0.1mm-2mm，通过将所述升降杆升起，以在所述石墨薄盖和/或石墨纸中形成作为所述气相原料通道的孔洞。
更可选地，所述升降杆的端面为圆弧形，端面的粗糙度不大于1.6um。
可选地，各存料仓室为同心圆环状结构或同心多边形环状结构，依内径大小在所述坩埚内由内至外依次设置；或各存料仓室的平面形貌选自三角形、四边形、六边形和圆形中的若干种，各存料仓室呈蜂窝状排布。
可选地，所述料仓的顶部为中间低边缘高的抛物线形。
可选地，所述坩埚的侧壁厚度为5mm-25mm，所述存料仓室的侧壁厚度为0.5mm-3mm；所述升降杆为石墨杆，直径为2mm-15mm。
可洗掉，所述坩埚底部设置有若干螺纹孔，若干升降杆一一对应设置于所述螺纹孔内而与坩埚底部螺纹配合，通过调整升降杆和坩埚底部的螺纹旋和长度，实现升降杆的升降。
本发明还提供一种基于PVT法生长碳化硅单晶的方法，包括：
1)提供如上述任一方案中所述的设备，将固定有碳化硅籽晶的籽晶托置于生长腔体内，并固定于料仓上方，存料仓室内放置原料，升降杆自坩埚底部向上插入存料仓室，并延伸到存料仓室顶部，使存料仓室顶部保持密封；
2)使坩埚处于热场中，待热场氛围达到预设温度和压力后，调整升降杆的高度，以使部分存料仓室顶部的气相原料通道释放气相原料，籽晶表面开始成核稳定生长第一时间；
3)使靠近料仓中心的存料仓室顶端释放气相原料，再次稳定生长第二时间；
4)重复步骤2)和3)，直至坩埚内的存料仓室由边缘向中心依次释放完毕，完成单晶生长。
可选地，在使用碳化硅籽晶生长表面的C向[0001]晶面与A向[1120]晶面偏转角度大于2°的晶体时，通过调整不同存料仓室的原料存储量，以可选择性地减少C向小面下方存料 仓室的气相原料释放数量，从而在轴对称温度分布下实现非轴对称浓度生长。
可选地，使坩埚处于热场中后，热场内初始气氛在500mbar-800mbar压力，将坩埚加热至2200-2450℃，稳定30min-5h后，利用1h-15h的时间将压力降低至0.5mbar至50mbar；第一时间和第二时间均为5h-50h；完成单晶生长后，向热场内充气至100mbar-600mbar，用5h-10h将加热功率降为0，自然冷却至室温，之后取出晶体。
可选地，所述方法生长的碳化硅单晶大于等于8英寸，单晶厚度大于等于15mm。
如上所述，本发明的基于PVT法生长碳化硅单晶的设备和方法，具有以下有益效果：本发明经改善的结构设计，将料仓分为多个独立的存料仓室，根据单晶不同生长阶段的需要，利用升降杆在不同的存料仓室顶部释放出气相原料通道，从而实现不同温区的原料逐步蒸发，确保整个单晶生长过程中，各组分浓度基本保持一致；因中心低温处原料也可以在晶体生长的后期全部利用，相较于采用现有设备，原料的利用率可提高10％以上。此外，在保证热场轴对称的情况下，可以更有效地实现非对称生长以抑制缺陷，且可以有效避免因应力不对称造成的晶体开裂，可显著提高晶体生长质量。
附图说明
图1显示为对比例中的典型的坩埚内气相运输示意图。
图2显示为对比例中的典型的坩埚等温云图。
图3显示为对比例中的非轴对称温度分布下的缺陷分布图。
图4显示为本发明实施例1中的例示性设备结构示意图。
图5显示为本发明实施例1中的料仓的例示性俯视图。
图6显示为本发明实施例1中的存料仓室和升降杆的位置关系示意图。
图7显示为本发明实施例2中的存料仓室和升降杆的位置关系的局部放大示意图。
图8显示为本发明实施例2中的轴对称温度分布非对称生长的缺陷分布图。
图9显示为本发明实施例3中的石墨纸密封存料仓室顶部的示意图。
具体实施方式
以下通过特定的具体实例说明本发明的实施方式，本领域技术人员可由本说明书所揭露的内容轻易地了解本发明的其他优点与功效。本发明还可以通过另外不同的具体实施方式加以实施或应用，本说明书中的各项细节也可以基于不同观点与应用，在没有背离本发明的精神下进行各种修饰或改变。如在详述本发明实施例时，为便于说明，表示器件结构的剖面图会不依一般比例作局部放大，而且所述示意图只是示例，其在此不应限制本发明保护的范围。 此外，在实际制作中应包含长度、宽度及深度的三维空间尺寸。
为了方便描述，此处可能使用诸如“之下”、“下方”、“低于”、“下面”、“上方”、“上”等的空间关系词语来描述附图中所示的一个元件或特征与其他元件或特征的关系。将理解到，这些空间关系词语意图包含使用中或操作中的器件的、除了附图中描绘的方向之外的其他方向。此外，当一层被称为在两层“之间”时，它可以是所述两层之间仅有的层，或者也可以存在一个或多个介于其间的层。
在本申请的上下文中，所描述的第一特征在第二特征“之上”的结构可以包括第一和第二特征形成为直接接触的实施例，也可以包括另外的特征形成在第一和第二特征之间的实施例，这样第一和第二特征可能不是直接接触。
需要说明的是,本实施例中所提供的图示仅以示意方式说明本发明的基本构想，遂图式中仅显示与本发明中有关的组件而非按照实际实施时的组件数目、形状及尺寸绘制，其实际实施时各组件的型态、数量及比例可为一种随意的改变，且其组件布局型态也可能更为复杂。为使图示尽量简洁，各附图中并未对所有的结构全部标示。
请参阅图4至图9。
如图4至图9所示，本发明提供一种基于PVT法生长碳化硅单晶的设备，包括生长腔体21、坩埚22、升降杆24和用于承载原料的料仓23，所述坩埚22、升降杆24和料仓23均位于生长腔体21内；所述料仓23位于所述坩埚22内，料仓23包括多个相互独立的存料仓室231，需要说明的是，此处“相互独立”的概念主要指各存料仓室231内存储的原料互不接触，供应过程中也互不干扰，因而在单晶生长过程中，可以根据需要选择由特定存料仓室231供应气相原料，而各存料仓室231在实体上可以是可拆卸出来的独立个体，各存料仓室231也可以是相互之间一体连接，或者也可以将各存料仓室231描述为通过间隔材料将一个完整的料仓23分割出的多个相互独立封闭的区域，本实施例中对各存料仓室231的实体形态并不做严格限制；升降杆24由坩埚22底部向上穿过所述存料仓室231的底部(存料仓室231的底部被密封)并延伸至存料仓室231的顶部234，通过上下升降所述升降杆24，可将所述存料仓室231的顶部234密封或在存料仓室231的密封顶部顶出气相原料通道；即，根据存料仓室231顶部的具体形态不同，升降杆24的升降产生的结果也不同，例如在一示例中，参考图5所示，所述存料仓室231的顶部234设置有作为气相原料通道的排气孔235，所述升降杆24顶部设置有与所述排气孔235相匹配的端面，将所述升降杆24上升至端面抵住所述排气孔235，可将所述排气孔235密封，将所述升降杆24下降至使升降杆24的端面远离所述排气孔235，使得所述存料仓室231可以通过所述排气孔235排出气相原料；而在另一示例中， 所述存料仓室231顶部234原本是封闭的，例如通过石墨薄盖233(参考图7所示)，更具体地，例如通过等压石墨薄盖，或通过单层或多层的石墨纸232实现密封，或如图9所示，同时采用石墨薄盖233和石墨纸232实现密封；通过将所述升降杆24升起，以在所述存料仓室231的顶部234，例如在所述石墨薄盖和/或石墨纸中形成作为所述气相原料通道的孔洞。本发明经改善的结构设计，将料仓分为多个独立的存料仓室，根据单晶不同生长阶段的需要，利用升降杆在不同的存料仓室顶部释放出气相原料通道，从而实现不同温区的原料逐步蒸发，确保整个单晶生长过程中，各组分浓度基本保持一致；因中心低温处原料也可以在晶体生长的后期全部利用，相较于采用现有设备，原料的利用率可提高10％以上。此外，在保证热场轴对称的情况下，可以更有效地实现非对称生长以抑制缺陷，且可以有效避免因应力不对称造成的晶体开裂，可显著提高晶体生长质量。
当所述存料仓室231顶部预先设置有排气孔235时，作为示例，所述排气孔235的直径较佳地为0.1mm-5mm，且在进一步的示例中，如图5所示，排气孔235的下部设置有与升降杆24的顶部端面相匹配的锥形面，锥形面的圆锥角例如为5°-85°，更加地为30°-60°；而为了使升降杆24与该排气孔235更好地匹配，较佳地，所述升降杆24的顶端设置有高度为1mm-5mm且直径为1mm-10mm的凸台，凸台下方连接有与所述排气孔235的锥形面相匹配的锥形面，升降杆24顶部的锥形面例如同样为圆锥形面，圆锥角例如为5°-85°，更加地为30°-60°。通过这样的设置，可以更好地控制排气孔235的打开或密封，便于更好地调节各存料仓室231的原料释放。
作为示例，当采用石墨薄盖将存料仓室231顶部封闭时，石墨薄盖的厚度较佳地为0.1mm-2mm(包括端点值，本说明书在涉及数值范围描述时，如无特殊说明，均包括端点值)，例如为0.1mm，0.5mm，1mm，2mm或这区间的任意值。
当同时采用石墨薄盖和石墨纸进行密封时，如图9所示，石墨薄盖233可以位于石墨纸232的下方，且石墨纸232的尺寸与存料仓室231顶部开口尺寸一致，即石墨纸232将存料仓室231顶部封闭，而石墨薄盖233的尺寸则小于存料仓室231顶部开口尺寸，例如石墨薄盖233可以为略大于与之接触的升降杆24的端面尺寸的圆盘结构，且该示例中，所述升降杆24的端面较佳地为圆弧形，端面的粗糙度Ra不大于1.6um，以使升降杆24能在存料仓室231顶部顶出一个较为规则的孔洞；当升降杆24上升时，先与石墨薄盖233接触，石墨薄盖233受到升降杆24的压力而将受力传递到石墨纸232，使石墨纸232对应石墨薄盖233的部分破裂形成作为气相原料通道的孔洞。因而通过这样的设置，可以使存料仓室231顶部不至于一下子全部破裂，更好地控制孔洞大小，从而更好地控制气相原料的释放，有助于提高原料利 用率和单晶生长质量。
在一示例中，参考图4所示，各存料仓室231为同心圆环状结构或同心多边形环状结构，依内径大小在所述坩埚22内由内至外依次设置。而在其他示例中，可参考图6所示，各存料仓室231的平面形貌选自三角形、四边形、六边形和圆形中的若干种，各存料仓室231呈蜂窝状排布，而同一料仓23的多个存料仓室231形状可以相同或不同。存料仓室231的数量以及各存料仓室231的具体尺寸可以根据需要设置，对此不做严格限制，但较佳地为至少分为3个存料仓室231，以分别对应料仓23中心、中间和边缘区域。在较佳的示例中，所述料仓23的顶部为中间低边缘高的抛物线形(参考图4)，以与单晶生长过程中的坩埚22等温线云图相对应，从而可以更好地控制热场分布，提高原料利用率。
所述存料仓室231与升降杆24可以是一一对应的关系，即每个存料仓室231对应设置有一个升降杆24，而在其他示例中，也可以是单个存料仓室231对应设置有多个升降杆24，例如在存料仓室231为前述的圆环状结构时，可以在同一存料仓室231的不同对应区域设置所述升降杆24，又或者根据需要，仅在部分存料仓室231设置升降杆24，本实施例中对此不做严格限制，但较佳地为一个存料仓室231至少对应设置一个升降杆24。
所述升降杆24需选择耐高温且耐腐蚀的材质，以避免因升降杆24的腐蚀磨损等原因引入杂质污染。较佳地，所述升降杆24为石墨杆，即为纯石墨材质，直径(除端面外的尺寸)较佳地为2mm-15mm。
所述坩埚22的侧壁厚度较佳地为5mm-25mm，所述存料仓室231的侧壁厚度较佳为0.5mm-3mm。
所述升降杆24的升降可以通过人工调节，也可以通过机械控制，优选机械控制。在一示例中，所述坩埚22底部设置有若干螺纹孔，坩埚22底部将各存料仓室231底部螺纹密封，各存料仓室231底部设置有通孔，而升降杆24与坩埚22底部螺纹配合，并自坩埚22底部深入各存料仓室231的通孔内，形成活塞式结构，通过调整升降杆24和坩埚22底部的螺纹旋和长度，实现升降杆24的升降，例如可通过机械方式旋动螺纹而实现升降杆24的升降。在其他示例中，也可以在坩埚22内设置与坩埚22底部相连通的波纹管等弹性结构，升降杆24从坩埚22底部向上穿过波纹管并向上延伸到存料仓室231以确保将存料仓室231顶部密封，使用升降装置(例如气缸的活塞杆)自升降杆24底部将升降杆24顶起，也可以调节升降杆24的升降。
所述设备还包括加热器和隔热装置等结构，由于此部分内容非本发明的重点，对此不做详细展开。
本发明提供的设备，可以有效避免因坩埚尺寸增加形成的径向温度梯度造成的原料输送的不均匀性，同时方便实现轴对称或非轴对称原料的输送，尤其对于晶体直径超过8英寸且晶体厚度超过15mm的晶体生长，在提供稳定的工艺条件的同时可有效提高原料利用率。
本发明还提供一种基于PVT法生长碳化硅单晶的方法，该方法尤其适合大尺寸碳化硅单晶生长，例如适于生长大于等于8英寸，单晶厚度大于等于15mm的碳化硅单晶，该方法包括：
1)提供如上述任一方案中所述的设备，前述对设备的相关介绍可以全文引用至此，出于简洁的目的不赘述；将固定有碳化硅籽晶26的籽晶托25置于生长腔体21内，并固定于料仓23上方，存料仓室231内放置原料，升降杆24自坩埚22底部向上插入存料仓室231，并延伸到存料仓室231顶部，使存料仓室231顶部保持密封；该步骤中，可以先将粘有8-12英寸碳化硅籽晶26的籽晶托25固定在生长腔体21上，然后将升降杆24插入各存料仓室231中，并加入合计3.5kg-12kg的原料(具体根据待生长的碳化硅单晶规格而定)，将整个料仓23放入坩埚22内，利用坩埚22底部螺纹密封各个存料仓室231，之后将坩埚22与生长腔体21固定，并将整个坩埚22投入热场；
2)使坩埚22处于热场中，待热场氛围达到预设温度和压力后，调整升降杆24的高度，以使部分存料仓室231顶部的气相原料通道释放气相原料，籽晶26表面开始成核稳定生长第一时间；
3)使靠近料仓23中心的存料仓室231顶端释放气相原料，再次稳定生长第二时间；
在较佳的示例中，步骤2)和3)包括：使坩埚22处于热场中后，热场内初始气氛在500mbar-800mbar压力，将坩埚22加热至2200-2450℃，稳定30min-5h后，利用1h-15h的时间将热场内的压力降低至0.5mbar至50mbar；调整升降杆24的高度，使靠近坩埚22边缘的存料仓室231顶端释放气相原料，籽晶26表面开始成核稳定生长5h-50h后；将温度提高0-50℃(若外侧温度足够高，不升温内部也已经开始蒸发，但由于内侧坩埚22密封，原料无法出来，如果外侧温度不够高，那么需要逐步升温，才能实现由外向内逐步蒸发，即该升温步骤是根据工艺需要可选的)，使靠近中心的料仓23顶端释放气相原料，并再次稳定生长5h-50h；较佳地，在使用碳化硅籽晶26生长表面的C向[0001]与A向[1120]偏转角度大于2°的晶体时，可选择性地减少C向小面下方存料仓室231的气相原料释放数量，例如在C向小面下方对着若干个存料仓室231，可以是正对的存料仓室231不放料，或者正对的存料仓室231少放料，也可以正对的存料仓室231中的某几个少放，或者不放，即通过调整不同存料仓室231的原料存储量，以可选择性地减少C向小面下方存料仓室231的气相原料释放数量，由此在轴对 称温度分布实现非轴对称浓度生长；
4)重复步骤2)和3)，直至坩埚22内的存料仓室231由边缘向中心依次释放完毕，完成单晶生长。
在一较佳示例中，完成单晶生长后，向热场内充入惰性气体，例如氩气，以使坩埚22内气压调整至100mbar-600mbar，用5h-10h将加热功率降为0，自然冷却至室温，之后取出晶体。
为使本发明的技术方案和优点更加突出，下面通过对比实验并结合附图对本发明做进一步说明。
对比例
如图1所示，将装有原料的坩埚11放入热场中，升温至2550℃时，坩埚内的温度分布等温线云图如图2所示(图2中的数字代表不同的温度，单位为开尔文)，从图2可以看到，等温线是抛物线型的，所以原料蒸发也是有次序的，中间为低温区，因而如果中间和边缘的气相原料一起释放，对应中间区域就会因温度低而产生结块，图1中，坩埚的高温区12的气相原料17逐步扩散至籽晶13，同时也在低温区14不断凝固。随着晶体15的不断生长，高温区12彻底空化，凝固的低温区原料将突然落入高温区12中，造成晶体生长条件发生突变。且由于原料的变化，晶体生长区16的碳化硅组分也在不断的改变，原料分解初期释放富硅气相原料成核，但随着生长继续，高温区12的硅不断减少，低温区14的原料结晶后难以分解，进一步加剧了生长条件的变化，造成晶体质量下降，且参考图3所示的非轴对称温度分布下的缺陷分布图(该图中的数字代表缺陷数量，同一深度的颜色代表应力缺陷分布情况相同，如果两个区域颜色深浅差异很大，代表这两个区域的应力缺陷分布情况差异很大)，因为籽晶存在4度偏角，所以晶体不是轴对称的，故而有的方案是通过不对称的热场去适应不对称的晶体，这样缺陷就是一头少一头多，导致生成的晶体开裂几率高。
实施例1
针对坩埚内热场的典型的等温线的分布情况，本发明对现有的设备结构进行了改进，例如本示例中，如图4所示，采用具有多个独立存料仓室231(例如包括第一存料仓室231a、第二存料仓室231b、第三存料仓室231c、第四存料仓室231d和第五存料仓室231e，各存料仓室依内径大小在坩埚22内由内之外同心设置)的料仓23，且料仓23顶面呈现为中间低边缘高的抛物线形，本实施例的碳化硅单晶生长步骤包括：
(1)继续参考图4所示，将8英寸籽晶26提前粘在籽晶托25上并固定在生长腔体21上；
(2)如图5所示，将升降杆24插入存料仓室231中，存料仓室231顶部234设置有直径 为2mm的排气孔235作为气相原料通道，排气孔235下方设置有圆锥角为15°的圆锥面，往料仓23中并加入5kg原料；将整个料仓23放入坩埚22中，利用坩埚底部螺纹向上旋转升降杆24，顶紧各个存料仓室231，以将各存料仓室231的顶部234的排气孔密封；将坩埚22与生长腔体21固定，并将整个坩埚22投入热场；
(3)热场内气氛在600mbar压力，将坩埚22加热至2350℃，稳定2h后，利用5h将压力降低至20mbar；
(4)将图4中最外侧的第一存料仓室231a的升降杆23下降3mm，使第一存料仓室231a顶端释放气相原料，籽晶26表面开始成核稳定生长10h并增加坩埚温度至2360℃，得到晶体后，再将图4中的第二存料仓室231b的升降杆24降低3mm，并再次稳定生长10h，同时升温至2370℃；
(5)重复步骤(4)直至坩埚内的第一存料仓室231a至第五存料仓室231e依次释放完毕；
(6)充气至100mbar，用10h将功率将为0，自然冷却至室温，取出晶体。
经检测，获得的8英寸碳化硅晶体厚度达到24mm，质量达到3.2kg，原料的转化效率达到64％。
实施例2
Figure PCTCN2022111456-appb-000001
Figure PCTCN2022111456-appb-000002
上述公式1为碳化硅分解与生成的公式，公式2为颗粒的热泳力公式，其中，F τ为热泳力，R为石墨粉半径，Cs为热滑移系数，
Figure PCTCN2022111456-appb-000003
为温度梯度，ρ为石墨密度，T为温度，Cm为动量交换系数，μ为气体分子自由程。
基于上述公式，为了获得较快的生长速度，当工艺温度接近2500℃时，原料表面附近的Si的压力将达到2mbar(1mbar＝100pa)左右，此时升降杆下落，在料仓顶部气孔剧烈进行碳化硅分解与生成，造成石墨粉化，由于热泳力与石墨粉颗粒直径R的平方和温度梯度
Figure PCTCN2022111456-appb-000004
成正比，同时由于料仓内压力与生长腔体压力存在差异，石墨颗粒进一步受到压力推动，当颗粒重力不足以克服两个推力时，石墨颗粒上升至籽晶处，引起晶体质量缺陷，鉴于此种情况，故进一步可以选用存料仓室顶部为0.5mm的薄板密封，由于密封作用温度达到2500℃时，原料轻微分解则保持仓内压力上升，原料无法持续分解。本实施例的晶体生长步骤为：
(1)将直径为200mm且生长表面C向[0001]晶面与A向[1120]晶面偏4度的碳化硅籽晶 26的籽晶托25固定在生长腔体22上(可继续参考图4)；
(2)参考图7所示，将升降杆24插入存料仓室231中，存料仓室231顶部采用石墨薄片233(也可以定义为薄石墨板)密封，升降杆24顶部为圆弧面，并加入5kg原料，并参考图6，在图6中标记有f的存料仓室231，即正对籽晶生长表面C向下方的料仓选择性地不投原料；将整个料仓23放入坩埚中，升降杆24顶紧各个存料仓室231顶部；将坩埚22与生长腔体21固定，并将整个坩埚22投入热场；
(3)热场内气氛在600mbar压力，将坩埚加热至2450℃，稳定2h后，利用5h将压力降低至5mbar；
(4)将最外侧的存料仓室的升降杆24上升5mm，顶破该存料仓室顶部的石墨薄片233，气相原料挥发到籽晶表面，开始成核稳定生长10h并增加坩埚温度至2460℃，得到晶体后，再将最外侧存料仓室中的升降杆上升5mm，并再次稳定生长10h，同时升温至2470℃；
(5)重复步骤(4)，直至由外至内将所有存料仓室的原料依次释放完毕；
(6)充气至100mbar，用10h将功率将为0，自然冷却至室温，取出晶体。
经检测，获得直径达200mm的碳化硅晶体厚度达到22mm，质量达到2.9kg左右，由于增加了原料的扩散面积，晶体内包裹物较少；同时，参考图8的轴对称温度分布非对称生长的缺陷分布图可以知晓，本实施例利用轴对称的温度分布实现非对称生长，可有效减少晶体的微观缺陷。
实施例3
在开启料仓的过程中，由于升降杆被原料的硅腐蚀，可能造成料仓开启异常的情况，因而本实施例中，存料仓室231采用如图9所示的结构进行顶部封闭，包括密封的1mm的石墨纸232和直径为5mm且厚度为2mm石墨薄片233，石墨薄片233位于石墨纸232下方，因而将先与升降杆24接触，升降杆24顶端为圆弧形且粗糙度为1.6um；生长过程中，升降杆24对石墨薄片233施加压力，可保证石墨纸232至少有直径5mm的开启面，保证各存料仓室仓有较为一致的原料蒸发面积，从而进一步稳定工艺过程。
综上所述，本发明经改善的结构设计，将料仓分为多个独立的存料仓室，根据单晶不同生长阶段的需要，利用升降杆在不同的存料仓室顶部释放出气相原料通道，从而实现不同温区的原料逐步蒸发，确保整个单晶生长过程中，各组分浓度基本保持一致；因中心低温处原料也可以在晶体生长的后期全部利用，相较于采用现有设备，原料的利用率可提高10％以上。此外，在保证热场轴对称的情况下，可以更有效地实现非对称生长以抑制缺陷，且可以有效避免因应力不对称造成的晶体开裂，可显著提高晶体生长质量。所以，本发明有效克服了现 有技术中的种种缺点而具高度产业利用价值。
上述实施例仅例示性说明本发明的原理及其功效，而非用于限制本发明。任何熟悉此技术的人士皆可在不违背本发明的精神及范畴下，对上述实施例进行修饰或改变。因此，举凡所属技术领域中具有通常知识者在未脱离本发明所揭示的精神与技术思想下所完成的一切等效修饰或改变，仍应由本发明的权利要求所涵盖。

Claims (14)

  1. 一种基于PVT法生长碳化硅单晶的设备，所述设备包括生长腔体、坩埚和用于承载原料的料仓，所述坩埚和料仓均位于生长腔体内，所述料仓位于所述坩埚内，其特征在于，料仓包括多个相互独立的存料仓室；所述设备还包括升降杆，所述升降杆位于生长腔体内，升降杆由坩埚底部向上穿过所述存料仓室的底部并延伸至存料仓室的顶部，通过上下升降所述升降杆，可将所述存料仓室的顶部密封或在存料仓室的密封顶部顶出气相原料通道。
  2. 根据权利要求1所述的设备，其特征在于，所述存料仓室的顶部设置有作为气相原料通道的排气孔，所述升降杆顶部设置有与所述排气孔相匹配的端面，将所述升降杆上升至端面抵住所述排气孔，可将所述排气孔密封，将所述升降杆下降至端面远离所述排气孔，使得所述存料仓室可以通过所述排气孔排出气相原料。
  3. 根据权利要求2所述的设备，其特征在于，所述排气孔的直径为0.1mm-5mm，排气孔的下部设置有与升降杆的顶部端面相匹配的锥形面，锥形面的圆锥角为5°-85°。
  4. 根据权利要求3所述的设备，其特征在于，所述升降杆的顶端设置有高度为1mm-5mm且直径为1mm-10mm的凸台，凸台下方连接有与所述排气孔的锥形面相匹配的锥形面。
  5. 根据权利要求1所述的设备，其特征在于，所述存料仓室顶部通过石墨薄盖和/或若干层石墨纸实现密封，石墨薄盖的厚度为0.1mm-2mm，通过将所述升降杆升起，以在所述石墨薄盖和/或石墨纸中形成作为所述气相原料通道的孔洞。
  6. 根据权利要求5所述的设备，其特征在于，所述升降杆的端面为圆弧形，端面的粗糙度不大于1.6um。
  7. 根据权利要求1所述的设备，其特征在于，各存料仓室为同心圆环状结构或同心多边形环状结构，依内径大小在所述坩埚内由内至外依次设置；或各存料仓室的平面形貌选自三角形、四边形、六边形和圆形中的若干种，各存料仓室呈蜂窝状排布。
  8. 根据权利要求1所述的设备，其特征在于，所述料仓的顶部为中间低边缘高的抛物线形。
  9. 根据权利要求1所述的设备，其特征在于，所述坩埚的侧壁厚度为5mm-25mm，所述存料仓室的侧壁厚度为0.5mm-3mm；所述升降杆为石墨杆，直径为2mm-15mm。
  10. 根据权利要求1-9任一项所述的设备，其特征在于，所述坩埚底部设置有若干螺纹孔，若干升降杆一一对应设置于所述螺纹孔内而与坩埚底部螺纹配合，通过调整升降杆和坩埚底部的螺纹旋和长度，实现升降杆的升降。
  11. 一种基于PVT法生长碳化硅单晶的方法，其特征在于，包括：
    1)提供如权利要求1-10任一项所述的设备，将固定有碳化硅籽晶的籽晶托置于生长腔体 内，并固定于料仓上方，存料仓室内放置原料，升降杆自坩埚底部向上插入存料仓室，并延伸到存料仓室顶部，使存料仓室顶部保持密封；
    2)使坩埚处于热场中，待热场氛围达到预设温度和压力后，调整升降杆的高度，以使部分存料仓室顶部的气相原料通道释放气相原料，籽晶表面开始成核稳定生长第一时间；
    3)使靠近料仓中心的存料仓室顶端释放气相原料，再次稳定生长第二时间；
    4)重复步骤2)和3)，直至坩埚内的存料仓室由边缘向中心依次释放完毕，完成单晶生长。
  12. 根据权利要求11所述的方法，其特征在于，在使用碳化硅籽晶生长表面的C向[0001]晶面与A向
    Figure PCTCN2022111456-appb-100001
    晶面的偏转角度大于2°的晶体时，通过调整不同存料仓室的原料存储量，以可选择性地减少C向小面下方存料仓室的气相原料释放数量，从而在轴对称温度分布下实现非轴对称浓度生长。
  13. 根据权利要求11所述的方法，其特征在于，使坩埚处于热场中后，热场内初始气氛在500mbar-800mbar压力，将坩埚加热至2200-2450℃，稳定30min-5h后，利用1h-15h的时间将压力降低至0.5mbar至50mbar；第一时间和第二时间均为5h-50h；完成单晶生长后，向热场内充气至100mbar-600mbar，用5h-10h将加热功率降为0，自然冷却至室温，之后取出晶体。
  14. 根据权利要求11-13任一项所述的方法，其特征在于，所述方法生长的碳化硅单晶大于等于8英寸，单晶厚度大于等于15mm。
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