CN109280964B - Thermal field structure for growing silicon carbide single crystal - Google Patents

Thermal field structure for growing silicon carbide single crystal Download PDF

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Publication number
CN109280964B
CN109280964B CN201811204668.2A CN201811204668A CN109280964B CN 109280964 B CN109280964 B CN 109280964B CN 201811204668 A CN201811204668 A CN 201811204668A CN 109280964 B CN109280964 B CN 109280964B
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crucible
silicon carbide
carbide single
single crystal
heat preservation
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CN109280964A (en
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高超
李长进
孙元行
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Shandong Tianyue Advanced Technology Co Ltd
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SICC Science and Technology Co Ltd
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Priority to CN201811204668.2A priority Critical patent/CN109280964B/en
Priority to KR1020197037936A priority patent/KR102331308B1/en
Priority to JP2019571512A priority patent/JP6937525B2/en
Priority to PCT/CN2018/123708 priority patent/WO2020077847A1/en
Priority to EP18922089.0A priority patent/EP3666933A4/en
Publication of CN109280964A publication Critical patent/CN109280964A/en
Priority to TW108136952A priority patent/TWI723579B/en
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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
    • C30B23/00—Single-crystal growth by condensing evaporated or sublimed materials
    • 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

Abstract

The application discloses a thermal field structure for growing silicon carbide single crystals, and belongs to the field of preparation of silicon carbide single crystals. The thermal field distribution of a PVT method is improved, the traditional method for manufacturing the axial temperature gradient through heat dissipation of the upper heat-insulating hole is changed, crucibles with different wall thicknesses and heat-insulating structures with different thicknesses are used for manufacturing the axial temperature gradient, and meanwhile, the heat-insulating structure on the upper side of the crucible is changed, so that the thermal field structure with uniform radial temperature distribution is manufactured; particularly, the thermal field in the large-size crucible can be uniformly distributed in the radial direction; as the electroactive impurity elements grow into the crystal along with the temperature gradient, the thermal field structure with uniform radial temperature distribution guides the electroactive impurity elements to be uniformly distributed along the radial direction, and then large-size high-purity semi-insulating silicon carbide single crystals and single crystal substrates with uniform radial resistivity and low stress are prepared.

Description

Thermal field structure for growing silicon carbide single crystal
Technical Field
The application relates to a thermal field structure for growing silicon carbide single crystals, belonging to the field of preparation of silicon carbide single crystals.
Background
semiconductor silicon carbide single crystal materials have evolved through the last 30 years since their commercialization in the 90 s of the last century as the preferred substrate material for power electronics and microwave radio frequency devices. With the continuous development of downstream device technology and the continuous promotion of industrialization degree, the quality requirement of the silicon carbide single crystal substrate is more and more severe.
At present, the most mature technology for preparing silicon carbide single crystals is a physical vapor transport method (PVT method for short), and the basic principle is that a graphite crucible arranged in the center of a coil is heated through medium-frequency induction, and the wall of the graphite crucible generates heat through induction and then transmits the heat to silicon carbide powder inside the graphite crucible and sublimes the silicon carbide powder. The center of the graphite heat-insulating felt on the upper side of the graphite crucible is provided with a through round hole, so that heat is dissipated through the round hole while temperature is measured through the round hole, and therefore an axial temperature gradient that the temperature of the lower part of the crucible is high and the temperature of the upper part of the crucible is low is caused, and sublimed gas phase is driven to be transmitted to a seed crystal area at the top of the crucible from a powder area in a growth chamber for crystallization. The silicon carbide single crystal produced by this method has been developed from 2 inches to 8 inches and is being used in downstream devices.
However, as the crystal size continues to increase, the diameter of the crucible also continues to increase. Because the crucible wall is used as a heating source in the medium-frequency induction heating mode, the radial temperature gradient along the crucible wall and the crucible center is increased continuously; in addition, the PVT method creates an axial temperature gradient by keeping a central circular hole at the upper side of the crucible as a heat dissipation center, which further causes non-uniformity of a thermal field inside the crucible in the radial direction, resulting in problems of large thermal stress of the crystal in the radial direction, non-uniform distribution of impurities and defects, and the like. The former has thermal stress which easily causes serious quality problems such as cracking in the crystal processing process, unqualified bending and warping degree in the substrate processing process, and the latter has impurity and defect maldistribution which also seriously restricts the resistivity uniformity of the substrate along the radial direction.
Disclosure of Invention
In order to solve the above problems, the present application provides a thermal field structure for growing a silicon carbide single crystal, which forms a thermal field structure uniform in a radial direction by redesigning a crucible and a heat insulating structure coated on the periphery of the crucible, thereby improving the radial uniformity of the silicon carbide single crystal and making it possible to prepare a large-sized high-purity semi-insulating silicon carbide single crystal substrate of high quality.
The thermal field structure for growing the silicon carbide single crystal comprises a crucible, a heating unit and a heat preservation structure, and is characterized in that the heat preservation structure comprises a heat preservation structure top, a heat preservation structure side and a heat preservation structure bottom, and the crucible is positioned in a sealed cavity of the heat preservation structure;
The wall thickness of the sidewall opening region of the crucible is greater than the wall thickness of the bottom region.
Optionally, the crucible and the holding structure are such that there is an axial temperature gradient within the crucible, and/or a radial temperature gradient near zero.
Preferably, the crucible is a graphite crucible.
Optionally, the sidewall of the crucible is linearly thickened along the bottom of the crucible to the opening.
Preferably, the wall of the side of the holding structure is linearly thickened along the direction from the opening of the crucible to the bottom.
Optionally, the open cross-section of the crucible has a first distance from the top inner surface of the holding structure above it, the first distance increasing in a direction from the center of the crucible to the edge of the crucible.
Preferably, the value of the variation value of the first distance is 5-50 mm. Optionally, the range of values of variation of the first distance has a lower limit selected from 10mm, 15mm, 20mm, 25mm or 30mmm and an upper limit selected from 15mm, 20mm, 25mm, 30mmm, 35mm, 40mm or 45 mm.
Optionally, the crucible and the insulating structure substantially share a first central axis;
The first central axis is approximately parallel to the inner surface of the side wall of the crucible and/or the outer surface of the side part of the heat preservation structure;
The first central axis and the outer surface of the side wall of the crucible form a first included angle, the first central axis and the inner surface of the side part of the heat preservation structure form a second included angle, and the first included angle and the second included angle are smaller than 90 degrees.
Further, the crucible and the heat preservation structure share a first central axis;
the first central axis is parallel to the inner surface of the side wall of the crucible and/or the outer surface of the side part of the heat preservation structure;
The first central axis and the outer surface of the side wall of the crucible form a first included angle, the first central axis and the inner surface of the side part of the heat preservation structure form a second included angle, and the first included angle and the second included angle are smaller than 90 degrees.
optionally, the first included angle has a value of 5 to 30 °, and the second included angle has a value of 5 to 30 °. Further, the lower limit of the values of the first and second angles is selected from 7 °, 10 °, 13 °, or 15 °, and the upper limit is selected from 28 °, 25 °, 23 °, 20 °, or 18 °.
optionally, the first included angle and the second included angle are substantially equal.
Optionally, the outer surface of the insulation structure is a cylinder, and the top of the insulation structure is not provided with an opening; the inner surface of the bottom of the heat preservation structure is approximately cylindrical; the inner surface of the side part of the heat preservation structure extends along the direction far away from the center of the crucible from the bottom of the crucible to the opening direction of the crucible; the top of the heat preservation structure is thickened along the direction from the edge to the center of the crucible;
The inner surface of the side wall of the crucible is approximately cylindrical, and the outer wall of the crucible has approximately the same extending direction as the inner surface of the side part of the heat preservation structure.
Optionally, the thermal field structure further comprises a seed crystal unit, the seed crystal unit is arranged above the crucible opening, and the heat preservation structure is not provided with an opening structure. The seed crystal unit includes a carbonized single crystal seed crystal.
According to another aspect of the present application, there is provided a method for producing a silicon carbide single crystal, characterized by producing using the thermal field structure of any one of the above.
According to another aspect of the present application, there is provided a crystal growth apparatus, comprising the thermal field structure of any one of the above.
Preferably, the crystal growth apparatus is used for producing a semi-insulating silicon carbide single crystal having a diameter of 4 to 12 inches and a substrate thereof. Further, the crystal growth apparatus is used for producing a semi-insulating silicon carbide single crystal having a diameter of more than 8 inches and 12 inches or less and a substrate thereof.
In the present application, the PVT method refers to a physical vapor transport method.
In the prior art, crystal growth is carried out by a PVT method, and a crystal growth thermal field is transmitted to the inside of a crucible after being heated by the crucible wall. The lower the temperature at locations further from the crucible wall, resulting in a larger radial temperature gradient inside the crucible. This situation is exacerbated as the crucible and crystal size increase. The resistivity of a high-purity semi-insulating silicon carbide single crystal substrate is determined by the concentration of an electrically active impurity in the crystal, and particularly, nitrogen, which is a shallow donor element, plays a decisive role in the value and distribution of the resistivity. Due to the distribution characteristics of the thermal field during the preparation of the silicon carbide single crystal by the PVT method, the nitrogen concentration is gradually reduced from the center to the edge of the crystal, so that the trend that the resistivity is increased from the center to the edge is easily formed in the radial direction, and the uneven resistivity distribution on the same substrate is caused.
Benefits of the present application include, but are not limited to:
According to the thermal field structure for growing the silicon carbide single crystal, the crucible and the heat preservation structure coated on the periphery of the crucible are redesigned to form a thermal field structure which is uniform along the radial direction, so that the radial uniformity of the quality of the silicon carbide single crystal is improved, and a high-quality large-size high-purity semi-insulating silicon carbide single crystal substrate can be prepared.
According to the thermal field structure, the thermal field distribution of a PVT method is improved, the traditional method for manufacturing the axial temperature gradient through heat dissipation of the upper heat-insulating hole is changed, the axial temperature gradient is manufactured by using crucibles with different wall thicknesses and heat-insulating structures with different thicknesses, and meanwhile, the heat-insulating structure on the upper side of the crucible is changed, so that the thermal field structure with the uniform radial temperature distribution is manufactured. As nitrogen grows into the crystal along with the temperature gradient, the thermal field structure with uniform radial temperature distribution guides the electroactive impurity elements, particularly the nitrogen, to be uniformly distributed along the radial direction, and the method is used for preparing high-purity semi-insulating silicon carbide single crystals and single crystal substrates with uniform radial resistivity.
Drawings
The accompanying drawings, which are included to provide a further understanding of the application and are incorporated in and constitute a part of this application, illustrate embodiment(s) of the application and together with the description serve to explain the application and not to limit the application. In the drawings:
Fig. 1 is a schematic view of a thermal field structure according to an embodiment of the present application.
Fig. 2 is a resistivity distribution diagram of a silicon carbide single crystal according to an embodiment of the present application.
Detailed Description
in order to more clearly explain the overall concept of the present application, the following detailed description is given by way of example in conjunction with the accompanying drawings.
so that the manner in which the above recited objects, features and advantages of the present application can be understood in detail, a more particular description of the invention, briefly summarized above, may be had by reference to the embodiments thereof which are illustrated in the appended drawings. It should be noted that the embodiments and features of the embodiments of the present application may be combined with each other without conflict.
in the following description, numerous specific details are set forth in order to provide a thorough understanding of the present application, however, the present application may be practiced in other ways than those described herein, and therefore the scope of the present application is not limited by the specific embodiments disclosed below.
in addition, in the description of the present application, it is to be understood that the terms "upper", "lower", "front", "rear", "left", "right", "inner", "outer", "axial", "radial", "circumferential", and the like, indicate orientations and positional relationships based on the orientations and positional relationships shown in the drawings, are only for convenience in describing the present application and simplifying the description, and do not indicate or imply that the device or element referred to must have a particular orientation, be constructed and operated in a particular orientation, and thus, should not be construed as limiting the present application.
furthermore, the terms "first", "second" and "first" are used for descriptive purposes only and are not to be construed as indicating or implying relative importance or implicitly indicating the number of technical features indicated. Thus, a feature defined as "first" or "second" may explicitly or implicitly include one or more of that feature. In the description of the present application, "a plurality" means two or more unless specifically limited otherwise.
In this application, unless expressly stated or limited otherwise, the terms "mounted," "connected," "secured," and the like are to be construed broadly and can include, for example, fixed connections, removable connections, or integral parts; the connection can be mechanical connection, electrical connection or communication; either directly or indirectly through intervening media, either internally or in any other relationship. The specific meaning of the above terms in the present application can be understood by those of ordinary skill in the art as appropriate.
In this application, unless expressly stated or limited otherwise, the first feature "on" or "under" the second feature may be directly contacting the first and second features or indirectly contacting the first and second features through intervening media. In the description herein, reference to the description of the term "one embodiment," "some embodiments," "an example," "a specific example," or "some examples," etc., means that a particular feature, structure, material, or characteristic described in connection with the embodiment or example is included in at least one embodiment or example of the application. In this specification, the schematic representations of the terms used above are not necessarily intended to refer to the same embodiment or example. Furthermore, the particular features, structures, materials, or characteristics described may be combined in any suitable manner in any one or more embodiments or examples.
referring to fig. 1, an embodiment of the present application discloses a thermal field structure for growing a silicon carbide single crystal, which includes a crucible 2, a heating unit, and a thermal insulation structure 6. The crucible 2 is arranged in the sealed heat insulation structure 6, the heating unit heats the outer wall of the crucible 2 in an induction mode, and the heating unit is arranged on the periphery of the heat insulation structure 6. A raw material 1 for growing a crystal is placed in a crucible 2.
The heating unit can heat the outer wall of the crucible 2, and consists of a power supply controller and a corresponding intermediate frequency induction coil 4; the induction coil 4 is positioned at the periphery of the side part of the heat insulation structure 6, surrounds the heat insulation structure 6 and shares a first central axis with the crucible 2. And the intermediate frequency induction coil heats the crucible 2 in an induction mode.
The crucible 2 may be a graphite crucible, but is not limited to a graphite crucible, and may be any material used for producing a silicon carbide single crystal.
The insulation 6 is made of a material having thermal insulation, such as graphite insulation felt, and the insulation 6 includes insulation sides 66, an insulation bottom 62, and an insulation top 64.
further, the thermal field structure is provided with a seed crystal unit 8, the seed crystal unit 8 is arranged on the inner side of the cover body of the graphite crucible 2, and the heat preservation structure 6 is not provided with an opening structure. The seed crystal unit 8 includes a carbonized single crystal seed crystal.
The crucible 2 and the heat preservation structure 6 share a first central axis A, and the first central axis A is parallel to the inner surface of the side wall of the crucible 2 and the outer surface of the wall of the heat preservation structure 6; the first central axis A and the outer surface of the side wall of the crucible 2, namely a schematic line B in the figure, have a first included angle, the first central axis A and the inner surface of the wall of the heat preservation structure 6, namely a schematic line C in the figure 1, have a second included angle, and the first included angle and the second included angle are less than 90 degrees.
According to the skin effect of the intermediate frequency heating of the graphite crucible 2, the outer wall of the graphite crucible 2 is a heat source when the graphite crucible 2 is heated at the intermediate frequency. The outer wall of the graphite crucible 2 in the embodiment is trapezoidal, the inner side of the graphite crucible 2 is in a straight cylinder shape, and the thickness of the wall of the graphite crucible 2 is reduced from the seed crystal to the bottom of the graphite crucible 2. The graphite heat preservation felt 6 on the periphery of the graphite crucible 2 consists of a heat preservation felt bottom 62, a heat preservation felt top 64 and a heat preservation felt side 66, wherein the heat preservation felt bottom 62 is in a regular cylinder shape; the thickness of the side part 66 of the heat preservation felt is in a trapezoidal structure along the outer diameter of the graphite crucible 2, namely the side part 66 of the heat preservation felt close to the upper part of the graphite crucible 2 has the smallest thickness and the thickness gradually increases along with the approach to the bottom of the graphite crucible 2; the side of the heat preservation felt top 64 close to the graphite crucible 2 is in a dome shape, a first distance X is formed from the opening surface of the graphite crucible 2 to the inner surface of the wall part of the heat preservation felt top 64 above the opening surface, the variation value of the first distance X is 5-50mm, a circular temperature measurement hole is not reserved on the heat preservation felt top 64, and further the variation value of the first distance X is 25 mm.
In the embodiment of the application, the thickness of the graphite crucible cylinder is linearly reduced from top to bottom, wherein the inner wall of the graphite crucible is in a vertical straight line shape, and the outer wall of the graphite crucible is in an oblique line shape. Because the outer wall surface layer of the graphite crucible is subjected to induction heating, the efficiency of the graphite crucible is lower than that of a thinner area at the lower part of the graphite crucible when heat is transferred to the inner cavity of the graphite crucible after the thicker graphite wall at the upper part of the graphite crucible generates heat, and then a higher temperature area at the lower part and a lower temperature area at the upper part can be formed in the cavity of the graphite crucible, so that an axial temperature gradient is formed. The angle formed by the straight lines of the inner and outer side sections of the wall of the graphite crucible is limited to 5-30 degrees, namely, the first included angle between the outer surface of the graphite crucible and the axis of the first central line is 5-30 degrees, and the formed temperature gradient and the heating efficiency of the graphite crucible can be balanced by the first included angle. Further, a first included angle between the outer surface of the graphite crucible and the first centerline axis is 20 °.
Further, the graphite crucible outside insulation structure in the embodiment of the present application is made of a graphite felt, the insulation structure is that the outside of the graphite felt is a cylindrical structure, the outer surface of the side portion of the graphite felt is a vertical straight line, and the inner surface of the side portion of the graphite felt is parallel to the outer wall of the graphite crucible. The included angle of the section of the inner surface of the side part of the graphite felt is 5-30 degrees, namely the second included angle between the inner surface of the side part of the graphite felt and the axis of the first central line is 5-30 degrees. The graphite felt of the thicker part is coated outside the thinner region at the lower part of the graphite crucible to reduce heat loss, so that a high-temperature region is further formed; the thinner region at the upper part of the graphite crucible is coated with the thinner graphite felt, so that the heat loss is more, and a low-temperature region is formed. Thereby, an axial temperature gradient can be further formed in the graphite chamber of the graphite crucible.
Furthermore, in the embodiment of the application, the side of the graphite felt on the upper side of the graphite crucible, which is close to the graphite crucible, adopts an arc-shaped design, and the center of the graphite crucible is not provided with an opening. According to the design of the graphite crucible and the heat preservation felt, an axial temperature gradient can be formed in a graphite crucible cavity, and the design of forming an axial temperature gradient by radiating heat through a central hole arranged on the upper heat preservation felt is replaced. However, due to the heat generated by the graphite crucible wall, there still exists a temperature gradient in the radial direction, in which the temperature of the region near the graphite crucible wall is high and the temperature of the center of the chamber far from the graphite crucible wall is low, so that there exists a temperature gradient in the radial direction. The arc design is adopted, so that the center of the upper side of the graphite crucible is closer to the graphite felt on the upper side, and the edge of the graphite crucible is farther from the heat preservation graphite felt on the upper side, therefore, the heat dissipation of the center of the graphite crucible is less, the heat dissipation of the edge is more, the heat dissipation of the center of the graphite crucible is mutually compensated with the heating condition of the wall of the graphite crucible, and the radial temperature gradient is reduced. The height difference of the arc-shaped surface of the upper side heat preservation felt is kept between 5mm and 50mm, and the radial temperature gradient can be reasonably controlled.
The thermal field structure with the radial temperature gradient close to zero can be formed when the silicon carbide single crystal is prepared by the thermal field structure obtained after the graphite heat preservation felt heat preservation structure and the graphite crucible are prepared according to the method. The prepared thermal field structure is used for growing high-purity silicon carbide single crystals, and the preparation method of the high-purity silicon carbide single crystals comprises the following steps:
Putting a certain amount of silicon carbide powder in a graphite crucible, wherein the purity of the silicon carbide powder is above 99.9999%, and the concentration of donor impurities with shallow energy level, such as nitrogen, contained in the silicon carbide powder is 1 multiplied by 1016cm-3The concentration of shallow level acceptor impurities such as boron and aluminum should be 1 × 1016cm-3The following;
Secondly, placing seed crystals for growing the silicon carbide single crystals on the upper part of the silicon carbide powder in the graphite crucible, and then sealing the graphite crucible; after the sealed graphite crucible is placed in the heat insulation structure of the graphite heat insulation felt, the whole graphite crucible is moved into single crystal growth equipment, and then a hearth is sealed;
Thirdly, vacuumizing the pressure in the hearth to 10 DEG-5pa for 5-10h to remove residual impurities in the furnace chamber, and gradually introducing protective atmosphere, such as argon or helium, into the furnace chamber;
fourthly, the pressure of the hearth is increased to 10 to 100mbar at the speed of 30 to 50mbar/h, simultaneously the temperature in the hearth is increased to 2100 ℃ and 2200 ℃ at the speed of 10 to 20 ℃/h, and the temperature is kept for 50 to 100h, thus finishing the growth process of the silicon carbide single crystal;
After the growth process of the single crystal is finished, stopping heating the hearth to naturally reduce the temperature of the hearth to room temperature, opening the hearth and taking out the graphite crucible to obtain the high-position silicon carbide single crystal.
The silicon carbide single crystal is prepared according to the method, and the specific preparation parameters are different from those of the method and are shown in table 1, so that the high-purity silicon carbide single crystal 1# -4# is prepared.
TABLE 1
Respectively carrying out the same cutting, grinding and polishing methods on the prepared silicon carbide single crystal 1#, silicon carbide single crystal 2#, silicon carbide single crystal 3#, silicon carbide single crystal 4#, silicon carbide single crystal 5#, silicon carbide single crystal 6#, silicon carbide single crystal D1#, silicon carbide single crystal D2# and silicon carbide single crystal D3# to respectively prepare a silicon carbide single crystal substrate 1#, a silicon carbide single crystal substrate 2#, a silicon carbide single crystal substrate 3#, a silicon carbide single crystal substrate 4#, a silicon carbide single crystal substrate 5#, a silicon carbide single crystal substrate 6#, a silicon carbide single crystal substrate D1#, a silicon carbide single crystal substrate D2# and a silicon carbide single crystal substrate D3 #; the silicon carbide single crystal substrate 1#, the silicon carbide single crystal substrate 2#, the silicon carbide single crystal substrate 3#, the silicon carbide single crystal substrate 4#, the silicon carbide single crystal substrate 5#, the silicon carbide single crystal substrate 6#, the silicon carbide single crystal substrate D1#, the silicon carbide single crystal substrate D2# and the silicon carbide single crystal substrate D3# have specifications of 4 to 12 inches, respectively.
Resistivity distributions of the prepared silicon carbide single crystal substrate 1#, silicon carbide single crystal substrate 2#, silicon carbide single crystal substrate 3#, silicon carbide single crystal substrate 4#, silicon carbide single crystal substrate 5#, silicon carbide single crystal substrate 6#, silicon carbide single crystal substrate D1#, silicon carbide single crystal substrate D2# and silicon carbide single crystal substrate D3# were respectively tested. The radial resistivity difference of the semi-insulating silicon carbide single crystal substrate is more than one order of magnitude, and the resistivity of the 4-8 inch semi-insulating silicon carbide single crystal substrate prepared by the embodiment of the application from No. 1 to No. 6 can reach 1 x 1010Omega cm or more, and the radial distribution of the resistivity is controlled within one order of magnitude, and further within 50%, thereby realizing the uniform distribution of the resistivity of the silicon carbide single crystal substrate. And the silicon carbide single crystal D1#, the silicon carbide single crystal D2# and the silicon carbide single crystal D3# have poor distribution uniformity of resistivity, and the radial distribution of resistivity is more than two orders of magnitude. The test structure was explained by taking a 4-inch silicon carbide single crystal substrate # 1 as an example, and the resistivity distribution of the silicon carbide single crystal substrate # 1 was shown in fig. 2, and the resistivity of the silicon carbide single crystal substrate # 2 was uniformly distributed.
because the radial temperature of the growth interface of the silicon carbide single crystal is kept consistent, impurities and intrinsic point defects in the crystal growth process are uniformly distributed in the radial direction, and further the semi-insulating high-purity silicon carbide single crystal substrate with larger size and uniformly distributed resistivity in the radial direction can be realized.
The bending and warping degree of the prepared silicon carbide single crystal substrate 1#, silicon carbide single crystal substrate 2#, silicon carbide single crystal substrate 3#, silicon carbide single crystal substrate 4#, silicon carbide single crystal substrate 5#, silicon carbide single crystal substrate 6#, silicon carbide single crystal substrate D1#, silicon carbide single crystal substrate D2# and silicon carbide single crystal substrate D3# are respectively tested. The bow and warp for the prepared silicon carbide single crystal substrates 1# -6# of 4-8 inches were within 10 μm. Because the crucible can provide the temperature gradient in the radial direction, the internal stress of the silicon carbide crystal is reduced at the same time, and the prepared silicon carbide single crystal substrate has smaller stress, and the bending degree and warping degree of the silicon carbide single crystal substrate are reduced, so that the silicon carbide single crystal substrate with higher quality is obtained. The bow and warp of the 8-inch silicon carbide single crystal substrate D1#, the silicon carbide single crystal substrate D2#, and the silicon carbide single crystal substrate D3# were 23.39 μm/31.74 μm, 19.27 μm/29.73 μm, and 27.84 μm/40.66 μm, respectively, which were much larger than 10 μm.
The resistivity of 8-12 inch semi-insulating silicon carbide single crystal substrate 1# -6# prepared by the embodiment of the application can reach 1 × 1010omega cm or more, and the radial distribution of the resistivity is controlled within one order of magnitude, and further within 80%, thereby realizing the uniform distribution of the resistivity of the silicon carbide single crystal substrate. For an 8-12 inch silicon carbide single crystal substrate, bow and warp can be controlled to be within 10 μm.
The above description is only an example of the present application, and the protection scope of the present application is not limited by these specific examples, but is defined by the claims of the present application. Various modifications and changes may occur to those skilled in the art. Any modification, equivalent replacement, improvement, etc. made within the technical idea and principle of the present application should be included in the protection scope of the present application.

Claims (6)

1. a thermal field structure for growing silicon carbide single crystals comprises a crucible, a heating unit and a heat preservation structure, and is characterized in that the heat preservation structure comprises a heat preservation structure top, a heat preservation structure side and a heat preservation structure bottom, the crucible is located in a sealed cavity of the heat preservation structure, and the heating unit heats the outer wall of the crucible in an induction mode;
The wall thickness of the side wall opening area of the crucible is larger than that of the bottom area;
The opening section of the crucible has a first distance from the inner surface of the top of the heat preservation structure above the opening section, the first distance is increased from the center of the crucible to the edge of the crucible, and the top of the heat preservation structure is thickened from the edge of the crucible to the center; the variation value of the first distance is 5-50 mm;
The side wall of the crucible is thickened linearly along the direction from the bottom of the crucible to the opening; along the direction from the bottom of the crucible to the opening of the crucible, the inner surface of the side part of the heat preservation structure extends along the direction far away from the central axis of the crucible; the inner surface of the side wall of the crucible is approximately cylindrical, and the outer wall of the crucible has the same extending direction with the inner surface of the side part of the heat preservation structure;
the outer surface of the heat insulation structure is a cylinder, and the wall part of the side part of the heat insulation structure is thickened linearly along the direction from the opening of the crucible to the bottom;
the crucible and the heat insulation structure share a first central axis;
The first central axis is approximately parallel to the inner surface of the side wall of the crucible and the outer surface of the side part of the heat preservation structure;
The first central axis and the outer surface of the side wall of the crucible are provided with a first included angle, the first central axis and the inner surface of the side part of the heat insulation structure are provided with a second included angle, the first included angle is 5-30 degrees, the second included angle is 5-30 degrees, and the first included angle and the second included angle are approximately equal.
2. The thermal field structure of claim 1, wherein the crucible is a graphite crucible.
3. the thermal field structure of claim 1, wherein the insulating structure has no opening at the top; the inner surface of the bottom of the insulation structure is approximately cylindrical.
4. A method for producing a silicon carbide single crystal, characterized by using the thermal field structure according to any one of claims 1 to 3.
5. A crystal growth apparatus comprising the thermal field structure of any of claims 1-3.
6. The crystal growth apparatus of claim 5, wherein the crystal growth apparatus is configured to produce a semi-insulating silicon carbide single crystal having a diameter of 4-12 inches.
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