CN113652749B

CN113652749B - Silicon carbide crystal with few small-angle crystal boundaries, substrate and preparation method thereof

Info

Publication number: CN113652749B
Application number: CN202110948698.XA
Authority: CN
Inventors: 张九阳; 李霞; 王永方; 王宗玉; 张红岩; 高超; 薛刚生; 杜其健; 苏丽娜
Original assignee: Shandong Tianyue Advanced Technology Co Ltd
Current assignee: Shandong Tianyue Advanced Technology Co Ltd
Priority date: 2021-08-18
Filing date: 2021-08-18
Publication date: 2022-07-12
Anticipated expiration: 2041-08-18
Also published as: CN113652749A

Abstract

The application discloses a silicon carbide crystal with few small-angle crystal boundaries, a substrate and a preparation method thereof. The silicon carbide crystal has an annular morphology extending from the first major surface through to the second major surface, the annular morphology including edge dislocations. The silicon carbide crystal containing the annular morphology is prepared and applied after mastering a related forming mechanism and a testing method thereof, so that waste is changed into valuable materials for optimizing the edge quality of the silicon carbide, the annular morphology, namely the edge dislocation wall, is used for preventing edge dislocation formed in the crystal growth process of the silicon carbide from slipping inwards and preventing edge small-angle crystal boundaries from extending inwards, and a high-quality silicon carbide substrate is obtained by means of special processing equipment and technology.

Description

Silicon carbide crystal with few small-angle crystal boundaries, substrate and preparation method thereof

Technical Field

The application relates to a silicon carbide crystal with few small-angle crystal boundaries, a substrate and a preparation method thereof, belonging to the field of semiconductor materials.

Background

Silicon carbide material has attracted much attention because of its excellent semi-insulating property, and especially for high-power semiconductor devices with special requirements, silicon carbide becomes a potential material of choice for these devices because of its high temperature, high frequency, high power, etc.

At present, silicon carbide crystal is produced by adopting a PVT method in industrial production, but because the requirement on the growth condition is higher, the improvement of the performance and the further application and development of the silicon carbide crystal are limited by defects introduced in the growth process. Therefore, improvement of defects is a primary prerequisite for improving the quality of the silicon carbide substrate.

The defects of silicon carbide crystals which we are familiar with at present are mainly: micropipes, triangular defects, voids and cracks, small-angle grain boundaries, traditional dislocations, and other defects (mainly including stacking faults, carrot defects, giant steps, particles, droppings, surface scratches, growth pits, and the like). These defects can have a certain effect on the quality of the material and further on the performance of devices made from the silicon carbide crystal, which fundamentally restricts the development of silicon carbide materials.

The preparation of semi-insulating silicon carbide single crystal which is industrialized at present is based on physical vapor phase method (PVT), which continuously optimizes the process and improves the quality of seed crystal, and further continuously explores for continuously improving the crystal quality to obtain the silicon carbide substrate with low defect density, large size and high quality.

At present, in the growth process of the silicon carbide crystal by the PVT method, edge dislocation can generate slip due to shear stress formed by temperature gradient, so that the slip is carried out from the edge to the center, and the high density of the dislocation at the center of a substrate, the local dislocation accumulation and the like are often caused.

During the crystal growth process, LAGB (small angle grain boundary) is formed at the crystal edge due to the fluctuation of crystal growth parameters, namely (edge dislocation) TED walls are formed. The formation of LAGB generally causes the local stress of a silicon carbide substrate to be poor, the crystallization quality to be poor, the FWHM value measured by corresponding XRD is large, the diffraction peak is widened or an impurity peak appears, and the use of a downstream device is interfered.

The grain boundary types can be divided into a small-angle grain boundary and a large-angle grain boundary, wherein the small-angle grain boundary refers to a grain boundary with a rotation included angle smaller than 10 degrees between two adjacent grains, and the large-angle grain boundary refers to a grain boundary with a rotation angle larger than 10 degrees.

For the seed crystal with local defects on the edge, the defects are transmitted to the grown crystal with high probability in the crystal growing process, so that the crystal always has the defects at the same position, and the high-quality silicon carbide crystal is not obtained.

Disclosure of Invention

In order to solve the problems, the silicon carbide crystal with the annular morphology is prepared and applied after a related forming mechanism and a testing method are mastered, so that waste is turned into wealth to optimize the edge quality of the silicon carbide, the annular morphology, namely the edge dislocation wall, is used for preventing edge dislocations formed in the silicon carbide crystal growth process from slipping inwards and preventing edge small-angle crystal boundaries from extending inwards, and a high-quality silicon carbide substrate is obtained by means of special processing equipment and special processing technology.

The silicon carbide crystal with few small-angle grain boundaries has a ring-shaped morphology extending throughout from the first major surface to the second major surface, the ring-shaped morphology including edge dislocations;

and forming a target silicon carbide crystal in a region surrounded by the annular appearance, wherein the dislocation density outside the annular appearance is greater than the dislocation density inside the annular appearance.

Optionally, the silicon carbide crystal is a 4H polytype silicon carbide crystal having a first major surface and a second major surface opposite the first major surface, the first major surface being a {0001} plane or a plane inclined at an off-angle greater than 0 ° and no greater than 8 ° with respect to the {0001} plane;

optionally, the ring-shaped topography blocks dislocations and small-angle grain boundaries from sliding inward;

the small-angle grain boundary outside the annular shape is larger than the small-angle grain boundary inside the annular shape.

Optionally, the stress of the annular feature is greater than the stress outside the annular feature is greater than the stress inside the annular feature.

Optionally, the crystalline quality outside the annular topography is lower than the crystalline quality inside the annular topography.

Optionally, the width of the annular feature is no greater than 5 mm.

Optionally, the silicon carbide crystal size in the annular topography is not less than 150 mm. The silicon carbide crystal size within the annular topography may be 150mm, 200mm, 250mm, 300mm, or 350 mm.

Optionally, the annular feature extends inwardly at least 3mm as an annular region that is a face that is inclined with respect to a {0004} face by an off-angle of no greater than 0.06 °;

and no small-angle grain boundary exists in the annular region, and the full width at half maximum of the crystallization quality of the annular region is not more than 20 arcsec. Preferably, the annular region and the central region have equal crystalline qualities such as off-angle, low angle grain boundaries, and full width at half maximum.

Optionally, the annular region is a face inclined with respect to an off-angle of {0004} face of no more than 0.05 °; the annular region is free of small-angle grain boundaries, and the full width at half maximum of the crystalline quality of the annular region is not more than 16.6 arcsec.

Optionally, the annular region has a width extending inward from the edge of the substrate of not less than 5 mm. Further, the annular region may have a width value or a width range extending inward from the edge of the substrate with upper and lower limits of 3mm, 4mm, 5mm, 6mm, 10mm, 15mm, or 20mm, respectively.

Optionally, the dislocation density in the annular region is no higher than 5500/cm²And the dislocation density in the central region is not higher than that in the annular region. Preferably, the upper limit of the dislocation density in the annular region is selected from 4400/cm²、4395/cm²、2600/cm²、2591/cm²。

Optionally, the stress is uniform in the central and annular regions.

According to another aspect of the present application, there is provided a method for producing a silicon carbide crystal with few small-angle grain boundaries according to any of the above, comprising the steps of:

1) assembling: providing a bearing raw material and a seed crystal arranged at the top in the crucible, placing the crucible in a heat preservation cavity formed by a heat preservation layer, and then moving the crucible into a crystal growth furnace; the heat-insulating layer comprises a heat-insulating ring arranged above the crucible, the heat-insulating ring at least covers the seed crystal and extends inwards from the edge by 0.5mm to 0.5r-0.5mm, and r is the radius of the seed crystal;

2) growing a crystal: and (3) preparing the silicon carbide crystal by crystal growth, wherein the edge of the prepared silicon carbide crystal forms an annular shape approximately corresponding to the covering position of the heat preservation ring.

Optionally, the crystal growth stage in step 2) comprises the following steps:

removing impurities: controlling the temperature and pressure of the crystal growth furnace and the flow of inert gas introduced into the crystal growth furnace so as to clean and remove impurities in the crystal growth furnace;

a temperature rise stage: adjusting the temperature of the crystal growth furnace to 2000-2400K, and controlling the pressure in the crucible to be 0.6 multiplied by 10⁵～3.3×10⁴Pa, the flow of inert gas introduced into the crystal growth furnace is 50-500mL/min, at the moment, the crucible moves upwards at the moving speed of 0.1mm/h, and rotates at the speed of 0.5 r/min;

a pressure reduction stage: the pressure is controlled from 0.6X 10⁵～3.3×10⁴Pa, down to 5X 10³Pa-1×10⁴Pa; during the pressure reduction, the crucible moves downwards at the speed of 1mm/h and rotates at the speed of 0.2 r/min; controlling the temperature to be 2400K-2600K;

crystal growth stage: the crystal growth temperature is 2600K-2800K, the crystal growth pressure is 100-; and keeping the reaction time for 80-120 h to obtain the silicon carbide crystal with the annular shape and the controllable diameter.

The invention discloses a ring shape based on the growth of silicon carbide crystal by the existing PVT method, which is applied after mastering the related formation mechanism and test method, thereby changing waste into valuable and optimizing the edge quality of silicon carbide, preventing the inward slippage of edge dislocation formed in the crystal growth process of silicon carbide and the inward extension of edge small-angle crystal boundary (LAGB) by the ring shape, namely a TED wall, and obtaining a high-quality silicon carbide substrate by special processing equipment and process.

The structure of heat preservation ring that this application provided and the position of setting can construct specific radial temperature gradient distribution in the top of carborundum seed crystal. Specifically, an air layer located above the seed crystal is surrounded on the inner side wall of the heat preservation ring, on one hand, the difference between the heat conductivity of air and the heat conductivity of the heat preservation layer is large, so that the radial temperature gradient of a temperature field generates sudden change at the position of the inner side wall of the heat preservation ring from inside to outside, and then a large temperature difference is formed between the inner side wall and the outer side of the inner side wall of the heat preservation ring, so that a large number of surface or penetrating defects are generated at the position of the inner side wall of the heat preservation ring with the temperature suddenly changed by the crystal in a centralized mode, a large number of defects are gathered to form an annular shape similar to a wall form, the annular shape can simultaneously prevent low-angle crystal boundaries outside the ring from extending inwards and the edge dislocations from sliding inwards, and the problem that the edge defects of the crystal extend or slide towards the middle part is solved; on the other hand, the air layer can also play the effect of homogenizing the temperature field, is favorable to adjusting the radial temperature ladder above the seed crystal, and then reduces or even eliminates the production of crystal middle part defect, promotes the quality of middle part crystal. Under the action of the two aspects, the quality of the middle area of the crystal within the position of the inner side wall of the heat preservation ring is improved, and the dislocation at the edge of the crystal is blocked and cannot slide into the middle area of the crystal at the inner side in the presence of the annular shape, so that the quality of the middle crystal of the silicon carbide crystal is obviously improved, and the silicon carbide crystal, namely the substrate with high quality at the middle part can be obtained after the annular shape and the outer part are removed.

According to still another aspect of the present application, there is provided a silicon carbide substrate with few small-angle grain boundaries, wherein any of the silicon carbide crystals described above or a method for producing any of the silicon carbide crystals described above further comprises the steps of:

the preparation method of the silicon carbide crystal comprises the following steps:

the silicon carbide crystal is subjected to the step of slicing to prepare a silicon carbide substrate with an annular shape;

preferably, the method further comprises the step of edging: and cutting the silicon carbide substrate along the annular shape or the inner side close to the annular shape to obtain the target silicon carbide substrate. Specifically, the silicon carbide crystal slicing further comprises grinding and polishing steps.

The preparation method for preparing the silicon carbide crystal is characterized in that an air layer is arranged between an upper insulating layer and a crucible besides an insulating ring structure.

1) assembling: providing a crucible for bearing raw materials and seed crystals, placing the crucible in a heat preservation cavity formed by a heat preservation layer, and then moving the crucible into a crystal growing furnace;

2) growing a crystal: and carrying out crystal growth under the condition that the distance between the top surface of the crucible and the inner surface of the upper heat-insulating layer of the heat-insulating layer is 30-50mm, and preparing the silicon carbide crystal.

Specifically, the seed crystal is installed the crucible of crucible is covered the below, and the diameter less than or equal to crucible of seed crystal covers the area, and the heat preservation ring sets up between the crucible lid of last heat preservation and crucible, the crucible top surface with the air bed that the distance between the last heat preservation internal surface of heat preservation formed. On the one hand, the air layer is arranged to homogenize the temperature field above the seed crystal, so that the radial temperature gradient of the target silicon carbide crystal above the seed crystal is further regulated and homogenized, and the quality of the target silicon carbide crystal is improved.

Optionally, a gap between the crucible side wall and the side insulating layer of the insulating layer is less than 1 mm. The crucible can not produce frictional getting and put the heat preservation intracavity promptly, but contactless nevertheless does not have obvious clearance between crucible and the heat preservation chamber, and this setting mode only forms the air bed between crucible top and last heat preservation, is favorable to guaranteeing the heat preservation effect of long brilliant in-process crucible lateral wall to guarantee radial temperature ladder and the axial temperature ladder of long brilliant in-process, prevent that the sublimed SiC atmosphere of PVT method from excessively leaking, be unfavorable for growing brilliant. The air layer is too large, which is not beneficial to the heat preservation of the crystal growth crucible, so that the atmosphere overflows, the shaft ladder is reduced, and the crystal growth is not beneficial.

As an implementation mode, the upper heat-insulating layer is provided with temperature measuring holes, the heat-insulating layer further comprises a lower heat-insulating layer, a heat-insulating ring and a transition heat-insulating layer, and the lower heat-insulating layer, the upper heat-insulating layer, the heat-insulating ring, the side heat-insulating layer and the transition heat-insulating layer enclose the heat-insulating cavity.

As an implementation mode, the upper heat-insulating layer is provided with temperature measuring holes, the heat-insulating layer further comprises a lower heat-insulating layer and a heat-insulating ring, and the lower heat-insulating layer, the upper heat-insulating layer, the heat-insulating ring and the side heat-insulating layer enclose the heat-insulating cavity.

Specifically, the shape of the transition insulating layer is not limited as long as the threaded connection portion is cylindrical, and may be, for example, a circular cylindrical structure or a cylindrical structure having an inwardly extending annular groove.

Preferably, the outer side wall of the side heat-insulating layer is provided with a thread structure, and the bottom end of the thread structure corresponds to the center of the crucible. The arrangement mode solves the problem of non-visualization in the crucible and the heat preservation layer, the central position of the thermal field is arranged in the crucible, the central position of the crucible can be obviously reflected, and the central position of the thermal field in the raw material in the crucible can be conveniently adjusted in the crystal growth process.

Optionally, as another embodiment, the growing crystal phase comprises the steps of:

removing impurities;

a temperature rising stage: adjusting the temperature of the crystal growth furnace to 1500-2200K, and controlling the pressure in the crucible to be 0.6 multiplied by 10⁵～3.3×10⁴Pa, introducing inert gas into the crystal growth furnace at a flow rate of 50-500 mL/min;

a step-by-step pressure reduction stage: controlling the pressure in the crucible to 3.3X 10⁴-2×10⁴Pa, raising the temperature to 2200-; ② controlling the pressure intensity in the crucible to be 2 multiplied by 10⁴Pa-1.2×10⁴Pa, raising the temperature to 2300K-2400K, and maintaining for 3 hours after reducing the pressure; thirdly, controlling the pressure intensity in the crucible to be 1.2 multiplied by 10⁴Pa-0.5×10⁴Pa, raising the temperature to 2400K-2500K, reducing the pressure, and maintaining for 5 hours, namely entering a crystal growth stage; the side heat-insulating layer drives the crucible to move downwards at the speed of 1mm/h in the step-by-step pressure reduction process, and the crucible rotates at the speed of 1r/min until the crucible is coincided with the center of a heating coil of the crystal growth furnace;

and (3) crystal growth stage: and controlling the crystal growth temperature to be 2500-2800K, the crystal growth pressure to be 5000-.

Specifically, the step-by-step pressure reduction is favorable for stably adjusting the pressure and the temperature in the crucible, impurities in the thermal field environment and the crucible can be further purified in the pressure reduction process, the silicon carbide powder loss of the silicon carbide crystal is prevented, the crucible is moved downwards in the pressure reduction process, the homogenization of a temperature field is favorable for the increase of an air layer at the top of the crucible, the internal stress of the silicon carbide crystal is reduced, and the cracking caused by the stress concentration is prevented.

The silicon carbide crystal prepared by the preparation method cannot generate annular appearance, and the middle area and the annular area of the silicon carbide crystal prepared by the air layer structure are few in defects and high in crystal quality, namely the dislocation density of the annular area at the edge is low, and the dislocation density of the central area is low. The annular area of the edge of the silicon carbide crystal prepared by the preparation method has no small-angle grain boundary generated by the edge effect, and the crystallization quality is high.

In the present application, the silicon carbide crystal has first and second opposed major surfaces, the annular feature extending across the silicon carbide crystal from the first major surface toward the second major surface in a direction generally perpendicular to the first major surface, the annular feature extending proximate a periphery of the silicon carbide crystal, e.g., a silicon carbide crystal having an annular feature that surrounds a region that includes a central region and an annular region; the ring shape can be observed by using a laser detector, a lattice defect detector, a microscope or a stress meter and the like; the ring-shaped topography includes edge dislocations.

Benefits of the present application include, but are not limited to:

1. according to the silicon carbide crystal with few small-angle crystal boundaries, the target silicon carbide crystal with the silicon carbide crystal has the advantages of high crystal quality, few dislocation, basically no small-angle crystal boundaries, small stress and high surface type quality.

2. According to the silicon carbide crystal with few small-angle grain boundaries, the dislocation density of the annular region at the edge of the target silicon carbide crystal is low, and the dislocation density of the central region is low; and the annular area at the edge does not generate small-angle grain boundaries, so that the crystallization quality is high, and the quality of the manufactured downstream device is high.

3. According to the preparation method of the silicon carbide crystal and the substrate with few small-angle crystal boundaries, the air layer is arranged to homogenize the temperature field above the seed crystal, and the radial temperature gradient above the seed crystal is further regulated and homogenized to further inhibit the generation of defects in the target silicon carbide crystal, so that the generation of edge defects of the target silicon carbide crystal is avoided.

4. According to the preparation method of the silicon carbide crystal and the substrate with few small-angle crystal boundaries, an annular shape is found and is applied after a related forming mechanism and a related testing method are mastered, so that waste is turned into wealth to optimize the edge quality of the silicon carbide, the annular shape, namely the edge dislocation wall, is used for preventing the inward slippage of edge dislocation formed in the crystal growth process of the silicon carbide and the inward extension of the edge small-angle crystal boundaries, and the high-quality silicon carbide substrate is obtained by means of special processing equipment and processes.

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 an insulation layer provided in example 1 of the present application;

FIG. 2 is a schematic view of another insulation layer provided in example 1 of the present application;

FIG. 3 is a schematic view of another insulation layer provided in example 1 of the present application;

FIG. 4 is a schematic view of an insulation layer provided in example 3 of the present application;

FIG. 5 is a schematic view of another insulation layer provided in example 3 of the present application;

FIG. 6 is a schematic view of yet another insulation layer provided in example 3 of the present application;

FIG. 7 is a schematic illustration of a primary silicon carbide substrate having an annular topography prepared in accordance with example 5 of the present application;

fig. 8 is a characteristic image of the ring-shaped morphology of the primary silicon carbide substrate a in a laser detector (Candela, equipment model CS920, equipment manufacturer) in example 5 of the present application;

fig. 9 is a characteristic image of the annular shape of the primary silicon carbide substrate a in a stress detector (instrument manufacturer, suzhou precision optical instrument ltd, equipment model number is qualitative portable polarization stress meter) in example 5 of the present application;

FIG. 10 is a test image of a ring-shaped lattice distortion detector (instrument manufacturer, soaring Crystal semiconductor technology Co., Ltd., equipment model CS10) for a primary silicon carbide substrate a according to example 5 of the present application;

fig. 11 is a polarization observation diagram (a) and a labeled diagram (b) of the ring shape of the primary silicon carbide substrate a in the SiC polished wafer in a microscope (the instrument manufacturer is olympus, equipment model MX63), and an observation diagram (c) and a labeled diagram (d) under a dark field in example 5 of the present application;

fig. 12 shows Raman mapping (HORIBA, equipment model: HREVOLUTION) of the ring profile of the primary silicon carbide substrate a in example 5 of the present application;

fig. 13 is a characteristic image (a) of the ring-shaped morphology of the primary silicon carbide substrate a in a laser detector (Candela, equipment model CS920, equipment manufacturer) in example 5 of the present application; an Atomic Force Microscope (AFM) (instrument manufacturer Park, equipment model NX20) of the annular appearance of the primary silicon carbide substrate a is used for testing (b);

FIG. 14 shows the results (b) of ring profile XRD test (instrument manufacturer is Bruker, equipment model is JV-DX) of the as-grown silicon carbide substrate a under a laser detector (equipment manufacturer is Candela, equipment model is CS920) for ring profile characterization image test (a) and ring profile bias angle XRD test (equipment manufacturer is Bruker, equipment model is JV-DX) for the as-grown silicon carbide substrate a according to example 5 of the present application;

FIG. 15 is an observation image of a microscope (manufactured by Olympus, model MX63) after ring shape stress KOH etching of a primary silicon carbide substrate a according to example 5 of the present application;

FIG. 16 is a statistical mapping image of dislocations after ring stress KOH corrosion of a ring shape of a primary silicon carbide substrate a according to example 5 of the present application;

fig. 17 is an observation image of the ring shape microscope (olympus, equipment model MX63) of the primary silicon carbide substrate a of example 5 of the present application under polarized light;

FIG. 18 is an image of a surface profile test (CORNING, FlatMaster200 Semi-Automated Wafer System) of the annular topography of a primary silicon carbide substrate a according to example 5 of the present application, wherein (a) is a wave-Bow surface profile image and (b) is LTV data;

in the figure: 101. an upper heat-insulating layer; 1011. a first external thread; 102. a transition heat-insulating layer; 2. a crucible; 3. silicon carbide seed crystals; 4. silicon carbide powder; 5. a side insulating layer; 501. a second external thread; 6. a temperature measuring hole; 7. an air layer; 701. the inner surface of the upper heat-insulating layer; 702. the inner surface of the transition insulating layer; a heat preservation ring 8; annular topography 91, silicon carbide substrate 92, annular region 93, central region 94.

Detailed Description

The present application will be described in detail with reference to examples, but the present application is not limited to these examples.

Unless otherwise specified, the raw materials and catalysts in the examples of the present application were all purchased commercially.

Example 1

The heat retaining ring structure is not shown in the drawings of this embodiment, and this embodiment mainly explains the structure of the air layer.

The crucible 2 is a graphite crucible, and the size of the silicon carbide seed crystal in the crucible 2 is 100-350 mm.

Referring to fig. 1-3, the insulating layer comprises a lower insulating layer, an upper insulating layer 101, a side insulating layer 5 and a transition insulating layer 102, the lower insulating layer, the upper insulating layer 101, the side insulating layer 5 and the transition insulating layer 102 enclose a heat insulating cavity, and the upper insulating layer 101 is provided with a temperature measuring hole; the transition insulating layer 102 is in threaded connection with at least one of the upper insulating layer 101 and the side insulating layer 5 and is integrally formed with the other, the upper insulating layer 101 is in threaded connection with the side insulating layer 5 through the transition insulating layer 102, and the distance between the crucible 2 arranged in the side insulating layer 5 and the inner surface of the upper insulating layer 101 is adjusted in a rotating manner.

Specifically, lower heat preservation and 5 fixed connection of side heat preservation, like integrated into one piece or screw connection etc. as long as realize that the heat preservation rotates can drive 5 rotations of side heat preservation simultaneously promptly. The crucible is placed on the lower heat-insulating layer, and the movement of the lower heat-insulating layer can drive the crucible to do the same movement. Specifically, the mode of relative rotation between the upper insulating layer 101 and the side insulating layer 5 through the threaded connection of the transition insulating layer 102 may be: the upper insulating layer 101 is fixed on the crystal growth furnace, and the lower insulating layer is installed on the rotary lifting unit. As an implementation mode, the rotary lifting unit comprises a motor, a rotary lifting platform and a supporting rod, the rotary lifting platform is fixed on the top of the supporting rod, the lower heat-insulating layer is fixed on the top of the rotary lifting platform, and the motor drives the supporting rod to drive the rotary lifting platform and the lower heat-insulating layer to rotate and lift. The rotary lifting mechanism can also be other rotary lifting units commonly used in the field as long as the rotary lifting unit can rotate and lift the side heat-insulating layer or the upper heat-insulating layer.

Referring to fig. 1, the inner surface 702 of the transition insulation layer is screw-coupled to the second external screw 501 outside the side insulation layer 5, the top of the transition insulation layer 102 is integrally formed with the upper insulation layer 101, and the transition insulation layer 102 and the side insulation layer 5 are relatively rotated to adjust the thickness of the air layer 7 between the top of the crucible 2 and the inner surface 701 of the upper insulation layer.

Referring to fig. 2, a first external thread 1011 is provided on the outer side of the upper insulation layer 101 and is in threaded connection with the inner surface 702 of the transition insulation layer, and the inner surface 702 of the transition insulation layer is in threaded connection with a second external thread 501 on the outer side of the side insulation layer 5. The transition insulating layer 102 and the side insulating layer 5 are adjusted to rotate relatively, and/or the transition insulating layer 102 and the upper insulating layer 101 are adjusted to rotate relatively to adjust the thickness of the air layer 7 between the top of the crucible 2 and the inner surface 701 of the upper insulating layer.

Specifically, the shape of the transition insulation layer 102 is not limited as long as the threaded connection portion is cylindrical, such as the circular ring cylindrical structure of fig. 2 or the cylindrical structure with an inwardly extending annular groove of fig. 3. The annular groove of the transition insulating layer 102 of fig. 3 is disposed to protrude from the side insulating layer 5 to form an air layer having a diameter significantly larger than that of the silicon carbide seed crystal 3 above the top opening of the side insulating layer 5, so as to further avoid edge defects of the grown silicon carbide crystal.

Specifically, the diameter of the air layer 7 is 0.2 to 30cm, preferably 1 to 20cm, more preferably 3 to 15cm larger than the diameter of the silicon carbide seed crystal. The thickness of the air layer is 10-60 mm. Further, the thickness of the air layer 7 in the crystal growth process is 20-50 mm; preferably, the thickness of the air layer 7 during the crystal growth is 30mm to 40 mm. The air layer is arranged in a mode which is beneficial to improving the crystal growth quality and reducing the generation of defects, particularly the defects at the edge of the crystal. Too thick air layer can lead to the reduction of the axis ladder, be unfavorable for guaranteeing the growth rate of crystal, too thin can lead to radial temperature ladder too big, and the shear stress increases, leads to stress concentration in the carborundum crystal.

As a preferred embodiment, it is preferable that the bottom end of the second external thread 501 provided on the outer sidewall of the side insulating layer 5 corresponds to the center position of the crucible 2. The arrangement mode solves the problem of non-visualization in the crucible 2 and the heat preservation layer, is difficult to adjust the central position of the crucible 2 in the thermal field, can obviously reflect the central position of the crucible 2, and can conveniently adjust the central position of the raw material in the crucible 2 in the thermal field in the crystal growth process.

Referring to fig. 1-3, in an assembled state, a crucible 2 is placed in a heat preservation cavity of a heat preservation layer, silicon carbide powder 4 is filled in the crucible 2, a silicon carbide seed crystal 3 is fixed on a crucible cover of the crucible 2, and the heat preservation cavity is of a sealed cavity structure with one position of a temperature measurement hole 6.

Specifically, the crucible 2 is a graphite crucible, and the heat-insulating layer is made of graphite felt.

Example 2

In this embodiment, a schematic view of adding a heat insulating ring structure is described in conjunction with embodiment 1, and in this embodiment, the portion not shown in embodiment 1 is only required to be capable of directly placing a heat insulating ring between the crucible and the upper heat insulating layer.

Referring to fig. 4, the embodiment is different from embodiment 1 in that the insulating layer includes a lower insulating layer, an upper insulating layer 101, a side insulating layer 5, and an insulating ring 8, the insulating ring 8 is connected between the upper insulating layer 101 and the side insulating layer 5, and the lower insulating layer, the upper insulating layer 101, the side insulating layer 5, and the insulating ring 8 enclose a heat insulating cavity.

Referring to fig. 5, the embodiment is different from the embodiment of fig. 1 of embodiment 1 in that the insulating layer further includes an insulating ring 8, the top of the insulating ring 8 is connected to the bottom of the upper insulating layer 101, and the bottom of the insulating ring 8 is connected to the top of the transition insulating layer 102. Specifically, the insulating ring 8 may be integrally formed with the upper insulating layer 101 and the transition insulating layer 102, respectively.

Referring to fig. 6, the embodiment is different from the embodiment of fig. 1 of embodiment 1 in that the insulating layer further includes an insulating ring 8, the inner surface of the insulating ring 8 is in threaded connection with the outer surface of the upper insulating layer 101, and the bottom surface of the insulating ring 8 is connected with the top surface of the transition insulating layer 102. Specifically, the bottom surface of the insulating ring 8 and the top surface of the transition insulating layer 102 are integrally formed.

Specifically, in any embodiment, the heat retaining ring 8 is arranged above the crucible, the heat retaining ring 8 at least covers 0.5mm to 0.5r-0.5mm of the seed crystal extending inwards from the edge, and r is the radius of the seed crystal.

Example 3

The method for producing a silicon carbide substrate using the crucible optionally containing the insulating layer and the crucible of example 2 includes the steps of:

1) assembling: providing a bearing raw material and a seed crystal arranged at the top in a crucible, placing the crucible in a heat preservation cavity formed by a heat preservation layer, and then moving the crucible into a crystal growth furnace; wherein, the heat preservation layer comprises a heat preservation ring arranged above the crucible, the heat preservation ring at least covers 0.5mm to 0.5r-0.5mm of the seed crystal extending inwards from the edge, and r is the radius of the seed crystal;

2) growing a crystal: preparing a silicon carbide crystal by crystal growth, wherein the edge of the prepared silicon carbide crystal forms an annular shape approximately corresponding to the covering position of the heat preservation ring;

3) preparing a primary silicon carbide substrate: carrying out steps including slicing on the silicon carbide crystal to obtain a primary silicon carbide substrate with an annular shape;

4) trimming: cutting the initial silicon carbide substrate along the inner side of the annular shape or close to the inner side of the annular shape to obtain a silicon carbide substrate;

wherein the crystal growth stage in step 3) comprises the following steps:

a temperature rising stage: adjusting the temperature of the crystal growth furnace to 2000-2400K, and controlling the pressure in the crucible to be 0.6 multiplied by 10⁵～3.3×10⁴Pa, introducing inert gas into the crystal growth furnace at a flow rate of 50-500mL/min, moving the crucible upwards at a moving speed of 0.1mm/h and rotating at a speed of 0.5 r/min;

a pressure reduction stage: the pressure is controlled from 0.6X 10⁵～3.3×10⁴Pa, down to 5X 10³Pa-1×10⁴Pa; during the depressurization, the crucible is moved down at a speed of 1mm/h and rotated at a speed of 0.2r/min(ii) a Controlling the temperature to be 2400K-2600K;

crystal growth stage: the crystal growth temperature is 2600K-2800K, the crystal growth pressure is 100-; the holding time is 80-120 h, and the silicon carbide crystal with the ring-shaped appearance and the controllable diameter is prepared.

Example 4

The method for preparing a silicon carbide substrate using the insulating layer and the crucible of fig. 5 in example 3 includes the steps of:

1) assembling: providing a bearing raw material and a seed crystal arranged at the top in a crucible, placing the crucible in a heat insulation cavity formed by a heat insulation layer, and then moving the crucible into a crystal growth furnace; wherein, the heat preservation layer comprises a heat preservation ring arranged above the crucible, the heat preservation ring at least covers the seed crystal, the width D of the seed crystal extending inwards from the edge is 0.5mm to 10mm, and the radius r of the seed crystal can be 24mm-85 mm;

2) growing a crystal: growing crystals to prepare the silicon carbide crystals, wherein the edges of the prepared silicon carbide crystals form an annular shape approximately corresponding to the covering position of the heat preservation ring;

3) preparing a primary silicon carbide substrate: carrying out steps including slicing on the silicon carbide crystal to prepare a primary silicon carbide substrate with an annular shape;

4) trimming: cutting the initial silicon carbide substrate along the inner side of the annular shape or close to the inner side of the annular shape to obtain a silicon carbide substrate a;

wherein the crystal growth stage in step 3) comprises the following steps:

a pressure reduction stage: the pressure is controlled from 0.6X 10⁵～3.3×10⁴Pa, down to 5X 10³Pa-1×10⁴Pa; the crucible was moved down at a speed of 1mm/h, 0.2 during the depressurizationrotating at the speed of r/min; controlling the temperature to be 2400K-2600K;

Example 5

The difference between this example and the preparation method of example 4 is that the width D of the seed crystal covered by the heat-retaining ring extending inward from the edge is different, and silicon carbide substrates b-g are prepared respectively. Comparative example 2 differs from example 5 in that there is no heat retaining ring, and comparative example 2 produces a comparative silicon carbide substrate Da.

TABLE 1

The wider the width of the heat-insulating ring, the larger the radial temperature gradient, when the inner diameter of the heat-insulating ring is smaller than the diameter of the crystal, the abrupt change of the radial gradient can occur at the junction of the heat-insulating ring and the air layer, so that the shearing stress at the junction is large, and the annular appearance is generated; the thickness of the heat preservation ring corresponds to the thickness of an air layer above the crucible, the thickness of the air layer is increased, namely the temperature field is homogenized, and the diameter ladder shaft ladder is reduced, so that the defect degree is reduced; the influence trend is as follows: the wider the width of the heat-insulating ring is, the smaller the diameter of the ring-shaped appearance is, and the farther away the ring-shaped appearance is from the edge; the narrower the width is, the larger the diameter of the annular shape is, and the closer the annular shape is to the edge; the larger the air layer is, the smaller the diameter ladder is, the lower the annular appearance degree is, and the narrower the width is; the smaller the air layer is, the larger the diameter ladder is, the more the annular appearance degree is intensified, and the wider the width is.

As can be seen from the data in the table, an annular shape is found, edge dislocation walls are used for preventing the inward slip of edge dislocations formed in the crystal growth process of the silicon carbide and the inward extension of edge small-angle grain boundaries, and a high-quality silicon carbide substrate is obtained by means of special processing equipment and processes.

Laser detection, stress detection characterization, lattice distortion detection, microscope polarization and observation under a dark field, Raman mapping test, AFM test and stress deflection angle test are respectively carried out on the initial silicon carbide substrates a-g, especially annular shape areas, of the prepared silicon carbide substrates a-g. The following description will be given taking a primary silicon carbide substrate a as an example.

Referring to fig. 7, a schematic view of a primary silicon carbide substrate a 92 having a ring-shaped profile 91 prepared in example 5 of the present application, which is a ring-shaped wall-like structure penetrating the primary silicon carbide substrate a 92 perpendicular to the {0001} plane. The initial silicon carbide substrate a can observe a circle of regular circular lines at the edge under a transmission light source, the distance between the circular lines and the edge of the substrate is 2-3 mm, and the distance can be adjusted through subsequent regulation and control. And the position and the distance from the ring line to the edge of the ring defect observed by the silicon carbide crystal can completely correspond to each other. After the locating edge cut, the annular feature can be machined away.

Referring to fig. 8, the primary silicon carbide substrate a was tested by laser and the ring-shaped topography was detected by a laser detector as a white ring from the edge of the primary silicon carbide substrate. The circular ring is completely visible, has an equal distance from the edge of about 2-3 mm, and completely corresponds to the position of the strong annular appearance of the detected substrate under the transmission light source in the graph 7.

Referring to fig. 9, the primary silicon carbide substrate a is tested by a stress detector, and the annular shape of the primary silicon carbide substrate a is locally characterized by the stress detector, and the annular shape is represented as a stress ring away from the edge of the silicon carbide substrate by the detection of the stress detector. According to the characterization result, the annular shape is a boundary line between the edge stress concentration region and the central stress good region, that is, the annular shape can be regarded as blocking the edge stress caused by the defect.

Referring to fig. 10, the primary silicon carbide substrate a was tested by a lattice distortion detector, and fig. 10 is an image obtained by testing the ring morphology using the lattice distortion detector. Through images, a stress concentration region caused by a large amount of lattice distortion exists on the primary substrate from the edge of the primary substrate to the annular appearance. When the lattice distortion defect extends to the annular shape, the lattice distortion defect is blocked by the annular shape and does not extend further to the inner part of the substrate.

Referring to fig. 11, the ring shape morphology in the primary silicon carbide substrate a was observed under polarized light and dark field of a microscope, and fig. 11(a) (b) are the ring shape morphology observed under bright field of a microscope for the wafer after grinding of the primary silicon carbide substrate a. Wherein the normal abrasive sheet is a rough matte surface that is observed under a microscope as a relatively uniform khaki color. Whereas the location with the ring-shaped topography appears as a distinct band with distinct dividing lines. FIG. 11(c) (d) shows that the annular shape has a contrast difference between the light and the shade on the SiC grinding plate and the normal area under the dark field, i.e. the annular shape area is a dark annular band.

Referring to fig. 12, for the circular stress Raman mapping test of the primary silicon carbide substrate a, a near-edge circular topography is selected for the Raman mapping test, and the test area and the result are shown in fig. 12(a) and fig. 12(b), respectively. The comparison of the test result and Raman sub-modes of various crystal forms of SiC shows that the crystal forms are 4H crystal forms in the test range, and multi-type defects of other crystal forms are included.

Referring to fig. 13(a) and (b), for the ring stress AFM test of the initial silicon carbide substrate a, fig. 13(b) 1, 2 and 3 respectively show the outer ring-shaped feature, the inner ring-shaped feature and the inner ring-shaped feature of fig. 13(a), and the atomic step and roughness of the region of the ring-shaped feature are continuously characterized by means of AFM, as shown in fig. 13 (b). The result shows that the atomic steps in the region are normal, and no abnormal broadening, narrowing or sharp change exists, which indicates that the atomic steps in the region are diffused normally; where the atomic step width at position 1 (outside the ring profile) is 0.165 μm, where the atomic step width at position 2 (ring profile) is 0.192 μm, and where the atomic step width at position 3 (inside the ring profile) is 0.22 μm. .

Referring to fig. 14(a) and (b), for the ring stress deflection angle test (a) and the result (b) of the primary silicon carbide substrate a, the crystal quality test was performed by XRD on the defect position and both the inner and outer sides, as shown in fig. 14. The XRD diffraction peak at the position 1 in the annular shape has shift and broadening, the cleaning quality gradually becomes better from the inside of the annular shape to the outside of the annular shape, and the FWHM value gradually decreases. The results of XRD measurements of the crystal quality and the off-angle are shown in Table 2, in which the crystal quality gradually becomes better from the edge inward and the off-angle gradually becomes smaller. The result is mainly due to the fact that the ring morphology blocks the LAGB and part of the dislocation out of the ring, and the LAGB and the dislocation are gathered to cause lattice distortion which is expressed by poor clean quality and increased deflection angle.

TABLE 2

Referring to fig. 15, the ring shape is etched for the initial silicon carbide substrate a using a molten KOH etchant at 500 ℃, and the defect is now a dislocation wall composed of TED, as shown in fig. 15. And various dislocations of TED, TSD and BPD exist outside the dislocation wall and close to one side of the edge, and the dislocation density is obviously higher than that in the TED dislocation wall, namely the TED dislocation wall blocks inward slip of the edge dislocation.

Referring to fig. 16, a dislocation statistics mapping image of a primary silicon carbide substrate with annular stress is obtained by performing KOH etching on a substrate with annular morphology, and mapping is performed to visually display dislocation density distribution. From the results, it was found that dislocation concentrated regions are mainly concentrated on the ring morphology and the outside thereof, and a uniform low density dislocation distribution can be formed inside, and therefore based on the results, edge dislocations can be blocked by the ring morphology, thereby suppressing inward slip of edge dislocations.

Referring to fig. 17, characterization observation of the annular shape 91 of the primary silicon carbide substrate a in the microscopic polarization mode is performed, and as shown in fig. 17, the annular stress is a continuous stress band corresponding to a TED wall after KOH etching. In the annular region 93 outside the annular topography, near the edge of the substrate, the stress performance is poor, corresponding to various dislocation densities outside the TED wall after KOH corrosion. While in the central region 94 within the annular topography, near the center of the substrate, the stress behavior is relatively good, corresponding to a dislocation density inside the etched TED wall that is lower than outside the TED wall.

Referring to fig. 18(a) (b), a face-type characterization was performed for a primary silicon carbide substrate a having a ring-shaped topography, as shown in fig. 18. As can be seen from the test images, the annular shape cannot cause the substrate surface type to be different, which is shown in FIG. 18(a), that is, the warp-bow graph still shows a 'steamed bun' shape with a high center and a low periphery, and there is no difference at a position of a circle near the edge corresponding to the annular shape. The annular shape LTV is further characterized, the edge is not different from the normal shape, and the abnormal LTV rise is avoided, namely, the defect is not caused by the substrate macroscopic surface type factors such as local unevenness.

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 to which the present application pertains. 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

1. A silicon carbide crystal with few small-angle grain boundaries, the silicon carbide crystal having a ring-shaped morphology extending from a first major surface through to a second major surface, the ring-shaped morphology comprising dislocations;

and forming the target silicon carbide crystal in the surrounding area in the annular shape, wherein the dislocation density outside the annular shape is greater than the dislocation density inside the annular shape.

2. The silicon carbide crystal with few small-angle grain boundaries of claim 1, wherein the silicon carbide crystal is a 4H polytype silicon carbide crystal having a first major surface and a second major surface opposite the first major surface, and wherein the first major surface is a {0001} plane or a plane inclined at an off-angle greater than 0 ° and not greater than 8 ° with respect to the {0001} plane.

3. The silicon carbide crystal with few small angle grain boundaries of claim 1 wherein the ring morphology blocks dislocations and small angle grain boundaries from sliding inward;

4. The silicon carbide crystal with few small-angle grain boundaries of claim 1, wherein the stress of the annular feature is greater than the stress outside the annular feature than the stress inside the annular feature; and/or

The crystallization quality outside the annular topography is lower than the crystallization quality inside the annular topography.

5. The silicon carbide crystal with few small grain boundaries of claim 1 wherein the width of the annular feature is no greater than 5 mm.

6. The silicon carbide crystal with few small-angle grain boundaries of any one of claims 1-5, wherein the silicon carbide crystal size in the annular morphology is not less than 150 mm.

7. The silicon carbide crystal with few small grain boundaries of claim 6 wherein the inward extension of the annular feature by at least 3mm is an annular region that is a surface inclined from a {0004} plane by an off-angle of no more than 0.06 °;

and no small-angle grain boundary exists in the annular region, and the full width at half maximum of the crystallization quality of the annular region is not more than 20 arcsec.

8. A method for producing a silicon carbide crystal with few small-angle grain boundaries according to any one of claims 1 to 7, comprising the steps of:

1) assembling: providing a bearing raw material and a seed crystal arranged at the top in a crucible, placing the crucible in a heat preservation cavity formed by a heat preservation layer, and then moving the crucible into a crystal growth furnace; the heat-insulating layer comprises a heat-insulating ring arranged above the crucible, the heat-insulating ring at least covers the seed crystal and extends inwards from the edge by 0.5mm to 0.5r-0.5mm, and r is the radius of the seed crystal;

2) growing a crystal: and (3) preparing the silicon carbide crystal by crystal growth, wherein the edge of the prepared silicon carbide crystal forms an annular shape corresponding to the covering position of the heat preservation ring.

9. The method according to claim 8, wherein the crystal growth stage in step 2) comprises the steps of:

10. A silicon carbide substrate with few small-angle grain boundaries, produced from the silicon carbide crystal according to any one of claims 1 to 7 or from a production method comprising the silicon carbide crystal according to claim 8 or 9, further comprising the steps of:

and the silicon carbide crystal is subjected to the step of slicing to prepare the silicon carbide substrate with the annular appearance.

11. The silicon carbide substrate with few small grain boundaries of claim 10 wherein the silicon carbide crystal further comprises the step of trimming: and cutting the silicon carbide substrate along the inner side of the annular shape or close to the inner side of the annular shape to obtain the target silicon carbide substrate.