CN113957533B

CN113957533B - Silicon carbide substrate with low dislocation density and preparation method thereof

Info

Publication number: CN113957533B
Application number: CN202110947945.4A
Authority: CN
Inventors: 张九阳; 李霞; 王永方; 高宇晗; 张红岩; 高超; 梁庆瑞; 李祥皓; 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: 2023-10-27
Anticipated expiration: 2041-08-18
Also published as: CN113957533A

Abstract

The application discloses a silicon carbide substrate with low dislocation density and a preparation method thereof, belonging to the field of semiconductor materials. The silicon carbide substrate is a 4H polytype silicon carbide substrate with a size not less than 100mm, the silicon carbide substrate having a first main surface and a second main surface opposite to the first main surface; the first main surface has a central region and an annular region surrounding the central region, the annular region being a face extending inward from the edge of the substrate by a width of not less than 5mm, the annular region being inclined with respect to a {0004} face by a deviation angle of not more than 0.06 °; and no small-angle grain boundary exists in the annular region, and the half-width of the crystallization quality of the annular region is not more than 20arcsec. The silicon carbide substrate has low dislocation density in the annular region of the edge and low dislocation density in the central region; and the annular area of the edge has no small angle grain boundary, and the crystallization quality is high, so that the quality of the manufactured downstream device is high.

Description

Silicon carbide substrate with low dislocation density and preparation method thereof

Technical Field

The application relates to a silicon carbide substrate with low dislocation density and a preparation method thereof, belonging to the field of semiconductor materials.

Background

Silicon carbide materials are of great interest because of their excellent semi-insulating properties, especially for high power semiconductor devices with special requirements, silicon carbide has become the potential material of choice for these devices due to its high temperature, high frequency, high power, etc.

At present, PVT method is adopted for industrial production of silicon carbide crystal, but the defects introduced in the growth process limit the improvement of the performance and the further application and development due to higher requirement of growth conditions. Therefore, improvement of defects becomes a primary premise for improving the quality of silicon carbide substrates.

The defects of silicon carbide crystals which we are familiar with at ordinary times are mainly: micropipes, triangular defects, voids and cracks, small angle grain boundaries, conventional dislocations, and other defects (including mainly stacking faults, carrot defects, giant steps, grains, falls, surface scratches and growth pits, etc.). These defects, to some extent, can have a certain effect on the quality of the material and further affect the performance of devices made from silicon carbide crystals, which fundamentally limits the development of silicon carbide materials.

The current industrialized semi-insulating silicon carbide single crystal preparation is based on a physical vapor deposition (PVT) method, the process is continuously optimized, the seed crystal quality is improved, and further the crystal quality is continuously improved to obtain a silicon carbide substrate with low defect density, large size and high quality.

At present, in the growth process of the PVT method silicon carbide crystal, edge dislocation can slip due to shear stress formed by temperature gradient, so that the edge is slipped to the center, and the dislocation density of the center of the substrate is high, or local dislocation is accumulated, and the like.

In the process of growing crystals, LAGB (small angle grain boundary) is formed at the edge of the crystals due to fluctuation of the crystal growth parameters, namely (edge dislocation) TED walls are formed. The formation of the LAGB generally results in poor local stress and poor crystallization quality of the silicon carbide substrate, large FWHM values as measured by XRD, broad diffraction peaks or occurrence of impurity peaks, which cause interference with the use of downstream devices.

The grain boundary type may be classified into a small angle grain boundary, which refers to a grain boundary having a rotation angle between two adjacent grains of less than 10 degrees, and a large angle grain boundary, which refers to a grain boundary having a rotation angle of more than 10 degrees.

For seed crystals with local defects at the edge, the defects are largely transmitted to the grown crystals in the crystal growth process, so that the crystals are always provided with the defects at the same position, and the high-quality silicon carbide crystals are not beneficial to obtaining.

Disclosure of Invention

In order to solve the above problems, the present application provides a silicon carbide substrate having not only a low dislocation density in an annular region of an edge but also a low dislocation density in a central region; and the annular area at the edge of the silicon carbide substrate has no small angle grain boundary, and the crystallization quality is high, so that the quality of the manufactured downstream device is high.

In order to solve the above-described problems, there is provided a silicon carbide substrate which is a 4H polytype silicon carbide substrate having a size of not less than 100mm, the silicon carbide substrate having a first main surface and a second main surface opposite to the first main surface;

the first main surface has a central region and an annular region surrounding the central region, the annular region being a face extending inward from the edge of the substrate by a width of not less than 3mm, the annular region being inclined with respect to a {0004} face by a deviation angle of not more than 0.06 °;

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

Optionally, the annular region is a face inclined with respect to a off angle of no more than 0.05 ° with respect to the {0004} face; and no small-angle grain boundary exists in the annular region, and the half-width of the crystallization quality of the annular region is not more than 16.6arcsec.

Optionally, the annular region is of a width extending inwardly from the edge of the substrate of no less than 5mm. Further, the upper and lower limits of the annular region, which are width values or width ranges extending inwardly from the edge of the substrate, may be 3mm, 4mm, 5mm, 6mm, 10mm, 15mm or 20mm, respectively.

Optionally, the size of the silicon carbide single crystal is not less than 150mm. The silicon carbide single crystal may have a size of 150mm, 200mm, 250mm, 300mm, or 350mm.

Optionally, the dislocation density in the annular region is not higher than 5500/cm ² The dislocation density in the central region is not higher than the dislocation density in the annular region. Preferably, the upper limit of dislocation density in the annular region is selected from 4400/cm ² 、4395/cm ² 、2600/cm ² 、2591/cm ² 。

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

According to another aspect of the present application, there is provided a method for producing a silicon carbide substrate as set forth in any one of the above, comprising the steps of:

1) And (3) 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 displacing the crucible into a crystal growth furnace;

2) Growing an ingot: growing crystals under the condition that the distance between the top surface of the crucible and the inner surface of the upper heat preservation layer of the heat preservation layer is 30-50mm, so as to obtain a silicon carbide crystal ingot;

3) Preparing a substrate: and carrying out a step comprising slicing on the prepared silicon carbide ingot to obtain the silicon carbide substrate.

Specifically, the preparation substrate of step 3) further comprises grinding and polishing steps after dicing.

Specifically, the seed crystal is installed the crucible lid below of crucible, and the diameter of seed crystal is less than or equal to the area of crucible lid, and the heat preservation sets up the outer of crucible, the crucible top surface with the air bed that the distance between the upper heat preservation internal surface of heat preservation formed not only can cover the width of seed crystal completely, and the width of air bed is greater than the seed crystal, can form the bigger air bed of diameter above the silicon carbide seed crystal of heat preservation intracavity. On one hand, the arrangement of the air layer can homogenize a temperature field above the seed crystal, further regulate a radial temperature gradient above the homogenized seed crystal, and further inhibit the generation of annular morphology in the crystal; on the other hand, the diameter of the air layer is larger than that of the silicon carbide seed crystal, so that the range of an air layer homogenizing temperature field covers the whole seed crystal, particularly the temperature field above the outer side of the edge of the seed crystal is homogenized, the temperature field above the edge position of the seed crystal is further ensured to be uniform and stable, the radial edge temperature gradient in the crystal growing process is reduced, the generation of an edge annular shape is avoided, and the effect of eliminating the annular shape is achieved.

Optionally, a gap between the side wall of the crucible and the side insulating layer of the insulating layer is smaller than 1mm. The crucible can be taken and placed in the heat preservation cavity without friction, but the crucible is not contacted with the heat preservation cavity without obvious gaps, and the arrangement mode only forms an air layer between the top of the crucible and the upper heat preservation layer, thereby being beneficial to ensuring the heat preservation effect of the side wall of the crucible in the crystal growth process, further ensuring the radial temperature gradient and the axial temperature gradient in the crystal growth process, preventing the excessive leakage of the SiC atmosphere sublimated by the PVT method and being unfavorable for crystal growth. The air layer is too large, which is unfavorable for the heat preservation of the crystal growth crucible, so that the atmosphere overflows, the shaft ladder is reduced, and the crystal growth is unfavorable.

Optionally, the upper heat-insulating layer is provided with a temperature measuring hole, the heat-insulating layer further comprises a lower heat-insulating layer and a transition heat-insulating layer, and the lower heat-insulating layer, the upper heat-insulating layer, the side heat-insulating layer and the transition heat-insulating layer enclose the heat-insulating cavity; the transition heat preservation layer is at least in threaded connection with one of the upper heat preservation layer and the side heat preservation layer, and is integrally formed with the other one, and the upper heat preservation layer is in threaded connection with the side heat preservation layer through the transition heat preservation layer, so that the distance between the crucible arranged in the side heat preservation layer and the inner surface of the upper heat preservation layer is adjusted in a rotating mode.

Specifically, the transition heat preservation respectively the upper heat preservation with side heat preservation threaded connection, and the transition heat preservation sets up in upper heat preservation and side heat preservation outside.

Specifically, the transition heat preservation layer is in threaded connection with the side heat preservation layer and is integrally formed with the upper heat preservation layer.

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

Preferably, a threaded structure is arranged on the outer side wall of the side heat-insulating layer, and the bottom end of the threaded structure corresponds to the center position of the crucible. The setting mode solves the problem of non-visualization in the crucible and the heat preservation layer, is difficult to adjust the central position of the crucible in the thermal field, can obviously reflect the central position of the crucible, and can conveniently adjust the central position of the thermal field of the raw material center in the crucible in the crystal growth process.

Optionally, the growing ingot stage comprises the steps of:

removing impurities;

and (3) heating: adjusting the temperature of the crystal growing furnace to 1500-2200K, and controlling the pressure in the crucible to be 0.6X10 ⁵ ～3.3×10 ⁴ Pa, and introducing inert gas into the crystal growth furnace at a flow rate of 50-500mL/min;

step-by-step depressurization stage: (1) controlling the pressure in the crucible to be 3.3X10 ⁴ -2×10 ⁴ Pa, raising the temperature to 2200-2300K, and maintaining for 1h after depressurization; (2) controlling the pressure in the crucible to be 2 multiplied by 10 ⁴ Pa-1.2×10 ⁴ Pa, raising the temperature to 2300K-2400K, and maintaining for 3h after depressurization; (3) controlling the pressure in the crucible to be 1.2 multiplied by 10 ⁴ Pa-0.5×10 ⁴ Pa, the temperature is increased to 2400K-2500K, and after depressurization, the temperature is maintained for 5 hours, namely, the crystal growth stage is entered; the side heat preservation layer drives the crucible to move downwards at a speed of 1mm/h in the step-by-step depressurization process, and the crucible rotates at a speed of 1r/min until the center of the crucible coincides with the center of the heating coil of the crystal growth furnace;

crystal growth stage: the crystal growth temperature is controlled to be 2500K-2800K, the crystal growth pressure is controlled to be 5000-4000Pa, and the holding time is controlled to be 80-120 h, so that the silicon carbide crystal ingot is obtained.

Specifically, the step-by-step depressurization is favorable for stably regulating the pressure and the temperature in the crucible, impurities in the thermal field environment and the crucible can be further purified in the depressurization process, the silicon carbide powder loss for preparing the silicon carbide crystal is prevented, and the crucible is downwards moved in the depressurization process to regulate the crucible, so that the air layer at the top of the crucible is increased by a small amount to be favorable for homogenization of the temperature field, the internal stress of the silicon carbide crystal is reduced, and the cracking caused by stress concentration is prevented.

The silicon carbide crystal prepared by the preparation method does not generate annular morphology, and the structure of an air layer is arranged to have few defects in the middle area and the annular area of the prepared silicon carbide crystal and high quality of the crystal, 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 edge effect, and the crystallization quality is high.

According to still another aspect of the present application, there is provided a method for producing a silicon carbide substrate as set forth in any one of the above, comprising the steps of:

1) And (3) assembling: providing bearing raw materials and seed crystals arranged at the top in the crucible, placing the crucible in a heat preservation cavity formed by a heat preservation layer, and then displacing the crucible in a crystal growth furnace; 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 an ingot: preparing a silicon carbide ingot by crystal growth, wherein the edge of the prepared silicon carbide ingot forms an annular shape approximately corresponding to the covering position of the heat preservation ring;

3) Preparing a primary silicon carbide substrate: performing a step comprising slicing the silicon carbide ingot to produce a primary silicon carbide substrate having an annular morphology;

4) Edge removal: and cutting the primary silicon carbide substrate along the annular shape or the inner side close to the annular shape to obtain the silicon carbide substrate.

Specifically, the ingot growing stage in step 3) includes the steps of:

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

and (3) heating: adjusting the temperature of the crystal growth furnace to 2000-2400K, and controlling the pressure in the crucible to be 0.6X10 ⁵ ～3.3×10 ⁴ Pa, the flow rate of inert gas introduced into the crystal growing furnace is 50-500mL/min, and at the moment, the crucible moves upwards at a moving speed of 0.1mm/h and rotates at a speed of 0.5 r/min;

step of depressurization: the pressure is controlled from 0.6X10 ⁵ ～3.3×10 ⁴ Pa, down to 5X 10 ³ Pa-1×10 ⁴ Pa; the crucible was moved down at a speed of 1mm/h during depressurization, and rotated at a speed of 0.2 r/min; the temperature is controlled at 2400K-2600K；

And (3) a crystal growth stage: the crystal growth temperature is 2600K-2800K, the crystal growth pressure is 100-5000Pa, and the crucible moves downwards at a speed of 0.05mm/h and rotates at a speed of 0.5 r/min; the holding time is 80-120 h, and the silicon carbide crystal ingot with the annular morphology with the controllable diameter is prepared.

The invention discovers an annular shape on the basis of the existing PVT method for growing silicon carbide crystal ingots, and applies the annular shape after grasping the related forming mechanism and testing method thereof, thereby changing waste into valuables for optimizing the edge quality of the silicon carbide, the annular shape, namely an edge dislocation (TED) wall, is used for preventing the edge dislocation formed in the silicon carbide crystal growing process from sliding inwards and the edge small angle crystal boundary (LAGB) from extending inwards, and the high-quality silicon carbide substrate is obtained by special processing equipment and technology.

The structure and the arrangement position of the heat preservation ring provided by the application can construct specific radial temperature gradient distribution above the silicon carbide seed crystal. Specifically, an air layer above the seed crystal is surrounded on the inner side wall of the heat preservation ring, on one hand, the thermal conductivity of the air and the thermal conductivity of the heat preservation layer are greatly different, so that the radial temperature gradient of a temperature field is suddenly changed at the inner side wall position of the heat preservation ring from inside to outside, and further, a larger temperature difference is formed at the inner side and the outer side of the inner side wall position of the heat preservation ring, so that a large number of surface or penetrating defects are intensively generated at the inner side wall position of the heat preservation ring, which is suddenly changed, a large number of defects are gathered to form an annular shape similar to a wall shape, and the annular shape can simultaneously prevent the low-angle grain boundary outside the ring from extending to the inner side of the ring and the edge dislocation from sliding to the inner side of the ring, and further, the problem that the edge defect of the crystal extends or slides to the middle part is solved; on the other hand, the air layer can also play a role in homogenizing the temperature field, which is beneficial to adjusting the radial temperature gradient above the seed crystal, thereby reducing or even eliminating the generation of defects in the middle of the crystal and improving the quality of the crystal in the middle. Under the actions of the two aspects, the quality of the middle area of the crystal positioned in the inner side wall of the heat preservation ring is improved, and dislocation positioned at the edge of the crystal is blocked in the presence of the annular morphology and cannot slide into the middle area of the crystal at the inner side, so that the quality of the middle crystal of the silicon carbide crystal is obviously improved, and the silicon carbide crystal with high quality at the middle part, namely the substrate, can be obtained after the annular morphology and the outer side part are removed.

Optionally, the ring topography comprises ring structures formed by edge dislocations perpendicular to the 0001 planes.

In the application, the silicon carbide substrate is provided with a first main surface and a second main surface which are opposite, the annular morphology extends from the first main surface of the silicon carbide substrate to the second main surface in a penetrating way, the extending direction is approximately perpendicular to the first main surface, the annular morphology extends near the periphery of the silicon carbide substrate, for example, one silicon carbide substrate is provided with an annular morphology, and a region surrounded by the annular morphology comprises a central region and an annular region; the annular appearance can be observed by using a laser detector, a lattice defect detector, a microscope or a stress meter, etc.; the annular topography includes edge dislocations.

The beneficial effects of the application include, but are not limited to:

1. according to the silicon carbide substrate of the present application, not only the dislocation density of the annular region having the edge but also the dislocation density of the central region is low; and the annular area of the edge has no small angle grain boundary, and the crystallization quality is high, so that the quality of the manufactured downstream device is high.

2. According to the preparation method of the silicon carbide substrate, the arrangement of the air layer can homogenize the temperature field above the seed crystal, so that the radial temperature gradient above the homogenized seed crystal is further regulated, and the generation of annular morphology in the crystal is further inhibited; on the other hand, the diameter of the air layer is larger than that of the silicon carbide seed crystal, so that the range of an air layer homogenizing temperature field covers the whole seed crystal, particularly the temperature field above the outer side of the edge of the seed crystal is homogenized, the temperature field above the edge position of the seed crystal is further ensured to be uniform and stable, the radial edge temperature gradient in the crystal growing process is reduced, the generation of an edge annular shape is avoided, and the effect of eliminating the annular shape is achieved.

3. The preparation method of the silicon carbide substrate has the advantages that the annular shape is found, the relevant forming mechanism and the testing method are mastered and then applied, so that waste is changed into valuable and the optimization of the edge quality of the silicon carbide is performed, the annular shape, namely the edge dislocation wall, is used for preventing edge dislocation formed in the silicon carbide crystal growth process from sliding inwards and the edge small-angle grain boundary from extending inwards, and the high-quality silicon carbide substrate is obtained by means of special processing equipment and special process.

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 specification, illustrate embodiments of the application and together with the description serve to explain the application and do not constitute a limitation on the application. In the drawings:

fig. 1 is a schematic view of an insulation layer according to embodiment 1 of the present application;

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

fig. 3 is a schematic view of another insulation layer according to embodiment 1 of the present application;

fig. 4 is a schematic view of an insulation layer according to embodiment 3 of the present application;

fig. 5 is a schematic view of another insulation layer according to embodiment 3 of the present application;

fig. 6 is a schematic view of another insulation layer according to embodiment 3 of the present application;

FIG. 7 is a schematic illustration of a primary silicon carbide substrate having an annular morphology prepared in accordance with example 8 of the present application;

FIG. 8 is a representation of the annular morphology of the silicon carbide substrate a of example 8 of the present application under a laser detector (instrument manufacturer Candela, device model CS 920);

FIG. 9 is a representation of the annular morphology of the silicon carbide substrate a of example 8 of the present application under a stress detector (instrument manufacturer is Suzhou Ming optical instruments Co., ltd., equipment model is qualitative portable polarization stress meter);

fig. 10 is a test image of a ring-shaped morphology lattice distortion detector (equipment model CS10, equipment manufacturer is Shanghai semiconductor technology limited) of a silicon carbide substrate a in example 8 of the present application;

fig. 11 is a polarized view (a) and a label (b) of a microscope (instrument manufacturer is olynbas, equipment model is MX 63) of the SiC ground wafer with the annular morphology of the primary silicon carbide substrate a of example 8 of the present application, and a view (c) and a label (d) under a dark field;

FIG. 12 shows the results of Raman imaging (HORIBA, HREVOLUTION) test (a) and (b) of the annular morphology of the silicon carbide substrate a of example 8 of the present application;

FIG. 13 is a representation of an image (a) of the annular morphology of a silicon carbide substrate a of example 8 of the present application under a laser detector (instrument manufacturer Candela, device model CS 920); an atomic force microscope AFM (Park, equipment model number NX 20) test (b) of the annular morphology of the primary silicon carbide substrate a;

FIG. 14 is a graph (a) showing the characterization of the annular morphology of the silicon carbide substrate a in example 8 of the present application under a laser detector (instrument manufacturer Candela, device model CS 920) and (b) showing the results of the annular morphology angle XRD test of the silicon carbide substrate a (instrument manufacturer Bruker, device model JV-DX);

FIG. 15 is an image of a microscope (Instrument manufacturer is Olympus, apparatus model MX 63) of the initial silicon carbide substrate a of example 8 after the annular stress KOH is corroded;

FIG. 16 is a statistical mapping image of dislocation after KOH etch of the annular topography of the primary silicon carbide substrate a of example 8 of the present application;

FIG. 17 is a view of the primary silicon carbide substrate a of example 8 of the present application under polarized light with a ring-shaped morphology microscope (Instrument manufacturer Olympic, apparatus model MX 63);

FIG. 18 is an image of a ring topography profile test (apparatus manufacturer CORNING, device model FlatMaster200 Semi-Automated Wafer System) of a silicon carbide substrate a of example 8 of the present application, wherein (a) is a Warp-Bow profile image and (b) is LTV data;

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

Detailed Description

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

The starting materials and catalysts in the examples of the present application were purchased commercially, unless otherwise specified.

Example 1

The embodiment of the application provides an insulating layer for eliminating the annular shape of the edge of silicon carbide and further preparing high-quality silicon carbide crystals, which is placed in a growth cavity of a crystal growth furnace together with a crucible during crystal growth and is used for wrapping and insulating the crucible containing silicon carbide materials when preparing the silicon carbide crystals by using a PVT method.

Preferably, in the following examples, crucible 2 is a graphite crucible and the size of the silicon carbide seed crystal in crucible 2 is 100 to 350mm.

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

Specifically, the lower heat-insulating layer is fixedly connected with the side heat-insulating layer 5, such as integrally formed or screwed, so long as the rotation of the lower heat-insulating layer is realized, the side heat-insulating layer 5 can be driven to rotate at the same time. The crucible is placed on the lower heat preservation layer, and the lower heat preservation layer can drive the crucible to do the same movement. Specifically, the manner of realizing the relative rotation between the upper heat-insulating layer 101 and the side heat-insulating layer 5 through the threaded connection of the transition heat-insulating layer 102 may be as follows: the upper heat-insulating layer 101 is fixed on the crystal growth furnace, and the lower heat-insulating layer is arranged on the rotary lifting unit. As one implementation mode, the rotary lifting unit comprises a motor, a rotary lifting table and a supporting rod, wherein the rotary lifting table is fixed at the top of the supporting rod, the lower heat-insulating layer is fixed at the top of the rotary lifting table, and the motor drives the supporting rod to drive the rotary lifting table and the lower heat-insulating layer to rotationally lift. The rotary lifting mechanism can also be other rotary lifting units commonly used in the field, so long as the rotation and lifting of the side heat insulation layer or the upper heat insulation layer can be realized.

Referring to fig. 1, the inner surface 702 of the transition heat-insulating layer is in threaded connection with the second external thread 501 on the outer side of the side heat-insulating layer 5, the top of the transition heat-insulating layer 102 is integrally formed with the upper heat-insulating layer 101, and the transition heat-insulating layer 102 and the side heat-insulating layer 5 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 heat-insulating layer.

Referring to fig. 2, a first external thread 1011 is provided on the outer side of the upper insulation layer 101 to be screwed with the inner surface 702 of the transition insulation layer, and the inner surface 702 of the transition insulation layer is screwed with the second external thread 501 outside the side insulation layer 5. The relative rotation of the transition insulation layer 102 and the side insulation layer 5 and/or the relative rotation of the transition insulation layer 102 and the upper insulation layer 101 is adjusted 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.

Specifically, the shape of the transition heat insulating layer 102 is not limited as long as the screw connection portion is cylindrical, for example, the torus structure of fig. 2 or the cylindrical structure of fig. 3 having an annular groove extending inward. The annular groove of the transition thermal insulation layer 102 of fig. 3 protrudes from the side thermal insulation layer 5 to form an air layer having a diameter significantly larger than that of the silicon carbide seed crystal 3 over the top opening of the side thermal insulation layer 5 to further avoid edge defects of the grown silicon carbide ingot.

Specifically, the diameter of the air layer 7 and the diameter of the silicon carbide seed crystal are larger by 0.2 to 30cm, preferably 1 to 20cm, more preferably 3 to 15cm. The thickness of the air layer is 10-60mm. Further, the thickness of the air layer 7 in the crystal growth process is 20-50mm; preferably, the thickness of the air layer 7 during the growth is 30mm-40mm. The arrangement mode of the air layer is beneficial to improving the crystal growth quality, reducing the generation of defects, and particularly reducing the defects of the edges of crystals. Too thick air layer can lead to the reduction of the shaft ladder, is unfavorable for ensuring the growth rate of the crystal, and too thin air layer can lead to the overlarge radial temperature ladder, the increase of the shear stress and the concentration of stress in the silicon carbide crystal.

As a preferred embodiment, it is preferable that the bottom end of the second external screw thread 501 provided on the outer side wall of the side insulating layer 5 corresponds to the center position of the crucible 2. The setting 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 thermal field of the raw material center in the crucible 2 in the crystal growth process.

Referring to fig. 1-3, in the 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 a temperature measurement hole 6.

Specifically, crucible 2 is graphite crucible, and the material of heat preservation is graphite felt.

Example 2

The method for producing a silicon carbide substrate using any one of the thermal insulation layers and the crucible of example 1 includes the steps of:

1) And (3) 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 displacing the crucible into a crystal growth furnace; wherein, the gap between the side wall of the crucible and the side heat preservation layer is smaller than 1mm;

2) Growing an ingot: growing crystals under the condition that the distance between the top surface of the crucible and the inner surface of the upper heat preservation layer of the heat preservation layer is not less than 40mm, and obtaining silicon carbide crystal ingots;

3) Preparing a substrate: performing a step including slicing on the prepared silicon carbide ingot to obtain a silicon carbide substrate;

wherein the growing ingot stage comprises the steps of:

removing impurities;

step-by-step depressurization stage: (1) controlling the pressure in the crucible to be 3.3X10 ⁴ -2×10 ⁴ PaRaising the temperature to 2200-2300K, and maintaining for 1h after depressurization; (2) controlling the pressure in the crucible to be 2 multiplied by 10 ⁴ Pa-1.2×10 ⁴ Pa, raising the temperature to 2300K-2400K, and maintaining for 3h after depressurization; (3) controlling the pressure in the crucible to be 1.2 multiplied by 10 ⁴ Pa-0.5×10 ⁴ Pa, the temperature is increased to 2400K-2500K, and after depressurization, the temperature is maintained for 5 hours, namely, the crystal growth stage is entered; the side heat-insulating layer drives the crucible to move downwards at a speed of 1mm/h in the step-by-step depressurization process, and the crucible rotates at a speed of 1r/min until the center of the heating coil of the crystal growth furnace coincides with the center of the heating coil of the crystal growth furnace;

Example 3

The method for preparing the silicon carbide substrate using the structure of the thermal insulation layer of fig. 2 in example 1 includes the steps of:

3) Preparing a substrate: performing a step including slicing on the prepared silicon carbide ingot to obtain a silicon carbide substrate 1#;

wherein the growing ingot stage comprises the steps of:

removing impurities; regulating the temperature to 1200-1500K, using a mechanical pump and a molecular pump to remove gas in the crystal growing furnace, and then introducing Ar gas for ventilation; repeating the process for 1-3 times to perform ventilation furnace washing so as to achieve the aim of removing impurities in the crystal growth furnace; and (3) heating: adjusting the temperature of the crystal growing furnace to 1500-2200K, and controlling the pressure in the crucible to be 0.6X10 ⁵ ～3.3×10 ⁴ Pa, and introducing inert gas into the crystal growth furnace at a flow rate of 50-500mL/min;

step-by-step depressurization stage: (1) controlling the pressure in the crucible to be 3.3X10 ⁴ -2×10 ⁴ Pa, heating to 2200-2300K, and reducing pressureMaintaining for 1h; (2) controlling the pressure in the crucible to be 2 multiplied by 10 ⁴ Pa-1.2×10 ⁴ Pa, raising the temperature to 2300K-2400K, and maintaining for 3h after depressurization; (3) controlling the pressure in the crucible to be 1.2 multiplied by 10 ⁴ Pa-0.5×10 ⁴ Pa, the temperature is increased to 2400K-2500K, and after depressurization, the temperature is maintained for 5 hours, namely, the crystal growth stage is entered; the side heat-insulating layer drives the crucible to move downwards at a speed of 1mm/h in the step-by-step depressurization process, and the crucible rotates at a speed of 1r/min until the center of the heating coil of the crystal growth furnace coincides with the center of the heating coil of the crystal growth furnace;

Example 4

The preparation method of this example is different from that of example 3 in that the thickness of the air layer above the silicon carbide seed crystal is different, and silicon carbide substrates 25# -are respectively prepared. Comparative example 1 differs from example 3 in that there is no air layer and the top of the crucible is in direct contact with the inner surface of the upper insulating layer, producing a comparative silicon carbide substrate d1#.

TABLE 1

As can be seen from the data of table 1, the silicon carbide substrate was low in dislocation density not only in the annular region of the edge but also in the central region; and the annular area of the edge has no small angle grain boundary, and the crystallization quality is high.

Example 5

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

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

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

Specifically, in any one of the embodiments, a heat-insulating ring 8 is disposed above the crucible, and the heat-insulating ring 8 covers at least 0.5mm to 0.5r-0.5mm of the seed crystal extending inward from the edge, where r is the radius of the seed crystal.

Example 6

The method for producing a silicon carbide substrate using any of the insulating layers and the crucible of example 5 includes the steps of:

1) And (3) assembling: providing bearing raw materials and seed crystals arranged at the top in a crucible, placing the crucible in a heat preservation cavity formed by a heat preservation layer, and then displacing the crucible in 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 seed crystal extending inwards from the edge, and r is the radius of the seed crystal;

3) Preparing a primary silicon carbide substrate: performing a step including slicing the silicon carbide ingot to produce a primary silicon carbide substrate having an annular morphology;

4) Edge removal: cutting the primary silicon carbide substrate along the annular shape or the inner side close to the annular shape to obtain the silicon carbide substrate;

wherein the growing ingot stage in step 3) comprises the steps of:

step of depressurization: the pressure is controlled from 0.6X10 ⁵ ～3.3×10 ⁴ Pa, down to 5X 10 ³ Pa-1×10 ⁴ Pa; the crucible was moved down at a speed of 1mm/h during depressurization, and rotated at a speed of 0.2 r/min; the temperature is controlled to be 2400K-2600K;

and (3) a crystal growth stage: the crystal growth temperature is 2600K-2800K, the crystal growth pressure is 100-5000Pa, and the crucible moves downwards at a speed of 0.05mm/h and rotates at a speed of 0.5 r/min; the holding time is 80-120 h, and the silicon carbide crystal ingot with the annular shape and controllable diameter is prepared.

Example 7

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) And (3) assembling: providing bearing raw materials and seed crystals arranged at the top in a crucible, placing the crucible in a heat preservation cavity formed by a heat preservation layer, and then displacing the crucible in a crystal growth furnace; 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 of the seed crystal can be 24mm to 85mm;

4) Edge removal: cutting the primary silicon carbide substrate along the annular shape or the inner side close to the annular shape to obtain a silicon carbide substrate a;

wherein the growing ingot stage in step 3) comprises the steps of:

Example 8

The preparation method of this example differs from that of example 7 in that the width D of the insulating ring covering the seed crystal extending inward from the edge is different, and silicon carbide substrates b to g are produced, respectively. Comparative example 2 differs from example 8 in that no heat retaining ring is present, and comparative silicon carbide substrate Da is produced in comparative example 2.

TABLE 2

The wider the width of the heat-insulating ring is, the larger the radial temperature gradient is, when the inner diameter of the heat-insulating ring is smaller than the diameter of the crystal, the radial gradient mutation can occur at the junction of the heat insulation layer and the air layer, so that the cutting stress at the junction is large, and the annular shape is generated; the thickness of the heat preservation ring corresponds to the thickness of an air layer above the crucible, and the thickness of the air layer is increased, namely, a temperature field is homogenized, and the diameter step shaft step is reduced, so that the defect degree is reduced; impact trend: the wider the heat preservation ring is, the smaller the diameter of the annular shape is, and the farther the heat preservation ring is away from the edge; the narrower the width, the larger the diameter of the annular morphology, the closer to the edge; the larger the air layer is, the smaller the diameter step is, the degree of annular morphology is weakened, and the width is narrower; the smaller the air layer is, the larger the diameter step is, the more the annular appearance degree is increased, and the wider the width is.

As can be seen from the data in the table, an annular morphology is found, by means of which edge dislocation walls are used to prevent edge dislocations formed during the growth of silicon carbide from slipping inward, edge small angle grain boundaries extend inward, and by means of special processing equipment and processes, high quality silicon carbide substrates are obtained.

The primary silicon carbide substrates a-g, especially annular morphology regions, from which the silicon carbide substrates a-g were prepared were subjected to laser detection, stress detection characterization, lattice distortion detection, microscopic polarization and observation in the dark field, raman mapping testing, AFM testing, and stress deflection angle testing, respectively. The primary silicon carbide substrate a will be described below as an example.

Referring to fig. 7, a schematic view of a primary silicon carbide substrate a 92 having a ring-shaped morphology 91, which is a ring-shaped wall-like structure extending through the primary silicon carbide substrate a 92 perpendicular to the {0001} plane, is prepared in example 8 of the present application. The primary silicon carbide substrate a can observe a circle of regular circular lines at the edge of the primary silicon carbide substrate a under a transmission light source, the circular lines are 2-3 mm away from the edge of the primary silicon carbide substrate, and the primary silicon carbide substrate a can be adjusted through subsequent regulation and control. And the ring line can completely correspond to the ring defect observed by the silicon carbide ingot in position and distance from the edge. After the locating edge cut, the annular topography can be machined away.

Referring to fig. 8, the primary silicon carbide substrate a was tested by laser and the annular topography was detected by a laser detector as a white ring from the edge of the primary silicon carbide substrate. The ring is fully visible and equidistant from the edge, about 2-3 mm, corresponding fully to the position of the annular topography of the substrate detected under the transmitted light source in fig. 7.

Referring to fig. 9, a primary silicon carbide substrate a was tested by a stress detector, and the annular topography of the primary silicon carbide substrate a was locally characterized using the stress detector, and the annular topography was detected by the stress detector as representing a stress ring one stress ring from the edge of the silicon carbide substrate. The characterization result shows that the annular appearance is a boundary line between the edge stress concentration area and the center stress good area, and the annular appearance 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 tester, and fig. 10 is an image obtained by testing the annular topography using the lattice distortion tester. From the image, the edge of the primary substrate reaches the annular shape, and a large amount of stress concentration areas caused by lattice distortion exist in the primary substrate. The lattice distortion defect is blocked by the annular morphology when extending to the annular morphology, and does not extend further into the substrate.

Referring to fig. 11, the annular morphology in the primary silicon carbide substrate a is observed under microscopic polarization and dark field, and fig. 11 (a) (b) is the annular morphology observed under microscopic bright field of the wafer after grinding the primary silicon carbide substrate a. Wherein the normal abrasive sheet is a rough matte surface and is observed under a microscope to be relatively uniform earthy yellow. And the location with the annular topography appears as a distinct band with distinct demarcation lines. Fig. 11 (c) (d) shows the difference in contrast between the annular topography on the SiC polishing sheet and the normal region in the dark field, i.e., the annular topography region is a dark annular band.

Referring to fig. 12, for the annular stress Raman mapping test of the primary silicon carbide substrate a, a near-edge annular topography was selected for Raman mapping test, and the test regions and results are shown in fig. 12 (a) and 12 (b), respectively. And comparing the test result with Raman sub-molds of each crystal form of SiC, wherein the crystal forms in the test range are all 4H crystal forms, and polytype defects of other crystal forms are included in the crystal forms.

Referring to fig. 13 (a) and (b), for the annular stress AFM test of the primary silicon carbide substrate a, fig. 13 (b) shows the annular outer-morphology, annular morphology and annular inner-morphology regions in fig. 13 (a), and atomic steps and roughness of the regions where the annular morphology regions are located are continuously characterized by means of AFM, as shown in fig. 13 (b). The result shows that the atomic steps in the area are normal, and no abnormal widening, narrowing or rapid increasing changes exist, which indicates that the atomic steps in the area are diffused normally; wherein the atomic step width at position 1 (outside the annular topography) is 0.165 μm, wherein the atomic step width at position 2 (inside the annular topography) is 0.192 μm, and wherein the atomic step width at position 3 (inside the annular topography) is 0.22 μm.

Referring to fig. 14 (a) and (b), for the annular stress deflection angle test (a) and the result (b) of the primary silicon carbide substrate a, XRD was performed on the defect positions and both the inner and outer sides, as shown in fig. 14. The XRD diffraction peak at the position 1 in the annular morphology is shifted and widened, the clean quality from the annular morphology to the annular morphology is gradually improved, and the FWHM value is gradually reduced. The XRD measured crystal quality and deflection angle results are shown in Table 3, and the crystal quality gradually became better from the edge to the inside, and the deflection angle also gradually became smaller. The cause of the result is mainly annular morphology to block the LAGB and part of dislocation outside the ring, and lattice distortion is caused by the aggregation of the LAGB and the dislocation, which is manifested by poor cleaning quality and increased deflection angle.

TABLE 3 Table 3

Referring to fig. 15, for the primary silicon carbide substrate a, the annular topography was etched with a molten KOH etchant at 500 ℃, which defect was now a dislocation wall of TED composition, as shown in fig. 15. Outside the dislocation wall, near one side of the edge, various dislocations of TED, TSD and BPD exist, and the dislocation density is obviously higher than that inside the TED dislocation wall, namely the TED dislocation wall blocks the edge dislocation from sliding inwards.

Referring to fig. 16, a dislocation statistics mapping image of a silicon carbide substrate with annular stress is formed by performing dislocation statistics after KOH etching on a substrate with annular morphology, and a mapping image is made to visually display dislocation density distribution. As a result, it was found that the dislocation density region was concentrated mainly in the annular morphology and the outside thereof, and a uniform low-density dislocation distribution could be formed inside thereof, and therefore, based on the result, edge dislocations could be blocked by the annular morphology, thereby inhibiting the edge dislocations from slipping inward.

Referring to fig. 17, the annular morphology 91 of the primary silicon carbide substrate a was characterized and observed in the microscopic polarization mode, as shown in fig. 17, as a continuous stress band corresponding to a TED wall after KOH etching. In the annular region 93 outside the annular morphology, near the edge of the substrate, the stress performance is poor, corresponding to the dense distribution of various dislocations outside the TED wall after KOH etching. While in the central region 94 within the annular topography, near the center of the substrate, the stress performs relatively well, corresponding to the lower dislocation density within the TED wall after etching than outside the TED wall.

Referring to fig. 18 (a) (b), a surface characterization was performed on a primary silicon carbide substrate a having a ring-shaped morphology, as shown in fig. 18. It is known from the test image that the annular morphology does not cause the substrate surface pattern to appear abnormal, and is shown in fig. 18 (a), namely, the warp-bow pattern still appears as a shape of a steamed bread with high center and low periphery, and the annular morphology does not have abnormal positions at the positions of the close edges corresponding to the annular morphology. Further characterization of the annular morphology LTV revealed that the edges were not different from normal and that no abnormal LTV was elevated, indicating that the defect was not due to substrate macroscopic surface factors such as local height variations.

The above description is only an example of the present application, and the scope of the present application is not limited to the specific examples, but is defined by the claims of the present application. Various modifications and variations of the present application will be apparent 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

1. A low dislocation density silicon carbide substrate, characterized in that the silicon carbide substrate is a 4H polytype silicon carbide substrate having a size of not less than 100mm, the silicon carbide substrate having a first main surface and a second main surface opposite to the first main surface;

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

2. The low dislocation density silicon carbide substrate as claimed in claim 1, wherein the annular region is a face inclined at an off angle of not more than 0.05 ° with respect to the {0004} face;

and no small-angle grain boundary exists in the annular region, and the half-width of the crystallization quality of the annular region is not more than 16.6arcsec.

3. The low dislocation density silicon carbide substrate as claimed in claim 1, wherein the annular region is of a width extending inwardly from the edge of the substrate of no less than 5mm; and/or

The silicon carbide substrate has a size of not less than 150mm.

4. A low dislocation density silicon carbide substrate as claimed in any one of claims 1 to 3, wherein the dislocation density in the annular region is not higher than 5500/cm ² The dislocation density in the central region is not higher than the dislocation density in the annular region.

5. The low dislocation density silicon carbide substrate as claimed in claim 4, wherein the dislocation density in the annular region is no higher than 4400/cm ² 。

6. The low dislocation density silicon carbide substrate as claimed in claim 5, wherein the dislocation density within the annular region is no higher than 2600/cm ² 。

7. A low dislocation density silicon carbide substrate as claimed in any one of claims 1 to 3, wherein the stress differential between the central region and the annular region is zero.

8. A method of preparing a low dislocation density silicon carbide substrate as claimed in any one of claims 1 to 7, comprising the steps of:

9. The method of claim 8, wherein a gap between the crucible sidewall and a side insulating layer of the insulating layer is less than 1mm; and/or

The upper heat-insulating layer is provided with a temperature measuring hole, the heat-insulating layer further comprises a lower heat-insulating layer and a transition heat-insulating layer, and the lower heat-insulating layer, the upper heat-insulating layer, the side heat-insulating layer and the transition heat-insulating layer enclose the heat-insulating cavity; the transition heat preservation layer is at least in threaded connection with one of the upper heat preservation layer and the side heat preservation layer, and is integrally formed with the other one, and the upper heat preservation layer is in threaded connection with the side heat preservation layer through the transition heat preservation layer, so that the distance between the crucible arranged in the side heat preservation layer and the inner surface of the upper heat preservation layer is adjusted in a rotating mode.

10. The method according to claim 9, wherein the outer side wall of the side insulating layer is provided with a screw structure, and the bottom end of the screw structure corresponds to the center position of the crucible.

11. The method of producing as defined in claim 8 wherein the growing ingot stage comprises the steps of:

removing impurities;

and (3) heating: adjusting the temperature of the crystal growth furnace to 1500-2200K, and controlling the pressure in the crucible to be 0.6X10 ⁵ ~3.3×10 ⁴ Pa, and introducing inert gas into the crystal growth furnace at a flow rate of 50-500mL/min;

step-by-step depressurization stage: (1) controlling the pressure in the crucible to be 3.3X10 ⁴ -2×10 ⁴ Pa, raising the temperature to 2200-2300K, and maintaining for 1h after depressurization; (2) controlling the pressure in the crucible to be 2 multiplied by 10 ⁴ Pa-1.2×10 ⁴ Pa, raising the temperature to 2300K-2400K, and maintaining for 3h after depressurization; (3) controlling the pressure in the crucible to be 1.2 multiplied by 10 ⁴ Pa-0.5×10 ⁴ Pa, temperature is increased to2400K-2500K, maintaining for 5h after depressurization, namely entering a crystal growth stage; the side heat preservation layer drives the crucible to move downwards at a speed of 1mm/h in the step-by-step depressurization process, and the crucible rotates at a speed of 1r/min until the center of the crucible coincides with the center of the heating coil of the crystal growth furnace;

12. A method of preparing a low dislocation density silicon carbide substrate as claimed in any one of claims 1 to 7, comprising the steps of:

1) And (3) assembling: providing bearing raw materials and seed crystals arranged at the inner top of the crucible, placing the crucible in a heat preservation cavity formed by a heat preservation layer, and then displacing the crucible in a crystal growth furnace; 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 an ingot: preparing a silicon carbide ingot by crystal growth, wherein the edge of the prepared silicon carbide ingot forms an annular shape corresponding to the covering position of the heat preservation ring;

13. The method of claim 12, wherein the annular topography comprises annular wall-like structures perpendicular to the {0001} planes formed by edge dislocations.