N-type silicon carbide single crystal, n-type silicon carbide substrate and semiconductor device

Abstract

The invention discloses an n-type silicon carbide single crystal, an n-type silicon carbide substrate and a semiconductor device, and belongs to the technical field of semiconductor materials. The through screw dislocation density in a 10mm annular range of the substrate edge obtained at the part, which is less than or equal to 10mm away from the seed crystal face, of the n-type silicon carbide single crystal is less than 300cm <-2 >, and the through screw dislocation density in a 130mm diameter range of the center is lt; 500 cm <-2 >, and the number of strip-shaped faults is less than 100; the through screw dislocation density within the 40mm annular range of the substrate edge obtained from the part, which is more than 10mm away from the seed crystal face, of the n-type silicon carbide single crystal is less than 100cm <-2 >, and the through screw dislocation density within the 130mm diameter range of the center is lt; 300 cm <-2 >, and the number of strip-shaped faults is less than 5. The n-type silicon carbide single crystal provided by the invention has low through screw dislocation density and low layer dislocation density, and compared with other n-type silicon carbide single crystals, the resistivity uniformity of a wafer prepared from the crystal is obviously improved; the n-type silicon carbide single crystal and the n-type silicon carbide substrate prepared from the n-type silicon carbide single crystal have relatively high quality and high uniformity.

Description

[0001] This application claims the priority of the Chinese patent application filed with the China Patent Office on April 29, 2024, with application number "202410530915.7" and invention name "A n-type silicon carbide substrate and silicon carbide crystal", all contents of which are incorporated by reference in this application. Technical Field

[0002] The present invention belongs to the technical field of semiconductor materials, and in particular relates to an n-type silicon carbide single crystal, an n-type silicon carbide substrate and a semiconductor device. Background Art

[0003] Silicon carbide (SiC) is a third-generation semiconductor material developed after the first-generation semiconductor materials silicon and germanium and the second-generation semiconductor materials gallium arsenide and indium phosphide. Due to its excellent physical, chemical, electrical and optical properties, silicon carbide (SiC) is also used as (but not limited to) the starting material for power electronic semiconductor components, high-frequency components and special light-emitting semiconductor components. For these components, the SiC substrate (=SiC wafer) is required to have the largest possible substrate diameter and the highest possible quality.

[0004] The basis of the silicon carbide substrate is a high-grade silicon carbide volume monocrystal (SiC volume monocrystal), which is usually produced by means of a physical vapour deposition treatment (PVT) method, in particular by means of a method disclosed in, for example, US 8865324 B2. In this growth method, a monocrystalline silicon carbide wafer (disc) is introduced into a growth crucible as a SiC seed crystal together with a suitable source material. Under controlled temperature and pressure conditions, the source material sublimates and gaseous substances are deposited on the SiC seed crystal, so that a SiC volume monocrystal grows therein.

[0005] However, there are still some problems in the current SiC PVT crystal growth: 1) The density of dislocations, stacking faults and other defects in the edge area of ​​the substrate is usually high, which will have an adverse effect on the performance of the device prepared in this area; 2) It is difficult to control the crystal to a stable slightly convex surface morphology when it grows thick, which easily leads to the generation of various defects such as polymorphism, polycrystalline, and microtubes. In particular, it is more difficult to stably control the morphology during the growth of crystals with a thickness greater than 30 mm. Therefore, the research on n-type SiC substrates with low through-screw dislocation density and low stacking fault density is of great significance. Summary of the invention

[0006] In view of the defects existing in the prior art, the purpose of the present invention is to provide an n-type silicon carbide single crystal and an n-type silicon carbide substrate. The n-type silicon carbide substrate provided by the present invention has low threading screw dislocation density and low stacking fault density, and has high quality and high uniformity.

[0007] According to one aspect of the present invention, there is provided an n-type silicon carbide single crystal, wherein the density of screw dislocations penetrating within a 10 mm ring range of the substrate edge obtained from a portion of the n-type silicon carbide single crystal ≤10 mm from the seed crystal surface is less than 300 cm -2 , the density of screw dislocations within the center 130mm diameter is <500cm -2 , the number of stripe stacking faults is less than 100; the density of screw dislocations penetrating within a 40mm ring range of the substrate edge obtained from the n-type silicon carbide single crystal crystal which is greater than 10mm from the seed crystal surface is less than 100cm -2 , the density of screw dislocations within the center 130mm diameter is <300cm -2 , the number of stripe stacking faults is less than 5.

[0008] Preferably, the screw dislocation density within the 10mm ring range of the substrate edge obtained from the n-type silicon carbide single crystal that is ≤10mm away from the seed crystal surface is less than 280cm -2 , the density of screw dislocations within the center 130mm diameter is <380cm -2 , the number of stripe stacking faults is less than 80; the density of screw dislocations penetrating within a 40mm ring range of the substrate edge obtained from the n-type silicon carbide single crystal crystal which is greater than 10mm from the seed crystal surface is less than 85cm -2 , the density of screw dislocations within the center 130mm diameter is <265cm -2 , the number of stripe stacking faults is ≤3.

[0009] Optionally, the density of screw dislocations within 40 mm of the substrate edge obtained from the n-type silicon carbide single crystal which is greater than 20 mm from the seed crystal surface is less than 50 cm -2 , the density of screw dislocations within the center 130mm diameter is <200cm -2 , the number of stripe stacking faults is ≤3.

[0010] Preferably, the screw dislocation density within 40 mm of the substrate edge obtained from the n-type silicon carbide single crystal which is greater than 20 mm from the seed crystal surface is less than 50 cm -2 , the density of screw dislocations within the center 130mm diameter is <155cm -2 .

[0011] Optionally, the central thickness of the n-type silicon carbide single crystal is greater than 10 mm;

[0012] Preferably, the central thickness of the n-type silicon carbide single crystal is greater than 30 mm.

[0013] Optionally, the resistivity of the n-type silicon carbide single crystal is less than 25 mΩ·cm, and the difference between the maximum and minimum values ​​of the resistivity is less than 2.4 mΩ·cm;

[0014] Preferably, the resistivity of the n-type silicon carbide single crystal is 19-21 mΩ·cm, and the difference between the maximum and minimum resistivity values ​​in any diameter line segment of the n-type silicon carbide single crystal in a 73-point test is less than 2 mΩ·cm.

[0015] Optionally, the difference between the maximum value and the minimum value of the refractive index of the n-type silicon carbide single crystal at the same wavelength in the range of 250-1800 nm is less than 2%.

[0016] Optionally, the difference between the maximum value and the minimum value of the absorption coefficient of the n-type silicon carbide single crystal at the same wavelength in the range of 250-650nm is less than 2%.

[0017] According to another aspect of the present invention, there is provided an n-type silicon carbide substrate, which is obtained by cutting, grinding and polishing the n-type silicon carbide single crystal crystal according to any one of claims 1 to 5, wherein the screw dislocation density within the 40mm annular range of the edge of the n-type silicon carbide substrate is less than 100cm -2 , the density of screw dislocations within the center 130mm diameter is <300cm -2 , the number of stripe stacking faults is less than 5;

[0018] Preferably, the screw dislocation density within the 40 mm annular range of the edge of the n-type silicon carbide substrate is less than 50 cm -2 , the density of screw dislocations within the center 130mm diameter is <200cm -2 , the number of stripe stacking faults is less than 3.

[0019] Optionally, the resistivity of the n-type silicon carbide substrate is less than 25 mΩ·cm, and the difference between the maximum and minimum values ​​of the resistivity is less than 2.4 mΩ·cm;

[0020] Preferably, the resistivity of the n-type silicon carbide substrate is 19-21 mΩ·cm.

[0021] More preferably, the difference between the maximum and minimum resistivity values ​​of the n-type silicon carbide substrate in a line segment of any diameter in a 73-point test is less than 2 mΩ·cm.

[0022] Optionally, the difference between the maximum value and the minimum value of the refractive index of the n-type silicon carbide substrate at the same wavelength in the range of 250-1800 nm is less than 2%.

[0023] Optionally, the difference between the maximum value and the minimum value of the absorption coefficient of the n-type silicon carbide substrate at the same wavelength in the range of 250-650nm is less than 2%.

[0024] Optionally, the basal plane dislocation density of the n-type silicon carbide substrate is less than 300 cm -2 , curvature <10μm.

[0025] Preferably, the basal plane dislocation density of the n-type silicon carbide substrate is less than 75 cm -2 , curvature <8.4μm.

[0026] Yet another aspect of the present invention provides a semiconductor device, comprising an n-type silicon carbide substrate prepared from any one of the n-type silicon carbide single crystal crystals described above or an n-type silicon carbide substrate described above.

[0027] The present application provides a growing device for growing n-type silicon carbide single crystals, comprising:

[0028] A crucible body, wherein the interior of the crucible body is hollow and formed into a growth chamber, the crucible body is divided into an upper crucible and a lower crucible, the wall thickness of the lower crucible is greater than the wall thickness of the upper crucible, a seed crystal is fixed on the top of the upper crucible, and at least two gas passages uniformly distributed along the circumference of the upper crucible are also provided on the top of the upper crucible, and the gas passages are provided between the seed crystal and the inner wall of the upper crucible;

[0029] A graphite support ring, which is arranged above the lower crucible and abuts against the inner wall of the upper crucible, and the wall thickness of the graphite support ring gradually decreases from bottom to top;

[0030] A graphite plate is arranged above the graphite support ring, the graphite plate is a porous structure and the pore area of ​​the graphite plate gradually decreases from the center to the edge.

[0031] Optionally, the growth device further comprises a heating coil and a heat-insulating structure, wherein the heating coil is used to heat the crucible body, and the heat-insulating structure is arranged outside the crucible body.

[0032] Optionally, the gas passage includes an air extraction path and a nitrogen supply path.

[0033] Optionally, the thickness of the graphite support ring at the thickest part is 1.5-5 mm, and the thickness of the graphite support ring at the thinnest part is 0.2-1 mm.

[0034] The present application provides a method for growing n-type silicon carbide single crystal, comprising the following steps:

[0035] (1) Assembling a growth device;

[0036] (2) Impurity removal: controlling the pressure in the growth device to be greater than 500 mbar, and raising the temperature in the crucible to 2000-2300° C.;

[0037] (3) Initial stage of crystal growth: reduce the pressure in the growth device to 100-300 mbar at a rate of 100-200 mbar / h and maintain it for 1-10 hours;

[0038] (4) Stable crystal growth: the pressure in the growth device is reduced to 1-20 mbar at a rate of 90-180 mbar / h, the device exhaust line 1# and exhaust line 2# are opened, and a doping gas containing nitrogen is continuously introduced, wherein the proportion of conventional nitrogen in the doping gas is 10%-50%, and after growing for 10-30 hours according to different temperature and pressure control, the device exhaust line 1# and exhaust line 2# are closed;

[0039] (5) Hydrogen etching: Raise the pressure to 100-500 mbar at a rate of 100-300 mbar / h, and at the same time lower the temperature to 1000-2000°C. Pass hydrogen, with the hydrogen accounting for 1%-20%, and etch for 3-10 hours.

[0040] (6) Restarting growth: Stop hydrogen introduction, reduce the pressure in the growth device to 1-20 mbar at a rate of 90-180 mbar / h, open nitrogen replenishment line 3# and nitrogen replenishment line 4# to replenish nitrogen, the replenished nitrogen introduction amount is 20%-50% of the normal nitrogen introduction amount, and at the same time, the temperature is raised to 2000-2300° C. At this time, the normal nitrogen introduction ratio is still the same as in step (4);

[0041] (7) End of growth: After the crystal continues to grow for 50-150 hours, the pressure is increased to 700-900 mbar and slowly dropped to room temperature. The crystal growth is completed and an n-type silicon carbide single crystal is obtained.

[0042] Optionally, the cooling rate of step (5) is 1-5°C / min.

[0043] Optionally, the crystal growth thickness in step (4) is 5 to 10 mm.

[0044] The beneficial effects of the present invention include at least one of the following:

[0045] 1. The n-type silicon carbide single crystal provided by the present invention has low threading screw dislocation density and low stacking fault density, improves the resistivity uniformity of the wafer prepared therefrom, and has high quality and high uniformity;

[0046] 2. The n-type silicon carbide single crystal provided by the present invention can convert TSD into basal plane defects because the crystal surface has more large step structures. At the same time, since the crystal convexity is gradually reduced after the growth is restarted, the large steps are also gradually reduced;

[0047] 3. The n-type silicon carbide single crystal provided by the present invention can obtain a lower TSD density in the edge area after the crystal edge reaches a thickness of 10-15 mm. At the same time, since the stacking faults in the crystal are mostly caused by TSD deflection, the TSD density at the edge of the crystal in the later stage is low, so few stacking faults can also be obtained;

[0048] 4. The n-type silicon carbide single crystal provided by the present invention increases the nitrogen doping amount in the edge area by an additional nitrogen supplement source, which effectively improves the crystal convexity control, atmosphere stability control and doping uniformity during the crystal growth process;

[0049] 5. The n-type silicon carbide single crystal provided by the present invention and the n-type silicon carbide substrate obtained by cutting the same have good yield, performance and reliability at the device end. BRIEF DESCRIPTION OF THE DRAWINGS

[0050] The drawings described herein are used to provide a further understanding of the present application and constitute a part of the present application. The illustrative embodiments of the present application and their descriptions are used to explain the present application and do not constitute an improper limitation on the present application. In the drawings:

[0051] Figure 1 This is a schematic diagram of the overall structure of the growth device involved in the embodiment of the present application;

[0052] Figure 2 This is a schematic diagram of the structure of a graphite support ring involved in an embodiment of the present application;

[0053] Figure 3 This is a schematic diagram of the structure of the graphite plate involved in the embodiment of the present application;

[0054] Figure 4 A schematic diagram of a base plane defect of TSD and its transformation during the substrate growth process involved in an embodiment of the present application;

[0055] Figure 5 A schematic diagram of the early substrate dislocation and stacking fault distribution involved in the embodiment of the present application;

[0056] Figure 6 A schematic diagram of the distribution of dislocations and stacking faults of a later stage substrate involved in an embodiment of the present application;

[0057] Figure 7 This is a 5-point test diagram involved in the embodiment of the present application;

[0058] Figure 8 This is a 73-point resistivity test diagram involved in the embodiment of the present application;

[0059] Fig. 9 This is a refractive index curve at the center of the substrate obtained at a distance of 15 mm from the seed crystal in Example 2 of the present application;

[0060] Fig.10 This is a refractive index curve at the center of the substrate obtained at a distance of 15 mm from the seed crystal in Comparative Example 2 of the present application;

[0061] Fig.11 This is a graph of the absorption coefficient at the center of the substrate obtained at a distance of 15 mm from the seed crystal in Example 2 of the present application;

[0062] Fig.12 This is a graph of the absorption coefficient at the center of the substrate obtained at a distance of 15 mm from the seed crystal in Comparative Example 2 of the present application.

[0063] List of parts and reference numerals:

[0064] 1-crucible body, 2-seed crystal, 3-silicon carbide raw material, 4-growth chamber; 1#-exhaust line, 2#-exhaust line, 3#-nitrogen supplement line, 4#-nitrogen supplement line, 5-graphite support ring, 6-graphite plate. DETAILED DESCRIPTION

[0065] In order to more clearly illustrate the overall concept of the present invention, a detailed description is given below by way of examples.

[0066] In the following description, many specific details are set forth to facilitate a full understanding of the present invention. However, the present invention may also be implemented in other ways different from those described herein. Therefore, the protection scope of the present invention is not limited to the specific embodiments disclosed below.

[0067] In the present invention, unless otherwise clearly specified and limited, the first feature "on" or "under" the second feature may be that the first and second features are in direct contact, or the first and second features are in indirect contact through an intermediate medium. In the description of this specification, the description with reference to the terms "one embodiment", "some embodiments", "example", "specific example", or "some examples" means that the specific features, structures, materials or characteristics described in conjunction with the embodiment or example are included in at least one embodiment or example of the present invention. In this specification, the schematic representation of the above terms does not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials or characteristics described may be combined in an appropriate manner in any one or more embodiments or examples.

[0068] Hereinafter, an n-type silicon carbide substrate and a silicon carbide crystal according to the present invention will be described in detail with reference to exemplary embodiments.

[0069] In an exemplary embodiment of the present invention, an n-type silicon carbide substrate and an n-type silicon carbide single crystal are provided in the present application.

[0070] In a specific embodiment, Figure 1 As shown, a growth device for growing n-type silicon carbide single crystal comprises a crucible body 1, a graphite support ring 5 and a graphite plate 6. The crucible body 1 is hollow inside to form a growth chamber 4. The crucible body is divided into an upper crucible and a lower crucible. The lower crucible is used to hold a silicon carbide raw material 3. The wall thickness of the lower crucible is greater than that of the upper crucible. A seed crystal 2 is fixed to the top of the upper crucible. The top of the upper crucible is also provided with at least two gas passages uniformly distributed along the circumference of the upper crucible, and the gas passages are arranged between the seed crystal and the inner side wall of the upper crucible; the graphite support ring 5 is arranged above the lower crucible and abuts against the inner side wall of the upper crucible, and the wall thickness of the graphite support ring 5 gradually decreases from bottom to top; the graphite plate 6 is arranged above the graphite support ring 5, and the graphite plate 6 is a porous structure and the pore area of ​​the graphite plate 6 gradually decreases from the center to the edge.

[0071] The gas passages are evenly distributed along the circumference of the upper crucible. Figure 1 Only two gas passages are shown, namely the first gas passage and the second gas passage. The first gas passage includes an exhaust passage 1# and a nitrogen replenishment passage 3#, and the second gas passage includes an exhaust passage 2# and a nitrogen replenishment passage 4#. In order to obtain a crystal with a larger convexity at the beginning of growth, it is necessary to open the switches of the exhaust passages 1# and 2# on both sides of the crystal during the crystal growth process, reduce the atmosphere on both sides of the crystal, reduce the edge growth rate, and then perform a hydrogen etching process. During the substrate growth process, the crystal needs to restore its normal morphology, so the switches of the exhaust passages 1# and 2# are closed, and the switches of the nitrogen passages 3# and 4# are opened at the same time, and nitrogen is introduced to increase the nitrogen content at the edge of the crystal and improve the uniformity of the substrate resistivity.

[0072] As a preferred embodiment, the gas passages are at least 4, and each gas passage includes an exhaust path and a nitrogen supply path. The exhaust path is opened during step (4) to reduce the edge growth atmosphere, so that the center thickness of the crystal is much larger than the edge thickness (increasing the crystal convexity). The nitrogen supply path is opened during step (6) to adjust the problem of the nitrogen doping amount at the edge of the crystal being less than that in the center area due to the radial temperature gradient, thereby improving the radial uniformity of nitrogen doping in the crystal.

[0073] It can be understood by those skilled in the art that the growth device of the present application mainly realizes that the crystal keeps a slightly convex morphology during the crystal growth process by evacuating gas or supplementing nitrogen through a graphite plate with pores and a gas passage, and realizes the control of crystal convexity, atmosphere stability control and improvement of doping uniformity by supplementing nitrogen. Growth devices with other structures or adjustment of production parameters can also be used to realize the control of crystal convexity, atmosphere stability control and improvement of doping uniformity to obtain the n-type silicon carbide single crystal of the present application. Therefore, the above-mentioned growth device and preparation method do not constitute a limitation to the present application.

[0074] like Figure 2 As shown, the wall thickness of the graphite support ring 5 gradually decreases from bottom to top, wherein the thickness of the thickest part of the wall is 1.5-5 mm, and the thickness of the thinnest part of the wall is 0.2-1 mm.

[0075] Figure 3 This is a pore distribution mode of the graphite plate 6, and the present application is not limited thereto. The graphite plate 6 may also have a variety of pore distribution modes. Figure 3 As shown, the pore area of ​​the graphite plate 6 gradually decreases from the center to the edge, so that the atmosphere in the center of the crystal is always greater than the atmosphere at the edge of the crystal, so that the crystal can always maintain a slightly convex morphology. The graphite plate 6 is supported by a graphite support ring 5 with uneven wall thickness. During the crystal growth process, the graphite support ring 5 gradually disappears from top to bottom, that is, the height of the graphite support ring 5 continues to decrease, and the graphite plate 6 will gradually move down with the growth of the crystal and maintain a relatively stable distance from the crystal surface.

[0076] Below the crystal, a graphite support ring with a wall thickness gradually decreasing from bottom to top and a graphite plate with pores are arranged. The pore area of ​​the graphite plate gradually decreases from the center to the edge. The function of the graphite plate is to protect the growth process from the atmosphere disorder problem caused by the fluctuation of the growth conditions and increase the stability of the atmosphere transmission. On the other hand, the atmosphere in the center of the crystal is always greater than the atmosphere at the edge of the crystal, so that the crystal can always maintain a slightly convex morphology. The graphite plate is supported by a graphite support ring with uneven wall thickness. During the crystal growth process, since the overall wall thickness of the graphite support ring is relatively thin and shows a trend of gradually decreasing wall thickness from bottom to top, the erosion of the silicon-rich atmosphere in the crucible causes the graphite support ring to gradually disappear from top to bottom, that is, the height of the graphite support ring continues to decrease, and the graphite plate with holes will gradually move down with the growth of the crystal, maintaining a relatively stable distance from the crystal surface. If the distance is too far, the effect on the crystal morphology is small; if the distance is too close, the pores have a greater impact on the local part of the crystal. Therefore, during the crystal growth process, the perforated graphite plate is kept at a close distance from the crystal surface, so that the crystal maintains a stable crystal shape during the entire growth process, solving the problem that the morphology is difficult to stably control during the growth of crystals with a thickness greater than 30 mm.

[0077] However, in addition to the graphite support ring, other support components can also be used to support the graphite plate and can adjust the graphite plate to gradually move downward with the growth of the crystal during the crystal growth process, thereby maintaining a relatively stable distance from the crystal surface. For example, a support member with a vertical slide groove is used to replace the graphite support ring. The support member may include an abutment plate and a support plate. The abutment plate is arranged above the lower crucible and abuts against the inner wall of the upper crucible, and a vertical slide groove is arranged on the abutment plate. The support plate can slide up and down along the vertical slide groove. The support plate is used to support the graphite plate. As the crystal grows, the support plate slides down along the vertical slide groove to maintain a relatively stable distance from the crystal surface.

[0078] However Figure 1-3 Only part of the structure of the growth device is shown. The gas passage arranged on the top of the upper crucible is an improvement on the crucible in the prior art. The structure that the crucible in the prior art should have is not shown. For example, there are other original gas pipelines for introducing or exhausting gas in the original crucible body, which are used to maintain the normal growth operation of n-type silicon carbide single crystal. During the growth process of the crystal, the original gas pipeline is used to realize the inflation and air intake for impurity removal, and the doping gas is introduced to realize N doping during stable crystal growth and restarting growth.

[0079] In a specific embodiment, the method for preparing an n-type silicon carbide substrate by using the above-mentioned growth device can be implemented by the following steps:

[0080] (1) Assembly of the growth device: Assemble the crucible body, silicon carbide raw material, graphite support ring, graphite plate, seed crystal, insulation structure and heating coil.

[0081] (2) Impurity removal: Control the pressure in the growth device to >500 mbar and increase the temperature in the crucible to 2000-2300°C.

[0082] (3) Initial stage of crystal growth: the pressure in the growth device is controlled to drop to 100-300 mbar at a rate of 100-200 mbar / h and maintained for 1-10 hours.

[0083] (4) Stable crystal growth: The pressure in the growth device is reduced to 1-20 mbar at a rate of 90-180 mbar / h, the exhaust port of the device is opened, and a doping gas containing nitrogen is continuously introduced. The proportion of conventional nitrogen in the doping gas is 10%-50%. After growing for 10-30 hours, the exhaust port of the device is closed according to different temperature and pressure control.

[0084] (5) Hydrogen etching: Raise the pressure to 100-500 mbar at a rate of 100-300 mbar / h, and at the same time lower the temperature to 1000-2000°C at a rate of 1-5°C / min. Pass hydrogen, with the hydrogen accounting for 1%-20%, and etch for 3-10 hours.

[0085] (6) Restarting growth: Stop hydrogen introduction, reduce the pressure in the growth device to 1-20 mbar at a rate of 90-180 mbar / h, open nitrogen replenishment line 3# and nitrogen replenishment line 4# to replenish nitrogen, the replenished nitrogen introduction amount is 20%-50% of the normal nitrogen introduction amount, and at the same time, the temperature is raised to 2000-2300°C.

[0086] (7) End of growth: After the crystal continues to grow for 50-150 hours, the pressure is increased to 700-900 mbar and slowly dropped to room temperature, and the crystal growth is completed.

[0087] In the process of stabilizing crystal growth and restarting growth, n-type element doping is used, which can be nitrogen doping or co-doping of nitrogen and other elements. The nitrogen introduction ratio is 10%-50%, and the nitrogen doping concentration is 1×10 18 cm -2 to 2×10 19 cm -2 .

[0088] At the beginning of growth, the crystal needs to have a larger convexity. When the crystal grows to 5 to 10 mm in the center, the pressure is increased and the temperature is lowered. Then hydrogen is introduced to etch the crystal at 1000°C-2000°C to generate more step aggregation. When the crystal growth process is restarted, the TSD can be converted into a basal plane defect because the crystal surface has more large steps. At the same time, since we gradually reduce the convexity of the crystal after restarting the growth, the large steps are also gradually reduced.

[0089] It is understood by those skilled in the art that, in addition to etching to generate more step aggregation during the above growth process, other growth parameters can also be used to control the formation of more large step structures, and then the crystal with more large step structures on the surface is restarted to obtain the n-type silicon carbide single crystal of the present application. Therefore, the above preparation method does not constitute a limitation to the present application.

[0090] In a specific embodiment, the n-type silicon carbide single crystal is prepared by the above-mentioned growth method or growth device. The stacking fault is tested by the PL method. In this test, the stacking fault is in the form of a strip, which is called a bar stacking fault (BSF). Figure 4 As shown, the overall outline indicates the final morphology of the grown crystal, the orange part indicates the crystal morphology when the furnace is shut down for the first time, the vertical line in the figure represents TSD, the horizontal line intersecting the vertical line represents the basal plane defect converted from TSD, and the two blue thick horizontal lines mark Figure 5 (the line below) and Figure 6(The upper line) The two defect diagrams are located in the crystal. After the crystal edge reaches 10-15mm thickness, a lower TSD density is obtained in the edge area. At the same time, since most of the stacking faults in the crystal are caused by TSD deflection, the TSD density at the edge of the crystal in the later stage is low, so there will be few stacking faults. The substrate formed in the early part of the crystal has more TSD conversion and more stacking faults. The number of substrate BSFs formed in the part of the crystal that exceeds the thickness of the first growth crystal by 2-5mm drops to less than 5.

[0091] From the early stage to the late stage of the crystal, the low density area of ​​the edge TSD gradually expands, and the overall density gradually decreases. The n-type silicon carbide single crystal can be 4 inches, 6 inches, 8 inches or more. Figure 5 As shown in the figure, the TSD density within the 10mm ring range of the n-type SiC substrate edge obtained within 10mm from the seed crystal surface is less than 300cm -2 , TSD density within the center 130mm diameter range <500cm -2 , BSF<100. Figure 6 As shown in the figure, the TSD density within the 40mm ring range of the edge of the n-type silicon carbide substrate obtained by the n-type silicon carbide single crystal crystal that is more than 10mm away from the seed crystal surface is less than 100cm -2 , TSD density within the center 130mm diameter range <300cm -2 , BSF < 5. Preferably, the obtained n-type silicon carbide substrate is > 20 mm and the TSD density within 40 mm of the substrate edge is < 50 cm -2 , TSD density within the center 130mm diameter range <200cm -2 , BSF<3.

[0092] In another specific embodiment, the resistivity of the n-type silicon carbide substrate obtained at any position of the n-type silicon carbide single crystal is less than 25mΩ·cm, and the difference between the maximum and minimum values ​​of the resistivity is less than 2.4mΩ·cm. Further, the resistivity of the n-type silicon carbide substrate obtained at any position of the n-type silicon carbide single crystal is 19-21mΩ·cm, and the difference between the maximum and minimum values ​​of the resistivity in any diameter line segment tested at 73 points is less than 2mΩ·cm.

[0093] In another specific embodiment, the difference between the maximum and minimum values ​​of the refractive index of the n-type silicon carbide substrate obtained at any position of the n-type silicon carbide single crystal at the same wavelength within the range of 200-1800 nm is less than 2%.

[0094] In another specific embodiment, the difference between the maximum value and the minimum value of the absorption coefficient of the n-type silicon carbide substrate obtained at any position of the n-type silicon carbide single crystal at the same wavelength in the range of 200-700 nm is less than 2%.

[0095] Example 1

[0096] This embodiment uses the above-mentioned growth method and growth device to prepare an n-type silicon carbide single crystal. The specific steps are as follows:

[0097] (1) Growth device assembly: Assemble the crucible body, insulation structure and heating coil.

[0098] (2) Impurity removal: Control the pressure in the growth device to >500 mbar and increase the temperature in the crucible to 2200°C.

[0099] (3) Initial stage of crystal growth: the pressure in the growth device was controlled to drop to 200 mbar at a rate of 100 mbar / h and maintained for 5 h.

[0100] (4) Stable crystal growth: The pressure in the growth device was reduced to 10 mbar at a rate of 90 mbar / h, and the device's exhaust lines 1# and 2# were opened to continuously introduce a doping gas containing nitrogen, with the ratio of conventional nitrogen in the doping gas being 30%. After 20 hours of growth, the device's exhaust lines 1# and 2# were closed.

[0101] (5) Hydrogen etching: The pressure was raised to 300 mbar at a rate of 100 mbar / h, and the temperature was lowered to 1500°C at a rate of 1-5°C / min. Hydrogen was introduced, with the hydrogen accounting for 5%, and the etching was carried out for 10 h.

[0102] (6) Restarting growth: Stop hydrogen introduction, reduce the pressure in the growth device to 10 mbar at a rate of 90 mbar / h, and replenish nitrogen through nitrogen replenishment line 3# and nitrogen replenishment line 4#. The replenished nitrogen introduction amount is 30% of the normal nitrogen introduction amount. At the same time, the temperature is raised to 2200°C, and the normal nitrogen introduction ratio is still 30%.

[0103] (7) End of growth: After the crystal continues to grow for 50 hours, the pressure is increased to 800 mbar and then slowly dropped to room temperature. The crystal growth is completed and an n-type silicon carbide single crystal is obtained.

[0104] Example 2

[0105] The difference between this embodiment and embodiment 1 is that the introduction ratio of conventional nitrogen in step (4) is 25%, and the rest is the same as embodiment 1.

[0106] Example 3

[0107] The difference between this embodiment and embodiment 1 is that the introduction ratio of conventional nitrogen in step (4) is 20%, and the other aspects are the same as those in embodiment 1.

[0108] Example 4

[0109] The difference between this embodiment and embodiment 1 is that the amount of nitrogen added in step (6) is 10% of the normal amount of nitrogen added, and the rest is the same as embodiment 1.

[0110] Example 5

[0111] The difference between this embodiment and embodiment 1 is that the amount of nitrogen added in step (6) is 65% of the normal amount of nitrogen added, and the rest is the same as embodiment 1.

[0112] Example 6

[0113] This embodiment uses the above-mentioned growth method and growth device to prepare an n-type silicon carbide single crystal. The specific steps are as follows:

[0114] (1) Growth device assembly: Assemble the crucible body, insulation structure and heating coil.

[0115] (2) Impurity removal: Control the pressure in the growth device to >500 mbar and increase the temperature in the crucible to 2000°C.

[0116] (3) Initial stage of crystal growth: the pressure in the growth device was controlled to drop to 100 mbar at a rate of 100 mbar / h and maintained for 1 hour.

[0117] (4) Stable crystal growth: The pressure in the growth device was reduced to 1 mbar at a rate of 90 mbar / h, and the device's exhaust lines 1# and 2# were opened to continuously introduce a doping gas containing nitrogen, with the ratio of conventional nitrogen in the doping gas being 50%. After 10 hours of growth, the device's exhaust lines 1# and 2# were closed.

[0118] (5) Hydrogen etching: The pressure was increased to 500 mbar at a rate of 300 mbar / h, and the temperature was reduced to 1000°C at a rate of 1°C / min. Hydrogen was introduced, with the hydrogen accounting for 1%, and the etching was carried out for 10 h.

[0119] (6) Restarting growth: Stop hydrogen introduction, reduce the pressure in the growth device to 1 mbar at a rate of 180 mbar / h, open nitrogen replenishment line 3# and nitrogen replenishment line 4# to replenish nitrogen, the replenished nitrogen introduction amount is 20% of the normal nitrogen introduction amount, and at the same time, the temperature is raised to 2200°C, at which time the normal nitrogen introduction ratio is still 50%.

[0120] (7) End of growth: After the crystal continues to grow for 100 hours, the pressure is increased to 700 mbar and slowly dropped to room temperature. The crystal growth is completed and an n-type silicon carbide single crystal is obtained.

[0121] Example 7

[0122] This embodiment uses the above-mentioned growth method and growth device to prepare an n-type silicon carbide single crystal. The specific steps are as follows:

[0123] (1) Growth device assembly: Assemble the crucible body, insulation structure and heating coil.

[0124] (2) Impurity removal: Control the pressure in the growth device to >500 mbar and increase the temperature in the crucible to 2300°C.

[0125] (3) Initial stage of crystal growth: the pressure in the growth device was controlled to drop to 300 mbar at a rate of 200 mbar / h and maintained for 10 h.

[0126] (4) Stable crystal growth: The pressure in the growth device was reduced to 20 mbar at a rate of 180 mbar / h, and the device's exhaust lines 1# and 2# were opened to continuously introduce a doping gas containing nitrogen, with the ratio of conventional nitrogen in the doping gas being 10%. After 30 hours of growth, the device's exhaust lines 1# and 2# were closed.

[0127] (5) Hydrogen etching: The pressure was raised to 100 mbar at a rate of 100 mbar / h, and the temperature was lowered to 2000°C at a rate of 5°C / min. Hydrogen was introduced, with the hydrogen accounting for 20%, and the etching was carried out for 3 h.

[0128] (6) Restarting growth: Stop hydrogen introduction, reduce the pressure in the growth device to 20 mbar at a rate of 90 mbar / h, open nitrogen replenishment line 3# and nitrogen replenishment line 4# to replenish nitrogen, the replenished nitrogen introduction amount is 50% of the normal nitrogen introduction amount, and at the same time, the temperature is raised to 2200°C, at which time the normal nitrogen introduction ratio is still 10%.

[0129] (7) End of growth: After the crystal continues to grow for 150 hours, the pressure is increased to 900 mbar and slowly dropped to room temperature. The crystal growth is completed and an n-type silicon carbide single crystal is obtained.

[0130] Comparative Example 1

[0131] This comparative example prepares a comparative n-type silicon carbide single crystal crystal, using the following method:

[0132] (1) Growth device assembly: Assemble the crucible body, insulation structure and heating coil.

[0133] (2) Impurity removal: Control the pressure in the growth device to >500 mbar and increase the temperature in the crucible to 2200°C.

[0134] (3) Initial stage of crystal growth: the pressure in the growth device was controlled to drop to 200 mbar at a rate of 100 mbar / h and maintained for 5 h.

[0135] (4) Stable crystal growth: The pressure in the growth device was reduced to 10 mbar at a rate of 100 mbar / h, and the doping concentration of nitrogen was 25%.

[0136] (5) End of growth: After the crystal has grown for 120 hours, the pressure is increased to 800 mbar and the temperature is slowly lowered to obtain a comparative n-type silicon carbide substrate.

[0137] Comparative Example 2

[0138] This comparative example prepares another comparative n-type silicon carbide single crystal, using a current growth device on the market instead of the growth device of the present application and using the following method to prepare:

[0139] (1) Growth device assembly: Assemble the crucible body, insulation structure and heating coil.

[0140] (2) Impurity removal: Control the pressure in the growth device to >500 mbar and increase the temperature in the crucible to 2200°C.

[0141] (3) Initial stage of crystal growth: the pressure in the growth device was controlled to drop to 200 mbar at a rate of 100 mbar / h and maintained for 5 h.

[0142] (4) Stable crystal growth: The pressure in the growth device was reduced to 10 mbar at a rate of 90 mbar / h, and the growth was continued for 120 h. The nitrogen introduction ratio was 25%.

[0143] (5) Hydrogen etching: The pressure was raised to 300 mbar at a rate of 100 mbar / h, and the temperature was lowered to 1500°C at a rate of 1-5°C / min. Hydrogen was introduced, with the hydrogen accounting for 5%, and the etching was carried out for 10 h.

[0144] (6) Restarting growth: Stop the introduction of hydrogen, reduce the pressure in the growth device to 10 mbar at a rate of 90 mbar / h, and at the same time increase the temperature to 2200° C., with the nitrogen introduction ratio being 25%.

[0145] (7) End of growth: After the crystal continues to grow for 50 hours, the pressure is increased to 800 mbar and the temperature is slowly lowered to obtain an n-type silicon carbide substrate.

[0146] Test Case

[0147] The n-type silicon carbide single crystals prepared in Examples 1 to 7 and the comparative n-type silicon carbide single crystals prepared in Comparative Examples 1 to 2 were cut, ground and polished to obtain n-type silicon carbide substrates, and performance tests were performed on the n-type silicon carbide substrates.

[0148] Among them, the resistivity test is carried out on all n-type silicon carbide substrates of the n-type silicon carbide single crystal. The resistivity of each n-type silicon carbide substrate is tested at 73 points in the surface using a low resistance tester. The point distribution is as follows: Figure 8 As shown, there is a maximum resistivity and a minimum resistivity on any straight line passing through the center of each n-type silicon carbide substrate. The difference between the maximum resistivity and the minimum resistivity on each straight line is calculated, and the maximum value of the difference obtained on all straight lines is taken as the difference between the maximum and minimum resistivity of the n-type silicon carbide substrate (named as the single-chip resistivity difference), and the resistivity values ​​obtained at all test points are averaged to calculate the resistivity of the n-type silicon carbide substrate (named as the single-chip resistivity). All n-type silicon carbide substrates obtained by cutting the n-type silicon carbide single crystal are compared, and the maximum value of the single-chip resistivity difference of all n-type silicon carbide substrates is taken as the maximum difference between the maximum and minimum resistivity of the n-type silicon carbide single crystal, and the single-chip resistivity of all n-type silicon carbide substrates is averaged to calculate the resistivity of the n-type silicon carbide single crystal. The test results are shown in Table 1.

[0149] like Figure 7 As shown, the refractive index and absorption coefficient are tested at 5 points evenly and symmetrically distributed in the silicon carbide substrate. Take 5 points of the substrate to test the refractive index at the same wavelength in the range of 200-1800nm, and obtain the five-point refractive index values ​​of the substrate at each wavelength. At each wavelength, the difference between the maximum and minimum refractive index at the wavelength is calculated according to the calculation formula: [(maximum refractive index-minimum refractive index) / maximum refractive index]×100%, and the maximum difference between the maximum and minimum refractive index at all wavelengths is taken as the difference between the maximum and minimum refractive index of the silicon carbide substrate (named as the single-piece refractive index difference), and the maximum value of the single-piece refractive index difference of all n-type silicon carbide substrates is taken as the maximum difference between the maximum and minimum refractive index of the n-type silicon carbide single crystal. The test results are shown in Table 1.

[0150] The absorption coefficient was tested at the same wavelength in the range of 200-700nm at 5 points of the substrate to obtain the five-point absorption coefficient values ​​of the substrate at each wavelength. The difference between the maximum and minimum absorption coefficients at the wavelength was calculated according to the calculation formula: [(maximum absorption coefficient-minimum absorption coefficient) / maximum absorption coefficient]×100% at each wavelength. The maximum difference between the maximum and minimum absorption coefficients at all wavelengths was taken as the difference between the maximum and minimum absorption coefficients of the silicon carbide substrate (named as the single-piece absorption coefficient difference). The maximum value of the single-piece coefficient absorption differences of all n-type silicon carbide substrates was taken as the maximum difference between the maximum and minimum absorption coefficients of the n-type silicon carbide single crystal. The test results are shown in Table 1.

[0151] The curvature is tested for each n-type silicon carbide substrate, and the maximum curvature of all n-type silicon carbide substrates is taken as the maximum curvature of the n-type silicon carbide single crystal.

[0152] The final performance test results are shown in Table 1-2. Figure 9-12 In Table 2, the TSD density is the through-screw dislocation density, and the BPD density is the basal plane dislocation density.

[0153] Table 1

[0154]

[0155]

[0156] Table 2

[0157]

[0158] As shown in Table 1, the evolution of stacking faults and TSD in the substrate (transformation of TSD and stacking faults, annihilation of TSD, etc.) is correlated with the N doping concentration, resulting in changes in TSD density and the number of stacking faults under different resistivities. The substrate resistivity of about 20 mΩcm is optimal.

[0159] The resistivity uniformity of the substrate is characterized by the maximum value of the difference on any diameter line segment in the 73-point test, and the difference on any diameter line segment is less than 2.4 mΩcm. The resistivity uniformity of Example 2 is significantly better than that of Comparative Example 2. It can be seen that the resistivity uniformity of the substrate obtained by the growth method of the present application is significantly improved.

[0160] The present invention achieves uniformity of refractive index and absorption coefficient by controlling the uniformity of resistivity and regulating defect distribution. Fig. 9 and Fig.10 As shown, the difference between the maximum and minimum values ​​of the refractive index uniformity of Example 2 is smaller than that of Comparative Example 2. Fig.11 and Fig.12As shown, the difference between the maximum and minimum values ​​of the uniformity of the absorption coefficient of Example 2 is smaller than that of Comparative Example 2.

[0161] The above description is only an embodiment of the present invention and is not intended to limit the present invention. For those skilled in the art, the present invention may have various modifications and variations. Any modification, equivalent substitution, improvement, etc. made within the spirit and principle of the present invention should be included in the scope of the claims of the present invention.

Claims

1. An n-type silicon carbide single crystal, characterized in that: The screw dislocation density within the 10mm ring range of the substrate edge obtained by the n-type silicon carbide single crystal that is ≤10mm away from the seed crystal surface is less than 300cm -2 , the density of screw dislocations within the center 130mm diameter is <500cm -2 , the number of stripe stacking faults is less than 100; The screw dislocation density within the 40mm ring range of the substrate edge obtained from the n-type silicon carbide single crystal crystal which is more than 10mm away from the seed crystal surface is less than 100cm -2 , the density of screw dislocations within the center 130mm diameter is <300cm -2 , the number of stripe stacking faults is less than 5.

2. The n-type silicon carbide single crystal according to claim 1, characterized in that: The density of screw dislocations within 40 mm from the edge of the substrate obtained by the n-type silicon carbide single crystal crystal which is more than 20 mm away from the seed crystal surface is less than 50 cm -2 , the density of screw dislocations within the center 130mm diameter is <200cm -2 , the number of stripe stacking faults is ≤3.

3. The n-type silicon carbide single crystal according to claim 1, characterized in that: The central thickness of the n-type silicon carbide single crystal is greater than 10 mm; Preferably, the central thickness of the n-type silicon carbide single crystal is greater than 30 mm.

4. The n-type silicon carbide single crystal according to claim 1, characterized in that: The resistivity of the n-type silicon carbide single crystal is less than 25 mΩ·cm, and the difference between the maximum and minimum values ​​of the resistivity is less than 2.4 mΩ·cm; Preferably, the resistivity of the n-type silicon carbide single crystal is 19-21 mΩ·cm, and the difference between the maximum and minimum resistivity values ​​in any diameter line segment of the n-type silicon carbide single crystal in a 73-point test is less than 2 mΩ·cm.

5. The n-type silicon carbide single crystal according to claim 1, characterized in that: The difference between the maximum and minimum refractive index of the n-type silicon carbide single crystal at the same wavelength in the range of 250-1800nm ​​is less than 2%; and / or The difference between the maximum value and the minimum value of the absorption coefficient of the n-type silicon carbide single crystal at the same wavelength within the range of 250-650nm is less than 2%.

6. An n-type silicon carbide substrate, characterized in that: It is obtained by cutting, grinding and polishing the n-type silicon carbide single crystal according to any one of claims 1 to 5, wherein the screw dislocation density within the 40mm annular range of the edge of the n-type silicon carbide substrate is less than 100cm -2 , the density of screw dislocations within the center 130mm diameter is <300cm -2 , the number of stripe stacking faults is less than 5; Preferably, the screw dislocation density within the 40 mm annular range of the edge of the n-type silicon carbide substrate is less than 50 cm -2 , the density of screw dislocations within the center 130mm diameter is <200cm -2 , the number of stripe stacking faults is less than 3.

7. The n-type silicon carbide substrate according to claim 6, characterized in that The resistivity of the n-type silicon carbide substrate is less than 25 mΩ·cm, and the maximum difference between the maximum value and the minimum value of the resistivity is less than 5 mΩ·cm; Preferably, the resistivity of the n-type silicon carbide substrate is 19-21 mΩ·cm; More preferably, the difference between the maximum and minimum resistivity values ​​of the n-type silicon carbide substrate in a line segment of any diameter in a 73-point test is less than 2 mΩ·cm.

8. The n-type silicon carbide substrate according to claim 6, characterized in that: The difference between the maximum and minimum refractive index of the n-type silicon carbide substrate at the same wavelength in the range of 250-1800nm ​​is less than 2%; and / or The difference between the maximum value and the minimum value of the absorption coefficient of the n-type silicon carbide substrate at the same wavelength within the range of 250-650nm is less than 2%.

9. The n-type silicon carbide substrate according to claim 6, characterized in that: The basal plane dislocation density of the n-type silicon carbide substrate is less than 300 cm -2 , curvature <10μm.

10. A semiconductor device, characterized in that: The semiconductor device comprises an n-type silicon carbide substrate prepared from the n-type silicon carbide single crystal crystal according to any one of claims 1 to 3 or the n-type silicon carbide substrate according to any one of claims 4 to 9.

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