CN112813499A - Preparation method and growth device of N-type silicon carbide crystal - Google Patents
Preparation method and growth device of N-type silicon carbide crystal Download PDFInfo
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- CN112813499A CN112813499A CN202011637816.7A CN202011637816A CN112813499A CN 112813499 A CN112813499 A CN 112813499A CN 202011637816 A CN202011637816 A CN 202011637816A CN 112813499 A CN112813499 A CN 112813499A
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- C—CHEMISTRY; METALLURGY
- C30—CRYSTAL GROWTH
- C30B—SINGLE-CRYSTAL GROWTH; UNIDIRECTIONAL SOLIDIFICATION OF EUTECTIC MATERIAL OR UNIDIRECTIONAL DEMIXING OF EUTECTOID MATERIAL; REFINING BY ZONE-MELTING OF MATERIAL; PRODUCTION OF A HOMOGENEOUS POLYCRYSTALLINE MATERIAL WITH DEFINED STRUCTURE; SINGLE CRYSTALS OR HOMOGENEOUS POLYCRYSTALLINE MATERIAL WITH DEFINED STRUCTURE; AFTER-TREATMENT OF SINGLE CRYSTALS OR A HOMOGENEOUS POLYCRYSTALLINE MATERIAL WITH DEFINED STRUCTURE; APPARATUS THEREFOR
- C30B29/00—Single crystals or homogeneous polycrystalline material with defined structure characterised by the material or by their shape
- C30B29/10—Inorganic compounds or compositions
- C30B29/36—Carbides
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- C—CHEMISTRY; METALLURGY
- C30—CRYSTAL GROWTH
- C30B—SINGLE-CRYSTAL GROWTH; UNIDIRECTIONAL SOLIDIFICATION OF EUTECTIC MATERIAL OR UNIDIRECTIONAL DEMIXING OF EUTECTOID MATERIAL; REFINING BY ZONE-MELTING OF MATERIAL; PRODUCTION OF A HOMOGENEOUS POLYCRYSTALLINE MATERIAL WITH DEFINED STRUCTURE; SINGLE CRYSTALS OR HOMOGENEOUS POLYCRYSTALLINE MATERIAL WITH DEFINED STRUCTURE; AFTER-TREATMENT OF SINGLE CRYSTALS OR A HOMOGENEOUS POLYCRYSTALLINE MATERIAL WITH DEFINED STRUCTURE; APPARATUS THEREFOR
- C30B23/00—Single-crystal growth by condensing evaporated or sublimed materials
- C30B23/002—Controlling or regulating
Abstract
The invention provides a preparation method and a growth device of an N-type silicon carbide crystal, wherein the method comprises the following steps of (1) placing raw materials in a high-temperature area of a crucible, placing seed crystals in a low-temperature area of the crucible, and inwards recessing the outer wall of the top of the crucible to form an annular gas groove; placing the assembled crucible in a furnace body of a crystal growth furnace, and enabling an annular gas tank to be close to a vent hole of the furnace body; (2) and in the crystal growth stage, introducing nitrogen source gas into the furnace body through the vent hole, controlling the crystal growth temperature and pressure, and growing the N-type silicon carbide crystal on the seed crystal. Through the annular gas tank near the air vent position department of furnace body, the gas that lets in can flow along annular gas tank, and the air current velocity of flow is very fast, and inside gas diffusion to the crucible for keep away from the central axis heat transfer in the crucible and accelerate, reduced the radial temperature gradient of crucible, improved crystal growth's quality.
Description
Technical Field
The invention relates to a preparation method and a growth device of an N-type silicon carbide crystal, belonging to the technical field of semiconductor material preparation.
Background
Silicon carbide material has attracted much attention because of its excellent semi-insulating property, and especially for high-power semiconductor devices with special requirements, silicon carbide becomes a potential material of choice for these devices because of its high temperature, high frequency, high power, etc.
At present, silicon carbide crystal is produced by adopting a PVT method in industrial production, but because the requirement on the growth condition is higher, the improvement of the performance and the further application and development of the silicon carbide crystal are limited by defects introduced in the growth process. Therefore, improvement of defects is a primary prerequisite for improving the quality of the silicon carbide substrate.
Dislocations, which are a type of line defect, can be classified into Threading Edge Dislocations (TED), Threading Screw Dislocations (TSD), and Basal Plane Dislocations (BPD) according to their formation mechanism and the resulting difference in the half atomic planes. The magnitude of the different dislocations and their density also have different effects on subsequent epitaxial growth. Most of the BPD is converted to TED during the early phase of epitaxial growth, and a small number of BPD penetrating the epitaxial layer has an effect on device performance. The TSD is prone to form pits, carrot defects and other defects on the surface of the epitaxial layer, and has important influence on the performance, yield and reliability of the device. The influence of the dislocation of the silicon carbide substrate on downstream devices is different from the influence of different types of dislocations, and the dislocation density is also one of important parameters for evaluating the quality of the silicon carbide substrate.
At present, the most mature growth mode of silicon carbide adopts a PVT method for growth, and the axial temperature gradient and the radial temperature gradient can generate shear stress in crystals, so that dislocation slippage is caused. For TSD and BPD, dislocation slip can occur, and when the TSD and BPD meet TED walls or other defects, the slip stops and dislocation accumulation is generated near the TED walls or the defects, so that the local dislocation density of the silicon carbide substrate is too high, and the performance and further application and development of the silicon carbide crystal are seriously influenced.
Disclosure of Invention
In order to solve the problems, the invention provides a preparation method and a growth device of an N-type silicon carbide crystal, wherein the axial temperature gradient is increased by controlling the flow of a nitrogen source gas to be not less than that of an inert gas and utilizing the fact that the heat conductivity of the nitrogen source gas is greater than that of the inert gas, the heat transmission rate above a crucible is higher, the dislocation concentration caused by dislocation slip in the silicon carbide crystal is reduced, and the crystal growth quality is improved.
According to one aspect of the application, a method for preparing an N-type silicon carbide crystal is provided, which is characterized by comprising the following steps:
(1) placing raw materials in a high-temperature area of a crucible, placing seed crystals in a low-temperature area of the crucible, and enabling the outer wall of the top of the crucible to be inwards sunken to form an annular gas tank; placing the assembled crucible in a furnace body of a crystal growth furnace, and enabling an annular gas tank to be close to a vent hole of the furnace body, wherein the furnace body is respectively provided with a first vent hole and a second vent hole from bottom to top;
(2) and in the crystal growth stage, introducing inert gas into the furnace body through the first vent hole, introducing nitrogen source gas into the furnace body through the second vent hole, controlling the flow of the introduced nitrogen source gas to be not less than the flow of the introduced inert gas, controlling the crystal growth temperature and pressure, and growing the N-type silicon carbide crystal on the seed crystal.
Further, the furnace body is respectively provided with a first vent hole and a second vent hole from bottom to top;
in the step (1), the assembled crucible is placed in the furnace body of the crystal growth furnace, so that the annular gas groove is close to the second vent hole of the furnace body.
Further, in the step (2), inert gas is introduced into the furnace body through the first vent hole, nitrogen source gas is introduced into the furnace body through the second vent hole, and the flow of the introduced nitrogen source gas is controlled to be not less than the flow of the introduced inert gas
Further, preferably, in the step (2), the flow rate of the nitrogen source gas is 150-500 mL/min, and the flow rate of the inert gas is 50-150 mL/min;
preferably, the flow rate of the nitrogen source gas is 200-300 mL/min, and the flow rate of the inert gas is 80-120 mL/min.
Further, in the step (2), along with the crystal growth process, the flow of the introduced nitrogen source gas is gradually increased, the flow of the introduced inert gas is kept unchanged, and the increasing rate of the flow of the introduced nitrogen source gas is 2-10 mL/h;
preferably, the increasing rate of the flow of the introduced nitrogen source gas is 5-8 mL/h;
preferably, the flow rate of the nitrogen source gas is controlled to be 150-500 mL/min and the flow rate of the inert gas is controlled to be 50-150 mL/min at the beginning of the crystal growth stage.
Furthermore, the outer wall of the top of the crucible is inwards sunken to form an annular gas groove, and the circle center of the annular gas groove is superposed with the circle center of the top of the crucible;
in the step (1), the assembled crucible is placed in the furnace body of the crystal growth furnace, so that the annular gas groove is close to the second vent hole of the furnace body.
Further, in the step (2), the crystal growth temperature is controlled to be 1800-2700 ℃, the crystal growth pressure is 1500-3000 Pa, and the crystal growth time is 80-200 h;
preferably, the crystal growth temperature is controlled to be 2000-2400 ℃, the crystal growth pressure is 1800-2200 Pa, and the crystal growth time is 100-150 h.
Further, in the step (2), in the crystal growth stage, the rotation and/or lifting of the crucible is controlled; preferably, the rotating speed of the crucible is controlled to be 5-20 r/min, and the lifting speed of the crucible is controlled to be 2-15 mm/min; preferably, the rotating speed of the crucible is controlled to be 10-15 r/min, and the lifting speed of the crucible is controlled to be 3-10 mm/min.
Further, in the step (2), in the crystal growth stage, introducing nitrogen source gas into a third vent hole, wherein the third vent hole is formed in the side wall of the furnace body and is positioned on the upper side of the second vent hole;
controlling the flow of the nitrogen source gas introduced into the third vent hole to be not more than the flow of the nitrogen source gas introduced into the second vent hole and not less than the flow of the inert gas introduced into the first vent hole;
preferably, the nitrogen source gas is selected from at least one of nitrogen gas, ammonia gas, and organic amines; and/or
The inert gas is at least one of helium, neon and argon;
preferably, the nitrogen source gas is nitrogen;
preferably, the inert gas is argon.
According to another aspect of the present application, there is provided an apparatus for growing an N-type silicon carbide crystal, the apparatus comprising:
the side wall of the furnace body is respectively provided with a first vent hole and a second vent hole from bottom to top, the first vent hole is used for introducing inert gas into the furnace body, and the second vent hole is used for introducing nitrogen source gas into the furnace body and is provided with vent holes;
the crucible, the crucible set up in the furnace body, the top outer wall of crucible inwards caves in and forms annular gas tank, the centre of a circle in annular gas tank and the centre of a circle coincidence at crucible top.
Furthermore, a plurality of annular gas grooves are concentrically arranged on the outer wall of the top of the crucible;
preferably, the depths of the plurality of annular gas grooves are increased from inside to outside in sequence;
preferably, the widths of the inner walls of the plurality of annular gas grooves are reduced from inside to outside in sequence;
preferably, the widths of the plurality of annular gas grooves increase from inside to outside in sequence;
preferably, the crucible is connected to a rotary lifting device.
Further, the furnace body is respectively provided with a first vent hole and a second vent hole from bottom to top, the first vent hole is used for introducing inert gas into the furnace body, and the second vent hole is used for introducing nitrogen source gas into the furnace body;
preferably, a plurality of second vent holes are formed in the peripheral side wall of the furnace body, and the second vent holes are symmetrically arranged by taking the axial direction of the furnace body as the center;
preferably, the furnace body is also provided with a third vent hole, the third vent hole is positioned above the second vent hole, and the third vent hole is used for introducing nitrogen source gas into the furnace body;
preferably, a plurality of third vent holes are formed in the peripheral side wall of the furnace body, and the third vent holes are symmetrically arranged by taking the axial direction of the furnace body as a center;
preferably, the heating coil is arranged on the outer side of the furnace body, and the furnace body is further provided with an air exhaust hole.
The beneficial effects of the invention include but are not limited to:
(1) according to the preparation method of the N-type silicon carbide crystal, the annular gas groove is close to the position of the vent hole of the furnace body, the introduced gas can flow along the annular gas groove, the gas flow velocity is high, and the gas is diffused into the crucible, so that the heat transmission in the crucible far from the central axis is accelerated, the radial temperature gradient of the crucible is reduced, and the crystal growth quality is improved.
(2) According to the preparation method of the N-type silicon carbide crystal, the flow of the introduced nitrogen source gas is controlled to be not less than the flow of the introduced inert gas, the heat conductivity of the introduced nitrogen source gas is greater than that of the introduced inert gas, the heat transmission rate above the crucible is high, the axial temperature gradient is increased, dislocation concentration caused by dislocation slip in the silicon carbide crystal is reduced, and the crystal growth quality is improved.
(3) According to the preparation method of the N-type silicon carbide crystal, the flow of the nitrogen source gas is gradually increased, so that the gas flow velocity above the crucible is gradually increased, the axial temperature gradient difference is gradually increased, the increase of the nitrogen source gas can also counteract the temperature rise of a crystal growth surface in the crystal growth process to be unfavorable for nitrogen doping, the dislocation defect of the silicon carbide crystal is further reduced, and the quality of the silicon carbide crystal is improved.
(4) The invention relates to a growth device of an N-type silicon carbide crystal, which is characterized in that inert gas is introduced into a furnace body through a first vent hole, and nitrogen source gas is introduced into the furnace body through a second vent hole; the thermal conductivity of the introduced nitrogen source gas is larger than that of the introduced inert gas, so that the axial temperature gradient of the crucible is increased, the crystal growth rate is ensured, and the crystal growth quality is improved.
Drawings
The accompanying drawings, which are included to provide a further understanding of the application and are incorporated in and constitute a part of this application, illustrate embodiment(s) of the application and together with the description serve to explain the application and not to limit the application. In the drawings:
FIG. 1 is a cross-sectional view of an apparatus for growing a silicon carbide crystal of the N-type according to the present application;
FIG. 2 is a cross-sectional view of a crucible in an apparatus for growing a silicon carbide crystal of the N-type according to the present application;
FIG. 3 is a schematic cross-sectional view of a crucible in an apparatus for growing a silicon carbide crystal of the N-type according to the present application;
FIG. 4 is a schematic representation of the dislocation density of a silicon carbide crystal produced by a comparative example of the present application;
FIG. 5 is a schematic representation of the dislocation density of a silicon carbide crystal produced in accordance with an embodiment of the present application;
wherein, 1, a furnace body; 11. a first vent hole; 12. a second vent hole; 13. a third vent hole; 14. an air exhaust hole; 2. a crucible; 21. an annular gas groove; 3. a heat-insulating layer; 31. a temperature measuring hole; 4. a graphite tray; 5. a support bar; 6. and a heating coil.
Detailed Description
The present application will be described in detail with reference to examples, but the present application is not limited to these examples.
In the following description, numerous specific details are set forth in order to provide a thorough understanding of the present application, however, the present application may be practiced in other ways than those described herein, and therefore the scope of the present application is not limited by the specific embodiments disclosed below.
In addition, in the description of the present application, it is to be understood that the terms "upper", "lower", "front", "rear", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", "outer", etc. indicate orientations or positional relationships based on those shown in the drawings, and are only for convenience of description and simplicity of description, and do not indicate or imply that the referred devices or elements must have a specific orientation, be constructed in a specific orientation, and be operated, and thus, should not be construed as limiting the present application.
The embodiments in the present specification are described in a progressive manner, and the same and similar parts among the embodiments are referred to each other, and each embodiment focuses on the differences from the other embodiments.
Furthermore, the terms "first", "second" and "first" are used for descriptive purposes only and are not to be construed as indicating or implying relative importance or implicitly indicating the number of technical features indicated. Thus, a feature defined as "first" or "second" may explicitly or implicitly include one or more of that feature. In the description of the present application, "a plurality" means two or more unless specifically limited otherwise.
In this application, unless expressly stated or limited otherwise, the terms "mounted," "connected," "coupled," and the like are to be construed broadly and include, for example, fixed or removable connections or integral parts; the connection can be mechanical connection, electrical connection or communication; either directly or indirectly through intervening media, either internally or in any other relationship. The specific meaning of the above terms in the present application can be understood by those of ordinary skill in the art as appropriate.
In this application, unless expressly stated or limited otherwise, the first feature "on" or "under" the second feature may be directly contacting the first and second features or indirectly contacting the first and second features through intervening media. In the description herein, reference to the description of the term "one embodiment," "some embodiments," "an example," "a specific example," or "some examples," etc., means that a particular feature, structure, material, or characteristic described in connection with the embodiment or example is included in at least one embodiment or example of the application. In this specification, the schematic representations of the terms used above are not necessarily intended to refer to the same embodiment or example. Furthermore, the particular features, structures, materials, or characteristics described may be combined in any suitable manner in any one or more embodiments or examples.
Example 1
Referring to fig. 1 to 3, the present embodiment provides an apparatus for growing an N-type silicon carbide crystal, the apparatus comprising a furnace body 1 and a crucible 2, the furnace body 1 being provided with a vent, the crucible 2 being provided in the furnace body 1; the outer wall of the top of the crucible 2 is inwards sunken to form an annular gas groove 21, and the circle center of the annular gas groove 21 is overlapped with that of the top of the crucible 2. The setting of annular gas tank 21 for gaseous can flow along annular gas tank 21, and the air current velocity of flow is very fast, and inside gas diffusion to the crucible, make keeping away from the central axis heat transfer in the crucible 2 and accelerate, reduced the radial temperature gradient of crucible, thereby reduced dislocation defect in the silicon carbide crystal, improved crystal growth's quality.
Specifically, the structure of the crucible 2 is not particularly limited, and a crucible conventionally used in the art may be used for the crucible 2. For example: the crucible 2 can be composed of a crucible body and a crucible cover at the top, or the crucible 2 can be composed of an upper crucible body and a lower crucible body, as long as the top outer wall of the crucible 2 is ensured to form the annular gas groove 21.
As an embodiment of the application, the top outer wall of the crucible is concentrically provided with a plurality of annular gas grooves. The plurality of annular gas grooves 21 form a plurality of gas channels, so that nitrogen source gas forms a uniform flow field above the crucible 2, the gas flow rate is accelerated, the radial temperature gradient is reduced, and the axial temperature gradient is increased.
As an embodiment of the present application, referring to fig. 2 in combination, the depth of the plurality of annular gas grooves 21 increases from inside to outside in sequence. Inside gas diffused crucible 2 through annular gas tank, the degree of depth of a plurality of annular gas tanks 21 increased from inside to outside in proper order for the heat transfer rate who keeps away from the central axis increased in proper order, further reduced radial temperature gradient.
As an embodiment of the present application, referring to fig. 3 in combination, the widths of the inner walls of the plurality of annular gas grooves 21 are sequentially decreased from inside to outside, so that the heat transfer rates from inside to outside through the annular gas grooves 21 are sequentially increased, and the radial temperature gradient of the crucible is further decreased.
As an embodiment of the present application, the widths of the plurality of annular gas grooves increase from inside to outside in sequence; the gas in the annular gas groove close to the edge can take more heat in unit time than the gas in the annular gas groove close to the center, so that the relative difference value of the temperature of the gas and the temperature of the gas in the center is reduced, and the radial temperature gradient is reduced.
As an embodiment of the present application, the crucible 2 includes a crucible body and a crucible cover, the crucible cover closing a top opening of the crucible body; the top of crucible cover inwards indent forms annular gas tank 2, and annular gas tank 21 sets up and covers at the crucible, convenient processing, and the sunken setting in annular gas tank 21 for inside the nitrogen source gas enters into the crucible cover, has further increased crucible 2's axial temperature gradient.
In one embodiment of the present application, the furnace body 1 is provided with a first vent hole 11 and a second vent hole 12 from bottom to top, the first vent hole 11 is used for introducing inert gas into the furnace body, and the second vent hole 12 is used for introducing nitrogen source gas into the furnace body. The introduced inert gas or nitrogen source gas can flow along the annular gas groove 21, the flow velocity of the gas flow is high, the heat conductivity of the introduced nitrogen source gas is higher than that of the introduced inert gas, the heat dissipation of the upper part of the crucible 2 is accelerated, the axial temperature gradient of the crucible 2 is increased, the radial gradient temperature is reduced, the dislocation concentration caused by dislocation slippage in the silicon carbide crystal is further reduced, and the crystal growth quality is improved.
Specifically, the shapes and the numbers of the openings of the first vent holes 11 and the second vent holes 12 are not specifically limited, and the shapes and the numbers of the annular gas grooves 21 are not specifically limited as long as the second vent holes 12 are communicated with the annular gas grooves 21, so that the nitrogen source gas can enter the annular gas grooves 21 through the second vent holes 12, and a gas flow field is formed above the crucible 2. The nitrogen source gas may be one conventionally used in the art, and is selected from at least one of nitrogen, ammonia, and organic amines, and preferably, the nitrogen source gas is nitrogen. The inert gas may be one conventionally used in the art, and is selected from at least one of helium, neon, and argon. Preferably, the inert gas is argon. The thermal conductivity of nitrogen at 100 ℃ is 7.5 cal/(cm.degree.C.s), the thermal conductivity of argon at 100 ℃ is 5.2 cal/(cm.degree.C.s), the thermal conductivity of the gas increases with the temperature, and the thermal conductivity of nitrogen is obviously higher than that of argon at the silicon carbide crystal growth temperature of 2000 ℃.
As an embodiment of the present application, a plurality of second ventilation holes 12 are arranged on the peripheral side wall of the furnace body 1, and the plurality of second ventilation holes 12 are symmetrically arranged by taking the axial direction of the furnace body 1 as the center, so that the nitrogen source gas uniformly enters the furnace body 1 from the side wall, the heat dissipation is faster around the crucible 2, and the radial temperature gradient is uniformly reduced.
In one embodiment of the present application, the furnace body 1 is further provided with a third vent hole 13, the third vent hole 13 is located above the second vent hole 12, and the third vent hole 13 is used for introducing a nitrogen source gas into the furnace body 1 and the nitrogen source gas introduced through the second vent hole 12 as a nitrogen source gas environment required for the growth of the N-type silicon carbide crystal.
As an embodiment of the present application, a plurality of third ventilation holes 13 are disposed on the peripheral side wall of the furnace body 1, and the plurality of third ventilation holes 13 are symmetrically disposed with the axial direction of the furnace body 1 as the center, so that the nitrogen source gas is uniformly introduced into the furnace body 1. And the flow of the nitrogen source gas in the second vent hole 1 is set to be larger than the flow of the nitrogen source gas in the third vent hole 13, so that the flow of the nitrogen source gas near the crucible 2 is increased, and the axial temperature gradient above the crucible 2 is further increased.
As an implementation mode of the application, the periphery of the crucible 2 is provided with a heat preservation layer 3, and the heat preservation layer 3 positioned at the top of the crucible 2 is provided with a temperature measuring hole 31; the temperature measuring hole 31 is located on the central axis of the annular gas groove 21. The temperature measuring holes 31 meet the requirement of temperature measurement in the crystal growth process of silicon carbide, and meanwhile, because the temperature of the raw material area in the furnace body 1 is high, the temperature measuring holes are far away from a high-temperature area, and the temperature is low, so that an axial temperature gradient is formed. The temperature measuring hole 31 is located on the central axis of the annular gas groove 21 so that a more uniform temperature gradient difference is formed in the axial direction.
As an embodiment of the present application, the apparatus further comprises a graphite tray 4, the graphite tray 4 is used for placing the crucible 2; the lower part of the graphite tray 4 is connected with a support rod 5, and the support rod 5 passes through the opening at the bottom of the furnace body 1 and is connected with an external rotary lifting device. The rotary lifting device is used for controlling the rotary lifting of the crucible 2 and comprises a motor, and the motor drives the supporting rod to drive the graphite tray 4 and the crucible 2 to rotate and lift so as to improve the uniformity of the gas flow rate in the crucible 2.
In one embodiment of the present application, the heating coil 6 is provided outside the furnace body 1, and the furnace body 1 is further provided with an extraction hole 14. The air exhaust hole can be arranged on the upper furnace cover at the top or the lower furnace cover at the bottom of the furnace body. The heating coil 6 is used for heating the crucible 2 to provide the temperature required by crystal growth, and the air exhaust hole 14 is used for exhausting air in the furnace body 1 to ensure that the furnace body 1 is at a certain pressure.
Example 2
A method of growing an N-type silicon carbide crystal using the apparatus of embodiment 1, comprising:
(1) and (3) assembling: placing a silicon raw material and a carbon raw material in a high-temperature area of a crucible, and placing seed crystals in a low-temperature area of the crucible; placing the assembled crucible in a furnace body of a crystal growth furnace;
(2) a temperature rising stage: regulating the temperature of the crystal growth furnace to 500-2000 ℃ for heating, and controlling the pressure in the crucible to be 0.2 multiplied by 105Pa is increased to 5X 105Pa, marking V1 as the flow rate of inert gas introduced into the first vent hole, V2 as the flow rate of nitrogen source gas introduced into the second vent hole, and V3 as the flow rate of nitrogen source gas introduced into the third vent hole; the flow rate of introducing inert gas in the temperature-raising stage V1 is 200mL/min, and the flow rate of introducing nitrogen source gas in the temperature-raising stage V3 or V2 is 100 mL/min; thereby forming an axial temperature gradient from top to bottom in the furnace body and providing a nitrogen environment required by the growth of the N-type silicon carbide;
(3) crystal growth stage: and the temperature of the crystal growth stage needs to be continuously increased to 2400-2600 ℃ on the basis of the temperature increase stage so as to meet the crystal growth requirement of the N-type silicon carbide. And in the crystal growth stage, the flow rate of the inert gas V1 is 50-150 mL/min, the flow rate of the nitrogen source gas V2 is 150-500 mL/min, the flow rate of the nitrogen source gas V3 is kept at 50-150 mL/min, the crystal growth pressure is 1500-3000 Pa, and the crystal growth time is kept at 100-150 h in the crystal growth stage, so that the N-type silicon carbide crystal is prepared. Wherein the flow rate of the V2 gas is larger than that of V1 and V3, the purpose of the method is mainly to increase the flow rate of nitrogen gas near the crucible, so that the nitrogen gas flow rate in the annular gas groove above the crucible is increased, and the axial temperature gradient above the crucible is further increased.
Or gradually increasing the flow of V2 nitrogen gas, wherein the increasing rate of the flow of the introduced nitrogen source gas is 2-10 mL/h, so as to gradually increase the flow of the introduced nitrogen source gas, gradually increase the flow rate of the gas above the crucible, counteract the temperature rise of the crystal growth surface during the crystal growth process, be not beneficial to nitrogen doping, and gradually increase the axial temperature gradient.
Or, in the crystal growth stage, the crucible can be controlled to lift near the second vent hole at the lifting speed of 0.1-1 mm/h, and can rotate in the lifting process to ensure the uniformity of the gas flow rate, and particularly, the crucible rotates at the speed of 10-15 r/min at the gas inlet groove of the upper cover of the crucible.
The concrete preparation parameters of each example and each comparative example are shown in Table 1, and N-type silicon carbide crystals 1# to 6# and comparative N-type silicon carbide crystals D1# to D2# are prepared. Wherein, the filled inert gas is argon, and the nitrogen source gas is nitrogen.
TABLE 1
Obtaining a comparative N-type silicon carbide crystal D3# according to a conventional crystal growth process, wherein inert gas vent holes and nitrogen vent holes of a crystal growth furnace body are arranged at the bottom of the furnace body;
the crystal growth process comprises the following steps: 1) a temperature rising stage: regulating the temperature of the crystal growth furnace to 500-2000 ℃ for heating, and controlling the pressure in the crucible to be 0.2 multiplied by 105Pa is increased to 5X 105Pa, introducing 150mL/min of inert gas vent hole and 80mL/min of nitrogen; 2) crystal growth stage: the temperature of the crystal growth stage needs to be continuously increased to 2400-2600 ℃ on the basis of the temperature increase stage so as to meet the crystal growth requirement of the N-type silicon carbide; introducing 150mL/min of inert gas through an air vent and 130mL/min of nitrogen; the rotation and movement of the crucible are not carried out in the crystal growth stage. A schematic diagram of the dislocation density of the resulting comparative silicon carbide crystal D3# is shown in FIG. 4.
The silicon carbide crystal 1# of N type obtained by the method of the present application is shown in FIG. 5. The dislocation density of the silicon carbide crystal prepared by the method is remarkably reduced, the dislocation distribution is sparse, and the phenomenon that dislocation concentration is caused by slippage due to shear stress caused by large diameter gradient in the crystal growing process is reduced.
The defects of the silicon carbide crystals of the N-type silicon carbide crystals 1# to 6# and the comparative N-type silicon carbide crystals D1# to D2# were detected, and the screw dislocations TSD, the plane dislocations BPD, the dislocation density and the like were detected, and the detection results are shown in Table 2.
TABLE 2
As can be seen from the results in Table 2, in the crystal growth stage, the N-type silicon carbide crystal obtained by the method has less dislocation defects and high crystal quality by controlling the flow of the nitrogen source gas to be not less than the flow of the inert gas and optimizing the increase ratio of the nitrogen gas.
The embodiments in the present specification are described in a progressive manner, and the same and similar parts among the embodiments are referred to each other, and each embodiment focuses on the differences from the other embodiments. In particular, for the system embodiment, since it is substantially similar to the method embodiment, the description is simple, and for the relevant points, reference may be made to the partial description of the method embodiment.
The above are merely examples of the present application, and the scope of the present application is not limited by these specific examples, but is defined by the claims of the present application. Various modifications and changes may occur to those skilled in the art. Any modification, equivalent replacement, improvement, etc. made within the technical idea and principle of the present application should be included in the protection scope of the present application.
Claims (10)
1. A preparation method of an N-type silicon carbide crystal is characterized by comprising the following steps:
(1) placing raw materials in a high-temperature area of a crucible, placing seed crystals in a low-temperature area of the crucible, and enabling the outer wall of the top of the crucible to be inwards sunken to form an annular gas tank; placing the assembled crucible in a furnace body of a crystal growth furnace, and enabling an annular gas tank to be close to a vent hole of the furnace body;
(2) and in the crystal growth stage, introducing nitrogen source gas into the furnace body through the vent hole, controlling the crystal growth temperature and pressure, and growing the N-type silicon carbide crystal on the seed crystal.
2. The method for preparing an N-type silicon carbide crystal according to claim 1, wherein the furnace body is provided with a first vent hole and a second vent hole from bottom to top;
in the step (1), the assembled crucible is placed in the furnace body of the crystal growth furnace, so that the annular gas groove is close to the second vent hole of the furnace body.
3. The method for preparing an N-type silicon carbide crystal according to claim 2, wherein in the step (2), an inert gas is introduced into the furnace body through the first vent hole, a nitrogen source gas is introduced into the furnace body through the second vent hole, and the flow rate of the introduced nitrogen source gas is controlled to be not less than the flow rate of the introduced inert gas;
preferably, in the step (2), the flow rate of the nitrogen source gas is 150-500 mL/min, and the flow rate of the inert gas is 50-150 mL/min;
preferably, the flow rate of the nitrogen source gas is 200-300 mL/min, and the flow rate of the inert gas is 80-120 mL/min.
4. The method for preparing an N-type silicon carbide crystal according to claim 3, wherein in the step (2), the flow rate of the introduced nitrogen source gas is gradually increased along with the growth process, the flow rate of the introduced inert gas is kept unchanged, and the increase rate of the flow rate of the introduced nitrogen source gas is 2-10 mL/h;
preferably, the increasing rate of the flow of the introduced nitrogen source gas is 5-8 mL/h;
preferably, the flow rate of the nitrogen source gas is controlled to be 150-500 mL/min and the flow rate of the inert gas is controlled to be 50-150 mL/min at the beginning of the crystal growth stage.
5. The method for preparing an N-type silicon carbide crystal according to claim 1, wherein in the step (2), the crystal growth temperature is controlled to be 1800-2700 ℃, the crystal growth pressure is controlled to be 1500-3000 Pa, and the crystal growth time is controlled to be 80-200 h;
preferably, the crystal growth temperature is controlled to be 2000-2400 ℃, the crystal growth pressure is 1800-2200 Pa, and the crystal growth time is 100-150 h.
6. The method for preparing a silicon carbide crystal according to claim 1, wherein in the step (2), the rotation and/or lifting of the crucible is controlled during the crystal growth stage;
preferably, the rotating speed of the crucible is controlled to be 5-20 r/min, and the lifting speed of the crucible is controlled to be 2-15 mm/min;
preferably, the rotating speed of the crucible is controlled to be 10-15 r/min, and the lifting speed of the crucible is controlled to be 3-10 mm/min.
7. The method for preparing an N-type silicon carbide crystal according to claim 1, wherein in the step (2), in the crystal growth stage, a nitrogen source gas is introduced into a third vent hole, the third vent hole is formed in the side wall of the furnace body, and the third vent hole is located above the second vent hole;
controlling the flow of the nitrogen source gas introduced into the third vent hole to be not more than the flow of the nitrogen source gas introduced into the second vent hole and not less than the flow of the inert gas introduced into the first vent hole;
preferably, the nitrogen source gas is selected from at least one of nitrogen gas, ammonia gas, and organic amines; and/or
The inert gas is at least one of helium, neon and argon;
preferably, the nitrogen source gas is nitrogen;
preferably, the inert gas is argon.
8. An apparatus for growing an N-type silicon carbide crystal, the apparatus comprising:
the side wall of the furnace body is provided with a vent hole;
the crucible, the crucible set up in the furnace body, the top outer wall of crucible inwards caves in and forms annular gas tank, the centre of a circle in annular gas tank and the centre of a circle coincidence at crucible top.
9. The apparatus for growing a silicon carbide crystal according to claim 8, wherein the crucible has a plurality of annular gas grooves concentrically formed in a top outer wall thereof;
preferably, the depths of the plurality of annular gas grooves are increased from inside to outside in sequence;
preferably, the widths of the inner walls of the plurality of annular gas grooves are reduced from inside to outside in sequence;
preferably, the widths of the plurality of annular gas grooves increase from inside to outside in sequence;
preferably, the crucible is connected to a rotary lifting device.
10. The device for growing N-type silicon carbide crystals according to claim 8, wherein the furnace body is provided with a first vent hole and a second vent hole from bottom to top, the first vent hole is used for introducing inert gas into the furnace body, and the second vent hole is used for introducing nitrogen source gas into the furnace body;
preferably, a plurality of second vent holes are formed in the peripheral side wall of the furnace body, and the second vent holes are symmetrically arranged by taking the axial direction of the furnace body as the center;
preferably, the furnace body is also provided with a third vent hole, the third vent hole is positioned above the second vent hole, and the third vent hole is used for introducing nitrogen source gas into the furnace body;
preferably, a plurality of third vent holes are formed in the peripheral side wall of the furnace body, and the third vent holes are symmetrically arranged by taking the axial direction of the furnace body as a center;
preferably, the heating coil is arranged on the outer side of the furnace body, and the furnace body is further provided with an air exhaust hole.
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