CN113897684B

CN113897684B - Silicon carbide seed crystal, silicon carbide seed crystal assembly, preparation method of silicon carbide seed crystal assembly and preparation method of silicon carbide crystal

Info

Publication number: CN113897684B
Application number: CN202010575275.3A
Authority: CN
Inventors: 蔡凯; 郭少聪; 王军; 周维
Original assignee: BYD Co Ltd
Current assignee: BYD Co Ltd
Priority date: 2020-06-22
Filing date: 2020-06-22
Publication date: 2023-08-08
Anticipated expiration: 2040-06-22
Also published as: CN113897684A

Abstract

The invention provides a silicon carbide seed crystal, a silicon carbide seed crystal assembly, a preparation method thereof and a method for preparing a silicon carbide crystal, wherein the method for preparing the silicon carbide seed crystal comprises the following steps: forming a silicon layer on the back surface of the silicon carbide seed crystal body; forming a prefabricated carbon layer on the surface of the silicon layer far away from the silicon carbide seed crystal, wherein the prefabricated carbon layer covers the surface of the silicon layer far away from the silicon carbide seed crystal body; and enabling the prefabricated carbon layer to react with the silicon layer to generate a silicon carbide transition layer and a carbon layer, so as to obtain the silicon carbide seed crystal. The method has simple steps and convenient operation, has no strict requirements on equipment and technicians, and the obtained silicon carbide seed crystal can effectively relieve the stress difference at the interface, so that the combination at the interface is firmer, and simultaneously, the problem of carbon layer falling caused by the difference of wettability and thermal expansion rate is remarkably improved, and the quality of the silicon carbide crystal grown by adopting the silicon carbide seed crystal can be further effectively improved.

Description

Silicon carbide seed crystal, silicon carbide seed crystal assembly, preparation method of silicon carbide seed crystal assembly and preparation method of silicon carbide crystal

Technical Field

The invention relates to the technical field of silicon carbide crystal growth, in particular to a silicon carbide seed crystal, a silicon carbide seed crystal assembly, a preparation method thereof and a method for preparing a silicon carbide crystal.

Background

Silicon carbide (SiC) is widely studied for application in fields of high temperature, high frequency, high power, radiation resistance, and the like due to its high saturated electron drift rate, high breakdown field strength, high thermal conductivity, and the like. In the existing process of preparing silicon carbide crystals, back evaporation is very easy to occur, so that planar hexagonal cavities are generated in the crystals, and the crystal quality is greatly affected. Moreover, as the crystal grows, voids induced by back evaporation continue to extend inside the crystal, eventually completely destroying the usability of the crystal. Therefore, solving the problem of back evaporation of the seed crystal is extremely important to improve the quality of the silicon carbide crystal.

At present, a scheme for inhibiting the back evaporation of the seed crystal is widely adopted, wherein a dense and high-temperature-resistant carbon film or a metal carbide protective layer is plated on the back surface of the seed crystal. Although the protective layer inhibits the back evaporation to a certain extent, the following problems also exist in the process of multiple heating and cooling in the production process: the protective layer is easy to crack between the protective layer and the silicon carbide seed crystal to cause the protective layer to fall off; internal stress of seed crystals can be increased, and quality of subsequent crystals is reduced; may be detrimental to the seed; the cost is high; foreign elements different from carbon and silicon are introduced to affect the crystal growth and the crystal purity.

Thus, the current silicon carbide crystal growth-related art still remains to be improved.

Disclosure of Invention

The present invention aims to solve at least one of the technical problems in the related art to some extent. Therefore, an object of the present invention is to provide a method for preparing a silicon carbide seed crystal capable of effectively improving the back evaporation problem, avoiding the falling of the film layer and improving the crystal quality.

In one aspect of the invention, a method of preparing a silicon carbide seed crystal is provided. According to an embodiment of the invention, the method comprises: forming a silicon layer on the back surface of the silicon carbide seed crystal body; forming a prefabricated carbon layer on the surface of the silicon layer, which is far away from the silicon carbide seed crystal body, wherein the prefabricated carbon layer covers the surface of the silicon layer, which is far away from the silicon carbide seed crystal body; and enabling the prefabricated carbon layer to react with the silicon layer to generate a silicon carbide transition layer and a carbon layer, so as to obtain the silicon carbide seed crystal. The method has simple steps, convenient operation and no strict requirements on equipment and technicians, carbon atoms in the prefabricated carbon layer permeate into the silicon layer to form a silicon carbide transition layer in the preparation process, and simultaneously, the silicon atoms in the silicon layer can permeate into the silicon carbide seed crystal body and react with the carbon atoms in the silicon carbide seed crystal body, so that the stress difference at an interface can be effectively relieved, the combination at the interface is firmer, the carbon film falling problem caused by the difference of wettability and thermal expansion coefficient is remarkably improved, and the quality of the silicon carbide crystal grown by adopting the silicon carbide seed crystal can be effectively improved.

In another aspect of the invention, a silicon carbide seed crystal is provided. According to an embodiment of the present invention, the silicon carbide seed crystal is prepared by the method described above. In the silicon carbide seed crystal, a layer close to the silicon carbide seed crystal body is a silicon carbide transition layer which is the same as the silicon carbide seed crystal body, the thermal expansion coefficient of a homogeneous material is similar, and the degree of thermal expansion and cold contraction which occur along with the change of temperature is similar, so that the influence on the internal stress of the silicon carbide seed crystal body is very weak, the binding force is strong, the falling risk is obviously reduced, meanwhile, the silicon carbide transition layer is also a compact high-temperature resistant material, the protection effect of the silicon carbide transition layer on the silicon carbide seed crystal body cannot be lost in the high-temperature environment of crystal growth, and in addition, a more compact protection layer can be provided by the carbon layer, so that the back evaporation problem is effectively avoided, and the quality of grown crystals is improved.

In yet another aspect of the invention, a method of preparing a silicon carbide seed crystal assembly is provided. According to an embodiment of the invention, the method comprises: preparing silicon carbide seed crystals by the method; forming an adhesion layer on at least one of a surface of a silicon carbide seed holder and a surface of the silicon carbide seed; and bonding the silicon carbide seed crystal holder and the silicon carbide seed crystal together through the bonding layer to obtain the silicon carbide seed crystal assembly. The method has simple and convenient steps, has no strict requirements on equipment and technicians, and the obtained silicon carbide seed crystal assembly can effectively improve the back evaporation problem, has stronger binding force between the silicon carbide transition layer and the silicon carbide seed crystal body and between the silicon carbide transition layer and the carbon layer, effectively relieves the stress difference at the interface, and obviously improves the problem of carbon layer falling caused by wettability, thermal expansion rate difference and the like.

In yet another aspect of the invention, a silicon carbide seed crystal assembly is provided. According to an embodiment of the present invention, the silicon carbide seed crystal assembly is prepared by the method described above. Therefore, the silicon carbide transition layer is in contact with the silicon carbide seed crystal body, the silicon carbide transition layer and the silicon carbide seed crystal body are made of homogeneous materials, the thermal expansion coefficients are similar, the degree of thermal expansion and cold contraction occurring along with the temperature change is similar, cracking and falling off cannot occur in the processing process due to the temperature change, the influence on the internal stress of the silicon carbide seed crystal body is small, meanwhile, the silicon carbide transition layer and the carbon layer are both high-temperature-resistant compact film layers, the back evaporation problem can be effectively prevented, and the quality of grown crystals is improved.

In another aspect of the invention, a method of preparing a silicon carbide crystal is provided. According to an embodiment of the invention, the method comprises: preparing a silicon carbide seed crystal assembly by the method; and growing a silicon carbide crystal on the surface of the silicon carbide seed crystal body away from the silicon carbide seed crystal holder by a physical vapor transport method. The silicon carbide crystal obtained by the method has smooth surface, no cavity and higher crystal quality.

Drawings

FIG. 1 is a flow chart of a method of preparing a silicon carbide seed crystal according to one embodiment of the invention.

FIG. 2 is a flow chart of a method of preparing a silicon carbide seed crystal according to one embodiment of the invention.

FIG. 3 is a schematic diagram of the structure of a silicon carbide seed crystal according to one embodiment of the invention.

FIG. 4 is a schematic structural view of a silicon carbide seed crystal assembly according to one embodiment of the present invention.

Reference numerals:

10: silicon carbide seed body 20: silicon carbide transition layer 31: preformed carbon layer 32: carbon layer 40: silicon layer 100: silicon carbide seed holder 200: silicon carbide seed crystal 300: adhesive layer

Detailed Description

Embodiments of the present invention are described in detail below. The following examples are illustrative only and are not to be construed as limiting the invention. The examples are not to be construed as limiting the specific techniques or conditions described in the literature in this field or as per the specifications of the product. The reagents or apparatus used were conventional products commercially available without the manufacturer's attention.

In one aspect of the invention, a method of preparing a silicon carbide seed crystal is provided. According to an embodiment of the invention, referring to fig. 1 and 2, the method comprises the steps of:

s100: a silicon layer 40 is formed on the back side of the silicon carbide seed body 10.

S200: a preformed carbon layer 31 is formed on the surface of the silicon layer 40 remote from the silicon carbide seed body 10, the preformed carbon layer 31 covering the surface of the silicon layer 40 remote from the silicon carbide seed body 10.

S300: the prefabricated carbon layer 31 and the silicon layer 40 are reacted to generate the silicon carbide transition layer 20 and the carbon layer 32, and the silicon carbide seed crystal is obtained.

Specifically, the silicon layer may be formed by a physical vapor deposition method, and in some embodiments, the silicon layer may be formed by a magnetron sputtering method. Therefore, the formed silicon layer has higher quality and purity, and is favorable for subsequent steps.

In some embodiments, the silicon layer may be a monocrystalline silicon layer. Thus, it is easy to prepare and react with the prefabricated carbon layer in the subsequent step to obtain the silicon carbide transition layer.

In some embodiments, the silicon layer 40 is fully reacted in step S300, i.e., the entire silicon layer is reacted to form a silicon carbide transition layer. In some embodiments, the thickness of the monocrystalline silicon layer is 0.05-0.1 microns, such as 0.05 microns, 0.06 microns, 0.07 microns, 0.08 microns, 0.09 microns, 0.1 microns, and the like. The single crystal silicon layer with the thickness range is easier to completely react with the prefabricated carbon layer in the subsequent step, so that a silicon carbide transition layer with a certain thickness is formed. If the single crystal silicon layer is too thick, the side adjacent to the silicon carbide seed body cannot react completely with the carbon atoms permeated from the prefabricated carbon layer, and unreacted silicon is melted into silicon droplets and then evaporated in the high temperature environment of subsequent crystal growth, which can lead to holes on the back surface of the silicon carbide seed body, and can greatly change the stress distribution state on the back surface of the silicon carbide seed body, which can have serious negative effects on crystal growth. If the thickness of the monocrystalline silicon layer is too thin, the formed silicon carbide transition layer is too thin, and the stress difference between the silicon carbide seed crystal body and the carbon layer in the high-temperature environment cannot be effectively buffered.

In some embodiments, the preformed carbon layer may be formed by: forming an organic adhesive layer on the surface of the silicon layer away from the silicon carbide seed crystal body; and carbonizing the organic adhesive layer to obtain the prefabricated carbon layer.

In some specific examples, the organic gel layer may be formed by spin coating, and specifically, the gel layer may be formed by spin coating at a rotation speed of 500 to 5000rpm (specifically, 500rpm, 1000rpm, 1500rpm, 2000rpm, 2500rpm, 3000rpm, 3500rpm, 4000rpm, 4500rpm, 5000rpm, etc.), and then drying the gel layer to evaporate a solvent in the gel layer, thereby obtaining the organic gel layer.

In particular, the specific kind of the organic glue may be selected according to actual needs, and in some specific examples, the organic glue with high carbon content may be selected, such as at least one of photoresist, epoxy resin, furfural resin and phenolic resin. While the thickness of the organic gel layer may be 10 to 20 μm (specifically, 10 μm, 11 μm, 12 μm, 13 μm, 14 μm, 15 μm, 16 μm, 17 μm, 18 μm, 19 μm, 20 μm, etc.). The thickness of the prefabricated carbon layer formed by the organic glue with the thickness after high-temperature curing and carbonization can be 5-10 mu m, and if the prefabricated carbon layer is too thick, the phenomena of peeling, chapping and falling easily occur; if the prefabricated carbon layer is too thin, perforation easily occurs in the subsequent process of forming the silicon carbide transition layer, the integrity is damaged, and the protection effect on the back surface of the silicon carbide seed crystal body is lost.

In some embodiments, carbonizing the organic glue layer is performed by heating the organic glue layer. Specifically, the heating rate of the carbonization may be 10 to 30 ℃/min (10 ℃/min, 12 ℃/min, 15 ℃/min, 18 ℃/min, 20 ℃/min, 22 ℃/min, 25 ℃/min, 28 ℃/min, 30 ℃/min, etc.), the carbonization temperature may be 700 to 1200 ℃ (specifically, such as 700 ℃, 800 ℃, 900 ℃, 1000 ℃, 1100 ℃, 1200 ℃, etc.), and the heat preservation time may be 1 to 5 hours (specifically, such as 1 hour, 2 hours, 3 hours, 4 hours, 5 hours, etc.). Under the condition, the organic glue can be quickly and comprehensively carbonized to form a compact prefabricated carbon layer, and the formed prefabricated carbon layer has a remarkable effect on improving the problem of back evaporation in the crystal growth process.

In some embodiments, the preformed carbon layer may have a thickness of 5 to 10 μm (e.g., 5 μm, 6 μm, 7 μm, 8 μm, 9 μm, 10 μm, etc., in particular). If the prefabricated carbon layer is too thick, the phenomena of skinning, chapping and falling easily occur; if the prefabricated carbon layer is too thin, perforation easily occurs in the subsequent process of forming the silicon carbide transition layer, the integrity is damaged, and the protection effect on the back surface of the silicon carbide seed crystal body is lost.

In one embodiment, the preformed carbon layer may be formed by: uniformly spin-coating (500-5000 rpm) organic glue (at least one of photoresist, epoxy resin, furfural resin and phenolic resin) with high carbon content on the surface of the silicon layer far away from the silicon carbide seed crystal body, wherein the thickness of the glue layer is 10-20 mu m, then drying to evaporate the solvent in the organic glue, then placing the silicon carbide seed crystal body spin-coated with the organic glue in a vacuum heating furnace, raising the temperature rising rate to 700-1200 ℃ at 10-30 ℃/min, and preserving the temperature for 1-5 h, so that the carbon-containing organic glue is fully decomposed and carbonized to form a prefabricated carbon film, and the thickness of the prefabricated carbon layer is 5-10 mu m.

It should be noted that the amount of silicon layer is much less than the amount of the preformed carbon layer, so that all silicon is guaranteed to react with carbon without damaging the outermost preformed carbon layer. If the amount of the silicon layer is too large to fully react, the prefabricated carbon layer fully participates in the reaction at the moment, so that the prefabricated carbon layer breaks and loses effect, the excessive silicon layer is melted into liquid silicon drops in a high-temperature environment for crystal growth, all protection layers are lost on the back of the silicon carbide seed crystal body, back evaporation cannot be inhibited, and the crystal quality is inevitably reduced. That is, in step S300, all of the silicon layer reacts to form a silicon carbide transition layer, while only a portion of the pre-carbon layer that is close to the silicon layer reacts to form a silicon carbide transition layer, a portion of the pre-carbon layer that is far from the silicon layer does not react, and the unreacted portion constitutes the carbon layer in the finally obtained silicon carbide seed crystal.

In some embodiments, reacting the pre-formed carbon layer with the silicon layer is performed by: the silicon carbide seed crystal body formed with the prefabricated carbon layer and the silicon layer is heated to 1200-1600 deg.c (specifically, 1200 deg.c, 1250 deg.c, 1300 deg.c, 1350 deg.c, 1400 deg.c, 1450 deg.c, 1500 deg.c, 1550 deg.c, 1600 deg.c, etc.), and maintained for a predetermined period of time. Specifically, under the high temperature condition, carbon atoms in the prefabricated carbon layer permeate to one side of the silicon layer and react with the silicon atoms to generate silicon carbide, and the concentration of the carbon atoms in the silicon layer is inversely proportional to the permeation distance, so that the closer to the carbon layer, the more carbon atoms are, the silicon carbide transition layer shows physical properties closer to the carbon layer; and the closer to the silicon carbide seed body the fewer carbon atoms, the closer to the physical properties of the silicon carbide seed body the silicon carbide transition layer therein. The silicon carbide transition layer formed in this way effectively relieves the stress difference at the interface, and ensures that the bonding at the interface is firmer.

In addition, on the one hand, the melting point of the simple substance silicon is lower (about 1410 ℃), and in the step, silicon atoms in the molten simple substance silicon can permeate to the side of the silicon carbide seed crystal body under the high-temperature condition and are bonded with carbon atoms in the silicon carbide seed crystal body, and the bonding force ensures that the silicon carbide transition layer and the silicon carbide seed crystal can be tightly bonded. On the other hand, the prefabricated carbon layer is formed by crosslinking and combining carbon atom chains, and carbon atoms react with silicon atoms in the silicon layer to generate silicon carbide, so that the bonding force between the silicon carbide transition layer and the carbon layer is increased, and as can be seen from the above, the silicon carbide transition layer which is closer to the carbon layer shows physical properties closer to the carbon layer due to the higher carbon content, and the problem of carbon layer falling caused by wettability and thermal expansion difference is greatly improved.

In some embodiments, during the process of forming the silicon carbide transition layer, the heating rate of the heating may be 50-100 ℃/min (such as 50 ℃/min, 60 ℃/min, 70 ℃/min, 80 ℃/min, 90 ℃/min, 100 ℃/min, etc.); the predetermined time may be 2 to 5 hours (specifically, 2 hours, 3 hours, 4 hours, 5 hours, etc.). Under the condition, the prefabricated carbon layer can fully react with the silicon layer to obtain the silicon carbide transition layer with better performance.

In one embodiment, the reacting of the pre-formed carbon layer with the silicon layer is performed by: after the carbonization treatment is finished, the temperature is raised to 1200-1600 ℃ at the heating rate of 50-100 ℃/min, and the heat is preserved for 2-5 hours, so that the prefabricated carbon layer and the silicon layer react at high temperature to form the high-temperature resistant silicon carbide transition layer. Because the silicon is far less than carbon, after the carbon-silicon reaction is complete, one side of the silicon carbide transition layer, which is far away from the silicon carbide seed crystal body, is provided with a denser and more high-temperature-resistant carbon layer.

The method has simple steps, convenient operation and no strict requirements on equipment and technicians, carbon atoms in the prefabricated carbon layer permeate into the silicon layer to form a silicon carbide transition layer in the preparation process, and simultaneously, the silicon atoms in the silicon layer can permeate into the silicon carbide seed crystal body and react with the carbon atoms in the silicon carbide seed crystal body, so that the stress difference at an interface can be effectively relieved, the combination at the interface is firmer, the carbon film falling problem caused by the difference of wettability and thermal expansion coefficient is remarkably improved, and the quality of the silicon carbide crystal grown by adopting the silicon carbide seed crystal can be effectively improved.

In another aspect of the invention, a silicon carbide seed crystal is provided. According to an embodiment of the present invention, the silicon carbide seed crystal is prepared by the method described above. Specifically, referring to fig. 3, the silicon carbide seed crystal includes: a silicon carbide seed body 10; a silicon carbide transition layer 20, the silicon carbide transition layer 20 overlying the back surface of the silicon carbide seed body 10; a carbon layer 32, the carbon layer 32 overlying a surface of the silicon carbide transition layer 20 remote from the silicon carbide seed body 10. In the silicon carbide seed crystal, a layer close to the silicon carbide seed crystal body is a silicon carbide transition layer which is the same as the silicon carbide seed crystal body, the thermal expansion coefficient of a homogeneous material is similar, and the degree of thermal expansion and cold contraction which occur along with the change of temperature is similar, so that the influence on the internal stress of the silicon carbide seed crystal body is very weak, the binding force is strong, the falling risk is obviously reduced, meanwhile, the silicon carbide transition layer is also a compact high-temperature resistant material, the protection effect of the silicon carbide transition layer on the silicon carbide seed crystal body cannot be lost in the high-temperature environment of crystal growth, and in addition, a more compact protection layer can be provided by the carbon layer, so that the back evaporation problem is effectively avoided, and the quality of grown crystals is improved.

It should be noted that, as used herein, the "back surface of the silicon carbide seed crystal body" refers to a surface facing away from the crystal growth surface, and specifically, when the silicon carbide seed crystal is used to prepare a silicon carbide crystal, the silicon carbide crystal grows on the crystal growth surface of the silicon carbide seed crystal body, and the silicon carbide transition layer and the carbon layer are disposed on the surface (i.e., back surface) of the silicon carbide seed crystal body facing away from the crystal growth surface.

According to an embodiment of the present invention, the atomic number ratio of carbon atoms to silicon atoms in the silicon carbide transition layer gradually decreases in the direction of the silicon carbide transition layer toward the silicon carbide seed body. That is, the silicon carbide transition layer is not uniform in the thickness direction (i.e., the direction of the silicon carbide transition layer toward the silicon carbide seed crystal body), its composition is gradually changed, and in particular, the closer to the carbon layer, the larger the carbon atom ratio in the silicon carbide transition layer is, the higher the carbon content is, exhibiting physical properties (such as thermal conductivity, thermal expansion rate, etc.) closer to the carbon layer; and the closer to the silicon carbide seed crystal body, the less the carbon atoms in the silicon carbide transition layer are in proportion, and the physical properties of the silicon carbide transition layer are closer to those of the silicon carbide seed crystal body. The silicon carbide transition layer formed in this way effectively relieves the stress difference at the interface, ensures that the combination at the interface is firmer, can effectively avoid the silicon carbide transition layer from falling off due to the cracking between the silicon carbide transition layer and the silicon carbide seed crystal body, and further improves the quality of the grown silicon carbide crystal.

According to some embodiments of the invention, the atomic number ratio of carbon atoms to silicon atoms in the silicon carbide transition layer is about 1:1 near the surface of the silicon carbide seed body. Therefore, the silicon carbide seed crystal has the properties closer to those of the silicon carbide seed crystal body, and the effects of improving the binding force and weakening the stress influence are better. The term "the atomic ratio of carbon atoms to silicon atoms is about 1:1" as used herein means that the atomic ratio of carbon atoms to silicon atoms may be 1:1, or may be slightly less than 1:1, or the latter may be slightly more than 1:1, or may be varied within a small range of about 1:1.

According to an embodiment of the invention, the silicon carbide transition layer satisfies at least one of the following conditions in a direction of the silicon carbide transition layer towards the silicon carbide seed body: the thermal conductivity of different positions in the silicon carbide transition layer is gradually increased; the thermal expansion coefficients of the silicon carbide transition layer at different positions gradually decrease. As previously mentioned, the silicon carbon number ratio in the silicon carbide transition layer is gradually changed, and thus the corresponding performance parameters are also changed with the gradual change of the composition.

It will be appreciated that the performance parameters of the homogeneous material are more closely related, and therefore, the difference between the thermal conductivity at different locations in the silicon carbide transition layer and the thermal conductivity of the silicon carbide seed body gradually decreases in the direction of the silicon carbide transition layer toward the silicon carbide seed body; the difference between the thermal expansion coefficients of the silicon carbide transition layer at different positions and the thermal expansion coefficient of the silicon carbide seed crystal body is gradually reduced. Therefore, the closer to the silicon carbide seed crystal body, the more similar the properties of the silicon carbide transition layer and the silicon carbide seed crystal body are, the stronger the bonding force between the silicon carbide transition layer and the silicon carbide seed crystal body is, and the silicon carbide transition layer cannot fall off due to different expansion degrees and other reasons in the temperature change process.

It should be noted that "the difference between the thermal conductivity at the different positions in the silicon carbide transition layer and the thermal conductivity of the silicon carbide seed body" described herein means that the larger one of the thermal conductivity at the different positions in the silicon carbide transition layer and the thermal conductivity of the silicon carbide seed body minus the difference obtained by the smaller one of the thermal conductivity at the different positions in the silicon carbide transition layer and the thermal conductivity of the silicon carbide seed body, that is, if the thermal conductivity at a certain position in the silicon carbide transition layer is greater than the thermal conductivity of the silicon carbide seed body, the difference between the thermal conductivity at the position in the silicon carbide transition layer and the thermal conductivity of the silicon carbide seed body = the thermal conductivity at the position in the silicon carbide transition layer-the thermal conductivity of the silicon carbide seed body; conversely, the difference between the thermal conductivity at the location of the silicon carbide transition layer and the thermal conductivity of the silicon carbide seed body = the thermal conductivity of the silicon carbide seed body-the thermal conductivity at the location of the silicon carbide transition layer. The differences between the other parameters described herein are the same and will not be described in detail.

It will of course also be appreciated that the difference between the thermal conductivity at different locations in the silicon carbide transition layer and the thermal conductivity of the carbon layer gradually decreases in the direction of the carbon layer towards the carbon layer; the difference between the thermal expansion coefficients of the silicon carbide transition layer and the carbon layer at different locations gradually decreases. Therefore, the closer to the carbon layer, the properties of the silicon carbide transition layer are similar to those of the carbon layer, the stronger the bonding force between the silicon carbide transition layer and the carbon layer is, and the carbon layer is not separated in the temperature change process due to different expansion degrees and the like, so that the back evaporation problem can be better improved, and the quality of the grown silicon carbide crystal is improved.

According to an embodiment of the present invention, in the silicon carbide seed crystal, the difference between the coefficients of thermal expansion of any two adjacent layers is not more than 4 to 6×10 ^-6 K ^-1 In particular 4X 10 ^-6 K ^-1 、4.2×10 ^-6 K ^-1 、4.5×10 ^-6 K ^-1 、4.8×10 ^-6 K ^-1 、5×10 ^-6 K ^-1 、5.2×10 ^-6 K ^-1 、5.5×10 ^-6 K ^-1 、5.8×10 ^-6 K ^-1 、6×10 ^-6 K ^-1 Etc. Therefore, the expansion and contraction degrees of the two materials are basically consistent in the temperature change process, the falling of the film layer can be effectively avoided, and the quality of the grown crystal is improved.

It should be noted that any two adjacent layers described herein may be the silicon carbide seed crystal body and the silicon carbide transition layer or the silicon carbide transition layer and the carbon layer, but as can be seen from the foregoing description, the composition and the performance parameters of the silicon carbide transition layer gradually change in the thickness direction, and the difference between the thermal expansion coefficients of any two adjacent layers is not more than 4 to 6×10 ^-6 K ^-1 The difference between the thermal expansion coefficient of the silicon carbide transition layer at any position in the thickness direction and the thermal expansion coefficient of the silicon carbide seed crystal body, and the difference between the thermal expansion coefficient of the silicon carbide transition layer at any position in the thickness direction and the thermal expansion coefficient of the carbon layer are all within the above range.

According to an embodiment of the present invention, the silicon carbide transition layer has a thickness of 0.1 to 0.5 μm, specifically, 0.1 μm, 0.2 μm, 0.3 μm, 0.4 μm, 0.5 μm, etc. The thickness range can well relieve the stress between the silicon carbide seed crystal body and the carbon layer, and improve the binding force between two adjacent layers.

According to an embodiment of the present invention, the thickness of the carbon layer is 2 to 7 μm, specifically, such as 2 μm, 3 μm, 4 μm, 5 μm, 6 μm, 7 μm, etc. The carbon layer in the thickness range can have good protection effect, improves the back evaporation problem, and is easy to wrinkle, crack and fall off if being too thick, and relatively reduces the protection effect if being too thin.

In yet another aspect of the invention, a silicon carbide seed crystal assembly is provided. According to an embodiment of the present invention, the silicon carbide seed crystal assembly is prepared by the method described above. Specifically, referring to fig. 4, the silicon carbide seed crystal assembly comprises: a silicon carbide seed holder 100; the silicon carbide seed 200 previously described; and an adhesive layer 300 disposed between the silicon carbide seed holder 100 and the silicon carbide seed 200 for adhering the silicon carbide seed 200 to the silicon carbide seed holder 100. Therefore, the silicon carbide transition layer is in contact with the silicon carbide seed crystal body, the silicon carbide transition layer and the silicon carbide seed crystal body are made of homogeneous materials, the thermal expansion coefficients are similar, the degree of thermal expansion and cold contraction occurring along with the temperature change is similar, cracking and falling off cannot occur in the processing process due to the temperature change, the influence on the internal stress of the silicon carbide seed crystal body is small, meanwhile, the silicon carbide transition layer and the carbon layer are both high-temperature-resistant compact film layers, the back evaporation problem can be effectively prevented, and the quality of grown crystals is improved.

According to the embodiment of the invention, the carbon layer and the silicon carbide transition layer described in the silicon carbide seed crystal may be identical to those described in the silicon carbide seed crystal, and will not be described in detail herein.

In another aspect of the invention, a method of preparing a silicon carbide crystal is provided. According to an embodiment of the invention, the method comprises: preparing a silicon carbide seed crystal assembly by the method; and growing a silicon carbide crystal on the surface of the silicon carbide seed crystal body away from the silicon carbide seed holder by a physical vapor transport method. The silicon carbide crystal prepared by the method basically has no hexagonal cavity caused by back evaporation, and has higher quality and better performance.

According to the embodiment of the invention, the specific steps, conditions and the like for bonding the silicon carbide seed crystal and growing the silicon carbide crystal can be performed by referring to the conventional technology, and are not described in detail herein.

Embodiments of the present invention are described in detail below.

Example 1

(1) Plating a monocrystalline silicon layer with the thickness of 0.05 mu m uniformly on the back surface of the silicon carbide seed crystal body by using magnetron sputtering;

(2) Spin-coating the photoresist solution at 1000rpm for 1min to uniformly spin-coat the monocrystalline silicon layer on the surface far away from the silicon carbide seed crystal body, and then drying the silicon carbide seed crystal body in a 160 ℃ oven to completely evaporate the solvent in the photoresist solution;

(3) Placing the obtained silicon carbide seed crystal body in a vacuum heating furnace, heating to 800 ℃ at a heating rate of 20 ℃/min under a vacuum environment, and preserving heat for 1h to fully decompose and carbonize the photoresist to form a prefabricated carbon layer;

(4) And then raising the temperature to 1400 ℃ at the heating rate of 50 ℃/min, and preserving the heat for 2 hours to enable part of the prefabricated carbon layer to react with the monocrystalline silicon layer at high temperature so as to form the high-temperature-resistant silicon carbide transition layer and the carbon layer.

(5) And fixing the obtained silicon carbide seed crystal on a graphite seed crystal support by using an adhesive, and observing the quality of the finally obtained silicon carbide crystal and the back surface of a seed crystal body.

Example 2

(2) Spin-coating the epoxy resin solution at 2000rpm for 1min to uniformly spin-coat the monocrystalline silicon layer on the surface far away from the silicon carbide seed crystal body, and then drying the silicon carbide seed crystal body in a 160 ℃ oven to completely evaporate the solvent in the epoxy resin solution;

(3) Placing the obtained silicon carbide seed crystal body in a vacuum heating furnace, heating to 1000 ℃ at a heating rate of 20 ℃/min under a vacuum environment, and preserving heat for 3 hours to fully decompose and carbonize the epoxy resin to form a prefabricated carbon layer;

(4) And then raising the temperature to 1500 ℃ at the heating rate of 50 ℃/min, and preserving the temperature for 5 hours, so that part of the prefabricated carbon layer reacts with the monocrystalline silicon layer at high temperature to form a high-temperature-resistant silicon carbide transition layer and a carbon layer.

(5) And fixing the obtained carbonized seed crystal on a graphite seed crystal support by using an adhesive, and observing the quality of the finally obtained silicon carbide crystal and the back surface of a seed crystal body.

Example 3

(1) Plating a monocrystalline silicon layer with the thickness of 0.1 mu m on the back surface of the silicon carbide seed crystal body by using magnetron sputtering;

(2) Spin-coating the phenolic resin solution at 4000rpm for 1min to uniformly spin-coat the monocrystalline silicon layer on the surface far away from the silicon carbide seed crystal body, and then drying the silicon carbide seed crystal body in a 160 ℃ oven to completely evaporate the solvent in the phenolic resin solution;

(3) Placing the obtained silicon carbide seed crystal body in a vacuum heating furnace, firstly raising the temperature to 1200 ℃ at the heating rate of 30 ℃/min, and preserving the temperature for 5 hours to fully decompose and carbonize the phenolic resin to form a prefabricated carbon layer;

(4) And then raising the temperature to 1600 ℃ at the heating rate of 80 ℃/min, and preserving the temperature for 5 hours, so that part of the prefabricated carbon layer reacts with the monocrystalline silicon layer at high temperature to form a high-temperature-resistant silicon carbide transition layer and a carbon layer.

Comparative example 1

(1) Depositing an yttrium oxide coating with the thickness of 0.2 mu m on the back surface of the silicon carbide seed crystal body by using a magnetron sputtering method;

(2) And (3) placing the silicon carbide seed crystal body and carbon powder under the atmosphere of Ar with 1 atmosphere, heating to 2100 ℃ and preserving heat for 30min, so that the carbon powder and yttrium oxide react, and a mixed coating of silicon carbide yttrium and yttrium carbide is obtained.

(3) And fixing the obtained silicon carbide seed crystal on a graphite seed crystal support by using an adhesive, and observing the quality of the finally obtained silicon carbide crystal and the back surface of a seed crystal body.

Performance test:

1. the testing method comprises the following steps: the four pieces of treated silicon carbide seed crystals obtained in examples 1 to 3 and comparative example 1 were used to grow silicon carbide crystals using the same process parameters, and the quality of the obtained crystals and the back surface of the seed crystal body were observed as to whether the crystals cracked or not, whether the back surface of the seed crystal body was smooth and bright, and whether or not there were voids resulting from back evaporation.

Test results:

examples	Crystal quality	Back of seed crystal body
			Example 1	Small stress and good processability	Smooth, bright and hole-free
Example 2	Small stress and good processability	Smooth, bright and hole-free
			Example 3	Small stress and good processability	Smooth, bright and hole-free
Comparative example 1	High stress and cracking during processing	Smooth, bright and has fine holes

The observation of whether the back surface of the obtained silicon carbide seed crystal body is smooth or not and whether holes exist or not can show that the silicon carbide crystal obtained by growth in the embodiments 1-3 of the application is good in quality, so that the silicon carbide transition layer and the carbon layer are not fallen off in the process of crystal growth, and a good protection effect is achieved.

2. Atomic number ratio test of carbon atoms and silicon atoms at different positions in the thickness direction of the silicon carbide transition layer: taking the cross section of the silicon carbide seed crystal prepared in the previous example, performing X-ray energy spectrum analysis (EDS) and Scanning Electron Microscope (SEM) element distribution test, and observing the distribution condition of two elements of carbon and silicon in the whole cross section in the direction of the carbon layer-silicon carbide transition layer-silicon carbide seed crystal body as follows: the presence of elemental silicon is not detected at the carbon layer; the carbon element accounts for more than 80 percent and the silicon element accounts for less than 20 percent at the position close to the carbon layer on the silicon carbide transition layer, the carbon element accounts for gradually decreasing from the side close to the carbon layer to the side close to the silicon carbide seed crystal body, the silicon element accounts for gradually increasing, and the more close to the silicon carbide seed crystal body, the more the two elements account for 50 percent; the carbon and silicon element ratio of the silicon carbide seed crystal body is about 50%.

In the description of the present specification, a description referring to terms "one embodiment," "some embodiments," "examples," "specific examples," 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 present invention. In this specification, schematic representations of the above terms are not necessarily directed 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. Furthermore, the different embodiments or examples described in this specification and the features of the different embodiments or examples may be combined and combined by those skilled in the art without contradiction.

While embodiments of the present invention have been shown and described above, it will be understood that the above embodiments are illustrative and not to be construed as limiting the invention, and that variations, modifications, alternatives and variations may be made to the above embodiments by one of ordinary skill in the art within the scope of the invention.

Claims

1. A method of making a silicon carbide seed crystal assembly, comprising:

forming a silicon layer on the back surface of the silicon carbide seed crystal body;

forming a prefabricated carbon layer on the surface of the silicon layer, which is far away from the silicon carbide seed crystal body, wherein the prefabricated carbon layer covers the surface of the silicon layer, which is far away from the silicon carbide seed crystal body;

reacting the prefabricated carbon layer with the silicon layer to generate a silicon carbide transition layer and a carbon layer, so as to obtain a silicon carbide seed crystal;

forming an adhesion layer on at least one of a surface of a silicon carbide seed holder and a surface of the silicon carbide seed;

bonding the silicon carbide seed crystal holder and the silicon carbide seed crystal together through the bonding layer to obtain a silicon carbide seed crystal assembly,

the thickness of the prefabricated carbon layer is 5-10 mu m,

the prefabricated carbon layer which is not reacted with the silicon layer constitutes the carbon layer, and the thickness of the carbon layer is 2-7 mu m.

2. The method of claim 1, wherein the silicon layer satisfies at least one of the following conditions:

the silicon layer is a monocrystalline silicon layer;

the thickness of the monocrystalline silicon layer is 0.05-0.1 micrometer;

the silicon layer is formed by a physical vapor deposition method.

3. The method of claim 2, wherein the silicon layer is formed by a magnetron sputtering method.

4. The method of claim 1, wherein the preformed carbon layer is formed by:

forming an organic adhesive layer on the surface of the silicon layer away from the silicon carbide seed crystal body;

and carbonizing the organic adhesive layer to obtain the prefabricated carbon layer.

5. The method of claim 4, wherein the organic glue layer is formed by a spin-coating process.

6. The method according to claim 5, wherein the spin-coating method has a rotation speed of 500 to 5000rpm.

7. The method of claim 4, wherein the organic glue comprises at least one of a photoresist, an epoxy resin, a furfural resin, and a phenolic resin.

8. The method according to claim 4, wherein the thickness of the organic glue layer is 10-20 μm.

9. The method according to claim 4, wherein the carbonization temperature is increased at a rate of 10 to 30 ℃/min, the carbonization temperature is 700 to 1200 ℃, and the heat preservation time is 1 to 5 hours.

10. The method of claim 1, wherein reacting the pre-formed carbon layer and the silicon layer is performed by:

and heating the silicon carbide seed crystal body with the prefabricated carbon layer and the silicon layer to 1200-1600 ℃, and preserving heat for a preset time.

11. The method of claim 10, wherein the heating is at a ramp rate of 50 to 100 ℃/min.

12. The method of claim 10, wherein the predetermined time is 2 to 5 hours.

13. The method of claim 1, wherein the silicon carbide transition layer satisfies at least one of the following conditions:

the thickness of the silicon carbide transition layer is 0.1-0.5 mu m;

the atomic number ratio of carbon atoms to silicon atoms in the silicon carbide transition layer gradually decreases in the direction of the silicon carbide transition layer toward the silicon carbide seed crystal body.

14. A silicon carbide seed crystal assembly prepared by the method of claim 1.

15. A method of preparing silicon carbide crystals, comprising:

preparing a silicon carbide seed crystal assembly using the method of claim 1;

and growing a silicon carbide crystal on the surface of the silicon carbide seed crystal body away from the silicon carbide seed crystal holder by a physical vapor transport method.