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CN114775046B - Silicon carbide epitaxial layer growth method - Google Patents

Silicon carbide epitaxial layer growth method Download PDF

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CN114775046B
CN114775046B CN202210710329.1A CN202210710329A CN114775046B CN 114775046 B CN114775046 B CN 114775046B CN 202210710329 A CN202210710329 A CN 202210710329A CN 114775046 B CN114775046 B CN 114775046B
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buffer layer
silicon carbide
silicon
epitaxial layer
carbon source
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CN114775046A (en
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王蓉
李佳君
皮孝东
李东珂
刘小平
杨德仁
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Hangzhou Jingchi Electromechanical Technology Co ltd
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ZJU Hangzhou Global Scientific and Technological Innovation Center
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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
    • C30B25/00—Single-crystal growth by chemical reaction of reactive gases, e.g. chemical vapour-deposition growth
    • C30B25/02—Epitaxial-layer growth
    • 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
    • C30B25/00—Single-crystal growth by chemical reaction of reactive gases, e.g. chemical vapour-deposition growth
    • C30B25/02—Epitaxial-layer growth
    • C30B25/18—Epitaxial-layer growth characterised by the substrate
    • C30B25/183—Epitaxial-layer growth characterised by the substrate being provided with a buffer layer, e.g. a lattice matching layer
    • 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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Abstract

The invention relates to the technical field of silicon carbide crystal growth, and discloses a silicon carbide epitaxial layer growth method.

Description

Silicon carbide epitaxial layer growth method
Technical Field
The invention relates to the technical field of growth of a silicon carbide epitaxial layer, in particular to a method for growing the silicon carbide epitaxial layer.
Background
The silicon carbide has excellent performance and has great application value in high-voltage and high-power application scenes. However, both device performance and yield are affected by the presence of dislocations.
In the state of the art, most of the basal plane dislocations of the silicon carbide substrate are converted into threading dislocations during the epitaxial formation of the silicon carbide epitaxial layer on the surface of the silicon carbide substrate, but the threading dislocations extend substantially entirely into the epitaxial layer. Therefore, the dislocation density of the epitaxial layer obtained by the conventional epitaxial process is not reduced, and the dislocation density is one of the key technical problems for limiting the performance optimization and the cost control of the silicon carbide device.
Disclosure of Invention
The invention aims to solve the problem of high dislocation density of an epitaxial layer obtained by a conventional epitaxial process, and provides a silicon carbide epitaxial layer growth method.
In order to achieve the above object, the present invention provides a method for growing a silicon carbide epitaxial layer, comprising the steps of:
providing a silicon carbide substrate slice, placing the silicon carbide substrate slice into an epitaxial furnace, introducing carrier gas, heating, setting pressure, introducing a carbon source with a first preset carbon source flow and a silicon source with a first preset silicon source flow, introducing doping gas, and growing a first buffer layer on the surface of the silicon carbide wafer; wherein the ratio of the first predetermined carbon source flow to the carbon-silicon in the first predetermined silicon source flow is in a range of 1:1 to 3:2, the flow range of the first predetermined carbon source is 10 sccm to 20 sccm; the carbon source with the first preset carbon source flow and the silicon source with the first preset silicon source flow enable the growth speed of the first buffer layer to be slow, and the threading dislocation continued from the silicon carbide substrate slice is converted into the stacking fault and the basal plane dislocation in the process of growing the first buffer layer, so that the dislocation is promoted to move transversely and move out of the surface of the first buffer layer;
stopping introducing the carbon source, the silicon source and the doping gas, introducing etching gas, etching the surface of the first buffer layer, removing carbon impurities on the surface of the first buffer layer, and preventing the carbon impurities from becoming a dislocation source;
and then continuously introducing the carbon source and the silicon source with corresponding flow rates, introducing doping gas, and growing on the surface of the first buffer layer after the impurities are removed to obtain the epitaxial layer with corresponding concentration parameters.
As an implementable manner, the steps of continuously introducing the carbon source and the silicon source with corresponding flow rates, introducing the doping gas, and growing on the surface of the first buffer layer after removing the impurities to obtain the epitaxial layer with corresponding concentration parameters specifically comprise;
continuously introducing a carbon source with a second preset carbon source flow rate and a silicon source with a second preset silicon source flow rate, introducing doping gas, and forming a second buffer layer on the surface of the first buffer layer, wherein the carbon source with the second preset carbon source flow rate and the silicon source with the second preset silicon source flow rate enable the growth speed of the second buffer layer to be fast, and in the process of growing the second buffer layer, residual basal plane dislocation continued from the first buffer layer is converted into threading dislocation, so that the dislocation moves longitudinally, and the dislocation extending from the second buffer layer to a subsequently formed epitaxial layer is threading dislocation;
and then continuously introducing the carbon source and the silicon source with corresponding flow rates, introducing doping gas, and growing on the surface of the second buffer layer after the impurities are removed to obtain the epitaxial layer with corresponding concentration parameters.
In one embodiment, the second predetermined carbon source flow rate ranges from: 60sccm to 100sccm, wherein the ratio of the second predetermined carbon source flow to the carbon to silicon in the second predetermined silicon source flow is in a range of 4:5 to 1:1.
as an implementation mode, setting the pressure range to be 30 to 80 Torr when the first buffer layer grows on the surface of the silicon carbide substrate slice; setting the pressure range to be 80 to 120 Torr when growing a second buffer layer on the surface of the first buffer layer; and setting the pressure range to be 80-120 Torr when the epitaxial layer grows on the surface of the second buffer layer.
As an implementation manner, the doping gas introduced during the growth of the first buffer layer has a first predetermined flow rate, and the doping gas with the first predetermined flow rate enables the first buffer layer to be formed to have a corresponding first predetermined doping concentration, and the first predetermined doping concentration is consistent with the doping concentration of the silicon carbide substrate slice, so as to prevent interface dislocation between the silicon carbide substrate slice and the first buffer layer caused by a large difference of the doping concentrations;
the doping gas introduced during the growth of the second buffer layer has a second preset flow rate, and the doping gas with the second preset flow rate enables the formed second buffer layer to have a corresponding second preset doping concentration, wherein the second preset doping concentration is smaller than the first preset doping concentration but larger than the doping concentration of the subsequently formed epitaxial layer, and is used for performing intermediate transition on the doping concentration of the first buffer layer and the doping concentration of the subsequently formed epitaxial layer, so that new defects caused by lattice distortion due to large difference of the doping concentrations are prevented.
As an implementation mode, the thickness range of the first buffer layer is 0.5 to 2.0 micrometers, and the thickness range of the second buffer layer is 0.5 to 2.0 micrometers.
As an embodiment, the threading dislocations include threading dislocations TSD and edge dislocations TED.
As one possible implementation mode, the silicon carbide substrate sheet is an N-type silicon carbide wafer, and the doping concentration range of the silicon carbide substrate sheet is 10 18 ~10 19 cm -3 The total dislocation density of the silicon carbide substrate piece is 10 3 ~10 4 cm -3 。
As one possible embodiment, the doping gas includes a nitrogen-containing gas including nitrogen; the carrier gas is hydrogen; the etching gas is hydrogen.
As an embodiment, the silicon source is one or both of silane and trichlorosilane; the carbon source is one or more of methane, ethylene and propylene.
The invention has the beneficial effects that: the invention provides a silicon carbide epitaxial layer growth method, which comprises the steps of generating a first buffer layer on the surface of a silicon carbide substrate by introducing a carbon source with a first preset carbon source flow rate and a silicon source with a first preset silicon source flow rate, so that through adjustment of the carbon-silicon flow rate ratio and the specific introduced carbon source flow rate, threading dislocations extending out of the silicon carbide substrate are promoted to be converted into faults and basal plane dislocations in the growth process of the first buffer layer, and the first buffer layer of a crystal is moved transversely and removed, thereby reducing the number of the dislocations entering an epitaxial layer from the first buffer layer; and a second buffer layer is generated on the surface of the first buffer layer by introducing a carbon source with a second preset carbon source flow and a silicon source with a second preset silicon source flow, so that the basal plane dislocation extending from the silicon carbide substrate is converted into a through dislocation in the growth process of the second buffer layer by adjusting the carbon-silicon flow ratio and the specific introduced carbon source flow, the dislocation density of the basal plane dislocation is reduced, the influence of the basal plane dislocation on the epitaxial layer is further reduced, the purpose of reducing the dislocation density in the silicon carbide epitaxial layer is finally realized, and the device performance is improved.
Drawings
FIG. 1 is a flow chart of steps of a method for growing a silicon carbide epitaxial layer according to an embodiment of the present invention;
FIG. 2 is a schematic illustration of dislocations in different layers in a silicon carbide epitaxial layer growth process according to an embodiment of the present invention;
fig. 3 is a schematic view showing the process of eliminating dislocation convergence in the method for growing a silicon carbide epitaxial layer according to the embodiment of the present invention.
Detailed Description
The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the drawings in the embodiments of the present invention, and it is obvious that the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.
Referring to fig. 1, the present embodiment provides a technical solution: a silicon carbide epitaxial layer growth method comprises the following steps:
step S100, providing a silicon carbide substrate slice, placing the silicon carbide substrate slice into an epitaxial furnace, introducing carrier gas, heating, setting pressure, introducing a carbon source with a first preset carbon source flow and a silicon source with a first preset silicon source flow, introducing doping gas, and growing a first buffer layer on the surface of the silicon carbide wafer; wherein the ratio of carbon to silicon in the first predetermined carbon source flow and the first predetermined silicon source flow ranges from 1:1 to 3:2, the flow range of the first predetermined carbon source is 10 sccm to 20 sccm; the carbon source with the first preset carbon source flow and the silicon source with the first preset silicon source flow enable the growth speed of the first buffer layer to be slow, and the threading dislocation continued from the silicon carbide substrate slice is converted into the stacking fault and the basal plane dislocation in the process of growing the first buffer layer, so that the dislocation is promoted to move transversely and move out of the surface of the first buffer layer;
step S200, stopping introducing the carbon source, the silicon source and the doping gas, introducing etching gas, etching the surface of the first buffer layer, removing carbon impurities on the surface of the first buffer layer, and preventing the carbon impurities from becoming dislocation sources;
and step S300, continuously introducing the carbon source and the silicon source with corresponding flow rates, introducing doping gas, and growing on the surface of the first buffer layer after the impurities are removed to obtain the epitaxial layer with corresponding concentration parameters.
Step S100 and step S200 are performed, in this embodiment, the silicon carbide substrate slice is an N-type silicon carbide wafer, and the doping concentration of the silicon carbide substrate slice is in the range of 10 18 ~10 19 cm -3 The total dislocation density of the silicon carbide substrate piece is 10 3 ~10 4 cm -3 In other embodiments, however, a different silicon carbide substrate piece may actually be selected.
The dopant gas includes nitrogen-containing gas and the like, and the nitrogen-containing gas includes nitrogen and the like; the carrier gas is high-purity hydrogen; the etching gas is hydrogen; the silicon source can be one or two of silane and trichlorosilane, or other specific materials which can be used as the silicon source; the carbon source is one or more of methane, ethylene, propylene and propylene, or other specific materials which can be used as the carbon source.
In this embodiment, the range of the first predetermined carbon source flow rate is: 10 sccm-20 sccm, and the ratio of the carbon to the silicon in the first predetermined carbon source flow and the first predetermined silicon source flow ranges from 3:1 to 1:2; the first preset silicon source flow of the introduced silicon source is adjusted through the fused first preset carbon source flow and the carbon-silicon ratio; specifically, in the present embodiment, the speed of growing the first buffer layer is slowed by introducing a lower carbon source flow; in the embodiment, by setting a high carbon-silicon flow ratio, that is, increasing the carbon-silicon ratio of the first predetermined carbon source flow to the first predetermined silicon source flow, that is, the carbon ratio is greater than the silicon ratio, the proportion of carbon in the generated first buffer layer is increased, so that threading dislocations continuing from the silicon carbide substrate sheet can be converted into stacking faults and basal plane dislocations during the growth of the first buffer layer, and the lateral movement of the stacking faults and dislocations is promoted under the slow growth of the first buffer layer, so that the stacking faults and dislocations can move out of the crystal under the lateral movement, and cannot rise into the epitaxial layer on the surface of the first buffer layer again without rising to the surface of the first buffer layer, thereby reducing the dislocation density in the epitaxial layer. Wherein, the stacking fault and the basal plane dislocation are grown transversely according to the growth direction of the step flow, and the threading dislocation is the dislocation which can grow longitudinally; the threading dislocations include threading dislocations TSD and edge dislocations TED.
Specifically, the speed of growing the first buffer layer is slowed, that is, the process of growing the first buffer layer is a low-speed step flow growth mode, in the growth mode, the size of the grown step is increased, so that the threading dislocation continued from the silicon carbide substrate sheet is promoted to move transversely in the process of growing the first buffer layer, and is converted into a transversely moving lamination fault and a basal plane dislocation, the transverse movement of the dislocation on the surface of the step is strengthened, so that part of the initial threading dislocation is promoted to move to the side surface of the crystal, and the other part of the initial threading dislocation is decomposed to form the lamination fault, so that the threading dislocation directly moves at an increased speed in the transverse growth direction of the lamination fault, and the threading dislocation can be promoted to escape from the crystal; and basal plane dislocations continued from the silicon carbide substrate slice can further move transversely along with the slow growth, so that the basal plane dislocations are moved out of the surface of the first buffer layer and do not extend to the surface of the first buffer layer.
Meanwhile, partial dislocations with opposite Bernoulli vectors can be converged and disappear, for example: the threading dislocation TSD is a screw dislocation, a left-handed threading dislocation TSD and a right-handed threading dislocation TSD are collided together and offset, and therefore convergence disappears, while the edge dislocation TED is a half-layer atom, and an edge dislocation TED in a left half-layer and an edge dislocation TED in a right half-layer are collided together and disappear; as shown in fig. 3, the solid black lines in the figure represent the movement of dislocation lines on the surface of the first buffer layer, the arrows represent the direction of the bernoulli vectors, the black dots represent the vertical direction to the surface, the hollow dots represent the convergence positions, as the epitaxial thickness of the first buffer layer increases, a part of the threading dislocations extend to the side of the crystal and escape, a part of the threading dislocations opposite to the bernoulli vectors approach each other and finally converge to each other and disappear, a part of the threading dislocations do not escape or converge, and the dislocation lines as residues may also move laterally in the direction of step flow in the first buffer layer without moving out of the first buffer layer.
In the embodiment, the heating temperature range in the process is 1500-1700 ℃; the pressure in the whole process can be set to be constant, but if the growth speed of the first buffer layer is further reduced; the pressure when the first buffer layer grows on the surface of the silicon carbide substrate slice can be set to be low pressure in a range of 30 to 80 Torr.
It should be noted that, because the ratio of the carbon source flow is high during the growth of the first buffer layer, carbon impurities may be generated on the surface of the first buffer layer, and if an epitaxial layer is grown on the surface of the first buffer layer without being removed, the carbon impurities may become dislocation sources of the epitaxial layer, and a new dislocation line is formed in the epitaxial layer, so that in order to reduce the influence of the impurities, the embodiment of the present invention further reduces the influence of dislocations on the epitaxial layer by etching the surface of the first buffer layer. Meanwhile, because the thickness of the first buffer layer is smaller, carbon impurities are mainly formed on the surface of the first buffer layer and are not formed in the first buffer layer, so that the carbon impurities on the surface of the first buffer layer are removed through an etching process, and dislocation sources of the epitaxial layer can be effectively reduced.
Step 300 is executed, a carbon source with a corresponding flow rate and a silicon source with a corresponding flow rate are introduced to perform epitaxial layer growth, the epitaxial layer with a target concentration parameter required to be obtained actually is determined, the growth thickness of the epitaxial layer is also directly determined according to the target thickness of the epitaxial layer required actually, the embodiment is not limited, for example, the flow rate of the carbon source can be 40 sccm to 80sccm, the carbon-silicon ratio in the flow rate of the carbon source and the flow rate of the silicon source can be set to 0.8 to 1, and the flow rate of the silicon source is adjusted through the flow rate of the carbon source and the carbon-silicon ratio.
In this embodiment, in order to further reduce the influence of the dislocation remaining on the surface of the first buffer layer on the epitaxial layer, in this embodiment, the carbon source and the silicon source with corresponding flows are continuously introduced, the doping gas is introduced, and the step of growing the epitaxial layer with corresponding concentration parameters on the surface of the first buffer layer after the impurities are removed specifically includes;
continuously introducing a carbon source with a second preset carbon source flow rate and a silicon source with a second preset silicon source flow rate, introducing doping gas, and forming a second buffer layer on the surface of the first buffer layer, wherein the carbon source with the second preset carbon source flow rate and the silicon source with the second preset silicon source flow rate enable the growth speed of the second buffer layer to be fast, and in the process of growing the second buffer layer, residual basal plane dislocations which are continued from the first buffer layer are converted into threading dislocations, so that the dislocations are promoted to move longitudinally, and the dislocations which extend from the second buffer layer to a subsequently formed epitaxial layer are threading dislocations;
and then continuously introducing the carbon source and the silicon source with corresponding flow rates, introducing doping gas, and growing on the surface of the second buffer layer after the impurities are removed to obtain the epitaxial layer with corresponding concentration parameters.
It should be noted that, in this embodiment, after the second buffer layer is generated, the surface of the second buffer layer is not etched, because the ratio of the first predetermined carbon source flow introduced into the second buffer layer to the carbon-silicon ratio in the first predetermined silicon source flow is not higher than that of the medium carbon source, carbon impurities are not formed on the surface of the second buffer layer, and an epitaxial layer may be directly grown without performing additional etching.
In this embodiment, the range of the second predetermined carbon source flow rate is: 60sccm to 100sccm, wherein the ratio of the second predetermined carbon source flow to the carbon to silicon in the second predetermined silicon source flow is in a range of 4:5 to 1:1; the flow rate of the introduced second predetermined silicon source is adjusted through the flow rate of the second predetermined carbon source of the introduced carbon source and the carbon-silicon ratio; specifically, in this embodiment, a higher carbon source flow is introduced, so that the growth speed of the second buffer layer is increased, and in addition, a low carbon source flow ratio is set, that is, the carbon content ratio of the second buffer layer is reduced compared to the carbon content ratio of the first buffer layer, so that residual basal plane dislocations continuing from the surface of the first buffer layer are converted into threading dislocations in the second buffer layer during the growth of the first buffer layer, so that the threading dislocations are accelerated to move longitudinally on the premise that the growth speed of the second buffer layer is increased, and finally the dislocations moving into the epitaxial layer are made to be threading dislocations, thereby reducing the influence of the basal plane dislocations on the epitaxial layer.
The purpose of converting residual basal plane dislocations extending from the first buffer layer into threading dislocations in the process of growing the second buffer layer, so that the dislocations extending from the second buffer layer into the epitaxial layer formed subsequently are threading dislocations, is that in the process of growing the first buffer layer, because some dislocations may exist or cannot move out, and the threading dislocations have smaller influence on the quality of the epitaxial layer than the basal plane dislocations, the influence of the dislocations on the epitaxial layer is further reduced, and the influence of the dislocations is reduced as a whole, so that the basal plane dislocations extending from the first buffer layer are converted into the threading dislocations again by arranging the second buffer layer; in other embodiments, however, the second buffer layer may be further designed to promote lateral movement of the basal plane dislocations, thereby promoting movement of the dislocations away from the surface of the second buffer layer, further reducing the number and density of dislocations in the epitaxial layer.
As shown in fig. 2, a first buffer layer 20 is grown on the surface of the silicon carbide substrate piece 10, a second buffer layer 30 is grown on the surface of the first buffer layer 20, and an epitaxial layer 40 is grown on the surface of the second buffer layer, wherein the solid lines shown in the figure can be regarded as dislocation lines, and the direction shown by the arrows is the direction of step flow, it can be seen that a plurality of dislocation lines exist in the silicon carbide substrate piece 10, and these dislocation lines directly extend into the generated first buffer layer 20, and since the present embodiment makes the growth speed of the first buffer layer 20 slow by adjusting the ratio of the flow rate of the introduced carbon to the silicon flow rate and the flow rate of the specifically introduced carbon source during the growth of the first buffer layer 20, and the threading dislocations in the silicon carbide substrate piece 10 are converted into basal plane dislocations moving laterally in the first buffer layer 20, and wherein the part of dislocation lines extend out of the right side of the first buffer layer 20 along with the growth of the first buffer layer 20, the number of dislocation lines that can extend to the surface of the first buffer layer 20 is reduced, and the second buffer layer 30 on the surface of the first buffer layer 20 can be adjusted by adjusting the flow rate of the carbon atoms introduced to the second buffer layer 30 and the flow rate of the second buffer layer 30 during the growth of the second buffer layer.
Further, the pressure range when the second buffer layer grows on the surface of the first buffer layer can be set to be 80 to 120 Torr, so that the speed of growing the second buffer layer is further increased; the pressure range when the epitaxial layer grows on the surface of the second buffer layer can be set to be 80-120 Torr, and the pressure range is used for improving the speed of growing the epitaxial layer.
Further, the doping gas introduced during the growth of the first buffer layer has a first predetermined flow rate, and the doping gas with the first predetermined flow rate enables the first buffer layer to be formed to have a corresponding first predetermined doping concentration, and the first predetermined doping concentration is consistent with the doping concentration of the silicon carbide substrate slice, so that interface dislocation caused by a large difference of the doping concentrations between the silicon carbide substrate slice and the first buffer layer is prevented;
the doping gas introduced during the growth of the second buffer layer has a second preset flow rate, and the doping gas with the second preset flow rate enables the formed second buffer layer to have a corresponding second preset doping concentration, wherein the second preset doping concentration is smaller than the first preset doping concentration but larger than the doping concentration of the subsequently formed epitaxial layer, and is used for performing intermediate transition on the doping concentration of the first buffer layer and the doping concentration of the subsequently formed epitaxial layer, so that new defects caused by lattice distortion due to large difference of the doping concentrations are prevented.
For example: when the doping concentration range of the silicon carbide substrate slice is 10 18 ~10 19 cm -3 And the doping concentration of the epitaxial layer to be grown is 10 15 cm -3 In this case, the doping concentration of the first buffer layer may be adjusted to 10 by adjusting the flow rate of the doping gas 18 cm -3 So that the doping concentration of the second buffer layer is reduced to 10 16 cm -3 Thereby enabling both the first buffer layer and the second buffer layer to function accordingly.
Specifically, as an example, first, a silicon carbide substrate sheet is provided, and the silicon carbide substrate sheet is cleaned, wherein, as the silicon carbide substrate sheet, a 4 ° obliquely cut N-type silicon carbide wafer may be selected with a doping concentration of 10 18 ~10 19 cm -3 Total dislocation density 10 3 ~10 4 cm -3 Cleaning based on standard RCA; after cleaning, sending the silicon carbide substrate into an epitaxial furnace, introducing high-purity hydrogen, and raising the temperature to 1600 ℃; adjusting the pressure of the reaction chamber to 40 Torr, adding trichlorosilane as a silicon source and propylene as a carbon source, wherein the flow of the propylene is 20 sccm, and adjusting the flow of the trichlorosilane to ensure that the flow ratio of the carbon to the silicon is 1:2, obtaining a low-speed step flow growth mode, adjusting the flow of high-purity nitrogen to ensure that the doping concentration is 10 18 cm -3 (ii) a Obtaining a first buffer layer with the thickness of 1.0 micron; in this mode, the epitaxial step size is increased, the lateral movement of the threading dislocations on the step surface is strengthened, and a part of the threading dislocations is promoted to move to the side of the crystal, and another part of the threading dislocations are decomposed into faults, so that the lateral growth speed is increased, and the threading dislocations can be promoted to escape from the crystal. Meanwhile, the dislocations with opposite Bernoulli vectors are close to each other, and finally converge and disappear. The high doping concentration can reduce lattice mismatch between the epitaxial layer and the substrate and avoid the generation of new interface dislocation.
Adjusting the pressure of the reaction chamber to be 100 Torr, the flow of propylene to be 60sccm, and adjusting the flow of trichlorosilane to ensure that the carbon-silicon ratio is 1:2, adjusting the flow rate of high-purity nitrogen gas to make the doping concentration of the second buffer layer 10 5 -10 6 cm -3 And growing to a thickness of 1.0 micrometer to obtain the buffer layer B, wherein the growth environment promotes the transition of basal plane dislocation to threading dislocation.
The pressure was maintained at 100 Torr, the flow rate of propylene was maintained at 60sccm, the flow rate of trichlorosilane was adjusted to reduce the carbon-silicon ratio to 0.9, and an epitaxial layer having a target thickness was grown to obtain an epitaxial thin film having a low dislocation density.
The invention provides a silicon carbide epitaxial layer growth method, which comprises the steps of generating a first buffer layer on the surface of a silicon carbide substrate sheet by introducing a carbon source with a first preset carbon source flow rate and a silicon source with a first preset silicon source flow rate, so that through adjustment of the carbon-silicon flow rate ratio and the specific introduced carbon source flow rate, threading dislocations extending from the silicon carbide substrate sheet are promoted to be converted into basal plane dislocations in the growth process of the first buffer layer, and the transverse movement is carried out to remove the first buffer layer of a crystal, so that the number of dislocations entering an epitaxial layer from the first buffer layer is reduced; and a second buffer layer is generated on the surface of the first buffer layer by introducing a carbon source with a first preset carbon source flow and a silicon source with a first preset silicon source flow, so that the basal plane dislocation extending from the silicon carbide substrate is converted into the threading dislocation in the growth process of the first buffer layer by adjusting the carbon-silicon flow ratio and the specific introduced carbon source flow, the dislocation density of the basal plane dislocation is reduced, the influence of the basal plane dislocation on the epitaxial layer is further reduced, the purpose of reducing the dislocation density in the silicon carbide epitaxial layer is finally realized, and the device performance is improved.
Although the present invention has been described with reference to the preferred embodiments, it is not intended to limit the present invention, and those skilled in the art can make variations and modifications of the present invention without departing from the spirit and scope of the present invention by using the methods and technical contents disclosed above.

Claims (10)

1. A method for growing a silicon carbide epitaxial layer is characterized by comprising the following steps:
providing a silicon carbide substrate slice, placing the silicon carbide substrate slice into an epitaxial furnace, introducing carrier gas, heating, setting the pressure range to be 30-80 Torr, introducing a carbon source with a first preset carbon source flow and a silicon source with a first preset silicon source flow, introducing doping gas, and growing a first buffer layer on the surface of the silicon carbide substrate slice; wherein the ratio of carbon to silicon in the first predetermined carbon source flow and the first predetermined silicon source flow ranges from 1:1 to 3:2, the flow range of the first predetermined carbon source is 10 sccm to 20 sccm; slowing down the growth speed of the first buffer layer, and converting the threading dislocation continuous from the silicon carbide substrate slice into a layer dislocation and a basal plane dislocation in the process of growing the first buffer layer, so as to promote the dislocation to move transversely and move out of the surface of the first buffer layer;
stopping introducing the carbon source, the silicon source and the doping gas, introducing etching gas, etching the surface of the first buffer layer, removing carbon impurities on the surface of the first buffer layer, and preventing the carbon impurities from becoming a dislocation source;
and then continuously introducing the carbon source and the silicon source with corresponding flow rates, introducing doping gas, and growing on the surface of the first buffer layer after the impurities are removed to obtain the epitaxial layer with corresponding concentration parameters.
2. The method for growing the silicon carbide epitaxial layer according to claim 1, wherein the step of continuing to introduce the carbon source and the silicon source at corresponding flow rates and introducing the doping gas to grow the epitaxial layer with the corresponding concentration parameter on the surface of the first buffer layer after the impurities are removed specifically comprises;
continuously introducing a carbon source with a second preset carbon source flow rate and a silicon source with a second preset silicon source flow rate, introducing doping gas, and forming a second buffer layer on the surface of the first buffer layer, wherein the carbon source with the second preset carbon source flow rate and the silicon source with the second preset silicon source flow rate enable the growth speed of the second buffer layer to be fast, and in the process of growing the second buffer layer, residual basal plane dislocations which are continued from the first buffer layer are converted into threading dislocations, so that the dislocations are promoted to move longitudinally, and the dislocations which extend from the second buffer layer to a subsequently formed epitaxial layer are threading dislocations;
and then continuously introducing the carbon source and the silicon source with corresponding flow rates, introducing doping gas, and growing on the surface of the second buffer layer after the impurities are removed to obtain the epitaxial layer with corresponding concentration parameters.
3. The method for growing the silicon carbide epitaxial layer according to claim 2, wherein the second predetermined carbon source flow rate ranges from 60sccm to 100sccm, and the ratio of the second predetermined carbon source flow rate to the carbon to silicon in the second predetermined silicon source flow rate ranges from 4:5 to 1:1.
4. the growth method of the silicon carbide epitaxial layer according to claim 2, wherein the pressure is set to be 80 to 120 Torr when the second buffer layer is grown on the surface of the first buffer layer; and setting the pressure range to be 80-120 Torr when the epitaxial layer grows on the surface of the second buffer layer.
5. The silicon carbide epitaxial layer growth method of claim 2, wherein the doping gas is introduced at a first predetermined flow rate during the growth of the first buffer layer, and the doping gas with the first predetermined flow rate enables the first buffer layer to be formed with a corresponding first predetermined doping concentration, and the first predetermined doping concentration is consistent with the doping concentration of the silicon carbide substrate slice, so as to prevent interface dislocation between the silicon carbide substrate slice and the first buffer layer caused by a large difference of the doping concentrations;
the doping gas introduced during the growth of the second buffer layer has a second preset flow rate, and the doping gas with the second preset flow rate enables the formed second buffer layer to have a corresponding second preset doping concentration, wherein the second preset doping concentration is smaller than the first preset doping concentration but larger than the doping concentration of the subsequently formed epitaxial layer, and is used for performing intermediate transition on the doping concentration of the first buffer layer and the doping concentration of the subsequently formed epitaxial layer, so that new defects caused by lattice distortion due to large difference of the doping concentrations are prevented.
6. The growth method of the silicon carbide epitaxial layer as claimed in claim 2, wherein the thickness of the first buffer layer ranges from 0.5 to 2.0 micrometers, and the thickness of the second buffer layer ranges from 0.5 to 2.0 micrometers.
7. The silicon carbide epitaxial layer growth method of claim 1, wherein the threading dislocations comprise threading dislocations TSD and edge dislocations TED.
8. The method of claim 1, wherein the silicon carbide substrate wafer is an N-type silicon carbide wafer and the silicon carbide substrate wafer has a doping concentration in the range of 10 18 ~10 19 cm -3 The total dislocation density of the silicon carbide substrate piece is 10 3 ~10 4 cm -3 。
9. The method of growing a silicon carbide epitaxial layer according to claim 1, wherein the dopant gas comprises a nitrogen-containing gas comprising nitrogen; the carrier gas is hydrogen; the etching gas is hydrogen.
10. The method for growing a silicon carbide epitaxial layer according to claim 1, wherein the silicon source is one or both of silane and trichlorosilane; the carbon source is one or more of methane, ethylene and propylene.
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