CN116623293B - Composite silicon carbide substrate and preparation method and application thereof - Google Patents

Composite silicon carbide substrate and preparation method and application thereof Download PDF

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CN116623293B
CN116623293B CN202310913101.7A CN202310913101A CN116623293B CN 116623293 B CN116623293 B CN 116623293B CN 202310913101 A CN202310913101 A CN 202310913101A CN 116623293 B CN116623293 B CN 116623293B
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silicon carbide
layer
monocrystalline silicon
bonding
layers
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CN116623293A (en
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郭超
黄秀松
母凤文
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Jc Innovative Semiconductor Substrate Technology Co ltd
Beijing Qinghe Jingyuan Semiconductor Technology Co ltd
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Jc Innovative Semiconductor Substrate Technology Co ltd
Beijing Qinghe Jingyuan Semiconductor Technology Co ltd
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Abstract

The invention provides a composite silicon carbide substrate and a preparation method and application thereof, belonging to the technical field of semiconductors, wherein the preparation method comprises the following steps: preparing monocrystalline silicon carbide thin layers on two sides of the surface of the middle sacrificial layer, respectively marking as a first monocrystalline silicon carbide thin layer and a second monocrystalline silicon carbide thin layer, and respectively bonding and connecting the first monocrystalline silicon carbide thin layer and the second monocrystalline silicon carbide thin layer with the middle sacrificial layer to obtain a bonding assembly; growing polycrystalline silicon carbide layers on two sides of the surface of the bonding assembly, wherein the polycrystalline silicon carbide layers contain free C phases; and removing the middle sacrificial layer in the bonding assembly to obtain two composite silicon carbide substrates. The preparation method can avoid the joint interface between the polycrystalline silicon carbide layer and the monocrystalline silicon carbide layer, and has high success rate and low cost. The composite silicon carbide substrate prepared based on the method has lower resistivity, the combination between the polycrystalline silicon carbide layer and the monocrystalline silicon carbide thin layer is tight and firm, and the industrial production can be realized.

Description

Composite silicon carbide substrate and preparation method and application thereof
Technical Field
The invention belongs to the technical field of semiconductors, and particularly relates to a composite silicon carbide substrate, and a preparation method and application thereof.
Background
The silicon carbide substrate is mainly applied to conductive substrates in the power fields of new energy automobiles, photovoltaics, industrial control, rail transit and the like, various power devices are manufactured on an epitaxial layer, or semi-insulating substrates in the radio frequency fields of 5G communication, national defense and the like are mainly used for manufacturing gallium nitride radio frequency devices.
The preparation of the silicon carbide substrate material mainly comprises links of raw material synthesis, silicon carbide crystal growth, ingot processing, crystal bar cutting, cutting piece grinding, grinding piece polishing, polishing piece cleaning and the like, wherein the preparation difficulty mainly comprises links of crystal growth, cutting, grinding and polishing, and is a bottleneck for limiting the yield and the productivity of the silicon carbide. In the crystal growth step, a physical vapor transport method (PVT) is generally used, the basic principle is that silicon carbide powder is heated to more than 2000 ℃, vapor phase components are transported under the action of concentration gradient after high-temperature sublimation, and finally the silicon carbide seed crystal is recrystallized on the surface of the silicon carbide seed crystal with lower temperature, so that the crystal growth is promoted. However, this method is costly and limits the large-scale application of silicon carbide substrates.
One way to reduce the cost of silicon carbide substrates is to bond a high quality single crystal silicon carbide layer to a low quality single crystal/polycrystalline silicon carbide substrate to form a composite silicon carbide substrate. Wherein bonding is generally performed by bonding. However, there is a certain probability of the bonding interface having the following problems: firstly, amorphous exists at the joint interface, so that the composite substrate cannot manufacture high-quality devices; and secondly, the joint interface can generate extra resistance, so that the overall resistivity of the composite substrate is increased.
Therefore, how to solve the adverse effect of the bonding interface in the current composite substrate is a technical problem to be solved.
Disclosure of Invention
Aiming at the defects of the prior art, the invention aims to provide a composite silicon carbide substrate and a preparation method and application thereof. The preparation method provided by the invention avoids the joint interface between the polycrystalline silicon carbide layer and the monocrystalline silicon carbide thin layer, and has high success rate and low cost. The composite silicon carbide substrate prepared based on the preparation method has lower resistivity, and the polycrystalline silicon carbide layer and the monocrystalline silicon carbide thin layer are tightly and firmly combined, so that industrial production can be realized.
In order to achieve the aim of the invention, the invention adopts the following technical scheme:
in a first aspect, the present invention provides a method for preparing a composite silicon carbide substrate, the method comprising the steps of:
(1) Preparing monocrystalline silicon carbide thin layers on two sides of the surface of the middle sacrificial layer, respectively marking as a first monocrystalline silicon carbide thin layer and a second monocrystalline silicon carbide thin layer, and respectively bonding and connecting the first monocrystalline silicon carbide thin layer and the second monocrystalline silicon carbide thin layer with the middle sacrificial layer to obtain a bonding assembly;
(2) Growing polycrystalline silicon carbide layers on two sides of the surface of the bonding assembly, wherein the polycrystalline silicon carbide layers contain free C phases;
(3) And removing the middle sacrificial layer in the bonding assembly to obtain two composite silicon carbide substrates.
The invention directly grows the polycrystalline silicon carbide layer on the surface of the monocrystalline silicon carbide thin layer, and a joint interface does not exist between the polycrystalline silicon carbide layer and the monocrystalline silicon carbide thin layer, so that the success rate is high and the cost is low. The composite silicon carbide substrate prepared based on the preparation method has lower resistivity, and the polycrystalline silicon carbide layer and the monocrystalline silicon carbide thin layer are tightly and firmly combined, so that industrial production can be realized.
As a preferred embodiment of the present invention, the material of the intermediate sacrificial layer in the step (1) includes any one or a combination of at least two of carbon, silicon oxide, silicon nitride and metal silicide.
In the invention, the material of the intermediate sacrificial layer is a substance which is easy to corrode, so that the intermediate sacrificial layer is convenient to remove in the later period.
Preferably, the thickness of the intermediate sacrificial layer in step (1) is 100-10000 μm, for example, 100 μm, 1000 μm, 3000 μm, 5000 μm, 7000 μm, 8000 μm or 10000 μm, etc., preferably 300-5000 μm.
Preferably, the thickness of the first and second thin layers of single crystal silicon carbide of step (1) is independently 0.1-10 μm, for example, 0.1 μm, 0.5 μm, 1 μm, 2 μm, 4 μm, 6 μm, 8 μm or 10 μm, etc.
As a preferred technical scheme of the present invention, the specific preparation method of the bonding assembly in the step (1) includes a first mode or a second mode, and the first mode includes the following steps:
(a1) Implanting ions into one surface of the monocrystalline silicon carbide layer to form a pre-buried weakening layer;
(b1) Bonding and connecting the ion implantation surface of the monocrystalline silicon carbide layer and one surface of the middle sacrificial layer;
(c1) Applying stress to fracture the monocrystalline silicon carbide layer along the weakened layer to obtain a layer to be recovered and an intermediate sacrificial layer bonded with a first monocrystalline silicon carbide thin layer;
(d1) Repeating steps (a 1) - (c 1), bonding a second monocrystalline silicon carbide thin layer on the other side of the intermediate sacrificial layer to obtain the bonding assembly;
the second mode comprises the following steps:
(a2) Respectively implanting ions into one surface of the first monocrystalline silicon carbide layer and one surface of the second monocrystalline silicon carbide layer to form 2 pre-buried weakening layers;
(b2) Bonding and connecting the first monocrystalline silicon carbide layer, the second monocrystalline silicon carbide layer and the middle sacrificial layer to obtain a sandwich structure;
(c2) And applying stress to fracture the sandwich structure along 2 weakened layers to obtain the bonding assembly.
In the invention, the bonding assembly is prepared in the first mode, the weakening layer is required to be broken twice before and after, the working procedures are more, but the operation difficulty is low, and the yield is higher; the bonding assembly is prepared in the second mode, only the weakening layer is required to be broken once, the working procedure is smaller, the operation difficulty is high, and the yield is lower. One or two modes can be selected according to the actual conditions of production and manufacture.
In the invention, the layer to be recovered obtained in the step (c 1) and the layer to be recovered obtained after the step (c 2) is broken can be recycled, so that the cost is reduced.
Preferably, the ions of step (a 1) and the ions of step (a 2) independently comprise hydrogen ions and/or helium ions.
Preferably, the ion implantation depth of step (a 1) and the ion implantation depth of step (a 2) are independently 0.15-10 μm, and may be, for example, 0.15 μm, 0.5 μm, 1 μm, 3 μm, 5 μm, 7 μm or 10 μm.
Preferably, the stressing of step (c 1) and the stressing of step (c 2) independently comprises a heat treatment and/or a mechanical separation.
The parameters of the heat treatment are not particularly limited in the present invention, and may be exemplified by heat treatment at a temperature of 900 to 1100 c for 0.5 to 2 hours, for example.
As a preferred technical scheme of the present invention, the intermediate sacrificial layer in step (1) includes an intermediate substrate and sacrificial layers located on two sides of the intermediate substrate, the sacrificial layers are respectively bonded and connected with the first monocrystalline silicon carbide thin layer and the second monocrystalline silicon carbide thin layer, and the specific step is performed in a third mode or a fourth mode, and the third mode includes the following steps:
(a3) Implanting ions into one surface of the monocrystalline silicon carbide layer to form a pre-buried weakening layer;
(b3) Growing a sacrificial layer on one surface of an intermediate substrate, and then bonding and connecting the ion implantation surface of the monocrystalline silicon carbide layer and the surface of the sacrificial layer;
(c3) Applying stress to fracture the single crystal silicon carbide layer along the weakened layer to obtain a component of a layer to be recovered and a first single crystal silicon carbide thin layer bonded;
(d3) Repeating the steps (a 3) - (c 3), and bonding a second monocrystalline silicon carbide thin layer on the surface of the sacrificial layer grown on the other surface of the intermediate substrate to obtain the bonding assembly;
the fourth mode comprises the following steps:
(a4) Respectively implanting ions into one surface of the first monocrystalline silicon carbide layer and one surface of the second monocrystalline silicon carbide layer to form 2 pre-buried weakening layers;
(b4) Respectively growing sacrificial layers on two sides of the intermediate substrate, and then respectively bonding and connecting the ion implantation surface of the first monocrystalline silicon carbide layer and the ion implantation surface of the second monocrystalline silicon carbide layer with the sacrificial layers on two sides of the intermediate substrate to obtain a sandwich structure;
(c4) And applying stress to fracture the sandwich structure along 2 weakened layers to obtain the bonding assembly.
In the invention, the bonding assembly is prepared in the third mode or the fourth mode, the sacrificial layer can be corroded in a chemical method later, and the intermediate substrate can be corroded together or not so as to be reused.
Preferably, the ions of step (a 3) and the ions of step (a 4) independently comprise hydrogen ions and/or helium ions.
Preferably, the ion implantation depth of step (a 3) and the ion implantation depth of step (a 4) are independently 0.15-10 μm, for example, may be 0.15 μm, 0.5 μm, 1 μm, 3 μm, 5 μm, 7 μm or 10 μm.
Preferably, the stressing of step (c 3) and the stressing of step (c 4) independently comprises heat treatment and/or mechanical separation.
The parameters of the heat treatment are not particularly limited in the present invention, and may be exemplified by heat treatment at a temperature of 900 to 1100 c for 0.5 to 2 hours, for example.
Preferably, the material of the intermediate substrate includes any one or a combination of at least two of silicon carbide, silicon or carbon.
Preferably, the thickness of the intermediate substrate is 100 to 10000 μm, for example, 100 μm, 1000 μm, 3000 μm, 5000 μm, 7000 μm, 8000 μm or 10000 μm, etc., preferably 300 to 5000 μm.
Preferably, the material of the sacrificial layer includes any one or a combination of at least two of carbon, silicon oxide, silicon nitride or metal silicide.
Preferably, the thickness of the sacrificial layer is 0.1-10 μm, and may be, for example, 0.1 μm, 0.5 μm, 1 μm, 2 μm, 4 μm, 6 μm, 8 μm, 10 μm, or the like.
As a preferable technical scheme of the invention, the polycrystalline silicon carbide layer in the step (2) is doped with N element.
Preferably, the doping concentration of N element in the polycrystalline silicon carbide layer is 1×10 18 -1×10 21 /cm 3 For example, it may be 1X 10 18 /cm 3 、5×10 18 /cm 3 、1×10 19 /cm 3 、5×10 19 /cm 3 、1×10 20 /cm 3 、5×10 20 /cm 3 Or 1X 10 21 /cm 3 Etc.
Preferably, the raw material doped with N element includes nitrogen and/or ammonia, preferably nitrogen.
Preferably, the nitrogen-silicon atomic ratio of the N-doped material to the polycrystalline silicon carbide layer-grown material is (0.7-1): 1, and may be, for example, 0.7, 0.75, 0.8, 0.85, 0.9, 0.95, or 1, and preferably (0.85-1): 1.
As a preferred technical solution of the present invention, the polycrystalline silicon carbide layer in the step (2) is grown in a fifth mode or a sixth mode, and the specific steps of the fifth mode include:
depositing polycrystalline silicon carbide layers on two sides of the surface of the bonding assembly, wherein the polycrystalline silicon carbide layers contain free C phases which are uniformly distributed;
the specific steps of the sixth mode include:
and firstly growing a transition layer and a homogeneous layer on two sides of the surface of the bonding assembly to obtain the polycrystalline silicon carbide layer.
In the invention, the mode five is adopted to directly grow the polycrystalline silicon carbide layer with evenly distributed free C phase, the process is simple, but the bonding strength between the monocrystalline silicon carbide thin layer and the polycrystalline silicon carbide layer is lower; and a transition layer is grown in a sixth mode, free C phase in the transition layer gradually increases along the direction close to the homogeneous layer, the process is more complex, and the bonding quality between the monocrystalline silicon carbide layer and the polycrystalline silicon carbide layer is better.
Preferably, the method for growing the polycrystalline silicon carbide layer comprises a chemical vapor deposition method.
Preferably, the raw material for growing the polycrystalline silicon carbide layer comprises a compound containing both a silicon element and a carbon element, or a compound comprising a combination of a silicon source and a carbon source.
Preferably, the compound containing both the silicon element and the carbon element includes trichloromethylsilane and/or methylsilane.
Preferably, the silicon source comprises a gaseous silicon source or a liquid silicon source.
Preferably, the liquid silicon source comprises silicon tetrachloride and/or trichlorosilane.
It should be noted that silicon tetrachloride and trichlorosilane are liquid at normal temperature and normal pressure, so that the silicon tetrachloride and trichlorosilane need to be transported by carrier gas in the vapor deposition process, specifically: by adopting a carrier gas bubbling method, silicon tetrachloride or trichlorosilane which is in a liquid state at normal temperature is converted into steam and is transported along with carrier gas.
The kind of carrier gas is not particularly limited in the present invention, and may be exemplified by hydrogen gas.
Preferably, the gaseous silicon source comprises dichlorosilane.
Preferably, the raw material for growing the polycrystalline silicon carbide layer further comprises a dilution gas, wherein the dilution gas comprises hydrogen and/or argon, preferably hydrogen.
Preferably, the carbon source comprises any one or a combination of at least two of methane, ethylene or propane, preferably ethylene.
Preferably, the thickness of the transition layer is 0.05-60 μm, for example, 0.05 μm, 0.1 μm, 1 μm, 5 μm, 10 μm, 20 μm, 30 μm, 40 μm, 50 μm or 60 μm, etc., preferably 0.5-30 μm.
In the invention, if the thickness of the transition layer is too small, the manufacturing difficulty is high, and the uneven thickness of the local part of the transition layer can lead to the direct combination of free C phase and monocrystalline silicon carbide thin layer, thereby affecting the combination quality of the polycrystalline layer and the monocrystalline silicon carbide thin layer; if the thickness of the transition layer is too large, the resistivity of the transition layer is high, and the proportion of the transition layer to the total thickness of the composite silicon carbide substrate is too large, so that the overall resistivity of the composite substrate can be increased.
In the fifth aspect of the present invention, the atomic ratio of the hydrogen element in the diluent gas to the silicon element in the silicon source, or the atomic ratio of the argon element in the diluent gas to the silicon element in the silicon source is independently (3-10): 1, and for example, may be 3:1, 4:1, 5:1, 6:1, 7:1, 8:1, 9:1, or 10:1, etc., preferably (6-10): 1.
Preferably, in the fifth mode, the carbon-silicon atomic ratio of the carbon source to the silicon source is (2.5-5): 1, for example, it may be 2.5:1, 3:1, 3.5:1, 4:1, 4.5:1 or 5:1, etc., and preferably (4-5): 1.
Preferably, in the fifth mode, the deposition temperature is 1400-1600 ℃, for example, 1400 ℃, 1450 ℃, 1500 ℃, 1550 ℃, 1600 ℃, or the like, preferably 1500-1600 ℃.
Preferably, in the fifth mode, the cavity pressure when depositing the polycrystalline silicon carbide layer is 10-40KPa, for example, 10KPa, 20KPa, 30KPa, 40KPa, or the like, and preferably 20-40KPa.
Preferably, in the sixth aspect, the specific step of growing the transition layer includes: the process parameter A is adopted first, and then the process parameter B is gradually changed into the process parameter B, so that the free C phase formed in the transition layer is gradually increased along the direction away from the bonding assembly.
Preferably, the specific manner of transition from the process parameter a to the process parameter B is as follows: and (3) regulating the carbon-silicon atomic ratio, the cavity temperature and the cavity pressure once every 1-30 min.
Preferably, in the process parameter a, the carbon-silicon atomic ratio is less than 2.5 or more than 5, for example, may be 2, 1.5, 1, 5.5, 6 or 6.5, etc., the cavity temperature is less than 1400 ℃ or more than 1600 ℃, for example, may be 1300 ℃, 1200 ℃, 1100 ℃, 1000 ℃, 1700 ℃, 1800 ℃, 1900 ℃, 2000 ℃, etc., and the cavity pressure is less than 10KPa or more than 40KPa, for example, may be 5KPa, 1KPa, 45KPa, 50KPa, 55KPa, etc.
Preferably, in the process parameter B, the carbon-silicon atomic ratio is 2.5-5, the cavity temperature is 1400-1600 ℃, and the cavity pressure is 10-40KPa.
Preferably, the process parameter B is used for growth during the growth of the homogenous layer.
In a second aspect, the present invention provides a composite silicon carbide substrate prepared by the preparation method according to the first aspect, wherein the composite silicon carbide substrate comprises a polycrystalline silicon carbide layer and a first monocrystalline silicon carbide thin layer, or comprises a polycrystalline silicon carbide layer and a second monocrystalline silicon carbide thin layer, and the polycrystalline silicon carbide layer contains free C phase;
preferably, the thickness of the polycrystalline silicon carbide layer is 50 to 800 μm, for example, 50 μm, 100 μm, 200 μm, 300 μm, 400 μm, 500 μm, 600 μm, 700 μm or 800 μm, etc., preferably 300 to 600 μm.
Preferably, the thickness of the thin layer of single crystal silicon carbide is 0.1-10 μm, and may be, for example, 0.1 μm, 0.5 μm, 1 μm, 2 μm, 4 μm, 6 μm, 8 μm, 10 μm, or the like.
Preferably, the resistivity of the single crystal silicon carbide thin layer is 0.01-0.03 Ω ∙ cm, and may be, for example, 0.01 Ω ∙ cm, 0.015 Ω ∙ cm, 0.02 Ω ∙ cm, 0.025 Ω ∙ cm, or 0.03 Ω ∙ cm, etc.
Preferably, the free C phase is of graphitic structure.
As a preferable technical scheme of the invention, the polycrystalline silicon carbide layer is doped with N element.
Preferably, the polycrystalline silicon carbide layer contains free C phases which are uniformly distributed, or the polycrystalline silicon carbide layer sequentially comprises a transition layer and a homogeneous layer along the direction away from the monocrystalline silicon carbide thin layer;
the transition layer gradually increases the free C phase along the direction away from the monocrystalline silicon carbide thin layer, and the homogeneous layer contains uniformly distributed free C phase;
the transition layer is characterized in that one side, close to the monocrystalline silicon carbide thin layer, does not contain free C phase, and one side, far away from the monocrystalline silicon carbide thin layer, contains free C phase which is uniformly distributed;
the homogeneous layer contains a homogeneous distribution of free C phase.
Preferably, the resistivity of the polycrystalline silicon carbide layer containing the free C phase distributed uniformly is less than 0.01Ω ∙ cm, and can be, for example, 0.008 Ω ∙ cm, 0.006 Ω ∙ cm, 0.004 Ω ∙ cm, 0.002 Ω ∙ cm, or 0.001 Ω ∙ cm.
Preferably, in the transition layer, the resistivity of the side close to the single crystal silicon carbide thin layer is greater than 0.05Ω ∙ cm, for example, may be 0.06Ω ∙ cm, 0.08Ω ∙ cm, 0.1Ω ∙ cm, 0.12Ω ∙ cm, or 0.14Ω ∙ cm, etc., and the resistivity of the other side far from the single crystal silicon carbide thin layer is less than 0.01Ω ∙ cm, for example, may be 0.008 Ω ∙ cm, 0.006 Ω ∙ cm, 0.004 Ω ∙ cm, 0.002 Ω ∙ cm, or 0.001 Ω ∙ cm, etc.
Preferably, the resistivity of the homogeneous layer is less than 0.01 Ω ∙ cm, and may be, for example, 0.008 Ω ∙ cm, 0.006 Ω ∙ cm, 0.004 Ω ∙ cm, 0.002 Ω ∙ cm, or 0.001 Ω ∙ cm, etc.
In a third aspect, the present invention provides a semiconductor device comprising a composite silicon carbide substrate as described in the second aspect.
The numerical ranges recited herein include not only the recited point values, but also any point values between the recited numerical ranges that are not recited, and are limited to, and for the sake of brevity, the invention is not intended to be exhaustive of the specific point values that the recited range includes.
Compared with the prior art, the invention has the following beneficial effects:
(1) The preparation method provided by the invention avoids the joint interface between the polycrystalline silicon carbide layer and the monocrystalline silicon carbide thin layer, and has high success rate and low cost.
(2) The composite silicon carbide substrate prepared by the preparation method provided by the invention has lower resistivity, the combination between the polycrystalline silicon carbide layer and the monocrystalline silicon carbide thin layer is tight and firm, and the industrial production can be realized.
Drawings
Fig. 1 is a schematic structural diagram of a composite silicon carbide substrate prepared in example 1 of the present invention.
Fig. 2 is a process flow diagram of preparing a composite silicon carbide substrate according to example 1 of the present invention.
FIG. 3 is a process flow diagram of the preparation of a bonded assembly according to example 1 of the present invention.
FIG. 4 is a process flow diagram of preparing a bonded assembly according to example 2 of the present invention.
Fig. 5 is a process flow diagram of preparing a composite silicon carbide substrate according to example 3 of the present invention.
FIG. 6 is a process flow diagram of preparing a bonded assembly according to example 3 of the present invention.
FIG. 7 is a process flow diagram of preparing a bonded assembly according to example 4 of the present invention.
Fig. 8 is a schematic structural diagram of a composite silicon carbide substrate prepared in example 5 of the present invention.
FIG. 9 is a process flow diagram of the preparation of a bonded assembly according to example 5 of the present invention.
Fig. 10 is a process flow diagram of preparing a composite silicon carbide substrate according to example 6 of the present invention.
Wherein the 1-single crystal silicon carbide layer; 10-a single crystal silicon carbide layer; 10' -layer to be recovered; 11-a first thin layer of single crystal silicon carbide; 12-a second thin layer of single crystal silicon carbide; 2-an intermediate sacrificial layer; 21-an intermediate substrate; 22-a sacrificial layer; a 3-polycrystalline silicon carbide layer; 31-a transition layer; 32-a homogeneous layer; 4-weakening layer.
Detailed Description
The technical scheme of the invention is further described by the following specific embodiments. It will be apparent to those skilled in the art that the examples are merely to aid in understanding the invention and are not to be construed as a specific limitation thereof.
Example 1
The embodiment provides a preparation method of a composite silicon carbide substrate, a process flow chart of which is shown in fig. 2, the preparation method comprises the following steps:
(1) Preparing monocrystalline silicon carbide thin layers 1 on two sides of the surface of an intermediate sacrificial layer 2 (made of silicon) with the thickness of 5000 mu m, namely a first monocrystalline silicon carbide thin layer 11 and a second monocrystalline silicon carbide thin layer 12 respectively, wherein the thickness of the monocrystalline silicon carbide thin layers is 5 mu m, the resistivity of the monocrystalline silicon carbide thin layers is 0.02 omega ∙ cm, and the first monocrystalline silicon carbide thin layer 11 and the second monocrystalline silicon carbide thin layer 12 are respectively connected with the intermediate sacrificial layer 2 in a bonding way to obtain a bonding assembly, and the specific method is shown in figure 3 and comprises the following steps:
(a1) Hydrogen ion implantation is carried out on one surface of the monocrystalline silicon carbide layer 10, and the hydrogen ions accelerated by an electric field enter a position 5.5 mu m away from an implantation surface to form a pre-buried weakening layer 4;
(b1) Bonding the ion implantation surface of the monocrystalline silicon carbide layer 10 and one surface of the intermediate sacrificial layer 2;
(c1) Performing a heat treatment at 950 ℃ for 1.5 hours to fracture the monocrystalline silicon carbide layer 10 along the weakened layer 4, obtaining a layer to be recovered 10' and an intermediate sacrificial layer 2 bonded with a thin layer 11 of a first monocrystalline silicon carbide;
(d1) Repeating steps (a 1) - (c 1), bonding a second thin monocrystalline silicon carbide layer 12 on the other side of the intermediate sacrificial layer 2, thereby obtaining the bonding assembly;
(2) Chemical vapor deposition is simultaneously carried out on two surfaces of the bonding assembly, so that a layer of polycrystalline silicon carbide layer 3 is respectively grown on the two surfaces, the thickness is 400 mu m, the polycrystalline silicon carbide layer 3 contains evenly distributed free C phase (graphite structure), and the concentration of doped polycrystalline silicon carbide layer 3 is 5 multiplied by 10 20 /cm 3 The specific growth steps comprise:
placing the bonding assembly in a reaction chamber of chemical vapor deposition, and introducing trichlorosilane, ethylene (carbon-silicon atomic ratio is 3.5:1), nitrogen (nitrogen-silicon atomic ratio is 0.85:1) and diluent gas (namely hydrogen gas and hydrogen-silicon atomic ratio is 6:1) into the reaction chamber under the conditions that the temperature of the chamber is 1500 ℃ and the pressure of the chamber is 25KPa, wherein the trichlorosilane is converted into steam from liquid state by a carrier gas bubbling method, and the carrier gas is hydrogen gas along with the carrier gas transmission;
(3) And removing the middle sacrificial layer 2 in the bonding assembly by adopting a mixed solution of hydrofluoric acid and nitric acid (the volume ratio is 1:1), and grinding and polishing to obtain the composite silicon carbide substrate.
Fig. 1 shows a schematic structural diagram of a composite silicon carbide substrate prepared in this example.
Example 2
The difference between this embodiment and embodiment 1 is that the method for preparing the bonding assembly in step (1) is shown in fig. 4, and the specific method includes:
(a2) Hydrogen ions are respectively injected into one surface of the two monocrystalline silicon carbide layers 10, and the hydrogen ions accelerated by the electric field enter a position 5.5 mu m away from the injection surface to form 2 pre-buried weakening layers 4;
(b2) Respectively bonding and connecting the ion implantation surfaces of the two monocrystalline silicon carbide layers 10 and the two side surfaces of the middle sacrificial layer 2 to obtain a sandwich structure;
(c2) A heat treatment at 1000 c for 1h causes the sandwich to fracture along 2 of the weakened layers 4, resulting in a bonded assembly.
The remaining preparation methods and parameters remain the same as in example 1.
Example 3
The embodiment provides a preparation method of a composite silicon carbide substrate, a process flow chart of which is shown in fig. 5, the preparation method comprises the following steps:
(1) Preparing monocrystalline silicon carbide thin layers 1 on two sides of the surface of an intermediate sacrificial layer 2, namely a first monocrystalline silicon carbide thin layer 11 and a second monocrystalline silicon carbide thin layer 12, respectively, wherein the thickness is 10 mu m, the resistivity is 0.01Ω ∙ cm, the intermediate sacrificial layer 2 comprises an intermediate substrate 21 (made of silicon carbide) with the thickness of 1000 mu m and sacrificial layers 22 (made of silicon) with the thickness of 5 mu m positioned on two sides of the intermediate substrate 21, and the sacrificial layers 22 are respectively bonded and connected with the first monocrystalline silicon carbide thin layer 11 and the second monocrystalline silicon carbide thin layer 12 to obtain a bonding assembly, and the specific method is as shown in fig. 6 and comprises the following steps:
(a3) Hydrogen ions are injected into one surface of the monocrystalline silicon carbide layer 10, and the hydrogen ions accelerated by the electric field enter a position 11 mu m away from the injection surface to form a pre-buried weakening layer 4;
(b3) Growing a sacrificial layer 22 on one surface of an intermediate substrate 21, and then bonding and connecting the ion implantation surface of the single crystal silicon carbide layer 10 and the surface of the sacrificial layer 22;
(c3) Performing a heat treatment at 1050 ℃ for 0.5h to fracture the monocrystalline silicon carbide layer 10 along the weakened layer 4, obtaining an assembly of a layer to be recovered 10' and a thin layer 11 of a first monocrystalline silicon carbide bonded thereto;
(d3) Repeating steps (a 3) - (c 3), growing a sacrificial layer 22 on the other surface of the intermediate substrate 21, and bonding a second thin layer 12 of single crystal silicon carbide to obtain the bonded assembly;
(2) Chemical vapor deposition is simultaneously carried out on two surfaces of the bonding assembly, so that a layer of polycrystalline silicon carbide layer 3 is respectively grown on the two surfaces, the thickness is 100 mu m, the polycrystalline silicon carbide layer 3 contains evenly distributed free C phase (graphite structure), and the concentration of doped polycrystalline silicon carbide layer 3 is 1 multiplied by 10 18 /cm 3 The specific growth steps comprise:
placing the bonding assembly in a reaction chamber of chemical vapor deposition, and introducing trichlorosilane, propane (carbon-silicon atomic ratio is 2.5:1), nitrogen (nitrogen-silicon atomic ratio is 0.7:1) and diluent gas (namely hydrogen-silicon atomic ratio is 3:1) into the reaction chamber under the conditions that the temperature of the chamber is 1400 ℃ and the pressure of the chamber is 10KPa, wherein the trichlorosilane is converted into steam from liquid by a bubbling method, and the carrier gas is hydrogen along with the carrier gas transmission;
(3) And removing the middle sacrificial layer 2 in the bonding assembly by adopting a mixed solution of hydrofluoric acid and nitric acid (the volume ratio is 1:1), and grinding and polishing to obtain the composite silicon carbide substrate.
Example 4
The difference between this embodiment and embodiment 3 is that the method for preparing the bonding assembly in step (1) is shown in fig. 7, and the specific method includes:
(a4) Hydrogen ions are respectively injected into one surface of the two monocrystalline silicon carbide layers 10, and the hydrogen ions accelerated by the electric field enter a position 11 mu m away from the injection surface to form 2 pre-buried weakening layers 4;
(b4) Respectively growing sacrificial layers 22 on two sides of the intermediate substrate 21, and then respectively bonding and connecting the ion implantation surface of the first monocrystalline silicon carbide layer 10 and the ion implantation surface of the second monocrystalline silicon carbide layer 10 with the sacrificial layers 22 on two sides of the intermediate substrate 21 to obtain a sandwich structure;
(c4) A heat treatment at 1050 c for 0.5h causes the sandwich to fracture along 2 of the weakened layers 4, resulting in a bonded assembly.
The remaining preparation methods and parameters remain the same as in example 3.
Example 5
The embodiment provides a preparation method of a composite silicon carbide substrate, which comprises the following steps:
(1) Preparing monocrystalline silicon carbide thin layers 1 on two sides of the surface of an intermediate sacrificial layer 2 (made of carbon) with the thickness of 10000 mu m, namely a first monocrystalline silicon carbide thin layer 11 and a second monocrystalline silicon carbide thin layer 12 respectively, wherein the thickness of the monocrystalline silicon carbide thin layers is 1 mu m, the resistivity of the monocrystalline silicon carbide thin layers is 0.03 omega ∙ cm, and the first monocrystalline silicon carbide thin layer 11 and the second monocrystalline silicon carbide thin layer 12 are respectively connected with the intermediate sacrificial layer 2 in a bonding way to obtain a bonding assembly, and the specific method is shown in fig. 9 and comprises the following steps:
(a1) Hydrogen ion implantation is carried out on one surface of the monocrystalline silicon carbide layer 10, and the hydrogen ions accelerated by an electric field enter a position which is 1.2 mu m away from an implantation surface to form a pre-buried weakening layer 4;
(b1) Bonding the ion implantation surface of the monocrystalline silicon carbide layer 10 and one surface of the intermediate sacrificial layer 2;
(c1) Performing a heat treatment at 900 ℃ for 1.5 hours to fracture the monocrystalline silicon carbide layer 10 along the weakened layer 4, obtaining a layer to be recovered 10' and an intermediate sacrificial layer 2 bonded with a first monocrystalline silicon carbide thin layer 11;
(d1) Repeating steps (a 1) - (c 1), bonding a second thin monocrystalline silicon carbide layer 12 on the other side of the intermediate sacrificial layer 2, thereby obtaining the bonding assembly;
(2) Firstly growing a transition layer 31 with the thickness of 30 mu m on two sides of the surface of the bonding assembly, and growing a homogeneous layer 32 with the thickness of 320 mu m to obtain the polycrystalline silicon carbide layer 3, wherein the polycrystalline silicon carbide layer 3 is doped with the concentration of 1 multiplied by 10 21 /cm 3 The specific steps include:
(i) The chemical vapor deposition method is adopted, namely, the process parameters A are firstly adopted, then the process parameters are adjusted every 10min, the process parameters B are changed into the process parameters B after 6 times of adjustment, the transition layer 31 is manufactured, the free C phase of the transition layer 31 is gradually increased along the direction far away from the monocrystalline silicon carbide thin layer 1, the free C phase is not contained at one side close to the monocrystalline silicon carbide thin layer 1, the resistivity is 0.1Ω ∙ cm, the uniformly distributed free C phase is contained at one side far away from the monocrystalline silicon carbide thin layer 1, and the resistivity is 0.005 Ω ∙ cm;
in the process parameter A, the carbon-silicon atomic ratio is 2:1, the cavity temperature is 1300 ℃, and the cavity pressure is 5KPa; in the process parameter B, the atomic ratio of carbon to silicon is 5:1, the cavity temperature is 1600 ℃, and the cavity pressure is 40KPa;
(ii) Growing a homogeneous layer 32 on the transition layer 31 by a chemical vapor deposition method, namely adopting the process parameter B, wherein the homogeneous layer 32 contains free C phases which are uniformly distributed, and the resistivity is 0.005 omega ∙ cm;
(3) And (3) introducing hot air with the temperature of 1000 ℃ to oxidize carbon into carbon dioxide, removing the middle sacrificial layer 2 in the bonding assembly, and grinding and polishing to obtain the composite silicon carbide substrate.
Fig. 8 shows a schematic structural diagram of a composite silicon carbide substrate prepared in this example.
Example 6
The present embodiment differs from embodiment 5 in that the method for preparing the bonding assembly in step (1) includes:
(a4) Hydrogen ions are respectively injected into one surface of the two monocrystalline silicon carbide layers 10, and the hydrogen ions accelerated by the electric field enter a position 1.2 mu m away from the injection surface to form 2 pre-buried weakening layers 4;
(b4) Respectively growing sacrificial layers 22 on two sides of the intermediate substrate 21, and then respectively bonding and connecting the ion implantation surface of the first monocrystalline silicon carbide layer 10 and the ion implantation surface of the second monocrystalline silicon carbide layer 10 with the sacrificial layers 22 on two sides of the intermediate substrate 21 to obtain a sandwich structure;
(c4) A heat treatment at 900 c for 1.5h causes the sandwich to fracture along 2 of the weakened layers 4, resulting in a bonded assembly.
The remaining preparation methods and parameters remain the same as in example 5.
Fig. 10 shows a process flow diagram of the present example for preparing a composite silicon carbide substrate.
Example 7
This embodiment differs from embodiment 5 in that the thickness of the transition layer 31 is made 0.02 μm by adjusting the time for deposition of the transition layer 31.
The remaining preparation methods and parameters remain the same as in example 7.
Example 8
This embodiment differs from embodiment 5 in that the thickness of the transition layer 31 is 65 μm by adjusting the time for deposition of the transition layer 31.
The remaining preparation methods and parameters remain the same as in example 7.
Example 9
The difference between this example and example 1 is that nitrogen is not added in step (2), i.e., N doping is not performed in the polycrystalline silicon carbide layer 3.
The remaining preparation methods and parameters remain the same as in example 1.
Comparative example 1
This example differs from example 1 in that the carbon to silicon atomic ratio in step (2) is 5.5:1.
The remaining preparation methods and parameters remain the same as in example 1.
Comparative example 2
This comparative example differs from example 1 in that the polycrystalline silicon carbide layer 3 does not contain free C phase, i.e., the carbon to silicon atomic ratio in step (2) is 2:1.
The remaining preparation methods and parameters remain the same as in example 1.
Comparative example 3
This comparative example differs from example 1 in that step (1) is not performed, but the polycrystalline silicon carbide layer 3 is deposited directly on the intermediate sacrificial layer 2.
The remaining preparation methods and parameters remain the same as in example 1.
Comparative example 4
This comparative example differs from example 1 in that step (2) is not performed, but the intermediate sacrificial layer 2 is directly removed after the bonded assembly is obtained.
The remaining preparation methods and parameters remain the same as in example 1.
Comparative example 5
The present comparative example provides a composite silicon carbide substrate comprising a thin layer of single crystal silicon carbide having a thickness of 5 μm and a layer of polycrystalline silicon carbide having a thickness of 400 μm bonded to the thin layer of single crystal silicon carbide, the single crystal silicon carbide having a resistivity of 0.02 Ω ∙ cm, the polycrystalline silicon carbide layer containing a uniform distribution of free C phase (graphite structure) and the polycrystalline silicon carbide layer being doped with a concentration of 5X 10 20 /cm 3 The specific steps of the N element with the resistivity of 0.005 omega ∙ cm comprise:
(1) Preparing a single crystal silicon carbide substrate having a thickness of 350 μm and a polycrystalline silicon carbide substrate having a thickness of 400 μm;
(2) Carrying out hydrogen ion implantation on one surface of the monocrystalline silicon carbide substrate, and enabling hydrogen ions accelerated by an electric field to enter a position 5.1 mu m away from an implantation surface to form a pre-buried weakening layer;
(3) Bonding and connecting the ion implantation surface of the monocrystalline silicon carbide substrate and one surface of the polycrystalline silicon carbide substrate;
(4) Performing heat treatment at 900 ℃ for 1.5 hours to fracture the monocrystalline silicon carbide substrate along the weakened layer to obtain a polycrystalline silicon carbide substrate bonded with a monocrystalline silicon carbide thin layer;
(5) And polishing the surface of the monocrystalline silicon carbide thin layer to obtain the composite silicon carbide substrate.
Performance testing
The composite silicon carbide substrates prepared in examples 1 to 9 and comparative examples 1 to 5 were subjected to resistivity test, bonding strength test between a single crystal silicon carbide thin layer and a polycrystalline silicon carbide layer.
Resistivity testing method: and (3) carrying out resistivity test on 5 sampling points (1 sampling point in the center and 4 uniformly distributed sampling points at the edge) of the composite substrate by using a non-contact vortex flow method sheet resistance meter, and taking the average value of the 5 resistivity values as the resistivity of the composite substrate.
The bonding strength test method comprises the following steps: the bonding strength between the monocrystalline layer and the polycrystalline layer was measured using a one-dimensional stretching method.
The test results are shown in Table 1.
TABLE 1
Analysis:
as can be seen from the above table, the preparation method provided by the invention can effectively reduce the resistivity of the composite silicon carbide substrate, the combination between the polycrystalline silicon carbide layer and the monocrystalline silicon carbide thin layer is tight and firm, and the industrial production can be realized.
From the data of examples 1 and 5, it can be seen that if a transition layer is grown first and a homogeneous layer is grown again on the surface of the bonded assembly, the bond strength between the single crystal silicon carbide layer and the polycrystalline silicon carbide layer is improved, and the overall resistivity of the composite substrate is increased, while still meeting the requirements of subsequent device fabrication.
As is clear from the data of examples 5 and examples 7 to 8, the thickness of the transition layer is too small, the manufacturing difficulty is great, the local thickness of the transition layer is uneven, so that the free C phase is directly combined with the monocrystalline silicon carbide thin layer, and the bonding strength between the monocrystalline silicon carbide layer and the polycrystalline silicon carbide layer is obviously reduced; and if the thickness of the transition layer is too large, the resistivity of the transition layer is higher, the proportion of the transition layer to the total thickness of the composite silicon carbide substrate is too large, the overall resistivity of the composite substrate is obviously increased, and the requirement of subsequent device manufacturing cannot be met.
As is clear from the data of examples 1 and 9, the resistivity of the polycrystalline silicon carbide layer increases without N-doping the polycrystalline silicon carbide layer, and thus the overall resistivity of the composite substrate increases.
From the data of example 1 and comparative example 1, it is evident that, when the carbon to silicon atomic ratio is too large, agglomerated large-size graphite is generated in the polycrystalline silicon carbide layer, and the bonding strength between the single crystal silicon carbide layer and the polycrystalline silicon carbide layer is greatly reduced.
As is apparent from the data of example 1 and comparative example 2, if the polycrystalline silicon carbide layer does not contain free C phase, the resistivity of the polycrystalline silicon carbide layer is excessively high, which results in a significant increase in the overall resistivity of the composite substrate, and thus the resistivity requirements for manufacturing semiconductor devices cannot be satisfied.
As is clear from the data of example 1 and comparative example 3, if the polycrystalline silicon carbide layer is directly deposited on the intermediate sacrificial layer, only a polycrystalline silicon carbide substrate is finally obtained, which cannot be used for manufacturing a semiconductor device.
As is clear from the data of example 1 and comparative example 4, if the intermediate sacrificial layer is directly removed after the bonded assembly is obtained, the thin single crystal silicon carbide layer becomes very brittle due to the too small thickness, and is difficult to handle, and the subsequent deposition of the polycrystalline silicon carbide layer cannot be performed, and any substrate cannot be obtained.
From the data of example 1 and comparative example 5, it is apparent that the polycrystalline silicon carbide layer was grown directly on the single crystal silicon carbide layer, and the bonding strength between the two was significantly greater than that of the composite substrate connected by bonding.
The applicant states that the process of the invention is illustrated by the above examples, but the invention is not limited to, i.e. does not mean that the invention must be carried out in dependence on the above process steps. It should be apparent to those skilled in the art that any modification of the present invention, equivalent substitution of selected raw materials, addition of auxiliary components, selection of specific modes, etc. fall within the scope of the present invention and the scope of disclosure.

Claims (9)

1. A method of preparing a composite silicon carbide substrate, the method comprising the steps of:
(1) Preparing monocrystalline silicon carbide thin layers on two sides of the surface of the middle sacrificial layer, respectively marking as a first monocrystalline silicon carbide thin layer and a second monocrystalline silicon carbide thin layer, and respectively bonding and connecting the first monocrystalline silicon carbide thin layer and the second monocrystalline silicon carbide thin layer with the middle sacrificial layer to obtain a bonding assembly;
(2) Growing polycrystalline silicon carbide layers on two sides of the surface of the bonding assembly, wherein the polycrystalline silicon carbide layers contain free C phases;
(3) Removing the middle sacrificial layer in the bonding assembly to obtain two composite silicon carbide substrates;
the polycrystalline silicon carbide layer in the step (2) is grown in a fifth mode or a sixth mode, and the specific steps of the fifth mode include:
directly depositing polycrystalline silicon carbide layers on two sides of the surface of the bonding assembly, wherein the polycrystalline silicon carbide layers contain free C phases which are uniformly distributed;
the specific steps of the sixth mode include:
firstly growing a transition layer and a homogeneous layer on two sides of the surface of the bonding assembly to obtain the polycrystalline silicon carbide layer;
the raw materials for the growth of the polycrystalline silicon carbide layer comprise compounds containing silicon elements and carbon elements at the same time or compounds containing a silicon source and a carbon source in combination;
the raw materials for growing the polycrystalline silicon carbide layer also comprise diluent gas, wherein the diluent gas comprises hydrogen and/or argon;
the thickness of the transition layer is 0.05-60 mu m;
the transition layer gradually increases the free C phase along the direction away from the monocrystalline silicon carbide thin layer, and the homogeneous layer contains the free C phase which is uniformly distributed.
2. The method of claim 1, wherein the material of the intermediate sacrificial layer in step (1) comprises any one or a combination of at least two of carbon, silicon oxide, silicon nitride, or metal silicide;
the thickness of the middle sacrificial layer in the step (1) is 100-10000 mu m;
the thickness of the first and second thin layers of single crystal silicon carbide of step (1) is independently 0.1-10 μm.
3. The method of claim 1, wherein the specific method of manufacturing the bonding assembly of step (1) comprises one or two modes, the one mode comprising the steps of:
(a1) Implanting ions into one surface of the monocrystalline silicon carbide layer to form a pre-buried weakening layer;
(b1) Bonding and connecting the ion implantation surface of the monocrystalline silicon carbide layer and one surface of the middle sacrificial layer;
(c1) Applying stress to fracture the monocrystalline silicon carbide layer along the weakened layer to obtain a layer to be recovered and an intermediate sacrificial layer bonded with a first monocrystalline silicon carbide thin layer;
(d1) Repeating steps (a 1) - (c 1), bonding a second monocrystalline silicon carbide thin layer on the other side of the intermediate sacrificial layer to obtain the bonding assembly;
the second mode comprises the following steps:
(a2) Respectively implanting ions into one surface of the first monocrystalline silicon carbide layer and one surface of the second monocrystalline silicon carbide layer to form 2 pre-buried weakening layers;
(b2) Bonding and connecting the first monocrystalline silicon carbide layer, the second monocrystalline silicon carbide layer and the middle sacrificial layer to obtain a sandwich structure;
(c2) And applying stress to fracture the sandwich structure along 2 weakened layers to obtain the bonding assembly.
4. The method according to claim 1, wherein the intermediate sacrificial layer in step (1) comprises an intermediate substrate and sacrificial layers located on two sides of the intermediate substrate, the sacrificial layers are respectively bonded and connected with the first monocrystalline silicon carbide thin layer and the second monocrystalline silicon carbide thin layer, and the specific step is performed in a third mode or a fourth mode, and the third mode comprises the following steps:
(a3) Implanting ions into one surface of the monocrystalline silicon carbide layer to form a pre-buried weakening layer;
(b3) Growing a sacrificial layer on one surface of an intermediate substrate, and then bonding and connecting the ion implantation surface of the monocrystalline silicon carbide layer and the surface of the sacrificial layer;
(c3) Applying stress to fracture the single crystal silicon carbide layer along the weakened layer to obtain a component of a layer to be recovered and a first single crystal silicon carbide thin layer bonded;
(d3) Repeating the steps (a 3) - (c 3), and bonding a second monocrystalline silicon carbide thin layer on the surface of the sacrificial layer grown on the other surface of the intermediate substrate to obtain the bonding assembly;
the fourth mode comprises the following steps:
(a4) Respectively implanting ions into one surface of the first monocrystalline silicon carbide layer and one surface of the second monocrystalline silicon carbide layer to form 2 pre-buried weakening layers;
(b4) Respectively growing sacrificial layers on two sides of the intermediate substrate, and then respectively bonding and connecting the ion implantation surface of the first monocrystalline silicon carbide layer and the ion implantation surface of the second monocrystalline silicon carbide layer with the sacrificial layers on two sides of the intermediate substrate to obtain a sandwich structure;
(c4) And applying stress to fracture the sandwich structure along 2 weakened layers to obtain the bonding assembly.
5. The method of claim 1, wherein the polycrystalline silicon carbide layer of step (2) is doped with N element;
the doping concentration of N element in the polycrystalline silicon carbide layer is 1 multiplied by 10 18 -1×10 21 /cm 3 ；
The raw materials doped with N element comprise nitrogen and/or ammonia.
6. The production method according to claim 1, wherein in the fifth mode, an atomic ratio of the hydrogen element in the diluent gas to the silicon element in the silicon source, or an atomic ratio of the argon element in the diluent gas to the silicon element in the silicon source is independently (3-10): 1;
in the fifth mode, the carbon-silicon atomic ratio of the carbon source to the silicon source is (2.5-5): 1;
in the fifth mode, the deposition temperature is 1400-1600 ℃;
in the fifth mode, the cavity pressure is 10-40KPa when the polycrystalline silicon carbide layer is deposited;
in the sixth mode, the specific step of growing the transition layer includes: firstly adopting a process parameter A, and then gradually transiting to a process parameter B, so that a free C phase formed in the transition layer gradually increases along a direction away from the bonding assembly;
in the process parameter A, the atomic ratio of carbon to silicon is less than 2.5 or more than 5, the cavity temperature is less than 1400 ℃ or more than 1600 ℃, and the cavity pressure is less than 10KPa or more than 40KPa;
in the process parameter B, the atomic ratio of carbon to silicon is 2.5-5, the cavity temperature is 1400-1600 ℃, and the cavity pressure is 10-40KPa;
and in the process of growing the homogeneous layer, adopting the process parameter B for growth.
7. A composite silicon carbide substrate prepared by the preparation method according to any one of claims 1 to 6, wherein the composite silicon carbide substrate comprises a polycrystalline silicon carbide layer and a monocrystalline silicon carbide thin layer, the monocrystalline silicon carbide thin layer is a first monocrystalline silicon carbide thin layer or a second monocrystalline silicon carbide thin layer, and the polycrystalline silicon carbide layer contains free C phase;
the free C phase is of a graphite structure.
8. The composite silicon carbide substrate of claim 7, wherein the polycrystalline silicon carbide layer is doped with N element;
the polycrystalline silicon carbide layer contains free C phases which are uniformly distributed, or the polycrystalline silicon carbide layer sequentially comprises a transition layer and a homogeneous layer along the direction away from the monocrystalline silicon carbide thin layer;
the transition layer is characterized in that one side, close to the monocrystalline silicon carbide thin layer, does not contain free C phase, and one side, far away from the monocrystalline silicon carbide thin layer, contains free C phase which is uniformly distributed;
the homogeneous layer contains a homogeneous distribution of free C phase.
9. A semiconductor device comprising the composite silicon carbide substrate of claim 7 or 8.
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