CN115074825A - Silicon carbide epitaxial structure, pulse type growth method and application thereof - Google Patents
Silicon carbide epitaxial structure, pulse type growth method and application thereof Download PDFInfo
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- 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
- C30B25/20—Epitaxial-layer growth characterised by the substrate the substrate being of the same materials as the epitaxial layer
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- C30B25/00—Single-crystal growth by chemical reaction of reactive gases, e.g. chemical vapour-deposition growth
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- C30B25/16—Controlling or regulating
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- C30B25/00—Single-crystal growth by chemical reaction of reactive gases, e.g. chemical vapour-deposition growth
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Abstract
The invention discloses a silicon carbide epitaxial structure, a pulse type growth method and application thereof, wherein a silicon carbide single crystal wafer containing a silicon carbide epitaxial layer is manufactured on a silicon carbide single crystal substrate by adopting a chemical vapor deposition method, when the growth condition of the silicon carbide epitaxial layer is reached in a growth reaction chamber, a carbon source and a silicon source are introduced into the reaction chamber, and the proportion of the carbon source and the silicon source is alternately changed at intervals of pulse time by adopting a pulse mode, so that the silicon carbide epitaxial layer is epitaxially grown by adopting a CVD method under the Si-rich atmosphere and the C-rich atmosphere respectively in a first time period and a second time period which are adjacent until the growth of the silicon carbide epitaxial layer is finished. Thereby combining the advantages of the CVD method and the ALD method to grow the silicon carbide epitaxial structure with good thickness and concentration uniformity.
Description
Technical Field
The invention relates to the field of silicon carbide, in particular to a silicon carbide epitaxial structure, a pulse type growth method and application thereof.
Background
Silicon carbide (SiC) as a wide bandgap semiconductor material has the characteristics of high breakdown voltage, high electron mobility, high thermal conductivity and the like, and compared with the traditional silicon (Si) based semiconductor device, the semiconductor device manufactured by the SiC semiconductor material has the advantages of small volume, low switching loss, higher power density and the like. With the future power system, the demands for high voltage resistance and low power consumption of power electronic devices and the vigorous development of emerging applications such as electric vehicles and charging piles, the SiC devices gradually replace Si-based devices, and show huge market potential.
In order to manufacture SiC devices that meet the requirements of practical applications, a SiC thin film is grown epitaxially on a SiC substrate by Chemical Vapor Deposition (CVD). On one hand, because the impurity content of the substrate is higher and the electrical property is not good enough, the SiC device is not directly manufactured on the SiC substrate; on the other hand, the doping difficulty is high, and even if an ion implantation mode is adopted, subsequent high-temperature annealing is required, so that the doping effect on the epitaxial layer is far less good. Epitaxial growth is therefore critical to the fabrication of SiC devices with doping concentrations and thicknesses that meet design requirements.
With the increasingly bright application prospect of SiC devices, the cost requirements of the industry on SiC devices are more and more stringent, and the large-diameter SiC epitaxial wafer can effectively reduce the manufacturing cost of subsequent devices, so that the SiC epitaxial wafer with the diameter of 6 inches or even 8 inches is expected. Meanwhile, the application of SiC is advantageous in high-voltage and ultra-high-voltage devices, and the withstand voltage degree of SiC devices is proportional to the thickness of epitaxial layers, so thick SiC epitaxial wafers are also a definite trend of industrial development. However, the increase of the size and thickness of the epitaxial wafer is often accompanied by the decrease of uniformity, and how to control the uniformity of the large-size epitaxial wafer is a key problem to be solved for improving the yield and reliability of the SiC device and further reducing the cost.
Disclosure of Invention
Aiming at the problems that the size and the thickness of the conventional SiC epitaxial wafer are increased and the uniformity is reduced, the embodiment of the application provides a silicon carbide epitaxial structure, a pulse type growth method and application thereof to solve the problems mentioned in the background technology.
In a first aspect, an embodiment of the present application provides a pulsed growth method of a silicon carbide epitaxial structure, including the following steps:
1) providing a silicon carbide substrate, wherein the silicon carbide substrate is provided with a plurality of off-axes (0001) with off-angles pointing to <11-20 >;
2) and placing the silicon carbide substrate into a reaction chamber, introducing a carbon source and a silicon source into the reaction chamber when the growth condition of the silicon carbide epitaxial layer is achieved in the reaction chamber, and alternately changing the proportion of the carbon source and the silicon source at intervals of pulse time in a pulse mode to epitaxially grow the silicon carbide epitaxial layer under the Si-rich and C-rich atmosphere in a first time period and a second time period which are adjacent to each other.
Preferably, the C/Si ratio is 0.5 or more and less than 1 in a Si-rich atmosphere, and the C/Si ratio is 1 or more and less than 2 in a C-rich atmosphere.
Preferably, in the step 2, the ratio of the carbon source to the silicon source is changed by changing the flow rates of the carbon source and the silicon source into the reaction chamber.
Preferably, in the step 2, the ratio of the carbon source to the silicon source is changed alternately at intervals of pulse time by a pulse mode, and the method specifically includes:
keeping the flow rate of the carbon source unchanged, and changing the flow rate of the silicon source at intervals; or alternatively
Keeping the flow rate of the silicon source unchanged, and changing the flow rate of the carbon source at intervals; or
And alternately changing the flow rates of the silicon source and the carbon source at intervals.
Preferably, the silicon source comprises silane and chlorosilane, wherein the silane comprises monosilane, and the chlorosilane comprises trichlorosilane, dichlorosilane or silicon tetrachloride; the carbon source includes ethylene and propane.
Preferably, the growth conditions of the silicon carbide epitaxial layer in the reaction chamber are achieved before the following steps are included:
evacuating the reaction chamber to 10 deg.C -4 Torr；
Introduction of H 2 And HCl mixed gas is used for enabling the reaction chamber to reach a certain pressure, the temperature is raised to the temperature required by etching, and H is controlled 2 And the flow of HCl is used for carrying out in-situ etching on the silicon carbide substrate so as to remove the sub-surface loss of the silicon carbide substrateA regular surface step structure is obtained.
Preferably, the pressure in the reaction chamber is 30-150 Torr during the in-situ etching, the temperature required by the etching is 1650 ℃, the time of the in-situ etching is 30-60 min, and silane with the flow rate of 1-10 mL/min is also introduced.
Preferably, the growth conditions in step 2 include any one or more of an epitaxial growth temperature, an epitaxial growth pressure, flow rates of a carrier gas and an etching gas, and a flow rate of a doping source, and when the growth conditions of the silicon carbide epitaxial layer are reached in the reaction chamber, the epitaxial growth temperature, the epitaxial growth pressure, the flow rates of the carrier gas and the etching gas are kept unchanged.
Preferably, the pulse time is 1-60 min.
Preferably, the reaction chamber is one of a horizontal hot-wall CVD reaction chamber, a hot-wall or warm-wall planetary CVD reaction chamber and a vertical hot-wall CVD reaction chamber.
Preferably, the silicon carbide substrate includes 3 to 8-inch conductive and semi-insulating silicon carbide substrates, and the off angle on the silicon carbide substrate is 2 to 8 ° in the <11-20> direction.
Preferably, the growth rate of the silicon carbide epitaxial layer is 60-100 μm/h.
In a second aspect, embodiments of the present application provide a silicon carbide epitaxial structure, which is fabricated by using the pulsed growth method of the silicon carbide epitaxial structure.
Preferably, the thickness range of the silicon carbide epitaxial layer is 1-100 mu m, and the thickness uniformity is more than 97%.
In a third aspect, embodiments of the present application propose the use of a silicon carbide epitaxial structure according to the above in a SiC device.
Compared with the prior art, the invention has the beneficial effects that:
the method combines the characteristics of high growth rate of a Chemical Vapor Deposition (CVD) method and good uniformity of an Atomic Layer Deposition (ALD) method, and approximately realizes a mode of one-layer silicon atom and one-layer carbon atom cyclic growth at the step of the off-axis SiC substrate by changing the flow rate of the epitaxial precursor or alternatively introducing the epitaxial precursor in different time intervals delta t, so that the grown SiC epitaxial layer has similar effects with a film grown by utilizing an atomic layer deposition mode, namely, the thickness is accurately controlled, the uniformity of a large area is good, the yield and the reliability of SiC devices are improved, the growth speed is higher, the rapid mass production of silicon carbide epitaxial wafers is facilitated, and the production speed is improved.
Drawings
The accompanying drawings are included to provide a further understanding of the embodiments and are incorporated in and constitute a part of this specification. The drawings illustrate embodiments and together with the description serve to explain the principles of the invention. Other embodiments and many of the intended advantages of embodiments will be readily appreciated as they become better understood by reference to the following detailed description.
Fig. 1 is a schematic view of a gas flow introduction process of a pulsed growth method of a silicon carbide epitaxial structure according to an embodiment of the present application;
fig. 2 is a schematic view of a gas flow introduction process of a growth mode of a silicon carbide epitaxial structure of a comparative example of the present application;
fig. 3 is a raman result graph of a silicon carbide epitaxial layer of the silicon carbide epitaxial structure of example 1 of the present application.
Detailed Description
The present application will be described in further detail with reference to the following drawings and examples. It is to be understood that the specific embodiments described herein are merely illustrative of the relevant invention and not restrictive of the invention. It should be noted that, for convenience of description, only the portions related to the related invention are shown in the drawings.
It should be noted that the embodiments and features of the embodiments in the present application may be combined with each other without conflict. The present application will be described in detail below with reference to the embodiments with reference to the attached drawings.
The epitaxial growth of SiC polytypes of the same type by chemical vapor deposition is currently the standard technique for making SiC devices. CVD methods allow better control of the thickness, doping concentration, and uniformity within the available area of the epitaxial layer than Liquid Phase Epitaxy (LPE) and sublimation methods, while possessing a faster growth rate than Molecular Beam Epitaxy (MBE) methods. At present, the mainstream SiC epitaxial growth equipment adopts a hot-wall CVD reaction chamber, because the hot-wall CVD reaction chamber requires less radio frequency power and has better temperature uniformity in the reaction chamber compared with a cold-wall CVD reaction chamber, and the structural design has three types, namely horizontal, vertical and planetary.
The embodiment of the invention provides a pulse type growth method of a silicon carbide epitaxial structure, which comprises the following steps:
(1) a silicon carbide substrate is provided having an off-axis (0001) oriented at an off-angle of a few degrees <11-20 >. Specifically, a (0001) Si-face silicon carbide substrate having an off-angle of 2 DEG to 8 DEG along a <11-20> direction is provided, and the silicon carbide substrate includes a 3-8 inch conductive type and semi-insulating type silicon carbide substrate. The silicon carbide substrate is then subjected to a standard clean.
(2) The cleaned silicon carbide substrate is placed in a reaction chamber, the reaction chamber is one of a horizontal hot-wall CVD reaction chamber, a hot-wall or warm-wall planetary CVD reaction chamber and a vertical hot-wall CVD reaction chamber, in a specific embodiment, the horizontal hot-wall CVD reaction chamber is adopted, and the silicon carbide substrate is placed on a susceptor in the hot-wall CVD reaction chamber, wherein the susceptor can have a rotating function or not. And then adjusting growth conditions, wherein the growth conditions comprise more than one of epitaxial growth temperature, epitaxial growth pressure, flow of carrier gas and etching gas and flow of a doping source. Firstly, the reaction chamber is vacuumized to 10 DEG -4 Torr; introduction of H 2 And HCl mixed gas to make the reaction chamber reach a certain pressure and raise the temperature to the temperature required by etching, wherein H 2 As carrier gas, continuously introducing HCl as etching gas and H during the whole epitaxial growth process 2 Together, the in-situ etching effect is realized, which is beneficial to obtaining a clean SiC surface without silicon drops. H 2 The flow rate is set to 5 to 100L/min, and the HCl flow rate is set to 5 to 100 mL/min. Control H 2 And carrying out in-situ etching on the silicon carbide substrate by the flow of HCl to remove the sub-surface loss of the silicon carbide substrate and obtain a regular surface step structure. Specifically, when in-situ etching is carried out, the pressure in the reaction chamber is 30-150 Torr, the temperature required by etching is 1650 ℃, the time of in-situ etching is 30-60 min, and silane with the flow rate of 1-10 mL/min is introduced. The in-situ etching can effectively control the crystal form of SiC, realize homoepitaxial growth and reduce the temperature of epitaxial growth.
(3) And when the growth condition of the silicon carbide epitaxial layer is reached in the reaction chamber, keeping the epitaxial growth temperature, the epitaxial growth pressure, the carrier gas and the etching gas flow unchanged. Introducing a carbon source and a silicon source into the reaction chamber, alternately changing the proportion of the carbon source and the silicon source at intervals of pulse time in a pulse mode, and specifically changing the proportion of the carbon source and the silicon source by changing the flow rate of the carbon source and the silicon source introduced into the reaction chamber, so that the silicon carbide epitaxial layer is epitaxially grown in the Si-rich atmosphere and the C-rich atmosphere in the adjacent first time period and the second time period respectively. Specifically, the silicon source comprises silane and chlorosilane, wherein the silane comprises monosilane, and the chlorosilane comprises trichlorosilane, dichlorosilane or silicon tetrachloride; carbon sources include ethylene and propane. The pulse time is 1-60 min, namely the flow of the carbon source and the silicon source introduced into the reaction chamber is changed every 1-60 min. The C/Si ratio is greater than or equal to 0.5 and less than 1 in a Si-rich atmosphere, and the C/Si ratio is greater than 1 and less than or equal to 2 in a C-rich atmosphere.
In the process of epitaxial growth, a silicon source and a carbon source are introduced in a pulse mode, namely the flow rates of the silicon source and the carbon source are changed along with time. According to the general rule of CVD growth of compound semiconductors, when the surface of the SiC substrate is in a Si-rich atmosphere, the growth rate is determined by the carbon supply; also under C-rich conditions, the growth rate is mainly determined by the silicon supply. When one growth source is excessive relative to the other, the excessive one waits for the other during the growth process, the flow rate of the growth source is controlled to change along with the time, which is actually equivalent to the cycle of the relative excessive condition, the first reaction gas and the surface of the substrate are subjected to chemical adsorption, then the inert gas is purged to discharge unadsorbed gas molecules or unreacted gas or reaction byproducts, then the second reaction gas and the surface of the substrate are subjected to chemical adsorption and purging again, and finally the cycle is repeated. The silicon source or the carbon source which is introduced in a pulse mode is equivalent to the first reaction gas and the second reaction gas for atomic layer deposition, and the silicon source and the carbon source are decomposed at high temperature to generate silicon atoms and carbon atoms after chemical adsorption; then, in the case of relative excess, either a layer of silicon atoms is grown first and then a layer of carbon atoms is grown, or vice versa; and finally, growing the silicon carbide epitaxial layer on the silicon carbide substrate layer by layer along with the growth time and the continuously introduced pulse growth source.
In a specific embodiment, the ratio of the carbon source and the silicon source in step 2 is changed alternately at intervals of the pulse time by a pulse mode, which specifically includes the following 3 cases:
(1) keeping the flow of the carbon source unchanged, and changing the flow of the silicon source at intervals;
(2) keeping the flow of the silicon source unchanged, and changing the flow of the carbon source at intervals;
(3) the flow rates of the silicon source and the carbon source are alternately changed at intervals.
The flow ratio of the silicon source and the carbon source, namely the ratio of C/Si, is controlled within a reasonable range so as to obtain better surface appearance and lower defect density.
When the growth of the silicon carbide epitaxial layer is finished, stopping introducing the silicon source, the carbon source and the HCl etching gas, and stopping introducing H 2 Cooling the sample in an atmosphere; after the reaction chamber is cooled, the reaction chamber is vacuumized again to 10 DEG -4 Repeatedly replacing with Torr or argon, and finally increasing the pressure in the reaction chamber to atmospheric pressure to take out the silicon carbide epitaxial wafer. In the examples of the present application, the growth rate of the silicon carbide epitaxial layer is 60 to 100 μm/h.
The embodiment of the application also provides a silicon carbide epitaxial structure, and the silicon carbide epitaxial structure is manufactured by adopting the pulse type growth method of the silicon carbide epitaxial structure. The thickness range of the silicon carbide epitaxial layer is 1-100 mu m, and the thickness uniformity is more than 97%. The silicon carbide epitaxial structure can be applied to SiC devices.
Example 1
Considering that the variables of the three cases only have the flow of the growth source, the embodiment of the application selects the case (2) as an embodiment to specifically illustrate the invention, and the growth process is shown in fig. 1; the invention is not limited to the contents of the following examples, but other examples are readily available by replacing variables.
(1) Providing edge<11-20>A silicon carbide substrate with an off-axis direction (0001) of an off-angle of 2-8 degrees comprises a 4-inch SiC substrate, an RCA standard cleaning process is carried out on the SiC substrate for removing pollutants, damaged layers and oxide layers on the surface of the substrate, and the used solution comprises: concentrated sulfuric acid, ammonia water, concentrated hydrochloric acid, hydrogen peroxide, hydrofluoric acid, absolute ethyl alcohol and acetone; after cleaning, the reaction chamber is placed on a susceptor and placed in a horizontal hot-wall CVD reaction chamber, and then the reaction chamber is vacuumized to 10 DEG -4 The Torr is less.
(2) Setting the pressure of the reaction chamber to be 30-150 Torr, and respectively introducing 5-100L/min of H into the reaction chamber 2 And 5-100 mL/min of HCl, and starting heating; after the growth temperature of 1650 ℃ in the reaction chamber is reached, SiH is added from t0 4 Introducing at a flow rate of 1-10 mL/min, and starting in-situ etching treatment; at this time, SiH 4 Relative to H 2 Proportion of carrier gas is 10 -2 Volume percent; the whole etching process is controlled within 30-60 minutes.
(3) From time t1, SiH is adjusted 4 The flow rate is 10-100 mL/min; simultaneously introducing 10-100 mL/min of C into the reaction chamber 3 H 8 (ii) a Wherein, two adjacent delta t times C 3 H 8 With different flow rates, e.g. C during t 1-t 1+ Δ t 3 H 8 The flow rate is 20mL/min (indicated as "high pulse"), and C is within the time of t1+ delta t-t 1+2 delta t 3 H 8 A flow rate of 5mL/min (indicated as "low pulse"), or vice versa; and then repeatedly switching C for the remaining growth time 3 H 8 Until the growth is finished, the delta t time can be controlled within 1 minute to 1 hour.
The switching of the traffic is not done instantaneously in view of the actual situation, but like in fig. 2 with a falling edge and a rising edge; therefore, the C/Si ratio in the reaction chamber also varies within a certain range, in accordance withAccording to the flow rate value set above, the C/Si ratio of the present embodiment is 0.5-2, which can satisfy the above-mentioned relative excess, i.e. C 3 H 8 At the time of the high pulse, the atmosphere of the surface of the SiC substrate is C-rich, the C/Si ratio is greater than 1 and less than or equal to 2, that is, C 3 H 8 And SiH 4 Is greater than 1:3 and not more than 2: 3; and C 3 H 8 At low pulse, it is Si-rich, the C/Si ratio is greater than or equal to 0.5 and less than 1, i.e. C 3 H 8 And SiH 4 The flow ratio of (1) or more: 6 and less than 1: 3. In particular, e.g. retention of SiH 4 Flow rate 30mL/min, high pulse C 3 H 8 The flow rate is 20mL/min, when C/Si is 2, and C is in low pulse 3 H 8 The flow rate was 5mL/min, and C/Si was 0.5. Meanwhile, in order to avoid the situation that the surface of the SiC substrate is graphitized within the first delta t time, a small amount of SiH is introduced in the in-situ etching stage 4 The method not only can effectively inhibit the generation of large steps on the surface, but also can avoid the high surface roughness and defect density of the SiC epitaxial layer caused by the over-high C/Si ratio.
At time t2, SiH is turned off 4 、C 3 H 8 And the switch of HCl into the reaction chamber stops growing. At H 2 Cooling the reaction chamber in a flow atmosphere; after the reaction chamber was cooled (time t 3), the reaction chamber was again evacuated to a high vacuum or repeatedly replaced with argon gas, and finally filled to atmospheric pressure, and the silicon carbide epitaxial wafer was taken out, and the Raman result thereof is shown in FIG. 3 where 203.7cm of the Raman spectrum existed -1 FTA mode at peak, 776.6cm -1 FTO mode sum at peak 964.3cm -1 Comparing the FLO model on the peak value with a standard map, the finally obtained silicon carbide is 4H-SiC with higher purity.
Example 2
Example 2 of the present application differs from example 1 in that a 6-inch silicon carbide substrate is provided in step (1).
Comparative example
The method takes a typical CVD epitaxial growth process as shown in FIG. 2 as a comparative example, and comprises an in-situ etching part and a main epitaxial growth part, wherein the flow rates of a carrier gas, an etching gas and a reaction gas are all fixed in the epitaxial growth process, and a silicon source and a carbon source are continuously introduced into a reaction chamber at a constant flow rate at the same time, and the method specifically comprises the following steps:
(1) off-axis (0001) SiC substrates with several degrees off-angle orientation <11-20>, including 2-8 inch conductive and semi-insulating SiC substrates, were selected, standard cleaned, and placed on a susceptor in a hot wall CVD chamber.
(2) The reaction chamber was evacuated to 10 deg.f -4 Torr, then H was introduced at time t0 2 And HCl mixed gas, and heating is started; h 2 Is used as carrier gas, is continuously introduced in the whole epitaxial growth process, uses HCl as etching gas, realizes the effect of in-situ etching together with H2, and is beneficial to obtaining a clean SiC surface without silicon drops. H 2 The flow rate is set to 5 to 100L/min, and the HCl flow rate is set to 5 to 100 mL/min.
(3) When the temperature in the reaction chamber reaches the epitaxial growth temperature, the temperature is maintained from t1 to t2, and in-situ etching is performed in order to remove the sub-surface damage of the substrate and obtain a regular surface step structure.
(4) Maintaining the temperature, pressure and H in the reaction chamber 2 The flow rate of the/HCl gas mixture is constant, and a silicon source and a carbon source, such as monosilane (SiH), are introduced at time t2 4 ) And propane (C) 3 H 8 ) (ii) a And controlling the flow ratio of the silicon source and the carbon source, namely the ratio of C/Si, within a reasonable range, and epitaxially growing a silicon carbide epitaxial layer by using the fixed flow ratio of the silicon source and the carbon source.
The results of the growth thickness and uniformity of the silicon carbide epitaxial layers of examples 1 and 2 of the present application are shown in table 1.
TABLE 1
As can be seen from table 1, the silicon carbide epitaxial layer grown by the pulse growth method according to the embodiment of the present disclosure can achieve a larger thickness and higher uniformity in different dimensions, which is beneficial to improving the yield and reliability of SiC devices.
In addition, 10 μm is the thickness most commonly produced in SiC epitaxy. The time required for growing the silicon carbide epitaxial layer by the conventional method in the comparative example was 1 hour, the growth rate was 10 μm/h, and the uniformity was 95%. The growth rate of the silicon carbide epitaxial layers grown by the methods of example 1 and example 2 was 80 μm/h, and the uniformity was 97% or more. Therefore, the silicon carbide epitaxial wafer has higher uniformity and higher growth speed, and is beneficial to the quick mass production of the silicon carbide epitaxial wafer.
While the present invention has been described with reference to the preferred embodiments, it will be understood by those skilled in the art that various changes and modifications may be made without departing from the spirit and scope of the invention as defined by the appended claims. Therefore, the protection scope of the present application shall be subject to the protection scope of the claims.
Claims (15)
1. A pulse type growth method of a silicon carbide epitaxial structure is characterized by comprising the following steps:
1) providing a silicon carbide substrate, wherein the silicon carbide substrate is provided with a plurality of off-axes (0001) with off-angles pointing to <11-20 >;
2) and placing the silicon carbide substrate into a reaction chamber, introducing a carbon source and a silicon source into the reaction chamber when the growth condition of the silicon carbide epitaxial layer is achieved in the reaction chamber, and alternately changing the proportion of the carbon source and the silicon source at intervals of pulse time in a pulse mode to epitaxially grow the silicon carbide epitaxial layer under the Si-rich and C-rich atmosphere in a first time period and a second time period which are adjacent to each other.
2. The pulsed growth method of a silicon carbide epitaxial structure according to claim 1, characterized in that the C/Si ratio in a Si-rich atmosphere is greater than or equal to 0.5 and less than 1, and the C/Si ratio in a C-rich atmosphere is greater than 1 and less than or equal to 2.
3. The pulsed growth method of silicon carbide epitaxial structure of claim 1, wherein the ratio of the carbon source and the silicon source is changed in step 2 by changing the flow rates of the carbon source and the silicon source into the reaction chamber.
4. The pulsed growth method of silicon carbide epitaxial structure according to claim 1, characterized in that the step 2 of varying the ratio of the carbon source and the silicon source alternately at pulse intervals by means of pulses comprises:
keeping the flow rate of the carbon source unchanged, and changing the flow rate of the silicon source at intervals; or
Keeping the flow rate of the silicon source unchanged, and changing the flow rate of the carbon source at intervals; or
And alternately changing the flow rates of the silicon source and the carbon source at intervals.
5. The pulsed growth method of silicon carbide epitaxial structure of claim 1, wherein the silicon source comprises silane and chlorosilane, wherein silane comprises monosilane and chlorosilane comprises trichlorosilane, dichlorosilane or silicon tetrachloride; the carbon source includes ethylene and propane.
6. The pulsed growth method of silicon carbide epitaxial structure according to claim 5, characterized in that the growth conditions of the silicon carbide epitaxial layer inside the reaction chamber are reached before comprising the following steps:
evacuating the reaction chamber to 10 deg.C -4 Torr；
Introduction of H 2 And HCl mixed gas is used for enabling the reaction chamber to reach a certain pressure, the temperature is raised to the temperature required by etching, and H is controlled 2 And carrying out in-situ etching on the silicon carbide substrate by the flow of HCl so as to remove the sub-surface loss of the silicon carbide substrate and obtain a regular surface step structure.
7. The pulsed growth method of the silicon carbide epitaxial structure of claim 6, wherein the pressure in the reaction chamber is 30-150 Torr during the in-situ etching, the temperature required for the etching is 1650 ℃, the time of the in-situ etching is 30-60 min, and silane with the flow rate of 1-10 mL/min is also introduced.
8. The pulsed growth method of silicon carbide epitaxial structure according to claim 1, characterized in that the growth conditions in step 2 include any one or more of epitaxial growth temperature, epitaxial growth pressure, flow rates of carrier gas and etching gas, and flow rate of dopant source, and when the growth conditions of silicon carbide epitaxial layer are reached in the reaction chamber, the epitaxial growth temperature, epitaxial growth pressure, flow rates of carrier gas and etching gas are kept constant.
9. The pulsed growth method of a silicon carbide epitaxial structure according to claim 1, characterized in that the pulse time is 1-60 min.
10. A method for pulsed growth of silicon carbide epitaxial structures according to claim 1, characterized in that the reaction chamber is one of a horizontal hot-wall CVD reaction chamber, a hot-wall or warm-wall planetary CVD reaction chamber, a vertical hot-wall CVD reaction chamber.
11. The pulsed growth method of silicon carbide epitaxial structure according to claim 1, wherein the silicon carbide substrate comprises 3-8 inch conductive and semi-insulating silicon carbide substrate, and the off angle on the silicon carbide substrate is 2-8 ° in the <11-20> direction.
12. The pulsed growth method of a silicon carbide epitaxial structure according to claim 1, characterized in that the growth rate of the silicon carbide epitaxial layer is 60-100 μm/h.
13. A silicon carbide epitaxial structure, characterized in that it is produced by a pulsed growth method of a silicon carbide epitaxial structure according to any one of claims 1 to 12.
14. The silicon carbide epitaxial structure of claim 13 wherein the silicon carbide epitaxial layer has a thickness in the range of 1 to 100 μm and a thickness uniformity of greater than 97%.
15. Use of a silicon carbide epitaxial structure according to any one of claims 13 to 14 in a SiC device.
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