Preparation method of silicon carbide epitaxial wafer and silicon carbide epitaxial growth equipment

Abstract

The invention provides a preparation method of a silicon carbide epitaxial wafer and silicon carbide epitaxial growth equipment. The method comprises the following steps: placing a silicon carbide substrate on a tray; a doping source gas path is used for conveying doping source gas to the gas source mixing area, a growth source gas path is used for conveying growth source gas to the gas source mixing area, the doping source gas comprises RxNHy, x and y are natural numbers, x + y = 3, R represents a group or an element, the temperature of the gas source mixing area is not smaller than a threshold temperature, and the growth source gas path is used for conveying growth source gas to the growth source mixing area. The threshold temperature characterizes a minimum temperature required for parasite production without SiNz (z represents a ratio between Si and N); and under the condition that the growth source gas and the doping source gas reach the gas source reaction region, controlling the growth source gas and the doping source gas to react so as to generate a silicon carbide epitaxial wafer on the surface, far away from the tray, of the silicon carbide substrate. The problem that in the prior art, due to the fact that the doping concentration of the n-type silicon carbide epitaxial layer is not uniform and the doping memory effect is high, the device performance is poor is solved.

Description

Technical Field

[0001] The present application relates to the field of SiC epitaxial technology, and in particular to a method for preparing a silicon carbide epitaxial wafer, a silicon carbide epitaxial growth device and a silicon carbide epitaxial wafer. Background Art

[0002] As a wide bandgap semiconductor material, silicon carbide has a series of superior properties such as large bandgap width, high breakdown electric field, high thermal conductivity and fast saturation drift velocity. It has broad application prospects in high-voltage, high-power, high-temperature and high-frequency applications, and is expected to solve the bottleneck faced by the development of silicon power semiconductor devices. In view of the needs of designing epitaxial layer structure and performance parameters of high-voltage SiC power devices, the preparation of high-quality lightly doped N epitaxial layers is crucial. Nitrogen is currently mainly used as a doping source in industry. However, due to the very high triple bond energy between N atoms in nitrogen and the difficulty in controlling the thermal decomposition process, it is difficult to achieve a uniform distribution of nitrogen partial pressure on the substrate surface; in addition, the nitrogen doping efficiency is low, and some nitrogen will be adsorbed by the reaction chamber deposits, so it has a strong memory effect, resulting in poor process repeatability. Therefore, in order to achieve low background doping concentration and further improve the uniformity of epitaxial layer doping concentration to reduce device performance discreteness and improve device reliability, selecting a more suitable n-doping source and mastering its growth process are key issues that urgently need to be broken through in silicon carbide epitaxy. Summary of the invention

[0003] The main purpose of the present application is to provide a method for preparing a silicon carbide epitaxial wafer, a silicon carbide epitaxial growth device and a silicon carbide epitaxial wafer, so as to solve the problems in the prior art of uneven doping concentration of an n-type silicon carbide epitaxial layer and strong doping memory effect leading to poor device performance.

[0004] In order to achieve the above-mentioned object, according to one aspect of the present application, a method for preparing a silicon carbide epitaxial wafer is provided, comprising: placing a silicon carbide substrate on a tray; delivering a doping source gas to a gas source mixing area by using a doping source gas path, and delivering a growth source gas to the gas source mixing area by using a growth source gas path, wherein the doping source gas comprises R x NH y , x and y are both natural numbers, x+y=3, R represents a group or element, the growth source gas includes at least a carbon source and a silicon source, the temperature of the gas source mixing zone is not less than a threshold temperature, and the threshold temperature represents the absence of SiN z(z represents the ratio between Si and N) the minimum temperature required for parasite generation; when the growth source gas and the doping source gas reach the gas source reaction zone, the growth source gas is controlled to react with the doping source gas to generate a silicon carbide epitaxial wafer on the surface of the silicon carbide substrate away from the tray, the temperature of the gas source reaction zone is not less than the growth temperature, and the growth temperature represents the minimum temperature required to generate the silicon carbide epitaxial wafer.

[0005] Optionally, after placing the silicon carbide substrate on the tray and before controlling the growth source gas to react with the doping source gas, the method further comprises: controlling the tray to rotate by using gas delivered to the bottom of the tray by a flotation gas path.

[0006] In order to achieve the above-mentioned purpose, according to one aspect of the present application, a silicon carbide epitaxial growth device is provided, and the silicon carbide epitaxial growth device is used for the preparation method of the silicon carbide epitaxial wafer, and the silicon carbide epitaxial growth device comprises: an air inlet channel, at least comprising a doping source gas path and a growth source gas path, the doping source gas path is used to convey the doping source gas, and the growth source gas path is used to convey the growth source gas; a tray, used to place the silicon carbide substrate; a gas source mixing zone, arranged at the outlet of the doping source gas path and the outlet of the growth source gas path, the doping source gas path is used to convey the doping source gas to the gas source mixing zone, the growth source gas path is used to convey the growth source gas to the gas source mixing zone, the temperature of the gas source mixing zone is not less than a threshold temperature, and the threshold temperature represents the absence of SiN z (z represents the ratio between Si and N) the minimum temperature required for parasite generation; a gas source reaction zone, which is arranged on the side of the silicon carbide substrate away from the tray, the temperature of the gas source reaction zone is not less than the growth temperature, and the growth temperature represents the minimum temperature required for generating a silicon carbide epitaxial wafer.

[0007] Optionally, the silicon carbide epitaxial growth equipment also includes: a first heating element, which is arranged on a side of the gas source reaction zone away from the tray, and the first heating element and the doping source gas path are arranged on the same side of the gas source reaction zone, and the first heating element is used to heat the gas source reaction zone so that the temperature of the gas source reaction zone is not less than the growth temperature.

[0008] Optionally, the silicon carbide epitaxial growth equipment further includes: a second heating element, the tray is arranged on a portion of the surface of the second heating element close to the gas source reaction zone, and the second heating element is used to heat the tray.

[0009] Optionally, the outlet of the doping source gas path is arranged in the first heating element, the gas source mixing zone and the gas source reaction zone are located in the same area, and the temperature of the gas source mixing zone is not less than the growth temperature.

[0010] Optionally, the outlet of the doping source gas path is arranged on one side of the first heating element, and the gas source mixing zone and the gas source reaction zone are located in different areas.

[0011] Optionally, the silicon carbide epitaxial growth equipment also includes: a spray port, which is arranged on a partial surface of the first heating element close to the gas source reaction zone, the spray port includes a plurality of spaced gas outlets arranged along its axial direction, and the outlet of the doping source gas path is arranged in the spray port.

[0012] Optionally, the air inlet channel also includes: a flotation gas path, which is arranged on a side of the growth source gas path away from the doping source gas path, and the outlet of the flotation gas path is arranged in the second heating element. The flotation gas path is used to transport gas to the bottom of the tray to rotate the tray.

[0013] Optionally, the silicon carbide epitaxial growth equipment further includes: a first heat insulating member, disposed on a surface of the first heating member away from the gas source reaction zone.

[0014] Optionally, the silicon carbide epitaxial growth equipment further includes: a second heat insulating member, disposed on a surface of the second heating member away from the gas source reaction zone.

[0015] Optionally, the silicon carbide epitaxial growth equipment further includes: a quartz cover, and the gas inlet channel, the tray, the gas source mixing zone and the gas source reaction zone are all arranged in the quartz cover.

[0016] According to another aspect of the present application, a silicon carbide epitaxial wafer is provided, wherein the silicon carbide epitaxial wafer is prepared by using the method for preparing the silicon carbide epitaxial wafer.

[0017] By applying the technical solution of the present application, a silicon carbide substrate is first placed on a tray, and then a doping source gas is transported to a gas source mixing area by a doping source gas path, and a growth source gas is transported to a gas source mixing area by a growth source gas path, and finally when the growth source gas and the doping source gas reach a gas source reaction area, the growth source gas is controlled to react with the doping source gas to generate a silicon carbide epitaxial wafer on a surface of the silicon carbide substrate away from the tray, wherein the doping source gas includes R x NH y , the temperature of the gas source mixing zone is not less than the threshold temperature. Compared with the problems of uneven doping concentration of n-type silicon carbide epitaxial layer and strong doping memory effect leading to poor device performance in the prior art, the present application selects R without high bond energy nitrogen-nitrogen double bonds and nitrogen-nitrogen triple bonds. x NH yAs the n-doping source, the low thermal decomposition energy can greatly reduce the memory effect and improve the problem of uneven nitrogen partial pressure distribution on the wafer surface, thereby achieving the effect of improving the in-plane uniformity of n-doping of silicon carbide epitaxial wafers; in addition, the doping source gas and the growth source gas are transported separately, and the gas source mixing zone ensures that there is no SiN z The temperature range of parasite growth ensures that there is no NH4Cl solid product and high stability nitrogen silicon parasite SiN z The generation of defects reduces the defect density of the prepared n-type epitaxial wafer, thereby ensuring better performance of the device. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] The drawings constituting part of the present application are used to provide a further understanding of the present application. The exemplary embodiments and descriptions of the present application are used to explain the present application and do not constitute an improper limitation on the present application. In the drawings:

[0019] Figure 1 A schematic flow chart of a method for preparing a silicon carbide epitaxial wafer according to an embodiment of the present application is shown;

[0020] Figure 2 A schematic structural diagram of a silicon carbide epitaxial growth device provided according to an embodiment of the present application is shown;

[0021] Figure 3 A schematic structural diagram of another silicon carbide epitaxial growth device provided according to an embodiment of the present application is shown;

[0022] Figure 4 A partial structural schematic diagram of a silicon carbide epitaxial growth device provided according to an embodiment of the present application is shown;

[0023] Figure 5 A partial structural schematic diagram of another silicon carbide epitaxial growth device provided according to an embodiment of the present application is shown.

[0024] The above drawings include the following reference numerals:

[0025] 10. Air inlet channel; 11. Tray; 13. Gas source mixing zone; 101. Doping source gas path; 17. First outlet; 102. Growth source gas path; 14. Gas source reaction zone; 15. First heating element; 16. Second heating element; 18. Spray port; 181. Gas outlet; 103. Air flotation gas path; 19. First thermal insulation element; 20. Second thermal insulation element; 21. Quartz cover. DETAILED DESCRIPTION

[0026] It should be noted that the following detailed descriptions are illustrative and are intended to provide further explanation of the present application. Unless otherwise specified, all technical and scientific terms used herein have the same meanings as those commonly understood by those skilled in the art to which the present application belongs.

[0027] It should be noted that the terms used herein are only for describing specific embodiments and are not intended to limit the exemplary embodiments according to the present application. As used herein, unless the context clearly indicates otherwise, the singular form is also intended to include the plural form. In addition, it should be understood that when the terms "comprise" and / or "include" are used in this specification, it indicates the presence of features, steps, operations, devices, components and / or combinations thereof.

[0028] It should be understood that when an element (such as a layer, film, region, or substrate) is described as being "on" another element, the element may be directly on the other element, or there may be intermediate elements. Moreover, in the specification and claims, when it is described that an element is "connected" to another element, the element may be "directly connected" to the other element, or "connected" to the other element through a third element.

[0029] As introduced in the background technology, the doping concentration of the n-type silicon carbide epitaxial layer in the prior art is uneven. To solve the above problem, the embodiments of the present application provide a method for preparing a silicon carbide epitaxial wafer, a silicon carbide epitaxial growth device and a silicon carbide epitaxial wafer.

[0030] The technical solutions in the embodiments of the present invention will be described clearly and completely below in conjunction with the accompanying drawings in the embodiments of the present invention.

[0031] Figure 1 1 is a flow chart of a method for preparing a silicon carbide epitaxial wafer according to an embodiment of the present application. Figure 1 As shown, the method comprises the following steps:

[0032] Step S101, placing a silicon carbide substrate on a tray;

[0033] Step S102, using a doping source gas path to deliver a doping source gas to a gas source mixing area, and using a growth source gas path to deliver a growth source gas to the gas source mixing area, wherein the doping source gas includes R x NH y , x and y are both natural numbers, x+y=3, R represents a group or element, the above-mentioned growth source gas includes at least a carbon source and a silicon source, and the temperature of the above-mentioned gas source mixing zone is not less than a threshold temperature, and the above-mentioned threshold temperature represents the absence of SiN z (z represents the ratio between Si and N) The minimum temperature required for parasite generation;

[0034] Step S103, when the above-mentioned growth source gas and the above-mentioned doping source gas reach the gas source reaction zone, the above-mentioned growth source gas and the above-mentioned doping source gas are controlled to react so as to generate a silicon carbide epitaxial wafer on the surface of the above-mentioned silicon carbide substrate away from the above-mentioned tray, and the temperature of the above-mentioned gas source reaction zone is not less than the growth temperature, and the above-mentioned growth temperature represents the minimum temperature required to generate the above-mentioned silicon carbide epitaxial wafer.

[0035] According to this embodiment, the silicon carbide substrate is first placed on the tray, and then the doping source gas is transported to the gas source mixing area by the doping source gas path, and the growth source gas is transported to the gas source mixing area by the growth source gas path, and finally when the growth source gas and the doping source gas reach the gas source reaction area, the growth source gas is controlled to react with the doping source gas to form a silicon carbide epitaxial wafer on the surface of the silicon carbide substrate away from the tray, wherein the doping source gas includes R x NH y , the temperature of the gas source mixing zone is not less than the threshold temperature. Compared with the problems of uneven doping concentration of n-type silicon carbide epitaxial layer and strong doping memory effect leading to poor device performance in the prior art, the present application selects R without high bond energy nitrogen-nitrogen double bonds and nitrogen-nitrogen triple bonds. x NH y As the n-doping source, the low thermal decomposition energy can greatly reduce the memory effect and improve the problem of uneven nitrogen partial pressure distribution on the wafer surface, thereby achieving the effect of improving the in-plane uniformity of n-doping of silicon carbide epitaxial wafers; in addition, the doping source gas and the growth source gas are transported separately, and the gas source mixing zone ensures that there is no SiN z The temperature range of parasite growth ensures that there is no NH4Cl solid product and high stability nitrogen silicon parasite SiN z The generation of defects reduces the defect density of the prepared n-type epitaxial wafer, thereby ensuring better performance of the device.

[0036] Specifically, R x NH y In the formula, R can be any substituent group such as CH3, C2H4, C2H5, C3H7, CO, C6H5, or any element such as Si, C, In, etc. For example, when x=0 and y=3, R x NH y is NH3; when x=1, y=2, R is CH3, R x NH y is CH3NH2; when x=1, y=2, R is CO, R x NH y is CONH2; when x=2, y=1, R is C6H5, R x NH y is (C6H5)2NH; when x=3, y=0, R is C5H5, R xNH y is (C5H5)3N; when x=1, y=2, R is Si, R x NH y It is SiNH2.

[0037] Specifically, SiN z It is an amorphous material whose properties depend on the ratio of Si to N, that is, the value of z.

[0038] Specifically, the threshold temperature is the temperature at which the thermodynamically stable phase is pure SiC. Pure SiC is different from silicon carbide epitaxial wafers (the ratio of Si to C and the crystal structure of the two are different).

[0039] It should be noted that choosing R x NH y (x and y are both natural numbers, x+y=3, R represents a group or element) as an n-doping source because such molecules contain doping atoms N but do not have high-energy nitrogen-nitrogen double bonds and nitrogen-nitrogen triple bonds, and are effective dopants for preparing high-quality n-type SiC epitaxial wafers. However, further research found that the actual process mainly has the following problems: 1) Generation of NH4C1-type solid products: In view of the needs of SiC thick epitaxy, a chlorine-based rapid epitaxy method is usually used to grow n-doped epitaxial layers. At room temperature, chlorine-based gases mixed with ammonia or its hydrocarbon-based substitutes will generate NH4C1-type solid products and adhere to the mass flow meter and process pipelines, causing blockage. Among them, the sublimation temperature of NH4C1 solid products is 338°C, and the melting point of monomethylamine hydrochloride is 220-230°C. This means that in order to avoid the occurrence of this problem, it is necessary to at least ensure that the mixing temperature of this type of doping source and the growth source gas is greater than the decomposition temperature; 2) High stability SiN z Generation: Ammonia or its hydrocarbon substituents are highly reactive and will react with silicon compounds to generate nitrogen-silicon compounds. These substances have excellent thermal stability and can remain stable under high temperature conditions. This means that once these substances are generated, they cannot be decomposed and eliminated. Therefore, we need to eliminate the generation of these substances from the beginning. Since the content of ammonia or its hydrocarbon substituents as doping sources is generally less than 1 / 10 of the C source gas flow rate, based on the C / Si / N / H phase diagram obtained by thermodynamic calculation in the reference literature, it can be seen that at this time, if the mixing temperature is greater than 800K, the thermodynamically stable product is pure SiC, without SiN z Impurities, which means that in order to avoid the occurrence of this problem, it is necessary to at least ensure that the mixing temperature of this type of doping source and growth source gas is higher than the temperature at which the thermodynamically stable phase is a nitrogen silicon compound, to ensure that the thermodynamically stable product at this time is pure SiC.

[0040] Specifically, the growth source gas also includes a chlorine-based gas. x NH y(x and y are both natural numbers, x+y=3, R represents a group or element) is transported separately from the growth source gas (carbon source / silicon source / chlorine-based gas) and mixed with the growth source gas within the temperature range where the thermodynamically stable phase is unique and is SiC (i.e., the threshold temperature) to prepare high-quality n-type silicon carbide epitaxial wafers.

[0041] In the embodiment of the present application, the threshold temperature is 520°C, and the growth temperature is 1000°C-1650°C.

[0042] In an optional solution, after placing the silicon carbide substrate on the tray and before controlling the growth source gas to react with the doping source gas, the method further includes: controlling the tray to rotate by using the gas delivered to the bottom of the tray by the flotation gas path. In this embodiment, by controlling the tray to rotate, the silicon carbide substrate is driven to rotate, further ensuring that the uniformity of n-doping of the obtained silicon carbide epitaxial wafer is good.

[0043] The present application also provides a silicon carbide epitaxial growth device, which is used in the above-mentioned method for preparing the silicon carbide epitaxial wafer. Figures 2 to 5 As shown, the above silicon carbide epitaxial growth equipment includes:

[0044] The gas inlet channel 10 at least comprises a doping source gas path 101 and a growth source gas path 102, wherein the doping source gas path 101 is used to transport the doping source gas, and the growth source gas path 102 is used to transport the growth source gas;

[0045] A tray 11, used for placing a silicon carbide substrate (not shown);

[0046] The gas source mixing zone 13 is arranged at the outlet (i.e., the first outlet 17) of the doping source gas path 101 and the outlet of the growth source gas path 102. The doping source gas path 101 is used to transport the doping source gas to the gas source mixing zone 13. The growth source gas path 102 is used to transport the growth source gas to the gas source mixing zone 13. The temperature of the gas source mixing zone 13 is not less than the threshold temperature. The threshold temperature indicates that there is no SiN z (z represents the ratio between Si and N) The minimum temperature required for parasite generation;

[0047] The gas source reaction zone 14 is disposed on a side of the silicon carbide substrate away from the tray 11 . The temperature of the gas source reaction zone 14 is not less than the growth temperature. The growth temperature represents the minimum temperature required to generate a silicon carbide epitaxial wafer.

[0048] Through the above embodiments, the silicon carbide epitaxial growth equipment includes an air inlet channel, a tray, a gas source mixing zone and a gas source reaction zone, wherein the air inlet channel includes at least a doping source gas path and a growth source gas path, the doping source gas path is used to transport the doping source gas to the gas source mixing zone, the growth source gas path is used to transport the growth source gas to the gas source mixing zone, and the temperature of the gas source mixing zone is not less than the threshold temperature. Compared with the problems of uneven doping concentration of n-type silicon carbide epitaxial layer and strong doping memory effect leading to poor device performance in the prior art, the present application separately transports the doping source gas and the growth source gas through the doping source gas path and the growth source gas path, and the gas source mixing zone ensures that the doping source gas and the growth source gas are not uniform in the absence of SiN. z The temperature range of parasite growth ensures that there is no NH4Cl solid product and high stability nitrogen silicon parasite SiN z The generation of defects can reduce the defect density of the prepared n-type silicon carbide epitaxial wafer, ensure the high quality of the silicon carbide epitaxial wafer, and thus ensure the good performance of the device.

[0049] In one alternative, Figures 2 to 5 As shown, the silicon carbide epitaxial growth device further includes: a first heating element 15, which is arranged on a side of the gas source reaction zone 14 away from the tray 11, and the first heating element 15 and the doping source gas path 101 are arranged on the same side of the gas source reaction zone 14, and the first heating element 15 is used to heat the gas source reaction zone 14 so that the temperature of the gas source reaction zone 14 is not less than the growth temperature. In this embodiment, the first heating element is used to heat the gas source reaction zone, which further ensures that the doping uniformity of the obtained n-type silicon carbide epitaxial wafer is good, thereby further ensuring that the quality of the silicon carbide epitaxial wafer is high.

[0050] In other embodiments, Figures 2 to 5 As shown, the silicon carbide epitaxial growth device further includes: a second heating element 16, the tray 11 is arranged on a portion of the surface of the second heating element 16 close to the gas source reaction zone 14, and the second heating element 16 is used to heat the tray 11. In this embodiment, the second heating element is used to heat the tray, thereby ensuring that the temperature of the bottom surface of the silicon carbide substrate is also high, ensuring that the temperature difference between the upper and lower surfaces of the silicon carbide substrate is small, and further ensuring that the quality of the obtained silicon carbide epitaxial wafer is high.

[0051] Specifically, the first heating element and the second heating element are both dense graphite elements, the outside of the dense graphite elements is surrounded by coils, alternating current is passed through the coils, and electromagnetic induction is used for heating.

[0052] Some other options, such as Figure 2 , Figure 4 and Figure 5As shown, the outlet of the doping source gas circuit 101 (i.e., the first outlet 17) is arranged in the first heating element 15, the gas source mixing zone 13 and the gas source reaction zone 14 are located in the same area, and the temperature of the gas source mixing zone 13 is not less than the growth temperature. In this embodiment, the outlet of the doping source gas circuit is arranged in the first heating element, which ensures that the outlet temperature of the doping source gas circuit is relatively high, thereby further ensuring that the doping source gas and the growth source gas can react well to form silicon carbide epitaxial wafers, further avoiding the absence of NH4Cl-based solid products and high-stability nitrogen-silicon parasites SiN z The generation of silicon carbide epitaxial wafers further ensures the high quality of the obtained silicon carbide epitaxial wafers.

[0053] Specifically, when the outlet of the doping source gas path is disposed in the first heating element, an anti-corrosion coating is disposed around the outlet of the doping source gas path to prevent R x NH y (x and y are both natural numbers, x+y=3, R represents a group or an element) the corrosion of the above-mentioned first heating element by the substance.

[0054] Specifically, Figure 4 (b) Figure 4 (a) The corresponding top view.

[0055] In some other options, such as Figure 3 As shown, the outlet of the doping source gas path 101 is disposed at one side of the first heating element 15 , and the gas source mixing zone 13 and the gas source reaction zone 14 are located in different areas.

[0056] In some exemplary embodiments, Figure 5 As shown, the silicon carbide epitaxial growth equipment further includes: a spray port 18, which is disposed on a portion of the surface of the first heating element 15 close to the gas source reaction zone (not shown), the spray port 18 includes a plurality of spaced gas outlets 181 arranged along its axial direction, and the outlet of the doping source gas path 101 (i.e., the first outlet 17) is disposed in the spray port 18.

[0057] Specifically, Figure 5 (b) Figure 5 (a) The corresponding top view.

[0058] Specifically, Figure 5 As shown, the outlet (ie, the first outlet 17 ) of the doping source gas path 101 completely overlaps with the spray port 18 , and the diameter of the spray port 18 is w.

[0059] Specifically, a spray port is provided on the bottom surface of the first heating element. The spray port is circular, and the diameter w of the spray port satisfies 0 < w < 1000 mm; preferably, 100 mm < w < 270 mm. The air outlet is circular, the number of air outlets is greater than or equal to 1, the diameter of the air outlet is greater than 0, and less than or equal to the diameter w of the spray port.

[0060] Specifically, by providing the spray port, gas vortices near the outlet of the doping source gas path can be suppressed, achieving a good effect of uniform gas mixing, and avoiding a large decrease in temperature near the outlet of the doping source gas path, thereby further suppressing the formation of solid products such as NH4Cl and parasitic silicon nitride SiN in the gas source mixing region. z in the gas source mixing region.

[0061] In some other exemplary embodiments, as Figures 2 to 5 shown, the above-mentioned intake passage 10 further includes: an air flotation gas path 103, which is arranged on the side of the above-mentioned growth source gas path 102 away from the above-mentioned doping source gas path 101. The outlet of the air flotation gas path 103 is arranged inside the above-mentioned second heating element 16. The air flotation gas path 103 is used to transport gas to the bottom of the above-mentioned tray 11 so that the above-mentioned tray 11 rotates. In this embodiment, the air flotation gas path is used to transport gas to the bottom of the tray so that the tray rotates, thereby driving the rotation of the silicon carbide substrate, further ensuring better uniformity of n-doping of the obtained silicon carbide epitaxial wafer.

[0062] Specifically, in the present application, the silicon carbide epitaxial growth equipment includes a growth chamber, a tray, and an intake pipeline. The intake pipeline has a doping source gas path, a growth source gas path, and an air flotation gas path. The doping source gas path is used to introduce a doping source gas R x NH y (both x and y are natural numbers, x + y = 3, and R represents a group or an element). The growth source gas path is used to introduce C-based gases (such as gases containing C atoms like propane, ethylene, methyltrichlorosilane, and methane), Si-based gases (such as gases containing Si atoms like silane, trichlorosilane, and methyltrichlorosilane), and other gases (such as hydrogen, hydrogen chloride, and argon) required for SiC epitaxial growth. The three types of gas path pipes are separated from each other, but each gas path pipe does not necessarily have to be a single pipe and can have multiple gas path pipes.

[0063] In still some other exemplary embodiments, as Figures 2 to 5 shown, the above-mentioned silicon carbide epitaxial growth equipment further includes: a first heat insulation member 19, which is arranged on the surface of the above-mentioned first heating element 15 away from the above-mentioned gas source reaction zone 14. In this embodiment, the first heat insulation member ensures that less heat generated by the first heating element is dissipated to the outside.

[0064] In other embodiments, as Figures 2 to 5As shown, the silicon carbide epitaxial growth device further includes: a second heat insulating member 20, which is disposed on the surface of the second heating member 16 away from the gas source reaction zone 14. In this embodiment, the second heat insulating member ensures that less heat is dissipated to the outside by the heat generated by the second heating member.

[0065] Specifically, the first thermal insulation member and the second thermal insulation member are thermal insulation graphite, and the thermal conductivity of thermal insulation graphite is very low.

[0066] In other embodiments, Figure 2 and Figure 3 As shown, the silicon carbide epitaxial growth device further includes: a quartz cover 21 , in which the gas inlet channel 10 , the tray 11 , the gas source mixing zone 13 and the gas source reaction zone 14 are all arranged.

[0067] The following will describe the method for preparing the silicon carbide epitaxial wafer of the present application in detail with reference to specific examples and comparative examples. Example 1 and Example 2 are examples of using the method for preparing the silicon carbide epitaxial wafer of the present application to prepare silicon carbide epitaxial wafers.

[0068] Example 1

[0069] The silicon carbide epitaxial growth equipment of the present application is used as SiC chemical vapor deposition equipment. The SiC epitaxial wafer growth source gas uses trichlorosilane and ethylene, which are introduced from the growth source gas path, and ammonia is selected as the n-doping source and introduced from the doping source gas path. The growth temperature is set to 1500°C, the pressure is set to 100mbar, the ammonia flow rate is 0.5sccm, and the SiC epitaxial layer is grown on the surface of the SiC substrate.

[0070] Comparative Example 1

[0071] Conventional horizontal SiC chemical vapor deposition equipment is used as SiC chemical vapor deposition equipment. Trichlorosilane and ethylene are used as the source gases for SiC epitaxial wafer growth, which are introduced from the growth source gas path. Ammonia is also selected as the n-doping source and is also introduced from the growth source gas path and directly mixed with the growth source gas. The growth temperature is set to 1500°C, the pressure is set to 100mbar, the ammonia flow rate is 0.5sccm, and SiC epitaxial wafers are grown on the surface of the SiC substrate. At this time, white ammonium chloride particles are found on the wall of the ventilation duct (i.e., the wall of the duct of the growth source gas path), and nitrogen silicon parasites are produced.

[0072] Comparative Example 2

[0073] The silicon carbide epitaxial growth equipment of the present application is used as SiC chemical vapor deposition equipment. Trichlorosilane and ethylene are used as the growth source gas for SiC epitaxial wafers, which are introduced from the growth source gas path, and nitrogen is selected as the n-doping source and introduced from the doping source gas path. The growth temperature is set to 1500°C, the pressure is set to 100mbar, the nitrogen flow rate is 80sccm, and SiC epitaxial wafers are grown on the surface of the SiC substrate. At this time, due to the difficulty in controlling the thermal decomposition of nitrogen, the distribution of nitrogen partial pressure on the surface of the substrate is uneven, and the in-plane uniformity of the surface doping concentration of the grown SiC epitaxial wafer is poor.

[0074] Example 2

[0075] The silicon carbide epitaxial growth equipment of the present application is used as SiC chemical vapor deposition equipment. Trichlorosilane and ethylene are used as the growth source gas for SiC epitaxial wafers, which are introduced from the growth source gas path. Ammonia is selected as the n-doping source and introduced from the doping source gas path. The gas is introduced from the outlet of the doping source gas path into the gas source mixing area to mix with the growth source gas. In addition, in order to solve the problems caused by uneven distribution of doping sources and nonlinear depletion, a small amount of ammonia can be appropriately added to the flotation gas path. At this time, the growth temperature is set to 1500°C, the pressure is 100mbar, and the ammonia flow rate is 0.5sccm, and SiC epitaxial wafers are grown on the surface of the SiC substrate.

[0076] In summary, in view of the problem that the nitrogen partial pressure distribution on the wafer surface is uneven due to the strong memory effect and difficult control of thermal decomposition of nitrogen using nitrogen as the n-doping source in the existing process, the present application selects R x NH y (x and y are both natural numbers, x+y=3, R represents a group or element) as the n-doping source gas, due to the low thermal decomposition energy, the memory effect can be greatly reduced and the problem of uneven distribution of nitrogen partial pressure on the wafer surface can be improved, thereby achieving the effect of improving the in-plane uniformity of n-doping of SiC epitaxial wafers. The effect of this invention can be illustrated by comparing the above embodiment 1 with the comparative example 2. Selecting R x NH y (x and y are both natural numbers, x+y=3, R represents a group or element) as n-doping source gas to manufacture silicon carbide epitaxial wafers, there are NH4Cl-based solid products and highly stable nitrogen-silicon parasites SiN zThe generation of nitrogen-free silicon parasites, combined with the previous analysis, shows that the temperature of the generation of nitrogen-free silicon parasites is higher than the decomposition temperature of NH4Cl-type solid products. Therefore, as long as the mixing temperature of the doping source gas and the growth source gas is at the temperature of the growth of nitrogen-free silicon parasites, the above two problems can be solved at the same time. Therefore, the present invention sets a separate doping source gas path, so that its outlet, that is, the mixing temperature of the two types of source gases (that is, the temperature of the gas source mixing zone), ensures that the thermodynamically stable phase is unique and is SiC (that is, the temperature is not less than the threshold temperature), thereby avoiding NH4Cl-type solid products and high-stability nitrogen silicon parasites SiN z The purpose of preparing n-type silicon carbide epitaxial wafers with low defect density and high doping uniformity is finally achieved. The effect of this invention can be illustrated by comparing the above embodiment 1 with comparative example 1.

[0077] The embodiment of the present application also provides a silicon carbide epitaxial wafer, and the silicon carbide epitaxial wafer is prepared by the above-mentioned method for preparing the silicon carbide epitaxial wafer.

[0078] In the above embodiment, the silicon carbide epitaxial wafer is prepared by a method for preparing a silicon carbide epitaxial wafer, wherein in the method for preparing a silicon carbide epitaxial wafer, a silicon carbide substrate is first placed on a tray, a doping source gas path is used to transport a doping source gas to a gas source mixing area, and a growth source gas path is used to transport a growth source gas to a gas source mixing area, and finally when the growth source gas and the doping source gas reach the gas source reaction area, the growth source gas is controlled to react with the doping source gas to generate a silicon carbide epitaxial wafer on a surface of the silicon carbide substrate away from the tray, wherein the doping source gas includes R x NH y , the temperature of the gas source mixing zone is not less than the threshold temperature. Compared with the problems of uneven doping concentration of n-type silicon carbide epitaxial layer and strong doping memory effect leading to poor device performance in the prior art, the present application selects R without high bond energy nitrogen-nitrogen double bonds and nitrogen-nitrogen triple bonds. x NH y As the n-doping source, the low thermal decomposition energy can greatly reduce the memory effect and improve the problem of uneven nitrogen partial pressure distribution on the wafer surface, thereby achieving the effect of improving the in-plane uniformity of n-doping of silicon carbide epitaxial wafers; in addition, the doping source gas and the growth source gas are transported separately, and the gas source mixing zone ensures that there is no SiN z The temperature range of parasite growth ensures that there is no NH4Cl solid product and high stability nitrogen silicon parasite SiN z The generation of defects reduces the defect density of the prepared n-type epitaxial wafer, thereby ensuring better performance of the device.

[0079] From the above description, it can be seen that the above embodiments of the present application achieve the following technical effects:

[0080] In the method for preparing a silicon carbide epitaxial wafer of the present application, a silicon carbide substrate is first placed on a tray, a doping source gas is then transported to a gas source mixing area using a doping source gas path, and a growth source gas is transported to a gas source mixing area using a growth source gas path, and finally when the growth source gas and the doping source gas reach a gas source reaction area, the growth source gas is controlled to react with the doping source gas to generate a silicon carbide epitaxial wafer on a surface of the silicon carbide substrate away from the tray, wherein the doping source gas includes R x NH y , the temperature of the gas source mixing zone is not less than the threshold temperature. Compared with the problems of uneven doping concentration of n-type silicon carbide epitaxial layer and strong doping memory effect leading to poor device performance in the prior art, the present application selects R without high bond energy nitrogen-nitrogen double bonds and nitrogen-nitrogen triple bonds. x NH y As the n-doping source, the low thermal decomposition energy can greatly reduce the memory effect and improve the problem of uneven nitrogen partial pressure distribution on the wafer surface, thereby achieving the effect of improving the in-plane uniformity of n-doping of silicon carbide epitaxial wafers; in addition, the doping source gas and the growth source gas are transported separately, and the gas source mixing zone ensures that there is no SiN z The temperature range of parasite growth ensures that there is no NH4Cl solid product and high stability nitrogen silicon parasite SiN z The generation of defects reduces the defect density of the prepared n-type epitaxial wafer, thereby ensuring better performance of the device.

[0081] The above description is only the preferred embodiment of the present application and is not intended to limit the present application. For those skilled in the art, the present application may have various modifications and variations. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present application shall be included in the protection scope of the present application.

Claims

1. A method for preparing a silicon carbide epitaxial wafer, characterized in that: include: placing the silicon carbide substrate on a tray; The doping source gas is transported to the gas source mixing area by using the doping source gas path, and the growth source gas is transported to the gas source mixing area by using the growth source gas path, wherein the doping source gas includes R x NH y , x and y are both natural numbers, x+y=3, R represents a group or element, the growth source gas includes at least a carbon source and a silicon source, the temperature of the gas source mixing zone is not less than a threshold temperature, and the threshold temperature represents the absence of SiN z The minimum temperature required for parasite generation, z represents SiN z The ratio between Si and N in When the growth source gas and the doping source gas reach the gas source reaction zone, the growth source gas and the doping source gas are controlled to react to generate a silicon carbide epitaxial wafer on the surface of the silicon carbide substrate away from the tray, and the temperature of the gas source reaction zone is not less than the growth temperature, and the growth temperature represents the minimum temperature required to generate the silicon carbide epitaxial wafer.

2. The method for preparing a silicon carbide epitaxial wafer according to claim 1, characterized in that: After placing the silicon carbide substrate on the tray and before controlling the growth source gas to react with the doping source gas, the method further includes: The tray is controlled to rotate by utilizing gas delivered to the bottom of the tray through an air flotation air path.

3. A silicon carbide epitaxial growth device, characterized in that: The silicon carbide epitaxial growth device is used in the method for preparing the silicon carbide epitaxial wafer according to claim 1 or 2, and the silicon carbide epitaxial growth device comprises: An air inlet channel at least comprising a doping source gas path and a growth source gas path, wherein the doping source gas path is used to transport the doping source gas, and the growth source gas path is used to transport the growth source gas; A tray for placing a silicon carbide substrate; A gas source mixing zone is provided at the outlet of the doping source gas path and the outlet of the growth source gas path, the doping source gas path is used to transport the doping source gas to the gas source mixing zone, the growth source gas path is used to transport the growth source gas to the gas source mixing zone, the temperature of the gas source mixing zone is not less than a threshold temperature, and the threshold temperature indicates that there is no SiN z The minimum temperature required for parasite generation, z represents SiN z The ratio between Si and N in A gas source reaction zone is arranged on a side of the silicon carbide substrate away from the tray, and a temperature of the gas source reaction zone is not less than a growth temperature, and the growth temperature represents a minimum temperature required to generate a silicon carbide epitaxial wafer.

4. The silicon carbide epitaxial growth device according to claim 3, characterized in that: The silicon carbide epitaxial growth equipment also includes: A first heating element is arranged on a side of the gas source reaction zone away from the tray, and the first heating element and the doping source gas path are arranged on the same side of the gas source reaction zone. The first heating element is used to heat the gas source reaction zone so that the temperature of the gas source reaction zone is not less than the growth temperature.

5. The silicon carbide epitaxial growth device according to claim 3, characterized in that: The silicon carbide epitaxial growth equipment also includes: A second heating element, wherein the tray is arranged on a portion of the surface of the second heating element close to the gas source reaction zone, and the second heating element is used to heat the tray.

6. The silicon carbide epitaxial growth device according to claim 4, characterized in that: The outlet of the doping source gas path is arranged in the first heating element, the gas source mixing zone and the gas source reaction zone are located in the same area, and the temperature of the gas source mixing zone is not less than the growth temperature.

7. The silicon carbide epitaxial growth device according to claim 4, characterized in that: The outlet of the doping source gas path is arranged at one side of the first heating element, and the gas source mixing zone and the gas source reaction zone are located in different areas.

8. The silicon carbide epitaxial growth device according to claim 6, characterized in that: The silicon carbide epitaxial growth equipment also includes: A spray port is arranged on a partial surface of the first heating element close to the gas source reaction zone, the spray port comprises a plurality of spaced gas outlets arranged along its axial direction, and the outlet of the doping source gas path is arranged in the spray port.

9. The silicon carbide epitaxial growth device according to claim 5, characterized in that: The air intake passage also includes: The flotation gas path is arranged on a side of the growth source gas path away from the doping source gas path, and the outlet of the flotation gas path is arranged in the second heating element. The flotation gas path is used to transport gas to the bottom of the tray to rotate the tray.

10. The silicon carbide epitaxial growth device according to claim 4, characterized in that: The silicon carbide epitaxial growth equipment also includes: The first heat insulating member is arranged on a surface of the first heating member away from the gas source reaction zone.

11. The silicon carbide epitaxial growth device according to claim 5, characterized in that: The silicon carbide epitaxial growth equipment also includes: The second heat insulating member is arranged on a surface of the second heating member away from the gas source reaction zone.

12. The silicon carbide epitaxial growth device according to claim 3, characterized in that: The silicon carbide epitaxial growth equipment also includes: A quartz cover, wherein the gas inlet channel, the tray, the gas source mixing zone and the gas source reaction zone are all arranged in the quartz cover.

13. A silicon carbide epitaxial wafer, characterized in that: The silicon carbide epitaxial wafer is prepared by the method for preparing the silicon carbide epitaxial wafer according to claim 1 or 2.

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