Silicon carbide epitaxial wafer and method of manufacturing the same

Abstract

The application discloses a silicon carbide epitaxial wafer and a preparation method thereof. The preparation method of the silicon carbide epitaxial wafer is used for preparing the silicon carbide epitaxial wafer, and comprises the following steps: placing a silicon carbide substrate in a reaction cavity; introducing an inert gas into the reaction cavity; increasing the temperature of the reaction cavity to a first preset temperature, and performing a first heat preservation step; growing a buffer layer, the buffer layer is located on one side of the silicon carbide substrate, and the buffer layer is an N-type doped buffer layer; growing an epitaxial layer, the epitaxial layer is located on a side of the buffer layer away from the silicon carbide substrate; and decreasing the temperature of the reaction cavity from the first preset temperature to a second preset temperature to obtain the silicon carbide epitaxial wafer. The preparation method of the silicon carbide epitaxial wafer provided by the application improves the quality of the silicon carbide epitaxial wafer.

Description

Technical Field

[0001] This application relates to the field of semiconductor manufacturing technology, specifically to a silicon carbide epitaxial wafer and its preparation method. Background Technology

[0002] Silicon carbide (SiC), as an excellent third-generation semiconductor material, boasts a bandgap of 2.3–3.3 eV. It possesses a breakdown electric field strength ten times that of silicon and a thermal conductivity three times that of silicon, making it uniquely attractive for high-power and high-temperature devices. The wide bandgap and high thermal stability of SiC allow certain types of SiC devices to operate indefinitely at junction temperatures of 300°C or higher, making SiC a key material for fabricating high-end power semiconductor devices. Summary of the Invention

[0003] The purpose of this application is to provide a method for preparing silicon carbide epitaxial wafers, thereby improving the quality of silicon carbide epitaxial wafers. A further purpose of this application is to provide a silicon carbide epitaxial wafer with excellent quality.

[0004] This application provides a method for preparing a silicon carbide epitaxial wafer, which includes:

[0005] The silicon carbide substrate is placed inside the reaction chamber;

[0006] An inert gas is introduced into the reaction chamber;

[0007] The temperature of the reaction chamber is raised to a first preset temperature, and a first heat preservation step is performed.

[0008] A buffer layer is grown, the buffer layer is located on one side of the silicon carbide substrate, and the buffer layer is an N-type doped buffer layer;

[0009] An epitaxial layer is grown on the side of the buffer layer opposite to the silicon carbide substrate;

[0010] The temperature of the reaction chamber is reduced from the first preset temperature to the second preset temperature to obtain the silicon carbide epitaxial wafer.

[0011] In some embodiments, the heating includes at least two heating steps to perform a gradient heating; the rate of the gradient heating is 1 to 2 °C / s, and a second holding step is performed every 10 to 15 °C increase in temperature, the time range of the second holding step being 20 to 30 seconds.

[0012] In some embodiments, the cooling includes at least two cooling steps to perform gradient cooling; the rate of gradient cooling is 1 to 2 °C / s, and a third holding step is performed every 10 to 15 °C decrease in temperature, the duration of the third holding step being 20 to 30 seconds.

[0013] In some embodiments, the step of growing the buffer layer includes:

[0014] A carbon source, a silicon source, and a nitrogen source are introduced into the reaction chamber to grow the buffer layer; the elements in the buffer layer include carbon and silicon, and the ratio of the number of carbon atoms to the number of silicon atoms ranges from 0.6 to 0.9.

[0015] In some embodiments, the carbon source includes at least one of ethylene, acetylene, methane, and propane.

[0016] In some embodiments, the silicon source includes at least one of trichlorosilane, tetrachlorosilane, dichlorosilane, and silane.

[0017] In some embodiments, the nitrogen source includes ammonia; or, the nitrogen source includes both ammonia and nitrogen.

[0018] In some embodiments, the gas flow rate of the carbon source is 60–70 sccm;

[0019] In some embodiments, the carrier gas of the silicon source is hydrogen, and the flow rate of the hydrogen is 184-190 sccm.

[0020] In some embodiments, when the nitrogen source is ammonia, the ammonia flow rate is 55-70 sccm; when the nitrogen source is ammonia and nitrogen, the ammonia flow rate is 45-55 sccm and the nitrogen flow rate is 15-25 sccm.

[0021] In some embodiments, the growth time of the buffer layer is 4 to 5 minutes during the step of growing the buffer layer.

[0022] In some embodiments, after the buffer layer is grown, the buffer layer has a first thickness L1 along the thickness direction of the silicon carbide epitaxial wafer, the first thickness L1 being in the range of 0.5 to 1.0 μm.

[0023] In some embodiments, the step of growing the epitaxial layer includes:

[0024] A carbon source, a silicon source, and a nitrogen source are introduced into the reaction chamber to grow the epitaxial layer; the elements in the epitaxial layer include carbon and silicon, and the ratio of the number of carbon atoms to the number of silicon atoms ranges from 0.72 to 1.17.

[0025] In some embodiments, the carbon source includes at least one of ethylene, acetylene, methane, and propane.

[0026] In some embodiments, the silicon source includes at least one of trichlorosilane, tetrachlorosilane, dichlorosilane, and silane.

[0027] In some embodiments, the nitrogen source includes ammonia; or, the nitrogen source includes both ammonia and nitrogen.

[0028] In some embodiments, the gas flow rate of the carbon source is 110–130 sccm.

[0029] In some embodiments, the carrier gas of the silicon source is hydrogen, and the flow rate of the hydrogen is 290–310 sccm.

[0030] In some embodiments, when the nitrogen source is ammonia, the ammonia flow rate is 120–580 sccm; when the nitrogen source is ammonia and nitrogen, the ammonia flow rate is 100–450 sccm and the nitrogen flow rate is 40–180 sccm.

[0031] In some embodiments, the growth time of the epitaxial layer is 10 to 13 minutes during the step of growing the epitaxial layer.

[0032] In some embodiments, after the epitaxial layer growth is completed, the epitaxial layer has a second thickness L2 along the thickness direction of the silicon carbide epitaxial wafer, the second thickness L2 being in the range of 10.5 to 12.5 μm.

[0033] In some embodiments, the first preset temperature is 1200–1600°C.

[0034] In some embodiments, the second preset temperature is 700–900°C.

[0035] In some embodiments, the step of introducing an inert gas into the reaction chamber includes:

[0036] After evacuating the reaction chamber, an inert gas is introduced.

[0037] In some embodiments, the inert gas includes argon, and the flow rate of the inert gas is 1 to 5 slm.

[0038] Accordingly, this application also provides a silicon carbide epitaxial wafer, comprising:

[0039] silicon carbide substrate;

[0040] A buffer layer is located on one side of the silicon carbide substrate; wherein the elements in the buffer layer include carbon and silicon, and the ratio of the number of carbon atoms to the number of silicon atoms ranges from 0.6 to 0.9; the buffer layer has a first thickness L1 along the thickness direction of the silicon carbide epitaxial wafer, and the first thickness L1 ranges from 0.5 to 1.0 μm; the carrier concentration of the buffer layer is 9.9E17 to 1.1E18 cm⁻¹. -3 ;

[0041] An epitaxial layer is located on the side of the buffer layer opposite to the silicon carbide substrate; wherein the elements in the epitaxial layer include carbon and silicon, and the ratio of the number of carbon atoms to the number of silicon atoms ranges from 0.72 to 1.17; along the thickness direction, the epitaxial layer has a second thickness L2, the second thickness L2 ranging from 10.5 to 12.5 μm; the carrier concentration of the epitaxial layer is 1.104E16 to 1.296E16 cm⁻¹. -3 .

[0042] The beneficial effects of this application are as follows: This application provides a method for preparing a silicon carbide epitaxial wafer, comprising: placing a silicon carbide substrate in a reaction chamber; introducing an inert gas into the reaction chamber; raising the temperature of the reaction chamber to a first preset temperature and performing a first heat preservation step; growing a buffer layer, the buffer layer being located on one side of the silicon carbide substrate, the buffer layer being an N-type doped buffer layer; growing an epitaxial layer, the epitaxial layer being located on the side of the buffer layer opposite to the silicon carbide substrate; and cooling the temperature of the reaction chamber from the first preset temperature to a second preset temperature to obtain a silicon carbide epitaxial wafer. The method for preparing a silicon carbide epitaxial wafer provided by this application improves the quality of the silicon carbide epitaxial wafer.

[0043] This application provides a silicon carbide epitaxial wafer, comprising: a silicon carbide substrate; a buffer layer located on one side of the silicon carbide substrate; wherein the elements in the buffer layer include carbon and silicon, and the ratio of the number of carbon atoms to the number of silicon atoms ranges from 0.6 to 0.9; the buffer layer has a first thickness L1 along the thickness direction of the silicon carbide epitaxial wafer, and the first thickness L1 ranges from 0.5 to 1.0 μm; the carrier concentration of the buffer layer is 9.9E17 to 1.1E18 cm⁻¹. -3 An epitaxial layer is located on the side of the buffer layer opposite to the silicon carbide substrate; the epitaxial layer contains carbon and silicon elements, with a carbon to silicon atomic ratio ranging from 0.72 to 1.17; the epitaxial layer has a second thickness L2 along the thickness direction, ranging from 10.5 to 12.5 μm; the carrier concentration of the epitaxial layer is 1.104E16 to 1.296E16 cm⁻¹. -3 The silicon carbide epitaxial wafer provided in this application has good quality. Attached Figure Description

[0044] Figure 1 A flowchart illustrating a method for preparing a silicon carbide epitaxial wafer provided in this application;

[0045] Figure 2 This application provides a silicon carbide epitaxial wafer;

[0046] Figure 3 The carrier concentration and thickness distribution diagram of a silicon carbide epitaxial wafer provided in this application;

[0047] Figure 4 This application provides a sampling point distribution diagram for a silicon carbide epitaxial wafer.

[0048] The attached diagram lists the components represented by each number as follows:

[0049] 10. Silicon carbide substrate; 20. Buffer layer; 30. Epitaxial layer; 100. Silicon carbide epitaxial wafer. Detailed Implementation

[0050] The technical solutions of this application will be clearly and completely described below with reference to the embodiments and accompanying drawings. Obviously, the described embodiments are only a part of the embodiments of this application, and not all of the embodiments. Based on the embodiments in this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application. Various embodiments of this application may exist in the form of a range; it should be understood that the description in the form of a range is only for convenience and conciseness, and should not be construed as a hard limitation on the scope of this application; therefore, it should be considered that the range description has specifically disclosed all possible sub-ranges and the single numerical value within that range. For example, it should be considered that the range description from 1 to 6 has specifically disclosed sub-ranges, such as from 1 to 3, from 1 to 4, from 1 to 5, from 2 to 4, from 2 to 6, from 3 to 6, etc., and the single digits within the range, such as 1, 2, 3, 4, 5, and 6, which applies regardless of the range. In addition, whenever a numerical range is indicated herein, it means including any referenced number (fraction or integer) within the indicated range.

[0051] While existing processes can improve carrier concentration and thickness uniformity through a series of complex techniques, such as variable-temperature growth, interrupted growth, and even a combination of growing multiple low-speed buffer layers with interrupted etching, the results are unsatisfactory. Therefore, this application proposes a method for preparing silicon carbide epitaxial wafers.

[0052] like Figures 1-2 As shown, this application provides a method for preparing a silicon carbide epitaxial wafer 100, which includes:

[0053] Step S1: Place the silicon carbide substrate 10 into the reaction chamber;

[0054] Step S2: Inert gas is introduced into the reaction chamber;

[0055] Step S3: Raise the temperature of the reaction chamber to the first preset temperature and perform the first heat preservation step;

[0056] Step S4: Grow a buffer layer 20. The buffer layer 20 is located on one side of the silicon carbide substrate 10 and is an N-type doped buffer layer.

[0057] Step S5: Grow epitaxial layer 30, which is located on the side of buffer layer 20 away from silicon carbide substrate 10;

[0058] Step S6: Cool the temperature of the reaction chamber from the first preset temperature to the second preset temperature to obtain the silicon carbide epitaxial wafer 100.

[0059] The present application provides a method for preparing a silicon carbide epitaxial wafer 100, which can improve the quality of the silicon carbide epitaxial wafer 100 and ultimately improve the product yield.

[0060] In some embodiments, the duration of the first heat preservation step is 14 to 18 minutes. It is understood that the duration of the first heat preservation step is the same as the growth time of the silicon carbide epitaxial wafer 100. Specifically, the duration of the first heat preservation step is one or a combination of 14 minutes, 15 minutes, 16 minutes, 17 minutes, and 18 minutes.

[0061] In some embodiments, the heating includes at least two heating steps to perform a gradient heating; the gradient heating rate is 1–2 °C / s, and a second holding step is performed for every 10–15 °C increase in temperature, the duration of the second holding step being 20–30 s. Specifically, the gradient heating rate is 1 °C / s or 2 °C / s. Specifically, the holding time is one or a combination of both of the following: holding for 20 s for every 10 °C increase, holding for 21 s for every 11 °C increase, holding for 23 s for every 12 °C increase, holding for 25 s for every 13 °C increase, holding for 28 s for every 14 °C increase, and holding for 30 s for every 15 °C increase.

[0062] This application uses a gradient heating method during the growth of the buffer layer 20 and the epitaxial layer 30 to reduce the surface stress of the epitaxial wafer 100 caused by excessively rapid heating, reduce the defect density, thereby improving the thickness uniformity of the silicon carbide epitaxial wafer 100 and ultimately improving the product yield.

[0063] In some embodiments, the cooling includes at least two cooling steps to perform gradient cooling; the gradient cooling rate is 1–2 °C / s, and a third holding step is performed for every 10–15 °C decrease in temperature, the duration of which is 20–30 s. Specifically, the gradient cooling rate is 1 °C / s or 2 °C / s. Specifically, the holding time is one or a combination of both of the following: holding for 20 s for every 10 °C decrease, holding for 21 s for every 11 °C decrease, holding for 23 s for every 12 °C decrease, holding for 25 s for every 13 °C decrease, holding for 28 s for every 14 °C decrease, and holding for 30 s for every 15 °C decrease.

[0064] This application uses a gradient cooling method during the growth of the buffer layer 20 and the epitaxial layer 30 to reduce the surface stress of the epitaxial wafer 100 caused by excessively rapid cooling, reduce the defect density, thereby improving the thickness uniformity of the silicon carbide epitaxial wafer 100 and ultimately improving the product yield.

[0065] In some embodiments, the step of growing the buffer layer 20 includes:

[0066] A carbon source, a silicon source, and a nitrogen source are introduced into the reaction chamber to grow a buffer layer 20. The buffer layer 20 contains carbon (C) and silicon (Si), with a carbon / Si ratio ranging from 0.6 to 0.9. The nitrogen source is used as a dopant source. The resulting buffer layer 20 contains carbon, silicon, and nitrogen.

[0067] Specifically, the C / Si ratio of the buffer layer 20 is in the range of one or both of 0.6, 0.7, 0.8, and 0.9. It is understood that the C / Si ratio of the buffer layer 20 is determined by the flow rates of the introduced carbon and silicon sources.

[0068] In some embodiments, the carbon source includes at least one of ethylene, acetylene, methane, and propane.

[0069] In some embodiments, the silicon source includes at least one of trichlorosilane, tetrachlorosilane, dichlorosilane, and silane.

[0070] In some embodiments, the nitrogen source includes ammonia; or, the nitrogen source includes both ammonia and nitrogen.

[0071] This application also uses chemically active ammonia or a mixture of ammonia and nitrogen as a nitrogen source during the growth of the buffer layer 20, which can reduce the memory effect of nitrogen in the reaction chamber and reduce the consumption of doping gas, thereby improving the uniformity of carrier concentration of the silicon carbide epitaxial wafer 100.

[0072] In some embodiments, during the step of growing the buffer layer 20, the gas flow rate of the carbon source is 60–70 sccm. Specifically, the gas flow rate of the carbon source is one or a combination of 60 sccm, 65 sccm, and 70 sccm.

[0073] In some embodiments, during the step of growing the buffer layer 20, the carrier gas for the silicon source is hydrogen, and the hydrogen flow rate is 184–190 sccm. Specifically, the hydrogen flow rate is one or a combination of two of the following: 184 sccm, 185 sccm, 186 sccm, 187 sccm, 188 sccm, 189 sccm, and 190 sccm.

[0074] In some embodiments, during the step of growing the buffer layer 20, when the nitrogen source is ammonia, the ammonia flow rate is 55–70 sccm. Specifically, the ammonia flow rate is one or a combination of 55 sccm, 60 sccm, 65 sccm, and 70 sccm.

[0075] In some embodiments, during the step of growing the buffer layer 20, when the nitrogen source is ammonia and nitrogen, the ammonia flow rate is 45–55 sccm, and the nitrogen flow rate is 15–25 sccm. Specifically, the ammonia flow rate is one or a combination of 45 sccm, 50 sccm, and 55 sccm. Specifically, the nitrogen flow rate is one or a combination of 15 sccm, 20 sccm, and 25 sccm.

[0076] In some embodiments, the growth time of the buffer layer 20 is 4 to 5 minutes. Specifically, the growth time of the buffer layer 20 is 4 minutes or 5 minutes.

[0077] In some embodiments, after the buffer layer 20 is grown, along the thickness direction Z of the silicon carbide epitaxial wafer 100, the buffer layer 20 has a first thickness L1, which ranges from 0.5 to 1.0 μm. Specifically, the thickness L1 of the buffer layer 20 is one or a combination of two of the following: 0.5 μm, 0.6 μm, 0.7 μm, 0.8 μm, 0.9 μm, and 1.0 μm.

[0078] In some embodiments, the step of growing the epitaxial layer 30 includes:

[0079] A carbon source, a silicon source, and a nitrogen source are introduced into the reaction chamber to grow an epitaxial layer 30. The epitaxial layer 30 contains carbon (C) and silicon (Si), with a carbon / Si ratio ranging from 0.72 to 1.17. The nitrogen source is used as a dopant source. The resulting epitaxial layer 30 contains carbon, silicon, and nitrogen.

[0080] Specifically, the C / Si ratio of the epitaxial layer 30 is a range of one or both of the following: 0.72, 0.75, 0.80, 0.85, 0.90, 0.95, 1.0, 1.05, 1.1, 1.15, and 1.17. It is understood that the C / Si ratio of the epitaxial layer 30 is determined by the flow rates of the introduced carbon and silicon sources.

[0081] In some embodiments, the carbon source includes at least one of ethylene, acetylene, methane, and propane.

[0082] In some embodiments, the silicon source includes at least one of trichlorosilane, tetrachlorosilane, dichlorosilane, and silane.

[0083] In some embodiments, the nitrogen source includes ammonia; or, the nitrogen source includes both ammonia and nitrogen.

[0084] This application also uses chemically active ammonia or a mixture of ammonia and nitrogen as a nitrogen source during the growth of the epitaxial layer 30 to prepare a silicon carbide epitaxial wafer 100 with a homogeneous epitaxial layer 30. This can reduce the memory effect of nitrogen in the reaction chamber and also reduce the consumption of doping gas, thereby improving the uniformity of carrier concentration of the silicon carbide epitaxial wafer 100.

[0085] In some embodiments, during the step of growing the epitaxial layer 30, the gas flow rate of the carbon source is 110 to 130 sccm. Specifically, the gas flow rate of the carbon source is one or a combination of two of 110 sccm, 115 sccm, 120 sccm, 125 sccm, and 130 sccm.

[0086] In some embodiments, during the step of growing epitaxial layer 30, the carrier gas for the silicon source is hydrogen, and the hydrogen flow rate is 290–310 sccm. Specifically, the hydrogen flow rate is one or a combination of two of the following: 290 sccm, 295 sccm, 300 sccm, 305 sccm, and 310 sccm.

[0087] In some embodiments, during the step of growing the epitaxial layer 30, when the nitrogen source is ammonia, the ammonia flow rate is 120–580 sccm. Specifically, the ammonia flow rate is one or a combination of two of the following: 120 sccm, 150 sccm, 180 sccm, 200 sccm, 220 sccm, 250 sccm, 280 sccm, 300 sccm, 320 sccm, 350 sccm, 380 sccm, 400 sccm, 420 sccm, 450 sccm, 480 sccm, 500 sccm, 520 sccm, 550 sccm, and 580 sccm.

[0088] In some embodiments, during the step of growing the epitaxial layer 30, when the nitrogen source is ammonia and nitrogen, the ammonia flow rate is 100–450 sccm, and the nitrogen flow rate is 40–180 sccm. Specifically, the ammonia flow rate is one or a combination of both of the following: 100 sccm, 120 sccm, 150 sccm, 180 sccm, 200 sccm, 220 sccm, 250 sccm, 280 sccm, 300 sccm, 320 sccm, 350 sccm, 380 sccm, 400 sccm, 420 sccm, and 450 sccm. Specifically, the nitrogen flow rate is one or a combination of both of the following: 40 sccm, 60 sccm, 80 sccm, 100 sccm, 120 sccm, 150 sccm, and 180 sccm.

[0089] In some implementations, the flow control methods for carbon sources, silicon sources, doped sources, and carrier gases are as follows: for gases, the flow rate is directly controlled by a mass flow meter; for liquids, the flow rate is controlled by controlling the flow rate of the carrier gas.

[0090] In some embodiments, the growth time of the epitaxial layer 30 is 10 to 13 minutes. Specifically, the growth time of the epitaxial layer 30 is one or a combination of 10 minutes, 11 minutes, 12 minutes, and 13 minutes.

[0091] In some embodiments, after the epitaxial layer 30 is grown, the epitaxial layer 30 has a second thickness L2 along the thickness direction Z of the silicon carbide epitaxial wafer 100, and the second thickness L2 ranges from 10.5 to 12.5 μm. Specifically, the thickness L2 of the epitaxial layer 30 is one or a combination of 10.5 μm, 11.0 μm, 11.5 μm, 12.0 μm, and 12.5 μm.

[0092] In some embodiments, the first preset temperature is 1200–1600°C. Specifically, the first preset temperature is a range of one or both of 1200°C, 1300°C, 1400°C, 1500°C, and 1600°C.

[0093] It is understandable that the first preset temperature of 1200-1600℃ is the growth temperature of the buffer layer 20 and the epitaxial layer 30.

[0094] In some embodiments, the second preset temperature is 700 to 900°C. Specifically, the second preset temperature is a range of one or both of 700°C, 750°C, 800°C, 850°C, and 900°C.

[0095] Understandably, the second preset temperature is the standby temperature of the epitaxial furnace reaction chamber.

[0096] In some embodiments, the step of introducing an inert gas into the reaction chamber includes:

[0097] After evacuating the reaction chamber, an inert gas is introduced. Specifically, after evacuating the reaction chamber, an inert gas is introduced to fill the reaction chamber with inert gas.

[0098] In some embodiments, the inert gas includes argon, and the inert gas flow rate is 1 to 5 slm. Specifically, the inert gas flow rate is one or a combination of two of the following: 1 slm, 2 slm, 3 slm, 4 slm, and 5 slm.

[0099] In some embodiments, the step of placing the silicon carbide substrate 10 within the reaction chamber includes:

[0100] Step S11: Use a robotic arm to place the silicon carbide substrate 10 into the reaction chamber.

[0101] In some embodiments, after the step of forming the silicon carbide epitaxial wafer 100, the method further includes:

[0102] Step S7: Use a robotic arm to remove the silicon carbide epitaxial wafer 100;

[0103] Step S8: Inspect, clean, and encapsulate the silicon carbide epitaxial wafer 100.

[0104] Accordingly, this application also provides a silicon carbide epitaxial wafer 100, including a silicon carbide substrate 10, a buffer layer 20, and an epitaxial layer 30; the buffer layer 20 is located on one side of the silicon carbide substrate 10; wherein the elements in the buffer layer 20 include carbon and silicon, and the ratio of the number of carbon atoms to the number of silicon atoms ranges from 0.6 to 0.9; along the thickness direction Z of the silicon carbide epitaxial wafer 100, the buffer layer 20 has a first thickness L1, the first thickness L1 ranging from 0.5 to 1.0 μm; the carrier concentration of the buffer layer 20 is 9.9E17 to 1.1E18 cm⁻¹. -3 The epitaxial layer 30 is located on the side of the buffer layer 20 opposite to the silicon carbide substrate 10; the elements in the epitaxial layer 30 include carbon and silicon, and the ratio of the number of carbon atoms to the number of silicon atoms ranges from 0.72 to 1.17; along the thickness direction Z, the epitaxial layer 30 has a second thickness L2, which ranges from 10.5 to 12.5 μm; the carrier concentration of the epitaxial layer 30 is 1.104E16 to 1.296E16 cm⁻¹. -3 .

[0105] The silicon carbide epitaxial wafer 100 provided in this application has good carrier concentration and thickness uniformity.

[0106] Example 1

[0107] This application provides a method for preparing a silicon carbide epitaxial wafer 100, which includes:

[0108] Step S1: Use a robotic arm to place the silicon carbide substrate 10 into the reaction chamber;

[0109] Step S2: After evacuating the reaction chamber, argon gas is introduced to fill the reaction chamber with argon gas. The flow rate of argon gas is 3slm.

[0110] Step S3: The reaction chamber is gradually heated at a rate of 1℃ / s, with a holding time of 25s for every 13℃ increase in temperature. When the temperature in the reaction chamber reaches 1400℃, it is held at that temperature.

[0111] Step S4: Ethylene, trichlorosilane, and a nitrogen source are introduced into the reaction chamber to grow a buffer layer 20. The buffer layer 20 is located on one side of the silicon carbide substrate 10 and is an N-type doped buffer layer. The flow rate of ethylene is 65 sccm, the carrier gas of trichlorosilane is hydrogen with a flow rate of 187 sccm, the nitrogen source is ammonia with a flow rate of 60 sccm, the growth time of the buffer layer 20 is 4 min, and the thickness of the buffer layer 20 is 0.7 μm.

[0112] Step S5: Ethylene, trichlorosilane, and a nitrogen source are introduced into the reaction chamber to grow an epitaxial layer 30. The epitaxial layer 30 is located on the side of the buffer layer 20 away from the silicon carbide substrate 10. The flow rate of ethylene is 120 sccm, the carrier gas of trichlorosilane is hydrogen with a flow rate of 300 sccm, the nitrogen source is ammonia with a flow rate of 300 sccm, and the growth time of the epitaxial layer 30 is 12 min.

[0113] Step S6: The reaction chamber is gradually cooled from 1400℃ at a rate of 1℃ / s, and the temperature is held for 25s for every 13℃ decrease. When the temperature in the reaction chamber drops to 800℃, a silicon carbide epitaxial wafer 100 is obtained.

[0114] Step S7: Use a robotic arm to remove the silicon carbide epitaxial wafer 100;

[0115] Step S8: Inspect, clean, and encapsulate the silicon carbide epitaxial wafer 100.

[0116] Example 2

[0117] The difference between Example 2 and Example 1 is that the reaction chamber is heated in a gradient manner with a heating rate of 2℃ / s and a holding time of 20s for every 10℃ increase in temperature; the reaction chamber is cooled in a gradient manner from 1400℃ with a cooling rate of 2℃ / s and a holding time of 20s for every 10℃ decrease in temperature.

[0118] Example 3

[0119] The difference between Example 3 and Example 1 is that the reaction chamber is heated in a gradient manner with a heating rate of 1℃ / s and a holding time of 30s for every 15℃ increase in temperature; the reaction chamber is cooled in a gradient manner from 1400℃ with a cooling rate of 1℃ / s and a holding time of 30s for every 15℃ decrease in temperature.

[0120] Example 4

[0121] The difference between Example 4 and Example 1 is that the nitrogen source for the growth buffer layer 20 is ammonia and nitrogen, with an ammonia flow rate of 50 sccm and a nitrogen flow rate of 20 sccm; the nitrogen source for the growth epitaxial layer 30 is ammonia and nitrogen, with an ammonia flow rate of 280 sccm and a nitrogen flow rate of 100 sccm.

[0122] Comparative Example 1

[0123] The difference between Comparative Example 1 and Example 1 is that the reaction chamber was connected and heated at a heating rate of 1°C / s; and the reaction chamber was connected and cooled from 1400°C at a cooling rate of 1°C / s.

[0124] Comparative Example 2

[0125] The difference between Comparative Example 2 and Example 1 is that the reaction chamber was connected and heated at a heating rate of 2°C / s; and the reaction chamber was connected and cooled from 1400°C at a cooling rate of 2°C / s.

[0126] Comparative Example 3

[0127] The difference between Comparative Example 3 and Example 1 is that the reaction chamber was connected and heated at a heating rate of 1°C / s; and the reaction chamber was connected and cooled from 1400°C at a cooling rate of 2°C / s.

[0128] Measurement methods:

[0129] The film thickness was measured using a Fourier transform infrared spectrometer, and the carrier concentration was measured using a mercury probe (mercury CV) tester.

[0130] Carrier concentration uniformity: standard deviation of carrier concentration at 10 measurement points on the epitaxial layer / arithmetic mean of carrier concentration at 10 measurement points on the epitaxial layer × 100%.

[0131] Thickness uniformity: standard deviation of thickness at 10 measurement points on the epitaxial layer / arithmetic mean of thickness at 10 measurement points on the epitaxial layer × 100%.

[0132] like Figure 3 The image shows the carrier concentration and thickness distribution of the epitaxial wafer 100 prepared in Example 1. The epitaxial wafer is six inches in size (1 inch = 2.54 cm). After removing the 5 mm edge, 10 measurement points were taken on the epitaxial wafer to measure the carrier concentration and thickness. The sampling method is as follows: Figure 4 As shown, the average thickness of the epitaxial layer was calculated to be 10.89 μm, and the average carrier concentration was 1.21E16 cm⁻¹. -3 .

[0133] Table 1 shows the measurement results of carrier concentration uniformity and thickness uniformity of the epitaxial wafers prepared in Examples 1-4 and Comparative Examples 1-3.

[0134] Example 1 1.02％ 0.39％ Example 2 2.03％ 0.85％ Example 3 1.64％ 0.55％ Example 4 1.28％ 0.47％ Comparative Example 1 3.06％ 0.95％ Comparative Example 2 3.59％ 1.01％ Comparative Example 3 3.31％ 1.07％

[0135] Results Analysis

[0136] As can be seen from the test results of Examples 1 and 4 and Table 1, when ammonia is used as the nitrogen source for the growth buffer layer and epitaxial layer, the prepared epitaxial wafer has less uniform carrier concentration and less uniform thickness.

[0137] As can be seen from the test results of Comparative Example 1, Examples 1-3 and Table 1, when gradient heating and gradient cooling are used to generate the buffer layer and epitaxial layer, the carrier concentration uniformity and thickness uniformity of the prepared epitaxial wafer are smaller.

[0138] As can be seen from the test results of Comparative Example 2, Example 1, and Table 1, when gradient heating and gradient cooling are used to generate the buffer layer and epitaxial layer, the carrier concentration uniformity and thickness uniformity of the prepared epitaxial wafer are smaller.

[0139] As can be seen from the test results of Comparative Example 3, Example 1, and Table 1, when gradient heating and gradient cooling are used to generate the buffer layer and epitaxial layer, the carrier concentration uniformity and thickness uniformity of the prepared epitaxial wafer are smaller.

[0140] The present application has been described in detail above. Specific examples have been used to illustrate the principles and implementation methods of the present application. The description of the above embodiments is only for the purpose of helping to understand the method and core ideas of the present application. At the same time, for those skilled in the art, there will be changes in the specific implementation methods and application scope based on the ideas of the present application. Therefore, the content of this specification should not be construed as a limitation of the present application.

Claims

1. A method for preparing a silicon carbide epitaxial wafer, used to prepare a silicon carbide epitaxial wafer (100), characterized in that, include: The silicon carbide substrate (10) is placed inside the reaction chamber; An inert gas is introduced into the reaction chamber; The temperature of the reaction chamber is raised to a first preset temperature, and a first holding step is performed. The temperature rise includes at least two temperature rise steps to perform gradient temperature rise. The gradient temperature rise rate is 1~2℃ / s, and a second holding step is performed every 10~15℃ increase in the temperature of the reaction chamber. The duration of the second holding step is 20~30s. The first preset temperature is 1200~1600℃. A carbon source, a silicon source, and a nitrogen source are introduced into the reaction chamber to grow a buffer layer (20); the buffer layer (20) is located on one side of the silicon carbide substrate (10), and the buffer layer (20) is an N-type doped buffer layer; the elements in the buffer layer (20) include carbon and silicon, and the ratio of the number of carbon atoms to the number of silicon atoms is in the range of 0.6 to 0.9; A carbon source, a silicon source, and a nitrogen source are introduced into the reaction chamber to grow an epitaxial layer (30). The epitaxial layer (30) is located on the side of the buffer layer (20) away from the silicon carbide substrate (10). The elements in the epitaxial layer (30) include carbon and silicon, and the ratio of the number of carbon atoms to the number of silicon atoms is in the range of 0.72 to 1.

17. The temperature of the reaction chamber is reduced from the first preset temperature to the second preset temperature to obtain the silicon carbide epitaxial wafer (100); the cooling includes at least two cooling steps to perform gradient cooling; the gradient cooling rate is 1~2℃ / s, and a third heat preservation step is performed every 10~15℃ decrease in the temperature of the reaction chamber, the time range of the third heat preservation step is 20~30s; the second preset temperature is 700~900℃.

2. The method for preparing a silicon carbide epitaxial wafer according to claim 1, characterized in that, In the step of growing the buffer layer (20), the carbon source includes at least one selected from ethylene, acetylene, methane, and propane; and / or, The silicon source includes at least one of trichlorosilane, tetrachlorosilane, dichlorosilane, and silane; and / or, The nitrogen source includes ammonia; or, the nitrogen source includes both ammonia and nitrogen.

3. The method for preparing a silicon carbide epitaxial wafer according to claim 2, characterized in that, The gas flow rate of the carbon source is 60~70 sccm; and / or, The carrier gas for the silicon source is hydrogen, and the flow rate of the hydrogen is 184~190 sccm; and / or, When the nitrogen source is ammonia, the ammonia flow rate is 55-70 sccm; when the nitrogen source is ammonia and nitrogen, the ammonia flow rate is 45-55 sccm and the nitrogen flow rate is 15-25 sccm.

4. The method for preparing a silicon carbide epitaxial wafer according to claim 1, characterized in that, In the step of growing the buffer layer (20), the growth time of the buffer layer (20) is 4~5 minutes; And / or, after the growth of the buffer layer (20) is completed, the buffer layer (20) has a first thickness L1 along the thickness direction (Z) of the silicon carbide epitaxial wafer (100), the first thickness L1 being in the range of 0.5~1.0 μm.

5. The method for preparing a silicon carbide epitaxial wafer according to claim 1, characterized in that, In the step of growing the epitaxial layer (30), the carbon source includes at least one selected from ethylene, acetylene, methane, and propane; and / or, The silicon source includes at least one of trichlorosilane, tetrachlorosilane, dichlorosilane, and silane; and / or, The nitrogen source includes ammonia; or, the nitrogen source includes both ammonia and nitrogen.

6. The method for preparing a silicon carbide epitaxial wafer according to claim 5, characterized in that, The gas flow rate of the carbon source is 110~130 sccm; and / or, The carrier gas for the silicon source is hydrogen, and the hydrogen flow rate is 290~310 sccm; and / or, When the nitrogen source is ammonia, the ammonia flow rate is 120~580 sccm; when the nitrogen source is ammonia and nitrogen, the ammonia flow rate is 100~450 sccm and the nitrogen flow rate is 40~180 sccm.

7. The method for preparing a silicon carbide epitaxial wafer according to claim 1, characterized in that, In the step of growing the epitaxial layer (30), the growth time of the epitaxial layer (30) is 10~13 min; And / or, after the epitaxial layer (30) is grown, along the thickness direction (Z) of the silicon carbide epitaxial wafer (100), the epitaxial layer (30) has a second thickness L2, the second thickness L2 being in the range of 10.5~12.5 μm.

8. The method for preparing a silicon carbide epitaxial wafer according to claim 1, characterized in that, The step of introducing an inert gas into the reaction chamber includes: After evacuating the reaction chamber, an inert gas is introduced.

9. The method for preparing a silicon carbide epitaxial wafer according to claim 1, characterized in that, The inert gas includes argon, and the flow rate of the inert gas is 1~5 slm.

10. A silicon carbide epitaxial wafer, characterized in that, The silicon carbide epitaxial wafer is prepared using the method for preparing a silicon carbide epitaxial wafer as described in any one of claims 1 to 9, and the silicon carbide epitaxial wafer comprises: Silicon carbide substrate (10); A buffer layer (20) is located on one side of the silicon carbide substrate (10); wherein the elements in the buffer layer (20) include carbon and silicon, and the ratio of the number of carbon atoms to the number of silicon atoms ranges from 0.6 to 0.9; along the thickness direction (Z) of the silicon carbide epitaxial wafer (100), the buffer layer (20) has a first thickness L1, the first thickness L1 ranging from 0.5 to 1.0 μm; the carrier concentration of the buffer layer (20) is 9.9E17 to 1.1E18 cm⁻¹. -3 ; An epitaxial layer (30) is located on the side of the buffer layer (20) facing away from the silicon carbide substrate (10); wherein the elements in the epitaxial layer (30) include carbon and silicon, and the ratio of the number of carbon atoms to the number of silicon atoms ranges from 0.72 to 1.17; along the thickness direction (Z), the epitaxial layer (30) has a second thickness L2, and the second thickness L2 ranges from 10.5 to 12.5 μm; the carrier concentration of the epitaxial layer (30) is 1.104E16 to 1.296E16 cm⁻¹. -3 .

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