Method for improving doping concentration uniformity of P-type silicon carbide epitaxial wafer

Abstract

The invention belongs to the technical field of silicon carbide epitaxial growth, and discloses a method for improving doping concentration uniformity of a P-type silicon carbide epitaxial wafer, which comprises the following steps of: introducing hydrogen with a preset flow into a reaction chamber, placing a silicon carbide substrate in the reaction chamber, keeping the input flow of the hydrogen unchanged, respectively adjusting the temperature and the pressure of the reaction chamber to a preset etching temperature and a preset etching pressure so as to etch the surface of the silicon carbide substrate to obtain the surface-etched silicon carbide substrate, and inputting ethylene gas and trichlorosilane gas into the reaction chamber through a lower channel of the layered gas homogenizing box so as to obtain the surface-etched silicon carbide substrate. Trimethylaluminum gas is input into the reaction chamber through an upper channel of the layered gas uniformizing box so as to promote the surface-etched silicon carbide substrate to grow an epitaxial layer, and a P-type silicon carbide epitaxial wafer with uniform doping concentration is prepared; reaction gas is separately input through the layered gas uniformizing box, the P-type silicon carbide epitaxial wafer with the uniform doping concentration is prepared, and the doping concentration uniformity of the P-type silicon carbide epitaxial wafer is improved.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of silicon carbide epitaxial growth, in particular to a method for improving the doping concentration uniformity of a P-type silicon carbide epitaxial wafer. BACKGROUND

[0002] As a key wide-bandgap semiconductor material, silicon carbide has become the core material for manufacturing high-voltage, high-frequency and high-temperature power devices due to its unique advantages such as large bandgap, high breakdown field strength, high thermal conductivity and high electron saturation drift speed, and is widely used in modern industrial applications such as new energy vehicle driving systems, 5G communication base stations, rail transit traction devices and smart grid power transmission and distribution equipment. In the manufacturing process of silicon carbide power devices, N-type or P-type chips need to rely on high-quality 4H-SiC epitaxial films (i.e. silicon carbide epitaxial wafers) as the basic platform. The epitaxial wafer forms the required electrical properties by doping specific impurity elements. Under current technical conditions, the thickness uniformity and doping concentration uniformity of N-type 4H-SiC epitaxial films have achieved a high level of control, and can be stably maintained within a fluctuation range of 3%, fully meeting the performance requirements of most unipolar devices. However, the uniformity control of P-type 4H-SiC epitaxial films still has significant bottlenecks, and the consistency of the thickness and doping concentration distribution is difficult to achieve ideal state, especially for bipolar devices such as insulated gate bipolar transistors, which require more optimal uniformity performance.

[0003] When P-type 4H-SiC epitaxial film is grown by using horizontal silicon carbide high-temperature epitaxial furnace, the doping concentration generally presents V-shaped distribution characteristics of low in the central region and high in the edge region. The root cause of this phenomenon is the temperature matching defect in the P-type doping process: the high-quality crystallization of 4H-SiC epitaxial film must rely on a process temperature higher than 1600℃, and the aluminum element in the P-type dopant trimethylaluminum has high chemical activity, which can be incorporated into the silicon carbide lattice in large quantities when the process temperature reaches 1400℃, which is much lower than the minimum temperature threshold required for crystallization. Inside the reaction chamber, the temperature distribution presents gradient characteristics of high in the center and low in the edge. In order to ensure that the edge region reaches the crystallization temperature (about 1600℃), the temperature in the central region must be raised to above 1630℃. According to the gas reaction kinetics principle, when ethylene, trichlorosilane and trimethylaluminum and other reaction gases are pre-mixed in the gas inlet pipeline and then enter the reaction chamber, the aluminum atoms are easy to replace silicon atoms and form stable covalent bonds with carbon atoms in the 1600℃ high-temperature environment when flowing through the edge region of the substrate. However, in the central region, due to the further increase of temperature, the bonding strength of carbon-silicon bond is significantly enhanced, and the aluminum atoms are difficult to effectively embed into the lattice structure, thereby causing the doping concentration in the central position to be significantly lower than that in the edge. Although the existing technology tries to weaken the steepness of the V-shaped distribution by optimizing process parameters such as gas flow and temperature distribution, it cannot fundamentally eliminate the concentration difference between the center and the edge, resulting in serious lack of doping uniformity of single epitaxial wafer, which greatly limits the reliability and mass production feasibility of high-performance P-type silicon carbide devices.

[0004] Therefore, in order to solve the technical problems that the existing P-type silicon carbide epitaxial wafer preparation method first mixes trimethylaluminum gas with ethylene gas and trichlorosilane gas, and makes aluminum atoms combine with carbon atoms by replacing silicon atoms in a high-temperature environment, resulting in uneven distribution of aluminum atoms, and thus the prepared P-type silicon carbide epitaxial wafer has uneven doping concentration distribution, an improved doping concentration uniformity method for P-type silicon carbide epitaxial wafer is urgently needed. SUMMARY

[0005] The purpose of the present application is to provide a method for improving the doping concentration uniformity of a P-type silicon carbide epitaxial wafer. The method involves inputting ethylene gas and trichlorosilane gas into a reaction chamber through the lower channel of a layered gas distribution box and inputting trimethylaluminum gas into the reaction chamber through the upper channel of the layered gas distribution box to promote the growth of a silicon carbide substrate and obtain a P-type silicon carbide epitaxial wafer with uniform doping concentration. The method solves the problem of uneven distribution of aluminum atoms caused by the combination of aluminum atoms with carbon atoms at high temperatures in the prior art method for preparing a P-type silicon carbide epitaxial wafer, which involves mixing trimethylaluminum gas with ethylene gas and trichlorosilane gas. The double-channel gas input method of the layered gas distribution box separates the dopant gas and the main reaction gas into layers, avoiding the local premature reaction caused by traditional mixing input and improving the doping concentration uniformity of the P-type silicon carbide epitaxial wafer.

[0006] In a first aspect, the present application provides a method for improving the doping concentration uniformity of a P-type silicon carbide epitaxial wafer. The method uses a layered gas distribution box to prepare a P-type silicon carbide epitaxial wafer with uniform doping concentration. The layered gas distribution box includes a gas distribution box and an upper channel and a lower channel arranged inside the gas distribution box. The method for improving the doping concentration uniformity of the P-type silicon carbide epitaxial wafer includes: Performing a vacuum operation on the reaction chamber of an epitaxial furnace; After inputting a predetermined flow rate of hydrogen gas into the reaction chamber, placing a silicon carbide substrate in the reaction chamber; Keeping the input flow rate of hydrogen gas unchanged, adjusting the temperature and pressure of the reaction chamber to the preset etching temperature and the preset etching pressure, respectively, to etch the surface of the silicon carbide substrate, obtaining a silicon carbide substrate after surface etching; Inputting ethylene gas and trichlorosilane gas into the reaction chamber through the lower channel of the layered gas distribution box and inputting trimethylaluminum gas into the reaction chamber through the upper channel of the layered gas distribution box to promote the growth of an epitaxial layer of the silicon carbide substrate after surface etching, obtaining a P-type silicon carbide epitaxial wafer with uniform doping concentration.

[0007] The method for improving the doping concentration uniformity of the P-type silicon carbide epitaxial wafer provided in the application can be used to prepare a P-type silicon carbide epitaxial wafer with a doping concentration. The ethylene gas and the trichlorosilane gas are input into the reaction chamber through the lower channel of the layered gas distribution box, and the trimethylaluminum gas is input into the reaction chamber through the upper channel of the layered gas distribution box, so as to promote the growth of the epitaxial layer of the silicon carbide substrate, and a P-type silicon carbide epitaxial wafer with a uniform doping concentration is prepared. The method solves the problem that, in the prior art, the trimethylaluminum gas is mixed with the ethylene gas and the trichlorosilane gas first, the aluminum atoms are combined with the carbon atoms under a high-temperature environment before the aluminum atoms replace the silicon atoms, and the aluminum atoms are not uniformly distributed, thereby causing the prepared P-type silicon carbide epitaxial wafer to have a non-uniform doping concentration. The dopant gas and the main reaction gas are input into the reaction chamber in a layered manner through the double-channel gas input mode of the layered gas distribution box, the local premature reaction caused by the traditional mixed input is avoided, and the doping concentration uniformity of the P-type silicon carbide epitaxial wafer is improved.

[0008] Optionally, after the hydrogen gas with the preset flow rate is input into the reaction chamber, the silicon carbide substrate is placed in the reaction chamber, including: The reaction chamber is adjusted to a preset preheating temperature, and hydrogen gas with a preset flow rate is input into the reaction chamber. The gas pressure of the reaction chamber is adjusted to atmospheric pressure, and the silicon carbide substrate is placed in the reaction chamber.

[0009] Optionally, the preset preheating temperature is 850-950℃, and the preset flow rate is 100-300slm.

[0010] Optionally, the preset etching temperature is 1650℃, and the preset etching pressure is 100mbar.

[0011] Optionally, the ethylene gas and the trichlorosilane gas are input into the reaction chamber through the lower channel of the layered gas distribution box, and the trimethylaluminum gas is input into the reaction chamber through the upper channel of the layered gas distribution box, so as to promote the growth of the epitaxial layer of the silicon carbide substrate after the surface etching, and a P-type silicon carbide epitaxial wafer with a uniform doping concentration is prepared, including: The temperature, the pressure and the input flow rate of the hydrogen gas are kept unchanged; Based on the preset ethylene input flow rate, the preset trichlorosilane input flow rate and the preset trimethylaluminum input flow rate, the ethylene gas and the trichlorosilane gas are input into the reaction chamber through the lower channel of the layered gas distribution box, and the trimethylaluminum gas is input into the reaction chamber through the upper channel of the layered gas distribution box, so as to promote the growth of the epitaxial layer of the silicon carbide substrate after the surface etching, and the silicon carbide epitaxial wafer after the epitaxial growth is obtained; The gas pressure of the reaction chamber is adjusted to atmospheric pressure, and the silicon carbide epitaxial wafer after the epitaxial growth is taken out from the reaction chamber after the reaction chamber naturally cools down to a preset extraction temperature, and a P-type silicon carbide epitaxial wafer with a uniform doping concentration is obtained.

[0012] The method for improving the doping concentration uniformity of the P-type silicon carbide epitaxial wafer provided in the application can realize the preparation of the P-type silicon carbide epitaxial wafer with a doping concentration, the structure characteristics of the layered gas distribution box are used to form a layered gas flow in the reaction chamber, which can avoid the premature consumption of trimethylaluminum in the central high-temperature zone and stabilize the gas flow field on the substrate surface through the carbon source gas flow in the lower channel, so as to promote the uniform incorporation of aluminum atoms into the lattice in each region of the substrate, thereby targetedly relieving the V-type distribution defect of the edge doping being too dense and the center doping being insufficient.

[0013] Optionally, the preset ethylene input flow rate includes a preset first ethylene input flow rate and a preset second ethylene input flow rate; the preset trichlorosilane input flow rate includes a preset first trichlorosilane input flow rate and a preset second trichlorosilane input flow rate; the preset trimethylaluminum input flow rate includes a preset first trimethylaluminum input flow rate and a preset second trimethylaluminum input flow rate; based on the preset ethylene input flow rate, the preset trichlorosilane input flow rate and the preset trimethylaluminum input flow rate, ethylene gas and trichlorosilane gas are input into the reaction chamber through the lower channel of the layered gas distribution box, and trimethylaluminum gas is input into the reaction chamber through the upper channel of the layered gas distribution box, so as to promote the growth of an epitaxial layer on the surface-etched silicon carbide substrate, and obtain a silicon carbide epitaxial wafer after epitaxial growth, including: Based on the preset first ethylene input flow rate, the preset first trichlorosilane input flow rate and the preset first trimethylaluminum input flow rate, in combination with a preset first growth time, ethylene gas and trichlorosilane gas are input into the reaction chamber through the lower channel of the layered gas distribution box, and trimethylaluminum gas is input into the reaction chamber through the upper channel of the layered gas distribution box, so as to promote the growth of a buffer layer on the surface-etched silicon carbide substrate, and obtain a silicon carbide substrate with a grown buffer layer; Based on the preset second ethylene input flow rate, the preset second trichlorosilane input flow rate and the preset second trimethylaluminum input flow rate, in combination with a preset second growth time, the ethylene gas and the trichlorosilane gas are input into the reaction chamber through the lower channel of the layered gas distribution box, and the trimethylaluminum gas is input into the reaction chamber through the upper channel of the layered gas distribution box, so as to promote the growth of an epitaxial layer on the silicon carbide substrate with a grown buffer layer, and obtain a silicon carbide epitaxial wafer after epitaxial growth.

[0014] The method for improving the doping concentration uniformity of the P-type silicon carbide epitaxial wafer provided in the application can realize the preparation of the P-type silicon carbide epitaxial wafer with a doping concentration, the structure characteristics of the layered gas distribution box are used to form a layered gas flow in the reaction chamber, which can avoid the premature consumption of trimethylaluminum in the central high-temperature zone and stabilize the gas flow field on the substrate surface through the carbon source gas flow in the lower channel, so as to promote the uniform incorporation of aluminum atoms into the lattice in each region of the substrate, thereby targetedly relieving the V-type distribution defect of the edge doping being too dense and the center doping being insufficient.

[0015] Optionally, the preset first ethylene flow rate is 20-100 sccm; the preset second ethylene flow rate is 50-200 sccm; the preset first trichlorosilane flow rate is 50-200 sccm; the preset second trichlorosilane flow rate is 100-400 sccm; the preset first trimethylaluminum flow rate is 100-300 sccm; and the preset second trimethylaluminum flow rate is 5-60 sccm.

[0016] Optionally, the preset first growth time is 5-10 min; and the preset second growth time is 10-20 min.

[0017] Optionally, the preset extraction temperature is 900℃.

[0018] Optionally, after the preparation of the P-type silicon carbide epitaxial wafer with uniform doping concentration by inputting the ethylene gas and the trichlorosilane gas into the reaction chamber through the lower channel of the layered gas distribution box and inputting the trimethylaluminum gas into the reaction chamber through the upper channel of the layered gas distribution box to promote the growth of the epitaxial layer on the etched silicon carbide substrate, the method further comprises: testing the doping concentration of the P-type silicon carbide epitaxial wafer to ensure that the doping concentration of the P-type silicon carbide epitaxial wafer is uniform.

[0019] Beneficial effects: The method for improving the doping concentration uniformity of the P-type silicon carbide epitaxial wafer provided by the present application promotes the growth of the epitaxial layer on the silicon carbide substrate by inputting the ethylene gas and the trichlorosilane gas into the reaction chamber through the lower channel of the layered gas distribution box and inputting the trimethylaluminum gas into the reaction chamber through the upper channel of the layered gas distribution box to prepare the P-type silicon carbide epitaxial wafer with uniform doping concentration, solves the problem that the existing P-type silicon carbide epitaxial wafer preparation method first mixes the trimethylaluminum gas with the ethylene gas and the trichlorosilane gas, so that the aluminum atoms combine with the carbon atoms before replacing the silicon atoms in the high-temperature environment, resulting in uneven distribution of the aluminum atoms and uneven doping concentration distribution of the prepared P-type silicon carbide epitaxial wafer, and the layered gas distribution box is used to input the dopant gas and the main reaction gas in layers, avoiding the local premature reaction caused by the traditional mixed input and improving the doping concentration uniformity of the P-type silicon carbide epitaxial wafer. BRIEF DESCRIPTION OF DRAWINGS

[0020] Figure 1 The flowchart of the method for improving the doping concentration uniformity of the P-type silicon carbide epitaxial wafer provided by the present application is shown.

[0021] Figure 2 The structure diagram of the layered gas distribution box of the present application is shown.

[0022] Figure 3A schematic diagram of a doping concentration distribution of a P-type silicon carbide epitaxial wafer according to an embodiment of the present application.

[0023] Figure 4 A schematic diagram of a doping concentration distribution of a P-type silicon carbide epitaxial wafer according to an embodiment of the present application after reducing the hydrogen flow.

[0024] Figure 5 A schematic diagram of a doping concentration distribution of a P-type silicon carbide epitaxial wafer prepared by a conventional preparation method.

[0025] Label description: 1, uniform gas box; 2, lower channel; 3, upper channel; 4, upper gas inlet pipe; 5, lower gas inlet pipe. DETAILED DESCRIPTION

[0026] The technical solutions in the embodiments of the present application will be clearly and completely described below with reference to the drawings in the embodiments of the present application. Obviously, the described embodiments are only part of the embodiments of the present application, rather than all the embodiments of the present application. The components of the embodiments of the present application described and shown in the drawings herein can be arranged and designed in various different configurations. Therefore, the following detailed description of the embodiments of the present application provided in the drawings is not intended to limit the scope of the claimed present application, but only represents selected embodiments of the present application. Based on the embodiments of the present application, all other embodiments obtained by those skilled in the art without creative work fall within the scope of the present application.

[0027] It should be noted that: similar labels and letters represent similar items in the following drawings, therefore, once an item is defined in one drawing, it does not need to be further defined and explained in subsequent drawings. Meanwhile, in the description of the present application, the terms "first", "second", etc. are only used for differentiation in description, and cannot be understood as indicating or implying relative importance.

[0028] Please refer to Figure 1 , Figure 1 A method for improving the doping concentration uniformity of a P-type silicon carbide epitaxial wafer in some embodiments of the present application, which uses a layered uniform gas box to prepare a P-type silicon carbide epitaxial wafer with uniform doping concentration. The layered uniform gas box (the specific structure is shown in Figure 2 ) includes a uniform gas box 1 and upper and lower channels 3 and 2 arranged inside the uniform gas box. The method for improving the doping concentration uniformity of the P-type silicon carbide epitaxial wafer includes: Step S1, performing a vacuum pumping operation on the reaction chamber of the epitaxial furnace; Step S2, after introducing a preset flow of hydrogen into the reaction chamber, placing a silicon carbide substrate in the reaction chamber; Step S3, keep the input flow rate of hydrogen unchanged, respectively adjust the temperature and pressure of the reaction chamber to the preset etching temperature and the preset etching pressure, to etch the surface of the silicon carbide substrate, to obtain a silicon carbide substrate after surface etching; Step S4, input ethylene gas and trichlorosilane gas into the reaction chamber through the lower channel of the layered gas distribution box, and input trimethylaluminum gas into the reaction chamber through the upper channel of the layered gas distribution box, to promote the growth of an epitaxial layer on the silicon carbide substrate after surface etching, to obtain a P-type silicon carbide epitaxial wafer with uniform doping concentration.

[0029] The method for improving the uniformity of the doping concentration of the P-type silicon carbide epitaxial wafer, by inputting ethylene gas and trichlorosilane gas into the reaction chamber through the lower channel of the layered gas distribution box, and inputting trimethylaluminum gas into the reaction chamber through the upper channel of the layered gas distribution box, to promote the growth of an epitaxial layer on the silicon carbide substrate, to obtain a P-type silicon carbide epitaxial wafer with uniform doping concentration, solves the problem of uneven distribution of aluminum atoms caused by the combination of aluminum atoms with carbon atoms at high temperature in the prior art P-type silicon carbide epitaxial wafer preparation method, which causes uneven distribution of aluminum atoms, and thus uneven distribution of the doping concentration of the prepared P-type silicon carbide epitaxial wafer. By the double-channel gas input method of the layered gas distribution box, the dopant gas and the main reaction gas are layered input, which avoids the local premature reaction caused by traditional mixed input, and improves the uniformity of the doping concentration of the P-type silicon carbide epitaxial wafer.

[0030] Specifically, as shown in Figure 2 , Figure 2 is a structural diagram of the layered gas distribution box, wherein the arrows represent the gas flow direction. In actual application, the upper inlet pipe 4 and the lower inlet pipe 5 are respectively used as the gas inlets of the upper channel 3 and the lower channel 2. The ethylene gas and the trichlorosilane gas (carbon source and silicon source) are first input into the lower inlet pipe 5 and then input into the reaction chamber through the lower channel 2. The trimethylaluminum gas (P-type dopant) is first input into the upper inlet pipe 4 and then input into the reaction chamber through the upper channel 3. This layered input strategy keeps different types of reaction gases separated before entering the reaction chamber, thereby avoiding premature mixing to prevent aluminum atoms from combining with carbon atoms first, which causes uneven distribution of aluminum atoms in the reaction chamber. This layered input strategy enables the trimethylaluminum gas to diffuse to the surface of the silicon carbide substrate in a more independent and more controlled manner after entering the reaction chamber, thereby promoting the more uniform embedding of aluminum atoms into the silicon carbide lattice on the entire substrate surface.

[0031] Therefore, the layered gas distribution box effectively separates the premature mixing of the trimethylaluminum gas and the ethylene gas and the trichlorosilane gas in space, and slows down the chemical reaction rate of the trimethylaluminum gas and the ethylene gas and the trichlorosilane gas in the reaction chamber, which is equivalent to inhibiting the rate of Al atoms incorporating into the 4H-SiC epitaxial film lattice. In this way, the Al atoms have more kinetic energy to move above the center of the silicon carbide substrate and then combine with C atoms to incorporate into the 4H-SiC epitaxial film lattice. In this way, the low doping concentration at the center of the 4H-SiC epitaxial wafer can be compensated for, and the P-type doping concentration of the 4H-SiC epitaxial wafer edge and center can be flattened, thereby solving the V-shaped distribution problem of the P-type silicon carbide epitaxial wafer doping concentration.

[0032] In some optional embodiments, the single-channel ports of the upper channel and the lower channel can be adjusted to multi-channel ports (i.e., multiple gas outlets) respectively, so that the gas flow output of different gas output positions can be adjusted according to actual conditions during the growth of the silicon carbide substrate, such as setting a baffle or a valve at each gas outlet to control the gas flow, so as to ensure the uniformity of the doping concentration of the P-type silicon carbide epitaxial wafer; or the upper channel and the lower channel can be adjusted to left and right channels (the upper gas inlet pipe and the lower gas inlet pipe are adjusted to left and right gas inlet pipes) respectively, so as to realize more ways of separate input.

[0033] Specifically, in step S1, the reaction chamber is vacuumized to remove residual gas and impurities in the reaction chamber, so as to provide a clean reaction environment for subsequent epitaxial growth, wherein the vacuum degree reaches 1E-4~9E-4 mbar, and the reaction chamber is ensured to be airtight.

[0034] Specifically, in step S2, after the preset flow of hydrogen gas is introduced into the reaction chamber, the silicon carbide substrate is placed in the reaction chamber, including: The reaction chamber is adjusted to a preset preheating temperature, and the preset flow of hydrogen gas is introduced into the reaction chamber; The gas pressure of the reaction chamber is adjusted to atmospheric pressure, and the silicon carbide substrate is placed in the reaction chamber.

[0035] In step S2, the reaction chamber is adjusted to a preset preheating temperature and a preset flow of hydrogen gas (within a certain range, the higher the hydrogen flow, the more uniform the doping concentration of the finally prepared silicon carbide epitaxial wafer), so that when the substrate enters the reaction chamber, the difference between the ambient temperature and the temperature of the substrate itself is reduced, thereby effectively reducing the thermal stress of the substrate due to sudden temperature change, avoiding the damage or defects of the substrate. After the hydrogen flow is stable, the gas pressure of the reaction chamber is adjusted to atmospheric pressure (i.e., 960 mbar), and the substrate placement operation is carried out under atmospheric pressure, which can provide a more stable and controllable operation environment, reduce the operation difficulty, and reduce the potential influence of the external environment on the cleanliness of the reaction chamber interior, thereby ensuring the accuracy and safety of the substrate placement process.

[0036] wherein the preset preheating temperature is 850-950℃; and the preset flow rate is 100-300 slm.

[0037] Specifically, in step S3, the reaction chamber is heated to a preset etching temperature and adjusted to a preset etching pressure while maintaining the continuous input of hydrogen, and the surface of the silicon carbide substrate is etched to remove the surface defect layer and activate the substrate surface active sites, thereby obtaining a silicon carbide substrate after surface etching.

[0038] Specifically, in step S4, the ethylene gas and trichlorosilane gas are input into the reaction chamber through the lower channel of the layered gas distribution box, and the trimethylaluminum gas is input into the reaction chamber through the upper channel of the layered gas distribution box to promote the growth of the epitaxial layer on the silicon carbide substrate after surface etching, thereby obtaining a P-type silicon carbide epitaxial wafer with uniform doping concentration, comprising: maintaining the temperature, pressure and hydrogen flow rate; based on the preset ethylene flow rate, the preset trichlorosilane flow rate and the preset trimethylaluminum flow rate, the ethylene gas and trichlorosilane gas are input into the reaction chamber through the lower channel of the layered gas distribution box, and the trimethylaluminum gas is input into the reaction chamber through the upper channel of the layered gas distribution box to promote the growth of the epitaxial layer on the silicon carbide substrate after surface etching, thereby obtaining a silicon carbide epitaxial wafer after epitaxial growth; adjusting the gas pressure of the reaction chamber to atmospheric pressure, and after the reaction chamber naturally cools to a preset extraction temperature, taking out the silicon carbide epitaxial wafer after epitaxial growth from the reaction chamber, thereby obtaining a P-type silicon carbide epitaxial wafer with uniform doping concentration.

[0039] In step S4, the temperature, pressure and hydrogen flow rate are kept stable, providing a constant physical and chemical environment for epitaxial growth, avoiding the adverse effects of growth condition fluctuations on the uniformity of the epitaxial layer. Based on the preset ethylene flow rate, trichlorosilane flow rate and trimethylaluminum flow rate, and using the channel separation input of the layered gas distribution box, the carbon source, silicon source and dopant can reach the substrate surface in precise and stable proportions and distribution. The precise control of the flow rate of trimethylaluminum as a dopant directly determines the number of dopant atoms, and the design of the layered gas distribution box ensures the uniform distribution of the dopant on the entire substrate surface, thereby fundamentally ensuring the high uniformity of the doping concentration of the epitaxial layer. In addition, after epitaxial growth, by adjusting the gas pressure of the reaction chamber to atmospheric pressure and naturally cooling to a preset extraction temperature, thermal stress, defects or surface contamination that may be introduced due to rapid cooling or improper operation are effectively avoided, which can all damage the uniformity of the formed epitaxial layer. The silicon carbide epitaxial wafer after epitaxial growth is taken out from the reaction chamber, thereby obtaining a P-type silicon carbide epitaxial wafer with uniform doping concentration.

[0040] Specifically, the preset ethylene flow rate includes a preset first ethylene flow rate and a preset second ethylene flow rate; the preset trichlorosilane flow rate includes a preset first trichlorosilane flow rate and a preset second trichlorosilane flow rate; the preset trimethylaluminum flow rate includes a preset first trimethylaluminum flow rate and a preset second trimethylaluminum flow rate; in step S4, based on the preset ethylene flow rate, the preset trichlorosilane flow rate, and the preset trimethylaluminum flow rate, the ethylene gas and the trichlorosilane gas are input into the reaction chamber through the lower channel of the layered gas distribution box, and the trimethylaluminum gas is input into the reaction chamber through the upper channel of the layered gas distribution box, to promote the growth of the epitaxial layer on the surface-etched silicon carbide substrate, to obtain the silicon carbide epitaxial wafer after epitaxial growth, including: Based on the preset first ethylene flow rate, the preset first trichlorosilane flow rate, and the preset first trimethylaluminum flow rate, in combination with the preset first growth time, the ethylene gas and the trichlorosilane gas are input into the reaction chamber through the lower channel of the layered gas distribution box, and the trimethylaluminum gas is input into the reaction chamber through the upper channel of the layered gas distribution box, to promote the growth of the buffer layer on the surface-etched silicon carbide substrate, to obtain the silicon carbide substrate with the grown buffer layer; Based on the preset second ethylene flow rate, the preset second trichlorosilane flow rate, and the preset second trimethylaluminum flow rate, in combination with the preset second growth time, the ethylene gas and the trichlorosilane gas are input into the reaction chamber through the lower channel of the layered gas distribution box, and the trimethylaluminum gas is input into the reaction chamber through the upper channel of the layered gas distribution box, to promote the growth of the epitaxial layer on the silicon carbide substrate with the grown buffer layer, to obtain the silicon carbide epitaxial wafer after epitaxial growth.

[0041] In step S4, the growth process of the P-type silicon carbide epitaxial wafer is divided into two stages of buffer layer growth and epitaxial layer growth. In the buffer layer growth stage, a layer of buffer layer is formed on the surface-etched silicon carbide substrate by using the preset first ethylene flow rate, the preset first trichlorosilane flow rate, and the preset first trimethylaluminum flow rate, in combination with the preset first growth time. The buffer layer can effectively absorb and alleviate the lattice mismatch stress between the substrate and the epitaxial layer, and act as a barrier to block the micro-defects (such as dislocations, stacking faults, etc.) existing in the substrate from extending to the subsequently grown epitaxial layer. It is precisely because of the existence of the buffer layer that a solid foundation is laid for the growth of the subsequent high-quality epitaxial layer. Secondly, in the epitaxial layer growth stage, based on the preset second ethylene flow rate, the preset second trichlorosilane flow rate, and the preset second trimethylaluminum flow rate, in combination with the preset second growth time, the epitaxial layer is continuously grown on the silicon carbide substrate with the grown buffer layer. At this time, since the buffer layer has optimized the growth interface, the epitaxial layer can grow under more stable conditions, thereby obtaining more excellent crystal quality and more uniform doping distribution.

[0042] The preset first ethylene flow rate is 20-100 sccm; the preset second ethylene flow rate is 50-200 sccm; the preset first trichlorosilane flow rate is 50-200 sccm; the preset second trichlorosilane flow rate is 100-400 sccm; the preset first trimethylaluminum flow rate is 100-300 sccm; the preset second trimethylaluminum flow rate is 5-60 sccm; and the preset extraction temperature is 900℃. The preset first growth time is 5-10 min; and the preset second growth time is 10-20 min.

[0043] Specifically, in step S4, the ethylene gas and the trichlorosilane gas are input into the reaction chamber through the lower channel of the layered gas distribution box, and the trimethylaluminum gas is input into the reaction chamber through the upper channel of the layered gas distribution box, so as to promote the growth of the epitaxial layer on the surface-etched silicon carbide substrate, and obtain the P-type silicon carbide epitaxial wafer with uniform doping concentration. After that, the method further comprises: The P-type silicon carbide epitaxial wafer is subjected to a doping concentration test to ensure that the doping concentration of the P-type silicon carbide epitaxial wafer is uniform.

[0044] In step S4, the doping concentration distribution of the epitaxial wafer is quantitatively analyzed, so as to provide objective data support to determine whether the epitaxial wafer truly meets the requirement of uniform doping concentration. Once the test result shows that the uniformity of the doping concentration does not meet the standard, timely corrective measures can be taken, such as adjusting the growth parameters of the subsequent batches or screening the unqualified products to avoid their flowing into the subsequent device manufacturing links. Thus, the test step converts the uniformity from an expected value to a verifiable index, which significantly improves the quality control level of the production process.

[0045] In practical applications, as shown in Figure 3 , Figure 4 , Figure 5 , Figure 3 is a doping concentration distribution diagram of a P-type silicon carbide epitaxial wafer of the embodiment of the present application (a preparation method using a layered gas distribution box to pre-separate the input gas), Figure 4 is a doping concentration distribution diagram of a P-type silicon carbide epitaxial wafer of the embodiment of the present application (a preparation method using a layered gas distribution box to pre-separate the input gas but reducing the hydrogen flow rate), Figure 5A schematic diagram of the doping concentration distribution of a P-type silicon carbide epitaxial wafer prepared by a traditional preparation method (a preparation method without pre-separation of input gas by a layered gas distribution box), wherein a is a doping concentration distribution curve of a P-type silicon carbide epitaxial wafer prepared by an embodiment of the present application, b is a doping concentration distribution curve of a P-type silicon carbide epitaxial wafer prepared by an embodiment of the present application after reducing the hydrogen flow rate (the hydrogen flow rate is 100 slm), and c is a doping concentration distribution curve of a P-type silicon carbide epitaxial wafer prepared by a traditional preparation method (the hydrogen flow rate is 100 slm), Figure 3 、 Figure 4 and Figure 5 The abscissa is a pre-set measurement point (the specific setting position of the measurement point is edge-center-edge), and the ordinate is the doping concentration, with a unit of E15 cm -3 . It can be known from Figure 3 、 Figure 4 that the average value of the doping concentration of the P-type silicon carbide epitaxial wafer prepared by using the method for improving the doping concentration uniformity of a P-type silicon carbide epitaxial wafer provided by the embodiment of the present application (the hydrogen flow rate is 120 slm) is 9.82E15 cm -3 , and the doping concentration non-uniformity is 1.13%. The average value of the doping concentration of the P-type silicon carbide epitaxial wafer prepared by using the method for improving the doping concentration uniformity of a P-type silicon carbide epitaxial wafer provided by the embodiment of the present application (the hydrogen flow rate is 100 slm) after reducing the hydrogen flow rate is 9.22E15 cm -3 , and the doping concentration non-uniformity is 1.56%. Therefore, the method of using a hydrogen flow rate of 120 slm can promote more Al atoms to move to the position above the center of the SiC substrate and combine with C atoms, which is helpful to continue improving the uniformity of the P-type 4H-SiC doping concentration. It can be known from Figure 4 、 Figure 5 that the average value of the doping concentration of the P-type silicon carbide epitaxial wafer prepared by using the method for improving the doping concentration uniformity of a P-type silicon carbide epitaxial wafer provided by the embodiment of the present application (the hydrogen flow rate is 100 slm) after reducing the hydrogen flow rate is 9.22E15 cm -3 , and the doping concentration non-uniformity is 1.56%. The average value of the doping concentration of the P-type silicon carbide epitaxial wafer prepared by using a traditional preparation method (the hydrogen flow rate is 100 slm) is 8.43E15 cm -3 , and the doping concentration non-uniformity is 23.85%. Therefore, the layered gas distribution box and the method for improving the doping concentration uniformity of a P-type silicon carbide epitaxial wafer provided by the embodiment of the present application can level the doping concentration of the edge and the center of the P-type silicon carbide epitaxial wafer and solve the V-shaped distribution problem of the doping concentration of the P-type silicon carbide epitaxial wafer.

[0046] From the above, the method for improving the doping concentration uniformity of the P-type silicon carbide epitaxial wafer, by vacuumizing the reaction chamber of the epitaxial furnace, introducing hydrogen gas with a preset flow rate into the reaction chamber, placing the silicon carbide substrate in the reaction chamber, keeping the input flow rate of hydrogen gas unchanged, adjusting the temperature and pressure of the reaction chamber to the preset etching temperature and the preset etching pressure respectively, etching the surface of the silicon carbide substrate to obtain the silicon carbide substrate after surface etching, inputting ethylene gas and trichlorosilane gas into the reaction chamber through the lower channel of the layered gas distribution box, and inputting trimethylaluminum gas into the reaction chamber through the upper channel of the layered gas distribution box to promote the growth of the epitaxial layer of the silicon carbide substrate after surface etching, and the P-type silicon carbide epitaxial wafer with uniform doping concentration is prepared; thereby, by inputting ethylene gas and trichlorosilane gas into the reaction chamber through the lower channel of the layered gas distribution box, and inputting trimethylaluminum gas into the reaction chamber through the upper channel of the layered gas distribution box to promote the growth of the epitaxial layer of the silicon carbide substrate, and the P-type silicon carbide epitaxial wafer with uniform doping concentration is prepared, the problem that the prepared P-type silicon carbide epitaxial wafer has uneven doping concentration distribution due to the fact that the aluminum atoms are combined with carbon atoms first under the high-temperature environment before the aluminum atoms replace silicon atoms, which is caused by the fact that the trimethylaluminum gas is mixed with ethylene gas and trichlorosilane gas in the prior method for preparing the P-type silicon carbide epitaxial wafer, the problem is solved, and the doping agent gas and the main reaction gas are inputted in layers through the double-channel gas input mode of the layered gas distribution box, which avoids the local premature reaction caused by the traditional mixed input, and improves the doping concentration uniformity of the P-type silicon carbide epitaxial wafer.

[0047] In this document, the term "only" is used to distinguish one entity or operation from another entity or operation, but does not necessarily require or imply that there is any such actual relationship or order between the entities or operations.

[0048] The above only describes the embodiments of the present application and is not used to limit the protection scope of the present application. For those skilled in the art, the present application can have various modifications and changes. 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 improving the doping concentration uniformity of a P-type silicon carbide epitaxial wafer, comprising using a layered gas homogenizing box to prepare a P-type silicon carbide epitaxial wafer with uniform doping concentration, characterized in that, The layered gas equalization box includes a gas equalization box and an upper channel and a lower channel disposed inside the gas equalization box; The method for improving the doping concentration uniformity of the P-type silicon carbide epitaxial wafer includes: Vacuuming is performed on the reaction chamber of the epitaxial furnace; After introducing hydrogen gas at a predetermined flow rate into the reaction chamber, the silicon carbide substrate is placed in the reaction chamber. Keeping the hydrogen input flow rate constant, the temperature and pressure of the reaction chamber are adjusted to a preset etching temperature and a preset etching pressure, respectively, to etch the surface of the silicon carbide substrate to obtain a silicon carbide substrate with surface etching. Ethylene gas and trichlorosilane gas are introduced into the reaction chamber through the lower channel of the layered gas equalization box, and trimethylaluminum gas is introduced into the reaction chamber through the upper channel of the layered gas equalization box to promote the growth of epitaxial layers on the silicon carbide substrate after surface etching, thereby preparing a P-type silicon carbide epitaxial wafer with uniform doping concentration.

2. The method for improving the doping concentration uniformity of P-type silicon carbide epitaxial wafers according to claim 1, characterized in that, After introducing hydrogen gas at a predetermined flow rate into the reaction chamber, a silicon carbide substrate is placed in the reaction chamber, including: The reaction chamber is adjusted to a preset preheating temperature, and hydrogen gas is introduced into the reaction chamber at a preset flow rate. The gas pressure in the reaction chamber is adjusted to atmospheric pressure, and the silicon carbide substrate is placed in the reaction chamber.

3. The method for improving the doping concentration uniformity of P-type silicon carbide epitaxial wafers according to claim 2, characterized in that, The preset preheating temperature is 850~950℃; the preset flow rate is 100~300slm.

4. The method for improving the doping concentration uniformity of P-type silicon carbide epitaxial wafers according to claim 1, characterized in that, The preset etching temperature is 1650℃; the preset etching pressure is 100mbar.

5. The method for improving the doping concentration uniformity of P-type silicon carbide epitaxial wafers according to claim 1, characterized in that, Ethylene gas and trichlorosilane gas are introduced into the reaction chamber through the lower channel of the layered gas homogenizer, and trimethylaluminum gas is introduced into the reaction chamber through the upper channel of the layered gas homogenizer to promote the growth of an epitaxial layer on the surface-etched silicon carbide substrate, thereby preparing a P-type silicon carbide epitaxial wafer with uniform doping concentration, comprising: Keep the temperature, pressure, and hydrogen flow rate constant; Based on preset ethylene flow rate, preset trichlorosilane flow rate, and preset trimethylaluminum flow rate, ethylene gas and trichlorosilane gas are introduced into the reaction chamber through the lower channel of the layered gas equalization box, and trimethylaluminum gas is introduced into the reaction chamber through the upper channel of the layered gas equalization box to promote the growth of an epitaxial layer on the surface-etched silicon carbide substrate, thereby obtaining an epitaxially grown silicon carbide epitaxial wafer. The gas pressure in the reaction chamber is adjusted to atmospheric pressure, and after the reaction chamber cools down naturally to the preset extraction temperature, the epitaxial silicon carbide wafer grown after epitaxial growth is taken out from the reaction chamber to obtain a P-type silicon carbide epitaxial wafer with uniform doping concentration.

6. The method for improving the doping concentration uniformity of a P-type silicon carbide epitaxial wafer according to claim 5, characterized in that, The preset ethylene flow rate includes a preset first ethylene flow rate and a preset second ethylene flow rate; the preset trichlorosilane flow rate includes a preset first trichlorosilane flow rate and a preset second trichlorosilane flow rate. The preset trimethylaluminum inlet flow rate includes a preset first trimethylaluminum inlet flow rate and a preset second trimethylaluminum inlet flow rate; Based on preset ethylene flow rates, preset trichlorosilane flow rates, and preset trimethylaluminum flow rates, ethylene gas and trichlorosilane gas are introduced into the reaction chamber through the lower channel of the layered gas homogenizer, and trimethylaluminum gas is introduced into the reaction chamber through the upper channel of the layered gas homogenizer to promote the growth of an epitaxial layer on the surface-etched silicon carbide substrate, resulting in an epitaxially grown silicon carbide wafer, comprising: Based on the preset first ethylene inlet flow rate, the preset first trichlorosilane inlet flow rate, and the preset first trimethylaluminum inlet flow rate, combined with the preset first growth time, ethylene gas and trichlorosilane gas are introduced into the reaction chamber through the lower channel of the layered gas equalization box, and trimethylaluminum gas is introduced into the reaction chamber through the upper channel of the layered gas equalization box, so as to promote the growth of the buffer layer on the surface-etched silicon carbide substrate, and obtain a silicon carbide substrate with a buffer layer grown. Based on the preset second ethylene inlet flow rate, the preset second trichlorosilane inlet flow rate, and the preset second trimethylaluminum inlet flow rate, combined with the preset second growth time, the ethylene gas and the trichlorosilane gas are introduced into the reaction chamber through the lower channel of the layered gas equalization box, and the trimethylaluminum gas is introduced into the reaction chamber through the upper channel of the layered gas equalization box, so as to promote the growth of the epitaxial layer on the silicon carbide substrate with the buffer layer, and obtain the epitaxially grown silicon carbide epitaxial wafer.

7. The method for improving the doping concentration uniformity of P-type silicon carbide epitaxial wafers according to claim 6, characterized in that, The preset first ethylene flow rate is 20~100 sccm; the preset second ethylene flow rate is 50~200 sccm; the preset first trichlorosilane flow rate is 50~200 sccm; the preset second trichlorosilane flow rate is 100~400 sccm; the preset first trimethylaluminum flow rate is 100~300 sccm; and the preset second trimethylaluminum flow rate is 5~60 sccm.

8. The method for improving the doping concentration uniformity of a P-type silicon carbide epitaxial wafer according to claim 6, characterized in that, The preset first growth time is 5-10 min; the preset second growth time is 10-20 min.

9. The method for improving the doping concentration uniformity of a P-type silicon carbide epitaxial wafer according to claim 5, characterized in that, The preset extraction temperature is 900℃.

10. The method for improving the doping concentration uniformity of a P-type silicon carbide epitaxial wafer according to claim 1, characterized in that, Ethylene gas and trichlorosilane gas are introduced into the reaction chamber through the lower channel of the layered gas homogenizer, and trimethylaluminum gas is introduced into the reaction chamber through the upper channel of the layered gas homogenizer to promote the growth of an epitaxial layer on the surface-etched silicon carbide substrate. After preparing a P-type silicon carbide epitaxial wafer with uniform doping concentration, the process further includes: The doping concentration of the P-type silicon carbide epitaxial wafer is tested to ensure that the doping concentration of the P-type silicon carbide epitaxial wafer is uniform.

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