Method for prolonging minority carrier lifetime of silicon carbide epitaxial wafer, silicon carbide epitaxial wafer and semiconductor device

Abstract

The invention provides a method for prolonging minority carrier lifetime of a silicon carbide epitaxial wafer, the silicon carbide epitaxial wafer and a semiconductor device. The method comprises the following steps: acquiring the silicon carbide epitaxial wafer; plasma bombardment treatment is carried out on the surface of the silicon carbide epitaxial wafer by adopting mixed gas, so that surface activation is carried out on the silicon carbide epitaxial wafer, and the mixed gas comprises hydrogen and inert gas; in an inert gas environment, performing laser scanning on the surface of the silicon carbide epitaxial wafer after plasma bombardment treatment so as to generate a nano carbon film on the surface of the silicon carbide epitaxial wafer; and at least in an inert gas environment, carrying out medium-temperature annealing on the silicon carbide epitaxial wafer on which the nano carbon film is generated. The problem that in the prior art, when a silicon carbide epitaxial wafer is applied to a bipolar high-voltage power device, the service life of minority carriers is short is solved.

Description

Technical Field

[0001] This application relates to the field of semiconductor technology, and more specifically, to a method for improving the minority carrier lifetime of a silicon carbide epitaxial wafer, a silicon carbide epitaxial wafer, and a semiconductor device. Background Technology

[0002] Silicon carbide (SiC), as a wide-bandgap semiconductor material, possesses advantages such as high thermal conductivity, high breakdown electric field, and high saturated electron drift velocity, making it widely used in high-temperature, high-frequency, high-power, and radiation-resistant applications. For bipolar silicon carbide power devices used under ultra-high voltage conditions, minority carrier lifetime can improve their conductivity modulation characteristics and reduce the device's on-resistance, playing a crucial role in improving and optimizing semiconductor device performance. Currently, silicon carbide epitaxial wafers exhibit relatively low minority carrier lifetimes in bipolar high-voltage power device applications. Summary of the Invention

[0003] The main objective of this application is to provide a method for improving the minority carrier lifetime of silicon carbide epitaxial wafers, as well as silicon carbide epitaxial wafers and semiconductor devices, to solve the problem of low minority carrier lifetime of silicon carbide epitaxial wafers in bipolar high-voltage power device applications in the prior art.

[0004] To achieve the above objectives, according to one aspect of this application, a method for improving the minority carrier lifetime of a silicon carbide epitaxial wafer is provided, comprising: obtaining a silicon carbide epitaxial wafer; subjecting the surface of the silicon carbide epitaxial wafer to plasma bombardment treatment with a mixed gas to activate the surface of the silicon carbide epitaxial wafer, wherein the mixed gas includes hydrogen and an inert gas; performing laser scanning on the surface of the plasma-bombarded silicon carbide epitaxial wafer in an inert gas environment to generate a nano-carbon film on the surface of the silicon carbide epitaxial wafer; and performing intermediate-temperature annealing on the silicon carbide epitaxial wafer with the nano-carbon film generated, at least in an inert gas environment.

[0005] Optionally, the hydrogen content in the mixed gas is 30%-80%.

[0006] Optionally, the gas flow rate of the plasma bombardment treatment is 50 sccm-100 sccm, the gas pressure is 10 Pa-50 Pa, the treatment time is 5 minutes-15 minutes, and the power of the radio frequency plasma machine used in the plasma bombardment treatment is 50 W-150 W.

[0007] Optionally, laser scanning is performed on the surface of the silicon carbide epitaxial wafer after plasma bombardment treatment, including: controlling the laser focus of the laser to be positioned at the center position of the surface of the silicon carbide epitaxial wafer, and starting from the center position, performing laser scanning on the surface of the silicon carbide epitaxial wafer in a direction pointing outward from the center position, wherein the scanning path unfolds in a spiral shape, and the laser energy density is 2J / cm². 2 -5J / cm 2 .

[0008] Optionally, in laser scanning, the scanning speed is 10mm / s-50mm / s, the scanning spacing is 10μm-45μm, and the laser spot diameter is 50μm-100μm.

[0009] Optionally, the annealing temperature for medium-temperature annealing is 700℃-1300℃, and the annealing time is 1 hour-10 hours.

[0010] Optionally, the silicon carbide epitaxial wafer on which the nano-carbon film is formed is subjected to intermediate-temperature annealing, at least in an inert gas environment, including: performing intermediate-temperature annealing on the silicon carbide epitaxial wafer in an environment in which silicon source gas and inert gas are mixed.

[0011] Optionally, the inert gas in the mixed gas includes argon, the inert gas in the laser scanning includes argon, and the inert gas in the intermediate-temperature annealing includes argon.

[0012] According to another aspect of this application, a silicon carbide epitaxial wafer is provided, which is prepared by any of the methods described above for improving the minority carrier lifetime of silicon carbide epitaxial wafers.

[0013] According to another aspect of this application, a semiconductor device is provided, comprising the aforementioned silicon carbide epitaxial wafer.

[0014] The technical solution of this application involves first obtaining a silicon carbide epitaxial wafer, then using a mixed gas including hydrogen and inert gas to bombard the surface of the silicon carbide epitaxial wafer with plasma to activate the surface of the silicon carbide epitaxial wafer, then performing laser scanning on the surface of the plasma-bombarded silicon carbide epitaxial wafer in an inert gas environment to generate a nano-carbon film on the surface of the silicon carbide epitaxial wafer, and finally performing medium-temperature annealing on the silicon carbide epitaxial wafer with the nano-carbon film generated, at least in an inert gas environment. Compared to the problem of low minority carrier lifetime in existing technologies for silicon carbide epitaxial wafers used in bipolar high-voltage power devices, this application utilizes plasma bombardment to activate the surface of silicon carbide epitaxial wafers. The use of a mixed gas of hydrogen and inert gas enhances the surface activity of the silicon carbide epitaxial wafer while removing surface impurities. Hydrogen in the plasma promotes chemical reactions, generating active Si-H bonds, increasing the dangling bond density on the silicon carbide epitaxial layer surface, thus enhancing surface activity and promoting subsequent carbon atom adsorption and nucleation. This provides favorable conditions for the uniform formation of subsequent nano-carbon films. The inert gas also acts as a physical cleaner, ensuring surface purity and reducing the possibility of deep-level defects. Laser scanning in an inert gas environment allows for precise control of the thermal effect region. This reduces the problem of uneven carbon layer distribution on the surface that may be caused by overall high-temperature heating. Laser scanning can locally heat the surface of silicon carbide epitaxial wafers, causing silicon atoms to sublimate, while carbon atoms aggregate on the surface to form a nano-carbon film. The formation of this nano-carbon film is not only controllable in thickness but also uniform in distribution, which is crucial for repairing carbon vacancy defects in the silicon carbide lattice. This is because the carbon atoms generated by the uniform nano-carbon film can more effectively fill these defects, reduce deep-level traps, and thus extend minority carrier lifetime. At least, medium-temperature annealing of the silicon carbide epitaxial wafer with nano-carbon film in an inert gas environment can promote the diffusion of carbon atoms. Carbon atoms diffuse into the silicon carbide lattice and repair carbon vacancies. That is, carbon defects are repaired by carbon atoms in the carbon film, reducing deep-level defects and ensuring a longer minority carrier lifetime. Attached Figure Description

[0015] The accompanying drawings, which form part of this application, are used to provide a further understanding of this application. The illustrative embodiments and descriptions of this application are used to explain this application and do not constitute an undue limitation of this application. In the drawings:

[0016] Figure 1 A schematic flowchart of a method for improving the minority carrier lifetime of a silicon carbide epitaxial wafer according to an embodiment of this application is shown.

[0017] Figure 2 A schematic diagram illustrating the process by which silicon atoms sublimate to form a nano-carbon film on the surface of a silicon carbide epitaxial wafer according to an embodiment of this application is shown.

[0018] Figure 3 A schematic diagram illustrating the process by which carbon atoms in a nano-carbon film and silicon atoms in a silicon source diffuse into a silicon carbide epitaxial wafer according to an embodiment of this application is shown.

[0019] Figure 4 The diagram shows a comparison of the minority carrier lifetime of a silicon carbide epitaxial wafer before and after processing using the method for improving minority carrier lifetime of silicon carbide epitaxial wafers according to this application.

[0020] Figure 5 A schematic diagram of a specific method for improving the minority carrier lifetime of a silicon carbide epitaxial wafer according to an embodiment of this application is shown.

[0021] The above figures include the following reference numerals:

[0022] 1. Silicon carbide epitaxial wafer; 2. Nanocarbon film; 3. First silicon atom; 4. Second silicon atom; 5. Carbon vacancy; 6. Silicon vacancy. Detailed Implementation

[0023] It should be noted that the following detailed descriptions are illustrative and intended to provide further explanation of this application. Unless otherwise specified, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application pertains.

[0024] It should be noted that the terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit the exemplary embodiments according to this application. As used herein, the singular form is intended to include the plural form as well, unless the context clearly indicates otherwise. Furthermore, it should be understood that when the terms "comprising" and / or "including" are used in this specification, they indicate the presence of features, steps, operations, devices, components, and / or combinations thereof.

[0025] It should be noted that the terms "first," "second," etc., in the specification, claims, and accompanying drawings of this invention are used to distinguish similar objects and are not necessarily used to describe a specific order or sequence. It should be understood that such data can be interchanged where appropriate for the embodiments of the invention described herein. Furthermore, the terms "comprising" and "having," and any variations thereof, are intended to cover non-exclusive inclusion; for example, a process, method, system, product, or apparatus that comprises a series of steps or units is not necessarily limited to those steps or units explicitly listed, but may include other steps or units not explicitly listed or inherent to such processes, methods, products, or apparatus.

[0026] It should be understood that when an element (such as a layer, film, region, or substrate) is described as being "on" another element, the element may be directly on the other element, or there may be an intermediate element present. Furthermore, in the specification and claims, when an element is described as being "connected" to another element, the element may be "directly connected" to the other element, or "connected" to the other element via a third element.

[0027] For ease of description, the following explains some of the nouns or terms used in the embodiments of this application:

[0028] As described in the background section, silicon carbide epitaxial wafers in the prior art have a low minority carrier lifetime in bipolar high-voltage power device applications. To solve the above problem, embodiments of this application provide a method for improving the minority carrier lifetime of silicon carbide epitaxial wafers, a silicon carbide epitaxial wafer, and a semiconductor device.

[0029] The technical solutions of the present invention will be clearly and completely described below with reference to the accompanying drawings in the embodiments of the present invention.

[0030] Figure 1 This is a flowchart of a method for improving the minority carrier lifetime of a silicon carbide epitaxial wafer according to an embodiment of this application. Figure 1 As shown, the method includes the following steps:

[0031] Step S201: Obtain a silicon carbide epitaxial wafer;

[0032] Specifically, the silicon carbide epitaxial wafer comprises a stacked substrate and an epitaxial layer. The silicon carbide epitaxial wafer is 4H-SiC, and its thickness is 300μm-600μm. The epitaxial layer has a thickness of 50μm-300μm and a doping concentration of 5×10⁻⁶. 14 cm - 3-1×10 17 cm - 3.

[0033] In this embodiment, the thickness of the silicon carbide epitaxial wafer is 350 μm, the thickness of the epitaxial layer is 100 μm, and the doping concentration of the epitaxial layer is 5 × 10⁻⁶. 15 cm - 3.

[0034] Step S202: The surface of the silicon carbide epitaxial wafer is subjected to plasma bombardment treatment using a mixed gas to activate the surface of the silicon carbide epitaxial wafer. The mixed gas includes hydrogen and an inert gas.

[0035] Specifically, hydrogen mainly plays a role in chemical activation. In this application, surface activation refers to the interaction between free electrons and ions in the plasma and the surface of the silicon carbide epitaxial wafer, reducing surface oxides and forming new chemical bonds (such as Si-H bonds). This increases the dangling bond density on the surface, improves surface activity, and makes the subsequent formation of nano-carbon films more uniform and dense.

[0036] Specifically, the surface of a silicon carbide epitaxial wafer refers to the surface of the epitaxial layer.

[0037] In practical applications, those skilled in the art can flexibly select appropriate inert gases according to actual needs, and this application does not impose specific limitations in this regard. In the embodiments of this application, argon is selected as the inert gas in the mixed gas.

[0038] Step S203: In an inert gas environment, the surface of the silicon carbide epitaxial wafer after the plasma bombardment treatment is laser scanned to generate a nano-carbon film on the surface of the silicon carbide epitaxial wafer.

[0039] Specifically, a nanocarbon film refers to a carbon film with a thickness on the nanometer scale. In the embodiments of this application, a uniform nanocarbon film with a thickness of 500nm-8000nm is obtained on the surface of a silicon carbide epitaxial wafer.

[0040] Step S204: The silicon carbide epitaxial wafer from which the above-mentioned nano-carbon film is generated is subjected to medium-temperature annealing, at least in an inert gas environment.

[0041] In this embodiment, a silicon carbide epitaxial wafer is first obtained. Then, a mixed gas including hydrogen and inert gas is used to bombard the surface of the silicon carbide epitaxial wafer with plasma to activate the surface of the silicon carbide epitaxial wafer. Next, in an inert gas environment, the surface of the plasma-bombarded silicon carbide epitaxial wafer is laser-scanned to generate a nano-carbon film on the surface of the silicon carbide epitaxial wafer. Finally, the silicon carbide epitaxial wafer with the nano-carbon film generated is subjected to medium-temperature annealing, at least in an inert gas environment. Compared to the problem of low minority carrier lifetime in existing technologies for silicon carbide epitaxial wafers used in bipolar high-voltage power devices, this application utilizes plasma bombardment to activate the surface of silicon carbide epitaxial wafers. The use of a mixed gas of hydrogen and inert gas enhances the surface activity of the silicon carbide epitaxial wafer while removing surface impurities. Hydrogen in the plasma promotes chemical reactions, generating active Si-H bonds, increasing the dangling bond density on the silicon carbide epitaxial layer surface, thus enhancing surface activity and promoting subsequent carbon atom adsorption and nucleation. This provides favorable conditions for the uniform formation of subsequent nano-carbon films. The inert gas also acts as a physical cleaner, ensuring surface purity and reducing the possibility of deep-level defects. Laser scanning in an inert gas environment allows for precise control of the thermal effect region. This reduces the problem of uneven carbon layer distribution on the surface that may be caused by overall high-temperature heating. Laser scanning can locally heat the surface of silicon carbide epitaxial wafers, causing silicon atoms to sublimate, while carbon atoms aggregate on the surface to form a nano-carbon film. The formation of this nano-carbon film is not only controllable in thickness but also uniform in distribution, which is crucial for repairing carbon vacancy defects in the silicon carbide lattice. This is because the carbon atoms generated by the uniform nano-carbon film can more effectively fill these defects, reduce deep-level traps, and thus extend minority carrier lifetime. At least, medium-temperature annealing of the silicon carbide epitaxial wafer with nano-carbon film in an inert gas environment can promote the diffusion of carbon atoms. Carbon atoms diffuse into the silicon carbide lattice and repair carbon vacancies. That is, carbon defects are repaired by carbon atoms in the carbon film, reducing deep-level defects and ensuring a longer minority carrier lifetime.

[0042] It should be noted that, in order to improve minority carrier lifetime, the existing technologies that use chemical deposition to introduce foreign carbon sources or inductive coupling to heat the epitaxial wafer may introduce foreign substances and cause contamination of the epitaxial wafer. Alternatively, the high-temperature treatment and cooling process of heating the entire epitaxial wafer at high temperatures may lead to uneven distribution of the surface carbon layer, affecting the consistency of minority carrier lifetime.

[0043] In one alternative embodiment, the hydrogen content in the mixed gas is 30%-80%. In this embodiment, hydrogen mainly plays a role in chemical activation. Controlling the hydrogen content ensures surface activation while avoiding surface damage caused by excessive hydrogen introduction.

[0044] In other embodiments, the gas flow rate of the plasma bombardment treatment is 50 sccm-100 sccm, the gas pressure is 10 Pa-50 Pa, the treatment time is 5 minutes-15 minutes, and the power of the radio frequency plasma machine used in the plasma bombardment treatment is 50 W-150 W. In this embodiment, the gas flow rate is in the range of 50 sccm to 100 sccm, which ensures that the generated plasma has sufficient density to promote surface reaction, while avoiding turbulence caused by excessive flow rate. Turbulence will interfere with the uniform distribution of plasma and affect the uniform nucleation of subsequent nano-carbon films. The treatment time and gas pressure directly affect the contact time between plasma and material surface and the stability of plasma. A treatment time of 5 minutes to 15 minutes allows sufficient time for plasma to act on the surface to achieve ideal cleaning and activation effects. A gas pressure range of 10 Pa to 50 Pa can maintain the plasma The plasma is in an optimal state, neither too low to make plasma generation difficult, nor too high to cause unnecessary side reactions or energy dissipation, ensuring a gentle and controllable surface activation process. If the power is too low, the plasma energy will be insufficient to generate enough active sites, while if the power is too high, high-energy particles will bombard the surface and produce micro-defects. Therefore, the power of the radio frequency plasma machine used in the plasma bombardment process of this application is 50W-150W, which not only ensures that enough active sites can be generated on the surface of the epitaxial layer, but also reduces the surface defects caused by plasma bombardment, further ensuring a longer lifespan for the final silicon carbide epitaxial wafer.

[0045] Specifically, a radio frequency plasma machine is used to bombard the surface of silicon carbide epitaxial wafers with plasma. When the radio frequency plasma machine is running at low power (50W-150W), the treatment of the wafer surface is an activation treatment.

[0046] Specifically, plasma bombardment is performed on the surface of a silicon carbide epitaxial wafer using a mixture of hydrogen and argon gases, with hydrogen comprising 30%-80%. Hydrogen primarily serves a chemical activation function, reducing surface oxides and generating active Si-H bonds. Argon plasma provides physical sputtering cleaning. The gas flow rate is 50-100 sccm. Insufficient flow rate results in low plasma density, poor surface activation, and potentially uneven carbon layer formation. Excessive flow rate creates turbulence, leading to uneven processing and surface hydrogenation, inhibiting subsequent carbon film growth. The power is 50-150W. Insufficient power results in insufficient plasma energy to generate enough active sites, while excessive power causes micro-defects due to high-energy particle bombardment. The gas pressure is 10-50 Pa, and the processing time is 5-15 minutes. Excessive pressure or time results in insufficient surface activation, while insufficient pressure or time leads to lattice distortion and introduces new defects. Preferably, in this embodiment of the application, hydrogen accounts for 70%, the gas flow rate is 60 sccm, the power is 75W, the gas pressure is 24Pa, the processing time is 10 minutes, and plasma bombardment of the silicon carbide epitaxial wafer surface can increase the dangling bond density on the silicon carbide epitaxial wafer surface and promote the uniform nucleation of subsequent nano-carbon films.

[0047] In an exemplary embodiment, laser scanning is performed on the surface of the silicon carbide epitaxial wafer after the plasma bombardment treatment. This includes: controlling the laser focus of the laser to be positioned at the center of the silicon carbide epitaxial wafer surface; starting from the center, laser scanning is performed on the surface of the silicon carbide epitaxial wafer in a direction pointing outwards from the center; wherein the scanning path unfolds in a spiral shape, and the scanning speed is 10 mm / s-50 mm / s. In this embodiment, a spiral scanning path is used, unfolding from the center outwards, which ensures that the laser energy is uniformly distributed across the entire epitaxial wafer surface. This reduces edge effects, ensures uniform formation of the nano-carbon film across the entire wafer, and improves material consistency. If the laser energy density is too low, it is insufficient to induce silicon atom sublimation, resulting in insufficient or uneven carbon film formation, thus affecting the improvement of minority carrier lifetime. If the energy density is too high, it can cause surface damage and micro-defects, which also affects the processing effect of subsequent processes and the optimization of minority carrier lifetime. The laser energy density in this application is set at 2 J / cm². 2 Up to 5J / cm 2 This process ensures the effective sublimation of silicon atoms while keeping carbon atoms in situ, thereby further forming a uniform and dense nano-carbon film.

[0048] In other embodiments, the laser scanning speed is 10mm / s-50mm / s, the scanning interval is 10μm-45μm, and the laser spot diameter is 50μm-100μm. In this embodiment, adjusting the laser scanning speed ensures that the laser heats each unit area consistently within a specific time, thereby controlling the sublimation rate of silicon atoms on the surface and achieving precise control of the thickness of the nano-carbon film. A reasonable scanning interval combined with the laser spot diameter ensures that each laser irradiation covers a sufficient but not excessively large area, thus avoiding uneven carbon film thickness caused by localized overheating and poor continuity of the carbon film due to excessive overlap or spacing between adjacent spots.

[0049] Specifically, the prepared silicon carbide epitaxial wafer is placed on a stage located in a sealed container with an inert gas environment, such as argon and nitrogen. In this embodiment, argon is used as the protective gas, and the gas flow rate ranges from 5 L / min to 20 L / min. The protective gas prevents high-temperature oxidation of the material surface during laser irradiation and also plays a certain role in blowing, improving the uniformity of the carbon film generated on the surface of the epitaxial wafer after laser treatment. If the gas flow rate is too high, the heat-affected zone will be smaller, resulting in a lower film thickness. If the gas flow rate is too low, it will be difficult to achieve the blowing effect, resulting in an uneven film and affecting the subsequent process.

[0050] Specifically, the laser is activated and the laser focus is positioned at the center surface of the silicon carbide epitaxial wafer. A single laser scan is performed, using a spiral path, starting from the center of the epitaxial wafer and scanning outwards sequentially. During this process, the wavelength of the pulsed laser is 532 nm, and the pulse energy density is 2 J / cm². 2 -5J / cm 2 The scanning speed is 10-50 mm / s, the laser repetition frequency is 10-50 Hz, the pulse width is 10-50 ns, the laser beam spot diameter is 50-100 μm, and the scanning spacing is 10-45 μm. This results in a uniform carbon nanofilm with a thickness of 500-8000 nm on the epitaxial wafer surface. The choice of laser power is primarily to ensure a uniform carbon nanofilm of ideal thickness. Inappropriate laser parameters may result in an excessively thick and uneven carbon film, making subsequent processes difficult, or an excessively thin film, affecting the improvement of minority carrier lifetime in subsequent processes. In this embodiment, a pulse energy of 5 J / cm² is used. 2 A laser with a scanning speed of 40 mm / s, a laser repetition frequency of 20 Hz, a pulse width of 15 ns, a laser spot diameter of 60 μm, and a scanning spacing of 20 μm was used to obtain a uniformly distributed carbon nanofilm with a thickness of 3000 nm.

[0051] According to some exemplary embodiments of this application, the annealing temperature for medium-temperature annealing is 700℃-1300℃, and the annealing time is 1 hour-10 hours. In this embodiment, a moderate annealing temperature and time can reduce energy consumption and improve production efficiency. Excessively high temperatures and excessively long times not only increase production costs but may also introduce new defects, while excessively low temperatures and times may not achieve the expected repair effect. The annealing temperature of 700℃-1300℃ and the duration of 1 hour-10 hours in this application ensure a balance between cost and efficiency while significantly improving the minority carrier lifetime of silicon carbide epitaxial wafers.

[0052] According to some other exemplary embodiments of this application, at least in an inert gas environment, the silicon carbide epitaxial wafer on which the above-mentioned nano-carbon film is generated is subjected to intermediate-temperature annealing, including: performing intermediate-temperature annealing on the silicon carbide epitaxial wafer in an environment containing a silicon source gas and an inert gas. In this embodiment, the silicon source gas decomposes during annealing, and the released silicon atoms can penetrate into the silicon carbide crystal, which helps to repair minor defects that may be caused by laser scanning, improve the integrity of the crystal structure, and at the same time, silicon atoms can act as fillers to reduce additional recombination centers that may be generated due to laser processing, further reduce the recombination center density, and further improve the minority carrier lifetime.

[0053] Specifically, a silicon carbide epitaxial wafer with a nano-carbon film is removed and placed in an inert gas containing a silicon source for medium-temperature annealing. The silicon source gas used is silane, and the inert gas doped with silicon source gas is argon. The main function of the inert gas is to prevent oxidation of the sample surface due to high temperatures. The volume fraction of silicon source gas is controlled, as too little silicon source gas is insufficient to repair defects, while too much may result in gas waste. The volume fraction of silicon source gas in the inert gas doped with silicon source gas is 0.1%-1%, and the volume fraction used in this embodiment is 0.3%. During the annealing process, the effects of annealing temperature, annealing time, heating rate, and cooling rate on the process effect must be fully considered. Effective coordination of these key process parameters is necessary to achieve the best defect repair effect. If the annealing temperature and annealing time are too low, the repair effect may be unsatisfactory, while if the annealing temperature and annealing time are too high, the sample will experience lattice distortion, altering the physical properties of the sample and affecting its electrical properties. Excessively rapid heating or cooling rates during annealing can lead to uneven heating of the sample, easily generating stress. This not only affects the repair effect but may also increase the risk of fragmentation. Conversely, excessively slow heating or cooling rates reduce production efficiency, increase production costs, and also affect the activation effect of carbon atoms in the carbon film. Therefore, in this application, the annealing temperature is 700-1300℃, the annealing time is 1-10 hours, the heating rate is 10-50℃ / min, and the cooling rate is 3-15℃ / min. In the embodiments of this application, the annealing temperature used is 850℃, the annealing time is 6 hours, the heating rate is 30℃ / min, the cooling rate is 10℃ / min, and the initial temperature in the annealing furnace is 650℃. This application involves medium-temperature annealing with an inert gas containing a silicon source. Carbon defects are repaired by carbon atoms in the carbon film, reducing deep-level defects. Meanwhile, silicon atoms in the silicon source can diffuse into the silicon carbide lattice, repairing micro-defects generated during laser scanning, improving crystal integrity, and reducing recombination center density.

[0054] Specifically, in addition to silane SiH4, the silicon source gas selected in this application can also be any one of tetraethoxysilane (TEOS), diethylsilane (DES), trichlorosilane (TCS).

[0055] Figure 2 This is a schematic diagram illustrating the process by which silicon atoms sublimate in a silicon carbide epitaxial wafer to form a nano-carbon film on its surface. Figure 2 As shown, after laser scanning of the surface of silicon carbide epitaxial wafer 1, silicon atoms (i.e., the first silicon atom 3) in silicon carbide epitaxial wafer 1 sublimate, thereby forming a nano-carbon film 2 on the surface of silicon carbide epitaxial wafer 1.

[0056] Figure 3This is a schematic diagram illustrating the diffusion of carbon atoms from the carbon nanofilm and silicon atoms from the silicon source into a silicon carbide epitaxial wafer. Figure 3 As shown, in an inert gas containing a silicon source, the silicon carbide epitaxial wafer 1 is annealed at a medium temperature, and carbon atoms in the nano-carbon film 2 and silicon atoms (i.e., second silicon atoms 4) in the silicon source diffuse into the carbon vacancy 5 and silicon vacancy 6 in the silicon carbide epitaxial wafer 1.

[0057] According to some other exemplary embodiments of this application, the inert gas in the above-mentioned mixed gas includes argon, the inert gas in laser scanning includes argon, and the inert gas in intermediate-temperature annealing includes argon. In this embodiment, argon is an inert gas that does not chemically react with silicon carbide or the carbon film or silicon source on its surface, effectively preventing oxidation of the material surface during various processing processes and maintaining the original properties and structural integrity of the material.

[0058] According to some exemplary embodiments of this application, after annealing the silicon carbide epitaxial wafer from which the above-mentioned nano-carbon film is formed, the method further includes: using a radio frequency plasma machine to perform plasma cleaning treatment on the annealed silicon carbide epitaxial wafer, wherein the gas flow rate of the plasma cleaning treatment is 55 sccm-200 sccm, the gas pressure is 0.1 Pa-5.0 Pa, the cleaning time is 5 minutes-20 minutes, the power of the radio frequency plasma machine is 300 W-700 W, and the frequency is 10 MHz-15 MHz. In this embodiment, by setting the gas flow rate between 55 sccm and 200 sccm and the gas pressure between 0.1 Pa and 5.0 Pa, it is possible to ensure that the plasma generated by the plasma generator has sufficient intensity and coverage to effectively remove residual carbon film, contaminants, and possible oxide layers from the surface. The cleaning time is between 5 and 20 minutes, which ensures that all residues are fully removed while avoiding unnecessary chemical corrosion to the silicon carbide epitaxial wafer surface that may be caused by prolonged cleaning. The power is set between 300 W and 700 W, which can generate sufficiently strong plasma to promote chemical reactions, but not so strong as to damage the silicon carbide surface, thereby maintaining the flatness and original structure of the epitaxial wafer surface. The plasma cleaning frequency is between 10 MHz and 15 MHz. This frequency range can promote the effective generation of active particles in the plasma, improve cleaning efficiency, and reduce equipment wear or electromagnetic interference problems that may be caused by using higher frequencies.

[0059] Specifically, the process performed by radio frequency plasma machines when operating at high power (300W to 700W) is a cleaning process.

[0060] Specifically, the equipment used for plasma bombardment treatment (surface activation) and plasma cleaning treatment in this application can both be radio frequency plasma machines, but the power of the radio frequency plasma machine is different in different treatments.

[0061] Specifically, the annealed silicon carbide epitaxial wafers undergo plasma cleaning to remove the carbon film from their surface. The plasma cleaning method utilizes a radio frequency plasma machine equipped with a mass flow controller and a vacuum system. The working gas is argon with a purity of 99.999%. The main difference between this and plasma-activated surface treatment is that plasma cleaning aims to completely remove surface contaminants and ensure the cleanliness of the wafer surface, while surface activation treatment primarily aims to increase the activity of the epitaxial wafer surface, facilitating the uniform formation of the subsequent carbon film. The gas flow rate during plasma cleaning is 55 sccm-200 sccm. If the gas flow rate is too low, the plasma activity and density will be insufficient, making it difficult to fully react with the carbon film, resulting in incomplete carbon film removal. If the gas flow rate is too high, the plasma will be overactive, causing unnecessary oxidation of the silicon carbide surface and affecting surface quality. Other specific parameters for plasma cleaning are: chamber pressure 0.1-5.0 Pa, power 300-700 W, frequency 10-15 MHz, and cleaning time 5-20 minutes. In this process, excessively low chamber pressure can make plasma generation and maintenance difficult, affecting the cleaning effect; excessively high pressure can lead to frequent particle collisions in the plasma, energy dispersion, reduced reaction efficiency with the carbon film, and even abnormal discharge, damaging the equipment and wafer. Insufficient power makes it difficult to generate plasma with enough energy to effectively remove the carbon film; excessive power can cause the plasma to bombard the silicon carbide surface too violently, causing surface damage and potentially overloading the equipment. Insufficient cleaning time also results in ineffective carbon film removal, while excessive time carries the risk of surface damage. In this embodiment, the plasma cleaning process uses argon gas at a pressure of 0.5 Pa, a power of 450 W, a frequency of 13.5 MHz, and a cleaning time of 8 minutes.

[0062] According to some other exemplary embodiments of this application, after performing plasma cleaning on the annealed silicon carbide epitaxial wafer, the method further includes: performing chemical mechanical polishing on the silicon carbide epitaxial wafer after the plasma cleaning treatment; and cleaning and drying the silicon carbide epitaxial wafer after the chemical mechanical polishing treatment. In this embodiment, the chemical mechanical polishing treatment can further remove minute defects on the surface of the silicon carbide epitaxial wafer, improve surface flatness, reduce surface roughness, and thus further improve minority carrier lifetime; the addition of the cleaning and drying steps further ensures the cleanliness of the silicon carbide epitaxial wafer surface and further reduces the risk of contamination in subsequent processes.

[0063] Specifically, the silicon carbide epitaxial wafers that have undergone plasma cleaning are subjected to conventional chemical mechanical polishing, cleaning, and drying, and then sealed and stored under an inert gas atmosphere.

[0064] In some alternative embodiments of this application, after obtaining the silicon carbide epitaxial wafer and before subjecting the surface of the silicon carbide epitaxial wafer to plasma bombardment treatment using a mixed gas, the method further includes: cleaning the silicon carbide epitaxial wafer using a standard RCA process to remove contaminants and metal ions from the surface of the silicon carbide epitaxial wafer; and etching the cleaned silicon carbide epitaxial wafer using hydrofluoric acid to remove oxides from the surface of the silicon carbide epitaxial wafer. In this embodiment, the use of the standard RCA process can effectively remove contaminants and metal ions from the surface of the silicon carbide epitaxial wafer, providing a clean surface for subsequent plasma bombardment treatment; the addition of hydrofluoric acid etching can remove surface oxides, further improving surface quality.

[0065] According to some exemplary embodiments of this application, after etching the cleaned silicon carbide epitaxial wafer and before performing plasma bombardment treatment on the surface of the silicon carbide epitaxial wafer using a mixed gas, the method further includes: cleaning the etched silicon carbide epitaxial wafer with deionized water and drying the cleaned silicon carbide epitaxial wafer. In this embodiment, cleaning with deionized water after etching can effectively remove residual chemical substances on the surface, such as byproducts of hydrofluoric acid reaction and other possible residual chemical reagents, further ensuring surface cleanliness and reducing the impact of chemical residues on material properties in subsequent processes; drying after cleaning with deionized water can remove surface moisture and prevent moisture from evaporating and generating steam during subsequent high-temperature treatment, which could lead to changes in the surface state or the formation of micro-defects.

[0066] Specifically, after obtaining the silicon carbide epitaxial wafer, the silicon carbide epitaxial wafer is cleaned using the standard RCA process to remove organic surface contaminants and metal ions. Then, it is etched with hydrofluoric acid (HF) to remove surface oxides. Finally, it is cleaned with deionized water and dried.

[0067] Specifically, in addition to argon, nitrogen or helium may also be used as the inert gas in this application, and this application does not impose any specific restrictions on this.

[0068] In summary, this application employs pulsed laser irradiation on the surface of a silicon carbide epitaxial wafer, causing silicon atoms to sublimate while retaining carbon atoms, thus generating a nano-carbon film in situ. The thickness of the generated nano-carbon film can be controlled by adjusting the laser scanning parameters. Laser scanning can generate high temperatures locally at the scanning area without affecting other areas. Controlling the laser parameters ensures the uniformity of carbon film formation. Subsequently, medium-temperature annealing in an inert gas containing a silicon source is performed. Carbon atoms in the carbon film repair carbon defects and reduce deep-level defects, while silicon atoms in the silicon source can diffuse into the silicon carbide lattice, repairing micro-defects generated during laser irradiation, improving crystal integrity, and reducing recombination center density. Finally, surface treatment through plasma surface cleaning and subsequent chemical mechanical polishing removes the carbon film, thus obtaining the final silicon carbide epitaxial wafer. Using the μ-PCD method to test silicon carbide epitaxial wafers, the minority carrier lifetime of existing silicon carbide epitaxial wafers is 1.2 ± 0.3 μs. However, after treatment with the method for improving the minority carrier lifetime of silicon carbide epitaxial wafers described in this application, the minority carrier lifetime of the epitaxial wafer is 17.5 ± 0.9 μs, representing a significant improvement. Figure 4 As shown in the figure. The thickness of the in-situ generated nano-carbon particle layer in this application is controllable, and silicon carbide epitaxial wafers with enhanced minority carrier lifetime can be prepared in a short time. Carbon vacancies and silicon vacancies are repaired simultaneously without introducing other deep-level defects, reducing recombination centers and achieving the goal of enhancing minority carrier lifetime.

[0069] To enable those skilled in the art to better understand the technical solution of this application, the implementation process of the method for improving the minority carrier lifetime of silicon carbide epitaxial wafers in this application will be described in detail below with reference to specific embodiments.

[0070] This embodiment relates to a specific method for improving the minority carrier lifetime of silicon carbide epitaxial wafers, such as... Figure 5 As shown, it includes the following steps:

[0071] Step S1: Surface activation: Plasma bombardment treatment is performed on the upper surface of the silicon carbide epitaxial wafer using a mixed gas of hydrogen and argon.

[0072] Step S2: Laser scanning: In an inert gas (such as argon) environment, turn on the laser and position the laser focus at the center surface of the silicon carbide epitaxial wafer. Use a single laser scan with a spiral path, starting from the center of the silicon carbide epitaxial wafer and scanning outwards sequentially.

[0073] Step S3: Medium-temperature annealing: The silicon carbide epitaxial wafer is annealed at a medium temperature in an inert gas containing a silicon source, the silicon source including silane SiH4, and the inert gas including argon.

[0074] Step S4: Plasma cleaning: The annealed silicon carbide epitaxial wafer is subjected to plasma cleaning, with argon as the working gas;

[0075] Step S5: The silicon carbide epitaxial wafer that has been plasma cleaned is chemically and mechanically polished, cleaned, and dried, and then sealed and stored under an inert gas (such as argon).

[0076] The technical features of the above embodiments can be combined in any way. For the sake of brevity, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0077] This application also provides a silicon carbide epitaxial wafer, which is prepared by any of the above-mentioned methods for improving the minority carrier lifetime of silicon carbide epitaxial wafers.

[0078] This application also provides a semiconductor device, including the silicon carbide epitaxial wafer described above.

[0079] As can be seen from the above description, the embodiments of this application achieve the following technical effects:

[0080] In the method for improving the minority carrier lifetime of silicon carbide epitaxial wafers disclosed in this application, a silicon carbide epitaxial wafer is first obtained. Then, a mixed gas including hydrogen and inert gas is used to bombard the surface of the silicon carbide epitaxial wafer with plasma to activate the surface of the silicon carbide epitaxial wafer. Next, in an inert gas environment, the surface of the plasma-bombarded silicon carbide epitaxial wafer is laser-scanned to generate a nano-carbon film on the surface of the silicon carbide epitaxial wafer. Finally, the silicon carbide epitaxial wafer with the nano-carbon film generated is subjected to intermediate-temperature annealing, at least in an inert gas environment. Compared to the problem of low minority carrier lifetime in existing technologies for silicon carbide epitaxial wafers used in bipolar high-voltage power devices, this application utilizes plasma bombardment to activate the surface of silicon carbide epitaxial wafers. The use of a mixed gas of hydrogen and inert gas enhances the surface activity of the silicon carbide epitaxial wafer while removing surface impurities. Hydrogen in the plasma promotes chemical reactions, generating active Si-H bonds, increasing the dangling bond density on the silicon carbide epitaxial layer surface, thus enhancing surface activity and promoting subsequent carbon atom adsorption and nucleation. This provides favorable conditions for the uniform formation of subsequent nano-carbon films. The inert gas also acts as a physical cleaner, ensuring surface purity and reducing the possibility of deep-level defects. Laser scanning in an inert gas environment allows for precise control of the thermal effect region. This reduces the problem of uneven carbon layer distribution on the surface that may be caused by overall high-temperature heating. Laser scanning can locally heat the surface of silicon carbide epitaxial wafers, causing silicon atoms to sublimate, while carbon atoms aggregate on the surface to form a nano-carbon film. The formation of this nano-carbon film is not only controllable in thickness but also uniform in distribution, which is crucial for repairing carbon vacancy defects in the silicon carbide lattice. This is because the carbon atoms generated by the uniform nano-carbon film can more effectively fill these defects, reduce deep-level traps, and thus extend minority carrier lifetime. At least, medium-temperature annealing of the silicon carbide epitaxial wafer with nano-carbon film in an inert gas environment can promote the diffusion of carbon atoms. Carbon atoms diffuse into the silicon carbide lattice and repair carbon vacancies. That is, carbon defects are repaired by carbon atoms in the carbon film, reducing deep-level defects and ensuring a longer minority carrier lifetime.

[0081] The above description is merely a preferred embodiment of the present application and is not intended to limit the present application. Various modifications and variations are possible for those skilled in the art. Any modifications, equivalent substitutions, or improvements made within the spirit and principles of the present application shall be included within the scope of protection of the present application.

Claims

1. A method for improving the minority carrier lifetime of a silicon carbide epitaxial wafer, characterized in that, include: Obtain silicon carbide epitaxial wafers; The surface of the silicon carbide epitaxial wafer is subjected to plasma bombardment treatment using a mixed gas to activate the surface of the silicon carbide epitaxial wafer, wherein the mixed gas includes hydrogen and an inert gas; In an inert gas environment, the surface of the silicon carbide epitaxial wafer after plasma bombardment treatment is laser scanned to generate a nano-carbon film on the surface of the silicon carbide epitaxial wafer. The silicon carbide epitaxial wafer from which the nano-carbon film is formed is subjected to medium-temperature annealing, at least in an inert gas environment.

2. The method for improving the minority carrier lifetime of silicon carbide epitaxial wafers according to claim 1, characterized in that, The hydrogen content in the mixed gas is 30%-80%.

3. The method for improving the minority carrier lifetime of silicon carbide epitaxial wafers according to claim 2, characterized in that, The gas flow rate of the plasma bombardment treatment is 50 sccm-100 sccm, the gas pressure is 10 Pa-50 Pa, the treatment time is 5 minutes-15 minutes, and the power of the radio frequency plasma machine used in the plasma bombardment treatment is 50 W-150 W.

4. The method for improving the minority carrier lifetime of silicon carbide epitaxial wafers according to claim 1, characterized in that, Laser scanning is performed on the surface of the silicon carbide epitaxial wafer after plasma bombardment treatment, including: The laser focus of the laser is positioned at the center of the surface of the silicon carbide epitaxial wafer. Starting from the center, a laser scan is performed on the surface of the silicon carbide epitaxial wafer in a direction pointing outwards from the center. The scanning path unfolds in a spiral shape, and the laser energy density is 2 J / cm². 2 -5J / cm 2 .

5. The method for improving the minority carrier lifetime of silicon carbide epitaxial wafers according to claim 3, characterized in that, In laser scanning, the scanning speed is 10mm / s-50mm / s, the scanning spacing is 10μm-45μm, and the laser spot diameter is 50μm-100μm.

6. The method for improving the minority carrier lifetime of silicon carbide epitaxial wafers according to claim 1, characterized in that, The annealing temperature for medium-temperature annealing is 700℃-1300℃, and the annealing time is 1 hour-10 hours.

7. The method for improving the minority carrier lifetime of silicon carbide epitaxial wafers according to claim 1, characterized in that, At least in an inert gas environment, the silicon carbide epitaxial wafer on which the nano-carbon film is formed undergoes intermediate-temperature annealing, including: The silicon carbide epitaxial wafer is subjected to medium-temperature annealing in an environment containing a mixture of silicon source gas and inert gas.

8. The method for improving the minority carrier lifetime of silicon carbide epitaxial wafers according to claim 1, characterized in that, The inert gas in the mixed gas includes argon, the inert gas in the laser scanning includes argon, and the inert gas in the intermediate temperature annealing includes argon.

9. A silicon carbide epitaxial wafer, characterized in that, The silicon carbide epitaxial wafer is prepared using the method for improving the minority carrier lifetime of silicon carbide epitaxial wafers as described in any one of claims 1 to 8.

10. A semiconductor device, characterized in that, Includes the silicon carbide epitaxial wafer as described in claim 9.

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