Reutilization method of substrate in silicon carbide epitaxial wafer

Abstract

The invention relates to the technical field of silicon carbide epitaxy, and provides a method for recycling a substrate in a silicon carbide epitaxial wafer, which comprises the following steps: obtaining a silicon carbide epitaxial wafer to be processed, the silicon carbide epitaxial wafer comprising a substrate, and a buffer layer and an epitaxial layer which are sequentially laminated on the substrate; determining the to-be-thinned thickness of the epitaxial layer, and performing at least one first thinning treatment on the epitaxial layer according to the to-be-thinned thickness to expose the buffer layer; the buffer layer is subjected to second thinning treatment, the substrate is exposed, and the first thinning treatment and the second thinning treatment comprise the step that the corresponding film layer is subjected to thinning treatment through laser; and sequentially cleaning and polishing the substrate. According to the method, the epitaxial layer and the buffer layer are thinned for multiple times by using laser, and the surface can be in a relatively flat state after each time of thinning treatment, so that the damage in the thinning treatment process can be reduced, and the reusable silicon carbide substrate with relatively good surface flatness degree can be obtained.

Description

Technical Field

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

[0002] In semiconductor manufacturing, silicon carbide (SiC) has attracted significant attention due to its excellent thermal conductivity, high critical breakdown electric field, high saturated electron velocity, good radiation resistance, and exceptional chemical stability. However, SiC power devices must be fabricated on an epitaxial layer of a SiC substrate, and the epitaxial growth process inevitably produces defective products, increasing costs and wasting resources. Therefore, processing these defective products for recycling and reuse is of great practical significance.

[0003] In the prior art, methods such as chemical etching, mechanical grinding, and chemical mechanical polishing (CMP) are commonly used to remove the epitaxial layer to obtain a recyclable silicon carbide substrate. However, the uniformity of the etching solution during chemical etching is difficult to ensure, which may lead to localized excessive or insufficient corrosion. Mechanical grinding and chemical mechanical polishing may introduce surface damage such as scratches. Although these can be repaired through annealing, this increases process complexity. The existing methods for removing the epitaxial layer are inefficient and it is difficult to ensure the quality of the silicon carbide substrate.

[0004] The above information disclosed in the background technology section is only used to enhance the understanding of the background technology of the technology described in this article. Therefore, the background technology may contain certain information that does not form the prior art known in this country to those skilled in the art. Summary of the Invention

[0005] The main purpose of this application is to provide a method for recycling the substrate in the silicon carbide epitaxial wafer, so as to solve the problem in the prior art that it is difficult to efficiently remove the epitaxial layer of unqualified silicon carbide epitaxial wafers and obtain high-quality silicon carbide substrates.

[0006] In order to achieve the above-mentioned purpose, according to one aspect of the present application, a method for reusing a substrate in a silicon carbide epitaxial wafer is provided, comprising: obtaining a silicon carbide epitaxial wafer to be processed, the silicon carbide epitaxial wafer comprising a substrate and a buffer layer and an epitaxial layer stacked in sequence on the substrate; determining the thickness of the epitaxial layer to be thinned, and performing at least one first thinning treatment on the epitaxial layer according to the thickness to be thinned to expose the buffer layer; performing a second thinning treatment on the buffer layer to expose the substrate, wherein the first thinning treatment and the second thinning treatment both comprise thinning the corresponding film layer using a laser; and sequentially cleaning and polishing the substrate.

[0007] In some embodiments of the present application, performing the first thinning treatment on the epitaxial layer at least once includes at least: performing thinning treatment on the epitaxial layer using a first laser; performing the second thinning treatment on the buffer layer includes: performing thinning treatment on the buffer layer using a second laser; wherein the energy density of the second laser is less than the energy density of the first laser.

[0008] In some embodiments of the present application, the first laser and the second laser satisfy at least one of the following: the frequency of the first laser is greater than the frequency of the second laser; the pulse energy of the first laser is greater than the pulse energy of the second laser; the spot diameter of the first laser is smaller than the spot diameter of the second laser; the line spacing of the first laser is smaller than the line spacing of the second laser; and the scanning speed of the first laser is smaller than the scanning speed of the second laser.

[0009] In some embodiments of the present application, the pulse energy of the first laser is 1J to 100J, and the spot diameter of the first laser is 10μm to 60μm.

[0010] In some embodiments of the present application, the pulse energy of the second laser is 1 mJ to 1 J, and the spot diameter of the second laser is 60 μm to 100 μm.

[0011] In some embodiments of the present application, the frequency of the first laser is 600kHz to 12MHz, the line spacing of the first laser is 0.1μm to 65μm, and the scanning speed of the first laser is 0.5mm / s to 500mm / s.

[0012] In some embodiments of the present application, the frequency of the second laser is 1 kHz to 600 kHz, the line spacing of the second laser is 70 μm to 100 μm, and the scanning speed of the first laser is 500 mm / s to 1000 mm / s.

[0013] In some embodiments of the present application, when performing the second thinning treatment on the buffer layer, the method further includes: placing the silicon carbide epitaxial wafer after the first thinning treatment in an inert protective gas environment.

[0014] In some embodiments of the present application, performing the first thinning treatment on the epitaxial layer at least once includes: performing the first thinning treatment on the epitaxial layer multiple times, and in the multiple first thinning treatments, except for the last first thinning treatment, each first thinning treatment is used to thin the epitaxial layer by 10 μm.

[0015] In some embodiments of the present application, the cleaning of the substrate includes: placing the substrate after the second thinning treatment in an ultrasonic cleaning machine for cleaning, wherein the ultrasonic cleaning machine is provided with a protective liquid, the substrate is immersed in the protective liquid, and the protective liquid includes deionized water or ethanol.

[0016] In some embodiments of the present application, performing the polishing process on the substrate includes: performing chemical mechanical polishing on the surface of the substrate from which the buffer layer is removed at least once until the surface roughness of the substrate reaches a set value;

[0017] In some embodiments of the present application, performing the polishing process on the substrate further includes: performing double-side polishing on the substrate.

[0018] The beneficial effects of this application are as follows:

[0019] The present application provides a method for reusing a substrate in a silicon carbide epitaxial wafer, comprising: obtaining a silicon carbide epitaxial wafer to be processed, the silicon carbide epitaxial wafer comprising a substrate and a buffer layer and an epitaxial layer sequentially stacked on the substrate; determining the thickness of the epitaxial layer to be thinned, and performing at least one first thinning process on the epitaxial layer according to the thickness to be thinned to expose the buffer layer; performing a second thinning process on the buffer layer to expose the substrate, wherein both the first thinning process and the second thinning process include thinning the corresponding film layer using a laser; and sequentially cleaning and polishing the substrate. The present application utilizes a laser to thin the epitaxial layer and the buffer layer multiple times, and the surface can be in a relatively flat state after each thinning process, which is beneficial for reducing damage during the thinning process and obtaining a silicon carbide substrate with a relatively good surface flatness and reusable. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] One or more embodiments are exemplarily described by the figures in the corresponding drawings. These exemplifications do not constitute limitations on the embodiments. Unless otherwise stated, the figures in the drawings do not constitute proportional limitations. In order to more clearly illustrate the embodiments of the present application or the technical solutions in the conventional technology, the following briefly introduces the drawings required for use in the embodiments. Obviously, the drawings described below are only some embodiments of the present application. For those of ordinary skill in the art, other drawings can be obtained based on these drawings without creative work. In the drawings:

[0021] Figure 1 A schematic flow chart of a method for reusing a substrate in a silicon carbide epitaxial wafer according to an embodiment of the present application;

[0022] Figure 2 A schematic structural diagram of a silicon carbide epitaxial wafer provided according to an embodiment of the present application;

[0023] Figure 3 A comparison table of thermal damage depths of substrates provided according to comparative examples and embodiments of the present application;

[0024] Figure 4 The following is a comparison table of the surface roughness of substrates provided in the comparative examples and embodiments of the present application.

[0025] Description of reference numerals:

[0026] 10. Substrate; 20. Buffer layer; 30. Epitaxial layer. DETAILED DESCRIPTION

[0027] It should be noted that the following detailed descriptions are illustrative and intended to provide further explanation of the present application. Unless otherwise specified, all technical and scientific terms used herein have the same meaning as commonly understood by those skilled in the art to which the present application belongs.

[0028] It should be noted that the terms used herein are only for describing specific embodiments and are not intended to limit the exemplary embodiments according to the present application. As used herein, unless the context clearly indicates otherwise, the singular form is also intended to include the plural form. In addition, it should be understood that when the terms "comprise" and / or "include" are used in this specification, they indicate the presence of features, steps, operations, devices, components and / or combinations thereof.

[0029] It should be noted that the terms "first," "second," and the like in the specification and claims of the present invention and the accompanying drawings are used to distinguish similar objects and are not to be construed as indicating or implying relative importance or implicitly specifying the quantity, specific order, or primary and secondary relationship of the technical features indicated. It should be understood that the terms used in this manner are interchangeable where appropriate to describe the embodiments of the present invention.

[0030] 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 an intermediate element may be present. Moreover, in the specification and claims, terms such as "installed", "connected", "connected", and "fixed" should be understood in a broad sense. For example, it can be a fixed connection, a detachable connection, or an integral whole; it can be a mechanical connection or an electrical connection; it can be directly connected or indirectly connected through an intermediate medium, and it can be the internal connection of two elements or the interaction relationship between two elements. For those of ordinary skill in the art, the specific meanings of the above terms in the embodiments of this application can be understood according to the specific circumstances.

[0031] Furthermore, references to "embodiments" herein mean that a particular feature, structure, or characteristic described in connection with the embodiments may be included in at least one embodiment of the present application. The appearance of such phrases in various locations in the specification does not necessarily refer to the same embodiment, nor do they constitute independent or alternative embodiments that are mutually exclusive of other embodiments. It is understood, both explicitly and implicitly, by those skilled in the art that the embodiments described herein may be combined with other embodiments.

[0032] For ease of description, some nouns or terms involved in the embodiments of the present application are explained below:

[0033] Laser energy density: The energy of the laser per unit volume. The higher the laser energy density, the more concentrated the laser is per unit volume. Laser energy density is proportional to the pulse energy and inversely proportional to the spot diameter, satisfying the following formula: Among them, E d Represents energy density, E p represents the pulse energy, and d represents the spot diameter.

[0034] Flatness: The degree to which the plane of an object conforms to an ideal perfect plane on a macro scale. It is usually expressed by the maximum height difference, that is, the vertical distance between the highest point and the lowest point measured on the plane. The lower the flatness, the closer the plane of the object is to a plane.

[0035] Roughness: The degree of irregularity of an object's surface on a microscopic scale. In this application, it is expressed as the arithmetic mean roughness. The lower the roughness, the smoother the surface of the object.

[0036] As described in the background technology, it is difficult to efficiently remove the epitaxial layer of unqualified silicon carbide epitaxial wafers and obtain high-quality silicon carbide substrates in the prior art. To solve the above problem, the embodiments of the present application provide a method for recycling the substrate in the silicon carbide epitaxial wafer. Figure 1 A schematic flow chart of a method for reusing a substrate in a silicon carbide epitaxial wafer according to an embodiment of the present application.

[0037] like Figure 1 As shown, the method for recycling a substrate in a silicon carbide epitaxial wafer provided in an embodiment of the present application includes the following steps S1 to S4:

[0038] Step S1: Obtain a silicon carbide epitaxial wafer to be processed. The silicon carbide epitaxial wafer to be processed may be a silicon carbide epitaxial wafer that does not meet product standards during the production process, or may be a silicon carbide epitaxial wafer that is damaged during transportation or use, but is not limited thereto.

[0039] For ease of understanding, the structure of the silicon carbide epitaxial wafer is described below: Figure 2Schematic diagram of the structure of a silicon carbide epitaxial wafer provided according to an embodiment of the present application, as shown in FIG. Figure 2 As shown, the silicon carbide epitaxial wafer includes a substrate 10 and a buffer layer 20 and an epitaxial layer 30 stacked in sequence on the substrate 10. The substrate 10, the buffer layer 20 and the epitaxial layer 30 are all made of silicon carbide (SiC). The substrate 10 is high-purity silicon carbide, and the buffer layer 20 and the epitaxial layer 30 are silicon carbide containing dopants, and the doping concentrations and thicknesses of the two are usually different. Among them, the buffer layer 20 has a lower doping concentration to reduce crystal defects and improve crystal quality, so that the buffer layer 20 can form a transition layer between the substrate 10 and the epitaxial layer 30 to reduce stress and defects caused by the difference in lattice constants between the two. The doping concentration of the epitaxial layer 30 can be adjusted according to specific application requirements to achieve the required electrical properties and device performance. The thickness of the buffer layer 20 as a transition is generally several microns, and the thickness of the epitaxial layer 30 can range from tens of microns to hundreds of microns depending on the design and performance goals of the device. The thickness of the epitaxial layer 30 is usually greater than that of the buffer layer 20.

[0040] Step S2: determining the thickness of the epitaxial layer to be thinned, and performing at least one first thinning process on the epitaxial layer according to the thickness to be thinned, so as to expose the buffer layer.

[0041] In step S2, the first thinning treatment includes thinning the epitaxial layer using a laser. Since the epitaxial layer is thick and difficult to remove at one time by laser, before performing the first thinning treatment, it is necessary to first determine the thickness of the epitaxial layer, thereby determining the number of first thinning treatments.

[0042] The thickness of the epitaxial layer to be thinned is the average thickness of the epitaxial layer, which can be obtained by selecting multiple points on the epitaxial layer, obtaining the thickness of the epitaxial layer at multiple points respectively, and then calculating the average value of the thickness at the above multiple points. For example, the silicon carbide epitaxial wafer is usually circular, and the 9-point method can be used to select points, selecting the center point of the epitaxial layer, the midpoint of each radius of the two perpendicular diameters (4 in total) and the end point (4 in total), or selecting 9 points arranged in a 3×3 matrix on the epitaxial layer, measuring the thickness of the epitaxial layer at the selected 9 points, and then calculating the average value to obtain the average thickness of the epitaxial layer. It should be understood that the method of selecting points on the epitaxial layer can be adjusted according to actual conditions, and the embodiments of the present application are not limited here.

[0043] Through the above method, the thickness of the buffer layer can also be measured in the same step. For example, after selecting the points, the thickness of the epitaxial layer and the buffer layer can be distinguished by ellipsometry technology or X-ray reflection technology. After measuring the thickness of the buffer layer at the above-mentioned multiple points, the average value of the thickness of the buffer layer at the above-mentioned multiple points is calculated to obtain the thickness of the buffer layer.

[0044] After determining the thickness of the epitaxial layer, the number of first thinning treatments can be determined. Taking into account the possible damage to the epitaxial wafer caused by the laser, when the thickness of the epitaxial layer is greater than 10 μm, the epitaxial layer needs to be subjected to two or more first thinning treatments. When the thickness of the epitaxial layer is less than 10 μm, the epitaxial layer only needs to be subjected to one first thinning treatment. In the embodiment of the present application, the thickness of the epitaxial layer or buffer layer thinned by laser each time is at most 10 μm. The thickness of each laser thinning treatment is controlled to 10 μm or less. The laser thinning process is more controllable, ensuring that the laser energy is fully absorbed without excessively penetrating into deeper film layers, causing additional damage, and avoiding surface unevenness caused by excessive one-time thinning, thereby reducing the complexity of subsequent processes. For example, after each first thinning treatment, the surface flatness of the epitaxial layer is less than or equal to 5 μm, and the surface roughness of the epitaxial layer is less than 2 nm, so that the surface of the epitaxial layer can be maintained in a relatively flat state after each first thinning treatment, which is conducive to improving the effect of subsequent thinning treatments.

[0045] Based on this, in some embodiments of the present application, performing at least one first thinning treatment on the epitaxial layer includes: performing multiple first thinning treatments on the epitaxial layer, and in the multiple first thinning treatments, except for the last first thinning treatment, each first thinning treatment is used to thin the epitaxial layer by 10μm. It can be understood that the thickness of the epitaxial layer required to be treated by the last first thinning treatment can be 10μm or less than 10μm.

[0046] Step S3: performing a second thinning process on the buffer layer to expose the substrate.

[0047] In step S3, the second thinning process includes thinning the corresponding film layer using a laser. Generally speaking, the thickness of the buffer layer is less than 10μm, so usually only one second thinning process is required to remove the buffer layer. However, it is understood that if the thickness of the buffer layer is greater than 10μm as measured in step S2, the buffer layer can be subjected to multiple second thinning processes, and except for the last second thinning process, each second thinning process is used to thin the buffer layer by 10μm.

[0048] The first thinning process and the second thinning process are described in detail below in conjunction with step S2 and step S3:

[0049] In some embodiments of the present application, each first thinning treatment can use a laser with the same process parameters, and each second thinning treatment can use a laser with the same process parameters. In this way, although the same film layer is treated in steps, the consistency of each thinning treatment can be guaranteed, which is beneficial to the control of product quality in mass production. In addition, setting laser parameters for the epitaxial layer and the buffer layer separately, and using the same process parameters for the same film layer can simplify the parameter setting and adjustment process in the process flow, reduce the complexity of the operation, make the process easier to manage and control, and eliminate the need to re-optimize the parameters for each thinning treatment, which helps to improve production efficiency.

[0050] In some embodiments of the present application, performing at least one first thinning treatment on the epitaxial layer includes at least: performing thinning treatment on the epitaxial layer using a first laser; performing a second thinning treatment on the buffer layer includes: performing thinning treatment on the buffer layer using a second laser; wherein the energy density of the second laser is less than the energy density of the first laser.

[0051] Due to its thickness and specific material properties, the epitaxial layer can withstand high-energy-density laser processing. Using a first laser with a higher energy density to process the epitaxial layer can ensure rapid and complete removal of the epitaxial layer. The buffer layer is thinner and closer to the substrate, requiring gentler processing to avoid damaging the substrate. Using a second laser with a lower energy density to process the buffer layer is conducive to precisely controlling the area affected by laser heat, while ensuring the efficiency of the thinning process while minimizing the impact of the laser on the substrate surface as much as possible, such as reducing surface microcracks, lattice distortion and other defects in the substrate, and maintaining the structural integrity of the substrate.

[0052] The energy density of the laser is related to the frequency, pulse capability, spot diameter, line spacing and scanning speed of the laser. In some embodiments of the present application, the first laser and the second laser satisfy at least one of the following conditions: the frequency of the first laser is greater than the frequency of the second laser; the pulse energy of the first laser is greater than the pulse energy of the second laser; the spot diameter of the first laser is smaller than the spot diameter of the second laser; the line spacing of the first laser is smaller than the line spacing of the second laser; and the scanning speed of the first laser is smaller than the scanning speed of the second laser.

[0053] The frequency and pulse energy of the first laser are set higher, which is conducive to the rapid and efficient removal of thicker epitaxial layers that require higher thermal energy to be effectively stripped. The high frequency and high pulse energy can accelerate the thermal effect of the material, thereby accelerating the epitaxial layer stripping process and improving production efficiency. The spot diameter and line spacing of the first laser are set smaller, which means that the energy of each laser irradiation is more concentrated and can act more accurately on the epitaxial layer. The spot diameter and line spacing of the second laser are larger, which can avoid excessive thermal effects on the buffer layer and reduce local overheating and damage caused by excessive laser energy concentration. The scanning speed of the first laser is set slower, so that the laser stays at each location longer, which helps to produce a more effective thermal effect in the epitaxial layer and facilitates more thorough removal of the epitaxial layer. The scanning speed of the second laser is set faster, which helps to reduce the thermal impact time on the buffer layer and avoid unnecessary damage to the substrate caused by heat diffusion. The embodiment of the present application can precisely control the thinning process of the epitaxial layer and the buffer layer by adjusting the frequency, pulse energy, spot diameter, line spacing and scanning speed. The differentiated parameter settings of the two ensure high precision of laser processing, which is conducive to reducing processing errors, improving yield and compatibility with subsequent processes.

[0054] In some embodiments of the present application, the pulse energy of the first laser is 1J to 100J. For example, the pulse energy of the first laser can be 1J, 10J, 20J, 30J, 40J, 50J, 60J, 70J, 80J, 90J, 100J or any other value within the above range; the spot diameter of the first laser is 10μm to 60μm. For example, the spot diameter of the first laser can be 10μm, 20μm, 30μm, 40μm, 50μm, 60μm or any other value within the above range. Setting the pulse energy and spot diameter of the first laser within the above range can make the first laser have a higher energy density, which helps to complete the thinning of the epitaxial layer in a shorter time and improve processing efficiency. In addition, the higher pulse energy can quickly increase the temperature of the material surface, promote the thermal decomposition and peeling of the silicon carbide epitaxial layer, thereby achieving rapid removal. The appropriate spot diameter can ensure that the laser energy is more evenly distributed on the surface of the epitaxial layer, avoiding local damage caused by excessive energy concentration due to a too small spot, and also avoids the decrease in processing efficiency caused by an overly large spot.

[0055] In some embodiments of the present application, the pulse energy of the second laser is 1mJ to 1J. For example, the pulse energy of the first laser can be 1mJ, 50mJ, 100mJ, 200mJ, 300mJ, 400mJ, 500mJ, 600mJ, 700mJ, 800mJ, 900mJ, 1J, or any other value within the above range; the spot diameter of the second laser is 60μm to 100μm. For example, the spot diameter of the second laser can be 60μm, 70μm, 80μm, 90μm, 100μm, or any other value within the above range. Setting the pulse energy and spot diameter of the second laser within the above range can control the energy density of the second laser to be within a lower range, thereby reducing the thermal impact on the buffer layer and avoiding damage to the microstructure of the substrate surface. At the same time, a larger spot diameter helps to disperse the energy of the second laser, further reducing the risk of thermal damage and improving the uniformity of the treatment. The embodiment of the present application can achieve precise control of the buffer layer thinning depth at lower pulse energy and larger spot diameter, which is beneficial to maintaining the integrity of the silicon carbide substrate, reducing the difficulty of subsequent processes and improving the substrate quality.

[0056] In some embodiments of the present application, the frequency of the first laser is 600kHz to 12MHz. For example, the frequency of the first laser can be 600kHz, 700kHz, 800kHz, 900kHz, 1MHz, 2MHz, 3MHz, 4MHz, 5MHz, 6MHz, 7MHz, 8MHz, 9MHz, 10MHz, 11MHz, 12MHz or any other value within the above range; the line spacing of the first laser is 0.1μm to 65μm. For example, the line spacing of the first laser can be 0.1μm, 1μm, 10μm, 15μm , 20μm, 25μm, 30μm, 35μm, 40μm, 45μm, 50μm, 55μm, 60μm, 65μm or any other value within the above range; the scanning speed of the first laser is 0.5mm / s to 500mm / s. Exemplarily, the scanning speed of the first laser can be 0.5mm / s, 1mm / s, 10mm / s, 50mm / s, 100mm / s, 150mm / s, 200mm / s, 250mm / s, 300mm / s, 350mm / s, 400mm / s, 450mm / s, or 500mm / s. High-frequency lasers can increase the number of pulses of energy transfer and improve the energy accumulation per unit time, thereby accelerating the thermal decomposition and peeling of the epitaxial layer material and significantly improving the removal efficiency of the epitaxial layer. The narrow line spacing and moderate scanning speed ensure that each laser scan can cover a sufficiently dense area, while not excessively reducing the scanning speed to cause excessive heat accumulation, thereby maintaining a reasonable processing time while ensuring the accuracy of material removal, and balancing the quality and efficiency of the thinning process. The embodiment of the present application can reduce surface damage after the first thinning treatment, such as scratches, microcracks, etc., by controlling the frequency, line spacing and scanning speed of the first laser within the above range. At the same time, it can also reduce surface roughness and improve the surface quality of the epitaxial layer after treatment, which is convenient for subsequent process flows.

[0057] In some embodiments of the present application, the frequency of the second laser is 1kHz to 600kHz. For example, the frequency of the second laser can be 1kHz, 10kHz, 50kHz, 100kHz, 150kHz, 200kHz, 250kHz, 300kHz, 350kHz, 400kHz, 450kHz, 500kHz, 550kHz, 600kHz or any other value within the above range; the line spacing of the second laser is 70μm to 100μm. For example, the line spacing of the second laser can be 70 μm, 75μm, 80μm, 85μm, 90μm, 95μm, 100μm or any other value within the above range; the scanning speed of the second laser is 500mm / s to 1000mm / s. Exemplarily, the scanning speed of the second laser can be 500mm / s, 550mm / s, 600mm / s, 650mm / s, 700mm / s, 750mm / s, 800mm / s, 850mm / s, 900mm / s, 950mm / s, 1000mm / s or any other value within the above range. A lower laser frequency means a lower heat density, which helps to reduce thermal damage to the buffer layer and is suitable for processing thinner buffer layers that are closer to the substrate. A larger line spacing means a larger spacing between laser beams, which reduces the possibility of local heat accumulation, helps to maintain the integrity of the substrate's microstructure, and avoids surface damage caused by thermal stress. A moderate scanning speed not only ensures processing efficiency, but also ensures that each laser path has enough time to dissipate heat, preventing local overheating caused by heat superposition between adjacent paths, helping to improve the overall uniformity of the second thinning process and reduce surface quality differences after the second thinning process. By setting the parameters of the second laser within the above range, rapid and gentle thinning of the buffer layer can be achieved without affecting the integrity of the material. By controlling the frequency, line spacing and scanning speed of the second laser within the above parameter range, the embodiment of the present application can not only save processing time, but also reduce substrate damage caused by excessive processing and improve substrate quality.

[0058] In some embodiments of the present application, when the buffer layer is subjected to a second thinning process, the method for reusing a substrate in a silicon carbide epitaxial wafer provided in embodiments of the present application may further include placing the silicon carbide epitaxial wafer after the first thinning process in an inert protective gas environment. For example, the inert protective gas may be nitrogen, argon, or a nitrogen-argon mixture. The introduction of the inert protective gas during the second thinning process effectively isolates oxygen from the air, preventing oxidation of the silicon carbide under the action of the laser, which could affect its performance, and also reducing the impact of laser thermal effects on areas other than the focal point.

[0059] In some embodiments of the present application, the flow rate of the inert shielding gas can be 10L / min to 50L / min, and illustratively, it can be 10L / min, 20L / min, 30L / min, 40L / min, 50L / min or any value within the above range. By setting the flow rate of the inert shielding gas within the above range, it helps to control the heat generated by the laser processing, ensure uniform temperature in the non-processed area, avoid local overheating or uneven cooling, and cause additional thermal stress damage to the material.

[0060] Step S4: cleaning and polishing the substrate in sequence.

[0061] In the present application, some impurities may still exist on the surface of the substrate after the second laser thinning treatment, so it needs to be cleaned. In step S4, cleaning the substrate includes: placing the substrate after the second thinning treatment in an ultrasonic cleaning machine for cleaning, wherein a protective liquid is provided in the ultrasonic cleaning machine, and the substrate is immersed in the protective liquid. The protective liquid may include deionized water or ethanol. The fluctuations generated by the ultrasonic wave in the liquid can efficiently remove residual impurities on the surface of the substrate. This non-contact cleaning method can reduce the risk of damage to the substrate surface due to physical friction, and can also remove some particles that are difficult to remove by traditional cleaning methods. Immersing the substrate in the protective liquid can not only clean the surface of the substrate, but also dissolve certain residues through chemical reactions, such as the oxide layer generated during the laser thinning process, thereby further improving the surface quality of the substrate. After post-cleaning, the cleanliness of the substrate surface is improved, which is conducive to reducing scratches caused by impurities in the subsequent polishing process, ensuring the smooth progress of subsequent processes and improving the yield rate and finished product quality.

[0062] In some embodiments of the present application, the ultrasonic frequency for cleaning the substrate is 20kHz to 40kHz, and illustratively, it can be 20kHz, 25kHz, 30kHz, 35kHz, 40kHz, or any value within the above range; the ultrasonic power is 30W to 500W, and illustratively, it can be 30W, 50W, 100W, 150W, 200W, 250W, 300W, 350W, 400W, 450W, 500W, or any value within the above range; the vibration The vibration time is between 30s and 10min, and can be 30s, 1min, 2min, 3min, 4min, 5min, 6min, 7min, 8min, 9min, 10min or any value within the above range; the vibration amplitude is between 3μm and 50μm, and can be 3μm, 5μm, 10μm, 15μm, 20μm, 25μm, 30μm, 35μm, 40μm, 45μm, 50μm or any value within the above range. By setting the parameters of ultrasonic cleaning within the above range, the surface residue of the substrate can be effectively removed while minimizing surface damage and reducing the risk of splitting during the substrate cleaning process. In one possible embodiment, the ultrasonic frequency is 30kHz, the ultrasonic power is 300W, the vibration time is 5min, and the vibration amplitude is 30μm.

[0063] After cleaning the substrate, the surface of the substrate needs to be polished to further reduce the roughness of the substrate surface. In step S4, polishing the substrate includes: performing at least one chemical mechanical polishing on the surface of the substrate from which the buffer layer has been removed, until the surface roughness of the substrate reaches a set value; and may also include: double-sided polishing of the substrate.

[0064] Chemical mechanical polishing involves placing a substrate, after the surface layer has been removed, on a polishing platen of a chemical mechanical polishing machine, with the surface, after which the buffer layer has been removed, facing upward. A polishing head is then used to press the substrate against the polishing platen, rotating the polishing head with the substrate at a predetermined speed. This, combined with a polishing fluid of appropriate flow rate, allows the substrate surface to be polished. In practical applications, multiple thinned substrates can be placed on the chemical mechanical polishing machine for simultaneous polishing to improve production efficiency. The number of polishing cycles can be determined based on the desired surface roughness, but this is not limited in this embodiment of the present application.

[0065] In some embodiments of the present application, the polishing liquid can be an aluminum oxide or silicon dioxide polishing liquid, and the polishing pressure applied by the polishing head to the substrate is 1kPa to 300kPa. Exemplarily, the polishing pressure can be 1kPa, 50kPa, 100kPa, 150kPa, 200kPa, 250kPa, 300kPa or any other value within the above range; the polishing head speed is 50r / min to 200r / min, and exemplary, it can be 50r / min, 100r / min, 150r / min, 200r / min or any other value within the above range; the polishing disk speed is 30r / min to 240r / min, and exemplary, it can be 30r / min, 60r / min, 90r / min, 120r / min in, 150r / min, 180r / min, 210r / min, 240r / min or any other value within the above range; polishing liquid flow rate 50mL / min~500mL / min, illustratively, it can be 50mL / min, 100mL / min, 150mL / min, 200mL / min, 250mL / min, 300mL / min, 350mL / min, 400mL / min, 450mL / min, 500mL / min or any other value within the above range; polishing time 5min~30min, illustratively, it can be 5min, 10min, 15min, 20min, 25min, 30min or any other value within the above range. In a possible embodiment, the polishing pressure is 30kPa, the polishing head speed is 100r / min, the polishing disk speed is 100r / min, the polishing liquid flow rate is 200mL / min, and the polishing time is 12min.

[0066] By selecting a suitable polishing liquid and setting the various parameters in the chemical mechanical polishing process within the above-mentioned range, the consistency of the effect on the substrate surface during the polishing process can be improved, local over-polishing or under-polishing can be avoided, and the uniformity and flatness of the substrate surface can be improved. In addition, while ensuring a good polishing effect, the integrity of the substrate is maintained and the occurrence of cracks and the like is prevented. Through the above-mentioned polishing process, the roughness of the polished surface of the substrate can reach 0.05nm to 0.18nm, and its flatness can be improved to a good level, preparing for subsequent processes.

[0067] In step S4, after completing chemical mechanical polishing, the substrate can also be double-sided polished. The double-sided polishing is completed in a double-sided polishing device. The substrate moves relative to the upper and lower polishing pads and cooperates with the polishing liquid to achieve double-sided polishing, making the surface of the substrate smoother and meeting the product requirements.

[0068] In some embodiments of the present application, the material of the polishing pad can be one of polyurethane, polyethylene, polypropylene, polyester, or a composite thereof; the polishing liquid can be an aluminum oxide or silicon dioxide polishing liquid; the particle size of the particles in the polishing liquid is 0.1 μm to 10 μm, and illustratively, it can be 0.1 μm, 1 μm, 2 μm, 3 μm, 4 μm, 5 μm, 6 μm, 7 μm, 8 μm, 9 μm, 10 μm, or any other value within the above range; the concentration of the particles in the polishing liquid is 1 wt% to 10 wt%, and illustratively, it can be 1 wt%, 2 wt%, 3 wt%, 4 wt%, 5 wt%, 6 wt%, 7 wt%, 8 wt%, 9 wt%, 10 wt%, or any other value within the above range. In one possible embodiment, the particle size of the particles in the polishing liquid is 1 μm and the concentration is 2 wt%.

[0069] By selecting an appropriate polishing pad and polishing slurry, and setting the various parameters of the polishing slurry within the above ranges, efficient and low-damage double-sided polishing of the substrate can be achieved, further improving the flatness of both sides of the substrate to meet product requirements, that is, it can be reused. After completing the above steps S1 to S4, the substrate can also be rinsed and dried, and placed in a sealed box filled with inert gas for storage and easy access.

[0070] To make the effect of the present application more intuitive, the present application also provides a comparative example for comparison with an embodiment of the present application. In the comparative example and the embodiment of the present application, the thickness of the epitaxial layer of the silicon carbide epitaxial wafer to be processed is 30 μm, and the thickness of the buffer layer is 3 μm.

[0071] Comparative Example: The epitaxial layer and the buffer layer are removed at one time using a laser. The laser frequency is 16 MHz, the pulse energy is 350 J, the spot diameter is 30 μm, the line spacing is 20 μm, and the scanning speed is 10 mm / s.

[0072] In an embodiment of the present application, the epitaxial layer is first removed by three first thinning treatments, with 10 μm removed each time. The frequency of the first laser used in the first thinning treatment is 8 MHz, the pulse energy is 50 J, the spot diameter is 30 μm, the line spacing is 20 μm, and the scanning speed is 10 mm / s. Then, the buffer layer is removed by a single second thinning treatment. The frequency of the second laser used in the second thinning treatment is 500 kHz, the pulse energy is 600 mJ, the spot diameter is 60 μm, the line spacing is 80 μm, and the scanning speed is 550 mm / s.

[0073] Figure 3 A comparison table of thermal damage depths of substrates provided according to the comparative examples and embodiments of the present application is provided. Figure 3 It can be seen that the removal of the epitaxial layer and the buffer layer by the method in the comparative example will cause 2.5±0.5μm of thermal damage to the silicon carbide substrate, while the step-by-step removal of the epitaxial layer and the buffer layer by the method in the embodiment of the present application can reduce the thermal damage depth of the silicon carbide substrate by 0.8±0.2μm. It can be seen that the method provided in the embodiment of the present application can alleviate the problem of deep thermal damage and poor edge accuracy caused by heat accumulation in single laser thinning, and improve the quality of the silicon carbide substrate to be recycled.

[0074] Figure 4 A comparison table of the surface roughness of substrates provided according to the comparative examples and embodiments of the present application, comprising Figure 4 It can be seen that when the epitaxial layer and the buffer layer are removed by the method in the comparative example, the roughness of the substrate surface is 3.2±0.5nm, while when the epitaxial layer and the buffer layer are removed by the method in the embodiment of the present application, the roughness of the substrate surface can be reduced to 0.12±0.03nm, which greatly improves the surface consistency of the silicon carbide substrate and facilitates reuse.

[0075] 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 recycling a substrate in a silicon carbide epitaxial wafer, characterized in that: include: Obtaining a silicon carbide epitaxial wafer to be processed, the silicon carbide epitaxial wafer comprising a substrate and a buffer layer and an epitaxial layer sequentially stacked on the substrate; Determining a thickness of the epitaxial layer to be thinned, and performing at least one first thinning process on the epitaxial layer according to the thickness to be thinned, so as to expose the buffer layer; Performing a second thinning process on the buffer layer to expose the substrate, wherein both the first thinning process and the second thinning process include performing a thinning process on the corresponding film layer using a laser; The substrate is cleaned and polished in sequence.

2. The method for recycling a substrate in a silicon carbide epitaxial wafer according to claim 1, wherein: Performing the first thinning process on the epitaxial layer at least once at least includes: performing a thinning process on the epitaxial layer using a first laser; Performing the second thinning process on the buffer layer includes: performing a thinning process on the buffer layer using a second laser; The energy density of the second laser is smaller than the energy density of the first laser.

3. The method for recycling a substrate in a silicon carbide epitaxial wafer according to claim 2, wherein: The first laser and the second laser satisfy at least one of the following: The frequency of the first laser is greater than the frequency of the second laser; The pulse energy of the first laser is greater than the pulse energy of the second laser; The spot diameter of the first laser is smaller than the spot diameter of the second laser; The line spacing of the first laser is smaller than the line spacing of the second laser; The scanning speed of the first laser is lower than the scanning speed of the second laser.

4. The method for recycling a substrate in a silicon carbide epitaxial wafer according to claim 2, wherein: The pulse energy of the first laser is 1J to 100J, and the spot diameter of the first laser is 10μm to 60μm.

5. The method for recycling a substrate in a silicon carbide epitaxial wafer according to claim 2, wherein: The pulse energy of the second laser is 1 mJ to 1 J, and the spot diameter of the second laser is 60 μm to 100 μm.

6. The method for recycling a substrate in a silicon carbide epitaxial wafer according to claim 2, wherein: The frequency of the first laser is 600 kHz to 12 MHz, the line spacing of the first laser is 0.1 μm to 65 μm, and the scanning speed of the first laser is 0.5 mm / s to 500 mm / s.

7. The method for recycling a substrate in a silicon carbide epitaxial wafer according to claim 2, characterized in that: The frequency of the second laser is 1 kHz to 600 kHz, the line spacing of the second laser is 70 μm to 100 μm, and the scanning speed of the first laser is 500 mm / s to 1000 mm / s.

8. The method for recycling a substrate in a silicon carbide epitaxial wafer according to claim 1, wherein: When performing the second thinning process on the buffer layer, the method further includes: The silicon carbide epitaxial wafer after the first thinning process is placed in an inert protective gas environment.

9. The method for recycling a substrate in a silicon carbide epitaxial wafer according to claim 1, wherein: Performing the first thinning treatment on the epitaxial layer at least once includes: performing the first thinning treatment on the epitaxial layer multiple times, and in the multiple first thinning treatments, except for the last first thinning treatment, each first thinning treatment is used to thin the epitaxial layer by 10 μm.

10. The method for recycling a substrate in a silicon carbide epitaxial wafer according to claim 1, characterized in that: Cleaning the substrate includes: The substrate after the second thinning treatment is placed in an ultrasonic cleaning machine for cleaning, wherein the ultrasonic cleaning machine is provided with a protective liquid, the substrate is immersed in the protective liquid, and the protective liquid includes deionized water or ethanol.

11. The method for recycling a substrate in a silicon carbide epitaxial wafer according to claim 1, wherein: Performing the polishing process on the substrate includes: The surface of the substrate from which the buffer layer is removed is subjected to at least one chemical mechanical polishing process until the surface roughness of the substrate reaches a set value.

12. The method for recycling a substrate in a silicon carbide epitaxial wafer according to claim 11, characterized in that: Performing the polishing process on the substrate further includes: The substrate is double-sided polished.

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