A method for thinning silicon carbide substrates based on thermal-assisted electrochemistry

Abstract

This invention provides a method for thinning silicon carbide substrates based on heat-assisted electrochemistry. Specifically, a pretreated silicon carbide substrate is placed in a high-temperature alkaline electrolyte, and a first voltage is applied to the pretreated substrate. The high-temperature alkaline electrolyte and the first voltage synergistically drive an electrochemical etching reaction on the surface of the silicon carbide substrate, forming a uniform nanoporous layer structure. Once the nanoporous layer structure reaches the target thickness, a second voltage, higher than the first voltage, is applied to induce further embrittlement of the nanoporous layer structure. The nanoporous layer is then peeled off using the impact of numerous bubbles generated during the high-voltage reaction, achieving precise thinning to the target thickness. The method provided by this invention enables high-precision thinning of silicon carbide substrates under non-contact and non-destructive conditions. The process is green, simple, low-cost, and fast, making it suitable for the fabrication of large-area, ultra-thin, high-performance, and flexible silicon carbide devices, and possesses promising application prospects and industrialization value.

Description

Technical Field

[0001] This invention relates to the field of semiconductor processing technology, and in particular to a method for thinning silicon carbide substrates based on thermally assisted electrochemistry. Background Technology

[0002] Silicon carbide (SiC), with its wide bandgap, high breakdown field strength, high thermal conductivity, high electron saturation drift velocity, and excellent radiation resistance, has become a core material for modern power electronic devices, radio frequency devices, optoelectronic devices, and quantum devices. To fully leverage the performance advantages of SiC power devices, after completing front-end manufacturing processes such as epitaxial growth, photolithography, and ion implantation, the production line needs to further thin the SiC substrate, originally several hundred micrometers thick (approximately 350-500 µm), to approximately 200 µm, or even less. The thinned substrate not only significantly shortens the current and heat transport path in the vertical direction, thereby greatly reducing substrate series resistance and Joule heat accumulation, effectively reducing device conduction losses and improving heat dissipation, but also facilitates the lightweight and miniaturized design of power modules. Therefore, how to achieve mass production of SiC substrates with thicknesses below 200 µm, or even 100 µm, at low cost and high yield has become one of the key technological challenges in constructing next-generation high-power-density, low-energy-consumption power modules.

[0003] Currently, the industry primarily employs back-side mechanical polishing with diamond wheels as the core process for thinning SiC power device substrates. This process is relatively mature and widely used. However, SiC, as a typical hard and brittle material with a Mohs hardness of 9.5, second only to diamond, presents extremely high machining challenges. The thinning process relies on diamond wheels for high-load, high-speed, and high-intensity physical removal of the substrate. While this achieves efficient thinning, it also leads to severe wear on the grinding wheel itself, significantly shortening its lifespan and drastically increasing the frequency of replacement and maintenance. Related literature and company statistics show that a grinding wheel needs to be replaced approximately every 50-60 6-inch SiC wafers processed. The associated consumables, such as abrasives and cooling / polishing fluids, also require frequent replenishment, making consumable costs significant. In the future, as SiC substrate sizes expand from 6 inches to 8 inches and even 12 inches, the area per wafer will increase significantly, processing time will lengthen, and yield control will become more difficult. The consumable consumption and equipment depreciation per wafer will increase exponentially, further driving up the overall thinning process cost. Meanwhile, mechanical polishing inevitably introduces structural defects such as mechanical damage, stress concentration, and microcracks into the surface and subsurface layers of silicon carbide substrates. When wafer thickness is further reduced to 200 µm or even below 100 µm, these defects significantly increase the wafer breakage rate during polishing, fundamentally limiting the safe and controllable thinning limit and severely impacting yield and cost. Even more critically, the core equipment and grinding wheels used for SiC back-side thinning are highly dependent on imports. Although the domestic semiconductor equipment industry is developing rapidly, mature independent alternatives have not yet been formed for thinning equipment and its key components and consumables. It is worth noting that this bottleneck in mechanical processing, stemming from the inherent hardness and brittleness of the material, is not unique to silicon carbide. With the rapid development of wide and ultra-wide bandgap power devices such as gallium nitride, aluminum nitride, and diamond, these materials also face the dilemmas of high damage, high cost, low yield, and difficulty in achieving ultra-thin processing due to traditional mechanical thinning processes. Especially for diamond, which has the highest Mohs hardness, the processing technology barriers far exceed those of silicon carbide. Therefore, the semiconductor industry also needs an innovative thinning solution to break this common dilemma.

[0004] In summary, traditional mechanical polishing processes face multiple bottlenecks when used for SiC substrate thinning, including high material costs, limited achievable thinning thicknesses, and insufficient domestic production of key equipment, making it difficult to support future large-scale, low-cost mass production demands. Therefore, there is an urgent need to develop a new thinning technology that is gentler, more efficient, less damaging, and has the potential for domestic substitution to support the development of SiC-based power devices towards higher integration, lower cost, and higher performance. The emergence of this new technology is also expected to provide a feasible technological reference and new solution for addressing the thinning challenges of other hard and brittle semiconductor materials (such as gallium nitride, gallium oxide, and diamond). Summary of the Invention

[0005] In view of the shortcomings of the prior art, the purpose of this invention is to provide a method for thinning SiC substrates based on thermally assisted electrochemistry, which aims to solve a series of problems caused by the mechanical polishing method commonly used in the back-side thinning process of SiC substrates in the prior art, such as high material costs, serious equipment dependence, and limited thinning thickness and other technical and equipment bottlenecks.

[0006] The technical solution of the present invention is as follows: A first aspect of the present invention provides a method for thinning a silicon carbide substrate based on thermally assisted electrochemistry, comprising the following steps: (1) The silicon carbide substrate to be thinned is pretreated to obtain the pretreated silicon carbide substrate; (2) The pretreated silicon carbide substrate is placed in an alkaline electrolyte or hydrofluoric acid solution (preferably a high-temperature alkaline electrolyte), and a first voltage is applied to the pretreated silicon carbide substrate to cause an electrochemical etching reaction on the surface of the pretreated silicon carbide substrate to be thinned, thereby forming a nanoporous layer structure on the surface to be thinned. (3) As the electrochemical etching reaction proceeds, after the nanoporous layer structure reaches the target thickness, a second voltage is applied to remove the nanoporous layer structure to obtain a thinned silicon carbide substrate.

[0007] Optionally, step (2) further includes: after placing the pretreated silicon carbide substrate in an alkaline electrolyte, heating the alkaline electrolyte to a temperature of 30-90°C, where the higher the temperature, the higher the etching rate.

[0008] Optionally, in step (2), the alkaline electrolyte includes one of the following: potassium hydroxide (KOH) aqueous solution, cesium hydroxide (CsOH) aqueous solution, rubidium hydroxide (RbOH) aqueous solution, sodium hydroxide (NaOH) aqueous solution, and lithium hydroxide (LiOH) aqueous solution; the concentration of the alkaline electrolyte is 0.1-5 mol / L. -1 The higher the concentration, the higher the etching rate.

[0009] Optionally, the alkaline electrolyte may further include functional additives, which may include one of methanol, ethanol, ferric nitrate, iodate, sodium dodecyl sulfate, and sodium fluoride.

[0010] Optionally, in step (2), the first voltage is applied in at least one of constant voltage, linear voltage scanning, step voltage, periodic pulse voltage, and constant current.

[0011] Optionally, in step (2), the first voltage is a constant voltage of 5-15V. The higher the voltage, the faster the etching rate.

[0012] Optionally, in step (2), the electrochemical etching reaction time is 10-180 minutes. The longer the etching time, the thicker the nanoporous layer structure. As the thickness of the nanoporous layer increases, the etching rate will decrease accordingly due to the limitation of mass transfer (the diffusion / escape of reaction ions / products in the pores is hindered).

[0013] Optionally, in step (3), the second voltage is 15-30V and the application time of the second voltage is 1-10s. The higher the selected second voltage, the shorter the application time.

[0014] Optionally, to improve the thinning rate, the silicon carbide substrate to be thinned can be subjected to multiple rounds of thinning. Multiple rounds of thinning can effectively reduce the influence of mass transfer limitation on the thinning rate. Specifically, in step (3), after obtaining the thinned silicon carbide substrate, the thinned silicon carbide substrate is repeated from step (2) to step (3) multiple times to obtain a silicon carbide substrate with multiple rounds of thinning.

[0015] Beneficial Effects: The method provided by this invention achieves non-contact, non-destructive thinning of SiC based on a thermo-assisted electrochemical reaction. Specifically, a nanoporous layer structure is generated on the back side of the SiC substrate under low-voltage conditions through thermo-assisted electrochemical action. A short-duration high-voltage pulse is then applied to induce further embrittlement of the nanoporous layer structure. The nanoporous layer is then peeled off using the impact of numerous bubbles generated during the high-voltage reaction, achieving gentle removal of the etched layer and vertical thinning of the substrate. The entire process does not rely on any mechanical contact and is carried out entirely within the liquid phase and electric field, avoiding the frictional impact and physical damage risks inherent in traditional mechanical grinding. This truly achieves a non-contact, non-destructive, low-stress, and high-integrity thinning method.

[0016] Compared with traditional mechanical grinding, the present invention has the following significant technical advantages: (1) The process is simple, the equipment threshold is low, and the cost of consumables is significantly reduced. The hardware required for this invention mainly consists of a standard electrochemical workstation, a constant-temperature water bath or heating device, a peristaltic pump, temperature sensors, and other conventional experimental equipment. All of these can be built using commercially available mature platforms, eliminating the need to purchase expensive, imported specialized back-end thinning equipment, or to perform high-frequency maintenance or precision grinding and calibration, significantly reducing initial investment and subsequent operating costs. The overall system structure is compact and occupies little space. In terms of consumables, this invention also demonstrates significant economic advantages. In traditional mechanical grinding, the high hardness of SiC accelerates the wear of diamond grinding wheels, leading to frequent replacements. Industry statistics show that a grinding wheel needs to be replaced for every 50-60 6-inch SiC wafers thinned, and a large amount of abrasive slurry and chemical cleaning agents are continuously consumed, resulting in continuous high-frequency costs. In contrast, the method provided by this invention relies only on a low-concentration alkaline electrolyte (e.g., 1 mol L...). -1 KOH), stable precious metal electrodes (such as Pt wire) that can be recycled for a long time, peristaltic pumps, heating devices and corresponding sensors, without any high-value consumables and complex post-cleaning processes, can significantly reduce the thinning cost per wafer.

[0017] (2) Continuously adjustable thickness, strong process adaptability, and support for batch processing: The method provided by this invention achieves dynamic adjustment of the oxidation and dissolution rate of the SiC substrate surface by precisely controlling multiple key process parameters such as applied voltage, solution temperature, ion concentration, and reaction time, thereby obtaining a continuously adjustable thinning thickness. Under given equipment conditions, by simply setting the voltage, temperature, and reaction time reasonably, a SiC substrate with an initial thickness of approximately 350 µm can be stably thinned to any target thickness (such as 50 µm, 120 µm, or 200 µm) to meet the fine requirements of different devices for substrate thickness. In addition, the entire thinning process does not rely on substrate rotation, polishing head, or high-rigidity positioning structure. The temperature field and electric field can be uniformly applied to the substrate surface, possessing excellent scalability and process compatibility. This invention is compatible with current mainstream 6-inch, 8-inch, and even 12-inch SiC substrates. The electrolyte circulation module is also rapidly expanded through proportional scaling. It supports both thinning of single large-size wafers and parallel batch processing of multiple substrates, and has good prospects for industrial scale-up and mass production applications.

[0018] (3) Supports the extreme thinning preparation of ultrathin (<50µm) SiC substrates In applications such as automotive power modules, high-power-density server power supplies, and photovoltaic / energy storage inverters, to simultaneously meet the requirements of low thermal resistance, low on-resistance, and high integration, SiC substrates typically need to be further thinned to 100 µm or even down to the tens of micrometer level. This places higher demands on the SiC substrate thickness. Traditional mechanical polishing processes are prone to substrate breakage, warping, and edge chipping when the thickness approaches 100 µm, making it difficult to guarantee reliability and yield. This invention constructs a non-contact, non-destructive, thermally assisted electrochemical etching thinning environment. In the later stages of the reaction, a multi-round "low-pressure etching – high-pressure removal" gradient thinning strategy is employed, enabling continuous and stable vertical substrate thinning without any mechanical contact. In each round of low-pressure etching, a nanoporous structure is formed on the surface. Subsequently, a high-voltage pulse is applied to induce further embrittlement of the interface and the impact of numerous bubbles, achieving gentle removal of the etched layer. This strategy offers high repeatability and precise control over the thinning depth, making it suitable for staged and safe substrate thickness reduction. Experiments have verified that this process platform can progressively thin SiC substrates with an initial thickness of approximately 350µm to 200µm, 100µm, and even stably control the thickness to 50µm and below, while maintaining the integrity of the substrate structure, surface uniformity, and no mechanical damage. This extreme thinning capability provides a feasible and scalable process path to meet the urgent need for ultra-thin SiC substrates in future advanced packaging (such as chip interconnects, 3D integration, and high-power-density modular designs).

[0019] (4) The core process mechanism is universal and applicable to non-destructive thinning of various material systems. The "pore-forming-peeling" core mechanism upon which this invention achieves thinning of silicon carbide materials inherently possesses strong technological transferability and scalability. Besides silicon carbide, for other semiconductor materials such as silicon and gallium nitride, only corresponding optimization and adaptation of the electrolyte system are needed to achieve non-destructive thinning using a similar process mechanism. This means that this invention has high application value and technological influence in the processing of various semiconductor substrates.

[0020] Therefore, the non-contact, non-destructive thinning process based on thermally assisted electrochemistry constructed in this invention achieves a replacement and breakthrough for traditional mechanical polishing solutions in several key aspects: it not only achieves substantial improvements in thinning limits, unit cost, and integration density, but also provides a novel solution for the large-scale mass production of SiC substrates with higher integration density, thinner wafers, and lower costs. This technical approach has high engineering feasibility and significant prospects for industrialization, and is applicable to the thinning processes of various types of high-performance SiC-based devices, such as power semiconductors, RF devices, and optoelectronic devices. Simultaneously, this invention also provides a feasible alternative and innovative approach for solving the thinning processing of other high-hardness and brittle semiconductor materials such as gallium nitride, aluminum nitride, and diamond. Attached Figure Description

[0021] Figure 1 Schematic diagrams of the overall non-contact thermally assisted electrochemical thinning reaction device and the electrochemical reaction cell; (a) Schematic diagram of the overall reaction device; (b) Schematic diagram of the electrochemical reaction cell device; wherein, 1-control computer, 2-electrochemical workstation or DC regulated power supply, 3-electrochemical reaction device, 4-vacuum pump switch, 5-vacuum pump, 6-constant temperature storage tank, 7, 13-electrolyte, 8-heating rod, 9, 10, 11-wire, 12-platinum sheet; 14-temperature sensor, 15, 17-peristaltic pump, 16, 18-peristaltic pump tube, 19-vacuum suction cup, 20-nickel plate, 21-fluoropolymer pad, 22-conductive sponge, 23-SiC, 24-electrochemical reaction cell shell, 25-screw.

[0022] Figure 2 The diagram shows the cross-sectional and surface morphology of the nanoporous layer after the electrochemical etching reaction in Example 1; (a) cross-sectional morphology of the nanoporous layer; (b) surface micromorphology.

[0023] Figure 3 The diagram shows the cross-sectional and surface morphology of the nanoporous layer after the electrochemical etching reaction in Example 2; (a) Cross-sectional morphology of the nanoporous layer, with the inset showing magnified details of the cross-sectional structure; (b) Surface micromorphology.

[0024] Figure 4 The diagram shows the cross-sectional and surface morphology of the nanoporous layer after the electrochemical etching reaction in Example 3; (a) Cross-sectional morphology of the nanoporous layer, with the inset showing magnified details of the cross-sectional structure; (b) Surface micromorphology.

[0025] Figure 5 The images show photographs of the ultrathin SiC substrate and the thickness measurement results in Example 4; (a) photograph of the ultrathin SiC substrate; (b) thickness measurement.

[0026] Figure 6 Comparison of physical images and thickness measurement results of commercial SiC MOSFET devices with different thicknesses in Examples 5 and 6; (a) Physical photos of devices with thicknesses of 350 µm, 120 µm and 47 µm; (b) Thickness measurement value of device with thickness of 47 µm.

[0027] Figure 7 The images show a comparison of two-inch SiC substrates of different thicknesses in Example 7, along with thickness measurement results and a macroscopic display of the flexibility of a 35 µm thick substrate. (a) Photographs of the 350 µm and 35 µm thick substrates; (b) Thickness measurement of the 35 µm thick substrate; (cd) Macroscopic flexibility characteristics of the 35 µm thick substrate at different angles. Detailed Implementation

[0028] This invention provides a method for thinning silicon carbide substrates based on thermally assisted electrochemistry. To make the objectives, technical solutions, and effects of this invention clearer and more explicit, the invention is further described in detail below. It should be understood that the specific embodiments described herein are merely illustrative of the invention and are not intended to limit the invention.

[0029] This invention provides a method for thinning silicon carbide substrates based on thermally assisted electrochemistry, comprising the following steps: (1) The silicon carbide substrate to be thinned is pretreated to obtain the pretreated silicon carbide substrate; (2) The pretreated silicon carbide substrate is placed in a high-temperature alkaline electrolyte, and a first voltage is applied to the pretreated silicon carbide substrate to cause an electrochemical etching reaction on the surface to be thinned of the pretreated silicon carbide substrate, thereby forming a nanoporous layer structure on the surface to be thinned. (3) After the nanoporous layer structure reaches the target thickness, a second voltage is applied to remove the nanoporous layer structure to obtain a thinned silicon carbide substrate.

[0030] This invention employs a method for thinning silicon carbide substrates based on heat-assisted electrochemistry. The SiC substrate to be thinned is placed in a high-temperature alkaline electrolyte, and a first voltage is applied to the substrate. Under the synergistic drive of the high-temperature alkaline electrolyte and the voltage, an electrochemical reaction occurs on the surface of the SiC substrate to be thinned. During the reaction, the surface of the SiC substrate to be thinned gradually oxidizes and dissolves, forming a uniform nanoporous layer structure. Once the nanoporous structure reaches the target thickness, a higher second voltage (i.e., second voltage > first voltage) is applied to stimulate a more vigorous chemical reaction, producing an effect similar to "electropolishing," thereby further embrittlement of the nanoporous layer structure. Simultaneously, the microscale mechanical disturbances generated by the local expansion and bursting of numerous microbubbles provide an upward thrust, promoting the peeling of the nanoporous layer structure and achieving the target thickness reduction. Furthermore, by adjusting the voltage and solution composition, the etching rate, pore size structure, and interface structure can be precisely adjusted to adapt to different thinning requirements.

[0031] By applying a first voltage in step (2) and a second voltage in step (3), this invention constructs a two-stage substrate thinning mechanism of "low-pressure etching + high-pressure removal". In step (2), a controllable nanoporous layer structure is generated on the surface of the SiC substrate under a lower voltage condition. Then, in step (3), a short-duration high-voltage pulse is applied to induce the impact effect caused by the local expansion and bursting of a large number of microbubbles in the interface structure, thereby achieving non-contact thinning of the substrate. In terms of electrochemical parameters, the specific values ​​of the "first voltage" and "second voltage" are not limited to a single value. For example, the preferred parameters can be low-pressure 10V etching and high-pressure 20V removal. Similar effects can also be achieved by appropriately adjusting the voltage amplitude and the action time: for example, a slightly higher voltage (such as 12V) can still stably form holes, or a higher voltage (such as 25V) combined with a shorter pulse time can also achieve effective removal. Similarly, parameters such as pulse frequency, duty cycle, and single pulse duration can be optimized and adjusted to achieve the same function. In other words, the selection and range of relevant parameters can be routinely optimized by those skilled in the art to achieve substantially the same technical effect. For example, when it is necessary to form a deeper porous structure or achieve a greater thinning thickness / higher thinning rate in a SiC substrate, a longer low-pressure etching time can be used in conjunction with multiple rounds of high-pressure pulse cycles; conversely, if the target thinning thickness and rate are low, a single short pulse can complete the stripping.

[0032] In addition, in step (2) when the first voltage is applied and in step (3) when the second voltage is applied, the electrochemical system can flexibly select a two-electrode or three-electrode configuration mode according to different process control requirements: (1) In the two-electrode system, the SiC substrate is used as the anode and the noble metal platinum wire (Pt) is used as the cathode to form the simplest reaction circuit; (2) In the three-electrode system, a standard mercury / mercury oxide electrode (Hg / HgO) is introduced as a reference electrode on the basis of the above two electrodes to achieve precise control of the anode potential, which is suitable for research-oriented or high-precision control of porous etching and thinning process analysis. All electrodes are connected to the electrochemical workstation through wires, which provides a stable voltage / current source and performs real-time monitoring and control of electrochemical parameters (including constant current control, constant potential control, step voltage control, linear cyclic voltammetry test, etc.). The specific reaction device is as follows: Figure 1 As shown. In some specific embodiments, a suitable electrode mode can be selected based on experimental complexity, etching uniformity requirements, and cost constraints.

[0033] It should be noted that although this invention uses silicon carbide as an example, this electrochemical treatment method for inducing the formation of a porous layer on the surface by applying a low voltage is not limited to silicon carbide. In other semiconductor material systems such as silicon, gallium nitride, and aluminum nitride, by adapting the corresponding electrolyte system, the same technical principle can be used to prepare porous structures. The process strategy of removing porous layers by changing electrical parameters has broad material applicability. For other material systems such as silicon, gallium nitride, gallium oxide, or diamond, only a corresponding second electrical parameter needs to be adapted according to the material characteristics to complete the removal of porous layers and thinning of the corresponding substrate using a similar process path.

[0034] In some embodiments, in step (1), the silicon carbide substrate to be thinned is one of 4H-SiC, 6H-SiC, and 3C-SiC.

[0035] In some embodiments, in step (1), the pretreatment includes: sequentially cutting, cleaning, and drying the silicon carbide substrate to be thinned.

[0036] To ensure the uniformity and repeatability of the etching reaction, the silicon carbide substrate needs to be cut and cleaned before electrochemical experiments. Specifically, the silicon carbide substrate to be thinned (such as a commercially conductive 4H-SiC substrate) is cut to the required size (12 mm * 12 mm). Cutting can be done using laser cutting, dicing, manual cutting with a diamond pen, or other precision cutting processes suitable for hard and brittle materials. After cutting, the sample is sequentially immersed in acetone, anhydrous ethanol, and deionized water, and ultrasonically cleaned for 10-20 minutes in each solution to remove any organic contaminants, particulate impurities, and micropowder generated during dicing. After cleaning, the sample is purged with dry nitrogen gas (for approximately 20-60 seconds) to ensure the surface is completely dry and free of residual liquid, providing a stable initial surface condition for subsequent etching steps.

[0037] Subsequently, the SiC substrate to be thinned is placed in an alkaline electrolyte, and the electrolyte is heated by an external heating device to create an etching environment with a uniform electric and thermal field. Specifically, the alkaline electrolyte can be heated to the target temperature (preferably 70-90°C) using a constant-temperature water bath or an electrically heated circulating tank to provide thermal activation conditions and accelerate the electrochemical reaction rate. The heated electrolyte is continuously circulated to the reaction tank by a peristaltic pump, keeping the liquid in the reaction area at a constant temperature and constantly replenishing it. This ensures the spatial uniformity of electrolyte temperature and ion concentration, improves reaction stability, and avoids uneven etching or etching rate fluctuations caused by local ion depletion or bubble accumulation.

[0038] In some embodiments, in step (2), the alkaline electrolyte includes one of KOH aqueous solution, CsOH aqueous solution, RbOH aqueous solution, NaOH aqueous solution, and LiOH aqueous solution, and its concentration is preferably 0.1-5 mol / L. -1 Within the above concentration range, a good balance can be achieved between etching rate, porous layer uniformity, and interface smoothness. Higher concentrations can effectively increase the etching rate, but excessively high concentrations may lead to interface coarsening; while controlling the concentration within 0.1-5 mol·L⁻¹ is preferable. - Within the range of ¹, it is more suitable for constructing a fine etching environment with controllable reaction and smooth interface, which meets the consistency requirements of the present invention for thinning efficiency and quality.

[0039] In some embodiments, functional additives may be added to the alkaline electrolyte. These functional additives include one or more of methanol, ethanol, ferric nitrate, iodate, sodium dodecyl sulfate, and sodium fluoride. These functional additives include various electron sacrificial agents used to regulate the anolyte reaction path, suppress side reactions, and improve hole utilization; or various surfactants that can reduce interfacial tension, promote rapid bubble desorption, optimize pore structure uniformity, and increase reaction rate; or various strong oxidants to improve the oxidation rate of the SiC surface. Furthermore, the introduction of fluorine-containing additives may be considered to further improve the oxide dissolution rate.

[0040] In some embodiments, the first voltage applied in step (2) is at least one of constant voltage, linear voltage scanning, step voltage, periodic pulse voltage, and constant current. When fabricating complex structures such as multilayer porous structures, achieving region-selective etching, or constructing functionally graded hole arrays, a periodic pulse voltage strategy is preferred. This strategy induces spatially selective removal through periodic electric field perturbation, enhancing etching accuracy and layer control. Furthermore, a constant current control mode can be used, providing dynamic adaptive current stabilization when electrolyte concentration fluctuates or local reaction is uneven. This helps maintain etching uniformity and system reaction stability, and is particularly suitable for automated or long-term continuous processing systems.

[0041] In some embodiments, the first voltage is a constant voltage of 5-15V.

[0042] In step (2), after the reaction system temperature stabilizes and the solution is fully circulated, a constant low voltage is applied to the SiC substrate, which serves as the working electrode, using an electrochemical workstation or power supply. The voltage range is typically set between 5-15 V (preferably 10 V) to initiate the electrochemical etching reaction driven by a weak electric field. Under the synergistic effect of the electric and thermal fields, a large number of electron-hole pairs are excited in the SiC substrate. Holes migrate to the surface under the drive of the applied electric field to participate in the anodic oxidation reaction, while electrons are transported to the counter electrode (such as a platinum wire) via an external circuit and trigger the cathode hydrogen evolution process, thereby forming a complete electrochemical circuit. This stage belongs to the "mild etching period," where the reaction rate is controlled, making it suitable for constructing a stable and uniform initial nanoporous layer, laying the structural foundation for subsequent high-voltage embrittlement of the interface structure and removal of the porous layer.

[0043] To ensure the continuity and uniformity of the reaction, the current density and temperature changes within the etching tank should be monitored in real time during the etching process. If necessary, the voltage can be adjusted through a program, or methods such as stirring and ultrasonication can be used to improve the uniformity of local etching and ensure the consistency of the reaction across the entire sample. The depth and morphology of the resulting nanoporous layer can be precisely controlled by adjusting parameters such as voltage, electrolyte concentration, reaction temperature, and time.

[0044] In some embodiments, in step (2), the preferred reaction time range for the electrochemical etching reaction is 10-180 minutes.

[0045] In some embodiments, in step (3), the second voltage is preferably in the range of 15-30V, and the application time of the second voltage is 1-10s, such as 5s. The higher the selected second voltage, the shorter the application time.

[0046] In some embodiments, in step (3), the second voltage is applied in at least one of constant voltage, linear voltage scanning, step voltage, and periodic pulse voltage.

[0047] In this invention, the method for removing the nanoporous layer structure includes the following steps: First, high voltage is applied to induce interfacial embrittlement and generate bubble disturbance; if necessary, one or more auxiliary methods such as ultrasonic treatment, mechanical disturbance, or directional liquid flow rinsing are combined to achieve the removal of the porous layer. For example, an ultrasonic coupling system can be used to accelerate bubble desorption and reactant transport, which can effectively suppress the bubble shielding effect and the formation of reactant depletion zones, thereby improving the uniformity of the pore structure, etching rate, and overall thinning quality. This invention uses interfacial embrittlement and bubble disturbance as the key mechanisms for porous layer removal, playing a core role in achieving non-contact SiC substrate thinning. Specifically, by applying high voltage to the anode, a violent chemical reaction is initiated between the nanoporous layer and the SiC interface, causing a further decrease in pore wall thickness and generating a large number of bubbles. The microscale mechanical disturbance generated by the local expansion and bursting of these bubbles can effectively destroy the weakened interfacial structure, thereby achieving non-contact removal of the etched layer.

[0048] In some embodiments, in step (3), after the nanoporous layer formed on the SiC substrate surface reaches a predetermined thickness, the etching process is stopped and preparations are made to enter the nanoporous layer removal stage. At this time, a short-term high voltage is applied to the working electrode through an electrochemical workstation, preferably in the range of 15-30 V, for a duration of several seconds. The specific parameters are optimized according to the sample size, pore depth, and required removal thickness. Under high voltage conditions, the electric field strength at the anode interface is significantly enhanced, and the reaction surface will enter a mode similar to "electropolishing", exhibiting multiple synergistic effects: (1) Etching rate jump: The voltage surge accelerates the etching reaction and greatly improves the removal efficiency of interface materials; (2) Triggering interface structure "embrittlement": Due to the thinning of the pore walls and the weakening of mechanical support between the nanoporous layer and the unetched area, the structural stability decreases, exhibiting a "brittle fracture tendency"; (3) Bubble-induced fracture: High voltage triggers a more intense interface reaction, and a large amount of gas is released (such as oxygen, carbon monoxide, carbon dioxide, etc.). Bubbles are rapidly generated, aggregated, expanded and ruptured in the pores, further destroying the connection area and promoting the removal of the porous layer. The above process is essentially a non-contact thinning mechanism based on the synergistic effect of multiple physical fields: electric field driving, structural embrittlement, and bubble disturbance. Specifically: (1) Electric field driving: High voltage forms a strong electric field in the anode region, which significantly enhances the anodic oxidation reaction rate, induces interfacial oxidation dissolution, and rapidly develops porous structures; (2) Structural embrittlement: Between the porous layer and the dense SiC interface, as the pore walls gradually thin and the stress concentration effect intensifies, the local structural strength and stability decrease; (3) Bubble disturbance: Accompanying the oxidation reaction process, a large amount of gas rapidly precipitates, accumulates, expands, and ruptures in the pore and interfacial regions, forming strong local disturbances. Under the coupling of the above three effects, the interfacial material is ultimately removed non-contactly. This coupling mechanism does not rely on the external force or tool intervention generated by traditional mechanical grinding, but achieves layer-by-layer thinning of the substrate in the vertical direction through the synergistic effect of electric field and bubbles in the nanoporous structure.

[0049] In some embodiments, the silicon carbide substrate to be thinned is subjected to multiple rounds of thinning, specifically including: in step (3), after obtaining the thinned silicon carbide substrate, the thinned silicon carbide substrate is repeated in steps (2) to (3) multiple times (e.g., 1-4 times) to obtain the silicon carbide substrate with multiple rounds of thinning.

[0050] By performing multiple thinning cycles on the silicon carbide substrate to be thinned, the impact of mass transfer limitation on the thinning rate can be effectively reduced, achieving ultra-thin SiC substrate fabrication while maintaining a high thinning rate. Through multiple cycles of "low-pressure etching + high-pressure removal," vertical material removal is gradually advanced to effectively reduce the SiC substrate thickness and avoid reaction stagnation and pore structure distortion caused by excessively deep etching in a single step. Ultimately, the target thickness of the SiC substrate is achieved to below 100µm.

[0051] In some embodiments, the thinned silicon carbide substrate is further cleaned.

[0052] After electrochemical etching and high-voltage removal of the nanoporous layer structure, the thinned silicon carbide substrate was removed from the alkaline electrolyte and immediately rinsed thoroughly with deionized water to remove any remaining alkaline electrolyte, preventing secondary deposition or salt marks during drying. The sample was then dried in an inert atmosphere such as nitrogen or argon to further remove residual moisture, ultimately obtaining a thinned SiC substrate.

[0053] This invention provides a thinned silicon carbide substrate, which has the following characteristics: (i) Low damage and low residual stress: There are no significant subsurface damage or amorphous damage layer on the surface, and the overall residual stress is basically zero, which can be directly adapted to subsequent process flow.

[0054] (ii) Ultra-thin specifications: Silicon carbide substrates with a thickness of ≤200µm can be prepared, and after multiple rounds of thinning, silicon carbide substrates with a thickness of ≤100µm can also be provided.

[0055] (iii) Thickness can be precisely controlled: it can be precisely thinned according to the target thickness, and the thickness consistency is excellent.

[0056] (iv) Capable of large-scale production: Supports large-scale production with high yield, controllable costs, and fast production speed.

[0057] Unless otherwise specified, the experimental methods used in the following examples are conventional methods, and the materials and reagents used are commercially available unless otherwise specified.

[0058] The present invention will be further described below through specific embodiments.

[0059] Example 1 This embodiment provides a method for thinning silicon carbide substrates based on thermally assisted electrochemistry, the specific steps of which are as follows: (1) Pretreatment of SiC material: To adapt to the size of the experimental reaction tank, a commercially available six-inch conductive 4H-SiC substrate with an original thickness of 350µm was cut into square samples of 12 mm*12 mm using a diamond pen. The samples were then immersed in 50 mL of acetone, 50 mL of anhydrous ethanol, and 50 mL of deionized water, and ultrasonically cleaned for 15 minutes in each step. After cleaning, the C-surface of the SiC sample was immediately blown with dry nitrogen for about 30 seconds to ensure that it was dry and clean, meeting the surface condition requirements of the subsequent etching steps.

[0060] (2) Preparation of alkaline electrolyte: Weigh 56.11 g of solid KOH, dissolve it in deionized water, and make up to 1000 mL. Stir thoroughly to ensure complete dissolution, obtaining a solution with a concentration of 1 mol / L. -1 An alkaline electrolyte.

[0061] (3) Electrode system setup: A typical two-electrode system was adopted, in which the C-side of the SiC sample was exposed to the alkaline electrolyte to participate in the reaction, and the Si-side was connected by a conductive sponge to ensure good electrical contact. Fluoropolymer gaskets were used for sealing and protection to prevent leakage of the alkaline electrolyte. Platinum wire was selected as the counter electrode, and both electrodes were connected to an electrochemical workstation to control the voltage application and monitor the reaction process.

[0062] (4) Formation process of porous structure: 1000 mL of the prepared 1mol L -1 An alkaline electrolyte was poured into a polytetrafluoroethylene (PTFE) container, and the temperature of the electrolyte was simultaneously heated to 70°C using a heating device and a temperature sensor, with continuous circulation achieved using a peristaltic pump. A constant voltage of 10V was applied to the SiC substrate. Under the dual coupling of the electric field and the high-temperature alkaline solution, the etching reaction lasted for 30 minutes. Under these conditions, a nanoporous layer structure could be stably formed on the SiC surface, with a surface morphology and thickness similar to... Figure 2 As shown, numerous etched pores are formed on the surface, with pore sizes ranging from approximately 30 to 60 nm and a pore density of approximately 40 µm. -2 The cross-sectional structure exhibits vertical columnar channels with a thickness of approximately 3.2 µm and an etching rate of approximately 0.11 µm / min. -1 (5) Termination of etching and removal of porous structure: After etching is completed, a short high-voltage pulse (20V, lasting about 3 s) is immediately applied to the working electrode to achieve rapid removal of the surface nanoporous layer. This process does not require any mechanical intervention and can effectively complete one thinning cycle.

[0063] (6) Sample cleaning and drying: After thinning, the reaction surface is thoroughly rinsed with deionized water to remove residual alkali and dissolved products, and then the surface is purged with dry nitrogen. Finally, the thinned SiC sample is obtained.

[0064] Example 2 This embodiment provides a method for thinning silicon carbide substrates based on thermally assisted electrochemistry, the specific steps of which are as follows: (1) Pretreatment of SiC material: To adapt to the size of the experimental reaction tank, a commercially available six-inch conductive 4H-SiC substrate with an original thickness of 350µm was cut into square samples with a size of 12 mm * 12 mm using a diamond pen. The samples were then immersed in 50 mL of acetone, 50 mL of anhydrous ethanol, and 50 mL of deionized water, and ultrasonically cleaned for 15 minutes in each step. After cleaning, the C-surface of the SiC sample was immediately blown with dry nitrogen for about 30 seconds to ensure that it was dry and clean, meeting the surface condition requirements of the subsequent etching steps.

[0065] (2) Preparation of alkaline electrolyte: Weigh 56.11 g of solid KOH, dissolve it in deionized water, and make up to 1000 mL. Stir thoroughly to ensure complete dissolution, obtaining a solution with a concentration of 1 mol / L. -1 An alkaline electrolyte.

[0066] (3) Electrode system setup: A typical two-electrode system was adopted, in which the C-side of the SiC sample was exposed to the alkaline electrolyte to participate in the reaction, and the Si-side was connected by a conductive sponge to ensure good electrical contact. Fluoropolymer gaskets were used for sealing and protection to prevent leakage of the alkaline electrolyte. Platinum wire was selected as the counter electrode, and both electrodes were connected to an electrochemical workstation to control the voltage application and monitor the reaction process.

[0067] (4) Formation process of porous structure: 1000 mL of the prepared 1mol L -1 An alkaline electrolyte was poured into a polytetrafluoroethylene container, and the temperature of the electrolyte was simultaneously heated to 90°C using a heating device and a temperature sensor, with continuous circulation using a peristaltic pump. A constant voltage of 10V was applied to the SiC substrate. Under the dual coupling of the electric field and the high-temperature alkaline solution, the etching reaction lasted for 30 minutes. Under these conditions, a nanoporous layer structure could be stably formed on the SiC surface, with surface morphology and thickness as shown in the figure. Figure 3 As shown, numerous etched pores are formed on the surface, with pore sizes ranging from approximately 20 to 50 nm and a pore density of approximately 12 µm. -2 The cross-sectional structure exhibits vertical columnar channels with a thickness of approximately 75.5 µm and an etching rate of approximately 2.5 µm / min. -1 .

[0068] (5) Termination of etching and removal of porous structure: After etching is completed, a short high-voltage pulse (20V, lasting about 3 s) is immediately applied to the working electrode to achieve rapid removal of the surface nanoporous layer. This process does not require any mechanical intervention and can effectively complete one thinning cycle.

[0069] (6) Sample cleaning and drying: After thinning, the reaction surface is thoroughly rinsed with deionized water to remove residual alkali and dissolved products, and then the surface is purged with dry nitrogen. Finally, the thinned SiC sample is obtained.

[0070] Example 3 This embodiment provides a method for thinning silicon carbide substrates based on photoelectrochemistry, and the specific steps are as follows: (1) Pretreatment of SiC material: To adapt to the size of the experimental reaction tank, a commercially available six-inch conductive 4H-SiC substrate with an original thickness of 350µm was cut into square samples with a size of 12 mm * 12 mm using a diamond pen. The samples were then immersed in 50 mL of acetone, 50 mL of anhydrous ethanol, and 50 mL of deionized water, and ultrasonically cleaned for 15 minutes in each step. After cleaning, the C-surface of the SiC sample was immediately blown with dry nitrogen for about 30 seconds to ensure that it was dry and clean, meeting the surface condition requirements of the subsequent etching steps.

[0071] (2) Preparation of alkaline electrolyte: Weigh 56.11 g of solid KOH, dissolve it in deionized water, and make up to 1000 mL. Stir thoroughly to ensure complete dissolution, obtaining a solution with a concentration of 1 mol / L. -1 An alkaline electrolyte.

[0072] (3) Electrode system setup: A typical two-electrode system was adopted, in which the C-side of the SiC sample was exposed to the alkaline electrolyte to participate in the reaction, and the Si-side was protected by a conductive sponge to ensure good electrical contact. To prevent leakage of the alkaline electrolyte, an alkali-resistant rubber gasket was used for sealing protection. Platinum wire was selected as the counter electrode, and both electrodes were connected to an electrochemical workstation to control the voltage application and monitor the reaction process.

[0073] (4) Formation process of porous structure: 1000 mL of the prepared 1mol L -1 An alkaline electrolyte was poured into a polytetrafluoroethylene container, and the temperature of the alkaline electrolyte was simultaneously heated to 90°C using a constant-temperature water bath system. A peristaltic pump was used for continuous circulation to maintain the uniformity and stability of the system temperature and ion concentration. A constant voltage of 15 V was applied to the SiC substrate. Under the dual coupling of the electric field and the high-temperature alkaline solution, the etching reaction lasted for 30 minutes. Under these conditions, a nanoporous layer structure could be stably formed on the SiC surface, with surface morphology and thickness as shown in the figure. Figure 4 As shown, under this voltage condition, lateral etching is severe, and most of the etched holes have been connected by drilling through the hole walls; the cross-sectional structure exhibits vertical columnar channels with a thickness of approximately 114.6 µm and an etching rate of approximately 3.8 µm / min. -1 .

[0074] (5) Termination of etching and removal of porous structure: After etching is completed, a short high-voltage pulse (25V, lasting about 3 s) is immediately applied to the working electrode to embrittle the interface structure and promote bubble disturbance, thereby achieving rapid removal of the surface nanoporous layer. This process does not require any mechanical intervention and can effectively complete one thinning cycle.

[0075] (6) Sample cleaning and drying: After thinning, the reaction surface is thoroughly rinsed with deionized water to remove residual alkali and dissolved products, and then the surface is purged with dry nitrogen. Finally, the thinned SiC sample is obtained.

[0076] Example 4 This embodiment provides a method for preparing ultrathin silicon carbide substrates based on thermally assisted electrochemical processes. Compared to Embodiment 2, the method in this embodiment uses multiple cycles of "low-pressure etching + high-pressure removal" to progressively remove vertical material, effectively reducing the SiC substrate thickness and avoiding reaction stagnation and pore structure distortion caused by excessive etching in a single step. Ultimately, the goal of thinning the SiC substrate to below 30µm is achieved. The specific steps are as follows: (1) Pretreatment of SiC material: To adapt to the size of silicon carbide devices in subsequent embodiments, a commercially available six-inch conductive 4H-SiC substrate with an original thickness of 350µm was cut into square samples with a size of 18.6 mm * 18.6 mm using a diamond pen. The samples were then immersed in 50 mL of acetone, 50 mL of anhydrous ethanol, and 50 mL of deionized water, and ultrasonically cleaned for 15 minutes in each step. After cleaning, the C-surface of the SiC sample was immediately blown with dry nitrogen for about 30 seconds to ensure that it was dry and clean, meeting the surface condition requirements of subsequent etching steps.

[0077] (2) Preparation of alkaline electrolyte: Weigh 56.11g of solid KOH, dissolve it in deionized water and bring the volume to 1000mL. Stir thoroughly until completely dissolved to prepare an alkaline electrolyte with a concentration of 1mol / L. -1 Prepare an alkaline electrolyte solution for later use.

[0078] (3) Electrode system construction: A typical two-electrode system was adopted, in which the C-side of the SiC wafer was used as the reaction region, and the Si-side was protected by a conductive sponge to ensure good electrical contact. To prevent leakage of alkaline electrolyte, an alkali-resistant gasket was used for sealing protection. A platinum wire was used as the counter electrode, and both electrodes were connected to an electrochemical workstation to control the voltage application and record the changes in electrical signals during the reaction process.

[0079] (4) Formation process of porous layer structure: 1000 mL of the prepared 1mol L -1 An alkaline electrolyte was poured into a polytetrafluoroethylene container and heated to 90°C using a constant-temperature water bath system. A peristaltic pump maintained the liquid circulation, while a constant voltage of 10V was applied to the SiC substrate. Under the dual coupling of the electric field and the high-temperature alkaline solution, the etching reaction lasted for 30 minutes, forming a regular nanoporous layer structure on the SiC surface. Since the low-pressure etching conditions in this embodiment are the same as in Example 2, the surface morphology and thickness of the resulting nanoporous layer are similar. Figure 3 The results are basically the same.

[0080] (5) Multiple low-pressure etching-high-pressure removal cycle: After the first round of etching, a short high-voltage pulse of 20V lasting for 3 seconds is applied to the working electrode to induce bubble disturbance and interface embrittlement, completing the spontaneous removal of the porous layer in the first round. The first round of thinning depth is the same as in Example 2, approximately 75µm. Subsequently, the same voltage and temperature conditions are repeated to carry out the second round of etching + removal process, removing approximately 75µm again. Based on the initial SiC substrate thickness of 350µm, this experimental example completes a total of four cycles, with a total thinning depth of 320µm, ultimately controlling the SiC substrate thickness to approximately 30µm.

[0081] (6) Sample cleaning and drying: After thinning, the reaction surface was thoroughly rinsed with deionized water to remove residual alkali and dissolution products, followed by purging the surface with dry nitrogen. The thinned SiC sample was finally obtained. The actual image of the ultrathin SiC substrate prepared in Example 4 and its corresponding thickness are shown below. Figure 5 As shown.

[0082] Example 5 This embodiment provides a method for fabricating a 120 µm thick SiC device based on a thermo-assisted electrochemical reaction. Compared to Example 4, the method in this embodiment is directly applied to a commercial SiC metal-oxide-semiconductor field-effect transistor (MOSFET) device, resulting in a 120 µm thick commercial SiC MOSFET device. The specific steps are as follows: (1) Preparation of alkaline electrolyte: Weigh 56.11g of solid KOH, dissolve it in deionized water and bring the volume to 1000mL. Stir thoroughly until completely dissolved to prepare an alkaline electrolyte with a concentration of 1mol / L. -1 Prepare an alkaline electrolyte solution for later use.

[0083] (3) Electrode system construction: A typical two-electrode system was adopted, in which the back of a commercial SiC MOSFET device was used as the reaction area, and the front was protected by a conductive sponge to ensure good electrical contact. To prevent leakage of alkaline electrolyte, an alkali-resistant rubber pad was used for sealing protection. A platinum wire was used as the counter electrode, and both electrodes were connected to an electrochemical workstation for controlling voltage application and recording changes in electrical signals during the reaction process.

[0084] (4) Formation process of porous layer structure: 1000 mL of the prepared 1mol L -1An alkaline electrolyte was poured into a polytetrafluoroethylene container and heated to 90°C using a constant-temperature water bath system. A peristaltic pump maintained the liquid circulation, while a constant voltage of 10V was applied to the SiC MOSFET device substrate. Under the dual coupling of the electric field and the high-temperature alkaline solution, the etching reaction lasted for 30 minutes, forming a regular nanoporous layer structure on the SiC surface. Since the low-pressure etching conditions in this embodiment are the same as in Example 2, the surface morphology and thickness of the resulting nanoporous layer are similar. Figure 3 The results are basically the same.

[0085] (5) Multiple low-pressure etching-high-pressure removal cycle: After the first round of etching, a short high-voltage pulse of 20V lasting for 3 seconds was applied to the working electrode to induce bubble disturbance and interface embrittlement, completing the spontaneous removal of the first round of porous layer. The first round of thinning depth was the same as in Example 2, approximately 75µm. Subsequently, the same voltage and temperature conditions were repeated to carry out the second round of etching + removal process, removing approximately 75µm again. This experimental example completed three cycles, ultimately controlling the SiC substrate thickness to approximately 120µm.

[0086] (6) Sample cleaning and drying: After thinning, the reaction surface was thoroughly rinsed with deionized water to remove residual alkali and dissolution products, followed by purging with dry nitrogen. The thinned SiC sample was finally obtained. A physical image of the 120µm commercial SiC MOSFET device prepared in Example 5 and its corresponding thickness are shown below. Figure 6 As shown.

[0087] Example 6 This embodiment provides a method for fabricating ultrathin (<50 µm) SiC devices based on a thermally assisted electrochemical reaction. The specific steps are as follows: (1) Preparation of alkaline electrolyte: Weigh 56.11g of solid KOH, dissolve it in deionized water and bring the volume to 1000mL. Stir thoroughly until completely dissolved to prepare an alkaline electrolyte with a concentration of 1mol / L. -1 Prepare an alkaline electrolyte solution for later use.

[0088] (3) Electrode system construction: A typical two-electrode system was adopted, in which the back of a commercial SiC MOSFET device was used as the reaction area, and the front was protected by a conductive sponge to ensure good electrical contact. To prevent leakage of alkaline electrolyte, an alkali-resistant rubber pad was used for sealing protection. A platinum wire was used as the counter electrode, and both electrodes were connected to an electrochemical workstation for controlling voltage application and recording changes in electrical signals during the reaction process.

[0089] (4) Formation process of porous layer structure: 1000 mL of the prepared 1mol L -1An alkaline electrolyte was poured into a polytetrafluoroethylene container and heated to 90°C using a constant-temperature water bath system. A peristaltic pump maintained the liquid circulation, while a constant voltage of 10V was applied to the SiC MOSFET device substrate. Under the dual coupling of the electric field and the high-temperature alkaline solution, the etching reaction lasted for 30 minutes, forming a regular nanoporous layer structure on the SiC surface. Since the low-pressure etching conditions in this embodiment are the same as in Example 2, the surface morphology and thickness of the resulting nanoporous layer are similar. Figure 3 The results are basically the same.

[0090] (5) Multiple low-pressure etching-high-pressure removal cycles: After the first round of etching, a short high-voltage pulse of 20V lasting for 3 seconds was applied to the working electrode to induce bubble disturbance and interface embrittlement, completing the spontaneous removal of the porous layer in the first round. The first round of thinning depth was the same as in Example 2, approximately 75µm. Subsequently, the same voltage and temperature conditions were repeated to carry out the second round of etching + removal process, removing approximately 75µm again. This experimental example completed a total of four cycles, ultimately controlling the SiC substrate thickness to approximately 50µm.

[0091] (6) Sample cleaning and drying: After thinning, the reaction surface was thoroughly rinsed with deionized water to remove residual alkali and dissolution products, followed by purging with dry nitrogen. The thinned SiC sample was finally obtained. A physical image of the 47µm ultrathin commercial SiC MOSFET device prepared in Example 5 and its corresponding thickness are shown below. Figure 6 As shown.

[0092] Example 7 This embodiment provides a method for preparing a two-inch ultrathin flexible SiC substrate based on a thermally assisted electrochemical reaction. The specific steps are as follows: (1) Preparation of alkaline electrolyte: Weigh 56.11g of solid KOH, dissolve it in deionized water and bring the volume to 1000mL. Stir thoroughly until completely dissolved to prepare an alkaline electrolyte with a concentration of 1mol / L. -1 Prepare an alkaline electrolyte solution for later use.

[0093] (3) Electrode system construction: A typical two-electrode system was adopted, with the back side of the two-inch SiC substrate serving as the reaction area, and the front side secured by a conductive sponge to ensure good electrical contact. To prevent leakage of the alkaline electrolyte, an alkali-resistant gasket was used for sealing protection. A platinum wire was used as the counter electrode, and both electrodes were connected to an electrochemical workstation for controlling voltage application and recording changes in electrical signals during the reaction process.

[0094] (4) Formation process of porous layer structure: 1000 mL of the prepared 1mol L -1An alkaline electrolyte was poured into a polytetrafluoroethylene container and heated to 90°C using a constant-temperature water bath system. A peristaltic pump maintained the liquid circulation, while a constant voltage of 10V was applied to the two-inch SiC substrate. Under the dual coupling of the electric field and the high-temperature alkaline solution, the etching reaction lasted for 40 minutes.

[0095] (5) Multiple low-pressure etching-high-pressure removal cycles: After the first round of etching, a short high-voltage pulse of 20V lasting for 3 seconds was applied to the working electrode to induce bubble disturbance and interface embrittlement, completing the spontaneous removal of the first porous layer. The first round of thinning depth was the same as in Example 2, approximately 75µm. Subsequently, the same voltage and temperature conditions were repeated to carry out the second round of etching + removal process, removing approximately 75µm again. This experimental example completed a total of four cycles, ultimately controlling the SiC substrate thickness to approximately 35µm.

[0096] (6) Sample cleaning and drying: After thinning, the reaction surface was thoroughly rinsed with deionized water to remove residual alkali and dissolution products, followed by purging with dry nitrogen. The thinned SiC sample was finally obtained. The actual image, corresponding thickness, and macroscopic flexibility characteristics of the ultrathin two-inch SiC substrate prepared in Example 7 are shown below. Figure 7 As shown.

[0097] The above embodiments do not introduce any mechanical polishing steps in the entire process, which fully verifies the feasibility of the thermally assisted electrochemical etching based on the present invention in the back-side thinning process of SiC substrate, and has good scalability and engineering potential.

[0098] In summary, the method provided by this invention is based on a thermally assisted electrochemical reaction on the back side of a conductive SiC substrate to generate a nanoporous layer structure under low voltage conditions. Then, a short-duration high-voltage pulse induces interfacial embrittlement and bubble impact, achieving gentle removal of the etched layer and vertical thinning of the substrate. The entire process does not rely on any mechanical contact and is carried out entirely within the liquid phase and electric field, avoiding the frictional impact and physical damage risks inherent in traditional mechanical grinding. This truly achieves a non-contact, low-cost, damage-free, low-stress, and high-integrity thinning method.

[0099] It should be understood that the application of the present invention is not limited to the examples above. Those skilled in the art can make improvements or modifications based on the above description, and all such improvements and modifications should fall within the protection scope of the appended claims.

Claims

1. A method for thinning silicon carbide substrates based on thermally assisted electrochemistry, characterized in that, Includes the following steps: (1) The silicon carbide substrate to be thinned is pretreated to obtain the pretreated silicon carbide substrate; (2) The pretreated silicon carbide substrate is placed in an alkaline electrolyte or hydrofluoric acid solution, and a first voltage is applied to the pretreated silicon carbide substrate to cause an electrochemical etching reaction on the surface to be thinned of the pretreated silicon carbide substrate, thereby forming a nanoporous layer structure on the surface to be thinned. (3) After the nanoporous layer structure reaches the target thickness, a second voltage is applied to remove the nanoporous layer structure to obtain a thinned silicon carbide substrate.

2. The method according to claim 1, characterized in that, Step (2) further includes: after placing the pretreated silicon carbide substrate in an alkaline electrolyte, heating the alkaline electrolyte to a temperature of 30-90°C.

3. The method according to claim 1, characterized in that, In step (2), the alkaline electrolyte includes one of KOH aqueous solution, CsOH aqueous solution, RbOH aqueous solution, NaOH aqueous solution, and LiOH aqueous solution; the concentration of the alkaline electrolyte is 0.1-5 mol / L. -1 .

4. The method according to claim 1 or 3, characterized in that, The alkaline electrolyte also includes functional additives, which include one of methanol, ethanol, silver nitrate, ferric nitrate, iodate, sodium dodecyl sulfate, and sodium fluoride.

5. The method according to claim 1, characterized in that, In step (2), the first voltage is applied in at least one of the following ways: constant voltage, linear voltage scanning, step voltage, periodic pulse voltage, and constant current.

6. The method according to claim 1 or 5, characterized in that, In step (2), the first voltage is a constant voltage of 5-15V.

7. The method according to claim 1, characterized in that, In step (2), the electrochemical etching reaction takes 10-180 minutes.

8. The method according to claim 1, characterized in that, In step (3), the second voltage is 15-30V and the application time of the second voltage is 1-10s.

9. The method according to claim 1, characterized in that, The silicon carbide substrate to be thinned is subjected to multiple rounds of thinning, specifically including: in step (3), after obtaining the thinned silicon carbide substrate, the thinned silicon carbide substrate is repeated from step (2) to step (3) multiple times to obtain the silicon carbide substrate thinned in multiple rounds.

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