Stripping method and stripping device for silicon carbide single crystal film

Abstract

The invention relates to the technical field of silicon carbide single crystal films, and provides a silicon carbide single crystal film stripping method and a silicon carbide single crystal film stripping device. An n-type silicon carbide substrate and a silicon carbide single crystal film on the surface of the n-type silicon carbide substrate are provided, and incident light is used for irradiating the surface of the n-type silicon carbide single crystal film; under the action of an internal electric field of a depletion region of an interface region of the n-type silicon carbide substrate and the silicon carbide single crystal thin film, photo-generated holes in the photo-generated hole-electron pair are enriched on one side, close to the silicon carbide single crystal thin film, of the depletion region and react with etching liquid; therefore, one side, close to the silicon carbide single crystal film, of the depletion region is selectively etched, and stripping of the silicon carbide single crystal film is achieved.

Description

Technical Field

[0001] The present invention relates to the technical field of silicon carbide single crystal thin films, and in particular to a stripping method and a stripping device for a silicon carbide single crystal thin film. Background Art

[0002] Silicon carbide materials have a series of excellent physical and electrical properties, such as wide band gap, high breakdown field strength, high electron saturation and drift rate, and high thermal conductivity. The silicon carbide power device industry is developing rapidly.

[0003] Silicon carbide homoepitaxial growth is the growth of a single-crystal silicon carbide film on a silicon carbide single-crystal substrate. The thickness and doping concentration of the silicon carbide epitaxial film determine the withstand voltage and conduction characteristics of the silicon carbide power device. At the same time, the defect control of the epitaxial layer has a vital impact on improving the performance and reliability of the device. Therefore, silicon carbide epitaxial wafers with unqualified thickness, doping concentration and defect indicators need to remove the epitaxial layer and re-epitaxial growth to improve the utilization rate of the silicon carbide substrate. Thin epitaxial layers can be removed by chemical mechanical polishing, while thick epitaxial layers require grinding and chemical mechanical polishing to remove the epitaxial layer. The above methods require different process flows and process parameters to be debugged according to the thickness of the epitaxial layer, which increases the production cost. In addition, in some existing technologies, the utilization rate of the silicon carbide substrate is improved by ion implantation to manufacture defective layers, annealing, laser irradiation, stripping, and polishing. The entire process is very cumbersome. At the same time, the processes of ion implantation, annealing, laser irradiation, and stripping greatly increase the production cost and reduce the production efficiency.

[0004] Moreover, the application of flexible electronic and optoelectronic devices in wearable devices, flexible displays and flexible detection has aroused great interest. Compared with organic materials, single-crystal silicon carbide, as a third-generation semiconductor, has excellent properties such as large bandgap, high breakdown field strength, high thermal conductivity, high electron mobility, thermal stability and chemical stability. It has shown important application potential in the fields of photoelectric detection, medium and high voltage power electronics and quantum sensing. However, due to the high hardness and high chemical inertness of silicon carbide, if a grinding and polishing process is used from top to bottom to prepare a qualified micro / nano-thick flexible silicon carbide single crystal, this not only has a long processing cycle and high processing cost, but also the obtained flexible silicon carbide single crystal is easy to break during the processing and is difficult to reach the micro / nano level. Summary of the invention

[0005] The purpose of the present invention is to overcome the problem of difficulty in removing the epitaxial layer, and to provide a method and a device for stripping a silicon carbide single crystal film. In order to achieve the above object, the present invention provides a method for stripping a silicon carbide single crystal film, comprising: A silicon carbide substrate is provided, wherein the silicon carbide substrate comprises an n-type silicon carbide substrate and a silicon carbide single crystal film located on a surface of the n-type silicon carbide substrate, an interface region between the n-type silicon carbide substrate and the silicon carbide single crystal film has a depletion region, and the depletion region has an internal electric field pointing from the n-type silicon carbide substrate to the silicon carbide single crystal film; The silicon carbide substrate is immersed in an etching solution, and the silicon carbide substrate is irradiated with incident light having a wavelength smaller than a critical value of the absorption light wavelength corresponding to the silicon carbide substrate, so as to form photogenerated hole-electron pairs in the silicon carbide substrate; under the action of the internal electric field of the depletion region, the photogenerated holes in the photogenerated hole-electron pairs are enriched on a side of the depletion region close to the silicon carbide single crystal film and react with the etching solution, thereby selectively etching the side of the depletion region close to the silicon carbide single crystal film until at least a portion of the thickness of the silicon carbide single crystal film is peeled off from the n-type silicon carbide substrate.

[0006] As an implementation method, a conductive layer is further provided on the surface of the n-type silicon carbide substrate, the silicon carbide substrate serves as an anode and is connected to a voltage output terminal through the conductive layer, a cathode is provided in the etching solution and is connected to a voltage input terminal, and the anode forms a circuit loop through the voltage output terminal, the voltage input terminal and the cathode; During the incident light irradiation process, a positive constant potential is provided to the n-type silicon carbide substrate through the voltage output terminal, the internal electric field of the depletion region is enhanced, and the photogenerated electrons are transferred to the cathode to undergo a reduction reaction with the etching solution, thereby accelerating the enrichment of photogenerated holes on the side of the depletion region close to the silicon carbide single crystal film and accelerating the peeling.

[0007] As an implementation method, the silicon carbide single crystal film is an n-type silicon carbide single crystal film or a p-type silicon carbide single crystal film, wherein when the silicon carbide single crystal film is an n-type silicon carbide single crystal film, the doping concentration of the n-type silicon carbide single crystal film is lower than the doping concentration of the n-type silicon carbide substrate.

[0008] As an implementation method, an insulating layer covering the conductive layer is further provided on the surface of the conductive layer.

[0009] As an implementation method, the step of irradiating the silicon carbide substrate with incident light having a wavelength smaller than a critical value of the absorption light wavelength corresponding to the silicon carbide substrate comprises: The surface of the silicon carbide single crystal film is vertically irradiated with incident light having a wavelength smaller than a critical value of the absorption light wavelength corresponding to the silicon carbide substrate.

[0010] As an implementation method, the crystal form of the silicon carbide substrate is 4H type or 6H type, wherein the critical values ​​of the absorption wavelength of light corresponding to 4H type and 6H type are 380nm and 410nm respectively.

[0011] As an implementable embodiment, the etching solution includes silicon oxide etching solution and an oxidant; The step of enriching the photogenerated holes on the side of the depletion region close to the silicon carbide single crystal film and reacting with the etching solution comprises: The photogenerated holes are enriched in the depletion region near the side of the silicon carbide single crystal film and react with SiC and an oxidant to generate silicon oxide. The silicon oxide etching solution reacts with the silicon oxide.

[0012] As an implementable method, the process of irradiating with the incident light further includes: The etching solution is stirred at a constant speed by a stirrer.

[0013] Accordingly, the present invention also provides a device for stripping a silicon carbide single crystal film, comprising: An electrolytic cell for containing an etching solution; A silicon carbide substrate immersed in the etching solution, wherein the silicon carbide substrate comprises an n-type silicon carbide substrate surface and a silicon carbide single crystal film located on the surface of the n-type silicon carbide substrate, an interface region between the n-type silicon carbide substrate and the silicon carbide single crystal film has a depletion region, and the depletion region has an internal electric field pointing from the n-type silicon carbide substrate to the silicon carbide single crystal film; A light source structure is arranged above the etching liquid, and is used to irradiate the surface of the silicon carbide single crystal film with incident light having a wavelength smaller than a critical value of the absorption light wavelength corresponding to the silicon carbide substrate, so as to form photogenerated hole-electron pairs in the silicon carbide substrate; under the action of the internal electric field of the depletion region, the photogenerated holes of the photogenerated hole-electron pairs are enriched on a side of the depletion region close to the silicon carbide single crystal film and react with the etching liquid, thereby selectively etching the side of the depletion region close to the silicon carbide single crystal film, until at least a portion of the thickness of the silicon carbide single crystal film is peeled off from the n-type silicon carbide substrate.

[0014] As an implementation method, the surface of the n-type silicon carbide substrate is further provided with a conductive layer; the silicon carbide substrate is used as an anode and connected to the voltage output terminal through the conductive layer, a cathode is provided in the etching solution and connected to the voltage input terminal, and the anode forms a circuit loop through the voltage output terminal, the voltage input terminal and the cathode; During the irradiation with the incident light, a positive constant potential is provided to the n-type silicon carbide substrate through the voltage output terminal, the internal electric field of the depletion region is enhanced, and the photogenerated electrons are transferred to the cathode to undergo a reduction reaction with the etching solution, thereby accelerating the enrichment of photogenerated holes on the side of the depletion region close to the silicon carbide single crystal film and accelerating the peeling.

[0015] Beneficial effects of the present invention: The present invention provides a method and device for stripping a silicon carbide single crystal film, which allows photogenerated holes to be enriched on the side of the depletion region close to the silicon carbide single crystal film under the action of the internal electric field of the depletion region and react with the etching solution, thereby selectively etching the side of the depletion region close to the silicon carbide single crystal film to achieve the stripping of the silicon carbide single crystal film. By selectively etching the silicon carbide substrate using photoelectrochemical corrosion, the surface of the n-type silicon carbide substrate will not be damaged. The stripped n-type silicon carbide substrate can be directly epitaxially grown, thereby improving the utilization rate of the silicon carbide substrate and reducing the production cost. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Figure 1 Schematic diagram of a silicon carbide substrate disclosed in some embodiments of the present invention; Figure 2 Schematic diagram of a preparation device disclosed in some embodiments of the present invention. DETAILED DESCRIPTION

[0017] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0018] Some embodiments of the present invention provide a method for preparing a flexible silicon carbide single crystal wafer, comprising: providing a silicon carbide substrate, wherein the silicon carbide substrate comprises an n-type silicon carbide substrate and a silicon carbide single crystal film located on a surface of the n-type silicon carbide substrate, an interface region between the n-type silicon carbide substrate and the silicon carbide single crystal film having a depletion region, and the depletion region having an internal electric field pointing from the n-type silicon carbide substrate to the silicon carbide single crystal film; The silicon carbide substrate is immersed in an etching solution, and the silicon carbide substrate is irradiated with incident light having a wavelength smaller than a critical value of the absorption light corresponding to the silicon carbide substrate, so as to form photogenerated hole-electron pairs in the silicon carbide substrate; under the combined action of energy band bending and the internal electric field of the depletion region, the photogenerated holes in the photogenerated hole-electron pairs are enriched on a side of the depletion region close to the silicon carbide single crystal film and react with the etching solution, thereby selectively etching the side of the depletion region close to the silicon carbide single crystal film until the silicon carbide single crystal film is peeled off from the n-type silicon carbide substrate.

[0019] In some embodiments, by controlling the depth of selective etching of the silicon carbide single crystal film, it can not only be used to remove unqualified silicon carbide single crystal film on the surface of n-type silicon carbide substrate when the indicators of the silicon carbide single crystal film are unqualified; it can also be used when it is necessary to peel off a qualified silicon carbide single crystal film from the surface of the n-type silicon carbide substrate, so that at least part of the thickness of the silicon carbide single crystal film can be naturally separated from the n-type silicon carbide substrate without the assistance of external force, so as to obtain a qualified micron / nanoscale single crystal silicon carbide flexible film.

[0020] In some embodiments, see Figure 1 , a silicon carbide substrate 1 is provided, wherein the silicon carbide substrate 1 includes an n-type silicon carbide substrate 100 and a silicon carbide single crystal thin film 200 located on a surface of the n-type silicon carbide substrate 100 .

[0021] In some embodiments, the size of the n-type silicon carbide substrate 100 is 2 to 12 inches, the thickness of the n-type silicon carbide substrate 100 is in the range of 200 μm to 500 μm, and the thickness of the silicon carbide single crystal film 200 is in the range of 5 μm to 500 μm. In some embodiments, the silicon carbide substrate 1 may be doped with nitrogen, and the doping concentration of nitrogen impurities in the silicon carbide substrate 1 is between 10 18 -10 19 cm -3 In some embodiments, the silicon carbide single crystal film 200 may be an n-type silicon carbide single crystal film or a p-type silicon carbide single crystal film. In some embodiments, when the silicon carbide single crystal film 200 is an n-type silicon carbide single crystal film, the layer doping concentration of the n-type silicon carbide single crystal film is less than the doping concentration of the silicon carbide single crystal film 200, and when the doping concentration of nitrogen impurities in the silicon carbide substrate 1 is between 10 18 -10 19 cm -3 The nitrogen impurity doping concentration of n-type silicon carbide single crystal film can be 10 14 -10 16 cm -3 In some embodiments, when the silicon carbide single crystal film 200 is a p-type silicon carbide single crystal film, the p-type silicon carbide single crystal film may be doped with aluminum, and the doping concentration of aluminum impurities in the p-type silicon carbide single crystal film is 10 14 -10 19 cm -3 .

[0022] In some embodiments, after a silicon carbide substrate 1 is formed by epitaxially growing a layer of silicon carbide single crystal film 200 on the surface of an n-type silicon carbide substrate 100, a depletion region 300 of a certain thickness will be spontaneously generated at the interface between the n-type silicon carbide substrate 100 and the silicon carbide single crystal film 200, and the depletion region has an internal electric field pointing from the n-type silicon carbide substrate to the silicon carbide single crystal film. In addition, the embodiments may also enhance the internal electric field by some technical means, such as forming a conductive layer on the surface of the n-type silicon carbide substrate 100, and providing a positive constant voltage to the n-type silicon carbide substrate 100 through the conductive layer, so as to generate an internal electric field that can meet the etching requirements.

[0023] Specifically, when the silicon carbide single crystal film 200 is a p-type silicon carbide single crystal film, after the p-type silicon carbide single crystal film is formed by epitaxy on the surface of the n-type silicon carbide substrate, since the free electrons in the n-type silicon carbide substrate are majority carriers and the holes are almost zero, which are called minority carriers, while the holes in the p-type silicon carbide single crystal film are majority carriers and the free electrons are minority carriers, a concentration difference between electrons and holes appears at their junction. Due to the concentration difference between free electrons and holes, some free electrons diffuse from the n-type silicon carbide substrate to the p-type silicon carbide single crystal film, and some holes diffuse from the p-type silicon carbide single crystal film to the n-type silicon carbide substrate. As a result of their diffusion, the p-type silicon carbide single crystal film loses holes, leaving impurity ions with negative charges, and the n-type silicon carbide substrate loses electrons, leaving impurity ions with positive charges. These immobile charged particles form a space charge region, i.e., a depletion region 300, near the interface between the p-type silicon carbide single crystal film and the n-type silicon carbide substrate due to the interaction between positive and negative charges. Figure 1 The direction of the internal electric field in the depletion region 300 is from the positively charged n-type silicon carbide substrate to the negatively charged p-type silicon carbide single crystal film. Obviously, the direction of this electric field is opposite to the direction of the diffusion movement of free electrons and holes, which further prevents the diffusion of electrons and holes, thereby forming a stable internal electric field in the depletion region 300.

[0024] When the silicon carbide single crystal film 200 is an n-type silicon carbide single crystal film, a low-doped n-type silicon carbide single crystal film will be formed by epitaxy on the surface of the highly doped n-type silicon carbide substrate. The free electrons in the highly doped n-type silicon carbide substrate are majority carriers, and the free electrons in the low-doped n-type silicon carbide single crystal film are also majority carriers, and the holes are all minority carriers. There is a concentration difference of electrons at the interface between the two. The free electrons diffuse from the n-type silicon carbide substrate to the n-type silicon carbide single crystal film, and positive space charges are generated on the side of the n-type silicon carbide substrate in the boundary area, and negative space charges appear on the side of the n-type silicon carbide single crystal film, generating a depletion region 300, and the depletion region has an internal electric field pointing from the n-type silicon carbide substrate to the n-type silicon carbide single crystal film.

[0025] In some embodiments, the crystal form of the n-type silicon carbide substrate is 4H type or 6H type, and the crystal form of the formed silicon carbide base is the corresponding 4H type or 6H type.

[0026] In some embodiments, the silicon carbide single crystal thin film 200 may be epitaxially formed on the surface of the n-type silicon carbide substrate 100 based on a chemical vapor deposition method or an ion implantation process.

[0027] In some embodiments, the thickness of the depletion region can be controlled by controlling the doping concentration, thereby controlling the depth of the selective etching of the silicon carbide single crystal film, and further controlling the thickness of the separated silicon carbide single crystal film.

[0028] In some embodiments, when the silicon carbide substrate 1 is immersed in the etching solution, the photogenerated holes are also affected by the energy band bending of the silicon carbide single crystal film 200, further accelerating the movement of the photogenerated holes to the side of the depletion region 300 close to the silicon carbide single crystal film 200. Specifically, the side of the silicon carbide single crystal film 200 close to the etching solution also has an energy band bending toward the n-type silicon carbide substrate, so that the side of the silicon carbide single crystal film close to the etching solution generates an electric field directed from the etching solution to the inside of the silicon carbide single crystal film 200, so that the electrons on the side of the silicon carbide single crystal film 200 close to the etching solution migrate to the surface of the silicon carbide single crystal film 200, and the remaining holes migrate to the inside of the silicon carbide single crystal film 200.

[0029] In some embodiments, the silicon carbide substrate 1 is irradiated with incident light having a wavelength smaller than a critical value of the absorption light wavelength corresponding to the silicon carbide substrate, so that photogenerated hole-electron pairs are formed in the silicon carbide substrate.

[0030] In some embodiments, the surface of the silicon carbide single crystal film may be irradiated with incident light having a wavelength smaller than the critical value of the absorption light wavelength corresponding to the silicon carbide substrate; further, see Figure 1 , you can use Figure 1 The incident light direction shown is that the incident light that is smaller than the critical value of the absorption light wavelength corresponding to the silicon carbide substrate is vertically irradiated on the surface of the silicon carbide single crystal film; wherein, the silicon carbide substrate has different critical values ​​of absorption light wavelength corresponding to different crystal forms, such as the critical values ​​of absorption light wavelength corresponding to 4H type and 6H type are 380nm and 410nm respectively.

[0031] In some embodiments, a xenon lamp, a mercury lamp or an LED lamp can be used as a light source at room temperature. The light source can be 5 cm to 15 cm above the etching liquid surface. After the light from the light source is filtered by a filter, the wavelength of the light reaching the surface of the silicon carbide epitaxial wafer is in the ultraviolet range (180 nm < λ 入射<380nm), so as to realize that the incident light with a wavelength smaller than the critical value of the absorption light wavelength corresponding to the silicon carbide substrate is irradiated on the surface of the silicon carbide single crystal film.

[0032] In some embodiments, the photogenerated holes in the photogenerated hole-electron pairs are generated in the silicon carbide single crystal film, and the photogenerated electrons in the photogenerated hole-electron pairs are generated in the n-type silicon carbide substrate. Specifically, the principle of forming the photogenerated hole-electron pairs in the silicon carbide substrate is: In the p-type silicon carbide single crystal film, Al atoms are used as doping atoms to replace Si atoms in the crystal lattice and are adjacent to the four surrounding C atoms. However, since the outer layer of Al has only three electrons, a hole is generated. When incident light with a wavelength less than the critical value of the absorption light wavelength corresponding to the silicon carbide substrate is irradiated on the surface of the p-type silicon carbide single crystal film, ionization occurs to form an immobile Al negative ion and a positively charged hole. In addition, the holes move randomly in the crystal lattice, and a part of the moving holes will be neutralized with the immobile Al negative ions. In the n-type silicon carbide substrate, N atoms serve as doping atoms to replace C atoms in the crystal lattice and are adjacent to the four surrounding Si atoms. However, since the outer layer of N has 5 electrons, there will be one extra electron. When incident light with a wavelength less than the critical value of the absorption light corresponding to the silicon carbide substrate is irradiated on the surface of the silicon carbide single crystal film, ionization will occur to form an immobile N positive ion and a negatively charged electron. In addition, the electrons move randomly in the crystal lattice, and at the same time, a part of the moving electrons will be neutralized with the immobile N positive ions.

[0033] That is, the holes in the depletion region and the silicon carbide single crystal film gather on the side of the depletion region close to the silicon carbide single crystal film, and the electrons in the depletion region move to the side of the n-type silicon carbide substrate.

[0034] After the photogenerated hole-electron pairs are formed in the silicon carbide substrate 1, due to the band bending of the interface between the silicon carbide single crystal film 200 and the etching solution, an electric field directed from the etching solution to the inner side of the silicon carbide single crystal film 200 is generated on the side of the silicon carbide single crystal film 200 close to the etching solution, which causes the photogenerated electrons in the silicon carbide single crystal film 200 close to the etching solution to migrate to the surface of the silicon carbide single crystal film 200, thereby inhibiting the corrosion of the surface of the silicon carbide single crystal film 200, while the remaining photogenerated holes migrate to the inside of the silicon carbide single crystal film 200; and due to the depletion region 300 at the interface between the silicon carbide single crystal film 200 and the n-type silicon carbide substrate 100, an electric field directed from the n-type silicon carbide substrate 100 to the silicon carbide single crystal film 200 is generated. The internal electric field of the film 200 causes the photogenerated electrons in the depletion region 300 to migrate to the side of the n-type silicon carbide substrate, while the photogenerated holes in the depletion region 300 are enriched on the side of the silicon carbide single crystal film; that is, the photogenerated holes in the silicon carbide single crystal film 200 and the photogenerated holes in the depletion region 300 are enriched on the side of the depletion region 300 close to the silicon carbide single crystal film 200 and react with the etching solution, thereby selective etching occurs to achieve stripping; and the energy band bending of the interface between the n-type silicon carbide substrate 100 and the etching solution and the internal electric field of the depletion region 300 cause the photogenerated electrons in the photogenerated hole-electron pairs to be enriched on the side of the depletion region 300 close to the n-type silicon carbide single crystal film 100. In some embodiments, the side of the depletion region 300 close to the n-type silicon carbide single crystal film 100 can also be directly understood as the area of ​​the depletion region 300 that originally belonged to the silicon carbide single crystal film 100.

[0035] In some embodiments, the etching solution includes a silicon oxide etching solution and an oxidant; in one embodiment, the silicon oxide etching solution can be hydrofluoric acid, and the oxidant can be hydrogen peroxide; specifically, the etching solution can be obtained by mixing and stirring hydrofluoric acid, hydrogen peroxide and anhydrous ethanol, wherein the concentrations of the aqueous solutions of hydrofluoric acid and hydrogen peroxide are 3% to 30%, respectively, and the mass ratio of the hydrofluoric acid solution to anhydrous ethanol is in the range of 1:0.5-1:2; the anhydrous ethanol has the effect of reducing the surface tension of the etching solution, and as the reaction proceeds, a tiny gap is formed at the interface of the silicon carbide substrate and the silicon carbide single crystal film, which is conducive to the etching solution to penetrate into the gap and continue to react.

[0036] In some embodiments, the step of enriching the photogenerated holes on the side of the depletion region close to the silicon carbide single crystal film and reacting with the etching solution comprises: The photogenerated holes are enriched in the depletion region near the side of the silicon carbide single crystal film and react with SiC and an oxidant to generate silicon oxide. The silicon oxide etching solution reacts with the silicon oxide.

[0037] Specifically, the photogenerated holes h +The chemical formula for the reaction with SiC is: SiC+2H2O2+4h + →SiO2+CO2↑+4H + ; Among them, H2O2 is used as an oxidant to accelerate the reaction, and H2O2 can be used selectively; After SiO2 is generated, SiO2 reacts with the hydrofluoric acid HF, wherein the chemical formula of the reaction between SiO2 and hydrofluoric acid HF is: SiO2+6HF→(SiF6) 2- +2H2O+ 2H + According to the method for stripping a silicon carbide single crystal film disclosed in the embodiment, unqualified silicon carbide single crystal films can be removed, and qualified micron / nanoscale flexible silicon carbide single crystal wafers can be obtained. After the silicon carbide single crystal film is stripped from the n-type silicon carbide substrate, the remaining n-type silicon carbide substrate can be reused.

[0038] In some embodiments, the process of irradiating with the incident light further includes: See also Figure 2 , the etching liquid is stirred at a constant speed by a stirrer 3; wherein, the rotation speed range of the stirrer 3 can be set to 300 r / min to 500 r / min according to the selection, so that the etching liquid flow rate is 1 mL / min to 5 mL / min, and further fully reacts.

[0039] In some embodiments, the selective etching of the side of the depletion region close to the silicon carbide single crystal film may specifically be: selective photoelectrochemical etching of the side of the depletion region close to the silicon carbide single crystal film; and, since the internal electric field spontaneously formed in the depletion region is weak and the potential barrier height is small, the internal electric field may be enhanced by other means to accelerate etching. For example, the n-type silicon carbide substrate may be connected to a positive voltage to enhance the internal electric field and increase the potential barrier height.

[0040] For details, see Figure 1A conductive layer 10 is provided on the surface of the n-type silicon carbide substrate 100, the silicon carbide substrate is used as an anode and is connected to a voltage output terminal through the conductive layer, a cathode is provided in the etching solution and is connected to a voltage input terminal, the voltage output terminal is used to connect to the positive electrode of an external power supply, and the voltage input terminal is used to connect to the negative electrode of an external power supply; thereby, in the subsequent process of irradiating with the incident light, a positive constant potential can be provided to the n-type silicon carbide substrate through the voltage output terminal, the internal electric field of the depletion region is enhanced, and the photogenerated electrons are transferred to the cathode to react with the etching solution for reduction, thereby accelerating the enrichment of photogenerated holes on the side of the depletion region close to the silicon carbide single crystal film, and accelerating the separation of the n-type silicon carbide substrate and the silicon carbide single crystal film. Specifically, the holes in the depletion region and the silicon carbide single crystal film will gather on the side of the depletion region close to the silicon carbide single crystal film, and the electrons in the depletion region will move to the side of the n-type silicon carbide substrate and, like the electrons in the n-type silicon carbide substrate, will be transferred along the current to the cathode to undergo a reduction reaction with the etching solution, thereby accelerating the enrichment of photogenerated holes on the side of the depletion region close to the silicon carbide single crystal film and accelerating the separation of the n-type silicon carbide substrate and the silicon carbide single crystal film.

[0041] Among them, the conductive layer 10 can be formed by sputtering a layer of metal on the bottom of the n-type silicon carbide substrate. The surface of the conductive layer 10 is also provided with an insulating layer 20 for protection and insulation. The metal can be pt, Au, Ti, Ni, etc., and the insulating layer 20 can be formed by coating with black wax, etc., so as to cover the conductive layer 10.

[0042] In some embodiments, the conductive layer 10 and the voltage output terminal 4 for connecting to the positive pole of the external power supply can be connected through a wire, and then the cathode and the voltage input terminal 5 for receiving the negative pole of the external power supply can be connected through a wire, and then the connected anode and cathode can be immersed in the etching solution.

[0043] In some embodiments, the cathode may be a graphite sheet or the like.

[0044] In some embodiments, the n-type silicon carbide substrate 100 can be used as an anode connected to a voltage output terminal based on a two-electrode system, and a cathode connected to a voltage input terminal can be set in the etching solution; or, the n-type silicon carbide substrate 100 can be used as a working electrode connected to a voltage output terminal based on a three-electrode system, and a counter electrode and a reference electrode can be set in the etching solution, and the counter electrode and the reference electrode are connected to a voltage input terminal. Specifically, the three-electrode system includes: a working electrode, a reference electrode, and a counter electrode. The three-electrode system contains two loops, one loop is composed of a working electrode and a reference electrode, and the other loop is composed of a working electrode and a counter electrode. Among them, in an electrochemical loop, the electrode surface where oxidation reaction occurs is the anode, and the electrode surface where reduction reaction occurs is the cathode. In some embodiments, a mercury / mercury oxide electrode can be used as a reference electrode, and a graphite electrode can be used as a counter electrode.

[0045] In some embodiments, during the irradiation process, an external power supply provides a positive constant potential to the n-type silicon carbide substrate 100 through a voltage output terminal, and the applied positive constant potential may be 1V to 15V, so that the photogenerated electrons enriched in the depletion region close to the side of the n-type silicon carbide single crystal film will be guided out of the silicon carbide substrate, thereby accelerating the speed of hole enrichment at the corrosion site and accelerating the etching stripping rate.

[0046] In some embodiments, due to the action of incident light and internal electric field, the photogenerated holes in the photogenerated hole-electron pairs are enriched on the side of the depletion region 300 close to the silicon carbide single crystal film 200, and the photogenerated electrons in the photogenerated hole-electron pairs are enriched on the side of the depletion region 300 close to the n-type silicon carbide single crystal film 100; and after voltage is applied at this time, the photogenerated electrons are transferred to the cathode through the voltage output terminal and the voltage input terminal in sequence to undergo a reduction reaction with the oxidant in the etching solution, the photogenerated holes react with the SiC on the side of the depletion region 300 close to the silicon carbide single crystal film 200 to generate silicon oxide, and the silicon oxide corrosive solution in the etching solution reacts with the silicon oxide, thereby selectively etching the side of the depletion region 300 close to the silicon carbide single crystal film 200, thereby removing the micron / nano-scale flexible silicon carbide single crystal film.

[0047] Among them, photogenerated electrons e - The chemical formula for the reduction reaction at the cathode is: 2H + +H2O2+2e - =2H2O Photogenerated holes h + The chemical formula for the reaction with SiC is: SiC+2H2O2+4h + →SiO2+CO2↑+4H + Among them, H2O2 is used as an oxidant to accelerate the oxidation reaction; After SiO2 is generated, SiO2 reacts with the hydrofluoric acid HF, wherein the chemical formula of the reaction between SiO2 and hydrofluoric acid HF is: SiO2+6HF→(SiF6) 2- +2H2O+ 2H + According to the method for preparing a flexible silicon carbide single crystal wafer provided in the embodiment, the internal electric field of the depletion region at the interface between the n-type silicon carbide substrate and the silicon carbide single crystal film can be used to accelerate the separation of photogenerated electron-hole pairs, so that the photogenerated holes are enriched on the side of the depletion region close to the silicon carbide single crystal film, and selective photoelectrochemical corrosion occurs on the side of the depletion region close to the silicon carbide single crystal film; the natural separation of the silicon carbide single crystal film and the n-type silicon carbide substrate is achieved without the assistance of external force, thereby obtaining a micron / nanometer-scale flexible silicon carbide single crystal film, and the thickness of the film can be controlled by adjusting the growth time of the epitaxial film; in addition, the n-type silicon carbide substrate remaining after the flexible silicon carbide single crystal film is peeled off can be reused for epitaxial growth.

[0048] In some embodiments, see Figure 2 , and also provides a stripping device for a silicon carbide single crystal film, comprising: An electrolytic cell 8, for containing an etching solution; A silicon carbide substrate 1, immersed in the etching solution, wherein the silicon carbide substrate comprises an n-type silicon carbide substrate surface and a silicon carbide single crystal film located on the surface of the n-type silicon carbide substrate, an interface region between the n-type silicon carbide substrate and the silicon carbide single crystal film has a depletion region, and the depletion region has an internal electric field pointing from the n-type silicon carbide substrate to the silicon carbide single crystal film; A light source structure is arranged above the etching liquid, and is used to irradiate the surface of the silicon carbide single crystal film with incident light having a wavelength smaller than a critical value of the absorption light wavelength corresponding to the silicon carbide substrate, so as to form photogenerated hole-electron pairs in the silicon carbide substrate; under the action of the internal electric field of the depletion region, the photogenerated holes of the photogenerated hole-electron pairs are enriched on a side of the depletion region close to the silicon carbide single crystal film and react with the etching liquid, thereby selectively etching the side of the depletion region close to the silicon carbide single crystal film, until at least a portion of the thickness of the silicon carbide single crystal film is peeled off from the n-type silicon carbide substrate.

[0049] In some embodiments, a conductive layer 10 is further provided on the surface of the n-type silicon carbide substrate 100; the silicon carbide substrate 1 serves as an anode and is connected to a voltage output terminal through the conductive layer 10; a counter electrode 3 and a reference electrode 2 are further provided in the etching solution and are respectively connected to voltage input terminals, wherein the counter electrode 3 can serve as a cathode; so that in the subsequent process of irradiating with the incident light, a positive constant potential is provided to the n-type silicon carbide substrate through the voltage output terminal 4, and photogenerated electrons are transferred to the cathode to undergo a reduction reaction with the etching solution, thereby accelerating the enrichment of photogenerated holes in the depletion region close to the side of the silicon carbide single crystal film, thereby accelerating the stripping.

[0050] In some embodiments, the electrolytic cell 8 may be a polytetrafluoroethylene electrolytic cell.

[0051] In some embodiments, the electrolytic cell 8 includes a water inlet 6 and a water outlet 7 , and the etching liquid is injected into the electrolytic cell 8 through the water inlet 6 , and the etching liquid is discharged through the water outlet 7 .

[0052] In some embodiments, the light source structure can be a combination of a light source and a filter. For example, a xenon lamp, a mercury lamp, or an LED lamp can be used as the light source. The light emitted from the light source is filtered by the filter, so that the incident light that is smaller than the critical value of the absorption light wavelength corresponding to the silicon carbide substrate is irradiated on the surface of the silicon carbide single crystal film.

[0053] In some embodiments, the etching liquid is further provided with a stirrer 9 for stirring the etching liquid at a constant speed.

[0054] Although the present invention has been disclosed as above in the form of a preferred embodiment, it is not intended to limit the present invention. Any person skilled in the art may make possible changes and modifications to the technical solution of the present invention by using the methods and technical contents disclosed above without departing from the spirit and scope of the present invention. Therefore, any simple modifications, equivalent changes and modifications made to the above embodiments based on the technical essence of the present invention without departing from the content of the technical solution of the present invention shall fall within the protection scope of the technical solution of the present invention.

Claims

1. A method for stripping a silicon carbide single crystal thin film, It is characterized in that include: A silicon carbide substrate is provided, wherein the silicon carbide substrate comprises an n-type silicon carbide substrate and a silicon carbide single crystal film located on a surface of the n-type silicon carbide substrate, an interface region between the n-type silicon carbide substrate and the silicon carbide single crystal film has a depletion region, and the depletion region has an internal electric field pointing from the n-type silicon carbide substrate to the silicon carbide single crystal film; The silicon carbide substrate is immersed in an etching solution, and the silicon carbide substrate is irradiated with incident light having a wavelength smaller than a critical value of the absorption light wavelength corresponding to the silicon carbide substrate, so as to form photogenerated hole-electron pairs in the silicon carbide substrate; under the action of the internal electric field of the depletion region, the photogenerated holes in the photogenerated hole-electron pairs are enriched on a side of the depletion region close to the silicon carbide single crystal film and react with the etching solution, thereby selectively etching the side of the depletion region close to the silicon carbide single crystal film until at least a portion of the thickness of the silicon carbide single crystal film is peeled off from the n-type silicon carbide substrate.

2. The method for peeling off a silicon carbide single crystal thin film according to claim 1, It is characterized in that A conductive layer is also provided on the surface of the n-type silicon carbide substrate, the silicon carbide substrate is used as an anode and is connected to the voltage output terminal through the conductive layer, a cathode is provided in the etching solution and is connected to the voltage input terminal, and the anode forms a circuit loop through the voltage output terminal, the voltage input terminal and the cathode; During the incident light irradiation process, a positive constant potential is provided to the n-type silicon carbide substrate through the voltage output terminal, the internal electric field of the depletion region is enhanced, and the photogenerated electrons are transferred to the cathode to undergo a reduction reaction with the etching solution, thereby accelerating the enrichment of photogenerated holes on the side of the depletion region close to the silicon carbide single crystal film and accelerating the peeling.

3. The method for peeling off a silicon carbide single crystal thin film according to claim 1, It is characterized in that The silicon carbide single crystal film is an n-type silicon carbide single crystal film or a p-type silicon carbide single crystal film, wherein when the silicon carbide single crystal film is an n-type silicon carbide single crystal film, the doping concentration of the n-type silicon carbide single crystal film is lower than the doping concentration of the n-type silicon carbide substrate.

4. The method for peeling off a silicon carbide single crystal thin film according to claim 2, It is characterized in that An insulating layer covering the conductive layer is also provided on the surface of the conductive layer.

5. The method for peeling off a silicon carbide single crystal thin film according to claim 1, It is characterized in that The step of irradiating the silicon carbide substrate with incident light having a wavelength smaller than a critical value of the absorption light wavelength corresponding to the silicon carbide substrate comprises: The surface of the silicon carbide single crystal film is vertically irradiated with incident light having a wavelength smaller than a critical value of the absorption light wavelength corresponding to the silicon carbide substrate.

6. The method for peeling off a silicon carbide single crystal thin film according to claim 4, It is characterized in that The crystal form of the silicon carbide substrate is 4H type or 6H type, wherein the critical values ​​of the absorption wavelength of light corresponding to 4H type and 6H type are 380nm and 410nm respectively.

7. The method for peeling off a silicon carbide single crystal thin film according to claim 1, It is characterized in that The etching solution includes silicon oxide etching solution and oxidant; The step of enriching the photogenerated holes on the side of the depletion region close to the silicon carbide single crystal film and reacting with the etching solution comprises: The photogenerated holes are enriched in the depletion region near the side of the silicon carbide single crystal film and react with SiC and an oxidant to generate silicon oxide. The silicon oxide etching solution reacts with the silicon oxide.

8. The method for peeling off a silicon carbide single crystal thin film according to claim 1, It is characterized in that The process of irradiating with the incident light also includes: The etching solution is stirred at a constant speed by a stirrer.

9. A device for peeling off a silicon carbide single crystal film, It is characterized in that include: An electrolytic cell for containing an etching solution; A silicon carbide substrate immersed in the etching solution, wherein the silicon carbide substrate comprises an n-type silicon carbide substrate surface and a silicon carbide single crystal film located on the surface of the n-type silicon carbide substrate, an interface region between the n-type silicon carbide substrate and the silicon carbide single crystal film has a depletion region, and the depletion region has an internal electric field pointing from the n-type silicon carbide substrate to the silicon carbide single crystal film; A light source structure is arranged above the etching liquid, and is used to irradiate the surface of the silicon carbide single crystal film with incident light having a wavelength smaller than a critical value of the absorption light wavelength corresponding to the silicon carbide substrate, so as to form photogenerated hole-electron pairs in the silicon carbide substrate; under the action of the internal electric field of the depletion region, the photogenerated holes of the photogenerated hole-electron pairs are enriched on a side of the depletion region close to the silicon carbide single crystal film and react with the etching liquid, thereby selectively etching the side of the depletion region close to the silicon carbide single crystal film, until at least a portion of the thickness of the silicon carbide single crystal film is peeled off from the n-type silicon carbide substrate.

10. The silicon carbide single crystal thin film peeling device according to claim 9, It is characterized in that A conductive layer is also provided on the surface of the n-type silicon carbide substrate; the silicon carbide substrate is used as an anode and connected to the voltage output terminal through the conductive layer; a cathode is provided in the etching solution and connected to the voltage input terminal; the anode forms a circuit loop through the voltage output terminal, the voltage input terminal and the cathode; During the irradiation with the incident light, a positive constant potential is provided to the n-type silicon carbide substrate through the voltage output terminal, the internal electric field of the depletion region is enhanced, and the photogenerated electrons are transferred to the cathode to undergo a reduction reaction with the etching solution, thereby accelerating the enrichment of photogenerated holes on the side of the depletion region close to the silicon carbide single crystal film and accelerating the peeling.

Images