Method for repairing defective unit of thyristor

Abstract

The invention discloses a method for repairing a defect unit of a thyristor, and the method comprises the steps: providing a wafer with a thyristor formed on the surface, covering a functional layer on the first surface, away from the wafer, of the thyristor, the material of the functional layer comprises a low-melting-point metal material, and the first surface is the surface of one side, provided with a cathode electrode, of the thyristor; the thyristor is tested under a target condition, a thyristor defect unit in the thyristor is heated, the thyristor defect unit is a cathode electrode of at least one thyristor unit in the thyristor, and the part, in contact with the thyristor defect unit, in the functional layer is alloyed with the thyristor defect unit and generates a recess, so that the thyristor defect unit is subjected to heat dissipation. The target condition comprises that the leakage current generated when the anode and the cathode of the thyristor are in a reverse bias state reaches a preset value; and removing the thyristor defect unit and the residual functional layer. Part of the functional layer and the thyristor defect unit are alloyed, the electrode can be completely removed in a physical removal mode, metal residues are avoided, and the repairing effect of the thyristor is improved.

Description

Technical Field

[0001] The present application relates to the field of semiconductor technology, and in particular to a method for repairing a defective thyristor unit. Background Art

[0002] High-power integrated gate-commutated thyristor (IGCT) devices are key modules in DC power grid transmission and transformation technology. The production of the array of comb-bar units (i.e., strip cathode electrodes) of gate-commutated thyristors (GCT) evenly distributed on the entire surface is difficult to process and requires high precision. During the GCT unit molding process, it is inevitable that there will be contamination, photolithography defects, film perforation, external stress damage, etc., which will cause defects in a single comb-bar unit, such as low gate cathode reverse breakdown voltage and large leakage current. Since the comb bars are arranged in parallel through metal pressing blocks, the defective thyristor units on the surface of the device will cause the overall failure of the device. It is of great significance to remove the defective thyristor units on the surface of the device. Therefore, it is necessary to screen the comb bar failure points in the test process in advance and remove the failed comb bars.

[0003] Manual measurement to eliminate defective thyristor units on the surface of GCT chips will take a lot of time and has low feasibility. The current more mature comb screening method is to use a stepping automatic detection platform, using stepper motors and image recognition to realize automatic scanning of each unit. Through point-by-point voltage scanning, the maximum current limit is used to screen the short circuit and failure areas of excessive leakage current of the GCT unit, and they are manually removed through ink marking. Despite this, the voltage test of thousands of combs will still take a lot of time and cost, and cannot meet the needs of batch device testing. In addition, the current method for comb repair mainly relies on manual scraping or micro-area grinding. Since the metal electrode is deposited on the comb table by electron beam evaporation, it has strong adhesion. When the metal electrode material on the surface of the comb is manually scraped, it is easy to produce electrode material residues, and the electrode material is difficult to completely peel off, resulting in device breakdown, short circuit and other serious consequences. Summary of the invention

[0004] The present application provides a method for repairing a defective thyristor unit to solve the problems in the related art of high cost and low efficiency of repairing a cathode electrode and easy residue of stripped electrode material.

[0005] According to one aspect of the present application, a method for repairing a thyristor defective unit is provided, comprising the following steps: providing a wafer with a thyristor formed on its surface, and covering a first surface of the thyristor away from the wafer with a functional layer, wherein the material of the functional layer comprises a low melting point metal material, and the first surface is a side surface of the thyristor having a cathode electrode; testing the thyristor under target conditions to heat the thyristor defective unit in the thyristor, wherein the thyristor defective unit is the cathode electrode of at least one thyristor unit in the thyristor, a depression is generated on a side surface of the functional layer corresponding to the thyristor defective unit and away from the thyristor defective unit, and a portion of the functional layer in contact with the thyristor defective unit is alloyed with the thyristor defective unit, and the target conditions include: a leakage current generated when the anode and cathode of the thyristor are in a reverse bias state reaches a preset value; and removing the remaining functional layer and thyristor defective unit.

[0006] Optionally, the target condition further includes: testing the thyristor in an environment below 20° C.

[0007] Optionally, the step of removing the remaining functional layer and the thyristor defective unit includes: heating the remaining functional layer to convert the functional layer from a solid state to a liquid state, and removing the functional layer; and removing the thyristor defective unit.

[0008] Optionally, the heating temperature of the remaining functional layer is greater than the melting point of the material of the functional layer and less than the heating temperature of the thyristor defective unit.

[0009] Optionally, the step of removing the functional layer includes: removing the liquid functional layer from the surface of the wafer by a purge process.

[0010] Optionally, the method for forming the functional layer includes a double-sided extrusion method, and the implementation steps of the double-sided extrusion method include: pouring liquid functional layer material and covering it on the wafer; using a cover plate to set it on the wafer and press it; cooling the functional layer material to form the functional layer, and removing the cover plate.

[0011] Optionally, the method of forming the functional layer includes: single-sided pressing method, spin coating method and brush coating method, wherein the implementation steps of the single-sided pressing method include: providing a substrate, pouring and covering the liquid functional layer material on the substrate, and cooling the functional layer material to form a preliminary functional layer; turning the substrate over so that the preliminary functional layer covers the wafer and applies pressure to the substrate, and removing the substrate.

[0012] Optionally, before removing the remaining functional layer and the defective thyristor unit, the repair method further comprises the step of screening the thyristor using image recognition software and an optical microscope to identify depressions generated in the functional layer.

[0013] Optionally, the material of the functional layer includes one or more of rubidium, cesium, gallium and gallium alloys, and the material of the cathode electrode of the thyristor includes aluminum.

[0014] Optionally, the removal method of the thyristor defective unit includes any one or more of scraper removal, ultrasonic removal, vibration removal, air flow removal and water flow flushing.

[0015] Through the present application, a functional layer is covered on the surface of one side of the wafer having a cathode electrode. Under target conditions, that is, the anode and cathode of the thyristor are in a reverse bias state, and the leakage current is set to a preset value. At this time, the defective cathode electrode, that is, the thyristor defect unit, generates a heating effect under this target condition. By utilizing the low melting point characteristics of the functional layer material, the heated thyristor defect unit heats the functional layer covering the unit and melts the part of the functional layer. Due to the surface tension of the liquid functional layer, the liquid functional layer shrinks into a more compact shape, and alloying with the thyristor defect unit also causes a part of the liquid functional layer to penetrate into the thyristor defect unit, reducing the volume of the functional layer, so that a depression is generated on the side of the surface that is away from the part corresponding to the thyristor defect unit, so that the depression can be identified and the liquid functional layer can be accurately detected. Identifying thyristor defective units improves the accuracy and reliability of screening, and can also achieve synchronous testing of all cathode electrodes on the wafer, thereby improving testing efficiency and reducing the testing cost of a single cathode electrode; at the same time, alloying will occur in the contact portion of the melted functional layer with the thyristor defective unit, wherein the thyristor defective unit in a heated state accelerates the alloying with the functional layer, and the alloyed thyristor defective unit becomes loose and brittle, reducing the adhesion to the thyristor, and when the thyristor defective unit is removed after removing the remaining functional layers, the alloyed thyristor defective unit is easier to remove, thereby avoiding metal residue, achieving precise repair of the thyristor defective unit, and solving the problems of high cost and low efficiency of cathode electrode repair and easy residue of stripped electrode material in related technologies. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] The drawings constituting a part of the present application are used to provide a further understanding of the present application. The illustrative embodiments and descriptions of the present application are used to explain the present application and do not constitute an improper limitation on the present application. In the drawings:

[0017] Figure 1 is a flow chart of a method for repairing a defective thyristor unit provided according to an embodiment of the present application;

[0018] Figure 2 It is a structural schematic diagram of a substrate after a functional layer is covered on a wafer formed with a thyristor in a method for repairing a thyristor defect unit provided in an embodiment of the present application;

[0019] Figure 3 Yes Figure 2 A schematic diagram of the structure of the substrate after a functional layer in contact with a defective unit of the thyristor is recessed during testing;

[0020] Figure 4 It is a flow chart of removing a functional layer and a thyristor defective unit in a method for repairing a thyristor defective unit provided in an embodiment of the present application.

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

[0022] 20. Thyristor; 21. Cathode electrode; 210. Thyristor defect unit; 30. Functional layer. DETAILED DESCRIPTION

[0023] It should be noted that, in the absence of conflict, the embodiments and features in the embodiments of the present application can be combined with each other. The present application will be described in detail below with reference to the accompanying drawings and in combination with the embodiments.

[0024] In order to enable those skilled in the art to better understand the solution of the present application, the technical solution in the embodiments of the present application will be clearly and completely described below in conjunction with the drawings in the embodiments of the present application. Obviously, the described embodiments are only part of the embodiments of the present application, not all of the embodiments. Based on the embodiments in the present application, all other embodiments obtained by ordinary technicians in this field without creative work should fall within the scope of protection of the present application.

[0025] It should be noted that the terms "first", "second", etc. in the specification and claims of the present application and the above-mentioned drawings are used to distinguish similar objects, and are not necessarily used to describe a specific order or sequential order. It should be understood that the data used in this way can be interchanged where appropriate, so that the embodiments of the present application described here. In addition, the terms "including" and "having" and any of their variations are intended to cover non-exclusive inclusions, for example, a process, method, system, product or device comprising a series of steps or units is not necessarily limited to those steps or units clearly listed, but may include other steps or units that are not clearly listed or inherent to these processes, methods, products or devices.

[0026] As introduced in the background technology, voltage testing of thousands of thyristor combs will still consume a lot of time and cost, and cannot meet the needs of batch device testing. The comb repair method mainly relies on manual scraping or micro-area grinding. Since the metal electrode is deposited on the comb by electron beam evaporation, it has strong adhesion. Manually scraping off the metal electrode material on the surface of the comb is likely to produce electrode material residues, and the electrode material is difficult to completely peel off, resulting in device breakdown, short circuit and other serious consequences.

[0027] In order to solve the above problems, according to the embodiments of the present application, Figure 1 is a flow chart of a method for repairing a thyristor defective unit according to an embodiment of the present application, such as Figure 1As shown, a method for repairing a defective thyristor unit is provided, comprising the following steps:

[0028] S1, providing a wafer with a thyristor formed on the surface, and covering a first surface of the thyristor away from the wafer with a functional layer, wherein the material of the functional layer includes a low melting point metal material, and the first surface is a side surface of the thyristor having a cathode electrode;

[0029] S2. Testing the thyristor under target conditions to heat the thyristor defective unit in the thyristor, the thyristor defective unit being the cathode electrode of at least one thyristor unit in the thyristor, a depression being generated on the surface of the side of the functional layer corresponding to the thyristor defective unit away from the thyristor defective unit, and a portion of the functional layer in contact with the thyristor defective unit being alloyed with the thyristor defective unit, the target conditions including: the leakage current generated when the anode and cathode of the thyristor are in a reverse bias state reaches a preset value;

[0030] S3. Removing the remaining functional layers and thyristor defective units.

[0031] Through the above implementation, the functional layer is covered on the first surface of the thyristor away from the wafer. Under the target condition, that is, the anode and cathode of the thyristor are in a reverse bias state, and the leakage current is set to a preset value. At this time, the defective cathode electrode, that is, the thyristor defective unit, generates a heating effect under this target condition. By utilizing the low melting point characteristic of the functional layer material, the heated thyristor defective unit heats the functional layer in contact with the thyristor defective unit and melts the part of the functional layer to produce a depression on its exposed surface, thereby accurately identifying the thyristor defective unit. The normal heating of the cathode electrode will not reach the melting point of the functional layer material, thereby improving the accuracy and reliability of the screening. In addition, the test of the thyristor under the target condition makes all cathode electrodes on the wafer Electrical performance tests are carried out simultaneously, and the functional layer covering all cathode electrodes can screen defects of all cathode electrodes on the wafer at the same time, realizing synchronous testing of all cathode electrodes on the wafer, improving testing efficiency, and reducing testing costs of single cathode electrodes; at the same time, the melted functional layer is alloyed with the thyristor defective unit, and the thyristor defective unit in a heated state accelerates alloying with the functional layer. The alloyed cathode electrode becomes loose and brittle, reducing adhesion to the thyristor, making it easier to remove the thyristor defective unit, thereby avoiding metal residue, realizing accurate repair of the thyristor defective unit, and solving the problems of high cost and low efficiency of cathode electrode repair and easy residue of stripped electrode material in related technologies.

[0032] The exemplary embodiments of the method for repairing a thyristor defective unit provided in accordance with the embodiments of the present application will be described in more detail below. However, these exemplary embodiments may be implemented in a variety of different forms and should not be construed as being limited to the embodiments described herein. It should be understood that these embodiments are provided to make the disclosure of the present application thorough and complete, and to fully convey the concepts of these exemplary embodiments to those of ordinary skill in the art.

[0033] First, step S1 is performed: providing a wafer with a thyristor 20 formed on the surface, and covering the first surface of the thyristor 20 away from the wafer with a functional layer 30, the material of the functional layer 30 includes a low melting point metal material, the first surface is a side surface of the thyristor 20 with a cathode electrode 21, and forming Figure 2 In the structure shown, the thyristor 20 includes a plurality of thyristor units.

[0034] In this embodiment, a functional layer of a low-melting-point metal material is covered on the first surface (the side surface with the cathode electrode) of the thyristor 20. In the subsequent testing of the thyristors on the wafer, the cathode electrodes on the entire wafer are simultaneously tested for electrical performance. Since the functional layer covers all the cathode electrodes, the cathode electrodes on the wafer can be simultaneously screened to see whether any cathode electrodes generate heat during the test. There is no need to position and electrically contact each one, which ensures that the test conditions are consistent for all cathode electrodes and reduces the instability caused by test contact points or positioning errors. This method significantly improves test efficiency and reduces dependence on complex test equipment through one-time coverage and subsequent global testing, thereby reducing test costs.

[0035] In some optional embodiments, the material of the functional layer includes one or more of rubidium, cesium, gallium and gallium alloys, and the material of the cathode electrode of the thyristor includes aluminum. These materials have low melting point characteristics, such as the melting point of gallium is 29.8°C, and the melting points of cesium and rubidium are also relatively low, which makes them remain liquid at room temperature or slightly higher temperatures, which is convenient for spreading and forming a uniform functional layer. The low melting point characteristic also means that during the detection process, a small amount of overheating is required to melt the material, so that the thyristor defective unit can be quickly identified through the molten area. The alloying characteristics with aluminum enable these materials to form alloys when in contact with the thyristor defective unit (the cathode electrode is an aluminum electrode), and the alloyed area contrasts with the surrounding unalloyed functional layer materials. The alloy area is easier to operate during subsequent removal, so that the thyristor defective unit can be easily removed by external force without residue.

[0036] Specifically, the type of thyristor in the embodiment shown in the present application includes one of IGCT and IGTO. Taking the IGCT device as an example, there are multiple GCT units on the wafer, and each GCT unit has a cathode electrode on the side away from the wafer.

[0037] Specifically, the cathode electrodes of multiple thyristor units can constitute a comb-bar electrode, that is, the comb-bar electrode includes multiple comb-bar units corresponding to the thyristor units one by one, the horizontal cross-section shape of each comb-bar unit is a long strip, and the arrangement methods include radial arrangement and staggered arrangement.

[0038] Since the uneven distribution of materials will introduce additional test errors and affect the accuracy and reliability of screening, in order to make the functional layer material evenly distributed on the wafer, in some optional embodiments, a double-sided extrusion method is used to cover the functional layer on the first surface of the thyristor away from the wafer.

[0039] Specifically, the implementation steps of the double-sided extrusion method may include: first, pouring and covering the liquid functional layer material on the wafer; by directly pouring the liquid material to cover the entire wafer, the material is quickly and evenly distributed, and the efficiency of material spreading is improved. At the same time, the fluidity of the liquid material helps it to form a uniform film on the wafer, reducing the additional testing and calibration due to uneven material distribution, and reducing the testing cost. Then, a cover plate is set on the wafer and pressed; applying pressure to the cover plate helps to eliminate bubbles in the material, reduce gaps, and make the functional layer form a denser structure on the surface of the thyristor, which helps to improve the adhesion of the material to ensure that the functional layer material is more tightly and evenly attached to the cathode electrode surface. Finally, the material of the functional layer is cooled to form a functional layer, and the cover plate is removed; the cooling process solidifies the liquid metal to form a solid functional layer, and the solid functional layer is used as a temperature-sensitive medium in the subsequent testing process to identify the heating position of the defective unit of the thyristor.

[0040] The double-sided extrusion method can ensure uniform distribution of the functional layer material on the wafer, thereby improving the accuracy and reliability of identifying thyristor defective units.

[0041] Exemplarily, the cover plate is a low-wettability substrate, including one or a combination of a quartz plate and a polyimide plate, but not limited to the above two. Those skilled in the art can reasonably select the type of cover plate according to actual needs, and this application does not make specific limitations.

[0042] Exemplarily, the material of the functional layer includes gallium. First, at an ambient temperature slightly higher than 30°C, liquid metal gallium is poured onto the center of the IGCT wafer that has been insulated, and a cover plate of comparable size is used to align the wafer and press it vertically. The vertical pressure applied is 50N to 100N to ensure that the liquid gallium metal is spread on the surface of the thyristor without holes, bubbles, or seepage. Then, the gallium metal is solidified at a low temperature of, for example, less than 20°C to form a functional layer. When removing the cover plate, due to the kinetic balance between the energy release rate and the tearing rate at the interface, the speed at which the wafer and the cover plate are separated directly affects the adhesion between the wafer and the gallium metal film. Therefore, a relatively low peeling speed of, for example, less than 1 mm / s is used here to lift the cover plate from the wafer. At this time, the wafer has a sufficiently strong adsorption force on the gallium metal film on its surface to ensure that the gallium metal film adheres to the surface of the thyristor, thereby completing the preparation of the gallium metal heating test film (i.e., the functional layer).

[0043] It should be noted that the method of covering the functional layer on the first surface of the thyristor facing away from the wafer is not limited to the double-sided extrusion method mentioned above. In some other optional implementations, the functional layer is covered by a single-sided pressing method.

[0044] Specifically, the implementation steps of the above-mentioned single-sided pressing method may include: first, providing a substrate, pouring and covering the material of the liquid functional layer on the substrate, and cooling the material of the functional layer to form a preliminary functional layer; by pouring the liquid material on the substrate, the surface properties of the substrate can be used to improve the fluidity and distribution uniformity of the material, ensuring that the preliminary functional layer forms a film with uniform thickness and smooth surface before cooling and solidification, and the low-melting-point metal material has a fast cooling and solidification speed, and can form a stable structure in a short time to form a preliminary functional layer. Finally, the substrate is turned over so that the preliminary functional layer covers the wafer and presses it, and the substrate is removed; after removing the substrate, the preliminary functional layer forms a functional layer on the surface of the thyristor, and by turning the substrate over and applying appropriate pressure, the preliminary functional layer can be tightly and evenly adhered to the surface of the thyristor, ensuring the precise transfer of the functional layer from the substrate to the wafer, and the preliminary functional layer has been solidified into a film before contacting the surface of the thyristor, and when the substrate is removed, the adhesion between the functional layer material and the substrate is small, and no residue of the substrate material will be left on the surface of the thyristor.

[0045] The above-mentioned single-sided pressing method forms a functional layer by forming a preliminary functional layer on a substrate, then transferring it to the surface of the thyristor, and removing the substrate after applying pressure. This not only improves the uniformity and quality of material spreading, but also simplifies the preparation steps before testing, reduces material and operating costs, and ultimately achieves higher screening efficiency.

[0046] Exemplarily, the material of the functional layer is gallium. Due to the high surface tension of the gallium metal film on the substrate, a substrate that can wet the gallium liquid metal needs to be selected for the spreading of the liquid metal. In this embodiment, copper is selected as the substrate. The substrate may also include other materials, which are not specifically limited in this application. Gallium liquid metal has a lower surface tension on the copper metal substrate and can be flatly adhered to the copper substrate. First, the gallium liquid metal is poured on the copper substrate, and the liquid metal is evenly spread on the copper substrate by spin coating, brush coating, etc., and the gallium metal is cooled and solidified at a low temperature of, for example, less than 20°C to form a gallium metal film to form a functional layer. Then, the copper substrate is turned over so that the side of the copper substrate covered with the functional layer is covered on the IGCT wafer and pressed tightly, wherein a vertical pressure of, for example, 50N-100N is applied, and the copper substrate is lifted by a lower peeling speed of, for example, less than 1mm / s, and the removal of the copper substrate is completed, and the preparation of the gallium metal heating test film (i.e., the functional layer) is completed.

[0047] In some other optional embodiments, the method of covering the first surface of the thyristor away from the wafer may also include spin coating and brush coating. Since the oxidized liquid metal has a lower surface tension, a layer of oxidized metal film (i.e., functional layer) can be generated on the surface under exposure to the natural environment. Before spreading the liquid metal, the liquid metal is stirred at a uniform speed to fully oxidize the liquid metal, so that the liquid metal with low surface tension can be spread on the surface of the thyristor by coating methods such as spin coating and brush coating to form a functional layer.

[0048] Exemplarily, before spreading the functional layer material, nanoparticles are coated on the surface of the thyristor. The nanoparticles are such as silicon dioxide (SiO2) microspheres. The slightly rough surface of the nanoparticles can provide more contact points, so that the gallium metal film can adhere more tightly to the surface of the thyristor when spreading. The nanoparticles can reduce the surface tension of the gallium metal, thereby improving its spreadability. This surface adjustment helps the gallium metal to form a thinner and more uniform film on the surface of the thyristor, reducing the formation of bubbles and discontinuities.

[0049] After the step of covering the functional layer, step S2 is performed: the thyristor is tested under target conditions, so that the thyristor defective unit 210 in the thyristor is heated, the thyristor defective unit 210 is the cathode electrode 21 of at least one thyristor unit in the thyristor, a depression is generated on the surface of the side of the functional layer 30 that is opposite to the thyristor defective unit 210, and the part of the functional layer 30 that contacts the thyristor defective unit 210 is alloyed with the thyristor defective unit 210. The above target conditions include: the leakage current generated when the anode and cathode of the thyristor are in a reverse bias state reaches a preset value, forming a Figure 3 The structure shown.

[0050] Under the target conditions, that is, when the leakage current generated by the anode and cathode of the thyristor in the reverse bias state reaches the preset value, only the defective thyristor unit will heat up to melt the functional layer, thereby improving the accuracy of screening and ensuring that only the defective thyristor unit is identified and marked. At the same time, the cathode electrode produces an alloying reaction with the melted functional layer. Among them, the cathode electrode accelerates the alloying with the functional layer material under local overheating, making the cathode electrode material loose and reducing the adhesion with the thyristor, which is easy to remove by external force (such as scraper) or chemical means. In addition, due to the difference in physical properties between the alloyed area and the surrounding unalloyed functional layer material, the removal operation can be more precise, avoiding damage to normal units. At the same time, it ensures that there is no residue of functional layer material after removal, avoiding defects such as device breakdown and short circuit.

[0051] In addition, this embodiment can simultaneously detect the electrical performance of all cathode electrodes on the wafer through a single testing process without the need to test each unit one by one, which greatly improves the testing efficiency. Since the number of test points is reduced, the demand for testing equipment and manpower is also reduced, thereby reducing the testing cost.

[0052] In addition, the above step S2 performs testing under specific target conditions and utilizes the heat generated by the thyristor defective unit to trigger the alloying reaction between the functional layer material and the aluminum electrode. The thyristor defective unit not only improves the test efficiency and reduces the test cost, but also ensures the accuracy and residue-free removal and repair process, ultimately improving the performance consistency and manufacturing yield of the entire chip.

[0053] Exemplarily, the target condition is: using a thyristor blocking voltage test bench to test the anode and cathode voltages corresponding to when the anode and cathode leakage current of the thyristor reaches 10mA. If gate cathode reverse bias leakage current occurs during the test, the cathode electrode in the thyristor that generates the leakage current is a defective thyristor unit, and its temperature will overheat, thereby exceeding the melting point of the low-melting-point metal.

[0054] Exemplarily, the material of the functional layer is gallium, and the heating temperature of the thyristor defect unit is greater than 50°C. Within this temperature range, gallium is in a completely liquid state, and as the temperature rises, the viscosity of liquid gallium becomes lower, and its fluidity and activity become stronger, making it easier to penetrate into the grain boundaries or surface defects of aluminum, thereby accelerating the alloying process of gallium and aluminum. High temperature will also significantly accelerate the diffusion process of gallium atoms in the aluminum lattice, allowing the aluminum metal electrode to alloy faster.

[0055] In some optional embodiments, the above target conditions also include: testing the thyristor in an environment below 20°C. In an environment below 20°C, the melting point characteristics of the functional layer material (such as the melting point of gallium is 29.8°C) make it so that only the defective thyristor unit will heat up to above the melting point, and the normal cathode electrode will not heat up and keep consistent with the ambient temperature. In this case, the defective cathode electrode (i.e., the defective thyristor unit) triggers an alloying reaction with the melted functional layer material to form an obvious mark, thereby avoiding misjudgment caused by ambient temperature fluctuations and improving the accuracy of the test.

[0056] In some optional embodiments, the above-mentioned repair method in the embodiment of the present application also includes the step of: using image recognition software and an optical microscope to screen the thyristor to identify the depressions produced in the functional layer. The image recognition software, in conjunction with the use of a microscope, can automatically analyze the depressions of the functional layer on the surface of the thyristor without the need for manual inspection one by one, greatly improving the screening efficiency. At the same time, automated screening reduces the need for manual operation, reduces labor costs, and also helps to reduce subjective errors that may be caused by manual inspection, thereby reducing costs. The optical microscope provides high-resolution images that can clearly display the depressions of the functional layer, and even tiny defects can be accurately identified. The image recognition software analyzes these images through algorithms, and can accurately locate the depression area, that is, the location of the thyristor defect unit, thereby improving the accuracy and consistency of recognition.

[0057] Illustratively, the microscope includes one or more of a dark field microscope, a laser confocal microscope, and a digital microscope. Those skilled in the art may select one according to actual needs, and this application does not make any specific limitation.

[0058] Exemplarily, a fluorescent marker is added to the functional layer material, and the fluorescent marker includes europium-doped yttrium oxide (Eu:Y2O3), and its fluorescence intensity increases significantly when the temperature rises. As an inorganic fluorescent material, europium-doped yttrium oxide not only has good temperature sensitivity, but also has good compatibility with gallium metal and does not affect the melting point and fluidity of gallium metal. Under the excitation of light of a specific wavelength, europium-doped yttrium oxide can produce bright and stable fluorescence signals, which facilitates the formation of significant visual contrast between alloyed areas and non-alloyed areas, avoiding image recognition software and microscopes from missing depressions, thereby improving the reliability and accuracy of screening.

[0059] After the step of alloying part of the functional layer with the thyristor defect unit, step S3 is performed: removing the remaining functional layer and thyristor defect unit. Through the previous alloying reaction, the thyristor defect unit has been accurately located. When removing these thyristor defect units, it can be carried out in a targeted manner, thereby improving the efficiency of the overall test, reducing the test cost, and ensuring the accuracy of the removal operation. Since the mark is accurately generated based on the electrical performance anomaly in the previous test, after removal and repair, the cathode electrodes with normal electrical performance are retained on the wafer, which further improves the accuracy of the screening. The alloying of the functional layer material and the cathode electrode of the thyristor defect unit changes the physical properties of these areas, making them loose and easy to remove. These alloyed areas can be easily removed using appropriate means without residue or damage to the surrounding normal units.

[0060] In some optional embodiments, such as Figure 4 As shown, the steps of removing the remaining functional layer and the thyristor defective unit include:

[0061] S01, heating the remaining functional layer to convert the functional layer from a solid state to a liquid state, and removing the functional layer;

[0062] S02. Remove defective thyristor units.

[0063] In the above embodiment, by heating the remaining functional layer, it is converted from solid to liquid at an appropriate temperature. After being heated to liquid, the functional layer material can be easily collected and recycled under the action of surface tension, thereby improving test efficiency and reducing costs. By removing the alloyed area, it can be ensured that only truly defective cathode electrodes are removed, thereby improving the accuracy of screening and repair, thereby ensuring the overall performance of the chip and improving the chip preparation yield.

[0064] An exemplary implementation of the steps of removing the remaining functional layer and the thyristor defective unit according to an embodiment of the present application will be described in more detail below.

[0065] First, execute step S01 to heat the remaining functional layer to convert the functional layer from solid to liquid, and remove the functional layer; the functional layer material has a low melting point, which means that at an appropriate temperature, these materials can be converted from solid to liquid, so that the remaining functional layer material melts and is convenient for subsequent removal.

[0066] Specifically, the step of removing the functional layer may include: tilting the wafer to remove the liquid functional layer from the surface of the wafer; or using a purge process to remove the liquid functional layer from the surface of the wafer. When the functional layer material is in a liquid state, its surface tension is high and its fluidity is improved. The liquid metal can be easily collected and recovered by tilting the wafer, purging or using other external force means, ensuring that the remaining functional layer is completely removed from the surface of the thyristor, avoiding the influence of residual materials on subsequent processes, and compared with polymer films, functional layer materials including low-melting-point metal materials have the characteristics of being easier to recycle, thereby reducing material waste and reducing testing costs.

[0067] Finally, step S02 is executed to remove the defective thyristor unit; in step S2, heating is performed to form an alloyed area between the functional layer and the defective thyristor unit, and the properties of the alloyed area change (such as becoming looser and more brittle, and the adhesion to the thyristor is weakened, etc.), making this part easy to be removed by external force, and the removal process will not cause damage to the normal thyristor unit, and the material residue in the removal process is also reduced. The removal operation is based on the previous marking and alloying process, with clear goals and controllable removal process, which reduces the accidental removal or damage caused by improper operation, improves the stability and accuracy of the removal repair, and thus improves the overall performance and manufacturing yield of the thyristor device.

[0068] In some optional embodiments, the removal method of the thyristor defective unit includes any one or more of scraper removal, ultrasonic removal, vibration removal, airflow removal, and water flushing. The scraper operation is relatively simple and easy to control, which reduces the uncertainty in the operation; the ultrasonic removal operation is fast and does not require additional physical tools, which reduces the tool cost and operation time; the vibration removal can affect multiple thyristor defective units at the same time, improve the processing speed, and by controlling the frequency and intensity of the vibration, the removal process can be finely controlled; the airflow or water flow removal operation is fast, and the removal effect is controlled by adjusting the direction and pressure of the airflow or water flow, which is suitable for large-scale wafer processing; the above methods can all guarantee the removal effect of the cathode electrode. Those skilled in the art should understand that the selection and application of each method must be determined according to the specific material properties, process requirements and equipment conditions. The removal of thyristor defective units also includes other methods. The above methods are used as examples and are not specifically limited in this application.

[0069] In some optional embodiments, the heating temperature of the remaining functional layer is greater than the melting point of the functional layer material and less than the heating temperature of the thyristor defect unit. The functional layer material (such as gallium or its alloy) has a specific melting point. Heating to a temperature above the melting point can make the functional layer material change from solid to liquid, and the material becomes easier to collect and remove. The low surface tension characteristics of liquid metal help it to form an easy-to-collect form after heating, avoiding leaving residues on the surface of the thyristor and reducing subsequent cleaning work. By accurately controlling the heating temperature above the melting point of the functional layer material but below the heating temperature of the thyristor defect unit, the complete melting of the functional layer material can be ensured. At the same time, when heating within this temperature range, the alloying of the remaining functional layer material and the thyristor cathode electrode is slow, avoiding misscreening or screening leakage due to improper temperature control, and avoiding the introduction of new defects, thereby significantly improving the chip preparation yield.

[0070] In some optional embodiments, after removing the defective thyristor unit, the method further includes the steps of: testing the thyristor again under target conditions, and using infrared thermal imaging monitoring to monitor the temperature distribution on the surface of the thyristor in real time. Infrared imaging can capture tiny temperature changes, detect whether there are overheated thyristor defective units in the cathode electrode during the test, accurately identify their location and overheating degree, and screen whether there are any missed thyristor defective units. Infrared imaging provides a more accurate, controllable and reliable screening method for mass production of high-power thyristor chips.

[0071] From the above description, it can be seen that the above embodiments of the present application achieve the following technical effects:

[0072] 1. Through the phenomenon that the defective thyristor unit melts and forms a depression when the functional layer covering the thyristor is overheated during the test under target conditions, the defective thyristor unit can be quickly and comprehensively screened. Compared with the point-by-point scanning method, the screening method has higher work efficiency and lower testing cost;

[0073] 2. During the test under target conditions, only defective thyristor units will overheat (the temperature of their heating exceeds the melting point of the functional layer). Combined with the melting point characteristics of liquid metal, which is extremely sensitive to temperature, accurate screening of thyristors can improve the accuracy and stability of defect screening;

[0074] 3. Since the liquid functional layer will alloy with the thyristor defective unit (cathode electrode), and accelerate the loosening and brittleness of the thyristor defective unit under the high temperature of the thyristor defective unit, and reduce the adhesion between the thyristor defective unit and the thyristor, it is easier to be removed by external force in the subsequent repair of the thyristor defective unit, and no obvious residue will occur, thus avoiding problems such as device breakdown and short circuit, and improving the consistency of thyristor chip performance and the preparation yield of thyristor chips.

[0075] It should also be noted that the terms "include", "comprises" or any other variations thereof are intended to cover non-exclusive inclusion, so that a process, method, commodity or device including a series of elements includes not only those elements, but also other elements not explicitly listed, or also includes elements inherent to such process, method, commodity or device. In the absence of more restrictions, the elements defined by the sentence "comprises a ..." do not exclude the existence of other identical elements in the process, method, commodity or device including the elements.

[0076] The above are only embodiments of the present application and are not intended to limit the present application. For those skilled in the art, the present application may have various changes and variations. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present application should be included within the scope of the claims of the present application.

Claims

1. A method for repairing a defective thyristor unit, characterized in that: The following steps are involved: Providing a wafer with a thyristor formed on the surface, and covering a first surface of the thyristor away from the wafer with a functional layer, wherein the material of the functional layer includes a low melting point metal material, and the first surface is a side surface of the thyristor having a cathode electrode; The thyristor is tested under target conditions to heat a thyristor defective unit in the thyristor, wherein the thyristor defective unit is a cathode electrode of at least one thyristor unit in the thyristor, a depression is generated on a surface of a side of the functional layer that is opposite to the portion corresponding to the thyristor defective unit, and a portion of the functional layer that contacts the thyristor defective unit is alloyed with the thyristor defective unit, and the target conditions include: a leakage current generated when the anode and cathode of the thyristor are in a reverse bias state reaches a preset value; The remaining functional layer and the thyristor defective unit are removed.

2. The method for repairing a defective thyristor unit according to claim 1, characterized in that: The target condition also includes: testing the thyristor in an environment below 20° C.

3. The method for repairing a defective thyristor unit according to claim 1, characterized in that: The step of removing the remaining functional layer and the thyristor defective unit comprises: heating the remaining functional layer to convert the functional layer from a solid state to a liquid state, and removing the functional layer; The defective thyristor unit is removed.

4. The method for repairing a defective thyristor unit according to claim 3, characterized in that: The heating temperature of the remaining functional layer is greater than the melting point of the material of the functional layer and is less than the heating temperature of the thyristor defective unit.

5. The method for repairing a defective thyristor unit according to claim 3, characterized in that: The step of removing the functional layer comprises: The liquid functional layer is removed from the surface of the wafer by a purge process.

6. The method for repairing a defective thyristor unit according to claim 1, characterized in that: The method for forming the functional layer includes a double-sided extrusion method, and the implementation steps of the double-sided extrusion method include: Pouring the liquid material of the functional layer onto the wafer; A cover plate is arranged on the wafer and pressed tightly; The material of the functional layer is cooled to form the functional layer, and the cover plate is removed.

7. The method for repairing a defective thyristor unit according to claim 1, characterized in that: Methods for forming the functional layer include: single-sided pressing method, spin coating method and brush coating method, wherein: The implementation steps of the single-sided pressing method include: Providing a substrate, pouring the liquid material of the functional layer onto the substrate and covering it, and cooling the material of the functional layer to form a preliminary functional layer; The substrate is turned over so that the preliminary functional layer covers the wafer and pressure is applied to the substrate to remove the substrate.

8. The method for repairing a defective thyristor unit according to claim 1, characterized in that: Before removing the remaining functional layer and the defective thyristor unit, the repair method further comprises the steps of: The thyristors were screened using image recognition software and an optical microscope to identify depressions created in the functional layer.

9. The method for repairing a defective thyristor unit according to any one of claims 1 to 8, characterized in that: The material of the functional layer includes one or more of rubidium, cesium, gallium and a gallium alloy, and the material of the cathode electrode of the thyristor includes aluminum.

10. The method for repairing a defective thyristor unit according to claim 1, characterized in that: The removal method of the thyristor defective unit includes any one or more of scraper removal, ultrasonic removal, vibration removal, air flow removal and water flow flushing.

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