Repair Method for Thyristor Defective Unit

Abstract

The present application discloses a method for repairing a defective thyristor unit, including: providing a wafer with a thyristor formed on its surface, covering a functional layer on a first surface of the thyristor facing away from the wafer, the material of the functional layer including a low-melting-point metal material, the first surface being the surface of the thyristor on the side with a cathode electrode; performing a test on the thyristor under target conditions to heat the defective thyristor unit in the thyristor, the defective thyristor unit being the cathode electrode of at least one thyristor unit in the thyristor, and a part of the functional layer in contact with the defective thyristor unit being alloyed with the defective thyristor unit to generate a depression, the target conditions including: the leakage current generated when the anode and cathode of the thyristor are in a reverse-biased state reaches a preset value; removing the defective thyristor unit and the remaining functional layer. A part of the functional layer in the present application is alloyed with the defective thyristor unit, and its electrode can be completely removed by physical removal, avoiding metal residue and improving the repair effect of the thyristor.

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 defective thyristor unit is provided, including the following steps: providing a wafer with a thyristor formed on its surface, and covering a functional layer on a first surface of the thyristor facing away from the wafer, the material of the functional layer including a low-melting-point metal material, the first surface being the surface of the thyristor having a cathode electrode; testing the thyristor under target conditions to heat the defective thyristor unit in the thyristor, the defective thyristor unit being the cathode electrode of at least one thyristor unit in the thyristor, a depression being generated on a side surface of the functional layer facing away from the part corresponding to the defective thyristor unit, and the part of the functional layer in contact with the defective thyristor unit being alloyed with the defective thyristor 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; removing the remaining functional layer and the defective thyristor unit.

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

[0007] Optionally, the step of removing the remaining functional layer and the defective thyristor 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; removing the defective thyristor 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 defective thyristor unit.

[0009] Optionally, the step of removing the functional layer includes: removing the liquid functional layer from the surface of the wafer by means of 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 and covering the material of the liquid functional layer on the wafer; setting a cover plate on the wafer and pressing it tightly; cooling the material of the functional layer to form the functional layer, and removing the cover plate.

[0011] Optionally, the method for forming the functional layer includes: a single-sided pressing method, a spin coating method, and a brush coating method. Among them, the implementation steps of the single-sided pressing method include: 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; flipping the substrate so that the preliminary functional layer covers the wafer and applying 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 includes the step of: screening the thyristor using image recognition software and an optical microscope to identify the depression generated in the functional layer.

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

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

[0015] In this application, a functional layer is covered on the surface of one side of the wafer with a cathode electrode. Under target conditions, that is, when the anode and cathode of the thyristor are in a reverse bias state and the set leakage current reaches a preset value, at this time, the defective cathode electrode, that is, the thyristor defect unit, generates a heating effect under this target condition. Utilizing the low melting point characteristic of the functional layer material, the heating thyristor defect unit heats and melts the functional layer covering the unit, and due to the surface tension of the liquid functional layer, the liquid functional layer will shrink into a more compact shape, and alloying with the thyristor defect unit will also cause a part of the liquid functional layer to penetrate into the thyristor defect unit, reducing the volume of the functional layer, causing a depression on the surface of the side opposite to the part corresponding to the thyristor defect unit. Thus, the thyristor defect unit can be accurately identified by recognizing this depression, improving the accuracy and reliability of screening. It can also achieve synchronous testing of all cathode electrodes on the wafer, improving the testing efficiency and reducing the testing cost of a single cathode electrode. At the same time, the contact part of the melted functional layer with the thyristor defect unit will undergo alloying, and the thyristor defect unit in the heating state accelerates the alloying with the functional layer. After alloying, the thyristor defect unit becomes loose and brittle, reducing the adhesion force with the thyristor. When removing the thyristor defect unit after removing the remaining functional layer, the alloyed thyristor defect unit is easier to remove, thus avoiding metal residue, achieving precise repair of the thyristor defect unit, and solving the problems of high repair cost, low efficiency, and easy residue of the peeled electrode material in the related technology. Description of the Drawings

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

[0017] Figure 1 is a flowchart of a method for repairing a thyristor defect unit provided according to an embodiment of this application;

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

[0019] Figure 3 is for Figure 2 testing the thyristor in, and is a schematic structural diagram of the substrate after a depression is generated in the functional layer in contact with the thyristor defect unit;

[0020] Figure 4 It is a flowchart for removing the functional layer and the thyristor defect unit in the repair method of the thyristor defect unit provided by the embodiments of the present application.

[0021] Among them, the above-mentioned drawings include the following reference numerals:

[0022] 20. Thyristor; 21. Cathode electrode; 210. Thyristor defect unit; 30. Functional layer. Detailed implementation manners

[0023] It should be noted that, without conflict, the embodiments in the present application and the features in the embodiments may be combined with each other. The present application will be described in detail below with reference to the drawings and in conjunction with the embodiments.

[0024] In order to enable those skilled in the art to better understand the solution of the present application, the technical solutions in the embodiments of the present application will be clearly and completely described below with reference to the drawings in the embodiments of the present application. Obviously, the described embodiments are only a part of the embodiments of the present application, rather than all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those of ordinary skill in the art without creative efforts shall fall within the protection scope 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 do not necessarily need to be used to describe a specific order or sequence. It should be understood that such data can be interchanged under appropriate circumstances so as to implement the embodiments of the present application described herein. In addition, the terms "include" and "have" and any variations thereof are intended to cover non-exclusive inclusions. For example, a process, method, system, product or device including a series of steps or units does not necessarily need to be limited to those steps or units clearly listed, but may include other steps or units not clearly listed or inherent to these processes, methods, products or devices.

[0026] As introduced in the background art, the voltage test of thousands of comb bars of the thyristor still consumes a large amount of time and cost, and cannot meet the requirements of batch device testing. The method of comb bar repair mainly relies on manual removal or micro-area grinding. Since the metal electrode is deposited on the comb bar by electron beam evaporation, its adhesion is relatively strong. When manually removing the metal electrode material on the surface of the comb bar, it is easy to have residues of the electrode material, and it is difficult for the electrode material to completely peel off, resulting in serious consequences such as device breakdown and short circuit.

[0027] To solve the above problems, according to the embodiments of the present application, Figure 1 It is a flowchart of the repair method of the thyristor defect unit provided by the embodiments of the present application, as Figure 1As shown, a method for repairing a defective thyristor unit is provided, including the following steps:

[0028] S1. Provide a wafer with a thyristor formed on its surface, and cover a functional layer on the first surface of the thyristor facing away from the wafer. The material of the functional layer includes a low-melting-point metal material, and the first surface is the surface of the thyristor on the side with the cathode electrode.

[0029] S2. Test the thyristor under target conditions to heat the defective thyristor unit in the thyristor. The defective thyristor unit is the cathode electrode of at least one thyristor unit in the thyristor. A depression is generated on the side surface of the part of the functional layer corresponding to the defective thyristor unit facing away, and the part of the functional layer in contact with the defective thyristor unit is alloyed with the defective thyristor unit. The target conditions include: the leakage current generated when the anode and cathode of the thyristor are in the reverse bias state reaches a preset value.

[0030] S3. Remove the remaining functional layer and the defective thyristor unit.

[0031] Through the above implementation, a functional layer is covered on the first surface of the thyristor facing away from the wafer. Under the target conditions, that is, when the anode and cathode of the thyristor are in the reverse bias state and the set leakage current reaches the preset value, at this time, the defective cathode electrode, that is, the defective thyristor unit, generates a heating effect under this target condition. Utilizing the low-melting-point characteristic of the functional layer material, the heating defective thyristor unit heats and melts the part of the functional layer in contact with the defective thyristor unit to make the exposed surface generate a depression, thereby accurately identifying the defective thyristor unit. The normal cathode electrode does not heat up to the melting point of the functional layer material, improving the accuracy and reliability of the screening. In addition, the test of the thyristor under the target conditions enables the simultaneous electrical performance test of all cathode electrodes on the wafer. The functional layer covering all cathode electrodes can simultaneously screen for defects in all cathode electrodes on the wafer, realizing the simultaneous test of all cathode electrodes on the wafer, improving the test efficiency, and reducing the test cost of a single cathode electrode; at the same time, the melted functional layer is alloyed with the defective thyristor unit. The defective thyristor unit in the heating state accelerates the alloying with the functional layer. After alloying, the cathode electrode becomes loose and brittle, reducing the adhesion force with the thyristor, and the defective thyristor unit is more easily removed, thus avoiding metal residue, realizing the precise repair of the defective thyristor unit, and solving the problems of high repair cost, low efficiency, and easy residue of the peeled electrode material in the related art.

[0032] Exemplary embodiments of the method for repairing thyristor defect cells provided according to the embodiments of the present application will be described in more detail below. However, these exemplary embodiments can be implemented in many different forms and should not be construed as being limited only to the embodiments set forth herein. It should be understood that these embodiments are provided so that the disclosure of the present application is thorough and complete, and the concept of these exemplary embodiments is fully conveyed to those of ordinary skill in the art.

[0033] First, perform step S1: Provide a wafer having a thyristor 20 formed on its surface, and cover a functional layer 30 on the first surface of the thyristor 20 facing away from the wafer. The material of the functional layer 30 includes a low-melting-point metal material. The first surface is the side surface of the thyristor 20 having the cathode electrode 21, and the structure shown in Figure 2 is formed, where the thyristor 20 includes a plurality of thyristor cells.

[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. During 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, it is possible to synchronously screen whether there is any cathode electrode that generates heat during the test on the cathode electrodes of the wafer, without the need for individual positioning and electrical contact, ensuring that the test conditions are consistent for all cathode electrodes, and reducing the instability caused by test contact points or positioning errors. This method significantly improves the test efficiency through one-time covering and subsequent global testing, reduces the dependence on complex test equipment, and thus reduces the test cost.

[0035] In some optional embodiments, the material of the functional layer includes one or more of rubidium, cesium, gallium, and alloys of gallium, and the material of the cathode electrode of the thyristor includes aluminum. These materials have low-melting-point characteristics. For example, the melting point of gallium is 29.8 °C, and the melting points of cesium and rubidium are also relatively low, which enables them to remain liquid at room temperature or slightly higher temperatures, facilitating spreading and forming a uniform functional layer. The low-melting-point characteristic also means that during the detection process, only a small amount of overheating is required to melt the material, so as to quickly identify the thyristor defect cells through the melted area. The alloying characteristics with aluminum enable these materials to form alloys when contacting the thyristor defect cells (the cathode electrode is an aluminum electrode). The alloyed area forms a contrast with the surrounding unalloyed functional layer material, and the alloy area is easier to operate during subsequent removal, making it easy to remove the thyristor defect cells by external force without residue.

[0036] Specifically, in the embodiments shown in the present application, the types of thyristors include one of IGCT and IGTO. Taking the IGCT device as an example, its wafer has a plurality of GCT cells, and each GCT cell has a cathode electrode on the side facing away from the wafer.

[0037] Specifically, the cathode electrodes of multiple thyristor units can form a comb electrode. That is, the comb electrode includes multiple comb units corresponding one-to-one to the thyristor units. The horizontal cross-sectional shape of each comb unit is strip-shaped, and its arrangement includes radial arrangement and staggered arrangement.

[0038] Since the non-uniform distribution of materials will introduce additional test errors and affect the accuracy and reliability of screening, in order to make the functional layer material uniformly distributed on the wafer, in some alternative 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 can include: First, pour and cover the liquid material of the functional layer on the wafer; by directly pouring the liquid material to cover the entire wafer, rapid and uniform distribution of the material is achieved, improving the efficiency of material spreading. At the same time, the fluidity of the liquid material helps it form a uniform thin film on the wafer, reducing the additional tests and calibrations increased due to uneven material distribution and lowering the test cost. Then, a cover plate is set on the wafer and pressed tightly; applying pressure to the cover plate helps eliminate air bubbles in the material, reduce voids, enabling the functional layer to form a denser structure on the surface of the thyristor, which helps improve the adhesion of the material to ensure that the functional layer material adheres more closely and uniformly to the surface of the cathode electrode. Finally, cool the material of the functional layer to form the functional layer and remove the cover plate; the cooling process solidifies the liquid metal to form a solid functional layer, and the solid functional layer serves as a temperature-sensitive medium in subsequent test processes to identify the heating positions of defective thyristor units.

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

[0041] Exemplarily, the cover plate is a low wettability substrate, including one or a combination of two of quartz sheet and polyimide sheet, but not limited to the above two. Those skilled in the art can reasonably select the type of the cover plate according to actual needs, and the present 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, and the substrate may also include other materials, which are not specifically limited in this application. The gallium liquid metal has a low surface tension on the copper metal substrate and can adhere flatly to the copper substrate. First, pour the gallium liquid metal on the copper substrate, and spread the liquid metal evenly on the copper substrate by means such as spin coating and brush coating, and cool and solidify the gallium metal into a gallium metal film at a low temperature of less than 20 °C, for example, to form a functional layer. Then, turn over the copper substrate so that the side of the copper substrate covered with the functional layer covers the IGCT wafer and press it tightly. Among them, apply a vertical pressure of 50 N - 100 N, for example, and lift the copper substrate at a low peeling speed of less than 1 mm / s, for example, to complete the removal of the copper substrate and complete the preparation of the gallium metal heating test film (i.e., the functional layer).

[0047] In some other alternative embodiments, the methods of covering the first surface of the thyristor facing 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., the functional layer) can be formed on the surface under the exposure of the natural environment. Before spreading the liquid metal, the liquid metal is subjected to a uniform stirring treatment 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, it also includes coating nanoparticles on the surface of the thyristor. The nanoparticles are, for example, silicon dioxide (SiO 2 2) microspheres. The micro-rough surface of the nanoparticles can provide more contact points, enabling the gallium metal film to 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 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 carried out: testing the thyristor under target conditions to heat the thyristor defect unit 210 in the thyristor. The thyristor defect 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 facing away from the part corresponding to the thyristor defect unit 210, and the part of the functional layer 30 in contact with the thyristor defect unit 210 is alloyed with the thyristor defect unit 210. The above target conditions include: the leakage current generated when the anode and cathode of the thyristor are in the reverse bias state reaches a preset value, forming a structure as shown in Figure 3 the figure.

[0050] Under target conditions, when the leakage current generated under the reverse bias state of the anode and cathode of the thyristor reaches a preset value, only the defective thyristor unit will heat up to melt the functional layer, improving the screening accuracy and ensuring that only the defective thyristor units are identified and marked. At the same time, an alloying reaction occurs between the cathode electrode and the melted functional layer. Among them, under local overheating, the alloying of the cathode electrode with the functional layer material is accelerated, making the material of the cathode electrode loose and reducing its adhesion to the thyristor, which is easy to remove by external means (such as a scraper) or chemical means. And because there are physical property differences between the alloying region and the surrounding unalloyed functional layer material, the removal operation can be more precise, avoiding damage to normal units and ensuring no residue of the functional layer material after removal, thus avoiding defects such as device breakdown and short circuit.

[0051] In addition, through one test process in this embodiment, the electrical performance of all cathode electrodes on the wafer can be detected simultaneously without testing each unit one by one, greatly improving the test efficiency. Since the number of test points is reduced, the requirements for test equipment and manpower are also reduced, thereby reducing the test cost.

[0052] Moreover, the above step S2 conducts the test under specific target conditions, triggering the alloying reaction between the functional layer material and the aluminum electrode by the heating of the defective thyristor unit. The defective thyristor unit not only improves the test efficiency and reduces the test cost, but also ensures the accuracy and residue-free of the removal and repair process, ultimately improving the performance consistency and preparation yield of the entire chip.

[0053] Exemplarily, the target conditions are as follows: Use a thyristor blocking voltage test bench to test the anode and cathode voltages corresponding to the anode and cathode leakage currents of the thyristor reaching 10 mA. During the test, if the gate-cathode reverse bias leakage current phenomenon occurs, the cathode electrode in the thyristor generating the leakage current is the defective thyristor unit, and its temperature will overheat, thus exceeding the melting point of the low-melting metal.

[0054] Exemplarily, the material of the functional layer is gallium, and the heating temperature of the defective thyristor unit is greater than 50 °C. In this temperature range, gallium is in a completely liquid state, and as the temperature increases, the viscosity of liquid gallium is lower, and its fluidity and activity are 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, making the aluminum metal electrode alloy faster.

[0055] In some alternative embodiments, the above-mentioned target conditions further 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 being 29.8°C) cause only the defective thyristor units to heat up above the melting point, and the normal cathode electrodes do not heat up and remain consistent with the ambient temperature. In this case, the defective cathode electrodes (i.e., the defective thyristor units) trigger an alloying reaction with the molten functional layer material, forming an obvious mark, avoiding misjudgment caused by ambient temperature fluctuations and improving the accuracy of the test.

[0056] In some alternative embodiments, the above-mentioned repair method in the embodiments of the present application further includes the step of screening the thyristor using image recognition software and an optical microscope to identify the depressions generated in the functional layer. The use of image recognition software in conjunction with the microscope can automatically analyze the depressions in the functional layer on the surface of the thyristor, eliminating 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, lowers labor costs, and also helps to reduce the subjective errors that may be brought about by manual inspection, thereby reducing costs. The optical microscope provides high-resolution images that can clearly show the depressions in the functional layer, and even tiny defects can be accurately identified. The image recognition software analyzes these images through algorithms and can precisely locate the depression areas, that is, the positions of the defective thyristor units, improving the accuracy and consistency of identification.

[0057] Exemplarily, the microscope includes one or more of a dark-field microscope, a laser confocal microscope, and a digital microscope, which can be selected by those skilled in the art according to actual needs, and the present application does not make specific limitations.

[0058] Exemplarily, a fluorescent labeling agent is added to the functional layer material. The fluorescent labeling agent includes europium-doped yttrium oxide (Eu:Y 2 O 3 ) whose fluorescence intensity will increase significantly when the temperature rises. Europium-doped yttrium oxide, as an inorganic fluorescent material, 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 with a specific wavelength, europium-doped yttrium oxide can produce a bright and stable fluorescent signal, facilitating a significant visual contrast between the alloying area and the non-alloying area, avoiding missed detection of depressions by the image recognition software and the microscope, and thus improving the reliability and accuracy of the screening.

[0059] After the step of alloying the part in the functional layer with the thyristor defect cells, step S3 is performed: removing the remaining functional layer and thyristor defect cells. Through the previous alloying reaction, the thyristor defect cells have been accurately located. When removing these thyristor defect cells, it can be carried out targeted, thereby improving the overall testing efficiency, reducing the testing cost, and ensuring the accuracy of the removal operation. Since the marking is accurately generated based on abnormal electrical performance in the previous test, after the defective ones are removed and repaired, the cathode electrodes with normal electrical performance are retained on the wafer, which further improves the accuracy of screening. The alloying of the functional layer material with the cathode electrodes of the thyristor defect cells changes the physical properties of these areas, making them loose and easy to remove. Appropriate means can easily remove these alloyed areas without residue and without damaging the surrounding normal cells.

[0060] In some alternative embodiments, such as Figure 4 shown, the step of removing the remaining functional layer and thyristor defect cells includes:

[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. Removing the thyristor defect cells.

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

[0064] Next, an exemplary embodiment of the step of removing the remaining functional layer and thyristor defect cells provided according to the embodiments of the present application will be described in more detail.

[0065] First, step S01 is executed, heating the remaining functional layer to convert the functional layer from a solid state to a liquid state and removing 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 a solid state to a liquid state, melting the remaining functional layer material for easy subsequent removal.

[0066] Specifically, the steps 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 purging 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 relatively high and its fluidity is improved. The liquid metal can be easily collected and recycled 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. Moreover, compared with polymer films, the functional layer material including low-melting-point metal materials has the characteristic of being more easily recycled, thus reducing material waste and lowering the test cost.

[0067] Finally, step S02 is executed to remove the defective thyristor units. In step S2, heating is performed to form an alloying region between the functional layer and the defective thyristor units. The properties of the alloying region change (such as becoming more porous and brittle, and the adhesion force with the thyristor weakening, etc.), making this part easy to be removed by external force means, and no damage is caused to normal thyristor units during the removal process, and material residues during the removal process are also reduced. The removal operation is based on the previous marking and alloying process, with a clear target and a controllable removal process, reducing misremoval or damage caused by improper operation, improving the stability and accuracy of removal and repair, and thus improving the overall performance and production yield of the thyristor device.

[0068] In some alternative embodiments, the removal methods of the defective thyristor units include any one or more of scraper removal, ultrasonic removal, vibration removal, air flow removal, and water flow flushing. The scraper operation is relatively simple and easy to control, reducing the uncertainty during operation; ultrasonic removal is fast and does not require additional physical tools, reducing tool costs and operation time; vibration removal can affect multiple defective thyristor units simultaneously, improving the processing speed, and by controlling the frequency and intensity of vibration, fine control of the removal process can be achieved; air flow or water flow removal is fast, and the removal effect can be controlled by adjusting the direction and pressure of the air flow or water flow, which is suitable for the processing of large-scale wafers. The use of the above methods can ensure the removal effect of the cathode electrode. Those skilled in the art should understand that the selection and application of each method need to be determined according to specific material characteristics, process requirements, and equipment conditions. The removal of defective thyristor units also includes other methods and ways. The above methods are taken as examples, and the present application does not make specific limitations.

[0069] In some alternative embodiments, the heating temperature of the remaining functional layer is greater than the melting point of the functional layer material and less than the heat generation 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 cause the functional layer material to change from a solid state to a liquid state, making the material easier to collect and remove. The low surface tension characteristic of the liquid metal helps it to form a shape that is easy to collect after heating, avoiding leaving residues on the surface of the thyristor and reducing subsequent cleaning work. By precisely controlling the heating temperature above the melting point of the functional layer material but below the heat generation temperature of the thyristor defect unit, it can ensure the complete melting of the functional layer material. Meanwhile, when heating in this temperature range, the alloying of the remaining functional layer material with the cathode electrode of the thyristor is slow, avoiding false screening or screening omission caused by improper temperature control, avoiding introducing new defects, and thus significantly improving the production yield of the chip.

[0070] In some alternative embodiments, after removing the thyristor defect unit, the method further includes the steps of: testing the thyristor again under target conditions and monitoring it using infrared thermal imaging 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 still overheated thyristor defect units in the cathode electrode during the test, accurately identify their positions and the degree of overheating, and screen for any missed thyristor defect units. Infrared imaging provides a more accurate, controllable, and reliable screening method for the 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 functional layer covering the thyristor melts and forms a depression when the thyristor defect unit overheats during the test under target conditions, rapid and overall screening of the thyristor defect unit can be achieved. Compared with the point-by-point scanning method, the screening method has higher working efficiency and lower test costs;

[0073] 2. During the test under target conditions, only the thyristor defect unit will have an overheating phenomenon (its heat generation temperature exceeds the melting point of the functional layer). Combining the extremely sensitive melting point characteristic of the liquid metal to temperature, precise screening of the thyristor can improve the accuracy and stability of defect screening;

[0074] 3. Since the liquid functional layer will alloy with the thyristor defect unit (cathode electrode), and accelerate the loosening and embrittlement of the thyristor defect unit at the high temperature when the thyristor defect unit generates heat, and reduce the adhesion force between the thyristor defect unit and the thyristor, making it easier to be removed by external force during the subsequent repair of the thyristor defect unit, and there will be no obvious residue, avoiding problems such as device breakdown and short circuit, improving the consistency of the thyristor chip performance, and the manufacturing yield of the thyristor chip.

[0075] It should also be noted that the term "including", "comprising" or any other variant thereof is intended to cover non-exclusive inclusion, so that a process, method, commodity or device including a series of elements not only includes those elements, but also includes other elements not expressly listed, or further includes elements inherent in such process, method, commodity or device. Without further limitation, an element defined by the statement "including one..." does not exclude the existence of another identical element in the process, method, commodity or device including the element.

[0076] The above are only the embodiments of the present application and are not used to limit the present application. For those skilled in the art, various changes and modifications can be made to the present application. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present application shall 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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