Silicon carbide corrosion device and working method thereof

Abstract

The invention relates to the technical field of defect characterization of silicon carbide single crystal substrate materials, in particular to a silicon carbide corrosion device and a working method thereof. The silicon carbide corrosion device comprises a crucible furnace, an inner lifting shaft and a basket; the crucible furnace comprises a furnace body and a furnace cover, a heating element is arranged outside the furnace body, the furnace body is provided with an oxygen inlet used for introducing oxygen and a gas discharge port used for discharging gas, the furnace cover covers the furnace body, the top of the furnace cover protrudes upwards to form an outer lifting shaft used for lifting the furnace cover, and the outer lifting shaft is provided with a through hole; the inner lifting shaft is inserted into the through hole of the outer lifting shaft, and the basket is installed at the bottom end of the inner lifting shaft and used for containing wafers. According to the method, different dislocation morphologies of the heavily nitrogen-doped substrate can be accurately distinguished, the corrosion efficiency is improved, the safety of operators is guaranteed, meanwhile, the operation process is simplified, and large-scale popularization and application are facilitated.

Description

Technical Field

[0001] The present invention relates to the technical field of defect characterization of silicon carbide single crystal substrate materials, and particularly to a silicon carbide etching device and its working method. Background Art

[0002] With the continuous progress of technology, many new scientific and technological devices need to work under special conditions of high frequency, high temperature, and strong radiation. As a representative material of the third-generation semiconductor, silicon carbide (SiC) has been widely used in new energy vehicles, rail transit, and smart grids due to its wide bandgap, high stability, high thermal conductivity, high critical breakdown voltage, etc., and has become one of the most promising new semiconductor materials at present. After nearly 30 years of development, significant breakthroughs have been made in silicon carbide single crystals in terms of microtube control and single crystal form control. However, in terms of dislocations, compared with silicon single crystals, the dislocation density in silicon carbide single crystals is still relatively high, which to a certain extent limits the performance of silicon carbide devices. Therefore, the accurate identification of silicon carbide wafer defects is of great significance for guiding single crystal growth processes.

[0003] Wet etching is currently the main method commonly used to characterize dislocations in silicon carbide. In wet etching, potassium hydroxide (KOH) is usually selected as the etchant. After heating it until it melts, the silicon carbide is placed in it for etching. Its etching principle is as follows: In a silicon carbide crystal, the stress at defects such as screw dislocations (TSD), edge dislocations (TED), and basal plane dislocations (BPD) is much greater than that at defect-free locations. Therefore, the etching rate at defect locations is faster than that at defect-free locations. Wet etching achieves selective etching in the material, and finally forms etching pits. Then, the microscopic defects of the wafer can be characterized using detection equipment.

[0004] The design concepts of existing silicon carbide etching furnaces can meet the etching conditions, but there are still many problems. For example, in CN217006621U, its design purpose is to improve the etching effect of silicon carbide wafers through a mesh frame structure and a magnetic stirrer, but it does not consider that the alkaline steam generated in the etching furnace will seriously affect the health of operators; for another example, in CN218994038U, although its designed double-chamber structure can block the leakage of alkaline steam, its horizontal design of the furnace body results in only one wafer being etched each time, with low efficiency and difficulty in replacing the etching solution. At the same time, to improve the etching efficiency of silicon carbide, most current choices are to add Na2O2 to KOH. However, this method requires considering the proportioning problems of different etchants. In addition, Na2O2 is a strong oxidizing chemical substance, which will affect the safety of operators and is not conducive to large-scale popularization and use.

[0005] For a doping concentration exceeding 1×10 19 cm -3For a heavily doped conductive SiC substrate, when using conventional KOH etching to characterize dislocations, it is found that the etching pits are difficult to appear, and thus the dislocations in the SiC substrate cannot be accurately characterized. This is because for a heavily doped conductive SiC substrate, during KOH etching, the etching process is no longer simply chemical etching, and the carriers in the substrate also participate in the reaction process, resulting in the failure of selective anisotropic etching of the substrate and the unclear distinction of etching pits for different dislocations. The method to solve this problem is to use electrochemical etching. For example, in Patent CN118392608A, by applying a bias voltage to the etching solution and the substrate to promote the generation of holes, the obvious distinction of the dislocation pit morphology can be achieved. However, the operation process of electrochemical etching is complex and is restricted by the uniformity of the current in the etching solution, and it cannot be currently applied to the dislocation characterization of large-sized heavily doped SiC substrates.

[0006] Therefore, the problems existing in the prior art are as follows:

[0007] ① For a heavily doped conductive SiC substrate, conventional KOH etching is difficult to show etching pits and cannot accurately characterize dislocations. Electrochemical etching has a complex operation process and is restricted by the uniformity of the current in the etching solution, making it difficult to be applied to the dislocation characterization of large-sized heavily doped SiC substrates.

[0008] ② The method of adding Na2O2 to accelerate the etching efficiency has problems with the etching agent ratio, and Na2O2 is a strong oxidizing chemical substance, which affects the safety of operators and is not conducive to large-scale popularization and use.

[0009] ③ In the existing etching methods, some etching devices have low efficiency. For example, the horizontal furnace body design results in only one wafer being etched each time, and it is difficult to replace the etching solution.

[0010] ④ The existing etching devices have potential health and safety hazards, and the alkaline steam generated in the etching furnace will seriously affect the health of operators. Summary of the Invention

[0011] Aiming at the deficiencies of the prior art, the purpose of the embodiments of the present invention is to provide an efficient and convenient silicon carbide etching device, which can accurately distinguish different dislocation morphologies of heavily nitrogen-doped substrates.

[0012] To achieve the above purpose, the embodiments of the present invention provide the following technical solutions:

[0013] A silicon carbide etching device, comprising: a crucible furnace, an inner lifting shaft and a basket; the crucible furnace includes a furnace body and a furnace cover, a heating element is arranged outside the furnace body close to the inner wall of the furnace body, an oxygen inlet for introducing oxygen and an oxygen outlet for discharging gas are arranged on the furnace body, the furnace cover covers the furnace body, and the top of the furnace cover bulges upward to form an outer lifting shaft for lifting the furnace cover, and the outer lifting shaft has a through hole; the inner lifting shaft is inserted into the through hole of the outer lifting shaft, and the basket is installed at the bottom end of the inner lifting shaft for holding wafers.

[0014] Optionally, the oxygen inlet is arranged at the upper outer extension part on one side of the furnace body, and the oxygen outlet is arranged at the bottom of the furnace body side wall. An oxygen channel is formed between the oxygen inlet and the oxygen outlet, and a one-way gas outlet device is also arranged at the oxygen outlet. This setting enables oxygen to enter the etching solution in the furnace body through the oxygen channel, and the one-way gas outlet device ensures that the etching solution will not flow back into the oxygen channel, ensuring the smooth introduction of oxygen and the stability of the etching solution, thereby improving the etching efficiency and safety.

[0015] Optionally, the one-way gas outlet device includes a rotating shaft and a cover plate. The rotating shaft is installed at the upper end of the oxygen outlet position on the inner wall of the furnace body, and the cover plate is rotatably installed on the rotating shaft, and the cross section of the cover plate is larger than the cross section of the oxygen outlet. This structure enables the pressure of oxygen to push the cover plate open when oxygen is introduced, allowing oxygen to enter the etching solution smoothly; after the oxygen supply stops, the cover plate automatically closes under the hydraulic pressure of the etching solution to prevent the etching solution from flowing back, forming a simple pneumatic valve, further improving the safety and reliability of the device.

[0016] Optionally, a fixing groove is arranged at the lower end of the inner lifting shaft, the fixing groove is T-shaped, the basket is suspended on the fixing groove of the inner lifting shaft, and a rangefinder is arranged on the lower cover surface of the furnace cover for measuring the height difference between the furnace cover and the liquid level. The design of the T-shaped fixing groove enables the basket to be stably suspended on the inner lifting shaft, ensuring the stability of the basket during the lifting process. The setting of the rangefinder can accurately measure the distance between the furnace cover and the etching solution liquid level, thereby providing an accurate basis for controlling the lifting of the basket, ensuring that the wafers can be accurately preheated and immersed in the etching solution, and improving the accuracy and uniformity of etching.

[0017] Optionally, a stirring device is installed on the inner lifting shaft through a clamping device. The clamping device includes a collar and a fixing screw. The fixing screw fixes the collar on the inner lifting shaft. The stirring device includes a connecting rod and a stirring plate. The upper end of the connecting rod is connected to the collar, and the stirring plate is arranged at the lower end of the connecting rod. The design of the stirring device enables the rotation of the stirring plate to be driven by the rotation of the inner lifting shaft during the corrosion process, thereby stirring the corrosion liquid, making the corrosion liquid fully mixed with oxygen, and improving the corrosion efficiency and uniformity. At the same time, the design of the clamping device enables the position of the stirring device to be adjusted as needed, increasing the flexibility and applicability of the device.

[0018] Optionally, a heat insulation layer is provided on the outer side of the furnace body. The heating element is installed in the heat insulation layer, and the heat insulation layer is made of alumina. The alumina heat insulation layer has good heat insulation performance, which can effectively reduce heat dissipation outside, improve the heating efficiency, and protect the safety of operators at the same time. The heating element is installed at a position close to the inner furnace body of the heat insulation layer, so that heat can be evenly transferred to the furnace body, ensuring the uniform temperature of the corrosion liquid and improving the stability and consistency of corrosion.

[0019] Optionally, a water inlet and a water outlet are provided on the furnace cover and are connected. The water outlet is arranged on the inner side wall of the furnace cover, and a drain pipe is provided on the furnace body and the heat insulation layer. After the corrosion is completed, water can be injected into the furnace body through the water inlet to dilute the corrosion liquid, and then the diluted waste liquid can be discharged through the drain pipe, which is convenient for the treatment of the waste liquid and the cleaning of the device, and improves the convenience and environmental protection of the device.

[0020] Optionally, the drain pipe includes a sub-drain pipe and a main drain pipe. Both the sub-drain pipe and the main drain pipe are arranged obliquely. There are multiple sub-drain pipes, all of which are arranged on the furnace body. The main drain pipe is arranged on the heat insulation layer. A partition plate is also provided in the furnace body to separate the sub-drain pipe and the main drain pipe. The layered drainage structure enables the sub-drain pipe to discharge the diluted waste liquid in time during the process of treating the waste liquid after corrosion, preventing the accumulation of the waste liquid from affecting the corrosion effect; the main drain pipe is used to discharge all the waste liquid centrally, improving the drainage efficiency and the stability of the device.

[0021] The embodiment of the present invention also provides a working method of the silicon carbide corrosion device as described above, including the following steps:

[0022] Simultaneously lift the inner lifting shaft and the outer lifting shaft to open the furnace cover. After pouring in solid pure potassium hydroxide, synchronously lower the inner and outer lifting shafts to close the furnace cover, heat up to the corrosion temperature and keep it warm;

[0023] Lift the inner and outer lifting shafts again to open the furnace cover, hang the basket carrying the substrate wafer, synchronously lower the inner and outer lifting shafts to close the furnace cover, preheat the wafer and then immerse it in the corrosion liquid to start corrosion;

[0024] At the beginning of corrosion, oxygen is introduced. After the predetermined corrosion time, heating and oxygen supply are stopped. The inner and outer lifting shafts are raised to take out the basket, and then the lifting shafts are lowered to close the furnace lid.

[0025] After the corrosion liquid cools and solidifies, water is injected for dilution until the potassium hydroxide solid is completely processed.

[0026] The corroded wafer substrate is tested, and the types and density information of dislocations are counted.

[0027] This working method realizes efficient and uniform corrosion of silicon carbide wafers by reasonably controlling the operating conditions and sequence of each step. At the same time, by introducing oxygen, the accuracy of dislocation identification and the corrosion efficiency are improved. The dilution and drainage operations facilitate waste liquid treatment and device cleaning. The whole process is safe, convenient and efficient.

[0028] Optionally, the oxygen flow rate is 5 sccm to 100 sccm, preferably 20 to 50 sccm. This enables oxygen to effectively mix with the corrosion liquid, accelerating the corrosion rate, while avoiding problems such as disorder of the corrosion liquid flow field caused by excessive oxygen flow rate or low corrosion efficiency caused by too small flow rate, ensuring the stability of the corrosion process and the accuracy of dislocation identification, and further optimizing the working effect of the silicon carbide corrosion device.

[0029] One or more technical solutions provided in the embodiments of the present invention have at least the following technical effects or advantages:

[0030] 1. The silicon carbide corrosion device includes a crucible furnace, an inner lifting shaft and a basket. The crucible furnace consists of a furnace body and a furnace lid. A heating element is provided outside the furnace body for heating. An oxygen inlet and a gas discharge port are provided on the furnace body. The top of the furnace lid forms an outer lifting shaft. The inner lifting shaft is inserted into the outer lifting shaft, and the basket is installed at the bottom of the inner lifting shaft for holding wafers. This structural design enables the device to perform the corrosion operation on silicon carbide wafers. The heating element heats the corrosion liquid in the furnace body. The oxygen inlet and outlet are used to introduce oxygen to assist corrosion, and the gas discharge port is used to discharge the gas generated during the corrosion process. The cooperation of the inner and outer lifting shafts realizes the lifting operation of the basket, thereby controlling the immersion and removal of the wafers. Through this device, different dislocation morphologies of the heavily nitrogen-doped substrate can be accurately distinguished, the corrosion efficiency is improved, the safety of operators is ensured, and at the same time, the operation process is simplified, which is convenient for large-scale popularization and application, so as to better meet the needs of defect characterization of silicon carbide single crystal substrate materials, and further guide the single crystal growth process and improve the performance of silicon carbide devices.

[0031] 2. There are two main advantages to introducing oxygen into the etching solution. One is that after adding oxygen, the reaction between the etching solution and the silicon carbide substrate becomes more intense, which can accelerate the rate of molten potassium hydroxide etching the silicon carbide substrate, thereby increasing the etching efficiency and facilitating subsequent large-scale etching. The other is that introducing oxygen is conducive to generating more holes during the etching process, promoting selective anisotropic etching at different defect sites (such as TSD, TED, and BPD), so that clearer and more obvious differences are shown in the morphology of the etching pits, realizing precise differentiation of different dislocation etching pits on the heavily doped silicon carbide substrate.

[0032] 3. In the nickel crucible furnace body of the present invention, an oxygen inlet and an oxygen outlet are provided, and an oxygen channel is formed between them, so that the function of introducing oxygen into the etching solution during the etching process can be realized. A one-way air outlet device is designed at the oxygen outlet to form a simple pneumatic valve, thus ensuring that the etching solution will not flow back into the oxygen channel. At the same time, a stirring plate is provided to fully stir the alkali solution to achieve full mixing of the introduced oxygen and the alkali solution, further improving the accuracy of dislocation identification.

[0033] 4. The lifting shaft of the present invention is designed in two parts. The inner lifting shaft controls the lifting and rotation of the basket, and the outer lifting shaft controls the lifting of the nickel furnace cover. During etching, the outer lifting shaft can be controlled to lower the nickel furnace cover to prevent the overflow of alkali vapor at high temperature, and then the inner lifting shaft can be controlled to slowly lower the basket, which can not only ensure the full preheating of the wafers in the basket, but also avoid the harm to the health of experimental personnel caused by the overflow of corrosive alkali vapor.

[0034] 5. Through the water inlet provided on the crucible cover and the drain pipe provided in the crucible of the present invention, water can be injected into the crucible in batches to dissolve solid potassium hydroxide and drain it after the crucible cools down after etching, which is convenient for replacing the waste liquid. Also, through the horizontal gas discharge port provided on the side wall of the nickel furnace cover, while preventing the cold precipitation and blockage of the discharge port when the alkali vapor is discharged, the corrosive gas and excess oxygen can be discharged from the nickel crucible, which is convenient for treatment.

[0035] 6. Compared with methods such as electrochemical etching and additional addition of Na2O2, the process flow of the method in the present invention is simpler, environmentally friendly, and conducive to popularization and application.

[0036] 7. The method in the present invention is applicable to N-type, P-type, and high-purity semi-insulating SiC substrates, especially suitable for conductive substrates with higher doping concentrations.

[0037] Advantages of additional aspects of the present invention will be given in the following description, some of which will become obvious from the following description, or be understood through the practice of the present invention. Brief Description of the Drawings

[0038] To more clearly illustrate the technical solutions in the embodiments of the present application or the prior art, the following will briefly introduce the drawings required for the description of the embodiments or the prior art. Obviously, the drawings described below are only some embodiments recorded in the present application. For those of ordinary skill in the art, without creative efforts, other drawings can also be obtained based on these drawings. In addition, the distances or sizes between components are exaggerated for showing their positions, and the schematic diagrams are only for illustration purposes.

[0039] Figure 1 is a schematic diagram of a silicon carbide etching device provided by an embodiment of the present invention;

[0040] Figure 2 is a schematic diagram of a unidirectional gas outlet device provided by an embodiment of the present invention;

[0041] Figure 3 is a schematic diagram of the dissolution situation of solid potassium hydroxide after water is injected into the nickel crucible furnace body after the corrosion ends in an embodiment of the present invention;

[0042] Figure 4 is an image of the optical microscope imaging after corrosion in Embodiment 1 of the present invention;

[0043] Figure 5 is an image of the optical microscope imaging after corrosion in Comparative Example 2 of the present invention;

[0044] Figure 6 is an image of the optical microscope imaging after corrosion in Comparative Example 3 of the present invention;

[0045] In the figure: 1. Nickel crucible furnace body; 2. Heat insulation layer; 3. Heating element; 4. Wafer; 5. Basket; 6. Corrosion liquid; 7. Oxygen inlet; 8. Oxygen outlet; 9. Oxygen channel; 10. Unidirectional gas outlet device; 11. Nickel furnace cover; 12. Gas discharge port; 13. Water inlet; 14. Water outlet; 15. Rangefinder; 21. Inner lifting shaft; 22. Outer lifting shaft; 23. Fixed groove; 31. Clamping device; 32. Fixed screw; 33. Connecting rod; 34. Stirring plate; 41. Sub-drain pipe; 42. Main drain pipe; 43. Nickel partition plate; 101. Rotating shaft; 102. Circular nickel cover plate; 201. Potassium hydroxide dilution solution; 202. Solid potassium hydroxide; Detailed implementation manners

[0046] It should be noted that the following detailed descriptions are all illustrative and are intended to provide further explanations for the present invention. Unless otherwise specified, all technical and scientific terms used in the present invention have the same meanings as those commonly understood by those of ordinary skill in the technical field to which the present invention belongs. In addition, it should also be understood that when the terms "include" and / or "comprise" are used in this specification, they indicate the presence of features, steps, operations, devices, components, and / or their combinations.

[0047] The following will specifically describe a silicon carbide etching device proposed in this embodiment, which is safe, efficient and conducive to subsequent dislocation detection, including the following structures: Figure 1 , Figure 2 Specifically describe a silicon carbide etching device proposed in this embodiment, which is safe, efficient and conducive to subsequent dislocation detection, including the following structures:

[0048] The nickel crucible furnace body 1 is used to hold KOH for etching. The outside of the furnace body is wrapped by a heat insulation layer 2, which can play a role in heat preservation during heating. A heating element 3 is provided on the side of the heat insulation layer 2 close to the furnace body. The heating element 3 is used to heat the nickel crucible furnace body 1 to heat the solid KOH in the crucible to a molten state. A circular oxygen inlet 7 is provided at the upper extension part on one side of the nickel crucible furnace body 1, and a circular oxygen outlet 8 is also provided near the bottom part of the nickel crucible furnace body. An oxygen channel 9 is formed between the oxygen inlet 7 and the oxygen outlet 8 for introducing oxygen from the outside into the etching solution, so as to accurately identify the dislocations of the heavily doped substrate and accelerate the etching rate.

[0049] The diameter of the crucible of the nickel crucible furnace body can be 250 mm to 450 mm, and the internal height is 300 mm to 600 mm. While ensuring that the etching basket can be accommodated, a space for the stirring plate to stir is left to ensure smooth stirring. The maximum diameter of the basket needs to be 40 - 80 mm smaller than the diameter of the crucible to facilitate normal stirring by the stirring plate. The side wall height of the nickel furnace cover can be 100 mm to 350 mm. If the side wall is too low, it is difficult to ensure enough lifting space during wafer preheating; if the side wall is too high, it will waste space.

[0050] The basket can be set to 1 - 6 layers, and the interval between the upper and lower layers of the basket can be 5 mm to 40 mm, and different numbers of wafers can be etched simultaneously according to the etching requirements.

[0051] The diameter of the oxygen inlet can be 1 mm to 25 mm. The diameter of the oxygen outlet can be 1 mm to 25 mm, and the diameter of the oxygen channel can be 1 mm to 25 mm. The diameters of the oxygen inlet, oxygen outlet and oxygen channel should be kept the same to ensure more uniform inflow of the introduced oxygen. If the diameters of the three are too small, it will cause too much pressure when oxygen is introduced into the etching solution, disturbing the flow field; if they are too large, it will cause the size of the unidirectional gas outlet device to be too large and the blocking effect to fail. The oxygen outlet can be set at a position 10 - 100 mm from the bottom of the crucible to ensure that the wafers in the basket can contact the introduced oxygen during etching. The diameter of the gas discharge port can be set to 5 mm to 25 mm. The gas discharge port is connected to an anti-corrosion exhaust pipe, and the exhaust pipe can be connected to a tail gas treatment device.

[0052] In the part where the oxygen outlet 8 contacts the etching solution 6 in this embodiment, a one-way gas outlet device 10 is also provided for blocking. The one-way gas outlet device 10 includes a rotatable rotating shaft 101 and a circular nickel cover plate 102 connected to the rotating shaft 101. The diameter of the circular nickel cover plate needs to be 5-20 mm larger than the diameter of the oxygen outlet. In actual use, when oxygen is not introduced, the nickel cover plate remains closed due to the hydraulic action of the etching solution 6 to prevent the molten KOH from entering the oxygen channel. After oxygen is introduced, when the air pressure of the oxygen on the circular nickel cover plate 102 is greater than the hydraulic pressure, the rotating shaft 101 will drive the circular nickel cover plate 102 to open, so that oxygen enters the etching solution 6 and mixes. After the etching is completed, oxygen supply is slowly stopped. When the hydraulic pressure is greater than the air pressure, the circular nickel cover plate 102 will close again, thus forming a simple pneumatic valve structure to prevent the etching solution 6 from entering the oxygen channel 9 before and after oxygen supply for etching.

[0053] The nickel furnace cover 11 is integrally in an inverted "C" shape with an open bottom. A gas discharge port 12 is provided on one side wall of the nickel furnace cover 11. The gas discharge port 12 is used to discharge corrosive gases and excess oxygen outside the nickel crucible furnace body for easy treatment. In this embodiment, the gas discharge port 12 is provided on the side wall instead of the top mainly because when the KOH alkali vapor sublimates to the vicinity of the nickel furnace cover, it may condense and solidify. If the gas discharge port 12 is provided on the top, the discharge port may be blocked. However, when it is provided on the side wall of the nickel furnace cover 11, if the alkali vapor condenses and solidifies, it will only solidify below the circular discharge port and will not block the entire discharge port. In this case, the gas discharge port 12 can still function normally.

[0054] The nickel furnace cover 11 of this embodiment is also provided with a water inlet 13 and a water outlet 14 for introducing water for diluting the etching solution into the nickel crucible furnace body 1 after etching. The water inlet 13 is provided at the joint of the nickel furnace cover 11 and the outer lifting shaft 22. There are two water outlets 14 in total, which are respectively arranged oppositely on the side wall of the nickel furnace cover 11 near the top. The purpose of arranging the water outlet 14 on the side wall near the top is to facilitate the water to flow down from the inside of the side wall and wash the inside of the nickel crucible furnace body 1 while diluting the solid KOH after etching. The water inlet 13 is connected to the two water outlets 14 respectively inside the nickel furnace cover. In actual use, after the etching is completed, the water inlet 13 is connected to a water pipe, and water for diluting the solidified KOH is introduced into the nickel crucible furnace body through the oppositely arranged water outlets 14.

[0055] In this embodiment, a distance measuring instrument 15 is also provided on the lower cover surface of the nickel furnace cover 11. In actual use, the height difference between the upper cover and the upper liquid level of the etching solution 6 is measured by the distance measuring instrument 15 and converted to obtain the distance between the lowermost wafer 4 and the liquid level, which is convenient for controlling the lifting distance of the basket 5 subsequently to achieve the effect of accurately controlling the wafer preheating.

[0056] The inner lifting shaft 21 and the outer lifting shaft 22 are coaxial structures. The inner lifting shaft 21 is used to control the lifting and uniform rotation of the basket, and can drive the stirring plate and the basket to lift or rotate together, so as to realize the stirring of the molten etching solution and ensure that the etching rates of all parts of the wafers in the basket are the same. The rotation speed during etching can be 0.1 - 5 r / min, and preferably 0.5 r / min - 2 r / min. If the rotation speed is too slow, it will lead to uneven etching; if the rotation speed is too fast, it will disrupt the flow field of the etching solution, resulting in poor etching effect. The outer lifting shaft 22 is used to control the lifting of the nickel furnace cover. A T-shaped fixing groove 23 is arranged at the lower part of the inner lifting shaft 21, which is used to hang and fix the basket 5 and control its lifting and rotation; the outer lifting shaft 22 is sleeved outside the inner lifting shaft 21 and is an integral structure with the nickel furnace cover 11, which is used to control the lifting of the nickel furnace cover.

[0057] During actual use, first control the inner lifting shaft 21 to rise so that the fixing groove 23 is at the same height as the lower surface of the nickel furnace cover 11. After the etching solution 6 reaches the set etching temperature, simultaneously control the inner lifting shaft 21 and the outer lifting shaft 22 to rise, open the nickel furnace cover 11, and then quickly hang the basket 5 carrying the wafers 4 onto the fixing groove 23. After hanging and fixing, control the inner lifting shaft 21 and the outer lifting shaft 22 to descend the same distance, so that the nickel furnace cover 11 covers the nickel crucible furnace body 1 to ensure that the corrosive alkaline vapor will not overflow. Then control the inner lifting shaft 21 to descend a certain distance but not touch the liquid surface of the etching solution 6, so that the wafers can be fully preheated, and then control the inner lifting shaft 21 to descend so that the wafers 4 are immersed in the etching solution 6 to start etching. This design can effectively prevent the continuous overflow of the corrosive alkaline vapor during wafer preheating.

[0058] The clamping device 31 is a circular collar, which is sleeved on the inner lifting shaft 21 and fixed at a certain fixed position on the inner lifting shaft 21 through a fixing screw 32. The clamping device 31 is connected to the stirring plate 34 through two connecting rods 33, which is used to stir the etching solution to make the etching and oxygen fully mixed. During actual use, before hanging the basket, first sleeve the clamping device 31 on the inner lifting shaft 21, and make the clamping device 31 fixed at a certain position on the inner lifting shaft 21 by tightening the fixing screw 32. The fixed position can be determined according to the liquid level height of the etching solution 6 and the depth that the stirring plate 34 wants to stir. During etching, the clamping device 31 will rotate together with the inner lifting shaft 21, and the connecting rods 33 and the stirring plate 34 will also rotate with the clamping device, playing a stirring role, which can make the etching solution and the introduced oxygen be fully stirred evenly. At the same time, because the stirring plate is fixed on the inner lifting shaft 21, the stirring plate 34 can rotate stably during stirring and will not bump into the nickel crucible furnace body 1 or the basket 5, so as to avoid the wafers 4 inside the basket 5 from being broken after the basket 5 is collided.

[0059] The ferrule, fixing screw, connecting rod, and stirring plate are made of materials such as nickel and platinum that are resistant to high-temperature corrosion by potassium hydroxide. The diameter of the stirring plate needs to be determined according to the diameter of the crucible, and the diameter of the stirring plate needs to be 20 mm to 40 mm smaller than the diameter of the crucible.

[0060] The sub-drain pipes 41 and the main drain pipe 42 are respectively arranged in the nickel crucible furnace body 1 and the heat insulation layer 2, and the two are separated by a nickel partition plate 43 arranged in the nickel crucible furnace body, and the two are used to discharge the diluted corrosion liquid 6 outward after corrosion. In this embodiment, a total of 8 sub-drain pipes 41 are arranged at intervals from top to bottom in sequence, and these sub-drain pipes 41 are inclined downward at the same angle until the boundary between the nickel crucible furnace body 1 and the heat insulation layer 2; the inclination direction of the main drain pipe 42 is the same as that of the sub-drain pipes 41.

[0061] The number of sub-drain pipes can be set from 3 to 15, and 8 to 10 are optimal. The interval between each sub-drain pipe depends on the quantity, but the interval between the upper and lower sub-drain pipes is fixed. The diameter of the sub-drain pipe is 1 to 15 mm, and 4 to 8 mm is optimal; the direction is inclined downward at 4° to 20°, and 5° to 10° is optimal. A nickel partition plate is provided between each sub-drain pipe and the main drain pipe to prevent the corrosion liquid from flowing out during corrosion.

[0062] The diameter of the main drain pipe is 1 to 15 mm, and 8 to 12 mm is optimal; the direction is inclined downward at 4° to 20°, and 5° to 10° is optimal. The main drain pipe can be connected to an external drain pipe and a waste liquid bucket. If the diameter and inclination angle of the sub-drain pipe and the main drain pipe are too small, it will cause drainage difficulties; if they are too large, it will cause the water flow rate to be too large and difficult to control.

[0063] During actual use, during the corrosion process, first insert the nickel partition plate 43 into the card slot in the nickel crucible furnace body 1 to prevent the corrosion liquid from flowing out through the sub-drain pipes 41. After the corrosion ends and the corrosion liquid 6 cools and solidifies, pull out the nickel partition plate 43, and repeatedly pass an appropriate amount of water into the nickel crucible furnace body 1 through the water inlet 13 and the water outlet 14, so that the solid potassium hydroxide near the solid surface dissolves into a solution and flows out of the nickel crucible furnace body 1 along the sub-drain pipes 41 and finally flows out from the main drain pipe 42.

[0064] As Figure 3 shown, when water is passed into the nickel crucible furnace body 1 to dilute the solid potassium hydroxide 202, since the concentration of the potassium hydroxide dilution liquid 201 continuously rises and finally reaches the dilution limit, only the potassium hydroxide solid with a certain thickness near the upper surface of the solid will finally dissolve and liquefy. Therefore, it is necessary to timely discharge this part of the potassium hydroxide dilution liquid 201 from the nickel crucible furnace body 1 and then repeat adding water to dilute it. Therefore, it is necessary to arrange multiple sub-drain pipes 41 at equal intervals up and down so as to timely discharge the potassium hydroxide dilution liquid 201.

[0065] Based on the above silicon carbide etching device, this embodiment also provides its working method, including:

[0066] Step 1: Control the inner lifting shaft and the outer lifting shaft to synchronously lift to the upper limit to open the nickel furnace cover, clean the inside of the nickel crucible furnace body and check whether the one-way gas outlet device is closed. Insert the nickel partition board, and connect the gas discharge port to an external waste gas treatment device. Pour 5 kg to 10 kg of solid pure potassium hydroxide into the nickel crucible furnace body, and then control the inner lifting shaft and the outer lifting shaft to synchronously descend until the nickel furnace cover is completely closed. Control it to gradually heat up to an etching temperature of 450 °C to 550 °C through the equipment program and keep it warm for 0.5 h to 10 h.

[0067] Step 2: Control the inner lifting shaft and the outer lifting shaft to synchronously lift to the upper limit to open the nickel furnace cover, quickly put the clamping device on the inner lifting shaft, and fix it with fixing screws after determining the position of the clamping device according to the required stirring depth. Hang the basket carrying the substrate wafer on the fixing groove, and then control the inner lifting shaft and the outer lifting shaft to synchronously descend until the nickel furnace cover is completely closed to ensure that the corrosive alkali vapor will not overflow. Read the reading of the rangefinder to determine the distance between the lowermost substrate wafer and the etching solution surface at this time, and then control the inner lifting shaft to descend a certain distance so that the lowermost wafer is 150 - 250 mm away from the liquid surface, wait for 3 - 10 min to preheat the wafer preliminarily, then control the inner lifting shaft to descend another certain distance so that the wafer is 50 - 130 mm away from the liquid surface, wait for 3 - 10 min to preheat the wafer again, and then control the inner lifting shaft to descend to the lower limit to immerse the wafer in the etching solution to start etching.

[0068] Step 3: Connect the oxygen tank to the oxygen inlet, and introduce oxygen with a flow rate of 5 sccm to 100 sccm into the etching solution simultaneously when the etching starts (if the introduced oxygen flow rate is too small, the etching rate will be too slow and the selective anisotropic etching of dislocations will not be obvious; if the introduced oxygen flow rate is too large, it will disrupt the etching solution flow field and lead to poor etching effect). The pressure of the oxygen will open the one-way gas outlet device, so that the oxygen can be smoothly mixed with the etching solution to accelerate the etching rate. During etching, set the rotation speed of the inner lifting shaft to 0.1 r / min to 5 r / min to drive the basket and the stirring plate to rotate.

[0069] Step 4: After 5 - 30 minutes from the start of etching, end the etching, stop heating, stop oxygen supply, and the one-way gas outlet device is closed under the influence of hydraulic pressure. Control the inner lifting shaft and the outer lifting shaft to synchronously lift to the upper limit, and quickly take out the basket. Then lower the inner lifting shaft and the outer lifting shaft and quickly close the nickel furnace cover to prevent the high-temperature alkali vapor from overflowing and harming the human body at this time.

[0070] Step Five: After the etching solution cools and solidifies, connect the water inlet to a water pipe and inject 500 ml to 2000 ml of water for dilution into the nickel crucible furnace body. At the same time, pull out the nickel partition plate so that the dilution solution can be discharged from the nickel crucible furnace body through the main drain pipe, and wait for 5 to 30 minutes for complete dilution. Then repeat the above dilution operation until all the potassium hydroxide solids in the nickel crucible furnace body are completely processed.

[0071] Step Six: Use a wafer flaw detector to test and count various dislocations on the etched wafer substrate, and obtain information such as the types and densities of dislocations on the substrate.

[0072] The following further illustrates the technical solutions claimed in the present invention through several examples and comparative examples:

[0073] Example 1

[0074] In this example, the crucible diameter of the nickel crucible furnace body 1 is set to 300 mm, and the internal height is 400 mm; the diameter of the basket 5 is 250 mm; the side wall height of the nickel furnace cover 11 is 200 mm. The diameters of the oxygen inlet 7, oxygen outlet 8 and oxygen channel 9 are all 10 mm, and the oxygen outlet 8 is set at a position 50 mm from the bottom of the crucible; the diameter of the circular nickel cover plate 102 is set to 20 mm; the diameter of the gas discharge port 12 is set to 10 mm; the diameter of the stirring plate 34 is set to 275 mm; eight sub-drain pipes 41 are arranged at intervals up and down, with an equal distance of 30 mm up and down. The lowermost sub-drain pipe 41 is set at the bottommost position of the inner side wall of the crucible. At the same time, the diameter of the sub-drain pipe 41 is set to 4 mm, and the direction is 8° obliquely downward; the diameter of the main drain pipe 42 is set to 8 mm, and the direction is 8° obliquely downward; the basket 5 is set to 4 layers in total, and the interval between the upper and lower layers of the basket 5 is 25 mm.

[0075] In this example, the size of the substrate wafer selected for etching is 8 inches, and the average nitrogen doping concentration is 1.2×10 19 cm -3 .

[0076] The specific operation process during etching using the device described in this example includes the following steps:

[0077] Step One: Control the inner lifting shaft and the outer lifting shaft to be lifted synchronously to the upper limit, open the nickel furnace cover, clean the inside of the nickel crucible furnace body and check whether the one-way air outlet device is closed. Insert the nickel partition plate well, and connect the gas discharge port to an external waste gas treatment device. Pour 8 kg of solid pure potassium hydroxide into the nickel crucible furnace body, and then control the inner lifting shaft and the outer lifting shaft to descend synchronously until the nickel furnace cover is completely closed. Use the program control equipment to raise the temperature from room temperature to the etching temperature of 550 °C within 4 hours and keep it warm for 1 hour.

[0078] Step 2: Control the inner lifting shaft and the outer lifting shaft to be lifted synchronously to the upper limit to open the nickel furnace cover. Quickly put the clamping device on the inner lifting shaft. After determining the position of the clamping device according to the required stirring depth, fix it with the fixing screw. Hang the basket carrying the substrate wafer on the fixing groove, and then control the inner lifting shaft and the outer lifting shaft to descend synchronously until the nickel furnace cover is completely closed to ensure that the corrosive alkaline vapor will not overflow. Read the reading of the rangefinder to determine the distance between the lowermost substrate wafer and the surface of the etching solution at this time. Then control the inner lifting shaft to descend a certain distance so that the lowermost wafer is 200 mm away from the liquid surface, wait for 5 minutes to preheat the wafer preliminarily, then control the inner lifting shaft to descend another certain distance so that the wafer is 80 mm away from the liquid surface, wait for 5 minutes to preheat the wafer again, and then control the inner lifting shaft to descend to the lower limit to immerse the wafer in the etching solution to start etching.

[0079] Step 3: Connect the oxygen tank to the oxygen inlet. While the etching starts, introduce oxygen with a flow rate of 5 sccm into the etching solution. The pressure of the oxygen will open the one-way gas outlet device, enabling the oxygen to mix with the etching solution smoothly and accelerating the etching rate. During the etching, set the rotation speed of the inner lifting shaft to 1 r / min to drive the basket and the stirring plate to rotate.

[0080] Step 4: Set the etching time to 11 minutes. After the etching is completed, stop heating and stop introducing oxygen. The one-way gas outlet device is closed under the influence of hydraulic pressure. Control the inner lifting shaft and the outer lifting shaft to be lifted synchronously to the upper limit, and quickly take out the basket. Then lower the inner lifting shaft and the outer lifting shaft again and quickly close the nickel furnace cover to prevent the high-temperature alkaline vapor from overflowing and harming the human body at this time.

[0081] Step 5: After the etching solution cools and solidifies, connect the water inlet to the water pipe and inject 1000 ml of water for dilution into the nickel crucible furnace body. At the same time, pull out the nickel partition board so that the dilution liquid can be discharged from the nickel crucible furnace body through the main drain pipe, and wait for 10 minutes for complete dilution. Then repeat the above dilution operation until all the potassium hydroxide solids in the nickel crucible furnace body are completely processed.

[0082] Step 6: Use a wafer flaw detector to test and count various dislocations on the etched wafer substrate to obtain information such as the types and densities of dislocations on the substrate.

[0083] The substrate wafer obtained after etching in Example 1 was cleaned and then placed under the wafer flaw detector for detection. The obtained image is as Figure 4 shown. The etching pits of TSD, TED, and BPD in the figure can be clearly distinguished, and there are obvious differences in size. It is confirmed that the method described in the present invention can effectively achieve the accurate identification of different types of dislocations in heavily doped silicon carbide, and at the same time can effectively accelerate the etching rate and improve the etching efficiency.

[0084] Example 2

[0085] The difference between this embodiment and Embodiment 1 is that the average nitrogen doping concentration of the selected wafer for etching is 1.4×10 18 cm -3 , the set etching temperature before etching is reduced to 450 °C, oxygen with a flow rate of 100 sccm is introduced at the beginning of etching, and the etching time is set to 30 min, and the rest is the same as Embodiment 1.

[0086] Embodiment 3

[0087] The difference between this embodiment and Embodiment 1 is that the nitrogen doping concentration of the selected wafer for etching is lower than the secondary ion mass spectrometry detection limit, indicating that the nitrogen doping concentration is lower than 1×10 15 cm -3 , the set etching temperature before etching is increased to 500 °C, oxygen with a flow rate of 50 sccm is introduced at the beginning of etching, and the etching time is set to 15 min, and the rest is the same as Embodiment 1.

[0088] The substrate wafers obtained after etching in Embodiment 2 and Embodiment 3 were cleaned and then placed under a wafer defect detector for inspection. The obtained images were similar to those obtained in Embodiment 1, further confirming that the method described in the present invention can effectively etch N-type and high-purity semi-insulating SiC substrates, especially for conductive substrates with a relatively high doping concentration, while accelerating the etching rate and improving the etching efficiency.

[0089] Comparative Example 1

[0090] The difference between this comparative example and Embodiment 1 is that no additional oxygen is introduced during the etching process, and the rest is the same as Embodiment 1.

[0091] The substrate wafer obtained after etching in Comparative Example 1 was cleaned and then placed under a wafer defect detector for inspection. It was found that the etching pits in the image were extremely small and had no characteristic appearance, and it was impossible to distinguish the types of dislocations. This shows that for heavily doped substrates, it is impossible to accurately identify the types of dislocations under the condition of not introducing oxygen.

[0092] Comparative Example 2

[0093] The difference between this comparative example and Embodiment 1 is that oxygen with a flow rate of 200 sccm is introduced at the beginning of etching, and the rest is the same as Embodiment 1.

[0094] The substrate wafer obtained after etching in Comparative Example 2 was cleaned and then placed under a wafer defect detector for inspection. The obtained image is as shown in Figure 5 . In the figure, the overlapping of etching pits is serious, and the dislocations are all circular in the same size, and it is impossible to accurately identify the types of dislocations. This shows that excessive oxygen introduction will lead to over-etching and it is impossible to effectively and accurately identify the types of dislocations.

[0095] Comparative Example 3

[0096] The difference between this comparative example and Example 1 is that oxygen with a flow rate of 1 sccm is introduced at the beginning of the corrosion, and the rest is the same as in Example 1.

[0097] The substrate wafer obtained after the corrosion in Comparative Example 3 was cleaned and then placed under a wafer flaw detector for inspection. The resulting image is as Figure 6 shown. In the figure, the number of corrosion pits is extremely small, and the dislocations are all oval in shape with the same size. This shows that too little oxygen supply will lead to under-corrosion and cannot effectively and accurately identify the dislocation types.

[0098] Although the specific implementation manners of the present invention have been described above in conjunction with the accompanying drawings, it is not a limitation to the protection scope of the present invention. Those skilled in the art should understand that various modifications or deformations that can be made without creative efforts on the basis of the technical solutions of the present invention are still within the protection scope of the present invention.

Claims

1. A silicon carbide etching device, characterized in that: include: Crucible furnace, internal lifting shaft and basket; The crucible furnace comprises a furnace body and a furnace cover, wherein a heating element is arranged outside the furnace body, an oxygen inlet for introducing oxygen and a gas discharge port for discharging gas are arranged on the furnace body, the furnace cover is covered on the furnace body, the top of the furnace cover protrudes upward to form an outer lifting shaft for lifting the furnace cover, and the outer lifting shaft has a through hole; The inner lifting shaft is inserted into the through hole of the outer lifting shaft, and the basket is installed at the bottom end of the inner lifting shaft for containing wafers.

2. The silicon carbide etching device according to claim 1, characterized in that: The oxygen inlet is arranged at the upper extension part of one side of the furnace body, an oxygen outlet is arranged at the bottom of the side wall of the furnace body, an oxygen channel is formed between the oxygen inlet and the oxygen outlet, and a one-way gas outlet device is also arranged at the oxygen outlet.

3. The silicon carbide etching device according to claim 2, characterized in that: The one-way gas outlet device comprises a rotating shaft and a cover plate. The rotating shaft is mounted on the upper end of the oxygen outlet position of the inner wall of the furnace body. The cover plate is rotatably mounted on the rotating shaft, and the cross section of the cover plate is larger than the cross section of the oxygen outlet.

4. The silicon carbide etching device according to claim 1, characterized in that: A fixing groove is arranged at the lower end of the inner lifting shaft, and the fixing groove is T-shaped. The basket is suspended on the fixing groove of the inner lifting shaft. A distance meter is arranged on the lower cover surface of the furnace cover for measuring the height difference between the furnace cover and the liquid level.

5. The silicon carbide etching device according to claim 1, characterized in that: A stirring device is installed on the inner lifting shaft through a fixing device, and the fixing device includes a ring and a fixing screw. The fixing screw fixes the ring on the inner lifting shaft. The stirring device includes a connecting rod and a stirring plate. The upper end of the connecting rod is connected to the ring, and the stirring plate is arranged at the lower end of the connecting rod.

6. The silicon carbide etching device according to claim 1, characterized in that: A heat insulation layer is arranged outside the furnace body, the heating element is installed in the heat insulation layer, and the heat insulation layer is made of aluminum oxide.

7. The silicon carbide etching device according to claim 6, characterized in that: The furnace cover is provided with a connected water inlet and a water outlet, the water outlet is arranged on the inner side wall of the furnace cover, and the furnace body and the heat insulation layer are provided with a drainage pipe.

8. The silicon carbide etching device according to claim 7, characterized in that: The drain pipe includes a branch drain pipe and a main drain pipe, both of which are arranged obliquely. There are multiple branch drain pipes, all of which are arranged on the furnace body. The main drain pipe is arranged on the insulation layer. A partition plate is also provided between the furnace body and the insulation layer to separate the branch drain pipe and the main drain pipe.

9. A method for operating a silicon carbide etching device according to any one of claims 1 to 8, characterized in that: The following steps are involved: The inner lifting shaft and the outer lifting shaft are raised synchronously to open the furnace cover, and after pouring in solid pure potassium hydroxide, the inner and outer lifting shafts are lowered synchronously to close the furnace cover, and the temperature is raised to the corrosion temperature and kept warm; Lift the inner and outer lifting shafts again to open the furnace cover, hang the frame basket carrying the substrate wafer, and simultaneously lower the inner and outer lifting shafts to close the furnace cover. After preheating the wafer, immerse it in the etching solution to start etching; At the beginning of corrosion, oxygen is introduced. After a predetermined corrosion time, heating and oxygen introduction are stopped. The inner and outer lifting shafts are lifted to take out the frame basket, and the shafts are lowered to close the furnace cover. After the corrosive liquid cools and solidifies, water is injected to dilute it until the potassium hydroxide solid is processed; Test the etched wafer substrate and collect statistics on dislocation types and density.

10. The working method according to claim 9, characterized in that: The oxygen inlet flow rate is 5 sccm to 100 sccm.

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