A fast recovery diode and a method for manufacturing the same

Abstract

The present application provides a fast recovery diode and a manufacturing method thereof. The fast recovery diode comprises a first conductive type substrate and a first conductive type drift layer. The first conductive type drift layer is located on the first conductive type substrate. And the first conductive type drift layer comprises multiple epitaxial layers. Among them, the doping concentration of the epitaxial layer closest to the first conductive type substrate is lower than the doping concentration of the first conductive type substrate. And in the direction from the first conductive type substrate to the first conductive type drift layer, the doping concentration of the multiple epitaxial layers gradually decreases, so that during the reverse recovery process, the sweeping speed of the carriers in the first conductive type drift layer gradually decreases. In the fast recovery diode, the carriers are evenly distributed through the structural design of the drift layer, reducing the on-resistance. At the same time, the electric field distribution is optimized to control the carrier behavior, realize the soft recovery process, and effectively reduce the switching loss. The overall process steps of the manufacturing method are simple and the cost is low.

Description

Technical Field

[0001] The present application belongs to the field of semiconductor devices and manufacturing technology, and relates to a fast recovery diode and a manufacturing method thereof. Background Art

[0002] A fast recovery diode (FRD) is a semiconductor device with good switching characteristics and short reverse recovery time. It is widely used in the field of power electronics, especially in high-frequency application scenarios, such as high-frequency rectifier diodes.

[0003] Compared with conventional diodes, fast recovery diodes have a base region I added between the P-type material layer and the N-type material layer to form a PIN diode structure. In this structure, the base region is thinner and the reverse recovery charge is very small, which makes the fast recovery diode have a shorter reverse recovery time and lower forward conduction resistance than conventional diodes, so it can more effectively control the flow of current. The above advantages of fast recovery diodes make it play an important role in systems such as switching power supplies, inverters, motor drives, and power transmission. Among them, the reverse recovery time refers to the time required for the fast recovery diode to switch from the on state to the reverse blocking state.

[0004] At present, due to the increasing demand for efficiency and response speed in modern power electronic systems, fast recovery diodes have become key devices in high-frequency power conversion and pulse signal processing. In these application scenarios, fast recovery diodes are not only responsible for freewheeling, but also directly affect the performance and reliability of the entire system. As the demand for high-power applications in power systems continues to grow, the comprehensive performance requirements for fast recovery diodes are becoming increasingly stringent. The reverse recovery characteristics and conduction characteristics of fast recovery diodes are key factors affecting the safety, efficiency and working stability of power electronic systems. However, the current fast recovery diode structure either cannot meet the actual application requirements at the same time in terms of reverse recovery time and conduction characteristics, or the improvement of reverse recovery characteristics will bring about large switching losses, and the reliability and stability of the device cannot be guaranteed.

[0005] Therefore, how to provide a fast recovery diode and a manufacturing method thereof to improve the comprehensive performance of the fast recovery diode has become an important technical problem to be solved urgently by those skilled in the art.

[0006] It should be noted that the above introduction to the technical background is only for the convenience of providing a clear and complete description of the technical solutions of the present application and for the convenience of understanding by those skilled in the art. It cannot be considered that the above technical solutions are well known to those skilled in the art simply because they are described in the background technology section of the present application. Summary of the invention

[0007] In view of the above-mentioned shortcomings of the prior art, the purpose of the present application is to provide a fast recovery diode and a manufacturing method thereof, so as to solve the problem that the comprehensive performance of the fast recovery diode in the prior art needs to be improved.

[0008] To achieve the above-mentioned purpose and other related purposes, in a first aspect, the present application provides a fast recovery diode, comprising a first conductive type substrate and a first conductive type drift layer, wherein the first conductive type drift layer is located on the first conductive type substrate, and the first conductive type drift layer comprises multiple epitaxial layers, wherein:

[0009] In the first conductive type drift layer, the doping concentration of the epitaxial layer closest to the first conductive type substrate is lower than the doping concentration of the first conductive type substrate, and in the direction from the first conductive type substrate to the first conductive type drift layer, the doping concentration of the multiple layers of the epitaxial layer gradually decreases, so that during the reverse recovery process, the sweeping speed of the carriers in the first conductive type drift layer gradually decreases.

[0010] Optionally, the resistivity range of the first conductive type substrate is 2×10 -3 Ω·m~5×10 -3 Ω·m, and the resistivity of the epitaxial layer in the first conductive type drift layer that is closest to the first conductive type substrate is in a range of 2Ω·m to 5Ω·m.

[0011] Optionally, the resistivity difference between any two adjacent epitaxial layers in the first conductive type drift layer is in the range of 2Ω·m to 10Ω·m.

[0012] Optionally, the first conductivity type drift layer includes at least seven epitaxial layers.

[0013] Optionally, in a direction from the first conductive type substrate to the first conductive type drift layer, the thicknesses of the multiple epitaxial layers decrease successively.

[0014] Optionally, a thickness of any one of the epitaxial layers in the first conductive type drift layer is in a range of 5 μm to 10 μm.

[0015] Optionally, the resistivity change rate of the first conductive type drift layer is controlled based on a first performance parameter of the fast recovery diode, wherein the first performance parameter includes at least one of a reverse recovery time and a reverse recovery softness.

[0016] Optionally, the resistivity of the epitaxial layer in the first conductive type drift layer is controlled based on a second performance parameter of the fast recovery diode, wherein the second performance parameter includes at least one of a withstand voltage performance and an on-state voltage drop performance.

[0017] In a second aspect, the present application also provides a method for manufacturing a fast recovery diode, comprising the following steps:

[0018] providing a first conductive type substrate;

[0019] A first conductive type drift layer is formed on the first conductive type substrate and is located on the first conductive type substrate. The first conductive type drift layer is located on the first conductive type substrate and includes multiple epitaxial layers.

[0020] In the first conductive type drift layer, the doping concentration of the epitaxial layer closest to the first conductive type substrate is lower than the doping concentration of the first conductive type substrate, and in the direction from the first conductive type substrate to the first conductive type drift layer, the doping concentration of the multiple layers of the epitaxial layer gradually decreases, so that during the reverse recovery process, the sweeping speed of the carriers in the first conductive type drift layer gradually decreases.

[0021] Optionally, the manufacturing method further comprises at least one of a carrier lifetime control step and a compensation injection step, wherein the carrier lifetime control comprises at least one of platinum diffusion, gold diffusion and electron irradiation.

[0022] As described above, in the fast recovery diode of the present application, the first conductive type drift layer includes multiple epitaxial layers, and the doping concentration of the multiple epitaxial layers gradually decreases in the direction from the first conductive type substrate to the first conductive type drift layer. On the one hand, by designing the gradual change of the doping concentration of each epitaxial layer, the carriers are evenly distributed, thereby reducing the on-resistance of the fast recovery diode. On the other hand, by designing the structure of the first conductive type drift layer, the electric field distribution in the fast recovery diode is optimized, thereby controlling the carrier behavior (including recombination and migration rate), thereby achieving a lower recovery current and soft recovery process during the reverse recovery process, thereby effectively reducing the switching loss, and at the same time ensuring the service life and long-term stability of the fast recovery diode. The manufacturing method of the fast recovery diode of the present application can realize a fast recovery diode with effectively improved comprehensive performance, and the overall process steps are simple, the cost is low, and it is easy to achieve large-scale production. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 Shown is a schematic structural diagram of a fast recovery diode provided as a comparative example.

[0024] Figure 2 Shown is a schematic diagram of the structure of a fast recovery diode provided in an embodiment of the present application.

[0025] Figure 3 Shown is a doping concentration curve diagram of a fast recovery diode provided by an embodiment of the present application;

[0026] Figure 4 A schematic diagram showing the variation of the anode current of the fast recovery diode provided in the embodiments of the present application and the comparative example with the reverse recovery time.

[0027] Description of reference numerals:

[0028] 101 - cathode layer, 102 - buffer layer, 103 - drift region, 104 - anode layer;

[0029] 10 - a first conductivity type substrate, 20 - a first conductivity type drift layer, 21 - an epitaxial layer, 30 - a second conductivity type semiconductor layer. DETAILED DESCRIPTION

[0030] The following describes the implementation of the present application through specific examples, and those skilled in the art can easily understand other advantages and effects of the present application from the contents disclosed in this specification. The present application can also be implemented or applied through other different specific implementations, and the details in this specification can also be modified or changed in various ways based on different viewpoints and applications without departing from the spirit of the present application.

[0031] See also Figures 1 to 4 It should be noted that the illustrations provided in this embodiment are only used to illustrate the basic concept of the present application in a schematic manner, and the drawings only show components related to the present application rather than being drawn according to the number, shape and size of components in actual implementation. In actual implementation, the type, quantity and proportion of each component may be changed arbitrarily, and the component layout may also be more complicated.

[0032] For a fast recovery diode, the fast recovery diode generally includes an anode, a cathode, and a first conductive type drift layer located between the anode and the cathode. In the freewheeling stage, the fast recovery diode is in a forward conduction state. Under the action of the forward voltage, due to the potential difference between the anode and the cathode, the anode injects holes into the first conductive type drift layer, and the cathode injects electrons into the first conductive type drift layer, and the carriers (i.e., holes and electrons) diffuse, recombine, and accumulate in the first conductive type drift layer. There are a large number of carriers in the first conductive type drift layer, which increases the conductivity in the first conductive type drift layer. Accordingly, the resistance of the first conductive type drift layer decreases, thereby reducing the forward conduction voltage drop of the fast recovery diode, so that the fast recovery diode has a lower forward voltage drop. When entering the reverse recovery stage, the application of reverse voltage causes the minority carriers (holes) at the PN junction between the first conductive type drift layer and the anode (i.e., the anode PN junction) of the fast recovery diode to begin to diffuse toward the cathode and be extracted and recombined at the same time, causing the carriers at the anode PN junction to be rapidly depleted. As the carriers at the anode PN junction are depleted, the electric field rapidly expands to the first conductive type drift layer. In this process, the carriers stored in the first conductive type drift layer during the freewheeling stage are quickly swept away, the reverse recovery current decreases rapidly, and the di / dt value (current change rate) is high. A large voltage spike may be generated in the circuit, which may easily cause the failure of the power device.

[0033] Comparative Example

[0034] See also Figure 1 , Figure 1 The schematic diagram of the structure of the fast recovery diode of the comparative example of the present application is shown. In the related art, in order to improve the reverse recovery characteristics of the fast recovery diode, a buffer layer 102 is arranged on the side of the drift region 103 away from the anode layer 104, and the doping concentration of the buffer layer 102 is between the doping concentration of the drift region 103 and the doping concentration of the cathode layer 101, so that in the reverse recovery process, the diffusion speed of the depletion region after extending to the buffer layer 102 is significantly reduced, and after experiencing the minority carrier storage time, there are still a large number of carriers that have not been recombined and extracted (increasing the storage charge in the drift region 103), and these carriers are used to support the recovery process, thereby increasing the reverse recombination time and improving the reverse recovery softness. At the same time, the introduction of the buffer layer 102 can also greatly reduce the thickness of the drift region 103, thereby shortening the reverse recovery time and reducing the forward voltage drop. However, although the fast recovery diode with the buffer layer 103 can improve the reverse recovery characteristics to a certain extent, it has a high voltage drop when forward conduction occurs, and the conduction loss increases, and it cannot achieve effective improvement of the comprehensive performance of the fast recovery diode.

[0035] The present application embodiment provides a fast recovery diode. Figure 2 , Figure 2The fast recovery diode is a schematic structural diagram. The fast recovery diode includes a first conductive type substrate 10 and a first conductive type drift layer 20 .

[0036] Specifically, the first conductive type drift layer 20 is located on the first conductive type substrate 10. The first conductive type drift layer 20 includes multiple epitaxial layers 21. Figure 3 , Figure 3 A schematic diagram showing the change in doping concentration of the fast recovery diode (along the Figure 2 In the first conductive type drift layer 20, the doping concentration of the epitaxial layer 21 closest to the first conductive type substrate 10 is lower than the doping concentration of the first conductive type substrate 10, and in the direction from the first conductive type substrate 10 to the first conductive type drift layer 20, the doping concentration of the multiple layers of the epitaxial layer 21 gradually decreases, so that during the reverse recovery process, the sweeping speed of the carriers in the first conductive type drift layer 20 gradually decreases.

[0037] In the embodiment of the present application, through the structural design of the first conductive type drift layer 20, that is, the first conductive type drift layer 20 includes multiple epitaxial layers 21, and the doping concentration of the multiple epitaxial layers 21 gradually decreases along the direction from the first conductive type substrate 10 to the first conductive type drift layer 20. During the reverse recovery process, the expansion speed of the electric field in the first conductive type drift layer 20 gradually slows down (that is, the electric field change will not be too drastic), so that the speed at which the carriers are swept out of the first conductive type drift layer 20 gradually decreases with the advancement of the reverse recovery process, so that the reverse recovery current decreases relatively slowly, thereby showing higher softness. And due to the gradual decrease in the speed at which the carriers are swept out, at the end of the reverse recovery stage, there are more carriers remaining in the first conductive type drift layer 20, and the recombination current (the current generated by the action of the recombination center in the PN junction) is large (that is, the recombination rate of the carriers is high), so that the reverse recovery current decreases more slowly, reduces the sharp change of the current, and thus significantly reduces the current oscillation effect (meaning that the voltage and power fluctuations are small), effectively ensuring the stable operation of the power electronic system.

[0038] Since the fast recovery diode needs to recover to the non-conducting state under the reverse bias state, a too fast carrier sweep speed may generate a large reverse recovery current, resulting in switching loss. In the embodiment of the present application, by designing the difference in resistivity (or doping concentration) of each epitaxial layer 21, the electric field distribution in the fast recovery diode can be optimized, thereby controlling the recombination and migration rate of carriers, thereby achieving a lower recovery current and a smoother recovery process (i.e., "soft recovery") during the reverse recovery process. This soft recovery feature effectively reduces switching loss, while extending the service life of the device, ensuring long-term stability, and improving efficiency. Please refer to Figure 4 , Figure 4 The reverse recovery curves of the fast recovery diodes provided in the embodiments of the present application and the comparative examples are shown. Figure 4 It can be seen from the dotted curve and the solid curve in that, under the condition of the same conduction voltage drop, the fast recovery diode provided in the embodiment of the present application has a lower reverse recovery peak current and a basically similar reverse recovery time compared to the fast recovery diode provided in the comparative example, that is, the fast recovery diode provided in the embodiment of the present application has lower conduction loss, which helps to further improve the comprehensive performance and reliability of the fast recovery diode.

[0039] In an optional embodiment, the resistivity range of the first conductive type substrate 10 is 2×10 -3 Ω·m~5×10 -3 Ω·m (including end points). For example, the resistivity of the first conductive type substrate 10 may be 3×10 -3 Ω·m or 4×10 -3 Ω·m. The resistivity range or doping concentration range of the first conductive type substrate 10 is selected based on the application field and performance requirements of the fast recovery diode and is not specifically limited here. The resistivity range of the epitaxial layer 21 closest to the first conductive type substrate 10 in the first conductive type drift layer 20 is 2Ω·m to 5Ω·m (including the endpoint values). For example, the resistivity of the epitaxial layer 21 closest to the first conductive type substrate 10 in the first conductive type drift layer 20 can be 3Ω·m or 4Ω·m.

[0040] Further, the resistivity difference between any two adjacent epitaxial layers 21 in the first conductive type drift layer 20 is in the range of 2Ω·m to 10Ω·m (including the end value). For example, the resistivity difference between any two adjacent epitaxial layers 21 in the first conductive type drift layer 20 is 3Ω·m, 6Ω·m or 8Ω·m. The resistivity difference between any two adjacent epitaxial layers 21 is appropriately selected based on the on-state voltage drop and withstand voltage performance of the fast recovery diode in the application field.

[0041] In an optional embodiment, in a direction from the first conductive type substrate 10 to the first conductive type drift layer 20 , the thicknesses of the multiple epitaxial layers 21 decrease successively.

[0042] Further, the thickness of any one of the epitaxial layers 21 in the first conductive type drift layer 20 is in the range of 5 μm to 10 μm (including the end value). For example, the thickness of any one of the epitaxial layers 21 may be 6 μm, 7 μm, and 8 μm. The thickness range of the epitaxial layer 21 is summarized based on the resistivity difference between any two adjacent epitaxial layers 21 mentioned above.

[0043] In an optional embodiment, the first conductive type drift layer 20 includes at least seven layers of the epitaxial layer 21. Since the thickness of the first conductive type drift layer 20 is directly related to the directional withstand voltage capability, on-resistance, breakdown voltage, carrier drift velocity and other performances of the fast recovery diode. Taking the reverse withstand voltage function in the fast recovery diode as an example, the thickness of the first conductive type drift layer 20 must be adjusted on the premise that the fast recovery diode has a certain reverse withstand voltage capability (or the above-mentioned other performances). Therefore, after actual verification, under the conditions of the thickness range of each epitaxial layer 21, the resistivity difference range between two adjacent epitaxial layers 21, the thickness change trend and the doping concentration change trend, when the first conductive type drift layer 20 has more than 7 epitaxial layers 21, the doping concentration (and thickness) of each epitaxial layer 21 is adjusted and controlled separately, and the smoothing degree of the overall doping concentration of the first conductive type drift layer 20 finally obtained can realize the soft recovery process, so as to effectively reduce the on-state voltage drop while effectively reducing the switching loss.

[0044] In an optional embodiment, when the fast recovery diode is applied to a high withstand voltage scenario, the number of epitaxial layers 21 in the first conductive type drift layer 20 is greater than 10. The high withstand voltage scenario includes a freewheeling diode in a switching power supply, a high frequency rectifier diode in a PWM pulse width modulator, a rectifier diode in a frequency converter, a rectifier diode in an inverter, etc. After actual verification, under the conditions of the thickness range of each epitaxial layer 21, the resistivity difference range between two adjacent epitaxial layers 21, the thickness variation trend, and the doping concentration variation trend, the number of epitaxial layers 21 in the first conductive type drift layer 20 is higher than 10, so as to ensure the withstand voltage performance requirements of the fast recovery diode in the high withstand voltage scenario.

[0045] In an optional embodiment, the resistivity change rate of the first conductive type drift layer 20 is controlled based on the first performance parameter of the fast recovery diode, the first performance parameter includes at least one of the reverse recovery time and the reverse recovery softness, and the resistivity change rate of the first conductive type drift layer 20 refers to the doping concentration gradient change rate of the first conductive type drift layer 20, specifically, the ratio of the doping concentration at any point in the first conductive type drift layer 20 to the distance between the point and the first conductive type substrate 10. For example, in the case where the fast recovery diode needs to have a lower reverse recovery time, the resistivity change rate of the first conductive type drift layer 20 can be set to be relatively large. For another example, in the case where the fast recovery diode needs to have a higher reverse recovery softness, the resistivity change rate of the first conductive type drift layer 20 can be set to be relatively low, so that the doping concentration gradient in the first conductive type drift layer 20 changes smoothly.

[0046] In an optional embodiment, the resistivity of the epitaxial layer 21 in the first conductive type drift layer 20 is controlled based on the second performance parameter of the fast recovery diode, and the second performance parameter includes at least one of the withstand voltage performance and the conduction voltage drop performance. For example, when the fast recovery diode needs to have a high withstand voltage performance, the resistivity of each epitaxial layer 21 in the first conductive type drift layer 20 can be set to be relatively high, and the epitaxial layer 21 with a lower resistivity can increase the width of the depletion region, thereby improving the withstand voltage performance. For another example, when the fast recovery diode needs to have a low conduction voltage drop, the resistivity of each epitaxial layer 21 in the first conductive type drift layer 20 can be set to be relatively low. That is, in the design stage of the fast recovery diode, the structural parameters (including resistivity change rate, resistivity, thickness and number of layers, etc.) in the first conductive type drift layer 20 are designed based on the application scenario of the fast recovery diode (performance requirements for the fast recovery diode) to ensure that the fast recovery diode manufactured based on the design parameters can meet the actual application requirements.

[0047] In an optional embodiment, the fast recovery diode further includes a second conductive type semiconductor layer 30, and the second conductive type semiconductor layer 30 is located on a side of the first conductive type drift layer 20 away from the first conductive type substrate 10. For example, the first conductive type substrate 10 and the first conductive type drift layer 20 are both N-type, and the second conductive type semiconductor layer 30 is P-type. Alternatively, the first conductive type substrate 10 and the first conductive type drift layer 20 are both P-type, and the second conductive type semiconductor layer 30 is N-type. The first conductive type substrate 10 serves as the cathode of the fast recovery diode, and the second conductive type semiconductor layer 30 serves as the anode of the fast recovery diode.

[0048] Since in the on state, the on voltage drop of the fast recovery diode is also closely related to the concentration and concentration distribution of the carriers in the first conductive type drift layer 20. In the embodiment of the present application, by designing the first conductive type drift layer 20 with a multi-layer epitaxial layer 21, and making the multi-layer epitaxial layer 21 in the first conductive type drift layer 20 have different doping concentrations and change in a gradient, the distribution of carriers is more uniform, further reducing the on resistance of the fast recovery diode, and improving the conductivity of the fast recovery diode. In addition, the structural design of the multi-layer epitaxial layer 21 can be targeted at the application scenarios and performance requirements of the fast recovery diode, so that each layer of the epitaxial layer 21 takes into account the optimization of the electric field distribution, carrier recombination and migration mechanism, so that the entire device can maintain a low on voltage drop in the on state. In addition, the multi-layer epitaxial structure of the first conductive type drift layer 20 (that is, the first conductive type drift layer 20 is made based on the multi-layer epitaxial process) can simplify the production process while ensuring that the fast recovery diode has excellent electrical performance, so that the production cost is greatly reduced, and the application competitiveness of the fast recovery diode is increased. Moreover, the structure of the multi-layer epitaxial layer 21 can precisely control the doping concentration at each position in the first conductive type drift layer 20, and the epitaxial growth process makes the material distribution in the crystal structure of each epitaxial layer 21 more uniform, which can improve the electrical characteristics and long-term stability of the fast recovery diode.

[0049] Furthermore, in the embodiment of the present application, due to the change in the doping concentration of the first conductive type drift layer 20, the doping concentration of the epitaxial layer 21 on the side of the first conductive type drift layer 20 close to the first conductive type substrate 10 is higher, and the epitaxial layer 21 can play a technical effect substantially similar to that of the buffer layer in the conventional fast recovery diode. And compared with the conventional fast recovery diode, since the doping concentration of the first conductive type drift layer 20 gradually increases from the anode to the cathode, there is a large energy level difference between the anode region and the first conductive type drift layer 20, and thus the anode is more easily injected with holes (more strongly diffused), and affected by the conductivity modulation response, the on-state voltage drop of the fast recovery diode is lower.

[0050] In addition, in order to obtain a first conductive type drift layer 20 structure with a gradual doping concentration, an attempt was also made to use a diffusion process to manufacture the first conductive type drift layer 20 structure in a fast recovery diode. However, after verification, it was found that the diffusion process had problems such as poor uniformity (including doping depth and doping concentration) when applied, too high material requirements for the first conductive type substrate 10, complex process and high cost. For example, due to temperature and time limitations, the diffusion process is usually difficult to achieve the required doping concentration accuracy control, which affects the reverse recovery time and conduction characteristics of the diode. In addition, the diode obtained based on the diffusion process has a slow recovery process during the switching process, which is prone to cause energy loss and thermal effects, affecting the efficiency and stability of the overall system, or the long reverse recovery time of the diode will cause a sudden change in current, thereby generating large electromagnetic noise, affecting the overall stability of the system. The existence of the above problems limits the further improvement of the performance of the fast recovery diode and the reduction of production costs, thereby restricting its practical application prospects. The drift layer 20 composed of multiple epitaxial layers 21 provided in this embodiment and the structural parameters of the drift layer 20 are limited, which can effectively solve the above-mentioned problems existing in the diffusion process. Compared with the diffusion process, the epitaxial process has lower cost and stronger manufacturability, and the actual operation of the multi-layer epitaxial process is more flexible. In the process of the multi-layer epitaxial process, other process applications that can further improve the performance of the fast recovery diode can be used. In addition, the doping concentration of each epitaxial layer 21 in the manufactured drift layer 20 can be accurately controlled, and a drift layer structure with a doping curve that is significantly better than that of the diffusion process can be obtained, thereby improving the comprehensive performance of the fast recovery diode based on the structure of the drift layer 20.

[0051] In the embodiment of the present application, in the design stage of the fast recovery diode, a suitable first conductive type substrate material is first selected based on the application platform of the fast recovery diode, and further, precise epitaxial growth conditions are formulated according to the performance requirements of the fast recovery diode required by the application platform, to ensure the structural uniformity of each epitaxial layer in the first conductive type drift layer and the precise control of the doping concentration. Then, the resistivity difference (and thickness difference) between each epitaxial layer is designed to optimize the electric field distribution and carrier behavior in the fast recovery diode in order to achieve the best electrical performance. After that, epitaxial layers with different electrical characteristics (mainly in doping concentration) are deposited layer by layer on the first conductive type substrate using an epitaxial growth process, so that the design of the multi-layer epitaxial layer can not only improve the conduction performance of the fast recovery diode, but also improve its reverse recovery characteristics. Next, a series of precise tests are performed on the electrical characteristics of the first conductive type drift layer to ensure that the fast recovery diode actually manufactured can meet the performance requirements of the target application platform (for example, a high-frequency power electronics application platform). Among them, in the design step of designing the resistivity difference between each epitaxial layer, the doping concentration (and thickness) of the epitaxial layer closest to the first conductive type substrate and the epitaxial layer farthest from the first conductive type substrate can be determined first, and the specific number of epitaxial layers can be determined on this basis, and the resistivity change rate (or doping concentration change rate) can be further controlled to achieve the structural design of the first conductive type drift layer.

[0052] In the fast recovery diode provided in the embodiment of the present application, the first conductive type drift layer includes multiple epitaxial layers, and the doping concentration of the multiple epitaxial layers gradually decreases in the direction from the first conductive type substrate to the first conductive type drift layer. On the one hand, by designing the gradual change of the doping concentration of each epitaxial layer, the carriers are evenly distributed, thereby reducing the on-resistance of the fast recovery diode. On the other hand, by designing the structure of the first conductive type drift layer, the electric field distribution in the fast recovery diode is optimized, thereby controlling the carrier behavior (including recombination and migration rate), thereby achieving a lower recovery current and soft recovery process in the reverse recovery process, thereby effectively reducing the switching loss, and at the same time extending the service life and long-term stability of the fast recovery diode.

[0053] The present invention also provides a method for manufacturing a fast recovery diode, which comprises the following steps:

[0054] Providing a first conductive type substrate 10;

[0055] A first conductive type drift layer 20 is formed on the first conductive type substrate 10 and is located on the first conductive type substrate 10. The first conductive type drift layer 20 is located on the first conductive type substrate 10 and includes a plurality of epitaxial layers 21.

[0056] In the first conductive type drift layer 20, the doping concentration of the epitaxial layer 21 closest to the first conductive type substrate 10 is lower than the doping concentration of the first conductive type substrate 10, and in the direction from the first conductive type substrate 10 to the first conductive type drift layer 20, the doping concentration of the multiple layers of the epitaxial layer 21 gradually decreases, so that during the reverse recovery process, the sweeping speed of the carriers in the first conductive type drift layer 20 gradually decreases.

[0057] In an optional embodiment, the manufacturing method also includes the step of forming a second conductive type doping layer on the first conductive type drift layer 20, and the second conductive type doping layer can be formed by ion implantation. After forming the second conductive type doping layer, the method also includes the step of annealing.

[0058] In an optional embodiment, the manufacturing method further includes performing at least one of a carrier lifetime control step and a compensation injection step, wherein the carrier lifetime control process includes at least one of platinum diffusion, gold diffusion and electron irradiation. The above steps can further improve the comprehensive performance of the fast recovery diode without changing the doping concentration (and gradient) of each epitaxial layer 21 in the first conductive type drift layer 20. Among them, the carrier lifetime control process can introduce uniformly distributed deep energy level impurities or irradiation defects in the first conductive type drift layer 20 to form a carrier recombination center, reduce the carrier lifetime, reduce the amount of charge stored in the first conductive type drift layer 20 during forward conduction, and accelerate the recombination of minority carriers during reverse shutdown, thereby further reducing the reverse recovery time. Compensation injection can adjust the injection efficiency of the anode by controlling the doping concentration and structure of the anode (i.e., the second conductive type semiconductor layer 30) to improve the reverse recovery characteristics and conduction characteristics of the fast recovery diode.

[0059] In an optional embodiment, the manufacturing method also includes the step of forming a cathode metal on a side of the first conductive type substrate 10 away from the first conductive type drift layer 20, and the step of forming an anode metal on a side of the second conductive type doped layer away from the first conductive type drift layer 20, thereby completing the manufacturing of the fast recovery diode.

[0060] The method for manufacturing a fast recovery diode provided in the embodiment of the present application can realize a fast recovery diode with effectively improved comprehensive performance, and the overall process steps are simple, the cost is low, and it is easy to realize large-scale production.

[0061] In summary, in the fast recovery diode of the present application, the first conductive type drift layer includes multiple epitaxial layers, and in the direction from the first conductive type substrate to the first conductive type drift layer, the doping concentration of the multiple epitaxial layers gradually decreases. On the one hand, the carriers are evenly distributed through the design of the gradual change of the doping concentration of each epitaxial layer, thereby reducing the on-resistance of the fast recovery diode. On the other hand, through the structural design of the first conductive type drift layer, the electric field distribution in the fast recovery diode is optimized, and the carrier behavior (including recombination and migration rate) is controlled, so as to achieve a lower recovery current and soft recovery process during the reverse recovery process, thereby effectively reducing the switching loss, and at the same time extending the service life and long-term stability of the fast recovery diode. The manufacturing method of the fast recovery diode of the present application can realize a fast recovery diode with effectively improved comprehensive performance, and the overall process steps are simple, low cost, and easy to achieve large-scale production. Therefore, the present application effectively overcomes the various shortcomings in the prior art and has a high industrial utilization value.

[0062] The above embodiments are merely illustrative of the principles and effects of the present application and are not intended to limit the present application. Anyone familiar with the technology may modify or change the above embodiments without violating the spirit and scope of the present application. Therefore, all equivalent modifications or changes made by a person of ordinary skill in the art without departing from the spirit and technical ideas disclosed in the present application shall still be covered by the claims of the present application.

Claims

1. A fast recovery diode, characterized in that: The invention comprises a first conductive type substrate and a first conductive type drift layer, wherein the first conductive type drift layer is located on the first conductive type substrate, and the first conductive type drift layer comprises multiple epitaxial layers, wherein: In the first conductive type drift layer, the doping concentration of the epitaxial layer closest to the first conductive type substrate is lower than the doping concentration of the first conductive type substrate, and in the direction from the first conductive type substrate to the first conductive type drift layer, the doping concentration of the multiple layers of the epitaxial layer gradually decreases, so that during the reverse recovery process, the sweeping speed of the carriers in the first conductive type drift layer gradually decreases.

2. The fast recovery diode according to claim 1, characterized in that: The resistivity range of the first conductive type substrate is 2×10 -3 Ω·m~5×10 -3 Ω·m, and the resistivity of the epitaxial layer in the first conductive type drift layer that is closest to the first conductive type substrate is in a range of 2Ω·m to 5Ω·m.

3. The fast recovery diode according to claim 1, characterized in that: The resistivity difference between any two adjacent epitaxial layers in the first conductive type drift layer is in the range of 2Ω·m to 10Ω·m.

4. The fast recovery diode according to claim 1, characterized in that: In a direction from the first conductive type substrate to the first conductive type drift layer, the thicknesses of the multiple epitaxial layers decrease in sequence.

5. The fast recovery diode according to claim 1, characterized in that: The thickness of any one of the epitaxial layers in the first conductive type drift layer is in the range of 5 μm to 10 μm.

6. The fast recovery diode according to any one of claims 1 to 5, characterized in that: The first conductive type drift layer includes at least seven layers of the epitaxial layer.

7. The fast recovery diode according to claim 1, characterized in that: The resistivity change rate of the first conductive type drift layer is controlled based on a first performance parameter of the fast recovery diode, wherein the first performance parameter includes at least one of a reverse recovery time and a reverse recovery softness.

8. The fast recovery diode according to claim 1, characterized in that: The resistivity of the epitaxial layer in the first conductive type drift layer is controlled based on a second performance parameter of the fast recovery diode, wherein the second performance parameter includes at least one of a withstand voltage performance and an on-state voltage drop performance.

9. A method for manufacturing a fast recovery diode, characterized in that: The following steps are involved: providing a first conductive type substrate; A first conductive type drift layer is formed on the first conductive type substrate and is located on the first conductive type substrate. The first conductive type drift layer is located on the first conductive type substrate and includes multiple epitaxial layers. In the first conductive type drift layer, the doping concentration of the epitaxial layer closest to the first conductive type substrate is lower than the doping concentration of the first conductive type substrate, and in the direction from the first conductive type substrate to the first conductive type drift layer, the doping concentration of the multiple layers of the epitaxial layer gradually decreases, so that during the reverse recovery process, the sweeping speed of the carriers in the first conductive type drift layer gradually decreases.

10. The method for manufacturing a fast recovery diode according to claim 9, characterized in that: The manufacturing method further includes performing at least one of a carrier lifetime control step and a compensation injection step, wherein the carrier lifetime control includes at least one of platinum diffusion, gold diffusion and electron irradiation.

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