Fast soft recovery diode with back hole injection and preparation method thereof

Abstract

The invention belongs to the technical field of power semiconductor devices, and particularly discloses a fast soft recovery diode with back hole injection and a preparation method. The structures of the p buffer layer, the n buffer layer and the p cathode region are optimized, the p buffer layer and the p + anode region are alternately arranged, and the doping of the p buffer layer is obviously lower than the doping of the p + anode of the PIN diode, so that the carrier extraction time in the reverse recovery process is obviously shortened. And the doping concentration of the n buffer region is lower than that of the n + cathode, so that the width of an electric field is effectively limited, the injection efficiency of the cathode is reduced, and the problems of long reverse recovery time and high reverse recovery current of the original PIN diode in the reverse recovery process are effectively solved.

Description

Technical Field

[0001] The present application belongs to the technical field of power semiconductor devices, and more specifically, relates to a fast soft recovery diode with back hole injection and a preparation method thereof. Background Art

[0002] Energy conversion devices based on power semiconductors play a vital role in advanced manufacturing industries, such as new energy, meeting the demands of high-voltage, high-power applications. Insulated-gate bipolar transistors (IGBTs) offer advantages such as high input impedance, fast switching frequency, low drive power, high current density, and low on-state voltage. IGBT modules constructed from IGBTs and fast-recovery diodes are widely used in AC motors, inverters, and energy storage applications. Fast-recovery diodes are typically connected in anti-parallel with the IGBT in various topologies. During the IGBT's off state, they provide a path for current flow, dissipating the high-voltage electromotive force induced by the inductive components within the topology and protecting the IGBT. To maximize IGBT performance, the fast-recovery diodes connected in anti-parallel with the IGBT must operate at currents of hundreds of amperes and maintain reverse recovery times in the microsecond range. Furthermore, to prevent damage to the IGBT module due to current resonance, electromagnetic compatibility, and electromagnetic interference, the fast-recovery diodes must control the peak reverse recovery current.

[0003] A PIN diode (a diode with a PIN structure), a traditional reverse recovery diode, features a highly doped p+ anode, an n+ cathode, and a lowly doped n-base region. Under forward bias, the p+ anode and n+ cathode inject holes and electrons, respectively. The concentration of holes injected into the n-base region increases with increasing forward voltage, creating an n-base conductivity modulation effect, resulting in a lower forward voltage. However, during the reverse recovery phase of a PIN diode, the carrier extraction time is too long, negatively impacting the reverse recovery speed and peak reverse recovery current. Furthermore, in practical applications, the distribution of the current path is closely related to device reliability. Current density concentration typically leads to localized heating and damage in the device. During the reverse recovery phase, current density concentration on the cathode side can form in a PIN diode, significantly impacting device reliability and requiring particular attention during the reverse recovery phase of the PIN diode. Summary of the Invention

[0004] In response to the defects of the prior art, the purpose of this application is to provide a fast soft recovery diode with back hole injection and a preparation method, aiming to solve the problems of traditional PIN diodes in the reverse recovery stage, such as slow reverse recovery speed, large reverse recovery peak current and low reliability due to the long carrier extraction time.

[0005] In a first aspect, the present application provides a fast soft recovery diode with back hole injection, comprising: an anode metal, an insulating oxide layer, a plurality of p+ anode regions, a p buffer layer, an n-base region, an n buffer layer, a plurality of p cathode regions, an n+ cathode region, and a cathode metal; The plurality of p+ anode regions are equally spaced and embedded in a p buffer layer; Each p+ anode region has a higher doping concentration than the p buffer layer, is connected to the anode metal near the anode side, and does not exceed the p buffer layer near the cathode side; An insulating oxide layer is provided between the anode metal and the p-buffer layer; A plurality of p cathode regions are formed by ion implantation at equal intervals in the n buffer layer; Each p cathode region contacts the n+ cathode region near the cathode side and does not exceed the n buffer layer near the anode side; The n+ cathode region has a higher doping concentration than the n buffer layer and is close to the cathode side and connected to the cathode metal.

[0006] Preferably, the number of the p+ anode regions and the p cathode regions are the same and are arranged correspondingly up and down.

[0007] Preferably, the distance between each p+ anode region ranges from 20 um to 100 um.

[0008] Preferably, the p+ anode region and the p cathode region are rectangular parallelepipeds of the same specifications, with a thickness ranging from 7um to 12um and a width ranging from 2um to 3um.

[0009] Preferably, the doping concentrations of the p+ anode region and the p cathode region are both above.

[0010] Preferably, the material of the p+ anode region is p-type SI-B, and the material of the p buffer layer is p-type SI-B.

[0011] Preferably, the material of the n-buffer layer is n-type SI-P, and the material of the p-cathode region is p-type SI-B.

[0012] Preferably, the insulating oxide is SiO2.

[0013] In a second aspect, the present application provides a method for preparing a fast soft recovery diode with back hole injection, comprising: S1. Forming an n-buffer layer on the cathode side of the n-base region by a diffusion process; S2. A p-buffer layer is formed on the anode side of the n-base region by a diffusion process; S3. Depositing an insulating oxide layer on the p-buffer layer by a PECVD deposition process; S4. forming a local insulating oxide layer on the insulating oxide layer by an etching process; S5. forming a p+ anode region on the local insulating oxide layer by an ion implantation process; S6. forming a local p cathode region on the n buffer layer by an ion implantation process; S7. forming an n+ cathode region on the n buffer layer by an epitaxial process; S8. The anode electrode is formed by depositing metal Al or Au through the insulating oxide layer on the p+ anode region and forming an ohmic contact. S9. The cathode electrode is deposited in sequence on the n+ cathode region by metal Al and Au and makes ohmic contact.

[0014] It can be understood that the beneficial effects of the second aspect mentioned above can be found in the relevant description of the first aspect mentioned above, and will not be repeated here.

[0015] In general, the above technical solutions conceived by this application have the following beneficial effects compared with the existing technologies: (1) Based on the existing PIN diode for reverse recovery, this application proposes a fast soft recovery diode with back hole injection. The p buffer layer, n buffer layer, and p cathode region structures are optimized. The p buffer layer and p+ anode region are arranged alternately. Since the p buffer layer doping is significantly lower than the p+ anode doping of the PIN diode, the carrier extraction time during the reverse recovery process is significantly shortened. The n buffer layer doping concentration is lower than the n+ cathode, which effectively limits the width of the electric field and reduces the cathode injection efficiency, effectively solving the problems of long reverse recovery time and high reverse recovery current of the original PIN diode during the reverse recovery process.

[0016] (2) This application proposes a fast soft recovery diode with back hole injection, which alternates the p buffer layer with the original p+ anode region and effectively isolates the p buffer layer from the anode metal with an insulating oxide layer. Therefore, under conditions of low current density and low hole injection efficiency, holes are mainly injected from the p buffer region on the anode side. Under conditions of high current density and high hole injection efficiency, holes are mainly injected from the p+ anode region on the anode side, thereby achieving the ability to dynamically adjust the current. This allows the diode of this application to have the ability to dynamically adjust the current in its forward conduction characteristics, and the forward conduction characteristics can be controlled to be equivalent to those of a PIN diode. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1 This is a schematic diagram of the traditional PIN diode structure provided in an embodiment of the present application.

[0018] Figure 2 This is a schematic diagram of the structure of a fast soft recovery diode with back hole injection provided in an embodiment of the present application.

[0019] Figure 3This is a comparison chart of the reverse withstand voltage characteristics of the fast soft recovery diode with back hole injection provided by the embodiment of the present application and the traditional PIN diode.

[0020] Figure 4 This is a comparison diagram of the cross-sectional electric field distribution of the fast soft recovery diode with back hole injection provided by this application and the traditional PIN diode.

[0021] Figure 5 This is a schematic diagram of an application circuit suitable for a reverse recovery diode provided in an embodiment of the present application.

[0022] Figure 6 This is a comparison chart of the forward conduction characteristics of the fast soft recovery diode with back hole injection provided by the embodiment of the present application and the traditional PIN diode.

[0023] Figure 7 This is a comparison chart of the reverse recovery voltage characteristics and reverse recovery current characteristics of the fast soft recovery diode with back hole injection provided by the embodiment of the present application and the traditional PIN diode.

[0024] Figure 8 This is a current density distribution diagram of a traditional PIN diode provided in an embodiment of the present application during the dynamic reverse recovery phase.

[0025] Figure 9 This is a current density distribution diagram of the fast soft recovery diode with back hole injection provided in an embodiment of the present application during the dynamic reverse recovery stage.

[0026] Throughout the drawings, the same reference numerals are used to denote the same elements or structures, wherein: 1 is the anode metal of the PIN diode, 2 is the p+ anode region, 3 is the n-base region, 4 is the n+ cathode region, 5 is the cathode metal, 6 is the anode metal of the fast soft recovery diode with back hole injection, 7 is the SiO2 oxide layer, 8 is the p+ anode region, 9 is the p buffer layer, 10 is the n-base region, 11 is the n buffer layer, 12 is the p cathode region, 13 is the n+ cathode region, and 14 is the cathode metal. DETAILED DESCRIPTION

[0027] In order to make the purpose, technical solutions and advantages of this application more clear, the following further describes this application in detail with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain this application and are not intended to limit this application.

[0028] For ease of understanding, the English abbreviations and related technical terms involved in the embodiments of this application are explained and described below.

[0029] p-type SI-B: A P-type semiconductor formed by doping boron into silicon semiconductor material.

[0030] n-type SI-P: N-type semiconductor formed by doping pentavalent element phosphorus into silicon semiconductor material.

[0031] PECVD deposition process: Plasma Enhanced Chemical Vapor Deposition, plasma enhanced chemical vapor deposition, promotes chemical reactions by utilizing the high energy characteristics of plasma, thereby achieving the deposition of high-quality thin films at lower temperatures.

[0032] The embodiments of the present application are described below in conjunction with the drawings in the embodiments of the present application.

[0033] The present application provides a fast soft recovery diode with back hole injection, comprising: an anode metal 6, an insulating oxide layer 7, a plurality of p+ anode regions 8, a p buffer layer 9, an n-base region 10, an n buffer layer 11, a plurality of p cathode regions 12, an n+ cathode region 13, and a cathode metal 14. The plurality of p+ anode regions 8 are embedded in the p buffer layer 9 at equal intervals. Each p+ anode region has a higher doping concentration than the p buffer layer 9, is connected to the anode metal 6 near the anode side, and does not exceed the p buffer layer 9 near the cathode side. The insulating oxide layer 7 is provided between the anode metal 6 and the p buffer layer 9. A plurality of p cathode regions 12 are formed by ion implantation at equal intervals in the n buffer layer 11. Each p cathode region 12 is in contact with the n+ cathode region 13 near the cathode side, and does not exceed the n buffer layer 11 near the anode side. The n+ cathode region 13 has a higher doping concentration than the n buffer layer 11, and is connected to the cathode metal 14 near the cathode side.

[0034] It should be noted that "holes" are a type of carrier in semiconductors, carrying a positive charge. "Hole injection" occurs because the hole concentration in the p-region is higher than in the intrinsic region. According to the principle of diffusion, holes diffuse from the high-concentration region to the low-concentration region. Simultaneously, the electric field accelerates the movement of holes, allowing them to enter the intrinsic region. "Ion implantation" is a process technology widely used in semiconductor manufacturing and other materials science fields. It is primarily used to precisely introduce impurity atoms (dopants) into semiconductors or other materials to modify their electrical, optical, or physical properties.

[0035] Since the doping of the p-buffer layer is significantly lower than the p+ anode doping of the PIN diode, the carrier extraction time during the reverse recovery process is significantly shortened, which can reduce the reverse recovery time and reverse recovery current.

[0036] The insulating oxide plays a role of passivation protection.

[0037] The doping concentration of the n buffer is lower than that of the n+ cathode, which effectively limits the width of the electric field and reduces the injection efficiency of the cathode, effectively solving the problems of long reverse recovery time and high reverse recovery current of the original PIN diode during the reverse recovery process.

[0038] The current density distribution during the reverse recovery process of the diode is limited to the p cathode region, so that the current density on the cathode side of the diode is evenly distributed, effectively avoiding device damage caused by current density concentration.

[0039] The p+ anode region 8 is provided with alternatingly distributed local high-doped ohmic contact regions, and the n+ cathode region 13 is provided with a high-doped ohmic contact region.

[0040] Preferably, the number of the p+ anode regions 8 and the p cathode regions 12 are the same and are arranged correspondingly up and down.

[0041] It should be noted that since the p+ anode region and the p cathode region are arranged in correspondence with each other, the current density is uniformly distributed and limited, which effectively solves the problem of uneven current density distribution, so that the current density of the diode of the present application is uniformly distributed during the reverse recovery process, effectively improving the dynamic reliability of the reverse recovery stage.

[0042] Preferably, the distance between each p+ anode region ranges from 20 um to 100 um.

[0043] It should be noted that the larger the spacing between the p+ anode regions, the higher the withstand voltage specification of the fast soft recovery diode.

[0044] Preferably, the p+ anode region 8 and the p cathode region 12 are rectangular parallelepipeds of the same specifications, with a thickness ranging from 7 um to 12 um and a width ranging from 2 um to 3 um.

[0045] It should be noted that, the larger the thickness-to-width ratio of the p+ anode region 8 and the p cathode region 12 is, the higher the withstand voltage specification of the fast soft recovery diode is.

[0046] Preferably, the doping concentrations of the p+ anode region 8 and the p cathode region 12 are both above.

[0047] Preferably, the material of the p+ anode region is p-type SI-B, and the material of the p buffer layer is p-type SI-B.

[0048] Preferably, the material of the n-buffer layer is n-type SI-P, and the material of the p-cathode region is p-type SI-B.

[0049] Preferably, the insulating oxide isolates the anode metal 6 and the p-buffer layer 9, including but not limited to SiO2.

[0050] The present application provides a method for preparing a fast soft recovery diode with back hole injection, comprising: S1. forming an n-buffer layer 11 on the cathode side of an n-base region 10 by a diffusion process; S2. forming a p-buffer layer 9 on the anode side of the n-base region 10 by a diffusion process; S3. depositing an insulating oxide layer on the p-buffer layer 9 by a PECVD deposition process; S4. forming a local insulating oxide layer 7 on the insulating oxide layer by an etching process; S5. forming a p+ anode region 8 on the local insulating oxide layer by an ion implantation process; S6. forming a local p-cathode region 12 on the n-buffer layer 11 by an ion implantation process; S7. forming an n+ cathode region 13 on the n-buffer layer 11 by an epitaxial process; S8. depositing an anode electrode by metal Al and Au through the insulating oxide layer from the bottom, and then sequentially depositing the anode electrode on the p+ anode region and making ohmic contact therewith; S9. depositing a cathode electrode by metal Al and Au sequentially on the n+ cathode region and making ohmic contact therewith.

[0051] Example In this embodiment, the performance of a conventional PIN diode and the PIN diode proposed in this application with the same specifications is compared and analyzed.

[0052] like Figure 1 The conventional PIN diode for reverse recovery has five main structures, namely, anode metal 1, p+ anode region 2, n-base region 3, n+ cathode region 4, and cathode metal 5. The PIN diode has n-base region 3, made of n-type SI-P, with a thickness of 265 μm, a width of 500 μm, and an n-doping concentration of The n+ cathode region 4 is formed on the cathode side of the n-base region 3 by epitaxial process. The material is n-type SI-P. The thickness of the n+ cathode region is 5um and the width is 500um. Its n+ doping concentration is On the anode side of the n-base region 3, the p+ anode region 2 is made by ion implantation. The material is p-type SI-B. The p+ anode region has a thickness of 7um and a width of 500um. Its p+ doping concentration is The anode electrode 1 is made of metal Al and Au deposited in sequence on the p+ anode region 2, with a thickness of 20 μm. The cathode electrode 5 is made of metal Al and Au deposited in sequence on the n+ cathode region 4, with a thickness of 20 μm.

[0053] like Figure 2 As shown, the PIN diode proposed in this application includes: an anode metal 6, an insulating oxide layer 7, multiple p+ anode regions 8, a p buffer layer 9, an n-base region 10, an n buffer layer 11, multiple p cathode regions 12, an n+ cathode region 13, and a cathode metal 14. Among them, the material of the p+ anode region is p-type SI-B, the p+ anode region has a thickness of 7um and a width of 2um, the spacing between each p+ anode region is 20um, and its p+ doping concentration is The material of the p-buffer layer is p-type SI-B, the p-buffer layer thickness is 15um, the width is 500um, and its p-doping concentration is The material of the n-base layer is n-type SI-P, the thickness of the n-base layer is 250um, the width is 500um, and its n-doping concentration is The material of the n-buffer layer is n-type SI-P, the thickness of the n-buffer layer is 15um, the width is 500um, and its n-doping concentration is The material of the p cathode region is p-type SI-B, the thickness of the p cathode region is 7um, the width is 2um, the spacing between each p cathode region is 20um, and the p doping concentration is The material of the n+ cathode region is n-type SI-P, the thickness of the n+ cathode region is 5um, the width is 500um, and its n+ doping concentration is The p-buffer layer is partially covered with a SiO2 oxide layer where it contacts the anode metal. Each local SiO2 oxide layer is 5 μm thick, 20 μm wide, and 2 μm apart. The anode electrode is sequentially deposited with metal Al and Au. The bottom passes through the SiO2 oxide layer and forms an ohmic contact with the p+ anode region. The thickness is 20 μm. The cathode electrode is sequentially deposited with metal Al and Au on the n+ cathode region, forming an ohmic contact. The thickness is 20 μm.

[0054] Figure 3 This chart compares the reverse withstand voltage characteristics of the fast soft recovery diode with back hole injection provided by this application and a conventional PIN diode. Given the same total thickness for both devices, the fast soft recovery diode with back hole injection provided by this application has a relatively lower reverse withstand voltage compared to the PIN diode, reducing it by 6.5% due to its thinner n-base region.

[0055] Figure 4 This figure compares the cross-sectional electric field distribution of the fast soft recovery diode with back hole injection provided by this application and a traditional PIN diode. The cross-sectional electric field of the fast soft recovery diode with back hole injection provided by this application is effectively confined between the p-buffer layer and the n-buffer layer, effectively reducing the spread of the electric field and facilitating further reductions in device thickness.

[0056] like Figure 5 As shown, the present application provides an application circuit suitable for a reverse recovery diode, including a fast soft recovery diode structure D, a DC voltage source , inductor L, switch S, DC current source . Connect the DC power supply After being connected in parallel with the diode D, it is then connected in series with the inductor L and the switch S, and then connected to the DC voltage source In the stable phase, the current source Current is applied through diode D and switch S is open. During the reverse recovery phase, switch S is closed and the DC voltage source A reverse voltage is applied to the diode D through the inductor L, causing the diode D to change from a forward conduction state to a reverse recovery state.

[0057] Figure 6 This is a comparison chart of the forward conduction characteristics of the fast soft recovery diode with back hole injection provided by this application and the traditional PIN diode. In the forward conduction characteristic chart, the forward voltage is usually used as the horizontal axis and the current density is used as the vertical axis. Figure 1 Compared with the PIN diode shown in the figure, since the n-base region of the fast soft recovery diode structure with back hole injection proposed in this application is narrower, the forward voltage of the device can be effectively reduced, and the conduction loss is lower at low current density.

[0058] Figure 7 This is a comparison chart of the reverse recovery voltage and reverse recovery current characteristics of the fast soft recovery diode with back hole injection provided by this application and the traditional PIN diode. Figure 1 Compared to the PIN diode shown in the figure, the reverse recovery time is shortened by 37.7% and the reverse recovery current peak is reduced by 48.4% because the doping concentration of the p-buffer layer of the diode proposed in this application is significantly lower than the p+ anode doping of the PIN diode. It can be concluded that the fast soft recovery diode proposed in this application has significantly reduced reverse recovery time and reverse recovery peak current, has the ability to dynamically adjust the current in the forward conduction characteristics, and the current density distribution is effectively controlled and uniformly distributed during the reverse recovery process, thereby improving the reverse recovery stability of the device.

[0059] Figure 8 This is the current density distribution diagram of the traditional PIN diode in the dynamic reverse recovery stage. ) conditions, traditional PIN diodes have current density concentration. This is due to uneven electric field distribution caused by local uneven doping of the cathode or anode, which leads to current density concentration, further causing local overheating of the device and the possibility of thermal failure.

[0060] Figure 9 This is the current density distribution diagram of the fast soft recovery diode with back hole injection provided by this application in the dynamic reverse recovery stage. ) conditions, holes are primarily injected from the multiple p+ anode regions on the anode side, resulting in a uniform distribution of current density across the multiple p+ anode regions. Furthermore, the current density distribution on the cathode side of the diode provided by this application exhibits a stable distribution characteristic, with the current density reliably fixed in the multiple p cathode regions formed by local injection in the n-buffer region. This is due to the high doping on both sides of the p-n+ junction. Under low reverse bias conditions, avalanche breakdown occurs at the p-n+ junction, and holes are injected into the n-base region. This improves the softness of the diode during reverse recovery and simultaneously controls the distribution of the current path.

[0061] The term "and / or" in this application describes an association relationship between associated objects, indicating that three relationships can exist. For example, A and / or B can represent: A exists alone, A and B exist simultaneously, or B exists alone. The symbol " / " in this application indicates that the associated objects are in an "or" relationship, for example, A / B means A or B.

[0062] In this application, the terms "first" and "second" are used to distinguish different objects, rather than to describe a specific order of objects. For example, the terms "first response message" and "second response message" are used to distinguish different response messages, rather than to describe a specific order of response messages.

[0063] In the embodiments of this application, words such as "exemplary" or "for example" are used to indicate examples, illustrations, or descriptions. Any embodiment or design described as "exemplary" or "for example" in the embodiments of this application should not be interpreted as being preferred or advantageous over other embodiments or designs. Rather, the use of words such as "exemplary" or "for example" is intended to present the relevant concepts in a concrete manner.

[0064] In the description of the embodiments of the present application, unless otherwise specified, "multiple" means two or more, for example, multiple processing units means two or more processing units, etc.; multiple elements means two or more elements, etc.

[0065] It should be understood that expressions such as "include" and "may include" used in this application indicate the existence of the disclosed functions, operations, or constituent elements, and do not limit one or more additional functions, operations, and constituent elements. In this application, terms such as "include" and / or "have" may be interpreted as indicating specific characteristics, numbers, operations, constituent elements, components, or combinations thereof, but may not be interpreted as excluding the existence or possibility of adding one or more other characteristics, numbers, operations, constituent elements, components, or combinations thereof.

[0066] In the description of the embodiments of the present application, it should be noted that, unless otherwise clearly specified and limited, the term "connection" should be understood in a broad sense. For example, "connection" can be a detachable connection or a non-detachable connection; it can be a direct connection or an indirect connection through an intermediate medium. Among them, "fixed connection" means that the two are connected to each other and the relative position relationship after the connection remains unchanged. "Rotational connection" means that the two are connected to each other and can rotate relative to each other after the connection. "Sliding connection" means that the two are connected to each other and can slide relative to each other after the connection. The directional terms mentioned in the embodiments of the present application, such as "top", "bottom", "inside", "outside", "left", "right", etc., are only reference to the directions of the accompanying drawings. Therefore, the directional terms used are for better and clearer explanation and understanding of the embodiments of the present application, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore cannot be understood as a limitation on the embodiments of the present application.

[0067] In addition, in the embodiments of the present application, the mathematical concepts mentioned include symmetry, equality, parallelism, and perpendicularity. These limitations are all for the current state of the art, rather than being absolutely strict definitions in a mathematical sense. A small amount of deviation is allowed, and it is possible to be approximately symmetric, approximately equal, approximately parallel, or approximately perpendicular. For example, A and B are parallel, which means that A and B are parallel or approximately parallel, and the angle between A and B can be between 0 and 10 degrees. A and B are perpendicular, which means that A and B are perpendicular or approximately perpendicular, and the angle between A and B can be between 80 and 100 degrees.

[0068] The above description is merely a specific embodiment of the present application, but the scope of protection of the present application is not limited thereto. Any changes or substitutions that can be easily conceived by a person skilled in the art within the technical scope disclosed in this application should be included in the scope of protection of this application. Therefore, the scope of protection of this application should be based on the scope of protection of the claims.

Claims

1. A fast soft recovery diode with back hole injection, characterized in that: include: Anode metal (6), insulating oxide layer (7), multiple p+ anode regions (8), p buffer layer (9), n-base region (10), n buffer layer (11), multiple p cathode regions (12), n+ cathode region (13), cathode metal (14); The plurality of p+ anode regions (8) are embedded in a p buffer layer (9) at equal intervals; Each p+ anode region has a doping concentration higher than that of the p buffer layer (9), is connected to the anode metal (6) near the anode side, and does not exceed the p buffer layer (9) near the cathode side; An insulating oxide layer (7) is provided between the anode metal (6) and the p buffer layer (9); A plurality of p cathode regions (12) are formed by ion implantation at equal intervals in the n buffer layer (11); Each p cathode region (12) contacts the n+ cathode region (13) near the cathode side and does not exceed the n buffer layer (11) near the anode side; The n+ cathode region (13) has a higher doping concentration than the n buffer layer (11) and is connected to the cathode metal (14) near the cathode side.

2. The fast soft recovery diode according to claim 1, characterized in that The number of p+ anode regions (8) and p cathode regions (12) is the same and they are arranged correspondingly up and down.

3. The fast soft recovery diode according to claim 2, characterized in that: The distance between each p+ anode region ranges from 20um to 100um.

4. The fast soft recovery diode according to claim 2, characterized in that: The p+ anode region (8) and the p cathode region (12) are rectangular parallelepipeds of the same specifications, with a thickness ranging from 7um to 12um and a width ranging from 2um to 3um.

5. The fast soft recovery diode according to claim 1, characterized in that: The doping concentrations of the p+ anode region (8) and the p cathode region (12) are both above.

6. The fast soft recovery diode according to claim 1, characterized in that: The material of the p+ anode region is p-type SI-B, and the material of the p buffer layer is p-type SI-B.

7. The fast soft recovery diode according to claim 1, characterized in that: The material of the n-buffer layer is n-type SI-P, and the material of the p-cathode region is p-type SI-B.

8. The fast soft recovery diode according to claim 1, characterized in that: The insulating oxide is SiO2.

9. A method for preparing a fast soft recovery diode with back hole injection, characterized in that: include: S1. forming an n-buffer layer (11) on the cathode side of the n-base region (10) by a diffusion process; S2. forming a p-buffer layer (9) on the anode side of the n-base region (10) by a diffusion process; S3. depositing an insulating oxide layer on the p-buffer layer (9) by a PECVD deposition process; S4. forming a local insulating oxide layer (7) on the insulating oxide layer by an etching process; S5. forming a p+ anode region (8) on the local insulating oxide layer by an ion implantation process; S6. forming a local p cathode region (12) on the n buffer layer (11) by an ion implantation process; S7. forming an n+ cathode region (13) on the n buffer layer (11) by an epitaxial process; S8. The anode electrode is formed by depositing metal Al or Au through the insulating oxide layer on the p+ anode region and forming an ohmic contact. S9. The cathode electrode is deposited in sequence on the n+ cathode region by metal Al and Au and makes ohmic contact.

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