A method for fabricating a fast recovery diode

Abstract

This invention discloses a method for fabricating a fast recovery diode (FRD). This method combines ion implantation and neutron transmutation processes to fabricate the FRD, significantly simplifying the fabrication process and reducing the fabrication cycle while ensuring the performance of the FRD. The method includes: fabricating the front-side structure of the FRD on the upper surface of an N-type substrate; implanting hydrogen ions and phosphorus ions from the back side of the N-type substrate using ion implantation and neutrons from the back side using neutron transmutation; annealing the N-type substrate at a preset temperature to form a multilayer field-stop layer with the same conductivity type as the N-type substrate, where hydrogen ions are located in the first field-stop layer, neutrons in the second field-stop layer, and phosphorus ions in the third field-stop layer; and fabricating the cathode region of the FRD on the lower surface of the N-type substrate.

Description

Technical Field

[0001] This invention relates to the field of semiconductor device technology, and in particular to a method for fabricating a fast recovery diode. Background Technology

[0002] A fast recovery diode (FRD) is a semiconductor diode characterized by good switching characteristics and short reverse recovery time. It is used in conjunction with three-terminal power switching devices such as insulated gate bipolar transistors (IGBTs) and integrated gate commutated thyristors (IGCTs) to conduct reactive current in the load, shorten the charging time of the capacitor, and suppress the high voltage induced by the instantaneous reverse current of the load. It is widely used in AC / DC converters, pulse width modulators, and other power electronics and communication equipment.

[0003] Currently, most fast recovery diodes are fabricated using multilayer epitaxial processes, which employ N-type epitaxial silicon wafers as the material and P-type active regions using ion implantation or diffusion. Therefore, the fabrication process involves oxidation, photolithography of the active region, ion implantation, junction pushing, photolithography of electrode holes, metallization, photolithography of metal, deposition of passivation layer, photolithography of passivation layer, silicon wafer thinning, and back-side metallization. The fabrication process requires multiple ion implantations, high-temperature junction pushing, and multiple photolithography processes.

[0004] It is evident that the existing technology of fabricating fast recovery diodes using multilayer epitaxial processes is not only complex and time-consuming, but also costly. Summary of the Invention

[0005] This invention provides a method for fabricating a fast recovery diode. This method combines ion implantation and neutron transmutation processes to fabricate the fast recovery diode. While ensuring the performance of the fast recovery diode, it greatly simplifies the fabrication process and reduces the fabrication cycle.

[0006] In a first aspect, embodiments of the present invention provide a method for fabricating a fast recovery diode, the method comprising:

[0007] The front-side structure of a fast recovery diode (FRD) is fabricated on the upper surface of an N-type substrate;

[0008] Hydrogen and phosphorus ions are implanted from the back side of the N-type substrate using ion implantation and neutrons are implanted from the back side of the N-type substrate using neutron transmutation. The N-type substrate is then annealed and activated at a preset temperature to form a multilayer field-stop layer with the same conductivity type as the N-type substrate. The implanted neutrons are used to convert some isotopes of silicon atoms in the N-type substrate into phosphorus atoms. The hydrogen ions are located in the first field-stop layer, the neutrons are located in the second field-stop layer, and the phosphorus ions are located in the third field-stop layer. The region inside the N-type substrate other than the first, second, and third field-stop layers is the N-drift region. The distances of the N-drift region, the first, second, and third field-stop layers from the upper surface of the N-type substrate increase sequentially, and the impurity concentrations also increase sequentially.

[0009] The cathode region of the FRD is prepared on the back side of the N-type substrate.

[0010] In this embodiment of the invention, firstly, the front structure of a fast recovery diode is fabricated on the upper surface of a provided N-type substrate. Then, hydrogen and phosphorus ions are implanted from the back side of the N-type substrate using an ion implantation process, and neutrons are implanted from the back side of the N-type substrate using a neutron transmutation process. Since the implanted neutrons can convert some isotopes of silicon atoms in the N-type substrate into phosphorus atoms, the first field-stop layer containing hydrogen ions, the second field-stop layer containing neutrons, and the third field-stop layer containing phosphorus ions maintain the same conductivity type as the N-type substrate. The region inside the N-type substrate other than the first, second, and third field-stop layers is the N-drift region, and the impurity concentrations corresponding to the N-drift region, the first field-stop layer, the second field-stop layer, and the third field-stop layer increase sequentially. Finally, the cathode region of the fast recovery diode is fabricated on the lower surface of the N-type substrate to complete the fabrication of the fast recovery diode. This method combines ion implantation and neutron transmutation processes to fabricate fast recovery diodes, greatly simplifying the fabrication process and reducing the fabrication cycle while ensuring the performance of the fast recovery diode.

[0011] Optionally, the energy of the hydrogen ions, the neutrons, and the phosphorus ions injected is in the megaelectron volt (Mev) range, and the injection dose is 1e14cm. -2 -1e15cm -2 The average injection depth is on the order of micrometers (µm).

[0012] In this embodiment of the invention, the injection energies of hydrogen ions, neutrons, and phosphorus ions reach the MeV level, and the injection dose reaches 1e14cm. -2 -1e15cm -2The average injection depth is in the micrometer range (µm). During the injection process, relevant parameters can be flexibly selected based on actual conditions to ensure that the concentration of impurities formed in each field-stop layer meets the performance requirements of the fast recovery diode.

[0013] Optionally, before implanting hydrogen and phosphorus ions from the back side of the N-type substrate via ion implantation and neutrons from the back side of the N-type substrate via neutron transmutation, the method further includes:

[0014] The back side of the N-type substrate is thinned, and the thinning process includes etching or a combination of grinding and etching, with the thickness of the thinning process being on the order of micrometers (µm).

[0015] In this embodiment of the invention, before implementing the ion implantation process and the neutron transmutation process, the back side of the N-type substrate can be thinned. For example, the back side of the N-type substrate can be thinned by etching or by a combination of etching and polishing, thereby reducing the thickness of the N-type substrate and thus reducing the on-state voltage drop of the fast recovery diode.

[0016] Optionally, the hydrogen ions, the neutrons, and the phosphorus ions are injected simultaneously.

[0017] In this embodiment of the invention, since hydrogen ions, neutrons, and phosphorus ions are implanted into different regions of the N-type substrate to form field cutoff layers of different concentrations, hydrogen ions, neutrons, and phosphorus ions can be implanted simultaneously, thereby shortening the fabrication time of the fast recovery diode.

[0018] Optionally, fabricating the front-side structure of the FRD on the surface of the N-type substrate includes:

[0019] An oxide layer is obtained by oxidizing the upper surface of the N-type substrate;

[0020] The terminal structure of the FRD is prepared based on the oxide layer;

[0021] An anode region is formed on the terminal structure by sputtering or depositing metal.

[0022] A passivation layer is formed by deposition on the anode region, and the passivation layer is etched to obtain the front structure of the FRD. The passivation layer is made of polyimide material.

[0023] In this embodiment of the invention, an oxide layer is first prepared on the upper surface of an N-type substrate, and a terminal structure of a fast recovery diode is formed based on the oxide layer. Then, an anode region is formed on the terminal structure by sputtering or depositing metal. Finally, a passivation layer is formed above the anode region by a deposition process to protect the anode region, and the front structure of the fast recovery diode is formed by an etching process.

[0024] Optionally, the oxidation treatment of the upper surface of the N-type substrate to obtain an oxide layer includes:

[0025] In a space filled with hydrogen and oxygen, the upper surface of the N-type substrate is subjected to high-temperature oxidation to form the oxide layer within a preset temperature range and a preset duration. The preset temperature range is 900℃-1100℃ and the preset duration is 1h-10h.

[0026] In this embodiment of the invention, an oxide layer can be generated on the upper surface of an N-type substrate in a space filled with hydrogen and oxygen, based on a preset temperature and a preset duration, so as to facilitate the subsequent photolithography process.

[0027] Optionally, the preparation of the terminal structure of the FRD based on the oxide layer includes:

[0028] Based on the oxide layer, a terminal protection ring region and a stop ring structure are prepared, and the terminal protection ring region and the stop ring structure together constitute the terminal structure.

[0029] In this embodiment of the invention, after forming an oxide layer on the upper surface of an N-type substrate, a terminal protection ring region and a cutoff ring structure can be fabricated based on the oxide layer, thereby forming the terminal structure of a fast recovery diode.

[0030] Optionally, the preparation of the terminal protection ring region based on the oxide layer includes:

[0031] Photoresist is coated on the oxide layer and exposed through a terminal ring mask to form a ring-shaped region;

[0032] P-type ion implantation and annealing processes are performed in the annular region to form a terminal protection ring structure. After removing excess photoresist and cleaning the formed terminal protection ring structure, the terminal protection ring region is obtained. The implantation energy of the P-type ions is 60keV-80keV, and the P-type ions are boron ions.

[0033] In this embodiment of the invention, a ring-shaped region can be formed on the oxide film by photolithography, and P-type ions, such as boron ions, are implanted in the ring-shaped region with a preset implantation energy. After removing and cleaning the excess photoresist in the photolithography process, the terminal protection ring region can be obtained.

[0034] Optionally, the preparation of the stop ring structure based on the oxide layer includes:

[0035] Photoresist is coated on the surface of the oxide layer, and exposure is performed through a stop ring mask to form a stop ring region.

[0036] A cutoff ring structure is formed by N+ ion implantation and annealing in the cutoff ring region, wherein the N+ ion implantation dose is 1e14cm. -2 -1e15cm -2 The annealing temperature is 900℃-1150℃.

[0037] In this embodiment of the invention, a cutoff ring region can be formed based on the formed oxide layer through photolithography, and after implanting N+ type ions into the cutoff ring region and annealing, a cutoff ring structure can be obtained.

[0038] Optionally, fabricating the cathode region of the FRD on the back side of the N-type substrate includes:

[0039] The cathode region of the FRD is formed on the back side of the N-type substrate by sputtering or depositing metal.

[0040] In this embodiment of the invention, the cathode region of the fast recovery diode can be formed on the back side of the N-type substrate by sputtering or depositing metal, thereby completing the fabrication of the fast recovery diode. Attached Figure Description

[0041] Figure 1 This is a schematic diagram of the structure of a fast recovery diode provided in an embodiment of the present invention;

[0042] Figure 2 A schematic flowchart illustrating a method for fabricating a fast recovery diode according to an embodiment of the present invention;

[0043] Figure 3 This is a schematic diagram of the structure for forming an oxide layer on an N-type substrate according to an embodiment of the present invention;

[0044] Figure 4 This is a schematic diagram of the structure for generating a terminal protection ring region on an N-type substrate according to an embodiment of the present invention;

[0045] Figure 5 This is a schematic diagram of generating a cutoff ring structure on an N-type substrate according to an embodiment of the present invention;

[0046] Figure 6 This is a schematic diagram of the structure for generating an anode region on an N-type substrate according to an embodiment of the present invention;

[0047] Figure 7This is a schematic diagram of the structure for forming a passivation layer on an N-type substrate according to an embodiment of the present invention;

[0048] Figure 8 This is a schematic diagram of a structure for generating a multilayer field cutoff layer in an N-type substrate, provided in an embodiment of the present invention. Detailed Implementation

[0049] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and embodiments.

[0050] In existing technologies, multilayer epitaxial processes are typically used to form fast recovery diodes. This means that fast recovery diodes need to be fabricated layer by layer, which requires multiple ion implantations, high-temperature junction pushing, and multiple photolithography processes. This results in complicated fabrication procedures, long production cycles, and high production costs in the fabrication of fast recovery diodes.

[0051] In view of this, embodiments of the present invention provide a method for fabricating a fast recovery diode. This method combines ion implantation and neutron transmutation processes, which enables the fabricated fast recovery diode to have high performance, greatly simplifies the fabrication process, reduces fabrication time, and saves fabrication costs.

[0052] The thickness and shape of each film layer in the attached figures do not reflect the actual proportions and are intended only to illustrate the content of the present invention.

[0053] Please see Figure 1 To facilitate understanding, a schematic diagram of a fast recovery diode according to an embodiment of the present invention will be introduced first. Figure 1 The fast recovery diode includes a front structure 101 (hereinafter referred to as front structure 101), an N-type substrate 102, a first field-stop layer 103, a second field-stop layer 104, a third field-stop layer 105, and a cathode region 106 (hereinafter referred to as cathode region 106). The front structure 101 is formed on the upper surface of the N-type substrate 102. The first field-stop layer 103, the second field-stop layer 104, and the third field-stop layer 105 are formed inside the N-type substrate 102. The region in the N-type substrate 102 other than the first field-stop layer 103, the second field-stop layer 104, and the third field-stop layer 105 is the N-drift region. Figure 1(Not shown), the cathode region 106 is formed on the back side of the N-type substrate 102. It should be understood that, relative to the front-side structure 101, the N-drift region, the first field-stop layer 103, the second field-stop layer 104, the third field-stop layer 105, and the cathode region 106 can all be considered to be formed on the back side of the N-type substrate 102. To ensure better performance of the fast recovery diode, the impurity concentration in the N-drift region, the first field-stop layer 103, the second field-stop layer 104, and the third field-stop layer 105 increases sequentially. The thickness of the N-type substrate 102 is 50µm-70µm, and the total thickness of the first field-stop layer 103, the second field-stop layer 104, and the third field-stop layer 105 is 15µm-20µm.

[0054] based on Figure 1 The diagram shows the structure of a fast recovery diode. The technical solution provided by the embodiments of the present invention will be described below with reference to the accompanying drawings. Please refer to... Figure 2 This invention provides a method for fabricating a fast recovery diode, the process of which is described as follows:

[0055] Step 201: Fabricate the front structure 101 of the fast recovery diode (FRD) on the upper surface of the N-type substrate 102.

[0056] In this embodiment of the invention, before fabricating the fast recovery diode, an N-type substrate 102 for fabricating the fast recovery diode is first required. For example, different N-type substrates 102 are selected based on resistivity. In this embodiment of the invention, an N-type substrate 102 with a specific resistivity can be selected according to actual needs, for example, an N-type substrate 102 with a resistivity of 30 ohm-cm or an N-type substrate 102 with a resistivity of 60 ohm-cm. No particular limitation is placed on the resistivity of the selected N-type substrate 102. After selecting an N-type substrate 102 with a specific resistivity, the front-side structure 101 of the fast recovery diode can be fabricated based on this N-type substrate 102.

[0057] As one possible implementation method, please refer to Figures 3-7 The front structure 101 of a fast recovery diode can be fabricated on the upper surface of the N-type substrate 102. The front structure 101 mainly includes an oxide layer 1011, a terminal protection ring region 1012, a stop ring structure 1013, an anode region 1014, and a passivation layer 1015.

[0058] In the process of fabricating the front structure 101, it is usually necessary to generate an oxide film layer on the N-type substrate so that the terminal structure of the fast diode can be generated subsequently through photolithography.

[0059] As one possible implementation method, please refer to Figure 3The upper surface of the N-type substrate 102 can be oxidized to obtain an oxide layer 1011.

[0060] Specifically, the cleaned N-type substrate 102 can be placed in a space filled with oxygen and hydrogen, and then subjected to high-temperature oxidation treatment based on a preset temperature and a preset duration. For example, the preset temperature can be in the range of 900℃-1100℃, and the preset duration can be in the range of 1h-10h. In this embodiment of the invention, appropriate parameters can be selected within the preset temperature range and preset duration range according to the actual situation; no special restrictions are placed on the preset temperature and preset duration here.

[0061] After forming the oxide layer 1011 on the N-type substrate 102, the termination structure of the fast recovery diode can be formed using photolithography. As one possible implementation, the termination structure of the fast recovery diode can be fabricated based on the oxide layer 1011.

[0062] Specifically, the termination structure of the fast recovery diode includes a termination protection ring region 1012 and a cutoff ring structure 1013. Typically, the termination protection ring region 1012 is fabricated first, followed by the cutoff ring structure 1013.

[0063] As one possible implementation method, please refer to Figure 4 Terminal protection ring region 1012 is prepared based on oxide layer 1011.

[0064] Specifically, photoresist is first coated onto the oxide layer 1011, and then exposed using a mask corresponding to the shape of the terminal protection ring region 1012 to form a ring-shaped region. After forming the ring-shaped region, P-type ions can be implanted into it to make it conductive. For example, the P-type ions can be boron ions or other types of ions; the type of P-type ions is not specifically limited here. The implantation energy for P-type ions is 60 keV-80 keV. It should be understood that the energy for implanting P-type ions is related to the implantation depth; the higher the energy, the greater the implantation depth; conversely, the lower the energy, the smaller the implantation depth. Therefore, the energy for implanting P-type ions can be selected according to actual needs.

[0065] After the implantation of P-type ions is completed, an annealing process can be performed to activate the implanted P-type ions. In other words, the annealing process makes the implanted P-type ions more active, resulting in a more uniform distribution within the formed annular region, which helps to improve the conductivity of the terminal protection ring region 1012.

[0066] After the terminal protection ring region 1012 is fabricated, the stop ring structure 1013 can be fabricated. For one possible implementation, please refer to [link to relevant documentation]. Figure 5 A cutoff ring structure 1013 can be fabricated based on the oxide layer 1011, thereby forming the terminal structure of the fast recovery diode.

[0067] Specifically, photoresist is first coated onto the surface of the terminal protection ring region. Then, the photoresist is exposed using a mask corresponding to the stop ring structure 1013 to form the stop ring region. After forming the stop ring region, N+ ions are implanted into it to make it conductive, thereby forming the stop ring structure 1013. For example, the dose of implanted N+ ions is 1e14cm⁻¹. -2 -1e15cm -2 To ensure a more uniform distribution of the implanted N+ ions within the stop ring structure 1013, an annealing process can be performed after N+ ion implantation, for example, at a temperature of 900℃-1150℃. It should be understood that the implantation dose of N+ ions and the annealing temperature can be selected according to actual needs during the preparation process; no specific restrictions are imposed on the above parameters here.

[0068] After the cutoff ring structure 1013 is fabricated, the termination structure of the fast recovery diode is complete. Based on this, the anode of the fast recovery diode can be further fabricated. For one possible implementation, please refer to... Figure 6 The anode region 1014 of the fast recovery diode can be formed on the terminal structure by sputtering or depositing metal.

[0069] Specifically, the metal used to form the anode region 1014 of the fast recovery diode can be aluminum or other types of metal; there are no special restrictions on the type of metal used to form the anode region.

[0070] After the anode region 1014 is fabricated, in order to protect the internal structure of the fast recovery diode (such as the termination protection ring region 1012 and the cutoff ring structure 1013, etc.) and prevent moisture in the air from corroding the internal structure of the fast recovery diode, an isolation film layer can be formed at the interface between the anode region 1014 and the oxide layer 1011 in this embodiment of the invention. As one possible implementation, please refer to... Figure 7 A passivation layer 1015 can be formed on the anode region 1014 and oxide layer 1011 of the fast recovery diode by deposition process. The passivation layer 1015 is mainly composed of polyimide material.

[0071] After a passivation layer 1015 is formed on the anode region 1014 by deposition, the passivation layer 1015 can be etched to reserve a wire bonding window in the passivation layer, so as to facilitate the subsequent encapsulation of the front structure of the fast recovery diode.

[0072] Step 202: Hydrogen ions and phosphorus ions are implanted from the back side of the N-type substrate 102 by ion implantation and neutrons are implanted from the back side of the N-type substrate 102 by neutron transmutation. The N-type substrate 102 is then annealed and activated at a preset temperature to form a multilayer field stop layer with the same conductivity type as the N-type substrate 102. The implanted neutrons are used to convert some isotopes of silicon atoms in the N-type substrate 102 into phosphorus atoms. Hydrogen ions are located in the first field stop layer 103, neutrons are located in the second field stop layer 104, and phosphorus ions are located in the third field stop layer 105. The area inside the N-type substrate 102 other than the first field stop layer 103, the second field stop layer 104, and the third field stop layer 105 is the N-drift region. The distances from the N-drift region, the first field stop layer 103, the second field stop layer 104, and the third field stop layer 105 to the upper surface of the N-type substrate 102 increase sequentially, and the impurity concentrations formed also increase sequentially.

[0073] In this embodiment of the invention, after the fabrication of the front-side structure 101 of the fast recovery diode is completed, the field-stop layer region of the fast recovery diode can be further fabricated. Considering that in the prior art, when fabricating the multilayer field-stop layer of the fast recovery diode, it is necessary to fabricate layer by layer, and each layer requires processes such as photoresist coating, exposure, development, etching, and ion implantation, resulting in a relatively complicated fabrication process and a long fabrication cycle.

[0074] Therefore, in this embodiment of the invention, the impurities to be doped can be implanted from the back side of the N-type substrate 102 into the N-type substrate 102. Furthermore, by controlling the energy, dosage, and implantation depth during impurity implantation, the concentration of impurities in each field cutoff layer can be controlled more accurately. This greatly simplifies the fabrication process of the field cutoff layer and reduces the fabrication time while ensuring rapid recovery of diode performance.

[0075] As one possible implementation method, please refer to Figure 8Hydrogen ions and phosphorus ions can be implanted from the back side of the N-type substrate 102 using ion implantation, and neutrons can be implanted from the back side of the N-type substrate 102 using neutron transmutation. In the regions implanted with hydrogen and phosphorus ions, a field cutoff layer with the same conductivity type as the N-type substrate 102 can be directly formed. After neutron implantation, the silicon atoms in the N-type substrate 102 are irradiated, causing some of the silicon atoms to be converted to phosphorus atoms, thus ensuring that the neutron-implanted regions also maintain the same conductivity type as the N-type substrate 102.

[0076] For example, the injected hydrogen ion region forms the first field cutoff layer 103, the injected neutron region forms the second field cutoff layer 104, and the injected phosphorus ion region forms the third field cutoff layer 105. It should be understood that the region inside the N-type substrate 102 excluding the first field cutoff layer 103, the second field cutoff layer 104, and the third field cutoff layer 105 is the N-drift region, and the distances of the N-drift region, the first field cutoff layer 103, the second field cutoff layer 104, and the third field cutoff layer 105 from the upper surface of the N-type substrate 102 increase sequentially. The three field cutoff layers are independent of each other, and each field cutoff layer contains only one type of impurity (hydrogen ions, neutrons, or phosphorus ions).

[0077] To ensure that the impurity concentrations in the three field-stop layers meet the performance requirements of the fast recovery diode, the energy, dose, and depth of hydrogen, neutron, and phosphorus ion implantation can be controlled. As one possible implementation, the implantation energy for hydrogen, neutron, and phosphorus ions is in the megaelectron volt (Mev) range, and the implantation dose is 1e14 cm⁻¹. -2 -1e15cm -2 The average injection depth is on the order of micrometers (µm).

[0078] It should be understood that in the actual preparation process, specific parameters can be selected for each impurity (hydrogen ions, neutrons, and phosphorus ions) to be injected according to actual needs. No special restrictions are placed on the parameters when injecting impurities (hydrogen ions, neutrons, and phosphorus ions) here.

[0079] Considering that the formation of multiple field stop layers in the N-type substrate 102 is independent, sequentially implanting the aforementioned impurities into different regions of the N-type substrate 102—for example, first implanting hydrogen ions, then neutrons, and finally phosphorus ions—to form multiple field stop layers, would result in a relatively long preparation cycle. Therefore, in this embodiment of the invention, the aforementioned impurities can be implanted into different regions of the N-type substrate 102 simultaneously using different implantation devices. As one possible implementation, hydrogen ions, neutrons, and phosphorus ions can be implanted simultaneously.

[0080] After implanting three types of impurities (hydrogen ions, neutrons, and phosphorus ions) into different regions of the N-type substrate 102, in order to make the impurities contained in each region more active and thus ensure the uniform distribution of impurities in each region, in this embodiment of the invention, the N-type substrate 102 can be annealed after each impurity is implanted into the corresponding field stop layer.

[0081] In one possible implementation, after hydrogen ions and phosphorus ions are implanted from the back side of the N-type substrate 102 by ion implantation process and neutrons are implanted from the back side of the N-type substrate 102 by neutron transmutation process, the N-type substrate 102 is annealed and activated at a preset temperature.

[0082] For example, the preset temperature for annealing activation is 300℃-400℃. In the actual annealing activation process, the preset temperature can be selected according to actual needs; no specific limit is placed on the exact value of the preset temperature here. It should be understood that the preset temperature cannot be too high, as this will affect the front-side structure 101 of the already fabricated fast recovery diode; conversely, the preset temperature cannot be too low, as this will fail to fully activate the impurities located in each field-stop layer, resulting in uneven impurity distribution in each field-stop layer, thus affecting the overall performance of the fast recovery diode.

[0083] In this embodiment of the invention, a multilayer field cutoff layer is formed by implanting impurities from the back side of the N-type substrate 102. Therefore, before implanting impurities, the N-type substrate 102 can be pretreated to keep the thickness of the N-type substrate 102 within a certain range. This thickness range can meet both the requirements of including a multilayer field cutoff layer and the performance requirements of the fast recovery diode for the N-type substrate 102.

[0084] As one possible implementation, the back side of the N-type substrate 102 can be thinned. For example, the back side of the N-type substrate 102 can be thinned by etching alone, or by a combination of etching and polishing. The thickness of the thinning process is in the micrometer (µm) range, and the specific thickness value can be selected according to actual needs; no specific limit is placed on the specific value of the thinning process here.

[0085] Step 203: Fabricate the cathode region 106 of the FRD on the back side of the N-type substrate 102.

[0086] In this embodiment of the invention, after the fabrication of the multilayer field cutoff layer in the N-type substrate 102 is completed, the cathode region in the fast recovery diode can be fabricated based on the N-type substrate 102 to form the final fast recovery diode.

[0087] As one possible implementation method, please continue to see Figure 1 The cathode region 106 of the fast recovery diode can be formed on the back side of the N-type substrate 102 by sputtering or depositing metal.

[0088] Specifically, the metal used to form the cathode region 106 of the fast recovery diode can be aluminum or other types of metal; there are no special restrictions on the type of metal used to form the cathode region 106.

[0089] Obviously, those skilled in the art can make various modifications and variations to this application without departing from the spirit and scope of this application. Therefore, if such modifications and variations fall within the scope of the claims of this application and their equivalents, this application also intends to include such modifications and variations.

Claims

1. A method for fabricating a fast recovery diode, characterized in that, The method includes: The front-side structure of a fast recovery diode (FRD) is fabricated on the upper surface of an N-type substrate; Hydrogen and phosphorus ions are implanted from the back side of the N-type substrate using ion implantation and neutrons are implanted from the back side of the N-type substrate using neutron transmutation. The N-type substrate is then annealed and activated at a preset temperature to form a multilayer field-stop layer with the same conductivity type as the N-type substrate. The implanted neutrons are used to convert some isotopes of silicon atoms in the N-type substrate into phosphorus atoms. The hydrogen ions are located in the first field-stop layer, the neutrons are located in the second field-stop layer, and the phosphorus ions are located in the third field-stop layer. The region inside the N-type substrate other than the first, second, and third field-stop layers is the N-drift region. The distances of the N-drift region, the first, second, and third field-stop layers from the upper surface of the N-type substrate increase sequentially, and the impurity concentrations also increase sequentially. The cathode region of the FRD is prepared on the back side of the N-type substrate; The step of implanting hydrogen ions and phosphorus ions from the back side of the N-type substrate through ion implantation and neutrons from the back side of the N-type substrate through neutron transmutation includes: simultaneously implanting the hydrogen ions, phosphorus ions and neutrons into different regions of the N-type substrate using different implantation devices.

2. The method as described in claim 1, characterized in that, The energy of the hydrogen ions, neutrons, and phosphorus ions injected is in the megaelectron volt (Mev) range, and the injection dose is 1e14cm. -2 -1e15cm -2 The average injection depth is on the order of micrometers (µm).

3. The method as described in claim 1, characterized in that, Before implanting hydrogen and phosphorus ions from the back side of the N-type substrate via ion implantation and neutrons from the back side of the N-type substrate via neutron transmutation, the procedure further includes: The back side of the N-type substrate is thinned, and the thinning process includes etching or a combination of grinding and etching, with the thickness of the thinning process being on the order of micrometers (µm).

4. The method as described in claim 1, characterized in that, The preset temperature is 300℃-400℃.

5. The method as described in claim 1, characterized in that, Fabricating the front-side structure of the FRD on the surface of an N-type substrate includes: An oxide layer is obtained by oxidizing the upper surface of the N-type substrate; The terminal structure of the FRD is prepared based on the oxide layer; An anode region is formed on the terminal structure by sputtering or depositing metal. A passivation layer is formed by deposition on the anode region, and the passivation layer is etched to obtain the front structure of the FRD. The passivation layer is made of polyimide material.

6. The method as described in claim 5, characterized in that, The oxidation process performed on the upper surface of the N-type substrate to obtain an oxide layer includes: In a space filled with hydrogen and oxygen, the upper surface of the N-type substrate is subjected to high-temperature oxidation to form the oxide layer within a preset temperature range and a preset duration. The preset temperature range is 900℃-1100℃ and the preset duration is 1h-10h.

7. The method as described in claim 5, characterized in that, The preparation of the terminal structure of the FRD based on the oxide layer includes: Based on the oxide layer, a terminal protection ring region and a stop ring structure are prepared, and the terminal protection ring region and the stop ring structure together constitute the terminal structure.

8. The method as described in claim 7, characterized in that, The preparation of the terminal protection ring region based on the oxide layer includes: Photoresist is coated on the oxide layer and exposed through a terminal ring mask to form a ring-shaped region; P-type ion implantation and annealing processes are performed in the annular region to form a terminal protection ring structure. After removing excess photoresist and cleaning the formed terminal protection ring structure, the terminal protection ring region is obtained. The implantation energy of the P-type ions is 60keV-80keV, and the P-type ions are boron ions.

9. The method as described in claim 7, characterized in that, The preparation of the stop-ring structure based on the oxide layer includes: Photoresist is coated on the surface of the oxide layer, and exposure is performed through a stop ring mask to form a stop ring region. A cutoff ring structure is formed by N+ ion implantation and annealing in the cutoff ring region, wherein the N+ ion implantation dose is 1e14cm. -2 -1e15cm -2 The annealing temperature is 900℃-1150℃.

10. The method as described in claim 1, characterized in that, Fabricating the cathode region of the FRD on the back side of the N-type substrate includes: The cathode region of the FRD is formed on the back side of the N-type substrate by sputtering or depositing metal.

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