FRD capable of improving reverse recovery characteristic and preparation method thereof

Abstract

The invention discloses an FRD capable of improving the reverse recovery characteristic and a preparation method, and relates to the field of semiconductor devices, the FRD comprises an N-type substrate, and the N-type substrate comprises a front surface and a back surface corresponding to the front surface; the front surface of the N-type substrate is correspondingly provided with a front surface structure, and the front surface structure comprises a plurality of P-type column regions which are prepared in the N-type substrate and are distributed at intervals; and the P-type column region is in ohmic contact with anode metal used for forming an anode above the N-type substrate. The FRD has a good reverse recovery characteristic.

Description

Technical Field

[0001] The present invention relates to the field of semiconductor devices, and in particular to an FRD capable of improving reverse recovery characteristics and a preparation method thereof. Background Art

[0002] Fast recovery diode (FRD) is one of the most commonly used basic components and is widely used in electronic circuits. Short reverse recovery time, high breakdown voltage, low reverse cut-off current, soft recovery characteristics and low forward conduction voltage drop are important requirements for fast recovery diodes. In particular, the switching speed of semiconductor power devices has increased rapidly in recent years, and higher and higher requirements have been placed on the reverse recovery speed of the diodes connected in parallel with them.

[0003] The structure of traditional FRD is as follows Figure 1 As shown in the figure, it consists of three parts: the anode P+ region, the base N- region and the cathode N+ region. When forward conduction occurs, the N- region stores a large number of carriers from the P+ region and the N+ region. The carriers injected into the N- region form excess carriers, resulting in a high conductivity modulation effect, which reduces the resistance of the N- region and thus reduces the forward conduction voltage drop of the FRD. When a reverse bias is applied, under the action of an external electric field, the carriers in the N- region are extracted to form a depletion region, and the diode is converted to a reverse blocking state.

[0004] It takes a certain amount of time for the carriers to be extracted from the N-region in the reverse direction. We call this process that affects the FRD turn-off speed reverse recovery, and the time required during this period is the reverse recovery time. Figure 2 As shown in Figure 2. The shorter the reverse recovery time, the higher the operating frequency of the FRD and the lower the energy consumption. Figure 2 As shown, the reverse recovery time t rr is the storage time t a and the fall time t b The sum of t b With t a The ratio is called the softness factor S. The larger S is, the better the reverse recovery softness is, that is, the device can effectively avoid voltage overshoot and oscillation caused by hard recovery, and has better stability and reliability.

[0005] At present, three life-time control technologies, namely heavy metal doping, electron irradiation and localization, are commonly used to improve the reverse recovery speed of diodes. Life-time control technology refers to an engineering method that introduces deep energy level recombination centers into the device to accelerate the recombination of carriers and reduce the minority carrier lifetime.

[0006] Among them, the heavy metal doping method usually diffuses heavy metals such as platinum or gold into the diode. The heavy metal diffuses into the inside of the device and exists in the form of substitutional atomic defects or interstitial atomic defects. The defects formed act as recombination centers to accelerate the recombination of carriers, thereby increasing the reverse recovery speed of the device. However, heavy metal doping will seriously pollute devices and production equipment on the one hand. On the other hand, the defects formed by doping are generally U-shaped distribution, and the defects will be concentrated on the surface of the device, thereby affecting the ohmic contact of the device, resulting in an increase in the forward conduction voltage drop and reverse cutoff current, which has a greater negative impact on device performance.

[0007] The electron irradiation method uses a high-energy electron beam to bombard the semiconductor, causing electrons to enter the semiconductor and collide with silicon atoms to form defects. These defects can act as recombination centers to control the minority carrier lifetime, thereby reducing the reverse recovery time of the diode. However, the defects caused by electron irradiation will attenuate or even decrease, which is extremely unstable. Moreover, compared with the traditional platinum diffusion process, the device generates greater leakage and poor high-temperature characteristics.

[0008] Local lifetime control technology refers to the process of converting H + or He 2+ Light ion irradiation-induced defects act as recombination centers to reduce minority carrier lifetimes. However, due to the limitation that a single light ion irradiation can only obtain a recombination center area of ​​fixed width inside the device, if you want to form a recombination center area distribution with any concentration, you have to irradiate the device multiple times, which greatly increases the device cost and reduces production efficiency, making it impossible to apply on a large scale.

[0009] In summary, it is urgent to find a more environmentally friendly, convenient and effective technology to improve the reverse recovery characteristics of devices, and this technology must take into account important performance parameters such as the forward conduction voltage drop, reverse cutoff current and reverse recovery softness of the diode. Summary of the invention

[0010] In view of the above problems and technical requirements, the inventors have proposed an FRD and a preparation method capable of improving reverse recovery characteristics. The technical solution of the present invention is as follows:

[0011] An FRD capable of improving reverse recovery characteristics comprises an N-type substrate, wherein the N-type substrate comprises a front surface and a back surface corresponding to the front surface;

[0012] A front structure is correspondingly arranged on the front side of the N-type substrate, and the front structure includes a plurality of P-type column regions prepared in the N-type substrate and distributed at intervals;

[0013] The P-type column region is in ohmic contact with an anode metal on the N-type substrate for forming an anode.

[0014] A further technical solution is that the front structure further includes an N-type doped region disposed between adjacent P-type column regions, and the N-type doped region is in contact with the corresponding P-type column region;

[0015] The doping concentration of the N-type doping region is greater than the doping concentration of the N-type substrate, and the N-type doping region is in ohmic contact with an anode metal for forming an anode above the N-type substrate.

[0016] A further technical solution is that the junction depth of the N-type doped region is smaller than the junction depth of the P-type column region.

[0017] A further technical solution is that a back surface structure is correspondingly provided on the back surface of the N-type substrate, and the back surface structure includes a plurality of N-type cathode regions prepared in the N-type substrate and distributed at intervals;

[0018] The N-type cathode region is in ohmic contact with a cathode metal disposed on the back side of the N-type substrate for forming a cathode.

[0019] A further technical solution is that the doping concentration of the N-type cathode region is greater than the doping concentration of the N-type substrate.

[0020] A further technical solution is that a filling groove is provided between adjacent N-type cathode regions, the sidewall of the filling groove is in contact with the corresponding N-type cathode region, and the filling groove is filled with an insulating medium.

[0021] A further technical solution is that the depth of the filling groove is not less than the junction depth of the N-type cathode region.

[0022] A further technical solution is that the insulating medium includes silicon dioxide.

[0023] A method for preparing an FRD capable of improving reverse recovery characteristics, characterized in that it is used to prepare the above-mentioned FRD, wherein the preparation method comprises:

[0024] Providing an N-type substrate, and performing a front process on the front side of the N-type substrate to prepare a desired front side structure, wherein the front side structure includes a plurality of P-type column regions prepared in the N-type substrate and distributed at intervals;

[0025] The P-type column region is in ohmic contact with an anode metal on the N-type substrate for forming an anode.

[0026] A further technical solution is to prepare a P-type column region through multiple ion implantation processes, and when multiple ion implantation processes are performed, the implantation energy of the ions is reduced successively.

[0027] The beneficial technical effects of the present invention are:

[0028] The FRD with improved reverse recovery characteristics provided by the present invention can avoid the problems of increased diode conduction voltage drop, increased reverse leakage, and poor high-temperature characteristics caused by traditional life control technology. The emission efficiency of the anode is controlled and the reverse withstand voltage is increased through the spaced P-type column area, the carrier storage capacity in the substrate is reduced, and the maximum reverse recovery current value and reverse recovery time are reduced. In addition, the present invention also controls the cathode emission efficiency through the back structure, further reduces the reverse recovery time, and improves the reverse recovery characteristics of the FRD without affecting the performance of the FRD. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] Figure 1 It is a cross-sectional schematic diagram of a traditional FRD structure.

[0030] Figure 2 It is the reverse recovery characteristic waveform of FRD.

[0031] Figure 3 FIG. 4 is a cross-sectional view of an embodiment of an FRD capable of improving reverse recovery characteristics provided by the present invention.

[0032] Figure 4-Figure 13 1 is a cross-sectional view of a process step of an embodiment of a method for preparing an FRD capable of improving reverse recovery characteristics provided by the present invention, wherein:

[0033] Figure 4 It is a cross-sectional view of an embodiment of the present invention after the first mask is prepared.

[0034] Figure 5 It is a cross-sectional view of an embodiment of the present invention after preparing an N-type doped region.

[0035] Figure 6 It is a cross-sectional view of an embodiment of the present invention after the second mask is prepared.

[0036] Figure 7 It is a cross-sectional view of an embodiment of the present invention after preparing a P-type column region.

[0037] Figure 8 It is a cross-sectional view of an embodiment of the present invention after the second oxide layer is deposited.

[0038] Fig. 9 It is a cross-sectional view of an embodiment of the present invention in which the oxide layer in the active area is etched.

[0039] Fig.10 It is a cross-sectional view of an embodiment of the present invention after the anode metal is prepared.

[0040] Fig.11 It is a cross-sectional view of an embodiment of the present invention after preparing an N-type preliminary doping region.

[0041] Fig.12It is a cross-sectional view of an embodiment of the present invention after the filling groove is prepared.

[0042] Fig.13 It is a cross-sectional view of an embodiment of the present invention after the filling groove is filled with oxide.

[0043] Explanation of the reference numerals: 1-N-type substrate, 2-P-type column region, 3-N-type doping region, 4-anode metal, 5-N-type cathode region, 6-filling groove, 7-insulating medium, 8-first mask, 9-second mask, 10-N-type pre-doping region. DETAILED DESCRIPTION

[0044] The specific implementation of the present invention will be further described below in conjunction with the accompanying drawings.

[0045] The present invention provides an FRD capable of improving reverse recovery characteristics, comprising an N-type substrate 1, wherein the N-type substrate 1 comprises a front surface and a back surface corresponding to the front surface;

[0046] A front structure is correspondingly arranged on the front side of the N-type substrate 1, and the front structure includes a plurality of P-type column regions 2 prepared in the N-type substrate 1 and distributed at intervals;

[0047] The P-type column region 2 is in ohmic contact with an anode metal 4 formed on the N-type substrate 1 for forming an anode.

[0048] Specifically, the N-type substrate 1 can be made of existing common materials, such as a silicon substrate, to meet application requirements. Figure 3 As shown, the P-type column region 2 is a P-type doped region with a deeper junction depth, and the P-type column region 2 extends vertically from the front side to the back side of the N-type substrate 1, and is arranged at intervals in a direction perpendicular to the thickness of the N-type substrate 1, forming a superjunction structure with the N-type substrate 1. The P-type column region 2 is in ohmic contact with the anode metal 4 to form an anode terminal.

[0049] When the FRD is reversely cut off, the ionized acceptors and donors of the P-type column region 2 and the N-type substrate 1 attract each other, forming lateral charge compensation, eliminating the longitudinal electric field, and increasing the reverse withstand voltage. On the basis of ensuring that the static reverse withstand voltage of the device is sufficient, the thickness of the N-type substrate 1 can be reduced, thereby reducing the carrier storage capacity in the N-type substrate 1, reducing the maximum reverse recovery current value, and increasing the reverse recovery speed. The longitudinal direction is perpendicular to the lateral direction, and the longitudinal direction is the thickness direction of the N-type substrate 1.

[0050] At the same time, compared with the traditional anode P+ region, the spaced P-type column region 2 can effectively reduce the emission efficiency of the anode, reduce the amount of holes injected from the anode into the N- region, i.e., the N-type substrate 1, and reduce the time it takes for carriers to be extracted from the N- region, thereby reducing the reverse recovery time and improving the reverse recovery characteristics.

[0051] Furthermore, the front structure further includes an N-type doping region 3 disposed between adjacent P-type column regions 2, wherein the N-type doping region 3 is in contact with the corresponding P-type column region 2;

[0052] The doping concentration of the N-type doping region 3 is greater than the doping concentration of the N-type substrate 1 , and the N-type doping region 3 is in ohmic contact with an anode metal 4 for forming an anode on the N-type substrate 1 .

[0053] Specifically, the N-type doping region 3 extends vertically from the front side of the N-type substrate 1 to the back side of the N-type substrate 1, and the junction depth of the N-type doping region 3 is less than the junction depth of the P-type column region 2, and the doping concentration of the N-type doping region 3 is greater than the doping concentration of the N-type substrate 1. The N-type doping region 3 is in contact with the corresponding P-type column region 2, that is, each N-type doping region 3 is in contact with the P-type column region 2 on both sides thereof. The N-type doping region 3 is also in ohmic contact with the anode metal 4 used to form the anode, which is used to reduce the forward conduction voltage drop and improve the reverse leakage problem caused by the spaced-injected P-type column region 2.

[0054] Furthermore, a back surface structure is correspondingly provided on the back surface of the N-type substrate 1, and the back surface structure includes a plurality of N-type cathode regions 5 prepared in the N-type substrate 1 and distributed at intervals;

[0055] The N-type cathode region 5 is in ohmic contact with a cathode metal disposed on the back side of the N-type substrate 1 for forming a cathode.

[0056] like Figure 3 As shown, in one embodiment of the present invention, the N-type cathode region 5 extends vertically from the back side of the N-type substrate 1 to the front side of the N-type substrate 1, and is arranged at intervals in the lateral direction, and the doping concentration of the N-type cathode region 5 is greater than the doping concentration of the N-type substrate 1. The N-type cathode region 5 is in ohmic contact with the cathode metal (not shown in the figure) on the back side of the N-type substrate 1 to form a cathode terminal. The back structure and the front structure are not in contact with each other, and the N-type cathode region 5 arranged at intervals can effectively reduce the emission efficiency of the cathode compared to the traditional cathode N+ region, that is, reduce the amount of holes injected by the cathode into the N- region, that is, the N-type substrate 1, thereby reducing the reverse recovery time. It should be noted that the N-type substrate 1 generally includes an active region and a terminal region surrounding the active region, and the above-mentioned front structure and back structure are both arranged in the active region.

[0057] Furthermore, a filling groove 6 is provided between adjacent N-type cathode regions 5 , a sidewall of the filling groove 6 is in contact with the corresponding N-type cathode region 5 , and the filling groove 6 is filled with an insulating medium 7 .

[0058] Specifically, the filling groove 6 extends vertically from the back side of the N-type substrate 1 to the front side of the N-type substrate 1, and the groove depth of the filling groove 6 is greater than or equal to the junction depth of the N-type cathode region 5, and the side wall of the filling groove 6 is in contact with the corresponding N-type cathode region 5, that is, the side wall of each filling groove 6 is in contact with the N-type cathode region 5 located on both sides thereof, so as to separate the adjacent N-type cathode regions 5 through the filling groove 6. Each filling groove 6 is filled with an insulating medium 7 to improve the reverse withstand voltage of the FRD and further improve the reliability of the FRD. The insulating medium 7 can be an oxide such as silicon dioxide, and the material of the insulating medium can be selected according to actual needs during specific implementation. The FRD with improved reverse recovery characteristics provided by the present invention does not need to use any existing lifetime control technology, retains the lifetime of carriers, reduces the reverse recovery speed of the FRD, increases the reverse recovery softness and reduces the reverse leakage, and improves the reliability of the FRD.

[0059] For the above-mentioned FRD capable of improving reverse recovery characteristics, the present invention also provides a method for preparing the FRD, the method comprising:

[0060] Providing an N-type substrate 1, and performing a front process on the front side of the N-type substrate 1 to prepare a desired front side structure, wherein the front side structure includes a plurality of P-type column regions 2 prepared in the N-type substrate 1 and distributed at intervals;

[0061] The P-type column region 2 is in ohmic contact with an anode metal 4 formed on the N-type substrate 1 for forming an anode.

[0062] Specifically, the specific form of the front structure is consistent with the above, and will not be repeated here. The P-type column region 2 is prepared by multiple ion implantation processes, and the ion implantation energy is reduced successively to form a P-type column region 2 with a deeper junction depth. In one embodiment of the present invention, a total of five ion implantation processes are performed to implant P-type doping ions into the N-type substrate 1 to prepare the P-type column region 2, wherein the ion implantation dose range of the first ion implantation process is 9.0e9cm -2 -1.4e10 cm -2 The implantation energy range of the first ion implantation process is 1200kev-1400kev; the implantation dose range of the second ion implantation process is 7.0e9cm -2 -1.2e10 cm -2 The second ion implantation process has an implantation energy range of 600kev-800kev; the third ion implantation process has an ion implantation dose range of 5.0e9cm -2 -7.5e9cm -2 The injection energy range of the third ion injection process is 300kev-500kev; the injection dose range of the fourth ion injection process is 2.0e9cm -2-5.5e10 cm -2 The implantation energy range of the fourth ion implantation process is 150kev-250kev; the implantation dose range of the fifth ion implantation process is 3.0e13cm -2 -6.0e13cm -2 The injection energy range of the fifth ion implantation process is 30kev-80kev. In specific implementation, the number of ion implantations and process conditions can be selected according to actual needs to meet the preparation requirements of the P-type column region 2.

[0063] The method for preparing the FRD includes a front process performed on the front side of the N-type substrate 1 and a back process performed on the back side of the N-type substrate 1. During preparation, the front process is generally performed first and then the back process. Figure 4-Figure 13 An embodiment of first performing the front process and then performing the back process is shown in FIG. Figure 4-Figure 13 The preparation method of the present invention is specifically described with reference to the process steps.

[0064] like Figure 4-Figure 5 As shown, an N-type substrate 1 with a resistance value of 65-90 ohm is provided, and a front process is performed on the N-type substrate 1, wherein the front process includes coating a photoresist and photolithography to form a first mask 8, and using the first mask 8 to implant N-type doping ions into the front of the N-type substrate 1 in the active region. After the implantation, the first mask 8 is removed and high-temperature furnace annealing is performed to activate the impurities, so as to prepare an N-type doping region 3. The implantation dose range of the N-type ions is 5.0e14 cm -2 -2.0e15 cm -2 , the implantation energy range is 30kev-100kev. The annealing temperature range of high temperature furnace tube annealing is 400℃-600℃, and the annealing time range is 30min-80min. In specific implementation, the process conditions of N-type ion implantation and high temperature furnace tube annealing can be selected according to actual needs to meet the preparation requirements of the N-type doping region 3.

[0065] like Figure 6-Figure 7 As shown, an oxide layer with a thickness of 1.0μm-1.6μm is deposited on the front of the above-mentioned N-type substrate 1, and a photoresist is coated. The area where the P-type ions need to be injected is defined by photolithography, and the oxide layer is etched accordingly and the photoresist is removed to form a second mask 9. The second mask 9 is used to inject P-type doped ions into the front of the N-type substrate 1 multiple times. In this embodiment, a total of 5 P-type ion injections are performed. The process conditions for each ion injection can refer to the above description and will not be repeated here. After the multiple ion injections are completed, the impurities are activated by high-temperature furnace tube annealing. The annealing temperature range of the high-temperature furnace tube annealing is 1000℃-1250℃, and the annealing time range is 150min-350min.

[0066] like Figure 8 and Fig. 9 As shown, an oxide layer with a thickness of 0.6 μm-1.2 μm is deposited on the front of the N-type substrate 1, and the oxide layer on the front of the N-type substrate 1 in the active area is removed by etching, leaving only the oxide layer in the terminal area. Fig.10 As shown, metal is deposited on the front side of the N-type substrate 1 to form an anode metal 4, and the anode metal 4 is in ohmic contact with the P-type column region 2 and the N-type doped region 3 to form an anode terminal, thus completing the front side process.

[0067] like Fig.11 As shown, a back process is performed on the back of the N-type substrate 1, including back thinning, thinning the thickness of the N-type substrate 1 to 70μm-120μm, and implanting N-type doping ions on the back of the thinned N-type substrate 1 and annealing at high temperature to prepare an N-type preliminary doping region 10 that crosses the active region. The implantation dose range of the N-type ions is 8.0e14 cm -2 -2.0e15 cm -2 , the injection energy range is 30kev-80kev. The annealing temperature range of high temperature furnace tube annealing is 350℃-450℃, and the annealing time range is 30min-50min. In specific implementation, the process conditions of N-type ion implantation and high temperature furnace tube annealing can be selected according to actual needs to meet the preparation requirements of the N-type preliminary doping area 10.

[0068] like Fig.12 As shown, photoresist is coated on the back side of the N-type substrate 1, and the area where the groove needs to be etched is defined by photolithography. A plurality of spaced filling grooves 6 are obtained by etching and the photoresist is removed. The filling grooves 6 penetrate the N-type preliminary doping region 10 to separate the N-type preliminary doping region 10 into a plurality of N-type cathode regions 5.

[0069] like Fig.13 As shown, oxide is deposited on the back side of the N-type substrate 1 in which the filling grooves 6 are prepared to fill all the filling grooves 6, the oxide layer on the back side of the N-type substrate 1 is removed, and metal is deposited on the back side of the substrate 1 to form a cathode metal (not shown in the figure), and the cathode metal is in ohmic contact with all the N-type cathode regions 5 to form a cathode terminal, thereby completing the back side process.

[0070] It should be noted that the words "front", "rear", "left", "right", "upper" and "lower" used in the above description refer to directions in the drawings of the present application specification, and the words "front" and "back", "inner" and "outer" refer to directions toward or away from a specific component, respectively. In addition, the terms "first" and "second" are used for descriptive purposes only and cannot be understood as indicating or implying relative importance or implicitly indicating the number of the indicated technical features.

[0071] The above is only a preferred embodiment of the present invention, and the present invention is not limited to the above embodiments. It is understood that other improvements and changes directly derived or associated by those skilled in the art without departing from the spirit and concept of the present invention should be considered to be included in the protection scope of the present invention.

Claims

1. An FRD capable of improving reverse recovery characteristics, characterized in that: An N-type substrate is included, wherein the N-type substrate includes a front surface and a back surface corresponding to the front surface; A front structure is correspondingly arranged on the front side of the N-type substrate, and the front structure includes a plurality of P-type column regions prepared in the N-type substrate and distributed at intervals; The P-type column region is in ohmic contact with an anode metal on the N-type substrate for forming an anode.

2. The FRD capable of improving reverse recovery characteristics according to claim 1, characterized in that: The front structure further includes an N-type doped region disposed between adjacent P-type column regions, wherein the N-type doped region is in contact with the corresponding P-type column region; The doping concentration of the N-type doping region is greater than the doping concentration of the N-type substrate, and the N-type doping region is in ohmic contact with an anode metal for forming an anode above the N-type substrate.

3. The FRD capable of improving reverse recovery characteristics according to claim 2, characterized in that: The junction depth of the N-type doping region is smaller than the junction depth of the P-type column region.

4. The FRD capable of improving reverse recovery characteristics according to claim 1, wherein: A back surface structure is correspondingly arranged on the back surface of the N-type substrate, and the back surface structure includes a plurality of N-type cathode regions prepared in the N-type substrate and distributed at intervals; The N-type cathode region is in ohmic contact with a cathode metal disposed on the back side of the N-type substrate for forming a cathode.

5. The FRD capable of improving reverse recovery characteristics according to claim 4, characterized in that: The doping concentration of the N-type cathode region is greater than the doping concentration of the N-type substrate.

6. The FRD capable of improving reverse recovery characteristics according to claim 4, characterized in that: A filling groove is arranged between adjacent N-type cathode regions, a side wall of the filling groove contacts the corresponding N-type cathode region, and the filling groove is filled with an insulating medium.

7. The FRD capable of improving reverse recovery characteristics according to claim 6, characterized in that: The depth of the filling groove is not less than the junction depth of the N-type cathode region.

8. The FRD capable of improving reverse recovery characteristics according to claim 6, wherein: The insulating medium includes silicon dioxide.

9. A method for preparing an FRD capable of improving reverse recovery characteristics, characterized in that: Used to prepare the FRD according to any one of claims 1 to 8, wherein the preparation method comprises: Providing an N-type substrate, and performing a front process on the front side of the N-type substrate to prepare a desired front side structure, wherein the front side structure includes a plurality of P-type column regions prepared in the N-type substrate and distributed at intervals; The P-type column region is in ohmic contact with an anode metal on the N-type substrate for forming an anode.

10. The method for preparing an FRD capable of improving reverse recovery characteristics according to claim 9, characterized in that: The P-type column region is prepared by multiple ion implantation processes, and when the multiple ion implantation processes are performed, the implantation energy of the ions is reduced successively.

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