Soft recovery FRD and manufacturing method thereof

Abstract

The invention relates to the technical field of semiconductor devices, and relates to a soft recovery FRD and a manufacturing method thereof, and the soft recovery FRD comprises an anode region of a first conduction type, which is formed by combining at least two first conduction type regions with different doping concentrations, and comprises a high-doping-concentration region and a low-doping-concentration region; the carrier injection suppression layer of the second conduction type is located below the anode region, and the doping concentration of the carrier injection suppression layer is higher than that of the drift region; the carrier injection suppression layer is formed through local injection and diffusion, and is used for suppressing minority carrier injection when working below a rated current, and the suppression effect is weakened when working at a large current. According to the invention, two or more first doping type region combinations with different doping concentrations are adopted, so that the performance of the device in different working states is effectively improved. The low-concentration doped region provides relatively low anode injection efficiency in rated and low-load working states, so that excellent softness characteristics are obtained; and the high-doping-concentration region provides enough carrier requirements during overload, so that the overload capacity of the product is remarkably enhanced.

Description

Technical Field

[0001] This invention relates to the field of semiconductor device technology, and in particular to a soft recovery FRD and its manufacturing method. Background Technology

[0002] When a switching device is in operation, it needs to be connected in parallel with a fast recovery diode (FRD). The fast recovery diode forms a loop with the load and is mainly used to provide freewheeling current to the load when the switching device is turned off. With the rapid development of power semiconductor device research and manufacturing technology, the performance of the main switching device in the circuit has been continuously improved. This requires that the FRD used with it must have better overall performance and a shorter reverse recovery time.

[0003] FS-FRD is currently the most common FRD structure in commercial applications, and its structure is as follows: Figure 1 As shown, region 101, representing the first doping type, is connected to the anode metal on the positive surface and is adjacent to region 102, representing the second doping type with the opposite doping type. Region 102, representing the second doping type, primarily bears the responsibility of handling high voltage during reverse blocking. Its doping concentration is relatively low; for products with voltages above 1200V, the doping concentration is below 1e14cm. -3 The electric field cutoff layer 103 is located below 102, and its doping type is the same as that of 102. The introduction of the electric field cutoff layer 103 can reduce the wafer thickness, thereby obtaining lower reverse recovery loss. The contact layer 104 is a second doping type, and its main purpose is to reduce the contact resistance between the back cathode metal and the semiconductor, so as to achieve better electrical interconnection.

[0004] To obtain a FRD with superior softness characteristics, a common practice is to suppress anode hole injection efficiency. There are generally two methods for suppressing anode hole injection efficiency. The first is to introduce light ion implantation into the front anode region, using the defects formed by light ion implantation to control the minority carrier lifetime, also known as local lifetime control technology. The second is to use a PIN-Schottky combined anode structure (MPS, Merged PIN Schottky Diode). Figure 2 As shown, introducing a Schottky contact 2012 into the anode region results in a smaller barrier voltage in the Schottky portion during diode conduction. The FRD current primarily enters the drift region 202 through the Schottky portion, thus reducing the front-side anode injection efficiency. Local lifetime control technology has high manufacturing costs, and introducing defects into the anode region can easily lead to a large reverse leakage current at high temperatures, severely impacting product reliability. In the MPS anode structure, the shielding effect of the PN junction is limited when the device is reverse biased, failing to completely eliminate the problem of large high-temperature leakage current in the Schottky contact, thus affecting product reliability. Summary of the Invention

[0005] The purpose of this invention is to address the problems existing in the background technology by proposing a soft recovery FRD and its manufacturing method, aiming to obtain better reverse recovery softness without sacrificing reliability.

[0006] The technical solution of this invention aims to achieve superior reverse recovery softness without sacrificing reliability. This invention proposes a soft recovery FRD and its manufacturing method. The proposed soft recovery FRD structure is as follows: Figure 3 As shown, the soft recovery FRD structure proposed in this invention has the following two main features: First, the anode region of the device is composed of two or more first doping type regions with different doping concentrations. The characteristics of the product under different operating conditions are controlled by the regions with different doping concentrations. The low-concentration doped region 3012 can provide lower anode injection efficiency under rated load and low load operating conditions, thereby obtaining better softness characteristics. The high-concentration doped region 3011 can provide sufficient carrier demand under overload, improving the overload capacity of the product. Second, an anode carrier injection suppression layer 305 is added below the anode region of the device. The carrier injection suppression layer has a strong minority carrier suppression effect when operating below rated current, but its suppression effect is weaker under high current and high injection conditions. The anode carrier injection suppression layer 305 is formed by local injection and diffusion. Its doping type is second doping type, and the doping concentration is higher than that of the drift region 302.

[0007] The soft recovery FRD proposed in this invention has a blocking capability comparable to the existing FS-FRD in the blocking state. Its combined anode structure and the introduction of the anode carrier injection suppression layer do not affect the reverse blocking capability of the product. Under high-temperature operation, the junctions in the surface anode region are all PN junctions, and the number of defects in the surface region is also within the rated range. Therefore, the soft recovery FRD proposed in this invention has low reverse leakage current and good reliability. In the forward conduction state, the lightly doped anode region 3012 preferentially conducts. The low doping concentration injects fewer minority carriers. The carriers injected into the body region from the lightly doped anode region 3012 first pass through the hole carrier injection suppression layer 305. When the minority carriers pass through the hole carrier injection suppression layer 305, some of them recombine with majority carriers and disappear, reducing the total amount of minority carriers injected into the body region. Under the same VF conditions, this reduces the amount of minority carriers stored on the front side and increases the amount of carriers stored on the back side. Lower front minority carrier storage and higher back carrier storage result in lower reverse recovery overshoot voltage, lower reverse recovery loss, and better reverse recovery softness during reverse recovery.

[0008] The present invention proposes a soft-recovery FRD top-view structure as follows: Figure 4As shown, 11 is the die cell region, and 21 and 22 together form the terminal withstand voltage region, where 21 is the terminal withstand voltage ring region and 22 is the terminal electric field cutoff region. The ring doping of the terminal withstand voltage ring region is formed together with 3011 and 3012 in the anode structure through injection diffusion, and the doping of the terminal electric field cutoff region is formed together with the anode carrier injection suppression layer 305.

[0009] This invention also includes a soft recovery FRD manufacturing method. Compared with conventional MPS FRD, the soft recovery FRD manufacturing method proposed in this invention does not increase the number of mask layers, and the manufacturing process is relatively simple, with each step consisting of conventional semiconductor manufacturing processes. The detailed manufacturing process is as follows: Select a suitable FZ substrate 501 with completed back sealing, clean and mark it, and grow a field oxide layer 502 on the substrate surface through a high-temperature oxidation process, such as... Figure 5a ; Photolithography is performed using the first photomask, and etching is performed according to the photolithographic pattern to open the field oxide layer in the die cell region 11, the terminal withstand voltage ring region 21, and the terminal electric field cutoff region 22, as follows: Figure 5b ; Depositing a dielectric layer such as SiN as a hard mask 503, such as Figure 5c ; After coating with photoresist 504, photolithography is performed using a second photomask to open the impurity injection opening region of the anode carrier injection suppression layer, such as... Figure 5d ; The hard mask 503 is dry-etched, and a second type of doping is performed using a high-energy, medium-speed ion implanter to form the impurity implantation region 505. Figure 5e ; Remove the photoresist 505, deposit another dielectric layer as a hard mask 506, and planarize the surface using CMP or other methods, such as... Figure 5f ; After removing the hard mask 503, the die cell region and the terminal withstand voltage ring are implanted with the first type of doping, such as... Figure 5g ; After removing the hard mask 506, high-temperature diffusion is performed on the implanted material to form a highly doped anode region 507 and an anode carrier injection suppression layer 5051, as shown below. Figure 5h ; First-type doped impurities are implanted, an ILD layer 508 is deposited, and the ILD layer is reflowed for smoothing. The reflow thermal process activates and diffuses the implanted impurities, forming a lightly doped anode region 509. Figure 5i ; The contact hole opening area is opened using photolithography with a third photomask, the ILD is etched to open the contact hole area, the front metal 510 is sputtered, the front metal is alloyed, and the front metal opening area is opened using a fourth photomask, forming the front anode metal 5101, the terminal withstand voltage ring metal 5102, and the terminal electric field cutoff region metal 5103, as shown. Figure 5j ; The back side is thinned, a second type of impurity is implanted into the back side, and laser annealing is performed to form a back side metal contact layer 511. Hydrogen ion implantation is performed on the back side, and electric field cutoff layer 512 is formed through furnace tube annealing. Electrical interconnection is formed by sputtering or evaporation of the back side metal 513. Figure 5k As shown.

[0010] The soft recovery FRD proposed in this invention involves four photolithography steps without a surface passivation layer, comparable to the conventional FS-FRD process, with lower manufacturing difficulty and greater feasibility. Furthermore, the method for forming the back-side electric field cutoff layer and contact layer of the soft recovery FRD proposed in this invention includes not only the hydrogen ion implantation method mentioned above, but also the following methods: using an epitaxial substrate as the substrate material, epitaxy is performed on a heavily doped substrate to form the electric field cutoff layer and device drift region, wherein the contact layer is formed directly with the substrate through a back-side metal; or using a diffusion wafer that has undergone long-term impurity diffusion as the substrate material, using a portion of the diffusion layer as the electric field cutoff layer, and the contact layer is still formed by impurity implantation combined with laser annealing.

[0011] The soft recovery FRD proposed in this invention uses a combination of two first-type doping regions with different doping concentrations in its anode region. The anode doping concentration distribution curve and the anode carrier injection suppression layer doping concentration distribution curve are shown below. Figure 6 As shown, the anode doping concentration distribution and the anode carrier injection suppression layer doping concentration distribution are exactly alternating. Below the high anode doping concentration is the lightly doped region of the anode carrier injection suppression layer, and below the lightly doped anode is the heavily doped region of the anode carrier injection suppression layer. This alternating doping distribution is beneficial for the product to obtain better overall performance.

[0012] The soft recovery FRD proposed in this invention exhibits lower front-side injection efficiency during forward conduction compared to existing MPS structure FRDs. Under the same VF conditions, the soft recovery FRD proposed in this invention has more holes distributed on the back side of the device, such as... Figure 7 As shown, Figure 7The simulation results for the proposed soft-recovery FRD and the existing MPS structure FRD under the same VF condition clearly show that the proposed invention has more holes concentrated on the back side, resulting in better softness characteristics. In the reverse recovery state, the greater distribution of holes on the back side of the device and the smaller hole distribution on the front side result in a smaller reverse recovery peak current for the proposed soft-recovery FRD. Figure 8 As shown, a smaller reverse recovery peak current can reduce IGBT turn-on losses to a certain extent, improve the safety of FRD devices under high current operation, and enable safe operation under more stringent conditions. Research on the low-current operating condition of the soft-recovery FRD proposed in this invention reveals that, compared to existing technologies, this invention is less prone to oscillation under low-current conditions. Figure 9 As shown, a smoother waveform that is less prone to oscillation enables the device to have a wider range of applications, and EMC problems will not occur in different applications.

[0013] Compared with the prior art, the present invention has the following beneficial technical effects: 1. This invention proposes a soft recovery FRD that, through a unique anode structure design, employs a combination of two or more first-doped regions with different doping concentrations, effectively improving the device's performance under various operating conditions. The low-doped region provides lower anode injection efficiency under rated and low-load operating conditions, thus achieving excellent softness characteristics; while the high-doped region provides sufficient carrier demand under overload conditions, significantly enhancing the product's overload capability. This design not only optimizes the device's dynamic performance but also broadens its application range. 2. This invention adds an anode carrier injection suppression layer below the anode region. This layer exhibits a strong minority carrier suppression effect when operating below the rated current, effectively reducing the total number of minority carriers in the anode injection body region. During reverse recovery, it significantly reduces the reverse recovery overshoot voltage, lowers reverse recovery losses, and achieves better reverse recovery softness. Simultaneously, the suppression effect of this layer is weaker under high current and high injection conditions, ensuring stable operation of the device under high current. 3. Compared with existing MPS structure FRDs, this invention exhibits lower front-side injection efficiency during forward conduction, resulting in a greater distribution of holes on the back side of the device and thus achieving better softness characteristics. In reverse recovery mode, this invention has a smaller reverse recovery spike current, reducing IGBT turn-on losses and improving the device's safety during high-current operation. Simultaneously, this invention is less prone to oscillation under low-current conditions, exhibiting a smoother waveform, thus enabling the device to have a wider range of applications and better EMC performance. Attached Figure Description

[0014] Figure 1This is a schematic diagram of the structure of a fast recovery diode (FRD) in the prior art; Figure 2 This is a schematic diagram of the existing anode MPS structure; Figure 3 This is a schematic diagram of a soft recovery FRD structure proposed in this invention; Figure 4 This is a top view schematic diagram of a soft recovery FRD structure proposed in this invention; Figure 5a -k is a flowchart of a soft recovery FRD manufacturing method proposed in this invention; Figure 6 This is a doping concentration distribution curve of a soft recovery FRD anode and a carrier injection suppression layer proposed in this invention; Figure 7 This is a comparison diagram of the hole distribution in the drift region between the soft recovery FRD proposed in this invention and existing technologies under the same VF. Figure 8 This is a comparison diagram of the reverse recovery current waveforms of the soft recovery FRD proposed in this invention and existing technologies under rated current. Figure 9 This is a comparison diagram of the reverse recovery current waveforms of the soft recovery FRD proposed in this invention and existing technologies under low current conditions; Figure 10 This is a schematic diagram of a soft recovery FRD proposed in Embodiment 1 of the present invention; Figure 11 This is a doping distribution diagram of the back surface region in Example 1; Figure 12 This is a schematic diagram of a soft recovery FRD proposed in Embodiment 2 of the present invention; Figure 13a -h is a flowchart of a soft recovery FRD manufacturing method proposed in Embodiment 2 of the present invention. Detailed Implementation

[0015] Example 1: This invention proposes a soft recovery FRD implementation case, as follows: Figure 10As shown, below the metal on the front side of the device is a combined anode structure of the first doping type, consisting of lightly doped 6012 and heavily doped 6011. Below the combined anode structure is an anode carrier injection suppression layer 605 of the second doping type. Under the combined anode structure and the anode carrier injection suppression layer 605, the minority carriers injected into the bulk region of the device are well suppressed, enabling the device to obtain better softness characteristics. Below the anode carrier injection suppression layer 605 are the conventional drift region 602 and the electric field cutoff layer 603. In this invention, a soft recovery FRD implementation example 1 introduces a minority carrier storage layer 306 between the electric field cutoff layer 603 and the contact layer 604. The introduction of the minority carrier storage layer 306 allows a certain amount of minority carriers to remain on the back side during the reverse recovery process of the device, thereby obtaining better softness characteristics. Under rated load and low load conditions, the low-doped anode region 6012 preferentially conducts, resulting in low anode injection efficiency. Simultaneously, the anode carrier injection suppression layer 605 beneath the anode activates, keeping the minority carrier level low and reducing the carrier storage on the anode side of the FRD during conduction, while increasing the carrier storage on the back side. During reverse recovery, the low carrier storage on the anode side results in a low reverse recovery overshoot, reducing reverse recovery losses. Due to the increased carrier storage on the back side, and the slower disappearance of minority carriers in the introduced minority carrier storage layer 606, there are always carriers supplying current to the FRD, improving the device's softness characteristics. Under overload conditions, the device current is high, primarily due to the operation of the heavily doped anode structure 6011. Under these conditions, the anode carrier injection suppression layer 605 is essentially ineffective, allowing the device to provide output current seven to eight times higher than the rated current, ensuring overcurrent capability under extreme conditions. Under reverse blocking conditions, the drift region provides sufficient reverse blocking capability. Even at high temperatures, the junctions in the surface anode region are all PN junctions, and the number of defects in the surface region is within the rated range. The soft recovery FRD proposed in this invention has low reverse leakage current, and the reverse blocking capability of the device is still relatively strong. Since the reverse leakage current of the device is relatively small even at high temperatures, the degradation of its raw materials is very slow, and the device has good long-term durability and reliability.

[0016] In the first implementation of the soft recovery FRD proposed in this invention, the electric field terminates at the electric field cutoff layer 603 in the reverse blocking state, and the carrier storage layer 606 will not be subjected to the electric field. Its thickness and doping concentration will not be affected by the device breakdown electric field. By optimizing the trade-off, a device with better softness characteristics is obtained.

[0017] The soft recovery FRD embodiment proposed in this invention can be fabricated using a uniformly doped FZ substrate or MCZ substrate. The front anode structures 6011 and 6012 and the anode carrier injection suppression layer 605 can be achieved through ion implantation combined with high-temperature annealing. The doping distribution curve of the region below the back electric field cutoff layer 603 in the soft recovery FRD embodiment proposed in this invention is shown in the figure below. Figure 11 As shown, the back electric field cutoff layer 603 can be achieved by multiple H-ion implantations combined with high-temperature annealing. The carrier storage layer can be obtained simply by controlling the energy of the back H-ion implantation during the preparation of the electric field cutoff layer 603 and the energy of the P-ion implantation and laser annealing during the preparation of the contact layer 606.

[0018] Example 2, a soft recovery FRD implementation case of the present invention, consists of a substrate 804, an electric field buffer layer 803, a drift region 802, an anode carrier injection suppression layer 805, and a composite anode structure 801, from cathode to anode. Figure 12 As shown. When the device is in forward conduction mode, the low-doped anode region 8012 preferentially conducts, resulting in low anode injection efficiency. Simultaneously, the anode carrier injection suppression layer 805 below the anode activates, keeping the minority carriers at a low level, reducing the carrier storage capacity on the anode side of the FRD during conduction, and increasing the carrier storage capacity on the back side. When the forward conduction current increases to a large level, the heavily doped anode structure 8011 mainly operates. Under this condition, the anode carrier injection suppression layer 805 essentially fails, and the device can provide an output capacity exceeding seven to eight times the rated current, ensuring the overcurrent capability of the device under extreme conditions. In reverse blocking mode, the drift region provides sufficient reverse blocking capability. Even at high temperatures, the junctions in the surface anode region are all PN junctions, and the number of defects in the surface region is within the rated range. The soft recovery FRD proposed in this invention has a small reverse leakage current, and the reverse blocking capability of the device is still relatively strong. Because the reverse leakage current is relatively small even at high temperatures, the raw materials degrade very slowly, and the device has good long-term durability and reliability. During the reverse recovery process, the low carrier storage on the anode side results in a low reverse recovery overshoot ratio, reducing reverse recovery loss and improving the device's softness characteristics.

[0019] This invention proposes a manufacturing method for a soft recovery FRD, as shown in Figure 13. This method involves forming the raw materials for device fabrication through multiple epitaxial layers. 804 is a heavily doped initial substrate, and 803 is the first epitaxial layer with a higher doping concentration than the second epitaxial layer 802. The second epitaxial layer 802 is a thick epitaxial layer with a lower doping concentration. The doping concentration and epitaxial thickness are related to the product's rated reverse blocking voltage. The anode and termination regions on the surface are implemented on the second epitaxial layer and its surface. The specific manufacturing process for this soft recovery FRD is as follows: Select a suitable bilayer epitaxial substrate, clean it, and complete laser marking, such as... Figure 13a ; The field oxide layer 907 is grown using a first photomask for photolithography, and then etched according to the photolithographic pattern to open the die cell and terminal block. Figure 13b ; A dielectric layer, such as SiN, is deposited as a hard mask 908, coated with photoresist 909, and photolithography is performed using a second photomask to open the impurity implantation opening region of the anode carrier implantation suppression layer. The hard mask 908 is then dry-etched, and a second type of doping is performed using a high-energy, medium-speed ion implanter to form the impurity implantation region. Figure 13c ; After removing the photoresist 909, another dielectric layer is deposited as a hard mask 910. The surface is then planarized using CMP or other methods, such as... Figure 13d ; After removing the hard mask 908, the die cell region and the terminal withstand voltage ring are implanted with the first type of doping, such as... Figure 13e ; After removing the hard mask 910, high-temperature diffusion is performed on the implanted material to form a highly doped anode region 9011 and an anode carrier injection suppression layer 905, as shown below. Figure 13f ; First-type doped impurities are injected, an ILD layer 911 is deposited, and the ILD layer is reflowed for smoothing. The reflow thermal process activates and diffuses the injected impurities, forming a lightly doped anode region 9012. Figure 13g ; The contact hole opening area is opened using photolithography with a third photomask, the ILD is etched to open the contact hole area, the front metal 912 is sputtered, and the front metal is alloyed. The front metal opening area is then opened using photolithography with a fourth photomask, forming the front anode metal 9121, the terminal withstand voltage ring metal 9122, and the terminal electric field cutoff region metal 9123. The back side is thinned, and the back metal 913 is sputtered or vapor-deposited to form electrical interconnects. Figure 13h As shown.

[0020] The embodiments of the present invention have been described in detail above with reference to the accompanying drawings. However, the present invention is not limited thereto. Various changes can be made within the scope of knowledge possessed by those skilled in the art without departing from the spirit of the present invention.

Claims

1. A soft recovery FRD, characterized in that, include: The anode region of the first conductivity type is composed of at least two first conductivity type regions with different doping concentrations, including a high doping concentration region and a low doping concentration region. A carrier injection suppression layer of the second conductivity type is located below the anode region, and its doping concentration is higher than that of the drift region; The carrier injection suppression layer is formed by local injection and diffusion. It is used to suppress minority carrier injection when operating below the rated current, and the suppression effect weakens when operating at high current.

2. The soft recovery FRD according to claim 1, characterized in that, The doping distribution of the carrier injection suppression layer is staggered with the doping distribution of the anode region.

3. The soft recovery FRD according to claim 2, characterized in that, Below the high-doping region of the anode lies the lightly doped region of the carrier injection suppression layer.

4. A soft recovery FRD according to claim 2, characterized in that, Below the low-doping region of the anode is the heavily doped region of the carrier injection suppression layer.

5. A soft recovery FRD according to claim 1 or 2, characterized in that, The anode region and the terminal withstand voltage ring region are formed through the same injection diffusion process; the carrier injection suppression layer and the terminal electric field cutoff region are formed through the same injection diffusion process.

6. A soft recovery FRD according to claim 1, characterized in that, It also includes a minority carrier storage layer located between the back electric field cutoff layer and the contact layer.

7. A method for manufacturing a soft recovery FRD, comprising manufacturing a soft recovery FRD as described in any one of claims 1-6, characterized in that, The specific steps include the following: S1. Provide a substrate to form a field oxide layer; S2. Open the oxide layer of the die area and the terminal area through the first photomask; S3. Deposit the first hard mask, and open the carrier injection suppression layer injection window through the second photomask; S4. Perform impurity injection of the second conductivity type to form a carrier injection suppression layer; S5. Deposit the second hard mask and planarize it; S6. Perform impurity implantation of the first conductivity type to form the anode region; S7. High-temperature diffusion forms the anode region and carrier injection suppression layer; S8. Perform light doping implantation of the first conductivity type, deposit interlayer dielectric and reflow to form a lightly doped anode region; S9. The contact holes and front metal patterning are completed through the third and fourth photomasks; S10, back side thinning, injection, annealing, forming back side metal.

8. A method for manufacturing a soft recovery FRD according to claim 7, characterized in that, The back electric field cutoff layer is formed by hydrogen ion implantation and annealing.

9. A method for manufacturing a soft recovery FRD according to claim 7, characterized in that, The back electric field cutoff layer is formed directly through the epitaxial substrate.

10. A method for manufacturing a soft recovery FRD according to claim 7, characterized in that, The back electric field cutoff layer is formed through a diffuser wafer.

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