Cell structure and device layout of Schottky diode
By designing a stepped contact surface and PN junction structure in the Schottky diode and optimizing the distribution of the doped region, the problem of large reverse leakage current in the Schottky diode was solved, and higher stability and conduction efficiency were achieved.
Patent Information
- Application Number
- CN202520468286.X
- Authority / Receiving Office
- CN · China
- Patent Type
- Utility models(China)
- Current Assignee / Owner
- Filing Date
- 2025-03-17
- Publication Date
- 2026-02-06
- Estimated Expiration
- 2035-03-17
AI Technical Summary
Silicon carbide Schottky diodes have a large leakage current when reverse blocked, which leads to a decrease in the efficiency of the power converter.
Design a cell structure for a Schottky diode, including a substrate, a drift layer and a first doped region. The contact surface between the doped region and the drift layer is stepped. A PN junction is formed by combining the doped region with a second doped region. Optimize the distribution of the doped region to reduce electric field concentration and enhance current conduction capability.
It effectively reduces leakage current, lowers the risk of breakdown, improves device stability and reliability, while maintaining forward conduction capability and enhancing conduction capability under high current.
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Figure CN223885547U_ABST
Abstract
Description
TECHNICAL FIELD
[0001] The present application relates to the field of semiconductor devices, in particular to a cell structure and device layout of a Schottky diode. BACKGROUND
[0002] In the prior art, a silicon carbide Schottky diode has a low voltage drop and on-resistance, and a low loss in a reverse recovery process, which is beneficial to improve the efficiency of a power converter, but due to the mirror barrier reduction effect, it will cause a large leakage current of the Schottky diode in reverse blocking. SUMMARY
[0003] The present application provides a cell structure and device layout of a Schottky diode to solve the problem of a large leakage current of a Schottky diode in the related art.
[0004] According to one aspect of the present application, a cell structure of a Schottky diode is provided, comprising: a substrate having a first doping type; a drift layer located on one side of the substrate, the drift layer having the first doping type; and a first doped region located on both sides of the drift layer in a first direction, the first doped region having a second doping type, the first direction being a vertical direction of the thickness direction of the drift layer, and the contact surface between the first doped region and the drift layer being a stepped surface.
[0005] Optionally, the drift layer comprises a first sub-drift region and a second sub-drift region, wherein: the second sub-drift region is located on the side of the first sub-drift region away from the substrate, the first doped region is located on both sides of the second sub-drift region in the first direction, and the orthographic projection of the second sub-drift region on the substrate is located within the orthographic projection of the first sub-drift region on the substrate.
[0006] Optionally, the surface of the second sub-drift region away from the substrate has a first orthographic projection on the substrate, and the surface of the second sub-drift region close to the substrate has a second orthographic projection on the substrate, and the first orthographic projection is located within the second orthographic projection.
[0007] Optionally, the cell structure of the Schottky diode further comprises a second doped region, the second doped region being located in the second sub-drift region, the second doped region having the second doping type, and the surface of the second doped region away from the substrate being located in the surface of the second sub-drift region away from the substrate.
[0008] Optionally, the projection shape of the second doped region on the substrate is at least one of the following: a regular polygon and a circle.
[0009] Optionally, the length of the second doped region in the thickness direction of the drift layer is 0.15-0.35 μm.
[0010] Optionally, the cell structure of the Schottky diode further comprises an anode and a cathode, wherein: the anode is located on the side of the drift layer away from the substrate, and the anode covers the first doped region; and the cathode is located on the side of the substrate away from the drift layer.
[0011] Optionally, the first doped region is formed by an epitaxial growth process.
[0012] Optionally, the doping concentration of the second doped region is greater than the doping concentration of the first doped region.
[0013] According to another aspect of the present application, a device layout of a Schottky diode is provided, comprising at least one cell structure of the Schottky diode.
[0014] By the cell structure of the Schottky diode provided by the present application, the cell structure comprises a substrate, a drift layer and a first doped region, wherein the first doped region is located on both sides of the drift layer, and the contact surface between the first doped region and the drift layer is a stepped surface. The first doped region can reduce the leakage current of the Schottky diode, and the stepped contact surface can reduce the problem of electric field concentration, further reduce the generation of leakage current, reduce the risk of breakdown, and improve the stability and reliability of the device. BRIEF DESCRIPTION OF DRAWINGS
[0015] The accompanying drawings, which form a part of this application, are included to provide a further understanding of the application and are incorporated in and constitute a part of this application. The embodiments of the present application illustrated in the drawings and their descriptions are used to explain the present application and are not intended to limit the present application. In the drawings:
[0016] Figure 1 is a schematic diagram of the cross-sectional structure of a cell structure of a Schottky diode according to an embodiment of the present application;
[0017] Figure 2 is a schematic diagram of the top view structure of a cell structure of a Schottky diode in Figure 1
[0018] Figure 3 is a schematic diagram of the top view structure of another cell structure of a Schottky diode in Figure 1
[0019] Figure 4 is a schematic diagram of the top view structure of a device layout of a Schottky diode according to an embodiment of the present application.
[0020] In the above drawings, the following reference signs are used:
[0021] 10, substrate; 20, drift layer; 21, first sub-drift region; 22, second sub-drift region; 30, first doped region; 40, second doped region; 50, anode; 60, cathode; 70, device layout. DETAILED DESCRIPTION
[0022] It should be noted that the embodiments and features of the embodiments in the present application can be combined with each other without conflict. The technical solutions in the embodiments of the present application will be described in detail below with reference to the accompanying drawings and in combination with the embodiments.
[0023] In order for those skilled in the art to better understand the scheme of the present application, the technical solutions in the embodiments of the present application will be described clearly and completely below in combination with the drawings in the embodiments of the present application. Obviously, the described embodiments are only a part of the embodiments of the present application, not all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative labor should be within the scope of protection of the present application.
[0024] It should be noted that the terms "first", "second" and the like in the specification and claims of the present application and the above-described drawings are used to distinguish similar objects, and do not necessarily have to describe a specific order or sequence. It should be understood that the data thus used can be interchanged under appropriate circumstances, so that the embodiments of the present application described herein can be implemented. In addition, the terms "include" and "have" and any variations thereof are intended to cover non-exclusive inclusion, for example, a process, method, system, product or device that includes a series of steps or units does not have to be limited to those steps or units clearly listed, but can include other steps or units not clearly listed or inherent to these processes, methods, products or devices.
[0025] As described in the prior art, silicon carbide Schottky diodes have lower voltage drop and on-resistance, and lower loss in reverse recovery process, which is beneficial to improve the efficiency of power converters, but due to the mirror barrier lowering effect, the Schottky diode has a large leakage current when blocking in the reverse direction. Therefore, the present application proposes a cell structure and device layout of a Schottky diode.
[0026] In order to solve the above technical problems, according to the embodiments of the present application, a cell structure of a Schottky diode is provided. Figure 1 is a schematic cross-sectional view of the cell structure of the Schottky diode according to the embodiments of the present application. As shown in the figure, the cell structure of the Schottky diode according to the embodiments of the present application comprises a substrate 10, a drift layer 20, a first sub-drift region 21, a second sub-drift region 22, a first doped region 30, a second doped region 40, an anode 50, a cathode 60 and a device layout 70. Figures 1 to 3As shown, the cell structure of the Schottky diode includes: a substrate 10 having a first doping type; a drift layer 20 located on one side of the substrate 10, the drift layer 20 having the first doping type; and first doped regions 30 located on both sides of the drift layer 20 in a first direction, the first direction being a vertical direction of the thickness direction of the drift layer 20, the first doped regions 30 having a second doping type, and the contact surface between the first doped regions 30 and the drift layer 20 being a stepped surface.
[0027] By setting the first doped regions in the cell structure of the Schottky diode and setting the contact surface between the first doped regions and the drift layer as a stepped surface, the area of the conduction electric field is increased so that the electric field is not concentrated in one point, and the problem of electric field concentration can be reduced. The first doped regions form ohmic contact with the anode of the Schottky diode, and the drift layer forms Schottky contact with the anode of the Schottky diode. The first doped regions can reduce the Schottky part of the electric field during reverse blocking, thereby reducing the reverse leakage current. Since the proportion of the first doped regions will increase, the Schottky contact part will decrease, resulting in a decrease in the forward conduction capability. Therefore, the Schottky diode in the present application can balance the forward characteristics and blocking characteristics. Specifically, the more the number of steps, the smaller the area of the Schottky contact between the drift layer and the anode. Reducing the number of steps can increase the area of the Schottky contact without greatly affecting the proportion of the first doped regions. Based on this, the number of steps of the stepped surface between the first doped regions and the drift layer can be reasonably selected according to the actual situation, so that the Schottky diode with the above cell structure can simultaneously consider the forward characteristics and blocking characteristics, weakening the trade-off between the blocking characteristics and the conduction characteristics in diode design, increasing the process window of the Schottky part, reducing the forward conduction resistance under the condition of ensuring small reverse leakage, better reducing the generation of leakage current, reducing the risk of breakdown, and improving the stability and reliability of the device.
[0028] In the above embodiment, as shown in Figure 1 the substrate 10 and the drift layer 20 have the same doping type, the doping concentration of the substrate 10 is 8x10 14 cm -3 ~ 8x10 16 cm -3 , the doping concentration of the drift layer 20 is 1x10 18 cm -3 ~ 1x10 20 cm -3 , if the substrate 10 and the drift layer 20 are N-type doped, the first doped regions 30 are P-type doped, and the doping concentration of the first doped regions 30 is 1x10 18 cm -3 ~ 1x10 19 cm -3 .
[0029] In some optional embodiments, as shown in FIG. 1, the first doped region 30 is formed by an epitaxial growth process. Figure 1
[0030] In the above optional embodiments, as shown in FIG. 1, the formation of the doped region in the drift layer 20 usually adopts an ion implantation process, but the ion implantation process will cause damage to the crystal lattice of the drift layer 20 and introduce defects, which will also affect the performance of the device. The use of an epitaxial growth process can avoid the generation of lattice defects in the structure of the device, effectively increase the ion activation rate of the first doped region 30, improve the conduction capacity of the diode under large surge conditions, and thus improve the performance of the device. Figure 1
[0031] In some optional embodiments, as shown in FIG. 1, the drift layer 20 includes a first sub-drift region 21 and a second sub-drift region 22, wherein: the second sub-drift region 22 is located on the side of the first sub-drift region 21 away from the substrate 10, the first doped region 30 is located on both sides of the second sub-drift region 22 in the first direction, and the orthogonal projection of the second sub-drift region 22 on the substrate 10 is located within the orthogonal projection of the first sub-drift region 21 on the substrate 10. Figure 1
[0032] In the above optional embodiments, as shown in FIG. 1, the first doped region 30 has a stepped contact surface on both sides of the second sub-drift region 22. As the number of steps increases, the thickness of the second sub-drift region 22 will also increase, but the contact surface with the anode will decrease, reducing the forward conduction. As the number of steps decreases, the thickness of the second sub-drift region 22 will also decrease, and the contact surface with the anode will increase, improving the forward conduction, reducing the Schottky part of the electric field in the reverse blocking, and reducing the reverse leakage current. Figure 1
[0033] In some optional embodiments, as shown in FIG. 1, the surface of the second sub-drift region 22 away from the substrate 10 has a first orthogonal projection on the substrate 10, and the surface of the second sub-drift region 22 close to the substrate 10 has a second orthogonal projection on the substrate 10, and the first orthogonal projection is located within the second orthogonal projection. Figure 1
[0034] In the above optional embodiments, as shown in FIG. 1, the surface of the second sub-drift region 22 away from the substrate 10 has a first orthogonal projection on the substrate 10, and the surface of the second sub-drift region 22 close to the substrate 10 has a second orthogonal projection on the substrate 10, and the first orthogonal projection is located within the second orthogonal projection. Figure 1 As shown, due to the stepped contact surface between the first doped region 30 and the second sub-drift region 22, the surface of the second sub-drift region 22 away from the substrate 10 gradually decreases in the direction away from the substrate 10, and the contact surface between the second sub-drift region 22 and the first sub-drift region 21 is the largest surface of the second sub-drift region 22. The adoption of the stepped structure in the thickness direction of the device can make the electric field transmission more uniform.
[0035] In some optional embodiments, as shown in Figures 1 to 3 As shown, the cell structure of the Schottky diode further includes a second doped region 40, the second doped region 40 is located in the second sub-drift region 22, the second doped region 40 has the second doping type, and the surface of the second doped region 40 away from the substrate 10 is located in the surface of the second sub-drift region 22 away from the substrate 10.
[0036] In the above optional embodiments, as shown in Figure 1 As shown, the second doped region 40 is further included in the second sub-drift region 22, and the second doped region 40 has the same doping type as the first doped region 30, as shown in Figures 2 to 3 As shown, in the top view of the Schottky diode, the second doped region 40 can be a regular polygon or a circle. The doping concentration of the second doped region 40 can be greater than or equal to the doping concentration of the first doped region 30, so that the first doped region 30 can further reduce the resistivity of the second sub-drift region 22 when the device is in forward conduction, and the current can be quickly conducted when passing through the second doped region 40 with high concentration of doping to the second sub-drift region 22, thereby avoiding heat accumulation. The first doped region 30 with high concentration of doping reduces the resistivity of the second sub-drift region 22 between the first doped regions 30, enhances the conductivity, further quickly conducts the current, and improves the surge resistance of the device.
[0037] In some optional embodiments, as shown in Figures 2 to 3 As shown, the projection shape of the second doped region 40 on the substrate is at least one of a regular polygon and a circle.
[0038] In the above optional embodiments, as shown in Figures 2 to 3 As shown, in the top view of the cell structure, the shape of the second doped region 40 in the second sub-drift region 22 can be a regular polygon or a circle.
[0039] In some optional embodiments, the length of the second doped region in the thickness direction of the drift layer is 0.15 μm to 0.35 μm.
[0040] In the above optional embodiments, as shown in Figure 1As shown, the thickness of the second doped region 40 in the thickness direction of the second sub-drift region 22 is 0.15 μm to 0.35 μm.
[0041] In some alternative embodiments, as shown in FIG. 2, the cell structure of the Schottky diode further comprises an anode 50 and a cathode 60, wherein: the anode 50 is located on the side of the drift layer 20 facing away from the substrate 10, and the anode 50 covers the first doped region 30; and the cathode 60 is located on the side of the substrate 10 facing away from the drift layer 20. Figure 1
[0042] In some alternative embodiments, as shown in FIG. 2, the cell structure of the Schottky diode further comprises an anode 50 and a cathode 60, wherein: the anode 50 is located on the side of the drift layer 20 facing away from the substrate 10, and the anode 50 covers the first doped region 30; and the cathode 60 is located on the side of the substrate 10 facing away from the drift layer 20. Figure 1
[0043] In some alternative embodiments, the doping concentration of the second doped region is greater than the doping concentration of the second doped region.
[0044] In some alternative embodiments, the doping concentration of the second doped region is 1 x 1018 cm-3 to 1 x 1020 cm-3. 19 cm -3 ~ 1 x 10 20 cm -3 .
[0045] The method for preparing the cell structure of the Schottky diode can be:
[0046] Step 1: providing a substrate;
[0047] Step 2: forming a preliminary drift layer on the substrate;
[0048] Step 3: etching the preliminary drift layer to make the preliminary drift layer have a stepped structure, forming a drift layer, and the part of the drift layer having the stepped structure is a second sub-drift region, and the part of the drift layer not etched is a first sub-drift region;
[0049] Step 4: Forming a first sub-doped region on the first sub-drift region by epitaxial growth process, so that the first sub-doped region covers the stepped structure and contacts the second sub-drift region;
[0050] Step 5: Forming a second doped region on the surface of the second sub-drift region away from the substrate by ion implantation process;
[0051] Step 6: Forming an anode on the side of the second sub-drift region away from the substrate, the anode covering the first doped region and the second doped region;
[0052] Step 7: Forming a cathode on the side of the substrate away from the drift layer.
[0053] The Schottky diode prepared by the preparation method has a first doped region in the cell structure, and the contact surface of the first doped region and the drift layer is set as a stepped contact surface, which can reduce the problem of electric field concentration. The first doped region forms an ohmic contact with the anode of the Schottky diode, and the drift layer forms a Schottky contact with the anode of the Schottky diode. The first doped region can reduce the Schottky part electric field during reverse blocking, thereby reducing the reverse leakage current. However, an increase in the proportion of the first doped region will reduce the Schottky contact part, resulting in poor forward conduction capability. Therefore, the number of steps of the stepped contact surface of the first doped region and the drift layer can be reasonably selected according to actual conditions. The more the number of steps is, the smaller the area of the Schottky contact between the drift layer and the anode is. Reducing the number of steps can increase the area of the Schottky contact without greatly affecting the proportion of the first doped region. Therefore, the cell structure of the Schottky diode can balance the forward characteristics and blocking characteristics, weaken the trade-off between the blocking characteristics and the conduction characteristics in the design of the diode, increase the process window of the Schottky part, reduce the forward conduction resistance under the condition of ensuring small reverse leakage, better reduce the generation of leakage current, reduce the risk of breakdown, and improve the stability and reliability of the device.
[0054] The second doped region and the drift layer form a PN junction, and there is an inherent electric field between the second doped region and the drift layer. When the diode is forward biased, the holes in the second doped region and the free electrons in the drift layer are attracted by the external voltage, thereby forming a conductive channel in the PN junction region, and the current can flow. The electrons and holes in the PN junction disappear in a recombination manner, so that the electric field at the PN junction can continue to maintain the flow of current. The second doped region has a high doping concentration and can be formed by an ion implantation process. The bipolar conduction capability is maintained under a large current, and the surge reliability of the device is improved.
[0055] In the optional embodiment, the second doped region can also be formed by epitaxial growth, and the first sub-drift region is first formed on the substrate, a second doped preliminary layer is formed on the first sub-drift region, the second doped preliminary layer is subjected to a patterning process to obtain a second doped region having a regular polygonal or circular projection on the substrate, a second sub-drift preliminary region is formed on the first sub-drift region, a surface of the second sub-drift preliminary region away from the substrate is located in the same surface as a surface of the second doped region away from the substrate, the second sub-drift preliminary region is subjected to an etching process to obtain a stepped structure, the first sub-doped region is formed on the first sub-drift region by epitaxial growth, the first sub-doped region and the second sub-drift region are in contact through the stepped structure, an anode is formed on a side of the second sub-drift region away from the substrate, the anode covers the first sub-doped region and the second doped region, and a cathode is formed on a side of the substrate away from the first sub-drift region.
[0056] According to another aspect of the present application, a device layout 70 of a Schottky diode is provided, as shown in Figure 4 including at least one of the above-mentioned cell structure of the Schottky diode.
[0057] By using the above-mentioned device layout of the Schottky diode, the area ratio of the first sub-doped region to the second sub-drift region of the above-mentioned cell structure is about 2:1, the first doped region with a large area is introduced into the cell structure, the device layout of the Schottky diode introduces the first doped region with a large area in the design of the cell structure, and the first doped region does not need to be separately introduced in the layout in the design of the device layout, thereby improving the wafer utilization efficiency of the diode, significantly improving the on-current capability of the device, significantly reducing the on-resistance, and reducing the junction temperature.
[0058] It should also be noted that the terms "comprising", "containing" or any other variant thereof are intended to cover non-exclusive inclusion, so that processes, methods, articles or devices that include a series of elements not only include those elements, but also include other elements not explicitly listed, or other elements inherent to such processes, methods, articles or devices. Without more limitations, the element defined by the statement "comprising a" does not exclude the presence of additional identical elements in the process, method, article or device including the element.
[0059] From the above description, it can be seen that the above-mentioned embodiments of the present application achieve the following technical effects:
[0060] 1) The embodiment of the present application provides a cell structure of a Schottky diode. The first doped region in the cell structure can reduce the electric field of the Schottky part when blocking in reverse direction, and reduce the reverse leakage current. However, the proportion of the first doped region will increase, which reduces the Schottky contact part, and causes the forward conduction ability to be poor. The forward characteristics and the blocking characteristics need to be balanced. The number of steps of the stepped contact surface between the first doped region and the drift layer can be reasonably selected according to actual conditions. The more the number of steps is, the smaller the area of the Schottky contact between the drift layer and the anode is. Reducing the number of steps can increase the area of the Schottky contact, and the proportion of the first doped region is not greatly affected. Therefore, the cell structure of the Schottky diode can balance the forward characteristics and the blocking characteristics, weakens the trade-off between the blocking characteristics and the conduction characteristics in the design of the diode, increases the process window of the Schottky part, reduces the forward conduction resistance under the condition of ensuring that the reverse leakage current is small, better reduces the generation of the leakage current, reduces the risk of breakdown, and improves the stability and reliability of the device.
[0061] 2) The embodiment of the present application provides a cell structure of a Schottky diode. The PN junction is formed between the second doped region and the drift layer, and the inherent electric field exists between the second doped region and the drift layer. When the diode is forward biased, the holes in the second doped region and the free electrons in the drift layer are attracted by the external voltage, so that the conductive channel is formed in the PN junction area, and the current can pass through. The electrons and holes in the PN junction disappear in a recombination manner, so that the electric field at the PN junction can continue to maintain the flow of the current. The second doped region has a high doping concentration, can be formed through an ion implantation process, maintains the bipolar conduction ability under a large current, and improves the surge reliability of the device.
[0062] 3) The embodiment of the present application provides a device layout of a Schottky diode. The first doped region with a large area is introduced into the cell structure. The device layout of the Schottky diode introduces the first doped region with a large area in the design of the cell structure. The first doped region does not need to be separately introduced in the layout in the design of the device layout, improves the wafer utilization efficiency of the diode, significantly improves the conduction ability of the device under a large current, significantly reduces the conduction resistance, and reduces the junction temperature.
Claims
1. A cell structure of a Schottky diode, characterized by, The Schottky diode comprises: a substrate having a first doping type; a drift layer located on one side of the substrate, the drift layer having the first doping type; first doped regions located on both sides of the drift layer in a first direction, the first direction being a direction perpendicular to a thickness direction of the drift layer, the first doped regions having a second doping type, and a contact surface of the first doped regions and the drift layer being a stepped surface.
2. The Schottky diode cell structure of claim 1, wherein, The drift layer comprises a first sub-drift region and a second sub-drift region, wherein: the second sub-drift region is located on a side of the first sub-drift region away from the substrate, the first doped regions are located on both sides of the second sub-drift region in the first direction, and a footprint of the second sub-drift region on the substrate is located within a footprint of the first sub-drift region on the substrate.
3. The Schottky diode cell structure of claim 2, wherein, a surface of the second sub-drift region away from the substrate has a first footprint on the substrate, and a surface of the second sub-drift region close to the substrate has a second footprint on the substrate, the first footprint being located within the second footprint.
4. The Schottky diode cell structure of any one of claims 2-3, wherein, The cell structure of the Schottky diode further comprises a second doped region, the second doped region being located in the second sub-drift region, the second doped region having the second doping type, and a surface of the second doped region away from the substrate being located in a surface of the second sub-drift region away from the substrate.
5. The Schottky diode cell structure of claim 4, wherein, A shape of a projection of the second doped region on the substrate is at least one of a regular polygon and a circle.
6. The Schottky diode cell structure of claim 4, wherein, A length of the second doped region in the thickness direction of the drift layer is 0.15 μm to 0.35 μm.
7. The Schottky diode cell structure of claim 1, wherein, The cell structure of the Schottky diode further comprises an anode and a cathode, wherein: the anode is located on a side of the drift layer away from the substrate, and the anode covers the first doped regions; the cathode is located on a side of the substrate away from the drift layer.
8. The Schottky diode cell structure of claim 1, wherein, The first doped regions are formed by an epitaxial growth process.
9. The Schottky diode cell structure of claim 4, wherein, A doping concentration of the second doped region is greater than a doping concentration of the second doped region.
10. A device layout for a Schottky diode, characterized by The Schottky diode comprises at least one cell structure according to any one of claims 1 to 9.