A composite-terminated vertical Schottky diode combining a BaTiO3 / Si3N4 dielectric field plate and ion implantation

Abstract

This invention discloses a composite-terminated vertical Schottky diode combining a BaTiO3 / Si3N4 dielectric field plate and ion implantation. A composite dielectric layer composed of Si3N4 and BaTiO3 layers is used, with an anode field plate disposed on the composite dielectric layer. Fluorine ions are implanted into a drift layer below the anode to form a fluorine implantation region. Part of the fluorine implantation region is located below the anode, and another part is located below the composite dielectric layer, forming a composite termination. This composite termination structure effectively modulates the electric field distribution on the device surface and within the device bulk, ultimately effectively reducing the electric field strength at the anode edge and achieving a higher breakdown voltage. This provides an effective solution for the termination design of high-performance high-voltage Schottky diode power devices.

Description

Technical Field

[0001] This invention relates to a composite-terminated vertical Schottky diode combining a BaTiO3 / Si3N4 dielectric field plate and ion implantation, belonging to the field of third-generation semiconductor power device technology. Background Technology

[0002] Third-generation wide-bandgap semiconductor materials, with their core advantages of wide bandgap and high breakdown electric field, break through the bottlenecks of traditional semiconductor devices in terms of voltage withstand and power density, enabling devices to operate stably at higher voltages, higher frequencies, and extreme temperatures, meeting the needs of high-voltage, high-frequency power electronics applications. Gallium nitride (GaN), as a core representative of this field, possesses excellent characteristics such as a large bandgap of 3.4 eV, a high breakdown electric field of 3.3 MV / cm, and high electron mobility.

[0003] Gallium nitride Schottky barrier diodes (GaN SBDs) are fundamental components in power conversion systems and have received increasing attention in recent years. A key parameter for evaluating the performance of power semiconductor devices is their reverse breakdown voltage; the device's breakdown voltage level is a crucial factor limiting the expansion of GaN power SBD applications. However, traditional planar Schottky diodes face inherent physical limitations when developing for high-voltage applications. One key limitation is the strong electric field concentration effect at the edge where the metal anode contacts the semiconductor surface. This localized electric field peak easily induces premature avalanche breakdown, resulting in an actual breakdown voltage that is far lower than the theoretical parallel-planar junction breakdown voltage of the semiconductor material itself.

[0004] Therefore, it is necessary to design and fabricate new structures at the edge of the Schottky junction in GaN Schottky barrier diodes to alleviate the electric field concentration phenomenon at the electrode edge. These structures are called termination structures. Commonly used termination technologies can generally be divided into two categories according to their basic structure: extended and truncated. Extended terminations include junction termination extensions, field plates, and field limiting rings, while truncated terminations include bevel terminations and trench terminations. Among them, field plate terminations are simple to process, do not require high-temperature annealing, and have no impact on forward characteristics, making them widely used in low-voltage discrete devices and high-voltage integrated circuits. The general operation involves depositing a dielectric layer on the semiconductor surface, and then depositing a metal on the dielectric. The electric field distribution is partly within the dielectric layer and partly within the semiconductor layer. Therefore, the introduction of BaTiO3 / Si3N4 as the field plate dielectric layer in this invention has significant technical advantages: BaTiO3 has a dielectric constant of over 180 to 240, which is much higher than that of traditional materials such as SiO2 (3.9) and Si3N4 (7.0), enabling it to generate a very strong electric field absorption effect. This effectively enhances the dispersion effect of the field plate on the electric field of the semiconductor surface, reduces the peak electric field in the semiconductor layer at the anode edge of the device, and thus improves the device's breakdown voltage. Si3N4 can form a low interface state coverage with the GaN drift layer, reducing the impact of interface defects. However, relying solely on various field plate designs cannot completely eliminate the electric field concentration effect at the electrode edge, because the field plate effect is outside the electrode and there is no mechanism to change it inside the device, so the device can still break down prematurely. In order to completely eliminate the electric field concentration effect at the electrode edge and reach the breakdown voltage limit that the material itself can support, it is also necessary to create a structure to disperse the electric field in the electrode edge region inside the device. In this invention, a novel terminal structure is further fabricated using ion implantation technology. The fluorine ion implantation structure is an extended edge terminal, where fluorine ions are injected into the device below the anode edge. Due to the strong negative charge of fluorine, fluorine ion implantation introduces a fixed negative charge at the Schottky junction edge, depleting free electrons and reducing the local carrier concentration at the anode edge. When the device operates in reverse, this region forms an expanded depletion region, dispersing the electric field from the edge to a larger area and reducing the electric field concentration at the anode edge. This implantation region, located at the anode edge, has no significant impact on the forward conduction of the device. The synergistic effect of these two mechanisms creates a high-resistivity region below the anode edge, widening the depletion region laterally, resulting in a smoother electric field distribution and a lower peak value. Subsequent data demonstrates that the peak electric field strength in Example 1 of this invention significantly decreases, approaching the same level as the bulk electric field, essentially eliminating the electric field concentration effect at the electrode edge, thereby improving the device's withstand voltage. Summary of the Invention

[0005] The purpose of this invention is to provide a composite terminal vertical Schottky diode combining a BaTiO3 / Si3N4 dielectric field plate and ion implantation, enabling the device to achieve a higher breakdown voltage.

[0006] The objective of this invention is achieved through the following technical solution: A composite-terminated vertical Schottky diode combining a BaTiO3 / Si3N4 dielectric field plate and ion implantation, the structure of which, from bottom to top, comprises: Substrate layer; Current spreading layer; Drift layer; Composite dielectric layer; It also includes a cathode and an anode, with the anode located on the drift layer and forming a Schottky contact with the drift layer; the cathode is located on the current spreading layer and forms an ohmic contact with the current spreading layer. The composite dielectric layer includes a first dielectric layer and a second dielectric layer. The first dielectric layer is located above the drift layer and is a Si3N4 layer. The second dielectric layer is located above the second dielectric layer and is a BaTiO3 layer. The anode extends above the second dielectric layer to form an anode field plate; Fluorine ions are injected into the drift layer below the anode to form a fluorine-injected region, part of which is located below the anode and the other part is located below the composite dielectric layer.

[0007] Preferably, the width of the fluorine-implanted region is 2-10 μm, the depth of the implanted region is 10-200 nm, the implantation energy is 10-100 keV, and the implantation dose is 1×10⁻⁶. 13 ~ 1×10 14 cm -2 .

[0008] Preferably, in the fluorine injection region, the width of the region below the anode is less than or equal to half the width of the entire fluorine injection region; more preferably, the injection is performed with the anode edge as the midpoint.

[0009] Preferably, the length of the anode field plate is 3% to 10% of the distance between the anode and cathode electrodes of the device, and the thickness is 0.05 to 3 μm.

[0010] Preferably, the thickness of the first dielectric layer is 10–50 nm, and the thickness of the second dielectric layer is 50–500 nm.

[0011] Preferably, the substrate is a sapphire substrate, a Si substrate, or a SiC substrate.

[0012] Preferably, the current spreading layer is n-type GaN with a thickness of 1~4 μm and a carrier concentration of 5×10⁻⁶. 18 ~1×10 20 cm -3 .

[0013] Preferably, the drift layer is n-type GaN with a thickness of 2 to 20 μm and a carrier concentration of 1 × 10⁻⁶.15 ~1×10 17 cm -3 .

[0014] The anode can be one of Ni, Au, Pt, Pd, Ir, Mo, Al, Ti, TiN, Ta, TaN, ZrN, VN, NbN or their stacked structure.

[0015] The cathode can be one of Ti, Al, Ni, Au, Mo, Ta, Zr, V, Nb or a stacked structure thereof.

[0016] This invention proposes a novel composite termination structure. Fluorine ions are implanted into a drift layer below the anode edge of the device, and an anode field plate is positioned above a BaTiO3 dielectric layer. BaTiO3, a high-dielectric-constant material, effectively reduces the electric field intensity on the semiconductor surface and optimizes the surface electric field distribution when used as the field plate dielectric layer. Fluorine ion implantation introduces fixed negative charges at the anode edge to deplete free electrons and form a high-resistivity region. This high-resistivity region widens the depletion region, resulting in a smoother internal electric field distribution and lower peak values. The field plate modulates the surface electric field distribution, improving breakdown voltage without significantly increasing lateral dimensions; fluorine ion implantation optimizes the bulk electric field and effectively suppresses new electric field peaks at the field plate edge. This invention combines field plate termination with fluorine ion implantation junction termination extension technology to form a composite termination, effectively modulating the electric field distribution on the device surface and within the bulk, ultimately reducing the electric field intensity at the anode edge and achieving a higher breakdown voltage. This provides an effective solution for edge termination design of high-performance high-voltage GaN power devices. Attached Figure Description

[0017] Figure 1 This is a schematic diagram of the structure of a vertical Schottky diode without a terminal structure, as shown in Comparative Example 1.

[0018] Figure 2 The diagram shows the electric field distribution of the device in Comparative Example 1 under a reverse bias of -500V, where (a) is the internal electric field distribution and (b) is the surface electric field distribution.

[0019] Figure 3 This is a schematic diagram of the structure of a vertical Schottky diode with only BaTiO3 / Si3N4 field plate terminals, as shown in Comparative Example 2.

[0020] Figure 4 The diagram shows the electric field distribution of the device in Comparative Example 2 under a reverse bias of -500V, where (a) is the internal electric field distribution and (b) is the surface electric field distribution.

[0021] Figure 5 This is a schematic diagram of the structure of a longitudinal Schottky diode with only fluorine ion implantation terminals, as shown in Comparative Example 3.

[0022] Figure 6 The diagram shows the electric field distribution of Comparative Example 3 device under reverse bias of -500V, where (a) is the internal electric field distribution and (b) is the surface electric field distribution.

[0023] Figure 7 This is a schematic diagram of the structure of a longitudinal Schottky diode with a complete BaTiO3 / Si3N4 field plate and a fluorine ion implantation composite terminal, according to Embodiment 1 of the present invention.

[0024] Figure 8 The electric field distribution diagrams of the complete design device of Example 1 under reverse bias of -500V are shown, where (a) is the internal electric field distribution and (b) is the surface electric field distribution diagram.

[0025] Figure 9 shows the device breakdown voltage variations in Comparative Examples 1-3 and Example 1.

[0026] Figure 10 It represents the change in device breakdown voltage across different fluorine-injected regions. Detailed Implementation

[0027] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only a part of the embodiments of the present invention, and not all of them. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0028] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains. The terminology used herein in the specification of this invention is for the purpose of describing particular embodiments only and is not intended to limit the invention. Furthermore, while this document provides examples of parameters containing specific values, it should be understood that the parameters need not be exactly equal to the corresponding values, but can approximate the corresponding values ​​within acceptable error tolerances or design constraints. Directional terms mentioned in the embodiments, such as “up,” “down,” “front,” “back,” “left,” “right,” etc., are only for reference to the accompanying drawings. Therefore, the directional terms used are for illustrative purposes and not for limiting the scope of protection of this invention.

[0029] Unless otherwise specified, all substances or instruments used in the following examples can be obtained from conventional commercial sources.

[0030] like Figure 1 As shown, a vertical Schottky diode structure without a terminal structure is provided, the structure of which includes: (1) Sapphire substrate; (2) Current spreading layer, GaN thickness is 3 μm, uniformly doped with 1×10⁻⁶ Si.19 cm -3 ; (3) Drift layer, GaN thickness is 9 μm, uniform Si doping 1.5×10 16 cm -3 ; (4) The first dielectric layer is a 50nm thick Si3N4 layer; (5) The second dielectric layer is a 200nm thick BaTiO3 layer; (6) Cathode, disposed on current spreading layer, is Ti / Al / Ni / Au alloy with thicknesses of 30 / 150 / 30 / 100nm respectively; (7) Anode, which is a Pt / Au metal combination with thicknesses of 50 / 300 nm, is set on the drift layer.

[0031] The distance between the anode and cathode of the device is 30 μm.

[0032] Under a reverse bias of -500V, the internal electric field distribution of Comparative Example 1 is as follows: Figure 2 As shown in (a), the electric field is highly concentrated at the edge of the anode metal, forming a sharp peak. Figure 2 (b) The surface electric field distribution curves show that the peak electric field strength in Comparative Example 1 is as high as 2.9 MV / cm, which easily induces premature breakdown, with a breakdown voltage of only 595 V. Figure 9 As shown.

[0033] like Figure 3 As shown, a vertical Schottky diode structure with only BaTiO3 / Si3N4 field plate terminals is described, the structure of which includes: (1) Sapphire substrate; (2) Current spreading layer, GaN thickness is 3 μm, uniformly doped with 1×10⁻⁶ Si. 19 cm -3 ; (3) Drift layer, GaN thickness is 9 μm, uniform Si doping 1.5×10 16 cm -3 ; (4) The first dielectric layer is a 50 nm thick Si3N4 layer; (5) The second dielectric layer is a BaTiO3 layer with a thickness of 200 nm; wherein, above the second dielectric layer, the anode extends towards the second dielectric layer to form an anode field plate with a length of 2 μm and a thickness of 0.1 μm; (6) Cathode, disposed on current spreading layer, is Ti / Al / Ni / Au alloy with thicknesses of 30 / 150 / 30 / 100nm respectively; (7) Anode, which is a Pt / Au metal combination with thicknesses of 50 / 300 nm, is set on the drift layer.

[0034] The distance between the anode and cathode of the device is 30 μm.

[0035] Under a reverse bias of -500V, the internal electric field distribution of Comparative Example 2 is as follows: Figure 4 As shown in (a), the introduction of the field plate effectively disperses the electric field lines at the edge of the anode, making the electric field distribution more gradual. The electric field peak at the original anode edge disappears, but a new electric field peak is introduced at the edge of the field plate. Figure 4 (b) The surface electric field distribution curves show that the peak electric field intensity in Comparative Example 2 decreased to 2.2 MV / cm, proving that the field plate structure alone can play a certain role in electric field modulation, but there is still a significant electric field concentration phenomenon within the device. The breakdown voltage increased to 1044 V, such as... Figure 9 As shown.

[0036] Comparative Example 3 like Figure 5 As shown, a vertical Schottky diode structure with only fluorine ion implantation terminals is described, the structure comprising: (1) Sapphire substrate; (2) Current spreading layer, GaN thickness is 3 μm, uniformly doped with 1×10⁻⁶ Si. 19 cm -3 ; (3) Drift layer, GaN thickness is 9 μm, uniform Si doping 1.5×10 16 cm -3 ; Fluorine ions were implanted into the drift layer, with an implantation region width of 4 μm, an overlap width of 2 μm with the area below the anode, and an additional 2 μm located below the first dielectric layer. The implantation depth was 100 nm, and the implantation dose was 5 × 10⁻⁶. 13 cm -2 .

[0037] (4) The first dielectric layer is a 50 nm thick Si3N4 layer; (5) The second dielectric layer is a 200 nm thick BaTiO3 layer; (6) Cathode, disposed on current spreading layer, is Ti / Al / Ni / Au alloy with thicknesses of 30 / 150 / 30 / 100nm respectively; (7) Anode, which is a Pt / Au metal combination with thicknesses of 50 / 300 nm, is set on the drift layer.

[0038] The distance between the anode and cathode of the device is 30 μm.

[0039] Under a reverse bias of -500V, the internal electric field distribution of Comparative Example 3 is as follows: Figure 6 As shown in (a), the high-resistivity region formed by fluorine injection causes the depletion region to expand laterally, and the electric field distribution becomes more gradual, but the electric field concentration phenomenon at the anode edge is still quite significant. Figure 6 (b) The surface electric field distribution curves show that the peak electric field intensity in Comparative Example 3 decreased to 2.4 MV / cm, verifying the effectiveness of the optimized bulk electric field distribution of the fluorine-implanted terminal structure. However, there is still a significant electric field concentration phenomenon within the device. The breakdown voltage was increased to 1298V, such as... Figure 9 As shown.

[0040] Example 1 like Figure 7 As shown, this vertical Schottky diode structure, which has a complete BaTiO3 / Si3N4 field plate and a fluorine ion implantation composite terminal, includes the following components from bottom to top: (1) Sapphire substrate; (2) Current spreading layer, GaN thickness is 3 μm, uniformly doped with 1×10⁻⁶ Si. 19 cm -3 ; (3) Drift layer, GaN thickness is 9 μm, uniform Si doping 1.5×10 16 cm -3 ; Fluorine ions were implanted into the drift layer, with an implantation region width of 4 μm, an overlap width of 2 μm with the area below the anode, and an additional 2 μm located below the first dielectric layer. The implantation depth was 100 nm, and the implantation dose was 5 × 10⁻⁶. 13 cm -2 .

[0041] (4) The first dielectric layer is a 50 nm thick Si3N4 layer; (5) The second dielectric layer is a BaTiO3 layer with a thickness of 200 nm; wherein, above the second dielectric layer, the anode extends towards the second dielectric layer to form an anode field plate with a length of 2 μm and a thickness of 0.1 μm; (6) Cathode, disposed on current spreading layer, is Ti / Al / Ni / Au alloy with thicknesses of 30 / 150 / 30 / 100nm respectively; (7) Anode, which is a Pt / Au metal combination with thicknesses of 50 / 300 nm, is set on the drift layer.

[0042] The distance between the anode and cathode of the device is 30 μm.

[0043] Under a reverse bias of -500V, the internal electric field distribution of this embodiment of the invention is as follows: Figure 8As shown in (a), due to the introduction of BaTiO3 / Si3N4 field plate and fluorine ion implantation composite terminal, the electric field distribution of this structure is the most gentle and the distribution area is the widest, and the electric field concentration at the anode edge and the field plate edge is significantly alleviated. Figure 8 (b) The surface electric field distribution curves show that the peak electric field intensity in this embodiment of the invention is significantly reduced to 1.8 MV / cm, lower than Comparative Examples 1, 2, and 3, and approximately 38% lower than the structure without termination (Comparative Example 1). It approaches the same as the bulk electric field, essentially completely eliminating the electric field concentration effect at the electrode edges, thereby improving the device's breakdown voltage. The breakdown voltage is significantly increased to 1845V, as shown in the figure. Figure 9 As shown.

[0044] Furthermore, the proportion of the overall fluorine-implanted region under the electrode also has a significant impact on the device breakdown voltage. The width of the implanted region under the electrode is W. OV By changing the distribution of the width of the injection region below the electrode and the width of the injection region outside the electrode, the breakdown voltage of the corresponding device can be obtained. For example... Figure 10 As shown, the overall fluorine injection area is kept constant at 4 mm, and the area under the electrode is W. OV When W is 1 mm, 2 mm, and 3 mm respectively, the results show that when W OV When the fluorine implantation area is less than or equal to 50% of the total fluorine content, the device breakdown voltage remains essentially unchanged; when it exceeds 50%, the device breakdown voltage decreases. Clearly, considering both the repeatability of the fabrication process alignment and the retention of device performance, centered on the anode edge in the fluorine implantation region is the optimal design, simultaneously ensuring both high device breakdown voltage and high reliability and repeatability of the fabrication process.

[0045] The above embodiments are preferred embodiments of the present invention, but the embodiments of the present invention are not limited to the above embodiments. Any changes, modifications, substitutions, combinations, or simplifications made without departing from the spirit and principle of the present invention shall be considered equivalent substitutions and shall be included within the protection scope of the present invention.

Claims

1. A composite-terminated vertical Schottky diode combining a BaTiO3 / Si3N4 dielectric field plate and ion implantation, the structure of which, from bottom to top, comprises: Substrate layer; Current spreading layer; Drift layer; Composite dielectric layer; It also includes a cathode and an anode, with the anode located on the drift layer and forming a Schottky contact with the drift layer; The cathode is located on the current spreading layer and forms an ohmic contact with the current spreading layer; The feature is that the composite dielectric layer includes a first dielectric layer and a second dielectric layer, wherein the first dielectric layer is located above the drift layer and is a Si3N4 layer, and the second dielectric layer is located above the second dielectric layer and is a BaTiO3 layer; The anode extends above the second dielectric layer to form an anode field plate; Fluorine ions are injected into the drift layer below the anode to form a fluorine-injected region, part of which is located below the anode and the other part is located below the composite dielectric layer.

2. The composite-terminated longitudinal Schottky diode according to claim 1, characterized in that: The fluorine implantation region has a width of 2–10 μm, an implantation depth of 10–200 nm, an implantation energy of 10–100 keV, and an implantation dose of 1 × 10⁻⁶. 13 ~ 1×10 14 cm -2 .

3. The composite-terminated longitudinal Schottky diode according to claim 2, characterized in that: In the fluorine injection region, the width of the region located below the anode is less than or equal to half the width of the entire fluorine injection region.

4. The composite-terminated longitudinal Schottky diode according to claim 1, characterized in that: The length of the anode field plate is 3% to 10% of the distance between the anode and cathode electrodes of the device, and the thickness is 0.05 to 3 μm.

5. The composite-terminated longitudinal Schottky diode according to claim 1, characterized in that: The thickness of the first dielectric layer is 10–50 nm, and the thickness of the second dielectric layer is 50–500 nm.

6. The composite-terminated longitudinal Schottky diode according to any one of claims 1-5, characterized in that: The substrate is a sapphire substrate, a Si substrate, or a SiC substrate.

7. The composite-terminated longitudinal Schottky diode according to any one of claims 1-5, characterized in that: The current spreading layer is n-type GaN with a thickness of 1~4 μm and a carrier concentration of 5×10⁻⁶. 18 ~1×10 20 cm -3 .

8. The composite-terminated longitudinal Schottky diode according to claim 7, characterized in that: The drift layer is n-type GaN with a thickness of 2 ~ 20 μm and a carrier concentration of 1 × 10⁻⁶. 15 ~1×10 17 cm -3 .

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