High-voltage gallium oxide Schottky diode with field-limiting ring termination structure

Abstract

The present invention proposes a high-voltage gallium oxide Schottky diode with a field-limiting ring terminal structure, comprising a cathode metal layer (1), a high-doped N-type gallium oxide substrate (2), a low-doped N-type gallium oxide epitaxial layer (3), and an anode metal layer (4) stacked sequentially from bottom to top; the anode metal layer is connected to a main junction (5) at the top of the low-doped N-type gallium oxide epitaxial layer; and a plurality of field-limiting rings (6) are further provided at the top of the low-doped N-type gallium oxide epitaxial layer. The present invention simplifies the process steps, enabling efficient industrial production. The device design of the present invention alleviates the electric field crowding phenomenon in the terminal region, improves the electric field distribution, and further improves the withstand voltage performance and reliability of the gallium oxide SBD device. Under this structure, the breakdown voltage of the device is greatly improved while the characteristic on-resistance is only slightly increased, ultimately achieving a high PFOM value.

Description

Technical Field

[0001] The present invention relates to the technical field of power semiconductors, in particular to a high-voltage gallium oxide Schottky diode under a field-limiting ring terminal structure. Background Art

[0002] Gallium oxide (Ga2O3) has been widely studied as a promising semiconductor material due to its wide bandgap (4.5-4.9 eV), high critical breakdown field (8 MV / cm), and high figure of merit (approximately 3000) for power performance. Furthermore, the cost of Ga2O3 single crystals is relatively low. Consequently, power devices based on Ga2O3 have attracted considerable attention in recent years. Conventional Ga2O3 SBDs (SBDs) are susceptible to electric field concentration at the anode edge. To address this issue, researchers have proposed incorporating edge termination structures into the device to mitigate this effect. These structures include field plates, ground angles, and stepped structures. Field-limiting rings (FLRs) are also a relatively effective approach. These FLRs can reduce peak electric fields and expand the depletion region, further enhancing the device's withstand voltage. However, due to the current lack of P-type doping technology for Ga2O3 materials, natural P-type semiconductor materials such as NiO or Cu2O can be used as FLRs.

[0003] To achieve a high power factor of merit (PFOM), gallium oxide Schottky diodes should have a low characteristic on-resistance during forward conduction and a high breakdown voltage during reverse conduction. However, due to the low barrier height of Schottky diodes, the breakdown voltage achieved by existing gallium oxide Schottky diodes is often low. Improving the device's breakdown voltage by implanting edge termination structures or modifying parameters such as the drift layer's doping concentration and thickness often increases the device's on-resistance. Therefore, balancing these two factors to maximize PFOM performance has become a core issue for gallium oxide power diodes. Summary of the Invention

[0004] This invention proposes a high-voltage gallium oxide Schottky diode with a field-limiting ring termination structure, simplifying the process steps and enabling efficient industrial production. The device design alleviates electric field crowding in the termination region, improving the electric field distribution and further enhancing the withstand voltage performance and reliability of the gallium oxide SBD device. With this structure, the device's breakdown voltage is significantly increased with only a slight increase in the characteristic on-resistance, ultimately achieving a high PFOM value.

[0005] The present invention adopts the following technical solutions.

[0006] A high-voltage gallium oxide Schottky diode with a field-limiting ring terminal structure comprises a cathode metal layer (1), a high-doped N-type gallium oxide substrate (2), a low-doped N-type gallium oxide epitaxial layer (3), and an anode metal layer (4) stacked sequentially from bottom to top; the anode metal layer is connected to a main junction (5) at the top of the low-doped N-type gallium oxide epitaxial layer; and a plurality of field-limiting rings (6) are also provided at the top of the low-doped N-type gallium oxide epitaxial layer.

[0007] The main junction (5) is placed at the edge of the anode metal layer (4).

[0008] The low-doped N-type gallium oxide epitaxial layer is a conductive drift layer having a plurality of P-type semiconductor ring regions that are arranged laterally and have a linearly increasing interval.

[0009] The field limiting ring is arranged on the top of the conductive drift layer.

[0010] The field limiting rings are spaced apart and arranged on the same horizontal plane at the top of the low-doped N-type gallium oxide epitaxial layer, and the distances between the field limiting rings increase linearly.

[0011] The thickness of the field limiting ring is no more than 1 μm.

[0012] The field limiting ring is a heavily doped structure, and the doping type is opposite to that of the conductive drift layer.

[0013] The impurity doping concentration in the field limiting ring is not less than 4.0×10 17 cm -3 .

[0014] The anode metal layer is made of Au, Ni, Pt and TiN; the cathode metal layer is made of Ti and Au; the thickness of the highly doped N-type gallium oxide substrate is 500-650 μm, and the doping concentration is 10 18 ~10 20 cm -3 The low-doped N-type gallium oxide epitaxial layer has a thickness of 5 to 15 μm and a doping concentration of 10 15 ~10 17 cm -3 gallium oxide materials.

[0015] A method for preparing a high-voltage gallium oxide Schottky diode with a field-limiting ring terminal structure comprises the following steps:

[0016] Step S1, epitaxially growing a low-doped N-type gallium oxide epitaxial layer on top of a highly doped N-type gallium oxide substrate using a hydride vapor phase epitaxy (HVPE) or metal organic chemical vapor deposition (MOCVD) process;

[0017] Step S2: spin-coating photoresist on the surface of the low-doped N-type gallium oxide epitaxial layer 3, forming a trench opening pattern in the terminal region using a standard photolithography process, and etching the low-doped N-type gallium oxide epitaxial layer using a reactive ion etching process to form a groove for depositing the field limiting ring;

[0018] Step S3: Soak the wafer in piranha solution for 15 minutes to remove dry etching damage. Then, soak the wafer in piranha solution for 15 minutes and then in buffered oxide etch (BOE) solution for 30 minutes to repair etching damage.

[0019] Step S4: Then, the cathode metal is evaporated by electron beam and annealed at 470° C. for 1 minute to form an ohmic contact at the bottom of the highly doped N-type gallium oxide substrate;

[0020] Step S5: spin-coating photoresist on the low-doped N-type gallium oxide epitaxial layer, and forming a field limiting ring opening pattern using a standard photolithography process;

[0021] Step S6: depositing a low-doped P-type NiO epitaxial layer and a field limiting ring structure at the groove according to the opening pattern by using a process including magnetron sputtering or electron beam evaporation;

[0022] Step S7: spin-coating photoresist on the surface of the low-doped N-type gallium oxide epitaxial layer and the field limiting ring, and forming an opening pattern of the anode metal layer using a standard photolithography process;

[0023] Step S8: depositing an anode metal layer on top of the low-doped N-type gallium oxide substrate and the P-type NiO main junction layer.

[0024] The solution described in this invention simplifies the process steps, enabling the device's production method to be effectively applied in industrial production. It also alleviates electric field crowding in the terminal region, improves the electric field distribution, and further enhances the withstand voltage performance and reliability of the gallium oxide SBD device. With this structure, the device's breakdown voltage is significantly improved with only a slight increase in the characteristic on-resistance, ultimately achieving a high PFOM value.

[0025] After the field-limiting ring layer is provided on top of the conductive drift layer of the gallium oxide Schottky diode of the present invention, the breakdown position inside the device can be shifted and the consumption zone can be expanded, thereby significantly improving the breakdown voltage of the device. However, the impact on the on-resistance is relatively small, which only slightly increases the on-resistance and alleviates the contradictory relationship between the breakdown voltage and the characteristic on-resistance.

[0026] The present invention expands the depletion region by combining the field-limiting ring terminal structure, reduces the peak electric field and improves the voltage resistance of the device, making the electric field distribution more uniform. Therefore, the device proposed by the present invention can optimize the electric field distribution while reducing process production costs, thereby significantly improving the voltage resistance performance of the device. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] The present invention is further described in detail below with reference to the accompanying drawings and specific embodiments:

[0028] Attachment Figure 1 1 is a schematic cross-sectional view of the structure of a high-voltage Schottky diode with a field limiting ring terminal structure provided by an embodiment of the present invention;

[0029] Attachment Figure 2 Schematic diagram of the withstand voltage relationship between a high-voltage gallium oxide Schottky diode with a field limiting ring terminal structure and a gallium oxide Schottky barrier diode without a field limiting ring structure under the same conditions;

[0030] Attachment Figure 3 Schematic diagram comparing forward conduction characteristic curves of a high-voltage gallium oxide Schottky diode with a field limiting ring terminal structure and a gallium oxide Schottky barrier diode without a field limiting ring structure under the same conditions;

[0031] In the figure: 1- cathode metal layer; 2- highly doped N-type gallium oxide substrate; 3- low doped N-type gallium oxide epitaxial layer (i.e., conductive drift layer); 4- anode metal layer; 5- main junction; 6- field limiting ring. DETAILED DESCRIPTION

[0032] The following will clearly and completely describe the technical solutions in the embodiments of the present invention in conjunction with the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making any creative efforts shall fall within the scope of protection of the present invention.

[0033] The technical solution of the present invention will be described in detail below with reference to the accompanying drawings.

[0034] It should be noted that the following detailed descriptions are illustrative and intended to provide further explanation of the present application. Unless otherwise specified, all technical and scientific terms used herein have the same meaning as commonly understood by those skilled in the art to which the present application belongs.

[0035] In the description of this application, it should be understood that the terms "center", "up", "down", "front", "back", "left", "right", "vertical", "horizontal", "top", "bottom", "inside", "outside", etc., indicating the orientation or position relationship, are based on the orientation or position relationship shown in the accompanying drawings, and are only for the convenience of describing this application and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore cannot be understood as a limitation on this application.

[0036] As shown in the figure, the high-voltage gallium oxide Schottky diode with a field-limiting ring terminal structure includes a cathode metal layer 1, a highly doped N-type gallium oxide substrate 2, a low-doped N-type gallium oxide epitaxial layer 3, and an anode metal layer 4 stacked sequentially from bottom to top; the anode metal layer is connected to the main junction 5 at the top of the low-doped N-type gallium oxide epitaxial layer; and a plurality of field-limiting rings 6 are also provided at the top of the low-doped N-type gallium oxide epitaxial layer.

[0037] The main junction 5 is placed at the edge of the anode metal layer 4 .

[0038] The low-doped N-type gallium oxide epitaxial layer is a conductive drift layer having a plurality of P-type semiconductor ring regions that are arranged laterally and have a linearly increasing interval.

[0039] The field limiting ring is arranged on the top of the conductive drift layer.

[0040] The field limiting rings are spaced apart and arranged on the same horizontal plane at the top of the low-doped N-type gallium oxide epitaxial layer, and the distances between the field limiting rings increase linearly.

[0041] The thickness of the field limiting ring is no more than 1 μm.

[0042] The field limiting ring is a heavily doped structure, and the doping type is opposite to that of the conductive drift layer.

[0043] The impurity doping concentration in the field limiting ring is not less than 4.0×10 17 cm -3 .

[0044] The anode metal layer is made of Au, Ni, Pt and TiN; the cathode metal layer is made of Ti and Au; the thickness of the highly doped N-type gallium oxide substrate is 500-650 μm, and the doping concentration is 10 18 ~10 20 cm -3 The low-doped N-type gallium oxide epitaxial layer has a thickness of 5 to 15 μm and a doping concentration of 10 15 ~10 17 cm -3 gallium oxide materials.

[0045] A method for preparing a high-voltage gallium oxide Schottky diode with a field-limiting ring terminal structure comprises the following steps:

[0046] Step S1, epitaxially growing a low-doped N-type gallium oxide epitaxial layer on top of a highly doped N-type gallium oxide substrate using a hydride vapor phase epitaxy (HVPE) or metal organic chemical vapor deposition (MOCVD) process;

[0047] Step S2: spin-coating photoresist on the surface of the low-doped N-type gallium oxide epitaxial layer 3, forming a trench opening pattern in the terminal region using a standard photolithography process, and etching the low-doped N-type gallium oxide epitaxial layer using a reactive ion etching process to form a groove for depositing the field limiting ring;

[0048] Step S3: Soak the wafer in piranha solution for 15 minutes to remove dry etching damage. Then, soak the wafer in piranha solution for 15 minutes and then in buffered oxide etch (BOE) solution for 30 minutes to repair etching damage.

[0049] Step S4: Then, the cathode metal is evaporated by electron beam and annealed at 470° C. for 1 minute to form an ohmic contact at the bottom of the highly doped N-type gallium oxide substrate;

[0050] Step S5: spin-coating photoresist on the low-doped N-type gallium oxide epitaxial layer, and forming a field limiting ring opening pattern using a standard photolithography process;

[0051] Step S6: depositing a low-doped P-type NiO epitaxial layer and a field limiting ring structure at the groove according to the opening pattern by using a process including magnetron sputtering or electron beam evaporation;

[0052] Step S7: spin-coating photoresist on the surface of the low-doped N-type gallium oxide epitaxial layer and the field limiting ring, and forming an opening pattern of the anode metal layer using a standard photolithography process;

[0053] Step S8: depositing an anode metal layer on top of the low-doped N-type gallium oxide substrate and the P-type NiO main junction layer.

[0054] Example:

[0055] This example proposes a high voltage Schottky diode with a field limiting ring terminal structure. Figure 1 As shown; the gallium oxide Schottky barrier diode includes a cathode metal layer 1, a highly doped N-type gallium oxide substrate 2, a low-doped N-type gallium oxide epitaxial layer 3, an anode metal layer 4, a NiO main junction layer 5 and a plurality of field limiting rings 6, characterized in that the cathode metal layer 1 is deposited below the highly doped N-type gallium oxide substrate 2, forms an ohmic contact with the highly doped N-type gallium oxide substrate 2, and serves as the cathode of the gallium oxide Schottky barrier diode. The cathode metal layer 1 is made of Ti; the highly doped N-type gallium oxide substrate 2 is made of Ti with a thickness of 300~650μm and a doping concentration of 10 18 ~10 20 cm -3 The low-doped N-type gallium oxide epitaxial layer 3 is arranged on the top of the high-doped N-type gallium oxide substrate 2; the low-doped N-type gallium oxide epitaxial layer 3 has a thickness of 5 to 15 μm and a doping concentration of 10 15 ~10 17 cm -3gallium oxide materials.

[0056] The anode metal layer 4 is arranged in the middle of the top of the low-doped N-type gallium oxide epitaxial layer 3; the field limiting ring is arranged on the top of the conductive drift layer. The edge of the anode metal layer 4 is etched to form a plurality of trench terraces with a certain width and depth; the linear spacing between the trench structures in the terminal region of the low-doped N-type gallium oxide epitaxial layer 3 is 0.75-2μm, and the number of field limiting rings N is selected according to product requirements; the etching depth of the trench structure in the terminal region of the low-doped N-type gallium oxide epitaxial layer 3 is 0.5-1μm, and the etching width is 7μm; the plurality of field limiting rings 6 are filled with P-type NiO in the trenches; the P-type NiO doping concentration in the plurality of field limiting rings 6 is 4.0×10 17 cm -3 And above; the anode metal layer can be selected from metals such as Au, Ni, Pt and TiN.

[0057] Reference Figure 1 This example also proposes a method for preparing a high-voltage Schottky diode with a field-limiting ring terminal structure.

[0058] The method for manufacturing the high-voltage Schottky diode based on a field-limiting ring terminal structure proposed in this example includes the following steps:

[0059] S1: An n-Ga2O3 epitaxial layer is formed on the substrate surface using hydride vapor phase epitaxy (HVPE) or metal organic chemical vapor deposition (MOCVD) technology.

[0060] S2: Clean with piranha solution (H2SO4: H2O2= 3:1).

[0061] S3: Then, trench rings and circular trench arrays are formed by dry etching

[0062] S4: The wafer is then immediately immersed in piranha solution for 15 minutes to remove dry etching damage. After that, the wafer is sequentially immersed in piranha solution for 15 minutes and then in buffered oxide etch (BOE) solution for 30 minutes to repair etching damage.

[0063] S5: Then, the titanium / gold (Ti / Au) cathode metal is evaporated by electron beam and annealed at 470°C for 1 minute to form an ohmic contact.

[0064] S6: Spin-coating photoresist on the low-doped N-type gallium oxide epitaxial layer (3), and forming an opening pattern of the field limiting ring (6) using a standard photolithography process;

[0065] S7: After completing the above process, p-type NiO is deposited on the groove ring and the circular groove array by magnetron sputtering to fill the circular groove array and the groove ring.

[0066] S8: Spin-coating photoresist on the surface of the low-doped N-type gallium oxide epitaxial layer (3) and the field limiting ring (6), and forming an opening pattern of the anode metal layer (4) using a standard photolithography process;

[0067] S9: depositing an anode metal layer (4) on the top of the low-doped N-type gallium oxide substrate (3) and on the top of part of the P-type NiO main junction layer (5).

[0068] In step S1, the thickness of the n-Ga2O3 epitaxial layer is 10 μm, and the doping concentration is 1.5×10 16 cm -3 .

[0069] Wherein, in step S3, the etching depth is 500 nm.

[0070] The magnetron sputtering method used in step S7 is performed in an Ar / O2 (2:3) mixed environment at room temperature.

[0071] In step S7, the doping concentration of p-NiO is 4.0×10 17 cm -3 .

[0072] Figure 2 and Figure 3 The current-voltage (IV) characteristics and reverse breakdown characteristics of a high-voltage Schottky diode with a field-limiting ring termination structure are shown. Compared to a high-voltage Schottky diode without a field-limiting ring termination, the breakdown voltage of the high-voltage Schottky diode with a field-limiting ring termination structure is increased by approximately 4000V.

[0073] The working principle of this example is: the present invention expands the depletion region by combining the field-limiting ring terminal structure, reduces the peak electric field and improves the voltage resistance of the device, making the electric field distribution more uniform. Therefore, the device proposed by the present invention can optimize the electric field distribution while reducing the process production cost, thereby significantly improving the voltage resistance performance of the device.

[0074] Figure 2 The comparison of the withstand voltage relationship between the GaO Schottky barrier diode with a terminal structure and a non-terminal structure under the same conditions is given in the present invention, in which the trench depth is 1 μm, the length of the field limiting ring is 7 μm, the recess depth is 1 μm, the ring spacing of the metal ring is 0.75-2 μm, and the number of field limiting rings M=8. Figure 2As can be seen, the breakdown voltage of the gallium oxide Schottky barrier diode without a terminal structure is only 752 V. The breakdown voltage of the gallium oxide Schottky barrier diode with a trench and metal ring composite terminal structure reaches 5340 V. With other parameters unchanged, the gallium oxide Schottky barrier diode with a trench and metal ring composite terminal structure achieves a 610% improvement over the gallium oxide Schottky barrier diode without a terminal structure, significantly improving the breakdown voltage of the gallium oxide Schottky barrier diode.

[0075] The metal organic chemical vapor deposition method, magnetron sputtering method, stripping method and other operating methods in this example are all existing technologies and will not be described in detail here.

[0076] In the description of this example, a large number of specific details are described. However, it is understood that embodiments of the present invention can be practiced without these specific details. In some instances, well-known methods, structures, and techniques are not shown in detail so as not to obscure the understanding of this description.

[0077] In the description of this example, reference to terms such as "one embodiment", "some embodiments", "example", "specific example", or "some examples" means that the specific features, structures, materials or characteristics described in conjunction with the embodiment or example are included in at least one embodiment or example of the present invention.

[0078] In this example, the schematic representations of the above terms do not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials, or characteristics described can be combined in any suitable manner in any one or more embodiments or examples. In addition, those skilled in the art can combine and integrate different embodiments or examples described in this specification, as well as features of different embodiments or examples, unless they are mutually inconsistent.

[0079] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it. Although the present invention has been described in detail with reference to the above embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the above embodiments, or make equivalent replacements for some or all of the technical features therein. These modifications or replacements do not deviate the essence of the corresponding technical solutions from the scope of the technical solutions of the embodiments of the present invention, and they should all be included in the scope of the claims and description of the present invention.

Claims

1. A high-voltage gallium oxide Schottky diode with a field-limiting ring terminal structure, characterized by: The invention comprises a cathode metal layer (1), a high-doped N-type gallium oxide substrate (2), a low-doped N-type gallium oxide epitaxial layer (3), and an anode metal layer (4) stacked sequentially from bottom to top; the anode metal layer is connected to a main junction (5) at the top of the low-doped N-type gallium oxide epitaxial layer; and a plurality of field limiting rings (6) are also provided at the top of the low-doped N-type gallium oxide epitaxial layer; The main junction (5) is placed at the edge of the anode metal layer (4); The low-doped N-type gallium oxide epitaxial layer is a conductive drift layer having a plurality of P-type semiconductor ring regions arranged laterally and having a linearly increasing spacing; The field limiting ring is arranged on the top of the conductive drift layer; The field limiting rings are spaced apart and arranged on the same horizontal plane at the top of the low-doped N-type gallium oxide epitaxial layer; The thickness of the field limiting ring is not greater than 1 μm; The anode metal layer is made of Au, Ni, Pt and TiN; the cathode metal layer is made of Ti and Au; the thickness of the highly doped N-type gallium oxide substrate is 500-650 μm, and the doping concentration is 10 18 ~10 20 cm -3 The low-doped N-type gallium oxide epitaxial layer has a thickness of 5 to 15 μm and a doping concentration of 10 15 ~10 17 cm -3 gallium oxide materials.

2. The high-voltage gallium oxide Schottky diode with a field-limiting ring terminal structure according to claim 1, characterized in that: The field limiting ring is a heavily doped structure, and the doping type is opposite to that of the conductive drift layer.

3. The high-voltage gallium oxide Schottky diode with a field-limiting ring terminal structure according to claim 1, characterized in that: The impurity doping concentration in the field limiting ring is not less than 4.0×10 17 cm -3 .

4. A method for preparing a high-voltage gallium oxide Schottky diode with a field-limiting ring terminal structure, characterized in that: A high-voltage gallium oxide Schottky diode for use in a field limiting ring terminal structure according to claim 1, comprising the following steps: Step S1, epitaxially growing a low-doped N-type gallium oxide epitaxial layer on top of a highly doped N-type gallium oxide substrate using a hydride vapor phase epitaxy (HVPE) or metal organic chemical vapor deposition (MOCVD) process; Step S2: spin-coating photoresist on the surface of the low-doped N-type gallium oxide epitaxial layer 3, forming a trench opening pattern in the terminal region using a standard photolithography process, and etching the low-doped N-type gallium oxide epitaxial layer using a reactive ion etching process to form a groove for depositing the field limiting ring; Step S3: soaking the wafer in piranha solution for 15 minutes to remove dry etching damage; then, soaking the wafer in piranha solution for 15 minutes, and then soaking the wafer in buffered oxide etchant (BOE) solution for 30 minutes to repair etching damage; Step S4: Then, the cathode metal is evaporated by electron beam and annealed at 470° C. for 1 minute to form an ohmic contact at the bottom of the highly doped N-type gallium oxide substrate; Step S5: spin-coating photoresist on the low-doped N-type gallium oxide epitaxial layer, and forming a field limiting ring opening pattern using a standard photolithography process; Step S6: depositing a low-doped P-type NiO epitaxial layer and a field limiting ring structure at the groove according to the opening pattern by using a process including magnetron sputtering or electron beam evaporation; Step S7: spin-coating photoresist on the surface of the low-doped N-type gallium oxide epitaxial layer and the field limiting ring, and forming an opening pattern of the anode metal layer using a standard photolithography process; Step S8: depositing an anode metal layer on top of the low-doped N-type gallium oxide substrate and the P-type NiO main junction layer.

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