High-voltage gallium oxide Schottky diode under field limiting ring terminal structure

Abstract

The invention provides a high-voltage gallium oxide Schottky diode under a field limiting ring terminal structure. The high-voltage gallium oxide Schottky diode comprises a cathode metal layer (1), a highly-doped N-type gallium oxide substrate (2), a lowly-doped N-type gallium oxide epitaxial layer (3) and an anode metal layer (4) which are sequentially stacked from bottom to top, the anode metal layer is connected with a main junction (5) at the top of the low-doped N-type gallium oxide epitaxial layer; a plurality of field limiting rings (6) are also arranged at the top of the low-doped N-type gallium oxide epitaxial layer; according to the gallium oxide SBD device, the process steps are simplified, effective industrial production can be achieved, the electric field crowding phenomenon of the terminal area is relieved through the device design, electric field distribution is improved, and the voltage resistance and reliability of the gallium oxide SBD device are further improved. Under the structure, the breakdown voltage of the device is greatly improved, only the characteristic on-resistance is slightly improved, and finally a high PFOM value is achieved.

Description

Technical Field

[0001] The 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 semiconductor material with broad prospects. It has the advantages of wide bandgap (4.5-4.9 eV), high critical breakdown field strength (8 MV / cm), high figure of merit of Balijah power (about 3000), and low cost of Ga2O3 single crystal. Therefore, power devices based on gallium oxide materials have attracted much attention in recent years. However, conventional gallium oxide SBDs are prone to electric field concentration effect at the edge of the anode. For this defect, researchers have proposed to implant edge terminal structures into the device to alleviate the electric field concentration effect. Its terminal structures include field plate structure, grinding structure, step structure, etc. In addition, field limiting ring structure is also one of the relatively effective methods. The addition of field limiting ring can better reduce the peak electric field and expand the depletion region, further improving the voltage resistance of the device. However, due to the lack of P-type doping technology for gallium oxide materials, we can choose to use natural p-type semiconductor materials such as NiO or Cu2O as field limiting ring materials.

[0003] In order to achieve a higher power quality factor (PFOM), the gallium oxide Schottky diode should have a lower characteristic on-resistance when forward conducting and a higher breakdown voltage when reversely turned off. However, due to the low barrier height of the Schottky diode, the breakdown voltage achieved by the existing gallium oxide Schottky diode is often low. By implanting an edge terminal structure or changing the parameters such as the drift layer doping concentration and thickness, while improving the device breakdown voltage, it often causes an increase in the device on-resistance. Therefore, how to balance the two to achieve the maximum increase in PFOM performance has become the core issue of gallium oxide power diodes. Summary of the invention

[0004] The present invention proposes a high-voltage gallium oxide Schottky diode under a field-limiting ring terminal structure, which simplifies the process steps and enables effective industrial production. The device design of the present invention alleviates the electric field crowding phenomenon in the terminal area, 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 and the characteristic on-resistance is only slightly increased, 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) which are sequentially stacked 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 which are arranged laterally and whose spacing presents a linear growth trend.

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

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

[0011] The thickness of the field limiting ring is not greater 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 metals; 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 of gallium oxide material.

[0015] A method for preparing a high-voltage gallium oxide Schottky diode under a field limiting ring terminal structure comprises 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 by 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 terminal region trench opening pattern by a standard photolithography process, and etching the low-doped N-type gallium oxide epitaxial layer by a reactive ion etching process to form a groove for depositing a field limiting ring; Step S3, soaking in piranha solution for 15 minutes to remove dry etching damage. After that, the wafer is soaked in piranha solution for 15 minutes, and then soaked in buffered oxide etching BOE solution for 30 minutes to repair etching damage; Step S4: Then, the cathode metal is evaporated by electron beam, and after annealing at 470° C. for 1 minute, an ohmic contact is formed 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 the top of the low-doped N-type gallium oxide substrate and the P-type NiO main junction layer.

[0016] The solution of the present invention simplifies the process steps, so that the production method of the device can be effectively applied to industrial production, and alleviates the electric field crowding phenomenon in the terminal area, 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 and the characteristic on-resistance is only slightly increased, and finally a high PFOM value is achieved.

[0017] After the field limiting ring layer is arranged on the 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 area can be expanded, so that the breakdown voltage of the device is greatly improved, while the effect on the on-resistance is small, which only slightly increases the on-resistance and alleviates the contradictory relationship between the breakdown voltage and the characteristic on-resistance.

[0018] The present invention expands the depletion region by combining a 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. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] The present invention is further described in detail below with reference to the accompanying drawings and specific embodiments: Attached Figure 11 is a schematic cross-sectional view of the structure of a high-voltage Schottky diode under a field limiting ring terminal structure provided by an embodiment of the present invention; Attached 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 in a preferred embodiment of the present invention under the same conditions; Attached Figure 3 A schematic diagram showing a comparison of 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 in a preferred embodiment of the present invention under the same conditions; In the figure: 1- cathode metal layer; 2- highly doped N-type gallium oxide substrate; 3- low doped N-type gallium oxide epitaxial layer (ie, conductive drift layer); 4- anode metal layer; 5- main junction; 6- field limiting ring. DETAILED DESCRIPTION

[0020] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are 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 creative work are within the scope of protection of the present invention.

[0021] The technical solution of the present invention is described in detail below in conjunction with the accompanying drawings.

[0022] It should be noted that the following detailed descriptions are illustrative and are intended to provide further explanation of the present application. Unless otherwise specified, all technical and scientific terms used herein have the same meanings as those commonly understood by those skilled in the art to which the present application belongs.

[0023] In the description of the present application, it should be understood that the terms "center", "up", "down", "front", "back", "left", "right", "vertical", "horizontal", "top", "bottom", "inside", "outside", etc., indicating orientations or positional relationships, are based on the orientations or positional relationships shown in the accompanying drawings, and are only for the convenience of describing the present 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 should not be understood as a limitation on the present application.

[0024] As shown in the figure, the high-voltage gallium oxide Schottky diode under the field limiting ring terminal structure includes 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 in sequence 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.

[0025] The main junction 5 is placed at the edge of the anode metal layer 4 .

[0026] The low-doped N-type gallium oxide epitaxial layer is a conductive drift layer having a plurality of P-type semiconductor ring regions which are arranged laterally and whose spacing presents a linear growth trend.

[0027] The field limiting ring is arranged on the top of the conductive drift layer.

[0028] The field limiting rings are arranged at intervals on the same horizontal plane at the top of the low-doped N-type gallium oxide epitaxial layer, and the distances between the multiple field limiting rings increase linearly.

[0029] The thickness of the field limiting ring is not greater than 1 μm.

[0030] The field limiting ring is a heavily doped structure, and the doping type is opposite to that of the conductive drift layer.

[0031] The impurity doping concentration in the field limiting ring is not less than 4.0×10 17 cm -3 .

[0032] The anode metal layer is made of Au, Ni, Pt and TiN metals; 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 of gallium oxide material.

[0033] A method for preparing a high-voltage gallium oxide Schottky diode under a field limiting ring terminal structure comprises 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 by 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 terminal region trench opening pattern by a standard photolithography process, and etching the low-doped N-type gallium oxide epitaxial layer by a reactive ion etching process to form a groove for depositing a field limiting ring; Step S3, soaking in piranha solution for 15 minutes to remove dry etching damage. After that, the wafer is soaked in piranha solution for 15 minutes, and then soaked in buffered oxide etching BOE solution for 30 minutes to repair etching damage; Step S4: Then, the cathode metal is evaporated by electron beam, and after annealing at 470° C. for 1 minute, an ohmic contact is formed 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 the top of the low-doped N-type gallium oxide substrate and the P-type NiO main junction layer.

[0034] Example: 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 comprises 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, and 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 300-650 μm 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 -3 of gallium oxide material.

[0035] The anode metal layer 4 is arranged at the middle position of the top of the low-doped N-type gallium oxide epitaxial layer 3; the field limiting ring is arranged at the top of the conductive drift layer. The edge of the anode metal layer 4 is etched to form a plurality of groove terraces with a certain width and depth; the linear spacing between the groove 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 groove 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 groove; the P-type NiO doping concentration in the plurality of field limiting rings 6 is 4.0×10 17 cm -3And above; the anode metal layer can be selected from metals such as Au, Ni, Pt and TiN.

[0036] Reference Figure 1 This example also proposes a method for preparing a high-voltage Schottky diode under a field-limiting ring terminal structure. The manufacturing method of the high-voltage Schottky diode based on a field limiting ring terminal structure proposed in this example comprises the following steps: S1: An n-Ga2O3 epitaxial layer is formed on the surface of the growth substrate by hydride vapor phase epitaxy (HVPE) or metal organic chemical vapor deposition (MOCVD) process.

[0037] S2: Wash with piranha solution (H2SO4: H2O2= 3:1).

[0038] S3: Then, a groove ring and a circular groove array are formed by dry etching. S4: Then immediately soak in piranha solution for 15 min to remove dry etching damage. After that, the wafer is sequentially soaked in piranha solution for 15 min and then soaked in buffered oxide etch (BOE) solution for 30 min to repair etching damage.

[0039] 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.

[0040] 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; 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.

[0041] 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; 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).

[0042] 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 .

[0043] Wherein, in step S3, the etching depth is 500 nm.

[0044] The magnetron sputtering method used in step S7 is performed in a room temperature mixed environment of Ar / O2 (2:3).

[0045] In step S7, the doping concentration of p-NiO is 4.0×10 17 cm -3 . Figure 2 and Figure 3 The current-voltage (IV) characteristics and reverse breakdown characteristics of a high-voltage Schottky diode based on a field-limiting ring terminal structure are shown respectively. Compared with a high-voltage Schottky diode without a field-limiting ring terminal, the breakdown voltage of a high-voltage Schottky diode based on a field-limiting ring terminal structure increases by about 4000V.

[0046] 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.

[0047] Figure 2 The comparison of the withstand voltage relationship between the terminal structure gallium oxide Schottky barrier diode with etched groove depth of 1μm, field limiting ring length of 7μm, recess depth of 1μm, metal ring spacing of 0.75-2μm, field limiting ring number M=8 and the gallium oxide Schottky barrier diode without terminal structure under the same conditions is given. Figure 2 It can be seen that 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 composite terminal structure of trench and metal ring reaches 5340 V. When other parameters remain unchanged, the gallium oxide Schottky barrier diode with a composite terminal structure of trench and metal ring achieves a 610% improvement compared to the gallium oxide Schottky barrier diode without a terminal structure, which greatly improves the breakdown voltage of the gallium oxide Schottky barrier diode.

[0048] The metal organic chemical vapor deposition method, magnetron sputtering method, stripping method and other operation methods in this example are all existing technologies and will not be described in detail here.

[0049] In the specification 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 specification.

[0050] In the description of this example, the description with 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.

[0051] 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 one or more embodiments or examples in a suitable manner. In addition, those skilled in the art can combine and combine different embodiments or examples and features of different embodiments or examples described in this specification without contradiction.

[0052] 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 aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or replace some or all of the technical features therein by equivalents. These modifications or replacements do not make the essence of the corresponding technical solutions deviate 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 specification of the present invention.

Claims

1. A high voltage gallium oxide Schottky diode with a field limiting ring terminal structure, characterized in that: It 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) which are sequentially stacked 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.

2. The high voltage gallium oxide Schottky diode with a field limiting ring terminal structure according to claim 1, characterized in that: The main junction (5) is placed at the edge of the anode metal layer (4).

3. The high voltage gallium oxide Schottky diode with a field limiting ring terminal structure according to claim 1, characterized in that: The low-doped N-type gallium oxide epitaxial layer is a conductive drift layer having a plurality of P-type semiconductor ring regions which are arranged laterally and whose spacing presents a linear growth trend.

4. The high voltage gallium oxide Schottky diode with a field limiting ring terminal structure according to claim 3, characterized in that: The field limiting ring is arranged on the top of the conductive drift layer.

5. The high voltage gallium oxide Schottky diode with a field limiting ring terminal structure according to claim 1, characterized in that: The field limiting rings are arranged at intervals on the same horizontal plane at the top of the low-doped N-type gallium oxide epitaxial layer, and the distances between the multiple field limiting rings increase linearly.

6. The high voltage gallium oxide Schottky diode with a field limiting ring terminal structure according to claim 1, characterized in that: The thickness of the field limiting ring is not greater than 1 μm.

7. 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.

8. The high voltage gallium oxide Schottky diode with a field limiting ring terminal structure according to claim 7, characterized in that: The impurity doping concentration in the field limiting ring is not less than 4.0×10 17 cm -3 .

9. The high voltage gallium oxide Schottky diode with a field limiting ring terminal structure according to claim 7, characterized in that: The anode metal layer is made of Au, Ni, Pt and TiN metals; 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 of gallium oxide material.

10. A method for preparing a high voltage gallium oxide Schottky diode with a field limiting ring terminal structure, characterized in that: The steps include: Step S1, epitaxially growing a low-doped N-type gallium oxide epitaxial layer on top of a highly doped N-type gallium oxide substrate by 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 terminal region trench opening pattern by a standard photolithography process, and etching the low-doped N-type gallium oxide epitaxial layer by a reactive ion etching process to form a groove for depositing a field limiting ring; Step S3, soaking in piranha solution for 15 minutes to remove dry etching damage; then, soaking the wafer in piranha solution for 15 minutes, and then soaking in buffered oxide etching BOE solution for 30 minutes to repair etching damage; Step S4: Then, the cathode metal is evaporated by electron beam, and after annealing at 470° C. for 1 minute, an ohmic contact is formed 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 the top of the low-doped N-type gallium oxide substrate and the P-type NiO main junction layer.

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