Vertical GaN Schottky diode and manufacturing method thereof

Abstract

The invention discloses a vertical GaN Schottky diode and a manufacturing method thereof, and relates to the technical field of semiconductors. The diode provided by the invention comprises a cathode metal layer, an n + GaN substrate layer, an n-GaN drift layer, a p-GaN slope junction termination extension structure and an anode metal layer which are arranged in sequence from bottom to top, wherein the cathode is in ohmic contact with the contact surface, the first anode and the second anode are in ohmic contact with the contact surface, and the third anode is in Schottky contact with the contact surface. The slope drift layer is used for reducing an edge electric field, a p-GaN slope junction terminal expansion structure is introduced, a built-in electric field of a p-n junction is used for restraining reverse leakage current, electric field distribution is regulated and controlled, the electric field edge collection effect is relieved, and therefore voltage resistance is improved. Further, an ohmic anode is added to create an additional current conduction path, increasing forward current density.

Description

Technical Field

[0001] The invention relates to a vertical GaN Schottky diode and a manufacturing method thereof, belonging to the technical field of semiconductors. Background Art

[0002] As a third-generation semiconductor, gallium nitride has many unique material properties, such as a wide bandgap, high saturated electron mobility, high breakdown field strength and high thermal conductivity, which give it significant advantages in the field of semiconductor devices.

[0003] At present, GaN Schottky diodes can be divided into planar and vertical types according to their structures. Planar SBDs are heterogeneously grown, so there are different degrees of lattice mismatch and high dislocation density, making it difficult to obtain high-quality and large-sized GaN bulk single crystals. Vertical SBDs are homogeneously grown, and their advantages include low dislocation density, small size, and high wafer utilization. In recent years, with the increasing maturity of GaN growth technology, especially homogeneous epitaxial technology, major breakthroughs have been made in high-quality GaN growth, so vertical structures have more potential for high-voltage and high-current applications.

[0004] However, in the traditional vertical GaN Schottky diode, the electric field will be concentrated at the edge of the Schottky diode, resulting in excessive local electric field strength, thereby reducing the breakdown voltage of the device. In order to improve the voltage resistance performance of the device, many terminal structures have been adopted, such as planar junction terminal extension JTE, insulating layer field plate, stepped terrace, guard ring, etc. However, the GaN Schottky diode under these structures still has the problems of uneven electric field distribution and large edge effect, which affects the voltage resistance characteristics of the diode and causes the reverse leakage to increase; in addition, the forward current density of the existing structure needs to be further optimized. Summary of the invention

[0005] In order to further reduce the electric field edge effect and increase the forward current density, the present invention provides a vertical GaN Schottky diode and a manufacturing method thereof. The technical solution is as follows:

[0006] The vertical GaN Schottky diode of the present invention comprises, arranged in order from bottom to top: a cathode metal layer 1, an n+GaN substrate layer 2, an n-GaN drift layer 3, a p-GaN bevel junction terminal extension structure, and an anode metal layer;

[0007] The p-GaN bevel junction terminal extension structure includes a first p-GaN bevel junction terminal extension structure 4 and a second p-GaN bevel junction terminal extension structure 5, which are respectively arranged at both ends of the upper surface of the n-GaN drift layer 3; the anode metal layer includes: a first anode 6, a second anode 7 and a third anode 8; the first anode 6 is in ohmic contact with the first p-GaN bevel junction terminal extension structure 4, the second anode 7 is in ohmic contact with the second p-GaN bevel junction terminal extension structure 5, and the third anode 8 is in Schottky contact with the first p-GaN bevel junction terminal extension structure 4, the second p-GaN bevel junction terminal extension structure 5 and the n-GaN drift layer 3 respectively.

[0008] Optionally, the thickness of the p-GaN bevel junction terminal extension structure is 1-1000 nm.

[0009] Optionally, the angle between the p-GaN bevel junction terminal extension structure and the horizontal plane is 0°-90°.

[0010] Optionally, the doping concentration of the p-GaN bevel junction terminal extension structure is 1×10 17 -1×10 20 cm -3 .

[0011] Optionally, the material of the first anode 6 and the second anode 7 is one or a combination of titanium, aluminum, nickel and gold.

[0012] Optionally, the material of the cathode metal layer 1 is one or more combinations of titanium, aluminum, nickel and gold.

[0013] Optionally, the thickness of the n+GaN substrate layer 2 is 1-10000 um, and the doping concentration is 1×10 17 -1×10 20 cm -3 .

[0014] Optionally, the thickness of the n-GaN drift layer 3 is 1-10000 um, and the doping concentration is 1×10 15 -1×10 18 cm -3 .

[0015] Optionally, the angle between the inclined surface of the n-GaN drift layer 3 and the horizontal plane is 0°-90°.

[0016] Optionally, the thickness of the first anode 6 and the second anode 7 is 1-10 um.

[0017] The method for preparing a vertical GaN Schottky diode of the present invention is used to prepare a vertical GaN Schottky diode as described in any one of the above items, comprising the following steps:

[0018] Step 1: providing an n+GaN substrate;

[0019] Step 2: forming an n-GaN drift layer on the n+GaN substrate;

[0020] Step 3: etching the n-GaN drift layer to form a slope structure;

[0021] Step 4: growing a p-GaN layer on the bevel structure, and etching to form a p-GaN bevel terminal extension structure;

[0022] Step 5: depositing materials on the above structure to form a first anode, a second anode and a third anode respectively; the first anode and the second anode are in ohmic contact with the p-GaN bevel terminal extension structure, and the third anode is in Schottky contact with the p-GaN bevel terminal extension structure and the n-GaN drift layer respectively;

[0023] Step 6: depositing materials under the n+GaN substrate to form a cathode, which is in ohmic contact with the contact surface.

[0024] The beneficial effects of the present invention are:

[0025] The present invention uses a bevel junction terminal extension structure to effectively improve the electric field distribution and alleviate the electric field edge effect of the vertical GaN Schottky diode, thereby increasing the breakdown voltage of the device; at the same time, an ohmic anode is introduced. Under a higher forward bias, due to the conduction of the pn junction, the JTE structure helps the conduction of the forward current and reduces the on-resistance, thereby increasing the forward current density of the device. Compared with the prior art, the reverse withstand voltage of the present invention can reach 1.2kV, which is 400V higher than the prior art level (800V), and the forward current density can reach 10 -1 -10 -2 A level, compared with the existing technology level (10 -3 -10 -4 A level) has been significantly improved. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] In order to more clearly illustrate the technical solutions in the embodiments of the present invention, the following briefly introduces the drawings required for use in the description of the embodiments. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without creative work.

[0027] Figure 1 This is a structural diagram of a vertical GaN Schottky diode device provided in Example 1 of the present invention.

[0028] Figure 2This is a reverse IV logarithmic coordinate curve of the vertical GaN Schottky diode device provided in the first embodiment of the present invention.

[0029] Figure 3 This is a forward IV characteristic curve of the vertical GaN Schottky diode device provided in the first embodiment of the present invention.

[0030] Figure 4 This is a comparison diagram of the electric field distribution of the vertical GaN Schottky diode device provided in the first embodiment of the present invention and the traditional vertical GaN Schottky diode device under a bias voltage of -500V. DETAILED DESCRIPTION

[0031] In order to make the objectives, technical solutions and advantages of the present invention more clear, the embodiments of the present invention will be further described in detail below with reference to the accompanying drawings.

[0032] Embodiment 1:

[0033] The present embodiment provides a vertical GaN Schottky diode, comprising, arranged in order from bottom to top: a cathode metal layer 1, an n+GaN substrate layer 2, an n-GaN drift layer 3, a p-GaN bevel junction terminal extension structure, and an anode metal layer.

[0034] The p-GaN bevel junction terminal extension structure includes a first p-GaN bevel junction terminal extension structure 4 and a second p-GaN bevel junction terminal extension structure 5, which are respectively arranged at both ends of the upper surface of the n-GaN drift layer 3; the anode metal layer includes: a first anode 6, a second anode 7 and a third anode 8; the first anode 6 is in ohmic contact with the first p-GaN bevel junction terminal extension structure 4, the second anode 7 is in ohmic contact with the second p-GaN bevel junction terminal extension structure 5, and the third anode 8 is in Schottky contact with the first p-GaN bevel junction terminal extension structure 4, the second p-GaN bevel junction terminal extension structure 5, and the n-GaN drift layer 3 respectively.

[0035] In this embodiment, the thickness of the n+GaN substrate layer 2 is 1 um, and the doping concentration is 1×10 18 cm -3 .

[0036] The n-GaN drift layer 3 is located on the upper surface of the n+GaN substrate 2, with a thickness of 5 μm and a doping concentration of 1×10 16 cm -3 , and the angle between the inclined surface of the n-GaN drift layer and the horizontal plane is 60°.

[0037] The thickness of the first p-GaN bevel junction terminal extension structure 4 and the second p-GaN bevel junction terminal extension structure 5 is 100 nm, and the doping concentration is 1×10 18 cm -3, and the angle between the p-GaN bevel junction terminal extension structure and the horizontal plane is 60°.

[0038] The third anode 8 is located on one side of the surface of the n-GaN drift layer 3, and the contact between the two is Schottky contact. The length of the overlapping part of the third anode 8 and the first p-GaN bevel junction terminal extension structure 4 and the second p-GaN bevel junction terminal extension structure 5 is set to 1um.

[0039] The first anode 6 and the second anode 7 are respectively located above the surface of the first p-GaN bevel junction terminal extension structure 4 and the second p-GaN bevel junction terminal extension structure 5 , and the contact mode is ohmic contact.

[0040] The cathode metal layer 1 is located at the bottom of the n+GaN substrate 2, and the two are connected through an ohmic contact.

[0041] The IV logarithmic coordinate curve of the vertical GaN Schottky diode device of this embodiment is as follows: Figure 2 As shown in the figure, it can be seen that the turn-on voltage of the device is about 0.6V and the reverse leakage is about 10 -8 Magnitude.

[0042] The forward IV characteristic curve of the vertical GaN Schottky diode device of this embodiment is shown in FIG. Figure 3 As shown in the figure, it can be seen that the current density has an inflection point at about 5V, and the current density increases significantly. The principle is that under a relatively small forward bias, the pn junction is not turned on, and the depletion region between the p-GaN and n-GaN drift layers will reduce the conduction of the current under the p-GaN; when the forward bias is high, the pn junction is turned on, and the forward current contributed by the pn junction helps to enhance current conduction. At the same time, the hole injection in the pn junction area can effectively reduce the on-resistance.

[0043] The comparison of the electric field distribution of the vertical GaN Schottky diode device of this embodiment and the traditional vertical GaN Schottky diode device under -500V bias is shown in the figure below. Figure 4 As shown in the figure, it can be seen that for the traditional vertical GaN Schottky diode, there is an obvious electric field edge collection effect at the anode edge, while the vertical GaN Schottky diode of this embodiment has two electric field peaks moving toward the p-GaN edge due to the effect of the bevel junction terminal extension structure, and the maximum electric field value is also significantly reduced.

[0044] Embodiment 2

[0045] This embodiment provides a method for preparing a vertical GaN Schottky diode, comprising the following steps:

[0046] Step 1: Provide an n+GaN substrate and clean it.

[0047] Step 2: epitaxially grow an n-GaN drift layer on the n+GaN substrate.

[0048] Step 3: dry-etching the n-GaN drift layer to form a slope structure.

[0049] Clean the epitaxial wafer: (1) use acetone ultrasound for 2 minutes; (2) stripping solution in a 60°C constant temperature water bath for 5 minutes; (3) use acetone ultrasound for 2 minutes; (4) use ethanol ultrasound for 2 minutes; (5) rinse with ultrapure water for 2 minutes, N 2 Blow dry.

[0050] The cleaned wafer is baked (hot plate 100°C, 2 minutes), then spin-coated with photoresist, and one side of the wafer is exposed obliquely using a mask, and then the other side of the wafer is exposed obliquely through other mask alignment marks. After exposure, it is post-baked (hot plate 100°C, 2 minutes), developed to obtain a photoresist with a sloped sidewall, and finally hardened.

[0051] Use an ICP etcher to etch to a set depth, place the etched sample in an acetone solution, remove the remaining unetched photoresist, and finally obtain the side wall bevel angle of the etched material to form a bevel structure.

[0052] Step 4: growing a p-GaN layer on the n-GaN drift layer, and etching using a UV lithography machine and an ICP etcher to form a p-GaN bevel terminal extension structure;

[0053] Step 5: Deposit materials on the above structure to form a first anode, a second anode and a third anode respectively; prepare the Schottky anode structure (third anode 8) by thermal evaporation technology or reactive magnetron sputtering technology, and deposit Ti / Al / Ni / Au on the first anode 6 and the second anode 7 by electron beam evaporation. 2 Annealing at 500°C in an ambient environment forms an ohmic contact with p-GaN.

[0054] Step 6: Deposit Ti / Al / Ni / Au below the n+GaN substrate by electron beam evaporation. 2 The cathode metal layer is formed by annealing at 850°C in an ambient environment.

[0055] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principle of the present invention should be included in the protection scope of the present invention.

Claims

1. A vertical GaN Schottky diode, characterized in that: It comprises, arranged in order from bottom to top: a cathode metal layer (1), an n+GaN substrate layer (2), an n-GaN drift layer (3), a p-GaN bevel junction terminal extension structure, and an anode metal layer; The p-GaN bevel junction terminal extension structure comprises a first p-GaN bevel junction terminal extension structure (4) and a second p-GaN bevel junction terminal extension structure (5), which are respectively arranged at two ends of the upper surface of the n-GaN drift layer (3); the anode metal layer comprises: a first anode (6), a second anode (7) and a third anode (8); the first anode (6) is in ohmic contact with the first p-GaN bevel junction terminal extension structure (4), the second anode (7) is in ohmic contact with the second p-GaN bevel junction terminal extension structure (5), and the third anode (8) is in Schottky contact with the first p-GaN bevel junction terminal extension structure (4), the second p-GaN bevel junction terminal extension structure (5) and the n-GaN drift layer (3), respectively.

2. The vertical GaN Schottky diode according to claim 1, characterized in that: The thickness of the p-GaN bevel junction terminal extension structure is 1-1000nm.

3. The vertical GaN Schottky diode according to claim 1, characterized in that: The angle between the p-GaN bevel junction terminal extension structure and the horizontal plane is 0°-90°.

4. The vertical GaN Schottky diode according to claim 1, characterized in that: The doping concentration of the p-GaN bevel junction terminal extension structure is 1×10 17 -1×10 20 cm -3 .

5. The vertical GaN Schottky diode according to claim 1, characterized in that: The material of the first anode (6) and the second anode (7) is one or a combination of titanium, aluminum, nickel and gold.

6. The vertical GaN Schottky diode according to claim 1, characterized in that: The material of the cathode metal layer (1) is one or a combination of titanium, aluminum, nickel and gold.

7. The vertical GaN Schottky diode according to claim 1, characterized in that: The thickness of the n+GaN substrate layer (2) is 1-10000 um, and the doping concentration is 1×10 17 -1×10 20 cm -3 .

8. The vertical GaN Schottky diode according to claim 1, characterized in that: The thickness of the n-GaN drift layer (3) is 1-10000 um, and the doping concentration is 1×10 15 -1×10 18 cm -3 .

9. The vertical GaN Schottky diode according to claim 1, characterized in that: The thickness of the first anode (6) and the second anode (7) is 1-10 um.

10. A method for preparing a vertical GaN Schottky diode, characterized in that: The method is used to prepare the vertical GaN Schottky diode according to any one of claims 1 to 9, comprising the following steps: Step 1: providing an n+GaN substrate; Step 2: forming an n-GaN drift layer on the n+GaN substrate; Step 3: etching the n-GaN drift layer to form a slope structure; Step 4: growing a p-GaN layer on the bevel structure, and etching to form a p-GaN bevel terminal extension structure; Step 5: depositing materials on the above structure to form a first anode, a second anode and a third anode respectively; the first anode and the second anode are in ohmic contact with the p-GaN bevel terminal extension structure, and the third anode is in Schottky contact with the p-GaN bevel terminal extension structure and the n-GaN drift layer respectively; Step 6: depositing materials under the n+GaN substrate to form a cathode, which is in ohmic contact with the contact surface.

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