JBS power diode based on self-assembled ni nano-islands and method of manufacturing the same

Abstract

The application provides a JBS power diode based on self-assembled Ni nano-islands and a preparation method thereof. The structure of the diode comprises, from bottom to top, a cathode, an N+ substrate, a JBS structure and an anode, the JBS structure comprises an N-drift layer, a PN heterojunction and Ni nano-islands, wherein the N-drift layer is provided with a groove structure, a P-type metal oxide on the inner side and the bottom of the groove forms a PN heterojunction with the N-drift layer; the Ni nano-islands are located on the top of the groove and form a Schottky contact with the N-drift layer; the PN heterojunction is connected in parallel with the Schottky contact. The self-assembled nano-islands formed by the Ni film under rapid thermal annealing are used to replace photoresist as a mask, so that the photoetching step is omitted, the preparation process is greatly simplified, the preparation period is shortened, and the cost is saved.

Description

Technical Field

[0001] This invention relates to the field of ultra-wide bandgap semiconductor power devices, specifically to a novel JBS power diode based on self-assembled Ni nanoislands and its fabrication method. Background Technology

[0002] Ultra-wide bandgap semiconductors, represented by materials such as diamond, Ga2O3, and AlN, exhibit bandgap widths far exceeding those of traditional wide bandgap semiconductors (GaN, SiC, etc.), and have broad application prospects in power devices, radio frequency devices, and other fields. Ga2O3, as an ultra-wide bandgap semiconductor, possesses a large bandgap (4.5-4.9 eV) and high breakdown field strength (8 MV / cm); its Baliga figure of merit is higher than 3000, approximately 5 to 10 times that of GaN and SiC; and it readily breaks down to 10... 16 cm -3 Up to 10 19 cm -3 The concentration range is controlled for n-type doping. Ga2O3 has five phases: α, β, γ, ε, and κ. Among them, β-Ga2O3 has the best thermal stability and is easy to prepare high-quality single crystals through melt growth. Therefore, most current research on Ga2O3 power devices is based on β-Ga2O3.

[0003] However, Ga2O3 research still faces many technical challenges. Currently, achieving stable P-type doping in Ga2O3 is difficult, so related research mainly focuses on unipolar devices such as Schottky diodes (SBDs). Although SBDs have advantages over PN junctions in terms of high switching speed and low forward voltage drop, their reverse breakdown voltage is relatively low, and their reverse leakage current is significant. In contrast, the junction-barrier Schottky diode (JBS) structure combines the advantages of low forward conduction loss of SBDs with the high reverse breakdown voltage and low off-state loss of PN junctions.

[0004] The current common implementation scheme for JBS structures is as follows: a pattern is formed on the substrate surface by photolithography; trenches are formed on the substrate using photoresist as a mask; P-type material is grown in the trenches; after removing the photoresist, metal is deposited by evaporation, forming a Schottky contact with the substrate. Under reverse bias, the P-type material forms a lateral PN junction with the N-type substrate, interrupting the current in the middle section, thereby shielding the lower barrier Schottky junction and obtaining better reverse characteristics than traditional SBDs. Alternatively, substrate etching can be omitted during fabrication; the P-type material can be grown directly using photoresist as a mask, and the metal is deposited after the photoresist is stripped.

[0005] JBS structures have been realized in Ga2O3 (e.g., Q. Yan, H. Gong, J. Zhang et al., Appl. Phys. Lett. 118, 122102 (2021), 2021). However, substrate etching and material growth inevitably require a mask to cover a portion of the area to form the JBS structure. Hard masks cannot achieve patterns of a few micrometers in size, thus requiring photolithography using photoresist as a mask. This makes the fabrication process relatively complex, requiring the design of photolithographic patterns and the execution of photolithography at a few micrometers in size. The technique of using self-assembled nanoislands as masks is currently mainly used for etching GaN or Ga2O3 nanopillars, but there has been no research on applying this technique to the fabrication of JBS. Summary of the Invention

[0006] To address the shortcomings of existing JBS structure fabrication methods, this invention utilizes the characteristic that Ni thin films can form nanoscale Ni particles under rapid thermal annealing. By using self-assembled Ni nano islands instead of photoresist as a mask, the JBS power diode structure can be fabricated, eliminating the need for photolithography.

[0007] The technical solution adopted in this invention is as follows:

[0008] The JBS power diode based on self-assembled Ni nanoislands includes a cathode, an N+ substrate, a JBS structure, and an anode arranged sequentially from bottom to top. The JBS structure includes an N-drift layer, a PN heterojunction, and Ni nanoislands. The N-drift layer has a trench structure, and the P-type metal oxide located on the inner side and bottom of the trench forms a PN heterojunction with the N-drift layer. The Ni nanoislands are located at the top of the trench and form a Schottky contact with the N-drift layer. The PN heterojunction is connected in parallel with the Schottky contact.

[0009] Furthermore, both the N+ substrate and the N- drift layer are made of β-Ga2O3 crystal.

[0010] Furthermore, the Ni nanoislands have a diameter of 100-500 nm and a spacing in the hundreds of nanometers.

[0011] Furthermore, the thickness of the P-type metal oxide is 100-300 nm, and the depth of the trench structure on the N-drift layer is 100-300 nm.

[0012] This invention provides a method for fabricating a JBS power diode based on self-assembled Ni nanoislands. The method comprises the following steps: depositing a Ni thin film on a substrate surface, followed by rapid thermal annealing; using the self-assembled Ni nanoislands formed by the rapid thermal annealing as a metal mask; etching an N-drift layer to form a trench structure; growing a P-type metal oxide in the trench structure; the metal oxide located on the inner side and bottom of the trench forming a lateral PN heterojunction with the N-drift layer; and the lateral PN heterojunction being connected in parallel with the Schottky contact formed by the Ni nanoislands at the top of the trench, thereby forming a JBS structure.

[0013] Further, the specific steps of the above method are as follows: (1) A Ni thin film with a thickness of 5-15 nm is deposited on the substrate surface using electron beam evaporation technology; (2) The sample deposited in step (1) is subjected to rapid thermal annealing at 850°C for 1-5 min to form self-assembled Ni nano islands; (3) Using the Ni nano islands as a mask, the N-drift layer is etched using ICP process to form a trench structure; (4) Ti and Au are deposited on the back side of the substrate using electron beam evaporation; (5) The sample deposited in step (4) is subjected to rapid thermal annealing to form a back side titanium-gold ohmic contact; (6) The sample surface is covered with a hard mask, and a hundred-nanometer-scale P-type metal oxide is grown on the trench structure using magnetron sputtering; (7) Ni and Au are deposited on the sample surface using electron beam evaporation to prepare a front side nickel-gold electrode.

[0014] Compared with existing methods for fabricating JBS structures using photoresist masks, the advantages of this invention are:

[0015] (1) The self-assembled nano-islands formed by Ni thin film under rapid thermal annealing are used to replace photoresist as a mask, eliminating the photolithography step, greatly simplifying the preparation process, shortening the preparation cycle and saving costs.

[0016] (2) The device prepared by the method of the present invention has better reverse characteristics, similar to a heterojunction; and exhibits double barrier characteristics in the forward direction. Attached Figure Description

[0017] Figure 1 This is a schematic diagram of the structure of the JBS power diode prepared in an embodiment of the present invention.

[0018] Figure 2 This is a morphology image of Ni self-assembled nanoislands under a scanning electron microscope in an embodiment of the present invention.

[0019] Figure 3 The diagram shows the current-voltage characteristics of the diode prepared in the embodiments of the present invention in linear and logarithmic coordinates.

[0020] Figure 4This is a diagram showing the reverse breakdown characteristics of the diode prepared in an embodiment of the present invention. Detailed Implementation

[0021] To make the objectives, technical solutions, and advantages of the present invention clearer, the embodiments of the present invention will be further described in detail 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. The described embodiments are for illustrative purposes only and are not intended to limit the scope of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the protection scope of the present invention.

[0022] The substrate used in this embodiment is a β-Ga2O3 HVPE epitaxial wafer. The substrate information is as follows: the thickness of the N+ heavily doped layer is 650 μm, and the doping concentration is 6 × 10⁻⁶. 18 cm -3 The surface drift layer is 10 μm thick, and the doping concentration is approximately 2 × 10⁻⁶. 16 cm -3 The substrate size is 5mm × 5mm. The fabrication method is as follows: First, a Ni thin film is deposited on the substrate surface, followed by rapid thermal annealing. The self-assembled Ni nano-islands formed under rapid thermal annealing are used as a metal mask to etch the β-Ga2O3 drift layer to form a trench structure. Then, P-type NiO (or other P-type metal oxides, such as Ir2O3, Cu2O, etc.) is grown in the trench structure. The NiO on the inner side and bottom of the trench forms a lateral PN heterojunction with Ga2O3. The NiO-Ga2O3 lateral PN heterojunction is connected in parallel with the Schottky contact formed by the Ni nano-islands at the top of the trench, thus forming a JBS power diode structure. The specific structure is as follows: Figure 1 As shown.

[0023] The specific fabrication process of the JBS power diode in this embodiment is as follows:

[0024] (1) A 10 nm Ni thin film was deposited on the substrate surface using electron beam evaporation technology.

[0025] (2) The sample from step (1) was subjected to rapid thermal annealing at 850℃ for 3 min to form a self-assembled Ni island structure in the Ni film. The morphology of the self-assembled Ni nanoislands formed after annealing under a scanning electron microscope is shown in the attached figure. Figure 2 As shown in the figure, this figure demonstrates that after high-temperature annealing, Ni thin films can form nano-island structures with diameters on the order of hundreds of nanometers, and their distribution is relatively uniform, illustrating the feasibility of this invention.

[0026] (3) Using the Ni island structure as a mask, the drift layer is etched with BCl3 to form a trench structure. The etching depth depends on the size of the Ni nanoislands and the etching gas used, and is approximately several hundred nanometers, to avoid the physical bombardment during etching having a significant impact on the Ni nanoisland mask. In this embodiment, the etching depth is 200 nm.

[0027] (4) Using electron beam evaporation technology, 500 nm of Ti and 500 nm of Au are deposited on the back side of the substrate.

[0028] (5) Perform rapid thermal annealing at 500°C for 1 min on the sample from step (4) to form a titanium ohmic contact on the back side of the sample.

[0029] (6) Cover the sample surface with a hard mask with a pattern of circles with a diameter of 200 μm, and grow 100 nm of P-type NiO on the sample surface using magnetron sputtering technology.

[0030] (7) A front-side nickel-gold electrode is prepared by depositing 20 nm of Ni and 90 nm of Au on the substrate surface using electron beam evaporation.

[0031] Figure 3 The current-voltage characteristics of the JBS power diode are shown in linear and logarithmic coordinates, revealing a turn-on voltage of 2.26V and exhibiting a double-barrier characteristic. The device achieves a current-on-displacement ratio as high as 2 × 10⁻⁶ at ±3V. 11 The on-resistance is 6.2 mΩ·cm 2 .

[0032] Figure 4 The reverse breakdown characteristics of the JBS power diode show a reverse breakdown voltage of 992V, from which the power factor (P-FOM) is calculated to be 160MW / cm². 2 .

Claims

1. A method for fabricating a JBS power diode based on self-assembled Ni nanoislands, characterized in that, The method involves the following steps: depositing a Ni thin film on the substrate surface, followed by rapid thermal annealing; using the self-assembled Ni nano-islands formed by the Ni thin film under rapid thermal annealing as a metal mask; etching the N-drift layer to form a trench structure; growing a P-type metal oxide in the trench structure; the metal oxide located on the inner side and bottom of the trench forming a lateral PN heterojunction with the N-drift layer; and connecting the lateral PN heterojunction in parallel with the Schottky contact formed by the Ni nano-islands at the top of the trench, thereby forming a JBS structure.

2. The preparation method according to claim 1, characterized in that, The specific steps of this method are as follows: (1) A Ni thin film is deposited on the substrate surface using electron beam evaporation technology; (2) Perform rapid thermal annealing on the sample deposited in step (1) to form self-assembled Ni nano islands in the Ni film; (3) Using the Ni nano islands as a mask, the N-drift layer is etched using ICP process to form a trench structure; (4) Electron beam evaporation is used to deposit Ti and Au on the back side of the substrate; (5) Perform rapid thermal annealing on the sample deposited in step (4) to form a titanium ohmic contact on the back side of the sample. (6) Cover the sample surface with a hard mask and grow a 100-nanometer-scale P-type metal oxide on the trench structure using magnetron sputtering; (7) Ni and Au are deposited on the sample surface by electron beam evaporation to prepare the front nickel-gold electrode.

3. The preparation method according to claim 2, characterized in that, In step (1), the thickness of the Ni film is 5-15 nm.

4. The preparation method according to claim 2, characterized in that, In step (2), the rapid thermal annealing time is 1-5 min and the annealing temperature is 850℃.

5. The preparation method according to claim 2, characterized in that, In step (2), the diameter of the Ni nanoislands is 100-500 nm, and the spacing between them is in the hundreds of nanometers.

6. The preparation method according to claim 2, characterized in that, In step (6), the thickness of the P-type metal oxide is 100-300 nm.

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