A deep ultraviolet LED flip chip and a preparation method thereof

Abstract

The present invention relates to a deep ultraviolet LED flip chip and a preparation method thereof. The deep ultraviolet LED flip chip includes an LED epitaxial wafer, an n-ohmic contact electrode (8) and a p-ohmic contact electrode (9) disposed on the LED epitaxial wafer. The p-ohmic contact electrode (9) presents a wavy shape with multiple branches being parallel and evenly distributed. The n-ohmic contact electrode (8) correspondingly surrounds the p-ohmic contact electrode (9), and the area difference between the p-ohmic contact electrode (9) and the n-ohmic contact electrode (8) is within 10%. On the one hand, it greatly enhances the lateral current expansion ability, reduces the phenomenon of current concentration and congestion in the flip structure, and greatly reduces the working voltage of the chip. On the other hand, it enhances the optical power. On the third hand, it is a chip with low voltage and high optical power, having high thermal stability and correspondingly improved lifespan.

Description

Technical Field

[0001] The present invention belongs to the technical field of semiconductor chip preparation, and relates to an LED (light-emitting diode) chip and a preparation method thereof, and particularly relates to a deep ultraviolet LED flip chip and a preparation method thereof. Background Art

[0002] In recent years, with the progress of the global LED industry technology, the LED emission band has been extended from the visible light band to the ultraviolet and deep ultraviolet bands. Deep ultraviolet LEDs have functions such as photocatalysis, medical light therapy, health care and air purification, and sterilization.

[0003] At present, after more than 10 years of research and development, the external quantum efficiency of deep ultraviolet LEDs below 280 nm has exceeded 10%, the corresponding luminous power is greater than 5 mW, and the service life reaches 5000 h. However, compared with the external quantum efficiency of nearly 60% of blue LEDs made of InGaN materials, there is still a big gap.

[0004] Currently, the electrodes of deep ultraviolet LED chips are usually made using a flip-chip structure. Due to the strong absorption of deep ultraviolet light by P-type GaN in the flip-chip structure, and at the same time, during the process of light transmitting from the back, due to the light absorption phenomenon between the internal contact layer material and the epitaxial layer structure in the deep ultraviolet LED epitaxial wafer, the luminous efficiency is low and the brightness is relatively low. Moreover, the n electrode and the p electrode are located on the same side of the epitaxial wafer, and the current congestion phenomenon still exists, which will lead to poor heat dissipation, low life, and low external quantum efficiency of the chip, resulting in most of the electrical energy being converted into heat.

[0005] For deep ultraviolet LED flip chips, in order to improve the optical power of the chip device, the usual method is to reduce the area of the n electrode and increase the area of the p electrode in the chip structure design to maximize the area of the active region, and finally achieve the purpose of improving the optical power of the chip device. However, such a structure causes the area of the n electrode to continuously decrease or even reach the limit in order to match the increased area of the p electrode, resulting in a large difference between the p / n electrode areas, often leading to concentrated current congestion and poor current spreading ability, and the voltage of the chip is relatively high. At the same time, in order to reduce the voltage, usually a layer of silicon oxide insulating medium is deposited under the n electrode as a current blocking layer. Although this can reduce the current ratio under the n electrode and increase the current diffusivity to a certain extent, adding the current blocking layer also limits the formation of the preparation process, increases the chip manufacturing process, and increases the production cost.

[0006] Therefore, it is necessary to provide an improved deep ultraviolet LED chip structure and a preparation method thereof to overcome the above problems. Summary of the Invention

[0007] To overcome the defects of the prior art, the present invention proposes a deep ultraviolet LED flip chip and a preparation method thereof, which can improve the optical power and reduce the voltage.

[0008] To achieve the above object, the present invention provides the following technical solutions:

[0009] A deep ultraviolet LED flip chip includes an LED epitaxial wafer and an n-ohmic contact electrode and a p-ohmic contact electrode disposed on the LED epitaxial wafer. It is characterized in that the p-ohmic contact electrode presents a plurality of parallel and uniformly distributed wavy shapes, the n-ohmic contact electrode surrounds the p-ohmic contact electrode accordingly, and the area difference between the area of the p-ohmic contact electrode and the area of the n-ohmic contact electrode is within 10%.

[0010] Preferably, each wavy-shaped p-ohmic contact electrode includes a plurality of discs and a cuboid connecting the discs.

[0011] Preferably, the n-ohmic contact electrode is made of a Ti / Al / Ti / Au film system and the thickness of the Ti / Al / Ti / Au film system is 20 / 60 / 50 / 20 nm.

[0012] Preferably, the p-ohmic contact electrode is made of a Ni / Au / Ti film system and the thickness of the Ni / Au / Ti film system is 10 / 200 / 20 nm.

[0013] Preferably, a current spreading electrode is fabricated on the n-ohmic contact electrode and the p-ohmic contact electrode, and the current spreading electrode is made of a Cr / Al / Ti / Au / Ti film system and the thickness of the Cr / Al / Ti / Au / Ti film system is 20 / 200 / 10 / 500 / 5 nm.

[0014] Preferably, a pad electrode is fabricated on the current spreading electrode.

[0015] Preferably, the LED epitaxial wafer includes a substrate and an aluminum nitride template layer, a superlattice stress buffer layer, an n-type AlGaN layer, a multi-quantum well structure layer, an electron blocking layer, and a P-type GaN hole conduction layer formed in sequence on the substrate, and the n-ohmic contact electrode is disposed on the n-type AlGaN layer, and the p-ohmic contact electrode is disposed on the P-type GaN hole conduction layer.

[0016] In addition, the present invention also provides a preparation method of a deep ultraviolet LED flip chip, which is characterized by including the following steps:

[0017] 1), growing an aluminum nitride template layer, a superlattice stress buffer layer, an n-type AlGaN layer, a multi-quantum well structure layer, an electron blocking layer, and a P-type GaN hole conduction layer in sequence on a substrate to obtain an LED epitaxial wafer;

[0018] 2), Etch part of the LED epitaxial wafer downward until the n-type AlGaN layer is reached to form an n-electrode mesa, and the unetched part forms a P-electrode mesa;

[0019] 3), Fabricate an n-ohmic contact electrode on the surface of the n-electrode mesa by photolithography and evaporation;

[0020] 4), Fabricate a p-ohmic contact electrode on the surface of the P-electrode mesa by photolithography and evaporation; wherein, the p-ohmic contact electrode presents a wavy shape with multiple parallel and evenly distributed branches, the n-ohmic contact electrode surrounds the p-ohmic contact electrode accordingly, and the area difference between the p-ohmic contact electrode and the n-ohmic contact electrode is within 10%;

[0021] 5), Fabricate a current spreading electrode on the n-ohmic contact electrode and the p-ohmic contact electrode by photolithography and evaporation processes;

[0022] 6), Fabricate a passivation layer by deposition, photolithography, and etching processes;

[0023] 7), Form a through hole opposite to the current spreading electrode on the passivation layer and evaporate a pad electrode connected to the current spreading electrode in the through hole.

[0024] Preferably, after obtaining the n-ohmic contact electrode, anneal the n-ohmic contact electrode in an N2 atmosphere, wherein the annealing temperature is 900 °C and the annealing time is 30 s.

[0025] Preferably, after obtaining the p-ohmic contact electrode, anneal the p-ohmic contact electrode in an N2 or air atmosphere, wherein the annealing temperature is 550 °C and the annealing time is 180 s.

[0026] Compared with the prior art, the deep ultraviolet LED flip chip and its manufacturing method of the present invention have one or more of the following beneficial technical effects:

[0027] 1. Its p-ohmic contact electrode adopts a wavy shape with multiple parallel and evenly distributed branches. Due to the lateral propagation of deep ultraviolet light and the independent multi-branch and uniform current conduction of this special structure of the P-ohmic contact electrode, the current injection efficiency is improved, thereby enhancing the optical power. At the same time, the multi-branch wavy uniform arrangement of the p-ohmic contact electrode increases its sidewall perimeter, thus enhancing the optical power of the chip sidewall;

[0028] 2. Its n-ohmic contact electrodes surround the p-ohmic contact electrodes correspondingly, and the area difference between the n-ohmic contact electrodes and the p-ohmic contact electrodes is within 10%. For such n-ohmic contact electrodes with a special structure, due to the comparable ohmic contact areas of the n / p-ohmic contact electrodes, the lateral current expansion ability is greatly enhanced, the phenomenon of current concentration and congestion in the flip-chip structure is reduced, and the operating voltage of the chip is significantly lowered.

[0029] 3. It belongs to a chip device with low voltage and high optical power, thereby improving the thermal stability and correspondingly increasing the lifespan.

[0030] 4. The processes involved in the present invention are all conventional processes and are easy to implement. Description of the Drawings

[0031] Figure 1 It is a schematic structural diagram of the LED epitaxial wafer of the deep ultraviolet LED flip-chip of the present invention.

[0032] Figure 2 It is a schematic plan view of the n-ohmic contact electrodes of the deep ultraviolet LED flip-chip of the present invention.

[0033] Figure 3 It is a schematic plan view of the p-ohmic contact electrodes of the deep ultraviolet LED flip-chip of the present invention.

[0034] Figure 4 It is a schematic plan view of the cooperation between the n-ohmic contact electrodes and the p-ohmic contact electrodes of the deep ultraviolet LED flip-chip of the present invention.

[0035] Figure 5 It is a schematic plan view of the cooperation between the n-ohmic contact electrodes and the p-ohmic contact electrodes of the deep ultraviolet LED flip-chip of the prior art.

[0036] Figure 6 It is a flowchart of the preparation method of the deep ultraviolet LED flip-chip of the present invention. Detailed Embodiments

[0037] The present invention will be further described below in conjunction with the drawings and embodiments. The content of the embodiments shall not be construed as a limitation to the protection scope of the present invention.

[0038] Aiming at the problems of high operating voltage and low external quantum efficiency existing in current deep ultraviolet LED flip chips, the present invention adopts a new chip structure design. Among them, the p ohmic contact electrode adopts a wavy shape with multiple branches parallel and evenly distributed. At the same time, the n ohmic contact electrode surrounds the p ohmic contact electrode correspondingly, and the area difference between the area of the p ohmic contact electrode and the area of the n ohmic contact electrode is within 10%. Such a structure design, on the one hand, due to the equivalent ohmic contact area of the n / p ohmic contact electrodes, greatly enhances the lateral current expansion ability, reduces the phenomenon of current concentration and congestion in the flip structure, and greatly reduces the operating voltage of the chip; on the other hand, due to the lateral propagation of deep ultraviolet light and the uniform current conduction of multiple branches, the current injection efficiency is improved, and thus the optical power is enhanced. At the same time, the uniform arrangement of the wavy shape of multiple branches of the P ohmic contact electrode increases the sidewall perimeter, thereby enhancing the sidewall optical power of the chip; on the third hand, it belongs to a chip device with low voltage and high optical power, the thermal stability is improved, and the lifespan is correspondingly extended.

[0039] Similar to the prior art, the deep ultraviolet LED flip chip of the present invention also includes an LED epitaxial wafer and an n ohmic contact electrode 8 and a p ohmic contact electrode 9 disposed on the LED epitaxial wafer.

[0040] Among them, as Figure 1 shown, the LED epitaxial wafer is similar to the existing LED epitaxial wafer, and includes a substrate 1 and an aluminum nitride template layer 2, a superlattice stress buffer layer 3, an n-type AlGaN layer 4, a multi-quantum well structure layer 5, an electron blocking layer 6, and a P-type GaN hole conduction layer 7 formed in sequence on the substrate 1.

[0041] The superlattice stress buffer layer 3 can be made of AlN or AlGaN. The electron blocking layer 6 can be a p-AlGaN layer.

[0042] The n ohmic contact electrode 8 is disposed on the n-type AlGaN layer 4. And, the p ohmic contact electrode 9 is disposed on the P-type GaN hole conduction layer 7.

[0043] Different from the prior art, in the present invention, as Figure 3 shown, the p ohmic contact electrode 9 presents a wavy shape with multiple branches parallel and evenly distributed. That is, the p ohmic contact electrode 9 is divided into multiple branches, each branch has the same structure and is in a wavy shape, and at the same time, the multiple branches are parallel to each other and evenly spaced apart.

[0044] Preferably, each wavy-shaped p ohmic contact electrode 9 includes a plurality of discs and a cuboid connecting the discs.

[0045] Due to the lateral propagation of deep ultraviolet light and the independent multi-branch and uniform current conduction of the P ohmic contact electrode 9 with this special structure, the current injection efficiency is improved, and thus the optical power is enhanced. At the same time, the uniform arrangement of the multi-branch wavy shape of the P ohmic contact electrode 9 increases its sidewall perimeter, thereby enhancing the optical power on the sidewall of the chip.

[0046] Meanwhile, as Figure 2 shown, the n ohmic contact electrode 8 has a shape corresponding to that of the p ohmic contact electrode 9. That is, the n ohmic contact electrode 8 has multiple parallel and uniformly distributed wavy-shaped notches to accommodate the p ohmic contact electrode 9.

[0047] Specifically, as Figure 4 shown, the n ohmic contact electrode 8 correspondingly surrounds the p ohmic contact electrode 9. That is, the n ohmic contact electrode 8 is also divided into multiple branches and respectively surrounds each branch of the p ohmic contact electrode.

[0048] Moreover, in the present invention, the area difference between the p ohmic contact electrode 9 and the n ohmic contact electrode 8 is within 10%.

[0049] The n ohmic contact electrode 8 with this special structure, due to the comparable ohmic contact areas of the n / p ohmic contact electrodes, greatly enhances the lateral current expansion ability, reduces the phenomenon of current concentration congestion in the flip-chip structure, and significantly reduces the operating voltage of the chip. Moreover, the ohmic contact electrode with this special structure is the basis for forming a chip with low voltage and high optical power, improving the thermal stability of the chip and correspondingly enhancing its lifespan.

[0050] Preferably, the n ohmic contact electrode 8 is made of a Ti / Al / Ti / Au film system and the thickness of the Ti / Al / Ti / Au film system is 20 / 60 / 50 / 20 nm. That is, the thickness of the bottom Ti film is 20 nm, the thickness of the Al film is 60 nm, the thickness of the middle Ti film is 50 nm, and the thickness of the Au film is 20 nm.

[0051] More preferably, the p ohmic contact electrode 9 is made of a Ni / Au / Ti film system and the thickness of the Ni / Au / Ti film system is 10 / 200 / 20 nm. That is, the thickness of the Ni film is 10 nm, the thickness of the Au film is 200 nm, and the thickness of the Ti film is 20 nm.

[0052] In addition, similar to the prior art, a current spreading electrode is fabricated on both the n ohmic contact electrode 8 and the p ohmic contact electrode 9.

[0053] Moreover, the current spreading electrode is formed by evaporating a high-reflection metal system. For example, the current spreading electrode is made of a Cr / Al / Ti / Au / Ti film system, that is, it is formed by stacking a Cr film, an Al film, an intermediate Ti film, an Au film, and a top Ti film.

[0054] Preferably, the thickness of the Cr / Al / Ti / Au / Ti film system is 20 / 200 / 10 / 500 / 5 nm.

[0055] Among them, Cr metal has good adhesion and relatively good conductivity, which is beneficial to current transmission. Moreover, the evaporation of Cr requires a lower vacuum degree, and a high-purity Cr source is easy to find. In the present invention, the thickness of the Cr film is 20 nm.

[0056] The reflectivity of Al metal in the deep ultraviolet band is 60%-70%, which is relatively high. At the same time, the cost of Al is very low, and Al acts as a reflective electrode. In the present invention, the thickness of the Al film is 200 nm.

[0057] The resistivity of Ti metal is relatively high, so the Ti film should not be too thick. In the present invention, the thickness of the intermediate Ti film is 10 nm.

[0058] Au metal is used as a protective layer and has good stability in air. In the present invention, the thickness of the Au film is 500 nm.

[0059] Since the wettability of Au and SiO2 is poor, the deep ultraviolet LED flip-chip process generally requires SiO2 passivation protection on the electrode. When the SiO2 protective layer exceeds 500 nm, cracks often appear when deposited on the Au layer, losing the meaning of passivation and reducing the leakage yield of the deep ultraviolet LED flip-chip. Therefore, a metal Ti that is stable in air and has good wettability with SiO2 is required on the Au layer. In the present invention, the thickness of the top Ti film is 5 nm.

[0060] Moreover, a pad electrode is fabricated on each of the current spreading electrodes. Through the pad electrode, it is convenient to connect an external power supply, thereby facilitating power supply to it for luminescence.

[0061] Finally, a passivation layer is provided between the two pad electrodes, between the two current spreading electrodes, and between the n-ohmic contact electrode 8 and the p-ohmic contact electrode 9. The passivation layer can prevent leakage caused by contact between the two pad electrodes, between the two current spreading electrodes, and between the n-ohmic contact electrode 8 and the p-ohmic contact electrode 9, thereby playing a protective role.

[0062] Preferably, the passivation layer is a SiO2 passivation layer.

[0063] Figure 4The deep ultraviolet LED flip chip with the above structure of the present invention has a difference in area between the p-ohmic contact electrode 9 and the n-ohmic contact electrode 8 of only 7.22%. Compared with Figure 5 the original chip structure formed by the existing n-ohmic contact electrode 10 and the existing p-ohmic contact electrode 11 shown, for a 20 mil * 20 mil chip, under a 100 mA current drive, the data are as shown in the following table. Among them, the operating voltage is reduced by 0.35 V, the optical power is increased by 26%, and the 168 h life maintenance rate is considered 100%.

[0064]

[0065] Note: In this table, p mm 2 represents the area of the p-ohmic contact electrode, with the unit of mm 2 ; n mm 2 represents the area of the n-ohmic contact electrode, with the unit of mm 2 ; the percentage difference in the p / n area represents the percentage difference in the areas of the p-ohmic contact electrode and the n-ohmic contact electrode.

[0066] The preparation method of the deep ultraviolet LED flip chip of the present invention is described below so that those skilled in the art can prepare the described deep ultraviolet LED flip chip according to the description of the present invention.

[0067] Figure 6 The flowchart of the preparation method of the deep ultraviolet LED flip chip of the present invention is shown. As Figure 6 shown, the preparation method of the deep ultraviolet LED flip chip of the present invention includes the following steps:

[0068] 1. Prepare an LED epitaxial wafer.

[0069] Similar to the prior art, when preparing an LED epitaxial wafer, it is necessary to provide a substrate 1 and sequentially grow an aluminum nitride template layer 2, a superlattice stress buffer layer 3, an n-type AlGaN layer 4, a multi-quantum well structure layer 5, an electron blocking layer 6, and a P-type GaN hole conduction layer 7 on the substrate 1.

[0070] 2. Prepare an n-electrode mesa and a p-electrode mesa.

[0071] Among them, before preparing the n-electrode mesa and the p-electrode mesa, the prepared LED epitaxial wafer can be cleaned first to facilitate the removal of impurities on the LED epitaxial wafer.

[0072] When cleaning, inorganic solvents, organic solvents (such as a sulfuric acid / hydrogen peroxide mixed solution, an isopropyl alcohol solution), etc. can be used for cleaning.

[0073] When preparing the n - electrode mesa and the p - electrode mesa, methods such as photolithography and dry etching can be used to etch part of the LED epitaxial wafer from top to bottom. Among them, during etching, it is necessary to etch down to the n - type AlGaN layer 4, that is, it is necessary to etch away the P - type hole - conducting layer 7, the electron - blocking layer 6, and the multi - quantum well structure layer 5 until the n - type AlGaN layer 4 is exposed, thereby forming the n - electrode mesa.

[0074] It should be noted that according to needs, during etching, it can be etched only to the surface of the n - type AlGaN layer 4, or a part of the n - type AlGaN layer 4 can be etched away, leaving only a part of the n - type AlGaN layer 4 with a certain thickness.

[0075] According to the thickness of each layer in the LED epitaxial wafer, preferably, when etching the LED epitaxial wafer, the etching depth is 500 - 800 nm. More preferably, the etching depth is 600 nm.

[0076] At the same time, the un - etched part forms the p - electrode mesa.

[0077] In the present invention, through etching, the formed n - electrode mesa is similar to Figure 2 the shape shown by the black part in Figure 2 And the un - etched p - electrode mesa is similar to

[0078] III. Preparation of the n - ohmic contact electrode 8.

[0079] In the present invention, the n - ohmic contact electrode 8 can be prepared on the exposed n - type AlGaN layer 4, that is, on the n - electrode mesa, through photolithography and evaporation processes.

[0080] Preferably, the n - electrode 8 is formed by evaporating a metal system of Ti / Al / Ti / Au, and the thickness of the bottom Ti film is 20 nm, the thickness of the Al film is 60 nm, the thickness of the middle Ti film is 50 nm, and the thickness of the Au film is 20 nm.

[0081] More preferably, after obtaining the n - ohmic contact electrode 8, the n - ohmic contact electrode 8 is subjected to high - temperature annealing in an N2 atmosphere. Among them, the annealing temperature is 900 °C, and the annealing time is 30 s.

[0082] Among them, the shape of the prepared n - ohmic contact electrode 8 is as shown by the black part in Figure 2

[0083] IV. Preparation of the p - ohmic electrode 9.

[0084] In the present invention, a p-ohmic contact electrode 9 can be fabricated on the P-type GaN hole conduction layer 7, that is, on the p-electrode platform, through a photolithography and evaporation process.

[0085] Among them, the fabricated p-ohmic contact electrode 9 is as Figure 3 shown by the black part in

[0086] In this way, as Figure 4 shown, the p-ohmic contact electrode 9 presents a wavy shape with multiple parallel and evenly distributed branches. The n-ohmic contact electrode 8 surrounds the p-ohmic contact electrode 9 accordingly, and the area difference between the p-ohmic contact electrode 9 and the n-ohmic contact electrode 8 is within 10%.

[0087] Preferably, the p-ohmic contact electrode 9 is formed by evaporating a metal system of Ni / Au / Ti, and the thickness of the Ni film is 10 nm, the thickness of the Au film is 200 nm, and the thickness of the Ti film is 20 nm.

[0088] More preferably, after obtaining the p-ohmic contact electrode 9, the p-electrode 9 is annealed in an N2 or air atmosphere. Among them, the annealing temperature is 550 °C and the annealing time is 180 s.

[0089] V. Fabricate a current spreading electrode.

[0090] In the present invention, a current spreading electrode can be fabricated on the n-ohmic contact electrode 8 and the p-ohmic contact electrode 9 respectively through a photolithography and evaporation process.

[0091] Among them, the current spreading electrode is formed by evaporating a high-reflection metal system. For example, it is formed by evaporating a metal system of Cr / Al / Ti / Au / Ti, that is, it is composed of a Cr film, an Al film, an intermediate Ti film, an Au film, and a top Ti film stacked together.

[0092] VI. Fabricate a passivation layer.

[0093] That is, after fabricating the current spreading electrode, a passivation layer is fabricated through deposition, photolithography, and etching processes.

[0094] Preferably, the passivation layer is a silicon oxide layer. By fabricating the passivation layer, it is possible to prevent leakage caused by contact between the two pad electrodes, between the two current spreading electrodes, and between the n-ohmic contact electrode 8 and the p-ohmic contact electrode 9, thereby being able to play a protective role.

[0095] VII. Fabricate pad electrodes.

[0096] Methods such as photolithography and dry etching can be used to form two vias on the passivation layer respectively opposite to the two current spreading electrodes. Then, pad electrodes connected to the current spreading electrodes are respectively deposited in the vias through an evaporation process.

[0097] After preparing the pad electrodes, the preparation process of the deep ultraviolet LED flip chip of the present invention is completed.

[0098] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than limiting the protection scope of the present invention. Those skilled in the art can modify or equivalently replace the technical solutions of the present invention according to the idea of the present invention, without departing from the essence and scope of the technical solutions of the present invention.

Claims

1. A deep ultraviolet LED flip chip, which comprises an LED epitaxial wafer and an n-ohmic contact electrode (8) and a p-ohmic contact electrode (9) arranged on the LED epitaxial wafer, and is characterized in that, The p-ohmic contact electrode (9) presents a wavy shape with multiple independent parallel and uniformly distributed branches. The n-ohmic contact electrode (8) surrounds the p-ohmic contact electrode (9) correspondingly, and the area difference between the p-ohmic contact electrode (9) and the n-ohmic contact electrode (8) is within 10%. A passivation layer is provided between the n-ohmic contact electrode (8) and the p-ohmic contact electrode (9). The n-ohmic contact electrode (8) has notches with a wavy shape of multiple independent parallel and uniformly distributed branches.

2. The flip-chip deep ultraviolet LED according to claim 1, characterized in that, Each wavy-shaped p-ohmic contact electrode (9) includes multiple discs and cuboids connecting the discs.

3. The flip-chip deep ultraviolet LED according to claim 1, characterized in that The n-ohmic contact electrode (8) is made of a Ti / Al / Ti / Au film system with a thickness of 20 / 60 / 50 / 20 nm for the Ti / Al / Ti / Au film system.

4. The deep ultraviolet LED flip chip according to claim 1, characterized in that, The p-ohmic contact electrode (9) is made of a Ni / Au / Ti film system with a thickness of 10 / 200 / 20 nm for the Ni / Au / Ti film system.

5. The deep ultraviolet LED flip chip according to claim 1, characterized in that, A current spreading electrode is fabricated on each of the n-ohmic contact electrode (8) and the p-ohmic contact electrode (9). The current spreading electrode is made of a Cr / Al / Ti / Au / Ti film system with a thickness of 20 / 200 / 10 / 500 / 5 nm for the Cr / Al / Ti / Au / Ti film system.

6. The flip-chip deep ultraviolet LED according to claim 5, characterized in that, A pad electrode is fabricated on each of the current spreading electrodes.

7. The flip-chip deep ultraviolet LED according to claim 1, wherein The LED epitaxial wafer includes a substrate (1) and an aluminum nitride template layer (2), a superlattice stress buffer layer (3), an n-type AlGaN layer (4), a multi-quantum well structure layer (5), an electron blocking layer (6), and a P-type GaN hole conduction layer (7) formed in sequence on the substrate (1). The n-ohmic contact electrode (8) is disposed on the n-type AlGaN layer (4), and the p-ohmic contact electrode (9) is disposed on the P-type GaN hole conduction layer (7).

8. A preparation method for a deep ultraviolet LED flip chip, characterized in that, It includes the following steps: 1). Grow an aluminum nitride template layer (2), a superlattice stress buffer layer (3), an n-type AlGaN layer (4), a multi-quantum well structure layer (5), an electron blocking layer (6), and a P-type GaN hole conduction layer (7) in sequence on the substrate (1) to obtain an LED epitaxial wafer. 2). Etch part of the LED epitaxial wafer downward to the n-type AlGaN layer (4) to form an n-electrode mesa, and the unetched part forms a P-electrode mesa. 3). Fabricate the n-ohmic contact electrode (8) on the surface of the n-electrode mesa by photolithography and evaporation. 4). Fabricate the p-ohmic contact electrode (9) on the surface of the P-electrode mesa by photolithography and evaporation. Among them, the p-ohmic contact electrode (9) presents a wavy shape with multiple parallel and uniformly distributed branches. The n-ohmic contact electrode (8) surrounds the p-ohmic contact electrode (9) correspondingly, and the area difference between the p-ohmic contact electrode (9) and the n-ohmic contact electrode (8) is within 10%. 5), fabricate a current spreading electrode on the n-ohmic contact electrode (8) and the p-ohmic contact electrode (9) respectively through photolithography and evaporation processes; 6), fabricate a passivation layer through deposition, photolithography, and etching processes; 7), form vias respectively opposite to the current spreading electrodes on the passivation layer and evaporate pad electrodes connected to the current spreading electrodes in the vias.

9. The preparation method of the deep ultraviolet LED flip chip according to claim 8, characterized in that, After obtaining the n-ohmic contact electrode (8), anneal the n-ohmic contact electrode (8) at a high temperature in an N2 atmosphere, where the annealing temperature is 900 °C and the annealing time is 30 s.

10. The manufacturing method of the deep ultraviolet LED flip chip according to claim 8, characterized in that, After obtaining the p-ohmic contact electrode (9), anneal the p-ohmic contact electrode (9) in an N2 or air atmosphere, where the annealing temperature is 550 °C and the annealing time is 180 s.

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