Metal electrode and deep ultraviolet LED chip having the metal electrode

Abstract

The present invention relates to a metal electrode and a deep ultraviolet LED chip having the metal electrode. The metal electrode comprises an adhesion layer (1), a reaction layer (2), a barrier layer (3) and a protective layer (4). The reaction layer (2) is a multilayer structure in which a Ti film (2.1) and an Al film (2.2) are alternately arranged, and the thickness ratio of the Ti film (2.1) to the Al film (2.2) in the reaction layer (2) is 1:10. The reaction layer is a multilayer design in which Ti and Al are arranged in a ratio of 1:10, so that Ti and Al can fully react in the annealing stage to form TiN and TiAl alloys with low work functions, thereby reducing the specific contact resistivity, and at the same time avoiding the internal diffusion of Al to form AlN with a high bandgap width and the external diffusion of Al, optimizing the surface morphology of the metal electrode, making the surface morphology of the metal electrode smooth, enhancing the light decay maintenance rate of the chip, and extending the chip life.

Description

Technical Field

[0001] The invention belongs to the technical field of semiconductors and relates to a metal electrode and a deep ultraviolet LED chip having the metal electrode. Background Art

[0002] In recent years, with the advancement of global LED industry technology, the LED light band has expanded from the visible light band to the ultraviolet and deep ultraviolet bands. Deep ultraviolet LEDs have the functions of photocatalysis, medical light therapy, health care, air purification, sterilization, etc. Deep ultraviolet LEDs have a broad market prospect due to their rapid sterilization and disinfection functions.

[0003] Different from blue LEDs, epitaxial wafers of deep ultraviolet LEDs have n-type electron layers with high Al content. For n-AlGaN layers with high Al content, energy level defects increase with the Al content, causing the ionization energy of Si donors to increase and mobility to decrease, resulting in relatively poor conductivity of n-AlGaN with high Al content. On the other hand, low electron affinity leads to high Schottky barriers at the metal-semiconductor interface and poor ohmic contact characteristics, which requires strict optimization of metal electrode structure and alloy annealing conditions. These two aspects limit the acquisition of low-resistance ohmic contact and keep chip voltage high.

[0004] As we all know, the contact between metal and semiconductor materials is generally divided into two types: rectifying contact and non-rectifying contact. Rectifying contact refers to a contact that exists in the barrier layer and has a pn junction-like rectifying effect on the current flowing through the contact. It is mainly used to form a Schottky barrier and is used in devices such as Schottky diodes. Non-rectifying contact, also known as ohmic contact, refers to a metal-semiconductor contact that does not produce obvious additional impedance, does not significantly change the equilibrium carrier concentration inside the semiconductor, and has almost no effect on the device current. Compared with the bulk resistance or extended resistance of the semiconductor, the contact resistance of the ohmic contact is very small.

[0005] Since semiconductor devices generally use metal electrodes to input or output current, this requires a good ohmic contact between the metal and the semiconductor. Good ohmic contact can reduce forward resistance and thermal resistance, and enhance reliability under continuous room temperature operation.

[0006] According to the metal-semiconductor contact barrier model, the barrier height is closely related to the metal work function and the electron affinity of the material. For n-A1GaN, to form a good ohmic contact, it is necessary to find a metal with a smaller work function, such as Ti / Al / Ti / Au, Cr / Al / Ti / Au, V / Al / V / Au, etc.

[0007] Currently, in actual processes, Ti / Al / Ti (Ni, Pt, Mo) / Au quaternary metal alloy or Cr / Ti / Al / Ti (Ni, Pt, Mo) / Au quinary metal alloy is the most common metal structure. Different metal structures require different annealing heat treatments to form ohmic contacts. However, whether it is Ti / Al / Ti / Au quaternary metal alloy or Cr / Ti / Al / Ti / Au quinary metal alloy, after thermal annealing, the surface of the n-electrode is very rough. This is because the reaction layer Ti and Al do not react sufficiently. Under high-temperature annealing conditions, Al diffuses into the outer Au layer, causing Al to surge out of the Au layer, forming bulges and making the surface rough. The rough surface of Al overflow not only increases the contact resistivity, but also weakens the chip light attenuation by 5%-10%.

[0008] In view of the above technical defects of the prior art, there is an urgent need to develop a new type of metal electrode and related deep ultraviolet LED chip. Summary of the invention

[0009] In order to overcome the defects of the prior art, the present invention proposes a metal electrode and a deep ultraviolet LED chip having the metal electrode, which can reduce the specific contact resistivity, improve the chip leakage yield, and enhance the chip reliability.

[0010] In order to achieve the above object, the present invention provides the following technical solutions:

[0011] A metal electrode comprises an adhesion layer, a reaction layer, a barrier layer and a protective layer, wherein the reaction layer is a multilayer structure in which Ti films and Al films are alternately arranged, and the thickness ratio of the Ti film to the Al film in the reaction layer is 1:10.

[0012] Preferably, the total thickness of all the Ti films in the reaction layer is 10-40 nm.

[0013] Preferably, the total thickness of all the Ti films in the reaction layer is 18 nm.

[0014] Preferably, the reaction layer is formed by alternating two layers of the Ti film and two layers of the Al film, and the thickness of a single layer of the Ti film is 9 nm.

[0015] Preferably, the reaction layer is formed by alternatingly arranging three layers of the Ti film and three layers of the Al film, and the thickness of a single layer of the Ti film is 6 nm.

[0016] Preferably, the protective layer includes an Au layer and a Ti layer located on the Au layer.

[0017] Preferably, the thickness of the Au layer is 40-50 nm, and the thickness of the Ti layer is 1-3 nm.

[0018] The thickness of the Au layer is 40 nm, and the thickness of the Ti layer is 2 nm.

[0019] Preferably, the adhesion layer is made of Cr and has a thickness of 1-30 nm.

[0020] Preferably, the thickness of the adhesion layer is 20 nm.

[0021] Preferably, the barrier layer is made of Ni or Ti.

[0022] Preferably, the barrier layer has a thickness of 40 nm.

[0023] In addition, the present invention also provides a deep ultraviolet LED chip, characterized in that its n-electrode is made of the metal electrode mentioned above.

[0024] Preferably, the n-electrode is disposed on an n-type AlGaN layer.

[0025] Preferably, the P electrode of the deep ultraviolet LED chip is arranged on a P-type GaN layer.

[0026] Compared with the prior art, the metal electrode of the present invention and the deep ultraviolet LED chip having the metal electrode have the following beneficial technical effects:

[0027] 1. The reaction layer is made of Ti and Al, and Ti and Al are designed in a multilayer according to a certain ratio, so as to form an n-electrode with a special structure, so that Ti and Al react fully in the annealing stage to form TiN and TiAl alloys with low work function, thereby reducing the specific contact resistivity, the forward resistance, and the thermal resistance. Under continuous room temperature operation, the reliability is enhanced, and at the same time, the internal diffusion of Al to form AlN with a high bandgap width and the external diffusion of Al are avoided, the surface morphology of the n-electrode is optimized, the surface morphology of the n-electrode is smooth, the light decay maintenance rate of the chip is enhanced, and the chip life is extended.

[0028] 2. Its protective layer is made of two metals, Au and Ti, which avoids the occurrence of cracks when the SiO2 passivation layer is deposited on the n-electrode when the SiO2 protective layer exceeds 500nm, thus losing the meaning of passivation, improving the chip leakage yield and enhancing the chip reliability. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] Figure 1 It is a schematic structural diagram of the metal electrode of the present invention.

[0030] Figure 2 It is a schematic structural diagram of a deep ultraviolet LED chip using the metal electrode of the present invention as an n-electrode.

[0031] Figure 3 The figure shows the change in the specific contact resistivity of the deep ultraviolet LED chip when the reaction layer of the n-electrode adopts different layer structures. DETAILED DESCRIPTION

[0032] The present invention is further described below in conjunction with the accompanying drawings and embodiments, and the contents of the embodiments are not intended to limit the protection scope of the present invention.

[0033] Aiming at the problem that the electrode surface of the quaternary metal alloy Ti / Al / Ti / Au and the quinary metal alloy Cr / Ti / Al / Ti / Au of the n-A1GaN ohmic contact in the current deep ultraviolet LED chip is rough after thermal annealing and the specific contact resistivity is relatively high, the inventor has found through research that the specific contact resistivity is relatively high because the reaction of Ti and Al in the reaction layer is not sufficient, and Al diffuses to the outer Au layer under high temperature annealing conditions, so that Al surges out of the Au layer to form a bulge, making the surface rough. The rough surface overflowed by Al not only increases the specific contact resistivity, but also weakens the chip light attenuation by 5%-10%. In view of this problem, the inventor proposes to design a multilayer of Ti and Al in the reaction layer according to a certain ratio, so that Ti and Al react fully in the annealing stage to form TiN and TiAl alloys with low work function, thereby reducing the specific contact resistivity, and at the same time avoiding the internal diffusion of Al to form AlN with a high bandgap width and the external diffusion of Al, destroying the surface morphology of the ohmic electrode, enhancing the light attenuation maintenance rate of the chip, and extending the chip life.

[0034] Figure 1 Schematic diagram of the structure of the metal electrode of the present invention is shown. Figure 1 As shown, the metal electrode of the present invention also includes an adhesion layer 1 , a reaction layer 2 , a barrier layer 3 and a protective layer 4 .

[0035] The adhesion layer 1 is used for adhesion. Since metal Cr has good adhesion and good conductivity, it is conducive to current transmission, and the evaporation of Cr has low vacuum requirements, and high-purity Cr sources are easy to find, therefore, in the present invention, the adhesion layer 1 is made of Cr.

[0036] Meanwhile, considering the size of the entire deep ultraviolet LED chip and its requirements for the n-electrode, in the present invention, the thickness of the adhesion layer 1 is 1-30 nm. Preferably, the thickness of the adhesion layer 1 is 20 nm.

[0037] The reaction layer 2 is used for reaction. Different from the single-layer structure in the prior art, in the present invention, the reaction layer 2 is a multi-layer structure in which Ti film 2.1 and Al film 2.2 are alternately arranged. In addition, the thickness ratio of the Ti film 2.1 and the Al film 2.2 in the reaction layer 2 is adjusted so that the thickness ratio of the Ti film 2.1 and the Al film 2.2 in the reaction layer 2 is 1:10.

[0038] Since the thickness of the Ti film 2.1 and the Al film 2.2 in the reaction layer 2 are designed in a multilayer manner according to a ratio of 1:10, Ti and Al are fully reacted in the annealing stage to form TiN and TiAl alloys with low work function, thereby reducing the specific contact resistivity. At the same time, the internal diffusion of Al to form AlN with a high bandgap width and the external diffusion of Al are avoided, the surface morphology of the n-electrode is optimized, and the surface morphology of the n-electrode is made smooth, thereby enhancing the light decay maintenance rate of the deep ultraviolet LED chip and extending the chip life.

[0039] It should be noted that, due to the high resistivity of the Ti film 2.1, the Ti film 2.1 should not be too thick. Generally, the total thickness of all the Ti films 2.1 is 10-40nm. Preferably, the total thickness of all the Ti films 2.1 is 18nm. Since the Al film 2.2 also acts as a reflective electrode, the total thickness of all the Al films 2.2 is generally greater than 100nm. According to the thickness ratio of the Ti film 2.1 to the Al film 2.2 of 1:10, the total thickness of all the Al films 2.2 is 100-400nm. Preferably, the total thickness of all the Al films 2.2 is 180nm. Thus, preferably, the thickness of the Ti film / Al film in the reaction layer 2 is 18 / 180nm.

[0040] In the present invention, preferably, the reaction layer 2 is formed by alternating two layers of the Ti film 2.1 and two layers of the Al film 2.2, and the thickness of the single layer of the Ti film 2.1 is 9 nm, and the thickness of the single layer of the Al film 2.2 is 90 nm. In this way, the structure of the reaction layer 2 is Ti film / Al film / Ti film / Al film, and the thickness of each film layer is 9 / 90 / 9 / 90 nm.

[0041] More preferably, the reaction layer 2 is formed by alternating three layers of the Ti film 2.1 and three layers of the Al film 2.2, and the thickness of a single layer of the Ti film 2.1 is 6 nm, and the thickness of a single layer of the Al film 2.2 is 60 nm. In this way, the structure of the reaction layer 2 is Ti film / Al film / Ti film / Al film / Ti film / Al film, and the thickness of each film layer is 6 / 60 / 6 / 60 / 6 / 60 nm.

[0042] The barrier layer 3 plays a blocking role. In the present invention, the barrier layer 3 is made of Ni or Ti. In this way, the barrier layer 3 can be used to block the diffusion between the metal layers. Preferably, the barrier layer 3 is made of Ni. More preferably, the thickness of the barrier layer 3 is 40nm. Thus, the barrier layer 3 can better block the diffusion between the metal layers.

[0043] The protective layer 4 plays a protective role. Normally, the protective layer 4 is made of an Au layer, and the thickness of the Au layer is generally 40-50nm. However, due to the poor wettability of Au and SiO2, the deep ultraviolet LED chip generally requires SiO2 passivation protection on the n-electrode. When the SiO2 protective layer exceeds 500nm, cracks often appear when it is deposited on the Au layer of the n-electrode, and the passivation meaning is lost, which reduces the leakage yield of the deep ultraviolet LED chip. Therefore, in the present invention, a metal Ti layer that is stable in the air and has good wettability with SiO2 is added to the Au layer. Therefore, in the present invention, the protective layer 4 includes an Au layer 4.1 and a Ti layer 4.2 located on the Au layer 4.1.

[0044] Preferably, the thickness of the Au layer 4.1 is 40-50 nm, and the thickness of the Ti layer 4.2 is 1-3 nm.

[0045] More preferably, the thickness of the Au layer 4.1 is 40 nm, and the thickness of the Ti layer 4.2 is 2 nm.

[0046] In the present invention, since the protective layer 4 is made of Au / Ti metals, cracks are avoided when the SiO2 passivation layer is deposited on the n-electrode to protect the n-electrode. When the SiO2 protective layer exceeds 500nm, the passivation meaning is lost, the chip leakage yield is improved, and the chip reliability is enhanced.

[0047] Therefore, when the reaction layer 2 is composed of two layers of the Ti film 2.1 and two layers of the Al film 2.2 arranged alternately, the overall structure of the metal electrode is Cr / Ti / Al / Ti / Al / Ni / Au / Ti. At this time, the corresponding preferred thickness is 20 / 9 / 90 / 9 / 90 / 40 / 40 / 2nm.

[0048] When the reaction layer 2 is composed of three layers of the Ti film 2.1 and three layers of the Al film 2.2 arranged alternately, the overall structure of the metal electrode is Cr / Ti / Al / Ti / Al / Ti / Al / Ni / Au / Ti. At this time, the corresponding preferred thickness is 20 / 6 / 60 / 6 / 60 / 6 / 60 / 40 / 40 / 2 nm.

[0049] Figure 2 FIG. 1 shows a schematic diagram of the structure of a deep ultraviolet LED chip using the metal electrode of the present invention as an n-electrode. Figure 2 As shown, the deep ultraviolet LED chip includes a substrate (sapphire), an LED epitaxial wafer, an n-electrode and a p-electrode. The n-electrode is the above-mentioned metal electrode.

[0050] The substrate may be a sapphire substrate, a silicon carbide substrate or a spinel substrate.

[0051] The LED epitaxial wafer comprises an AlN template layer, an AlN / AlGaN superlattice stress buffer layer (AlN / AlGaN SLs), an n-type AlGaN layer (n-AlGaN), a multi-quantum hydrazine structure layer (MQW), P-AlGaN and P-type GaN (P-GaN) which are sequentially formed on the substrate.

[0052] Wherein, the n-electrode is arranged on the n-type AlGaN layer, and the p-electrode is arranged on the p-type GaN layer.

[0053] Figure 3 The figure shows the change in the specific contact resistivity of the deep ultraviolet LED chip when the reaction layer of the n-electrode adopts different hierarchical structures. Figure 3 It can be seen that as the reaction layer of the n-electrode increases from one layer of Ti film and Al film to two layers of Ti film and Al film, and then to three layers of Ti film and Al film, the specific contact resistivity of the deep ultraviolet LED chip decreases in order of magnitude. Therefore, using the metal electrode with a multi-layer reaction layer of the present invention as the n-electrode can significantly reduce the specific contact resistivity of the deep ultraviolet LED chip.

[0054] Finally, it should be noted that the above embodiments are only used to illustrate the technical solution of the present invention, rather than to limit the scope of protection of the present invention. Those skilled in the art can modify or replace the technical solution of the present invention according to the idea of ​​the present invention without departing from the essence and scope of the technical solution of the present invention.

Claims

1. A metal electrode comprising an adhesion layer (1), a reaction layer (2), a barrier layer (3) and a protective layer (4), characterized in that: The reaction layer (2) is a multilayer structure composed of Ti films (2.1) and Al films (2.2) arranged alternately, the thickness ratio of the Ti films (2.1) to the Al films (2.2) in the reaction layer (2) is 1:10, and the total thickness of all the Ti films (2.1) in the reaction layer (2) is 10-40 nm; The Ti film and Al film in the reaction layer are designed as a multilayer with a thickness ratio of 1:10, so that Ti and Al can fully react in the annealing stage to form TiN and TiAl alloys with low work function.

2. The metal electrode according to claim 1, characterized in that The total thickness of all the Ti films (2.1) in the reaction layer (2) is 18 nm.

3. The metal electrode according to claim 2, characterized in that The reaction layer (2) is formed by alternating arrangement of two layers of the Ti film (2.1) and two layers of the Al film (2.2), and the thickness of a single layer of the Ti film (2.1) is 9 nm.

4. The metal electrode according to claim 2, characterized in that The reaction layer (2) is formed by alternating arrangement of three layers of the Ti film (2.1) and three layers of the Al film (2.2), and the thickness of a single layer of the Ti film (2.1) is 6 nm.

5. The metal electrode according to any one of claims 1 to 4, characterized in that The protective layer (4) comprises an Au layer (4.1) and a Ti layer (4.2) located on the Au layer (4.1).

6. The metal electrode according to claim 5, characterized in that The thickness of the Au layer (4.1) is 40-50 nm, and the thickness of the Ti layer (4.2) is 1-3 nm.

7. The metal electrode according to claim 6, characterized in that The thickness of the Au layer (4.1) is 40 nm, and the thickness of the Ti layer (4.2) is 2 nm.

8. The metal electrode according to claim 7, characterized in that The adhesion layer (1) is made of Cr and has a thickness of 1-30 nm.

9. The metal electrode according to claim 8, characterized in that The thickness of the adhesion layer (1) is 20 nm.

10. The metal electrode according to claim 9, characterized in that The barrier layer (3) is made of Ni or Ti.

11. The metal electrode according to claim 10, characterized in that The barrier layer (3) has a thickness of 40 nm.

12. A deep ultraviolet LED chip, characterized in that: The n-electrode is the metal electrode according to any one of claims 1 to 11.

13. The deep ultraviolet LED chip according to claim 12, characterized in that: The n-electrode is provided on the n-type AlGaN layer.

14. The deep ultraviolet LED chip according to claim 13, characterized in that: Its P electrode is arranged on the P-type GaN layer.

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