A ruthenium metal electrode film layer for flip-chip LED chips and a method for preparing the same
By employing a multi-layer structure of aluminum-copper alloy film, ruthenium metal film, and bonding layer in flip-chip LEDs, the problems of high cost of precious metals and low work function of ruthenium are solved, thereby achieving improved reliability and cost reduction of ruthenium metal electrode film, and improving luminous efficacy and process yield.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2026-03-26
- Publication Date
- 2026-06-23
AI Technical Summary
In the existing technology, precious metals gold and platinum are expensive to use as electrode materials in flip-chip LEDs, and ruthenium has a work function lower than the threshold required to form an ideal ohmic contact, which leads to electrode reliability problems.
A multi-layer structure consisting of an aluminum-copper alloy film, a ruthenium metal film, an adhesion layer, and a bonding layer is adopted. The ruthenium metal electrode film is formed by a vapor deposition process. The reliability is improved and the cost is reduced by adjusting the work function of ruthenium and setting the bonding layer.
The reliability and stability of the ruthenium metal electrode film were achieved, the diffusion of precious metals was avoided, the manufacturing cost was reduced, and the luminous efficiency and process yield were improved.
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Figure CN122269908A_ABST
Abstract
Description
Technical Field
[0001] This invention relates to the field of LED semiconductor electronics technology, and in particular to a ruthenium metal electrode film for flip-chip LEDs and its preparation method. Background Technology
[0002] In the manufacturing of light-emitting diode (LED) chips, the design of the electrode structure and the selection of materials have a critical impact on the device's photoelectric performance, reliability, and manufacturing cost.
[0003] Currently, the industry commonly uses gold (Au) and platinum (Pt) with high work functions (greater than 5.0 eV) as electrode materials to form low-resistance ohmic contacts with P-type GaN. However, both gold and platinum are precious metals with high prices, and the cost of precious metals cannot be ignored in the total cost during large-scale production.
[0004] From the perspective of raw material cost alone, ruthenium (Ru) is cheaper than gold and platinum, giving it a significant advantage in cost control. However, ruthenium's work function (approximately 4.7 eV) is lower than the common threshold (greater than 5.0 eV) required to form an ideal ohmic contact, making it difficult to achieve good electrical contact performance when using ruthenium directly. Summary of the Invention
[0005] The technical problem to be solved by the present invention is: how to provide a ruthenium metal electrode film for flip-chip LEDs and its preparation method, so as to reduce the electrode manufacturing cost without affecting the electrode reliability.
[0006] To solve the above-mentioned technical problems, the present invention adopts the following technical solution: a ruthenium metal electrode film layer for flip-chip LEDs, comprising an aluminum-copper alloy film layer, a ruthenium metal film layer, an adhesive layer, and a bonding layer; the aluminum-copper alloy film layer comprises a first aluminum-copper alloy film layer and a second aluminum-copper alloy film layer; the first aluminum-copper alloy film layer is disposed on the adhesive layer; the bonding layer is disposed between the aluminum-copper alloy film layer and the ruthenium metal film layer; the second aluminum-copper alloy film layer or at least two ruthenium metal film layers are disposed between two adjacent bonding layers.
[0007] Furthermore, the bonding layer includes a first bonding layer and a second bonding layer; the first aluminum-copper alloy film layer is provided with the first bonding layer, two ruthenium metal film layers, the first bonding layer, two ruthenium metal film layers, the first bonding layer, two ruthenium metal film layers, and the second bonding layer stacked sequentially from bottom to top on the first aluminum-copper alloy film layer.
[0008] Furthermore, the bonding layer also includes a third bonding layer and a fourth bonding layer; the second bonding layer is provided with a second aluminum-copper alloy film layer, the third bonding layer, four ruthenium metal film layers and the fourth bonding layer stacked sequentially from bottom to top.
[0009] Furthermore, the ruthenium metal film has a thickness of 200 Å, and the ruthenium metal film is a ruthenium-based alloy or a conductive oxide.
[0010] Furthermore, the ruthenium-based alloy is Ni / Ru; the conductive oxide is ruthenium dioxide (RuO2).
[0011] Furthermore, the aluminum-copper alloy film layer has a thickness of 3000 Å to 8000 Å; the bonding layer is a titanium film layer with a thickness of 500 Å to 2000 Å; and the adhesion layer is a chromium film layer with a thickness of 25 Å.
[0012] Furthermore, a method for preparing the aforementioned ruthenium metal electrode film for flip-chip LEDs is provided, comprising the steps of forming an aluminum-copper alloy film, a ruthenium metal film, an adhesion layer, and a bonding layer using a vapor deposition process.
[0013] Furthermore, the plating rate of the adhesion layer is 0.1 Å / s, and the cooling time after evaporation is 2 s; the plating rate of the aluminum-copper alloy film layer is 6 Å / s, and the cooling time after evaporation is 3 s; the plating rate of the ruthenium metal film layer is 1 Å / s, and the cooling time after evaporation is 10 s; the plating rate of the bonding layer is 1 Å / s, and the cooling time after evaporation is 10 s.
[0014] Furthermore, the total pre-melting time of each of the ruthenium metal films is 215 seconds.
[0015] The beneficial effects of this invention are as follows: a ruthenium metal electrode film for flip-chip LEDs and its preparation method, through a bonding layer disposed between a copper-aluminum alloy film and a ruthenium metal layer, provides reliable bonding force for ruthenium to films of different metals; using ruthenium instead of gold and platinum in the traditional structure, due to ruthenium's chemical inertness, its diffusion rate is several orders of magnitude slower than that of gold and platinum, avoiding the diffusion (including electromigration and thermal migration) of gold and platinum atoms into the GaN layer or encapsulation material under long-term working environments of high temperature, high current, and high humidity, thus improving luminous efficiency and reliability; furthermore, ruthenium has a melting point of 2334°C, higher than the melting point of gold (1064°C) and platinum (1768°C), so in the back-end processes of LED chip manufacturing (such as annealing and bonding) or high-temperature working environments, the ruthenium electrode can maintain structural stability and is less prone to spheroidization or deformation, thereby ensuring the provision of a reliable metal electrode film while significantly reducing manufacturing costs. Attached Figure Description
[0016] Figure 1 This is a schematic diagram of the structure of a ruthenium metal electrode film layer for flip-chip LEDs according to the present invention; Label Explanation: 1. Adhesive layer; 2. Copper-aluminum alloy film layer; 3. Bonding layer; 4. Ruthenium metal film layer; 21. First copper-aluminum alloy film layer; 22. Second copper-aluminum alloy film layer; 31. First bonding layer; 32. Second bonding layer; 33. Third bonding layer; 34. Fourth bonding layer. Detailed Implementation
[0017] To explain in detail the technical content, objectives, and effects of the present invention, the following description is provided in conjunction with the embodiments and accompanying drawings.
[0018] Before detailing the embodiments of this application, some related concepts are explained: Ni / Ru refers to nickel / ruthenium; RuO2 refers to ruthenium dioxide; and the pre-melting time refers to the time set by the electron beam inside the machine to pre-melt each metal at a high temperature before coating.
[0019] Table 1
[0020] Please refer to Table 1. Taking a 12-layer existing technology as an example, the P-type electrode uses gold and platinum to form an ohmic contact with the P-GaN layer. However, under long-term working conditions of high temperature, high current, and high humidity, gold atoms will diffuse into the GaN layer or encapsulation material, including electromigration and thermal migration, which will lead to increased contact resistance, decreased luminous efficiency, and even short-circuit failure, seriously affecting the long-term reliability of the LED chip.
[0021] To at least solve the above problems, please refer to Figure 1 This invention provides a ruthenium metal electrode film layer for flip-chip LEDs, comprising an aluminum-copper alloy film layer, a ruthenium metal film layer, an adhesive layer, and a bonding layer; the aluminum-copper alloy film layer includes a first aluminum-copper alloy film layer and a second aluminum-copper alloy film layer; the first aluminum-copper alloy film layer is disposed on the adhesive layer; the bonding layer is disposed between the aluminum-copper alloy film layer and the ruthenium metal film layer; the second aluminum-copper alloy film layer or at least two ruthenium metal film layers are disposed between two adjacent bonding layers.
[0022] As can be seen from the above description, the beneficial effects of the present invention are as follows: A ruthenium metal electrode film layer for flip-chip LEDs provides reliable bonding force between ruthenium and different metal films through a bonding layer disposed between a copper-aluminum alloy film layer and a ruthenium metal layer; ruthenium is used instead of gold and platinum in the traditional structure. Due to its chemical inertness, the diffusion rate of ruthenium is several orders of magnitude slower than that of gold, platinum, etc., thereby avoiding the diffusion of gold atoms into the GaN layer or encapsulation material (including electromigration and thermal migration), improving luminous efficiency and enhancing reliability; and ruthenium has a melting point of 2334°C, which is higher than the melting point of gold (1064°C) and platinum (1768°C). In the back-end processes of LED chip manufacturing (such as annealing and bonding) or high-temperature operating environments, the ruthenium electrode can maintain structural stability and is less prone to spheroidization or deformation, thereby ensuring the provision of a reliable metal electrode film layer while significantly reducing manufacturing costs.
[0023] Furthermore, the bonding layer includes a first bonding layer and a second bonding layer; the first aluminum-copper alloy film layer is provided with the first bonding layer, two ruthenium metal film layers, the first bonding layer, two ruthenium metal film layers, the first bonding layer, two ruthenium metal film layers, and the second bonding layer stacked sequentially from bottom to top on the first aluminum-copper alloy film layer.
[0024] Furthermore, the bonding layer also includes a third bonding layer and a fourth bonding layer; the second bonding layer is provided with a second aluminum-copper alloy film layer, the third bonding layer, four ruthenium metal film layers and the fourth bonding layer stacked sequentially from bottom to top.
[0025] Furthermore, the ruthenium metal film has a thickness of 200 Å, and the ruthenium metal film is a ruthenium-based alloy or a conductive oxide.
[0026] Furthermore, the ruthenium-based alloy is Ni / Ru; the conductive oxide is ruthenium dioxide (RuO2).
[0027] As can be seen from the above description, this structure avoids the problem that the work function of ruthenium (approximately 4.7 eV) is lower than that of gold (approximately 5.1 eV) and platinum (approximately 5.65 eV). By forming a ruthenium-based alloy (such as Ni / Ru) or using a conductive oxide (such as RuO2), its work function and band structure are adjusted to achieve ohmic contact with the P-GaN layer, and the contact resistance meets the requirements. The thickness of the ruthenium metal film of 200 Å and its segmented ruthenium plating structure are combined with the cooling time in the subsequent process.
[0028] Furthermore, the aluminum-copper alloy film layer has a thickness of 3000 Å to 8000 Å; the bonding layer is a titanium film layer with a thickness of 500 Å to 2000 Å; and the adhesion layer is a chromium film layer with a thickness of 25 Å.
[0029] As can be seen from the above description, the specific thickness range of each film layer defined in this structure, and the thickness parameters given (such as 3000-8000 Å for the aluminum-copper alloy film layer, 500-2000 Å for the bonding layer, and 25 Å for the adhesion layer), are the optimal ranges verified by experiments. The aluminum-copper alloy film layer provides high reflectivity and conductivity. The bonding layer uses titanium, which provides strong adhesion while its thickness plays a role in stress buffering and blocking. The adhesion layer uses chromium, which saves costs while ensuring bonding with the P-GaN layer.
[0030] Furthermore, a method for preparing the aforementioned ruthenium metal electrode film for flip-chip LEDs is provided, comprising the steps of forming an aluminum-copper alloy film, a ruthenium metal film, an adhesion layer, and a bonding layer using a vapor deposition process.
[0031] Furthermore, the plating rate of the adhesion layer is 0.1 Å / s, and the cooling time after evaporation is 2 s; the plating rate of the aluminum-copper alloy film layer is 6 Å / s, and the cooling time after evaporation is 3 s; the plating rate of the ruthenium metal film layer is 1 Å / s, and the cooling time after evaporation is 10 s; the plating rate of the bonding layer is 1 Å / s, and the cooling time after evaporation is 10 s.
[0032] As can be seen from the above description, the beneficial effects of the present invention are as follows: It provides a method for preparing a ruthenium metal electrode film for flip-chip LEDs. The multilayer film structure of the present invention is achieved through a vapor deposition process. This process has good compatibility and is easy to implement and promote on existing LED chip production lines. It can stably deposit materials such as aluminum, copper, ruthenium, titanium, and chromium. The low deposition rate design facilitates the full migration of atoms on the P-GaN layer, forming a dense and uniform film. The set cooling time works in conjunction with the corresponding film thickness to fully release the film stress and avoid excessive stress and peeling.
[0033] Furthermore, the total pre-melting time of each of the ruthenium metal films is 215 seconds.
[0034] As can be seen from the above description, due to the high melting point of ruthenium, sufficient pre-melting is required before coating. A sufficient total pre-melting time (215s) is set to allow ruthenium to fully melt, providing the preconditions for subsequent atomic evaporation.
[0035] Please refer to Figure 1 This embodiment provides a ruthenium metal electrode film for flip-chip LEDs and its preparation method.
[0036] Traditional P-type electrodes often use gold or platinum to form good ohmic contacts with P-type GaN. However, under long-term operating environments of high temperature, high current, and high humidity, Au atoms diffuse into the GaN layer or encapsulation material through electromigration and thermal migration, leading to increased contact resistance, decreased luminous efficiency, and even short-circuit failure, seriously affecting the long-term reliability of LED chips.
[0037] Table 2
[0038] Please refer to Figure 1 Table 2 shows the film layer sequence and process parameters of the ruthenium metal electrode film in this embodiment. This invention uses 19 layers, replacing platinum and gold with ruthenium. Among commonly used electrode materials, gold is generally more expensive than platinum, and platinum is significantly more expensive than ruthenium (Ru). Ruthenium, as a platinum group metal, possesses good chemical stability, a high melting point, and relatively low resistivity, making it a potential electrode material in terms of both electrical and thermal properties, and it also has a significant cost advantage.
[0039] It is worth noting that in this embodiment, the thicknesses of the first bonding layer, the second bonding layer, the third bonding layer, and the fourth bonding layer are 1000 Å, 1200 Å, 2000 Å, and 500 Å, respectively. The 1000 Å thick titanium metal (Ti) is mainly used to separate ruthenium metal (Ru), because a one-time plating of 1200 Å Ru may cause excessive stress from Ru, resulting in the entire electrode being pulled apart and the flip electrode being detached due to stress. The 1200 Å and 2000 Å Ti are used as adhesive layers between AlCu and Ru, considering that AlCu and Ru are not easy to bond directly and may cause film separation. Ti is used as an adhesive layer between the two. The 500 Å Ti is the outermost film layer of the entire electrode structure, which is used as an adhesion layer for the electrode and the protective silicon dioxide layer deposited in the next process.
[0040] Tables 3, 4, and 5 present reliability verification data for the structure of this invention. Table 3 shows a comparison of various electrical test data between the experimental group (using the electrode structure of this patent in a chip) and the chip BASE group (using the original electrode structure). Table 3
[0041] Referring to Table 3, it can be seen that the overall yield of the present invention is 0.5% higher than that of BASE (the prior art shown in Table 1), and there are no significant differences in various electrical properties VF1, VF3, WLD, and IR. The normalized LOP@454nm of the experimental group is 1.83% higher than that of BASE. Among them, VF1 and VF3 represent the voltage of the chip under different test currents, WLD represents the emission wavelength of the chip, and IR represents the reverse current applied to the chip under the reverse voltage, which is used to detect whether the chip is leaking current.
[0042] Table 4
[0043] Please refer to Table 4. It can be seen that the thrust values of the experimental group and the BASE group (the prior art shown in Table 1) of this invention are consistent with the control results and there is no significant difference.
[0044] Table 5
[0045] Please refer to Table 5. It can be seen that the deterioration and aging verification results of the experimental group and the BASE group (the prior art shown in Table 1) of this invention are all OK.
[0046] In summary, the ruthenium metal electrode film for flip-chip LEDs and its preparation method provided by the present invention have the following beneficial effects: 1. By using ruthenium metal (Ru) to replace gold (Au) and platinum (Pt) in traditional electrodes, a reliable metal electrode film is provided while reducing the material cost of the chip, resulting in significant economic benefits. 2. The chemical inertness of ruthenium prevents gold atoms from diffusing into the GaN layer or packaging material (including electromigration and thermal migration), improving optical efficiency and ensuring the long-term reliability of the chip. 3. By utilizing the high melting point of ruthenium, the ruthenium electrode maintains structural stability during the later stages of LED chip manufacturing or in high-temperature operating environments, and is less prone to spheroidization or deformation. 4. By setting a bonding layer to enhance the bonding force between ruthenium and the aluminum-copper alloy film, and by adopting a segmented ruthenium plating method to extend the cooling time, internal stress is fully released, preventing the electrode film from peeling or falling off, thereby improving process yield and product reliability. 5. By setting different plating rates and cooling times, atoms can migrate fully to form a dense film, and the stress in each film layer can be fully released, avoiding stress accumulation.
[0047] The above description is merely an embodiment of the present invention and does not limit the patent scope of the present invention. Any equivalent modifications made based on the content of the present invention specification and drawings, or direct or indirect applications in related technical fields, are similarly included within the patent protection scope of the present invention.
Claims
1. A ruthenium metal electrode film for flip-chip LEDs, characterized in that, It includes an aluminum-copper alloy film layer, a ruthenium metal film layer, an adhesive layer, and a bonding layer; the aluminum-copper alloy film layer includes a first aluminum-copper alloy film layer and a second aluminum-copper alloy film layer; the first aluminum-copper alloy film layer is disposed on the adhesive layer; the bonding layer is disposed between the aluminum-copper alloy film layer and the ruthenium metal film layer; the second aluminum-copper alloy film layer or at least two ruthenium metal film layers are disposed between two adjacent bonding layers.
2. The ruthenium metal electrode film layer for flip-chip LEDs according to claim 1, characterized in that, The bonding layer includes a first bonding layer and a second bonding layer; the first aluminum-copper alloy film layer is provided with the first bonding layer, two ruthenium metal film layers, the first bonding layer, two ruthenium metal film layers, the first bonding layer, two ruthenium metal film layers and the second bonding layer stacked sequentially from bottom to top on the first aluminum-copper alloy film layer.
3. The ruthenium metal electrode film layer for flip-chip LEDs according to claim 2, characterized in that, The bonding layer further includes a third bonding layer and a fourth bonding layer; the second bonding layer is provided with a second aluminum-copper alloy film layer, the third bonding layer, the four ruthenium metal film layers and the fourth bonding layer stacked sequentially from bottom to top.
4. The ruthenium metal electrode film layer for flip-chip LEDs according to claim 1, characterized in that, The ruthenium metal film has a thickness of 200 Å and is a ruthenium-based alloy or a conductive oxide.
5. A ruthenium metal electrode film layer for flip-chip LEDs according to claim 4, characterized in that, The ruthenium-based alloy is Ni / Ru; the conductive oxide is ruthenium dioxide (RuO2).
6. The ruthenium metal electrode film layer for flip-chip LEDs according to claim 1, characterized in that, The aluminum-copper alloy film layer has a thickness of 3000Å to 8000Å; the bonding layer is a titanium film layer with a thickness of 500Å to 2000Å; and the adhesion layer is a chromium film layer with a thickness of 25Å.
7. A method for preparing a ruthenium metal electrode film for flip-chip LEDs as described in any one of claims 1 to 6, characterized in that, The process includes steps such as forming an aluminum-copper alloy film, a ruthenium metal film, an adhesion layer, and a bonding layer using a vapor deposition process.
8. A ruthenium metal electrode film for flip-chip LEDs according to claim 7, characterized in that, The coating rate of the adhesion layer is 0.1 Å / s, and the cooling time after evaporation is 2 s; the coating rate of the aluminum-copper alloy film layer is 6 Å / s, and the cooling time after evaporation is 3 s; the coating rate of the ruthenium metal film layer is 1 Å / s, and the cooling time after evaporation is 10 s; the coating rate of the bonding layer is 1 Å / s, and the cooling time after evaporation is 10 s.
9. A ruthenium metal electrode film for flip-chip LEDs according to claim 7, characterized in that, The total pre-melting time of each of the ruthenium metal films is 215 seconds.