A front-mounted LED chip with improved moisture resistance and a method for manufacturing the same

Abstract

The application relates to the technical field of LED, in particular to a positive LED chip with improved moisture resistance and a preparation method thereof. The positive LED chip comprises a substrate, an epitaxial layer, a P-type electrode, an N-type electrode and a passivation layer. The P-type electrode and the N-type electrode each have an electrode wire bonding area for wire bonding. The passivation layer covers part of the surface of the chip except the electrode wire bonding area. The height of the electrode wire bonding area in the direction perpendicular to the substrate is higher than the upper surface of the surrounding passivation layer. The application has the beneficial effect that the electrode wire bonding area of the electrode is physically lifted to be higher than the surrounding passivation layer. This fundamentally changes the stress interface of the solder ball during packaging and wire bonding, so that the force of the solder ball is completely borne by the solid electrode metal, thereby completely avoiding the problem of crushing and shearing the brittle passivation layer due to the offset or oversize of the solder ball, guaranteeing the integrity of the passivation layer from the source of structure and improving the moisture resistance and reliability of the chip.

Description

Technical Field

[0001] This invention relates to the field of LED technology, and in particular to a positive-mounted LED chip with improved moisture resistance and its preparation method. Background Technology

[0002] LED (Light Emitting Diode) is a solid-state semiconductor device that converts electrical energy into light energy. It is widely used in display and lighting fields due to its advantages such as high luminous efficiency, long lifespan, energy saving, and environmental friendliness. High-precision LED chips, due to their mature technology and relatively low cost, occupy an important position in outdoor displays. Outdoor environments place extremely high demands on the reliability of LED devices, especially their resistance to moisture.

[0003] To improve moisture resistance, a common practice is to deposit a passivation layer (such as SiO2, SiN, etc.) on the chip surface, covering the electrode edges and other sensitive areas of the chip to isolate moisture corrosion and prevent "dead LEDs" caused by electrode oxidation or electrochemical corrosion. However, in the critical process of chip packaging—wire bonding—a wire bonding machine is used to sinter the ends of metal wires (gold wires, alloy wires, etc.) into balls and then bond them to the chip electrodes. Due to factors such as equipment precision and process fluctuations, the solder balls may shift in position, or due to excessively large ball diameters, their edges may press against the passivation layer around the electrodes. The brittle passivation layer is extremely prone to cracking or even peeling off under enormous pressure and ultrasonic energy (e.g., ...). Figure 1 , Figure 2 As shown in the image, this leads to the failure of the moisture barrier, causing a sharp decline in the chip's moisture resistance. This problem is particularly prominent in outdoor display applications that require smaller pixel pitch and higher reliability.

[0004] In existing technologies, there are solutions to improve packaging reliability by optimizing the electrode structure. For example, Chinese invention patent CN201210587583.3 discloses an LED chip that fabricates bumps on P-type and N-type electrodes, with the tips of the two bumps located on the same horizontal plane, to solve the chip misalignment and cold solder joint problems caused by the height and area differences of the electrode pads in the flip-chip bonding (SMT) process. However, this solution focuses on the very different packaging form of flip-chip bonding, where the bumps are used for surface array bonding to the substrate. It addresses the surface tension balance and eutectic bonding issues during the bonding process, without addressing or considering the risk of mechanical damage to the passivation layer by the solder balls in the conventional wire bonding process.

[0005] Therefore, how to fundamentally avoid the damage to the passivation layer caused by wire bonding process by starting with chip structure design, and thus significantly improve the inherent moisture resistance of upright LED chips without increasing additional packaging costs, has become a technical problem that urgently needs to be solved. Summary of the Invention

[0006] The technical problem to be solved by the present invention is to overcome the defect that the passivation layer around the electrode is easily damaged due to the offset of the solder balls or the excessive diameter of the solder balls during the wire bonding process of existing upright LED chips, which leads to a decrease in the moisture resistance and reliability of the chip.

[0007] To solve the above-mentioned technical problems, the present invention adopts the following technical solution: providing a positive-mounted LED chip with improved moisture resistance, comprising a substrate, an epitaxial layer, a P-type electrode, an N-type electrode, and a passivation layer, wherein the P-type electrode and the N-type electrode each have an electrode bonding area for wire bonding; the passivation layer covers the portion of the chip surface excluding the electrode bonding area; the height of the electrode bonding area in the direction perpendicular to the substrate is higher than the upper surface of the passivation layer surrounding it.

[0008] Another technical solution of the present invention is: a method for preparing a positive-mounted LED chip with improved moisture resistance, comprising the following steps: forming a raised boss made of GaN material on the LED epitaxial layer; A protruding electrode is formed on the lifting boss, and the electrode wire bonding area of ​​the protruding electrode is located on the lifting boss.

[0009] Another technical solution of the present invention is: a method for preparing a positive-mounted LED chip with improved moisture resistance, comprising the following steps: An electrode body is formed on the LED epitaxial layer; A passivation layer is formed on the electrode body, and the thickened area on the electrode body is exposed by photolithography and etching processes; A thickened electrode is formed on the exposed thickened region.

[0010] The beneficial effects of this invention are as follows: By physically raising the electrode wire bonding area (wire bonding point) of the electrode, making it higher than the surrounding passivation layer, this fundamentally changes the force interface of the solder ball during packaging wire bonding. The force exerted by the solder ball is entirely borne by the robust electrode metal, thus completely avoiding the problem of damaging or shearing the brittle passivation layer due to solder ball misalignment or excessive size. This ensures the integrity of the passivation layer from the structural source and improves the chip's moisture resistance reliability. Attached Figure Description

[0011] Figure 1 This is a schematic diagram illustrating the damage to the passivation layer caused by the misalignment of wire bonding balls in existing technologies. Figure 2 This is a schematic diagram of the structure of a positive-mounted LED chip with improved moisture resistance according to Embodiment 1 of the present invention (based on GaN raised bosses); Figure 3 This is a schematic diagram of the fabrication process of the upright LED chip in Embodiment 1 of the present invention; Figure 4This is a schematic diagram of the structure of the upright LED chip with improved moisture resistance according to Embodiment 2 of the present invention (based on thickened electrodes); Figure 5 This is a schematic diagram of the fabrication process of the upright LED chip in Embodiment 2 of the present invention; 1. Wire bonding balls; 2. Passivation layer; 3. Electrode; 41. First GaN layer; 42. First insulating barrier layer; 43. First current spreading layer; 44. Protruding electrode; 45. First passivation layer; 51. Second GaN layer; 52. Second insulating barrier layer; 53. Second current spreading layer; 54. Electrode body; 55. Second passivation layer; 56. Thickened electrode. Detailed Implementation

[0012] 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.

[0013] Figure 1 This is a schematic diagram illustrating how wire bonding ball misalignment leads to passivation layer damage in existing technologies. Figure 1 Misalignment of the wire bonding ball 1 can easily damage the passivation layer 2 around the electrode 3, leading to a decrease in the chip's moisture resistance and reliability.

[0014] This invention physically isolates the wire bonding stress from the passivation layer through structural design, ensuring that the passivation layer remains intact after encapsulation, thus fully leveraging its moisture barrier function and greatly reducing the risk of failure caused by moisture intrusion.

[0015] This invention provides a positive-mounted LED chip with improved moisture resistance, comprising a substrate, an epitaxial layer, a P-type electrode, an N-type electrode, and a passivation layer. The P-type electrode and the N-type electrode each have electrode bonding regions for wire bonding. The passivation layer covers the portion of the chip surface excluding the electrode bonding regions. The height of the electrode bonding regions in the direction perpendicular to the substrate is higher than the upper surface of the passivation layer surrounding them.

[0016] The beneficial effects of this invention are as follows: By physically raising the electrode wire bonding area (wire bonding point) of the electrode, making it higher than the surrounding passivation layer, this fundamentally changes the force interface of the solder ball during packaging wire bonding. The force exerted by the solder ball is entirely borne by the robust electrode metal, thus completely avoiding the problem of damaging or shearing the brittle passivation layer due to solder ball misalignment or excessive size. This ensures the integrity of the passivation layer from the structural source and improves the chip's moisture resistance reliability.

[0017] Furthermore, in the aforementioned positive-mounted LED chip with improved moisture resistance, the height difference between the electrode wire bonding area and the upper surface of the passivation layer is 1 μm to 3 μm.

[0018] As described above, the height difference range ensures sufficient protection distance, effectively accommodating fluctuations in conventional wire bonding processes and solder ball size tolerances. At the same time, this height difference avoids abnormal gold wire deformation or stress concentration during wire bonding due to excessive lifting, achieving the best balance between ensuring reliability and process feasibility.

[0019] Furthermore, in the aforementioned positive-mounted LED chip with improved moisture resistance, a raised boss made of GaN material from the epitaxial layer is provided below the electrode wire bonding area.

[0020] As described above, using the epitaxial GaN material of the chip itself to form raised bumps eliminates the need for introducing additional heterogeneous materials. This results in a structure with strong integration with the chip body, good thermal matching, and high stability. This method can be achieved through local masking and etching processes, exhibits good compatibility with existing processes, and has controllable costs.

[0021] Furthermore, in the aforementioned upright LED chip with improved moisture resistance, the sidewalls of the raised boss are covered with an insulating barrier layer.

[0022] As described above, since the raised boss (GaN) is conductive, placing an insulating barrier layer on its sidewalls effectively prevents lateral short circuits between the subsequently formed electrode metal and the boss sidewalls, ensuring the reliability of the device's electrical performance. The insulating barrier layer can be a film layer with insulating properties, such as SiO2, Al2O3, or SiN.

[0023] Furthermore, in the aforementioned positive-mounted LED chip with improved moisture resistance, the P-type electrode and / or the N-type electrode includes an electrode body and a thickened electrode located on the electrode body, with the top surface of the thickened electrode serving as the electrode wire bonding area.

[0024] As described above, this setup provides another core lifting method. Through a stacked design of "electrode body + thickened electrode," metal is locally thickened in designated areas after the passivation layer is formed. The thickened electrode is specifically designed to withstand wire bonding impact and provide a high-quality wire bonding interface, while the underlying passivation layer is completely covered and protected. This design is flexible and particularly suitable for applications requiring extremely thick wire bonding layers.

[0025] Furthermore, in the aforementioned positive-mounted LED chip with improved moisture resistance, the thickened electrode is made of gold and has a thickness of 10,000 Å to 25,000 Å; the total thickness of the electrode body is 3,500 Å to 10,000 Å.

[0026] As described above, gold is an ideal wire bonding material, and gold layers of this thickness range can provide excellent wire bonding performance and sufficient mechanical strength. Thickened electrodes can fully utilize their functions as "sacrificial layers" and "buffer layers," effectively isolating wire bonding stress and protecting the underlying electrode body and passivation layer.

[0027] Furthermore, in the aforementioned upright LED chip with improved moisture resistance, the projection of the thickened electrode in the direction parallel to the substrate falls entirely within the top surface area of ​​the electrode body below it.

[0028] As described above, this arrangement ensures that the thickened electrode is completely positioned above the electrode body, guaranteeing that its edges are well supported by the electrode body and preventing edge warping, peeling, or stress concentration caused by suspension. This feature guarantees the stability and long-term reliability of the thickened electrode structure.

[0029] Furthermore, in the aforementioned upright LED chip with improved moisture resistance, the thickness of the passivation layer is 600 Å to 3000 Å.

[0030] As described above, the aforementioned passivation layer thickness range can effectively block water vapor while avoiding problems such as increased internal stress, easy cracking, and decreased light extraction efficiency caused by excessively thick membranes. Combined with the lifting structure, a dual moisture-resistant optimization of "active protection (structure) + passive protection (membrane)" is achieved.

[0031] Another technical solution of the present invention is: a method for preparing a positive-mounted LED chip with improved moisture resistance, comprising the following steps: forming a raised boss made of GaN material on the LED epitaxial layer; A protruding electrode is formed on the lifting boss, and the electrode wire bonding area of ​​the protruding electrode is located on the lifting boss.

[0032] As described above, the method directly utilizes epitaxial layer materials to form a raised structure through "selective retention" rather than "addition". The process steps are simple and it is seamlessly integrated with standard LED chip manufacturing processes. While significantly improving product reliability, it effectively controls production costs and process complexity, and has high industrial application value.

[0033] Another technical solution of the present invention is: a method for preparing a positive-mounted LED chip with improved moisture resistance, comprising the following steps: An electrode body is formed on the LED epitaxial layer; A passivation layer is formed on the electrode body, and the thickened area on the electrode body is exposed by photolithography and etching processes; A thickened electrode is formed on the exposed thickened region.

[0034] As described above, the thickened electrode not only raises the wire bonding surface, but its excellent metallic properties also effectively buffer the wire bonding pressure, reduce the impact on the underlying structure, and provide an excellent gold-gold bonding interface, further improving the wire bonding quality and reliability.

[0035] Example 1 (Based on a structure with protruding electrodes) This embodiment provides a positively packaged LED chip with improved moisture resistance, such as... Figure 2 The diagram illustrates the structure of a top-mounted LED chip with improved moisture resistance according to this embodiment (based on GaN raised protrusions). The top-mounted LED chip includes a first GaN layer 41, a first insulating barrier layer 42, a first current spreading layer 43, a raised electrode 44, and a first passivation layer 45. From bottom to top, it comprises a sapphire substrate, an N-type GaN layer, a multi-quantum-well light-emitting layer, and a P-type GaN layer. Through photolithography and inductively coupled plasma (ICP) etching processes, a portion of the epitaxial GaN material is selectively retained in the first GaN layer 41 directly below the area designated for forming the bonding regions of the P and N electrodes, forming a raised protrusion. The retained thickness of this protrusion is approximately 13000 Å, adjustable within the range of 8000 Å to 18000 Å. This thickness provides sufficient basis for subsequent electrode raising.

[0036] Since the raised bump itself is conductive GaN, to prevent short circuits between the subsequently formed electrodes and its sidewalls, a first insulating barrier layer 42 of SiO2 with a thickness of approximately 1000 Å (greater than 600 Å) is formed on its sidewalls using chemical vapor deposition (CVD). Next, a first current spreading layer 43 (ITO, approximately 1500 Å thick) is deposited and patterned on the P-type GaN layer. Subsequently, P-type and N-type electrodes (raised electrodes 44) are formed in the region including the top of the raised bump through evaporation and patterning processes. The final electrode layer is titanium (Ti), approximately 50 Å thick; this thin titanium layer significantly enhances the adhesion between the electrodes and the subsequent passivation layer. Finally, a first passivation layer 45 (SiN, approximately 2000 Å thick, ranging from 600-3000 Å) is deposited across the entire chip surface, and windows in the electrode bonding region are opened by photolithography etching.

[0037] Ultimately, the bonding region of the protruding electrode 44 is supported by the solid GaN lifting boss beneath it, creating a height difference H between its surface and the upper surface of the surrounding passivation layer. This H value is controlled to be approximately 2 μm (range 1-3 μm). During bonding, the wire bond ball 1 can only land in the raised metal region of the protruding electrode 44, and the edge of the passivation layer is safely "hidden" below the plane of action of the bond ball, thus receiving effective protection.

[0038] like Figure 3 The diagram shown is a schematic of the fabrication process of the standard-mount LED chip in this embodiment, including the following steps: We provide LED epitaxial wafers with N-type GaN layers, light-emitting layers, and P-type GaN layers grown on them. The process involves coating, exposure, and development to form a photoresist mask that patterns the bonding regions for the protective electrodes.

[0039] Step 1: Perform ICP etching using a mixed gas of Cl2, BCl3, and Ar (flow ratio approximately 3:1:1) at approximately 150W power. This etches away the P-type GaN layer, the light-emitting layer, and even part of the N-type GaN layer in the areas not protected by photoresist. This results in the first GaN layer 41 below the bonding area protected by photoresist and below the electrode wire bonding area. Figure 3 The black part in process one is retained, which raises the position of the electrode wire bonding point to form a lifting boss.

[0040] Step 2: The GaN layer retained below the electrode wire bonding area needs to be covered with the first insulating barrier layer 42 ( Figure 3 The yellow section (which is additional in process two compared to the previous process) is protected to prevent leakage and short circuits after electrode deposition. This insulating barrier layer can be an insulating film such as SiO2, Al2O3, or SiN. The thickness must be at least 600 Å, and can range from 600 Å to 5000 Å. Step 3: Deposit the first current extension layer 43 ( Figure 3 The green section that appears in step three compared to the previous step. Step 4: Perform electrode evaporation to obtain protruding electrode 44 ( Figure 3 The blue section that appears in step four compared to the previous step. The electrode after vapor deposition has GaN underneath, which raises the electrode wire bonding area. This prevents the passivation layer around the electrode from being damaged during the packaging wire bonding process, and can greatly improve the moisture resistance of the LED chip. The last metal layer of the electrode vapor deposition is Ti, and the thickness of Ti can be 5~500Å. This metal can effectively make the passivation layer adhere better to the electrode, thereby improving the moisture resistance of the LED. Step 5: Deposit the first passivation layer 45 ( Figure 3 The orange section in step five (which is the extra part compared to the previous step) is used to protect the LED chip.

[0041] Example 2 (Based on a structure with thickened electrodes) This embodiment provides another type of upright LED chip with improved moisture resistance, such as... Figure 4 As shown, it is a schematic diagram of the structure of a positive-mounted LED chip with improved moisture resistance in this embodiment (based on thickened electrodes). The positive-mounted LED chip includes a second GaN layer 51, a second insulating barrier layer 52, a second current spreading layer 53, an electrode body 54, a second passivation layer 55, and a thickened electrode 56.

[0042] The epitaxial layer structure of the LED chip in this embodiment is similar to that in Embodiment 1. First, a second GaN layer 51, a second insulating barrier layer 52, and a second current spreading layer 53 are formed, and an electrode body 54 is formed by vapor deposition. The electrode body 54 is a multilayer metal stack with a total thickness controlled at approximately 7000 Å (range 3500-10000 Å). Its top layer is a titanium (Ti) layer with a thickness of approximately 100 Å (range 5-500 Å) to enhance adhesion; below it are other metal layers such as a gold (Au) layer.

[0043] Next, a second passivation layer 55 (Al2O3, approximately 1500 Å thick) is deposited on the entire chip surface, and a precise window is opened only in the bonding area where wire bonding is required, exposing the underlying electrode body 54 through photolithography etching.

[0044] On the exposed bonding region, a very thick layer of thickened electrode 56 is selectively deposited by vapor deposition. This layer is made of pure gold (Au) and is approximately 20,000 Å thick (range 10,000-25,000 Å), significantly thicker than the electrode body 54. During vapor deposition, the mask must be strictly controlled to ensure that the boundary of the thickened electrode 56 falls entirely within the top surface of the electrode body 54, and its area is approximately 90% or less of the corresponding area on the electrode body 54, without covering the surrounding passivation layer.

[0045] Finally, the thickened electrode 56 raises the bonding surface high, forming the required height difference H (approximately 2.5 μm). Wire bonding balls are then bonded to this thick gold layer. The excellent ductility of the thick gold layer effectively absorbs wire bonding stress, protecting the underlying electrode body 54 and the second passivation layer 55. The second passivation layer 55 is sandwiched in between and protected by the upper and lower metal layers.

[0046] Please see Figure 5 The method for manufacturing a positive-mounted LED chip with improved moisture resistance in this embodiment includes the following steps: Step 1: Using ICP etching, expose the second GaN layer 51. Figure 5 (The black part in process one) Step 2: Deposition of the second insulating barrier layer 52 ( Figure 5 The yellow section is the additional part of process two compared to the previous process. Step 3: Deposit the second current extension layer 53 ( Figure 5 The green section that appears in step three compared to the previous step. Process 4, Evaporation of Electrode Body 54 ( Figure 5(Note: "electrode layer 1" in the text). In the structure of the electrode body 54, the last metal layer is Ti, and the thickness of Ti can be 5~500 Å. The second to last metal layer is Au. This Au layer is not used as a wire bonding layer, so its thickness can be 100~5000 Å. The total thickness can be 3500~10000 Å. Step 5: Deposit the second passivation layer 55 to protect the LED chip ( Figure 5 The orange section in step five that is additional compared to the previous step); Process 6: Evaporation to thicken electrode 56 ( Figure 5 (Note: This is referred to as "electrode layer 2"). The thickened electrode 56 is made of Au, and the thickness of Au is 10,000~25,000 Å, and the thickness of the thickened electrode 56 is greater than the thickness of the electrode body 54.

[0047] In summary, the beneficial effects of the improved moisture resistance LED chip described in this invention are as follows: It clearly identifies and solves the specific technical problem of passivation layer damage during the wire bonding process, providing two specific technical means: "GaN raised bumps" and "thickened electrodes." Neither of these structures has been disclosed or inspired by existing technologies. Furthermore, this invention has conducted extensive experiments and optimizations to limit key parameters such as height difference (1-3 μm), GaN bump thickness, insulating layer thickness, electrode and wire bonding layer thickness and their proportional relationship, and passivation layer thickness. These specific numerical ranges are necessary conditions for achieving the optimal effect of this solution and are not common knowledge or conventional choices in the field. Mechanistically, it completely blocks the path to passivation layer damage, thereby significantly improving the chip's lifespan and reliability in high-temperature and high-humidity environments, meeting the stringent quality requirements of the high-end LED display market.

[0048] 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 positive-mounted LED chip with improved moisture resistance, comprising a substrate, an epitaxial layer, a P-type electrode, an N-type electrode, and a passivation layer, characterized in that, The P-type electrode and the N-type electrode each have an electrode bonding area for wire bonding; the passivation layer covers the portion of the chip surface other than the electrode bonding area; the height of the electrode bonding area in the direction perpendicular to the substrate is higher than the upper surface of the passivation layer surrounding it.

2. The positive-mounted LED chip with improved moisture resistance according to claim 1, characterized in that, The height difference between the electrode wire bonding area and the upper surface of the passivation layer is 1 μm to 3 μm.

3. The positive-mounted LED chip with improved moisture resistance according to claim 1, characterized in that, Below the electrode wire bonding area, there is a raised boss made of GaN material from the epitaxial layer.

4. The positive-mounted LED chip with improved moisture resistance according to claim 3, characterized in that, The sidewalls of the raised boss are covered with an insulating barrier layer.

5. The positive-mounted LED chip with improved moisture resistance according to claim 1, characterized in that, The P-type electrode and / or the N-type electrode includes an electrode body and a thickened electrode located on the electrode body, wherein the top surface of the thickened electrode serves as the electrode wire bonding area.

6. The positive-mounted LED chip with improved moisture resistance according to claim 5, characterized in that, The thickened electrode is made of gold and has a thickness of 10,000 Å to 25,000 Å; the total thickness of the electrode body is 3,500 Å to 10,000 Å.

7. The positive-mounted LED chip with improved moisture resistance according to any one of claims 5 to 6, characterized in that, The projection of the thickened electrode in the direction parallel to the substrate falls entirely within the top surface area of ​​the electrode body below it.

8. The positive-mounted LED chip with improved moisture resistance according to claim 1, characterized in that, The thickness of the passivation layer is 600 Å to 3000 Å.

9. A method for preparing a positive-mounted LED chip with improved moisture resistance as described in claim 3 or 4, characterized in that, Includes the following steps: A raised protrusion made of GaN material is formed on the LED epitaxial layer; A protruding electrode is formed on the lifting boss, and the electrode wire bonding area of ​​the protruding electrode is located on the lifting boss.

10. A method for preparing a positive-mounted LED chip with improved moisture resistance as described in any one of claims 5 to 6, characterized in that, Includes the following steps: An electrode body is formed on the LED epitaxial layer; A passivation layer is formed on the electrode body, and the thickened area of ​​the electrode body is exposed by photolithography and etching processes; A thickened electrode is formed on the exposed thickened region.

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