Flip-chip LED chip and method for manufacturing the same

Abstract

The application relates to the technical field of optoelectronic manufacturing, and particularly discloses a flip LED chip and a preparation method thereof. The flip LED chip comprises a substrate, an epitaxial layer, an insulating protective layer, a reflection layer, a first insulating layer, a P-type metal conductive layer, an N-type metal conductive layer, a second insulating layer, a P-type pad layer and an N-type pad layer which are stacked on the substrate; the reflection layer is arranged above the P-type semiconductor layer; the reflection layer comprises an electromigration-resistant part, a reflection part and a protective part; the electromigration-resistant part and the reflection part are arranged adjacently, the electromigration-resistant part is arranged close to the N-type conductive step, and the protective part covers the electromigration-resistant part and the reflection part; the electromigration-resistant part comprises an electromigration-resistant main part and a first oxidation-resistant part which are stacked in sequence; each group of metal pairs comprises an Ag metal layer and an AgNi alloy layer which are stacked in sequence; and the first oxidation-resistant part is made of one or more of Ni, Au, Ti and Cr. By implementing the application, the reliability can be improved.

Description

Technical Field

[0001] This invention relates to the field of optoelectronic manufacturing technology, and in particular to a flip-chip LED and its fabrication method. Background Technology

[0002] Flip-chip LEDs are widely used due to their advantages such as back-emitting light, good solderability, high thrust, and high reliability. Large-size flip-chip LEDs often use Ag metal as the reflective layer, which has higher luminous efficiency and better heat dissipation compared to traditional DBR reflective layers. However, Ag metal is prone to migration, especially in areas with congested current, and poor control can easily affect the reliability of the flip-chip LED. Summary of the Invention

[0003] The technical problem to be solved by the present invention is to provide a flip-chip LED with high reliability.

[0004] Accordingly, the present invention also provides a method for preparing the above-mentioned flip-chip LED.

[0005] To solve the above-mentioned technical problems, the present invention provides a flip-chip LED, comprising: a substrate, an epitaxial layer, an insulating protective layer, a reflective layer, a first insulating layer, a P-type metal conductive layer, an N-type metal conductive layer, a second insulating layer, a P-type pad layer and an N-type pad layer stacked on the substrate;

[0006] The epitaxial layer comprises an N-type semiconductor layer, a light-emitting layer, and a P-type semiconductor layer sequentially stacked on the substrate. A light-emitting structure, an isolation trench, and an N-type conductive step are formed on the epitaxial layer. The N-type conductive step is disposed on one side of the light-emitting structure and exposes the N-type semiconductor layer. An insulating protective layer covers the N-type conductive step, the isolation trench, and the sidewall of the light-emitting structure. The first insulating layer covers the insulating protective layer and the reflective layer.

[0007] The reflective layer is disposed above the P-type semiconductor layer; the reflective layer includes an anti-electromigration portion, a reflective portion, and a protective portion; the anti-electromigration portion and the reflective portion are disposed adjacent to each other, the anti-electromigration portion is disposed close to the N-type conductive step, and the protective portion covers the anti-electromigration portion and the reflective portion; the anti-electromigration portion includes an anti-electromigration body and a first anti-oxidation portion stacked sequentially; the anti-electromigration body is composed of multiple metal pairs, each metal pair including an Ag metal layer and an AgNi alloy layer stacked sequentially; the first anti-oxidation portion is made of one or more of Ni, Au, Ti, and Cr.

[0008] As an improvement to the above technical solution, in the anti-electromigration unit, the metal pair near the P-type semiconductor layer is the first group of metal pairs, the metal pair near the first insulating layer is the last group of metal pairs, and the rest are intermediate metal pairs; the thickness of the Ag metal layer in the first group of metal pairs is less than the thickness of the Ag metal layer in the intermediate metal pairs and less than the thickness of the Ag metal layer in the last group of metal pairs, and the thickness of the AgNi alloy layer in the first group of metal pairs is equal to the thickness of the AgNi alloy layer in the intermediate metal pairs and less than the thickness of the AgNi alloy layer in the last group of metal pairs.

[0009] As an improvement to the above technical solution, the thickness of the AgNi alloy layer in the last metal pair is 100 to 200 times the thickness of the AgNi alloy layer in the first metal pair.

[0010] The thickness of the Ag metal layer in the last metal pair is 20 to 50 times the thickness of the Ag metal layer in the first metal pair.

[0011] As an improvement to the above technical solution, the anti-electromigration head includes 3 to 5 metal pairs;

[0012] In the first metal pair, the thickness of the Ag metal layer is 50 Å to 100 Å, and the thickness of the AgNi alloy layer is 10 Å to 15 Å.

[0013] The thickness of the Ag metal layer in the intermediate metal pair is 200 Å to 500 Å, and the thickness of the AgNi alloy layer is 10 Å to 15 Å; the thickness of the Ag metal layer and the thickness of the AgNi alloy layer are the same in different intermediate metal pairs; the thickness of the Ag metal layer in the last metal pair is 1000 Å to 2000 Å, and the thickness of the AgNi alloy layer is 1500 Å to 2000 Å.

[0014] The first antioxidant portion is made of Ti and has a thickness of 300 Å to 500 Å.

[0015] As an improvement to the above technical solution, the reflective part includes an Ag reflective layer and a second antioxidant part stacked sequentially; the thickness of the Ag reflective layer is 1200Å~2000Å; and the thickness of the second antioxidant part is 300Å~500Å.

[0016] As an improvement to the above technical solution, the protective part includes alternating layers of Ni metal and TiW alloy, with a cycle number of 3 to 5; the thickness of the Ni metal layer is 1000 Å to 2000 Å, and the thickness of the TiW alloy layer is 3000 Å to 5000 Å.

[0017] As an improvement to the above technical solution, the distance between the sidewall of the anti-electromigration part away from the N-type conductive step and the sidewall of the light-emitting structure is 20μm~40μm;

[0018] The distance between the sidewall of the anti-electromigration portion near the N-type conductive step and the sidewall of the light-emitting structure is 5μm~7μm.

[0019] As an improvement to the above technical solution, the anti-electromigration portion and the reflective portion at least partially overlap, with an overlap width of 3μm to 5μm, and in the overlap region, the reflective portion is located above the anti-electromigration portion.

[0020] As an improvement to the above technical solution, the insulating protective layer is made of SiO2 and has a thickness of ≥5000Å;

[0021] The first insulating layer comprises an Al2O3 layer and a SiO2 layer stacked sequentially, wherein the thickness of the Al2O3 layer is 600 Å to 1200 Å and the thickness of the SiO2 layer is 8000 Å to 10000 Å.

[0022] Accordingly, the present invention also discloses a method for preparing a flip-chip LED, which includes:

[0023] (1) An epitaxial layer is formed on a substrate, the epitaxial layer comprising an N-type semiconductor layer, a light-emitting layer and a P-type semiconductor layer sequentially stacked on the substrate;

[0024] (2) Etching forms multiple N-type conductive steps and isolation trenches that expose the N-type semiconductor layer, forming multiple light-emitting structures disposed on the substrate;

[0025] (3) An insulating protective layer is formed on the N-type conductive step, the isolation groove and the sidewall of the light-emitting structure;

[0026] (4) An anti-electromigration portion is formed on the P-type semiconductor layer at the top of the light-emitting structure;

[0027] (5) A reflective portion is formed on the P-type semiconductor layer at the top of the light-emitting structure; the reflective portion is disposed adjacent to the anti-electromigration portion;

[0028] (6) A protective portion is formed on the anti-electromigration portion and the reflective portion to obtain a first intermediate;

[0029] (7) A first insulating layer is formed on the first intermediate body, and a first through hole is formed to expose the protective part and a second through hole is formed to expose the N-type conductive step;

[0030] (8) A P-type metal conductive layer and an N-type metal conductive layer are formed on the first insulating layer to obtain a second intermediate;

[0031] (9) A second insulating layer is formed on the second intermediate, and a third through-hole and a fourth through-hole are formed to expose the P-type metal conductive layer and the N-type metal conductive layer, respectively.

[0032] (10) A P-type pad layer and an N-type pad layer are formed on the second insulating layer.

[0033] Implementing this invention has the following beneficial effects:

[0034] In one embodiment of the present invention, a flip-chip LED includes: a substrate, an epitaxial layer, an insulating protective layer, a reflective layer, a first insulating layer, a P-type conductive metal layer, an N-type conductive metal layer, a second insulating layer, a P-type pad layer, and an N-type pad layer stacked on the substrate; wherein, the reflective layer is disposed above the P-type semiconductor layer; the reflective layer includes an anti-electromigration portion, a reflective portion, and a protective portion; the anti-electromigration portion and the reflective portion are disposed adjacent to each other, the anti-electromigration portion is disposed near the N-type conductive step, and the protective portion covers the anti-electromigration portion and the reflective portion; the anti-electromigration portion includes an anti-electromigration body and a first anti-oxidation portion stacked sequentially; the anti-electromigration body is composed of multiple metal pairs, each metal pair including an Ag metal layer and an AgNi alloy layer stacked sequentially; the first anti-oxidation portion is made of one or more of Ni, Au, Ti, and Cr. The above-mentioned anti-electromigration portion can effectively prevent Ag migration and improve the reliability of the flip-chip LED. Attached Figure Description

[0035] Figure 1 This is a schematic diagram of the structure of a flip-chip LED in one embodiment of the present invention;

[0036] Figure 2 This is a schematic diagram of the anti-electromigration part in one embodiment of the present invention;

[0037] Figure 3 This is a schematic diagram of the substrate structure after step (3) in one embodiment of the present invention;

[0038] Figure 4 This is a schematic diagram of the structure of the first intermediate after step (7) in one embodiment of the present invention;

[0039] Figure 5 This is a schematic diagram of the structure of the second intermediate after step (9) in one embodiment of the present invention;

[0040] In the diagram, 100 is the substrate, 210 is the N-type semiconductor layer, 220 is the light-emitting layer, 230 is the P-type semiconductor layer, 240 is the N-type conductive step, 250 is the isolation trench, 260 is the light-emitting structure, 300 is the transparent conductive layer, 400 is the insulating protective layer, 500 is the reflective layer, 510 is the anti-electromigration section, 511 is the anti-electromigration body, 5111 is the first metal pair, 5112 is the intermediate metal pair, and 5113 is the last metal pair. 511a is an Ag metal layer, 511b is an AgNi alloy layer, 512 is a first anti-oxidation layer, 520 is a reflective layer, 530 is a protective layer, 600 is a first insulating layer, 610 is a first through-hole, 620 is a second through-hole, 710 is a P-type conductive metal layer, 720 is an N-type conductive metal layer, 800 is a second insulating layer, 810 is a third through-hole, 820 is a fourth through-hole, 910 is a P-type pad layer, and 920 is an N-type pad layer. Detailed Implementation

[0041] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings. It is hereby declared that the directional terms such as up, down, left, right, front, back, inside, and outside used in this text are based solely on the accompanying drawings and are not intended to specifically limit the invention.

[0042] Please see Figure 1 , Figure 2 An embodiment of the present invention provides a flip-chip LED, which includes a substrate 100, an epitaxial layer, an insulating protective layer 400, a reflective layer 500, a first insulating layer 600, a P-type metal conductive layer 710, an N-type metal conductive layer 720, a second insulating layer 800, a P-type pad layer 910 and an N-type pad layer 920.

[0043] In the vertical direction (i.e., the thickness direction of the substrate 100), the epitaxial layer includes an N-type semiconductor layer 210, a light-emitting layer 220, and a P-type semiconductor layer 230 sequentially stacked on the substrate 100. A light-emitting structure 260, an isolation trench 250, and an N-type conductive step 240 are formed on the epitaxial layer. The isolation trench 250 is used to separate the substrate 100 and the epitaxial layer to form multiple flip-chip LEDs. The N-type conductive step 240 is located on one side of the light-emitting structure 260, exposing the N-type semiconductor layer 210, and is used to form an electrical connection with the N-type metal conductive layer 720 and the N-type pad layer 920. The light-emitting structure 260 emits light, and its top is a P-type semiconductor layer 230, which is used to form an electrical connection with the P-type metal conductive layer 710 and the P-type pad layer 910.

[0044] Specifically, the substrate 100 is a sapphire substrate, a silicon substrate, or a SiC substrate, but is not limited to these. The N-type semiconductor layer 210 can be an N-type GaAs layer, an N-type GaN layer, or an N-type AlGaN layer, but is not limited to these. The light-emitting layer 220 can be an InGaN-GaN type multiple quantum well layer, an InGaN-AlGaN type multiple quantum well layer, an AlGaN-AlGaN type multiple quantum well layer, or an AlGaInP-AlGaInP type multiple quantum well layer, but is not limited to these. The P-type semiconductor layer 230 can be a P-type GaN layer, a P-type AlGaInP layer, or a P-type AlGaN layer, but is not limited to these. Preferably, in some embodiments, the substrate 100 is a sapphire substrate, the N-type semiconductor layer 210 is an N-type GaN layer, the light-emitting layer 220 is an InGaN-GaN type multiple quantum well layer, and the P-type semiconductor layer 230 is a P-type GaN layer.

[0045] The insulating protective layer 400 covers the N-type conductive step 240, the isolation groove 250, and the sidewall of the light-emitting structure 260. That is, the surfaces exposed during the etching process to form the light-emitting structure 260, the isolation groove 250, and the N-type conductive step 240 are all covered with the insulating protective layer 400 to passivate the dangling bonds formed by etching and improve the reliability of the flip-chip LED.

[0046] Specifically, the insulating protective layer 400 is composed of SiO2 and SiN. x It may be made of Al2O3, but is not limited to this. The thickness of the insulating protective layer 400 is ≥5000 Å. Preferably, in some embodiments, the insulating protective layer 400 is made of SiO2 and has a thickness of 5000 Å to 8000 Å.

[0047] Specifically, the reflective layer 500 is disposed above the P-type semiconductor layer 230 on top of the light-emitting structure 260, and is used to reflect the light emitted by the light-emitting layer 220 so that the light is emitted from the substrate 100 side. The reflective layer 500 includes an anti-electromigration portion 510, a reflective portion 520, and a protective portion 530. The anti-electromigration portion 510 and the reflective portion 520 are disposed adjacent to each other, and the protective portion 530 covers the anti-electromigration portion 510 and the reflective portion 520. The anti-electromigration portion 510 is disposed near the N-type conductive step 240. The anti-electromigration portion 510 includes an anti-electromigration body 511 and a first anti-oxidation portion 512 stacked sequentially. The anti-electromigration body 511 is composed of multiple metal pairs, each metal pair including an Ag metal layer 511a and an AgNi alloy layer 511b stacked sequentially. The first anti-oxidation portion 512 is made of one or more of Ni, Au, Ti, and Cr. In this technical solution, the reflective layer 500 has an anti-electromigration body 511 and a first anti-oxidation part 512 formed by alternating Ag metal layer 511a and AgNi alloy layer 511b on the side near the N-type conductive step 240. This can effectively prevent Ag migration, improve the reliability of flip-chip LEDs, and at the same time ensure that the reflective layer 500 has a high reflectivity and does not reduce the light extraction efficiency.

[0048] Specifically, the reflective portion 520 is a stacked structure formed by one or more of Ag, Al, or Au reflective layers, but is not limited thereto. The thickness of the reflective portion 520 is 1500 Å to 3000 Å. It should be noted that the reflective portion 520 is disposed adjacent to the anti-electromigration portion 510 and covers the top surface of the light-emitting structure 260 to completely reflect the light emitted by the light-emitting structure 260.

[0049] Preferably, in some embodiments, the reflective portion 520 includes a sequentially stacked Ag reflective layer and a second anti-oxidation portion, wherein the thickness of the Ag reflective layer is 1200 Å to 2000 Å, and the second anti-oxidation portion is made of one or more of Ni, Au, Ti, and Cr, with a thickness of 300 Å to 500 Å. The second anti-oxidation portion can effectively prevent the reflective portion 520 from being oxidized after the vapor deposition is completed and the first insulating layer 600 is formed, further improving the reliability of the flip-chip LED. More preferably, the thickness of the Ag reflective layer is 1500 Å to 2000 Å, and the second anti-oxidation portion is made of Ti with a thickness of 300 Å to 400 Å.

[0050] Specifically, the protective portion 530 is a stacked structure formed by one or more of Ni metal layers, TiW alloy layers, and Pt / Pd alloy layers, but is not limited thereto. The thickness of the protective portion 530 is 10,000 Å to 40,000 Å. The protective portion 530 completely covers the reflective portion 520 and the anti-electromigration portion 510 to form complete protection for both.

[0051] Preferably, in some embodiments, the protective layer 530 includes alternating layers of Ni metal and TiW alloy, with a cycle number of 3 to 5; in each cycle, the thickness of the Ni metal layer is 1000 Å to 2000 Å, and the thickness of the TiW alloy layer is 3000 Å to 5000 Å. This protective layer composition further enhances reliability. More preferably, the thickness of the Ni metal layer is 1500 Å to 2000 Å, and the thickness of the TiW alloy layer is 4000 Å to 5000 Å.

[0052] Specifically, the first insulating layer 600 covers the insulating protective layer 400 and the reflective layer 500, and a first through-hole 610 exposing the reflective layer 500 and a second through-hole 620 exposing the N-type conductive step 240 are formed on the first insulating layer 600. Specifically, the first insulating layer 600 is a SiO2 layer or a SiN layer. x The first insulating layer 600 is a stacked structure composed of one or more of the following: an Al2O3 layer, a SiO2 layer, etc., but is not limited thereto. The thickness of the first insulating layer 600 is 6000 Å to 12000 Å. Preferably, in some embodiments, the first insulating layer 600 includes sequentially stacked Al2O3 layers and SiO2 layers, wherein the thickness of the Al2O3 layer is 600 Å to 1200 Å; and the thickness of the SiO2 layer is 8000 Å to 10000 Å. This first insulating layer 600 can better improve the luminous brightness.

[0053] Specifically, both the P-type conductive metal layer 710 and the N-type conductive metal layer 720 are disposed above the first insulating layer 600. The P-type conductive metal layer 710 contacts the reflective layer 500 through the first through-hole 610, and the N-type conductive metal layer 720 contacts the N-type conductive step 240 through the second through-hole 620. Both the P-type conductive metal layer 710 and the N-type conductive metal layer 720 are common single-layer or multi-layer metal structures in the art, for example, they can be made of one or more of Cr, Al, Ti, Pt, Ni, Au, Cu, and Ag, but are not limited thereto. Preferably, in some embodiments, both the P-type conductive metal layer 710 and the N-type conductive metal layer 720 include sequentially stacked Al layers, Ti layers, Al layers, Ti layers, Al layers, Ti layers, Ni layers, Au layers, and Ti layers. The thicknesses of each layer are: 500Å~1000Å, 500Å~1000Å, 500Å~1000Å, 500Å~1000Å, 500Å~1000Å, 500Å~1000Å, 1000Å~2000Å, 5000Å~10000Å and 1000Å~2000Å.

[0054] Specifically, the second insulating layer 800 covers the P-type metal conductive layer 710, the N-type metal conductive layer 720, and the first insulating layer 600. A third through-hole 810 exposing the P-type metal conductive layer 710 and a fourth through-hole 820 exposing the N-type metal conductive layer 720 are formed on the second insulating layer 800. Specifically, the second insulating layer 800 is a SiO2 layer or a SiN layer. x The structure is a multilayer structure consisting of one or more of the following: an Al2O3 layer, but is not limited thereto. The thickness of the second insulating layer 800 is 5000 Å to 12000 Å.

[0055] Specifically, both the P-type pad layer 910 and the N-type pad layer 920 are disposed above the second insulating layer 800. The P-type pad layer 910 contacts the P-type metal conductive layer 710 through a third via 810, and the N-type pad layer 920 contacts the N-type metal conductive layer 720 through a fourth via 820. Specifically, the P-type pad layer 910 and the N-type pad layer 920 are common metal pad structures in the art, such as a stacked structure composed of one or more of Ti, Sn, Ni, and Au, but are not limited thereto. Preferably, both the P-type pad layer 910 and the N-type pad layer 920 include sequentially stacked Ti, Ni, and Au layers with thicknesses of 1000 Å~2000 Å, 10000 Å~15000 Å, and 200 Å~2000 Å, respectively.

[0056] Preferably, in some embodiments, the light-emitting structure 260 further includes a transparent conductive layer 300 disposed above the p-type semiconductor layer 230. This layer may be an ITO layer, an IZO layer, or an AZO layer, but is not limited to these. The projection of the transparent conductive layer 300 onto the substrate 100 is located inside the projection of the p-type semiconductor layer 230 onto the substrate 100, meaning there is a predetermined distance between the sidewalls of the transparent conductive layer 300 and the sidewalls of the light-emitting structure 260.

[0057] Preferably, in some embodiments, in the anti-electromigration section 511, the metal pairs near the P-type semiconductor layer 230 are the first group of metal pairs 5111, the metal pairs near the first insulating layer 600 are the last group of metal pairs 5113, and the rest are intermediate metal pairs 5112; the thickness of the Ag metal layer 511a in the first group of metal pairs 5111 is less than the thickness of the Ag metal layer 511a in the intermediate metal pairs 5112 and less than the thickness of the Ag metal layer 511a in the last group of metal pairs 5113, and the thickness of the AgNi alloy layer 511b in the first group of metal pairs 5111 is equal to the thickness of the AgNi alloy layer 511b in the intermediate metal pairs 5112 and less than the thickness of the AgNi alloy layer 511b in the last group of metal pairs 5113. Based on this arrangement, the reflectivity of the anti-electromigration section 510 can be effectively improved, thereby increasing the light extraction efficiency of the flip-chip LED.

[0058] Specifically, in some embodiments, the thickness of the Ag metal layer 511a in the last metal pair 5113 is 20 to 50 times the thickness of the Ag metal layer 511a in the first metal pair 5111, exemplarily 22, 25, 30, 35, 40, or 45 times, but not limited thereto. Preferably, the thickness of the Ag metal layer 511a in the last metal pair 5113 is 30 to 40 times the thickness of the Ag metal layer 511a in the first metal pair 5111.

[0059] Specifically, in some embodiments, the thickness of the AgNi alloy layer 511b in the last metal pair 5113 is 100 to 200 times the thickness of the AgNi alloy layer 511b in the first metal pair 5111, exemplarily 115, 130, 145, 160, 175, or 190 times, but not limited thereto. Preferably, it is 120 to 180 times.

[0060] More specifically, the anti-electromigration head 511 includes 3 to 5 metal pairs, preferably 4 to 5 metal pairs.

[0061] More specifically, the thickness of the Ag metal layer 511a in the first metal pair 5111 is 50 Å to 100 Å, exemplarily 60 Å, 70 Å, 80 Å or 90 Å, but not limited thereto. Preferably it is 60 Å to 100 Å.

[0062] More specifically, the thickness of the AgNi alloy layer 511b in the first metal pair 5111 is 10 Å to 15 Å, exemplary of which are 11 Å, 11.5 Å, 12 Å, 12.5 Å, 13 Å, 14 Å or 14.5 Å, but not limited thereto. Preferably, it is 12 Å to 15 Å.

[0063] More specifically, the thickness of the Ag metal layer 511a in the intermediate metal pair 5112 is 200 Å to 500 Å, exemplary of 250 Å, 300 Å, 350 Å, 400 Å or 450 Å, but not limited thereto. Preferably it is 250 Å to 400 Å.

[0064] Preferably, in some embodiments, when the anti-electromigration unit 511 includes a plurality of intermediate metal pairs 5112, the Ag metal layer 511a in different intermediate metal pairs 5112 has the same thickness, and the AgNi alloy layer 511b has the same thickness.

[0065] More specifically, the thickness of the Ag metal layer 511a in the last metal pair 5113 is 1000 Å to 2000 Å, exemplary of 1100 Å, 1300 Å, 1500 Å, 1700 Å or 1900 Å, but not limited thereto. Preferably it is 1500 Å to 2000 Å.

[0066] More specifically, the thickness of the AgNi alloy layer 511b in the last metal pair 5113 is 1500 Å to 2000 Å, exemplary of 1550 Å, 1600 Å, 1700 Å, 1850 Å, 1900 Å, or 1950 Å, but not limited thereto. Preferably, it is 1600 Å to 2000 Å.

[0067] Preferably, in some embodiments, the first antioxidant portion 512 is made of Ti and has a thickness of 300 Å to 500 Å, exemplarily 340 Å, 380 Å, 420 Å, 460 Å or 480 Å, but is not limited thereto.

[0068] Preferably, in some embodiments, the distance between the sidewall of the anti-electromigration portion 510 away from the N-type conductive step 240 and the sidewall of the light-emitting structure 260 (i.e., Figure 1 The distance L is 20μm to 40μm. When L < 20μm, the anti-migration capability decreases significantly; while when L > 40μm, the reliability growth trend tends to level off. Preferably, L is 30μm to 40μm. It should be noted that, due to the etching process, the sidewalls of the anti-migration portion 510 and the sidewalls of the light-emitting structure 260 are both inclined, and L refers to the distance between the bottoms of the inclined sidewalls. In addition, when the light-emitting structure 260 includes a transparent conductive layer 300, the reflective layer 500 is disposed above the transparent conductive layer 300, the insulating protective layer 400 covers the sidewalls of the transparent conductive layer 300, and L is the distance between the bottom of the inclined sidewall of the anti-migration portion 510 and the bottom of the inclined sidewall of the transparent conductive layer 300.

[0069] Preferably, in some embodiments, the distance between the sidewall of the anti-electromigration portion 510 near the N-type conductive step 240 and the sidewall of the light-emitting structure 260 is ( Figure 1 L1 is 5μm to 7μm, exemplarily 5.4μm, 5.8μm, 6.2μm, 6.6μm or 6.8μm, but not limited thereto. Preferably it is 5μm to 6μm, as this range better prevents Ag migration. It should be noted that when the light-emitting structure 260 includes a transparent conductive layer 300, L1 is the distance between the sidewall of the anti-electromigration portion 510 and the sidewall of the transparent conductive layer 300.

[0070] Preferably, in some embodiments, the anti-electromigration portion 510 and the reflective portion 520 at least partially overlap, the overlap width being ( Figure 1 The reflective portion 520 (L2) is 3μm to 5μm in diameter, and in the overlapping region, the reflective portion 520 is located above the anti-electromigration portion 510. Based on the above structure, the anti-electromigration capability can be further improved.

[0071] Accordingly, the present invention also discloses a method for preparing a flip-chip LED, which specifically includes the following steps:

[0072] (1) Forming an epitaxial layer on a substrate;

[0073] Specifically, an epitaxial layer is obtained by sequentially forming an N-type semiconductor layer 210, a light-emitting layer 220, and a P-type semiconductor layer 230 on a substrate 100 using methods such as MOCVD, MBE, and PVD.

[0074] (2) Etching forms multiple N-type conductive steps and isolation trenches that expose N-type semiconductor layers, forming multiple light-emitting structures on the substrate;

[0075] Specifically, a mask (photoresist layer or SiO2 layer) can be formed on the epitaxial layer first, and then the P-type semiconductor layer 230, the light-emitting layer 220 and the N-type semiconductor layer 210 of a preset thickness in the preset area can be removed by wet etching or dry etching to form an N-type conductive step 240, an isolation trench 250 and a light-emitting structure 260, but it is not limited to this.

[0076] Preferably, in some embodiments, after etching to form the N-type conductive step 240 and the isolation trench 250, a transparent conductive layer 300 is formed on the surface of the N-type conductive step 240, the isolation trench 250 and the light-emitting structure 260. Then, photolithography is used to remove the transparent conductive layer 300 on the sidewall of the N-type conductive step 240, the isolation trench 250 and the light-emitting structure 260, leaving only the transparent conductive layer 300 on the P-type semiconductor layer 230.

[0077] (3) An insulating protective layer is formed on the sidewalls of the N-type conductive step, the isolation groove, and the light-emitting structure;

[0078] Specifically, in some implementations, an insulating protective layer 400 is formed by PECVD, and then the insulating protective layer 400 above the P-type semiconductor layer 230 / transparent conductive layer 300 is removed by photolithography etching.

[0079] (4) An anti-electromigration portion is formed on the P-type semiconductor layer at the top of the light-emitting structure;

[0080] Specifically, the anti-electromigration part 510 can be obtained by forming a metal stack through electron beam evaporation or PVD processes, but is not limited to these methods.

[0081] Preferably, in some embodiments, a photoresist layer is first formed using a negative photoresist, then the photoresist layer on top of the light-emitting structure 260 is removed by exposure and development, then multiple metals are sequentially deposited by electron beam evaporation to form an anti-electromigration part 510, then the metals located on the photoresist layer are removed by blue film stripping, and finally the photoresist layer is removed.

[0082] (5) A reflective portion is formed on the P-type semiconductor layer at the top of the light-emitting structure;

[0083] Specifically, the reflective part 520 can be obtained by forming a metal stack through electron beam evaporation or PVD processes, but is not limited to these methods.

[0084] Preferably, in some embodiments, a photoresist layer is first formed using a negative photoresist, and then the photoresist layer on the P-type semiconductor layer 230 at the top of the light-emitting structure 260 and the photoresist layer of a predetermined width on the anti-electromigration portion 510 are removed by exposure and development. Then, multiple metals are sequentially deposited by electron beam evaporation to form the reflective portion 520. Then, the metals located on the photoresist layer are removed by blue film stripping process, and finally the photoresist layer is removed.

[0085] (6) A protective part is formed on the anti-electromigration part and the reflective part to obtain the first intermediate;

[0086] Specifically, the protective layer 530 can be obtained by forming a metal stack through electron beam evaporation or PVD processes, but is not limited to these methods.

[0087] Preferably, in some embodiments, a photoresist layer is first formed using a negative photoresist, and then the photoresist layer on the reflective part 520 and the anti-electromigration part 510 is removed by exposure and development. Then, a variety of metals are sequentially deposited by electron beam evaporation to form a protective part 530. Then, the metals located on the photoresist layer are removed by blue film stripping process, and finally the photoresist layer is removed.

[0088] (7) A first insulating layer is formed on the first intermediate body, and a first through hole for exposing the protective part and a second through hole for exposing the N-type conductive step are formed;

[0089] Specifically, the first insulating layer 600 can be formed by processes such as ALD, PECVD, and LPCVD, and then etched to form the first through hole 610 and the second through hole 620, but it is not limited to this.

[0090] Preferably, in some embodiments, an Al2O3 layer is first formed on the first intermediate by ALD, and then a SiO2 layer is formed on the Al2O3 layer by PECVD to obtain the first insulating layer 600. Then, a photoresist layer is formed on the first insulating layer 600, and the first insulating layer 600 in a predetermined area is exposed by exposure and development. Then, the first via 610 and the second via 620 are formed by etching, and then the photoresist layer is removed.

[0091] (8) A P-type metal conductive layer and an N-type metal conductive layer are formed on the first insulating layer to obtain a second intermediate;

[0092] Specifically, metal stacks can be formed through electron beam evaporation or PVD processes to obtain a P-type metal conductive layer 710 and an N-type metal conductive layer 720, but are not limited to these methods.

[0093] Preferably, in some embodiments, a photoresist layer is first formed in the first insulating layer 600, the first through-hole 610, and the second through-hole 620. Then, the photoresist layer in the preset area is removed by exposure and development. Then, a metal stack is deposited by electron beam evaporation to form a P-type metal conductive layer 710 and an N-type metal conductive layer 720. Then, the metal on the photoresist layer is removed by blue film stripping. Finally, the photoresist is removed to obtain the second intermediate.

[0094] (9) A second insulating layer is formed on the second intermediate, and a third through-hole exposing the P-type metal conductive layer and a fourth through-hole exposing the N-type metal conductive layer are formed;

[0095] Specifically, the second insulating layer 800 can be formed by processes such as ALD, PECVD, and LPCVD, and then the third through-hole 810 and the fourth through-hole 820 can be etched, but it is not limited to these.

[0096] Preferably, in some embodiments, a SiO2 layer is first formed on the second intermediate by PECVD as the second insulating layer 800. Then, a photoresist layer is formed on the second insulating layer 800, and the second insulating layer 800 in a predetermined area is exposed by exposure and development. Then, the third via 810 and the fourth via 820 are etched, and then the photoresist layer is removed.

[0097] (10) A P-type pad layer and an N-type pad layer are formed on the second insulating layer.

[0098] Specifically, metal layers can be formed through electron beam evaporation or PVD processes to obtain P-type pad layer 910 and N-type pad layer 920, but are not limited to these.

[0099] Preferably, in some embodiments, a photoresist layer is first formed in the second insulating layer 800, the third through-hole 810 and the fourth through-hole 820, and then the photoresist layer in the preset area is removed by exposure and development. Then, a metal stack is deposited by electron beam evaporation to form a P-type pad layer 910 and an N-type pad layer 920. Then, the metal on the photoresist layer is removed by blue film stripping process, and finally the photoresist is removed.

[0100] Preferably, in some embodiments, the method for preparing flip-chip LEDs further includes: splitting the wafer obtained in step (10) along the isolation groove, and then sorting it by testing to obtain flip-chip LEDs.

[0101] Testing showed that the aging time of the flip-chip LED in this technical solution can reach over 2256 hours, while the aging time of traditional flip-chip LEDs is less than 864 hours. Specifically, the aging time testing method is as follows: The flip-chip LED is fabricated into a sample with a size of 1200μm×1200μm, and subjected to a long-term high-current aging test at room temperature (25℃). The high current is three times the operating current (700mA). During the aging process, the turn-on voltage of the chip at a current of 1μA is tested every 48 hours. When the turn-on voltage is less than 2.1V, the chip is considered to have failed.

[0102] The above description is a preferred embodiment of the invention. It should be noted that, for those skilled in the art, several improvements and modifications can be made without departing from the principle of the invention, and these improvements and modifications are also considered to be within the scope of protection of the invention.

Claims

1. A flip-chip LED, characterized in that, include: Substrate, an epitaxial layer, an insulating protective layer, a reflective layer, a first insulating layer, a P-type metal conductive layer, an N-type metal conductive layer, a second insulating layer, a P-type pad layer and an N-type pad layer stacked on the substrate; The epitaxial layer comprises an N-type semiconductor layer, a light-emitting layer, and a P-type semiconductor layer sequentially stacked on the substrate. A light-emitting structure, an isolation trench, and an N-type conductive step are formed on the epitaxial layer. The N-type conductive step is disposed on one side of the light-emitting structure and exposes the N-type semiconductor layer. An insulating protective layer covers the N-type conductive step, the isolation trench, and the sidewall of the light-emitting structure. The first insulating layer covers the insulating protective layer and the reflective layer. The reflective layer is disposed above the P-type semiconductor layer; the reflective layer includes an anti-electromigration portion, a reflective portion, and a protective portion; the anti-electromigration portion and the reflective portion are disposed adjacent to each other, the anti-electromigration portion is disposed close to the N-type conductive step, and the protective portion covers the anti-electromigration portion and the reflective portion; the anti-electromigration portion includes an anti-electromigration body and a first anti-oxidation portion stacked sequentially; the anti-electromigration body is composed of multiple metal pairs, each metal pair including an Ag metal layer and an AgNi alloy layer stacked sequentially; the first anti-oxidation portion is made of one or more of Ni, Au, Ti, and Cr.

2. The flip-chip LED as described in claim 1, characterized in that, In the anti-electromigration unit, the metal pair closest to the P-type semiconductor layer is the first group of metal pairs, the metal pair closest to the first insulating layer is the last group of metal pairs, and the rest are intermediate metal pairs; the thickness of the Ag metal layer in the first group of metal pairs is less than the thickness of the Ag metal layer in the intermediate metal pairs and less than the thickness of the Ag metal layer in the last group of metal pairs, and the thickness of the AgNi alloy layer in the first group of metal pairs is equal to the thickness of the AgNi alloy layer in the intermediate metal pairs and less than the thickness of the AgNi alloy layer in the last group of metal pairs.

3. The flip-chip LED as described in claim 2, characterized in that, The thickness of the AgNi alloy layer in the last metal pair is 100 to 200 times the thickness of the AgNi alloy layer in the first metal pair. The thickness of the Ag metal layer in the last metal pair is 20 to 50 times the thickness of the Ag metal layer in the first metal pair.

4. The flip-chip LED as described in claim 2, characterized in that, The anti-electromigration core comprises 3 to 5 metal pairs; In the first metal pair, the thickness of the Ag metal layer is 50 Å to 100 Å, and the thickness of the AgNi alloy layer is 10 Å to 15 Å. The thickness of the Ag metal layer in the intermediate metal pair is 200 Å to 500 Å, and the thickness of the AgNi alloy layer is 10 Å to 15 Å; the thickness of the Ag metal layer and the thickness of the AgNi alloy layer are the same in different intermediate metal pairs; the thickness of the Ag metal layer in the last metal pair is 1000 Å to 2000 Å, and the thickness of the AgNi alloy layer is 1500 Å to 2000 Å. The first antioxidant portion is made of Ti and has a thickness of 300 Å to 500 Å.

5. The flip-chip LED as described in claim 1, characterized in that, The reflective portion includes an Ag reflective layer and a second antioxidant portion stacked sequentially; the thickness of the Ag reflective layer is 1200 Å to 2000 Å; and the thickness of the second antioxidant portion is 300 Å to 500 Å.

6. The flip-chip LED as described in claim 1, characterized in that, The protective part comprises alternating layers of Ni metal and TiW alloy, with a period of 3 to 5; the thickness of the Ni metal layer is 1000 Å to 2000 Å, and the thickness of the TiW alloy layer is 3000 Å to 5000 Å.

7. The flip-chip LED as described in claim 1, characterized in that, The distance between the sidewall of the anti-electromigration portion away from the N-type conductive step and the sidewall of the light-emitting structure is 20μm~40μm; The distance between the sidewall of the anti-electromigration portion near the N-type conductive step and the sidewall of the light-emitting structure is 5μm~7μm.

8. The flip-chip LED as described in claim 1, characterized in that, The anti-electromigration portion and the reflective portion at least partially overlap, with an overlap width of 3μm to 5μm, and in the overlap region, the reflective portion is located above the anti-electromigration portion.

9. The flip-chip LED as described in claim 1, characterized in that, The insulating protective layer is made of SiO2 and has a thickness of ≥5000 Å; The first insulating layer comprises an Al2O3 layer and a SiO2 layer stacked sequentially, wherein the thickness of the Al2O3 layer is 600 Å to 1200 Å and the thickness of the SiO2 layer is 8000 Å to 10000 Å.

10. A method for fabricating a flip-chip LED, used to fabricate the flip-chip LED as described in any one of claims 1 to 9, characterized in that, include: (1) An epitaxial layer is formed on a substrate, the epitaxial layer comprising an N-type semiconductor layer, a light-emitting layer and a P-type semiconductor layer sequentially stacked on the substrate; (2) Etching forms multiple N-type conductive steps and isolation trenches that expose the N-type semiconductor layer, forming multiple light-emitting structures disposed on the substrate; (3) An insulating protective layer is formed on the N-type conductive step, the isolation groove and the sidewall of the light-emitting structure; (4) An anti-electromigration portion is formed on the P-type semiconductor layer at the top of the light-emitting structure; (5) A reflective portion is formed on the P-type semiconductor layer at the top of the light-emitting structure; the reflective portion is disposed adjacent to the anti-electromigration portion; (6) A protective portion is formed on the anti-electromigration portion and the reflective portion to obtain a first intermediate; (7) A first insulating layer is formed on the first intermediate body, and a first through hole is formed to expose the protective part and a second through hole is formed to expose the N-type conductive step; (8) A P-type metal conductive layer and an N-type metal conductive layer are formed on the first insulating layer to obtain a second intermediate; (9) A second insulating layer is formed on the second intermediate, and a third through-hole and a fourth through-hole are formed to expose the P-type metal conductive layer and the N-type metal conductive layer, respectively. (10) A P-type pad layer and an N-type pad layer are formed on the second insulating layer.

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