Flip chip LED and method for manufacturing the same

Abstract

The application discloses an inverted LED chip, and relates to the technical field of semiconductors, comprising a substrate, an epitaxial structure and a light reflection structure; the epitaxial structure is provided with a plurality of first openings, which expose the sidewalls of a P-GaN layer, an MQW layer and an N-GaN layer; a sidewall protection layer, a primary passivation layer and a sidewall reflection layer are sequentially arranged along the first openings; the sidewall protection layer comprises a plurality of insulating film layers which are stacked to form a Bragg reflection mirror; the sidewall reflection layer comprises a sidewall metal adhesion layer and a sidewall Ag reflection layer, the sidewall metal adhesion layer is arranged on the primary passivation layer, and the sidewall Ag reflection layer is arranged on the sidewall metal adhesion layer; the sidewall reflection layer is connected with the N-GaN layer and overlaps with the projection part of the light reflection structure on the substrate. The sidewall protection layer which is stacked into a Bragg reflection mirror is combined with the sidewall reflection layer, the emergent light of the sidewall is reflected to the substrate, and the light emission efficiency and brightness are significantly improved.

Description

Technical Field

[0001] This invention relates to the field of semiconductor technology, and more specifically to a flip-chip LED and its fabrication method. Background Technology

[0002] like Figure 1 As shown, existing flip-chip LEDs include a substrate 1, an epitaxial structure (including an N-GaN layer 2, an MQW layer 3, and a P-GaN layer 4), and a metal reflective layer 100. The MQW layer 3 in the epitaxial structure emits light in all directions. The metal reflective layer 100 in the upper region of the epitaxial structure can reflect the light emitted by the MQW layer 3 on the side facing away from the substrate 1 and allow it to exit from the substrate 1. However, no metal reflective layer 100 is grown on the sidewalls 200 of the epitaxial structure and the middle opening. Some light will be emitted from the sidewalls 200 of the epitaxial structure. This light will be blocked and absorbed by the flip-chip LED support, reducing the light extraction efficiency and brightness of the flip-chip LED. Summary of the Invention

[0003] The purpose of this invention is to overcome the shortcomings of the prior art. This invention provides a flip-chip LED and its fabrication method. By stacking a sidewall protective layer and a sidewall reflective layer to form a Bragg reflector, the light emitted from the sidewall of the epitaxial structure is reflected to the substrate and emitted, which significantly improves the light extraction efficiency and brightness of the flip-chip LED.

[0004] This invention provides a flip-chip LED, which includes a substrate, an epitaxial structure disposed on the substrate, and a light-reflecting structure disposed on the epitaxial structure;

[0005] The epitaxial structure includes an N-GaN layer, an MQW layer disposed on the N-GaN layer, and a P-GaN layer disposed on the MQW layer;

[0006] The epitaxial structure is provided with a plurality of first openings, the first openings exposing the sidewalls of the P-GaN layer, the MQW layer and the N-GaN layer; a sidewall protection layer, a primary passivation layer and a sidewall reflective layer are sequentially provided along the sidewalls of the first openings;

[0007] The sidewall protective layer includes a plurality of stacked insulating film layers, which form a Bragg reflector.

[0008] The sidewall reflective layer includes a sidewall metal adhesion layer and a sidewall Ag reflective layer. The sidewall metal adhesion layer is disposed on the primary passivation layer, and the sidewall Ag reflective layer is disposed on the sidewall metal adhesion layer. The sidewall reflective layer is in contact with the N-GaN layer.

[0009] The sidewall reflective layer overlaps with the projection portion of the light-reflecting structure on the substrate.

[0010] Specifically, the insulating film layer includes a first SiO2 layer, a Ti3O5 layer, and a second SiO2 layer. The first SiO2 layer and the Ti3O5 layer are stacked alternately to form a Bragg reflector, and the second SiO2 layer covers the Bragg reflector.

[0011] Specifically, the thickness ratio of the first SiO2 layer to the Ti3O5 layer is 1:0.8, and the number of layers of the first SiO2 layer and the Ti3O5 layer stacked is 3 to 5.

[0012] Specifically, the thickness of the second SiO2 layer is

[0013] Specifically, the primary passivation layer includes a bottom layer and a top layer, wherein the bottom layer mainly consists of a SiO2 layer and a SiN layer. x Layer or SiO x N y One or more components in a layer.

[0014] Specifically, the surface film is an Al2O3 layer with a thickness of [missing information].

[0015] Specifically, the work function of the sidewall metal adhesion layer is J1, the work function of the N-GaN layer is J2, and the relationship between J1 and J2 is: -0.5eV≤J1-J2≤0.5eV;

[0016] The sum of the atomic numbers of the materials of the sidewall metal adhesion layer is Z1, and the sum of the atomic numbers of the materials of the N-GaN layer is Z2. The relationship between Z1 and Z2 is: -10≤Z1-Z2≤10.

[0017] Specifically, the material of the sidewall metal adhesion layer includes Zr or Zn, and the thickness of the sidewall metal adhesion layer is [missing information].

[0018] Specifically, the sidewall Ag reflective layer includes The sidewall Ag metal layer and The sidewall secondary metal layer is mainly composed of one or more of Ti, W, Al, Ni, and Pt.

[0019] This invention also provides a method for fabricating a flip-chip LED, comprising the following steps:

[0020] A substrate is provided, on which an epitaxial structure is formed by sequentially stacking an N-GaN layer, an MQW layer and a P-GaN layer;

[0021] A plurality of first openings are formed in a predetermined region in the epitaxial structure, and the first openings extend from the P-GaN layer to a predetermined depth in the N-GaN layer;

[0022] Several insulating film layers are sequentially stacked along the sidewall of the first opening to form a sidewall protective layer;

[0023] A light-reflecting structure is formed on a predetermined region of the P-GaN layer;

[0024] A primary passivation layer is formed along the sidewall protective layer and the surface of the light-reflecting structure;

[0025] A sidewall metal adhesion layer and a sidewall Ag reflective layer are sequentially stacked on a predetermined area of ​​the primary passivation layer to form a sidewall reflective layer; the sidewall reflective layer is in contact with the N-GaN layer.

[0026] Compared with the prior art, the beneficial effects of the present invention are:

[0027] By setting a sidewall reflective layer on the sidewall of the epitaxial structure to fill the area not covered by the light-reflecting structure, the emitted light from the sidewall of the epitaxial structure is reflected to the substrate and emitted, thereby improving the light extraction efficiency and brightness of the flip-chip LED.

[0028] By stacking several insulating film layers, the sidewall protective layer forms a Bragg reflector structure, which enhances the reflection effect of the emitted light from the sidewall of the epitaxial structure, thereby improving the light extraction efficiency and brightness of the flip-chip LED.

[0029] By combining the sidewall protective layer and the sidewall reflective layer, which are stacked to form a Bragg reflector, two reflections are formed, which significantly improves the light extraction efficiency and brightness of the flip-chip LED. Attached Figure Description

[0030] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0031] Figure 1 This is a schematic diagram of the structure of an existing flip-chip LED;

[0032] Figure 2 This is a schematic diagram of the flip-chip structure in an embodiment of the present invention;

[0033] Figure 3 yes Figure 1 Enlarged view of region a in the middle;

[0034] Figure 4 This is a schematic diagram of the fabrication process of the flip-chip LED in an embodiment of the present invention.

[0035] In the attached figures, 1 is the substrate; 100 is the metal reflective layer; 2 is the N-GaN layer; 200 is the sidewall; 3 is the MQW layer; 4 is the P-GaN layer; 5 is the sidewall protective layer; 6 is the primary passivation layer; 7 is the sidewall reflective layer; 701 is the sidewall metal adhesion layer; 702 is the sidewall Ag reflective layer; 8 is the secondary passivation layer; 9 is the N-type current conductive layer; 10 is the N-electrode pad; 11 is the P-electrode pad; 12 is the P-type current conductive layer; 13 is the first N-electrode window; 20 is the ITO transparent conductive layer; 30 is the light reflection structure; 31 is the Ag mirror reflective layer; 32 is the Ag mirror protective layer; 41 is the first opening; and 42 is the second opening. Detailed Implementation

[0036] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0037] Example 1:

[0038] Figure 2 This diagram illustrates the structure of a flip-chip LED in an embodiment of the present invention. The flip-chip LED includes a substrate 1, an epitaxial structure disposed on the substrate 1, and a light-reflecting structure 30 disposed on the epitaxial structure. The epitaxial structure includes an N-GaN layer 2, an MQW layer 3 disposed on the N-GaN layer 2, and a P-GaN layer 4 disposed on the MQW layer 3. The epitaxial structure has a plurality of first openings 41, which expose the sidewalls of the P-GaN layer 4, the MQW layer 3, and the N-GaN layer 2. A sidewall protection layer 5, a primary passivation layer 6, and a sidewall reflective layer 7 are sequentially disposed along the sidewalls of the first openings 41. The sidewall reflective layer 7 overlaps with the projection portion of the light-reflecting structure 30 on the substrate 1.

[0039] By providing a sidewall reflective layer 7 on the sidewall of the epitaxial structure to fill the area not covered by the light reflective structure 30, the emitted light from the sidewall of the epitaxial structure is reflected to the substrate 1 for emission, thereby improving the light extraction efficiency and brightness of the flip-chip LED.

[0040] The sidewall protective layer 5 includes several stacked insulating film layers, which form a Bragg reflector.

[0041] By stacking several insulating film layers, the sidewall protective layer 5 forms a Bragg reflector structure, which enhances the reflection effect of the emitted light from the sidewall of the epitaxial structure, thereby improving the light extraction efficiency and brightness of the flip-chip LED.

[0042] The aforementioned stacked insulating film layers include at least two different materials. Several pairs of insulating film layers of two or more materials are staggered and stacked to achieve high reflectivity for a certain optical band, thus forming a Bragg reflector structure. A commonly used type is a quarter-wave mirror, where the thickness of each insulating film layer corresponds to one-quarter of the wavelength (wavelength refers to the wavelength of light in the material). This wavelength is the wavelength for which the reflectivity is specifically increased, and the greater the difference in refractive index between the two materials, the higher the reflection efficiency.

[0043] Specifically, the insulating film layer includes a first SiO2 layer, a Ti3O5 layer, and a second SiO2 layer. The first SiO2 layer and the Ti3O5 layer are stacked alternately to form a Bragg reflector, and the second SiO2 layer covers the Bragg reflector.

[0044] The Bragg reflector structure formed by the staggered stacking of the first SiO2 layer and the Ti3O5 layer can enhance the reflection effect of the emitted light from the sidewall of the epitaxial structure and improve the brightness of the flip-chip LED. The staggered stacking of the first SiO2 layer and the Ti3O5 layer also improves the structural density and passivation of the sidewall protection layer 5, so that the sidewall protection layer 5 can effectively protect the sidewall of the epitaxial structure, prevent Ag from migrating from the sidewall of the epitaxial structure to the MQW layer 3 and causing leakage current in the flip-chip LED, and improve the stability and yield of the flip-chip LED.

[0045] Furthermore, the thickness ratio of the first SiO2 layer to the Ti3O5 layer is 1:0.8, and the number of stacked layers of the first SiO2 layer and the Ti3O5 layer is 3 to 5. The first SiO2 layer is formed first, and then the Ti3O5 layer is formed on the first SiO2 layer to form a SiO2 / Ti3O5 composite layer, and the number of SiO2 / Ti3O5 composite layers is 3 to 5. If the number of stacked layers of the first SiO2 layer and the Ti3O5 layer is small and the thickness after stacking is too thin, the light reflection effect of the sidewall protective layer 5 will be reduced, and the compactness of the sidewall protective layer 5 will also be reduced. If the number of stacked layers of the first SiO2 layer and the Ti3O5 layer is large and the thickness after stacking is too thick, the wet etching difficulty of the sidewall protective layer 5 will be increased, resulting in incomplete removal of the sidewall protective layer 5 in the preset area, which will affect the subsequent deposition and processing of the film layer.

[0046] By combining the sidewall protective layer 5, which is stacked to form a Bragg reflector, with the sidewall reflective layer 7, two reflections are formed, which significantly improves the light extraction efficiency and brightness of the flip-chip LED.

[0047] Furthermore, the total thickness of the sidewall protective layer 5 is The thickness of the second SiO2 layer is If the second SiO2 layer is too thin, its adhesion to the primary passivation layer 6 will be poor; if the second SiO2 layer is too thick, it will absorb light emitted from the sidewall of the epitaxial structure, reducing the brightness of the flip-chip LED. The thick second SiO2 layer can form a good adhesion with the primary passivation layer 6, so that the sidewall protective layer 5 and the primary passivation layer 6 are tightly bonded.

[0048] refer to Figure 3 The sidewall reflective layer 7 includes a sidewall metal adhesion layer 701 and a sidewall Ag reflective layer 702. The sidewall metal adhesion layer 701 is disposed on the primary passivation layer 6, and the sidewall Ag reflective layer 702 is disposed on the sidewall metal adhesion layer 701. By setting the sidewall metal adhesion layer 701, the sidewall Ag reflective layer 702 is firmly bonded to the primary passivation layer 6, reducing the risk of the sidewall Ag reflective layer 702 falling off or bubbling.

[0049] refer to Figure 2 The sidewall reflective layer 7 is connected to the N-GaN layer 2. Specifically, the bottom of the first opening 41 exposes the N-GaN layer 2. At the bottom of the first opening 41, part of the sidewall reflective layer 7 is in direct contact with the N-GaN layer 2. More specifically, part of the sidewall metal adhesion layer 701 is in direct contact with the N-GaN layer 2.

[0050] Due to the presence of the sidewall metal adhesion layer 701, the sidewall reflective layer 7 and the N-GaN layer 2 form a good ohmic contact, which reduces the operating voltage of the flip-chip LED and enables higher brightness.

[0051] In some specific embodiments, the work function of the sidewall metal adhesion layer 701 is J1, the work function of the N-GaN layer 2 is J2, and the relationship between J1 and J2 is: -0.5eV≤J1-J2≤0.5eV;

[0052] The work function, also known as the work function or work function, is defined in solid-state physics as the minimum energy required to move an electron from the interior of a solid to its surface. The work function difference between the sidewall metal adhesion layer 701 and the N-GaN layer 2 should not exceed 0.5 eV; otherwise, the ohmic contact between them will deteriorate, resulting in higher contact resistance and increased voltage in the flip-chip LED.

[0053] Furthermore, the sum of the atomic numbers of the materials of the sidewall metal adhesion layer 701 is Z1, and the sum of the atomic numbers of the materials of the N-GaN layer 2 is Z2. The relationship between Z1 and Z2 is: -10≤Z1-Z2≤10.

[0054] "Sum of atomic numbers" refers to the sum of the atomic numbers of each element in the film layer. The sum of atomic numbers between the sidewall metal adhesion layer 701 and the N-GaN layer 2 should not differ by more than 10; otherwise, the ohmic contact between the two will deteriorate, resulting in higher contact resistance and increasing the voltage of the flip-chip LED.

[0055] Specifically, the sidewall metal adhesion layer 701 is made of Zr or Zn, with Zr having an atomic number of 40 and Zn having an atomic number of 30, meaning the sum of the atomic numbers of the sidewall metal adhesion layer 701 is 40 or 30; the N-GaN layer 2 includes N and Ga, with N having an atomic number of 7 and Ga having an atomic number of 31, meaning the sum of the atomic numbers of the N-GaN layer 2 is 38; the difference in the sum of the atomic numbers between the two layers does not exceed 10.

[0056] Specifically, the thickness of the sidewall metal adhesion layer 701 is... If the sidewall metal adhesive layer 701 is too thin, the adhesion between the sidewall metal adhesive layer 701 and the N-GaN layer 2 will be poor, resulting in a high contact voltage; if it is too thick, it will absorb the light emitted from the sidewall of the epitaxial structure, reducing the brightness of the flip-chip LED. If the sidewall metal adhesive layer 701 is too thin, the adhesion between the sidewall Ag reflective layer 702 and the primary passivation layer 6 will not be tight enough, making the sidewall Ag reflective layer 702 prone to bubbling or even falling off.

[0057] The sidewall metal adhesion layer 701 of appropriate thickness can form a good ohmic contact with the N-GaN layer 2, reducing the voltage of the flip-chip LED; it can also make the sidewall Ag reflective layer 702 firmly bonded to the primary passivation layer 6, reducing the risk of the sidewall Ag reflective layer 702 falling off or bubbling.

[0058] In some specific embodiments, the sidewall Ag reflective layer 702 includes The sidewall Ag metal layer and A sidewall sub-metal layer is disposed on the sidewall Ag metal layer to protect the sidewall Ag metal layer from oxidation.

[0059] The sidewall submetallic layer is mainly composed of one or more of Ti, W, Al, Ni, and Pt. Preferably, Ti is used to compose the sidewall submetallic layer, which has good adhesion and facilitates contact and adhesion of the current conductive layer.

[0060] In some specific embodiments, the thickness of the primary passivation layer 6 is 1–1.5 μm. If the thickness is too thin, the density is poor, leading to leakage current in the flip-chip LED and reducing the chip yield; if the thickness is too thick, the manufacturing cost is high and the manufacturing efficiency is reduced. The primary passivation layer 6 includes a bottom film layer and a surface film layer. The bottom film layer mainly consists of a SiO2 layer and a SiN layer. x Layer or SiO x N y One or more components of the layer have good insulation properties; the surface film is an Al2O3 layer, which has good adhesion and is used to adhere the sidewall reflective layer 7, so that the sidewall reflective layer 7 is tightly attached to the primary passivation layer 6. The thickness of the surface film is... If it is too thin, the adhesion effect will be poor, which will easily cause the sidewall reflective layer 7 to fall off; if it is too thick, it will absorb the light emitted from the sidewall of the epitaxial structure and reduce the brightness of the flip-chip LED.

[0061] Example 2:

[0062] Figure 4 This invention illustrates a schematic flowchart of a method for fabricating a flip-chip LED, including the following steps:

[0063] S1. Provide a substrate, and sequentially stack an N-GaN layer, an MQW layer and a P-GaN layer on the substrate to form an epitaxial structure.

[0064] A patterned substrate 1 is provided, and an N-GaN layer 2, an MQW layer 3, and a P-GaN layer 4 are sequentially grown on the patterned substrate 1 by MOCVD to form the epitaxial structure of a flip-chip LED.

[0065] S2. A plurality of first openings are formed in a predetermined region in the epitaxial structure, the first openings extending from the P-GaN layer to a predetermined depth in the N-GaN layer.

[0066] Using a thick photoresist as a mask, the epitaxial structure is etched by ICP (inductively coupled plasma etching) to form several first openings 41 with an etching depth of about 1 to 1.5 μm. The first openings 41 penetrate a certain distance into the N-GaN layer 2, exposing the sidewalls of the P-GaN layer 4, MQW layer 3 and N-GaN layer 2. The bottom of the first openings 41 exposes the N-GaN layer 2. After etching, the thick photoresist is removed.

[0067] Furthermore, another thick photoresist is used as a mask, and then ICP is used to etch the bottom of the first opening 41 in the preset area to form a number of second openings 42. The second openings 42 are located at the edge of the flip LED chip and extend into the surface of the patterned substrate 1, exposing the entire sidewall surface of the epitaxial structure; the thick photoresist is removed after etching.

[0068] Furthermore, an ITO transparent conductive layer 20 is deposited on the first opening 41, the second opening 42, and the P-GaN layer 4 using electron beam deposition or magnetron sputtering deposition techniques. Then, using photoresist as a mask, the ITO transparent conductive layer 20 on the surfaces of the first opening 41 and the second opening 42 is etched away using chemical solutions such as ITO etchant, and a predetermined amount of the ITO transparent conductive layer 20 on the P-GaN layer 4 is also etched away; the photoresist is then removed after etching.

[0069] S3. Several insulating film layers are sequentially stacked along the sidewall of the first opening to form a sidewall protective layer.

[0070] Specifically, a number of insulating film layers are sequentially deposited on the first opening 41, the second opening 42, the P-GaN layer 4, and the ITO transparent conductive layer 20 using PECVD (plasma-enhanced chemical vapor deposition), magnetron sputtering, or electron beam evaporation to form a sidewall protective layer 5; in subsequent steps, part of the sidewall protective layer 5 is etched away.

[0071] The insulating film layer includes a first SiO2 layer, a Ti3O5 layer, and a second SiO2 layer. A Bragg reflector is first formed by alternately stacking several first SiO2 layers and several Ti3O5 layers, and then the second SiO2 layer is deposited on the Bragg reflector structure. The thickness ratio of the first SiO2 layer to the Ti3O5 layer is 1:0.8, and 3 to 5 layers of the first SiO2 layer and Ti3O5 layer are alternately stacked. The thickness of the second SiO2 layer is...

[0072] The Bragg reflector structure formed by the staggered stacking of the first SiO2 layer and the Ti3O5 layer can enhance the reflection effect of the emitted light from the sidewall of the epitaxial structure and improve the brightness of the flip-chip LED. The staggered stacking of the first SiO2 layer and the Ti3O5 layer also improves the structural density and passivation of the sidewall protection layer 5, so that the sidewall protection layer 5 can effectively protect the sidewall of the epitaxial structure, prevent Ag from migrating from the sidewall of the epitaxial structure to the MQW layer 3 and causing leakage current in the flip-chip LED, and improve the stability and yield of the flip-chip LED.

[0073] The second SiO2 layer can enhance the adhesion between the sidewall protective layer 5 and the subsequent primary passivation layer 6.

[0074] S4. A light-reflecting structure is formed on a predetermined area of ​​the P-GaN layer.

[0075] Using a negative photoresist as a mask, the sidewall protective layer 5 on the preset area of ​​the P-GaN layer 4, i.e. the sidewall protective layer 5 on the ITO transparent conductive layer 20, is removed by a wet etching process using chemical solutions such as BOE etch solution. The negative photoresist mask is retained, and Ag mirror reflective layer 31 and Ag mirror protective layer 32 are sequentially deposited on the ITO transparent conductive layer 20 by techniques such as magnetron sputtering or electron beam evaporation to form a light reflective structure 30. Then the negative photoresist is removed.

[0076] The Ag mirror reflective layer 31 is generally prepared using magnetron sputtering technology and mainly consists of an Ag mirror metal layer. and associated metal layer The constituent elements of the auxiliary metal layer include metals such as Ti, W, Al, Ni or Pt, and the auxiliary metal layer protects the Ag mirror metal layer from oxidation.

[0077] The Ag mirror protective layer 32 is generally prepared using electron beam evaporation technology and is mainly composed of highly conductive metallic elements such as Cr, Al, Ni, Ti, Pt, or Au; the overall thickness of the Ag mirror protective layer 32 is generally [missing information]. This is used to enhance the conductivity of the Ag mirror reflective layer 31; simultaneously, the outermost metal of the Ag mirror protective layer 32 is made of an etching-resistant metal material such as Pt or Ni, and the thickness of this outermost metal is... To prevent subsequent etching processes from damaging the underlying metal layer and Ag mirror reflective layer 31.

[0078] S5. A primary passivation layer is formed along the sidewall protective layer and the surface of the light-reflecting structure.

[0079] A dense primary passivation layer 6 is deposited along the surface of the sidewall protective layer 5 and the light-reflecting structure 30 using PECVD (plasma-enhanced chemical vapor deposition). Then, using photoresist as a mask, a dry etching process is used to etch away the primary passivation layer 6 and the sidewall protective layer 5 on the second opening 42; a predetermined amount of the primary passivation layer 6 and the sidewall protective layer 5 on the N-GaN layer 2 are etched away, wherein a first N-electrode window 13 is formed in the first opening 41 where there is no second opening 42; a portion of the primary passivation layer 6 on the light-reflecting structure 30 is etched away to form a first P-electrode window; and the photoresist is removed after etching.

[0080] The primary passivation layer 6 possesses excellent density, insulation, and high light transmittance. It is mainly composed of a bottom layer and a top layer. The bottom layer primarily consists of a SiO2 layer and a SiN layer. x Layer, SiO2 / SiN x Composite layer or SiO x N y The flip-chip LED is composed of passivation and insulating layers with a thickness of 1 to 1.5 μm. If the thickness is too thin, the density will be poor, which will make the flip-chip LED prone to leakage and reduce the yield of the chip. If the thickness is too thick, the manufacturing cost will be high and the manufacturing efficiency will be reduced.

[0081] The surface film is an Al2O3 layer, used to adhere subsequent film layers, ensuring a tight bond between the subsequently grown film layers and the primary passivation layer 6; the thickness of the surface film is... If the film is too thin, the adhesion will be poor, which will easily lead to the subsequent growth of the film layer falling off; if it is too thick, it will absorb the light emitted from the sidewalls of the epitaxial structure, reducing the brightness of the flip-chip LED.

[0082] S6. A sidewall metal adhesion layer and a sidewall Ag reflective layer are sequentially stacked on the preset area of ​​the primary passivation layer to form a sidewall reflective layer; the sidewall reflective layer is in contact with the N-GaN layer.

[0083] Using photoresist as a mask, a sidewall metal adhesion layer 701 and a sidewall Ag reflective layer 702 are sequentially deposited on the primary passivation layer 6 of the first opening 41 to form a sidewall reflective layer 7. The sidewall reflective layer 7 covers at least the area above the light-reflecting structure 30 and the sidewall of the epitaxial structure, and is also in contact with the N-GaN layer 2. That is, the sidewall reflective layer 7 surrounds the area above and to the side that the light-reflecting structure 30 does not cover, and can reflect the light emitted from the sidewall of the epitaxial structure to the substrate 1 for emission, thereby improving the light emission efficiency of the flip-chip LED, i.e., improving its brightness. After deposition, the photoresist is removed.

[0084] Specifically, at the bottom of the first opening 41, a portion of the sidewall reflective layer 7 directly covers the N-GaN layer 2; more specifically, a portion of the sidewall metal adhesion layer 701 directly contacts the N-GaN layer 2; the sidewall reflective layer 7 fills the first N-electrode window 13.

[0085] The sidewall metal adhesion layer 701 firmly bonds the sidewall Ag reflective layer 702 to the primary passivation layer 6, reducing the risk of the sidewall Ag reflective layer 702 falling off or bubbling; the sidewall metal adhesion layer 701 also enables the sidewall reflective layer 7 to form a good ohmic contact with the N-GaN layer 2, reducing the operating voltage of the flip-chip LED and achieving higher brightness.

[0086] Furthermore, using photoresist as a mask, current-conducting layers are deposited in the corresponding areas by electron beam evaporation, including depositing a P-type current-conducting layer 12 on the first P-electrode window, depositing an N-type current-conducting layer 9 in the first opening 41 without the second opening 42, and on the primary passivation layer 6 without exposing the light-reflecting structure 30; the P-type current-conducting layer 12 and the N-type current-conducting layer 9 are separated from each other, and the P-type current-conducting layer 12 does not contact the sidewall reflective layer 7, while the N-type current-conducting layer 9 is in contact with the sidewall reflective layer 7.

[0087] The current-conducting layer is mainly composed of metal elements with good conductivity such as Cr, Al, Ni, Ti, Pt or Au; the current-conducting layer uses Cr or Ti as the bottom metal to facilitate good adhesion contact with the Ag mirror protective layer 32 and the sidewall reflective layer 7; the current-conducting layer uses Ti as the surface metal to facilitate good adhesion contact with the subsequently deposited secondary passivation layer 8.

[0088] The total thickness of the current-conducting layer is 1-2 μm. If it is too thin, the conductivity will be poor, and if it is too thick, the manufacturing cost will be high and the manufacturing efficiency will be low.

[0089] Furthermore, a secondary passivation layer 8 is deposited along the surface of the second opening 42, the sidewall reflective layer 7, and the current conductive layer using PECVD (plasma-enhanced chemical vapor deposition). Then, using a negative photoresist as a mask, a predetermined amount of the secondary passivation layer 8 is removed from the N-type current conductive layer 9 and the P-type current conductive layer 12 using wet etching or dry etching, forming the N-electrode pad 10 window and the P-electrode pad 11 window, respectively. Next, with the negative photoresist mask retained, electrode pads are deposited on the current conductive layer by electron beam evaporation, that is, N-electrode pads 10 are deposited in the N-electrode pad 10 window and P-electrode pads 11 are deposited in the P-electrode pad 11 window.

[0090] The secondary passivation layer 8 possesses excellent density, insulation, and high light transmittance, and can be composed of SiO2 layers, SiN... x Layer, SiO2+SiN x Composite layer, SiO x N y The electrode pads are composed of passivation and insulating layers such as Ti2O5 layer; the electrode pads are mainly composed of metal elements with good conductivity such as Cr, Ni, Ti, Pt, Au, Sn or Au, and the bottom metal of the electrode pads is made of Cr or Ti, which has good adhesion to the current conductive layer.

[0091] Furthermore, the substrate 1 is thinned by grinding using conventional processes, and then cut along the second opening 42 to complete the fabrication of the flip-chip LED.

[0092] This invention provides a flip-chip LED and its fabrication method. By setting a sidewall reflective layer 7 on the sidewall of the epitaxial structure to fill the area not covered by the light-reflecting structure 30, the emitted light from the sidewall of the epitaxial structure is reflected to the substrate 1 for emission, thereby improving the light extraction efficiency and brightness of the flip-chip LED. By forming a Bragg mirror structure with several stacked insulating film layers, the sidewall protective layer 5 enhances the reflection effect of the emitted light from the sidewall of the epitaxial structure, thereby improving the light extraction efficiency and brightness of the flip-chip LED. By combining the sidewall protective layer 5, which is stacked to form a Bragg mirror, with the sidewall reflective layer 7, a double reflection is formed, which significantly improves the light extraction efficiency and brightness of the flip-chip LED.

[0093] By using several layers of insulating film, the structural density and passivation of the sidewall protection layer 5 are improved, so that the sidewall protection layer 5 can effectively protect the sidewall of the epitaxial structure. This can prevent Ag from migrating from the sidewall of the epitaxial structure to the MQW layer 3, which would cause leakage current in the flip-chip LED, and improve the stability and yield of the flip-chip LED.

[0094] By setting the sidewall metal adhesion layer 701, a good ohmic contact is formed between the sidewall reflective layer 7 and the N-GaN layer 2, reducing the operating voltage of the flip-chip LED and achieving higher brightness. The sidewall metal adhesion layer 701 also ensures a strong bond between the sidewall Ag reflective layer 702 and the primary passivation layer 6, reducing the risk of the sidewall Ag reflective layer 702 detaching or blistering. By selecting suitable materials to form the bottom or top film layers, good adhesion between the film layers is achieved, improving the stability of the flip-chip LED.

[0095] The flip-chip LED of this invention improves brightness by 5-10%, yield by 3-6%, and stability by 50-80%, as detailed in Table 1:

[0096] Table 1

[0097] Grouping Brightness / mW Yield stability Existing technology 1030.6 84.7％ 14.5％ This invention 1100.4 89.3％ 90.6％ contrast 6.8％ 4.6％ 76.1％

[0098] The foregoing has provided a detailed description of a flip-chip LED and its fabrication method according to embodiments of the present invention. Specific examples have been used to illustrate the principles and implementation methods of the present invention. The descriptions of the above embodiments are only for the purpose of helping to understand the method and core ideas of the present invention. At the same time, for those skilled in the art, there will be changes in the specific implementation methods and application scope based on the ideas of the present invention. Therefore, the content of this specification should not be construed as a limitation of the present invention.

Claims

1. A flip-chip LED, characterized in that, The flip-chip LED includes a substrate, an epitaxial structure disposed on the substrate, and a light-reflecting structure disposed on the epitaxial structure; The epitaxial structure includes an N-GaN layer, an MQW layer disposed on the N-GaN layer, and a P-GaN layer disposed on the MQW layer; The epitaxial structure is provided with a plurality of first openings, the first openings exposing the sidewalls of the P-GaN layer, the MQW layer and the N-GaN layer; a sidewall protection layer, a primary passivation layer and a sidewall reflective layer are sequentially provided along the sidewalls of the first openings; The sidewall protective layer includes a plurality of stacked insulating film layers, the plurality of stacked insulating film layers including a first SiO2 layer, a Ti3O5 layer and a second SiO2 layer, the first SiO2 layer and the Ti3O5 layer are stacked alternately to form a Bragg reflector, the Bragg reflector directly covers the sidewall of the first opening, and the second SiO2 layer directly covers the Bragg reflector. The sidewall reflective layer includes a sidewall metal adhesion layer and a sidewall Ag reflective layer. The sidewall metal adhesion layer is disposed on the primary passivation layer, and the sidewall Ag reflective layer is disposed on the sidewall metal adhesion layer. The material of the sidewall metal adhesion layer includes Zr or Zn, and the thickness of the sidewall metal adhesion layer is 20–100 Å. The sidewall Ag reflective layer includes a 2000–4000 Å sidewall Ag metal layer and a 3000–5000 Å sidewall secondary metal layer. The sidewall secondary metal layer is composed of one or more of Ti, W, Al, Ni, and Pt. The sidewall Ag metal layer directly covers the sidewall metal adhesion layer, and the sidewall secondary metal layer directly covers the sidewall Ag metal layer. The sidewall metal adhesion layer is in contact with the N-GaN layer, and the sidewall metal adhesion layer and the N-GaN layer form an ohmic contact. The sidewall reflective layer overlaps with the projection portion of the light-reflecting structure on the substrate. The primary passivation layer comprises a bottom film layer and a top film layer. The bottom film layer consists of a SiO2 layer and a SiN layer. x Layer or SiO x N y One or more components of the layer; the surface film is an Al2O3 layer with a thickness of 200–500 Å; the surface film directly covers the bottom film, the bottom film is in contact with the second SiO2 layer and the light-reflecting structure, and the surface film is in contact with the sidewall metal adhesion layer.

2. The flip-chip LED as described in claim 1, characterized in that, The thickness ratio of the first SiO2 layer to the Ti3O5 layer is 1:0.8, and the number of the first SiO2 layer and the Ti3O5 layer stacked is 3 to 5.

3. The flip-chip LED as described in claim 1, characterized in that, The thickness of the second SiO2 layer is 500–1000 Å.

4. The flip-chip LED as described in claim 1, characterized in that, The work function of the sidewall metal adhesion layer is J1, and the work function of the N-GaN layer is J2. The relationship between J1 and J2 is: -0.5eV≤J1-J2≤0.5eV; The sum of the atomic numbers of the materials of the sidewall metal adhesion layer is Z1, and the sum of the atomic numbers of the materials of the N-GaN layer is Z2. The relationship between Z1 and Z2 is: -10≤Z1-Z2≤10.

5. A method for preparing the flip-chip LED according to any one of claims 1 to 4, characterized in that, Includes the following steps: A substrate is provided, on which an epitaxial structure is formed by sequentially stacking an N-GaN layer, an MQW layer and a P-GaN layer; A plurality of first openings are formed in a predetermined region in the epitaxial structure, and the first openings extend from the P-GaN layer to a predetermined depth in the N-GaN layer; A plurality of insulating film layers are sequentially stacked along the sidewall of the first opening to form a sidewall protective layer; the plurality of insulating film layers include a first SiO2 layer, a Ti3O5 layer and a second SiO2 layer, the first SiO2 layer and the Ti3O5 layer are stacked alternately to form a Bragg reflector, the Bragg reflector directly covers the sidewall of the first opening, and the second SiO2 layer directly covers the Bragg reflector. A light-reflecting structure is formed on a predetermined region of the P-GaN layer; A primary passivation layer is formed along the sidewall protective layer and the surface of the light-reflecting structure; the primary passivation layer includes a bottom film layer and a top film layer, the bottom film layer being composed of a SiO2 layer and a SiN layer. x Layer or SiO x N y One or more components of the layer; the surface film is an Al2O3 layer with a thickness of 200–500 Å; the surface film directly covers the bottom film, and the bottom film is in contact with the second SiO2 layer and the light-reflecting structure; A sidewall reflective layer is formed by sequentially stacking a sidewall metal adhesion layer and a sidewall Ag reflective layer on a predetermined region of the primary passivation layer. The sidewall metal adhesion layer is made of Zr or Zn and has a thickness of 20–100 Å. The sidewall metal adhesion layer directly covers the surface film layer. The sidewall Ag reflective layer includes a 2000–4000 Å sidewall Ag metal layer and a 3000–5000 Å sidewall secondary metal layer. The sidewall secondary metal layer is composed of one or more of Ti, W, Al, Ni, and Pt. The sidewall Ag metal layer directly covers the sidewall metal adhesion layer, and the sidewall secondary metal layer directly covers the sidewall Ag metal layer. The sidewall metal adhesion layer is in contact with the N-GaN layer, and the sidewall metal adhesion layer and the N-GaN layer form an ohmic contact. The sidewall reflective layer overlaps with the projection portion of the light-reflecting structure on the substrate.

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