CN112768582B - Flip LED chip comprising high-reflection n-GaN ohmic contact and manufacturing method thereof - Google Patents

Flip LED chip comprising high-reflection n-GaN ohmic contact and manufacturing method thereof Download PDF

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CN112768582B
CN112768582B CN202110275172.XA CN202110275172A CN112768582B CN 112768582 B CN112768582 B CN 112768582B CN 202110275172 A CN202110275172 A CN 202110275172A CN 112768582 B CN112768582 B CN 112768582B
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electrode
led chip
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metal layer
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CN112768582A (en
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周玉刚
郭焱
许朝军
潘赛
张�荣
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Nanjing University
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    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
    • H01L33/00—Semiconductor devices having potential barriers specially adapted for light emission; Processes or apparatus specially adapted for the manufacture or treatment thereof or of parts thereof; Details thereof
    • H01L33/36—Semiconductor devices having potential barriers specially adapted for light emission; Processes or apparatus specially adapted for the manufacture or treatment thereof or of parts thereof; Details thereof characterised by the electrodes
    • H01L33/40—Materials therefor
    • H01L33/405—Reflective materials
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
    • H01L33/00—Semiconductor devices having potential barriers specially adapted for light emission; Processes or apparatus specially adapted for the manufacture or treatment thereof or of parts thereof; Details thereof
    • H01L33/005—Processes
    • H01L33/0062—Processes for devices with an active region comprising only III-V compounds
    • H01L33/0066—Processes for devices with an active region comprising only III-V compounds with a substrate not being a III-V compound
    • H01L33/007—Processes for devices with an active region comprising only III-V compounds with a substrate not being a III-V compound comprising nitride compounds
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
    • H01L33/00—Semiconductor devices having potential barriers specially adapted for light emission; Processes or apparatus specially adapted for the manufacture or treatment thereof or of parts thereof; Details thereof
    • H01L33/36—Semiconductor devices having potential barriers specially adapted for light emission; Processes or apparatus specially adapted for the manufacture or treatment thereof or of parts thereof; Details thereof characterised by the electrodes
    • H01L33/40—Materials therefor
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
    • H01L2933/00—Details relating to devices covered by the group H01L33/00 but not provided for in its subgroups
    • H01L2933/0008—Processes
    • H01L2933/0016—Processes relating to electrodes

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Abstract

The invention discloses a flip LED chip containing high-reflection n-GaN ohmic contact and a manufacturing method thereof. The flip LED chip comprises an epitaxial structure layer, a p electrode and an n electrode, wherein the epitaxial structure layer comprises an n-type layer, a quantum well layer and a p-type layer which are sequentially stacked, the p electrode is arranged on the p-type layer, and the n electrode is arranged on the n-type layer; the n electrode comprises a high-reflection n-GaN ohmic contact structure, the high-reflection n-GaN ohmic contact structure comprises a first metal layer and a second metal layer which are arranged in a laminated mode, the first metal layer is arranged on the n-type layer and forms ohmic contact with the n-type layer, and the first metal layer comprises metal Mg. The flip LED chip adopts a flip structure, so that the thermal resistance and the junction temperature during working of the flip LED chip with high-reflection p and n ohmic contact of the same material can be effectively reduced, and the luminous efficiency of a device is improved.

Description

Flip LED chip comprising high-reflection n-GaN ohmic contact and manufacturing method thereof
Technical Field
The invention relates to a flip LED chip, in particular to a flip LED chip containing high-reflection n-GaN ohmic contact and a manufacturing method thereof, belonging to the technical field of photoelectrons.
Background
GaN is widely used in optoelectronic devices due to its direct and wide bandgap, high electron mobility and high carrier density. Good ohmic contact is very important for manufacturing reliable and efficient LEDs. The main mechanisms for forming an n-type ohmic contact are two, i.e., the work function of metal is lower than that of semiconductor and the formation of ohmic contact is caused by the tunneling effect due to the narrow width of the barrier. The flip LED chip can improve heat dissipation, luminescence, reliability and current distribution characteristics. The optical output power of the flip-chip LED chip is affected not only by the p-electrode but also by the n-electrode. However, the reflectivity of common n-GaN ohmic contact structures (such as Ti/Al, Ti/Al/Ni/Au and Cr/Au) is very low, which limits the light efficiency of the flip-chip LED chip to be further improved.
Disclosure of Invention
The invention mainly aims to provide a flip LED chip comprising a high-reflection n-GaN ohmic contact and a manufacturing method thereof, so as to overcome the defects in the prior art.
In order to achieve the purpose, the technical scheme adopted by the invention comprises the following steps:
the embodiment of the invention provides a flip LED chip comprising a high-reflection n-GaN ohmic contact, which comprises an epitaxial structure layer, a p electrode and an n electrode, wherein the epitaxial structure layer comprises an n-type layer, a quantum well layer and a p-type layer which are sequentially stacked, the p electrode is arranged on the p-type layer, and the n electrode is arranged on the n-type layer;
the n-electrode high-reflection n-GaN ohmic contact structure comprises a first metal layer and a second metal layer which are arranged in a laminated mode, wherein the first metal layer is arranged on the n-type layer and forms ohmic contact with the n-type layer, and the first metal layer comprises metal Mg.
The embodiment of the invention also provides a manufacturing method of the flip LED chip containing the high-reflection n-GaN ohmic contact, which comprises the following steps:
providing an epitaxial structure layer, wherein the epitaxial structure layer comprises an n-type layer, a quantum well layer and a p-type layer which are sequentially stacked;
processing the surface of the epitaxial structure layer to form a step structure, wherein the step structure divides the surface of the epitaxial structure layer into a p area and an n area;
forming a p electrode in the p region and an n electrode in the n region;
the n electrode comprises a high-reflection n-GaN ohmic contact structure, the high-reflection n-GaN ohmic contact structure comprises a first metal layer and a second metal layer which are arranged in a laminated mode, the first metal layer is arranged on the n-type layer and forms ohmic contact with the n-type layer, and the first metal layer comprises metal Mg.
Compared with the prior art, the invention has the advantages that:
1) according to the flip LED chip comprising the high-reflection n-GaN ohmic contact, which is provided by the embodiment of the invention, by adopting a flip structure, the thermal resistance and the junction temperature during working of the flip LED chip with the high-reflection p and n ohmic contact made of the same material can be effectively reduced, and the luminous efficiency of a device is improved;
2) the Mg metal layer in the flip LED chip containing the high-reflection n-GaN ohmic contact has good reflectivity from near ultraviolet to visible light, and Mg can form good ohmic contact with an n-type layer, so that the flip LED chip has extremely high reflectivity and light emission on the basis of ensuring good ohmic contact.
Drawings
FIG. 1 is a schematic structural diagram of a flip-chip LED chip including a highly reflective n-GaN ohmic contact provided in embodiment 1 of the present invention;
FIG. 2 is a schematic structural diagram of a flip-chip LED chip including a highly reflective n-GaN ohmic contact provided in embodiment 2 of the present invention;
FIG. 3 is a schematic structural diagram of a flip-chip LED chip including a highly reflective n-GaN ohmic contact provided in embodiment 3 of the present invention;
FIG. 4 is an IV characteristic of n-GaN electrodes having a highly reflective n-GaN ohmic contact structure with Mg-containing metal at different annealing temperatures according to an exemplary embodiment of the invention;
FIG. 5 is a graph showing the reflectance at different temperatures of an n-GaN electrode having a highly reflective n-GaN ohmic contact structure containing Mg metal in an exemplary embodiment of the invention.
Detailed Description
In view of the deficiencies in the prior art, the inventors of the present invention have made extensive studies and extensive practices to provide technical solutions of the present invention. The technical solution, its implementation and principles, etc. will be further explained as follows.
The embodiment of the invention provides a flip LED chip comprising a high-reflection n-GaN ohmic contact, which comprises an epitaxial structure layer, a p electrode and an n electrode, wherein the epitaxial structure layer comprises an n-type layer, a quantum well layer and a p-type layer which are sequentially stacked, the p electrode is arranged on the p-type layer, and the n electrode is arranged on the n-type layer;
the n electrode comprises a high-reflection n-GaN ohmic contact structure, the high-reflection n-GaN ohmic contact structure comprises a first metal layer and a second metal layer which are arranged in a laminated mode, the first metal layer is arranged on the n-type layer and forms ohmic contact with the n-type layer, and the first metal layer comprises metal Mg.
Further, the first metal layer is an Mg metal layer.
Further, the thickness of the first metal layer is 10-200 nm.
Further, the second metal layer includes any one or a combination of two or more of Al, Ti/Al (i.e., stacked Ti layer, Al layer), Ti/Au (i.e., stacked Ti layer, Au layer), and Ni/Au (i.e., stacked Ni layer, Au layer).
Further, the thickness of the second metal layer is 100-300 nm.
Furthermore, a step structure is formed on the surface of the epitaxial structure layer, the surface of the epitaxial structure layer is divided into a p area and an n area by the step structure, wherein the p electrode is arranged in the p area, and the n electrode is arranged in the n area.
Furthermore, the n region is provided with an n region contact hole, the n-type layer is exposed from the n region contact hole, and the n electrode is arranged in the n region contact hole.
Further, the p region is disposed at a top end side of the stepped structure, and the n region is disposed at a bottom end side of the stepped structure.
Furthermore, a passivation layer is arranged between the n electrode and the step structure and is isolated from each other through the passivation layer.
Further, an electron barrier layer is arranged between the quantum well layer and the p-type layer; preferably, the material of the electron blocking layer includes AlGaN.
Further, the flip LED chip is a GaN-based ultraviolet LED chip or a visible LED chip.
The embodiment of the invention also provides a manufacturing method of the flip LED chip containing the high-reflection n-GaN ohmic contact, which comprises the following steps:
providing an epitaxial structure layer, wherein the epitaxial structure layer comprises an n-type layer, a quantum well layer and a p-type layer which are sequentially stacked;
processing the surface of the epitaxial structure layer to form a step structure, wherein the step structure divides the surface of the epitaxial structure layer into a p area and an n area;
forming a p electrode in the p region and an n electrode in the n region;
the n electrode comprises a high-reflection n-GaN ohmic contact structure, the high-reflection n-GaN ohmic contact structure comprises a first metal layer and a second metal layer which are arranged in a laminated mode, the first metal layer is arranged on the n-type layer and forms ohmic contact with the n-type layer, and the first metal layer comprises metal Mg.
Further, the manufacturing method specifically comprises the following steps:
forming p-electrode metal in the p region, forming n-electrode metal in the n region, and annealing the p-electrode metal and the n-electrode metal for 10 s-3 min under the conditions of a protective atmosphere and 350 ℃ at 100 ℃ so as to form ohmic contact between the n-electrode metal and the n-type layer.
Further, the manufacturing method specifically comprises the following steps: firstly, processing an n region on the surface of the epitaxial structure layer to form an n region contact hole, and manufacturing an n electrode in the n region contact hole.
In a more specific embodiment, a method for fabricating a flip-chip LED chip including a highly reflective n-GaN ohmic contact may include the steps of:
step S1, growing an epitaxial structure layer on the substrate, wherein the epitaxial layer comprises main structure layers including a buffer layer, an n-type layer, a quantum well layer and a p-type layer;
step S2, etching the surface of the epitaxial structure layer to form a step through photoetching, etching and other processes, wherein the two sides of the step are respectively a p-region table top and an n-region contact hole;
step S3, depositing p-electrode metal on the p-type layer through photoetching, evaporation or sputtering, etching and other processes, and annealing to form a p-electrode;
step S4, depositing a Mg metal layer and an upper cover metal layer (namely the second metal layer, the same below) on the n-type layer through photoetching, evaporation or sputtering, etching and other processes, and rapidly annealing at 100-350 ℃ in an argon atmosphere to form ohmic contact between the Mg metal layer and the n-type layer.
Optionally, after step S4, the following steps may be further included:
step S5, growing SiO on the surface of the epitaxial structure layer by PECVD or electron beam evaporation2Or Si3N4The passivation layer covers the p region, the n region and the step of the epitaxial structure layer, and then holes are respectively formed in the passivation layer corresponding to the n region and the p region through photoetching, etching and other processes to respectively form an n electrode hole and a p electrode hole;
step S6, preparing a pad metal layer through photoetching, metal evaporation or sputtering and other processes, wherein the pad metal layer comprises an n-pole pad metal layer and a p-pole pad metal layer which are isolated from each other, the n-pole pad metal layer is electrically connected with the upper cover metal layer through an n-electrode hole, and the p-pole pad metal layer is electrically connected with the p-electrode metal layer through a p-electrode hole.
Furthermore, the n and p electrodes can be electrically connected with the outside through bumps, solder, conductive adhesive or metal bonding wires.
In a more specific embodiment, a method for fabricating a flip-chip LED chip including a highly reflective n-GaN ohmic contact may include the steps of:
step S1, growing an epitaxial structure layer on the substrate, wherein the epitaxial structure layer comprises main structure layers including a buffer layer, an n-type layer, a quantum well layer and a p-type layer;
step S2, etching the surface of the epitaxial structure layer to form a step through photoetching, etching and other processes, wherein the two sides of the step are respectively a p-region table top and an n-region contact hole;
step S3, depositing p-electrode metal on the p-type layer through photoetching, evaporation or sputtering, etching and other processes, and annealing to form a p-electrode;
step S4, growing SiO on the epitaxial structure layer by PECVD or electron beam evaporation2Or Si3N4The passivation layer covers the p region, the n region and the step of the epitaxial structure layer; and then, forming holes on the passivation layer corresponding to the n region and the p region respectively by photoetching, etching and other processes to form an n-type layer hole and a p-electrode hole respectively.
Step S5, preparing an Mg metal layer and an upper cover metal layer by photolithography, metal evaporation or sputtering, and the like, using the Mg metal layer and the upper cover metal layer as pad metal layers, wherein the pad metal layers are divided into an n-pole pad metal layer (the n-pole pad metal layer also serves as an n-electrode) and a p-pole pad metal layer which are isolated from each other, the n-pole pad metal layer is electrically connected with the n-pole layer through an n-pole layer hole and forms ohmic contact, and the p-pole pad metal layer is electrically connected with the p-pole metal layer through a p-pole hole.
Furthermore, the n and p electrodes can be electrically connected with the outside through bumps, solder, conductive adhesive or metal bonding wires.
The technical solution, the implementation process and the principle thereof will be further explained with reference to the drawings and the specific embodiments, and unless otherwise specified, the processes of photolithography, evaporation, sputtering, etching, MOCVD process and the like used in the present invention can be known to those skilled in the art.
Mg has a low work function (3.68eV) and a high reflectivity (> 91.6% in the wavelength range 250 to 550 nm), and is therefore capable of forming highly reflective ohmic contacts on n-GaN.
Example 1
Referring to fig. 1, a flip-chip LED chip including a high-reflective n-GaN ohmic contact has the following structure from top to bottom: the sapphire substrate 101 and an epitaxial structure layer, wherein the surface of the epitaxial structure layer comprises a p region, an n region and a step (namely the step structure, the same below); the epitaxial structure layer corresponding to the p region sequentially comprises a GaN buffer layer 102 with the thickness of 2.5-3 mu m, an n-GaN layer (namely the n-type layer, the same below) 103 with the thickness of 1-3 mu m, a quantum well layer 104 with the thickness of about 20nm, an AlGaN electronic barrier layer 105 with the thickness of about 8nm and a p-GaN layer (namely the p-type layer, the same below) 106 with the thickness of 40nm from top to bottom; the epitaxial structure layer corresponding to the n region sequentially comprises a GaN buffer layer 102 with the thickness of 2.5-3 mu m and an n-GaN layer 103 with the thickness of 1-3 mu m from top to bottom; the boundary of the p region and the n region is a step a; a p-electrode 107 is correspondingly disposed in the p-region surface portion region, a 100nm Mg metal layer (i.e., the first metal layer) 108 and a 200nm Al cap metal layer (i.e., the second metal layer, the same applies below) 109 are correspondingly disposed in the n-region surface portion region, and the Mg metal layer 108 and the n-GaN layer 103 form ohmic contact.
The steps of fabricating the flip-chip LED chip are described in detail below:
the manufacturing method of the flip LED chip specifically comprises the following steps:
step S1: sequentially growing a GaN buffer layer 102 with the thickness of 2.5-3 microns, an n-GaN layer 103 with the thickness of 1-3 microns, an InGaN/GaN quantum well layer 104 with the thickness of about 20nm, an AlGaN electronic barrier layer 105 with the thickness of about 8nm and a p-GaN layer 106 with the thickness of 40nm on a sapphire substrate 101 through an MOCVD (metal organic chemical vapor deposition) process;
step S2: etching the surface of the epitaxial structure layer to form a step a by the processes of photoetching, etching and the like, wherein the two sides of the step a are a p-region table top and an n-region contact hole respectively;
step S3: depositing a p-electrode metal layer on the p-GaN layer 106 of the p region by photolithography, evaporation or sputtering (preferably sputtering), etching, or the like, and annealing to form a p-electrode 107;
step S4: sequentially depositing a 10-200nm (preferably 100nm) Mg metal layer 108 and a 200nm Al upper cover metal layer 109 on the n-GaN layer 103 in the n region by the processes of photoetching, evaporation or sputtering (preferably sputtering), etching and the like, and rapidly annealing for 10 s-3 min (preferably 60s) under the condition of 100-350 ℃ (preferably 200 ℃) in Ar atmosphere to enable the Mg metal layer 108 to form ohmic contact with the n-GaN layer 103, thereby forming an n electrode;
step S5: thinning, polishing and cutting a sample to form a discrete LED chip;
step S6: the p-electrode and the n-electrode on the LED chip can be electrically connected with the bonding pad on the flip-chip substrate through bumps or solder.
Example 2
Referring to fig. 2, a structure of a flip-chip LED chip including a high-reflective n-GaN ohmic contact includes a sapphire substrate 201 and an epitaxial structure layer sequentially disposed from top to bottom, where the surface of the epitaxial structure layer includes a p region, an n region, and a step (i.e., the step structure, the same applies to the following) a; the epitaxial structure layer corresponding to the p region sequentially comprises a GaN buffer layer 202 with the thickness of 2.5-3 mu m, an n-GaN layer (namely the n-type layer, the same below) 203 with the thickness of 1-3 mu m, a quantum well layer 204 with the thickness of about 20nm, an AlGaN electronic barrier layer 205 with the thickness of about 8nm and a p-GaN layer (namely the p-type layer, the same below) 206 with the thickness of 40nm from top to bottom; the epitaxial structure layer corresponding to the n region sequentially comprises a GaN buffer layer 202 with the thickness of 2.5-3 mu m and an n-GaN layer 203 with the thickness of 1-3 mu m from top to bottom; the boundary of the p region and the n region is a step a; a p-electrode 207 is provided in the p-region surface region, and a 100nm Mg metal layer (i.e., the first metal layer) 208 and a 200nm Al cap metal layer (i.e., the second metal layer, the same applies below) 209 are provided in a stacked manner in the n-region surface region; the Al upper cover metal layer 209, the p electrode 207, the p region surface partial region, the n region surface partial region and the step a are sequentially covered with a passivation layer 210 of 300nm and a pad metal layer 211 of 400 nm.
The steps of fabricating the flip-chip LED chip will be described in detail below with reference to the accompanying drawings:
the manufacturing method of the flip LED chip specifically comprises the following steps:
step S1: sequentially growing a GaN buffer layer 202 with the thickness of 2.5-3 microns, an n-GaN layer 203 with the thickness of 1-3 microns, an InGaN/GaN quantum well layer 204 with the thickness of about 20nm, an AlGaN electronic barrier layer 205 with the thickness of about 8nm and a p-GaN layer 206 with the thickness of 40nm on a sapphire substrate 201 through an MOCVD process;
step S2: etching the surface of the epitaxial structure layer to form a step a by the processes of photoetching, etching and the like, wherein the two sides of the step a are a p-region table top and an n-region contact hole respectively;
step S3: depositing a p-electrode metal layer on the p-GaN layer 206 of the p region by photolithography, evaporation or sputtering (preferably sputtering), etching, etc., and annealing to form a p-electrode 207;
step S4: depositing a 10-200nm (preferably 100nm) Mg metal layer 208 and a 200nm Al upper cover metal layer 209 on the n-GaN layer 203 of the n region through the processes of photoetching, evaporation or sputtering (preferably sputtering), etching and the like, and rapidly annealing for 10-3 min (preferably 60s) under the condition of 100-350 ℃ (preferably 200 ℃) in Ar atmosphere, thereby forming an n electrode;
step S5: growing SiO with a thickness of 300-500 nm (preferably 300nm) on the surface of the epitaxial structure layer by PECVD or electron beam evaporation (preferably PECVD)2Or Si3N4Passivation layer (preferably SiO)2)210, the passivation layer 210 at least covers the n region, the p region and the step of the epitaxial structure layer, and then the passivation layer 210 corresponding to the n region and the p region is respectively provided with a hole by the processes of photoetching, etching and the like, so as to form an n electrode hole and a p electrode hole;
step S6: preparing a 400-600 nm (preferably 400nm) pad metal layer (preferably Ni/Au)211 by photoetching, metal evaporation or sputtering (preferably sputtering) and other processes, wherein the pad metal layer 211 is divided into an n-pole pad metal layer and a p-pole pad metal layer which are isolated from each other, the n-pole pad metal layer is electrically connected with the Al upper cover metal layer 209 through an n-electrode hole, and the p-pole pad metal layer is electrically connected with the p-electrode 207 through a p-electrode hole;
step S7: thinning, polishing and cutting a sample to form a discrete LED chip;
step S8: and the p electrode and the n electrode on the LED chip are electrically connected with the bonding pad on the flip substrate through bumps or solder.
Example 3
Referring to fig. 3, a structure of a flip-chip LED chip including a high-reflective n-GaN ohmic contact includes a sapphire substrate 301 and an epitaxial structure layer sequentially disposed from top to bottom, where the surface of the epitaxial structure layer includes a p region, an n region, and a step (i.e., the step structure, the same applies to the following) a; the epitaxial structure layer corresponding to the p region sequentially comprises a GaN buffer layer 302 with the thickness of 2.5-3 mu m, an n-GaN layer (namely the n-type layer, the same below) 303 with the thickness of 1-3 mu m, a quantum well layer 304 with the thickness of 20nm, an AlGaN electronic barrier layer 305 with the thickness of 8nm and a p-GaN layer (namely the p-type layer, the same below) 306 with the thickness of 40nm from top to bottom; the epitaxial structure layer corresponding to the n region sequentially comprises a GaN buffer layer 302 with the thickness of 2.5-3 mu m and an n-GaN layer 303 with the thickness of 1-3 mu m from top to bottom; the boundary of the p region and the n region is a step a; the p-electrode 307 with the thickness of about 500nm is correspondingly arranged on the partial region of the p-region surface, and a passivation layer 310 with the thickness of about 300nm, a Mg metal layer 308 with the thickness of about 100nm and an Al upper cover metal layer 309 with the thickness of about 200nm are sequentially covered on the p-electrode 307, the step a and the n-region surface.
The steps of fabricating the flip-chip LED chip will be described in detail below with reference to the accompanying drawings:
the manufacturing method of the flip LED chip specifically comprises the following steps:
step S1: sequentially growing a GaN buffer layer 302 with the thickness of 2.5-3 mu m, an n-GaN layer 303 with the thickness of 1-3 mu m, an InGaN/GaN quantum well layer 304 with the thickness of about 20nm, an AlGaN electronic barrier layer 305 with the thickness of about 8nm and a p-GaN layer 306 with the thickness of 40nm on a sapphire substrate 301 through an MOCVD process;
step S2: etching the surface of the epitaxial structure layer to form a step a by the processes of photoetching, etching and the like, wherein the two sides of the step a are a p-region table top and an n-region contact hole respectively;
step S3: depositing a p-electrode metal layer on the p-GaN layer 306 of the p region by photolithography, evaporation or sputtering (preferably sputtering), etching, and the like, and annealing to form a p-electrode 307;
step S4: growing SiO (300-500 nm, preferably 300nm) on the surface of the epitaxial structure layer and the p electrode by PECVD or electron beam evaporation (preferably PECVD)2Or Si3N4Passivation layer (preferably SiO)2)310, wherein the passivation layer 310 at least covers the n region, the p region and the step of the epitaxial structure layer; then, holes are respectively formed in the passivation layer 310 corresponding to the n region and the p region through the processes of photoetching, etching and the like to form an n-type layer hole and a p-electrode hole;
step S5: preparing and depositing a 10-200nm (preferably 100nm) Mg metal layer 308 and a 200nm Al upper cover metal layer 309 by the processes of photoetching, metal evaporation or sputtering (preferably sputtering), and the like, wherein the Al upper cover metal layer 309 is used as a pad metal layer, the pad metal layer is divided into an n-pole pad metal layer and a p-pole pad metal layer which are isolated from each other, the n-pole pad metal layer is electrically connected with the upper cover metal layer 309 through an n-electrode hole, and the p-pole pad metal layer is electrically connected with a p-electrode 307 through a p-electrode hole;
step S6: thinning, polishing and cutting a sample to form a discrete LED chip;
step S7: and the electrodes on the LED chip are electrically connected with the bonding pads on the flip substrate through bumps or solder.
In the embodiment, one of the purposes of forming the Mg metal layer and the upper cover metal layer in the p region or the p electrode hole is used as pad to lead out the p electrode, and one of the purposes of forming the Mg metal layer and the upper cover metal layer in the n-type layer hole is used as an n electrode and is used as pad metal layer at the same time; example 3 differs from the structures of examples 1 and 2 mainly in that: the Mg metal layer and the upper cover metal layer are used as an n electrode and a pad metal layer at the same time, and the n electrode is manufactured after a passivation layer is formed.
One of the purposes of the Mg metal layer as the pad metal layer is: because the pad metal of the flip-chip LED chip is generally low-reflectivity metal, but the pad metal layer needs to cover the step and the step has no electrode, if the pad metal is low-reflectivity metal, the light in the area cannot be reflected and output, so that the light in the area can be output by using the Mg metal layer and the upper cover metal layer as the pad, and the light output efficiency of the device is increased.
Specifically, Mg is taken as an active metal, belongs to a dangerous metal, and because the active property of Mg is easily reacted with moisture in the air and oxygen to generate an insulating precipitate, the reliability of a manufactured device is poor, so that Mg is rarely deeply researched as an electrode material; mg has a low work function (3.68eV), can form good ohmic contact when used as an n-GaN electrode without annealing, and has ultrahigh reflectivity of a visible light wave band, so that the light emitting of a flip LED chip manufactured by using Mg as an electrode is increased. The IV characteristics of the n-GaN electrode with the high-reflection n-GaN ohmic contact structure (Mg/Al) containing Mg metal at different annealing temperatures are shown in fig. 4, and the reflectance of the n-GaN electrode with the high-reflection n-GaN ohmic contact structure containing Mg metal at different temperatures is shown in fig. 5, so that the Mg metal layer in the flip-chip LED chip with the high-reflection n-GaN ohmic contact structure (Mg/Al) provided by the embodiment of the present invention has good reflectance from near ultraviolet to visible light, and Mg can form good ohmic contact with the n-type layer, and has extremely high reflectance to increase light emission on the basis of ensuring good ohmic contact.
According to the flip LED chip comprising the high-reflection n-GaN ohmic contact, which is provided by the embodiment of the invention, by adopting a flip structure, the thermal resistance and the junction temperature during working of the flip LED chip with the high-reflection p and n ohmic contact made of the same material can be effectively reduced, and the luminous efficiency of a device is improved.
It should be understood that the above-mentioned embodiments are merely illustrative of the technical concepts and features of the present invention, which are intended to enable those skilled in the art to understand the contents of the present invention and implement the present invention, and therefore, the protection scope of the present invention is not limited thereby. All equivalent changes and modifications made according to the spirit of the present invention should be covered within the protection scope of the present invention.

Claims (13)

1. A flip LED chip containing high-reflection n-GaN ohmic contact is characterized by comprising an epitaxial structure layer, a p electrode and an n electrode, wherein the epitaxial structure layer comprises an n-type layer, a quantum well layer and a p-type layer which are sequentially stacked, the p electrode is arranged on the p-type layer, and the n electrode is arranged on the n-type layer;
the n electrode comprises a high-reflection n-GaN ohmic contact structure, the high-reflection n-GaN ohmic contact structure comprises a first metal layer and a second metal layer which are arranged in a laminated mode, the first metal layer is arranged on the n type layer and forms ohmic contact with the n type layer, and the first metal layer is an Mg metal layer.
2. The flip-chip LED chip containing highly reflective n-GaN ohmic contacts of claim 1, wherein: the thickness of the first metal layer is 10-200 nm.
3. The flip-chip LED chip containing highly reflective n-GaN ohmic contacts of claim 1, wherein: the second metal layer comprises any one or the combination of more than two of Al, Ti/Au and Ni/Au.
4. The flip LED chip containing highly reflective n-GaN ohmic contacts according to claim 1 or 3, wherein: the thickness of the second metal layer is 100-300 nm.
5. The flip-chip LED chip containing highly reflective n-GaN ohmic contacts of claim 1, wherein: the surface of the epitaxial structure layer is further provided with a step structure, the surface of the epitaxial structure layer is divided into a p area and an n area by the step structure, the p electrode is arranged in the p area, and the n electrode is arranged in the n area.
6. The flip-chip LED chip containing highly reflective n-GaN ohmic contacts according to claim 5, wherein: the n-region is provided with an n-region contact hole, the n-type layer is exposed out of the n-region contact hole, and the n-electrode is arranged in the n-region contact hole.
7. The flip-chip LED chip containing highly reflective n-GaN ohmic contacts according to claim 6, wherein: and a passivation layer is also arranged between the n electrode and the step structure and is mutually isolated through the passivation layer.
8. The flip-chip LED chip containing highly reflective n-GaN ohmic contacts of claim 1, wherein: and an electron barrier layer is also arranged between the quantum well layer and the p-type layer.
9. The flip-chip LED chip containing highly reflective n-GaN ohmic contacts of claim 8, wherein: the electron blocking layer is made of AlGaN.
10. The flip-chip LED chip containing highly reflective n-GaN ohmic contacts of claim 1, wherein: the flip LED chip is a GaN-based ultraviolet LED chip or a visible light LED chip.
11. The method of fabricating a flip-chip LED chip containing highly reflective n-GaN ohmic contacts according to any of claims 1 to 10, comprising:
providing an epitaxial structure layer, wherein the epitaxial structure layer comprises an n-type layer, a quantum well layer and a p-type layer which are sequentially stacked;
processing the surface of the epitaxial structure layer to form a step structure, wherein the step structure divides the surface of the epitaxial structure layer into a p area and an n area;
forming a p electrode in the p region and an n electrode in the n region;
the n-electrode comprises a first metal layer and a second metal layer which are arranged in a laminated mode, the first metal layer is arranged on the n-type layer and forms ohmic contact with the n-type layer, and the first metal layer is an Mg metal layer.
12. The manufacturing method according to claim 11, characterized by specifically comprising:
forming p-electrode metal in the p region, forming n-electrode metal in the n region, and annealing the p-electrode metal and the n-electrode metal for 10 s-3 min under the conditions of a protective atmosphere and 350 ℃ at 100-.
13. The method of manufacturing according to claim 12, wherein: the manufacturing method specifically comprises the following steps: firstly, processing an n region on the surface of the epitaxial structure layer to form an n region contact hole, and manufacturing an n electrode in the n region contact hole.
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